A gel polymer electrolyte film based on chitosan derivative and ionic liquid for the LiFePO4 cathode solid Li metal battery

Solid electrolytes can improve the safety of Li metal batteries. However, the performance of solid electrolyte is still not satisfactory due to its poor high-temperature stability, low ionic conductivity, and poor interface stability/compatibility with electrodes. By combining chitosan-based polymer substrates with ionic liquids, we designed and synthesized two types of solid gel polymer electrolyte (SGPE, i.e., HA-BF4 and HA-TFSI) films. The optimal SGPE film (i.e., HA-BF4-80) exhibited good high-temperature stability (270 °C), high ionic conductivity (2.03 × 10−3 S cm−1 at 35 °C), and excellent interface stability/compatibility with electrodes. It had a wide electrochemical window of 4.60 V and high Li+ transport number of 0.54. With LiFePO4 as the cathode, the HA-BF4-80 SGPE film as solid electrolyte, and the Li metal as anode, the Li|HA-BF4-80|LiFePO4 displayed a higher specific capacity of 152 mAh g−1 and excellent cycle performance with a capacity retention of 82% even after 100 cycles underscoring the significant potential applications of HA-BF4-80 SGPE film in solid lithium metal batteries. This work would have an important value in the design and development of the high-performance SGPE films.