Redox behavior of Li-S cell with PP14-TFSI ionic liquid electrolyte Spectroscopic study on speciation of polysulfides during charge/discharge processes

Abstract: Li-S batteries, having one of highest theoretical energy densities possible, havebeen suggested as a way to improve on the current state of the art. However, thedissolution of intermediate polysulfide species in the electrolyte has so far greatlyreduced the cycleabilty of these batteries. One proposed solution is to use an ionicliquid electrolyte to decrease the solubility of the polysulfides.This work investigates the polysulfide speciation in Li-S cells with an ionicliquid electrolyte during charge and discharge. Four different room temperatureionic liquids were studied and found to dissolve polysulfides in small concentrations.One of the ionic liquids, PP14-TFSI, was examined further using UV-Visspectroscopy to identify the polysulfide ions present in the electrolyte at differentpoints of the charge/discharge cycle.It was found that the first step of the reaction during discharge produces S2