To investigate the impact of pressure, a second cell was cycled at 100 °C and ~ 180 MPa. The voltage-capacity plots as well as the trends of specific capacity and energy efficiency against the cycle number can be found in Figure ) and b). In first discharge, a specific capacity of about 222 mAh/g, 73 % of the theoretical capacity of BiF3 (302 mAh/g) was delivered, which is remarkably close to the first discharge capacity of the cell with no external pressure applied.