Rich Se Vacancies Mo _x V _1‐x Se ₂ Nanosheets with Synergistic Optimization of Electronic and Lattice Structures for Accelerating Sulfur Redox Kinetics in Mg─S Batteries

ABSTRACT Rechargeable magnesium–sulfur (Mg─S) batteries are considered promising next‐generation energy storage solutions because of their high volumetric energy density. However, they often suffer from severe performance degradation due to the well‐known polysulfide shuttle effect and sluggish reaction kinetics. Defective materials are widely employed in metal‐sulfur battery systems due to their unique adsorptive and catalytic properties, which effectively address the challenges of polysulfide shuttle and sluggish conversion kinetics during charge‐discharge processes. Nevertheless, studies systematically correlating defect concentration with the adsorptive‐catalytic properties of electrodes remain scarce. In this study, Mo x V 1‐x Se 2 (x = 0‐0.1) with tunable selenium‐vacancy concentrations is employed as a model system to modulate its electronic structure and enhance catalytic performance. A quantitative correlation is further established between selenium‐vacancy concentration and adsorption‐catalytic properties to regulate sulfur redox kinetics. Experimental and theoretical findings indicate that a higher density of selenium vacancies effectively provides additional active sites and promotes electron accumulation, leading to reduced energy barriers for MgS nucleation/decomposition as well as faster kinetics in polysulfide conversion reactions. Thus, the Mo 0.075 V 0.925 Se 2 with abundant selenium vacancies concentrations exhibits exceptional performance as a sulfur host, delivering the highest reversible capacity (1127 mAh g −1 ) and remarkable cycling stability (200 cycles with ∼99.7% capacity retention). This study contributes to advancing the practical implementation of defect engineering with quantitative control for application in Mg─S batteries.