Insights into corrosion behaviour and discharge performance improvement in Mg-Air batteries using sodium acetate

The discharge behaviour of Mg-air batteries with pure Mg anodes is presented, highlighting the improved anodic utilization efficiency and specific capacity in sodium acetate (NaOAc) electrolyte over sodium chloride (NaCl) electrolyte. Moreover, only a modest reduction in discharge potential was noted at increased current densities in half-cell tests. NaOAc electrolyte, containting less aggressive acetate ions, enables the formation of a homogeneous and protective oxide layer, in contrast to the chloride ions in NaCl electrolyte, which promote oxide breakdown and localized corrosion. The protective layer formed in NaOAc electrolyte limits Mg degradation, reduces H₂ evolution rate, and enhances discharge performance. The surface characterizations by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) reveal a denser corrosion layer formed on the surface of pure Mg anode in the NaOAc electrolyte, contributing to improved corrosion resistance and increased anodic utilization efficiency. Full-cell discharge tests using pure Mg, Mg-0.2Ca, and AZ31 alloy show that the anodic utilization efficiency and specific energy are improved in NaOAc electrolyte, particularly for Mg-0.2Ca, with energy density of 2066 Wh/kg at 2 mA/cm². These findings suggest that NaOAc is a promising electrolyte for improving the performance of Mg-air batteries for different Mg-based anode materials.