A battery electrochemical impedance spectroscopy detection method and device

Abstract

The application discloses a battery electrochemical impedance spectrum detection method and device, and relates to the field of battery state detection. The method comprises the following steps: connecting a to-be-detected battery to a test system in a Kelvin mode; determining the specific form of a sampling function according to a low-frequency test frequency band and an internal resistance of the to-be-detected battery, so as to obtain a sampling signal; testing a high-frequency band of the to-be-detected battery by using a sine sweep excitation method, and obtaining an impedance spectrum of the high-frequency band; controlling the test system to test the low-frequency band of the to-be-detected battery according to the designed sampling signal, obtaining an excitation current signal and a response voltage signal of the to-be-detected battery in the low-frequency band, and performing Fourier transform to obtain an impedance spectrum of the low-frequency band; and splicing the impedance spectrum of the high-frequency band and the impedance spectrum of the low-frequency band to form a complete electrochemical impedance spectrum of the to-be-detected battery. Whether static test or online measurement is performed, the application can significantly improve the test efficiency of the battery electrochemical impedance spectrum and ensure the test precision.

Description

TECHNICAL FIELD

[0001] The application relates to the field of battery state detection, in particular to a battery electrochemical impedance spectroscopy detection method and device. BACKGROUND

[0002] Lithium / sodium ion batteries are favored as the mainstream electrochemical energy storage method, but they frequently have safety problems during operation. The existing battery management system (BMS) only realizes the detection of voltage, current and external temperature, and the reflection sensitivity of potential or sudden events such as metal deposition and thermal runaway is not enough. Related research results to improve the "state perception" ability of the battery during operation include the application of new detection technologies such as distributed optical fiber sensor measurement of battery internal temperature and ultrasonic reflection detection to evaluate the state of charge of the battery. However, these detection technologies may change the internal structure of the battery or have high requirements for the detection conditions, making it difficult to realize online application. Electrochemical impedance spectroscopy (EIS) has a good mapping relationship with various electrochemical processes in the battery at different time scales, and as a non-destructive detection method, it can provide important clues for the state estimation and fault diagnosis of the battery.

[0003] At present, most EIS tests are carried out in the laboratory on batteries after standing, which is called static electrochemical impedance spectroscopy (SEIS). In contrast, dynamic electrochemical impedance spectroscopy (DEIS) is a test carried out during the charging and discharging process of the battery, which can reveal the complex electrochemical processes inside the battery under different working conditions, and therefore contains more information about the state of the battery. However, the effectiveness and accuracy of impedance spectroscopy testing depend on the three basic conditions of causality, linearity and stability of the measured system, and the internal state of the battery changes constantly during the charging and discharging process, which makes DEIS testing face greater challenges.

[0004] The traditional swept frequency measurement method based on single-frequency sinusoidal excitation is too time-consuming, especially the acquisition of impedance information in the low-frequency band requires a long time, which cannot meet the test requirements. Therefore, reducing the time of low-frequency impedance testing and completing the test when the battery state is approximately unchanged is a key challenge to achieve accurate EIS measurement. In recent years, a variety of excitation signals have been proposed to accelerate EIS testing, such as multiple sinusoidal signals, chirp signals, pseudo-random sequence signals, step signals and white noise signals. However, while the detection speed is improved, the accuracy of the impedance test is inevitably affected. The spectrum leakage problem that occurs in the signal processing of chirp signals and pseudo-random sequences will lead to a decrease in test accuracy, and the improvement of the low-frequency impedance test speed by the two is still limited. Step signals and white noise signals can obtain low-frequency information within tens of seconds, but because their spectral energy is too low, it affects the measurement accuracy of the impedance spectrum.

[0005] Therefore, it is urgent to find a suitable excitation signal that meets the stability conditions of the system during the test and keeps the spectrum energy stable within the test frequency band, and propose a battery DEIS test method that takes into account both test efficiency and test accuracy. Summary of the Invention

[0006] The purpose of this application is to provide a battery electrochemical impedance spectroscopy detection method and device, which can improve the test efficiency and test accuracy of the battery electrochemical impedance spectroscopy.

[0007] To achieve the above objectives, this application provides the following solutions:

[0008] In a first aspect, the present application provides a battery electrochemical impedance spectroscopy detection method and device, comprising: connecting the battery to be tested to the test system in a Kelvin manner; establishing an expression for a sampling function; the parameters of the sampling function include length, compression coefficient and amplitude; determining the value of the amplitude according to the internal resistance of the battery to be tested; determining the value of the length according to the lowest frequency in the low frequency band of the battery to be tested; the low frequency band is a frequency range in the test frequency band that is less than the frequency domain threshold; determining the value of the compression coefficient according to the low frequency band; and combining the values ​​of the length, the compression coefficient and the amplitude. The numerical value of is substituted into the expression of the sampling function to obtain a sampling signal; a sinusoidal sweep frequency excitation method is used to test the high frequency band of the battery to be tested to obtain an impedance spectrum in the high frequency band; the test system is controlled to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal to obtain an excitation current signal and a response voltage signal of the battery to be tested in the low frequency band; the excitation current signal and the response voltage signal are Fourier transformed to obtain an impedance spectrum in the low frequency band; the impedance spectrum in the high frequency band and the impedance spectrum in the low frequency band are spliced ​​to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a dynamic electrochemical impedance spectrum or a static electrochemical impedance spectrum.

[0009] In a second aspect, the present application provides a battery electrochemical impedance spectroscopy detection device, comprising: a test system and a computer. The test system is connected to the battery to be tested using a Kelvin method; and the computer is connected to the test system.

[0010] The computer is used to establish an expression of a sampling function; the parameters of the sampling function include length, compression coefficient and amplitude; the value of the amplitude is determined according to the internal resistance of the battery to be tested; the value of the length is determined according to the lowest frequency in the low frequency band of the battery to be tested; the low frequency band is a frequency range in the test frequency band that is less than the frequency domain threshold; the value of the compression coefficient is determined based on the low frequency band; the value of the length, the value of the compression coefficient and the value of the amplitude are substituted into the expression of the sampling function to obtain a sampling signal.

[0011] The test system uses a sinusoidal sweep frequency excitation method to test the high frequency band of the battery to be tested, obtains the impedance spectrum of the high frequency band, and transmits it to a computer; the test system is also used to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal, obtains the excitation current signal and response voltage signal of the battery to be tested, and transmits them to a computer.

[0012] The computer is further used to perform Fourier transform on the excitation current signal and the response voltage signal to obtain an impedance spectrum in the low-frequency band; and to splice the impedance spectrum in the high-frequency band and the impedance spectrum in the low-frequency band to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a dynamic electrochemical impedance spectrum or a static electrochemical impedance spectrum.

[0013] According to the specific embodiments provided in this application, this application has the following technical effects:

[0014] The present application provides a battery electrochemical impedance spectrum detection method and device. According to the low frequency band, the lowest frequency (frequency resolution) and the internal resistance in the test frequency band of the battery to be tested, a suitable sampling signal is determined as the excitation signal. The excitation signal meets the stability conditions of the system during the test, and the spectrum energy remains stable within the test frequency band. The present application uses the stable frequency spectrum of the sampling function to accurately obtain multiple low-frequency information in a short period of time. Compared with the traditional sinusoidal sweep excitation method, it greatly improves the test speed of the low frequency band, thereby greatly improving the test efficiency of the battery electrochemical impedance spectrum; at the same time, compared with excitation measurement methods such as chirp signals and pseudo-random binary sequences, since the present application has a more stable spectrum, it improves the test accuracy of the battery electrochemical impedance spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 A schematic diagram of a flow chart of a battery electrochemical impedance spectroscopy detection method provided in one embodiment of the present application;

[0017] Figure 2 Schematic diagram of the performance of the sampling signal in the time domain and frequency domain provided in Case 1 of this application;

[0018] Figure 3 Schematic diagram of the measured excitation current and response voltage signal provided in Case 1 of this application;

[0019] Figure 4 Schematic diagram of the 1kHz-0.05Hz dynamic electrochemical impedance spectroscopy of a battery provided in Case 1 of this application;

[0020] Figure 5 Schematic diagram of the multi-segment excitation signal designed for Case 2 of this application;

[0021] Figure 6 Schematic diagram of battery EIS in the 1kHz to 0.05Hz frequency band provided for Case 2 of this application;

[0022] Figure 7 This is a schematic diagram for verifying the accuracy of the sampling signal acceleration test proposed in this application, provided in Case 2 of this application. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0024] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0025] In an exemplary embodiment, Figure 1 As shown, a battery electrochemical impedance spectroscopy detection method is provided, including the following steps 101 to 110. In which:

[0026] Step 101: Connect the battery to be tested to the test system using the Kelvin method.

[0027] Step 102: Establish an expression of a sampling function; the parameters of the sampling function include length, compression coefficient and amplitude.

[0028] Step 103: Determine the value of the amplitude according to the internal resistance of the battery to be tested.

[0029] Step 104: Determine the value of the length according to the lowest frequency in the low frequency band of the battery to be tested; the low frequency band is a frequency range in the test frequency band that is less than the frequency domain threshold.

[0030] Step 105: Determine the value of the compression coefficient according to the low frequency band.

[0031] Step 106: Substitute the value of the length, the value of the compression coefficient, and the value of the amplitude into the expression of the sampling function to obtain a sampling signal.

[0032] Step 107: Use a sine sweep excitation method to test the high frequency band of the battery to be tested, and obtain an impedance spectrum of the high frequency band.

[0033] Step 108: Control the test system to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal, and obtain an excitation current signal and a response voltage signal of the battery to be tested in the low frequency band.

[0034] Step 109: Perform Fourier transform on the excitation current signal and the response voltage signal to obtain an impedance spectrum in a low-frequency band.

[0035] Step 110: combining the impedance spectrum of the high frequency band and the impedance spectrum of the low frequency band to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a static electrochemical impedance spectrum or a dynamic electrochemical impedance spectrum.

[0036] Static electrochemical impedance spectroscopy refers to the electrochemical impedance spectroscopy measured when the battery is at rest, and dynamic electrochemical impedance spectroscopy refers to the electrochemical impedance spectroscopy measured when the battery is charging and discharging.

[0037] Whether performing static testing or online measurement, this application can significantly improve the test efficiency of battery electrochemical impedance spectroscopy and ensure test accuracy.

[0038] Implement the above steps 101 to 110, and determine a suitable sampling signal as an excitation signal based on the low frequency band, the lowest frequency (frequency resolution) and the internal resistance in the test frequency band of the battery to be tested. The excitation signal meets the stability conditions of the system during the test, and the spectrum energy remains stable within the test frequency band. The present application uses a stable frequency spectrum of a sampling function to accurately obtain multiple low-frequency information in a short time. Compared with the traditional sinusoidal sweep excitation method, the test speed of the low frequency band is greatly improved, thereby greatly improving the test efficiency of the battery electrochemical impedance spectrum. At the same time, compared with excitation measurement methods such as chirp signals and pseudo-random binary sequences, since the present application has a more stable spectrum, the test accuracy of the battery electrochemical impedance spectrum is improved.

[0039] In another exemplary embodiment of the present application, to ensure that the collected signal is an accurate battery signal and does not include line losses, it is necessary to connect the battery to the test system in a Kelvin manner. Then the above step 101 can be replaced by the following steps 201 to 202:

[0040] Step 201: Setting up a test system including an excitation source, a current detector, and a voltage detector.

[0041] Step 202: Connect the positive pole of the excitation source to one end of the current detector, the other end of the current detector to the positive pole of the battery to be tested, the negative pole of the excitation source to the negative pole of the battery to be tested, and the positive and negative ends of the voltage detector to the positive and negative ends of the battery to be tested respectively.

[0042] The current detector is responsible for measuring the current signal of the battery, and the voltage detector is responsible for measuring the voltage change at the battery terminal.

[0043] In another exemplary embodiment of the present application, the sampling function, namely the Sa(t) signal, is a function formed by the ratio of a sine function to an independent variable, and its core parameters are length t, compression coefficient K, and amplitude A. Sa(Kt) is the sampling signal, and the formula is expressed as follows:

[0044]

[0045] The Sa(t) signal in the time domain is expressed as a rectangular window in the frequency domain. The frequency domain spectrum energy is high and stable. Its expression is shown in formula (2):

[0046]

[0047] Among them, ε(ω) is a unit step function, that is, the spectrum of Sa(t) is a width of ω c This makes the energy in the frequency domain concentrated in a specific frequency range and evenly distributed at each frequency point.

[0048] Figure 2Part (a) shows the time domain waveform. Figure 2 Part (b) in represents the frequency spectrum. Figure 2 As shown in Figure 1, the Sa(t) signal appears symmetrical in the time domain. The peak portion of the signal is called the mainlobe, while the remaining gradually decaying bands are called sidelobes. The signal's resolution, width, and spectral energy in the frequency domain are determined by the sampling function parameters.

[0049] The frequency resolution of EIS determines the length t of the Sa(t) signal, that is, the lowest frequency point ω min =1 / t. As t increases, the sampling function's time domain width increases, the wave number increases, the signal's frequency domain width widens, the lowest frequency point becomes lower, the frequency resolution becomes higher, and the spectral energy decreases. While increasing t can obtain lower-frequency EIS information, the reduction in spectral energy will affect the accuracy of impedance testing.

[0050] The frequency domain width of the EIS determines the choice of the compression factor, K. As K increases, the sampling function has more time-domain wavenumbers, the decay from the main lobe to the side lobes is faster, the frequency response becomes wider, and the spectral energy decreases. While increasing K increases the frequency response width of the signal, it also reduces the spectral energy.

[0051] The amplitude A of the applied Sa(t) signal is determined by the battery's internal resistance R. According to the basic principles of EIS testing, 1mV ≤ A × R ≤ 10mV must be met. As A increases, the sampling function's time-domain waveform remains unchanged, but is simply stretched vertically by a factor of A. Its frequency-domain function remains unchanged, except for a factor of A in which the spectral energy increases.

[0052] In summary, based on the characteristic analysis of Sa(t) signal excitation, the signal amplitude of the DEIS test is determined according to the internal resistance of the battery to be tested, the signal length is determined by the lowest point of the battery test frequency, and the signal compression coefficient is determined according to the low-frequency impedance frequency range.

[0053] For example, the process of determining the value of the compression coefficient in step 105 can be replaced by the following steps 301 to 306:

[0054] Step 301: Set the initial value of the compression coefficient to 1.

[0055] Step 302: Substitute the value of the length, the initial value of the compression coefficient, and the value of the amplitude into the expression of the sampling function to obtain a time domain signal of the sampling function.

[0056] Step 303: Convert the sampling function time domain signal into a frequency domain spectrum.

[0057] Step 304: If the maximum frequency in the frequency domain spectrum is equal to the highest frequency in the low frequency band, the initial value of the compression coefficient is determined as the value of the compression coefficient.

[0058] Step 305: If the maximum frequency in the frequency domain spectrum is not equal to the highest frequency in the low frequency band, adjust the value of the compression coefficient.

[0059] Step 306: Update the initial value of the compression coefficient to the adjusted value of the compression coefficient, and return to the step of "substituting the numerical value of the length, the initial value of the compression coefficient and the numerical value of the amplitude into the expression of the sampling function to obtain the sampling function time domain signal."

[0060] This application designs appropriate sampling function parameters to generate Sa(t) signals for excitation based on the internal resistance of the battery under test and the required EIS frequency range and frequency resolution. The excitation signal meets the stability conditions of the system during the test and the spectrum energy remains stable within the test frequency band.

[0061] In another exemplary embodiment of the present application, an additional excitation current of the Sa(t) signal is applied to the battery, and the change in the battery terminal voltage is detected to separate the response voltage. Then the above step 108 can be replaced by the following steps 401 to 404:

[0062] Step 401: Before performing an excitation test, record the current value and voltage value of the battery under test; when performing a dynamic electrochemical impedance spectroscopy test on the battery under test, the recorded current value is the operating current value of the battery under test during the charge and discharge process, and the recorded voltage value is the operating voltage value of the battery under test during the charge and discharge process; when performing a static electrochemical impedance spectroscopy test on the battery under test, the recorded current value is 0, and the recorded voltage value is the initial terminal voltage of the battery under test after it is at rest.

[0063] Step 402: After the excitation test is performed, the current signal and voltage signal of the battery under test measured by the test system are recorded.

[0064] Step 403: Subtract the recorded current value from the measured current signal to obtain an excitation current signal.

[0065] Step 404: Subtract the recorded voltage value from the measured voltage signal to obtain a response voltage signal.

[0066] The method of the present application can be applied to both dynamic battery electrochemical impedance spectroscopy testing and static battery electrochemical impedance spectroscopy testing.

[0067] Signal detection during battery charging / discharging:

[0068] ① The excitation current is the additional Sa(t) signal applied. At the beginning of the test, record the operating current value of the battery IC When the excitation current is applied, the current signal measured by the current detection device is subtracted from I C The excitation current signal i can be obtained E (t).

[0069] ② The response voltage is the response of the excitation current. At the beginning of the test, record the working voltage value of the battery U C When the excitation current is applied, the battery terminal voltage signal measured by the voltage detection device is subtracted from U C The response voltage signal u can be obtained E (t).

[0070] In addition, the method of the present application can also be used when the battery is at rest: since the battery is at rest and no charge or discharge operation is performed, the initial current value is 0 and the initial terminal voltage is a constant value U C After the EIS test starts, the excitation current signal i can be directly measured. E (t). Due to the Kelvin wiring method, the battery voltage test value does not include the voltage drop of the line, and is the accurate battery terminal voltage value. Subtract U from the measured battery terminal voltage signal C The response voltage signal u can be obtained E (t).

[0071] In another exemplary embodiment of the present application, since Sa(t) contains information of multiple frequency components, the impedance values ​​corresponding to multiple frequency points can be obtained by excitation of one signal and an impedance spectrum can be formed. E (t) and the response voltage signal u E (t) is subjected to Fourier transform and decomposed into n different frequency components {ω k , k=1,2,…n}, the impedance spectrum of the low frequency band can be further obtained, and the above step 109 is replaced by the following steps 501 to 503:

[0072] Step 501: Perform Fourier transform on the excitation current signal and the response voltage signal respectively to obtain the frequency domain expression of the excitation current signal and the frequency domain expression of the response voltage signal:

[0073]

[0074] Where U E (ω) is the spectrum of the response voltage signal, I E (ω) is the spectrum of the excitation current signal, ω is the frequency, ω k is the kth frequency, |U E (ω k )| is the amplitude of the response voltage signal at the kth frequency, |I E(ω k )| is the amplitude of the excitation current signal at the kth frequency, ψ U (ω k ) is the phase angle corresponding to the response voltage signal at the kth frequency, ψ I (ω k ) is the phase angle of the excitation current signal at the kth frequency, and n is the number of frequencies.

[0075] Step 502: Obtain the imaginary part and the real part of the impedance at each frequency according to the frequency domain expression of the excitation current signal and the frequency domain expression of the response voltage signal according to formula (4);

[0076]

[0077] In the formula, |Z(ω k )| is the impedance modulus of the battery under test at the kth frequency, Z real (ω k ) is the imaginary impedance part of the battery under test at the kth frequency, Zim(ωk) is the real impedance part of the battery under test at the kth frequency, θ(ω k ) is the phase difference between the response voltage signal and the excitation current signal at the kth frequency.

[0078] Step 503: Establish a coordinate system with the real part of the impedance as the X-axis and the negative imaginary part of the impedance as the Y-axis, and fill the imaginary part and real part of the impedance at each frequency into the coordinate system to obtain the impedance spectrum of the low frequency band.

[0079] In another exemplary embodiment of the present application, if the DEIS test frequency is low, in order to maintain the spectrum energy of the Sa(t) signal and ensure the accuracy of the impedance test, a multi-segment signal can be designed to test the low-frequency impedance. The method can also include the following steps 601 to 604.

[0080] Step 601: When the frequency range of the low frequency band is greater than a preset frequency range, the low frequency band is divided into a plurality of sub-frequency bands, and a sampling signal of each sub-frequency band is obtained.

[0081] Step 602: Control the test system to perform an excitation test on the battery under test according to the sampling signals of each sub-frequency band, and obtain the excitation current signal and response voltage signal of the battery under test in each sub-frequency band.

[0082] Step 603: Perform Fourier transform on the excitation current signal and the response voltage signal to obtain the impedance spectrum of each sub-band.

[0083] Step 604: combining the impedance spectrum of the high frequency band and the impedance spectra of each sub-frequency band to form an electrochemical impedance spectrum of the battery to be tested.

[0084] The specific embodiments of the present application will be described below through actual cases.

[0085] Case One: Rapid detection of dynamic electrochemical impedance spectroscopy

[0086] The experimental object is a 26650 battery of A123 Company, with a rated capacity of 2500 mAh and an internal resistance of about 5-10 Ω. The working current is 1.5 A. The battery is discharged at full capacity, and after 5 minutes of discharge, when the state of charge of the battery is about 95%, an excitation signal is additionally applied for testing. The testing target is the DEIS of the 1 kHz-0.05 Hz frequency band.

[0087] Firstly, the Sa(t) signal is generated by designing appropriate sampling function parameters for excitation. Considering that the period of the sine signal itself is short and fast in the middle and high frequency impedance test, the traditional sine sweep excitation method can be maintained in the 1 kHz-1 Hz frequency band, and only the Sa(t) signal is used in the frequency band below 1 Hz to accelerate the impedance spectroscopy test. In addition, since the frequency spectrum energy of Sa(t) will decrease with the increase of signal length t, if only one Sa(t) signal with a long time length is used for excitation, the test accuracy of the impedance in some frequency bands may be reduced. Therefore, the impedance test in the 1 Hz-0.05 Hz frequency band is divided into two sections, 1 Hz-0.1 Hz and 0.1 Hz-0.05 Hz, and different parameters of Sa(t) signals are designed for excitation according to the characteristics of the lowest frequency and the frequency domain width of each section. The specific parameters are as follows: the Sa(t) signal parameters for the 1 Hz-0.1 Hz frequency band are t1=20 s, K1=2.2, and A1=1; the Sa(t) signal parameters for the 0.1 Hz-0.05 Hz frequency band are t2=50 s, K2=0.88, and A2=1. This excitation signal design can ensure that the frequency spectrum energy of each Sa(t) signal maintains at a high level, improving the test speed while ensuring the accuracy of DEIS test. Among them, in order to maintain the highest accuracy of the test results, the values of the above two t are larger than the actual calculated values.

[0088] Then, the excitation current and response voltage signals are obtained as shown in Figure 3

[0089] Finally, the excitation current and response voltage are calculated according to formula (3) and formula (4), and the 1 kHz-0.05 Hz battery dynamic electrochemical impedance spectroscopy is obtained as shown in Figure 4

[0090] Case Two: Rapid detection of static electrochemical impedance spectroscopy

[0091] The experimental object is a 26650 battery of A123 Company, with a rated capacity of 2500 mAh and an internal resistance of about 5-10 Ω. The testing target is the EIS of the 1 kHz-0.05 Hz frequency band when the battery is at rest. ​​

[0092] First, connect the batteries in Kelvin.

[0093] Then, the excitation signal is designed based on the required EIS in the 1kHz to 0.05Hz frequency band. Since the sinusoidal signal for medium and high frequency impedance testing has a short period and fast speed, the traditional sinusoidal sweep excitation method can be maintained in the 1kHz to 1Hz frequency band, and the Sa(t) signal is only used to accelerate the impedance spectrum test in the frequency band below 1Hz. In addition, considering that the required spectrum is relatively wide, in order to ensure the accuracy of the test, a multi-segment Sa(t) signal is used to test the low-frequency impedance. Specifically: the Sa(t) signal parameters for the 1Hz to 0.1Hz frequency band are t1 = 20s, K1 = 2.2, A1 = 1; the Sa(t) signal parameters for the 0.1Hz to 0.05Hz frequency band are t2 = 50s, K2 = 0.88, A2 = 1.

[0094] Furthermore, the designed Figure 5 The multi-segment excitation signal is shown, and the excitation current and response voltage signals are collected.

[0095] Then, the obtained excitation current and response voltage signals are calculated according to formula (3) to formula (4), and the following is obtained: Figure 6 The battery EIS in the 1kHz to 0.05Hz frequency band is shown.

[0096] Finally, to verify the accuracy of the proposed method, we also compared its error with the traditional sine sweep test method. Since only the low-frequency band was used for the accelerated test using the Sa(t) signal, the error comparison analysis was performed in the low-frequency band.

[0097] Figure 7 Part (a) shows the low-frequency impedance obtained by the traditional sine sweep excitation method and the new Sa(t) signal excitation method, respectively. Figure 7 Part (b) shows the error analysis of the new method proposed in this application compared to the traditional method. The EIS test of the low frequency band of 1Hz to 0.05Hz using the traditional sine sweep method took 890 seconds, and the test results are as follows: Figure 7 The red curve in part (a) is shown, and the black curve is the accelerated test result using the Sa(t) signal method for excitation. It can be seen that the impedance spectra obtained by the two methods are very consistent. Figure 7 As shown in part (b), the maximum modulus error is 0.32mΩ, and the phase error is less than 1.87°. The impedance RMSE of the Sa(t) signal excitation test result is 1.1025×10 -4 , which verifies the accuracy of the method proposed in this invention, and the Sa(t) signal excitation test method increases the low-frequency EIS test speed by 92.13%.

[0098] Based on the same inventive concept, the present application also provides a battery electrochemical impedance spectroscopy detection device for implementing the aforementioned battery electrochemical impedance spectroscopy detection method. The solution provided by this device is similar to the solution described in the aforementioned method. Therefore, the specific limitations of one or more battery electrochemical impedance spectroscopy detection device embodiments provided below can be found in the above-mentioned limitations of the battery electrochemical impedance spectroscopy detection method and will not be repeated here.

[0099] In an exemplary embodiment, a battery electrochemical impedance spectroscopy detection device is provided, comprising: a test system and a computer. The test system is connected to a battery to be tested using a Kelvin method; and the computer is connected to the test system.

[0100] The computer is used to establish an expression of a sampling function; the parameters of the sampling function include length, compression coefficient and amplitude; the value of the amplitude is determined according to the internal resistance of the battery to be tested; the value of the length is determined according to the lowest frequency in the low frequency band of the battery to be tested; the low frequency band is a frequency range in the test frequency band that is less than the frequency domain threshold; the value of the compression coefficient is determined according to the low frequency band; the value of the length, the value of the compression coefficient and the value of the amplitude are substituted into the expression of the sampling function to obtain a sampling signal.

[0101] The test system uses a sinusoidal sweep frequency excitation method to test the high frequency band of the battery to be tested, obtains the impedance spectrum of the high frequency band, and transmits it to the computer; the test system is also used to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal, obtains the excitation current signal and response voltage signal of the battery to be tested, and transmits them to the computer.

[0102] The computer is also used to perform Fourier transform on the excitation current signal and the response voltage signal to obtain an impedance spectrum in the low-frequency band; the impedance spectrum in the high-frequency band and the impedance spectrum in the low-frequency band are spliced ​​together to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a static electrochemical impedance spectrum or a dynamic electrochemical impedance spectrum.

[0103] As an optional implementation, in order to realize the functions of the above-mentioned test system, the test system may include: a sinusoidal swept frequency excitation test device, an excitation source, a current detector, and a voltage detector.

[0104] The sinusoidal swept frequency excitation test device uses the sinusoidal swept frequency excitation method to test the high frequency band of the battery to be tested and obtain the impedance spectrum of the high frequency band.

[0105] The positive terminal of the excitation source is connected to one end of the current detector, the other end of the current detector is connected to the positive terminal of the battery under test, the negative terminal of the excitation source is connected to the negative terminal of the battery under test, and the positive and negative terminals of the voltage detector are connected to the positive and negative terminals of the battery under test, respectively. The excitation source, current detector, and voltage detector are used to perform an excitation test on the low-frequency band of the battery under test according to the sampling signal, thereby obtaining an excitation current signal and a response voltage signal of the battery under test.

[0106] The sinusoidal swept frequency excitation test device may include a signal generator, a power amplifier, an exciter, a sensor, and a data acquisition system. The signal generator is used to generate a frequency-adjustable sinusoidal excitation signal. The power amplifier is used to amplify the signal generated by the signal generator to provide sufficient energy to drive the exciter. The exciter converts the electrical signal into mechanical vibration and applies an excitation force to the object under test. The sensor is used to monitor the response of the object under test, such as an accelerometer or velocity sensor. The data acquisition system collects the sensor data and transmits it to a computer.

[0107] This application has the following advantages:

[0108] ① Compared with the existing dynamic electrochemical impedance spectroscopy testing technology that can only obtain impedance data in the high-frequency band, the method proposed in the present invention can achieve the acquisition of broadband EIS during the online operation of the battery.

[0109] ② Moreover, compared with the traditional sinusoidal excitation measurement method, the method proposed in the present invention increases the test speed by 90% or more, greatly improving the EIS test efficiency.

[0110] ③In addition, compared with new excitation measurement methods such as chirp signals and pseudo-random binary sequences proposed in recent years, the excitation measurement method based on sampling function proposed in the present invention has better test accuracy due to its more stable spectrum.

[0111] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A battery electrochemical impedance spectroscopy detection method, characterized in that: The battery electrochemical impedance spectroscopy detection method comprises: Connect the battery to be tested to the test system using the Kelvin method; Establishing an expression of a sampling function; the parameters of the sampling function include length, compression coefficient and amplitude; Determining a value of the amplitude according to the internal resistance of the battery to be tested; Determine the value of the length according to the lowest frequency in the low frequency band of the battery to be tested; the low frequency band is a frequency range in the test frequency band that is less than the frequency domain threshold; Determining a value of the compression coefficient according to the low frequency band; Substituting the value of the length, the value of the compression coefficient and the value of the amplitude into an expression of a sampling function to obtain a sampling signal; The high frequency band of the battery under test is tested using a sine sweep excitation method to obtain the impedance spectrum of the high frequency band; Controlling the test system to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal, and obtaining an excitation current signal and a response voltage signal of the battery to be tested in the low frequency band; Perform Fourier transform on the excitation current signal and the response voltage signal to obtain the impedance spectrum in the low frequency band; Splicing the impedance spectrum of the high frequency band and the impedance spectrum of the low frequency band to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a static electrochemical impedance spectrum or a dynamic electrochemical impedance spectrum; The expression of the sampling function is: ； Where, is the sampling signal, A is the amplitude, K is the compression coefficient, t is the length; The numerical determination constraint formula of the amplitude is: 1mV≤ A × R ≤10mV; Where, R is the internal resistance of the battery to be tested; The formula for determining the value of the length is: ； Where, is the lowest frequency in the low frequency band; Determining a value of the compression coefficient according to the low frequency band specifically includes: Set the initial value of the compression coefficient to 1; Substituting the value of the length, the initial value of the compression coefficient and the value of the amplitude into an expression of a sampling function to obtain a sampling function time domain signal; Convert the sampling function time domain signal into frequency domain spectrum; If the maximum frequency in the frequency domain spectrum is equal to the highest frequency in the low frequency band, then determining the initial value of the compression coefficient as the value of the compression coefficient; If the maximum frequency in the frequency domain spectrum is not equal to the highest frequency in the low frequency band, adjusting the value of the compression coefficient; Updating the initial value of the compression coefficient to the adjusted value of the compression coefficient, and returning to the step of "substituting the value of the length, the initial value of the compression coefficient, and the value of the amplitude into the expression of the sampling function to obtain the sampling function time domain signal"; Controlling the test system to perform an excitation test on the low frequency band of the battery under test according to the sampling signal to obtain an excitation current signal and a response voltage signal of the battery under test in the low frequency band, specifically including: Before conducting the excitation test, record the current value and voltage value of the battery under test; when conducting a dynamic electrochemical impedance spectroscopy test on the battery under test, the recorded current value is the operating current value of the battery under test during the charge and discharge process, and the recorded voltage value is the operating voltage value of the battery under test during the charge and discharge process; when conducting a static electrochemical impedance spectroscopy test on the battery under test, the recorded current value is 0, and the recorded voltage value is the initial terminal voltage of the battery under test after it is at rest; After the excitation test is performed, the current signal and voltage signal of the battery under test measured by the test system are recorded; Subtract the recorded current value from the measured current signal to obtain the excitation current signal; Subtracting the recorded voltage value from the measured voltage signal to obtain a response voltage signal; The battery electrochemical impedance spectroscopy detection method further includes: When the frequency range of the low frequency band is greater than the preset frequency range, dividing the low frequency band into a plurality of sub-frequency bands, and obtaining a sampling signal of each sub-frequency band; The control test system performs an excitation test on the battery under test according to the sampling signal of each sub-frequency band, and obtains the excitation current signal and response voltage signal of the battery under test in each sub-frequency band; Perform Fourier transform on the excitation current signal and the response voltage signal to obtain the impedance spectrum of each sub-band; The impedance spectrum of the high-frequency band and the impedance spectrum of each sub-band are spliced ​​together to form the electrochemical impedance spectrum of the battery to be tested.

2. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: Connect the battery to be tested to the test system using the Kelvin method, including: Setting up a test system including an excitation source, a current detector, and a voltage detector; Connect the positive pole of the excitation source to one end of the current detector, the other end of the current detector to the positive pole of the battery to be tested, the negative pole of the excitation source to the negative pole of the battery to be tested, and the positive and negative ends of the voltage detector to the positive and negative ends of the battery to be tested respectively.

3. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: Perform Fourier transform on the excitation current signal and the response voltage signal to obtain the impedance spectrum in the low-frequency band, including: Perform Fourier transform on the excitation current signal and the response voltage signal respectively, and obtain the frequency domain expression of the excitation current signal and the frequency domain expression of the response voltage signal as follows: Where, U E ( ω ) is the frequency spectrum of the response voltage signal, I E ( ω ) is the spectrum of the excitation current signal, ω is the frequency, ω k For the k frequencies, | U E ( ω k )| is the response voltage signal in the first k The corresponding amplitude at the frequency, | I E ( ω k )| is the excitation current signal in the first k The corresponding amplitude at the frequency is In response to the voltage signal k The corresponding phase angle at the frequency is The excitation current signal is k The corresponding phase angle at the frequency is n is the number of frequencies; According to the frequency domain expression of the excitation current signal and the frequency domain expression of the response voltage signal, according to the formula , obtain the imaginary part and real part of impedance at each frequency; where |Z( ω k )| is the battery under test in the k The impedance modulus at a frequency, For the battery under test k The imaginary part of the impedance at a frequency, For the battery under test k The real part of the impedance at a frequency, In response to the voltage signal and the excitation current signal k The corresponding phase angle difference at the frequency; A coordinate system is established with the real part of the impedance as the X-axis and the negative imaginary part of the impedance as the Y-axis, and the imaginary part and real part of the impedance at each frequency are filled into the coordinate system to obtain the impedance spectrum in the low frequency band.

4. A battery electrochemical impedance spectroscopy detection device, characterized in that: The battery electrochemical impedance spectroscopy detection device adopts the battery electrochemical impedance spectroscopy detection method according to claim 1, and the battery electrochemical impedance spectroscopy detection device includes: a test system and a computer; The test system is connected to the battery under test using the Kelvin method; Connecting the computer to the test system; The computer is used to establish an expression for a sampling function; the parameters of the sampling function include length, compression coefficient, and amplitude; the value of the amplitude is determined based on the internal resistance of the battery to be tested; the value of the length is determined based on the lowest frequency in a low frequency band of the battery to be tested; the low frequency band is a frequency range within the test frequency band that is less than a frequency domain threshold; the value of the compression coefficient is determined based on the low frequency band; the values ​​of the length, the compression coefficient, and the amplitude are substituted into the expression for the sampling function to obtain a sampled signal; The test system uses a sine sweep excitation method to test the high frequency band of the battery to be tested, obtains the impedance spectrum of the high frequency band, and transmits it to the computer; The test system is further configured to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal, obtain an excitation current signal and a response voltage signal of the battery to be tested, and transmit the signals to a computer; The computer is also used to perform Fourier transform on the excitation current signal and the response voltage signal to obtain an impedance spectrum in the low-frequency band; splice the impedance spectrum in the high-frequency band and the impedance spectrum in the low-frequency band to form an electrochemical impedance spectrum of the battery to be tested; the electrochemical impedance spectrum is a static electrochemical impedance spectrum or a dynamic electrochemical impedance spectrum.

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