High capacity and cycling stability of sulfur cathode built of zeolite-templated 3D graphene-like ordered microporous carbon possessing secondary mesopores

Abstract

Two main issues regarding lithium-sulfur batteries (LSBs) are the insulating nature of sulfur and the dissolution of lithium polysulfides into the electrolyte. These problems cause poor sulfur utilization and serious capacity fading in LSBs, especially at high current densities [1]. Herein, we approached these problems by confining the sulfur inside a zeolite-templated ordered microporous carbon, which was synthesized using a nanocrystalline beta zeolite as a template (Fig. 1) [2,3]. The microporous carbon framework was built with single-walled graphene-like sp2 carbon atoms, reminiscent of a carbon Schwarzite. This carbon possessed secondary mesopores between the nanocrystal-like microporous domains. Sulfur was melt infiltrated into the carbon micropores using capillary forces, but not into the mesopores. The sulfur in the extremely narrow pore environment (diameter = 0.9 nm) could react with Li+ ions under solvent-deficient conditions, suppressing the problematic polysulfide dissolution. The lithium-sulfur reactions occurred efficiently even under fast discharge conditions. This is interpreted as a result of rapid diffusion of Li+ ions into the narrow micropores via wide mesopores. Thus, the sulfur/hierarchical carbon hybrid cathode exhibited high capacity and excellent cycling stability at a wide range of current densities, demonstrating its potential use in future LSBs.