SEI Characterization Using XPS: Resolving Rinsing Effects through Cryogenic Implementation

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• The chemical environment of the battery anode's solid electrolyte interphase (SEI) under operando conditions is not well understood.
• Traditional X-ray photoelectron spectroscopy (XPS) is limited by SEI evolution during analysis.
• Cryogenic XPS (cryo-XPS) offers a breakthrough for preserving SEI integrity during measurements.

Purpose of the Study:

• To evaluate different sample preparation protocols for ex situ XPS analysis of the SEI.
• To determine the optimal method for preserving operando-relevant chemical speciation.
• To leverage cryo-XPS to identify protocol-induced differences in SEI characterization.

Main Methods:

• Utilized cryo-XPS with instant plunge freezing to preserve the SEI interface.
• Compared two sample preparation protocols: unwashed blotted SEI (w-SEI) and rinse-dried cryo-sample (d-SEI).
• Analyzed the impact of sample preparation on SEI chemical composition and probe depth certainty.

Main Results:

• Cryo-XPS demonstrated significant differences between sample preparation methods.
• The rinse-dried cryo-sample (d-SEI) protocol provides a more accurate representation of operando-relevant SEI chemical composition.
• The d-SEI protocol ensures probe depth certainty and reveals more buried SEI species compared to w-SEI.

Conclusions:

• Sample preparation is critical for accurate surface-sensitive XPS characterization of the SEI.
• The controlled, rinse-dried cryo-sample (d-SEI) protocol is the preferred method for operando-relevant SEI analysis using cryo-XPS.
• This finding enhances the reliability of SEI chemical state analysis in battery research.