Controlled synthesis of sulfur-vacancy-enriched sheet-like Ni₃S₂@ZnS composites for asymmetric supercapacitors with ultralong cycle life

To improve the electrochemical performance of supercapacitors, pseudocapacitive electrode materials must be synthesized with high surface activity, high electrical conductivity, and ultralong cycle life, which presents a significant challenge. In this study, we reported on the synthesis of sulfur-vacancy-enriched sheet-like Ni₃S₂ @ZnS composites based on 3D network porous nickel foam (NF) using a two-step electrodeposition protocol. The Ni₃S₂ @ZnS/NF exhibited a specific capacitance of 1141.9 C g⁻¹ (241.0 mC cm⁻²) at a current density of 19 A g⁻¹ (5 mA cm⁻²). The Ni₃S₂ @ZnS/NF positive electrode was used to fabricate an all-solid asymmetric supercapacitor, which demonstrated an ultrahigh energy density of 12.0 μWh cm⁻² at a power density of 7.2 mW cm⁻², as well as an ultrahigh capacitance retention rate of 86.7% after 50,000 cycles. Experimental and theoretical results indicated that the introduction of sulfur vacancies could improve the surface activity of the electrode, as well as its hydroxide diffusion and adsorption ability by adjusting the surrounding local electron concentration of cations around them. This accelerated the interfacial redox reaction and resulted in remarkable electrochemical performance for the Ni₃S₂ @ZnS/NF electrode. This research provides a pathway for the controlled synthesis of 2D nanosheets with vacancy-rich structures and their potential electrochemical applications.