發(fā)布時(shí)間：2018-07-08 11:18

  本文選題：鋰空氣電池 + 非水電解液體系��； 參考：《國(guó)防科學(xué)技術(shù)大學(xué)》2014年博士論文

【摘要】：隨著人們對(duì)高能量密度儲(chǔ)能系統(tǒng)的需求日益迫切,具有極高理論能量密度的鋰空氣電池(11300 Wh kg-1)自問(wèn)世起便得到了研究人員的廣泛關(guān)注。非水鋰空氣電池因具有結(jié)構(gòu)簡(jiǎn)單、電極反應(yīng)可逆的特點(diǎn),已成為目前鋰空氣二次電池領(lǐng)域的研究熱點(diǎn)。雖然具有諸多優(yōu)勢(shì),但非水鋰空氣電池在實(shí)際應(yīng)用過(guò)程中依然面臨著電解液體系不穩(wěn)定、電池循環(huán)性能較差,空氣電極結(jié)構(gòu)和表面性質(zhì)對(duì)電極放電性能影響機(jī)制不明確等問(wèn)題,導(dǎo)致目前非水鋰空氣電池實(shí)用化進(jìn)程面臨著嚴(yán)峻挑戰(zhàn)。針對(duì)上述問(wèn)題,本文首先利用循環(huán)伏安、恒流充放電測(cè)試及離線光譜測(cè)試對(duì)三種有機(jī)電解液體系—碳酸酯類(lèi)(碳酸乙烯酯,EC和碳酸二乙酯,DEC)、醚類(lèi)(乙二醇二甲醚,DME)和酰胺類(lèi)(N-甲基-2-吡咯烷酮,NMP)溶劑在鋰空氣電池中的穩(wěn)定性進(jìn)行系統(tǒng)研究。研究結(jié)果表明,碳酸酯類(lèi)分子易于被O2-親核進(jìn)攻發(fā)生分解生成Li2CO3和烷基碳酸鋰;醚類(lèi)分子的自氧化反應(yīng)則會(huì)導(dǎo)致醚類(lèi)電解液在長(zhǎng)時(shí)間放電過(guò)程中發(fā)生分解,副反應(yīng)產(chǎn)物為L(zhǎng)i2CO3。由于存在不穩(wěn)定分解,兩種溶劑分子均不適用于非水鋰空氣電池。在研究的三種溶劑分子中,酰胺類(lèi)溶劑具有最好的穩(wěn)定性,其首次放電產(chǎn)物為L(zhǎng)i2O2,首次循環(huán)過(guò)程的庫(kù)倫效率達(dá)到97%。NMP在放電過(guò)程中對(duì)O2-良好的穩(wěn)定性為后續(xù)O2還原電極過(guò)程研究提供了穩(wěn)定的電解液體系。但對(duì)采用NMP電解液鋰空氣電池的循環(huán)性能進(jìn)一步研究表明,充電過(guò)程中,NMP在空氣電極表面會(huì)發(fā)生電化學(xué)氧化分解,生成Li2CO3和LiNOx;同時(shí)在鋰負(fù)極表面發(fā)生電化學(xué)還原,生成亞胺基醚鋰、氨基酸鋰和LiOH。充電過(guò)程中NMP在正負(fù)極兩側(cè)的分解均會(huì)導(dǎo)致電池循環(huán)性能的衰退。以兩種標(biāo)準(zhǔn)平板電極金(Au)電極和玻碳(GC)電極為研究對(duì)象,綜合考慮O2還原電極過(guò)程中,O2異相電荷轉(zhuǎn)移過(guò)程、O2-均相轉(zhuǎn)化過(guò)程和Li2O2沉積三個(gè)步驟間的相互影響。利用穩(wěn)態(tài)極化曲線,陰極極化條件下的交流阻抗譜和整體電解法系統(tǒng)研究了兩種電極表面O2還原過(guò)程的特征。研究結(jié)果表明,O2在不同電極材料表面上的還原過(guò)程存在顯著差異。相對(duì)于GC電極,Au電極表面O2具有更快的異相電荷轉(zhuǎn)移速度和較慢的O2-均相轉(zhuǎn)化速率,Li2O2在其表面的沉積傾向于垂直表面生長(zhǎng)。電化學(xué)還原產(chǎn)物O2-在Li2O2表面的富集導(dǎo)致O2還原過(guò)程中,沉積的Li2O2電阻率水平顯著低于其本體電阻率。O2的電荷轉(zhuǎn)移過(guò)程越快,O2-的消耗速率越慢,Li2O2電阻率水平越低,因此Au電極表面沉積的Li2O2具有較小的電阻率數(shù)值。為進(jìn)一步研究多孔空氣電極中材料表面性質(zhì)同電極放電性能間的關(guān)系,本文利用溶液浸漬方法制備了一種全碳納米管(CNT)空氣電極。在不改變電極宏觀孔道結(jié)構(gòu)的前提下,通過(guò)改變熱處理溫度,控制CNT表面性質(zhì),系統(tǒng)分析了CNT電極表面性質(zhì)對(duì)O2還原電極過(guò)程的影響。結(jié)果表明,CNT表面具有吸電子能力的含氧基團(tuán)會(huì)抑制O2的異相電荷轉(zhuǎn)移過(guò)程,同時(shí)含氧基團(tuán)的引入會(huì)提高O2-的均相轉(zhuǎn)化過(guò)程速率。在含氧官能團(tuán)含量較高,表面孔道孔徑較小的CNT電極表面,Li2O2表現(xiàn)出傾向平行電極表面生長(zhǎng)的特征。降低CNT表面含氧官能團(tuán)含量,擴(kuò)大表面孔道孔徑,Li2O2在CNT表面垂直生長(zhǎng)的趨勢(shì)增強(qiáng)。根據(jù)CNT表面Li2O2電阻率水平和不同熱處理?xiàng)l件下CNT電極表面形貌隨放電深度的變化規(guī)律,本文確定了放電過(guò)程中電極電子傳導(dǎo)能力并不是導(dǎo)致放電終止的主要因素,電極放電性能主要決定于O2在Li2O2表面的后續(xù)還原過(guò)程。在含氧官能團(tuán)含量低,表面孔道孔徑較大的CNT電極表面,較高的相對(duì)生長(zhǎng)指數(shù)使得Li2O2具有橢球狀形貌結(jié)構(gòu),該形貌結(jié)構(gòu)有利于O2在Li2O2顆粒表面的后續(xù)電荷轉(zhuǎn)移過(guò)程,這使得上述CNT電極體現(xiàn)了良好的放電性能。結(jié)合上一部分的研究結(jié)果,電極材料表面性質(zhì)直接決定了電極表面O2還原過(guò)程特征。因此,電極材料表面性質(zhì)是影響電極放電性能的根本性關(guān)鍵因素之一。本文還在現(xiàn)有單一電解液體系無(wú)法同時(shí)滿足充電過(guò)程中鋰空氣電池正負(fù)極穩(wěn)定性需求的研究結(jié)果基礎(chǔ)上,探索了一種新型雙電解液體系在非水鋰空氣電池中的應(yīng)用。以CNT電極為空氣電極,金屬鋰為負(fù)極,引入固體電解質(zhì)LAGP,正負(fù)極兩側(cè)分別采用NMP和碳酸酯類(lèi)電解液,構(gòu)成具有雙電解液結(jié)構(gòu)的鋰空氣電池(Li|1 mol L-1 LiPF6-EC\DEC|LAGP|0.1 mol L-1 LiClO4-NMP|CNT)。測(cè)試結(jié)果表明,通過(guò)利用固體電解質(zhì)的隔離作用避免非水電解液在正負(fù)極的副反應(yīng)歷程,該電池體系在限制3000 mAh g-1比容量的條件下,40次后的循環(huán)性能無(wú)明顯衰減。該結(jié)構(gòu)體系的提出,為現(xiàn)有鋰空氣電池的應(yīng)用探索了一條可行途徑。
[Abstract]:With the increasing demand for high energy density energy storage systems, lithium air batteries with high theoretical energy density (11300 Wh kg-1) have been widely concerned by researchers since they were asked. The non lithium ion battery has become the research of the two battery field of lithium air because of its simple structure and reversible electrode reaction. Although it has many advantages, the non water lithium air battery still faces the problems of the instability of the electrolyte system, the poor performance of the battery cycle, the unclear influence mechanism of the air electrode structure and the surface properties on the discharge performance of the electrode, which leads to the severe choice of the practical process of the current non water lithium air battery. In order to solve the above problems, the stability of three organic electrolyte systems - carbonate (ethylene carbonate, EC and two ethyl carbonate, DEC), ethers (ethylene glycol two methyl ether, DME) and amides (N- methyl -2- pyrrolidone, NMP) solvents in lithium air batteries The results show that the carbonic acid esters are easily decomposed by O2- nucleophilic attack to produce Li2CO3 and alkyl lithium carbonate, and the self oxidation of ether molecules will result in the decomposition of the ether electrolyte during the long discharge process. The side reaction product is Li2CO3. because of the existence of unstable decomposition, the two solvents are discomfort. For the non water lithium air battery. Among the three solvent molecules studied, amides have the best stability, the first discharge product is Li2O2, the Kulun efficiency of the first cycle process reaches 97%.NMP and the good stability of O2- during the discharge process provides a stable electrolyte system for the subsequent O2 reduction electrode process. Further study on the cyclic performance of NMP electrolyte lithium air battery shows that in the charging process, the electrochemical oxidation of NMP will occur on the surface of the air electrode to produce Li2CO3 and LiNOx, and the electrochemical reduction on the surface of the lithium anode produces imino ether lithium, and the decomposition of NMP on both sides of the positive and negative poles during the charging process of amino acid lithium and LiOH. will be all Two standard flat electrode gold (Au) electrode and glassy carbon (GC) electrode are used as the research object. The interaction between the O2 heterphasic charge transfer process, the O2- homogeneous transformation process and the Li2O2 deposition in the O2 reduction electrode process is taken into consideration. The stable polarization curve and the AC impedance under the cathodic polarization condition are used. The characteristics of the O2 reduction process on the surface of the two electrodes are studied by the spectrum and the whole electrolysis system. The results show that there is a significant difference in the reduction process of O2 on the surface of different electrode materials. Relative to the GC electrode, O2 has a faster rate of heterogeneous charge transfer and slower O2- phase transformation rate on the surface of Au electrode, and the deposition of Li2O2 on the surface of the electrode has been deposited on the surface of the electrode. The growth of the electrochemical reduction product O2- on the Li2O2 surface leads to the O2 reduction process, and the resistivity of the deposited Li2O2 is significantly lower than that of its bulk resistivity.O2, the faster the charge transfer process, the slower the O2- consumption rate, the lower the Li2O2 resistivity, so that the Li2O2 deposited on the Au electrode surface has a smaller number of resistivity. In order to further study the relationship between the surface properties of porous materials and the performance of electrode discharge in the porous air electrode, a kind of full carbon nanotube (CNT) air electrode was prepared by solution impregnation. Under the premise of changing the macro channel structure of the electrode, the surface properties of CNT were controlled by changing the temperature of heat treatment, and the CNT electrode table was systematically analyzed. The effect of surface properties on the process of O2 reduction electrode shows that the oxygen - containing groups with the ability of absorbing electrons on the surface of CNT will inhibit the heterogeneous charge transfer process of O2, and the introduction of oxygen containing groups will increase the rate of the homogeneous transformation process of O2-. In the CNT electrode surface with higher oxygen functional group content and smaller pore diameter of the surface, the Li2O2 shows the dip. The characteristics of the growth of the parallel electrode surface. Reducing the content of oxygen functional groups on the surface of CNT, expanding the pore diameter of the surface and increasing the vertical growth of Li2O2 on the CNT surface. According to the Li2O2 resistivity of the CNT surface and the change law of the surface morphology of the CNT electrode with the discharge depth under different heat treatment conditions, the electrode electricity in the discharge process is determined. The conductivity is not the main factor that leads to the termination of the discharge. The discharge performance of the electrode is mainly determined by the subsequent reduction process of O2 on the surface of Li2O2. In the CNT electrode surface with a low oxygen functional group content and a larger surface pore diameter, the higher relative growth index makes the Li2O2 elliptically shaped structure, which is beneficial to O2 in Li2O. The following charge transfer process on the surface of 2 particles makes the CNT electrode exhibit good discharge performance. Combining the results of the previous part, the surface properties of the electrode directly determine the characteristics of the O2 reduction process on the electrode surface. Therefore, the surface properties of the electrode material are one of the key factors affecting the discharge performance of the electrode. On the basis of the research results that the existing single electrolyte system can not meet the positive and negative stability requirements of the lithium air battery in the charging process, a new dual electrolyte system is used in the non water lithium air battery. The CNT electrode is used as the air electrode, the metal lithium is negative, the solid electrolyte LAGP is introduced and the positive and negative poles are divided. The lithium air battery (Li|1 mol L-1 LiPF6-ECDEC|LAGP|0.1 mol L-1 LiClO4-NMP|CNT) with double electrolyte structure is not used in the electrolyte of NMP and carbonate. The test results show that the negative reaction process of non water electrolyte in positive and negative electrode is avoided by the isolation effect of solid electrolyte, and the battery system is limited to 3000 mAh g-1 specific capacitance. Under the condition of volume, the cycle performance of the 40 cycles is not obviously attenuated. The proposed structure system has explored a feasible way for the application of the existing lithium air battery.
【學(xué)位授予單位】：國(guó)防科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TM911.41

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