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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.
Faraday Discussions
|July 27, 2026
Summary
Understanding the electric double layer (EDL) is key to controlling solid electrolyte interphase (SEI) formation in lithium batteries. This study uses operando ATR-SEIRAS to reveal EDL evolution and guide SEI composition control.
Area of Science:
- Electrochemistry
- Materials Science
- Spectroscopy
Background:
- The electric double layer (EDL) at the electrode-electrolyte interface (EEI) dictates solid electrolyte interphase (SEI) formation in batteries.
- Studying the EDL is crucial for controlling SEI composition and morphology, but it remains challenging due to its nanoscale dimensions and complex dependencies.
Purpose of the Study:
- To investigate the dynamic evolution of the EDL in non-aqueous lithium electrolytes using advanced spectroscopic techniques.
- To develop and refine models of EDL evolution with changing cell voltage.
- To leverage EDL insights for controlled SEI formation in lithium-metal batteries.
Main Methods:
- Utilized *operando* attenuated-total-reflectance (ATR) surface-enhanced infrared absorption spectroscopy (SEIRAS) for real-time EDL analysis.
- Examined two distinct electrolyte systems: LiPF6 in EC:EMC and LiFSI in DME, within Li‖Cu half cells.
- Collected spectroscopic data across a voltage range of 0 V to 3 V *vs.* Li/Li+.
Main Results:
- Observed and analyzed the evolution of EDL species composition as a function of applied cell voltage for both electrolyte systems.
- Advanced detailed models describing EDL composition changes over time and voltage.
- Successfully demonstrated control over SEI composition in an ether-based electrolyte using a constant potential protocol informed by EDL models.
Conclusions:
- The study provides critical insights into the dynamic nature of the EDL and its direct influence on SEI formation mechanisms.
- The developed EDL models offer a pathway to predictable control over SEI properties.
- This work represents a significant advancement towards optimizing lithium-metal battery performance through precise SEI engineering.
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