An integrated approach to improve the performance of lean–electrolyte lithium–sulfur batteries

Abstract

While the sulfur conversion reaction kinetics in Li–S batteries is nowadays improved by the use of appropriate electrocatalysts, it remains a challenge for the batteries to perform well under the lean electrolyte condition where polysulfide shuttle, electrode passivation and the loss of electrolyte due to side reactions, are aggravated. These challenges are addressed in this study by the tandem use of a polysulfide conversion catalyst and a redox–targeting mediator in a gel sulfur cathode. Specifically, the gel cathode reduces the polysulfide mobility and hence the polysulfide shuttle and the passivation of the lithium anode by the crossover polysulfides. The redox mediator restrains the deposition of inactive sulfur species in the cathode thereby enabling the Fe–N and Co–N co–doped carbon catalyst to prolong its catalytic activity. Consequently, the integrated catalytic system is able to increase the discharge capacity of high–loading (6.8 mg cm−2) lean–electrolyte (4.0 µL mg−1) Li–S batteries from ∼630 to ∼1316 mAh g−1, concurrently with an improvement of the cycle life (600 cycles with 46% capacity retention at 1.0 mA cm−2). Redox mediator assisted catalysis in a gel cathode is therefore an effective strategy to extend the application of the sulfur conversion catalyst in lean electrolyte Li–S batteries.