Effects of Al and Sn on microstructure, corrosion behavior and electrochemical performance of Mg–Al-based anodes for magnesium-air batteries

Three types of Mg–Al-based anodes Mg–3Al–Zn, Mg–6Al–Zn, and Mg–6Al–Sn (wt.%) alloys were produced. The influences of Al and Sn on microstructure, corrosion behavior, electrochemical property, and battery performance were studied. The experimental results show that the introduction of Al and Sn leads to the significant grain refinement and the decrease of hydrogen evolution rate of Mg–Al-based anodes. The more Al element added in alloy, the more β-Mg17Al12 phases scattered at the grain boundaries, which can accelerate the dissolution of magnesium matrix. Thus, Mg–6Al–Zn manifests stronger discharge activity than Mg–3Al–Zn. The added Sn is capable to propagate Mg2Sn phases along the grain boundaries and to suppress the precipitate of coarse β-Mg17Al12 phases in Mg–6Al–Sn. Significantly, the fine grain with tiny second phases existed in Mg–6Al–Sn is beneficial to facilitate the self-peeling of discharge products by forming the micro-cracks on the alloy surface during discharge process. The results suggest that Mg–6Al–Sn exhibits a higher electrochemical activity and utilization efficiency, specifically, a better discharge stability at the large current density for long-time. The average cell voltage, power density, specific capacity and anodic efficiency of Mg–6Al–Sn anode for Mg-air battery within 12 h at 50 mA cm−2 were 1.097 V, 54.85 mW cm−2, 1423 mA h g−1 and 63.7%, respectively.