Controllable Synthesis of Three-Dimensional β-NiS Nanostructured Assembly for Hybrid-Type Asymmetric Supercapacitors

The process of energy storage in supercapacitors via the surface reaction of the electrode can lead to a significant perfecting of the electrochemical performance of supercapacitors, for developing the morphologies of materials and increasing the specific surface areas of the electrodes. Three-dimensional nickel sulfide (NiS) superstructures with nanomorphologies, viz. coral-like, urchin-like, flake-like, and flower-like, are synthesized through simple solvothermal methods, without any template. The nanostructured flower-like β-NiS demonstrates, not only a remarkable specific capacitance of 2425.89 F·g^-1 at the current densities of 1 A·g^-1, but also an excellent cycling stability of approximately 100% (at the current density of 10 A·g^-1 over 5000 cycles). Moreover, the hybrid-type asymmetric supercapacitor, constructed from the flower-like β-NiS positive electrode and active carbon negative electrode, exhibits an energy density of 42.12 Wh·kg^-1 at a power density of 28.8 kW·kg^-1.