Abstract
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.
Highlights
Advanced numerical simulation tools are important for the understanding of existing battery systems as well as the development and the optimization of future battery systems
The tortuosity of the here used Celgard 2500 separator (τ = 2.5) which is necessary for the calculation of the binary diffusion coefficient D±(c0), is taken from Landesfeind et al.,[2] where it was determined from single separator layers
Calculation of the tortuosity from the high frequency resistance measured before each pulse experiment (20 Ohm) of a cell filled with 20 layers of the Celgard 2500 separator and the 0.5 M electrolyte yields a tortuosity of 2.65, which is in good agreement with the value for an individual layer of the separator of 2.5
Summary
Advanced numerical simulation tools are important for the understanding of existing battery systems as well as the development and the optimization of future battery systems. The binary diffusion coefficients D±|plounlsge−term and D±|slotenagd−y−tersmtate refer to the values calculated from the long-term relaxation behavior after a pulse and a steady-state polarization experiment, respectively
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