Abundant adsorption and catalytic sites of the CoS2/MoS2 heterostructure for enhanced reversible kinetics in polysulfide conversion

Abstract

The practical application of lithium-sulfur (Li-S) batteries is hindered by the sluggish redox kinetics of sulfur, significant volume expansion, and the shuttle effect of lithium polysulfides (LiPSs). To address these challenges, this study utilizes hollow carbon spheres (HCS) as a matrix, incorporating a heterojunction of transition metal sulfides (CoS₂/MoS₂) as the sulfur host. The HCS, with their ultrahigh specific surface area, effectively mitigate structural damage to the cathode caused by sulfur’s volume expansion during charge and discharge cycles. Meanwhile, the CoS₂/MoS₂ heterojunction provides abundant chemical adsorption and reaction sites, which accelerate the redox kinetics of sulfur and alleviating the shuttle effect of LiPSs. Density functional theory (DFT) calculations reveal that the coupling effect at the CoS₂/MoS₂ heterointerface significantly enhances charge transfer and adsorption interactions between CoS₂/MoS₂ and LiPSs. Experimental results demonstrate that Li-S batteries with S/CoS₂/MoS₂@HCS composites as the cathode exhibit an exceptionally low capacity decay rate of only 0.023% per cycle after 1200 cycles at 2.0 C. Even with high sulfur loading (7.9 mg cm⁻²) and a low electrolyte-to-sulfur (E/S) ratio (6.0 μL mg⁻¹), the battery achieves an outstanding areal capacity of 6.86 mA h cm⁻². This study develops a highly efficient CoS₂/MoS₂ heterojunction within HCS for the adsorption and conversion of LiPSs, providing valuable insights into the design of high-performance cathode materials for Li-S batteries.