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. 2025 Nov 11;122(45):e2514652122.
doi: 10.1073/pnas.2514652122. Epub 2025 Nov 6.

Direct and in situ examination of Li+ transport kinetics in an isotope-labeled solid-electrolyte interphase

Affiliations

Direct and in situ examination of Li+ transport kinetics in an isotope-labeled solid-electrolyte interphase

Xiaofei Yu et al. Proc Natl Acad Sci U S A. .

Abstract

Solid-electrolyte interphase (SEI) is the critical component in all advanced battery chemistries, whose ionic transport and electron leakage behaviors remain least understood among all battery components. Here, using unique in situ liquid secondary ion mass spectroscopy on isotope-labeled SEI, assisted by cryogenic transmission electron microscopy and constrained ab initio molecular dynamics simulation, we answer the question regarding the Li+ transport mechanism across SEI and quantitatively determine the Li+ mobility therein. We unequivocally unveil that Li+ transport in SEI mainly follows a mechanism of successive displacement. We further reveal that in accordance with the spatial dependence of SEI structure across the thickness, the apparent Li+ self-diffusivity continuously drops from the SEI-electrolyte side to the SEI-electrode side (6.7 × 10-19 m2/s to 1.0 × 10-20 m2/s), setting a quantitative gauging of both ionic transport behavior of the SEI layer against the underlying electrode and the rate-limiting step of battery operation. This direct study on Li+ kinetics in SEI fills part of the decade-long knowledge gap about the most important component in advanced batteries and provides more precise guidelines for the tailoring of interphasial chemistries for future battery chemistries.

Keywords: Li battery; Li ion transport; in situ liquid SIMS; isotope labeling; solid–electrolyte interphase.

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Conflict of interest statement

Competing interests statement:The authors declare no competing interest.

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