An alternative electrolyte of deep eutectic solvent by choline chloride and ethylene glycol for wide temperature range supercapacitors

In present work, we present a novel deep eutectic solvent electrolyte for supercapacitors simply by mixing choline chloride and ethylene glycol. It unveils that the molar ratio of choline chloride and ethylene glycol exerts crucial effect on the viscosity, electrical conductivity and capacitive behaviors under extreme conditions (−40–115 °C). With the increase of temperature, the viscosity of electrolyte decreases along with the enhancement of electrical conductivity; similar phenomenon toward capacitive behaviors under extreme conditions also occurs. The electrolyte with molar ratio of 1:2 (choline chloride:ethylene glycol) under 115 °C shows a specific capacitance of 362 F g−1 (with energy density of 50.33 Wh kg−1), which can remain as 102 F g−1 (with energy density of 14.13 Wh kg−1) even at −40 °C. In addition, density functional theory also confirms that the electrolyte with molar ratio of 1:2 has larger absolute value of adsorption energy as 4.42 eV. The present deep eutectic solvent by choline chloride and ethylene glycol can extend to other electrolytes especially for wide temperature range supercapacitors.