金属化合物—碳类复合材料的制备及其用作锂离子电池负极的研究

【作者】 王刚；

【导师】 王惠；

【作者基本信息】 西北大学 ， 材料化学， 2012， 博士

【摘要】 本论文在碳质微纳米材料改性金属化合物复合材料的制备方面开展了一系列工作,研究内容可分为两部分：第一部分主要针对金属氧化物(MxOy)用于锂离子电池负极材料时出现的首次库伦效率偏低,储锂性能较差等问题,用石墨烯(Graphene nanosheets)和球形碳(CSs)对金属氧化物微纳米材料Fe304、Fe203和Ce02进行改性研究,在对该类型材料物相组成、形貌和结构以及电化学性能分析和测试的基础上,对石墨烯、球形碳以及碳包覆层在改善金属氧化物储锂能力方面所起作用进行归纳和总结；第二部分主要针对碱式碳酸盐类镧系化合物LaOHCO3的可控制备以及其与石墨烯的复合方面展开研究,并对该类型材料的荧光性能进行检测和比较。具体研究内容如下：利用石墨烯作为改性元素,以水热法合成出两种担载型纳米复合材料Fe3O4/graphene和CeO2/graphene和一种掺杂型微纳米复合材料Fe2O3-graphene。三种复合材料均显示出优于其本体的电化学性能,对于Fe3O4/graphene,首次充放电比容量分别高达2315和1160mAh/g,50次循环后可逆比容量771mAh/g,相比于单一Fe304,比容量提升107%；对于Fe2O3-graphene,首次充放电比容量分别高达1800和1420mAh/g,100次循环后可逆比容量为567mAh/g,相比于单一Fe203,比容量提升46%；对于CeO2/graphene,首次充放电比容量分别高达1469和991mAh/g,100次循环后可逆比容量为605mAh/g,相比于单一CeO2,比容量提升63%。利用球形碳作为改性元素,利用水热法合成出一种掺杂型碳包覆的微纳米复合材料Fe2O3@C-CSs,以浸渍法并结合高温煅烧手段合成出一种担载型碳包覆的纳米复合材料Fe2O3@C/graphene。两种材料均显示出优于其本体的电化学性能,对于Fe2O3@C-CSs,首次充放电比容量分别高达1507和978mAh/g,50次循环后可逆比容量为550mAh/g,相比于单一Fe203,比容量提升37%；对于Fe2O3@C/graphene,首次充放电比容量分别为1530和1016mAh/g,50次循环后可逆比容量为1027mAh/g,相比于Fe2O3/graphene,比容量提升34%。以聚乙烯吡咯烷酮(PVP)作为软模板,利用水热法并精确调控反应时间,制备出不同形貌的LaOHCO3微纳米颗粒,在优化出层级结构LaOHCO3合成工艺的基础上对其与石墨烯复合进行研究。对合成的不同形貌LaOHCO3以及不同石墨烯含量的层级结构LaOHCO3-graphene进行荧光测试发现前者均可在365nm激发下于420nm处出现一荧光发射峰,而后者荧光性能的存在与否和石墨烯的添加量有关。对于LaOHCO3样品,其荧光强度呈现一定规律性,粒度越大,荧光强度越强；粒度同等大小情况下,经180℃水热反应24h得到的层级结构LaOHCO3微米球的荧光强度最强。对于LaOHCCO3-graphene,随石墨烯含量增加,荧光强度逐渐减弱直至发生淬灭。更多还原

【Abstract】 A series of composites related to the modification of metal compounds by micro-or nano-carbonaceous materials has been synthesized and studied in this paper. The detailed research work is composed of two parts. Part one is focoused on the modification of metal oxides (MxOy=Fe3O4, Fe2O3and CeO2) by graphene nanosheets and carbon spheres to overcome their defects such as low coulombic efficiency at the initial cycle and poor lithium storage properties and improve their electrochemical performance when used as anode materials for lithium ion batteries. The influence of graphene nanosheets and carbon spheres as modifying elements on lithium storage performance of the MxOy is summarized after systematically investigating the phase composition, the morphology and structure, and the electrochemical perforamance of the MxOy-graphene composites. Part two is focoused on the synthesis of lanthanum carbonate hydroxides (LaOHCO3) and LaOHCO3-graphene composites with controlled morphology and the further comparation of their luminescence properties. The main contents of the paper are presented as follows:Preparation of two supported nanocomposites of Fe3O4/graphene and CeO2/graphene, and a doped micro/nanocomposite of Fe2O3-graphene is realized by utilization of graphene nanosheets as modifying elements through hydrothermal treatment. The three composites show much better electrochemical performance than the MxOy used in each system. For the Fe3O4/graphene, it shows a discharge capacity of2315mAh/g and charge capacity of1160mAh/g in the first cycle. After50cycles, the reversible capacity still remained771mAh/g. The rate of capacity increased is107%when compare with pure Fe3O4electrode. For the Fe2O3/graphene, it shows a discharge capacity of1800mAh/g and charge capacity of1420mAh/g in the first cycle. After100cycles, the reversible capacity still remained567mAh/g. The rate of capacity increased is46%when compared with pure Fe2O3electrode. For the CeO2/graphene, it shows a discharge capacity of1469mAh/g and charge capacity of991mAh/g in the first cycle. After100cycles, the reversible capacity still remained605mAh/g. The rate of capacity increased is63%when compared with pure CeO2electrode.Preparation of a doped micro/nanocomposite with carbon coated (Fe2O3@C-CSs) is realized by utilization of carbon spheres as modifying elements through hydrothermal treatment. Preparation of a supported nanocomposite with carbon coated (Fe2O3@C/graphene) is realized by utilization of carbon spheres as modifying elements through immersion method and high temperature calcination. The two composites show much better electrochemical performance than the Fe2O3or Fe2O3/graphene used in each system. For the Fe2O3@C-CSs, it shows a discharge capacity of1507mAh/g and charge capacity of978mAh/g in the first cycle. After50cycles, the reversible capacity still remained550mAh/g. The rate of capacity increased is37%when compare with pure Fe2O3electrode. For the Fe2O3@C/graphene, it shows a discharge capacity of1530mAh/g and charge capacity of1016mAh/g in the first cycle. After50cycles, the reversible capacity still remained1027mAh/g. The rate of capacity increased is34%when compare with Fe2O3/graphene.In the presence of polyvinylpyrrolidone (PVP), LaOHCO3with various morphologies are synthesized successfully via a facile hydrothermal process. The novel hierarchical nest-like architectures of LaOHCO3are obtained based on the time-controlled experiment during the process. Hierarchical LaOHCO3-graphene composites with different amounts of graphene nanosheets are synthesized subsequently. The optical properties of LaOHCO3microparticles with different morphologies and LaOHCO3-graphene composites with different amounts of graphene nanosheets are measured. For the pure LaOHCO3, it shows that all the samples exhibite emission spectrum centered at～420nm using an excitation wavelength of365nm. Their luminescence properties are very sensitive to the morphology and strongly dependent on the size. The larger the particle size, the stronger the intensity of luminescence. Comparing the particles that have the same size, the hierarchical LaOHCO3obtained at180℃in24h exhibite the highest luminescence intensity. For the LaOHCO3-graphene composites, it shows that the luminescence intensity decreased gradually and finally the fluorescence quenching occured with the amounts of graphene increased.更多还原