【作者】 李迪；

【导师】 蒋凯；

【作者基本信息】 华中科技大学 ， 新能源科学与工程， 2016， 硕士

【摘要】 随着常规能源的有限性以及环境问题的日益突出,以环保和可再生为特质的新能源的发展越来越受到各国的重视。以锂离子电池为代表的电化学储能最有希望解决新能源发电技术中的储能问题。近年来,电动汽车市场发展迅猛,而拥有高能量及功率密度的锂离子电池倍受青睐,成为新能源汽车储能环节的首选技术。以上引起了锂离子电池在全球范围内的研究热潮。锂离子电池研究的关键在于电极材料,拥有理论容量高、成本低廉、环境友好、安全可靠等诸多优点的过渡金属化合物受到了研究者的广泛青睐。但过渡金属化合物做锂离子电池负极材料时也有一些缺陷需要克服,如导电性不好,嵌锂脱锂过程中材料容易发生体积变化,进而导致结构坍塌,严重降低锂离子电池的电化学性能。解决这些问题的途径主要有两种,一种是改变材料的微观形貌,另一种是与碳基材料复合。本文将结合这两种途径通过多种方法改善铁基氧化物、锰基氧化物及二硫化钼的电化学性能。主要内容如下:通过使用“原位”固相还原法合成Fe3O4/FeO/Fe/C复合物。用葡萄糖做碳源,和纳米级Fe2O3粉末混合充当前躯体,并在不同温度下反应。将反应产物用XRD、XPS、SEM、TG等成分及形貌测试方法进行测试分析,发现在700°C温度下合成的材料成分为Fe3O4、FeO、少量Fe和无定形碳,其中各组分之间接触紧密,碳均匀地包覆在颗粒周围并形成了整个材料的基底,能够在充放电过程中缓冲氧化物颗粒的体积变化。对这个Fe3O4/FeO/Fe/C复合物进行电化学测试后发现,其作为负极材料在0.1 A g-1电流下可逆容量达到1400 mAh g-1,在1 A g-1电流下循环500圈仍保留900 mAh g-1的可逆容量,表现出了出色的循环稳定性和倍率性能。其中,材料中少量的单质Fe可显著提高材料的导电性,对材料电化学性能的改善起到至关重要的作用。再次运用“原位”固相还原法在锰基氧化物上使用,将MnO2和葡萄糖作为前躯体进行不同温度下的热处理。将样品进行XRD、SEM等测试,对比分析反应温度对材料成分及电化学性能的影响。用各组样品制备锂离子电池并进行测试,发现在800°C下制备出的MnO/C复合物有非常优异的电化学性能,该样品在1 A g-1的大电流充放电下从第50圈到第500圈容量持续增加,在第500圈时得到845 mAh g-1的可逆容量,表现出了出色的循环稳定性和倍率性能。将水热法与CVD法相结合,在用CVD法生成的三维泡沫石墨烯(GF)上水热沉积MoS2,制备出MoS2@GF复合材料。通过调整水热反应时间控制MoS2的载量,发现在180°C下反应24 h可得到载量为1:1的MoS2@GF样品。此样品可以直接作为Binder-free的电极材料进行电池的封装,省去了粘结剂、导电剂等添加剂,简化了电池制备过程。将MoS2@GF复合物作为锂离子电池负极材料进行电化学测试后发现,在100 mA g-1充放电电流下样品可以获得接近900 mAh g-1的可逆容量,且在50圈以内几乎没有容量衰减,表现出了稳定的循环性能和出色的倍率性能。通过对比分析可以看出,MoS2@GF复合物集合了MoS2与GF双方的优点,其中MoS2本身就具有较高的理论容量,而GF显著提高了复合物的导电性,弥补了MoS2在这一方面的不足。更多还原

【Abstract】 With the limition of conventional energy sources and increasingly prominent environmental problems, more and more attention is paid to the development of environmental protection and renewable new energy sources by many nations. Lithium ion batteries, as the representative of an electrochemical energy storage, is the most promising new energy technologies to solve the energy storage problems in new energy power generation. In recent years, with the booming of electric automobile market, lithium ion battery, which has high energy and power density, is acclaimed as the preferred technology in new energy automotive sectors energy storage. These attract research boom about lithiumion batteries worldwide. The key of the lithium-ion battery research is electrode materials. Transition metal compound, which owns a high theoretical capacity, low cost, ecofriendliness, natural abundant, safety and many other advantages, has been widely investigated by researchers. However, there are also some drawbacks of transition metal compound to be overcome when acting as anode material for lithium-ion battery, such as poor electrical conductivity, huge volume change during lithium ion insertion/extraction, which lead to pulverization of the initial particle morphology and breakdown of electrical connection of such anode materials from current collectors, seriously hindered the direct use of raw Fe3O4 material in commercial batteries. Two main strategies are commonly used to solve these problems. One is to synthesis nanostructured materials with various morphologies. The other one is to incorporate with carbonaceous materials. In this article the electrochemical properties of iron-based oxide, manganese oxide and molybdenum disulfide group will be improved through a variety of methods related to these two strategies. The main contents are as follows:Fe3O4/FeO/Fe nanoparticles coated with amorphous carbon is prepared via a facile and scalable in situ-reduction solid synthesis route. Glucose is prepared as carbon source. it is mixed with nanosized Fe2O3 powder as precursor, then heated at different temperatures. The reaction products are tested by XRD, XPS, SEM, TG and other testing methods. It is found that, the sample synthesized under 700 °C is Fe3O4, FeO, a small amount of Fe and amorphous carbon. What’s more, the components are closely contacted and the carbon can form the substrate throughout the material by coating the particles uniformly, which can buffer the volume change during charge and discharge. When used as anode materials in lithium ion batteries, the as-prepared Fe3O4/FeO/Fe/Carbon composite shows super high rate capability(685, 543, and 401 mAh/g at 2, 5, and 10 C, respectively, 1 C = 1 A/g) and extremely excellent cycling performance at high rates(capacity remains 900 mAh/g after 500 cycles at 1 C). It proves that the composite has excellent cycling stability and rate capability. Wherein a small amount of elemental Fe in the material can significantly improve electrical conductivity of the material, and it plays a crucial role to improve the electrochemical properties.By using in situ-reduction solid synthesis route on another transition metal compound material, manganese-based oxide, samples are synthesized by adding MnO2 and glucose powders as precursors at different temperatures. XRD and SEM tests are performed, followed by the comparison and analysis of how reaction temperature affects the composition and electrochemical properties are made. Electrochemical tests of each group of samples are performed. It is found that that MnO/C composite synthesized at 800 °C has an excellent electrochemical performances. The reversible capacity of this sample continues to increase from 50 th cycle to 500 th cycle in a current as high as 1 A g-1, and reaches 845 mAh g-1 at 500 th cycle, showing excellent cycling stability and rate performance.Hydrothermal method and CVD are combined in this part. MoS2@GF sample is synthesized by depositing MoS2 on the three-dimensional graphene foam(GF) generated using CVD method. By adjusting the duration of hydrothermal reaction process, the deposition amount of MoS2 can be controlled. The 180 °C sample can be used directly as a Binder-free electrode material, getting rid of the need for binder and conductive agent, simplifing the fabrication process of battery. When used as anode material for lithium ion battery, MoS2@GF composite obtains a reversible capacity of 900 mAh g-1, showing a stable cycle performance and excellent rate capability. Through the comparison and analysis of different samples, it can be seen that MoS2@GF composite combines the advantages of both GF and MoS2, among which MoS2 has a high theoretical capacity, while GF can significantly improve the conductivity of composites.更多还原