Insights into electrolyte reactivity at the Li metal surface from density functional theory

Understanding interfacial reactivity and electrolyte degradation is critical for designing functional solid electrolyte interphase (SEI) layers in lithium-ion batteries (LIBs). This work employs density functional theory (DFT) calculations to model the adsorption and degradation mechanisms of two common electrolyte solvents—ethylene carbonate (EC) and propylene carbonate (PC)—and two widely used additive molecules — vinylene carbonate (VC) and fluoroethylene carbonate (FEC)—on the Li metal anode surface. Our findings reveal that solvent molecules exhibit stronger adsorption on the Li metal surface compared to additive molecules. Nudged elastic band calculations are employed to study two distinct C–O bond dissociation pathways, providing insights into the preferred degradation mechanisms and the resulting early-stage SEI products. EC and PC predominantly decompose to form Li2CO3 and C2H4, whereas FEC and VC follow alternate ring-opening pathways that yield intermediates prone to polymerization or further decomposition into CO and CO2. To validate our computational approach, we benchmarked three DFT functionals (r2SCAN, rVV10, and PBE) against hybrid functionals (HSE06 and PBE0). Among them, r2SCAN achieved the closest agreement with hybrid-level results, while rVV10 notably underestimated activation barriers. We also examined charge transfer using two different partitioning schemes, finding the Bader scheme more reliable than the Lowdin scheme, which significantly underpredicted charge transfer. These results provide a detailed mechanistic understanding of electrolyte degradation at the Li metal surface, offering valuable insights for the design of stable SEI layers in LIBs.