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In-Operando FTIR Study to Investigate the Effect of Varying Lithium Salts on Solid Electrolyte Interface (SEI) Evolution in Lithium Metal Batteries
Journal article   Open access   Peer reviewed

In-Operando FTIR Study to Investigate the Effect of Varying Lithium Salts on Solid Electrolyte Interface (SEI) Evolution in Lithium Metal Batteries

Samia Rahman, Rhyz Pereira, Jantakan Nedsaengtip and Vibha Kalra
Advanced science, e23503
16 Mar 2026
PMID: 41837871
Featured in Collection :   Drexel's Newest Publications
url
https://doi.org/10.1002/advs.202523503View
Published, Version of Record (VoR)CC BY V4.0 Open

Abstract

Chemistry Chemistry, Multidisciplinary Materials Science, Multidisciplinary Nanoscience & Nanotechnology Science & Technology Science & Technology - Other Topics Materials Science Physical Sciences Technology
Lithium Metal Batteries (LMBs) offer exceptional energy density but suffers from unstable Solid Electrolyte Interface (SEI). This study employs in-operando Fourier transform infrared (FTIR) spectroscopy, coupled with post-mortem XPS, to deconstruct the real-time evolution of the SEI in Li||Li symmetric cells at a practical current density of 3 mA/cm2. We investigate three lithium salts in a DME: DOL solvent - 1m LiTFSI, 1m LiClO4, and 1m LiDFOB. In- operando FTIR reveals distinct, salt-dependent SEI formation dynamics. The results reveal that LiTFSI interacts instantaneously with the lithium surface, creating a robust, hybrid SEI composed of both organic (e.g., ROLi, ROCO2Li) and inorganic species (e.g., Li2O, Li3N, LiF). This stable interface correlates with superior electrochemical performance, exhibiting the lowest and most stable overpotential. In contrast, LiClO4 shows a delayed interaction, with SEI formation commencing minutes into plating and featuring decomposition products such as LiCl. The LiDFOB electrolyte proves to be the least effective, yielding an unstable, organic-rich SEI that results in high overpotential and poor performance. This study establishes a clear correlation between SEI composition and electrochemical performance, offering a molecular-level understanding to inform rational electrolyte design and salt selection strategies for stable lithium metal batteries.

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