Modeling And Analysis Of Single Flow Zinc-Nickel Battery

Single flow zinc-nickel battery is a kind of deposition redox flow battery with alkaline electrolyte.It only uses one electrolyte and one electrolyte storage tank,and does not use ion exchange membrane.It has a high application prospect in large-scale energy storage technology because of its advantages of flexible site selection,simple structure and low cost.The modeling research is of great significance for studying the internal mechanism,facilitating the performance improvement of redox flow battery.From the perspective of experiment and mechanism,the fourth-order equivalent impedance model was established by electrochemical impedance spectroscopy(EIS),and the two-dimensional dynamic electrochemical model was established based on electrochemical principle,which provides guidance for the follow-up research work such as state estimation and structure optimization of single flow zinc-nickel battery.Based on EIS measurement experiment,a fourth-order equivalent impedance model of single flow zinc-nickel battery was established and its component parameters were identified.Firstly,the EIS of single flow zinc-nickel battery was measured.Then,aiming at the problem that the structure of the equivalent circuit model of the battery is not accurate enough to depend on experience,the fourthorder equivalent impedance model of the single flow zinc-nickel battery was established by using the relaxation time distribution technique,which provides a feasible experimental reference for the structure determination of the equivalent circuit model of the battery.Finally,an improved gray wolf optimization algorithm(Gr GWO)was proposed to identify the element parameters of the fourth-order equivalent impedance model.The average relative error of the fourth-order equivalent impedance model identified by the algorithm is less than1%,and the average relative error of the imaginary part is less than 6%.Based on the electrochemical mechanism,a two-dimensional dynamic electrochemical model of single flow zinc-nickel battery was established.In order to study the phenomenon of concentration distribution and potential polarization,aimed at the problem of hard to through the experiment to measure the ion concentration distribution of single flow zinc-nickel battery,a two-dimensional transient electrochemical model was set up combined with the fluid flow equation,mass transfer equation,potential distribution equation and electrode kinetics equation.The model was simulated by finite element analysis software,and compared with the output voltage-time curve measured by constant current charge-discharge experiment of the single flow zinc-nickel battery,the reliability of the model was verified.The dynamic distribution characteristics of ion concentration and over potential were simulated.Modelling the influence of different electrolyte inlet velocity and different electrode porosity on ion concentration and over potential distribution,results showed that the concentration polarization and potential polarization of the ions near the cathode boundary can be reduced by increasing the electrolyte inlet velocity.Increasing the porosity of the porous electrode will increase the concentration polarization and decrease the potential polarization in the porous positive domain.