Preparation And Performance Of Lithium-Ion Battery Separator With Thermal Shutdown Function

In recent years,the accidents such as ignition and explosion of lithiumion batteries occur frequently.The safety of lithium-ion batteries has gradually become the focus of attention.It is an effective way to solve the safety problem by preparing a functional separator of lithium-ion battery.The separator with thermal shutdown function can cut off the transmission path of lithium-ion at a certain temperature,thus ensuring the safety of lithium-ion batteries.The functional composite membrane is obtained by combining the polymer microspheres layer with low melting point and the polymer nanofibers membrane.It can be thermally shut down when the internal temperature of the battery increases,and the microspheres melt to form a dense polymer layer that can block ion transmission.In this paper,EVA microspheres with smooth surface and uniform size,were prepared by suspension dispersion method.The EVA microspheres were combined with PVDF electrospinning nanofiber membrane by dipping coating.The microspheres on the surface of the composite membranes are evenly distributed.EVA microsphere composite membranes with 5 wt%,8 wt% and10 wt% dip coating concentration are prepared by adjusting the concentration of EVA microsphere solution,and then the wettability and thermal shutdown property of the EVA microsphere composite membranes are investigated.Through a series of comparative analysis,it is concluded that the comprehensive performance of 8 wt% EVA microsphere composite membrane is the best,and its electrolyte uptake can reach 436 %.After heat treatment at90 ℃ for 20 min,its ionic conductivity can be reduced to 1.7 % of the original.Its discharge capacity decreases to 0.2 m Ah/g,this indicates that the battery has been shut off and cannot charge and discharge normally.The lithium-ion battery assembled with the composite membrane has good cycle rate performance.After 100 charge-discharge cycles,the capacity retention rate of the battery can reach 90.1 %,and the capacity retention rate at 4 C rate is56.9 %.The PVDF/PE/PVDF sandwich composite membrane with thermal shutdown function is prepared by combining PE particles with PVDF nanofiber film by electrostatic spraying.The porosity of the composite membrane is68.8 %,and the electrolyte uptake can reach 484 %.After heat treatment at110 ℃ for 20 minutes,the ionic conductivity decreases to 0.3 % of that before heat treatment.Its discharge capacity decreases to 0.03 m Ah/g at 110℃,it can effectively shut off the battery.The battery assembled by the sandwich composite membrane has excellent cycle and rate performance.After 100charge-discharge cycles,the capacity retention rate of the battery can reach92.2 %,the performance at higher rate is also very excellent.The capacity retention rate can reach 63.3 % at 4 C.In summary,EVA microsphere composite membrane and sandwich composite membrane are suitable for lithium-ion battery separators,they have good electrolyte wettability and cycle rate performance,which can effectively ensure the safety of lithium-ion battery.