An amorphous carbon-coated α-Fe2O3/expanded natural graphite (ENG) composite as an anode active material for lithiumion batteries was successfully synthesized by a simple hydrothermal method. The ENG anode material used as a matrix showed better cycling performance but a larger irreversible capacity than pristine NG anode material due to the large amount of solid electrolyte interface film. The reversible capacity of the ENG anode material increased by approximately 26% through impregnation of α-Fe2O3 nanoparticles. Nevertheless, the capacity retention significantly decreased from 98.9 to 74.9% after 63 cycles due to volume expansion and microstructural change caused by aggregation of Fe and Li2O during the chargedischarge process. This degradation of cycling performance was overcome by the surface coating of amorphous carbons. The reversible capacity of an amorphous carbon-coated α-Fe2O3/ENG composite increased with cycling and reached 576 mAh/g at the 95th cycle and 524 mAh/g at the 350th cycle, showing 99% capacity retention. The favorable cycling performance was attributed to suppression of nanoparticle aggregation, a fast charge transfer, and lowering of the contact resistance by the conductive amorphous carbon coating.

Keywords: Lithium ion batteries, Natural graphite, Fe2O3, Expanded graphite, Anode active materials