具有多重缓冲机制的锂离子电池硅基负极
发布时间：2018-08-22 13:18
【摘要】：开发高比能、长寿命、低成本的二次电池是构建新能源社会的核心工作。硅(Si)因具有十倍于现有商业化石墨负极的理论比容量,被认为是新一代锂离子电池的理想负极。但其锂化/去锂化过程中巨大的体积变化容易引起活性颗粒粉化、电极结构破坏以及表面SEI膜的重复生长。这些问题严重制约了 Si负极的商业化应用和高比能锂离子电池的发展。本论文工作以开发高循环稳定性Si基负极材料为目的,以构建多重缓冲机制为手段,设计并制备了两种新型Si基复合负极材料,FeSi/C复合纳米纤维和Si@SiOx@C复合物。主要研究内容及结果如下:1.FeSi/C复合纳米纤维的制备与表征。以纳米FeSi合金和聚丙烯腈(PAN)为原料,通过静电纺丝及后续高温热解,制备出FeSi/C纳米复合纤维,并优化了其制备条件。实验结果表明,将FeSi与PAN以1:0.5的质量比混纺,然后在热解产物FeSi/C纤维表面再化学气相沉积(CVD)一层碳,得到的FeSi/C/C复合纤维产物具有最优的电化学性能。电化学测试结果表明,FeSi/C/C复合纤维电极的初始比容量为953 mAh g-1循环200周后仍有60%的容量保持率,且循环过程中库伦效率保持在99.5%左右;在1000mAg-1的大电流密度下,材料仍有700 mAh g-1以上的比容量。FeSi/C/C复合纤维材料优异的电化学性能主要得益于它的多重缓冲结构,包括FeSi合金中惰性FeSi2相、主体PAN热解碳纤维和CVD沉积碳,有效缓冲了活性Si的体积膨胀,保持了纤维结构及表面SEI膜的稳定性。2.Si@SiOx@C复合材料的制备与表征。利用聚丙烯酸(PAA)与Si表面羟基的氢键作用,通过高温热解Si@PAA复合物,一步法直接制备出具有双层包覆结构的Si@SiOx@C复合材料。由于双包覆层在充放电过程中有效缓冲了活性Si内核的体积膨胀,维持了电极/电解液界面和表面SEI膜的稳定性,使得复合材料展现出良好的循环性能。充放电测试结果表明,材料的首周比容量为1110 mAh g-1;循环150周后仍有664mAhg-1的比容量,对应的容量衰减率仅为0.27%/周。
[Abstract]:Developing high specific energy, long-life, low-cost secondary batteries is the core work of building a new energy society. Silicon (Si) is considered to be the ideal anode for a new generation of lithium ion batteries because of its theoretical specific capacity of 10 times that of commercial graphite anode. However, the huge volume change in the process of lithiation / delithiation can easily cause the active particles to be powdered, the electrode structure destroyed and the surface SEI film to grow repeatedly. These problems seriously restrict the commercial application of Si anode and the development of high specific energy lithium ion battery. In order to develop high cycle stable Si-based negative electrode materials and to construct multiple buffer mechanism, two new Si-based composite negative electrode materials, FeSi- / C nanofibers and Si@SiOx@C composites, have been designed and fabricated in this paper. The main contents and results are as follows: 1. Preparation and characterization of FeSi- / C nanofibers. FeSi/C nanocomposite fibers were prepared by electrospinning and pyrolysis of polyacrylonitrile (PAN) and FeSi alloy. The preparation conditions were optimized. The experimental results show that FeSi and PAN are blended at 1: 0.5 mass ratio and then redeposited on the surface of pyrolytic FeSi/C fiber by chemical vapor deposition of a layer of (CVD) carbon. The obtained FeSi/C/C composite fiber has the best electrochemical performance. The results of electrochemical measurement show that the initial specific capacity of FeSi-C / C composite fiber electrode is 953 mAh / g ~ (-1), and the capacity retention rate is still 60%, and the Coulomb efficiency is about 99.5% during the cycle, and at the high current density of 1000mAg-1, the initial specific capacity of FeSi-C / C composite fiber electrode is 953 mAh / g ~ (-1). The excellent electrochemical properties of Fesi / C / C composite fiber with a specific capacity of more than 700 mAh g ~ (-1) are mainly due to its multilayer buffer structure, including inert FeSi2 phase in FeSi alloy, PAN pyrolytic carbon fiber and carbon deposited by CVD. The volume expansion of active Si was effectively cushioned, and the stability of fiber structure and surface SEI film was maintained. The Si@SiOx@C composites with double-layer coating structure were directly prepared by pyrolysis of Si@PAA composites at high temperature by hydrogen bonding between polyacrylic acid (PAA) and hydroxyl groups on Si surface. Because the double cladding layer effectively buffers the volume expansion of the active Si core during charge and discharge, the stability of the electrode / electrolyte interface and the surface SEI film is maintained, which makes the composite exhibit good cycling performance. The results of charge-discharge test show that the specific capacity of the material is 1110 mAh g ~ (-1) in the first cycle, and the specific capacity of 664mAhg-1 is still in existence after 150 weeks of cycle, the corresponding capacity attenuation rate is only 0.27 / week.
【学位授予单位】：武汉大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
本文编号：2197213
[Abstract]:Developing high specific energy, long-life, low-cost secondary batteries is the core work of building a new energy society. Silicon (Si) is considered to be the ideal anode for a new generation of lithium ion batteries because of its theoretical specific capacity of 10 times that of commercial graphite anode. However, the huge volume change in the process of lithiation / delithiation can easily cause the active particles to be powdered, the electrode structure destroyed and the surface SEI film to grow repeatedly. These problems seriously restrict the commercial application of Si anode and the development of high specific energy lithium ion battery. In order to develop high cycle stable Si-based negative electrode materials and to construct multiple buffer mechanism, two new Si-based composite negative electrode materials, FeSi- / C nanofibers and Si@SiOx@C composites, have been designed and fabricated in this paper. The main contents and results are as follows: 1. Preparation and characterization of FeSi- / C nanofibers. FeSi/C nanocomposite fibers were prepared by electrospinning and pyrolysis of polyacrylonitrile (PAN) and FeSi alloy. The preparation conditions were optimized. The experimental results show that FeSi and PAN are blended at 1: 0.5 mass ratio and then redeposited on the surface of pyrolytic FeSi/C fiber by chemical vapor deposition of a layer of (CVD) carbon. The obtained FeSi/C/C composite fiber has the best electrochemical performance. The results of electrochemical measurement show that the initial specific capacity of FeSi-C / C composite fiber electrode is 953 mAh / g ~ (-1), and the capacity retention rate is still 60%, and the Coulomb efficiency is about 99.5% during the cycle, and at the high current density of 1000mAg-1, the initial specific capacity of FeSi-C / C composite fiber electrode is 953 mAh / g ~ (-1). The excellent electrochemical properties of Fesi / C / C composite fiber with a specific capacity of more than 700 mAh g ~ (-1) are mainly due to its multilayer buffer structure, including inert FeSi2 phase in FeSi alloy, PAN pyrolytic carbon fiber and carbon deposited by CVD. The volume expansion of active Si was effectively cushioned, and the stability of fiber structure and surface SEI film was maintained. The Si@SiOx@C composites with double-layer coating structure were directly prepared by pyrolysis of Si@PAA composites at high temperature by hydrogen bonding between polyacrylic acid (PAA) and hydroxyl groups on Si surface. Because the double cladding layer effectively buffers the volume expansion of the active Si core during charge and discharge, the stability of the electrode / electrolyte interface and the surface SEI film is maintained, which makes the composite exhibit good cycling performance. The results of charge-discharge test show that the specific capacity of the material is 1110 mAh g ~ (-1) in the first cycle, and the specific capacity of 664mAhg-1 is still in existence after 150 weeks of cycle, the corresponding capacity attenuation rate is only 0.27 / week.
【学位授予单位】：武汉大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
【参考文献】
相关期刊论文 前3条
1 张双虎;迟彩霞;张盛武;;锂离子电池预锂化技术的最新研究进展[J];电源技术;2015年07期
2 Delong Ma;Zhanyi Cao;Anming Hu;;Si-Based Anode Materials for Li-Ion Batteries:A Mini Review[J];Nano-Micro Letters;2014年04期
3 艾新平;杨汉西;;浅析动力电池的技术发展[J];中国科学:化学;2014年07期
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