Achieving Ultrahigh Anodic Efficiency via Single-Phase Design of Mg-Zn Alloy Anode for Mg-Air Batteries.

Magnesium-air battery has been considered promising for electrochemical energy storage or as a conversion device due to its high theoretical energy density and low cost. However, the experimental energy density is far lower than the theoretical value due to the intense hydrogen evolution of the Mg anode upon discharging. Herein, we have successfully developed a novel Mg64Zn36 (at. %) alloy via single-phase design. The as-prepared Mg64Zn36 anode possesses a high discharge specific capacity of 1302 ± 70 mAh g-1 and extraordinarily high efficiency of 94.8 ± 4.9%, which breaks the records of efficiency among all of the reported Mg anodes. The superior high efficiency is attributed to the anodic hydrogen evolution being inhibited by Zn alloying, which passivates the Mg matrix. The intermediate ion Mg+ produced during discharging is dramatically limited by the integrated passive film and is totally converted into Mg2+ electrochemically through the film. Meanwhile, the uniform discharging products due to the homogeneous microstructure of Mg64Zn36 co-contribute to the high efficiency. The design of the Mg-Zn alloy may open a new avenue for the development of Mg-air batteries.