Development of a Mg/O ReaxFF Potential to describe the Passivation Processes in Magnesium-Ion Batteries

Creators: Fiesinger, Florian; Gaissmaier, Daniel; van den Borg, Matthias; Bessner, Julian; van Duin, Adri C. T.; Jacob, Timo

Abstract

One of the key challenges preventing the breakthrough of magnesium-ion batteries (MIB) is the formation of a passivating boundary layer at the Mg anode. To describe the initial steps of Mg anode degradation by O2 impurities, we have developed a Mg/O ReaxFF reactive force field description capable of accurately modeling the bulk, surface, adsorption, and diffusion properties of both metallic Mg and the salt MgO. We show that O2 immediately dissociates upon first contact with the Mg anode (modeled as Mg(0001), Mg(10m10)A, and Mg(10m11)), heating the surface to several 1000 K. The high temperature assists the further oxidation and forms a rocksalt interphase intersected by several grain boundaries. Among the Mg surface terminations, Mg(10m10)A is the most reactive, forming an MgO layer with a thickness of up to 25 Å. We also demonstrate the recrystallization of an amorphous MgO particle, which is obtained performing grand-canonical Monte Carlo simulations, into the rocksalt structure by thermal annealing at elevated temperatures. Our force field can be used to model the ongoing reactions in Mg-air batteries and constitutes an important step towards modeling the solid--electrolyte interface formation at the Mg anode.

Additional Information

The content is available under CC BY 4.0 License. This work contributes to the research performed at the Center for Electrochemical Energy Storage Ulm-Karlsruhe (CELEST) and was partly funded by the German Research Foundation (DFG) under Project-ID 390874152 (POLiS Cluster of Excellence). Further support through the DFG-research unit FOR-5065 (ELSICS) under Project-ID 428906592 is gratefully acknowledged. The authors acknowledge support by the state of Baden-Württemberg through bwHPC and the DFG through grant no INST 40/575-1 FUGG (JUSTUS 2 cluster). F.F. sincerely thanks Dr. Björn Kirchhoff and Dr. Christoph Jung for helpful discussions and comments on the manuscript. A.C.T.v.D. acknowledges funding from a grant from the U.S. Army Research Laboratory through the Collaborative Research Alliance (CRA) for Multi-Scale Multidisciplinary Modeling of Electronic Materials (MSME) under Cooperative Agreement No. W911NF-12-2-0023. The authors declare no conflict of interest. Author Contributions. F.F. performed all the calculations except of the force field training of the magnesium–magnesium interactions which was performed by D.G. F.F. analyzed and discussed all results together with D.G., M.B., and J.B. A.C.T.v.D. and T.J. supervised the research. The manuscript was written by F.F. and all authors commented on the manuscript. Data Availability Statement. The data that support the findings of this study are openly available in zenodo at https://doi.org/10.5281/zenodo.7074790. Furthermore, the KVIK optimization routine is openly available in the GitHub repository at https://github.com/shk11/KVIKOptimizer.

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