【摘要】：鋰空氣電池,作為比能量最高的電池,有望解決電動汽車及能量存儲問題,近年來備受全世界矚目。在影響其商業(yè)化的眾多問題中,正極鈍化,電解液的降解,含氧量低及放電產(chǎn)物溶解度小等是最主要因素。但是正極的鈍化和電解液的降解是現(xiàn)階段限制鋰空氣電池發(fā)展的關(guān)鍵原因。穩(wěn)定性差的電解液,例如有機碳酸酯等,在電池運行過程中無法可逆形成Li2O2,并且電解液會分解成諸多不可逆產(chǎn)物,例如甲酸鋰,乙酸鋰及烷基化鋰等,同時許多不溶的副產(chǎn)物會沉積在孔空氣正極孔隙,堵塞O2傳輸通道,加劇電池極化。電池極化增大(過電壓)造成電解液的電化學(xué)不穩(wěn)定,從而改變電解液體系的成分并導(dǎo)致電池反應(yīng)機理發(fā)生改變。有機電解液又稱為非質(zhì)子極性溶劑,在反應(yīng)體系中不能給出質(zhì)子——不會釋放H+腐蝕鋰負(fù)極;又能使陽離子,特別是金屬陽離子(Li+)溶劑化,Li+在電解液中都是以溶劑化的形式Li+(S)n遷移。同時具有電化學(xué)窗口寬,熔點高不易揮發(fā),低粘度等優(yōu)點,有望解決鋰空氣電池商業(yè)化問題。本文采用1 M LiTFSI作為鋰鹽,通過對有機溶劑環(huán)丁砜(TMS)、N,N-二甲基乙酰胺(DMA)和四乙二醇二甲醚(TEGDME)的熔點、閃點、介電常數(shù)、粘度、電導(dǎo)率、溶氧量、電化學(xué)窗口等理化性質(zhì)研究,并運用交流阻抗測試,循環(huán)伏安測試、充放電測試表征采用三組單一電解液鋰空氣電池性能進(jìn)行對比,提出DMA+TMS作為鋰空氣電池混合電解液溶劑,確認(rèn)了LiTFSI-20DMA:80TMS適合作為鋰空氣電池電解液。最后根據(jù)DMA和TMS之間的協(xié)同作用,分別采用這兩種電解液對TEGDME進(jìn)行混合改性研究。(1)LiTFSI-TMS在三種電解液中粘度最高(25.26 mPa·s@28℃),離子電導(dǎo)率最低(1.91×10-3 S cm-1),在4℃~44℃粘度變化了43.56 mPa·s,因此溫度對TMS的離子電導(dǎo)率影響很大;LiTFSI-TEGDME的粘度適中(9.01mPa·s@28℃),但由于其結(jié)構(gòu)導(dǎo)致TEGDME離子電導(dǎo)也較低(2.06×10-3 S cm-1),其粘度隨溫度變化也比較明顯;LiTFSI-DMA的粘度最小(2.70 mPa·s@28℃),且粘度隨溫度變化不大,LiFTSI-DMA的離子電導(dǎo)率達(dá)到了TMS和TEGDME的四倍以上(8.87×10-3 S cm-1)。CV曲線OER起始電位大小依次為DMA(3.0 V)TMS(3.2 V)TEGDME(3.3 V)。在電流密度為0.3 mA cm-2/1.77 mA gcarbon-1,比容量為1000 mAh gcarbon-1,三種溶劑循環(huán)性能大小為TMS(200圈)TEGDME(80圈)DMA(50圈),但是TEGDME和TMS循環(huán)過程中存在嚴(yán)重的極化。(2)本文采用DMA:TMS混合制備鋰空氣電池電解液。通過粘度、離子電導(dǎo)率、CV、氣質(zhì)聯(lián)用技術(shù)(GCMS)對混合電解液體系分析優(yōu)化后發(fā)現(xiàn),TMS鋰空氣電池具有較高的穩(wěn)定性能。添加20%DMA進(jìn)入TMS電解液中制備混合電解液,在電流密度為0.3 mA cm-2,比容量為1000 mAh gcarbon-1,其充電過電壓比環(huán)丁砜鋰空氣電池低0.2 V~0.6 V,庫倫效率保持在100%,并且DMA改善了環(huán)丁砜的理化性質(zhì)。(3)用掃描電子顯微鏡(SEM)、X射線衍射(XRD)以及核磁共振氫譜(1H NMR)對放電產(chǎn)物進(jìn)行表征,TMS鋰空氣電池放電后的產(chǎn)物比較密集,正極表面附著了許多塊狀的Li2O2,20DMA:80TMS鋰空氣電池的產(chǎn)物是細(xì)小的顆粒,Li2O2本身不導(dǎo)電,因此會鈍化正極。20DMA:80TMS鋰空氣電池產(chǎn)物較高的比表面積加快了Li2O2的充電分解。研究表明,得益于TMS穩(wěn)定性能和DMA對電池極化的改善,首次提出DMA/TMS組成的雙功能電解液溶劑。綜合而言,DMA與TMS的協(xié)同作用使得電池的性能得到明顯改善。(4)根據(jù)DMA和TMS改性研究,分別用兩種溶劑對TEGDME鋰空氣電池進(jìn)行探索。結(jié)果表明,TMS對TEGDME電池性能并無顯著改善,而DMA同樣使TEGDME電池充電電壓有較為明顯的降低。
[Abstract]:Lithium-air batteries, as the most energy-specific batteries, have attracted worldwide attention in recent years. Among the problems affecting the commercialization of lithium-air batteries, cathode passivation, electrolyte degradation, low oxygen content and low solubility of discharge products are the main factors. Bad stability electrolytes, such as organic carbonates, are unable to form Li2O2 reversibly during battery operation, and the electrolyte decomposes into irreversible products, such as lithium formate, lithium acetate and lithium alkylate, and many insoluble by-products are deposited in pore air. The increase of cell polarization (overvoltage) results in the electrochemical instability of the electrolyte, thus changing the composition of the electrolyte system and leading to changes in the reaction mechanism of the cell. Lithium anode can be corroded and the cations, especially the metal cations (Li+) can be solvated. Li + is solvated in the electrolyte form of Li + (S) n migration. At the same time, it has the advantages of wide electrochemical window, high melting point, high volatility, low viscosity, and so on, it is expected to solve the commercial problems of lithium-air batteries. The melting point, flash point, dielectric constant, viscosity, conductivity, dissolved oxygen content, electrochemical window and other physical and chemical properties of solvent sulfolane (TMS), N, N-dimethylacetamide (DMA) and tetraethylene glycol dimethyl ether (TEGDME) were studied. The AC impedance test, cyclic voltammetry test and charge-discharge test were used to characterize the performance of three groups of single electrolyte lithium air batteries. Finally, according to the synergistic effect between DMA and TMS, two kinds of electrolytes were used to modify TEGDME. (1) LiTFSI-TMS had the highest viscosity in the three electrolytes (25.26 mPa @ s @ 28 C). The ionic conductivity is the lowest (1.91 *10-3 S cm-1), and the viscosity changes 43.56 mPa s at 4 44 C, so the temperature has a great influence on the ionic conductivity of TMS; the viscosity of LiTFSI-TEGDME is moderate (9.01 mPa s @ 28 C), but the ionic conductivity of TEGDME is also lower (2.06 10-3 S cm-1) because of its structure, and its viscosity changes obviously with temperature. The ionic conductivity of LiFTSI-DMA is more than four times that of TMS and TEGDME (8.87 *10-3 S cm-1). The starting potential of OER in CV curve is DMA (3.0 V) TMS (3.2 V) TEGDME (3.3 V). The current density is 0.3 mA cm-2/1.77 mA gcarbon-1, and the specific capacity is 1000 mAh carbon-1. 1. The performance of three solvents is TMS (200 cycles) TEGDME (80 cycles) DMA (50 cycles), but there is serious polarization in the process of TEGDME and TMS cycling. (2) In this paper, the electrolyte of lithium-air batteries was prepared by mixing DMA: TMS. Adding 20% DMA into the TMS electrolyte to prepare the mixed electrolyte, the current density is 0.3 mA cm-2, the specific capacity is 1000 mAh gcarbon-1, the charge overvoltage is 0.2 V~0.6 V lower than that of the sulfolane lithium air battery, the coulomb efficiency is maintained at 100%, and the physical and chemical properties of sulfolane are improved by DMA. Microscope (SEM), X-ray diffraction (XRD) and nuclear magnetic resonance hydrogen spectroscopy (1H NMR) were used to characterize the discharge products. After discharging, the products of the lithium-air battery were dense. The positive surface of the lithium-air battery was coated with many pieces of Li2O2,20DMA:80TMS particles. Li2O2 itself was not conductive, so the cathode would be passivated.20DMA:80TMS lithium-air battery. The high specific surface area of the gas cell products accelerated the charge decomposition of Li2O2. The results showed that the stability of TMS and the improvement of cell polarization by DMA were beneficial to the improvement of the performance of the battery. The results show that the performance of TEGDME battery is not improved significantly by using TMS, and the charging voltage of TEGDME battery is also decreased significantly by DMA.
【學(xué)位授予單位】：深圳大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TM911.41

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