In situ composite NiCoO2 sphere of nanosheets on wood chip for supercapacitor

The low electrical conductivity of nickel–cobalt layered oxides and single Ni, Co metal oxides led to the low rate capability and poor cycling stability, which thus limits the commercial application in practical supercapacitor. Here, NiCoO2/WCC composite electrode materials were prepared by employing wood chips carbon (WCC) with the high specific surface area and low cost as the conductive layer, where hierarchical spherical structure of laminar NiCoO2 interspersed as homogeneous and was oriented and constructed on the surface of carbon by hydrothermal and calcination. The strategy provided abundant frameworks and active sites for the in situ growth of NiCoO2, which prevented the aggregation of spherical structures to a certain extent; furthermore, the layered spherical structure exposed more active sites, which thus enhanced the electrochemical performance of the capacitor. The NiCoO2/WCC electrode (RNi:Co = 1) possessed a high specific capacitance of 1053.6 F g−1 at 0.5 A g−1 due to the synergistic effect between the bimetallic oxide and WCC, and the specific capacitance of the electrode remained 906 F g−1 even at a high current density of 10 A g−1 by the lamellar structure with more electrochemical sites. In addition, the asymmetric supercapacitor based on the NiCoO2/WCC cathode and the WCC anode delivers a high specific capacitance of 134.4 F g−1 at 1 A g−1, a high specific energy of 36.6 Wh kg−1 at 1 A g−1, and good cycling performance (~ 94.3% retention after 5000 cycles), where the above properties were superior to existing and similar electrode materials.