Microwave synthesis of three-dimensional nickel cobalt sulfide nanosheets grown on nickel foam for high-performance asymmetric supercapacitors.

A facile and cost-effective microwave method is developed to prepare ternary nickel cobalt sulfide (NiCo2S4) interconnected nanosheet arrays on nickel foam (NF). When acting as an electrochemical supercapacitor electrode material, the as-prepared NiCo2S4/NF shows a high specific capacitance of 1502 F g-1 at a current density of 1 A g-1, and outstanding cycling stability of 91% capacitance retention after 8000 cycles. In addition, a asymmetric supercapacitor (ASC) is composed of NiCo2S4/NF as positive electrode and activated carbon as negative electrode, which exhibits a high energy density of 34.7 W h kg-1 at a power density of 750 W kg-1 and long-term cyclic stability (83.7% capacity retention after 8000 cycles). Even at a high power density of 15 kW kg-1, it still remains an energy density of 17.9 W h kg-1, which is able to light up a light-emitting diode. These findings provide a new and facile approach to fabricate high-performance electrode for supercapacitors.