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The presence of H₂O has been linked to enhancements in the reactivity of cathodes for Mg²⁺ electrochemistry. If the enhancements were mimicked by nonaqueous solvents, they could enable Mg batteries with transformational energy density. However, the extent to which H₂O may boost actual intercalation of Mg²⁺, as opposed to competing reactions, has not been elucidated. Here, in this paper, we evaluate its role as additive in the electrochemistry of a tunnel polymorph of V₂O₅ in a nonaqueous Mg²⁺ electrolyte. The electrochemical response and V reduction in the cathodes positively correlated with H₂O concentration, but it was not concurrent with commensuratemore » changes in cell volume and Mg content. These observations indicate that H₂O does not enhance Mg²⁺ intercalation, but rather, it promotes competing pathways. This work shows the importance of accurately probing reactions in multivalent electrolytes. Importantly, it indicates that H₂O is not a universal solution to the challenge of Mg²⁺ intercalation in oxides.« less

Nanometric ζ-V ₂ O ₅ displayes an enhanced ability to reversibly store Mg ²⁺ , yielding a better understanding of kinetic limiting factors in reversible magnesiation reactions of oxide electrode materials.

While α-V₂O₅ has traditionally been considered as a promising oxide to reversibly intercalate high levels of Mg²⁺ at high potential, recent reports indicate that previously observed electrochemical activity is dominated by intercalation of H⁺ rather than Mg²⁺, even in moderately dry nonaqueous electrolytes. Consequently, the inherent functionality of oxides to intercalate Mg²⁺ remains in question. By conducting electrochemistry in a chemically and anodically stable ionic liquid electrolyte, we report that, at 110 °C, layered α-V₂O₅ is indeed capable of reversibly intercalating 1 mol Mg²⁺ per unit formula, to accumulate capacities above 280 mAh g^–1. Multimodal characterization confirmed intercalation of Mg²⁺more » by probing the elemental, redox, and morphological changes undergone by the oxide. After cycling at 110 °C, the electrochemical activity at room temperature was significantly enhanced. The results renew prospects for functional Mg rechargeable batteries surpassing the levels of energy density of current Li-ion batteries.« less