Designing Hysteresis Free High-Valent Redox Cathode Materials for Electrochemical Applications

Type Thesis

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Summary

Advances in electrochemical devices such as batteries, fuel cells, and water-splitting membranes are making global transition towards clean and renewable energy more possible than ever. Foundational to (electro)chemical and catalytic transformations in these devices are a stable and reversible high-valent redox couples. In particular, the phenomenon of high-valent oxygen redox (anionic redox) in lithium- and sodium-ion positive electrodes has the potential to significantly improve cell energy density by providing additional high voltage capacity beyond that of most transition metal redox couples. However, the additional capacity from (anionic redox) has come at the expense of reduced reversibility in the form of voltage hysteresis and voltage fade. As a result, high valent redox couples have been historically avoided. After providing historical context of lithium- and sodium-ion battery technologies in Chapter 1, my thesis, will outline the mechanism and the framework for understanding the source of poor electrochemical reversibility in high-valent redox (Chapter 2 and 3). In Chapter 4 and 5, I will demonstrate mechanisms and design rules where structural disorder and voltage hysteresis can either be completely avoided or mitigated, respectively. Finally, I will conclude by summarizing the main findings and their implications to the future of (electro)chemistry, solid-state chemistry and condensed matter physics (Chapter 6).