Bruce-Vincent transference numbers from molecular dynamics simulations

TL;DR

This paper derives a theoretical framework linking the Bruce-Vincent transference number to Onsager coefficients, enabling calibration of molecular dynamics simulations to predict true transference numbers in electrolyte solutions.

Contribution

It provides a new formulation for the Bruce-Vincent transference number in terms of Onsager coefficients, facilitating the use of MD simulations for accurate transference number prediction.

Findings

Derived the Bruce-Vincent transference number using Onsager coefficients.

Applied the formulation to PEO-LiTFSI electrolyte system.

Enabled MD simulations to predict true transference numbers.

Abstract

Transference number is a key design parameter for electrolyte materials used in electrochemical energy storage systems. However, the determination of the true transference number from experiments is rather demanding. On the other hand, the Bruce-Vincent method is widely used in the lab to measure transference numbers of polymer electrolytes approximately, which becomes exact in the limit of infinite dilution. Therefore, theoretical formulations to treat the Bruce-Vincent transference number and the true transference number on an equal footing are clearly needed. Here we show how the Bruce-Vincent transference number for concentrated electrolyte solutions can be derived in terms of the Onsager coefficients, without involving any extrathermodynamic assumptions. By demonstrating it for the case of PEO-LiTFSI system, this work opens the door to calibrating molecular dynamics (MD) simulations via reproducing the Bruce-Vincent transference number and using MD simulations as a predictive tool for determining the true transference number.