Bimetallic sulfide NiCo2S4 yolk–shell nanospheres as high-performance cathode materials for rechargeable magnesium batteries

Abstract

Constructing bimetallic sulfides with ideal structures could effectively alleviate the poor cycling stability of rechargeable Mg batteries due to a bimetallic synergistic effect. An exquisite yolk–shell structured bimetallic sulfide NiCo₂S₄ synthesized via a two-step solvothermal hydrothermal method is investigated as a cathode material for rechargeable Mg batteries. With the bimetallic strategy and well-designed architecture, the as-synthesized yolk–shell NiCo₂S₄ exhibits outstanding Mg-storage performance, demonstrating a superior reversible capacity (270 mA h g⁻¹ at 50 mA h g⁻¹), a high rate capability, and a specific capacity retention of 91% over 400 cycles (2.2% capacity decay per cycle). The in-depth mechanism investigation reveals the two-step conversion reaction process and the bimetallic synergistic effect in the Mg-storage process. Based on DFT calculations and kinetic investigations, the bimetallic synergistic effect effectively alleviates the Jahn–Teller effect and distortion in the crystal lattices and increases active reaction sites, thus largely enhancing the electrochemical Mg-storage performance. The superior electrochemical performance of NiCo₂S₄ not only demonstrates the viability of the bimetallic strategy but also sheds light on the use of nanostructure design for high-performance cathode research.