Prediction of Carbonate Solvent Stability on Lithiated Si Anode

Silicon (Si) is a highly promising material for advanced Li-ion batteries (LIBs) due to its high theoretical capacity and low electrochemical potential. However, challenges such as significant volumetric expansion during cycling and the electrochemical instability of electrolytes, leading to the formation of the solid electrolyte interphase (SEI), present obstacles. To overcome these issues, understanding stable SEI formation from a computational perspective using first-principles calculations is invaluable. In this study, we employ density functional theory (DFT) and ab initio molecular dynamics (AIMD) to uncover the mechanisms behind stable reduction processes. We investigate novel electrolyte compositions, specifically focusing on lithium hexafluorophosphate (LiPF6) salts paired with different solvent molecules, to capture the atomistic changes during electrolyte decomposition and SEI layer formation. Additionally, we examine the effects of varying degrees of lithiation in Si anodes (LiSi and Li15Si4) and how these stages influence the reduction mechanism at the atomic level. Our findings reveal that the LiPF6 electrolyte with vinylene carbonate (VC) added to ethyl methyl carbonate (EMC) is the most thermodynamically stable configuration. The impact of fluoroethylene carbonate (FEC) and VC on stability varies depending on whether the primary solvent is EMC or a mixture of ethylene carbonate (EC) and EMC. These insights into interfacial reactivity offer guidance for designing more thermodynamically stable LIB electrolyte solvents for Si anodes.