Enhancing the Cycling\nand Rate Performance of NaNi<sub>1/3</sub>Fe<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub> Cathodes by\nLa/Al Codoping

O3-type layered oxides hold significant promise as the\nmaterial\nfor cathodes in sodium-ion batteries for their favorable electrochemical\nproperties, while irreversible structural degradation and harmful\nphase transitions during cyclic operation limit the practical application\nof these materials. In this work, we proposed a La<sup>3+</sup>/Al<sup>3+</sup> codoping strategy in O3-Na(Ni<sub>1/3</sub>Mn<sub>1/3</sub>Fe<sub>1/3</sub>)O<sub>2</sub> cathode materials and found that batteries\nwith the Na (Ni<sub>1/3</sub>Mn<sub>1/3</sub>Fe<sub>1/3</sub>)<sub>0.998</sub>­La<sub>0.001</sub>Al<sub>0.001</sub>O<sub>2</sub> (NFM-La/Al) cathodes exhibited not only promoted capacity from 135.80\nto 170.42 mAh g<sup>–1</sup> at 0.2 C but also significantly\nenhanced cycling stability, with a 10% improvement in capacity retention\ncompared with NFM cathodes after 300 cycles. Particularly, their rate\nperformance was significantly improved as well. XRD and XPS tests\nindicated that La could expand the <i>c</i>-axis of NFM\ndue to its larger ionic radius and thus significantly increased Na<sup>+</sup> ion diffusion efficiency, and in addition, Al doping could\neffectively increase the content of Ni<sup>2+</sup> and Mn<sup>4+</sup> and thus greatly alleviated the negative Jahn–Teller effect\ncaused by Mn<sup>3+</sup>. Moreover, consistent with XRD analyses,\nDFT calculations further substantiated the effectiveness of the La/Al\ncodoping strategy by demonstrating the detailed atom substitution\nmechanism in the NFM crystal lattice. The boosted structure stability\nand Na<sup>+</sup> diffusion kinetics may enhance the potential for\npractical applications of O3-type oxide cathodes.