Ionic Liquid-Derived N-Doped Carbon/Sulfur Composite Cathodes with Tailored Nanostructure for High-Performance Li/S Batteries

Batteries are one of the key technologies in the field of energy storage and conversion. Among the broad range of available cathode active materials, elemental sulfur has the highest theoretical specific capacity (1675 mAh/g) and thus holds great promise as positive electrode material in rechargeable Li-batteries.^[1] There are, nevertheless, major safety and performance issues that need to be addressed before commercialization of Li/S batteries can be contemplated. Recently, significant progress has been made by incorporating sulfur into nano-structured carbons. Such carbon/sulfur composites seem to be capable of providing a stable cathode performance by somewhat hindering the lithium polysulfides from leaving the architecture (through specific chemical and/or physical interactions).^[2] Furthermore, nanostructured carbons have been shown to have the potential to preserve the electrode integrity by better accomodating the volume changes of sulfur during conversion to lithium sulfide. Here, we report on the use of hierarchically structured N-doped carbon/sulfur composites for long-life and high-performance Li/S batteries.^[3] Highly conductive carbon with tailored porosity was fabricated by silica templating followed by sulfur melt infiltration to produce carbon/sulfur nanocomposites. Cathodes with a sulfur content of 60% and sulfur loadings ranging from 1 to 4 mg/cm² were tested electrochemically both in coin and pouch cells. At a moderate C-rate of C/5, stable specific capacities of approx. 700 mAh/g can be achieved over hundreds of cycles; and cathodes with a sulfur loading of 4 mg/cm² demonstrate areal capacities approaching 3.0 mAh/cm². Literature reports on sulfur cathodes providing similar areal capacities are scarce, especially when the electrolyte-to-sulfur mass ratio is <15:1.^[4] Overall, we show that our ionic liquid-derived carbon/sulfur composite possesses a beneficial microstructure for Li/S battery applications.

[1]      Manthiram, A. Acc. Chem. Res. 2013, 46, 1125–1134.

[2]      Ji, X.; Lee, K.T.; Nazar, L. Nature Materials 2009, 8, 500-506

[3]      Schneider, A.; Weidmann, C.; Suchomski, C.; Sommer, H.; Janek, J.; Brezesinksi T. Chem. Mater. 2015, DOI: 10.1021/cm504460p.

[4]      Song, J.; Wang, D. Adv. Funct. Mater. 2013, 24, 1243–1250.