Sulfur encapsulation into yolk-shell Fe2N@nitrogen doped carbon for ambient-temperature sodium-sulfur battery cathode

Room temperature sodium-sulfur (RT-Na-S) battery represents an advanced energy storage technology because of low cost and large theoretical energy density. However, RT-Na-S battery technology is facing severe challenges such as dissolution of sodium polysulfide, loss of active material on the surface of anode, serious shuttle effect and poor cycle stability. Herein, we synthesis hollow polar iron nitride nanoparticle encased N-doped carbon yolk shell (YS-Fe₂N@NC) as sulfur carrier. The synergistic effect of YS-Fe₂N@NC as well as wide void can be effectively trap polysulfides and improve the conductivity of sulfur-based cathode. The reversible reaction mechanism of Na-S battery is studied by in/ex-situ characterizations, catalytic behaviour of YS-Fe₂N@NC and Density functional theory (DFT) calculations. The as made S/YS-Fe₂N@NC composite exhibit promising specific capacity of 1123 mAh g⁻¹ at the rate of 1C for the initial cycle, good rate capability (845 mAh g⁻¹ at 2C) and ultra-stable cycling performance with an ultra-low capacity decay of 0.0724% per cycle. The present work highlights the importance of introducing the Fe₂N to catalyse the conversion reactions of polysulfide within NC shell for boosting the RT-Na-S battery in term of high storage capacity, rate capability and stability.