Battery shell detection method

Abstract

The present invention provides a battery cell shell detection method, which relates to the field of battery technology. The battery cell shell detection method first performs a tensile test on a sample with a welding area on the battery cell shell. When the tensile strength of the sample exceeds a preset strength threshold and the fracture of the sample is located in a non-welding area, the battery cell shell of the corresponding batch of the sample is a semi-qualified product; then the battery cell shell of the same batch as the semi-qualified product is sealed and ventilated, and the welding area is immersed in water to observe whether bubbles are generated in the welding area. If no bubbles are generated in the welding area, the battery cell shell is a qualified product. The battery cell shell detection method described in the present invention first performs a tensile test on the welding area of ​​the battery cell shell, and performs a sealing test on the battery shell of the same batch in which the welding area is not broken in the tensile test, which is conducive to identifying the welding strength and airtightness of the welding area, thereby improving the detection accuracy of defects in the welding area of ​​the battery shell, and further facilitating the safety of the battery cell.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for detecting a battery cell shell. Background Art

[0002] As the main body of the battery cell, the performance of the battery cell shell is the key to the performance of the battery cell. After the processing is completed, the battery cell shell needs to be tested before assembly to ensure that qualified battery cell shells enter the next process and unqualified battery cell shells are removed to prevent unqualified battery cell shells from entering the next assembly process and producing defective products, thereby causing waste of battery cells.

[0003] The battery cell shell is mainly formed by bending a plate multiple times, aligning the two sides of the plate, and then welding them through a high-frequency welding process. Among them, high-frequency welding uses high-frequency current to generate resistance heat on the metal surface, heating the surface of the workpiece to a molten state, and at the same time applying extrusion force to make the metal fuse together for welding. When conducting quality inspection on battery cell shells, the most common inspection method is helium inspection. However, helium inspection (the standard is a leakage rate less than 1*10 -7 / Pa.m 3 / s) can detect the size of the leak rate at the weld, but due to the low pressure provided by the helium test itself, it cannot identify non-penetrating weld crack defects, so that the battery shell with non-penetrating weld crack defects enters the next process as qualified products, resulting in low detection accuracy. Increasing the helium test pressure will increase the amount of helium used, thereby increasing the detection cost. Summary of the invention

[0004] In view of this, the present invention aims to provide a battery cell shell detection method to improve the detection accuracy of the battery cell shell.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for detecting a battery cell shell, wherein the battery cell shell is formed by bending a sheet of plate, and the two side edges of the battery cell shell at the head and tail are aligned and connected together by high-frequency welding. The method for detecting the battery cell shell comprises firstly performing a tensile test on a sample having a welding area on the battery cell shell to apply tensile force to the parts located on two opposite sides of the welding area. When the tensile strength of the sample exceeds a preset tensile strength threshold and the fracture of the sample is located in a non-welding area, the battery cell shell of the corresponding batch of the sample is a semi-qualified product; then the battery cell shell of the same batch as the semi-qualified product is sealed and ventilated, and then the welding area is immersed in water to observe whether bubbles are generated in the welding area. If no bubbles are generated in the welding area, the battery cell shell is a qualified product.

[0007] Furthermore, when ventilating the battery cell shell, the pressure in the battery cell shell is first increased to a first pressure threshold, and is completely released after maintaining the pressure for a first time, and then the battery cell shell is re-inflated so that the pressure in the battery cell shell is increased to a second pressure threshold and then maintained for a second time; wherein the first pressure threshold is 1.2Mpa-1.4Mpa, and the first time is: 30s-90s; and / or the second pressure threshold is 0.4Mpa-0.6Mpa, and the second time is 4min-6min.

[0008] Furthermore, the pressure in the battery cell housing is gradually increased to the first pressure threshold at a pressure increasing rate of 0.05 MPa-0.1 MPa / time.

[0009] Furthermore, before the welding area is immersed in water, the battery cell casing is clamped by a clamping tool, and at least a portion of the clamping tool is immersed in water together with the welding area.

[0010] Furthermore, a ratio C of a clamping width A of the clamping tool to a thickness of the battery cell housing B satisfies: 0.95≤C<1.

[0011] Furthermore, the preset tensile strength threshold is 150 MPa.

[0012] Furthermore, a marking line is drawn on the battery cell shell to mark the position where the bubbles are generated.

[0013] Furthermore, the welding area immersed in water is arranged upward.

[0014] Furthermore, the gas introduced into the battery cell shell includes air.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The battery cell shell detection method described in the present invention first performs a tensile test on the welding area of ​​the battery cell shell, and then performs a sealing test on the battery shells of the same batch in which the welding area is not broken during the tensile test. Compared with the solution of only using helium for airtightness detection in the prior art, this dual testing method of tension and airtightness is conducive to identifying the welding strength and airtightness of the welding area, thereby improving the detection accuracy of defects in the welding area of ​​the battery shell, preventing unqualified battery cell shells from entering the next process, and further helping to improve the safety of the battery cell.

[0017] In addition, during the ventilation process, the cell shell is first increased to the first pressure threshold and then released after maintaining the pressure, and then charged to the second pressure threshold, which is conducive to simulating the state of the battery shell when thermal runaway occurs during use, so that non-penetrating weld cracks can increase and leak, which is conducive to identifying potential risks in the welding area, and then it is conducive to evaluating the safety of the cell shell when the cell is thermally runaway. The boost speed in the cell shell is conducive to simulating the change of pressure in the cell shell when the cell is thermally runaway, and improving the leakage effect at the non-penetrating weld cracks, so as to further improve the test accuracy of the cell shell.

[0018] In addition, clamping the cell shell by a clamping tool is conducive to simulating the state of the cell in the battery pack, thereby further improving the detection accuracy. The setting of the ratio range of the clamping width A of the clamping tool to the thickness of the cell shell B is conducive to simulating the capacity division process in the formation stage of the cell forming process. In this way, the coordination of the clamping tool and the water inspection is conducive to the performance of non-penetrating cracks. Marking the position of the bubble with a marking line is conducive to further checking the leakage point after detection. The welding area immersed in water is set upward to facilitate checking whether there are bubbles in the welding area. Air has the advantages of being easy to implement and having a better pressure increase effect than helium. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 A top view of a sample according to an embodiment of the present invention;

[0021] Figure 2 for Figure 1 Metallographic image at the AA section.

[0022] Description of reference numerals:

[0023] 1. Sample; 100. Welding area; 101. Fracture. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0025] In the description of the present invention, it should be noted that if there are terms indicating orientation or positional relationship such as "upper", "lower", "inner", "back", etc., they are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, if there are terms such as "first", "second", etc., they are also used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0026] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0027] The present embodiment relates to a battery cell shell detection method to overcome the problem in the prior art that the battery cell shell welding area 100 is only tested for airtightness using helium detection, which is unable to identify non-penetrating weld cracks that are prone to cause problems during the use of the battery cell shell, thereby facilitating the improvement of the detection accuracy of the battery cell shell and the safety of the battery cell.

[0028] In general, in the present embodiment, a method for detecting a battery cell shell is described, wherein the battery cell shell is formed by bending a sheet, and the two side edges of the battery cell shell are aligned and connected together by high-frequency welding. The method for detecting a battery cell shell includes firstly performing a tensile test on a sample 1 having a welding area 100 on the battery cell shell to apply a tensile force to the parts located on two opposite sides of the welding area 100. When the tensile strength of the sample 1 exceeds a preset tensile strength threshold, and the fracture 101 of the sample 1 is located in the non-welding area 100, the battery cell shell of the corresponding batch of the sample 1 is a semi-qualified product.

[0029] Then, the cell casings from the same batch as the semi-qualified products are sealed and ventilated, and then the welding area 100 is immersed in water to observe whether bubbles are generated in the welding area 100. If no bubbles are generated in the welding area 100, the cell casing is a qualified product.

[0030] The battery cell shell detection method described in the present embodiment first performs a tensile test on the welding area 100 of the battery cell shell, and then performs a sealing test on the battery shells of the same batch in which the welding area 100 is not broken during the tensile test. Compared with the solution of only using helium for airtightness detection in the prior art, this dual testing method of tension and airtightness detection is beneficial to converting non-penetrating weld cracks with potential risks into penetrating weld cracks by detecting the welding strength and airtightness of the welding area 100, thereby generating bubbles in the process of airtightness detection and identifying them, thereby improving the detection accuracy of defects in the welding area 100 of the battery shell, preventing unqualified battery cell shells from entering the next process, and further improving the safety of the battery cell.

[0031] In this embodiment, the battery cell shell can be a welded shell made of other alloy materials such as aluminum shell, steel shell, etc. The battery cell shell is specifically formed by bending a plate multiple times, aligning the two side edges at the head and tail, and then welding them through a high-frequency welding process. When the battery cell shell detection method in this embodiment performs a tensile test on the sample 1, it is usually required to cut multiple samples 1 with welding areas 100 from the same batch of battery cell shells. Among them, the two side edges at the head and tail after bending are respectively located at two opposite sides of the welding area 100, and the two side edges are in the same plane after welding.

[0032] For example, the number of samples 1 can be 4 to 8, and the length and width of sample 1 can be determined according to the use requirements. For example, the length of sample 1 can be 80 mm to 120 mm, and the width can be 20 mm to 30 mm. In specific implementation, Figure 1 As shown in , the length of the sample 1 may be 100 mm and the width may be 25 mm. Preferably, the welding area 100 is located in the middle of the sample 1, which is conducive to improving the test accuracy.

[0033] Among them, a tensile test machine is used to perform a tensile test on sample 1. During the specific operation, Figure 1 As shown in , the tensile machine clamps the parts of sample 1 located on both sides of the welding area 100 for stretching, and records the tensile force value. Considering that the tensile force value standard of different materials is affected by the wall thickness of the battery shell and the size of sample 1. Therefore, the tensile strength is used as a measure to determine whether the tensile test result of sample 1 is qualified. When calculating specifically, the formula P=F / S is used for calculation, where P is the tensile strength, F is the tensile force used when breaking, and S is the area of ​​sample 1 taken.

[0034] After multiple tests, it was verified that the tensile strength of the valve core welding area 100 is below 150Mpa. That is to say, during the tensile test, if the tensile strength of sample 1 reaches or exceeds 150Mpa, the tensile test will break at the welding area 100, and the battery cell shell of the batch of sample 1 is judged to be unqualified. If the tensile strength of sample 1 reaches or exceeds 150Mpa, the tensile test will not break at the welding area 100, and the battery cell shell of the batch of sample 1 is judged to be semi-qualified. Whether there is a non-penetrating weld crack in the welding area 100 requires water inspection for airtightness testing to further explore. Whether the fracture position is located in the welding area 100 needs to be checked with the help of metallographic testing.

[0035] Table 1 shows the test results of tensile strength exceeding 150 MPa when tensile tests were performed on multiple samples 1.

[0036]

[0037] Table 2 shows the test results of tensile strength less than 150 MPa when tensile tests were performed on multiple samples 1.

[0038]

[0039] It can be seen from Table 1 that when the tensile strength exceeds 150Mpa, all samples 1 break, and when the preset tensile strength is less than 150Mpa, the welding area 100 will not break, so setting the preset tensile strength to 150Mpa has a good reference significance. Figure 2 An example in which the fracture 101 is located in the non-welding area 100 is illustrated in FIG.

[0040] Specifically, Figure 2 The figure is a metallographic image of the fracture 101 on sample 1. The part on the left side of the welding area 100 is fractured. The fracture 101 is specifically located between the two areas. The welding area 100 is located on the sheet area on the right. Obviously, the fracture 101 is not located at the welding area 100. Figure 2 When the fracture 101 is located at the welding area 100, it can be judged that the sample 1 is a substandard product.

[0041] When the air tightness test is performed on the cell shells of the same batch as the semi-qualified products, a plugging plate can be welded on the open end of the cell shell to seal the cell shell, as long as the cell shell can be sealed. In specific implementation, both ends of the cell shell are open, and plugging plates are set at both ends of the cell shell (the plugging plates can be fixed on the cell shell by welding).

[0042] In order to facilitate ventilation into the battery cell housing for water inspection, an air inlet pipe can be provided on one of the plugging plates, and an air outlet pipe can be provided on the other plugging plate. The air inlet pipe and the air outlet pipe are both connected to the external air supply part through pipelines. The external air supply part flows into the battery cell housing through the air inlet pipe and flows out through the air outlet pipe. A first control valve is provided between the air inlet pipe and the external air supply part, and a second control valve is provided between the air outlet pipe and the external air supply part.

[0043] As a preferred embodiment, the gas introduced into the battery cell housing includes air. In this case, the gas outputted by the external air supply unit may be compressed air. Compared with the conventional solution of introducing helium, the introduction of air is conducive to increasing the pressure in the battery cell housing, thereby facilitating the transformation of non-penetrating weld cracks with potential risks into penetrating weld cracks, thereby identifying them through water inspection, and further facilitating the improvement of the inspection accuracy of the battery cell housing.

[0044] In order to simulate the state of the cell shell in use in the battery pack, the cell shell is clamped by a clamping tool before the welding area 100 in this embodiment is immersed in water, and at least part of the clamping tool is immersed in water together with the welding area 100. Specifically, the cells are arranged side by side in the battery pack, and the two cells arranged at intervals can clamp the cell located between them. The clamping tool here specifically simulates the clamping force of the cells on both sides on the test cell shell.

[0045] As a feasible implementation method, the clamping tool in this embodiment includes two clamping plates arranged in the thickness direction of the battery cell shell, and the two clamping plates are detachably connected together in the circumferential direction by a bolt pair composed of multiple bolts and nuts. A space for clamping the battery cell shell is formed between the two clamping plates to facilitate the installation and removal of the battery cell shell between the two clamping plates. In addition, by adjusting the position of the nut on the bolt, the thickness of the cover plate clamping space can be adjusted, so that battery cell shells of different thicknesses can be clamped with better flexibility of use. It should be noted that in the clamping state, when the battery cell shell is in a ventilated state, the clamping plates on both sides are not displaced or deformed.

[0046] During specific implementation, the clamping tool is immersed in water along with the battery cell housing. In order to facilitate observation of whether bubbles are generated in the welding area 100, in this embodiment, the welding area 100 immersed in water is arranged upward.

[0047] As a preferred embodiment, the ratio C of the clamping width A of the clamping tool to the thickness of the battery shell B satisfies: 0.95≤C<1. Such a setting is conducive to simulating the formation stage of the battery cell forming process. In the mode of cooperation between the clamping tool and the water inspection, it is conducive to the more prominent performance of non-penetrating cracks. In specific implementation, the ratio C can be, for example, 0.95, 0.96, 0.97, 0.98 or 0.99.

[0048] In this embodiment, when ventilating the battery cell housing, the pressure in the battery cell housing is first increased to a first pressure threshold, and then all released after maintaining the pressure for a first time, and then the battery cell housing is re-inflated so that the pressure in the battery cell housing is increased to a second pressure threshold and then maintained for a second time. The first pressure threshold is 1.2Mpa-1.4Mpa, and the first time is 30s-90s. The second pressure threshold is 0.4Mpa-0.6Mpa, and the second time is 4min-6min.

[0049] In specific implementation, the first pressure threshold may be 1.2Mpa, 1.3Mpa or 1.4Mpa, etc. The first duration may be 30s, 40s, 50s, 60s, 70s, 80s or 90s, etc. The second pressure threshold may be 0.4Mpa, 0.5Mpa or 0.6Mpa, etc. The second duration may be 4min, 5min or 6min, etc.

[0050] Considering that the standard value of the bursting pressure of the battery shell in the natural state is 1.2Mpa, it is of good reference significance to use 1.2Mpa as the pressure reference value for the first inflation. In addition, the pressure is increased to 0.4Mpa during the second inflation, which is the lower limit pressure value of the explosion-proof valve. When this pressure is reached, the explosion-proof valve will explode.

[0051] During the inflation process, the first control valve is first opened and the second control valve is closed. When the pressure in the battery cell housing is released, the first control valve is closed and the second control valve is opened. When the battery cell housing is re-inflated, the first control valve is opened again and the second control valve is closed.

[0052] As a preferred embodiment, the pressure in the battery cell shell is gradually increased to the first pressure threshold at a boosting rate of 0.05Mpa-0.1Mpa / time. The pressure in the battery cell shell is increased to the first pressure threshold in multiple times, so that the pressure in the battery cell shell gradually increases according to a gradient. Specifically, the pressure in the battery cell shell is gradually increased to the first pressure threshold at a boosting rate of 0.1Mpa / time. Such a setting can further expand the state of microcracks in the weld, which is specifically manifested as water leakage. Of course, in specific implementation, the pressure increase rate can also be 0.05Mpa / time, 0.07Mpa / , 0.09Mpa / time or 0.1Mpa / time, etc.

[0053] In the present embodiment, in particular, during the first inflation, the pressure in the battery cell shell is increased to 1.2 MPa, maintained for a first period of time, and then released, and then re-pressurized to 0.4 MPa for a second period of time, which is beneficial to simulating thermal runaway of the battery cell, and focuses on simulating whether leakage occurs at the welding part of the battery cell shell when the battery cell has thermal runaway, thereby causing side spraying, thereby helping to improve the reference significance of the detection results.

[0054] In addition, in order to mark the location where bubbles are generated during the water inspection, a marking line can be drawn on the battery cell shell to mark the location where bubbles are generated. The structure of the welding area 100 where air leakage occurs in this embodiment is shown in the figure.

[0055] In addition, in order to verify the accuracy of the test method in this embodiment, a verification test was performed on the battery cell casing measured by this method after it was assembled into a battery cell. The verification results are shown in Figure 3.

[0056] Table 3 shows the test results using the test method of this embodiment:

[0057]

[0058] As can be seen from Table 3, for Examples 3, 6, 7, and 10 to 12, which failed the tensile test, bubbles appeared during the ventilation test, and the welding area 100 also had leakage problems during the use of the battery cells, thereby verifying that the detection method in this embodiment can detect unqualified welding products. For the semi-qualified products, no bubbles appeared after the ventilation test for the samples corresponding to Examples 1 and 2, 5, 8, and 9, and the corresponding samples did not have leakage problems at the welding area 100 during use. For the semi-qualified products, Examples 4 and 13, bubbles appeared at the welding area 100 during the ventilation test, and the batteries made of the corresponding samples had leakage problems at the welding area 100 during use. Therefore, the qualified products detected by the method of combining the tensile test and the ventilation test have a high reference value.

[0059] Table 4 shows the test results using the traditional helium test method:

[0060]

[0061] Among them, each comparative example in Table 4 corresponds to the sample of the embodiment in Table 3 one by one. For example, the sample in embodiment 1 and the sample in comparative example 1 are from the same batch.

[0062] It can be seen from Table 4 that when the comparative examples were subjected to helium inspection, only comparative examples 4 and 12 failed the helium inspection, and the battery cells made of the corresponding samples all had leakage in the welding area 100 during use. However, the battery cells corresponding to comparative examples 3, 11 and 13 that passed the helium inspection respectively had leakage in the welding area 100 during use. Obviously, even the welding area 100 that passed the helium inspection will have the problem of low detection accuracy. In the present application, the combination of tensile testing and ventilation testing can amplify potential non-penetrating weld crack defects, thereby facilitating the identification of defective products that cannot be detected by traditional helium testing.

[0063] In addition, the battery cell shell detection method in this embodiment can detect and identify unqualified battery cell shells before battery cell preparation, which is helpful to prevent leakage of products due to unqualified quality of battery cell shell welding. Moreover, when using this detection method, only part of the samples of the same batch need to be tested. Compared with the solution in the prior art that can only perform helium inspection on assembled battery cells, it is helpful to reduce the production cost of battery cells.

[0064] The detection method of this embodiment, based on the characteristics of the welding area 100 of the battery cell shell, integrates the two methods of tensile test and water inspection sealing test to evaluate whether the welding area 100 of the battery cell shell is qualified. It is not only easy to implement, but also conducive to improving the detection accuracy. In particular, it can magnify non-penetrating weld crack defects with potential leakage risks and combine them with the water inspection sealing test, which is conducive to timely and accurate identification of the specific leakage location on the welding area 100, and further confirm it by obtaining the metallographic diagram of the leakage location. It has high detection accuracy, effectively preventing battery cell shells with non-penetrating weld cracks and penetrating weld cracks from entering the next assembly process, thereby facilitating the safety of the battery cells.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting a battery cell shell, wherein the battery cell shell is formed by bending a sheet of material, and the two side edges of the battery cell shell are aligned and connected together by high-frequency welding, characterized in that: The battery cell shell detection method includes firstly performing a tensile test on a sample having a welding area on the battery cell shell to apply a tensile force to the parts located on two opposite sides of the welding area. When the tensile strength of the sample exceeds a preset tensile strength threshold and the fracture of the sample is located in a non-welding area, the battery cell shell of the corresponding batch of the sample is a semi-qualified product. Then the battery cell casing of the same batch as the semi-qualified product is sealed and ventilated, and then the welding area is immersed in water to observe whether bubbles are generated in the welding area. If no bubbles are generated in the welding area, the battery cell casing is a qualified product; When ventilating the battery cell housing, firstly increase the pressure in the battery cell housing to a first pressure threshold, and then release all the pressure after maintaining the pressure for a first time, and then re-inflate the battery cell housing so that the pressure in the battery cell housing increases to a second pressure threshold and then maintains the pressure for a second time; Wherein, the preset tensile strength threshold is 150Mpa; the first pressure threshold is 1.2Mpa-1.4Mpa, and the first duration is: 30s-90s; and / or, the second pressure threshold is 0.4Mpa-0.6Mpa, and the second duration is 4min-6min; The pressure in the battery cell housing is gradually increased to the first pressure threshold at a pressure increasing rate of 0.05 MPa-0.1 MPa / time.

2. The method for detecting a battery cell shell according to claim 1, characterized in that: Before the welding area is immersed in water, the battery cell housing is clamped by a clamping tool, and at least a portion of the clamping tool is immersed in water together with the welding area.

3. The method for detecting a battery cell shell according to claim 2, characterized in that: The ratio C of the clamping width A of the clamping tool to the thickness of the battery cell shell B satisfies: 0.95≤C<1.

4. The method for detecting a battery cell shell according to claim 1, characterized in that: Marking lines are drawn on the battery cell casing to mark the locations where bubbles are generated.

5. The method for detecting a battery cell shell according to claim 1, characterized in that: The welding area immersed in water is arranged upward.

6. The method for detecting a battery cell shell according to any one of claims 1 to 5, characterized in that: The gas introduced into the battery cell casing includes air.

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