四氧化三铁颗粒的制备及其石墨烯复合材料锂电性能研究

发布时间：2018-06-04 03:00

本文选题：溶剂热法 + 四氧化三铁　；参考：《兰州大学》2014年硕士论文

【摘要】：近年来,随着科学技术的不断进步,人们对能源的需求也越来越大。锂离子电池作为一种常用的便携式储能设备,受到越来越多的关注。如何提高锂离子电池的循环稳定性、电容量和效率,是当前研究面临的主要问题。四氧化三铁由于具有较高的理论电容量、低成本和环境友好等特点,已经开始被应用于锂离子电池负极材料。石墨烯以及基于石墨烯的复合材料,被认为是作为锂离子电池的电极的不二选择。因为这类材料具有很好的导电性,大的比表面积,耐腐蚀性,高透明度和较宽的电化学窗口等优点。本论文主要采用溶剂热法制备了实心和空心四氧化三铁微球,并对分别对其结构、形貌和磁性能进行了研究。同时还讨论了反应时间以及尿素含量对其结构和磁性能的影响。在此基础上,采用了三种不同的方法,将四氧化三铁与石墨烯进行了复合,并对其锂电性能进行了研究。主要的研究内容和成果如下：(1)在不需要任何模板的前提下,通过溶剂热法,可以制备出具有空心结构的四氧化三铁微球。实验表明,颗粒的粒径在400nm左右,内径尺寸约为230nm,具有很好的分散性和表面形貌。VSM测试表明,所制备的空心微球具有室温亚铁磁性,其饱和磁化强度接近于块体材料。(2)不同的反应时间对四氧化三铁空心结构的形成有着重要的影响。随着反应时间的增长,颗粒逐渐形成空心结构。当反应时间为8小时时,四氧化三铁为实心微球；当反应时间增加到20小时时,便形成了空心结构。(3)尿素含量会影响四氧化三铁微球的形貌。尿素含量为1.0g时,颗粒尺寸约为800nm；随着含量的增加,颗粒尺寸开始减小,但是,其形貌的不规则也愈发严重。当尿素含量为2.0g时,具有最佳形貌。由此我们总结出制备空心四氧化三铁微球的最佳条件是反应时间20小时,尿素含量2.0g。(4)通过对实心四氧化三铁微球和空心四氧化三铁微球的微波吸收能力的研究发现,空心结构的确可以提高对微波的吸收能力。空心Fe304微球的最小反射吸收在5.7GHz处可达-42.6dB,远高于实心Fe304微球的-29.1dB (3.2GHz处)。同时,其反射损耗小于-18dB的吸波宽度为6.6GHz,也大于实心微球的4.8GHz。 (5)我们采用石墨烯直接包覆制备好的四氧化三铁颗粒(实心和空心)的方法制备了Fe304/石墨烯的复合材料。实验表明：采用这种办法,四氧化三铁颗粒可以很好的保持其原有形貌,同时石墨烯有更好的还原效果,其锂电性能也得到了提高。 (6)同时还发现,用KH550对四氧化三铁表面进行修饰,然后用石墨烯对修饰后的四氧化三铁颗粒进行二次包覆,颗粒的分散性得到了改善,此外还可以增强颗粒与石墨烯的结合,进而增加对四氧化三铁颗粒的保护能力,提高电容量和稳定性。修饰后的空心微球与未经修饰的相比,其50次循环后的放电电容量提高了15%,更为重要的是其稳定性也有了大幅提高。
[Abstract]:In recent years, with the continuous progress of science and technology, the demand for energy is also increasing. As a portable energy storage device, lithium ion battery has attracted more and more attention. How to improve the cycle stability, capacitance and efficiency of lithium-ion battery is the main problem. Due to its high theoretical capacity, low cost and environmental friendliness, iron trioxide has been used as anode material for lithium ion batteries. Graphene and graphene-based composites are considered to be the best electrode for lithium-ion batteries. Because of its good conductivity, large specific surface area, corrosion resistance, high transparency and wide electrochemical window. In this paper, solid and hollow iron trioxide microspheres were prepared by solvothermal method, and their structure, morphology and magnetic properties were studied. The effects of reaction time and urea content on the structure and magnetic properties were also discussed. On this basis, three different methods were used to compound iron trioxide with graphene, and the lithium electrical properties were studied. The main research contents and results are as follows: (1) without any template, iron trioxide microspheres with hollow structure can be prepared by solvothermal method. The results show that the particle size is about 400nm and the inner diameter is about 230 nm. The hollow microspheres prepared have ferromagnetic properties at room temperature due to their good dispersion and surface morphology. The saturation magnetization is close to that of bulk material. The different reaction time has an important effect on the formation of iron trioxide hollow structure. With the increase of reaction time, the particles gradually formed hollow structure. When the reaction time was 8 hours, Fe _ 2O _ 3 was a solid microsphere, and when the reaction time was increased to 20 hours, the hollow structure was formed. The urea content would affect the morphology of Fe _ 2O _ 3 microspheres. When the urea content is 1.0 g, the particle size is about 800 nm, and with the increase of urea content, the particle size begins to decrease, but the irregular morphology becomes more and more serious. When urea content is 2.0 g, the optimum morphology is obtained. The optimum conditions for the preparation of hollow iron trioxide microspheres were as follows: reaction time 20 hours, urea content 2.0 g 路L ~ (4). The microwave absorption capacity of solid iron trioxide microspheres and hollow iron trioxide microspheres was studied. The hollow structure can improve the absorption ability of microwave. The minimum reflectance absorption of hollow Fe304 microspheres can reach -42.6 dB at 5.7GHz, which is much higher than that at -29.1dB / 3.2GHz for solid Fe304 microspheres. At the same time, the absorption width with reflection loss less than -18dB is 6.6 GHz, which is also larger than that of solid microsphere (4.8 GHz). 5) Fe304/ graphene composites were prepared by direct coating of graphene with iron trioxide particles (solid and hollow). The experimental results show that the Fe _ 2O _ 4 particles can maintain their original morphology, and graphene has a better reduction effect, and its lithium electrical properties are also improved. At the same time, it was found that the surface of Fe _ 2O _ 3 was modified by KH550, and then the modified Fe _ 2O _ 3 particles were twice coated with graphene, the dispersion of the particles was improved, and the combination of the particles with graphene was also enhanced. Furthermore, the capacity and stability of Fe _ 2O _ 3 particles were improved. Compared with the unmodified hollow microspheres, the discharge capacity of the modified hollow microspheres increased by 15% after 50 cycles, and more importantly, the stability of the modified hollow microspheres was greatly improved.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

【参考文献】