Synergy Strategy of Electrical Conductivity Enhancement and Vacancy Introduction for Improving the Performance of VS₄ Magnesium-Ion Battery Cathode

The development of cathode materials with a high electric conductivity and a low polarization effect is crucial for enhancing the electrochemical properties of magnesium-ion batteries (MIBs). Herein, Mo doping and nitrogen-doped tubular graphene (N-TG) introduction are carried out for decorating VS4 (Mo-VS4/N-TG) via the one-step hydrothermal method as a freestanding cathode for MIBs. The results of characterizations and density functional theory (DFT) reveal that rich sulfur vacancies are induced by Mo doping, and N-TG as a high conductive skeleton material serves to disperse the active material and forms a tight connection, all of which collectively improved the electrical conductivity of electrode and increased the adsorption energy of Mg2+ (−6.341 eV). Furthermore, the fast reaction kinetics is also confirmed by the galvanostatic intermittent titration technique (GITT) and the pesudocapacitance-like contribution analysis. Benefiting from the synergistic effect of electrical conductivity enhancement and rich vacancy introduction, Mo-VS4/N-TG delivers a steady Mg2+ storage specific capacity of about 140 mAh g–1 at 50 mA g–1, outstanding cycle stability (80.6% capacity retention ratio after 1200 cycles under 500 mA g–1), and excellent rate capability (specific capacity reaches 77.1 mAh g–1 when the current density reaches 500 mA g–1). In addition, the reversible reaction process, intercalation mechanism, and structural stability during the Mg2+ insertion/extraction process are confirmed by a series of ex situ characterizations. This research provides a sustainable and scalable strategy to spur the development of MIBs.