Boston-based startup Fourth Power, says its 2400°C thermal battery will be 10X cheaper than lithium-ion

The technology is reportedly ten times cheaper than lithium-ion batteries and far more powerful and efficient than any other thermal battery.

Which isn't saying much, really. It exposes "solar" cells to the white hot bricks to regain the energy, but that's going to be maybe 30% efficient. It also uses tin as the heating fluid, at least in the prototype, which is (in spite of popular confusion) a very rare metal.

It's an interesting idea, but I doubt this is going anywhere. Even pumped water or solid weights seems more practical, and sodium ion battery is apparently coming on the market as an option.