NiCo alloy-decorated nitrogen-doped carbon double-shelled hollow polyhedrons with abundant catalytic active sites to accelerate lithium polysulfides conversion.

Lithium-sulfur (Li-S) batteries have received significant attention due to their high theoretical energy density. However, the inherent poor conductivity of S and lithium sulfide (LiS), coupled with the detrimental shuttle effect induced by lithium polysulfides (LiPSs), impedes their commercialization. In this study, we develop NiCo alloy-decorated nitrogen-doped carbon double-shelled hollow polyhedrons (NC/NiCo DSHPs) as highly efficient catalysts for Li-S batteries. The distribution of NiCo alloy on both the inner and outer shells provides abundant catalytic active sites, effectively adsorbing LiPSs, mitigating the shuttle effect, and promoting the conversion between LiPSs and LiS, even at high sulfur loadings. This results in enhanced redox kinetics within the Li-S system. Moreover, the highly conductive carbon material framework, enriched with carbon nanotubes and graphitic carbon layers, can greatly promote the efficient electron transportation. Additionally, the improved ion diffusion rates benefiting from the hollow structure can also be realized. By harnessing these synergistic effects, Li-S batteries incorporating the double-shelled NC/NiCo DSHP catalysts achieved a high specific capacity of 1310 mAh/g at 0.2C and a superior rate performance of 621 mAh/g at 4C. Furthermore, excellent cycling performance with ultralow capacity fading rate of only 0.045 % per cycle after 800 cycles at 1C was achieved. When sulfur loading reaches 6 mg cm, a high capacity of 4.6 mAh cm at 0.1C after 100 cycles further validates the practical potential of this design. This study presents an innovative approach to alloy catalyst design, offering valuable insights for future research of Li-S batteries.