【作者】 王国增；

【导师】 单忠强；

【作者基本信息】 天津大学 ， 应用化学， 2008， 硕士

【摘要】 随着能源与环境问题的日益突出以及现代科技的快速发展,对电池的性能提出了更高的要求。锂离子电池以其工作电压高、体积小、质量轻、比能量高、无记忆效应、无污染、自放电小、循环寿命长等特点而受到人们的重视和青睐。目前,商业化的锂离子电池正极材料主要是钴酸锂。由于钴资源有限且对环境有害,钴酸锂价格较高,热稳定性和安全性能较差。因而研究开发成本低、环境友好、电化学性能好、安全性能佳的新型锂离子电池正极材料成为研究热点。磷酸铁锂具有原料来源广泛、价格低廉、热稳定性好、比能量高、循环性能好、安全性能突出及对环境无污染的特点。其理论容量为170 mAh/g,工作电压为3.45 V左右,是最具潜力的正极材料之一。然而,磷酸铁锂正极材料仍存在两个不足之处:一是其电导率低和离子扩散系数低。二是材料的堆积密度小。目前用来提高LiFePO4电化学性能的方法主要有三种:改进合成方法得到颗粒小且分布均匀的产物;掺杂导电剂,主要是掺杂碳或者金属粉末;掺杂金属离子,从本质上提高材料的导电性。本文采用了液相共沉淀法-碳热还原法合成出了体积比容量较高的球形LiFePO4材料,并采用XRD、SEM、TEM、CV等手段对材料进行表征,在不同条件下测试了材料的电化学性能。结果表明,550℃下锻烧10 h制得的样品表现出较好的电化学性能,0.1C的电流密度下首次放电比容量为141.8mAh/g。同时对材料的改性进行了研究,通过对碳源、掺碳量、以及掺碳方式的研究发现,使用过量5%葡萄糖作为碳源,在550℃下制得的材料综合性能较好,当采用0.1C放电时,其比容量达到154.6mAh/g。本文还将微波加热与液相共沉淀-碳热还原法相结合,制得的球形LiFePO4材料粒径在50~200nm。用LiFePO4作正极材料进行了电池的充放电测试和循环伏安测试,结果显示,在0.5C下首次放电比容量达到129.7mAh/g,循环100次后,仍然可以保持在125.4 mAh/g,在50℃下,其首次放电容量为143.3mAh/g。更多还原

【Abstract】 The increasing concerns on energy, environment and the rapid development of modern science and technology have more demands on batteries. Lithium ion batteries (LIB) are favorable because of the properties of high vlltage, high energy density, long cycling life, little local action, non-memory effect and pollution-free. Currently, the cathode material that commercialized is mainly LiCoO2. However, because of its pollution, high price, poor thermal stability and security, the development of new cathode materials which are low cost, environment-friendly, and have better electrochimecal properties and better security are becoming the focus of resent research.LiFePO4 is one of the most potential cathode materials which has a high theoretical capacity (170mAh/g) and voltage (about 3.5V versus Li/Li). It also have good stability both at room temperature and high temperature. Besides, it is environmentally benign and inexpensive. However, LiFePO4 have some fatal problems including its low electronic conductivity, low lithium ion diffusivity, and low tap density. In order to overcome these defaults, the first way is to synthesize small fine particles of LiFePO4 through improved methods, the second way is to coat LiFePO4 with electronically conductive materials such as carbon or metal powder, the final way is to substitute Li or Fe by other metal ions to enhance the inherent electronic conductivity.Spherical LiFePO4 was obtained by liquid co-deposited-carbonthermal reduction. The LiFePO4 was characterized by XRD, SEM, TEM, CV analysis. We also studied the electrochemical properties of the product at different conditions. The results indicated that the sample synthesized by co-deposited-carbonthermal reduction sintered at 550℃for 10 hours showed the best electrochemical properties. The first discharge capacity was 141.8mAh/g with a current density of 20mA/g.And we also researched the modification by coating LiFePO4 materials with different carbon sources, such as acetylene black, glucose and sucrose. Studies on carbon sources, mixing accounts and mixing styles indicated that the sample coated with 5% excess glucose sintered at 550℃for 10 hours has the most optimized electrochemical properties with a discharge capacity of 154.6mAh/g under a current density of 20mA/g. The spherical material LiFePO4 was synthesized by liuqid-microwave method with 50~200nm particle diameter. The results of charge-discharge test of the products coated with sucrose showed a lithium insertion plateau around 3.5V vs. Li together with a specific capacity of 129.7mAh/g with a current density of 100mA/g. After 100 cycles, it remains a specific capacity of 125.4mAh/g. And under the temperature of 50℃, it also have a specific capacity of 143.3mAh/g.更多还原