Fe1-xS@S-Doped Carbon Core-Shell heterostructured Hollow Spheres as Highly Reversible Anode Materials for Sodium Ion Batteries

Iron sulfide (Fe1-xS) has been considered as a promising anode material for sodium ion batteries (SIBs) because of its high theoretical capacity. However, Fe1-xS suffers from large volume change and sulfur dissolution issues during sodiation/desodiation process, which lead to a poor cycle performance. Here, heterostructured Fe1-xS@S-doped carbon (Fe1-xS@SC) hollow spheres (HSs) have been prepared as SIB anode material. The Fe1-xS@SC HSs show a high reversible capacity of 776.2 mAh g-1 at 0.2 A g-1 and 454.3 mAh g-1 at 1.0 A g-1 after 500 cycles. The constructed Fe1-xS/SC heterojunctions play a key role in alleviating the large volume variation and stabilizing the reaction products Fe0 and Na2S, thus enhancing the conversion reaction kinetics of Fe0 and Na2S and ultimately resulting in a highly reversible conversion reaction. This work provide a possibility to solve the reversibility issue of conversion-type anode materials.