本文選題：富鋰錳基氧化物 + 形貌修飾�。� 參考：《紹興文理學(xué)院》2017年碩士論文

【摘要】：富鋰錳基氧化物xLi_2MnO_3·(1-x)LiMO_2(M=Co,Ni和Mn等)因比容量高(250 mAh·g~(-1))、價(jià)格低廉、和環(huán)境友好等特點(diǎn),成為提高鋰離子電池高能量密度的關(guān)鍵。然而,該材料具有在諸多問題:首次充放電效率低;充放電過程中的相變化造成材料的晶格扭曲;高電位下電解液分解;以及電子導(dǎo)電率低等。這導(dǎo)致材料較差的倍率性能與循環(huán)穩(wěn)定性,也制約了材料的產(chǎn)業(yè)化應(yīng)用。本論文研究從形貌、晶格和界面等方面對(duì)富鋰錳基氧化物進(jìn)行修飾,研究其對(duì)材料電化學(xué)性能的影響:一、采用陽離子Na~+摻雜替代Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2中的部分Li~+,形成Li_(1.2-x)Na_x Mn_(0.54)Ni_(0.13)Co_(0.13)O_2(x=0,0.05,0.10和0.20)。研究發(fā)現(xiàn)Na~+的摻入可以預(yù)活化Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2,材料晶體結(jié)構(gòu)中出現(xiàn)尖晶石相,且隨著Na~+摻雜量從x=0增加到x=0.20,尖晶石相也越來越明顯,材料首的次庫倫效率也從76%提高到了94%。同時(shí),隨著Na~+摻雜量的從x=0.05到x=0.20,Li~+嵌脫通道的層間距漸漸變大,Li~+在層間的擴(kuò)散系數(shù)得到提高,因而材料的倍率性能得以改善,在500 mA·g~(-1)時(shí),未摻雜Na~+材料的放電比容量是54 mAh·g~(-1),而Li_(1.1)Na_(0.1) Mn_(0.54)Ni_(0.13)Co_(0.13)O_2(x=0.1)的放電比容量達(dá)到128 mAh·g~(-1)。此外,摻雜Na還能阻止充放電過程中過渡金屬離子遷入鋰位,抑制晶體結(jié)構(gòu)畸變,從而改善循環(huán)穩(wěn)定性。二、基于軟硬酸堿理論,采用軟硬堿度不同的F-、Cl-、Br-和I-對(duì)富鋰錳基氧化物進(jìn)行協(xié)同摻雜,替代晶格中的部分O_2-,分別制得FCl、FBr和FI協(xié)同摻雜的Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料。陰離子摻雜材料的首次庫倫效率都有不同程度的提高,首次庫倫效率從Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2的73.4%提高到了FCl協(xié)同摻雜Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2的81.5%,這應(yīng)歸于摻雜陰離子替代了部分O_2-導(dǎo)致電化學(xué)活化過程中氧的析出減少。由于F-具有比O_2-對(duì)過渡金屬離子更強(qiáng)的相互作用,一定程度上抑制了材料在充放電過程中的相轉(zhuǎn)變,改善了富鋰錳基材料的電壓降問題,同時(shí)還使得過渡金屬離子向鋰位遷移可能性變小,循環(huán)性能變好。三、從控制Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2與電解液直接接觸界面的角度,采用釩氧化物對(duì)Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料表面進(jìn)行修飾。研究發(fā)現(xiàn)釩氧化物可以預(yù)活化富鋰錳基氧化物,與材料中Li~+發(fā)生作用形成Li)3VO)4。Li)3VO)4的形成不僅可以減少首次充電過程中的不可逆脫鋰量,而且Li_3VO_4還能在放電過程中產(chǎn)生額外的放電容量,致使釩氧化物包覆的材料具有103.1%的首次充放電效率。此外,包覆層降低了富鋰錳基氧化物與電解液的副反應(yīng),從而可以減輕電解液對(duì)材料的腐蝕,使材料的循環(huán)穩(wěn)定性得到提高。四、采用棉花纖維作為犧牲性反應(yīng)載體,制得了由納米粒子構(gòu)筑成的Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2多孔纖維。材料在25 mA·g~(-1)(0.1 C)時(shí)的放電比容量是250.3 mAh·g~(-1),在1250 mA·g~(-1)(5 C)下的循環(huán)100圈后的比容量為110.3 mAh·g~(-1)。材料好的充放電性能歸于纖維中的孔道使材料擁有大的表面去充分浸潤電解液,以及構(gòu)筑粒子的納米粒徑賦予Li~+短的遷移路徑。
[Abstract]:The lithium rich manganese oxide xLi_2MnO_3 (1-x) LiMO_2 (M=Co, Ni and Mn, etc.) has the characteristics of high specific capacity (250 mAh. G~ (-1)), low price, and environmentally friendly characteristics. It has become the key to improve the high energy density of lithium ion batteries. However, the material has many problems: the initial charge discharge efficiency is low, and the phase change in the charge discharge process causes the lattice lattice. Distortion, decomposition of electrolyte at high potential and low electronic conductivity, which leads to the poor ratio and cyclic stability of materials and the industrial application of materials. This paper studies the modification of lithium manganese rich oxide from morphology, lattice and interface, and studies its effect on the electrochemical properties of materials: first, the use of Yang Ionic Na~+ is substituted for partial Li~+ in Li_ (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2, and Li_ (1.2-x) Na_x Mn_ (0.54) Ni_ (0.13) Ni_ (0.13) (0.20). With the increase of x=0.20, the spinel phase is becoming more and more obvious, and the secondary Kulun efficiency of the material increases from 76% to 94%.. With the Na~+ doping from x=0.05 to x=0.20, the spacing of the Li~+ inlay channel becomes larger and the diffusion coefficient of the Li~+ is increased in the interlayer, thus the performance of the material is improved, and at the time of 500 mA. G~ (-1), it is not doped. The discharge specific capacity of the Na~+ material is 54 mAh. G~ (-1), while the discharge ratio of Li_ (1.1) Na_ (0.1) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 (x=0.1) is 128 mAh. Besides, the doping can also prevent the transition metal ions into the lithium position in the charge discharge process and inhibit the crystal structure distortion, thus improving the cyclic stability. Two, based on the soft and hard acids and bases. On the other hand, F-, Cl-, Br- and I- are used to Co doped lithium rich manganese based oxides with different soft and hard basicity, instead of partial O_2- in the lattice, and FCl, FBr and FI Co doped Li_ (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13). The first Kulun efficiency of the anionic doping material has been improved to a different degree, and the first Kulun efficiency is from 1. 2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 73.4% increased to FCl Co doped Li_ (1.2) Mn_ (0.54) Ni_ (0.13) Co_ (0.13) O_2 81.5%, which should be attributed to doping anions instead of partial O_2- leading to the reduction of oxygen precipitation in the electrochemical activation process. The phase transition of material in charge and discharge improves the voltage drop of lithium rich manganese based materials. At the same time, the possibility of transition metal ion migration to lithium position becomes smaller and the cycle performance becomes better. Three, Li_ (1.2) Mn_ (0.54) N is used by vanadium oxide from the angle of controlling the direct contact interface between Li_ (1.2) (0.54) Ni_ (0.13) Co_ (0.13) O_2 and electrolysis solution. The surface of i_ (0.13) Co_ (0.13) O_2 is modified. It is found that the vanadium oxide can preactivate the lithium manganese rich oxide, and the formation of Li) 3VO) 4.Li) 3VO with the Li~+ in the material. The formation of the O_2 3VO) not only reduces the irreversible lithium removal in the first charging process, but also can produce extra discharge capacity during the discharge process. The vanadium oxide coated material has 103.1% first charge and discharge efficiency. In addition, the coating reduces the side reaction of the lithium rich manganese oxide and the electrolyte, thus reduces the corrosion of the electrolyte to the material and improves the cyclic stability of the material. Four, the cotton fiber is used as the sacrificial reaction carrier, and the nanoparticles are prepared. The Li_ (1.2) (1.2) Mn_ (0.54) (0.54) Ni_ (0.13) Co_ (0.13) O_2 porous fiber. The discharge specific capacity of the material at 25 mA. G~ (0.1 C) is 250.3 mAh. G~ (-1). The specific capacity of the material after 100 cycles of 100 cycles is 1250. The charge discharge performance of the material is attributed to the large surface of the material to be fully immersed. Wetting the electrolyte and the nanoparticle diameter of the particles give Li~+ a short migration path.

【學(xué)位授予單位】：紹興文理學(xué)院
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM912;O646
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本文編號(hào)：1876873