Study On Electrochemical Reaction Mechanism Of Porous Electrode Of Single-flow Battery Based On REV Scale LBM

The energy depletion and environmental pollution problems caused by the excessive use of conventional fossil energy have made renewable clean energy technology develop rapidly.In order to solve the intermittent and stability problems of new energy technology,large-scale energy storage technology came into being.The redox flow battery,as an effective technical means for large-scale energy storage technology,has been widely developed in recent years because of its unique advantages.Zinc-nickel single-flow battery is a type of redox flow battery,and it is a single-flow battery system proposed by the Institute of Chemical Control in 2007.It has the characteristics of simple system,high energy efficiency,low cost and long cycle life,and has become an effective technical means for large-scale energy storage.In order to further optimize its working performance,it is particularly important to simulate and analyze its chemical reaction mechanism.Based on this,and on the basis of this research group,this paper uses the REV scale lattice Boltzmann to analyze and study the internal flow and mass transfer process.The work done includes the following:1)Based on the analysis of the shape characteristics and seepage characteristics of the positive electrode of zinc-nickel single flow battery.Selecting the appropriate mathematical model of REV scale LBM.In the main influencing parameters of the model,namely the equilibrium distribution function and the force processing of the evolution process,the force processing method of the micropore seepage model proposed by Guo et al.The parameters required for calculation were obtained through experiments and pore-scale simulation,and a complete mathematical model of seepage inside the porous electrode was established.2)At the same time,considering the structural characteristics of the battery stack,a part of a single flow channel(including the porous positive electrode material)is delineated as the calculation domain of the seepage calculation.Using the above model,on the basis of ensuring that it can be accurately expanded into the macro-control equation,the REV scale lattice Boltzmann method is used to solve the distribution of the flow field in the calculation domain.The changes of the internal seepage flow by changing the conditions such as the width of the flow channel and the thickness of the positive electrode were investigated,and the change of the average flow velocity in the direction of the flow channel and the thickness of the electrode was analyzed.The simulation results show that changing the two conditions does not affect the basic structure of the flow field inside the porous electrode,but it will change the overall seepage velocity.The greater the thickness of the electrode,the lower the overall seepage velocity.The larger the width of the flow channel,the smaller the overall seepage velocity.3)A REV scale model that can describe the mass transfer and electrochemical reaction in the positive porous medium of the zinc-nickel single-flow battery is established,and the lattice Boltzmann method is used to analyze and calculate the transient charging process of the battery.The distribution rule of the concentration in the pores during charging is obtained.Explored the transient process of battery charging,the influence rules of charging current density,porous positive electrode thickness and porous electrode porosity on the concentration difference of hydroxide ion along the flow channel direction on the near flow channel side,the far flow channel side and between the two sides.The influence of the above three factors on the mass transfer and chemical reaction inside the battery is analyzed and compared.And the simulation results show that increasing the current density can reduce the charging time,but the effect of reducing the charging time gradually decreases with the increase of the current density.Excessive current density may cause excessive concentration difference in the thickness direction of the electrode Polarization;and the increase of the electrode thickness will increase the diffusion resistance of-ions from the near channel side to the far channel side.Excessive electrode thickness will cause excessive concentration polarization;when the porosity is small,The diffusion resistance of-ions will increase,so that the concentration polarization will increase,and when the transmission resistance of-increases,it will adversely affect the electrochemical reaction inside the electrode.And through analysis,it is found that the thickness of the electrode has the greatest influence on the mass transfer and electrochemical reaction of the porous electrode among the above three factors.After research and analysis of the above work,some general rules about the mass flow in the positive electrode of zinc-nickel single-flow battery are obtained.