A Thermally Conductive Separator for Safe Lithium Metal Batteries

Lithium metal batteries (LMBs) have demonstrated potential for energy storage but face significant thermal safety concerns. Here, we report a thermally conductive trifunctional separator, composed of hexagonal boron nitride and poly(vinylidene fluoride)-hexafluoropropylene (BN/PH), as a dendrite suppression layer, temperature regulation layer, and thermal protection layer to enhance the thermal safety and electrochemical performance of LMBs. The customized BN/PH separator shows a Li+ transference number (0.55) and promotes uniform lithium deposition, resulting in 1800 h cycles in the Li/Li symmetric cell with low overpotential (14 mV). Importantly, it demonstrates a thermal conductivity of 117.76 W m–1 K–1 in the XY-plane for rapid heat dissipation and prevents short circuits at elevated temperature (>180 °C), significantly increasing the thermal runaway onset temperature from 119.3 to 196.7 °C in cycled pouch cells. This work underscores the critical role of thermally conductive separators in ensuring the thermal safety of LMBs.