Design and construction of nickel-cobalt-sulfide nanoparticles in-situ grown on graphene with enhanced performance for asymmetric supercapacitors

We synthesized NiCo2S4@rGO for electrode applications using a facile one-step solvothermal method. NiCo2S4@ rGO exhibited excellent electrochemical activity due to abundance of active sites and had a higher capacitance than other unitary metal oxides or sulfides. The synthesized electrode achieved a specific capacitance of 2418 F g(-1) at a current density of 1 A g(-1). In the asymmetric supercapacitor, NiCo2S4@rGO and N-doped graphene are used as the cathode and anode, respectively, and an extended potential working window of 1.6 V can be obtained. A combination of pseudocapacitance and double layer capacitance resulted in NiCo2S4@rGO achieving good rate performance and excellent cyclic stability. The device delivered a maximum energy density of 34.1 Wh kg(-1) at a power density of 411 W kg(-1). In addition, the device possessed acceptable cyclic stability, with 86.4% capacitance retention after 5000 cycles. The proposed method provides a general route for assembling supercapacitors with high capacitance and wide voltage window.