Enhancing the Safety of Lithium-Ion Batteries with a Multifunctional Organic-Inorganic Hybrid Separator

As lithium-ion batteries (LIBs) pursue higher energy density, safety concerns grow due to the limited thermal stability of polyolefin separators. Most improvements suffer from a trade-off between thermal safety and electrochemical performance. Herein, we report an organic-inorganic hybrid flame-retardant (HFR) separator. A hierarchical porous layer of boehmite particles within a phosphorus-based polymer network is coated onto a polyethylene (PE) substrate via vapor-induced phase separation (VIPS) process. Ion transport is preserved by the hierarchical porosity and anion-interacting boehmite, while thermal shrinkage is effectively suppressed. Flame retardancy stems from phosphorus-based radical quenching and boehmite's endothermic decomposition. Furthermore, the HFR layer forms a phosphorus-rich cathode-electrolyte interphase (CEI) that stabilizes the cathode and improves cycling. This scalable design simultaneously enhances safety and performance for high-safety batteries.