碳纳米管薄膜在锂离子电池中的应用研究

发布时间：2018-10-18 11:32

【摘要】：能源问题、环境问题的不断加剧迫使人们开发新的供能体系与储能系统。电池因其能量转换率高、污染小等特点,成为了替代化石燃料能源的一个重要途径。这其中,锂离子电池由于具有输出电压高、比容量大等优势,得到了日益广泛的关注与应用。随着便携式电子设备、电动汽车、智能电网等锂离子电池应用领域对电池性能的要求不断提高,如何进一步提高电池的比容量与能量密度成为发展锂电技术的核心问题之一。受限于目前电极材料的性质,锂离子电池中往往不得不引入导电剂、集流体、粘结剂等无电化学活性的组分。因而,如何有效的减少这些组分的比重对于提高锂离子电池的比容量以及能量密度具有重要的意义。本工作利用超顺排碳纳米管排列整齐、表面洁净、管间范德瓦尔斯力强的特点,将这一性能优异的材料应用于锂离子电池的导电剂、集流体等领域,实现了电池比容量与能量密度的提高。在导电剂方面,通过表征包含不同种导电剂的电极性能,证明导电剂的尺寸、长径比、分散性是影响导电剂性能的重要因素,同时发现兼顾长程与短程电荷输运的复合结构是一种更高效的导电剂体系。基于此结论,利用铺膜结合冷轧的工艺开发了一种导电炭黑—超顺排碳纳米管复合导电剂,实现了导电剂的充分分散与利用,在碳纳米管引入量不足0.01 wt%的的前提下改善了电极的导电性能,提高了极片力学强度并获得了优异的循环与倍率性能。在集流体方面,利用交叉超顺排碳纳米管薄膜制备一种柔性、轻质的超薄集流体。相比于金属箔集流体,碳纳米管膜集流体不但具有非常小的质量与体积,还具有更好的电极—集流体界面性能,提高了电池的比容量,并实现了能量密度的显著提升。同时,超顺排碳纳米管由于管间相互作用强,避免了文献报道中碳基集流体常见的厚度偏大、碳纳米管引入量偏多的问题。此外,针对超顺排碳纳米管薄膜本征电导率偏低的问题,利用蒸镀金属的方法,在保持集流体极小的质量与体积的前提下,进一步降低了碳纳米管膜的面电阻,提高了大电流工作条件下的电池性能,并使碳纳米管膜集流体能够满足圆柱形电池等大容量锂电池对极片的要求。设计了一种基于超顺排碳纳米管薄膜的全新电极结构,使碳纳米管同时承担起导电剂、粘结剂以及集流体的作用,将电极中活性物质的比重提升至95 wt%以上,同时利用碳纳米管优异的电学与力学性能、以及交叉碳纳米管薄膜特有的多孔结构,改善了电极的反应动力学。此外,基于这种新型的电极结构,制备出了一种柔性薄膜全电池,实现了高的面积比容量。
[Abstract]:Energy and environmental problems are becoming more and more serious, forcing people to develop new energy supply systems and energy storage systems. Because of its high energy conversion rate and low pollution, battery has become an important alternative to fossil fuel energy. Among them, lithium ion battery has been paid more and more attention because of its advantages of high output voltage and large specific capacity. With the development of portable electronic devices, electric vehicles, smart grids and other lithium ion battery applications, the requirements of battery performance are constantly increasing. How to further improve the specific capacity and energy density of the battery has become one of the core issues in the development of lithium technology. Limited by the current properties of electrode materials, lithium ion batteries often have to introduce conductive agent, fluid collection, binder and other non-electrochemical active components. Therefore, how to effectively reduce the specific gravity of these components is of great significance to improve the specific capacity and energy density of lithium ion batteries. In this work, the supercis carbon nanotubes are arranged neatly, the surface is clean, and the van der Waals force between tubes is strong. This material with excellent performance is applied in the field of conducting agent and fluid collecting of lithium ion battery. The specific capacity and energy density of the battery are improved. In the aspect of conductive agent, it is proved that the size, aspect ratio and dispersity of conductive agent are the important factors that affect the performance of conductive agent by characterizing the electrode performance of different kinds of conductive agents. It is also found that the composite structure with both long range and short range charge transport is a more efficient conductive agent system. Based on this conclusion, a conductive carbon black-supercis carbon nanotube composite conductive agent was developed by using film laying and cold rolling process, which realized the full dispersion and utilization of the conductive agent. The conductivity of the electrode was improved, the mechanical strength of the electrode was improved and the excellent cycling and rate properties were obtained under the condition that the carbon nanotube was introduced less than 0. 01 wt%. In the aspect of collecting fluid, a kind of flexible and light ultrathin carbon nanotube thin film was prepared by using cross supercis carbon nanotube film. Compared with the metal foil, the carbon nanotube membrane not only has a very small mass and volume, but also has a better performance of the electrode / fluid collector interface, improves the specific capacity of the battery, and achieves a remarkable increase in the energy density. At the same time, because of the strong interaction between tubes, the supercis carbon nanotubes avoid the problems of the large thickness and the large amount of carbon nanotubes introduced in the literature. In addition, in order to solve the problem of low intrinsic conductivity of supercis carbon nanotube film, the surface resistance of carbon nanotube film is further reduced by the method of metal evaporation, while keeping the mass and volume of collecting fluid very small. The performance of the battery under the condition of high current operation is improved, and the carbon nanotube film can meet the requirements of the electrode of the large capacity lithium battery such as cylindrical battery. A novel electrode structure based on supercis carbon nanotube film is designed, which enables carbon nanotubes to act as a conductive agent, a binder and a fluid collector at the same time. The specific gravity of active substances in the electrode is increased to more than 95 wt%. At the same time, the electrode reaction kinetics was improved by using the excellent electrical and mechanical properties of carbon nanotubes and the unique porous structure of the cross-carbon nanotubes film. In addition, based on the new electrode structure, a kind of flexible thin film whole cell is fabricated, which can achieve high area specific capacity.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TM912;TB383.1

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