Magnesium (Mg)-air battery, which is an important category of metal-air batteries, has been considered as the promising energy storage in various areas as a primary battery. However, low utilization efficiency due to the serious hydrogen evolution of the Mg anode impairs its discharge performance. Herein, we successfully achieve a high-energy-capacity Mg-air battery that reaches record-breaking 2134 ± 88 mAh g−1 and 2279 ± 55 mAh g−1 with magnetron-sputtered Mg50Al50 and Mg30Al70 anodes in a traditional NaCl electrolyte. The superior high capacity of this new battery can be attributed to the suppression of hydrogen evolution without inhibiting the discharge process of the anode. Display omitted •Mg50Al50 and Mg30Al70 alloy anodes were magnetron-sputtered for a Mg-air battery.•The primary batteries with the anodes had record-breaking high specific capacity.•The passive films of the anodes effectively inhibited anodic hydrogen evolution.•The supersaturated Al in the anodes improved the capacity and reduced the activity.