炭包覆高容量负极材料的设计合成及性能研究

发布时间：2018-03-12 12:26

本文选题：储能　切入点：锂离子电池　出处：《大连理工大学》2017年博士论文　论文类型：学位论文

【摘要】：随着新能源产业的不断发展,发展具有长循环稳定性、高可逆容量、良好的安全性能和快速充放电能力的储能材料,是世界能源发展趋势,符合我国能源战略需求,成为研究者关注的热点。金属基纳米材料在储能领域扮演重要角色,特别是在锂离子电池负极材料应用方面,其微观结构决定了其储锂性能。面临的共性问题是循环过程中体积变化大,容量衰减严重,特别是过渡金属氧化物材料存在电子导电率低的问题。炭材料具有高的电子导电性,结构形貌可控,表面化学性质可调且环境友好,将炭材料与金属基纳米材料进行复合能有效改善锂离子电池负极材料的性能。本论文以高容量负极材料的结构设计合成为目标,旨在提高炭材料与活性组分的紧密接触,并结合氮掺杂和创造多孔结构,发展了三种炭包覆负极材料的有效新方法,构筑了一系列具有新颖结构的炭包覆纳米复合材料,并将其应用于锂离子电池,显示出高的可逆容量、循环稳定性和倍率性能。在此基础上,系统研究了炭包覆纳米复合材料的结构特点对其电化学性能的影响。具体包括如下几个方面:(1)以纳米二元金属氧化物(ZnSnO_3)和2-甲基咪唑为前驱体靶向生长金属有机骨架ZIF-8制备了三维连续的氮掺杂炭包覆高含量(82.3 wt%)纳米锡材料。根据软硬酸碱理论,2-甲基咪唑作为交界碱优先与交界酸Zn~(2+)结合生成ZIF-8包覆层,将高分散锡的氧化物引入ZIF-8网络中。后续的热解使ZIF-8转变为含有丰富氮元素(5.3wt%)的高导电连通的炭包覆网络,同时,锡的氧化物炭热还原为Sn纳米粒子,被还原的低沸点的Zn在后续的热解过程中挥发并产生丰富且开放的孔道结构,实现离子和电子的快速高效传输。锂离子电池测试结果表明,Sn/C复合材料在0.2 A g~(-1)电流密度下首次放电容量为1321mAhg~(-1),库伦效率高达80.1%。在0.2和1Ag~(-1)下分别循环150次后可逆容量可保持为901和690 mA hg~(-1)。此外,这种方法还可以扩展到氮掺杂炭包覆氧化锰复合材料的合成,同样展现出优异的电化学性能。(2)从生物质出发,利用真菌木耳自身特有的可溶胀特性和多细胞网格结构吸附Mn~(2+)溶液构筑了三维高度交联的MnO@C纳米片网络结构。木耳细胞壁主要成分几丁质中富含羟基官能团,利用其与金属离子的络合作用将MnO纳米粒子原位生成并固载于连通的炭纳米片中,有效防止颗粒聚集长大。此外木耳细胞壁中的几丁质在通过后续干燥收缩和高温热解,可以转变为连续的氮掺杂炭导电包覆层,提高复合材料的导电性和结构稳定性。这种纳米片网络结构不仅可以减小离子扩散路径,还能有效缓冲MnO在充放电过程中的体积变化。电化学测试结果表明,采用此方法合成的MnO@C复合材料在0.2 A g~(-1)电流密度下循环300次可逆容量为868 mAh g~(-1),在1 A g~(-1)下循环500次可逆容量为668 mAh g~(-1),证明其具有高的可逆容量和优异的循环稳定性。此外,这种可持续绿色的合成方法易于规模化且为高性能纳米片网络结构的设计合成提供了新的思路。(3)采用聚多巴胺包覆的过渡金属碳酸盐晶体在自身生成的弱氧化气氛中限域热解的方法构筑炭包覆过渡金属氧化物介孔微纳结构。以聚多巴胺包覆的MnCO_3晶体为例,热解使外部的包覆层转变为导电炭保护壳,同时MnCO_3晶体在自身生成的CO_2气体压力推动下爆裂为超小的纳米MnO。原位生成的CO_2不仅作为造孔剂分别在材料内部产生由内而外贯通的介孔和在炭包覆层形成丰富的微孔,其还可以为过渡金属氧化物的形成提供一个弱的氧化性气氛,有效中和聚多巴胺热解过程中产生的还原性气氛,防止金属相生成。采用这种方法分别制备了具有介孔微纳结构的炭包覆氧化锰、氧化钴和氧化铁材料。MnO@C复合材料在0.2和2 A g~(-1)电流密度下分别循环200和300次可逆容量高达886和770 mA h g~(-1),炭包覆氧化钴和氧化铁材料在0.2 A g~(-1)电流密度下可逆容量分别可达1058和770mAhg~(-1),同时具有良好的循环稳定性。这种合成方法可以同时实现炭包覆核壳结构、贯通的介孔结构和微纳结构的多级结构优势,有效缓冲过渡金属氧化物在充放电过程中的体积膨胀,从而提高循环稳定性。
[Abstract]:With the continuous development of new energy industry development, has long cycle stability, high reversible capacity, good safety performance and fast charging and discharging capacity of the energy storage material is the development trend of world energy demand, in line with China's national energy strategy, become the focus of attention of researchers. Kinami metal materials in the field of energy storage plays an important role, especially in the application of lithium ion battery anode material, the microstructure determines its lithium storage performance. Facing common problems is the volume cycle changes, the capacity of serious decay, especially transition metal oxide materials have low electronic conductivity. Carbon materials with high electronic conductivity structure, controllable morphology, surface the chemical properties of adjustable and environmentally friendly, carbon materials and metal based nano composite materials can effectively improve the performance of anode materials for lithium ion batteries. In this paper, high capacity anode The structure of the material design and synthesis as the goal, to improve the close contact of carbon materials and active components, combined with nitrogen doped porous structure and the creation of new and effective methods, development of three kinds of carbon coated anode materials, construct a series of novel structured carbon coated nano composite material and its application in lithium ion the battery shows high reversible capacity, cycle stability and rate performance. On this basis, influence the structural characteristics of the system of carbon coated nano composite material on its electrochemical performance. Specifically including the following aspects: (1) to two yuan of nano metal oxide (ZnSnO_3) and 2- methyl imidazole as the precursor target to the growth of metal organic frameworks ZIF-8 prepared N-doped carbon coated three-dimensional continuous high content (82.3 wt%) nano tin material. According to the HSAB theory, 2- methyl imidazole as base junction priority and border acid (2+) combined with Zn~ Generation of ZIF-8 coating, the highly dispersed tin oxide is introduced into the ZIF-8 network. The subsequent pyrolysis ZIF-8 change rich nitrogen (5.3wt%) high conductive carbon coated connected network, at the same time, reduction of carbon oxides for Sn Hot Tin nanoparticles, the reduction of the low boiling point Zn volatilization in subsequent pyrolysis process the pore structure and generate rich and open, efficient transport of ions and electrons. Lithium ion battery test results show that the Sn/C composite materials in 0.2 A g~ (-1) current density discharge capacity of 1321mAhg~ (-1), Kulun's efficiency is as high as 80.1%. in 0.2 and 1Ag~ (-1) respectively under 150 cycles after the reversible capacity can maintain for 901 and 690 mA hg~ (-1). In addition, this method can also be extended to the synthesis of nitrogen doped carbon coated manganese oxide composite material, also exhibited excellent electrochemical performance. (2) starting from the raw material, the use of wood fungi The unique ear swelling characteristics and multicellular grid structure for adsorption of Mn~ (2+) solution to build a three-dimensional net structure of nano MnO@C highly cross-linked. Rich in hydroxyl groups of main components of fungus cell wall chitin, the complexation of metal ions and MnO nanoparticles in situ and immobilized on carbon nano sheet connected in, effectively prevent the nanoparticles from agglomeration. In addition of chitin in the cell wall of the fungus in the subsequent drying shrinkage and pyrolysis can be transformed into continuous nitrogen doped carbon conductive coating layer, improve the conductivity and stability of composite structure. The nano network structure can not only reduce the ion diffusion path, can effectively buffer the volume change in MnO the charge and discharge process. The electrochemical test results show that the MnO@C composite material of this synthesis method in 0.2 A g~ (-1) at a current density of 300 cycles can be The inverse capacity of 868 mAh g~ (-1), 1 A g~ (-1) 500 cycles the reversible capacity of 668 mAh g~ (-1), has proved its high reversible capacity and excellent cycle stability. In addition, the sustainable green synthesis method is easy to scale and high performance nano network node design the synthesis structure provides a new way of thinking. (3) by using the method of domain limit weak oxidizing atmosphere pyrolysis of transition metal carbonate crystal polydopamine coated in self generated structure in carbon coated mesoporous transition metal oxides micro nano structure. Polydopamine coated with MnCO_3 crystal as an example, the pyrolysis coating layer for an external change conductive carbon shell, and MnCO_3 crystal nano MnO. burst in-situ ultra small CO_2 gas pressure in its generation under the impetus of CO_2 not only as a pore forming agent in mesoporous material to produce from the inside through the cladding and carbon in shape A rich micropores, a weak oxidizing atmosphere which can also transition metal oxides, reducing atmosphere and effective poly dopamine producing in the process of pyrolysis, prevent metal phase formation. Were prepared with mesoporous nano structured carbon coated manganese oxide by using this method, cobalt oxide and iron oxide.MnO@C composite at 0.2 and 2 A g~ (-1) current density respectively 200 and 300 times circulation reversible capacity as high as 886 and 770 mA h g~ (-1), carbon coated cobalt oxide and iron oxide materials in 0.2 A g~ (-1) current density under the reversible capacity is respectively 1058 and 770mAhg~ (-1). At the same time has a good cycle stability. This method can also achieve the carbon coated core-shell structure, mesoporous structure and micro nano structure through a multi-level structure of advantage, effectively buffer the transition metal oxide in the process of charging and discharging volume expansion, thereby improving High cycle stability.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912;TB383.1

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