Understanding the Impact of Precipitation Kinetics on the Electrochemical Performance of Lithium-Sulfur Batteries by Operando X-ray Diffraction

Abstract

The complex reaction mechanism of the lithium-sulfur battery system consists of repetitive dissolution and precipitation of the sulfur-containing species in the positive electrode. In particular, the precipitation of lithium sulfide (Li2S) during discharge has been considered a crucial factor for obtaining a high degree of active material utilization. Here, the influence of electrolyte amount, electrode thickness, applied current, and electrolyte salt on the formation of Li2S is systematically investigated in a series of operando X-ray diffraction experiments. Through a combination of simultaneous diffraction and resistance measurements, the evolution of Li2S is directly correlated to the variation in internal resistance and transport properties inside the positive electrode. The correlation indicates that at different stages the Li2S precipitation both facilitates and impedes the discharge process. This information about the kinetics of Li2S formation offers mechanistic explanations for the strong impact of different electrochemical cell parameters on the cell performance and, thus, directions for holistic optimizations to achieve high sulfur utilization.