Effect of Surface Heterogeneity on Electrolyte Stability in Mg-metal Batteries: Insights from Ab Initio Molecular Dynamics

Magnesium (Mg) metal batteries are widely regarded as a sustainable and high-capacity alternative to lithium-ion batteries. Despite their promise, their practical implementation is hindered by electrolyte instability at Mg metal anodes, which limits reversible Mg deposition and battery performance. In particular, widely-used Mg salts such as Mg(TFSI)2 and Mg(PF6)2 have been the subject of conflicting experimental and computational reports, leaving the origins of electrolyte decomposition poorly understood. In this work, we address this critical knowledge gap by systematically examining interfacial stability of three representative salts, namely, Mg(TFSI)2, Mg(PF6)2, and Mg(CB11H12)2 on three Mg anode surface models: metallic Mg (m-Mg), stoichiometric MgO (s-MgO), and non-stoichiometric MgO (ns-MgO), using ab initio molecular dynamics simulations. Our results demonstrate that oxide chemistry and surface heterogeneity critically dictate electrolyte stability. While m-Mg and s-MgO remain largely inert, ns-MgO surface triggers rapid anion decomposition, charge transfer, and irreversible passivation, explaining the experimental observations. Among the salts, Mg(CB11H12)2 shows exceptional stability across all surfaces, aligning with its reported cycling efficiency. Importantly, our study not only resolves the longstanding discrepancies between theory and experiment but also establishes a new computational framework that closely reflects experimental realities and provides critical atomistic insights into salt decomposition pathways.