Employing Redox-Active Additives for Enhanced Charge Polarization and Twofold Higher Energy Density in Supercapacitor

Abstract

Remarkable improvement in the polarization and charge transport at the solid–solid electrode–electrolyte interface due to the incorporation of a redox-active additive sodium molybdate (Na2MoO4) is demonstrated. The presence of the electrochemically active oxide center along with Na+ facilitates the hopping-based charge transport of the ionic liquid leading to higher ionic conductivity and a twofold increase in specific capacitance (0.009 to 0.018 F cm−2). This drives a 200% increase in the energy density (0.76–1.7 µW h cm−2) and a 2.5 times improvement in the rate capability (10 000 mV s−1) of the solid-state supercapacitor. Importantly, the power density, non-Faradic nature, and cyclability remain unaltered, resulting in performance exceeding several solid-state and liquid electrolyte-based supercapacitors. Thus, the results established here through the use of redox-active additive establish the robustness of the approach and practicality of the resulting device besides providing transformative opportunities in tuning the performance of solid-state devices.