Method for verifying assembly force of fuel cell stack in situ

Abstract

The invention discloses a method for verifying the assembly force of a fuel cell stack in situ, which effectively simulates the actual operation environment of a fuel cell by performing gradient pressurization and electrochemical testing in a continuous discharge state of the stack. By synchronously collecting output voltage and impedance spectrum parameters, direct association between assembly force change and electrochemical response is established, and the limitation of traditional static testing is broken through. The in-situ verification mode avoids the interference of the disassembly and assembly process on the galvanic pile structure, more accurately reflects the actual influence of different assembly forces on the battery performance, provides a real and reliable basis for optimization, constructs a three-level priority decision mechanism of the output voltage, the ohmic resistance and the gas mass transfer resistance, and improves the reliability of the system. And the electrical property output, the internal loss and the reaction gas transmission efficiency of the electric pile are comprehensively considered. According to the method, an assembly force threshold value is gradually explored through a gradient pressurization process, and the contradiction between conductive contact improvement and runner pressure loss control is systematically balanced on the premise that the structural safety of the membrane electrode is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell manufacturing technology, specifically relating to an in-situ verification method for fuel cell stack assembly force. Background Technology

[0002] Assembly force is a core parameter in fuel cell stack manufacturing, directly affecting the contact resistance of the membrane electrode interface and the uniformity of gas diffusion. Proton exchange membrane fuel cells directly convert chemical energy into electrical energy through a hydrogen-oxygen electrochemical reaction, and their energy conversion efficiency is not limited by the Carnot cycle. During stack operation, specific assembly forces must be applied to ensure tight contact between the bipolar plates and the membrane electrode, reducing efficiency losses caused by contact resistance.

[0003] Current assembly force setting methods have significant drawbacks. Traditional methods require disassembling the fuel cell stack to measure contact resistance, which disrupts assembly consistency and leads to large deviations between measurement results and actual operating conditions. In addition, existing technologies only focus on minimizing ohmic resistance and ignore the synchronous changes in gas mass transfer resistance. Therefore, it is necessary to develop an in-situ, multi-parameter coordinated dynamic verification method for assembly force.

[0004] Chinese patent literature discloses a system and method for online verification of the optimal assembly force of a fuel cell stack [Application No.: 202311555721.4, Publication No.: CN117423873A]. It includes a compressor system, a load, and a testing system. The compressor system is used to apply the assembly force to the stack and cooperates with the testing system to perform online performance testing. The load is used to control the pressure and performance of the stack. Although this patent can achieve the characteristic of testing the optimal assembly force, it does not involve gradient pressurization process and dynamic monitoring of gas mass transfer resistance, and still lacks accuracy in electrochemical response under real working conditions. Summary of the Invention

[0005] A method for in-situ verification of fuel cell stack assembly capability, characterized by comprising the following steps: (a) Place the fuel cell stack in a pressurized fixture and apply an initial assembly force; (b) Connect the fuel cell test bench to the electrochemical workstation and apply a constant current to the fuel cell stack for continuous discharge; (c) After the output voltage of the fuel cell stack stabilizes, record the voltage value and perform electrochemical impedance spectroscopy to obtain the ohmic resistance and gas mass transfer resistance. (d) Gradually increase the assembly force on the fuel cell stack using clamps; (e) Repeat step (c) after each increase in assembly force; (f) Compare the output voltage, ohmic resistance and gas mass transfer resistance under different assembly forces, and determine the optimal assembly force by prioritizing the highest output voltage as the first priority, the lowest ohmic resistance as the second priority and the lowest gas mass transfer resistance as the third priority.

[0006] Preferably, the pressurizable clamp is any one of a cylinder clamp, a pneumatically driven clamp, or a mechanical press.

[0007] The above technical solutions enable accurate control and optimization of fuel cell stack assembly force in situ, meeting assembly pressure requirements under different specifications and installation environments, and improving operational flexibility and adaptability.

[0008] Specifically, the aforementioned pressurized clamps can apply stable, controllable, and repeatable assembly forces to the fuel cell stack, enabling gradient pressurization. During each pressurization step, real-time test parameters such as stack output voltage and electrochemical impedance spectroscopy can be used to directly reflect the internal contact state and operating performance of the stack, effectively avoiding problems such as increased contact resistance due to insufficient assembly force or component deformation and performance degradation caused by excessive pressurization.

[0009] In practical applications, the fixture structure and testing process of this invention facilitate the rapid selection of the optimal assembly force range, ensuring that the fuel cell stack is in its best operating state, thereby improving its performance consistency and service life. At the same time, the fixture has the advantages of simple structure, convenient operation, and easy large-scale application, which can better meet the different needs of fuel cell manufacturing and testing, and is of great significance for improving the overall reliability and economy of fuel cell systems.

[0010] Preferably, before applying a constant current in step (b), it is necessary to confirm that the pressure holding and sealing of the three chambers of the fuel cell stack is qualified. The criteria for qualified pressure holding are: the pressure drop of the anode chamber, cathode chamber and coolant chamber is ≤0.5kPa after holding the pressure for 3 minutes under the test pressure.

[0011] The above technical solutions can effectively ensure the sealing reliability of each functional cavity of the fuel cell stack and promptly detect and eliminate potential leakage hazards.

[0012] Specifically, by independently testing the sealing performance of the three chambers of the fuel cell stack, defects in installation, sealing components, or the manufacturing process can be identified before electrochemical performance testing. This prevents leaks of reactant gases or coolant due to poor airtightness, which could affect the safety of the fuel cell and the accuracy of test data. Furthermore, setting appropriate holding times and pressure drop thresholds helps determine the conformity of the sealing component assembly, standardizes operating procedures, and improves testing efficiency.

[0013] In practical applications, the aforementioned three-chamber pressure-holding and sealing test, as a key pretreatment step before constant current discharge, can significantly improve the reliability and consistency of fuel cell stack test results, prevent invalid testing and resource waste, lay a solid foundation for subsequent assembly force optimization and performance analysis, and is of great significance for improving the quality control of the fuel cell production process and the long-term stability of system operation.

[0014] Preferably, the stable output voltage of the fuel cell stack in step (c) means that the voltage fluctuation amplitude is ≤ ±1% and lasts for ≥ 3 minutes.

[0015] The above technical solution can ensure that highly stable and representative voltage data are collected during the fuel cell stack performance test, which is beneficial to effectively eliminate the influence of external environmental interference and the transient response of the fuel cell stack itself.

[0016] Specifically, defining the criteria for judging voltage stability can avoid large fluctuations in data obtained during the initial startup phase or before the fuel cell stack has reached a steady state after voltage adjustment, thus improving the accuracy and comparability of test data. Strict monitoring of voltage stability provides a direct reflection of the actual operating state of the fuel cell stack, offering a reliable data foundation for subsequent testing of electrochemical performance parameters such as ohmic resistance and gas mass transfer resistance.

[0017] In practical applications, this stability assessment method helps standardize fuel cell testing procedures, ensures the consistency and scientific rigor of performance parameter acquisition such as voltage, and thus improves the reliability and engineering application value of assembly force optimization results. This plays a positive role in enhancing the assembly quality control and operational stability of fuel cell stacks.

[0018] Preferably, the gradient pressurization in step (d) is performed according to the following segmented process: First stage of pressurization: pressurize at a rate of 500-1000 N / s to 110%-130% of the initial assembly force; The second stage of pressurization: pressurize at a rate of 200-500 N / s to 150%-180% of the initial assembly force; The third stage of pressurization: pressurize at a rate of 100-300 N / s to 200%-250% of the initial assembly force; After each pressurization, let it stand for 1-3 minutes to allow the pressure to be evenly distributed.

[0019] The above technical solution enables scientific, precise and controllable phased adjustment of the assembly force during the fuel cell stack assembly process. It adopts a gradient pressurization method, sets reasonable pressurization rates and target assembly forces according to different stages, and sets a resting time after each pressurization stage to ensure that the pressure is uniformly transmitted to each contact surface inside the stack.

[0020] Specifically, the assembly force is gradually increased in three stages, from 110%-130% of the initial assembly force to 200%-250%, and matched with the corresponding pressurization rate. This effectively reduces the risk of component stress and structural deformation caused by excessively rapid or uneven pressurization, and helps improve the consistency and compactness of the internal structure of the fuel cell stack. In addition, the static operation after each stage of pressurization allows the clamping force to be fully distributed, eliminates local stress concentration, and further improves contact resistance and the overall performance of the fuel cell stack.

[0021] In practical applications, gradient pressurization technology helps operators precisely control the assembly process. Combined with real-time performance test data, it allows for the rapid selection of optimal assembly force parameters that match the stack structure and material properties, effectively improving the consistency, reliability, and final operational performance of fuel cell assembly. This control method is of significant technical importance for ensuring the quality of mass production of fuel cells and their long-term stable operation.

[0022] Preferably, the initial assembly force is 50%-70% of the maximum assembly force designed for the fuel cell stack.

[0023] The above technical solutions enable the rational distribution and adjustment of assembly force while ensuring the structural safety and functional integrity of the fuel cell stack. This facilitates the gradual increase of pressure during subsequent gradient pressurization, reducing the adverse effects on internal components of the stack caused by excessive one-time pressurization.

[0024] Specifically, a lower initial assembly force helps ensure the initial positioning of the fuel cell stack and the effective bonding of each component, reserving sufficient adjustment space for subsequent staged pressurization; it also effectively reduces the risks of component damage and seal failure during assembly. By gradually increasing the assembly force according to the established process in subsequent operations, it is possible not only to better promote assembly uniformity and eliminate stress concentration within the structure, but also to further optimize the contact state of each layer of the fuel cell stack, improving conductivity and service life.

[0025] In practical applications, this initial assembly force setting, combined with a gradient pressurization process, can significantly improve the consistency, safety, and controllability of fuel cell stack assembly, effectively ensuring excellent electrochemical performance and stability of the stack during subsequent operation. This method of graded pressurization and reasonable initial force setting also has significant promotional value and practical significance for the mass assembly and engineering application of fuel cells.

[0026] Preferably, when repeating step (c) as described in step (e), the constant current value remains unchanged, and the discharge duration is ≥10 minutes to ensure data stability.

[0027] The above technical solution ensures the objectivity and comparability of test data under each assembly force gradient, keeps the constant current value unchanged, and ensures that the test conditions are consistent at different stages, thereby enabling accurate evaluation of the impact of different assembly forces on the performance of the fuel cell stack; at the same time, it stipulates that the discharge duration is not less than 10 minutes to fully eliminate system fluctuations or short-term interference, and ensure the stability and representativeness of the test data.

[0028] Specifically, constant current helps eliminate performance evaluation bias caused by differences in operating parameters, making performance comparison more scientific and intuitive; a discharge duration of no less than 10 minutes can stabilize the internal temperature, flow field, and reaction of the fuel cell stack, reducing data errors caused by instantaneous or periodic fluctuations, and facilitating the analysis of the fuel cell stack's actual working performance under different assembly forces.

[0029] In practical applications, this solution can generate complete and traceable performance change curves, support scientific decision-making for assembly force optimization, improve the precision of fuel cell stack assembly quality control, and lay a solid foundation for subsequent mass production and engineering applications.

[0030] Compared with the prior art, the present invention has the following advantages: 1. This invention effectively simulates the actual operating environment of a fuel cell by performing gradient pressurization and electrochemical testing under continuous discharge conditions. By simultaneously acquiring output voltage and impedance spectrum parameters, a direct correlation between assembly force changes and electrochemical response is established, overcoming the limitations of traditional static testing. This in-situ verification method avoids interference with the fuel cell structure during disassembly and assembly, more accurately reflects the actual impact of different assembly forces on battery performance, and provides a reliable basis for optimization.

[0031] 2. This invention constructs a three-level priority decision mechanism based on output voltage, ohmic resistance, and gas mass transfer resistance, comprehensively considering the electrical performance output, internal losses, and reactant gas transport efficiency of the fuel cell stack. This method gradually explores the assembly force threshold through a gradient pressurization process, systematically balancing the contradiction between improving conductive contact and controlling flow channel pressure loss while ensuring the safety of the membrane electrode structure. This multi-parameter collaborative optimization strategy significantly improves the scientific rigor and reliability of the assembly force setting. Attached Figure Description

[0032] Figure 1 This is a system flowchart of the present invention; Figure 2 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1 (Single Cell Stack Verification) Step 1: Initial setup; The single-cell stack is placed in the hydraulic press fixture, and an initial assembly force of 18000N is applied.

[0035] Connect to the fuel cell test bench and confirm that the three chambers are pressure-holding qualified: the anode chamber / cathode chamber / coolant chamber are held at a test pressure of 150 kPa for 3 minutes, and the pressure drop is ≤0.4 kPa.

[0036] A constant current of 80A is applied through the test bench, and the discharge is carried out for ≥12 minutes.

[0037] Step 2: First round of data collection; Monitor output voltage: After 12 minutes, the voltage stabilized at 0.68V (fluctuation ≤ ±0.5%).

[0038] Perform electrochemical impedance spectroscopy (EIS) testing: Ohmic resistance = 0.22Ω, gas mass transfer resistance = 0.35Ω Step 3: Gradient pressure application; The pressurization rates of gradient pressurization and the corresponding test values ​​are shown in Table 1: Table 1 Pressurization phase pressurization rate Target value resting time Output voltage Ohm resistor First paragraph 800N / s 21600N 2 minutes 0.69V 0.20Ω Second paragraph 400N / s 28800N 2.5 minutes 0.71V 0.18Ω Third paragraph 200N / s 36000N 3 minutes 0.67V 0.17Ω Step 4: Data Comparison; Create a comparison table and filter the results. The comparison table is shown in Table 2: Table 2 Assembly force (N) Output voltage (V) Ohm resistance (Ω) 18000 0.68 0.22 21600 0.69 0.20 28800 0.71 0.18 36000 0.67 0.17 Filtering results: Output voltage TOP3: 28800N (0.71V) > 21600N (0.69V) > 18000N (0.68V); The lowest ohmic resistance among the TOP3: 21600N (0.20Ω); Optimal assembly force: 21600N.

[0039] Example 2 (Multi-cell stack verification) Step 1: Initial setup; Five battery cells were placed in a hydraulic press fixture, and an initial assembly force of 50,000 N was applied.

[0040] Connect to the fuel cell test bench and confirm that the three chambers are pressure-holding qualified: the anode chamber / cathode chamber / coolant chamber are held at a test pressure of 150 kPa for 3 minutes, and the pressure drop is ≤0.3 kPa.

[0041] A constant current of 200A is applied to the test bench, and the discharge is carried out continuously for ≥15 minutes.

[0042] Step 2: Gradient pressure application and data acquisition; The pressurization rates and corresponding test values ​​for gradient pressurization are shown in Table 3: Table 3 stage pressurization rate Target value resting time Output voltage Ohm resistor First paragraph 800N / s 60000N 2 minutes 3.25V 0.95Ω Second paragraph 400N / s 80000N 2.5 minutes 3.40V 0.85Ω Third paragraph 200N / s 110000N 3 minutes 3.20V 0.82Ω Step 3: Compare data to determine the optimal value; A comparison table is created, as shown in Table 4: Table 4 Assembly force (N) Output voltage (V) Ohm resistance (Ω) Gas mass transfer resistance (Ω) 50000 3.15 1.05 1.20 60000 3.25 0.95 1.35 80000 3.40 0.85 1.60 110000 3.20 0.82 2.10 Screening process: Output voltage TOP3: 80000N (3.40V) > 60000N (3.25V) > 110000N (3.20V); The lowest ohmic resistance among the TOP3: 80,000N (0.85Ω); Optimal assembly force: 80,000 N.

[0043] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for in-situ verification of fuel cell stack assembly force, characterized in that, Includes the following steps: (a) Place the fuel cell stack in a pressurized fixture and apply an initial assembly force; (b) Connect the fuel cell test bench to the electrochemical workstation and apply a constant current to the fuel cell stack for continuous discharge; (c) After the output voltage of the fuel cell stack stabilizes, record the voltage value and perform electrochemical impedance spectroscopy to obtain the ohmic resistance and gas mass transfer resistance. (d) Gradually increase the assembly force on the fuel cell stack using clamps; (e) Repeat step (c) after each increase in assembly force; (f) Compare the output voltage, ohmic resistance and gas mass transfer resistance under different assembly forces, and determine the optimal assembly force by prioritizing the highest output voltage as the first priority, the lowest ohmic resistance as the second priority and the lowest gas mass transfer resistance as the third priority.

2. As described in claim 1, characterized in that, The pressurizable clamp is any one of a cylinder clamp, a pneumatically driven clamp, or a mechanical press.

3. As described in claim 1, characterized in that, Before applying a constant current in step (b), it is necessary to confirm that the pressure holding and sealing of the three chambers of the fuel cell stack is qualified. The criteria for qualified pressure holding are: the pressure drop of the anode chamber, cathode chamber and coolant chamber is ≤0.5kPa after holding the pressure for 3 minutes under the test pressure.

4. As described in claim 1, characterized in that, The stable output voltage of the fuel cell stack in step (c) means that the voltage fluctuation amplitude is ≤ ±1% and lasts for ≥ 3 minutes.

5. As described in claim 1, characterized in that, The gradient pressurization in step (d) is performed according to the following segmented process: First stage of pressurization: pressurize at a rate of 500-1000 N / s to 110%-130% of the initial assembly force; The second stage of pressurization: pressurize at a rate of 200-500 N / s to 150%-180% of the initial assembly force; The third stage of pressurization: pressurize at a rate of 100-300 N / s to 200%-250% of the initial assembly force; After each pressurization, let it stand for 1-3 minutes to allow the pressure to be evenly distributed.

6. The method according to claim 5, characterized in that, The initial assembly force is 50%-70% of the maximum assembly force designed for the fuel cell stack.

7. As described in claim 1, characterized in that, When repeating step (c) in step (e), the constant current value remains unchanged, and the discharge duration is ≥10 minutes to ensure data stability.

Images