<scp>PVDF</scp> ‐ <scp>HFP</scp> / <scp>PI</scp> ‐ <scp> SiO ₂ </scp> composite sandwich separators for lithium‐ion batteries: Fabrication and post‐processing

Abstract PVDF‐HFP/PI‐SiO 2 three‐layer sandwich separators of lithium‐ion battery were fabricated by electrospinning and post‐processing. PI‐SiO 2 composite side layers were electrospun with 5, 10, and 15 wt% SiO 2 , while PVDF‐HFP was used as the middle layer. Then, mechanical/thermal post‐processing was applied on electrospun sandwich separators. Results showed that the addition of SiO 2 reduced fibers diameter, increased wettability, and improved mechanical strength of the PVDF‐HFP/PI separator. The separator with 10% SiO 2 has shown the highest tensile strength (21.1 MPa) and puncture strength (1.573 KgF). Differential scanning calorimetric, thermo‐gravimetric analysis, thermal shrinkage, and flammability results showed that PI‐SiO 2 /PVDF‐HFP/PI‐SiO 2 separators had excellent thermal stability with respect to PP separator, while these properties were improved with SiO 2 content. The fabricated sandwich separators had high air permeability and volumetric porosity of more than 63%. The discharge capacity of PI‐SiO 2 /PVDF‐HFP/PI‐SiO 2 was enhanced at high current densities, as it was improved from 117 to 125 mAh/mg at the discharge rate of 2C, by increasing the percentage of SiO 2 from 0 to 15 (wt%). Highlights Tensile strength was improved more than 500% by applying post‐processing. SiO 2 reduced fibers diameter, and improved wettability and mechanical strength. Capacity was improved from 117 to 125 mAh/mg at the rate of 2C with SiO 2 . Fabricated separators had ignition resistance compared to commercial separators.