原位生长FeS纳米结构薄膜及其在锂离子电池中的应用

发布时间：2018-07-01 12:26

本文选题：FeS微米片阵列 + 微米球　；参考：《浙江大学》2015年硕士论文

【摘要】：本文采用溶液法在铁基底上原位生长出四方硫铁矿型FeS微米片阵列和FeS微米球薄膜,并研究其电化学性能。利用单一变量法改变实验参数,研究Fe3+离子浓度、硫源和溶剂对FeS形貌结构的影响机制。通过对不同反应时间下合成产物的形貌和结构表征,探索FeS微米片阵列和FeS微米球的生长机制,并为其他金属硫化物的合成提供参考。分别将FeS微米片阵列和FeS微米球组装成锂离子半电池,并测其电化学性能,分析不同结构形貌对电极材料电化学性能的影响。另外,本文采用原位透射电子显微镜观察分析方法,研究FeS在充放电过程中的形变和相变机理,进一步分析形貌结构对电极材料可逆性优劣的影响。对于生长机理的研究中发现,溶液中Fe3+浓度大小对FeS的形貌没有影响,但是与片的密集程度有直接关系,Fe3+浓度越大,产物越密集；硫源种类对生长规则形貌和单一相产物具有关键作用,不同硫源释放S2-的速率不同,从而影响晶体生长速度,S2-释放速率越快,反应越不可控,越容易产生杂质相且形貌越不规则；乙二胺分子具有很强的协调能力和金属螯合力,生成FeS·mEDA后可作为模板控制晶体的定向生长,阻止片状自组装,使最终形成FeS片状阵列。故乙二胺是形成FeS片状阵列的关键。FeS生长过程为在反应初期,溶液中的Fe3+与铁基底反应,在铁基底表面形成Fe2+,然后与溶液中的S2-离子生成FeS在基底表面形核,晶核垂直基底生长成片状FeS晶体。最终,在不同的实验条件下得到不同形貌的FeS薄膜。将FeS纳米结构薄膜作为锂离子电池电极材料,并测其电化学性能。实验发现FeS微米片阵列电极表现出很好的储锂性能(首次放电容量为772 mAh g-1,循环20次后放电容量为697 mAh g-1),远远优于FeS微米球电极的储锂性能,研究表明电极材料的储锂性能与其结构形貌有关。FeS微米片阵列电极具有很好的电化学性能,原因有以下几点：微米片结构可以缩短Li+和电子的扩散长度并且具有较大的比表面；FeS微米片阵列是片相互交叉形成的网状结构,这种结构存在大量的空间,可以有效缓冲Li+脱嵌过程中带来的体积变化,抑制薄膜开裂和粉化；与传统的锂离子电池电极材料相比,在集流体上原位生长片状阵列的电极材料的方法,可以为电极材料和集流体提供很好的电接触和很强的结合力,这有利于电子和离子的传输,并大大简化了电池组装工艺。本文采用原位TEM分析方法,进一步研究FeS在充放电过程中的形变和相变机理。结果显示FeS纳米片电极在电化学循环过程中能保持很好的结构稳定性。在首次锂化过程中,体积仅为锂化前的129%,形变很小。经过三次循环后,纳米片体积为初始体积的112.6%,说明纳米片在电化学循环过程中形变量很小,且没有发生开裂和粉化现象,这主要是由于纳米片具有大的比表面和短的扩散长度,使反应均匀快速的进行,并且很好的解释了其循环稳定性能好的原因。其次,FeS纳米片电极在首次锂化过程中的相变是不可逆的,首次完全锂化后形成Li2S和Fe纳米晶,Fe纳米晶尺寸为2-3 nm,分散在Li2S中。首次完全退锂化形成Li1.13FeS2单一相,之后的循环则为Li2S/Fe的混合相与Li1.13FeS2单一相之间的相互转变。
[Abstract]:In this paper, a four square pyrite type FeS microchip array and a FeS microsphere film were grown on the iron base by solution method, and the electrochemical properties were studied. The influence mechanism of the Fe3+ ion concentration, the sulfur source and the solvent on the morphology of the FeS was studied by the single variable method. In appearance and structural characterization, the growth mechanism of FeS micron array and FeS microsphere is explored, and the reference for the synthesis of other metal sulfides is provided. The FeS micron array and FeS microspheres are assembled into lithium ion semi batteries, respectively, and their electrochemical properties are measured, and the effects of different structure morphology on the electrochemical properties of the electrode materials are analyzed. The deformation and phase transition mechanism of FeS during charge discharge were investigated by in-situ transmission electron microscopy, and the effect of morphology and structure on the reversibility of the electrode material was further analyzed. In the study of the growth mechanism, it was found that the concentration of Fe3+ in the solution had no effect on the morphology of FeS, but it was direct to the density of the film. The larger the concentration of Fe3+, the more dense the product is. The species of the sulfur source plays a key role in the growth rule and the single phase product. The rate of the release of S2- is different from the sulfur source, which affects the growth speed of the crystal. The faster the S2- release rate is, the more uncontrollable the reaction is, the more easily the hetero phase is produced and the more irregular the morphology is. The ethylenediamine molecule is very strong. Coordination ability and metal chelation force, after producing FeS. MEDA, can be used as a template to control the directional growth of crystal, prevent flaky self assembly, and eventually form a FeS sheet array. Therefore, ethylenediamine is the key.FeS growth process of forming a FeS flake array in the initial reaction, the reaction of Fe3+ in the solution with the iron substrate, and the formation of Fe2+ on the surface of the iron base, and then the.FeS The S2- ion in the solution generates FeS on the surface of the substrate, and the crystal nucleus grows into a slice like FeS crystal. Finally, the FeS thin films with different morphologies are obtained under different experimental conditions. The FeS nano structure film is used as the lithium ion battery electrode material and its electrochemical performance is measured. The experimental results show that the FeS micron array electrode has shown good performance. The lithium storage performance (the first discharge capacity is 772 mAh g-1, the discharge capacity is 697 mAh g-1 after 20 cycles), which is far superior to the FeS microsphere electrode's lithium storage performance. The study shows that the lithium storage properties of the electrode materials and their structure morphology related to the.FeS micron slice array electrode have good electrical properties. The reasons are the following several points: microchip structure can be used. It can shorten the diffusion length of Li+ and electrons and have a larger specific surface; FeS micron array is a network structure formed by intersecting pieces. This structure has a lot of space, which can effectively buffer the volume change brought by the process of Li+ deinterlay and inhibit the film cracking and pulverization. Compared with the traditional lithium ion battery electrode materials, The method of in situ growth of electrode materials in a flaky array can provide good electrical contact and strong binding force for the electrode material and the collection of fluids. This is beneficial to the transmission of electrons and ions and greatly simplifies the battery assembly process. In this paper, in situ TEM analysis method is used to further study the deformation and phase of FeS during the charge discharge process. The results show that the FeS nanoscale electrode can maintain a good structural stability during the electrochemical cycle. In the first lithium process, the volume is only 129% before lithium, and the deformation is very small. After three cycles, the volume of the nanoscale is 112.6% of the volume of the initial volume, indicating that the shape variables of the nanoscale are very small in the electrochemical cycle. The phenomenon of cracking and pulverization is mainly due to the large specific surface and short diffusion length of the nanoscale, which makes the reaction uniform and rapid, and explains well the reason for its good cycling stability. Secondly, the phase transition of the FeS nanoscale electrode in the first lithium process is irreversible, and the first complete lithium is Li2S and Fe after the first complete lithium-ion. Nanocrystalline, Fe nanocrystalline size is 2-3 nm, dispersed in Li2S. The first complete lithialization to form a single phase of Li1.13FeS2, and the subsequent cycle is the transformation between the Li2S/Fe mixture and the Li1.13FeS2 single phase.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2;TM912

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