Making Economical, Green, High-Energy Nickel- Manganese (NiMn) Batteries Small Scale/DIY Battery Making

Transcription

Making Economical,
Green, High-Energy NickelManganese (NiMn) Batteries
Small Scale/DIY Battery Making
the Turquoise Battery Project
PRELIMINARY
by Craig Carmichael, December 30th, 2013
TurquoiseEnergy.com
Quick Summary: These flooded cells utilize a new "moderately alkaline" chemistry, charging to about 2.6 volts and
nominally giving about 2.2 volts and high amp-hours per weight, for high energy storage (potentially better than
lithium ion) and very long or indefinite cycle life, from economical chemicals and supplies.
It should be noted that while the chemistries have been developed and tested, the author has not been able to
produce batteries that come even close to making good percentage utilization of the active chemicals - of any
chemistry. These instructions must therefore be taken as a starting point for battery making, not an end point.
The metallic manganese "negatrode" (-) side is similar in reactions to familiar metals cadmium, zinc or iron,
except for 3 things:
1. The voltage is higher than any other, being around -1.4 volts.
2. It's completely stable: in no state of charge is it an insulator or soluble. It should last forever.
3. Manganese has never been made to hold its high voltage charge before. Normally, it spontaneously discharges to
Mn(OH)2 + H 2 gas. A pH below 14, and 'trace' additives Sb2S3 (1%) and ZrSiO4 (3%), have been found to allow it to
hold its charge.
Zinc has been used for current collectors and conductivity enhancement powders. (Most metals would bubble
hydrogen and discharge the electrode.)
The nickel plus manganese oxides "positrode" (+) side is a modified version of the typical 'nickel' oxides alkaline
electrode. The addition of manganese (~60% Ni to 40% Mn by element) causes mixed valence charging to nickel
manganate to increase amp-hours per weight and to reduce cost. (Mn is cheap - the stuff of throw-away dry cells.
Too much manganese per nickel would however form soluble KMnO4 and deteriorate the electrode with cycling.) The
lower pH of the electrolyte raises the voltage of the reactions. It uses graphite materials for current collectors and
conductivity enhancements. These materials are improved during fabrication. (All metals will oxidize in the
positrodes, so carbon materials are necessary.)
The Electrolyte is potassium chloride (KCl) salt, with the possible addition of calcium hydroxide (Ca(OH)2, lime),
which sets the pH to about 12.7. W ithout the lime, the pH generally drifts from 7 up to 12 or 13 over several
charge-discharge cycles. Since lime is only slightly soluble, extra lime can be added, which will simpy sit on the
bottom unless it's needed. (Lime may also be an additive layer in the positrode to improve oxygen overvoltage
characteristics and conductivity.)
DISCLAIMER: This information is provided freely and is in no instance or detail guaranteed as to accuracy or veracity.
Any use made of the information is at the sole risk of the user. No liability will be accepted by the author. The author
warns the reader that his highest formal chemical education is a 74% grade in Chemistry 30 in grade 12, in 1972. Most
everything learned about the subject since then has been self-directed web based studies and experimentation.
Note that preliminary editions are being written in bits and pieces as research proceeds, and the text may not be
consistent within itself: one statement might say "is expected to" or "should", while somewhere else, text written later may
simply say "this is how it works", or perhaps mentions that "it doesn't work", or simply omits further reference to an earlier
idea that didn't work. One piece of writing may contradict another.
READ THIS ==> THIS BOOK IS NOT COMPLETE AT THIS TIME AND IT CONTAINS MANY OUTDATED
INSTRUCTIONS. Only chapters 1 and 2, and "electrodes overview" in chapter 3, are up to date. SEE TURQUOISE
ENERGY NEWS #60 TO #69 FOR THE MOST UP TO DATE INSTRUCTIONS AND FORMULAS. PAY ATTENTION TO
converted by Web2PDFConvert.com
LATEST ELECTRODE INGREDIENTS, CURRENT COLLECTOR AND CONDUCTIVITY ENHANCEMENT MATERIALS,
AND VARIOUS DETAILS.
http://www.saers.com/recorder/craig/TENewsV2/index.html
TE News #60, #61: step-by-step procedure - with pictures (#60), revised but no pictures (#61)
TE News #66: Breakthrough additive (zirconium silicate) addition to negative electrode
TE News #69: Latest positive electrode formula... sufficient nickel oxides in comparison to manganese oxides
Check editions of TurquoiseEnergy.com/news/ later than the date of this document for newer information and progress.
Contents
1. Foreward and Backward
2. Electrochemistry Overview
The water-based battery cell environment
Battery Electrochemistry
Specific Electrode Substances
- Nickel
- Manganese
- Nickel plus Manganese (Nickel Manganate?)
- Silver
- Vanadium
- Perchlorate
- Zinc
- Current Collectors
3. Battery Construction Overview
Electrodes Overview
Battery Layout(s)
Chosen Layout
Electrode Binder "glue"
Separators and Capacitors
4. Making the Case and Fittings
Case
Electrode Current Collector Grills & Terminal Leeds
5. Making Perforated Plastic Pocket Electrode Enclosures
Perforating the plastic
Forming the square cylinder
End caps
'Glue'/solvent
6. Making the Positrode
6.a Permanganate/Nickel Hydroxide Positrode
6.b Monel Positrode
6.c Vanadium Pentoxide Positrode
7. Making the Negatrode
7.a Zinc Negatrode
7.b Manganese Negatrode
8. The Electrode Separators
9. Electrolyte and Cell Assembly
10. Charging, "Forming" and Testing
Initial Rest Period
Initial charge
Initial cycling
Testing Specs
11. Appendices
A. Creating Unusual Substances
B. Materials and Chemicals Supply Sources
C. Equipment & Supplies
D. Survey of Some Battery Electrode Materials
1. Foreward and Backward
[This section is an overview of the state of battery affairs and my own developments. If that's just a digression to
your prupose, skip to section 2.]
In one sense, batteries are a well known technology, intellectual property of mankind. In another, they are almost
a lost art. Factories churn out inferior lead-acid cells and small cells for portable electronic devices and cordless
tools, but the employees are just workers. W hile the theory of operation and the chemical reactions aren't hard to
undersatnd, there are a few important details needed for successful construction that are hardly mentioned
anywhere, much less all in one place. I'd say very few people know anything practical about battery design or
battery construction principles. I started this project knowing as little as anybody else, and it took six years of part
time study, experiments and frustration to finally get usable cells - and even then they're not meeting the
potentials of the chemistries, the percentage utilization of the active substances still being poor. I wish to save
future battery makers from such trouble.
A great need has long existed for long lived, economical, high energy batteries for electric transport and off-grid
power. I decided to try my hand at creating some way to make some sort of batteries at home.
I soon felt sure that some better chemistries, probably much better, than existing types could be created, and
potentially for lead-acid or throw away dry cell prices, or not so much more.
Battery research and commercialization have been sidelined by human propensity to "go with the flow", to limit
thoughts into narrow structured channels, good or (more often) inferior, and to extend that channel to the exclusion
of wider possibilities, including superior ones.
Thus for example, when Jungner found in about 1899 that nickel wouldn't oxidize at pH 14 and could be used as a
current collector for alkaline batteries, subsequent research went into pH 14 alkaline chemistries with potassium
hydroxide electrolyte almost to the exclusion of all others.
Later, with large, higher-energy alkaline batteries such as nickel-metal hydride having been killed commercially by
corrupt interests in the late 1990 s via "dog in the manger" corporate patent wielding (the most important, most
common, and most heinous use of patents - which were created to give inventors, not corporate megaliths, rights to
their inventions), and with the single-minded recognition that lithium is the lightest atomic weight metal, most
research today has been working on trying to develop better lithium batteries, despite the cost and the complex
problems of making lithium work well, and despite the fact that patents on the best developments are acquired to
kill each one as it emerges. This insanity won't continue for a second 100 years - the world is evolving - but in the
meantime, DIY battery making of non-patented chemistries provides the rest of us a way to take matters into our
own hands.
Making 'normal' water based batteries is a rather involved but fascinating "DIY " project touching on several
distinct specialties, and it creates a product valuable to civilization at this time. The process of learning and making
will challenge and broaden your base of knowledge and abilities.
How was I to write this? Should it be just "do this" and "do that" and you'll have a battery, should I provide a
little background, or should the reader be given all the gory details, the reasons and reasoning behind the
instructions? Knowledge is power! I'm telling all that I can think of to say. But I'm organizing it into various sections
so the reader can read as much or as little as desired - the basic instructions, a good theoretical overview, or
complete detail.
In other material, even the most basic information is lacking. For example, why is the positive electrode in a
standard dry cell a conductive carbon rod instead of metal as in all other batteries? You'll dig long and deep and still
not find the simple answer: that every common metal will corrode away in the positive electrode in salty electrolyte
- including nickel, which sits inert in and enables all the various KOH saturated alkaline cells. A lower pH, only
carbon or graphite works. Obviously battery makers know this (or once did), but it took me over two years of
corroded electrodes in every test cell to figure it out for myself, because no one mentions it anywhere. (I put it on
W ikipedia, but it was soon erased.)
Much of the info herein has been acquired gradually, and often painfully, in my battery research over the past 4
years. A tidbit of basic info is casually mentioned in one publication or another, most of which assume the reader is
well versed in the battery making arts - and few people are.
For example, it was only after 2-1/2 years that I finally saw for the first time an actual figure for the amount of
pressure used to compact a battery electrode into a "briquette" - for one type of electrode in one experiment. W hen
I started, I wasn't even aware of the vital role of compaction, and after eventually deducing it indirectly from some
material density specs, it took a another year to figure out a simple way to get enough pressure.
And it wasn't until January 2012 that I discovered the essential "Pourbaix diagrams" that show the relationship
between alkalinity, voltage and reaction products. These seem to show that a somewhat alkaline electrolyte is best
for virtually all of the chemicals discussed. This can evidently be obtained by using salt but adding calcium
hydroxide to the positrode. The slightly soluble Ca(OH)2 raises the pH to (theoretically) 12.3, an "ideal" moderately
alkaline pH, tho still caustic enough to be somewhat hazardous.
Likewise, it wasn't until February 2012 and four years of mysterious self-discharge problems that I understood
that the wires in the negative electrode had to have as high a hydrogen overvoltage as the electrode substance
itself charges to. Most anything goes for iron, cadmium or hydride, but few common things work with a higher
voltage chemical - zinc or manganese. For the Mn negatrode, it has to be zinc - not copper, brass, nickel, iron, ...
(...or perhaps graphite, lead or bismuth might work. These I have not tried.)
My original minimum battery goal was to copy proven and relatively economical NiMH EV battery chemistry, by the
simplest techniques I could find or work out, and thus create a "DIY " means of making batteries. But I also started
to think that coming into the field as a newcomer without formal training in the field as to "that's how it is", I
might, in stumbling around, uncover overlooked information or ideas that could lead to a better battery.
That would have the additional advantage that being developed by me, freely and openly published by me, and
designated by me as the inventor to be free technology. There would be no patent restrictions on it for vested
interests to kill commercialization with. (Patents aside, it would be very difficult to make a decent hydride alloy at
home.)
I did indeed do a good bit of stumbling around in my ignorance, getting wild ideas and then seeing the flaws, and
gradually learning many broad basics and fine details in no particular sequence. And I did uncover a few key
overlooked things.
I also developed some "DIY " battery construction tools and techniques, such as a bolt-down electrode compactor,
and perforating rigid plastic sheets with a heavy sewing machine to make solid "pocket" electrodes. Finally I have
been rather successful: nickel-manganese batteries are in principle economical, "green", and superior to what's on
the market today, including being quite economical and having about the highest feasible energy density,
theoretically on a par or greatr than lithium ion types. I picked the reacting substances out of a considerable number
of possibilities because they seem to be the best. The fact that they are also common and relatively economical is
an excellent bonus.
2. Electrochemistry Overview
Unless otherwise specified, quantities given as a percentage, eg "1% antimony sulfide", mean percent by weight
("wt%"). Sometimes this is in addition to the otherwise complete chemicals. So if an electrode has 65% nickel
hydroxide and 35% graphite powder, and "1% Sb 2S3 is added", the total weight is 101%.
I'm introducing here some new terminology - more accurately, two terms and a new spelling. Most literature uses
the terms "anode" and "cathode". The meaning of these terms is reversed when the battery is charging from when it
is discharging, and while there is a convention that "anode" refers to the negative electrode (while it is the positive
terminal of a diode or a non-rechargeable battery), this is not universally adhered to, and there is often confusion
about what is meant - I often get mixed up myself. As electrodes are ubiquitous to the subject and a specific one is
so often referred to, herein I will call them "positrode" and "negatrode", which terms should be self explanatory. I
also insist on spelling terminal wires as "leeds" to differentiate connections and wires from the metal "lead", the
guy "in the lead", and at least a couple of other uses of the same four letter sequence, hoping not to "lead" anyone
astray.
Once an electrochemical design has been worked out, the physical design and construction becomes the more
important to making a battery that works. But the electrochemisty is the premiere part, the fascinating part, so it
gets the first chapter.
I've tried to explain less common, specifically electrochemical terms herein, but the reader will understand the
text better if he still remembers his high school chemistry. If you don't know what an "ion" or a "sulfate" are, just
look them up on W ikipedia. If anyone asks, I'll try to answer things I haven't made clear.
T he Water-based Battery Cell Environment
Aqueous batteries tend to charge water into O 2 (positrode) and H2 (negatrode) gasses. In acid, hydrogen
generation starts to occur at 0.0 volts or anything negative: this is the reference voltage against which all other
reactions are measured. W hether a substance can be used inside a rechargeable cell depends on it charging below
the voltage where gas is produced instead.
Gas generation is more and more likely with increasing voltage above 1.23 volts, but the exact voltage varies
considerably with electrode substance and additives, temperature, and pH. Any amount over the theoretical gassing
limit, at which gas isn't generated, is called the "overvoltage".
In acid, gas generation voltages shift to inhibit oxygen generation and hydrogen generation occurs more easily.
Eg, a lead-acid battery allows the lead oxide to lead sulfate reaction to work at +1.7 volts. The lead dioxide would
spontaneously discharge itself at that voltage in salt or alkaline solution. However, the lead metal to sulfate
reaction is just under the hydrogen generation limit at -.35 volts.
On the other hand, in alkali, oxygen gas generation is encouraged and hydrogen more inhibited. The common
alkaline nickel positrode (+.49 volts) is just below the "oxygen overvoltage" at room temperature, and zinc just
works at -1.24 volts. The 0.0 volts in acid hydrogen voltage, in alkali is -.833 volts. The inverse of this voltage plus
the +.49 volts of nickel gives us a theoretical open circuit voltage of the nickel-metal hydride alkaline battery, 1.32
volts.
Oxygen overvoltage falls a bit with temperature, and above 40ºC simple nickel electrodes won't charge properly.
The electrode substance is also significant, and small amount of a high overvoltage potential substance as an
additive can increase the overvoltage so that the main substance works better, or works at higher temperatures. To
improve zinc's performance in alkaline solution (-1.24 volts), the traditional additive was 2.5-4% mercury oxide.
Later, owing to mercury's toxicity, transition metals (gallium, indium, tin and bismuth) or their oxides were tried and
found to work well even in amounts under .5%. In an Indian experiment with sealed Ni-Fe alkaline cells, .5%
bismuth sulfide (Bi2S3) was used to reduce the hydrogen bubbling in the iron negatrode. Heavy transition metals
such as antimony are also used to improve lead-acid cell charge performance.
In the case of manganese as a negatrode, lowering the pH even a little lowers the reaction voltage - from -1.57v
towards -1.18v at pH 8. That's the start, but it's not enough.
Then, adding 1% antimony sulfide raises the hydrogen overvoltage above manganese's charging voltage -- as long
as the temperature is under about 20°c. I discovered this worked in February 2012. Eureka! I was sure I had it!
Then later I got poor results. In July 2013 I figured out the problem by putting the cell in the fridge. It didn't work
at 25°c. It worked fine at 6 or 8°. I considered that cells with manganese electrodes might have to be kept in air
conditioned spaces.
Then I tried adding 3% zirconium silicate as well as the antimony sulfide, and this raised the stable temperature
to at least 30°c. (...probably considerably higher, but that was as high as I happened to test it at.)
The additives are the only reason it works at all. W ithout them, the overvoltage seems to be right on the edge
even at low temperatures: the manganese may or may not charge, but it bubbles hydrogen as it does, and gradually
discharges itself to hydroxide. Thus manganese has never been used before as a negatrode. But its high reaction
voltage gives a "-Mn" battery an edge in energy density over any other. (Ni-Mn is higher voltage and far longer
lasting than Ni-Zn, making higher energy cells of about 2.2 or 2.3 nominal volts. In fact, NiMn moderately alkaline
cells may last indefinitely.)
There are lots of even higher voltage reactions, but it's hard to conceive of making any of them work with any
additive. For example, aluminum to aluminum hydroxide is -2.33 volts in alkali. That would make for fantastic
energy density, but I doubt that will ever be enticed to charge or to hold a charge in any aqueous solution.
The gas produces pressure inside the cell, and the pressure problem increases with battery size, so sealed
batteries are small. In addition, H2 has proven almost impossible to get rid of in sealed cells. Pressure would just
build up until the cell burst. So sealed alkaline batteries are made with the negatrodes larger than the positrodes.
The positrodes bubble oxygen first, and the cells are also made as dry cells with empty spaces that gas can pass
through. The oxygen migrates to the negatrode, discharges some of the substance (making heat), and prevents
complete charging of the negatrode. This gets rid of the oxygen, and prevents the negatrode from bubbling
hydrogen gas, preventing mild overcharging from bursting the cell.
Vented cells (a) dry out and need refilling, and (b) absorb carbon dioxide from the air, which may gradually
degrade substances within, turning them from active chemicals into carbonates. Various caps and valves can
minimize the problems and vented cells aren't impractical, but they're second best to sealed.
To make sealed cells bigger than dry cells, some means to keep gas pressure low has to be found. Recent work
with catalysts to recombine O2 and H2 into water has been successful, but I haven't explored it at this point. I've
also read that antimony is almost unique in its ability to react with small molecules - like hydrogen - and I picked it
as an electrode material additive hopefully as a recombinant catalyst as well as for raising hydrogen overvoltage,
but I don't know if it works, or if I've employed it well to do so. Antimony sulfide is cheap.
I've given up on sealed cases for now. W ith alkaline liquid electrolyte, sealed cells are very dangerous, since a
spray of postassium hydroxide out a leak can blind. "Blindness is for life"... one cell almost got me - only takes one
- and I've met a blind chemistry professor. A vented case reduces the dangers, but using potassium salt for
electrolyte makes it much safer.
I hated the thought of using potassium hydroxide or acid electrolytes. They're dangerous! I was using a salt
based electrolyte of neutral pH, potassium chloride. (KCl) It's a fast electrolyte (allowing high current flow), and
less hazardous to handle than potassium hydroxide - it's edible. However, the cells turn quite alkaline with cycling.
The caustic OH- ions are much less concentrated, but it's still about pH 13.
In addition to chemistry, there were (and are) other novel improvements begging to be made. If one could find a
chemically inert but electrically conductive or even semiconductive binder 'glue' to hold the electrode powders
together, it could permit higher current flow than the usual insulating binders, and intense compacting of the
electrodes would be less critical to obtaining good current capacity... If a small, economical, high energy battery
could supply enough current to start a car engine, that would be a marvel!
Battery Electrochemistry
First I'd like to point out a misleading quirk of terminology. Back in the beginning of understanding atomic
particles, someone decided electrons had a "negative" charge while protons were "positive". It doubtless all seemed
pretty arbitrary, perhaps even using the words "positive" and "negative". Of course, these two words have other, well
known meanings. Here they have been applied backwards.
Consider that protons are stationary, within atoms, while free electrons move around between atoms... like banks
and money. W ith a surplus of electrons, paradoxically the charge is "negative", while if there is a deficit, it becomes
"positive". The more money you spend, the higher your account balance; the more you earn, the higher your debt.
The negatrode deposits electrons during charging and then supplies them to a load, while the positrode is "short" of
them when charged and soaks them up on discharge. This is all counterintuitive, and in some situations, a
hindrance to figuring out what's going on. Now back to our regularly scheduled program...
W hen a positive battery electrode is charged, it is "oxidized". W hen it discharges, it is "reduced". The negatrode
is the opposite. These confusing names indicate electrochemical reactions that involve loss and gain of electrons,
which on this planet are frequently but not always related to oxygen reactions. (Remember the obnoxious "OIL RIG"
- Oxidation Involves Loss, Reduction Involves Gain [of electrons].) Pushing electrons around is what batteries are all
about. (Hmm, "Reduction is gain!" -- another lovely little paradox of nomenclature!) A shorthand used for reduction
and oxidation is "redox", and battery reactions are redox reactions.
The electrochemical reactions at each electrode are called "half reactions", and the two half reactions of a battery
must balance each other. If the negative terminal supplies "x gazillion" electrons to an external circuit, the positive
terminal must soak up "x gazillion" electrons. And, the ions released internally by one electrode when the electron
flow must complement those released by the other or be absorbed into it. After all, no atoms are being added to or
removed from a battery in use.
The chemicals used in a battery are chosen both for complementing ions and such that the positive side is a
chemical that gives energy when reducing while the negative chemical is one that gives energy when oxidizing - at
least relative to each other, within the cell's closed environment.
Usually the negatrode material reduces to the pure metal form when charged: iron, cadmium, zinc, lead,
manganese, and oxidizes to an oxide or hydroxide during discharge.
The positrode is likely to go between two oxide forms with charge and discharge, a higher and a lower oxide or
hydroxide.
There are exceptions, and many other possibilities. In lead-acid batteries, the negatrode metallic lead oxidizes to
lead sulfate, and the positrode lead dioxide reduces to lead sulfate, the sulfate ions being stored as excess acid (or
sodium bisulfate) in the electrolyte when the battery is charged, and absorbed as it's discharged. More examples
appear below.
Usually these positrode oxide forms aren't very good electrical conductors. Some oxides, like titanium and
zirconium, are virtually insulators, so they can't convert easily between forms by electrical action as battery
elements. Often additives are used to improve the conductivity of the oxides. Zinc and cobalt oxides have been
used to make nickel hydroxide electrodes conductive enough to use, as have nickel powders and flakes, and
powdered graphite.
The number of amp hours depends on how many electrons the substance will release or absorb during oxidation or
reduction, and the energy of each reaction is indicated by its voltage. A substance which naturally wants to oxidize
(in the battery environment) will have a more negative reaction voltage than one that wants to reduce. The energy
in watt-hours is the amp-hours (the number of electrons) times the voltage (the pressure behind each electron). The
voltage of both electrodes is subtracted for the total battery voltage, eg +.5 - -.93 = 1.43 open circuit volts for a
nickel-iron alkaline battery. The amp-hours or number of electrons isn’t additive: it should match. The current flow
stops and the cell is discharged when either electrode has been depleted to its un-energetic state and will pump no
more electrons and ions.
For a given number of electrons moved per reaction, the lighter the atomic weights of the reacting elements, the
more amp-hours per kilogram will be available, because there are more molecules to react in that kilogram. Oxygen
and especially hydrogen are quite light, so the metal is usually the dominating factor. If a heavier element is
chosen, it must move more electrons per reaction, or have a higher reaction voltage, to provide equal energy
density. If the advantages are less than the added weight, as with lead, cadmium or mercury, batteries with these
heavier elements have lower energy densities. Heavier elements are also more costly. Thus my own searches (once I
understood this) were mainly for lighter atom metals.
Lightness of metallic substance is pursued to the ultimate in lithium battery types. But lithium has to be used in
thin film electrodes, often with non-aqueous electrolyte, and the substrates to hold all the thin films add their own
bulk and weight.
Usually it is required that reaction products of both charge and discharge be solid, that is, that they don't dissolve
(...or melt or turn into a gas). This greatly limits the choices. Most chlorides are soluble, so the electrodes of a
battery using hydrochloric acid would dissolve and thus would be hard to recharge. The old 'standard' nonrechargeable dry cell uses ammonium chloride electrolyte, and the zinc electrode dissolves to zinc chloride in use.
Most lighter elements dissolve in sulfuric acid, but lead, lead sulfate and lead dioxide are all non-soluble - hence
the lead-acid battery.
Just to prove the point, I looked for an acid that lighter metals wouldn't dissolve in. I found oxalic acid seemed to
qualify, and I made a nickel-zinc test battery in oxalic acid: nickel oxide, nickel oxalate, zinc and zinc oxalate are all
insoluble. Similar in concept to lead-acid, it worked and could be charged. (The voltage was lower than the tables
indicated, about 1.4 volts.) But I didn't think this was the battery I was looking for. I suspected there would be
unforseen complications over many cycles, and took it no farther.
Zinc has been known as a frustrating battery negatrode element. It's energy is the highest available for pH 14
alkaline cells and its electrical conductivity is good, and the charge and discharge products are both solids. However,
in use there is a temporary dissolved state, the zincate ion, in which form the zinc can and does gradually migrate.
This causes the negatrode to gradually lose capacity, and the zinc grows dendrites, "tentacles" of zinc crystal, which
usually short out dry cell batteries, often after only 10-50 charge-discharge cycles. Cadmium, underneath zinc on the
periodic table, has the same problem to a lesser extent, and in my experience Ni-Cd dry cells rarely last anywhere
close to their supposed cycle life as cadmium crystals poke through the separator sheet and short the cell. NiZn and
NiCd pocket cell batteries fare much better. But it would seem that NiZn dry cells in recent years have improved, as
a company making AA cells (available on Amazon.com) claims 500 to 1000 charge-discharge cycles.
It's possible that in salt electrolyte, zinc doesn't form zincate ion. Thus switching to salt might solve the problem,
allowing use of this high energy density substance in long-life batteries. Somehow I doubt it.
There are several choices with somewhat less energy than zinc - eg, iron, cadmium and hydride - but none with
"just a little less". Next up, manganese at about .3 volts higher than zinc and with apparently ideal characteristics
for a battery negatrode, sat enticingly on the voltage threshold between usable and not for a negatrode. After much
time, frustration and confusion, I got it to work as explained herein.
The electrolyte doesn’t conduct electrons between the electrodes, it only conducts charged dissolved ions. It's the
one place where protons are on the move. To have the oxidations and reductions take place, both ions and electrons
must flow, as will be seen in the redox (reduction-oxidation) reactions coming up.
A circuit connected to the battery lets the electrons flow between the electrodes - externally. This is of course
what the battery is for. W hen an external circuit is connected, the electron flow, the ion flow and the discharge
reactions proceed spontaneously and simultaneously, releasing the chemically stored energy as electricity. The ions
flow mainly by diffusion through the electrolyte, spreading because like charges repel, and by attraction to the
opposite electrode as they reach it. The current capacity of the battery depends partly on how fast the ions diffuse
through the electrolyte. Potassium chloride salt is supposed to be very fast.
The discharging reactions release chemically stored energy electrically. The recharging reactions require electrical
energy from the external circuit - the battery charger. Charging restores the 'spent' lower energy substances to their
higher energy oxidation states and valences.
There are many solutions and some solids that can pass ions, but the best - fastest - solvent is a polar liquid such
as water, with an acid, salt or alkali electrolyte dissolved in it. There is, however, one serious limitation to using
water as an electrolyte, as mentioned previously:
"The use of aqueous battery electrolytes theoretically limits the choice of electrode reactants to those with decomposition voltages less than that of water, 1.23 V
at 25 ºC, although because of the high "overvoltage" potential normally associated with the decomposition of water, the practical limit is some 2.0 V. The liquid
state offers very good contacts with the electrodes and high ionic conductivities."
Lead-acid batteries are theoretically 2.05 open circuit volts, and many earlier cells were about 2 volts. The 2.6
open circuit volts of the Ni-Mn cell have raised the "practical limit" considerably.
The voltage delivered to a load circuit is somewhat lower than the open circuit voltage, depending on the internal
resistances of the battery relative to the amount of current flowing. Hence batteries are given a "nominal" voltage
rating which might be expected in typical heavier use, such as "1.2 volts" for Ni-Fe, Ni-Cd, and Ni-MH, which read
more typically 1.33 to 1.43 volts with no load. Heavy loads may drop the output even more, eg to 1.0 volts. If such
loads are expected, it's usually best to add more batteries in parallel to reduce the load on each one, or to use
bigger cells, which is effectively about the same thing. Ni-Mn should be rated when someone has made one that
utilizes at least 1/4 of the potential active material. (Mine so far, of any chemistry, are generally below 1/10th.)
If the positrode has lesser amp-hours capacity on discharge than the negative it is depleted first. The negatrode
still could have supplied more current and the battery is said to be positive limited. Vice-versa if it's the negatrode
that runs out first. It may also be positive or negative limited on charging, and not necessarily in the same
direction. It's also possible for the electrodes to be entirely off balance - one discharged and the other charged. It
could be hard to either charge or discharge this cell.
There are often good reasons for preferring one reactant to deplete first. For example, if there's no recombination
catalyst in a sealed dry cell, oxygen gas is much better to generate than hydrogen if the cell is overcharged. In a dry
cell, it travels over form the positrode to the negatrode and there discharges an atom of metal to hydroxide, making
a bit of heat. Thus the cell stops charging - it just gets warm. Hydrogen doesn't readily discharge at the positrode
and the gas would accumulate until the cell bursts, so it's best to have the positrode charge first and not get any
hydrogen. W ith the catalyst, starting to generate both gasses at about the same time when the charge is complete
should be advantageous, since they can then start recombining to make water before the pressure of either gas
builds up much. But that depends on having an effective catalyst and a design that utilizes it effectively.
Electrode Substances
Besides lead in lead-acid cells and lithium, there are two common positrode substances: nickel oxyhydroxide
(NiOOH) and manganese dioxide (MnO2).
Manganese dioxide has been strictly the substance of one-use dry cells, so-called "carbon-zinc" but actually
manganese-zinc, the carbon (as graphite or "carbon black") being in fact simply a conductivity improving additive. In
salty solution (pH 7) the energy is about +.5 volts, but in alkaline solution (pH 14) it's only +.15 volts.
Lower voltage cells might be okay given that manganese is cheap, except that when charged it doesn't readily
stop charging at MnO2, valence 4. Unless charged very slowly with little voltage above the charged cell voltage, it
continues to charge to potassium permanganate (KMnO4), valence 7, with the "K" from the electrolyte. And that's a
little soluble, so the manganese migrates and the electrode deteriorates.
So makers of rechargeable alkaline batteries prefer virtually insoluble nickel oxyhydroxide, with +.5 volts.
In "moderately alkaline" cells, nickel oxyhydroxide's voltage, increasing as the pH drops, works great and makes
2+ volt cells. But there's a third alternative: adding manganese to the nickel seems to cause "mixed valence"
charging to nickel manganate, to provide the highest energy density. Others have noted the higher amp-hours when
manganese is added to the nickel (at pH 14), but they explain it as "helping the nickel charge to a higher valence",
which is probably not accurate. The proportion of manganese to nickel should be under about 40%, to avoid leftover manganese oxides and probable formation of potassium permanganate.
In alkaline negatrodes, iron, cadmium, zinc and metal hydride alloys have been used. Utilization of iron is poor,
and it very gradually forms ferric oxide or hydroxide and the electrode decreases in capacity. Ni-Fe is nevertheless a
long life battery chemistry. Cadmium crystals gradually grow owing to temporary solubility of cadmate (cadmiate?)
ions. This tendency is however most pronounced in the element above camium - zinc. Flooded Ni-Cd cells last much
longer than the dry cells, which often short out long before the 'advertised' time. However, being a heavier element
(atomic weight 112) and lower voltage (-.82), the energy density is lower than with zinc (atomic weight 65.4 and 1.24v).
Metal hydrides are alloys with mixed crystalline spacings that leave lots of nooks and crannies for hydrogen "-"
ions to hide in without creating much pressure buildup. A typical alloy is Ni:La:Co in proportions 10:2:1. Amazingly,
when the cell is charged, the H- ions can be packed in more densely than in liquid hydrogen itself. Since Ni(OH)2 (or
'NiOHOH') charges to NiOOH using up one water molecule to release two "OH-" ions, and since the hydride stores
one "H-" instead of "OH-", leaving one "HOH" - water, the water content of the cell doesn't change between charge
and discharge as it does with the other types where the metal converts to its hydroxide. (eg, Cd + 2 OH- ->
Cd(OH)2, effectively absorbing an H2O.)
Lanthanum will spontaneously form La(OH)3 on contact with water, so the hydride gradually deteriorates and
many surface treatment tricks are used to try to slow this. As with Ni-Fe, Ni-MH cells will last a very long time substantially longer than Ni-Cd or Ni-Zn. However, all of them have finite lives for known reasons.
Until now zinc has been known as the most energetic negatrode element at -1.24 volts and 820 amp-hours/gram
of Zn, or 1016 watt-hours/kilogram. This is much better than iron or cadmium and on a par with the best hydrides in
alkali. However, its rather rapid deterioration owing to the temporary formation of zincate ions makes it unattractive
for lasting batteries.
Manganese, now that it's working, appears to be an ideal negatrode, and the only one that should last
indefinitely. It has even higher energy density than zinc: theoretically 976 amp-hours per gram of Mn at around -1.4
volts or 1366 watt-hours per kilogram.
Nickel
Nickel hydroxide [Ni(OH)2] is the common positrode material used in most rechargeable alkaline batteries with
various negative electrode materials: Ni-Cd, Ni-Fe, Ni-MH and Ni-Zn. Dry and pure, it's a very fine, fluffy, turquoise
green powder. The nickel will happily stay in the hydroxide form in the battery environment. It thus has no usable
energy. To convert it to a more energetic chemical, energy must be put into it.
To charge it, the nickel hydroxide is further oxidized to nickel oxyhydroxide by grabbing one electron from it. It
doesn’t willingly give up the electron: the charger has to supply the energy to cause it to happen, exceeding +.52
volts. This disengages a hydrogen ion (H +), which jumps over to an immediately adjacent hydroxide ion (OH- ) in the
electrolyte to form water. The nickel is 'oxidized' from valence +2 to +3, by losing an electron (to the charging
circuit) and a hydrogen rather than by adding oxygen. The basic half reaction is shown as:
(beta) Ni(OH)2(s) + OH- (aq) <==> (beta) NiO(OH)(s) + H2O(l) + e -
[+0.49 V in alkali; ~ +1 V in salt]
(discharged <==> charged)
Note that the "Ni" compounds are solids on both sides of the reaction -- not dissolved, liquid or gas. It is usually
a prime requirement that the electrode doesn't dissolve. Normally if it does, the battery won't recharge. The valence
of the nickel goes from II to III as it's charged, indicating that one electron is removed per molecule, as shown.
(We'll touch on the crystalline forms "beta", "alpha" and "gamma" further on.)
But in fact, not all of the oxyhydroxide [III] gets converted back into hydroxide [II]. W hen there's some of each,
the nickel valence is expressed as a fraction. (which we will not attempt to describe with traditional Roman
numerals) W hen it gets below 2.25 or so, the resistance rises and the user considers the battery to be "pretty much
dead". So really, only 3/4 of an electron is moved per nickel atom, reducing the capacity below the theoretical value.
The two voltages shown (+.49, +.52) are as listed by different sources as being the "open circuit" voltage for this
reaction. Voltages seem to vary slightly with different electrode additives, and perhaps with temperature.
A major advantage of salty electrolyte is that the nickel reaction voltage is substantially higher, giving it more
watt-hours per kilogram than the pH 14 alkaline cell. This alone was a good reason to attempt to create working
salt solution batteries.
The nickel oxyhydroxide is an "energized" substance: it would rather be just plain hydroxide and given a chance
will revert and give off energy in doing so. But it needs an electron and a hydrogen ion to do so. The amount of
energy per electron is seen in the voltage. It can get the hydrogen "H+" ions from the water, leaving OH- in the
water. This is balanced with the negative electrode grabbing the "OH-" ions, but it will only perform this reaction
when an external electrical load is connected to give it an electron.
Nickel redox chart.
Paradoxically not shown is the chief reaction of battery interest, between valences 2 and 3
in alkali (base) Ni(OH)2 to NiOOH, which has the same reaction voltage as the 2 to 4: +0.49 volts...
or +0.52 depending where you read. If some of the nickel is oxidized to NiO 2, valence 4, as shown
on the chart, it raises the number of electrons transferred and hence the amp-hours capacity.
Notice on the chart that nickel hydroxide can be reduced as well as oxidized, to become elemental nickel. Again,
it would rather be hydroxide in the wet battery environment, and it takes energy to reduce it to elemental nickel
metal. Thus, this reaction would make a "-Ni" negatrode. The reduction reaction is:
Ni(OH)2(s) + 2 e- ==> Ni(s) + 2 OH - (aq)
[-0.72 V]
Again the nickel keeps a solid form, so a working Ni-Ni battery could be created... except that nickel metal won't
oxidize in pH 14 solution. It does work in salt electrolyte, at a somewhat lower voltage.
A "Pourbaix" diagram shows the reaction products at different pHes and voltages.
A Ni negatrode might discharge to Ni(OH)2 between -.4 and -.6 volts depending on
the pH of the electrolyte.
A NiOOH positrode will discharge to Ni(OH)2 between +.49 and maybe +.9 depending on pH.
If the pH falls below about 8, the nickel can dissolve when it discharges.
(I'm not aware that Ni(OH)3- is ever mentioned in literature...
but it's even less likely to form in moderately alkaline pH.
I suspect this chart is very approximate in all its aspects.)
The valence of the nickel goes from II to 0, adding two electrons to each nickel atom. This charging reaction gives
off the negatively charged hydroxide ions that were bonded to the Ni(OH)2, the same as with iron, cadmium, zinc
and manganese, each at its own voltage. Moving two electrons instead of one, at -0.5 volts (instead of +0.5),
provides 2 times the theoretical energy storage. Nickel hydroxide in moderate alkali, though the most common
positrode material, makes a more energetic negatrode than it does a positive one! And it should have no limit to its
cycle life.
Notwithstanding this, the voltage and energy of the reaction are lower than the usually used substances.
Manganese has three times the energy, indefinite life, and is much cheaper.
So why is nickel [oxy]hydroxide so popular as a positrode chemistry if it has so little energy beside the common
negative electrode materials? Well, it boils down to ... try and find something better, that doesn't cost a fortune!
Manganese dioxide, while cheap, is only +.15 volts in alkaline solution. That means more cells to attain a given
voltage. In salt, it's .5 volts, and it might be a more economical solution for stationary batteries, eg for off-grid
home power storage. It is easy however, and considered deleterious, to charge it to a higher oxide form. (The zircon
ion and-or chelation of the Mn ions shield might alleviate this concern.)
For transport where light weight counts, nickel's +1 volt in salt is better despite the cost. Anyway, the only
required nickel in the salty battery is the actual active chemical, whereas in alkaline batteries nickel or nickel plating
is used for all internal metallic structures. (That could be changed with grafpoxy.)
But the traditional basic reaction doesn't reveal nickel's full potential. Nowadays, manganese is added to the
positrode as a major additive, perhaps 35 to 40% by weight ("wt%") of Mn to Ni. W hat this supposedly does is raise
the oxygen overvoltage, which evidently allows the nickel to charge to "alpha" nickel oxyhydroxide, wherein some
portion of the nickel actually charges to NiO 2, valence IV, moving two electrons instead of one. Another thought is
that permanganate is a "powerful oxidizer", and it may be this that allows or causes the nickel to oxidize to a higher
valence. On the other hand, the two ideas may just possibly amount to the same thing expressed differently.
Maximum attainable overall valence appears to be about 3.8. The actual nickel valence thus might change from
about, say, 2.25 to 3.75 from discharged to charged, thus moving 1.5 electrons per nickel atom, twice as much as
with the old pure Ni(OH)2 simple formulation. This doesn't double energy density by weight because of the added
mass of the manganese, but it does improve it, and the nickel - the costly and main ingredient - does twice as
much work.
Multiplying the theoretical value 289 AH/Kg * 1.5 = 433 AH/Kg. Naturally however, the theoretical maximum isn't
going to be attained. (Experimentally about 350 AH/Kg has been attained, the forms being alpha hydroxide and
gamma oxyhydroxide, which both occupy about the same volume of space. Although it's a higher volume form than
the beta forms, the constancy is very desirable for long cycle life.)
NiMH "AA" battery capacities have increased from 1.5 to 2.5 amp-hours in recent years. (This is after sintered
nickel cadmium "AA" batteries of just 0.5 AH in the 1970s.) Since the NiMH AA cells with this high energy weigh 30
grams, and the nickel hydroxide (educated guess) probably weighs up to about half of it, an attainable figure in an
actual battery of around 166-200 milliamp-hours/gram (= amp-hours/Kg) is suggested.
Squeezing the most out of the nickel is important both for economy and because the nickel is the bulkier, heavier
electrode, and anything that improves it can notably improve the entire energy density of the battery. For homebrew
salty batteries, I'm expecting actual attainment of around 100 AH/Kg will be doing well.
The negatrode substances being much higher energy, the energy density of the whole cell will be mostly limited
by the nickel and the voltage obtained. A 1.8 nominal volts nickel-zinc/salt cell then will be somewhat under 180
W H/Kg, eg maybe 120-170. For 2.1V with a manganese negatrode, if that can be made to work, 130-190 W H/Kg
might be attained. These figures seem dissappointing after reading the theoretical maximums, but they're still
better than commercial NiMH dry cells and as good as or better than lithium ion types. And it's not impossible that
with good design, chemicals, technique, workmanship and high compaction, even higher energy might be attained.
Other metal oxides or hydroxides besides manganese that have been tried and appear to work (and may bear
further experimentation) include: aluminum, cobalt, yttrium, ytterbium, erbium, and gadolinium. Other rare earths
hydroxides such as samarium, neodymium and even lanthanum might be better, or at least fine, in salt solution. I'm
not sure why manganese is supposed to be "especially preferred" (or even why it should work well), or indeed what
the selection criteria are, but I've used Mn in my positrodes as well. I believe the Mn charges to higher oxides
(potassium permanganate) that won't discharge until the nickel has finished discharging, and then at a lower
voltage. (Manganese has so many reactions at various voltages that it's confusing to try and figure out what will
actually happen in many situations, and I as far as I can see commercial battery designers often don't know exactly
what they're doing either. Certainly in Alkaline Storage Batteries (Falk and Salkind 1969), there was a lot of
speculation about some of the main chemical reactions. And battery substance reactions in salty electrolyte are
relatively unexplored compared to alkaline.)
It's not clear to me at the moment whether the only effect of the manganese compound is supposed to be to
raise oxygen overvoltage in the postirode. If it is, the samarium or whatever, probably in considerably lesser
quantity percentage-wise, should replace it entirely, providing highest energy density. (For a while I thought the
KMnO4 reacted at virtually the same voltage as the nickel and would be an active chemical along with the NiOOH,
but it appears it's somewhat lower and thus wouldn't start to discharge unless the nickel had completely
discharged.)
The element nickel is the biggest cost in nickel-alkaline batteries - it's not only the postrode substance, but
composes over 3/4 of the hydride alloy, and the plating or substance of all the metal conductors within the cell. In
the salty cell, it's just the positrode chemical, so the cell should be more economical.
Neither nickel hydroxide, oxyhydroxide nor potassium permanganate is a very good electrical conductor. The
battery's current capacity would be extremely limited if these were the only ingredients. Powdered graphite has
been added for better conductivity, as in the standard and alkaline single use dry cells.
Edison put in 80 layers per inch of alternating nickel hydroxide and ultra-thin nickel metal flakes, crammed solidly
into perforated metal tubes about the size of a pencil. The nickel flakes were made by electroplating alternate
layers of copper and nickel onto something, then dissolving away the copper. That costly arrangement was the best
he could come up with that worked well. He tried graphite flakes and found the performance was unpredictable - I
think Edison didn't expect powder could be a good conductor across an electrode, but above a critical proportion it
is.
The sintered electrode is another good form for conductivity in alkali, the sintered nickel sponge connecting well
across the whole electrode for very high current capacity. NiCd cells get some of their high current ratings from this.
But I discovered that for any salty cell battery, all metals oxidize rapidly in the salty positrode. Sintered metal
electrodes are out. And graphite powder is cheap at any art supply store.
But up to 5% cobalt hydroxide has been added to alkaline cells with good effect to improve conductivity without
graphite or nickel flakes, and I've been trying starting with monel alloy, which puts (25-33%) copper hydroxide in
solid solution with the (67%) nickel hydroxide. (The monel I'm using also contains 2% Mn and 3% Fe, so the copper
is 28%. Obviously Mn doesn't hurt, and the iron either, I trust.)
On a practical note, it's worth mentioning that a nickel electrode can be discharged chemically to Ni(OH)2 by
immersing it in a small pool of hydrogen peroxide - the 3% drug store stuff is fine. It makes zillions of very tiny
bubbles as excess oxygen comes out. W hen it's done, rinse out the H2O2 with clean water.
In addition, the nickel can be charged to NiOOH using bleach, sodium hypochlorite. I haven't done this myself. 3%
grocery store bleach should work fine. Again rinse out the bleach when done.
These procedures give you a way to equalize the charge if you've ended up with one charged electrode and one
discharged for a sealed battery. For an unsealed one, charging and letting gas bubble off one electrode works.
Manganese Positrode
Manganese dioxide is a dark gray, blackish powder, fairly dense. It can be scrounged from [non-alkaline] dry cells,
or purchased at pottery supply stores. The dry cell is probably the better source - it's known to be pure enough for
batteries and it's "pre-mixed" with conductive graphite powder. In the open, dioxide is the usual state of
manganese, but in the typical cell it's the charged state. An even better form for use in positrodes is as potassium
permanganate.
Sometimes the discharge product is given as MnOOH and sometimes as Mn 2O 3. It matters little as both are
valence three after moving one electron, the difference only affecting the amount of water released or absorbed
during charge and discharge.
The literature says the discharge reaction in alkaline solution is:
MnO 2(s) + H2O(l) + e - <==> Mn2O 3(s) + OH- (aq)
[+0.15 V]
In salt solution, however, the voltage is much higher, and all literature I've managed to find shows this reaction:
MnO 2(s) + H2O(l) + e - <==> MnOOH(s) + OH- (aq)
[~+0.5 V]
Manganese Redox chart.
Manganese *can* be recharged to dioxide, and some "renewable" alkaline cells make use of this. However, just a
little extra charging voltage will cause it to charge to potassium permanganate (KMnO4), with the MnO4- ion being
soluble. The soluble ion deteriorates the electrode, and it discharges to Mn(OH)2 when it touches the negatrode.
The Mn(OH)2 gradually builds up in the separators and shorts out the cell. Thus manganese positrodes are known
for short cycle life.
The only listed permanganate that isn't soluble is silver permanganate, but some manganates (MnO4--) are
insoluble. Notably nickel manganate is probably insoluble, and we'll get to the mixed nickel-manganese positrode
further down.
Manganese Negatrode
Another manganese reaction of great interest is the one on the right end of the chart, going between valence 0
and +2. If one simply uses manganese powder in water, this reaction is just high enough in voltage that it gradually
but spontaneously discharges into Mn(OH)2. This has always precluded the use of manganese as a negatrode.
However, at any pH below 14 the voltage of this reaction drops a little. Combined with that, certain additives, in
particular heavier transition metals or their compounds, are known to raise the voltage at which hydrogen starts to
be generated. They have been used to help zinc electrodes charge better and work at higher temperatures.
Traditionally about 2.5-4% mercury oxide was used. Now smaller amounts of less toxic transition metals are
substituted: eg, gallium, indium, tin, or bismuth.
I got the idea that if zinc could be improved in voltage and temperature performance with transition metal
additives, perhaps manganese - tantalizingly just out of range - could go from "doesn't work" to "works" by the
same route.
I tried antimony oxide (Sb2O3, stibia) with uncertain results. In February 2012 I tried antimony sulfide (Sb2S3,
stibnite). It worked! (BTW the usual ore of antimony is stibnite.) I believe the Sb2S3 converts to keresemite
(Sb2S2O) or possibly to Sb2S in the cell, and it works better. W hatever happens, adding 1% antimony sulfide raised
the hydrogen overvoltage enough to allow manganese to charge and hold its charge... just enough, at lower
temperatures.
Later - in summer - it didn't seem to work and a puzzling year went by. Finally in July 2013 I tried putting a cell
that wouldn't charge in the refrigerator, and lo and behold it worked! It only worked up to maybe 20°c. (I didn't
measure the transition temperature.) Then I added 3% zirconium silicate (ZrSiO4, zircon) as well as the stibnite.
This raised the working temperature at least as far as I tried it, which was to 29°c. (Yes, I should have tried higher
to verify that it would work up to at least, say, 35 or 40°c. At the time, I was ecstatic to find that it worked at 29°.
I also didn't try any other concentration of zircon besides 3%.)
Charging Mn to metallic state and having it hold its charge was doubtless a first, and is probably my biggest
contribution to battery technology. The reaction voltage of almost -1.5 volts, makes it the most energetic alkaline
electrode ever, and the reduced pH works better than pH 14 for both electrodes. W ith no soluble or insulating states
in the negatrode, the cells may last virtually indefinitely.
Nickel and Manganese (Nickel Manganate?)
In late February 2012 I ran across a potentially better form of nickel for electrodes than nickel hydroxide: nickel
manganate [NiMn 2O 4], a synthesis of nickel and manganese. This little known substance (but not unknown - it's
used to make thermistors) is of repute for its "spinel" crystalline structure, which gives it a much lower electrical
resistance than most oxides. At first I thought it might make a good conductivity improving additive. It was far
more conductive than Ni(OH)2... but nowhere near as good as graphite.
Then I thought of using it in place of nickel hydroxide as the main electrode substance. Finally, I started to expect
that if one placed both nickel hydroxide and potassium permanganate oxides in the electrode, they might
spontaneously form nickel manganate via substitution reactions, or that nickel hydroxide and manganese dioxide
might well form nickel manganate when the cell is charged - or both - without any formation of slightly soluble
potassium permanganate.
At first I thought it might charge to nickel permanganate [Ni(MnO 4)2]. Both substances have one nickel and two
manganese ions. However, one has 4 oxygen ions while the other has 8. Charging nickel manganate to nickel
permanganate would release 8 electrons and use up 8 OH- ions from the charging negatrode (Four become the other
four "O--" ions in the permanganate, the other four become H2O). The voltage for that reaction would be around
+.65 volts in alkaline solution. It would be fantastic energy density... maybe too good to be true.
Then I thought that the nickel would be more likely to change since its reaction voltages are lower, probably
similarly to the reactions discussed for nickel hydroxide. A nickel valence 3 compound might be formed, for example,
Ni(OH)Mn2O4, or even valence 4, eg Ni(O)Mn2O4. It'd probably get a bit more mileage out of the nickel - because of
the high conductivity, it might discharge down to nickel valence 2.0, whereas nickel hydroxide pretty much stops
supplying current when the average valence is down to 2.25 owing to increasingly poor conductivity.
Later I considered that nickel manganate was the likely result, probably giving a combined effect and increasing
the amp-hours, and (it would seem) the voltage.
Before considering that it might form naturally with charging the two-oxide electrode, I looked but couldn't find
nickel manganate to buy. I tried making it chemically, but it was slow, messy and smelly. Then I mixed appropriate
amounts of dry NiO and MnO2 powders (both from the pottery supply) in a stainless steel pot and simply heated
them red hot with a propane torch (outdoors, with a respirator). This gave a lower resistance product (*probably*
nickel manganate) and was fast and pretty simple to do. I only got 15 grams, so I guess the torch blew 7 or 8
grams of powder out of the pot. Later I made another batch and 'only' lost 25% of the mass.
But if it didn't form naturally with charging of the electrode, it would probably separate into the two oxides on
discharge anyway, negating the point of having made it. And in that case, the solubility of KMnO4 would cause
problems that aren't apparently observed except in my electrodes with too much manganese compared to nickel, the
60:40 ratio having been carelessly ignored or ignored for the higher theoretical amp-hours of more manganese.
The most likely thought is that nickel manganate is the charge product. W ho knows about discharge? But
whatever exactly is happening in the mixed valence electrode, the combination of nickel and manganese oxides
seems to make a stable electrode evidently with higher amp-hours, higher conductivity and perhaps higher oxygen
overvoltage than than nickel oxides alone.
Silver
Silver oxide works well in strong alkali, but moving up to 1.5 electrons (later ones at lower voltages) doesn't
entirely make up for its higher atomic weight. It's also quite costly, and it tends to degrade separator sheets, so it's
not used a lot except for tiny cells like hearing aid batteries.
Dissolving at pHes lower than 12 (per Pourbaix diagram) would make it almost impractical to use with Mn
negatrodes. It could work if the pH was fixed to about 12.7 by calcium hydroxide in the electrolyte, but overall it
appears less effective than NiOOH or the combining of NiOOH and MnO2.
One good point is that the internal conductivity, and hence current capacity per unit area of interface, should be
fabulous. Silver oxides are quite conductive... but even more especially when some of the oxide has been reduced to
metallic silver - the best conductor of all the elements.
Vanadium
I 2011 I made a battery with a vanadium electrode. It was supposed to be the negatrode, but it didn't seem to
work - unexpectedly, the vanadium seemed to become soluble and to migrate. (This was also the first cell I'd made
with transparent plexiglass sides, and I could see the vanadium pentoxide yellow color appearing on the other
electrode.) I reversed the charges, and found that the cell charged to about 2.2 volts. The vanadium positrode side
would have made up around 3/4 of that, and it seems surprising that it didn't just bubble oxygen and spontaneously
discharge itself to a lower oxide. It seemed to charge and discharge well, but at the time I hadn't made the
grafpoxy yet and it deteriorated like my other cells of that period, as the "flexible graphite" backing sheet swelled
and lost conductivity and good contact with the electrode and the carbon terminal post. Judging by the voltage and
the chart, the likely half-reaction was:
V2O5 + H2O + 2e- <==> V2O4 + 2 OH- [+1.6? V]
Unlike the case for either alkali or acid solution, and unlike it's unexpected behavior as a negatrode, the oxides
appeared to me to remain in solid form, not dissolve, in the salt electrolyte. This appears to make it a good
positrode, moving one electron per vanadium atom, hopefully with good stability from the double vanadium
molecular center.
Taking the average of the acid and alkali voltages as being the approximate salt voltage, the voltage obtained in
the cell indicates the single valence change to V2O4 seems to apply. (average of (1.0V [acid] + 2.19V [base]) / 2 =
1.6V [salt])
The table shows that vanadium's higher oxides are "amphoteric", that is, they'll dissolve in either acid or alkali.
However, they don't seem to dissolve or break down in neutral pH salty solution even with a valence of +5.
Vanadium may have the potential to be a good positrode in salt water electrolyte. Theoretical amp-hours works
out to be almost identical to the theoretical 289 amp-hours/Kg of beta nickel oxyhydroxide. The potential double
valence change that is achieved by some of the nickel to alpha oxyhydroxide molecules wouldn't seem to be
possible with vanadium, but the voltage appears to be higher.
According to the electrochemical table, we might
suppose that vanadium might also make a good
negatrode in alkali at the same potential as cadmium (.82) and hydride (-.833), providing it wasn't
overdischarged, which might form the higher oxides, (eg
V2O3) which might cause problems.
But it didn't seem to work right for me - at least not in
salt electrolyte. There's a unique line straight from
valence 0 to 5 that probably messes things up.
However, the "Pourbaix" state diagram from W ikipedia
seems different from the above table. It looks pretty
scary.
I don't see the common V2O5 form (or VO for that
matter) anywhere in the pourbaix diagram, and the
voltages don't match the table above, nor do they appear
to jibe with my experimental results.
Vanadium may deserve more research in salt electrolyte
for use as a positrode (and maybe in alkali as a
negatrode), but I have no present plans for doing it
myself. After I found the Pourbaix diagram, I figured
there's probably soluble ions somewhere during charge or
discharge, which might make for limited cycle life.
Rare Earth Perchlorate?
Chlorine ion, Cl - , oxidizes to perchlorate, ClO 4- , moving 8 electrons with its very own electrochemical reactions
regardless of the metal + ion it's attached to. This idea may have some obvious problem and be ridiculous... or not.
(I did warn that I'm not a chemist!)
I once tried to make a positrode of lanthanum perchlorate, La(ClO 4)3, which would reduce on discharge to
lanthanum chloride: LaCl 3 + 24 OH-. The lanthanum was (per my intent, anyway) chelated into the substance of the
electrode so that, even being in dissolved form, the heavy La +++ ions wouldn't be mobile. (There is precident for
this last, an article saying chelated dissolved lanthanum behaved about the same as undissolved, tho I can't
remember where I read of it.) In addition, perchlorate is often much less soluble than chloride, as with only slightly
soluble potassium perchlorate versus potassium chloride salt.
As I've said, if heavier elements were used, they'd have to move more electrons to attain the same energy
density. Lanthanum perchlorate, potentially with 12 O -- ions forming 24 OH - ions on contact with water, is a super
example: 24 electrons per reaction where nickel moves one or two. That much would more than make up for the
atomic weight of La(ClO4)3 being almost five times that of Ni(OH)2, and - if I'm not overlooking anything - suggests
some theoretical possibility of a much higher energy density electrode than nickel hydroxide.
Unless a real chemist knows of reasons this wouldn't work, it may deserve more research. (Next time, I think I'll
try converting lanthanum hydroxide straight to perchlorate with perchloric acid instead of first to chloride with
hydrochloric acid.) (Perchloric acid is called a "super acid" - yow! I must read the MSDS again before I start. and
someone says I should get rid of it so it doesn't turn explosive.)
Zinc
Note: Zinc is superseded by manganese with 1% stibnite and 3% zircon added to raise its hydrogen overvoltage.
Manganese is the better choice in every way.
Zinc's reactions make it suitable only for a negatrode, but quite a high energy one. The dissolved ion form found
in discharge and shown in the diagram is clarified in the Pourbaix diagram beneath it.
The conductivity of zinc oxide or hydroxide is better than most, and cells with zinc are usually high-rate for both
discharge and charge.
Addition of a transition metal or its oxide is used to raise the hydrogen gas generation voltage (the "hydrogen
overvoltage") to improve charging characteristics. 2.5% to 4% mercury oxide is 'traditional' in alkaline cells. 1%
antimony sulfide is better and environmentally benign.
It was long debated whether the zinc forms Zn(OH)2 as shown or ZnO as it discharges, but as usual the
difference is merely the water content of the battery charged versus discharged, since Zn(OH)2 = ZnO + H2O. (IIRC
the general consensus is that it's ZnO.)
The troublesome zincate ion that limits
the life of NiZn alkaline cells is best seen in
the Zinc Pourbaix diagram. Here it is
revealed that this ion probably won't form
below about pH 13.5, and it's the pH 14
electrolyte that's the problem: it would be
fine at about pH 8 to 13.
Evidently, adding some manganese oxide
to the zinc to lower the pH to 13, as the
manganese negatrode does for itself, should
stop zincate from forming and allow long life
zinc negatrodes.
The question then is, is there any point to
making zinc negatrodes when manganese
ones have more energy and are just as
cheap? One possible reason is to get close
to a specific battery voltage. For example, if
NiMn cells are 1.7 volts, 6 volts is hard to
attain:
1.7 * 3 = 5.1
1.7 * 4 = 6.8
whereas four NiZn is closer:
1.6 * 4 = 6.4
or to get very close, use 3 NiZn and one NiMH:
1.6 * 3 + 1.2 = 6.0
Thus it would seem that NiZn could have uses in specific situations.
For general application however, including 12 volts, the NiMn would seem to be the winner, needing only 7 cells for
11.9 volts, while zinc is way off at 11.2 or 12.8 with 7 or 8 cells. NiMH takes 10 cells.
"Active" high surface area zinc oxide (ZnOxide.org)
An issue with zinc in salt solution is that zinc powder
and zinc oxide powder both absorb CO2 out of the air and
form zinc carbonate on the surface, which is passive in a
battery and (I think) an insulator. The carbonate however
can be removed by immersing the powder or the electrode
in a hydroxide: KOH, NaOH or Ca(OH)+ (lime). The lime is
the best and safest one. A bit of the Ca(OH)2 will become
carbonate (CaCO3, limestone). This should help
strengthen the brittle zinc electrode.
Not only does the carbonate become zinc oxide,
evidently it becomes the finest, high surface area "active"
zinc oxide, ideal for a battery electrode.
In traditional manufacture of alkaline batteries with zinc
electrodes, the finished electrodes are placed in KOH for a
day, and the "carbonated" electrolyte is replaced before
charging. But the soluble zincate ion causes zinc
electrodes to degrade rapidly enough that NiZn hasn't
been a very popular choice, lasting as few as 10 to 50
charges, followed by a shorted cell being the norm in dry
cells.
However, according to W ikipedia, NiZn alkaline cells with "stabilized" negatrodes have been much improved since
Y 2K and are now commercially viable, attaining 400-1000 charge-discharge cycles at 100 W H/Kg, probably at a
substantially lower cost than NiMH or lithium. W hen the patents run out, they might become available in vehicle
battery sizes instead of just small dry cells.
Cadmium also forms a soluble ion and NiCd dry cells often don't fare much better than zinc, cadmium being right
under zinc in the same column of the periodic table. They do have zinc's high conductivity. NiCd pocket cells,
however, like other pocket cell batteries, have a good reputation for longevity. Since the atomic weight of cadmium
is 112.5 versus 65.5 for zinc, and since its voltage in alkaline solution is -.82 instead of -1.25, the energy density of
cadmium is only 38% that of zinc. Hydride is much higher even with the same voltage. (-.83) Nickel-iron is probably
better too, even tho utilization of the iron isn't high, as it tends to agglomerate into larger particles with less
surface area with cycling. (Additives such as cadmium help, and it was from using cadmium as an Fe additive to
NiFe that NiCd was developed. I can't help but wonder if a sufficient quantity of graphite would keep the iron
particles from merging.) But I digress.
3. Battery Construction Overview
For batteries, one thinks immediately of electrochemistry, but the construction of a battery is no trivial part of
making it work. A good part of the effort of six years of battery R & D was trying to come up with workable ways to
actually make a battery, any battery, as a feasible DIY project. And even at the end of that time, my cells often
don't have 10% of the amp hours they ought to have for the amount of active material they contain - counting
"ought to have" as 50% of the theoretical. (That's for any chemistry, not just ones I've created.) If I get a chance to
get back to the battery project, increasing the performance will be the main priority.
In the end, the prime cause of performance that doesn't match reasonable expectations must be active material
electronically poorly connected or unconnected to the terminal post, or (less common) active material the electrolyte
can't reach. Reasons for these may be many and varied.
Electrodes Overview
Everything else depends on the electrodes. Besides the chemistry, what's in an electrode? how is it made? W hat are
its properties?
First, all points inside an electrode must be electronically connected together, that is, connected for electron flow.
Ideally it is one total "short circuit" from every point to every other point. All the active material is electrically
connected straight to the battery terminal. In practice there may be resistance, even considerable resistance,
between points because many active materials are semiconductors, but there can't be any insulated points. Parts of
an electrode that become insulated from the rest cease to function; they are "passivated" like sulfated lead-acid
battery plates gradually become. The lower the resistance within the electrode, the more current can flow with less
voltage drop.
Again, electronic conduction refers to conduction of electrons, wet or dry, not ions. Conduction only by ion flow
when it's wet may read "connected" on an ohm meter, but it won't work.
Second, all active points of the electrode must be wetted by the electrolyte. The reactions only take place when
the electrolyte ions can interact with the active chemical. Again, any parts of an electrode where the electrolyte is
blocked are passivated and do nothing.
These two requirements, electron flow and electrolyte penetration, are in conflict for actual physical construction.
A good battery requires an immense active surface area in contact with the electrolyte. The surface area of a sheet
of metal is small, and all but the very surface atoms of the sheet are wasted, out of contact with the electrolyte. A
vast multiplication of minute particles to make a porous substance is required in order that the battery electrodes
need not span a gymnasium to supply much current or store much energy.
On the other hand, these many minute particles must all be in electrical contact with each other and they can't
physically fall apart. To achieve this, they must be "glued" and compacted from loose powder into something more
like a dense piece of sandstone or brick - a porous electrode "briquette". The briquette must be well compacted so
the particles electronically connect, and yet consist of open pores so they all also contact the electrolyte. And the
binder 'glue', if used, can't interfere or coat the particles with a waterproof layer.
Since connections are generally still poor though the maze of particles over much distance (and increasingly poor
with oxidation level), some sort of continuous metal or carbon conductor spans the entire area of the electrode, the
"current collector". The briquette is compacted around this for good contact throughout. None of the grains are more
than the electrode thickness away from this plate, mesh or conductive sponge that is connected straight to the
battery terminal.
Obviously there's an optimum compacting pressure to achieve the best compromise between electronic
conductivity and pores for ionic conductivity. Doubtless this varies with the ingredients in the electrode mix. An
electrode with fluffy nickel hydroxide and considerable graphite powder may have a different optimum pressure than
a dense zinc electrode with few additives.
The only figure I've seen for compacting pressure was in one research paper where the authors mentioned an
"optimum" pressure of 675 Kg/sq.cm - 9600 pounds per square inch - for an iron oxide electrode. For the chosen 1.5"
x 3" electrode size, that would be 21.5 tons. Perhaps this may be taken as a maximum pressure requirement. (On
the other hand, maybe a reason my cells don't perform better is insufficient compaction.) I describe some electrode
compactors and ways to get sufficient pressure in the appendices. (I hope to offer a good compactor press with a
"steering wheel" type tightening handle - but it can be done by tightening some bolts with a wrench, too.) Getting
the pressure is one of the chief keys to making batteries.
Current Collector Materials & Conductivity Enhancement Powders
The material chosen for the current collector and the terminal leed is important. More particularly, the surface of
the material, in contact with the electrolyte, is important. Likewise, with battery active chemicals usually being
poorly conductive, some sort of powder or powders are usually added to the mix to improve it. These materials
share the requirements of the collectors.
Positrode
In the salty battery with neutral pH, every metal I tried for a current collector in the positrode dissolved. After 3
years of frustration, I realized only conductive carbon based current collectors would work. W hat worked were carbon
rods from dry cells, but they weren't shaped for my flat electrodes. Graphite sheets seemed to swell and lose
contact with the electrode.
At one point, I created "grafpoxy", a 1 to 1 (by weight) mixture of epoxy resin and graphite powder. The resistance
was rather high, but workable. I tried various ways to make it work. A relatively fine metallic screen (around 30
mesh), with a terminal riveted or welded to it, was coated in grafpoxy for use as the current collector. The epoxy
protected the metal from contact with the electrolyte, and the graphite let the electrode substance electrically
contact with the mesh. The mix should have about as much graphite (by weight) as epoxy. This generally makes
rather thick for painting or dipping, so some solvent is added, eg, 10% toluene, to thin it. (The solvent evaporates.)
I found that two coats are needed, and it should be inspected in a good light. If any trace of copper color is visible,
the metal will dissolve away until the cell quits working.
Then I found cheap, thin graphite sheets with low electrical resistance. They come in rolls, sold as gasket
material. Instead of trying to connect them to metal within the cell, I cut them with a long "finger" tab to stick out
a slit in the top of the cell. This is bolted to a matching exterior plastic tab to support the flimsy graphite, and the
bolt is the terminal. The slit is sealed with heat glue.
Other expedients such as a brushed on dopant layer of osmium in acetaldehyde, and a dousing with toluene
(methyl benzene) or "Diesel Kleen" (contains trimethyl benzene) improved surface conductivity to better connect the
electrode briquette. The methyl benzenes dissolve graphite, and when they evaporate, it can solidify into more
conductive forms such as nanotubes and lamilae. This is especially helpful for the conductivity enhancing graphite
powder: Electrodes read 30-40% lower resistance after being doused than before. The liquid can also be added
instead of water when the electrode is mixed and compacted.
Another improvement, since there's no "graphite mesh" current collector, is to punch the plate (except for the
finger) full of holes, to give more surface area and grip between the active briquette and the current collector. A
device called a "pin frog" or "flower frog" is available at florist shops. The many parallel pins that stick straight out
of the thick metal base (for sticking flower stems into) can be pressed into the graphite to make many holes at
once. Anything that helps make good and durable contact with the electrode briquette should improve performance.
Negatrode
In a high voltage negatrode like
manganese, a material with sufficient
hydrogen overvoltage must be chosen.
(Hydrogen voltage is -.833 volts in pH 14
alkali.) I tried many manganese and zinc
electrodes with copper or nickel plated mesh
that would self discharge and bubble
hydrogen. I could understand this for the
experimental manganese, but zinc was a
known, working electrode chemical. It was
ages before I finally realized it was the
current collector doing the bubbling, and not
the active chemical substance itself.
Zinc metal itself, or silver, evidently works
well. Recent research in Iran showed that a tin-zinc mixture also corrodes. But this research showed that an alloy of
copper, tin and zinc, "optalloy" evidently "acts as a noble metal" with a high overvoltage and works well.
I thought that the simplest thing to do would be to use a long, thin zinc plated or galvanized nail or bolt in the
square cylinder pocket electrode. However, these proved to cause a fair bit of self discharge. (which was probably
the plating corroding through in the initial charging, as I think about it.)
In normal use, the zinc remains in metallic form because the reaction voltage of manganese is higher. Opposite to
most usage of zinc, the manganese forms a "sacrificial anode" (if it may be so termed) which protects the zinc.
Then, I got "zincate solution" for 'priming' aluminum, and zinc coated an aluminum rod (after shining it up with a
nylon scouring pad). This seemed to work... at least on a second try after the electrode was initially charged. The
solution can be found at Caswell Plating [.com], or can probably be mixed from sodium hydroxide (caution: very
caustic! especially protect your eyes!) and zinc oxide. I found a very simple way to electroplate zinc onto metal in
an on-line instructional "How to Electroplate a Penny", which I copied into an issue of Turquoise Energy News.
A problem with the plating is that the initial reactions with manganese oxides used in the briquette, which are
"overdischarged" for a negatrode, will oxidize the plating. A freshly plated piece works the second time, after
initially charging the electrode, where the first plated piece on the uncharged electrode has failed and cause self
discharge.
Up to this point, I had been unable to find pure zinc except in fat lumps, rods and bars. Then I found that thin
zinc sheet metal is available in rolls at roofing or building supply stores! And it's cheap. It's placed on roofs to kill
moss. The solid zinc metal is a much better choice than plated material and it can withstand the initial oxidation
problem. I shaped these like the graphite with a long "finger" tab to poke up through a slit in the top cover of the
cell. Holes can be punched in the thin zinc sheets with the same pin frog as the graphite to improve conductivity.
Fine zinc powder and flakes can be used to improve the conductivity of the manganese briquette.
I note that even solid zinc seems to need protection where it's in contact with electrolyte but away from the
manganese: especially near the bottom of the finger. I had one finger/tab corrode right off in a month. If graphite
doesn't bubble hydrogen, it might be a better choice for the current collector. Zinc powder is probably still a better
conductivity additive. Then again...
Electrode Constructions - maintaining compaction
After the compacting there's the wetted electrode in the cell, before and after charging. Electrodes want to swell
when wetted (especially nickel hydroxide), and if they are able to do so, they lose their conductivity and become
pretty much useless. This was a major problem through most of my battery research. There has to be virtually no
space they can expand into.
There are at least 3 types of electrode construction: Pocket, Sintered Plate, and Paste Electrodes. All of them use
powders of the active material, usually with additives mixed in.
Pocket electrodes consisting of thin perforated metal enclosures, "pockets", to hold the electrode briquettes, were
invented in the 1890s. These work great and are highly conductive but with metal pouches holding the electrode
materials they're expensive to manufacture and heavier, with low energy densities by weight.
Nevertheless nickel-iron alkaline pocket batteries were much better than lead-acid and Edison's best version was
in common use in early electric cars by 1910 or so.
The pockets had to be nickel plated (at least in the positive electrode) to avoid dissolving away even in caustic
alkali solution. Since all common metals including nickel dissolve in salty electrolyte (anything lower than pH 14),
metal pocket cells are out for Ni-Mn designs.
However, perforated rigid plastic pocket electrodes may be a good choice for homemade DIY batteries, especially
if one can coax a 3D printer into producing ABS pieces with very, very small holes. The extra weight of the electrode
and battery case structures is compensated and more by better, higher energy chemistries.
I tried making some of these. A 3D printer owned by Camosun College made some very fine-holed "porous" plastic
pieces, but mine were too coarse and allowed material leakage.
As another possible process, something like epoxy or thermoplastic (ABS?) could have a fine powder added to it
that would dissolve. It would be formed into thin sheets or whole pockets, then the powder would be dissolved out
to render it finely porous.
Sintered electrodes were invented in the late 1920's as a better way, but their manufacture and use only spread
gradually. The carbonyl or a powder of the metal, usually nickel and cadmium for Ni-Cd's, would be sintered (heated
until it softens and flows a bit, and the particles just barely melt together where they touch) into a porous "metal
sponge" structure full of minute open cavities -- 80 - 95 % empty space. The electrode active particles would be
impregnated into these spaces, then the whole thing compacted. As the conductive metal permeates every little
recess of the entire electrode, these are highly conductive and have great current capacity from small cells, eg ~20
amps from ~"AA" sizes. The sintered metal also holds the compaction without an external shell. Energy density is
reduced by the heavy inert sintered "sponge", which would make up a considerably greater percentage of the
electrode volume after compaction than prior. The Ni-Cd sintered "AA" size cell might have up to around one amphour capacity. Again the sintered metals would dissolve in salty electrolyte, making this type impractical - unless
perhaps a porous sponge of 'grafpoxy' material could be created. I have little confidence in this idea.
In alkaline paste electrodes, the powders are simply compacted around a nickel or nickel plated metal mesh or
perforated foil "collector plate", with a binder "glue" in the mix. The compacted briquette is the finished electrode,
with a nickel leed welded to an edge of the foil or mesh. Since there's not much there besides the active chemical
and its additives, the highest energy density by weight is attained. The metal case of the dry cell prevents
decompaction of the electrodes, which virtually fill the entire space within the cell. Generally the current capacity is
lower per square centimeter of electrode than sintered types. The amazing 2.6 AH Ni-MH size "AA" (100 W H/Kg) will
only put out about 7 amps. (There are 2.0 AH "high rate" NiMH's that are good for 20 amps. Perhaps these are the
sintered type.) Powder/paste is also the newest type, the easiest to make, and the most fragile electrodes to
handle for insertion. Zinc electrodes are especially crumbly. But electrodes harden up in use inside the cell as
pathways establish themselves.
Common binders for the nickel oxide positrode briquette include CMC (AKA CMC gum, AKA sodium[?] carboxy
methyl cellulose).
For the negative, PVA (poly vinyl alcohol) PTFE (AKA teflon, AKA poly tetra fluoro ethene, AKA poly tetra fluoro
ethylene, AKA (C 2F 2)n) suspension, with a fairly coarse particle size, have been used. But as often, nothing is used.
I've variously tried in different mixes with different techniques, sometimes for different reasons: Sunlight
dishsoap, fried beans (to the point of them catching fire and burning for up to 60 seconds), acetaldehyde, VeeGum
(a bentonite clay mixture), and agar agar gel.
After many experiments, I read that CMC should be "under 1%" of the electrode substance. PVA of up to 2% has
been used in zinc electrodes. These figures mean I was using substantially too much of whatever I tried.
I hear that PTFE is the best for "ordinary chemistry" alkaline electrodes, but it seems hardest to get. Also because
a substance works well in alkaline cells doesn't mean it'll necessarily work well in salty cells, as is illustrated by
nickel platings of electrode structures.
I consider that the organic sulfates and sulfonates in "Lemon Fresh Sunlight" dishsoap act to chelate the
substances into place and stop them from moving around, extending indefinitely the life of the electrode.
An important consideration is how thick to make the electrodes. There are two considerations limiting the
thickness of flat plate electrodes: electronic conductivity and ion conductivity.
Naturally, with an electrode that has semiconductor active material connected to a collector sheet or grill, the
thicker it is, the more the internal resistance from the surface layer to the collector.
And, the thicker an electrode is, the farther removed its back recesses are from the other electrode and the
farther the ions have to travel. Thus thinner electrodes may be expected to effectively have lower resistance and
higher current capacity even for highly conductive electrodes. Voltage with thicker ones will drop off more at high
currents when their charge is lower, as the remaining charged material at rear must come into play.
I estimate that for flat plate electrodes with good conductivity in KCl, reasonable thicknesses are around 3mm for
high rate, 6mm for medium rate, and 9mm for low rate batteries. For electric transport, they should probably be
under 6mm unless there are quite a lot of batteries sharing the load. These are all considered very thick electrodes
in most batteries. Typical alkaline cell electrodes may be around 1mm. Lithiums generally have thin films.
For square cylinder pocket electrodes, a .5" square will have substantially higher resistance than the .375" (3/8")
square, but both types will be substantially higher resistance than a thinner flat plate. A larger diameter of central
current collector wire will reduce the distance to the particles and lower the resistance, but unless it's hollow, it'll
add weight without adding storage capacity.
If the internal resistance can be lowered, and-or if the electrolyte can penetrate better, larger diameter cylinders
will perform better.
The manganese standard dry cell "+" electrode occupies almost the whole diameter of the cell - the construction
does work, but is generally for low current rates. Pulling an amp from a D cell is taxing it.
Of course, the taller the cylinder pocket is, the more electrode cylinders there are in the cell, and the more cells
that are in parallel, the lower the overall resistance will be and the higher the current that can be driven, but they
will still charge and discharge at about the same rate.
Another aspect to this problem is the speed of ion diffusion through the electrolyte. If an electrolyte diffuses ions
twice as quickly, the electrodes may be considerably thicker and still have the same current capacity. Potassium
chloride is, I believe, about the fastest electrolyte. Potassium compounds (KCl, KOH) are known to be faster than
their sodium equivalents (NaCl, NaOH).
Battery Layouts
One common type of battery construction is wrapped, spiral electrodes, common in "AAA" to "D" NiMH dry cells. A
"V" of separator paper encloses one electrode.
Another common type is "prismatic", where alternate positive and negative flat plates, separated by sheets, are
connected together in parallel to each terminal. This is usually used in flooded cells such as lead-acid.
These constructions have the advantage of providing the maximum interface area between electrodes, each plate
being adjacent on both sides through separators to an opposite electrode, except of course for the two end plates,
or the outside of the spiral.
An older construction is "pocket electrodes", wherein a minutely perforated, nickel plated shell of thin metal holds
the electrode chemicals compacted. (Nickel is the only metal that doesn't corrode away in the positrode in KOH or
NaOH alkaline electrolyte.) Typically there's a wall every 1 to 2 cm, dividing the pocket plates up into rows or
columns - they would bulge out if wider. These plates, just over a couple of millimeters thick, are then used in
"prismatic" form with spacers between the electrodes. The metal pockets are thin and perforated, but they do add
some weight to the battery. Nonetheless, the prototypical pocket electrode battery dating back to about 1902,
nickel-iron, substantially outperforms lead-acid and lasts far longer - some decades old NiFe batteries still work
today.
Chosen Battery Layout:
T he Checkerboard of Perforated Plastic Square Cylinder Pocket Electrodes
First battery with two 1/2"
square cylinder electrodes
At the start of February 2012 I suddenly
conceived of a completely new construction,
easier and more certain to succeed as DIY
construction: the Perforated Plastic Pocket
Electrode. This harkens back to the early
days of batteries - but they didn't have plastic
back then. A number of previous ideas came
together, and a couple of new ones were soon
developed, to make this work. A battery of
any size could be assembled from easy to
make, square cylinder plastic pocket
electrodes, layed out checkerboard style. Each
electrode was a separate unit, individually
compacted and held that way. Initially the
biggest problems were bursting of the
perforated cylinders and high internal
electrode resistance.
The first plastic cylinders were 1/2" square
inside. This made electrodes that were just
too fat, and the conductivity was very poor. So
this electrode size was changed to 1/4"
square, more in keeping with the
electrochemical requirements (see "Electrodes
Overview", next section), and it increased
conductivity an order of magnitude. The cost
was making four times as many electrodes. I
may try 5/16" and see how that works, but
they'll probably be pretty low rate cells. At that point, I decided a special jig to
help compact the powders into the small tubes was needed to speed things up.
Right jig: channel for folding the plastic around a 1/4" steel rod, after heating it in an oven (rod shown is 5/16")
Left jig: electrode stuffing jig. Powder is dropped/brushed into slot,
1/4" rod pushes it in, and then tamps it down (not too hard).
After the top is glued on, a zinced nail is driven in.
Right electrode is the original 1/2" size, replaced by four 1/4" size.
The sides of the first square tubes were made from .063" ABS sheet plastic. Next will be tougher .020" styrene
plastic to cut waste space, weight, and the distance between electrodes. They are perforated with a heavy-duty
sewing machine.
The perforated plastic is cut into sections about 25 x 65 mm. This is heated in a kitchen oven on an unwanted
cookie sheet or shallow baking pan to 350 degrees F, for about 3 minutes if the oven is preheated. (The longer it's
left in, the more it shrinks.) In 3 minutes, it should be pretty much limp and can be formed into any desired shape.
That shape is a four walled cylinder of 1/4" square inside dimensions, by 60mm tall, formed around a 1/4" square
steel rod with a jig. A bottom and a top end cap close the ends. The top cap has a hole for the connection wire. The
overlapped seam and the end caps are glued with methylene chloride, a solvent which dissolves the plastic, thus
making the plastic its own glue as it evaporates.
Filling the electrode is to be done with an "Electrode Stuffing Jig" having a slot for electrode powder mix to fall into
place for a 1/4" square steel plunger rod to stuff it into the cylinder and tamp it down. Once it's filled, the end caps
are glued on.
The straight connection wire runs right through the cylinder from top to bottom, and sticks out the top far enough
to poke through the top of the battery to solder to. At the roof of the battery, it's sealed with RTV cement, or epoxy.
For the negatrode, the connection wire is a galvanized box nail, pounded into the electrode after both caps are
glued on. The zinc coating on the nail has the required hydrogen overvoltage.
For the positrode, a nail is used to make a hole, then a grafpoxy (or "nimangapoxy"?) wire (too fragile for
pounding) is stuffed into the hole.
Like the carbon rod in the manganese center of a "carbon"-zinc dry cell, a single grafpoxy coated wire sticks out the
center of the top of the electrode for connection, for both polarity of electrodes, of any chemistry. The electrode
chemical mix is compacted by tamping it directly into the plastic shell with a hammer and a punch. (The punch has a
center hole to fit around the wire.) Once the bottom is glued on, there's nowhere the chemicals can expand except
by bulging the stiff plastic sides. (A bit of expansion ability is vital for most pocket electrodes, depending on the
chemistry, temperature, etc.)
Separator Sheets
Separator sheets up until the 1970s were pretty simple: any insulator to keep the
two electrodes from touching. Recently there have been developments of interest.
The first is the zircon (ZrSiO4) or zirconia (ZrO2, which becomes Zr(OH)4 when
wetted) ion shield. While allowing the passage of chlorine (Cl-) or hydroxyl ions (OH-)
in neutral to alkaline solution, a layer of zircon prevents migration of metallic cations.
Depending on how effective this shield really is, that can mean that not all reaction
products need to be solids.
The first potential use is to prevent migration of zincate ions, which should greatly
extend the life of NiZn batteries even if the shield is only partly effective.
The second potential use, if the shield proves fully effective, is to permit new chemistries where either
the charge of discharge product is partly or primarily a dissolved ion. A prime example might again be
zinc, which forms soluble zinc chloride on discharge in the standard salt electrolyte dry cell. If these can be
blocked from crossing the separator, the standard MnZn dry cell might become rechargeable.
Another possible use is according to the diagram - for a single use battery where some of the products
are dissolved ions.
A very good separator sheet is Arches 90# watercolor paper, tho various papers from coffee filters to
writing paper to cardboard might work. The Arches is uniformly thick and even.
To make an ion shield on this, it is simply necessary to buy zircon powder ("Ultrox" is a pottery trade
name for the purest type - use the purest), wet it, and paint it onto the paper with an artist's paintbrush.
Be sure the target electrode is fully wrapped so no electrolyte can get around the shield. Zirconium oxide
costs more and is less readily available.
For the perforated pocket electrodes, separator sheets are hard to place, and a space between the
electrodes can be enough. It does make it hard to try any of the fancy things!
Working Up
The battery isn't ready to use immediately on assembly and filling. First it should be left to soak for a
day or so - at least overnight. For a monel electrode, the color will change from purple water to bluegreen solid as the monel is oxidized by the permanganate and swells up to fill the available space.
4. Making the Case and Fittings
I had hoped to simply buy suitable cases of molded plastic, but I couldn't find any. Then I thought I'd look for
rectangular plastic tubing of a suitable size to cut to length and glue in bottom pieces, but I couldn't find any of
that, either.
It's frustrating because round ABS and PVC plumbing pipe and fittings are everywhere. These could be heated in
an oven (about 300ºF) to soften them, and bent into rectangular shape, but it's hard to control the dimensions
properly and consistently so everything fits without leaking.
The latest plan, using the encapsulated perforated plastic electrodes, reverts to the earliest: cut flat pieces of
ABS plastic, available in sheets from 1/16" to at least 3/8" (textured on one side - so what?), and cement them
together into cases with methylene chloride or other solvent. The difference between the first plan and the last is I
gave up trying to make sealed cells and have adopted vented ones that don't pressurize (at least, not much). That
way the plastic doesn't bulge until it leaks.
For the present time for DIY experiments, I'm preferring to put the tops on with screws (or even just friction fit)
rather than gluing them. This allows inspection and even replacement of electrodes.
Cell/Piece Sizes
W ith 1/2" square I.D. cylinder electrodes of 'wrapped' .030" PVC plastic, and leaving a bit of space for bulging
electrode sides, separator paper wrap, and bubbling electrolyte, the electrode 'footprint' in the case is about 11/16"
(17mm) square per electrode. This could probably be trimmed down a bit for best density, eg to 16 x 17, but it's
easier with a bit of slack. So far I'm going with 17mm. I found 3/4" (19mm) dimensions seemed to leave excessive
empty space, which when filled with water makes the cell needlessly heavier.
So the number of electrodes and their arrangement times 17mm for each one defines the inside cross section
dimensions. For example, for a 12 electrode cell arranged 3 by 4, it would be 51mm by 68mm (2.0625" by 2.75").
This is the dimensions of the base piece. The side wall lengths must be chosen to fit the base with corners
matching the wall material thicknesses.
For the base, I recommend 1/4" thick ABS, or perhaps 3/16" for small cells. The walls must glue securely to the
edges of this and not leak. The end walls need to be thick enough to glue the side walls to the edges of. I've used
1/4" and 3/16" for end walls.
The side walls glue flat onto the base and the end walls. 1/8" thick should be good for most cells. For small cells
1/16" seems okay.
The top has two pieces. The inner piece is identical to the base piece. The outer one is cut to the outside
dimensions, accounting for the wall thicknesses. For the outer piece 1/16" is thick enough.
These two pieces are glued together. Then they are drilled 17mm (11/16") apart for each electrode terminal,
starting about 8.5mm (11/32") in from one corner and presumably ending up the same distance in from each corner,
measuring on the inside piece. W hen the battery is assembled, the holes can be filled around each electrode post
with "RTV" cement, and all the positrode posts are soldered together with wires, then all the negative ones. (Or
they can be left separate until individually tested.)
Another hole is made in the center, between four electrodes, for the filler/pressure release cap (which has yet to
be designed).
Since these are liquid filled cells, the inside height must accommodate the electrodes and "slosh room" above
them. This headroom should be bigger for larger cells, and bigger for vehicle batteries than is necessary for
stationary use. For 60mm tall electrode cylinders and small cells (my presently selected size standard), I suggest a
minimum of 70mm,10mm headroom. Since the 1/4" bottom and 3/16" top decrease the inside height by 10mm, the
minimum height of the walls is 80mm. 90 or taller is better for larger cells.
I checked a two electrode, 3/4" x 1.5" cell having 3/16" base, end walls and inner lid, and 1/16" side walls and
outer lid, and it weighed 41 grams. If the electrode fillers are 20 grams each, the electrode posts and perforated
plastic pockets 10, and the water 20, the necessary supporting materials dilute the energy density of the chemicals
by 3 to 1 (not considering conductivity additives within the electrodes). Finding numbers like "393 watt-hours per
kilogram" for the chemicals is more exciting without considering making an actual battery with them, which will
probably be down to 100 for our DIY flooded cells.
Still, various trimmings each have their effect. W hen I cut the case size down to 17 x 34mm internally, it weighed
34 grams, a 17% reduction, and the 'extra' water in it would probably be cut by 2/3.
Of course, for a specific voltage battery such as 6 or 12 volts, 3 or 6 cells may be made on a common base and or
with some common walls, saving a little plastic and weight.
OLD WAY (Before pocket electrodes)
I finally decided that the best flat material to make a rectangular case from seems to be acrylic plastic
("plexiglass") or lexan. I prefer to use clear stuff so the quality of the seam joins can be inspected, as well as the
battery inside. The edges can be 1/2" or 5/8" thick acrylic/lexan turned sideways, so the battery is exactly 1/2" or
5/8" thick inside with no gaps around the edges and no need to sand everything flush. The edge pieces can be cut
about 3/8" wide.
Electrodes are fragile and keeping even 1.5" x 3" ones intact until they're in the cell can be challenging. But a
4mm thick electrode this size has as much active material as one 3" x 8" that's only .75mm thick, as is typical of
alkaline. By the time some paper is wrapped around one and maybe things are a little off dimensionally, the case
needs to be preferably about 3.2" x 1.8" on the inside so they go in readily.
Prototype battery case of acrylic plastic,
with prototype grafpoxy coated electrode collector screens.
I tried ABS before acrylic, but in sealed cells I found it kept leaking at the seams - it seems a little too
flexible, so it deforms a bit under pressure, putting high stress on the seam bonds. It would probably work
well for vented cases, but at the moment I'm using the clear acrylic for one-off cases. ABS faces with
acrylic edges might also work.
Face Pieces: 1/8" or 3/16" acrylic or lexan plastic (plexiglass), or 3/16" or 1/4" ABS, cut size: 4" x 2-3/8".
Left and Right Edge Pieces: 1/2" acrylic, cut size: 3/8" x 2".
Bottom piece: 1/2" acrylic, cut size 3/8" x 4".
Top Piece: Here for my prototypes I prefer to cut a custom piece of plexi with some sort of lip at both
ends.
For gluing plastic cell wall pieces together from sheets of plastic, it's about 4" x 2.4" x .8". Cut the main
faces 4" x 2.4" or 100mm x 60mm. Using 1/2"/12mm thick plastic for the edges, cut them about .3" wide.
Turning them sideways, the 1/2" uniform thickness goes between the wide sides as the internal width, and
your cuts won't have to be perfect or sanded down to exact uniform thickness, except the bottom ends of
the two side pieces should contact the edge of the bottom piece well. The chief place to watch for leaks is
the bottom corners.
I would LOVE to have injection molded cases and lids, and I hope I can make the molds some day, or
perhaps two or three of them of different thicknesses. (January 11th 2012 note: I've just acquired a milling
machine and ordered a kit to make it into a CNC milling machine - the vital tool for making injection
molds.)
Molded ABS (or other plastic) boxes would eliminate the seams except around the lid. A molded ABS lid
with a lip made to fit over would solve that. They'd be my ideal for production - sealed or vented - when
the visual inspection aspect loses its meaning.
A possible way to do seamless rectangular boxes without injection molds would be to make a simple
mold from a solid block of polyethylene, wrap polypropylene fabric ("landscaping fabric") around it, and
epoxy it. When it sets, add more layers if needed to get to the desired thickness. Spray the mold block
with wax to help release the finished box from around it. I would think making the block taller than
required and putting in a handle hole to pull on would be the way to go.
Grafpoxy Current Collector Grills and Terminal Leeds
The first thing needed is a compatible metal. Nickel is suitable but for some reason seems harder to get
than gold. Copper seems to work, but is very hard to tack-weld. Stainless steel mesh doesn't seem to
work.
The grafpoxy is a one to one mixture of epoxy resin and graphite. It's rather thick with West System
epoxy, so I'm going to try diluting it. Evidently acetone is a common solvent, also MEK, xylene... Let's
see... I have toluene. I guess I'll try that.
Electrode Current Collector Grills & Terminal Leeds
Current collectors first and foremost must not corrode away in the electrolyte during charging and
discharging. Since every common metal corrodes away in salty electrolyte (very quickly in the positrode),
only conductive carbon substances such as graphite can be used. This is why the standard dry cell has a
conductive carbon rod for a terminal. But these rods are hard to make and brittle, and graphite isn't as
conductive as one might wish. Graphite sheets or even flakes tend to degrade in the cell during charging.
Fine graphite powder fares better, also as demonstrated by the standard dry cell.
In 2011 I invented 'grafpoxy', simply a 50-50 (by weight) mixture of epoxy resin and graphite powder.
The resin makes it impervious to the electrolyte, and the graphite makes it at least somewhat conductive.
This could possibly be used and molded by itself, but metal is still a much better conductor. So the
grafpoxy is used to coat a metal current collector and the parts of the terminal inside the cell.
The best current collectors are those that provide the best conductance to every bit of the electrode, yet
allow electrolyte to pass though so they can be in the middle of the thickness, and to which the electrode
substance will remain affixed. A fine grill, eg, 20 to 40 wires per inch, is ideal. Compatible metals include
(at least) copper, brass, nickel-brass (AKA "nickel-silver"), monel or other copper-nickel alloy, and nickel.
Pure copper is so conductive it's hard to tack weld. My ersatz tack welder won't make any sort of join to
copper.
Rivetted copper grills before grafpoxy coating,
and electrode compactor revised to work with book (or hydraulic) press.
Left electrode grill has one installed rivet,
one not yet spread with center punch and hammer,
and one empty 1/8" hole
I got some expanded copper mesh for
my prototypes at an art supply store, but
it's only about 10 x 15 'wires' per inch,
which is rather coarse, and I'm riveting it
to copper foil for the terminal leed. I'm
still looking for something better. Here I
scrunched up the mesh somewhat (and
then hammered it flat again) to get a few
more wires per unit area. The small
rivets, 'post and cap' (IIRC) rivets, are
available from leather supply stores (i.e.
Tandy Leatherword). I only use the posts,
spreading the thin end with a center
punch and then hammering it flat (see
foto - the fat 'head' end of all the rivets is
underneath).
With this third batch of electrodes, I went back to using a wire for the terminal instead of the foil, and I
made the slot in the compactor for wires only. The inner end is flattened and runs the length of the
electrode inside the foil.
If the electrolyte gets through the grafpoxy and inside the foil, it'll spread along the wire and it'll all
dissolve from the inside. I did two coats of grafpoxy, and touched up some spots with a third.
I used some toluene solvent to thin the grafpoxy. It seemed about right at first, but it gradually became
thicker as I worked, as the solvent evaporated.
I would very much like to automate production of the grills, as making and coating them is very tedious.
With nickel or perhaps brass alloys, one could at least tack-weld the wire and mesh together and skip the
foil and rivets.
5. Making Electrodes & the Positrode
Square Cylinder Pocket Making
Electrode Making Procedure (NEW)
The pocket electrodes make things simpler, but eliminate a couple of options. Yay for simpler!
1. Make or otherwise obtain a perforated square cylinder pocket with a bottom on it.
2. Mix the dry chemicals/substances per recipes below.
3. Add about 1-2% by weight of Lemon Fresh Sunlight dishsoap for glue/binder. (accept no substitutes - it's got the
right things in it.)
4. Add just enough water to make a dry, stiff paste.
5. Place the pocket in the slot in the plunging jig.
6. Spoon a little of the mix into the slot.
7. W ith the square rod, push the mix into the cylinder.
8. Repeatedly plunge the rod in hard to compact down the electrode mix. If it oozes out the perforations, it has too
much liquid. Leave it somewhere warm for a while and let some evaporate.
9. Repeat 6,7,8 until the pocket is full of well compacted mix, leaving a little room for the cap.
10. Dig a drill bit in to make a hole to the bottom.
11. Force the (slightly wedge shaped) post in. If it goes in too easily, it's probably not making good electrical
contact with the chemicals.
12. If the electrode contains graphite, pour a little toluene in the top and let it soak through the electrode, then
evaporate. (Toluene dissolves graphite, and as it evaporates, the graphite forms random lamilae/carbon nanotube
conductive paths through the electrode, improving the conductivity.) ABS plastic will soften when wetted and harden
up again when it evaporates. Acrylic plastic will crack. The PVC seems unaffected.
13. Put a top cap with a hole over the post, and push it down firmly into place and glue it, or plastic weld it (eg with
a soldering iron). Alternative: melt some hard wax on. In the positrode, this can be graphited wax, but not in the
negatrode.
Now it's ready for placing in a battery cell. Now you can look at the instructions below from before the pocket
electrodes and see what fun you're missing out on.
Electrode Making Procedure (OLD - Before Pocket Electrodes)
My general procedure for making an electrode briquette, positive or negative, is:
1. Make a grafpoxied mesh grid collector grill with a terminal leed sticking out one corner.
2. Put a 1.5 x 3" piece of thin polyethylene plastic sheet into the electrode compactor. Put in the current collector
grill on top of it. (Instructions are elsewhere in this book for making compactor boxes and the grills.)
3. Have all ingredients prepared and on hand, a sub-gram weigh scale, and lightweight plastic "dishes" for weighing
ingredients on the scale.
4. Measure and mix the dry ingredients. If necessary, grind them with a mortar and pestle to get a fine, uniform
powder. (I ordered a glass mortar and pestle through a local drug store. A pestle ("4 oz") one size smaller than the
mortar ("8 oz") was helpful.)
5. Add the liquid ingredients and mix thoroughly. The mix should seem barely damp. If there is too much liquid, it
will simply ooze out the cracks instead of compacting. You should be able to tamp it down in the mortar and check
electrical conductivity with an ohm meter. If it's above 100 ohms, you might want to let it dry a bit until you can
tamp it down harder, or if it seems dry enough, add more graphite. If it's too dry of 'diesel kleen', the graphite won't
process properly in the compactor.
6. Put about 1/2 of the mix into the compactor. Try to get it evenly spread around in the box. Put in the current
collector grill on top of it, putting the terminal leed through its slot in a corner of the box. (Instructions for making
the grills are .)
7. Put a 1.5" x 3" sheet of polyethylene plastic over top, then put the die in over that.
8. Put the lid on and do up the bolts (or clamp the box in a heavy book press or 20+ ton hydraulic press) to compact
the electrode into a "briquette". Leave it in with the top tightened for 1/2 an hour or more. During this time, the
graphite will dissolve in the diesel kleen (probably the methyl benzene is the active ingredient) and form lamillae random linear formations that connect the active elements randomly across the electrode for the best short circuit
conductivity throughout.
9. Remove the briquette from the compactor.
The next steps show what fun you miss by using perforated plastic pocket electrodes. Skip to step 13.
10. For positrodes only, paint calcium oxide on the surface. (Making calcium oxide from calcium carbonate is in the
appendix.)
11. Dry it in a toaster oven outdoors (not indoors - the diesel kleen reeks) for over an hour at about 100ºC/212ºF.
12. Play a propane torch over the surface for about 5 seconds to sinter and hence harden the surface layer. The
battery will last longer. If the electrode isn't wholly dry, it may suddenly pop apart from steam pressure - hence the
oven step above.
13. Drip some toluene onto the briquette. This will absorb in and dissolve a bit of graphite, which will (theoretically)
form into carbon nano-tubes as the toluene (or turpentine) evaporates, creating the best connections.
Naturally, you'll save considerable effort by making multiple identical electrodes at a time. (It wouldn't hurt to
have two, or even three, compactor boxes.) If some of this seems rather intricate and involved, it's because it is.
It's more than has traditionally been done to create electrodes, but they should (I hope) be the best they can be
and extremely long lasting.
On the other hand, measuring the resistance of the compacted substance will tell whether it needs more or less
graphite. If it's above mid tens of ohms without pushing too hard on the test probes, add more and try again. If it's
below 10 ohms, there's probably more than needed - unless maybe you're making a very high rate cell.
Instead of Diesel Kleen, an electrode can be wetted with water. Before putting the top cap on, pour in a bit of
toluene (methyl benzene). This will soak through. (and soften the ABS plastic bottom.) It evaporates relatively
quickly. At the moment I prefer this, but I'd like to check conductivities of a few electrodes made using water versus
Diesel Kleen during the compaction.
I caution that some of the steps are just my own ideas which aren't all verified as to their efficacy or even their
actual effect. And they were written before the idea of perforated plastic pocket electrodes. Some of them can't be
or don't need to be applied to them. It should be realized that I have created these things on my own on a very low
budget with very minimal equipment, concurrently with other inventive projects. In no case am I certain all the
ingredients are given in optimum proportions - many are just fair guesses. The amount of compaction is just
whatever the box can do - it's probably below optimum pressure in most cases. Sintering with a torch to toughen
the surface is a theoretical idea. The diesel kleen and toluene do appear to improve conductivity. But to verify fine
scale graphite lamillae surely needs at least a microscope, and to verify carbon nanotubes would require an electron
microscope. A calcium layer has also been used by others to help with toughness and oxygen overvoltage, but
whether oxide (lime) is the best form I can't verify. (It's likely to turn into calcium carbonate if left exposed to the
air too long. This must be what happens to bags of cement.) Torched barium carbonate (turns to oxide on heating)
might be better. Thiamin to chelate the rare earth and ions is experimental, as is the specific choice of antimony
sulfide, to raise hydrogen overvoltage.
Nickel Manganate Positrode
I presently think this is the best choice. It has high voltage and I believe should have very long life, and the high
amp hours of manganese.
I won't try to give a formula this time - instead a principle. Measure out 'X' amount of NiMnO4(?), then add some
graphite powder. Add 1 or 2% Sunlight dishsoap, a few % rare earth oxide or hydroxide, and a bit of water.
Mix it well then tamp it down. Measure the resistance. If it's well tamped down and the resistance is over tens of
ohms, add more graphite and try again. If it doesn't tamp down well, add more water or let some evaporate to get a
better consistency.
Manganese Positrode
A great powder mix for Mn positive electrodes is the positive electrode powder salvaged from throw-away dry
cells.
To this, add perhaps about 1-2% Sunlight dishsoap added to help permanently glue the powder together, and
enough Diesel Kleen to dampen it to a dry paste. The paste becomes more moist as it is compacted into the
electrode cylinder since liquid doesn't compress.
Add a few percent rare earth oxide or hydroxide to raise the oxygen/chlorine overvoltage (especially in warm
climates).
Come to think of it, with the graphite forming conductive nanotubes, it might be worth experimenting with lesser
amounts of graphite in the mix, eg by adding a percentage of pure MnO2 to it to dilute the graphite. The ohm meter
says whether more graphite powder is needed, or whether less can be used.
Since I've already written instructions for making some nickel hydroxide electrode types, I'll leave them in here.
But I no longer recommend them.
Nickel Positrode
The main dry ingredients, except for the graphite powder, each can take more than one form. See the list of
supply sources to find each form of each metallic element.
Nickel can be had as fine nickel powder, nickel oxide (NiO), nickel hydroxide (Ni(OH)2, nickel sulfate, or nickel
carbonate. The recommended form is NiO, followed by Ni(OH)2. The sulfate or carbonate have to be converted to
Ni(OH)2 in alkali. Unless you have a pre-existing stash, why bother? Ni(OH)2 can be converted to the charged form,
NiOOH with bleach, and back again with hydrogen peroxide. (see appendix)
In the salty battery it's not clear (to me) whether the nickel will take the typical alkaline forms above or: NiO,
Ni2O3 and NiO2 for valence states 2, 3 and 4. I suspect NiO is the discharged form, and NiO2 is most likely the
valence four form. For valence 3, toss a coin.
Remember these various oxide and hydroxide forms only affect the consumption and release of water during
charge and discharge. It's probably relevant in a 'dry' cell, but not really in a flooded cell.
The manganese is best added as potassium permanganate, which is likely what it'll become when the cell is
charged anyway. That way, it already has its potassium and there's no chlorine left over from charging with the
potassium form the potassium chloride electrolyte. But if that's too hard to obtain (owing to bizarre substance laws
or local supply) it can also be added as manganese dioxide. That will charge to KMnO4, but in the process use up
some of the KCl salt electrolyte, releasing a bit of chlorine gas. (doubtless undesirable in a sealed cell.)
Many of the rare earth oxides (REO) might work fine. I'd say the order of preference is: samarium, neodymium or
lanthanum. Cerium is one that should probably be avoided, owing to a possible charging reaction from valence 3 to
4 (Ce(OH)3 <-> CeO2). Mischmetal (unseparated blend of rare earth metals) oxides should be avoided because
they'd contain cerium.
Dry ingredients:
30g - NiO (or 37g Ni(OH)2)
20g - KMnO4 (= 9g MnO2)
22g - fine graphite powder
1g - Sm(OH)3 (or other rare earth oxide/hydroxide)
Liquid ingredients:
2.5g - Diesel Kleen
.5g - Lemon Fresh Sunlight dishsoap - no other dishsoap (or PVA or teflon powder)
Monel Positrode
The monel positrode is still somewhat experimental as to ingredients and proportions. It is essentially a nickel
positrode in which the nickel and manganese mix is replaced by nickel and copper oxides in solid solution. In order
to attain the solid solution state, the nickel and copper are purchased as fine monel alloy powder. A typical monel
alloy is about 2/3 nickel. The powder I obtained contains: Ni 67%, Cu 28%, Fe 3%, Mn 2%.
All of these metals will oxidize/hydroxidize when the battery is charged. The copper oxide in solid solution
improves the conductivity of the nickel oxide, hence less graphite is added. The manganese is at worst benign.
(Perhaps one should add more.) The iron is probably benign as well.
The only form to obtain the substance in is as metal alloy powder.
As with the other nickel electrode formulations, a rare earth oxide/hydroxide is added to increase the oxygen
overvoltage, in the same order of preference as to element. Some thiamin (bean sauce) is added to chelate the
ingredients and make the electrode very long lasting.
Dry ingredients:
40g - fine monel powder
10g - fine graphite powder
1g - Sm(OH)3 (or other rare earth oxide/hydroxide)
Liquid ingredients:
2.5g - Diesel Kleen
2g - tinned bean/bean sauce
.5g - Lemon Fresh Sunlight dishsoap - no other dishsoap (or PVA or teflon powder)
The torching step is extra important to "bake the beans" and set the thiamin.
Vanadium Positrode
This electrode is very speculative as to ingredients and proportions. The voltage appears to be somewhat higher
than for nickel.
Half reactions. (charged <==> discharged)
V2O5 + 2 H2O + 4e- <==> V2O3 + 4 OH- [~ +1 V]
The reason for adding nickel oxide is to complement the vanadium in the structure and (perhaps) to provide a
means to raise oxygen overvoltage. I'm not quite certain of the exact forms the nickel or its reactions will take.
Here are the chief possibilities as I see them:
NiOOH + H2O + e- <==> Ni(OH)2 + OH- [~ +1 V] (same as in alkaline cells but voltage is higher.)
NiOOH + e- <=====> NiO + OH[~ +1 V]
NiO2 + 2e<=====> NiO + 2 OH[+1.1 V ?]
It's less likely that NiO2 will be formed, and that instead the nickel will provide some oxygen overvoltage
protection, to the voltage level required to form it. At least, I suspect that's how it works.
Antimony has an almost unique ability to interact with small molecules like hydrogen and oxygen. The antimony
sulfide is added as a catalyst to recombine O2 and H2 gasses that get generated during charging (in spite of all
measures to stop or reduce them) especially towards the end of the charge, keeping gas pressure from bursting the
cell and allowing larger sealed cells. Adding this Sb2S3 to the electrode materials allows O2 & H2 to be recombined
wherever they happen to meet, easing requirements for gas transport to specific locales.
The main chemicals used in the positive electrode briquette are:
- 66wt% (% by weight) Vanadium pentoxide, V2O5 (Caution: very POISONOUS if ingested)
- 33wt% Nickel oxide or hydroxide, NiO or Ni(OH)2
- 1wt% Stibnite = antimony sulfide, Sb2S3 (also very POISONOUS)
Also in the mix:
- fine graphite powder - about 50wt% as much as the total of the above ingredients
- a small wad of chopped carbon fibers, immersed in Diesel Kleen (If it looks too hairy after compacting, use less.)
- Lemon Fresh Sunlight dishsoap
- enough Diesel Kleen to dampen. Not much - too much and the substance will ooze out of the compactor when
attempting to compact it, and it evaporates more slowly than water. Too little and the metallic looking surface with
high conductivity won't appear. (pictures later.)
The Sunlight solidifies during charging and discharging into a sort of binder ('glue') to hold the electrode together
and keep active ingredients from migrating. This should extend cycle life 'ad infinitum'.
The graphite powder and carbon (graphite) fibers are to improve the conductivity. The nickel and vanadium oxides
are are poorly conductive, and the battery would scarcely work without some means to improve it. The Diesel Kleen
disperses the graphite and helps it to form a connective network throughout the electrode and into the expanded
graphite backing sheet (current collector sheet) as the electrode is compacted from loose powder into a "briquette".
- Calcium Hydroxide ("slaked lime")
The vanadium is the active ingredient, with higher amp-hours by weight and volume than nickel oxyhydroxide.
The graphite powder improves conductivity.
Cobalt improves the conductivity of nickel hydroxide positrodes, in "solid solution" with it. I'm only guessing that it
will help with vanadium as well, and thinking it might fuse with it in some useful way. Perhaps it's just wishful
thinking...
The dishsoap ingredients 'freeze out' and form the 'glue' to hold the electrode together.
The calcium is supposed to raise the oxygen overvoltage to reduce self discharge and improve higher temperature
performance.
Chemically made Ni(OH)2 is of about 50% beta and 50% alpha forms. The alpha form is an electrical insulator or
poor conductor and there shouldn't be too much of it in the battery. There is a chemical means to convert it. First,
pour in bleach and leave it for a while. (10 minutes?) This oxidizes it, converting it chemically to nickel
oxyhydroxide. Pour that off and rinse it thoroughly. Then pour in some hydrogen peroxide and leave it a while. Tiny
bubbles come off it. This reduces it to nickel hydroxide again, but preferentially to the beta form. Again pour this
out and rinse thoroughly. The beta form is also substantially denser than the alpha, so more can be packed into the
battery.
I bought nickel hydroxide from Palm Inc (palminc.com). I had to get a 10 Kg bag, which cost about $400. The bag
says it came from OMG Harjavalta Oy in Finland, with an e-mail address of [email protected] . (It's probably
only about as hazardous as any fine, dusty stuff, but check the MSDS.)
The cobalt oxide (ceramics/pottery supplies store) is prepared as well (rats, and you thought you could just dump it
in!), by heating it to about 500ºF in the kitchen oven for an hour or two. This turns more of it from Co3O4
(structurally Co2O3:CoO) into the Co2O3 form. (gloves - I think cobalt is poisonous.) This is added in the amount
of about 1% to the Ni(OH)2, and then enough dishsoap (grocery) is added to make a paste. Use only the yellow
"Lemon Fresh Sunlight", not Ivory, etc. Use no more than necessary: the denser the powder the better. Ni(OH)2 has
a listed capacity of 289 mAH/g, and more grams of powder stuffed into the same space also conduct electrons
better.
This paste is plastered in as-is. Once it is in the battery (or in the jar if left there), the dishsoap hardens, "gluing"
the electrode together. Also, zinc, a desirable element for increasing the conductivity in nickel hydroxide electrodes,
leaches out from the nickel-brass cell wall sheet into the paste. This is in fact a main reason for using nickel-brass
instead of straight nickel plates.
According to some recent literature, it might also be beneficial to add some yttrium oxide to this mix to improve
performance at higher temperatures. At the moment, the experiment seems academic for Victoria BC's climate, and
too pricey, there being none at Victoria Clay Arts. (160 $/Kg from HEFA Rare Earths Sept 2008.) In a hot climate, or
if the batteries prove to heat up notably when in use, it might make a notable difference.
6. Making the Negatrode
Zinc Negatrode
The electrode briquette is prepared similarly to the positrode, see chapter 5, except for the actual ingredients in
the mix. Zinc electrodes are especially crumbly and fragile.
Dry ingredients:
50g - zinc oxide powder (theoretical maximum: 35 amp-hours)
5-10g - graphite powder
.5g - antimony sulfide (stibnite) or antimony oxide (stibia) (sulfide preferred)
Liquid ingredients:
1.5g - Diesel Kleen
1g - Lemon Fresh Sunlight dishsoap - no other dishsoap (or PVA or teflon powder)
Vary the diesel kleen as required to get the best amount of dampness. Add graphite if required to get lower
resistance readings on tamped-down mix or finished electrodes. Make electrode as per instructions in chapter 5.
After putting the electrode together, it is wrapped in zircon painted separator paper (next chapter). Then it's
immersed for several hours in a solution of calcium hydroxide (slaked lime). (Calcium carbonate can be purchased at
a pottery supply. Making lime from calcium carbonate in a kiln and dissolving it is detailed in an appendix.) Then the
Ca(OH)2 is rinsed or diluted out. The alkali removes passivating carbonate from the zinc oxide, purifying it.
Some Ca(OH)2 absorbs the carbonate from the zinc and becomes calcium carbonate, CaCO3 - limestone. If it
doesn't rinse out, this probably will, if anything, contribute a bit of strength to the fragile electrode.
Manganese Negatrode
This is (if it works) one of my major battery making coups. No one has been able to make a manganese negatrode
before, because its voltage is just a little over the hydrogen generation voltage. Thus, hydrogen bubbles up as it
charges, and continues to do so until the electrode has discharged itself to Mn(OH)2 or MnO.
Hydrogen generation voltage varies with electrode ingredients (as well as pH). Zinc is "improved" by ingredients
to raise the hydrogen generation voltage. Manganese is "enabled" only by ingredients that sufficiently raise the
hydrogen generation voltage to where it will charge effectively and stay charged without excessive self discharge.
If it works, manganese makes a better electrode all round: it doesn't form a soluble ion, it's higher voltage (-1.37
vs -1.05), probably more amp-hours per weight (being a lighter element: 56 versus 65.5), and it's stronger and
better consistency. It also doesn't appear, from what I can see, that it forms carbonate, so it shouldn't need the
alkali treatment - the compacted briquette is ready to use.
Dry ingredients:
50g - manganese oxide powder (theoretical maximum: 35 amp-hours)
10g - graphite Powder(?)
.5g - antimony sulfide (stibnite)
Liquid ingredients:
1.5g Diesel Kleen (this is used as an additive in diesel engines, but it has what's needed!)
1g Lemon Fresh Sunlight dishsoap - no other dishsoap (or PVA or teflon powder)
Vary the diesel kleen as required to get the best amount of dampness. Add graphite if required to get lower
resistance readings on tamped-down mix or finished electrodes. Make electrode as per instructions in chapter 5.
7. Electrode Separators
The electrode separator consist of three layers:
separator paper
Paste: zirconium oxide ("zirconia", 8 parts) and ferric oxide ("rust", 1 part) powders,
in "Sunlight".
separator paper
Sheets
Chemicals
Fabrication
8. Electrolyte and Cell Assembly
dd
9. Working it up
dd
10. Charging, "Forming" and Testing
Once everything is put together, the cell might not work very well at first. Here are my results with an early
manganese negatrode, placed in alkali with a commercial nickel electrode in a nickel-iron battery case, kept on
charge for several days. At first, it seemed it had too much self discharge to really be useful, and little capacity. (I
thought my 90:10 tin-silver solder coated current collector - stuck in later - must be bubbling hydrogen, and also
that it wasn't making a very good connection.) It seemed like _your_favorite_expletive_here_. But it gradually
improved. It needed a lot of patience. Then it started stay up above 1.8 volts longer and longer when the charge
was removed, drifting down more and more slowly. Most of the improvements were after charging overnight, and I've
skipped mentioning some cycles I tried too soon after the previous one. The figures for the first 6 cycles are from
memory (I didn't record them at the time) and are only reliable as far as showing a general trend. The cell voltage
could be seen gradually dropping, but occasionally it would jump up a bit and restart the drop from there, probably
as little new connections formed within the electrode. This became more frequent with each passing cycle, and
voltages stayed higher longer.
Discharge cycle. Held > 1.5 volts for ___ seconds/minutes, and 1.0 volts for ___ with 25Ω load, then after discharge
continued to .9 volts, recovered to ___ volts.
1. 60 s, ?, 1.4 v
2. 90 s, ?, 1.45 v
3. 2 m, 6m, 1.5 v
4. 5 m, 10 m, 1.6 v
5. 6 m, 12 m, 1.63 v (and only 1-1/2 hours after test 5.)
Electrodes are pretty soft when made, but they harden up with forming. They might not even need the plastic
enclosures, tho I suspect they'd gradually fall apart without them. Evidently it's common to replace the electrolyte
after the electrodes are formed, or even to form a bunch of electrodes in a bath before putting them into a battery
cell. This seems like especially good advice for DIY with chemicals that might not be completely clean by the time
they're in an electrode.
11. Appendices
"Acetal Polyester" Electrode Binder
Once the electrode powders are mixed, they need a binder, "glue" to help hold them together and also to prevent
migration of the "solid" chemicals during charge and discharge cycles.
Various binders have been used: PTFE (teflon) powder and CMC (sodium carboxy methyl cellulose gum) among
others. PTFE is the preferred choice.
But these are insulators. A conductive, or perhaps even a semiconductive, binder would not only help hold things
together, but improve the current handling capacity of the electrode.
A great advantage of the sintered type of electrode was that the sintered metal conductor ran through the whole
electrode. Thus we would find old Ni-Cd cells for portable power tools, in the "AA" size range, that would put out 25
amps. A modern high capacity Ni-MH "AA" cell may hold over twice the energy, but it won't put out 10 amps.
A conductive binder would be a great replacement for the sintered metal "sponge".
I decided to try polymerizing acetal ester hoping to gain this effect. This is the real "chemistry lab" part of making
the battery. It's a four step process:
1. Convert potassium dichromate (AKA potassium bichromate) into potassium chlorochromate (AKA "chromic acid")
with hydrochloric acid (AKA "muriatic acid").
2. Convert alcohol (AKA "ethanol", AKA "triple distilled vodka") into acetaldehyde (AKA "ethanal") with the
potassium chlorochromate.
3. Convert the acetaldehyde into acetal ester (monomer solvent) with hydrochloric acid.
4. Use the acetal ester as the liquid to mix the electrode powders together with.
5. Compact the electrode.
6. Cook the electrode at 110ºc (225ºf ) to polymerize the acetal ester into acetal polyester. Also freeze it. (One of
these must do it...)
(You were going to mix the electrode powders with some liquid and compact the electrode anyway, so it's only four
additional steps, not six.)
Making the Potassium Chlorochromate
It's hard to buy "ethanal" because it's evidently an explosion risk during shipping. To make the unavailable "ethanal"
(CH 3CHO) from available though pricey ethanol (CH3CH 2OH) without accidentally reducing it all the way to acetic
acid (vinegar, CH 3CHOOH) we need another unavailable chemical: KClCrO
3 (AKA KCrO 3Cl).
Web info for reducing alcohols to aldehydes invariably says to use pyridinium chlorochromate, but that's pricey and
also considered hazardous to ship, so it's even less available. (And don't bother to look up "pyridinium" in the
periodic table of the elements - it's not there.) But the important thing is the hexavalent chromium, so we skip the
imaginary pyridinium and use potassium chlorochromate. This is very poisonous and acidic, so be careful.
Nobody is likely to have potassium chlorochromate either, but this can be readily made. A ceramics supply store will
have potassium dichromate (or -bichromate, K 2Cr2O 7, also very poisonous and acidic), bright orange pottery glaze
crystals. Now, where do we get the chlorine, and how do we put it in? Turns out hydrochloric acid, HCl, has chlorine
and works well. Since the dichromate is losing some oxygen and stealing the chlorine from the acid, the obvious
byproduct with the hydrogen from the acid is HOH (AKA water), so according to my reckoning we're left with the
desired product and water. Of course, some acid will be left over... or potassium dichromate if there wasn't enough
HCl. (Actually, one could probably calculate the correct proportions. According to the hygrometer, my HCl from Rona
is about 33% strength, and the K2Cr2O7 is 100%. I should probably figure out what atomic weights of the active
ingredients per gram that gives.)
Pour a little HCl (RUBBER GLOVES, GOGGLES, do it in the sink; avert your nose!) into a jar and add K2Cr2O7
crystals. Heat it, stirring gently, in a shallow pot of hot water on the stove until the solids dissolve. This takes quite
hot water. If the crystals don't completely dissolve, that probably means the acid is used up and there'll be some
dichromate left over. Add more acid. At some point in the process, put the lid on. Then label it "KClCrO 3, POISON!"
and put it in a safe fridge where no one might think it's food. The KClCrO 3 will precipitate out and the acidy water
can be gently drained off and flushed down the sink. Label it, let it dry out, and put it in your secure chemical
cupboard.
Making the Acetaldehyde
The "aldehyde" is considered a hazardous substance to ship - better to make your own.
Put 20 parts (by volume) of Alberta "triple distilled" Vodka (40% pure ethanol dissolved in 60% water by any other
name) and 1 part potassium chlorochromate into a small jar and heat it in a shallow pot of hot water on a stove
burner, stirring constantly. Once it’s heated, screw the lid on - acetaldehyde boils at about room temperature.
(rubber gloves, goggles: KClCrO 3 is acidic and poisonous... and acetaldehyde is the hangover chemical.) Shake the
jar as it heats and continue until the KClCrO 3 dissolves. The end product should have a strong "fruity" smell (seeing
it's a major component in the smell of ripe fruit) and should be a clear liquid when everything settles. Label it
carefully and put it in a fridge to cool. (Preferably not a food fridge. Label it "Aldehyde, POISON!" and take whatever
precautions are necessary to ensure it’s clear that it isn’t food and to make it unavailable to young children. Again,
with the chrome stuff in there, it's poisonous.)
If you could just drink the vodka and somehow extract the acetaldehyde from your body before it gave you a
hangover, you wouldn’t need the nasty hexavalent chromium stuff. But the end product is unavailable. You feel
lousy, and the alcohol in vodka costs more by weight than lanthanum "rare earth" metal - a sobering thought!
Making the Acetal Ester
This is made from the acetaldehyde by simply adding hydrochloric acid to it (HCl - RUBBER GLOVES, EY E
PROTECTION). No heat is necessary. After it sits a while it should be a blue-greenish liquid, still with a fruity smell.
A. Materials and Chemicals Supply Sources (Not all materials listed are applicable to the Ni-Mn chemistry.
Obtaining Manganese: permanganate, dioxide, and metal powder.
Potassium permanganate is used in swimming pool and other water filters to eliminate iron rust staining.
For that reason, is may often be found at water treatment supply stores. [Victoria Water Treatment] Be
prepared to buy at least a 5 pound, 60$ plastic jug of it. It's more than you'll need unless you're opening a
battery factory, but most customers want 20 pounds or more. KMnO4 has also been used as a medical
poultice for certain skin conditions. It turns water purple and stains skin and other things brown. If you
can't obtain permanganate for positrodes, you can use the oxide. Oxide is the prefered initial form for a
manganese negatrode.
Battery quality "electrolytic manganese dioxide" or its (equally useful) discharged forms, Mn2O3 or
MnOOH, can be salvaged for free from "carbon zinc" dry cells (use non-alkaline - alkali is corrosive to skin,
and the zinc paste used can get mixed in), complete with graphite powder (the "carbon" of the name)
added to improve its conductivity. Snip a bit of the outer zinc can of a D, F or C cell with sidecutters or
something, or saw it with a hacksaw, and then take needlenose pliers, grab the flap, twist, and peel it
open like a sardine can.
For your own edification, check the resistance of the compacted powder with an ohm meter, and note its
density and consistency by scraping and breaking it. If your electrodes turn out as well compacted, you're
doing very well.
Remove extra stuff and bits from the manganese/graphite mix and dump the compacted powder from
some cells into a jar, and fill the jar with water. In a few hours or a day, drain the water and put in fresh
water. About 3 dilutions with plenty of water should pretty much eliminate the ammonium chloride
electrolyte and any dissolved zinc chloride.
Around 35% of the weight of the salvaged manganese/graphite mix is graphite; 65% is manganese. This
should be taken into consideration when measuring out ingredients. The graphite is less dense, and
actually accounts for about 55% of the volume of the mix.
Manganese dioxide can also be purchased from a pottery or ceramics supply store. I'm not sure of the
purity, but it has no graphite added, for use in the negative side.
For a negatrode charged form, manganese metal powder is available from www.micronmetals.com /
Atlantic Equipment Engineers.
This is not an exhaustive list. It's just where I got my stuff plus a few other sources I know of.
[applicable to Victoria BC]
Drug Stores, Natural Food Stores
Potassium Chloride Salt (KCl)
Ceramics Supply Store [Victoria Clay Arts; gets stuff from Seattle Pottery Supply] - good source of many powdered chemicals:
mostly oxides, carbonates, sulfates.
potassium dichromate (a.k.a. potassium bichromate) - small qty
nickel oxide, manganese oxide
Zirconium Silicate ("Ultrox" is the purest)
MicronMetals.com
Monel powder
Manganese powder
Pyrotechnics Suppliers
Antimony sulfide (stibnite, "chinese needles", Sb2S3)
Arts Supply Store [Opus Framing]
Arches Watercolour paper 90#, electrode separator paper
expanded copper grill (used for modelling)
Plastics Supply Store [Industrial Plastics & Paints]
16oz, 20oz plastic (PE) "Cosmetics Jars" as battery cases
ABS plastic sheets, 1/4 inch thickness to make battery case from
(Prefer white for "+" end, black for "-" end. Choice of Bk or Wh for middle parts.)
Methylene Chloride solvent to melt/glue the ABS
Methyl Ethyl Ketone (solvent): a small amount is used in the electrolyte.
(it also seems to glue ABS - I used some by accident,
so maybe you could skip the methylene chloride?)
Syringe
methylene chloride dispenser (has a very fine syringe-like metal tube. Careful not to get any plastic in it or it'll clog.)
Hardware Store [Baywest Rona, Capital Iron, Canadian Tire...]
Brass bolts, 5/16" x 1.5" hex or flat head for battery terminal posts.
Brass or stainless steel nuts and washers.
Hydrochloric Acid (a.k.a. "Muriatic" acid)
Hygrometer
HEFA Rare Earths (Richmond BC Canada)
Samarium Oxide
Lanthanum (2 Kg Ingots)
Zirconium Oxide (a.k.a. zirconia. powder, small qty or 1 Kg.)
(Or try "yttria stabilized zirconia" - might give better high temperature performance.)
B. Equipment & Supplies
Rubber Gloves (grocery etc)
Safety Goggles (hardware etc)
Syringe (Plastics Store - grind the sharp point off of it)
Hygrometer (Auto parts & supplies store)
Litmus Paper (Science/lab supplies store)
Paper Towels, cloths, dish towels (grocery)
Jars and Plastic Containers (grocery etc.)
Adhesive labels, marker pen
Sink, Stove, Fridge, Oven
sintering "furnace" (see instructions for making)
pressure cooker or autoclave (the La(OH)3 this is for making will be supplied premade)
C. Survey of Simple Battery Electrode Materials
This charts a few possible rechargeable battery electrode materials. It includes only basic chemicals without getting into more complex
organic chemistry such as the lanthanum perchlorate I've made that uses a couple of organic adjuncts for a positive electrode with better
energy density.
Why do I put the words "negative" and "positive" in quotes? While it may have seemed an arbitrary thing when someone decided that an
electron had a "negative" charge and a proton's was "positive", it's the electrons that move - especially in a battery - while protons essentially
stay put. The more electrons you have, the more "negative" your charge. A deficit of electrons is a "positive" charge. If it worked that way with
other things, it would be really simple to keep, for example, a positive bank balance: just spend more money to prevent accumulating a
negative balance and stay in the positive! Hence my objection in principle to this reversed terminology: it confuses proper comprehension of
elemental relationships.
Electron Receiving ("Positive") Electrode Materials
Nickel [Oxy]hydroxide
This is the "Ni" of Ni-Cd, Ni-Fe, Ni-MH, Ni-Zn, etc. The energy density isn't very good and it limits the energy density of the whole family of
rechargeable alkaline batteries, but there aren't many simple things known that work very well over a lot of cycles for a positive electrode and
this does.
Electron Emitting ("Negative") Electrode Materials
Nickel [Hydroxide]
Any metal hydroxide that conducts electrons, can be reduced to the metal in an alkaline environment, and with a potential of under about 2
volts, can be used as an electron emitting ("negative") electrode material, and the same stuff that oxidizes to oxyhydroxide will also reduce to
the metal.
Chemical
Voltage AH/Kg WH/Kg Density*
NiOOH <-> Ni(OH)2 +0.52
289
150
1.3 - 2.2
Ni(OH)2 <-> Ni
-0.72
578
Fe(OH)3 <-> Fe
-0.9
Cd(OH)2 <-> Cd
Metal <-> Metal-Hydride -0.83
Zn(OH)2 <-> Zn
-1.24
Ca(OH)2.Zn(OH)2 <-> ? -1.69
416
1.3 - 2.2
* The density of powders in pastes depends on several things, especially how hard the particles are crammed together. The higher the
density, the better they conduct electrons, so higher density is best unless it doesn't provide room for any expansion that may be necessary.
The most densely packed beta nickel hydroxide can cause trouble as some changes into alpha nickel hydroxide. This crystalline form is said
to occupy 44% more space than the beta form. Big Edison cells have no problem with it, but a tightly packed dry cell can burst and leak.
Any metal hydroxide that conducts electrons, can be reduced to the metal in an alkaline e
Incidental Chemical Processes
Making Potassium Permanganate:
High Temperature Method
It seems it requires a license, for some reason, from "Health Canada" to purchase potassium permanganate, KMnO4. I'm not sure why this
should be, as it doesn't look especially toxic according to MSDS sheets, and it's unrestricted in the USA. Instead we have to produce it
ourselves, using a hazardous chemical and process.
Required are:
1. Manganese Dioxide, MnO2
2. Potassium Hydroxide, KOH
3. An oven capable of 180-200ºc (360-390ºf).
I generally suggest a toaster oven plugged in outside if available,
though in this reaction no hazardous fumes are generated.
1. Mix a 50% w/w solution of KOH and water. (FACE SHIELD, RUBBER GLOVES, cover bare skin!) Mix it in or over a sink. Add the KOH
slowly to the water, a bit at a time, as dissolving it generates considerable heat. If you add it too quickly or all at once the container will
become too hot to hold. A plastic jar may melt and a glass one could perhaps crack.
2. The MnO2 powder should be in a ratio of two molar to one with the KOH (assuming pure MnO2.) (Figure out how much of each to use!)
Essentially, we want to combine all the KOH and the MnO2 we put together.
3. The mixture should become K3MnO4, potassium hypomanganate.
4. Heat it in the oven at around 200ºc until all the water boils off. This turns it into K2MnO4, potassium manganate.
Now we're done. The astute reader will note this still isn't potassium PERmanganate.
Fortunately, the final part of the process is electrolysis, and for us it happens automatically: When the K2MnO4 is mixed with the electrode
material, put in the battery and the battery is charged, the manganate, K2MnO4, will "automatically" become permanganate, KMnO4. (Hmm...
but what happens to the other "K"?)
The existing processes for manufacturing potassium permanganate (both so-called roasting processes and liquid-phase processes) are
significantly limited in their operability by problems of corrosion and wear of equipment, protracted residence time of materials being
processed (slow rate of conversion), limited versatility in the use of ores which vary in their richness in MnO.sub.2 and in the level and type of
impurities and, specifically in the case of liquid-phase processes, the need to operate with a large excess of potassium hydroxide (mole ratio
MnO.sub.2 /KOH equal to or less than 1/10).
In general, the process of conversion of the manganese ore to potassium permanganate consists of a series of stages, comprising:
The preparation of the ore (drying and grinding).
Mixing with potassium hydroxide (KOH) in precise proportions.
The attack and disintegration of the ore through the effect of the potassium hydroxide under suitable conditions of concentration and
temperature.
The oxidation of the disintegrated ore in an oxidizing atmosphere to the valency Mn6+, in the form of K2MnO4.
The dissolution in water of the potassium manganate (K.sub.2 MnO.sub.4) obtained and the separation of impurities originating from the ore.
The oxidation of manganate (Mn.sup.6+) to permanganate (Mn.sup.7+) via electrolysis.
The crystallization of the potassium permanganate obtained and the separation and drying of the crystals.
Making Potassium Permanganate:
Lower Temperature Electrolysis Method
1. Prepare an electrolytic tank. Use an anode plate of: pure nickel metal or stainless steel or iron or monel (eg); and an iron plate as a
cathode.
2. Mix manganese dioxide and KOH powders. (FACE SHIELD for KOH, RUBBER GLOVES, AVOID BREATHING DUSTS) Put it in the tank.
(figure out the quantities! Or do you just need "plenty" of KOH?)
3. Add HOH until the concentration OF KOH is about 15 to 25% by weight. (FACE SHIELD, RUBBER GLOVES, (figure out the quantities!)
4. Heat the tank/water to higher than 60° c, preferably about 80-90ºc. Eg, put it on a stove burner and simmer it very gently. Take all
precautions with the KOH, especially FACE SHIELD! Avoid splashes and popping bubbles!
5. Turn on the power (power adapter? battery charger?). The manganese dioxide is electrolytically oxidized in the slurry of KOH using a direct
current of 50 to 500 amps/m2 of anode and a current concentration of 3 to 30 amps/liter. The electrolytic conditions may be varied to suit.
6. [I presume] the KMnO4 precipitates out or rises to the surface. (A certain amount will stay dissolved.) This probably means any remaining
KOH is irrelevant (except insofar as it's still dangerously corrosive). Pour it down the drain and flush some water down after it to dilute it.
"It is astonishing and unexpected that when the tetra-valent manganese oxide is electrolytically oxidized in a caustic alkali slurry having a
concentration of 10 to 25% by weight at a temperature of higher than 60° C, the manganese oxide is directly oxidized into the alkali
permanganate."
Tables
Energies of Common Negatrode Materials ( /Kg of metal element only)
Element
Voltage (in
alkali)
Amp-Hours /
Kg
Watt-Hours /
Kg
Cd
H (as in
MH)
0.82
0.83
477
500-1000
391
830 (max)
Fe
Zn
0.93
1.24
961
820
894
1017
Mn
1.56
976
1523
Notes:
Cd - toxic, grows crystals that short out the cells giving poor cycle life.
MH - metal hydrides store a lot of hydrogen at low pressure - the voltage is the same as for 'H' alone. The
batteries work very well with long to exceptional life.
Fe - grows into larger clumps, reducing surface area, hence it has less available energy density than the
figure indicates. Otherwise, the chemistry works very well with exceptional cycle life. Mixing with cadmium
reduces clumping.
Zn - grows crystal "tentacles" (dendrites) that short out the cells giving poor cycle life.
Mn - any long-term issues with manganese are undetermined so far, but it looks like it might well be as
close to "perfect" as it gets.
Some Overvoltage Potentials
The table below, while describing acid solution and a limited selection of materials, illustrates the differing
overvoltage ("overpotential") of different substances. So while the theoretical voltage of hydrogen (the
reference for all other electrochemical voltages) is 0.00 volts, it takes different voltages to actually
generate it depending on the material of the electrode. Although the alkaline voltages in which zinc with
mercury have been used aren't shown, one can see why mercury would be an additive to a zinc electrode,
which charges to -.79 volts (in acid), to raise the hydrogen overvoltage from -.77 volts to -.85 volts. The
zinc would discharge itself without such an additive.
Activation overpotential for the evolution of selected gases
on various electrode materials at 25 °C in acid solution. (from wikipedia; Hydrogen "table 2" from unknown source. The reason for the large
discrepancies between gold and lead is unknown. Neither table listed copper.)
Material of Hydrogen Oxygen Chlorine Hydrogen
the electrode
(Table 2)
Platinum,
Hydrogen will bubble off a negatrode current collector or electrode
−0.07 V +0.77 V +0.08 V
platinized
substance
when it reaches a certain potential. The difference in
Palladium
−0.07 V +0.93 V
potential
between
the material and a hydrogen electrode at
Gold
−0.09 V +1.02 V
-0.36
equilibrium
in
the
same
solution is defined as hydrogen overvoltage.
Iron
−0.15 V +0.75 V
This
overvoltage
decreases
with increasing temperature and surface
Platinum,
−0.16 V +0.95 V +0.10 V -0.12
shiny
roughness. The overvoltage needed for hydrogen evolution for some
Aluminum
-0.19
common metals is found in the table below.
Silver
−0.22 V +0.91 V
-0.29
In pH 14 alkaline solution, hydrogen evolves at -.833 volts if the
Iron
-0.27
hydrogen overvoltage is zero. Thus with zinc:
Nickel
−0.28 V +0.56 V
-0.24
-.833 + -.75 = 1.583 volts.
Silver
-0.33
By
itself, this is just high enough not to bubble H2 gas and discharge
Graphite,
-0.35
the -1.56 volts manganese electrode. Nothing else will work for the
artificial
Graphite
-0.62 V +0.95 V +0.12 V
current collector but zinc or an alloy containing zinc.
Lead
−0.71 V +0.81 V
-0.42
For graphite powder, on the other hand (and unfortunately for this
Tin
-0.49
one substance the two tables differ widely):
Cadmium
-0.50
-.833 + -.35 = 1.183 ... or ... -.833 + -.62 = 1.453 volts
Magnesium
-0.59
Neither of these figures is high enough not to cause self discharge of
Zinc
−0.77 V
-0.75
the -1.56 volt manganese.
Mercury
−0.85 V
But transition metal compounds will raise the hydrogen overvoltages, and the 1% antimony sulfide
increases the margin for the zinc, and indeed changes the margin for the manganese itself from a negative
to a positive margin. It doesn't, however, appear to raise the overvoltage quite enough to allow use of
graphite as a conductivity enhancer.
Oxygen and chlorine overvoltages work similarly. The overvoltage for the manganate or permanganate
positrode is likely to be near the oxygen limit, but I haven't found values for Mn yet. I know that nickel
hydroxide charges at near the limit, and doesn't hold charge well above about 40ºC without an
overvoltage raising additive. I also understand that rare earth oxides or hydroxides will raise the oxygen
overvoltage, eg, 5% samarium oxide should be quite effective. Ironically, sometimes a considerable
percentage of MnO2 is used for this purpose. Graphite has a high oxygen overvoltage, and so may easily
be used as a conductivity enhancer in the positrode. Indeed, it's about the only thing that won't corrode
away to oxide.
I haven't worried much about chlorine overvoltages, if only because I haven't noticed any problems
developing from that or smelled chlorine.
MISC NOTES
Diesel Kleen/Hexadecane
The bottle labelled "Diesel Kleen" contains not only hexadecane but unspecified "petroleum distillates"
(from MSDS... probably Ethylbenzene, Naphthalene, Xylene and 1,2,4-Trimethylbenzene) and "slick
diesel", in unspecified proportions. Whatever it exactly is, it seems to work great!
I believe it's forming random lamellae of graphite (graphine?) and electrode active substance(s), a
random conductive network.
Lemon Fresh Sunlight Dish Soap (other soaps are not good substitutes)
Contains: sodium dodecylbenzene sulfonate, sodium lauryl ether sulfate, sodium xylene sulfonate,
ethanol.
This seems to be good binder/glue/chelator for electrodes. Add 1-2% to the electrode mix. Its use is
suggested by the stability of sulfonates and the industrial use of methlysulfonic acid as an elecrode binder.
Osmium-acetaldehyde separator sheet doping
Osmium by itself is a very good metal hydride, able to store hydrogen ions (AKA protons) quite densely.
It is however far too costly to consider making into an electrode. But by lightly doping the thin cellophane
separator sheet with it, it divides the cell into two halves: a vanadium-metal hydride half and a metal
hydride-nickel half. The protons pass easily through the sepator sheet, increasing current capacity.
The acetaldehyde is the means of chelating, 'gluing', the osmium particles into place in the sheet.
To prevent the osmium from oxidizing, and the cellophane from disintegrating, the thin film osmium
doped cellophane is best placed between the negatrode and the paper separator sheet, contacting (if
anywhere) with the negative voltage rather than the positive.
3. The Negative Electrode (OLDE)
Chemicals
The chemicals in the negative electrode are:
monel powder (Ni:Cu ~60%:40%)
graphite powder
lanthanum hydroxide powder (Neodymium oxide/hydroxide is probably better, and Samarium
oxide/hydroxide is probably best.)
cobalt oxide
thiamin mononitrate (tinned bean sauce)
Sunlight yellow dishsoap
eggwhite
Monel is an alloy of nickel and copper. The fine monel powder should be purchased as such, though it can
be tediously ground from solid monel with a fine sanding belt or fine (#120 or finer) grinding wheel, the
dust being collected. It can be separated from the grinder grit with a supermagnet: monel is slightly
magnetic. The only supplier I've found to date is www.micronmetals.com .
I bought two 1Kg lanthanum ingots at HEFA Rare Earths (Richmond BC, www.baotou-rareearth.com). To
turn that into lanthanum hydroxide powder, I cut it into slices with an angle grinder cutting wheel and put
it in a pressure cooker of hot water on the stove. Occasionally I opened the pressure cooker and removed
and dried the white precipitate, adding water as necessary. It took weeks. An autoclave to get a hotter
temperature would speed the process. Slicing the ingots made some fiery arcing tails behind the grinder:
Lanthanum is what gives flint its spark, and its fiery oxidation gives a demonstration of the energy
potential hidden within!
I prefer to buy some chemicals from ceramics supply stores than from chemical companies as it's local and
the cost is much less. Cobalt carbonate ("cobalt blue" pottery glaze, powder) is available at ceramics
supply stores but not cobalt chloride. The carbonate may be converted to chloride simply by placing it in
hydrochloric acid. (Cobalt is poisonous, acid is acid: rubber gloves, goggles, at a sink!) Hydrochloric acid is
available at hardware or building supply stores under the confusing code name "muriatic acid". It fizzes
until the carbonate (or the acid) is used up. Refrigerate and pour the acid off the from the precipitated
cobalt chloride. Rinse the sink - acid is hard on stainless steel. Use jars with plastic lids. LABEL
EVERYTHING. If you don't you will soon start running across things that you can't remember what they
are, or which jar is which.
After it's "dry", it's a hydrated crimson powder, CoCl2:6H2O. Get rid of the latter (or at least four of them)
by heating the powder in an oven above about 70ºC for an hour or two. It will then be a blue powder. Put
a lid on it or it will soon reabsorb 4 H2O's back out of the air.
Sintering Procedure
The monel and lanthanum hydroxide are mixed in a ratio of about 3 to 1 by volume. About 1% cobalt
chloride is added. To the powder is added enough "glue", tinned beans in their sauce, to make it all into a
paste. This is rolled (rolling pin - grocery store etc.) into thin (1-2mm) sheets on thin pieces of aluminum
sheet (eg, pieces of roofing flashing - building supplies store) and dried.
The sheets are then placed in an oven and heated until the bean sauce catches fire and burns off. Do it
outside - the smoke is thick and unpleasant. The whole procedure should take less than about 90 seconds.
Sometimes you don't see the blue flame, more often you do. Longer than a couple of minutes will oxidize
the chemicals too much. When it cools, the crusty powder is scraped into a container. Dumping in powders
with an 80cc scoop, I find I usually have around 8 sheets to burn in a "session".
The "oven" I use uses a 1500 watt electric barbecue (Value Village - doubtless available new somewhere,
though I confess I've never seen another one) built up with pottery kiln bricks (Victoria Clay Arts) sliced
into shapes with an abrasive cutting wheel on the radial arm saw (hardware store - kiln bricks cut like
butter) to form a floor under the burner, walls, and removable roof pieces. Leave some air gaps for
ventilation.
Fabrication
The powder is mixed with just enough "Lemon Fresh Sunlight" dishsoap (grocery) to make a paste.
Acetaldehyde (a.k.a. ethanal, ethyl aldehyde, aldehyde, "the hangover chemical", ALcohol
DEHYDrogenated) is poured in. Add a little HCl (Eye Protection, Rubber Gloves) and churn vigorously to
turn the aldehyde into acetal ester. This is then dished into the battery.
Making the Acetaldehyde
Putting the electrode together is easy enough, but where do you get this "aldehyde" stuff? Turns out it's
not very stable, so it doesn't keep very well and it's considered a hazardous substance to ship. (What, just
because it can explode?!?) It's better to make your own. That doesn't mean it's especially easy or cheap
to do so. This is the real "chemistry lab" part of making the battery.
Put 20 parts (by volume) of Alberta "triple distilled" Vodka (40% pure ethanol dissolved in 60% water by
any other name) to 1 part potassium chlorochromate into a small jar and heat it in a shallow pot of water
on a stove burner, stirring constantly. Once it's heated, screw the lid on - acetaldehyde boils at about room
temperature. (rubber gloves, goggles: KClCrO3 is acidic and poisonous... and acetaldehyde is the
hangover chemical.) Shake the jar as it heats and continue until the KClCrO3 dissolves. The end product
should have a strong "fruity" smell. Label it carefully and put it in a fridge. (Preferably not a food fridge.
Take whatever precautions are necessary to ensure it's clear that it isn't food and to make it unavailable to
young children.)
If you could just drink the vodka and somehow extract the acetaldehyde from your body before it gave
you a hangover, you wouldn't need the nasty hexavalent chromium stuff. As it is, the end product is
unavailable. You feel lousy, and the alcohol in vodka costs more by weight than lanthanum "rare earth"
metal - a sobering thought!
Making the Potassium Chlorochromate
Now we've got the unavailable "ethanal" but to make it we needed in its place another unavailable
chemical, KClCrO3.
Web info says to use pyridinium chlorochromate, but that's pricey and also is considered hazardous to ship.
But don't bother to look up "pyridinium" in the periodic table of the elements. It's not there. The important
thing is the hexavalent chromium, so we skip the imaginary pyridinium and use potassium
chlorochromate.
Nobody has potassium chlorochromate. (AFAIK) So again we have to make it. The ceramics supply store
to the rescue! They have potassium dichromate (or -bichromate, K2Cr2O7, also very poisonous and
acidic), bright orange pottery glaze crystals. (I was told that the last person to buy some was a high school
student making rocket fuel a few years previously, proving that ceramics supplies are the right place to get
the cool chemicals. He was planning to hit the stratosphere with his next rocket.) Now, where do we get
the chlorine, and how do we put it in? Turns out hydrochloric acid, HCl, has chlorine and works well. Since
the dichromate is losing some oxygen and stealing the chlorine from the acid, the obvious byproduct with
the hydrogen from the acid is H2O, so according to my reckoning we're left with the desired product and
water. Of course, some acid will be left over... or potassium dichromate if there wasn't enough HCl.
(Actually, one could probably calculate the correct proportions. According to the hygrometer, the HCl from
Rona is about 33% strength, and the K2Cr2O7 is 100%. Figure out what atomic weights of the active
It's made just about the same way as the aldehyde: Pour a little HCl (RUBBER GLOVES, GOGGLES, do it in
the sink; avert your nose!) into a jar and add K2Cr2O7 crystals. Heat it, stirring gently, in a shallow pot of
water on the stove until the solids dissolve. This takes quite hot water. If the crystals don't completely
dissolve, that probably means the acid is used up and there'll be some dichromate left over. Add more
acid. At some point in the process, put the lid on. Then label it and put it in a safe fridge. The KClCrO3 will
precipitate out and the acidy water can be gently drained off and flushed down the sink. Label it, let it dry
out, and put it in your secure chemical cupboard.
Making the Acetal Ester
This is made from the acetaldehyde in the presence of the negative electrode mix, which include
lanthanum hydroxide. Pour some acetaldehyde into the mix. Then pour in a little HCl (RUBBER GLOVES,
EYE PROTECTION). Some lanthanum chloride is formed, and this substance is called "a mild lewis acid,
able to convert aldehydes to acetals in a neutral [non acidic] environment". Herein lies the unique
advantage of using lanthanum over other possible metals with similar valences.
Making Monel-Lanthanum Aspic
Okay, having thrown all these ingredients into the negative electrode, there's one more thing to do: gel it.
The positive electrode became a paste with the addition of the Sunlight, but that doesn't work for the
negative mixture. Agar agar [a.k.a. "agar"; natural foods stores] is a white powder or flakes made from
some kinds of red seaweed. It's used for a neutral microscope slide culture gel base... and for aspics and
jellies that are stable at and above room temperature. This second use is of interest. The battery won't
charge if the lanthanum hydroxide molecules are free to migrate. A cheesy gel holds them in place.
Take a dish. Put in ____ cc of the negative electrode mix with the acetal ester solvent in it, and add ____
grams of agar. Stir in ____ cc of water. (A lot of experimentation is due here to determine optimum
proportions.) Stir or whip vigorously for a few minutes to dissolve the agar. Heat a shallow pot of water to
about boiling on the stove in put the dish in it. Stir. Once it's hot, pour it into a flat tray about 6mm (1/4")
deep and put it in the chemical fridge. Let it cool and gel.
Cut it into squares that fit in the battery and use a spatula to put them in. One possibility, especially for
larger cell sizes, is to use trays the size of the electrodes, eg, 6" x 12", and put a cell wall sheet in the
bottom. Then the gel is already on the cell wall plate, which will be easy to remove intact from the tray.
Or, make the trays from the wall plates with ABS or other insulating edges, ready to pull out and stick into
the battery without removing the gel at all.

Making Economical, Green, High-Energy Nickel- Manganese (NiMn) Batteries Small Scale/DIY Battery Making

Transcription

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