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Determination of the Solid Electrolyte Interphase Structure Grown on a Silicon Electrode Using a Fluoroethylene
Gabriel M Veith1, Mathieu Doucet2, Robert L Sacci3
1Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA. veithgm@ornl.gov.
Scientific Reports
|July 26, 2017
Summary
Fluorinated ethylene carbonate (FEC) additive dynamically modifies the silicon anode solid electrolyte interphase (SEI) thickness and composition during battery cycling. This electrolyte additive creates a stable, responsive SEI layer crucial for battery performance.
Area of Science:
- Materials Science
- Electrochemistry
- Battery Technology
Background:
- Silicon anodes are promising for high-capacity lithium-ion batteries but suffer from poor cycling stability due to uncontrolled solid electrolyte interphase (SEI) formation.
- Electrolyte additives can significantly influence SEI properties, impacting battery performance and longevity.
Purpose of the Study:
- To investigate the in situ role of fluorinated ethylene carbonate (FEC) as an electrolyte additive in mediating the thickness and composition of the SEI on silicon anodes.
- To elucidate the dynamic changes in SEI structure during battery cycling as a function of state-of-charge.
Main Methods:
- In situ analysis of SEI formation and evolution on silicon anodes with and without FEC electrolyte additive.
- Electrochemical measurements to determine SEI thickness and composition changes during lithiation and delithiation.
Main Results:
- FEC addition leads to the formation of a ~50 Å thick SEI layer composed of C-O containing polymeric species.
- The SEI thickness dynamically changes during cycling: it thickens to ~70 Å upon lithiation (becoming more organic) and thins to ~57 Å upon delithiation (becoming more inorganic, e.g., LiF).
- This reversible thickening and thinning demonstrates the dynamic nature of the FEC-mediated SEI, contrasting with thicker (~280 Å) SEI layers formed without FEC.
Conclusions:
- Fluorinated ethylene carbonate (FEC) acts as a crucial electrolyte additive, enabling the formation of a dynamic and responsive solid electrolyte interphase on silicon anodes.
- The observed reversible SEI thickness and compositional changes mediated by FEC are key to improving the stability and performance of silicon-based lithium-ion batteries.
