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

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.