Highly stable core-shell heterostructures by homologous metal sulfides for supercapacitors

Transition metal sulfide (TMS) demonstrates significant potential as an anode material for supercapacitors due to its abundant REDOX reaction capabilities and high conductivity. This paper presents the design and construction of a homologous TMS core-shell heterostructure using a hydrothermal method for asymmetric supercapacitor (ASC) cathode materials. The anion-exchange reaction produces a one-dimensional NiCo₂S₄ nanowire array featuring enhanced structural stability and increased active sites, along with a three-dimensional heterogeneous structure incorporating two-dimensional NiCo₂S₄ nanosheets. This configuration creates a synergistic effect that yields higher conductivity and accelerated REDOX kinetics. Furthermore, the utilization of homologous TMS in both core and shell structures results in superior lattice matching and more uniform physicochemical properties, thereby minimizing stress concentration issues related to material compatibility, improving stability, and delivering higher specific capacitance and cycle life. The NiCo₂S₄@NiCo₂S₄ electrode, functioning as a binder-free electrode for the supercapacitor, achieves a high specific capacitance of 677.3 C g^-1 at a current density of 1 A g^-1. It maintains impressive capacitance retention rates of 82.7 % and 79.2 % at 10 A g^-1 (560.3 C g^-1) and 15 A g^-1 (536.2 C g^-1), respectively. Additionally, at a current density of 1 A g^-1, the battery demonstrates extended cycle life of 5,000 cycles with a capacitor retention rate of 92.3 % at a current density of 5 A g^-1. The assembled NiCo₂S₄@NiCo₂S₄//AC battery exhibits exceptional electrochemical performance (43.46 Wh kg^-1 at 770.7 W kg^-1). However, how to ensure the uniformity and high quality of the core-shell structure through post-processing during the preparation process, and how to improve the packaging technology during use to ensure the integrity of metal sulfides in extreme environments remain a key issue. We will continue to explore this in subsequent experiments. This study introduces innovative prospects for the large-scale industrial manufacturing of positive electrode materials tailored for supercapacitors and applications involving energy storage.