Effect of reference frame and ion-pair lifetime on the transport coefficients of polymer electrolytes

The transport coefficients of electrolyte solutions are important design parameters for electrochemical energy storage devices. The experimental measurements and simulations thereof help to understand the factors limiting the performance of electrolyte materials. We demonstrate the critical role of reference frame (RF) in reconciling the recent experimental observation of negative transference numbers in the polymer electrolyte PEO-LiTFSI, and establishing the link between experiment and simulation. We show that the quantitative comparison of transport coefficients is only possible upon proper RF transformation, and highlight the impact of anion mass fraction and anion-anion interaction on the reported transference numbers. By tuning the solvent polarity of the polymer electrolyte, we reveal two regimes characterized by different ion-pair lifetime with distinct ion-pair kinetics and ion-ion correlation.