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.