Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

Abstract

One of the technological barriers to electrification of transport is the insufficient storage capacity of the Li-ion batteries on which the current electric cars are based. The lithium-sulfur (Li-S) battery is an advanced technology whose successful commercialization can lead to significant gains in the storage capacity of batteries and promote wide-spread adoption of electric vehicles. Recently, important Li-S intermediates, including polysulfides, S₃^•-, and Li₂S, have been shown to present unique X-ray absorption near edge structure (XANES) features at the sulfur K-edge. As a result, a combination of XANES characterization with electrochemistry has the potential to contribute to the understanding of Li-S chemistry. In this study, we present an <em>operando</em> XANES cell design, benchmark its electrochemical and spectroscopic performance, and use it to track reaction intermediates during the discharge of the battery. In particular, by employing electrolyte solvents with either a high or a low dielectric constant, we investigate the influence of the solvent on the conversion of polysulfide species to Li₂S. Our results reveal that Li₂S is already formed after similar to 25-30% discharge in both types of electrolyte solvents, but that further conversion of polysulfides to Li₂S proceeds more rapidly in a solvent with a low dielectric constant.