Stabilizing effects of Al-doping on Ni-rich LiNi_0.80Co_0.15Mn_0.05O₂ cathode for Li rechargeable batteries

Ni-rich layered oxide cathodes with Ni content above 80% have considerable potential for Li rechargeable batteries due to their high capacity and low cost. However, what with stability issues, inferior cycle performance and thermal instability, studies are still underway to improve their performance. Herein, Al-doped Ni-rich (LiNi_0.80Co_0.15Mn_0.05O₂) cathode is investigated to stabilize structural, electrochemical, and thermal properties. Compared to undoped one, Al-doped Ni-rich cathode exhibits lower polarization potential, better rate capability, and cyclability. This can be attributed to the alleviation of anisotropic lattice changes and volume changes during cycling. More importantly, Al-doped Ni-rich cathode maintains a wider LiO₆ interslab thickness without collapse at highly charged states, allowing Li-ions to be deintercalated/intercalated reversibly. This indicates that rigid structural integrity contributes to enhanced electrochemical performance. Furthermore, Al-doping improves thermal stability by delaying the onset temperatures of phase transformations during the heating process. These results demonstrate that Al-doping plays a major role in stabilizing the structure by suppressing abrupt lattice changes during cycling and the formation of a rock-salt phase during thermal decomposition reaction. Therefore, this study provides structural aspects of Al-doping effects on the stabilization of layered cathode materials for the high energy density of rechargeable batteries.