Immobilization and kinetic promotion of polysulfides by molybdenum carbide in lithium-sulfur batteries

The shuttle effect of lithium polysulfides (LiPSs) intermediates is mainly responsible for the poor cycling stability of lithium sulfur (Li-S) batteries. Accelerating the reaction kinetics of the LiPSs conversion is proved to be effective in suppressing the migration of LiPSs. Herein, we propose an effective KB/Mo2C-modified separator for enabling stable Li-S batteries. The Mo2C shows both favorable anchoring capability and catalysis activity for LiPSs conversion due to its strong chemical affinity with LiPSs. The reaction kinetics of LiPSs reduction are facilitated on the Mo2C surface, and the activation potential of lithium sulfide (Li2S) oxidation is reduced. The battery using the modified separator shows high active material utilization and long-term cycling stability with a low decay rate of 0.076% per cycle up to 600 cycles at 1C. Moreover, when the sulfur loading increases to 6.5 mg cm−2, a high areal capacity of 5.2 mAh cm−2 can be maintained after 60 cycles with a capacity retention of 87%, demonstrating the feasibility for practical applications in Li-S batteries.