One-step construction of δ-MnO2 cathodes with an interconnected nanosheet structure on graphite paper for high-performance aqueous asymmetric supercapacitors

Abstract

Among various supercapacitor materials, transition metal oxides have attracted wide attention due to their high theoretical capacitance, and however a great challenge associated with the related materials is to fabricate nanostructured electrodes with high comprehensive performance including high capacitance, excellent cycle stability and good rate performance by a simple and green method. Herein, a high-performance self-supporting cathode consisting of interconnected δ-MnO2 nanosheets on graphite paper (GP) is developed by water bath only at 40°C. Benefiting from the synergetic effects from the interconnected and open nanosheet structure of δ-MnO2 and the GP substrate including effective contact with the electrolyte, a large specific surface area, efficient stress relief, improved ion diffusion and charge transfer, and small equivalent series resistance, a high specific capacitance of 446.6 F g–1 at 1 A g–1, 1.3 V potential window, and outstanding cycle stability with the capacitance retention of ~ 86.1% after 10000 cycles at 8 A g–1 and Columbic efficiency around 100% during cycling can be achieved for the cathodes. The aqueous asymmetric supercapacitors assembled using the δ-MnO2 cathode and active carbon anode and 1 M NaNO3 aqueous solution electrolyte can deliver a specific energy of 47.2 and 19.8 W h kg−1 at 1150 and 115000 W kg−1, respectively. Moreover, long cycle stability with 87.2% capacitance retention even after 30000 cycles at 4 A g−1 can be maintained by the ASCs. Thanks to the simple and green preparation and high performance of the electrodes, valuable exploration of developing high-performance ASCs can be provided by this work.