Hierarchical nanostructure-tuned super-high electrochemical stability of nickel cobalt sulfide

Abstract

In this work, microstructure-controlled synthesis of NiCo₂S₄ grown on nickel foam by a facile microwave-assisted hydrothermal/solvothermal approach is reported. Based on the basic principle of Faraday supercapacitors, the hierarchical nanostructure of NiCo₂S₄ is tuned by the supersaturation determined by the polarity of the solvent and the solubility of the product in the solvent. The results of electrochemical measurements indicate that the as-prepared aggregated NiCo₂S₄ with ordered nanosheets grown on nanospheres have high electrochemical performance and cycling stability. The material presents a high specific capacitance of 2070.5 F g⁻¹ at a current density of 2.2 A g⁻¹. It also exhibits super-high cycling stability (81.2% capacitance retention after 100 000 electrochemical charge–discharge cycles). The asymmetric supercapacitors with nanostructured NiCo₂S₄ and active carbon used respectively as positive and negative electrode materials also present high energy density (53.6 W h kg⁻¹ at a power density of 601.5 W kg ⁻¹). These results indicate that the hierarchical nanostructure-tuned NiCo₂S₄ could be a promising electrode material for high performance supercapacitors.