Search

Electrospun fibrous membranes have been widely used for research of lithium-ion battery separators because of the high porosity, large specific surface area as well as excellent electrolyte wettability. However, little research has been focused on the puncture strength, which influences the safety of lithium-ion battery seriously. PPESK fibrous membranes with different thicknesses were fabricated by electrospinning technique, and the mechanical properties were improved by heat treatment, and the puncture strength of heat-treated PPESK membrane was tested using universal tensile testing machine and the linear relationship between the puncture strength of heat-treated PPESK fibrous membrane and the thickness was established. The further microscopic analysis of the puncture failure region was carried out to explore the puncture failure mechanism of heat-treated PPESK fibrous membranes. The result shows that the puncture process of isotropic heat-treated PPESK fibrous membrane is much tempered compared with PP microporous separator. The penetration of the heat-treated PPESK fibrous membranes was caused by the bend, deformation and fracture of PPESK fibers. The failure region of heat-treated PPESK fibrous membrane appears a circular hole, while the PP separator is long cracks. The puncture mechanism of heat-treated PPESK fibrous membrane is beneficial to prevent the destruction of lithium dendrites, but the puncture strength of heat-treated PPESK fibrous membrane remains to be enhanced.

In order to improve the mechanical property of traditional electrospinning fibrous membranes, PPESK-fiber/PVDF-bead composite membranes were prepared via simultaneously electrospinning of PPESK concentrated solution and electrospraying of PVDF dilute solution, and then hot pressed at 160℃. The membrane structure, tensile strength, ionic conductivity and cycling performance of lithium-ion batteries were measured by scanning electron microscope, universal tensile test machine, electrochemical work station and battery cycle system. The results show that the hot-pressed PPESK/PVDF composite membrane separator exhibits excellent liquid electrolyte wettability, ionic conductivity reaches 1.92mS·cm-1 at room temperature,PVDF beads are uniformly dispersed in PPESK fibers. The interfacial strength of PPESK fibers is effectively enhanced due to the melt of PVDF beads during the hot press process, hence the mechanical strength of composite membrane is leached 13.2MPa. In addition, cells assembled with PPESK/PVDF composite membrane show high discharge capacity and stable cycling performances.