NiCo2S4 is one of the most promising bimetallic sulfides for use in energy-storage systems, but more studies are needed to endow NiCo2S4 with a high electrochemical reaction capability and reversibility. In this work, we present rationally materials design of an optimal NiCo2S4 nanoparticle in a reduced graphene oxide (RGO) matrix as a NiCo2S4/RGO nanocomposite. Furthermore, we report the improvements in the materials technology, demonstrating the NiCo2S4/RGO nanocomposite electrode with an excellent specific capacitance of 963–700 F g−1 at 1–15 A g−1, high capacitance retention of 70%, and long cycle life of 3000 cycles. The practical application is showcased in an asymmetric supercapacitor with a high active-material loading. The NiCo2S4/RGO nanocomposite shows a high energy density of 31 Wh kg−1 at a power density of 987 W kg−1 and maintains an excellent density of 23 Wh kg−1 at a high power density of 7418 W kg−1. The outstanding electrochemical utilization and stability of the NiCo2S4/RGO nanocomposite confirm that our systematic optimization in the materials science and technology in terms of the active-material synthesis, the electrode development, and the device design/fabrication would benefit the future development of high-performance supercapacitors.
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