Strategically optimized diffusion dynamics in Ni9S8 nanoflower architectures for high-performance asymmetric supercapacitors

The growing demand for sustainable solutions in future electronic systems has accelerated the replacement of outdated devices with more efficient and reliable technologies. In this context, surface-controlled Ni9S8 was synthesized using a hydrothermal method. An orthorhombic crystal structure was verified through x-ray diffraction analysis, while field emission scanning electron microscopy revealed nano-scale platelets with a distinctive flower-like morphology, ideal for storage mechanisms. Energy-dispersive x-ray spectroscopy further confirmed the phase purity and all possible constituents. Cyclic voltammetry demonstrated high reversibility and a diffusion-controlled charge storage mechanism, interpreted using Dunn's model. Galvanostatic charge–discharge analysis showed a significant specific capacity (Qsp) of 952 C/g at a current density (J) of 11.8 A/g. The optimized material delivered an outstanding energy density (Ed) with a value of 66.1 Wh/kg alongside a power delivery (Pd) of 2941.2 W/kg, maintaining 98.6% of its initial capacity value and 97.6% coulombic efficiency after 3000 cycles. Electrochemical impedance spectroscopy revealed a low charge transfer resistance of 0.28 Ω, a high ionic conductivity of 0.12 S/cm, highlighting the electrode's fast kinetics. The asymmetric device exhibited a Qsp of 104.2 C/g at a J value of 0.7 A/g with Ed of 17.3 Wh/kg and Pd of 423.5 W/kg. Furthermore, the diffusion coefficient was optimized under varying current densities and molar concentrations, with the best results being 7.1 × 10−15 cm2/s at a 2 M solution and 5 mA current. These findings demonstrate the potential of the material for hybrid energy storage systems, smart electronics, and sensor applications.