| The researching for the new kind of electrode material with high performance and low cost is always the purpose of Lithium-ion battery. Nowadays, the conventional LiCoO2 cathode material for Lithium-ion batteries(LIB) was losing the momentum for its safety hazard and high cost. As one substitution for LiCoO2 in many electrode materials, multi-element compound oxide cathode material LiNi1/3Co1/3Mn1/3O2, it not only has mostly near electrochemical performance, but also has superior thermal stability and relatively low cost, so this kind of material is regarded as the most promising and new cathode material to substitute for LiCoO2. At present this kind of cathode material is facing the market gradually, especially, in the field of electric vehicle(EV) and hybrid electric vehicle(HEV), it still has very large space to develop.The precursor Ni1/3Co1/3Mn1/3(OH)2 was prepared by chemical coprecipitation process in this paper, and LiNi1/3Co1/3Mn1/3O2 was synthesized by solid state reaction method. Taking LiNi1/3Co1/3Mn1/3O2 as researching object, the synthesis method, cycle performance, doping, surface coating and the intercalation and de-intercalation of lithium ion were researching carefully. Mainly using X-ray diffraction(XRD) analysis, scanning electron microscope(SEM) analysis, TG-DTA analysis, galvanostatic charge/discharge testing method to observe and do research about the particle morphology, lattice structure and electrochemical performance.During the process of making Ni1/3Co1/3Mn1/3(OH)2 precursor by chemical coprecipitation method, a lot of work was done about the generation principle of spherical particle, the action of precipitator and complexant during the chemical coprecipitation process. As a result, the range of PH value was about 10.5, metal ion concentration was 2 mol·L?1, precipitator concentration was 4 mol·L?1, complexing agent was 3 mol·L?1, the Ni1/3Co1/3Mn1/3(OH)2 precursor has a narrow particle distribution, moreover, the particles were ball-like and tap density was 1.54 g·cm-3。About the test phase of cathode material LiNi1/3Co1/3Mn1/3O2 which was synthesized by solid state reaction, a lot of work was done on different sinter time, calcination temperatures and various Li/(Ni+Co+Mn) mole value. At last, getting the best solid phase reaction situation: the mole ratio of Li/M(Ni+Co+Mn) was 1.12/1, the mixed materials were calcined at 480℃for 6 h, 620℃for 8 h and then calcined at 840℃for 12 h. The cathode materials LiNi1/3Co1/3Mn1/3O2 synthesized at above situations showed that the initial discharge capacity was 154.50 mAh·g?1 in 2.754.3V at 0.2 C rate and after 20 cycles the capacity retention rate was 91.91%.The kinetics of LiNi1/3Co1/3Mn1/3O2 cathode materials was studied. According the method of cyclic voltammetry, oxidation peak and reduction peak was mostly symmetrical, it was proved that the cathode materials had steady structure and good capacity retentiont, the surface of electrode material had excellent stabilization. The AC impedance picture of LiNi1/3Co1/3Mn1/3O2 was made up of three parts, film impedance of SEI, electrochemical impedance and Warburg impedance caused by diffusion of Li+, the electrochemical impedance is increased with the reducing of voltage.At last, LiNi1/3Co1/3Mn1/3O2 cathode materials were doping and surface coating. The particle morphology, lattice structure was studied, the charge/discharge testing by the electrochemical testing equipment was researched comparing with the unadulterated and uncoated material.Li[Ni1/3Co1/3Mn1/3]0.99La0.01O2 cathode materials showed better capacity retention than Li[Ni1/3Co1/3Mn1/3]0.99La0.01O2 materials after 20 cycles, but the discharge capacity was 120.10 mAh·g?1, 78 % of the unadulterated cathode materials. When LiNi1/3Co1/3Mn1/3O2 was coated with TlO, the cycle performance was improved, the initial discharge capacity was 142.40 mAh·g?1 in 2.754.3 V at 0.2 C rate and after 20 cycles the capacity retention rate was 93.13 %. |
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