Battery Inspection Equipment

Abstract

The quality of the battery is determined by measuring impedance in the high frequency band. The impedance of a secondary battery is measured at two or more different measurement frequencies within a frequency range of 100 kHz to 100 MHz, and the state of the secondary battery is determined based on the difference or ratio between the impedance measurements at the different measurement frequencies.

Description

[Technical Field]

[0001] The present invention relates to a battery inspection device that can be used to determine whether a battery is good or bad. [Background technology]

[0002] A secondary battery state determination method for determining a micro-short circuit tendency state, which is a state in which a micro-short circuit is likely to occur in a secondary battery, has been disclosed (Patent Document 1). The method includes an electron transfer resistance measurement step in which a voltage or current is applied to an electrode system of the secondary battery at a stepwise changing frequency with a small amplitude, and measurements are made using an AC impedance method to output a Nyquist plot to measure the electron transfer resistance Rs of the secondary battery. The method also includes an electrode distance determination step in which the electron transfer resistance Rs obtained in the electron transfer resistance measurement step is compared with a predetermined lower threshold Rsmin, and a secondary battery state determination step in which, if the electron transfer resistance Rs in the electrode distance determination step is equal to or greater than the lower threshold Rsmin, the electrode distance is determined to be good and the secondary battery is determined to be a good product. The method also includes an electrolyte determination step in which the electron transfer resistance Rs obtained in the electron transfer resistance measurement step is compared with a predetermined upper threshold Rsmax, and the secondary battery is determined to be a good product if the electron transfer resistance Rs obtained in the measurement step is less than the predetermined upper threshold Rsmax. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-174729 Summary of the Invention [Problem to be solved by the invention]

[0004] During the manufacturing process of lithium-ion batteries, uneven pressure on the electrode surface or the inclusion of foreign matter can cause unexpected chemical reactions, resulting in defective batteries with metal deposits on the electrode surface. Metal deposits on the electrode surface are known to originate from metallic lithium, which originates from the battery's carrier, the lithium ion, and from metallic foreign matter that has entered the battery. These deposits can cause micro-short circuits within the battery, adversely affecting battery performance. In particular, metallic lithium is known to lower the thermal runaway temperature of the battery, adversely affecting battery safety.

[0005] In the above-mentioned conventional technology, pass / fail judgment is performed by comparing the electron transfer resistance Rs obtained from the Nyquist plot with a preset threshold value. To obtain the electron transfer resistance from the Nyquist plot, measurements must be taken at multiple frequency points in a relatively low frequency range (approximately 0.1 Hz to 1 kHz) so that an arc can be drawn. To achieve high-precision measurements, repeated measurements at each frequency point are required to cancel out the white noise, but this takes a long time. Furthermore, the self-discharge test performed prior to measuring the electron transfer resistance requires an even longer testing period, which increases the cost of battery manufacturing.

[0006] Therefore, there is a demand for a battery inspection device that can more easily determine whether a battery is good or bad. [Means for solving the problem]

[0007] One aspect of the present invention is a battery inspection device for a secondary battery, characterized in that the impedance of the secondary battery is measured at two or more different measurement frequencies within a frequency range of 100 kHz or more and 100 MHz or less, and the state of the secondary battery is determined based on the difference or ratio of the measured impedance values ​​at the different measurement frequencies.

[0008] Here, it is preferable to determine the state of the secondary battery based on the difference or ratio between the measured values ​​of the real part components of the impedance at the different measurement frequencies.

[0009] Preferably, the secondary battery is a lithium ion secondary battery, and the secondary battery having metal deposits or metal foreign matter therein is detected.

[0010] It is also preferable to include an impedance measuring device that measures the impedance, and a connection wire that electrically connects the impedance measuring device and the secondary battery. [Effects of the Invention]

[0011] According to the present invention, the quality of a battery can be more easily determined by measuring impedance in a high frequency band during the battery manufacturing process. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of a battery inspection device according to an embodiment of the present invention; [Figure 2] 10 is a flowchart showing a peak hold process according to an embodiment of the present invention. [Figure 3] FIG. 4 is a graph showing the frequency dependence of the high-frequency resistance value of the battery according to the embodiment of the present invention. [Figure 4] FIG. 3 is an enlarged view showing the frequency dependence of the high-frequency resistance value of the battery according to the embodiment of the present invention. [Figure 5] FIG. 4 is a diagram showing relative resistance values ​​of a battery according to an embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing the slope of the resistance value of a battery with respect to frequency in an embodiment of the present invention. [Figure 7] FIG. 10 is a graph showing the frequency dependency of the slope of the relative resistance value / frequency of a battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Battery inspection equipment configuration] As shown in Fig. 1, a battery inspection device 100 according to an embodiment of the present invention includes an impedance measuring instrument 10, a coaxial cable 12, and a measurement terminal 14. The battery inspection device 100 is designed to measure the impedance of a battery 200, which is the object to be measured. By measuring the impedance using the battery inspection device 100, the internal resistance and reaction characteristics of the battery 200 can be known, which makes it possible to evaluate the quality and lifespan of the battery 200.

[0014] The impedance measuring instrument 10 is a device for measuring the impedance of the battery 200. The impedance measuring instrument 10 applies an AC signal to the battery 200 and calculates the impedance by analyzing the response. The frequency of the applied AC signal is set to two or more points between 100 kHz and 100 MHz. The impedance measuring instrument 10 can be, for example, an impedance meter or a network analyzer.

[0015] The coaxial cable 12 is used to connect the impedance measuring instrument 10 and the measurement terminal 14. The coaxial cable 12 is less susceptible to external noise and is capable of transmitting signals with high accuracy.

[0016] The measurement terminal 14 connects the impedance measuring instrument 10 and the battery 200 via the coaxial cable 12. A signal is applied to the battery 200, which is the object to be measured, via the measurement terminal 14, and the response is returned to the impedance measuring instrument 10. Methods for contacting the measurement terminal 14 with the terminal of the battery 200 include, for example, bolting, pressing a high-frequency probe against the terminal, or contacting the electrode surfaces. The measurement terminal 14, together with the coaxial cable 12, constitutes a connecting wiring.

[0017] The impedance measuring instrument 10 is connected to a measurement terminal 14 via a coaxial cable 12. The measurement terminal 14 is further connected to a battery 200 to be measured. Through this connection, the impedance measuring instrument 10 sends a signal to the battery 200, receives the response, and measures the impedance.

[0018] 2 shows an example of a configuration in which an impedance measuring instrument 10 is mounted on a printed circuit board or the like. In this example, a coaxial cable 12 is not used, and measurement terminals 14 on the impedance measuring instrument 10 are brought into contact with terminals of a battery 200, which is the object to be measured. The measurement terminals 14 form connecting wiring.

[0019] [Example] A total of six battery cells were prepared: five with low self-discharge (referred to as OK cells) and one with high self-discharge (referred to as NG cell), and the high-frequency resistance between the positive and negative terminals of the battery cells was measured using a vector network analyzer. The high-frequency resistance was measured in the frequency range of 100 kHz to 100 MHz.

[0020] Figure 3 shows the frequency dependence of the measured resistance value R in the high frequency band. Figure 4 shows an enlarged view of the frequency dependence of resistance value R in the frequency band above 5 MHz. As shown in Figures 3 and 4, the resistance value R of the NG cell is smaller than the resistance of the OK cell in the frequency band above approximately 10 MHz. The prominent resistance value R around 60 MHz is a measurement error caused by resonance with the cable, etc.

[0021] Figure 5 shows the results of calculating the average value μ and standard deviation σ of the resistance values ​​R of six battery cells at each frequency, and then calculating the evaluation value [(R-μ) / σ] by dividing the difference (R-μ) between the resistance value R of each cell and the average value μ by the standard deviation σ.

[0022] As shown in Figure 5, the evaluation values ​​of the OK cells did not show any significant trend in the frequency band from 100 kHz to 100 MHz. In contrast, the evaluation values ​​of the NG cells showed a continuous decreasing trend in the frequency band from 100 kHz to 10 MHz. Furthermore, the evaluation values ​​of the NG cells were lower than the evaluation values ​​of the other four OK cells except for one OK cell in the frequency band above 1 MHz. Furthermore, the evaluation values ​​of the NG cells were lower than the evaluation values ​​of all OK cells in the frequency band above 5 MHz.

[0023] As shown in Figure 3, the resistance value R of a battery cell tends to increase as the frequency band increases. Also, as shown in Figure 5, the evaluation value of a battery cell, which represents the relative resistance value, tends to decrease as the frequency band increases. Therefore, as shown in Figure 6, the slope of the resistance value R with respect to frequency f (dR / df) decreases relatively as the frequency increases.

[0024] Figure 7 shows the results of calculating the average μa and standard deviation σa for the slope (dR / df) of six battery cells at each frequency, and then dividing the difference {(dR / df)-μa} between the slope (dR / df) and the average μa for each battery cell by the standard deviation σa to obtain an evaluation value [{(dR / df)-μa} / σa]. In the frequency band from 3 MHz to 40 MHz, the evaluation value of a non-compliant cell is approximately twice the standard deviation σa of the evaluation value of a non-compliant cell.

[0025] As described above, the resistance values ​​R of a plurality of battery cells are measured in a frequency band ranging from 100 kHz to 100 MHz, and if the resistance value R of the battery cell being evaluated is significantly different from the resistance values ​​R of the other cells, the battery cell being evaluated can be determined to be an NG cell.

[0026] For example, the resistance value R of a battery cell is measured in a frequency band ranging from 100 kHz to 100 MHz, preferably from 1 MHz to 100 MHz, and more preferably from 3 MHz to 40 MHz, and if the deviation from the average value μ is equal to or greater than a predetermined threshold, the battery cell can be determined to be an NG cell. For example, if the deviation of the resistance value R of the battery cell to be evaluated from the average value R of the resistance values ​​R of the other cells is equal to or greater than a standard deviation σ, the battery cell to be evaluated can be determined to be an NG cell. In particular, it is preferable to determine the battery cell as an NG cell when the deviation from the average value R is -σ or greater.

[0027] Instead of the average value μ, the evaluation may be performed using the median value of a plurality of battery cells.

[0028] Furthermore, it is sufficient if the battery cell to be evaluated can be evaluated as either a good cell or a bad cell based on the difference or ratio between the impedance of the battery cell to be evaluated and the impedance of other battery cells. For example, as shown in Fig. 5, the evaluation value of a bad cell shows a tendency to continuously decrease in the frequency band from 100 kHz to 10 MHz, so the slope of the evaluation value of the battery cell to be evaluated with respect to frequency may be calculated, and the cell to be evaluated may be determined to be a bad cell if the slope of the decrease with respect to frequency is greater than or equal to a predetermined threshold value compared to the slope of the evaluation values ​​of other battery cells.

[0029] [Configuration of the present invention] [Configuration 1] A battery inspection device for a secondary battery, characterized in that it measures the impedance of a secondary battery at two or more different measurement frequencies within a frequency range of 100 kHz or more and 100 MHz or less, and determines the state of the secondary battery based on the difference or ratio of the measured impedance values ​​at the different measurement frequencies. [Configuration 2] The battery inspection device according to configuration 1, A battery inspection device characterized in that the state of the secondary battery is determined based on a difference or ratio between measured values ​​of the real part components of the impedance at the different measurement frequencies. [Configuration 3] The battery inspection device according to configuration 1, the secondary battery is a lithium ion secondary battery, A battery inspection device characterized by detecting the secondary battery having metal deposits or metallic foreign matter therein. [Configuration 4] The battery inspection device according to any one of configurations 1 to 3, an impedance meter for measuring the impedance; a connection wire that electrically connects the impedance measuring instrument and the secondary battery; A battery inspection device comprising: [Explanation of symbols]

[0030] 10 Impedance measuring instrument, 12 Coaxial cable, 14 Measuring terminal, 100 Battery testing equipment, 200 Batteries.

Claims

1. A battery inspection device for a secondary battery, characterized in that the impedance of the secondary battery is measured at two or more different measurement frequencies within a frequency range of 100 kHz or more and 100 MHz or less, and the state of the secondary battery is determined based on the difference or ratio of the measured impedance values ​​at the different measurement frequencies.

2. The battery inspection device according to claim 1, A battery inspection device characterized in that the state of the secondary battery is determined based on a difference or ratio between measured values ​​of the real part components of the impedance at the different measurement frequencies.

3. The battery inspection device according to claim 1, the secondary battery is a lithium ion secondary battery, A battery inspection device characterized by detecting the secondary battery having metal deposits or metallic foreign matter therein.

4. The battery inspection device according to any one of claims 1 to 3, an impedance meter for measuring the impedance; a connection wire that electrically connects the impedance measuring instrument and the secondary battery; A battery inspection device comprising:

Images