A simple and general approach for: In situ synthesis of sulfur-porous carbon composites for lithium-sulfur batteries

Abstract

Porous carbon materials constitute an excellent conductive matrix for the immobilization of sulfur in the cathode of lithium-sulfur batteries. Herein, we provide a novel, easy, sustainable, general and scalable procedure for the preparation of such cathodes, which combines in the same process both the generation of a S-doped porous carbon and the incorporation of elemental sulfur within the pores. To achieve this, a biomass-based substance (i.e., tannic acid) is activated with sodium thiosulfate, yielding a carbonized solid that includes a high-surface area carbon (up to 2550 m2 g-1) and sodium polysulfides. Once this solid is immersed in an acid medium, the polysulfides generated as activation by-products are oxidized in situ to elemental sulfur that spontaneously diffuses into the pores of the carbon, which gives rise to the hybrid sulfur-carbon composite. When tested as cathodes in lithium-sulfur batteries, these hybrid materials exhibit high sulfur utilization (∼80%) even for the composites with a sulfur content as high as 82%, as well as an excellent rate performance (590 mA h g-1 S at 5C). The cycling stability of the batteries was confirmed by their low capacity fading (0.049% of capacity decay per cycle), maintaining 85% of their initial capacity after 300 charge-discharge cycles at 1C. Cathodes with a high sulfur loading (7.1 mg S per cm2) were steady cycled providing reversible areal capacities of 4.4 mA h cm-2 at 0.2C after 100 charge-discharge cycles.