Construction of ZnCo2S4@Ni(OH)2 core–shell nanostructures for asymmetric supercapacitors with high energy densities

Abstract

ZnCo₂S₄ nanoneedle clusters are uniformly grown as a core on foamed nickel and then are coated with Ni(OH)₂ nanosheets as shell layers. The formed ZnCo₂S₄@Ni(OH)₂ core–shell structures as electrode materials exhibit high specific capacitance (1193 C g⁻¹ at 1 A g⁻¹) and superior cycle rate performance (a capacity retention rate of 92% after 8000 cycles). The ZnCo₂S₄@Ni(OH)₂//AC asymmetric supercapacitor composed of AC//NF as the negative electrode, ZnCo₂S₄@Ni(OH)₂ as the positive electrode, porous glass fiber paper as the separator and 3 mol L⁻¹ KOH as the electrolyte shows a specific capacitance of 215 F g⁻¹ at 1 A g⁻¹ with 70% capacitance retention and 100% coulombic efficiency even after 5000 cycles at a scan rate of 5 A g⁻¹, evidencing the excellent energy storage capacitance and electrochemical performance. Besides, the ZnCo₂S₄@Ni(OH)₂//AC device exhibits an exceptional energy density of ∼44 W h kg⁻¹ at a power density of ∼0.83 kW kg⁻¹.