Supercapacitors aren't that useful for grid storage. The energy density is very low. They have a very high power density which allows them to produce or store

Supercapacitors aren't that useful for grid storage. The energy density is very low. They have a very high power density which allows them to produce or store enormous amounts of energy in a short time, but that's not really a problem that needs to be solved if you're already using some sort of lithium ion battery which already have a power density that's way beyond what you'd need in that application. Cylindrical cells are fine as long as they can be made cheaply and the costs (economic and environmental) can be amortized over a long life. We'll probably start seeing more LFP batteries in coming years, which are more ideal for grid storage. (They're cheap and have a long life.) Battery recycling needs to improve, but we'll probably get there eventually. Right now the volume of batteries that need to be recycled is just not very big. The Nissan Leaf, for instance, was only just released in 2010. Most of the EVs that have ever been manufactured are only a few years old.