| Renewable energy has the characteristics of randomness,intermittency and volatility.Large-scale energy storage technology occupies a very important position in the large-scale utilization of renewable energy.Vanadium redox flow battery is one of the most promising large-scale energy storage technologies due to its many advantages.The rational flow field design is expected to play an important role in improving the overall performance and reducing the system cost of vanadium redox flow battery.The spacing between neighboring interdigitated channels is one key design parameter of the interdigitated flow field for vanadium redox flow batteries,since it directly influences the flow distribution and velocity magnitude of the electrolyte across the entire porous electrode,thus simultaneously impacting on the pumping loss and mass transport loss.It is not clear how channel spacing affects overall battery performance（including energy efficiency,pumping losses,and electrolyte utilization）and equipment costs under a wide range of operating conditions,including flow rates and operating current density.The negative redox electric pair exhibits poor kinetic performance on carbon electrode,resulting in activation loss and poor performance,resulting in large battery stack size,high cost and difficult to large-scale application.In order to improve the battery performance and reduce the cost of the battery system,the following work is carried out in this paper:Firstly,a CFD model is developed to calculate the pressure drop and pumping loss of the batteries based on interdigitated flow field with different channel spacing and flow rates.The pressure drop and pump power analysis of the battery were carried out,and the experiment was determined at the channel spacing of 13,20,26 and 38 mm.The distribution of flow velocity and pressure inside the electrode shows good periodicity and symmetry.Based on this,the representative unit of the interdigitated flow field is selected to design the graphite plates.Secondly,representative unit of the cells with different channel spacings were designed and fabricated.An experimental platform was built to conduct electrochemical tests on the battery under different working conditions to investigate the output cell performance with different temperature,operating current density,flow rate and channel spacing.The optimal operating temperature of the battery is 35°C.With the increase of current density,voltage efficiency and energy efficiency decrease,coulomb efficiency increases,electrolyte utilization and pump-based voltage efficiency decreases.With the increase of electrolyte specific flow rate,voltage efficiency and electrolyte utilization increases,pumping loss increases,and the pump-based voltage efficiency and energy efficiency increases first and then decreases.With the increase of the channel spacing,the voltage efficiency,electrolyte utilization and the pumping loss increases,the pump-based voltage efficiency and energy efficiency first increases and then decreases.Thirdly,based on the electrochemical behavior and pumping loss,cost-performance analysis of vanadium redox flow batteries is conducted to reveal the mechanism how the design and operation parameters quantitatively impact on the overall performance and cost of the battery.It is concluded that the optimal flow channel spacing of the battery based on the interdigital flow field is 26 mm under different discharge scenarios.The battery system is operated with a fixed specific flow,the vanadium redox flow battery with the channel spacing of 26 mm can achieve the lowest device cost of$205 k Wh-1 with the electrolyte utilizaiton of 67.3%at the operating current density of 132.6 m A cm-2 and the specific flow rate of 1.0 m L min-1 cm-2 with the energy efficiency of 81.4%for 4 MWh discharge duration.A method of battery operation under the mode of changing specific flow is proposed.In this way,the optimal specific flow combination is 0.5-1.0 m L min-1 cm-2.The case of 26-mm channel spacing has the lowest device cost of$208 k Wh-1 with the electrolyte utilizaiton of72.5%for 4 MWh discharge duration,and the pump-based energy efficiency is 80.1%and operating current density is 110.2 m A cm-2.Finally,the electrodeposition conditions of bismuth catalysts were studied on the optimal interdigitated flow field structure.The effects of electrodeposition current density and ion concentration on battery performance were explored.When the bismuth catalyst loading is 1 mg cm-2,the initial concentration of bismuth catalyst is 4 mmol L-1,and the electrodeposition current density is 9.65 m A cm-2,the vanadium redox flow battery has the highest efficiency.At the current density of 280 m A cm-2,the voltage efficiency of the battery is as high as 83.7%.In the 4 MWh discharge scenario,the pump-based energy efficiency reaches 82.5%,the operating current density is increased to 159.50 m A cm-2,the electrolyte utilization rate is as high as 70.8%,and the battery system cost is reduced to$180 k Wh-1. |
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