1-Ethyl-2,3-dimethylimidazolium tetrafluoroborate ionic liquid mixture as electrolyte for high-voltage supercapacitors

Abstract

A novel ionic liquid (IL) 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate ([Emmim][BF4]) with trialkyl substitution imidazolium cation was synthesized, and its binary system blended with acetonitrile (ACN) under different concentrations were prepared and investigated as possible electrolytes for supercapacitors. The physico-chemical properties such as density, viscosity, and electrical conductivity of the binary mixture system were measured from 288.15 to 333.15 K. The temperature dependences of density, viscosity, and electrical conductivity were illustrated and discussed by the Vogel-Fulcher-Tamman (VFT) equation and Arrhenius equation. It was found that the VFT equation was more suitable to [Emmim][BF4] + ACN system. Further, the important characteristics of this IL-based electrolyte for supercapacitors including the maximum operative voltage, the capacitance, the energy density, and power density were measured and calculated by cyclic voltammetry (CV), electrochemical impedance spectrum (EIS), and galvanostatic charge-discharge. The results show that the performance of the electrolyte can be improved with appropriate ratio of IL. When the concentration of the IL increased to 0.8 mol L−1, the maximum operative voltage increased to 5.9 V, and the specific capacitance achieves 142.6 F g−1. It shows the IL-based mixtures with excellent characteristics are applicable as high-voltage electrolytes for supercapacitors.