Developing high anti-corrosion dilute Mg-La-Ca-Ge alloy as promising anode for primary Mg-air batteries

Two of the main challenges facing the current development of primary Mg-air batteries are the actual operating voltage far below the theoretical value and the severe self-corrosion. Herein we report the new micro-alloyed Mg-0.5La-0.3Ca-0.3Ge (wt%) alloys as the promising candidate for anodes of Mg-air batteries, which can provide relatively high cell voltage at low current density and can be stored for a long time, especially in marine environments. The as-cast alloy exhibits remarkably high corrosion resistance (0.15 mm·y⁻¹) and its discharge performance is slightly lower than that of heat-treated alloy (C5 alloy), while C5 alloy with corrosion rate of 1.04 mm·y⁻¹ presents superior discharge performance. The C5 anode has the highest cell voltage of 1.50 V (2.5 mA·cm⁻²) and anodic efficiency of 63.5% (20 mA·cm⁻²), as compared to 1.48 V and 57.4% for as-cast anode at the same current density. The C5 anode also has high specific energy of 1875.7 mWh·g⁻¹ (2.5 mA·cm⁻²) and high specific capacity of 1408.5 mAh·g⁻¹ (20 mA·cm⁻²). The results indicate that the formation of dense protective product containing GeO is the main reason for the high corrosion resistance of the as-cast alloy, and does inhibit the self-corrosion during discharge, but it is also responsible for the lower discharge performance of the as-cast alloy than that of C5 alloy. Our study suggests that the nature of the product film is critical for the development of anodes with high corrosion resistance and high discharge performance.