锗碳复合锂离子电池负极材料的制备及其储锂电化学性能
发布时间：2018-07-29 20:22
【摘要】：随着高容量、高倍率、高安全性锂离子电池发展的要求，石墨因其理论容量较低限制了其进一步的研究和改善空间。而锗基负极材料因嵌锂容量高、嵌锂电位适中和锂离子扩散系数大等优点得到越来越多研究者们的关注。但成本高及嵌锂过程中体积膨胀过大并导致循环性能差是阻碍其商业化应用的关键问题。本文以发展综合性能优良的Ge基体系负极材料为目标，采用高能机械球磨法特别是首次引入介质阻挡放电等离子体（DBDP）辅助高能球磨来制备Ge-C体系复合负极材料，主要研究了不同球磨方法和工艺对Ge-C复合材料的微观结构及电化学性能的影响。 本研究分别采用常规高能球磨法和介质阻挡放电等离子体(DBDP)辅助高能球磨法，将纯Ge粉和天然石墨粉直接混合球磨，，分别制备了不同形态的石墨包覆纳米Ge颗粒结构的Ge50C50材料。DBDP辅助球磨将石墨剥离成性能优良的少层石墨烯，这种少层石墨烯对Ge基负极材料的结构稳定性和电化学性能的改善作用优于常规球磨法中得到的团絮状石墨。在100mA/g的充/放电电流密度下，DBDP辅助球磨得到的复合材料Ge50C50经过50次循环后容量仍保持为812.1mAh/g。将上述两种球磨方法制备的Ge50C50材料分别添加还原氧化石墨烯(RGO)，并对比各自添加RGO前后的结构和电化学性能，发现经过50次循环后两种Ge50C50RGO10复合材料的放电容量均提高约150mAh/g，但首次库伦效率降低，被认为是化学法制备少层石墨烯容易引入杂质官能团，导致电极材料首次循环的不可逆容量损失。 将膨胀石墨(EG)与预磨5h后的纯Ge进行DBDP辅助球磨10h，得到10层左右的少层石墨烯(FLG)包覆尺寸为150nm的纯锗颗粒的Ge@FLG复合结构。Ge@FLG复合材料阻抗约90，循环50次后放电比容量为846.3mAh/g。随球磨时间延长，Ge@FLG材料的Ge颗粒尺寸无明显变化，膨胀石墨被剥离成为少层石墨烯，储锂容量增加，循环更加稳定，材料内部阻抗降低，锂离子扩散动力学性能提高。但DBDP辅助球磨能量输出较大，球磨时间超过15h时Ge@FLG复合材料性能反而下降。
[Abstract]:With the development of high capacity, high rate and high safety lithium ion batteries, graphite has limited its further research and improvement due to its low theoretical capacity. However, germanium based anode materials have attracted more and more attention due to their high lithium intercalation capacity, moderate lithium intercalation potential and large lithium ion diffusion coefficient. However, high cost and excessive volume expansion in the process of lithium intercalation lead to poor cycle performance, which is a key problem that hinders its commercial application. The aim of this paper is to develop GE based negative electrode materials with good comprehensive properties. The high energy mechanical ball milling method, especially the introduction of dielectric barrier discharge plasma (DBDP) assisted high energy ball milling for the first time, is used to prepare Ge-C composite negative electrode materials. The effects of different ball milling methods and processes on the microstructure and electrochemical properties of Ge-C composites were studied. In this study, the pure GE powder and natural graphite powder were mixed directly by conventional high energy ball milling and dielectric barrier discharge plasma (DBDP) assisted high energy ball milling. Ge50C50 materials with different forms of graphite coated with nanocrystalline GE particles were prepared. DBDP-assisted ball milling was used to peel graphite into low-layer graphene with excellent properties. The structure stability and electrochemical performance of the Ge-base anode material were improved by using this kind of low-layer graphene, which was better than that obtained by conventional ball milling method. Under the charge / discharge current density of 100mA/g, the capacity of the composite Ge50C50 obtained by ball-milling is still 812.1mAh / g after 50 cycles. The structure and electrochemical properties of the Ge50C50 materials prepared by the two ball milling methods were compared by adding reduced graphene (RGO), and comparing the structure and electrochemical properties before and after the addition of RGO. It was found that after 50 cycles, the discharge capacity of the two Ge50C50RGO10 composites was increased by about 150mAh/ g, but the first Coulomb efficiency was decreased. It is considered that it is easy to introduce impurity functional groups into the preparation of less layer graphene by chemical method. The irreversible capacity loss of the electrode material is caused by the first cycle. The expanded graphite (EG) and the pure GE after 5 h pre-grinding were milled with DBDP for 10 h. The composite structure of 10 layers of (FLG) coated with pure germanium particles of 150nm was obtained. The impedance of the composite was about 90, and the specific discharge capacity of the composite was 846.3mAh. g after 50 cycles. With the prolongation of ball milling time, the GE particle size of Ge@ FLG material has no obvious change, and the expanded graphite is stripped into less layer graphene, the lithium storage capacity increases, the cycle becomes more stable, the internal impedance of the material decreases, and the diffusion kinetic properties of lithium ion are improved. However, the energy output of DBDP assisted ball milling is large, and the properties of Ge@FLG composites decrease when milling time exceeds 15 h.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912
本文编号：2153898
[Abstract]:With the development of high capacity, high rate and high safety lithium ion batteries, graphite has limited its further research and improvement due to its low theoretical capacity. However, germanium based anode materials have attracted more and more attention due to their high lithium intercalation capacity, moderate lithium intercalation potential and large lithium ion diffusion coefficient. However, high cost and excessive volume expansion in the process of lithium intercalation lead to poor cycle performance, which is a key problem that hinders its commercial application. The aim of this paper is to develop GE based negative electrode materials with good comprehensive properties. The high energy mechanical ball milling method, especially the introduction of dielectric barrier discharge plasma (DBDP) assisted high energy ball milling for the first time, is used to prepare Ge-C composite negative electrode materials. The effects of different ball milling methods and processes on the microstructure and electrochemical properties of Ge-C composites were studied. In this study, the pure GE powder and natural graphite powder were mixed directly by conventional high energy ball milling and dielectric barrier discharge plasma (DBDP) assisted high energy ball milling. Ge50C50 materials with different forms of graphite coated with nanocrystalline GE particles were prepared. DBDP-assisted ball milling was used to peel graphite into low-layer graphene with excellent properties. The structure stability and electrochemical performance of the Ge-base anode material were improved by using this kind of low-layer graphene, which was better than that obtained by conventional ball milling method. Under the charge / discharge current density of 100mA/g, the capacity of the composite Ge50C50 obtained by ball-milling is still 812.1mAh / g after 50 cycles. The structure and electrochemical properties of the Ge50C50 materials prepared by the two ball milling methods were compared by adding reduced graphene (RGO), and comparing the structure and electrochemical properties before and after the addition of RGO. It was found that after 50 cycles, the discharge capacity of the two Ge50C50RGO10 composites was increased by about 150mAh/ g, but the first Coulomb efficiency was decreased. It is considered that it is easy to introduce impurity functional groups into the preparation of less layer graphene by chemical method. The irreversible capacity loss of the electrode material is caused by the first cycle. The expanded graphite (EG) and the pure GE after 5 h pre-grinding were milled with DBDP for 10 h. The composite structure of 10 layers of (FLG) coated with pure germanium particles of 150nm was obtained. The impedance of the composite was about 90, and the specific discharge capacity of the composite was 846.3mAh. g after 50 cycles. With the prolongation of ball milling time, the GE particle size of Ge@ FLG material has no obvious change, and the expanded graphite is stripped into less layer graphene, the lithium storage capacity increases, the cycle becomes more stable, the internal impedance of the material decreases, and the diffusion kinetic properties of lithium ion are improved. However, the energy output of DBDP assisted ball milling is large, and the properties of Ge@FLG composites decrease when milling time exceeds 15 h.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912
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