Molecular Dynamics of Lithium Ion Transport in a Model Solid Electrolyte Interphase

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Solid electrolyte interphase (SEI) layer composition in lithium-ion batteries is crucial for performance but challenging to study.
• Dilithium ethylene dicarbonate (Li2EDC) is identified as a dominant SEI component.
• Molecular dynamics (MD) studies of Li+ transport in SEI layers face limitations due to compositional control.

Purpose of the Study:

• To investigate Li+ transport characteristics in a model SEI layer composed of Li2EDC using a parameterized non-polarizable MD force field.
• To compare Li+ dynamics in Li2EDC with liquid ethylene carbonate (EC).
• To provide analytical methods for evaluating Li+ ion transport in new battery materials.

Main Methods:

• Development and application of a parameterized, non-polarizable MD force field for Li2EDC.
• Long-time MD simulations at moderate temperatures to study Li+ dynamics.
• Analysis of mean-squared displacements, van Hove self-correlation functions, and vibrational modes.

Main Results:

• Identified three distinct Li+ transport regimes in Li2EDC: ballistic, trapping, and diffusive.
• Observed significantly longer nanosecond trapping times in Li2EDC compared to liquid EC, which decrease with increasing temperature.
• Characterized Li2EDC as a glassy material based on non-Gaussian van Hove functions and mean-squared displacements, validated by vibrational mode analysis.

Conclusions:

• The non-polarizable MD model for Li2EDC is effective for studying Li+ dynamics, consistent with polarizable force field results.
• Longer trapping times in Li2EDC highlight the need for materials with smaller trapping regions for fast-charging batteries.
• The analytical methods presented can guide the development and testing of novel battery materials for improved Li+ ion transport.