锂离子电池高电压电解液体系的构建及电化学性能的研究

发布时间：2018-03-12 20:06

本文选题：锂离子电池　切入点：高电压电解液　出处：《兰州理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着高电压体系的迅速发展,高电压电解液的研发已经成为锂离子电池技术研究的热点。目前,商业使用的常规高电压电解液主要是由LiPF_6和碳酸酯类溶剂构成,其氧化分解电压在4.5 V(vs.Li/Li~+)附近。但是,LiPF_6在使用的过程中会发生自催化作用产生酸性物质,溶蚀正极材料。正极中溶蚀的过渡金属离子又会进一步沉积在负极石墨层中,造成容量迅速衰减。本文选用兼具LiBOB和LiBF_4优点的Li DFOB作为电解质锂盐,并利用其在镍锰酸锂LiNi_(0.5)Mn_(1.5)O_4正极材料表面成膜性好的优点对高电压电解液体系进行改性研究。首先,为了研究ADN添加剂对高电压电解液的作用机理,构建了Li DFOB-DEC/EC/ADN电解液体系。相较于不含添加剂的体系,含有添加剂的电解液体系的容量保持率升至81.2%,循环效率升至72.8%。结合实验数据,对ADN在LMNO正极表面的作用机理提出了两种猜想。第一,XPS的测试结果认为ADN会富集在正极表面对其它溶剂产生空间位阻从而减少电解液的分解;第二,量子化学计算方法分析ADN分解产物认为较为稳定的分解产物会阻碍高价Ni~(4+)氧化电解液。随后,本文结合ADN的作用机理对LiDFOB-DEC/EC/ADN体系在室温下放电比容量低的缺陷进行优化,通过在体系中引入含硫试剂优化正负极表面界面膜,研究改进的界面膜对ADN在负极分解的抑制作用。通过对含硫试剂ES、DMS以及SL在正负电极作用效果的分析,得到LiDFOB-ES和Li DFOB-SL的适配体系,并认为在正极上,LiDFOB-ES形成了稳定的界面膜,提高了电池的放电比容量;在负极上,LiDFOB-SL优先在负极表面成膜减少ADN的分解,提高了电池的容量保持率(72.5%)。上述研究为高电压电解液的设计及研发提供了新的思路。
[Abstract]:With the rapid development of high voltage system, the research and development of high voltage electrolyte has become a hot spot in lithium ion battery technology. At present, the conventional high voltage electrolyte for commercial use is mainly composed of LiPF_6 and carbonate solvents. The oxidation decomposition voltage is around 4.5 V / v 路L / L ~. But during the process of use, LiPFS6 will produce acid substances and dissolve the cathode materials. The transition metal ions dissolved in the positive electrode will be further deposited in the graphite layer of the negative electrode. In this paper, Li DFOB, which has the advantages of LiBOB and LiBF_4, is chosen as the electrolyte lithium salt, and the high voltage electrolyte system is modified by the advantage of good film-forming property on the surface of lithium nickel manganese LiNi_(0.5)Mn_(1.5)O_4 cathode material. In order to study the action mechanism of ADN additive on high voltage electrolyte, Li DFOB-DEC/EC/ADN electrolyte system was constructed. The capacity retention rate of the electrolyte system containing additives rose to 81.2 percent, and the cycle efficiency rose to 72.8 percent. Two conjectures about the mechanism of ADN acting on the surface of positive electrode of LMNO are put forward. First, the results of LMNO test show that ADN can enrich on the surface of positive electrode to produce steric resistance to other solvents, thus reducing the decomposition of electrolyte. The analysis of ADN decomposition products by quantum chemistry method shows that the more stable decomposition products will hinder the high valence Ni~(4) oxidation electrolyte. Subsequently, the defects of LiDFOB-DEC/EC/ADN system with low discharge specific capacity at room temperature are optimized in combination with the mechanism of ADN. By introducing sulfur-containing reagents into the system to optimize the interface film on the surface of positive and negative electrodes, the inhibitory effect of the improved interfacial membrane on the decomposition of ADN in the negative electrode was studied, and the effect of the sulfur-containing reagent ESS-DMS and SL on the positive and negative electrode was analyzed. The adaptive system of LiDFOB-ES and LiDFOB-SL was obtained, and it was considered that LiDFOB-ES formed a stable interfacial film on the positive electrode, which increased the specific discharge capacity of the battery, and LiDFOB-SL preferentially formed a film on the negative electrode surface to reduce the decomposition of ADN. The capacity retention rate of the battery is improved by 72.5. The above research provides a new idea for the design and development of high voltage electrolyte.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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