金属氧（硫）纳米结构的构筑及电化学性能研究

发布时间：2018-05-20 22:39

本文选题：锂离子电池 + 负极材料　；参考：《青岛科技大学》2017年硕士论文

【摘要】：锂离子电池因其具有能量密度高、循环寿命长和对环境友好等优点,被认为是最具发展前景的电能存储技术之一。目前商业化锂离子电池中普遍采用石墨类型的碳负极材料,但其理论容量低、能量密度小、安全隐患多等缺点已不能满足人们对高性能、氋安全性的锂离子电池的需求。因此,研究和开发新型的、具有高性能表现的锂离子电池负极材料具有极其重要的现实意义。过渡金属氧(硫)化物在众多备选材料中具有理论容量高、资源丰富、环境友好、安全性高等优点得到了广泛关注。然而它们也存在着导电性差、首次库伦效率低和充放电过程中体积变化大导致循环稳定性差的问题。此外,以二硫化钼为代表的过渡金属硫化物表现出了优异的电催化析氢性能。但二硫化钼的催化活性位点数量较少且是一种半导体材料,导电性较差,因此与铂族贵金属相比性能仍有很大差距。石墨烯具有电子迁移率高、比表面积大、柔韧性好等独特的性质,在纳米电子器件、电化学储能和能源转换等领域具有广泛的应用。本论文针对过渡金属氧(硫)化物的特点和存在的缺陷,结合石墨烯材料的优点,分别从材料纳米化、电极结构、形貌调控等方面对其进行了研究以提高其电化学储锂和电催化析氢性能,具体的研究工作如下:1.首次设计并制备了夹层石墨烯纸@Fe_3O_4纳米棒阵列@石墨烯(GPFG)复合材料,作为高性能锂离子电池的集成电极。Fe_3O_4纳米棒阵列直接生长在导电的石墨烯纸上,确保了快速反应动力学与高可逆性。石墨烯包覆层不仅加速电子转移,还可以缓冲体积变化。因此,电极表现出相当大而稳定的储锂容量,良好的倍率性能和长久的循环寿命。遗憾的是,石墨烯包覆层只是物理沉积在纳米阵列表面,机械稳定性较脆弱,在电极充放电过程中容易破碎。在此基础上,又利用碳膜作为包覆层来制备新颖的夹心状石墨烯纸@Fe_3O_4纳米棒阵列@碳(GFC)自支撑电极。碳膜是通过沉积的聚苯胺(PANI)薄膜原位转化得到,因而具有良好的机械稳定性,可很好地包裹纳米棒阵列并有效抑制破碎的纳米棒进入电解液。正是由于此种独特的复合结构,此类具有内部阵列结构的夹心状电极展现出出色的电化学储锂性能,尤其是在高电流密度(在2 A g-1循环1000圈后852 mA g-1)下有着高容量,稳定,持久的循环性能,使其有望作为一种高性能集成电极。2.利用多面体CoSn(OH)_6作为前驱体,构造了石墨烯包裹SnO_2-Co_3O_4立方体(G/SnO_2-Co_3O_4)的柔性集成电极,并用于锂离子电池。复合电极组分的合理选择,材料独特的多面体纳米结构和适当的复合材料构建方法成功产生了协同储锂效应,实现了SnO_2和石墨烯界面储锂的部分可逆转换,使电极在100 mA g-1下循环100圈后可逆容量仍高达1665 mAh g-1。在1 A g-1大电流密度下,电极依然保持高容量、稳定的循环性能和长效的循环寿命(循环1000圈后容量为1208 mAh g-1)。更重要的是,本实验制备的自支撑电极在反复300次电化学循环后能很好地保持它的柔韧性,这使其有望作为高效而又稳定的柔性锂离子电池电极材料之一。3.利用蒸发诱导自组装的方法首次合成了用作锂离子电池负极材料的介孔正八面体Fe Co_2O_4。尖晶石型混合过渡金属氧化物中部分金属被替代可以提高其储锂性能。各向异性的正八面体结构可以保持结构的稳定性,提高循环性能。介孔结构能够缩短电荷传输路径,促进电解液的流动和浸润,提供更多的表面积吸附锂离子,还可以提供更多空间缓冲体积变化。拥有多组分的协同效应,稳定的正八面体结构和介孔结构,使得样品表现出良好的电化学性能,包括高容量,快速充放电和稳定的循环性能(1 A g-1循环200圈后为1101 mAh g-1),以及曾报道的Fe Co_2O_4最好的倍率性能(在10 A g-1下为518 m Ah g-1)。4.通过水热法合理设计并成功制备了石墨烯量子点掺杂的MoS_2纳米片(GQDs/MoS_2),并利用XRD,SEM,TEM和拉曼技术等对其结构进行表征。掺杂GQDs扩大了MoS_2的层间距,加速电化学动力学,并缓冲体积效应,有助于同时增强MoS_2在结构和组成上的优势,提高储锂性能。当作为一种锂离子电池负极材料时,GQDs/MoS_2表现出高容量、良好的循环性能和倍率性能。掺杂到MoS_2中的GQDs在纳米片边缘和基底平面形成大量缺陷,这是其提高催化活性和电导率的关键因素。正因为如此,样品对电化学析氢反应的催化性能有着显著提高,其中包括较大的阴极电流(在200 mV的低过电位时为10 mA cm-2和在300mV的低过电位时为74 mA cm-2)和较低的起始电位(140 mV)。
[Abstract]:Lithium ion batteries are considered to be one of the most promising energy storage technologies because of their high energy density, long cycle life and friendly environment. At present, graphite type carbon negative materials are widely used in commercial lithium ion batteries, but their shortcomings such as low theoretical capacity, small energy density and many hidden dangers are not satisfied. Therefore, it is of great practical significance to study and develop a new type of lithium ion battery anode material with high performance. The transition metal oxygen (sulfur) compounds have the advantages of high theoretical capacity, rich resources, friendly environment and high safety in many alternative materials. There is a wide range of concerns. However, they also have poor conductivity, the first Kulun low efficiency and the large volume change in the charge discharge process lead to poor circulation stability. In addition, the transition metal sulfide represented by molybdenum disulfide shows excellent electrocatalytic hydrogen evolution performance. But the number of catalytic active sites of two molybdenum sulfide is less and is less than that of molybdenum sulfide. A semiconductor material has poor conductivity, so there is still a big gap in performance compared with platinum group precious metals. Graphene has a unique property, such as high electron mobility, large specific surface area, good flexibility and so on. It is widely used in the fields of nanoscale electronic devices, electrochemical energy storage and energy conversion. The characteristics and existing defects, combined with the advantages of graphene materials, have been studied in terms of material nanoscale, electrode structure, morphology control, etc. to improve their electrochemical lithium storage and electrocatalytic hydrogen evolution performance. The specific research work is as follows: 1. the first design and preparation of sandwich graphene @Fe_3O_4 nanorod array @ graphene (GP) FG) composites, as an integrated electrode.Fe_3O_4 nanorod array of high performance lithium ion batteries, grow directly on the conductive graphene paper, which ensures fast reaction kinetics and high reversibility. The graphene coating not only accelerates electron transfer, but also can buffer volume change. Therefore, the electrode shows considerable and stable lithium storage capacity. It is regrettable that the graphene coating is only physically deposited on the surface of nanowire arrays, and the mechanical stability is fragile and easily broken during the charge discharge process of the electrode. On this basis, the carbon film is used as a coating to prepare a novel sandwich like graphene paper @Fe_3O_4 nanorod array @ carbon (GFC). Self supporting electrode. The carbon film is obtained by in situ transformation of the deposited polyaniline (PANI) film, thus having good mechanical stability. It can well wrap the nanorod array and effectively suppress the broken nanorods into the electrolyte. It is because of this unique composite structure that the sandwich electrodes with internal array structure show out. The electrochemical lithium-ion storage properties of color, especially at high current density (2 A g-1 cycle 1000 cycles after 852 mA g-1), have high capacity, stable and lasting cycling performance, which makes it promising to use polyhedral CoSn (OH) _6 as a precursor for a high performance integrated electrode.2., and to construct the soft of a graphene wrapped SnO_2-Co_3O_4 cube (G/SnO_2-Co_3O_4). The rational selection of the lithium ion battery, the rational selection of the composition of the composite electrode, the unique polyhedron nanostructure and the appropriate composite material construction method successfully produced the synergistic lithium storage effect, and realized the partial reversible conversion of the SnO_2 and Shi Moxi interface lithium storage, and the reversible capacity of the electric pole was still high after 100 cycles under 100 mA g-1. At the high current density of 1665 mAh g-1. at 1 A g-1, the electrode remains high capacity, stable cycle performance and long effective cycle life (1208 mAh g-1 after 1000 cycles). More importantly, the self supporting electrode prepared in this experiment can maintain its flexibility well after repeated 300 cycles of electrochemical cycle, which makes it expected to be high. One of the effective and stable flexible lithium ion battery electrode materials.3. first synthesized the mesoporous positive eight surface body Fe Co_2O_4. spinel mixed transition metal oxide used as the anode material for lithium ion batteries by the method of evaporation induced self assembly. The replacement of the partial metals in the mixed transition metal oxide of the spinel type of the mesoporous Fe Co_2O_4. can improve the lithium storage property. The structure can maintain the stability of the structure and improve the cycle performance. The mesoporous structure can shorten the charge transmission path, promote the flow and infiltration of the electrolyte, provide more surface area for the adsorption of lithium ion, and provide more space buffer volume. The product showed good electrochemical properties, including high capacity, rapid charge discharge and stable cycling performance (1 A g-1 cycle 200 cycles after 1101 mAh g-1), and the best ratio performance of Fe Co_2O_4 (518 m Ah g-1 under 10 A g-1), which was reasonably set up by hydrothermal method and successfully prepared the graphene quantum dots doped nanoparticle. XRD, GQDs/MoS_2, SEM, TEM and Raman techniques are used to characterize the structure. Doping GQDs expands the spacing of MoS_2, accelerates the electrochemical kinetics, and buffers the volume effect. It helps to enhance the advantages of MoS_2 in the structure and composition and improve the lithium storage energy. As a negative material for lithium ion batteries, GQDs/MoS_2 table High capacity, good cycling performance and multiplying performance. The GQDs doped into MoS_2 forms a large number of defects in the edge and base plane of the nanoscale, which is the key factor to improve the catalytic activity and electrical conductivity. At a low overpotential of 200 mV, it was 10 mA cm-2 and 74 mA cm-2 at low overpotential of 300mV and a low initial potential (140 mV).
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1;TM912

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