Consistency testing method for secondary batteries

Abstract

The present invention provides a consistency detection method for a secondary battery, comprising: providing a battery to be tested and a plurality of reference batteries; obtaining the Nyquist spectrum of each reference battery; obtaining the first characteristic frequency in the Nyquist spectrum of each reference battery, the first characteristic frequency being the frequency corresponding to the ohmic internal resistance of the reference battery in the Nyquist spectrum; obtaining a first average characteristic frequency according to the first characteristic frequency of each reference battery; using a first test current of the first average characteristic frequency to input the battery to be tested, and obtaining a corresponding first response voltage; obtaining the ohmic internal resistance of the battery to be tested according to the first response voltage and the first test current of the first average characteristic frequency, and judging the consistency of the battery to be tested by the ohmic internal resistance of the battery to be tested. The consistency detection method provided by the present invention can efficiently and accurately detect the consistency of a secondary battery.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary battery performance testing, and in particular to a secondary battery consistency detection method. Background Art

[0002] As energy crisis and environmental pollution become increasingly prominent, it is increasingly important to develop sustainable new energy and build a low-carbon society. The significance of new energy vehicles in alleviating energy crisis and environmental protection has been widely recognized and valued. The large-scale commercial popularization of electric vehicles has put forward high requirements on the service life and safety performance of power cells and module packs. The ohmic internal resistance parameter is one of the important indicators reflecting the power characteristics and internal electrochemical state of power cells. It is also an important data basis for the power characteristics, capacity attenuation, and life attenuation evaluation of the battery system in the power battery BMS system management.

[0003] At present, battery manufacturers mainly detect the consistency of batteries through ohmic internal resistance. There are three main ways to measure ohmic internal resistance: (1) charge (or discharge) the battery under a constant pulse current to measure the voltage change, and use Ohm's law R=U / I to calculate the DC internal resistance (DCR) as the battery's ohmic internal resistance; (2) apply a small-amplitude AC sinusoidal signal with a wide frequency range (from microhertz to megahertz) to the battery, and use a spectrum analyzer to convert the output current and potential signals to obtain the impedance, impedance modulus and phase angle at different frequencies, so as to analyze the different electrochemical reaction processes of the battery system and obtain the battery's ohmic internal resistance; (3) input a fixed 1KHz sine wave frequency to the battery, and then pass it through an effective conversion circuit to collect a series of data such as voltage, rectification and filtering, so as to accurately measure the actual impedance value at the characteristic frequency of 1KHz to replace the battery's ohmic internal resistance.

[0004] In the prior art (1), the pulse current is relatively large, and the tested battery may cause irreversible damage to the battery itself after passing through a large pulse current, and there are certain safety risks; the large pulse current will cause the battery to polarize, and the result is difficult to reflect the true ohmic internal resistance; the test process requires the tested battery to be charged to a specific state of charge (SOC), which increases the test time. In the prior art (2), it is necessary to convert the effective value of the AC signal into a voltage value, and the test frequency ranges from microhertz to megahertz, which not only increases the production cost of the test equipment, but also has a long test cycle, and it is not feasible to directly apply it to mass production battery testing. (3) The actual impedance value at the characteristic frequency of 1KHz includes ohmic internal resistance, electrochemical reaction impedance and inductive reactance, which cannot reflect the true ohmic internal resistance of the battery.

[0005] In summary, it is difficult for the existing technology to efficiently and accurately detect the consistency of secondary batteries. Summary of the invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that it is difficult to efficiently and accurately detect the consistency of secondary batteries, thereby providing a consistency detection method for secondary batteries.

[0007] The present invention provides a consistency detection method for a secondary battery, comprising: providing a battery to be tested and a plurality of reference batteries; obtaining the Nyquist spectrum of each reference battery; obtaining a first characteristic frequency in the Nyquist spectrum of each reference battery, the first characteristic frequency being the frequency corresponding to the ohmic internal resistance of the reference battery in the Nyquist spectrum; obtaining a first average characteristic frequency according to the first characteristic frequency of each reference battery; using a first test current of the first average characteristic frequency to input the battery to be tested to obtain a corresponding first response voltage; obtaining the ohmic internal resistance of the battery to be tested according to the first response voltage and the first test current of the first average characteristic frequency; and / or obtaining a second characteristic frequency in the Nyquist spectrum of each reference battery, the second characteristic frequency being the frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; obtaining a second average characteristic frequency according to the second characteristic frequency of each reference battery; using a first test current of the second average characteristic frequency to input the battery to be tested to obtain a corresponding second response voltage; obtaining the electrochemical reaction resistance of the battery to be tested according to the second response voltage and the first test current of the second average characteristic frequency; judging the consistency of the battery to be tested by the ohmic internal resistance of the battery to be tested and / or the electrochemical reaction internal resistance of the battery to be tested.

[0008] Optionally, the number of the batteries to be tested is several; the average ohmic internal resistance of the several batteries to be tested is obtained according to the ohmic internal resistance of the several batteries to be tested; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the batteries to be tested is greater than or equal to the average ohmic internal resistance of the batteries to be tested times a first threshold value, the battery to be tested does not meet the test battery consistency requirements; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the batteries to be tested is less than the average ohmic internal resistance of the batteries to be tested times a first threshold value, the battery to be tested meets the test battery consistency requirements; the first threshold value multiple is less than or equal to 0.005.

[0009] Optionally, the first threshold multiple is 0.003.

[0010] Optionally, the number of the batteries to be tested is several; the average electrochemical reaction resistance of the several batteries to be tested is obtained according to the electrochemical reaction resistance of the several batteries to be tested; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is greater than or equal to the average electrochemical reaction resistance of the battery to be tested times a second threshold value, the battery to be tested does not meet the test battery consistency requirement; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is less than the average electrochemical reaction resistance of the battery to be tested times a second threshold value, the battery to be tested meets the battery consistency requirement; the second threshold value multiple is less than or equal to 0.005.

[0011] Optionally, the second threshold multiple is 0.003.

[0012] Optionally, the ohmic internal resistance of each reference battery is obtained, and the average ohmic internal resistance of the reference batteries and the standard deviation of the ohmic internal resistance of the reference batteries are obtained based on the ohmic internal resistance of each reference battery; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is greater than or equal to the standard deviation of the ohmic internal resistance of the reference battery times a third threshold value, the battery to be tested does not meet the consistency requirements of the test battery; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is less than the standard deviation of the ohmic internal resistance of the reference battery times a third threshold value, the battery to be tested meets the consistency requirements of the test battery; the third threshold value is less than or equal to 5.

[0013] Optionally, the third threshold multiple is 3.

[0014] Optionally, the electrochemical reaction resistance of each reference battery is obtained, and the average electrochemical reaction resistance of the reference battery and the standard deviation of the electrochemical reaction resistance of the reference battery are obtained according to the electrochemical reaction resistance of each reference battery; if the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is greater than or equal to the electrochemical reaction resistance of the reference battery multipled by a fourth threshold value, the battery to be tested does not meet the consistency requirements of the test battery; if the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is less than the standard deviation of the electrochemical reaction resistance of the reference battery multipled by a third threshold value, the battery to be tested meets the consistency requirements of the test battery; the fourth threshold value multiple is less than or equal to 5.

[0015] Optionally, the fourth threshold multiple is 3.

[0016] Optionally, a method for obtaining the Nyquist spectrum of any reference battery includes: inputting a first test current signal to the reference battery, obtaining a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies within a test frequency band; obtaining the internal resistance of the reference battery according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; obtaining the Nyquist spectrum of the reference battery according to the internal resistance of the reference battery and the corresponding frequency; the test frequency band range is 10KHz to 0.1Hz.

[0017] Optionally, the method further includes: before obtaining the Nyquist spectrum of each reference battery, performing a static treatment on each reference battery; the static treatment time is 2 hours to 10 hours; and the static treatment ambient temperature is -30°C to 60°C.

[0018] Optionally, the ambient temperature of the reference battery during the process of obtaining the Nyquist spectrum of each reference battery is consistent with the ambient temperature of the static treatment.

[0019] Optionally, after each reference battery is subjected to a static treatment and before the Nyquist spectrum of each reference battery is obtained, the reference battery is charged to a reference state of charge; the reference state of charge is 20%-80%.

[0020] Optionally, before obtaining the first characteristic frequency and / or the second characteristic frequency, the method further includes: performing a static treatment on the battery to be tested; after the static treatment on the battery to be tested, charging the battery to be tested to a reference state of charge; the time conditions for performing the static treatment on the battery to be tested are the same as the time conditions for performing the static treatment on each reference battery; the ambient temperature for performing the static treatment on the battery to be tested is the same as the ambient temperature for performing the static treatment on each reference battery.

[0021] The technical solution of the present invention has the following advantages:

[0022] The consistency detection method of a secondary battery provided by the technical solution of the present invention, in the process of obtaining the Nyquist spectrum of each reference battery, causes less damage to the reference battery and does not cause more obvious battery polarization of the reference battery. When the first average characteristic frequency obtained according to the Nyquist spectrum of the reference battery is used as the frequency of the first test current of the test battery, the ohmic internal resistance of the test battery can be accurately obtained, and the ohmic internal resistance of the test battery contains less other interference impedances. When the second characteristic frequency obtained according to the Nyquist spectrum of the reference battery is used as the frequency of the first test current of the test battery, the electrochemical reaction resistance of the test battery can be accurately obtained, and the electrochemical reaction resistance of the test battery contains less other interference impedances. The real ohmic internal resistance and / or electrochemical reaction resistance of the battery to be tested can be accurately reflected respectively, so that the consistency screening result of the test battery is more accurate. In summary, the consistency detection method of a secondary battery provided by the present invention can efficiently and accurately detect the consistency of a secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A flow chart of a method for detecting consistency of a secondary battery provided in Embodiment 1 of the present invention;

[0025] Figure 2 It is the electrochemical impedance spectroscopy equivalent circuit diagram in Example 1 of the present invention;

[0026] Figure 3 The histogram of the ohmic internal resistance test results of the battery to be tested 30 times with an ohmic internal resistance of 0.3382 mΩ in Example 2 of the present invention;

[0027] Figure 4 This is a relationship diagram between the number of tab cracks and ohmic internal resistance of Example 2 of the present invention;

[0028] Figure 5 The ohmic internal resistance of the battery to be tested in Example 3 of the present invention and the distribution diagram of the internal resistance of the battery to be tested in Comparative Example 1 are shown;

[0029] Figure 6 This is a graph showing the relationship between the average ohmic internal resistance of the reference battery in Test Example 1 of the present invention and the corresponding frequency and temperature;

[0030] Figure 7 This is a graph showing the relationship between the average electrochemical reaction resistance of the reference battery in Test Example 1 of the present invention and the corresponding frequency and temperature;

[0031] Figure 8 This is a graph showing the relationship between the average ohmic internal resistance and temperature of a reference battery in Test Example 1 of the present invention;

[0032] Fig. 9 This is the ohmic internal resistance distribution diagram of the battery to be tested in Test Example 2 of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example 1

[0038] This embodiment provides a secondary battery consistency detection method, referring to Figure 1 ,include:

[0039] S1: Provide a battery to be tested and several reference batteries;

[0040] S2: Obtain the Nyquist spectrum of each reference battery;

[0041] S3: Obtaining the first characteristic frequency in the Nyquist spectrum of each reference battery, where the first characteristic frequency is the frequency corresponding to the ohmic internal resistance of the reference battery in the Nyquist spectrum; obtaining a first average characteristic frequency according to the first characteristic frequency of each reference battery; inputting a first test current of the first average characteristic frequency into the battery to be tested to obtain a corresponding first response voltage; obtaining the ohmic internal resistance of the battery to be tested according to the first response voltage and the first test current of the first average characteristic frequency; and / or,

[0042] S4: Obtaining a second characteristic frequency in the Nyquist spectrum of each reference battery, where the second characteristic frequency is the frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; obtaining a second average characteristic frequency according to the second characteristic frequency of each reference battery; inputting a first test current of the second average characteristic frequency into the battery to be tested to obtain a corresponding second response voltage; obtaining the electrochemical reaction resistance of the battery to be tested according to the second response voltage and the first test current of the second average characteristic frequency;

[0043] S5: Determine the consistency of the battery to be tested by the ohmic internal resistance of the battery to be tested and / or the electrochemical reaction internal resistance of the battery to be tested.

[0044] The consistency detection method for secondary batteries provided in this embodiment, in the process of obtaining the Nyquist spectrum of each reference battery, causes less damage to the reference battery and does not cause more obvious battery polarization of the reference battery. When the first average characteristic frequency obtained according to the Nyquist spectrum of the reference battery is used as the frequency of the first test current of the test battery, the ohmic internal resistance of the test battery can be accurately obtained, and the ohmic internal resistance of the test battery contains less other interference impedances. When the second average characteristic frequency obtained according to the Nyquist spectrum of the reference battery is used as the frequency of the first test current of the test battery, the electrochemical reaction resistance of the test battery can be accurately obtained, and the electrochemical reaction resistance of the test battery contains less other interference impedances. The real ohmic internal resistance and / or electrochemical reaction resistance of the battery to be tested can be accurately reflected respectively, so that the consistency screening results of the test battery are more accurate. In summary, the consistency detection method for secondary batteries provided by the present invention can efficiently and accurately detect the consistency of secondary batteries.

[0045] In this embodiment, the method for obtaining the Nyquist spectrum of any reference battery includes: inputting a first test current signal to the reference battery, obtaining a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies within a test frequency band; obtaining the internal resistance of the reference battery according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; and obtaining the Nyquist spectrum of the reference battery according to the internal resistance of the reference battery and the corresponding frequency.

[0046] In this embodiment, the method for obtaining the frequency corresponding to the ohmic internal resistance (i.e., the first characteristic frequency) in the Nyquist spectrum of each reference battery is based on the equivalent circuit diagram of the electrochemical impedance principle (such as Figure 2 As shown, L1: represents the inductive reactance of the battery, R1 represents the ohmic internal resistance of the battery, R2 represents the electrochemical reaction impedance of the battery, C2 represents the capacitance of the battery, and W3 represents the diffusion impedance of the battery) decomposes the Nyquist spectrum of the reference battery to obtain the ohmic internal resistance corresponding frequency, which is the frequency point corresponding to the point where the Nyquist spectrum curve intersects with the real part of the Nyquist spectrum, and the resistance value at the intersection point is the ohmic internal resistance of the reference battery.

[0047] In this embodiment, the method for obtaining the corresponding frequency of the electrochemical reaction resistance in the Nyquist spectrum of each reference battery (i.e., the second characteristic frequency) is based on the electrochemical impedance principle equivalent circuit diagram (such as Figure 2 The frequency corresponding to the electrochemical reaction resistance obtained by decomposing the Nyquist spectrum of the reference battery (as shown) is the frequency corresponding to the first approximate semicircle inflection point of the Nyquist spectrum curve, and the impedance corresponding to the real part of the inflection point is the electrochemical reaction resistance of the reference battery.

[0048] In this embodiment, the test frequency band ranges from 10 KHz to 0.1 Hz, for example, 10 KHz to 0.1 Hz, or 1000 Hz to 0.1 Hz.

[0049] In this embodiment, the consistency detection method of the secondary battery also includes: before obtaining the Nyquist spectrum of each reference battery, each reference battery is subjected to a static treatment, wherein the static treatment time is 2h to 10h, for example: 3h, 4h, 8h or 10h; the ambient temperature of the static treatment is -30℃ to 60℃, for example: -20℃, 0℃, 10℃, 30℃ or 45℃. Static treatment of the reference battery can make the performance of the test battery relatively stable and avoid the adverse effect of the uneven temperature of the test battery itself on the test results. The static treatment time is further determined by the size and original temperature of the test battery. The temperature of the static treatment is determined by the use temperature of the reference battery.

[0050] In this embodiment, the ambient temperature of the reference battery during the process of obtaining the Nyquist spectrum of each reference battery is consistent with the temperature of the static treatment.

[0051] In this embodiment, after each reference battery is placed in a static state and before the Nyquist spectrum of each reference battery is obtained, the reference battery is charged to a reference state of charge; the reference state of charge is 20% to 80%, for example, 20%, 30%, 50% or 75%. In order to accurately test, the reference batteries need to be adjusted to the same state of charge to avoid different battery polarizations due to different states of charge, which makes the comparison of the test results poor.

[0052] In this embodiment, before obtaining the first characteristic frequency and / or the second characteristic frequency, the method further includes: performing a static treatment on the battery to be tested; after the static treatment on the battery to be tested, charging the battery to be tested to a reference state of charge; the time conditions for performing the static treatment on the battery to be tested are the same as the time conditions for performing the static treatment on each reference battery; the ambient temperature for performing the static treatment on the battery to be tested is the same as the ambient temperature for performing the static treatment on each reference battery.

[0053] In one embodiment of the present invention, the number of batteries to be tested is several; the average ohmic internal resistance of the several batteries to be tested is obtained according to the ohmic internal resistance of the several batteries to be tested; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the battery to be tested is greater than or equal to the average ohmic internal resistance of the battery to be tested times a first threshold value, the battery to be tested does not meet the test battery consistency requirement; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the battery to be tested is less than the average ohmic internal resistance of the battery to be tested times a first threshold value, the battery to be tested meets the test battery consistency requirement; the first threshold value multiple is less than or equal to 0.05, for example, 0.05, 0.01, 0.005 or 0.003; in this embodiment, the first threshold value multiple is 0.003.

[0054] In another embodiment of the present invention, the number of the batteries to be tested is several; the average electrochemical reaction resistance of the several batteries to be tested is obtained according to the electrochemical reaction resistance of the several batteries to be tested; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is greater than or equal to the average electrochemical reaction resistance of the battery to be tested times the second threshold value, the battery to be tested does not meet the test battery consistency requirement; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is less than the average electrochemical reaction resistance of the battery to be tested times the second threshold value, the battery to be tested meets the battery consistency requirement; the second threshold value multiple is less than or equal to 0.05, for example, 0.05, 0.01, 0.005 or 0.003; in the present embodiment, the second threshold value multiple is 0.003.

[0055] In another embodiment of the present invention, the ohmic internal resistance of each reference battery is obtained, and the average ohmic internal resistance of the reference battery and the standard deviation of the ohmic internal resistance of the reference battery are obtained based on the ohmic internal resistance of each reference battery; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is greater than or equal to the standard deviation of the ohmic internal resistance of the reference battery multipled by a third threshold value, the battery to be tested does not meet the consistency requirements of the test battery; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is less than the standard deviation of the ohmic internal resistance of the reference battery multipled by a third threshold value, the battery to be tested meets the consistency requirements of the test battery; the third threshold value multiple is less than or equal to 5, for example, 1, 2, 3 or 5; in the present embodiment, the third threshold value multiple is 3.

[0056] In another embodiment of the present invention, the electrochemical reaction resistance of each reference battery is obtained, and the average electrochemical reaction resistance of the reference battery and the standard deviation of the electrochemical reaction resistance of the reference battery are obtained according to the electrochemical reaction resistance of each reference battery; if the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is greater than or equal to the electrochemical reaction resistance of the reference battery multiple times a fourth threshold value, the battery to be tested does not meet the consistency requirements of the test battery; if the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is less than the standard deviation of the electrochemical reaction resistance of the reference battery multiple times a third threshold value, the battery to be tested meets the consistency requirements of the test battery; the fourth threshold multiple is less than or equal to 5, for example, 1, 2, 3 or 5; in the present embodiment, the fourth threshold multiple is 3.

[0057] Example 2

[0058] Ten square batteries of the same model for pure electric vehicles in good condition are provided as reference batteries. After the reference batteries are allowed to stand at 25°C for 6 hours, the charge state of the reference batteries is adjusted to a 50% charge state. At 25°C, a first test current signal is input into the test reference battery through a BT4560 variable frequency Hioki internal resistance meter to obtain a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in a frequency range of 1000 Hz to 0.1 Hz (wherein, a point is collected every 1 Hz in the frequency range of 1000 to 10 Hz, and a point is collected every 0.1 Hz in the frequency range of 10 to 0.1 Hz). The internal resistance of the reference battery is obtained according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; and the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

[0059] The equivalent circuit model based on the electrochemical impedance spectroscopy principle of the reference battery (reference Figure 2) and the Nyquist spectrum of the reference battery to obtain the frequency corresponding to the ohmic internal resistance of each reference battery, as well as the ohmic internal resistance. The average ohmic internal resistance corresponding frequency of the reference battery is 66 Hz, the average ohmic internal resistance of the reference battery is 0.3061 mΩ, the standard deviation of the ohmic internal resistance of the reference battery is 0.001 mΩ, and the third threshold multiple is 3.

[0060] Provide 10 batteries to be tested that are the same model as the reference battery but have different degrees of tab cracking (including 2 batteries in good condition, 2 batteries with two layers of tab cracking, 2 batteries with four layers of tab cracking, 2 batteries with six layers of tab cracking, and 2 batteries with eight layers of tab cracking), let the batteries to be tested stand at 25°C for 6 hours, adjust the state of charge of the test batteries to a 50% state of charge, input a first test current signal of 66 Hz to the batteries to be tested through a BT4560 variable frequency Hioki internal resistance meter at 25°C, obtain a corresponding first response voltage, and obtain the ohmic internal resistance of the battery to be tested according to the first response voltage and the first test current of the first characteristic frequency.

[0061] The ohmic internal resistance values ​​of the tested batteries are in the order of increasing number of tab cracking layers (0, 2, 4, 6, 8) as follows: 0.3052mΩ, 0.3051mΩ, 0.3187mΩ, 0.3183mΩ, 0.3262mΩ, 0.3264mΩ, 0.3315mΩ, 0.3317mΩ, 0.3382mΩ, 0.3387mΩ. By comparison, it can be found that the ohmic internal resistance values ​​of the tested batteries can be divided into 5 groups, corresponding to batteries in good condition, batteries with two tab cracking layers, batteries with four tab cracking layers, batteries with six tab cracking layers, and batteries with eight tab cracking layers. By comparing the difference between the ohmic internal resistance value of the tested battery and the average ohmic internal resistance of the reference battery and the standard deviation of the ohmic internal resistance, it can be found that when the number of tab cracking layers is 2, the battery does not meet the consistency requirements of the tested battery.

[0062] The battery to be tested with an ohmic internal resistance of 0.3382 mΩ was tested 30 times using a BT4560 variable frequency Hioki internal resistance meter (the test conditions are the same as those described above). The histogram of the frequency and ohmic internal resistance using Minitab software (such as Figure 3 shown), from Figure 3 It can be seen that the ohmic internal resistance of the battery to be tested conforms to the normal distribution, and the standard deviation value is small, indicating that the measurement system has small fluctuations, high sensitivity, and low test error.

[0063] Each battery to be tested is tested 10 times using a BT4560 variable frequency Hioki internal resistance meter (the test conditions are the same as those described above), and the corresponding ohmic internal resistance is recorded. A relationship diagram between the number of tab cracks and the ohmic internal resistance is plotted using Minitab software (see Figure 1). Figure 4). Figure 4 It can be seen that as the number of cracked layers of the tab increases, the ohmic internal resistance basically shows a linear growth relationship, and the ohmic internal resistance growth rate can reach up to about 10%, indicating that when the difference in ohmic internal resistance is small, this method can be used for accurate and effective identification, thereby improving the accuracy of ohmic internal resistance identification, effectively solving the problem of battery ohmic internal resistance consistency screening, and increasing the finished product shipment rate.

[0064] Example 3

[0065] Ten square batteries of the same model and in good condition for hybrid electric vehicles are provided as reference batteries. After the reference batteries are left to stand at 25° C. for 6 hours, the charge state of the reference batteries is adjusted to a 50% charge state. A first test current signal is input to the test reference battery through an electrochemical workstation at 25° C. to obtain a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in a frequency range of 10 kHz to 10 mHz. The internal resistance of the reference battery is obtained according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; and the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

[0066] The equivalent circuit model based on the electrochemical impedance spectroscopy principle of the reference battery (reference Figure 2 ) and the Nyquist spectrum of the reference battery to obtain the frequency corresponding to the ohmic internal resistance of each reference battery, and the average frequency corresponding to the average ohmic internal resistance of the reference battery is 245 Hz by average calculation.

[0067] Provide 100 test batteries of the same model as the reference battery (number the test batteries from 1 to 100), let the test batteries stand for 6 hours at 25°C, adjust the charge state of the test batteries to 50% charge state, input a first test current signal of 245Hz to the test batteries through a mass production line variable frequency internal resistance meter at 25°C, obtain the corresponding first response voltage, obtain the ohmic internal resistance of each test battery according to the first response voltage and the first test current of the first characteristic frequency, calculate the average ohmic internal resistance of the test batteries, compare the ohmic internal resistance of each test battery with the average ohmic internal resistance, if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance is greater than or equal to 0.3% of the average ohmic internal resistance, then the test battery does not meet the test battery consistency; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance is less than 0.3% of the average ohmic internal resistance, then the test battery meets the test battery consistency. Test result reference Figure 5 .

[0068] Two batteries to be tested that do not meet battery consistency are screened out.

[0069] Comparative Example 1

[0070] The 100 batteries in Example 3 were tested. After the tested batteries were allowed to stand for 6 hours at 25°C, the charge state of the tested batteries was adjusted to a 50% charge state. A first test current signal of 1000 Hz was input to the tested batteries through a mass production line internal resistance meter at 25°C to obtain a corresponding first response voltage. The ohmic internal resistance of each tested battery was obtained based on the first response voltage and the first test current of the first characteristic frequency. The average ohmic internal resistance of the ohmic internal resistance of the tested batteries was calculated on average. The ohmic internal resistance of each tested battery was compared with the average ohmic internal resistance. If the absolute value of the difference between the ohmic internal resistance of the tested battery and the average ohmic internal resistance is greater than or equal to 0.3% of the average ohmic internal resistance, the tested battery does not meet the test battery consistency. If the absolute value of the difference between the ohmic internal resistance of the tested battery and the average ohmic internal resistance is less than 0.3% of the average ohmic internal resistance, the tested battery meets the test battery consistency. Test result reference Figure 5 .

[0071] Four batteries to be tested that do not meet battery consistency are screened out.

[0072] Since the internal resistance obtained under the first test current signal of 1000 Hz includes a large amount of inductive reactance, the internal resistance fluctuates greatly, and it is easy to screen out the batteries to be tested that meet the battery consistency.

[0073] Test Example 1

[0074] The 10 reference batteries in Example 3 are left to stand at 25°C for 6 hours, the charge state of the reference battery is adjusted to a 50% charge state, a first test current signal is input to the test reference battery through an electrochemical workstation at 25°C to obtain a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in the frequency range of 10kHz to 10mHz, the internal resistance of the reference battery is obtained according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; and the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

[0075] The equivalent circuit model based on the electrochemical impedance spectroscopy principle of the reference battery (reference Figure 2 ) and the Nyquist spectrum of the reference battery to obtain the frequency corresponding to the ohmic internal resistance and the frequency corresponding to the ohmic internal resistance and the electrochemical reaction resistance of each reference battery, and the average ohmic internal resistance corresponding frequency, the average ohmic internal resistance, and the average electrochemical reaction resistance corresponding frequency of the reference battery are obtained by average calculation.

[0076] According to the above method, the average ohmic internal resistance corresponding frequency, the average ohmic internal resistance, and the average electrochemical reaction resistance corresponding frequency of the above 10 reference batteries at -30°C, -25°C, -20°C, -10°C, 0°C, 10°C and 25°C are obtained in turn.

[0077] The relationship between the average ohmic internal resistance and the frequency and temperature is shown in Figure 6 The relationship between the average electrochemical reaction resistance and the frequency and temperature is shown in Figure 7 .

[0078] The relationship between the average ohmic internal resistance and temperature is shown in Figure 8 ,pass Figure 8 It can be seen that the relationship between the average ohmic internal resistance and temperature conforms to the Arrhenius equation:

[0079] σT=Ae -Ea / RT

[0080] Among them, σ represents the ion migration rate, σ = L / (R×S); T represents temperature, Ea represents activation energy; k is a constant; A is the pre-exponential factor, L represents the length of the electrode material, S represents the area of ​​the electrode material; R represents resistance (ohmic internal resistance or electrochemical reaction resistance).

[0081] pass Figure 8 This indicates that within a wider temperature range, the test value of the average ohmic internal resistance is relatively accurate. The consistency detection method for a secondary battery provided by the present invention can efficiently and accurately detect the consistency of a secondary battery within a wider temperature range.

[0082] Test Example 2

[0083] Ten square batteries of the same type and in good condition for hybrid vehicles are provided as reference batteries. After the reference batteries are left to stand at 25° C. for 6 hours, the charge state of the reference batteries is adjusted to a 50% charge state. At 25° C., a first test current signal is input into the test reference battery through a BT4560 variable frequency Hioki internal resistance meter to obtain a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in a frequency range of 1000 Hz to 0.1 Hz (wherein, a point is collected every 1 Hz in the frequency range of 1000 to 10 Hz, and a point is collected every 0.1 Hz in the frequency range of 10 to 0.1 Hz). The internal resistance of the reference battery is obtained according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; and the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

[0084] The equivalent circuit model based on the electrochemical impedance spectroscopy principle of the reference battery (reference Figure 2 ) and the Nyquist spectrum of the reference battery to obtain the frequency corresponding to the ohmic internal resistance of each reference battery, as well as the ohmic internal resistance, and the average ohmic internal resistance corresponding frequency of the reference battery is obtained by average calculation as 300Hz.

[0085] 9 batteries of the same model to be tested are randomly provided (with battery numbering). After the batteries to be tested are left to stand at 25°C for 6 hours, the state of charge of the test batteries is adjusted to 50% state of charge. At 25°C, a 300Hz first test current signal is input to the batteries to be tested through a BT4560 variable frequency Hioki internal resistance meter to obtain the corresponding first response voltage. The ohmic internal resistance of the batteries to be tested is obtained according to the first response voltage and the first test current of the first characteristic frequency. The test results are shown in Fig. 9 .

[0086] pass Fig. 9 It can be seen intuitively that there are certain differences in the ohmic internal resistance of mass-produced batteries of the same model. By accurately and effectively identifying the ohmic internal resistance of the battery, mass-produced batteries that do not meet the battery consistency requirements can be screened out to improve the shipment rate of good products.

[0087] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for detecting consistency of a secondary battery, characterized in that: include: Provide a battery to be tested and several reference batteries; Obtain the Nyquist spectrum of each reference battery; Obtaining a first characteristic frequency in the Nyquist spectrum of each reference battery, where the first characteristic frequency is a frequency corresponding to the ohmic internal resistance of the reference battery in the Nyquist spectrum; Acquire a first average characteristic frequency according to the first characteristic frequency of each reference battery; Using a first test current with a first average characteristic frequency to input into the battery to be tested, and obtaining a corresponding first response voltage; Obtaining the ohmic internal resistance of the battery to be tested according to the first response voltage and the first test current of the first average characteristic frequency; and / or, Obtaining a second characteristic frequency in the Nyquist spectrum of each reference battery, where the second characteristic frequency is a frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; obtaining a second average characteristic frequency according to the second characteristic frequency of each reference battery; Using a first test current of a second average characteristic frequency to input into the battery to be tested, and obtaining a corresponding second response voltage; Obtaining an electrochemical reaction resistance of the battery to be tested according to a second response voltage and a first test current of a second average characteristic frequency; Determining the consistency of the battery under test by the ohmic internal resistance of the battery under test and / or the electrochemical reaction internal resistance of the battery under test; Obtaining the ohmic internal resistance of each reference battery, and obtaining the average ohmic internal resistance of the reference batteries and the standard deviation of the ohmic internal resistance of the reference batteries according to the ohmic internal resistance of each reference battery; If the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is greater than or equal to the standard deviation of the ohmic internal resistance of the reference battery at a third threshold multiple, the battery to be tested does not meet the test battery consistency requirements; if the absolute value of the difference between the ohmic internal resistance of the test battery and the average ohmic internal resistance of the reference battery is less than the standard deviation of the ohmic internal resistance of the reference battery at a third threshold multiple, the battery to be tested meets the test battery consistency requirements; the third threshold multiple is less than or equal to 5; Obtaining the electrochemical reaction resistance of each reference battery, and obtaining the average electrochemical reaction resistance of the reference battery and the standard deviation of the electrochemical reaction resistance of the reference battery according to the electrochemical reaction resistance of each reference battery; If the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is greater than or equal to the electrochemical reaction resistance of the reference battery multiple times the fourth threshold value, the battery to be tested does not meet the consistency requirements of the test battery; if the absolute value of the difference between the electrochemical reaction resistance of the test battery and the average electrochemical reaction resistance of the reference battery is less than the standard deviation of the electrochemical reaction resistance of the reference battery multiple times the third threshold value, the battery to be tested meets the consistency requirements of the test battery; The fourth threshold multiple is less than or equal to 5; The method for obtaining the Nyquist spectrum of each reference battery includes: inputting a first test current signal to the reference battery, obtaining a first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies within a test frequency band; obtaining the internal resistance of the reference battery according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test electrical signal; obtaining the Nyquist spectrum of the reference battery according to the internal resistance of the reference battery and the corresponding frequency; the test frequency band range is 10KHz~0.1Hz.

2. The method for detecting consistency of a secondary battery according to claim 1, characterized in that: The number of the batteries to be tested is several; the average ohmic internal resistance of the several batteries to be tested is obtained according to the ohmic internal resistance of the several batteries to be tested; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the batteries to be tested is greater than or equal to the average ohmic internal resistance of the batteries to be tested times a first threshold value, the battery to be tested does not meet the consistency requirements of the test batteries; if the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance of the batteries to be tested is less than the average ohmic internal resistance of the batteries to be tested times a first threshold value, the battery to be tested meets the consistency requirements of the test batteries; the first threshold value is less than or equal to 0.

05.

3. The method for detecting consistency of a secondary battery according to claim 1, characterized in that: The number of the batteries to be tested is several; the average electrochemical reaction resistance of the several batteries to be tested is obtained according to the electrochemical reaction resistances of the several batteries to be tested; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is greater than or equal to the average electrochemical reaction resistance of the battery to be tested times a second threshold value, the battery to be tested does not meet the test battery consistency requirement; if the absolute value of the difference between the electrochemical reaction resistance of the battery to be tested and the average electrochemical reaction resistance of the battery to be tested is less than the average electrochemical reaction resistance of the battery to be tested times a second threshold value, the battery to be tested meets the battery consistency requirement; the second threshold value multiple is less than or equal to 0.

05.

4. The method for detecting consistency of a secondary battery according to claim 1, characterized in that: Also includes: Before obtaining the Nyquist spectrum of each reference battery, each reference battery is subjected to a static treatment; the static treatment time is 2 hours to 10 hours; and the static treatment environment temperature is -30°C to 60°C.

5. The method for detecting consistency of a secondary battery according to claim 4, characterized in that: In the step of obtaining the Nyquist spectrum of each reference battery, the ambient temperature of the reference battery is consistent with the ambient temperature of the static treatment.

6. The method for detecting consistency of a secondary battery according to claim 4, characterized in that: After each reference battery is subjected to a static treatment and before the Nyquist spectrum of each reference battery is obtained, the reference battery is charged to a reference state of charge; the reference state of charge is 20% to 80%.

7. The method for detecting consistency of a secondary battery according to claim 6, characterized in that: Before obtaining the first characteristic frequency and / or the second characteristic frequency, the method also includes: performing a static treatment on the battery to be tested; after the static treatment on the battery to be tested, charging the battery to be tested to a reference state of charge; the time conditions for the static treatment on the battery to be tested are the same as the time conditions for the static treatment on each reference battery; the ambient temperature for the static treatment on the battery to be tested is the same as the ambient temperature for the static treatment on each reference battery.

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