Designing the large-format cell

[kirk]

@Vorg

@Vorg said in Designing the large-format cell:

I'm 99% sure this is not possible, but maybe tossing it out there would give someone an idea for another direction to look. This problem of a shunt current makes my envision some sort of FET like object with a passage between source and drain to allow fluid to flow through it while a "gate voltage" pinches off current flow through it.

There are A LOT of different approaches out there for dealing with shunt currents---right now the approach I'm taking is "we'll cross that bridge when we come to it"---and the "long manifold" approach that balances the overall sum of [pressure drop] + [shunt current losses] seems like a promising passive approach, ie. not requiring moving parts or actively driven auxiliary electrodes. It is the most common approach I've seen commercial entities take, but that's not to say it's the best.

Like you describe, an "ionic diode" of sorts would be ideal!

There are approaches where people have passed "protective" currents through the manifold to cancel out the shunt currents, but it is an active control method if I understand correctly.

The shunt current protective currents were then passed through the protective electrodes inserted at the first and last channel/manifold node point connections. The shuntage currents through the channels were reduced/eliminated. The effects with the passage of protective current for a charge mode are shown in Figure 5. Similar data at other conditions are given in Zahn, Grimes, and Bellows, 1980.

Source: White, R.E. (1984). Electrochemical Cell Design, Springer US, Boston, MA

Chapter: SHUNT CURRENT CONTROL METHODS IN ELECTROCHEMICAL SYSTEMS - APPLICATIONS
Patrick G. Grimes and Richard J. Bellows
Advanced Energy Systems Laboratory
Exxon Research & Engineering Company Linden, New Jersey 07036

[danielfp248]

Just wanted to say I've made the first successful flow test of the large scale system. Kirk modified the flow frames to a much more simplified design for the flow path, which greatly reduced pressure and allowed flow without leaking. You can see the simpler flow path in the image below. Barbs were also added to the entry ports to prevent leaks around the hose due to pressure. Both flow frames printed water tight on my Prusa Core One.

For the first test I used a single pump and flowed tap water through both chambers. I used 4 layers of photopaper as a membrane material.

I tightened everything by hand and was actually missing washers on the backside (forgot to order enough, lol). Test went well, with over 30 minutes of flow at 5-10L/min with no leaks. At very high flow ~40L/min, I did start to see some leaks through the 0.1mm silicone gasket due to overpressure. With that said, this flow rate is extremely high, ready far above anything that we would ever need and was just a stress test.

For future reference I attach the configuration file used for these prints. large_scale_flowframe_config.txt

This is the filament I normally use https://www.smartmaterials3d.com/pp-filamento#/25-color-natural/27-diametro-285_mm/239-tamano-m_650g

[sepi]

@danielfp248 Amazing! You rock! Now I wanna see this power some real world device

[kirk]

Some preliminary CFD of the simplified flow frame (U in m/s and P in Pa if I understand OpenFOAM correctly)

Conditions

• 4 L/min volumetric flowrate through one half-cell, inlet is on the top left, outlet on the lower right.
• Ambient pressure on cell outlet
• No-slip wall
• File containing CAD and CFD simulation setup is here
  Blue is inlet, red outlet, pink is porous zone
  !

Close-up of mesh:

Flow Distribution (m/s)

Pletcher and Walsh say a range of 0.05-0.4 m/s linear velocity is a good design range for electrolyte flow, if I apply a smaller range for velocity with 0.05 m/s as the upper limit, we see which areas in red have sufficient flow and where the dead zones are (in the corners, predictably)

Pressure Drop (Pa)

Big Caveat

Still need to calculate the Darcy-Forchheimer coefficients to do the porous zone simulation in the graphite felt, right now I am using the default values, which are almost certainly not correct. If anyone feels like finding that data (https://openfoamwiki.net/index.php/DarcyForchheimer). I think Antoni Forner-Cuenca's group has measured a lot on this recently. This could change the results quite a bit as far as flow distribution and pressure drop. I've mostly so far just been getting familiar with the simulation pipeline in FreeCAD --> CfdOF --> OpenFOAM --> ParaView.

Design is far from final, and I'm probably doing the CFD incorrectly, BUT it prints and doesn't leak! We will keep optimizing the flow frame later.

[muntasirms]

Hey! This is incredible work. I noticed you guys are exploring the shunt current/pressure drop/residence time distribution issue of manifold design. This is well outside my expertise, but I did run into this paper a while back from Kyle Smith, who offered a manifold design (and methodology) to resolve at least the pressure drop/residence time issue. Here's the paper - let me know if you have trouble accessing it and I'm happy to send it along.

They use a tapered header channel with straight diffuser channels and achieve very even flow rate distributions (at Reynolds numbers < 10)

Not sure how well this prevents shunt currents but I hope this helps.

[kirk]

@muntasirms oh this looks great, I hadn't seen the paper! It's exactly what we need for the non-shunt-current related issues (which are another bridge for us anyway, down the road). An efficient manifold seems like it could be decoupled from the shunt current protection scheme also. I will try to implement it in FreeCAD.

[kirk]

The current collectors and endplates as-received from SendCutSend in the US, laser-cut and milled, respectively:

Some more pics:

[kirk]

Quick video of Daniel's leak test: https://spectra.video/w/bSYUyYpJVr34N92261cd6K

[muntasirms]

Out of curiosity, how are you guys attaching the tubing to the cell stack? are they glued on? hose barbs? Threaded piping?

I ask because leaks are my bane in a lot of my lab setups, even with super tight bolts and threaded fittings. I'm impressed at how well you guys have managed with flexible tubing!

[danielfp248]

@muntasirms They are just barbed fittings. These have worked surprisingly well at both scales.

[quinnale]

@kirk Had a few thoughts that I hope are helpful or probing at least. Disclaimer, fluids are not my strength. I'd be happy to hear more about your insights or goals here.

Colleague pointed out to me that there are correlations for different porous media geometries (e.g., see Fig 4 & Equation 2.6 and a bit more surrounding context in this paper for details https://link.springer.com/article/10.1007/s11242-020-01423-y). So if you have the permeability (and make some assumptions), you can have some bounded estimates of the coefficient.

I'm trying to digest the utility of the Forchheimer part of Darcy-Forchheimer. For a first-pass estimate of pressure drop, I'm willing to bet using Darcy's law is sufficient to approximate pressure drop (maybe the computational expense is smaller, and it's more instructive for a general audience IMO).

Regarding flow distribution: relating flow to performance I think will be challenging (there could be a lot of cell performance that is determined by other electrode complexities beyond whatever "inertial flow" does to transport of active species).

I'd also note that measuring the pressure drop directly could be relatively easy. We've done them with cheap pressure sensors such as these before: link. Maybe that could be of use and might be a way to check for inertial effects?

In any case, excited for the next steps in the modeling!

[danielfp248]

I'm finishing printing of the flowframes necessary for building the first stacked implementation. This will be a battery with three stacked cells. Each stack takes around 6mm of thickness. These are the files you have to print if you want a stacked implementation:

First would be blocked, then on top of that alternating through/mirrored as many times as you wish and then finally barbed at the end. For a 1kWh battery using Zn-I you would need 40 cells, so a total thickness of 24cm. I will start with a 3 cell stack, which will have a total thickness of around 2cm (counting current collectors).

[danielfp248]

All flow frames are ready now. I'll have to wait a couple of weeks for some graphoil to cut the bipolar plate material that goes between the cells. Picture of the 6 finished flow frames below. I won't be running this with any active material, as I have no place to safely do so, I will just be testing for leaks to test the basics of the stacked design.

If ran with active material the expected voltage of this system with Zn-I would be ~3.6V and the current needed to charge it in a reasonable time would be around 3.5A. The system would produce around 12.6W, power capacity would be around 60Wh, would require around 1.5L of catholyte and 1.5L of anolyte. This would be enough capacity to run a raspberry pi for 12 hours.

[sepi]

Wow, amazing news! Especially being able to power some real world device sounds almost unreal. I guess you didn't factor in the pump consumption though.

About the safe place to run it in. Could you not just put it in a plastic container? I'm not sure if it's easy to buy large PP containers that are not IBC containers.

[sepi]

said in Designing the large-format cell:

About the safe place to run it in. Could you not just put it in a plastic container? I'm not sure if it's easy to buy large PP containers that are not IBC containers.

https://www.fasswulf.de/products/300-l-ibc-container-kunststoff-palette-150-50-un-zulassung

This LDPE container might work (after cutting the top off ) even if LDPE might not be ideal for mong term storage of triiodide.

[danielfp248]

@sepi The problem is not so much finding containers that can be used, but what happens if there is any issue. If some hose unhooks or breaks or there is a leak, it is not safe to have 1L of concentrated iodine solution spilled at your house. I live in an apartment, so I'm unable to test anything that involves meaningful amounts of active material, just because it's unsafe to do so as leaks would put me and my family's health at risk. To test a prototype like this - with a lot of potential for leaks and problems at high volumes - I would require a safe working space where leaks can be handled appropriately and without contaminating areas I am in contact with on a daily basis.

[Vorg]

Don't know what you have there, but Target, Walmart, Home Depot, or even order from Amazon, Plastic storage bins. Just set the whole project in one. They come in clear so you can see in if there is a problem without removing the lid. If it spills, the fluid stays in the bin.

[danielfp248]

@Vorg A spill of a container full of charged electrolyte would off gas a lot of I2, which at those amounts is a big health risk. I sadly don't have a space where I could have that happen and then be able to ventilate that safely, nor do I have a spare room I could dedicate entirely to the project. So as far as I go, I will test with just water. We will likely get a space to do active material testing safely, but probably not until sometime next year. If any of you guys can do this testing safely and feel comfortable doing so, you can also take a shot! As with our kit, all the materials for this are open source.