Synergy Strategy of Electrical Conductivity Enhancement and Vacancy Introduction for Improving the Performance of VS 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 VS (Mo-VS/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 Mg (-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-VS/N-TG delivers a steady Mg storage specific capacity of about 140 mAh g at 50 mA g, outstanding cycle stability (80.6% capacity retention ratio after 1200 cycles under 500 mA g), and excellent rate capability (specific capacity reaches 77.1 mAh g when the current density reaches 500 mA g). In addition, the reversible reaction process, intercalation mechanism, and structural stability during the Mg insertion/extraction process are confirmed by a series of characterizations. This research provides a sustainable and scalable strategy to spur the development of MIBs.