A Joint DFT-kMC Study To Model Ethylene Carbonate Decomposition Reactions: SEI Formation, Growth, and Capacity Loss during Calendar Aging of Li-Metal Batteries

The solid electrolyte interphase (SEI) is a multistructured thin layer that forms at the anode (e.g., lithium-metal)/electrolyte (e.g., ethylene carbonate EC) interface due to electrolyte reduction. At the initial battery cycles, the SEI protects the electrolyte from further reduction. However, the SEI continues to grow with time, leading to capacity loss and eventually the death of the battery. In this work, we modeled the battery-aging process at storage conditions (calendar aging). We studied EC decomposition reactions using density functional theory (DFT) simulations in the gas-phase in isolation and over the inorganic layer found inside the SEI composed of Li2CO3. We used the values obtained from DFT alongside diffusion coefficients from the literature to explore the temporal evolution of the concentration of the species by kinetic Monte Carlo (kMC) simulations. We found that reactions occurring over Li2CO3 (001) led to a relatively slow SEI growth which is compatible with the general use of carbonate-based solvents in LIBs for protection/passivation purposes. Our simulations over Li2CO3 (001) predict the formation of a multilayered structured SEI. Moreover, our kMC simulations predict the shift from a nonlinear initial behavior to a linear behavior for the capacity loss induced by the formation and growth of the SEI over time which was reported in previous experimental and theoretical studies for lithiated graphite-based batteries. We extended our analysis to the decomposition reactions over the Li2O (111) surface, which could form from the decomposition of Li2CO3. We found that the selectivity of the decomposition reactions strongly depends on the inorganic surface. The main conclusion of this study is to highlight the crucial role played by surface reactions inside the SEI on the nature and selectivity of the decomposition kinetics of EC for the SEI growth.