锂离子电池正极材料磷酸铁锂的合成和性能研究

发布时间：2018-04-28 23:21

  本文选题：湿法磷酸 + 磷酸铁　； 参考：《武汉工程大学》2014年硕士论文

【摘要】：随着社会的发展，，能源问题的日益突出，人们对资源利用率的提高越来越重视。锂离子电池由于工作电压高、循环寿命长、能量密度大、对环境友好等优点而受到广泛的关注。因此,大力发展价格低廉、能量密度高的可充式锂离子电池,具有积极重要的科学意义，而且具有可观的潜在商业价值。其中含铁系列正极材料以其价格低廉、原料丰富易得、绿色环保等优点,受到电池行业的广泛关注,特别是磷酸铁锂正极材料。 磷酸铁锂正极材料具有放电比容量高、循环性能优良、较好的热稳定性等诸多优点，而致国内外争相研究。而磷酸铁作为合成磷酸铁锂的重要原料也越来越受到关注。 本文以湿法磷酸和硫酸亚铁分别为磷源和铁源，通过合成、沉淀过程制备磷酸铁，研究了摩尔投料比、反应pH、氨水滴加速度、表面活性剂PEG（10000）添加量和煅烧温度等对合成磷酸铁的影响，并以制备的磷酸铁为磷源和铁源通过溶胶-凝胶法制备了磷酸铁锂材料。采用了粒度分布、振实密度、比表面积、红外光谱（IR）、X射线衍射(XRD)和扫描电子显微镜(SEM)等手段对合成的磷酸铁及磷酸铁锂材料的结构和微观形貌进行表征，同时通过电池测试系统及电化学工作站对磷酸铁锂材料的电化学性能进行检测。 结果表明：制备磷酸铁的最佳工艺条件为：磷铁摩尔投料比为1.0:1，PEG用量为原料硫酸亚铁质量的3.0%，氨水滴加速率为35.62ml/h，反应的pH控制在2.5。在此工艺条件下制备得到的磷酸铁为无定型二水磷酸铁粉体，经450℃煅烧后为斜方晶系的纳米片磷酸铁粉体，磷酸铁微粒厚度约为70-100nm，平均粒径1000nm，分散性好，粒度分布均匀。该工艺具有原料廉价，操作简单，合成时间短和能耗小等优点，是一种节能且经济的新方法。 通过优化条件下制备的磷酸铁为原料通过溶胶-凝胶法制得的产物为磷酸铁锂/碳的复合材料，通过表征可得磷酸铁锂正极材料结晶度良好，晶形完整，为橄榄石晶体，粒度分布均匀，团聚现象少，磷酸铁锂表面疏松多孔，比表面积可达13.61m2/g，D50=3.6μm，粒度分布窄，振实密度为1.24g/cm3。磷酸铁锂/碳复合材料通过电化学性能检测具有较好的首次放电比容量和稳定的循环性能。在0.1C倍率下首次放电最高能到达到145.5mAh/g，40次充放电循环后保持在143.1mAh/g，衰减率为1.61%；样品分别在0.2C，0.5C，1.0C三种倍率下的首次放电比容量分别为138.7mAh/g、129.1mAh/g和119.2mAh/g，通过40次循环后比容量分别下降至128.9mAh/g、115.8mAh/g和101.5mAh/g，衰减率分别为7.1%、10.3%和17.5%。电荷转移阻抗小，该工艺制作的材料可逆性好，极化较小，电化学性能较稳定。
[Abstract]:With the development of society and the increasingly prominent energy problem, people pay more and more attention to the improvement of resource utilization ratio. Lithium-ion batteries have attracted wide attention due to their high operating voltage, long cycle life, high energy density and environmental friendliness. Therefore, the development of rechargeable lithium ion batteries with low price and high energy density has positive and important scientific significance and has considerable potential commercial value. Due to its low price, abundant raw materials and green environmental protection, iron containing series cathode materials have attracted wide attention in battery industry, especially lithium iron phosphate cathode materials. Lithium iron phosphate cathode material has many advantages, such as high discharge capacity, good cycling performance, good thermal stability and so on. Iron phosphate as an important raw material for the synthesis of lithium iron phosphate has attracted more and more attention. In this paper, wet-process phosphoric acid and ferrous sulfate were used as phosphorous source and Tie Yuan, respectively, to prepare ferric phosphate through synthesis and precipitation process. The molar ratio of feed, pH of reaction, acceleration of ammonia droplet were studied. The effect of the amount of surfactant PEG 10000) and calcination temperature on the synthesis of iron phosphate was studied. The lithium iron phosphate material was prepared by sol-gel method using the prepared iron phosphate as the phosphorus source and Tie Yuan as the source. Particle size distribution, vibrational density, specific surface area, IR spectra, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structure and microstructure of the synthesized iron phosphate and lithium iron phosphate materials. At the same time, the electrochemical performance of lithium iron phosphate was tested by battery test system and electrochemical workstation. The results showed that the optimum technological conditions for the preparation of iron phosphate were as follows: the molar ratio of phosphorus to iron was 1.0: 1g as the mass fraction of ferrous sulfate, the dropping rate of ammonia water was 35.62 ml / h, and the pH of the reaction was 2.5. The ferric phosphate powder prepared under this condition is amorphous iron dihydrate powder. After calcined at 450 鈩

本文编号：1817358