Advances in electrolyte chemistry and the development of electrolyte systems have revealed that electrolyte concentration significantly affects battery performance. However, the relationship between electrolyte concentration, polysulfide formation, and lithium−sulfur (Li−S) battery performance remains unclear, which hinders the developmental progress of practical Li−S batteries. In this study, we compared the electrolyte structures and performance of Li−S batteries with various electrolyte concentrations and developed a method that links microscopic interactions, apparent electrolyte parameters, and battery performance. The relationship between polysulfides and the electrolyte system was analyzed at various concentrations, which revealed that systems with a low lithium-salt concentration, especially below 1 M, are better suited to practical Li−S batteries and that polysulfides play crucial roles in ion-transport processes under practical conditions. This study supports the development of electrolytes for practical Li−S batteries and provides guidance for controlling ion-transport processes in liquid electrolytes for other secondary batteries.