Mapping the Free Energy of Lithium Solvation in the Protic Ionic Liquid Ethylammonuim Nitrate: A Metadynamics Study

TL;DR

This study uses metadynamics simulations to map the free energy landscape of lithium ion solvation in ethylammonium nitrate, revealing key conformations and transition barriers relevant for electrochemical applications.

Contribution

It provides a detailed free-energy landscape of lithium solvation in a protic ionic liquid using first-principles metadynamics, aligning with experimental data.

Findings

Lowest free energy conformations involve 3 or 4 nitrate ions solvating lithium.

Transition barrier between these conformations is approximately 0.2 eV.

Additional less probable solvation conformations are also characterized.

Abstract

Understanding lithium solvation and transport in ionic liquids is important due to their possible application in electrochemical devices. Using first-principles simulations aided by a metadynamics approach we study the free-energy landscape for lithium ions at infinite dilution in ethylammonium nitrate, a protic ionic liquid. We analyze the local structure of the liquid around the lithium cation and obtain a quantitative picture in agreement with experimental findings. Our simulations show that the lowest two free energy minima correspond to conformations with the lithium ion being solvated either by three or four nitrate ions with a transition barrier between them of 0.2 \eV. Other less probable conformations having different solvation pattern are also investigated.