科琴黑及二氧化铈改性锂硫电池隔膜的研究

发布时间：2018-05-31 10:38

本文选题：锂硫电池 + 隔膜改性　；参考：《江苏大学》2017年硕士论文

【摘要】：从1990年开始,锂电池就成为了主流电子产品的电源。但是随着市场对电子产品续航能力要求的提高以及环境问题导致的电动汽车研究热潮,众多学者开始研究更高能量密度的电池体系。因此以硫为正极,锂为负极的高能量密度的锂硫电池(2600 Wh kg-1)开始成为研究热点。但是锂硫电池(Li-S电池)体系自身的缺陷使其商业化进程受到了极大的限制。其中包括硫和硫的放电终产物的低离子/电子电导,充放电过程中活性物质严重的体积膨胀/收缩,以及反应中产物聚硫化锂(LiPS)溶解于有机电解液并扩散到负极形成的穿梭效应。本文针对Li-S电池体系中由于LiPS的穿梭效应引起的正极活性物质利用率低,电池极化严重,循环稳定性差的问题,研究隔膜改性对于锂硫电池性能的提升。论文研究的主要内容和研究成果包括:1)科琴黑改性锂硫电池隔膜的研究。实验通过对比KB改性隔膜与商用隔膜的电池电化学性能,研究了KB涂层对电池电化学反应过程的影响并探索其作用机理。研究发现:KB涂层是一个由纳米颗粒均匀堆叠而成一个疏松多孔的碳层;KB涂层疏松多孔的结构能够有效吸附多硫化物,抑制穿梭效应;KB涂层优异的导电性能使得浸入涂层的“失活”硫化物能被“活化”再次参与反应;KB涂层作为一个二次集流体,促进反应中离子、电子的迁移。因此,KB改性隔膜的电池表现出较好的循环性能与倍率性能。此改性电池在0.1 C下能够达到1318 mAh g-1的比容量。即便是在1 C下循环100圈以后,放电比容量也只是从946 mAh g-1降低到815 mAh g-1。此改性电池在2 C的倍率下放电比容量依然能够保持在934 mAh g-1。而当电流强度降到0.1 C时,KB改性隔膜的电池与传统隔膜的电池的可逆容量分别为1173 mAh g-1与605 mAh g-1。2)二氧化铈改性锂硫电池隔膜的研究。实验利用喷雾造粒法制备出中空的氧化铈,并进行隔膜的涂布改性。通过对比二氧化铈改性隔膜与商用隔膜、Super-P改性隔膜的电池的电化学性能,研究了稀土金属氧化物的掺杂对锂硫电池电化学反应过程的影响并探索其作用机理。研究发现:CeO_2涂层不仅对LiPS起到了物理阻隔的作用,还有一定的化学吸附的作用;CeO_2涂层能够催化浸入其中的多硫化物的还原反应,提升反应动力学,降低电池极化;CeO_2涂层还能因为其特殊的核外电子排布能够在Ce~(3+)与Ce~(4+)价之间自由转化并且稳定存在,增加浸入涂层的活性物质的导电性。因此,二氧化铈改性隔膜的电池具有更优异的循环稳定性。CeO_2改性隔膜的电池在1 C下的首次放电比容量达到1004 mAh g-1。即便循环500圈,放电比容量还能保持在625 mAh g-1。该电池在2 C的大倍率下充放电时,比容量也能达到760 mAh g-1。而当充放电倍率再次调整至0.5C时,电池的可逆放电比容量能达到960 mAh g-1,与首次在0.5 C下充放电的970 mAh g-1几乎一致。
[Abstract]:Lithium batteries have been the mainstay of electronics since 1990. However, with the increasing demand of the market for the ability of electronic products to live and the upsurge of research on electric vehicles caused by environmental problems, many scholars have begun to study battery systems with higher energy density. Therefore, the high energy density lithium-sulfur battery with sulfur as positive electrode and lithium as negative electrode has become a hot research topic. However, the commercial process of Li-S battery system has been greatly restricted due to its own defects. These include the low ion / electron conductance of the discharge end product of sulfur and sulfur, and the serious volume expansion / contraction of the active substance during the charge-discharge process. And the shuttle effect of poly-lithium-sulphide LiPSs dissolved in the organic electrolyte and diffused to the negative electrode. In order to solve the problems of low utilization of positive active substances, serious polarization and poor cycle stability caused by the shuttle effect of LiPS in Li-S battery system, the improvement of lithium-sulfur battery performance by membrane modification was studied in this paper. The main contents and results of this paper include: 1) study on the membrane of black modified lithium-sulfur battery. The effect of KB coating on the electrochemical reaction process of the battery was studied by comparing the electrochemical performance of the KB-modified membrane with the commercial membrane and the mechanism of its action was explored. It is found that the porous structure of a porous carbon layer formed by a homogeneous stacking of nano-particles can effectively adsorb polysulfides. The excellent conductivity of KB coating makes the "inactivated" sulfides immersed in the coating can be "activated" again to participate in the reaction of KB coating as a secondary collecting fluid, which can promote the ion and electron migration in the reaction. Therefore, the battery with modified membrane of KB showed better cycling performance and rate performance. The specific capacity of the modified battery can reach 1318 mAh g-1 at 0. 1 C. Even after 100 cycles at 1 C, the specific discharge capacity was reduced from 946 mAh g ~ (-1) to 815 mAh g ~ (-1). The specific discharge capacity of the modified battery can still be kept at 934 mAh g-1 at the rate of 2 C. However, when the current intensity is reduced to 0.1C, the reversible capacity of the modified membrane is 1173 mAh g-1 and 605 mAh g-1.2 respectively) the membrane of the lithium-sulfur cell modified by cerium oxide is 1173 mAh / g ~ (-1) and the reversible capacity of the conventional membrane is 1173 mAh / g ~ (-2) respectively. The hollow cerium oxide was prepared by spray granulation and modified by coating. The effects of rare earth metal oxide doping on the electrochemical reaction of lithium-sulfur batteries were studied by comparing the electrochemical performance of cerium oxide modified membrane and commercial super-P modified membrane. It is found that the CEO _ 2 coating not only acts as a physical barrier to LiPS, but also has a certain chemisorption effect. CeO _ 2 coating can catalyze the reduction reaction of polysulfide immersed in it and enhance the reaction kinetics. The reduction of the polarization of CEO _ 2 coating can also increase the conductivity of the active substances immersed in the coating because of the free conversion and stable existence of its special extranuclear electron arrangement between Ce~(3) and Ce~(4. Therefore, the battery with cerium oxide modified diaphragm has better cycle stability. The initial discharge specific capacity of the battery with CeO-2 modified diaphragm reaches 1004 mAh g-1 at 1 C. The specific discharge capacity can be kept at 625 mAh g-1 even if the cycle is 500 cycles. The specific capacity of the battery can also reach 760 mAh g-1 when charged and discharged at a large rate of 2 C. When the charge / discharge ratio is adjusted to 0.5 C again, the reversible discharge specific capacity of the battery can reach 960 mAh g-1, which is almost the same as that of 970 mAh g ~ (-1) charged and discharged at 0.5C for the first time.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912;TB383.2

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