【作者】 项良顺；

【导师】 高明霞；

【作者基本信息】 浙江大学 ， 材料学， 2010， 硕士

【摘要】 本论文在详细综述了国内外锂离子电池及其相关材料,尤其是Si基负极材料的研究进展基础上,针对Si具有最大的嵌锂理论容量,但是由于在循环过程中具有不可避免的严重的体积效应,提出以纳米Si粉为原材料,采用溶胶-凝胶法和热气相分解法分别制备Li4Ti5O12和碳不同包覆,具有核壳结构的(Si/Li4Ti5O12和Si/C)硅基复合材料作为锂离子电池负极材料。运用XRD、SEM和TEM等技术对合成材料的微观结构和形貌进行了分析,采用恒流充放电、循环伏安法和交流阻抗技术测试其电化学性能。论文系统研究了主要制备工艺对合成材料的微观形貌结构和电化学性能的影响。论文采用溶胶-凝胶法,以钛酸丁酯、乙酸锂和纳米硅粉体为原材料,在烧结温度为500-1000℃的条件下,成功制备了数纳米厚度的Li4Ti5O12包覆纳米Si的Si/Li4Ti5O12复合材料,Li4Ti5O12相在600-800℃下结晶化程度很高,其余温度下出现杂相。干凝胶球磨预处理可降低合成材料的颗粒团聚度,改善其分散性,有效提高复合材料的电化学性能。Li4Ti5O12部分抑制了首次嵌锂过程中生成SEI膜的反应,缓解了Si在脱嵌锂过程中体积的变化,从而改善材料的循环性能。1000℃合成的样品,具有更好的循环稳定性,但含有较多的非活性杂质相,其容量相对较低。Si和Li4Ti5O12的质量比为8,在700℃合成材料具有最大的可逆容量,为2075 mAh/g,经50次循环后,容量保持为490 mAh/g,比初始Si的容量(245 mAh/g)高一倍。采用热气相分解法成功制备了具有均匀碳包覆层的纳米Si/C复合材料。乙炔在700-900℃的温度下经不同时间(15-90 min)分解,分解为无定形的碳包覆于纳米颗粒表面,包覆碳厚度在数十纳米,并随分解温度及分解时间的延长而增加,含量在1-40wt%。碳包覆明显提高了Si电极的循环稳定性,纳米Si在乙炔中经800℃保温30 min合成样品经50次循环后容量为705 mAh/g,为未包覆碳的纳米Si样品的3倍多。更多还原

【Abstract】 In this thesis, the recent research development on the related materials for lithium-ion batteries (LIB) at home and abroad, especially Si-based anode materials, are detailed reviewed. Based on the advantages and disadvantages of Si as anode material, two Si-based nanocomposites (Si/Li4Ti5O12 and Si/C) with a core-shell structure were synthesized through Sol-Gel method and thermal vapor decomposition method, respectively. The microstructures of the synthesized Si-based nanocomposites were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) as well as element analysis, etc. The electrochemical properties of the composites were studied by galvanostatic charge-discharge, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) methods. The effects of the fabrication parameters on the microstructures and electrochemical properties of the synthesized Si-based nanocomposites were systematically studied.The Si/Li4TisO12 composites with a thin shell of Li4Ti5O12 coating on the surface of silicon nanoparticle core were synthesized via a Sol-Gel method by using nano-Si powders, tetrabutyl titanate and lithium acetate as the starting materials. Sintering temperatures ranging 500-1000℃were used. The agglomeration of the synthesized Si/Li4Ti5O12 composites was reduced by the pre-treatment of the dry-Gel by ball milling with conductive agent, and hence, the electrochemical properties were improved effectively. The purity of the synthesized Li4Ti5O12 was high in the sintering conditions of 600-800℃, a few impurity phases would exist when the sintering temperature was too high or too low. The presence of Li4Ti5O12 coating-layer bated the formation of SEI film as well as weakened the silicon volume variation during Si alloying/dealloying with lithium, so that the cycle performance of composite materials was effectively improved. The reversible capacity of the synthesized composite with the sintering temperature of 700℃is 2075 mAh/g for the first cycle which is the largest of the synthesized samples, and 490 mAh/g after fiftieth cycle, which is two times of 245 mAh/g for the bare Si. The synthesized composite with the sintering temperature of 1000℃has a high initial Coulomb efficiency (80%) and better cycling stability, though its reversible capacity is relatively lower. The causation may be that there are more impurities which are inactive or weaker active.The Si/C nanocomposites with a uniform layer of carbon-coated were successfully prepared through thermal vapor decomposition method. Acetylene decomposed into amorphous carbon which through the temperature of 700-900℃for different time (15-90 min). The thickness of carbon coating was a few nanometers, and the carbon content increased from 1 wt%to 40 wt%along with the extention of the decomposition temperature and time. The cycle stability of nano-Si was significantly improved through the carbon uniformly coated on the surface of the Si nanoparticles. For example, the Si/C nanocomposite synthesized at 800℃for 30 min has a capacity of 705 mAh/g after 50 cycles, which is 3 times of the bare Si sample.更多还原