Enhancing the Cycling and Rate Performance of NaNi1/3Fe1/3Mn1/3O2 Cathodes by La/Al Codoping

O3-type layered oxides hold significant promise as the material for cathodes in sodium-ion batteries for their favorable electrochemical properties, while irreversible structural degradation and harmful phase transitions during cyclic operation limit the practical application of these materials. In this work, we proposed a La3+/Al3+ codoping strategy in O3-Na­(Ni1/3Mn1/3Fe1/3)­O2 cathode materials and found that batteries with the Na (Ni1/3Mn1/3Fe1/3)0.998­La0.001Al0.001O2 (NFM-La/Al) cathodes exhibited not only promoted capacity from 135.80 to 170.42 mAh g–1 at 0.2 C but also significantly enhanced cycling stability, with a 10% improvement in capacity retention compared with NFM cathodes after 300 cycles. Particularly, their rate performance was significantly improved as well. XRD and XPS tests indicated that La could expand the c-axis of NFM due to its larger ionic radius and thus significantly increased Na+ ion diffusion efficiency, and in addition, Al doping could effectively increase the content of Ni2+ and Mn4+ and thus greatly alleviated the negative Jahn–Teller effect caused by Mn3+. Moreover, consistent with XRD analyses, DFT calculations further substantiated the effectiveness of the La/Al codoping strategy by demonstrating the detailed atom substitution mechanism in the NFM crystal lattice. The boosted structure stability and Na+ diffusion kinetics may enhance the potential for practical applications of O3-type oxide cathodes.