A freeze-thaw molten salt battery for seasonal storage

Grid-level storage of seasonal excess can be an important asset to renewable electricity. By applying the freeze-thaw thermal cycling strategy, here, we report Al-Ni molten salt batteries with effective capacity recovery over 90% after a period of 1-8 weeks as a proof-of-concept. We explore three activation methods of the nickel cathode in a molten-salt battery: (1) heat treating the cathode granules under H-2/N-2, (2) incorporating a partially charged NiCl2/Ni cathode, and (3) doping the molten salt electrolyte with sulfur. In particular, sulfur doping, a cost-efficient method suitable for large-scale applications, is not only effective in activating the Ni cathode initially but also invaluable for energy retention during thermal cycling. Overall, these Al-Ni molten salt batteries under thermal cycling show high retention in cell capacity over weeks, setting a direction for scalable seasonal storage.