Coupling bimetallic selenides with homogeneous mediators synergistically accelerating overall sulfur redox kinetics for high-performances lithium–sulfur batteries

Abstract

The practical applications of lithium-sulfur batteries (LSBs) are hampered by poor electrical conductivity, severe shuttling of intermediate lithium polysulfides (LiPSs) and sluggish redox kinetics. Herein, we introduce a multifunctional catalytic system by integrating bimetallic ZnSe-CoSe2 with CoCp2 mediators, aimed at serving as redox kinetic accelerators in LSBs. In this design, the ZnSe-CoSe2 heterostructure with hierarchical pores and large surface area, is capable of immobilizing both soluble LiPSs and CoCp2 mediators, but also provides abundant active sites for catalyzing LiPSs conversions. Concurrently, the soluble CoCp2 mediators contribute to promoting the high-dimensional growth of Li2S and reducing the interface polarization. Electrochemical experiments and theoretical analyses reveal that the ZnSe-CoSe2/CoCp2 system synergistically accelerates overall sulfur redox kinetics. Consequently, the cell with the ZnSe-CoSe2/CoCp2 system under a sulfur loading of 2.3 mg cm−2 exhibits superior long-term cycling stability at 1.0C. Additionally, it achieves a remarkable areal capacity of 6.5 mAh cm−2 under a high sulfur loading of 8.0 mg cm−2 and a low electrolyte-to-sulfur ratio of 5.0 µL mg−1.