Flower-like NiCo2S4/rGO composites directly grown on Ni Foam as highly efficient electrode for long cycling stability supercapacitor

NiCo2S4 and reduced graphene oxide(rGO) were directly grown on Ni foam by a two-step hydrothermal method to form NiCo2S4/rGO composite material with hierarchical structures. The resulting samples displayed flower-like NiCo2S4 particles formed by interconnected NiCo2S4 nanosheets with the conductive rGO sheets interspersing among them. This unique structure can provide a much rougher surface, rich two-phase interface, and porous channels exposed to electrolytes with fast ion diffusions and electron transmissions, as well as effectively relieve the expansion/contractions during charging and discharging. The electrochemical test results show that NiCo2S4/rGO composite prepared at 120 ℃ with 8.1 mg mass loading on Ni foam exhibits a specific capacitance (1974.7 F·g-1) at a current density of 10 mA·cm-2. An asymmetric supercapacitor device assembled by NiCo2S4/rGO and activated carbon can provide an energy density high up to 46.8 Wh·kg-1 at a power density of 219.5 W·kg-1. Even if the power density is increased up to 731.6 W kg-1, it still can achieve the energy density superior to 31.8 Wh kg-1. Moreover, the asymmetric supercapacitor device exhibits an outstanding cycling stability with 87.8% capacitance retention after 5000 cycles, which confirms its potential application in the energy storage.