Engineering Electrolyte Strong-Weak Coupling Effect toward Wide-Temperature Supercapacitor

Developing highly reliable electrochemical energy storage (EES) devices over a wide-temperature range are urgent for some extreme application. Conventional electrolytes commonly make EES operate at only −30-60°C since they suffer from sluggish ion-transport kinetics at low temperature while decomposition failure at high temperature. Herein we report a strong-weak coupled electrolyte to develop wide-temperature supercapacitor. Specifically, fluoroethylene carbonate as strong-solvation solvent acts on enhancing the ionic conductivity by dissociation the ion pairs while ethyl acetate as a weak-solvation solvent plays a role in taming the affinity between solvents and ions. As a result, the as-prepared electrolytes exhibit a considerably high conductivity (1.17-29.40 mS cm−1 at −70 to 80°C). This strong-weak coupled electrolyte-based supercapacitor can operate stably over a wide temperature range from −70°C to 80°C. Also, the strong-weak coupling effect endows wide-temperature supercapacitor with excellent electrochemical properties including energy density of 35.7 Wh kg−1, power density of 21.1 kW kg−1, 82.4% capacitance retention after 50, 000 cycles, and low self-discharge rate.