Magnesium alloys as anodes for neutral aqueous magnesium-air batteries

Magnesium (Mg) is abundant, green and low-cost element. Magnesium-air (Mg-air) battery has been used as disposable lighting power supply, emergency and reserve batteries. It is also one of the potential electrical energy storage devices for future electric vehicles (EVs) and portable electronic devices, because of its high theoretical energy density (6.8 kWh•kg−1) and environmental-friendliness. However, the practical application of Mg-air batteries is limited due to the low anodic efficiency of Mg metal anode and sluggish oxygen reduction reaction of air cathode. Mg metal as an anode material is facing two main challenges: high self-corrosion rate and formation of a passivation layer Mg(OH)2 which reduces the active surface area. In last decades, a number of Mg alloys, including Mg-Ca, Mg-Zn, commercial Mg-Al-Zn, Mg-Al-Mn, and Mg-Al-Pb alloys, have been studied as anode materials for Mg-air batteries. This article reviews the effect of alloying elements on the battery discharge properties of Mg alloy anodes. The challenges of Mg-air batteries are also discussed, aiming to provide a depth understanding for the theoretical and practical development of high-performance Mg-air batteries.