A novel NiS/Ni(PO₃)₂ composite material for high-power-density asymmetric solid state supercapacitor

Nickel-based compounds have emerged as promising electrode materials for hybrid energy storage systems due to their rich redox activity and high specific capacity. In this study, nickel sulfide (NiS), nickel phosphate (Ni(PO₃)₂), and their composites (NiS/(Ni(PO₃)₂)) with varying weight ratios (1:1, 1:2, and 2:1) were synthesized via a facile hydrothermal route. Electrochemical studies (CV, GCD, and EIS) confirm that the NiS/(Ni(PO₃)₂ (1:1) composite delivers the most efficient charge-storage behavior, predominantly governed by a faradaic mechanism, with a specific capacity of 457.25C/g (762.08 F/g) at 2 A/g. The enhanced electrochemical performance was attributed to the synergistic coupling between NiS and Ni(PO₃)₂, which enhanced electrical conductivity, ion diffusion, and redox activity. Furthermore, a hybrid supercapattery device was fabricated with the optimized composite, which achieved an energy density of 21.31 Wh/kg and a power density of 1875 W/kg, demonstrating energy-power balance. The fabricated device exhibited 89% coulombic efficiency and 86% cyclic stability. The practical applicability was shown by constructing a solid-state supercapacitor that successfully powered a hygrometer. These findings highlight the strong potential of NiS/Ni(PO₃)₂ composites as efficient and stable electrode materials for advanced supercapacitors and hybrid energy storage applications.