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.