Dr. Narayanan - Computational design of electrolytes for high-performance lithium-sulfur batteries

Speaker: Dr. Narayanan, University of Louisville Mechanical Engineering

Abstract: Lithium-sulfur (Li-S) batteries hold tremendous promise in electric transportation owing to their high theoretical specific energy and low-cost of sulfur. However, techno-economic studies show that they need to operate under lean-electrolyte conditions (low electrolyte-to-sulfur ratio E/S<1 mL/g) to compete effectively with existing Li-ion technology. Developing long-lived Li-S batteries with high capacity at low E/S ratio has remained extremely challenging owing to (a) reliance of traditional Li-S chemistry on large excess of electrolytes (>10 mg/L) to solubilize the intermediate lithium polysulfide reaction products, and (b) uncontrolled parasitic reactions at the Li-anode. In this seminar, I will demonstrate that an emerging class of electrolytes containing high concentration of Li-salts (called sparingly solvating electrolytes, SSE in short) could provide a way to mitigate these longstanding challenges. Using first-principles molecular dynamics simulations, and quantum chemical calculations, we find that within a SSE, the local solvation structure around Li+ ion, and long-range electrolyte structure can be precisely controlled by varying composition of the electrolyte. In combination with electrochemical experiments and spectroscopic measurements, our computations show that extended network structures can be engineered within a SSE by optimizing its composition. These network structures facilitate a quasi-solid-state speciation pathway that enables low E/S operation, while simultaneously inhibiting parasitic reactions at the anode. I will discuss these results in the context of designing electrolytes for long-lived, stable, and high-energy density Li-S batteries.