金属有机框架材料（MOFs）的制备、改性及其在锂硒电池中的应用

发布时间：2018-05-03 18:06

本文选题：金属有机框架 + 多孔碳骨架　；参考：《西南大学》2017年硕士论文

【摘要】：锂硒电池是继锂硫电池之后的一种新型高能量密度电池体系,极具发展前景。与锂硫电池一样,容量衰减迅速、库伦效率低也是阻碍锂硒电池实现产业化的关键问题,因此对锂硒电池的研究重点和热点主要集中在探索具有高导电性、高比表面积、适宜孔结构及孔尺寸的多孔碳骨架,与硒复合后得到比能量高、循环性能优异的硒基正极材料,以此提高硒正极的电化学活性和循环稳定性,使硒负载量和硒利用率协同作用并达到最大值,这对于高能量密度锂硒电池的发展具有重要的理论意义及实用价值。本文以金属有机框架材料为研究对象,将其作为多孔碳骨架的前驱体,成功制备了三种比表面积理想、孔径适宜的多孔金属有机框架,分别为Ni2O(BDC)2、Ni3(BTC)2和Zn2ONi2O(BDC)2(BDC=对苯二甲酸,BTC=均苯三甲酸),通过高温碳化进一步改性得到三种电化学性能优异的多孔碳骨架,进而通过熔融-扩散过程实现多孔碳骨架与活性物质硒的高效复合,分别合成了硒/介孔碳复合正极材料(meso-C@Se),硒/空心分级多孔碳微球复合正极材料(MHPCS/Se)以及硒/分级多孔碳立方体复合电极材料(Se/CMCs),研究其物理化学和电化学性能,获得结果如下:1.硒/介孔碳复合正极材料:以MOF-Ni为前驱体,利用一步碳化法得到具有介孔碳特性的基体,经过熔融浸渍封装硒后作为锂硒电池的正极材料。热重分析结果显示硒高度均匀地分布在复合材料中,其质量百分含量高达48%。电化学性能测试发现,在3 C的高电流密度下,meso-C@Se初始放电比容量为599.7 mAh g-1,100次循环后仍保持有417 mAh g-1,库仑效率一度高达99.9%,其优异的电化学性能归因于MOFs衍生碳骨架导电性能的提升和多孔通道结构。2.硒/空心分级多孔碳微球复合正极材料(MHPCS/Se):采用溶剂热法和高温碳化过程成功制备了一种空心分级多孔碳微球(MHPCS),研究显示MHPCS既具有介孔结构又存在大量微孔结构,微米碳球由彼此紧密堆积的半径约20 nm、厚度约5 nm的纳米碳空心气泡组成。MHPCS/Se复合材料作为Li-Se电池正极,在0.5 C的电流密度下提供高达588.2 mAh g-1的初始比容量,在500次循环过程中表现出突出的循环稳定性,其衰减速率低至0.08%,即使在1C电流密度下循环1000次后依然能够保持大于200 mAh g-1的比容量。改善的电化学性能应该归功于MHPCS的分级多孔结构,介孔有利于硒的大量浸入及离子传输,而微孔有利于固定硒,使其不会在充放电过程中由于体积膨胀而溶解流失。3.硒/分级多孔碳立方体复合电极材料(Se/CMCs):选取双金属离子(Ni2+,Zn2+)作为中心,溶剂热反应得到Zn/Ni-MOF-2立方块,氩气中高温煅烧后CMCs高度保持了前驱体的立方体形貌特征。CMCs具有分级多孔结构,比表面积高达1013.6 m2 g-1,这使得Se负载量高达50 wt%。在碳酸盐基电解质中,Se/CMCs复合材料表现出超高的初始放电比容量及循环可逆容量。值得一提的是,CMCs多孔结构有效地缓解了体积膨胀效应,同时因其具有优异的导电性,能有效降低电荷转移电阻并抑制碳酸盐基电解液中多硒化物的溶解,从而使硒基正极的电化学性能得到显著改善。综上所述,我们以金属有机框架材料为前驱体构建了多种分级多孔碳骨架,对活性物质硒具有较好的负载和固定作用,可以用于改善锂硒电池存在的“穿梭效应”和体积膨胀问题,为锂硒电池高容量正极复合材料的制备提供了新的思路。
[Abstract]:Lithium selenium battery is a new type of high energy density battery system after lithium sulfur battery. It has a great development prospect. As the lithium and sulfur battery, the capacity attenuation is rapid and the low efficiency of Kulun is the key problem that hinders the industrialization of lithium selenium battery. Therefore, the focus and focus of research on lithium selenium battery is to explore high conductivity and high performance. The specific surface area, porous carbon skeleton suitable for pore structure and pore size, and selenium based positive material with high specific energy and excellent cycling performance are obtained after combined with selenium, in order to improve the electrochemical activity and cyclic stability of the selenium positive pole, make the selenium load and selenium utilization synergistic and reach the maximum value, which is the development of the high energy density lithium selenium battery. It has important theoretical significance and practical value. In this paper, three kinds of porous metal organic frameworks with ideal specific surface area and suitable aperture are prepared by using metal organic frame materials as precursors of porous carbon skeleton, which are Ni2O (BDC) 2, Ni3 (BTC) 2 and Zn2ONi2O (BDC) 2 (BDC= terephthalic acid, BTC= mean three formic acid), respectively. Three porous carbon frameworks with excellent electrochemical properties were further modified by high temperature carbonization, and then the efficient recombination of the porous carbon skeleton and the active substance selenium was achieved through the melt diffusion process. The selenium / mesoporous carbon composite positive electrode (meso-C@Se), the selenium / hollow fractional porous carbon microsphere composite positive material (MHPCS/Se) and selenium / selenium were synthesized respectively. A graded porous carbon cube composite electrode material (Se/CMCs) was used to study its physicochemical and electrochemical properties. The results were as follows: 1. selenium / mesoporous carbon composite cathode material: using MOF-Ni as the precursor, the matrix with mesoporous carbon properties was obtained by one step carbonization, and after the melt impregnation and encapsulation of selenium as the cathode material for lithium selenium batteries. The results show that selenium is highly distributed in the composite. Its mass content is up to 48%. electrochemical performance test. At the high current density of 3 C, the initial discharge ratio of meso-C@Se is 417 mAh g-1 and the coulomb efficiency is as high as 99.9%, and its excellent electrochemical performance is attributed to MO. The conductivity of Fs derived carbon framework and the porous channel structure.2. selenium / hollow graded porous carbon microsphere composite positive material (MHPCS/Se): a hollow graded porous carbon microsphere (MHPCS) was successfully prepared by solvothermal method and high temperature carbonization. The study shows that MHPCS has both mesoporous structure and a large number of microporous structures, and the microsphere carbon spheres are composed of microspheres. The tightly packed radius of 20 nm, and the nano carbon hollow bubbles with a thickness of about 5 nm, made up of.MHPCS/Se composites as the positive pole of the Li-Se battery, provided the initial specific capacity of up to 588.2 mAh g-1 under the current density of 0.5 C, and showed a prominent cyclic stability during the 500 cycle process, and its attenuation rate was as low as 0.08%, even in the 1C current density. The specific capacity of more than 200 mAh g-1 can still be maintained after 1000 cycles. The improved electrochemical performance should be attributed to the hierarchical porous structure of MHPCS, which is beneficial to a large amount of immersion and ion transmission of selenium, and the micropores are beneficial to the fixation of selenium, so that it will not dissolve and lose.3. Se / graded porosity during the charge discharge process by volume expansion. Carbon cube composite electrode material (Se/CMCs): select the bimetallic ion (Ni2+, Zn2+) as the center, the solvent thermal reaction to get the Zn/Ni-MOF-2 cubic block. After the high temperature calcined in the argon, the CMCs height keeps the cube morphology of the precursor,.CMCs has a hierarchical porous structure, and the specific surface area is up to 1013.6 M2 g-1, which makes the Se load up to 50 wt%.. In the carbonate base electrolyte, the Se/CMCs composite exhibits high initial discharge specific capacity and reversible reversible capacity. It is worth mentioning that the porous structure of CMCs effectively alleviates the volume expansion effect and can effectively reduce the electric charge transfer resistance and inhibit the polyselenide in the carbonate base electrolyte because of its excellent conductivity. In conclusion, a variety of graded porous carbon frameworks have been constructed with metal organic frame materials as precursors, which have good load and fixed effect on active substance selenium, and can be used to improve the "shuttle effect" and volume expansion of lithium selenium batteries. The preparation of high capacity cathode composite materials for lithium selenide batteries provides a new way of thinking.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O641.4;TM912

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