High-Performance Li-S Batteries with a Minimum Shuttle Effect: Disproportionation of Dissolved Polysulfide to Elemental Sulfur Catalyzed by a Bifunctional Carbon Host

A long cycle-life Li-S battery (boththe coin cell and pouch cell)is reported with minimum shuttle effect. The performance was achievedwith a bifunctional carbon material with three unique features. Thecarbon can catalyze the disproportionation of dissolved long-chainpolysulfide ions to elemental sulfur; the carbon can ensure homogeneousprecipitation of Li sulfide on the host carbon, and the carbon hasa honeycomb porous structure, which can store sulfur better. All thefeatures are demonstrated experimentally and reported in this paper.Few dissolved polysulfides are found by high-performance liquid chromatographyin the electrolyte of the Li-S batteries during cycling, and onlydissolved elemental sulfur is detected. The unique porous structureof the carbon made from raw silk is revealed by scanning electronmicroscopy. The N-containing functionalities that were introducedto carbon from the amino acids of raw silk can catalyze the disproportionationof the dissolved S- n (2-) to solid S-8 at the cathode side, thereby mitigating theshuttle effect. In addition, the hierarchical honeycomb porous structuresgenerated by a carbonization process can physically trap high-orderlithium polysulfides and sustain the volume change of sulfur. Withthe synergistic effects of the unique structures and characteristicsof the carbon prepared at 800 & DEG;C, the sulfur/carbon compositedelivers a high reversible capacity of over 1000 mAh g(-1) after 100 cycles with a sulfur content of 1.2 mg cm(-2) in a pouch cell.