Effect of mass loading and fabrication of VARTM-based high-performance solid-state supercapacitor device with MXene-NiCo₃S₄ nanocomposite

Transition metal sulfides with binary compositions have recently regained attention as promising electrode materials for supercapacitors with high energy density. However, their electrochemical performance suffers significantly as mass loading increases due to their limited electrical and ionic conductivities, which restrict their practical energy output. This study used a one-pot hydrothermal process to synthesize NiCo₃S₄ nanoparticles directly onto a two-dimensional Ti₃C₂ (Mxene) surface, forming MXene-NiCo₃S₄ nanocomposites (NCs). Through electrostatic interaction, positively charged nickel ions and negatively charged Mxene enable uniform dispersion of NiCo₃S₄ on Ti₃C₂. We investigated the effect of mass loading of Mxene-NiCo₃S₄ NCs electrodes on a carbon woven fiber substrate. It was observed that increasing the mass loading of MXene-NiCo₃S₄ NCs electrodes from 1.2 mg/cm² to 2.8 mg/cm² resulted in an initial increase in specific capacitance, followed by a decrease, with the optimal specific capacitance achieved at 2.5 mg/cm². The resulting electrode shows remarkable areal capacitance, reaching 0.862 F cm⁻² at 0.58 mA cm⁻² in neutral aqueous electrolytes using Mxene-NiCo₃S₄ NCs. Moreover, we demonstrate practical applicability by integrating MXene-NiCo₃S₄ NCs onto woven carbon fiber and fabricating a symmetric supercapacitor device using the VARTM technique with polyvinyl alcohol-EMIBF₄ gel electrolyte as the electrolyte and electrode separator. This device achieves a specific capacitance of 0.30 F /cm² at 2.4 mA/cm², along with a maximum energy density of 69.42 Wh/kg at a power density of 1000 W/kg while maintaining excellent cycle stability for up to 10,000 cycles with 91 % retention of its initial capacitance. Findings at lower mass loadings reveal mechanisms that limit performance in thicker electrodes, such as enhanced ion transport and reduced resistance. This knowledge informs the design of high-mass loading electrodes by addressing issues like poor electrolyte penetration and sluggish ion dynamics. Future work will build on these insights to optimize high-mass loading configurations for practical applications, bridging the gap between laboratory results and industrial use.