Modeling Research Of All Vanadium Redox Flow Battery

The modeling and simulation of all vanadium redox flow battery (VRB) is the foundation for the design, scale-up, control and optimization. According to the complexity of the VRB models, they can be divided into three types:namely empirical models, semi-empirical models and theoretical ones. In this paper, the progress on the study each model has been reviewed. Meanwhile, a VRB single cell has been experimentally investigated by the transient boundary voltage method and Electrochemical Impedance Spectroscopy (EIS), two equivalent circuit models have been developed and analyzed.The relationship of current excitation and voltage response of a VRB single cell is carried out, and a new equivalent circuit model is presented using the transient boundary voltage method. The model parameters are calculated by curve fitting with a high degree of agreement, and the relative error was up to10-3order of magnitude. The effects of current density and electrolyte flowrate on polarizations during the charge and discharge processes are investigated. The model results indicate that ohm resistances in charge and discharge process are1.465Ω·cm2and1.537Ω·cm2respectively. The increase of current density results in the increase of electrochemical polarization, the sharply raise of electrochemical polarization occurred in the end of charge and discharge process is caused by the insufficiency of active substances. When the electrolyte flowrate increase within certain range, three polarizations decreases slightly and the battery performance can be improved. Based on the polarization analysis, the ohm polarization is the most part of total polarization, and the battery voltage efficiency can be improved by the decease of ohm resistance.The Electrochemical Impedance Spectroscopy of VRB single cell and corresponding plausible equivalent circuit model have been investigated, the accuracy of the model (chi square) reach to10-6. The model contains ohm resistance, a constant phase angle element (CPE) standing for double electrical layer on porous electrode, charge transfer resistance and Warburg resistance. It is found that the EIS charge and discharge ohm resistance are2.316Ω·cm2and2.375Ω·cm2respectively, which are larger than the values that calculated by transient boundary voltage method. It is can be explained that the former is AC resistance while the latter is DC resistance.The two equivalent circuit models are similar, they are not only can be used for battery performance analysis and operation monitor, but also for coupling with power generation module, building up a power generation and energy storage hybrid system and the management of the system energy.