Crystal reconstruction of V2O3/carbon heterointerfaces via anodic hydration for ultrafast and reversible Mg-ion battery cathodes

Magnesium-ion batteries (MIBs) have promising applications because of their high theoretical capacity and the natural abundance of magnesium Mg. However, the kinetic performance and cyclic stability of cathode materials are limited by the strong interactions between Mg ions and the crystal lattice. Here, we demonstrate the unique Mg²⁺-ion storage mechanism of a hierarchical accordion-like vanadium oxide/carbon heterointerface (V₂O₃@C), where the V₂O₃ crystalline structure is reconstructed into a MgV₃O₇∙H₂O phase through an anodic hydration reaction upon first cycle, for the improved kinetic and cyclic performances. As verified by in situ/ex situ spectroscopic and electrochemical analyses, the fast charge transfer kinetics of the V₂O₃@C cathode were due to the crystal-reconstruction and chemically coupled heterointerface. The V₂O₃@C demonstrated an ultrahigh rate capacity of 130.4 mAh g⁻¹ at 50 000 mA g⁻¹ and 1000 cycles, achieving a Coulombic efficiency of 99.6%. The high capacity of 381.0 mA h g⁻¹ can be attributed to the reversible Mg²⁺-ion intercalation mechanism observed in the MgV₃O₇∙H₂O phase using a 0.3 M Mg(TFSI)₂/ACN(H₂O) electrolyte. Additionally, within the voltage range of 2.25 V versus Mg/Mg²⁺, the V₂O₃@C exhibited a capacity of 245.1 mAh g⁻¹ when evaluated with magnesium metal in a 0.3 M Mg(TFSI)₂ + 0.25 M MgCl₂/DME electrolyte. These research findings have important implications for understanding the relationship between the Mg-ion storage mechanism and reconstructed crystal phase of vanadium oxides as well as the heterointerface reconstruction for the rational design of MIB cathode materials.