Method, test fixture, and test system for testing swelling force of battery cell

Abstract

ABSTRACT METHOD, TEST FIXTURE, AND TEST SYSTEM FOR TESTING SWELLING FORCE OF BATTERY CELL A method, a test fixture, and a test system for testing a swelling force of a battery cell are provided. The present disclosure relates to battery technology and addresses the problem in which a measured swelling force greatly differs from the actual swelling force within a system. The battery cells are not uniformly tested using test fixtures of identical stiffness. Instead, the plurality of cells of a battery module are divided into multiple units. During testing, each unit is assigned a corresponding test fixture based on its position in the module, such that the closer the unit is to the center, the higher the stiffness of the assigned fixture. This approach simulates real swelling conditions after system assembly, ensuring consistent results and improved design accuracy.

Description

Test methods, test fixtures, and test systems for cell expansion force

[0001] This application claims priority to Chinese Patent Application No. 2025104530804, filed with the Chinese Patent Office on April 10, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a method, fixture, and system for testing the expansion force of a battery cell. Background Technology

[0003] Cell expansion force refers to the mechanical stress generated in a battery (especially a lithium-ion battery) due to changes in the volume of its internal materials during charge-discharge cycles, aging, or abnormal operating conditions. Specifically, lithium-ion batteries, with their high energy density, high charging efficiency, long cycle life, and mature technology, have become the preferred energy unit for new energy vehicles. During the manufacturing and use of lithium-ion batteries, the insertion or extraction of lithium ions causes an expansion phenomenon resulting in localized changes in the cell's thickness. Simultaneously, the gas produced by internal chemical reactions further enhances this expansion phenomenon.

[0004] Before assembling battery cells into a battery system, especially during system design, it is generally necessary to test the cell expansion force. This test result can guide system simulation and material selection. Current testing methods do not consider the different conditions of the cells within the system; they all use the same fixture for testing. This results in a significant discrepancy between the measured cell expansion force and the actual expansion force observed within the system. Consequently, the measured expansion force does not reflect the true expansion force within the system, leading to insufficient structural strength in the designed battery system and causing issues such as steel strip breakage and end plate cracking due to expansion. Technical issues

[0005] The technical problem to be solved by this application is that the cell expansion force tested in related technologies differs greatly from the actual tested and exhibited expansion force in the system, resulting in insufficient structural strength of the designed battery system and many defects such as steel strip breakage and end plate cracking due to expansion. This application provides a cell expansion force testing method, testing fixture, and testing system. Technical solutions

[0006] The technical solution adopted by this application to solve its technical problem is:

[0007] Firstly, a method for testing the expansion force of battery cells is provided, for testing the expansion force of battery cells in a battery module to be assembled into a battery system. The battery module includes multiple battery cells. The method includes:

[0008] Provide at least two test fixtures with different stiffnesses;

[0009] Multiple battery cells are divided into multiple units, and a unit includes one or multiple battery cells arranged in a continuous manner;

[0010] Based on the position of the unit in the battery module, a corresponding test fixture is assigned to the unit so that the unit closer to the center of the battery module is assigned a test fixture with higher rigidity.

[0011] After placing the battery cells in the unit into the test fixture assigned to the unit, the test is performed to obtain the cell expansion force.

[0012] In this application, the battery cells are not tested uniformly using test fixtures of uniform stiffness. Instead, the multiple cells of the battery module are divided into multiple units. During testing, a corresponding test fixture is assigned to each unit based on its position within the battery module. The allocation follows the principle that the closer the unit to the center of the battery module, the higher the stiffness of the assigned test fixture. In other words, this application uses at least two test fixtures, and the stiffness of the fixture is not fixed but related to the position of the assigned unit within the battery module. This allows the application to simulate the actual expansion force of the assembled battery system, ensuring consistency between the cell expansion force test results and the system's internal tests. This improves the accuracy of the system's expansion force design parameter input and ultimately ensures that the cell lifespan matches the system's lifespan. Furthermore, using cell testing to simulate system testing reduces system-level testing, improves testing efficiency, saves testing resources and materials, and reduces costs.

[0013] One possible implementation is to have an odd number of units, with the center of the innermost unit coinciding with the center of the battery module, and the other units symmetrically distributed in pairs on either side of the battery module center; alternatively, to have an even number of units, also symmetrically distributed in pairs on either side of the battery module center. Considering that within the same battery module, the forces acting on symmetrically arranged cells are essentially the same, based on the battery module center, the units can be divided symmetrically.

[0014] One possible implementation is to assign a corresponding test fixture to the unit, including: assigning the same test fixture to two units that are symmetrically distributed with each other; or assigning a separate test fixture to a unit if there are no other units distributed opposite to it.

[0015] This application takes into account that, with the center of the battery module as the reference, the forces on the symmetrical cells in the same battery module are basically the same. Therefore, symmetrical units can be assigned to the same test fixture, which can make full use of the test fixture.

[0016] As one possible implementation, the battery system includes a module frame for assembling battery modules, and the stiffness of one of the at least two test fixtures is also related to the stiffness of the module frame.

[0017] Assign corresponding test fixtures to the units, including: assigning test fixtures related to the stiffness of the module frame to the units located at both ends.

[0018] This application provides a test fixture with unit allocation at both ends related to the stiffness of the module frame. When the battery cell is clamped in the fixture, it is equivalent to simulating the scenario where the battery cells are bound by the module frame after the system is assembled. By fully simulating the real environment of the battery cells in the system, the accuracy of the test is improved.

[0019] As one possible implementation, the test fixture includes a cell placement slot for placing the cell and multiple clamps distributed at both ends of the cell placement slot;

[0020] In the test fixtures assigned to the units at both ends: the stiffness of the clamping plate located on the first side of the cell placement space is consistent with the stiffness of the clamping plate located on the second side of the cell placement space of the target test fixture; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame.

[0021] The target test fixture is the test fixture corresponding to the unit adjacent to the unit in the head.

[0022] This application is a cell allocation and module frame located at both ends. One end simulates the module frame environment, and the other end simulates the internal expansion force of the battery, which is more in line with the real environment of the battery cell, thereby ensuring the accuracy of the test results.

[0023] As one possible implementation, each test fixture, except for the test fixtures assigned to the units at both ends, satisfies:

[0024] The test fixture has multiple clamps with the same stiffness, which can ensure test accuracy and reduce costs; or, the clamp of the test fixture located on the first side of the cell setting space has greater stiffness than the clamp of the test fixture located on the second side of the cell setting space, which can more realistically simulate the different forces on both sides of the cell and improve test accuracy.

[0025] As one possible implementation, there are two test fixtures, with the first test fixture having less stiffness than the second test fixture; there are three units, with the center of the battery module falling into the middle unit.

[0026] Assigning corresponding test fixtures to units includes: assigning the first test fixture to units located at both ends, and assigning the second test fixture to units located in the middle.

[0027] This method is simple, low-cost, and can cover most testing needs while ensuring that the differences between the test results and the system tests are within a reasonable range.

[0028] As one possible implementation, the battery system includes a module frame for assembling battery modules, and the test fixture includes cell placement slots for placing battery cells and multiple clamps distributed at both ends of the cell placement slots.

[0029] In the first test fixture, the stiffness of the clamping plate located on the first side of the cell placement space is consistent with the stiffness of the second test fixture; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame.

[0030] The second test fixture has multiple clamps with consistent stiffness, which is greater than that of the module frame.

[0031] As one possible implementation, the method also includes applying a preload force to both sides of the battery cell after placing it in the test fixture.

[0032] As one possible implementation, the battery module also includes multiple buffer structures, with one buffer structure distributed on each side of each cell; the buffer structure is configured for the cell when it is placed in the test fixture;

[0033] If the thickness of the buffer structure of the battery system is determined, a pre-tightening force is applied to both sides of the battery cell, including: using the sum of the thicknesses of N battery cells and N buffer structures after the battery system is assembled as the expansion force clamping distance, adjusting the clamping distance of the test fixture to the expansion force clamping distance, thereby applying the pre-tightening force; where N is the number of battery cells currently placed in the test fixture.

[0034] This application incorporates a buffer structure between actual battery cells and also includes a buffer structure for the battery cells in the fixture to simulate the real environment of the battery cells under test and improve measurement accuracy.

[0035] As one possible implementation, the battery module also includes multiple buffer structures, with one buffer structure distributed on each side of each cell; the buffer structure is configured for the cell when it is placed in the test fixture;

[0036] If the buffer structure of the battery system is not determined, a preload force is applied to both sides of the cell, including: applying the preload force according to the initial value set by the test fixture; if the preset standard is not met, the preload force is adjusted until the preset standard is met.

[0037] The preset standards include: after each application of preload, the test fixture should allow a preset time for rest, and the stress change reported by the fixture should be less than the set value.

[0038] This application allows for cell testing even before the system design is complete, particularly when the buffer structure is undetermined. The test results can be fed back to the system design for optimization.

[0039] One possible implementation involves placing the cells in the unit into the test fixture assigned to the unit and then performing a test to obtain the cell expansion force. This includes: placing the cells in the unit into the test fixture all at once and then performing a test to obtain the cell expansion force; or placing the cells in the unit into the test fixture in multiple batches and performing a test in each batch to obtain the cell expansion force, with each batch including at least one cell.

[0040] After dividing the application into units, it is possible to test the entire unit or to take one or more cells from the unit for testing, which fully ensures the accuracy of the test. It is also possible to take different numbers of cells for testing, which can cross-verify the accuracy of the test.

[0041] As one possible implementation, the method also includes:

[0042] Configure the initial state of charge of the cells held in the test fixture to be consistent with the initial state of charge of the cells after the battery system is assembled.

[0043] The initial state of charge affects the cell thickness; therefore, ensuring a consistent initial state of charge ensures consistency with the testing conditions within the system.

[0044] As one possible implementation, the method also includes:

[0045] Based on the environment in which the reference cells are located after the battery system is assembled, the corresponding environment is configured for the cells placed in the test fixture to simulate the environment in which the cells are located after the battery system is assembled.

[0046] As one possible implementation, configuring the appropriate environment for the battery cell placed in the test fixture includes:

[0047] When placing the battery cell into the test fixture, a buffer structure is configured for the battery cell. The stress-strain curve of the buffer structure configured for the battery cell is consistent with that of the buffer structure configured for the battery cell after the battery system is assembled.

[0048] In this way, the change in the force exerted on the battery when the environmental conditions of the cell affect the thickness of the buffer structure can be simulated.

[0049] In its simplest form, the material of the buffer structure configured for the battery cell in the test fixture is the same as the material of the buffer structure configured for the battery cell after the battery system is assembled. Therefore, as one possible implementation, the material of the buffer structure configured for the battery cell in the test fixture is the same as the material of the buffer structure configured for the battery cell after the battery system is assembled.

[0050] Of course, the buffer structure in the test fixture can also be changed to be on both sides of the cell. Therefore, as a possible implementation, the buffer structure is configured for the cell, including: configuring a buffer structure on one side of the cell in the test fixture, and the thickness of the configured buffer structure is consistent with the thickness of the buffer structure configured for the cell after the battery system is assembled; or, configuring buffer structures on both sides of the cell in the test fixture, and the sum of the thicknesses of the buffer structures on both sides is consistent with the thickness of the buffer structure configured for the cell after the battery system is assembled.

[0051] As one possible implementation, the appropriate environment is configured for the battery cell placed in the test fixture, including any one or any combination of the following:

[0052] Place the test fixture holding the battery cell into the temperature chamber. Referencing the highest temperature of the battery cell during the charging process after the battery system is assembled, adjust the temperature chamber temperature so that the highest temperature of the battery cell in the test fixture during the charging process is consistent with the highest temperature during the charging process after the battery system is assembled.

[0053] Thermal insulation material is placed on the outside of the test fixture;

[0054] A cold plate may be placed on top of the battery cell in the test fixture, or on the bottom of the battery cell, or both the top and bottom of the battery cell may be placed on the cold plate.

[0055] As one possible implementation, the method also includes using a charge / discharge strategy that is consistent with the charge / discharge strategy after the battery system is assembled.

[0056] When the battery cell is clamped in the fixture, the present application is equipped with a buffer structure, temperature chamber, cold plate, insulation material, etc., and the charging and discharging strategy is consistent with the test in the system, which fully simulates the real environment of the battery cell in the system and improves the accuracy of the test.

[0057] Secondly, a test fixture is provided for use in the method of this application; the stiffness of the test fixture is related to the position of the assigned unit in the battery module: the closer the assigned unit is to the center of the battery module, the higher the stiffness of the test fixture.

[0058] As one possible implementation, the battery system includes a module frame for assembling battery modules, and a test fixture includes cell placement slots for placing battery cells and multiple clamps distributed at both ends of the cell placement slots, wherein:

[0059] The stiffness of multiple clamps is related to the position of the unit assigned to the test fixture in the battery module;

[0060] Alternatively, the stiffness of the clamping plate located on the first side of the cell placement space is related to the position of the cell assigned to the test fixture in the battery module; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame.

[0061] As one possible implementation, the multiple clamping plates include a back plate, an intermediate clamping detection plate, and a front plate, all of which are vertically arranged and sequentially arranged along a first direction. The back plate and the front plate are connected by a guide shaft extending along the first direction, and the guide shaft moves through the intermediate clamping detection plate. A drive mechanism for pushing the intermediate clamping detection plate to move along the guide shaft is installed on the front plate.

[0062] A cell placement space is formed between the intermediate clamping detection plate and the back plate. After the cell is placed in the cell placement space, the thickness direction of the cell is parallel to the first direction.

[0063] As one possible implementation, it also includes any or any combination of the following: connecting rod, support plate;

[0064] The back panel and the front panel are positioned opposite each other along the first direction, and their four corners are connected by guide shafts.

[0065] The tray connects the back plate and the front plate and is located at the bottom of the cell placement space;

[0066] The connecting rod connects the back plate and the front plate and is located at the top of the cell mounting space.

[0067] As one possible implementation, the first end face of the tray is locked to the side of the back plate facing the centrally clamped detection plate in a first direction, and the second end face of the tray is locked to the side of the front plate facing the centrally clamped detection plate in a first direction.

[0068] As one possible implementation, the top edge of the back panel protrudes upward near the center to form a first flange, the top edge of the front panel protrudes upward near the center to form a second flange, and at least one connecting rod is connected between the first flange and the second flange.

[0069] As one possible implementation, the intermediate clamping detection plate includes a clamping plate and a pressure plate, the clamping plate and the pressure plate are connected and a sensor is installed between them.

[0070] As one possible implementation, the stiffness of the clamping plate and the pressure plate is consistent with the stiffness of the front plate;

[0071] Wherein: the stiffness of the clamping plate is the same as that of the back plate; or, the stiffness of the back plate is less than that of the clamping plate.

[0072] As one possible implementation, the stiffness of the backplate is consistent with the stiffness of the module frame.

[0073] As one possible implementation, the drive mechanism includes a drive rod threaded to the front plate for applying a preload, and a pressure head for contacting and pushing the intermediate clamping detection plate; the drive rod passes through the front plate in a first direction and is connected to the pressure head.

[0074] As one possible implementation, the front plate has a sleeve on the side opposite to the middle clamping detection plate, through which the drive rod passes and is threadedly engaged.

[0075] As one possible implementation, a positioning through hole is provided on the sleeve, and a positioning groove is provided on the drive rod, wherein at least one of the positioning holes and positioning grooves is provided in multiple quantities;

[0076] After the drive rod is preloaded, it is locked to the rod sleeve by the limiting component, so that the drive rod cannot rotate. The limiting component is inserted into the positioning through hole and positioning groove that are closest to each other.

[0077] As one possible implementation, the test fixture also includes a locking nut mounted on the drive rod and located on the side opposite to the front plate, for reverse locking after the drive rod is preloaded, thereby preventing the drive rod from rotating.

[0078] Thirdly, a testing system is provided, comprising a test execution system and at least two test fixtures with different stiffnesses, wherein the test execution system is used to electrically connect to the battery cells in the test fixtures and perform an expansion force test on the battery.

[0079] The beneficial effects of the second and third aspects described above can be referred to the first aspect or any possible implementation of the first aspect, and will not be elaborated here. Based on the implementations provided in the above aspects, this application can also combine them to provide more implementations. Beneficial effects

[0080] The cell expansion force testing method, fixture, and system provided in this application do not utilize uniform fixtures with the same stiffness for testing. Instead, they divide the multiple cells of a battery module into multiple units. During testing, a corresponding test fixture is assigned to each unit based on its position within the battery module. The allocation follows the principle that the closer the assigned unit is to the center of the battery module, the higher the stiffness of the assigned fixture. In other words, this application uses at least two test fixtures, and the stiffness of the fixture is not fixed but related to the position of the assigned unit within the battery module. This allows the application to simulate the actual expansion force of the assembled battery system, ensuring consistency between the cell expansion force test results and the system's internal testing, improving the accuracy of the system's expansion force resistance design parameter input, and ultimately ensuring that the cell lifespan matches the system's lifespan. Furthermore, using cell testing to simulate system testing reduces system-level testing, improves testing efficiency, saves testing resources and materials, and reduces costs. Attached Figure Description

[0081] Figure 1 is a schematic diagram of the structure of the test fixture in one of the embodiments of this application;

[0082] Figure 2 is a second schematic diagram of the structure of the test fixture in the embodiment of this application;

[0083] Figure 3 is a third schematic diagram of the test fixture in the embodiments of this application;

[0084] Figure 4 is a fourth schematic diagram of the test fixture in the embodiments of this application;

[0085] Figure 5 is a simulated stress cloud diagram of long cell expansion in an embodiment of this application;

[0086] Figure 6 is a schematic diagram of the unit division;

[0087] Figure 7 is a schematic diagram of assigning 3 sets of fixtures to 6 units;

[0088] Figure 8 is a flowchart of the cell expansion force testing method provided in an embodiment of this application;

[0089] Figure 9 shows the cycle life test results;

[0090] Explanation of icon numbers:

[0091] 1. Battery cell; 2. Backplate; 3. Guide shaft; 4. Support plate; 5. Clamping plate; 6. Sensor; 7. Pressure plate; 8. Connecting rod; 9. Front plate; 10. Drive rod; 11. Rod sleeve; 12. Pressure head; 10-1 position component; 13. Crowbar; 14. Locking nut. Embodiments of the present invention

[0092] To address the significant discrepancy between the cell expansion force measured by related technologies and the actual expansion force observed within the system, leading to insufficient structural strength in the designed battery system and numerous defects such as steel strip breakage and end plate cracking due to expansion, this application provides a method, test fixture, and test system for testing cell expansion force. This application provides at least two test fixtures with different stiffnesses; it divides multiple cells into multiple units, each unit comprising one or multiple cells arranged consecutively; based on the unit's position within the battery module, it assigns a corresponding test fixture, ensuring that units closer to the center of the battery module receive test fixtures with higher stiffness—that is, the stiffness of the test fixture assigned to a unit is negatively correlated with the distance of the unit from the center of the battery module; after placing the cell in the assigned test fixture, the cell expansion force is obtained through testing. Thus, this application can simulate the actual expansion force of the battery system after assembly, ensuring that the expansion force test results of the cells are consistent with those of the system tests, improving the accuracy of the system expansion force resistance design parameter input, and ultimately ensuring that the cell lifespan is consistent with the system lifespan. Moreover, using cell testing to equivalently test the system can also reduce system-level testing, improve testing efficiency, save testing resources and materials, and reduce costs.

[0093] The terminology used in the implementation section of this application is only for explaining specific embodiments of this application and is not intended to limit this application. A brief introduction to some concepts that may be involved in this application is given below.

[0094] System assembly: refers to the final actual assembly of the battery system.

[0095] In-system testing: refers to the expansion force test performed on the batteries after the battery system is assembled.

[0096] Battery module: consists of multiple battery cells;

[0097] Module frame: refers to the structure for mounting battery modules, which binds and fixes the cells arranged in the battery module together. It includes end plates and side plates. The end plates and side plates are set along the direction of cell arrangement. The end plates and side plates are generally perpendicular to each other, and the cells at both ends face the end plates.

[0098] Consistent stiffness: refers to stiffness differences that are within the error range.

[0099] This application discloses a method for testing the cell expansion force of battery cells, which is used to test the cell expansion force of battery cells to be assembled into a battery system. This method can be performed before the battery system is assembled, for example, after the battery system design simulation is completed or during the design simulation process. It should be noted that this method requires at least two test fixtures, the main difference between which is their stiffness. The specific structure of the test fixtures is not limited; existing fixture structures can be used. This application only needs to set the material stiffness of the fixtures for use in its method. To better understand this method, the test fixtures of this application are described below.

[0100] Referring to Figures 1-3, Figures 1 and 2 show two examples of the fixture, while Figures 2 and 3 show different perspectives of the same fixture example; Figure 2 is a top-down view, and Figure 3 is a bottom-up view. The function of the test fixture in this application is to clamp the battery cells and apply preload. The battery cells assembled in the test fixture can then be used for subsequent testing. Considering that the cells at different locations in the battery module experience different compressive forces after the battery system is assembled (e.g., the closer to the center of the battery module, the higher the compressive force), this application divides the battery module into multiple units. At least two test fixtures with different stiffnesses are assigned to each unit in the battery module (each unit includes one or multiple consecutively arranged battery cells). The stiffness of the test fixture is related to the position of the assigned unit within the battery module; the closer the assigned unit is to the center of the battery module, the higher the stiffness of the test fixture. This will be explained in detail in subsequent method embodiments.

[0101] Since battery modules are assembled using a module frame in a battery system, the cells located at both ends of the battery module will contact the module frame and be subjected to forces applied by the module frame. Therefore, in order to simulate the actual stress conditions after the battery system is assembled as much as possible, in some embodiments, the stiffness of the corresponding test fixture for the cells located at both ends of the battery module is related not only to the assigned cell position but also to the stiffness of the module frame.

[0102] Referring again to Figure 1-3, the test fixture includes cell placement slots for placing battery cells and multiple clamping plates distributed at both ends of the cell placement slots. The rigidity of the test fixture is mainly reflected in the rigidity of the clamping plates. If the unit assigned to the test fixture is not one of the two ends, the rigidity of the multiple clamping plates is related to the position of the unit assigned to the test fixture within the battery module. If the unit assigned to the test fixture is one of the two ends, the rigidity of the clamping plate located on the first side of the cell placement slot is related to the position of the unit assigned to the test fixture within the battery module; the rigidity of the clamping plate located on the second side of the cell placement slot is related to the rigidity of the module frame.

[0103] In some embodiments, the plurality of clamping plates includes a back plate 2, an intermediate clamping detection plate, and a front plate 9. The back plate 2, the intermediate clamping detection plate, and the front plate 9 are all vertically arranged and sequentially arranged along a first direction. The back plate 2 and the front plate 9 are generally rectangular plates, facing each other, and connected by at least one guide shaft 3 extending along the first direction, with the guide shaft 3 movably passing through the intermediate clamping detection plate. In some embodiments, the back plate 2 and the front plate 9 are facing each other along the first direction, and their four corners are connected by guide shafts 3 respectively. A drive mechanism for pushing the intermediate clamping detection plate to move along the guide shafts 3 is mounted on the front plate 9.

[0104] A cell placement space is formed between the intermediate clamping detection plate and the back plate 2. After the cell is placed in the cell placement space, the thickness direction of the cell is parallel to the first direction, that is, the dimension of the cell along the first direction after being placed in the cell placement space is the thickness dimension. By driving the intermediate clamping detection plate to move closer to the back plate 2 through the drive mechanism, the cell to be tested placed in the cell placement space can be clamped, and a preload force can be applied to the cell to be tested.

[0105] In some embodiments, the guide shaft 3 is axially (the axial direction is parallel to the first direction) threadedly connected to the back plate 2 and the front plate 9, and there are circular holes of the same diameter as the guide shaft 3 on the intermediate clamping detection plate to ensure that the four guide shafts 3 are parallel, thereby ensuring that the drive mechanism drives the intermediate clamping detection plate to slide smoothly on the guide shaft 3 without jamming.

[0106] In some embodiments, the intermediate clamping detection plate includes a clamping plate 5 and a pressure plate 7. The clamping plate 5 and the pressure plate 7 are generally rectangular plates. The clamping plate 5 and the pressure plate 7 are connected and a sensor 6 is installed between them. The sensor 6 can detect the preload applied to the battery cell by the pressure plate 7.

[0107] In some embodiments, the drive mechanism includes a drive rod 10 threadedly connected to the front plate 9 for applying a preload, and a pressure head 12 for contacting and pushing the pressure plate 7 in the intermediate clamping detection plate. The pressure head 12 may or may not be connected to the pressure plate 7. The drive rod 10 passes through the center of the front plate 9 along a first direction and connects to the pressure head 12. The shape and material of the pressure head 12 are not limited, as long as it can achieve rigid contact with the pressure plate 7 and transmit thrust. For example, the pressure head 12 may be funnel-shaped, facing the pressure plate 7, to facilitate a steady pushing of the pressure plate 7.

[0108] In some embodiments, a rod sleeve 11 is located at the center of the side of the front plate 9 away from the intermediate clamping detection plate. The rod sleeve 11 is fixedly connected to the front plate 9 or integrally formed therein. The drive rod 10 passes through the rod sleeve 11 and is threadedly engaged with it. To facilitate rotation of the drive rod 10, a pry bar 13 is also connected to the end of the drive rod 10 away from the front plate 9. The pry bar 13 and the drive rod 10 form an angle with each other, which facilitates rotation of the drive rod 10 by the pry bar 13.

[0109] Due to the threaded connection between the drive rod 10 and the sleeve 11, rotating the pry bar 13 will drive the pressure head 12 to apply preload to the pressure plate 7, clamping plate 5, and sensor 6. The preload is controlled by reading the value from sensor 6 during the application of preload by the drive rod 10.

[0110] Because the cell expansion force test cycle is long, and the expansion force always changes approximately periodically with charging and discharging, there is a possibility that the threaded fit between the drive rod 10 and the sleeve 11 may experience untwisting, leading to a loss of cell preload and affecting the test. Therefore:

[0111] To prevent twisting, referring to Figure 2, in some embodiments, the sleeve 11 has a positioning through hole, and the drive rod 10 has a positioning groove. At least one of the positioning holes and positioning grooves is multiple; for example, there may be one positioning hole and multiple positioning grooves, or multiple positioning holes and one positioning groove, or multiple positioning holes and multiple positioning grooves. After the drive rod 10 is preloaded, it is locked to the sleeve 11 by a limiting member 10-1, thus preventing the drive rod 10 from rotating. The limiting member 10-1 can be a pin, inserted into the closest positioning through hole and positioning groove.

[0112] To prevent torque slippage, referring to Figure 4, in some embodiments, the test fixture further includes a locking nut 14 mounted on the drive rod 10 and located on the side opposite to the front plate 9. This nut is used to lock the drive rod 10 in the reverse direction after a preload is applied, thus preventing the drive rod 10 from rotating. In this way, at the start of the test, the locking nut 14 is tightly locked against the drive rod 10 on the inside, thus preventing loosening and torque slippage.

[0113] As shown in Figures 1-3, the battery cell releases expansion force to both sides. One side consists of a pre-tensioning structure including a clamping plate 5, a sensor 6, and a drive rod 10, while the other side is a back plate 2. This structure simulates the environment of the battery cell within a battery module. Therefore, the test fixture structure of this application has low stability risk, high flexibility, and is closer to real-world conditions.

[0114] It is understood that the test fixture of this application is not limited to testing a single cell. If more cells are to be expanded, the length of the guide shaft 3 and the drive rod 10 can be adjusted to meet the testing requirements.

[0115] Due to the diverse requirements of various automotive types for onboard battery packs, longer batteries have emerged, necessitating the corresponding adjustment of battery cells to longer lengths. Because of their longer structure, these longer cells experience more pronounced expansion in the middle during charge / discharge cycles. If traditional expansion force testing fixtures are used, the backplate 2 will also be lengthened to accommodate the longer cell, resulting in a longer distance between the guide shafts 3 on both sides of the backplate 2. This creates a simply supported beam structure with reduced stiffness. In this case, the larger expansion in the middle of the long cell is largely absorbed by the deformation of the backplate 2, leading to a significant deviation between the measured expansion force and the actual force. As shown in Figure 5, finite element analysis software simulations of cell expansion demonstrate that the expansion force in the middle of the long cell is particularly pronounced. Therefore, the backplate 2 may deform significantly during testing, causing a substantial deviation in the expansion force measured by the sensor 6.

[0116] To address the aforementioned drawback of potentially severe deviations in the expansion force testing of long battery cells, referring to Figure 3, in some embodiments, the test fixture further includes a tray 4. The tray 4 is horizontally positioned and perpendicular to the back plate 2 and the front plate 9. The tray 4 connects the back plate 2 and the front plate 9 and is located at the bottom of the battery cell placement space. When the battery cell to be tested is placed in the battery cell placement space, it rests on the tray 4. In some embodiments, the tray 4 is positioned near the middle of the bottom of the back plate 2 and the front plate 9.

[0117] Referring to Figure 1, in some embodiments, the bottom edge of the back plate 2 is vertically locked to the surface of the support plate 4 near the first end face, and the bottom edge of the front plate 9 is vertically locked to the surface of the support plate 4 near the second end face. That is, the back plate 2 and the front plate 9 are situated on the surface of the support plate 4. The locking method can be, but is not limited to, using bolts, for example, by screwing bolts from bottom to top through the support plate 4 and into the bottom edges of the back plate 2 and the front plate 9.

[0118] Referring to Figures 2-3, in some embodiments, the first end face of the support plate 4 is locked to the side of the back plate 2 facing the centrally clamped detection plate along a first direction, and the second end face of the support plate 4 is locked to the side of the front plate 9 facing the centrally clamped detection plate along a first direction. That is, the support plate 4 is clamped between the back plate 2 and the front plate 9. The locking method can be, but is not limited to, using bolts. For example, assuming the first direction is left-right, and the front plate 9 is on the left side of the back plate 2, bolts are used to pass through the front plate 9 from left to right and screwed into the first end face of the support plate 4, and bolts are used to pass through the front plate 9 from right to left and screwed into the second end face of the support plate 4. Compared to the vertical bottom-up locking in the example of Figure 1, the axial (parallel to the first direction) locking in the example of Figure 2 uses the preload of the bolt connection itself to pull the back plate 2 and the front plate 9, thereby compensating for the weakening of the rigidity of the back plate 2 in the lower middle region.

[0119] To address the significant deviation in the expansion force test of long battery cells, referring to Figures 2-3, in some embodiments, the test fixture further includes connecting rods 8. Connecting rods 8 connect the back plate 2 and the front plate 9, and are located at the top of the empty space where the battery cell is installed. The number of connecting rods 8 is not limited; Figure 2 illustrates two. The two connecting rods 8 are connected between the top center of the back plate 2 and the top center of the front plate 9, and are fixed by bolts. The bolt connection is axially locked, the purpose of which is to use the preload of the bolt connection itself to pull the back plate 2 and the front plate 9 together, thereby compensating for the reduced stiffness of the back plate 2 in the upper middle region. Here, there are no circular holes of the same diameter as the connecting rods 8 in the back plate 2 and the front plate 9 to avoid interference during installation. The reason for choosing to connect the rods 8 to the top of the back plate 2 and the front plate 9, rather than a plate connection, is to leave space for the operation and wiring of the sensor 6 and the battery cell 1.

[0120] In some embodiments, the top edge of the back plate 2 protrudes upward near the center to form a first flange, as shown in Figures 2-3 where the top of the back plate 2 is convex; the top edge of the front plate 9 protrudes upward near the center to form a second flange, as shown in Figure 3 where the top of the front plate 9 is convex. At least one connecting rod 8 is connected between the first flange and the second flange to avoid interference during installation.

[0121] To more realistically simulate the stress on the cells after the battery system is assembled, the materials of the back plate 2, clamping plate 5, pressure plate 7, and front plate 9 of the test fixture can be determined according to the battery module in which the cell is located, so as to make the test more realistic.

[0122] For example, for the cells at both ends of the battery module, in the corresponding test fixture: the stiffness of the back plate 2 is less than the stiffness of the clamping plate 5, and the stiffness of the back plate 2 is consistent with the stiffness of the module frame.

[0123] For example, for cells that are not located at either end of the battery module, the stiffness of the front plate 9 and the back plate 2 in the corresponding test fixture can be the same, or the stiffness of the back plate 2 can be less than the stiffness of the clamping plate 5. The specific stiffness depends on the assigned cell position, which will be explained in subsequent method embodiments.

[0124] The stiffness of the clamping plate 5 and the pressure plate 7 is the same as that of the front plate 9.

[0125] The testing methods for this application are described below.

[0126] Referring to Figure 8, in some embodiments, the method for testing cell expansion force includes:

[0127] S101: Provide at least two test fixtures with different stiffnesses;

[0128] The test fixtures can be found in the test fixture examples section above, and will not be repeated here. In most scenarios, providing two test fixtures is sufficient. If more refined testing is required, more test fixtures can be provided.

[0129] It should be noted that the term "provided" here means that these fixtures are available during testing, or that they are prepared for testing.

[0130] S102: Divide multiple battery cells into multiple units, each unit comprising one or multiple battery cells arranged in a continuous sequence.

[0131] The specific scheme for dividing multiple battery cells into multiple units is not limited, as long as the battery cells in the divided units are arranged continuously in the battery module, they are all within the protection scope of this application. For example, starting from the first battery cell, the required number of battery cells can be used as the first unit, and then the required number of battery cells can be used as the second unit, and so on, until all battery cells have been divided.

[0132] The number of cells assigned to a unit is not limited. It can be uniform, for example, in the partitioning scheme of Figure 6(a), the number of cells in units A11, A12, and A13 is 4 each; and in the partitioning scheme of Figure 6(b), the number of cells in units A21, A22, A23, and A24 is 3 each. It can also be non-uniform, for example, in the partitioning scheme of Figure 6(c), the number of cells in units A31, A32, and A33 is 3, 6, and 3 respectively; and in the partitioning scheme of Figure 6(d), the number of cells in units A41, A42, and A43 is 2, 7, and 3 respectively. Therefore, the partitioning of multiple units can result in various scenarios: for example, all units may have the same number of cells, some units may have the same number of cells, or all units may have different numbers of cells.

[0133] In some embodiments, the number of units is odd, with the center of the middle unit coinciding with the center of the battery module, and the other units symmetrically distributed in pairs on both sides of the center of the battery module. In some embodiments, the number of units is even, and they are symmetrically distributed in pairs on both sides of the center of the battery module. This is because, within the same battery module, the forces acting on symmetrical cells are essentially the same with respect to the center of the battery module, so symmetrical units can be assigned to the same test fixture, thus making full use of the test fixture.

[0134] Symmetrical distribution refers to two units where not only are the number of cells in each unit the same, but the distance from each cell in one unit to the center of the battery module is also the same as the distance from each cell in the other unit to the center of the battery module. For example, in scheme (a) of Figure 6, A11 and A13 are symmetrically distributed, each with 4 cells, and the distances from cells 1, 2, 3, and 4 to the center of the battery module are the same as the distances from cells 12, 11, 10, and 9 to the center of the battery module; in scheme (b) of Figure 6, A21 and A24 are symmetrically distributed, and A22 and A23 are symmetrically distributed; in scheme (c) of Figure 6, A31 and A33 are symmetrically distributed.

[0135] S103: Based on the position of the unit in the battery module, assign the corresponding test fixture to the unit so that the unit closer to the center of the battery module is assigned a test fixture with higher rigidity.

[0136] The number of cells is greater than or equal to the number of test fixtures. In some embodiments, if two cells are symmetrically distributed about the center of the battery module, the same test fixture is assigned to the two symmetrically distributed cells. If a cell does not have a symmetrical counterpart, a separate test fixture is assigned to it.

[0137] Taking Figure 6 as an example, for instance, in scheme (a) of Figure 6, A11 and A13 are symmetrically distributed, and A11 and A13 are assigned to the same test fixture T11; A12 is assigned to a separate test fixture T12, as shown in Table 1 below:

[0138]

[0139] For example, in scheme (b) of Figure 6, A21 and A24 are symmetrically distributed, so A21 and A24 are assigned to the same test fixture T21. A22 and A23 are symmetrically distributed, so A22 and A23 are assigned to the same test fixture T21, as shown in Table 2 below:

[0140]

[0141] For example, in scheme (c) of Figure 6, A31 and A33 are symmetrically distributed. Therefore, A31 and A33 are assigned to the same test fixture T31, while A32 is assigned to a separate test fixture T32, as shown in Table 3 below:

[0142]

[0143] For example, in scheme (d) of Figure 6, there is no symmetrical distribution between the units. Therefore, A41, A42, and A43 are each assigned test fixtures T41, T42, and T43, as shown in Table 4 below:

[0144]

[0145] Because the closer a unit is to the center of the battery module, the higher the stiffness of the test fixture it is assigned to, which means that: (a) in the scheme, the stiffness of test fixture T11 is less than that of test fixture T12; (b) in the scheme, the stiffness of test fixture T21 is less than that of test fixture T22; (c) in the scheme, the stiffness of test fixture T31 is less than that of test fixture T32; (d) in the scheme, the stiffness of test fixture T41 is less than that of test fixture T42, and the stiffness of test fixture T43 is less than that of test fixture T42.

[0146] In conjunction with the test fixture embodiment section, the rigidity of the test fixture is mainly reflected in the rigidity of the clamping plates, primarily the rigidity of the back plate 2 and the clamping plate 5. The rigidity of the clamping plate 5 and the pressure plate 7 is consistent with the rigidity of the front plate 9.

[0147] In some embodiments, for units that are not at both ends, the stiffness of the clamping plates of their corresponding test fixtures is consistent and related to the position of the unit assigned to the test fixture in the battery module. For example, in the test fixture for non-two-end units, the stiffness of the clamping plate 5 is consistent with the stiffness of the back plate 2. For example, in the fixtures T12, T22, T32, and T42 in Table 1-4, the stiffness of the back plate 2, clamping plate 5, pressure plate 7, and front plate 9 inside each fixture is consistent and is high stiffness. The specific stiffness value can be set according to experience or simulation data. The closer to the center of the battery module, the higher the stiffness. For example, referring to Figure 7, which illustrates the case where 3 sets of fixtures are needed, the stiffness of the back plate 2, clamping plate 5, pressure plate 7, and front plate 9 of fixture T52 is consistent at S1, and the stiffness of the back plate 2, clamping plate 5, pressure plate 7, and front plate 9 of fixture T53 is consistent at S2. Then S1 is less than S2 because fixture T53 is closer to the center of the battery module.

[0148] In some embodiments, for units that are not at both ends, the clamping plates of the corresponding test fixtures can have a stiffness greater than that of the clamping plates located on the first side of the cell placement space, for example, the stiffness of the back plate 2 is less than that of the clamping plate 5. Therefore, when placing the cell, the side of the cell closest to the center of the battery module should face the clamping plate 5, and the side facing away from the center of the battery module should face the back plate 2. The stiffness value can be set based on experience or simulation data. For example, in fixtures T12, T22, T32, and T42, the stiffness of the back plate 2 inside each fixture is less than the stiffness of the clamping plate 5, pressure plate 7, and front plate 9 inside each fixture.

[0149] Since the cells located at both ends come into contact with and are subjected to force by the module frame of the battery system's battery module assembly, the stiffness of at least one of the two test fixtures is also related to the stiffness of the module frame. Accordingly, when assigning corresponding test fixtures to the cells, test fixtures related to the stiffness of the module frame are assigned to the cells located at both ends. For example, the stiffness of test fixture T11 in scheme (a) of Figure 6, test fixture T21 in scheme (b) of Figure 6, test fixture T31 in scheme (c) of Figure 6, and test fixtures T41 and T43 in scheme (d) of Figure 6 are all related to the stiffness of the module frame. Specifically, referring to the test fixture embodiment section, the test fixtures assigned to the cells at both ends include:

[0150] (1) The stiffness of the clamping plate located on the first side of the cell placement space is consistent with the stiffness of the clamping plate located on the second side of the cell placement space of the target test fixture. The target test fixture is the test fixture corresponding to the unit adjacent to the head unit. For example, the stiffness of the clamping plate 5 of T11 is consistent with the stiffness of the back plate 2 of T12, the stiffness of the clamping plate 5 of T21 is consistent with the stiffness of the back plate 2 of T22, the stiffness of the clamping plate 5 of T31 is consistent with the stiffness of the back plate 2 of T32, the stiffness of the clamping plate 5 of T41 is consistent with the stiffness of the back plate 2 of T42, and the stiffness of the clamping plate 5 of T43 is consistent with the stiffness of the back plate 2 of T42.

[0151] (2) The stiffness of the clamping plate located on the second side of the cell setting space is related to the stiffness of the module frame. For example, the stiffness of the back plate 2 of T11, T21, T31, and T41 is consistent with the stiffness of the module frame, specifically the stiffness of the module frame end plate.

[0152] In most scenarios, the battery module is divided into three units, with the center of the battery module falling into the middle unit. Two test fixtures are sufficient. The two test fixtures represent the strongest and weakest points of stiffness within the system, respectively, and are typically designed with the stiffness of the center and end positions selected. For example, in some embodiments, the stiffness of the first test fixture (end fixture) is less than the stiffness of the second test fixture (middle fixture). In this case, corresponding test fixtures are assigned to the units, including: end fixtures for units at both ends and middle fixtures for units in the middle.

[0153] In the intermediate fixture, the stiffness of multiple clamping plates (back plate 2, clamping plate 5) is consistent and greater than that of the module frame. The stiffness of the intermediate fixture satisfies the requirement that the expansion displacement be ≤0.1mm under a stress of 3MPa.

[0154] In the end clamp, the stiffness of the clamping plate (clamping plate 5) located on the first side of the cell placement space is consistent with the stiffness of the intermediate clamp; the stiffness of the clamping plate (back plate 2) located on the second side of the cell placement space is related to the stiffness of the module frame. For example, the back plate 2 is made of the same material and thickness as the end plate of the module frame. In this way, the stiffness of the back plate 2 of the end clamp is the same as that of the end plate of the module frame, which can simulate the actual stress of the end cell.

[0155] S104: After placing the battery cell in the unit into the test fixture assigned to the unit, perform the test to obtain the battery cell expansion force.

[0156] In some embodiments, the battery cells in the unit can be placed into the test fixture all at once and then the test can be performed to obtain the cell expansion force. For example, the four battery cells of unit A11 in Figure 6 can be placed into fixture T11 all at once.

[0157] In some embodiments, the battery cells in the unit are placed into the test fixture in multiple batches, and the battery cell expansion force is obtained by performing tests in batches. Each batch includes at least one battery cell. For example, the four battery cells in unit A11 in Figure 6 can be tested in four batches. First, battery cell 1 is placed in fixture T11 for testing, then battery cell 2 is placed in fixture T11 for testing, and so on. Alternatively, battery cells 1 and 2 can be placed in fixture T11 for testing first, and then battery cells 3 and 4 can be placed in fixture T11 for testing. Or, battery cell 1 can be placed in fixture T11 for testing first, then battery cells 2 and 3 can be placed in fixture T11 for testing, and then battery cell 4 can be placed in fixture T11 for testing.

[0158] It should be noted that it is not necessary to test all battery cells. You can select representative cells for testing as needed.

[0159] Because the initial state of charge (SOC) affects cell thickness, in some embodiments, the method further includes configuring the initial SOC of the cells held in the test fixture to be consistent with the initial SOC of the cells after the battery system is assembled. Other indicators meet the incoming material requirements for system assembly.

[0160] In some embodiments, the method further includes: configuring a corresponding environment for the cells placed in the test fixture, based on the environment in which the cells are located after the battery system is assembled, to simulate the environment in which the cells are located after the battery system is assembled. The aim is to ensure that the average temperature during charging, the average temperature during discharging, and the maximum temperature remain consistent with those within the system. Therefore, configuring a corresponding environment for the cells placed in the test fixture can be achieved primarily through the following aspects:

[0161] 1) When placing the battery cell into the test fixture, a buffer structure is configured for the battery cell. The stress-strain curve (compression curve) of the buffer structure configured for the battery cell is consistent with that of the buffer structure configured for the battery cell after the battery system is assembled. The consistency of the stress-strain curve means that the amount of deformation is the same when subjected to the same force.

[0162] In the simplest case, the material of the buffer structure configured for the battery cell in the test fixture is the same as the material of the buffer structure configured for the battery cell after the battery system is assembled.

[0163] After the battery system is assembled, each cell in the battery module has a buffer structure distributed on both sides. Therefore, this application configures the buffer structure for the cell when placing it into the fixture, including two methods:

[0164] Method 1: Maintain consistency with the specifications used in the system, configure a buffer structure on one side of the cell in the test fixture, and the thickness of the configured buffer structure is consistent with the thickness of the buffer structure configured for the cell after the battery system is assembled. Typically, one cell corresponds to one piece of buffer material.

[0165] Method 2: Configure buffer structures on both sides of the battery cell in the test fixture, and ensure that the sum of the thicknesses of the buffer structures on both sides is consistent with the thickness of the buffer structures configured for the battery cell after the battery system is assembled. For example, use materials with half the thickness on both sides of the battery cell, but ensure that the stress-strain curve of the halved buffer material is consistent with that of the buffer material in the system.

[0166] 2) Place the test fixture holding the battery cell into the temperature chamber. Refer to the highest temperature of the battery cell during the charging process after the battery system is assembled, and adjust the temperature chamber temperature so that the highest temperature of the battery cell in the test fixture during the charging process is consistent with the highest temperature during the charging process after the battery system is assembled.

[0167] 3) Install thermal insulation material on the outside of the test fixture;

[0168] 4) A cold plate is placed on top of the battery cell in the test fixture, or a cold plate is placed on the bottom of the battery cell, or both the top and bottom of the battery cell are placed on cold plates.

[0169] In some embodiments, the method further includes using a charge / discharge strategy that is consistent with the charge / discharge strategy after the battery system is assembled.

[0170] In some embodiments, the method further includes: applying a preload force to both sides of the battery cell after placing it into the test fixture; there are two scenarios:

[0171] Scenario 1: If the thickness of the buffer structure of the battery system is determined, then a pre-tightening force is applied to both sides of the battery cell, including: using the sum of the thicknesses of N battery cells and N buffer structures after the battery system is assembled as the expansion force clamping distance, adjusting the clamping distance of the test fixture to the expansion force clamping distance, thereby applying the pre-tightening force; where N is the number of battery cells currently placed in the test fixture.

[0172] Taking the test of a single battery cell placed in the fixture as an example, in this scenario, the actual thickness of a single battery cell and a single buffer material after the system is assembled is used as the expansion force clamping distance. Rotate the drive rod 10 so that the distance between the back plate 2 and the clamping plate 5 is the expansion force clamping distance, and the preload can be determined.

[0173] Scenario 2: If the system has not yet been designed and is mainly due to the undetermined buffer structure of the battery system, a pre-tightening force is applied to both sides of the cell. This includes: applying the pre-tightening force at the initial value set by the test fixture. If the preset standard is not met, the pre-tightening force is adjusted until the preset standard is met. The preset standard includes: after each application of the pre-tightening force, the test fixture sensor 6 is allowed to stand for a preset time, and the stress change reported by the sensor 6 is less than the set value.

[0174] For example, the initial preload is typically selected between 100 and 6000 N, with a typical value of 3000 N used in experiments. After each application of force, the settling time is set to 10-15 minutes. The system is considered to have reached the preset standard when the stress change is less than the set value of 1 kgf / 10 minutes (meaning mechanical relaxation). After reaching the preset standard, the distance between the back plate 2 and the clamping plate 5 can be measured as an auxiliary parameter for later system design.

[0175] It should be noted that after the battery cell is placed in the fixture and pre-tightened, it can be placed in the temperature chamber. Then, the battery cell is electrically connected to the test execution system to perform the test. The specific test is achieved by periodically charging and discharging the battery, which is common knowledge in this field and will not be elaborated here.

[0176] Taking the aforementioned three units with two test fixtures (intermediate fixture and end fixture) as an example, the back plate 2, clamping plate 5, pressure plate 7, and front plate 9 of the intermediate fixture are made of steel, while the clamping plate 5, pressure plate 7, and front plate 9 of the end fixture are made of aluminum. The back plate 2 of the end fixture is made of the same aluminum as the end plate of the module frame, and its thickness is consistent with that of the end plate of the module frame. During testing, individual cells are sequentially placed into their corresponding fixtures and clamped for testing. Referring to Figure 9, which shows the cell cycle life test curve, the horizontal axis represents the number of charge-discharge cycles, and the vertical axis represents the capacity ratio. The thick line represents the system test results after the actual battery system is assembled, the thin solid line represents the test results of the intermediate cell clamped by the intermediate fixture (both sides of the cell are steel), and the dashed line represents the test results of the end cells clamped by the end fixture (both sides of the cell are silver and steel, respectively). As can be seen, the test results of this application are very close to the system test results. Therefore, the testing method of this application is equivalent to the testing method for cell expansion force within the system, ensuring consistency between the cell expansion force test results and those within the system, and improving the accuracy of the system's expansion force resistance design parameter input. Furthermore, using a single cell as an equivalent system for testing reduces system-level testing, improves testing efficiency, saves testing resources and materials, and achieves cost reduction.

[0177] It should be noted that this application is applicable to all battery systems, and expansion force testing within the equivalent system of the cell can be achieved in each battery system.

[0178] It should be understood that although the steps in the flowchart are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated in this application, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the diagram may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0179] Based on the same concept, this application also claims protection for a testing system, which includes a test execution system and at least two test fixtures with different stiffnesses. The test execution system is used to electrically connect to the battery cells in the test fixtures and perform expansion force tests on the batteries. The test execution system can be connected to the battery / cell under test and obtain expansion force data by cyclically charging and discharging the battery / cell under test. Since the test execution system is an existing system, it will not be described in detail here. The test fixtures used in this application and the specific test methods can be found in the method embodiments.

Claims

1. A method for testing the expansion force of battery cells, used to test the expansion force of battery cells in a battery module to be assembled into a battery system, the battery module comprising multiple battery cells, the method comprising: Provide at least two test fixtures with different stiffnesses; The plurality of battery cells are divided into a plurality of units, wherein each unit comprises one or a plurality of battery cells arranged in a continuous manner; Based on the position of the unit in the battery module, a corresponding test fixture is assigned to the unit, such that the unit closer to the center of the battery module is assigned a test fixture with higher rigidity. After placing the battery cell in the unit into the test fixture assigned to the unit, the test is performed to obtain the battery cell expansion force.

2. The method according to claim 1, wherein, The plurality of units is an odd number, with the center of the middle unit coinciding with the center of the battery module, and the other units symmetrically distributed in pairs on both sides of the center of the battery module; or, the plurality of units is an even number and symmetrically distributed in pairs on both sides of the center of the battery module.

3. The method according to any one of claims 1-2, wherein, The step of assigning a corresponding test fixture to the unit includes: assigning the same test fixture to two units that are symmetrically distributed with each other; if there are no other units that are distributed opposite to the unit, then assigning a separate test fixture to the unit.

4. The method according to any one of claims 1-3, wherein, The battery system includes a module frame configured to assemble the battery module, and the stiffness of one of the at least two test fixtures is also related to the stiffness of the module frame. The step of assigning the corresponding test fixture to the unit includes: assigning the test fixture related to the stiffness of the module frame to the units located at both ends.

5. The method according to claim 4, wherein, The test fixture includes a cell placement slot configured to place a cell and multiple clamping plates distributed at both ends of the cell placement slot. In the test fixtures assigned to the units at both ends: the stiffness of the clamping plate located on the first side of the cell placement space is consistent with the stiffness of the clamping plate of the target test fixture located on the second side of the cell placement space; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame. The target test fixture is the test fixture corresponding to the unit adjacent to the unit in the head.

6. The method according to claim 5, wherein, Except for the test fixtures assigned to the units at both ends, each of the other test fixtures satisfies: The multiple clamps of the test fixture have the same stiffness; or, the stiffness of the clamp of the test fixture located on the first side of the cell placement space is greater than the stiffness of the clamp of the test fixture located on the second side of the cell placement space.

7. The method according to any one of claims 1-6, wherein, The number of test fixtures is two, wherein the stiffness of the first test fixture is less than that of the second test fixture; the number of units is three, and the center of the battery module falls into the middle unit; The step of assigning the corresponding test fixture to the unit includes: assigning the first test fixture to the units located at both ends, and assigning the second test fixture to the units located in the middle.

8. The method according to claim 7, wherein, The battery system includes a module frame configured to assemble the battery module, and the test fixture includes a cell placement slot configured to place the cell and a plurality of clamps distributed at both ends of the cell placement slot. In the first test fixture, the stiffness of the clamping plate located on the first side of the cell placement space is consistent with the stiffness of the second test fixture; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame. The second test fixture has a plurality of clamps with uniform stiffness that is greater than that of the module frame.

9. The method according to any one of claims 1-8, further comprising: After the battery cell is placed in the test fixture, a preload force is applied to both sides of the battery cell.

10. The method according to claim 9, wherein, The battery module also includes multiple buffer structures, with one buffer structure distributed on each side of each cell; the buffer structure is configured for the cell when it is placed in the test fixture. If the thickness of the buffer structure of the battery system is determined, the pre-tightening force applied to both sides of the battery cell includes: using the sum of the thicknesses of N battery cells and N buffer structures after the battery system is assembled as the expansion force clamping distance, adjusting the clamping distance of the test fixture to the expansion force clamping distance, thereby applying the pre-tightening force; where N is the number of battery cells currently placed in the test fixture.

11. The method according to any one of claims 9-10, wherein, The battery module also includes multiple buffer structures, with one buffer structure distributed on each side of each cell; the buffer structure is configured for the cell when it is placed in the test fixture. If the buffer structure of the battery system is not determined, the preload applied to both sides of the cell includes: controlling the test fixture to apply the preload at an initial value; if the preset standard is not met, the preload is adjusted until the preset standard is met. The preset standard includes: after each application of preload, the test fixture is allowed to stand for a preset time, and the stress change reported by the test fixture is less than the set value.

12. The method according to any one of claims 1-11, wherein, The step of placing the battery cells in the unit into the test fixture assigned to the unit and then performing a test to obtain the battery cell expansion force includes: placing the battery cells in the unit into the test fixture all at once and then performing a test to obtain the battery cell expansion force; or placing the battery cells in the unit into the test fixture in multiple batches and performing a test to obtain the battery cell expansion force in batches, with each batch including at least one battery cell.

13. The method according to any one of claims 1-12, further comprising: The initial state of charge of the battery cell held in the test fixture is configured to be consistent with the initial state of charge of the battery cell after the battery system is assembled.

14. The method according to any one of claims 1-13, further comprising: Referring to the environment in which the battery cell is located after the battery system is assembled, a corresponding environment is configured for the battery cell placed in the test fixture to simulate the environment in which the battery cell is located after the battery system is assembled.

15. The method according to claim 14, wherein, The process of configuring a suitable environment for the battery cell placed in the test fixture includes: When the battery cell is placed in the test fixture, a buffer structure is configured for the battery cell. The stress-strain curve of the buffer structure configured for the battery cell is consistent with that of the buffer structure configured for the battery cell after the battery system is assembled.

16. The method according to claim 15, wherein, The material of the buffer structure configured for the battery cell in the test fixture is the same as the material of the buffer structure configured for the battery cell after the battery system is assembled.

17. The method according to any one of claims 15-16, wherein, The provision of a buffer structure for the battery cell includes: configuring a buffer structure on one side of the battery cell in the test fixture, wherein the thickness of the configured buffer structure is consistent with the thickness of the buffer structure configured for the battery cell after the battery system is assembled; or, configuring buffer structures on both sides of the battery cell in the test fixture, wherein the sum of the thicknesses of the buffer structures on both sides is consistent with the thickness of the buffer structure configured for the battery cell after the battery system is assembled.

18. The method according to any one of claims 14-17, wherein, The provision of a suitable environment for the battery cell placed in the test fixture includes any one or any combination of the following: The test fixture holding the battery cell is placed in the temperature chamber, and the temperature chamber temperature is adjusted so that the highest temperature of the battery cell in the test fixture during the charging process is consistent with the highest temperature of the battery system during the charging process after assembly. Thermal insulation material is provided on the outside of the test fixture; A cold plate is provided on the top of the battery cell in the test fixture, or a cold plate is provided on the bottom of the battery cell, or both the top and bottom of the battery cell are provided with cold plates.

19. The method according to any one of claims 1-18, further comprising: The charging and discharging strategy used during the test is consistent with the charging and discharging strategy after the battery system is assembled.

20. A test fixture for use in the method of any one of claims 1-19; wherein the stiffness of the test fixture is related to the position of the unit to which it is assigned in the battery module: the closer the unit to which the test fixture is assigned is to the center of the battery module, the higher the stiffness of the test fixture.

21. The test fixture according to claim 20, wherein, The battery system includes a module frame configured to assemble the battery modules, and the test fixture includes cell placement slots configured to place battery cells and multiple clamping plates distributed at both ends of the cell placement slots, wherein: The stiffness of each of the multiple clamping plates is related to the position of the unit to which the test fixture is assigned in the battery module; Alternatively, the stiffness of the clamping plate located on the first side of the cell placement space is related to the position of the unit assigned to the test fixture in the battery module; the stiffness of the clamping plate located on the second side of the cell placement space is related to the stiffness of the module frame.

22. The test fixture according to any one of claims 21-22, wherein, The plurality of clamping plates include a back plate, an intermediate clamping detection plate, and a front plate, all of which are vertically arranged and sequentially arranged along a first direction. The back plate and the front plate are connected by a guide shaft extending along the first direction, and the guide shaft movably passes through the intermediate clamping detection plate. A drive mechanism configured to push the intermediate clamping detection plate to move along the guide shaft is mounted on the front plate. The intermediate clamping detection plate and the back plate form a cell placement space. After the cell is placed in the cell placement space, the thickness direction of the cell is parallel to the first direction.

23. The test fixture according to any one of claims 22-23, further comprising any one or any combination of the following: a connecting rod and a support plate; in: The back plate and the front plate are arranged facing each other along the first direction, and their four corners are connected by the guide shafts respectively. The tray connects the back plate and the front plate and is located at the bottom of the cell mounting space; The connecting rod connects the back plate and the front plate and is located at the top of the cell mounting space.

24. The test fixture according to claim 23, wherein, The first end face of the tray is locked to the side of the back plate facing the intermediate clamping detection plate along the first direction, and the second end face of the tray is locked to the side of the front plate facing the intermediate clamping detection plate along the first direction.

25. The test fixture according to any one of claims 23-24, wherein, The top edge of the back panel protrudes upward near the center to form a first flange, and the top edge of the front panel protrudes upward near the center to form a second flange. At least one of the connecting rods is connected between the first flange and the second flange.

26. The test fixture according to any one of claims 22-25, wherein, The intermediate clamping detection plate includes a clamping plate and a pressure plate, the clamping plate and the pressure plate are connected and a sensor is installed between them.

27. The test fixture according to claim 26, wherein, The stiffness of the clamping plate and the pressure plate is the same as that of the front plate; Wherein: the stiffness of the clamping plate is the same as the stiffness of the back plate; or, the stiffness of the back plate is less than the stiffness of the clamping plate.

28. The test fixture according to claim 27, wherein, The stiffness of the back plate is consistent with the stiffness of the module frame.

29. The test fixture according to any one of claims 22-28, wherein, The drive mechanism includes a drive rod threadedly connected to the front plate and configured to apply a preload, and a pressure head configured to contact and push the intermediate clamping detection plate; the drive rod passes through the front plate in a first direction and is connected to the pressure head.

30. The test fixture according to claim 29, wherein, The front plate has a sleeve on the side opposite to the intermediate clamping detection plate, and the drive rod passes through the sleeve and is threaded into it.

31. The test fixture according to claim 30, wherein, The sleeve has a positioning through hole, the drive rod has a positioning groove, and at least one of the positioning holes and positioning grooves is multiple; After the drive rod is preloaded, it is locked to the rod sleeve by the limiting member, so that the drive rod cannot rotate. The limiting member is inserted into the positioning through hole and the positioning groove that are closest to each other.

32. The test fixture according to any one of claims 30-31 further includes a locking nut mounted on the drive rod and located on the side opposite to the front plate, configured to reverse-lock the drive rod after a preload is applied, thereby preventing the drive rod from rotating.

33. A testing system comprising a test execution system and at least two test fixtures of different stiffnesses as described in any one of claims 20-32, the test execution system being configured to be electrically connected to a cell in the test fixture and to perform an expansion force test on the battery.