Application Of Organic System Electrolyte In Electric Double Layer Capacitors

The purpose of this paper is to prepare the electrolytes for Electric Double Layer Capacitors(EDLCs)with high specific capacitance and high working voltage.The research work of N,N-Dimethylpyrrolidinium tetrafluoroborate(P11-BF4),N-Ethyl-N-methylpyrrolidinium tetrafluoroborate(P12-BF4),Tetraethylammonium Tetrafluoroborate(TEA-BF4),1-Butyl-1-methylpyrrolidinium tetrafluoroborate(P14-BF4),N-(2-Methoxyethyl)-N-methylpyrrolidinium tetrafluoroborate(P12O1-BF4)electrolytes has been carried out.This work studied the influence of the size of electrolyte salt ions,the introduction of ether bonds on cationic alkyl chains on the conductivity of electrolyte,the electrochemical window,further the influence of these factors for voltage withstanding characteristics and mass specific capacitance characteristics of EDLCs were systematically studied.In this work,all electrolyte salts were prepared by two step method.With propylene carbonate(PC)as the solvent,the electrolyte salts were arranged into PC with the concentration of I mol/L.The EDLCs were assembled with activated carbon(YP-50F)as the electrodes.First,1 mol/L P11-BF4/PC,1 mol/L P12-BF4/PC and 1 mol/L TEA-BF4/PC were used to study the effect of the size of electrolyte salt on the electrochemical performance of EDLCs by cyclic voltammetry.constant current charge discharge test and AC impedance test and so on.Then 1 mol/L P14-BF4/PC and 1 mol/L P12O1-BF4/PC electrolytes are compared to study the influence of the ether bond on the working voltage and Specific capacitance on the cationic alkyl side chain.The results show that:(1)The electrolytes of 1 mol/L P11-BF4/PC.1 mol/L P12-BF4/PC and 1 mol/L TEA-BF4/PC were prepared respectively as electrodes to assemble EDLCs,the effects of electrolyte size on the electrochemical performance of EDLCs were investigated.The results show that:these three electrolytes have almost the same electrochemical window(5.3V).At the low current density,the specific capacitance of the three kinds of EDLCss are P11-BF4/PC>P12-BF4/PC>TEA-BF4/PC,while at the large current density,those become P12-BF4/PC>P11-BF4/PC>TEA-BF4/PC,both the electrolyte ion size and cation symmetry affect the specific capacitance of the EDLCs.The withstand voltage characteristics of the three kinds of EDLCs are P11-BF4/PC>P12-BF4/PC>TEA-BF4/PC in sequence.The smaller the electrolyte ion size is,the(2)better the voltage withstanding characteristic of the electrolyte is,and the higher the working voltage of EDLC is.(3)Preparation of 1 mol/L P14-BF4/PC and 1 mol/L P12O1-BF4/PC electrolyte,the conductivity,viscosity and electrochemical window were tested.Then the influence of the introduction of the ether bond on the electrolyte cation alkyl side chain on the electrochemical performance of EDLCs was investigated in detail.The research found that the introduction of the ether bond can improve the conductivity of electrolyte,reduce the viscosity of the electrolyte,but can not improve the electrochemical window of the electrolyte,meanwhile it can increase the compatibility of electrolyte with activated carbon electrode,improve specific capacitance and working voltage of EDLCs.The EDLCs,which were assembled by the electrolyte with an ether bond,has better capacitance characteristics.