A two-step hydrothermal synthesis approach to synthesize NiCo2S4/NiS hollow nanospheres for high-performance asymmetric supercapacitors

In this work, a high-performance asymmetric supercapacitor device based on NiCo2S4/NiS hollow nanospheres as the positive electrode and the porous activated carbon as the negative electrode was successfully fabricated via a facile two-step hydrothermal synthesis approach. This NiCo2S4/NiS//activated carbon asymmetric supercapacitor achieved a high energy density of 43.7 Wh kg(-1) at a power density of 160 W kg(-1), an encouraging specific capacitance of 123 F g(-1) at a current density of 1 mA cm(-2), as well as a long-term performance with capacitance degradation of 5.2% after 3000 consecutive cycles at 1 mA cm(-2). Moreover, the NiCo2S4/NiS electrode also demonstrated an excellent specific capacitance (1947.5 F g(-1) at 3 mA cm(-2)) and an outstanding cycling stability (retaining 90.3% after 1000 cycles). The remarkable electrochemical performances may be attributed to the effect of NiS doping on NiCo2S4 which could enlarge the surface area and increase the surface roughness. (C) 2017 Elsevier B.V. All rights reserved.