Predominant P3-Type Solid–Solution Phase Transition Enables High-Stability O3-Type Na-Ion Cathodes

Layered O3-type oxides are one of the most promising cathode materials for Na-ion batteries owing to their high capacity and straightforward synthesis. However, these materials often experience irreversible structure transitions at elevated cutoff voltages, resulting in compromised cycling stability and rate performance. To address such issues, understanding the interplay of the composition, structure, and properties is crucial. Here, we successfully introduced a P-type characteristic into the O3-type layered structure, achieving a P3-dominated solid–solution phase transition upon cycling. This modification facilitated a reversible transformation of the O3–P3–P3′ structure with minimal and gradual volume changes. Consequently, the Na0.75Ni0.25Cu0.10Fe0.05Mn0.15Ti0.45O2 cathode exhibited a specific capacity of approximately 113 mAh/g, coupled with exceptional cycling performance (maintaining over 70% capacity retention after 900 cycles). These findings shed light on the composition–structure–property relationships of Na-ion layered oxides, offering valuable insights for the advancement of Na-ion batteries.