锂离子电池电极材料石墨烯以及磷酸铁锂的制备与电化学性能研究

发布时间：2018-05-10 16:47

  本文选题：锂离子电池 + 磷酸铁锂　； 参考：《天津大学》2014年博士论文

【摘要】：锂离子电池由于具有快速充放，无记忆效应以及高容量等优势，已经成为新能源发展主要的方向。磷酸铁锂作为锂离子电池正极材料，由于原料来源广泛，对环境友好，使用安全等诸多优点逐渐成为动力型锂离子电池的主要材料。但是磷酸铁锂因为自身较低的电导率与能量密度限制了其在锂离子电池中的大规模应用，因此对磷酸铁锂进行改性使其具有优秀的倍率性能与循环性能成为本文研究的主要内容。本文主要的研究内容包括石墨烯(GS)与磷酸铁锂的制备，并以碳和石墨烯两种不同类型的碳源对其进行改性，优化制备出性能优越的磷酸铁锂/石墨烯复合正极材料。 在石墨烯的制备过程中，本文首次采用一种在室温环境下，以LiAlH4与PBr3作为双重还原剂还原氧化石墨来快速制备石墨烯的方法。结果表明所制备的石墨烯层数较少，约为三层左右。作为负极材料应用于锂半电池，在电流密度为100mA/g下，首次充放电比容量分别为1029.4，855.1mAh/g，库伦效率可以达到83.1%。经过21次循环后，，可逆放电比容量仍然可以达到760.7mAh/g，显示出了优秀的循环稳定性能。 在LiFePO4前驱体的制备过程中，本文分别采用溶胶-凝胶、溶剂热两种方法。研究发现采用溶剂热法制备的LiFePO4/C样品具有非常优秀的微观形貌与电化学性能，并对反应时间、反应温度以及碳含量进行了详细的考察。结果表明在130℃反应5h，葡萄糖加入量为15%时制备的样品具有较好的结晶度与分散性。在0.2，0.5，1，3C倍率下，放电比容量分别为159.4，155.6，151.9，141.9mAh/g，具有非常优秀的倍率性能。在5，10，20，30C倍率下循环100次，容量保持率分别为97.0%，99.6%，97.1%，95.6%，显示出优秀的循环稳定性能。 在LiFePO4/GS复合电极材料的制备过程中，主要研究了石墨烯的加入量对复合材料形貌与电化学性能的影响。研究发现在制备LiFePO4/GS复合材料过程中，石墨烯加入量过少会导致晶体具有较大颗粒；石墨烯加入量过多会在LiFePO4颗粒表面包裹较厚的石墨烯层，导致电化学性能下降。结果表明当石墨烯加入量为5%时制备的LiFePO4/GS样品表现最佳，晶体颗粒大小约为100nm，在LiFePO4表面所包裹的石墨烯层数约为4~5层。在0.2，0.5，1，5C倍率下，放电比容量分别为154.4，150.5，145.9，124.3mAh/g；在5C倍率下循环200次容量保持率为99.1%，说明复合材料具有非常好的倍率性能与循环寿命。
[Abstract]:Li-ion batteries have become the main direction of new energy development due to their advantages of rapid charging, memory free and high capacity. As the cathode material of lithium ion battery, lithium iron phosphate has become the main material of power lithium ion battery because of its wide source, friendly to the environment, safe use and so on. However, lithium iron phosphate has limited its large-scale application in lithium-ion batteries because of its low conductivity and energy density. Therefore, the modification of lithium iron phosphate to make it have excellent rate performance and cycle performance has become the main content of this paper. The main research contents in this paper include the preparation of graphene glutathione (GSH) and lithium ferric phosphate, and the modification of them with two different carbon sources, carbon and graphene, to optimize the preparation of lithium iron phosphate / graphene composite cathode material with superior properties. In the process of preparation of graphene, a method of rapid preparation of graphene by reducing graphite oxide with LiAlH4 and PBr3 at room temperature was used for the first time. The results show that the number of graphene layers is less, about three layers. The first charge / discharge capacity is 1029.4855.1 mg / g at current density of 100mA/g, and the Coulomb efficiency can reach 83.1%. After 21 cycles, the specific capacity of reversible discharge can still reach 760.7 mg / g, showing excellent cyclic stability. In the preparation of LiFePO4 precursors, sol-gel and solvothermal methods were used in this paper. It was found that the LiFePO4/C samples prepared by solvothermal method had excellent micromorphology and electrochemical properties, and the reaction time, reaction temperature and carbon content were investigated in detail. The results show that the samples prepared at 130 鈩

本文编号：1870087