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题名: 石墨烯复合一维二氧化钛纳米材料的合成、表征和电化学嵌锂性能
作者: 侯娟
答辩日期: 2013-05-27
导师: 常爱民
专业: 微电子学与固体电子学
授予单位: 中国科学院大学
授予地点: 北京
学位: 博士
关键词: 锂离子电池 ; 一维二氧化钛纳米材料 ; 石墨烯复合材料 ; 电化学性能 ; 浓碱水热法
摘要:

一维纳米结构的二氧化钛作为锂离子电池负极材料具有较高的理论比容量(335mAhg-1),安全性能好,Li+嵌脱过程中结构变化小(4%),循环性能好,环境友好等优点,还具有因高度异向的几何形状及尺寸所限制的独特性质,因而逐渐成为锂离子电池新型负极材料研究的热点。但单纯的二氧化钛由于较低的电导率和较差的导锂能力,限制了其在锂离子的电池方面实际应用的进一步发展。具有良好电子导电特性、高比表面积和卓越机械强度的石墨烯与一维二氧化钛纳米材料的复合有望实现二者优势的协同作用,使电极材料具有良好的电化学性能。本论文的研究内容主要集中在石墨烯与一维二氧化钛纳米材料复合物为研究目标,将二氧化钛电极材料纳米化,形成一维纳米管或纳米线的特殊微观结构,提高Li+的存储能力,缩短Li+的输运距离,改善二氧化钛材料的电化学性能。以二维石墨烯作为优良的柔性基底,与一维二氧化钛纳米材料复合,构建石墨烯复合一维二氧化钛纳米复合材料。高导电性的石墨烯的引入可增强电子电导,导致高的嵌锂容量和良好的循环稳定性。论文对复合电极材料的制备工艺、表征及其电化学嵌锂性能做了系统的研究。1、利用TG-DSCXRDTEMN2吸附-脱附分析及恒电流充放电测试等方法研究了一维二氧化钛纳米管负极材料的浓碱水热合成工艺。通过分析合成过程中钛源、水热反应温度、后期焙烧温度等工艺参数对材料结构、形貌及电化学性能的影响,确定了合成一维的TiO2纳米管较佳的工艺条件。2、采用Hummers方法合成了褶皱状的氧化石墨,经超声剥离后得到氧化石墨烯,再通过10M NaOH溶液水热处理获得具有褶皱和半透明薄纱层状的完整的单层或少层结构的还原石墨烯(rG),作为合成复合材料的基底。XRD结果表明经浓碱水热还原后,氧化石墨在2θ=11.3°的衍射峰消失,而rG2θ=24.9°43.2°的衍射峰再次表明得到的rG大部分为几个单片层叠加的少层结构,由于GO表面含氧基团的还原脱去导致rG层间距的明显减小。XPS结果分析表明氧化石墨表面上大量的C-OC=OO=C-O 等含氧基团被大部分去除,说明采用浓碱水热法可以很好的实现氧化石墨的还原剥离。 3、采用浓碱水热法实现了rG薄片上均匀负载二氧化钛纳米管的复合材料。以锐钛矿TiO2为钛源合成的rG5.1%/TiO2纳米管复合物中,TiO2纳米管呈多壁形态,均匀分布在完整的大面积rG片上。进一步探讨了rG的复合量对合成的rG/ TiO2纳米管复合材料的相结构、热稳定性、形貌和电化学性能的影响。电化学测试表明rG5.1%/TiO20.1C倍率,首次充放电容量分别高达358mAhg-1379mAhg-15次循环后至0.2C时,仍具有较高的充放电容量(分别为330 mAhg-1315 mAhg-1),而且复合电极材料高倍率下的循环性能也有了显著的改善。而以P25粉末为钛源合成的rG3 %/TiO2纳米管复合材料虽然首次放电和充电容量只有281mAhg-1278 mAhg-1,但远远高于没有rG复合的Ti02纳米管电极材料。结果分析表明具有较高电导率的rGTiO2纳米管组合形成导电网络,有助于电子的传输和电解质离子的快速扩散。复合电极中一定量rG的引入在充放电过程中不仅作为高导电性的添加剂缩短了Li+扩散和快速的相转移反应时间,而且对嵌锂容量也有一定的贡献。4、通过简单的浓碱水热方法处理GO- TiO2 复合凝胶,获得了rG薄片上负载一维TiO2(B)纳米线的新型复合材料。测试结果表明得到的复合材料为TiO2(B)结构纳米线,完全不同于没有rG复合的样品的锐钛矿结构的TiO2纳米管。结合TG-DSC手段重点考察了焙烧温度对复合材料相结构和形貌的影响,结果显示约为9.6% rG的复合不仅改变了TiO2的相结构,还促进了纳米管——纳米线的转变过程,材料的热稳定性提高。电化学测试表明,在0.1C下复合样品的首次放电容量为304mAhg-1,但在1C衰减至146 mAhg-12C衰减至124mAhg-1,当达到5C时容量仅为78 mAhg-1。这表明还需进一步优化复合材料的合成条件从而更好的提高其高倍率性能。但是相比于同条件下合成的纯锐钛矿TiO2纳米管,由于二维rG和一维TiO2(B)纳米线的协同作用,复合电极材料在相同倍率下的放电的比容量和循环性能都有了显著的提高和改善。

英文摘要: One dimensional nanostructure titania have been regarded as the most promising new anode materials for lithium ion batteries(LIB), due to their huge theoretical capacity (335 mAhg-1), high safety,excelent cyclability, environmental benignity,small structural change (<4%) during Li+ reversible insertion/extraction and also their unique properties associated with highly anisotropic geometry and size confinement. However, pristine titania electrode materials in LIB are limited by slow Li-ion diffusion and poor electron transport in electrodes limit their further advancements in promising applications. The combination of one dimensional nanostructures titania and graphene with high specific surface area, good conducting property and exceptional mechanical strength has been proposed as perfect electrode materials with good electrochemical properties for LIB due to the synergistic effect of graphene and one dimensional nanostructures titania. Hence, this thesis is aimed at system research of the preparation and characterization of the graphene-based one dimensional nanostructures titania composites and their application in LIB.    The technics of synthesized one-dimensional titania nanotubes cathode materials via strongly alkaline hydrothermal process was studied by using TG-DSC, XRD, TEM, Nitrogen adsorption–desorption isotherm measurements and galvanostatic charge-discharge tests. Effects of the preparation conditions, such as titanium source, hydrothermal reaction temperature, and calcination temperature on the structure, morphology and electrochemical performance of the titania nanotubes were investigated to optimize one dimensional nanostructures titania production process.    Paper-like shap graphite oxide with wrinkles was prepared by a modified Hummers method, and it was hydrothermal treated in 10M NaOH aqueous solution after ultrasonic exfoliating. We can obtain the rG displays translucent-chiffon-like shapes with wrinkles and it has large surface structure composed of single-layer or few-layer sheets. The obtained rG with large surface is especially suitable to the substrate of composite materials. The XRD results show that the diffraction peaks at 2θ = 11.3°corresponding to graphite oxide was disappeared after strongly alkaline hydrothermal treatment. As for the peaks observed at 2θ= 24.9°and 43.2°in the XRD of rG indicated that most of the reduced graphene are few-layer sheets which stack with single-layer. The interlayer distance of the rG decreased due to the elimination of the oxygen-containing groups on the GO sheets. XPS results indicated that a considerable number of C-O、C=O、O=C-O groups on the GO were removed, which revealed that exfoliated GO can undergo fast deoxygenating in strongly alkaline solutions with hydrothermal treatment.    The one dimensional nanostructure tubular titania was successfully dispersed onto the surface of rG uniformly through the strongly alkaline hydrothermal treatment. For rG(5.1%)/TiO2 nanotubes composite synthesized by alkaline hydrothermal treatment of anatase precursors, the walls of the nanotube consisting of more shells and well-distributed on the complete large rG. The effect of rG amounts on the synthesized rG/TiO2 nanotubes composites phase structure, thermal stability, morphology and electrochemical performance was discussed. Electrochemical results demonstrated that the synthesized rG(5.1%)/TiO2 nanotubes has the high first charge capacity 358mAhg-1and discharge capacity of 379 mAh g-1 at 0.1C, and after 5 cycles, charge-discharge capacity still has high (330 and 315 mAhg-1, respectively) at 0.2C. The cycle performance at high rates of the composite electrode materials has also significantly improved. As for commerical P25-produced rG(3%)/ Ti02 nanotubes composite, the initial charge and discharge capacities are only 278 and 281mAhg-1 at 0.1C, respectively, but they were larger than the values for the Ti02 nanotubes without rG. Results show that the formation of rG with high conductivity and Ti02 nanotube hybrid conductive network facilitated rapid transportation of electron and diffusion of electrolyte ion. And, a appropriate amount of rG in the composit not only as a high conductivity additive to decreased the Li+ diffusion and phase transfer reaction time in the process of charge and discharge but also contribution to the lithium insertion capacity.    We designed a simple strongly alkaline hydrothermal treated GO-hybrid titania gel synthesis route obtained well-dispersed TiO2(B) nanowires loaded on graphene sheets novel composite material. The results demonstrated that the obtained composite can be assigned to TiO2(B) nanowires, completely different from the anatase TiO2 nanotubes without rG. Effects of calcination temperature on phase structure and morphology of composite materials were studied by TG-DSC. The results showed that titania compound with graphene could improve the thermostability of the composite, and therefore increased TiO2(B)-anatase phase transformation temperature and accelerated the nanotube-nanowire transformation process. Electrochemical results demonstrated that the initial discharge capacity of rG/TiO2(B) nanowires composite is 304mAhg-1 at 0.1C, and decreases to 146 mAhg-1 at 1C, 124mAhg-1 at 2C, and 78 mAhg-1 at 5C, respectively. Hence, the performance of composite electrode at high discharge/charge rates needs improvement by optimization of the preparation conditions. However, the electrochemical performances of composite electrode materials superior to the pure anatase TiO2 nanotubes synthesized at the same experimental conditions, which may attribute to the synergistic effect of graphene and TiO2(B) nanowires.
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/2502
Appears in Collections:材料物理与化学研究室_学位论文

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作者单位: 中国科学院新疆理化技术研究所

Recommended Citation:
侯娟. 石墨烯复合一维二氧化钛纳米材料的合成、表征和电化学嵌锂性能[D]. 北京. 中国科学院大学. 2013.
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