Enhanced cyclability of O3-NaNi0.33Fe0.31Mn0.36O2 by Mg and Cu synergistic doping with strengthened MnO bonds

Among some practical O3-type layered oxide cathodes, NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM) features a high specific capacity and moderate cyclability. However, sluggish Na + transfer kinetics, low structural stability, and rapid capacity loss during long-term cycling, are still posing a challenge to commercial applications of this material. In this work, we propose a Mg and Cu co-doped O3-type NaMg 0.02 Cu 0.02 Ni 0.33 Fe 0.27 Mn 0.36 O 2 (MC-NFM) with a stable structure and good cycling stability. It was found that the Mn O bonds in MC-NFM are obviously reinforced by synergistic doping with small amounts of Mg and Cu, leading to enhanced structural robustness, decreased Na + migration barrier, and delayed O3-P3 phase transition. As a result, longer cycle life and enhanced rate performance are achieved. MC-NFM can yield a specific capacity of 142.1 mAh g −1 at 0.1C and 116.0 mAh g −1 at 5C, and maintain 83.6 % of its initial capacity after 400 cycles at 1C. This work provides a promising design of O3-type cathode for sodium-ion batteries.