Cathode properties of MgV2O4 spinel for magnesium rechargeable batteries: effect of synthesis route on structure and electrochemical performance

Abstract

Magnesium rechargeable batteries (MRBs) are promising candidates for next-generation energy storage owing to their high volumetric capacity and safety. Herein, we investigate spinel-type MgV₂O₄ (MVO) as a cathode material and elucidate the correlation between its crystal structure and electrochemical performance. An ordered spinel was synthesized via a solid-state route and subsequently subjected to mechanical milling (MM), while a solvothermal (ST) method was employed to prepare a comparative sample. Rietveld refinement revealed that MM induces a transition from an ordered to a disordered spinel structure, accompanied by partial V occupancy at the interstitial 16c site, which obstructs Mg²⁺ migration between 8a sites. Despite particle size reduction, MM-MVO exhibited poor reversibility due to this structural disorder. Complementary computational analysis confirmed the energetic favorability of V migration into the 16c site by MM, explaining the origin of the diffusion barrier. In contrast, ST-MVO retained a relatively ordered structure with minimal V occupation at 16c sites and delivered a reversible capacity of 175 mAh g⁻¹ at 2 V when paired with a high-voltage electrolyte. These findings highlight the critical role of spinel ordering in enabling efficient Mg²⁺ transport and provide design guidelines for high-performance MRB cathodes.