Electrochemical insertion of lithium, sodium, and magnesium in molybdenum(VI) oxide

The electrochemical insertion of divalent magnesium cations into orthorhombic molybdenum(VI) oxide was studied with regard to their use as electroactive species in ion-transfer battery systems and compared to the insertion of Li+ and Na+. Specific charges of up to 300 and 240 Ah kg−1 were obtained in organic, propylene carbonate-based electrolytes for the lithium and sodium insertion, respectively, in the first reduction half-cycle. Reversible Mg2+ insertion could be demonstrated in a room temperature molten salt electrolyte consisting of 3 wt.% MgCl2, 41 wt.% 1-ethyl-3-methylimidazolium chloride, and 56 wt.% AlCl3. Specific charges of up to 160 Ah kg−1 were obtained with MoO3 in the first reduction half-cycle. The Mg2+ insertion process can be enhanced using an organic electrolyte with traces of H2O. In 1 M Mg(ClO4)2/acetonitrile with 3 mol% of H2O, specific charges of up to 210 Ah kg−1 were measured in the first reduction.