In situ approach of cementite nanoparticles encapsulated with nitrogen-doped graphitic shells as anode nanomaterials for Li-ion and Na-ion batteries.

Novel Fe3C nanoparticles encapsulated with nitrogen-doped graphitic shells were synthesized by floating catalytic pyrolysis. Due to the short synthesis time and controllable pyrolytic temperature, the diameters of Fe3C core nanoparticles ranged from 5 to 15 nm (Fe3C@NGS900 prepared at 900 °C) and the average thickness of N-doped graphitic shells was ∼1.2 nm, leading to their high electrochemical performance: specific capacity of 1300 mA h g-1 at current density 0.2 A g-1, outstanding rate capability of 939 mA h g-1 at 3 A g-1, improved initial coulombic efficiency (Fe3C@NGS900: 72.1% vs. NGS900 (pure graphitic shells): 52%) for lithium ion batteries (LIBs), and impressive long-term cycle performance (1399 mA h g-1 maintained at 3 A g-1 after 500 cycles for LIBs; 214 mA h g-1 maintained at 1 A g-1 after 500 cycles for sodium ion batteries).