Influences of chemical reactions on polysulfide reduction reaction process on promotor surface in Li-S batteries

Polar promotors have been proven effective in catalyzing the polysulfide (PS) reduction reaction (PSRR) process in lithium-sulfur (Li-S) batteries. However, the promotor surface tends to be poisoned due to the accumulation of insoluble discharging products of lithium disulfide (Li₂S₂) and lithium sulfide (Li₂S) during Li-S battery operation. Herein, we investigate the detailed PSRR mechanism on the surface of manganese sulfides (MnS) as a representative promoter by performing in-situ Raman mapping measurements. The catalytic ability of MnS enables thorough electrochemical reduction of PSs to Li₂S₂ and Li₂S on the MnS surface. The generated Li₂S₂ and Li₂S then adsorb the dissolved PSs via chemical reactions among sulfur species during the subsequent PSRR process. This phenomenon mitigates promotor poisoning and continuously improves the reversible capacity. Consequently, the assembled Li-S cell demonstrates excellent electrochemical performance after introducing a conductive interlayer containing a thin piece of carbon nanotube film and MnS promotors.