CO₂-Derived Synthesis of Hierarchical Porous Carbon Cathode and Free-Standing N-Rich Carbon Interlayer Applied for Lithium–Sulfur Batteries

The combination of a porous carbon cathode and an interlayer having strong interactions with polysulfides is a very promising strategy for advanced lithium–sulfur batteries. This work prepares a hierarchical porous carbon through CO2 conversion using a reduction agent of NaBH4 with a CaCO3 nanotemplate. A free-standing carbon sheet is also synthesized by the CO2 treatment by adding NaBH4 to the conventional electrospinning process, which leads to significant porosity with a high nitrogen content of 15.5 atom % in the carbon paper and 30% reduced weight due to its meso-porosity, compared to typical electrospun fibers. This modified method induces lower density and higher active sites, different from the typical process involving further treatment and a mass increase to generate additional active sites to existing carbon surfaces. The hierarchical carbon is used as a cathode of the lithium–sulfur battery to provide high sulfur content and facile transport of the lithium ions. The resultant carbon paper for the interlayer suppresses the polysulfide shuttle and accelerates the kinetics of redox reactions. As a result, the cells assembled with them have a capacity of 707 mAh g–1 after 500 cycles at 0.5 C. In addition, it can maintain a capacity of 697 mAh g–1, even at a high current density of 7.0 C.