Delocalized Li 2 MnO 3 ‐Like Domains for Enhanced Structural Stability in 4.2 V‐Class O3‐Type Sodium Layered Cathodes

ABSTRACT Ni/Mn‐based O3‐type layered oxides are promising high‐energy‐density cathodes for sodium‐ion batteries, yet their practical application at high voltages is hindered by irreversible oxygen redox and structural degradation. Herein, we demonstrate that Li/Sn co‐doping in O3‐NaNi 0.5 Mn 0.5 O 2 induces the formation of delocalized Li 2 MnO 3 ‐like domains, deviating from the conventional random substitution model. These domains comprise spatially dispersed Li‐centered local configurations (e.g., LiMn 6 , LiNiMn 5 , LiSnMn 5 ) and serve as structural pillars within the layered framework. Multimodal characterizations reveal that these domains regulate both local structure and electronic configuration. Charge compensation is dominated by Ni redox, while lattice oxygen participation, irreversible oxygen redox, and O–O dimer formation are effectively suppressed. Meanwhile, the stabilized local structure inhibits transition metal migration, mitigates layer gliding, and suppresses c ‐axis contraction, enabling a reversible O3‐P3‐O3 phase transition. The optimized cathode delivers 98.06% capacity retention after 100 cycles at 0.1C and 82.42% after 200 cycles at 1C. This work provides atomic‐scale insights and a promising strategy for designing high‐performance sodium layered cathodes.