Mn‐Mediated Reduction Coupling Mechanism Stabilizes Anion Redox Chemistry Toward High‐Performance P2‐Type Na‐Layered Oxide Cathodes

ABSTRACT Unlocking anionic redox reactions represents a promising route to boost the energy density of cathode materials for sodium‐ion batteries (SIBs). However, excessive oxygen participation often induces irreversible lattice oxygen loss and structural reconstruction, leading to degraded electrochemical performance and sluggish reaction kinetics. Herein, we present a Mn‐mediated reductive coupling mechanism (Mn‐RCM) activated by Ca doping in the P2‐Na _0.64 Ca _0.03 Ni _0.33 Mn _0.67 O ₂ cathode. The mechanism involves an uncommon electron transfer from oxygen to manganese ions, which enhances the reversibility and kinetics of anionic redox. Synchrotron‐based X‐ray absorption spectroscopy captures this electron transfer behavior, while theoretical calculations suggest that Ca incorporation lowers the crystal field splitting of Mn 3d orbitals and facilitates charge transfer from O 2p to Mn e _g orbitals at high voltage. Additionally, Ca ²⁺ ions in the Na layers act as rigid pillars, inhibiting P–O phase transitions to ensure a single P2 solid‐solution reaction and minimize lattice strain. Consequently, the P2‐Na _0.64 Ca _0.03 Ni _0.33 Mn _0.67 O ₂ cathode demonstrates improved structural stability and long‐cycling performance, with 80% capacity retention after 800 cycles within a high cutoff voltage of 4.3 V at 1.0 C. This work provides new insights into enhancing the reversibility and kinetics of anionic redox chemistry, facilitating the development of stable high‐voltage cathodes for SIBs.