Mixed valence Mo2C-MoC/C catalyst enhances polysulfides conversion kinetics in lithium–sulfur batteries

Abstract

Lithium-sulfur batteries have received extensive attention in the field of electrochemical energy storage systems due to their extremely high theoretical energy density (2600 Wh·kg−1) and low cost. However, poor electrical conductivity, shuttle effect, and volume expansion effect still need to be addressed. Here, we controllably synthesized hollow spherical Mo2C-MoC/C structure as the cathode material for lithium-sulfur batteries. Through high-temperature calcination, the synthesis of graphitized reticular carbon matrix and the loading of Mo2C and MoC nanoparticles with mixed valence of Mo2+ and Mo3+ were simultaneously achieved. The two synergistically improved the electronic conductivity and ensured excellent battery performance. From the experimental results, Mo2C-MoC/C structure strongly adsorbed polysulfides and promoted the conversion of polysulfides to lithium sulfide, accelerating the reaction kinetics and enhancing the battery performance. The initial discharge specific capacity of Mo2C-MoC/C electrode with 57.12 wt% sulfur content was 870.4 mAh·g−1 at 0.2 C, and remained at 770.7 mAh·g−1 at 0.5 C, which was significantly better than that of Mo2C/C/S. The rational design of the Mo2C-MoC/C structure in this study can be generalized to the advanced electrode materials of other Mo-based nanomaterials.