A method for detecting the compression deformation of the flow field area of ​​a flexible graphite bipolar plate of a fuel cell

Abstract

The present invention discloses a method for detecting the compression deformation of the flow field area of ​​a flexible graphite bipolar plate for a fuel cell, and relates to the field of fuel cell testing. The present invention proposes for the first time to evaluate the rigidity and impregnation uniformity of a bipolar plate through a compression deformation curve, filling the gap in the quantitative detection of mechanical properties. The present invention combines mechanical testing with quality control to solve the single-dimensional defect of traditional detection methods. It quantitatively evaluates deformation behavior through dynamic compression testing, directly associates it with defects in the preparation process, and can reversely optimize the preparation process (such as adjusting the molding pressure and impregnation parameters) based on the deformation data to improve the yield of the bipolar plate. The present invention provides an efficient and quantifiable detection method, which can screen out plates with uneven impregnation or insufficient rigidity through the compression deformation curve. It is suitable for rapid screening in large-scale production and is superior to traditional manual visual inspection or single parameter testing.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell testing, and in particular to a method for detecting the compression deformation of a flow field region of a flexible graphite bipolar plate of a fuel cell. Background Art

[0002] As a core component of proton exchange membrane fuel cells (PEMFCs), bipolar plates fulfill multiple functions, including separating reactant gases, conducting current and heat, and supporting the membrane electrode structure. Their performance directly impacts the stack's energy density, durability, and manufacturing cost. Currently, bipolar plate materials fall into four main categories: traditional artificial graphite plates, metal surface-modified plates, composite plates, and flexible expanded graphite plates. Flexible expanded graphite bipolar plates are becoming the mainstream choice due to their lightweight, high conductivity, and corrosion resistance.

[0003] Flexible expanded graphite bipolar plates are molded from natural flake graphite through oxidation intercalation and high-temperature expansion. Their loose, porous structure requires resin impregnation to enhance mechanical strength and airtightness. However, the uneven particle size and irregular shape of the expanded graphite raw material can easily lead to defective areas with large local voids after molding. During the impregnation process, the resin has difficulty evenly penetrating the pores, resulting in uneven bipolar plate rigidity and insufficient airtightness, which in turn affects the stability of the stack assembly and long-term operational reliability.

[0004] Existing bipolar plate testing technologies mainly focus on electrical performance testing and surface defect detection, but lack quantitative evaluation methods for mechanical properties. Specifically,

[0005] Electrical performance testing: Measuring the bipolar plate's bulk resistance or contact resistance assesses conductivity, but this does not reflect the material's deformation behavior under pressure. During stack assembly, the bipolar plates must withstand stacking pressures ranging from tens to hundreds of kPa. Insufficient rigidity or uneven impregnation can lead to localized collapse, resulting in a surge in contact resistance or gas leakage.

[0006] Air tightness test: Helium leak detection or differential pressure method is used to detect the sealing performance of bipolar plates. However, such methods can only locate macroscopic leak points and cannot identify microscopic pore defects caused by uneven impregnation, nor can they predict the performance degradation of materials after long-term pressure.

[0007] Surface defect detection: Detects surface defects such as flow channel size deviation and cracks based on machine vision or eddy current sensors, but cannot quantitatively evaluate the uniformity of the material's internal structure.

[0008] Mechanical properties testing: Existing technologies (such as the three-point bending test) can only obtain the overall bending strength of the bipolar plate, but cannot detect the compression deformation in different regions, making it difficult to identify local areas of weak rigidity.

[0009] The existing technology makes it impossible to reversely optimize key process parameters such as molding pressure and impregnation time through detection data; visual inspection or single parameter testing can easily miss defective products with uneven impregnation but intact surfaces; and bipolar plates with insufficient rigidity are prone to deformation during stack assembly or operation, causing problems such as increased contact resistance and gas cross leakage, shortening the stack life.

[0010] Therefore, there is an urgent need for a detection method that can quantitatively evaluate the rigidity and impregnation uniformity of flexible graphite bipolar plates to improve the reliability and service life of the battery stack assembly. Summary of the Invention

[0011] Because the existing technology has not solved the problem of uneven impregnation of flexible graphite bipolar plates due to their porous structure, the present invention provides a method for detecting the compressive deformation of the flow field area of ​​fuel cell bipolar plates. The compressive displacement under different test forces is detected by the lifting device of a universal testing machine, and plates with insufficient rigidity and poor impregnation consistency are screened out based on the compressive deformation and curve trend.

[0012] The purpose of the present invention can be achieved by the following ways:

[0013] The present invention provides a method for detecting the compressive deformation of a flow field region of a flexible graphite bipolar plate of a fuel cell, comprising the following steps:

[0014] S1. Determine the reference point: Fix the flexible graphite bipolar plate to be tested on a universal testing machine and apply an initial test force at a constant test force loading speed. When the compression deformation reaches the set threshold, record the corresponding test force as the reference point.

[0015] S2. Regional compression test: Starting from the reference point, apply increasing test force to at least three independent regions of the bipolar plate flow field area, maintain a constant test force loading speed and preset hold time in each test force stage, and measure the compression deformation of each region in real time;

[0016] S3. Data analysis and judgment: Generate a curve of the change in compression deformation of each area with the test force, use the least squares method to fit the equation, observe the slope change, and calculate the range of compression deformation in different areas under the same test force. If the slope trend of the curve deviates significantly or the range exceeds the preset threshold, it is judged as an unqualified bipolar plate.

[0017] As a preferred solution, the surface density of the flexible graphite bipolar plate of the fuel cell to be tested in the embodiment of the present invention is 50-70 mg / cm 2 As an example, but not limited to.

[0018] Furthermore, in step S1, in an example of an embodiment of the present invention, the setting threshold of the reference point is selected to be a compression deformation of 0, and the corresponding initial test force range is 0.05-0.15KN.

[0019] Furthermore, in step S2, the incremental test force range is 0.283-2.83 KN, the test force loading speed is 0.005-0.1 KN / s, and the preset holding time of each test force stage is 2-30 s.

[0020] Specifically, in step S2, at least three independent areas are symmetrically and evenly selected from the bipolar plate flow field area, including a central area and symmetrically distributed edge areas, and the area of ​​each area accounts for 5%-20% of the total area of ​​the flow field area; preferably, in the embodiment of the present invention, the area of ​​each area accounts for 9.9% of the total area of ​​the flow field area as an example, but is not limited to this.

[0021] As a preferred solution, in step S3, the preset threshold is that the range of deformation of different regions under the same test force is controlled within 0~0.0090mm, and the product exceeding the threshold is judged as unqualified.

[0022] As a preferred solution, the condition for determining whether the curve trend deviates significantly is that the difference between the slope of the compression deformation in any area as the test force changes and the slope of other areas is ≤0.002.

[0023] The present invention also provides a system for implementing the detection method, comprising:

[0024] A universal testing machine, including a lifting device for raising and lowering a pressure-applying device, a displacement sensor, a pressure sensor, and a programmable controller;

[0025] Data acquisition module, real-time recording of test force and compression deformation;

[0026] The analysis module generates the compression deformation-test force curve and calculates the range and trend deviation.

[0027] Furthermore, the programmable controller can set the corresponding test force range according to the contact area between the indenter and the bipolar plate. The test force formula is: F=P·S (where P is pressure, MPa; S is contact area, cm 2 ; F is the test force, KN)

[0028] Beneficial effects of the present invention:

[0029] Existing technologies focus more on electrical properties (such as volume resistance) or surface defects, while the present invention proposes for the first time to evaluate the rigidity and impregnation uniformity of bipolar plates through compression deformation curves, filling the gap in quantitative detection of mechanical properties.

[0030] The present invention combines mechanical testing with quality control to address the single-dimensional defects of traditional detection methods. It quantitatively evaluates deformation behavior through dynamic compression testing and directly links it to defects in the manufacturing process. Based on the deformation data, the manufacturing process can also be reversely optimized (such as adjusting the molding pressure and impregnation parameters) to improve the yield of bipolar plates.

[0031] The present invention provides an efficient and quantifiable detection method, which can screen out plates with uneven impregnation or insufficient rigidity through the compression deformation curve. It is suitable for rapid screening in large-scale production and is superior to traditional manual visual inspection or single parameter testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a compression deformation-test force curve generated from the data measured in Example 1.

[0033] Figure 2 This is a compression deformation-test force curve generated from the data measured in Example 2.

[0034] Figure 3 This is a compression deformation-test force curve generated from the data measured in Example 3. DETAILED DESCRIPTION

[0035] Example 1

[0036] 50 mg / cm 2 The area density of the flexible graphite bipolar plate region 1 is placed in the test position of the universal testing machine, the open-loop displacement control speed is 10 mm / min, and then the test force is loaded at a speed of 0.02 KN / s and the speed is decreased. When the test force reaches 0.1 KN, the deformation is zero;

[0037] Continue to descend at a speed of 0.02KN / s. When the test force reaches 0.283KN, maintain the test force for 10s. Repeat the above operation until the test force reaches 2.83KN. Maintain the test force for 10s and record the compression deformation between 0.283 and 2.83KN. Area 2 and Area 3 are operated in the same way as Area 1. The measurement data are shown in Table 1. The compression deformation-test force curve generated according to Table 1 is shown in Figure 1 shown.

[0038] Table 1

[0039]

[0040] Least squares fitting of the data revealed a slope of 0.0072 for region 1, 0.0054 for region 2, and 0.0066 for region 3. The slopes of region 2 differed from those of regions 1 and 3 by 0.0018 and 0.0012, respectively, all ≤0.002. The three curves exhibit similar trends with minimal deviation.

[0041] In addition, as shown in Table 1 and Figure 1 As shown, in Example 1, under a test force of 0.283-2.83 kN, the range of the deviation of Regions 1, 2, and 3 is 0.0013-0.0063 mm, which is included in the range of 0-0.0090 mm, and the discrete amplitude is relatively small. In summary, it shows that the flexible graphite bipolar plate has strong rigidity and good consistency of impregnation effect.

[0042] Example 2

[0043] 60 mg / cm 2 The area 1 of the flexible graphite bipolar plate with areal density is placed in the test position of the universal testing machine. The open-loop displacement control speed is 10 mm / min, and then it is lowered at a speed of 0.02 KN / s. When the test force reaches 0.1 KN, the deformation is zero.

[0044] Continue to descend at a speed of 0.02KN / s. When the test force reaches 0.283KN, maintain the test force for 10s. Repeat the above operation until the test force reaches 2.83KN. Maintain the test force for 10s and record the compression deformation between 0.283 and 2.83KN. Area 2 and Area 3 are operated in the same way as Area 1. The measurement data are shown in Table 2. The compression deformation-test force curve generated according to Table 2 is shown in Figure 2 shown.

[0045] Table 2

[0046]

[0047] Least squares fitting of the data revealed slopes of 0.0091 for region 1, 0.0089 for region 2, and 0.0121 for region 3. The slopes of region 3 differed from those of regions 1 and 2 by 0.0030 and 0.0032, respectively, both exceeding 0.002. The curve for region 3 deviated significantly from the trends of regions 1 and 2.

[0048] In addition, as shown in Table 2 and Figure 2 As shown, in Example 2, under the test force of 0.283-2.83 KN, the range of region 1, region 2, and region 3 is 0.0076-0.0126 mm, which is not included in the range of 0-0.0090 mm. The discrete amplitude is too large, indicating that the rigidity of the flexible graphite bipolar plate is insufficient and the impregnation effect is consistently poor.

[0049] Example 3

[0050] 70 mg / cm 2 The area 1 of the flexible graphite bipolar plate with areal density is placed in the test position of the universal testing machine. The open-loop displacement control speed is 10 mm / min, and then it is lowered at a speed of 0.02 KN / s. When the test force reaches 0.1 KN, the deformation is zero.

[0051] Continue to descend at a speed of 0.02KN / s. When the test force reaches 0.283KN, maintain the test force for 10s. Repeat the above operation until the test force reaches 2.83KN. Maintain the test force for 10s and record the compression deformation between 0.283 and 2.83KN. Area 2 and Area 3 are operated in the same way as Area 1. The measurement data are shown in Table 3. The compression deformation-test force curve generated according to Table 3 is shown in Table 3. Figure 3 shown.

[0052] Table 3

[0053]

[0054] Least squares fitting of the data revealed a slope of 0.0147 for Region 1, 0.0098 for Region 2, and 0.00143 for Region 3. The slopes of Region 2 differed from those of Regions 1 and 3 by 0.0049 and 0.0045, respectively, both exceeding 0.002. The curve for Region 2 deviated significantly from the trends of Regions 1 and 3.

[0055] In addition, as shown in Table 3 and Figure 3 As shown, in Example 3, under a test force of 0.283-2.83 kN, the range of variation for Regions 1, 2, and 3 was 0.0088-0.0189 mm, not within the range of 0-0.0090 mm, indicating a large dispersion. In summary, this indicates that the rigidity of the flexible graphite bipolar plate is insufficient, resulting in poor consistency in the impregnation effect.

Claims

1. A method for detecting the compressive deformation of a flexible graphite bipolar plate in a fuel cell flow field region, characterized in that: The detection method comprises the following steps: S1. Determine the reference point: Fix the flexible graphite bipolar plate to be tested on a universal testing machine and apply an initial test force at a constant test force loading speed. When the compression deformation reaches the set threshold, record the corresponding test force as the reference point. S2. Regional compression test: Starting from the reference point, apply increasing test force to at least three independent regions of the bipolar plate flow field area, maintain a constant test force loading speed and preset hold time in each test force stage, and measure the compression deformation of each region in real time; S3. Data Analysis and Judgment: Generate a curve based on the compression deformation of each region versus the test force. Use the least squares method to fit the data to obtain the slope value. Calculate the range of compression deformation in different regions under the same test force. If the slope trend of the curve deviates significantly or the range exceeds a preset threshold, the bipolar plate is judged to be unqualified. The criterion for determining whether the slope trend of the curve deviates significantly is that the difference between the slope of the compression deformation in any area as the test force changes and the slope of other areas is greater than 0.

002.

2. The detection method according to claim 1, wherein The surface density of the flexible graphite bipolar plate to be tested is 50-70 mg / cm 2 .

3. The detection method according to claim 1, wherein In step S1 , the threshold value of the reference point is set to a compression deformation of 0, and the corresponding initial test force range is 0.05-0.15 KN.

4. The detection method according to claim 1, wherein In step S2, the incremental test force range is 0.283-2.83 KN, the test force loading speed is 0.005-0.1 KN / s, and the preset holding time of each test force stage is 2-30 s.

5. The detection method according to claim 4, characterized in that In step S2, at least three independent areas are symmetrically and evenly selected from the bipolar plate flow field area, including a central area and symmetrically distributed edge areas, and the area of ​​each area accounts for 5%-20% of the total area of ​​the flow field area.

6. The detection method according to claim 1, characterized in that In step S3, the preset threshold is that the deformation range of different areas under the same test force is controlled within 0-0.009mm, and the product exceeding the threshold is judged as unqualified.

7. A system for implementing any detection method according to claim 1, characterized in that: include: A universal testing machine, including a lifting device for raising and lowering a pressure-applying device, a displacement sensor, a pressure sensor, and a programmable controller; Data acquisition module, real-time recording of test force and compression deformation; The analysis module generates the compression deformation-test force curve and calculates the range and trend deviation.

8. The system according to claim 7, characterized in that The programmable controller sets the corresponding test force range according to the contact area between the pressure head and the bipolar plate. The test force formula is: F=P·S, Where P is the pressure in MPa; S is the contact area in cm 2 ; F is the test force, unit is KN.

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