A Composite Separator Combining High‐Temperature Resistance, Flame Retardancy, and Interfacial Regulation for High Safety Lithium Metal Batteries

The separator plays a vital role in preventing internal short circuits and thermal runaway in lithium metal batteries (LMBs). In the event of thermal runaway, an intrinsically flame‐retardant separator is of paramount importance for suppressing fire ignition and combustion, thereby enhancing the safety performance of the battery. In this study, an intrinsically flame‐retardant composite separator is prepared by coating flame‐retardant poly(pentabromobenzyl acrylate) (PPBBA) onto a polyethylene separator using an inorganic binder, lithium polysilicate (LSO). It has the advantages of high‐temperature resistance, flame retardancy, and interfacial regulation, greatly enhancing the cycling durability and safety performance of the battery. This composite separator exhibits no thermal shrinkage at 200°C and demonstrates excellent flame‐retardant characteristics. Meanwhile, PPBBA can weaken the coordination interaction between Li + and solvent molecules, improving Li + transport kinetics. Furthermore, PPBBA and LSO preferentially induce the formation of an inorganic‐rich solid electrolyte interphase layer containing LiBr and Li x SiO y , improving the interfacial stability of lithium metal anodes (LMAs). As a result, the Li||Li symmetric cell operated stably for over 1200 h, and the Li||LiFePO 4 battery exhibited a capacity retention of 88.8% after 600 cycles at 0.5 C . This work provides an effective strategy for the design of high‐safety separators for long‐life LMBs.