砜类作为高电压锂离子电池电解液添加剂的研究

发布时间：2018-07-05 14:23

本文选题：锂离子电池 + 高电压　；参考：《浙江大学》2017年硕士论文

【摘要】：随着锂离子电池的广泛应用,高电压锂离子电池体系成为研究热点。电解液作为锂离子电池中的重要组成部分正面临着挑战,一方面传统的碳酸酯电解液在4.5V以上就会发生氧化分解；另一方面新型高电压电解液由于存在各种问题未能得到普遍应用。而电解液在高压下的稳定性直接影响着电池的电化学性能,是制约高电压锂离子电池发展的关键因素之一。据文献报道,现阶段有效而又经济的解决方法之一就是在电解液中引入一定量(5%)的功能性添加剂,可以稳定高电压锂离子电池体系从而提高电化学性能。本论文选用极性大、氧化电位高、热稳定性好的砜类作为研究对象,在1M LiPF6-EC:DMC(1:1)参比电解液(Standard, STD)体系中加入不同量的添加剂,通过对LiNi1/3CO1/3Mn1/3O2/Li、石墨/Li以及LiNi1/3Co1/3Mn1/3O2/石墨电池体系在不同电解液体系中的循环性能和倍率性能测试,并结合线性扫描伏安(Linear sweep voltammetry, LSV)、循环伏安(Cyclic voltammetry, CV)、电化学阻抗(Electrochemical impedance spectroscopy, EIS)以及扫描电子显微镜(Scanning electron microscopy, SEM)、能量色散X射线光谱学(Energy dispersive X-ray spectroscopy, EDS)和X射线光电子能谱(X-ray photoelectron spectroscopy, XPS)等材料表征手段,探讨不同结构的砜作为添加剂对电池的影响。主要结果如下：1、环丁砜作为高电压电解液添加剂：(1)研究发现当添加量为2%(体积比)时,环丁砜能够提高参比电解液的电化学窗口以及增强电解液在高压下的氧化稳定性,并在一定程度上减少溶剂碳酸乙烯酯(Ethylene carbonate, EC)的还原分解。(2)含有环丁砜的电解液对LiNi1/3CO1/3Mn1/3O2正极、石墨负极的相容性较好,LiNi1/3Co1/3Mn1/3O2/Li、石墨/Li以及LiNi1/3Co1/3Mn1/3O2/石墨电池体系的放电容量、循环性能和倍率性能都得到提高。(3)结合多种分析手段发现：环丁砜对电池电化学性能的改进的机理是含有环丁砜的电解液能够在正负极表面形成均一紧密的膜层,消除膜层表面的裂痕从而抑制电解液的持续分解,提高了循环过程中电解液和电极的稳定性,减少电池体系在循环过程中的阻抗增加,从而使电池性能得到提升。2、乙基异丙基砜(Ethyl isopropyl sulfone, EIS)、乙基乙烯基砜(Ethyl vinyl sulfone, EVS)作为添加剂：(1) 乙基异丙基砜作为添加剂时,能够提高参比电解液的电化学窗口至4.5V, LiNi1/3Co1/3Mn1/3O2正极材料在4.6V的截止电压下充放电100次的放电容量更大、循环更稳定；但发现电池在循环过程中的阻抗的增加幅度比参比电解液大,且石墨负极在含该添加剂的体系中的电化学性能并不理想。(2)乙基乙烯基砜作为添加剂时,LiNi1/3Co1/3Mn1/3O2/Li电池的充放电容量不稳定,并且库伦效率持续低于100%,初步原因分析为加入EVS后,LiNi1/3Co1/3Mn1/3O2在充放电过程的不可逆程度增大以及电化学极化较严重。虽然EVS在1.2V左右能够先于EC进行还原反应,但是未能对电池体系起到稳定作用,对石墨负极的兼容性较差。
[Abstract]:With the wide application of lithium ion batteries, the system of high voltage lithium ion batteries has become a hot topic. As an important part of lithium ion batteries, electrolyte is facing challenges. On the one hand, the oxidation decomposition of the traditional carbonate electrolyte over 4.5V will occur. On the other hand, the new high voltage electrolyte has a variety of problems because of various problems. The stability of the electrolyte at high pressure directly affects the electrochemical performance of the battery. It is one of the key factors restricting the development of high voltage lithium ion batteries. According to the literature, one of the effective and economical solutions at the present stage is the introduction of a certain amount of functional additives (5%) in the electrolyte, which can stabilize the electrolyte. The high voltage lithium ion battery system improves the electrochemical performance. In this paper, the sulfone, which has high polarity, high oxidation potential and good thermal stability, is used as the research object, adding different additives in the 1M LiPF6-EC:DMC (1:1) reference electrolyte (Standard, STD) system through LiNi1/3CO1/3Mn1/3O2/Li, graphite /Li, and LiNi1/3Co1/3Mn1/3O2/ The cyclic voltammetry (Linear sweep voltammetry, LSV), cyclic voltammetry (Cyclic voltammetry, CV), electrochemical impedance (Electrochemical impedance spectroscopy, EIS), and scanning electron microscopy (Scanning) are used to test the cycle performance and ratio performance of the graphite battery system in different electrolyte systems. ), energy dispersive X ray spectroscopy (Energy dispersive X-ray spectroscopy, EDS) and X ray photoelectron spectroscopy (X-ray photoelectron spectroscopy, XPS) are used to characterize the effects of sulfone as additives on batteries. The main results are as follows: 1, sulfoxide as a high voltage electrolyte additive: (1) research When the addition amount is 2% (volume ratio), sulfoxide can improve the electrochemical window of the reference electrolyte and the oxidation stability of the enhanced electrolyte at high pressure, and reduce the reduction decomposition of the solvent carbonate (Ethylene carbonate, EC) to a certain extent. (2) the electrolyte containing sulfoxide is on the positive pole of the LiNi1/3CO1/3Mn1/3O2, Shi Mofu The discharge capacity, cycle performance and multiplying performance of LiNi1/3Co1/3Mn1/3O2/Li, graphite /Li and LiNi1/3Co1/3Mn1/3O2/ graphite battery systems are improved. (3) the mechanism of the improvement of the electrochemical performance of the sulphone battery is that the electrolyte containing sulphone can be on the positive and negative surface. A homogeneous membrane is formed to eliminate the cracks on the surface of the membrane and inhibit the continuous decomposition of the electrolyte, improve the stability of the electrolyte and electrode during the cycle, and reduce the increase of the impedance of the battery system during the cycle process, so that the battery performance is enhanced by.2, ethyl isopropyl sulfone (Ethyl isopropyl sulfone, EIS), ethyl vinyl group Ethyl vinyl sulfone (EVS) is used as additive: (1) when ethyl isopropyl sulfone is used as an additive, the electrochemical window of the reference electrolyte can be increased to 4.5V, and the discharge capacity of the LiNi1/3Co1/3Mn1/3O2 positive electrode charging and discharging at the cut-off voltage of 4.6V is greater and the ring is more stable, but the impedance of the battery in the cycle process is found. The increase amplitude is larger than that of the reference electrolyte, and the electrochemical performance of the graphite negative electrode in the system containing the additive is not ideal. (2) when ethyl vinyl sulfone is used as an additive, the charge and discharge capacity of LiNi1/3Co1/3Mn1/3O2/Li battery is unstable and the efficiency of Kulun continues to be less than 100%. The initial reason is that after adding EVS, LiNi1/3Co1/3Mn1/3O2 is in the process. The irreversible degree of charge and discharge process increases and the electrochemical polarization is serious. Although EVS can be reduced to EC before 1.2V, it can not play a stable role in the battery system, and the compatibility of graphite negative electrode is poor.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

【参考文献】