Preparation Of Nano-modified Uhmwpe Lithium Battery Separator

The separator is an important part of lithium-ion battery,which provides electrical insulation and microporous channels for the role of ion transport between the positive electrode and negative electrode.Capacity,cycle performance and safety performance of the battery have a direct relationship with the separator.Ultra high molecular weight polyethylene?UHMWPE?with its good performance has been widely used in the preparation of lithium-ion battery separator.However,UHMWPE separator also has some problems,such as low porosity,poor thermal stability and poor wettability,which need be modified.This paper describes the modified method of UHMWPE separator through electrospraying.In this paper,PVDF/UHMWPE composite separator,PVDF/SiO₂/UHMWPE composite separator and PVDF/KH570#SiO₂/UHMWPE?Silane coupling agent KH570 modified nano-SiO₂,referred to be as KH570#SiO₂?composite separator were prepared via electrospraying method.The surface morphology,porosity,thermal stability and electrochemical performance were thoroughly studied.First,the optimal electrospraying parameters of polyvinylidene fluoride solution,such as mass fraction of PVDF and electrospraying voltage were successfully determined by adjusting the voltage value and concentration of PVDF solution.The composite separator was prepared by electrospraying PVDF particles on the UHMWPE separator.The analytical results show that the porosity rate of the composite separator is increased from 46%to 73%.The first specific discharge capacity of the composite separator is increased by4.2%,and the separator has good cycle stability after 50 cycles,which could be used as lithium ion battery separator.Second,the addition ratio of SiO₂/PVDF was 0.1wt%,which was determined by studying the effect of the amount of nano-SiO₂ in the PVDF solution.The optimal electrospraying voltage was 23 kV,which was determined by studying the effects of different voltage on SiO₂/PVDF solution.The PVDF/SiO₂/UHMWPE composite separator was prepared by electrospraying under the optimal conditions.The analytical results show that the porosity rate of the composite separator is increased from 46%to 63%,and the contact angle is reduced from 30oto 10o.The composite separator was applied to assemble lithium-ion battery,and the results show that the first discharge capacity increases by 32.5%.The last,in order to improve the dispersion of nano-SiO₂ in PVDF solution and the microspheres reunification,nano-SiO₂ was grafted by the silane coupling agent KH570?CH₂=C?CH₃?COO?CH₂?Si?OCH₃?₃?.The PVDF/KH570#SiO₂/UHMWPE composite separator was prepared by electrospraying under the optimal conditions.The analytical results show that the first discharge capacity of PVDF/KH570#SiO₂/UHMWPE composite separator is increased by nearly 12%,exhibiting good stability after 50 cycles,which satisfied the requirements of lithium-ion batteries.