| As a "zero strain" material used for Li-ion power battery, Lithium titanate(Li4Ti5O12) is one of the most potential cathode materials, comparing to the commercial carbon materials so far. Solid-state synthesis method was primarily used in this paper, and then the material was disposed by metal doping and surface modification, so as to improve the electrical conductivity and enhance the electrochemical properties. Detailed work were done as follows:In our study, the process of solid-state synthesis and the influence of different materials to the Li4Ti5O12 preparation were investigated in the first instance. The structure, morphology and electrochemical performan-ce of the sample was characterized by X-ray diffractometry(XRD), scanning electron microscopy(SEM), laser particle analysis, galvanostatic charge-discharge test, electrochemical impedance spectroscopy (EIS) and cyclic voltammeter(CV). The result showed that Li4Ti5O12 with the best performance was achieved when using Anatase-TiO2 and LiCO3 as the original material, and preheated at 750℃for 4 h followed by 850℃for 20 h. The as-prepared sample was well-crystallized single-phase, and its particle was well-distributed with a narrow size distribution from 0.2 to 0.6μm. On charge/discharge at 0.2 C, the initial specific discharge capacity was 163.4 mAh·g-1, and the specific capacity still kept at 160 mAh·g-1 after 30 cycles. At the room temperature, on charge/discharge at the rate of 0.5,1 and 3 C after 50 cycles, the retention rate in discharge capacity was 96.2,94.1,86.0% respectively. And the possible formation mechanism of Li4Ti5O12 was explored as well.On the bases of the study on preparing the pure samples, the doping of the metallic icons such as Y3+, Yb3+, Er3+, V5+, Mg2+ was conducted. The electrochemical test indicated that their electrochemical performance were quite different from each other although the electron transfer resistance of them were greatly reduced. The samples doped Y3+, Yb3+ Er3+, V5+, Mg2+ had the capacity of 132.6,110.1,102.4,86.2,139.6 mAh·g-1 respectively at 1 C after 50 cycles.Based on the solid-phase synthesis and metal doping, the composite materials Li3.9Mg0.1Ti5O12/C and Li4Ti5O12/(Cu+C) were fabricated by glucose and copper acetate which was used as carbon and copper source. The galvanostatic charge-discharge test showed that when the content of carbon in Li3.9Mg0.1Ti5O12/C was 3,5,10 and 15 wt%, the samples had the discharge capacity of 166.5,156.3,153.7 and 149.4 mAh·g-1 for the first cycle, respectively. For Li4Ti5O12/(Cu+C) materials, The capacity retention were 90.4,88.4 and 82.0% respectively at 0.5,1 and 3 C after 50 cycles, and the corresponding discharge capacity were 155,151.7 and 140.6 mAh·g-1.The diffusion coefficient of Li+ for Li4Ti5O12 and Li4Ti5O12/(Cu+C) were 4.3×10-10 cm2·s-1 and 1.2×10-9 cm2·-1 respectively, which were calculated from CV analysis. |
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