One-step synthesis of architectural Ni3S2 nanosheet-on-nanorods array for use as high-performance electrodes for supercapacitors

Abstract

Although a wide variety of three-dimensional porous electrode architectures have been created for supercapacitors to markedly enhance the charge and mass transfer associated with cycling, their low volumetric energy densities limit applications in many energy storage systems. In this work, we report a unique electrode architecture consisting of Ni3S2 nanosheet-onto-Ni3S2-nanorods grown on nickel foam and prepared using a simple one-step hydrothermal method. When tested as an electrode for a supercapacitor (using a three-electrode configuration), this material exhibited excellent rate capability and cycling stability at high cycling rates. The obtainable capacitance decreased by <42% as the current density was increased from 20 to 240 mA cm−2, and the capacity retained 89.3% of its initial value after 5000 cycles at a cycling rate of 120 mA cm−2. Further, an asymmetric supercapacitor consisting of the Ni3S2 nanosheet-onto-Ni3S2-nanorods electrode and an activated carbon (AC) electrode displayed a volumetric energy density as high as ~1.96 mWh cm−3, with the potential to bridge the performance gap between thin-film Li batteries and commercial AC//AC supercapacitors. The outstanding electrochemical performance is attributed to the good mechanical adhesion and electrical connection with the substrate, high contact area with the electrolyte and alleviated structural pulverization during the ion insertion/desertion process. It is predicted that the architectural Ni3S2-nanosheet-on-nanorods array prepared with this facile method offers great potential promise in large-scale energy storage device applications. An electrode material for considerably enhanced storage of electrical energy in supercapacitors has been developed by an international team. Supercapacitors offer high charge storage capacities and rapid energy release, but they typically have lower volumetric energy storage densities than rechargeable batteries, making them bulkier in comparison. Supercapacitor electrodes having high surface areas through nanoscale morphologies offer a solution but can be difficult to fabricate. Now, Meilin Liu from Georgia Institute of Technology in the USA, Chenghao Yang from South China University of Technology in China, and their colleagues have used a simple one-step hydrothermal method to fabricate an architecture based on nickel sulfide (Ni3S2) nanosheets and nanorods. Supercapacitors made from these materials showed a high volumetric energy density and a long durability. The researchers anticipate that this architecture will be useful for large-scale energy storage devices. Three kinds of Ni3S2 nanostructures, namely Ni3S2 nanorods, Ni3S2 nanosheet@nanorods and Ni3S2 multi-connected nanorods were prepared using a one-step hydrothermal process via controlling the temperature. Owing to the good mechanical adhesion and electrical connection with the substrate, high contact area with the electrolyte and alleviated structural pulverization during the ion insertion/desertion process, Ni3S2 nanosheet-onto-Ni3S2 nanorods exhibited excellent rate capability and cycling stability. Asymmetric supercapacitor consisting of Ni3S2 nanosheet @nanorods electrode and activated carbon (AC) electrode displayed a volumetric energy density of 1.96 mWh cm−3, which can be used to bridge the performance gap between thin-film Li batteries and commercial AC//AC supercapacitors.