Sodium-sulfur batteries are available commercially. They have good energy density but they have to be heated to 350C which makes them impractical for vehicles.

Sodium-sulfur batteries are available commercially. They have good energy density but they have to be heated to 350C which makes them impractical for vehicles. They're commonly used for grid storage. https://en.m.wikipedia.org/wiki/Sodium%E2%80%93sulfur_battery https://en.m.wikipedia.org/wiki/Sodium%E2%80%93sulfur_batter...