@kirk So my thesis is specifically on slurry/suspension electrodes (instead of using a graphite felt/porous electrode, you suspend conductive carbons with the electrolyte - which also allow you to run solid-phase chemistries in flow) in a way that's sort of chemistry-agnostic. Basically applying chemical reactor design principles to designing slurry electrodes. But here are some salient idiosyncrasies of all-iron cells:

• iron plating in porous electrodes is annoying (acidic = HER, basic = whole host of nasty iron oxides, many of which are quite stable. Plating on carbon substrates is also a pain - most studies I've seen plate onto copper. Also volume expansion is a big pain in static cells. In flow batteries, any time you have plating you end up re-tying power density and energy density through that half cell. Iron plating kinetics are also quite slow, especially in relation to zinc plating.
• Bunch of folks (Savinell and Wainright groups) at case western used slurry electrodes and plated iron onto the slurry particles (ostensibly). They attempted to scale but really struggled with having a performant enough slurry electrode that wasn't too viscous. But plating on suspended particles re-de-couples power and energy density.
• Have you guys looked into water-in-salt electrolytes? They involve dissolving a ton of a supporting electrolyte to the point where they lower the activity of water and suppress HER. I've seen some work using acetate salts and this one using magnesium chloride to support even iron plating - and I've replicated it successfully. The study plates on copper like I mentioned earlier, but I also got it to plate on grafoil.

Solving that performance/viscosity tradeoff in slurry electrodes is part of my thesis! And so is improving the power density of otherwise crappy flow battery chemistries. I'm still working on getting some of it out, but I'd love to share soon or help in any other way.

Material choice from the perspective of mineral centralization and cost is another problem I think regularly about - I did a little study collecting the centralization/governance of various metals and ranked aqueous battery chemistries by cost and "criticality". If that's of interest let me know too!

I have started the first tests with the RFB. I have encountered the problem that the electrolyte migrates from one reservoir to the other. I assume that a better separator material would help. I am currently using three pieces of photo paper. Could more layers of photo paper reduce the effect?
The pumps I use are probably a little too big, which certainly doesn't help.
I assume that with larger cells, the problem will intensify and that a better separator material than photo paper will be necessary.

It seems to me that there is no way to obtain small quantities of a proper separator. At least, I couldn't find any online.

Now to my actual questions:
What other materials could be used as separators?
Which one would be the most suitable to buy at the moment?
Has anyone of you been able to obtain small quantities of a separator material?

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?

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.

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!

Hi Guys,

as promised I also want to document my journey on building the kit. Yesterday I started with the very simple endplates:
The right one was the first, printed with 15% infill, the left one with 60%, but still just 2 wall loops. Of course, you can feel the difference in the weight.

One problem I noticed was, that I had a PEI textured print plate only. Therefore the surfarce looks fine, but it might not be the best to seal the chamber.

To solve this I ordered a flat "high temp" plate from Amazon, which arrived today. Of course, next print cycle was in the queue. This time with 5 wall loops:

On the right the initial version, on the left the new one. You can see the difference immediately. Well, the picture still gives the impression that it is not flat, but it is:

This is how the old one was looking:

BTW, I printed all of them in Geeetech PLTG on a Bmboo Lab P1S with AMS. The printing time for version with 15% infill was arround 25min, 48min for the version with 60%. Printed with 0.2mm layer height.

Looking forward to print my first parts in PP in the next days...

Yeah… That went well.

On December 14, 2024 – three weeks after I published the last exciting installment in this series of posts – our new Redflow ZCell battery, which replaced the original one which had developed a leak in the electrode stack, itself failed due to a leak in the electrode stack. With Redflow in liquidation there was obviously no way I was getting a warranty replacement this time around. Happily, Aidan Moore from QuantumNRG put me in touch with Jason Litchfield from GrazAg, who had obtained a number of Redflow’s post-liquidation stock of batteries. With the Christmas holidays coming up, the timing wasn’t great, but we were ultimately able to get the failed unit replaced with a new ZBM3.

At this point the obvious question from anyone who’s been following the Redflow saga is probably going to be: why persevere, especially in light of this article from the ABC which speaks of ongoing reliability issues and disturbingly high failure rates for these batteries. That’s a good question, and like many good questions it has a long and complicated answer.

[…]

#redflow #solar #victron

Inspired by Gus to share my journey. Some quite useful info in that thread. I expect my journey to be a bit more "scrappy", given I'm trying to make this work with some items I have lying around. I also might deviate on the first chemistry I test: we'll see.

For now here's a picture of some of the components I've printed, including two peristaltic pump heads that interface with NEMA-17 stepper motors and that use bearings as the rollers. Links to them here:

• https://www.myminifactory.com/object/3d-print-peristaltic-pump-63137
• https://makerworld.com/en/models/497147-peristaltic-pump-\_-nema-17-\_-608-bearings#profileId-622582

Small steps, hoping my next post is me showing whether I can get the pumps to work. I'd be curious if anyone has had success with such 3D-printed pumps. I'll try to provide some more feedback in the coming posts too.

Hi all,

It's been very exciting to see the FBRC community grow these past months! We have come a long way from just two people tinkering in their respective apartments. If we are going to develop a practical battery technology in this way, having a strong open-source community will be crucial.

So far, all the interactions here have been positive to my knowledge. We've only had one blatant spam post so far. A few people I spoke with recommended adopting a code of conduct, such as the well-used Contributor Covenant. I have uploaded it to the FBRC website here and added the contact info for the current mod team (right now, me and @danielfp248).

I'm not adding this in response to any recent incident, rather, I think it's good to have it established and in-place as the community continues to grow.

If you have any comments or feedback on this, please feel free to discuss here! It's not a static document; we can change it as we see fit.

TL;DR: Don't be a jerk, let the mods know if someone is causing trouble, and let's make open-source batteries happen!

Hey all! If everything goes well, we'll soon have a bit bigger cell and maybe cell stack to play with. This will be another step towards building an actually useful energy storage. This also means that overall systems efficiency starts becoming an important issue. In order to know what to focus on in the development but also to understand questions of dimensioning and parts selection, it would make sense to be able to model the whole RFB system including Pumps, Inverters, plumbing and cell and its chemistry.

Did anyone look into this already? I was exploring a bit what tools we could use and figured that Libreoffice Calc would be the very simplest tool, followed by python with SymPy and finally by OpenModelica. What do you think? Is this the right time to think about these things or am I overthinking it?

Hello all, I'm trying to gather parts but I'm not sure about some of the suppliers/products I have an eye on. Could you maybe give me some feedback about the following products? (I also added more specific questions to the screenshots).

Also, do you have any good sources for the chemical reagents that are accessible to amateurs?

Did I understand correctly that there is a 12V and a 24V version with vastly different prices? The 12V one is 17€ while the 12/24V one 68€?

Many thanks for your help!

Making a thread for a potential all-copper chemistry, which came up in discussion during our regular meeting today as a potential safe chemistry for testing, particularly as we scale to larger electrolyte volumes/cell areas. H/t to @danielfp@chemisting.com !

The voltage is too low to be of major commercial interest (~ 0.6 V), but in the charged state it's not volatile like iodine-containing complexes.

It also fulfills our emerging criteria:

1. Safe (in comparison to vanadium or lead-based aqueous systems)
2. Accessible (low-cost and available to amateur chemists)
3. Compatible with porous separators (no requirement for ion-exchange membrane)

From Roth et al. chapter 38 on all-copper [1]:

The CuFB is a novel aqueous system based on the three oxidation states of copper, achieved by stabilizing the Cu(I) complexes (CuCl2−, CuCl32−) in concentrated chloride solutions. The resulting cell has a hybrid configuration with the chemical reactions shown in Eqs. (38.1) and (38.2).

And the self-discharge reaction for completeness:

We are considering testing this in the dev kit and then in our first large-format cells, as it could be cheaper and safer on the 100-1,000 mL scale than zinc-iodide.

[1] Roth, C. et al. (eds.) (2023). Flow Batteries: From Fundamentals to Applications, Wiley.

Hi, was observing this theme long time and also I've seen the problems.
I have made two sketches for a possible solution what prevent probmems of security and efficiency.
So the water filled capsuled system prevent too high wasting of energy by senseless level differences because the reservoirs can swim up and down. So you can in one case use level differences and in the other case you can prevent senseless level differences.
In small testing systems it plays not so a big role, but in bigger systems and it does and lead also to senseless pressure on the pipes.
Also prevent the setup any leakage of chemicals in this closed setup. On leakages on pumps or so, the chemicals flowing back in it's reservoir. Also the water does prevent leakages of the salt solution outside of the box.
Also electrical elements are secure because all can be installed above the chemicals ways.

This are only sketches, but eventually helpful?

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.

I tried ordering the MyStat off of PCBWay assembled and it seems like the components cost almost 1k$. Is this normal? Could I leave out a component and have the component cost come down to a normal price range? Did you always solder the components on yourselves?

During the past couple of years we have been working on the design of a small flow battery kit for the study of flow batteries (you can read a previous post about it here). With the help of an NLNet grant, we have fully developed the first two versions of our small scale kit – with the second one achieving even longer scale tests – and are now working on the development of a larger surface area kit that can be used to study flow batteries or build flow battery applications at a relevant scale for practical power storage.

This new large area setup – which we have discussed in our forum – is now moving out of the design stage thanks to the acquisition of new systems for both 3D printing (Prusa Core One) and vinyl cutting (Cricut Maker4) that are allowing us to move to their in-house fabrication and testing. The new cell is designed to be compatible with the area of 3D printing beds and features an active area of 13.5×13.5cm, which is 182.5cm2. In practice this means a single cell will be able to handle a capacity of nearly 22Wh when using the Zn-I chemistry used in our small scale design.

We borrow some of the features that worked great for our small scale kit – like using a polypropylene enclosed flow frame – and add features that are needed for a scalable design (like all entry/exit points on the same side, stacking compatible design, etc).

The fabrication of these pieces is especially challenging due to their size and the complexity of the flow fields in them. The flow fields have to follow complex paths to prevent the creation of large shunt currents within the device. A really good 3D printer with a heated enclosure is required to be able to print this in polypropylene with no warping and good enough resolution. Even with such a printer, a lot of fine tuning is still required to achieve the low level of surface roughness and high level of water tightness that is needed for this particular application.

While we are thinking about the potential of using heat welding or even adhesives to be able to put the cell together, the easiest first approach will be to use the same silicon gaskets as we used for the fabrication of our initial cells. To cut our gaskets in house we are using a Cricut Maker4 vynil cutter, which is able to make this high precision cuts without any problems.

With these materials now fabricated, we are now close to putting together our first tests of a larger scale flow battery cell. The idea of these initial tests will be to test the cell for leaks and make sure we can circulate water without problems before we try to run any active materials. We will be using thick wood as endplates for this initial test, as this is the easiest to source, hard material, that can be used. Thanks to our use of fully enclosed gaskets, the end plates will also have zero contact with any water or active materials.

This flow battery kit work is being funded by the Financed by Nlnet’s NGI0 Entrust Fund. We are also collaborating with the FAIR Battery project.

After I look around, I can't find much data of performance.

I take a look also in principes and now I know. I was wrong. I ever tought it is pumped from one side to other, but istn't.
So my diagram in the other thread is nonsense...

But, I think about the efficiency to totally mix it in one unstructured container on each side. My thinking here, it will press down the efficiency?

Is there anywhere a diagram of load and unload process?
Yes, you can optimize the cell but would think, also the storage management could be a factor to make the system more efficient.
So the unleaded flowing back could be a bad thing...?
A test with a really long pipe instead of big tubes/container could be a good idea for a better sorting of loaded an unloaded salt solution. So that not the fresh used stuff flows directly back and possibly damages the efficiency ot the cells work.
Eventually a leaded flow could do the trick?

If it is so, later could be used a cheap leveled grid into a tube the leading element for a flow in row.

So on load would be the goal to use the most unloaded stuff at first and on unload using the most loaded stuff at first.
But I'm not a physics expert for electrical poteincial, I only try to go a simple way of my normal logic.

Here is a link to his presentation, thank you to Sanli for his support of our project! Useful if you are new to FBRC and trying to get a quick overview of what we are attempting to do.

Here are the PeerTube and YouTube links.

Building a rechargeable battery is not an easy task. Although many great technologies are available (like LiFePO4 or even lead acid batteries), building these batteries isn’t trivial because of the technological hurdles, manufacturing requirements, chemical substances, knowledge and safety requirements. It would be ideal if we had access to an open source rechargeable battery technology that was easy to construct in practice with readily available materials, robust and at low cost.

In a previous post I talked about Cu/Mn batteries and how several different papers describe batteries using Cu sulfate and Mn sulfate along with sulfuric acid to create robust batteries with significant capacities, even above 40Ah/L. Such batteries would be close to ideal as they are easy to build, use earth abundant materials and – in theory – are very robust. However, my efforts to reproduce these batteries were plagued with failure as I was unable to reproduce both their reversibility and their capacities.

Furthermore, this Cu/Mn technology using sulfuric acid has been patented by a French company (years before the Chinese articles started sharing the chemistry in 2017). This means that this chemistry is not open source and significant battles could arise from the use of this technology at a wide scale. This also explains why the patent applications mentioned by some of the Chinese researchers in their papers cannot be found (probably the patents were denied because of the preceding French patent).

To tackle my problems reproducing this chemistry, the hurdles with intellectual property and some issues dealing with the solubility limit of copper/manganese sulfate mixes, I have modified this technology to use methansulfonic acid (CH₃SO₃H) instead of sulfuric acid. Methanesulfonic acid is easier to get than sulfuric acid – because it has no regulatory restrictions – and the solubility of both copper and manganese mesylates is higher than that of their sulfates, meaning that even higher capacities than with sulfuric acid should be possible.

The above experimental results show cycling of the cell shown in the first picture. This chemistry achieves a CE above 90% with an EE above 65%, the cycling is also very stable with very reversible MnO₂ formation in the highly acidic media. The electrolyte tested is roughly 0.8m Cu, 0.8m Mn and 1m CH₃SO₃H. I haven’t tried changing the acid concentration or preparing more highly concentrated electrolytes yet, as I am still fine tuning the cell fabrication process to enhance reproducibility. The cells right now can be charged to 20Ah/L, which is already an interesting level of capacity, although 40Ah/L should be possible.

A very important issue I’ve noticed is that dendrites tend to appear around the edges of my Cu anodes due to electric field instabilities, as the Cu prefers to grow in the free solution rather than through the polypropylene separator. This can cause the battery to short when charging to very high capacities). Cells without separators – with just the electrodes hanging parallel as in the case of some of the Chinese papers – could help alleviate the issue. I am also trying passivating the edges using nail polish, to see if this fully solves the issue.

While the Cu/Mn battery chemistry using H₂SO₄ is clearly patented, the innovation using CH₃SO₃H is not protected, neither covered by the scope of the current patent. The publication of this blog post should ensure that this technology will remain patent-free.