Improving redox kinetics of sulfur cathode via bidirectional catalysis enhanced by nitrogen vacancy

Abstract

The high-energy-density lithium-sulfur (Li-S) batteries (2600 Wh kg−1) are seriously hampered by the slow redox reaction kinetics and obnoxious shuttle effects of sulfur cathode. Introducing a catalytic host to promote sulfur redox kinetics is a promising way to inhibit polysulfide shuttling. Previous studies mainly focus on the unidirectional catalysis conversion from S8 to Li2S, and usually ignore the inverse reaction. Herein, defective vanadium nitride (VN1−x) is designed to promote the conversion of sulfur. The catalytic analysis suggests that introducing nitrogen vacancies effectively improves the nucleation and decomposition kinetics of Li2S, and prefers to promote the nucleation process, leading to superior capacity. Benefit from the bidirectional enhanced sulfur redox kinetics, the VN1−x/S composite electrode presents an impressively high capacity of 1417 mAh g−1 at 0.1 C at the first charge/discharge process, which is very close to the theoretical capacity of sulfur cathode (1675 mAh g−1). The Coulombic efficiency of the composite electrode reaches 99.89% even after 1000 cycles, showing reversible redox reactions. The pouch cell using VN1−x/S cathode shows a high initial discharge capacity (1180.3 mAh g−1) and can stably cycle over 100 cycles. This work can support the development of bidirectional catalytic host design for high-loading Li-S batteries.