Year

2021

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

The rapid development of electric vehicles has been intensifying the need for high-energy-density rechargeable batteries. The traditional lithium-ion batteries based on intercalation-type electrodes, however, are approaching the theoretical limit of their energy densities, and hence, they cannot satisfy the ever-growing demand for power sources with high energy and power densities. Replacing the current anode with lithium (Li) metal, which has a high theoretical capacity (3860 mAh g−1) and the lowest electrochemical potential (−3.04 V vs. standard hydrogen electrode), has been widely regarded as the “ultimate strategy” to boost the performance of next-generation energy storage systems. Unfortunately, Li metal is thermodynamically unstable against electrolytes, and thus, the electrolyte will be reductively decomposed to form a solid-electrolyte interphase (SEI) on every electron-conductive surface of the Li. Even though the SEI blocks electron tunnelling on the Li surface and thus suspends the further decomposition of electrolyte, the uneven deposition of Li could damage the SEI, and the side reactions between Li and electrolyte restart until the exposed fresh Li is completely passivated. The continuous breakage and repair of the SEI lead to electrolyte dry-out and the exhaustion of electrochemically active Li, fundamentally damaging the electrochemical performance of the Li metal batteries (LMBs). Worse still, Li+ is prone to deposition in dendritic morphology, which may pierce the separator to trigger an internal short circuit and a series of exothermic reactions. Before the commercialization of LMBs, these challenges need to be addressed.

The properties of the Li/electrolyte interface have a decisive influence on the stability of the Li metal electrode and the performance of LMBs. In this doctoral thesis, by using chemical pre-treatment and electrolyte engineering strategies, a series of nitrided interfaces are developed on Li metal electrode to regulate the uniform deposition of Li and passivate the reductive surface of Li metal. With the protection of the nitrided interfaces, the safety, capacity retention, and lifespan of LMBs have been effectively improved.

This thesis is unavailable until Thursday, January 12, 2023

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.