Research On Solid-state Electrolyte Based On New Polymeric Ionic Liquid

Polymer solid-state batteries have wide application prospects in electrochemical energy storage devices due to their high safety,flexible design,and the like.However,the traditional polymer-based solid electrolyte has low ionic conductivity at room temperature because of its high crystallinity and poor lithium solubility,which leads to its high temperature dependence and limits its application.Therefore,it is an inevitable trend to seek new conductive polymers.Polymeric ionic liquids?PILs?,as a new type of conductive polymer,are a class of ionic liquid polymers formed by the polymerization of ionic liquid monomers,having anionic and cationic groups on the repeating unit,and combining the excellent performance of ionic liquids and polymers.PILs not only overcome the fluidity of ionic liquids,but also have the advantages of high electrical conductivity,good thermal stability,and controllable structure.As a conductive substrate for solid electrolytes,PILs can improve the ionic conductivity and electrochemical performance of solid electrolytes at room temperature.In this paper,two kinds of PILs were designed and synthesized,and the solid electrolytes were prepared by blending it with PVDF-HFP to study its electrochemical performance.The main research contents are as follows:?1?PIL-1:the poly(methyl methacrylate-1-vinyl-3-ethyl-imidazolium bis?trifluoromethylsulfonimide?][TFSI]was designed and synthesized,and its structure and physical properties were characterized by spectroscopic analysis.Solid state electrolytes were prepared by blending PIL-1 with PVDF-HFP.The effect of different content of PIL on the electrochemical performance of the electrolyte was investigated,and the electrochemical properties of the supercapacitor were measured.The results showed that the content of PIL-1 increased with the increase of the content of PIL-1.When the content of PIL-1 was 25 wt%,the supercapacitor showed excellent electrochemical performance.After 2000 weeks of cycle,the capacity retention rate was more than 80%.This shows that the superelectric properties of the blend solid electrolyte are improved effectively by adding PIL?2?PIL-2:the ether-functionalized poly(methyl methacrylate-1-vinyl-3-methylether-imidazoliumbis?trifluoromethanesulfonimide?[P?MMA+VIm+CH₂OCH₂CH₃?][TFSI]was designed and synthesised.The structure and physical properties were characterized by spectra.Several kinds of PIL PVDF-HFP blend solid electrolyte were prepared.The effects of plasticizer and lithium salt PIL on the conductivity of the mixed solid electrolyte were investigated.The mixed solid electrolyte with the highest conductivity was selected to be used in the lithium ion battery.The optimized conditions results showed that the mass ratio of polymer matrix,plasticizer and lithium salt was 1:1:0.2,and the PIL content is 20 wt%.Here,the room temperature ionic conductivity of the solid polymer electrolyte blend is up to 2.8×10^-4 S·cm^-1,and the Li⁺transference number is 0.76.Under the optimized conditions,the electrochemical performance of the blending solid-state electrolyte was studied in Li/LiFePO4 lithium battery.At 60°C,the discharge specific capacity still remained at138.5 mAh·g^-1,with 80%of the capacity retention,and the coulomb efficiency was91.3%after 100 cycles at 0.1 C in lithium battery.This means that the functional PIL-2 conductive polymer substrate can improve the electrochemical performance and cyclic stability of solid-state lithium batteries.