High capacity micro-mesoporous carbon-sulfur nanocomposite cathodes with enhanced cycling stability prepared by a solvent-free procedure

The use of elemental sulfur as a cathode active material is challenging. Besides the complex electrochemical conversion mechanism there are negative side effects added to the system by application of solvent-based cathode preparation, such as chemical incompatibility caused by solvent contamination, sulfur evaporation and morphology change during drying as well as limited active material loading. Therefore we present a solvent-free, highly versatile pressing/thermal treatment method for the fast and reproducible production of mechanically stable and highly flexible freestanding carbon-sulfur composite cathode foils with tunable sulfur loading, high in-plane conductivity and enhanced cycling stability. Utilizing an optimized cathode composition consisting of sulfur, a porous carbon host material and a carbon nanotube conducting agent, a stable capacity >740 mA h g(-1)-S as well as high coulombic efficiency >96% was achieved over 160 cycles in our experiments at a moderate rate of C/10. Moreover, reversible cycling was possible up to a high rate of 1C due to the tuned carbon matrix properties as well as the highly conductive carbon nanotube percolation network. Thus not only a long-lasting electrical contact to insulating sulfur precipitates is provided but also the agglomeration of active material is restrained. To achieve even higher energy densities and improved corrosion resistance, the application of highly conductive freestanding cathode foils without a metallic current collector is a promising feature.