Abstract
Li-S batteries have attracted a lot of attention in the past decade due to their very high theoretical energy density of 2567 Wh.kg-1. Although several developments have been made to improve the performance of Li-S batteries, the assessment of some of their phenomena and limitations still remain challenging. In my PhD work, we have developed multiple mathematical models, which assist with assessment and optimization of some the Li-S batteries phenomena. We developed a novel 3D kinetic Monte-Carlo (kMC) model, which simulates the discharge of carbon/sulfur (C/S) composites at the mesoscopic level. Our kMC model also provides insights into the impacts of the discharge rate and sulfur loading on the mesoscale properties of the Li2S(s) deposits over the carbon surface. We also developed a multi-scale continuum model to investigate the impacts of the C/S cathode design parameters on the discharge of Li-S batteries. In order to determine the reaction mechanism of the solvated polysulfides in our experimental electrolyte (1 M LiTFSI in TEGDME:DOL (v/v=1:1)), we carried out cyclic voltammetry measurements of different electrolyte solutions containing solvated sulfur and polysulfides. A mathematical model was used to interpret the reactions behind the characteristics of experimental cyclic voltammograms. Furthermore, we also developed a nucleation and growth model to understand the phenomena behind the Li2S(s) electrodeposition in a simplified Li-S cell. Finally, we carried out some galvanostatic experiments using Li-S coin cells to validate our discharge model