Lithium intercalation into α-Fe 2O 3 obtained by mechanical milling of α-FeOOH

Abstract

Crystalline α-Fe 2O 3 powder was prepared by the mechanical milling of crystalline α-FeOOH at room temperature in air. This result means that crystalline α-FeOOH is dehydrated by mechanical milling at room temperature. The obtained α-Fe 2O 3 powder worked as a rechargeable electrode material in lithium ion conductive organic electrolytes. The electrodes exhibited high discharge capacities of over 1000 mAh g −1 corresponding to 6 Li per α-Fe 2O 3 at potentials ranging from the open circuit potential to 0.5 V (versus Li +/Li) in the first discharging (lithium insertion) process. This suggests that the valence deviation from Fe 3+ in α-Fe 2O 3 to Fe 0 may be caused by electrochemical reduction. In contrast, after the first discharge, the electrodes exhibited high charge capacities of more than 700 mAh g −1 corresponding to 4.2 Li per α-Fe 2O 3 in the first charging (lithium extraction) process. The coulombic efficiency at the first cycle was about 70%, suggesting a valence deviation from Fe 0 to Fe 2+ or Fe 3+ caused by electrochemical oxidation.