An internal short circuit boundary test assembly for an electric cell, a test device and a test method thereof

Abstract

The application provides an internal short circuit boundary testing assembly of an electric core, a testing device and a testing method thereof, and belongs to the field of battery fault detection. The internal short circuit boundary testing assembly of the electric core comprises a positive electrode to-be-tested structure, a negative electrode to-be-tested structure, a first diaphragm and a second diaphragm. The first diaphragm is located between the positive electrode to-be-tested structure and the negative electrode to-be-tested structure, and the first diaphragm is provided with a through hole corresponding to the positive electrode to-be-tested structure and the negative electrode to-be-tested structure. The second diaphragm covers the through hole. Through the internal short circuit boundary testing assembly of the electric core, a relatively accurate internal short circuit boundary of the electric core can be obtained, so that the advantages and disadvantages of the safety of the electric core can be judged more accurately.

Description

Technical Field

[0001] This application relates to the field of battery fault detection, and more specifically, to a short-circuit boundary test component, test device, and test method for a battery cell. Background Technology

[0002] In existing technologies, thermal runaway of batteries is mainly caused by short circuits within the cell. The short circuit boundary within the cell is an important parameter indicator. By measuring the short circuit boundary within the cell, the safety boundary of the cell can be determined, thereby revealing the quality of the cell's safety.

[0003] However, existing testing methods are unable to obtain accurate short-circuit boundaries within the battery cell, making it difficult to effectively determine the safety level of the battery cell. Summary of the Invention

[0004] The purpose of this application is to provide a short-circuit boundary test component, test device and test method for battery cells, which can obtain a more accurate short-circuit boundary within the battery cell, thereby enabling a more accurate judgment of the safety quality of the battery cell.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, embodiments of this application provide a short-circuit boundary testing assembly for a battery cell, including a positive electrode test structure, a negative electrode test structure, a first separator, and a second separator. The first separator is located between the positive electrode test structure and the negative electrode test structure, and the first separator has through holes corresponding to both the positive electrode test structure and the negative electrode test structure; the second separator covers the through holes.

[0007] In the above technical solution, the second diaphragm is used to cover the through holes on the first diaphragm. Through the cooperation of the positive electrode test structure, the negative electrode test structure, the first diaphragm, and the second diaphragm, a complete normal cell structure can be simulated. At this time, by removing the second diaphragm, a cell short circuit can be achieved to test the cell internal short circuit boundary under the corresponding condition. Compared with existing detection devices (which usually require heating to cause an internal short circuit, while actual cell internal short circuits usually occur at room temperature), the detection device provided in this application embodiment can simulate an internal short circuit condition that is closer to the actual cell internal short circuit condition. Correspondingly, the detected cell internal short circuit boundary is also more accurate, thereby enabling a more accurate judgment of the cell's safety quality.

[0008] In some alternative implementations, the cross-sectional shape of the through hole is rectangular.

[0009] In the above technical solution, the use of through holes with regular shapes makes it easier to adjust the area of ​​the fault region compared to the use of through holes with irregular shapes.

[0010] In some alternative implementations, the positive electrode structure to be tested includes a positive current collector and a positive active material layer, and the negative electrode structure to be tested includes a negative current collector and a negative active material layer.

[0011] The cell internal short-circuit boundary test component provided in this application embodiment is applicable to the internal short-circuit mode of the positive electrode material area (in this application, the material area refers to the area where the active material is located - the active material layer) - the negative electrode material area.

[0012] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥40mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥50mm.

[0013] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which can relatively easily test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode thermal runaway without fire state.

[0014] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway fire state are both ≥60mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway fire state are both ≥80mm.

[0015] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0016] In some alternative implementations, the positive electrode structure to be tested includes a positive current collector and a positive active material layer, and the negative electrode structure to be tested includes a negative current collector.

[0017] The cell internal short-circuit boundary test assembly provided in this application embodiment is applicable to the internal short-circuit mode of the positive electrode material area-negative electrode current collector.

[0018] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the cross-sectional dimensions of the through hole in the thermal runaway state without ignition are both ≥70mm; and / or, when the cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole in the thermal runaway state without ignition are both ≥90mm.

[0019] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which can relatively easily test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode thermal runaway without fire state.

[0020] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway fire state are both ≥80mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway fire state are both ≥100mm.

[0021] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0022] In some alternative implementations, the positive electrode structure under test includes a positive current collector, and the negative electrode structure under test includes a negative current collector and a negative electrode active material layer.

[0023] The cell internal short-circuit boundary test assembly provided in this application embodiment is applicable to the internal short-circuit mode of the positive current collector-negative electrode material region.

[0024] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥10mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥30mm.

[0025] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which can relatively easily test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode thermal runaway without fire state.

[0026] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway fire state are both ≥15mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway fire state are both ≥35mm.

[0027] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0028] In some optional implementations, the test assembly is a test assembly for octet ternary lithium-ion batteries. When the battery is fully charged, the length and width of the cross-sectional dimensions of the through-hole in the thermal runaway state without ignition are both ≥5mm.

[0029] In the above technical solution, for the 8-series ternary system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0030] In some optional implementations, the test assembly is a test assembly for octet ternary lithium-ion batteries, where the length and width of the through-hole are both ≥10mm when the battery is fully charged and under thermal runaway fire conditions.

[0031] In the above technical solution, for the 8-series ternary system battery cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0032] In some optional implementations, the test assembly is a test assembly for LFP system cells, where the length and width of the through-hole are both ≥20mm when the cell is fully charged and in a thermal runaway state without ignition.

[0033] In the above technical solution, for LFP system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0034] In some optional implementations, the test assembly is a test assembly for LFP system cells, where the length and width of the through-hole are both ≥30mm when the cell is fully charged and under thermal runaway fire conditions.

[0035] In the above technical solution, for LFP system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0036] In some alternative implementations, the positive electrode structure under test includes a positive current collector, and the negative electrode structure under test includes a negative current collector.

[0037] The cell internal short-circuit boundary test assembly provided in this application embodiment is applicable to the internal short-circuit mode of positive current collector-negative current collector.

[0038] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥40mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway state without ignition are both ≥50mm.

[0039] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which can relatively easily test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode thermal runaway without fire state.

[0040] In some optional implementations, the test assembly is a test assembly for a ternary lithium battery cell. When the cell is fully charged, the length and width of the through-hole in the thermal runaway fire state are both ≥60mm; and / or, when the cell is 50% charged, the length and width of the through-hole in the thermal runaway fire state are both ≥80mm.

[0041] In the above technical solution, for the five-element ternary system battery cell, the test is carried out according to a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0042] In some optional implementations, the in-cell short-circuit boundary test assembly satisfies either condition A or B:

[0043] A. The short-circuit boundary test component inside the cell is a wound structure, and the through hole is opened in any one of the second to fourth turns starting from the outer turn of the first diaphragm.

[0044] B. The short-circuit boundary test assembly inside the cell is a stacked structure, and the through-hole is opened in any of the second to fourth layers, starting from the outer layer of the first separator.

[0045] In the above technical solution, when dealing with the two different structures of battery cells, the through holes are opened in specific positions. Compared with the form of opening them closer to the inside of the battery cell, this can effectively avoid causing more damage to the battery cell structure, thereby reducing the failure rate of the battery cell. Compared with the form of opening them closer to the outside of the battery cell, this can ensure the accuracy of the test results (there is a temperature difference between the inside and outside of the battery cell. If the fault area is too close to the outside of the battery cell, it will lead to insufficient representativeness of the test results).

[0046] In some alternative implementations, the cross-sectional dimensions of the second diaphragm are larger than the cross-sectional dimensions of the through-hole.

[0047] In the above technical solution, the second diaphragm has a larger cross-sectional size. Compared with the form where the two have the same cross-sectional size, the former is easier to remove the second diaphragm.

[0048] Secondly, embodiments of this application provide a short-circuit boundary testing device for a battery cell, including a test container, a short-circuit boundary testing component as provided in the first aspect embodiment, an electrolyte, a thermometer, and a voltage meter. The short-circuit boundary testing component is housed within the test container; the electrolyte is housed within the test container; the thermometer is housed within the test container and is used to test the temperature of the short-circuit boundary testing component; the voltage meter is housed within the test container and is used to test the voltage of the short-circuit boundary testing component.

[0049] In the above technical solution, the cell internal short-circuit boundary test device includes the cell internal short-circuit boundary test component as provided in the first aspect embodiment. Compared with conventional test devices, it can obtain a more accurate cell internal short-circuit boundary, thereby enabling a more accurate judgment of the cell's safety performance.

[0050] Thirdly, embodiments of this application provide a method for testing the short-circuit boundary within a battery cell, using the short-circuit boundary testing device provided in the second aspect embodiment, comprising the following steps:

[0051] The initial temperature and initial voltage of the short-circuit boundary test component inside the battery cell were tested and recorded using a thermometer and a pressure gauge.

[0052] The second diaphragm is removed to short-circuit the short-circuit boundary test assembly within the cell.

[0053] The short-circuit temperature and short-circuit voltage of the short-circuit boundary test component inside the battery cell were tested and recorded using a thermometer and a pressure meter.

[0054] The type of thermal runaway is determined by the changes between the initial temperature and the short-circuit temperature, as well as the changes between the initial voltage and the short-circuit voltage.

[0055] In the above technical solution, the test method for the short-circuit boundary inside the cell adopts the short-circuit boundary test device inside the cell provided in the second aspect embodiment, which can accurately determine the thermal runaway type of the cell, and thus obtain the short-circuit boundary inside the cell under the corresponding thermal runaway type more accurately according to the thermal runaway type.

[0056] In some alternative implementations, the test container is filled with an inert gas.

[0057] In the above technical solution, the test container is filled with inert gas, which can effectively prevent the battery cell from undergoing oxidation-reduction reactions with water, oxygen or air, thereby effectively preventing the overall electrical performance of the battery cell from being affected. Attached Figure Description

[0058] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 A schematic diagram of the structure of a short-circuit boundary test assembly within a battery cell provided in an embodiment of this application;

[0060] Figure 2 This is a schematic diagram of the structure of a first diaphragm provided in an embodiment of this application from another perspective.

[0061] Icons: 10 - Cell internal short circuit boundary test assembly; 100 - Positive electrode structure under test; 200 - Negative electrode structure under test; 300 - First separator; 310 - Through hole; 400 - Second separator. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0063] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0064] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0065] In the description of this application, it should be noted that the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0066] In existing technologies, the testing of short-circuit boundaries within a battery cell is mainly conducted through the following two methods:

[0067] (1) By implanting an L-shaped nickel-titanium deformation memory alloy inside the cell, when the temperature is low, the memory alloy will not deform between the cells. This can be understood as the cell being a normal cell. When the cell is heated, the memory alloy will deform, resulting in an internal short circuit, so as to obtain the internal short circuit boundary of the cell under the corresponding short circuit state.

[0068] (2) By conducting destructive tests on the membranes corresponding to the positive and negative electrodes, that is, creating damaged areas of different sizes on the membranes, then coating the damaged areas with paraffin wax, and then assembling them into a battery cell; then, heating the battery cell will melt the graphite, thereby causing a short circuit inside the battery cell, so as to obtain the short circuit boundary inside the battery cell under the corresponding short circuit state.

[0069] Both of the above testing methods require heating the battery cell to achieve this. However, actual short circuits in battery cells usually occur at room temperature. Therefore, the above two testing methods do not match the actual situation of short circuits in battery cells, making it difficult to obtain a relatively accurate short circuit boundary in the battery cell.

[0070] Based on this, the inventors discovered through creative research that by opening through holes of different sizes on the separator and by using an additional separator that can cover the through holes, the internal short circuit state of the battery cell can be simulated by artificially controlling whether the through holes are covered by the additional separator. This allows for testing and obtaining a more accurate internal short circuit boundary of the battery cell that is closer to the actual internal short circuit situation without heating the battery cell.

[0071] See Figure 1 and Figure 2 In a first aspect, embodiments of this application provide a short-circuit boundary test assembly 10 for a battery cell, including a positive electrode test structure 100, a negative electrode test structure 200, a first separator 300, and a second separator 400. The first separator 300 is located between the positive electrode test structure 100 and the negative electrode test structure 200, and the first separator 300 has through holes 310 corresponding to both the positive electrode test structure 100 and the negative electrode test structure 200; the second separator 400 covers the through holes 310.

[0072] It should be noted that, in this field, a complete battery cell = battery positive electrode + battery negative electrode + separator, which is equivalent to the positive electrode test structure 100 + negative electrode test structure 200 + first separator 300 + second separator 400 in this application.

[0073] It should be noted that thermal runaway typically includes two modes: thermal runaway without ignition and thermal runaway with ignition. Generally speaking, the short circuit boundary within the cell corresponding to thermal runaway without ignition is smaller than the short circuit boundary within the cell corresponding to thermal runaway with ignition.

[0074] It should be noted that "covering" here means that the cross-sectional size of the second diaphragm 400 is greater than or equal to the cross-sectional size of the through hole 310.

[0075] In this application, the second diaphragm 400 is used to cover the through hole 310 on the first diaphragm 300. Through the cooperation of the positive electrode test structure 100, the negative electrode test structure 200, the first diaphragm 300 and the second diaphragm 400, a complete normal cell structure can be simulated. At this time, by removing the second diaphragm 400, a cell short circuit can be achieved to test the cell internal short circuit boundary under the corresponding condition. Compared with the existing detection device (which usually requires heating to cause an internal short circuit, while the actual cell internal short circuit usually occurs at room temperature), the detection device provided in this application embodiment can simulate an internal short circuit condition that is closer to the actual cell internal short circuit condition. Correspondingly, the result of detecting the cell internal short circuit boundary is also more accurate, thereby enabling a more accurate judgment of the cell safety quality.

[0076] It should be noted that the cross-sectional shape of the through hole 310 is not limited and can be adjusted according to actual needs.

[0077] As an example, the cross-sectional shape of the through hole 310 is rectangular.

[0078] In this embodiment, a through hole 310 with a regular shape is used, which makes it easier to adjust the area of ​​the fault region compared to using an irregularly shaped through hole 310.

[0079] In other possible implementations, the cross-sectional shape of the through hole 310 can also be circular or triangular, etc.

[0080] It is understandable that different battery cell systems use different materials, and consequently, the boundary size corresponding to the occurrence of internal short circuits is also different. In order to test the internal short circuit boundary of different battery cell systems more quickly, the size of the through hole 310 can be adjusted accordingly.

[0081] It should be noted that the specific applicable internal short circuit mode of the battery cell internal short circuit boundary test component 10 provided in this application embodiment is not limited, and can be adjusted accordingly according to actual needs. In this application embodiment, the rectangular through hole 310 is used as an example.

[0082] As an example, the positive electrode test structure 100 includes a positive current collector and a positive active material layer, and the negative electrode test structure 200 includes a negative current collector and a negative active material layer.

[0083] In this embodiment, the cell internal short-circuit boundary test component 10 provided in this application is applicable to the internal short-circuit mode of the positive electrode material area (in this application, the material area refers to the area where the active material is located - the active material layer) - the negative electrode material area.

[0084] It should be noted that there are no restrictions on the type of battery cell; adjustments can be made according to actual needs.

[0085] As an example, the test component is a test component for a ternary lithium battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥40mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥50mm.

[0086] It should be noted that ternary system cells refer to cells in which the positive electrode active material layer includes metals such as nickel, cobalt, and manganese.

[0087] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0088] As an example, the test component is a test component for a five-element ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥60mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥80mm.

[0089] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0090] As an example, the positive electrode test structure 100 includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode test structure 200 includes a negative electrode current collector. This configuration is equivalent to removing the active material layer on the negative electrode of the battery.

[0091] In this embodiment, the cell internal short-circuit boundary test component 10 provided in this application is suitable for the internal short-circuit mode of the positive electrode material area-negative electrode current collector.

[0092] As an example, the test component is a test component for a ternary lithium battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥70mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥90mm.

[0093] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0094] As an example, the test component is a test component for a five-element ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥80mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥100mm.

[0095] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0096] As an example, the positive electrode test structure 100 includes a positive electrode current collector, and the negative electrode test structure 200 includes a negative electrode current collector and a negative electrode active material layer. This configuration is equivalent to removing the active material layer on the positive electrode of the battery.

[0097] In this embodiment, the cell internal short-circuit boundary test component 10 provided in this application is suitable for the internal short-circuit mode of the positive current collector-negative electrode material region.

[0098] It should be noted that there are no restrictions on the type of battery cell; adjustments can be made according to actual needs.

[0099] As an example, the test component is a test component for a ternary lithium battery cell. When the cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥10mm; and / or, when the cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥30mm.

[0100] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0101] As an example, the test component is a test component for a five-element ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥15mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥35mm.

[0102] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0103] As an example, the test component is a test component for an octet ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥5mm.

[0104] It should be noted that the difference between 8-series and 5-series battery cells lies in the proportion of nickel in the cathode material, with 8-series cells having a higher proportion of nickel.

[0105] In this embodiment, for the 8-series ternary system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0106] As an example, the test component is a test component for an eight-series ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire conditions are both ≥10mm.

[0107] In this embodiment, for the 8-series ternary system battery cell, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0108] As an example, the test component is a test component for LFP system cells. When the cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥20mm.

[0109] It should be noted that LFP system cells refer to cells in which the positive electrode active material layer includes lithium iron phosphate material.

[0110] In this embodiment, for LFP system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0111] As an example, the test component is a test component for LFP system cells. When the cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire conditions are both ≥30mm.

[0112] In this embodiment, for LFP system cells, testing is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0113] As an example, the positive electrode test structure 100 includes a positive current collector, and the negative electrode test structure 200 includes a negative current collector. This configuration is equivalent to removing the active material layer from both the positive and negative electrodes of the battery.

[0114] In this embodiment, the cell internal short-circuit boundary test component 10 provided in this application is suitable for the internal short-circuit mode of positive current collector-negative current collector.

[0115] As an example, the test component is a test component for a ternary lithium battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥40mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 in the state of thermal runaway without ignition are both ≥50mm.

[0116] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the corresponding internal short circuit mode under thermal runaway without fire.

[0117] As an example, the test component is a test component for a five-element ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥60mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole 310 under thermal runaway fire state are both ≥80mm.

[0118] In this embodiment, for the five-element ternary system battery cell, the test is carried out starting from a specific range of dimensions, which makes it relatively easy to test the internal short circuit boundary of the battery cell in the thermal runaway fire state under the corresponding internal short circuit mode.

[0119] It is understandable that the test results may vary depending on the location of the internal short-circuit region in the cell. Considering the accuracy of the test results and the safety of the test process, the position of the internal short-circuit region (i.e., through-hole 310) can be adjusted.

[0120] As an example, the cell-internal short-circuit boundary test assembly 10 satisfies either the following condition A or B:

[0121] A. The short-circuit boundary test component 10 inside the cell is a wound structure (i.e., the cell is made by a winding process), and the through hole 310 is opened in any one of the second to fourth turns starting from the outer ring of the first diaphragm 300.

[0122] B. The short-circuit boundary test component 10 of the battery cell is a stacked structure (i.e., the battery cell is made by stacking process), and the through hole 310 is opened in any of the second to fourth layers starting from the outer layer of the first separator 300.

[0123] In this embodiment, when dealing with the two different cell structures mentioned above, the through hole 310 is opened at a specific location. Compared with the form of opening it closer to the inside of the cell, it can effectively avoid causing more damage to the cell structure, thereby reducing the failure rate of the cell. Compared with the form of opening it closer to the outside of the cell, it can ensure the accuracy of the test results (there is a temperature difference between the inside and outside of the cell. If the fault area is too close to the outside of the cell, it will lead to insufficient representativeness of the test results).

[0124] It should be noted that, for ease of testing, the relative cross-sectional dimensions of the second diaphragm 400 and the through hole 310 can be adjusted.

[0125] As an example, the cross-sectional dimension of the second diaphragm 400 is larger than the cross-sectional dimension of the through hole 310.

[0126] In this embodiment, the second diaphragm 400 has a larger cross-sectional dimension, which makes it easier to remove the second diaphragm 400 compared to forms where both have the same cross-sectional dimension.

[0127] Secondly, embodiments of this application provide a short-circuit boundary testing device for a battery cell, including a test container, a short-circuit boundary testing component as provided in the first aspect embodiment, an electrolyte, a thermometer, and a voltage meter. The short-circuit boundary testing component is housed within the test container; the electrolyte is housed within the test container; the thermometer is housed within the test container and is used to test the temperature of the short-circuit boundary testing component; the voltage meter is housed within the test container and is used to test the voltage of the short-circuit boundary testing component.

[0128] In this application, the cell internal short-circuit boundary testing device includes the cell internal short-circuit boundary testing component as provided in the first aspect embodiment. Compared with conventional testing devices, it can obtain a more accurate cell internal short-circuit boundary, thereby enabling a more accurate judgment of the cell's safety performance.

[0129] It should be noted that there are no restrictions on the type and material of the test container; it can be selected and set according to the conventional methods used in this field.

[0130] As an example, the test container is an aluminum-plastic film sealed bag.

[0131] It should be noted that the specific composition of the electrolyte is not limited and can be adjusted according to the different battery cell systems.

[0132] It should be noted that for functional units in the cell short-circuit boundary test device that are not specifically described (such as temperature measuring instruments, pressure measuring instruments, etc.), they can be set according to the conventional selection in this field.

[0133] Thirdly, embodiments of this application provide a method for testing the short-circuit boundary within a battery cell, using the short-circuit boundary testing device provided in the second aspect embodiment, comprising the following steps:

[0134] The initial temperature and initial voltage of the short-circuit boundary test assembly within the cell are tested and recorded using a thermometer and a voltmeter. The second diaphragm is removed to short-circuit the short-circuit boundary test assembly within the cell. The short-circuit temperature and short-circuit voltage of the short-circuit boundary test assembly within the cell are tested and recorded using a thermometer and a voltmeter. The type of thermal runaway is determined by the changes between the initial temperature and the short-circuit temperature, as well as the changes between the initial voltage and the short-circuit voltage.

[0135] In this application, the method for testing the short-circuit boundary within the battery cell adopts the short-circuit boundary testing device within the battery cell provided in the second aspect embodiment, which can more accurately determine the thermal runaway type of the battery cell, and thus obtain the short-circuit boundary within the battery cell under the corresponding thermal runaway type more accurately according to the thermal runaway type.

[0136] It should be noted that in this field, temperature, temperature change rate, voltage, and voltage change rate are usually used to determine whether a battery cell has experienced thermal runaway. The criteria for these four indicators are as follows: temperature greater than or equal to 60°C, temperature rise rate greater than 1°C / min, voltage less than or equal to 2.5V, and voltage change rate decreasing by 25% or more within 2 seconds. If any two of these conditions are met, the battery cell is judged to be in a state of thermal runaway.

[0137] It is understandable that the electrodes of the battery cell are prone to oxidation-reduction reactions with water, oxygen or air. In order to obtain a more accurate short-circuit boundary within the battery cell, the test conditions can be optimized.

[0138] As an example, the test container was filled with inert gas.

[0139] In this embodiment, the test container is filled with inert gas, which can effectively prevent the battery cell from undergoing oxidation-reduction reactions with water, oxygen or air, thereby effectively preventing the overall electrical performance of the battery cell from being affected.

[0140] It should be noted that the type of inert gas is not limited and can be selected and set according to the conventions in this field.

[0141] As an example, the inert gas includes at least one of nitrogen and argon.

[0142] To better understand the technical solution, the following specific examples will be used for illustration:

[0143] Example 1

[0144] This application provides a method for preparing a short-circuit boundary testing device for a battery cell, including the following steps:

[0145] The battery cell is disassembled from the battery. Then, a through hole is opened in the preset short-circuit area of ​​the first separator. Then, a second separator is set and the through hole is covered to obtain the short-circuit boundary test assembly of the battery cell.

[0146] Then, the short-circuit boundary test component inside the cell is encapsulated in an aluminum-plastic film sealed bag, and a temperature measuring instrument and a pressure measuring instrument are set in sequence. Then, electrolyte is injected. Then, the aluminum-plastic film sealed bag is evacuated and argon gas is introduced to obtain the short-circuit boundary test device inside the cell.

[0147] Experimental Example 1

[0148] Cell internal short circuit boundary test

[0149] Test method:

[0150] The short-circuit boundary test device for the battery cell was assembled according to the preparation method of Example 1. Then, the initial temperature and initial voltage of the short-circuit boundary test component for the battery cell were tested using a thermometer and a pressure meter, respectively. The test component is a test component system for a ternary lithium battery cell. The positive current collector is Cu, the positive active material layer is large single crystal lithium nickel cobalt manganese oxide-NCM523, the negative current collector is Al, the negative active material layer is graphite, and the short-circuit point (i.e., through hole) is set in the second ring starting from the outer ring. The negative current collector is scraped off with a sharp tool, and the positive current collector is wiped with NMP.

[0151] The second diaphragm is removed to short-circuit the short-circuit boundary test component inside the cell. Then, the short-circuit temperature and short-circuit voltage of the short-circuit boundary test component inside the cell are tested and recorded by a thermometer and a voltmeter. The cell is judged to be thermally runaway by any two of the four thermal runaway judgment indicators. At the same time, the specific thermal runaway type is determined by whether the cell catches fire.

[0152] By setting up through holes of different sizes (i.e., internal short-circuit regions of different areas) and repeating the above test method, we can obtain different thermal runaway boundaries of the battery cell under different charge levels.

[0153] Table 1. Test results of short-circuit boundary within the battery cell.

[0154]

[0155] It should be noted that the ">" in the table represents the area of ​​thermal runaway ignition being larger than the corresponding size of the area of ​​thermal runaway non-ignition, but the specific size value has not been tested.

[0156] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A short-circuit boundary test assembly for battery cells, characterized in that, include: Positive electrode structure to be tested; Negative electrode structure under test; A first diaphragm is located between the positive electrode test structure and the negative electrode test structure, and the first diaphragm has through holes corresponding to both the positive electrode test structure and the negative electrode test structure. as well as A second diaphragm covers the through-hole; The cell-internal short-circuit boundary test assembly meets either of the following conditions A or B: A. The short-circuit boundary test assembly inside the cell is a wound structure, and the through hole is opened in any one of the second to fourth turns with the outer ring of the first diaphragm as the starting point. B, the cell short-circuit boundary test assembly is a stacked structure, and the through hole is opened in any of the second to fourth layers with the outer layer of the first separator as the starting point; The positive electrode structure under test includes a positive electrode current collector and a positive electrode active material layer, and the negative electrode structure under test includes a negative electrode current collector. The test component is a test component for a five-element ternary system battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole in the thermal runaway state without ignition are both ≥70 mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole in the thermal runaway state without ignition are both ≥90 mm. The test assembly is a test assembly for a ternary lithium battery cell. When the battery cell is fully charged, the length and width of the cross-sectional dimensions of the through hole under thermal runaway fire state are both ≥80 mm; and / or, when the battery cell is 50% charged, the length and width of the cross-sectional dimensions of the through hole under thermal runaway fire state are both ≥100 mm.

2. The cell-internal short-circuit boundary test assembly according to claim 1, characterized in that, The cross-sectional shape of the through hole is rectangular.

3. The cell-internal short-circuit boundary test assembly according to claim 1 or 2, characterized in that, The cross-sectional dimension of the second diaphragm is larger than the cross-sectional dimension of the through hole.

4. A short-circuit boundary testing device for a battery cell, characterized in that, include: Test container; The cell-in-short-circuit boundary test assembly as described in claim 1 or 2, wherein the cell-in-short-circuit boundary test assembly is housed within the test container; Electrolyte, which is contained within the test container; A thermometer, which is housed within the test container and is used to test the temperature of the short-circuit boundary test component inside the battery cell; as well as A voltage tester, housed within the test container, is used to test the voltage of the short-circuit boundary test assembly within the battery cell.

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