Carbon-wrapped amorphous Ni–Co binary oxide nanosheet for high-performance pseudocapacitors

The development of high-energy density supercapacitor demands that the electrode has the characteristic of good conductivity for electron and open framework structure and ion transfer. NiCo2O4 already exhibits superior electric conductivity among the multi-metal oxides. Here, carbon-wrapped amorphous Ni–Co oxide nanosheet is prepared by a hydrothermal method, followed by an annealing process in Ar atmosphere. The conductivity is further improved by carbon coating and it also has a more open structure, which is verified by extended X-ray absorption fine structure analysis. Owing to the advantage of its structure, the carbon-wrapped amorphous Ni–Co oxide shows large capacitance of 1775 F g−1 at 1 A g−1 in three-electrode aqueous system, high energy density of 73.5 Wh kg−1 and power density of 806.7 W kg−1 in asymmetric supercapacitors. The open framework feature of the amorphous would promote the wide exploration of amorphous Ni–Co oxide material as the electrode for energy storage devices.