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 this 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 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. [Background technology]

[0003] In the case of medium-sized and large batteries in which multiple mono cells are stacked, some of the mono cells inside may exhibit low voltage defects (a phenomenon in which the potential of a specific mono cell decreases) for unknown reasons, resulting in a defect in which the capacity of the entire cell deteriorates.

[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 product.

[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 were limitations to the HPCD test method's detection capabilities.

[0006] Therefore, a test method that can detect low-voltage defective cells using existing test methods and that can inspect all cells in a short time is required. 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 multiple 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 high-speed battery defect inspection method 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 impedance of the analysis target battery; 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. [Effects of the Invention]

[0010] The high-speed defective battery testing method of the present invention can detect low-voltage defective batteries in a short time, and can test several thousand to several tens of thousands of batteries per second.

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

[0012] The high-speed battery defect inspection method of the present invention dramatically reduces the inspection time compared to conventional methods, and can also determine whether a battery is defective even if it has not been inspected. [Brief explanation 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; [Figure 2] 1 is a graph showing a general Nyquist diagram. [Figure 3] 10 is a graph comparing impedance values ​​of a normal battery and a defective battery. [Figure 4] FIG. 10 is a block diagram showing another embodiment of the method for high-speed battery defect inspection of the present invention. [Figure 5] FIG. 1 is a block diagram showing a set frequency stage. DETAILED DESCRIPTION OF THE INVENTION

[0014] The high-speed battery defect inspection method 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 impedance of the analysis target battery; 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 It is also available in kHz to 7MHz.

[0016] In the high-speed battery defect inspection method 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, before 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 multiple reference impedances for multiple frequencies; and a set frequency calculating step (step s20) of calculating the set frequency based on the multiple reference impedances.

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

[0019] In the high-speed battery defect inspection method of the present invention, the set frequency calculation step (step s20) calculates the plurality of reference impedances as real part values ​​Z SR and the imaginary part value is Z SI A variable separation step (step s21) for separating Z SR and Z SI and a set frequency obtaining step (step s23) of obtaining 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]

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[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 frequencies that satisfy the following Equation 2 for an interval in which .function..times ...

[0023]

number

[0024] In the setting frequency step of the high speed battery defect testing method of the present invention, 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 equation 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 charge / discharge step, a pre-inspection step of pre-inspecting the activation target battery by performing the above-described high-speed battery defect inspection method using the activation 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 description, the size and shape of components shown in the drawings may be exaggerated for clarity and convenience. Furthermore, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intentions or practices of users and operators. Definitions of such terms should be based on the overall content of this specification.

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

[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 high-speed battery defect detection method 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 impedance of the analysis target battery; 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.

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

[0033] The monocell is a unit cell in which one or more positive electrodes and one or more negative electrodes are stacked with a separator sandwiched between them to form an electrode assembly, and the electrodes located on both outermost surfaces are different in type. For example, the monocell is a unit cell having an electrode assembly structure in which the positive electrode, separator, and negative electrode are stacked in this order. As another example, the monocell is a unit cell having an electrode assembly structure in which the positive electrode, separator, negative electrode, separator, positive electrode, separator, and 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 kHz to 7MHz. A low-voltage defective battery has a different impedance value from 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 such as that shown in Figure 2 can be obtained. Specifically, the imaginary part of the impedance value corresponding to each frequency is multiplied by (-) and the real part is plotted on a coordinate system to obtain a Nyquist diagram such as that shown in Figure 2. The high-speed battery defect detection method of the present invention can quickly determine whether a battery has a low-voltage defect based on the real part values ​​on two quadrants of the graph shown in Figure 2.

[0039] Figure 3 is a graph showing the impedance spectroscopy measurement results for 15 batteries. In Figure 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. The E-grade defective batteries are defective batteries that exhibit absolute OCV reduction. The L-grade defective batteries are defective batteries that exhibit relative OCV reduction. In Figure 3, the graphs for EIS measurements of low-voltage defective batteries (E-grade defective batteries and L-grade defective batteries) regardless of the defective grade are seen to overlap with each other, but the graphs for normal batteries show different behavior from the graphs for defective batteries. Specifically, the impedance value measured at about 10 kHz appears in the A region for a normal battery, and in the B region for a defective E-class battery and a defective L-class battery. In the E-class and L-class defective batteries, it is seen that the real part has a maximum value in the B region. 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 range of 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 high-speed battery defect testing method of the present invention further includes, before 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 multiple reference impedances for multiple frequencies; and a set frequency calculating step (step s20) of calculating the set frequency based on the multiple reference impedances.

[0041] The high-speed battery defect testing method of the present invention can obtain an optimal set frequency that can accurately detect low-voltage defective batteries 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 if its dOCV (delta open circuit voltage) is 300 mV or more or 3 sigma or more. The reference battery that is determined to be a low-voltage defective battery is obtained as a battery that has been inspected as a defective battery during mass production or a battery that has been subjected to defective conditions such as electrode bending or a defective active material coating area.

[0043] The reference impedance measurement step (step s10) is performed by impedance spectroscopy (EIS), so that reference impedance values ​​corresponding to 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 is Z SI A variable separation step (step s21) for separating Z SR and Z SI 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 relation f is the real part value 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 setting frequency acquisition step (step s23), the setting frequency is SI is selected from among frequencies that satisfy the following Equation 2 for an interval in which .function..times ...

[0049]

number

[0050] In the setting frequency step, the ε is also 0. That is, the relation f is 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 value is 30% or more of the value, the battery to be analyzed is determined to be a defective battery. As described above for low-voltage defective batteries, the relational expression f has a maximum value at 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 equation 2 is SI If the value is 30% or more or 50% or more, the battery being analyzed is determined to be a low-voltage defective battery.

[0052] A battery activation method applying the high-speed battery defect inspection 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 high-speed battery defect inspection method of the present invention using the battery to be activated as the analysis target battery and finally screening out defective batteries.

[0053] The battery to be activated 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 significantly reduce the time required for battery defect inspection before shipping.

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

[0056] The battery activation method of the present invention can prevent defective batteries from being subjected to the charge-discharge and aging processes by first screening out defective batteries before the charge-discharge and aging processes, and can also prevent defective batteries from being subjected to the charge-discharge and aging processes by second screening out defective batteries after the aging process, thereby removing defective batteries generated during the SEI layer formation process, etc.

[0057] Experimental example Fifteen 100Ah 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 at a frequency of 10kHz, which corresponds to the set frequency, while the real resistance values ​​of the five E-class defective batteries were measured at 1160μΩ, 1140μΩ, 1110μΩ, 1130μΩ, and 1110μΩ 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 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] While the embodiments of the present invention have been described above, they are merely illustrative, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of the present invention should be determined by the following claims. [Industrial Applicability]

[0062] The high-speed defective battery testing method of the present invention can detect low-voltage defective batteries in a short time, and can test several thousand to several tens of thousands of batteries per second.

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

[0064] The high-speed battery defect inspection method of the present invention dramatically reduces the inspection time compared to conventional methods, and can also determine whether a battery is defective even if it has not been inspected.

Claims

1. A reference impedance measurement step (step s10) of applying an AC current to a reference battery while changing the frequency to obtain multiple reference impedances for multiple frequencies; a set frequency calculation step (step s20) of calculating a set frequency based on the plurality of reference impedances; an analysis target impedance measuring step (step s30) of applying an AC current of the set frequency to the 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 a defect determination step (step s50) of determining whether the battery to be analyzed is defective based on the real part resistance, the set frequency is a frequency when an imaginary part resistance, which is an imaginary part value of the impedance to be analyzed, is greater than 0; The set frequency calculation step (step s20) a variable separation step (step s21) of separating the plurality of reference impedances into real part values ​​ZSR and imaginary part values ​​ZSI; a function fitting step (step s22) for obtaining a relational expression f between the ZSR and the ZSI; a set frequency acquisition step (step s23) of acquiring the set frequency based on the relational expression f; In the function fitting step (step s22), The relational expression f is fitted by the following Equation 1: [Equation 1] In the setting frequency acquisition step (step s23), The set frequency is selected from frequencies that satisfy the following Equation 2 for a section in which Z SI has a value greater than 0: [Equation 2] The method for high-speed battery defect inspection, wherein ε is 0 to 0.

2.

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

3. The method for rapid battery defect testing according to claim 1 , wherein the battery to be analyzed includes a plurality of mono-cells.

4. 2. The high-speed battery defect inspection method according to claim 1, wherein the reference battery is a low-voltage defective battery having a dOCV of 300 mV or more or 3 sigma or more in the reference impedance measurement step (step s10).

5. In the setting frequency acquisition step (step s23), 2. The method for high-speed battery defect inspection according to claim 1, wherein the ε is 0.

6. In the defect determination step (step s50), The real part resistance satisfies the formula 2. ＳＩ 6. The method for high-speed battery defect inspection according to claim 5, wherein the battery to be analyzed is determined to be a defective battery when the value is 30% or more of the value.

7. an activation battery 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 inspecting defective batteries using the target battery for activation as the target battery for analysis, and finally sorting out defective batteries; A battery activation method comprising:

8. Between the activated battery preparation step and the charge / discharge step, 8. The battery activation method according to claim 7, 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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