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1、 博士学位论文锂离子电池石墨类碳负极的容量衰减机制研究RESEARCH ON CAPACITY LOSS MECHANISMSOF GRAPHITIC CARBON ANODES IN LITHIUMION BATTERIES杨丽杰哈尔滨工业大学2014年 10月 国内图书分类号：TM912.9学校代码：10213国际图书分类号：621.355密级：公开工学博士学位论文锂离子电池石墨类碳负极的容量衰减机制研究博士研究生：杨丽杰导 师：尹鸽平教授申请学位：工学博士学科：化学工程与技术所在单位：化工学院答辩日期：2014年 10月授予学位单位：哈尔滨工业大学 Classified Index: T
2、M912.9U.D.C: 621.355Dissertation for the Doctoral Degree in EngineeringRESEARCH ON CAPACITY LOSS MECHANISMSOF GRAPHITIC CARBON ANODES IN LITHIUMION BATTERIESCandidate：Yang LijieSupervisor：Prof. Yin GepingAcademic Degree Applied for：Speciality：Doctor of EngineeringChemical Engineering and TechnologyS
3、chool of Chemical Engineering and Technology Affiliation：October, 2014 Date of Defence：Degree-Conferring-Institution：Harbin Institute of Technology 摘要摘要锂离子电池具有电压高、能量密度高、污染小等优点，在电子产品和电动车领域已经得到应用。锂离子电池的容量在使用过程中逐渐降低，如果能够探究出导致电池容量衰减的原因，那么可以有针对性地对电池的制备进行改善，从而获得具有高容量、长寿命的锂离子电池，这将具有十分重要的意义。本文研究了锂离子电池常用的负极材
4、料中间相碳微球（ MCMB）和石墨的容量衰减机制，通过电化学交流阻抗（EIS）和循环伏安（CV）测试考察负极材料的电化学性能在长期充放电循环过程中的变化，采用扫描电子显微镜（SEM）、X射线光电子能谱（XPS）、X射线衍射谱（XRD）等测试手段对负极材料表面固体电解质界面（SEI）膜的生长、负极材料的结构变化以及锂沉积物的生长进行研究。通过对 MCMB扣式半电池进行长期充放电循环，研究了 MCMB材料的容量衰减机制。研究表明，随着充放电循环的进行，MCMB材料体相的 d002和 Lc出现小幅度的增加，石墨化程度小幅度地下降，d110和 La未出现明显变化，MCMB材料表面的无序化度增加。MCM
5、B材料表面的 SEI膜随着循环的进行不断生长，Li2O先生成，LiF后生成。由于 SEI膜的不断生长，锂离子通过 SEI膜的迁移过程变得更加困难，引起膜电阻（Rf）的增加，而且 LiF含量的增加表明 SEI膜的生长过程中不断消耗电解质盐 LiPF6，引起电池的欧姆电阻（Rb）增加。这些阻抗的增加使得电极脱嵌锂反应的极化增大，反应电流降低，表现为负极容量的衰减。研究了长期循环过程中 LiCoO2/MCMB电池的 MCMB负极容量衰减机制。在前 200次充放电循环过程中，LiCoO2/MCMB电池的容量快速衰减，发现负极极耳附近的单面涂覆区域中电极材料从集流体上剥离，结合力测试结果表明此区域中负极
6、材料与集流体之间的结合力较小，这是电池循环前期容量快速衰减的原因之一。Li2CO3、ROCO2Li等碳酸盐出现在循环后期形成的 SEI膜中。在长期循环过程中，MCMB电极材料的 d002和 Lc小幅度增加，石墨化程度小幅度下降，d110和La未出现明显变化。随着长期循环的进行，负极表面 SEI膜对容量损失的影响增加，MCMB材料结构变化对容量损失的影响小于 SEI膜。循环初期和后期生成的SEI膜对电化学阻抗的影响由大到小的顺序均为 Rf、传荷电阻（Rct）、Rb。MCMB负极表面的锂沉积物随着循环的进行不断生长，首先出现在与集流体相邻的表面，然后在与隔膜相邻的表面生长。上层和下层沉积物的外部区
7、域均由 Li2CO3、LiOH、ROCO2Li和ROLi组成。被刻蚀的下层沉积物的内部主要含有Li2O、LiF和Li2CO3，上层沉积物的内部主要含有 Li2CO3、ROCO2Li、ROLi和 LiF。负极 MCMB表面的 SEI膜明显阻碍锂离子向碳层中的嵌入，正极 LiCoO2产生过充而脱出较多的锂I 哈尔滨工业大学工学博士学位论文离子，这两个因素引起长期循环过程中锂沉积物的生成。锂沉积物的厚度可达几十到上百微米，阻碍了锂离子的嵌入，并引起 MCMB层从集流体上的局部剥离，使得电池的 Rb略有增加，Rf和 Rct明显增加，导致负极容量的衰减。2400次循环后负极 MCMB的容量衰减大于正极
8、LiCoO2，负极表面 SEI膜的生长是负极容量衰减的主要原因，占容量损失的 68%。在长期充放电循环过程中，LiCoO2/石墨电池负极材料的 d002小幅度增加，Lc小幅度降低，La未出现明显变化。循环至 600次时，石墨表面出现不均匀分布的锂沉积物，而且随着循环的进行不断生长。锂沉积物表面的 SEI膜成分和石墨表面的 SEI膜成分相似。锂沉积物的出现消耗电池中的电解液，降低电池的离子导电性，而且其本身的形成也会消耗电池中的活性锂，引起电池的容量衰减。随着充放电循环的进行，石墨材料的剥落引起负极活性材料的减少，使得锂沉积物出现在石墨电极表面。LiCoO2/石墨电池的正极和负极对电池长期循环容
9、量衰减的影响最大，其次是电解液，负极对电池性能衰减的影响大于正极。关键词：锂离子电池；碳材料；容量衰减；SEI膜；锂沉积物II AbstractAbstractThe lithium ion battery has some advantages such as high voltage, high energydensity, few pollution and so on. It has been applied in the fields of electronic productsand electric vehicle. The capacity of lithium ion bat
10、tery decreased gradually during use.If the reasons for the capacity loss were explored, the preparation of the battery wouldbe improved targetedly and lithium ion batteries with high capacity and long life couldbe obtained, which is of great importance. In this paper, capacity loss mechanisms ofmeso
11、carbon microbeads (MCMB) and graphite anodes applied in lithium ion batterywidely were studied. The changes of electrochemical properties of the anodes during thelong-term charge/discharge cycling were examined by electrochemical impedancespectroscopy (EIS) and cyclic voltammetry (CV) tests. Then th
12、e growth of solidelectrolyte interface (SEI) film on the surface of the anode, structure changes and thegrowth of the lithium deposits were studied using scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and so on.The capacity fade behaviors of MCMB w
13、ere studied by the long-term charging anddischarging of MCMB coin cells. The results indicated that d002 and Lc of MCMB bulkincreased and the degree of graphitization decreased slightly with the cycling, while d110and La did not change obviously, and the disorder extent of MCMB surface increased.Li2
14、O was formed firstly, and then LiF was formed in SEI film on the surface of MCMB.Due to the growth of SEI film, it was more difficult for lithium ions to transfer throughSEI film, which contributed to the increase of film resistance. Moreover, the increase ofLiF content indicated that LiPF6 was cont
15、inously consumed during the growth of SEIfilm, leading to the increase of ohmic resistance. The increase of these resistances led tothe polarization increase of the lithium insertion and deinsertion reaction, and thedecline of reaction current, which contributed to the capacity loss of the anode.The capacity loss mechanism of MCMB anode in LiCoO2/MCMB battery
