Toward quantifying capacity losses due to solid electrolyte interphase evolution in silicon thin film batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Understanding lithium-ion battery (LIB) failure is crucial for improving cycle life.
• Capacity fading in LIBs results from active material loss and solid electrolyte interphase (SEI) evolution, which are difficult to distinguish.
• Current electrochemical methods cannot separate these two capacity loss mechanisms.

Purpose of the Study:

• To quantitatively link capacity-fading mechanisms to electrochemical and chemical processes in LIBs.
• To differentiate and quantify capacity loss due to SEI evolution versus active material loss.
• To identify the primary contributor to capacity fading in LIBs.

Main Methods:

• Utilized a model system of amorphous silicon (a-Si) thin film on silicon carbide in a half-cell configuration.
• Employed precision measurements of Coulombic efficiency via electrochemical experiments.
• Applied X-ray reflectivity measurements to quantify active material losses.

Main Results:

• Quantified capacity loss attributed to SEI evolution in each cycle.
• Identified SEI growth as the major contributor to capacity fading.
• Observed increased overpotentials and reduced lithiation extent due to SEI growth.
• Found that SEI growth is exacerbated by prolonged periods at low voltages where electrolyte decomposition is favored.
• Determined a proportionality constant for SEI growth following a parabolic law.

Conclusions:

• SEI growth is the dominant factor in LIB capacity fading.
• The developed methodology quantitatively separates lithium-ion loss mechanisms within active materials and the SEI.
• This approach provides a powerful tool for understanding and mitigating LIB degradation.