Anomalous diffusion of lithium-anion clusters in ionic liquids.

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• Lithium-ion transport is crucial for battery performance but is often hindered in ionic liquids (ILs).
• Understanding the mechanisms of ion transport in ILs is essential for developing advanced energy storage devices.

Purpose of the Study:

• To investigate the kinetics of lithium-ion transport in ionic liquids using molecular dynamics simulations.
• To develop and validate a two-state model for lithium-ion transport, comparing it with machine learning approaches.

Main Methods:

• Extensive molecular dynamics simulations of lithium ions in [N-methyl-N-propylpyrrolidium][bis(trifluoromethanesulfonyl)imide] with LiNtf[Formula: see text].
• Analysis of transport mechanisms, including train size distributions and shell exchange dynamics.
• Development of a two-state (soft and hard) model and application of graph neural networks to identify ion states.

Main Results:

• Lithium-ion transport is characterized by non-Poissonian, bursty shell exchanges of the bis(trifluoromethanesulfonyl)imide anion.
• A two-state model accurately describes the transition probabilities of lithium-ion shells.
• The 'shell-soft' state significantly contributes to lithium-ion transport, particularly at lower temperatures.

Conclusions:

• The 'shell-soft' state is the primary driver of lithium-ion transport in these ionic liquids.
• Increasing the fraction of the 'shell-soft' state is a key strategy for enhancing lithium-ion conductivity.
• This research provides fundamental insights into ion dynamics in ILs for battery applications.