Formation and Evolution of the Solid Electrolyte Interphase on Silicon Electrodes from Fluorine-Free Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Growing demand for sustainable energy storage solutions.
• Need for environmentally compatible electrolytes in lithium-ion batteries.
• Lithium bis(oxalato)borate (LiBOB) as a promising fluorine-free electrolyte component.

Purpose of the Study:

• Investigate SEI formation and evolution on Si wafers using LiBOB-based electrolytes.
• Elucidate the impact of vinylene carbonate (VC) additive on SEI properties and cycling stability.
• Understand Si wafer (de)lithiation processes and lithium trapping mechanisms.

Main Methods:

• Operando X-ray reflectivity (XRR) for in-situ structural analysis.
• Ex situ X-ray photoelectron spectroscopy (XPS) for surface chemical characterization.
• Cycling of Si wafer model systems with LiBOB electrolytes, with and without VC.

Main Results:

• Identified three distinct SEI evolution stages: formation, densification/growth, and thickness decrease during delithiation (SEI breathing).
• VC additive mitigates LiBOB decomposition and promotes a smoother SEI layer.
• Observed lithium trapping in Si wafers, reduced by VC addition.

Conclusions:

• The study provides fundamental structural and chemical insights into SEI behavior in LiBOB electrolytes.
• Demonstrated the beneficial effect of VC in enhancing SEI stability and reducing lithium loss.
• Offers implications for designing safer and more efficient environmentally friendly lithium-ion batteries.