Phase Transformations in Layered O and P Type Metal Oxide Na-Ion Battery Cathodes

Current state of the art Na-ion battery cathodes are selected from the broad chemical space of layered first row transition metal (TM) oxides. Unlike their lithium ion counterparts, seven first row layered TM oxides can intercalate Na ions reversibly. Their voltage curves also indicate significant and numerous reversible phase transformations during electrochemical cycling. These transformations are not yet fully understood, but arise from Na-ion vacancy ordering and metal oxide slab glide. In this study, we investigate the nature of vacancy ordering transformations within the O3, P3 and P2 lattice frameworks. We generate predicted electrochemical voltage curves for each of the Na-ion intercalating layered single TM oxides using a high-throughput framework of density functional theory (DFT) calculations. We determine a set of vacancy ordered phases appearing as ground states in all Na\textsubscript{x}MO\textsubscript{2} systems, and investigate the effect of ordering interactions between adjacent layers. We further investigate the role of TM choice and TM mixing in mitigating phase transformations and synthesis of O3 and P2 type materials.