Inherent inhibition of oxygen loss by regulating superstructural motifs in anionic redox cathodes

The capacity of the layered oxide cathode in a sodium ion battery can be increased by harnessing anionic redox. However, the extra capacity induced by anionic redox comes at the expense of reversibility due to the irreversible oxidation and subsequent loss of oxygen. Here, we report a universal strategy of improving the reversibility of oxygen redox in sodium layered oxides by regulating the superstructural motifs. The intrinsic chemical properties of superstructural motifs can be directionally altered by modulating the interionic interactions, and the rational integration of selected superstructural motifs can result in advanced materials with target performance. As a demonstration, a novel cathode comprising both Mg@Mn6 and Li@Mn6 superstructural motifs is designed and synthesized with inherently inhibited oxygen loss and significantly improved cyclic reversibility. Detailed characterizations on the atomic-level structure and chemistry of materials revealed that the pinning effect of the Mg@Mn6 superstructural motif is critical to maintain a stable layered structure. The findings from this work open up new routes for the design and development of next-generation high energy cathodes with target performance.