H2O assisted in improving the electrochemical performance of a deep eutectic electrolyte formed by choline chloride and magnesium chloride hexahydrate†

Abstract

Introduction of H₂O provides an effective strategy to tailor conductivity and viscosity in an electrolyte based on a deep eutectic solvent (DES), as well as customizing the energy storage performance. Herein, a novel DES as a suitable electrolyte is prepared by means of choline chloride (ChCl) and with crystalline magnesium chloride (MgCl₂·6H₂O), with different amounts of H₂O added as additives to investigate its effect on the electrolyte's electrochemical properties. These novel DESs are systematically studied both theoretically and experimentally, as well as being utilized as electrolytes in supercapacitors. The results show that the addition of H₂O significantly optimized the ion conductivity and the viscosity of the prepared DES electrolyte. The proposed mechanism is that introduction of H₂O ‘dilutes’ the interaction between ions and hydrogen bonds, and enhances the capacity of ion transport and diffusion in the electrolyte system. The supercapacitor assembled with the optimized DES electrolyte (DES-1-1.0) exhibits superior electrochemical properties within a voltage range of 0–2.6 V, delivering a remarkable energy density of 87.7 W h kg⁻¹ at a high power density of 1.69 kW kg⁻¹ and retains 90.25% of its initial capacitance after undergoing 30 000 cycles at 10 A g⁻¹.