The Simulation Study Of Vanadium Redox Flow Battery With Carbon Paper Electrode

The application of energy storage technology can effectively solve the intermittent problem associated with the utilization of renewable energy.The vanadium redox flow battery has attracted great attention for medium and large-scale energy storage.A suitable flow field structure can be helpful to reduce the concentration polarization in the battery and it is an important way to improve the battery performance of vanadium redox flow battery.In this paper,a 3-D steady model of vanadium redox flow battery with carbon paper electrode is developed by taking into account the coupling processes of flow,mass transfer and electrochemical reactions.The battery performance,electrolyte distribution and pressure drop with different flow fields were studied in detail by the mathematical model.The purpose of this paper is to provide some theoretical references for the flow field design of vanadium redox flow battery.By comparing the serpentine and interdigitated flow field,it is shown that the convection flow in the electrode of the serpentine flow field is stronger than that in the interdigitated flow field,which causes the concentration of reactive ions at the electrode surface of serpentine flow field is higher.The cell performance with serpentine flow field is thus better than that with interdigitated flow field because of lower concentration polarization.However,the longer flow path and higher flow velocity lead to a larger pressure drop in the serpentine flow field.On the other hand,the interdigitated flow field has a better uniformity of electrolyte distribution in the electrode because of its structure with multi-channel branches.The effect of channel depth on the battery performance with serpentine flow field was studied.It is shown that the battery performance with smaller channel depth is higher.When the channel depth is smaller,the convection flow in the electrode is stronger and the mass transfer resistance of the electrolyte is smaller,which results in both higher surface concentration and pore concentration of the reactive ions,thus the concentration polarization is reduced and the battery performance is improved as the channel depth decreases.However,the velocity in the electrode increases with the decrease of flow depth,which causes larger pressure drop.The effect of channel and rib width on the battery performance with serpentine flow field was further studied.It is shown that a smaller channel width and rib width is beneficial to improve the battery performance.This is because when the channel width is fixed,a larger rib width makes the mass transfer in the electrode area under the rib get worse,resulting in lower pore concentration and surface concentration of the reactive ions,leading to a poor battery performance.When the rib width is fixed,a smaller channel width causes higher velocity of the electrolyte in both channel and electrode,therefore the mass transfer is enhanced and the concentration polarization is reduced.In addition,compared with the change of rib width,the battery performance is more sensitive to the change of channel width.This is because the change of channel width can lead to a larger change of velocity in the electrode than the change of rib width.However,when the channel width and rib width are small,the pressure drop is significantly high.The influence of operating conditions on the battery performance was studied by using serpentine flow field.The results show that the increase of SOC,the concentration of vanadium ions,electrolyte flow rate and the permeability of the electrode are all helpful to reduce concentration polarization in discharge process,leading to better performance of the battery.This is because as SOC and the concentration of vanadium ions increase,the concentration of reactive ions in the electrolyte increase significantly.As the electrolyte flow rate and the electrode permeability increase,the mass transfer resistance within the electrode is reduced.