Polypyrrole-coated cobalt sulfide as an effective host for sulfur cathode

Owing to the high theoretical energy density, lithium-sulfur batteries (LSBs) stand out from various batteries. However, the slow electrochemical dynamics, the shuttle of lithium polysulfides (LiPSs), and the uncontrolled growth of lithium dendrites seriously affect the cycling performance of LSBs. In this work, we prepared a polypyrrole-coated cobalt sulfide (CoS@PPy) composite through a hydrothermal method followed by in situ polymerization reaction. The internal CoS exhibits strong chemisorption and catalytic conversion ability toward LiPSs. The external PPy can further inhibit the migration of LiPSs through its rich functional groups, thereby improving the electronic conductivity and alleviating the volume expansion of the sulfur electrodes. Therefore, after S loading, the CoS@PPy/S electrode exhibits superior cycling stability, and after 500 cycles at 1 C, its capacity decay is only 0.092% and the satisfactory coulombic efficiency is above 98%. Moreover, the CoS@PPy/S electrode delivers a high reversible capacity of 605 mA h g-1 at 3 C. The present work provides a feasible solution for the synthesis of polymer-metal compound composites and offers a new idea for the construction of efficient sulfur-hosting materials for LSBs. The CoS@PPy not only shows excellent chemisorption toward lithium polysulfides, but also can accelerate their conversion.