Performance Test Of All Vanadium Flow Battery And Influence Of Assembly Stress

All-Vanadium Redox Flow Battery(VRB)is a new technology that can be used in large-scale energy storage.Because of its long service life,large battery capacity,and high battery efficiency,it has been widely used.in new energy source power supply,remote power supply systems,and island management and maintenance.However,since the energy density of the all-vanadium redox flow battery is not high enough and it is difficult to operate stably under extreme temperature conditions,so that it is difficult to apply in wider fields.The study found that there are two main ways to increase the energy density of the flow battery,namely improving the polarization phenomenon and improving the electrochemical reaction process.In order to understand the energy loss during the charging process and the distribution characteristics of vanadium ions in VRB,this article used the experimental and numerical simulation methods to study the charge and discharge process and the inherent laws of mass transfer process of the electrolyte in VRB.This article first introduced the basic theories of electrochemical thermodynamics and electrode process dynamics involved in the research of vanadium redox flow battery.Then we established a VRB test platform consisting of charging device,electronic load,electrolyte storage tank,peristaltic pump,battery monitoring system,computer management system,etc.After the successful commissioning,a variety of VRB flow field plates were installed for testing,and emphasized the procedures and precautions to be followed in the operation of the test platform.Using the test platform above,the charge and discharge process and AC impedance of VRB were tested.The parameters of charge and discharge characteristics,battery impedance,and battery efficiency of the battery were analyzed under different flow field conditions and electrolytes flow.The study found that:Comparing traditional parallel and serpentine flow field plates with self-designed turtle-shaped and spiral flow field plates,the battery's charge and discharge performance is improved,the rate of chemical reactions is accelerated,and the time for charge of VRB is shortened,faraday impedance decreases,battery Coulomb efficiency,voltage efficiency,and energy efficiency increase;the electrolyte flow distribution during the electrode reaction is improved,reducing the concentration polarization and electrochemical polarization of the electrolyte during the reaction;When the state of charge of' the flow battery is the same,the discharge duration of the battery is positively correlated with the flow rate of the electrolyte,and the corresponding voltage efficiency and energy efficiency are improved.The change of the flow field structure enhances the overall performance of the vanadium redox flow battery and impoves the efficiency of battery,which is of impetus in the follow-up study of all-vanadium redox flow battery.Basing on solid mechanics,fluid dynamics,mass transfer and electrochemical principle,a hybrid model was established by coupling different physics fields using COMSOL software.The stress distribution,deformation distribution,effective porosity distribution of graphite felts and the current distribution for vanadium redox flow batteries were analyzed using COMSOL software,and analyzed the influence of assembly prestress on the above parameters.The study found that under the action of assembly prestress,the stress and deformation of the graphite felt under the flow ridge is larger than the stress and deformation of the graphite felt under the flow channel,and inhomogeneity of the stress and deformation distribution of the graphite felt is increased with the increase of the assembly prestress,which resulting the porosity in the electrode is reduced and unbalanced;porosity in the graphite felt under flow ridges is reduced more,and porosity in graphite felts under the flow path is reduced less.Due to the non-uniformity of the porosity in the graphite felt,the reaction resistance of reactants and products in the electrode of VRB is not uniform,so the current density distribution in the graphite felt is not uniform,and the greater the assembly prestress,the more uneven the current density in the graphite felt.When the electrode reacts,the total electrolyte flow is constant,the assembly force increases,the electrolyte flow at the flow ridge compression site decreases,and the electrolyte flow rate at the proton exchange membrane increases,so that the electrode reaction current density near the proton exchange membrane increases,the current density of the electrode reaction decreases at the ridge compression.