Insights into Electrolyte Reactivity and Solid Electrolyte Interphase Formation at the Li Metal Anode Surface from DFT Simulations

Solid electrolyte interphase (SEI) is a critical component of lithium ion batteries, yet is poorly characterized and not well understood. We use plane wave density functional theory simulations to perform a comprehensive study of the degradation reaction mechanisms of four electrolyte solvents and additives, ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC), at the Li (001) metal anode surface. The calculations provide fundamental insights into electrolyte decomposition and spontaneous SEI formation. Utilizing automated workflows implemented in the Schrödinger Materials Science Suite, we compute the adsorption energies and calculate the reaction energies for each decomposition pathway. Furthermore, we employ nudged elastic band calculations to compute the decomposition reaction barriers and provide mechanistic insights into the onset of SEI formation. We analyze trends in decomposition reaction energies and the relationships between the reaction energies and the activation barriers for the various electrolyte molecules as a function of applied bias potential. We find that the preferred decomposition pathways are different for the solvent molecules (EC and PC) than for the additives (FEC and VC). Calculations also suggest that applied bias reduces decomposition reaction barriers thus enhancing SEI formation. Such a comprehensive dataset of reaction energies and activation barriers provides useful benchmarks for the development and validation of reactive machine learned force fields for modeling advanced battery chemistries at a larger scale.