Role of micro-Ca/In alloying in tailoring the microstructural characteristics and discharge performance of dilute Mg-Bi-Sn-based alloys as anodes for Mg-air batteries

The influence of micro-Ca/In alloying on the microstructural characteristics, electrochemical behaviors and discharge properties of extruded dilute Mg-0.5Bi-0.5Sn-based (wt.%) alloys as anodes for Mg-air batteries are evaluated. The grain size and texture intensity of the Mg-Bi-Sn-based alloys are significantly decreased after the Ca/In alloying, particularly for the In-containing alloy. Note that, in addition to nanoscale Mg₃Bi₂ phase, a new microscale Mg₂Bi₂Ca phase forms in the Ca-containing alloy. The electrochemical test results demonstrate that Ca/In micro-alloying can enhance the electrochemical activity. Using In to alloy the Mg-Bi-Sn-based alloy is effective in restricting the cathodic hydrogen evolution (CHE) kinetics, leading to a low self-corrosion rate, while severe CHE occurred after Ca alloying. The micro-alloying of Ca/In to Mg-Bi-Sn-based alloy strongly deteriorates the compactness of discharge products film and mitigates the "chunk effect" (CE), hence the cell voltage, anodic efficiency as well as discharge capacity are greatly improved. The In-containing alloy exhibits outstanding discharge performance under the combined effect of the modified microstructure and discharge products, thus making it a potential anode material for primary Mg-air battery.