Effect of calcium on the electrochemical behaviors and discharge performance of Al-Sn alloy as anodes for Al-air batteries

Abstract The effect of calcium on the microstructure, electrochemical behaviors and discharge properties of Al–0.1Sn alloys as anodes for alkaline Al–air batteries are investigated. Addition of calcium to Al–0.1Sn alloys promotes the precipitation of CaSn phase and Al4Ca phase in the matrix. The Al–0.1Sn alloys with calcium (≤ 0.16 wt%) exhibit better discharge performance and higher anode efficiency, which is due to the oxidation of CaSn phases introducing one layer of Ca(OH)2-containing film that inhibits the hydrogen evolution reaction of the anode. The Al–0.1Sn–0.08Ca alloy shows a discharge capacity as high as 2495.75 Ah kg−1 (83.75% anode efficiency) and a peak energy density of 3793.54 Wh kg−1 at 20 mA cm−2, which are 24.8% and 18.9% higher than for the Al–0.1Sn alloy. By contrast, the Al4Ca phase formed by excessive calcium strongly aggravates the hydrogen evolution reaction of the Al–0.1Sn alloy, which is not conducive to its discharge performance. Furthermore, at high current densities, the discharge behaviors of calcium-containing alloys are significantly suppressed by the Ca(OH)2-containing film. Therefore, the Al–0.1Sn–0.08Ca alloy is suitable to serve as anode materials for Al-air batteries at low current densities.