boundary of particles was clear and dispersion was good. When the higher the temperature, the longer the time of the hydrothermal, the better the crystallinity of the ferric phosphate was. When the iron source was ferrous sulfate, the ferric phosphate was orthorhombic FePO4·2H2O, which contains a certain amount of impurity such as Fe2(NH4)(OH)(PO4)2·2H2O, FeH2P3O10·H2O, Fe(H2PO4)3, and the content of impurity Fe2(NH4)(OH)(PO4)2·2H2O with space group P21/n of the monoclinic system was relatively higher; When the iron source was ferric nitrate, ferric phosphate containing both orthorhombic FePO4·2H2O and monoclinic system FePO4·2H2O, also contained some other iron-phosphorus compound impurities, when the hydrothermal temperature rised, the content of impurity of orthorhombic Fe5(PO4)4(OH)3·2H2O also be increased. When the iron source was ferrous sulfate, ferric phosphate was in a larger particle size, the average particle size was distribution in the range of 10-15 μm; When the iron source was ferric nitrate, ferric phosphate had relatively small particle size of about 6μm, but the particle size distribution is uneven, the distribution was wide. When the iron source was ferrous sulfate, the ferric phosphate particles were spherical, when the synthesis temperature was up to 180 ℃, the particle became ellipsoidal; When the iron source was ferric nitrate, the ferric phosphate particles were ellipsoid or peanut like morphology. When the iron source was ferrous sulfate, lithium iron phosphate synthesized by the ferric phosphate which prepared under 120 ℃ for 2 hours had the highest discharge capacity at 0.2 C rate of 142 mAh/g, lithium iron phosphate synthesized by the ferric phosphate which prepared under 150 ℃ for 10 hours had the highest discharge capacity at 5 C rate of 78 mAh/g; When the iron source was ferric nitrate, lithium iron phosphate synthesized by the ferric phosphate which prepared under 120 ℃ for 6 hours had the highest discharge capacity both at 0.2 C and 5 C rate of 124.5 mAh/g and 66 mAh/g.
(3) When the iron source was the ferrous sulfate, using the hydrothermal synthesis method, the ferric phosphate would have better crystallinity and spherical morphology under the reaction for 6-10 hours at 150-180 ℃, the lithium iron phosphate would have better overall performance.
Key Words: Lithium-ion battery; Lithium iron phosphate; Ferric phosphate; Precipitation method; Hydrothermal synthesis method
目 录
第一章 绪论 ................................................................................................................................. 1
§1.1 引言 ................................................................................................................................ 1 §1.2 锂离子电池概述 ............................................................................................................ 2
1.2.1 锂离子电池发展简介 ........................................................................................... 2 1.2.2 锂离子电池组成结构及工作原理 ....................................................................... 2 §1.3 锂离子电池正极材料LiFePO4研究进展 .................................................................... 4
1.3.1 正极材料的选择依据 ........................................................................................... 5 1.3.2 LiFePO4正极材料的结构 ..................................................................................... 5 1.3.3 LiFePO4的电化学性能 ......................................................................................... 6 1.3.4 LiFePO4的合成方法 ............................................................................................. 7 §1.4 FePO4研究进展 .............................................................................................................. 9
1.4.1 FePO4的结构和性质 ........................................................................................... 10 1.4.2 FePO4的合成方法 ............................................................................................... 10 §1.5 本论文的选题背景及研究内容 .................................................................................. 11 第二章 以沉淀法合成的磷酸铁(FePO4·xH2O)制备磷酸铁锂及其性能研究 ........................ 13
§2.1 实验部分 ...................................................................................................................... 13
2.1.1 实验试剂 ............................................................................................................. 13 2.1.2 实验仪器 ............................................................................................................. 13 2.1.3 磷酸铁(FePO4·xH2O)的制备 .............................................................................. 14 2.1.4 磷酸铁锂的制备 ................................................................................................. 15 2.1.5 电池正极的制作及电池的组装 ......................................................................... 16 §2.2 材料表征测试方法 ...................................................................................................... 16
2.2.1 XRD分析 ............................................................................................................ 16 2.2.2 TG-DSC分析 ....................................................................................................... 16 2.2.3 粒度检测 ............................................................................................................. 16 2.2.4 SEM分析 ............................................................................................................. 16 2.2.5 电池充放电性能测试 ......................................................................................... 17 §2.3 结果分析 ...................................................................................................................... 17
2.3.1 FePO4·xH2O及LiFePO4/C的XRD分析 ........................................................... 17 2.3.2 FePO4·xH2O的TG-DSC分析 ............................................................................ 18 2.3.3 FePO4·2H2O的粒度分析 .................................................................................... 19 2.3.4 磷酸铁的扫描电镜分析 ..................................................................................... 21 2.3.5 磷酸铁锂充放电性能分析 ................................................................................. 22 本章小结 ............................................................................................................................... 26
第三章 以水热法合成的磷酸铁(FePO4·xH2O)制备磷酸铁锂及其性能研究 ........................ 28
§3.1 实验部分 ...................................................................................................................... 28
3.1.1 实验试剂 ............................................................................................................. 28 3.1.2 实验仪器 ............................................................................................................. 28 3.1.3 磷酸铁(FePO4·xH2O)的制备 .............................................................................. 29 3.1.4 磷酸铁锂的制备 ................................................................................................. 30 3.1.5 电池正极的制作及电池的组装 ......................................................................... 30 §3.2 结果分析 ...................................................................................................................... 30
3.2.1 FePO4·xH2O及LiFePO4/C的XRD分析 ........................................................... 30 3.2.2 FePO4·xH2O的TG-DSC分析 ............................................................................ 33 3.2.3 FePO4·2H2O的粒度分析 .................................................................................... 34 3.2.4 磷酸铁的扫描电子显微镜分析 ......................................................................... 37 3.2.5 磷酸铁锂充放电性能分析 ................................................................................. 39 本章小结 ............................................................................................................................... 43 第四章 结论与展望 ................................................................................................................... 44
§4.1 结论 .............................................................................................................................. 44 §4.2 展望 .............................................................................................................................. 45 致 谢 ........................................................................................................... 错误！未定义书签。 参考文献 ....................................................................................................................................... 46
XX大学全日制硕士专业学位论文 1
第一章 绪论
§1.1 引言
能源、新材料、生物工程以及信息技术是现代社会新技术的四大支柱。如今，能源是推动经济发展和社会进步的重要基础，是人类社会可持续发展战略的核心。随着工业化进程的不断加快及人口的快速增长，人们对能源的需求也日益增加。有数据表明，世界人口相比于上世纪增长了将近2倍，而能源的消耗则增长了10倍之多，其中石油、天然气和煤炭这类不可再生的化石燃料的消费占世界一次能源消耗的八成以上[1]。但是化石燃料存在着环境污染大、能量转化率低和资源有限等明显缺点，因此，在追求环保及循环经济的时代背景下，开发绿色新能源是当今各国关注的重点。
如今，研究人员正在致力于水利、太阳能、潮汐能、风能和核能等无污染可持续利用能源的开发利用，这些能源会以电能的形式输出，但是电能的产生和利用并不是持续的，如果要大规模的利用这些电能，则必须有与之相匹配的能量储存装置[2]，而且，随着笔记本电脑、手机等便携式电子产品的广泛应用及电动汽车和军用电子设备的大力开发，人们对轻便的移动电源需求快速增长，这进一步促进了高容量二次电池的快速发展。
锂离子二次电池是第三代可充二次电池，因具有工作电压高、比容量较高、循环寿命长、对环境污染小等特点，近年来成为化学电源领域的研究热点，具有广阔的应用前景。相对于Ni-Cd、Ni-MH及铅酸电池这类传统的二次电池来说，锂离子电池具有不可比拟的优点。表1-1为各二次电池参数对比[3-5]。
表1-1 常用二次电池的参数对比
Table1-1 Performance comparison of common secondary batteries
性能参数 工作电压(V) 质量比能量(Wh/Kg) 体积比能量(Wh/L) 循环寿命(次) 使用温度范围(℃) 自放电率(每月)
毒性 记忆效应
铅酸电池
2 30-50 50-80 500 -20-60 5% 有毒 无
Ni-Cd电池
1.2 70 130-150 500 -20-65 20% 有毒 有
Ni-MH电池
1.2 80 200 500 -20-65 20-30% 低毒 无
锂离子电池
3.6 100-150 240-260 500-1000 -20-60 <10% 低毒 无
但目前锂离子电池还存在成本过高、安全性较差、功率密度低等不足，这些都限制了