NiCo2(SxSe1-x)4 sulfoselenide microspheres with optimized S/Se ratio for asymmetric supercapacitors

Composition-engineered multi-anion transition-metal chalcogenides are promising electrode materials for high-performance supercapacitors because their anion chemistry can tune charge-transfer characteristics and redox utilization. In this study, a series of NiCo2(SxSe1-x)4 sulfoselenide microspheres with different S/Se ratios (NCSSe-0.4, NCSSe-0.5, and NCSSe-0.6) was synthesized by a hydrothermal route followed by post-annealing to establish how anion composition governs structure, kinetics, and device-level performance. The samples were characterized by XRD, SEM, N2 adsorption-desorption, and XPS, and their electrochemical behavior was evaluated in 6 M KOH by CV, GCD, EIS, and Dunn's kinetic analysis. Among the series, NCSSe-0.5 exhibited the best overall performance, delivering 835.7 F g−1 at 10 mV s−1 and 471.3 F g−1 at 1 A g−1. Kinetic analysis revealed diffusion-dominated battery-type charge storage for NCSSe-0.5, with a b-value of 0.38 and a diffusion contribution of 90.25% at 10 mV s−1. An asymmetric supercapacitor assembled using NCSSe-0.5 as the positive electrode and activated carbon as the negative electrode operated over 0.0–1.5 V, achieving 8.6 Wh kg−1 at 750 W kg−1 and 3.1 Wh kg−1 at 7500 W kg−1. These results show that tuning the S/Se ratio is an effective strategy for optimizing Nisingle bondCo sulfoselenide electrodes and clarifying the composition–structure–kinetics relationship relevant to asymmetric supercapacitor applications.