Internment of polysulfide in fractal carbon structure for high rate lithium-sulfur batteries

Highlights: • Fractal like interconnected candle soot coated over glass fiber is used as an interlayer. • Activated candle soot is used to host sulfur for carbon–sulfur composite cathode. • Excellent reversible capacities of 865 and 485 mAh g⁻¹ are attained at 2C and 7C rate. • Cell shows ~96% coulombic efficiency for a high sulfur loading of 4.2 mg cm⁻². The development of Lithium-Sulfur (Li-S) batteries was hindered due to the insulating nature of sulfur and the high shuttling of Li-polysulfide in electrolytes. To address these stumbling blocks, we introduced a highly dense fractal-like candle soot (CS) carbon cloud on the three-dimensional (3D) glass fiber paper as an interlayer that adsorbs and provides sufficient sites for Li-polysulfide accommodation. The interlayer also retains the electrolyte with soluble Li-polysulfides and converts them into insoluble lower-order polysulfide (Li₂S and Li₂S₂) without losing the electrical contact. Li-S cell is fabricated with activated candle soot (ACS) and sulfur (S) composite (ACS-S) as an electrode material. The candle soot-glass fiber interlayer (CS_IL) attained a high initial discharge capacity of 1139 mAh g⁻¹ at a 0.5C rate and displayed excellent cyclic stability with reversible capacity of 865 mAh g⁻¹ at the current rate of 2C for 100 cycles with coulombic efficiency of 95%. Further, the same cell was tested at a high charge/discharge rate of 7C, and exhibit excellent reversible capacity of 485 mAh g⁻¹ with a long life of 400 cycle and high coulombic efficiency of 95%. The overall improvement of Li-S battery also evident with impedance analysis, H-cell adsorption testing, and shuttle factor calculations.