Linking the discharge behavior and microstructure of ternary Mg–Ca–Zn alloy anodes for magnesium-air cells

Abstract

Three Mg–1Ca–1Zn (wt.%) alloy anodes with distinct microstructure characteristics (As-cast, water-cooled (WC) and furnace-cooled (FC)) are prepared by casting and homogenization treatment followed by different cooling methods. The relationship between microstructure and discharge behavior is systematically investigated. Due to the severe self-corrosion and discharge products adhesion caused by the formation of a large number of micro-galvanic couples, the As-cast anode shows the worst discharge performance. After homogenization treatment, the FC anode possesses an increased peak anodic efficiency of 56.6% and discharge capacity of 1250.11 mAh g−1 at 10 mA cm−2, however, the “chunk effect" induced by the linkage of discharge channels at the triple line boundary restricts cell efficiency. The WC anode exhibits the highest cell voltage at all discharge current densities, which is attributed to the high electrochemical activity and easily exfoliated discharge product layers. A novel discharge mechanism of the linear dissolution of α-Mg across grain boundaries results in uniform dissolution of the anode matrix, mitigative hydrogen evolution and smooth discharge pits. The WC anode exhibits the highest anodic efficiency of 62.9% and specific capacity of 1388.9 mA h g−1 at 10 mA cm−2, making it a promising anode material for Mg-air cells.