锂离子二次电池的改进与研究

发布时间：2018-04-08 21:27

本文选题：锂离子二次电池隔膜　切入点：微孔膜　出处：《南京大学》2016年硕士论文

【摘要】：锂离子二次电池和其它电池相比,它的循环寿命更长、能量密度更高、并且电池也更加轻便,除此以外安全可靠、快速的充电放电也是它的优点。如今传统铅酸蓄电池和镍镉蓄电池已经逐渐被性能优异的锂离子二次电池替代,锂离子二次电池已经成为动力电池的主要选择。作为锂离子二次电池的核心部件,隔膜在电池中对电子绝缘,并且它允许电解液中正负离子自由通过从而使得离子可以正常传导,在电池温度过高时,隔膜还可以关闭自身孔洞,阻隔电流的传导,使电池停止工作,从而对电池起到一定的保护作用。隔膜的性能对于电池容量、循环寿命和安全性能起着重要的作用。根据物理、化学性质的不同,常见的锂离子二次电池隔膜材料有：微孔膜、复合膜、织造膜、隔膜纸、无纺布、碾压膜等。聚烯烃材料化学性能的相对稳定和较好的力学性能,使得它适合作为一种热塑性材料。在温度高于熔融温度的条件下,多孔的聚烯烃可以收缩孔隙并自动闭合,电池的阻抗会显著上升、电子停止传导,这样可以有效地防止电池温度过高从而引起电池爆炸。目前聚烯烃是一种安全可靠的锂离子二次电池隔膜材料。基体材料的选择和造孔技术工艺是目前隔膜技术的主要难点。隔膜产品质量不仅与造孔的技术相关,也取决于生产设备的稳定性。基体材料主要是聚丙烯、聚乙烯等聚烯烃和各类的添加剂。隔膜厚度不均、强度差、孔隙率不足是目前造孔技术的主要难点。本文介绍了常用制备隔膜工艺,并把所制备的电池隔膜性能进行对比和论述。本文选用1μm-100μm的聚丙烯隔膜,通过拉光纤法制备六角结构的光纤模板,然后在熔融温度下进行加热,孔径大小会随着热压的时间改变而改变。热压法制备隔膜具有制备方法简单,孔径结构、孔尺寸、孔隙率、透气率均匀可调等优点,并且制备的隔膜质量高,膜孔形状均匀,可应用于锂离子二次电池、燃料电池、水处理等多种领域。除此以外还使用相转换法,用纳米氧化铝涂层制备的陶瓷聚乙烯复合隔膜。通过涂覆Al2O3涂层,可以使得PE隔膜在孔隙率、吸液率、接触角、热稳定性、电导率、电化学稳定性和电池循环方面的性能都得到显著提升。通过实验我们发现：当Al2O3质量含量为30%时,各项性能提升最为明显。最后在不同煅烧温度下制备单分散Nano-Fe2O3,将制得的Nano-Fe2O3用固相烧结的方法制备LiFePO4。我们发现单分散Nano-Fe2O3颗粒的直径会随着温度的升高而不断升高,并且在较低的温度时,颗粒的球形形貌最为完整。较低煅烧温度制备的LiFePO4的放电容量在低倍率下的性能能够得到一定的提升。
[Abstract]:Compared with other batteries, Li-ion secondary battery has longer cycle life, higher energy density and lighter battery. In addition, it is safe and reliable, and has the advantage of fast charge and discharge.Nowadays, traditional lead-acid batteries and nickel-cadmium batteries have been gradually replaced by lithium ion secondary batteries with excellent performance. Lithium ion secondary batteries have become the main choice of power batteries.As a core component of the lithium ion secondary battery, the diaphragm is electrically insulated in the battery, and it allows positive and negative ions to pass freely through the electrolyte so that the ions can conduct normally, when the cell temperature is too high.The diaphragm can also close its own holes, block the conduction of the current, make the battery stop, and thus play a protective role on the battery.The performance of diaphragm plays an important role in battery capacity, cycle life and safety performance.According to the physical and chemical properties, the common materials of lithium ion secondary battery diaphragm are: microporous membrane, composite membrane, weaving film, diaphragm paper, non-woven cloth, rolling film, etc.Polyolefin materials have relatively stable chemical properties and good mechanical properties, which make them suitable for thermoplastic materials.When the temperature is higher than the melting temperature, the porous polyolefin can shrink the pores and close automatically, the impedance of the cell will increase significantly, and the electron conduction will stop, which can effectively prevent the cell from exploding because of the excessive temperature of the cell.At present, polyolefin is a safe and reliable membrane material for lithium ion secondary battery.The selection of matrix material and pore making technology are the main difficulties of diaphragm technology at present.The quality of diaphragm products is not only related to the hole making technology, but also depends on the stability of production equipment.The main matrix materials are polypropylene, polyethylene and other polyolefin and various additives.Uneven thickness of diaphragm, poor strength and insufficient porosity are the main difficulties of current pore making technology.In this paper, the common preparation process of the membrane is introduced, and the performance of the prepared membrane is compared and discussed.In this paper, the hexagonal fiber template was prepared by using 1 渭 m -100 渭 m polypropylene diaphragm, and then heated at melting temperature. The pore size changed with the time of hot pressing.The preparation of diaphragm by hot pressing method has the advantages of simple preparation method, pore size, pore size, porosity and uniform air permeability, etc. The prepared diaphragm has high quality and uniform pore shape. It can be used in lithium ion secondary battery and fuel cell.Water treatment and other fields.In addition, the ceramic polyethylene composite diaphragm prepared by nano-alumina coating was also prepared by phase conversion method.The properties of PE membrane in porosity, liquid absorption, contact angle, thermal stability, conductivity, electrochemical stability and battery cycle can be significantly improved by coating with Al2O3 coating.The experimental results show that when the mass content of Al2O3 is 30%, the performance improvement is the most obvious.Finally, monodisperse Nano-Fe _ 2O _ 3 was prepared at different calcination temperatures, and LiFePO _ 4 was prepared by solid-state sintering method.It is found that the diameter of monodisperse Nano-Fe2O3 particles increases with the increase of temperature, and the spherical morphology of the particles is the most complete at lower temperatures.The discharge capacity of LiFePO4 prepared at low calcination temperature can be improved at low rate.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM912

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