Na + ‐Gradient Spatial Functionalization Enhances Structural Stability of Ultrahigh‐Ni Layered Cathodes

Abstract Ultrahigh‐Ni layered cathode materials (LiNi x Co y Mn 1−x−y O 2 , x ≥ 0.9) have attracted intense research interest for high‐energy‐density lithium‐ion batteries owing to their high specific capacity and cost advantages; however, severe interfacial side reactions and bulk structural degradation under high‐voltage operation continue to limit practical applications. Here a spatially functionalized doping strategy is presented that constructs a Na + ‐doped layer with a surface‐to‐bulk gradient in LiNi 0.90 Co 0.05 Mn 0.05 O 2 , achieving synergistic optimization of surface structure and bulk capacity. The architecture forms a Na‐rich stable interfacial buffer near the surface that effectively suppresses oxygen loss and phase transitions and mitigates electrolyte side reactions; the bulk preserves active lithium sites to the maximum extent, maintaining high specific capacity. Experimental measurements and characterizations indicate that graded Na + doping markedly suppresses H2/H3 two‐phase coexistence and the c ‐axis contraction and anisotropic volumetric strain occurring during phase transitions, thereby inhibiting microcrack formation, improving Li + transport kinetics, and concurrently enhancing cycling stability and rate capability. The modified cathode retains 90.4% of its capacity after 200 cycles at 1 C and still delivers 159.1 mAh g −1 at 10 C. This composition‐gradient surface buffering approach establishes a new spatially functionalized lattice‐engineering paradigm for advanced ultrahigh‐Ni cathodes.