Microstructure and electrochemical properties of Mg/Nb/Zr co-doped LiNi0.94Mn0.04Al0.02O2 cathode materials

The increasing oil scarcity and environmental awareness have accelerated the rise of the new energy vehicle industry, but range and cost issues have hindered the rapid popularization of new energy vehicles. The Co-free Ni-rich layered cathode materials have received a wide attention due to their high energy density, low cost, and stable raw material supply. However, its structure and electrochemical stability still need to be further improved. In this study, the electrochemical properties of LiNi0.94Mn0.04Al0.02O2 (NMA), a Co-free Ni-rich layered cathode material, have been improved by co-doping of Mg, Nb, and Zr. Also, the effects of co-doping on the crystal structure, morphology and electrochemical properties of NMA cathode materials were investigated, too. The results show that the NMA material (NMA-333) with 0.9 mol% doping amount has the best electrochemical performance. The discharge-specific capacity in the first cycle at 1 C was 199.6 mAh g-1, and the capacity retention after 200 cycles reached 73.94%, which is nearly 24% higher than that of the original material (NMA-1.03). Meanwhile, the NMA-333 material has a relatively better rate performance, with a discharge-specific capacity of 125.2 mAh g-1 at 10 C. Moreover, the structure and morphology of the modified material were represented by SEM, TEM, XRD, and XPS. And the results showed that the co-doping modification could refine the primary particles of the NMA material, reduce the lithium-nickel mixing, and increase the lattice spacing. The XPS, SEM, and XRD of the post-cycle electrodes further showed that co-doping had stabilized the crystal structure, inhibited the generation and expansion of microcracks, and reduced the occurrence of harmful side reactions, thus improving the cycling performance of the NMA materials at high voltage. The method could be a feasible way to improve the electrochemical performance of layered high-nickel cobalt-free cathode materials.