Reversible transformation between solid and liquid states of Na2S2O3·5H2O leads to supercapacitor electrolytes with low volatilization and low self-discharge

Abstract

The self-discharge and effumability of supercapacitors with aqueous electrolytes are prevalent problems. In this study, we used Na₂S₂O₃·5H₂O as the electrolyte for aqueous supercapacitors. Na₂S₂O₃ in Na₂S₂O₃·5H₂O can dissolve in crystalline water molecules by itself and the transformation between the solid and liquid states of Na₂S₂O₃·5H₂O electrolytes is reversible. The electrolyte based on liquating Na₂S₂O₃ in 5H₂O electrolytes has better thermal stability than that based on 2 M Na₂S₂O₃ and 2 M KOH electrolytes. The electrochemical result indicates that the energy storage mechanism of a supercapacitor based on liquating Na₂S₂O₃ in 5H₂O leads to a double-layer supercapacitor via Na⁺ and S₂O₃²⁻ ion adsorption. The self-discharge behavior of the supercapacitor using liquating Na₂S₂O₃ in 5H₂O is effectively suppressed by the slow charge redistribution of Na⁺ and S₂O₃²⁻ ions in solid electrolytes formed from the liquid state. Finally, the supercapacitor using liquating Na₂S₂O₃ in 5H₂O has good cycling stability.