The Mg-air batteries face limitations with pronounced hydrogen evolution and low anodic utilization efficiency from Mg anodes in conventional NaCl electrolytes. The corrosion performance, surface composition, and discharge properties of commercial purity Mg anodes were thoroughly investigated in KNO₃ electrolytes with and without sodium 5-sulfosalicylate and compared to NaCl electrolyte. The addition of sodium 5-sulfosalicylate to KNO₃-based electrolyte results in efficient inhibition of H₂ evolution, consequently enhancing anodic utilization efficiency to 84% and specific capacity to 1844 mAh/g, compared to NaCl (24% and 534 mAh/g, respectively) under discharge condition of 10 mA/cm² in half cell. Furthermore, the chelating ability of sodium 5-sulfosalicylate can significantly improve the Mg surface dissolution kinetics and discharge product deposition rate at the Mg anode / electrolyte interface, yielding formation of a thinner discharge layer as confirmed by time-of-flight secondary ion mass spectrometry. The discharge voltage is increased to 1.60 V, compared to 1.35 V in KNO₃ at 0.5 mA/cm² in full cell. However, higher concentration of sodium 5-sulfosalicylate can accelerate Mg anode dissolution, impeding the improvement of anodic utilization efficiency, specific capacity, and energy density. Hence, determining optimal additive concentration and current density is crucial for enhancing the discharge properties of Mg-air batteries and mitigating excessive Mg dissolution in chloride-free electrolytes.

Mg-air batteries have attracted tremendous attention as a potential next-generation power source for portable electronics and e-transportation due to their remarkable high theoretical volumetric energy density, environmental sustainability, and cost-effectiveness. However, the fast hydrogen evolution reaction (HER) in NaCl-based aqueous electrolytes impairs the performance of Mg-air batteries and leads to poor specific capacity, low energy density, and low utilization. Thus, the conventionally used NaCl solute was proposed to be replaced by NaNO₃ and acetic acid additive as a corrosion inhibitor, therefore an electrolyte engineering for long-life time Mg-air batteries is reported. The resulting Mg-air batteries based on this optimized electrolyte demonstrate an improved discharge voltage reaching ~1.8 V for initial 5 h at a current density of 0.5 mA/cm² and significantly prolonged cells' operational lifetime to over 360 h, in contrast to only ~17 h observed in NaCl electrolyte. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were employed to analyse the composition of surface film and scanning electron microscopy combined with transmission electron microscopy to clarify the morphology changes of the surface layer as a function of acetic acid addition. The thorough studies of chemical composition and morphology of corrosion products have allowed us to elucidate the working mechanism of Mg anode in this optimized electrolyte for Mg-air batteries.