Functional separator with 1 T/2H-MoSe2 nanosheets decorated nitrogen and sulfur co-doped mesoporous hollow carbon spheres for high-performance Li-S batteries

Due to the dissolution, shuttling, and tardy kinetics conversion of lithium polysulfides (LiPSs) during cycling, there are serious defects in the utilization of active material and capacity retention ability for lithium-sulfur batteries (LSBs). To inhibit effectively the shuttling effect of LiPSs, herein, we propose the dual design strategies, using 1 T/2H mixed phase MoSe2 (1 T/2H-MoSe2) nanosheets uniformly growing on the external surface and inner wall of nitrogen and sulfur co-doped mesoporous hollow carbon spheres (MoSe2-NSHC) as both sulfur host and modified material of conventional polypropylene (PP) separator. The hollow structure of MoSe2-NSHC has a large specific surface area and internal space, which not only loads a large amount of sulfur, but also buffers severe volume expansion of sulfur during charge/discharge process. Meanwhile, 1 T/2H-MoSe2 and co-doped nitrogen and sulfur in the carbon skeleton effectively anchor LiPSs and accelerate the kinetics conversion of LiPSs by forming chemical bond. Density-functional theory calculations indicate the corresponding mechanisms. Based on these advantages, lithium-sulfur battery assembled with a MoSe2-NSHC/S cathode and a MoSe2-NSHC-PP separator delivers an initial discharge capacity of 1402 mAh/g at 0.2C, and also exhibits the first discharge capacity of 1155 mAh/g at 0.5C with a capacity retention rate of 79 % after 100 cycles. And after 800 cycles at 1C, the outstanding long-term cyclability with a low capacity decay per cycle of 0.039 % is also obtained. Notably, even in case of sulfur loading of 3.2 mg cm-2 and electrolyte/sulfur ratio of 6 mu L mg-1, lithium-sulfur battery still exhibits a good electrochemical performance. Importantly, this work provides a feasible approach for commercial application of LSBs.

Automated summary

In this work, the dual design strategies of using 1 T/2H mixed phase MoSe2 nanosheets growing on nitrogen and sulfur co-doped mesoporous hollow carbon spheres (MoSe2-NSHC) are proposed to inhibit the shuttling effect of lithium polysulfides. The hollow structure of MoSe2-NSHC can load a large amount of sulfur and buffer the volume expansion. Additionally, 1 T/2H-MoSe2 and co-doped nitrogen and sulfur in the carbon skeleton can effectively anchor lithium polysulfides and accelerate their conversion. The lithium-sulfur battery assembled with MoSe2-NSHC/S cathode and MoSe2-NSHC-PP separator shows excellent electrochemical performance and long-term cyclability.