Manipulating polysulfide catalytic conversion through edge site construction, hybrid phase engineering, and Se anion substitution for kinetics-enhanced lithium-sulfur battery

Abstract

Applying catalytic materials in Li-S batteries can effectively enhance the lithium polysulfides (LiPSs) conversion kinetics and suppress the severe LiPSs shuttle effect. However, optimizing the catalytic activity of catalysts through synchronous geometrical/electronic structure design remains challenging. Here, we demonstrate that the highly stable MoSSe@graphene (MoSSe@rGO) electrocatalyst, with vertically aligned geometry configuration, 1T/2H hybrid phase engineering, and Se anion substitution, can effectively trap and catalyze the LiPSs conversion. The vertically grown MoSSe nanosheets on rGO expose abundant active edge sites and ensure that every MoSSe nanosheet participates in chemical adsorption and catalytic reaction. The 1T/2H hybrid phase possesses high electronic conductivity, enabling direct and fast adsorption/catalyzing of LiPSs. Moreover, the Se anion substitution in 1T/2H-MoS2 enhances the Li+ diffusion kinetics and accelerates the LiPSs redox reaction. Due to the synergy of geometrical (edge sites) and electronic (1T/2H phase and Se substitution) engineering, the 1T/2H-MoSSe@rGO affords strong chemical adsorption and enhanced bidirectional catalytic activity toward LiPSs, endowing the Li-S batteries with ultra-small voltage hysteresis (125 mV at 0.2 C), ultrahigh rate capability (747.2 mAh g−1 at 3 C), and long cycle life over 500 cycles. Further, theoretical simulation and ex-situ measurements verify the catalysis mechanism of 1T/2H-MoSSe@rGO and demonstrate its ultra-stable operation upon cycling. This work provides a geometrical/electronic multi-construction strategy to design superior Li-S catalysts.