Li-diffusion at the interface between Li-metal and [Pyr₁₄][TFSI]-ionic liquid: Ab initio molecular dynamics...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• The solid electrolyte interface (SEI) is crucial for lithium-ion battery performance.
• Understanding ion transport within the SEI is key to improving battery stability and efficiency.
• Previous work established SEI composition and structure using density functional theory-molecular dynamics (DFT-MD).

Purpose of the Study:

• To investigate lithium-ion diffusion rates within the SEI compact layer and the Li-electrode region.
• To determine the activation energies for lithium-ion diffusion in different battery interface regions.
• To compare diffusion characteristics in smaller and larger simulation systems.

Main Methods:

• Employed density functional theory-molecular dynamics (DFT-MD) simulations.
• Analyzed diffusion constants and activation energies for lithium ions.
• Utilized systems of varying sizes: 83Li/2[TFSI] and 164Li/4[TFSI] at 400 K.

Main Results:

• Lithium-ion diffusion is approximately one order of magnitude slower in the SEI (0.22–0.33 × 10^-10 m²/s) compared to the Li-electrode region (1.35–5.64 × 10^-10 m²/s).
• Lithium diffusion in the SEI is primarily governed by hopping between fluorine or oxygen neighbor shells.
• Activation energies for Li-diffusion varied: 0.03–0.11 eV in the Li-region and 0.06–0.09 eV in the SEI.

Conclusions:

• The SEI compact layer presents a significant kinetic barrier to lithium-ion transport.
• Understanding diffusion mechanisms and activation energies is vital for designing advanced solid electrolytes.
• Simulation results provide critical insights into SEI properties influencing battery performance.