Nickel-Iron Battery/Prototype

Prototypes

It looks as though using a high surface area electrode made from nickel or another conductive material which is acceptable from a chemistry standpoint, then causing the oxyhydroxide to deposit on it electrochemically could be done. But there are a great many ways to make the electrodes, and some may be more suitable. A great number of patents are available with what look like better options. See the research page for links.

All of them include some "plaque" or conductive matrix with fairly high surface area which extends throughout the active material. Nickel sponge, sintered nickel powder, and nickel fabric cloth like material, have been used.

A typical fibrous mesh for a battery that performs well at 0.2 C might use fibers 15 microns in width, usually not circular but their cross section might be 15 x 30 microns, which fill 20-10% of the volume of the electrode, which entails a void width of 60 microns ( (1000*(1-f)/((f*1000)/w) where f is the fill fraction, and w is the average width of the average fiber). Fibers as small as 2 microns have been used and they provide superior performance that might be good for a starting battery.

Other documents indicate that around 10-100 micron fibers with voids 100 to 200 microns apart in which the conductive material consumes 10 to 30 percent of the volume of the electrode is reasonable, so that's about the right range, the documents are talking about different contexts and from different eras so it's no surprise there is that variation.

A polymer binder loaded with graphite or other carbon particles which is then carbonized (not the same as pyrolized, entails changes in crystal structure and interconnection of the carbon mass which increases strength and conductivity) can be made, with the carbonized polymer being the conductive grid. Polymer binders (not carbonized) filled with conductive particles and hydrophobic plastic (e.g. teflon) spacer particles are often used in modern batteries. The mix is made, then pressed with great force onto a nickle or nickel plated grid or cloth. The polymer mix material can also be applied to a thin textured sheet of metal.

Fine flakes ("flitts") or fibers of nickel metal can be mixed with active material, pressed into a plate, and heated to melt or diffusion bond the flakes/fibers together, producing a conductive matrix surrounded and filled by a porous mass of oxyhydroxide.

Nickel wool or other low density fibrous masses of conductive material which are chemically acceptable might do as well. It is stated in patents that nickel plated steel wool works well. In this case the active material has to be applied in a paste or though more complex means like electrodeposition, in which the active material is precipitated by electrolysis in the electrode volume.

The so called pocket electrode is still used in modern batteries; conductive powder or fibers or flakes (graphite, nickel or nickel cobalt alloy flitts) a couple millimeters in size are mixed with the active material and pressed into "pockets" formed from perforated metal sheets. The pressing is needed to get good electrical contact between the particles and conductive material.

For the iron electrode high surface area solid iron electrode may be used with small amounts of something to activate it, such as sulfide ions like magnesium sulfide, iron sulfide or even elemental sulfur, to cause activation of the electrode (removal of the iron monoxide layer as the sulfur is more electronegative than the iron and for some reason suppresses hydrogen gas production). Other additives in the iron electrode might be possible and desirable but sulfur is the main one (see additives section) and accomplishes several things at once. For high purity powder like carbonyl iron the sulfide needs to be added. Otherwise it can be present in high enough amounts for some batteries as an impurity (see other reactions section). The appropriate surface area of both electrodes which will give a reasonably low internal resistance needs to be calculated or tested. References indicate it should be on the order of 10 sq meters per gram, which is about 26 micron average particle diameter (density of NiOOH is 4 so 40 square meters or 400,000 sq cm per cc, so pi*r^2*4/(4*pi*r^3/3)=1/(r/3)=400,000 so r=1/133,333 cm or 13.3 microns, so diameter is 26.6 microns. This same reference source, the battery handbook 3rd edition, says that 200 mesh (0.075 or 75 micron diameter) particles are used for pocket plate technology so there is some disconnect there.

Loose powder is not ever used, because the conductivity of the mass is too low. In the the case of the nickel electrode, they must be at least pressed together with the flits (pocket type) or surrounded with a fine conductive matrix and have quite small size area and then during the initial charge/discharge cycles they tend to bond together so the bulk conductivity of the mass increases to an acceptable level (pasted). Nickel hydroxide is even less conductive than the oxyhydroxide (how much?). This may help to explain why the electrodes are rarely loaded with the hydroxide initially, as the lower conductivity combined with the poor level of inter-particle contact before the particles are bonded together would make the initial charge/discharge cycles take that much longer but that's not a major problem for us.

In at least one of the Edison batteries he chose to use mercury to increase the conductivity between iron particles but that is not used in modern batteries and there are better ways to get the improved performance. It does not seem to have been done with the batteries that were eventually mass produced by the edison battery company either. Commercial batteries like the Changhong batteries intended for solar use are rated for 0.2 C but they make batteries capable of starting locomotives too. The C ratings are only guidelines however and can be exceeded greatly at cost of efficiency and effective battery capacity - 6 C produces a capacity of 65% rated capacity for the battery in the sealed battery testing doc. See related pages section for more about high rate batteries.

Over time the electrode shape could change in undesirable ways, reducing surface area and increasing the battery's internal resistance to an excessive value. It appears that this occurs to a relatively small degree in nickel iron batteries, and in fact this is mainly what gives them their much longer life compared with other batteries. Mostly it is limited by the very low solubility of the reactants and reaction products, they cannot travel far in the electrolyte before being redeposited (precipitating out of solution). In fact the nickel electrode reactions are thought to occur almost all in the solid state.

This is one of the reasons deep discharging of lead acid is a problem. Although there are many different types of lead acid battery there is usually alloy of antimony and lead used to form the electrode scaffold for one or both electrodes, which reacts more slowly than the lead that is supposed to cover it. But if discharged too deeply the scaffold will react too, and it cannot be reformed in the shape it was, rendering the battery damaged. Similarly during recharge some battery types form dendrites from one electrode to another - thin shafts of metal. As the finger of metal protrudes towards the opposing electrode the resistance between the tip of the finger and the opposing electrode gets lower, resulting in a higher current at the tip of the dendrite, causing metal to be preferentially deposited at the tip of it, lengthening it until it touches the opposite electrode, shorting the battery. Clearly over many charge/discharge cycles the cumulative effects that result from the relative effect size of these processes can cause substantial changes in electrode shape if they are not understood and accounted for, which is hard to do.

In the nickel iron battery the fact that this occurs very little allows the iron electrode metal scaffold (plaque, current collector) to be made of the reactant itself while still getting long life (sintered electrode). The surface can get converted to the reaction product and back again many times without changing the shape of the internal iron structure. Usually, if you did this with e.g. a zinc anode the zinc would get out of shape pretty fast due to dendrite growth etc. and become useless. A sintered block with 3 to 4 times the amount of iron than stoichiometric is typical, so 1/3 to 1/4 of the iron is used in each full charge/discharge.

In patents it appears to be universally assumed that for both nife electrodes, if they have a high surface area at manufacture they continue to have a high surface area thereafter so this may not be a problem.

Suggested contributions

We could use the documents below.

Then these can be legally shared by e.g. zippyshare.com with other developers who ask for a copy under the fair use doctrine. See the library section for what we already have.

We basically want all papers that mention nickel iron specifically and most of the others that relate to battery electrodes made from nickel oxyhydroxide(very frequently referred to as only "hydroxide" in the context of NiMH especially), and metallic iron and/or iron oxides. The electrode ones may not mention "nickel iron" per se because e.g. a good iron electrode can also be used in several other battery chemistries.

Most important:

6V, 60Ah nickel-iron battery. (http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=2274533EA) Periasamy, P | Ramesh Babu, B | Jegannathan, S | Muralidharan, S | Chakkravarthy, C | Vasu, K I Bulletin of Electrochemistry. Vol. 6, no. 2, pp. 263-265. 1990

Nickel--Iron Battery Development in CECRI. (Abstract Only) ,Periasamy, P | Babu, B R | Jegannathan, S Trans. SAEST. Vol. 24, no. 3, pp. 6.19. July-Sept. 1989

Alkaline Ni--Fe battery development is undertaken in CECRI under the sponsorship of the Defence Ministry (India). Dry powder sintering technique using the concerned metal powder is followed to fabricate porous Fe negatives and Ni positives. With carbonyl-nickel powder as the starting material, porous Ni positive plates (17.4 x 13.8 x 0.2 cm) were prepared by sintering in hydrogen atmosphere to get the Ni matrix of porosity 8-85%, followed by impregnation of nickel hydroxide into the pores of the Ni matrix. Porous Fe electrode was fabricated from electrolytic Fe powder by sintering in H atmosphere and activation of the sintered porous Fe plate (17.4 x 13.8 x 0.15 cm). A 6 V, 60 A/h Ni/Fe battery consisting of five individual cells in series is assembled with five positives and six negatives in each cell. The electrolyte is 30% KOH solution containing 50 g/l of LiOH. The separator is woven nylon fabric. The 6 V, 60 A/h Ni/Fe battery is charged at the 2 h (C/2) rate and discharged at different rates ranging from 1 h (C) to 5 h (C/5) rate to realise the A/h capacity in each case. In addition to carrying out life cycle test on the battery, self-discharge and effect of temperature on the output have been carried out. Special features of the Ni/Fe battery developed in CECRI are: high charging efficiency (80%), approx 50% capacity output at 0 deg C, high rate of charge and discharge and deep discharge up to 90-95%, without affecting the battery.--AA

Less important but still highly desirable:

• Westinghouse nickel-iron battery performance, 1981 Yeki
• Creator/Author Rosey, R.
• Publication Date 1981 Jan 01
• OSTI Identifier OSTI ID: 6394222; Legacy ID: DE83008901
• Report Number(s) CONF-811010-9
• DOE Contract Number W-31-109-ENG-38
• Other Number(s) Other: ON: DE83008901
• Resource Type Conference/Event
• Specific Type Technical Report
• Resource Relation 6. electric vehicle council symposium, Baltimore, MD, USA, 21 Oct 1981; Other Information: Portions are illegible in microfiche products
• Research Org Westinghouse Electric Corp., Pittsburgh, PA (USA). Advanced Energy Systems Div.
• Subject 33 ADVANCED PROPULSION SYSTEMS; 25 ENERGY STORAGE; ELECTRIC-POWERED VEHICLES; IRON-NICKEL BATTERIES; LIFE-CYCLE COST; PERFORMANCE; CAPACITY; DESIGN; ELECTRODES; ENERGY DENSITY; COST; ELECTRIC BATTERIES; ELECTROCHEMICAL CELLS; METAL-METAL OXIDE BATTERIES; VEHICLES
• Description/Abstract An advanced nickel-iron battery system is currently being developed by Westinghouse for energy storage applications which include on and off road electric vehicles, emergency standby power systems and deep water submersibles. The thrust of a present development program, sponsored by the Department of Energy under the Electric/Hybrid Vehicle Act, is to demonstrate battery system performance characteristics in an electric vehicle to achieve a 100 mile range on the SAE J227a D cycle. The 1981 nickel-iron battery performance objectives established by Westinghouse required to meet this range are: 54 wh/kg gravimetric energy density; 120 wh/l volumetric energy density; and 150 w/kg peak power density. Additional requirements are > 60% charge efficiency, selling price of $80/kWh, and 1000 cycles life to provide a system with acceptable operating life cycle cost. Demonstrated results for electrodes, cells, and batteries will be presented. These include charge/discharge voltage profiles, thermal effects on performance, power characteristics, cyclic stability, and vehicular mission profiles. The design and operating features of the battery system will also be reviewed.

There are some even less important ones on the research page.

See the Library section for a list of documents that we already have (these lists of what we need and what we have share no documents in common at this point on june 30 2011.)

factors affecting cost

1. Active material utilization fraction.

Not all of the active material actually gets used in the electrode. Obviously we want it to be high in the nickel electrode in particular because the cost of the material is high.

In the Edison cell the fraction of mass utilized can be calculated from the weights and composition of the electrodes Edison gives in the patents and this should be done. It can be increased with the addition of conductive carbon (like graphite) particles to the active material. Documents indicate that the homogeneity of the particle sizes is important in pocket cells to increase mass utilization, which should be no surprise as it would entail a smaller number of particles in between the gaps of large particles that are not compressed in any way against their neighbors, leading to high contact resistance and therefore low electrical coupling to the current collector.

For pasted electrodes it can be very high for both the iron and the nickel electrodes, patents indicate that it could be 80% without cobalt additive and almost 100% with it for the nickel. Smaller particle sizes and finer denser mesh helps too. Similar figures apply to the iron but since iron is cheap that will probably not be a deciding factor in the iron electrode design.

For sintered iron electrodes it is typically 1/3 or 1/4 of the total mass. The rest forms the conductive matrix of the current collector.

If the active material or a precursor that is later converted the the active material (like nickel oxide, probably NiO) is added before sintering the current collector that would need to be checked, but it would likely be high.

With electrodeposition and molten salt it should be very high.

For the nickel electrode the amount of conductive metallic material used (if metal is used, carbon works too) is typically 30% to 10 by volume of the electrode, so this will have a significant impact on cost if it is solid nickel. This may be a good reason to use a nickel plated steel of some sort or some other material as a current collector.

From patent number 00880978 Edison indicates that about 8 grams of the material the composition of which is described in number 839,371 is used per tube. The composition could be checked and the other patents searched (see research page for and archive of searchable pdfs of edison's patents) to find what the ampere hour capacity of each tube was, which I remember seeing but now forget, and then the efficiency of material utilization can be calculated. It is probably fairly low but can be improved by mixing in conductive particles of carbon and using a more uniform particle size. Mostly likely a pocket plate battery would be relatively expensive when made at a small scale, for these and other reasons.

The homogeneity of the materials is important apparently according to one of the journal articles and may be cheaper than additives.

2.Charge/discharge (round trip) efficiency (distinct from charge only efficiency).

This has a major impact on the cost of a solar power system that the batteries are included in. See [Impact of battery efficiency on cost]. To a rough approximation it can be represented as an addition to the $/Wh cost of the battery, and could add an additional $0.2 per Wh or more, which given that $0.2 per Wh is about the cost of lead acid AGM batteries (the normal type used in solar installations) that is a real problem.

However lead acid batteries are not that much better, actually, in real-world conditions. Nevertheless, the efficiency is one of the major considerations that should be optimized for. References indicate this can range from 50 to 65% depending on battery design, so it is not a given. Methods of enhancement so far identified include the addition of activators to the iron electrode like sulfur, selenium or tellurium compounds (which is best? Sulfur is the only one references seem to describe being used so experimentation or in depth knowledge of chemistry may be required here).

Forum posts and other information indicates that the efficiency actually rises over time to 80% or so after a few years of use, but this needs to be verified with other sources. Ideally the mechanisms could be identified and used to get this performance right off the bat.

This seems like one of the things an individual highly knowledgeable about chemistry could be particularly helpful with.

As the cost of the collector goes down over time this will become less important.

3. Cycle life. Although they get much longer cycle life than lead acid batteries, and it is to some degree inherent to the chemistry, it is not a given, and references indicate it can vary from 1500 to 3500 cycles, depending on the design of the battery, and up to 4000 with "good care" (issues which cause cycle life loss due to lack of good maintenance should be identified but this refers to non-sealed batteries so some of them might not apply to a sealed battery).

Cycle life unsurprisingly has a major impact on long term cost, so it should be maximized. It would be hard to test due to the time requirements, so this is a case where the higher quality references and perhaps in-depth knowledge of chemistry will be particularly needed.

Financial calculations should be done to determine how valuable very long lives are, although this is also important as part of OSE specs.

4. Calendar life.

Marketing material[www.nickel-iron-batteries.com] indicates that there are significant mechanisms that causes capacity loss independent of charge/discharge cycling. Some ideas on what it/they might be are included in the other reactions section.

In Edison cells one of the problems was the make-up electrolyte had impurities in it, and dust from the air would get into the battery and cover the electrode material particles. A sealed battery would of course avoid this, so there is another reason to do a sealed battery.

Problems with an unsealed cell

Ingress of stuff: Dust, carbon dioxide in the air which reacts with the electrolyte to form carbonate salts using up the electrolyte and possible being a problem chemically (need access to better references to know) Contaminants from the replacement electrolytes added, but from the solutes and that less than perfectly pure water is used. To some extent these will be expelled along with the electrolyte. May include some particulate matter.

Need to calculate how much of a problem these things would be without any sort of precautions, e.g. just a hole in the case.

Egress of stuff: Electrolyte solute, a mist is produced when bubbles break the surface of the water and this can result in loss of electrolyte solute as the water droplets that escape contain it.

Electrolyte solvent, due to the escape of mist and the conversion of the water to gas.

fortunately the active materials stay put, since they are hardly soluble in the electrolyte.

Prevention methods assuming lack of gas recombination ability: Gas permeable plastic film (polyethylene might do) allows only gasses to pass, keeping solute in and particulates out. Can be chosen to reduce the permeability of co2 relative to the other gasses.

Pressure regulated valve helps with ingress by only opening when the pressure inside the battery is higher than the atmosphere, thus preventing dust etc getting in by brownian motion as would occur with a simple hole in the battery case. Could also maybe be just a one way valve. In VRLA batteries they do not activate until a substantial pressure has built up because the hope is that most of the gasses will recombine in the electrode separator or if there is a catalytic recombiner, and the valve is more of a safety device. If there is no hope of recombination at all there may be little point in pressure regulated valve instead of just a one way valve. Maybe could be a liquid valve but then over the years the liquid might escape as mist etc. even if a nonvolatile liquid is used.

Design the vent hole to have a path that makes dust getting in harder, and as small as possible.

A porous material like the material used in doulton ceramic water filters, or plastic microporous material film (or a mini sterilizing filter as used in home brewing on the aerator air lines which use them) or fibrous mat could help filter dust and mist out of the air to prevent ingress and egress of those things.

An anti-mist filter like used on air pumps to remove oil mist could help prevent escape of mist.

Use high purity materials when replenishing electrolyte to reduce the addition of contaminants, could cost extra and/or be harder to obtain though.

Sealing the battery

The evolution of hydrogen and oxygen gas is a problem to a greater or lesser extent in all batteries with an aqueous electrolyte. This includes lead acid, NiMH and nicad, but the problem is particularly bad in nickel iron due to the quantity of gas produced being higher and for some reason the chemistry apparently not being amenable to the cheaper approaches used in the other types, possibly including that hydrogen is evolved even when the battery is not being overcharged.

This problem can be dealt with in a number of ways to the extent the battery can be considered "sealed" in that there should be no need to add electrolyte over the course of the batteries intended lifetime, which includes:

-Reducing it to an acceptable level so low that the supply of electrolyte is not the limiting factor in battery life. Especially helps if the battery life is not that long. Depends on clever chemistry, making the iron electrode (where hydrogen is evolved on overcharge) extra large to prevent formation of hydrogen gas until well after the battery is fully charged (because the nickel electrode is fully charged well before the iron one is, preventing the battery from storing any more energy after that point).

-Recombining the gasses There are a wide range of approaches used to do this in batteries of various sizes and types, see the research page for links and patents and notes. In sealed lead acid batteries they can get the gases to recombine in the porous electrode separator by getting the oxygen evolved to the other electrode, where it promptly recombines with the hydrogen for some reason.

The other common method is catalytic combiner caps, also called "hydro caps" which catalyze the conversion of hydrogen and oxygen to water. The big problem with this is that they usually use platinum group metals which are extremely rare and expensive, albeit in small amounts. Research needs to be done to determine if the relevant metals might be recoverable in the very small amounts needed locally. Patents indicate it might be possible to use the cheaper more common metals like osmium.

Research also needs to be done to determine if different more readily available catalysts like Raney nickel or something might be made to work.

The design of such caps is also not entirely trivial, as the catalyst surface must be kept free of liquid water and any mist from the electrolyte. A lot of heat can also be produced, especially during overcharge conditions.

It might be possible to ignite the mixture in a controlled and safe way with a spark gap or heated nichrome element, thereby eliminating the catalyst metals.

Whatever method is chosen there is also the choice of shared gas space and non-shared. In shared gas space the cells share the same atmosphere and so the water that is produced by recombination needs to be distributed equitably back to the cells again, or water or electrolyte solutes will accumulate in one cell or another. And thermal gradient will also result in redistribution of the water by evaporation and condensation. Non-shared gas space is the simplest in this regard, with each cell having it's own atmosphere, but then you need a separate combiner mechanism for each cell (although of fractional capacity), which may be more complex to manufacture.

Combiner caps made for lead acid batteries might work for us for now, and are readily available. But there may or may not be some minor snags with e.g. access to the catalyst being blocked by the solutes in the electrolyte accumulating, whereas in lead acid the electrolyte solute is also a volatile liquid itself rather than a solid in NiFe. Purchasing ones made for NiFe specifically has the problem that they would likely not be readily available and the supply might dry up in the future if the manufacturer stops making them or puts the price up.

However the battery could be designed, with some compromises, to work in either sealed or non-sealed mode.

Also, sometimes the gasses are not produced in stoichiometric proportions, usually there is an excess of hydrogen because the oxygen reacts with other components in the cell or electrolyte instead of going to O2 gas. Obviously this can't continue forever or it would cause major problems with the battery chemistry and limit battery life. It usually only happens for a while until equilibrium is (nearly) achieved, with the ratio of evolved gasses getting closer and closer to stoichiometric for recombination to water as time goes on, either during the charge cycle or with time after the battery is built. Thus there still needs to be provisions to allow some gas escape, even aside from the safety issues.

If it occurs cyclically (not clear yet form information available) then if venting the excess occurs every cycle, it would cause some loss of electrolyte. Unless it is quite low this is bad. Instead the container will probably have to be made to stand these transient pressures and contain the gas until the other of the pair is also evolved and recombination can proceed.

The need to add water to an unsealed cell is a substantial problem with NiFe batteries because they convert a particularly large amount of water to H2 an O2 no mattery how well they are treated.

The hydrogen and oxygen produced can be catalyticaly recombined with so-called catalytic combiner caps, which are available for lead acid batteries and also specifically for nickel iron although they may be the same. The sealed battery document details a method of making catalytic material. It is usually a platinum catalyst with significant amounts of platinum (~2%) so that is a problem unless it could greatly reduced or less could be used, and finding another catalyst is important.

A piece of catalytic converter from a car might work but they still involve expensive rare metals.

In AGM batteries the gasses are to some extent recombined in the glass mat, and during overcharge the gas generation would be substantial. In NiMH batteries it recombines in some way through certain reactions in the electrolyte and metal hydride electrode [battery handbook 3rd edition]. I recall seeing some patents that apparently did not involve catalysts.

Over time if either oxygen or hydrogen is consumed in a way other than forming water there may end up being an excess of the other, which could accumulate to the point where venting to the atmosphere is needed, and the recombination mechanism could malfunction, so even a "sealed" battery needs a pressure activated release valve, and water loss can occur in that way as well.

Potential options that do not include platinum, and should be investigated more: A spark gap surrounded by anti-flash mesh. Causes combustion of the gasses but when the flame front propogates through a mass of stainless steel wool, heat is lost by conduction to the extent that combustion ceases. Therefore the combustion is confined to the small volume around the spark gap which is surrounded by the wool, but gas can still flow to and from the area. The electrical properties of the spark gap and the spark discharge could maybe be used to determine the pressure of gases in the battery, thereby allowing a microcontroller to estimate the spark frequency needed. Only one control module for a large battery bank would be needed so it could be manageable. One problem is perhaps the risk of detonation initiation. If detonation were initiated the shockwave would not be stopped by the wool, I think, and could cause the other gas in the cell to detonate. This may be manageable with informed design. In welding there are arrestors attached to the acetylene tanks which can arrest a shockwave so they should be investigated and maybe that mechanism used .

Another option might be to have a very small volume of gas space in the battery so even if it did detonate there is no harm done. Spak gap erosion has to be taken into account but it may be too slow to be a concern.

Maybe turn electrodes so they are horizontal instead of veritical so taht o2 bubbles up to the other electrode so it is present when h formed and helps recombination

Electrode production options

There are many different ways to make the physical electrodes given active material. The Edison process involved tubes packed with powdered active material, nickel or graphite flakes, molasses and some additives such as cobalt hydroxide (see other reactions and additives section) under about 4000 PSI and with about 8 grams of the mixture per tube, each of which was about a quarter of an inch in diameter and formed of nickel plated perforated sheet metal and reinforced with rings of metal in some areas. See his patents for details. These are then connected together to form the nickel electrode. He made the iron is in either a similar way or by compressing iron active material into a brick with copper crystals, mercury and other additives.

A very similar process is was still used as lately as the nineties by some manufactures, who may still be using it. For some reason they use smaller tubes only a few millimeters wide.

The changhong batteries are pocket-plate type. Verification is needed on exactly what pocket plate indicates. It can include tubular but there seems to be a distinct method as well in use which involves essentially denting the surface into pockets, much like a tv dinner tray. This could be easier and cheaper.

Other current collectors that are described as being or having been used commercially are: Nickel fiber mesh and paper

Sintered nickel powder

A foil or mesh on nickel or nickel plated steel which is covered in powder then sintered to bond the particles to it, increasing surface area

Foil (for teflon bonded) can be bend or scored or etched to increase surface area

Nickel foam- nickel powder is mixed with e.g. polyurethane foam particles the surface of which they coat, packed together and heated at greater than 700 degrees, removing the polyurethane and leaving the nickel.

Nickel plated steel wool

Others described in patents but which don't seem to be used:

Carbonized polymer material, heat some polymers to 900 degrees and they carbonize into a relatively durable and conductive material which is chemically compatible more or less with both the nickel and iron electrodes. Carbon particles of activated carbon are mixed in too.

There may be others as well

Other ideas:

conductive plastics?

Getting the material onto the substrate:

Active material includes additives etc.

Used commercially: Mix the active material with teflon or another hydrophobic plastic particles, graphite particles, and some elastomer and a thickener. Exact compositions described in patents. Apply to mesh or foil and press hard, like 700 kg per cm2.

Mix it into a paste and apply to a mesh or foam by running the foam or cloth through rollers along with the paste. Apparently it stays put in the foam without any additives like thickeners or binders though I would have though it would slowly fall out. de-emulsifiers, thickeners and other additives are sometimes used to make the details of production easier.

A common method called vacuum impregnation is to dip the mesh or foam in melted nickel nitrate and then into hot sodium hydroxide solution, converting the nitrate to hydroxide. Presumably it is done under a vacuum else the air in the foam would prevent entry of the liquids.

Electrochemical impregnation, there are several ways to do it and a chemist could probably come up with more, but basically the right nickel compound precipitates out of solution in fine particles on the surface of the nickel matrix. The source of the nickel can be either the metallic nickel matrix (beefed up with extra nickel of course) or the surrounding solution.

Described in patents but not apparently used: In some cases the active material can be mixed with e.g. nickel fibers or fibers of the polymer to be carbonized, then the whole thing heated, bonding the fibers, flakes, whatever, together into a continuous mesh. The heating does not damage the active material if it is formulated right and done in the right atmosphere (not hard though).

list of tasks that need to be completed

If you can do any of the things below please do, and put a link to the location where the completed work is, or promote that item to a new section on this page. When the Pivotal tracker comes online these can be moved there.

-Decide between pocket plate and nickel plated steel wool: Can we get away without the diffusion bonding? Diffusion bonding takes hours at very high temperature, leading to high capital and energy costs. Other methods could maybe be used: ultrasonic welding, resistive welding, the fibers may be connected during the electroplate process satisfactorily. Also, the diffusion bonding's purpose is to reduce the bulk resistance of the steel wool but maybe we don't absolutely need to do so.

-look into electroless plating instead of electroplating. It looks as though it would require a lot of chemical and produce a lot of waste which would be somewhat toxic, compared with electroplating. For the iron electrode the pocket plate should be relatively easy because it doesn't have to be under such pressure, and it is more conductive. The battery handbook 3rd edition says they are made with stamped pockets from a steel sheet (much like a TV dinner tray). -Identify active material usage fraction for various electrode designs -come up with some reasonably good and workable battery designs that mesh with OSE specs - calculate materials and estimate manufacturing cost for them and pick what looks like would be the cheapest - hash out what would be the production process so have a reasonable idea of the complexity of what it will be before finalizing decision to use this design. If seems to be getting ungainly, go back and do likewise for a different design and maybe it will be more makeable. - produce bill of materials for prototype -identify suppliers -build and test it well -repeat thrice integrating knowledge gained in previous prototypes while hashing out the details of the eventual production line. -design production line -track down suppliers and produce bill of materials -prototype pieces of it -build the line and get it working.

Notes on interpreting patents and other documentation

Chemists have a terrible habit of interchanging the names of compounds as if they were synonyms based on family relations, and glossing over details. Nickel Oxyhydroxide if often referred to as nickel hydroxide in this context. Incidentally so is actual nickel hydroxide, which can get confusing for someone with limited knowledge of the art.

A nickel-iron battery likewise may use not just iron as the negative electrode but can also make use of the higher iron oxides like Fe3O4 (ferric oxide) called iron oxide as a reactant (need to check details on this). Similarly FeO (ferrous oxide or iron monoxide) is a problem in the batteries but is likewise called iron oxide. Similarly there are a couple nickel oxides and the name is often used to refer to several.

Note that often the individual electrodes are sometimes talked about (like with the iron plateau thing) in the absence of the other, which can happen because sometimes you can think of the battery to some degree as 2 half cells and many reactions proceed almost independently of what is going on at the other electrode.

Also it is a convenient way to talk about what happens if the electrode is completely charged/discharged or whatever which might not happen in a real battery. But they can never be fully separate, reactions at one usually end up influencing the other at least a bit, and sometimes important ones are basically prerequisite for certain reactions at the other. But it is interesting partly because they can get "out of sync" to some degree sometimes and be in different states of charge.

Basically you have to step away with the simplistic view of batteries that we are usually presented with and think of it in terms of the complex electrochemical system that is is.

See wikipedia "cathode" for an explanation of which is the cathode in an electrochemical cell.

Current project status

Basically, having gone through all those patents and documents and so much more (check the edit history) my recommendation as to how to proceed is:

1. Obtain a a changhong battery. 2. Performance test it with a battery analyzer fr maybe 20 cycles to collect a bunch of data regarding charge discharge efficiency at various states of charge etc. This should be available from the manufacturer, but I have found that it is not in fact. Probably for marketing reasons. They figure you will just cross your fingers and buy it anyway.

We need this info anyway so we know what we are competing against in the market.

3. Dismantle the electrodes to look at their construction. In all my travels I have not been able to determine how pocket plate electrodes are made exactly this [1] is about it. Although there are many different ways and the basic idea is just to pack the material in at 2000 to 4000 psi (it becomes a solid mass probably a bit like soapstone) and then hold it at a pressure of about 40 psi. The main purpose of the pressures is to decrease the contact resistance between the constituent parts.

4. If the performance is higher than expected they may have developed new additives, especially if the efficiency is better than 60%. Check the battery for patent numbers. Contact the company to see if the battery or any part of it is patented. Look up the patents.

Under US patent system, they cannot conceal this information in the slightest - it must be fully made known - or the patent is not enforceable. That is why stuff usually has "protected by patent x" on it.

5. If there are not patent problems, analyze the active material by microscopic and chemical analysis to determine what the additives are so we can copy them. Fear not, this is not unethical as this is SOP in manufacturing.

6. Design battery Open battery prototype I while keeping the production line in mind. To keep costs low there will probably need to be a bit of custom equipment for electroplating etc which can be made with the replab but not really be part of it.

7. Build, test.

I think it is most probably by a ways that pocket plate is the best, for a variety of reasons, mostly simplicity of manufacture, not tubular and not sintered and not mesh and not teflon bonded and not nickel plated steel wool. Changhong even uses pocket plates for their starting lighting ignition batteries so it should be good.