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.