Dual‐Strategy Induced Near‐Surface Reconstruction Enabling Highly Stable P2‐Layered Oxide Cathodes for Sodium‐Ion Batteries

Abstract Layered oxide cathodes have garnered increasing attention in the field of sodium‐ion batteries (SIBs) owing to high specific capacity, excellent cyclability, and scalable synthesis processes. However, residual alkali species accumulate on the surface during the synthesis process, accompanied by irreversible lattice oxygen release and unstable cathode‐electrolyte interface, which trigger structural degradation. Herein, we propose a carbonate buffer solution to remove residual alkalis, construct a disordered sodium‐enriched layer, reducing the initial Mn oxidation state increases the discharge capacity by 67.1% (136.7 mAh g ⁻¹ ). Near‐surface reconstruction not only blocks the direct contact between electrolyte and bulk structure, but also provides a low‐energy barrier channel for ion transport. Dual strategy combining an additional electrochemical presodiation enhances the cycling stability, yielding 90.1% capacity retention after 100 cycles (versus 58.6% in pristine sample). Active Na ⁺ injected into P2‐type NLMFO (Na _0.7 Li _0.2 Mn _0.7 Fe _0.1 O ₂ ) activates fully Mn ⁴⁺ /Mn ³⁺ redox reaction and retaines O ^{2 −} /O ^{n −} (n<2) lattice oxygen activity, suppresses the Jahn‐Teller effect and compensates for Na deficiencies. The lattice structure recovery effect renders phase transition more reversible, reduces internal stress accumulation and improves structural stability. The results demonstrate that washing and presodiation dual synergistic strategy achieves surface reconstruction, meets requirements for energy density, durability, and safety of next‐generation SIBs.