Room-temperature solid-state metallic lithium batteries based on high-content boron nitride nanosheet-modified polymer electrolytes

Polyethylene oxide (PEO)-based solid-state electrolytes have great potential in the development of solid-state metallic lithium batteries. However, it is difficult to apply them in metallic lithium batteries at room temperature because of the poor ionic conductivity and the lithium dendrite-induced safety problem. Herein, high-performance composite polymer electrolytes (CPEs) are developed by filling high-content boron nitride (BN) nanosheets with well dispersity in the PEO-LiTFSI matrices. Theoretical calculations and experimental characterizations reveal that the BN nanofillers with a strong Lewis acid property can capture TFSI− to release more free Li+, reduce the polymer crystallinity, and facilitate the generation of rich BN/PEO-LiTFSI fast-ion interfaces. Thus, the ionic conductivity and the Li+ transference number of the CPEs at room temperature greatly increase to 4 and 2 times those of the pristine electrolyte, respectively. Hence, the Li/CPE/Li batteries can operate steadily at 0.05 mA/cm2 (0.05 mAh/cm2) and 30 °C for 1200 h. Furthermore, the LiFePO4/CPE/Li batteries show higher initial capacity of 132 mAh/g and capacity retention of 84 % after 90 cycles at 0.3C and 30 °C than the pristine electrolyte-based batteries (29 %). This study provides a feasible case to prepare excellent-performance CPE films containing high nanofiller content for room-temperature solid-state metallic lithium batteries.