  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.
