Electrochemical reduction mechanism of sulfur particles electrically isolated from carbon cathodes of lithium-sulfur cells

This work presents a new insight into the reduction mechanism of solid sulfur during the first step of cell discharge, that is, a 2.4V plateau in Li-S batteries, by testing a specially designed cell with the solid sulfur electrically isolated from the carbon cathode and comparing it with a conventional cell. Importantly, the cell with the electrically isolated sulfur particles confined between two separators shows very normal operation even during the first cycle and provides the same result as a conventional cell after several cycles. Based on the controlled potentiostatic and galvanostatic experiments, we propose a reasonable reaction route: a portion of the electrically isolated solid sulfur (S₈) is dissolved in the electrolyte solution to form sulfur molecules, which can be electrochemically reduced to polysulfides on the carbon surface.