Phytic acid-mediated multiscale reconstruction stabilizes high-voltage anionic redox in P2-type Mn-based layered oxide cathodes

ABSTRACT P2-type sodium-deficient Mn-based layered oxides with anionic oxygen redox are promising cathodes for high-energy sodium-ion batteries, yet their practical application is hindered by irreversible oxygen loss, transition-metal migration, parasitic interfacial reactions, and rapid structural degradation under high-voltage operation. Herein, we propose a phytic acid (PA)-mediated multiscale reconstruction strategy to regulate the surface to near-bulk structure of P2-type Na 0.72 Li 0.24 Mn 0.76 O 2 (NLM). Upon secondary annealing, PA transforms the residual surface alkali into an ion-conductive Na 3 PO 4 outer layer. Meanwhile, the annealing-induced localized reductive environment promotes oxygen-vacancy ( V O ) formation and gradient P 5+ doping in the near-bulk region. The P 5+ preferentially coordinates as [PO 4 ] tetrahedra to replace [MO 6 ] octahedra, enlarging the charge-transfer gap ( Δ ) via the inductive effect. Concurrently, the charge compensation effect drives local Mn 4+ reduction, which lowers the Hubbard U . This dual band regulation thermodynamically stabilizes the lattice oxygen. Furthermore, the V O -enriched environment and P 5+ doping synergistically drive the migration and subsequent oxidation of the reduced Mn species, triggering the formation of a Li 2 MnO 3 -like buffer interphase. Consequently, the modified PA-NLM delivers an improved rate capability of 99.19 mAh·g -1 at 5 C and enhanced long-term cycling stability, retaining 124.3 mA·h·g –1 within 1.8–4.7 V after 150 cycles at 1 C. This work provides a viable surface-to-near-bulk stabilization paradigm for durable high-voltage sodium-ion cathodes.