Fe2O3 nanoparticles encapsulated with N-doped porous graphitic shells approached by oxidizing Fe3C@C precursor for high-performance sodium-ion batteries

Fe2O3 nanoparticles encapsulated with N-doped porous graphitic shells (Fe2O3@PWSs) were successfully prepared through a facile approach as anodes for SIBs. In such approach, owing to the short synthetic time, ∼7 nm precursor (Fe3C@N-doped graphitic shells core-shell nanoparticles) were prepared by floating catalytic pyrolysis, leading to in situ doped N atoms were well distributed. By partially removing homogeneous N-doped structure, lots of nanopores were created on the shell of the precursor, which made Fe3C cores efficiently oxidized without violently destroying graphitic shells. The excellent structural characteristics of Fe2O3@PWSs could effectively prevent pulverization/agglomeration of Fe2O3 and accommodate its volume changes during long-term cycling processes, exhibiting distinct cycling stability (at current density of 5000 mA g−1, 3000 cycles: a fading rate of only 0.007% per cycle for SIBs). Additionally, small size of Fe2O3 nanoparticles (average size of 5 nm) and higher porosity of carbon shells could offer more diffusion pathway which facilitate the transportation of Na+/Li+ and electrolyte leading to significantly improved electrochemical activity toward Na+/Li+ storage (the specific capacity: 637 and 525 mAh g−1 at current density of 100 and 3000 mA g−1, respectively, for SIBs; the specific capacity: 1506 and 1310 mAh g−1 at current density of 200 and 3000 mA g−1, respectively, for LIBs).