(Invited) A Tale of Spinels: From Li-Ion to Mg Battery Electrodes

Since the discovery by Thackeray and co-workers of their ability to reversibly intercalate Li, spinel oxides have become a canonical electrode material in battery technologies. Phases with this structure typically present very stable cycle life in the bulk and fast kinetics. When used as positive electrodes, the downside of spinel electrodes is their fairly low capacity and their interfacial instability. In Li-ion batteries, the best performance is obtained with significant amounts of Mn in the structure. Ions of these element, when redox active, are prone to corrosion processes that undermine the cyclability of the electrochemical cell. Further, while full intercalation from M₂O₄ (M=Mn, Ni, Co...) to Li₂M₂O₄ is possible, it is also poorly reversible. As a result, practical applications limit the utilization to processes between M₂O₄ and LiM₂O₄. In other words, this material highlights the barrier of two electron reactivity that is pervasive in battery electrodes based on intercalation reactions.

In this talk, we will overview the strategies we have followed to expand the versatility of spinel oxides as reversible intercalation electrodes. We will discuss our efforts to understand the kinetic limitations of the Mn₂O₄-Li₂Mn₂O₄ transition using high resolution chemical imaging. We will describe strategies to understand and impart interfacial stability, especially against corrosion processes that damage full battery performance. Finally, we will introduce evidence that this family of oxides could provide a path to explore positive electrodes for emerging multivalent technologies, with emphasis on Mg batteries.