ZnCo2O4-reduced graphene oxide composite with balanced capacitive performance in asymmetric supercapacitors

ZnCo2O4-rGO composite with intertwined sheets grown onto nickel foam substrate is prepared through a facile hydrothermal deposition and followed thermal annealing treatment, which can be directly employed as binder free electrode of supercapacitor. The hierarchically porous texture of ZnCo2O4-rGO composite with high specific surface area and efficient ions diffusion channels ensures sufficient faradic reaction of ZnCo2O4 component, therefore enables an ultrahigh electrode specific capacitance (Cs) of 3222 F g−1 at 1 A g−1 in alkali electrolyte, and the Cs still retains to be 860 F g−1 at 20 A g−1. When used as positive electrode of full cell, the ZnCo2O4-rGO//activated carbon (AC) asymmetric supercapacitor can offer a maximum device specific capacitance (Ccell) of 139 F g−1 at 0.5 A g−1 and therefore an energy density (Ecell) of 49.1 Wh kg−1 at power density (Pcell) of 400 W kg−1. Even at high Pcell of 7625 W kg−1, the Ecell of the asymmetric device can still retain to be 18.8 Wh kg−1. More significantly, the asymmetric supercapacitor demonstrates only 6% Ccell fade subjected to 5000 successive charge-discharge cycles. The balanced Ecell, Pcell delivery abilities and high cycleability highlight the potential of the faradic ZnCo2O4-rGO composite in high performance and long lifetime energy storage devices.