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 (NaMnO_2−x) as highly capable supercapacitor electrodes. The NaMnO_2−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 NaMnO_2−x electrode and activated carbon electrode as positive and negative electrodes, respectively. The NaMnO_2−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.