Atomic Resolution of Solid-Electrolyte Interphase Formation via Off-Lattice On-the-Fly Kinetic Monte Carlo

Complex reactions occurring at the electrode/electrolyte interface in Li metal batteries lead to the formation of a solid-electrolyte interphase (SEI), which plays a vital role in stabilizing batteries' performance. An in-depth understanding of the SEI formation mechanism thus is crucial for battery optimization. Kinetic Monte Carlo (KMC) simulations can offer detailed information on the interfacial reaction processes over multiple time scales. However, conventional KMC methods employing on-lattice models and predefined event lists are inappropriate for modeling SEI formation due to the complex chemical environment at materials interfaces. In this work, we propose an off-lattice on-the-fly KMC (OTF-KMC) method integrated with a machine learning force field (MLFF) to investigate SEI growth at the atomic level. We study a system comprising a Li(100) surface and an electrolyte containing the ethylene carbonate (EC) molecules and Li salts and identify various decomposition pathways of EC molecules and PF₆^- anions to generate the SEI. Our results show that the SEI features a spatial distribution of an inorganic inner layer near the Li electrode with organic products relatively far from the surface, aligning closely with experimental evidence. More importantly, we present a versatile and robust computational framework for modeling interfacial reactions in electrochemical systems.