Stabilization of Phase Transition Process and Lattice Oxygen of O3‐Layered Oxide Cathode for Sodium‐Ion Battery via Dual‐Doping Strategy

Abstract Satisfying stable cycling under high voltage and efficient ion extraction/insertion kinetics are important factors in constructing high‐energy density sodium‐ion batteries. O3‐layered oxide cathodes draw significant attention due to their high specific capacity and mature synthesis processes. However, these materials are plagued by stress accumulation from phase transitions, sluggish sodium ion diffusion kinetics, and irreversible lattice oxygen oxidation at high voltage. Herein, a Na(Ni 1/3 Fe 1/3 Mn 1/3 ) 0.98 Al 0.02 B 0.02 O 2 material is reported that addresses the inherent limitations of O3‐layered oxides under high voltage through a rationally designed dual‐element doping mechanism. Al 3 ⁺ that occupies the transition metal layer, can strengthen TM─O bonds as well as inhibit interlayer sliding and phase transition. Meanwhile, B 3 ⁺ doping at the interstitial sites between the transition metal layer and oxygen layer stabilizes lattice oxygen via robust B─O covalent interactions, thereby reducing lattice oxygen release and avoiding excessive decomposition of electrolyte catalyzed by reactive oxygen. Furthermore, this dual‐element doping cathode achieves expanded Na─O interlayer spacing and an elevated c/a ratio, synergistically enhancing Na‐ion diffusion kinetics. The Na(Ni 1/3 Fe 1/3 Mn 1/3 ) 0.98 Al 0.02 B 0.02 O 2 cathode exhibits a stable and reversible sodium storage structure, so that it significantly improves high‐rate capability, and cycling performance. This bulk‐interface synergistic bond‐energy engineering provides a novel perspective for high‐voltage cathodes in sodium ion batteries.