Biomimetic Molecule Catalysts to Promote the Conversion of Polysulfides for Advanced Lithium-Sulfur Batteries

To overcome the shuttle effect in Li-S batteries, novel biomimetic molecule catalysts are synthesized by grafting hemin molecules to three functionalized carbon nanotube systems (CNTs-COOH, CNTs-OH, and CNTs-NH2). The Li-S battery using the CNTs-COOH@hemin cathode exhibits the optimal initial specific capacity (1637.8 mAh g(-1)) and cycle durability (up to 1800 cycles). Various in situ characterization techniques, such as Raman spectroscopy, Fourier-transform infrared reflection absorption spectroscopy, and UV-vis spectroscopy, combined with density functional theory computations are used to investigate the structure-reactivity correlation and the working mechanism in the Li-S system. It is demonstrated that the unique structure of the CNTs-COOH@hemin composite with good conductivity and adequate active sites resulting from molecule catalyst as well as the strong absorption to polysulfides entrapped by the coordinated Fe(III) complex with Fe-O bond enables the homogeneous dispersion of S, facilitates the catalysis and conversion of polysulfides, and improves the battery's performance.