Preparation And Surface Coating Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials For Li-Ion Batteries

Owning to developments of Hybrid-Electric Vehicle (HEV) and Electric Vehicle (EV) and demands to the energy storage device for nature energy such as solar energy and wind energy, lithium ion batteries with high capacity have turned into a main research focus. However, flaws of the commercial-used LiCoO₂ material make it no longer competitive. Therefore finding new type cathode materials for lithium ion batteries should be put down on research schedule. LiNi_0.8Co_0.1Mn_0.1O₂, with a mass specific capacity as large as 200mAh/g, becomes an ideal cathode material for the HEV of 40-km class. Nevertheless its safety performance and cycling performance need to be ameliorated. This thesis introduces the preparation of LiNi_0.8Co_0.1Mn_0.1O₂ and Ni_0.69Co_0.14Mn_0.17O₂, synthesized by Ni_0.8Co_0.1Mn_0.1(OH)₂ and Ni_0.69Co_0.14Mn_0.17- (OH)₂ the under different calcination temperature and calcination time. The affection of parameters of precursor fabrication on material morphology and the influence of calcination temperature on performance of LiNi_0.8Co_0.1Mn_0.1O₂ were mainly studied. The final performance of Ni_0.69Co_0.14Mn_0.17O₂ material was examined after the optimum synthesis conditions were settled.Scanning electronic microscopy, X-ray diffraction, Inductive coupled plasma emission spectroscopy, Energy dispersive X-ray spectroscopy, Galvanostatic charge/discharge measurement and tap density test were employed to study the particle morphology, lattice parameter, elements content and the electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ material. Also affects of the ammonia concentration, pH value and feeding rate in coprecipitation process on morphology of Ni_0.8Co_0.1Mn_0.1(OH)₂ were investigated. The result showed that Ni_0.8Co_0.1Mn_0.1(OH)₂ material was the best sphere-shaped when pH value equals 10.5, proportion of ammonia and metal ion equals 2 and reacting duration lasts 15h. Via control experiment, heat treatment parameters in different sections were determined and how different calcination temperature and Li/M²⁺ proportion would affect the electrochemical performance was studied. When Li/M²⁺ proportion equals 1.02 and precursor was sintered 20h under 750℃in atmosphere, material possessed the best electrochemical performance, with an initial discharge capacity of 181mAh/g when cycled between 3.0-4.4V under a current density of 200mA/g and a capacity retention rate of 95.6% after 50 cycles. The enhanced thermal and lithium intercalation stability of the Li[Ni_0.69Co_0.14Mn_0.17]O₂ was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.