Optimization of CNT-induced Ni9S8 nanoplates for balanced charge-transfer kinetics and conductivity in high-performance battery-type supercapacitors.

The growing need for sustainable and eco-friendly energy solutions has intensified the efforts to develop advanced electrode materials with superior electrochemical traits. In this study, we synthesized Ni9S8 (NS), and its carbon nanotube (CNT) based composites containing 3, 6, and 9% CNTs (NS-3, NS-6, and NS-9) for supercapacitor applications. NS exhibited an initial plate-like morphology, which transformed into a CNT-entangled structure in composites. NS-6 showed an increased surface area of 61.72 m2 g-1, reflecting the coexistence of both micro and mesopores. Cyclic voltammetry revealed well-defined redox peaks across multiple scans, signifying a hybrid charge storage behavior, as validated through Dunn's model analysis. Among all composites, NS-6 showed the best electrochemical performance, achieving a specific capacity of 1382.47 C g-1 at 2.0 A g-1 and excellent cyclic stability with 95.5% retention after 10 000 cycles. The composite also presented enhanced ionic conductivity (4.4 × 10-2 S cm-1), reduced charge transfer resistance (2.51 Ω), and a diffusion coefficient of 7.48 × 10-11 cm2 s-1. Based on these optimized results for NS-6, an asymmetric device was assembled, delivering 301.11 C g-1, an energy density of 50.18 Wh kg-1, and a power density of 705.88 W kg-1. These results highlight NS-6 as a leading contender for efficient electrode materials for future energy solutions.