  Numerical simulations are a powerful tool for the development and improvement
of Li-ion batteries. Modeling the mass transport of the involved electrolytic
solutions requires precise determination of the corresponding electrolyte
parameters. In this work, we attempt to measure the conductivity, the diffusion
coefficient, the transference number and the thermodynamic factor for a system
of 0.5$\,$M LiPF$_6$ dissolved in a blend of ethylene carbonate and ethyl
methyl carbonate (EC:EMC, 3:7 weight) at 20$\,${\deg}C and 50$\,${\deg}C.
Applying galvanostatic polarization experiments to symmetrical metal Li |
electrolyte + separator | Li metal cells reveals, however, a potential response
qualitatively deviating from theoretical expectations. Impeded diffusion
processes indicate the presence of additional, undesired porous structures on
the Li electrodes, preventing a reliable evaluation of the electrolyte
parameters. To spectrally resolve the diffusive processes, we conduct
very-low-frequency impedance spectroscopy. The impedance in fact exhibits
multiple interfering diffusive features. In our measurements, an explicit
identification of the impedance for the sole diffusion through the separator is
however not feasible. Therefore, the authors doubt that polarizing experiments
using Li metal electrodes yield accurate parameters for electrolytes.
