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

Abstract

Abstract The high electrochemical performance of Li 2 MnO 3 ‐derived Li‐rich layered oxides suggests that Na 2 MnO 3 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 Na 2 MnO 3 has not been established. In the present work, the structural and thermal stability, and the anionic oxygen redox mechanism of Na 2 MnO 3 were studied by using first‐principle calculations based on density functional theory. About 1.75 Na + per formula unit were extracted from Na 2‐ x MnO 3 through partial O 2− 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, Na 2 MnO 3 and its derived Na‐rich layered oxides might be considered promising cathode materials for sodium ion batteries.