Cobalt Nanoparticles Embedded in Nitrogen-doped Carbon Nanofibers to Enhance Redox Kinetics for Long-Cycling Sodium-Sulfur Batteries

The shuttle effect resulting from severe volume expansion and polysulfide dissolution imposes limitations to the application of sodium-sulfur (Na-S) batteries. Herein, a three-dimensional self-supported electrode comprised of cobalt nanoparticles embedded in nitrogen-doped carbon nanofibers (CoNCNF) is constructed to accommodate sulfur as cathode for Na-S batteries. The carbon fiber framework facilitates direct electrons transmission and reduces overall contact impedance of electrode. The abundant pore structure not only promotes electrolyte infiltration but also ensures high loading of sulfur, and provides space for volume expansion during charging and discharging. Most significantly, CoNCNF carrier accelerate the conversion rate of sodium polysulfides (NaPSs) into NaS and guide NaS deposition on its surface in a three-dimensional progressive nucleation (3DP) mode, resulting in a high NaS deposition capacity and outstanding long-term cycling performance. When coupled with a Na metal anode, the CoNCNF/S composite cathode exhibits stable electrochemical properties with a capacity up to 1030.2 mA h g after 300 cycles at 0.2C and excellent rate performance.