Enhanced electrochemical performance of Li-rich low-Co Li1.2Mn0.56Ni0.16Co0.08−x Al x O2 (0≤x≤0.08) as cathode materials

Layered Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 (0 ≤ x ≤ 0.08) cathode materials were successfully synthesized by a sol-gel method. X-ray diffraction and the refinement data indicate that all materials have typical α-NaFeO2 structure with R -3 m space group, and the a -axis has almost no change, but there is a slight decrease in the c lattice parameter as well as the cell volume. Scanning electron microscopy and high resolution transmission electron microscopy prove that all the samples have uniform particle size of about 200–300 nm and smooth surface. The energy-dispersive X-ray spectroscopy mapping shows that aluminum has been homogeneously doped in the Li1.2Mn0.56Ni0.16Co0.08O2 cathode material. The cyclic voltammetry and electrochemical impedance spectroscopy reveal that appropriate Al-doping contributes to the reversible lithium-ion insertion and extraction, and then reduces the electrochemical polarization and charge transfer resistance. Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) shows the lowest charge transfer resistance and the highest lithium-ion diffusion coefficient among all the samples. The Li-rich electrodes with low-level Al doping shows a much higher discharge capacity than the pristine one, especially the Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) sample, which exhibits greater rate capacity and better fast charge-discharge performance than the other samples. Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) also exhibits higher discharge capacity than the pristine one at each cycle at 55°C. These results clearly indicate that the high rate capacity together with a good high rate cycling performance and high-temperature performance of the low-Co Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x =0.05) is a promising alternative to next-generation lithium-ion batteries.