High-Entropy Electrolyte Design for Low-Temperature Supercapacitors.

Abstract

Supercapacitors (SCs) are high-power energy storage devices but often experience reduced electrochemical performance at low temperatures, especially below -30 °C, due to the high freezing points of conventional electrolytes. In this study, we introduce a novel high-entropy electrolyte (HEE) for supercapacitors that extends operational capabilities over a wide temperature range. The high entropy of the HEE results in an exceptionally low freezing point of -116 °C. With an increased number of solvent molecules in the cation solvation structures, the HEE exhibits high conductivity (3.9 mS cm^-1 at -50 °C) and low de-solvation energy (14.1 kJ mol^-1). When incorporated into a carbon-based SC, the HEE enables a capacitance retention of 58 % at temperatures below -30 °C, compared to 25 °C, while conventional single-solvent electrolytes retain only 38 %. Additionally, the HEE provides superior high-rate performance and excellent cycling stability, maintaining 88 % capacitance after 15,000 cycles, compared to 73 % with conventional electrolytes.