石墨烯基纳米复合材料在锂二次电池中的应用研究

发布时间：2018-12-24 11:54

【摘要】：随着移动电子设备、电动汽车、智能电网以及航空航天等领域的迅猛发展,商用锂离子电池受其传统电极材料理论比容量限制,已无法满足日益增长的能源需求,开发具有高能量密度、高功率密度和环保经济的电极材料体系以及其他锂二次电池体系迫在眉睫。目前研究者致力于探索应用于锂离子电池、锂有机电池和锂硫电池等锂二次电池的新型电极材料,对推动能源存储系统的科学可持续性发展具有重要意义。针对电极材料存在的瓶颈问题,包括氧化锡负极材料充放电过程中的巨大体积变化、有机电极材料在电解液中的溶解以及锂硫电池循环过程中多硫阴离子的“穿梭效应”等,本课题旨在探索和挖掘具有独特各向异性、高电荷迁移率等优异特性的石墨烯基二维材料在电极材料改性中的应用价值。研究主要内容和结果如下:1.通过在水热碳化蔗糖的过程中引入含硼前驱体(硼酸或苯硼酸),对负载有氧化锡纳米颗粒的石墨烯纳米片进行包覆,最后对包覆中间产物进行热处理,制备了一种具有二维核壳结构的硼掺杂碳包覆氧化锡/石墨烯纳米片。得益于掺杂碳材料和二维核壳结构的协同效应,该石墨烯基二维复合材料被应用于锂离子电池负极材料,既可以有效缓解氧化锡的体积膨胀又能够提供更多活性储锂位点,极大提高了电极材料的稳定性、导电性和电化学活性,以苯硼酸为前驱体制备得到的复合材料表现出最优电化学性能。2.以聚丙烯腈修饰的石墨烯为模板,采用离子热方法(以氯化锌为溶剂和催化剂),通过调节不同单体(邻、间、对苯二腈)和合成温度制备了具有纳米级别厚度、超高比表面积、可控孔径分布以及共价键合的石墨烯-多孔聚三嗪衍生骨架。这种石墨基二维多孔材料作为锂二次电池正极材料,能够促进电子和离子的快速传输以及有效抑制电活性基团在电解液中的溶解问题,表现出超长循环寿命和超高比容量,其优异性能远胜于先前文献报道的非无机类正极材料。3.鉴于上述石墨烯基二维多孔碳材料具有诸多结构优势,如纳米厚度、高比表面积、可控孔结构、氮掺杂特性和优异导电性等,进一步将其选作负载单质硫的理想载体,采用融化扩散方法制备了石墨烯基二维多孔碳/硫复合材料。这种对硫正极材料改性的方法能够有效调控硫分子在多孔结构中的存在形式,极大提高孔结构对硫的吸附作用,从而有助于缓解多硫阴离子的“穿梭效应”。此外,复合材料的二维构造和氮掺杂特性能够促进充放电过程中电子和离子的快速传输,对提高硫正极的导电性有显著作用。
[Abstract]:With the rapid development of mobile electronic devices, electric vehicles, smart grids, aerospace and other fields, commercial lithium ion batteries have been unable to meet the increasing energy demand due to their theoretical specific capacity of traditional electrode materials. It is urgent to develop electrode materials and other lithium secondary battery systems with high energy density, high power density and environmental protection. At present, researchers are devoting themselves to exploring new electrode materials for lithium ion batteries, lithium organic batteries and lithium sulfur batteries, which are of great significance to promote the sustainable development of energy storage system. In view of the bottleneck problems existing in electrode materials, including the huge volume change of tin oxide anode materials during charge and discharge, the dissolution of organic electrode materials in electrolyte and the "shuttle effect" of polysulfide anions during the cycle of lithium-sulfur batteries, etc. The purpose of this paper is to explore and explore the application value of graphene based two-dimensional materials with unique anisotropy and high charge mobility in the modification of electrode materials. The main contents and results are as follows: 1. By introducing boron precursor (boric acid or phenylboric acid) in the process of hydrothermal carbonization of sucrose, the graphene nanoparticles loaded with tin oxide nanoparticles were coated, and the intermediate products were heat treated. A boron doped carbon coated tin oxide / graphene nanochip with two dimensional core-shell structure was prepared. Due to the synergistic effect of doped carbon materials and two-dimensional core-shell structures, the graphene based two-dimensional composites have been used as anode materials for lithium ion batteries, which can effectively reduce the volume expansion of tin oxide and provide more active lithium-storage sites. The stability, conductivity and electrochemical activity of the electrode material were greatly improved. The composite prepared with phenylboric acid as precursor showed the best electrochemical performance. 2. Using graphene modified with polyacrylonitrile as template, nanocrystalline thickness was prepared by ion-thermal method (using zinc chloride as solvent and catalyst) by adjusting different monomers (o, m, p-phthalonitrile) and synthesizing temperature. Ultrahigh specific surface area, controllable pore size distribution and covalently bonded graphene-porous polytriazine derived skeleton. As a cathode material of lithium secondary battery, this graphite-based two-dimensional porous material can promote the rapid transfer of electrons and ions and effectively inhibit the dissolution of electroactive groups in the electrolyte, showing an ultra-long cycle life and ultra-high specific capacity. Its excellent performance is much better than that of non-inorganic cathode materials reported in previous literatures. 3. In view of the many structural advantages of the graphene based two-dimensional porous carbon materials, such as nanometer thickness, high specific surface area, controllable pore structure, nitrogen doping characteristics and excellent conductivity, they are further selected as ideal carriers for supporting elemental sulfur. Graphite-based two-dimensional porous carbon / sulfur composites were prepared by melting diffusion method. This method can effectively regulate the existence of sulfur molecules in the porous structure and greatly improve the adsorption of sulfur on the pore structure, thus helping to alleviate the "shuttle effect" of polysulfide anions. In addition, the two-dimensional structure and nitrogen doping characteristics of the composites can promote the rapid transfer of electrons and ions during charge and discharge, and play an important role in improving the conductivity of sulfur positive electrode.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM912;TB383.1

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