多孔钴酸铁非碳正极的制备及其在锂空气电池中的应用研究

发布时间：2018-01-16 06:11

本文关键词：多孔钴酸铁非碳正极的制备及其在锂空气电池中的应用研究　出处：《深圳大学》2017年硕士论文　论文类型：学位论文

【摘要】：新型锂空气电池由于具备极高的理论能量密度而受到了广泛的关注。但是,锂空气电池离实际应用还存在着很大的差距,其较大的充放电过电势导致了较差的循环性能和倍率性能,这与空气正极的氧还原反应(ORR)和氧析出反应(OER)过程的钝化密切相关。通过改善空气正极的结构并结合催化剂的使用是促进锂空气电池ORR与OER过程的有效途径。本文中,为避免碳基正极的各种弊端,采用水热法和热处理法使金属氧化物催化剂钴酸铁(FeCo_2O_4)薄片原位生长在泡沫镍(Ni)上构筑大孔/介孔并存的多孔非碳正极FeCo_2O_4@Ni并应用到锂空气电池中,大孔提供放电产物Li2O2储存的空间和O2的扩散通道;而FeCo_2O_4薄片上的介孔则为ORR/OER提供充足的催化活性位点。而后通过使用贵金属金(Au)来修饰FeCo_2O_4@Ni,制备出新型复合空气正极Au/FeCo_2O_4@Ni,以进一步降低充放电过电势,提升电池循环性能。两种非碳正极具体的性能考察如下:(1)通过水热反应和热处理两个过程制备非碳正极FeCo_2O_4@Ni,并通过改变水热溶剂和煅烧温度(300-400℃)来调控FeCo_2O_4的形貌、结构。采用SEM、BET、XRD等手段对材料的理化性能进行表征,最后将空气正极分别组装成CR2032型扣式电池,并进行多种电化学性能测试。结果表明乙二醇能够起到减少催化剂堆叠和团聚的作用,350℃下煅烧得到的空气正极FeCo_2O_4@Ni具有较大的比表面积和最大孔容,并且结晶程度良好,同时拥有最大的放电容量和最优的充放电平台。因此,确定水热溶剂中含有乙二醇和煅烧温度为350℃是制备大孔/介孔并存的FeCo_2O_4@Ni的最佳条件,后续的FeCo_2O_4@Ni均在此条件下制备。(2)继续对非碳正极FeCo_2O_4@Ni在锂空气电池中的应用进行深入的研究。经TEM和XPS表征进一步确认了FeCo_2O_4@Ni为大孔/介孔并存的三维多孔结构和其氧空位的存在。将所制备的非碳正极FeCo_2O_4@Ni与碳基正极KB/FeCo_2O_4/Ni进行电化学性能比较,发现前者的充放电过电势低于后者,前者的循环运行次数也高于后者,充分证明了非碳正极FeCo_2O_4@Ni对ORR和OER过程的促进作用。通过SEM形貌表征发现,空气正极FeCo_2O_4@Ni的放电产物主要为无定形的低维度的Li2O2,并且相较于结晶型的Li2O2,无定形的Li2O2在充电过程中更容易被分解。然而,尽管非碳正极FeCo_2O_4@Ni在一定程度上缓解空气正极的钝化问题,但随着电池的循环运行,放电电压下降较快,这是由于非碳正极FeCo_2O_4@Ni的导电性比较差,需要进一步改善电极的导电性。(3)最后,将所制备的FeCo_2O_4@Ni浸泡在四氯金酸溶液中形成新型复合空气正极Au/FeCo_2O_4@Ni。经SEM、XRD和XPS表征,确认复合电极上贵金属金(Au)的成功添加和FeCo_2O_4结构的保留。此外,通过电化学性能测试,表明了添加贵金属金后提高了电极的导电性,稳定了电极的放电电压,并且在循环充放电的中后期过程中显著降低了充放电过电势,提高了电池循环性能。综上所述,本论文制备了两种以钴酸铁催化剂为主体的多孔非碳正极,并系统地研究了其在锂空气电池中的催化机理和电化学性能,证实了相较于对应的碳基正极,两种非碳正极有效降低了电池的充放电过电势和提高了电池的循环性能。
[Abstract]:The new lithium air batteries have attracted much attention due to the theory of energy density with very high. However, lithium air battery from practical application there are still a large gap between the large overpotential leads to the charge discharge cycle performance and rate performance is poor, and the air cathode oxygen reduction reaction (ORR) and oxygen precipitation the reaction (OER) process of passivation is closely related. By improving the structure of air cathode and combined with the use of catalysts is an effective way to promote the lithium air battery ORR and OER process. In this paper, in order to avoid the disadvantages of carbon based anode, by hydrothermal method and heat treatment method of the metal oxide catalyst of cobalt iron (FeCo_2O_4) in situ growth on nickel foam sheet (Ni) on the structure of porous macroporous / mesoporous carbon cathode FeCo_2O_4@Ni non coexist and applied to lithium air battery, macroporous diffusion discharge products Li2O2 storage space and O2. Tao; provide adequate catalytic active sites of mesoporous FeCo_2O_4 thin sheet is ORR/OER. Then through the use of precious metal (Au) modified FeCo_2O_4@Ni prepared Au/FeCo_2O_4@Ni composite cathode air, to further reduce the charge discharge potential, enhance the cycle performance of battery. Two kinds of non carbon anode performance of specific investigation are as follows: (1) through hydrothermal reaction and heat treatment process of the preparation of two non carbon anode FeCo_2O_4@Ni, and by changing the hydrothermal solvent and calcination temperature (300-400 DEG C) to control the morphology, the structure of FeCo_2O_4. Using SEM, BET, physicochemical properties are characterized by means of XRD material, the air cathode respectively. Assemble type CR2032 button battery, and various electrochemical performance test. The results showed that ethylene glycol can reduce stacking and agglomeration effects of the catalysts calcined at 350 FeCo_2O_4@Ni with a positive air The large surface area and maximum pore volume, and the crystallization degree is good, the charge and discharge platform also has the largest discharge capacity and optimal. Therefore, determination of hydrothermal solvents containing ethylene glycol and calcination temperature to 350 degrees is the best conditions for preparing macroporous / mesoporous FeCo_2O_4@Ni coexistence, subsequent FeCo_2O_4@Ni here under the condition of preparation. (2) to continue in-depth study on the application of non carbon anode in lithium air battery in FeCo_2O_4@Ni. The TEM and XPS characterization confirmed the three-dimensional porous structure of FeCo_2O_4@Ni macroporous / mesoporous coexist and the presence of oxygen vacancies. The preparation of non carbon anode and carbon FeCo_2O_4@Ni comparison of KB/FeCo_2O_4/Ni based cathode electrochemical performance, found that the former charge discharge potential is lower than the latter, cycle running times are higher than the former to the latter, fully proved that the non carbon anode FeCo_2O_4@Ni on ORR and OER in the process of promoting The role of the SEM morphology characterization shows that the discharge products mainly for air cathode FeCo_2O_4@Ni amorphous low dimension Li2O2, and compared with crystalline Li2O2, amorphous Li2O2 more easily in the process of charging is decomposed. However, despite the non carbon anode passivation of FeCo_2O_4@Ni to some extent alleviate the air anode, but with the circulation of the battery, the discharge voltage decreases rapidly, this is because the conductivity of non carbon anode FeCo_2O_4@Ni is relatively poor, need to further improve the conductivity of the electrode (3). Finally, the FeCo_2O_4@Ni prepared by immersion in four gold chloride acid solution to form a new type of composite air cathode Au/FeCo_2O_4@Ni. by SEM, XRD and XPS. Confirm, composite electrode precious metal (Au) retained successfully added and FeCo_2O_4 structure. In addition, the electrochemical performance tests show that the addition of conductive, precious metal after high electrode Stable discharge voltage, electrode, and in the later process of charge discharge cycle in significantly reduced the charge discharge potential, improve the cycle performance of battery. To sum up, this thesis synthesized two cobalt iron catalyst as the main body of the non porous carbon cathode, and studied its catalytic mechanism in a lithium air battery and the electrochemical properties, demonstrated that carbon based cathode compared to the corresponding to the two kinds of non carbon anode effectively reduces the battery charge and discharge overpotential and improve the cycle performance of the battery.

【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TM911.41

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