Homebrewed Electricity > Storage

So I went down the Nickel-Iron battery rabbit hole...

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SimonMester:
So after a lot of reading, I have a pretty good idea on the pros and cons of this type of battery (aka Edison battery).
I'm sure most of you reading this will be aware of at least the broad strokes. Low energy density, slow charge and discharge, some maintenance needed, but pros being it not needing lithium, simple construction, not being a literal bomb waiting to explode and century long battery life.
It seems nowadays there is a bit more resurgence for off grid applications especially.
It is not a straight up attractive proposition however, for a couple reasons. The main one being the surprisingly high price. It's not really due to the materials needed, it's more due to almost no R&D, manufacturing, as it has remained very niche, thus costs are that of a niche product.

This is where I have begun with search for other hobbyists. I have seen many DIY attempts, all super small scale, and quite arbitrary in their measurements. I'd like to give it a go myself, but preferably one that is a bit more thought out in terms of chemistry and construction.
I have one modification over the usual idea. The electrolyte that is usually used is KOH. It's quite hard to get here for some reason, and luckily NaOH is a good, cheap and available substitution.
I have managed to find some conductivity tables, and turns out 20% wt NaOH has the highest electrical conductivity. It's about two thirds of that of KOH, so I expect a lower voltage at the end, but for my purposes, I'd like to figure out a practical, cheap manufacture, and then the scaling of that, so I'm not super concerned with lesser efficiencies or outputs.

For the electrodes, one the one side we have black Nickel III oxide, on the other we have Iron III oxide, Fe3O4. I have this in the form of fine magnetite powder already.
There are several proposed ways of making the electrodes. Usually involving nickel plated steel as a base to put the oxides on. This achieves corrosion resistance, and deposition of oxides aims to maximize surface area of the oxides and thus overall conductivity and efficiency.

This is probably the biggest question in manufacturing. How to maximize surface area, while not making manufacture really complex or energy intense.
Here are my ideas: Usage of epoxy for binding bits of the oxides, essentially making 'sandpaper' electrodes. Turns out epoxy is really resistant to the caustic environment, so it should stand up to the task. The problem is that the oxide has to be accessible by the NaOH, and covering it with epoxy would defeat the whole thing.
This would mean the fine powders would have to be turned into smaller grains, and the epoxy layer would need to be quite thin, probably pressing the grains into it until bound.

I have seen other suggestions with making mixtures, pastes of the oxides, usually mixing them with some form of graphite, interestingly. I haven't found really clear reasoning as to why, but I did read some references to spacing out the oxides, leaving 'voids' between them being good, and carbon being employed to that end.

Electroplating steel wool with nickel, and then coating it with such paste might be a really nice solution, once a decent mixture is identified.

I have a few questions, to anyone who might be a knower:

- How would one come to calculate the ratios of Nickel, Iron and Electrolyte for each cell. I have found references to oversizing the iron side by 20-30% being healthy to prevent battery damage while charging/discharging, but I have very little clue on what amount of electrolyte would be needed.

- I have read nickel wires are a must in this caustic environment, which makes sense, but I have never used those. Do they refer to nickel coated copper wires?

- I hardly find references to positioning of the electrodes in relation to each other. What relevance does that have?

MattM:
Can you get enough adhesion using enamel?  There is a nylon fibrous non-uniform mesh called Flo-free that perhaps could be doped with enamel, and as its drying but still has tack, coated with your iron powder.  The material is sold in 6" or 36" wide rolls.  If you need more uniform material then perhaps you could use screen material doped in a similar way using different screen fiber sizes between layers to prevent blockages.

If only there was a way to use a pair of water acid neutralizer canisters to circulate your liquid between anode and cathode, where you could just fill both up and use a membranes in the pipes connecting the two for keeping them separated.  Its never that easy.

Edit:  Nevermind my ramblings.  I was thinking this was a flow battery.  Nickel-iron has a very narrow gap required.  Literally more similar to lead-acid battery than a flow battery.  Even has significant off gassing, so no way to completely seal them.

SimonMester:
Yeah, it has off gassing so significant, there is research on capturing the Hydrogen to be used.
The problem of the materials is also that it will be sitting in a super caustic environment, so I'll definitely need information on whether they can put up with it, before I buy anything.
Nickel and Nickel plated things work, and epoxy does too. Polypropylene does too, but thats quite expensive and annoying to get.
I'll have a little read into those meshes, but I'm not sure how could I coat them without sealing up the holes. It's all done by hand and fine powders.

SimonMester:
I'm also thinking, maybe something like this: https://www.easycomposites.co.uk/polypropylene-plastic-sheet
It could be the base of the plates, and then maybe bind with epoxy on the surface. That way I at least have rigid plates to work with that are easier to position as well?
I'm not sure how to avoid the fine powder just clumping together though. Maybe thats where some additive, such as carbon can be useful to space them out.

Nvm I'm an idiot, the big reason people use nickel plated sheets is not just chemical resistance, but you need it to be a conductor to attach your wires to of course.

Mary B:
Going to toss in a word of caution. Caustic materials are VERY dangerous to handle. They will turn your skin to soap in seconds sloughing it off... and you won't feel it because it doesn't burn like acid does!

I used to handle 55 gallon drums of caustic soda. I had to wear a full coverage protective suit with helmet in case of splashes... the neutralizer for it was hydrochloric acid! After that a bath in a baking soda based neutralizer then the emergency shower... we had to use it once when I worked at that feed testing lab, one of the girls mixed things wrong and a liter of it blew up in her face, she needed lower face, neck, and upper chest skin grafts over a period of 2 years and the scarring was bad... wasn't the first bad accident while I worked there... one of the other girls did the same with a gallon of sulfuric acid she was supposed to dilute... she added water to acid... bad idea... it boils and creates a LOT of heat.

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