The influence of interface polarization on the determination of lithium transference numbers of salt in polyethylene oxide electrolytes

Lithium transference numbers, salt diffusion coefficients and effective lithium conductivities are investigated with the steady state polarization method for poly(ethylene oxide) (PEO) based polymer electrolytes containing lithium bis(oxalato)borate (LiBOB) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We compare the commonly used evaluation technique with our approach. Here, the focus is laid on the potential relaxation of the polarized sample which delivers information about the salt diffusion and the potential distribution in symmetric Li/electrolyte/Li cell. The new approach circumvents the well-known initial current issue and thus increases the reliability of the experiment. The temperature dependence of the lithium transference numbers and the importance of data acquisition time are also discussed. The highest lithium transference numbers are 0.19 for P(EO)60·LiTFSI at 90 °C.