Interconnected δ-MnO2 nanosheets anchored on activated carbon cloth as flexible electrode for high-performance aqueous asymmetric supercapacitors

Abstract For aqueous supercapacitors, the working voltage is normally limited below 2 V because of the electrochemical stability of water, which limits improvement of the energy density and thus severely hinders their practical application. Herein, a flexible electrode of interconnected δ-MnO2 nanosheets anchored on activated carbon cloth with a potential window (vs Ag/AgCl) extending to 1.2 V is developed using simple one-step water bath only at 40 °C. A high specific capacitance up to 360.5 F g−1 at 1 A g−1 combining with good rate performance and electrochemical stability is delivered. Folding test indicates that the charge storage performance of the electrode has neglected degradation during the 2000 times of folding. Furthermore, a 2.4 V aqueous asymmetric supercapacitor is assembled based on the device configuration of activated carbon//δ-MnO2 and a high energy density of 49.8 Wh kg−1 at the power density of 1198.4 W kg−1 and good electrochemical stability, i.e., 90.6% capacitance retention after 5000 cycles can be achieved. Thanks to the good energy storage performance, high flexibility and simple preparation of the material, it is believed that this work provides a valuable exploration to develop high-performance flexible aqueous asymmetric energy storage devices.