Mitigating Interfacial Capacity Fading in Vanadium Pentoxide by Sacrificial Vanadium Sulfide Encapsulation for Rechargeable Mg-Ion Batteries

Rechargeable Mg-ion Batteries (RMB) containing a Mg metal anode offer the promise of higher specific volumetric capacity, energy density, safety, and economic viability than lithium-ion battery technology, but their realization is challenging. The limited availability of suitable inorganic cathodes compatible with electrolytes relevant to Mg metal anode restricts the development of RMBs. Despite the promising capability of some oxides to reversibly intercalate Mg⁺² ions at high potential, its lack of stability in chloride-containing ethereal electrolytes, relevant to Mg metal anode hinders the realization of a full practical RMB. Here the successful in situ encapsulation of monodispersed spherical V₂O₅ (≈200 nm) is demonstrated by a thin layer of VS₂ (≈12 nm) through a facile surface reduction route. The VS₂ layer protects the surface of V₂O₅ particles in RMB electrolyte solution (MgCl₂ + MgTFSI in DME). Both V₂O₅ and V₂O₅@VS₂ particles demonstrate high initial discharge capacity. However, only the V₂O₅@VS₂ material demonstrates superior rate performance, Coulombic efficiency (100%), and stability (138 mA h g⁻¹ discharge capacity after 100 cycles), signifying the ability of the thin VS₂ layer to protect the V₂O₅ cathode and facilitate the Mg⁺² ion intercalation/deintercalation into V₂O₅.