Year

2023

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

Lithium (Li) metal batteries have recently gained tremendous attention owing to their high energy capacity compared to other rechargeable batteries. Nevertheless, Li dendritic growth causes low Coulombic efficiency, thermal runaway, and safety issues, all of which hinder the practical application of Li metal as a promising anodic material. From the material development aspect, new and creative solutions are required to resolve the current technical issues on advanced Li batteries and improve their safety during operation.

The research encompassed in this work spans a broad investigation of utilizing Zeolitic imidazolate framework derived carbon (ZIF-C) as a 3D host material in Li metal batteries. The reason behind choosing ZIF-C in this thesis not only relies on its flexibility with which constituents’ geometry, size, and functionality can be modified to match application needs, but also because it exhibits several outstanding properties, such as robust mechanical strength, large surface area and pore volume, and adequate electrical conductivity, making it a potential candidate for cost-effective practical usage. These host materials, however, could suffer from poor Li wettability, which results in significant nucleation barriers and upper surface electrodeposition of Li metal, leading to dendritic growth and safety concerns.

This thesis covers multiple aspects related to ZIF-C material. Firstly, the physical properties of porous ZIF-C, which can be controlled by the inorganic components, were thoroughly studied. This provided the basis of enhancing the properties of ZIF-C by varying the ratios of zinc/cobalt ion metallic precursors. A key finding from this study is that the initiation of carbon nanotubes growth and the pore size on the surface of ZIF-C is highly dependent on the Co/Zn ratio. Secondly, we theoretically demonstrated and experimentally correlated the growth mechanism of Li clusters on the surface of Co/Zn ZIF-C by employing different heteroatoms (pyridinic N, pyrrolic N, quaternary N, and Co-N4). As a key feature, the Co-N4 affects the Li deposition behavior with axial Li growth on the surfaces of the carbon frameworks, while the other heteroatoms (i.e., nitrogen defects) induce unfavorable vertical Li growth. Thirdly, we functionalized the Co/Zn ZIF-C with oxidized nitrogen groups by utilizing nitric acid. We found that the functionalized porous carbon demonstrated an enhanced wettability compared to its non-functionalized counterpart. Moreover, by functionalizing the carbon surface with oxidized nitrogen during Li plating and stripping, catalyzed Li nitride (Li3N) formed in the solid electrolyte interphase which effectively enhanced the surface morphology of Li deposition. The electrochemical measurements showed a massive improvement in the capacitive behavior of the functionalized porous carbon and an enhanced electrochemistry performance in terms of cyclability and reversibility.

Some additional theoretical and experimental work, involving advanced computational simulations and in situ characterization techniques, opens the door to further work in developing high-performance battery materials for the advance of a new generation of Li-based batteries.

FoR codes (2008)

0299 OTHER PHYSICAL SCIENCES, 0399 OTHER CHEMICAL SCIENCES, 0904 CHEMICAL ENGINEERING, 0912 MATERIALS ENGINEERING

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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.