过渡金属化合物与碳纳米纤维复合材料的合成及其电化学性能研究

发布时间：2018-02-01 10:29

本文关键词： 锂离子电池碳纳米纤维 CoO/CNF FeCO_3/CNF Fe_2O_3/CNF　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：锂离子电池凭借其能量密度较高、循环性能优良、使用寿命较长、安全环保、无记忆效应等特点,成为新能源材料的研究热点,目前已被广泛应用于智能手机、笔记本电脑等电子产品行业以及动力汽车、混合动力汽车行业。然而,随着人们对锂离子电池需求量的日益增加,开发出能量密度更高、循环性能更好、使用寿命更长的新型锂离子电池已经成为新能源领域最具有价值的研究之一。负极材料作为锂离子电池的核心材料之一,是决定锂离子电池储锂性能的关键材料。目前商业上通常采用循环稳定性优良的碳材料作为负极材料,但是,碳材料理论容量较低,仅372 mAh g~(-1),其较低的储锂性能并不能满足人类对锂离子电池日益增长的需求。近十年,过渡金属化合物由于其较高的理论容量受到国内外研究人员的广泛关注,然而,这类材料受SEI膜和体积效应限制,循环稳定性能较差,同样无法满足人类的需求。本文综合考虑碳材料及过渡金属化合物材料的优缺点,结合前人经验,首次提出将碳纳米纤维与过渡金属化合物复合,采用不同方法制备出过渡金属化合物/碳纳米纤维柔性膜,打破传统拌浆工艺,简化电池组装流程,实现了负极材料可逆容量与循环稳定性能的双重突破。本论文具体内容如下:(1)通过静电纺丝技术制备碳纳米纤维(CNF),结果表明:该方法合成的CNF表面光滑,呈现网状结构,循环稳定性能优异,可逆容量偏低,在200mA g~(-1)的电流密度下循环150圈以后,材料比容量为285.6 mAh g~(-1)。(2)以CNF为基底、硝酸钴为金属源、尿素为配体、去离子水和乙醇为溶剂,采用冷凝回流法合成了CoO/CNF复合材料,结果表明:在CoO/CNF复合材料中,CoO纳米片团聚成柳絮状CoO微米球镶嵌在CNF纤维中,表现出优秀的电化学性能,在200 mA g~(-1)的电流密度下循环150圈以后,材料比容量为579.7mAh g~(-1),其中,CoO为整个材料提供的比容量高达774.1 mAh g~(-1)。(3)以CNF为基底、氯化铁为金属源、尿素为配体、抗坏血酸为还原剂、去离子水为溶剂,采用传统水热法合成了FeCO_3/CNF复合材料,结果表明:该方法合成的FeCO_3/CNF复合材料呈现蜂窝状结构,表现出优秀的电化学性能,在200 mA g~(-1)的电流密度下循环200圈以后,材料比容量为546.2 mAh g~(-1),其中,FeCO_3为整个材料提供的比容量高达919.7 mAh g~(-1)。(4)以CNF为基底、氯化铁为金属源、尿素为配体、乙醇为溶剂,采用微波水热法合成了Fe_2O_3/CNF复合材料,结果表明:该方法合成的Fe_2O_3/CNF复合材料呈现蜂窝状结构,表现出优秀的电化学性能,在200 mA g~(-1)的电流密度下循环150圈以后,材料比容量为673.8 mAh g~(-1),其中,Fe_2O_3为整个材料提供的比容量高达926.2 mAh g~(-1)。
[Abstract]:Li-ion battery has become the research focus of new energy materials because of its high energy density, good cycling performance, long service life, safety and environmental protection, no memory effect and so on, and has been widely used in smart phones. However, with the increasing demand for lithium ion batteries, higher energy density and better cycle performance have been developed. New lithium-ion batteries with longer service life have become one of the most valuable research fields in the field of new energy. Negative electrode materials as one of the core materials of lithium-ion batteries. Carbon materials with good cyclic stability are usually used as negative electrode materials, but the theoretical capacity of carbon materials is relatively low. Its low lithium storage performance can not meet the increasing demand for lithium-ion batteries in recent ten years. Transition metal compounds have attracted much attention because of their high theoretical capacity. However, due to the limitation of SEI film and volume effect, the cyclic stability of transition metal compounds is poor. In this paper, we consider the advantages and disadvantages of carbon materials and transition metal compounds, combined with previous experience, the first time to put forward the carbon nanofibers and transition metal compounds composite. Transition metal compounds / carbon nanofiber flexible films were prepared by different methods to break the traditional slurry mixing process and simplify the battery assembly process. The reversible capacity and cyclic stability of negative electrode materials have been achieved. The main contents of this thesis are as follows: (1) carbon nanofibers CNF were prepared by electrospinning technology. The results show that the CNF synthesized by this method has a smooth surface, a reticular structure, excellent cyclic stability and low reversible capacity, after the current density of 200mA / g ~ (-1). The specific capacity of the material is 285.6 mAh / g ~ (-1) / L ~ (-1)) based on CNF, cobalt nitrate as metal source, urea as ligand, deionized water and ethanol as solvent. CoO/CNF composites were synthesized by condensation reflux method. The results showed that the CoO/CNF composites were agglomerated to form cataclysmic CoO microspheres embedded in CNF fibers. It showed excellent electrochemical performance, and the specific capacity of the material was 579.7 mAh / g ~ (-1) after 150 cycles under the current density of 200 Ma / g ~ (-1), in which the specific capacity of the material was 579.7 mAh / g ~ (-1). The specific capacity of CoO for the whole material was as high as 774.1 mAh / g ~ (-1) / L ~ (3)) based on CNF, ferric chloride as metal source, urea as ligand, ascorbic acid as reducing agent. FeCO_3/CNF composites were synthesized by conventional hydrothermal method using deionized water as solvent. The results show that the FeCO_3/CNF composites synthesized by this method have honeycomb structure. It shows excellent electrochemical performance, and the specific capacity of the material is 546.2 mAh / g ~ (-1) after cycling at a current density of 200mA / g ~ (-1), in which the specific capacity of the material is 546.2 mAh / g ~ (-1). The specific capacity of FeCO_3 for the whole material is as high as 919.7 mAh / g ~ (-1) / L ~ (4). CNF is used as the substrate, ferric chloride as metal source, urea as ligand and ethanol as solvent. Fe_2O_3/CNF composites were synthesized by microwave hydrothermal method. The results show that the Fe_2O_3/CNF composites prepared by this method have honeycomb structure. It shows excellent electrochemical performance, and the specific capacity of the material is 673.8 mAh / g ~ (-1) after the current density of 200mA / g ~ (-1) is circulated in 150th cycle, in which the specific capacity of the material is 673.8 mAh / g ~ (-1). The specific capacity of Fe_2O_3 for the whole material is up to 926.2 mAh / g ~ (-1).
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB332;TM912

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