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 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 VO (≈200 nm) is demonstrated by a thin layer of VS (≈12 nm) through a facile surface reduction route. The VS layer protects the surface of VO particles in RMB electrolyte solution (MgCl + MgTFSI in DME). Both VO and VO@VS particles demonstrate high initial discharge capacity. However, only the VO@VS material demonstrates superior rate performance, Coulombic efficiency (100%), and stability (138 mA h g discharge capacity after 100 cycles), signifying the ability of the thin VS layer to protect the VO cathode and facilitate the Mg ion intercalation/deintercalation into VO.