Investigation of Electrolyte-Dependent In-Situ SEI on Lithium Metal Anodes for Lithium-Sulfur Batteries

Abstract

This thesis investigates the electrochemical performance of lithium symmetrical cells and lithium-sulfur (Li-S), emphasizing the role of various electrolyte additives on the formation and stability of the solid electrolyte interphase (SEI) and their overall impact on battery performance. Extensive experimental studies were conducted to understand how different additives influence SEI characteristics, Coulombic efficiency, and cell longevity. Key findings reveal that fluoroethylene carbonate (FEC) significantly enhances the electrochemical stability and operational efficiency of Li-S cells, outperforming other tested additives by promoting consistent SEI formation and reducing capacity loss over extended cycling. FEC enhanced cells resulted in lower the impedance values compared to other additives tested in this study. The study also highlighted the challenges associated with high current densities in lithium symmetrical cells, leading to early micro-short circuits and unstable voltage behaviors, suggesting the need for milder testing conditions to avoid overestimating cell degradation. The research underscores the critical role of electrolyte composition in developing high-performance Li-S batteries and points towards promising strategies for future electrolyte enhancement. The outcomes of this study not only contribute to the scientific understanding of SEI dynamics in Li-S batteries but also pave the way for further improvements in battery technologies, aiming for higher efficiency and longer life cycles in real-world applications.