Decorating CoSe2 on N-doped carbon nanotubes as catalysts and efficient polysulfides traps for Li-S batteries

Lithium-sulfur batteries (LSBs) have attracted wide attention as one of the most potential secondary batteries in the next generation. However, the low sulfur utilization, serious "shuttle effect", and large volume expansion of the sulfur cathode restrict the performance of LSBs. Here, CoSe2 decorated hollow N-doped carbon nanotubes (CoSe2/hNCTs) were synthesized firstly, and then the CoSe2/hNCTs were used as a sulfur host to prepare a multifunctional CoSe2/hNCTs/S cathode. DFT calculations confirm that the CoSe2 not only efficiently adsorbs lithium polysulfides (LiPSs), but also exhibits good catalytic performance for the conversion of LiPSs. SEM and TEM images indicate that the CoSe2 uniformly disperses on the surface of the polypyrrole nanotube-derived hNCTs, like plum blossoms. The hNCTs with a morphology of plum blossom branches provide a high conductive network and prohibit large volume expansion during the electrochemical process. And the plum petal-like CoSe2 on the hNCTs surface acts as a catalyst and an efficient polysulfides trap. The CoSe2/hNCTs/S cathode delivers a satisfactory lithium storage performance, which presents reversible capacities of 1156 and 640 mA h g-1 at 0.5 and 5C, respectively. Simultaneously, the cathode demonstrates excellent cycle stability with a slow capacity decay rate of 0.069% per cycle in 1000 cycles at 1C rate. This work provides a new idea for constructing composites of transition metal selenides and carbon materials, promoting the practical applications of LSBs.