Two-State Bursty Dynamics of Li+-Anion Solvation Shells in Ionic Liquid Electrolytes

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Understanding ion transport in ionic liquids (ILs) is key for advanced battery electrolytes.
• Connecting local coordination dynamics to macroscopic ion mobility remains a challenge.

Purpose of the Study:

• To investigate the dynamics of lithium-ion (Li+) solvation shells in ionic liquids.
• To develop a framework linking local coordination dynamics to Li+ mobility.

Main Methods:

• Polarizable-force-field molecular dynamics simulations of Li+/Pyr14+ with FSI-, TFSI-, and BETI- anions.
• Analysis using a two-state bursty dynamics framework and likelihood-based model comparisons.
• Temperature-dependent analysis across 298-423 K.

Main Results:

• Li+-anion solvation shell dynamics are non-Poissonian and bursty.
• A two-state model (soft and hard states) effectively describes the dynamics.
• The soft state, with lower coordination and higher anion exchange, shows greater Li+ mobility.
• Kinetic barriers increase with anion size and for hard-state transitions.

Conclusions:

• The soft-state fraction serves as a local kinetic descriptor for Li+ mobility.
• This finding provides a link between solvation dynamics and ion transport in ILs.
• Future experiments can validate these simulation-based insights.