锂离子电池用纳米碳纤维—硅复合负极材料

发布时间：2018-01-12 22:19

本文关键词：锂离子电池用纳米碳纤维—硅复合负极材料　出处：《东华大学》2014年硕士论文　论文类型：学位论文

【摘要】：锂离子电池(LIB)的无记忆效应、能量密度高以及自放电率低等优点使其在工业领域迅猛发展。随着其在便携式设备和动力汽车中的应用,人们对于锂离子电池的负极材料提出了更高的要求。目前石墨作为商用锂离子电池的负极材料,在充放电过程中锂的嵌入量较低,理论容量只有372mAh/g。同时由于过充或其他原因引起的锂枝晶影响电池的安全性。 Sn、Si、A1、 Pb等金属与锂形成金属间化合物,表现出较好的电化学性能。这些高容量的负极材料还没有商业化的原因是其在嵌锂时发生较大的体积膨胀,超过100%。这会造成材料结构发生严重的破坏甚至粉化,使材料失去电接触,导致容量的迅速衰减。因此消除因金属材料在充放电过程中的体积变化而造成的电池失效成为负极材料研究重点。目前的研究表明,三维网络电极结构能有效缓冲硅在嵌锂时产生的体积变化,同时这种结构为锂离子提供了传输通道,提高电极的倍率充放电性。热解细菌纤维素(Pyrolyzed Bacterial cellulose, PBC)保留了细菌纤维素(BC)的三维多孔结构,将上述金属材料担载到PBC的三维网络中,形成金属／纳米碳纤维复合三维电极是提高LIB负极材料电化学综合性能的有效途径。因此,将PBC与硅材料复合制备新型锂离子电池负极材料,对于将硅负极材料商用化具有重要意义。本论文以BC为前驱体,通过高温烧结制备了具有三维网络结构的纳米碳纤维(PBC)。在此基础上通过打浆法和溶胶凝胶法分别制备了PBC/碳纳米管(CNTs、PBC/Si和PBC/SiO2复合负极材料,利用FESEM、TG、XRD以及循环测试等方法详细研究了其结构和性能的关系。主要研究内容和结论如下： 1.PBC及PBC/CNTs的结构与性能。PBC具有三维多孔网状结构,存在石墨化碳。电性能测试显示PBC的电池容量略低于石墨,但加入羧基化碳纳米管可以提高PBC的导电性以及电池的容量。PBC/CNTs复合材料的首次充电容量达到1280.6mAh/g,库伦效率为45.7%。循环20次后可逆容量达到433mAh/g,不仅优于PBC,同时超过了石墨的理论容量。 2.打浆法制备的PBC/Si复合材料的结构与性能。PBC/Si的电化学性能较好,首次充电容量达到3375mAh/g,经过65次循环后后可逆容量为1369mAh/g。只要适当的控制硅的含量及其分散,PBC的特殊三维结构可以作为充放电过程中硅体积膨胀的缓冲区。 3.溶胶凝胶法制备PBC/SiO2复合材料的结构与性能。PBC/SiO2复合材料的导电性差、容量低,存在严重的粉化现象。仅仅用二氧化硅作为碳-硅复合负极材料的硅源不是十分有效。
[Abstract]:Li-ion battery (Lib) has many advantages, such as memoryless effect, high energy density and low self-discharge rate, which makes it develop rapidly in industrial field, with its applications in portable devices and power vehicles. At present, graphite is the negative electrode material of commercial lithium ion battery, and the intercalation of lithium in the process of charge and discharge is low. The theoretical capacity is only 372mAh / g, and lithium dendrites due to overcharge or other causes affect the safety of the battery. The metals such as Sn-SiOA1, Pb and so on form intermetallic compounds with lithium. These high capacity anode materials have not been commercialized because of their larger volume expansion in lithium intercalation. More than 100. This can cause serious damage to the structure of the material or even powdered, resulting in the loss of electrical contact with the material. Therefore, eliminating the battery failure caused by the volume change of metal materials during charge and discharge has become the research focus of negative electrode materials. Current studies have shown that the three-dimensional network electrode structure can effectively buffer the volume change of silicon in lithium intercalation, and this structure provides a transport channel for lithium ion. The pyrolytic bacterial cellulose was Pyrolyzed Bacterial cellulose. PBCs retained the three-dimensional porous structure of bacterial cellulose (BC) and loaded the above metal materials into the three-dimensional network of PBC. The formation of metal / carbon nanocomposite three-dimensional electrode is an effective way to improve the electrochemical properties of LIB anode materials. Therefore, a new type of cathode materials for lithium ion batteries is prepared by combining PBC with silicon materials. It is of great significance to commercialize silicon anode materials. In this thesis, BC was used as the precursor. PBC / CNTs with three-dimensional network structure were prepared by high temperature sintering, and PBC / CNTs were prepared by beating and sol-gel methods respectively. PBC/Si and PBC/SiO2 composite negative electrode materials, using Fesemer TG. The relationship between structure and performance is studied in detail by XRD and loop testing. The main contents and conclusions are as follows: 1. The structure and performance of PBC and PBC/CNTs. PBC has a three-dimensional porous network structure, and there is graphitized carbon. The electrical performance test shows that the battery capacity of PBC is slightly lower than that of graphite. However, the addition of carboxylated carbon nanotubes can improve the conductivity of PBC and the initial charging capacity of the composite. The Coulomb efficiency is 45.7 and the reversible capacity is 433mAh / g after 20 cycles, which is not only superior to PBC, but also exceeds the theoretical capacity of graphite. 2. The structure and properties of PBC/Si composites prepared by beating pulping method. The electrochemical properties of PBC / Si are better, and the initial charging capacity is 3375mAh/ g. After 65 cycles, the reversible capacity is 1369 mg 路h / g. The content of silicon and its dispersion should be controlled properly. The special three-dimensional structure of PBC can be used as a buffer for volume expansion of silicon during charging and discharging. 3. The structure and properties of PBC/SiO2 composites prepared by sol-gel method. The conductivity and capacity of PBC / SiO2 composites are poor. There is a serious pulverization phenomenon. It is not very effective to use silicon dioxide as the silicon source of carbon-silicon composite negative electrode material.
【学位授予单位】：东华大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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