Synergistic capture and conversion of polysulfides in cathode composites with multidimensional framework structures.

ABSTRACT

The application of lithium-sulfur batteries are seriously hindered by their poor cycle stability and low sulfur utilization due to their inevitable polysulfide shuttle effect and slow reaction kinetics. Here, Mo2C nanorods that were surface-decorated with metallic-organic framework-derived nitrogen-doped carbon and ultrasmall cobalt nanoparticles (NC-Co@Mo2C) were used as the materials for lithium-sulfur battery cathodes. The prepared NC-Co@Mo2C@S composites had the specific capacity of 1073 mAh·g-1 (0.2 C) and the retained 806 mAh·g-1 after 200 cycles, thus showing excellent discharge specific capacity and cycling stability. The Mo2C nanorods can adsorb lithium polysulfides (LiPSs) through the formation of MoS bonds. Cobalt nanoparticles electrocatalytically accelerated the redox kinetic conversion of LiPSs. Nitrogen doping can effectively reduce the energy potential barrier. The interconnected multidimensional backbone of NC-Co@Mo2C composites contributed to electrolyte permeation, fast electron/Li+ transport, and sufficient volume change buffering. Therefore, the synergistic effect of the adsorption ability of Mo2C nanorods and the catalytic ability of cobalt nanoparticles can effectively improve the sulfur fixation ability of the composites and greatly suppress the shuttle effect.