The commercial polyolefin separators still possess two well-known drawbacks: poor wettability and thermal stability. Herein, a thin and lightweight silica filled in polyimide (PI) nanofibers membrane is prepared by electrospinning. Without any binders, the nano-silica particles are firmly embedded in the PI nanofibers with high structure stability. The PI-SiO2 membrane with high porosity (90%) presents enhanced conductivity due to the excellent electrolyte wettability and large electrolyte uptake (about 2400%). In addition, the PI-SiO2 membrane displays good mechanical flexibility and enhanced thermal stability up to 250 degrees C, which significantly improve the safety of lithium-ion batteries when used as a separator. The LiMn2O4/Li cell with the PI-SiO2 separator exhibits highly improved rate capability and cycling stability at different temperatures (25 degrees C and 55 degrees C), which make PI-SiO2 membrane as a promising secure separator candidate for high-performance and safety lithium-ion batteries.