Effect of the Charging Conditions on the Cycle Performance of Fe2O3/C Composite Anodes for Iron-Air Batteries

A Fe2O3/C composite material obtained by dry-type ball milling was applied as a negative electrode in iron-air batteries. The effects of charge current density and charge cutoff capacity on the electrochemical behavior of the Fe2O3/C electrode in KOH electrolyte with or without a K2S additive were investigated. In KOH electrolyte, the redox currents decreased with repeated cycling because of the increased resistance of the Fe2O3/C electrode and the aggregation of iron species to form large particles during cycling. Various charge current densities from 0.5 mA cm(-2) to 100 mA cm(-2) in KOH aqueous solutions with and without K2S additives were used and the results revealed that higher charge current density facilitated the redox reaction of the Fe/Fe(OH)(2) redox couple, discharge capacity increased with the increase in charge current density. The discharge capacity of the electrode was larger in the presence than in the absence of S2- additives, and the redox reactions of Fe/Fe(II) and Fe(II)/Fe(III) improved as evidenced by lengthened plateaus on the charge-discharge curves. In the coulostatic charge process, various cutoff capacities were applied from 300 mA h g(-1)-Fe2O3 to 1007 mA h g(-1)-Fe2O3, and results showed that the discharge capacities of the Fe2O3/C electrode increased with increasing cutoff capacity. Thus, the practical capacities of iron-air batteries could be increased through the suppression of hydrogen evolution by optimizing the charge current density, charge cutoff capacity, and additives of the batteries.