Electrochemical performance of the all-solid-state lithium battery at 60°C with the polymer-in-salt electrolyte, the lithium-metal anode, and the LiFePO4 cathode. (a) Charge/discharge profiles of the cell at different current rates. (b) Specific discharge capacity and coulombic efficiency of the cell at different current rates. (c) Charge/discharge cycling stability of the cell at 0.2 C rate. (d) Electrochemical impedance spectra of the cell before and after the charge/discharge cycling test.