Battery Capacity: How High Can We Reach?

Battery Capacity: How High Can We Reach?

Battery capacity (energy):
How high can we reach?
Oct 16, 2014
Dr. Denis Y.W. Yu
Assistant Professor
School of Energy and Environment
How many batteries are you carrying with you?
Remote control
Alkaline
Mn dry cell
Hearing
aid
Zinc
air
Ni-MH
Li-ion
Alkaline
Ni-Cd
CD Player
Primary
• Alkaline battery
• Li battery
Laptop
Camera
Cordless
phone
Ni-Cd
Hand
cleaner
Ni-MH
Li-ion
Cell phone
PDA
Alkaline
dry cell
Alkaline
Lead-acid
Ni-Cd
Ni-MH
Li coin cell
Secondary
• Lead-acid battery
• Ni-Cd battery
• Ni-mH battery
• Li-ion battery
http://www.baj.or.jp/knowledge/stage.html
School of Energy and Environment, City University of Hong Kong
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What are the trends?
Gets bigger and bigger
Gets smaller and smaller
School of Energy and Environment, City University of Hong Kong
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What are the trends?
Need efficient energy storage for sustainability
School of Energy and Environment, City University of Hong Kong
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What do consumers want?
Life
Power
Cost
Safety
Capacity
Depending on applications
School of Energy and Environment, City University of Hong Kong
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Battery capacity (energy)
Definition
History
Current status
Where do you go from here?
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Battery capacity (energy) – definition
V – Voltage
E – Energy = VxQ
Q – Capacity (mAh)
Type of battery
Ampere [A] = charge (Coulomb) per second
Battery capacity (ampere hour)  amount of charge that is stored
e.g. Typical cell phone batteries has capacity = 1000 mAh
Means it contains a charge of 3600 Coulomb
The higher the capacity, the longer the battery will last for
same current
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Battery energy (Wh/kg or Wh/L)
V – Voltage
E – Energy = VxQ
Q – Capacity (mAh)
Type of battery
Capacity depends on size (mass or volume) of the battery
Better to compare specific energy density:
Gravimetric energy density (Wh/kg) = energy/mass
Volumetric energy density (Wh/L) = energy/volume
School of Energy and Environment, City University of Hong Kong
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History of batteries
1785 Coulomb, first report on Electricity and Magnetism
1800
Volta: Voltaic pile (Zn/Cu/brine)
1820s Andre-Maria Ampere, papers on electrodynamics
1827 Georg Ohm, Ohm's law
1836
Daniell cell (Zn/Zn2+ Cu/Cu2+)
1859
Lead-acid battery (Pb/PbO2/H2SO4)
1865 John Newlands, only 62 elements discovered
1866
Zinc-carbon cell (Zn/MnO2/NH4Cl)
1869 Dmitri Mendeleev, first periodic table
1880s Thomas Edison, carbon filaments for light bulb
1897 J.J. Thomson, discovery of electrons
1899
Nickel-cadmium cell (Ni/Cd/KOH)
1947 Bell Labs, invention of transitor
1967
Nickel-metal hydride (Ni/MH/KOH)
1979 Apple II+ personal computer
1991
Li-ion battery (LiCoO2/C)
1991 World Wide Web
School of Energy and Environment, City University of Hong Kong
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Energy density comparison of various battery systems
How much energy can be stored?
Gravimetric energy density (Wh/kg) = energy/mass
Volumetric energy density (Wh/L) = energy/volume
Wants lowest
mass and volume
Energy
density
http://www.epectec.c
om/batteries/cellcomparison.html
Lithium-ion battery  highest energy density
School of Energy and Environment, City University of Hong Kong
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Effect of energy density on battery size
Cell phone development
<1990
Ni-Cd
50-150Wh/L
1991
Li-ion
200 Wh/L
2013
Li-ion
600-700 Wh/L
Decrease in size of electronics
Decrease in size of battery
School of Energy and Environment, City University of Hong Kong
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Inside a lithium-ion battery
eV
Al
e
Cu
Li+
Positive
electrode
Electrolyte
Negative
electrode
+
Li
Basic principle: store energy by moving Li+ back and forth between the electrodes
Typical cathode: LiCoO2
Typical anode:
Li1-xCoO2 + xLi+ + xe-
C + xLi+ + xe-
LixC
Cell voltage
3.7V
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Limitations of battery capacity/energy
Chemistry vs. engineering
Capacity  allowable # of
e-
Cap (+)
transfer
separator
LiCoO2
Li1-xCoO2 + xLi+ + xe-
(~160mAh/g)
C + xLi+ + xe-
LixC
cathode
Can (-)
anode
(~370mAh/g)
Voltage ~3.7-3.8V
Theoretical energy density ~ 400 Wh/kg
Inactive material – can, metal foil,
electrolyte
Practical energy density ~ 200 Wh/kg
Material only
Cell level
Need to develop new materials to further increase capacity
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DY091116D_5
21E-6:Ab:L-B-90:5:5
Examples of material development
(cathode)
LiCoO2
~160 mAh/g
Li-rich material
LiMO2 – Li2MnO3
“composite”
~250 mAh/g
Li/Li+)
Potential
vs. Li/Li+)
(V vs.
Potential(V
5
Li layer
Transition
metal layer
4.5
4
3.5
3
2.5
2
2C
1.5
0
50
100
1C
0.5C
0.2C
150
200
Capacity (mAh/g)
0.1C
0.05C
250
300
Capacity (mAh/g)
Yu et al. J. Electrochem. Soc. 157 (2010) A1177-A1182
Challenge:
• Voltage drop during cycling
• Poor rate capability
• Requires surface coating to prevent electrolyte decomposition
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Example of material development (anode)
Graphite
370 mAh/g
900
e.g. Sb2S3
Optimized binder + electrolyte
800
Capacity (mAh g-1)
Technologies to
improves
structural and
chemical stability
Metal sulfide
>700 mAh/g
700
600
New binder +
conventional electrolyte
500
400
300
200
0-2.5V
250mA g-1
100
Commercial
graphite
0
0
Yu et al. Scientific Reports 4
(2014), doi:10.1038/srep04562
10
20
30
Cycle number
School of Energy and Environment, City University of Hong Kong
40
50
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Future outlook (Li-ion battery)
Alternative anode materials
e.g. Si, Ge, Sn – alloy with Li
Challenge – volume expansion
Capacity
Volume
change
Graphite
372mAh/g (C6Li)
12%
Silicon
4200mAh/g (Li22Si5)
320%
Expected increase in energy
Cathode: 160  250 mAh/g
Anode: 370  2000 mAh/g
Energy density  ~50% UP
Zhang, W.-J. J. Power Sources, 196, 13-24 (2011)
School of Energy and Environment, City University of Hong Kong
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Future outlook (Li-Sulfur battery)
S + 2 Li+ + 2 e- → Li2S
Feature:
• Uses Li metal as anode
• Uses S as cathode
• Both Li and S are lightweight
Capacity = 1670 mAh/g
Potential = 2V vs. Li/Li+
Theoretical energy density ~ 2300 Wh/kg
http://www.vorbeck.com/energy.html
Challenges:
• Electrical conductivity of S
• Dissolution of polysulfide into electrolyte (self discharge)
• Reactivity of Li metal (Li plating)
Research:
Nano-composite; carbon-coating; etc.
Prototypes of about
500 Wh/kg made
School of Energy and Environment, City University of Hong Kong
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Future outlook (Li-Oxygen battery)
O2 + 2 Li+ + 2 e- → Li2O2
Feature:
• Uses Li metal as anode
• Oxygen can be obtained from air
Capacity = 3850 mAh/g (Li only)
Potential = 2.6V vs. Li/Li+
Theoretical energy density ~ 10000 Wh/kg
Challenges:
• How to enable reversible oxygen reaction
• Electrolyte type
• Reactivity of Li metal (Li plating)
• Real applicability in air
Research:
Nano-structure; solid electrolyte; etc.
School of Energy and Environment, City University of Hong Kong
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Battery capacity: how high can we reach?
Theoretical
Practical
~400 Wh/kg
~200 Wh/kg
600-700 Wh/kg
300-350 Wh/kg
Li-sulfur
2300 Wh/kg
500 Wh/kg
(prototype)
Li-oxygen
10000 Wh/kg
??
Li-ion (existing technology)
Li-ion (new materials)
Must include supporting battery
structure (inactive material)
• Need new materials and technologies to increase battery energy
Petrol: energy density = 13000 Wh/kg
•Caution when comparing energy density values
School of Energy and Environment, City University of Hong Kong
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Future outlook - applications
Electric
vehicles
Renewables
Nissan
Leaf
Tesla
Model S
Size
24kWh
Weight
(Battery+module)
218kg
Size
85kWh
544kg
e.g. 350kW PV for 12h = 4200kWh
Need 21ton LIB
Spiderman: “With great power comes great responsibility”
Battery scientists: “With great energy comes great safety
responsibility”
School of Energy and Environment, City University of Hong Kong
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