Synergistic Vacancy Engineering and Electronic Reconstruction Enables Reversible Oxygen Redox in P2‐Type Sodium Cathodes With Ultralow Strain

ABSTRACT Sodium layered transition‐metal (TM) oxides are considered promising cathode materials for sodium‐ion batteries owing to their high energy density. However, their practical application is severely hindered by detrimental phase transformations and irreversible oxygen redox at high voltages. Herein, we report a P2‐type layered oxide Na 0.67 Li 0.15 Co 0.15 Mn 0.6 Ti 0.1 O 2 (NLCMT) and decipher the dual‐functional role of Li in regulating both structural and electronic evolution. We demonstrate that electrochemically induced Li migration generates local coordination vacancies in the TM layers. These vacancies stabilize the layered framework through triggering the formation of a Na pillar‐like configuration, which effectively suppresses high‐voltage phase transitions and lattice strain accumulation. Meanwhile, the vacancy‐induced local environment enhances Co 3 d –O 2 p hybridization and facilitates adaptive ligand‐to‐metal charge transfer (LMCT). This process effectively redistributes oxygen hole density, preventing the localized accumulation of oxidized oxygen species and suppressing oxygen dimerization. Consequently, the NLCMT electrode delivers an exceptionally high discharge capacity of 197 mAh g −1 at 0.1C with remarkable reversibility. This work demonstrates an effective vacancy‐mediated strategy for developing highly reversible oxygen redox cathode materials.