Direct calculation of Li-ion transport in the solid electrolyte interphase.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• The solid electrolyte interphase (SEI) is critical for lithium-ion battery performance and longevity.
• The precise mechanism of Li(+) transport through the SEI remains poorly understood.
• Typical SEI films comprise porous organic outer layers and dense inorganic inner layers.

Purpose of the Study:

• To elucidate the mechanism of Li(+) transport within SEI films using a multiscale theoretical methodology.
• To investigate Li(+) diffusion in crystalline Li(2)CO(3), a major component of the inner SEI layer.
• To develop a predictive model for Li(+) transport properties in SEI layers.

Main Methods:

• Development of a multiscale theoretical methodology combining first-principles calculations and mesoscale diffusion equations.
• Utilizing density functional theory (DFT) to determine dominant diffusion carriers and mechanisms in Li(2)CO(3).
• Formulating a two-layer/two-mechanism diffusion model (pore diffusion and knock-off diffusion) informed by experimental data.

Main Results:

• Density functional theory identified excess interstitial Li(+) as the dominant diffusion carrier in Li(2)CO(3).
• A 'knock-off' diffusion mechanism, maintaining O-coordination, was determined to be prevalent over direct hopping.
• The multiscale model accurately predicted the measured Li-isotope ratio profile across the SEI layer without fitting parameters.

Conclusions:

• The study elucidates the atomic-scale mechanism of Li(+) transport in crystalline Li(2)CO(3) within SEI layers.
• A novel multiscale model successfully describes Li(+) transport across different SEI layers and mechanisms.
• The methodology provides a framework for predicting SEI transport properties and understanding battery aging.