CO_Thème 1 - Société Chimique de France

Transcription

Congrès de la Société Chimique de France – 2015
SCF Congress - 2015
Use of an electroactive organic binder as active material for
high energy density supercapacitors.
Liant organique modifié pour supercondensateurs à haute densité
d’énergie.
C. Benoit1, D. Bélanger2, C. Cougnon1*
1
Laboratoire MOLTECH Anjou, UMR-CNRS 6200, Université d’Angers, 2 Boulevard Lavoisier 49045, Angers Cedex,
France
2 Département de Chimie, Université du Québec à Montréal, case postale 8888, succursale centre-ville, Montréal,
Québec H3C 3P8, Canada
* Corresponding author: [email protected]
______________________________________________________________
Résumé :
Grace à leurs propriétés physiques et chimiques uniques, les carbones activés sont un matériau de choix pour la
fabrication de supercondensateurs. Ils présentent typiquement des capacités de 100 à 150F/g. Une des stratégies
les plus utilisées pour améliorer cette capacité de stockage consiste à greffer des molécules redox sur le substrat
carboné. Malheureusement le greffage altère la capacité de double couche du carbone. Nous proposons d’étudier un
liant organique modifié avec des unités redox pour améliorer les performances des dispositifs et empêcher la perte
de la capacité de double couche.
________________________________________________________________________
Summary:
Activated carbons are attractive materials for supercapacitors due to their physical and chemical proprieties. They
present a typical capacitance comprises between 100 and 150F.g-1. One of the most popular strategies to improve
the capacitance consists in adding faradaic contribution by grafting redox molecules. However, both the double-layer
capacitance of the carbon and the internal resistance suffer from the grafting. In this work, we propose to graft binder
with redox molecules instead of carbon, in order to prevent decrease of the double layer capacitance of carbon and
improve the performances of devices.
Keywords: Supercapacitors; activated carbon; organic binder; grafting
Les supercondensateurs sont de nos jours utilisés dans de nombreux domaines, comme l’aviation (ouverture d’urgence),
l’automobile (récupération d’énergie au freinage) ou encore pour le stockage d’énergie électrique. Ils présentent la
capacité à stocker en quelques secondes une quantité importante de charges grâce à leur résistance interne très faible.
Malheureusement leur capacité de stockage encore trop faible limite leur utilisation à grande échelle, et c’est dans ce
cadre que s’inscrivent nos recherches
1
Introduction
Activated carbons are attractive material for
supercapacitors due to the extremely low
separation of ions and electron charges associated
with a large specific surface area. However,
because it can’t be easily handled as electrodes
component, carbon powder are generally mixed to
an organic binder and conductive additive to obtain
a carbon paste with suitable mechanical and
electrical proprieties.
To increase the specific capacitance value of
the activated carbon, a popular strategy is to graft
redox molecules to add a faradaic contribution to
the capacitive one of the carbon. [1,2] In this
approach, the binder is considered as a deadweight for the charge storage. In this work, we
propose to use the binder as a charge storage
component, by grafting electroactive molecules
onto its polymeric skeleton. Such redox binder is
expected to have the dual functionality of both
binder and active material.
2
Experimental/methodology
Polystyrene used as binder was modified by
reaction
in
THF
with
O-protected
3,4dimethoxyaniline in situ diazotized. After 108h
stirring at room temperature, the solvent was
removed under vacuum. The residue was purified
by chromatography on silica gel (eluents
CH2CL2/MEOH 99/1, CH2CL2/MEOH 95/5 and pure
MEOH) affording a brown powder.
Electrodes were prepared by mixing carbon
powder (YP80F, KURAKAY) with modified or raw
binder (10 w% in N-methyl pyrrolidinone) and
carbon black (superior graphite) with a ratio of
80:10:10. The mixture was stirred for one day until
a homogenous ink was obtained. As counter
electrodes, unmodified carbon and polystyrene
were used and 0,2ml of carbon ink was deposited
onto the gold disk. As working electrodes modified
and unmodified carbon was mixed with modified or
unmodified polystyrene and 0,1ml of the carbon ink
was deposited onto a platinum disk. After drying at
120°C for 3 hours, thin films of 1-3 mg were
obtained.
Electrochemical measures were performed at
room temperature in an aqueous sulfuric acid (1M)
electrolyte with a three-electrode test cell ECC-
AQU (EL-ELL, Germany). Potential are referred to
Ag/AgCl reference electrode. A potentiostatgalvanostat model VSP (Bio-Logic) monitored by
EC-lab software was used.
4
unmodified electrode
modified carbon
3
modified binder
2
Current (Ag-1)
3
Results and discussion
Here, we propose to reconsider the binder for
the charge storage by grafting molecules onto its
polymeric skeleton. This original approach was
tested with a modified binder prepared by reaction
between O-protected 3,4-dimethoxyaniline in situ
diazotized and polystyrene. The resultant carbon
electrode was compared to an electrode based on
modified carbon powder to study the performances
according to the way molecules were attached (i.e.,
onto the organic binder or carbon powder). The
scheme in Figure 1 resumes the different
combinations of the two modified components used
as active materials in this work.
Figure 1 shows typical cyclic voltammograms (CVs)
recorded in 1 M H2SO4 on working electrodes
prepared from modified binder or modified carbon
powder, compared to the response of an
unmodified electrode. Note that, just before use,
carbon electrodes were first cyclized between 0 V
and 1.1 V vs. Ag/AgCl in 1 M H2SO4 to remove the
two methyl protecting groups by electrochemical
oxidation and restore the well-known redox activity
of the catechol. At relative low scan rate, the CV
recorded on the unmodified electrode shows a
quasi-rectangular shape, which is characteristic of a
nearly pure capacitive behavior. With the electrode
based on modified carbon, the CV is characterized
by an intense reversible electrochemical system
centered at around 0.1 V, accompanied to a
retarded current when the potential sweep is
reversed. When the working electrode contains the
modified binder, the CV reveals a similar redox
system, whilst the current intensity is highly
increased over the entire potential domain scanned.
The global specific capacitance values determined
by integrating the area under the CVs are 110 Fg-1
for the unmodified electrode, 180 Fg-1 for the
modified-carbon-based electrode and 240 Fg-1 for
the modified-binder-based electrode.
As it was expected, when redox molecules are
introduced, an additional faradaic capacitance is
obtained over a narrow potential window where the
redox reaction occurs. However, it is noteworthy
that the best result is obtained with the modifiedbinder-based electrode, which contain only 10
weight % of redox binder, compared to the carbon
powder, which is the main component (80 weight
%). This unprecedented result can be explained by
the fact that the grafting onto the binder does not
damage the double-layer capacitance of the
carbon, and by an improved wettability of the
composite network that increases the pores
accessibility and favors the ions adsorption
processes.
1
0
-1
-2
-3
-4
-0.4
-0.2
0
0.2
0.4
0.6
Potential (V)
Fig. 1. Cyclic voltammograms recorded in 1M H2SO4 at
10mV.s-1 on unmodified electrode, modified-carbon-based
electrode and modified-binder-based electrode.
4
Conclusions
This work points the interest of using an
electroactive organic binder as active material. By
this strategy, the total capacitance can be doubled,
the equivalent series resistance decreased, while a
good stability was obtained.
Acknowledgements
This work is supported by the Centre National
de la Recherche Scientifique (CNRS-France) and
the Agence National de la Recherche (ANR)
through the project ICROSS
References
1.
2.
Pognon, G., et al., Catechol-Modified Activated
Carbon Prepared by the Diazonium Chemistry for
Application as Active Electrode Material in
Electrochemical Capacitor. ACS Applied Materials &
Interfaces, 2012. 4(8): p. 3788-3796.
Pognon, G., et al., Performance and stability of
electrochemical capacitor based on anthraquinone
modified activated carbon. Journal of Power Sources,
2011. 196(8): p. 4117-4122.
SCF Congress - 2015
Ionic liquids and γ-butyrolactone
mixtures as electrolytes
γ
supercapacitors operating over extended temperature ranges
for
Mélanges binaires de liquides ioniques et γ-butyrolactone pour
applications aux supercondensateurs sur une gamme de température
étendue
L. Dagousset1,2, G. T. M. Nguyen1, F. Vidal1, C. Galindo2, G. Pognon2, P-H.
Aubert1*
1
Laboratoire de Physicochimie des Polymères et des Interfaces (EA 2528), Université de
Cergy-Pontoise, 5 mail Gay-Lussac, 95031 Cergy-Pontoise Cedex, France
2
Thales Research & Technology, 1 avenue Augustin Fresnel, 91767, Palaiseau, France
______________________________________________________________
Résumé :
Les propriétés physico-chimiques et électrochimiques de trois liquides ioniques ont été étudiées et comparées avec
celles des mélanges binaires de ces trois liquides ioniques avec de la γ-butyrolactone (GBL). Les conductivités optimales
mesurées à température ambiante concernent les trois mélanges à 50% massique en solvant. Ils ont donc été
sélectionnés pour être étudiés de manière plus approfondie et comparés avec les liquides ioniques purs. Il a ainsi été
observé que l’ajout de solvant augmente fortement la fluidité et la conductivité des solutions ioniques, et supprime
également les pics de transitions de phase dans la gamme de température de -50°C à 100°C. Ces électrolytes binaires
sont donc particulièrement intéressants pour des applications à basse température. Nous avons cependant noté une
diminution de la fenêtre électrochimique de 0.5 à 1V par rapport aux liquides ioniques purs.[1]
________________________________________________________________________
Summary:
Physicochemical and electrochemical properties of three pyrrolidinium or imidazolium based ionic liquids were
investigated and compared with binary mixtures of those ionic liquids with γ-butyrolactone (GBL). It was found that the
highest conductivity for each mixture was obtained for a concentration close to 50 wt%. Then thermal and transport
properties for the three neat ionic liquids and the three mixtures with GBL at 50 wt% were evaluated from 50°C to 100°C.
The addition of GBL enhances the conductivity and fluidity of the mixtures, especially at low temperature. Another
advantage of the solvent addition is that it suppresses the melting transition and allows applications down to -50 °C. A
drawback is the slight reduction of the electrochemical stability window of the electrolyte.[1]
Keywords: Supercapacitors, electrolytes, ionic liquids
Dans le domaine des supercapacités, des besoins spécifiques ne peuvent pas être satisfaits par les technologies
commercialisées actuellement. Parmi eux, un fonctionnement sur une gamme de température étendue (-50°C à 100°C),
et des résistances internes très faibles pour atteindre des puissances importantes des domaines tels que l’avionique.
Les électrolytes étudiés (TRL 3) permettent des utilisations dans de telles conditions sans pertes drastiques des
performances, on envisage donc de faire de nouveaux prototypes (démonstrateur de laboratoire (TRL 4)).
1
Introduction
During recent years, the interest in ionic liquids
(ILs) as an electrolyte has been growing,
concerning multiple applications like electrical
double layer capacitors (EDLCs) [1],[2],[3], lithium
ion batteries, electrochemical actuators[4],[5], dye
sensitized solar cells[6] or electrochromic
devices.[7] The attraction of ILs is due to their
numerous advantages such as a high thermal and
chemical stability in addition to a low volatility which
improves the safety of electrochemical devices, a
good conductivity, and a wide electrochemical
potential window which increases the device
efficiency. However ionic liquids exhibit a high
viscosity and the melting transition usually lies
within the temperature range [-50°C ; +100°C].
Those two drawbacks can be eliminated by the
addition of an organic solvent. In that perspective,
Chagnes et al.[8] and Anouti et al.[9] studied
GBL/IL mixtures, and more particularly the thermal
analysis of an aprotic ionic liquid (1-butyl-3-methylimidazolium) and a protic ionic liquid (pyrrolidinium
nitrate) respectively. Ruiz et al.[3]. and Nishida et
al.[10] studied the ionic conductivity of binary
mixtures of different ionic liquids with acetonitrile,
propylene carbonate or γ-butyrolactone.
2
-1
The ionic conductivity (σ, mS cm ) of IL/GBL
mixtures varying from 0 to 100 wt% in ionic liquid
was evaluated at room temperature with a Mettler
Toledo conductivity meter FE30 placed inside a
glove box under nitrogen. The ionic conductivity as
a function of temperature was recorded every 10 °C
from -50°C to 100°C, by Electrochemical
Impedance Spectroscopy (EIS) using a potentiostat
VMP3 multi-channel (Bio-Logic Instruments). The
measurement was realized in a three electrode cell,
using an Ag wire as a pseudo-reference electrode,
a Pt wire as a counter electrode and a glassy
carbon working electrode. Electrochemical setup
was assembled in a glove box and transferred into
a thermostatic chamber. The ionic conductivity was
calculated using the equation σ=k/Z, where Z is the
real part of the complex impedance (ohms) and k is
the cell constant, considered to be unchanged over
the temperature range. Electrochemical windows
(EW) measurements were carried out in the same
three-electrode setup. The cyclic voltammograms
-1
(CV) were recorded at 20 mV.s with current
-2
density boundaries set to +/-0.28 mA cm .
3
For all mixtures the maximum of the ionic
conductivity is reached for a composition Cσ,max,
close to 50 wt%, which corresponds to a molar
-1
concentration of 2 mol.L and an ionic conductivity
-1
-1
of 21.9 mS.cm for Pyr13FSI, 1.7 mol L and 20.5
-1
-1
-1
mS.cm for EMITFSI, 1.5 mol.L and 14.4 mS.cm
for Pyr14TFSI. A concentration of 50 wt% has been
selected for the forthcoming results. The ionic
conductivity and the viscosity is then measured
over the temperature range [-50°C; +100°C] for
neat ionic liquids and 50 wt% IL/GBL mixtures and
all measurements follow the the Vogel–Tamman–
Fulcher behavior.
Viscosity and ionic conductivity data were used
along with density data in order to evaluate the
ionicity of all electrolytes. Indeed Angell et al.[10]
have classifed ILs depending on where they stand
regarding the ideal line on the Walden plot (Fig.1).
All six electrolytes exhibit a good ionicity : the ions
are dissociated.
The electrochemical characterization of neat ionic
liquids was performed over their liquid temperature
range, and below 100°C. As their viscosity increase
dramatically for temperatures lower than 0°C, no
electrochemical measurement could be performed
for lower temperatures, whereas extremely wide
electrochemical windows (up to 8V) were measured
for all three binary mixtures à -50°C. However, the
electrochemical window is 0.5V to 1V lower than
that of neat ionic liquids, whatever the temperature.
Fig.1. Walden plot of log(molar conductivity, L) against
log(reciprocal viscosity, h_1), for: Pyr14TFSI ( ), EMITFSI ( ),
Pyr13FSI ( ), Pyr14- TFSI/GBL ( ), EMITFSI/GBL ( ) and
Pyr13FSI/GBL ( ).
4
Conclusions
The addition of an organic solvent upon ionic
liquids dramatically improves the fluidity and the
ionic conductivity of the system and can lead to a
device with extremely good performances at low
temperature, but a slight drawback is the reduction
of the electrochemical window for binary mixture,
within the temperature range [20°C – 100°C]
Acknowledgements
The authors thank the ANRT for the financial
support through the L. Dagousset PhD thesis, and
François Tran-Van (PCM2E University of Rabelais,
Tours, France), for the densitometer studies.
References
[1]
L.Dagousset, G.T.M. Nguyen, F.Vidal, P-H. Aubert, C.
Galindo, RSC Adv., 2015, 5, 13095–13101
[2] R. Palm, H. Kurig and K. T˜onurist, Electrochem. Commun.,
2012, 22, 203.
[3] V. Ruiz and T. Huynh, RSC Adv., 2012, 2, 5591.
[4] A. Maziz, C. Plesse, C. Soyer, C. Chevrot, D. Teyssi´e, E.
Cattan and F. Vidal, Adv. Funct. Mater., 2014, 24(30),
4851.
[5] R. Temmer, A. Maziz, C. Plesse, A. Aabloo, F. Vidal and T.
Tamm, Smart Mater. Struct., 2013, 22, 104006.
[6] D. Qin, Y. Zhang, S. Huang, Y. Luo, D. Li and Q. Meng,
Electrochim. Acta, 2011, 56, 8680.
[7] A. S. Shaplov, D. O. Ponkratov, P.-H. Aubert, E. I.
Lozinskaya, C. Plesse, F. Vidal and Y. S. Vygodskii, Chem.
Commun., 2014, 50(24), 3191.
[8] A. Chagnes, H. Allouchi and B. Carren, Solid State Ionics,
[9] M. Anouti and L. Timperman, Phys. Chem. Chem. Phys.,
2013
[10] T. Nishida, Y. Tashiro and M. Yamamoto, J. Fluorine
Chem.,2003, 120, 135 15, 6539–6548.
[11] W. Xu, E. I. Cooper and C. A. Angell, J. Phys. Chem. B,
2003, 107, 6170.
SCF Congress - 2015
Two-Dimensional Ti3C2-Based MXene for Energy Storage
Ti3C2-MXene bidimensionnel pour le stockage de l’Énergie
Yohan Dall’Agnese1,2,3, Maria R. Lukatskaya3, Kevin M. Cook3, Pierre-Louis
Taberna1, Yury Gogotsi3, Patrice Simon1,2
1
Université Paul Sabatier, CIRIMAT UMR CNRS 5085, 118 route de Narbonne, 31062
Toulouse, France.
2
Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459,
France.Université Paul Sabatier, CIRIMAT UMR CNRS 5085, 118 route de Narbonne, 31062
Toulouse, France.
3
A. J. Drexel Nanomaterials Institute & Department of Materials Science and Engineering,
Drexel University, Philadelphia, PA 19104, USA.
______________________________________________________________
Résumé :
Les MXènes sont une nouvelle famille de matériaux bidimensionnels à base de métaux de transition carbonée. Une
dizaine de MXènes ont déjà été synthétisés. Certains sont remarquables grâce à leurs performances en tant
qu’électrodes pour le stockage électrochimique de l’énergie, pour les applications telles que les batteries et les
supercondensateurs.
Le MXène Ti3C2 est étudié pour les supercondensateurs dans un électrolyte acide. L’effet des groupes de surface sur
les performances électrochimiques est analysé. Cette étude montre que le Ti3C2 contenant des groupes de fonction
3
riches en oxygène a des capacitances très élevées de 520F/cm à 2 mV/s.
________________________________________________________________________
Summary:
Recently, a new family of two-dimensional early transition metal carbides, called MXenes, was discovered. To date,
more than 10 MXenes have been successfully synthetized and quickly attracted the attention as promising electrodes
materials for energy storage applications such as batteries and supercapacitors.
Here, we report on Ti3C2-based MXene performances for electrochemical capacitor in acidic electrolyte. We
investigate the effect of the surface chemistry on the electrochemical performances. The study revealed that Ti 3C2
with oxygen containing functional groups have an extraordinary capacitance of 520F/cm3 at 2mV/s, with high power
rate and high reversibility.
Keywords: Electrochemical capacitors; two-dimensional materials; XPS; surface chemistry
The development of electric cars, telephones, as well as the need for storing renewable energy drive the development of
electrochemical energy storage devices. Batteries can deliver high energy but cannot be charged quickly.
Supercapacitors can be charged faster with lower energy density. MXenes are a new family of materials that are
promising for energy storage thanks to suitable properties. They are two-dimensional materials composed of carbon and
early transition metals and can host a variety of ion between layers which leads to higher energy than commercials
electrodes.
Les batteries des nouveaux appareils électriques mobiles qui demandent des niveaux d'énergies élevées se chargent
lentement. Les supercondensateurs qui ont l’avantage de se charger rapidement délivrent cependant une énergie
encore faible. Les MXènes, nouveaux matériaux, permettent d'augmenter le niveau de stockage d’énergie. Grâce à
leurs propriétés bidimensionnelles, ces MXènes stockent des ions entre leurs feuillets, délivrant ainsi rapidement plus
d’énergie que les matériaux actuellement industrialisés.
1
Introduction
Supercapacitors (SCs) have higher power
density than Li-ion batteries but lower energy
density. The challenge SCs are currently facing is
the improvement of their energy density. It was
recently shown that fast, non-diffusion limited
intercalation reaction offers a solution. [1,2].
In this work, we investigate electrochemical
performance of Ti3C2 as electrodes for
supercapacitors in acidic electrolyte. Ti3C2 is a
member of a new family of 2D materials called
MXenes that have demonstrated promising results.
As synthetized, these MXenes are electrically
conductive layers with some –F surface termination
which is not known to have any pseudocapacitive
energy storage mechanism. Our strategy is to
chemically tune the surface termination of Ti3C2 in
order to increase the energy density with
pseudocapacitive effect. We analyze the influence
of the surface chemistry on the performance [3,4].
2
As synthetized multilayers, noted Ti3C2Tx, were
modified by either chemical intercalation of
potassium salts, potassium hydroxide and
potassium acetate (denoted KOH-Ti3C2 and KOAcTi3C2), or by delamination of Ti3C2 layers (d-Ti3C2).
The samples were characterized using an X-ray
photoelectron spectrometer (VersaProbe 5000,
Physical Electronics Inc., USA), a scanning electron
microscope (Zeiss, Supra 50VP, Oberkochen,
Germany) and an X-ray diffractometer (Rigaku
SmartLab).
The electrochemical performance was tested by
cyclic voltammetry, galvanostatic charge discharge
and impedance spectroscopy using a VMP3
potentiostat (Biologic, S.A.)
3
The Scanning Electron Microscopy images and
X-Ray Diffraction patterns revealed that the
chemical modifications of Ti3C2Tx lead to different
morphologies. The c-lattice parameter increase in
the order Ti3C2Tx, KOAc-Ti3C2, KOH-Ti3C2 and dTi3C2, the latter being separated layers.
The X-ray photoelectron spectroscopy results
demonstrated that the different treatment lead to
different surface chemistries. The fluorinated
functional groups were replaced by hydroxyl and
oxygen-containing
termination.
KOAc-Ti3C2
+
contains electrosorbed K ions while KOH-Ti3C2
and d-Ti3C2 spectra reveal mainly oxidation of the
surface of the material.
Fig.1 shows the electrochemical performances
of the samples. The difference in performances
between Ti3C2Tx, KOH-Ti3C2 and KOAc-Ti3C2 can
only be explained with the difference in surface
chemistry, while the difference between KOH-Ti3C2
and d-Ti3C2 is believed to be due to the higher
specific surface area and lower thickness of dTi3C2.
As expected, Ti3C2Tx exhibits moderate
capacitance due to its inactive fluorinated
termination. KOAc-Ti3C2 and KOH-Ti3C2 have
higher capacitance thanks to the replacement of Fgroups by oxygen-terminated groups, including –
OOH, =O and –OH, which can be responsible for
well-known pseudocapacitive behavior in acidic
electrolyte.
Fig.1. Electrochemical performance of Ti3C2-based electrodes
in 1M H2SO4 [3].
4
Conclusions
The surface chemistry of the Ti3C2 (MXene) was
tuned by chemical intercalation or delamination.
The fluorinated surface was replaced with
oxygenated functional groups. This change led to a
4-fold increase in capacitance, thanks to the
pseudocapacitive contribution. D-Ti3C2 shows
excellent electrochemical behavior with high
volumetric capacitance, high rate stability and
reversibility.
Ti3C2 is only one of the first synthetized
members of the new family of two-dimensional
transition metal carbides/nitrides called MXenes. It
can be expected the other MXenes can achieve
even higher capacitance values.
Acknowledgements
This work was supported by the Partnership
Universities Fund (PUF) of French Embassy. YDA
was supported by the European Research Council
(ERC, Advanced Grant, ERC-2011-AdG, Project
291543 – IONACES). PS acknowledges the
funding from the Chair of Excellence of the Airbus
group foundation “Embedded multi-functional
materials”
References
[1]
[2]
[3]
[4]
P. Simon, et al. Science, 343 (2014), 1210-1211.
V. Augustyn, et al. Nat Mater, 12 (2013), 518-522.
M. R. Lukatskaya, et al. Science, 341 (2013), 1502-1505.
Y. Dall'Agnese, et al. Electrochem. Commun., 48 (2014),
118-122.
SCF Congress - 2015
Polyaniline prepared from anilinium salt: synthesis, characterization
and application for electrochemical energy storage
Polyaniline préparée à partir de sel d’anilinium : synthèse, caractérisation et
application pour le stockage électrochimique
F. Al Zohbi1, F. Ghamouss1, B. Schmaltz1, M.Oyharçabal2, M. Abarbri3, K.
Cherry4, M.Tabcheh5, F. Tran Van1
1
Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (EA 6299),
Université François Rabelais de Tours, Parc Grandmont, 37200 Tours, France.
2
RESCOLL Société de Recherche, 8 Allée Geoffroy Saint Hilaire, 33600 Pessac, France.
3
Laboratoire ISP (UMR INRA 1282), Université François Rabelais de Tours, Equipe «Recherche
et Innovation en Chimie Médicinale», Parc Grandmont, 37200 Tours, France
4
Laboratoire Matériaux, Catalyse, Environnement et Méthodes Analytiques (MCEMA) Campus
Universitaire de Hadath, Liban.
5
Laboratoire de chimie appliquée, Faculté des sciences III, Université Libanaise, Kobbeh Tripoli - LIBAN
______________________________________________________________
Résumé : La polyaniline (Pani) a été synthétisée par voie oxydative du sel d’anilinium [Ani][X] dans l’eau en utilisant
le persulfate d’ammonium comme oxydant. L’effet de l’anion dopant et l’ajout de graphène sur la morphologie, la
stabilité thermique, la conductivité électrique et la chimie de la Polyaniline (Pani) seront présentés et discutés sur la
base des observations MEB, ATG, IR et analyse Raman. La Pani ainsi synthétisée sous différentes conditions
expérimentales est ensuite utilisée comme matériau d’électrode dans un supercondensateur, dont les performances
en termes d’énergie et de puissance seront discutées et corrélées aux autres résultats de caractérisations physicochimiques.
_____________________________________________________________________
Summary: Polyaniline (Pani) was synthesized by oxidative polymerization of anilinium salt [Ani][X] in water using
ammonium persulfate as oxidant. The effect of dopant size and graphene ratio on the morphology, thermal stability,
electronic conductivity and chemical structure of Pani will be presented and discussed based on SEM observation,
TGA, IR and Raman characterizations. The obtained polymer will be used as electrode material supercapacitor
application. The performances of the supercapacitor (energy and power) will be presented and discussed.
Keywords: Polyaniline; protic ionic liquid; oxidative polymerization, supercapacitor
1
Introduction
La Polyaniline (Pani) est un polymère
conducteur intrinsèque qui a attiré une grande
attention du fait de
ses propriétés: stabilité
thermique, conductivité électronique, performance
électrochimique [1]. Dans le domaine du stockage
de l’énergie, la Pani est utilisée comme matériaux
d'électrode dans des supercondensateurs[2]. La
recherche de performances de plus en plus
importantes de ces dispositifs (capacité de
stockage particulièrement) a motivé une recherche
intensive ces deux dernières décennies afin
d’améliorer
les
propriétés
des
polymères
conducteurs et de la Pani en particulier[3].
L’objectif de ce travail consiste à préparer par voie
oxydative et à caractériser la Pani dopée par
différents
anions.
Des
nanocomposites
graphène/Pani sont également préparés et étudiés.
Nous montrons ainsi, que les propriétés de la Pani
sont fortement influencées par la composition du
milieu de synthèse.
2 Résultats et discussion
La Pani a été synthétisée à partir de quatre
sels d’aniline obtenus par une simple réaction
acido-basique
entre
l’aniline
et
l’acide
correspondant (acide chlorhydrique HCl, acide
sulfurique H2SO4, acide para-toluène sulfonique
APTS ou l’acide camphre sulfonique ACS) (Fig.1).
Les quatre acides utilisés dans la préparation du
sel d’aniline sont structurellement différent : HCl est
un acide diatomique ayant une petite masse
molaire (36.4M), H2SO4 est un acide diprotique,
l’APTS possède un cycle benzènique et l’ACS est
une molécule bicyclique.
Fig.1. Synthèse du sel d’anilinium
Bien que les différents polymères synthétisés
présentent une composition chimique similaire, les
observations par imagerie électronique montrent
des différences significatives d’un point de vue
morphologique. L’effet de l’anion dopant de la Pani
sur son comportement électrochimique a été étudié
dans une configuration de supercondensateur
symétrique. Les supercondensateurs ont été
caractérisés par voltamétrie cyclique (CV) sur une
gamme de potentiel comprise entre 0 à 0,55V afin
d’évaluer le comportement capacitif des matériaux,
et par cyclage galvanostatique (GCPL) dans un
électrolyte à base de liquide ionique protique
PyrHSO4. Les propriétés de l’électrolyte ont été
optimisées en termes de conductivité ionique et de
viscosité pour atteindre les performances optimales
du supercondensateur. Les supercondensateurs
assemblés montrent un comportement pseudocapacitif
caractéristique
des
polymères
conducteurs. La capacitance spécifique des
dispositifs, déterminée à partir des cycles de
charge et décharge galvanostatiques présentée en
fonction du courant sur la fig.2. Les résultats,
donnés par masse active des deux électrodes
montrent une tendance similaire de la capacitance
mesurée des différents supercondensateurs. La
capacitance diminue en effet quand le courant de
décharge augmente. Cette diminution peut être
directement liée à l’impédance totale des
supercondensateurs. Toutefois, il est intéressant de
remarquer que l’amplitude de cette diminution est
plus importante dans le cas de Pani-Cl et Pani
HSO4, pourtant plus conductrice (tableau 1). Ce
phénomène serait alors lié à des phénomènes
d’interface
électrode/électrolyte
(diffusion
et
résistance de transfert de charge). A faible courant
de décharge, les capacitances spécifiques de la
Pani-PTS, CS et HSO4 sont quasi-identiques. A
2A/g, la capacité de la Pani-PTS (320F/g) est
similaire à celle de la Pani-CS (316F/g) qui est
supérieure à celle de la Pani-HSO4 (274F/g). A ce
même courant, la plus faible capacitance est
attribuée à la Pani-Cl (247F/g). Pour la Pani-PTS,
la capacitance diminue de 369 à 320F/g quand le
courant augmente de 0,25 à 2A/g, la rétention de
la capacitance est de 87%. Sur cette même gamme
de courant, la rétention de la capacitance est de
87%, pour la Pani-CS et de 77% pour la Pani-Cl et
la Pani-HSO4 En conclusion, les capacitances
spécifiques et leurs retentions sont plus
importantes pour des polymères préparés à partir
de sels à base d’anions volumineux.
Les résultats du tableau.1 montrent cependant que
la conductivité électrique mesurée par la méthode
de quatre pointes est indépendante de la taille des
anions utilisés pour la préparation du sel d’anilinium
choisi. Des valeurs très proches sont obtenus pour
la Pani-Cl et la Pani-PTS pourtant très différentes
concernant l’anion du sel d’aniline de départ.
Tableau.1
Conductivité électrique de la Pani dopée avec Cl-, HSO4-, PTS- ou CSPolymer
 (S.cm-1)
Pani-Cl
2.4
Pani-HSO4
0.18
Pani-PTS
2
Pani-CS
0.6
La dernière partie de la présentation sera
consacrée à l’étude de l’effet de l’incorporation de
graphène dans la préparation du matériau. Le
graphène, obtenue par exfoliation chimique de
graphite est dispersé dans ce cas dans le mélange
contenant les précurseurs de polymérisation et
constitue donc un support nanostructuré pour la
polymérisation. Les mesures de conductivité
électrique montre que celle-ci augmente avec
l’ajout de graphène. Dans le cas de la Pani-PTS
cette valeur est augmentée de 2 à 25S/cm avec
22%
de
graphène.
Le
comportement
électrochimique est étudié en fonction du
pourcentage de graphène dans le matériau. La
fig.3 montre l’amélioration de la densité de courant
en présence de 3% de graphène dans la Pani-PTS.
(
(
Fig.3. CV à 15mV/s dans H2SO4 (0.1M) (
)de la Pani,
) PaniI-Graphene (78:22), (
) Pani-graphene (92:8) et
) Pani-graphène (97 :3)
Conclusions
La polyaniline a été préparée dans l’eau en
utilisant diffèrents sel d’anilinium. Nous avons
étudié l’effet de l’anion dopant de la Pani sur ses
propriétés. Les performances électrochimiques et la
morphologie de la Pani dépendent de la nature des
anions du sel d’aniline de départ. Les anions de
grande
taille
présentent
les
meilleurs
comportements capacitifs. L’ajout de graphène
améliore la conductivité électrique et les propriétés
capacitives de la Pani.
Références
Fig.2. Capacité en fonction du courant de la ( ) Pani-Cl, ( )
Pani-HSO4, ( )Pani-PTS et ( ) Pani-CS dans PyrHSO4-59% eau
[1] S. Bhadra et al; Prog. Polym. Sci. 34 (2009) 783.
[2] J. Qiang et al; Synthetic Metals 158 (2008) 544.
[3] J. Liu et al; Electrochim. Acta 55 (2010) 5819.
SCF Congress - 2015
Preparation and physico-chemical study
electrolytes for solid-state Li-ion systems
of
polymer
Préparation et étude physico-chimique d’électrolytes polymères pour
systèmes solides de type Li-ion
V. Chaudoy1,3, F. Ghamouss*,1, E. Luais2, J-C. Houdbert3, M. Deschamps4, F.
Tran Van1
1
Université de Tours, Laboratoire PCM2E, Parc de Grandmont, 37200 Tours
2
Université de Tours, Laboratoire GREMAN, Parc de Grandmont, 37200 Tours
3
STMicroelectronics, Rue Pierre et Marie Curie, BP7155, 37071 Tours cedex 2
4
CEMHTI-CNRS UPR3079, CS 90055, 1D de la Recherche Scientifique, 45071 Orléans
______________________________________________________________
Résumé :
Cette étude présente l’impact du confinement d’un liquide ionique (N-Propyl-N-methylpyrrolidinium
bis(flurosulfonyl)imide – P13FSI) et d’un sel de lithium (Lithium bis(trifluorosulfonyl)imide - LiTFSI) sur la mobilité de
l’ion lithium dans deux types de polymères. L’un est de type physique (PVdF-co-HFP) tandis que l’autre est de type
chimique (réseau à base de poly (oxyde d’éthylène)). Pour caractériser l’impact du confinement sur la mobilité, des
caractérisations de types physico-chimiques, morphologiques, mécaniques et électrochimiques ont été réalisées.
L’objectif étant de montrer cet impact sur les performances des systèmes solides de type batterie et
supercondensateur hybride.
________________________________________________________________________
Summary:
This study illustrates the impact of containment of an ionic liquid (N-Propyl-N-methylpyrrolidinium
bis(flurosulfonyl)imide – P13FSI) with a lithium salt (Lithium bis(trifluorosulfonyl)imide - LiTFSI) on lithium ion mobility
in two types of polymers. We used a linear polymer (PVdF-co-HFP) and poly (ethylene oxide) based networks. To
characterize the impact of containment on mobility, various characterizations such as physico-chemical, imaging,
mechanical and electrochemical were realized. The objective is to present the impact of lithium mobility on
electrochemical performances in electrochemical devices such as battery and hybrid supercapacitor.
Keywords: Polymers, Electrolytes, Ionic liquids, Solid-state devices, Li-Ion Batteries, Supercapacitors
1
Introduction
La technologie Li-ion est aujourd’hui considérée
comme l’une des technologies de stockage
d’énergies les plus importantes car elle s’adapte à
de nombreuses applications. Le système Li-ion le
plus mature est basé sur la technologie C/LiCoO2
commercialisé par Sony en 1991. Ce type de
système utilise un électrolyte liquide de type
organique composé d’alkyl carbonate linéaire et
cyclique de type EC, DMC, PC, EMC. Cependant
l’utilisation de ces types de solvant pose un
problème majeur de sécurité intrinsèquement lié à
leurs natures inflammables et volatiles. Pour
résoudre ce problème, de nouvelles batteries de
type solide voient le jour grâce à l’utilisation de
poly(oxyde d’éthylène) et de sel de lithium dissous .
Cependant la faible conductivité de ce système à
température ambiante limite son utilisation [4].
L’intégration de nouveaux électrolytes à base de
liquide ionique et de sel de lithium confiné au sein
d’un polymère pourrait permettre de palier les
problèmes de sécurité (Liquides ioniques : non
inflammables et non volatiles). De plus, la
conductivité ionique élevée des liquides ioniques
ouvre la voie à l’utilisation de systèmes solides à
l’ambiante.
Dans cette perspective, nous présenterons
l’utilisation d’électrolytes polymères incorporant le
liquide ionique et le sel de lithium confiné dans des
systèmes
de
type
Li-ion
(batterie
et
supercondensateur hybride). Nous comparerons
l’impact de l’utilisation de deux types de polymères
pour l’encapsulation du liquide ionique en termes
de propriétés physico chimiques (conductivité
ionique et diffusion des ions), mécaniques,
thermiques, morphologiques et électrochimiques
(cyclage galvanostatique et voltampérométrie
cyclique). Les différents systèmes Li-ion présentés
seront des batteries réalisées en système de type
Li/LiNi1/3Mn1/3Co1/3O2 et des supercondensateurs
hybrides en systèmes Li/Carbone activé.
.
2
Résultats et discussion
Les électrolytes étant de natures différentes ont
été préparés selon plusieurs voies (voir tableau 1).
En effet, l’électrolyte 1 à base de PVdF-co-HFP fut
préparé par homogénéisation du copolymère en
présence de liquide ionique, de sel de lithium et
d’acétone. L’électrolyte fut ensuite déposé par
méthode de coulé-évaporation. Dans le cas de
l’électrolyte à base POE, le polymère précurseur
(poly(éthylène glycol) diméthacrylate) sous forme
liquide a été mélangé avec le liquide ionique et le
sel de lithium. Il est ensuite mis en forme puis
réticulé grâce à un traitement thermique.
Tableau 1
Electrolytes polymères étudiés
Electrolyte
Polymère
1
PVdF-co-HFP
Poly(éthylène
Diméthacrylate
2
Liquide ionique
P13FSI
glycol)
P13FSI
La figure 1 présente les résultats de conductivité
ionique des deux électrolytes étudiés ainsi que le
liquide ionique avec son sel de lithium en tant que
référence en fonction de la température. A 25°C,
l’électrolyte polymère 1 montre une conductivité
-3
-1
ionique de 1.88 x 10 S.cm tandis que l’électrolyte
-4
-1
polymère 2 atteint 8.91 x 10 S.cm . La référence
-3
indique une conductivité ionique de 4.81 x 10
-1
S.cm .
Fig. 1. Conductivité ionique des électrolytes polymères en
fonction de la température
Cette plus faible conductivité ionique de
l’électrolyte 2 par rapport au 1 pourrait être
expliquée par l’interaction O-Li qui limiterait la
mobilité de l’ion lithium et par la réticulation du
réseau de POE qui limite la mobilité du LI.
Fig. 2. Courbes de charge/décharge cellules NMC/Li à un
régime de C/10 à 25°C
Ces résultats sont à mettre en parallèle avec les
résultats de RMN à gradients de champs pour
déterminer les coefficients de diffusion des ions.
Comme le montre la figure 1, les propriétés de
transport plus élevées pour l’électrolyte 1 vont se
traduire directement sur les performances
électrochimiques en système Li-ion.
La figure 2 présente une courbe de
charge/décharge à un régime de C/10 à 25°C pour
les 2 électrolytes polymères en cellules de type
NMC/Li. L’utilisation de l’électrolyte 2 à base POE
réticulable montre une plus forte polarisation du
système et une plus grande chute ohmique qui
abaisse la plage de potentiel d’utilisation de la
batterie.
De
plus,
les
performances
-1
électrochimiques se limitent à 100 mA.h.g tandis
-1
que l’électrolyte 1 atteint les 145 mA.h.g .
Il est intéressant de montrer l’utilisation
potentielle de ce type d’électrolyte polymère dans
un système de type supercondensateur hybride
(CA/Li) ou supercondensateur Li-ion. En effet, la
figure 3 montre différentes courbes de
voltampérométrie cyclique d’une cellule CA/Li à
différentes vitesses de balayage (20, 15, 10, 5 et 2
-1
mV.s ) sur une plage de potentiel comprise entre
1.9V et 4.2V.
Fig. 3. Courbes de voltampérométrie cyclique des cellules
CA/Li à différentes vitesses de balayage pour l’électrolyte à base
de PVdF-co-HFP
L’utilisation de ce type d’électrolyte permet
-1
-1
d’atteindre des capacités de 70 F.g à 20 mV.s et
-1
-1
92 F.g à 2 mV.s
4
Conclusions
Cette étude présente une comparaison des
propriétés de transport et des performances
électrochimiques en systèmes Li-ion entre deux
électrolytes
polymères.
On
constate
que
l’électrolyte à base de PVdF-co-HFP permet
d’obtenir une meilleure conductivité ionique et un
meilleur coefficient de diffusion des ions lithium. La
plus grande mobilité de l’ion lithium dans cet
électrolyte se traduit par une amélioration des
performances électrochimiques en système Li-ion.
Acknowledgements
Les
auteurs
souhaitent
remercier
STMicroelectronics pour leur soutien financier.
SCF Congress - 2015
A study of lithiation/delithiation process of graphite in
lithium-ion batteries in the dinitriles: impact and role of
additives on the performance and the SEI formation.
Etude du processus de Lithiation/délithiation du graphite dans les
batteries Li-ion dans les dinitriles : impact et rôle des additifs sur les
performances et la formation de la SEI.
Douaa FARHAT, Charles ESNAULT, Fouad GHAMOUSS, Jesus SANTOS PENA,
Daniel LEMORDANT, François TRAN-VAN.
Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (PCM2E), EA
6299. Université François Rabelais-département de chimie, Parc de Grandmont,
37200 Tours, France
[email protected]
______________________________________________________________
Résumé :
La compatibilité des dinitriles contenant LiTFSI comme un sel, sur les électrodes de graphites seront élucidés. Ces
solvants seront utilisés seuls ou en mélange avec des additifs.
Le but de ce travail est d'améliorer la performance électrochimique et la qualité de la couche de passivation (SEI)
formée sur les électrodes de graphite.
La microbalance à quartz, la spectroscopie d'impédance électrochimique, et la voltammétrie cyclique seront utilisées
afin d'étudier les performances de l'anode de graphite et les processus irréversibles à l’interface. La morphologie et la
nature de la couche formée seront caractérisées par la microscopie électronique à balayage (MEB), spectroscopie IR
et XPS.
________________________________________________________________________
Summary:
The Compatibility of dinitriles containing LiTFSI as a salt, with graphite negative electrode will be studied.
These solvents are used alone or in mixture with additives.
The aim of this work is to improve the electrochemical performance and the quality of the passivation layer (SEI) on
the graphite electrodes.
The quartz crystal microbalance, the electrochemical impedance spectroscopy, and cyclic voltammetry will be used to
investigate the graphite anode performance and the irreversible processes at the interface. The morphology and
nature of the layer formed will be characterized by scanning electron microscopy (SEM), IR and XPS.
Keywords: Li-ion batteries, Graphite, Dinitriles, SEI, Additives.
Dans les systèmes Li-ion, l'électrolyte standard
utilisé par les concepteurs de batteries est
composé d'un mélange ternaire d’alkyle carbonate
aprotique (PC, EC, et DMC ou DEC). Le lithium est
utilisé sous forme ionique dont la source est un sel
de lithium soluble tel que LiPF6 ou LiTFSI. L'énergie
stockée provient des réactions électrochimiques
réversibles
et
la
double
intercalation/déintercalation des ions Li+ se produisant sur les
électrodes. La grande majorité des systèmes
actuellement commercialisés utilise une négative à
base de graphite associée à une positive constituée
d'un oxyde métallique comme le LiCoO2. Les
systèmes « classiques » à anode en graphite sont
très largement décrits dans la littérature
scientifique, et aujourd’hui le fonctionnement de ces
électrodes est relativement bien maitrisé.
Cependant, un des verrous majeurs à lever dans
les systèmes Li-ion actuels concerne les problèmes
de sécurité liés à l'utilisation de solvants organiques
inflammables, et pouvant se décomposer sur les
électrodes en générant des gaz dans le cœur du
dispositif de stockage. En effet, à l'état chargé,
l'électrolyte inflammable se trouve au contact d'une
électrode positive hautement oxydante (E > 4V vs
Li/Li+) et une négative fortement réductrice. De
plus, dans des conditions adiabatiques, l'autoéchauffement entraîne un emballement thermique
qui peut conduire à une destruction de la batterie.
Des études sont alors menées depuis plusieurs
années afin de proposer des alternatives aux
solvants habituellement utilisés. Toutefois,
les
études engagées pour améliorer et résoudre les
problèmes liées à l’inflammabilité et à la réactivité
des électrolytes dans les batteries Li-ion conduisent
souvent à des pertes significatives des
performances (cyclabilité, énergie, puissance,
rendement faradique, impédance interne). C’est le
cas par exemple des liquides ioniques, solvant non
inflammable, et possédant, pour certains d’entre
eux, des fenêtres électrochimiques supérieurs à 5
V, mais présentant le plus souvent des
performances électrochimiques bien en deçà de
celles des électrolytes classiques.
De par leur faible tension de vapeur, et de leur
inertie électrochimique (fenêtre électrochimique > 6
V), les dinitriles (NC(CH2)nCN) sont aujourd’hui
proposés comme solvants alternatifs aux alkyle
carbonate dans les batteries Li-ion [1]. Ces solvants
peuvent dissoudre des sels de lithium à des
concentrations relativement élevées, et possèdent
des viscosités modérées. L’adiponitrile (n=4), et le
glutaronitrile (n=3) ont ainsi été utilisées pour la
formulation d’électrolytes compatibles avec les
systèmes Li-ion et les supercondensateurs [1-4].
Toutefois, l’utilisation de co-solvants capables de
former une couche de passivation stable sur
l’électrode négative est jugée nécessaire pour le
fonctionnement des batteries.
L’objectif de notre travail est d’étudier le
comportement et la compatibilité des électrolytes à
base de dinitrile sur des négatives à base de
graphite. Ces solvants seront utilisés seuls ou en
mélange avec des additifs, dont le rôle sera
d’améliorer la qualité de la couche de passivation
(SEI). La faculté de ces électrolytes à former une
SEI stable et conductrice sera étudiée et suivie par
plusieurs
moyens
physico-chimiques.
La
microbalance
à
quartz,
la
spectroscopie
d’impédance électrochimique et la voltammétrie
cyclique seront utilisée afin d’identifier tous les
processus irréversibles se produisant à l’interface
et tout particulièrement lors de la première
lithiation : prise en masse lors de la première
réduction, correspondance entre quantité de charge
consommée lors de la première réduction et la
prise de masse sur l’électrode, identification des
potentiels de réduction des solvants et additifs sur
le graphite, évolution de l’impédance de la cellule
en fonction du solvant et de l’additif . La
microscopie électronique à balayage sera utilisée
afin d’identifier la morphologie des couches de
passivation formées sur l’électrode. La nature
chimique des SEI en fonction des dinitriles utilisés
et l’effet de l’incorporation de certains additifs
fluorés seront élucidés par spectroscopies IR et
XPS. Enfin, les performances électrochimiques
(capacité spécifiques, cyclabilité et rendement
faradique) seront présentées et discutées en
fonction de la nature des dinitriles utilisés et la
présence ou non d’additifs.
Fig. Première et deuxième charge/décharge galvanostatique à
C/20 d’une électrode de graphite ainsi que les images MEB
enregistrées en fin de charge (délithiation) dans : a1, et a2
adiponitrile+1M LiTFSI, b1 et b2, adiponitrile +1M LiTFSI +2%
F2EC (2% en masse).
References:
[1]
[2]
[3]
[4]
Y. Abu-Lebdeh et al. Journal of The Electrochemical
Society. (2009)156 1 A60
A. Brandt. Journal of The Electrochemical Society.
(2012)159 (12) A2053
F. Ghamouss et al J Appl Electrochem (2013) 43, 375–385
F. Ghamouss et al J. Phys. Chem. C, 2014, 118 (26), pp
14107
SCF Congress - 2015
Surface-fluorination
for
active
electrode
protection
technology - a glance at fluorinated titanium dioxide
materials
Fluoration de surface pour technologie de protection active
d’électrode - un coup d’œil sur les matériaux à base de dioxyde de
titane fluorés
Nicolas Louvain,1* Katia Guérin,2 Marc Dubois,2 Delphine Flahaut,3 Hervé
Martinez,3 and Laure Monconduit3
Institut Charles Gerhardt UMR CNRS 5253, Université Montpellier 2, CC1502, place E.
Bataillon, 34095 Montpellier cedex 5, France
1
Institut de Chimie de Clermont-Ferrand UMR CNRS 6296, Clermont Université, Université
Blaise Pascal, Chimie 5, BP80026, 24, avenue des Landais, 63171 Aubière cedex, France
2
3
Institut des Sciences Analytiques et de Physicochimie pour l’Environnement et les
Matériaux UMR CNRS 5254, Université de Pau et des Pays de l’Adour, Hélioparc, 2 avenue
Président Angot, 64053 Pau Cedex 09, France
* [email protected]
______________________________________________________________
Résumé :
La fluoration surfacique de matériaux d’électrodes de batteries à ions lithium est présentée comme la meilleure
manière de protéger les électrodes contre une consommation indésirable de lithium. Les dioxydes de titane ont été
sélectionnés comme de parfaits exemples pour démontrer l’efficacité de notre méthode.
________________________________________________________________________
Summary: text in english
Surface fluorination of electrode materials of Li-ion batteries is presented as the best way to protect
electrodes from being subject to unwanted lithium consumption. Titanium dioxides have been selected as
perfect examples to demonstrate the efficiency of our approach.
Keywords: fluorination, titanium dioxide, electrochemistry, lithium-ion batteries, surface study
1
Introduction (font style: Arial bold 10pt)
In all domains, materials need protection:
protection against corrosion, weathering, or
scratches. Our objective is to provide protection to
metal oxides in the field of energy storage. Used as
electrode, metal oxides are extremely sensitive to
their chemical environment.1,2 For instance, in Liion batteries, metal oxides are slowly degraded by
the electrolyte. Such degradation, coupled with
other inherent problems of batteries, leads to what
is tagged as irreversible capacity: a lost
electrochemical capacity that cannot be brought
back. We propose a solution to protect metal oxides
materials by surface fluorination, an innovative
concept applied to metal oxides. In Li-ion
batteries, the surface fluorination of metal
oxides will provide a surface protection against
capacity fading by preventing its cause: the
unwanted lithium consumption. To put it simply,
it may be possible to get your mobile running for a
longer period of time.
We endeavoured to work on titanium oxides to
demonstrate the efficiency of our approach. Indeed,
titanium oxides are attractive anode energy
materials owing to their versatile redox chemistry,
relative abundance, and nontoxic nature, and,
worth mentioning, they are industrially produced on
a wide scale, up to 5 million metric tons worldwide
in 2010,3 as they found many applications,
including pigments, sunscreen and UV-absorber,
photocatalysis and photovoltaics.4,5 In theory, they
are able to deliver a capacity of 1342.5 mAh g-1
upon complete reduction of the metal, and
335.6 mAh g-1 when only one lithium ion is
considered.
Some recent reports claim that fluorination of TiO2
is a process that could improve their
electrochemical properties,6-9 but such an
apparently simple chemical reaction is poorly
documented, and hence the motivation of our
current project: first we investigated the synthesis
and properties of the bulk material TiOF2 and, as a
second step, the surface fluorination of TiO 2
samples is undertaken in Montpellier, in
collaboration with the team of Marc Dubois at
Clermont-Ferrand’s ICCF.10
2
First step: BULK
Reactivity of pure molecular fluorine F2 allows
the creation of new materials with unique
electrochemical properties. We demonstrated that
titanium oxyfluoride TiOF2 can be obtained under
molecular fluorine from anatase titanium oxide
TiO2, while the fluorination of rutile TiO2 leads only
to pure fluoride form TiF4.10
Contrary to most fluorides, TiOF2 is air-stable
and hydrolyses poorly in humid conditions. That
makes it a potential electrode material for Li-ion
secondary batteries systems. It shows capacities as
high as 220 mAh g-1 and good cyclability at high
current rates at an average potential of 2.3 V vs
Li+/Li. At such a potential, only Li+ insertion occurs,
as proven by in operando XRD/electrochemistry
experiments.10
3
Second step: SURFACE
The idea behind this is as simple as it seems:
re-enforce the surface of TiO2 electrode surface
with fluorine, the same way toothpaste acts
everyday on your own teeth!
The main objective is to study the influence of
the surface fluorination (through molecular or
atomic fluorine) on the electrochemical behaviour of
TiO2 electrodes under operating conditions. In Liion batteries, one of the main drawbacks for
titanium oxides is the large irreversible capacity on
the first charge/discharge cycle that is associated
with surface reactions between the electrolyte and
the electrode. Thus, surface fluorination is the key,
as presented on Figure 1.
Fig. 1. Galvanostatic charge-discharge curves for TiO2/Li (a)
and TiO2-F/Li (b) half-cells, at C/20 current density; electrolyte is
LiPF6 EC:PC:3DMC 1M.
References
1. S. K. Martha, E. Markevich, V. Burgel, G. Salitra, E.
Zinigrad, B. Markovsky, H. Sclar, Z. Pramovich, O.
Heik, D. Aurbach, I. Exnar, H. Buqa, T. Drezen, G.
Semrau, M. Schmidt, D. Kovacheva and N. Saliyski,
J. Power Sources, 2009, 189, 288-296.
2. Y. B. He, B. Li, M. Liu, C. Zhang, W. Lv, C. Yang,
J. Li, H. Du, B. Zhang, Q. H. Yang, J. K. Kim and F.
Kang, Sci. Rep., 2012, 2, 913.
3. TDMA, Cefic - The European Chemical Industry
Council, 2010.
4. G. Bedinger, in US Geological Survey - Mineral
commodity summaries, 2013, pp. 172-173.
5. X. Chen and S. Mao, Chem. Rev., 2007, 107, 28912959.
6. M. Saito, Y. Nakano, M. Takagi, T. Maekawa, A.
Tasaka, M. Inaba, H. Takebayashi and Y. Shodai,
Key Eng. Mater., 2014, 582, 127-130.
7. Y. Zeng, W. Zhang, C. Xu, N. Xiao, Y. Huang, D. Y.
Yu, H. H. Hng and Q. Yan, Chem. Eur. J., 2012, 18,
4026-4030.
8. L. Chen, L. Shen, P. Nie, X. Zhang and H. Li,
Electrochim. Acta, 2012, 62, 408-415.
9. D. Dambournet, K. Chapman, P. Chupas, R. Gerald,
N. Penin, C. Labrugere, A. Demourgues, A. Tressaud
and K. Amine, J. Am. Chem. Soc., 2011, 133, 1324013243.
10. N. Louvain, Z. Karkar, M. El-Ghozzi, P. Bonnet, K.
Guerin and P. Willmann, J. Mater. Chem. A, 2014, 2,
15308-15315.
SCF Congress - 2015
Single-ion copolymers as electrolytes for Lithium-Metal
Batteries
Copolymères à blocs anioniques comme électrolytes solides pour les
Batteries au Lithium métallique
A. Ferrand*1, R. Bouchet2, S. Maria1, T.N.T. Phan1, D. Gigmes*1
1
Aix Marseille Université, CNRS, Institut de Chimie Radicalaire – UMR 7273, 13397
Marseille, Cedex 20, France
2
Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces (LEPMI)
UMR CNRS 5279, Grenoble Universités, 1130 rue de la piscine, 38402 St. Martin d’Hères,
France
* Corresponding author: [email protected], [email protected]
______________________________________________________________
Résumé : Des électrolytes solides sous forme de copolymères à blocs anioniques sont élaborées pour des batteries
au lithium métallique. Ces électrolytes ont pour objectif de supprimer, d’une part, le phénomène de croissance
dendritique, qui est le principal inconvénient de cette technologie, et d’autre part, améliorer les performances des
batteries en terme d’autonomie, de puissance, de durée de vie… Suite aux résultats prometteurs obtenus avec des
[1],[2]
copolymères à blocs à base de dérivés polystyrène anioniques et poly(oxyde d’éthylène) (POE),
nous avons
synthétisé de nouveaux copolymères à blocs à base de dérivés poly(méth)acrylate anioniques dans le but d’évaluer
leurs propriétés électrochimiques dans des dispositifs de type batterie au lithium-métal.
________________________________________________________________________
Summary: Solid electrolytes as anionic blocks copolymers are developed for lithium-metal batteries. These
electrolytes are designed to remove the dendritic growth phenomenon, which is the main drawback of this
technology, as well as to improve the electrochemical performances of the battery like the ionic conductivity, the
cyclability… Following the promising results obtained by block copolymers based of anionic polystyrene derivatives
[1],[2]
and poly(ethylene oxide) (PEO),
we have synthesized new block copolymers based of poly(meth)acrylate
derivatives to evaluate their electrochemical properties in lithium-metal batteries.
Keywords: Lithium-Metal Battery, Solid polymer electrolyte, Dendritic growth.
Alternative mode of transportation such as fully electric or hybrid vehicles are a matter of primary importance for a
sustainable long-term development. In line with this societal context, the elaboration of cheap and safe batteries with a
high specific energy suitable for the mass-market of electric vehicles is stimulating the scientific community since many
[3]
years. Among different battery technologies, Lithium-Metal Battery is very well positioned thanks to the high energy
density of lithium vs its weight and volume.
Le développement de modes de transport alternatifs comme les véhicules hybrides ou électriques est un enjeu majeur
dans le contexte actuel de développement durable. L’élaboration de batteries performantes, sures, économiquement
viables… stimule la communauté scientifique depuis plusieurs années. Parmi les différentes technologies de batteries,
[3]
celle basée sur une anode de lithium métallique est une des plus attractive grâce à la densité électrique du lithium très
élevée associée à un poids et un volume réduit.
1
Introduction
Dans le contexte actuel de diminution des
ressources fossiles et de préservation de
l’environnement, le développement de modes de
transport alternatifs répondant aux exigences de
technologies éco-compatibles est plus que
nécessaire. Dans cette optique, les véhicules
électriques s’inscrivent comme une des solutions
les plus crédibles. Toutefois, le stockage de
l’énergie électrochimique dans des batteries
performantes, fiables et à faible coût de revient
demeure un défi d’actualité. Parmi les différentes
technologies de batteries, celle basée sur une
anode de lithium métallique est une des plus
attractive grâce à une densité électrique du lithium
très élevée associée à un poids et un volume
[3]
réduits.
Cependant,
l’utilisation
de
cette
technologie n’est pas encore très répandue pour
des problèmes de sécurité qu’elle peut présenter
dans certaines conditions. En effet, lors de la
recharge, une électrodéposition irrégulière du
lithium à la surface de l’électrode métallique est
parfois observée. Ce phénomène conduit à la
formation de dendrites susceptibles de mettre la
batterie en court-circuit et conduire à une
destruction voire une explosion de celle-ci. Afin de
supprimer ce phénomène, de nombreux travaux
sont consacrés à l’élaboration d’électrolytes
polymères solides (EPS) combinant à la fois une
conductivité ionique élevée et des propriétés
mécaniques suffisantes pour empêcher la
croissance dendritique. Par exemple, nous avons
2
Méthodologies
Les copolymères sont synthétisés par
polymérisation radicalaire contrôlée par les
nitroxydes (NMP). D’une manière générale, nous
avons synthétisé les copolymères triblocs en 3
étapes, Fig1. La première étape consiste à
préparer un POE-diacrylate par estérification du
POE correspondant en présence de chlorure
d’acryloyle et de triéthylamine. La deuxième étape
consiste à faire réagir un POE-diacrylate dans une
réaction d’addition radicalaire intermoléculaire de
[4]
type 1,2 en présence de MAMA-SG1
pour
conduire
à
la
di-alkoxyamine
de
POE
correspondante. Enfin, dans une dernière étape, le
tribloc est obtenu par polymérisation du monomère
anionique, préparé au préalable, dans les
conditions de NMP à partir de la di-alcoxyamine de
POE.
Fig. 1. Synthèse du macroamorceur POE-di(MAMA-SG1)
Fig. 2. - (a) Evolution du ln [M]0/[M]t en fonction du temps et (b)
Evolution des masses molaires moyennes en nombre
théoriques, calculées par RMN 1H, en fonction de la conversion.
(a) ln[M]0/[M]t = f (t)
1,2
1
ln [M]0/[M]t
Toutefois, de nombreux efforts restent encore à
accomplir pour améliorer la puissance, l’autonomie,
la vitesse de charge ou encore la température de
fonctionnement de ces dispositifs. Dans ce
contexte, nos travaux consistent à concevoir et
préparer des copolymères triblocs basés sur des
blocs de POE, pour les propriétés de conductivité
ionique, associés à des blocs de type
poly(méth)acrylate anioniques pour apporter des
propriétés mécaniques appropriées au cahier des
charges de l’application visée.
Lors de la synthèse des copolymères à blocs,
effectuée en présence soit d’Acrylate poly(éthylène
glycol) ou de Styrène-trifluorométhanesulfonimide
comme co-monomères, les évolutions de la
conversion au cours du temps, ainsi que celle de la
masse molaire en fonction de la conversion sont
conformes avec un processus de polymérisation
[5],[6]
radicalaire contrôlée (Fig.2).
0,8
y = 0,0039x - 0,0892
R² = 0,9815
0,6
0,4
0,2
0
0
50
100
150
Temps (min)
200
250
300
(b) Mn th = f (conversion)
60000
50000
Mn (g.mol-1)
démontré le remarquable potentiel de copolymères
à blocs anioniques basés sur des dérivés de
polystyrène et de poly(oxyde d'éthylène) comme
EPS pour la technologie des batteries au lithium
[1],[2]
métallique.
y = 299,6x + 36880
R² = 0,945
40000
30000
20000
10000
0
10
20
30
Conversion
40
50
Au
cours
de
cette
présentation,
les
caractérisations des propriétés électrochimiques et
morphologiques des électrolytes seront également
discutées.
Etape 1
Etape 2
Etape 3
4
Conclusions
Une large gamme d’électrolytes solides, sous
forme de copolymères triblocs à base de POE, a
été synthétisée par NMP. Les processus de
polymérisation sont bien contrôlés et permettent
d’envisager
l’établissement
de
corrélations
composition/architecture/performances pertinentes
pour développer des EPS aux propriétés
optimisées.
Références
[1]
La caractérisation des matériaux s’effectue par
analyse RMN et SEC.
3
La synthèse de la macroalkoxyamine de POE
est caractérisée par RMN à chaque étape. Le taux
de couplage, des fonctions acrylates sur le POE,
1
calculé par RMN H, est quantitatif.
L’efficacité de l’addition radicalaire 1,2 de la
MAMA-SG1 sur le POE-diacrylate est confirmée en
1
RMN H par disparition des signaux correspondant
aux protons acrylates.
[2]
[3]
[4]
[5]
[6]
R.Bouchet, S.Maria, R.Meziane, A.Aboulaich, L.Lienafa, JP.Bonnet, T.N.T.Trang, D.Bertin, D.Gigmes, D.Devaux,
R.Denoyel, M.Armand. Nature Materials, 12 (2013) 452457.
R.Bouchet,
T.N.T.Trang,
E.Beaudoin,
D.Devaux,
P.Davidson, D.Bertin, R.Denoyel. Macromolecules, 47,
(2014) 2659-2665.
M.Armand, J-M.Tarascon. Nature, 451 (2008) 652-657.
D.Gigmes,
P-E.Dufils,
D.Glé,
D.Bertin,
C.Lefay,
Y.Guillaneuf. Polym. Chem., 2 (2011) 1624.
S.Brusseau,
J.Belleney,
S.Magnet,
L.Couvreur,
B.Charleux. Polymer Chemistry, 1, (2010) 720-729.
J.Nicolas, S.Brusseau, B.Charleux. J. Polym. Sci, 48,
(2010) 34-47.
SCF Congress - 2015
Stabilization of the electrode/electrolyte interface in new Liion battery negative electrodes based on silicon
Stabilisation de l’interface électrode/électrolyte avec de nouvelles
électrodes pour batteries lithium-ion à base de silicium
S. Sayah, F. Ghamouss, J. Santos-Peña, D. Lemordant, F. Tran Van
Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (PCM2E),
UFR Sciences et Techniques, 37200 Tours Parc de Grandmont
* [email protected]
______________________________________________________________
Résumé : Cette étude vise à comprendre le mécanisme de formation des couches de passivation
sur une nouvelle électrode négative pour batteries lithium-ion. Ce matériau est un composite comprenant
silicium, étain, aluminium, graphite et une matrice intermétallique. Du fait des changements de volume associés aux
réactions des trois premiers avec le lithium, la couche de passivation est instable. Dans cette communication nous
étudions l’impact de la formulation des électrolytes dans la stabilisation d’une interface solide/électrolyte stable. Dans un
premier temps l’utilisation de solvants inertes électrochimiquement est employée. Dans un deuxième temps l’ajout
d’additifs, qui forment la SEI, à des solvants classiques (mélanges d’alkylcarbonates linéaire ou cycliques) est proposé.
________________________________________________________________________
Summary: The goal of our study is to understand the formation of the passivation films on a new
lithium ion battery negative electrode. Such material is a composite consisting of silicon, tin, aluminum,
graphite and an intermetallic matrix. Due to the volume changes associated to the lithium alloying with the
three first species, the passivation film is unstable. In this communication we study the effect of the
electrolyte formulation in stabilizing the electrode/electrolyte interface. First, we propose the use of
electrochemically inactive solvents. Secondly, we study the addition of selected SEI-building species to
classic, reactive solvents (based on mixtures of linear or cyclic alkylcarbonates).
Keywords: Li-ion Batteries; silicon negative electrode; electrolytes; SEI building additives; ionic liquids
L’un des aspects essentiels dans le domaine
des batteries Li-ion est la compréhension des
interfaces
électrodes/électrolytes
lors
des
processus de charge/décharge. La bonne
cyclabilité des batteries n’est pas seulement le
reflet de la réversibilité des processus d’insertion
+
des ions Li dans les matériaux d’électrode positive
et négative mais est également liée aux interfaces.
Lors du fonctionnement d’une pile, des produits de
réduction de l’électrolyte sont formés sur l’électrode
négative, créant ce qu’on appelle une SEI (solid
electrolyte interface). Selon les matériaux
d’électrode et l’électrolyte, la SEI peut être plus ou
moins stable. D’ailleurs la SEI sera efficacement
passivante si elle est fortement isolante
8
électronique (sa résistivité est estimée à 4·10
2
W·cm [1]) et en même temps conductrice ionique.
La première caractéristique permet l’arrêt de la
décomposition électrochimique de l’électrolyte et la
+
deuxième permet le passage des ions Li en
provenant de l’électrolyte et allant vers l’électrode
pour assurer la réaction redox responsable de
l’utilisation du matériau dans la batterie.
Une couche de passivation instable implique
une consommation continue de l’électrolyte. Pour
certains matériaux d’électrode comme ceux à base
de silicium, il est connu que lors des cycles
d’expansion/contraction de volume, la surface du
matériau est exposée à l’électrolyte contribuant à
cette consommation. Le résultat final après cyclage
est une pénurie en électrolyte et une baisse de
l’efficacité coulombique qui conduit à une perte de
capacité de l’électrode au bout de quelques cycles.
Dans le cadre du projet NEWMASTE (ANR),
l’équipe du CNRS-ICMPE (Thiais) prépare une
électrode négative à la base d’un composite
Si0.32Ni0.14Sn0.17Al0.04C0.35 avec du carbone graphite
-1
[2]. Le matériau fournit 700 mAh·g pendant 300
cycles sous un régime de C/50 à 25°C. Le
composite contient des nanoparticules agrégées
incorporées dans une matrice nanostructurée
principalement constituée de l’intermétallique
Ni3Sn4. L’interface électrode/électrolyte de ce
matériau est donc sensible aux changements de
volume dus au silicium mais aussi à l’étain et à
l’aluminium. En tant que partenaires du projet
NEWMASTE, le PCM2E travail sur l’amélioration
de ces interfaces. Notre laboratoire propose de
nouvelles formulations d’électrolyte visant à
construire une couche stable et fine de passivation
sur l’électrode.
Cette communication présente les premiers
résultats obtenus avec des électrolytes à la base de
LiTFSI comme sel de lithium et différents solvants.
Parmi ces derniers, nous avons choisi quelques
solvants ayant une stabilité électrochimique dans la
fenêtre de potentiel de travail de l’électrode
négative (0.0-2.0V). Dans ce contexte, le
tétrahydrofurane (THF) et le dimethoxyéthane
(DME) ont été appliqués dans la préparation des
électrolytes.
L’utilisation
de
ces
solvants
impliquerait la formation d’une SEI fine par
réduction de l’anion du sel. Une autre famille de
composés intéressants est celle des liquides
+
ioniques contenant un cation pyrrolidium (Pyr14 ,
+
+
Pyr13 …) ou tétraalkylammonium (N1114 ) ainsi qu’un
anion
délocalisé
comme
le
bis
(trifluoromethylsufonyl)imide (TFSI , FSI ). Ceux-ci
sont très stables et le seul processus générant une
couche serait la réduction du cation à de très bas
potentiels.
Une autre solution pour optimiser la couche de
passivation est l’ajout d’additifs aux solvants
traditionnels
basés
sur
des
mélanges
d’alkylcarbonates. Par exemple, on suppose que
l’ajout d’espèces comme le vinylène carbonate
(VC) à l'électrolyte, qui a un effet positif sur la SEI
formée sur le graphite (une électrode traditionnelle
dans les batteries à ions lithium), devrait être aussi
une alternative intéressante pour améliorer
l’interface du système à base de silicium. L’idée est
de copolymériser des additifs pour modifier les
propriétés conductrices, mécaniques et de
couverture des couches.
Les solutions électrolytiques contiennent LiTFSI
dans une concentration 1M. Les propriétés
physicochimiques (conductivité, densité, viscosité)
de ces solutions ont été étudiées. Leurs impacts
sur la performance électrochimique du composite
de NEWMASTE ont été analysés par différents
mesures
électrochimiques
(galvanostatiques,
voltammetries
cycliques,
spectroscopie
d’impédance électrochimique).
A titre d’exemple on présente avec la Figure 1 la
variation de conductivité du système LiTFSI 1M
dans solvants DME, THF, propylène carbonate
(PC) et diméthylcarbonate (DMC). La conductivité
jouera un rôle dans la réponse des systèmes sujets
à des fortes sollicitations (dans notre cas, aux
régimes dépassant C/5, c’est à dire, 5 heures pour
le passage d’une mole de lithium par mole de
composite).
Cette première étude montre bien l’impact positif
de l’utilisation du THF comme solvant dans la
formulation de l’électrolyte. En effet, d’après la
Figure 2, cette formulation conduit à des fortes
retentions de la capacité à régimes rapides tel que
-1
-1
2C (600 mAh·g ) et pouvant récupérer 200 mAh·g
en retournant à un régime de C/20. Ceci fait du
THF un solvant prometteur et même un co-solvant
intéressant en le rajoutant à EC, une espèce
créatrice d’une SEI stable. Les différents interfaces
crées avec ou sans l’EC ont d’ailleurs été
confirmées
par
mesures
d’impédance
électrochimique.
Fig. 1. Variation de la conductivité des électrolytes formulés
dans cette communication avec la température.
Fig. 2. Variation de la capacité en lithiation des demi-cellules
Li/composite en fonction de différents régimes de cyclage et du
nombre des cycles (T=25°C).
Ces resultats confirment la pertinence de notre
étude des interfaces électrode/électrolyte, sachant
que, à haut régime, le matériau composite
développe de capacités inférieures dans un
éléctrolyte traditionnal LiPF6 1M (EC,DMC,PC),
Acknowledgements
Les auteurs remercient l’ANR pour la
concession du contrat NEWMASTE, le ICMPE pour
la préparation des matériaux d’électrode et la SAFT
pour la confection des électrodes.
References
[1]
[2]
M. Park, X. Zhang, M. Cheung, G.B. Less, A.M. Sastry, J.
Power Sourc. 195 (2010) 7904
Z.Edfouf, F. Cuevas, M. Latroche, C.Georges, C. Jordy, T.
Hézèque, G. Caillon, J.C. Jumas, M.T. Sougrati, J. Power
Sourc. 196 (10) (2011) 4762.
SCF Congress - 2015
Radiolysis as a solution for accelerated ageing studies of
electrolytes in Lithium-ion-batteries
D. Ortiz1, S. Legand2, J.P. Baltaze,3 J-F Martin,4 J. Belloni,5 M. Mostafavi,5
and S. Le Caër1.
1
Institut Rayonnement Matière de Saclay, NIMBE, UMR 3685 CNRS/CEA, LIONS, Bâtiment
546 91191 Gif-sur-Yvette Cedex, France.
2
CEA/Saclay, DEN/DANS/DPC/SECR/LRMO 91191, Gif-sur-Yvette Cedex, France.
3
Laboratoire de Chimie-Physique, UMR 8000 CNRS Université Paris Sud, Faculté des
Sciences, Bâtiment 349, 91405 Orsay Cedex, France.
4
CEA/LITEN/DEHT/SCGE, Grenoble, France.
5
Laboratoire de Chimie-Physique/ELYSE, UMR 8000 CNRS Université Paris Sud 11, Faculté
des Sciences, 91405 Orsay Cedex, France.
* [email protected], [email protected]
________________________________________________________________________
Summary:
The ageing phenomena occurring in electrolytes are studied using radiolysis as a tool to generate the same species as
the ones in electrolysis. This approach entails indeed important benefits: (i) the time to degradate the electrolyte is
shortened as compared to electrolysis studies (hours instead of weeks or months), (ii) both short-time (ps-μs) and longtime (minutes-days) processes can be studied, offering then an understanding on multiple temporal scales and (iii) the
possibility to study each solvent with/without the salt to understand its reactivity, which is not necessarily possible in a
real battery approach. The reaction mechanisms accounting for the degradation of electrolytes can then be proposed.
Finally, in order to demonstrate the utility of the approach, the radiolytic results are compared with classical
charge/discharge experiments. This comparison illustrates the interest of the radiolysis approach.
Keywords: alkyl carbonates, Lithium-ion battery, degradation products, reaction mechanisms, picosecond pulse
radiolysis, mass spectrometry.
In order to improve electronic storage devices, it is critical to find the more robust electrolyte. The slow degradation of the
electrolyte represents a barrier to its safe use. We show that radiolysis can mimic the effects of electrolysis. It can
therefore be used to screen rapidly a large number of electrolyte systems.
1
Introduction
The rechargeable Li-ion battery (LIB) technology is
dominating the electronic market. It is an essential
component in portable electronic applications. In this
context, the ageing process is a growing concern [1].
Many efforts have been devoted to improve the stability
of electrolytes, which can be a serious problem
particularly in large-scale LIBs such as electric vehicles.
Over the last years, a large number of studies have been
devoted to the identification of decomposition products
[2]. These studies are typically based on classical
“charge/discharge” experiments and they need weeks or
months to prepare a sample. As a result, ageing studies
can be lengthy, costly and usually remain purely
qualitative.
We present here results obtained on diethylcarbonate
(DEC, C2H5OCOOC2H5), a solvent usually used in
-3
mixtures in LIB with/without LiPF6 (1 mol.dm ). At shorttime scale, picosecond pulse radiolysis experiments were
performed in order to explore the primary radiation
effects on alkyl carbonate/LiPF6 systems. Then, the longtime decomposition products were analyzed both in the
gas and liquid phase. To this end, a wide variety of
analytical techniques have been used [3].
In order to demonstrate the usefulness of this
method, we have carried out a similar set of experiments
in a real cell with DEC/LiPF6 1 M.
2
In order to identify stable degradation products,
137
irradiation was performed using a Gammacell ( Cs) or a
linear electron accelerator (10 ns electrons of 10 MeV
energy).
The ultrafast kinetics of the solutions was accessed
by picosecond pulse radiolysis with the laser driven
electron accelerator ELYSE. A detailed set-up
configuration is described elsewhere [4].
The gas phase was analyzed and quantified by Gas
Chromatography-Electron Impact-Mass spectrometry
(GC-EI-MS) whereas a combination of Electrospray-High
Resolution Mass Spectrometry (ESI-HRMS) with both Ion
Mobility Spectroscopy (IMS), Infrared Multi-Photon
19
31
Dissociation (IRMPD) spectroscopy and F and P
Nuclear Magnetic Resonance (NMR) experiments have
been used to characterize the products formed in the
liquid phase.
3
can form directly small molecules and also lead to
different homolytic bond cleavages.
Pulse radiolysis experiments give information on the
reactivity of the electron which is detected at 1100 nm
(Figure 2). The electron decay becomes faster when the
LiPF6 concentration increases (Figure 2).
At long time-scales, the gas phase decomposition
products formed upon irradiation are presented in Figure
1. Different types of molecules are produced under
irradiation: alkanes, alkenes and alkynes (for example
C2H6, C2H4 and C2H2); oxygenated molecules (aldehyde;
ether; carboxylic acid). Moreover, fluorinated molecules
such as C2H5F are also formed. HF is indirectly detected
by the presence of SiF4 which is the result of the
interaction between HF and SiO2, present in the walls of
the pyrex glass ampoule [5].
Fig. 1. Gas decomposition products of DEC/LiPF6 1M measured
by GC-EI/MS after a 20 kGy irradiation
The liquid phase is much more complex to analyze
and different techniques were needed. Mass
spectrometry results point out the formation of three
different families of decomposition products: (i) linear
lengthening of the alkyl carbon chain of DEC, (ii)
compounds with a C2H5-O-CO-O-CnH2n-CO-C2H5 type
structure and (iii) branching in the alkyl chain such as
C2H5-O-CO-O-CH(CH3)-CH3. It was also possible to
identify fluorinated and molecules with a phosphorus
atom such as POF(OEt)2 or (F)2(OCO2C2H5)P=O. The
19
presence of these species was also confirmed by F and
31
P NMR experiments.
Picosecond pulse radiolysis experiments provide
important information concerning the mechanism
pathways. Upon irradiation, DEC reacts according to
reaction (a):
+· (a) DECvvv  DEC*, DEC , e
+·
Previous results [6] indicate that DEC and the
electron will recombine very fast, underlying the
*
importance of the excited state of DEC in the reactivity. It
Fig. 2. Kinetics of the electron decay at 1100 nm in neat DEC
(black) and in DEC/LiPF6 with increasing LiPF6 concentration.
+
The solvated electron does not react with Li ions
+
because of the lower redox potential of the Li /Li couple
as compared to the redox potential implying the solvated
electron. This means that the solvated electron reacts
with the PF6 anion as written below (b).
-·
(b) e sol + PF6  F + PF5
+
The PF6 anion can also react with DEC (c):
·
+·
(c) DEC + PF6  F + PF5
The decomposition products observed both in the gas
and in the liquid phase are then mainly attributed to the
intermediates arising from the excited state of DEC* and
to the reactive species coming from (b) and (c) reactions
(the fluoride anion and, of course, the fluorine atom). The
fluorine atom will then react forming different POFR1R2
species (R = F, OH, OC2H5), and, at the end, oligomer as
evidenced by NMR experiments.
The decomposition products produced by electrolysis
in the DEC/LiPF6 1 M cell were also analyzed. It is
important to point out that products detected both in the
liquid and in the gas phase are consistent with those
evidenced in the radiolysis experiments, highlighting the
interest of the present approach
4
Conclusions
Radiolysis can be used to generate stable
degradation products of neat linear alkyl carbonates that
can be compared to those formed in “real” Lithium-ion
batteries. It is a useful tool to screen new potential
electrolytes in order to explore their properties in a very
fast and efficient way.
Acknowledgements
The authors want to thank DSM-Energie under
project “Age” for financial support.
References
[1]
[2]
[3]
[4]
[5]
[6]
Xu, K. Chem. Rev. 2004, 104 (10), 4303-4417
Gireaud, L. et al. Anal. Chem. 2006 78, 3688-3698
Ortiz, D. et al submitted.
Schmidhammer, U., et al. Rad. Phys.Chem.2012, 1, 1715.
Lux, S. F. et al. Electrochem. Comm. 2012 14, 47-50.
Torche, et al. J. Phys. Chem. A 2013, 117, 10801-10810.
SCF Congress - 2015
Ink-jet printing NiO for efficient p-type and tandem DSSC.
Impression par voie jet d’encre du NiO pour des cellules solaires à
colorant de type p et tandem.
R. Brisse1,*, R. Faddoul1, N. Kaeffer2, S. Palacin1, V. Artero2, B. Geffroy1,
T. Berthelot1, T. Gustavsson3 and B. Jousselme1.
1
CEA Saclay, IRAMIS/DSM/NIMBE/LICSEN, 91191 Gif-Sur Yvette.
2
Laboratoire de Chimie et Biologie des Métaux (UMR 5249 CEA – CNRS – Université
Grenoble Alpes), Grenoble, France.
3
CEA Saclay, IRAMIS/LIDYL/LPP, URA 2453 91191 Gif-sur-Yvette
______________________________________________________________
Résumé: Dans ce travail, une nouvelle voie de synthèse de NiO, par impression jet d’encre d’une encre à base de
NiCl2, est présentée. Le NiO a été sensibilisé avec succès par un nouveau colorant organique push-pull. Les photocathodes ainsi synthétisées ont alors été incorporées dans des cellules solaires à colorant de type p, en vue d’une
application en cellule tandem, mais également en photo-production d’hydrogène. Les premiers résultats montrent
que le dépôt par voie jet d’encre de NiO est une nouvelle alternative viable. L’ensemble des possibilités de contrôle
qu’offre cette technique la rend prometteuse.
________________________________________________________________________
Summary: In this work, ink-jet printing NiO, with a NiCl2 based ink is presented. NiO was successfully sensitized with
a new push-pull organic dye. The as fabricated photocathodes were incorporated into p-type Dye Sensitized Solar
Cells (p-DSSCs), the final goal being their use into tandem DSSCs and also into hydrogen photo-production devices.
The first results show that ink-jet printing NiO is a new viable way of deposition. Due to high degree of tunability, inkjet printing NiO is promising.
Keywords: Ink-jet printing, Photovoltaic, DSSC, NiO, push-pull systems, solvatochromism.
Introduction
Over the last twenty years, through the study of ntype Dye Sensitized Solar Cells (n-DSSCs) [1],
photosensitization of n-type semiconducting oxides
(like TiO2) with dye compounds (metal-organic or
purely organic) has been widely investigated. This
type of solar cell is a mix between organic and
inorganic: a TiO2 dye sensitized photo-anode and a
platinum cathode, sandwiching an iodine based
electrolyte. With PCE yields reaching 13% [2], nDSSCs represent a promising, low cost, alternative
to traditional silicon solar cells. On the other hand,
p-type DSSCs, based on a p-type semiconducting
oxide (like NiO) have not met such a success.
Indeed, their PCE yield is low: the record is 1.3 %
[3]. NiO low capability to collect charges compared
to TiO2, is often emphasized as an important
inefficiency factor. Then, charges recombinations
are important in p-DSSCs and, photo-generated
currents are lower than for their n-type equivalent.
However, p-DSSCs desserve further studies. In
fact, they can be implemented into tandem devices
or into PEC hydrogen production cells. Tandem
structures combine a TiO2 photo-anode and a NiO
photo-cathode. They have caught researchers’
eyes as they have a theoretical efficiency which is
higher than “classical” DSSCs [4]. However, due to
NiO, PCE yields of such solar cells are still low (2%
maximum [5]).
Some have tried to replace NiO but no
breakthrough has been done in that direction [6].
Employing a push-pull type dye, in order to
increase charge separation at the surface of NiO
has been a first solution to challenge the charge
recombination issue and gave substantial
enhancement of the PCE yields [7]. Recently, a
more crystalline, transparent and nano-structured
NiO was depicted to give higher photocurrents [8].
In the present work, the deposition of
NiO through ink-jet printing was
investigated. Controlled, transparent
and crystalline NiO micrometer films
could be obtained. A new push-pull
system (so called RBG174) was also
synthesized, so as to sensitize the
ink-jet printed NiO and to test
the properties of the as
Fig. 1. An example
of ink-jet printed
deposited oxide into p-DSSCs
NiO film, sensitized
device.
with RBG174
Fig. 2. The new push-pull dye
synthesized : RBG174.
RBG174 is shown in
fig.2.
Triphenylamine, the
donor
group
is
covalently linked to
an acceptor group,
a
naphtalimide
derivate, thanks to a bithiophene bridge. Then, two
carboxylic acids ensure grafting of the dye, via the
triphenylamine moiety, onto the NiO surface.
NiO was deposited onto a FTO substrate by an inkjet printing method. The NiO precursor was a NiCl2
salt. A Dimatix printer (DMP 2800 series) was used
for the deposition of one to four layers of
mesoporous NiO. Efficient dying of the NiO
mesoporous film was performed and optimized by
immersion of the film into a saturated RBG174
solution in methanol, during one hour and in the
dark. P-type DSSCs were finally fabricated as
described in literature [3] and their photovoltaic
performances
were
tested:
current-voltage
measurements were performed under the
illumination of a simulated AM 1.5G solar light (100
-2
mW.cm ) connected to a computer-controlled
Keithley 2635 source measurement.
Steady-state absorption and emission spectra were
recorded
with
a
double-beam
UV-visible
spectrophotometer (Perkin Elmer lambda 900) and
a spectrofluorimeter (SPEX Fluorolog 3, Horiba
Jobin Yvon) in 1 cm optical path cells.
Fluorescence spectra over the whole UV-visible
spectral region were recorded with excitation at 425
nm. RBG174 was studied into three different
solvents:
MeOH,
acetonitrile
and
toluene
(spectrophotometric grade, Aldrich).
Electrochemical and photo-physical properties
of RBG174
Photo-physical and electrochemical properties of
RBG174 were assessed. The compound has two
reversible oxidation peaks, and one reversible
reduction wave. They were respectively attributed
to the donor and the acceptor moieties. The dye’s
HOMO is below the NiO
valence band. Injection
of a hole from the dye,
to
NiO
is
then
thermodynamically
favorable. The molar
extinction
coefficient
was also determined to
-1
-1.
be 11 000 mol .cm L.
Fig. 3. Normalized absorption
and fluorescence spectra in
various solvents (toluene,
acetonitrile, methanol).
RBG174
has
two
absorption
bands
around 370 and 430
nm (see fig.3). The
λA,max λF,max ΔνA,F
Solvent
(nm)
(nm)
(nm)
low energy band
Methanol
446
688
242
was
red-shifted
Acetonitrile 432
624
192
when the solvent
Toluene
429
571
142
polarity
was
increased
(see
Table
Table
1
Absorption
and
1). Upon excitation of
emission band maxima (λA,max,
λF,max) for the charge transfer
this
band
was
band, Stokes shift (ΔνA,F) in
strongly dependent
various solvents.
on solvent polarity.
Actually, in polar solvents, fluorescence is not
intense and strongly shifted to high wavelengths. In
apolar toluene solvent, fluorescence is intense and
happens at lower wavelengths. This solvatochromic
behavior points out a photo-induced intra-molecular
charge transfer and confirms the push-pull nature of
RBG174.
Photovoltaic performances of ink-jet printed
NiO dyed with RBG174
Ink-jet printed NiO was implemented into p-DSSCs
with RBG174 as the sensitizer. For one layer
deposited by ink-jet printing, the PCE yield was
0.059 % (see fig.4), a value which is comparable
Fig. 4. Current density-voltage characteristic for a 1 layer
of NiO inkjet printed, RBG174 sensitized p-DSSC.
with those found in recent literature [9]. For thicker
films (2 to 4 layers ink-jet printed), no photocurrent
rise was observed (cf. table 2), we attributed this
phenomenon to the low hole conductivity of NiO.
Number of
layers
PCE (%)
Jsc (mA.cm-1)
VOC (mV)
Fill Factor (%)
1
2
3
4
0.059
1.428
111
36.96
0.046
1.122
111
37.18
0.040
1.030
103
37.23
0.040
0.969
111
37.64
Table 2 – Summary of the photovoltaic properties for
various number of NiO layers deposited
The results presented here showed that ink-jet
printed NiO films are adapted to incorporation into
p-DSSC. Eventually, the high degree of tunability
and control for this deposition technique is very
promising for future improvements of NiO .
Acknowledgements
This work was supported by the FCH Joint Undertaking
(ArtipHyction Project, Grant Agreement n.303435) and the CEA
DSM Energy program.
References
[1] B. O’Regan, M. Grätzel, Nature 353 (1991) 737–740.
[2] S. Mathew et al., Nat. Chem. 6 (2014) 242–247.
[3] S. Powar et al., Angew. Chem. Int. Ed. 52 (2013) 602–605
[4] J. He, H. Lindström, A. Hagfeldt, S.-E. Lindquist, Solar
Energy Materials and Solar Cells 62 (2000) 265–273.
[5] A. Nattestade et al., Nat. Mater. (2010) 9, 31–35.
[6] M. Yu, G. Natu, Z. Ji, Y. Wu, J. Phys. Chem. Lett. 3 (2012)
1074–1078.
[7] M. Weidelener et al., J. Mater. Chem. 22 (2012) 7366–7379.
[8] S. Powar et al., Energy Environ. Sci. 5 (2012) 8896–8900.
[9] C. J. Wood, K.C.D. Robson, P.I.P. Elliott, C.P. Berlinguette,
E. A. Gibson, RSC Adv. 4 (2014) 5782–5791.
SCF Congress - 2015
Toward the III-V/Si high-efficiency tandem solar cell
Vers les cellules solaires à haut rendement à base de composés III-V
sur substrats bas-couts de silicium
S. Almosni1, M. Da Silva1, C. Cornet1, A. Létoublon1, C. Levallois1, A.
Rolland1, J. Even1, L. Pédesseau1, S. Loualiche1, P. Rale2, L. Lombez2 and J.F. Guillemoles2,3, F. Mandorlo4, M. Lemiti4, and O. Durand1,*
1
UMR FOTON, CNRS, INSA de Rennes, F-35708 Rennes, France
2
Institut de Recherche et Développement sur l'Energie Photovoltaïque (IRDEP), UMR 7174 CNRS-EDF-ENSCP, EDF R&D, 6 quai Watier, 78401 Chatou Cedex, France
3
NextPV, LIA CNRS-RCAST/U. Tokyo-U. Bordeaux, 4-6-1 Komaba, Meguro-ku, Tokyo 1538904, Japan
4
University of Lyon, Lyon Institute of Nanotechnology (INL) UMR CNRS 5270, INSA de Lyon,
Villeurbanne
______________________________________________________________
Résumé :
GaAsPN est un matériau très prometteur pour l’élaboration de cellules solaires double-jonctions sur substrat
monocristallin de silicium, bas-coût. Nous passons en revue les différentes étapes technologiques que nous avons
développées, dans l’optique d’élaborer ce type de cellule solaire des cellule solaire à haute efficacité sur substrat de
silicium
________________________________________________________________________
Summary:
GaAsPN is a promising material for development of tandem solar cells on low-cost silicon substrates. We review our
studies of the different building blocks toward the development of high efficiency tandem solar cell on silicon.
Keywords: Tandem solar cell, III-V compound on Si substrates, Molecular Beam Epitaxy, dilute-nitrides. Latticematched coherent growth.
The PV cells efficiency is one of the most important parameters for the final cost of electricity, since it impacts the ratio
between produced energy and production cost. With 22% efficiency modules based on c-Si, the technology reaches its
limits. Our aim is to provide low-cost and high-efficiency tandem solar cells (association of two different absorbing layers
in the same cell) grown on c-Si substrates, developed with both Si and III-V materials which displays high light
absorbance.
1
Introduction
To date, the highest efficiency conversions have
been reached by using III-V monocrystalline
multijunction solar cell (MJSC) under concentrated
sunlight. SOITEC and Fraunhofer Institute have
pushed solar cell record to 44.7% for terrestrial
applications [1], with a wafer bonded four-junction
GaInP/GaAs//GaInAsP/GaInAs solar cell under
concentration of 297 suns, and announced very
recently a 46% efficiency under concentration of
508 suns, in the SOITEC website. Moreover, a III-V
triple junction coherently grown (lattice-matched)
onto GaAs substrate has been performed by Solar
Junction. This solar cell has shown a 44 %
efficiency under 942 suns (AM1.5D spectra)
(description of the Solar cell structure: Derkacs et
al. 2012) [2], and contains a highly rewarded 1 eV
GaInAsNSb diluted-nitride junction. However,
maintaining the GaAs, or Ge, substrates to build
these high efficiency III-V solar cells, undoubtedly
incurs a substantial cost associated with such
substrates. To realize the strategic challenge of
cost of 0.25-0.5 Euro/Wp, we have chosen to use
the abundantly available on earth, and therefore
low cost, silicon material as a substrate. Indeed, a
true monolithic integration of the III-V compound
semiconductor heterostructures with silicon is
receiving great interest since it will enable
simultaneous both high efficiency and low cost
production.
2
Methodology
A tandem solar cell, made of a 1.7 eV III-V top
and a 1.1 eV c-Si bottom cell, would theoretically
reach an efficiency of 37%, under an AM 1.5G [3].
However, efficiency of MJSC is very sensitive to the
structural defects such as misfit dislocations,
appearing during metamorphic growth, since they
dramatically reduce the carrier lifetime, and thus the
current extraction, and therefore reduction of the
solar cell performance. Therefore, combination of
both the III-V and Si technologies through a perfect
lattice-matched epitaxial PV structure on silicon
substrate, would allow increasing significantly the
efficiency, as well as reducing the overall cost of
the PV multi-junction cell.
100
IQE (%)
80
2
0
-2
-4
-1,0
-0,5
0,0
Bias (V)
0,5
1,0
Fig. 2. J-V under AM1.5G solar spectrum, of a GaP/GaAsPN
300 nm/GaP PIN junction grown on GaP(001) substrate
4
Conclusions
A clear pathway to higher efficiency of the top
GaAsPN cell would require a thorough optimization
of both the MBE growth and the post-growth
annealing step, accompanied by a PIN junction
architecture improvement, similarly to the
development of the GaInAsN 1eV subcell on GaAs
substrates [2]. These results are promising and
validate our approach for the elaboration of a
lattice-matched dual junction solar cell on silicon
substrate. The TJ and, hence, the overall tandem
cell with a purposely designed bottom Si subcell, is
currently under development.
Acknowledgements
This research was supported by “Région
Bretagne” through the PONANT project including
FEDER funds and by the French national project
MENHIRS (2011-PRGE-007-01)
60
40
20
0
Current density (mA/cm²)
3
The tandem GaAsPN/Si double-junction solar
cell will be electrically connected with a tunnel
junction (TJ) and one of the main issues for the
dual junction solar cell development is obtaining an
efficient TJ. Modeling of which has shown high
theoretical current densities for both GaP(n+)/Si(p+)
and Si(n+)/Si(p+) TJ with doping levels
experimentally attained in the GaP alloy, and
considering a n-doped Si bottom absorber [4].
Considering
the
top-PIN-junction
GaAsPN
absorber, tight binding calculation crossed with
critical thickness modeling pointed out that a
GaAsPN alloy with a composition 9% of As and 4%
of N is interesting due to its expected bandgap
energy (1.81 eV) and its critical thickness which
allow the pseudomorphic growth of a 1 µm-thick
absorber [5]. Therefore, to get an assessment of
the material quality, independently of defects
potentially generated at the GaP/Si interface, a 100
nm-thick GaAsPN alloy has been grown latticematched on a GaP(001) substrate. After a postgrowth annealing step, this alloy displays a strong
absorption around 1.8-1.9 eV, and efficient
photoluminescence at room temperature suitable
for the targeted solar cell top junction development.
References
1.5
2.0
2.5
3.0
Energy (eV)
3.5
4.0
[1]
Fig. 1. Internal quantum efficiency of a GaP/ GaAsPN 1µm /GaP
PIN junction grown on GaP(001) substrate
Early stage GaP/GaAsPN/GaP PIN solar cell
prototypes have been elaborated by MBE on a GaP
(001) substrate, prior to the elaboration on a
GaP/Si(001) pseudo-substrate [6]. The quantum
efficiency (IQE around 40%) shows that carriers
have been extracted from a 1 µm-thick GaAsPN
alloy absorber (fig.1). I-V measurements performed
on this sample shows a remarkable open-circuit
voltage record at 1.18V. Our best cell was obtained
using a 300nm-thick absorber with 2.25% efficiency
under AM1.5G (fig.2). This cell exhibits a
remarkable Fill Factor of 71%, and short-circuit
current of 3.77 mA/cm² but relatively low Voc
(0.89V). Assuming that a 1 µm thick GaAsPN layer
is necessary to absorb the main part of the solar
spectrum and considering the absence of any antireflective coating, this last results is promising.
[2]
[3]
[4]
[5]
[6]
F. Dimroth, M. Grave, P. Beutel, U. Fiedeler, C. Karcher, T.
N. D. Tibbits, E. Oliva, G. Siefer, M. Schachtner, A.
Wekkeli, A. W. Bett, R. Krause, M. Piccin, N. Blanc, C.
Drazek, E. Guiot, B. Ghyselen, T Salvetat, A. Tauzin, T.
Signamarcheix, A. Dobrich, T. Hannappel and K.
Schwarzburg, Prog. Photovolt: Res. Appl. 22, 277–282,
2014.
D. Derkacs, R. Jones-Albertus, F. Suarez, O. Fidaner, J.
Photon. Energy 2, 021805, 2012.
S.R. Kurtz, P. Faine, J.M. Olson ,"Modeling of two-junction,
series-connected tandem solar cells using top-cell
thickness as an adjustable parameter". J. Appl. Phys. 68,
1890, 1990.
Alain Rolland, Laurent Pedesseau, Jacky Even, Samy
Almosni, Cedric Robert, Charles Cornet, Jean Marc Jancu,
Jamal Benhlal, Olivier Durand, Alain Le Corre, Pierre Rale,
Laurent Lombez, Jean-Francois Guillemoles, Eric Tea,
Sana Laribi, Opt Quant Electron 46, 2014.
S. Almosni, C. Robert, T. Nguyen Thanh, C. Cornet, A.
Létoublon, T. Quinci, C. Levallois, M. Perrin, J. Kuyyalil, L.
Pedesseau, A. Balocchi, P. Barate, J. Even, J. M. Jancu, N.
Bertru, X. Marie, O. Durand, and A. Le Corre, J. Appl.
Phys. 113, 123509, 2013.
O. Durand, S. Almosni, Y. Ping Wang, C. Cornet, A.
Létoublon, C. Robert, C. Levallois, L. Pedesseau, A.
Rolland, J. Even, J.M. Jancu, N. Bertru, A. Le Corre, F.
Mandorlo, M. Lemiti, P. Rale, L. Lombez, J.-F. Guillemoles,
S. Laribi, A. Ponchet, J. Stodolna. “Monolithic integration of
diluted-nitride III-V-N compounds on silicon substrates:
toward the III-V/Si Concentrated Photovoltaics”, Energy
Harvesting and Systems. Special Issue Article. ISSN
(Online) 2329-8766, ISSN (Print) 2329-8774, 2014.
SCF Congress - 2015
Study of hybrid heterojunction solar cells containing
CH3NH3PbI3 and ZnO compounds
Etude de cellules solaires hybrides constituées de pérovskite en
interface avec du ZnO
W. Hadouchi1,*, J. Rousset2, B. Geoffroy3, D. Tondelier1, D. Lincot2, Y.
Bonnassieux1
1
LPICM, Ecole Polytechnique, CNRS UMR-7647, 91128 Palaiseau
2
IRDEP,EDF , 78400 Chatou
LICSEN, NIMBE UMR 3685, CEA Saclay, 91191 Gif sur Yvette
3
______________________________________________________________
Résumé : texte en français
Récemment une nouvelle génération de cellules solaires a vu le jour : les cellules solaires à base de pérovskite.
Ces cellules solaires hybrides à base d’un tri-halogénure organométallique, une pérovskite de type CH3NH3PbI3
déposée sur du TiO2 nanostructuré, ont atteint des rendements records qui atteignent environ 20% [1]. Grâce la forte
absorbance de ces matériaux et à leur caractéristique ambipolaire, ainsi qu’à la facilité de fabrication de ces cellules,
cela ouvre une nouvelle voie vers des cellules à coût faible et à hauts rendements.
Dans ce travail, nous avons étudié le remplacement du TiO2 par le ZnO dont la mobilité des électrons est plus
élevée. Les effets de l’utilisation de ZnO en tant que couche bloqueuse de trous a été étudié dans les cellules à base de
pérovskite dans une architecture plane et nanostructurée. La couche compacte de ZnO dont le rôle est de collecter les
trous est déposée par sputtering ou par électrochimie sur un substrat de verre recouvert de SnO2:F. Dans l’architecture
nanostructurée une couche de ZnO nanoporeux est déposée sur la couche compacte de ZnO par voie électrochimique.
________________________________________________________________________
Summary: text in english
Recently has emerged a new solar cells class: perovskite solar cells. Solid-state hybrid solar cells based on
organometal trihalide CH3NH3PbI3 perovskite absorbers deposited on TiO2 nanostructured achieved record efficient
about of 20 % [1]. Thanks to the high absorbance of the perovskite material, its capacity to act as hole conductor, and to
the ease of their fabrication, this new type of cells open a way to a low-cost and high efficiency solar cells.
In this work we studied the deposition of CH3NH3PbI3 on zinc oxide substrate which has higher electron mobility than
that of TiO2. The effects of ZnO-blocking layer (BL) in perovskite solar cells were investigated in planar and
nanostructured heterojunction. The BL is generated through sputtering or electrochemical deposition onto fluorine tin
oxide (FTO). For the nanostructured architecture a nanoporous ZnO is deposited on a ZnO-BL by electrochemistry.
Keywords: Solar cells, perovskite, Zinc Oxyde
Perovskite solar cells have many advantages that could facilitate their development principally thanks to their ease of
manufacture. They could play a crucial role in the future of solar power. In fact, these new devices can be fully fabricated
without the need for high temperature annealing steps so costs of processing and infrastructure required for manufacture
are considerably reduced compared to other types of solar cells.
These constitute a serious alternative to silicon-based cells. It would also be possible to build a hybrid silicon or CIGS
panel / perovskite. Finally, thanks to their ability to get different colors, they could be installed on various surfaces.
However, several issues must still resolved before the possibility to commercialize these cells. First, stability needs to be
improved during production because the performances of perovskite cells produced in same conditions can vary. In
addition, the best performances were obtained by associating a toxic material, lead which could be a barrier to
marketing. So the safety of the cells remains problematic.
Les cellules solaires pérovskite ont de nombreux avantages qui pourraient faciliter leur développement. L’un de ces
avantages est leur facilité de fabrication. Elles pourraient jouer un rôle crucial dans le future de l’énergie solaire. En effet,
ce nouveau genre de cellules pouvant être entièrement fabriquées sans passer par des étapes de recuit à haute
température, cela permettrait de réduire considérablement les coûts de leur production en comparaison aux autres types
de cellules solaires.
Cependant, elles présentent quelques problèmes qui doivent être résolus avant de pouvoir les commercialiser. Tout
d’abord, la stabilité doit être améliorée durant l’étape de production puisque les performances des cellules produites
dans les mêmes conditions peuvent varier. De plus, les meilleures performances ont été obtenues par association de
plomb dans la pérovskite qui est un matériau toxique ce qui fait barrière à la commercialisation. La sureté de ces cellules
reste encore problématique.
Introduction
Les cellules solaires pérovskite ont connus une
évolution remarquable durant ces deux dernières
années notamment avec l’utilisation de TiO2
comme substrat.
L’étude présentée a pour but de remplacer le TiO2
par du ZnO que ce soit dans une architecture plane
ou nanostructurée. La couche bloqueuse de trous
(BL) est une couche compacte de ZnO déposée
par sputtering ou électrochimie et la couche
nanoporeuse est déposée par électrochimie.
2
Dark
Light
8
4
0
-4
-8
-12
-0,2
Sur un substrat transparent conducteur (SnO2 :F),
une couche compacte de ZnO de 100 nm est
déposée
par
sputtering
ou
par
voie
électrochimique.
Dans le cas d’un dépôt dense de ZnO par
électrochimique, celui se fait dans une solution
contenant du KCl à 0.1M, du ZnCl2 à 5 mM. Lors de
la déposition, la température est maintenue à 75°C.
La croissance de la couche de ZnO nanoporeuse
s’effectue par électrochimie dans les mêmes
conditions que pour la couche dense excepté que
l’on ajoute de l’Eosin Y à 50µm.
-1
Une solution de PbI2 dans du DMF (460 mg.mL )
est ensuite déposée par spin-coating [2] sur le
substrat de ZnO dense ou nanoporeux à 6000 rpm
pendant 30s. Après un recuit à 70°C pendant
30min, l’échantillon est trempé dans une solution
de 2-propanol pendant 15s puis dans une solution
de CH3NH3I pendant 40s et enfin nettoyé une
solution de 2-propanol pendant 2s. Après un recuit
à 70°C pendant 50min, le transporteur de trou (une
solution de Spiro-OMETAD, 4-tert-butylpyridine,
lithium bis(trifluoromethylsulphonyl)imide et tris(2(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III)
bis(trifluoromethylsulphonyl)imide
dans
le
chlorobenzene) est déposé par spin-coating.
3
12
Current Density (mA.Cm^2)
1
Cette étude a permis d’aboutir à des résultats
assez
encourageant
spécialement
pour
l’architecture plane où l’on obtient des cellules
ayant des rendements de l’ordre de 6% après
optimisation.
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Fig. 1. Courbe I-V de Voltage
la cellule
(V) ayant les meilleures
performances dans une architecture plane dans laquelle le ZnO
est déposé par sputtering.
Table 1 : Résultats opto-électroniques de la cellule la plus
performante en structure plane.
VOC (V)
JSc (mA.Cm-2)
PCE (%)
0.93
11
5.62
4
Conclusions
FF (%)
55
Le remplacement du TiO2 par du ZnO dans les
cellules pérovskite CH3NH3PbI3 dans une
architecture plane donne des premiers résultats qui
sont assez encourageants. Cependant, les
performances peuvent encore être améliorées d’où
l’intérêt d’ajouter une couche de ZnO nanoporeuse.
Acknowledgements
Financement: IDEX Paris-Saclay
References
[1] National Renewable nergy Laboratory (NREL),
Research
Cell
Efficiency
Records,
http://www.nrel.gov/ncpv/images/efficiency
chart.jpg.
[2] J. Burschka, N. Pellet, S-J Moon, R. HumphryBaker, P. Gao, M.K. Nazeeruddin & M. Grätzel,
doi:10.1038/nature12340.
SCF Congress - 2015
Microfluidic enzymatic biofuel cells to generate electrical
energy.
Biopiles enzymatiques microfluidiques pour la génération d’énergie.
S. Tingry1*, D. Desmaël1, L. Renaud2
1
Institut Européen des Membranes, Place Eugène Bataillon, Université de Montpellier 2,
ENSCM, CNRS, cc047, 34095 Montpellier
2
Institut des Nanotechnologies de Lyon, Université Claude Bernard, Lyon 1, 43 bd du 11
novembre1918, 69 622 Villeurbanne
______________________________________________________________
Résumé : Ce travail présente la fabrication et l'évaluation d'une biopile enzymatique microfluidique fonctionnant à
partir de glucose et d’O2 et constituée de deux micro-canaux empilés verticalement. Pour la première fois, des films
minces de polyester ont été utilisés comme support flexible d'électrodes modifiés par de l’or. Notre prototype est
fabriqué avec des matériaux biocompatibles via un procédé rapide sans l’utilisation d’une salle blanche. Connecté à
un convertisseur d’élévateur de tension fournissant une tension de sortie de 3,1 V, ce prototype peut être exploité
pour fournir de l'énergie électrique à un capteur sans fil pour transmettre des données de température à un
ordinateur distant.
__________________________________________________________
Summary: This work presents the fabrication and evaluation of a novel three-dimensional microfluidic enzymatic
biofuel cell working from glucose and O2, and made of two microchannels vertically stacked one above the other. For
the first time, thin polyester films have been used as flexible electrode substrates modified by gold. Our prototype can
be fabricated with biocompatible materials via rapid prototyping and without the need to access a clean room.
Connected to a voltage boost converter providing an output voltage of 3.1 V, we demonstrate that our current
prototype can be exploited to supply electrical energy to a wireless sensor for transmitting temperature data to a
remote computer.
Keywords: Enzyme, Microfluidics, 3D biofuel cells, Polyester films, Flexible Stack
Microfluidic biofuel cells can be fabricated via processes derived from the microelectronic industry that provides high
capabilities of integration. These devices are thus inherently well adapted to miniaturization and appear as an ideal
configuration to supply power to a wireless electronic sensor that would broadcast the local temperature of a site,
indicative of infection of an internal wound for example.
Les biopiles microfluidiques peuvent être fabriquées par des procédés issus de l’industrie électronique qui permet
d’intégrer plusieurs fonctionnalités sur un substrat. Ces dispositifs sont donc bien adaptés à la miniaturisation et
apparaissent comme une configuration idéale pour alimenter un capteur électronique sans fil afin de diffuser la
température locale d’un site, indicative d’une plaie interne par exemple.
1
Introduction
Biofuel cells (BFCs) are today recognized as
promising alternative energy sources that work from
enzyme catalysts [1]. Compared to conventional
biofuel cell architectures, membraneless BFCs can
exploit the properties of the laminar flow regime that
dominates in microfluidic channels [2, 3]. The
resulting devices, called also microfluidic BFCs, are
now considered as micro sources able to supply
power for portable electronic systems [4].
This work presents the preliminary results
towards the development of a novel architecture
based on the use of thin and flexible double-sided
adhesive tape and transparent thin polyester films
to construct the micro-channels and the electrode
substrates. The height of the channels is defined by
the film thickness of the laminated materials [5].
The prototype is built from two microfluidic biofuels
vertically stacked one above the other. The
resulting device is a three dimensional architecture
containing 2 microchannels, 4 pairs of electrodes
and an in-reservoir that drives the fluid in a
cascade-like fashion toward both microchannels.
This prototype exhibits a high degree of
flexibility, and can be entirely assembled via a low
cost, scalable fabrication process which is entirely
based on rapid prototyping.
We demonstrate the potential of our prototype to
supply electrical energy to a wireless sensor
transmitting temperature values to a remote
computer.
2
The microfluidic biofuel cell proposed is a three
dimensional chip, composed of two T-shaped
microfluidic channels superposed one above the
other. The resulting device, depicted in Fig.1, is a
laminated structure that comprises 2 double sided
pressure adhesive (DSPA) films sandwiched
between 3 Polyethylene naphthalate (PEN) layers.
Gold layers (≈200 nm thick) were directly sputtered
on the PEN as electrode substrates. Each electrode
exposed to the electrolyte solutions was 25 mm
long, 1 mm wide. The interspace between the
electrodes was 1 mm. The anolyte consisted of
glucose (10 mM) prepared in neutral phosphate
buffers (saturated by N2), in the presence of
−1
Glucose oxidase from Aspergillus Niger (1 mg.ml ,
−1
198000 U.mg solid) and hexacyanoferrate (10
mM). The catholyte consisted of 2,2 -azinobis (3−1
ethylbenzothiazoline-6-sulfonate) (1 mg.ml ) and
−1
laccase from Trametes Versicolor (1 mg.ml , 20
−1
U.mg solid) in 0.1 M citrate buffers (pH 5.0) under
O2.
continuously broadcast temperature values every 2
min.
Au electrodes
Fig. 2. Power-current profiles for the 3D-microfluidic biofuel cell
with a single pair of electrodes (dotted lines) and with 4 pairs of
electrodes connected in parallel (common anodes, common
cathodes).
micro
channel
Fig. 1. Flexible three-dimensional device based on the stacking
of 2 microfluidic biofuel cells.
3
The feasibility of the constructed 3D microfluidic
biofuel cell, based on laminated materials, was
characterized by running the system at room
temperature with glucose and oxygen solutions in
the presence of enzymes. At the anode, glucose
was oxidized by the glucose oxidase, and oxygen
was reduced at the cathode by the laccase, in the
presence of specific redox mediators to enhance
the electron transfer from the active site of the
enzymes and the electrode surface.
Power curves obtained for the reference flow
−1
rate of 150 μl.min are presented in Fig.2. With all
electrodes connected in parallel, the maximum
power achieved is ≈ 12.5 μW for a current of ≈ 66
μA and a voltage of ≈ 0.19 V. This level of power is
reached despite a low level of fuel utilization (1%) in
accordance with previous results [6]. Via the
integration of top and bottom electrodes for each
microchannel, this 425 μm thick prototype can
improve the output power by a factor >3 when
compared to a similar membraneless biofuel cell
including a single pair of electrodes.
When the device was connecting to a voltage
boost converter (VBC), the voltage was increased
to 3.1 V but the current at the output of the VBC
dropped to ≈ 2 μA as the amplification of the
voltage comes at the expense of a significant
current consumption. Nevertheless, this low current
value proved to be sufficient for the 3D-microfluidic
biofuel cell to produce enough power to
4
Conclusions
This work showed the construction of a
membraneless-biofuel cell resulting from the
vertical stacking of two microfluidic channels
equipped with top and bottom electrodes in a
flexible package. When connecting to a voltage
converter, the resulting device has potential to
supply enough electrical energy to a wireless
sensor for transmitting temperature data to a
remote computer.
There is still room for improvements. In
particular, increasing the open circuit voltage
appears highly desirable to improve the overall
performance of the biofuel cell.
Acknowledgements
This work was supported by the ANR program
”International II” under project ”Hybiocell”.
References
[1]
[2]
[3]
[4]
[5]
[6]
Minteer SD, Liaw BY, Cooney MJ, Curr Opin Biotechnol. 18
(2007) 228.
E. Kjeang, N. Djilali, D. Sinton , J. Power Sources 186
(2009) 353.
A. Zebda, L. Renaud, M. Cretin, C. Innocent, F. Pichot, R.
Ferrigno, S. Tingry, J. Power Sources 309 (2009) 602.
J. wook Lee, E. Kjeang, Biomicrofluidics 4 (2010) 041301.
S. Shaegh, NT. Nguyen, SH. Chan, W. Zho, Int J Hydrog
Energy 37 (2012) 3466.
E. R. Choban, L. J. Markoski, A. Wieckowski, P. J. Kenis,
J. Power Sources 128 (2004) 54.
SCF Congress - 2015
Functionalized carbon nanotubes for the realisation of
Lithium/sulfur accumulators
Nanotubes de carbone fonctionnalisés pour la réalisation
d’accumulateurs Lithium/soufre
G.CHARRIER 1, C.BARCHASZ 2, B.JOUSSELME 1, S.CAMPIDELLI
1*
1
CEA Saclay, IRAMIS, Laboratoire d’Innovation en Chimie des Surfaces et Nanosciences,
91191 Gif sur Yvette, France2
2
CEA Grenoble, LITEN, Laboratoire des Générateurs Innovants, 38054 Grenoble, France
______________________________________________________________
Résumé :
Un inconvénient majeur des batteries lithium/soufre (Li/S) classiques est la dissolution progressive de la matière active
dans l’électrolyte, qui entraine une perte de capacité importante, un phénomène d’autodécharge et finalement la fin de
vie prématurée de la batterie.
Dans ce travail, de nouveaux matériaux d’électrodes positives pour accumulateurs Li/S ne présentant pas de
phénomène de dissolution de la matière active en cours de décharge ont été développés.
Pour cela, des molécules présentant des ponts disulfures ont été greffées sur des nanotubes de carbone et du
graphène. Les matériaux carbonés assurent une bonne conductivité électronique à l’électrode positive, tout en servant
de point d’accroche pour la matière active. Les systèmes obtenus présentent une excellente tenue en cyclage et une
capacité spécifique encourageante.
________________________________________________________________________
Summary:
One of the main issues regarding lithium/sulfur accumulators is the progressive dissolution of the active material in the
electrolyte, which causes an important loss of capacity, a self-discharge phenomenon and finally the end of the battery.
In this work, new positive electrode materials for Li/S accumulators have been developed, avoiding the dissolution of the
active material in the electrolyte during the discharge phase.
To this end, molecules bearing disulfide bonds were grafted to carbon nanotubes and graphene. The carbon materials at
once bring a good electronic conductivity to the positive electrode and serve as a template for a covalent immobilization
of the active material. The resulting systems remain very stable over cycling and present a promising specific capacity.
Keywords:
Lithium/sulfur batteries
Energy storage
Carbon nanotubes
Covalent grafting
Positive electrode
This work has been done through a collaboration between the fundamental and the technological research departments
at the CEA. We studied the contribution of the nanomaterials for energy applications. This work is currently quite
fundamental (TRL 2-3) but concrete fallouts in the field of Li/S batteries are expected in the long run.
Ce travail est une collaboration entre la recherche fondamentale et la recherche technologique au CEA qui étudie
l’apport des nanomatériaux pour des applications dans le domaine de l’énergie. Nous sommes actuellement encore au
stade fondamental (TRL 2-3) mais des retombées concrètes dans le domaine des batteries Li/S sont attendues à long
terme.
Les systèmes lithium-ion (Li-ion) sont
aujourd’hui largement intégrés aux appareils
électroniques portables. Leurs performances en
termes de capacité et d’énergie spécifiques
semblent cependant atteindre progressivement un
palier et ces systèmes pourront difficilement
répondre aux exigences identifiées pour les
batteries
de
véhicules
électriques.
Les
accumulateurs lithium/soufre (Li/S) constituent une
alternative prometteuse en raison de la forte
capacité de stockage massique de l’électrode
positive de soufre élémentaire [1] qui permettrait
d’atteindre des densités d’énergie allant jusqu’à
-1
-1
500 Wh.kg (vs 250-300 Wh.kg pour le Li-ion au
maximum). Ce type d’accumulateur présente un
mécanisme de décharge non conventionnel, sans
réactions d’insertion/désinsertion d’ions lithium
comme pour les systèmes Li-ion. Le soufre
élémentaire réagit avec le lithium selon la réaction
électrochimique : 16 Li + S8  8 Li2S [2].
Cette technologie présente cependant un
inconvénient majeur qui explique pourquoi elle n’est
pas encore commercialisée : le soufre élémentaire
S8 et les intermédiaires réactionnels de type
polysulfures de lithium Li2Sn (2≤n≤8) sont solubles
dans les électrolytes organiques classiquement
utilisés dans les batteries [3]. La matière active
solubilisée peut diffuser à travers l’électrolyte et
venir réagir à l’électrode négative, entrainant une
perte de capacité ainsi qu’un phénomène
d’autodécharge. De plus, le soufre élémentaire
étant isolant, l’ajout d’un conducteur électronique à
l’électrode positive est obligatoire.
2. Résultats et discussion
Dans ce travail, nous avons synthétisé de
nouveaux matériaux d’électrode positive pour
accumulateurs Li/S ne présentant pas de
phénomène de dissolution de la matière active
dans l’électrolyte en cours de cyclage. Des
matériaux carbonés (SWCNT, DWCNT, MWCNT,
graphène) ont été utilisés à la fois pour apporter la
conduction électronique nécessaire et pour servir
de substrat au greffage covalent de molécules
présentant des groupements électro-actifs soufrés
[4].
Nous avons choisi de travailler avec des
molécules portant un pont disulfure. Ainsi, en
fonctionnement, la réaction électrochimique avec le
lithium se produit comme dans un accumulateur
classique par rupture de la liaison S-S, tout en
MWCNT non greffés
MWCNT greffés avec la molécule soufrée
3,5
3,0
+
Dans le contexte actuel de transition
écologique, la problématique du stockage de
l’énergie revêt une importance particulière,
notamment dans l’optique de la production et de
l’utilisation d’énergies intermittentes et délocalisées.
Pour cela, la réalisation de batteries possédant une
grande capacité spécifique ainsi qu’un faible coût
est un enjeu majeur.
conservant un point d’accroche de la matière active
à l’électrode positive par le biais du greffage
covalent aux nanotubes de carbone ou au
graphène.
Après synthèse et greffage des molécules
cibles aux nanotubes de carbone (ou au graphène),
les nouveaux matériaux d’électrode ont été intégrés
en tant que cathode dans des batteries Li/S de
format pile-bouton, et des tests de charge/décharge
ont été réalisés (un exemple est donné à la Figure
1), montrant l’apport essentiel du greffage covalent,
aussi bien sur la capacité et l’énergie spécifiques
des accumulateurs que sur la stabilité du système
dans la durée. Des valeurs de capacité spécifique
jusqu’à vingt fois plus importantes ont pu être
-1
obtenues après greffage, de l’ordre de 100 mAh.g
d’électrode (pour des valeurs théoriques situées
-1
autour de 300 mAh.g de molécule soufrée).
E (V vs Li /Li)
1. Introduction
2,5
2,0
1,5
20
40
60
80
t (h)
100
120
Figure 1 : Profils de charge/décharge de piles-boutons pour
des échantillons de MWCNT greffés et non greffés avec l’une
des molécules cibles
3. Conclusions
De nouveaux matériaux d’électrode positive
pour accumulateurs Li/S ont été développés dans
ce travail, par greffage covalent de molécules
électro-actives sur des nanotubes de carbone et du
graphène. Cette méthode permet d’éviter la
dissolution de la matière active dans l’électrolyte
pendant le fonctionnement de l’accumulateur.
Les systèmes ainsi obtenus présentent une
excellente stabilité (jusqu’à 98% de leur capacité
initiale après 50 cycles) et une capacité spécifique
prometteuse.
4. Références
[1] X.Ji, K.T.Lee, L.F.Nazar, Nat. Mater., 2010, 20, 98219826
[2] P.G.Bruce1, S.A.Freunberger, L.J. Hardwick,
J.M.Tarascon, Nat. Mater., 2012, 11, 19-29
[3] Y.X.Yin, S.Xin, Y.G.Guo, L.J.Wan,
Angew.Chem.Int.Ed., 2013, 52, 13186-13200
[4] G.Charrier et al., en préparation
SCF Congress - 2015
Elaboration
and
characterization
of
membranes
Application in aqueous Li-air batteries
Li+
conducting
Elaboration et caractérisation de membranes conductrice du Li+
Application dans les batteries Li-air aqueuses
G. Lancel*,1,2,3, D. Bregiroux1,2, G. Toussaint3, P. Stevens3, C. LabertyRobert1,2
1
Sorbonne Universités, UPMC Univ Paris 06, CNRS, Collège de France, Laboratoire de Chimie de la
Matière Condensée de Paris, 11 place Marcelin Berthelot, 75005 Paris, France
3
EDF R&D, LME, M29 Groupe Batteries, 77818 Moret sur Loing Cedex, France
______________________________________________________________
Résumé : L’accumulateur lithium-air, particulièrement étudié ces dernières années, permettrait au véhicule
électrique d’avoir une autonomie comparable au véhicule thermique. Un certain nombre de défis restent encore à
relever pour rendre cette technologie fonctionnelle, mais l’usage d’un électrolyte aqueux répond à plusieurs d’entre
eux. Cela nécessite cependant l’usage d’une anode de lithium protégée. Alors que l’état de l’art est l’utilisation d’une
vitrocéramique rigide, une approche différente est ici proposée. Elle consiste à fabriquer une membrane hybride, qui
combine simultanément étanchéité, flexibilité et conduction du lithium.
___________________________________________________________________
Summary: Lithium-air batteries have attracted a lot of research interest recently because they can close the gap
between the electric vehicle and the internal combustion engine vehicle. Several challenges remain before making
this technology fully functional, but using an aqueous electrolyte addresses several of them. However, it requires the
use of a PLA (Protected Lithium Anode). While the state of the art is using a fragile glass-ceramic membrane, a
+
different approach is reported here. It consists in a hybrid membrane, combining water-tightness, flexibility and Li
conduction.
Keywords: lithium-air battery, membrane, separator, protected lithium anode, hybrid material, energy storage
To enable widescale deployment of the electric vehicle, it is essential to develop new energy storage technologies. One
of these, the aqueous lithium-air battery, can directly use ambient oxygen from the air on discharge and regenerate it
during charge. This “breathing”, combined with a metallic lithium electrode enables extremely high energy densities,
approaching gasoline engines. Furthermore, the use of an aqueous electrolyte makes it more reliable, ecological and
cheaper than a standard battery.
Pour permettre le déploiement massif du véhicule électrique, il est essentiel de développer de nouvelles technologies de
stockage de l’énergie, notamment le lithium-air aqueux. Ce type d’accumulateur puise sa matière active, l’oxygène,
directement dans l’environnement et le restitue à la recharge. Cela permet d’obtenir des énergies spécifiques
extrêmement élevées, et d’approcher l’autonomie des voitures à essence. De plus, l’utilisation d’un électrolyte aqueux le
rend plus fiable, plus économique et plus écologique qu’un accumulateur classique.
1
Introduction
Lithium-ion battery technology has been a
revolution in the field of electrochemical energy
storage, and is integrated in multiple applications
including portable electronics and electric vehicle.
Fig. 1.Specific energy, estimated driving range and costs of
several battery technologies for electric vehicles.[1]
The development of these systems is still active,
and significant advances are expected. Despite
these prospects, massive
electric
vehicle
development will still need a real breakthrough in
battery technologies to simultaneously increase the
specific energy and decrease the costs. Several
systems are studied, including Li-S, but also metalair and especially Li-air.
In such system, the capacity of the negative
electrode is no more limited by the positive
electrode: the latter harvests its reactant, oxygen,
directly from the environment at discharge and
releases it during charge. Specific energy is then
drastically increased. This promising technology is
still at the laboratory scale, and several challenges
remain to be addressed. In organic lithium-air
technologies (“aprotic lithium-air”), pure oxygen
must be used at the positive electrode to avoid
moisture and CO2 [2]. Reaction products are stored
in the positive electrode porosity. Furthermore, the
use of an organic electrolyte causes stability and
safety issues.
Aqueous based lithium-air [3,4] addresses these
issues, but requires the use of a PLA (Protected
+
Lithium Anode) [5], i.e, a solid Li ionic conductor is
used to isolate the metallic lithium from the
aqueous electrolyte. An example of PLA uses a 1µm layer of LiPON (Lithium Phosphorous
OxyNitride) in contact with the lithium, and a 150µm
Li1+x+zAlx(Ti,Ge)2-xSizP3-zO12 glass-ceramic.
However, the integration of glass-ceramic makes
the system more fragile and limits its cyclability.
We propose here a different approach to protect the
lithium electrode. It consists in producing a hybrid
membrane [6] which combines watertightness,
+
flexibility and Li conductivity. This membrane is
+
made from an Li conducting inorganic nanofiber
mat, embedded in hydrophobic polymer.
2
The critical step for producing a hybrid membrane
is the electrospinning. This versatile process uses
an electric field to break the surface tension of a
liquid, and extrude it into a solid fiber [7]. Originally
designed for polymers, its use for producing
ceramic nanofibers is constantly increasing [8].
Either a suspension or sol-gel precursors can be
used. Multiple parameters belong to both the hybrid
solution,
the
electrospinning
parameters
(temperature, relative humidity, injection speed,
electric field, spinneret/counter electrode distance
and counter electrode geometry.) influence the
membrane properties including conductivity,
mechanical strength and tightness
A solution containing both a supporting polymer
and inorganic precursors is injected under an
electric field to yield hybrid nanofibers. These fibers
are then thermally treated to calcine the organic
binder and drive crystallization of the lithiumconducting ceramic phase.
The inorganic fibers are then impregnated with a
polymer to achieve the final mechanical resistance
and watertightness.
Electrospun fibers with various morphologies were
studied by scanning electron microscope and
energy-dispersive X-ray spectroscopy, to determine
fiber density, fiber diameter and organic/inorganic
homogeneity.
Then, the impact of thermal treatment on phase
purities, fiber mat morphology and fiber sintering
will be discussed based on X-Ray diffraction,
inductively coupled plasma, scanning electron
microscopy
and
energy-dispersive
X-Ray
spectroscopy.
Finally, the impregnation step and availability of the
surface fibers was studied by scanning electron
microscopy
and
energy-dispersive
X-Ray
spectroscopy. Watertightness was tested by
+
conductimetry. Li ionic conductivity was measured
by electrochemical impedance spectroscopy.
3
A new sol-gel synthesis was successfully
developed to meet the requirements of
electrospinning, for both the Li3xLa2/3-xTiO3
perovskite and the Li1+xAlxTi2-x(PO4)3 NASICON.
Formulation and thermal treatment optimization
resulted in a pure-phase. Lithium content in the
perovskite-phase can vary due to Li2O evaporation
during thermal treatment. It was adjusted by ICPMS analysis.
Fig. 2.a Fibers after electrospinning 1b Fibers after thermal treatment.
Impregnation was optimized to reach the desired
properties. The amount of polymer added by dropcasting was small enough to leave surface+
nanofibers available for Li conduction, but
sufficient to provide mechanical strength and water-6
-1
tightness. We measured 2,6.10 S.cm on a
130µm membrane.
4
Conclusions
Lithium-air batteries could play a key role in
transports electrification and energetic transition.
Several issues still remain to be addressed. The
hybrid membranes fabrication described here is a
simple process, using low-cost and versatile
electrospinning as main equipment. All materials
are low-cost and abundant, especially for the
Li1+xAlxTi2-x(PO4)3 phase. Measured conductivities
are promising for final integration into the Li-air
battery.
Acknowledgements
The authors would like to thank Domitille
Giaume (IRCP) for the ICP-MS analysis.
References
[1]
[2]
P.G. Bruce, S. A. Freunberger, L.J. Hardwick, J.M.
Tarascon, Nature Mat, 11 (2012) 19.
Christensen, J.; Albertus, P.; Sanchez-Carrera, R.S.;
Lohmann, T.; Kozinsky, B.; Liedtke, R.; Ahmed, J Journal
of The Electrochemical Society, 159 (2) R1-R30 (2012)
[3]
[4]
[5]
[6]
[7]
[8]
P. Stevens, G. Toussaint, G. Caillon, P. Viaud, P. Vinatier,
C. Cantau, O. Fichet, C. Sarrazin, M. Mallouki, ECS Trans.
28 (2010) 1.
P. Stevens, G. Toussaint, L. Puech, P. Vinatier, ECS
Trans., 50 (2013) 1.
S.J.Visco, Y. Nimon, US Patent 20070117007. 2007.
C. Laberty-Robert, K. Vallé, F. Pereira, C. Sanchez, Chem
Soc Rev, 40 (2011) 961.
A. Greiner, J. H. Wendorff, Angew. Chem. Int. Ed.2007, 46,
5670-5703.
Y. Dai, W. Liu, E. Formo, Y. Sun, Y. Xia, Polym. Adv.
Technol. 2011, 22 326-338.
SCF Congress - 2015
Nucleation of LiFePO4 and Li2FeSiO4 into porous carbons and
their application as positives electrodes in Li-ion batteries
Nucléation de LiFePO4 et Li2FeSiO4 dans des carbones poreux et leur
utilisation comme électrodes positives de batteries Li-ion
S. Sun1,2,3, C. Matei-Ghimbeu1,3, C. Vix-Guterl1,3, C. Masquelier2,3, R. Janot2,3
1
Institut de Science des Matériaux de Mulhouse, UMR CNRS 7361, Université de Haute
Alsace, 15 Rue Jean Starcky, 68057 Mulhouse, France
2
Laboratoire de Réactivité et Chimie des Solides, UMR CNRS 7314, Université de Picardie
Jules Verne, 33 rue Saint Leu, 80039 Amiens Cedex 1, France
3
Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, 33 rue Saint
Leu, 80039 Amiens Cedex, France
______________________________________________________________
Résumé : Des matériaux composites mésoporeux LiFePO4–carbone et Li2FeSiO4-carbone sont préparés par une
synthèse en une étape « soft templating » ou par imprégnation d’un carbone poreux conducteur et leurs
performances électrochimiques sont rapportées en tant qu’électrodes positives de batteries Li-ion. Les effets de la
nature des précurseurs de Fe/Li et de la température de traitement thermique sur la formation des phases,
l’arrangement mésostructural du carbone et le degré d’oxydation du fer sont systématiquement étudiés grâce à un
large éventail de techniques d’analyse. La préparation de nanocristallites de LinFeXO4 (∅ < 20 nm), bien dispersées
dans la matrice carbonée conductrice, permet une bonne tenue en cyclage à fort régimes de charge/décharge.
_______________________________________________________________________
Summary: LiFePO4–carbon and Li2FeSiO4-carbon mesoporous composites are prepared either by one-pot softtemplate approach or by impregnation of a porous conductive carbon and their electrochemical performances as
positive electrodes of Li-ion batteries are reported. The effects of the Fe/Li precursor types and the thermal annealing
temperature on the phase formation, mesostructural regularity, porosity and Fe oxidation state were systematically
investigated by a large panel of analysis techniques. The successful preparation of LinFeXO4 nanocrystals (∅ < 20
nm), well dispersed in the carbon conductive matrix, allows a high rate capability for the polyanionic cathode
materials.
Keywords: composites; porous carbons; nanocrystallites, Li-ion battery; cyclability
This project concerns the development of positive electrode materials for Li-ion batteries able to cycle at high
charge/discharge rates and, therefore, able to reach the targets for power applications. This study is mainly related to a
fundamental research with the main objectives being a better understanding of the formation mechanisms of highly
divided electrode materials in a porous carbon and a better understanding of their electrochemical responses.
Ce projet vise à développer des électrodes positives de batteries Li-ion capable de cycler à des régimes de
charge/décharge rapides et pouvant ainsi répondre à des demandes en application de puissance. L’étude s’inscrit
essentiellement dans le domaine fondamental avec pour objectifs principaux des meilleures compréhensions des
mécanismes de formation de matériaux d’électrodes très divisés et de leurs signatures électrochimiques.
1
Introduction
Nowadays, lithium-ion batteries are being
developed for large scale applications. Batteries
with lower cost, higher reversibility and enhanced
safety are becoming increasingly important. Since it
was demonstrated that lithium could be reversibly
extracted from LiFePO4 at 3.4 V [1], this compound
quickly became one of the most promising
materials for Li-ion batteries positive electrode.
LiFePO4 is of particular interest for large-scale
applications due to its high theoretical capacity (170
mAh/g) and its intrinsic structural and chemical
stability that leads to safe and long cycle life
batteries. Since then, a large variety of polyanion
Fe-based compounds such as silicates, sulfates
and borates has emerged as potential electrode
materials [2]. In principle, the extraction of 2 Li+ per
formula for Li2MSiO4 (M=Fe, Mn, Co, etc.) with a
theoretical capacity as high as 330 mAh/g is
possible, which makes silicates more appealing.
Among these silicates, the most studied is
Li2FeSiO4 [3], with iron and silicon being among the
most abundant and lowest cost elements. However,
Li2FeSiO4 and LiFePO4 suffer from extremely poor
electronic conductivity (10-14 S/cm and 10-9 S/cm at
25°C, respectively) [4]. To overcome this severe
issue, many methods have been reported with the
carbon coating being the most wide-spread one [5].
In this work, we report the synthesis of LiFePO4/C
composites
by
simple
and
Li2FeSiO4/C
impregnation routes of porous carbons or even by
one-step “soft-template” method.
2
For the synthesis of mesoporous LiFePO4–C
composites, a one-pot soft-template route was
developed. Environmentally benign phloroglucinol
and glyoxal (instead of phenol and formaldehyde as
usually reported in the literature) were used as
carbon precursors. In addition, instead of expensive
and unstable ferrous salts, cheaper ferric salts were
employed as Fe sources. The synthesis was based
on the multi-constituent coassembly of triblock
copolymers, resol and LiFePO4 precursors. The
polymerization of phloroglucinol and glyoxal in the
presence of the structure directing agent led to the
formation of a resol, then the addition of LiFePO4
precursors followed by annealing under Ar gave
rise to the mesoporous LiFePO4–C composites.
The preparation of Li2FeSiO4/C composites was
performed through an impregnation route of porous
conductive carbons. In a typical synthesis,
stoichiometric amounts of Fe(III) nitrate, LiNO3 and
TEOS were dissolved in 20 mL of ethanol to form a
transparent solution. Then, commercial porous
carbon KB-600 (1.0 g) was added into this solution,
stirred overnight at room temperature to evaporate
the solvent. After being dried at 80 °C, the resultant
powder was calcinated in a tubular furnace under
Ar flow at different temperatures to get the
Li2FeSiO4/C composites.
3
mesoporous
For
the
LiFePO4–carbon
composites prepared in one step, a crystallization
mechanism of LiFePO4 was proposed based on
TEM observations: round amorphous particles of
150–500 nm are first formed in the carbon matrix
(cf. Fig. 1a) and then a crystallization/breaking
process occurs, leading to the formation of well
dispersed LiFePO4 nanocrystallites (20–30 nm) (cf.
Fig. 1c).
Fig. 1. TEM images illustrating the crystallization mechanism of
the LiFePO4 nanoparticles in the carbon matrix.
crystallized in the space group Pmn21, were found
well dispersed in the carbon matrix. The presence
of carbon not only plays an important role in the
formation of the Li2FeSiO4 phase, but also can
stabilize the initial crystal structure of Li2FeSiO4.
The carbon can therefore delays the lowering of the
Fe3+/Fe2+ redox voltage (from 3.1/3.0 to 2.8/2.7 V
vs. Li+/Li) usually reported for Li2FeSiO4 upon
electrochemical cycling. In viewpoint of practical
application, the present Li2FeSiO4/C composite
exhibits excellent high-rate capacity and cycling
stability, as it delivers an initial discharge capacity
at 55 °C as high as 82 mAh/g at the rate of 2 C,
with 86 % capacity retention after 500 cycles (cf.
Fig. 2). This good performance is attributed to the
nanocrystalline character and good dispersion of
Li2FeSiO4 in the conductive carbon matrix.
Fig. 2. Discharge capacity of a Li2FeSiO4/C composite (80/20
wt. ratio) at 2 C and 55°C upon 500 cycles.
4
Conclusions
New energy- and time- saving synthesis methods
were developed to prepare LiFePO4/C and
Li2FeSiO4/C composites. Excellent high-rate
capacity and cycling stability were obtained due to
the nanocrystalline character and good dispersion
of the active materials in the conductive carbon
matrix. These versatile synthesis methods can be
easily extended to synthesize other electroactive
material-carbon composites.
References
Our
optimized
mesoporous
LiFePO4–C
composite exhibits an excellent lithium storage
performance [6], i.e. a capacity of 52 mA/g
(including the carbon weight) at a high current rate
of 10 C without any conductive carbon additive or
binder, hence a capacity decrease of only 20%
when increasing the current from C/10 to 10C. This
LiFePO4–carbon mesoporous composite shows
good cycling performances since, after 100 cycles
at C/20, the capacity retention is about 75 %.
About the nucleation of Li2FeSiO4 into porous
carbons, high purity and nanocrystalline Li2FeSiO4,
[1] A.K. Padhi, K.S. Nanjundaswamy, J.B. Goodenough, J.
Electrochem. Soc. 144 (1997) 1188
[2] C. Masquelier, L. Croguennec, Chem. Rev. 113 (2013) 6552
[3] A. Boulineau, C. Sirisopanaporn, R. Dominko, R. Armstrong,
P. Bruce, C. Masquelier, Dalton Trans. 39 (2010) 6310
[4] S.-Y. Chung, J. T. Bloking and Y.-M. Chiang, Nat. Mater. 1
(2002) 123
[5] N. Ravet, J. Goodenough, S. Besner, M. Simoneau, P.
th
Hovington, M. Armand, 196 Meeting ECS, Abstract 127 (1999).
[6] S. Sun, C. Ghimbeu, R. Janot, J-M. Le Meins, A. Cassel, C.
Davoisne, C. Masquelier, C. Vix-Guterl, Micro. Meso. Mat. 198
(2014) 175
SCF Congress - 2015
Synthesis, structure and electrochemical properties of 3dmetal organic polyanion compounds
Synthèse, structure et propriétés électrochimiques de composés
polyanioniques à base de métaux de transition
H. Ahouaria, G. Rousseb,c, Y. Kleinc, J-N. Chotarda, M-T. Sougratid, Matthieu
Courtya, N. Recham*,a and J-M. Tarasconb
a
LRCS, UMR CNRS 7314, 33 Rue Saint Leu, 80039 Amiens Cedex.
Collège de France, Chimie du Solide et de l’Energie, FRE 3677, 11 place Marcelin Berthelot,
75231 Paris Cedex 05, France
c
Sorbonne Universités - UPMC Univ Paris 06, 4 Place Jussieu, F-75005 Paris, France.
d
Institut Charles Gerhardt - UMR 5253, 34095 Montpellier Cedex 5, France
*Corresponding author: [email protected]
b
______________________________________________________________
Résumé : Une nouvelle famille de malonates de sodium et de métaux de transition a été préparée par voie
hydrothemale. La structure cristalline a été résolue par diffraction des rayons X sur poudres et sur monocristal.
Toutes ces phases appartiennent au même groupe d’espace Pbca et sont formées de couches alternées de
malonates de métaux de transition et de sodium. Il a été montré que le processus de déshydratation et d’hydratation
est réversible et que ces composés sont inactifs électrochimiquement vs. Li.
Summary: We report here a series of new malonate compounds Na2M(H2C3O4)2×2H2O with M= Mn, Fe, Co, Ni, Zn
and Mg, whose structure and electrochemical performances are presented. Metal malonate compounds crystallize in
an orthorhombic structure built upon MO6 octahedra connected with malonate groups to form a layered structure. The
removal/uptake of water from the malonate members was found to be reversible and the crystal structure of the
anhydrous Na2Mn(H2C3O4)2 is solved from powder diffraction and presents similarities with the hydrated phase.
However, these Na-metal malonates compounds are not electrochemically active.
Keywords: Hydrothermal synthesis, oxalates, malonates, electrochemical properties
The massive use of fossil fuel is now at the origin of growing economical and political concerns since the resources are
limited and are on the way of depletion. Consequently, it is necessary to explore other energy resources more abundant
and renewable. However, most of these sustainable energies are intermittent and require storage system in particular Liions batteries. Searching new materials acting as positive electrode for lithium-based batteries with minimum footprint in
nature and made through eco-efficient processes became one of the areas of interest of the scientific communities.
En raison de la diminution des énergies fossiles, il est impératif de trouver d’autres sources d’énergie. Un grand espoir
réside dans l’utilisation des énergies renouvelables. Cependant, ces dernières ont un caractère intermittent ce qui
nécessite le développement de systèmes de stockage d’électricité, tels que les batteries Li-ions. Dans ce contexte, la
recherche de nouveaux matériaux naturels, d’électrodes reposant sur l’utilisation d’éléments chimiques abondants
préparés par des procédés peu énergivores dans le contexte du développement durable devient une priorité. C’est dans
ce cadre que s’inscrit cette étude.
.
1
Introduction
Since the commercialization of Li-ions
batteries in the early 1990s, searching for new
cathode materials have always been the main area
of interest of the scientific community to improve
the energy density, the rate capability and the
cost[1]. Most studies have been devoted to
transition metal oxides having either layered LixMO2
or spinel LiMn2O4 structures, and more recently to
polyanionic compounds which were first brought to
the scene by J. B. Goodenough. Among them,
LiFePO4 stands as the most suitable positive
electrode for the next generation of Li-ions batteries
+
0
as it could operate at 3.45 V vs. Li /Li with a
-1
theoretical capacity of 170 mAh.g while also
presenting the added benefit of improved safety
performances.
Aside from the inorganics polyanionic
compounds, we have recently shown the cost-wise
attractiveness of some 3d-metals based phases
having organic polyanions such as carbonates,
oxalates, malonates, etc. which display a wide
range of attractive physical properties. Among the
dicarboxylates
ligands,
3d-metal
oxalate
Na2M2(C2O4)3×2H2O have already been reported in
the literature together with their magnetic properties
discussed[2]. In parallel, specific attention was also
placed on the use of malonate rather than oxalate
ligands leading to compounds of general formulae
Na2M(H2C3O4)2×2H2O for which the Cu member
-1
3
Using XRD single crystal, we confirm that
Na2M2(C2O4)3×2H2O compounds crystallize within a
monoclinic unit cell (P21/c) and the structure is built
upon MO6octahedra out of which five of the oxygen
ligands are oxalates, while the sixth one belongs to
2+
+
the water molecule that bridges both M and Na
cations (Figures 1a). However, for the malonates
the
crystal
members
Na2M(H2C3O4)2·2H2O,
structure was solved using both X-Rays powder
and single crystal diffraction and all these
compounds crystallize within a Pbca orthorhombic
space group. The crystal structure shown in Figure
1b consists of sheets made of MO6 octahedra and
tridentate malonate compounds alternating with Nawater malonate units. The crystal structure of the
malonates phases indicates that water molecules
are present in the space between 3d-metal
malonates layers which suggests that getting the
anhydrous phase is easy. For this purpose, Mnmalonate compound was heated at 200°C under
argon for 20min. This treatment induces a
departure of two water molecules and formation of
the anhydrous phase with the corresponding crystal
structure solved using Rietveld refinement carried
out on the XRD powder pattern recorded at 200°C.
The compound crystallize in a monoclinic unit cell
with P21/c space group and the structure shown in
Figure 1c is built upon MnO6 octahedra linked
through tridentate malonate groups, so as to form
the same layers as in the hydrated phase.
The aforementioned compounds were
tested for their electrochemical performances
versus lithium. Solely the Fe-based phases show
an electrochemical activity worth being reported.
The voltage versus capacity curves of iron oxalate
(Figure 1d) and iron malonate (Figure 1e)
compounds, realized between 2.0 and 4.2 V at
C/10 rate shows an electrochemical activity
+
0
centered around 3.3 V vs. Li /Li . A reversible
a)
Voltage (V vs. Li)
Capacity(mAh/g)
c
0
10
20
Capacity(mAh/g)
30
40 0
10
20
30
40
4.0
3.0
(1)
50
60
(5)
(2)
4.0
3.0
(4)
d)
(a)
2.0 (3)
e)
(b)
(6)
1.00
b
1.00
0.98
c)
b)
5%Fe 3+
95%Fe2+
(1)
0.96
15%Fe 3+
85%Fe 2+
(4)
0.98
6%Fe 3+
94%Fe2+
18%Fe3+
0.98
82%Fe2+
0.96
0.98
a
b
(5)
(2)
0.96
1.00
7%Fe3+
93%Fe 2+
20%Fe 3+
(3)
0.96
c
-4
0.99
0.98
1.00
1.00
1.00
c
2.0
Voltage (V vs. Li)
2
Transmission
Both
family
of
compounds
and
Na2M(H2C3O4)2×2H2O
Na2M2(C2O4)3×2H2O
were synthesized by hydrothermal method.
Typically MCl2×nH2O, H2C2O4×2H2O or H4C3O4,
CH3COONa×3H2O and NaCl were mixed in 5-8 ml
of distilled water with a suitable molar ratios. The
mixture was then heated to 225-250°C for the
oxalates and 100-150°C for the malonates in a 23
ml capacity Teflon-lined autoclave for 2.5 hours
followed by slow cooling to room temperature. The
resulting powders or crystals were washed (i) with
distillated water or methanol to dissolve the sodium
chloride salt, (ii) with acetone and (iii) oven dried at
50°C for 3 hours.
-1
capacity of about 35 mAh.g and 20 mAh.g was
reached for the oxalate and the malonate phases,
57
respectively. Based on the ex situ Fe Mössbauer
spectra collected for the electrochemically charged
and discharged samples we concluded that the
3+
2+
capacity observed is not related to Fe /Fe redox
couple and may results from the oxalate or
malonate anionic network.
-2
0
2
Velocity (mm/s)
4
0.99
80%Fe 2+
-4
-2
(6)
0
2
Velocity (mm/s)
Fig.1. (a) Structure of sodium oxalates Na2 M2(C2O4)3·2H2O
projected along the a axis. (b) Structure of sodium malonates
Na2M(H2C3O4)2·2H2O projected along the a axis and (c)
Structure of sodium malonates anhydrous Na2 M(H2C3O4)2
projected along the b axis. MO6 octahedra are depicted in blue
and sodium is shown as yellow spheres. Oxygen, carbon and
hydrogen atoms are shown in red, brown and black,
respectively.
Electrochemical
performances:
(d)
Na2Fe2(C2O4)3·2H2O and (e) Na2Fe(H2C3O4)2·2H2O compounds
together with room temperature Mössbauer spectra.
4
Conclusions
New
malonate
compounds
Na2M(H2C3O4)2×2H2O,
whose
structure
was
determined using both powder and single crystal Xray diffraction, are reported. These compounds
crystallize in an orthorhombic structure with Pbca
space group which consists of layers of metal
malonates that sandwiches sodium and water
groups. The crystallographic structure of the
manganese malonate anhydrous phase (monoclinic
P21/c space group) is built upon MnO6 octahedra
linked through tridentate malonate groups, so as to
form the same layers as in the hydrated phase.
However, Na-metal oxalates/malonate compounds
show no electrochemical activity.
Acknowledgements
The authors would like to acknowledge Ludovic
Delbes and Benoît Baptiste (IMPMC) for help in
setting
up
the
high
temperature
XRD
measurements. H.A. acknowledges ALISTORE-ERI
for her Ph.D. grant
References
[1] M. Ati, B.C. Melot, J.N. Chotard, G. Rousse, M. Reynaud,
J.M. Tarascon, Electrochem. Commun. 13 (2011) 1280.
[2] C. Mennerich, H.-H. Klauss, A.U.B. Wolter, S. Sullow, F.J.
Litterst, C. Golze, R. Klingeler, V. Kataev, B. Buchner, M.
Goiran, H. Rakoto, J.-M. Broto, O. Kataeva, D.J. Price,
Condens. Matter. (2007) 1.
4
0.98
Transmission
was solely reported. In both cases, whatever the
nature of the metal or organic ligands, nothing was
specified upon their electrochemical performances,
although their framework structure was indicative of
possible insertion reactions.
SCF Congress - 2015
Bacteria-Assisted Synthesis of Fe-Based Electrode Materials
for Li batteries.
Utilisation de Bactéries pour la Synthèse et la Texturation de
Matériaux d’Electrodes, à base de Fer, pour Batteries au Lithium.
B. Mirvaux*,1,2, N. Recham1,2, J. Miot3, M-T. Sougrati2,5, M. Courty1,2, C.
Davoisne1,2, J-M. Tarascon2,4 , D. Larcher1,2
1
Laboratoire de Réactivité et Chimie des Solides, UMR CNRS 7314, Université de Picardie
Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France.
2
Réseau sur le Stockage Electrochimique de l'Energie (RS2E), FR CNRS 3459, France.
3
Institut de Minéralogie, Physique des Matériaux et Cosmochimie (IMPMC), Université Paris
6, Muséum National d'Histoire Naturelle, CNRS UMR 7590, IRD 206, 4 place Jussieu, 75252
Paris cedex 05.
4
Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France.
UICGM - UMR5253- Equipe AIME Université Montpellier II, 2 Place Eugène Bataillon – CC
1502, 34095 Montpellier.
5
______________________________________________________________
Résumé :
La précipitation à température ambiante et en milieu aqueux de FePO4·xH2O amorphe (a-FePO4·xH2O) a été menée en
présence de bactéries (Sporosarcina Pasteurii). Il en résulte la croissance de particules submicroniques (50-80 nm) de
a-FePO4·xH2O à la surface des dites bactéries. Ensuite, un traitement thermique à température modérée est appliqué
pour décomposer la bactérie, ce qui n’altère ni le caractère amorphe ni la texture/organisation alvéolaire du matériau
inorganique. Bien que provoquant une déshydratation partielle souvent reportée comme néfaste à l’activité
électrochimique de cette famille de matériaux d’électrodes, ce traitement s’avère ici nécessaire pour activer cette
réactivité électrochimique et il améliore à la fois l’étendue et la réversibilité de l’insertion de Li dans a-FePO4·xH2O.
________________________________________________________________________
+
Summary:
The room-temperature precipitation from aqueous media of amorphous FePO4·xH2O (a-FePO4·xH2O) has been
conducted in presence of a bacteria (Sporosarcina pasteurii), which results in the growth of sub-micrometer particles (5080 nm) deposited at the surface of the bacteria. Then, a mild heat treatment is applied to decompose these bacteria
without affecting neither the amorphous nature nor the alveolar texture/organization of the inorganic material. Even
though coming with a partial dehydration generally reported as negatively impacting the electrochemical performances of
this family of electrode compounds, this treatment is here found mandatory to promote the electrochemical activity and to
improve both the extent and the reversibility of the Li insertion into a-FePO4·xH2O.
Keywords: Li battery; iron phosphates; electrode material; bio-mineralization; bacteria;
Presently, the production of high-energy Li-based batteries comes with large energy consumption and environmental
impact, mostly coming from the production of the electrode materials generally requiring high temperatures. However,
some living beings are able to concentrate and transform soluble species, leading to precipitates with specific size,
morphology, texture and so at ambient temperature. This prompted our present strategy aimed at using bacteria to
assist in the synthesis of textured active electrode materials towards more eco-friendly routes.
La production d’accumulateurs électrochimiques (Li-ion) a un coût énergétique / environnemental élevé, notamment en
raison des hautes températures de synthèse requises pour la synthèse des matériaux d’électrodes. Pourtant, certains
êtres vivants sont capables de concentrer et de précipiter des matériaux, à température ambiante, tout en contrôlant leur
taille, morphologie et organisation. Ceci a motivé notre stratégie visant à tirer bénéfice de ces mécanismes pour
synthétiser et texturer des matériaux d’électrode de manière plus « éco-compatible ».
(a-FePO4·xH2O). Notons que ces deux classes de
matériaux partagent le même point faible : leur
tenue en puissance.
2
Volet expérimental
La synthèse s’effectue en deux étapes : i)
multiplication des bactéries dans un « milieu de
culture », ii) transfert de ces bactéries dans un
« milieu de minéralisation » aqueux où sont dissous
+
3les précurseurs inorganiques (Li , PO4 …). Après
20 h, la poudre récupérée (« bactériomorphe ») est
caractérisée par microscopies électroniques (MEB,
TEM),
diffraction
des
rayons
X
(DRX),
spectroscopies (Raman, IR, Mössbauer, STXM),
analyses thermiques et de surfaces (BET/porosité).
Les tests électrochimiques sont réalisées vs Li° (20
m% Sp, 1M LiPF6 EC/DMC, 20°C). Un matériau de
référence, dit « abiotique », est précipité dans les
mêmes conditions mais sans bactéries.
3
a)
b)
Fig. 1. Images de Microscopie Electronique en Balayage de aFePO4·xH2O (a) « bactériomorphe » précipité en présence de
Sporosarcina pasteurii et (b) « abiotique » précipité en l'absence
de bactéries.
La Figure 1 permet de comparer la texture, la
morphologie et la taille du composite Bactérie / aFePO4·xH2O (« bactériomorphe ») et du matériau
« abiotique ». Ces matériaux sont amorphes (DRX)
III
et 100% Fe
(STXM, Mössbauer) mais se
distinguent par la taille et la texturation : les
bactériomorphes sont constitués de petites
particules (50-80 nm) déposées à la surface des
bactéries, tandis que le matériau « abiotique » est
constitué de particules non-organisées et de plus
grande taille (200-300 nm). La Figure 2 présente
les performances électrochimiques en cyclage
galvanostatique des bactériomorphes avant (a) et
après (b) avoir subi un traitement thermique à
température modérée. On note une nette
amélioration des performances avec i) l’apparition
de la signature spécifique de a-FePO4·xH2O et ii)
une excellente réversibilité. L’absence d’activité des
bactériomorphes non traités est due au caractère
isolant électrique de la matière organique.
Bacteriomorphs après traitement thermique
Bacteriomorphs 50°C
4
4
(a)
3,5
(b)
3,5
3
3
80
1,5
1
0,5
120
2,5
60
100
Capacity (mA/g of MA)
100
2
U (Volts)
2,5
Capacity (mAh/g of AM)
U (Volts)
1
Introduction
La production de matériaux d’électrodes pour
accumulateurs au lithium (Li-ion, Li-polymère)
consomme beaucoup d’énergie car requiert de
hautes températures de synthèse (ex : graphite,
NMC, LMO,..). Actuellement, plusieurs voies sont
parallèlement explorées pour résoudre ce
problème : i) la mise au point de nouvelles voies de
synthèses moins énergivores, ii) la recherche de
nouveaux
matériaux
préparés
à
basses
températures, iii) le développement du recyclage.
Nous proposons ici de profiter de l’assistance de
bactéries pour synthétiser et texturer des matériaux
d’électrode, à base d’éléments abondants et peu
toxiques, à température ambiante. Cela peut donc
constituer une nouvelle voie de synthèse plus écocompatible. Suite aux très bons résultats obtenus
lors d’une précédente étude (-Fe2O3, réaction de
conversion [1]), nous illustrerons ici l’intérêt de
cette démarche pour les réactions d’insertion grâce
à l’exemple du phosphate ferrique amorphe hydraté
2
1,5
40
1
20
0
0
5
10
15
20
0,5
25
80
60
40
20
0
0
Cycle number
10
20
30
40
Cycle number
50
0
0
0
20
40
60
80
Capacity (mAh/g of iron phosphate)
100
0
20
40
60
80
100
Capacity (mAh/g of iron phosphate)
Figure 2. Courbes Potentiel-Composition en mode
galvanostatique des bactériomorphes (vs Li°, 20 m% Sp, 1 Li /
20h, 20°C), avant (a) et après (b) traitement thermique.
Un
traitement
thermique
s’avère
donc
nécessaire bien qu’il soit largement reporté que la
déshydratation (voire cristallisation) du matériau qui
en résulte soit néfaste à son activité
électrochimique [2]. Néanmoins, les performances
atteintes sont équivalentes à celles obtenues après
broyage intense de a-FePO4·xH2O non texturé
avec du carbone conducteur. Ce point sera
largement discuté et illustré par de nombreuses
caractérisations, de même que les aspects
Capacité vs Puissance de ces matériaux.
4
Conclusions et perspectives
La présence de Sporosarcina pasteurii dans le
milieu de précipitation permet une forte texturation
du matériau a-FePO4·xH2O et une faible taille des
particules. La bactérie est ensuite décomposée afin
d’améliorer la conductivité électrique du composite.
Ce traitement thermique provoque de nombreuses
modifications chimiques et structurales qui ont été
suivies par diverses techniques dont nous
présenterons les résultats. Cependant, dans une
optique d’utilisation en accumulateurs Li(Na)-ion, la
bio-minéralisation directe de composés ternaires
demeure un des objectifs majeurs de notre projet.
Remerciements
Les auteurs remercient tous les acteurs du
projet (LRCS, IMPMC, RS2E, CRRBM, UM2) pour
leur aide et leur soutien.
Références
[1]
[2]
Miot, J. et al. Energy & Environmental Science 7, 451
(2014).
C.Masquelier et al, J. Electrochem. Soc. 149(8) A1037
(2002)
SCF Congress - 2015
Sputtered LiMn1.5Ni0.5O4 thin film for Li-ion microbattery
Dépôt de film mince de LiMn1.5Ni0.5O4 par pulvérisation cathodique
pour microbatterie Li-ion
M. Létiche1, 2*, E. Eustache1, 3, 4, T. Brousse3,4, P. Roussel2 and C. Lethien1, 4
1
Institut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN), Université Lille
1, CNRS UMR 8520 Avenue Poincaré, BP 60069, 59652 Villeneuve d’Ascq cedex, France
2
Unité de Catalyse et de Chimie du Solide (UCCS), CNRS UMR 8181, Université Lille 1,
59655 Villeneuve d’Ascq Cedex, France
3
Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la
Houssinière, BP32229, 44322 Nantes Cedex 3, France
4
Réseau sur le Stockage Electrochimique de l’Energie (RS2E), CNRS FR 3459, 33 rue SaintLeu, 80039, Amiens CEDEX, France
______________________________________________________________
Résumé :
Une électrode en film mince (LiMn1.5Ni0.5O4) pour microbatterie à ions lithium a été étudiée et développée par
pulvérisation cathodique radiofréquence. La morphologie ainsi que les propriétés structurales et électrochimiques
des couches ont été étudiées en fonction des paramètres de dépôt (puissance, pression et débit d’argon) ainsi que
de la température de recuit. Les couches minces obtenues possèdent une capacité de stockage de l’ordre de 100
-1
-2
-1
3
mAh.g , soit 40 µAh.cm .µm pour une densité de 4 g/cm .
________________________________________________________________________
Summary:
LiMn1.5Ni0.5O4 cathode material has been deposited by Radio Frequency sputtering for implementing in a Li-ion
microbattery. The morphology as well as the structural and electrochemical properties of the thin films have been
studied according to the deposition parameters (power, pressure, argon flow) and to the temperature of the post
-2
-1
deposition annealing. The resulting thin films exhibit high rate capability, high capacity (40 µAh.cm .µm ) with a
3
density assumed to be close to 4 g/cm and good retention capacity upon cycling.
Keywords: RF sputter deposition, Li-ion microbattery, LiMn1.5Ni0.5O4, high voltage spinel cathode, thin film
Today, with the fast development of portable technology and miniaturized devices, there is a need for energy sources for
powering them. Currently, Li-ion batteries are the energy storage devices the most widely used. Hence, the fabrication of
Li-ion microbatteries is already well developed, especially with the use of thin film technology. To enhance the
performances, high potential cathode material (LMNO) has been deposited by RF sputtering (TRL 2).
1
Introduction
The transition metal oxide with spinel structure,
LiMn1.5Ni0.5O4 (LMNO) is a promising candidate for
high energy density devices due to its high cut-off
+
potential (4.7 V vs Li/Li ) and its theoretical
-1
gravimetric capacity of 147 mAh.g [1]. In this
study, thin films of LNMO, which are free of binders
and additives, have been successfully deposited in
a two-step process by RF sputtering followed by a
post deposition annealing and they have been
characterized [2,3].
2
All the LMNO thin films have been sputtered on
silicon wafer for morphological and structural
analysis, but also on platinum – alumina – silicon
substrate
stacking
for
electrochemical
characterization using a 4 inches LMNO target
under argon atmosphere. The substrate-target
distance was kept close to 5 cm and the thin films
deposition was performed at room temperature.
LMNO films with different thicknesses (ranging from
0.1 to 1 µm) were obtained depending on the
deposition parameters. To reach the requested
LMNO spinel phase, the as-deposited thin films
have been annealed between 650 °C and 800 °C
under air atmosphere for 2 hours.
The surface morphology and microstructure
were carried out by atomic force microscopy (AFM)
and scanning electron microscopy (SEM). The
structure of the films was identified by X-ray
diffraction analysis (XRD). Cyclic voltammetry
experiments (CV) of the thin films have been
+
performed between 3.8 and 4.9 V vs Li/Li (0.2
mV/s) in a flat cell. The thin film was used as the
working electrode. A lithium foil was used both as
reference and counter electrode in LiClO4 (1M) in
EC:DMC (1:1) as the electrolyte.
3
In this study, two main parameters have been
mainly investigated: the pressure in the chamber
during the deposition process and the postannealing temperature. The argon flow rate and the
RF power have been respectively kept at 50 sccm
and 100 W. The deposition time was constant for all
the LMNO thin films (2h). The figure 1 (green area)
shows the cross-section of the as-deposited LMNO
-3
films at different deposition pressures, from 5.10
-2
mbar to 9.10 mbar. At low pressure, thin films are
very dense and they turn columnar and more
porous at higher pressure. According to the AFM
images (top view) grains are unregularly dispersed
on the surface and growing under higher pressure
which induces an increase of the surface
roughness.
Further
investigations
have
demonstrated that it was favorable to work at higher
deposition pressure: the LMNO thin films will then
be deposited at 0.09 mbar. The cross sections of
the LMNO layers deposited at 0.09 mbar as a
function of the post annealing temperature are
depicted in Fig 1 – brown area.
+
-1
4.9 V vs Li/Li at a scan rate of 0.2 mV.s . The CV
of the four samples annealed at different
temperatures are plotted on figure 3. The samples
were deposited at 0.09 mbar and the thickness was
about 1 µm. The 650, 700 and 750°C annealed
samples exhibit typical electrochemical responses
for LNMO material, meaning two oxidation peaks at
+
4.72 and 4.78 V vs Li/Li and two reduction peaks
+
2+
at 4.69 and 4.62 V vs Li/Li corresponding to Ni
4+
oxidation to Ni and then reduction.
Fig.2. XRD diffractogramms of the target, the as-deposited and
the annealed samples under air atmosphere at 650 700, 750
and 800°C for 2h. The evolution of the I400/I111 ratio is shown in
the inset.
The sample annealed at 700°C (black line)
presents higher discharge current (0.16 mA) which
means higher discharge capacity. The sample
annealed at 800°C exhibits only one broad
reduction peak at 4.56V probably correlated with
the observed change in the structure already
noticed by XRD analysis.
Fig.1. SEM and AFM images (scale 5µm x 5µm) show the
influence of pressure (green area) on the morphology of the
surface and the microstructure at room temperature. The
influence of the annealing temperature (brown area) on the
microstructure is also depicted, using a constant deposition
pressure (0.09 mbar).
The film morphology changes from columnar at RT
to granular and dense at 650°C, and then to
granular with voids. At high temperature, a growth
of the particle size is highlighted. The influence of
the annealing temperature on the structure was
investigated by XRD. The XRD patterns of the
LMNO target and the deposited samples are
displayed in figure 2. It clearly shows that LNMO
polycrystalline spinel structure is obtained after a
post deposition annealing at 650°C and 700°C. At
higher temperatures (750 and 800°C), a new phase
(peaks at 30° and 34°) appears in the thin film and
the peak intensities of the LMNO XRD patterns are
increased. The evolution of the (111) to (400)
diffraction peak integrated intensities ratio is shown
in the inset of fig. 2. A preferred orientation along a
<100> direction at temperatures higher than 700°C
is clearly evidenced. The electrochemical behavior
has been studied by cyclic voltammetry from 3.8 to
Fig.3. CV curves of the annealed samples at 0.2 mV.s-1 between
3.8 and 4.9 V vs Li/Li+.
4
Conclusions
Annealing temperature are key parameters to
obtain LNMO by RF sputtering. Structural
investigations showed that the spinel compound
LMNO was obtained polycrystalline when annealed
below 750°C. The film annealed at 700°C exhibits
the best electrochemical performance.
References
[1]
[2]
[3]
R. Santhanam et al, J. Power Sources 195 (2010) 54425451.
L Baggetto et al, Power Sources 211 (2012) 108-118
P. Soudan, T. Brousse, G. Taillades, J. Sarradin, ECS
spring meeting (2003)
SCF Congress - 2015
Electrochemical Reactivities of new n- and p-type Organic
Materials for Positive Electrode in Rechargeable Batteries
Réactivités Electrochimiques de Nouveaux Matériaux Organiques de
type n et p pour des Applications en tant qu’électrode positive dans
des Accumulateurs Rechargeables
Elise Deunf*,1, Anne-Lise Barrès1, Dominique Guyomard1, Franck Dolhem2,3,
Philippe Poizot1,4
1
Institut des Matériaux Jean Rouxel (IMN), UMR CNRS 6502, Université de Nantes, 2 rue de
la Houssinière, B.P. 32229, 44322 Nantes Cedex 3, France
2
Laboratoire de Glycochimie, des Antimicrobiens et des Agroressources (LG2A), FRE CNRS
3517, Université́ de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens, France
3
Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, France
4
Institut Universitaire de France (IUF), 103 bd Saint-Michel, 75005 Paris Cedex 05, France
______________________________________________________________
Résumé :
Dans le but de promouvoir un stockage électrochimique à plus faible empreinte environnementale, on assiste depuis
quelques années au développement de matériaux organiques pour une application en accumulateur. Nos efforts
dans ce domaine se sont surtout portés sur des composés de type n possédant des fonctions redox diénolates
lithiées capables d’être oxydées réversiblement (avec extraction d’ions lithium) et jouer ainsi le rôle de matériau
d’électrode positive. Plus récemment, nous avons également mis au point de nouveaux matériaux organiques de
+
0
type p, cette fois, pour permettre d’atteindre un potentiel moyen de charge au-dessus de 3 V vs Li /Li .
___________________________________________________________________________
Summary:
To promote electrochemical storage systems while limiting the demand on metal-based raw materials, a possible
parallel research to inorganic-based batteries consists in developing organic batteries. Along this line, we have
mainly designed and prepared n-type redox organic structures based on the reactivity of lithiated dienolate functions.
Upon charging, such compounds are able to extract reversibly lithium ions and can act as positive electrode
materials. More recently, we have also developed and assessed new p-type organic host materials to enable a
+
0
reversible electrochemical activity at an average charge potential above 3 V vs Li /Li .
Keywords: organic electrode materials, lithium-ion batteries, organic battery
The necessity to develop renewable electricity has markedly increased the need for high-performance and affordable
electrochemical generators, particularly the rechargeable ones. However, most common electrode materials are based
on inorganic materials obtained from non-renewable resources. To fulfill the actual market demands as well as the
emerging environmental concern, there is a need to design “greener” battery technologies. Switching to organic
structures may offer potentialities and environmental benefits. This communication will be an opportunity to present
recent advances in the field especially in terms of organic cathode materials offering interesting electrochemical
properties.
Pour répondre de manière durable aux besoins énergétiques actuels et futurs, il devient impératif de décarboner notre
ingénierie énergétique en favorisant nettement l’intégration des sources d’énergies renouvelables. Or, le fonctionnement
des accumulateurs actuels repose sur les propriétés électrochimiques de matériaux inorganiques non renouvelables,
issus de l’extraction minière. Dans le but de promouvoir des accumulateurs moins polluants, une voie de recherche
alternative consiste à recourir à des composés électroactifs organiques, pouvant dériver d’agro-ressources et plus
facilement recyclables. Cette communication sera l’occasion de présenter une série de matériaux organiques innovants.
1
Introduction
Li-ion batteries (LIBs) appear nowadays as
flagship technology able to power an increasing
range of applications starting from small portable
electronic devices to advanced electric vehicles.
Therefore, the world production of secondary
batteries is expected to keep on growing for a long
time. In this context, redox-active organic
compounds could play a significant role in the
forthcoming battery technologies notably because
composed of more abundant chemical elements [13]. Although the low cyclability of numerous organic
electrode materials has been pointed out due to
solubility issues in common electrolytes used in Libatteries, a few solutions have been proposed to
overcome this failure and drastically improve the
solid-state stability [1-3]. Additionally, the diversity
of organic compounds coupled with the easy
modification of the molecular framework from
classic synthetic routes offer a wide range of
possibilities for getting toward voltage tuning [4,5].
This contribution will be an opportunity to present
some n-type and p-type organic materials
(Figure 1) showing reversible electrochemical
activities for possible application in organic
rechargeable batteries.
Fig. 1. General p/n-type redox-active organic systems.
2
Synthesized
organic
compounds
were
1
characterized using several techniques (e.g., H
13
C NMR, FTIR, HRMS, TG-DSC).
and
Electrochemical measurements were performed in
conventional Swagelok-type cells using a Li metal
disc as negative electrode and a fiberglass
separator soaked with 1 M LiPF6 solution (in
ethylene carbonate:dimethyl carbonate / 1:1 in
volume ratio) as the electrolyte. Carbon additive:
33 wt%.
3
The electrochemistry of lithiated enolate
functions as n-type redox centers were first
investigated vs Li in a half cell configuration. Ionic
substitutents under the form of carboxylate groups
were incorporated to the structures for overcoming
the solubilization of such organic molecules in
classic batteries electrolytes. The para isomer of
the dienolate backbone in Li4-p-DHT (Figure 2a) is
able to reversibly de-intercalate the lithium at
+
0
2.55 V vs Li /Li with quite good electrochemical
performance. To go further and taking into account
an expected positive potential shift with the ortho
regio-isomer, Li4-o-DHT was then synthesized.
Interestingly, a positive shift of about 300 mV was
measured (Figure 2b). This gain is assigned to the
extended conjugation in the ortho backbone, a wellknown
phenomenon
in
the
molecular
electrochemistry
field
for
semiquinone
/
hydroquinones moieties.
Fig. 1. Galvanostatic cycling curve of a Li half-cell using (a) Li4p-DHT and (b) Li4-o-DHT as positive electrode material
(T = 20°C). Cycling rate: 1 Li+ exchanged in 5 h (adapted from
[5,6]).
In order to get towards higher voltages, we recently
investigated p-type organic materials and the
electrochemistry of their anion intercalation/release
reactions. Particularly, N-containing conjugated
structures appeared to exhibit quite interesting
reversible electrochemical properties with an
+
0
average voltage above 3 V vs Li /Li .
4
Conclusions
Novel and efficient electrode materials have
been designed and synthesized to promote
alternative organic batteries. Enolate and nitrogenbased functional groups were investigated as redox
center for Li insertion/de-insertion and anion
intercalation/release
reactions.
Interesting
electrochemical performances were observed with
fast kinetics, high voltages and good capacity
retention upon cycling.
Acknowledgements
This work was partially funded by the Region Pays
de la Loire and the Agence Nationale de la
Recherche (ANR Volta). The authors deeply thank
E. Quarez and P. Moreau (IMN), M. Becuwe
(LRCS, Amiens) and O. Ouari (ICR, Marseille) for
their help in this research project.
References
[1]
[2]
[3]
[4]
[5]
[6]
P. Poizot, F. Dolhem. Energy Environ. Sci. 4 (2011) 2003.
Y. Liang, Z. Tao, J. Chen. Adv. Energy Mater. 2 (2012)
769.
Z. Song, H. Zhou. Energy Environ. Sci. 6 (2013) 2280.
S. Nishida, Y. Yamamoto, T. Takui, Y. Morita.
ChemSusChem 6 (2013) 794.
S. Gottis, A.-L. Barrès, F. Dolhem, P. Poizot, ACS Appl.
Mater. Interfaces 6 (2014) 10870.
S. Renault, S. Gottis, A.-L. Barrès, M. Courty, O. Chauvet,
F. Dolhem, P. Poizot. Energy Environ. Sci. 6 (2013) 2124.
SCF Congress – 2015
Na3V2(PO4)2F3: crystal structure and phase transformations
upon Na+ extraction of a promising positive electrode
Na3V2(PO4)2F3 : structure cristalline et tranformations de phase
pendant l’extraction du Na+ d’une électrode positive prometteuse
M. Bianchini1,2,3,4, F. Fauth5, N. Brisset2, F. Weill2,4, T. Broux1,2, E. Suard3,
L. Croguennec2,4, C. Masquelier*1,4
1
Laboratoire de Réactivité et de Chimie des Solides,
CNRS-UMR#7314, Université de Picardie Jules Vernes, F-80039 Amiens Cedex 1, France
2
CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France
3
Institut Laue-Langevin, 71 Av. Des Martyrs, F-38000 Grenoble, France
4
RS2E, Réseau Français sur le Stockage Electrochimique de l’Energie, FR CNRS#3459,
F-80039 Amiens Cedex 1, France
5
CELLS - ALBA synchrotron, E-08290 Cerdanyola del Vallès, Barcelona, Spain
______________________________________________________________
Résumé : Ce travail présente l’étude détaillée de Na3V2(PO4)2F3, un matériau prometteur en tant qu’électrode
positive pour les batteries Na-ion de prochaine génération. Le contrôle de sa composition, de sa structure et de ses
propriétés électrochimiques est critique, ce qui explique les désaccords présents dans la littérature. Nous avons ainsi
récemment montré que le matériau stœchiométrique (sans substitution partielle de l’oxygène au fluor) présentait une
structure orthorhombique décrite dans le groupe d’espace Amam, jamais rapportée jusque-là, et une signature
électrochimique également originale, présentant une série de transitions de phase qui ont pu être reliées
principalement à des (dés)ordres sodium/lacune. La diffraction des rayons X synchrotron s’est révélée indispensable
pour mener cette étude.
________________________________________________________________________
Summary: This work is devoted to the detailed study of Na3V2(PO4)2F3, a material of great interest as positive
electrode for next-generation Na-ion batteries. The fine control of its composition, structure and electrochemical
properties is critical, explaining the discrepancies reported in literature. We have recently demonstrated that the
stoichiometric material (i.e. without any partial substitution of oxygen for fluorine) is characterized by an orthorhombic
structure described in the Amam space group, never reported before, and also by an original electrochemical
signature, showing a series of phase transitions associated to sodium/vacancy (dis)orderings. Synchrotron X-ray
diffraction was shown to be critical to the success of this study.
Keywords: Na-ion, Na3V2(PO4)2F3 , electrode, synchrotron, diffraction, in situ.
Li-ion is now the technology of choice for portable electronics and possibly transportation, but since lithium resources are
limited new technologies need to be developed. Na-ion is akin to Li-ion and can benefit from this similarity since much
research has been already done. However new electrodes are needed, combining high energy density and facile Na
extraction/insertion. Na3V2(PO4)2F3 has these properties and we work to get a full understanding of the way it reacts in a
battery, on a basic physico-chemistry level but also to bring it from laboratories to a commercial reality.
1
Introduction
Although Li-ion is now the technology of choice
for portable applications and it is spreading to the
automotive world, concerns have been recently
raised about the future availability and prize of
lithium resources [1]. Many alternatives are
explored and a large amount of research is
presently dedicated to the Na-ion technology, due
to the fact that sodium is cheap, abundant and that
the knowledge reached on lithium’s intercalation
chemistry makes the development of materials for
Na-ion batteries faster. We focused our efforts on
the
vanadium
polyanionic
compound
Na3V2(PO4)2F3. It presents an extraordinary
theoretical capacity of 192 mAh/g for the extraction
of 3 Na+, although only the extraction of 2 of them
has been experimentally demonstrated when the
material is cycled vs. Na [2]. The material is also
challenging from the crystal structure point of view,
since the whole family of compositions
Na3V2O2x(PO4)2F3-2x (0 ≤ x ≤ 1, with vanadium’s
oxidation state ranging from 3+ to 4+), shows an
extremely rich set of phase transformations vs.
temperature and composition, i.e. a rich phase
diagram. In the case of Na3V2(PO4)2F3 (x=0), the
crystal structure was established in 1999 by Le
Meins et al. [3], who described it in the tetragonal
space group P42/mnm, used until now, although
important discrepancies are found in literature.
2
We
used
electrochemical
techniques
(galvanostatic cycling, GITT) in combination with
diffraction ones (X-Rays, neutrons and electrons) to
determine in detail the electrochemical and
crystallographic properties of Na3V2(PO4)2F3. To
understand the material’s phase diagram upon Na+
extraction, we used synchrotron radiation diffraction
operando, i.e. in situ and during battery operation.
3
We reported on our finding of a small
orthorhombic
distortion
in
Na3V2(PO4)2F3
(a=9.028Å, b=9.044Å) that could only be observed
thanks to very high angular resolution synchrotron
radiation diffraction [4]. This led to a new structural
determination in the Amam space group, preserving
the structural framework but inducing a different
arrangement of sodium ions. Interestingly, we also
showed an orthorhombic-tetragonal transition
determined by the disordering of sodium ions at
high temperature. Regarding the sodium extraction
mechanism, this has always been reported to be a
simple solid solution described in the tetragonal
space group P42/mnm, with shrinkage of the unit
cell. However, different facts suggest otherwise:
firstly, the above-mentioned finding of a different
space group to describe the structure of
Na3V2(PO4)2F3; secondly, a recent theoretical work
suggesting that the phase diagram is more
complicated than a simple solid solution [5]: finally,
in situ experiments were performed by other groups
on materials of the family Na3V2O2x(PO4)2F3-2x
(x = 0.8, 1), showing a complex behavior [6]. We
decided to re-investigate the phase diagram of
Na3V2(PO4)2F3, thanks to in-situ (operando)
synchrotron radiation diffraction upon Na+
extraction. We observed for the first time an
extremely complicated sequence of biphasic and
monophasic reactions between the compositions
Na3V2(PO4)2F3 and NaV2(PO4)2F3, with several
intermediate phases formed upon charge [7].
Fig. 2. Comparison between laboratory (blue) and synchrotron
radiation (red) XRD data of Na3V2(PO4)2F3, showing how the
high angular resolution of synchrotron data allows to resolve the
orthorhombic splitting.
Fig. 3. Distribution of Na+ ions in the z = 0 plane in the structure
of Na3V2(PO4)2F3 described in the Amam space group.
4
Conclusions
Our work showed how Na3V2(PO4)2F3 is an
incredibly interesting material both for applications
in Na-ion batteries and scientifically for the rich
crystal chemistry it presents. Further analysis are
undertaken to get more insight into its properties
and to develop it as a commercial electrode.
Acknowledgements
This research was performed in the frame of the
French network RS2E and partly funded by the
French National Research Agency ANR (Descartes
project SODIUM).
References
[1]
[2]
[3]
[4]
[5]
Fig. 1. Galvanostatic cycling of a Na3V2(PO4)2F3 // Na battery,
showing the extraction of 2 Na+ at C/50 rate. Inverse derivative
curve (inset) reveals several electrochemical processes.
[6]
[7]
J. M. Tarascon, Nature Chemistry., 2, (2010), 510.
R. K. B. Gover, A. Bryan, P. Burns and J. Barker, Solid
State Ionics, 177 (2006), 1495.
J. M. Le Meins, M. P. Crosnier-Lopez, A. Hemon-Ribaud
and G. Courbion, Journal of Solid State Chemistry, 148(2),
(1999), 260.
M. Bianchini, N. Brisset, F. Fauth, F. Weill, E. Elkaim, E.
Suard, C. Masquelier and L. Croguennec, Chemistry of
Materials, 26(14), (2014), 4238.
Y.-U. Park, D.-H. Seo, H. Kim, J. Kim, S. Lee, B. Kim and
K. Kang, Advanced Functional Materials, 24(29), (2014),
4603.
N. Sharma, P. Serras, V. Palomares, H. E. A. Brand, J.
Alonso, P. Kubiak, M. L. Fdez-Gubieda and T. Rojo,
Chemistry of Materials, 26(11), (2014), 3391.
M. Bianchini, F.Fauth, N. Brisset, F. Weill, E. Suard, C.
Masquelier and L. Croguennec, Submitted.
SCF Congress - 2015
Iron fluoride synthesis for Li-ion batteries applications
Synthèses de fluorures de fer pour batteries lithium ion
D. Delbègue1,2, K. Guérin*,1,2, P. Bonnet1,2 , M. T. Sougrati3, B. Laik4, J.P.
Pereira-ramos4,C. Morthe-Cenac5
1
Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP
10448, F-63000 Clermont-Ferrand, France
2
CNRS, UMR 6296, Institut de Chimie de Clermont-Ferrand, F-63177 Aubière, France
3
Institut Charles Gerhardt Montpellier, AIME, CNRS UMR5253, Université Montpellier 2,
Place Eugène Bataillon - CC 004, 34095 Montpellier cedex 05, France.
4
Université Paris Est Créteil, Institut de Chimie et des Matériaux Paris-Est, UMR CNRS 7182
Thiais, France.
5
Centre National d’Etudes Spatiales, Toulouse, France.
______________________________________________________________
Résumé : Les batteries lithium ions sont la technologie de référence pour le stockage électrochimique de l’énergie.
Cependant, les matériaux cathodiques de ces batteries comme LiCoO2, LiMn2O4 ou LiFePO4 présentent une
capacité spécifique limitée (<160 mAh/g). De nombreux composés sont à l’étude pour améliorer cette performance
-1
dont le fluorure de fer 3 en raison de sa capacité théorique de 711 mAh.g .
Ce travail présentera la synthèse de FeF3 par différentes méthodes de fluoration de précurseurs choisis pour la
modularité de la liaison impliquant le fer. Les matériaux obtenus seront comparés en termes de structures et de
liaison (DRX, Mössbauer, spectroscopies IR et Raman) mais aussi de texture (isothermes d’adsorption à l’azote à
77K). Les propriétés électrochimiques des matériaux obtenus seront également comparées.
________________________________________________________________________
Summary: The lithium-ion batteries are the current solution for electrochemical energy storage. However, their
performances are limited by the cathode materials, such as LiCoO2, LiMn2O4 or LiFePO4 of specific capacity lower
than 160 mAh/g. Many materials are good candidate to improve this capacity such as iron trifluoride of theoretical
-1
capacity of 711 mAh.g .
This work will present the synthesis of FeF3 through different fluorination ways using various precursors chosen
with different iron bonding. The resulting materials will be characterized owing to their structure by XRD, Mössbauer,
Raman and IR spectroscopies and their texture by nitrogen adsorption isotherms at 77K. Finally the electrochemical
properties will be evaluated and compared.
Keywords: Iron trifluoride ; Li-ion Batteries ; Mossbauer; solid-gas fluorination
Le réchauffement climatique et l’épuisement des ressources fossiles montrent l’importance des énergies renouvelables.
La demande en énergie étant toujours croissante, ces énergies nécessitent donc d’être stockées, il est nécessaire de
trouver de nouveaux matériaux capables d’allier performances et durée de vie. L’utilisation de fluorures de fer pourrait
permettre d’améliorer la durée d’utilisation des batteries afin par exemple d’augmenter l’autonomie des véhicules
électriques. Cela nécessite de mettre en œuvre des méthodes de synthèse inédites de ces composés et de corréler la
structure et la texture de ces matériaux à leurs propriétés.
Congrès de la Société Chimique de France –
2015
SCF Congress - 2015
An “All-solid-state” sodium-ion battery using NASICON-type
materials and operating at 200°C
Batterie sodium-ion « tout-solide » à base de matériaux de structure
NASICON et fonctionnant à 200°C
F. Lalère1,2, J.B. Leriche1,2, M. Courty1,2, S. Boulineau1,2, V. Viallet1,2,
C. Masquelier1,2, V.Seznec*1,2
Laboratoire de Réactivité et Chimie des Solides (UMR 7314), Université de Picardie Jules
Verne, 33 rue Saint Leu, 80039 Cedex Amiens, France.
1
Réseau sur le Stockage Electrochimique de l’Energie (CNRS FR3459), 33 rue Saint Leu,
80039 Cedex Amiens, France.
2
Résumé : Une batterie monolithique “tout-solide” Na-ion fonctionnant à 200°C et utilisant des matériaux de structure
NASICON a été étudiée. Na3V2(PO4)3 est utilisé aux deux électrodes comme matériau actif tandis que Na3Zr2Si2PO12
sert d’électrolyte solide au sodium. La batterie complète est assemblée en une seule étape de frittage flash à 900°C
pendant 10’. Les caractéristiques électrochimiques à haute température (200°C) ont été évaluées grâce à un nouvel
appareil expérimental développé au laboratoire. La batterie fonctionne à un potentiel de 1,8 V et délivre 85% de la
capacité théorique pour un régime de C/10. Celle-ci présente une bonne rétention de capacité pour une densité
d’énergie de 1,87x10-3 W.h/cm2 et une capacité surfacique de 1,04 mA.h/cm2.
Summary: An all-solid state symmetric monolithic Na-ion battery operating at 200°C is described, using NASICONtype materials for electrodes and electrolyte. Na3V2(PO4)3 is used at both electrodes as the active material while
Na3Zr2Si2PO12 stands the role of the Na+ solid electrolyte. The full battery was assembled in a 10’ single step by
spark plasma sintering at 900°C. The electrochemical characteristics at high temperature (200°C) were evaluated
thanks to a new experimental set-up developed at the laboratory. The battery operates at 1.8 V with 85% of the
theoretical capacity attained at C/10 with satisfactory capacity retention, for an overall energy density of 1.87x10 -3
W.h/cm2 and a capacity of 1.04 mA.h/cm2.
Keywords: solid state battery ; sodium ; solid electrolyte ; NASICON ; energy storage ; high temperature
Le stockage et la restitution de l’énergie de manière sûre, peu chère et efficace est un enjeu majeur pour de nombreuses
applications (véhicule électrique, multimédia… .). De part le faible coût et l’abondance du sodium, la technologie Naion suscite un intérêt grandissant vis-à-vis du Li-ion. De plus, les batteries « tout-solide » présentent à la fois des
avantages en termes de sécurité mais aussi d’un point de vue environnemental du fait de l’absence de solvants dans
cette technologie.
Energy storage and conversion is a key factor for many applications (electric vehicle, multimedia… .) and have to be
safe, low cost and efficient. The low cost and abundance of sodium make the Na-ion technology more and more
attractive versus Li-ion. Moreover, “all-solid” state batteries are safer and more environment-friendly due to the absence
of solvents in this technology.
1
Introduction
Les batteries Na-ion ont récemment suscité un vif
intérêt dans le domaine du stockage électrochimique
de l’énergie [1-3] et commencent à être perçues
comme une alternative envisageable aux
technologies Li-ion dans le cadre d’applications
spécifiques. En particulier, de récents travaux sur les
matériaux d’électrode positive au sodium à base de
phosphate
tels
que
Na3V2(PO4)3 [4]
et
Na3V2(PO4)2F3 [5] ont démontré d’excellentes
performances. Néanmoins, de même que pour la
technologie Li-ion, les problèmes de sécurité liés à
l’utilisation d’électrolytes liquides inflammables
demeurent et deviennent même plus importants du
fait de la réactivité accrue du sodium vis-à-vis de
l’humidité et de l’oxygène. Des batteries « toutsolide » utilisant des électrolytes solides non
inflammables plutôt que des électrolytes organiques
se présentent alors comme de bonnes candidates
pour ces systèmes de stockage d’énergie [6-8]. En
suivant une démarche similaire à celle développée
précédemment pour les batteries Li-ion « toutsolide » [9,10], nous avons assemblé une batterie
Na-ion « tout-solide » monolithique.
2
Expérimental
Les matériaux d’électrodes et d’électrolyte solide
sont obtenus par voie céramique et sol-gel
respectivement et présentent tout deux une
structure NASICON. La fabrication de la batterie
s’opère en une seule étape de frittage flash (Spark
Plasma Sintering) à 900°C en 10 minutes (Fig. 1).
Le Ministère de l’Education Nationale et de
l’Enseignement Supérieur est grandement remercié pour
le support financier de F.L. via un Contrat Doctoral à
l’UPJV d’Amiens. Nous souhaitons également remercier J.
M. Tarascon et M. Morcrette pour leurs précieux conseils.
Fig. 1. (haut) photo et dimensions de la batterie et (bas) cliché
MEB en électrons rétrodiffusés d’une tranche de la batterie.
3
Résultats et Discussion
Na3V2(PO4)3 (NVP) tient à la fois le rôle de matériau
d’électrode positive (couple V4+/V3+) et négative
(couple V3+/V2+) tandis que Na3Zr2Si2PO12 (NZSP)
sert de matériau d’électrolyte solide. Les composés
présentent tous deux des transitions de phases
ordre-désordre et démontrent des conductivités de
1,5 x10-3 S.cm-1 et 1,9 x10-4 S.cm-1 à 200°C pour
Na3Zr2Si2PO12 et Na3V2(PO4)3, respectivement
Un nouveau dispositif expérimental mis au point au
laboratoire nous a permis de reporter pour la
première fois les caractéristiques électrochimiques
d’une batterie Na-ion « tout-solide » opérant à 200°C
[11]. Celle-ci se présente sous la forme d’une pastille
monolithique d’environ 500 m d’épaisseur totale,
les électrodes positive et négative contenant
chacune environ 60% massique d’électrolyte solide,
25% de matière active et 15% de Carbone SP. La
batterie délivre une tension de 1,8 V avec 85% de la
capacité théorique pour un régime de courant de
C/10 (Fig. 2.). Celle-ci montre une bonne rétention
de capacité avec une densité d’énergie totale de
1,87 x10-3 W.h.cm-2 et une capacité surfacique de
1,04 mA.h.cm-2.
4
Conclusions
Sur la base de ces travaux et à des fins de
compréhension et d’optimisation, différentes études
sont menées sur la préparation des matériaux, la
composition des électrodes, la fabrication de la
batterie par exemple. Enfin, des études post-mortem
(après cyclage) sont menées pour étudier le
vieillissement des batteries « tout-solide ».
5
Remerciements
Fig. 2. (à gauche) cyclage galvanostatique à 200°C à des
régimes de courant de C/2 ou C/10 pour un potentiel limite de 2,2
V pour les 3ème, 6ème et 26ème cycles et (à droite) rétention de
capacité au cours du dit cyclage.
6
Références
[1] K.B. Hueso, M. Armand, T. Rojo, Energy & Environmental
Science, 6 (2013) 734.
[2] H. Pan, Y.-S. Hu, L. Chen, Energy & Environmental Science,
6 (2013) 2338.
[3] B.L. Ellis, L.F. Nazar, Current Opinion in Solid State and
Materials Science, 16 (2012) 168-177.
[4] K. Saravanan, C.W. Mason, A. Rudola, K.H. Wong, P. Balaya,
Advanced Energy Materials, 3 (2013) 444-450.
[5] A. Ponrouch, R. Dedryvere, D. Monti, A.E. Demet, J.-M. Ateba
Mba, L. Croguennec, C. Masquelier, P. Johansson, M.R. Palacin,
Energy & Environmental Science, 6 (2013) 2361-2369.
[6] M. Nagao, Y. Imade, H. Narisawa, T. Kobayashi, R. Watanabe,
T. Yokoi, T. Tatsumi, R. Kanno, Journal of Power Sources, 222
(2013) 237-242.
[7] T. Ohtomo, A. Hayashi, M. Tatsumisago, Y. Tsuchida, S.
Hama, K. Kawamoto, Journal of Power Sources, 233 (2013) 231235.
[8] S. Boulineau, J.-M. Tarascon, J.-B. Leriche, V. Viallet, Solid
State Ionics, 242 (2013) 45-48.
[9] A. Aboulaich, R. Bouchet, G. Delaizir, V. Seznec, L. Tortet, M.
Morcrette, P. Rozier, J.M. Tarascon, V. Viallet, M. Dollé,
Advanced Energy Materials, 1 (2011) 179-183.
[10] G. Delaizir, V. Viallet, A. Aboulaich, R. Bouchet, L. Tortet, V.
Seznec, M. Morcrette, J.-M. Tarascon, P. Rozier, M. Dollé,
Advanced Functional Materials, 22 (2012) 2140-2147.
[11] F. Lalère, J.B. Leriche, M. Courty, S. Boulineau, V. Viallet, C.
Masquelier, V. Seznec, Journal of Power Sources, 247 (2014)
975-980.
SCF Congress - 2015
Charge storage in nanoporous carbons: The molecular origin
of supercapacitance
Stockage de charge dans les
moléculaire de la super-capacité
carbones
nanoporeux:
L'origine
B. Rotenberg1,2, C. Merlet1,2, C. Péan1,2 et M. Salanne1,2
1
Laboratoire PHENIX, CNRS et UPMC, 4 place Jussieu, 75005 Paris
2
RS2E (Réseau sur le Stockage Electrochimique de l'Energie)
______________________________________________________________
Résumé :
Très performants en puissance, les supercondensateurs sont utilisés pour récupérer l’énergie de freinage dans
certaines voitures ou tramways. Ils fonctionnent grâce à deux électrodes en carbone plongées dans une solution
ionique ou un liquide ionique pur. C’est l’adsorption d’ions à la surface qui permet de stocker l’électricité, mais le
mécanisme microscopique à l'origine des performances exceptionnelles des carbones dérivés de carbures (CDC)
pour le stockage de la charge restait à établir. Par simulation moléculaire d'électrodes de structure réaliste et
maintenues à potentiel constant, nous étudions les effets du confinement et de la solvatation sur le mécanisme de
charge. Nous précisons également la dynamique du processus de charge et faisons le lien avec les modèles utilisés
par les électrochimistes.
________________________________________________________________________
Summary:
Supercapacitors are electric devices able to deliver a large power, enabling their use e.g. for the recovery of breaking
energy in cars. This is achieved by using two carbon electrodes and an electrolyte solution or a pure ionic liquid
(Room Temperature Ionic Liquid, RTIL). Energy is stored by the adsorption of ions at the surface of the electrodes,
but the microscopic mechanism underlying the exceptional performance of Carbide Derived Carbon (CDC)
electrodes remained unknown. Using molecular simulation with realistic electrode structures and under constant
voltage conditions, we investigate the effect of confinement and solvation on the microscopic charging mechanism.
We further analyse the dynamics of the charging process and make the link with equivalent circuit models used by
electrochemists.
Keywords: Supercapacitors, Molecular Dynamics, Adsorption, Ion exchange, Electrode, Nanoporous carbon
This basic research approach explores the microscopic mechanisms at the origin of macroscopic observations that
remained to date unclear. Molecular simulation provides the theoretical tools necessary to address this fundamental
issue for which only limited experimental techniques on this scale are available. The insights gained on the molecular
scale can then be used to optimize the choice of carbon structure / electrolyte combination and provide new ideas for the
design of supercapacitors with improved performances.
Ce travail de recherche fondamentale explore les mécanismes microscopiques à l'origine d'observations
macroscopiques qui restaient jusqu'ici incomprises. La simulation moléculaire fournit les outils théoriques permettant de
s'attaquer à ces questions que peu de techniques expérimentales permettent d'aborder à cette échelle. Les
connaissances acquises à l'échelle moléculaire permettront d'optimiser le choix de la combinaison structure de carbone /
électrolyte et fournissent de nouvelles idées pour le design de supercondensateurs aux performances améliorées.
1
Introduction
Supercapacitors are electric devices able to
deliver a large power, enabling their use e.g. for the
recovery of breaking energy in cars and tramways
or the emergency door opening in the A380 airliner.
This is achieved by using two carbon electrodes
and an electrolyte solution or a pure ionic liquid
(Room Temperature Ionic Liquid, RTIL). Energy is
stored by the adsorption of ions at the surface of
the electrodes, but the microscopic mechanism
underlying the exceptional performance of Carbide
Derived Carbon (CDC) electrodes remained
unknown [1].
2
Methodology
Using molecular simulation, we investigated the
effect of confinement and solvation on the
microscopic charging mechanism, by taking two
essential features into account: Simulations are
performed under constant voltage and a realistic
structure of the electrode is used. The high
computational cost for the description of the
electrode is compensated by the use of a coarsegrained model for the electrolyte (butyl-methylimidazolium hexafluorophosphate, BMIPF6), either
as a pure ionic liquid or dissolved in acetonitrile.
Comparing planar graphite electrodes with CDC
allows us to uncover how charge separation occurs
in the latter [2] as well as the influence of the
degree of confinement on the charge storage
efficiency [3]. Comparing a RTIL with the same ions
in acetonitrile further allows investigating the
influence of solvation on charge storage (see Fig.
1). Finally, we used molecular simulations to
analyse the dynamics of the charging process and
to make the link with equivalent circuit models used
by electrochemists [4].
Fig. 1. Molecular simulation strategy: Comparing graphite and
nanoporous carbon electrodes allows us to uncover the role of
confinement, while comparing pure ionic liquids and organic
electrolytes we can assess the role of solvation.
3
Using a realistic model for the EDLC cell, we
report capacitances in quantitative agreement with
experimental results. We show that this increase is
not merely due to a larger surface area and
demonstrate the key role of the pore size and
microstructure. The electrode is wetted by the
electrolyte at null potential and the charging
process involves the exchange of ions with the bulk
electrolyte without changing the volume of liquid
inside the electrode. This exchange is accompanied
by a partial decrease of the coordination number of
the ions rendered possible by the charge
compensation by the electrode. The efficiency of
the storage process over that of planar graphite
electrodes arises from the confinement, which
prevents the occurrence of overscreening effects
[2].
We further provide a detailed analysis of the
various environments experienced by the ions. We
pick out four different adsorption types, and we,
respectively, label them as edge, planar, hollow and
pocket sites upon increase of the coordination of
the molecular species by carbon atoms from the
electrode. We show that both the desolvation and
the local charge stored on the electrode increase
with the degree of confinement [3].
Nanoporous carbon electrodes, which give
larger capacitances than simpler geometries, might
be expected to show poorer power performances
because of the longer times taken by the ions
to access the electrode interior. Experiments do not
show such trends, however, and this remains to
be explained at the molecular scale. We show
using molecular dynamics that carbide-derived
carbons exhibit heterogeneous and fast charging
dynamics. The system, originally at equilibrium in
the uncharged state, is suddenly perturbed by the
application of an electric potential difference
between the electrodes. The electrodes respond by
charging progressively from the interface to the bulk
as ions are exchanged between the nanopores and
the electrolyte region. The simulation results are
then injected into an equivalent circuit model, which
allows us to calculate charging times for
macroscopic-scale devices [4].
Recently, we have also explored new venues for
the accurate determination of the differential
capacitance with molecular simulations and the
prediction of the evolution of the interfacial
properties with voltage. This new strategy exploits
the equilibrium charge fluctuations in nanoscale
capacitors [5] and has already allowed to link peaks
in differential capacitance with voltage-induced
transitions in the adsorbed electrolyte [6].
4
Conclusions
Classical molecular dynamics simulation is a
powerful tool to investigate the microscopic
mechanisms underlying the exceptional ability of
nanoporous carbon electrodes to store charge in
supercapacitors. The insights gained on the
molecular scale will now be used to optimize the
choice of carbon structure / electrolyte combination
and provide new ideas for the design of
supercapacitors with improved performances.
Acknowledgements
The authors thank Paul Madden, Patrice Simon,
Pierre-Louis Taberna and Barbara Daffos. CM
acknowledges financial support from ANR under
grant ANR-2010-BLAN-0933-02, CP from ERC
under grant 102539. We are grateful for the
computing resources on JADE (CINES, French
National HPC) obtained through the project
c2013096728. We acknowledge PRACE for
awarding us access to resource CURIE based in
France at TGCC.
References
[1] Chmiola et al., Science 313, 1760–1763 (2006)
[2] Merlet et al., Nature Materials 11, 306 (2012)
[3] Merlet et al., Nature Communications 4, 2701 (2013)
[4] Péan et al., ACS Nano 8, 1576 (2014)
[5] Limmer et al., Phys. Rev. Lett. 111, 106012 (2013)
[6] Merlet et al., J. Phys. Chem. C 118, 12891 (2014)
SCF Congress - 2015
An intuitive and efficient method for cell voltage
prediction of lithium and sodium-ion batteries
Méthode Théorique Intuitive et Efficace pour la Prédiction du
Potentiel des Batteries Li/Na-Ion
M. Saubanère1,2,4, M. Ben Yahia1,4, S. Lebègue3,4, M.-L. Doublet*1,4
1
Institut Charles Gerhardt – Université Montpellier et CNRS – UMR5253 Place E. Bataillon,
34095 Montpellier, France
2
Collège de France – FRE3677 “Chimie du Solide et Energie”, 11 Place Marcelin Berthelot,
75231 Paris Cedex 05, France
3
Laboratoire CRM2 Institut Jean Barriol, CNRS—Université de Lorraine, BP 239, Boulevard des
Aiguillettes, 54506 Vandoeuvre-lès-Nancy
4
______________________________________________________________
Résumé : La tension délivrée par une batterie rechargeable au lithium ou au sodium est un paramètre clé pour
désigner le dispositif comme potentiellement prometteur pour de futures applications. Nous présentons une nouvelle
formulation du potentiel basée sur des grandeurs chimiques intuitives qui permet d’accéder rapidement et
précisément au potentiel d’une batterie, à partir de la structure cristalline des matériaux d’électrode. Le modèle –
validé sur une large famille de matériaux de cathode existants – fournit de nouvelles connaissances sur les
caractéristiques physiques et chimiques d'une structure cristalline qui influencent le potentiel d’un matériau et ouvrent
de nouvelles directions pour la conception de nouvelles batteries.
________________________________________________________________________
Summary: The voltage delivered by rechargeable Lithium- and Sodium-ion batteries is a key parameter to qualify the
device as promising for future applications. Here we report a new formulation of the cell voltage in terms of
chemically intuitive quantities that can be rapidly and quantitatively evaluated from the alkaliated crystal structure of
the electrode materials. The model – validated on a wide series of existing cathode materials – provides new insights
into the physical and chemical features of a crystal structure that influence the material potential and opens new
directions for the design of novel batteries.
Keywords: Theoretical chemistry, concepts et methods, Li/Na-ion batteries.
The method presented in this work opens new directions for the challenging project of material design in
rechargeable batteries. It allows a rapid assessment of battery cell voltage, is fully predictive and easy-handling,
thus utilizable by a large scientific community.
La méthode théorique présentée dans ce travail ouvre de nouvelles perspectives pour la conception de nouveaux
matériaux pour batteries. Elle permet d’accéder de manière rapide et prédictive au potentiel d’une batterie. Facile
à mettre en œuvre, elle est utilisable par une large communauté scientifique.
1 Introduction
Over the past 20 years, intensive research has
been devoted to the design of new promising
materials for positive electrodes in Li-ion batteries.
The candidates have to be safe, cheap and
environmentally friendly along with exhibiting high
energy density and good rate capability. Beside the
economic and ecologic aspects on which chemists
can act to meet the industrial specifications of ideal
materials, theoretical and computational chemistry
can also be used to improve the electrochemical
performances of electrodes in terms of energy
density. In principle, the battery energy density
should not be difficult to control (that is, improve) as
it depends on two thermodynamic quantities — the
capacity C (mAh/g) and the working voltage E (V)
— which are both fundamentally understood and
therefore easily tunable. In practice, however, the
literature teaches us that these two quantities are
not so easy to improve simultaneously. So far, the
calculation of a material potential requires the
computation of accurate reaction enthalpies within
the Density Functional Theory (DFT) framework.
Although this may appear much easier to conduct
than experiments, the procedure still requires a
significant amount of work: both the alkali-rich and
the alkali-poor compositions have to be computed
within a reasonable numerical accuracy for their
energy difference to be meaningful. To overcome
these limitations and provide an efficient and
affordable tool to experimentalists to evaluate
material potentials, a direct link between some of
the material properties and the operating cell
voltage of the battery is strongly needed. This
implies understanding which and how the different
constituents of a material contribute to the
amplitude of the potential, that is, how the
electronic structure of the material is linked to the
intrinsic nature of its constituting elements and to
the way they interact all together in the crystal.
2 Methodology
Following standard perturbation theory, we derived
a new formulation of the cell voltage in terms of
chemically intuitive quantities that can be rapidly
and quantitatively evaluated from the alkaliated
crystal structure with no need of first-principles
calculations.[1] The method is utilizable by any
solid-state chemist, is fully predictive and allows
rapid assessment of material potentials, thus
opening new directions for the challenging project
of material design in rechargeable batteries.
3 Results and Discussion
The decomposition we propose allows dissecting
the different factors controlling the material potential
in terms of electronic versus ionic and short-range
versus long-range contributions. Therefore, it brings
out which quantity is controlled by the chemical
nature of the redox active centre (redox couple) or
by the crystal structure (polymorph).
We
demonstrate that the potential of electrode
materials decomposes into one on-site contribution
directly linked to the chemical potential and
chemical hardness of the material redox centre and
two inter-site electrostatic contributions due to the
positive (Li+) and negative (e―) added charges. In
the specific case of strongly ionic systems, these
terms reduce to two Madelung contributions that
can be rapidly evaluated using simple formal
punctual charges that are very familiar to chemists,
and which linearly correlate with the battery cell
voltage (see Figure 1). This new formulation not
only discards the two-step DFT procedure required
so far to accurately compute cell voltages but is
also valid for any crystal structure, any ligand, any
transition metal and any alkali type and
stoichiometry.
The method also provides with a tractable
treatment of disorder such as cationic metal/Li
intermixing whose effect is here demonstrated to
substantially increase the material potential
compared with ordered materials displaying
equivalent ligand field.
Fig. 1. Theoretical vs. experimental cell voltages for a series of
Fe- (plain symbols) and Co-based (empty symbols) insertion
materials using formal charges.
Owing to its generalized expansion into meaningful
and easily tunable quantities, our approach
provides solid-state chemists new recipes for
designing new electrode materials for Li-ion (or Naion) batteries. It also rationalizes why potential and
capacity cannot be improve simultaneously or why
high-energy density materials are structurally
unstable. [2] In regards to the challenges our
society faces in terms of energy, this finding may
appear alarmist and appeals new paradigm and/or
new redox concepts to improve the battery
performances. Among these, the regeneration of
the redox centre upon cycling [3] or the valorization
of material structural instability and interfaces
reactivity [4] are some directions that deserve to be
investigated.
4
Conclusions
The model presented in this work is the first
quantitative model, free of first-principles DFT
calculations, allowing an accurate and nonparameterized evaluation of potential variations in
cathode materials, with an excellent accuracy.
Since the needed ingredients of the model require
insignificant numerical cost and corresponds to
easy handling quantities that can be manipulated
by any solid-state chemist, it is expected to
accelerate significantly the discovery of new
materials suitable for being used as electrodes in
lithiumor
sodium-ion
batteries.
More
fundamentally, the model dissects all the leading
parameters governing the material potentials in
terms of ionic versus electronic and short-range
versus long-range effects, thus providing recipes
going beyond the inductive effect to design new
materials.
References
[1]
[2]
[3]
[4]
Saubanère et al. Nature Commun. 5 (2014) 5559
Sathyia et al. Nature Materials 12, 2013, 827-835
Bichat et al. Chem. Mater. 16 (2004) 1002-1013
Dalverny et al. J. Mat. Chem. 114, 2010, 21750-21756
SCF Congress - 2015
Myths versus Facts in the Multiscale Modeling of
Electrochemical Devices for Energy Conversion and Storage
Mythes versus Réalités dans la Modélisation Multiéchelle des
Dispositifs Electrochimiques pour la Conversion et le Stockage de
l’Energie
A.A. Franco*1,2,3, Y. Yin1,2,3, G. Shuckla1,2,3, K.H. Xue1,2,3, T.K. Nguyen1,2,3, M.
Quiroga1,2,3, A. Torayew1, H. Huang1
1
Laboratoire de Réactivité et Chimie des Solides (LRCS), UMR CNRS 7314, Université de
Picardie Jules Verne, 80039 Amiens Cedex, France
2
3
ALISTORE-ERI, European Research Institute, FR CNRS 3104, F-80039 Cedex 1, France
______________________________________________________________
Résumé : Nous exposons nos développements de modèles multiéchelles pour l'analyse des mécanismes
physicochimiques dans les dispositifs électrochimiques pour la conversion et le stockage de l'énergie. Ces modèles,
inventés par nous il y a 14 ans, permettent de relier la chimie/microstructure de matériaux et composants avec leur
efficacité et durabilité macroscopique. En combinaison avec des expériences modèles, ils permettent concevoir et
optimiser les cellules de nouvelle génération. Les fondamentaux et aspects pratiques de nos modèles sont présentés
dans le contexte d'une littérature du domaine constituée par de réalisations concrètes mais aussi de mythes. Les
fonctionnalités puissantes de nos modèles sont illustrées par des exemples dans la R&D des batteries lithium
ion/air/soufre et les piles à combustible.
________________________________________________________________________
Summary: We provide here a comprehensive review on our developments of multiscale models for the analysis of
physicochemical mechanisms in electrochemical devices for energy conversion and storage. These models,
pioneered by us 14 years ago, allow linking the chemical/microstructural properties of materials and components with
their macroscopic efficiency and durability. In combination with “model” experiments, they can provide tremendous
progress in designing and optimizing the next-generation cells. Fundamentals and practical aspects of our models
are discussed within the context of a literature in the field composed of concrete achievements but also of myths.
Powerful capabilities of our models are concretely illustrated through examples in the lithium ion/air/sulfur batteries
and fuel cells R&D.
______________________________________________________________
Keywords: electrochemical energy conversion and storage, multiscale modeling, numerical simulation, rechargeable
batteries, fuel cells.
Devices for electrochemical energy conversion and storage exist at many different levels of development, from the early
stages of R&D to mature, deployed technologies. Our work consists on developing flexible, transferable and widely
available multiscale and multiphysics modeling tools of practical use by both academia and industry, including
manufacturers and end-users of these zero-emission and nomad devices. Thus our work falls at TRL1-TRL6 (R&D to
prototyping) strengthening the European energy sustainability.
Les dispositifs électrochimiques pour la conversion et le stockage de l’énergie existent à différents niveaux de
développement. Notre travail consiste à développer des outils de modélisation multiéchelles et multiphysiques flexibles,
transférables et disponibles pour leur utilisation pratique par le milieu universitaire et l'industrie, y compris les fabricants
et les utilisateurs finaux de ces dispositifs. Ainsi, notre travail s’inscrit aux niveaux TRL1 à TRL6 (R&D au prototypage)
contribuant au renforcement des stratégies européennes d’énergies soutenable.
1
Introduction
Electrochemical devices for energy conversion
and storage are called to play a significant role in
our future societies as they offer a great potential to
become cost competitive, highly efficient and
environmentally
benign.
However,
several
performance and durability challenges need still to
be overcome for their widespread application.
Because of the numerous competing mechanisms
at multiple scales, their design reveals to be a
complex optimization problem where different
scales have to be considered simultaneously.
We provide here a comprehensive review on the
fundamentals and practical aspects of an in-house
multiscale modeling approach for the analysis of
physicochemical mechanisms in this type of
devices. This approach, pioneered by us 14 years
ago [1-3] and boosted thanks to recent progresses
in computational science, allow linking the
chemical/microstructural properties of materials and
components with their macroscopic efficiency and
durability. In combination with “model” experiments,
it can provide significant progress in designing and
optimizing the next-generation cells [4].
2
Our modeling approach
Our approach generally results in bottom-up
continuum cell models describing mathematically
the physicochemical processes in multiple spatial
scales in the components (e.g. composite
electrodes) [5]. The mathematical descriptions
consist on a set of coupled partial and ordinary
differential equations translating the conservation of
reactants/products mass and charge as well as the
constitutive thermodynamic flux/effort relationships
associated to the transport and electrochemical
mechanisms. These equations contain parameters
related to the physicochemical and microstructural
properties of the components materials. In our
approach, their values are given by databases
generated from numerical “mining” simulations
based on the Density Functional Theory (activation
energies of relevant electrochemical reaction steps)
and Coarse Grain Molecular Dynamics (pore size
distributions and other relevant microstructural
features in composite electrodes, together with the
associated effective transport properties) [6-7].
These models are devoted to be merged into a
single in-house multifaceted cell simulator
called MS LIBER-T [8]. This is a flexible code,
supported in Python/C/Matlab, which can also
couple on the fly the numerical resolution of
continuum transport models with discrete models
(e.g. Kinetic Monte Carlo models describing the
elementary reaction kinetics on a catalyst surface).
lithium air batteries (LABs), lithium sulfur batteries
(LSBs) and polymer electrolyte membrane fuel cells
(PEMFCs) [9-12]. Calculated outputs include
observables (e.g. potential vs. time) and state
variables providing insights on the evolution of
intermediate reaction species, reactants, products,
charges concentrations during the cell operation, at
different scales in the components. Moreover, by
taking into account the on-the-fly feedback between
performance models and elementary kinetic models
describing materials degradation, our approach is
also able to predict the cell performance evolution
and durability as function of operation conditions
(e.g. applied current density or temperature) [7, 13].
4
Our approach allows predicting the behavior of
the materials in realistic electrochemical conditions,
and thus goes beyond prediction capabilities of the
widely
available
quantum
chemistry-only
computational methods. Aspects related to the
robustness and parameters transferability between
scales in our models are discussed in comparison
with literature models composed by both concrete
achievements but also myths. Finally, through one
example on phase transformation kinetics in LIBs, it
is demonstrated that rigorous analysis of
experimental data is only possible when the model
developed can be “simplified” to match the
“conceptual model” used by the experimentalist to
characterize the system under study.
Acknowledgements
We deeply acknowledge the Conseil Regional
de Picardie, the European Regional Development
Fund, the ANR and the European Commission for
the funding support through the projects
MASTERS, ALIBABA, PUMA MIND and EUROLIS.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
3
Results
The analysis and prediction capabilities of our
models are illustrated through concrete examples in
relation to the R&D on lithium ion batteries (LIBs),
Concluding remarks
[12]
[13]
a) A.A. Franco, PhD thesis, Université Claude Bernard
Lyon 1 (2005) ; b) A.A. Franco, Habilitation (H.D.R.)
manuscript, Université Claude Bernard Lyon 1 (2010).
A.A. Franco, P. Schott, C. Jallut, B. Maschke, J.
Electrochem. Soc., 153 (6) (2006) A1053.
A.A. Franco, P. Schott, C. Jallut, B. Maschke, Fuel
Cells, 7 (2007) 99.
A.A. Franco, Multiscale modeling of electrochemical
devices for energy conversion and storage, book chapter
in: Encyclopedia of Applied Electrochemistry, edited by R.
Savinell, K.I. Ota, G. Kreysa (publisher: Springer) (2013).
A.A. Franco, RSC Advances, 3 (32) (2013) 13027.
R. Ferreira de Morais, D. Loffreda, P. Sautet, A. A.
Franco, Electrochim. Acta, 56 (28) (2011) 10842.
K. Malek, A.A. Franco, J. Phys. Chem. B, 115 (2011) 8088.
www.modeling-electrochemistry.com
K. H. Xue, E. McTurk, L. Johnson, P.G. Bruce, A.A.
Franco, J. Electrochem. Soc., 162 (4) (2015) A614.
K.H. Xue, T.K. Nguyen, A.A. Franco, J. Electrochem.
Soc., 161 (8) (2014) E3028.
A.A. Franco, K.H. Xue, ECS Journal of Solid State Science
and Technology, 2 (10) (2013) M3084.
M.A. Quiroga, K.H. Xue, T.K. Nguyen, M. Tułodziecki, H.
Huang, A.A. Franco, J. Electrochem. Soc., 161 (8) (2014)
E3302.
L. F. L. Oliveira, S. Laref, E. Mayousse, C. Jallut, A.A.
Franco, PCCP, 14(29) (2012) 10215.
SCF Congress - 2015
Development of a new simulation method to model diffusion
and NMR spectra in porous carbons: insights into ion
adsorption in supercapacitors
Développement d'une nouvelle méthode de simulation pour modéliser
la diffusion et les spectres RMN au sein des carbones poreux : étude
de l'adsorption des ions dans les supercondensateurs
C. Merlet1,*, A. C. Forse1, J. M. Griffin1, D. Frenkel1, C. P. Grey1
1
Department of Chemistry, University of Cambridge, Lensfield road, Cambridge CB2 1EW,
UK
______________________________________________________________
Résumé : Au sein des supercondensateurs, l'énergie est stockée par adsorption des ions à l'interface
carbone/électrolyte. L'utilisation de carbones poreux possédant de larges surfaces accessibles permet d'obtenir de
grandes capacités et donc de grandes densités énergétiques. Néanmoins, la surface accessible n'est pas la seule
propriété qui compte. Ce travail vise à combiner des techniques de RMN in situ, qui fournissent des informations sur
la structure et la dynamique de l'électrolyte au sein de la porosité, avec une méthode de simulation originale,
développée en vue d'interpréter finement les résultats expérimentaux, pour mieux comprendre les mécanismes du
stockage de charge dans ces systèmes.
________________________________________________________________________
Summary: Supercapacitors are electrochemical energy storage systems which store energy at the carbon/electrolyte
interface through ion adsorption. The use of porous carbon materials with large surface areas leads to high
capacitances, and thus large energy densities. Nevertheless, the surface area is not the only material property that
matters. This work aims at combining in situ NMR techniques, which can provide information about the structure and
dynamics of the liquid electrolyte confined inside the porosity, with an original lattice simulation method, developed to
interpret the experimental results in details, in order to gain insights into the mechanisms of charge storage in these
systems.
Keywords: supercapacitors, adsorption, porous carbon, in situ NMR, lattice simulation, diffusion
This work is done in the context of the fundamental research on energy storage and more particularly on carbon/carbon
supercapacitors. The combination of theory and experiments aims at getting insights into the mechanisms of charge
storage at the electrode/electrolyte interface in order to suggest new materials with optimised properties. The developed
methods can be extended to other systems such as batteries.
Ce travail entre dans le contexte de la recherche fondamentale sur le stockage de l'énergie et en particulier sur les
supercondensateurs carbone/carbone. La combinaison de la théorie et des expériences vise à mieux comprendre les
mécanismes du stockage de charge à l'interface électrode/électrolyte afin de proposer de nouveaux matériaux aux
propriétés optimisées. Les méthodes développées pourront être étendues à d'autres systèmes tels que les batteries.
1
Introduction
This project focuses on the characterisation of
the electrode/electrolyte interface in supercapacitors through the combination of in situ NMR
techniques and lattice simulations. The idea is to
bridge the gap between molecular simulations,
which provide information about quantities such as
energy landscapes and locally induced magnetic
fields, and NMR experiments which correspond to
averages over relatively long times and length
scales compared to molecular simulations. In the
case of supercapacitors, the active material for the
electrodes consists in porous carbons with high
surface areas to maximise ion adsorption, which is
at the origin of energy storage in these systems.
The carbon materials commonly used are
disordered which renders the description of their
structure and the electrode/electrolyte interface
very difficult although this characterisation is an
essential step in order to understand the relation
between the structural properties of the materials
and the obtained electrochemical performances.
2
Methodology
This work relies on the development of a new
coarse-grained model able to use input from
molecular simulations to predict NMR spectra
corresponding to these input data. Here, we
propose a new lattice simulation method to predict
NMR spectra of ions diffusing in porous carbons.
The method is made very numerically efficient
through the use of the 'moment-propagation'
approach [1], a method that allows us to account for
all possible trajectories that particles could follow in
a discretised model of a porous network. The model
is parametrised using input from molecular
dynamics simulations such as the free-energy
profile for ionic adsorption [2], and densityfunctional theory calculations are used to predict
the NMR chemical shift of the diffusing ions [3].
3
Advanced Fellowship to CPG) for funding. ACF and
JMG thank the NanoDTC Cambridge for travel
funding. DF acknowledges EPSRC Gran No.
EP/I000844/1.
In this work, parametrisation was performed for
an organic electrolyte confined in slit mesopores of
various pore sizes (from 2 nm to 10 nm) and we
could show that, while a number of environments
would be observed if the diffusion of probed
species was ultra-slow, the exchange rates
involved in experiments lead to the detection of a
single resonance. This peak is observed for an
average chemical shift which depends both on the
pore size and on the adsorption profile of the
studied species.
The model is also parametrised in order to
represent a carbon particle with a realistic pore size
distribution. The lattice model allows us to explore
various spatial distributions of the pore sizes and
various conditions such as applying different
temperatures and magnetic fields, which can be
related to experimental conditions. While some
parameters are known from microscopic simulations, others can be estimated by comparing
computed and experimental spectra for a range of
temperatures and magnetic fields. Such a comparison yields novel insights into the structure of
porous carbon materials, and the structure and dynamics of the liquid inside the pores.
4
Conclusions
The technique presented in this work provides a
tool to extract information about the spatial
distribution of pore sizes from NMR spectra. Such
information is difficult to obtain from other
characterisation techniques. This new lattice model
is expected to provide new insights into in situ NMR
experiments performed on supercapacitors. Moreover, because of its versatility, the lattice model is a
powerful tool to investigate a full range of materials,
for which NMR parameters can be determined,
including battery and fuel cell materials.
Fig. 1. The method developed in this work allows us to model
carbon particles using input from both experimental and
molecular simulation data, and to predict NMR spectra for ions
diffusing in these model particles. a) Pore size distribution used
in the model. b) The pore sizes can be distributed randomly or
following a gradient in one of the three dimensions. Different
colors represent different chemical shifts (corresponding to
different pore sizes). c) The resulting spectra depend on both the
spatial distribution of the pore sizes and the barrier height to
jump from one pore size to another (activation energies are
equal to 1.7 or 11.8 kJ/mol in the case represented here).
Acknowledgements
CM acknowledges the School of the Physical
Sciences of the University of Cambridge for funding
through an Oppenheimer Research Fellowship.
CM, ACF, JMG and CPG acknowledge the Sims
scholarship (ACF), EPSRC (via the Supergen
consortium, JMG), and the EU ERC (via an
References
[1]
[2]
[3]
D. Frenkel, Phys. Lett A 121 (1987) 385.
C. Merlet, M. Salanne, B. Rotenberg, P. A. Madden,
Electrochim. Acta, 101 (2013) 262.
A. C. Forse, J. M. Griffin, V. Presser, Y. Gogotsi,
C. P. Grey, J. Phys. Chem. C 118 (2014) 7508.
SCF Congress - 2015
The structural defect in over-stoichiometric LiCoO2:
a solid-state chemistry investigation
Le défaut structural de LiCoO2 sur-stoechiométrique :
une investigation de chimie du solide
M. Ménétrier*, D. Carlier, C. Delmas
CNRS, Univ. Bordeaux, ICMCB, UPR9048 F33600 Pessac
______________________________________________________________
Résumé : LiCoO2 est toujours le matériau de positive le plus utilisé dans les batteries Li-ion. Sa structure lamellaire
est très simple, mais la RMN du Li a montré qu’il peut comporter un défaut paramagnétique s’il est préparé avec un
excès de Li, sans que la diffraction ne soit affectée. La courbe électrochimique est affectée par ce défaut.
Nous discutons les caractérisations et les expériences menées pour proposer la présence de Li excédentaire en
substitution du Co, avec autant de lacunes d’oxygène pour la compensation des charges, ce qui conduit a quelques
3+
ions Co en site pyramidal à base carrée au lieu d’octaédrique. Des simulations par DFT confirment de plus la
plausibilité de cette hypothèse de défaut.
_______________________________________________________________________
Summary: LiCoO2 is still the most widely used positive material for Li-ion batteries. It exhibits a quite simple layered
structure but Li NMR showed that it can contain a paramagnetic defect when prepared with excess Li, without change
in diffraction patterns. The electrochemical curve is altered by the presence of this defect.
We discusses various characterizations and experiments we have carried out leading to propose the presence of
3+
excess Li in substitution for Co, with as many oxygen vacancies for charge compensation. This leads to some Co
ions with a square-based pyramidal instead of octahedral environment. DFT simulations also confirm the likelihood of
such a defect.
Keywords: LiCoO2 ; Li-ion Batteries ; Structural defect ; overstoichiometry, MAS NMR
This work highlights a basic solid state chemistry strategy on an application-wise very important material: using solid
state chemistry synthesis and characterization methods, with additional help from theoretical simulation, to understand
structural defects that control the operation of one of the most important Li-ion battery materials.
Ce travail illustre l’intérêt d’une démarche fondamentale de chimie du solide sur un matériau très important au niveau
application : Mettre en œuvre des méthodes de caractérisation et de synthèse de chimie de solide, associées à la
simulation, pour comprendre les défauts structuraux qui contrôlent le fonctionnement d’un des plus importants matériaux
pour batteries Li-ion.
1
Introduction
LiCoO2 has been used in commercial Li-ion
batteries ever since their introduction by Sony in
1991. It still is the most widely used positive
electrode material, at least for portable consumer
electronics. Its structure is very simple and very
+
suitable to deintercalation/intercalation of Li ions
3+
accompanied by oxidation/reduction of Co ions,
as proposed by Goodenough in 1980 [1]. It consists
of an NaCl-type arrangement where Li and Co are
ordered in alternate atomic layers perpendicular to
the [111] cubic direction. This leads to a trigonal R3m space group whith alternate layers of edgesharing LiO6 and CoO6 octahedra (diamagnetic LS
Co3+ ions) packed along the [001] hexagonal
direction.
Deintercation of Li from LiCoO2 during the
charge of the battery is accompanied by oxidation
3+
4+
of Co to formally Co (the reverse spontaneous
phenomena occurring during discharge thus
provide the wanted current, and therefore energy).
However, we showed in 1999 using Li NMR, that
the electrons are actually delocalized (itinerant),
3+
4+
between formally Co and Co ions, the partially
filled t2g orbitals of edge sharing octahedral Co ions
being able to overlap and form a metallic-like
conduction band, in agreement with Goodenough’s
general criterion [2,3]. This electronic delocalization
is the driving force for a phase separation between
a metallic phase with composition Li0.75CoO2 and a
4+
phase with few Co ions leading to small-polarontype hopping. Actually, the maximum amount of
4+
such Co ions before phase separation strongly
depends upon the actual composition i.e. on the
defects content of the material.
We had indeed shown in 2000 that LiCoO2
prepared with excess Li2CO3 does not lead to the
phase
separation
during
electrochemical
deintercalation, while “stoichiometric” LiCoO2
phase-separates for Li0.94CoO2 [4]. We showed
more recently that “very stoichiometric” LiCoO 2 can
also be prepared and separates into the metallic
phase as early as x = 0.99 [5].
Extra Li NMR signals are present in the overstoichiometric material, revealing the presence of
paramagnetic defects in the material. We initially
2+
hypothesized the presence of Co ions associated
to extra Li ions [4]. Then, we proposed that extra Li
3+
ions are present in substitution for Co ions, with
as many oxygen vacancies that compensate the
charges. This leads to a structural defect consisting
3+
of Co ions in square-based pyramids where they
have an intermediate spin configuration [6].
In this communication, we propose an overview
of the steps that led to our hypothesis, with an
emphasis on recent results based on XAS
measurements and on simulation of the defect
using DFT calculations [7].
2
LiCoO2 samples were prepared from Co3O4 and
Li2CO3 using different ratios and different thermal
treatments. Very stoichiometric LiCoO2 requires a
very long 900°C annealing in O2 of nominally
stoichiometric LiCoO2. Over stoichiometric LiCoO2
is prepared using large excess of Li2CO3 and
washing of the unreacted portion of the material
after 900°C thermal treatments.
7
Li MAS NMR (including 2D EXSY-RFDR
through
space
dipolar
Li-Li
correlation
measurements), magnetic measurements (SQUID),
Mössbauer spectroscopy (of Fe-doped samples)
are
used,
as
well
as
electrochemical
characterization in cells with a Li metal negative
electrode.
DFT calculations use a pseudo-potential method
with GGA+U approximation in the VASP code.
3
Only in very stoichiometric LiCoO2 does Li NMR
(very long T1) and susceptibility data confirm fully
3+
6
diamagnetic LS CO
with t2g
electronic
configuration.
In Li-overstoichiometric samples, a Curie-Weiss
behavior is observed while NMR shows the
presence of Li ions associated to a paramagnetic
ion as defects within the material (figure 1).
A series of investigations led us to propose the
3+
formula Li1+tCo1-tO2-t with 2t intermediate spin Co
ions.
Co K-edge XAS suggests Co-Co and Co-O
coordination numbers in agreement with the
hypothesis.
O K-edge spectra show additional pre-edge
features vs. the stoichiometric compound,
suggesting additional O 2p-related empty states.
VASP calculations for a Li25Co23O47 supercell
3+
(corresponding to t = 0.04) lead to pairs of IS Co
ions with a peculiar electronic configuration (figure
2).
Analysis of the Co 3d and O 2p partial DOS
shows the existence of hybrid additional empty
levels, in very good agreement with the O K-edge
observation.
Li
z
Co dyz
y
Co dyz
Fig. 2. The modeled structural defect in Li1+tCo1-tO2-t:
a pair of intermediate spin state Co3+ ions in square-based
pyramids with electron spins in the dyz and dz2 orbitals.
4
Conclusions
Although without a strict proof, we believe we
have elucidated the nature of the defect in
overstoichiometric LiCoO2, via a panel of
experiments and characterizations, with help of
theoretical simulation.
Acknowledgements
C. Denage, I. Saadoune, S. Levasseur, Y.
Shao-Horn, A Wattiaux, B.J. Huang, M.
Deschamps, R. Messinger, E. Salager for
participation in various steps of the work. Umicore
and Région Aquitaine for financial support.
References
[1]
[2]
[3]
[4]
[5]
[6]
Fig. 1. 2D EXSY-RFDR 7Li MAS NMR map showing crosspeaks for all the signals, and therefore dipolar proximity of all the
Li species in the material.
[7]
K. Mizushima, P. C. Jones, P. J. Wiseman and J. B.
Goodenough, Mater. Res. Bull. 15 (1980) 783.
J. B. Goodenough, Prog. Solid State Chem. 5 (1971) 278.
M. Ménétrier, I. Saadoune, S. Levasseur and C. Delmas
J. Mater. Chem. 9 (1999) 1135
S. Levasseur, M. Ménétrier, E. Suard and C. Delmas
Solid State Ionics 128 (2000) 11
M. Ménétrier, D. Carlier, M. Blangero and C. Delmas
Electrochemical and Solid State Letters 11 (2008) A179
S. Levasseur, M. Ménétrier, Y. Shao-Horn, L. Gautier, A.
Audemer, G. Demazeau, A. Largeteau and C. Delmas
Chem. Mater. 15 (2003) 348
D. Carlier, J-H. Cheng, C-J. Pan, M. Ménétrier, C. Delmas
and B-J. Hwang, J. Phys. Chem..C 117 (2013) 26493
SCF Congress - 2015
Capacitive Charge Storage Behavior of Carbon Based
Electrodes Investigated By Fast Electrogravimetric Methods
Stockage des Charges Capacitives d'électrodes à base de Carbone
étudié par des Méthodes d'Electrogravimétrique Rapide
O. Sel1,2, H. Perrot1,2, I. T. Lucas1,2, M. Lahcini3, M. Raihane3, A. El Kadib,4 H.
Goubaa1,2, F. Escobar1,2, I. Ressam1,2,3
1
Sorbonne Universités UPMC Univ Paris 06, UMR 8235, LISE, F-75005, Paris, France
CNRS, UMR 8235, LISE, F-75005, Paris, France
3
Laboratoire de Chimie Organométallique et Macromoléculaire Matériaux Composites, Faculté
des Sciences et Techniques, Université Cadi Ayyad, B.P 549 Marrakecch Morocco
4
Euromed Research Institute, Engineering Division, Euro-Mediterranean University of Fes
(UEMF), Fès-Shore, Route de Sidi Hrazem, 30070 Fès, Morocco
2
______________________________________________________________
Résumé : L'efficacité des dispositifs de stockage d'énergie, (ex : supercondensateurs), dépend en grande partie des
propriétés physiques des matériaux d'électrode (surface spécifique, propriétés d'interface, porosité, morphologie). Il
est donc nécessaire de caractériser ces paramètres qui jouent un rôle prépondérant pour les performances. Dans ce
travail, nous avons étudié l’électroadsorption d'ions au sein des électrodes de carbone (à base d'oxyde de graphène
réduit et de nanotubes de carbone). Pour ce faire, un outil de caractérisation a été proposé en couplant une
microbalance à quartz rapide et la spectroscopie d'impédance. Cela permet de fournir des informations sur l'aspect
cinétique et thermodynamique relatives aux transferts des ions/du solvant au niveau des interfaces
électrode/électrolyte.
________________________________________________________________________
Summary: The efficiency of energy storage devices, including supercapacitors, depends largely on the physical
properties of the electrode materials (the specific surface area, interfacial properties, porosity and/or morphology). It
is therefore necessary to characterize and to control the parameters that play a predominant role for the performance
of these materials. In this work, we have studied the electroadsorption of ions on carbon electrodes, including
electrochemically reduced graphene oxide and carbon nanotube based thin films. To do so, an alternative
characterization tool was proposed which couples fast quartz crystal microbalance and electrochemical impedance
spectroscopy which provided information on the kinetic and energetic aspect of ion transfer at the carbon
electrode/electrolyte interfaces.
Keywords: Electric double-layer capacitors, carbon nanotubes, electrochemically reduced graphene oxides,
electrogravimetry, ac-electrogravimetry, quartz crystal microbalance
Electric double-layer capacitors (EDLCs), store
charges through reversible ion adsorption at
electrolyte-electrode interfaces upon applying a
voltage [1]. Carbon materials (carbon nanoparticles,
nanotubes, graphene) have been extensively
studied as supercapacitor electrodes. Among these
carbons, graphene and graphene-like materials
have shown great application potential. However,
producing graphene with desirable properties is still
a significant challenge. Synthesis route from
graphene oxides (GO) is considered to be the most
economical, but often includes hazardous
chemicals. Therefore, electrochemical methods are
often preferred as a green strategy for the reduction
of graphene oxides to produce graphene-like
materials [2].
Since the efficiency of energy storage devices,
including EDLCs, depends largely on the physical
properties of the materials that are constituted of,
such as the specific surface area, interfacial
properties, porosity and/or morphology [3,4]. It is
therefore necessary to characterize and to control
the parameters that play a predominant role for the
performance of these materials. Particularly, the
morphology dependent performance, and kinetic or
dynamic aspects of ion electroadsorption behaviour
of carbon based electrodes is not a quite solved
issue. In the literature, the interaction of ions with
carbon based electrodes was investigated by in situ
and ex situ characterization techniques, including
electrochemical and gravimetric methods. However,
none of these methods alone provides the
information on the exact identification of the
electroadsorbed ionic species, their dynamics of
transfer at the interfaces, as well as the role of
electrolyte composition and the effect of ions
solvation on the charge storage phenomena.
Therefore,
in
this
work,
an
alternative
characterization tool was proposed which couples
fast quartz crystal microbalance (QCM) and
electrochemical impedance spectroscopy (EIS) (acelectrogravimetry). This method has recently been
employed for studying transfer and transport
phenomena in materials for charge storage [5]. This
coupled method, so called ac-electrogravimetry
differs from classical EQCM and measures the
usual electrochemical impedance, ΔE/ΔI (ω), and
the mass variations of the film under a sinusoidal
potential perturbation, Δm/ΔE (ω), simultaneously
[6]. This coupling has the ability to detect the
contribution of the charged or uncharged species
and to separate the anionic, cationic, and the free
solvent
contributions
during
the
various
(pseudo)capacitive processes.
Specifically, the capacitive charge storage
behavior of electrochemically reduced graphene
oxide (ERGO) and carbon nanotube based
electrodes were examined. GO films were
elaborated on the gold electrode of a quartz
resonator which was followed by a subsequent
electrochemical reduction step. The reduced film
was
then
characterized
with
structural
characterization methods such as FEG-SEM, EDX,
XRD, HR-TEM and in-situ Raman spectroscopy
during electro-reduction of GO films. The
supercapacitive charge storage was evaluated by
classical electrochemical methods such as cyclic
voltammetry in aqueous electrolytes. Since EDLCs
store energy by accumulating positive or negative
charges from electrolytes on the surface of the
electrodes, the understanding of the dynamics of
the ion transfer at the electrode/electrolyte
interfaces is highly important to further improve the
performance of these electrodes. Under a potential
perturbation, ERGO electrode mass varies due to
the electroadsorption/desorption process at the
electrolyte/film interface to ensure electroneutrality.
This phenomenon was investigated with acelectrogravimetry in various aqueous electrolytes
(LiCl, NaCl and KCl, thus varying the cation size).
Our findings indicate that there are two different
charged species are transferred (solution cations
and their hydrated counterparts) and free solvent
molecules indirectly intervene in the charge
compensation, suggesting a more complex charge
storage behavior than envisaged. Our comparative
+
study shows that the transfer of K cations is more
+
+
rapid than that of Na , and Li ions are the slowest
species transferred. This kinetic behavior can be
attributed to the differences in the dehydration
+
energies of the present cations. The transfer of K
is faster, most likely due to its easier dehydration
(easier removal of its hydration shell). In contrast,
+
Li is strongly attached to its hydration shell, making
its transfer slower. The same trend in the dynamic
behavior of ion electroadsorption have been
observed in carbon nanotube based electrodes (for
a variety of CNTs, single, double, multi wall CNTs).
To the best of our knowledge, this study is the
first experimental attempt to understand the ion
transfer
dynamics
in
ERGO
by
fast
electrogravimetric methods, which might have
significant implications on the supercapacitive
charge storage mechanisms and to
subtleties unreachable with classical tools.
extract
References
[1]
[2]
[3]
[4]
[5]
[6]
J. Chmiola, C. Largeot, P. L. Taberna, P. Simon, Y.
Gogotsi, Science 328 (2010) 480.
H. Guo, X. Wang, Q. Qian, F. Wang, X. Xia, ACS Nano, 9,
(2009) 2653.
P. Simon, Y. Gogotsi, Nature Mater. 7 (2008) 845.
J. R. Miller, P. Simon, Science 321 (2008) 651.
C. Ridruejo Arias, C. Debiemme-Chouvy, C. Gabrielli, C.
Laberty-Robert, A. Pailleret, H. Perrot, O. Sel, J. Phys.
Chem. C, 118 (2014) 26551.
C. Gabrielli, J. J. Garcia-Jareno, M. Keddam, H. Perrot, F.
J. Vicente, Phys. Chem. B. (2002) 106, 3182.
SCF Congress - 2015
Operando Neutron Diffraction Studies of Li-ion battery
electrodes
Etudes de diffraction des neutrons operando au sein de batteries Li-ion
M. Bianchini1,2,3,4, E. Suard3, L. Croguennec2,4, C. Masquelier*1,4
1
Laboratoire de Réactivité et de Chimie des Solides, CNRS-UMR#7314,
Université de Picardie Jules Vernes, F-80039 Amiens Cedex 1, France
2
CNRS, Univ. Bordeaux, ICMCB, UPR 9048, F-33600 Pessac, France
3
Institut Laue-Langevin, 71 Av. Des Martyrs, F-38000 Grenoble, France
4
RS2E, Réseau Français sur le Stockage Electrochimique de l’Energie, FR CNRS#3459,
F-80039 Amiens Cedex 1, France
______________________________________________________________
Résumé : L’objectif de cette étude est de démontrer la possible utilisation de la diffraction de neutrons operando au
sein de cellules électrochimiques type « Li-ion » afin de pouvoir extraire des données expérimentales de qualité pour
une étude fine des évolutions structurales des matériaux au cours du cyclage charge/décharge. Nous avons
développé une nouvelle cellule à base d’alliage « Ti,Zr » (transparent aux neutrons) particulièrement efficace et qui,
utilisée sur la ligne D20 de l’ILL de Grenoble, permet d’obtenir des diagrammes de diffraction de haute qualité, en un
temps de mesure raisonnable. Des déterminations structurales par affinements Rietveld ont pu être réalisées sur
plusieurs systèmes physico-chimiques en cours de cyclage, tels que LiFePO4, Li1+xMn2-xO4 (x=0, 0.05, 0.1) ou
LiNi0.5Mn1.5O4.
________________________________________________________________________
Summary: Our work aims at applying neutron diffraction for the study of electrode materials for Li-ion batteries, and
importantly to do so operando, namely in situ & during battery operation. We thus developed a new electrochemical
cell (manufactured with a neutron-transparent (Ti,Zr) alloy) that combined with deuterated electrolytes gives good
electrochemical properties and high quality neutron diffraction patterns. This allows detailed structural determinations
of electrode materials by Rietveld refinement during operation. After validating the cell with well-known battery
materials such as LiFePO4, we used it to study new ones, as the series of spinel materials Li1+xMn2-xO4 (x=0, 0.05,
0.1) or high-voltage mixed Ni-Mn spinels such as LiNi0.5Mn1.5O4.
Keywords: Neutron diffraction, in situ, operando, electrodes, Li-ion batteries, Rietveld
This work gives us the possibility to use a non-standard diffraction technique (in the sense that neutrons are less widely
used than X-Rays for materials characterization) to understand how an electrode material for Li-ion batteries reacts
during battery operation. Neutrons have the advantage of being the best radiation to be diffracted in order to “see”
lithium. This is the first time, to our knowledge, that such a neutron transparent cell is proposed, which allows high quality
structural refinements of Li-battery materials under operation.
1
Introduction
In situ techniques proved to be exceptionally useful
tools to understand electrode materials for Li-ion
batteries [1]. Despite the great interest generated
by neutrons’ sensitivity to lithium, in situ neutron
diffraction (ND) knew a slow development due to
the intrinsic difficulties it held [2].
2
We recently designed an electrochemical cell
manufactured
with
a
completely neutrontransparent (Ti,Zr) alloy [3]. Used with deuterated
electrolytes, the cell is able to combine good
electrochemical properties and the ability to collect
ND patterns operando, with good statistics and no
other Bragg peaks than those of the electrode
material of interest. Importantly, this allows detailed
structural determinations by Rietveld refinement
during operation. The cell was validated using wellknown battery materials such as LiFePO4 and
Li1.1Mn1.9O4 [3] demonstrating real operando
experiments conducted on the D20 high flux
neutron powder diffractometer at ILL Grenoble,
France.
3
The cell was used to study challenging materials.
We report here in particular on a series of spinel
materials Li1+xMn2-xO4 (x = 0, 0.05, 0.1). The wellknown difference in electrochemical performances
(capacity fading) observed in this family of materials
was thoroughly investigated
neutron diffraction [4].
using
operando
of key importance for understanding and therefore
improving Li-ion battery materials.
Fig. 1. Scheme of the developed in situ cell.
Fig. 3. Left: Phase diagram observed operando upon charge
(Li+ extraction) for LiMn2O4 (top), Li1.05Mn1.95O4 (middle) and
Li1.10Mn1.90O4 (bottom). Right: focus on a narrow 2θ angular
range of the respective neutron diffraction patterns, showing the
peaks’ evolution.
4
Fig. 2. 3D view of the operando charge of a LiFePO4 electrode
measured on the D20 diffractometer. The LiFePO4 phase can be
observed to disappear, while the FePO4 charged phase appears.
Our study shows that not only the volume change
induced by the delithiation is reduced while going
from LiMn2O4 to Li1.10Mn1.90O4, but more importantly
+
that the mechanism of Li extraction from these
Li1+xMn2-xO4 (x = 0, 0.05, 0.1) compositions is highly
dependent on the initial value of x. In fact, while
Li1.10Mn1.90O4 reacts though a “simple” monophasic
reaction (a solid solution), Li1.05Mn1.95O4 shows the
existence of a solid solution process followed by a
biphasic reaction. LiMn2O4 shows a sequence of
two biphasic reactions. Both the above mentioned
features
contribute
to
make
overlithiated
Li1.10Mn1.90O4 a much better candidate for use in Liion batteries than the standard stoichiometric
LiMn2O4.
In more details, neutrons allow to refine lithium’s
atomic parameters, such as atomic coordinates and
even site occupancy factors (SOFs), and thus to
include them in our analysis by the Rietveld method
to increase the accuracy of our time-dependent
structural model. In the specific case of Li1+xMn2-xO4
spinels, this meant the possibility to correlate, for
the first time, the evolution of lithium’s SOF with the
electrochemical features of the materials, which is
Conclusions
Our developed operando electrochemical cell has
clearly demonstrated to be an useful tool to study
(de)intercalation reactions in Li-ion battery
electrodes. The insight we can get is unique and
complementary to information obtained by other
characterization techniques. The cell has also been
used for several new in situ experiments in late
2014, performed in charge and in discharge for a
number of positive and negative electrodes for Liion batteries. The first results of these experiments
will be shown and discussed.
Acknowledgments
The authors are grateful to Thomas Hansen (ILL)
for scientific support on the D20 beamline at ILL, to
P. Dagault, L. Etienne and E. Lebraud (ICMCB),
J.B. Leriche (LRCS) for technical help and
discussion, to Région Aquitaine for financial support
and to the Institut Laue-Langevin for the funding
PhD thesis of Mattéo Bianchini (PhD-ILL Grant)
References
[1]
[2]
[3]
M. Morcrette, Y. Chabre, G. Vaughan, G. Amatucci, J. B.
Leriche, S. Patoux, C. Masquelier and J. M. Tarascon,
Electrochimica Acta, 47 (2002), 3137.
M. Roberts, J. J. Biendicho, S. Hull, P. Beran, T.
Gustafsson, G. Svensson and K. Edstrom, Journal of
Power Sources, 226 (2013), 249.
M. Bianchini, J. B. Leriche, J.-L. Laborier, L. Gendrin, E.
Suard, L. Croguennec and C. Masquelier, Journal of The
Electrochemical Society, 160 (2013), A2176.
[4] M. Bianchini, E. Suard, L. Croguennec and C.
Masquelier, Journal of Physical Chemistry C, 118(42),
(2014), 25947.
SCF Congress - 2015
High Temperature Steam Electrolysis and Co-electrolysis
Results at stack and System levels
Résultats d’Electrolyse Haute Température et de Co-Electrolyse à
l’échelle du stack et du système
M. Reytier*, S. Di Iorio, A. Chatroux, M. Petitjean, J. Mougin
CEA-LITEN, 17 rue des Martyrs, F-38054 Grenoble Cedex 9, FRANCE
______________________________________________________________
Résumé : Couplée à une électricité décarbonée et à une source de chaleur bon marché, l’électrolyse de la vapeur
d’eau à haute température, basée sur la technologie à oxydes solides, est un moyen pour produire massivement de
l'hydrogène à haut rendement et à faible empreinte carbone. Cette technologie peut aussi produire du gaz de synthèse
(CO + H2) par co-électrolyse d’un mélange de vapeur d’eau et CO2 offrant ainsi un recyclage très prometteur du CO2.
Des essais à l’échelle du stack en mode électrolyse et co-électrolyse ont été réalisés. Un empilement de 25 cellules a
produit jusqu'à 1.9 Nm3 / h d'hydrogène à 800 ° C en dessous de 1,3 V pour toutes les cellules et une conversion de la
vapeur de l’ordre de 50%. Le mode co- électrolyse a également été validé. Enfin, cette conception de stack a été
installée dans un système, démontrant les potentialités de cette technologie avec une consommation électrique totale
3
de 3,9 kWe / Nm d’hydrogène.
________________________________________________________________________
Summary: High Temperature Steam Electrolysis, based on solid oxide technology is a high efficient way to produce
massively hydrogen with low carbon footprint, if coupled to a CO2-free electricity and a low cost heat. Moreover, it can
also produce syngas (H2 + CO) by co-electrolyzing a mix of steam and CO2 .This syngas constitutes the basis of further
synthetic fuels, offering therefore a very promising CO2 reuse. Here experiments at stack level in both electrolysis and
3
co-electrolysis modes have been carried out. A 25-cell stack has produced up to1.9 Nm /h of hydrogen at 800°C below
1.3V for all the cells and a steam conversion around 50%. The co-electrolysis mode has also been validated. Finally, this
stack design has been plugged in a system, demonstrating these technology potentialities with a total electrical
3
consumption of 3.9 kWe/ Nm of hydrogen.
Keywords: Solid Oxide Stack, Hydrogen, Syngas, System,
Introduction
1
Increasing needs of energy worldwide require the
development of energy sources alternative to fossil
fuels, as regards to CO2 emissions. To develop the
hydrogen economy, its production should therefore
present a low carbon footprint, which is not the case
with steam methane reforming (SMR) massively
used today. Hydrogen production through water
electrolysis is one of most favored production
processes for that purpose and High Temperature
Steam Electrolysis (HTSE) appears as the most
efficient electrolysis way [1]. Based on solid oxide
technology (as the Solid Oxide Fuel Cells, SOFCs),
it is operated above 700°C. If this technology offers
several advantages, high levels of performance and
durability, in association with cost-effective stack
and system components are still the key points [2-9].
Thanks to the high operating temperature, this
HTSE technology is also liable to electrolyze
different compounds such as a mixture of H2O and
CO2 to produce syngas (H2+CO) [10] that can be
transformed into synthetic fuels (methane, diesel,
methanol, DME, etc) according to the H2/CO ratio at
the electrolysis outlet. These synfuels complement
hydrogen for the storage of intermittent renewable
energies through the power to gas concept that
currently raises growing interest.
In the present paper, experimental results in
steam electrolysis and co-electrolysis (steam and
CO2) modes are presented, at the scale of a 25-cell
stack and of a system.
2
Experiments
Figure 1. View of the stack installed into the test rig and
instrumented before testing
The cells tested were hydrogen electrode
supported cells. The H2 electrode (cathode) was a
NiO-8YSZ cermet (nickel oxide NiO + 8mol% Yttria
Stabilized Zirconia YSZ) with a thickness of 500
µm. The electrolyte, having a thickness of 5 µm,
was 8YSZ. The O2 electrode (anode), was made of
LSC (Lanthanum–Strontium-Cobaltite) having a
thickness of 20 µm, with a diffusion barrier layer of
CGO (Gadolinia doped Ceria) applied between YSZ
and LSC.
The stack is based on thin interconnects using
0.2 mm AISI441 ferritic stainless steel sheets
(Figure 1). The active area was 100 cm². A nickelmesh and a LSM contact element were used in the
hydrogen and oxygen compartment respectively. A
cross flow design was chosen. Sealing was
achieved with a commercial ceramic glass. A mica
foil was added to ensure the electrical insulation
between two adjacent interconnects,
This low-weight thus cost efficient stack design
developed by CEA-LITEN has been evaluated with
25 cells. It leads to one of the best performances at
this scale level. In HTSE it reaches more than -1.5
A/cm² at 800°C without exceeding 1.3V at a steam
conversion rate around 50% and -1 A/cm² at 700°C
with a steam conversion rate of 32%.
The
presented prototype is perfectly tight and therefore
offers optimum performances and complete
recovery of the produced gases. The homogeneity
of all the cells in the stacks confirms a good
electrical contact and a good gas distribution. The
average value of the ASR is 0.24 Ohm.cm². A
power of 5.6 kW for this 25-cell stack has been
obtained. These performances constitute one of the
best results published at this stack level.
These results validate the CEA stack design for
both HTSE and co electrolysis mode, since in this
latter mode performances close to pure steam
electrolysis were obtained.
Moreover, a system (Figure 2) based on this
design has been performed. It is based on a single
stack and the necessary auxiliaries, including high
temperature exchangers to preheat the inlet flows
from heat recovered in the exhaust gases. It has
3
produced 1.2 Nm /h of H2 with a total electrical
3
consumption of 3.9 kWh/Nm , achieving 92% of
efficiency (electrical consumption of the system vs
HHV of the produced hydrogen). It also demonstrates
that a 150°C heat source temperature is sufficient for
the steam generation, and that a slightly exothermic
operating mode of the stack is sufficient to preheat
the inlet gas up to 700°C and compensate the system
heat losses.
These results confirm the potential of this technology
to store the carbon-free electricity into hydrogen: very
high efficiencies thanks to the high temperature
operation, but no high temperature heat source
required, and a very promising help to recycle the
CO2 into synthetic fuels.
Figure 2. View of the system
3
Acknowledgements
This work has been supported by the Carnot
Institute for future energies. Moreover, colleagues
from CEA, Philippe Szynal, Michel Planque, Bruno
Oresic and Thomas Donnier-Maréchal are greatly
thanked for their participation to this work.
References
C. Graves et al., Sustainable Energy Reviews, 15, 1 (2011)
J.E. O'Brien et al., J. Fuel Cell Sci. Technol., 3 (2), 213
(2006).
[3] C.M. Stoots et al., Nucl. Technol. 166 (1), 32 (2009).
[4] S.H. Jensen et al., Int. J. Hydrogen Energy, 32 (15), 3253
(2007).
[5] A. Brisse et al., Int. J. Hydrogen Energy, 33 (20), 5375
(2008).
[6] L. Zhou et al., Electrochimica Acta, 53 (16), 5195 (2008)
[7] V.N. Nguyen et al., Int. J. Hydrogen Energy, 38 (11), 4281
(2013).
[8] M.A. Laguna-Bercero, J. Power sources, 203, 4 (2012).
[9] S.H. Jensen et al., Int. J. Hydrogen Energy, 35 (18), 9544
(2010).
[10] C. Graves et al., Solid State Ionics 192, 398–403 (2011)
[1]
[2]
SCF Congress - 2015
Development of high performance components for PEMFC
Développement de composants hautes performances pour PEMFC
Th. Priem*, P. A. Jacques, A. Morin, G. Gebel
CEA-LITEN, 17 rue des Martyrs, F-38054 Grenoble Cedex 9, FRANCE
______________________________________________________________
Résumé : Afin d’atteindre les objectifs industriels pour les piles à combustible de type PEMFC (performances,
durabilité, coût…), les activités de R&D du CEA couvrent à la fois les matériaux (catalyseurs à faible chargement en
métaux nobles, membranes…), les composants (électrodes, couches de diffusion, Assemblages MembraneElectrodes), la conception des stacks (plaques bipolaires) et systèmes intégrés. Dans ce but, les approches
expérimentales et modélisation sont menées simultanément.
________________________________________________________________________
Summary: To reach industrial targets for PEMFC (performances, durability, costs…), R&D activities at CEA cover
materials (low noble metal catalyst, membranes…), components (electrodes, GDL, Membrane-Electrode
Assemblies), stack design (bipolar plates) and integrated systems. For this purpose, both experimental and modelling
approaches are done in parallel.
Keywords: PEM Fuel cells, catalyst, electrodes, membrane, bipolar plates
1
Introduction
Even though PEMFC is a rather mature
technology
close
to
commercialization,
improvements are still required for fulfilling the
industrial specifications. The main remaining
2
challenges are a power density up to 1 W/cm for
automotive applications, a lifetime up to 40 000
hours for stationary applications and a system cost
lower than 30 $ per kW for private cars.
To reach these targets, R&D activities at CEA
cover materials (catalyst, membranes…), stack
design (bipolar plates) and integrated system
management including hybridization with Li-ion
battery.
2
Research on Catalysts
In a PEMFC, both hydrogen oxidation reaction
(HOR) at the anode and oxygen reduction reaction
(ORR) at the cathode need to be catalysed. The
most efficient catalyst used to date is platinum
which allows accelerating the kinetic of the HOR
and ORR and thus increases the efficiency of the
Membrane Electrode Assembly (MEA). However, in
2009 IPHE has published a study showing that the
platinum cost could be responsible of 20% of the
global cost of the PEMFC system. We have shown
in addition that the cathode requires 4 times more
Pt than the anode [1]; therefore, major attention has
been given to the design of catalysts for ORR with
decreased Pt content.
Research
activities
at
CEA
integrate
fundamental developments on low Pt content
catalysts within full size MEAs.
The structuration of Pt in order to make each Pt
atom active towards ORR is scaled-up and tested.
A
specifically
designed
electro-deposition
techniques has allowed grafting Pt nanoparticles on
a full size electrode with a mass activity twice
higher than reference commercial catalyst. The
fabrication of Pt nanotubes either by electrodeposition on sacrificial Silicon template, direct
liquid injection metal organic chemical vapour
deposition (DLI-MOCVD) or atomic layer deposition
(ALD) is also investigated [2]. This new family of
self-supported catalysts shows promising results in
term of specific activity and gas accessibility even if
the mass activity is still to be increased (4.5 A/gPt).
One additional concept to reduce Pt content is
its alloying with a non-noble metal. Co was found to
be the most promising and nano-clusters of
Pt 0.6 Co 0.4 have been produced allowing reaching
mass activity of 16 A/gPt @0.9 V, which is two
times higher than pure Pt. Thermal treatment
allowed the nano-structuration of Pt 3 Co core-shell
particles with the shell (active part of the
nanoparticle) made of Pt and the core made of
PtCo alloy. However, characterization of these
core/shell catalysts by HR-TEM (High Resolution
Transmission Electron Microscopy), performed after
ageing tests, showed the formation of hollow
particles attributed to non-noble metal leaching by
Kirkendall effect [3].
In the above described approach, the MEA is
considered as a whole and the catalyst as a
component which has to be evaluated in situ taking
into account its interaction with the carbon based
support material and other components such as
membrane material. Furthermore, the up-scalability
of the catalyst synthesis and the electrode
preparation are also considered. Finally, on line
with recent conclusions of European consortium
including CEA, we aim at reducing the Pt content
(g/kW) maintaining the MEA power density (W.cm
2
) optimal. This approach is specific to CEA which
covers the entire field from catalyst to PEMFC
system.
3
Research on Membrane electrode
Assemblies (MEAs)
The development of Membrane Electrode
Assembly at a scale representative of industry with
high performances and high durability requires a
complete understanding of the link between local
operating conditions and global performances as
well as a deep knowledge of the different
phenomena occurring at micro-scale level within
the electrodes. For that reason, research’s activities
on MEAs at CEA have been developed jointly at
experimental and modelling levels with a strong
focus on two major issues, i.e. water management
and degradation phenomena.
Fig. 1. Cross section imaging of a MEA showing the various
layers of electrodes (gas diffusion layer, microporous layer and
active layer) surrounding the electrolyte.
Current mapping of large surface MEAs was
developed in order to follow upon aging the
evolution with time of the current density along the
electrodes. Additionally, advanced TEM techniques
were used to identify the main degradation
mechanisms occurring inside the membrane and
along the electrodes. These studies highlighted a
heterogeneous degradation of the active layers
between gases inlet and outlet which might be
related to heterogeneity of working conditions
(gases partial pressure, relative humidity, current
density…) as observed in water transport or current
mapping experiments. In addition, TEM images
coupled to chemical mapping allowed identifying
the modifications of Platinum or Pt alloys
nanoparticles due to ageing depending on both
global and local conditions [4].
Multi-scale and multi-physics modelling has
been developed in the last years to complement the
experimental approach for understanding at every
level the reactions occurring during operation [5]. It
is based on a full multi-scale approach in which the
nano/micro continuum scales are coupled with abinitio calculation (from external collaborations) and
fundamental
mechanisms
(electrochemical,
transport) are studied and integrated (Figure 2).
Effective parameters and degradation mechanisms
are calculated at the scale of the rib/channel and of
the cell. These scales are mainly used to calculate
the impact of local conditions on performance and
reversible
and
irreversible
degradation
mechanisms. For that purpose an electrochemical
double layer model has been developed to
understand locally the competition between the
different irreversible and reversible degradation
mechanisms. In addition, models focused on fluidic
phenomena or based on pore network simulation
give inputs for electrode and gas diffusion layer
processing in order to improve water management
within the fuel cell [6].
Fig. 2. Modelling multi-scale approach on the nano and microscale of the active layer and the GDL.
These coupled models describing performance,
degradation mechanisms and fluids transport have
allowed simulating the distribution of gases in
channels and of current density upon operation,
opening the door for iterative optimisation
approach.
Main results so far are i) a decrease of platinum
loading within large area MEA from 0.6 to 0.2
-2
mgPt.cm keeping same performances, ii) tuned
active layer with adapted polymer composition and
newly developed catalysts limiting local flooding, iii)
the development of tuned gas diffusion electrode
with properties adapted to various operating
conditions representative of targeted applications,
iv) MEAs reproducible durability over 2500 hours
under load cycling operation, an accelerated
degradation protocol representative of transport
conditions.
4
Conclusions
Most of the components for PEMFC are already
well known technologies that deserve adaption and
improvement for fulfilling the new specifications of
the hydrogen-energy application. In particular,
several key bottlenecks still remain such as
performance and durability in representative
transient operations due to new applications such
as automotive drive chain or micro-cogeneration. In
addition, cost reduction is a highly challenging
target for entering the market place.
Material science associated with scaling-up and
system integration is a most promising way to
overcome these issues and to reach the industrial
targets. Consequently, CEA will continue in the
coming years, its R&D activities on material
science.
References
[1]
[2]
[3]
[4]
[5]
[6]
Billy E. et al., J. Power Sources, 2010.
Lazar F. et al., Electrochim. Acta, 2012 ; Galbiati S. et al.,
Electrochim. Acta, 2014.
Lepesant, PhD thesis, 2014 ; Dubau L. et al., Appl. Catal.,
B, 2013; Dubau L. et al., Electrochim. Acta, 2011.
Guétaz L. et al., J. Power Sources, 2012
Robin C. et al., Int. J. of Hydrogen Energy, 2013.
Pauchet J. et al., J. Power Sources, 2011
SCF Congress - 2015
Autonomous glass sealant for high temperature application
Matériaux vitreux autocicatrisants pour application à haute
température
Montagne L.1* Carlier T.1, Mear F.O.1, Podor R.2, Saitzek S.1, Castanié S.1
1 Université Lille Nord de France, UCCS UMR CNRS 8181, Villeneuve d’Ascq, France
2 Institut de Chimie Séparative de Marcoule, UMR 5257 CEA-CNRS-UM2-ENSCM, Marcoule, France
* Corresponding author:[email protected]
______________________________________________________________
Résumé : Les verres et vitrocéramiques constituent une solution technologique efficace pour réaliser des
scellements ou des joints devant fonctionner à haute température. On peut citer en exemple la réalisation de joints
d’étanchéité pour pile à combustible à oxyde solide (SOFC solid oxide fuel cell) dont la température de
fonctionnement est comprise entre 700 et 900 °C. Toutefois, la longévité de ces joints est limitée par différents
facteurs, en particulier par la formation de fissures consécutives aux cycles thermiques. Nous illustrons ici comment
le concept d’autocicatrisation peut être mis en œuvre dans le cadre des joints de verre SOFC.
________________________________________________________________________
Summary: Glass and glass-ceramic provide an effective technology solution for producing seals or joints to operate
at high temperature. One example is the production of seals for solid oxide fuel cell (SOFC) whose operating
temperature is 700–900 °C range. However, the life time of these joints is limited by several factors, and particularly
by the formation of cracks due to consecutive thermal cycles. We illustrate in the paper how the concept of selfhealing can be implemented within the SOFC glass joints.
Keywords: Glass and glass-ceramic / SOFC / seals / self-healing / active particle
1
Introduction
Une nouvelle stratégie en recherche et
développement de matériaux innovants se base sur
la gestion des dommages, permettant ainsi la
production de matériaux plus solides et plus fiables.
Ces matériaux ont la capacité d’autoréparer des
dommages se produisant pendant leur utilisation.
En effet, lorsqu’un dommage d’origine
thermique, mécanique ou chimique se produit, le
matériau a la capacité de cicatriser et de retrouver
son état d’origine. L’autocicatrisation peut ainsi être
réalisée de deux façons distinctes : extrinsèque ou
intrinsèque. L’autocicatrisation intrinsèque exige
une intervention extérieure, comme l’augmentation
de la température, par exemple. L’autocicatrisation
extrinsèque nécessite l’ajout d’un agent cicatrisant
dans le matériau, dont la réactivité est activée par
une contrainte dont l’origine peut être mécanique,
thermique ou chimique. White et al. [1] qui avaient
introduit
des
innovations
majeures
dans
l’autocicatrisation des matériaux polymères, ont
mentionné que leur approche pouvait être étendue
aux céramiques et autres matériaux fragiles.
En effet, nous avons montré au laboratoire
qu’une autocicatrisation extrinsèque autonome
dans les verres et les vitrocéramiques peut être
réalisée [2]. Pour cela, un choix approprié de
l’agent cicatrisant permet à la fissure de se
cicatriser à la température de fonctionnement de la
pile, ce qui prévient tout risque de dégradation de la
structure.
2
Le procédé d’autocicatrisation d’une matrice
vitreuse a été mis en évidence dans un verre de
formulation 47,62mol.% SiO2–28,57 mol.% BaO–
9,52 mol.% Al2O3–14,29 mol.% CaO. Pour cela,
Nous utilisons des particules cicatrisantes de
borure de vanadium (VB) dispersées dans la
matrice vitreuse. Le choix de VB est justifié par sa
réactivité et par ses caractéristiques thermiques en
adéquation avec celles du verre [2, 3, 4]. Quand
une fissure se produit sur la surface de l’échantillon
et se propage dans la matrice vitreuse, les
particules de VB réagissent au contact de l’oxygène
contenu dans l’atmosphère pour produire un
nouveau verre qui remplit la fissure [2, 4].
3
Les analyses obtenues par ATD confirment que
les particules de VB s’oxydent à une température
inférieure au Tg du verre, permettant ainsi
l’autocicatrisation sans déformation du verre ; ceci
confirme le caractère extrinsèque du procédé
d’autocicatrisation car il ne nécessite pas
d’intervention extérieure. L’oxydation des particules
de VB peut être obtenue dans un délai compatible
avec l’application. Nous avons en effet observé par
gravimétrie que l’oxydation de VB à 700 ◦C était
quasi-totale
après
seulement
30
min.
L’identification des phases formées a été réalisée
par RMN-MAS des noyaux 51V et 11B. Les
résonances identifiées sur les différents spectres
sont caractéristiques de V2O5. Et de B2O3
(respectivement δiso = −610 ppm ;δiso = −15,2
ppm). Ces résultats montrent donc que le borure de
vanadium peut être utilisé comme un agent
cicatrisant pour des matériaux vitreux présentant
une Tg ou une température de ramollissement
supérieure à 700 ◦C. Nous avons ensuite démontré
la faisabilité du procédé in situ par microscopie
environnementale à l’ICSM sur un composite verreparticules de VB (20 %vol. VB). La figure 1 montre
les micrographies d’une fissure, préalablement
réalisée par indentation Vickers, enregistrées en
fonction du temps à température ambiante (Fig.
1A), puis à 700 ◦C après 5 (Fig. 1B), 15 (Fig. 1C) et
45 min (Fig. 1D). Après 15 min de traitement
thermique (Fig. 1C), les particules sont
partiellement oxydées, comme le montre la
modification de la forme des particules. Les
analyses par RMN ont montré que VB s’oxydait en
B2O3 et V2O5, en 30min à 700 ◦C. Ces oxydes
présentent une faible viscosité à l’état fondu et
peuvent ainsi s’écouler dans la fissure. La
cicatrisation complète de la fissure est obtenue
après 45 min comme le montre l’encart (Fig. 1D)
par un nouveau verre issu de B2O3 et V2O5 dont la
composition est un aluminoborosilicate mixte de
baryum et de calcium.
La capacité d'un composite Verre/VB à assurer
l'étanchéité du joint a été mise en évidence par la
mesure du taux de fuite de gaz en fonction du
temps (fig. 2), Pour accélérer la formation de
fissures dans le joint composite (Figure 2.), la
pression est augmentée à 950 mbar. Une
dégradation du joint est observée à 120h à 800°C
sous 950 mbar, comme le montre le taux de fuite. A
partir de 125h, le joint est remis sous aux
conditions normales d’utilisation en pression, ce qui
permet au procédé d’auto-cicatrisation autonome
de se produire et l’étanchéité totale du joint est
retrouvée en quelques heures (à partir de 142h).
Ces expériences démontrent l'efficacité de
l'auto-cicatrisation autonome en conditions réelles
d'utilisation du matériau.
Fig.2. Mise en évidence du taux de fuite en fonction du
traitement thermique utilisé pour un joints de scellement
composite Verre-VB
4
En conclusion, nous avons démontré qu’il est
possible de réaliser l’autocicatrisation extrinsèque
d’un verre, c’est-à-dire d’obtenir son autoréparation
sans intervention extérieure par l’ajout de particules
choisies selon des critères de réactivité (rapidité et
température). Les résultats de mesure de tests
d’étanchéité du joint ont montré que la mise en
place du processus de cicatrisations autonome
permet de retrouver, en quelques heures, une
étanchéité totale du joint. Ces résultats démontrent
bien l’intérêt de ce type de composite innovant
comme joint de scellement dans les piles SOFC.
References
[1]
[2]
[3]
[4]
Fig.1.
Micrographies
obtenues
par
microscopie
environnementale mettant en évidence in situ l’autocicatrisation.
Conclusions
S.R. White, N.R. Sottos, P.H. Geubelle, J.S. Moore, M.R.
Kessler, S.R. Sriram, E.N.Brown, S. Viswanathan, Nature
409 (2001)
D. Coillot, F.O. Méar, L. Montagne, Composition vitreuse
autocicatrisante, procédé de préparation et utilisations,
Brevet, 2010, patent WO2010/136721.
D. Coillot, R. Podor, F.O. Méar, L.Montagne, J. Electron
Microsc. 59 (2010) 359-366
D. Coillot, F.O. Méar, R. Podor, L.Montagne,Adv. Funct.
Mater. 20 (2010) 4371-4374
SCF Congress - 2015
Lan+1NinO3n+1 (n=1, 2 and 3) nickelates as IT-SOFC cathode
materials: screen printing vs. electrostatic spray deposition
Nickélates de lanthane, Lan+1NinO3n+1 (n = 1, 2 et 3) en vue d’être
utilisés comme matériaux de cathode pour PAC-IT : sérigraphie et
atomisation électrostatique
R. K. Sharma1, 2, M. Burriel1, 3, L. Dessemond1, 2, J.M. Bassat4, E. Djurado1, 2,*
1
Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France
2
CNRS, LEPMI, F-38000 Grenoble, France
Catalonia Institute for Energy Research (IREC), Department of Advanced Materials for
Energy, Jardins de les Dones de Negre 1, 2nd floor, 08930-Sant Adriá del Besòs,
Barcelona, Spain
4
ICMCB-CNRS, Institut de Chimie de la Matière Condensée de Bordeaux, 87 Av. du Dr,
3
33 608 PESSAC Cedex (France)
______________________________________________________________
Résumé : Dans ce travail, des films de Lan + 1NinO3n + 1 (n = 1, 2 et 3) ont été déposés sur Ce0.9Gd0.1O2-δ (CGO) par
atomisation électrostatique (ESD) et par sérigraphie pour évaluer l’influence de la microstructure et de n (nombre de
couches perovskite dans la structure) sur les propriétés électrochimiques. Des études par diffraction des rayons X
(DRX), par spectroscopie à dispersion d'énergie aux rayons X (EDX) et par microscopie électronique à balayage
(MEB) ont permis de caractériser la nature des phases cristallines, la composition et la morphologie des dépôts. Des
valeurs inédites de résistances spécifiques (les plus faibles actuellement répertoriées pour les nickelates de lanthane
La2NiO4+) seront présentées, en lien avec des microstructures originales.
________________________________________________________________________
Summary: In this work, Lan+1NinO3n+1 (n=1, 2 and 3) films were prepared on Ce0.9Gd0.1O2-δ (CGO) substrates both
by electrostatic spray deposition (ESD) and by screen-printing to evaluate the effect of the microstructure and of the n
(number of perovskite layers in the structure) on the electrochemical properties. X-Ray Diffraction (XRD), energydispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) were used for the characterization of
the phase, composition and morphology of the coatings. The lowest values of area specific resistance (ASR) reported
to date for these compositions will be presented versus original microstructures.
Keywords: Ruddlesden–Popper (RP) oxides; IT-SOFC; XRD; SEM; EDX; impedance spectroscopy
Solid oxide fuel cells (SOFCs) are devices which convert chemical energy into electrical energy with low emissions. The
main objective of current research on Solid Oxide Fuel Cells is to reduce the operating temperature to the intermediate
range (500-700°C) without compromising the performances to be able to commercialize such devices by bringing down
the cost and increasing the life time.
1
Introduction
The main objective of current research on Solid
Oxide Fuel Cells is to reduce the operating
temperature down to intermediate temperatures
(500-700°C)
without
compromising
the
performances of the device. However the reduction
of the operating temperature leads to a significant
decrease of the electrode performances and
therefore the choice of suitable cathode materials
becomes more critical and important. Recently,
Lan+1NinO3n+1 (n=1, 2 and 3) (LNO) oxides based
Ruddlesden–Popper (RP) oxides have attracted
considerable attention as promising intermediate
temperature solid oxide fuel cell (IT-SOFC) cathode
materials. These nickelates possess high electronic
and ionic conductivity, similar thermal expansion
coefficient (TEC) to the most commonly used solid
electrolyte,
at
intermediate
temperatures,
Ce0.9Gd0.1O2-δ (CGO), and high electrocatalytic
activity under oxidizing conditions [1]. Both the
composition as well as the microstructural design of
the cathode film play an important role in obtaining
optimal performances [2, 3]. In this work,
Lan+1NinO3n+1 (n=1, 2 and 3) films have been
prepared on CGO substrates by Electrostatic Spray
Deposition (ESD) as well as screen-printing (SP)
and their electrochemical properties have been
studied.
2
Predetermined amounts of nitrate hexahydrate
[Ni(NO3)2·6H2O, 99.9%, Aldrich], Lanthanum nitrate
hexahydrate [La(NO3)3 6H2O, 99.9%, Alfa Aesar],
citric acid [C6H8O7, 99.9%, Alfa Aesar], water and
ethanol (CH3CH2OH, >99.9%, prolabo) were mixed
to prepare a solution of concentration 0.02M.
The LNO films were deposited on CGO
substrates by ESD under ambient atmosphere
using a vertical set-up configuration [3] and were
subsequently calcined in air at different
temperatures (see Fig. 1). The deposition time, flow
rate, substrate temperature, nozzle to substrate
distance and voltage were optimized to
approximately 180 min., 1.5 mL/L, 350°C, 50 mm
and 8.5 kV respectively. A second batch of LNO
coatings was deposited on CGO by SP. Terpineolbased slurries were prepared with each nickelate
material and sintered at 1000°C for 6 h under air.
Lan+1NinO3n+1 cathodes has been investigated using
AC impedance spectroscopy at open circuit
potential. Measurements were carried out between
500 and 800°C in air using a Solartron (SI 1280B)
potentiostat/galvanostat
frequency
response
analyzer with frequencies between 0.01 Hz and 20
kHz.
3
The X-Ray diffraction patterns of all the LNO
films are shown in Fig. 1. All coatings are highly
crystalline with no trace of impurities or secondary
phases.
* CGO o La2NiO4+
+ La
3Ni2O7+
1100°C/6h/air
- La Ni O
3
4
*
10+
10m
La4Ni3O10
Fig. 2 SEM micrographs of ESD La2NiO4+δ films a) Top view
b) cross-section
*
*
*--
Intensity (a.u.)
-
-
*
-
-
--
- - --
1100°C/6h/air
La3Ni2O7
*
+
+
*
+
+*
*
+
++
++
o
++
o
o
o
o oo
o
o
30
o
o
*
o
40
2degree
*
+
*
*
*
+
La2NiO4
950°C/6h/air
o
20
++
+
50
o
*
60
Fig. 1. XRD patterns of the Lan+1NinO3n+1 films
EDX analysis as shown in table 1 confirms the
La/Ni ratio in the film to be 2:1, 3:2 and 4:3 for the
different compositions, in good agreement with
those of the starting precursor solution.
Table 1
Elemental analysis
La2NiO4
Element
[norm. at.%]
La
Ni
21.17
10.07
La3Ni2O7
[norm. at.%]
26.51
15.95
10m
La4Ni3O10
[norm. at.%]
19.99
13.56
A uniform porous morphology was observed by
FEG-SEM for both the ESD and SP La2NiO4+
cathodes of 28 and 37 m thickness, respectively,
with an original 3D porous coral-type microstructure
for ESD specimen (Fig.2).
The influence of the microstructure on the
electrochemical performances of the SP and ESD
The ASR values at 700°C were found to
increase with n (Lan+1NinO3n+1) for SP samples
(from 0.58, 1.03 to 1.55 Ω.cm² for La2NiO4,
La3Ni2O7 and La4Ni3O10, respectively). In the case
of the ESD samples, the reverse was observed
from 2.38, 2.33 to 1.85 Ω.cm², respectively, and
could be interpreted by a different microstructural
approach. When a La2NiO4+current collector was
screen-printed on top of the ESD La2NiO4
electrode, a decrease of the ASR value down to as
low as 0.077 Ω.cm² at 700°C was found, being this
the lowest value up to now reported in the literature
for this composition. Measurements for other both
compositions with current collector are in progress.
4
Conclusions
Lan+1NinO3n+1 (n=1, 2 and 3) films were prepared
on CGO substrates by ESD and by SP and
systematically characterized. The preparation
process and composition have been evaluated for
their possible application as IT-SOFC cathodes
materials. To conclude, the microstructure has
shown to play a very important role in the
electrochemical performance of the LNO cathode.
The best cathodic performance at 700°C was
observed for ESD La2NiO4+ with a current
collecting layer of the same composition.
Acknowledgements
The authors would like to thank CMTC
(Grenoble INP, France) for XRD and EDX
analyses.
References
[1]
[2]
[3]
S. Choi, S. Yoo, J.-Y. Shin, G. Kim, Journal of the
Electrochemical Society 158 (2011) B995.
D. Marinha, L. Dessemond, E. Djurado, J. Power Sources
197 (2012) 80.
D. Marinha, L. Dessemond, E. Djurado, Current Inorganic
Chemistry 3 (2013) 2.
SCF Congress - 2015
Accelerated stability test of materials for electrolysers, fuel
cells or CO2 converters
Tester en accéléré la stabilité des matériaux pour électrolyseurs, piles
à combustible ou convertisseurs de CO2
Ph. Colomban1,2, A. Slodczyk1,2
1
Sorbonne Universités, UPMC Univ Paris 06, UMR 8233, MONARIS, 75005, Paris, France
2
CNRS, UMR 8233, MONARIS, IP2CT, F-75005, Paris, France
______________________________________________________________
Résumé : La production intermittente des sources renouvelables impose une filière avec stockage. L’hydrogène peut
être produit et stocké de façon propre. La combinaison électrolyse-pile ou électrolyse+convertisseur CO2 en
hydrocarbures, etc. offre une solution pérenne. La très forte réactivité de l’hydrogène et du proton et la nécessité
économique de longue durée de vie des dispositifs nécessitent des matériaux très stables. L’étude ex situ (Raman,
IR, diffraction/diffusion neutronique) et in situ (Raman, conductivité) sous très forte pression de vapeur d’eau, de
CO2, etc. permet de comparer et de sélectionner les meilleurs matériaux et assemblages en accéléré.
________________________________________________________________________
Summary: Intermittent production of renewable energies requires an economic plant with storage. Hydrogen is an
energy vector which can be stored and produced environment friendly. The combinations of electrolyser – fuel cell or
electrolyser + CO2/hydrocarbon converter, offer sustainable solutions. Very high reactivity of hydrogen and protons
together with economic long life time requirements of devices need very stable materials. The ex situ (Raman, IR,
neutron diffraction/diffusion) and in situ (Raman, conductivity) study under high water vapour pressure and/or CO2
allow to compare and select rapidly the most stable materials/electrochemical devices.
Keywords: chemical stability; structural stability; proton; hydrogen; lifetime; corrosion
The long life time of production, conversion and storage systems of energy is the crucial point of economic and practical
interest. The materials used as electrolytic membranes must withstand harsh conditions, especially if high performance is
requested. Modelling requires accelerated but representative aging tests. The presence of significant corrosion film/layer
that can be analyzed by multiple and effective techniques makes the ageing study easier.
La durée de vie des systèmes de production, conversion et stockage de l’énergie est le point critique de leur intérêt
économique et pratique. Les matériaux utilisés doivent supporter des conditions difficiles, d’autant plus que de hautes
performances leur sont demandées. La modélisation du vieillissement nécessite des tests en accéléré mais
représentatifs. L’étude est facilitée si l’épaisseur du film de corrosion est suffisante pour être analysée par des
techniques variées.
1
Introduction
The production of hydrogen by water electrolysis
from intermittent (renewable) and peak-off
electricity, its storage and conversion (H2/air Fuel
Cell) or even reaction with CO2 giving Syngas/‘oil’
or more advanced chemicals [1-4] appear as very
promising solutions. Pressurized cells/systems are
more efficient from industrial points of view [3].
More or less advanced prototypes of
Electrolysers (Es), Fuel Cells (FCs) and CO2
converters (CCs) working at intermediate 500600°C (proton conducting electrolyte) or at high
800-1000°C (oxygen ion conducting electrolyte)
temperatures have been proposed [1-11]. The
working temperature range is sufficient high to
avoid expansive catalysers. Operating below 600°C
provides additional economic advantages (no need
of very expansive steel, H2 security regulation).
Since an important/stable conductivity of the
electrolyte, cathode and anode is a key point,
compromises should be made between a material
thicknesses (decreasing the resistivity), a
mechanical strength, electric/chemical gradients, a
processing temperature(s), a material compatibility
(thermal expansion mismatch), etc. However, the
material selection is often made separately and
conductivity tests are performed in conditions very
far from the operando ones. This is especially the
case of systems based on proton conductors [1-14].
Proton size is intermediate between that of
+
electron and the smallest ion, Li . Consequently its
physics and chemistry are unique [1,13]. Small
proton doping (10-2 mole/mole) is sufficient to
modify electrolyte structure (e.g. substituted
perovskite) but makes its characterization difficult
[15,16]. Surface conduction is neglected by many
scientists although its contribution could be
dominant for porous membrane, even if the porosity
is low. Consequently the literature should be read
with caution.
2
Methodology
Selected electrolytes or electrodes of Es, FCs or
CCs were thermally treated in autoclave in
operating conditions, e.g. at 550-600°C under 20 to
80 bar of water vapor pressure [11,12,14-18]. In the
case of 1mm-thick dense perovskite ceramic, the
protonation, e.g. proton incorporation, requires a
few days and is controlled by TGA, neutron
scattering,
neutronography
and/or
Raman
profilometry [11,19]. The ceramic mass variation as
a function of autoclave treatment duration and of
(CO2) water pressure value is used to compare the
chemical stability [14,17]. Raman, ATR FT-IR, XRD
and neutron diffraction/scattering allow identifying
the structural/chemical changes involved by the
proton doping and the presence of different phases
(non protonated, proton-doped and corroded film).
3
Fig. 1 compares the mass variation of a few
electrode candidates as a function of autoclave
treatment duration. Since the mass variation mainly
depends on corroded film ((oxo)hydroxides and
carbonates) formed at the ceramic surface, the
corrosion rate can be determined. The results show
that the LSCF and NNO ceramics exhibit the
highest structural/chemical stability whereas
important, fast ageing is detected for LNO.
(Fig. 2b). Note, the most important volume change
– contraction, is observed after 1st protonation.
4
Conclusions
The autoclave treatment at high temperature
and under high water vapour pressure makes the
incorporation/diffusion of protonic species easier
but simultaneously may facilitate the hydroxylation
and, in the presence of CO2, the hydrocarbonation,
especially at the grain boundary [18]. The
comprehension of subtle structural modifications
caused by proton doping and of ageing
mechanisms requires specific analysis methods
such as vibrational spectroscopy and neutron
scattering performed ex situ at the first time but
especially in situ and operando.
Acknowledgements
Drs G. André, P. Batocchi, P.M. Geffroy, F. Grasset, O.
Lacroix, F. Mauvy, A. Pons, B. Sala, O. Zaafrani, and M. S.
Setakorn are kindly acknowledged for their contribution and
many fruitful discussions.
References
[1]
[2]
[3]
[4]
[5]
20000
SZE
--- 1H
--- 1DH
b)
286
284
3
Intensity (arb. units)
a)
unit cell volume (A )
Fig. 1. Mass variation by surface unit vs. time for different
electrode materials (dense ceramics) with perovskite structure:
La2NiO4+δ (LNO), Pr2NiO4+δ (PNO), Nd2NiO4+δ (NNO) and
La0.6Sr0.4Co0.2Fe0.8O3-δ; (LSCF6428) treated at 550°C under 20
bar of CO2-free water pressure [20].
10000
0
[6]
[7]
[8]
[9]
NH
H1
H2
[10]
282
280
[11]
278
[12]
276
20
40
60
80
2 theta (deg)
100
200
400
600
800
Temperature (°C)
Fig. 2. a) RT neutron diffraction patterns of de-protonated (1DH)
and 40 bar H2O protonated (1H) anhydrous perovskite
(SrZr0.9Er0.1O3-δ); b) Unit-cell volume vs. temperature of non
st
nd
protonated (NH), 1 time 40 bar H2O protonated (H1) and 2
time 40 bar H2O protonated (H2) SrZr0.9Er0.1O3-δ.
The proton doping of a ceramic (e.g. less than a
% mole/mole for an electrolyte membrane:
SrZr0.9Yb0.1O2.95H0.003) gives rise to very subtle, but
measurable, structural modifications. The bulk and
surface protonation can be determined by the
variation of incoherent background intensity
proportional to the protonic species content (Fig.
2a) and by small changes of the unit-cell volume
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
Ph. Colomban Ed.: Proton Conductors Solids, membranes
and gel – materials and devices. Cambridge University
Press, Cambridge (1992, 2008, 2011).
Ph. Knauth, M.L. Di Vona,. Eds.: Solid State Proton
Conductors. Properties and Applications in Fuel Cells, John
Wiley & Sons, Chichester (2012)
B. Sala, O. Lacroix, S.Willemin, K. Rhamouni, H.Takenouti,
A. van der Lee, P. Goeuriot, B Bendjeriou, Ph.Colomban,
PCT Patent WO 2008/152317 A2 (18-12-2008); ibidem
French Patent FR 1159221, 12/11/2011.
F Forrat, G. Dauge, P. Trevoux. G. Danner, M. Christan,
Acad. Sci. Paris 259 (1964) 2813
O. Lacroix, K. Rahmouni, A. Sirat, H. Takenouti, C.
Deslouis, M. Keddam, B. Sala, J. Power Sources 270 506
(2014)
K.D. Kreuer, Ann. Rev. Mater. Res. 33 (2003)333. .
T. Kobayashi, K. Abe, Y. Ukyo, H. Matsumoto, Solid State
Ionics 138 (2001) 243.
S. Tao, J.T.S. Irvine, J.A Kilner, Advanced Materials 17
1734 (2005).
S. Ricote, N. Bonanos, G. Caboche Solid State Ionics 180
(2009) 990.
A. Grimaud, J.M.Bassat, F. Mauvy, P. Simon, A. Canizares,
B. Rousseau, M.Marrony, J.C.Grenier, Solid State Ionics
191 (2011) 24.
Ph. Colomban, O. Zaafrani, A. Slodczyk, Membranes 2(3)
(2012) 493.
Ph.Colomban, C. Tran, O Zaafrani, A. Slodczyk, J. Raman
Spectrosc. 44 (2013) 312.
Ph. Colomban, Fuel Cells 13 (2013) 6.
A. Slodczyk, O. Zaafrani, M.D. Sharp, J.A. Kilner, B.
Dabrowsky, O. Lacroix, Ph. Colomban, Membranes 3(4)
311 (2013)
Ph. Colomban, A. Slodczyk, European Physical J. Special
Topics 213 (2012) 171.
A. Slodczyk, Ph. Colomban, F. Grasset, J. Phys Chem.
Solids, submitted.
S. Upasen, P. Batocci, F. Mauvy, A. Slodczyk, Ph.
Colomban, J. Alloys Comp. 622 1074 (1015).
A. Slodczyk, M.D. Sharp, S. Upasen, Ph. Colomban, J.
Kilner, Solid State Ionics 262 (2014) 870
A Slodczyk, Ph Colomban, S. Willemin, O. Lacroix, B. J.
Raman Spectrosc. 40 513 (2009)
S. Upasen, P. Batocci, F. Mauvy, A. Slodczyk, Ph.
Colomban, J. Alloys Comp., submitted.
SCF Congress - 2015
Modelling the HCOOH/CO2 Electrocatalytic Reaction: When
Details Are Key
Modélisation de la réaction électrocatalytique HCOOH/CO 2: Quand les
détails sont les clés
Stephan N. Steinmann,1 Carine Michel,1,2 J.-S. Filhol,3 Philippe Sautet1,2*
1
Lab oratoire de Chimie de l'ENS de Lyon, Ecole Normale Supérieure de Lyon, Lyon, France.
CNRS, Lyon, France.
3
CTMM, Institut Charles Gerhardt Montpellier, Université Montpellier 2, Montpellier, France.
2
______________________________________________________________
Résumé :
La transformation électrocatalytique du CO2 en acide formique (HCOOH) et inversement est d'un grand intérêt en
raison de caractéristiques uniques, notamment pour le stockage d'énergie e t pour des piles à combustibles. Dans
cette présentation nous exposerons des chemins réactionnels pour l'oxydation électrocatalytique de l'acide formique
sur Ni(111). Nous montrerons que les barrières d'activation changent significativement sous des conditions
électrochimiques par rapport à des calculs dans le vide et que donc le potentiel électrochimique doit être inclus dans
le calcul DFT, ce qui est rarement fait dans les études théoriques. L'a pproche utilisée est généralement applicable et
ce niveau de description est nécessaire pour comprendre les étapes élémentaires qui limitent l'efficacité des
réactions électrocatalytiques hétérogènes.
______________________________________________________________ __________
Summary:
Our first principles simulations of the electro-oxidation of formic acid over nickel identify important reaction barriers
involved in the re-orientation of the formate intermediate and in the desorption of CO2. Although not associated with
an electron transfer step, these barriers are strongly modified when explicitly accounting for the electrochemical
potential and when modelling the influence of the solvent. Such a level of modelling is hence key to understand the
kinetic limitations that penalize the reaction.
Keywords: électrochimie; electrocatalyse hétérogène; modélisation DFT à potentiel constant; chemins réactionnels ;
acide formique
Electrocatalysis is the principle behind the conversion of cheap molecules (e.g., CO2) and electricity into useful
chemicals like fules (and vice versa in fuel cells), polymers and fine chemicals. Our research is situated at the interface
between fundamental and applied science. We model
the fundamental processes and elucidate important
characteristics of electrocatalysis by first principles computations. The provided insight might lead to increased ecoefficiency of existing processes.
L'électrocatalyse permet de transformer grâce à l'électricité des molécules abondantes comme le CO2 en produits
chimiques utiles comme des carburants (et inversement dans des piles à combustibles), en polymères et en produits de
chimie fine. Notre recherche se situe à l'interface entre les sciences fondamentales et les sciences appliquées. Nous
modélisons les processus fondamentaux et identifions les caractéristiques importantes de l'électrocatalyse. La
compréhension détaillée que nous apportons pourraient améliorer l'éco -efficacité des procédures existants .
1
Introduction
La transformation électrocatalytique du CO 2 en
acide formique (HCOOH) et invers ement est d'un
grand intérêt en raison de caractéristiques uniques.
Tout d’abord, la façon la plus simple de recycler le
CO2 est de former HCOOH, car cette réaction ne
nécessite que deux électrons et deux protons, et
conserve la connectivité du CO 2. Par ailleurs,
l'acide formique pourrait être utilisé plus facilement
que H2 pour des piles à combustibles. Néanmoins,
les procédés actuels ne sont pas très efficaces, ce
qui se traduit par des pertes énergétiques.
Malgré des progrès récents en modélisation de
réactions électrocatalytiques, la dét ermination du
mécanisme et la rationalisation des sélectivités
posent t oujours de maints problèmes. Dans cette
présentation, nous exposerons des chemins
réactionnels pour l'oxydation électrocatalytique de
l'acide formique sur Ni(111) en appliquant deux
modèles de prise en compte de l'environnement
électrochimique
(Figure
1).[1]
L'électrode
computationnelle à hydrogène (CHE) de Norskov
[2] est l'approche la plus simple, car elle ne prend
en compte que l'énergie de l'électron. Dans la
méthode de Filhol et Neurock[3], l'électrode est
chargée explicitement et la cellule périodique
neutralisée par une charge de fond uniforme. De
cette manière, l'électrode est polarisée et toutes les
étapes élémentaires peuvent être influencées par le
potentiel électrochimique.
Fig. 1. Chemin réactionnel pour l'oxydation électrocatalytique
de l'acide formique sur Ni(111). Les espèces 2-5 correspondent
à des formiates, tandis que 6 et 7 sont du CO2 chimisorbé. Les
lignes fines indiquent les énergies libre selon le modèle CHE,
tandis que les lignes épaisses sont calc ulé en prenant
explicitement en compte le potentiel électrochimique par des
charges de surface. Le changement de la couleur du fond
symbolise les étapes formellement électrochimiques, c'est-à-dire
les étapes ou le nombre de H++e- dans le système change.
2
Résultats and discussion
Nos résultats montrent qu’il existe une barrière
importante pour la réorientation du formiate (3),
étape nécessaire à la rupt ure de la liaison C-H. Par
ailleurs, la désorption du CO2 (TSdes ) est une étape
fortement activée. Même si ni l'une ni l'autre de ces
deux étapes ne sont formellement électrochimiques
(le nombre d'électrons et de protons est constant ),
ces barrières sont fortement modifiées quand on
traite le potentiel électrochimique explicitement. La
raison de cette dépendance au potentiel se trouve
dans le changement du dipôle de surface, qui
entraîne une variation de charge pour garder le
potentiel électroc himique constant. Il est donc
indispensable d'inclure le potentiel directement
dans les calculs DFT pour identifier et comprendre
les
étapes
limitantes
des
réactions
électrocatalytique.
3
Conclusions
La comparaison de la méthode populaire CHE
et du modèle plus réaliste SC pour l'électrooxydation de l'acide formique sur Ni montre
clairement la sous-estimation de l'influence du
potentiel dans la méthode CHE. La désorption du
CO2, ainsi que la réorient ation défavorable du
formiate ent rainent des valeurs de barrières
prohibitives, qui expliquent l'activité faible du Ni.
Les changements importants de l'intensité du
dipôle de surface entraînent l'influence dramatique
du potentiel électrochimique sur les étapes
élémentaires. Comme le travail de s ortie est
intimement lié au dipôle de surface et que celui-ci
ne change pas exclusivement pendant les étapes
dites "électrochimiques", les simulations à potentiel
constants (SC) modifient significativement les
étapes dites "chimiques", contrairement aux
hypothès es habituelles. Ainsi, il est impératif
d'inclure le potentiel électrochimique explicitement
dans les calculs pour comprendre l'électrocat alyse
hétérogène dans tout e sa complexité.
Remerciements
Nous remercions Solvay pour le financ ement de
ce projet. Le PSMN nous a généreusement donné
accès à des ressources HPC. Ces travaux ont
bénéficié d’un accès aux moyens de calcul du
CINES et de l’IDRIS au travers de l’allocation de
ressourc es 2014-080609 attribuée par GE NCI.
References
[1]
[2]
[3]
[1] S. N. Steinmann, C. Michel, R. Schw iedernoch, J.-S.
Filhol, P. Sautet, submitted.
[2] J. K. Norskov, J. Rossmeisl, A. Logadottir, L.
Lindqvist, J. R. Kitchin, T. Bligaard, H. Jonsson,
J.
Phys. Chem. B 108 (2004) 17886.
M. Mamatkulov, J. S. Filhol, Phys. Chem. Chem. Phys. 13
(2011) 7675.
SCF Congress - 2015
CO2 reduction to methanol using fomic acid as a C-H bond
shuttle
Utilisation de l'acide formique comme relais de liaison C-H pour la
réduction du CO2 en méthanol
S. Savourey1, G. Lefèvre1, J.C. Berthet1, P. Thuéry1, C. Genre1, T. Cantat1*
1
CEA SACLAY, LCMCE, IRAMIS, NIMBE 91191 Gif-sur-Yvette Cedex.
______________________________________________________________
Résumé : La disproportionation de l’acide formique en méthanol a été décrite pour la première fois en 2013 avec un
catalyseur à l’iridium. Cette réaction est cependant en compétition avec la déshydrogénation de l’acide formique (en
H2 et CO2) ce qui limite les rendements en méthanol à 2%. Nous proposons ici la conversion de l’acide formique en
méthanol avec des rendements allant jusqu’à 50% grâce à un catalyseur composé de ruthénium(II) et d’un ligand
phosphoré tridentate. Les études théoriques et mécanistiques ont à la fois permis de discerner deux chemins
réactionnels convergents et d’isoler et de caractériser les intermédiaires pour mieux comprendre la chimie impliquant
le complexe de ruthénium.
________________________________________________________________________
Summary: The disproportionation of formic acid to methanol was unveiled in 2013 using iridium catalysts. Although
attractive, this transformation suffers from very low yields; methanol was produced in less than 2 % yield, because the
competitive dehydrogenation of formic acid (to CO2 and H2) is favored. We report herein the efficient and selective
conversion of HCOOH to methanol in 50 % yield, utilizing ruthenium(II) phosphine complexes. Experimental and
theoretical results show that different convergent pathways are involved in the production of methanol. Reaction
intermediates have been isolated and fully characterized and the reaction chemistry of the resulting ruthenium
complexes has been studied.
Keywords: methanol; formic acid, homogeneous catalysis, hydrogenation, disproportionation.
85% of today’s energy originates from hydrocarbon, oil or coal. Designing new fuels based on renewable resources is a
challenge to stop relying on these fossil fuels. Methanol can be used in fuel cells or in combustion engine. Being able to
efficiently convert CO2 into methanol would therefore mean that a high energy density fuel could be available from
renewable resources.
La fabrication de nouveaux carburants utilisant des énergies renouvelables et décarbonées s’inscrit dans une optique
d’indépendance face aux énergies fossiles qui produisent aujourd’hui 85% de l’énergie consommée. Le méthanol est
utilisable aussi bien dans les piles à combustible que dans les moteurs à combustion. L’approche développée ici vise à
convertir efficacement le CO2 en méthanol afin de produire ce carburant à haute densité énergétique, à partir de
ressources renouvelables.
1
Introduction
Efficient conversion of CO2 to methanol is a key
process to reach a methanol economy, based on a
closed carbon cycle.[1] Such goal could be
achieved by the 6-electron reduction of CO2 or its
hydrogenation to methanol. However both solutions
currently suffer from low faradaic efficiencies. An
interesting alternative would consist in utilizing
formic acid as a C–H bond shuttle in the reduction
of CO2 to methanol. This strategy relies on the 2–
electron reduction of CO2 to formic acid, in an
electrochemical cell, and this methodology is now
technically and economically available, thanks to
efficient electrocatalysts.[2] Disproportionation of
formic acid is then required to produce methanol.
Miller et al. showed, for the first time in 2013, that
an iridium molecular complex could promote the
disproportionation of formic acid to methanol.[3]
Though promising, this strategy currently suffers
from the use of expensive iridium catalysts and the
yields of methanol do not exceed 1.9 %.[3] We
present the efficient disproportionation of formic
acid to methanol, with methanol yields of up to
50.2%, using ruthenium molecular catalysts.[4]
2
Ruthenium complexes are well–established
catalysts in reduction chemistry and their potential
was recently illustrated in the hydrogenation of a
variety of reluctant substrates, such as CO2,
carbonates, carbamates and amides.[5] In addition,
ruthenium benefits from a lower cost compared to
iridium (75 vs 830 $/oz in 2013). The
disproportionation of formic acid was thus
investigated, utilizing ruthenium(II) complexes
supported by external phosphine ligands (Table 1).
To our delight, we observed that heating a THF
solution of formic acid in a sealed vessel at 150 °C,
resulted in the complete conversion of formic acid
to produce methanol in 5.0 % yield, after 1 h (Entry
1, Table 1). The remaining 95% formic acid
underwent dehydrogenation. To understand the
competition
between
dehydrogenation
and
disproportionation the intermediates involved in the
reaction were isolated and characterized in order to
elucidate the reaction’s mechanism.
pathways. Additional work is underway in our
laboratories to translate these conclusions into the
design of earth abundant metal catalysts with
increased selectivity for the production of methanol
from formic acid.
Table 1
Disproportionation of formic acid.
Entry
FA
[mmol]
Additive
T
t
CH3OH
[1.5 mol%]
[°C]
[h]
Yield [%]
1
1
0.6
–
150
5.0
2
2.4
–
80
17
7.6
3
2.4
–
40
72
1.0
4
2.4
–
150
1
11.9
5
4.8
–
40
72
1.0
4.8
–
80
17
26.7
6
7
0.8
–
150
1
0.5
8
1.6
–
150
1
7.5
1
50.2
9
2.4
MSA
150
Reaction conditions: cat. [Ru(COD)(methylallyl)2] + triphos (0.6
mol%); yields determined by 1H NMR spectroscopy in
deuterated solvents, using mesitylene as an internal standard.
3
DFT studies, based on the characterized
intermediates,
emphasized
that
the
rate
determining intermediate was common to both
dehydrogenation and disproportionation pathways
(Figure
1).
Dehydrogenation
is
also
thermodynamically favored, however since only 4
kcal/mol distinguishes the two reactions (Figure 1)
we decided to play on the pressure to favor
methanol production. Indeed dehydrogenation of 3
moles of formic acid leads to 6 moles of gases
when disproportionation leads to 2 moles of gases.
At high pressure, disproportionation is thus favored.
In fact, increasing the formic acid loading in a
sealed vessel (which means reaching higher
pressure through dehydrogenation) yielded up to
27% methanol (Table 1).
Furthermore,
detailed
experimental
and
mechanistic studies by Klankermayer, Leitner et. al.
have shown that acid promoters, such as
methanesulfonic acid (MSA), could significantly
boost
the
catalytic
activity
of
([Ru(COD)(methylallyl)2]+triphos). This strategy has
been successfully utilized by the groups of Leitner
and Klankermayer, to promote the hydrogenation of
CO2 with H2.[5c] Following this approach, the
disproportionation of formic acid was achieved in up
to 50% yield (Table 1).
4
Conclusions
As a result, the selectivity for the production of
MeOH is under thermodynamic control. While the
dehydrogenation of one molecule of formic acid is
favored at low pressure (∆G = –9.9 kcal/mol vs –7.4
kcal/mol for the disproportionation route), the
formation of methanol by transfer hydrogenation is
favored at high pressure, in agreement with the
experimental findings. Acidic additives further
increase the yield by avoiding catalyst deactivation
Fig. 1. Computed pathways for the dehydrogenation and
disproportionation of formic acid.
Acknowledgements
For financial support of this work, we acknowledge
the CEA, the CNRS, the University Paris-Saclay
(Fellowship to X.F.), the CHARMMMAT Laboratory
of Excellence and the European Research Council
(ERC Starting Grant Agreement no. 336467). T.C.
thanks the Fondation Louis D. – Institut de France
for its formidable support.
References
[1] G. Olah, A. Goeppert, G. K. Surya Prakash, Beyond Oil and
Gas: The Methanol Economy, Wiley-VCH, Weinheim, 2009.
[2] H.-R. Jhong, S. Ma, P. J. A. Kenis, Curr. Opin. Chem. Eng.
2013, 2, 191.
[3] A. J. M. Miller, D. M. Heinekey, J. M. Mayer, K. I. Goldberg,
Angew. Chem. Int. Ed. 2013, 52, 3981; Angew. Chem. 2013,
125, 4073.
[4] S. Savourey, G. Lefèvre, J.-C. Berthet, P. Thuéry, C. Genre,
T. Cantat, Angew. Chem., Int. Ed., 2014, 53, 10466.
[5] a) E. Balaraman, C. Gunanathan, J. Zhang, L. J. W.
Shimon, D. Milstein, Nat. Chem. 2011, 3, 609; b) P. P. M.
Schleker, R. Honeker, J. Klankermayer, W. Leitner, Chem.
Cat. Chem, 2013, 5, 1762; c) K. Beydoun, T. vom Stein, J.
Klankermayer, W. Leitner, Angew. Chem. Int. Ed., 2013, 52,
9554; Angew. Chem., 2013, 125, 9733; d) Y. Li, I. Sorribes,
T. Yan, K. Junge, M. Beller, Angew. Chem. Int. Ed., 2013,
52, 12156; Angew. Chem., 2013, 125, 12378; e) J. Coetzee,
D. L. Dodds, J. Klankermayer, S. Brosinski, W. Leitner, A. M.
Z. Slawin, D. J. Cole-Hamilton, Chem. Eur. J. 2013, 19,
11039.

CO_Thème 1 - Société Chimique de France

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