Importance of the ion-pair lifetime in polymer electrolytes

Abstract

Ion-pairing is commonly considered as a culprit for the reduced ionic conductivity in polymer electrolyte systems. However, this simple thermodynamic picture should not be taken literally, as ion-pairing is a dynamical phenomenon. Here we construct model PEO-LiTFSI systems with different degree of ion-pairing by tuning solvent polarity, and examine the relation between the cation-anion distinct conductivity $σ^\rm{d}_{+-}$ and the lifetime of ion-pairs ${\tau }_{+-}$ using molecular dynamics simulations. It is found that there exist two distinct regimes where $σ^\rm{d}_{+-}$ scales with $1/{\tau }_{+-}$ and ${\tau }_{+-}$ respectively, and the latter is a signature of longer-lived ion-pairs which contribute negatively to the total ionic conductivity. This suggests that ion-pairs are kinetically different depending on the solvent polarity, which renders the ion-pair lifetime highly important when discussing its effect on ion transport in polymer electrolyte systems.

References in corpus (2)

• Canonical sampling through velocity-rescaling
• Temperature effects on the ionic conductivity in concentrated alkaline electrolyte solutions

Cited by in corpus (2)

• Bruce-Vincent transference numbers from molecular dynamics simulations
• Effect of Succinonitrile on Ion Transport in PEO-based Lithium Ion Battery Electrolytes