Controllable synthesis and coating-thickness-dependent electrochemical properties of mesoporous carbon-coated α-Fe2O3 nanoparticles for lithium-ion batteries

Abstract Mesoporous carbon-coated iron oxide (α-Fe2O3@C) nanoparticles were hydrothermally synthesized by using α-Fe2O3 nanospheres (ca. 50 nm) as the cores and resorcinol as the carbon source of the shells. The formation of the mesoporous carbon coatings was confirmed by means of SEM, TEM, FT-IR, TG, XPS and BET measurements. Moreover, the coating thickness was easily adjusted to be 4, 7 and 10 nm by changing the amount of resorcinol. When used as the anodes for lithium-ion batteries (LIBs), the α-Fe2O3@C nanoparticles exhibited significantly improved electrochemical properties as compared to pure α-Fe2O3 nanoparticles. With the increase of the coating thickness, the α-Fe2O3@C electrodes presented an initial increase and subsequent decrease in their cycling stability and rate performance. Especially, the α-Fe2O3@C-7 nanoparticles displayed a high reversible capacity of 1223 mA h/g at 1 A/g, a good cycling stability retaining 1093 mA h/g at 1 A/g after 100 cycles as well as a remarkable rate performance of 570 mA h/g at 5 A/g. The quantitative kinetic analysis revealed that 58% of the charge storage was contributed by the capacitive process at 0.5 mV/s. The well-defined core-shell structure and superior electrochemical performance of the α-Fe2O3@C-7 nanoparticles will make them a promising anode for LIBs.