Unravelling the peculiar role of Co and Al in highly Ni-rich layered oxide cathode materials

Currently, the limited availability of cobalt resources has had a negative impact on the progress of commercial batteries, prompting the development of cobalt-free Ni-rich cathodes. However, the complete replacement of cobalt has faced challenges due to the lack of understanding the influence of dopants on cathode material performance. In this study, we aimed to address this knowledge gap by designing and preparing LiNi_0.95Co_0.05-xAl_xO₂ (x = 0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) cathode materials. The impact of cobalt and aluminum doping on the morphology, crystallographic structure and electrothermal performance of Ni-rich cathode materials has been systematically investigated. Our findings confirmed the significant role of cobalt in increasing energy density and mitigating cationic disordering. However, it is found that cobalt doping contributes to the release of lattice oxygen during cycling, leading to rapid capacity fading. Conversely, aluminum doping could stabilize the crystal structure of the cathode material, resulting in slower capacity degradation. Furthermore, the substitution of aluminum effectively mitigates the crystal growth during the synthesis of highly Ni-rich cathode materials, leading to a reduced Li⁺ diffusion length and thereby excellent rate performance. Specifically, LiNi_0.95Al_0.05O₂ could deliver a high discharge capacity of around 163 mAh g⁻¹ at 10C. This study provides valuable insights for the design of cobalt-free Ni-rich cathodes and sheds light on the possibility of cobalt elimination.