【作者】 夏洋；

【导师】 杨毅夫；

【作者基本信息】 武汉大学 ， 物理化学， 2011， 博士

【摘要】 在能源问题和环境问题日益严重的今天,各国政府越来越重视电动汽车的发展,而混合动力电动汽车则是目前技术最为成熟的电动汽车。作为混合动力电动汽车最重要的配套动力化学电源,MH/Ni动力电池具有较好的综合性能,随着MH/Ni动力电池产业化速度的不断加快,我们仍要不断提高MH/Ni动力电池的比容量、比功率、使用寿命等性能并降低电池的生产成本,而这些问题的解决则强烈的依赖于MH/Ni动力电池应用性技术的基础研究。对MH/Ni动力电池正极活化过程的研究就属于这一范畴,针对氢氧化镍电极的活化机制,本论文在氢氧化镍材料活化过程本质的研究、活化速度较快的含Ni(Ⅲ)的氢氧化镍材料的研究、添加剂Co和CoO的氧化过程及其对氢氧化镍电极性能的影响、活化后的MH/Ni动力电池长时间搁置后的特性研究等方面开展了一些创新性的工作：1.利用改进的单颗粒微电极实验装置研究了氢氧化镍的活化过程,现场观察到单颗粒氢氧化镍在充放电过程中自身颜色的变化,结果表明当电化学还原反应进行完后,仍有一部分Ni(Ⅲ)存在于颗粒中。活化过程的研究表明循环伏安法可以有效的活化氢氧化镍颗粒,颗粒在活化过程中充电效率的变化表明在初始阶段,氢氧化镍主反应的活化速度大于副反应氧析出反应的活化速度,随后,主反应的活化速度和副反应的活化速度基本一致,主反应和副反应的竞争关系是活化过程的一个重要性质。通过对氢氧化镍归一化输出能力的分析,表明活化过程并没有改善颗粒的电化学反应速率。综合实验数据的分析后,我们提出了单颗粒氢氧化镍的活化模型,氢氧化镍材料活化过程的本质就是一层特殊的导电性更好的活性物质的形成过程。2.采用在碱液中用强氧化剂氧化氢氧化镍的方法合成了部分氧化的氢氧化镍。通过增加反应温度和反应时间可以增加氢氧化镍的氧化程度,高温条件可以加剧氧化反应的进行。强氧化剂改变了氢氧化镍颗粒的表面成分和形貌,含5%Ni(Ⅲ)的氢氧化镍的表面Co、Zn元素的含量有一定程度的增加,含10%Ni(Ⅲ)的氢氧化镍的表面颗粒之间的接触不再紧密,含20%Ni(Ⅲ)的氢氧化镍表面已被强氧化剂严重破坏。部分氧化的氢氧化镍,由于其表面Ni(Ⅲ)的存在改善了材料的导电性,使得这些材料的活化速度在活化过程的初期都要比母体氢氧化镍的活化速度快,这进一步证实了我们提出的氢氧化镍材料的活化本质。由于强氧化剂对含10%Ni(Ⅲ)和含20%Ni(Ⅲ)的氢氧化镍表面的过度作用,使得这两种材料的循环性能很差。含5%Ni(Ⅲ)的氢氧化镍材料的电化学综合性能最好。3.研究了CoO和Co在50℃的浓碱中首次电化学氧化的过程,并详细分析了CoO和Co在电化学氧化过程中结构和形貌的变化,提出了钻的电化学氧化机理,探讨了CoO和Co作为正极的添加剂对MH/Ni电池性能的影响。实验结果表明：当初始反应物为CoO时,氧化产物是Co304的单相,而当初始反应物为Co时,氧化产物则是CoOOH和C0304的两相混合物。CoO和Co的电化学氧化机理揭示了钴在电解液中的溶解性和消耗CoOOH的反应的动力学这两个因素可以在很大程度上影响反应产物C0304和CoOOH的量。Co的氧化产物CoOOH可以很好地连接泡沫镍集流体与氢氧化镍颗粒,进而增强MH/Ni电池的大电流充放电性能。CoO的氧化产物C0304可以很好地在氢氧化镍颗粒与颗粒之间建立导电连接,提高正极对β-Ni(OH)2的利用率,进而增强MH/Ni电池的容量性能。因此,CoO和Co需要同时作为添加剂添加到MH/Ni电池的正极中。4.以搁置两年后的分别添加了CoO和添加了Co的电池作为研究对象,从正极板、电解液及隔膜的性质分析了经过长时间搁置后的电池的性能。搁置两年后两种电池的正极板仍保持其本来的电化学性能,表明通过第四章中的方法在电池高温化成过程中形成的钻导电网络能够长时间的稳定存在,并能够保持良好的导电性。搁置两年后的电池显示,添加CoO的正极板中活性物质堆积得很致密,而添加Co的正极板中活性物质堆积得很松散。添加CoO的正极板表面和正极活性物质表面钴元素的含量都要大于添加Co的电极的情况。由于负极合金的腐蚀而溶解进入电解液中的Al、Ce、La、Mn元素的浓度很低,不会对电池的性能产生影响。由于析氧副反应对添加Co的电池正极的影响强烈,导致其隔膜内填充入大量的正极活性物质颗粒,而添加CoO电池的隔膜内正极活性物质的数量较少。更多还原

【Abstract】 More and more national governments around the world have been realizing the importance of the development of electric vehicle due to the increasingly serious problems of environmental pollution and energy consumption. Among the electric vehicles, the hybrid electric vehicle is the most mature one at the present time. As the most mature electrochemical power sources for hybrid electric vehicle, Ni/MH power batteries have good comprehensive electrochemical performance. However, with the fast development of Ni/MH power batteries industrialization, the specific energy, the specific power and cycle life of Ni/MH power batteries should be further promoted and the production cost of the batteries should be reduced. The settlement of these issues strongly depends upon basic research of applicable technology of Ni/MH power batteries. The study of the activation process of Ni/MH power batteries positive electrode belongs to this basic research. Focusing on the activation process of Ni(OH)2 electrode, some innovative works referring to the activation behavior of electrode material Ni(OH)2, the study of Ni(OH)2 containing Ni(Ⅲ), differences in the effects of Co and CoO additions on the performance of Ni(OH)2 electrode, the performance of Ni/MH power batteries after long time storage have been done in this thesis. The main progress of this thesis is summarized as follows:1. The activation process of Ni(OH)2 was studied by a single particle microelectrode method with an improved apparatus. The color change of the single particle could be seen during the charging and discharging process. The result indicates that the Ni(Ⅲ) formed in the charging process cannot be completely reduced under nonnal reduction conditions. The study of the activation process manifests that CV is an effective way to activate the Ni(OH)2 particle. The variation of charge efficiency during the activation process means that in the initial stage the major reaction has faster activation speed than that of the side reaction (oxygen evolution), and then the activation speed of these two reactions become the same. The competition between the major and side reactions is an important characteristic of the activation process. The analysis of normalized output rate reveals that the activation process does not improve the electrochemical reaction rate of the particle. A model to describe the activation process of a single particle is proposed from an overall perspective. The intrinsic characteristic of the activation process is that a layer of active mass with better electric conductivity is formed starting from the surface and is finally dispersed in the whole particle.2. Partially oxidized Ni(OH)2 was prepared by oxidizing Ni(OH)2 with strong oxidant in an alkaline medium. The oxidation degree of Ni(OH)2 can be increased by raising reaction temperature and increasing reaction time. Elevated temperature can expedite proceeding of the oxidation reaction. The surface composition and morphology of Ni(OH)2 particles are changed by strong oxidant. Compared with the original Ni(OH)2, the content of cobalt and zinc on the surface layer of Ni(OH)2 particle containing 5% Ni(Ⅲ) increases. The tiny particles on the surface of Ni(OH)2 containing 10% Ni(Ⅲ) have loose contact with each other. The surface of Ni(OH)2 containing 20% Ni(Ⅲ) has been severely damaged by strong oxidant. Because Ni(Ⅲ) existed in the surface layer of Ni(OH)2 can improve the electric conductivity of the material, this has resulted in a faster activation of the Ni(OH)2 containing Ni(Ⅲ) than the original Ni(OH)2 in the initial activation process. This result has further confirmed the intrinsic nature of the activation of Ni(OH)2 that has been revealed in the chapter 2. Because the particle surface of Ni(OH)2 containing 10% Ni(Ⅲ) and 20% Ni(Ⅲ) has been excessively oxidized, the cycle performance of both these two materials become worse. The Ni(OH)2 containing 5% Ni(Ⅲ) has good comprehensive electrochemical performance.3. The electrochemical behavior of Co and CoO as additives in the positive electrode of Ni/MH power batteries in an alkaline medium during first charging at 50°C was analyzed. The structural and textural evolutions of Co and CoO during charging were studied, and an oxidation mechanism was proposed. Moreover, the effects of the two additives in the positive electrode on the performance of Ni/MH power batteries were investigated. The experimental results reveal that different oxidation products can be obtained according to the type of starting material. When the starting material is CoO, only Co3O4 is formed. A CoOOH phase is present together with a Co3O4 phase when Co is used as a starting material. The oxidation mechanism of Co and CoO reveals that two factors, the solubility of cobalt and kinetics of the reaction that consumes CoOOH, can significantly influence the amounts of Co3O4 and the remaining CoOOH. According to the electrochemical performance of the CoO-added and Co-added batteries and the cobalt oxidation behavior, the highly compact CoOOH phase, which works well in connecting the nickel foam and Ni(OH)? particles, enhances the high rate charge and discharge performance of the Ni/MH power battery. The Co3O4 phase, which works well in connecting Ni(OH)2 particles with each other, increases the utilization of Ni(OH)2, consequently improving the capacitive performance of the Ni/MH power battery. Therefore, both additives are necessary to create a power battery.4. CoO-added battery and Co-added battery which have stored for two years were chosen as research objects. The performance of the two batteries was studied by analyzing the physical properties and electrochemical performance of positive electrodes as well as the physical properties of electrolyte and separator. The electrochemical performance of the two positive electrodes still remains unchanged comparing with that of the two positive electrodes before storage. This result manifests that the cobalt conductive networks which fomied in the first charging at 50°C have good electric conductivity and stability after the long time storage. The Ni(OH)2 particles in the CoO-added positive electrode stack compactly, whereas the Ni(OH)2 particles in the Co-added positive electrode stack loosely. The content of cobalt in the surface of CoO-added positive electrode is larger than the content of cobalt in the surface of Co-added positive electrode. And the content of cobalt in the surface of Ni(OH)2 particles is still larger in the case of CoO-added positive electrode than that in the case of Co-added positive electrode. The concentration of Al、Ce、La、Mn elements which dissolved from the negative electrode is very low. This has little effect on the performance of the two batteries. Because the oxygen evolution has significant effect on the positive electrode of Co-added battery, this results in the penetration of large amount of Ni(OH)2 particles into the separator. However, in the case of CoO-added battery there is only a small amount of Ni(OH)2 particles that have inserted into the separator.更多还原