Flow Battery Research Collective

hey @DDM ! It's moving along slowly but surely. I had to move my lab around a couple times in the last months which has slowed things down a lot, just starting to get back to things! Doing some initial leak tests with water, seems like we may need beefier centrifugal pumps than initially thought to get sufficient flow (and/or I did a poor job on designing the flow frame!). I'll be ordering the next couple sizes up of the same type of pump to see how much of a difference that makes. Once we have good flow conditions the plan is to test the same Zn-I chemistry as the benchtop scale, but with about a liter of total electrolyte. Also need to get a battery cycler working for the larger currents needed at this scale, have two solutions for this right now, most likely is a MightyWatt electronic load I already have set up as a cycler (like here: http://kaktuscircuits.blogspot.com/2015/09/mightywatt-as-li-ion-charger.html).

Hi all, and apologies for the delay! This year has started off with quite a lot of administrative burden for me and I haven't had as much time for research as I anticipated. @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: Elektrolyte: The group noticed that two slightly different electrolyte compositions are mentioned. Sorry for the confusion, the correct mass composition can be found in the documentation here: https://fbrc.codeberg.page/rfb-dev-kit/electrolyte.html, the masses listed will prepare approximately 10 mL of electrolyte. @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: They assume an 880 ml volume for one single cell. Do you estimate this volume to maintain the obtained results until now? Is this the volume foreseen to achieve the 22 Wh/single large-format cell? Yes this would be correct volume scaling for the large-format cell, although of course still a lot smaller than an eventual life-size system! It is basically t]e volume that we will end up using for our tests of the large-format cell (still to come). @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: The group is assuming the EE value to estimate this. This value does not include energy demand from pumps and electronics, correct? Correct, these losses are often summed up in RFB literature as "balance-of-plant" or BoP if you want to search for some values. @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: Meaning: to store 1 Wh, 1.56 Wh needs to be taken from the grid (excluding electronics and pumps). Does this make sense, or are we oversimplifying here? You've got it exactly! @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: Used electricity For the same purpose of modelling the use phase, it is important to define from which country and what type of energy/electricity is being used to charge the electrolyte. Since the users of the FBRC battery can be anywhere, but are currently mostly centered in Europe, the group has decided to choose the European electricity grid mix data to represent the current FBRC reality. This makes sense to me. @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: The separator, for instance, would be one of these peripheral impacts, since it would need to be replaced after some cycles (probably faster than the electrolyte). Since cycle durability of photo paper is still unknown, the group will model different scenarios from 10–100 cycles in steps of 30 cycles. Do you feel this is a reasonable range? Do you already now conditions such as density and flow rate the larger cell will work with? The group will assume 4 layers for the larger cell although in some parts are 3 layers stated. While separators can be replaced, I am doubtful in an industrial system that they would, due to the labor costs. From my understanding, Li-ion lifetimes are often given as 2,000 cycles to 80% of initial capacity; for flow batteries, the data isn't as solid, but for VRFB the lifetime claims are more on the scale of 20,000 cycles or 20 years, whichever comes sooner (taken with a grain of salt...). We haven't done any testing that long-term, so don't have much for your to extrapolate, but RFB technoeconomic papers with operation and maintenance (O&M) costs incorporated would give you a good idea of membrane/pump replacement frequency (if ever). I would increase the cycle range to much longer terms, with the upper end in the 1,000s at least. We aren't yet locked-in on flow rates for the large cell as we are still settling on choice of pumps and flow field design. @Santiago-Eduardo said in Life Cycle Assessment (LCA) for the FBRC redox-flow battery: The current BOM and building instructions do not provide specific links to purchase the necessary chemicals. To model the electrolyte production, including the transportation of each chemical, the group has assumed the following production locations based on market data and worldwide production trends. If your own experience differs in this, please do not hesitate to comment. These assumptions all make sense to me; Daramic separator (which we also use in addition to paper depending on the test) can/is produced in the EU though not exclusively. I hope this clears things up for you all somewhat, and again, sorry for the delay!

@danielfp248 I always performed more cycles before starting 40 mA / 100 mAh charging (10 half-cycles at 20 mA / 10 mAh + 4–10 half-cycles at 30 mA / 10 mAh). The cell was also wet with demineralized water (leakage test). Could this also be the cause? I was also always using the membrane frame. Wouldn't the electrolyte leak through the paper membrane? @kirk Apart from solving the electrolyte leakage issue, does this "pulling-through configuration" improve the total capacity of the system in any other way? Also, I am wondering whether you are using the default membrane frame from the documentation (2 mm thick, right?) or a different one with another thickness and the 0.1 mm silicone gaskets.

Hi sepi, your refactor-modular works on my PCs: my mainPC (Kubuntut 2404) and two Notebooks for measurements (Kubuntu 2404 and Win11), thanks. I'm waiting for your calibration wizard. My hardware is waiting incl. Mystat, but till now I did not do tests.

@sepi Without the four-wire control the pump speeds are definitely harder to manage, sorry to hear that, though the PWM regulator may help. Can you visually see how different the rotation speeds are? That should be rough proxy for volumetric flowrate. I am not surprised they won't spin below 11 V. @sepi said in My build (very slowly progressing): Is this 20-40ml/min measured with the cell in line or just the pump. Ideally best to measure with the cell inline, to be closer to the actual conditions. However, as the tubing wears, this can drift, just FYI. Not a huge deal but something to be aware of. @sepi said in My build (very slowly progressing): Is the figure obtained with water or electrolyte? Water for now, just as a proxy, minimize exposure to electrolyte. This is kind of a 1, maybe 2 significant digit measurement, no more (the volumetric flowrate). @sepi said in My build (very slowly progressing): What would you recommend doing against the excess flow? @sepi said in My build (very slowly progressing): the left passing up to 40% more water at the same voltage. At the same voltage, is the left pump spinning at (nearly) the same rate as the right? if they are spinning at the same rotational speed and the left is passing 40% more water, it sounds like there is some flow restriction in the right pump's flow loop. If they have identical flow loops (in terms of pressure drop), and are set at the same voltage, I would guess that they should rotate at similar speeds, but this may not be the case for the brushed motors (e.g. variance in motor properties). What is important for testing, is that both pumps are above a minimum flowrate to ensure good mass transfer, and that the pressure imbalance between the two sides isn't too great as to cause transfer of electrolyte from one side to another through the separator. If the flowrates aren't perfectly matched but those two previous conditions are met, it's not a big issue, although it's just better for repeatability for them to be the same.

The tubing is gone now, thanks for buying at my store

@doho that's a great idea, I'll give it a try!

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!

@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.