A water-sulfolane hybrid electrolyte enabling ultra-low-temperature flexible magnesium-ion supercapacitors

Abstract With the continuous development of wearable electronics, flexible energy storage devices have received widespread attention. Aqueous magnesium-ion supercapacitors (MSCs) have attracted great attention due to their high safety and low cost. However, the freeze of aqueous electrolytes will lead to rapid deterioration of aqueous MSCs performances, which hinders their application in wearable electronics. Herein, we propose a water-sulfolane hybrid electrolyte based on low-concentration Mg(ClO 4 ) 2 and sulfolane exhibiting excellent low-temperature properties. By investigating the physical characterization and electrochemical performance testing of the hybrid electrolyte revealed that sulfolane contains functional groups disrupting the hydrogen-bond network between water molecules, resulting in superior anti-freezing properties. The hybrid electrolytes endow flexible aqueous MSCs with a wider temperature operating range (-50 °C~25 °C), high specific capacitance of 22 F/g at -30 °C, and superior flexibility. This work provides an effective and feasible strategy for flexible energy storage systems operating in ultra-low temperatures environments.