Chemically Anchored Lattice Oxygen Enables Stability in Layered Sodium Cathodes

The long-term performance of P2-type layered transition metal oxides is often compromised by irreversible oxygen redox and lattice instability, resulting in rapid capacity degradation. This work proposes a dual-site La³⁺ substitution strategy to stabilize the lattice oxygen and improve the electrochemical durability. The substitution of La³⁺ into the transition metal layer forms strong La─O covalent interactions that anchor lattice oxygen while simultaneously lowering the O 2p orbital energy to suppress parasitic oxygen evolution. This electronic and structural modulation enables controlled anionic redox behavior and enhances phase reversibility under deep charge. In situ XRD reveals a minimal volume change (0.9%) during cycling, indicative of an apparent structural resilience. The optimized 0.02La-doped cathode exhibits stable full-cell performance when paired with commercial hard carbon, achieving 80.2% capacity retention over 600 cycles at 5C. These findings demonstrate a viable path toward stable sodium-ion cathodes via rare-earth-assisted lattice oxygen regulation.