Synthesis and electrochemical performance of lithium-rich cathode material Li[Li_0.2Ni_0.15Mn_0.55Co_0.1-xAl_x]O₂

Lithium-rich layered Li[Li_0.2Ni_0.15Mn_0.55Co_0.1-xAl_x]O₂ (0≤x<0.1) cathode materials have been synthesized by a sol-gel method followed by high temperature annealing at two stages of 850 °C and 900 °C, respectively. Thermal gravity analysis (TGA), Powder X-ray diffraction (XRD) and Scanning electron microscope (SEM) characterizations prove that the materials have a typical α-NaFeO₂ structure, uniform particle size and smooth surface. Electrochemical performance has been investigated by charge-discharge test and the results show that the initial discharge capacity of Li[Li_0.2Ni_0.15Mn_0.55Co_0.1-xAl_x]O₂ (0≤x<0.1) decreases slightly with the increasing content of Al, but the cycling performance and rate performance have been significantly improved. The optimum amount of Al for the Co is x = 0.05 in consideration of the higher specific capacity and good cyclability. As a consequence, the doped material(x = 0.05) delivers an initial discharge capacity of 231.7mAh·g⁻¹ at 25 °C with the first columbic efficiency of 75% and 275.8mAh·g⁻¹ at 55 °C with the first columbic efficiency of 89%, respectively, both at 0.1C within the cut-off voltage range of 2.0 and 4.8 V, which is higher than that of non-substituted material. After 30 cycles, the specific capacity retains 219.1mAh·g⁻¹ with a capacity retention of 98% for 25 °C, and 248.2mAh·g⁻¹ with a capacity retention of 96% for 55 °C at 0.5C within the potential range from 2.0 to 4.8 V. These demonstrate that suitable amount of Al³⁺ substitute for Co³⁺ in Li[Li_0.2Ni_0.15Mn_0.55Co_0.1]O₂ facilitates the improvement of the structural stability of materials.