I just figured out that they are called “Aqueous Hybrid Ion Battery” in English, so they are not the molten ones.

I didn’t find a lot about them, but this website seems to have an overview about them (although they are the main manufacturer of the batteries, so they are probably biased): https://www.aquionenergy.com/technology/aqueous-hybrid-ion-ahi/#What_Are_Saltwater_Batteries_and_How_Are_They_Different