α-Fe₂O₃ nanoflakes as an anode material for Li-ion batteries

Abstract

Nanoflakes of α-Fe₂O₃ were prepared on Cu foil by using a thermal treatment method. The nanoflakes were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The reversible Li-cycling properties of the α-Fe₂O₃ nanoflakes have been evaluated by cyclic voltammery, galvanostatic discharge-charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature. Results show that Fe₂O₃ nanoflakes exhibit a stable capacity of (680±20) mA h g⁻¹, corresponding to (4.05±0.05) moles of Li per mole of Fe₂O₃ with no noticeable capacity fading up to 80 cycles when cycled in the voltage range 0.005-3.0 V at 65 mA g⁻¹ (0.1 C rate), and with a coulombic efficiency of > 98 % during cycling (after the 15th cycle). The average discharge and charge voltages are 1.2 and 2.1 V, respectively. The observed cyclic voltammograms and impedance spectra have been analyzed and interpreted in terms of the 'conversion reaction' involving nanophase Fe⁰-Li₂O. The superior performance of Fe₂O₃ nanoflakes is clearly established by a comparison of the results with those for Fe₂O₃ nanoparticles and nanotubes reported in the literature.