Sulfur film sandwiched between few-layered MoS2 electrocatalysts and conductive reduced graphene oxide as a robust cathode for advanced lithium-sulfur batteries

摘要

Improving the capacity retention and reaction kinetics of sulfur cathodes is critical to realizing high-performance lithium-sulfur (Li-S) batteries. In this contribution, few-layered MoS2 nanosheets as electrocatalysts are introduced into the Li-S system by developing a novel sandwich-type MoS2/sulfur/reduced graphene oxide (MoS2/S/rGO) composite cathode. The sandwiched sulfur film has a synergistic coupling effect with both the MoS2 electrocatalyst layer and the conductive rGO substrate, enabling a robust hybrid structure with strong interfacial interactions for physical entrapment of intermediate lithium polysulfides (LiPSs) during cycling. More importantly, the MoS2 electrocatalysts are bifunctional in regulating sulfur reaction chemistry, and could chemically immobilize LiPSs via Li-S bonds and also kinetically accelerate sulfur redox reactions, especially for the mutual conversions between soluble LiPSs and solid Li2S2/Li2S. These merits with regard to structure and chemistry enable the MoS2/S/rGO cathode with superior rate capability (reversible capacities of 657 and 553 mA h g(-1) at high rates of 7 and 10C, respectively), and long-term cycling stability (a slow capacity decay of 0.037% per cycle at 2C over 1000 cycles). This work provides a new pathway to establish a multifaceted cathode structure by rationally integrating the concepts of physical confinement, chemical adsorption and electrocatalysis for advanced Li-S batteries.