Sn content effect mediated by segregation: dendrite/secondary phase evolution and discharge performance optimization of Mg-0.2Ca-xSn alloys

The primary objective of this work was to investigate how segregation-induced dendrites and secondary phases influence the discharge dissolution behavior and product desorption of magnesium alloy (Mg-0.2Ca- x Sn) electrode materials by adjusting the Sn/Ca addition ratio under low Ca doping conditions. The results indicated that when the alloy microstructure contains both a small amount of dispersively distributed short rod-like CaMgSn phases and a limited quantity of dendrites, a dynamic balance is established between the micro-galvanic corrosion induced by the former (acting as cathodic sites) and the grain-boundary corrosion associated with the latter. Instead of exacerbating localized corrosion, the synergistic interaction between these two microstructural features complemented each other, thereby achieving uniform corrosion of the alloy during the discharge process and providing critical microstructural assurance for the stable discharge of the electrode. The full-cell test results demonstrate that among the Mg-Ca-Sn series electrode materials, the MC06 alloy (Mg-0.2Ca-0.6Sn) exhibits the most promising anode performance for magnesium-air batteries. At a current density of 10 mA‧cm⁻², the MC06 alloy delivers an average discharge voltage of 1.251 V, a specific capacity of 1042.2 mAh‧g⁻¹, a specific energy of 1332.3 mWh‧g⁻¹, and an anode efficiency of 44.79%.