本文選題：高電壓鋰離子電池　切入點(diǎn)：界面膜　出處：《北京科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：隨著石油資源的逐漸枯竭,以及汽車尾氣排放帶來的環(huán)境污染等問題,使得新能源汽車成為未來汽車的主要發(fā)展方向,成為行業(yè)研究熱點(diǎn)。鋰離子電池作為新能源汽車的核心零部件得到越來越多的關(guān)注。為了更好的滿足用戶需求,解決里程焦慮的問題,開發(fā)更高比能量的電池來延長汽車?yán)m(xù)航里程成為必然。提高鋰離子電池的比能量需要提高活性材料的克容量發(fā)揮,擴(kuò)寬電池的電壓窗口,開發(fā)高電壓鋰離子電池。本文以開發(fā)高電壓鋰離子電池化學(xué)體系為目標(biāo),將關(guān)鍵原材料的研發(fā)和正負(fù)極界面膜優(yōu)化等過程關(guān)鍵參數(shù)的識(shí)別有機(jī)結(jié)合起來,首先研究了決定高電壓鋰離子電池能量的正極富鋰材料和決定電壓窗口的電解液體系;然后為了高電壓鋰離子電池?fù)碛懈觾?yōu)異的性能,識(shí)別了適用于高電壓鋰離子電池負(fù)極表面界面膜精修的低電位恒壓化成參數(shù)和正極表面可控生長界面膜的高電位下高壓化成參數(shù),并研究了加工過程中不可避免帶入的痕量水分對(duì)整個(gè)電池體系穩(wěn)定性的影響;最后將優(yōu)化的正極富鋰材料、耐高壓分解的電解液和界面膜優(yōu)化有機(jī)結(jié)合起來,開發(fā)了性能優(yōu)異的高電壓鋰離子電池化學(xué)體系,并對(duì)體系的壽命衰減機(jī)理進(jìn)行了分析,進(jìn)一步優(yōu)化了高電壓鋰離子電池化學(xué)體系。富鋰材料具備較高的克容量發(fā)揮,是開發(fā)高電壓高能量鋰離子電池優(yōu)異的正極材料。但富鋰材料在充放電過程中,由于Mn元素的變價(jià),會(huì)發(fā)生類似尖晶石結(jié)構(gòu)的相變,導(dǎo)致性能的快速劣化。本文采用Cu~(2+)元素?fù)诫s的方法,取代一部分Mn~(4+),增強(qiáng)材料的結(jié)構(gòu)穩(wěn)定性和導(dǎo)電性,從而提高材料的電化學(xué)性能。通過液相共沉淀和球磨法,合成了含有不同比例Cu~(2+)的富鋰材料0.5Li2MnO3·0.5Li(Ni0.5Mn0.5-xCux)O2,采用XRD,SEM,粉末電子電導(dǎo)和電化學(xué)充放電等測(cè)試方法對(duì)摻雜Cu~(2+)的富鋰材料進(jìn)行了表征。研究表明:摻雜Cu~(2+)之后,材料形貌由顆粒狀變?yōu)轭惏魻?材料的層間距增大,克容量發(fā)揮降低,隨著摻雜Cu~(2+)比例的提高,材料電子電導(dǎo)率逐漸增大,克容量發(fā)揮隨之提高,壽命改善也越明顯。摻雜能明顯增加富鋰材料的晶胞體積和層間距,有利于鋰離子在循環(huán)過程中的脫嵌,增強(qiáng)材料的結(jié)構(gòu)穩(wěn)定性,進(jìn)而改善循環(huán)性能。為了拓寬電池的工作電壓窗口,本文研究了基于氟代溶劑D2的耐氧化分解的電解液體系,研究各溶劑組成、鋰鹽濃度對(duì)有機(jī)電解液的電導(dǎo)率、飽和蒸汽壓、熱穩(wěn)定性、電化學(xué)窗口、正極耐高壓穩(wěn)定性和負(fù)極成膜穩(wěn)定性的影響。結(jié)果表明:隨著電解液中鋰鹽濃度的增大,電導(dǎo)率先增大再降低,飽和蒸汽壓降低,熱穩(wěn)定性變差;隨著電解液中D2比例的增大,電導(dǎo)率逐漸降低,飽和蒸汽壓逐漸升高;D2溶劑明顯提升了電解液的耐氧化分解特性,并參與了碳酸酯類溶劑在負(fù)極上的還原反應(yīng)。識(shí)別化成參數(shù)可以優(yōu)化電池正負(fù)極在首次充放電過程中所形成的界面膜,提升高電壓鋰離子電池的循環(huán)性能。對(duì)于負(fù)極,本文研究低電位下恒壓精修SEI膜的化成方法,識(shí)別了關(guān)鍵控制參數(shù),發(fā)現(xiàn)在3.3V下恒壓60min,能夠在負(fù)極表面上形成致密、低阻抗、良好均一性的界面SEI膜。針對(duì)正極在高電位下持續(xù)氧化分解電解液造成電池性能劣化的問題,本文尋找合適的恒壓電位,控制電解液中VC的含量,從化成參數(shù)優(yōu)化的角度,研究VC在電解液中的最佳比例,促使VC添加劑在正極表面充分、有序、可控分解,形成穩(wěn)定的界面SEI膜,阻止電解液進(jìn)一步的氧化分解,從而提高高電壓鋰離子電池高壓下的循環(huán)壽命。研究發(fā)現(xiàn)當(dāng)電解液中VC含量為0.8%,首次充電截止電壓為4.63V,恒壓40min,電池的循環(huán)性能最佳,300次循環(huán)后容量保持率達(dá)到70%。痕量水分對(duì)電池體系的穩(wěn)定性有較大影響。本文研究了痕量水分對(duì)電池體系穩(wěn)定性的影響,研究發(fā)現(xiàn):水分對(duì)于正極,主要影響了電解液在正極表面發(fā)生氧化分解反應(yīng)的電位,水分含量越高,電解液的氧化分解電位越低,氧化分解的產(chǎn)物在正極表面沉積,導(dǎo)致正極界面膜阻抗增大,而對(duì)正極材料結(jié)構(gòu)沒有影響;水分在石墨負(fù)極表面參與SEI的形成反應(yīng),改變了負(fù)極界面膜的組成和形貌,水分含量高的負(fù)極形成較厚的、疏松多孔的界面膜;不同水份含量全電池的壽命測(cè)試顯示,負(fù)極水分含量的增大對(duì)電池循環(huán)壽命的影響要比正極水分含量增大顯著的多;通過三電極分析發(fā)現(xiàn),負(fù)極界面膜Rf的增大是電池阻抗增大的主要原因,負(fù)極水分含量越高,Rf隨循環(huán)增長就越快,最終導(dǎo)致電池壽命衰減加劇。最后,本文采用摻Cu~(2+)改性后的富鋰材料為正極,普通人造石墨為負(fù)極,常規(guī)PP/PE/PP三層復(fù)合聚烯烴隔膜,匹配D2氟化溶劑為主體成分的耐高壓分解電解液,并采用負(fù)極界面SEI膜精修的低電位恒壓化成參數(shù)和高電位下正極表面可控生長界面膜的高壓化成參數(shù),嚴(yán)格控制過程水分在合理的區(qū)間范圍,制備了高電壓鋰離子電池,并對(duì)壽命衰減機(jī)理進(jìn)行分析,進(jìn)一步優(yōu)化了高電壓鋰離子電池的化學(xué)體系。
[Abstract]:With the gradual depletion of oil resources, and vehicle emissions caused by environmental pollution and other issues, making the new energy vehicles have become the main direction of future car development, become a hot research area. Lithium ion batteries as the core components of new energy vehicles to get more and more attention. In order to better meet the needs of users, solve the mileage anxiety problems. The development of more high energy battery to prolong the vehicle mileage become inevitable. Improve the lithium ion battery than the energy needed to improve the active material capacity per gram of play, widening the battery voltage window, the development of high voltage lithium ion battery. In this paper, the development of high voltage lithium ion battery chemistry system as the goal, the key raw materials research and development and the positive and negative polar circle mask key parameters optimization process identification organically, firstly studies the positive decision of high voltage lithium ion battery energy The electrolyte lithium rich materials and then to determine the voltage window; high voltage lithium ion battery have more excellent performance and recognition for high voltage lithium ion battery cathode surface film refinement of low potential parameters and constant pressure into the anode surface controlled growth bounded in the high potential and high voltage forming parameters, and the effects of the trace the water in the process of the inevitable into the whole cell system stability; cathode lithium rich materials will finally be optimized, high pressure decomposition of the electrolyte and the film optimization combine the development of excellent high voltage lithium ion battery chemical system, and the system lifetime decay mechanism is analyzed, further optimization of the high voltage lithium ion battery chemistry system. Lithium rich materials have relatively high capacity, is the development of high voltage high energy lithium ion battery is excellent The electrode materials for lithium rich materials. But in the process of charge and discharge, because the Mn element valence, phase transition occurs similar to spinel structure, leading to rapid deterioration of the performance. This paper uses the method of Cu~ (2+) doped, replacing a part of Mn~ (4+), enhanced structural stability and conductivity of the material, so as to improve the the electrochemical properties of materials through liquid phase coprecipitation and ball milling method, with different proportion of synthesis of Cu~ (2+) of the lithium rich materials (Ni0.5Mn0.5-xCux), 0.5Li2MnO3 0.5Li O2, by XRD, SEM, test method of powder electronic conductivity and electrochemical charge discharge of doped Cu~ (2+) of the lithium rich materials were characterized. Research shows that the doping of Cu~ (2+), the material morphology from granular into class bar, materials increased the interlayer spacing, G capacity decreased with the doping of Cu~ (2+) the increase in the proportion of materials, electronic conductivity increases grams capacity play increase, improve service life Is more obvious. Doping can obviously increase the cell volume and the layer spacing of lithium rich materials, for lithium ions in the circulation process disembedded, enhance the structural stability of materials, and improve the cycle performance. In order to broaden the battery voltage window, in this paper the fluorinated solvent resistance of D2 electrolyte decomposition oxidation based on the study of the solvent composition, the conductivity of lithium salt concentration on the organic electrolyte, saturated vapor pressure, thermal stability, electrochemical window, positive and negative effects of high pressure resistant stability of membrane stability. The results show that: with the increase of salt concentration in the electrolyte, the conductivity increased first and then decreased, reducing the saturated vapor pressure and thermal stability becomes worse; with the increase of the proportion of D2 in the electrolyte, the conductivity decreased gradually, the saturated vapor pressure gradually increased; D2 solvent significantly enhance the oxidation decomposition of the electrolyte, and part of the carbonate dissolution The reduction reaction in the cathode of the battery can be optimized. Formed in the first charge discharge process to identify parameters of interfacial film, improved cyclic performance of high voltage anode for lithium ion batteries. In this paper, the formation process of low potential under constant refinement of the SEI film, identify the key control parameters, found in 3.3V constant pressure 60min, can form a dense, in the anode on the surface of low impedance, good uniformity of interface of SEI films. For the positive continuous oxidative decomposition of electrolyte caused by the deterioration of the battery performance in high potential, the potential for constant pressure fit, to control the content of VC in electrolyte, a parameter optimization point of Conghua, the best ratio of VC in the electrolyte, the VC additive in the cathode surface is sufficient, orderly, controllable decomposition, interface form stable SEI film, prevent further oxidation electrolyte decomposition, so as to improve high voltage lithium Ion battery cycle life under high pressure. The study found that when the content of VC in the electrolyte is 0.8%, the first charging voltage is 4.63V, voltage 40min, cell cycle performance, after 300 cycles the capacity retention rate has great influence on the stability of 70%. trace water battery system. This paper investigates the influence of trace water on the battery system the study found that: the stability of water on the cathode, the main impact of the electrolyte on the cathode surface potential oxidation decomposition reaction, the higher water content, electrolyte oxidation potential is low, product decomposition oxidation deposition on the cathode surface, resulting in the increase of cathode interface impedance, but no effect on the structure of cathode material; water formation reaction in the surface of graphite anode in SEI, changed the composition and morphology of the cathode film anode, high moisture content to form thick, porous film; not Life test with moisture content of whole cell showed negative effect on the moisture content increase the battery cycle life than the cathode water content increased significantly more; through the three electrode analysis showed that the increase of Rf cathode film is the main reason for the battery impedance increase, anode water content is higher, with the cycle of growth is more Rf fast, resulting in increased battery life attenuation. Finally, this paper uses Cu~ (2+) doped modified lithium rich materials of the cathode, the common artificial graphite as anode, conventional PP/PE/PP three layer composite polyolefin diaphragm, high pressure resistance, solvent based electrolyte decomposition D2 fluoride, body composition, and surface controlled cathode high potential growth sector mask of the high voltage forming low potential and formation parameters of constant parameters using SEI membrane anode surface refinement, strict control of water in a reasonable range, high voltage lithium ion battery was prepared, and the life The mechanism of life attenuation is analyzed, and the chemical system of high voltage lithium ion battery is further optimized.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM912

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