Exploration and Optimization of Thiol-containing Conductive Polymer and Covalent Organic Frameworks as Cathode Materials in Lithium-Sulfur Batteries: Synthesis, Operando Analysis, and Simulation

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Lithium-sulfur (Li-S) batteries hold promise for future energy storage, with polymers like poly(4-(thiophene-3-yl) benzenethiol) (PTBT) playing key roles. However, achieving high sulfur loading and maintaining optimal conductivity present challenges. Covalent organic frameworks (COFs) provide potential solutions, offering porous structures for sulfur storage and transport. Despite promising initial studies, fundamental issues such as electrochemical interactions between sulfur and COFs and the impact of pore structures on sulfur loading remain unexplored. In addition to the scientific challenges, practical aspects such as scalability, compatibility with industrial processes, and degradation mechanisms during transition to industrially relevant cell formats need addressing. Advanced characterization technologies and operando methods offer deeper understanding of electrochemical mechanisms in electrode materials, though COFs have had limited exposure to multi-method modeling studies. The proposed research combines experimental and theoretical investigations to optimize PTBT and thiol-functionalized COFs (SH-COFs) as cathode materials, aiming to enhance the efficiency, stability, and energy density of Li-S batteries. The work program includes experimental investigations, comprehensive operando analysis, and mechanistic studies using simulations and theoretical calculations. The program involves optimizing the up-scale synthesis of PTBT-based sulfur cathodes for pouch cell application, creating SH-COFs with controllable pore size and -SH groups, performing multimodal operando analysis of Li-S cells (both coin cells and pouch cells), and attaining a theoretical understanding of thiol-containing COF-based sulfur hosts. Techniques like X-ray imaging will track active material distributions, while spectroscopic methods will study the release of polysulfide species into the electrolyte during cell cycling. A mechanistic study of thiol-containing COFs, based on multiscale simulations and theoretical modeling, will provide a microscopic understanding of these materials. Molecular structure, dynamics, and the impact of varied solvent compositions and pore sizes will be investigated.