發(fā)布時間：2018-06-18 22:30

  本文選題：鋰氧氣電池 + 過氧化鋰��； 參考：《南京大學》2016年博士論文

【摘要】：隨著電動汽車和智能電網(wǎng)市場規(guī)模的不斷擴大,電化學儲能技術越來越受到人們的關注。鋰氧氣電池理論比能量極高,是鋰離子電池的數(shù)倍,并且成本低廉、環(huán)境友好,因而被普遍認為是極具希望的下一代儲能系統(tǒng)。和鋰離子電池的研究方式一樣,目前普遍采用基于正極材料質(zhì)量的比容量來評估鋰氧氣電池的電化學性能。因此,有必要探究鋰氧氣電池是否合適采用這種方式來評估電化學性能,即是否滿足電池容量和正極材料質(zhì)量呈線性關系的前提條件。此外,目前實際比容量低、充電過電位大、循環(huán)性能差等問題嚴重限制了鋰氧氣電池的實用化進程。就我們所知,鋰氧氣電池的電化學性能主要取決于氧氣電極的結(jié)構(gòu)和固有化學性質(zhì)。因此,本論文中我們在優(yōu)化氧氣電極的多孔結(jié)構(gòu)和提高其穩(wěn)定性方面進行了一系列研究。此外,我們還綜合利用X射線衍射(XRD)、掃描電子顯微鏡(SEM)、X射線光電子能譜(XPS)、差分電化學質(zhì)譜(DEMS)等手段重點研究了鋰氧氣電池的充電反應機理。主要研究內(nèi)容如下：首先,我們探究了影響鋰氧氣電池放電容量的因素。通過驗證鋰離子電池的容量隨LiCoO2的質(zhì)量線性增加,說明采用質(zhì)量比容量這一參數(shù)來評估鋰離子電池的電化學性能是合理的。同時,我們發(fā)現(xiàn)鋰氧氣電池的放電容量也隨正極SP炭黑的質(zhì)量增加而增加,但是兩者不再呈線性關系。XRD的分析結(jié)果表明Li202是主要的放電產(chǎn)物,從而保證鋰氧氣電池的反應機理。考慮到氧氣是放電過程的反應物,我們進一步研究了氧氣窗口面積對電池放電容量的影響。實驗結(jié)果表明,鋰氧氣電池的放電容量隨氧氣窗口面積的增大線性增加。通過SEM觀察到鋰氧氣電池放電過程中Li202的沉積幾乎只發(fā)生在電極暴露在氧氣氛圍下的區(qū)域,因此,我們將電極暴露在氧氣氛圍的區(qū)域稱為Li202沉積的有效區(qū)域。此外,我們還合理地提出了鋰氧氣電池氧氣電極有效區(qū)域的形成途徑�；谏鲜鰧嶒灲Y(jié)果,我們通過一步法成功合成了具有自支撐和多階孔道結(jié)構(gòu)的石墨烯氣凝膠,并直接用作鋰氧氣電池不含粘結(jié)劑的正極材料。石墨烯氣凝膠的三維多階孔道結(jié)構(gòu)方便電解液的滲透、氧氣的擴散和電子的轉(zhuǎn)移,大比表面積能夠提供足夠多的活性反應位置,高孔容可以存儲更多的放電產(chǎn)物。因此,基于石墨烯氣凝膠的放電比容量高達10000mAhg-1. Ru納米顆粒進一步修飾在石墨烯片層的表面(Ru-GA),表現(xiàn)出對氧氣析出反應(OER)很好的催化活性。Ru-GA正極可以有效增加鋰氧氣電池的放電比容量(12000 mAh g-1),降低充電過電位,提升循環(huán)穩(wěn)定性(在500 mAh g-1的容量截止條件下可以循環(huán)50圈)。更重要的是,根據(jù)原位DEMS的分析結(jié)果,我們提出了鋰氧氣電池的充電過程可分為三個氧化階段的反應機理。再者,為了解決循環(huán)過程中碳腐蝕的問題,我們通過硬模板法制備了孔徑不同的有序多孔Ru02材料,并用作鋰氧氣電池的無碳正極。同時,我們還系統(tǒng)研究了有序多孔Ru02材料的孔隙結(jié)構(gòu)參數(shù)對鋰氧氣電池性能的影響。電化學測試和分析結(jié)果表明,基于孔徑為16nmRuO2(RuO2-16)正極的鋰氧氣電池放電比容量最大,能量轉(zhuǎn)換效率最高,并且在100 mAg-1電流密度和2.5-4.0 V電壓區(qū)間內(nèi)可以穩(wěn)定循環(huán)70圈。鋰氧氣電池如此優(yōu)異的電化學性能得益于Ru02-16正極良好的電子導電性、較大的BET比表面積、合適的孔徑大小和對OER良好的催化活性。原位DEMS的分析結(jié)果表明,和碳材料正極相比,RuO2-16無碳正極能夠有效減少副反應的產(chǎn)生。最后,我們深入研究了具有高比表面積的活化石墨烯吸附的水汽對鋰氧氣電池電化學性能和反應機理的影響。活化石墨烯用作正極的鋰氧氣電池在充電過程中出現(xiàn)了兩個電壓平臺。通過XRD和SEM對不同充放電階段的產(chǎn)物進行表征,我們發(fā)現(xiàn)鋰氧氣電池的放電產(chǎn)物中既有Li2O2,也有LiOH,并且生成的LiOH會在電池充電至3.5 V時完全分解。這與原位DEMS的分析結(jié)果吻合。但是,當SP炭黑用作正極時,并沒有發(fā)現(xiàn)LiOH。這表明LiOH的形成與活化石墨烯有關。卡爾-費休滴定的結(jié)果表明,活化石墨烯由于極高的比表面積,吸附了空氣中大量的水汽。因此,H20與放電產(chǎn)物Li202反應生成LiOH, LiOH的分解造成了較低的充電電壓平臺。
[Abstract]:With the expansion of the market size of electric vehicles and smart grid, the electrochemical energy storage technology has attracted more and more attention. The theory of lithium oxygen battery is more than energy, many times the lithium ion battery, and the cost is low, and the environment is friendly. Therefore, it is generally considered as the very promising next generation energy storage system. And the lithium ion battery research In the same way, it is widely used to evaluate the electrochemical performance of lithium Oxygen Batteries Based on the mass specific capacity of positive materials. Therefore, it is necessary to explore whether lithium oxygen batteries are suitable for evaluating the electrochemical performance, that is, whether the battery capacity and the material quantity of positive electrode have a linear relationship. The problems of low specific capacity, large overpotential and poor cycling performance seriously restrict the practical process of lithium oxygen batteries. As we know, the electrochemical performance of the lithium oxygen cell depends mainly on the structure and natural chemical properties of the oxygen electrode. Therefore, in this paper, we are optimizing the porous structure of the oxygen electrode and improving its stability. In addition, X ray diffraction (XRD), scanning electron microscope (SEM), X ray photoelectron spectroscopy (XPS) and differential electrochemical mass spectrometry (DEMS) are used to study the reaction mechanism of lithium oxygen batteries. The main contents are as follows: first, we explored the influence of lithium oxygen battery discharge. By verifying that the capacity of the lithium ion battery increases linearly with the mass of LiCoO2, it is reasonable to use the mass specific capacity to evaluate the electrochemical performance of the lithium ion battery. At the same time, we find that the discharge capacity of the lithium oxygen battery increases with the increase of the quality of the positive SP carbon black, but both of them are no longer linear. The analysis of the relationship.XRD shows that Li202 is the main discharge product, thus ensuring the reaction mechanism of the lithium oxygen battery. Considering the oxygen is the reactant of the discharge process, we further study the effect of the oxygen window area on the discharge capacity of the battery. The experimental results show that the discharge capacity of the lithium oxygen battery increases with the increase of the oxygen window area. By SEM, it is observed that the deposition of Li202 in the discharge process of the lithium oxygen cell is almost only in the area exposed to the oxygen atmosphere by the electrode, so we call the area of the oxygen atmosphere of the electrode known as the effective region of the Li202 deposition. In addition, we also reasonably put forward the shape of the oxygen electrode in the lithium oxygen battery. Based on the above experimental results, we successfully synthesized graphene aerogels with self support and multistage channel structure by one step method and directly used as cathode materials for lithium oxygen batteries without adhesives. The three-dimensional multi-channel structure of graphene aerogels is convenient for the permeation of the electrolyte, the diffusion of oxygen and the transfer of electrons. The specific surface area can provide enough active reaction position, and the high pore volume can store more discharge products. Therefore, the discharge specific capacity of the graphene aerogel is up to 10000mAhg-1. Ru nanoparticles to be further modified on the surface of the graphene lamellar (Ru-GA), showing a good catalytic active.Ru-GA positive electrode for the oxygen exhalation reaction (OER). It can effectively increase the discharge specific capacity of the lithium oxygen battery (12000 mAh g-1), reduce the overpotential and improve the cycle stability (50 cycles can be circulate under the capacity cut-off condition of 500 mAh g-1). Furthermore, in order to solve the problem of carbon corrosion in the cycle process, we have prepared porous Ru02 materials with different pore sizes by hard template method and used as carbon free cathode of lithium oxygen batteries. At the same time, we also systematically studied the effect of pore structure parameters of ordered porous Ru02 materials on the performance of lithium oxygen batteries. The results show that the discharge capacity of the lithium oxygen battery based on the aperture of 16nmRuO2 (RuO2-16) is the highest, the energy conversion efficiency is the highest, and the 70 cycles can be stabilized in the 100 mAg-1 current density and the 2.5-4.0 V voltage range. The excellent electrochemical properties of the lithium oxygen battery can benefit from the good electronic conductivity of the Ru02-16 positive electrode. The large BET specific surface area, suitable aperture size and good catalytic activity for OER. In situ DEMS analysis shows that RuO2-16 carbon free positive electrode can effectively reduce the production of the side reaction. Finally, we have studied the electrochemical properties of the lithium oxygen battery adsorbed by activated graphene with high specific surface area. There are two voltage platforms in the charging process of the living fossil ink as the positive electrode. Through XRD and SEM, the products of different charge discharge stages are characterized. We find that the discharge products of the lithium oxygen battery have both Li2O2 and LiOH, and the generated LiOH will finish when the battery is charged to 3.5 V. Full decomposition. This coincides with the analysis of in situ DEMS. However, when SP carbon black is used as a positive pole, no LiOH. is found to indicate that the formation of LiOH is associated with the living fossil graphene. The results of Carle - Fischer titration showed that the living fossil graphene adsorbed a large amount of water vapor in the air because of its high specific surface area. Therefore, H20 was reacted with the discharge product Li202. The decomposition of LiOH and LiOH results in a lower charging voltage platform.
【學位授予單位】：南京大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TM911.41
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本文編號：2037084