【作者】 陈晓燕；

【导师】 刘宾虹；

【作者基本信息】 浙江大学 ， 锂离子电池材料（专业学位）， 2014， 硕士

【摘要】 锂离子电池因其较高的能量密度和优异的性能受到广泛关注。随着中小型便携式电子产品以及电动汽车的高速发展,对低成本,高性能和高安全性的锂离子电池需求越来越大。传统的碳系负极材料由于比容量较低(372mAh-g-1),已经无法满足下一代新型锂离子电池对负极材料的要求。因此,开发出一种新型的比容量高、稳定性好、安全性好、成本低廉的负极材料显得尤为迫切。铁基氧化物Fe2O3, Fe3O4由于具有理论容量高,成本低廉、对环境友好等优点成为锂离子电池负极材料研究的关注焦点。但这些材料目前还存在着倍率放电性能差、循环寿命短等问题。一般情况下,材料的晶体结构、微观形貌及纳米尺寸等对其电化学性能均有重要的影响。所以本文开展了对铁基化合物纳米材料及其碳复合材料的制备、表征以及电化学性能研究,主要工作分为以下几部分：一.采用水热法制备LiFePO4/C正极材料。在反应中加入抗坏血酸调节晶粒的生长,制备出分散性良好的片状纳米材料,研究不同的水热温度与时间对LiFePO4纳米颗粒大小、形貌及其电化学性能的影响。185℃,10h为水热合成的最佳温度和时间,该条件下的LiFePO4/C样品的电化学性能最优。二.采用水热法制备α-Fe2O3纳米颗粒作为锂离子电池负极材料。通过改变反应物配比制备成棱锥状,中空球状等不同形貌的Fe2O3纳米颗粒,测试结果表明其电化学性能衰减严重,表面碳包覆后有所改善。增加电极涂片中乙炔黑的含量后,电化学性能明显提高,表明要改善Fe2O3负极材料循环寿命短的问题,还需要增加其碳包覆的含量。三.通过制备铁基干凝胶并将其热处理炭化得到Fe3O4与介孔碳的复合材料。比较不同铁含量,不同胶凝剂含量,不同溶剂配比对干凝胶形貌的影响,研究不同的热处理条件对得到的复合材料的形貌、比表面积及电化学性能的影响。研究表明600℃,4h热处理的P2-2X样品的电化学性能最优,这主要归功于形成了尺寸均匀的Fe3O4纳米颗粒在三维多孔碳基体中均匀分布这一理想的纳米结构。更多还原

【Abstract】 Lithium-ion batteries have attracted extensive interest due to high energy densities and excellent performance. With the rapid developments of portable electronics and electric vehicles, lithium-ion batteries with low-cost, high performance, and high safety are in great demand. Traditional carbon anode materials can not meet the requirements of the next generation lithium-ion battery due to a low capacity of372mAh-g-1. Consequently, developments of novel anode materials with higher capacity, high stability, high safety and low cost are particularly urgent.Because of their high theoretical capacity, low cost and environment friendly advantages, iron oxides Fe2O3, Fe3O4as anode materials of the lithium-ion battery are becoming the focus of attention. However, these materials are currently with some problems such as low rate capability and short cycle life. Composites of iron oxides and carbon with designed nanostructures are expected to enhance the electrochemical performance. In general, crystal structure, morphology and nanosize of composites have significant influences on their electrochemical properties. Therefore in this thesis, several iron-based compounds and their carbon composites were synthesized, characterized and electrochemically evaluated.1. Nano-plate LiFePO4as cathode materials was synthesized by hydrothermal method through adding ascorbic acid to inhibit particle’s growth. The reaction temperature and time of hydrothermal treatments on LiFePO4nanoparticles’ morphology and electrochemical performance were examined. The optimum hydrothermal conditions of180℃,10h were found to achieve the best electrochemical performance.2. Fe2O3nanoparticles as anode materials for lithium-ion batteries were prepared by the hydrothermal method. Different morphologies such as pyramid, porous spheres were achieved through the addition of surfactants such as EDTA. But the Fe2O3nanoparticles demonstated limited cycle life. The cycle performance was found to be sensitive to the ratio of acetylene black added in the anode. To improve the cycle life of Fe2O3anode materials, it is important to synthesize composites of oxides with carbon.3. The nanocomposites of Fe3O4and mesoporous carbon were synthesized by heating iron-based xerogels in N2. Varying the amounts of iron compounds, gelation agents and solvents affected the morphology of xerogels and resulting Fe3O4/C composites. The effects of heat treatment conditions on morphology, specific surface area and electrochemical properties are also examined. The results showed that the best electrochemical performance was achieved on the600℃,4h heat treated P2-2X sample, which is attributed to the favorable nanostructure in which Fe3O4nanoparticles dispersed homogeneously in the mesoporous carbon matrix.更多还原