Dual-Functional Multichannel Carbon Framework Embedded with CoS 2 Nanoparticles: Promoting the Phase Transformation for High-Loading Li-S Batteries.

Lithium-sulfur batteries have been considered as one of the most promising energy storage devices due to their high theoretical capacity and low cost. They go through complicated multistep electrochemical reactions from solid (sulfur)-liquid (soluble polysulfide) to liquid (soluble polysulfide)-solid (LiS) during discharge process. Actually, during this process, the transition from liquid phase (LiS) to solid phase (LiS) at 2.1 V plateau is a difficult step with sluggish kinetics, thus leading to low sulfur utilization and discharge capacity. To promote the transition processes and enhance the sulfur utilization, CoS@multichannel carbon nanofiber composites (CoS@MCNFs) serving as sulfur host were successfully synthesized. Herein, CoS catalysts are proven to be beneficial not only for enhancing the phase transition kinetics, but also for adsorbing soluble polysulfide. Besides, unlike other carbon materials, MCNFs have plenty of hollow channels and thus enhance sulfur loading and conductivity. Accordingly, the discharge capacity increases 32% more than that of electrode without CoS. And a very low capacity fade rate of 0.03% per cycle (over 450 cycles) is obtained at 0.5 C rate. This work has opened up new ideas for enhancing sulfur utilization for high sulfur loading electrode.