LiFePO₄化合物的水热合成、改性及电化学性能研究

【作者】 张静；

【导师】 黄可龙；

【作者基本信息】 中南大学 ， 无机化学， 2005， 硕士

【摘要】 本文采用传统高温固相法、机械化学活化法和水热法三种方法制备正极材料LiFePO₄。研究发现,三种方法都可以得到橄榄石型的LiFePO₄正极材料。其中,水热法制备的LiFePO₄为纯相,并且材料颗粒呈规整的片状,粒径分布均匀,都为2μm左右,小倍率下的充放电比容量和循环性能都明显优于其他两种方法所得的LiFePO₄材料。 系统研究了水热法制备LiFePO₄时,反映温度、反应时间和填充度对所得LiFePO₄材料晶体结构、外观形貌和电化学性能的影响。结果表明,将反应釜填充90%,并于190℃下反应6h,所得样品的电性能最好,小倍率（0.1C）充放电时比容量可以达到140.2mAh·g^-1和132.9mAh·g^-1。 为提高材料的电性能,在制备LiFePO₄后掺杂导电碳黑和在制备过程中掺加金属离子,得到了LiFePO₄/C复合物、LiFe_0.9Mg_0.1PO₄和LiFe_0.9Mn_0.1PO₄,并研究了改性方法对材料的影响。研究表明,两种改性方法都不会影响材料的晶体结构,并且掺碳可以提高材料的小倍率下的比容量和循环性能;掺杂金属离子,杂质离子可以增大Li⁺在晶格中的扩散系数,从而改善材料的倍率性能和大倍率下的循环性能。更多还原

【Abstract】 LiFePO₄ powders were synthesized by three different reacting conditions （solid state reactions at high temperatures, mechanochemical activation and hydrothermal synthesis）. The samples were characterized by XRD, SEM, granularity analysis etc. Results showed that only the LiFePO₄ powders gotten by hydrothermal processes were pure phase, regular sheet with 2 urn, better performance compared with the products prepared by the other methods.In the process of the hydrothermal synthesis, we researched the effect of technological conditions on crystal structure and electrochemical performance. The results showed that the reaction temperature, reaction time and fill rate were important factors. The optimum process of synthesizing LiFePO₄ read as follows: the mixture was reactioned at 190℃ for 6 h, and the fill rate was 90%. The low rate recharge-discharge characteristic of the sample is best, the 1st recharge-discharge capacity at 0.1C rate were 140.2 mAh.g^-1 and 132.9 mAh.g^-1.In order to improve the electrochemical performance of products, prepared LiFePO₄/C by doping carbon and LiFe₀.9Mg₀.1PO₄ （LiFe₀.9Mn₀.1PO₄） by doping metal ion. The effect of doping ways on the materials was investigated. The experiment results showed that doping carbon and doping metal ion would not change the crystal structure; doping carbon can enhance the specific capacity and cycle characteristic at low rate. The chemical diffusion coefficient of lithium ion in the crystal lattice was increased and high rate characteristic of the materials was improved after doping metal ion.更多还原