Flow Battery Research Collective

Hello! I'll try to document my building experience here while I impatiently wait for parts to arrive. This is mostly to document and motivate myself to continue. Don't expect super interesting stuff in here.

After having ordered most of the material from aliexpress and amazon.de, I finally got around printing the endplates yesterday. I opted for PLA on my old ender 3. As described in the docs I went for the 60% infill and managed to produce some pretty decent parts. The layer height of 0.25 looks good too. Each plate took around 1h30 on this antique machine. There might have been a tiny bit of warping on one edge but I hope it won't be enough to cause issues.

Anyways, I still need to print the arduino case and the stand (which I might modify in order to use less material). On the ordering front, I still need to order most reagents from synthetica and some PP-filament.

I have so many questions that are related to RGBs but don't really fit into existing threads. I'll poste here and hope that we can collect those random questions in one thread such that we don't pollute the other threads too much.

1. I read about the history of batterie and it seems that for a long time, terracotta or other ceramics were used as membranes/separators. Have you investigated their use? Once I have a functioning system I will surely try it out. The advantages would be that they are tough (at least physically) and potentially easy to produce almost anywhere in the world.

2. I noticed that some designs of for FBs don't have flow frame like in the dev kit but rather a thin meandering channel. What's the reason for these two designs an why did you select the flow frame

3. What would happen if you just removed the membrane in the Zn/I cell, would the iodine anions just progressively oxidize the metallic zinc and produce heat?

4. Do I understand correctly that the Nernst equation can be used to predict at what temperature and relative concentration between oxidized and reduced ion of two species a redox reaction takes place? Do I also understand that this does not predict or influence kinetics?

Many thanks for your precious insights!

Hello everyone! I've had the idea floating in my head for quite a while to make my own barbed connectors/fittings for connecting tubing as used in the dev kit. I finally got around printing a series of prototypes in PLA. The results are promising, even if the value of printed ones is questionable. Designed them so that you print them lying flat in order to optimise lengthwise strength. To get them watertight, you just need to sand the barbs a tiny bit.

I have two main reasons to print these parts myself, first of all, I forgot to order them and secondly, the more parts of the dev kot can be printed, the less people will have difficulties sourcing them.

I'll publish a Freecad file once I have it tested and printed in PP.

Hey everyone, i just read an article about your project on a german tech site and watched your fosdem video and I'm super stoked about this project. I've been interested in energy storage and in particular flow batteries since years and envisioned building one at some point. Unfortunately just by reading academic paper, I couldn't go forward so I gave up. That's why I'm super excited to see that someone did the tough work of creating libre plans for an experimental cell.

I'm an electical and computer science engineer by training but more of a programmer and sysadmin by trade. On top of that I'm a 3d printing enthusiast (sometimes going as far as writing my own albeit simple slicer) with quite some experience with FreeCAD. I'm based in Luxembourg so I hope I can source all the required materials easily.

I'll try to build the experimental cell in the upcoming months if time and motivation lasts and family life allows it to. After and during that process I would love to give you feedback (and maybe improve) on the documentation.

I already miss two sections which I unfortunately cannot supply. 1. Flow battery basics 2. Operation of the flow battery.

In the future I would love to store my excess PV power in my basement using my self built cell :D.

Congrats on this excellent project!

@danielfp248 that makes a lot of sense. Being a complete newb, I slowly gather an understanding of the individual components of the cell.

The chemicals have all arrived. Unfortunately I'm still waiting for the glass vials to store the finished electrolyte. I'll have to wait a bit until I can take out my old lab coat :).

I finally managed to mill the current collectors. I started off with 0.9mm brass but had an accident with the second collector. I'm pretty sure it would work, but to be sure I went to the crafts shop next door and got some 0.8mm copper and re-milmed the collectors. .

The cell starts to come together!

I also received the titanium foil which needs to be milled into the right shape to work as a bipolar plate. As a backup I also have generic grafoil being delivered.

The only things I'm missing now is the pumps, proper PTFE lined tubing and PP-Filament.

In the meantime I'll print my modified jig which tries to reduce print time and adds some printability features like hexagonal holes for the pumps and drop shaped holes for screws. It also features a little basin that can catch a bit of liquid that might spill.

@kirk about the jig, yeah I modified the FreeCAD version. It's probably prone to tipping. I'll see that once I get the pumps and hobo modify it and then modify my model and share it.

My Mystat finally arrived, yay! No I need to figure out how to flash that pic (hopefully no programmer neede) and get rid of the remaining 5 PCBs.

Does anyone need a MyStat PCB and is based ln the EU? It's probably useless to most people who donct have an oven and advanced SMT soldering skills. Anyways, if you're interested, I can send one over for free.

Hello fellow flow battery enthusiasts! I bought 15m of Tygon Chemical tubing with PTFE lining suitable for the Zn/I chemistry as used in the devkit. I only need around 2m and someone else wanted to take 5m, that's 8m left to be distributed amongst people who need some. I ship in the whole EU and the price is 23€/m (thats what I paid incl. shipping). Just send me a PM if you're interested.

Thanks for the good explanations! Now I need to actually source alls those parts!

@danielfp248 ahh, I had't caught those two caveats. Especially the oxygen sensitivity seems to be a big issue to me. That makes it very unfriendly to tinkering. The temperature requirement is off course also problematic, probably also from an efficiency point of view.

On top of that it's also a hybrid, so I guess has all the problems with dendrites etc.

Could you please document how the potentiostat is connected to the cell? Is it connected only on the two current collectors? Does that not mean that you could substitute it using a constant voltage source and just log current?

Sorry, I'm a total newcomer in battery testing, so this might be obvious to others.

Congratulations, that's great to hear!

Do I understand correctly that microporous membranes mostly let pass small ions and "try" to contain the active speices like I and Zn? In reality though they might let them pass in non-negligable qunatities, no? Is this what you call migration?

Thanks a lot for the digging! You're probably right about getting potentiostat. I got the quote from PCBWay down to around 314$ for one fully assembled PCB and 4 extra ones. This is acceptable for me even if still quite expensive. I guess I could drive down the cost by ordering and soldering on the expensive parts by myself.

This sounds very exciting but to be honest, as an outsider, I can't really judge. Could you explain how this chemistry compares to others and how the results are promising, etc? Also, is the low voltaic efficiency due to overpotentials because of relatively bad kinetics?

I ordered most parts now. Fingers crossed they are correct. I went for the Ti foil instead of the graphoil since it was way cheaper. Fingers crossed

Thanks for the comprehensive reply, that sounds indeed very nice! I have more questions still:

1. Do you do anything differently than what is already published or is the challenge mostly to get something kind of proven working in the FBRC devkit?
2. Would it in general be an issue to just never charge the battery to high SoCs? Sure your volumetric energy density will go down but you might avoid all kinds of trouble this way. I imagine habing a very simple or lowtech battery of mediocre efficiency and density could still be of a lot of value to many people.
3. Are the low voltages due to ohmic losses in the separator and maybe electrolyte?
4. How is the patent situation around this technology?