Asymmetric Activated Carbon-Manganese Dioxide Capacitors in Mild Aqueous Electrolytes Containing Alkaline-Earth Cations

Manganese dioxide exhibits the ideal capacitive behavior in aqueous electrolytes containing alkaline-earth cations ( , , or ). A specific capacitance value as high as was obtained in electrolyte at . The ideal capacitive behavior, high specific capacitance, good coulombic efficiency, and rate ability of manganese dioxides in aqueous electrolytes containing bivalent cations ( , , or ) indicate that these alkaline-earth cations might be good alternatives for the state-of-the-art univalent alkaline cations. Moreover, activated carbon/ asymmetric capacitors with operating voltage were built up based on the aqueous electrolytes containing these alkaline-earth cations. The energy density of the asymmetric capacitor with cation at a current density of was found to be .