Finite Element Modelling of Mg Anode- Electrolyte Interface in Aqueous Primary Mg-Air Batteries

Magnesium–air (Mg–air) batteries are promising eco-friendly energy systems, yet their practical performance remains far below theoretical expectations due to low operating voltage and rapid anode degradation. This work integrates experimental studies and finite element method (FEM) simulations to investigate the evolution of the Mg-based anode–electrolyte interface (Mg-AEI) during discharge. A two-dimensional model was established to describe the coupled processes of surface film formation, hydrogen evolution, and interfacial degradation, with special consideration of the negative differential effect (NDE). The model was validated by comparison with experiments on high-purity magnesium (HP Mg) and Mg-Ca alloy anodes. The results reveal that discharge current density critically governs surface film growth, porosity, and pH distribution, which together determine voltage behavior. A semi-empirical expression was derived to correlate anode voltage drop with interfacial characteristics and current density. Additionally, the study explored electrolyte modification using salicylic acid (SAL) as an Mg²⁺-complexing additive, demonstrating that SAL stabilizes pH, alters the surface layer, and enhances discharge uniformity and voltage stability. Overall, this thesis provides a combined experimental–computational framework for understanding Mg-AEI dynamics, evaluating Mg-based anode materials, and optimizing electrolytes for improved Mg–air battery performance.

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