Thesis Defense: Yuchi Tsao, Bao & Cui Groups
"Probing the effect of polymer coating, carbon material and molecular engineering of redox organic molecules for durable lithium-sulfur batteries"
Abstract: Lithium-sulfur (Li-S) batteries charge by oxidizing solid lithium sulfide (Li2S) into sulfur (S8) through soluble lithium polysulfide intermediates (Li2Sx), enabling a high energy density of 2500 Wh kg-1, a five-fold increase compared to traditional Lithium ion Batteries (LiBs). However, significant challenges remain in order to build practical Li-S batteries, which are primarily attributed to the dissolution of intermediate species (LiPSs) in the electrolytes as well as the insulating nature of both sulfur and Li2S. Therefore, strategies to durability of the Li-S batteries is key to their successful application in commercial batteries.
In my talk, the use of polymer coating, electrolyte additive, and carbon materials were used to address and understand issues of Li-S batteries. In the first part, I will talk about employing a solution-processable isoindigo-based polymers incorporating polar substituents to prevent the dissolution of LiPSs problem. In the second part, I will talk about applying the redox chemistry of a quinone derivative to realize efficient, fast, and stable operation of Li-S batteries using Li2S microparticles. Through understanding different property of redox mediator (e.g. oxidation potential, solubility, and electrochemical stability in the electrolyte), I found out a quinone derivative could resolve the overpotential problem for Li2S electrode. Lastly, to understand a better carbon structure that could be used in low E/S ratio, I employed a carbon flower to be a host to stabilize sulfur batteries. My work improves the durability of Li-S cycle life through understanding the effect polymer coating, electrolyte additives and carbon materials to Li-S batteries.