Achieving ultrahigh anodic-efficiency and energy-density Mg–air battery via the discharge product film design of bulk Mg anode

• A design strategy of achieving superior performance of Mg anode is proposed based on the addition of the alloying elements. • The Mg-air battery with bulk AZ63X anode achieves ultra-high anodic efficiency (85.7% and 81.1%) and discharge capacity (1801 mAh g-1 and 1720 mAh g-1) at 0.5 mA cm-2 and 1 mA cm-2. • The addition of Re and Ca elements contributes to the formation of a dense and thin discharge product film, inhibiting the anodic hydrogen evolution significantly. This study exhibits a design of the discharge product film of a bulk AZ63-Ce-La-Ca (AZ63X) anode for Mg-air battery. An ideal discharge product film for Mg anode is that it could inhibit the anodic hydrogen evolution but does not hinder the transfer of the electrons at the interface. Fortunately, the addition of Ce, La, and Ca into AZ63 alloy achieves this goal. The Mg-air battery with AZ63X anode in 3.5% NaCl has an ultrahigh anodic efficiency of 85.7 ± 1.7% and energy-density of 2431 ± 53 mWh g -1 with the unique discharge product film, surpassing the values of most reported Mg-air batteries. Furthermore, the alloying elements reduce the anode delamination effect significantly by transforming the block Mg 17 Al 12 phase into the connected Mg 17 Al 12 structure and fine rod Al 2 RE and Al 2 Ca.