Growing Magnetic NiCo-LDH Nanosheets on the Ni@CoSe2 Surface to Enhance Energy Storage Capacity in Asymmetric Supercapacitors

Abstract

Nickel–cobalt layered double hydroxide (NiCo-LDH) shows great potential as an electrode material for various applications; however, single NiCo-LDH layered electrode materials are poorly stabilized and prone to agglomeration, which hampers ion transport. In this study, three-dimensional composite electrode materials with high specific surface area and abundant redox active sites were prepared by loading spherical CoSe₂ on the surface of nickel foam and realizing the in situ growth of NiCo-LDH nanosheets derived from ZIF-67 on the Ni@CoSe₂ skeleton. The results show that the CoSe₂@NiCo-LDH electrode achieves an area-specific capacitance of 6.06 F cm^–2 at a current density of 6 mA cm^–2. Compared with CoSe₂ and NiCo-LDH, CoSe₂@NiCo-LDH electrodes have a 0.265 eV narrow bandgap. It is demonstrated that the composite heterojunction of CoSe₂ and NiCo-LDH enhances the electrical conductivity, and the built-in electric field triggered by efficient electron migration promotes the conductivity and electrochemical activity of the electrode materials. The charge density distribution and density of states further confirm that the interaction between CoSe₂ and NiCo-LDH heterojunctions mainly relies on the hybridization of d orbitals of Co atoms, Ni atoms, and p orbitals of Se atoms, which facilitates charge transport and ion diffusion. Molecular dynamics simulations show that the composite exhibits excellent ion adsorption capacity in KOH electrolyte. An asymmetric supercapacitor assembled from this electrode with activated carbon exhibits an area capacitance of 0.51 F cm^–2 to 0.33 F cm^–2 over a current density range of 6 mA cm^–2 to 20 mA cm^–2, with an 0.183 mWh cm^–2 energy density and 40 mW cm^–2 power density, and retained 97.82% of its initial capacitance over 5000 cycles.