| The exhaustion of traditional energy resources and the enhancement of awareness of environment protection offer a good opportunity for the lithium ion battery. However, the lithium ion battery can't be used in the new energy vehicles and the energy storage devices because of the high cost and the poor safety. The cathode material occupies more than 30 % of the lithium ion battery cost, so it's very important to produce the cathode material with good performance and low cost.As a promising kind of cathode material, LiNi1-x-yCoxMnyO2 gets more and more attention. This kind of cathode material LiNi1/3Co1/3Mn1/3O2 has been widely used. Another kind of cathode material LiNi0.5Co0.2Mn0.3O2 is being developed. With higher Ni content, LiNi0.5Co0.2Mn0.3O2 has higher capacity per gram and energy density. However, the cation mixing is severe to some extent, the structure is not very stable and the cycling performance is relative poor.In this thesis, the LiNi0.5Co0.2Mn0.3O2 was coated with SiO2 and CeO2 in wet chemical and high temperature calcination method. X-ray diffraction?XRD?, scanning electron microscope?SEM? and transmission electron microscope?TEM? were used to prove the coating of SiO2 and CeO2. The results of initial charge/discharge, cycling test and rate test showed good electrochemical performance. After 100 cycles at 10 C?20 C?, the 0.5 wt% SiO2-coated sample and 2 wt% CeO2-coated sample can deliver 100.6 mAh·g-1?90.0 mAh·g-1? and 97.4 mAh·g-1?59.2 mAh·g-1?, while the uncoated sample only deliver 23.5 mAh·g-1?9.0 mAh·g-1?. The coating of SiO2 can form a complete layer, decreasing the side reactions, stabling the structure of LiNi0.5Co0.2Mn0.3O2, improving the cycling performance. With good conductivity, cerium oxide can form a rough coating which can decrease the polarization, slower the increase of charge transfer resistance, weaken the corrosion degree of LiNi0.5Co0.2Mn0.3O2 by HF and stable the structure of the material, resulting in good electrochemical performance. |
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