锂离子电池中高分子复合固态电解质薄膜的研究
日期：2022/11/21 - 2022/11/21
博士论文答辩：锂离子电池中高分子复合固态电解质薄膜的研究
主讲人：Xintong Mei, Ph.D. candidate at UM-SJTU Joint Institute
时间：2022年11月21日（周一）上午9:00
地点：密院龙宾楼403会议室
讲座摘要
Solid-state electrolytes, as an essential component in solid-state batteries, have received extensive attention. Solid polymer electrolytes are one of the representative solid-state electrolytes and possess the properties of good flexibility, lightweight and easy scale-up production. However, the ionic conductivity (~10-6 S/cm) is not yet able to meet the requirements of practical applications. Meanwhile, due to the complexity of polymers and their composites, essential ion transport mechanisms are not fully understood, and quantitative characterization is unavailable. Therefore, this dissertation is devoted to investigating ion transport mechanism through the correlation between ion conduction and polymer crystallization, micro dynamics and microstructure and developing highly conductive solid polymer composite electrolytes based on these fundamentals.
Firstly, from the scientific level, this dissertation demonstrates the quantitative relationship between the crystallinity of polymer and the ionic conductivity of composite electrolytes. Although crystallization is generally considered detrimental to ion conduction, whether there are any quantitative correlations between polymer crystallinity and ionic conductivity is unknown. Therefore, mastering the correlation between crystallization and ion conduction can directly lead to a better understanding of ion conduction mechanisms. This dissertation first discovers a novel quantitative correlation between ionic conductivity and crystallinity, which is also applicable to other polymer-ceramic composites reported in the literature. On the other hand, it is also found that ion transport is quantitatively coupled with the chain segment motion of the polymer and the interfacial polarization, which elucidates the ion transport mechanism from the perspective of micro dynamics.
From the engineering level, this dissertation fabricates polymer blend electrolytes in which continuous and abundant polymer-polymer interfaces are created. Existing studies have shown that polymer/polymer interfaces may provide a rapid pathway for ion transport. However, recent work is still qualitative and the effect of interfaces remains to be investigated. In this dissertation, polymer/polymer interfaces are designed and manipulated by thermodynamic interaction between two polymers. The effect of the interface on ionic conductivity is analyzed and evaluated by such material systems. The strong interactions between components suppress local concentration fluctuations and reduce the scale of polymer-polymer interfaces. By constructing polymer-polymer interfaces of molecule level and gradually accelerating the relaxation processes of chain segments and interfaces, the ionic conductivity of polymer blend electrolyte is enhanced to a promising and applicable level of 1.4×10-4 S/cm at room temperature.
Furthermore, from the processing level, this dissertation proposes an electric-field-assisted method to prepare polymer-ceramic composite films. The external electric field can effectively regulate the microscopic distribution of ceramic particles in the composite system. Particles are rearranged in the direction of the electric field to form a chain-like microstructure directly connecting the cathode and anode, which contribute to fast ion transport. Meanwhile, polar groups on the polymer chains tend to be orderly arranged along the direction of the electric field, and crystallization is effectively inhibited. The regulated internal structure increases ionic conductivity by 3.33 times.
This dissertation quantitatively models ionic conductivity by crystallization and micro dynamics and reveals how microstructure impacts ion conduction. The results provide novel comprehensions of ion transport mechanisms which can aid the design of solid polymer composite electrolytes with improved ionic conductivities toward practical application of solid-state batteries.
主讲人简介
Xintong Mei received her B.S. degree in College of Mechanical and Vehicle Engineering from Hunan University, China, in 2016. Now, she is a Ph.D. candidate student at University of Michigan-Shanghai Jiao Tong University Joint Institute, supervised by Professor Yunlong Guo. Her current research focuses on the solid polymer composite electrolytes in Lithium-ion batteries.