LAUSR

Abstract A comprehensive understanding of sulfur reduction pathways is critical to developing high-performance lithium-sulfur (Li-S) batteries. However, to date even the polysulfide intermediates are not fully understood with their distinct forms under debate. In this work, electrochemical impedance spectroscopy is employed to study the polysulfide evolution in a Li-S cell using the free-standing film with a sulfur loading of 6 mg cm−2 and ether-based electrolyte. The impedance data reveal the presence of soluble Li2S3 intermediate, and two major obstacles in the discharge processes. One obstacle is the sluggish kinetics of Li2S4 reduction reaction at 25% depth of discharge (DoD), and the other is Li2S nucleation observed at 50% DoD requiring to overcome an energy barrier. This clarification provides a new prospect for making a better Li-S battery, i.e. to develop effective sulfur reduction catalysts that circumvent the two major obstacles.