In this study, PPESK/PVDF/PPESK tri-layer composite separators for lithium-ion batteries were prepared by electrospinning technique. The physical properties, electrochemical performances and thermal properties of composite separators were investigated. Results indicate that PPESK/PVDF/PPESK separator displays good wettability in liquid electrolyte. The electrolyte uptake of PPESK/PVDF/PPESK separator is much higher than that of electrospun PVDF, which leads to higher ionic conductivity of PPESK/PVDF/PPESK separator than PVDF separator. Discharge capacity of the cell assembled with PPESK/PVDF/PPESK separator is increased by 50 % than that with PVDF separator. Initial charge-discharge efficiency and capacity retention property of the cell with PPESK/PVDF/PPESK are better than those with PVDF separator or PPESK separator. In addition, when the mass ratio between PPESK and PVDF resins is increased to 4:3, PPESK/PVDF/PPESK separators show good thermal dimensional stability even thermally treated at 180 A degrees C for 1 h.