Li+ solvation and transport properties in ionic liquid/lithium salt mixtures: a molecular dynamics simulation study

Area of Science:

• Physical Chemistry
• Materials Science
• Computational Chemistry

Background:

• Ionic liquids (ILs) like N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([pyr(13)][Ntf(2)]) are promising electrolytes.
• Understanding the behavior of lithium salts ([Li][Ntf(2)]) within ILs is crucial for battery applications.

Purpose of the Study:

• To investigate the structural and transport properties of [pyr(13)][Ntf(2)]/[Li][Ntf(2)] mixtures using molecular dynamics.
• To elucidate the influence of lithium salt concentration on ion coordination, diffusion, and conductivity.

Main Methods:

• Molecular dynamics (MD) simulations employing a polarizable force field.
• Simulations conducted at various lithium salt mole fractions (0-33%) and temperatures (363 K, 423 K).
• Analysis of densities, ion self-diffusion coefficients, and ionic conductivities.

Main Results:

• Simulated properties closely matched experimental data.
• Li(+) cations were coordinated by approximately 4.1 oxygen atoms from Ntf(2) anions.
• Anion sharing by Li(+) increased with salt concentration, leading to cluster formation and reduced ion diffusivity.
• Ionic conductivity decreased with increasing salt concentration, particularly at higher temperatures.
• Li(+) contribution to conductivity saturated at higher concentrations.

Conclusions:

• The study provides detailed insights into the molecular mechanisms governing ion transport in IL-based electrolytes.
• Findings highlight the trade-offs between lithium concentration and electrolyte performance.
• Results are valuable for designing advanced electrolytes for electrochemical devices.