Boosting Mg-Air Primary Battery Performance Via Addition of Complexing Agents in the Electrolyte: A Mechanistic View on the Effect of EDTA

Abstract

Diverse novel energy conversion and storage systems have developed rapidly in the last few decades to address the growing demand for sustainable and environmentally friendly energy sources. In this respect, aqueous Mg-air batteries have drawn much attention for their high energy density, cost-effectiveness, and environmental friendliness.A primary Mg-air battery can theoretically provide a relatively high voltage and specific energy density of 3.1 V and 6.8 kW.h.kg-1, respectively [1]. However, the high wasteful self-corrosion rate of Mg alloys during discharge in aqueous electrolytes and fouling of the anode surface with corrosion products significantly reduce the delivered voltage and the specific energy of the Mg-air battery. These drawbacks are exacerbated by the anodic polarization due to the well-known phenomenon called Negative Difference Effect (NDE). Recently, pioneered by Höche et al. [2], the use of Mg complexing agents in the battery electrolyte has revolutionized the performance of Mg-air batteries by mitigating the mentioned shortcomings. However, the understanding of the enhancement mechanism, which may differ for different complexing agents, is at its nascent stage.In this work, sodium salt of ethylendiaminetetraacetic acid (EDTA) is used as the additive for the electrolyte of a primary Mg-air battery with a commercially pure Mg anode [3]. The electrolyte pH was taken as the main parameter to explore the effect of EDTA on the discharge performance of the Mg anode.The battery voltage was improved at all tested electrolyte pH values, which ranged from 7.0 to 11.0. The utilization efficiency (UE) of the discharged Mg anode is also enhanced by the presence of EDTA in the electrolyte at pH of 11, resulting in a 10-fold increase in the full-cell battery discharge time as compared to the reference battery in NaCl electrolyte without EDTA.Different methods, including EIS, local pH and dissolved O2 measurements, and H2 evolution tests were employed to study the interaction of EDTA with the Mg anode surface during discharge. Several mechanisms of enhancement in the UE have been concluded, including suppressing the chunk effect, weakening the detrimental NDE, and promoting the formation of a more protective layer on the Mg anode surface.The findings of this study provides an improved understanding of the interaction of the complexing agents with the Mg anode in Mg-air batteries, which further helps finding the tuning parameters to optimize its performance.[1] T. Zhang, Z. Tao, J. Chen, Magnesium-air batteries: From principle to application, Materials Horizons, 1 (2014) 196-206.[2] D. Höche, S.V. Lamaka, B. Vaghefinazari, T. Braun, R.P. Petrauskas, M. Fichtner, M.L. Zheludkevich, Performance boost for primary magnesium cells using iron complexing agents as electrolyte additives, Sci Rep, 8 (2018) 7578.[3] B. Vaghefinazari, D. Snihirova, C. Wang, L. Wang, M. Deng, D. Höche, S.V. Lamaka, M.L. Zheludkevich, Exploring the effect of sodium salt of Ethylenediaminetetraacetic acid as an electrolyte additive on electrochemical behavior of a commercially pure Mg in primary Mg-air batteries, Journal of Power Sources, 527 (2022) 231176.