MgCr_2-XV_xO₄ High Voltage Spinel Oxide Cathodes for Mg-Ion Batteries

Theoretical and experimental evidences have revealed that Cr-spinel oxides fulfill the cationic mobility requirements of Mg-ion cathode with a suitable activation energy, while V-spinel oxides with lower redox potentials are moderate to the operating potentials of current candidates of non-aqueous high voltage electrolyte. By controlling structure, composition and complexity, a largely solid-solution MgCrVO4 spinel was synthesized which unlike nanocomposites can bring together the advantages of each transition metal. The spinel was successfully prepared by a simple solid-state reaction with minor inactive Cr or V rich components which was confirmed via 25Mg MAS NMR and high resolution X-ray diffraction analyses. A thermally stable Mg(TPFA)2/triglyme electrolyte was utilized for high temperature electrochemistry, lowering kinetic barriers at and across interfaces so as to observe reversible intercalation in the designed oxide. Multimodal characterization confirmed an apparent bulk demagnesiation from MgCrVO4 with partial reversibility, by probing evolution of the local and long range structure as well as vanadium and chromium electronic states within the lattice. Characterization experiments also provided direct evidence of (de)intercalation reactions that occurred without any major competitive conversion reactions or insertion of protons into the lattice. These findings expand materials composition and complexity design opportunities for Mg-ion cathodes while highlighting the need to identify the origins of reversibility challenges due to but not limited to phase stability particularly for the charged states, barriers at the interface, electrolyte stability and desolvation phenomena.