Inspection method for bipolar secondary battery

Abstract

To provide an inspection method for a bipolar secondary battery capable of accurately inspecting quality of deposition in a seal part.SOLUTION: An inspection method is provided for a bipolar secondary battery configured by laminating a power storage module comprising: a pair of electrodes including a cathode and an anode; a separator provided between the pair of electrodes; and a seal part which is provided so as to enclose the pair of electrodes and the separator, thereby forming a sealed space in which a liquid electrolyte is stored. In the inspection method for the bipolar secondary battery, a temperature of the seal part is measured on the basis of a wavelength region different from a wavelength region with heating while heating and depositing the seal part of power storage modules which are adjacent to each other in a lamination direction, and a defect of deposition in the seal part is detected on the basis of a temperature change.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for inspecting a bipolar secondary battery. [Background technology]

[0002] Bipolar secondary batteries are known as batteries mounted on hybrid electric vehicles or electric vehicles. In bipolar secondary batteries, seals are welded between power storage modules to retain an electrolyte. In the manufacturing process of bipolar secondary batteries, the quality of the welded seals is inspected.

[0003] For example, Patent Document 1 discloses an inspection method for inspecting the welded portion between the housing and the cover of an electricity storage device. In the inspection method disclosed in Patent Document 1, the temperature of the welded portion after welding is measured with an infrared thermometer to inspect the quality of the weld. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-021601 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inspection method disclosed in the above-mentioned Patent Document 1 can measure the temperature at the seal portion of a bipolar secondary battery after welding, but cannot measure the temperature during welding, and is therefore insufficient for inspecting the quality of welding.

[0006] The present disclosure has been made in consideration of the above circumstances, and provides a method for inspecting a bipolar secondary battery that can accurately inspect whether welding at a seal portion is good or not. [Means for solving the problem]

[0007] The method for inspecting a bipolar secondary battery according to the present disclosure includes: A method for inspecting a bipolar secondary battery in which storage modules are stacked, the storage modules including a pair of electrodes including a positive electrode and a negative electrode, a separator provided between the pair of electrodes, and a seal portion provided so as to surround the pair of electrodes and the separator to form an enclosed space for accommodating a liquid electrolyte, the method comprising the steps of: While heating and fusing the seal portions of the power storage modules adjacent to each other in a stacking direction, a temperature of the seal portions is measured based on a wavelength range different from a wavelength range associated with the heating; Based on the temperature change, a welding defect in the seal portion is detected.

[0008] In the bipolar secondary battery inspection method according to the present disclosure, the temperature is measured based on a wavelength range different from the wavelength range associated with heating. With this configuration, the temperature can be measured even while the seal is being welded, so that welding defects can be detected and the quality of the welding of the seal can be inspected with high accuracy. Effect of the Invention

[0009] The present disclosure provides a method for inspecting a bipolar secondary battery that can accurately inspect whether welding at a seal portion is good or bad. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view (xz plan view) of a bipolar secondary battery. [Diagram 2] 4 is a flowchart illustrating a method for inspecting a bipolar secondary battery according to the first embodiment. [Diagram 3] 5A and 5B are diagrams showing an example of the results of measuring the temperature of the sealed portion during and after welding by the method for inspecting a bipolar secondary battery according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and for clarity of explanation, duplicate explanations are omitted as necessary. In addition, some reference numerals are omitted so as not to make the drawings complicated. Naturally, the right-handed xyz Cartesian coordinate system shown in the drawings is for the convenience of explaining the positional relationship of the components. Usually, the positive direction of the z axis is vertically upward, and the xy plane is a horizontal plane.

[0012] (Embodiment 1) <Structure of bipolar secondary battery> First, an example of the configuration of a bipolar secondary battery will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view (xz plan view) of a bipolar secondary battery. Fig. 1 illustrates only the parts of the bipolar secondary battery related to charging and discharging, and omits members such as a restraining plate. The bipolar secondary battery 10 is, for example, a secondary battery such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The bipolar secondary battery 10 is used as a battery for various vehicles such as a forklift, a hybrid vehicle, and an electric vehicle.

[0013] As shown in Fig. 1, the bipolar secondary battery 10 is configured by stacking a plurality of power storage modules 12. In the example shown in Fig. 1, the bipolar secondary battery 10 is configured by stacking a plurality of power storage modules 12 in the z-axis direction. Hereinafter, the z-axis direction in the drawing will be referred to as the stacking direction.

[0014] The electricity storage module 12 includes a pair of electrodes including a positive electrode 17 and a negative electrode 18, a separator 14 provided between the pair of electrodes, and a seal portion 11. The seal portion 11 is provided so as to surround the pair of electrodes including the positive electrode 17 and the negative electrode 18, and the separator 14, thereby forming a sealed space SP that contains a liquid electrolyte.

[0015] In other words, the bipolar secondary battery 10 is configured such that the liquid electrolyte does not leak to the outside of the bipolar secondary battery 10 by welding the seal parts 11 of the power storage modules 12 adjacent in the stacking direction. In addition, the seal parts 11 seal the bipolar secondary battery 10 so that hydrogen, oxygen, and coolant supplied for power generation by the bipolar secondary battery 10 do not leak to the outside of the bipolar secondary battery 10.

[0016] Here, it can be said that the bipolar secondary battery 10 is configured by alternately stacking the bipolar electrodes 13 and the separators 14. In the example shown in Fig. 1, the power storage module 12 has a plurality of bipolar electrodes 13 and a plurality of separators 14 stacked alternately in the stacking direction.

[0017] The bipolar electrode 13 will be described. The bipolar electrode 13 has a positive electrode current collector 15a, a negative electrode current collector 15b, a positive electrode 17 provided on one surface of the positive electrode current collector 15a, and a negative electrode 18 provided on one surface of the negative electrode current collector 15b. The bipolar electrode 13 has a structure in which the positive electrode 17, the positive electrode current collector 15a, the negative electrode current collector 15b, and the negative electrode 18 are stacked in this order.

[0018] A positive electrode current collector 15a and a negative electrode current collector 15b are provided between the positive electrode 17 and the negative electrode 18 in the bipolar electrode 13. The positive electrode current collector 15a and the negative electrode current collector 15b are in contact with each other on one side. The positive electrode current collector 15a is in contact with the positive electrode 17 on the other side, and the negative electrode current collector 15b is in contact with the negative electrode 18 on the other side. The positive electrode current collector 15a and the negative electrode current collector 15b are made of, for example, a conductive metal foil. The positive electrode current collector 15a is, for example, a copper foil. The negative electrode current collector 15b is, for example, an aluminum foil. In the example shown in FIG. 1, the stacking end of the bipolar secondary battery 10 is the negative electrode current collector 15b on the z-axis positive side, and the positive electrode current collector 15a on the z-axis negative side.

[0019] The power storage module 12 is electrically connected to a conductive plate (not shown), and charging and discharging of the bipolar secondary battery 10 is performed via the positive electrode 17 and the negative electrode 18.

[0020] <Inspection method for bipolar secondary batteries> Next, a method for inspecting a bipolar secondary battery according to embodiment 1 will be described with reference to Fig. 2. Fig. 2 is a flow chart illustrating an example of the method for inspecting a bipolar secondary battery according to embodiment 1. In the following, the method will be described with reference to Fig. 1 as well.

[0021] First, while the seal parts are being heat-welded, the temperature of the seal parts is measured using a wavelength range different from the wavelength range associated with heating (step ST1). A more detailed explanation will be given with reference to Fig. 1. As shown in Fig. 1, while the seal parts 11 of the power storage modules 12 adjacent in the stacking direction are being heat-welded, the temperature of the seal parts 11 is measured based on a wavelength range different from the wavelength range associated with heating. The temperature is measured using, for example, a thermal camera.

[0022] The wavelength range different from the wavelength range associated with heating refers to a wavelength range different from the wavelength emitted by a heating device used to heat the seal portion 11. An example will be described in which the seal portion 11 is made of a polyolefin resin having an absorption wavelength peak at around 3.4 micrometers.

[0023] Here, it is assumed that the heating device is a carbon heater that has a peak at about 2 to 3 micrometers and emits wavelengths from about 0.5 micrometers to about 5.8 micrometers. Other examples of the heating device may include an infrared heater, a ceramic heater, a graphite heater, a halogen heater, etc., capable of welding the seal portion 11 without contact. The heating method may be a method in which the heating device is placed at an appropriate location and a pair of electrodes is heated while rotating, or a method in which the heating devices are placed at multiple locations and heated simultaneously. The peak wavelength of the heating device is preferably within 5 micrometers of the peak wavelength of the absorption wavelength of the material, and more preferably within 2.5 micrometers.

[0024] To increase the measurement accuracy, it is preferable to use a thermo camera capable of measuring wavelengths close to the absorption wavelength of the seal portion 11 when measuring the temperature during welding of the seal portion 11. However, if a thermo camera capable of measuring wavelengths around the absorption wavelength of 3.4 micrometers is used, the wavelength emitted by the carbon heater will also be measured. Therefore, by using a thermo camera capable of measuring wavelengths outside the wavelength range emitted by the carbon heater, for example, around 6 micrometers, the temperature during welding of the seal portion can be measured accurately. It is more preferable that the wavelength used for measurement is higher than the absorption wavelength of the seal portion.

[0025] In order to increase the measurement accuracy, it is preferable to use a thermo camera capable of measuring a wavelength close to the peak absorption wavelength of the seal portion when measuring the temperature after welding of the seal portion 11.

[0026] Next, the quality of welding is judged based on the temperature change of the seal portion (step ST2). A more detailed explanation will be given with reference to FIG. 3. FIG. 3 is a diagram showing an example of the results of measuring the temperature of the seal portion during and after welding by the inspection method for a bipolar secondary battery according to embodiment 1. The upper part of FIG. 3 shows an example in which no welding defect occurs in the seal portion. The middle part of FIG. 3 shows an example in which a welding defect occurs in the seal portion during welding. The lower part of FIG. 3 shows an example in which a welding defect occurs in the seal portion after welding.

[0027] In the upper, middle, and lower parts of FIG. 3, the horizontal axis indicates time, and the vertical axis indicates temperature. In the upper, middle, and lower parts of FIG. 3, the dashed line on the horizontal axis indicates the boundary between welding by the heating device and after welding. The heating device is activated during welding, and is not activated after welding. In the upper, middle, and lower parts of FIG. 3, the temperature distributions 20 and 30 of the sealing part measured by two thermo cameras 1 and 2 that can measure different wavelength ranges, the reference range 40 in which no defects occur in welding of the sealing part, and the actual temperature 50 of the sealing part are shown using different types of lines. The actual temperature 50 of the sealing part is measured, for example, by attaching a sheet-type thermocouple to the sealing part.

[0028] As mentioned above, during welding, in order to avoid being affected by the wavelengths emitted by the heating device, the thermo camera 2 capable of measuring wavelengths around 6 micrometers is used. On the other hand, after welding, since the heating device is not activated, the thermo camera 1 capable of measuring wavelengths around 3.4 micrometers is used.

[0029] First, the upper part of Fig. 3 will be described. The temperature distribution 30 measured by the thermo camera 2 during welding is within the reference range 40. Therefore, no defects occur during welding. In addition, the temperature distribution 20 measured by the thermo camera 1 after welding is also within the reference range 40. Therefore, no defects occur even after welding.

[0030] Next, the middle part of Fig. 3 will be described. In the temperature distribution 30 measured by the thermo camera 2 during welding, a part of the distribution indicated by the arrow is outside the reference range 40. Therefore, a defect occurs during welding. In this way, when a defect such as a void occurs during welding, the seal part is not heated by the surrounding air, and the temperature drops. On the other hand, the temperature distribution 20 measured by the thermo camera 1 after welding is within the reference range 40. Therefore, no defects occur after welding.

[0031] In this way, since the temperature of the sealed portion is measured based on a wavelength range different from the wavelength range associated with heating, even during welding of the sealed portion, welding defects can be detected based on the temperature change.

[0032] Next, the lower part of Fig. 3 will be described. The temperature distribution 30 measured by the thermo camera 2 during welding is within the reference range 40. Therefore, no defects occur during welding. On the other hand, the temperature distribution 20 measured by the thermo camera 2 after welding has a portion of the distribution indicated by the arrow that is outside the reference range 40. Therefore, defects have occurred during welding. In this way, when defects such as voids occur after welding, the temperature drops in the same way as during welding.

[0033] As shown in the middle of Figure 3, during welding, the temperature is measured using a thermo camera 2 that can measure a wavelength range different from the wavelength range associated with heating. Also, as shown in the bottom of Figure 3, after welding, the temperature is measured using a thermo camera 1 that can measure a wavelength close to the absorption wavelength that depends on the material and amount of the seal part. With this configuration, welding defects can be detected not only after welding but also during welding.

[0034] In Fig. 3, the temperature of the sealed portion is measured by switching between two thermo cameras during and after welding. However, this is not limited to this, and the temperature of the sealed portion may be measured using one thermo camera that can measure multiple wavelengths by dispersing light into different wavelengths. In other words, the temperature of the sealed portion may be measured by switching the measurement wavelength of one thermo camera during and after welding.

[0035] Here, a thermo camera was used to measure the temperature of the sealed portion, but a radiation thermometer may also be used. Temperature measurement may also be performed on a part of the sealed portion. Furthermore, the temperature measurement points may be divided according to the shape of the sealed portion.

[0036] In this way, in the bipolar secondary battery inspection method according to the first embodiment, the temperature is measured based on a wavelength range different from the wavelength range associated with heating. With this configuration, the temperature can be measured even while the seal is being welded, so that welding defects can be detected and the quality of the welding of the seal can be inspected with high accuracy.

[0037] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. In other words, the above description has been omitted or simplified as appropriate for the purpose of clarity, and a person skilled in the art can easily modify, add, or convert each element of the embodiment within the scope of the present invention. [Explanation of symbols]

[0038] 10 Bipolar secondary battery 11 Seal part 12 Energy storage module 13 Bipolar Electrode 14 Separator 15a Positive electrode current collector 15b Negative electrode current collector 17 Positive electrode 18 negative electrode 20, 30 temperature distribution 40 Reference range 50 Actual temperature of the seal SP closed space

Claims

[Claim 1] A method for inspecting a bipolar secondary battery in which storage modules are stacked, the storage modules including a pair of electrodes including a positive electrode and a negative electrode, a separator provided between the pair of electrodes, and a seal portion provided so as to surround the pair of electrodes and the separator to form an enclosed space for accommodating a liquid electrolyte, the method comprising the steps of: While heating and fusing the seal portions of the power storage modules adjacent to each other in a stacking direction, a temperature of the seal portions is measured based on a wavelength range different from a wavelength range associated with the heating; detecting a welding defect in the seal portion based on the temperature change; A method for inspecting bipolar secondary batteries.

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