Honeycomb-like metallic nickel selenide nanosheet arrays as binder-free electrodes for high-performance hybrid asymmetric supercapacitors

Abstract

Of all the novel electrode materials that can be used to enhance the electrochemical performance of supercapacitors, the most promising one is ordered nanoarray structures, which can be used as binder-free electrodes. Honeycomb-like metallic nickel selenide (Ni_0.85Se) nanosheet arrays supported on nickel foams were successfully synthesized via a one-step hydrothermal approach. Characterization results reveal that the as-obtained Ni_0.85Se nanosheets belong to the hexagonal crystal phase with a thickness of ∼15 nm. By virtue of their intrinsic metallicity, super-hydrophilic surface and unique honeycomb-like structure composed of interconnected ultrathin nanosheets, the Ni_0.85Se nanosheet arrays exhibit splendid electrochemical properties, e.g. higher specific capacitance (3105 F g⁻¹ at 1 A g⁻¹ and 1460 F g⁻¹ at 10 A g⁻¹), outstanding cycling stability (90.1% capacitance retention after 5000 cycles), and remarkable conductivity. More importantly, hybrid asymmetric supercapacitors are assembled with Ni_0.85Se nanosheet arrays as the binder-free positive electrode and activated carbon as the negative electrode, and show remarkable energy-storage characteristics, including an energy density of 65.02 W h kg⁻¹ at a power density of 103.33 W kg⁻¹, only 6.3% capacitance loss after 10 000 cycles, and a wider voltage window of 0–1.6 V. In addition, two asymmetric supercapacitors based on Ni_0.85Se nanoarrays connected in series can be charged and easily drive two light emitting diodes or a mini fan. Such excellent performance evidently proves that Ni_0.85Se nanosheet arrays are a promising electrode material for energy storage applications.