锂离子动力电池负极材料钛酸锂的制备与性能研究

【作者】 蒋志军；

【导师】 刘开宇；

【作者基本信息】 中南大学 ， 应用化学， 2011， 硕士

【摘要】 钛酸锂(Li4Ti5O12),作为一种“零应变”材料,与目前商品化的碳材料相比,是更具潜力的锂离子动力电池负极材料。本文以固相法合成电极材料Li4Ti5O12,旨在通过金属掺杂、表面修饰途径,提高电导率进而改善其电化学性能,具体工作如下：本文首先考察了制备Li4Ti5O12的固相工艺和不同原料的影响。采用XRD、SEM、激光粒度对材料进行了表征,及恒流充放电、交流阻抗、循环伏安测试方法研究了材料的电化学性能。结果表明：原料为锐钛型Ti02和Li2CO3,先于750℃预烧4h,再于850℃煅烧20 h得到的材料性能最佳,样品为结晶完好的单一物相,颗粒分布均匀,粒径分布窄,粒度分布在0.2～0.6μm之间。以0.2 C的倍率进行充放电,首次放电比容量为163.4mAh·g-1,30次循环后,容量依然保持在160mAh·g-1,常温下,分别以0.5、1和3C倍率进行充放电循环50次后,容量保持率分别为96.2、94.1、86.0%。并探索了Li4Ti5O12可能的形成机理。在合成纯样的研究基础上,进行了Y3+、Yb3+、Er3+、V5+、Mg2+金属离子的掺杂。电化学测试表明：金属离子掺杂后电极材料的电荷转移阻抗都显著减小,但电化学性能却显示出很大的差异。在1C倍率下循环50次后,掺杂Y3+、Yb3+、Er3+、V5+、Mg2+的比容量分别为132.6、110.1、102.4、86.2、139.6mAh·g-1。在固相合成和金属掺杂的基础上,分别以葡萄糖和乙酸铜作为碳源和铜源制备了Li3.9Mg0.1Ti5O12/C和Li4Ti5O12/(Cu+C)复合材料。恒电流充放电结果表明,在0.1 C的倍率下放电时,Li3.9Mg0.1Ti5O12/C(C含量分别是3、5、1 0、15wt%)的首次放电容量依次为166.5、156.3、153.7和149.4mAh·g-1。对于Li4Ti5O12/(Cu+C),在0.5、1和3C倍率下,经50次充放电循环,容量保持率分别为90.4、88.4、82.0%,其放电比容量依次为155、151.7、140.6mAh·g-1。通过循环伏安测试技术得到Li4Ti5O12和Li4Ti5012/(Cu+C)电极材料的Li+扩散系数分别为4.3×10-10cm2.s-1和1.2×10-9cm2.s-1。更多还原

【Abstract】 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.更多还原