A cation/anion co-doped Li1.12Na0.08Ni0.2Mn0.6O1.95F0.05 cathode for lithium ion batteries

Highlights: • We proposed a novel cation/anion (sodium/fluorine) co-doping methode for lithium rich Li_1.2Ni_0.2Mn_0.6O₂ cathode. • The cation/anion (sodium/fluorine) co-doping mechanism was studied in-depth. • Excellent cycling stability and superior rate performance have been achieved with the co-doping process. -- Abstract: Lithium-rich layered structure cathode materials are arousing significant attention in the next-generation commercial lithium ion batteries owing to their high capacity and energy density. However, the poor rate performance and inferior cycle stability stand in the way of its large-scale applications. In this study, we pioneer a novel cation/anion (sodium/fluorine) co-doping approach to address the above issues for lithium rich Li_1.2Ni_0.2Mn_0.6O₂ cathode. Consequently, the cation/anion co-doped cathode material could keep the advantages of both cation (sodium) and anion (fluorine), which can significantly enhance the stability by suppressing the phase transformation from layered to spinel structure and rate performance through decreasing resistance of Li diffusion and the electrons migration. The co-doped Li_1.12Na_0.08Ni_0.2Mn_0.6O_1.95F_0.05 exhibits an excellent cycling stability (100% after 100 cycles at 0.2 C) and a superior rate performance (167 mAh g⁻¹ at 5 C). The mechanism of the dramatic improvement is also systematic investigated for the first time. Furthermore, we also believe that the cation/anion co-doping approach could be employed to improve the performance of other classes of layered cathode materials.