A thermally managed separator for lithium metal batteries operating safely above 100 °C

Safety is an essential concern in the ongoing pursuit of high-energy-density batteries. As one of the most promising energy storage systems, lithium metal batteries (LMBs) are still plagued by the dendrite growth and associated high risk especially in high-temperature environments. Herein, we have designed a thermally managed separator by hybridizing polybenzimidazole (PBI) with AlN nanowires (PBI-AlN), which shows the merits of heat resistance, nonflammability, and enhanced thermal conductivity. This design promotes dendrite-free plating and ensures the safe operation of LMBs over 100 °C. At room temperature, the Li|Li symmetric cell with the optimal PBI-AlN700 separator presents an ultralong lifetime over 10000 h with an ultralow overpotential of ≈16 mV at 5 mA cm⁻² with 5 mAh cm⁻². At the high temperature of 120 °C, the Li|LiFePO₄ coin cell with PBI-AlN700 separator still has a large specific capacity of 148.9 mAh g⁻¹ at 1 C. The corresponding pouch cell can steadily light the lamp arrays under repeated bending/restoring states and work safely over 100 °C, showing the flexibility and high-temperature stability of the PBI-AlN separator. This study provides a novel separator to enable the safe operation of LMBs at high temperatures and proposes a strategy for separator design from a thermal management perspective.