Direct Observation of Magnesium Ion Intercalation into a Spinel-Structured λ-Manganese Oxide at the Multi Length Scale

The growing market of electric vehicles and grid storage requires the current battery technology to be further advanced. However, LIBs, the best energy storage system based on redox reactions, are intrinsically limited in their charge storage capacity by structural and/or electronic factors. 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. In particular, Mg-ion batteries are of great interest to surpass the current performance barriers of Li-ion technology. There is only one proven working positive electrode material, Chevrel phase, for Mg ion battery at a relatively low working voltage window.^{1, 2} When searching for high voltage Mg-intercalation positive electrodes, most previous studies of the possible electrochemistry of oxide compounds Mg²⁺ electrolytes have provided little information on the reaction mechanisms leading to the electrochemical data.³  In this work, direct evidence of the reversible intercalation of Mg²⁺ into a spinel host was obtained. The structural changes observed after intercalation/deintercalation into the cubic spinel structure, λ-MnO₂, and from tetragonal Mg_xMn_3-xO₄ nanoparticles will be discussed.  Experimental observations by XRD, XAS, STEM-EDX, PDF and NMR were used to provide a robust understanding of the electrochemical reactions (see representative STEM-EDX in Figure 1).  The results confirm that spinel oxides are a potential cathode material for Mg batteries. They point at needs in the understanding of the mechanisms involved in multivalent ion storage, as well as the most efficient ways to characterize these reactions.

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2.            H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, and D. Aurbach, Energ Environ Sci, 6 (8), 2265-2279 (2013).

3.            C. Yuan, Y. Zhang, Y. Pan, X. Liu, G. Wang, and D. Cao, Electrochimica Acta, 116 (0), 404-412 (2014).