Diagnostic method and production method for a cell stack of an electrochemical energy converter

Abstract

The present invention relates to a diagnostic method (100) for diagnosing a state of a cell stack (300) of an electrochemical energy converter. The diagnostic method (100) comprises: - connecting (101) a plurality of bipolar plates (301) of the cell stack (300) to a cell voltage measurement system (311), - ascertaining (103) measurement values for each cell (303) of the plurality of cells (303) by means of the cell voltage measurement system (311), - determining (105) a characteristic value for each cell (303) of the plurality of cells (303) on the basis of measurement values ascertained by means of the cell voltage measurement system (311), - comparing (107) the characteristic value with a specified quality criterion, - outputting (109) an error message if the characteristic value does not satisfy the quality criterion, wherein the ascertaining of measurement values is carried out in a dry state of the cell stack (300).

Description

[0001] Description

[0002] title

[0003] Diagnostic method and manufacturing method for a cell stack of an electrochemical energy converter

[0004] The presented invention relates to a diagnostic method for diagnosing a condition of a cell stack of an electrochemical energy converter and a manufacturing method for manufacturing a cell stack of an electrochemical energy converter according to the appended claims.

[0005] State of the art

[0006] Electrochemical energy converters, such as fuel cell systems or electrolysis systems, are based on a cell stack consisting of a large number of electrochemical cells that are connected by bipolar plates or supplied with operating media.

[0007] The functionality of each individual cell is crucial for the functionality of an entire cell stack. A cell can fail due to, among other things, a lack of electrical or ionic contact or a short circuit.

[0008] When assembling a cell stack, individual cells can be damaged, so it is advisable to check the function of individual cells after assembly.

[0009] In order to monitor the individual cells of an electrochemical energy converter during operation, a cell voltage monitoring system can be provided that measures and records the cell voltage of individual or all cells. It is known to use such a cell voltage monitoring system during operation of an electrochemical energy converter filled with operating media.

[0010] Disclosure of the invention

[0011] Within the scope of the invention presented, a diagnostic method for diagnosing the condition of a cell stack of an electrochemical energy converter and a manufacturing method for manufacturing an electrochemical energy converter are presented. Further features and details of the invention emerge from the respective subclaims, the description, and the drawings. Features and details described in connection with the diagnostic method according to the invention naturally also apply in connection with the manufacturing method according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0012] The invention presented serves in particular to provide a robust electrochemical energy converter.

[0013] Thus, according to a first aspect of the invention presented, a diagnostic method for diagnosing a state of a cell stack of an electrochemical energy converter is presented.

[0014] The presented diagnostic method comprises connecting a plurality of cells, in particular bipolar plates of the cell stack, to a cell voltage measuring system, determining measured values ​​for each cell of a plurality of cells using the cell voltage measuring system, determining a characteristic value for each cell of the plurality of cells based on measured values ​​determined using the cell voltage measuring system, comparing the characteristic value with a predetermined quality criterion, and outputting an error message if the characteristic value does not meet the quality criterion, wherein the determination of measured values ​​is carried out in a dry state of the cell stack. In the context of the presented invention, a dry state of a cell stack is understood to mean a state in which the cell stack is not yet filled with operating fluids, in particular not with water, or in which the respective cells are dry.

[0015] In the context of the invention presented, a cell voltage measurement system is understood to mean, in particular, a so-called "cell voltage monitoring" system. The cell voltage measurement system can be part of the electrochemical energy converter or an external system for connecting to the electrochemical energy converter.

[0016] The presented diagnostic method is based on a cell voltage measurement system that is connected to a number of bipolar plates, in particular all bipolar plates of a cell stack for an electrochemical energy converter. Using the cell voltage measurement system, a measurement is performed on a specific cell, more precisely on the bipolar plates surrounding or forming the cell.

[0017] A characteristic value is determined based on the measured values ​​obtained by the cell voltage measurement system. The measured values ​​can be used directly to form the characteristic value or values. Alternatively, a characteristic value can be assigned to the measured values ​​using an assignment scheme, such as a mathematical transformation. The respective characteristic values ​​determined in this way are then compared with a predefined quality criterion, such as a threshold value or a permissible variance.

[0018] If the characteristic value does not meet the quality criterion, an error message is issued, which marks the respective measured cell as faulty.

[0019] Of course, even if the characteristic value is

[0020] If the quality criterion is met, a plausibility message is issued that identifies the respective measured cell as error-free or OK. It can be provided that each bipolar plate of the plurality of bipolar plates is connected to a multiplexer, and the multiplexer connects all of the plurality of bipolar plates one after the other to a single impedance bridge.

[0021] By using a multiplexer, a single measuring bridge can be used for a large number of cells, eliminating the need for a complex measuring system with a large number of measuring bridges or impedance bridges.

[0022] It may also be provided that the measured values ​​are determined by electrochemical impedance spectroscopy.

[0023] Electrochemical impedance spectroscopy (EIS) determines the impedance, i.e., the alternating current resistance, of electrochemical systems as a function of the frequency of an alternating voltage or current. Accordingly, an alternating voltage or current can be applied to a respective bipolar plate using the cell voltage measurement system to measure it.

[0024] It can further be provided that the characteristic value comprises a cell potential of a cell formed by the respective bipolar plate.

[0025] A cell potential has proven to be a robust measure for assessing the functionality of a cell in a cell stack of an electrochemical energy converter.

[0026] It may further be provided that the characteristic value includes a frequency-dependent resistance.

[0027] A frequency-dependent resistance, such as an AC resistance, has proven to be a robust measure for assessing the functionality of a cell in a cell stack of an electrochemical energy converter.

[0028] It may also be provided that the characteristic value is a

[0029] AC resistance, wherein the AC resistance is determined at a number of predetermined frequencies, the number being less than 50, preferably less than 10, in particular 1.

[0030] By using a small number of frequencies of an electrical current induced in each cell to perform EIS, the EIS can be performed particularly quickly.

[0031] It may also be provided that the measured values ​​are determined over a specified period of time and / or for induction currents with different frequencies.

[0032] By evaluating a temporal progression of the respective measured values, the behavior of a respective bipolar plate or cell can be evaluated over time or at different induction currents, so that a reliable measure of the functionality of the bipolar plate or cell in real operation can be determined.

[0033] It may further be provided that an electrolysis cell stack or a fuel cell stack is selected as the cell stack.

[0034] According to a second aspect, the presented invention relates to a manufacturing method for producing an electrochemical energy converter.

[0035] The presented manufacturing method comprises providing a cell stack comprising a plurality of electrochemical cells and a plurality of bipolar plates, carrying out a possible embodiment of the presented diagnostic method, and filling the cell stack with at least one operating fluid after the diagnostic method has been carried out.

[0036] The proposed manufacturing process is based on performing the diagnostic procedure before each cell stack is filled. Accordingly, the diagnostic procedure is performed while the cell stack is dry, so that the cell stack can be inspected, for example, while still on the respective production line. Accordingly, operating media for filling a defective cell stack are avoided, and only inconspicuous cell stacks—i.e., those that do not show any abnormalities or are not faulty during the diagnostic procedure—are released for filling.

[0037] In particular, it is intended that a fuel cell stack or an electrolysis cell stack is selected as the cell stack in the manufacturing process presented.

[0038] Advantages described in detail with respect to the diagnostic method for diagnosing a condition of a cell stack of an electrochemical energy converter according to the first aspect of the invention equally apply to a manufacturing method for manufacturing an electrochemical energy converter according to the second aspect of the invention.

[0039] Further advantages, features, and details of the invention will become apparent from the following description, which describes exemplary embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination.

[0040] They show:

[0041] Figure 1 shows a possible design of the presented diagnostic procedure.

[0042] Figure 2 shows a possible design of the presented manufacturing process.

[0043] Figure 3 shows an arrangement of a cell voltage measuring system on a cell stack according to a possible embodiment of the presented diagnostic method.

[0044] Figure 1 shows a diagnostic method 100 for diagnosing a condition of a cell stack of an electrochemical energy converter.

[0045] The diagnostic method 100 comprises a connection step 101 in which a plurality of bipolar plates of the cell stack are connected to a cell voltage measuring system, a determination step 103 in which measured values ​​for each cell of the plurality of cells are determined by means of the cell voltage measuring system, a determination step 105 in which a characteristic value for each cell of the plurality of cells is determined based on measured values ​​determined by means of the cell voltage measuring system, a comparison step 107 in which the characteristic value is compared with a predetermined quality criterion, and an output step 109 in which an error message is output in the event that the characteristic value does not meet the quality criterion.

[0046] According to the diagnostic method 100, the determination of measured values ​​is carried out in a dry state of the cell stack. Subsequently, the cell stack can be filled with operating media in a filling step 111.

[0047] For the determination step 103, the cell stack or a respective bipolar plate can be subjected to an electric current having an alternating voltage with low amplitudes around the resting potential of a respective cell of the cell stack.

[0048] Figure 2 shows a manufacturing method 200.

[0049] The manufacturing method 200 comprises a provision step 201 in which a cell stack is provided, ie, for example, assembled from a number of cells in a stacking process.

[0050] Following the provision step 201, the diagnostic method 100 according to Figure 1 is carried out in a diagnostic step 203.

[0051] Finally, in a filling step 205, the cell stack is filled with operating media.

[0052] Accordingly, if the diagnostic method 100 results in an error message, a corresponding cell stack can be excluded from the filling step 205. Figure 3 shows a cell stack 300. The cell stack 300 comprises a number of bipolar plates 301, which form a number of cells 303. A multiplexer 307 is electrically coupled to each of the bipolar plates 301 via connecting lines 305, so that each of the bipolar plates 301 can be connected to an impedance bridge 309 of a cell voltage measuring system 311 via the multiplexer 307.

Claims

Claims 1 . Diagnostic method (100) for diagnosing a condition of a cell stack (300) of an electrochemical energy converter, the diagnostic method (100) comprising: Connecting (101) a plurality of cells (303) of the cell stack (300) to a cell voltage measuring system (311), Determining (103) measured values ​​for each cell (303) of the plurality of cells (303) by means of the cell voltage measuring system (311), Determining (105) a characteristic value for each cell (303) of the plurality of cells (303) based on measured values ​​determined by means of the cell voltage measuring system (311), Comparing (107) the characteristic value with a given quality criterion, Outputting (109) an error message in the event that the characteristic value does not meet the quality criterion, wherein the determination of measured values ​​is carried out in a dry state of the cell stack (300).

2. Diagnostic method (100) according to claim 1, characterized in that each bipolar plate (301) of the plurality of bipolar plates (301) is connected to a multiplexer (307) of the cell voltage measuring system (311), and the multiplexer (307) connects all cells (303) of the plurality of cells (303) one after the other to a single impedance bridge (309) 3. Diagnostic method (100) according to claim 1 or 2, characterized in that the determination (103) of measured values ​​is carried out by electrochemical impedance spectroscopy.

4. Diagnostic method (100) according to one of the preceding claims, characterized in that that the characteristic value comprises a cell potential of a cell (303) formed by respective bipolar plates (301).

5. Diagnostic method (100) according to one of the preceding claims, characterized in that the characteristic value comprises a frequency-dependent resistance.

6. Diagnostic method (100) according to one of the preceding claims, characterized in that the characteristic value comprises an alternating current resistance, wherein the alternating current resistance is determined at a number of predetermined frequencies, wherein the number is less than 50, preferably less than 10, in particular 1.

7. Diagnostic method (100) according to one of the preceding claims, characterized in that the measured values ​​are determined over a predetermined period of time and / or with induction currents having different frequencies.

8. Diagnostic method (100) according to one of the preceding claims, characterized in that an electrolysis cell stack or a fuel cell stack is selected as the cell stack (300).

9. Manufacturing method (200) for producing an electrochemical energy converter, the manufacturing method (200) comprising: Providing (201) a cell stack (300) comprising a plurality of electrochemical cells (303) and a plurality of bipolar plates (301), Carrying out (203) a diagnostic method (100) according to one of claims 1 to 8, Filling (205) the cell stack (300) with at least one operating fluid after the diagnostic method (100) has been carried out.

10. Manufacturing method (100) according to claim 9, characterized in that a fuel cell stack or an electrolysis cell stack is selected as the cell stack (300).

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