【作者】 阮艳莉；

【导师】 唐致远；

【作者基本信息】 天津大学 ， 应用化学， 2005， 博士

【摘要】 磷酸铁锂（LiFePO₄）作为新型锂离子电池正极材料具有高安全性、低成本、高温性能好、环境友好等优点,因而成为目前电池界竞相开发与研究的热点。本文以磷酸铁锂作为研究目标,系统地对其合成工艺、材料改性、结构表征、电化学性能以及电极动力学性能等方面进行了研究。利用TG-DSC、XRD、SEM、LSD、CV、EIS以及充放电测试等方法研究了橄榄石型LiFePO₄正极材料的合成工艺。通过单因素实验及正交实验对合成过程中所用原料、焙烧温度、焙烧时间、惰性气氛流量等工艺参数进行了优化,确定了合成磷酸铁锂最佳的工艺条件。首次将TG-DTA热分析技术应用于研究LiFePO₄正极材料固相合成的动力学过程。运用Doyle-Ozawa法和Kissinger法计算合成过程中各个反应阶段的表观活化能、反应级数、频率因子等动力学参数,为磷酸铁锂固相合成过程的进一步放大和研究提供了预测依据。采用不同类型的碳导电剂前驱物对LiFePO₄正极材料进行表面包覆改性。实验表明,葡萄糖及甘油等有机导电剂前驱物具有较好的改性效果。考虑到适当的掺碳量对于LiFePO₄正极材料容量和密度的综合优化是十分必要的,本文对葡萄糖的加入量进行了筛选。结果表明,当葡萄糖的加入量为10%时,样品具有良好的充放电动力学特性,具有较高的充放电容量及稳定的循环性能。本文对磷酸铁锂正极材料的离子掺杂改性进行了系统的研究。从产物的结构和电化学性能方面考察了掺杂离子的改性效果,并尝试从金属离子半径、价态和LiFePO₄晶格内部缺陷等方面分析离子掺杂改性的机制,提出了离子选择的标准,即采用离子半径与Li⁺相近,但具有更高价态的金属离子进行Li位掺杂能够取得较好的改性效果。尝试对共沉淀法进行改进,利用自制的加料装置通过控制原料的滴加速度从而控制前驱物沉淀的生成速率,最终达到均匀沉淀。并成功利用该法对LiFePO₄进行表面包覆改性,取得了较好的效果。测定了锂离子在LiFePO₄中脱嵌的OCV曲线及微分容量曲线。运用EIS技术测定了LiFePO₄正极材料中锂离子的固相扩散系数。对橄榄石型LiFePO₄材料中锂离子的扩散系数随锂离子在材料中嵌入组成的变化规律进行了探讨。更多还原

【Abstract】 Lithium iron phosphate, LiFePO₄, has recently attracted significant interest because of its low hygroscopicity, low cost and environmentally friendly components. The aim of the present study were to focus on the preparation processes, the modification of materials, the structural characterization, the electrochemical properties, and the kinetics behaviors of the olivine lithium iron phosphate as cathode materials for rechargeable lithium batteries.Effects of the preparation conditions, such as precursor material, annealing temperature and time, atmosphere and grinding process et al., on the structure, particle size and electrochemical properties of LiFePO₄ were studied by using TG-DSC, XRD, SEM, LSD, CV, EIS and electrochemical charge-discharge tests to optimize LiFePO₄ production process.Attempts were made for the first time to use TG-DTA to study the solid state reaction processes of LiFePO₄. The activation energies of each reaction process, reaction orders and frequency factors were determined by making use Doyle-Ozawa method and Kissinger method. The method provides reliable predication for further scale-up and research of the process.The effects of different carbon source on the performance of LiFePO₄ were systematically investigated. The results demonstrate that pyrogenation and glycerin, added as conductive precursor before the formation of the crystalline phase, can optimize the performance of LiFePO₄ effectively. The carbon content was optimized, and the results show that the material obtained by adding 10 wt. % C have much higher discharge capacity. The material also displays a more stable cycle-life than the others.The effects of cation doping on the physicochemical structure and electrochemical performance of produced cathode were systematically investigated. at different doping position. The doping mechanism was discussed from the aspects of cation valence, cation radius and the crystal defect of LiFePO₄. And the criterion to choose the cations was proposed, that is the supervalent cations, which have the similar radius with Li+, have good doping effects.Attempts were made for the first time to improve the co-precipitation method by designing feed-in device to control the growth speed of the deposit, which could make deposit well-proportioned. The results indicated that the improved co-precipitationmethod was an effective route to improve the electrochemical of LiFePO₄/C material.The open circuit voltage and the differential capacitance plot for LiFePO₄ with the change of intercalation compositions have been measured. The lithium ion diffusion coefficients have been obtained by EIS method and the results indicate that its values are change with the change of lithium ion intercalation compositions.更多还原