Flow Battery Research Collective

Just wondering, you are using water, but are you using distilled, or de-ionized, or just tap? The reason for the question is, when/if this becomes a doable project for home battery system, our tap water is very hard. It is a mix of ground water which is some what hard and CAP water which is water that has flowed for some 336 miles across the desert in an open canal diverted from the Colorado river making it VERY hard. Seems likely it would throw off the chemistry.

Don't know what you have there, but Target, Walmart, Home Depot, or even order from Amazon, Plastic storage bins. Just set the whole project in one. They come in clear so you can see in if there is a problem without removing the lid. If it spills, the fluid stays in the bin.

Maybe that is what the video was talking about when they said the biggest problem is ion lock, or maybe it was electron lock. But basicly it's very hard to get the charge out at a useful rate. I'm sure there is more to Tesla's secret sauce, but they said Tesla's fix was very thin aluminum with carbon pressed into it creating a battery that gave it's charge better, could be charged in 5 minutes, and produced far less heat then lithium batteries with no thermal runaway problem. It sounded like they won't even use battery cooling for it because what heat it does produce makes it work better. A lot of "sounds good", but will see when it hits the road.

@sepi It's the pressure difference that rupture the separator correct? So what I was talking about is some kind of double bypass valve (one for each side) that is linked together to keep the pressure the same on each side. Might be too complicated and likely yuo can already buy something like that though $$$. Anyway, just a thought.

Fuel injection works this way on cars. They use a bypass regulator to give you a smooth continuous flow. Pump is always pumping and extra goes back to the tank.

Another thought, someone might be able to come up with a regulator that balances each side. Pressure goes up on one side, it reduces that side and raises the other.

Question, what about using some sort aluminum oxide? Tesla is rumored to be using a new aluminum battery the developed in place of LFOP for the new model 2. They said something about aluminum holding 3 ions? per molecule instead of 1. I poked around and there are groups working on aluminum flow batteries. Seem they don't have the dendrite problem.

I see a number of groups working on aluminum flow batteries. Seems they don't have the dendrite problem.

Just a thought when using oversized pumps, try adding a bypass valve. With the valve fully open, the output of the pump just goes right back to the input. Close the valve a little at a time to get the pressure you want.

For a pointless waste of time search, I tried in google: "what is the best cheapest redox flow battery chemistry"
Came back with:

High-energy and low-cost membrane-free chlorine flow battery:
https://www.nature.com/articles/s41467-022-28880-x#:~:text=To meet the needs of,La France in 188428.

A high-energy and low-cost polysulfide/iodide redox flow battery:
https://www.sciencedirect.com/science/article/abs/pii/S2211285516304153#:~:text=Highlights * • The polysulfide/iodide redox flow,reversibility of polysulfide and iodide redox chemistries.

Air-Breathing Aqueous Sulfur Flow Battery for Ultralow-Cost Long-Duration Electrical Storage:
https://www.sciencedirect.com/science/article/pii/S2542435117300326

And 2 Google search options with a lot of results over my head:
Sulfur-Air Hybrid Redox Flow Batteries: https://www.google.com/search?num=10&cs=1&sca_esv=db6c98fd308e1745&q=Sulfur-Air+Hybrid+Redox+Flow+Batteries&sa=X&ved=2ahUKEwjS8bKDhoGPAxXpL0QIHXvhGwgQxccNegQIEhAB&mstk=AUtExfDy0ZazObNsltp9BYwtpQylX9u5AJT5yaQVQRbdARMJvJuEzcAf-Z2d4utwzTSnhCKcn4qOInT9b9zVkToTFJswogvnK4pun2X3x25KeDNW8dbrTS5jwMmIp6riqcFc6wG0Rm8FPMwC2B67TUxmok7FRMfFyfzTWq_Ub_BP2zY5rP4&csui=3

All-Iron Redox Flow Batteries: https://www.google.com/search?num=10&cs=1&sca_esv=db6c98fd308e1745&q=All-Iron+Redox+Flow+Batteries&sa=X&ved=2ahUKEwjS8bKDhoGPAxXpL0QIHXvhGwgQxccNegQIIhAD&mstk=AUtExfDy0ZazObNsltp9BYwtpQylX9u5AJT5yaQVQRbdARMJvJuEzcAf-Z2d4utwzTSnhCKcn4qOInT9b9zVkToTFJswogvnK4pun2X3x25KeDNW8dbrTS5jwMmIp6riqcFc6wG0Rm8FPMwC2B67TUxmok7FRMfFyfzTWq_Ub_BP2zY5rP4&csui=3

Google sure like long URL's

I was hoping there was something here. Lithium batteries cost way too much tripling or more the cost of a solar system and are way to dangerous with their high fire risk. But it really takes a battery to make solar worth doing because it averages out the load to make better use of the input even when not looking for extending through the night. I Just saw a 12kW split phase (we use 240 split phase in the US) hybrid inverter for under $500 which is cheep. Solar panels are also getting down if you look. But the battery is still a project killer.

I thought these were full flow batteries you guys were working on

But a .25kWh battery is hardly worth messing with. Need at least in the 10's of kWh. Last month we used 1271.84kWh (Summer time with record temps 110+) which comes to ~43kW/day. On 7/10/25 we used 47.36kWh.
And you can only collect during the day. Assuming an off the wall number of 30% of useable daylight, that leaves you needing to store ~25-28kWh for night.

I am confused, The big advantage of flow batteries is that the capacity is decoupled from the cells putting it in the size of the tanks. Need more kWh, use bigger/more tanks. Need more amp's, then you need more/bigger cells.

Oh, and solar with battery systems tend to use 48v because you need less amperage for a given amount of wattage.

My dad bought stocks in an Iron/Salt "flow" battery. But after seeing videos on it, it's not really a flow battery. They are using gels instead with no external tanks.

@danielfp248 So 2 small tanks with switching VS 1 large tank of the same volume wouldn't mater? Just use one big tank for each side?

I know this is something for way down the road, but it seems to me there will be some kind of tank size limit. Because the bigger the tank, the more diluted the remaining charge would be when it gets low to the point that it would be of no use.

So any thoughts on what the upper useful limit would be on tank size before diminished returns kicks in?

If you are looking at ceramics, I stumbled across this YT video using a kind of cement. But seems to me thickness would be just one of many problems.

I know we kinda got off topic, so bringing it back. When Kirk in the Op said iodine is volatile, i googled I iodine explosive and got this:

"Iodine forms explosive or shock-sensitive compounds when mixed with REDUCING AGENTS (such as LITHIUM, SODIUM, ALUMINUM and their HYDRIDES) and liquid AMMONIA. Iodine will ignite POWDERED METALS (such as ANTIMONY, MAGNESIUM and ZINC) in the presence of WATER."

I read this to say that if that membrane ruptured, the two sides would mix and BOOM. I don't know much about photo paper as opposed to regular paper. I'm thinking it's paper with some kind of polymer coating. When paper gets wet, it breaks down. So prolonged setting between two fluids, seems like the boom is just a matter of time.

So with this copper, If you get air in it, say need to work on it, is it all ruined? or do you just put a vacuum on it and repressurize with something like Argon and you're good to go again? As for the temperature it needs, I live in tucson, We hit 113 a couple weeks ago with normal daily temps 100+ in the summer, so only a problem in the winter.

@danielfp248 Any reason making a membrane was abandon? Seemed like you were making progress and without it you seem more limited on chemistry.

I didn't know iodine was explosive. Did a google and yea, when mixed with other stuff like zinc oxide and water :(. So, googled ion exchange membrane for sale and was seeing what looked like rolls of it at amazon. But those rolls were small, some ~50cm square and still pushing $100.

The googled diy. There are a lot of YT vids. Think I'll be watching some of those tonight.

I'm 99% sure this is not possible, but maybe tossing it out there would give someone an idea for another direction to look. This problem of a shunt current makes my envision some sort of FET like object with a passage between source and drain to allow fluid to flow through it while a "gate voltage" pinches off current flow through it.

I know, crazy, but maybe now that it's out there, the thought will stop bouncing around in my head

There is RTV silicone used in automotive to put carbs together back when cars had carbs