PVdF/SiO2 composite nonwoven membranes exhibiting high safety (thermal stability), high ionic conductivity and excellent electrochemical performances are firstly prepared by electrospinning poly(vinylidene fluoride) (PVdF) homopolymer and silicon dioxide (SiO2) sol synchronously for the separators of lithium-ion batteries (LIBs). Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and hot oven tests show that the PVdF/SiO2 composite nonwoven membranes are thermally stable at a high temperature of 400 °C while the commercial Celgard 2400 PP membrane exhibits great shrinkage at 130 °C, indicating a superior thermal stability of PVdF/SiO2 composite nonwoven membranes than that of Celgard membrane. Moreover, the composite membrane exhibits fairly high ionic conductivity (7.47 × 10−3 S cm−1) that significantly improves the performance of LIBs. The PVdF/SiO2 composite membranes are also evaluated to have higher level of porosity (75−85%) and electrolyte uptake (571−646 wt%), lower interfacial resistance compared to the Celgard separator. The lithium-ion cell (using LiFePO4 cathode) assembled with the composite membrane exhibits more stable cycle performance, higher discharge capacity (159 mAh g−1) and excellent capacity retention which proves that they are promising candidates for separators of high performance rechargeable LIBs.