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?
