Application Of Acetonitrile Electrolyte Based On Pyyole And Imidazolium Ionic Liquids For Supercapacitor

Six kinds of pyrrole and imidazolium ionic liquids,l-ethyl-2,3-dimethylimidazoliumbistriflimide(EDMITFSI),1-ethyl-2,3-dimethyl imidazolium tetrafluoroborate(EDMIBF4).N.N-dimethylpyrrolidinium bistriflimide(DMPTFSI),N,N-dimethylpyrrolidinium tetrafluoroborate(DMPBF4),1-ethyl-1-methylpyrrolidiniumbistriflimide(EMPTFSI)and 1-ethyl-1-methylpyrrolidiniumtetrafluoroborate(EMPBF4).were designed and synthesized.These compounds were chracterized by 1H NMR and IC spectra.The testing results of trace impurities showed that the synthesized ionic salts met the quality requirements of supercapacitor electrolyteIt was found that high conductivity could be obtained when these pyrrole and imidazolium ionic liquids dissolved in acetonitrile.By comparing the conductivity of electrolyte based on TFSI and BF4 systems,there existed systematic bias in comparison with molar concentration,where mass concentration was more objective.Through the study of the conductivity of the electrolyte,the following results were obtained:(Ⅰ)it.was found that the conductivity of electrolyte of ionic salts was parabolic with concentration at a certain temperature;(Ⅱ)the conductivity was linear with temperature at a certain concentration;(Ⅲ)there was a model(σ=A1 x C2+B1×C+B2×C×T+C1×T+C2),which could better express the relationship between the concentration,temperature and conductivity of pyrrolidine and imidazole ionic liquids acetonitrile-based electrolyte.The model can be used for calculating the conductivity of electrolyte.The results showed that this function model has the recovery of 95%-107%in temperature range of-40～40℃,which was reliable enough to replace the observed data.Based on the model,the 95%max conductivity-temperature-concentration diagram was established to simplify the optimization work of electrolyte recipe.Supercapacitors were prepared from the electrolyte with optimized formulation,and their charge-discharge performance were studied at 2.7 V,100 C,20000 and 3.0 V,100 C,15000 cycles.The performance of capacitance,internal resistance,capacitance drop rate and internal resistance rise rate were analyzed,which showed that the electrolytes prepared by pyrrolidine tetrafluoroborates were significantly better than those by imidazole bistriflimides.The electrolyte prepared by DMPBF4 showed excellent performance in capacity and internal resistance.In this thesis,the electrolyte extract was obtained by dismantling the capacitor after different cycling conditions.The di/dV-V curve derived from LSV performance of these ionic liquids electrolyte after high voltage cycling was studied.Redox fluctuation of the di/dV-V curve derived from LSV showed that pyrrolidine tetrafluoroborates had smaller fluctuation size than bis(trifluoromethylsulfonyl)imines,proving the pyrrolidine tetrafluoroborate system was better in matching with materials of this kind supercapacitor.It is found that the comparison of redox fluctuation of cell extract-electrolyte is a new evaluation method to judge the matching between electrolyte and material.