Performance of AZ31 Alloy as Anodes for Primary Magnesium-Air Batteries under High Current Discharge

The discharge behavior of Mg-air battery consisting of AZ31 Mg alloy anode and a graphite-based air cathode was investigated under constant discharge current densities of up to 40 mA cm(-2). Discharge with higher current density increased the power density, which reached its maximum value of 25 mW cm(-2) at 30 mA cm(-2). Further discharge caused the cell voltage to drop and fluctuate. Electrochemical impedance spectra of the Mg anode revealed specific trajectories according to the discharge current. A new electrical equivalent circuit modeling the dissolution at the Mg anode was proposed. After checking its validity, the dependence of the circuit elements on the discharge current was analyzed. A discharge product in the form of hydrotalcite was preferentially formed under high current discharge, which was gradually transformed to Mg(OH)(2) and Al2O3. Higher discharge current promoted uniform dissolution of the Mg anode and improved the anodic efficiency. The removal of Al-Mn intermetallic particles was considered as the cause, which was verified by SEM/EDS analysis. Considering the anode kinetics and the performance of the air cathode, the optimal operation condition of 30 mA cm(-2) discharge was proposed for the present Mg-air battery configuration.