Recovery from self-assembly: a composite material for lithium-sulfur batteries

Abstract

A highly ordered mesoporous carbon, AlCMK, with an assembly of carbon rods and a bimodal pore system is used for sulfur encapsulation, and the AlCMK/S composite is observed to be able to accommodate volume expansion during a discharge process and recover its original structure when recharged. It is proved that the assembly structure of AlCMK makes it "breath" during the redox reaction of lithium and sulfur. Such a novel ability greatly benefits the maintenance of electrode construction during a repeated discharge-charge process. Moreover, a long heating time (e. g. 20 h) at 300 degrees C in a two-step melt diffusion method is found to contribute to the uniform dispersion of sulfur in the AlCMK carbon matrix. Using this featured composite, a Li-S cell retains 627 mA h g(-1) after 450 cycles at 0.1 C-rate with a coulombic efficiency close to 100% and also shows good rate capability up to 5 C-rate, demonstrating a significant improvement of reversible capacity and cycle stability of Li-S cells.