【作者】 唐宇峰；

【导师】 杨立；

【作者基本信息】 上海交通大学 ， 应用化学， 2010， 博士

【摘要】 锂离子电池具有开路电压高、能量密度大、使用寿命长、少污染等优点,它在总体性能上优于其它传统二次电池。电动汽车(EV、HEV)等环境负荷较低的“新一代汽车”要求搭载的储能器件具备高速充放电能力,所以动力型锂离子电池高功率化的研发不可或缺也十分紧迫。实现高功率锂离子电池的关键是开发性能优异的电池材料。Li4Ti5O12负极材料具有充放电过程中体积变化小、可逆性好等优点。然而,作为高功率动力型锂离子电池负极材料,其倍率性能还有待进一步提高。纳微分级结构不仅能够提供大的比表面积和短的离子扩散路径,而且热力学稳定,易于制备,是一种较为理想的结构体系,可有效提高电极材料的倍率性能。我们将Li4Ti5O12材料本身所具有的优越的循环性能和安全性能,与纳微分级结构有利于提高电极材料倍率性能的特点结合起来,设计合成出了一系列具有新型纳微分级结构的Li4Ti5O12,从而获得具有高功率、高安全性和长寿命的负极材料。主要研究内容如下:利用乙二醇-水混合溶剂热法制备了纳米片构成的花状Li4Ti5O12微球。循环伏安测试结果表明,该结构体系通过缩短锂离子的扩散路径,增强了材料中锂离子嵌/脱动力学性能。通过充放电测试,花状Li4Ti5O12表现出了高的可逆容量和较好的倍率性能,在8 C倍率下的首次放电容量为165 mAhg-1。鉴于纳米片自组装结构的良好性能,我们利用无定型水合二氧化钛微球作为前驱体,通过简单的水热合成及后续热处理,制备了新型Li4Ti5O12纳米片自组装空心微球。所合成的微球直径约400 nm,球体内中空,球壳由厚度约2-5 nm的Li4Ti5O12纳米片组成。通过考察分级结构空心微球的形成过程,提出其形成过程中可能存在着柯肯达尔效应(Kirkendall effect)。由于空心结构有利于离子快速传输,该结构Li4Ti5O12展现了更为优异的倍率性能和较高的容量,即使在50 C倍率下材料的放电容量仍可达到131 mAhg-1,显示出应用于高功率锂离子电池的潜力,值得期待。以水合二氧化钛微球作为前驱体,通过乙醇-水混合溶剂热以及后续热处理制备了介孔Li4Ti5O12微球,讨论了介孔微球的形成机理。研究了反应体系中乙醇含量对样品形貌的影响,结果表明:当溶液中乙醇含量低于30%,难以得到形貌均一的介孔Li4Ti5O12微球。将介孔Li4Ti5O12微球用于锂离子电池,研究了该结构Li4Ti5O12的充放电倍率性能。与微米级Li4Ti5O12颗粒相比,介孔Li4Ti5O12微球不仅倍率性能优异,30 C倍率下的放电容量为114 mAhg-1,而且具有非常好的容量保持率,在20 C倍率下200次循环后容量仍保持在125 mAhg-1左右,容量保持率接近100%。通过将H2O2引入反应体系,在低碱性溶液中,水热制备了钛酸钠纳米管自组装空心微球。水热后的钛酸钠用稀盐酸中和后,可得到相似结构的钛酸。进而以钛酸为反应前驱物,通过直接热处理或水热锂离子交换反应得到TiO2纳米管和Li4Ti5O12纳米管的自组装空心微球。将材料用于锂离子电池,研究了纳米管自组装结构Li4Ti5O12和TiO2的充放电性能。结果表明,纳米管自组装结构有利于提高电极材料的电化学性能,尤其TiO2纳米管自组装微球表出很好的倍率性能和循环可逆性:1 C倍率下100次循环后放电容量保持在160 mAhg-1左右,而8 C倍率的放电容量仍可达到90 mAhg-1。更多还原

【Abstract】 Lithium ion battery has many merits (e.g., higher voltage, higher energy density, and longer cycle life) compared with traditional rechargeable batteries. Considerable attention has been paid to electrochemical energy storage devices with the ability to withstand fast charge-discharge over an adequate cycle life, because of their potential use in future electric vehicle (EV) or hybrid EV (HEV). Thus, the research and development of Lithium ion battery with outstanding high-rate performance is desirable and significative.As the performance of high–rate lithium ion battery these devices depends intimately on the properties of their materials, considerable attention has been paid to the research and development of key materials. Although spinel Li4Ti5O12 has a good reversibility and exhibits a very small volume change during charge–discharge process, the future importance of high-power applications encourages investigation of the high-rate performance of the material. Electrode materials with nano/micro hierarchical structures are the best systems of choice to improve high rate capability, because they have large specific surface area, short distance for lithium ion diffusion, good stability and easy of fabrication. Novel Li4Ti5O12 with nano/micro hierarchical structure may give an ideal host material for the rapid intercalation and deintercalation of Lithium ions and provide the possibility of efficient transport of electrons in the high-rate lithium ion batteries. The major research content is as follows: The flower-like spinel Li4Ti5O12 consisting of nanosheets was synthesized by a hydrothermal process in glycol solution and following calcination. The cycle voltammetric results of the electrodes indicate enhanced electrochemical kinetics for lithium insertion by reducing the distance of lithium ion diffusion in solid-state body. The capacity of the sample used as anode material for lithium ion battery was measured. This structured Li4Ti5O12 exhibited a high reversible capacity and an excellent rate capability of 165 mAhg-1 at 8 C. Besides the flower-like Li4Ti5O12, the Li4Ti5O12 hollow microspheres consisting of nanosheets have also been synthesized via a hydrothermal route and following calcination. The formation mechanism for the hollow microspheres was studied by tracking the crystallization and morphology of the product at different reaction stages. Because of the favorable transport properties of this hollow structure, when the Li4Ti5O12 hollow microspheres assembled by nanosheets were used as the anode material in lithium ion battery, they exhibited superior rate performance and high capacity even at a very high rate (131 mAhg-1 at 50 C), indicating potential application for high-rate lithium ion batteries.Mesoporous spinel lithium titanate Li4Ti5O12 microspheres were prepared by template-free hydrothermal process in ethanol-water mixed solution and subsequent heat treatment. The role of ethanol helps the formation of a mesoporous structure during the hydrothermal process. In general, well-defined mesoporous spheres can hardly be produced when r(EtOH vol% in the solvent of EtOH-H2O) is lower than 30%. A mechanism analogous to the Kirkendall effect was proposed to account for the template-free formation of these mesoporous nanostructures. As anode materials for high-rate lithium ion battery, the Li4Ti5O12 mesoporous spheres exhibited superior high-rate performance of 114 mAhg-1 at 30 C and good capacity retention of 125mAhg-1 after 200 cycles at 20 C.A facile synthesis route was developed to prepare hierarchical hollow microspheres assembled by titanate nanotubes. Especially, H2O2 was found to be an efficient agent that can facilitate the roll of titanate sheets into nanotubes under low concentrated NaOH conditions. And the similar structured hydrogen titanate was prepared via acid washing of sodium titanate. After calcination, the hydrogen titanate can be transformed into TiO2 nanotube-based hollow spheres, and similar structured Li4Ti5O12 can be prepared by hydrothermal ion-exchange between lithium ion with hydrogen titanate and following calcination. When the hierarchical structured TiO2 were used as the anode material in lithium ion battery, they exhibited a high capacity and cycle stability of 160 mAhg-1 after 100 cycles at 1 C and a good rate performance of 90 mAhg-1 at 8 C.更多还原