Synergistic modulation of capacitive-diffusive charge storage kinetics in an Ni-SnS2@SnO2 nanocomposite for advanced micro-supercapacitor applications.

Metal sulfide/oxide nanocomposites are promising electrode materials for high-performance supercapacitors; however, the charge-storage kinetics of Ni-doped SnS2@SnO2 remain insufficiently explored. Moreover, previous studies on SnO2-based electrodes have mainly focused on enhancing capacitance, while the underlying charge-storage kinetics, particularly the distinction between capacitive and diffusion-controlled contributions, remain largely unexplored. Herein, an Ni-SnS2@SnO2 nanocomposite was synthesized by a simple, cost-effective one-step solvothermal method and characterized by XRD, FESEM, EDX, and HR-TEM. SnS2, SnS2@SnO2, and Ni-SnS2@SnO2 electrodes were evaluated in 1 M Na2SO4 using CV, GCD, and EIS in a three-electrode configuration. Structural analysis confirmed the formation of the SnS2@SnO2 heterostructure, while Ni incorporation induced lattice expansion and increased interlayer spacing, facilitating ion accessibility and rapid intercalation/deintercalation. At 0.5 mA cm-2, Ni-SnS2@SnO2 delivered an areal capacitance of 202.63 mF cm-2, superior to the 66.32 and 108.06 mF cm-2 delivered by SnO2 and SnS2@SnO2, respectively. Kinetic analysis revealed a mixed capacitive-diffusion-controlled mechanism arising from heterostructure formation and Ni doping, which enhanced charge transport and introduced additional redox-active sites. The electrode retained ∼85% of its capacitance after 5000 cycles and achieved 18.01 mW h cm-2 energy density at 199.98 mW cm-2 power density. A coulombic efficiency of 85.05-99.93% further demonstrates excellent reversibility and rate capability. These results highlight Ni-SnS2@SnO2 as a promising electrode for advanced micro-supercapacitors and next-generation energy storage systems.