Design And Multi-physics Simulation Of Flow Battery For Long-Term Energy Storage Applications

The flow battery is one of the preferred technologies in the field of long-term energy storage in power systems.Combined with renewable energy,it can meet the requirements of smart grid for high security,low cost and environmentally friendliness.However,the most mature all-vanadium flow battery has limited the further commercial development of all-vanadium flow battery with high power density in recent years,due to the rising price of vanadium and the high flow resistance and high polarization of the stack.Therefore,solving the problems of high flow resistance and high polarization of the stack and developing a new generation of low-cost and transformative flow battery energy storage technology are effective ways to break through the existing industrialization bottleneck.Among them,all-iron flow battery with obvious cost advantage has attracted the attention of some scholars.However,due to the uneven deposition of iron under neutral conditions,the reversibility of deposition and dissolution is poor,and the side reaction of hydrogen evolution is serious,there is still a certain distance from commercial large-scale application.Therefore,this paper carries out research from the following two aspects:Firstly,this paper adopts the method of combining simulation and experiment,and uses the flow channel design to synergically reduce the concentration polarization and pressure drop to improve the power density and reduce the pump loss in accordance with the problem of high flow resistance and high polarization of the all-vanadium flow battery under high current density.Secondly,aiming at the problem of poor reversibility of deposition and dissolution in the charging process of the iron negative electrode of neutral all-iron flow battery,the influence factors of the deposition process are also analyzed though the combination of experiment and simulation,so as to provide theoretical guidance for improving the reversibility of deposition and dissolution.Firstly,two different types of flow channels,interdigitated and parallel were designed on the carbon felt electrode for all-vanadium flow battery,and compared with the original carbon felt.The finite element simulation results show that the pressure drop of carbon felt designed with interdigitated and parallel channels is significantly reduced,the reactant distribution is more uniform,and the flow rate along the channel is accelerated.On the basis of measuring the local mass transfer coefficients,at a high current density of up to 200 mA cm-2,the finger and parallel channel designs greatly reduce the concentration polarization,and the parallel channel is superior to the finger channel design.Finally,the dynamic model prediction results of industrial-scale stack highlight a desirable system efficiency of ca.70%for the parallel channel design at 200 mA cm-2,which benefits largely from minimized pumping energy losses and lowered concentration polarizations at the end of charge/discharge.In order to improve the reversibility of deposition and dissolution of low-cost alliron flow battery and promote its further development,the effects of Fe2+ concentration,operating temperature and applied current density on the electrodeposition process of iron in neutral environment were investigated by scanning electron microscopy,atomic force microscopy and simulation.Scanning electron microscopy and atomic force microscopy showed that the concentration of 0.4 mol L-1,the temperature of 40℃ and the low current density of 10 mA cm-2 were favorable to obtain uniform and compact morphology of iron deposition.The further simulation results help to reveal that the reason for the uneven deposition at high concentration,low temperature and high current density is that the reaction consumption rate of Fe2+near the substrate is greater than the diffusion rate of Fe2+ from the solution body to the electrode surface,which makes the concentration polarization larger.On this basis,when the current density distribution on the electrode surface is not uniform,Fe2+ preferentially deposits and accumulated on the top of the bulge with high current density,and even formed dendrites.Therefore,properly reducing the concentration of iron salt,increasing the temperature and decreasing the applied current density will be beneficial to obtain uniform and dendrite-free deposition morphology,improve the reversibility of deposition and dissolution,thus extending the cycle life and promoting the further development of cost-effective and environmentally friendly all-iron flow battery.