Direct and in situ examination of Li+ transport kinetics in isotope labelled solid electrolyte interphase

TL;DR

This study uses advanced in-situ techniques and simulations to elucidate Li+ transport mechanisms in the solid electrolyte interphase, revealing a successive displacement process and quantifying Li+ mobility, which informs battery design.

Contribution

It provides the first direct in-situ evidence of Li+ transport mechanism in SEI and quantifies Li+ diffusivity, advancing understanding of ionic transport in battery interfaces.

Findings

Li+ transport follows a successive displacement mechanism.

Li+ self-diffusivity varies from 6.7×10^-19 to 1.0×10^-20 m^2/s.

Quantitative insights into SEI ionic transport behavior.

Abstract

Here, using unique in-situ liquid secondary ion mass spectroscopy on isotope-labelled solid-electrolyte-interphase (SEI), assisted by cryogenic transmission electron microscopy and constrained ab initio molecular dynamics simulation, for the first time we answer the question regarding Li+ transport mechanism across SEI, and quantitatively determine the Li+-mobility therein. We unequivocally unveil that Li+ transport in SEI follows a mechanism of successive displacement, rather than "direct-hopping". We further reveal, in accordance with spatial-dependence of SEI structure across the thickness, the apparent Li+ self-diffusivity varies from 6.7*10-19 m2/s to 1.0*10-20 m2/s, setting a quantitative gauging of ionic transport behavior of SEI layer against the underlining electrode as well as 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 to the tailoring of interphasial chemistries for future battery chemistries.