锂离子电池负极材料Li₄Ti₅O₁₂的制备与性能研究

【作者】 周晓玲；

【导师】 戴永年； 黄瑞安；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2011， 硕士

【摘要】 尖晶石型钛酸锂Li4Ti5O12材料由于具有优异的循环寿命,安全性能好,容易制备,对环境友好等特点,被认为是目前最有前途的锂离子电池负极材料之一。然而,Li4Ti5O12材料由于电导率低而导致倍率性能较差,成为其商业化应用的最大障碍。本文在制备纯相Li4Ti5O12材料的基础上,通过表面改性改善其倍率性能。以Li2CO3和Ti02为原料,采用高温固相法在850℃下焙烧12小时制备了尖晶石型Li4Ti5O12负极材料。实验结果表明：合成的Li4Ti5O12颗粒密实且堆积在一起,晶粒分布不均匀,粒径为1-4微米左右,测试电池的首次放电容量为145.4mAh/g,100次循环后容量保持率约为80%采用溶胶-凝胶法制备了Li4Ti5Ol2负极材料,探讨了焙烧温度、保温时间、不同锂盐及分散剂聚乙二醇(PEG)对Li4Ti5O12电化学性能的影响。XRD测试表明,制备的Li4Ti5Ol2为尖晶石结构；恒流充放电测试表明,随着焙烧温度的升高和保温时间的延长,合成的Li4Ti5O12放电比容量随之增大,但当焙烧温度高于700℃,保温时间超过6h时,产物的放电比容量反而有所降低；采用金属锂比采用乙酸锂做锂源合成的Li4Ti5O12材料颗粒小,放电比容量高,团聚现象严重；采用聚乙二醇(PEG)作为分散剂,有效地阻止了粒子的团聚长大,从而改善了由于材料颗粒较小而引起的团聚现象,提高了Li4Ti5012材料颗粒的分散性和比表面积,不仅增加了电极-电解液的接触面积,活性材料和碳黑的混合也更加均匀,从而提高了Li4Ti5O12材料的倍率性能。因此得出最佳工艺条件为：以金属锂为锂源,聚乙二醇(PEG)为分散剂,焙烧温度为700℃,保温时间为6h。用此工艺合成的材料首次放电比容量为168.3mAh/g,100次循环后容量保持率为97%,电化学性能优于高温固相法制备的材料。通过在Li4Ti5O12材料表面包覆导电物质碳、氮化钛、锑锡氧化物(ATO)的方法来改善Li4Ti5O12负极材料的倍率性能。实验结果表明：包覆碳、氮化钛、锑锡氧化物(ATO)后,提高了材料的首次放电容量；在5C倍率下放电,10次循环后放电容量分别为127.3 mAh/g.111.0 mAh/g、88.1 mAh/g,较之纯相Li4Ti5O12材料的5C倍率放电容量76.0mAh/g,倍率性能得到了不同程度的提高,其中改善效果包覆碳最好,氮化钛次之,ATO效果不明显。更多还原

【Abstract】 The spinel Li4Ti5O12 has been demonstrated as one of the most promising anode material candidates for lithium ion batteries, due to its excellent cyclability, very good safety, easy preparation, environmental friendliness and so on. However, a major obstacle to its commercial application is the low conductivity of Li4Ti5O12 which exhibited poor rate performance. In the paper, pure Li4Ti5O12 was symhesized by different methods and the rate performance of Li4Ti5O12 was improved by coating substance which has good conductivity.Spinel Li4Ti5O12 was synthesized by solid state reaction using Li2CO3 and TiO2 as raw materials for 850℃,12 hours. The results showed that particle of Li4Ti5O12 were dense and the particle size was 1～4μm. The initial discharge capacity of the cell was 145.4 mAh/g, it retained 80% after 100 cycles.The effect of sintering temperature, sintering time, Li materials and polyethylene glycol(PEG) to Li4Ti5O12 which synthesized by sol-gel method were studied. The XRD test indicated that the spinel lithium titanate composite Li4Ti5O12 was successfully synthesized. The charge-discharge test showed that the capacity of Li4Ti5O12 was increased with elevation of heating temperatures and time. However, the capacity of Li4Ti5O12 was fall when the temperature over 700℃and the time over 6 hours. The particle was smaller, more disperse when using lithium than CH3COOLi·2H2O. By adding PEG to improve the dispersivity and the specific surface area of the Li4Ti5O12, the electrode-electrolyte contact area was increased; meanwhile, more homogeneous mixing of the active materials with carbon black was achieved. Thus the high rate performance of Li4Ti5O12 was improved. Therefore, the ideal experiment parameters are 700℃,6 hours, using lithium as raw materials, and adding PEG as a dispersant.The rate performance of Li4Ti5O12 was improved by coating carbon, TiN and antimony doped Tin oxide(ATO) which increased the electronic conductivity of Li4Ti5O12. The results showed that initial discharge capacity of the cell was increased. When tested at a rate of 5C, they still retained a discharge capacity of 127.3 mAh/g,111.0 mAh/g,88.1 mAh/g, respectively, after 10 cycles, better than 76.0 mAh/g of the pure Li4Ti5O12 Obviously, the material coating carbon got the best performance, and the rate performance of Li4Ti5O12 by coating antimony doped Tin oxide(ATO) was not obvious.更多还原