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(PF 6 ) 2 have been the subject of conflicting experimental reports and computational studies , leaving the origins of electrolyte decomposition poorly understood. In this work, we address this critical knowledge gap by systematically examining the interfacial stability of three representative salts, namely, Mg(TFSI) 2 , Mg(PF 6 ) 2 , and Mg(CB 11 H 12 ) 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 triggers rapid anion decomposition, charge transfer, and irreversible passivation, consistent with the experimental observations. Among the salts, Mg(CB 11 H 12 ) 2 shows exceptional stability across all surfaces, aligning with its reported cycling efficiency. Importantly, our study resolves longstanding discrepancies between theory and experiment and also establishes a new computational framework that closely reflects experimental realities and provides critical atomistic insights into salt decomposition pathways.