本文選題：鋰離子電池　切入點：正極材料　出處：《北京科技大學》2017年博士論文　論文類型：學位論文

【摘要】：富鋰錳基固溶體正極材料由于其大于280 mAh g-1的超高比容量以及低成本等優(yōu)勢被認為是最有潛力的下一代鋰離子電池正極材料,其超高比容量與特殊的充放電機制引起了科研工作者的濃厚興趣。富鋰材料的高容量與首次充電過程中4.5 V處氧的脫出有關,然而氧的脫出會造成材料的首次不可逆容量損失過大,以及氧空位的形成和局域離子遷移、重排,從而引起循環(huán)過程中的結(jié)構(gòu)衍變,導致電壓降與容量衰減,同時富鋰材料的倍率性能較差,因此阻礙了其產(chǎn)業(yè)化道路。本論文以富鋰錳基固溶體材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2為對象,以實現(xiàn)富鋰材料的高能量密度和高功率密度,提高其比容量、倍率性能和循環(huán)結(jié)構(gòu)穩(wěn)定性為目標,就以下幾個方面展開工作:采用高壓靜電紡絲法制備一維納米纖維狀的富鋰材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2,同時采用共沉淀法合成納米顆粒狀材料作為對照,對納米纖維狀富鋰材料與顆粒狀富鋰材料在形貌、比表面積、晶體結(jié)構(gòu)、電化學性能與氧化還原機理之間的關系進行了全面的研究與報道,BET測試結(jié)果表明納米纖維狀富鋰材料的比表面積為6.537 m2 g-1,大于納米顆粒狀材料(4.388 m2g-1),由于納米纖維狀材料具有更好的鋰離子擴散動力學條件,在5 C倍率下能夠釋放126.6 mAh g-1的容量,大于納米顆粒狀材料的101.1 mAhg'1。此外,創(chuàng)新性地采用分段循環(huán)伏安法對首次氧化還原過程進行區(qū)別對比考察,利用電化學方法更好的解釋了富鋰層狀正極材料在首次充放電過程中的O脫出與Mn活化的氧化還原機理。在靜電紡絲法制備納米纖維狀富鋰材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2的過程中,在對前驅(qū)體采取不同的熱處條件時,其終產(chǎn)物會表現(xiàn)出不同的形貌,得出升溫速度影響終產(chǎn)物的微觀形貌這一結(jié)論,即當以1℃ min-1的速度升溫時終產(chǎn)物表現(xiàn)出以為一維納米纖維形貌,當升溫速度為5 ℃ min-1時終產(chǎn)物會表現(xiàn)出花瓣狀納米片的微觀形貌。樣品在800℃鍛燒8 h后表現(xiàn)出良好的倍率性能,這歸因于其具有良好的動力學條件,5 C的放電容量達到127 mAh g-1。納米線狀與花瓣狀納米片材料具備納米材料特有的尺寸效應小的特點,能縮短鋰離子的遷移時間,另外,材料較大的比表面積能夠使電極與電解液充分接觸,減小電極在大電流密度下充放電時的極化現(xiàn)象。對富鋰正極材料進行酸浸出處理會使材料發(fā)生鋰離子與氧離子的化學脫出,即Li2O從晶格中脫出,這種方法可以有效降低富鋰正極材料的首次不可逆容量損失,然而高濃度的酸浸出處理會對材料表面晶體結(jié)構(gòu)造成較大破壞從而導致電極的循環(huán)性能惡化。本論文首次報道了采用稀釋后的低濃度的酸溶液(0.01moL-lHNO3溶液)對富鋰材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2進行溫和的浸出處理,在將材料的首次庫倫效率從82.4%提高到89.7%的同時,可以避免對材料表面晶格結(jié)構(gòu)的破壞。為了探究稀酸處理對材料首次庫倫效率提升的作用機理,創(chuàng)新性地設計并實施了工作電極在不同氣氛下(O2或Ar)的原位循環(huán)伏安法測試,利用電化學手段第一次發(fā)現(xiàn)富鋰材料中的氧可以被可逆還原,經(jīng)過酸處理后的材料在充電時脫出的氧的還原催化活性得到了提高。本論文首次采用一種低溫固相—電化學循環(huán)法對富鋰材料Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2進行表面修飾,修飾物質(zhì)在電化學循環(huán)過程中逐漸形成一層完整連續(xù)的保護層,同時聚陰離子BF4-逐漸介入到材料表面晶體結(jié)構(gòu)中,抑制富鋰材料表面處氧空位的形成與過渡金屬離子的遷移,從而達到抑制晶體結(jié)構(gòu)在循環(huán)過程中的衍變、抑制電化學循環(huán)中的電壓降的目的。經(jīng)過處理后的材料,放電比容量達到308.7mAhg-1,5C倍率下放電比容量為140 mAh g-1。經(jīng)過55次循環(huán)后,處理后的材料電壓降為65 mV,遠小于原始材料的202mV,55次循環(huán)后容量為286.9mAhg-1。HRTEM測試說明表面處理能夠有效阻止材料表面處晶格缺陷的形成。XPS測試表明,在首次放電至2.0 V時,經(jīng)過處理的材料負二價氧離子明顯增加,負一價氧離子顯著減少,說明表面處理可以有效提高氧的可逆還原。
[Abstract]:Lithium rich manganese based solid solution cathode material due to its high specific capacity is more than 280 mAh g-1 and low cost advantages are considered to be the most promising cathode materials for the next generation of lithium ion battery, its high specific capacity and special charge discharge system has aroused great interest of researchers at 4.5 V high oxygen. The capacity of lithium rich materials and for the first time in the process of charging off, however, oxygen will cause the material from the initial irreversible capacity loss is too large, and the formation of oxygen vacancies and local ion migration, rearrangement, resulting in structural evolution during the cycle, resulting in voltage drop and capacity attenuation, poor rate capability and rich lithium the material, which has prevented the road of industrialization. The lithium rich manganese based solid solution materials Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 as the object, in order to achieve the high energy density of lithium rich materials and high power density, improve The specific capacity and rate performance and cycle structure stability as the goal, to start work on the following aspects: the preparation of one-dimensional nanofibers by electrospinning method of lithium rich materials Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 as control, co precipitation synthesis of nano granular materials used at the same time, the nano fibrous and granular material rich lithium lithium rich materials in morphology, surface area, crystal structure, electrochemical properties and redox mechanism between the studied and reported comprehensive, BET test results show that the lithium rich materials nano fibrous surface area of 6.537 M2 g-1, more than 4.388 (nano granular materials m2g-1), due to lithium ion nano fibrous material has better diffusion kinetic conditions, can release 126.6 mAh g-1 capacity at a rate of 5 C, more than 101.1 mAhg'1. nano granular material in addition, innovative. The difference of comparative study on the first redox process by using cyclic voltammetry, electrochemical method to better explain the oxidation Li rich layered cathode materials in the first charge discharge in the process of removal of the O and Mn activation reduction mechanism. The preparation of nano fibrous materials in lithium rich Li_ electrospinning (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 in the process of taking heat at different conditions of the precursor, the final product will exhibit different morphology, the conclusion that the morphology effect of temperature rising speed of the end product, namely when 1 DEG min-1 speed of heating end products showed that one morphology, when the heating rate is 5 DEG min-1 when the final product will exhibit the morphology of petal shaped nano sheet. The sample at 800 C for 8 h after calcination showed good rate capability, which is attributed to its favorable dynamic conditions, the discharge of 5 C Capacity of 127 mAh g-1. nanowires and petal nanosheets possess the characteristics of unique small size effect of nanometer materials, can shorten the migration time, lithium ions in the material larger than the surface area of the electrode and the electrolyte can fully contact electrode polarization at high current density discharge to the rich. Lithium acid leaching treatment will make the material chemistry hernia lithium ion and oxygen ion, the removal of the Li2O from the crystal lattice, this method can effectively reduce the rich lithium cathode material the first irreversible capacity loss, but high concentration of acid leaching treatment will cause greater damage resulting in a deterioration of the cycle performance of electrode of crystal materials the surface structure. This is the first report of the acid solution of low concentration after dilution (0.01moL-lHNO3 solution) of lithium rich materials Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 For leaching mild, the material for the first time in Kulun, the efficiency is increased from 82.4% to 89.7% at the same time, can avoid the damage on the surface of the material crystal structure. In order to explore the mechanism of dilute acid treatment on the material for the first time in Kulun to promote efficiency, innovative design and implementation of the working electrode in different atmospheres (O2 or Ar) the in situ cyclic voltammetry using electrochemical method first discovered lithium rich materials in oxygen can be reversible reduction, by reducing the catalytic activity from acid treated materials in charge of oxygen is improved. This paper firstly adopts a low temperature solid state electrochemical cycling method of lithium rich materials Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 surface modification, modification of material gradually formed a layer of continuous protective layer on the electrochemical cycle, at the same time the polyanion BF4- gradually involved in crystal material surface In the structure, inhibit the formation of surface migration rich lithium oxygen vacancies and transition metal ions, thus inhibiting crystal structure evolution during the cycle, suppress the voltage drop in the electrochemical cycle. After processing the material discharge capacity reached 308.7mAhg-1,5C rate discharge capacity of 140 mAh after 55 g-1. cycles, material processing after the voltage is reduced to 65 mV, far less than the original material 202mV, after 55 cycles the capacity of 286.9mAhg-1.HRTEM test shows that surface treatment can effectively prevent the formation of.XPS test showed that the material surface defects, the first discharge at 2 V after treatment, the material price of two negative oxygen ions significantly increase of negative valence oxygen ion was significantly reduced, the surface treatment can effectively improve the reversible oxygen reduction.

【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TM912

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相關博士學位論文 前1條

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本文編號：1619350