Method for detecting and analyzing foreign substance in battery cell

Abstract

The present invention provides a method for detecting and analyzing a foreign substance in a battery cell, comprising the steps of: preparing a battery cell to be inspected; disassembling the battery cell to be inspected, so as to obtain a separator from an electrode assembly; and putting the separator into X-ray fluorescence analysis equipment to analyze the presence or absence of a metal foreign substance on the surface of the separator, wherein the metal foreign substance is present in the electrode assembly before disassembly by penetrating a surface of the separator facing a positive electrode and a surface of the separator facing a negative electrode.

Description

Method for detecting and analyzing foreign substances in battery cells

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0124328 dated September 11, 2024, the entire contents of which are incorporated herein.

[0003] Technology field

[0004] The present invention relates to a method for detecting and analyzing foreign substances within a battery cell, and more specifically, to a method for detecting and analyzing foreign substances within a battery cell using X-ray fluorescence analysis.

[0005] Recently, rechargeable secondary batteries are being widely used as an energy source for wireless mobile devices. Furthermore, secondary batteries are attracting attention as an energy source for electric vehicles and hybrid electric vehicles, which are being proposed as solutions to address air pollution caused by conventional gasoline and diesel vehicles that use fossil fuels. Consequently, the types of applications utilizing secondary batteries are becoming highly diversified due to their advantages, and it is expected that secondary batteries will be applied to a wider range of fields and products in the future than they are today.

[0006] Secondary batteries are classified according to the structure of the electrode assembly, which consists of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes. Representative examples include a jelly-roll (wound-type) electrode assembly in which long sheet-type positive and negative electrodes are wound with a separator interposed; a stack-type (laminated-type) electrode assembly in which multiple positive and negative electrodes cut into units of a predetermined size are sequentially stacked with a separator interposed; and a stack-folding type electrode assembly in which unit cells such as bi-cells or full cells, formed by stacking units of positive and negative electrodes with a separator interposed, are wound. Additionally, a secondary battery can be manufactured by injecting an electrolyte while the electrode assembly is housed in a battery container and sealing the battery container.

[0007] These secondary batteries may experience various types of defects due to various causes during the manufacturing process or use. In particular, some finished secondary batteries exhibit a voltage drop behavior exceeding their self-discharge rate, a phenomenon referred to as low voltage.

[0008] The low-voltage failure phenomenon in these secondary batteries is largely caused by the ingress of metal foreign matter during the manufacturing process and poor electrolyte impregnation. Among these, when low-voltage failures occur due to the ingress of metal foreign matter, the metal can cause an internal short circuit in the secondary battery, which can lead to battery failure or damage, and in severe cases, cause ignition.

[0009] Conventionally, to identify the type and location of foreign matter in battery cells with such low-voltage defects, workers had to disassemble the cells and perform analysis by visually inspecting the electrode and separator surfaces; however, this method had problems such as large variability among workers and low repeatability and reproducibility.

[0010] Attempts were made to analyze electrode and separator surfaces using a Scanning Electron Microscope (SEM) to compensate for the limitations of visual inspection, but these attempts suffered from low accuracy and the need for a large workforce.

[0011] The present invention aims to provide a method for detecting and analyzing foreign substances within a battery cell that can accurately and quickly determine whether the cause of a low voltage failure is due to the ingress of metal foreign substances.

[0012] The present invention provides a method for detecting and analyzing foreign substances within a battery cell, comprising the steps of: preparing a battery cell to be inspected; disassembling the battery cell to be inspected to obtain a separator from an electrode assembly; and introducing the separator into an X-ray fluorescence analysis device to analyze the presence of a metal foreign substance on the surface of the separator, wherein the metal foreign substance is characterized in that, prior to disassembly, the separator exists by penetrating the surface facing the positive electrode and the surface facing the negative electrode in the electrode assembly.

[0013] The present invention enables the detection and analysis of foreign substances in a separator obtained by disassembling a battery cell using X-ray fluorescence analysis, thereby allowing for the detection and analysis of even small foreign substances, reducing differences in analysis between operators, and increasing repeatability and reproducibility, which can improve the accuracy and reliability of foreign substance detection and analysis within the battery cell.

[0014] If the cause of a low voltage defect is accurately and quickly identified as being due to a metallic foreign object through the method for detecting and analyzing foreign objects within a battery cell of the present invention, it is advantageous to be able to select and take action only on the problematic parts without inspecting all equipment in each manufacturing process.

[0015] FIG. 1 is a schematic diagram of an X-ray transmission image according to one embodiment of the invention.

[0016] The present invention will be described in detail below. Prior to this, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they must be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0017] In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0018]

[0019] The method for detecting and analyzing foreign substances within a battery cell according to the present invention includes the step of preparing a battery cell to be inspected. As long as the battery cell is a conventional lithium secondary battery, there are no special restrictions on its shape and structure. Specifically, cylindrical, prismatic, or pouch-type battery cells may all be used. The battery cell has a structure in which an electrolyte and an electrode assembly are housed within a battery case. Specific details regarding other components constituting the battery cell are known to those skilled in the art, so a detailed description is omitted.

[0020]

[0021] The battery cell subject to inspection described above may be a battery cell that has a low-voltage defect. Determining a low-voltage defect in a battery cell can be performed by various methods, for example, by measuring the open circuit voltage (OCV) of the battery cell. Specifically, if the change in open circuit voltage observed while aging the battery cell after charging and discharging it a certain number of times exceeds a predetermined value, it can be determined to be a low-voltage defect. Alternatively, this can be performed by applying a predetermined voltage or current while pressurizing the battery cell and measuring the leakage current value measured from the battery cell. Other specific methods for determining whether a battery cell has a low-voltage defect are known to a person skilled in the art, so a detailed explanation is omitted.

[0022]

[0023] The method for detecting and analyzing foreign substances within a battery cell according to the present invention includes the step of disassembling the battery cell to be inspected. In the present invention, the disassembly of the battery cell may be performed by opening the battery case using a tool or the like and extracting the electrode assembly inside the battery case to the outside of the battery case. Furthermore, the electrode assembly may be disassembled into individual units, such as electrodes and separators. A jelly-roll type electrode assembly must be disassembled into individual units by unwinding the wound electrode assembly.

[0024] The method for detecting and analyzing foreign substances within a battery cell according to the present invention includes the step of disassembling the electrode assembly to obtain individual separators. At this time, for the safety of the worker, the disassembly of the battery cell may be performed in a sealed space while separated from the worker. The present invention has the advantage of being able to more accurately analyze the cause of low voltage by analyzing the separator among the components within the battery cell. This is because, in the case of low voltage caused by metallic foreign substances, a short circuit occurs when the metallic component penetrates the separator located between the positive and negative electrodes and connects.

[0025] When individual separators are separated from the battery cell, a drying process may be additionally performed to remove the electrolyte remaining on the surface of the separator.

[0026]

[0027] The method for detecting and analyzing foreign substances within a battery cell according to the present invention includes the step of introducing a separated individual separator into an X-ray fluorescence analysis device and irradiating it with X-rays to analyze the presence of metallic foreign substances on the surface of the separator. At this time, the metallic foreign substances are present by penetrating the surface of the separator facing the positive electrode and the surface facing the negative electrode in the electrode assembly prior to disassembly. If such metallic foreign substances are present, it can be determined that the cause of the low voltage failure is due to the metallic foreign substances. If such metallic foreign substances are not present, other causes of the low voltage failure, such as electrolyte impregnation defects, can be analyzed.

[0028] In X-ray fluorescence analysis equipment, X-rays can be irradiated under the following conditions.

[0029] X-ray generator

[0030] - Voltage: 50kV

[0031] - Current: 1000μA

[0032] <Coefficient>

[0033] - Max 150,000 cps

[0034]

[0035] Specifically, the separated individual separator is placed into an X-ray fluorescence analysis device, and an X-ray transmission image is acquired for the entire separator. At this time, both sides of the separated individual separator are scanned to identify points A and A' with identical X and Y coordinates on the upper and lower surfaces of the separator, as shown in FIG. 1. The upper and lower surfaces of the separator correspond, respectively, to the surface facing the anode and the surface facing the cathode in the electrode assembly prior to disassembly. Points A, A', B, C, D, and E shown in FIG. 1 are all points formed by metallic foreign matter, and their shapes may appear as dots, spots, stains, etc. Unlike points A and A', points B, C, D, and E were not formed by metallic foreign matter penetrating the separator; therefore, no points with identical X and Y coordinates exist on the opposite side of the separator.

[0036] Metal foreign matter, such as points A and A' in Fig. 1, where points with identical X and Y coordinates are formed on the upper and lower surfaces of the separator, exists by penetrating the surface of the separator facing the positive electrode and the surface facing the negative electrode in the electrode assembly before disassembly. Various metal foreign matter may exist on the surface of the separator due to the battery cell manufacturing process and components included in the battery cell itself. Among these, metal foreign matter existing by penetrating the separator becomes the direct cause of a short circuit between the positive and negative electrodes as it passes through the separator, thereby allowing for the accurate identification of the cause of the low voltage failure.

[0037] The point formed on the surface of the separator by penetrating the above metal foreign matter may have a diameter of 100㎛ or less, 90㎛ or less, 80㎛ or less, 70㎛ or less, 60㎛ or less, or 20㎛ or more and 50㎛ or less. Since the method for detecting and analyzing foreign matter in a battery cell according to the present invention can observe even very small metal foreign matter that is difficult to observe with the naked eye, the cause of low voltage failure can be accurately identified.

[0038]

[0039] The method for detecting and analyzing foreign substances within a battery cell according to the present invention may include a step of analyzing the components of the metal foreign substances.

[0040] The step of analyzing the composition of the metal foreign matter described above is performed by measuring the X-ray fluorescence spectrum obtained by irradiating X onto the metal foreign matter present through the surfaces of the separator facing the anode and the cathode in the electrode assembly prior to disassembly. At this time, the method may be characterized by detecting the type of foreign matter from the position of the peak appearing in the X-ray fluorescence analysis spectrum. Analyzing the composition of the introduced metal foreign matter in this manner has the advantage of enabling rapid and accurate action to identify which part of the manufacturing process equipment is problematic.

[0041] The step of analyzing the components of the metal foreign matter described above can be performed by moving the stage within the X-ray fluorescence analysis equipment that analyzes the presence of metal foreign matter on the surface of the separator, rather than by moving the separator to another analysis device. For this reason, the method for detecting and analyzing foreign matter within a battery cell according to the present invention has the advantage of saving analysis time and manpower.

[0042] The detection of the type of foreign substance described above can be performed by comparing the spectrum of the separator with the spectrum of a reference separator. Here, the reference separator refers to a normal electrode or normal separator in which no foreign substance is detected. By comparing the measured spectrum with the reference spectrum, if an unknown peak is found, it can be determined that a foreign substance has been detected, and the type of foreign substance can be detected from the wavelength indicated by the unknown peak.

[0043] The components of the metallic foreign matter analyzed through the above X-ray fluorescence analysis equipment may be one or more selected from the group consisting of Fe, Cr, Cu, Zn, Ni, Mn, Fe, Co, and alloys thereof.

[0044] If the component of the analyzed metallic foreign matter is Fe or an alloy of Fe and Cr, it can be determined that there is a defect in the equipment or bearing steel coated with Fe or Cr among the cell manufacturing equipment.

[0045] If the component of the analyzed metallic foreign matter is Cu or an alloy of Cu and Zn, it can be determined that there is a defect in the equipment made of brass. For example, it can be determined that there is a defect in the cylinder, air chuck, floating joint, spring, rotary joint of the cell assembly equipment, or the cylinder, rod end bearing, air chuck, floating joint, spring, etc. of the electrode assembly winder equipment.

[0046]

[0047] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0048]

[0049] Examples

[0050] Three cells determined to have low voltage defects were disassembled to obtain separators from the electrode assemblies. The number of visible metallic foreign object spots on the obtained separators was counted and recorded in Table 1 below.

[0051] In addition, regarding the obtained separator, the surface facing the anode and the surface facing the cathode in the electrode assembly before disassembly were each scanned with X-rays, and the number of dots of metallic foreign matter penetrating the surface was counted and listed in Table 1 below.

[0052] X-rays were irradiated again on the points of the specified metallic foreign matter to measure the X-ray fluorescence spectra emitted from them. At this time, the number of points where the composition of the metallic foreign matter was Fe or an alloy of Fe and Cr, and the number of points where the composition was Cu or an alloy of Cu and Zn were counted and listed in Table 1 below.

[0053] Number of points observed visually Number of points analyzed by X-ray Number of points where the metallic foreign matter is composed of Fe or an alloy of Fe and Cr Number of points where the metallic foreign matter is composed of Fe or an alloy of Cu or Zn Separator 10 1 10 Separator 27 1 4 1 13 Separator 30 4 40

[0054] As can be seen in Table 1 above, the number of points analyzed by X-ray was greater than the number of points of metal foreign matter observed with the naked eye. When analyzing metal foreign matter using the foreign matter detection and analysis method within a battery cell of the present invention, accurate and rapid inspection was possible compared to visual inspection.

Claims

1. Step of preparing the battery cell to be inspected; The step of disassembling the battery cell subject to inspection to obtain a separator from the electrode assembly; and A method for detecting and analyzing foreign substances in a battery cell, comprising the step of inserting the separator into an X-ray fluorescence analysis device and irradiating X-rays to analyze the presence of metallic foreign substances present on the surface of the separator. A method for detecting and analyzing foreign substances in a battery cell, characterized in that the above-mentioned metallic foreign substance exists by penetrating the surface facing the positive electrode and the surface facing the negative electrode in the electrode assembly prior to disassembly.

2. In Claim 1, A method for detecting and analyzing foreign substances within a battery cell, wherein the battery cell subject to inspection is a battery cell that has a low voltage defect.

3. In Claim 1, A method for detecting and analyzing foreign substances in a battery cell, wherein the diameter of a dot formed on the surface of a separator by penetrating the above-mentioned metal foreign substance is 100㎛ or less.

4. In Claim 1, A method for detecting and analyzing foreign substances in a battery cell, further comprising the step of analyzing the components of the metal foreign substances.

5. In Claim 4, A method for detecting and analyzing foreign substances in a battery cell, wherein the step of analyzing the composition of the above-mentioned metal foreign substances includes the step of measuring an X-ray fluorescence spectrum for metal foreign substances present through the surface of the separator facing the anode and the surface facing the cathode in the electrode assembly before decomposition.

6. In Claim 5, The step of analyzing the composition of the above-mentioned metal foreign matter is, A method for detecting and analyzing foreign substances in a battery cell, characterized by detecting the type of foreign substance from the position of a peak appearing in an X-ray fluorescence analysis spectrum.

7. In Claim 6, A method for detecting and analyzing foreign substances in a battery cell, wherein the detection of the type of foreign substance is performed by comparing the spectrum of the separator with the spectrum of a reference separator.

8. In Claim 5, A method for detecting and analyzing foreign substances in a battery cell, wherein the components of the analyzed metallic foreign substances are one or more selected from the group consisting of Fe, Cr, Cu, Zn, Ni, Mn, Fe, Co, and alloys thereof.

9. In Claim 8, A method for detecting and analyzing foreign substances in a battery cell, further comprising the step of determining that there is a defect in the equipment or bearing steel coated with Fe or Cr among the cell manufacturing equipment when the component of the analyzed metal foreign substance is Fe or an alloy of Fe and Cr.

10. In Claim 8, A method for detecting and analyzing foreign substances in a battery cell, further comprising the step of determining that there is a defect in one or more of the cylinder, air chuck, floating joint, spring, rotary joint of a cell assembly facility; or the cylinder, rod end bearing, air chuck, floating joint, spring of an electrode assembly winder facility, when the component of the analyzed metal foreign substance is Cu or an alloy of Cu and Zn.

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