Flow Battery Research Collective

@kirk said in Following your documentation – feedback & questions: Could you share the file you modified? It looks like you added a big cylinder. I have send you an email, @kirk said in Following your documentation – feedback & questions: The program here * should * work on linux when run as root (in order to have proper USB access). You can control the pump speeds via the Arduino with the software, even without the MYSTAT connected (under the "charge/discharge" tab) (this will all hopefully be in a video soon!) Thank you. I am planning to use a Raspberry Pi for long-term tests. Are you using a Raspberry Pi too, or a PC? @kirk said in Following your documentation – feedback & questions: In the CAD files we have specified a 2D endplate (https://codeberg.org/FBRC/RFB-dev-kit/src/branch/main/CAD/exports/Metal Endplate.step), that could be laser cut or milled from aluminum. @danielfp@chemisting.com has received endplate versions of this in aluminum, the only catch is then you need insulating washers so as to not short them. Another rigid polymer could work too. Thank you. For now, if there are no leaks during the long-term tests, I will not change these endplates. And also, I wanted to ask you about the current collector's material – is brass a better option than pure copper? What was the criterion for the material type and thickness selection?

Updates from @danielfp@chemisting.com during today's meeting: I started a test with 2M KI, 1M ZnCl2, 2M NH4Cl, 5% Trieg with Daramic and felt on both sides. Going to charge to 1.6V at 10mA/cm2, see if it makes any difference regarding stability with Trieg on subsequent cycles. I did one cycle at 10mA/cm2, charged to around 240mAh (noticed a dip indicating start of solid I2 buildup, so cut it there), discharged 180mAh. I am now charging to 150mAh at 30mA/cm2, normally I would see drops in capacity with cycling with Trieg at this level, we'll see if they happen. [image: 1747325869007-57810618-3e33-4f12-ad81-bc93fc620bcd-image.png] Seems to be stable now at 30mA/cm2. I will leave it cycling here longer, see if it starts decaying. [image: 1747325889390-778d48dc-3d94-4012-9de2-a0c45a4727b0-image.png] ok, went for 9 cycles with no issues at all. I am now going to cycle it to 1.65V, to the Nernst limit, see if it continues working equally well. Charging to 1.65V showed the weird start for the discharge curve, although with no apparent deterioration of the cycle characteristics after the first cycle. No evidence for solid iodine formation was present, so the solution is very well behaved. [image: 1747325914186-cc5413ce-ad2d-4ae5-b64d-ed8939f213cf-image.png] Test at 15mA/cm2 of the same cell. Some deterioration is now evident, charging to 1.55 V [image: 1747325934195-2dbc77b1-de09-4492-a3e2-5997e2517c81-image.png]

From Roth et al., Aalto University built a (sizable!) stack for all-copper and used ABS for their flow frames - I'd imagine it would play better with BPT tubing than the Zn-I chemistry also.

@gus @SamAuc ABS may work with an all-copper chemistry!

Hi Otmar! I think it would be helpful to see a rough schedule of the workshop and time allocations per topic/activity - then it would be easier to give feedback for the site, based on specifics of the activity the site is meant to complement!

Cloning the https://codeberg.org/FBRC/RFB-dev-kit repository, opening the assembly in FreeCAD, fixing part of it, then pushing the changes with VSCodium. As part of the Flow Battery Research Collective project at https://fbrc.dev 0:00 Cloning repository 3:29 Opening assembly file 4:09 Fixing the cell assembly 20:20 Pushing changes to repository

Doing some preliminary design for a flow frame that could be printed with a common FDM printer - side length 200 mm. More to come soon! [image: 1746549456826-0a9be9ec-5073-4eb6-b3c0-52c7a42e9e3c-image.png]

@kirk@spectra.video made a quick attempt at filming the assembly of a cell, in order to help out someone who was asking for more detail on the steps

Hi Otmar, welcome to FBRC and the project, looking forward to working with you!

@kirk said in How should we control the centrifugal pumps? TRIAC/thyristor etc? Need help from controls/electrical people: It seems to work! At least enough for testing purposes. Here is a video: https://spectra.video/w/8xipM8aXnBkDXnu4kkRpqT Here is the code for this test: https://codeberg.org/FBRC/RFB-test-cell/src/commit/d10834bc7dd67736e708c9a33832a5602ab3ca28/firmware/FlowrateRampTest.ino

Nice work, Daniel. I am thinking of plumbing solutions to the imbalance issue: From A review of all-vanadium redox flow battery durability: After studying the capacity fade for mixed acid electrolyte, UET [154] found that, during long‐term operation, the ratio of catholyte and anolyte concentration remained constant: 1.3:1. Based on this finding, they designed an overflow system with different volume (volume ratio: 1.3:1) anolyte and catholyte tanks, in which the volume ratio and total vanadium were kept constant. With the new design, the VRFB achieved long term capacity and efficiency stability. However, this design is only valid for the mixed acid electrolyte system. Recently, Wang et al [152] developed an electrolyte reflow method to solve the electrolyte imbalance issue for the sulfuric acidvanadium electrolyte system. Figure 10 shows the schematic of their method; without reflow, eventually all of the anolyte will move to the catholyte tank, while with reflow, the anolyte tank will always contain some electrolyte. Similar to the UET method, the volume ratio of catholyte to anolyte is a key parameter affecting the capacity stability and is highly dependent on the operating current density. Cycle life and total capacity were all improved with the reflow method. There is also Capacity balancing for vanadium redox flow batteries through electrolyte overflow but it was retracted - they think they accidentally had a pinhole in their membrane for the test. But they did build a real overflow system: [image: 1739741378711-aceadcdb-fb4d-4387-b6c6-9b95a79cc192-image.png]

That's great! Do you have a link to one or know where we could procure one to test?

Stephen Hawes of Opulo has compiled some of their tools here: https://midscale.io/docs The AutoBOM one seems to be based on those workflows above and looks pretty interesting

Reading the posts about the different pump designs, it makes more sense. More background reading to do. TY

Excited to try this in the dev kit one day... Though you mentioned that Mn(III)-EDTA might cause some trouble

@H4K1 no need to build the flow battery and test chemistry to help the project out! You can also build and test just with water, especially the larger cell we'll build. But if you can do CI/CD and firmware now then that's great! You'd be the only one on the project now with those capabilities, so a huge bonus. It will help make a framework that we'll benefit from as the project advances and hopefully save us some time as we improve and develop, so we can focus on what we're all best at and enjoy!