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锂离子电池正极材料LiFePO4的液相法制备及性能研究
李传玲
学位类型硕士
导师康雪雅 ; 吐尔迪·吾买尔
2011-05-31
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业材料物理与化学
关键词锂离子电池 正极材料 Lifepo4 水热法 液相还原法
摘要磷酸铁锂(LiFePO4)是一种有潜力的锂离子电池正极材料,具有比容量相对较高、热稳定性好、安全环保、原料丰富、成本低等突出优点。但其导电率和离子扩散速率均较低,在大电流充放电的条件下,循环性能有待改善。本论文主要集中在橄榄石型LiFePO4的液相法制备、材料形貌和结构表征、晶体生长机理以及电化学性能研究。 以LiOH•H2O,FeSO4•7H2O和H3PO4作为起始原料,采用水热法以制备纯相LiFePO4为目的,考察了主要影响因素如溶剂、蔗糖添加量、加料顺序、前驱体pH等的最佳选择。 在水热法制备LiFePO4中,通过前驱体pH的调节,制备了多种形貌的纯相LiFePO4。并探讨了前驱体pH对LiFePO4的形貌和电化学性能的影响及其机理。结果表明:当不用添加剂调节前驱体pH时(pH=6.50),生成菱形形貌。在中性和碱性条件下,随着前驱体pH的增加,生成了多层的菱形,继而生成了团聚的微粒。在酸性条件下,随着前驱体pH的降低,首先生成尺寸较小的粒子,接着生长成为棒状物并连接组合在一起,生成了凹陷形,最后生长为由棒状物组成的空心球。通过控制LiFePO4的制备条件,使LiFePO4得颗粒细小、分布均匀以及抑制[010]方向上的生长,使其尽可能多的暴露(010)面,有助于提高LiFePO4的电化学性能。当pH=6.00时得到的LiFePO4电化学性能优越,放电比容量在0.1 C时为163 mAh•g-1,在5 C时为100 mAh•g-1,可以作为一种制备LiFePO4正极材料的方法。 以LiOH•H2O,H2C2O4•2H2O和FePO4•2H2O作为起始原料,采用液相还原法制备LiFePO4,考察了主要影响因素如碳源、铁源和磷源以及烧结时间的最佳选择,通过工艺优化研究确定了纯相LiFePO4最佳的制备条件。测试结果表明:在0.1 C和10 C充放电循环时,首次放电比容量分别为169 mAh•g-1和90 mAh•g-1,且具备良好的循环性能。
其他摘要The olivine-like material lithium iron phosphate (LiFePO4) has attracted broad attention as a promising positive electrode material for lithium ion batteries. LiFePO4 has many advantages of high potential, good thermal stability, high safety, environment friendly performance, rich sources and low cost. However, relatively low electric conductivity and ionic diffusion coefficient limit the application of LiFePO4, especially with large charge/discharge current, the cycle ability needs improvement. The aim of the present study were to focus on the liquid phase synthesis, the morphology of materials, the structural characterization, the mechanism of crystal growth, and the electrochemical properties of the olivine lithium iron phosphate as cathode materials for rechargeable lithium batteries. Using LiOH·H2O, FeSO4·7H2O and H3PO4 as starting materials, LiFePO4 samples were synthesized through hydrothermal method. The parameters such as solvent, sucrose addition, charging sequence and precursor pH value were optimized. Pure phase of LiFePO4, which displays interesting morphologies, was prepared by hydrothermal method with precursor pH value varying. The mechanism and influences of precursor pH on the morphology and electrochemical behavior of LiFePO4 were investigated. The results show that the LiFePO4 samples crystallize well in an olivine-type structure, and display hollow microsphere and concave morphologies made up by rods, as well as rhombic and multilayer rhombic morphologies. To prepare small and monodisperse particles and inhibit the growth in [010] orientation to make the most exposure of (010) face can be important to improve the electrochemical property of LiFePO4. LiFePO4 samples with different morphologies exhibit different electrochemical properties, especially LiFePO4 obtained at precursor pH=6.00, which delivers initial discharge capacities of 163 mAh·g-1 and 75 mAh·g-1 at 0.1 C and 10 C rate, respectively. Using LiOH·H2O, H2C2O4·2H2O and FePO4·2H2O as starting materials, LiFePO4 samples were synthesized through liquid reduction method, and the effects of carbon sources, iron and phosphorus sources, and sintering time on the electrochemical properties of LiFePO4 were studied. LiFePO4 prepared in the optimum condition exhibits initial discharge capacities of 169 mAh·g-1 and 90 mAh·g-1 at 0.1 C and 10 C, as well as good static cycle life.
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4448
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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李传玲. 锂离子电池正极材料LiFePO4的液相法制备及性能研究[D]. 北京. 中国科学院研究生院,2011.
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