Optimization And Modification Of PVDF-HFP System Gel Electrolyte On Lithium-ion Battery

Lithium-ion batteries have attracted attention from many researchers,because of many advantages,such as high specific energy,high battery voltage,low self-discharge,long service life,and environmental friendliness.They have been widely used in electronic products,power tools,aerospace power and large-scale energy storage.Electrolyte is a key component of lithium-ion battery,and the gel electrolyte has both high conductivity of liquid electrolyte and high safety of solid electrolyte,and it is considered as the most promising electrolyte.In this paper,PVDF-HFP was chosen as the polymer matrix of the gel electrolyte,and the preparation and performance characterization of the PVDF-HFP system gel electrolyte on Lithium-ion battery were systematically studied.The gel electrolyte was prepared by solvent evaporation method and immersion precipitation method,and assembled into a lithium-ion button cell to test performance.It lays an experimental foundation for the optimization and modification of PVDF-HFP gel electrolyte,and innovatively attempts to influence the performance of gel electrolyte by urea and PVP co-doping.PVDF-HFP gel electrolyte was prepared by solvent evaporation method.By preparing three kinds of electrolytes with different raw material ratios,the effect of the ratio between PVDF-HFP,solvent,and plasticizer on electrolyte and battery performance was investigated.The best performance sample obtained was an electrolyte composed of10 wt%PVDF-HFP:80 wt%THF/acetone:10 wt%1 mol/L LiClO₄-EC/DEC,and its electrical conductivity was 1.06×10^-3 S cm^-1,and its chemical window was 4.5V,and the Coulomb efficiency of the assembled button cell was above 98%after 10 cycles of charge and discharge.The PVDF-HFP gel electrolyte was also prepared by immersion precipitation method.The best performance sample was obtained:the concentration of PVDF-HFP in the solution was 15 wt%,and the solvent was DMAC,and the coagulation bath was ethanol:water=4:6,v/v,and the solvent was immersed in the coagulation bath after volatilization for 30 s.its conductivity was 4.26×10^-3 S cm^-1,and electrochemical window was 4.6 V,and the Coulomb efficiency of the assembled button cell was close to 100%after 20 cycles of charge and discharge.In this paper,the two preparation methods of PVDF-HFP gel electrolytes were systematically studied,and the electrolyte properties of the prepared PVDF-HFP gel electrolytes were compared.Compared with the immersion precipitation method,the solvent evaporation method is simple,but it needs to be operated in the glove box all the time,which increases the difficulty of the experiment and is easily affected by other volatile solvents in the glove box during solvent evaporation,thus increasing uncontrollable factors.Caused the problem of low repetition rate of the experiment.The immersion precipitation method needs to submerge the coagulation bath,which increases the complexity of the experiment and has many experimental parameters,but the experimental repetition rate is higher than the solvent evaporation method.The PVDF-HFP gel electrolyte was optimized and modified by added urea and polyvinylpyrrolidone?PVP?on the basis of immersion precipitation method.The electrolyte prepared by added urea and the electrolyte prepared by added PVP were quite different in terms of structure,and this result was confirmed the effect of additives on the structure and properties of the electrolyte.When the additive is urea and PVP co-doped with the same ratio,the electrolyte performance is optimal:conductivity is 6.10×10^-3S cm^-1,electrochemical window is 5V,the assembled battery is still normal after 20 cycles.