[gpm]

I don't think it's a dumb question at all. Storing thermal energy separately from electrical energy would make plenty of sense if we could store the thermal energy better (cheaper, lighter) than the electrical energy.

A quick search suggests that sodium acetate used like this stores 230kj/kg (i.e. 64 Wh/kg in the units used for batteries) [1] which is significantly worse than the sodium ion batteries being discussed. Same order of magnitude though, so maybe there's a better material that would make it work.

[1] https://www.sciencedirect.com/science/article/abs/pii/S13594...