Abstract: Lithium-ion batteries, renowned for their high energy density, robust cycle life, and environmentally friendly profile, have found extensive applications in sectors such as electric vehicles, consumer electronics, and energy storage systems. Despite their widespread adoption, the increasing frequency of safety incidents during lithium-ion battery usage in recent years has cast doubt on the safety and reliability of this clean energy technology. Polyethersulfone (PES) membranes demonstrate superior dimensional stability at elevated temperatures, along with exceptional flame-retardant properties. In this work, PES-based separators were fabricated via electrospinning, yielding membranes with optimized porosity and enhanced electrolyte wettability. Through the application of in-situ growth techniques, a SiO₂ layer was uniformly coated onto the PES nanofibers, enhancing both the mechanical properties and thermal stability of the separators. The inorganic SiO₂ nanoparticles undergo polycondensation and cross-linking under high temperatures, forming a Si—O—Si network that effectively inhibits combustion, thus imparting flame-retardant capabilities to the membranes. The microstructure of the composite membranes was systematically characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).Flame retardancy was assessed via ignition testing, revealing that the PES/SiO2-1.5 membrane demonstrated superior flame resistance, along with remarkable electrochemical performance.