Tri-sulfur radical trapping in lithium–sulfur batteries

Lithium-sulfur (Li–S) batteries have emerged as a next-generation battery technology owing to their prospects of high capacity and energy density. They, however, suffer from rapid capacity decay due to the shuttling of reaction intermediate species: Li polysulfides (LiPSs). One of the more important and intriguing PSs is the tri-sulfur radical (S3•−), observed mainly in high-donor number (DN) solvent-based electrolytes. Although this radical has been proposed to be crucial to full active material (AM) utilization, there is currently no direct evidence of the impact of S3•− on cycling stability. To gain more insight into the role of the S3•−, we studied the use of radical traps in low and high DN solvent-based electrolytes by operando Raman spectroscopy. The traps were based on nitrone and iminium cation, and S3•− was indeed successfully trapped in ex situ analysis. However, it was the ionic liquid-based trap, specifically pyridinium, that effectively suppressed S3•− during battery operation. Overall, the PS formation was altered in the presence of the traps and we confirmed the impact of S3•− formation on the Li–S battery redox reactions and show how the trapping correlates with Li–S battery performance. Therefore, stabilization of the S3•− might be a path to improved Li–S batteries.