Mechanochemical Synthesis of MgV₂O₄: Reactivity Pathways Driven by Milling Energy and Precursors

Magnesium spinels such as MgAl₂O₄ and MgFe₂O₄ have been widely explored for energy storage and sensing applications, but MgV₂O₄ remains relatively unexplored despite its promising potential, e.g., as a battery electrode material. In this study, we report the first mechanochemical synthesis of MgV₂O₄ at room temperature using either MgO or Mg with various vanadium oxides as reactants. Directed by thermodynamic calculations on a DFT level, only the self-sustaining reaction between V₂O₅ and Mg led to MgV₂O₄ within 20 min of milling, along with MgO as a side product. With increasing rotational speed, an earlier reaction ignition after a few minutes of milling, smaller crystallite sizes in the nanometer range, and increased strain in MgV₂O₄ were observed. In addition, harsh milling conditions induce increasing nonstoichiometry in both phases, leading to a magnesium-rich spinel and a vanadium-containing rock salt phase, as supported by X-ray diffraction and electron paramagnetic resonance measurements. Acid washing after synthesis removed MgO, and electrochemical impedance spectroscopy showed that milder grinding conditions increased the conductivity of MgV₂O₄ due to the smaller number of defects.