Synergistic Microstructure and Thermal Regulation via Multifunctional Flame-Retardant Separator Design for High-Safety Lithium Metal Batteries

Lithium metal batteries (LMBs) are expected to increase energy density due to the high capacity and low electrode potential of lithium metal. However, lithium dendrite growth and organic liquid electrolytes exacerbate the risk of thermal runaway. To improve the safety of the battery, a multifunctional flame-retardant separator was developed through the synergistic effect of decabromodiphenyl ethane (DBDPE)/Al 2 O 3 nanoparticle composite modification. Among these, DBDPE acts as a flame retardant to reduce the combustibility of the battery, while Al 2 O 3 with high mechanical strength inhibits dendrite growth, and its amphiphilic nature favors the uniform distribution of lithium ions. Thus, a multifunctional flame-retardant separator simultaneously achieves excellent flame suppression, enhanced thermal conductivity (71.3 mW·m –1 k –1 ), and excellent electrochemical performance. Lithium (Li) symmetrical batteries based on this separator stably run over 500 h at a current density of 0.5 mA·cm –2, and Li/LiFePO 4 batteries retain a capacity of 138 mAh g –1 capacity over 100 cycles at a rate of 0.5 C. This flame-retardant separator design, leveraging synergistic regulation of microstructure and thermal properties, provides a groundbreaking roadmap for suppressing thermal runaway while maintaining electrochemical performance, thereby redefining safety paradigms for next-generation high-energy-density battery systems.