NaMnO2-x thin nanosheets assembled microspheres as electrode for aqueous asymmetric supercapacitor

Abstract

This study proposes MnO2 thin nanosheets assembled microspheres with oxygen vacancies and pre-insertion of Na ions (NaMnO2-x) as highly capable supercapacitor electrodes. The NaMnO2-x electrode can reach a stable potential window of 1.2 V without oxygen evolution reactions in three-electrode configuration. The voltage window of the assembled aqueous ASC device can be expanded to 2.4 V (1 M Na2SO4) by using NaMnO2-x electrode and activated carbon electrode as positive and negative electrodes, respectively. The NaMnO2-x electrode delivers a good specific capacitance of 215 F • g-1 at current density of 1 A • g-1. It displays high-rate capability and an excellent cycling stability, maintaining 95.5% of its initial specific capacitance at 2 A • g-1 after 2500 cycles. The ASC device shows a high energy density and power density of 28.56 W • h • kg-1 and 1246 W • kg-1, respectively, at a current density of 1 A • g-1,.