Galvanostatic cycling was performed either using a Solartron 1400 CellTest System or a Biologic VSP 150 potentiostat. The BiF3/BaSnF4/Sn-cell was cycled at 100 °C under ~180MPa stack pressure with a current density of 35 µA/cm 2 , and cutoff voltages 0.05 V and 1.2 V were set considering electrochemical stability of electrolyte material. Before cycling, the cell was heated up to the desired temperature and held for at least 4 hrs to reach thermal equilibrium.