Tailoring Surface Chemistry for Robust and Ambient‐Stable Sodium Layered Oxide Cathodes

ABSTRACT Layered transition metal oxides represent a pivotal class of cathode materials for high‐energy sodium‐ion batteries (SIBs), yet their practical application is severely hindered by interfacial instability. To circumvent these degradation pathways, we demonstrate a novel synergistic Nb‐Ti surface modification strategy to construct a multifunctional surface on Na _2/3 Mn _2/3 Cu _1/3 O ₂ (NMCO) cathode. Through comprehensive multimodal characterizations, we provide direct evidence that the in situ constructed Nb‐Ti modified surface layer serves as a “defense barrier” that suppresses irreversible lattice oxygen redox and transition metal dissolution. Consequently, the tailored surface architecture significantly reinforces the structural integrity and facilitates Na‐ion diffusion kinetics, resulting in exceptional cycling stability and ambient robustness. Theoretical calculations further corroborate that the preferential adsorption of Nb/Ti species at active lattice sites significantly elevates the energetic barriers for surface degradation. This synergistic modification strategy offers a promising and extensible approach to achieving high‐performance layered oxide cathodes for sustainable energy storage.