基于石墨烯改性的锂（钠）离子电池负极材料与正极材料的研究

发布时间：2018-04-02 19:46

本文选题：石墨烯　切入点：硫化镍　出处：《浙江大学》2014年硕士论文

【摘要】：石墨烯是一种碳原子以sp2杂化轨道呈蜂巢晶格排列构成的单层二维材料,具有优异的电学、力学以及热学性能,是与电化学活性物质复合的理想基体,在锂(钠)离子电池电极材料上具有良好的应用前景。本文通过水(溶剂)热法,制备石墨烯基负极、正极复合材料,详细研究了石墨烯的引入对材料微观结构的影响,复合材料微观结构与电化学性能之间的关系,并探索了石墨烯在改善正、负极材料储锂(钠)性能上的作用机理。电极材料的微观结构对其性能有很大影响,利用石墨烯(G)可以获得具有特殊微观形貌的电极材料。本文采用一步水热法制备了超薄NiS/G二维复合材料,并详细分析了其生长机理。相对于单纯NiS展现出的由纳米棒团聚而成的纳米花形结构,NiS/G复合材料展现出独特的片-片复合二维层状结构,NiS片层厚度小于5nm,石墨烯层数小于8层。研究发现,在水热反应过程中,石墨烯表面的含氧残基与NiS纳米棒表面的含硫残基形成新的共价键,将NiS纳米棒逐步剥离成纳米片,形成新型超薄二维复合材料。本文研究了NiS/G复合物作为负极材料在锂离子及钠离子电池上的应用。研究表明,在储锂方面,NiS/G复合物在50mA/g充放电流密度下,经过100次循环依然保持481mAh/g的可逆容量,高达其理论容量(约500mAh/g)的96.2%；而单纯NiS在10次循环后容量迅速衰减为140mAh/g。在储钠方面,NiS/G复合物在400mA/g的充电流密度下经过10次循环后,容量保持在150mAh/g以上,而单纯NiS则不到80mAh/g。在负极复合材料中,石墨烯不仅可以缓冲充放电过程中的体积效应,还能形成导电网络提升导电性,并且在长时间循环过程中保持材料良好的分散性,从而显著提高材料的循环稳定性及倍率性能。本文采用溶剂热法合成了LiFePO4/G复合材料。研究发现,LiFePO4颗粒均匀地镶嵌在石墨烯片层上,尺寸在100nm以下。在5C电流密度下,LiFePO/G复合材料的可逆容量高达105mAh/g,而单纯LiFePO4仅有65mAh/g的容量。在正极复合材料中,石墨烯形成的柔性三维连续导电网络不仅弥补了LiFePO4导电性较差的不足,并且改善了电极材料与电解液的浸润性,使得复合材料表现出良好的大电流倍率性能。
[Abstract]:Graphene is a carbon atom with SP2 hybrid orbital honeycomb lattice of two-dimensional monolayer material formed, with excellent electrical, mechanical and thermal properties, is an ideal substrate composite and electrochemical active material, lithium (sodium) has a good application prospect of electrode material ion battery. The heat water (solvent) method for preparing graphene based anode, cathode material, a detailed study of the introduction of graphene on the microstructure of the materials, the relationship between the microstructure and electrochemical properties of composite materials, and explored the graphene in improving, anode materials for lithium storage (NA) mechanism performance.
The microstructure of the electrode material has great influence on its performance, the use of graphene (G) can obtain the electrode materials with special morphology. The two-dimensional ultrathin NiS/G composites were prepared by one-step hydrothermal method, and a detailed analysis of the growth mechanism. Compared with the pure NiS nano show by nanorods and agglomeration the flower shaped structure, NiS/G composite materials show a unique piece of film composite two-dimensional layered structure, NiS layer thickness is less than 5nm, less than 8 layers of graphene. The study found that during the hydrothermal process, the graphene surface oxygen containing residues and NiS nanorod surface sulfur residues forming a new covalent bond the NiS nanorods gradually stripped into nanosheets, forming new ultra-thin two-dimensional composite materials.
This paper studies the NiS/G compounds were used as anode materials in lithium ion and sodium ion batteries. Research shows that in the lithium storage, NiS/G complex on current density at 50mA/g, after 100 cycles still maintain a reversible capacity of 481mAh/g, up to its theoretical capacity (about 500mAh/g) and only 96.2%; at NiS after 10 cycles the rapid decay of the capacity for 140mAh/g. in sodium storage, NiS/G complexes in the 400mA/g charging current density after 10 cycles, the capacity retention was more than 150mAh/g, but the NiS is less than 80mAh/g. in the anode composite material, graphene can not only buffer the volume effect of the charge and discharge process. Can enhance the conductivity of conductive network formation, and maintain a good dispersion of materials in long time cycle, so as to improve the performance of the cycle stability and rate of the material.
In this paper, LiFePO4/G composite materials were prepared by solvothermal method. The study found that LiFePO4 particles embedded in the graphene layers, size below 100nm. In the current density of 5C, the reversible capacity of LiFePO/G composites reached 105mAh/g, while the capacity of pure LiFePO4 65mAh/g. Only in anode composite materials, graphene the formation of flexible three-dimensional continuous conductive network not only overcomes the shortcoming of LiFePO4 poor conductivity, and improve the wettability of the electrode and the electrolyte, the composites exhibit a high current ratio of good performance.

【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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