Prediction of SEI Formation in All‐Solid‐State Batteries: Computational Insights from PCL‐based Polymer Electrolyte Decomposition on Lithium‐Metal

Abstract Identifying the solid electrolyte interphase (SEI) components in all‐solid‐state lithium batteries (ASSLBs) is essential when developing strategies for improving this battery technology. However, a comprehensive understanding of the interfacial stability and decomposition reactions of solid polymer electrolyte with lithium metal anode remains a challenge, not least outside the dominating poly(ethylene oxide)‐based materials. Here, we report the reactivity of an electrolyte system composed of a polyester (poly‐ϵ‐caprolactone, PCL) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt on Li (100) surface, and the subsequent SEI formation, using ab initio molecular dynamics (AIMD) simulations. The step‐by‐step electrolyte decomposition on the anode surface is monitored, and the resultant major SEI components are analyzed by Bader charges to correlate with X‐ray photoelectron (XPS) signal. The presence of PCL at the Li surface promotes a rapid initial reduction of LiTFSI salt via cleavage of S−N and C−S bonds, and its complete dissociation and formation of major SEI components such as LiF, Li 2 O, Li 2 S, and C‐containing species. Furthermore, a computational analysis of relevant XPS spectra is performed to support the degradation compounds.