Redox Mediator: A New Strategy in Designing Cathode for Prompting Redox Process of Li–S Batteries

Abstract

The multistep redox reactions of lithium–sulfur batteries involve undesirably complex transformation between sulfur and Li2S, and it is tough to spontaneously fragmentate polysulfides into shorter chains Li2S originating from the sluggish redox kinetics of soluble polysulfide intermediates, causing serious polarization and consumption of sulfur. In this work, 3,4,9,10-perylenetetracarboxylic diimide (PTCDI)/G is employed as sulfur host to accelerate the conversion process between polysulfides and sulfur, which could facilitate the process of both charging and discharging. Moreover, PTCDI has strong adsorption capacity with polysulfides to restrain shuttle effect, resulting in promotional kinetics and cycle stability. A high initial capacity of 1496 mAh g−1 at 0.05 C and slight capacity decay of 0.009% per cycle at 5 C over 1500 cycles can be achieved. Moreover, the cathode could also achieve a high energy efficiency over 85% at 0.5 C. This research extends the knowledge into an original domain for designing high-performance host materials.