Effect of Al substitution sites on Li1−xAlx(Ni0.5Co0.2Mn0.3)1−yAlyO2 cathode materials for lithium ion batteries

The effects of various Al concentration and substitution sites (including Li layer and transition metal layer) on the structural and electrochemical properties of LiNi0.5Co0.2Mn0.3O2 (NMC) materials are systematically investigated. X-ray diffraction, X-ray photoelectron spectroscopy and electrochemical tests confirm that LiAlO2 phase appears in Li1−xAlxNi0.5Co0.2Mn0.3O2 samples and contributes to better lithium ion diffusion coefficient. While Al prefer to form AlO solid solution in Li(Ni0.5Co0.2Mn0.3)1−yAlyO2 samples, which can improve the structural stability of NMC. As expected, Al substituted samples with suitable dopant concentration exhibit remarkably enhanced electrochemical performances compared with pristine LiNi0.5Co0.2Mn0.3O2. Particularly, the Li0.99Al0.01Ni0.5Co0.2Mn0.3O2 sample maintains 172.3 mAh g−1 (1 C) with 90.9% capacity retention after 100 high-voltage cycles at 4.6 V charge cut-off. These results demonstrate that substitution of Li with low Al content has superior advantages for LiNi0.5Co0.2Mn0.3O2 cathodes.