Dendritic microstructure-driven discharge behavior of micro-alloyed Mg–Sn binary alloys for Mg-air batteries

In cast magnesium alloys, the segregation of alloying elements often leads to the formation of dendrites and the subsequent precipitation of second phases. However, previous studies on magnesium anodes for Mg-air batteries have predominantly focused on the effects of second phases, largely overlooking the role of dendrites. In this investigation, micro-alloyed Mg–Sn binary alloys were designed to evaluate their discharge behavior and underlying mechanism as anodes for Mg-air batteries. The Sn atoms tend to dissolve and segregate within the matrix of as-cast alloys, forming dendrites that establish galvanic coupling with the Mg matrix and promote dissolution of the anode during discharge. The micro-alloyed Mg-0.5 wt% Sn, featuring refined dendritic structures, exhibited the optimal discharge performances, which achieved an anode utilization efficiency of 60.5 ± 0.7 % and a specific capacity of 1330.7 ± 15 mAh·g⁻¹ at 50 mA·cm⁻², along with an energy density of 1779.6 ± 45 mWh·g⁻¹ at 10 mA·cm⁻². This work provides new insights into the design of advanced Mg-air batteries through microstructural control of the anode.