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 (NaxMnO₂, 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 Nae and face-shared Naf) 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 Nae/Naf ratio. The theoretical simulation confirms that the P'2 structure can accommodate more Na⁺ at the Nae 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-Na0.67Ti0.1Fe0.05Mn0.85O₂ cathode. Quenching enables the formation of P'2-structure with a high Nae/Naf 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, Ti⁴⁺ (3d⁰, unfilled) and Fe³⁺ (3d⁵, half-filled) are introduced into P'2-Na0.67MnO₂ 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.