【摘要】：鋰-氧氣電池(或鋰-空氣電池)由于具有超高的理論比容量而獲得全世界眾多研究者的廣泛關注,被認為是極具發(fā)展?jié)摿Φ南乱淮鷥δ荏w系之一。在過去十年中,科研人員對有機體系鋰-氧氣電池的相關基本理論進行了深入研究并取得了一定成果。但是,要真正實現(xiàn)該電池體系的應用化,還需要解決很多棘手的關鍵技術問題。其中最大的難題就是,由于不溶性放電產物過氧化鋰自身的低電子電導率和ORR/OER反應中過于緩慢的動力學造成的充放電過程中過電壓較大,尤其是充電過程。這不僅會直接降低電池的能量轉換效率,還會促進電解液在高電位下嚴重分解,從而削減電池的循環(huán)壽命。目前,研究人員主要通過開發(fā)各種正極催化劑來減小充放電的極化作用,降低充放電過電壓,從而提高電池的能量轉換效率和循環(huán)穩(wěn)定性。但迄今為止,開發(fā)具有高效率且長循環(huán)性能的催化劑仍然是科研界面臨的主要任務。因此,對催化劑類型和結構進行最優(yōu)化的設計,獲得具有高能量轉換效率和優(yōu)異循環(huán)穩(wěn)定性能的鋰-氧氣電池體系,是當前很值得深入研究的課題,具有重要的實際意義。本論文從當前鋰-氧氣電池固體催化材料面臨的關鍵問題出發(fā),提出了利用可溶解的添加劑來催化分解固體放電產物的實驗設計思路來大幅提高鋰-氧氣電池的能量轉換效率、可逆性能和循環(huán)穩(wěn)定性能。在此基礎上,分別構筑并研究了具有三明治式結構的Fe2O3/石墨烯復合雙功能催化劑和自支撐結構的泡沫鎳負載Ru(即Ru@UNF)催化劑用作鋰-氧氣電池正極的電化學性能,取得了以下成果:1、高效可溶性催化劑N-甲基吩噻嗪(MPT)的研究:在最初研究階段,我們系統(tǒng)總結了氧化還原介質型添加劑作為鋰-氧氣電池可溶性催化劑的基本條件,并初步篩選了若干氧化電位小于4.0 V的氧化還原穿梭添加劑。通過對MPT的物理特性和電化學性能進行實驗研究,發(fā)現(xiàn)MPT具有合適的氧化電位,較大的分子擴散系數(shù),是一種潛在的鋰-氧氣電池可溶性催化劑。后來,深入研究了 MPT的添加對鋰-氧氣電池充放電的影響。實驗表明,MPT的加入雖然沒有改變放電電壓平臺,卻明顯降低了充電過電位(0.67V),從而提高了相應電池的能量轉換效率(75.7%)。借助一系列非原位表征技術(如SEM、XRD等)和原位DEMS技術來研究MPT在鋰-氧氣電池充放電過程中的作用機制。結果表明,添加MPT的電池在充放電過程中實現(xiàn)了 Li2O2的可逆形成與分解,其中MPT在充電過程中對 Li2O2 的催化作用機理為:(1)2MPT = 2MPT++2e-;(2)2MPT + Li2O2=2MPT + 2Li+ + 02↑。此外,還發(fā)現(xiàn)MPT的使用大大改善了電池的循環(huán)穩(wěn)定性能,抑制了高電位下碳和電解液的不穩(wěn)定副反應。在此,我們還深入討論了影響MPT循環(huán)催化利用效率的因素,總結出提高此類可溶性催化劑循環(huán)效率的方法途徑。最后,嘗試設計出具有高能量效率和優(yōu)異循環(huán)穩(wěn)定性的鋰-氧氣電池體系。2、高效可溶性催化劑LiI的研究:深入研究了可溶性LiI的添加對鋰-氧氣電池充放電過程的影響。研究表明,LiI的使用明顯降低了鋰-氧氣電池充電電位至3.5 V左右,從而提高電池的能量轉換效率至74.3%,這一值遠遠高于未添加LiI的相應電池效率(59.7%)。采用非原位SEM和XPS表征技術發(fā)現(xiàn),含LiI的鋰-氧氣電池表現(xiàn)出良好的Li2O2可逆形成與分解特性。而且將電化學石英微天平技術與循環(huán)伏安測試結合定量檢測含LiI的鋰-氧氣電池在充放電過程中電極表面納克級質量的變化,以此來探究LiI的催化作用機理,如下:放電時,LiI不影響Li2O2的生成;充電時,I-離子優(yōu)先在電極表面失去電子被氧化為I3-(3.2V左右),然后I3-繼續(xù)被氧化為I2(3.5V左右),并擴散至固體放電產物Li2O2表面,在固-液界面處通過化學反應(12 + Li2O2 = 2Li+ + 21-+O2↑)氧化分解Li2O2,釋放氧氣并再次生成其還原態(tài)I-。此外,LiI的使用明顯改善了電池的循環(huán)穩(wěn)定性能。3、三明治式結構Fe2O3/石墨烯復合正極催化劑:采用簡單的熱鑄法成功設計并制備了多層、三明治式結構的Fe2O3/GNS復合材料,并將其用作鋰-氧氣電池正極催化劑。結果表明,與純的GNS相比,Fe2O3/GNS的充電過電位明顯得到改善,且具有良好的可逆性、能量效率、庫倫效率和循環(huán)穩(wěn)定性能。我們也嘗試將可溶性催化劑MPT加入電池體系,測試后發(fā)現(xiàn)電池充電電壓降至3.7 V左右,且具有優(yōu)異的循環(huán)穩(wěn)定性。通過一系列非原位和原位的表征,發(fā)現(xiàn)以Fe2O3/GNS復合材料用作正極催化劑時,鋰-氧氣電池放電產物主要是環(huán)狀固體Li202,且再次充電時Li2O2被氧化分解。利用DEMS技術研究了以Fe2O3/GNS為正極的鋰-氧氣電池在充電過程的反應機理。我們認為,電池表現(xiàn)出如此好的性能主要歸因于雙功能催化劑的獨特三明治結構,該結構不僅提供了較多的催化活性位點,更重要的是,能夠有效減少碳基底與Li2O2的接觸反應,從而抑制副產物Li2C03的生成,提高電池循環(huán)性能。4、自支撐結構的無碳正極催化劑Ru@UNF:采用Cu模板法制備出超輕泡沫鎳(UNF)基底,后用電沉積法制備得到三維自支撐結構的無碳正極Ru@UNF催化劑。該材料具有多孔結構,且在Ru優(yōu)異的ORR和OER催化性能作用下,催化劑表現(xiàn)出優(yōu)異的電化學性能。在電流密度密度為150mAg-1下,以Ru@UNF為正極的鋰-氧氣電池首圈可逆比容量達到2410 mAh g-1,且放電電壓在2.66 V左右,充電平臺在3.56V,相應能量轉換效率為74.7%。同時,還具有良好的循環(huán)穩(wěn)定性能(可循環(huán)100圈以上)。通過原位DEMS研究了以Ru@UNF為正極的鋰-氧氣電池在充電過程中的反應機理。電池具有如此優(yōu)異的性能應該歸因于兩點:(1)Ru的優(yōu)異催化性能,降低充放電過電位,提高能量效率;(2)無碳正極材料的使用能夠避免碳腐蝕引起的副反應,大大提升了電池的循環(huán)性能。以上結果為解決有機體系鋰-氧氣電池面臨的充放電過電位大、能量轉換效率低和循環(huán)穩(wěn)定性差等問題指出了 一條全新的突破思路和方向,對于發(fā)展高性能、可實用化的鋰-氧氣電池具有重要意義。
[Abstract]:Lithium oxygen battery (or lithium air battery) has received extensive attention from many researchers all over the world because of its high theoretical specific capacity. It is considered to be one of the next generation energy storage systems with great potential. In the past ten years, researchers have studied and obtained the basic theory of lithium oxygen battery in organic system. However, in order to realize the application of the battery system, there are many key technical problems to be solved. The biggest problem is that the overvoltage in the charge and discharge process caused by the low electron conductivity of the insoluble discharge product and the slow dynamics of the ORR/OER reaction is larger, especially in the process of charge discharge. It is a charging process. This will not only directly reduce the energy conversion efficiency of the battery, but also promote the serious decomposition of the electrolyte at high potential, thus reducing the cycle life of the battery. At present, the researchers mainly develop a variety of positive catalysts to reduce the polarization effect of charge and discharge, lower the charge and discharge overvoltage, and thus improve the energy conversion of the battery. But so far, the development of catalysts with high efficiency and long cycle performance is still the main task in the scientific research community. Therefore, the optimal design of the type and structure of the catalyst to obtain a lithium oxygen battery system with high energy conversion efficiency and excellent cyclic stability is currently worth it. The subject of in-depth study is of great practical significance. In this paper, starting from the key problems facing the current solid catalytic materials for lithium oxygen batteries, the experimental design idea of using soluble additives to catalyze the decomposition of solid discharge products is proposed to greatly improve the energy conversion efficiency of the lithium oxygen battery, the reversible performance and the cycle stability. On this basis, the electrochemical performance of Fe2O3/ graphene composite double functional catalyst with sandwich structure and self supporting structure of nickel foam Ru (Ru@UNF) catalyst used as the cathode of lithium oxygen battery was constructed and studied respectively. The following achievements were obtained: 1, the research of the high efficiency soluble catalyst N- methyl phenothiazine (MPT) In the initial stage, we systematically summarized the basic conditions of the oxidation-reduction medium additive as the soluble catalyst for the lithium oxygen battery, and preliminarily screened some oxidation-reduction shuttle additives with the oxidation potential less than 4 V. Through the experimental study of the physical and electrochemical properties of MPT, it was found that MPT was suitable. The oxidation potential, the larger molecular diffusion coefficient, is a potential lithium oxygen battery soluble catalyst. Later, the effect of the addition of MPT on the charge and discharge of lithium oxygen batteries was deeply studied. The experiment shows that, although the addition of MPT does not change the discharge voltage platform, the charge overpotential (0.67V) is obviously reduced, thus the corresponding battery is improved. The energy conversion efficiency (75.7%). Using a series of non in-situ characterization techniques (such as SEM, XRD etc.) and in situ DEMS technology, the mechanism of MPT in the charge and discharge process of lithium oxygen battery is studied. The results show that the Li2O2 is reversible and decomposed in charge and discharge process, and MPT is charged to Li2O2 during the charging process. The mechanism of the action is: (1) 2MPT = 2MPT++2e-; (2) 2MPT + Li2O2=2MPT + 2Li+ + 02. Furthermore, it is found that the use of MPT greatly improves the cycle stability of the battery and inhibits the unstable side reaction of carbon and electrolyte at high potential. Here, we also discuss the factors affecting the utilization efficiency of the MPT cycle, and summarize the improvement of this kind. In the end, an attempt was made to design a lithium oxygen battery system.2 with high energy efficiency and excellent cycling stability, and a study of the high efficiency soluble catalyst LiI. The effect of the addition of soluble LiI on the charge and discharge process of lithium oxygen batteries was investigated. The study showed that the use of LiI was significantly reduced. The charge potential of lithium oxygen battery is about 3.5 V, thus increasing the energy conversion efficiency of the battery to 74.3%. This value is far higher than that of the corresponding battery efficiency (59.7%) without the addition of LiI. The non in situ SEM and XPS characterization techniques showed that the LiI containing lithium oxygen battery showed good Li2O2 reversible formation and decomposition characteristics. Moreover, the electrochemical quartz was Microsoft. Balance technique and cyclic voltammetry test combine the quantitative detection of the changes in the quality of the electrode surface of the lithium oxygen battery containing LiI in the process of charging and discharging, in order to explore the catalytic mechanism of LiI, as follows: when the discharge is discharged, the LiI does not affect the formation of the Li2O2; when the charge is charged, the I- ion loses electrons on the electrode surface to be oxidized to I3- (3.2V), Then I3- continues to be oxidized to I2 (3.5V), and diffuses to the surface of the solid discharge product Li2O2, and spreads to the surface of the solid discharge product Li2O2. The chemical reaction (12 + Li2O2 = 2Li+ + 21-+O2) is used to oxidize Li2O2, release oxygen and regenerate its reductive I-.. The use of LiI has obviously improved the cycle stability of the battery, and the sandwich structure Fe2O3. / graphene composite positive catalyst: a simple heat casting method was used to successfully design and prepare multi-layer, sandwich structure Fe2O3/GNS composites and use it as a lithium oxygen battery positive catalyst. The results show that the overpotential of Fe2O3/GNS is obviously improved compared with pure GNS, and has good reversibility, energy efficiency and library. We also try to add the soluble catalyst MPT to the battery system. After testing, it is found that the charge voltage of the battery is reduced to about 3.7 V and has excellent cyclic stability. By a series of non in situ and in situ characterization, the lithium oxygen battery discharge production is found when Fe2O3/GNS composite is used as a positive catalyst. The main object is a circular solid Li202, and the Li2O2 is decomposed when recharged. The reaction mechanism of the lithium oxygen battery with Fe2O3/GNS as the positive electrode is studied by DEMS technology. We think that the performance of the battery is mainly attributable to the single special sandwich structure of the dual function catalyst, which not only provides much more. The catalytic active sites, more importantly, can effectively reduce the contact reaction between the carbon base and Li2O2, thus inhibit the formation of the Li2C03 and improve the battery cycle performance.4. The carbon free catalyst Ru@UNF: of the self supporting structure is prepared by Cu template method to prepare the base of the super light foam nickel (UNF), and then the three-dimensional self support is prepared by electrodeposition. The structure has a carbon free positive Ru@UNF catalyst. The material has a porous structure, and the catalyst exhibits excellent electrochemical performance under the excellent catalytic performance of ORR and OER. Under the current density density of 150mAg-1, the reversible specific volume of the first coil of the lithium oxygen battery with Ru@UNF as the positive pole reaches 2410 mAh g-1, and the discharge voltage is about 2.66 V. The charging platform at 3.56V, with the corresponding energy conversion efficiency of 74.7%., also has good cyclic stability (100 cycles or more). Through in situ DEMS, the reaction mechanism of the lithium oxygen battery with Ru@UNF as the positive electrode is studied. The excellent performance of the battery should be attributed to two points: (1) the excellent catalytic performance of Ru. To reduce the overcharge and discharge overpotential and improve the energy efficiency, (2) the use of carbon free cathode materials can avoid the secondary reaction caused by carbon corrosion and greatly improve the cycle performance of the battery. The above results have pointed out a problem that the charge discharge overpotential, the low energy transfer efficiency and the poor circulation stability are pointed out in the organic system of lithium oxygen batteries. The new breakthrough ideas and directions are of great significance for the development of high-performance, practical lithium oxygen batteries.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TM911.41;O643.36

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