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Published on: November 10, 2014
Operando surface-enhanced infrared spectroscopy reveals electric double layer evolution during solid electrolyte
Thanh Nguyen1, Ziqi Liu2, Jeffrey Lopez1
1Department of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208, USA. jlopez@northwestern.edu.
Abstract:
The electric double layer (EDL) determines the species present at the electrode-electrolyte interface (EEI) and the distribution of reactants that will form the solid electrolyte interphase (SEI). Knowledge of the species in the EDL at the onset of formation and the change in the EDL composition with time provides valuable insight into SEI formation mechanisms and improves control over the SEI composition and morphology. Despite this significance, the EDL remains challenging to study with length scales on the order of 10s of nanometers and a complex dependence on electrolyte formulation and electrode potentials. In this work, we use operando attenuated-total-reflectance (ATR) surface-enhanced infrared absorption spectroscopy (SEIRAS) to study the EDL in non-aqueous lithium electrolytes. We report operando ATR-SEIRAS on 1 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC) : ethyl methyl carbonate (EMC) 3 : 7 wt/wt and 1 M lithium bis(fluorosulfonyl)imide (LiFSI) in 1,2-dimethoxyethane (DME) in Li‖Cu half cells to observe the evolution of the species in the EDL as a function of cell voltage. We use these data to advance detailed models of the EDL evolution between 0 V and 3 V vs. Li/Li+. We then use this model to control the SEI composition for the ether-based electrolyte via a constant potential protocol. This work serves as an important step towards understanding the evolution of the EDL structure and how it determines the composition of the SEI in lithium-metal batteries during cycling.
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