High-speed battery defect inspection method

Abstract

The present invention relates to a high-speed battery defect inspection method, and more specifically, to a high-speed battery defect inspection method that predicts the degradation characteristics of a battery formed by stacking a plurality of mono-cells and determines whether the battery is defective within a short period of time.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0140870 dated October 28, 2022, and all contents disclosed in the documents of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a high-speed battery defect inspection method, and more particularly to a high-speed battery defect inspection method for predicting the degradation characteristics of a battery formed by stacking a plurality of mono-cells and determining whether the battery is defective within a short period of time. [Background technology]

[0003] In the case of medium- to large-sized batteries in which multiple mono cells are stacked, some of the internal mono cells may exhibit a low voltage defect (a decrease in the potential of a specific mono cell) for unknown reasons, resulting in a defect that reduces the capacity of the entire cell.

[0004] Products such as ESS and vehicle batteries that are shipped and equipped with low-voltage defective cells will show significant instability in performance over the long term, reducing the reliability of the products.

[0005] Previously, battery voltage was tracked to detect low-voltage defective batteries at the battery shipping stage. This typically required a long period of time, more than two weeks. Furthermore, there is a high pressure current detection (HPCD) test method, which considers the main cause of low-voltage defects to be bending of the separator, but there was a limit to what the HPCD test method could detect.

[0006] Therefore, a test method is required that can detect low-voltage defective cells using existing test methods and can inspect all cells in a short time. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a high-speed battery defect inspection method, and more specifically, to provide a high-speed battery defect inspection method that predicts the degradation characteristics of a battery formed by stacking a plurality of mono-cells and determines whether the battery is defective within a short period of time.

[0008] The technical problems that the present invention aims to solve are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0009] The method for rapid battery defect inspection of the present invention includes an analysis target impedance measuring step (step s30) of applying an AC current of a set frequency to an analysis target battery to obtain an analysis target impedance, which is the analysis target battery impedance; a real part resistance extracting step (step s40) of extracting a real part value from the analysis target impedance as a real part resistance; and a defect determination step (step s50) of determining whether the analysis target battery is defective based on the real part resistance, wherein the set frequency is selected from among frequencies at which the imaginary part resistance, which is the imaginary part value of the analysis target impedance, is greater than 0. Effect of the Invention

[0010] The high-speed battery defect inspection method of the present invention is capable of detecting low-voltage defective batteries in a short time, and is capable of inspecting several thousand to several tens of thousands of batteries per second.

[0011] The method for high speed battery defect inspection according to the present invention is capable of non-destructive inspection of completed batteries and is applicable to mass production line batteries and already manufactured batteries.

[0012] The high speed battery defect inspection method of the present invention dramatically reduces the inspection time compared to the conventional methods, and is capable of determining defects even in uninspected batteries. [Brief description of the drawings]

[0013] [Figure 1] 1 is a block diagram showing a method for high-speed battery defect inspection according to the present invention; [Diagram 2] 1 is a graph showing a general Nyquist diagram. [Diagram 3] 1 is a graph comparing impedance values ​​of a normal battery and a defective battery. [Figure 4] FIG. 13 is a block diagram showing another embodiment of the method for high-speed battery defect inspection of the present invention. [Diagram 5] FIG. 2 is a block diagram showing a set frequency step. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The method for rapid battery defect inspection of the present invention includes an analysis target impedance measuring step (step s30) of applying an AC current of a set frequency to an analysis target battery to obtain an analysis target impedance, which is the analysis target battery impedance; a real part resistance extracting step (step s40) of extracting a real part value from the analysis target impedance as a real part resistance; and a defect determination step (step s50) of determining whether the analysis target battery is defective based on the real part resistance, wherein the set frequency is selected from among frequencies at which the imaginary part resistance, which is the imaginary part value of the analysis target impedance, is greater than 0.

[0015] In the high-speed battery defect inspection method of the present invention, the set frequency is 10 -2 Also available in kHz to 7MHz.

[0016] In the method for rapid battery defect inspection of the present invention, the battery to be analyzed includes a plurality of mono-cells.

[0017] The high-speed battery defect testing method of the present invention further includes, prior to the analysis target impedance measuring step (step s30), a reference impedance measuring step (step s10) of applying an AC current to a reference battery while changing the frequency to obtain a plurality of reference impedances for a plurality of frequencies, and a set frequency calculating step (step s20) of calculating the set frequency based on the plurality of reference impedances.

[0018] In the high speed battery defect inspection method of the present invention, the reference battery has a dOCV of 300mV or more or 3sigma or more.

[0019] In the high-speed battery defect inspection method of the present invention, the set frequency calculation step (step s20) is performed by dividing the plurality of reference impedances by real part values ​​Z SR and the imaginary part value Z SI A variable separation step (step s21) for separating Z SR and Z SI and a function fitting step (step s22) of acquiring a relational expression f for the above relational expression, and a set frequency acquisition step (step s23) of acquiring the set frequency based on the relational expression.

[0020] In the function fitting step (step s22) of the high speed battery defect inspection method of the present invention, the relational expression f is fitted by the following Equation 1.

[0021]

number

[0022] In the step of acquiring the set frequency (step s23) of the high-speed battery defect inspection method of the present invention, the set frequency is SI is selected from among the frequencies that satisfy the following Equation 2 for a section in which is greater than 0.

[0023]

number

[0024] In the step of setting the frequency of the battery defect high speed inspection method of the present invention, the ε can be 0.

[0025] In the defect determination step (step s50) of the battery defect high speed inspection method of the present invention, the real part resistance satisfies the formula 2.SI If the value is 30% or more, the battery to be analyzed is determined to be a defective battery.

[0026] The battery activation method of the present invention includes a battery preparation step of preparing a battery to be activated through an assembly process; a charge / discharge step of charging or discharging the battery to be activated; a stabilization step of stabilizing the battery to be activated by storing the battery to be activated at the set temperature and set humidity for a certain period of time; and a defect screening step of performing the above-described high-speed battery defect inspection method using the battery to be activated as the analysis target battery to finally screen out defective batteries.

[0027] The battery activation method of the present invention further includes, between the activation battery preparation step and the charging / discharging step, a pre-inspection step of pre-inspecting the target battery by performing the above-described high-speed battery defect inspection method using the target battery as an analysis target battery.

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this process, the size and shape of components shown in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intention or practice of a user or operator. The definition of such terms should be based on the overall content of this specification.

[0029] Fig. 1 is a block diagram showing a method for high-speed battery defect inspection of the present invention. Fig. 2 is a graph showing a general Nyquist diagram. Fig. 3 is a graph comparing impedance values ​​of normal and defective batteries. Fig. 4 is a block diagram showing another embodiment of the method for high-speed battery defect inspection of the present invention. Fig. 5 is a block diagram showing a setting frequency stage.

[0030] Hereinafter, the method for high speed battery defect inspection of the present invention will be described in detail with reference to FIGS.

[0031] As shown in FIG. 1, the method for rapid battery defect inspection of the present invention includes an analysis target impedance measuring step (step s30) of applying an AC current of a set frequency to an analysis target battery to obtain an analysis target impedance, which is the analysis target battery impedance; a real part resistance extracting step (step s40) of extracting a real part value from the analysis target impedance as a real part resistance; and a defect determining step (step s50) of determining whether the analysis target battery is defective based on the real part resistance, wherein the set frequency is selected from among frequencies when the imaginary part resistance, which is the imaginary part value of the analysis target impedance, is greater than 0.

[0032] In the method for rapid battery defect inspection of the present invention, the battery to be analyzed includes a plurality of mono-cells.

[0033] The mono cell is a unit cell having different types of electrodes located on both outermost surfaces when one or more positive electrodes and one or more negative electrodes are stacked with a separator sandwiched therebetween to form an electrode assembly. For example, the mono cell is a unit cell having an electrode assembly structured such that a positive electrode-separator-negative electrode are stacked in this order. As another example, the mono cell is a unit cell having an electrode assembly structured such that a positive electrode-separator-negative electrode-separator-positive electrode-separator-negative electrode are stacked in this order.

[0034] The positive electrode is formed by applying a positive electrode active material to a positive electrode current collector.

[0035] The negative electrode is formed by applying a negative electrode active material to a negative electrode current collector.

[0036] The separation membrane is an insulator that allows ions to pass through.

[0037] In the analysis target impedance measurement step (step s30), the set frequency is 10 -2 A low-voltage defective battery has an impedance value that is different from that of a normal battery at high frequencies, and the difference is particularly evident in the real component of the impedance value.

[0038] When impedance spectroscopy (EIS) is performed on a battery, a graph on a complex plane as shown in Fig. 2 can be obtained. Specifically, for the impedance value corresponding to each frequency, the imaginary part is multiplied by (-) and the real part is plotted on a coordinate system to obtain a Nyquist diagram as shown in Fig. 2. The method for high-speed battery defect inspection of the present invention is capable of quickly determining low voltage defects of a battery based on the real part values ​​on two quadrants of the graph in Fig. 2.

[0039] FIG. 3 is a graph showing the impedance spectroscopy measurement results for 15 batteries. In FIG. 3, five graphs A_1, A_2, A_3, A_4, and A_5 are graphs for normal batteries, five graphs E_1, E_2, E_3, E_4, and E_5 are graphs for E-grade defective batteries, and five graphs L_1, L_2, L_3, L_4, and L_5 are graphs for L-grade defective batteries. E-grade defective batteries are defective batteries that show absolute OCV reduction. L-grade defective batteries are defective batteries that show relative OCV reduction. In FIG. 3, it can be seen that the graphs for EIS measurements for low-voltage defective batteries (E-grade defective batteries and L-grade defective batteries) regardless of the defective grade are overlapped with each other, but the graphs for normal batteries show different behavior from the graphs for defective batteries. Specifically, in the case of a normal battery, the impedance value measured at about 10 kHz appears in region A, and in the case of a defective battery of E grade and a defective battery of L grade, it appears in region B. In the case of a defective battery of E grade and a defective battery of L grade, it is seen that there is a maximum value for the real part value in region B. Therefore, in the step of measuring the impedance to be analyzed (step s30), the set frequency is set to 10 -2 The frequency is selected from the range of 10 kHz to 7 MHz. -1 ~10 2 The frequency is selected from 10 kHz. -2 In the frequency band from kHz to 7 MHz, a low-voltage defective battery exhibits an abnormal increase in the real part of the resistance value, which can be used to identify the battery as a low-voltage defective battery.

[0040] As shown in FIG. 4, the method for high speed battery defect testing according to the present invention further includes, prior to the analysis target impedance measuring step (step s30), a reference impedance measuring step (step s10) of applying an AC current to a reference battery while changing the frequency to obtain a plurality of reference impedances for a plurality of frequencies, and a set frequency calculating step (step s20) of calculating the set frequency based on the plurality of reference impedances.

[0041] The method for rapid battery defect testing of the present invention can obtain an optimal set frequency for accurately detecting a low-voltage defective battery by performing a reference impedance measurement step (step s10) and a set frequency calculation step (step s20) before the analysis target impedance measurement step (step s30).

[0042] In the reference impedance measurement step (step s10), the reference battery is determined to be a low-voltage defective battery when its delta open circuit voltage (dOCV) is 300 mV or more or 3 sigma or more. The reference battery that is a low-voltage defective battery is obtained as a battery that is inspected as a defective battery during mass production or a battery that is subjected to defective conditions such as bending of electrodes or defects in the active material coating area.

[0043] The reference impedance measuring step (step s10) is performed by impedance spectroscopy (EIS), so that reference impedance values ​​corresponding to each of a plurality of frequency values ​​can be obtained.

[0044] As shown in FIG. 5, the set frequency calculation step (step s20) calculates the plurality of reference impedances as real part values ​​Z SR and the imaginary part value Z SI A variable separation step (step s21) for separating Z SR and Z SI and a function fitting step (step s22) of acquiring a relational expression f for the above relational expression, and a set frequency acquisition step (step s23) of acquiring the set frequency based on the relational expression.

[0045] In the function fitting step (step s22), the relational expression f is fitted by the following Equation 1.

[0046]

number

[0047] That is, in the function fitting stage (step s22), the relational expression f is expressed as Z SR is the dependent variable, and the imaginary part value Z SI is obtained in the form of a function with

[0048] In the set frequency acquisition step (step s23), the set frequency is SI is selected from among the frequencies that satisfy the following Equation 2 for a section in which is greater than 0.

[0049]

number

[0050] In the setting frequency step, the ε is also 0. That is, the relation f is expressed as Z SI The frequency when the value differentiated by f is 0 can be obtained as the set frequency. More specifically, the frequency value when the relational expression f has a maximum value can be obtained as the set frequency.

[0051] In the defect determination step (step s50), the real part resistance satisfies Equation 2. SIWhen the resistance of the real part of the low-voltage defective battery is 30% or more, the battery is judged to be a defective battery. As described above for the low-voltage defective battery, the relational expression f has a maximum value for the set frequency, and the real part resistance value may have an abnormally large value. According to an experimental example described later, the real part resistance value of a low-voltage defective battery at the set frequency is more than twice as large as the real part resistance value of a normal defective battery. Therefore, the real part resistance Z that satisfies the above formula 2 is SI If the measured voltage is 30% or more or 50% or more of the value, the battery being analyzed is determined to be a low-voltage defective battery.

[0052] A battery activation method to which the rapid battery defect inspection method of the present invention is applied includes: an activation battery preparation step of preparing a battery to be activated through an assembly process; a charge / discharge step of charging or discharging the battery to be activated; a stabilization step of stabilizing the battery to be activated by storing the battery to be activated at the set temperature and set humidity for a certain period of time; and a defect screening step of performing the rapid battery defect inspection method of the present invention using the battery to be activated as the analysis target battery and finally screening out a defective battery.

[0053] The target battery to be activated, which is prepared in the activated battery secretion step, is a battery that has been completed up to the packaging process.

[0054] The high speed battery defect inspection method of the present invention is applied to the battery activation process to greatly reduce the time that batteries need to be inspected for defects before shipping.

[0055] The battery activation method of the present invention further includes, between the activation battery preparation step and the charging / discharging step, a pre-inspection step of pre-inspecting the target battery by performing the high-speed battery defect inspection method of the present invention on the target battery as an analysis target battery.

[0056] The battery activation method of the present invention can prevent the charge / discharge process and the aging process from being performed on the defective battery by first screening out the defective battery before the charge / discharge process and the aging process, and can also screen out the defective battery secondarily after the aging process to remove the defective battery generated during the process of forming the SEI layer.

[0057] Experimental Example Fifteen 100 Ah class batteries that had undergone the activation process were prepared, of which five were normal batteries, five were E class defective batteries, and five were L class defective batteries.

[0058] EIS was performed on 15 batteries, and the results shown in Figure 3 were obtained.

[0059] The real resistance values ​​of the five normal batteries were measured at 500μΩ, 480μΩ, 470μΩ, 490μΩ and 520μΩ respectively at a frequency of 10kHz, which corresponds to the set frequency, the real resistance values ​​of the five E-class defective batteries were measured at 1160μΩ, 1140μΩ, 1110μΩ, 1130μΩ and 1110μΩ respectively at a frequency of 10kHz, which corresponds to the set frequency, and the real resistance values ​​of the five L-class defective batteries were measured at 1120μΩ, 1070μΩ, 1150μΩ, 1140μΩ and 1170μΩ respectively at a frequency of 10kHz, which corresponds to the set frequency.

[0060] That is, it can be seen that the real part resistance value measured for a low-voltage defective battery is more than twice as large as that of a normal battery at the set frequency.

[0061] Although the embodiment of the present invention has been described above, it is merely an example, and a person skilled in the art will understand that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of the present invention should be determined by the claims. [Industrial Applicability]

[0062] The high-speed battery defect inspection method of the present invention is capable of detecting low-voltage defective batteries in a short time, and is capable of inspecting several thousand to several tens of thousands of batteries per second.

[0063] The method for high speed battery defect inspection according to the present invention is capable of non-destructive inspection of completed batteries and is applicable to mass production line batteries and already manufactured batteries.

[0064] The high speed battery defect inspection method of the present invention dramatically reduces the inspection time compared to the conventional methods, and is capable of determining defects even in uninspected batteries.

Claims

1. an analysis target impedance measuring step (step s30) of applying an AC current of a set frequency to an analysis target battery to obtain an analysis target impedance, which is the impedance of the analysis target battery; A real part resistance extraction step (step s40) of extracting a real part value as a real part resistance from the analysis target impedance; and determining whether the battery is defective based on the real part resistance (step s50). The set frequency is a frequency at which an imaginary part resistance, which is an imaginary part value of the impedance to be analyzed, is greater than 0.

2. The set frequency is 10 －２ 3. The method for high speed battery defect inspection according to claim 1, wherein the frequency is from kHz to 7 MHz.

3. 2. The method of claim 1, wherein the battery to be analyzed includes a plurality of mono-cells.

4. Prior to the analysis target impedance measurement step (step s30), A reference impedance measuring step (step s10) of applying an AC current to the reference battery while changing the frequency to obtain a plurality of reference impedances for a plurality of frequencies; A set frequency calculation step (step s20) of calculating the set frequency based on the plurality of reference impedances; The method for rapid battery defect inspection according to claim 1 , further comprising:

5. 5. The method for high speed battery defect inspection according to claim 4, wherein the reference battery has a dOCV of 300 mV or more or 3 sigma or more.

6. The set frequency calculation step (step s20) The plurality of reference impedances are expressed as real part values ​​Z ＳＲ and the imaginary part value Z ＳＩ A variable separation step (step s21) for separating Said Z ＳＲ and Z ＳＩ A function fitting step (step s22) for obtaining a relational expression f for The method for high speed battery defect inspection according to claim 4, further comprising: a set frequency acquisition step (step s23) of acquiring the set frequency based on the relational expression.

7. In the function fitting step (step s22), The method of claim 6 , wherein the relational expression f is fitted by the following Equation 1: [0010] 。

8. In the setting frequency acquisition step (step s23), The set frequency is Z ＳＩ The method for high speed battery defect inspection according to claim 7, wherein the frequency is selected from frequencies that satisfy the following Equation 2 for a section in which t is greater than 0: [0025] The ε is 0 to 0.

2.

9. In the setting frequency acquisition step (step s23), 9. The method for high speed battery defect inspection according to claim 8, wherein the ε is 0.

10. In the defect determination step (step s50), The real part resistance satisfies the formula 2. ＳＩ 10. The method for rapid battery defect inspection according to claim 9, wherein the battery to be analyzed is determined to be a defective battery when the battery defect rate is 30% or more of the value.

11. a preparation step of preparing a battery to be activated through an assembly process; a charging / discharging step of charging or discharging the activation target battery; a stabilization step of storing the target battery at a set temperature and a set humidity for a certain period of time to stabilize the target battery; a defective sorting step of performing the method of claim 1 for quickly testing a defective battery using the target battery for activation as the target battery for analysis, and finally sorting out a defective battery; A method for activating a battery comprising:

12. Between the activated battery preparation stage and the charging and discharging stages, The battery activation method according to claim 11, further comprising a pre-inspection step of pre-inspecting the target battery by performing the high-speed battery defect inspection method according to claim 1 on the target battery as an analysis target battery.

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