Molten salt electrolyte based high-temperature calcium metal batteries?

Clever electrolyte design is crucial for any next generation battery (NGB) technology in its infancy to enable leapfrogging. Using molten salt electrolytes (MSEs) in calcium metal batteries (CMBs) opens possibilities in terms of safety, abundance, and high-temperature applications. Herein, equimolar compositions of Ca(FSI) 2 together with the analogous Li-, Na-, and KFSI salts are combined in three ternary and one unique quaternary MSE, for which the mechanisms and limiting processes of metal plating and stripping in symmetric Ca||Ca cells are evaluated, using both a classic set-up and a method inspired by symmetric cathode tests. While Ca metal anodes still face issues with passivation layers, using MSEs can be feasible under the right conditions, and the combination represents a small steppingstone towards practical high-temperature CMBs. • High temperature galvanostatic cycling of symmetric calcium cells. • Compositional effects in cycling by multi-cationic molten salt electrolytes. • Reproducible cycling at high and moderate temperatures. • Unconventional symmetric anode tests inspired by symmetric cathode tests.