Effects of external field treatment on the electrochemical behaviors and discharge performance of AZ80 anodes for Mg-air batteries

In this work, the effects of external field treatment on electrochemical behaviors and discharge performance of as-cast Mg-8%Al-0.5%Zn (wt%) anodes for Mg-air batteries are systematically investigated in 3.5 wt% NaCl solution. The external field treatment particularly the variable-frequency ultrasonic field can dramatically refine the alpha-Mg grains and beta phases. The grain size decreases from 1594.8 + 43 mu m (untreated billet) to 140.6 + 15 mu m after variable-frequency ultrasonic field treatment. The values of open circuit potential, electrochemical activity and corrosion resistance of Mg-8%Al-0.5%Zn anode are improved with external field treatment, which should be attributed to refined grains and dispersive p phase. The external field treatment especially the variable-frequency ultrasonic field improves stability and the value of cell voltage, and enhances the discharge performance of the Mg-8%Al-0.5%Zn anode. The variable-frequency ultrasonic field treated anode has the best discharge capacity and anodic efficiency at current density of 45 mA cm(-2), with the values of 1417 mA h g(-1) and 63.3%, respectively. The ultrasonic field vibration changes the dissolution behavior of alpha-Mg matrix during the discharge process, showing the oriented surface morphologies. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.