Enhanced Electrochemical Kinetics with Highly Dispersed Conductive and Electrocatalytic Mediators for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are promising energy-storage devices because of their high theoretical energy densities. However, the practical application of Li-S batteries is still impeded by the poor cycling performance and rate capability at practical conditions. In order to improve the performance of practical Li-S batteries, a hierarchical Mo2 C nanocluster/carbon nanosheets hybrid based hollow spherical material (Mo2 C/CHS) is designed and prepared. The hollow spheres composed of stacked carbon nanosheets can facilitate the infiltration of electrolyte. The ultrasmall and highly conductive Mo2 C nanocrystals are confined in the carbon nanosheets and expose more active sites for anchoring and conversion of lithium polysulfides and increase the number of the nuclei for Li2 S2 /Li2 S precipitation. Benefitting from the synergistic effects, Mo2 C/CHS greatly promotes electrochemical kinetics in Li-S batteries with high sulfur loading (5 mg cm-2 ). Even under lean electrolyte conditions (E/S = 7 μL mgsulfur -1 ), the Li-S batteries with Mo2 C/CHS added exhibit a discharge capacity of 904 mAh g-1 at the high current rate of 0.5 C, and with 894 mAh g-1 maintained after 200 cycles. This work provides a fundamental understanding of the electrochemical processes and guides the rational design of host and additive materials for practical Li-S batteries.