磷酸铁锂正极材料的制备及其性能研究

发布时间：2018-06-29 04:14

  本文选题：锂离子电池 + LiFePO_4/C正极材料　； 参考：《昆明理工大学》2017年硕士论文

【摘要】：橄榄石型磷酸铁锂(LiFePO4)正极材料,因其具有环境友善、资源丰富、价格便宜和安全性能好等优点,被认为是极具有发展前景的锂离子电池正极材料。但由于本身晶体结构的限制,导致较差的电导性和离子扩散性能,导致实际比容量低且大电流放电性能差,因此提高其材料的电子传导性和离子扩散性已成为研究人员关注的焦点。本文分别采用了碳热还原法和混合溶剂热法来合成LiFePO4材料,并通过碳包覆对其进行改性。运用过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、元素分析仪、交流阻抗和充放电循环测试等对产物的物相、表面形貌、碳含量和电化学性能等方面进行检测和分析。碳热还原法主要采用磷酸铁为铁源和磷源、碳酸锂为锂源,研究不同磷酸铁原料、烧结温度、碳源和碳包覆量对合成材料形貌和电化学性能的影响。研究发现:当采用葡萄糖为碳源,无水FePO4、碳酸锂、葡萄糖的摩尔比为2:1.03:0.35,烧结温度为700 ℃时为合成LiFePO4/C的最佳条件,所得样品在0.2 C和10 C倍率下的首次放电比容量分别为160.0和104.9 mAh/g;当碳包覆量为0.40时,二者合成的LiFePO4/C材料在10 C的高倍率下的放电比容量分别为106.3 mAh/g,且1 C倍率下200次循环后的放电比容量保持在99.2%。混合溶剂热法主要采用磷酸锂(Li3PO4)、磷酸(H3PO4)和七水硫酸亚铁(FeSO4·7H2O)为原料制备磷酸铁锂,并探讨了不同溶剂、溶剂配比和模板剂加入量对合成材料形貌和电化学性能的影响。研究发现:当以有机溶剂30 ml聚乙二醇(PEG)和30 ml去离子水混合作为溶剂时制备的LiFePO4/C材料明显的(020)晶面衍射峰很强,其结晶性非常好,且显示出优异的电化学性能;当模板剂的加入量为3 mmol时,合成LiFePOO4/C样品的(020)晶面的结晶度最高,其在0.2 C倍率下的首次放电比容量为152.3 mAh/g,在10 C倍率下的放电比容量仍能够达到 99.2 mAh/g。
[Abstract]:Olivine type lithium ferric phosphate (LiFePO4) cathode material is considered to be a promising cathode material for lithium-ion batteries because of its advantages of friendly environment, abundant resources, low price and good safety performance. However, due to the limitation of crystal structure, it leads to poor conductivity and ion diffusion, which leads to low specific capacity and poor discharge performance of large current. Therefore, improving the electron conductivity and ion diffusion of the materials has become the focus of attention. LiFePO4 materials were synthesized by carbothermal reduction method and mixed solvothermal method, and modified by carbon coating. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), elemental analysis, AC impedance and charge-discharge cycle measurements were used to detect and analyze the phase, surface morphology, carbon content and electrochemical properties of the products. The effects of different raw materials of iron phosphate, sintering temperature, carbon source and amount of carbon coating on the morphology and electrochemical properties of the synthesized materials were studied by using iron phosphate as Tie Yuan and phosphorus source and lithium carbonate as lithium source. The results show that when glucose is used as carbon source, anhydrous FePO _ 4, lithium carbonate, glucose molar ratio is 2: 1.03: 0.35, sintering temperature is 700 鈩，

本文编号：2080803