Influence of cycling stability on structure and properties of MnCo2S4 nanocomposite for high-performance supercapacitors

Abstract

Mesoporous MnCo2S4 composites directly grown on porous Ni foam were prepared by a facile hydrothermal method for high-performance supercapacitors. The nanostructure of MnCo2S4 composite electrodes plays an important role in achieving desirable electrical properties by providing a large surface area that greatly improves the electrode/electrolyte contact area and shortens the ion diffusion paths. As a result, the MnCo2S4 electrode exhibits the advantages of high conductivity and a fast-redox reaction rate. Moreover, metal sulfides are receiving more attention for use in supercapacitors owing to their higher electrical conductivity than those of metal oxides/hydroxides. However, these sulfides are difficult to apply in practice owing to a low potential window. In this study, to compensate for these shortcomings, we experimented with adding glycerol and ethylene glycol to the MnCo2S4 composite. Among the obtained composites, the glycerol-MnCo2S4 electrodes showed high-capacity retention after many cycles and a remarkable maximum specific capacitance of 1218.7 F g−1 at 3 A g−1, which was significantly higher than that of other electrodes. The cycling stability of the glycerol-MnCo2S4 composite electrode was also measured to be the highest at 92.4% after 5000 cycles. In addition, the glycerol-MnCo2S4 composite was confirmed to have the highest specific capacitance, after 5000 cycles (484.2 F g−1 at 3 A g−1). In addition, we fabricated an asymmetric supercapacitor employing the glycerol-MnCo2S4 composite as the positive electrode and graphene as the negative electrode, which exhibited a high energy density of 32.9 W h kg−1 at a power density of 295.2 W kg−1 and a remarkable cycling stability, with 87.7% capacitance retention after 5000 cycles. These advantages show that the glycerol-MnCo2S4 electrodes prepared by the hydrothermal method could be a promising positive electrode material for high-performance asymmetric supercapacitors.