Mediator–Assisted Catalysis of Polysulfide Conversion for High–Loading Lithium–Sulfur Batteries Operating Under the Lean Electrolyte Condition

Abstract

The kinetics of S ↔ Li2S conversion in lithium–sulfur (Li–S) batteries can be improved with electrocatalysts to increase the application performance. The effectiveness of electrocatalysis reduces under the lean electrolyte condition due to the preponderance of solid reaction products (sulfur and Li2S) in a small amount of electrolyte; and the difficulty of catalyzing solid sulfur and Li2S. In this report, we describe the development of a mediated catalytic pathway in which a solid cathode catalyst is used alongside a soluble mediator to enable a cooperative catalysis that increases the sulfur utilization from 44% to 61% for high–loading (5.6 mg cm–2) lean–electrolyte (5.0 µL mg–1) Li–S batteries. The improved sulfur utilization is due primarily to the mediator working as a scavenger to capture and reutilize the otherwise “inactive” sulfur species (S/Li2S) in the cathode. Mediated catalysis is therefore a new strategy to noticeably improve polysulfide catalysis and sulfur utilization beyond what is possible with conventional use of catalysts.