【作者】 王娟；

【导师】 梁继才；

【作者基本信息】 吉林大学 ， 材料学， 2016， 硕士

【摘要】 随着能源短缺和环境恶化,开发新型清洁能源已经迫在眉睫,锂离子电池具有能量密度大,工作电压高,循环寿命长等优点,越来越受到研究者们的重视。近年来,由于石墨烯具有大的比表面积和良好的导电性,与其他材料复合形成纳米复合材料电池用作锂离子电池的负极材料,既可以克服传统材料自身的缺点,同时发挥了石墨烯材料的特有性质。因此石墨烯基复合材料在催化剂、光电和储能等领域都有很好的应用前景。在紫外光的照射下,二氧化钛可以分解难降解、有毒有害的污染物,并且二氧化钛廉价、无毒、不会产生二次污染,受到广泛研究和应用。然而未经优化处理的二氧化钛材料带隙较宽,光生载流子容易复合,极大地影响了二氧化钛的光催化性能。本文利用石墨烯良好的导电性和空心结构的优点,把石墨烯-二氧化钛空心球纳米复合材料作为研究对象,在实验过程中制备了不同比例的石墨烯-二氧化钛空心球纳米复合材料,并研究了光催化性能和电学性能。二氧化锡作为锂离子电池负极材料具有高的理论容量(790 m Ahg-1),没有记忆效应,对环境无污染。但在长时间充放电条件下,二氧化锡体积膨胀严重,电子电导率变差,导致其循环稳定性和倍率性能变差。因此,纯二氧化锡不适合实际应用。本文制备了石墨烯-Sn O2-Ti O2纳米复合材料,引入石墨烯既能提高电导率,又能减少二氧化锡纳米颗粒的团聚。而二氧化钛纳米颗粒可以形成更多的空间,可以缓冲二氧化锡的体积膨胀,从而提高石墨烯-Sn O2-Ti O2纳米复合材料的电化学性能。(1)采用改进的Hummers方法制备氧化石墨烯,并对氧化石墨烯进行形貌结构的表征。通过透射电镜发现所制备的氧化石墨烯具有薄片结构并且有褶皱,氧化石墨烯并不是单层的而是由几层组成。(2)利用石墨烯良好的导电性和二维立体结构,以氢氧化钛为前驱体,采用一步水热法还原氧化石墨烯并制备了石墨烯-二氧化钛空心球纳米复合材料。结果表明所制备的纳米复合材料中二氧化钛为空心球结构,空心球的直径小于20nm,空心部分的直径大约为3-5 nm,石墨烯和二氧化钛很好的复合在了一起,石墨烯-二氧化钛空心球纳米复合材料的比表面积为111m2g-1。(3)实验过程中改变石墨烯的量,合成G0-Ti O2、G0.5-Ti O2、G1-Ti O2、G2-Ti O2和G5-Ti O2这六种不同重量比的石墨烯-二氧化钛空心球纳米复合材料。对比研究它们的光催化性能和电化学性能。研究表明G1-Ti O2这一复合比例的纳米复合材料具有最好的光催化性能,光催化降解亚甲基蓝25 min后,可以达到98.02%,光催化降解甲基橙30min后,可以达到99%。所制备的G1-Ti O2这一复合比例的纳米复合材料具有最好的循环稳定性,在充放电倍率为0.2C下循环100圈后,比容量达到217.2 m Ahg-1,远高于二氧化钛的理论容量(168 m Ahg-1)。(4)以SnCl2·2H2O为原料,通过水热法合成了石墨烯-SnO2复合材料,研究了石墨烯的复合对二氧化锡的微观纳米结构和电化学性能的影响。实验结果表明,Sn O2纳米颗粒在石墨烯的表面分散的不均匀,有明显的团聚现象,Sn O2纳米颗粒粒径约为5 nm,石墨烯-Sn O2复合材料表现出良好的循环稳定性,在充放电倍率为0.2C下,循环50圈后,比容量为1024 m Ahg-1。(5)以钛酸四丁酯和Sn Cl2·2H2O为原料,采用溶剂热结合水热两步法合成石墨烯-Sn O2-Ti O2三元纳米复合材料,研究它们的微观纳米结构和电化学性能。实验结果表明,在加入极少量Ti O2后,Sn O2纳米颗粒和石墨烯很好的复合在了一起,并且没有发生团聚,Sn O2纳米颗粒粒径约为5 nm,石墨烯-Sn O2-Ti O2三元复合材料表现出较高的可逆容量和更好的循环稳定性,在充放电倍率为0.2C下,循环50圈后,比容量为1073 m Ahg-1。更多还原

【Abstract】 Lithium-ion batteries(LIBs) are wide-spreadly used in portable electronic devices and electrical vehicles for their large energy density, high operation voltage and long cycle life. As the energy shortages and environmental degradation, exploring new clean alternative sources of energy has become a development trend, the research of lithium-ion batteries also draw more and more attention of the researchers. In recent years, graphene because of its large specific surface area and good electrical conductivity, could form nanocomposites with other materials as anode materials for lithium ion batteries. This kind of nanocomposites materials can not only get rid of disadvantages of traditional material itself, but also play the unique properties of graphene materials. Therefore graphene/oxide nano composites materials, in the catalyst, photoelectric, energy storage and other fields have good application prospects.Under the irradiation of ultraviolet light, Ti O2 can be decomposed hardly degradable substance, poisonous and harmful pollutants, and Ti O2 is cheap and non-toxic, does not produce secondary pollution, so Ti O2 has been widely researched and used. However, the band gap of Ti O2 without optimization process is wider. Furthermore, light carrier is easy to compound and greatly affected the photocatalytic properties of Ti O2. Based on the good electrical conductivity of graphene and hollow structure, in this work, the graphene- Ti O2 hollow nanocrystals nanocomposites were researched and syntheticed. Different hybrids were prepared by adjusting the weight ratio of graphene of mixture in the process of experiment, then their photocatalytic properties and electrical properties are studied.Sn O2 is considered as one of the most promising lithium-ion battery anode materials because of its high theoretical capability(790 m Ahg-1), no memory effect and environmental benignity. However, it has serious drawbacks of huge volume change and poor electronic conductivity during the charge and discharge process, which displays poor cycle life and rate performance. So, bulk Sn O2 isunsuitable for the practical application. In this paper, the graphene-Sn O2-Ti O2 nanocomposites were prepared by hydrothermal method. In general, introducing graphene can effectively improve the electrical conductivity and possibly mitigatethe agglomeration of nanoparticles.(1) Graphite oxide was prepared by improved Hummers method using natural flake graphite as raw material, then graphene oxide was got after the ultrasonic dispersion of graphite oxide. Morphology of graphene oxide structure was analysised by observing TEM and SEM. It is found that GO has a flake-like structure with wrinkles. Furthermore, graphene oxide is composed of several layers instead of a single one.(2) Using the two-dimensional structure and good electrical conductivity of grapheme, three-dimensional graphene-Ti O2 hollow nanocrystal composites were synthesised via a simple one-step hydrothermal method with hydrogen in titanium oxide as the precursor. Our results show that Ti O2 hollow nanocrystals are evenly dispersed nanoparticles on graphene. The diameter of Ti O2 hollow nanocrystals is smaller than 20 nm and the diameter of the hollow part is approximately from 3 to 5 nm. The specific surface area of G1-Ti O2 is calculated to be higher than 111 m2g-1.(3) The amount of grapheme was changed in the process of experiment, six kinds of different weight ratio of graphene-Ti O2 hollow nanocrystal composites, such as G0-Ti O2, G0.5-Ti O2, G1-Ti O2, G2-Ti O2 and G5-Ti O2, were synthesized. Their photocatalytic performance and electrochemical properties were studied. Experiments have shown that the G1-Ti O2 composite material display the best photocatalytic performance. Using methylene blue as degradation compounds, after degradation for 25 min, the degradation rate can reach 98.02%, while photocatalytic degradation of methyl orange for 30 min, the degradation rate can reach 99%.G1-Ti O2 composite material has the best cycle stability, a high initial reversible capacity of 217.2 m Ahg-1 for the G1-Ti O2 composite material is obtained at 0.2 C after 100 cycles, which is far higher than theoretical capacity of Ti O2(168 m Ahg-1).(4) By Sn Cl2· 2H2 O as raw materials, graphene-Sn O2 composites were synthesized through the hydrothermal method, their nanometer micro-structure and electrochemical performance were studied. The experiment results show that Sn O2 nanoparticles dispersed on the surface of graphene unevenly, there is a clear phenomenon of agglomeration, the size of Sn O2 nanoparticle is about 5 nm, graphene-Sn O2 composites exhibited good cycle stability, a high specific capacity of 1024 m Ah-1 is obtained at 0.2 C after 50 cycles.(5) By tetrabutyl titanate and Sn Cl2·2H2O as raw materials, a solvothermal method combined with a hydrothermal two-step method is developed to synthesize grapheme-Sn O2-Ti O2 ternary nanocomposite, their nanometer micro-structure and electrochemical performance were studied. The experiment results show that after joining extremely small amount of Ti O2, Sn O2 nanoparticles evenly dispersed on the surface of graphene, and there is no agglomeration, the size of Sn O2 nanoparticle is about 5 nm, graphene-Sn O2-Ti O2 ternary nanocomposite exhibited higher reversible capacity and better cycle stability, a high specific capacity of 1073 m Ah-1 is obtained at 0.2 C after 50 cycles.更多还原