Straightforward synthesis of Sulfur/N,S-codoped carbon cathodes for Lithium-Sulfur batteries.

An upgrade of the scalable fabrication of high-performance sulfur-carbon cathodes is essential for the widespread commercialization of this technology. Herein we present a simple, cost-effective and scalable approach for the fabrication of cathodes comprising sulfur and high-surface area, N,S-codoped carbons. The method involves the use of a sulfur salt, i.e. sodium thiosulfate, as activating agent, sulfur precursor and S-dopant, and polypyrrole as carbon precursor and N-dopant. In this way, the production of the porous host and the incorporation of sulfur are combined in the same procedure. The porous hosts thus produced have BET surface areas in excess of 2000 m g, a micro-mesoporous structure, as well as sulfur and nitrogen contents of 5-6 wt% and ~2 wt%, respectively. The elemental sulfur content in the composites can be precisely modulated in the range of 24 to ca. 90 wt% by controlling the amount of sodium thiosulfate used. Remarkably, these porous carbons are able to accommodate up to 80 wt% sulfur exclusively within their porosity. When analyzed in lithium-sulfur batteries, these sulfur-carbon composites show high specific capacities of 1100 mAh g at a low C-rate of 0.1 C and above 500 mAh g at a high rate of 2 C for sulfur contents in the range of 50-80 wt%. Remarkably, the composites with 51-65 wt% S can still provide above 400 mAh g at an ultra-fast rate of 4 C (where a charge and discharge cycle takes only ten minutes). The good rate capability and sulfur utilization was additionally assessed for cathodes with a high sulfur content (65-74%) and a high sulfur loading (>5 mg cm). In addition, cathodes of 4 mg cm successfully cycled for 260 cycles at 0.2 C showed only a low loss of 0.12%/cycle.