Sustainable Cathodic Performances of VS₄ in Rechargeable Magnesium Batteries by Cobalt Substitution

Vanadium tetrasulfide (VS₄) is one of the most promising cathodic materials for rechargeable magnesium battery systems (RMBSs). Elemental substitution to expand layers, creation of sulfur vacancies, and reduction of particle sizes of VS₄ are undoubtedly effective strategies to enhance cathodic performances. Experimental and DFT analysis revealed that valence states of vanadium and cobalt have been elevated from V²⁺ to V³⁺ and Co²⁺ to Co³⁺ in VS₄ and that the Co-S bond length shortened due to cobalt substitution, which resulted in enhanced overall internal polarization in the layered atomic structure of VS₄ by increasing cobalt concentrations. This phenomenon of charge accumulation contributes toward regulated magnesiation and accommodated volume expansion while cycling, resulting in the enormous structural stability of VS₄ and sustainable battery performance during a long and stable cycling at a cost of 20% capacity diminution as compared to pristine VS₄ in RMBS. Hence, 9% CoVS₄ demonstrated a capacity of 158 mAh g^-1 at a current density of 500 mA g^-1 with approximately 98% capacity retention after 1000 cycles. Sustainable cathodic performance is the most desirous feature for commercialization. This work provides insight realization regarding structural limitations and opportunities of VS₄ for sustainable cathodic performances in RMBS with non-nucleophilic 0.25 mol/L (R-PhOMgCI)₂-A1Cl₃/THF (PMC) electrolyte and has laid a theoretical plus experimental foundation for future developments.