Influence of heat treatment on the discharge performance of Mg-Al and Mg-Zn alloys as anodes for the Mg-air battery

• Heat treatment was used to improve the discharge performance of Mg anode. • The improvement mechanism of heat treatment was clarified. • Heat treatment can be considered an effective process for advanced Mg anodes. This work investigated the use of heat treatment to improve the battery performance of cast Mg-6Zn and Mg-8Al anodes for primary Mg-air batteries. The reason for anodic efficiency drop was quantitively analyzed. Anodes after heat treatment had a discharge voltage that was higher and more-stable than that of cast anodes, attributed to a higher open circuit voltage and smoother exfoliation of discharge products. The solution heat-treated Mg-6Zn had the best discharge capacity of 1185 mAh g −1 and an anodic efficiency of 56 % at 40 mA cm −2 , compared with 928 mAh g −1 and 44 % for as-cast Mg-6Zn at the same current density. The T6 treated (solution and annealing) Mg-8Al anodes produced the best discharge capacity of 1418 mAh g −1 and anodic efficiency (at 40 mA cm −2 ) of 63 %. Heat treatment also enhanced the peak energy density from 926 mWh g −1 (2.5 mA cm −2 ) to 1463 mWh g −1 (at 10 mA cm −2 after solution treatment) for Mg-6Zn and from 1501 mWh g −1 (20 mA cm −2 ) to 1736 mWh g −1 (at 20 mA cm −2 after the T6 heat treatment) for Mg-8Al. These improvements were caused by suppressing the anodic hydrogen reaction and dissolving harmful large-sized precipitates. Heat treatment should be considered essential in the production of high-performance anodes for Mg-air batteries.