Regulating Na-Ion Occupations of P-Type Na 0.67 Ti 0.10 Fe 0.05 Mn 0.85 O 2 for Improving Electrochemical Reversibility and Kinetics

P′2-type manganese-based layered oxides (Na x MnO 2, 0.5 < x < 0.8 usually) have emerged as promising cathode materials for sodium-ion batteries (SIBs), primarily due to their ability to deliver higher capacity compared to P2-type layered oxides. However, the underlying mechanism behind this high capacity still remains unclear, and the cycling stability has been a challenge. Given that distinct Na + occupation environments (edge-shared Na e and face-shared Na f ) in P-type cathodes have different electrochemical kinetics, this study establishes a direct correlation between the high capacity of the P′2 structure and the high Na e /Na f ratio. The theoretical simulation confirms that the P′2 structure can accommodate more Na + at the Na e site, which features a lower migration energy barrier and enhanced migration. Guided by this insight, a dual-approach rational design─combining quenching treatment and Ti/Fe codoping─is proposed to harvest the high-capacity and high-stability P′2-Na 0.67 Ti 0.1 Fe 0.05 Mn 0.85 O 2 cathode. Quenching enables the formation of P′2-structure with a high Na e /Na f ratio of 2.1 (compared to the typical ∼ 1.00), delivering a higher capacity of 190.3 mAh g –1 at 0.1 C between 2.0 and 4.0 V (the naturally cooled cathode only exhibits 130.2 mAh g –1 at 0.1 C); Furthermore, Ti 4+ (3d 0, unfilled) and Fe 3+ (3d 5, half-filled) are introduced into P′2-Na 0.67 MnO 2 for suppressing Na + /vacancy ordering and stabilizing the structure, resulting in excellent cycle stability with 96.9% capacity retention after 350 cycles at 5 C. This strategy provides a pathway to improve the reversible capacity of Mn-based layered cathodes for sodium-ion batteries.