Lithium battery AC impedance spectrum time domain and frequency domain conversion method and system

Abstract

The invention discloses a lithium battery AC impedance spectroscopy time domain and frequency domain conversion method and system, and relates to the technical field of battery data processing, and the method comprises the steps: carrying out the electrochemical impedance spectroscopy measurement of a to-be-measured lithium battery module, and obtaining the discrete impedance data of the electrochemical impedance spectroscopy; simulating the lithium battery module to be tested by using a preset equivalent circuit to obtain a fitting relationship between the circuit parameters of the preset equivalent circuit and the discrete impedance data; based on the discrete impedance data and the fitting relationship, constructing a target loss function about a regularization coefficient; determining an optimal regularization coefficient by taking the minimum value of the target loss function and combining relaxation time distribution precision meeting a preset condition as an optimization target; and converting the discrete impedance data into a continuous function on a time domain by using a regularization method based on an optimal regularization coefficient to obtain relaxation time distribution of the lithium battery module to be tested. According to the method, the technical problem that the polarization process in a battery electrochemical system cannot be effectively identified by traditional electrochemical impedance spectroscopy analysis is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery data processing, and in particular to a method and system for converting a lithium battery AC impedance spectrum into a time domain and a frequency domain. Background Art

[0002] Electrochemical Impedance Spectroscopy (EIS) is a method to reveal the kinetic characteristics of different processes inside the battery and is widely used in the field of battery research. In practical applications, due to the lack of transparency of the reaction process mechanism inside the battery, the current application scope of EIS is mainly limited to applied research; in the study of the internal mechanism of the battery, equivalent circuit analysis is often used. At the same time, due to the high degree of coupling of the internal kinetic process of the battery, it is difficult to achieve a comprehensive study of the influencing factors of each process. It can be seen that the current research is generally fragmented and lacks systematicity, and cannot effectively identify the polarization process in the battery electrochemical system. Summary of the invention

[0003] The purpose of the present invention is to provide a method and system for converting the time-domain and frequency-domain of the AC impedance spectrum of a lithium battery in order to solve at least one of the above technical problems.

[0004] In the first aspect, an embodiment of the present invention provides a method for converting the time domain and frequency domain of the alternating current impedance spectrum of a lithium battery, comprising: performing electrochemical impedance spectrum measurement on a lithium battery module to be tested to obtain discrete impedance data of the electrochemical impedance spectrum; simulating the lithium battery module to be tested using a preset equivalent circuit to obtain a fitting relationship between circuit parameters of the preset equivalent circuit and the discrete impedance data; constructing a target loss function regarding a regularization coefficient based on the discrete impedance data and the fitting relationship; determining an optimal regularization coefficient with the minimum value of the target loss function and the relaxation time distribution accuracy meeting preset conditions as the optimization target; and transforming the discrete impedance data into a continuous function in the time domain using a regularization method based on the optimal regularization coefficient to obtain a relaxation time distribution of the lithium battery module to be tested.

[0005] Furthermore, the discrete impedance data includes: a test frequency, and a real part of impedance and an imaginary part of impedance corresponding to the test frequency.

[0006] Furthermore, the preset equivalent circuit includes a Voigt equivalent circuit; and the fitting relationship includes:

[0007]

[0008] Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance of the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

[0009] Furthermore, the objective loss function includes:

[0010]

[0011] Wherein, N is the total amount of discrete impedance data; y n is the frequency point n n The discrete impedance data measured at M ,f n ) is the preset equivalent circuit for the discrete impedance data y n The fitting result of ; λ is the regularization coefficient, and λ≥0; P(x1,x2,…,x M ) is the penalty function, M is the total amount of data of the fitting result, x n is the nth fitting result, and p is a preset constant greater than or equal to 1.

[0012] Furthermore, the relaxation time distribution accuracy meets a preset condition, including: a real-imaginary part difference test function and a real-imaginary part cross validation test function calculated based on the relaxation time distribution are both less than a preset threshold; wherein the real-imaginary part difference test function includes:

[0013] The real-imaginary cross validation test function includes:

[0014]

[0015] Among them, DRT Re,λ DRT is the relaxation time distribution result calculated using the real part of the discrete impedance data; Im,λ is the relaxation time distribution result calculated using the imaginary part of the discrete impedance data; Z' is the real part of the discrete impedance data; Z'' (DRT Im,λ ) is the imaginary part of the impedance calculated using the relaxation time distribution result; Z'' is the imaginary part of the discrete impedance data; Z'(DRT Re,λ ) is the real part of the impedance calculated using the relaxation time distribution results.

[0016] Further, the discrete impedance data is transformed into a continuous function in the time domain, including:

[0017] Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; R0 is the ohmic internal resistance of the battery that is independent of frequency; Z pol (ω) is the frequency-dependent polarization resistance in the battery; g(τ) is the relaxation time distribution; τ is the relaxation time; j is the imaginary unit; ω is the angular frequency.

[0018] In a second aspect, an embodiment of the present invention further provides a lithium battery AC impedance spectrum time-domain frequency-domain conversion system, comprising: a measurement module, an equivalent module, a construction module, a determination module and a conversion module; wherein the measurement module is used to perform electrochemical impedance spectrum measurement on a lithium battery module to be measured to obtain discrete impedance data of the electrochemical impedance spectrum; the equivalent module is used to simulate the lithium battery module to be measured using a preset equivalent circuit to obtain a fitting relationship between the circuit parameters of the preset equivalent circuit and the discrete impedance data; the construction module is used to construct a target loss function about a regularization coefficient based on the discrete impedance data and the fitting relationship; the determination module is used to determine an optimal regularization coefficient with the minimum value of the target loss function and the relaxation time distribution accuracy meeting preset conditions as the optimization target; the conversion module is used to transform the discrete impedance data into a continuous function in the time domain using a regularization method based on the optimal regularization coefficient to obtain the relaxation time distribution of the lithium battery module to be measured.

[0019] Furthermore, the preset equivalent circuit includes a Voigt equivalent circuit; and the fitting relationship includes:

[0020]

[0021] Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance of the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

[0022] In a third aspect, an embodiment of the present invention further provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method provided in the embodiment of the present invention when executing the computer program.

[0023] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and when the computer instructions are executed by a processor, the method provided in the embodiment of the present invention is implemented.

[0024] The embodiment of the present invention provides a method and system for time-domain and frequency-domain conversion of the alternating current impedance spectrum of a lithium battery. The method uses electrochemical impedance spectroscopy to extract battery data, and transforms discrete impedance data based on an equivalent circuit method and a regularization transformation method to achieve time-domain and frequency-domain conversion of the battery electrochemical impedance spectrum, thereby alleviating the technical problem that traditional electrochemical impedance spectroscopy analysis cannot effectively identify the polarization process in the battery electrochemical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 A flow chart of a method for converting the time domain to the frequency domain of an AC impedance spectrum of a lithium battery provided by an embodiment of the present invention; Figure 2 A basic structural diagram of an equivalent circuit provided by an embodiment of the present invention; Figure 3 A diagram of electrochemical impedance spectroscopy simulation results of a basic equivalent circuit model provided in an embodiment of the present invention; Figure 4 A schematic diagram of a Voigt equivalent circuit structure provided by an embodiment of the present invention; Figure 5 An electrochemical impedance spectrum image of a lithium battery after importing measured data provided by an embodiment of the present invention; Figure 6 A comparison diagram of an electrochemical impedance spectrum curve obtained by simulating an equivalent circuit model provided in an embodiment of the present invention and the actual result; Figure 7 A lithium battery relaxation time distribution image conversion result diagram provided by an embodiment of the present invention; Figure 8 A schematic diagram of a lithium battery AC impedance spectrum time-domain and frequency-domain conversion system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0027] The following detailed description is an exemplary description, which is intended to provide further detailed description of the present invention. Unless otherwise specified, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present invention.

[0028] Embodiment 1 Figure 1 1 is a flow chart of a method for converting the time domain to frequency domain of a lithium battery AC impedance spectrum provided by an embodiment of the present invention. Figure 1 As shown, the method specifically comprises the following steps: Step S102 , performing electrochemical impedance spectroscopy measurement on the lithium battery module to be measured to obtain discrete impedance data of the electrochemical impedance spectroscopy.

[0029] Optionally, the discrete impedance data includes: a test frequency, and a real part of impedance and an imaginary part of impedance corresponding to the test frequency.

[0030] Step S104, using a preset equivalent circuit to simulate the lithium battery module to be tested, and obtaining a fitting relationship between circuit parameters of the preset equivalent circuit and discrete impedance data.

[0031] Step S106, constructing a target loss function with respect to a regularization coefficient based on the discrete impedance data and the fitting relationship.

[0032] Step S108, taking the minimum value of the target loss function and the relaxation time distribution accuracy satisfying the preset conditions as the optimization target, and determining the optimal regularization coefficient.

[0033] Step S110, using a regularization method based on an optimal regularization coefficient, the discrete impedance data is transformed into a continuous function in the time domain to obtain the relaxation time distribution of the lithium battery module to be tested.

[0034] In an optional implementation provided by an embodiment of the present invention, the preset equivalent circuit includes a Voigt equivalent circuit; the Voigt equivalent circuit is composed of a plurality of parallel elements of differential resistors and capacitors. Optionally, the fitting relationship includes:

[0035]

[0036] Where Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance in the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

[0037] In an optional implementation provided by an embodiment of the present invention, the target loss function includes:

[0038]

[0039] Where N is the total amount of discrete impedance data; y n is the frequency point n n The discrete impedance data measured at M ,f n ) is the preset equivalent circuit for discrete impedance data y n The fitting result of ; λ is the regularization coefficient, and λ≥0; P(x1,x2,…,x M ) is the penalty function, M is the total amount of data of the fitting result, x n is the nth fitting result, and p is a preset constant greater than or equal to 1.

[0040] Specifically, in an embodiment of the present invention, the relaxation time distribution accuracy is determined by minimizing the real-imaginary difference test function and the real-imaginary cross-validation test function, and the specific method is to calculate the DRT calculated independently using the real and imaginary parts of the data Re,λ and DRT Im,λ The difference between , and the difference between the imaginary and real parts of the impedance calculated using the real and imaginary parts of the experimental data and the relaxation time distribution.

[0041] Specifically, the relaxation time distribution accuracy meets the preset conditions, including: the real part-imaginary part difference test function and the real part-imaginary part cross validation test function calculated based on the relaxation time distribution are both less than a preset threshold; wherein the real part-imaginary part difference test function includes:

[0042] The real-imaginary cross validation test functions include:

[0043]

[0044] Among them, DRT Re,λ DRT is the relaxation time distribution result calculated using the real part of the discrete impedance data; Im,λ is the relaxation time distribution result calculated using the imaginary part of the discrete impedance data; Z' is the real part of the discrete impedance data; Z'' (DRT Im,λ ) is the imaginary part of the impedance calculated using the relaxation time distribution results; Z'' is the imaginary part of the discrete impedance data; Z'(DRT Re,λ) is the real part of the impedance calculated using the relaxation time distribution results.

[0045] Specifically, in step S110, the discrete impedance data is transformed into a continuous function in the time domain, including:

[0046] Where Z(ω) is the total impedance of the lithium battery module to be tested; R0 is the ohmic internal resistance of the battery that is independent of frequency; Z pol (ω) is the frequency-dependent polarization resistance in the battery; g(τ) is the relaxation time distribution; τ is the relaxation time; j is the imaginary unit; ω is the angular frequency.

[0047] Specifically, the method provided in the embodiment of the present invention adopts a regularization method in the transformation between continuous functions in the discrete impedance data domain and the time domain, and the core function of the regularization is the above-mentioned target loss function: It can be seen that the transformation equation must include the regularization coefficient. The regularization coefficient is added to prevent oscillation caused by excessive errors between experimental data and equivalent circuit fitting data during the iteration process; therefore, the optimal regularization parameter is solved and substituted into the target loss function to obtain the relaxation time distribution result.

[0048] In an optional implementation provided by an embodiment of the present invention, in actual working conditions, factors such as temperature and the SOC and SOH of the battery will affect the electrochemical impedance spectroscopy test of the battery, so it is necessary to accurately determine the state parameters of the battery. This embodiment performs an electrochemical impedance spectroscopy test on a lithium battery at 25°C, 50% SOC, and 98% SOH, and the results are shown in Table 1: Table 1 Simulation data of electrochemical impedance spectroscopy of parallel lithium batteries

[0049] Table 1 shows the electrochemical impedance spectroscopy test results of lithium batteries at 1kHz-0.1Hz, which measures the impedance, real part of impedance, imaginary part of impedance, phase angle and battery terminal voltage at the corresponding frequency of the battery.

[0050] The three parameters of frequency, real impedance part and imaginary impedance part in Table 1 are extracted to obtain the original data of time-frequency domain conversion.

[0051] In an optional implementation provided by an embodiment of the present invention, the equivalent circuit is used to extract parameters and perform regularization transformation: In the embodiment of the present invention, the equivalent circuit (ECM) method is a circuit model used to describe the impedance characteristics of the electrochemical system. A series of basic circuit elements such as resistors, capacitors, and inductors are combined in different ways such as series and parallel to achieve frequency domain simulation of the electrochemical impedance spectrum. The basic simulation principle is as follows: 1. Establish the internal reaction process of the battery. For common batteries, the internal part is usually composed of electrodes and electrolytes. The basic reactions may include: oxidation of compounds in the battery, migration from the bulk of the solution to the electrode / solution interface; adsorption of the oxidized state of the compound on the electrode surface; obtaining electrons on the electrode and being reduced; desorption of the reduced state of the compound from the electrode surface; migration of the reduced state of the compound from the electrode / solution interface to the bulk of the solution.

[0052] 2. Establishment of equivalent circuit elements. Impedance is assigned according to the internal reaction process of the battery, which may include: internal resistance of the working electrode, solution resistance between electrodes, resistance of the interface between electrode and solution, and double-layer capacitance generated by the double-layer structure of the electrode / solution interface.

[0053] 3. Establishment of circuit structure. Construct an equivalent circuit model by combining the electrode reaction process and equivalent circuit elements. Since the working electrode resistance and the solution resistance are equivalent to a series structure, and the solution resistance is much larger than other resistances, this part is often equivalent to the solution resistance; for the battery double-layer structure, since the double-layer capacitance and the electrode / solution interface contact resistance are generated at the same position, they can be regarded as a parallel state. Therefore, the basic equivalent circuit model of the battery can be composed of two parts: a resistor and a resistor / capacitor parallel structure, such as Figure 2 shown.

[0054] 4. Equivalent circuit model calculation. Calculate according to the equivalent circuit structure. By converting the resistance and capacitance elements into admittance expressions and performing certain mathematical processing, the expression can be obtained:

[0055] Where Z' is the real impedance of the battery, R s is the battery solution resistance, R ct is the battery electrode / solution interface contact resistance, and Z'' is the battery imaginary impedance.

[0056] Plotting the above expression on the Nyquist diagram gives a basic semicircular arc, such as Figure 3 shown.

[0057] Figure 4 Schematic diagram of a Voigt equivalent circuit diagram provided according to an embodiment of the present invention. Figure 4As shown, for the Voigt equivalent circuit, it can be regarded as a model with multiple RC parallel structures built in. Each RC structure will be represented as a semicircular structure on the Nyquist diagram. By differentiating the resistance, the electrochemical impedance spectrum simulation can be approximated and a simulation image closest to the actual result can be drawn.

[0058] In the embodiment of the present invention, regularization transformation is performed according to equivalent circuit parameters.

[0059] In order to solve the relaxation time distribution using discrete impedance data, it is first necessary to solve the ill-posed problem. The present invention adopts a regularization method to solve the ill-posed problem. The regularization method is implemented by adding a regularization term to the loss function of the model. The regularization term is usually based on the size of the model parameters to limit the number or amplitude of the model parameters. The specific regularization method adopts the L2 regularization algorithm. The L2 regularization uses the sum of the squares of the model parameters as the regularization term. It achieves regularization by adding the L2 norm term to the loss function, encouraging the model to generate smooth weights, that is, adjusting the weight of the feature to a smaller value and tending to minimize all items. Since individual outliers are inevitable in impedance data in actual tests, the use of the L2 regularization algorithm will be more robust to outliers and reduce the problem of over-reliance on a single feature parameter in the calculation. The L2 regularization calculation formula is as follows:

[0060] The formula is the sum of two parts. The left side is the mean square error loss function, which is the true value; the right side is the regularization term, which is used as a penalty function to control the calculation results and prevent oscillation; λ is the regularization coefficient, which is used to control the strength of the regularization term.

[0061] In an optional implementation provided by an embodiment of the present invention, a minimization loss function is solved, a suitable regularization coefficient is determined, and a relaxation time distribution result is obtained.

[0062] Optionally, a regularization solution method is designed based on the MATLAB language environment. The specific steps are as follows: 1. Data import. Read the location where the data is saved, import the frequency, real part of impedance, and imaginary part of impedance into MATLAB, and pre-process the data: transform the second column (real part of impedance) and the third column (imaginary part of impedance) of the imported data into the form of total impedance expression, and call the data to present it in the image. Data supports reading .txt and .csv format files; 2. Design the relaxation time distribution image format. Since the relaxation time and the corresponding frequency are inversely proportional to each other, the relaxation time distribution image can be output in gamma-τ format or gamma-frequency format; 3. Regularization parameter design. Users can customize the size of the regularization parameter and determine whether the regularization parameter is appropriate based on the regularization parameter results and equivalent circuit simulation effects; 4. Solution method. When solving the relaxation time distribution integral, the FWHM half-maximum full width method can be used for calculation. The expression of FWHM is:

[0063] Here, σ is the standard deviation of the data.

[0064] 5. Calculation. Use the L2 regularization method to perform regularization calculations, and call the quadprog function to implement quadratic programming of the loss function. Among them, the quadratic programming needs to import the real part and imaginary part of the experimental data impedance, the real part and imaginary part of the impedance after equivalent circuit fitting, and the regularization parameters; 6. Results. After regularization calculation, the relaxation time distribution image is derived. The rationality of the result is judged by referring to the frequency domain simulation effect of the equivalent circuit and the characteristic values ​​such as peak area and relaxation time in the relaxation time distribution image.

[0065] From the above description, it can be seen that the embodiment of the present invention provides a method for converting the time domain and frequency domain of the AC impedance spectrum of a lithium battery, which realizes the rapid calculation and conversion of the impedance information of the lithium battery through an equivalent circuit, and systematically summarizes the impedance spectrum data of the lithium battery under different conditions, so as to provide a reliable data source for processing battery data in large quantities and performing battery state analysis. Due to its high-resolution characteristics, the relaxation time distribution can observe more subtle polarization processes than the electrochemical impedance spectrum in the process of analyzing the battery kinetic characteristics. The joint application of relaxation time distribution and electrochemical impedance spectrum can not only realize the rapid transformation of the battery impedance information in the time and frequency domain, but also realize the accurate decoupling of the battery kinetic reaction process under different conditions. By observing the electrochemical impedance in a specific frequency band, the battery kinetic reaction process under the influence of a single factor can be decoupled, providing theoretical support for the real-time monitoring of electrochemical systems in actual complex working conditions.

[0066] Embodiment 2 In order to facilitate further understanding of the method provided by the present invention, a group of lithium batteries to be tested is taken as an example for description below.

[0067] 1. Obtain the electrochemical impedance spectrum of the lithium battery module to be tested, obtain the electrochemical impedance spectrum data of the lithium battery module, organize the data, select the frequency, real part of impedance, and imaginary part of impedance as the original data, import and obtain the electrochemical impedance spectrum experimental results, such as Figure 5 As shown; 2. Yes Figure 5 Perform equivalent circuit simulation analysis to obtain the simulation results of the real part and imaginary part of impedance. The simulation results are as follows: Figure 6As shown, the red data points are the original data, and the black curve is the simulation result of the equivalent circuit; 3. Input the regularization coefficient. Taking 1E-3 as an example, regularize the above data and complete the relaxation time distribution conversion of the electrochemical impedance spectrum of the lithium battery. The result is as follows: Figure 7 The simulation accuracy is determined by comparing the electrochemical impedance spectroscopy simulation results. Some simulation results are shown in Table 2: Table 2 Simulation data of lithium battery electrochemical impedance spectroscopy

[0068] The real and imaginary part errors of the impedance in the 24 data sets are all within the 5% error range except for some data points with large errors. The reason for the large error data points is related to the actual test. In the actual test process, some abnormal values ​​may appear in the results due to accidental factors or equipment wiring. However, the simulation results use the L2 regularization method to make the overall data changes smooth. Therefore, the simulation results and the actual data results will have large errors at the abnormal value positions. This phenomenon is acceptable, so the simulation results are considered to meet the requirements. Figure 7 The result can be regarded as the optimal relaxation time distribution result.

[0069] Embodiment 3 Figure 8 Schematic diagram of a lithium battery AC impedance spectrum time domain frequency domain conversion system provided according to an embodiment of the present invention. Figure 8 As shown, the system includes: a measuring module 10 , an equivalent module 20 , a building module 30 , a determining module 40 and a converting module 50 .

[0070] Specifically, the measuring module 10 is used to measure the electrochemical impedance spectrum of the lithium battery module to be measured to obtain discrete impedance data of the electrochemical impedance spectrum; The equivalent module 20 is used to simulate the lithium battery module to be tested by using a preset equivalent circuit to obtain a fitting relationship between the circuit parameters of the preset equivalent circuit and the discrete impedance data; A construction module 30 is used to construct a target loss function about a regularization coefficient based on the discrete impedance data and the fitting relationship; A determination module 40 is used to determine an optimal regularization coefficient by taking the minimum value of the target loss function and combining the relaxation time distribution accuracy to meet the preset conditions as the optimization target; The conversion module 50 is used to transform the discrete impedance data into a continuous function in the time domain by using a regularization method based on an optimal regularization coefficient, so as to obtain the relaxation time distribution of the lithium battery module to be tested.

[0071] Optionally, the preset equivalent circuit includes a Voigt equivalent circuit; and the fitting relationship includes:

[0072]

[0073] Where Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance in the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

[0074] The present invention further provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method provided in the embodiment of the present invention when executing the computer program.

[0075] The present invention also provides a computer-readable storage medium, which stores computer instructions. When the computer instructions are executed by a processor, the method provided in the embodiment of the present invention is implemented.

[0076] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

[0077] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0078] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 processor, or other programmable data processing device to produce 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.

[0079] 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 including 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.

[0080] 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.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for converting the time domain to frequency domain of the AC impedance spectrum of a lithium battery, characterized in that: include: Conduct electrochemical impedance spectroscopy measurement on the lithium battery module to be tested to obtain discrete impedance data of the electrochemical impedance spectroscopy; Simulating the lithium battery module to be tested by using a preset equivalent circuit to obtain a fitting relationship between the circuit parameters of the preset equivalent circuit and the discrete impedance data; Based on the discrete impedance data and the fitting relationship, constructing a target loss function with respect to a regularization coefficient; Taking the minimum value of the objective loss function and the relaxation time distribution accuracy satisfying the preset conditions as the optimization goal, determining the optimal regularization coefficient; The discrete impedance data is transformed into a continuous function in the time domain by using a regularization method based on the optimal regularization coefficient to obtain the relaxation time distribution of the lithium battery module to be tested.

2. The method according to claim 1, characterized in that The discrete impedance data includes: a test frequency, and a real impedance part and an imaginary impedance part corresponding to the test frequency.

3. The method according to claim 1, characterized in that The preset equivalent circuit includes a Voigt equivalent circuit; and the fitting relationship includes: Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance of the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

4. The method according to claim 1, characterized in that: The objective loss function includes: Wherein, N is the total amount of discrete impedance data; y n is the frequency point n n The discrete impedance data measured at M ,f n ) is the preset equivalent circuit for the discrete impedance data y n The fitting result of ; λ is the regularization coefficient, and λ≥0; P(x1,x2,…,x M ) is the penalty function, M is the total amount of data of the fitting result, x n is the nth fitting result, and p is a preset constant greater than or equal to 1.

5. The method according to claim 1, characterized in that The relaxation time distribution accuracy meets the preset conditions, including: The real-imaginary part difference test function and the real-imaginary part cross-validation test function calculated based on the relaxation time distribution are both less than a preset threshold; wherein the real-imaginary part difference test function includes: The real-imaginary cross validation test function includes: Among them, DRT Re,λ DRT is the relaxation time distribution result calculated using the real part of the discrete impedance data; Im,λ is the relaxation time distribution result calculated using the imaginary part of the discrete impedance data; Z' is the real part of the discrete impedance data; Z'' (DRT Im,λ ) is the imaginary part of the impedance calculated using the relaxation time distribution result; Z'' is the imaginary part of the discrete impedance data; Z'(DRT Re,λ ) is the real part of the impedance calculated using the relaxation time distribution results.

6. The method according to claim 1, characterized in that The discrete impedance data is transformed into a continuous function in the time domain, comprising: Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; R0 is the ohmic internal resistance of the battery that is independent of frequency; Z pol (ω) is the frequency-dependent polarization resistance in the battery; g(τ) is the relaxation time distribution; τ is the relaxation time; j is the imaginary unit; ω is the angular frequency.

7. A lithium battery AC impedance spectrum time domain frequency domain conversion system, characterized in that: include: measurement module, equivalent module, construction module, determination module and conversion module; among them, The measuring module is used to measure the electrochemical impedance spectrum of the lithium battery module to be measured to obtain discrete impedance data of the electrochemical impedance spectrum; The equivalent module is used to simulate the lithium battery module to be tested by using a preset equivalent circuit to obtain a fitting relationship between the circuit parameters of the preset equivalent circuit and the discrete impedance data; The construction module is used to construct a target loss function about a regularization coefficient based on the discrete impedance data and the fitting relationship; The determination module is used to determine the optimal regularization coefficient by taking the minimum value of the target loss function and combining the relaxation time distribution accuracy to meet the preset conditions as the optimization target; The conversion module is used to transform the discrete impedance data into a continuous function in the time domain by using a regularization method based on the optimal regularization coefficient, so as to obtain the relaxation time distribution of the lithium battery module to be tested.

8. The system according to claim 7, characterized in that The preset equivalent circuit includes a Voigt equivalent circuit; and the fitting relationship includes: Wherein, Z(ω) is the total impedance of the lithium battery module to be tested; n is the number of parallel elements of differential resistance and capacitance of the preset equivalent circuit; dR i is the ith differential resistance; j is the imaginary unit; ω is the angular frequency; C i is the i-th capacitor; dτ i is the discrete relaxation time differential expression.

9. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 1 to 6 when executing the computer program.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and when the computer instructions are executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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