Interface Structure in Li-Metal/[Pyr₁₄][TFSI]-Ionic Liquid System from ab Initio Molecular Dynamics Simulations

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• Ionic liquids (ILs) are advanced materials for next-generation lithium (Li) batteries.
• ILs can function as electrolytes or interlayers, enhancing battery performance.
• A stable solid electrochemical interface (SEI) is crucial for Li battery longevity, preventing electrode oxidation and electrolyte decomposition.

Purpose of the Study:

• To computationally investigate the composition and structure of the SEI layer formed between a Li anode and [Pyr14][TFSI] ionic liquid.
• To elucidate the detailed SEI structure, overcoming experimental limitations.

Main Methods:

• Density functional theory (DFT)-based molecular dynamics simulations were employed.
• The study focused on the SEI compact layer formed at the Li anode/[Pyr14][TFSI] interface.

Main Results:

• The [TFSI] anions decomposed upon reaction with Li, forming the SEI layer.
• [Pyr14] cations remained stable and were not incorporated into the SEI.
• The SEI layer exhibited a nonhomogeneous structure, composed of atomized S, N, O, F, and C from oxidized anions.

Conclusions:

• The SEI layer's composition is primarily derived from the decomposition of [TFSI] anions.
• The stability of [Pyr14] cations contributes to the SEI's protective properties.
• Understanding the SEI's nonhomogeneous, anion-derived structure is key to optimizing Li battery electrolytes.