【作者】 魏召唤；

【导师】 孙克宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 硕士

【摘要】 锂离子电池具有质量轻、比能量高、寿命长及无记忆效应等优点,不仅在民用领域的应用发展迅速,而且在军用通信、航天等高科技领域也有很广的应用前景。由于其特殊使用环境,这些领域对锂离子电池的性能提出了更高的要求。目前限制锂离子电池使用主要因素之一是锂离子电池的低温性能比较差,石墨负极在低温下嵌锂过程极为困难。造成这一现象的主要原因是在低温下石墨负极中锂离子扩散速率小、嵌锂过程中电极/电解液界面上的电荷传递阻抗较大。因此本论文从这两个限制因素入手,分别采用膨胀化处理和氧化处理两种手段对中间相碳微球(mesophase carbon microbeads, MCMB)进行改性,并通过扫描电镜、X射线衍射、电化学交流阻抗等表征手段考察改性后MCMB表面形貌、结构、嵌锂过程阻抗的变化情况,借此探讨了负极低温性能改善的原因。膨胀化处理MCMB主要目的是增大MCMB石墨层间距,提高锂离子在MCMB中的迁移能力。结果发现,随着膨胀化程度的增加,MCMB的低温性能得到明显改善。阻抗结果分析发现膨胀化中间相碳微球锂离子扩散系数比未经处理的中间相碳微球高三个数量级,达到1.36×10-10cm2s-1,-40℃循环容量可达到38mAh.g-1,经过热处理,-40℃循环容量可进一步达到101mAh.g-1。氧化处理MCMB目的在于改变石墨表面官能团的种类和数量,进而调控MCMB充放电过程中形成的固体电解质(Solid Electrolyte Interface, SEI)膜的厚度与组成,增加SEI膜电导率。同时,氧化可能会引起表面形貌的变化,形成孔道结构,增大锂离子扩散系数。试验结果发现,氧化后SEI膜阻抗增大,扩散系数增大,表面微观结构基本无变化,对低温容量的提高作用很小。因此单纯表面氧化不能使石墨负极的低温脱嵌锂性能得到提高。更多还原

【Abstract】 Li-ion battery has the advantages of low equivalent weigh, high theoretical capacity, long cycle life, no memory effection and so on. So it can be applied not only in civilian areas, but also in military communications, aerospace and other high-tech fields, thus the performance of li-ion battery has to fit these fields. One of the main factors restricts the use of li-ion battery is its poor performance at low temperature. The main reasons for this phenomenon are the low lithium ion diffusion rate and large charge transfer resistance. In this work the mesophase carbon microbead (MCMB) was modified to investigate the influences of expanding and oxidation effection on the low temperature performance of li-ion battery. Scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) were used to characterize the surface morphology, structural characteristics and resistance of the modified MCMB.Expanded MCMB was prepared to increase the li-ion diffusion coefficient. It was found that the low temperature performance of MCMB had been significantly improved with the increase of expansion. The study of EIS found that the li ion diffusion coefficient of expanded MCMB was three orders magnitude higher than that of unmodified. The capacity of expanded MCMB at -40℃could reach to 38mAhg-1. By heat treated, the capacity of expanded MCMB at -40℃could reach to 101mAhg-1.Oxidate treated MCMB was prepared to change the types and quantities of surface groups, and change the thickness and composition of the solid electrolyte formed on the anode, to increase the conductivity of Solid Electrolyte Interface (SEI). Meanwhile, Oxidation might leads to changes in surface morphology, to form the pore structure and increase the li ion diffusion coefficient. The results showed that after oxidation, the resistance of SEI and the diffusion coefficient increased, but the improvement of low temperature performance was unsatisfied. As a result, just simply surface oxidation treatment couldn’t improve the low temperature performance of graphite anodes.更多还原