Multivalent ion storage systems are attractive among the alternative systems because, while they closely resemble systems using Li-ion, they can store more charge per mol of intercalated species, which creates the opportunity for less dramatic structural rearrangements in the host materials, and therefore enhanced stability. In particular, Mg-ion batteries are of great interest to surpass the current performance barriers of Li-ion technology. The electrochemical intercalation of Mg ions into several compounds has been investigated. Most previous studies about the multivalent ion electrochemistry in oxide compounds have provided little information on the reaction mechanisms leading to the electrochemical data. The proof of Mg2+ intercalation was mainly based on the existence of an electrochemical response or indirect manners. In this paper, by using combinatorial characterization tools, reversible multivalent ion (Mg) intercalation into spinel structure has been confirmed. Tetragonal phase MgMn2O4 is achieved by the intercalation of Mg into the cubic spinel structure, λ-MnO2, and reversibly oxidized back to the cubic spinel structure by deintercalation of Mg. The experimental observations by XRD, XAS, STEM-EDX, and NMR, all verify that the intercalation reaction occurred. Our work has great importance in several aspects. First, the reaction mechanism of Mg intercalation into the spinel λ-MnO2 has been confirmed, which will potentially work as an active cathode material for Mg-ion batteries. Second, our work will assist future understanding of the mechanisms involved in multivalent ion storage, as well as the most efficient ways to characterize these reactions.

Direct observation of magnesium ion intercalation into a spinel-structured λ-manganese oxide at the multilength scale

249th National Meeting (2015)

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