Date of Graduation

7-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor

Jie Xiao

Committee Member

Xiangbo (Henry) Meng

Second Committee Member

Ryan Tian

Third Committee Member

Uche Wejinya

Fourth Committee Member

Rick Wise

Keywords

Electrochemical deposition, Energy storage devices, Lithium metal battery, Microelectrode, Organic electrolyte, Silver metal deposition

Abstract

Metals, whether in a solid or soluble ion form, are a vital part of any electrochemical storage system. More so, Li metal is widely considered as the ideal anode because of its low density and low electrochemical potential (-3.04 V vs. the standard hydrogen electrode – SHE). However, just like most metals, it does not plate or strip evenly during cycling which can lead to cycling performance issues, short cycling lifespans, and even safety concerns brought about by dendrites that can cause internal short-circuiting within cells. This research focused on investigating the electroplating of metals in both aqueous and non-aqueous systems. The diffusion process and electrochemical kinetics of metal cations have been quantified and correlated to the microstructures of electrochemically deposited metals. To simplify the deposition process and exclude the interference from solid electrolyte interface (SEI), this work started from depositing Zn and Ag in an aqueous electrolyte in a “clean” system to understand the fundamental correlations among concentration, concentration gradient, solvation structure (additive), and the electroplated metal morphologies in the model system. A microelectrode was further used to quantify the diffusion process and electrochemical reaction rate of Li+ in a variety of non-aqueous electrolytes to develop a tool for fast screening of compatible electrolytes for a lithium metal anode. Based on the knowledge gathered, a series of novel benzene (PhH) based electrolytes have been identified and validated in a lithium sulfur battery system. Optimized PhH based electrolyte recipes were found to appreciably improve the cycling performance of the Li metal anode and the overall performance of the LiS cells over the conventional ether-based electrolyte, confirming the effectiveness of the proposed methodology for fast testing of electrolytes.

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