Molecular insights into temperature-driven transport mechanisms in EC-LiTFSI electrolytes.

Abstract

Understanding the temperature dependence of electrolyte properties is crucial for optimizing the performance of rechargeable batteries, as temperature directly influences ion transport and electrochemical efficiency. We investigate how the properties of ethylene carbonate-based electrolytes containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) evolve with temperature across the range of 300 K to 600 K. Using molecular dynamics simulations, we evaluate the interaction between viscosity, ionic conductivity, and ion transport, and the results align with experimental findings. We find that the Nernst-Einstein ionic conductivity (<i>σ</i>_NE) displays an Arrhenius behavior with temperature, yielding an activation energy of 13 kJ mol^-1, while the viscosity and ion-pair relaxation times increase exponentially with temperature. The <i>σ</i>_NE follows a power-law dependence on viscosity with a scaling relation <i>σ</i>_NE ∼ <i>η</i>^-0.91, closely matching the ideal Walden relation, a rarely observed result in molecular simulations. Interestingly, we observe that the ionic conductivity is somewhat weakly related to the ion-pair relaxation timescales described by <i>σ</i>_NE ∼ <i>τ</i>_c^-0.63, indicating that slower dynamics associated with ion pairs reduce ionic conductivity. In order to obtain a better understanding of the dynamics of EC-LiTFSI electrolytes, we calculate the non-Gaussian parameter. Our study not only establishes the interplay between viscosity and ionic conductivity but also links temperature-driven ion-pair dynamics to conductivity limitations, offering a new framework for tuning electrolyte properties in energy storage applications.