Determination of transport parameters in liquid binary lithium ion battery electrolytes - I. Diffusion coefficient

Various numerical methods for the simulation of ion-transport in concentrated binary electrolyte solutions can be found in the literature, whereas the corresponding transport parameters are rarely discussed. In this contribution, a polarization cell consisting of two electrodes separated by a porous separator is proposed to determine the concentration dependent binary diffusion coefficient of non-aqueous electrolyte solutions. Therefore, two different electrochemical methods are extended so that they can be applied to electrolyte solutions in a porous medium. Additionally, the different methods are compared with each other by means of numerical simulations. The proposed experimental setup is used to determine the concentration dependent binary diffusion coefficient of an exemplary electrolyte, lithium perchlorate dissolved in a mixture of ethylene carbonate and diethyl carbonate, and the data are compared to those available in the literature. It will be shown that the most reliable method to determine concentration dependent binary diffusion coefficients are long-term relaxation experiments in a two-electrode cell using a porous separator.