纳米结构锌基复合金属氧化物的可控构筑与储锂性能研究

发布时间：2018-03-19 21:27

本文选题：锂离子电池　切入点：负极材料　出处：《华中科技大学》2014年博士论文　论文类型：学位论文

【摘要】：随着电子科技的飞速发展,移动设备如手机、笔记本电脑、电子阅读器等便携设备随着功能的丰富耗电量逐渐增加,其对于锂离子电池在比容量,使用寿命和充电速度方面的要求越来越严苛。随着传统化石燃料的日益衰竭,对于新型能源如风能,太阳能的储存显得尤为重要,锂离子电池被视为理想候选者之一。而目前传统的材料钴酸锂和石墨已不能满足现在的需求。因而开发高容量、高倍率、长循环寿命,廉价环保的新型电极材料迫在眉睫。本文以锌基金属氧化物为研究对象,采用纳米化和碳材料杂化等手段合成了一系列具有纳米结构的复合材料,并对其电化学性能进行了研究。具体内容包括以下几个方面：采用醋酸锌和氧化锗为反应物,在水和叔丁胺的混合溶剂中进行水热反应合成锗酸锌,通过调控反应物浓度和溶剂中水和叔丁胺的比例,合成了具有海胆状形貌的锗酸锌纳米材料,构成分级结构的纳米棒直径约为20nm,长度约为500nm,这种一维结构有利于电荷的传输,提高传输效率。且纳米棒之间的空隙可在一定程度上缓解储锂过程中的体积膨胀,提高结构稳定性。电化学表征结果表明其具有较高的比容量和较好的倍率性能。与此同时,还对材料的生长机理进行了研究,研究结果对于合成类似结构的氧化物具有一定的参考价值。采用微波辅助水热法,利用锗酸锌-乙二胺杂化物纳米带作为前驱体,将其均匀分散在氧化石墨烯(GO)悬浮液中,通过微波加热手段在短时间内(15分钟)合成锗酸锌/氮掺杂石墨烯复合物。在反应过程中,微波引发的分子间高频率的振动可以极大地加速化学反应的进行,使得锗酸锌—乙二胺杂化物中的乙二胺分子迅速脱离出本体,与氧化石墨烯进行反应,在将其还原为石墨烯的同时进行氮原子掺杂。在最终产物中,锗酸锌纳米棒被氮掺杂石墨烯紧紧包裹,电化学测试结果表明,相比在同样反应条件下合成的无石墨烯包覆的锗酸锌纳米棒,其性能得到了显著的提升。Zn2GeO4/氮掺杂石墨烯复合材料在100mAg-1的电流密度下进行放—充电循环100次仍可保持1044mAhg-1的可逆比容量。即使在电流密度高达3.2Ag-1的条件下,其比容量也远高于传统石墨材料,达到531mAh g-1。开发了一种廉价环保的方法,在室温下利用离子交换反应成功制备了具有三明治结构的锗酸锌/氧化石墨烯复合材料。合成的复合材料中,锗酸锌纳米棒均匀地嵌入在氧化石墨烯层间,其在储锂过程中产生的体积膨胀可以得到很好的缓冲。得益于结构的保持,复合物在首次放电过程中产生的Li20可以在随后的充电过程中部分可逆转化为锂离子和金属氧化物,通过计算,Li20的可逆程度可达64%,比容量得到极大提升。得到的复合材料无论在容量、循环寿命还是倍率性能方面都表现出优异的性能。此外,锗酸锌纳米棒的嵌入避免了氧化石墨烯层间的堆叠,提高了氧化石墨烯的利用率,有效降低了复合物中的碳含量,从而提升了材料的体积能量密度,为将来大规模应用提供可能。利用空心八面体结构的金属有机框架材料作为前驱体,在氮气气氛下进行热处理得到了介孔结构的氧化锌/铁酸锌/碳的空心八面体。归功于金属有机框架的特殊结构,其在热处理过程中,有机配体碳化后可均匀的包覆在由金属元素形成的氧化物纳米颗粒表面。金属氧化物颗粒由于受到碳层的限制,颗粒尺寸仅为5nm左右,形成的八面体结构壁厚仅为10nm左右,孔径大小为7.5nm。将其作为锂离子电池负极材料表现出极为优异的性能,在500mA g-1的电流密度下,首次循环过程中可逆比容量高达1047mAh g-1,库仑效率达到75.6%,较其他类似氧化物有所提升,且100次循环之后比容量增至1390mAh g-1,即使在电流密度增加至1OAg-1的情况下,可逆比容量仍高达762mAh g-1。如此出色的性能要归功于其特殊的结构,小尺寸的氧化物纳米颗粒加上均匀的碳包覆层可以有效缓解充放电过程中的体积膨胀,多孔空心结构有利于电解液的浸润,增加电解液与颗粒之间的接触面,提高电化学反应动力学,极薄的壁厚可以有效缩短锂离子的传输路径,提高材料的倍率性能。
[Abstract]:With the rapid development of electronic technology, mobile devices such as mobile phone, notebook computer, electronic reader and other portable devices increases gradually with rich power consumption function, the specific capacity for lithium ion batteries in terms of life, and the speed of the charging requirements more stringent. With the traditional fossil fuel depletion, for new energy such as wind energy the solar energy storage, it is particularly important, the lithium ion battery is regarded as one of the ideal candidates. At present, the traditional material LiCoO2 and graphite has been unable to meet the demand. So the development of high capacity, high rate, long cycle life, imminent new electrode materials for environmental protection. Cheap
Based on zinc based metal oxides, a series of nanostructured composites were synthesized by means of Nanocrystallization and carbon material hybridization, and their electrochemical properties were studied.
Using zinc acetate and germanium oxide as reactants, synthesis of germanium hydrothermal reaction of acid zinc in the mixed solvent of water and tert butylamine, by regulating the concentration of reactant and solvent water and tert butylamine proportion of zinc germanate nanometer material with sea urchin like morphology were synthesized, a hierarchical structure of the nanorod diameter is about 20nm. The length is about 500nm, the one-dimensional structure is conducive to the transmission of charge, improve the transmission efficiency. The gap between the nanorods and storage during lithium expansion to ease to a certain extent, improve the stability of structure. Electrochemical characterization results show that it has high specific capacity and good rate performance. At the same time, also on the growth mechanism of materials the research results have certain reference value for the synthesis of the similar structure of the oxide.
By microwave assisted hydrothermal method using zinc germanate ethylenediamine hybrid nanoribbons as precursor, which are evenly dispersed on graphene oxide (GO) suspension, by means of microwave heating in a short period of time (15 minutes) the synthesis of zinc germanate / nitrogen doped graphene complex in the reaction process. In the inter molecular microwave high frequency vibration can greatly accelerate the chemical reaction, the ethylenediamine germanate zinc - ethylenediamine hybrid in rapidly out of body, react with graphene oxide, in the reduction of graphene doping of nitrogen atoms. At the same time. In the final product. Germanate ZnO nanorods by nitrogen doped graphene wrapped tightly, the electrochemical test results show that compared with the same reaction conditions without the graphene coated zinc germanate nanorods synthesized, its performance has been significantly improved.Zn2GeO4/ nitrogen doped graphene composite Under the current density of 100mAg-1, the charging cycle of 1044mAhg-1 can maintain the reversible specific capacity of 3.2Ag-1 for 100 times. Even at the current density of 3.2Ag-1, its specific capacity is much higher than that of traditional graphite material, reaching 531mAh g-1..
The development of a low-cost method of environmental protection, the use of acid / Zinc Germanium ion with sandwich structure of graphene oxide composite materials were prepared successfully in the exchange reaction at room temperature. The synthesis of composite materials, zinc germanate nanorods were uniformly embedded in the graphene oxide layer, the lithium storage in the process of volume expansion can get good buffer. Due to the structure, compound produced in the first discharge process of Li20 in the process of charging into partially reversible lithium ion and metal oxide, through calculation, up to 64% degree of reversibility of Li20, greatly enhance the specific capacity. The resulting composite materials both in capacity the life cycle, or rate performance has shown excellent performance. In addition, zinc germanate nanorods embedded avoid stacked graphene oxide layers, improve the utilization rate of graphene oxide, effectively reduced The carbon content in the compound is lower and the volume energy density of the material is enhanced, which provides the possibility for large-scale applications in the future.
Metal organic framework materials with hollow structure eight as precursor, heat treatment in nitrogen atmosphere were obtained mesoporous structure Zinc Oxide / zinc ferrite / carbon hollow eight face. Due to the special structure of metal organic frameworks, in the process of heat treatment, the organic ligands after carbonization can be uniformly in the coating formed by the metal elements in the surface oxide nano particles. The metal oxide particles due to the carbon layer, the particle size is only about 5nm, eight structure formed wall thickness is only about 10nm, the pore size of 7.5nm. anode materials for lithium ion batteries are shown as extremely excellent performance in current the density of 500mA g-1, the first cycle reversible capacity up to 1047mAh g-1, the coulombic efficiency reached 75.6%, compared with other similar oxide has improved, and after 100 cycles the specific capacity of 1390mAh to g-1, even in The current density is increased to 1OAg-1, the reversible capacity is still as high as 762mAh g-1. so excellent performance due to its special structure, the small size of the oxide nanoparticles with uniform carbon coating can effectively alleviate the charge and discharge process of the volume expansion, porous hollow structure is conducive to the increase of electrolyte infiltration. The contact surface between the electrolyte and the particles, improve the electrochemical reaction kinetics, transmission path of thin wall thickness can effectively shorten the lithium ion, improve the rate performance of the material.

【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TQ127.11;TM912

【共引文献】