Dependence of Impedance Response of Li-S Battery on Polysulfide Solubility of Electrolyte II - Mid - End Stage of Discharge

摘要

Sulfur is a promising cathode material for the lithium based battery because of its advantages such as eco-friendness, abundance in nature, and high theoretical capacity of 1675 mAh g~(-1). However, sulfur cathodes are not without their own intrinsic problems such as low ionic and electronic conductivity, large volumetric expansion upon lithiation from S_8 to Li_2S, and the dissolution of so-called polysulfide intermediates (Li_2S_x where x represents a value between 4 and 8). In previous studies, glyme-Li~+ solvent ionic liquid (SIL) and polypyrrole film containing ionic liquid were proposed to mitigate dissolution of polysulfide. Meanwhile, dependence of sulfur cathode's reaction mechanism on polysulfide solubility of electrolyte is still unclear. In this study, electrochemical impedance spectroscopy (EIS) at various depth of discharge was performed in two types of lithium-sulfur batteries using electrolytes with different polysulfide solubility. This paper describes that polysulfide solubility in electrolyte largely influences the impedance response at mid - end stage of discharge in Li-S batteries.