Enhancing the electrochemical properties of LiNi_0.92Co_0.05Mn_0.03O₂ cathode material via co-doping aluminium and fluorine for high-energy lithium-ion batteries

Ni-rich cathode materials LiNi_xCo_yMn_1-x-yO₂ (NCM) are widely used in Li-ion batteries because of their high energy density and low material cost. However, the cycle and safety performance are poor due to internal structure instability, cation mixing, and surface instability. The Al-O bond and TM-F bond are higher than the TM-O bond, which is beneficial to the stable layered structure of NCM cathode material. In this paper, Ni-rich layered Li[(Ni_0.9Co_0.05Mn_0.03)_1-xAl_x]O_2-zF_z (NCMAF) cathode material was prepared by a high-temperature solid-state method. When compared to NCM, the co-doped NCMAF shows excellent rate performance with the discharge capacity (177 mAh/g) at 10C and better cycle performance with a capacity retention of 72.7% after 200 cycles. According to XRD, Rietveld refined, and TEM analysis, the lithium layer distance of co-doped NCMAF is broader than that of pristine NCM. The capacity differential (dQ/dV) proves that the H₂-H₃ phase transition is inhibited during the charging and discharging process of NCMAF. Analysis of EIS reveals that the modified NCMAF has lower polarization and increases the diffusion coefficient (8.59 × 10⁻¹⁴ cm²/s) of lithium-ion than pristine NCM.