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

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 mg_sulfur ^-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.