Three-Dimensional Porous Nitrogen-Doped Carbon Nanosheet with Embedded Ni_xCo_{3- x}S₄ Nanocrystals for Advanced Lithium-Sulfur Batteries

The shuttle effect of lithium polysulfides (Li₂S_n) in electrolyte and the low conductivity of sulfur are the two key hindrances of lithium sulfur (Li-S) batteries. In order to address the two issues, we propose a three-dimensional porous nitrogen-doped carbon nanosheet with embedded Ni_xCo_3-xS₄ nanocrystals derived from metal-organic frameworks for the durable-cathode host material in Li-S batteries. Experiments and density functional theory simulations show that the large porosity, robust N-doped carbon framework, and evenly embedded Ni_xCo_3-xS₄ nanocrystals with high polarity act as strong "traps" for the immobilization of Li₂S_n, which leads to an effective suppressing of the shuttle effect and promotes efficient utilization of sulfur. The Ni_xCo_3-xS₄/N-doped carbon hybrid material exhibits a high reversible capacity of 1122 mAh g^-1 at a current density of 0.5 C after 100 cycles. Even at high areal sulfur loadings of 10 and 12 mg cm^-2, the hybrid cathode materials can maintain good areal capacities of 7.2 and 7.6 mAh cm^-2 after 100 cycles. The present study sheds light on the principles of the anchoring behaviors of Li₂S_n species on bimetallic sulfide hybrid materials and reveals an attractive route to design the highly desirable cathode materials for Li-S batteries.