Once solid state batteries are produced at scale it will truly be game over for ICE vehicles. Meanwhile the European and US manufacturers just whine and cry for protectionism while sitting on their hands.
Which will also mean a renaissance for classic vehicles for EV conversions. Currently the EV market is too small to really support them, but as EVs start hitting junkyards, it will become a big deal.
There are multiple US firms that are actively researching solid state batteries. I think at least one is in the manufacturing scaleup research phase. The auto manufacturers aren't generally into the cell research business and they don't need to be. Once a firm begins mass manufacturing, the autos will buy the output and use it in their cars. Protectionism is needed for other reasons. Meanwhile they're all working on their platforms.
That would be QuantumScape. It seems like they are well on the way to commercialisation but with stuff like that it's always "I'll believe it when i see it".
Depends on who you ask. The main advantage is better cycle life and being able to charge faster. That will address the concerns most people have about EVs. There will also be advantages in energy density and manufacturing cost but right now it's really difficult to say where we'll land in that regard.