Void space expanded hierarchical battery-type composite material for high-capacity hybrid supercapacitors

Synergetic modulation of battery-type materials with excellent electrochemical activity is an important feature to elevate the energy storage performance in the hybrid supercapacitors (HySCs). In this study, we synthesized a void space expanded nickel sulfide@nickel molybdenum oxysulfide on Ni foam (Ni_xS_y@NiMoO_x-1S_y/Ni foam) using wet-chemical sulfurization technique. The growth solution, composed of sulfur ions, partially converts NiMo DHs into NiMoO_x-1S_y and the Ni foam substrate into Ni_xS_y, resulting in the formation of a hybrid-composite. Increased mass-loading growth of Ni_xS_y@NiMoO_x-1S_y/Ni foam and multi-oxidation states of nickel species in the composite were confirmed using the X-ray photoelectron spectroscopy analysis. The binder-free Ni_xS_y@NiMoO_x-1S_y/Ni foam electrode was electrochemically cycled in aqueous KOH electrolyte, demonstrating battery-type redox behavior with enhanced capacity (310.6 mAh/g) compared to the Ni_xS_y/Ni foam (221.1 mAh/g) and NiMo DHs/Ni foam (142.5 mAh/g) electrodes, which could be ascribed to the improved electrical conductivity, adequate electrolyte diffusivity, and fast charge transfer properties. Furthermore, a two-electrode system based HySC was assembled using the battery-type Ni_xS_y@NiMoO_x-1S_y/Ni foam and capacitive-type activated carbon, enabling a maximum energy density (58.8 Wh/kg) and power density (2666.7 W/kg) with good cycling stability and coulombic efficiency. The high-performance HySCs were used to power-up portable lighting devices, demonstrating their practical use in real-time applications.