Flow Battery Research Collective

Here is a video of assembling the large-format cell. https://spectra.video/w/m9RKg1QWrFdkkn9qUBFMTS FYI, you are meant two use two endplates per side (I used one here), I intentionally left the graphite felt out as this was for leak-testing, and the cell is missing washers on one side. The video illustrates the basic process of assembling our cell and how it is designed and seals. All the design files are available at https://codeberg.org/FBRC/RFB-large-format-cell. The setup is essentially there, waiting on chemicals and sorting out the power electronics set up and we should be able to run our first real charge/discharge tests with this large-format cell! The work to get to this point has been supported by the NGI0 Entrust Fund, a fund established by NLnet, to whom we are very grateful!

@gus said in Following your documentation – feedback & questions: I’ve returned to testing the flow cell and even built a second one to check repeatability. I’m wondering what could cause such a large difference in performance between them. Hey, welcome back! As sepi said, please upload the correct firmware to the MYSTAT as an outdated version was previously present in the repo, also be sure to recalibrate your MYSTAT before cycling again, this is likely the source IMO. It wouldn't be bad to add some sort of calibration reminder/routine into the MYSTAT software... @sepi said in Following your documentation – feedback & questions: Good luck with your further investigations! You might want to rzun your future experiments in a transparent PP box in the future. I will for sure once I'm ready for actual electrolyte. Definitely a good idea! @gus said in Following your documentation – feedback & questions: The next day, when I returned to the workshop, both tubes from the pumps had detached from the cell, and the electrolyte had spilled on the table. Do you have any idea what might have happened? Ah shoot, sorry to hear this. I suspect if the MYSTAT was out of calibration it may have caused issues with the cycling. An issue with the iodide-containing chemistries is possible clogging of the felts with iodine if something goes wrong; normally the triethylene glycol should prevent this by forming a soluble complex, but it's possible your system got outside the normal operating range. I'd try again fresh (in a PP box/spill tray/secondary containment), with a calibrated MYSTAT running the latest firmware. Tagging @danielfp248 in case he has any suggestions.

No worries! Good luck and let us know how it goes. Internal leakage is a pretty common issue to have when you're getting your first cells set up and debugged!

Charging to 6Ah/L at 30mA/cm2 and discharging at 5mA/cm2. At most we only get 2-3 Ah/L of available capacity, same as if we charged to 4Ah/L. [image: 1758211363268-f3e1b8fc-98a1-4c8b-b305-b4d4a5bedee6-image.png]

This test showed some deterioration on cycling: [image: 1758097795042-c586de1d-8d24-4884-bd7a-a00afb789080-image.png] I took out the catholyte and anolyte when charged (you can see the anolyte (left) and catholyte (right) in the pictures below). There isn't any hydroxide precipitation in either one. However there are some pieces of detached Fe metal on the anolyte, which I think are what causes the slight loss in capacity and increases in ohmic resistance as a function of time. [image: 1758097834649-5ee56443-1754-4f62-9a96-83d6194304ca-image-resized.png]

My pumps didn't have them, only the ones built into the pump. I saw that on some of your pictures, you have additional fittings between the different elements, I guess to make it easier to connect and disconnect the cell. In the end, it might make more sense to just shrink the barbs on the flowframe and/or tank a bit so the tubing comes off mor easily.

Congratulations, that's great to hear!

@sepi Thanks for trying this. I understand what you mean, I had similar issues when I tried to do this before. The main issue is that the fit is quite tight, so depending on the resolution of both the sleeve and the hole on the endplate, you can have too low of a tolerance for it to work. The easiest fix is probably to increase the size of the holes on the endplate around 0.25mm, so that this works regardless of the printer. We will make the modification on the official endplate exported files so that this approach works more easily.

@danielfp248 huh, that makes a lot of sense.

@danielfp248 ah, that makes sense as a last resort measure but would it not be nice to not lose charge? Well it all depends on how easiy it is to counteract by setting a different flow for the different electrolytes.

@Vorg We will slowly get there but no, right now we don't have any kWh capacity battery. As I mentioned, it will be several years before we get there. The fun is to walk this path and make everything open source on the way.

@sepi Hi, if you do the selling of the tube, I would order 2 (two) meters.

@danielfp248 sorry, my question was not well formulated. I meant a potential between the electrolytes inside the cell independently the possibility of measuring them using an electrode. Or to formulate it differently, if you cut through the cell (lile you cut a sandwich) and plotted the electrical potential between the electrodes, how would it look like?

@czahl I am a huge fan of trying this, especially for the larger format where setups are likely to be more permanent. As kirk mentioned we have never actually tried it, so please let us know if you do!