锂硫电池用具有选择锂离子通过性聚合物电解质的研究

发布时间：2018-05-23 23:51

本文选题：锂硫电池 + 聚合物电解质　；参考：《国防科学技术大学》2014年博士论文

【摘要】：作为兼具高能量密度、低成本和环境友好等优点的新型二次电池,锂硫电池相关技术逐渐成为近年来化学电源领域的研究热点。但是,由于锂硫电池放电中间产物聚硫离子Sn2-(4≤n≤8)易溶于电解液,在浓度梯度作用下会逐渐向金属锂负极扩散并与之反应,导致电池内部产生飞梭现象;同时,其放电最终产物Li2S2或/和Li2S不溶于电解液,将沉积于金属锂负极表面,使负极表面腐蚀钝化,最终造成锂硫电池活性物质利用率低、循环性能差、库仑效率低等问题,延缓了其实用化的步伐。为此,本论文提出使用具有选择Li+通过性的聚合物电解质,以提高锂硫电池的循环性能和库仑效率。其中,具有选择Li+通过性的聚合物电解质的关键在于尽量提高聚合物电解质的,使其在传导Li+的同时抑制Sn2-(4≤n≤8)的通过,避免Sn2-(4≤n≤8)与Li负极的直接接触,从而达到提高电池硫利用率和循环性能的目的。本论文首先采用向聚合物电解质中添加有机Lewis酸PEGn-B的方式提高聚合物电解质的,然后直接使用接近于1的全氟锂离子聚合物作为电解质材料。系统开展了含PEGn-B添加剂的CPL电解质的性能及其改善锂硫电池性能研究,以及全氟锂离子聚合物电解质的性能及其改善锂硫电池性能的研究,并对全氟锂离子聚合物电解质具有选择Li+通过性的机理进行了系统研究。主要研究工作包括:研究了聚合体系中PEGn-B的-EO-链段长度及添加比例对CPL电解质的离子电导率和锂离子迁移数的影响,确定了使CPL电解质的离子电导率和锂离子迁移数达最大时的聚合体系,并结合分子模拟计算,对CPL电解质传导Li+机理,以及PEGn-B提高CPL电解质的、阻隔负离子通过的机理进行了研究。结果表明,CPL电解质膜的最佳聚合配比为PME400:PDE600:PEG3-B的质量比为1:1:5,此时所得的CPL电解质的离子电导率为3.3×10-4 S/cm,为0.54。含PEGn-B的CPL电解质主要依靠CPL分子以及PEGn-B分子中-EO-链段的弛豫运动传导Li+,而其提高并对负离子的传输具有阻隔性依靠PEGn-B中的中心原子B与电解质中负离子之间的Lewis酸-碱作用。论文系统研究了使用含PEGn-B添加剂的CPL电解质对锂硫电池循环性能的影响以及该电池循环性能仍缓慢衰减的原因。Li|CPL|S电池以0.1C倍率恒流充放电时,50次循环后容量保持率为87%,库仑效率一直保持在90%以上,对比使用液态电解质的锂硫电池,其循环性能和库仑效率得到了明显改善。通过SEM、EDS、XPS等测试Li|CPL|S电池循环前后电解质膜以及Li负极表面的形貌和组成变化的分析,表明受限于PEGn-B在CPL电解质中的浓度和分布,CPL电解质的小于1,Sn2-(4≤n≤8)在PEGn-B中B所形成的双电层有效范围之间的空隙空间中借助于-EO-链段的弛豫运动所产生的自由体积,最终穿过CPL电解质,造成使用CPL电解质的锂硫电池放电比容量缓慢衰减。论文制备了Li-PFSA型锂离子聚合物电解质,系统研究了Li-PFSA电解质对锂硫电池循环性能和倍率性能的影响。研究结果表明,使用由Li+交换得到的Li-PFSA电解质,由于其高的(0.986),使用Li-PFSA电解质的锂硫电池的循环性能得到了改善,当以0.1C倍率恒流充放电时,100次循环后放电比容量保持率达78%,且库仑效率也一直稳定于95%以上。验证了接近于1的全氟锂离子聚合物电解质改善锂硫电池循环性能的可行性。但由于其较低的离子电导率(1.2×10-5 S/cm),使用Li-PFSA电解质的锂硫电池的倍率性能不佳,以1C倍率恒流充放电时,放电比容量仅130 m Ah/g左右。论文合成了Li-PFSD和Li-PFSI两种新型全氟锂离子聚合物,系统研究了溶液流延法成膜对这两种离子聚合物结晶性能和电化学性能的影响。结果表明,随着成膜温度的升高,Li-PFSD电解质膜和Li-PFSI电解质膜的结晶度均减少,而结晶规整度均升高;随着热处理温度的升高或热处理时间的延长,Li-PFSD电解质膜和Li-PFSI电解质膜的结晶度均先减少后增加,而结晶规整度均一直升高。同时,Li-PFSD电解质膜和Li-PFSI电解质膜的结晶度越低,所对应电解质的离子电导率越高。而Li-PFSD电解质膜和Li-PFSI电解质膜的结晶规整度越高,所对应电解质的越高。Li-PFSD电解质膜的最佳成膜方式为180℃下成膜后再于220℃下热处理4 h,此时Li-PFSD电解质的离子电导率为2.12×10-4 S/cm,为0.96,Li-PFSI聚合物膜的最佳成膜方式为180℃下成膜后再于220℃下热处理4 h,此时Li-PFSI电解质的离子电导率为4.74×10-4 S/cm,为0.98。论文系统开展了Li-PFSD电解质和Li-PFSI电解质对锂硫电池循环性能和倍率性能的研究。研究表明,Li|Li-PFSD|S电池同时获得了良好的循环性能和倍率性能,以0.1C倍率恒流充放电时,Li|Li-PFSD|S电池100次循环后放电比容量保持率达82.9%,且库仑效率一直稳定于97%以上;以1C倍率恒流充放电时,其放电比容量稳定在530 m Ah/g左右。Li|Li-PFSI|S电池也获得良好的循环性能和倍率性能,当以0.1C倍率恒流充放电时,100次循环后放电比容量保持率达88.1%,且库仑效率一直稳定于97%以上;以1C倍率恒流充放电时,放电比容量稳定于700 m Ah/g左右,以2C倍率恒流充放电时,放电比容量稳定于620 m Ah/g左右。对Li|Li-PFSI|S电池以0.2C倍率进行长循环恒流充放电,经210次循环后其放电比容量保持率为80%,500次循环后其放电比容量的保持率仍达68%。论文分析了使用全氟锂离子聚合物电解质提高锂硫电池循环性能和库仑效率的原因。通过对循环过程中锂硫电池各界面的阻抗变化情况,以及循环前后正、负极的形貌变化以及电解质膜的形貌和性能变化的分析,表明使用全氟锂离子聚合物电解质的锂硫电池循环性能和库仑效率的提高的原因是全氟锂离子聚合物电解质具有选择Li+通过性,能有效抑制Sn2-(4≤n≤8)通过,从而减少了电池中与Li负极反应所消耗的活性物质以及飞梭现象的产生。论文分析了三种不同的全氟锂离子聚合物电解质膜在不同有机溶剂中吸液率以及所对应电解质的离子电导率的变化,研究了溶剂性质以及锂离子聚合物的末端离子基团的结构对电解质离子电导率的影响,以及全氟锂离子聚合物膜的静电效应和微结构对电解质的影响。研究表明,当全氟锂离子聚合物不变时,所形成的聚合物膜的结晶度越小,所吸胀的有机溶剂的介电常数和施主数越大、黏度越小,该电解质的离子电导率越高;而对于不同的全氟锂离子聚合物,聚合物末端离子基团的离域趋势越大,在相同条件下该电解质离子电导率越高。
[Abstract]:As a new type of two battery with the advantages of high energy density, low cost and friendly environment, the related technology of lithium sulfur battery has gradually become a hot spot in the field of chemical power supply in recent years. However, as the intermediate product of polysulfide ion Sn2- (4 < < < 8) of the lithium sulfur battery is easily dissolved in the electrosolution, it will gradually be negative to the metal lithium under the concentration gradient. At the same time, the final product Li2S2 or / and / and Li2S insoluble in the electrolyte will be deposited on the surface of the metal lithium anode, and the negative electrode surface is corroded and passivated, which eventually causes the low utilization of the active material of the lithium sulfur battery, the poor circulation performance and the low coulomb efficiency. In this paper, we propose to use the polymer electrolyte with the choice of Li+ to improve the cycle performance and coulomb efficiency of the lithium sulfur battery. Among them, the key of the polymer electrolyte with the choice of the Li+ passing ability is to improve the polymer electrolyte as much as possible to prevent the passing of Sn2- (4 < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < 4 >). The direct contact between the Sn2- (4 < < n < < < < 8) and the negative electrode of Li can improve the sulfur utilization and cycle performance of the battery. In this paper, the polymer electrolyte is improved by adding organic Lewis acid PEGn-B into the polymer electrolyte, and then directly using the perfluoro lithium ion polymer near to 1 as the electrolyte material. The properties of the CPL electrolyte containing PEGn-B additive and the improvement of the performance of the lithium sulfur battery, the performance of the perfluoro lithium ion polymer electrolyte and the improvement of the performance of the lithium sulfur battery were studied. The mechanism of the perfluoro lithium ion polymer electrolyte has been studied systematically. The main research work includes: The effect of the length and proportion of -EO- segment of PEGn-B on the ionic conductivity and lithium ion migration number of CPL electrolyte is investigated. The polymerization system which makes the ionic conductivity and the lithium ion migration number of the CPL electrolyte is maximum is determined. The mechanism of Li+ conduction to the CPL electrolyte and the PEGn-B to improve the CPL electricity are also determined by the molecular simulation calculation. The results show that the mass ratio of the optimum polymerization ratio of CPL electrolyte membrane to PME400:PDE600:PEG3-B is 1:1:5, and the ionic conductivity of the CPL electrolyte is 3.3 x 10-4 S/cm at this time, and the CPL electrolyte containing PEGn-B in 0.54. is mainly dependent on the CPL molecule and -EO- chain in the PEGn-B molecule. The relaxation motion conduction Li+, and its enhancement and the transmission of negative ions is dependent on the Lewis acid alkali effect between the central atom B in PEGn-B and the negative ions in the electrolyte. This paper systematically studies the effect of CPL electrolyte containing PEGn-B additive on the cycle performance of the lithium sulfur battery and the slow attenuation of the cycle performance of the battery. The capacity retention rate of the.Li|CPL|S battery was 87% after 50 cycles, and the coulomb efficiency remained above 90%. The cycle performance and coulomb efficiency of the battery were improved obviously. The electrolyte membrane and Li negative electrode before and after the Li|CPL|S battery cycle were tested by SEM, EDS, XPS and so on. The analysis of the surface morphology and composition changes shows that the concentration and distribution of the PEGn-B in the CPL electrolyte is limited, and the CPL electrolyte is less than 1, and the Sn2- (4 < < n < 8) is in the void space between the effective range of the double layer of the B formed in PEGn-B, and the free volume produced by the relaxation motion of the -EO- chain section is finally passed through the CPL electrolyte, resulting in the result. The discharge of lithium sulfur battery with CPL electrolyte attenuates slowly. A Li-PFSA type lithium ion polymer electrolyte is prepared in this paper. The influence of Li-PFSA electrolyte on the cycle performance and ratio performance of lithium sulfur battery is systematically studied. The results show that the use of Li-PFSA electrosolution obtained by Li+ exchange is high (0.986), using Li-PFSA electrolysis The cycle performance of the lithium sulfur battery is improved. The discharge ratio of the discharge is 78% and the coulomb efficiency is stable over 95% when the discharge of the 0.1C ratio constant current is 78%, and the coulomb efficiency is more than 95%. The feasibility of improving the cycle performance of the lithium sulfur battery is verified. The conductivity (1.2 x 10-5 S/cm), the ratio performance of the lithium sulfur battery using Li-PFSA electrolyte is not good. The discharge specific capacity is only about 130 m Ah/g when charging and discharging at the constant current of 1C multiplier. The paper synthesizes two new types of perfluoro lithium ion polymers with Li-PFSD and Li-PFSI. The crystallization properties of these two kinds of ionic polymers are systematically studied. The results show that the crystallinity of the Li-PFSD electrolyte membrane and the Li-PFSI electrolyte membrane decreases with the increase of the film forming temperature. The crystallinity of the Li-PFSD electrolyte membrane and the Li-PFSI electrolyte membrane increases with the increase of heat treatment temperature or the prolongation of the heat treatment time. At the same time, the lower the crystallinity of the Li-PFSD electrolyte membrane and the Li-PFSI electrolyte membrane, the higher the ionic conductivity of the corresponding electrolyte, the higher the crystallinity of the Li-PFSD electrolyte membrane and the Li-PFSI electrolyte membrane, the best film forming way of the higher.Li-PFSD electrolyte membrane of the corresponding electrolyte is the film forming at 180 degrees C and then after the formation of the film. At 220 C, the heat treatment was 4 h, at this time the ionic conductivity of the Li-PFSD electrolyte was 2.12 x 10-4 S/cm, which was 0.96. The best film forming method of the Li-PFSI polymer film was at 180 C and then at 220 C at 4 h, and the ionic conductivity of the Li-PFSI electrolyte was 4.74 * 10-4 S/cm, and Li-PFSD electrolyte and Li-PFSI electrolysis were carried out for 0.98. paper system. The study of the cycle performance and ratio performance of the lithium sulfur battery shows that the Li|Li-PFSD|S battery has good cycle performance and multiple performance. The discharge ratio of the Li|Li-PFSD|S battery after 100 cycles is 82.9%, and the coulomb efficiency has been stable over 97% when the 0.1C rate constant current charging and discharging. The discharge ratio is stable at about 530 m Ah/g and the.Li|Li-PFSI|S battery has good cycle performance and multiple performance. When charging and discharging with 0.1C constant current, the discharge ratio of discharge is 88.1%, and the coulomb efficiency is stable over 97%. The discharge capacity is stable at 700 m A with 1C multiple constant current charging and discharging. At about h/g, the discharge capacity is stable at about 620 m Ah/g with the constant current of 2C multiplying constant current. The Li|Li-PFSI|S battery is charged with a long cycle and constant current with 0.2C multiplying, after 210 cycles the discharge ratio of the discharge ratio is 80%, and the retention rate of the discharge specific capacity after the 500 cycle is still up to 68%. paper analysis of the use of the perfluoro lithium ion polymer. The reasons for the improvement of the cycle performance and coulomb efficiency of lithium sulfur batteries by electrolytes are analyzed. The cyclic properties of lithium sulfur batteries using perfluoro lithium ion polymer electrolytes are shown by the analysis of the changes in the impedance of the lithium sulfur batteries and the changes in the morphology and the morphology and properties of the electrolyte membrane. The reason for the improvement of the coulomb efficiency is that the perfluoro lithium ion polymer electrolyte has the selectivity of Li+ and can effectively inhibit the passing of Sn2- (4 < < n < 8), thus reducing the production of active substances and the shuttle phenomenon in the battery with Li negative electrode reaction. In this paper, three different kinds of perfluoro lithium ion polymer electrolyte membranes are analyzed in different ways. The effect of the properties of the solvent and the structure of the terminal ionic group on the ionic conductivity of the lithium ion polymer, as well as the electrostatic effect of the perfluoro lithium polymer film and the influence of the microstructure on the electrolyte, are studied. The smaller the crystallinity of the polymer film is, the smaller the crystallinity of the polymer film, the greater the dielectric constant and the donor number of the dilated organic solvents, the smaller the viscosity, the higher the ionic conductivity of the electrolyte, and the greater the ionization trend of the polymer terminal ionic groups for different perfluorium-ion polymers, the electrolyte is separated under the same conditions. The higher the electrical conductivity of the sub.
【学位授予单位】：国防科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

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