高能量密度锂空气电池的相关研究

发布时间：2018-05-25 04:23

本文选题：锂空气电池 + 树叶状氧化石墨烯　；参考：《复旦大学》2014年硕士论文

【摘要】：非水系锂空气电池的理论能量密度是现有锂离子电池的5到10倍,可与汽油相媲美,因此近几年来锂空气电池受到了人们的广泛关注。锂空气电池主要由三部分组成：负极金属锂,电解液和空气催化电极。锂空气电池的储能原理是基于金属锂与氧气的反应。然而由于锂空气电池体系中所发生的反应是气液固三相参与的反应,因此影响锂空气电池的电池性能的因素有很多。本论文以开发高性能的锂空气电池为目标,对锂空气电池的主要组成进行了研究,并运用非原位的XRD,红外以及SEM等分析测试手段对锂空气电池充放电过程中的反应机理进行了分析与探讨,对于发展锂空气电池具有极其重要的意义。而在这篇论文中我们主要研究以下几个方面：空气催化电极碳材料,离子液体电解液及湿度的影响。论文的三部分工作内容如下：1.空气电极碳材料的研究以VGCF为原料,采用传统的Hummers法制备了一种新型的含碳纳米管中脉的树叶状氧化石墨烯,作为锂空气电池的空气催化电极材料进行了研究。并且与含商业的碳纳米管和普通的氧化石墨烯以及两者质量比1：1的简单混合物的锂空气电池进行了电性能比较。采用改进的Hummers法制备的树叶状氧化石墨烯能够有效综合氧化石墨烯和碳纳米管的优点,因此具有了碳纳米管的优良导电性和氧化石墨烯的多反应活性位点性,从而表现出极其优异的循环性能和大容量性能。因此得出结论,具有优良导电性和多反应活性位点的材料具有更高的催化活性,能够使Li202和O2之间相互转换,从而提高锂空气电池的性能。另外,材料的孔道结构也会影响锂空气电池的性能。研究表明,有序的介孔通道可以为电解液的浸润和锂离子的传输提供了便利,而大孔则不仅有利于氧气的扩散,也为Li2O2和O2之间的相互转换提供了空间。因此我们采用模板法合成了介孔大孔多级孔的碳球阵列。由于锂空气电池充放电过程中发生的反应是气液固三相参与的反应,而我们合成的产物的分层次多孔结构可以为其提供有序的三相反应活性界面,从而提高锂空气电池的性能。另外,其有序的分层次多孔结构在充放电过程中能够较好地保持其原有的形貌,而这种结构上的稳定性改善了锂空气电池的循环性能。以不同含量的介孔大孔多级孔碳为活性物质的锂氧电池在相同条件下均获得高于用Super P炭黑为活性物质的锂氧电池的比容量。综合考虑循环和容量性能,该材料的最佳含量为30%。另外,其含量为30%时在不同电流密度下电压极化差值均小于Super P炭黑的。并运用非原位的XRD,红外以及SEM等手段对充放电过程进行分析,也证实了上述推测的介孔大孔多级孔碳性能优异的原因。2.一种离子液体电解液的研究锂空气电池的电解液主要包含电解质和溶剂两部分组成,其中溶剂的不稳定性是限制锂空气电池发展的一大障碍。有机电解液是目前锂空气电池中研究最多的电解液体系。然而,最近的研究表明,高催化活性的氧自由基能够分解大部分的有机电解液,包括在锂离子电池中最常用的有机电解液。而离子液体由于其固有的低挥发性,不易燃性和对氧高稳定性等特点而有可能成为锂空气电池电解液的希望。我们以γ-MnOOH纳米棒为催化剂,在新型的EMIMBF4-LiNTf2离子液体对锂空气电池的电池性能进行测试。结果表明,在EMIMBF4-LiNTf2离子液体中,锂空气电池表现超大的放电容量和较好的循环稳定性。同时我们还在该电解液中,对以γ-MnOOH纳米棒和α-MnO2纳米棒为催化剂以及没有催化剂的锂空气电池进行了比较,发现含γ-MnOOH纳米棒催化剂的锂空气电池在相同电流密度下表现出优于含α-MnO2纳米棒催化剂或不含催化剂的锂空气电池的放电容量以及放电电压平台。因此,我们得出初步结论以EMIMBF4-LiNTf2离子液体为电解液,用γ-MnOOH纳米棒为催化剂,两者的综合实用能够有效地改善锂空气电池的电化学性能。其超长的循环稳定性归因于该离子液体对氧气的稳定性和较宽的电化学耐压窗口,而且γ-MnOOH纳米棒能够催化离子液体中的氧气还原进程,从而提高了锂空气电池的放电电压平台和放电容量。这一结果表明合适的离子液体电解液和高催化性能的催化剂对发展可充放锂空气电池十分重要。3.湿度对锂氧电池电化学性能的影响为了发展真正意义上的锂空气电池,即氧气来自于周围空气中,所以研究湿度对锂氧电池性能的影响是十分必要的。因此,我们分别在干燥的纯氧中,相对湿度为15%的纯氧中以及相对湿度为50%的空气中比较了锂氧电池性能,并分析了湿度对碳基空气催化电极所发生的反应的影响。电化学研究表明锂空气电池的放电容量随着相对湿度数值的升高而增大,而循环性能和倍率性能却随相对湿度数值的升高而变差。而非原位的XRD,红外以及SEM测试结果表明湿度不仅影响Li2O2/O2,LiCO3/O2的转换以及LiOH的形成,也直接影响着充放电过程中多孔催化电极上放电产物的形貌。此外,根据上述研究结果可以明显地看出不同湿度对负极的腐蚀影响不同,从而逐渐加重了这些电池的电化学性能之间的差别,而湿度对负极的影响将是我们下一步研究的方向。上述结果对发展锂空气电池十分重要。
[Abstract]:The theoretical energy density of the non-aqueous lithium air battery is 5 to 10 times that of the existing lithium ion battery, which is comparable to that of the gasoline. Therefore, the lithium air battery has attracted wide attention in recent years. The lithium air battery consists mainly of three parts: anode metal lithium, electrolyte and air accelerating electrode. The energy storage principle of lithium air battery is based on gold. However, there are many factors affecting the performance of lithium air batteries because of the reaction in the lithium air battery system because of the reaction of the gas-liquid solid three-phase. This paper aims at developing the high performance lithium air battery, and studies the main composition of the lithium air battery, and uses the insitu. XRD, infrared and SEM analysis methods have been analyzed and discussed for the reaction mechanism of lithium air battery charging and discharging. It is of great significance for the development of lithium air batteries. In this paper, we mainly study the following aspects: the influence of the air catalytic electrode carbon material, the ionic liquid electrolyte and the humidity. The three parts of the work are as follows: 1. the study of air electrode carbon materials is made of VGCF as the raw material. A new type of leaf like graphite oxide in the middle vein of carbon nanotubes is prepared by the traditional Hummers method. It is studied as the air catalytic electrode material of the lithium air battery. The electrical properties of the fossil graphene and the lithium air batteries with a simple mixture of 1:1 are compared. The leaves like graphene oxide prepared by the improved Hummers method can effectively integrate the advantages of the oxidation of graphene and carbon nanotubes, thus having the excellent conductivity of the carbon nanotubes and the multi reaction active site of the graphene oxide. Therefore, it is concluded that materials with excellent conductivity and reactive active sites have higher catalytic activity, can make Li202 and O2 convert to each other, thus improve the performance of lithium air batteries. The study shows that the ordered mesoporous channels can provide convenience for the infiltration of electrolyte and the transfer of lithium ion. The large pore is not only beneficial to the diffusion of oxygen, but also provides space for the mutual conversion between Li2O2 and O2. Therefore, we use template method to synthesize the carbon sphere array of mesoporous large pore and multistage holes. The reaction in the charging and discharging process is the reaction of the gas-liquid solid three-phase, and the hierarchical porous structure of the synthesized products can provide an orderly three-phase reactive interface, thus improving the performance of the lithium air battery. In addition, the ordered hierarchical porous structure can keep its original in the charge and discharge process. The structural stability improves the cycle performance of lithium air batteries. Lithium oxygen cells with different content of mesoporous macroporous carbon as active substances obtain the specific capacity of lithium oxygen batteries with Super P carbon black as active substances under the same conditions. The optimum content of the material is comprehensive considering the cycle and capacity properties. For 30%., the voltage polarization difference at 30% at different current densities is less than Super P carbon black. The charge discharge process is analyzed by using non in-situ XRD, infrared and SEM methods. It is also proved that the above speculated that the high carbon performance of the mesoporous macroporous multistage pores is studied by.2. an ionic liquid electrolyte. The electrolyte of a gas battery consists mainly of two parts of electrolyte and solvent, in which the instability of solvent is a major obstacle to the development of lithium air batteries. Organic electrolyte is the most important electrolyte system in lithium air batteries. However, recent research shows that most of the oxygen free radicals of high catalytic activity can be decomposed. Electromechanical solution, including the most commonly used organic electrolyte in lithium ion batteries, and the ionic liquid may be the hope of the lithium air battery electrolyte due to its inherent low volatility, non flammability and high oxygen stability. We use gamma -MnOOH nanorods as the catalyst in the new EMIMBF4-LiNTf2 ionic liquid to the lithium air The performance of the battery was tested. The results showed that the lithium air battery showed great discharge capacity and good cyclic stability in the EMIMBF4-LiNTf2 ionic liquid. Meanwhile, we also compared the lithium air batteries with gamma -MnOOH nanorods and alpha -MnO2 nanorods as well as the lithium air batteries without catalyst in the electrolyte. The lithium air battery containing a gamma -MnOOH nanorod catalyst shows the discharge capacity of the lithium air battery with an alpha -MnO2 nanorod catalyst or no catalyst at the same current density, as well as the discharge voltage platform. Therefore, we draw a preliminary conclusion that the EMIMBF4-LiNTf2 ionic liquid is used as the electrolyte, and the gamma -MnOOH nanorods as the catalyst, two The comprehensive utility can effectively improve the electrochemical performance of the lithium air battery. Its ultra long cycle stability is attributed to the stability of the ionic liquid to oxygen and the wide electrochemical voltage resistance window, and the gamma -MnOOH nanorods can catalyze the process of oxygen reduction in the ionic liquid, thus increasing the discharge voltage of the lithium air battery. The results show that the suitable ionic liquid electrolyte and the high catalytic performance catalyst are very important for the development of the lithium air battery. The influence of.3. humidity on the electrochemical performance of the lithium oxygen cell is the real significance of the lithium air battery, that is, the oxygen comes from the ambient air, so the humidity is studied on the lithium oxygen. The effect of the battery performance is very necessary. Therefore, we compare the performance of the lithium oxygen battery in the dry oxygen, the relative humidity of 15% and the relative humidity of 50%, and analyze the effect of the humidity on the reaction of the carbon based air catalytic electrode. With the increase of relative humidity, the cyclic performance and multiplying performance varies with the increase of relative humidity. The results of XRD, IR and SEM show that humidity not only affects the conversion of Li2O2/O2, LiCO3/O2 and the formation of LiOH, but also affects the discharge production on the porous catalytic electrode in the process of charging and discharging. In addition, according to the above results, it is obvious that the influence of different humidity on the corrosion of the negative electrode is different, which gradually aggravates the difference between the electrochemical properties of these batteries, and the influence of humidity on the negative electrode will be our next research direction. The above results are very important for the development of the lithium air battery.
【学位授予单位】：复旦大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM911.41

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