Consideration of Suitable Sodium Battery Cathode Materials

Interest in sodium based batteries is motivated by several factors including the low cost and high earth abundance of sodium. However, to realize the benefits envisioned by the adoption of this lithium alternative chemical system for energy storage, the other battery components must also provide similar desirable features of low cost and high earth abundance. Therefore, cathode materials must be chosen judiciously to not offset the potential gains due to the selection of sodium as the mobile cation. Thus, cathode materials based on select transition metals are of interest.
Manganese oxide materials are appealing as battery cathodes due to their high specific capacity, low cost, earth abundance, and environmental compatibility. Further, there is significant structural design flexibility as manganese is capable of forming a wide range of manganese oxide polymorphs with multiple stable manganese oxidation states and a variety of central cations. Notably, manganese oxides can adopt both layer structured phases proving 2D ion diffusion as well as 1D tunnel-type structures with a diversity of tunnel sizes and configurations. Deliberate synthesis of several manganese oxide structures and compositions was accomplished. The electrochemical behavior of the materials and their material evolution under electrochemistry in lithium based systems and sodium systems will be presented and contrasted to shed light on important features to consider in suitable material design for sodium based batteries.