富锂锰基氧化物的制备及电化学性能研究

发布时间：2018-05-12 03:16

  本文选题：富锂锰基氧化物 + 形貌修饰　； 参考：《绍兴文理学院》2017年硕士论文

【摘要】：富锂锰基氧化物xLi_2MnO_3·(1-x)LiMO_2(M=Co,Ni和Mn等)因比容量高(250 mAh·g~(-1))、价格低廉、和环境友好等特点,成为提高锂离子电池高能量密度的关键。然而,该材料具有在诸多问题:首次充放电效率低;充放电过程中的相变化造成材料的晶格扭曲;高电位下电解液分解;以及电子导电率低等。这导致材料较差的倍率性能与循环稳定性,也制约了材料的产业化应用。本论文研究从形貌、晶格和界面等方面对富锂锰基氧化物进行修饰,研究其对材料电化学性能的影响:一、采用阳离子Na~+掺杂替代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)。研究发现Na~+的掺入可以预活化Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2,材料晶体结构中出现尖晶石相,且随着Na~+掺杂量从x=0增加到x=0.20,尖晶石相也越来越明显,材料首的次库伦效率也从76%提高到了94%。同时,随着Na~+掺杂量的从x=0.05到x=0.20,Li~+嵌脱通道的层间距渐渐变大,Li~+在层间的扩散系数得到提高,因而材料的倍率性能得以改善,在500 mA·g~(-1)时,未掺杂Na~+材料的放电比容量是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)的放电比容量达到128 mAh·g~(-1)。此外,掺杂Na还能阻止充放电过程中过渡金属离子迁入锂位,抑制晶体结构畸变,从而改善循环稳定性。二、基于软硬酸碱理论,采用软硬碱度不同的F-、Cl-、Br-和I-对富锂锰基氧化物进行协同掺杂,替代晶格中的部分O_2-,分别制得FCl、FBr和FI协同掺杂的Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料。阴离子掺杂材料的首次库伦效率都有不同程度的提高,首次库伦效率从Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2的73.4%提高到了FCl协同掺杂Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2的81.5%,这应归于掺杂阴离子替代了部分O_2-导致电化学活化过程中氧的析出减少。由于F-具有比O_2-对过渡金属离子更强的相互作用,一定程度上抑制了材料在充放电过程中的相转变,改善了富锂锰基材料的电压降问题,同时还使得过渡金属离子向锂位迁移可能性变小,循环性能变好。三、从控制Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2与电解液直接接触界面的角度,采用钒氧化物对Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2材料表面进行修饰。研究发现钒氧化物可以预活化富锂锰基氧化物,与材料中Li~+发生作用形成Li)3VO)4。Li)3VO)4的形成不仅可以减少首次充电过程中的不可逆脱锂量,而且Li_3VO_4还能在放电过程中产生额外的放电容量,致使钒氧化物包覆的材料具有103.1%的首次充放电效率。此外,包覆层降低了富锂锰基氧化物与电解液的副反应,从而可以减轻电解液对材料的腐蚀,使材料的循环稳定性得到提高。四、采用棉花纤维作为牺牲性反应载体,制得了由纳米粒子构筑成的Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2多孔纤维。材料在25 mA·g~(-1)(0.1 C)时的放电比容量是250.3 mAh·g~(-1),在1250 mA·g~(-1)(5 C)下的循环100圈后的比容量为110.3 mAh·g~(-1)。材料好的充放电性能归于纤维中的孔道使材料拥有大的表面去充分浸润电解液,以及构筑粒子的纳米粒径赋予Li~+短的迁移路径。
[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.

【学位授予单位】：绍兴文理学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912;O646
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本文编号：1876873