离子液体微观结构及其锂离子电池体系的原位透射电镜研究

Room-temperature ionic liquids are a special class of liquids solely composed of cations and anions. Even though bulk properties of ionic liquids are still under intense investigations, the study of the microstructure of ionic liquids in low dimensional system is an exciting challenge and has attracted great attention due to their relevance in catalytic processes, separation, lubricants, electrochemistry, lubricants, biomass conversion, etc. High resolution transmission electron microscopy (HRTEM) is a powerful technique for probing the structure of materials deep into nanometer scale and molecular level. Unfortunately, the normal molecular liquid samples preclude any direct HRTEM observations due to their volatilities. Ionic liquids are unique liquid materials with almost zero vapor pressure, Thus they are ideal liquid samples which can be characterized by HRTEM directly. In this project, we design a bottom-up approach to insight into the microstructure of ionic liquid. We will carry out the in-situ HRTEM observations on a series of ionic liquids in 1D space, 2D thin film states and bulk phase. The microstructure, packing fashion and phase behavior of ionic liquids will be studied systematically. It is anticipated to explore not only the new concepts on liquid behavior in nanoscale, but also a solid understanding on the nature of ionic liquids. .On the other hand, during the last few years, there has been increasing interest in ionic liquids as electrolytes for lithium ion batteries, due to their high ionic conductivity, wide electrochemical window and nonflammable/nonvolatile properties. However, some important issues still unclear, such as lithium transportation in ionic liquids, solid electrolyte interface formation process, stability, microstructure and phase behavior of ionic liquid during battery working. Here, we will build up a lithium ion battery system inside HRTEM by using ionic liquid as electrolyte. The structure and behavior of ionic liquid during the charge/discharge circles will be investigated. Through this direct and in-situ analysis, combining with other electrochemical and spectroscopic techniques, many surface/interface problem, dynamic process and micro mechanisms can be revealed in detail, which will give some guidance on the utilization of ionic liquids in this field.

作为一类新型介质，离子液体在催化、分离、润滑、电化学、生物质转化等诸多领域展现出优异的应用前景，在这些领域中离子液体的微观结构起决定性作用，但目前对其微观结构特性的认识还很有限。高分辨透射电镜是一种在纳米尺度、分子水平上研究材料微观结构的强有力工具。本项目拟采取从一维空间到二维薄膜再到本体这种自下而上的研究策略，利用高分辨电镜探测多尺度下离子液体的微观结构、分子排列和相变行为等，了解离子液体的本质。在此基础上，考虑到近年来离子液体已被广泛用于新型锂离子电池的开发，然而在其应用过程中很多科学问题尚不清楚。我们将在高分辨透射电镜内部构筑以离子液体为电解质的锂离子电池原位表征系统，在线监测在电池充放电过程中，离子液体电解质的微观结构和物化行为。结合电化学方法和其他波谱技术，深入考察该体系的表界面科学问题、动态过程和微观机制，为开发离子液体在锂离子电池领域中的应用提供指导。

离子液体在催化、分离、润滑、电化学、生物质转化等诸多领域展现出优异的应用前景，在这些领域中离子液体的微观结构起决定性作用，但目前对其微观结构特性的认识还很有限。本项目采取从一维空间到二维薄膜再到本体这种自下而上的研究策略，利用高分辨电镜并结合多种波谱技术，探测多尺度下离子液体的微观结构、分子排列和相变行为等。例如，我们发现了离子液体在碳纳米管受限空间内熔点升高、自发还原等现象，对深入认识离子液体的本质及理解其在相关领域中的应用具有重要意义。. 考虑到近年来离子液体已被广泛用于新型锂离子电池的开发，然而在其应用过程中很多科学问题尚不清楚。本项目执行期间，我们开发了系列高性能电极材料，并利用合成的材料和离子液体电解液，在高分辨透射电镜内部构筑以离子液体为电解质的锂离子电池原位表征系统，在线监测在电池充放电过程中，离子液体电解质的微观结构和物化行为。结合电化学方法和其他波谱技术，深入考察该体系的表界面科学问题、动态过程和微观机制，例如我们发现一些仿生结构的负极材料，由于其结构的协同效应，可以大幅提高电极材料的循环、倍率等性能；设计合成的弹性致密碳包覆的硅球复合材料，可以大大提高硅碳负极材料的首次效率和循环稳定性，相关工作为开发离子液体在锂离子电池领域中的应用提供了指导。. 受此项目资助，发表SCI论文13篇，申请专利4项。