A model study on effects of vanadium ion diffusion through ion exchange membranes in a non-aqueous redox flow battery

Abstract

A simple charge-discharge model of a nonaqueous vanadium redox flow battery (VRFB) was introduced in this study to analyze the diffusion coefficients of active materials permeating an electrolyte membrane. Using this model, the effects of diffusion coefficients on the long-term performance, efficiency, and capacity of the system have been studied. Based on a literature review, the diffusion coefficients of approximately 10−7–10−6 cm2 s−1 were applied and the results were analyzed to determine relevant parameters for this study. Through this study, it has been confirmed that the capacity of the system was maintained at 100% under ideal conditions in the long-term operation, whereas that of the system reduced by more than half when only one vanadium species moved and is 10 mAh when all vanadium species moved. In addition, the simulation clarified the effect of diffusion coefficients on coulombic efficiency. In most conditions of the various diffusion coefficients, coulombic efficiency enhanced through cycle had been operated. In the case of voltage efficiency, the value was not largely changed regardless of diffusion coefficients since it was affected more by other factors. One important factor revealed through this model study is that electrolyte membrane performance of the VRFB system was not only affected by the diffusion coefficient of a specific ion, but also by the relationship between the diffusion coefficients of all active ions involved in the reaction. This study provides guidance for the development of an electrolyte membrane to improve the performance of VRFB systems.