Fabrication and post-processing of PI/PVDF-HFP/PI electrospun sandwich separators for lithium-ion batteries

PI/PVDF-HFP/PI sandwich separators were prepared by electrospinning, and subsequent pressing and heat treatment were used to improve their properties. Morphology, porosity, air permeability, contact angle, and other specifications of the separators were evaluated. The results showed that heat treatment changed separator porosity and permeability. The pressed and heat-treated PI/PVDF-HFP/PI separators showed suitable air permeability (313.49 s) and higher porosity (71.57%) compared to commercial PP separators. Subsequent heat treatment improved tensile strength from 3.48 to 19.09 MPa. The use of polyimide as the sandwich in PI/PVDF-HFP/PI sandwich separator causes improved flame retardant properties and minimizes thermal shrinkage (2%). On the other hand, the use of PVDF-HFP as an intermediate layer with a melting temperature of 148-155 degrees C makes for a safe condition to shut down ta lithium-ion battery and prevents an explosion. Finally, a coin cell assembled with a pressed and heat-treated PI/PVDF-HFP/PI separator showed a discharge capacity of 176 mAh/g at the rate of 0.1C and had higher capacity at the rates above 2C in comparison to the commercial separator (PP).