Research On Electrochemical Performance Of Polymer Electrolyte Based On Ion Liquid And Its Application In Rechargeable Battery

Due to the advantages of large specific surface area,high flexibility and good compatibility with electrode,the application of polymer electrolyte in battery has always been a hot topic.However,the low ionic conductivity and poor electrochemical stability of polymer electrolyte hinder its development,so it needs further modification.In this paper,two kinds of polymer electrolytes based on ionic liquid were prepared with Poly(methyl methacrylate)(PMMA)as polymer matrix by solvent-free preparation process and different modification methods,which were applied in lithium-ion battery and dual-ion battery systems respectively.The electrochemical properties of polymer electrolytes and the energy storage mechanism of batteries were analyzed and discussed.The specific research contents are as follows:(1)The gel polymer electrolyte was prepared by blending PMMA with Pyr₁₄TFSI adding Li_0.33La_0.56Ti O₃(LLTO)and nano Si O₂as fillers,and used in Li Fe PO₄/Li battery.The effects of different proportions of LLTO on the electrochemical performance of polymer electrolytes were investigated,and the prepared polymer electrolytes were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetry(TG),infrared spectroscopy(FTIR).The results showed that LLTO is evenly embedded in the electrolyte,and the addition of LLTO and Si O₂can reduce the crystallinity of the electrolyte,and enhance the movement of the segments,further enhance the ion conductivity.The electrochemical workstation and electrochemical test system were used to characterize the electrochemical performance of the battery.The results showed that MMA-Pyr₁₄TFSI-3 wt%LLTO polymer electrolyte exhibited the best performance,its ionic conductivity reached4.51×10^-3S/cm,the initial discharge specific capacity reached 150 m Ah g^-1,and the capacity retention rate reached 90.7%.And the electrochemical window reached 5.0 V,which showed good electrochemical performance.(2)A polymer electrolyte was prepared by blending PMMA with ionic liquid EMIm TFSI in a certain proportion,which was applied in dual-ion graphite batteries.Scanning electron microscopy(SEM),X-ray diffraction(XRD)and Raman spectroscopy(Raman)were used to characterize the positive and negative graphite electrodes under different charging and discharging conditions and before and after cycles.It was found that the cation EMIm⁺and anion TFSI^-in the electrolyte had reversible intercalation and exfoliation reactions on the positive and negative graphite electrodes respectively,and even performed well after 100cycles.Meanwhile,the dual-ion battery was characterized by electrochemical test system and electrochemical workstation.The results of electrochemical experiments showed that the specific discharge capacity of 46 m Ah g^-1can be obtained at 100 m A g^-1current density under the electrochemical window of 1.0-4.0 V,and the battery still showed good cycle stability after 100 cycles,and showed a wide electrochemical window of 4.5 V.Compared with the pure ionic liquid EMIm TFSI,the self discharge phenomenon of the polymer electrolyte dual-ion battery has been significantly improved.