Unraveling the Microstructure of Organic Electrolytes for Applications in Lithium-Sulfur Batteries

Abstract

Lithium batteries have revolutionized emerging electronic applications and will play more important roles in the future. Unfortunately, the energy density of commercial lithium-ion batteries (100-265 Wh kg-1) cannot satisfy the fast-growing demand for energy storage technologies. Lithium-sulfur (Li-S) batteries stand out for high energy density (2567 Wh kg-1), low-cost, and environmentally benign attributes. However, the development of Li-S full-batteries is still hindered by the dissolution of polysulfides into the organic electrolytes and poor ions transfer at the interfaces of electrolytes and lithium-intercalated electrodes (e.g., lithiated graphite). Improving the electrolytes is a crucial aspect for the development of battery technologies, but the knowledge concerning the electrolyte microstructures remains elusive. This dissertation unravels the microstructures of organic electrolytes and paves the way to the development of Li-S batteries. Firstly, we demonstrate the key role of electrolyte chemistry in the battery performances by showing a synergetic effect of electrolytes coupled with designed sulfur cathodes. Secondly, we investigate the microstructure of electrolytes and discover previously unexplored solvent-solvent and solvent-anion interactions. We show that the interactions are useful to elucidate important battery operations, such as ions transfer at electrolyte-electrode interfaces, and reveal a potential probe for developing battery electrolytes. Thirdly, we optimize the electrolyte composition to obtain a highly reversible Li+ intercalation/deintercalation at the graphite anode, giving high performances of Li-S full-batteries in a dilute electrolyte concentration. Finally, we unravel the key role of additives in suppressing Li+ solvation in the electrolytes. Nitrate (NO3-) anions are observed to incorporate into the solvation shells, change the local environment of Li+ cations, and then lead to an effective Li+ desolvation followed by improved battery performances. Key significances of this dissertation are (i) observation of detailed electrolyte microstructures showing a potential probe for developing battery electrolytes; (ii) evidences of the electrolyte chemistry plays a predominant role in the electrolyte-electrode interfacial reactions, which prevails over the role of commonly believed solid electrolyte interphase (SEI); and (iii) new mechanistic insights into the key role of additives in the electrolyte microstructures. Furthermore, the presented methodology paves the way for developing electrolytes for broad electrochemical applications.

Date of Award	Jun 30 2021
Original language	English (US)
Awarding Institution	Physical Sciences and Engineering
Supervisor	Thomas Anthopoulos (Supervisor)