Preparation And Modification Of A Novel PVDF/HDPE Separator For Lithium Ion Battery By Non-solvent Induced Phase Separation(NIPS)Method

In recent years, widely attention has been paid to the safety problem of the liquid lithium ion battery, thus more and more studies which aim to improve the safety performance on the lithium ion battery are transferring to the separator or the polymer electrolyte. Until now, researches about the separator or polymer electrolyte are focused on two aspects:physical or chemical modification of macro-porous polyethylene separator and exploration of PVDF-based polymer electrolyte. In this paper, novel PVDF/HDPE separator for lithium ion battery was prepared by non-solvent induced phase separation method. HDPE, widely used as the substrates of separator, was made to particles and added to the PVDF to form the homogeneous casting solution for the first time. Also, the prepared separator was modified by metal oxide (alumina) and non-metal oxide (silica). The structures of prepared separator were characterized by SEM, XRD and TG, while the electro-chemistry performances were detected by LSV, EIS and charge-discharge tests, etc.First, the effect of PVDF concentration, PVP addition and HDPE addition on the structure and performance on the lithium ion battery was researched and the optimal condition of membrane preparation was determined. The results show that separator shows best performance is got when PVDF concentration is15wt.%, PVP2.5wt.%, HDPE1.5wt.%. Separator prepared under this condition has high ionic conductivity of2.2mS/cm, wide electrochemical stability window with decomposition voltage higher than4.5V. Half cells comprised of prepared membrane and LiCoO2shows good cycalbility and rate capability:initial discharge capacity of near150mAh/g, and91.4%of the capacity (from128mAh/g to117mAh/g) is maintained after50cycles under1.0C rates.Second, the modified membranes were prepared with inorganic particles of silica and alumina as additives, and the effect of addition on the thermal properties and electrochemical performance was also investigated. The results show that silica can significantly improve the battery performance of membrane and95.14%of the capacity (from131.7mAh/g to125.3mAh/g) is maintained after50cycles under1.0C rates when SiO2addition is1.0%; while Al2O3has no obvious contribution to the improvement of battery performance, and membrane show better performance when A12O3addition is1.5%:88.75%of the capacity (from130.7mAh/g to116mAh/g) is maintained after50cycles under1.0C rates. Thus, silica is more suitable for using in modification of PVDF/HDPE membrane.