Mesopore channel length control in ordered mesoporous carbon hosts for high performance lithium-sulfur batteries

Ordered mesoporous carbons (OMCs) with different mesopore channel length, prepared by using corresponding size-tuned ordered mesoporous silicas as templates, are explored as hosts for sulfur (S) in cathode to investigate the effect of the mesopore length on Li-S battery (LSB) performance. The well-developed mesopores in the OMCs provide an excellent ion transport path, enhancing mass transport capability and thus demonstrating better cycling performance and rate capability. Particularly, platelet OMC (pOMC) with thin hexagonal prism shape and short mesopore length demonstrates the high reversible discharge capacity of 1419 mAh g⁻1 at a current density of 168 mA g⁻¹ and excellent cyclability. Based on the specific capacity, cycle efficiency, and rate capability, the pOMC-S outperforms considerably its mesoporous carbon peers, rod-like OMC-S (rOMC-S) and spherical OMC-S (sOMC-S) with longer mesopore length. This superb behavior is attributed to better and more utilization of short mesopore channels for active sulfur species, which induce higher sulfur utilization, and are also supported by low electrochemical resistances in electrochemical impedance spectroscopy. The improved cell performance can be understood in terms of utilization efficiency of the mesopore channels for sulfur loading and polysulfide dissolution, which improves with decreasing channel length.