高能量密度锂离子电池硅基负极材料的性能和应用研究

发布时间：2018-01-19 10:38

本文关键词： 高能量密度锂离子电池硅基负极材料电化学性能　出处：《湖南工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：锂离子电池已广泛应用于便携式电子设备,电动汽车以及储能领域,但受制于常规正负极活性物质的比容量,目前商业化的锂离子电池很难满足更高能量密度的需求。根据中国汽车动力电池发展路线的规划要求,至2015年动力电池模块的能量密度达到150Wh/kg(单体在170~190Wh/kg),目前已经达到要求;至2020年动力电池模块的能量密度达到250Wh/kg(单体在300Wh/kg以上),以现有的材料体系已经无法满足未来发展的需求,所以必须要发展高能量密度的电极材料。硅的理论比容量高达4200mAh/g,是传统石墨负极的十倍多(石墨的理论比容量为372mAh/g),其应用可以大幅地提高锂离子电池的能量密度,因此,硅被认为有望成为下一代锂离子电池大容量负极材料。然而,硅负极颗粒在充放电过程中,其体积变化率超过300%,导致活性物质结构粉化、脱离集流体而失去活性,以及不稳定固体电解质界面膜(Solid Electrolyte Interface,简称SEI膜)的产生,使得硅基负极材料的库伦效率低、循环性能较差,影响其在全电池中的使用。本文对锂离子电池的结构与组成、工作原理以及所用负极材料的进展进行概述,通过对比微米硅、硅碳复合、硅铁合金、硅氧合金四种不同类型的硅基负极材料的结构和电化学性能,得到硅氧合金材料中的SiOx可以有效抑制硅颗粒的体积膨胀,循环性能较好(半电池中0.2C倍率下循环20次后容量保持率70%),嵌锂容量较高(首次嵌锂容量可达1600mAh/g以上),是比较有希望商业化应用的材料。针对硅氧合金材料的首次效率低、导电性能差的问题,以Si/SiOx为研究对象,采用包覆无定形碳的方式对其进行表面改性,得到的Si/SiOx/C的首次库伦效率提高了10%,循环容量保持率提高了11%。为进一步提高Si/SiOx/C材料的导电性,通过研究Super P、CNTs、Graphene三种单一导电剂和Super P+CNTs、Super P+CNTs+Graphene两种复合导电剂的导电网络结构对Si/SiOx/C材料的导电性能和电化学性能的影响,得出综合性能最好是SP+CNTs复合导电剂,它具有三维立体导电网络结构,Si/SiOx/C电极的体电阻率较小,倍率性能最优、循环性能最佳(半电池中0.5C倍率下循环20次后容量保持率55%)。为改善Si/SiOx/C与导电剂、集流体之间的粘结性能,研究常规SBR/CMC常规粘结剂体系和PAALi新型粘结剂对Si/SiOx/C极片的性能影响,在使用Si/SiOx/C/石墨复合材料的聚合物锂离子电池(型号为418281)中进行对比,得出新型PAALi粘结剂能提升极片的剥离强度,降低电池的内阻、提高电池的倍率、循环、高低温性能等。通过对硅基负极材料的改性、所用导电剂和粘结剂的优化,最终开发出能量密度高达737Wh/L,循环300次后容量保持率为80%,满足锂离子电池商业化应用的基本要求,推进硅基负极材料在高能量密度锂离子电池中的应用。
[Abstract]:Lithium ion batteries have been widely used in portable electronic equipment, electric vehicles and energy storage, but limited by the specific capacity of conventional positive and negative active substances. It is difficult to meet the demand of higher energy density for commercial lithium-ion batteries at present. According to the planning requirements of the development route of automobile power battery in China. By 2015, the energy density of the power battery module was 150? In 2020, the energy density of the power battery module reached 250Wh/ kg (the monomer is more than 300Wh/ kg / kg), the existing material system can not meet the future development needs. Therefore, it is necessary to develop high energy density electrode materials. The theoretical specific capacity of silicon is as high as 4200mAh/ g, more than ten times that of the traditional graphite negative electrode (the theoretical specific capacity of graphite is 372mAh/ g). Its application can greatly increase the energy density of lithium-ion batteries. Therefore, silicon is expected to become the next generation of lithium ion batteries large capacity anode materials. However, silicon anode particles in charge and discharge process. Its volume change rate is more than 300, resulting in the structure of the active substances powdered, away from the fluid collection and lose activity. The formation of solid Electrolyte interface (SEI membrane) makes the Coulomb efficiency of silicon-based anode materials low. In this paper, the structure and composition of Li-ion battery, the working principle and the development of anode materials are summarized, and the micron silicon and silicon-carbon composite are compared. The structure and electrochemical properties of four different types of silicon-based negative electrode materials, ferrosilicon alloy and silicon oxide alloy, the SiOx in silicon-oxygen alloy materials can effectively inhibit the volume expansion of silicon particles. The cycle performance is better (the capacity retention is 70 and the lithium intercalation capacity is high (the first lithium intercalation capacity can be more than 1600mAh/ g) after 20 cycles in the semi-battery with 0.2C ratio). It is a promising material for commercial application. Aiming at the problems of low efficiency and poor conductivity of silicon-oxygen alloy materials, Si/SiOx is taken as the research object. The first Coulomb efficiency of Si/SiOx/C was improved by 10% by coating amorphous carbon on the surface. In order to further improve the electrical conductivity of Si/SiOx/C materials, the cyclic capacity retention rate was increased by the study of Super. Three kinds of Graphene single conductive agent and Super P CNTs. The effect of conducting Network structure of Super P CNTs Graphene on the Conductive and Electrochemical Properties of Si/SiOx/C Materials. It is concluded that the best comprehensive property is SP CNTs composite conductive agent, which has a three-dimensional conducting network structure, the volume resistivity of Si / Sio _ x / C electrode is smaller, and the rate performance is the best. In order to improve the adhesion between Si/SiOx/C and conductive agent, the capacity retention rate is 550.In order to improve the adhesion between Si/SiOx/C and conductive agent, the capacity retention rate is 55% after 20 cycles at 0.5C ratio in the semi-battery, in order to improve the bonding performance between the Si/SiOx/C and the conductive agent. The effects of conventional SBR/CMC binder system and new PAALi binder on the properties of Si/SiOx/C plates were studied. Compared with the polymer lithium-ion battery (type 418281) using Si / Sio _ x / C / graphite composite, the new PAALi binder can improve the peeling strength of the electrode. Reduce the internal resistance of the battery, improve the rate of the battery, cycle, high and low temperature performance. Through the modification of silicon-based anode materials, the use of conductive agent and binder optimization. Finally, the energy density is as high as 737Wh/ L, and the capacity retention rate is 80 after 300 cycles, which meets the basic requirements of commercial application of lithium-ion batteries. Application of silicon based anode materials in high energy density lithium ion batteries.
【学位授予单位】：湖南工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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