Method for calculating contact resistance of bipolar plate of fuel cell

Abstract

The invention discloses a method for calculating the contact resistance of a bipolar plate of a fuel cell, and the method comprises the steps: testing the relation between the resistance value of a single piece of carbon paper and the number of pressing times, and carrying out linear fitting to obtain an intercept value; calculating the contact resistance between the carbon paper and the copper electrode according to the measured intercept value, and calculating the body resistance of the carbon paper by using the contact resistance; and obtaining the sum of the body resistance of the sample, the body resistance of the two pieces of carbon paper, the contact resistance between the two samples and the carbon paper, the contact resistance between the two pieces of carbon paper and the copper electrodes and the body resistance of the two copper electrodes, and calculating the contact resistance of the sample and the carbon paper according to the sum. According to the method, the contact resistance between the bipolar plate and the carbon paper is calculated by accurately measuring the body resistivity of different batches of carbon paper, so that the problem of body resistance fluctuation caused by material batch difference is effectively solved, and the test efficiency and the result reliability are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly relates to a method for calculating the contact resistance of a fuel cell bipolar plate. Background Art

[0002] In a fuel cell, carbon paper plays a crucial role. It is usually located at the diffusion layer positions of the anode and the cathode, between the bipolar plate and the catalytic layer. On the anode side, hydrogen enters the fuel cell from the anode gas inlet and is evenly distributed to the surface of the anode carbon paper under the action of the flow field. The carbon paper provides a channel for the diffusion of hydrogen, enabling hydrogen to smoothly reach the anode catalytic layer for oxidation reaction. On the cathode side, oxygen enters from the cathode gas inlet, reaches the cathode carbon paper under the guidance of the flow field, and then diffuses through the carbon paper to the cathode catalytic layer to participate in the reduction reaction. At the same time, the carbon paper also plays a role in collecting and conducting current, transferring the electrons generated by the cathode catalytic layer to the bipolar plate, and then outputting electrical energy.

[0003] The bulk resistance of carbon paper is part of the internal resistance of the fuel cell. The size of the battery internal resistance directly affects the output voltage and power performance of the battery. By calculating the bulk resistance of carbon paper, its contribution to the battery internal resistance can be accurately understood, so as to take targeted measures to reduce the internal resistance and improve the battery performance.

[0004] Currently, when calculating the bulk resistance of carbon paper (refer to the standard of "GB / T 20042.7-2014"), the conventional calculation formula is as follows:

[0005]

[0006] However, in actual calculation, due to the existence of pores between carbon fibers, when measuring the thickness of carbon paper, the carbon paper will undergo slight deformation, and the thickness compression rate can reach 10% - 15% (for example, the initial thickness of 300 μm is compressed to 270 μm), resulting in the measured values of the cross-sectional area (A) and thickness (L) deviating from the true values. At the same time, when dust or lint (particle size > 10 μm) adheres to the surface of the carbon paper in the test room, the contact resistance fluctuation can reach ±5% or even more.

[0007] In order to reduce the influence caused by deformation, a new carbon paper needs to be replaced for each test to avoid the decrease in contact resistance caused by excessive pressing of the carbon paper and avoid the influence of resistance differences caused by multiple uses of the carbon paper on the repeatability of test results.

[0008] However, when testing the resistance of a large number of bipolar plates, frequently replacing the carbon paper will significantly extend the test cycle, and the difference in the bulk resistance between carbon papers is not taken into account. Currently, the difference in the bulk resistance of carbon papers with good uniformity is usually within 5%, which may lead to an error in the contact resistance of the bipolar plate within ±3% - 5%. For carbon papers with poor uniformity, the difference in bulk resistance may exceed 10%, resulting in a test error in the contact resistance of the bipolar plate within ±8% - 12%. Especially in the test of low contact resistance (such as <10 mΩ), the proportion of the error is higher. Summary of the Invention

[0009] To solve the above problems, the present invention provides a method for calculating the contact resistance of a fuel cell bipolar plate, which can accurately and quickly calculate the contact resistance between the bipolar plate and the carbon paper.

[0010] For this purpose, the technical solution of the present invention is: a method for calculating the contact resistance of a fuel cell bipolar plate, comprising the following steps:

[0011] 1) Test the relationship between the resistance value of a single piece of carbon paper and the number of pressing times, perform linear fitting, and obtain the intercept value R 1截距 ;

[0012] 2) Calculate the contact resistance R c-cu between the carbon paper and the copper electrode according to the measured intercept value, and the formula is as follows:

[0013]

[0014] where: ρ is the resistivity of the carbon paper in the vertical direction, and d0 is the initial thickness of the carbon paper;

[0015] 3) Obtain the sum R1 of the bulk resistance of one carbon paper body, the contact resistances between two carbon papers and the copper electrodes, and the bulk resistances of two copper electrodes during the process of obtaining the contact resistance between the test sample and the carbon paper, and calculate the bulk resistance R 体 of the carbon paper based on this, and the formula is as follows:

[0016] R 体 = R1 - 2×R c-cu

[0017] 4) Obtain the sum R2 of the bulk resistance of the sample body, the bulk resistances of two carbon papers, the contact resistances between two samples and the carbon papers, the contact resistances between two carbon papers and the copper electrodes, and the bulk resistances of two copper electrodes, and calculate the contact resistance R between the sample and the carbon paper based on this. The formula is as follows:

[0018] R = (R2 - R1)×S - R 体

[0019] where: S is the contact area of the carbon paper.

[0020] Based on the above solution and as an optimized solution of the above solution: The specific steps of step 1) are as follows: Place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and measure the current resistance value of a single piece of carbon paper; Repeat the downward pressing multiple times, measure the resistance value of a single piece of carbon paper after each downward pressing, and finally obtain the relationship between the resistance value of a single piece of carbon paper and the number of downward pressings.

[0021] Based on the above solution and as an optimized solution of the above solution: Use the resistance value of a single piece of carbon paper as the Y-axis and the number of downward pressings as the X-axis to draw a relationship curve. After linear fitting, derive the slope value a by minimizing the sum of squared residuals, and calculate the intercept value R 1截距 ;

[0022] R 1截距 = y’ - ax’

[0023] Where: y’ is the average value of the resistance value of a single piece of carbon paper, and x’ is the average value of the number of downward pressings.

[0024] Based on the above solution and as an optimized solution of the above solution: In step 3), place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and the total resistance R1 of a carbon paper body resistance, two contact resistances between the carbon paper and the copper electrodes, and two copper electrode body resistances can be measured.

[0025] Based on the above solution and as an optimized solution of the above solution: In step 4), stack two pieces of carbon paper and the sample between two copper electrodes, apply a pressure of 1.5 MPa, and the total resistance R2 of the sample body resistance, two carbon paper body resistances, two contact resistances between the sample and the carbon paper, two contact resistances between the carbon paper and the copper electrodes, and two copper electrode body resistances can be measured.

[0026] Compared with the prior art, the beneficial effects of the present invention are: By accurately measuring the volume resistivity of carbon paper in different batches, and then calculating the contact resistance between the bipolar plate and the carbon paper, the problem of volume resistance fluctuation caused by material batch differences is effectively solved. Compared with the traditional method, it can not only reduce the test error, but also greatly shorten the test cycle, save the test cost, and significantly improve the test efficiency and result reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a relationship diagram of the resistance value of a single piece of carbon paper and the number of downward pressings;

[0028] Figure 2 It is a fitting diagram of the resistance value of a single piece of carbon paper and the number of downward pressings;

[0029] Figure 3 It is a test relationship diagram of the present invention and the existing test method;

[0030] Figure 4Graph of repeated test results for four different samples. Detailed implementation method

[0031] Refer to the attached drawings. The calculation method for the contact resistance of the fuel cell bipolar plate in this embodiment includes the following steps:

[0032] 1) Test the relationship between the resistance value of a single piece of carbon paper and the number of pressing times, perform linear fitting, and obtain the intercept value R 1截距 ; The specific steps are as follows:

[0033] 1.1) Place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and measure the current resistance value of the single piece of carbon paper;

[0034] 1.2) Repeat pressing multiple times and measure the resistance value of the single piece of carbon paper after each pressing;

[0035] 1.3) Draw a relationship curve with the resistance value of the single piece of carbon paper as the Y-axis and the number of pressing times as the X-axis (such as Figure 1 ), after linear fitting (such as Figure 2 ), derive the slope value a by minimizing the sum of squared residuals,

[0036]

[0037] x is the number of pressing times, x' is the average value of x;

[0038] y is the resistance value of the single piece of carbon paper, y' is the average value of y;

[0039] ∑xy is the sum of the products of x and y;

[0040] ∑x 2 is the sum of the squares of x, ∑x is the sum of x, and ∑y is the sum of y;

[0041] n is the number of data points;

[0042] 1.4) Calculate the intercept value;

[0043] R 1截距 = y' - ax'

[0044] where: y is the average value of the resistance value of the single piece of carbon paper, x is the average value of the number of pressing times, and the unit of R 1截距 is milliohm mΩ.

[0045] 2) Calculate the contact resistance R between the carbon paper and the copper electrode according to the measured intercept value c-cu (unit: milliohm square centimeter mΩcm 2 ), the formula is as follows:

[0046]

[0047] Where: ρ is the resistivity of the carbon paper in the vertical direction, with the unit of milliohm - centimeter (mΩcm), and d0 is the initial thickness of the carbon paper, with the unit of centimeter (cm);

[0048] 3) Place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and the total resistance R1 (unit: milliohm, mΩ) of a carbon paper body resistance, two contact resistances between the carbon paper and the copper electrodes, and two copper electrode body resistances can be measured, and the carbon paper body resistance R (unit: milliohm - square centimeter, mΩcm) is calculated therefrom. The formula is as follows: 体 (unit: milliohm - square centimeter, mΩcm 2 ) The formula is as follows:

[0049] R 体 = R1 - 2×R c-cu

[0050] 4) Stack two pieces of carbon paper and the sample between two copper electrodes, apply a pressure of 1.5 MPa, and the total resistance R2 (unit: milliohm, mΩ) of the sample body resistance, two carbon paper body resistances, two contact resistances between the sample and the carbon paper, two contact resistances between the carbon paper and the copper electrodes, and two copper electrode body resistances can be measured, and the contact resistance R between the sample and the carbon paper is calculated therefrom. The formula is as follows:

[0051] R=(R2 - R1)×S - R 体

[0052] Where: S is the contact area of the carbon paper, with the unit of square centimeter (cm 2 ).

[0053] Experimental verification 1:

[0054] Use the traditional method (the test method recorded in the standard of "GB / T 20042.7 - 2014") and the new method (the test method adopted in this embodiment) to conduct ten - time tests on the same sample respectively. It can be seen that the test results of the new method are on average 24.9% smaller than those of the traditional method, and the difference is relatively large. It is considered that this is mainly due to the different inter - body resistances of the carbon papers; in terms of variance and range, the test standards of the new method are smaller than those of the traditional method, indicating that the new method is more stable and accurate compared with the traditional method; in terms of the test cycle, 58% of the time cost is saved; in terms of the cost of replacing carbon paper, 90% of the money cost is saved.

[0055] Name Traditional method New method Optimization rate <![CDATA[Average mΩcm 2 > 2.8980 2.1575 Variance 0.3264 0.0456 ↓85.9％ <![CDATA[Extreme difference mΩcm 2 > 1.0646 0.1520 Time min 60 25 ↓58.3％ Cost of replacing carbon paper (5 yuan per time) 50 5 ↓90％

[0056] Example verification 2:

[0057] Through multiple tests on different samples, the following test results are obtained in the chart. It can be seen that for different samples in the 40 - 60 - time tests, the test results are very stable, with variances all < 0.05, and the ratio of the difference between the maximum value and the minimum value is also all < 3%.

[0058]

[0059] In this embodiment, by dynamically correcting the difference in the body resistance of the carbon paper, the contact resistance error is controlled within ±3%; the frequency of carbon paper replacement is reduced, the test cycle is shortened by 58%, and the cost is reduced by 90%; it has strong universality, can be compatible with silicon-based / metal / graphite / composite bipolar plates, and is suitable for carbon papers of different batches; it can fit the actual working conditions of fuel cells, and the data traceability is high.

[0060] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the concept of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for calculating the contact resistance of a fuel cell bipolar plate, characterized in that: It includes the following steps: 1) Test the relationship between the resistance value of a single-piece carbon paper and the number of pressing times, perform linear fitting, and obtain the intercept value R 1截距 ; 2) Calculate the contact resistance R between the carbon paper and the copper electrode according to the measured intercept value c-cu , and the formula is as follows: Where: ρ is the resistivity of the carbon paper in the vertical direction, and d0 is the initial thickness of the carbon paper; 3) During the process of obtaining the contact resistance between the test sample and the carbon paper, the sum of the resistance of one carbon paper body, the contact resistances between the two carbon papers and the copper electrodes, and the resistances of the two copper electrode bodies is R1, and the carbon paper bulk resistance R is calculated therefrom. 体 , and the formula is as follows: R 体 = R1 - 2×R c-cu 4) Obtain the sum R2 of the sample body resistance, the two carbon paper body resistances, the two contact resistances between the sample and the carbon paper, the two contact resistances between the carbon paper and the copper electrode, and the two copper electrode body resistances, and calculate the contact resistance R between the sample and the carbon paper according to the following formula: R = (R2 - R1) × S - R 体 Where: S is the contact area of the carbon paper.

2. The calculation method of the contact resistance of a fuel cell bipolar plate according to claim 1, characterized in that: The specific steps of step 1) are as follows: Place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and measure the current resistance value of the single-piece carbon paper; Repeat the pressing multiple times, measure the resistance value of the single-piece carbon paper after each pressing, and finally obtain the relationship between the resistance value of the single-piece carbon paper and the number of pressings.

3. The calculation method of the contact resistance of a fuel cell bipolar plate according to claim 2, characterized in that: Taking the resistance value of a single piece of carbon paper as the Y-axis and the number of pressing times as the X-axis, a relationship curve is plotted. After linear fitting, the slope value a is derived by minimizing the sum of squared residuals, and the intercept value R is calculated. 1截距 ; R 1截距 = y' - ax' Where: y’ is the average value of the resistance value of the single-piece carbon paper, and x’ is the average value of the number of pressings.

4. The calculation method of the contact resistance of a fuel cell bipolar plate according to claim 1, characterized in that: In step 3), place a piece of carbon paper between two copper electrodes, apply a pressure of 1.5 MPa, and the sum R1 of a carbon paper body resistance, the two contact resistances between the carbon paper and the copper electrode, and the two copper electrode body resistances can be measured.

5. The calculation method of the contact resistance of a fuel cell bipolar plate according to claim 1, characterized in that: In step 4), stack two pieces of carbon paper and the sample between two copper electrodes, apply a pressure of 1.5 MPa, and the sum R2 of the sample body resistance, the two carbon paper body resistances, the two contact resistances between the sample and the carbon paper, the two contact resistances between the carbon paper and the copper electrode, and the two copper electrode body resistances can be measured.

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