Microcapsule Modification Strategy Empowering Separator Multifunctionality to Enhance Safety of Lithium‐Metal Batteries

Abstract The uncontrollable growth of lithium dendrites and the flammability of electrolytes are the direct impediments to the commercial application of high‐energy‐density lithium metal batteries (LMBs). Herein, this study presents a novel approach that combines microencapsulation and electrospinning technologies to develop a multifunctional composite separator (P@AS) for improving the electrochemical performance and safety performance of LMBs. The P@AS separator forms a dense charcoal layer through the condensed‐phase flame retardant mechanism causing the internal separator to suffocate from lack of oxygen. Furthermore, it incorporates a triple strategy promoting the uniform flow of lithium ions, facilitating the formation of a highly ion‐conducting solid electrolyte interface (SEI), and encouraging flattened lithium deposition with active SiO 2 seed points, considerably suppressing lithium dendrites growth. The high Coulombic efficiency of 95.27% is achieved in Li–Cu cells with additive‐free carbonate electrolyte. Additionally, stable cycling performance is also maintained with a capacity retention rate of 93.56% after 300 cycles in LFP//Li cells. Importantly, utilizing P@AS separator delays the ignition of pouch batteries under continuous external heating by 138 s, causing a remarkable reduction in peak heat release rate and total heat release by 23.85% and 27.61%, respectively, substantially improving the fire safety of LMBs.