Discharge performance of the Al–Mg–Sn alloy anodes with different Sn content for Al-air batteries

In this paper, the discharge performance of the Al–Mg–Sn alloy anodes with different Sn content for Al-air batteries is investigated in 4 mol L−1 NaOH solution, and their microstructure, corrosion behavior and discharge properties are discussed in detail. It shows that Sn-rich phases in the Al matrix act as cathode to promote the anode dissolution of the Al matrix and increase the electrochemical activity. The electrochemical impedance spectroscopy (EIS) results reveal that the value of hydroxide film resistance (Rc) increases as Sn content increases to 0.5 wt%, indicating that Sn addition can improve the corrosion resistance and therefore reduce the hydrogen evolution rate (HER). As a result, the Al-0.6Mg-0.2Sn alloy shows good discharge performance at low current density and its peak energy density reaches 2858.6 mWh∙g−1 at 20 mA cm−2 with the discharge capacity of 2341.9 mAh∙g−1. The Al-0.6Mg-0.5Sn alloy presents good discharge performance at high current density and its peak anode efficiency reaches 93.21% at 40 mA cm−2. When Sn content is up to 0.8 wt%, excessive Sn-rich phases aggravate the hydrogen evolution corrosion and intergranular corrosion, which results in more weight loss. This is responsible for the unsatisfactory discharge performance of Al-0.6Mg-0.8Sn alloy at all current density.