Master of Engineering Science
Mechanical and Materials Engineering
All-solid-state lithium-sulfur batteries (ASSLSBs) have emerged as a highly promising energy storage solution for next-generation applications, particularly electric vehicles. ASSLSBs offer several advantages compared to their lithium-ion battery counterparts, including economic feasibility, high theoretical energy density, and intrinsic safety. However, despite their potential, there remain significant challenges that hinder the widespread adoption of ASSLSB technology. The first part of this thesis focuses on investigating the reaction mechanism of ASSLSBs, with a particular focus on their discharge products. Advanced characterization techniques such as X-ray absorption spectroscopy and time-of-flight secondary ion mass spectroscopy are employed to probe the discharge products of ASSLSBs. Contrary to previous reports that suggest the formation of only lithium sulfide (Li2S), we discover that the discharge products of ASSLSBs consist of a mixture of Li2S and lithium disulfide (Li2S2). Building on this insight, we propose a strategy to induce a Li2S2-dominant discharge product while incorporating a trace mount of solid-state catalyst. This approach leads fully reversible ASSLSBs with long cycle life. The second part of this thesis investigates the relationship between the sulfide solid-state electrolyte (SSE) degradation in the cathode composite and the resulting impact on the electrochemical behavior of ASSLSBs. We reveal that the electrochemical performance of ASSLSBs is influenced by the type of SSE used in the cathode composite, primarily due to variations in their degradation products. In summary, this thesis provides valuable insights into the fundamental aspects of ASSLSBs and offers feasible strategies to improve their performance. The findings presented in this thesis contribute to the development of next-generation energy storage technologies, paving the way for the widespread adoption of ASSLSB technology in various applications and devices.
Summary for Lay Audience
The sudden paradigm shift toward electric vehicles (EVs) has resulted in the surging demand for rechargeable batteries, a cardinal component of EVs that determines factors such as driving distance, charge time, overall cost, and safety. Currently, lithium-ion batteries (LIBs) are the leading industry-standard battery technology, and all mass- produced EVs utilize LIBs. However, it remains unclear whether this decades-old technology can sustain the rapid, worldwide growth of EVs. This concern regarding LIBs stems from: 1) the threats to safety that arise from using a highly flammable liquid electrolyte component; 2) heavy reliance on expensive, unevenly distributed, and environmentally limited materials such as nickel and cobalt; and 3) the fast-approaching theoretical energy limit of traditional LIB materials such as graphite. In this regard, all- solid-state lithium-sulfur batteries (ASSLSBs) have been identified as a next-generation energy storage technology that could potentially be used in a variety of applications instead of traditional LIBs, such as electric vehicles (EVs) and grid-scale energy storage. ASSLSBs possess several distinct advantages compared to their liquid LIB counterparts. First, ASSLSBs utilize abundant, evenly distributed, and cheap sulfur as the cathode material. This enables indigenous supply chains that can circumvent materials sourcing from conflict-based countries and/or environmentally harmful mines. Second, ASSLSBs can deliver energy densities nearly ten times higher than traditional LIBs, enabling considerably longer driving ranges and lighter weight EVs. Third, ASSLSBs replace the flammable liquid electrolyte with a non-flammable solid-state electrolyte (SSE), mitigating the thermal runaway concerns inherent to LIBs. Despite its many advantages, ASSLSB technology is, unfortunately, nascent; there are several challenges hindering its fruition. The research presented in this thesis aims to elucidate the underlying reaction mechanisms of ASSLSBs. A mechanistic understanding of ASSLSBs will enable the identification of new engineering solutions and facilitate the practical implementation of ASSLSBs in next-generation devices and applications.
Kim, Jung Tae, "Mechanistic Insights into High Performance All-Solid-State Li-S Batteries" (2023). Electronic Thesis and Dissertation Repository. 9352.
Available for download on Tuesday, April 01, 2025