Battery electrochemical impedance spectroscopy detection method and device

Abstract

The invention discloses a battery electrochemical impedance spectroscopy detection method and device, and relates to the field of battery state detection. The method comprises the steps that a to-be-tested battery is connected with a test system in a Kelvin mode; determining a specific form of a sampling function according to the low-frequency test frequency band and the internal resistance of the to-be-tested battery so as to obtain a sampling signal; testing the high frequency band of the battery to be tested by adopting a sine frequency sweep excitation method to obtain an impedance spectrum of the high frequency band; controlling the test system to perform excitation test on the low-frequency band of the to-be-tested battery according to the designed sampling signal to obtain an excitation current signal and a response voltage signal of the to-be-tested 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 battery to be detected. No matter whether standing test or online measurement is carried out, the test efficiency of the electrochemical impedance spectroscopy of the battery can be remarkably improved, and the test precision can be ensured.

Description

Technical Field

[0001] The present application relates to the field of battery status detection, and in particular to a battery electrochemical impedance spectroscopy detection method and device. Background Art

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

[0003] At present, most EIS tests are conducted on static batteries in the laboratory, which is called static electrochemical impedance spectroscopy (SEIS). In contrast, dynamic electrochemical impedance spectroscopy (DEIS) is a test conducted during the battery charging and discharging process, which can reveal the complex electrochemical processes inside the battery under different working conditions, and therefore contains richer battery status information. However, the effectiveness and accuracy of impedance spectroscopy testing depends on the three basic conditions of causality, linearity and stability being met by the tested system, and the internal state of the battery is constantly changing during the charging and discharging process, which makes DEIS testing face greater challenges.

[0004] The traditional sweep frequency measurement method based on single-frequency sinusoidal excitation is too time-consuming, especially the acquisition of impedance information in the low-frequency band takes 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 improving the detection speed, the accuracy of the impedance test is inevitably affected. The spectrum leakage problem of chirp signals and pseudo-random sequences during signal processing 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 spectrum energy is too low, the measurement accuracy of the impedance spectrum is affected.

[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 the present 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 the first aspect, the present application provides a battery electrochemical impedance spectrum detection method and device, including: connecting the battery to be tested to the test system in a Kelvin manner; establishing an expression of 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; the value of the length, the value of the compression coefficient and the amplitude are combined. Substitute the value of into the expression of the sampling function to obtain a sampling signal; use a sine sweep excitation method to test the high frequency band of the battery to be tested to obtain an impedance spectrum in the high frequency band; 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 to obtain 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 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 dynamic electrochemical impedance spectrum or a static electrochemical impedance spectrum.

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

[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 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 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 an 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 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, because the present application has a more stable spectrum, the test accuracy of the battery electrochemical impedance spectrum is improved. 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 drawings required for use in the embodiments will be briefly introduced below. 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 paying 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 A schematic diagram showing the performance of the sampling signal in the time domain and frequency domain provided in Case 1 of this application;

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

[0019] Figure 4 Schematic diagram of 1kHz~0.05Hz battery dynamic electrochemical impedance spectroscopy 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 A schematic diagram of battery EIS in the frequency range of 1kHz to 0.05Hz 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 the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0024] In order to make the above-mentioned objects, 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, comprising the following steps 101 to 110. Among them:

[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 frequency 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: 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.

[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 it is a static test or an online measurement, the present application can significantly improve the test efficiency of the battery electrochemical impedance spectroscopy and ensure the test accuracy.

[0038] Implement the above steps 101 to 110, and determine a suitable sampling signal as an excitation signal 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. 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, the present application has a more stable spectrum, thereby improving the test accuracy of the battery electrochemical impedance spectrum.

[0039] In another exemplary embodiment of the present application, in order to ensure that the collected signal is an accurate battery signal rather than including the loss in the line, the battery and the test system need to be connected 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, connect the other end of the current detector to the positive pole of the battery to be tested, connect the negative pole of the excitation source to the negative pole of the battery to be tested, and connect 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, amplitude A, and Sa(Kt) is the sampling signal, which 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 the figure, the Sa(t) signal appears as a symmetrical signal in the time domain. The part with the highest peak in the middle of the signal is called the main lobe, and the remaining gradually attenuated bands are called side lobes. The resolution, width and spectrum energy of the signal in the frequency domain are jointly determined by the sampling function parameters.

[0049] The frequency resolution of EIS determines the length t of the Sa(t) signal, i.e., the lowest frequency point ω min =1 / t. When t increases, the time domain width of the sampling function increases, the wave number increases, the width of the signal frequency domain increases, the lowest frequency point is lower, the frequency resolution is higher, and the spectrum energy decreases. Although increasing t can obtain lower-frequency EIS information, the reduction of spectrum energy will affect the accuracy of impedance testing.

[0050] The frequency domain width of the EIS dominates the choice of the compression factor K. When K increases, the sampling function has more time domain wave numbers, the decay rate from the main lobe to the side lobe is faster, the frequency response is wider, and the spectrum energy is reduced. Although increasing K can increase the frequency response width of the signal, it also reduces the spectrum energy of the signal.

[0051] The amplitude A of the applied Sa(t) signal is determined by the internal resistance R of the battery. According to the basic principle of EIS testing, 1mV≤A×R≤10mV must be satisfied. When A increases, the time domain waveform shape of the sampling function remains unchanged, but is stretched A times in the vertical direction, and its frequency domain function does not change except that the spectrum energy increases A times.

[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] Exemplarily, 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, adjusting 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] The present application designs appropriate sampling function parameters to generate Sa(t) signals for excitation according to 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 of 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 to be tested; when performing a dynamic electrochemical impedance spectroscopy test on the battery to be tested, the recorded current value is the working current value of the battery to be tested during the charge and discharge process, and the recorded voltage value is the working voltage value of the battery to be tested during the charge and discharge process; when performing a static electrochemical impedance spectroscopy test on the battery to be tested, the recorded current value is 0, and the recorded voltage value is the initial terminal voltage of the battery to be tested after being left at rest.

[0063] Step 402: After the excitation test is performed, the current signal and the 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 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 frequency 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: According to the frequency domain expression of the excitation current signal and the frequency domain expression of the response voltage signal, the imaginary part of the impedance and the real part of the impedance at each frequency are obtained 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 impedance as the X-axis and the negative imaginary part of impedance as the Y-axis, and fill the imaginary part and real part of 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 test for low-frequency impedance can also be designed. The method can also include the following steps 601 to 604. Among them:

[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-frequency band.

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

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

[0085] Case 1: Rapid detection of dynamic electrochemical impedance spectroscopy

[0086] The experimental object is A123's 26650 battery, with a rated capacity of 2500mAh, an internal resistance of about 5-10Ω, and an operating current of 1.5A. The battery starts to discharge when it is fully charged, and after 5 minutes of discharge, when the battery charge state is about 95%, an additional excitation signal is applied for testing, and the test target is DEIS in the frequency band of 1kHz to 0.05Hz.

[0087] First, design appropriate sampling function parameters to generate Sa(t) signals for excitation. Considering that the sinusoidal signal of medium and high frequency impedance test has a short period and fast speed, the 1kHz~1Hz frequency band can maintain the traditional sinusoidal sweep excitation method, and only use Sa(t) signals to accelerate impedance spectrum testing in the frequency band below 1Hz. In addition, since the spectrum energy of Sa(t) decreases with the increase of signal duration t, if only a longer duration Sa(t) signal is used for excitation, the test accuracy of impedance in some frequency bands may be reduced. Therefore, the impedance test in the 1Hz~0.05Hz frequency band is further divided into two sections: 1Hz~0.1Hz and 0.1Hz~0.05Hz, and Sa(t) signals with different parameters are designed for excitation according to the characteristics of the lowest frequency and frequency domain width of each section. The details are as follows: the parameters of the Sa(t) signal in the 1Hz~0.1Hz frequency band are t1=20s, K1=2.2, A1=1; the parameters of the Sa(t) signal in the 0.1Hz~0.05Hz frequency band are t2=50s, K2=0.88, A2=1. This excitation signal design can ensure that the spectrum energy of each segment of the Sa(t) signal is maintained at a high level, which can ensure the accuracy of the DEIS test while improving the test speed. 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 test is as follows Figure 3 The excitation current and response voltage signals are shown.

[0089] Finally, the excitation current and response voltage are calculated according to formula (3) to (4) to obtain Figure 4 The 1kHz~0.05Hz battery dynamic electrochemical impedance spectrum is shown.

[0090] Case 2: Rapid detection of static electrochemical impedance spectroscopy

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

[0092] First, connect the batteries in Kelvin.

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

[0094] Furthermore, the designed Figure 5 The multiple excitation signals shown in the figure are used to collect the excitation current and response voltage signals.

[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 range is shown.

[0096] Finally, to verify the accuracy of the proposed method, the error comparison between the proposed method and the traditional sine sweep test method is also analyzed. Since only the low frequency band uses the Sa(t) signal for accelerated testing, the error comparison analysis is 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 with the traditional method. The 1Hz to 0.05Hz low frequency EIS test using the traditional sine sweep method took 890 seconds. The test results are as follows: Figure 7 The red curve in part (a) is shown in Figure 1, 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 have good consistency. Figure 7 As shown in part (b) of the figure, the maximum value of the modulus error is 0.32 mΩ, and the phase error is less than 1.87°. The RMSE of the impedance value of the Sa(t) signal excitation test result is calculated to be 1.1025×10 -4 , which verifies the accuracy of the method proposed in the present 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 embodiment of the present application also provides a battery electrochemical impedance spectrum detection device for implementing the battery electrochemical impedance spectrum detection method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in one or more battery electrochemical impedance spectrum detection device embodiments provided below can refer to the limitations of the battery electrochemical impedance spectrum detection method above, and will not be repeated here.

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

[0102] The computer is also used to perform Fourier transform on the excitation current signal and the response voltage signal to obtain the 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 the 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 sine swept frequency excitation test device, an excitation source, a current detector and a voltage detector.

[0104] The sine sweep frequency excitation test device uses a sine sweep 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 pole 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 pole of the battery to be tested, the negative pole of the excitation source is connected to the negative pole of the battery to be tested, and the positive and negative ends of the voltage detector are respectively connected to the positive and negative ends of the battery to be tested. The excitation source, the current detector and the voltage detector are used to perform an excitation test on the low frequency band of the battery to be tested according to the sampling signal to obtain the excitation current signal and the response voltage signal of the battery to be tested.

[0106] Among them, the sine sweep 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. Exciter: converts electrical signals into mechanical vibrations to apply excitation force to the object under test. Sensor: used to monitor the response of the object under test, such as accelerometers, velocity sensors, etc. The data acquisition system collects the data from the sensor and transmits it to the 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 may 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 article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will 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 the expression of the sampling function to obtain a sampling signal; The high frequency band of the battery to be tested is tested using a sine sweep excitation method to obtain an impedance spectrum in 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; The impedance spectrum of the high frequency band and the impedance spectrum of the low frequency band are spliced ​​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.

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: The expression of the sampling function is: Where Sa(Kt) is the sampling signal, A is the amplitude, K is the compression coefficient, and t is the length.

4. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: The numerical determination constraint formula of the amplitude is: 1mV≤A×R≤10mV; Where A is the amplitude and R is the internal resistance of the battery to be tested.

5. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: The formula for determining the value of the length is: In the formula, ω min is the lowest frequency in the low frequency band, and t is the length.

6. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: 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 the expression of the sampling function to obtain a sampling function time domain signal; Convert the sampling function time domain signal into a frequency domain spectrum; 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; 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; 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".

7. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: 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 to obtain an excitation current signal and a response voltage signal of the battery to be tested in the low frequency band, specifically including: Before the excitation test, the current value and voltage value of the battery to be tested are recorded; when the dynamic electrochemical impedance spectroscopy test is performed on the battery to be tested, the recorded current value is the working current value of the battery to be tested during the charging and discharging process, and the recorded voltage value is the working voltage value of the battery to be tested during the charging and discharging process; when the static electrochemical impedance spectroscopy test is performed on the battery to be tested, the recorded current value is 0, and the recorded voltage value is the initial terminal voltage of the battery to be tested after being left 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 an excitation current signal; The measured voltage signal is subtracted from the recorded voltage value to obtain the response voltage signal.

8. 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: The excitation current signal and the response voltage signal are respectively subjected to Fourier transform, and the frequency domain expressions of the excitation current signal and the response voltage signal are obtained 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 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 corresponding to the excitation current signal at the kth frequency, and 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 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; A coordinate system is established with the real part of impedance as the X-axis and the negative imaginary part of impedance as the Y-axis, and the imaginary part and real part of impedance at each frequency are filled into the coordinate system to obtain the impedance spectrum in the low frequency band.

9. The battery electrochemical impedance spectroscopy detection method according to claim 1, characterized in that: The battery electrochemical impedance spectroscopy detection method also 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 to be tested according to the sampling signals of each sub-frequency band, and obtains the excitation current signal and the response voltage signal of the battery to be tested 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 ​​to form the electrochemical impedance spectrum of the battery to be tested.

10. A battery electrochemical impedance spectroscopy detection device, characterized in that: The battery electrochemical impedance spectrum detection device comprises: a test system and a computer; The test system is connected to the battery under test using the Kelvin method; The computer is connected to the test system; 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; 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 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, obtain the excitation current signal and the response voltage signal of the battery to be tested, and transmit them to the 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.

Images