Enhancing Polysulfide Conversion in Lithium-Sulfur Batteries through the Synergistic Effect of 2,6-Dihydroxyanthraquinone and Co Atoms

Currently, lithium-sulfur batteries for wider applications are challenged by both the shuttle effect in the cathodes as well as the slow kinetics of the sulfur redox reactions. Although metal compounds have been reported to suppress the shuttle effect of lithium polysulfides (LiPSs) by chemically adsorbing LiPSs and catalyzing their conversion, current methods for sulfur fixation on cathode materials remain insufficient. In this work, 2,6-dihydroxyanthraquinone (DHAQ) is tightly adsorbed on a Co-doped porous carbon (Co-C) substrate through pi-pi stacking. The abundant oxygen-containing functional groups in DHAQ form Li-O bonds with lithium in the LiPSs and enable in situ covalent fixation. Meanwhile, cobalt in Co-C forms Co-S bonds with sulfur in LiPSs, providing an efficient pathway for electron transfer and promoting LiPS conversion. Thus, the DHAQ/Co-C composite provides dual chemical adsorption capabilities that mitigate the "shuttle effect" of LiPSs. Additionally, the conductive merits of the DHAQ and Co-C networks accelerate electron transfer, enhance LiPS redox kinetics, and increase the battery's specific capacity. In the end, the optimized S@DHAQ/Co-C composite demonstrates an initial discharge capacity (1385 mAh g-1) at 0.1C. After 600 cycles, the electrode displays a capacity decay rate of 0.062% at 1C. Compared with metal-based materials that rely solely on chemical sulfur fixation, the synergistic effect of organic oxygen atoms and metals in sulfur fixation offers significant improvements.