| Lithium cobalt oxide (LiCoO2) is the most widely used one of the cathode materials in commercial lithium-ion batteries at present. However, its high cost and toxicity limit its further use in newly developed multifunctional portable devices and electric vehicle systems. Thus, extensive research has been carried out to explore alternative cathode materials. Li(Ni1/3Co1/3Mn1/3)O2 has become a focus of research because of its low cost, higher reversible capacity, and milder thermal stability. However, the fabrication process of Li(Ni1/3Co1/3Mn1/3)O2 is complex and cation mixing tends to reduce the electrochemical properties. The topics of this thesis are concentrated on the synthesized of Li(Ni1/3Co1/3Mn1/3)O2 by co-precipitation method and ultrasonic spray method and characteristic of them. The main results are as follow:(1) Li(Ni1/3Co1/3Mn1/3)O2 was prepared by sintering the mixture of LiNO3 and the precursor (Ni1/3Co1/3Mn1/3)(OH)2 obtained via co-precipitation method. Effects of a variety of synthesis conditions, including aging time, feeding rate, pH and ammonia concentration, on the morphology of (Ni1/3Co1/3Mn1/3)(OH)2 particles were investigated. Low feed rate, moderate pH and high ammonia concentration could reduce the supersaturation of the transition metal ion in the reaction solution, such that the nucleation rate was reduced and the morphology of precursor was significantly improved. Effects of different sintering temperatures on the structural and electrical performance were investigated. The cathode synthesized at 800℃ showed high discharge capacity of 186.93 mAhg-1 as well as stable cycling performance in the voltage range 2.8-4.5V Li/Li+, remaining 95.6% of initial capacity after 75 cycles at a rate of 2C.(2) Li(Ni1/3Co1/3Mn1/3)O2 was prepared by a ultrasonic spray method via two routes. Effects of thermal decomposition temperature, the initial concentration of the precursor solution and the carrier air flow rate on the morphology of the precursor were investigated. On the basis of the study, a mechanism models that how droplet transformed into solid particles had been proposed. The model is described as follows: When the droplet was heated, the solvent of the surface layer was evaporated and the solute started to precipitate, forming a shell while droplets shrink. If the evaporation rate of the solvent of the surface layer was greater than the diffusion rate of the solvent inside the droplet to the surface, a spherical shell structure would be obtained. The effects of different synthesis routes of ultrasonic spray method on the morphology and electrochemistry of Li(Ni1/3Co1/3Mn1/3)O2 were investigated. Li(Ni1/3Co1/3Mn1/3)O2 prepared via Route One (without LiNO3 in the precursor solution) had a higher initial discharge capacity (178.32mAh/g), better cycle performance but worse high-rate performance than the sample prepared via Route Two (with LiNO3 in the precursor solution).(3) A series of oxides was synthesized by an ultrasonic spray method. With the same synthesized conditions, the particles of different metal oxides showed exhibit different morphologies. |
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