Ultra-high-purity Mg-Ge anodes enable a long-lasting, high energy-density Mg-air battery

The primary Mg-air battery shows extraordinary theoretical energy density to satisfy the requirements that traditional rechargeable batteries cannot reach. However, the battery has failed to live to its potential due to its low operating discharge voltage, parasitical anodic hydrogen reaction and irreversible corrosion. To address these issues, we devised a process to generate ultra-high-purity (UHP) Mg-Ge anodes for Mg-air batteries. The Ge addition enhances the anodic reaction activity and suppresses the anodic hydrogen evolution reaction (AHER). Hence, the fabricated UHP Mg-0.5Ge anode exhibited a remarkably high discharge voltage of 1.69 V (0.5 mA cm-2) coupled with a high energy density of 2272 mWh g-1 (20 mA cm-2). These values are higher than all the reported Mg-based anodes in the literature. Furthermore, the minimal impurity content and the development of a Ge-bearing surface layer contribute to the UHP Mg-0.5Ge anodes achieving a 95% intermittent discharge efficiency, which is 3.5 times higher than that of the commonly employed AZ31 anode. The outstanding properties of the fabricated UHP Mg-Ge anode set the stage for advancing the next generation of Mg-air batteries.