Author: Madison R. Tuttle

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

The ability to store energy in a scalable, profitable, and environmentally benign manner is a key challenge in the global transition to clean energy. Unfortunately, lithium-ion batteries (LIBs) and other conventional energy storage systems depend on metal-based electrode materials and the large-scale mining of metal ores, which is environmentally costly and ultimately unsustainable. Organic electrode materials (OEMs) offer an intriguing alternative to metal-based electrode materials, as OEMs benefit from abundant feedstocks, unparalleled synthetic modularity, and rich redox chemistry. However, reported OEMs lack the fast charging rates and long cycle lifetimes of metal-based electrode materials, likely due to low electrical conductivity and dissolution in battery electrolytes. To address these issues, we have focused on understanding fundamental relationships between the molecular structure of OEMs and battery performance, which can serve as design guidelines for the development of next-generation sustainable energy storage systems. Using benzoquinone as our OEM scaffold, we first investigated the impact of discrete synthetic modifications, such as incorporating thiazyl (-S=N-) moieties or hydrogen bonding motifs, to uncover new structure-performance trends for OEMs in LIBs. Through theoretical calculations and experimental studies, we established a positive correlation between non-covalent intermolecular interaction strength and performance for thiazyl and hydrogen bonding functional groups. In particular, we found that increasing the number of thiazyl S atoms or hydrogen bonding groups leads to stronger intermolecular interactions, resulting in enhanced charging rates and prolonged battery lifetimes. These works showcase molecular modification as a tool for systematically tuning battery performance, presenting two possible design strategies for improving conductivity and stability in future OEMs. Aside from LIBs, aqueous Zn-ion batteries (AZIBs) have become promising candidates for grid-scale renewable energy storage due to the low cost of Zn metal and safety of aqueous electrolytes. Toward this end, we designed and synthesized two low-cost Zn-thiolate OEMs, utilizing our molecular modification approach to tune the electrochemical performance. Through detailed mechanistic investigation and optimization of the electrolyte and separator, we were able to identify and inhibit a detrimental H+ insertion redox process, extending the battery lifetime appreciably. This work identifies a new thiolate/disulfide redox platform for designing low-cost electrode materials for sustainable energy storage. In each of these studies, chemical intuition and experimental testing were necessary to identify, synthesize, and evaluate each OEM candidate. Although this approach has led to useful insights and design trends in our case, it is inherently time-intensive, and a good outcome is not guaranteed. With this in mind, we have begun developing a statistical model for predicting OEM performance based on easily obtained physical organic features. We aim to use this model to identify key factors that govern the performance of OEMs, which will significantly reduce the time and cost of OEM development.