A Sb2O3-modified poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) fibrous membrane is prepared via a sequential electrospinning technique and used as a safe separator for lithium-ion batteries. A small amount of 2% Sb2O3 nanoparticles can effectively improve mechanical strength of the PVDF-CTFE membrane. Besides, the Sb2O3 modified PVDF-CTFE electrospun fibrous membrane exhibited synergistic flame retardancy as well as outstanding thermal stability without shrinkage at 160 degrees C for 2 h. Furthermore, the Sb2O3-modified PVDF-CTFE membrane as a composite separator possessed superior wettability toward nonaqueous electrolyte, higher ionic conductivity, lower interfacial resistance and well electrochemical stability compared to the commonly used polyethylene separator. Therefore, the Li||LiFePO4 cell using this type of composite separator exhibits excellent cycling stability and superior rate capability. These results suggest that the Sb2O3-modified PVDF-CTFE electrospun fibrous membrane is attractive for high-performance and high-safety lithium-ion batteries.