Composite Separator with Superior Thermal Shrinkage Resistance for the Safety of Lithium Metal Batteries

High‐energy‐density batteries have raised numerous safety concerns, particularly thermal runaway. Separators play an indispensable role in battery safety. Herein, an Al 2 O 3 ‐coated composite separator (LSO‐Al 2 O 3 @PE) with superior thermal shrinkage resistance is prepared with lithium polysilicate (LSO) as a binder. Different from the common organic binder, the binding force of inorganic LSO binder to Al 2 O 3 particles can be further strengthened through the in situ dehydration and condensation at elevated temperatures, significantly enhancing the thermal shrinkage resistance of the composite separator (∼ zero thermal shrinkage at 200°C). The LSO‐Al 2 O 3 @PE separator also demonstrates thermal shutdown and acid impurity scavenging properties, effectively improving the safety and cycling performance of lithium metal batteries. The Li|LSO‐Al 2 O 3 @PE|LiFePO 4 cells retains 70% capacity after 1000 cycles, and the Li|LSO‐Al 2 O 3 @PE|LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells retains 81% capacity after 200 cycles. This work provides a new solution to improve the thermal shrinkage resistance of commercial polyolefin separators.