An electrochemical impedance test equivalent circuit and fitting method

Abstract

The present application discloses an electrochemical impedance test equivalent circuit and fitting method, which relates to the field of battery technology and can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working state of the battery. An electrochemical impedance test equivalent circuit includes: an electrolyte membrane resistor; at least two-order equivalent circuits connected in series with the electrolyte membrane resistor, each of the at least two-order equivalent circuits is connected in series, and each of the equivalent circuits includes linear elements and nonlinear elements.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an electrochemical impedance test equivalent circuit and a fitting method. Background Art

[0002] PEMFC (Proton Exchange Membrane Fuel Cell) is a power supply device that can convert chemical energy into electrical energy by chemical reactions under certain catalytic conditions. It has the characteristics of low temperature, high efficiency, and zero emissions, such as hydrogen fuel cells. However, the unclear electrochemistry and transmission mechanism inside PEMFC has restricted its development. Its internal resistance is one of the important factors affecting the performance, efficiency and service life of PEMFC. EIS (Electrochemical Impedance Technology) is a transient electrochemical measurement technology that belongs to the category of AC signal measurement. It has the characteristics of fast measurement speed and low interference. The principle of EIS is to apply a small amplitude AC signal with different frequencies to the electrochemical system, measure the ratio of the AC signal voltage to the current (this ratio is the electrochemical impedance of the battery) with the change of the sine wave frequency ω, or the change of the impedance phase angle Φ with ω, and then analyze and study the working state of the battery.

[0003] At present, the electrochemical impedance of the battery can be tested by inferring the equivalent circuit diagram of the impedance spectrum based on the fitting results, and analyzing the working state of the battery through the basic circuit components and physical meanings.

[0004] However, the equivalent circuit of the existing electrochemical impedance test is difficult to accurately fit the electrochemical impedance spectrum inside the battery, and thus it is difficult to accurately reflect the working status of the battery. Summary of the invention

[0005] The embodiment of the present application provides an electrochemical impedance test equivalent circuit and fitting method, which can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working status of the battery.

[0006] In a first aspect of an embodiment of the present application, an electrochemical impedance spectroscopy equivalent circuit is provided, comprising:

[0007] Electrolyte membrane resistance;

[0008] At least two-order equivalent circuits are connected in series with the electrolyte membrane resistor, each order of the at least two-order equivalent circuits is connected in series with each other, and each order of the equivalent circuits includes a linear element and a nonlinear element.

[0009] In some embodiments, the electrochemical impedance spectroscopy equivalent circuit comprises:

[0010] A third-order equivalent circuit is connected in series with the electrolyte membrane resistor, and each order of the equivalent circuits of the third-order equivalent circuit is connected in series with each other.

[0011] In some embodiments, during the fitting process of the electrochemical impedance spectrum of the fuel cell, each order of the equivalent circuit corresponds to a frequency band of a different AC test current of the fuel cell.

[0012] In some embodiments, the third-order equivalent circuit includes a first-order equivalent circuit, a second-order equivalent circuit, and a third-order equivalent circuit connected in series in sequence, wherein the first-order equivalent circuit is connected in series with the electrolyte membrane resistor;

[0013] The frequency band of the AC test current corresponding to the first-order equivalent circuit is greater than the frequency band of the AC test current corresponding to the second-order equivalent circuit, and the frequency band of the AC test current corresponding to the second-order equivalent circuit is greater than the frequency band of the AC test current corresponding to the third-order equivalent circuit.

[0014] In some embodiments, the linear element comprises a resistor, and / or the nonlinear element comprises a constant phase angle element.

[0015] In some implementations, the linear element and the nonlinear element of each order equivalent circuit are connected in parallel.

[0016] A second aspect of the embodiment of the present application provides an electrochemical impedance test equivalent circuit fitting method, using the electrochemical impedance test equivalent circuit as described in the first aspect, the fitting method comprises:

[0017] Conducting a power-on test on the fuel cell to obtain impedance test data of the fuel cell;

[0018] Using Zview software, based on the impedance test data, the initial value of the element impedance in the electrochemical impedance test equivalent circuit is fitted;

[0019] The Zview software is used to fit the electrochemical impedance spectrum of the fuel cell based on the initial value of the element impedance.

[0020] In some embodiments, the impedance test data includes the imaginary part and the real part of the impedance expression of the electrochemical impedance test equivalent circuit, and the frequency of the AC test current applied to the fuel cell during the power-on test of the fuel cell;

[0021] The Zview software is used to fit the initial impedance value of the element in the electrochemical impedance test equivalent circuit based on the impedance test data, including:

[0022] The real part and the imaginary part corresponding to the different frequency bands of the AC test current are input into the Zview software. After fitting by the Zview software, the initial value of the element impedance of each order equivalent circuit is obtained respectively, wherein each order equivalent circuit corresponds to a different frequency band of the AC test current.

[0023] In some embodiments, the using the Zview software to fit the electrochemical impedance spectrum of the fuel cell based on the initial value of the element impedance includes:

[0024] Based on the initial value of the element impedance, construct an electrochemical impedance test equivalent circuit model;

[0025] The electrochemical impedance test equivalent circuit model is imported into the Zview software to perform overall fitting on the internal impedance of the fuel cell to obtain the electrochemical impedance spectrum.

[0026] In some embodiments, the electrochemical impedance spectroscopy equivalent circuit fitting method further comprises:

[0027] Based on the electrochemical impedance spectroscopy, the operating state of the fuel cell is evaluated.

[0028] The electrochemical impedance test equivalent circuit and fitting method provided in the embodiment of the present application are provided by setting at least two equivalent circuits, each order of the at least two equivalent circuits is connected in series, and each order of the equivalent circuit includes linear elements and nonlinear elements. By setting linear elements and nonlinear elements in each order of equivalent circuits, the phenomenon of impedance arc deformation caused by uneven distribution of porosity on the electrode surface can be represented. By setting at least two equivalent circuits, the anode and cathode impedances can be separated into different arcs in the electrochemical impedance spectrum, so that the anode impedance can be tested, thereby improving the accuracy of the electrochemical impedance test. Using the embodiment of the present application, an electrochemical impedance test equivalent circuit is provided, which can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working state of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic structural block diagram of an electrochemical impedance test equivalent circuit provided in an embodiment of the present application;

[0030] Figure 2 A schematic structural block diagram of another electrochemical impedance spectroscopy equivalent circuit provided in an embodiment of the present application;

[0031] Figure 3 A schematic structural block diagram of another electrochemical impedance test equivalent circuit provided in an embodiment of the present application;

[0032] Figure 4A schematic flow chart of an electrochemical impedance spectroscopy equivalent circuit fitting method provided in an embodiment of the present application;

[0033] Figure 5 A schematic diagram of electrochemical impedance spectroscopy analysis of a fuel cell provided in an embodiment of the present application;

[0034] Figure 6 Schematic diagrams of three electrochemical impedance spectroscopy provided in the embodiments of the present application. DETAILED DESCRIPTION

[0035] In order to better understand the technical solutions provided by the embodiments of this specification, the technical solutions of the embodiments of this specification are described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of this specification and the specific features in the embodiments are detailed descriptions of the technical solutions of the embodiments of this specification, rather than limitations on the technical solutions of this specification. In the absence of conflict, the embodiments of this specification and the technical features in the embodiments can be combined with each other.

[0036] In this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the statement "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements. The term "more than two" includes two or more than two situations.

[0037] PEMFC is a power supply device that can convert chemical energy into electrical energy by chemical reaction under certain catalytic conditions. It has the characteristics of low temperature, high efficiency and zero emission, such as hydrogen fuel cells. However, the unclear electrochemistry and transmission mechanism inside PEMFC restricts its development. Its internal resistance is one of the important factors affecting the performance, efficiency and service life of PEMFC. EIS is a transient electrochemical measurement technology, which belongs to the category of AC signal measurement and has the characteristics of fast measurement speed and low interference. The principle of EIS is to apply a small amplitude AC signal with different frequencies to the electrochemical system, measure the ratio of the voltage to the current of the AC signal (this ratio is the electrochemical impedance of the battery) with the change of the sine wave frequency ω, or the change of the phase angle Φ of the impedance with ω, and then analyze and study the working state of the battery. At present, the test method of the electrochemical impedance of the battery can be used to reverse the equivalent circuit diagram of the impedance spectrum based on the fitting results, and analyze the working state of the battery through the basic circuit components and physical meanings. However, the equivalent circuit of the existing electrochemical impedance test is difficult to accurately fit the electrochemical impedance spectrum inside the battery, and thus it is difficult to accurately reflect the working state of the battery.

[0038] In view of this, the embodiments of the present application provide an electrochemical impedance test equivalent circuit and a fitting method, which can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working state of the battery.

[0039] In a first aspect of an embodiment of the present application, an electrochemical impedance test equivalent circuit is provided, comprising: an electrolyte membrane resistor and at least two-order equivalent circuits, wherein the at least two-order equivalent circuits are connected in series with the electrolyte membrane resistor, and each order of the at least two-order equivalent circuits is connected in series with each other, and each order of the equivalent circuit comprises linear elements and nonlinear elements.

[0040] For example, Figure 1 A schematic structural block diagram of an electrochemical impedance test equivalent circuit provided in an embodiment of the present application. The electrochemical impedance test equivalent circuit includes: an electrolyte membrane resistor Rm and at least two-order equivalent circuits, at least two-order equivalent circuits are connected in series with the electrolyte membrane resistor Rm, and the two-order equivalent circuits may include a first-order equivalent circuit 100 and a second-order equivalent circuit 200, the first-order equivalent circuit 100 is connected in series with the second-order equivalent circuit 200, and the first-order equivalent circuit 100 is connected in series with the electrolyte membrane resistor Rm. Each order equivalent circuit includes linear elements and nonlinear elements. The power source E is connected in series with the electrolyte membrane resistor Rm.

[0041] It should be noted that PEMFC is a typical nonlinear black box system. At present, most of the research focuses on the diagnosis of PEMFC internal faults through different detection methods. The methods used are mostly model identification methods based on signal analysis in the time domain and frequency domain. There are generally two methods for analyzing impedance spectra. One is to establish a mathematical model and find the model parameters to infer the kinetic process and mechanism of the electrode system. This method can perfectly present the characteristics of the data, but it is very difficult to derive and assume the reaction mechanism. The second method is to reverse the equivalent circuit diagram of the impedance spectrum based on the fitting results, and judge the electrode process and mechanism through the basic circuit components and physical meaning. The difficulty lies in the connection between the basic components and the internal battery. At present, the application of EIS in the field of PEMFC mainly adopts the latter, but the different equivalent fitting circuits used will also significantly affect whether the experimental data can truly and accurately reflect the influence of external factors such as operating conditions on the internal impedance of PEMFC.

[0042] Usually, the electrochemical impedance test equivalent circuit is composed of the parallel connection of the electrolyte membrane resistance, double-layer capacitance and reaction resistance. The values ​​of these resistances and capacitances will vary greatly with the performance of the battery and the power generation state. The method of using EIS to measure the impedance of each component of the equivalent circuit is to superimpose a small measurement AC current on the discharge DC current of the fuel cell, measure and calculate the voltage and current, and obtain the impedance value through calculation. Usually, the equivalent circuit composed of the electrolyte membrane resistance, double-layer capacitance and reaction resistance can only be used for basic analysis. When considering more sophisticated electrochemical reaction processes, there will be large errors. For example, it cannot represent the phenomenon of impedance arc deformation caused by uneven distribution of porosity on the electrode surface.

[0043] In order to solve the problem that the equivalent circuit composed of electrolyte membrane resistance, double layer capacitance and reaction resistance cannot represent the impedance arc deformation caused by the uneven distribution of electrode surface porosity, nonlinear elements are introduced. With the help of nonlinear elements, the impedance arc deformation caused by the uneven reaction components caused by the porous structure of the electrode surface can be characterized. However, in actual situations, the cathode impedance may be significantly greater than the anode impedance, thereby masking the anode impedance. If the time constants of the anode reaction and the cathode reaction overlap, such overlap will also occur. If the activation impedance of the anode is extremely small, the frequency corresponding to the anode time constant may exceed the limit of most impedance elements, resulting in the anode impedance being unable to be measured.

[0044] In view of the above problems, the electrochemical impedance test equivalent circuit provided in the embodiment of the present application is provided by setting at least two equivalent circuits, and each order of the at least two equivalent circuits is connected in series, and each order of the equivalent circuit includes linear elements and nonlinear elements. By setting linear elements and nonlinear elements in each order of equivalent circuits, the phenomenon of impedance arc deformation caused by uneven distribution of porosity on the electrode surface can be represented. By setting at least two equivalent circuits, the anode and cathode impedances can be separated into different arcs in the electrochemical impedance spectrum, so that the anode impedance can be tested, thereby improving the accuracy of the electrochemical impedance test. Using the embodiment of the present application, an electrochemical impedance test equivalent circuit is provided, which can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working state of the battery.

[0045] In some embodiments, the electrochemical impedance test equivalent circuit may include: a third-order equivalent circuit, the third-order equivalent circuit is connected in series with the electrolyte membrane resistance, and each order of the third-order equivalent circuit is connected in series with each other. In the fitting process of the electrochemical impedance spectrum of the fuel cell, each order of the equivalent circuit corresponds to a frequency band of a different AC test current of the fuel cell.

[0046] For example, Figure 2 A schematic structural block diagram of another electrochemical impedance test equivalent circuit provided in an embodiment of the present application. The third-order equivalent circuit includes a first-order equivalent circuit 100, a second-order equivalent circuit 200, and a third-order equivalent circuit 300 connected in series in sequence, and the first-order equivalent circuit 100 is connected in series with the electrolyte membrane resistance Rm.

[0047] Exemplarily, the frequency band of the AC test current corresponding to the first-order equivalent circuit 100 is greater than the frequency band of the AC test current corresponding to the second-order equivalent circuit 200, and the frequency band of the AC test current corresponding to the second-order equivalent circuit 200 is greater than the frequency band of the AC test current corresponding to the third-order equivalent circuit 300. For example, the first-order equivalent circuit corresponds to a high frequency band, the second-order equivalent circuit corresponds to a medium frequency band, and the third-order equivalent circuit corresponds to a low frequency band.

[0048] In some embodiments, the linear element may include a resistor, and the nonlinear element may include a constant phase angle element. The linear element and the nonlinear element of each order equivalent circuit may be connected in parallel.

[0049] For example, Figure 3 This is a schematic structural block diagram of another electrochemical impedance test equivalent circuit provided in the embodiment of the present application. Figure 3 As shown, the first-order equivalent circuit includes a first constant phase angle element CPE1 and a first resistor Rct1 in parallel, the second-order equivalent circuit includes a second constant phase angle element CPE2 and a second resistor Rct2 in parallel, and the third-order equivalent circuit includes a third constant phase angle element CPE3 and a third resistor Rct3 in parallel.

[0050] The electrochemical impedance test equivalent circuit provided in the embodiment of the present application is composed of linear elements and nonlinear elements, wherein the first-order equivalent circuit 100, the second-order equivalent circuit 200 and the third-order equivalent circuit 300 correspond to the high frequency band, the medium frequency band and the low frequency band of the AC test current, respectively, and can represent the phenomenon of impedance arc deformation caused by the uneven distribution of the porosity of the electrode surface. By setting a three-level equivalent circuit, the anode and cathode impedances can be separated into different arcs in the electrochemical impedance spectrum, so that the anode impedance can be tested, thereby improving the accuracy of the electrochemical impedance test. Using the embodiment of the present application, an electrochemical impedance test equivalent circuit is provided, which can accurately fit the electrochemical impedance spectrum inside the battery, and thus truly approach the nonlinear working phenomenon of the fuel cell.

[0051] A second aspect of the embodiment of the present application provides an electrochemical impedance spectroscopy equivalent circuit fitting method, using the electrochemical impedance spectroscopy equivalent circuit as described in the first aspect, Figure 4 This is a schematic flow chart of an electrochemical impedance test equivalent circuit fitting method provided in an embodiment of the present application. Figure 4 As shown, an electrochemical impedance test equivalent circuit fitting method includes:

[0052] S101: Conducting a power-on test on the fuel cell to obtain impedance test data of the fuel cell. Exemplarily, the fuel cell is powered on and tested using an impedance test device, a small measurement AC current is superimposed on the discharge DC current of the fuel cell, i.e., an AC test current is superimposed, and then the voltage and current of the fuel cell are tested, and the impedance value is obtained through calculation, i.e., the impedance test data is obtained.

[0053] S102: Using Zview software, based on the impedance test data, the initial impedance value of the element in the electrochemical impedance test equivalent circuit is fitted. Zview software is an impedance analysis software, and the impedance test data can be imported into Zview software. Zview software fits the impedance to obtain the initial impedance value of the element in the electrochemical impedance test equivalent circuit described in the first aspect. The initial impedance value of the element is the initial electrical parameter of each element in the electrochemical impedance test equivalent circuit.

[0054] S103: Using Zview software, based on the initial value of the element impedance, the electrochemical impedance spectrum of the fuel cell is fitted. The initial value of the element impedance in the electrochemical impedance test equivalent circuit is imported into the Zview software, and the electrochemical impedance spectrum of the fuel cell can be fitted.

[0055] The electrochemical impedance test equivalent circuit fitting method provided in the embodiment of the present application sets at least two equivalent circuits in the electrochemical impedance test equivalent circuit, and each order of the at least two equivalent circuits is connected in series, and each order of the equivalent circuit includes linear elements and nonlinear elements. By setting linear elements and nonlinear elements in each order of equivalent circuits, the phenomenon of impedance arc deformation caused by uneven distribution of porosity on the electrode surface can be represented. By setting at least two equivalent circuits, the anode and cathode impedances can be separated into different arcs in the electrochemical impedance spectrum, so that the anode impedance can be tested, thereby improving the accuracy of the electrochemical impedance test. Using the embodiment of the present application, an electrochemical impedance test equivalent circuit is provided, which can accurately fit the electrochemical impedance spectrum inside the battery, thereby accurately reflecting the working state of the battery.

[0056] In some embodiments, the impedance test data includes the imaginary part and the real part of the impedance expression of the electrochemical impedance test equivalent circuit, and the frequency of the AC test current applied to the fuel cell during the power-on test of the fuel cell.

[0057] Step S102 may include:

[0058] The real part and imaginary part corresponding to the frequency band of different AC test currents are input into the Zview software, and after fitting by the Zview software, the initial value of the element impedance of each order equivalent circuit is obtained respectively, wherein each order equivalent circuit corresponds to the frequency band of different AC test currents. In step S101, the real part and imaginary part under different AC test current frequency bands can be measured by different AC test currents. The real part and imaginary part corresponding to the frequency band of different AC test currents are input into the Zview software, and after fitting by the Zview software, the initial value of the element impedance of each order equivalent circuit is obtained respectively, and then the initial value of the element impedance of each order equivalent circuit can be fitted respectively. The initial value of the element impedance corresponds to the resistance value of the electrolyte membrane resistor, the impedance value of the first constant phase angle element CPE1, the resistance value of the first resistor Rct1, the impedance value of the second constant phase angle element CPE2 and the resistance value of the second resistor, the impedance value of the third constant phase angle element CPE3 and the resistance value of the third resistor Rct3.

[0059] In some implementations, step S103 may include:

[0060] Based on the initial value of the component impedance, an electrochemical impedance test equivalent circuit model is constructed. The electrochemical impedance test equivalent circuit described in the first aspect is only a circuit structure. By substituting the initial value of the component impedance into the electrochemical impedance test equivalent circuit, an electrochemical impedance test equivalent circuit model with clear parameters of each component can be obtained.

[0061] The electrochemical impedance test equivalent circuit model is imported into the Zview software to perform an overall fit on the internal impedance of the fuel cell and obtain the electrochemical impedance spectrum. The electrochemical impedance test equivalent circuit model is imported into the Zview software, which can iteratively calculate the electrochemical impedance test equivalent circuit model to accurately calculate the impedance of each component in the electrochemical impedance test equivalent circuit model, so as to better characterize the internal impedance of the fuel cell.

[0062] In some embodiments, the electrochemical impedance spectroscopy equivalent circuit fitting method further comprises:

[0063] The working state of the fuel cell is evaluated based on electrochemical impedance spectroscopy.

[0064] For example, since the measurement equipment uses a low-noise optimization algorithm during the EIS test, the impact of the inductive reactance of the internal and external circuits of the fuel cell on the test will be significantly reduced. Therefore, when constructing the equivalent circuit model, no inductive element can be set in the main circuit. In order to obtain accurate and comprehensive internal parameter information at different frequency bands, a third-order equivalent circuit model is used to fit the EIS test results. The third-order equivalent circuit describes the electrochemical reaction process inside the fuel cell when the AC test current is tested in the high frequency band, medium frequency band and low frequency band respectively. The impedance Z of the constant phase angle element is generally expressed as formula (1):

[0065]

[0066] Among them, Z 0 is the impedance factor, Z 0 It can change with the change of a, ω is the angular frequency; n is the frequency factor; a is the impedance angle. When the constant phase angle element is connected in parallel with the purely linear resistance element, the relationship is as follows:

[0067]

[0068] Formula (2) represents a circle with (R / 2, -R(ctg(a / 2)) / 2) as the center and R / 2sina as the radius on the complex plane. The arc in the first quadrant can be regarded as a part of a semicircle with a radius of R / 2sina and a center in the fourth quadrant. The deflection angle is (n-1)π / 2, where n is a natural number. Therefore, the constant phase angle can be used to fit several arcs in the EIS test results. R is the resistance value of the resistor as a linear element.

[0069] In the parameter fitting process of the third-order equivalent circuit model, the setting of the initial value of the component impedance should ensure that the same component parameters in different links have sufficient discrimination and cannot deviate too much from the measured values. Since RQ components are used in the high-frequency, medium-frequency and low-frequency bands, if the initial parameters are set too close, the fitting software will not be able to correctly distinguish and correspond, which may easily cause errors in fitting multiple RQ links to a certain frequency band curve at the same time. In addition, if only the discrimination of the three frequency bands is considered when setting the initial value, and the degree of conformity with the actual value is ignored, it is easy to produce a large fitting error, resulting in fitting failure.

[0070] For example, Figure 5 This is a schematic diagram of electrochemical impedance spectroscopy analysis of a fuel cell provided in an embodiment of the present application. Figure 5 As shown in the electrochemical impedance spectrum of the fuel cell, the horizontal axis is the real part Re(z) in the impedance expression of the fuel cell, and the unit is Ω·cm 3 , the ordinate is the imaginary part Im(z), the unit is Ω·cm 3 The electrochemical impedance spectrum is divided into four parts: ohmic consumption impedance R Ω , Anode activation characteristic impedance R fA , cathode activation consumption impedance R fC and mass transfer characteristic impedance, the coordinate values ​​corresponding to the horizontal axis are Z Ω , Z Ω +Z fA and Z Ω +Z fA +Z fC .

[0071] Exemplarily, the electrochemical impedance spectroscopy equivalent circuit fitting method provided in the embodiment of the present application has the following process:

[0072] First, the impedance test data of the fuel cell obtained from the test is imported into the Zview software. According to the original shape corresponding to the impedance test data, segmented fitting is performed to obtain the initial values ​​of the third-order equivalent circuit, that is, the impedance of Rm, Rct and CPE of each order equivalent circuit, and Rm is classified as the first-order equivalent circuit. After fitting the initial values ​​of each parameter, the electrochemical impedance test equivalent circuit model with the initial value of the component impedance is imported into the Zview software for overall fitting, and finally the EIS curve and the corresponding different impedance values ​​are obtained. The fitting results are exported, and the results can include four parts, combined with Figure 5, R1 can be used to characterize the ohmic resistance of the fuel cell system, corresponding to the ohmic consumption, which mainly reflects the difficulty of charge transfer to the external circuit. Its value is independent of the current density, including the ionic resistance of the electrolyte, the contact resistance between the electrolyte and the electrode, and the electronic resistance of the electrode, current collection layer and electrode lead. R2 can be used to characterize the anode activation impedance, corresponding to the anode activation characteristics. R3 can be used to characterize the cathode activation impedance, corresponding to the cathode activation consumption. R2 and R3 together reflect the kinetic characteristics of the electrochemical reaction. The influencing factors are mainly the reaction environment on the electrode surface and the activity of the reaction gas in the catalytic layer. R4 can be used to characterize the mass transfer impedance, corresponding to the mass transfer characteristics, reflecting the difficulty of gas mass transfer in the fuel cell stack.

[0073] For example, Figure 6 Schematic diagrams of three electrochemical impedance spectroscopy provided in the embodiments of the present application. Figure 6 The three curves shown may correspond to three electrochemical impedance spectra, which may be electrochemical impedance spectra of a fuel cell in three working states, or electrochemical impedance spectra of three fuel cells, which are not specifically limited in the embodiments of the present application.

[0074] The electrochemical impedance test equivalent circuit fitting method provided in the embodiment of the present application adopts a third-order equivalent circuit fitting method, and the segmented identification of the EIS test results with the help of Zview software can better approximate the true value of the internal impedance of the fuel cell, and can compare the differences in the internal impedance values ​​of the fuel cell under different frequency bands and different current densities, thereby better exploring the mechanism of the influence of external working conditions on the internal of the fuel cell, so as to propose targeted improvement measures.

[0075] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0076] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-readable program code.

[0077] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0078] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0079] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0080] An embodiment of the present application also provides a computer program product, which includes computer software instructions. When the computer software instructions are executed on a processing device, the processing device executes the process of the electrochemical impedance test equivalent circuit fitting method.

[0081] The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on the computer, the process or function according to the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, a computer, a server or a data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (digital subscriber line, DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium can be any available medium that a computer can store or a data storage device such as a server or a data center that includes one or more available media integration. Available media can be magnetic media, (e.g., floppy disk, hard disk, tape), optical media (e.g., DVD), or semiconductor media (e.g., solid state disk (solid state disk, SSD)), etc.

[0082] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0083] In the several embodiments provided in the present application, it should be understood that the disclosed devices, apparatuses and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0084] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0085] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0086] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0087] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

[0088] Although the preferred embodiments of this specification have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of this specification.

[0089] Obviously, those skilled in the art can make various changes and modifications to this specification without departing from the spirit and scope of this specification. Thus, if these modifications and variations of this specification fall within the scope of the claims of this specification and their equivalents, this specification is also intended to include these modifications and variations.

Claims

1. An electrochemical impedance test equivalent circuit, characterized in that: include: Electrolyte membrane resistance; A third-order equivalent circuit is connected in series with the electrolyte membrane resistance, each order of the three-order equivalent circuits is connected in series with each other, and each order of the three-order equivalent circuits includes a linear element and a nonlinear element to separate the anode and cathode impedances into different arcs in the electrochemical impedance spectrum; In the fitting process of the electrochemical impedance spectrum of the fuel cell, each order equivalent circuit corresponds to the frequency band of different AC test currents of the fuel cell, wherein the third-order equivalent circuit includes a first-order equivalent circuit, a second-order equivalent circuit and a third-order equivalent circuit connected in series in sequence, the first-order equivalent circuit is connected in series with the electrolyte membrane resistance, the first-order equivalent circuit corresponds to a high frequency band, the second-order equivalent circuit corresponds to a medium frequency band, and the third-order equivalent circuit corresponds to a low frequency band.

2. The electrochemical impedance spectroscopy equivalent circuit according to claim 1, characterized in that: The frequency band of the AC test current corresponding to the first-order equivalent circuit is greater than the frequency band of the AC test current corresponding to the second-order equivalent circuit, and the frequency band of the AC test current corresponding to the second-order equivalent circuit is greater than the frequency band of the AC test current corresponding to the third-order equivalent circuit.

3. The electrochemical impedance spectroscopy equivalent circuit according to any one of claims 1 to 2, characterized in that: The linear element includes a resistor, and / or the nonlinear element includes a constant phase angle element.

4. The electrochemical impedance spectroscopy equivalent circuit according to any one of claims 1 to 2, characterized in that: The linear element and the nonlinear element of each order equivalent circuit are connected in parallel.

5. A method for fitting an equivalent circuit of an electrochemical impedance test, characterized in that: Using the electrochemical impedance test equivalent circuit according to any one of claims 1 to 4, the fitting method comprises: Conducting a power-on test on the fuel cell to obtain impedance test data of the fuel cell; Using Zview software, based on the impedance test data, the initial value of the element impedance in the electrochemical impedance test equivalent circuit is fitted; The Zview software is used to fit the electrochemical impedance spectrum of the fuel cell based on the initial value of the element impedance.

6. The electrochemical impedance spectroscopy equivalent circuit fitting method according to claim 5, characterized in that: The impedance test data includes the imaginary part and the real part of the impedance expression of the electrochemical impedance test equivalent circuit, and the frequency of the AC test current applied to the fuel cell during the power-on test of the fuel cell; The Zview software is used to fit the initial impedance value of the element in the electrochemical impedance test equivalent circuit based on the impedance test data, including: The real part and the imaginary part corresponding to the different frequency bands of the AC test current are input into the Zview software. After fitting by the Zview software, the initial value of the element impedance of each order equivalent circuit is obtained respectively, wherein each order equivalent circuit corresponds to a different frequency band of the AC test current.

7. The electrochemical impedance spectroscopy equivalent circuit fitting method according to claim 6, characterized in that: The method of using the Zview software to fit the electrochemical impedance spectrum of the fuel cell based on the initial value of the element impedance includes: Based on the initial value of the element impedance, construct an electrochemical impedance test equivalent circuit model; The electrochemical impedance test equivalent circuit model is imported into the Zview software to perform overall fitting on the internal impedance of the fuel cell to obtain the electrochemical impedance spectrum.

8. The electrochemical impedance spectroscopy equivalent circuit fitting method according to claim 6, characterized in that: Also includes: Based on the electrochemical impedance spectroscopy, the operating state of the fuel cell is evaluated.

Images