CN115184823A - Method for detecting consistency of secondary battery - Google Patents

Abstract

The invention provides a consistency detection method of a secondary battery, which comprises the following steps: providing a battery to be tested and a plurality of reference batteries; acquiring a Nyquist map of each reference battery; acquiring a first characteristic frequency in a Nyquist map of each reference battery, wherein the first characteristic frequency is a frequency corresponding to the ohm internal resistance of the reference battery in the Nyquist map; acquiring a first average characteristic frequency according to the first characteristic frequency of each reference battery; inputting a first test current with a first average characteristic frequency into a battery to be tested to obtain a corresponding first response voltage; and acquiring 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 according to the ohmic internal resistance of the battery to be tested. The consistency detection method provided by the invention can efficiently and accurately detect the consistency of the secondary battery.

Description

Consistency testing method for secondary batteries

technical field

The invention relates to the technical field of performance testing of secondary batteries, in particular to a method for detecting consistency of secondary batteries.

Background technique

With the increasingly prominent problems of energy crisis and environmental pollution, it is more and more important to develop sustainable new energy and build a low-carbon cost society. The significance of new energy vehicles for alleviating the energy crisis and environmental protection has been widely recognized and valued. The large-scale commercial popularization of electric vehicles puts 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 symbols reflecting the power characteristics and internal electrochemical state of the power cell, and it is also an important data basis for evaluating the power characteristics, capacity decay and life decay of the battery system in the management of the power battery BMS system.

At present, battery manufacturers mainly test 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 change in voltage, Use Ohm's law R=U/I to calculate the DC internal resistance (DCR) as the ohmic internal resistance of the battery; (2) apply a small-amplitude AC sinusoidal signal with a wide frequency range (from the microhertz level to the megahertz level) to the battery, Use a spectrum analyzer to convert the output current and potential signals to obtain impedance at different frequencies, impedance modulus and phase angle, so as to analyze different electrochemical reaction processes of the battery system and obtain the ohmic internal resistance of the battery; (3) Input a fixed 1KHz sine wave frequency to the battery, and then pass 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 ohmic internal resistance of the battery.

In the prior art (1), the pulse current is relatively large, and the battery under test may cause irreversible damage to the battery itself after passing the large pulse current, and there is a certain safety risk; the large pulse current will cause the battery to polarize. , the result is difficult to reflect the real ohmic internal resistance; the test process needs to charge the battery under test 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 the microhertz level to the megahertz level, which not only increases the production cost of the test equipment, but also has a long test period. Production battery testing is not feasible. (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 real ohmic internal resistance of the battery.

In conclusion, it is difficult to efficiently and accurately detect the consistency of the secondary battery in the prior art.

SUMMARY OF THE INVENTION

Therefore, the technical problem to be solved by the present invention is to overcome the difficulty of efficiently and accurately detecting the consistency of secondary batteries in the prior art, thereby providing a method for detecting consistency of secondary batteries.

The invention provides a method for detecting the consistency of secondary batteries, comprising: providing a battery to be tested and several reference batteries; acquiring the Nyquist spectrum of each reference battery; acquiring the No. 1 Nyquist spectrum of each reference battery a characteristic frequency, the first characteristic frequency is the frequency corresponding to the ohmic internal resistance of the reference battery in the Nyquist spectrum; the first average characteristic frequency is obtained according to the first characteristic frequency of each reference battery; the first characteristic frequency of the first average characteristic frequency is adopted; A test current is input to the battery to be tested, and the corresponding first response voltage is obtained; the ohmic internal resistance of the battery to be tested is obtained according to the first response voltage and the first test current of the first average characteristic frequency; and/or, the ohmic internal resistance of each reference battery is obtained The second eigenfrequency in the Nyquist spectrum, the second eigenfrequency is the frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; the second average eigenfrequency is obtained according to the second eigenfrequency of each reference battery Adopt the first test current of the second average characteristic frequency to input the battery under test, and obtain the corresponding second response voltage; Obtain the electrochemical reaction resistance of the battery under test according to the first test current of the second response voltage and the second average characteristic frequency ; Judge the consistency of the battery to be tested by the ohmic internal resistance of the battery to be tested and/or the internal resistance of the electrochemical reaction of the battery to be tested.

Optionally, the number of the batteries to be tested is several; the average ohmic internal resistance of the batteries to be tested is obtained according to the ohmic internal resistances of the batteries to be tested; If the absolute value of the difference of the average ohmic internal resistance is greater than or equal to the average ohmic internal resistance of the battery to be tested which is a multiple of the first threshold value, the battery to be tested does not meet the consistency requirements of the tested battery; If the absolute value of the difference between the average ohmic internal resistance of the battery under test is less than the average ohmic internal resistance of the battery under test with a multiple of the first threshold value, then the battery under test meets the consistency requirements of the test battery; the multiple of the first threshold value is less than or equal to 0.005 .

Optionally, the first threshold multiple is 0.003.

Optionally, the number of the batteries to be measured is several; the average electrochemical reaction resistance of the batteries to be measured is obtained according to the electrochemical reaction resistances of the batteries to be measured; If the absolute value of the difference between the average electrochemical reaction resistance of the battery under test is greater than or equal to the average electrochemical reaction resistance of the battery under test with a multiple of the second threshold, the battery under test does not meet the consistency requirements of the test battery; If the absolute value of the difference between the electrochemical reaction resistance 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 with a multiple of the second threshold value, the battery to be tested meets the battery consistency requirements; the second Threshold multiple is less than or equal to 0.005.

Optionally, the second threshold multiple is 0.003.

Optionally, obtain the ohmic internal resistance of each reference battery, and obtain the average ohmic internal resistance of the reference battery and the standard deviation of the ohmic internal resistance of the reference battery according to the ohmic internal resistance of each reference battery; If the absolute value of the difference of the average ohmic internal resistance is greater than or equal to the standard deviation of the ohmic internal resistance of the reference battery that is a multiple of the third threshold, the battery to be tested does not meet the test battery consistency requirements; if the ohmic internal resistance of the test battery is different from the reference battery The absolute value of the difference of the average ohmic internal resistance is less than the standard deviation of the ohmic internal resistance of the reference battery with the third threshold multiple, then the battery to be tested meets the test battery consistency requirements; the third threshold multiple is less than or equal to 5.

Optionally, the third threshold multiple is 3.

Optionally, obtain the electrochemical reaction resistance of each reference cell, and obtain the average electrochemical reaction resistance of the reference cell and the standard deviation of the electrochemical reaction resistance of the reference cell according to the electrochemical reaction resistance of each reference cell; If the absolute value of the difference between the reaction resistance and the average electrochemical reaction resistance of the reference battery is greater than or equal to the electrochemical reaction resistance of the reference battery that is a multiple of the fourth threshold, the battery to be tested does not meet the test battery consistency requirements; If the absolute value of the difference between the chemical reaction resistance 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 at a multiple of the third threshold, the battery to be tested meets the test battery consistency requirements; the fourth Threshold multiple is less than or equal to 5.

Optionally, the fourth threshold multiple is 3.

Optionally, the method for obtaining the Nyquist spectrum of any reference battery includes: inputting a first test current signal to the reference battery, and obtaining a first response of the reference battery corresponding to the first test current signal of different frequencies within the test frequency range. voltage signal; obtain 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; obtain the Nyquis of the reference battery according to the internal resistance of the reference battery and the corresponding frequency Special map; the test frequency range is 10KHz ~ 0.1Hz.

Optionally, the method further includes: before acquiring the Nyquist spectrum of each reference battery, performing a stationary treatment on each reference battery; the stationary treatment time is 2 h to 10 h; the ambient temperature of the stationary treatment is -30℃～60℃.

Optionally, the ambient temperature of the reference battery in the process of acquiring the Nyquist spectrum of each reference battery is consistent with the ambient temperature of the stationary process.

Optionally, after each reference battery is left to stand, and before acquiring the Nyquist spectrum of each reference battery, the reference battery is charged to a reference state of charge; the reference state of charge is 20% -80%.

Optionally, before acquiring the first characteristic frequency and or the second characteristic frequency, the method further includes: performing a resting process on the battery to be tested; after the battery to be tested is rested, charging the battery to be tested to a reference state of charge; The time conditions for the stationary treatment are the same as the time conditions for the stationary treatment for each reference battery; the ambient temperature for the stationary treatment for the battery to be tested is the same as the ambient temperature for the stationary treatment for each reference battery.

The technical scheme of the present invention has the following advantages:

In the method for detecting the consistency of the secondary battery provided by the technical solution of the present invention, in the process of acquiring the Nyquist spectrum of each reference battery, the damage to the reference battery is small and the reference battery will not cause obvious battery polarization. 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. Interference impedance is less. 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. Other interference impedances are less. The real ohmic internal resistance and/or electrochemical reaction resistance of the battery to be tested can be accurately reflected respectively, and the consistency screening results of the test battery are more accurate. In conclusion, the consistency detection method of the secondary battery provided by the present invention can efficiently and accurately detect the consistency of the secondary battery.

Description of drawings

In order to illustrate the specific embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description The drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

1 is a flowchart of a method for detecting consistency of a secondary battery provided in Embodiment 1 of the present invention;

2 is an equivalent circuit diagram of the electrochemical impedance principle in Embodiment 1 of the present invention;

FIG. 3 is a histogram of 30 times of ohmic internal resistance detection results of a battery to be tested with 2 ohm internal resistance of 0.3382mΩ according to the embodiment of the present invention;

4 is a graph showing the relationship between the number of cracks in different tabs and ohmic internal resistance in Embodiment 2 of the present invention;

5 is a distribution diagram of the ohmic internal resistance of the battery to be tested in Example 3 of the present invention and the internal resistance of the battery to be tested in Comparative Example 1;

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

Fig. 7 is the relation diagram of frequency and temperature corresponding to the average electrochemical reaction resistance of the reference cell of Test Example 1 of the present invention;

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

FIG. 9 is a distribution diagram of the ohmic internal resistance of the battery to be tested in Test Example 2 of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must have a specific orientation or a specific orientation. construction and operation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first", "second", and "third" are used for descriptive purposes only and should not be construed to indicate or imply relative importance.

In the description of the present invention, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense, unless otherwise expressly specified and limited, for example, it may be a fixed connection or a detachable connection Connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific situations.

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.

Example 1

This embodiment provides a method for detecting the consistency of a secondary battery, referring to FIG. 1 , including:

S1: Provide the battery to be tested and several reference batteries;

S2: Obtain the Nyquist spectrum of each reference battery;

S3: Obtain 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; according to the first characteristic frequency of each reference battery Obtain the first average characteristic frequency; use the first test current of the first average characteristic frequency to input the battery under test to obtain the corresponding first response voltage; obtain the under test according to the first response voltage and the first test current of the first average characteristic frequency the ohmic internal resistance of the battery; and/or,

S4: Obtain the second characteristic frequency in the Nyquist spectrum of each reference battery, and the second characteristic frequency is the frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; according to the second characteristic of each reference battery The frequency obtains the second average characteristic frequency; the first test current of the second average characteristic frequency is used to input the battery to be tested, and the corresponding second response voltage is obtained; the first test current to be tested is obtained according to the second response voltage and the second average characteristic frequency Measure the electrochemical reaction resistance of the battery;

S5: Judging the consistency of the battery to be tested by the ohmic internal resistance of the battery to be tested and/or the internal resistance of the electrochemical reaction of the battery to be tested.

In the method for detecting the consistency of secondary batteries provided in this embodiment, in the process of acquiring the Nyquist spectra of each reference battery, the damage to the reference battery is relatively small and the reference battery will not cause obvious battery polarization. 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. Interference impedance is less. 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 includes The other interference impedance is less. The real ohmic internal resistance and/or electrochemical reaction resistance of the battery to be tested can be accurately reflected respectively, and the consistency screening results of the test battery are more accurate. In conclusion, the consistency detection method of the secondary battery provided by the present invention can efficiently and accurately detect the consistency of the secondary battery.

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, and obtaining the first test current signal of the reference battery corresponding to the first test current signal of different frequencies within the test frequency range. a response voltage signal; obtain 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; obtain the nanometer of the reference battery according to the internal resistance of the reference battery and the corresponding frequency Quest map.

In this embodiment, the method for obtaining the frequency corresponding to the ohmic internal resistance (ie, the first characteristic frequency) in the Nyquist spectrum of each reference battery is an equivalent circuit diagram based on the principle of electrochemical impedance (as shown in FIG. 2 , wherein, 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, W3 represents the diffusion impedance of the battery) Decompose the Nyquist spectrum of the reference battery to get the ohmic resistance The frequency corresponding to the resistance is the frequency point corresponding to the point where the Nyquist spectrum curve and the real part of the Nyquist spectrum intersect, and the resistance value of the intersection point is the ohmic internal resistance of the reference battery.

In this embodiment, the method for obtaining the corresponding frequency (ie, the second characteristic frequency) of the electrochemical reaction resistance in the Nyquist spectrum of each reference battery is to decompose the equivalent circuit diagram (as shown in FIG. 2 ) based on the principle of electrochemical impedance. The frequency corresponding to the electrochemical reaction resistance obtained from the Nyquist spectrum of the reference battery is the frequency corresponding to the inflection point of the first approximate semicircle of the Nyquist spectrum curve, and the corresponding impedance of the real part of the inflection point is the electrochemical reaction resistance of the reference battery. .

In this embodiment, the test frequency range is 10KHz～0.1Hz, for example, 10KHz～0.1Hz, or 1000Hz～0.1Hz.

In this embodiment, the method for detecting the consistency of the secondary battery further includes: before acquiring the Nyquist spectrum of each reference battery, performing a resting treatment on each reference battery, wherein the resting treatment time is 2h to 10h, For example: 3h, 4h, 8h or 10h; the ambient temperature of the stationary treatment is -30°C to 60°C, for example: -20°C, 0°C, 10°C, 30°C or 45°C. The performance of the test battery can be relatively stable by standing the reference battery, and the uneven temperature of the test battery itself can be prevented from adversely affecting the test results. The rest processing time is determined by testing the size of the battery and the original temperature. The temperature of the standstill treatment is determined by the reference battery usage temperature.

In this embodiment, the ambient temperature of the reference battery in the process of acquiring the Nyquist spectrum of each reference battery is consistent with the temperature of the resting process.

In this embodiment, after each reference battery is left to stand, and before acquiring the Nyquist spectrum of each reference battery, 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 test accurately, it is necessary to adjust the reference battery to the same state of charge, so as to avoid different battery polarizations due to different states of charge, resulting in poor comparison of test results.

In this embodiment, before acquiring the first characteristic frequency and or the second characteristic frequency, the method further includes: performing a resting process on the battery to be tested; after the resting process on the battery to be tested, charging the battery to be tested to a reference state of charge; The time conditions for the standstill treatment of the test battery are the same as the time conditions for the standstill treatment of each reference battery; the ambient temperature of the standstill treatment of the battery to be tested is the same as the ambient temperature of the standstill treatment of each reference battery.

In this embodiment, the number of the batteries to be tested is several; the average ohmic internal resistance of the batteries to be tested is obtained according to the ohmic internal resistances of the batteries to be tested; If the absolute value of the difference between the average ohmic internal resistance of the battery under test is greater than or equal to the average ohmic internal resistance of the battery under test that is a multiple of the first threshold, the battery under test does not meet the test battery consistency requirements; If the absolute value of the difference between the resistance 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 with a multiple of the first threshold value, the battery to be tested meets the test battery consistency requirements; the multiple of the first threshold value 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 multiple is 0.003.

In another embodiment, the number of the batteries to be measured is several; the average electrochemical reaction resistance of the batteries to be measured is obtained according to the electrochemical reaction resistances of the batteries to be measured; If the absolute value of the difference between the resistance and the average electrochemical reaction resistance of the battery under test is greater than or equal to the average electrochemical reaction resistance of the battery under test with a multiple of the second threshold, the battery under test does not meet the test battery consistency requirements; If the absolute value of the difference between the electrochemical reaction resistance of the battery under test and the average electrochemical reaction resistance of the battery under test is less than the average electrochemical reaction resistance of the battery under test with a multiple of the second threshold, the battery under test meets the battery consistency requirements; The second threshold multiple is less than or equal to 0.05, such as 0.05, 0.01, 0.005 or 0.003; in this embodiment, the second threshold multiple is 0.003.

In another embodiment, 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 according to the ohmic internal resistance of each reference battery; If the absolute value of the difference between 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 that is a multiple of the third threshold, the battery to be tested does not meet the test battery consistency requirements; if the ohmic internal resistance of the test battery If the absolute value of the difference with the average ohmic internal resistance of the reference battery is less than the standard deviation of the ohmic internal resistance of the reference battery with the 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, for example, 1, 2, 3, or 5; in this embodiment, the third threshold multiple is 3.

In another embodiment, the electrochemical reaction resistance of each reference cell is obtained, and the average electrochemical reaction resistance of the reference cell and the standard deviation of the electrochemical reaction resistance of the reference cell are obtained according to the electrochemical reaction resistance of each reference cell; The absolute value of the difference between the electrochemical reaction resistance of the reference 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 with the fourth threshold multiple, then the battery to be tested does not meet the test battery consistency requirements; If the absolute value of the difference between the electrochemical reaction resistance of the 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 that is a multiple of the third threshold, the battery to be tested meets the test battery consistency requirements; The fourth threshold multiple is less than or equal to 5, such as 1, 2, 3, or 5; in this embodiment, the fourth threshold multiple is 3.

Example 2

Provide 10 square batteries of the same model for pure electric vehicles in good condition as reference batteries. After the reference batteries are left standing at 25 °C for 6 hours, the state of charge of the reference batteries is adjusted to 50% state of charge, and passed at 25 °C. The BT4560 variable frequency daily built-in internal resistance meter inputs the first test current signal to the test reference battery to obtain the first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in the frequency range of 1000Hz ~ 0.1Hz (wherein 1000 ~ 10Hz One point is collected every 1Hz within the frequency range, and one point is collected every 0.1Hz within the frequency range of 10-0.1Hz), obtained according to the first response voltage signal and the corresponding first test electrical signal of the reference battery at different frequencies The internal resistance of the reference battery; the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

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

Provide 10 batteries to be tested with the same type as the reference battery but with different degrees of tab cracking (2 of them are in good condition, 2 are two-layer batteries with cracked tabs, 2 are four-layer batteries with cracked tabs, and 2 are Six-layer battery with cracked tabs, 2 are eight-layer batteries with cracked tabs), after the battery to be tested is allowed to stand at 25 °C for 6 hours, the state of charge of the test battery is adjusted to 50% state of charge, at 25 °C Input the first test current signal of 66Hz to the battery under test through the BT4560 variable frequency daily built-in internal resistance meter, obtain the corresponding first response voltage, and obtain the ohm of the battery under test according to the first response voltage and the first test current of the first characteristic frequency. internal resistance.

The ohmic internal resistance value of the battery to be tested is in the increasing order of the number of cracked layers of the tab (layer 0, layer 2, layer 4, layer 6, layer 8): 0.3052mΩ, 0.3051mΩ, 0.3187mΩ, 0.3183mΩ, 0.3262mΩ , 0.3264mΩ, 0.3315mΩ, 0.3317mΩ, 0.3382mΩ, 0.3387mΩ, through comparison, it can be found that the ohmic internal resistance of the test battery can be divided into 5 groups, corresponding to the battery in good condition, the two-layer battery with cracked electrode, and the cracked electrode Four-layer battery, six-layer battery with tab cracking, and eight-layer battery with tab cracking. By comparing the difference between the ohmic internal resistance value of the battery to be tested 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 cracks in the tabs is 2, the battery does not meet the test battery consistency requirements .

The battery to be tested with ohmic internal resistance of 0.3382mΩ was tested 30 times through the BT4560 variable frequency daily internal resistance test (the test conditions are the same as the above test conditions), and the frequency and ohmic internal resistance histogram of the Minitab software was used (as shown in Figure 3). ), it can be seen from Figure 3 that the ohmic internal resistance of the battery to be tested conforms to a normal distribution, and the standard deviation value is small, indicating that the measurement system has small fluctuations, high sensitivity and low test error.

Each battery to be tested is tested 10 times with the BT4560 variable frequency daily internal resistance meter (the test conditions are the same as the above test conditions), and the corresponding ohmic internal resistance is recorded, and the number of tab cracks and the ohmic internal resistance are plotted by Minitab software Relationship diagram (shown in Figure 4). It can be seen from Figure 4 that with the increase of the number of cracked layers of the tab, the ohmic internal resistance basically increases linearly, and the maximum ohmic internal resistance growth rate can reach 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 ohmic internal resistance identification accuracy, effectively solving the battery ohmic internal resistance consistency screening problem, and improving the finished product shipment rate.

Example 3

10 prismatic batteries of the same model for hybrid electric vehicles in good condition were provided as reference batteries. After the reference batteries were allowed to stand at 25 °C for 6 h, the state of charge of the reference batteries was adjusted to 50% state of charge, and the state of charge of the reference batteries was adjusted to 50% at 25 °C. Input the first test current signal to the test reference battery through the electrochemical workstation to obtain the first response voltage signal of the reference battery corresponding to the first test current signal at different frequencies in the frequency range of 10kHz to 10mHz. The internal resistance of the reference battery is obtained from the first response voltage signal and the corresponding first test electrical signal; the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

Based on the equivalent circuit diagram model of the electrochemical impedance principle of the reference battery (refer to Figure 2) and the Nyquist spectrum of the reference battery, the corresponding frequency of the ohmic internal resistance of each reference battery is obtained, and the average ohmic internal resistance corresponding frequency of the reference battery is obtained by averaging calculation. is 245Hz.

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

Screen out 2 batteries to be tested that do not meet the battery consistency.

Comparative Example 1

The 100 batteries in Example 3 were tested, and after the battery to be tested was allowed to stand at 25°C for 6 hours, the state of charge of the test battery was adjusted to 50% state of charge, and the internal resistance of the mass production line was passed at 25°C. The instrument inputs the first test current signal of 1000Hz to the battery under test, obtains the corresponding first response voltage, obtains the ohmic internal resistance of each battery under test according to the first response voltage and the first test current of the first characteristic frequency, and calculates the average Measure the average ohmic internal resistance of the ohmic internal resistance of the battery, and compare the ohmic internal resistance of each battery to be tested with the average ohmic internal resistance. If the absolute value of the difference between the ohmic internal resistance of the battery to be tested and the average ohmic internal resistance is greater than or equal to 0.3% of the average ohmic internal resistance, the battery under test does not meet the consistency of the test battery; 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, then The battery to be tested conforms to the test battery consistency. Refer to Figure 5 for the test results.

Screen out 4 batteries to be tested that do not meet the battery consistency.

Because the internal resistance obtained under the first test current signal of 1000Hz contains a large amount of inductive reactance, the internal resistance fluctuates greatly, and it is easy to screen the battery to be tested that conforms to the battery consistency.

Test Example 1

After providing 10 reference batteries in Example 3 and standing at 25°C for 6 hours, the state of charge of the reference battery was adjusted to 50% state of charge, and the first test current was input to the test reference battery through an electrochemical workstation at 25°C The signal obtains the first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in the frequency range of 10kHz～10mHz, according to the first response voltage signal of the reference battery at different frequencies and the corresponding first test voltage signal. The signal obtains the internal resistance of the reference battery; the Nyquist spectrum of the reference battery is obtained according to the internal resistance of the reference battery and the corresponding frequency.

Based on the equivalent circuit diagram model of the electrochemical impedance principle of the reference battery (refer to Figure 2) and the Nyquist spectrum of the reference battery, the corresponding frequency of the ohmic internal resistance and the corresponding frequency of the ohmic internal resistance and the electrochemical reaction resistance of each reference battery are obtained, and the average Calculate and obtain the frequency corresponding to the average ohmic internal resistance of the reference battery, the average ohmic internal resistance, and the corresponding frequency of the average electrochemical reaction resistance.

According to the above method, obtain the frequency corresponding to the average ohmic internal resistance, the average ohmic internal resistance, and The average electrochemical reaction resistance corresponds to frequency.

The relationship between the frequency and temperature corresponding to the average ohmic internal resistance is shown in Figure 6, and the relationship between the frequency and temperature corresponding to the average electrochemical reaction resistance is shown in Figure 7.

The relationship between the average ohmic internal resistance and temperature is shown in Figure 8. It can be seen from Figure 8 that the relationship between the average ohmic internal resistance and temperature conforms to the Arrhenius equation:

^σT=Ae-Ea/RT

Among them, σ represents the ion mobility rate, σ=L/(R×S); T represents the temperature, Ea represents the activation energy; k is a constant; A represents the prefactor, L represents the length of the electrode material, and S represents the area of the electrode material; R Represents resistance (ohmic internal resistance or electrochemical reaction resistance).

8 , it can be shown that in a wide temperature range, the test value of the average ohmic internal resistance is relatively accurate, and the consistency detection method of the secondary battery provided by the present invention can efficiently and accurately detect the secondary battery in a wide temperature range consistency.

Test case 2

Provide 10 prismatic batteries for hybrid vehicles of the same model in good condition as reference batteries. After the reference batteries are allowed to stand at 25 °C for 6 h, the state of charge of the reference batteries is adjusted to 50% state of charge, at 25 °C. Input the first test current signal to the test reference battery through the BT4560 variable frequency daily internal resistance meter to obtain the first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies in the frequency range of 1000Hz～0.1Hz (wherein, 1000～ A point is collected every 1Hz within the frequency range of 10Hz, and a point is collected every 0.1Hz within the frequency range of 10-0.1Hz), according to the first response voltage signal and the corresponding first test electrical signal of the reference battery at different frequencies Obtain the internal resistance of the reference battery; obtain the Nyquist spectrum of the reference battery according to the internal resistance of the reference battery and the corresponding frequency.

Based on the equivalent circuit diagram model of the electrochemical impedance principle of the reference battery (refer to Figure 2) and the Nyquist spectrum of the reference battery, obtain the corresponding frequency of the ohmic internal resistance of each reference battery, as well as the ohmic internal resistance, and calculate the average to obtain the average value of the reference battery. The ohmic internal resistance corresponds to a frequency of 300Hz.

9 batteries to be tested of the same type are randomly provided (for battery numbering), after the battery to be tested is placed at 25°C for 6 hours, the state of charge of the test battery is adjusted to 50% state of charge, and passed BT4560 at 25°C The 300Hz first test current signal is input to the battery under test, the corresponding first response voltage is obtained, and the ohmic internal resistance of the battery under test is obtained according to the first response voltage and the first test current of the first characteristic frequency. . The test results are shown in Figure 9.

Figure 9 shows that the ohmic internal resistance of mass-produced batteries of the same model is different to a certain extent. By accurately and effectively identifying the ohmic internal resistance of the battery, it is possible to screen out the mass-produced batteries that do not meet the battery consistency requirements, so as to improve the output of good products. rate.

Obviously, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. And the obvious changes or changes derived from this are still within the protection scope of the present invention.

Claims (10)

1. the consistency detection method of secondary battery, is characterized in that, comprises: Provide the battery to be tested and several reference batteries; Obtain the Nyquist spectrum of each reference battery; 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 the first average characteristic frequency according to the first characteristic frequency of each reference battery; The first test current of the first average characteristic frequency is used to input the battery under test, and the corresponding first response voltage is obtained; Obtain the ohmic internal resistance of the battery under test according to the first response voltage and the first test current of the first average characteristic frequency; and/or, Obtain the second eigenfrequency in the Nyquist spectrum of each reference battery, and the second eigenfrequency is the frequency corresponding to the electrochemical reaction resistance of the reference battery in the Nyquist spectrum; obtain according to the second eigenfrequency of each reference battery the second average characteristic frequency; the first test current of the second average characteristic frequency is used to input the battery under test, and the corresponding second response voltage is obtained; the battery under test is obtained according to the second response voltage and the first test current of the second average characteristic frequency The electrochemical reaction resistance of ; The consistency of the battery to be tested is judged by the ohmic internal resistance of the battery to be tested and/or the internal resistance of the electrochemical reaction of the battery to be tested. 2. The method for detecting the consistency of secondary batteries according to claim 1, wherein the number of the batteries to be tested is several; the ohmic internal resistances of the batteries to be tested are obtained Average ohmic internal resistance; 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 that is a multiple of the first threshold, the battery to be tested will not be tested. Meets 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 battery to be tested is less than the average ohmic internal resistance of the battery to be tested that is a multiple of the first threshold, the battery to be tested meets the Test battery consistency requirements; the first threshold multiple is less than or equal to 0.05. 3. The consistency detection method of a secondary battery according to claim 1, wherein the number of the batteries to be tested is several; several batteries to be tested are 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 that is a multiple of the second threshold, Then the battery under test does not meet the test battery consistency requirements; if the absolute value of the difference between the electrochemical reaction resistance of the battery under test and the average electrochemical reaction resistance of the battery under test is less than the second threshold multiple of the average charge of the battery under test. chemical reaction resistance, the battery to be tested meets the battery consistency requirements; the second threshold multiple is less than or equal to 0.05. 4. The method for detecting consistency of secondary batteries according to claim 1, wherein the ohmic internal resistance of each reference battery is obtained, and the average ohmic internal resistance of the reference battery and the reference battery are obtained 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 that is a multiple of the third threshold, the battery to be tested will be 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 that is a multiple of the third threshold, the battery to be tested meets the requirements Test battery consistency requirements; the third threshold multiple is less than or equal to 5. 5. The consistency detection method of secondary battery according to claim 1, is characterized in that, obtains the electrochemical reaction resistance of each reference cell, obtains the average electrochemical reaction resistance of reference cell according to the electrochemical reaction resistance of each reference cell and the standard deviation of the electrochemical reaction resistance of the reference cell; if the absolute value of the difference between the electrochemical reaction resistance of the test cell and the average electrochemical reaction resistance of the reference cell is greater than or equal to the electrochemical reaction resistance of the reference cell that is a multiple of the fourth threshold, Then the battery to be tested does not meet the test battery consistency requirements; 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 third threshold multiple of the reference battery's electrochemical reaction resistance standard poor, the battery to be tested meets the test battery consistency requirements; the fourth threshold multiple is less than or equal to 5. 6 . The consistency detection method of a secondary battery according to claim 1 , wherein the method for obtaining the Nyquist spectrum of the reference battery comprises: inputting a first test current signal to the reference battery, and obtaining a test frequency band. 7 . The first response voltage signal of the reference battery corresponding to the first test current signal of different frequencies within the range; the internal resistance of the reference battery is obtained according to the first response voltage signal and the corresponding first test electrical signal of the reference battery at different frequencies ; Obtain the Nyquist spectrum of the reference battery according to the internal resistance of the reference battery and the corresponding frequency; the test frequency range is 10KHz～0.1Hz. 7 . The method for detecting the consistency of secondary batteries according to claim 1 , further comprising: before acquiring the Nyquist spectrum of each reference battery, performing a resting process on each reference battery; The standing treatment time is 2h to 10h; the ambient temperature of the standing treatment is -30°C to 60°C. 8 . The method for detecting the consistency of secondary batteries according to claim 7 , wherein the ambient temperature of the reference battery in the step of acquiring the Nyquist spectrum of each reference battery is consistent with the ambient temperature of the stationary treatment. 9 . 9 . The method for detecting the consistency of secondary batteries according to claim 7 , wherein after each reference battery is left to stand, and before acquiring the Nyquist spectrum of each reference battery, the reference The battery is charged to a reference state of charge; the reference state of charge is 20% to 80%. 10 . The consistency detection method of a secondary battery according to claim 9 , wherein before acquiring the first characteristic frequency and or the second characteristic frequency, the method further comprises: performing a static treatment on the battery to be tested; After the standstill treatment, the battery to be tested is charged to the reference state of charge; the time conditions for the standstill treatment of the battery to be tested are the same as the time conditions for the standstill treatment of each reference battery; the ambient temperature and The ambient temperature at which each reference battery was left to stand was the same.

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