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 Technolog
3、ySchool 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
4、负极材料中间相碳微球（ 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
5、增加。MCMB 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（R b）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
6、试结果表明此区域中负极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、ROCO 2Li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（R ct）、R b。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
7、生长。上层和下层沉积物的外部区域均由 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Li2CO 3，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 LiCoO 2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
8、后负极 MCMB的容量衰减大于正极 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，L a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
9、/石墨电池的正极和负极对电池长期循环容量衰减的影响最大，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IIAbstractAbstractThe 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
10、of lithium ion battery 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
11、 mechanisms ofmesocarbon 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 (
12、CV) tests. Then the 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 b
13、ehaviors of MCMB were 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 sur
14、face increased.Li2O 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 t
15、hat LiPF6 was continously 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 los
16、s of the anode.The capacity loss mechanism of MCMB anode in LiCoO2/MCMB battery duringthe long-term cycling was studied. The capacity of LiCoO2/MCMB battery declinedquickly during the first 200 charge/discharge cycles. The MCMB materials in thesingle-side coated area near the plate lug of anode deta
17、ched from current collector.Adhesion between anode material and current collector in the single-side coated areawas small from test result of adhesion. Detachment of anode material from currentcollector was considered as one of the reasons for quick capacity loss at the early stageof cycling. Li2CO3
18、 and ROCO2Li appeared in the SEI film generated in the later periodof cycling. d002 of MCMB increased slightly, and d110 and La did not change during thelong-term cycling. The effect of SEI film on the capacity loss increased with the cyclingand the effect of the structure change of MCMB material on
19、 the capacity loss wasIII哈尔滨工业大学工学博士学位论文smaller than that of SEI film. The effects of SEI film generated in the both earlier andlater periods of cycling on the electrochemical resistances from big to small were Rf, Rctand Rb. Lithium deposition on the MCMB anode grew gradually with the cycling. Thed
20、eposition appeared on the surface next to the current collector firstly, and then on thesurface next to the separator. The outer region of both lower and upper deposition layersconsisted of Li2CO3, LiOH, ROCO2Li and ROLi. The inner region of etched lowerdeposition layer mainly consisted of Li2O, LiF
21、 and Li2CO3, and that of etched upperdeposition layer mainly consisted of Li2CO3, ROCO2Li, ROLi and LiF. SEI filmhindered the intercalation of lithium ions into carbon layers obviously and ovchargedLiCoO2 cathode provided more lithium ions, which brought up the formation of thelithium deposition dur
22、ing long-term cycles. The thickness of the deposition ranged fromtens to several hundreds of micrometres. The deposition hindered the intercalation oflithium ions, and it made MCMB layer peeled off from current collector locally. Rb ofthe cell increased slightly, and Rf and Rct increased significant
23、ly, leading to the capacitydecline of the anode. The capacity loss of anode was larger than that of cathode after2400 cycles. The growth of SEI film on the anode was the main reason for the capacitydecline, and it accounted for 68% of the capacity loss of the anode.d002 of the anode in the LiCoO2/gr
24、aphite battery increased and Lc decreased slightly,and La did not change obviously during the long-term charge/discharge cycling. Whenthe battery was charged and discharged for 600 cycles, lithium deposition began toappeare unevenly on the surface of graphite anode and the deposition grew continuous
25、lywith the cycling. The composition of SEI film on the surface of lithium deposition wassimilar with that on the surface of graphite. The appearance of lithium deposition couldconsume the electrolyte of the battery and decrease the ionic conductivity of the battery.Moreover, the formation of lithium
26、 deposition itself would also consume the activelithium of the battery and led to the capacity loss. The exfoliation of graphite materialled to the decline of anode active material with the charge/discharge cycling, makingmetal lithium deposition appear on the surface of graphite anode. The effect o
27、f cathodeand anode on the LiCoO2/graphite battery capacity loss was the first largest and that ofelectrolyte was the second largest. Moreover, the effect of anode on the property declineof the battery was greater than that of cathode.Keywords: Lithium ion battery, Carbon anode, Capacity loss, SEI fi
28、lm, LithiumdepositionIV目 录目录摘要 .IAbstract. III第 1章绪论. 11.1课题研究的目的和意义 11.2锂离子电池容量衰减机制研究概况 21.2.1正极材料 21.2.2电解液 41.2.3集流体 71.2.4负极材料 71.3石墨类碳负极容量衰减机制的研究进展 81.3.1石墨类碳负极表面 SEI膜的研究进展 81.3.2石墨类碳负极中锂沉积物的研究进展 111.3.3石墨类碳负极结构变化的研究进展 131.3.4石墨类碳负极寿命提高的研究概况 151.4本文的主要研究内容 16第 2章实验材料和研究方法 182.1实验药品和实验仪器 182.1.1
29、实验药品 182.2.2实验仪器 182.2电池的制备 192.2.1 MCMB扣式半电池的制 备 192.2.2 LiCoO2/MCMB全电 池的制备 192.2.3 LiCoO2/石墨全电池的制备 202.2.4全电池拆解及扣式半电池的制备 202.3电化学性能测试 202.3.1恒流充放电测试 202.3.2电化学交流阻抗测试 202.3.3循环伏安测试 212.4电池材料的物理性能表征 212.4.1扫描电子显微镜 21V哈尔滨工业大学工学博士学位论文2.4.2 X射线光电子能谱 . 212.4.3 X射线衍射谱 . 222.4.4拉曼光谱 222.4.5傅里叶红外光谱 222.4.6
30、原子力显微镜 222.4.7示差扫描量热法 222.4.8结合力测试 23第 3章扣式半电池中 MCMB 电极材料的容量衰减机制研究 . 243.1半电池中 MCMB表面 SEI膜的生长 243.2半电池中 MCMB的结 构变化 313.3 MCMB半电池电化学性能的演 变 353.4 MCMB半电池组成对容量 损失的影响 383.5本章小结 40第 4章 LiCoO2/MCMB电 池中 MCMB 负极的容量衰减机制研究 414.1 LiCoO2/MCMB电池循 环前期的容量衰减行为研究 414.2 LiCoO2/MCMB电池电 化学性能在长期循环中的演变及正负极对容量衰减的影响 . 454.
31、3 LiCoO2/MCMB电池中 MCMB表面 SEI膜和 MCMB结构在长期循环中的演变 . 484.3.1长期循环中 MCMB 表面 SEI膜的生长 484.3.2长期循环中 MCMB 材料结构的变化 574.3.3长期循环中 MCMB 表面 SEI膜生长和 MCMB结构变化对电化学性能的影响 594.4长期循环中 MCMB负 极表面的锂沉积现象 664.4.1长期循环中 MCMB 负极表面沉积物的生长 664.4.2长期循环中 MCMB 负极表面沉积物的形貌 694.4.3沉积物对 MCMB负 极电化学性能的影响 714.4.4沉积物的组成和生成机制 724.5 MCMB负极中各因素对
32、容量衰减的影响大小 804.6本章小结 83第 5章 LiCoO2/石墨电池中石墨负极的容量衰减机制研究 845.1 LiCoO2/石墨电池在长期循环中的电化学性能演变 845.2正负极与电解液对 LiCoO2/石墨电池性能衰减的影响 85VI目 录5.2.1正负极对电池性能衰减的影响 855.2.2正负极与电解液对电池容量衰减的影响 885.3石墨负极的形貌和结构在长期循环中的演变 895.3.1石墨负极的形貌在长期循环中的演变 905.3.2石墨负极的结构在长期循环中的变化 925.4石墨负极表面的锂沉积现象及其对容量衰减的影响 945.4.1石墨负极表面锂沉积物的生长 945.4.2石墨
33、负极表面锂沉积物的组成及其对容量衰减的影响 975.5全电池中 MCMB和石墨 负极容量衰减机制的比 较 995.5.1 MCMB和石墨负极结 构变化的比较 995.5.2 MCMB和石墨负极中 锂沉积物的比较 1005.6提高石墨类碳负极寿命的改进措施分析 1015.6.1提高 SEI膜锂离子导电性的改进措施分析 1015.6.2抑制锂沉积物生成的改进措施分析 1025.7本章小结 103结论. 105创新点. 107展望. 108参考文献. 109攻读博士学位期间发表的论文及其它成果. 122哈尔滨工业大学博士学位论文原创性声明. 123哈尔滨工业大学博士学位论文使用授权书. 123致谢.
34、 124个人简历. 125VII哈尔滨工业大学工学博士学位论文ContentsAbstract (In Chinese)IAbstract (In English) .IIIChapter 1 Introduction 11.1 Objectives and meaning of the dissertation. 11.2 Research progress of capacity loss mechanism of lithium ion battery 21.2.1 Positive electrode material 21.2.2 Electrolyte 41.2.3 Current
35、 collector 71.2.4 Anode electrode material. 71.3 Research progress of capacity loss mechanism of the graphitic carbon anode. 81.3.1 Research progress of SEI film on the surface of the graphitic carbonanode. 81.3.2 Research progress of lithium depositions in the graphitic carbon anode 111.3.3 Researc
36、h progress of structure change of the graphitic carbon anode 131.3.4 Research progress of improving the life of the graphitic carbon anode 111.4 Main research contents of the dissertation 16Chapter 2 Experimental materials and methods 182.1 Experimental materials and instruments 182.1.1 Main reagent
37、s 182.1.2 Instruments 182.2 Preparation of lithium ion battery 192.2.1 Preparation of MCMB coin half-cell. 192.2.2 Preparation of LiCoO2/MCMB full battery. 192.2.3 Preparation of LiCoO2/graphite full battery 202.2.4 Disassembling of full battery and preparation of coin half cell 202.3 Electrochemica
38、l property tests. 202.3.1 Constant-current charge/discharge test 202.3.2 Electrochemical impedance spectroscopy test 202.3.3 Cyclic voltammetry test. 212.4 Physical properties characterization of battery materials 212.4.1 Scanning electron microscopy. 212.4.2 X-ray photoelectron spectroscopy. 212.4.
39、3 X-ray diffraction 22VIIIContents2.4.4 Raman spectroscopy 222.4.5 Fourier transform infrared spectroscopy . 222.4.6 Atomic force microscope. 222.4.7 Differential scanning calorimetry 222.4.8 Adhension test . 23Chapter 3 Study on the capacity loss mechanism of MCMB electrode material in thecoin half
40、-cell . 243.1 Growth of SEI film on the surface of MCMB in the half cell. 243.2 Structural change of MCMB in the half cell . 313.3 Electrochemical property evolution of MCMB half cell. 353.4 Effect of half cell components on the capacity loss 383.5 Chapter summary. 40Chapter 4 Study on the capacity
41、loss mechanism of MCMB anode in LiCoO2/MCMBbattery 414.1 Study on the capacity loss action of LiCoO2/MCMB battery at the early stageof the cycling . 414.2 Electrochemical property evolution of LiCoO2/MCMB battery during thelong-term cycling and the effects of positive and negative electrodes on the
42、capacityloss. 454.3 Evolution of SEI film on the surface of MCMB and the structure of MCMB inLiCoO2/MCMB battery during the long-term cycling 484.3.1 Growth of SEI film on the surface of MCMB during the long-termcycling 484.3.2 Structure change of MCMB material during the long-term cycling . 574.3.3
43、 Effects of SEI film and structure change on electrochemical propertiesduring the long-term cycling 594.4 Lithium depositing phenomenonon the surface of MCMB anode during thelong-term cycling. 664.4.1 Growth of the deposition on the surface of MCMB anode during thelong-term cycling 664.4.2 Morpholog
44、y of the deposition on the surface of MCMB anode during thelong-term cycling 694.4.3 Effect of the deposition on the electrochemical properties of MCMBanode. 714.4.4 Compositions of the deposition and its formation mechanism . 724.5 Effects of each element in MCMB anode on the capacity loss. 80IX哈尔滨
45、工业大学工学博士学位论文4.6 Chapter summary. 83Chapter 5 Study on the capacity loss mechanism of graphite anode inLiCoO2/graphite battery 845.1 Electrochemical property evolution of LiCoO2/graphite battery during thelong-term cycling. 845.2 Effects of positive and negative electrodes, and the electrolyte on the
46、 propertyfade of LiCoO2/graphite battery 855.2.1 Effects of positive and negative electrodes on the property fade ofthebattery. 855.2.2 Effects of positive and negative electrodes, and the electrolyte on thecapacity loss 885.3 Evolution of the morphology and structure of graphite anode duringthelong
47、-term cycling 895.3.1 Morphology evolution of graphite anode during the long-term cycling .905.3.2 Structure change of graphite anode during the long-term cycling 925.4 Phenomenon of lithium deposition on the surface of graphite anode and itseffect on the capacity loss 945.4.1 Growth of lithium depo
48、sition on the surface of graphite anode 945.4.2 Composition of lithium deposition on the surface of graphite anode andits effect on the capacity loss 975.5 Comparation of the capacity loss mechanisms of MCMB and graphite anodes infull battery . 995.5.1 Comparation of structure change of MCMB and gra
49、phite anodes 995.5.2 Comparation of depositions in MCMB and graphite anodes 1005.6 Measures analysis of improving the life of the graphitic carbon anode 1035.6.1 Measures analysis of improving the lithium ion conductivity of SEI film1005.6.2 Measures analysis of restraining the formation of lithium deposition 1005.7 Chapter summary. 103Conclusions 105Innovation 107Outlook. 108References 109Papers published in the period of Ph D education 122XContentsState
