Apploications Of High Voltage-Resist Poly(Ionic Liquid)s In The Electrolytes Of Lithium Ion Batteries

With the growing popularity of 5G applications,and the huge demand for safety batteries in electric vehicles,people put forward higher requirements for rechargeable lithium-ion batteries in terms of safety,energy density and environmental protection However.the traditional organic electrolytes have drawbacks,such as flammability,leakage and enviromnet toxity,which limits the development of lithium-ion batteries.Therefore,it is very necessary to develop an alternative advanced lithium-ion battery electrolyte.Room temperature ionic liquids composed of anions and cations have extremely low volatility,high ionic conductivity,high flame retardancy and excellent electrochemical stability have attracted much attention.The excellent physical and chemical properties of ionic liquids have a broad application prospect of the designing of green and safe,high energy(power)density and long-life lithium-ion batteries.In this paper,the effect of the chemical structure of ionic liquids on the electrochemical stability of ionic liquids was investigated,and the ionic liquid electrolytes which could withstand the high voltage of more than 5V were prepared and applied to lithium ion batteries.The ionogel electrolytes doped with inorganic solid electrolytes were prepared by selecting the optimal ionic liquid structure,and their physical and chemical properties and electrochemical properties were studied.The specific research contents are as follows(1)A series of ionic liquids with different N-substituents(cyano,benzyl,butyl,hexyl and octyl)were synthesized,and their electrochemical stability and degradation mechanism at high voltage were investigated.The influence of N-position of pyrrolidinium and piperidinium cations on their high voltage resistance were studied through theoretical simulation and experimental investigation.With the enhancement of the electron-donating ability of the substitutes,the high voltage resistance of ionic liquids is also improved Among them,1-hexyl-1-methylpyrolidinium bis(trifluoromethylsulfonyl)imide([C6Py][TFSI])exhibited excellent resistance to high voltage decomposition(>5.12V),showed great application potential in high voltage lithium ion battery electrolytes.(2)Organic-inorganic ionogel electrolytes composed of inorganic solid electrolyte Li1.4Al0.4Ti1.6(PO4)3(LATP),crosslinked polypyrrolium organic skeleton and ionic liquid/LiTFSI mixture were prepared,and its structure and physicochemical properties were studied.The results show that the ionogel electrolyte has excellent high temperature stability,high flame retardancy and electrochemical stability(decomposition voltage more than 5V)and compatibility with lithium metal.Among them,the addition of inorganic solid electrolyte can improve the mechanical strength of ionogel and provide a physical barrier for inhibiting the formation of lithium dendrite.When the content of inorganic solid electrolyte in ionic gel electrolyte is 5 wt%,the ionic conductivity increases significantly from 1.57 × 10-3 S cm-1 to 3.03 × 10-3 cm-1 S cm-1(80?),which shows great application potential in high voltage lithium metal battery applications in the future.