Effect of Sn/Ca Mass Ratio on the Second Phase, Corrosion Behavior and Discharge Performance of Mg–xSn–1Ca Mg–Air Battery Anodes

Abstract

Mg–Sn–Ca alloys are promising candidates for Mg–air battery anodes. In this study, the influence of Sn/Ca mass ratio on the formation of the second phase, corrosion behavior and discharge performance of Mg-xSn-1Ca (x = 0.5, 1.0, 2.5, 4.0 wt%) alloys, has been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical characterizations. The results reveal that the CaMgSn phase forms in four Mg–xSn–1Ca alloys, the Mg2Ca phase precipitates in low Sn/Ca mass ratio alloys (Mg-0.5Sn-1Ca and Mg–1Sn–1Ca), and the Mg2Sn phase precipitates in the Mg-4Sn-1Ca alloy. Low Sn/Ca mass ratio alloys present better corrosion resistance than high Sn/Ca mass ratio alloys (Mg-2.5Sn-1Ca and Mg-4Sn-1Ca). The improvement in the corrosion resistance of the Mg2Ca phase is more than that of the Mg2Sn and CaMgSn phases. The highest average discharge voltage, anodic efficiency, power density, specific capacity, and specific energy of 1.188 V, 58.3%, 23.78 mW cm−2, 1225.5 mA h g−1, and 1389.8 mW h g−1, respectively, are found for the Mg-0.5Sn-1Ca alloy at an Sn/Ca mass ratio of 0.34, at a current density of 20 mA cm−2. This is attributed to better corrosion resistance and good electrochemical activity of the alloy. For the TX01 alloy, the current of discharge failure is calculated to be 93.6 mA.