Flow Battery Research Collective

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

A google for "graphoil sheet" comes up with some stuff under the brand name "Grafoil". Saw a number of sources including Ebay. Might try starting with google and then narrow it down. There was also some that included Ti foil in the layering

I'm no expert ether. We used quick setting plaster a lot in construction for repairs on a lot of things and now they have a "wood epoxy" which is an epoxy for wood repairs. You have a thing epoxy you brush on onto wood which provides a good bonding surface for dry rotted wood and then you mix an epoxy that works more like the quick setting plaster and creates a strong enough repair that you can nail it. These plasters and epoxies could be formed or poured to create a nice mold. For the quickset we could build up an area, then carve and shape it before it fully set. The surface is very smooth and with a spray sealer of some kind should be even better for molds.

A quick look into casting, it looks like the most common is using silicon for making the mold. Yes it lets you do detail, but it is also soft and flexible. Not good for making thin plates without warpage.

The other post I was referring to was in "Designing the large-format cell". I was wondering if there are option to cast using resins or other material instead of printing. Would solve the problem of trying to print large plates without warping.

I was thinking of casting (posted in the other thread), but if you are printing enclosed complex channels, that would be a problem. I didn't think you could print horizontal channels without the material sagging into the channel.

I can see that unless the gasket was supper thin, it could squeeze into the channels in a layered design. But something applied in a thin liquid form such as an adhesive might work. I just googled the printer and cutter you're using to make the plates and gaskets. Some $1300 for both, ouch.

From the way I looked at the plate, it has open channels that become enclosed when placed against the next plate.

I've never done any 3d printing, but from what I read, they don't do overhangs well because the hot plastic would not have any support under it and adding supports in the channels would restrict flow.

I saw the blog post which also mentioned the problems of 3d printing the panels of that size without warping. I did a quick google on injection molding and that could also get $$$ and a bit beyond some DIYers with the need for pressure.

But what about casting? Are there resin based or other low temp materials that could be cast? Because making the mold would be easy. A dummy part could be printed from any material and it could be made in, say forths that could be glued together. And for the mold there is a quick setting plaster like material we use in construction for repairs (one brand is "Quickfix) that dries to a porcelain like material, very hard, and very fast. It's sold with set times in minutes. Make your dummy part and put it on some wax paper or plastic wrap on a flat surface with a frame around the part. fill with plaster and when cured, spray with a sealer that wont react to the resin to seal the micro pores. Then with it flipped over and the dummy back in, and the frame around it, pour the other half. You have a simple and cheap to make mold for casting.

Hi, Timothy from the US. Casual interest in the project. Would like to build a battery for house backup at some point, but give the additional cost of inverters and solar for charging, permits, etc., it's likely more of a pipe dream.