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Preparation And Modification Of LiNi0.6Co0.2Mn0.2O2 As Cathode Material For Lithium Ion Battery

Posted on:2016-05-19Degree:MasterType:Thesis
Country:ChinaCandidate:S T SunFull Text:PDF
GTID:2311330485458597Subject:Chemical engineering
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Lithium ion battery cathode material Li[Ni-Co-Mn]O2 systems have been widely studied since of its high theoretical capacity, good thermal stability, low cost and environment friendly. This system inherit the merits of LiCoO2, LiMnO2 and LiNiO2, and even better than any kind of these materials. But the poor electrochemical performance and high rate cycle performance when charged to high voltage of Li[Ni-Co-Mn]O2 systems also limits its use for hybrid electric vehicles. This paper mainly studied the synthesis method of the asymmetric three element cathode material LiNi0.6Co0.2Mn0.2O2. The important influence factors in the synthesis process were optimized, and the structure and electrochemical characteristics of the synthetic materials under different conditions were studied. The effect of Li2ZrO3 coating on the electrocheemical properties and thermal stability of LiNi0.6Co0.2Mn0.2O2 was studied in detail.The synthesis of LiNi0.6Co0.2Mn0.2O2 via sol-gel method using metal acetate as raw material and glycine as complexing agent was studied. The significant factors influencing the discharging capacity of LiNi0.6Co0.2Mn0.2O2 such as calcination temperature, calcination time, pre synthesis time, glycine :?Ni+Co+Mn? molar ratio were studied. XRD and charge/discharge test shows that the optimized synthesis conditions for LiNi0.6Co0.2Mn0.2O2 are 450? for 6h, 900? for 18 h and glycine:?Ni+Co+Mn? molar ratio at 2:1.The LiNi0.6Co0.2Mn0.2O2 was hexagonal ?-NaFeO2 structure with a space group of R-3m. Within the cut-off voltage of 2.6-4.8V, the sample exhibited an initial discharge capacity of 180 mAh/g and with a capacity retention about 85.5% after 30 cycles at 0.1C.The synthesis of LiNi0.6Co0.2Mn0.2O2 via solid-state method using metal acetate as raw material was studied. The significant factors influencing the discharging capacity of LiNi0.6Co0.2Mn0.2O2 such as calcination temperature, calcination time, pre synthesis time were studied. XRD, and charge/discharge test shows that the optimized synthesis conditions for LiNi0.6Co0.2Mn0.2O2 are 400? for 5h, 600? for 2h, 750? for 6h and 850? for 10 h.The LiNi0.6Co0.2Mn0.2O2 was hexagonal ?-NaFeO2 structure. Within the cut-off voltage of 2.6-4.8V, the sample exhibited an initial discharge capacity of 170 mAh/g and with a capacity retention about 79.8% after 30 cycles at 0.5C.To improve the high-rate capacity and cycle ability, Li2ZrO3 was successfully coated on LiNi0.6Co0.2Mn0.2O2 materials via wet chemical method. The crystal structure and electrochemical properties of the bare and coated material are studied by X-ray diffractometry?XRD?, scanning electron microscope?SEM?, transmission electron microscopy?TEM?, cyclic voltammetry and electrochemical impedance spectroscopy?EIS?. The XRD and SEM results indicated that the lattice structure of Li2ZrO3-coated materials were the same as the pristine one. Transmission electron microscopy showed that there was a thin Li2ZrO3 coating layer on the surface. Li2ZrO3-coating improves the rate performance and cycling stability. Minor Li2ZrO3 modification plays an important role to enhance the high-rate capability and cycle ability of LiNi0.6Co0.2Mn0.2O2. Within the cut-off voltage of 2.6-4.8V, the 1 wt.% Li2ZrO3 coated samples exhibited an initial discharge capacity of 190 mAh/g and with a capacity retention about 85% after 50 cycles at 0.1C.
Keywords/Search Tags:Lithium ion battery, cathode material, LiNi0.6Co0.2Mn0.2O2, sol-gel method, solid-state method, Li2ZrO3 coating
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