Electrochemical behaviors and discharge properties of Al–Mg–Sn–Ca alloys as anodes for Al-air batteries

The effects of Calcium (Ca) content on the electrochemical behaviors and discharge properties of Al-0.5Mg-0.1Sn alloys is investigated in 4 M NaOH solution. Adding Ca component to the Al-0.5Mg-0.1Sn alloy generates CaxSny phases or Al4Ca phases in the matrix so that refining grains. Compared with the properties of Al-0.5Mg-0.1Sn alloys, Al-0.5Mg-0.1Sn-0.05/0.1Ca alloys exhibit a better discharge activity and a lower self-corrosion rate, since the CaxSny phase could refine grains and enhance its discharge activity. Also, the oxidation of CaxSny phases provides one layer of Ca(OH)2-containing film, which restrains the self-corrosion behavior of the anode (hydrogen evolution reaction). However, Al-0.5Mg-0.1Sn-0.2/0.4Ca alloys have a higher self-corrosion rate, since the Al4Ca phase in the matrix accelerates the hydrogen evolution reaction. Among them, Al-0.5Mg-0.1Sn-0.1Ca alloys reach its peak energy density (4081.64 Wh kg−1) at 20 mA cm−2 with a discharge capacity of 2619.42 Ah·kg−1 (anode efficiency of 87.9%). Therefore, Al-0.5Mg-0.1Sn-0.1Ca alloys can serve as a promising anode material for Al-air batteries.