Flow field structure of bionic monocotyledon vein and application of flow field structure in all-vanadium redox flow battery

Abstract

The invention discloses a flow field structure of a bionic monocotyledon vein and application of the flow field structure in an all-vanadium redox flow battery, the flow field structure comprises a rib part of the flow field structure, a flow branch, a flow field inlet, a flow field outlet and a main channel, the main channel is arranged between the flow field inlet and the flow field outlet, flow branches with a certain distance are arranged on the two sides of the main channel, and ribs of a flow field structure are arranged between the flow branches. The unique flow field structure design improves the battery performance in principle by optimizing the electrolyte flow path, has huge potential in the practical engineering application of a large-scale energy storage system, and has the core advantages of improving the electrolyte distribution uniformity, reducing concentration polarization and the like. A reliable technical scheme is provided for improving the overall performance of the battery, and the high requirements of a large-scale energy storage scene for the performance and stability of the battery can be effectively met.

Description

Technical Field

[0001] The present invention relates to the technical field of all-vanadium redox flow batteries (VRFBs), and in particular to a flow field structure that mimics the veins of monocotyledonous plants and its application in all-vanadium redox flow batteries, for optimizing electrolyte distribution, reducing pump power loss, and improving battery system efficiency. Background Art

[0002] Against the backdrop of global dual-carbon goals and energy restructuring, many countries are actively increasing new capacity from renewable energy sources such as wind and solar. However, these renewable energy sources are characterized by randomness and intermittency, which inevitably impacts the stability and quality of power output. To address this issue, energy storage technology has become crucial, and vanadium oxide flow batteries (VRFBs), as a mature technology, have attracted considerable attention.

[0003] As a device capable of storing large amounts of energy, flow batteries offer the advantages of rapid response and flexible regulation. However, their performance is affected by the design of their internal flow field. Careful design of the flow field is essential to reduce system losses, optimize electrolyte distribution, and mitigate the effects of concentration polarization.

[0004] However, flow field design also faces some challenges and limitations. First, uneven flow may cause local changes in electrolyte concentration, thereby affecting the performance and cycle stability of the battery. Second, in order to ensure the constancy of the flow, the flow field design usually requires a certain level of pressure, which may cause the battery to lose more power. In addition, the electrolyte flow must overcome the flow resistance, which also causes energy loss and reduces the overall efficiency of the battery. In addition, due to the instability of the flow, problems such as eddy currents or turbulence may occur, resulting in local pressure changes and uneven electrolyte distribution, which in turn affects the performance and service life of the battery.

[0005] Therefore, in the development of flow battery technology, it is necessary to continuously optimize the flow field design to overcome these challenges, improve the performance and reliability of the battery, and thus better meet the requirements of the global dual carbon goals.

[0006] Many scholars have worked hard to study and overcome the shortcomings of these flow fields. They have improved the performance of the battery flow field and minimized energy loss by optimizing the flow field design, improving the electrode structure, using advanced computational simulation technology, and selecting more optimized materials. Chu et al. designed a double-sided cross flow field (IFF) to improve mass transfer behavior. The results showed that the double-sided IFF has higher output net power, system efficiency, and distribution uniformity. Guo et al. proposed a bifurcated cross flow field that separates the electrolyte by layers and transports it into branch channels, thereby reducing pumping losses and enhancing the uniformity of electrolyte distribution. Hao et al. adjusted the flow field design on the carbon felt electrode, significantly reducing concentration polarization and achieving a high efficiency at 200 mA cm -2 The results significantly improved discharge capacity and power density and have great potential for scaling up to practical flow battery stacks. Pan et al., based on a traditional serpentine flow field design, gradually reduced the channel depth from the inlet to the outlet and found that an optimized gradient at 25% resulted in the highest pump-based voltage efficiency. Sun et al. summarized the progress and prospects of flow field design and optimization, focusing on the scale-up process. Sun Jie et al. modified the distribution of hydraulic resistance under the ribs to improve distribution uniformity and designed three different simulation verification methods. Wei et al. proposed and fabricated a flow field for convection enhancement of aqueous redox flow batteries to enhance sub-rib convection between adjacent flow channels. Wang et al. proposed a novel pluggable current collector for in-service current distribution measurement, which greatly simplified the process of measuring current density distribution in VRFBs with flow fields. Huang et al. used a variable flow rate and current density charge-discharge method to improve energy efficiency and system efficiency by 9.07% and 8.34%, respectively, thereby significantly improving energy storage capacity. Chai et al. proposed a novel double-helix flow channel design to evaluate performance by introducing different flow patterns within the VRFB. Duan et al. investigated the effects of electrode parameters and operating conditions on the performance of serpentine and interdigitated flow fields and discussed the influence of electrode porosity on these two structures. Zhong et al. designed a novel biomimetic lung-shaped flow field that reduced the charge voltage, increased the discharge voltage, and improved mass transfer performance. Akuzum et al. investigated the effects of varying flow channel depth, showing that adding a slope resulted in a significant 40% decrease in the required pumping pressure. Summary of the Invention

[0007] All-vanadium redox flow battery (VRFB) is an important technology that can achieve large-scale, large-capacity, long-term energy storage. In the battery structure, flow field design plays a vital role, which can significantly improve the uniformity of electrolyte distribution while minimizing pumping losses. Inspired by the excellent nutrient transport process of leaf veins in nature, the present invention proposes a flow field design for a flow battery with a bionic leaf vein structure. Through extensive research, another novel flow field design was obtained by innovatively adding obstructions in the main channel, which demonstrated the superior advantage of achieving uniform distribution of electrolyte concentration. Improve the pump-based efficiency of the system and increase the average concentration of active substances. These results demonstrate the advantages of these two new designs in high-performance VRFBs. At the same time, the simple, effective and easily scalable design mechanism enhances the potential of VRFBs in engineering applications.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] A flow field structure of a bionic monocot leaf vein includes ribs of the flow field structure, flow branches, a flow field inlet, a flow field outlet, and a main channel. The main channel is arranged between the flow field inlet and the flow field outlet, and flow branches are arranged at a certain distance on both sides of the main channel. The ribs of the flow field structure are arranged between each flow branch.

[0010] Furthermore, flow branches with a distance of 0.5 mm are provided on both sides of the main channel.

[0011] Furthermore, there is one main channel and 16 flow branches.

[0012] Furthermore, each flow branch 3 is distributed at an angle of 45° to the main channel 6, and the flow branches on both sides of the main channel are completely symmetrical.

[0013] Furthermore, the main channel is 1.5 mm wide.

[0014] Furthermore, the spacing and angles of the flow branches follow the fractal formula to ensure the self-similarity of the flow channel network:

[0015] L n =L0·r n ,θ n =θ0·cosα

[0016] Among them, L n is the length of the n-th branch, r is the fractal scaling factor, θ n is the branch angle, and α is the fluid diffusion angle.

[0017] Furthermore, the pressure gradient equation of the flow field structure is: the flow-blocking structure reduces the overall pressure difference by changing the local flow velocity:

[0018]

[0019] Among them, μ is the viscosity of the electrolyte, q is the flow rate, L is the length of the flow channel, w and h are the width and height of the flow channel, A i / A0 is the cross-sectional area ratio of the flow branch to the main channel.

[0020] Furthermore, the area size of the entire flow field structure is a square of 20 mm×20 mm.

[0021] Furthermore, the flow channel depth is 1 mm.

[0022] The present invention also provides an application of a flow field structure of a bionic monocot leaf vein (abbreviated as: bionic leaf vein flow field structure) in an all-vanadium liquid flow battery. The all-vanadium liquid flow battery system includes a positive electrode liquid storage tank, a first peristaltic pump, a first end plate, a first current collecting plate, a first fixing frame, a first flow channel, a first porous electrode, a proton exchange membrane, a second porous electrode, a second flow channel, a second fixing frame, a second current collecting plate, a second end plate, a second peristaltic pump, and a negative electrode liquid storage tank.

[0023] Compared with the prior art, the present invention has the following technical advantages:

[0024] (1) LFF significantly reduces the flow field pressure drop and pumping energy consumption through the bionic hierarchical branching structure. The flow channel design based on Murray's law makes the main channel and the branch channel form an optimized geometric ratio (satisfying r1 3 =∑r2 3 The branching network shortens the flow path by 48%, reducing pump power to 13.1 mW at 180 mL / min (compared to 46.7 mW for SFF), and energy loss by 65%, effectively suppressing the nonlinear growth of energy consumption at high flow rates.

[0025] (2) LFF significantly optimizes the uniformity of active material concentration distribution and alleviates the concentration polarization effect. In the concentration gradient analysis in the electrode depth direction (2L / 3 section), the gradient value of LFF at 120mL / min is only 1.3mol·m-3 / mm, which is 65% lower than that of SFF at 3.71mol·m-3 / mm. Its branching structure enhances the convection under the ribs, which increases the lateral penetration depth of the electrolyte by 40%. At SOC=0.6, the average electrode concentration is 3.5% higher than that of SFF, and the concentration depletion phenomenon in the outlet area is eliminated, especially at high flow rates (180mL / min), ensuring the effective utilization of deep electrode active materials.

[0026] (3) LFF has achieved a breakthrough in overall battery efficiency. The polarization curve shows that at 100 mA cm-2 At the current density, the LFF output voltage reaches 1.32574V, which is 0.18% higher than that of SFF, and the voltage fluctuation is reduced by 30%. The charge and discharge test shows that the LFF discharge voltage (1.318V) is 0.7% higher than that of SFF at SOC = 0.6, and the power efficiency is 60mA·cm -2 The SFF is 0.82774, and the system efficiency is improved by 10%, ultimately achieving an overall leap in battery energy conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the flow field structure of the bionic monocotyledonous plant vein of the present invention.

[0028] Figure 2 Schematic diagram of the flow direction of the electrolyte in the flow field.

[0029] Figure 3 Schematic diagram of the VRFB system composition.

[0030] Figure 4 Schematic diagram of the bionic leaf vein 3D model.

[0031] Figure 5 Polarization curve diagram.

[0032] Figure 6 It is a charge and discharge curve diagram.

[0033] Figure 1 In the figure, 1 is the confluence of the branch ends of the flow field structure, 2 is the rib of the flow field structure, 3 is the flow branch of the flow field structure, 4 is the flow field inlet, 5 is the flow field outlet, and 6 is the main channel. DETAILED DESCRIPTION

[0034] like Figure 1 、 2 As shown, the present invention draws inspiration from leaf veins and proposes a bionic leaf vein flow field (LFF). The flow field has a main channel 6 between the flow field inlet (4) and the flow field outlet (5), similar to the central vein in a leaf. On both sides of the main channel 6, there are flow branches 3 with a fixed distance (0.5 mm) leading to the flow field outlet (5). The flow field structure ribs 2 are provided between each flow branch 3, and the branch ends of the flow field structure converge at 1.

[0035] The flow field has a main channel (6) and 16 flow branches (3). The main channel is 1.5 mm wide, and each flow branch (3) is 0.5 mm wide. The overall flow channel area is a 20 mm × 20 mm square, and the flow channel depth is 1 mm. Each flow branch 3 is distributed at a 45° angle to the main channel 6. The flow branches 3 on both sides of the main channel 6 are completely symmetrical. The lower left is the electrolyte flow field inlet 4, and the upper right is the electrolyte flow field outlet 5. The flow field inlet 4 and the flow field outlet 5 are connected by a peristaltic pump in the all-vanadium redox flow battery (VRFB) system to achieve the flow of electrolyte in the flow field.

[0036] The structure of the main channel and flow field branches: imitating the hierarchical fractal distribution of monocot leaf veins, the main channel (main vein-like) connects the flow field inlet and the flow field outlet, and the secondary branch flow branches extend symmetrically on both sides at intervals of 0.5 mm.

[0037] Fractal geometry model: The spacing and angles of flow branches follow the fractal formula to ensure the self-similarity of the flow channel network:

[0038] L n =L0·r n ,θ n =θ0·cosα

[0039] Among them, L n is the length of the n-th branch, r is the fractal scaling factor (taken as 0.7), θ n is the branch angle, and α is the fluid diffusion angle (optimized to 15°).

[0040] Pressure gradient equation: The flow-blocking structure reduces the overall pressure difference by changing the local flow velocity:

[0041]

[0042] Among them, μ is the viscosity of the electrolyte, q is the flow rate, L is the length of the flow channel, w and h are the width and height of the flow channel, A i / A0 is the cross-sectional area ratio of the flow branch to the main channel.

[0043] Improved mass transfer efficiency: The flow-blocking structure enhances the convection term (Nernst-Planck equation) and reduces concentration polarization:

[0044]

[0045] Where j is the material flux, D is the diffusion coefficient, and v is the flow velocity.

[0046] like Figure 3As shown, the entire all-vanadium redox flow battery (VRFB) system includes a positive electrode liquid storage tank (for storing electrolyte), a first peristaltic pump, a first end plate, a first current collecting plate, a first fixing frame, a first flow channel, a first porous electrode, a proton exchange membrane, a second porous electrode, a second flow channel, a second fixing frame, a second current collecting plate, a second end plate, a second peristaltic pump, and a negative electrode liquid storage tank (for storing electrolyte). The first end plate, the first current collecting plate, the first fixing frame, the first flow channel, the first porous electrode, the proton exchange membrane, the second porous electrode, the second flow channel, the second fixing frame, the second current collecting plate, and the second end plate are arranged in sequence. The positive electrode liquid storage tank is connected to the first end plate via an upper pipeline (first pipeline) and a lower pipeline (second pipeline), and the lower pipeline (second pipeline) is equipped with a first peristaltic pump; the negative electrode liquid storage tank is connected to the second end plate via an upper pipeline (third pipeline) and a lower pipeline (fourth pipeline), and the lower pipeline (fourth pipeline) is equipped with a second peristaltic pump.

[0047] The location of the flow field structure of the bionic monocotyledonous plant vein proposed in the present invention is the red circular frame.

[0048] 3D models such as Figure 4 As shown, the pink highlight shows the 3D structure diagram of the flow field structure of the bionic monocot leaf vein.

[0049] like Figure 5 As shown in Table 1-4, the polarization curve shows that at 100mA·cm -2 At the current density, the LFF output voltage reaches 1.32574V, which is 0.18% higher than that of SFF, and the voltage fluctuation is reduced by 30%. The charge and discharge test shows that the LFF discharge voltage (1.318V) is 0.7% higher than that of SFF at SOC = 0.6, and the power efficiency is 60mA·cm -2 The SFF is 0.82774, and the system efficiency is improved by 10%, ultimately achieving an overall leap in battery energy conversion efficiency.

[0050] Table 1 Polarization curve data (V)

[0051] Current density SFF LFF 25 1.3494 1.3504 50 1.3404 1.3422 75 1.33187 1.33397 100 1.32334 1.32574 125 1.31474 1.31874 150 1.3067 1.31174 175 1.298 1.30374 200 1.2875 1.29572

[0052] Table 2 Output power efficiency (%)

[0053] Current density SFF LFF 60 0.82774 0.91896 120 0.80691 0.89583 180 0.76264 0.89423

[0054] Table 3 System efficiency (%)

[0055] Current density SFF LFF 60 0.76392 0.86428 120 0.71403 0.84391 180 0.6316 0.81161

[0056] Table 4 Charge and discharge curve (V)

[0057] SOC LFF-discharge SFF-Discharge LFF-Charging SFF-Charging 0.9 1.4055 1.4237 1.47497 1.46727 0.8 1.3664 1.3843 1.4318 1.42495 0.7 1.34 1.3577 1.403 1.39719 0.6 1.318 1.3358 1.38108 1.37462 0.5 1.2977 1.3154 1.36 1.35405 0.4 1.2772 1.2949 1.34008 1.33362 0.3 1.2546 1.2724 1.319 1.31152 0.2 1.2268 1.2446 1.29164 1.28482 0.1 1.184 1.2022 1.25282 1.24521

[0058] like Figure 6 As shown in the figure, the numerical comparison of the charge voltage and discharge voltage of the simulation data and the experimental data, where the current density is 40mA / cm 2 , the inlet flow rate is 180ml / min.

[0059] The present invention uses 3D multi-physics simulation to verify that the proposed LFF flow field can better improve the average reactant concentration and distribution uniformity coefficient of the porous electrode. When the flow rate is low (0.5 ml / s) and the current density is 40 mA / cm2, the output power-based efficiency of OLFF is 1.5% higher than that of LFF. When the flow rate is high (3 ml / s) and the current density is 40 mA / cm2, the pump-based efficiency of OLFF is 4.5% higher than that of LFF. Under various conditions, V 2+ The concentration of electrolytes increases by an average of approximately 3%. Due to the obstruction blocks in the OLFF, the electrolyte is forced to flow through the branches. The distribution of active species within the projected region of the main channel is roughly the same as that in the surrounding area. This significantly improves the uniformity of electrolyte distribution and further reduces the impact of concentration polarization on the overall battery performance. Therefore, the overall performance of the battery can be significantly improved due to the innovative design of the flow field. This design has great potential for practical engineering applications in large-scale energy storage systems.

Claims

1. A flow field structure of a bionic monocot leaf vein, characterized in that: It includes ribs of flow field structure, flow branches, flow field inlet, flow field outlet and main channel. A main channel is set between the flow field inlet and the flow field outlet, flow branches are set at a certain distance on both sides of the main channel, and ribs of flow field structure are set between each flow branch.

2. The flow field structure of the bionic monocot leaf vein according to claim 1, characterized in that: Flow branches with a distance of 0.5 mm are set on both sides of the main channel.

3. The flow field structure of the bionic monocot leaf vein according to claim 2, characterized in that: There is one main channel and 16 flow branches.

4. The flow field structure of the bionic monocot leaf vein according to claim 3, characterized in that: Each flow branch 3 is distributed at an angle of 45° to the main channel 6, and the flow branches on both sides of the main channel are completely symmetrical.

5. The flow field structure of the bionic monocot leaf vein according to claim 4, characterized in that: The main channel is 1.5 mm wide.

6. The flow field structure of the bionic monocot leaf vein according to claim 3, characterized in that: The spacing and angles of the flow branches follow the fractal formula to ensure the self-similarity of the flow channel network: L n =L0·r n ,i n =θ0·cosα Among them, L n is the length of the n-th branch, r is the fractal scaling factor, θ n is the branch angle, and α is the fluid diffusion angle.

7. The flow field structure of the bionic monocot leaf vein according to claim 6, characterized in that: Pressure gradient equation of flow field structure: The flow-blocking structure reduces the overall pressure difference by changing the local flow velocity: Among them, μ is the viscosity of the electrolyte, q is the flow rate, L is the length of the flow channel, w and h are the width and height of the flow channel, A i / A0 is the cross-sectional area ratio of the flow branch to the main channel.

8. The flow field structure of the bionic monocot leaf vein according to any one of claims 1 to 7, characterized in that: The area size of the entire flow field structure is a square of 20 mm × 20 mm.

9. The bionic monocot leaf vein flow field structure according to claim 8, characterized in that: The flow channel depth is 1 mm.

10. Application of the bionic monocot leaf vein flow field structure according to any one of claims 1 to 9 in an all-vanadium redox flow battery, characterized in that: The all-vanadium liquid flow battery system includes a positive electrode liquid storage tank, a first peristaltic pump, a first end plate, a first current collecting plate, a first fixing frame, a first flow channel, a first porous electrode, a proton exchange membrane, a second porous electrode, a second flow channel, a second fixing frame, a second current collecting plate, a second end plate, a second peristaltic pump, and a negative electrode liquid storage tank.

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