Nanoscale Characterization of Oxide Materials and Interfaces for High Performance Lithium Ion BatteriesPublic
The start of the 21st century brought the sweeping proliferation of portable electronics such as laptops, tablets, and smartphones. These technologies were largely enabled by advances in energy storage methods – lithium ion batteries in particular. Society's push for more advanced energy storage applications, such as electric vehicles, stresses the need for lithium ion batteries with improved performance and availability. Reaching new performance heights largely requires developing new materials for the battery electrodes, and understanding the impact of their crystal structure and materials chemistry on the electrochemical phenomena which directly affect battery performance. The work in this dissertation probes how nanoscale changes to the structure and composition of metal oxide electrode materials drive increases in charge capacity. The challenges and complications these changes bring to the materials system are also examined, especially when undergoing reduction-oxidation reactions due to lithiation and delithiation. These challenges are most prominent in materials that undergo a conversion reaction with lithium, resulting in large charge capacities but limited reversibility and significant morphology changes. Multilayer nickel/nickel oxide structures are utilized as an anode model system and testing ground for controlling structural evolution, lithiation mechanisms, and kinetics of the conversion reaction. Key to these studies is the deep implementation of electron microscopy imaging and spectroscopy techniques for the characterization of chemical and structural evolution, and their correlation with surface-sensitive x-ray techniques. These same techniques are applied to studying oxygen coordination and electronic structure in lithium-rich intercalation cathode materials. The reactivity and participation of oxygen in charge compensation mechanisms during electrochemical (de)lithiation is carefully considered. Furthermore, an extended methodology of electron energy loss spectroscopy is explored for the study of lithium ion battery materials when limited by constraints in electron beam sensitivity or sample thickness and morphology. Overall, these studies illustrate the diverse and complex electrochemical reactivity of metal oxides that together deepen our understanding of the atomic-scale and nano-scale structure-composition effects on phenomena critical to battery performance.
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