Electronic Properties, Phase Transformation, and Anionic Redox of Monoclinic Na2MnO3 Cathode Material for Sodium‐Ion Batteries: First‐Principle Calculations

The high electrochemical performance of Li2MnO3‐derived Li‐rich layered oxides suggests that Na2MnO3 might be a promising cathode material for sodium‐ion batteries for its effective anionic oxygen redox. However, experimental and theoretical evidence for anionic redox and enhanced Na+ capacity of Na2MnO3 has not been established. In the present work, the structural and thermal stability, and the anionic oxygen redox mechanism of Na2MnO3 were studied by using first‐principle calculations based on density functional theory. About 1.75 Na+ per formula unit were extracted from Na2‐xMnO3 through partial O2− oxidation while the local structure remained intact, resulting in a large theoretical capacity of 315 mA h g−1. Surface Na+ was extracted before bulk Na+, which might have led to oxygen loss and structural transformation from the surface to the material bulk. Given the importance of high capacity in practical applications, Na2MnO3 and its derived Na‐rich layered oxides might be considered promising cathode materials for sodium ion batteries. The structural and thermal stability and the anionic oxygen redox mechanism of Na2MnO3 are studied by first‐principle calculations. About 1.75 Na+ is extracted from Na2‐xMnO3 through partial O2− oxidation while the local structure remains intact, resulting in a large theoretical capacity. Surface Na+ is extracted before bulk Na+, which might lead to oxygen loss and structural transformation from the surface to the material bulk.