Solid state isn’t so much a new battery built from the ground up, rather the use of some form of pure Silcon, carbons or metal, as the batteries Anode material, instead of most commonly used graphite.
Semisolid state batteries, which use a gel type material for rapid ion diffusion are also another type of solid state battery. Battery manufactures see semi solid state batteries as offering nearly the same benefit as solid batteries but with an advantage: They are closer to commercialization and will allow 600 -700 miles between charges. WeLions new battery can go upto 621 miles and is expected in 2025or sooner. Nio will use WeLion.