Boosting sulfur redox kinetics by a pentacenetetrone redox mediator for high-energy-density lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) battery is considered as a promising energy storage system due to its ultrahigh theoretical energy density of 2,600 Wh·kg−1. Redox mediation strategies have been proposed to promote the sluggish sulfur redox kinetics. Nevertheless, the applicability of redox mediators in practical high-energy-density Li-S batteries has seldomly been manifested. In this work, 5,7,12,14-pentacenetetrone (PT) is proposed as an effective redox mediator to promote the sulfur redox kinetics under practical working conditions. A high initial specific discharge capacity of 993 mAh·g−1 is achieved at 0.1 C with high-sulfur-loading cathodes of 4.0 mgS·cm−2 and low electrolyte/sulfur (E/S) ratio of 5 µL·mgS−1. More importantly, practical Li-S pouch cells with the PT mediator realize an actual initial energy density of 344 Wh·kg−1 and cycle stably for 20 cycles wih a high capacity retention of 88%. This work proposes an effective redox mediator and further verifies the redox mediation strategy for practical high-energy-density Li-S batteries.