Investigation of Solid Electrolyte Interphase Regarding Extra Capacity in Fe‐Fe₃C as a Superior Sodium‐Ion Anode Material

Sodium-ion batteries (SIBs) offer promising advantages over lithium-ion batteries (LIBs) due to sodium's abundance and lower cost. However, challenges like thick solid electrolyte interphase (SEI) layers and the larger radius of sodium (1.02 Å vs. 0.76 Å for lithium) make graphite, the most common LIB anode, unsuitable for SIBs. To realize the maximum potential of carbon anode for SIBs, one of the main strategies is to fabricate carbon materials with tailored microstructures and to enhance redox reactivity by incorporating catalytic metals. In this work, the Fe-Fe3C nanoparticles embedded in worm-like graphitic carbon (Fe-Fe3C@GC) were synthesized by a simple chemical vapor deposition. This hybrid structure promotes the catalytic activity to achieve additional capacities through the reversible SEI layer formation, in detail, by the reversible interconversion of ester and ether derivatives as well as conductivity enhancement. Furthermore, in situ formed Fe2O3 from Fe(0) contributed extra capacity. The Fe-Fe3C@GC showed a large reversible discharge capacity of 376.2 mAh g^-1 with a fading rate of 0.013% per cycle after 1000 cycles at a current density of 50 mA g^-1. A full cell coupled with an FeOF cathode delivered a high energy density of 602.8 Wh kg^-1.