Evaluation of Impurities in Aluminum Anodes for Al-Air Batteries

Aluminum anodes with various purity grades (2N8, 3N6, 3N8, 4N6, and 5N) are characterized and investigated as anodes for aluminum-air batteries. The effects of impurity elements (Fe, Si, Ga, Zn, etc.) and the associated microstructure change on battery performance are evaluated through microstructure and surface potential analysis and electrochemical and battery measurements. The results reveal that the decrease in contents of Fe and Si in Al anodes can alleviate the self-corrosion and boost the anode utilization. Moreover, the Al anode with a higher purity shows a more negative open-circuit potential to realize a larger open-circuit voltage for the Al-air battery, except the 3N6 Al anode. The 3N6 Al anode displays a higher electrochemical activity than the 4N6 Al anode due to the activation from Zn and Ga elements. The Al-air batteries with 5N Al and 4N6 Al display large discharge voltages and specific capacities at 20 mA cm–2. The Al-air batteries with 2N8 Al and 3N8 Al exhibit better discharge characteristics than those with 5N Al and 4N6 Al at a higher current density because of smaller polarization resistances. The Al-air battery with 3N6 Al shows larger discharge voltages at both low and high current densities. Finally, the energy cost of various Al anodes is evaluated, and the result reveals that the 3N6 Al anode is the most cost-effective anode for Al-air batteries in this study.