Fine-tuned molecular design toward a stable solid electrolyte interphase on a lithium metal anode from in silico simulation

Electrolyte engineering has emerged as a promising approach for enhancing the performance of lithium (Li) metal batteries, with recent advancements in novel electrolytes contributing to improved battery performance. Nevertheless, the intricate electrochemical interface poses significant challenges for experimental studies, resulting in a limited fundamental understanding of interface phenomena. To address this issue, we utilize hybrid ab initio and reactive molecular dynamics (HAIR) simulations to examine the solid electrolyte interphase (SEI) formation process and chemical composition at the atomic level in a series of fluorinated pseudo-localized high-concentration electrolytes (LHCEs). Our detailed analysis uncovers that ionic conductivity, the abundance of LiF, and oligomer length are three pivotal factors influencing cell performance. The simulations not only corroborate the -CF2- fluorinated backbone scheme, aligning with experimental findings but also reveal new opportunities for enhancing performance through the introduction of -CHF- moieties based on the concept of incremental design. Consequently, we propose a novel solvent molecule, fluorinated 1,2,3,4,5,6-hexa-1,6-dimethoxylhexane (FHDH), and demonstrate that FHDH maintains desirable physicochemical properties and high F concentration while exhibiting superior SEI physicochemical properties in terms of ionic conductivity, relative amount of LiF, and long-chain oligomers. Our findings offer a rational explanation for experimental design strategies and suggest further electrolyte optimization based on these insights, paving the way for the development of high-performance Li metal batteries.