Surface Sulfurization and Self‐Reconstruction Strategy for Decorating Carbon Nanofibers to Fabricate Sheet‐Like NiCo₂S₄ Grown on Ni₃S₂ Electrode for High‐Energy Density Asymmetric Supercapacitor

Abstract In this study, transition metal sulfide‐based binder‐free hybrid electrodes were grown in‐situ on Ni foam using hydrothermal method. However, it still remains a challenge for designing a heterostructure with sufficient electroactive sites to improve electrochemical performance. Herein, effects of CNF@NSNCS on Ni foam binder‐free composites were investigated for developing high‐performance, low‐cost supercapacitors. By avoiding the use of additive binding polymers, the purity of the electrodes was enhanced, resulting in excellent electrochemical behavior. The prepared binder‐free CNF@NSNCS composite electrode exhibited an ultrahigh specific capacitance of 2739 F/g at a current density of 1 A/g, with superior capacitance retention charge‐discharge cycle stability of 100 % over continuous 14,000 cycles at 10 A/g. Furthermore, an asymmetric supercapacitor (ASC) was assembled using CNF@NSNCS binder‐free composites as the positive electrode and Activated carbon (AC) as the negative electrode. The assembled devices demonstrated superior electrochemical performance, delivering a high energy density of 77.5 Wh/kg at a power density of 748.4 W/kg. This work may contribute to advancing the development of low‐cost, high‐performance energy storage applications for the next generation of portable electronic devices.