Effect of ethanol solvent on the energy storage of imidazolium acetate ionic liquid supercapacitors

Abstract

Supercapacitors are gaining more and more attention in the field of energy storage technology due to their superior power density. However, their development is limited by the low energy density. Ionic liquids (ILs) have wide electrochemical windows as electrolytes, which can effectively enhance the energy density of supercapacitors. However, the viscosity of ILs is generally large, which affects the power density of supercapacitors. Adding solvents is a simple and effective method to reduce the viscosity, which can effectively improve the dielectric constant and conductivity of ions. Here, we make an in-depth theoretical investigation of the IL-electrolyte systems by molecular dynamics simulations, with the cations of 1-ethyl-3-methylimidazole ([EMIM]⁺), 1,3-dimethylimidazolium ([MMIM]⁺), or 1- methylimidazolium ([MIM]⁺), and the acetate ion ([AC]^-). Then, we use ethanol as the organic solvent to explore the effects of solvents. The conductivity and double layer capacitance of these three IL-systems with/without ethanol solvent were systematically calculated from the perspective of improving power and energy density. Among them, the [EMIM][AC] - ethanol system shows the best performance, with the conductivity of 194.9 mS/cm². The maximum value of the double layer capacitance is enhanced from 5.4 μF/cm² (+1.5 V) to 6.1 μF/cm² (+1 V) with the addition of 35 % ethanol.