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

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.