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The formation and evolution of the dynamic solid electrolyte interphase (SEI) at the Si anode/electrolyte interface are yet to be completely understood to solve irreversible capacity loss and increase battery cycle life. Herein, the evolution of SEI and its dynamic properties at the Si anode/electrolyte interface are investigated in two electrolyte systems, a 1.2 M LiPF 6 in EC: EMC 3:7 (wt%) electrolyte (referred to as Gen2) and a 1.2 M LiTFSI in EC: EMC 3:7 (wt%) electrolyte (referred to as LiTFSI). Two lithiation stages are studied: the pre-lithiation ( pre-Li ) SEI stage and the post-lithiation ( post-Li ) stage. Findings reveal at the pre-Li , SEI formation starts at an early potential and contributes to the greater mass gain in the Si/Gen2, and it is dominated by the formation of a non-uniform F- and P-rich layer in Si/Gen2, in contrast to a homogeneous F- and C-containing layer at the Si/LiTFSI interphase. The initially formed SEI in LiTFSI further benefits the charge transfer kinetics. At the post-Li stage, a more substantial SEI evolution is observed at Si/LiTFSI. This study offers a foundational understanding of the SEI dynamic evolution with electrolyte dependence. Findings from this report offer important insights into solving the complex SEI stability issues on Si.
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This content will become publicly available on June 3, 2027
Identifying Electrolyte Reduction Intermediates in Lithium Metal Batteries with Spin Trapping
Despite promising developments in liquid electrolyte engineering for lithium metal batteries, solid electrolyte interphase (SEI) formation mechanisms from electrolyte components remain challenging to study. Here, we establish an approach employing spin trapping to identify radical intermediates formed during electrolyte reduction. We use electron paramagnetic resonance spectroscopy to identify three distinct radical intermediates formed during fluoroethylene carbonate reduction that confirm a ring-opening mechanism. Our spin trapping approach further enables confirmation of radical identity with liquid chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The resulting SEI formed in the spin-trapped system is investigated with titration and spectroscopic techniques to observe how stunting organic SEI formation reduces SEI stability and increases anion decomposition. Overall, this is the first time that radical intermediates in battery interphase formation reactions have been directly characterized, affording insight into the complex mechanisms of electrolyte reduction and establishing a new approach for studying SEI formation and function.
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- Award ID(s):
- 2338202
- PAR ID:
- 10710672
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 148
- Issue:
- 23
- ISSN:
- 1943-2984
- Page Range / eLocation ID:
- 24240 to 24249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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