In order to prepare a separator which had high electrolyte uptake and good thermal dimensional stability, the poly(phthalazinone ether ketone)(PPEK)/SiO2 electrospun membranes were prepared by electrospinning technology. The structures and properties of electrospun membranes and batteries were tested by SEM, electrochemical workstation, LAND battery cycle systerm and so on. The structures and thermal properties of the electrospun membranes with different SiO2 content were studied. The electrospun membranes were used as separators to assemble lithium ion batteries, and electrochemical performances and battery performances were studied. The results showed that electrospun membranes’ porosity, electrolyte uptake, ionic conductivity increased gradually with the increase of SiO2 content. The thermal shrinkage rate of PPEK electrospun membranes were 0 when heat treated at 200 °C for 1 h, which displayed good thermal dimensional stability. When the mass fraction of SiO2 was 6%, the porosity and electrolyte uptake reached 179% and 1031%, and ionic conductivity was 2.63×10-3 S/cm. Morever, the discharge capacity of electrospun membrane was 332~350 mAh/g, which exhibited better cycle performance and excellent capacity retention.