Chemomechanical Interactions Dictate Lithium Surface Diffusion Kinetics in the Solid Electrolyte Interphase.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Materials Science

Background:

• The solid electrolyte interphase (SEI) is crucial for fast ion transport and electrode protection in rechargeable batteries.
• Mechanical failure of the SEI due to lithium electrode volume changes can lead to electrolyte degradation and battery performance issues.

Purpose of the Study:

• To investigate the mechanical properties of lithium fluoride (LiF) and lithium oxide (Li2O) nanofilms, key components of the SEI.
• To quantify the effect of mechanical strain on lithium (Li) surface diffusion kinetics over these SEI materials.
• To establish a correlation between SEI properties and lithium plating behavior for dendrite-free electrodeposition.

Main Methods:

• Density functional theory (DFT) calculations were employed to study SEI nanofilms.
• Mechanical properties (Young's modulus, ideal strength) of LiF and Li2O nanofilms were analyzed as a function of thickness and crystallographic direction.
• Lithium surface diffusion kinetics were quantified under varying mechanical strain conditions.

Main Results:

• SEI mechanical properties are dependent on nanofilm thickness and crystallographic orientation.
• Mechanical strain significantly alters Li surface diffusion: a 4% strain decreased Li diffusion on Li2O by two orders of magnitude but increased it twofold on LiF.
• A direct link between intrinsic SEI characteristics and lithium plating behavior was identified.

Conclusions:

• The mechanical stability of the SEI is a critical, tunable parameter for rechargeable metal battery design.
• Strain-induced changes in Li diffusion kinetics on different SEI materials have profound implications for anode morphological stability.
• SEI modulation offers a promising strategy for achieving dendrite-free lithium electrodeposition and enhancing battery safety and longevity.