I ask this because we are always talking about pack level energy density. I feel like a significant amount of weight comes from the tons of redundant metal battery casings. Yes, I know this is why Tesla is developing the 4680 to help alleviate this issue, but I've got to assume someone else is working on this. The only issue I can see is that most plastics would (even with excellent chemical corrosion resistance) be not suitable due to thermal decomposition tendencies of lithium ion cells. I do know that some plastics have extremely high melting points but probably pretty low glass transition temps. I figure carbon fiber may even be a good candidate, but we're trying to lower the cost per kWh, not send it to outer space. Perhaps fiberglass? I realize that plastics and related materials have much poorer thermal conductivity than metals and that'd present a cooling issue. I've got to think that some plastics have better thermal properties than others, though it could be that nothing really exists that has good thermal and chemical resistance as well as is a good thermal conductor. And yes I know the terminals of the cell would still have to be alloy.

Any thoughts? As I mentioned before I'm sure this has been thoroughly investigated already I just want to know what is preventing us from using something other than metals.