Bio-Derived Phytic Acid-Based Organic-Inorganic Hybrid Coating for Flame-Retardant and Thermally Stable Separators...

As lithium-ion batteries (LIBs) continue to evolve toward higher energy densities, increasing amounts of energy are stored within limited volumes, raising critical safety concerns. Among various battery components, separators play a critical role in battery safety by preventing internal short circuits, yet commercially used polyolefin separators suffer from severe thermal shrinkage and high flammability under elevated temperatures, which can accelerate thermal runaway. Herein, we report a flame-retardant separator by introducing an organic-inorganic hybrid coating onto a commercial polyethylene (PE) separator. The coating consists of boehmite inorganic particles and a cross-linked organic network incorporating bio-derived, phosphorus-rich phytic acid. Owing to synergistic condensed- and gas-phase flame-retardant mechanisms, arising from phosphorus-rich char formation and radical scavenging by phytic acid together with the endothermic reaction and ceramic barrier formation of boehmite, the resulting separator exhibits significantly enhanced thermal stability and flame retardancy. In addition, improved electrolyte wettability and interfacial stabilization enable favorable electrochemical performance and long-term cycling stability. This work presents a multifunctional separator design that simultaneously enhances thermal stability, flame retardancy, and cycling stability, providing a promising strategy for developing safe separator systems for LIBs.