Doctor of Philosophy (PhD)
Lithium ion battery (LIB) is a lightweight, rechargeable and powerful battery that is used widely from mobile phones to laptops to electric cars. It has many exceptional advantages such as high energy density, high output power, relatively low self-discharge, etc. However, it has some disadvantages such as safety issues, capacity loss, and expensive manufacture. LIB is composed of three main components: electrolytes, positive and negative electrodes. Researchers have been working on improving the performance of LIB for the past decade, but only a few have focused on investigating the electrolytes at the molecular level. In addition, the molecular mechanisms behind the macroscopic properties of LIB are yet to be explored. The vibrational stretch of the solvent molecule is selected as the infrared probe in order to investigate the structure and dynamics in LIE at the molecular level via linear and non-linear infrared spectroscopies. Ultrafast laser spectroscopy has emerged as a powerful tool of studying the structure and dynamics at the molecular level because it offers unique advantages of time and frequency resolutions. DFT calculation, classical and ab initio MD simulations are also employed to assist the interpretation of experimental data. Three projects of LIE are detailed in this dissertation. The first project focused on lowering the flammability of the electrolyte by replacing carbonate solvent with urea solvent, where it is found that the molecular interactions in urea-based electrolytes are similar to the carbonate-based electrolytes. The aim of second project was to reveal the molecular mechanism behind the dynamics of solvent molecules around Li ion in acetonitrile-based electrolytes, where it is shown that the angle between Li ion and acetonitrile plays the most important role in the molecular dynamics around Li ion. The last project investigated a less conventional LIE, which is the concentrated electrolyte composed of Li sulfonylimide salt and acetonitrile, where a highly correlated network is proposed to form in the mixtures. In addition, the molecular origin of the macroscopic properties in a family of concentrated electrolytes is studied through both experimental and theoretical methods.
Chen, Xiaobing, "Investigation on the Structure and Dynamics of Lithium Ion Solvation Shell by Linear and Non-Linear Infrared Spectroscopy" (2021). LSU Doctoral Dissertations. 5563.
Kuroda, Daniel G.