Expanding the potential window of aqueous electrochemical capacitors with binder-free electrostatically sprayed manganese oxide composite cathode films

Abstract

In this study, three binder-free manganese oxide-carbon nanotube (MnOx-CNT) composite films were synthesized using electrostatic spray deposition (ESD) and evaluated as electrochemical capacitor (EC) electrodes in aqueous media. The MnOx-CNT 9-1 composition exhibited superior electrochemical performance as compared to both the pristine MnOx and MnOx-CNT 8-2 composite films, exhibiting a high specific capacitance of 281 F g−1 in addition to excellent rate handling and cyclability. In order to investigate the practical viability of the MnOx-CNT 9-1 electrodes, a comprehensive two-electrode analysis was performed using activated carbon (AC) counter electrodes for different mass ratios to obtain optimal energy-power trade-off. The asymmetric capacitor with the AC electrode with a mass 2.6 times that of the MnOx-CNT 9-1 electrode exhibited the best energy-power characteristics reaching a maximal gravimetric energy density of 30.3 Wh kg−1; the excellent electrochemical performance of the asymmetric capacitor is attributed to the wider cell voltage of 2V as well as the high gravimetric capacitance of the ESD- based MnOx-CNT composite cathode.