Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Sun, Xueliang

Abstract

Li metal batteries have been widely regarded as the next stage of energy storage technology, which is enabled by the low electrochemical potential (-3.04 V vs. the standard hydrogen electrode) and high specific capacity (3860 mAh g-1) of the Li metal anode. However, the implementation of Li metal anodes has been hindered by several issues including parasitic side reactions with electrolyte, large volume fluctuations, and dendrite formation which can cause short-circuits and safety issues. This thesis will cover some novel Li anode stabilization strategies while using advanced characterization techniques to provide critical information on the working mechanisms of Li metal anodes and their modes of failure.

The first part of this thesis covers the design of a conductive 3D copper nanowire host for Li metal. A simple and facile fabrication process yields a lithiophilic surface that enables molten Li infusion into the 3D host. The 3D structure is shown to lower the localized current density and minimize electrode volume change, thus allowing for high performance and long-life Li metal anodes.

The second part of this thesis investigates the temperature-dependent behavior and failure mechanisms of Li metal anodes in carbonate electrolytes. Several electrochemical testing methodologies are used to study the cycling behavior of Li metal anodes cycled between 0-60 °C. Furthermore, advanced synchrotron characterization techniques including in-situ X-ray tomography and energy-dependent X-ray fluorescence mapping are used for the first time to study Li metal anode chemical and physical structure changes under different operating conditions.

The third part of this thesis explores the application of molecular layer deposition (MLD) Zircone films on Li metal anodes. The nanoscale zircone coatings are able to improve the air stability and processability of the Li metal anode while enabling operation at higher current densities with improved stability. The application of the coating is shown in Li-O2 batteries which have a 10-fold improvement in cycle life.

The fourth part of this thesis investigates the mechanism of atomic layer deposition (ALD) coating growth on Li metal anodes and compares it to Cu current collectors for anode-free applications. The chemical and physical structure of the coatings are explored and it is shown that the reactive Li surface results in non-ideal surface structures with unexpected chemical compositions that differ from other substrates with the same deposition parameters.

The final part of this thesis studies three superionic halide solid-state electrolytes and their electrochemical reactivity towards Li metal anodes. The reactions are studied through advanced characterization techniques and their failure modes are explored.

Summary for Lay Audience

The ever-growing need for higher performance electronic devices and electric vehicles has led to the need for batteries with higher energy density than modern Li ion batteries. As a result, Li metal batteries have been proposed as the next step in energy storage technology. Li metal can enable several next-generation battery systems while offering energy densities that supersede that of conventional anode materials. However, several problems have prevented the commercialization of Li metal anodes, including unwanted reactions and dendrite formation which cause safety hazards. This thesis includes strategies to stabilize the Li metal anode and improve their safety. Novel Li anode designs and thin film coatings are developed to prevent dendrite formation, enhance safety, and improve battery lifetime. Moreover, advanced characterization techniques are used to study Li metal anodes in different environments, including liquid and solid-state electrolyte systems, to provide a better understanding of their failure mechanisms.

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Available for download on Saturday, August 12, 2023

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