The exploration of highly efficient catalysts for the oxygen reduction reaction to improve sluggish kinetics still remains a great challenge for advanced energy conversion and storage in metal/air batteries. In this work, ultrafine Mn3O4 nanowires/three-dimensional graphene/single-walled carbon nanotube catalysts with an electron transfer number of 3.95 (at 0.60 V vs Ag/AgCl) and kinetic current density of 21.7-28.8 mA cm-2 were developed via a microwave-irradiation-assisted hexadecyl trimethylammonium bromide (CTAB) surfactant procedure to greatly enhance the overall catalytic performance in Mg/air batteries. To match the electrochemical activity of the cathode catalysts, a large-scale Mg anode prepared with micropersimmon-like particles via a mechanical disintegrator and Mg(NO3)2-NaNO2-based electrolyte containing 1.0 wt % trihexyl(tetradecyl)phosphonium chloride ionic liquid were applied. Combining the ultrafine Mn3O4 nanowires/three-dimensional graphene/single-walled carbon nanotube as an efficient electrocatalyst for the oxygen reduction reaction and an Mg micro-/nanoscale anode in the novel electrolyte, the advanced Mg/air batteries demonstrated a high cell open circuit voltage (1.49 V), a high plateau voltage (1.34 V), and a long discharge time (4177 min) at 0.2 mA cm-1, showing a high energy density. Therefore, it is believed that this device configuration has great potential for application in new energy storage technologies.