0
$\begingroup$

I'm a tech hobbyist, I'm not an engineer, I'm just a IT tech guy that edits Wikipedia and answers tech questions for fun. I am aware that pure solid nanocrystal formation is the primary cause of loss of rechargeable battery storage capacity over time. Rechargeable lithium-ion cells are typically operated in the 20% to 80% charge range, to avoid highly purified cell chemistry at the extremes of charge state that contribute to crystal growth.

These nanocrystals can also form tiny dendrite branches or spikes that burrow through and puncture cell separators, and then reach across and short the anode to the cathode, killing the cell and potentially leading to thermal runaway in consolidated parallel cell groups or large prismatic pouch/slab batteries.

Much of the work that goes into rechargeable battery engineering involves trying to prevent crystals from forming, with either in-solution chemical additives or nanoengineered surfaces that resist crystal growth. For example:

Understanding and Controlling the Nucleation and Growth of Zn Electrodeposits for Aqueous Zinc-Ion Batteries - https://pubs.acs.org/doi/10.1021/acsami.1c06131

 

Typically crystals will most easily come out of solution when there are nucleation zones, usually due to rough or sharp edges, or surface contamination.

It seems to me like the sharp cut or stamped edges of anode and cathode plates may be a significant contributing factor for nucleation. Is this an actual problem contributing cell aging and failure? If so, is there anything that can be done to prevent it?

There are some possible solutions that I can think of, but I don't know if these are feasible at a sub-millimeter scale with thin foil:

  • Physically roll the plate edge, to tuck the sharp edge inside a folded curl. Probably would not work for tight inside or outside angles beyond about 30 degrees, leaving an exposed sharp cut/stamp edge at the corners.

  • Apply a dip or paint coating along the edges of the plates to encapsulate the sharp edges. Could be done with liquid plastic, varnish, etc. This might be easiest before the plate is coiled into a cell structure, but it may also work after the cell plates have been assembled into a multilayer stack or coiled.

  • Smooth or deburr the cell plate edge after cutting/stamping. Is it possible to mechanically deburr thin and fragile metal foil without tearing it? Use a laser to heat, melt, and round off the edge of the foil?

  • Rather than cold-rolling thick metal plates into thin foil and then cutting/stamping the foil into the final tabbed cell plate shape, is it feasible to directly cast a thin metal foil cell plate with tabs, in a casting that is several meters long? (I'm assuming it's not possible, since the mold ejection mechanism may apply enough force to dent the casting and by itself create rough nucleation edges where the plate was ejected from the mold.)

$\endgroup$
2
  • $\begingroup$ Many problems with your casting idea. The first and most obvious: have you ever actually seen what finish a cast part has? Then shrinkage. Guess what that means for something super thin? Not to mention be horrendously expensive because you're casting one. at. a. time. Shrinkage is typically handled with risers but for risers to work the part has to cool towards the riser so that the reserve metal from the riser can replenish the parts that are shrinking. With very wide, thin part, that's probably not happening. Ejection is the least of your worries. $\endgroup$
    – DKNguyen
    Sep 25, 2021 at 5:23
  • $\begingroup$ "Thin wall casting" is only a google search away and nowhere near what could be considered to be a foil. $\endgroup$
    – DKNguyen
    Sep 25, 2021 at 5:26

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.