Method for establishing relationship between hot-spot temperature and working parameters of all-vanadium redox flow battery

Abstract

The invention discloses a method for establishing a relationship between hot-spot temperature and working parameters of an all-vanadium redox flow battery. The method comprises the following steps: establishing a single battery three-dimensional geometric model suitable for representing temperature distribution by utilizing modeling software; performing electrochemical-flow-thermal coupling setting on the model, solving a battery temperature model and extracting the highest temperature; changing three working parameters of battery current density, inlet flow velocity and environment temperature, and respectively fitting relation equations of the battery hot-spot temperature and the three parameters by utilizing a least square method; establishing a multivariate linear regression equation of the three parameters and the hot-spot temperature of the battery to obtain a change rule of the hot-spot temperature of the battery, and giving working parameter setting suggestions of the all-vanadium redox flow battery based on temperature control in combination with engineering practice; according to the method, the characteristics of flexible setting and visual result of finite element simulation are fully utilized, the hot-spot temperature values of the battery under different working parameters can be accurately obtained, and data and method support is provided for theoretical research, design, operation and maintenance and the like of the all-vanadium redox flow battery.

Description

Technical Field

[0001] This invention belongs to the field of vanadium redox flow battery design and operation, specifically, it relates to a method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery. Background Technology

[0002] Vanadium redox flow batteries (VRBs) possess advantages such as high safety, long charge-discharge cycle life, recyclable electrolyte, and environmental friendliness, making them a promising candidate for long-term energy storage. However, temperature variations have a significant impact on VRB performance. For instance, in practical applications, higher temperatures can cause pentavalent vanadium ions to hydrolyze, forming insoluble V₂O₅ precipitates. These crystals or precipitates not only reduce the concentration of active materials in the battery but, more problematicly, can clog porous electrodes or flow channels, directly leading to battery failure. Therefore, studying the influence of battery operating parameters on temperature under steady-state conditions and identifying parameter settings that minimize hotspot temperatures during normal operation is of great significance.

[0003] Currently, research on vanadium redox flow batteries, both domestically and internationally, mainly focuses on the battery's electrochemical performance, including changing electrolyte composition and adjusting reaction mechanisms. Temperature monitoring is also largely limited to the effects of charging and discharging on battery temperature, with little exploration of the impact of battery operating parameters on temperature. Therefore, establishing an electrochemical-fluid-thermal finite element model of a vanadium redox flow battery is necessary to study the above aspects, providing a theoretical basis for the theoretical research and design of vanadium redox flow batteries.

[0004] To address the above issues, this invention establishes a method for determining the relationship between hotspot temperature and operating parameters of a vanadium redox flow battery. This method is used to determine the battery hotspot temperature under different current densities, inlet flow rates, and ambient temperatures, and provides parameter configuration suggestions. Summary of the Invention

[0005] In view of the shortcomings of the prior art, this invention proposes a method for establishing the relationship between the hot spot temperature and operating parameters of a vanadium redox flow battery. This method can solve problems such as the unclear influence of different current densities, inlet flow velocities, and ambient temperatures on the battery hot spot and the difficulty in calculation. It provides suggestions for optimizing parameter settings under the condition of ensuring normal battery operation, and provides data and methodological support for the theoretical research, design, construction, and operation and maintenance of vanadium redox flow batteries.

[0006] To solve the above technical problems, the present invention provides a method for establishing the relationship between the hot spot temperature and operating parameters of a vanadium redox flow battery, characterized in that the method includes:

[0007] Step S101: Determine the structure and actual size of the battery cell, and use modeling software to establish a three-dimensional geometric model of the vanadium redox flow battery cell;

[0008] Step S102: Set up the electrochemical-fluid-thermal coupling of the model, establish a temperature characterization model for a single vanadium redox flow battery cell, and solve and extract the highest battery temperature during the charging and discharging process;

[0009] Step S103: Change the battery current density, inlet flow rate, and ambient temperature, and plot the curves of the battery hot spot temperature changing with the three parameters and fit the equations.

[0010] Step S104: Compare the hot spot temperature distribution patterns of the battery under different parameters, and based on engineering practice, provide suggestions for setting the working parameters of the vanadium redox flow battery based on temperature control.

[0011] Furthermore, in step S101, the structure and actual dimensions of the battery cell are determined, and a three-dimensional geometric model of the vanadium redox flow battery cell is established using modeling software. Specifically, this includes:

[0012] Step S1011: Determine the structure and dimensions of the vanadium redox flow battery to be studied, including the location and size of its inlet and outlet channels;

[0013] Step S1012: Establish the geometric model of the battery using the geometry module of the finite element software, and note whether the electrode and the ion exchange membrane are clamped structures.

[0014] Furthermore, in step S102, the electrochemical-fluid-thermal coupling of the model is set up to establish a temperature characterization model for a single vanadium redox flow battery cell, and the highest battery temperature during charge and discharge is solved and extracted. Specifically, this includes:

[0015] Step S1021: Determine the simulation software, such as Comsol or similar computer-aided design software, select the steady-state analysis type, and select appropriate physical fields according to the software settings to complete the settings in electrochemistry, fluid flow, and heat transfer.

[0016] Step S1022: Set the manifestation of the porous structure of the positive and negative electrodes in the electrochemical field, flow field, and heat transfer field, and set its porous matrix and fluid characteristics;

[0017] Step S1023: Set up the electrochemical coupling between the positive and negative electrodes and the ion exchange membrane, and set up the coupling of electrochemical heat, non-isothermal flow electrochemistry and heat transfer, and fluid flow and heat transfer in the model through multi-physics field nodes.

[0018] Step S1024: Select material parameters for different regions of the battery. By consulting the material manual, set the material parameters such as dynamic viscosity, density, and thermal conductivity for each region.

[0019] Step S1025: Based on the operating characteristics of the vanadium redox flow battery, grounding is set on the outer surface of the negative electrode of the battery, and electrode current excitation is applied to the outer surface of the positive electrode to set the positive and negative reaction equilibrium potential of the battery.

[0020] Step S1026: Set the SOC change range during steady-state charging / discharging of the battery, select an appropriate SOC value as the basis for analyzing the hot spot temperature change under the influence of multiple parameters, set the inflow electrolyte temperature, and calculate and export the hot spot temperature data.

[0021] Step S1027: Given that the thickness of the ion exchange membrane is much smaller than that of the electrode, its grid should be set separately. The inlet and outlet of the flow channel should be set separately and the grid should be refined. The grid size and accuracy should be appropriate to ensure calculation speed and accuracy.

[0022] Furthermore, in step S103, the battery current density, inlet flow rate, and ambient temperature are changed, and curves showing the battery hotspot temperature changing with these three parameters are plotted and equations are fitted. Specifically, this includes:

[0023] Step S1031: Divide the range of values ​​of the three parameters under normal battery operating conditions into n equal parts, where n is an integer not less than 5, and take n+1 values ​​as observation points for battery current density, inlet flow rate and ambient temperature.

[0024] Step S1032: Fix these three parameters in pairs and solve for the battery hot spot temperature value under the influence of current density, inlet flow rate and ambient temperature.

[0025] Step S1033: Let the battery current density, inlet flow rate, and ambient temperature be independent variables X, and the hot spot temperature value be the dependent variable Y, respectively. Use plotting software to draw the curve of hot spot temperature changing with different parameters.

[0026] Step S1034: Use the least squares method to obtain the fitting equations respectively;

[0027] Furthermore, in step S104, a multiple linear regression equation is established between the three parameters and the battery hotspot temperature. Based on engineering practice and the hotspot temperature variation pattern, suggestions for setting the operating parameters of the vanadium redox flow battery based on temperature control are given, specifically including:

[0028] Step S1041: Use data analysis software to establish a multiple linear regression equation for battery current density, inlet flow rate, ambient temperature and battery hot spot temperature.

[0029] Step S1042: Compare the temperature change patterns of battery hotspots under the influence of different parameters;

[0030] Step S1043: Based on the hot spot temperature change pattern, provide suggestions for setting battery operating parameters;

[0031] The beneficial effects of this invention are as follows: 1. By fully utilizing the characteristics of the finite element analysis method, a finite element model of the vanadium redox flow battery can be accurately and quickly established, and the battery hot spot temperature values ​​under different operating parameters can be accurately obtained; 2. This invention overcomes the disadvantages of using formula methods, such as difficulty in calculation, large errors, and complex and costly physical experiments; 3. This invention can find the optimal parameter setting method for the vanadium redox flow battery under the influence of multiple parameters, providing data support for the theoretical research, design, construction, and operation and maintenance of the vanadium redox flow battery. Attached Figure Description

[0032] Figure 1 A flowchart illustrating a method for establishing the relationship between hot spot temperature and operating parameters of an all-vanadium redox flow battery;

[0033] Figure 2 This is a structural diagram of a single vanadium redox flow battery model.

[0034] Figure 3 This is a diagram showing the result of mesh generation.

[0035] Figure 4 This is a diagram showing the initial battery temperature distribution.

[0036] Figure 5 Diagram showing battery operating parameter settings;

[0037] Figure 6 shows the temperature change curves of the battery hotspot under the influence of the three parameters respectively; Detailed Implementation

[0038] The flowchart of the method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery provided by this invention is as follows: Figure 1 As shown. To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0039] The following is an example.

[0040] This invention provides a method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery, using a 2*2cm vanadium redox flow battery cell under normal operating conditions as an example for calculation.

[0041] 1. Establish a three-dimensional geometric model of a single vanadium redox flow battery cell.

[0042] A single vanadium redox flow battery cell consists of three parts: positive and negative electrodes made of porous graphite material, a Nafion ion exchange membrane, and an external flow channel. A finite element geometric model is established based on its actual structure, as follows: Figure 2 As shown, from front to back are the negative electrode, the ion exchange membrane, and the positive electrode, with a clamping structure between the electrode and the ion exchange membrane.

[0043] 2. Establish an electrochemical-fluid-thermal coupled model for the all-vanadium redox flow battery, solve for and extract the battery's highest temperature.

[0044] The finite element analysis method allows for flexible excitation settings, so Comsol finite element analysis software was chosen for simulation, and the steady-state analysis type was selected.

[0045] Electrochemical settings were achieved by adding three current distribution fields to the positive and negative electrodes and the ion exchange membrane, respectively. Flow field settings were achieved by adding Brinkman equation fields to the positive and negative electrodes, and heat transfer field settings were achieved by adding a fluid-solid heat transfer field to the entire model. The porous structure of the positive and negative electrodes was set in three physical fields, and their porous matrix and fluid properties were configured.

[0046] Electrochemical coupling between the positive and negative electrodes and the ion exchange membrane is established, and the coupling of electrochemical heat, electrochemical and heat transfer of non-isothermal flow, and fluid flow and heat transfer is set through multiphysics field nodes.

[0047] Select material parameters for different areas of the battery. By consulting the material manual, set material parameters such as dynamic viscosity, density, and thermal conductivity for each area.

[0048] The material parameters of each part of the vanadium redox flow battery are shown in Table 1. Table 1 Material parameters of various parts of the vanadium redox flow battery Material Name Dimensions (mm*mm) Thermal conductivity (W / (m·K)) Density (kg / m³) Graphite positive / negative electrodes 20×20×3 0.15 2000 Nafion ion exchange membrane 20×20×0.125 0.67 1970 Graphite flow channel 2×2×3 0.15 2000

[0049] The electrolyte material parameters for vanadium redox flow batteries are shown in Table 2. Table 2. Electrolyte material parameters for all-vanadium redox flow batteries Parameter name numerical values Dynamic viscosity 4.298*10 -3 Pa·s Initial vanadium concentration (positive electrode) 1500 mol*m -3 ]] Initial vanadium concentration (negative electrode) 1500 mol*m -3 ]] Initial proton concentration (positive electrode) 6000 mol*m -3 ]]> Initial proton concentration (negative electrode) 6000 mol*m -3 ]]> V 2+ diffusion coefficient 2.4*10 -10 ]]> V 3+ diffusion coefficient 2.4*10 -10 ]]> <![CDATA[VO 2+ Diffusion coefficient <![CDATA[3.9*10 -10 ]]> <![CDATA[VO2 + Diffusion coefficient <![CDATA[3.9*10 -10 ]]>

[0050] Grounding is set on the outer surface of the negative electrode of the battery, and electrode current excitation is applied to the outer surface of the positive electrode. The positive and negative reaction equilibrium potentials of the battery are set to 1.004V and -0.255V, respectively.

[0051] The SOC variation range during steady-state charging / discharging of the battery was set, and the discharge SOC=0.5 state was selected as the basis for analyzing the hot spot temperature change under the influence of multiple parameters. The electrolyte inflow temperature was set to 298.15K, and the initial current density was set to 180mA / cm². 2 With the flow rate set to 1.3 ml / s and the ambient temperature at 298.15 K, the battery hotspot temperature data was calculated and exported.

[0052] The mesh is generated using a sweeping method. Since the ion exchange membrane is much thinner than the electrode, its mesh distribution is set to a fixed number of cells (5). The remaining areas have a predefined mesh distribution of 5 cells. The inlet and outlet of the flow channel are separately meshed using free triangular grids for refinement. Figure 3 As shown.

[0053] 3. Change the battery current density, inlet flow rate, and ambient temperature, and plot the curves of the battery hot spot temperature as a function of the three parameters, and fit the equations.

[0054] Based on the actual engineering requirements, the range of battery operating parameters is set as follows: Figure 5 As shown, the current density is set to 60-240 mA / cm². 2 Step length 40mA / cm 2 The inlet flow rate was set to 0.9-1.9 ml / s with a step size of 0.2 ml / s, and the ambient temperature was set to 268.15-318.15 K with a step size of 10 K.

[0055] Let battery current density, inlet flow rate, and ambient temperature be the independent variables X, and hot spot temperature value be the dependent variable Y. Use plotting software to draw the curves of hot spot temperature changing with different parameters and obtain the trend of change, as shown in Figure 6.

[0056] The least squares method yields the following fitted equation:

[0057] (1)

[0058] (2)

[0059] (3) Equations (1) to (3) are the fitting equations for the hot spot temperature as a function of current density, inlet flow velocity, and ambient temperature.

[0060] 4. Fit the battery hotspot temperature equation under the combined effect of three parameters, and based on the actual engineering situation and the hotspot temperature change law, give suggestions on the setting of working parameters of the vanadium redox flow battery based on temperature control.

[0061] The following multiple linear regression equations were established for current density, inlet flow velocity, ambient temperature, and battery hot spot temperature:

[0062] (4)

[0063] Combining equations (1)-(4) Figure 5 It can be seen that the maximum temperature of the battery increases almost linearly with the increase of current density, decreases with the increase of inlet flow rate, and increases with the increase of ambient temperature.

[0064] Therefore, when using a battery, it is necessary to consider the actual needs and the influence of different parameters on the battery hot spot temperature. For example, if the inlet flow rate and ambient temperature are known, a lower current density should be selected; if the ambient temperature and current density are known, a higher inlet flow rate should be selected; if the current density and inlet flow rate are known, the ambient temperature should be reduced as much as possible, and the parameter combination that makes the battery hot spot temperature as low as possible should be selected.

[0065] Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention and not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific embodiments of the present invention, but such modifications or alterations are all within the scope of protection of the pending claims.

Claims

1. A method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery, characterized in that, The method comprises the following steps: Step S101, determining the structure and actual size of the battery monomer, and establishing a three-dimensional geometric model of the vanadium flow battery monomer by using modeling software; Step S102, performing electrochemical-flow-heat coupling setting of the model, establishing a temperature characterization model of the vanadium flow battery monomer, and solving and extracting the highest temperature of the battery in the charging and discharging process; Step S103, changing the battery current density, inlet flow rate and environmental temperature, respectively drawing the curves of the battery hot spot temperature changing with the three parameters and fitting equations; Step S104, establishing a multiple linear regression equation of the three parameters and the battery hot spot temperature, and giving suggestions for setting the working parameters of the vanadium flow battery based on temperature control according to the hot spot temperature variation law and the engineering practice.

2. The method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery according to claim 1, characterized in that, In the step S101, the structure and actual size of the battery monomer are determined, and a three-dimensional geometric model of the vanadium flow battery monomer is established by using modeling software, which specifically comprises: Step S1011, determining the structure and size of the vanadium flow battery to be studied, including the position and size of the flow channel inlet and outlet; Step S1012, establishing the geometric model of the battery by using the geometric module of the finite element software, and paying attention to whether the electrode and ion exchange membrane are clamped structures.

3. The method of claim 1, wherein the method further comprises: In the step S102, the electrochemical-flow-heat coupling setting of the model is performed, the temperature characterization model of the vanadium flow battery monomer is established, and the highest temperature of the battery in the charging and discharging process is solved and extracted, which specifically comprises: Step S1021, determining the simulation software such as Comsol and similar computer-aided design software, selecting the steady-state analysis type, and selecting appropriate physical fields according to the software setting to complete the setting of the electrochemical, fluid flow and heat transfer aspects; Step S1022, setting the embodiment of the porous structure of the positive and negative electrodes in the electrochemical field, flow field and heat transfer field, setting the porous matrix and fluid characteristics thereof; Step S1023, setting the electrochemical coupling between the positive and negative electrodes and the ion exchange membrane, and setting the electrochemical heat, the coupling of electrochemistry and heat transfer of non-isothermal flow, and the coupling of fluid flow and heat transfer of the model through the multi-physical field node; Step S1024, selecting material parameters for different regions of the battery, setting material parameters such as dynamic viscosity, density and thermal conductivity of each region through the query of a material manual; Step S1025, setting the grounding on the outer surface of the negative electrode and the electrode current excitation on the outer surface of the positive electrode according to the operating characteristics of the vanadium flow battery, and setting the positive and negative reaction equilibrium potentials of the battery; Step S1026, setting the SOC change range of the battery in the steady-state charging / discharging process, selecting appropriate SOC values as the basis for analyzing the hot spot temperature change under the influence of multiple parameters, setting the temperature of the inflow electrolyte, and calculating and exporting the hot spot temperature data; Step S1027, since the ion exchange membrane is far smaller in thickness than the electrode, the grid thereof should be set separately, the grid of the inlet and outlet of the flow channel should be set separately for encryption, and the grid size and accuracy should be appropriate to ensure the calculation speed and accuracy.

4. The method for establishing the relationship between hot spot temperature and operating parameters of a vanadium redox flow battery according to claim 1, characterized in that, In the step S103, the battery current density, inlet flow rate and environmental temperature are changed, the curves of the battery hot spot temperature changing with the three parameters are drawn respectively, and equations are fitted, which specifically comprises: Step S1031, dividing the value range of the three parameters under normal working condition of the battery into n equal parts, n is an integer not less than 5, and n+1 values are taken as observation points of the battery current density, inlet flow rate and environmental temperature; Step S1032, fixing two of the three parameters respectively, and solving the hot spot temperature value of the battery under the influence of the current density, inlet flow rate and environmental temperature; Step S1033, taking the battery current density, inlet flow rate and environmental temperature as independent variables X and the hot spot temperature value as dependent variable Y, and drawing a curve of the hot spot temperature changing with different parameters by using drawing software; Step S1034, obtaining fitting equations by using least square method respectively.

5. The method of claim 1, wherein the method further comprises: In the step S104, a multiple linear regression equation of the three parameters and the battery hot spot temperature is established, and based on the engineering practice, the working parameter setting suggestion of the all-vanadium redox flow battery based on temperature control is given according to the hot spot temperature change law, which specifically includes: Step S1041, establishing a multiple linear regression equation of the battery current density, inlet flow rate, environmental temperature and battery hot spot temperature by using data analysis software; Step S1042, comparing the hot spot temperature change law under the influence of different parameters; Step S1043, giving the battery working parameter setting suggestion according to the hot spot temperature change law.

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