Microstructure of Pure Magnesium and AZ31 Magnesium Alloy Anodes after Discharge/Charge Cycles for Rechargeable Magnesium Batteries

Abstract

This study investigated the microstructure of pure magnesium (Mg) and AZ31 (Al—3 wt%; Zn—1 wt%) Mg alloy anodes after different discharge/charge cycles in an all phenyl complex (APC) electrolyte for rechargeable Mg batteries. When discharging the as-immersed Mg metal electrodes, the stripping morphologies of pure Mg and AZ31 Mg alloy electrodes are inhomogeneous with numerous discharge holes. In the subsequent charge stage, the plated Mg preferentially deposits along the circumferences of the discharge holes, which could be related to the distribution of Mg and Cl complex ions near the electrode surface after discharge. Later discharge/charge cycles on pure Mg show that both the plated Mg and the pure Mg substrate are stripped during discharge, resulting in an incomplete stripping of the plated Mg and a non-uniform electrode surface morphology after cycles. In contrast, AZ31 Mg alloy shows a higher stripping resistance than pure Mg, so the plated Mg is preferentially stripped during discharge. Near complete stripping of the plated Mg on AZ31 Mg alloy electrode results in a more uniform electrode surface morphology after cycles and a mitigated increase in the difference between the discharge and charge potentials.