Controlled synthesis of unique Co9S8 nanostructures with carbon coating as advanced electrode for solid-state asymmetric supercapacitors

Abstract

Stimulated by both the rich electrochemical properties and unique structural merits, much attention is directed to construct novel cobalt sulfides nanoarchitectures for energy storage devices. Here, carbon-coated cobalt sulfide nanostructures are fabricated with the assistance of polyvinylpyrrolidone during hydrothermal process. The morphology of carbon-coated cobalt sulfide can evolve from well-defined uniform nanooctahedrons, nanoflowers to nanospheres by simply controlling the polyvinylpyrrolidone amount. Remarkably, the unique carbon-coated cobalt sulfide configuration takes full advantage of the synergistic contributions from both the homogeneous incorporated carbon layer and the ideal hierarchical flowerlike structures, thereby making it to be a suitable electrode for supercapacitors. By virtue of the intriguing structural features of carbon-coated cobalt sulfide, a solid asymmetric supercapacitor based on carbon-coated cobalt sulfide nanoflowers as the positive electrode and active carbon as the negative electrode achieves remarkable cycling stability (around 86% capacitance retention even up to 10,000 times), and outstanding energy density of 40 Wh kg−1 at power density of 850 W kg−1. The exceptionably electrochemical performance of the asymmetric supercapacitor is related to the enhanced electrical conductivity and increased electrode/electrolyte contact area of carbon-coated cobalt sulfide. Thus, the as-prepared carbon-coated cobalt sulfide nanoflowers is demonstrated to be a promising electrode for asymmetric supercapacitors.