Department of Chemistry – Physical Chemistry Seminar – Qing Guo

About the event

Speaker: Qing Guo, Postdoctoral Research Associate in Aurora Clark’s lab

Title: Exploration of lithium polysulfides solid phase – a first-principles study

Abstract: The lithium-sulfur battery is considered a promising substitute for the current Lithium-ion battery due to its high theoretical energy density and relatively low cost. However, the discharge progress of lithium-sulfur batteries is still not fully understood because of the complexity of intermediate polysulfides products. It is believed that the intermediate products (long-chain polysulfides) are highly soluble in the traditional organic electrolytes, e.g., Tetraethylene glycol dimethylether (TEGDME), 1,2-dimethoxyethane (DME), etc. However, with a well-engineered cathode microstructure, the lithium polysulfides could be confined within the cathode without dissolving into the electrolytes. This provides the feasibility of solid polysulfides formation. In this work, we have employed the particle swarm optimization (PSO) based structure prediction method for a systematical investigation of the possible lithium polysulfides solid phases. Then, we continue to explore the structural, mechanical, and electronic properties of the low-energy solid lithium polysulfide structures. Our DFT results indicate the van der Waals term is essential in polysulfides crystalline structures study, and the predicted S K-edge X-ray absorption near-edge structure (XANES) well explained the experimental observations. Besides that, the calculated thermodynamics and mechanical properties also provide an important baseline study for Li-S battery cathode materials design.