P'2-type manganese-based layered oxides (NaxMnO2, 0.5 x + 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.
Xiao et al. (Thu,) studied this question.