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1、河北工业大学硕士学位论文磷酸铁锂包覆特性研究姓名：米增财申请学位级别：硕士专业：材料物理与化学指导教师：梁广川2011-03河北工业大学硕士学位论文 i 磷酸铁锂包覆特性研究 摘 要 磷酸铁锂包覆特性研究 摘 要 针对目前 LiFePO4正极材料改性存在的包覆工艺复杂、碳包覆不均匀以及颗粒粒径偏大等问题，采用淀粉为碳源，利用其加热糊化形成稳定胶体实现对前躯体均匀包覆，碳热还原法制备得到微细 LiFePO4/C 复合材料。利用程控恒流充放电测试系统，结合 XRD、SEM、TEM、TG-DTA 等表征手段，研究了焙烧温度和焙烧时间等合成工艺参数对材料的结构、形貌和电化学性能的影响，进一步通过正交实
2、验确定了最佳的合成工艺条件。并且研究了采用复合碳源碳热还原法合成高性能的 LiFePO4/C 复合材料。 实验发现，以淀粉为碳源合成的 LiFePO4/C 复合材料不仅具有微细类球形颗粒形貌，一次粒径为 500nm 左右，而且网络丝状的导电碳均匀包覆于颗粒表面。相对于传统固相包覆工艺，不仅减小了颗粒粒径，而且有效地减小极化，提高了 LiFePO4的电化学性能。 通过正交实验确定的最佳合成工艺条件为：焙烧温度：750，焙烧时间：4h，掺碳量：FePO4Li2CO3C= 21.021。以最佳工艺合成的 LiFePO4/C 复合材料结晶良好，具有高的电导率，为 5.1210-2S/m 和振实密度（1
3、.25g/cm3） 。同时材料表现出优良的电化学性能，0.2C 和 3C 下首次放电容量分别为 155.8mAh/g 和 129.2mAh/g，3C 循环 100 次容量保持率高达 97.8%。 为了实现材料颗粒表面具有致密均匀的全面导电碳体系，进一步来提高 LiFePO4/C 复合材料的导电率。以淀粉和 PEG 作为复合碳源碳热还原法合成 LiFePO4/C 复合材料。实验发现，合成材料颗粒微细呈类球形，粒径仅为 400nm，不仅致密的导电碳均匀包覆于颗粒表面，而且颗粒之间充满了网络丝状的碳，这种全面的导电体系有效地提高了材料颗粒表面和之间的电导率，高达 2.3810-1S/cm。经过放电测
4、试，所制备的样品表现出优良的电化学性能，0.2C 和 1C 放电容量分别为 156.8mAh/g、140.8mAh/g。 关键词：关键词：LiFePO4/C，碳热还原法，包覆改性，微细材料，复合碳源 磷酸铁锂包覆特性研究 ii STUDY ON COATING CHARACTERISTICS OF LITHIUM IRON PHOSPHATE ABSTRACT For the existing problems in the modification of LiFePO4 cathode materia, such as coating process complex, carbon-coat
5、ed uneven and particle size too large and so on, using starch as carbon source, which can be heated to form a stable colloid achieving the uniform coated precursor. Superfine LiFePO4/C composite material was synthesized by carbothermal reduction. The electrochemical performances were evaluated by th
6、e programmable constant-current charge-discharge test system. The structure and morphology of material were characterized by means of X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), and Thermogravimetry/differential thermal analysis (TG-DTA). The
7、effect of calcining temperature and time synthetic process parameters was investigated. The best synthetic conditions were determined by the orthogonal experiment. And the study was done on the high-performance LiFePO4/C composite material synthesized by carbothermal reduction with using composite c
8、arbon sources. It was found that LiFePO4/C composite material synthesized by using starch as carbon source not only had superfine spherical particle morphology, a particle size of about 500nm, but also the particle surface of which was coated by the network filaceous conductive carbon evenly. Compar
9、ed with traditional solid-phase coating process, not only it reduced the particle size, but also effectively reduced polarization to improve the electrochemical performance of LiFePO4. The best synthetic process conditions determined by the orthogonal experiment are as follows: calcining temperature
10、: 750, calcining time: 4h, the ratio of doped carbon: FePO4: Li2CO3: C=2: 1.02: 2. The LiFePO4/C composite material synthesized under the best synthetic process conditions had good crystalline, high specific conductance (5.1210-2S/m) and tap density (1.25g/cm3). Meanwhile, the result indicated that
11、it had excellent electrochemical performances. The discharge tests were taken at 0.2C rate and 3C rate. The first discharge specific capacity is 155.8mAh/g and 129.2mAh/g, while the capacity retention at 3C ratio in 100 times circulation reach as high as 97.8%. In order to form comprehensive compact
12、 and uniform carbon conductivity system on the surface of material, the specific conductance of LiFePO4/C composite material is further 河北工业大学硕士学位论文 iii improved. With starch and polyethylene glycol (PEG) as composite carbon sources, LiFePO4/C composite material was synthesized by carbothermal reduc
13、tion. The result indicated that the synthesized material had superfine spherical particle morphology, a particle size of about 500nm. Not only the surface of material was coated by compact conductive carbon evenly, but the gap of particle was filled by the network filaceous conductive carbon. Such a
14、 comprehensive conductive system had effectively increased the conductivity of material on the surface and between the particles, up to 2.3810-1S/cm. The discharge tests found that the synthesized samples had excellent electrochemical performances. The discharge tests were taken at 0.2C rate and 1C
15、rate. The first discharge specific capacity is 156.8mAh/g and 140.8mAh/g. KEY WORDS: LiFePO4/C, carbothermal reduction, coating modification, subtle material, composite carbon sources 磷酸铁锂包覆特性研究 vi 符号说明符号说明 C 充放电倍率 d 直径，cm R 电阻， m 质量，g V 体积，cm3 振实密度，g/cm3 电导率，S/cm wt% 质量百分含量 PEG 聚乙二醇 XRD X射线衍射 SEM 扫
16、描电子显微镜 TEM 透射电子显微镜 TG-DTA 热重-差热分析 DSC 差示扫描量热分析 PTFE 聚四氟乙烯 EC 碳酸乙烯酯 DMC 二甲基碳酸酯 河北工业大学硕士学位论文 1 第一章 绪 论 1.1 引言 随着社会的进步，能源和环境问题成为人类面临的两个最严峻的挑战。进入 21 世纪后，对能源体系提出了新的更高要求，建立高效、清洁、经济、安全的能源体系成为当下的重要目标。首当其冲，寻求新能源，开发新能源材料成为全球的热点和共同的科技战略。这样给科技工作者提供了一个机遇，同时也是一个很大的挑战。 新能源汽车成为新能源产业的热点，而新能源汽车里的关键是动力电池。目前，能否突破价廉、安全、环境友好的二次化学电源技术已是制约新能源汽车发展的瓶颈。锂离子电池自 20 世纪 90 年代初问世以来，因其高能密度和良好的循环性能已成为迅速成长的二次电池产业链。正极材料作为锂离子电池的重要组成部分，是决定电池的安全性、容量和价格的关键因素。因此，寻找锂离
