One-step hydrothermal synthesis of flower-like MnO2–NixCo1−x(OH)2@carbon felt positive electrodes with 3D open porous structure for high-performance asymmetric supercapacitors

Abstract

In this study, nickel–cobalt-layered double hydroxides nanosheets combined with manganese dioxide directly coated on the carbon felt (MnO2–NixCo1−x(OH)2@CF) are prepared by a facile and novel one‐step hydrothermal process with the help of potassium permanganate (KMnO4). The CF not only plays the role of 3D open porous skeleton and current collector, but also serves as the reducing agent and anchor sites to generate OH− and MnO2 coated on the surface of CF by in situ reacting with KMnO4. The morphology and electrochemical performance of the as-prepared MnO2–NixCo1−x(OH)2@CF electrodes with different feeding molar ratio of Ni–Co are investigated and the optimum feeding molar ratio of Ni–Co is confirmed to be 8:2. The resulted MnO2–Ni0.8Co0.2(OH)2@CF electrode with a 3D open porous structure contains a large number of interconnected MnO2–Ni0.8Co0.2(OH)2 nanosheets and well-defined flower-like aggregations, which exhibits a high areal specific capacitance of 1018.6 mF cm−2 at 4 mA cm−2. Furthermore, the asymmetric supercapacitor based on the MnO2–Ni0.8Co0.2(OH)2@CF as the positive electrode and activated carbon-coated CF as the negative electrode has a maximum energy density of 49.5 μWh cm−2 and remarkable cycling stability (70.2% retention after 10,000 cycles at 20 mA cm−2).