# Identifying the Mechanism of Continued Growth of the Solid-Electrolyte Interphase

## TL;DR

This paper identifies Li-interstitial diffusion as the key mechanism behind the continued growth of the solid electrolyte interphase in lithium-ion batteries, explaining capacity fade.

## Contribution

It differentiates potential-dependent growth mechanisms and confirms Li-interstitial diffusion as the primary cause through comparison with experimental data.

## Key findings

- Li-interstitial diffusion matches experimental potential dependence
- Solvent diffusion, electron conduction, and tunneling do not match experiments
- Identifies the primary transport mechanism for long-term SEI growth

## Abstract

Continued growth of the solid electrolyte interphase (SEI) is the major reason for capacity fade in modern lithium-ion batteries. This growth is made possible by a yet unidentified transport mechanism that limits the passivating ability of the SEI towards electrolyte reduction. We, for the first time, differentiate the proposed mechanisms by analyzing their dependence on the electrode potential. Our calculations are compared to recent experimental capacity fade data. We show that the potential dependence of SEI growth facilitated by solvent diffusion, electron conduction, or electron tunneling qualitatively disagrees with the experimental observations. Only diffusion of Li-interstitials results in a potential dependence matching to the experiments. Therefore, we identify Li-interstitial diffusion as the cause of long-term SEI growth.