Hierarchical iron sulfide-graphene nanocubes consisting of multiple nanoparticles with superior sodium ion storage properties

Hierarchical iron sulfide nanocubes consisting of multiple iron sulfide-carbon core-shell nanoparticles coated with few-layer graphene (Fe1-xS@C/rGO) were prepared by a two-step in-situ transformation strategy employing Prussian blue (PB) as a starting material. The hierarchical nanocubes delivered an outstanding rate capability of 323 mAh g−1 at the current density of 10 A g−1 when used as the anode of sodium ion half cells. An iron-based sodium-ion full cell composed of a hierarchical Fe1-xS@C/rGO anode and PB cathode had a capacity of 323 mAh g−1 for 150 cycles. We attributed the good sodium ion storage properties of the Fe1-xS@C/rGO nanocubes to the stable hierarchical building structures and the high graphitization degree of carbon obtained during the transformation process. The graphene-coated nanocube structures inhibited the agglomeration of iron sulfide-carbon core-shell nanoparticles and accommodated the huge volume expansion that occurred during cycling. The high graphitization degree of carbon endowed Fe1-xS@C/rGO nanocubes with high electronic conductivity, facilitated sodium ion accessibility, and increased mechanical durability.