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 electrochem. conversion mechanism there are neg. side effects added to the system by application of solvent-based cathode prepn., such as chem. incompatibility caused by solvent contamination, sulfur evapn. and morphol. 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 prodn. of mech. stable and highly flexible freestanding carbon-sulfur composite cathode foils with tunable sulfur loading, high in-plane cond. and enhanced cycling stability. Utilizing an optimized cathode compn. consisting of sulfur, a porous carbon host material and a carbon nanotube conducting age nt, a stable capacity >740 mA h g-1-S as well as high coulombic efficiency >96% was achieved over 160 cycles in our expts. 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 elec. contact to insulating sulfur ppts. 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.