A Sulfur-Host design for Adsorption/Catalysis strong synergy on polysulfide conversions via CoB/NCPS composites inheriting the polyhedron morphology of Metal-Organic framework

As a promising option for next-generation energy storage systems, the high specific capacity and energy density of lithium-sulfur (Li-S) battery have attracted significant attention. Actually, high-energy–density lithium-sulfur batteries face challenges due to the "shuttle effect" and slow conversion kinetics of lithium polysulfides (LiPSs), which can be successfully circumvented by multifunctional materials. Here, we report a sulfur cathode based on a new type of cobalt boride (CoB) alloy which is uniformly distributed on the nitrogen-doped carbon polyhedral shell (CoB/NCPS). In our conception, ZIF-67 is partially reduced to form the CoB alloy as catalyst while still retains its original polyhedron morphology as the catalyst supporter, which would be much beneficial to the electrochemical performance of the sulfur cathode through further pyrolysis. As expected, the resultant S@CoB/NCPS cathode enables an initial discharge specific capacity as high as 1022.3 mAh/g at 1C, and can even endure a high rate up to 5C with an initial capacity of 782.7 mAh/g and deliver an ultralow capacity decay rate of 0.06 % per cycle over 1000 cycles. This study not only demonstrates that the CoB/NCPS composites as sulfur host have the extraordinary adsorption performance and excellent electrocatalysis activity in the redox conversion reaction of sulfur/Li2S, but also provides a tractable strategy for the fabrication of metal borides with perfect morphology in lithium-sulfur batteries.