In Situ UV-Vis Analysis of Polysulfide Shuttling in Ionic Liquid-Based Li-FeS2 Batteries

ABSTRACT: Herein, a combination of in situ and ex situ UV-Vis spectroscopy is used to study the formation and shuttling of polysulfides (PSs) in Li-FeS2 batteries. We find three key results. First, PS shuttling significantly decreases (similar to 4x) when an ionic liquid electrolyte (1.0 M LiFSI in PYR14TFSI; ILE) is used in place of a conventional organic electrolyte (1.0 M LiTFSI in 1:1 DOL:DME). Furthermore, when the Li salt anion in the ILE is changed from FSI- to TFSI-, PS shuttling is effectively suppressed. Second, the total amount of PSs formed using the ILE is approximately double the amount shuttled. This result has implications for battery aging as solubility of PSs could conceivably increase upon extended storage. Third, the majority of PS shuttling occurs during the first cycle. Together, these findings provide important insights for understanding and thus preventing PS shuttling in Li-FeS2 batteries.

Automated summary

In this study, a combination of in situ and ex situ UV-Vis spectroscopy is used to investigate the formation and shuttling of polysulfides in Li-FeS2 batteries. The results show that PS shuttling can be significantly reduced when an ionic liquid electrolyte is used instead of a conventional organic electrolyte, and changing the Li salt anion in the ionic liquid electrolyte effectively suppresses PS shuttling. The majority of PS shuttling occurs during the first cycle, and the total amount of PSs formed using the ionic liquid electrolyte is approximately double the amount shuttled.