钼掺杂炭气凝胶正极材料制备及其锂硫电池性能的研究

发布时间：2018-05-17 06:04

本文选题：锂硫电池 + 炭气凝胶　；参考：《合肥工业大学》2017年硕士论文

【摘要】：单质硫作为锂硫电池的电极材料具有很高的理论容量(1675 mAh·g-1)和能量密度(2600 Wh·kg-1),并且资源丰富、价廉、无毒等优势,锂硫电池成了广泛关注的热点。但硫单质本质属性也给锂硫电池的发展带来一些挑战。比如单质硫的绝缘性,多硫离子中间产物的溶解性导致的穿梭效应等问题。为了解决相关问题,从碳材料的制备入手,形成特定的同轴电缆结构的炭气凝胶(CNCA),采用钼氧化物和钼硫化物的原位掺杂进行材料改性。在此基础上采用与硫单质复合形成锂硫电池的正极。论文工作中采用X射线衍分析,X射线电子能谱分析,场发射扫描电镜分析,场发射透射电镜分析,氮气吸脱附分析等多种现代结构分析方法,对材料的组成、形貌、元素价态、孔结构、吸附能力等进行测试和表征,获得材料结构特征和丰富信息。同时采用恒流充放电、循环伏安和交流阻抗等电化学方法进行测试,获得的碳硫及其掺杂材料电化学性能。结合对材料结构表征和电化学测试,对碳硫复合材料的结构与电化学性能间的关系进行了深入的研究。基于碳纳米管(CNT)引导所制备的炭气凝胶,具有互连特征,呈现出同轴电缆3维网状结构。金属钼化物掺杂的炭气凝胶具有优良的导电性、较高的比表面积和孔容,同时呈现出对硫和多硫化物的有效的固定和吸附作用,可以抑制多硫化物溶解于电解液,有效提高电极材料的循环寿命。结果研究表明,所制得的同轴电缆结构的炭气凝胶作为锂硫电池的正极,具有良好的电化学性能,不仅具有较高的初始容量,而且具有优异的循环性能和优良的倍率性能,同时呈现低的阻抗值。MoS2修饰的同轴电缆3维网状结构炭气凝胶(MoS2-n/CNCA)对多硫化物具有良好的锚牵作用,再加上较高的比表面积、孔容量和导电性能,作为电极材料具有良好的循环稳定性、较高的放电容量、优异的高倍率性能。其中MoS2-8/CNCA/S的在0.2C条件下初始放电容量为1384mAh·g-1,200圈后的容量保持率为83%;在5C条件下的放电容量也高达723 mAh·g-1。以MoO2纳米颗粒均匀的镶嵌在具有同轴电缆3维网状结构碳材料的管壳上制得的MOO2-n/CNCA,具有良好的导电性能和对多硫化物的牵引作用,使MOO2-n/CNCA/S电极材料具有良好的电化学性能,其中M0O2-6/CNCA/S在0.2C条件下初始放电容量为1308 mAh·g-1,200圈后的容量保持率为80%;在5C条件下的放电容量也高达为686 mAh·g-1;以此表现出优异的电化学性能。
[Abstract]:As the electrode material of lithium sulfur battery with high theoretical capacity (1675 mAh g-1) and energy density of 2600 Wh 路kg -1, simple sulfur has many advantages, such as abundant resources, low price and non-toxicity, so the lithium sulfur battery has become the focus of attention. However, the essential properties of sulfur also bring some challenges to the development of lithium-sulfur batteries. Such as the insulation of elemental sulfur, the solubility of polysulfide intermediate products caused by the shuttle effect and so on. In order to solve the related problems, the carbon aerogel CNCA (carbon aerogel) with specific coaxial cable structure was formed from the preparation of carbon materials and modified by in-situ doping of molybdenum oxides and molybdenum sulfides. On this basis, the lithium-sulfur battery cathode was formed by combining with sulfur. In this paper, X-ray diffraction analysis, field emission scanning electron microscopy, field emission transmission electron microscopy, nitrogen absorption and desorption analysis were used to analyze the composition, morphology and valence of elements. The pore structure and adsorption capacity were measured and characterized to obtain the material structure characteristics and abundant information. At the same time, constant current charge and discharge, cyclic voltammetry and AC impedance were used to test the electrochemical properties of carbon and sulfur and their doped materials. The relationship between the structure and electrochemical properties of carbon and sulfur composites was studied by means of structural characterization and electrochemical test. Carbon aerogels based on carbon nanotube (CNT) guidance have interconnect characteristics and present a three dimensional network structure of coaxial cable. Carbon aerogels doped with molybdenum metal have excellent conductivity, high specific surface area and pore volume, and exhibit effective fixation and adsorption to sulfur and polysulfide, which can inhibit the dissolution of polysulfide in electrolyte. Effectively improve the cycle life of electrode materials. The results show that the carbon aerogel with coaxial cable structure has good electrochemical performance, not only has high initial capacity, but also has excellent cycling performance and excellent rate performance as the cathode of lithium-sulfur battery. At the same time, MoS2 modified coaxial cable with low impedance value. MoS2 modified carbon aerogel MoS2-n / CNCA has good anchoring effect on polysulfide, plus high specific surface area, pore capacity and conductivity. As an electrode material, it has good cycling stability, high discharge capacity and excellent performance of high rate. The initial discharge capacity of MoS2-8/CNCA/S is 83 after 1384mAh g-1200 cycles at 0.2C, and the discharge capacity at 5C is as high as 723 mAh g-1. MOO2-n / CNCA, which is made of MoO2 nanoparticles uniformly embedded on the tube and shell of carbon material with three dimensional network structure of coaxial cable, has good electrical conductivity and traction to polysulfide, which makes the MOO2-n/CNCA/S electrode material have good electrochemical performance. The initial discharge capacity of M0O2-6/CNCA/S at 0.2C was 1308 mAh g-1200 cycles and the discharge capacity at 5C was as high as 686 mAh g-1, which showed excellent electrochemical performance.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ427.26;TM912

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