Battery cell swelling stiffness test method

Abstract

This invention relates to the field of battery testing technology, and in particular to a method for testing the expansion stiffness of a battery cell, comprising the following steps: measuring the free expansion deformation t0 during the charging and discharging process of the battery cell; setting the values ​​of the reserved gap t1, t2...tn for the battery cell, wherein 0 < t1 < t2 < ... < tn ≤ t0; placing the battery cell between a fixed plate and a measuring plate, ensuring that the distance between the measuring plate and the battery cell is equal to the reserved gap; charging and discharging the battery cell, measuring the displacement a and the force F of the measuring plate when the SOC of the battery cell is a preset value b; repeating the above operation to obtain the corresponding displacements a1, a2...an and the force F1, F2...Fn when the reserved gaps are t1, t2...tn; calculating n expansion deformation ΔS based on n sets of reserved gap and displacement values, plotting the curve of force value versus expansion deformation, and the slope of the curve is the expansion stiffness of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of battery testing technology, and in particular to a method for testing the expansion stiffness of battery cells. Background Technology

[0002] During the charging and discharging process, the battery cell expands due to factors such as increased electrode thickness, SEI film growth, and gas generation, directly affecting the battery's safety performance. Assessing the expansion characteristics of the battery cell during charging and discharging plays a crucial role in the safe design of battery modules. Expansion stiffness refers to the cell's ability to resist elastic deformation during expansion. The expansion stiffness is influenced by factors such as the state of charge, charge / discharge rate, and the amount of expansion deformation. Testing and accurate calculation of expansion stiffness are key to evaluating the cell's expansion characteristics, and an accurate and effective method is needed for its measurement and calculation.

[0003] There are two existing methods for testing and calculating the expansion stiffness of battery cells: the reverse testing method and the constant force measurement method. The reverse testing method involves compressing the battery cell and recording the relationship between the compression displacement and pressure to obtain the compression stiffness under different compression deformation amounts, which is then approximated as the expansion stiffness. However, since the compression process of a battery cell under a fixed state of charge is completely different from the expansion process during charging, using the compression stiffness as the expansion stiffness introduces a certain degree of error. The constant force measurement method requires constant force testing equipment, which is difficult to maintain a constant expansion force during cell expansion. This places high demands on the accuracy of the constant force testing equipment, making it prone to errors due to insufficient equipment precision.

[0004] Therefore, there is an urgent need for a method to test the cell expansion stiffness in order to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the expansion stiffness of a battery cell, which can test the expansion stiffness of the battery cell and avoid the inherent errors of the reverse testing method and the equipment errors of the constant force measurement method.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] A method for testing the expansion stiffness of a battery cell is provided, comprising the following steps:

[0008] S1. Measure the free expansion deformation t0 of the battery cell during the charging and discharging process;

[0009] S2. Set the values ​​of the reserved gap of the battery cell to t1, t2...tn, where 0 < t1 < t2 < ... < tn ≤ t0;

[0010] S3. Place the battery cell between the fixed plate and the measuring plate, ensuring that the distance between the measuring plate and the battery cell is equal to the reserved gap. Charge and discharge the battery cell. When the SOC of the battery cell is a preset value b, measure the displacement a of the measuring plate and the force F of the measuring plate. Repeat the above operation to obtain the displacement a1, a2...an and the force F1, F2...Fn corresponding to the reserved gaps t1, t2...tn.

[0011] S4. Based on the values ​​of the n reserved gaps and the displacement, calculate n expansion deformation amounts ΔS, and plot the curve of the force value versus the expansion deformation amount. The slope of the curve is the expansion stiffness of the battery cell.

[0012] As a preferred method for testing the expansion stiffness of battery cells, the charging and discharging processes of the battery cells in steps S1 and S3 satisfy the following: the initial SOC and the charge / discharge rate of the battery cells are the same in different measurement processes.

[0013] As a preferred method for testing the expansion stiffness of battery cells, the initial state of charge (SOC) of the battery cell is 0.

[0014] As a preferred method for testing the expansion stiffness of battery cells, b≥90%.

[0015] As a preferred embodiment of the cell expansion stiffness testing method, step S1 includes: placing the cell vertically, placing a first displacement sensor and a second displacement sensor on both sides of the cell respectively, charging and discharging the cell, and summing the maximum displacement values ​​of the sidewalls of the cell measured by the first displacement sensor and the second displacement sensor to obtain the free expansion deformation t0.

[0016] As a preferred method for testing the expansion stiffness of battery cells, the test ends of the first displacement sensor and the second displacement sensor are located on the same horizontal line.

[0017] As a preferred method for testing the expansion stiffness of battery cells, in step S4, the expansion deformation ΔS is the sum of the reserved gap and the displacement.

[0018] As a preferred method for testing the expansion stiffness of battery cells, in step S3, the displacement of the measuring plate is measured by a third displacement sensor, and the force on the measuring plate is measured by a pressure sensor.

[0019] As a preferred embodiment of the cell expansion stiffness testing method, the equipment in step S3 further includes a stabilizing plate, a pushing plate, and a connecting rod. The connecting rod passes through the threaded hole of the stabilizing plate, and the external thread of the connecting rod mates with the threaded hole. One end of the connecting rod is connected to the pushing plate, and the pressure sensor is clamped between the measuring plate and the pushing plate.

[0020] As a preferred embodiment of the cell expansion stiffness testing method, the device in step S3 further includes a rolling plate, with multiple rollers disposed below the rolling plate, and the cell placed on the rolling plate.

[0021] The beneficial effects of this invention are:

[0022] This invention provides a method for testing the expansion stiffness of a battery cell, comprising the following steps: S1, measuring the free expansion deformation t0 during the charging and discharging process of the battery cell; S2, setting the values ​​of the reserved gap t1, t2…tn for the battery cell, wherein 0 < t1 < t2 < … < tn ≤ t0; S3, placing the battery cell between a fixed plate and a measuring plate, ensuring that the distance between the measuring plate and the battery cell is equal to the reserved gap, charging and discharging the battery cell, and measuring the displacement a and the force F of the measuring plate when the SOC of the battery cell is a preset value b. Repeating the above operation to obtain the corresponding displacements a1, a2…an and the force F1, F2…Fn when the reserved gaps are t1, t2…tn; S4, calculating n expansion deformations ΔS based on n sets of reserved gap and displacement values, plotting the curve of force value versus expansion deformation, and the slope of the curve is the expansion stiffness of the battery cell. This cell expansion stiffness testing method can test the expansion stiffness of the cell, avoids the inherent error of the reverse testing method, and does not require the use of constant force testing equipment, thus avoiding the equipment error of the constant force measurement method. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of step S1 of the cell expansion stiffness testing method provided in the embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of step S3 of the cell expansion stiffness testing method provided in the embodiment of the present invention;

[0025] Figure 3 This is a graph showing the relationship between the stress value and the expansion deformation (any working condition) provided in the embodiments of the present invention.

[0026] Figure 4 This is a graph showing the relationship between the stress value and the expansion deformation (specific working condition) provided in the embodiments of the present invention.

[0027] In the picture:

[0028] 1. First displacement sensor; 2. Second displacement sensor; 3. Auxiliary side plate; 4. Fixing plate; 5. Measuring plate; 6. Third displacement sensor; 7. Pressure sensor; 8. Stabilizing plate; 9. Pushing plate; 10. Connecting rod;

[0029] 100. Battery cells. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present invention are shown in the accompanying drawings, not all of them.

[0031] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0032] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0033] like Figures 1-2 As shown, the cell expansion stiffness test method in this embodiment is not only simple to operate and relatively accurate in test results, but also can simultaneously consider the influence of factors such as SOC, charge / discharge rate and expansion deformation on expansion stiffness.

[0034] The method for testing the expansion stiffness of battery cells includes the following steps:

[0035] S1. First, measure the free expansion deformation t0 of cell 100 during the charging and discharging process.

[0036] Preferably, step S1 includes: as follows Figure 1As shown, the battery cell 100 is placed vertically, and the first displacement sensor 1 and the second displacement sensor 2 are placed on both sides of the battery cell 100 respectively. The battery cell 100 is charged and discharged. The maximum displacement values ​​of the sidewalls of the battery cell 100 measured by the first displacement sensor 1 and the second displacement sensor 2 are summed to obtain the free expansion deformation t0.

[0037] Preferably, the test ends of the first displacement sensor 1 and the second displacement sensor 2 are located on the same horizontal line to measure the displacement of the most convex point on the symmetrical side walls of the battery cell 100. Since the subsequent measuring plate 5 will contact the most convex point on the side of the battery cell 100, preferably, the test ends of the first displacement sensor 1 and the second displacement sensor 2 are both located at the most convex point of the expansion deformation on the side of the battery cell 100, so that the obtained free expansion deformation amount t0 has reference value for the subsequent setting of the reserved gap.

[0038] Preferably, multiple sets of the first displacement sensor 1 and the second displacement sensor 2 can be set at intervals to facilitate finding the most protruding point and ensure the accuracy of the free expansion deformation amount t0.

[0039] Preferably, the measuring device further includes two auxiliary side plates 3 arranged opposite to each other. The two auxiliary side plates 3 are respectively arranged on both sides of the battery cell 100 to assist in fixing the first displacement sensor 1 and the second displacement sensor 2, so as to eliminate the error caused by the movement of the first displacement sensor 1 and the second displacement sensor 2 themselves.

[0040] S2. Set the values ​​of the reserved gap t1, t2...tn for cell 100, where 0 < t1 < t2 < ... < tn ≤ t0. The larger the value of n, the smoother the curve of force value-expansion deformation will be, and the more accurate the calculation result of expansion stiffness will be.

[0041] S3. Place the battery cell 100 between the fixed plate 4 and the measuring plate 5, ensuring that the distance between the measuring plate 5 and the battery cell 100 is equal to the reserved gap. Charge and discharge the battery cell 100. When the SOC of the battery cell 100 is the preset value b, measure the displacement a of the measuring plate 5 and the force F of the measuring plate 5. Repeat the above operation to obtain the corresponding displacements a1, a2...an and force values ​​F1, F2...Fn when the reserved gaps are t1, t2...tn.

[0042] Preferably, the charging and discharging processes of the battery cell 100 in steps S1 and S3 satisfy the requirement that the initial SOC and charge / discharge rate of the battery cell 100 are the same in different measurement processes, so as to eliminate errors caused by differences in the initial SOC and charge / discharge rate of the battery cell 100. Preferably, the initial SOC of the battery cell 100 is 0, and setting the initial state to an empty state is the easiest to control, which can reduce the difficulty of operation and avoid errors caused by operation. Preferably, in this embodiment, b ≥ 90% to ensure that the force and displacement are large, avoiding the problem of low accuracy of subsequent calculation results due to small test values. Preferably, b is 100% to obtain the maximum force and displacement.

[0043] Since the measuring plate 5 may be displaced when pressed against the side wall of the battery cell 100, it is necessary to detect the displacement of the measuring plate 5. Preferably, in step S3, the displacement of the measuring plate 5 is measured by the third displacement sensor 6. Alternatively, preferably, the force value of the measuring plate 5 is measured by the pressure sensor 7.

[0044] Preferably, the device in step S3 further includes a stabilizing plate 8, a pushing plate 9, and a connecting rod 10. The connecting rod 10 passes through a threaded hole in the stabilizing plate 8, and the external thread of the connecting rod 10 mates with the threaded hole. One end of the connecting rod 10 is connected to the pushing plate 9, and the pressure sensor 7 is clamped between the measuring plate 5 and the pushing plate 9. Rotating the connecting rod 10 adjusts the distance between the measuring plate 5 and the battery cell 100 to match the reserved gap value. During the expansion of the sidewall of the battery cell 100, the battery cell 100 abuts against the measuring plate 5, and a force is generated between the measuring plate 5 and the pushing plate 9. The magnitude of this force is equal to the force applied to the measuring plate 5.

[0045] During the charging and discharging process, when the side of the battery cell 100 near the fixed plate 4 expands, the battery cell 100 will be subjected to the reaction force of the fixed plate 4. At this time, the bottom surface of the battery cell 100 will be subjected to frictional force in the opposite direction. In order to prevent the frictional force from affecting the measurement of the force value, preferably, the device in step S3 also includes a rolling plate (not shown in the figure). Multiple rollers are provided below the rolling plate, and the battery cell 100 is placed on the rolling plate to eliminate the frictional force on the bottom surface of the battery cell 100.

[0046] S4. Based on the values ​​of n sets of reserved gaps and displacement, calculate n expansion deformation amounts ΔS, and plot the curve of force value versus expansion deformation amount. The slope of the curve is the expansion stiffness of cell 100.

[0047] Preferably, in step S4, the expansion deformation ΔS is the sum of the reserved gap and the displacement, i.e., ΔS = t + a. Therefore, the expansion deformation ΔS1, ΔS2, ..., ΔSn can be calculated based on the reserved gaps t1, t2…tn and the corresponding displacements a1, a2…an.

[0048] Based on the basic theory of expansion stiffness calculation

[0049] F=k(ΔS0-ΔS) (1)

[0050] k=F / (ΔS0-ΔS) (2)

[0051] Formulas (1)-(2) are the formulas for calculating the average stiffness of the battery cell 100 during the expansion process. F is the expansion force of the battery cell 100 during the expansion process, which is the force value F of the measuring plate 5 mentioned above. k is the expansion stiffness. ΔS0 is the free expansion deformation, which is t0 in the above test steps. ΔS is the expansion deformation of the battery cell 100 under the constraint state. Furthermore, substituting F1, ΔS1, F2, and ΔS2 into formula (1):

[0052] F1 = k(ΔS0 - ΔS1)

[0053] F2=k(ΔS0-ΔS2)

[0054] F2-F1=k(ΔS1-ΔS2)

[0055] k=(F2-F1) / (ΔS1-ΔS2) (3)

[0056] Formula (3) is the calculation expression for the expansion stiffness k by calculating the expansion deformation ΔS and the measured force F. When ΔS1-ΔS2 approaches 0, the expansion stiffness value under a certain expansion deformation can be obtained. The absolute value of the slope of the curve at a certain point corresponding to ΔS is the expansion stiffness under that expansion deformation.

[0057] Organize the data on the expansion deformation ΔS and the corresponding force F, and plot a curve with the expansion deformation ΔS on the horizontal axis and the force F on the vertical axis, as shown below. Figure 3 As shown in the figure, the absolute value of the slope of the tangent line at the corresponding point on the curve when different expansion deformation values ​​are selected on the horizontal axis is the expansion stiffness value under that expansion deformation amount.

[0058] Taking b as 100% and the charge / discharge rate as 0.33C as an example, the thickness of cell 100 was measured to be 15.0 mm when the SOC was 0% and 15.8 mm when the SOC was 100%. The reserved gap values ​​were set to 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, and 0.8 mm. The table below shows the expansion force of the measuring board 5 and the corresponding expansion deformation of cell 100 when cell 100 is fully charged under different reserved gaps.

[0059] Reserved gap t / mm Displacement value a / mm Force value F / N Expansion deformation ΔS / mm 0.1 0.031 10335 0.131 0.2 0.025 6525 0.225 0.3 0.022 4493 0.322 0.4 0.022 3015 0.422 0.5 0.018 1997 0.518 0.6 0.015 1210 0.615 0.7 0.010 482 0.710 0.8 0 0 0.800

[0060] The corresponding curves of F and ΔS obtained from the above data are as follows: Figure 4 As shown, when the expansion deformation is 0.3 mm, the slope of the tangent line at this point is 17241.4, that is, the expansion stiffness is 17241.4 N / m.

[0061] Of course, different initial SOC, b, and charge / discharge rates can be used to obtain the expansion stiffness under different working conditions, as well as the influence of these parameters on the expansion stiffness.

[0062] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method of testing cell expansion stiffness, characterized by, Includes the following steps: S1. Measure the free expansion deformation t0 of the battery cell (100) during the charging and discharging process; S2. Set the values ​​of the reserved gap of the battery cell (100) to t1, t2...tn, where 0 < t1 < t2 < ... < tn ≤ t0; S3. Place the battery cell (100) between the fixing plate (4) and the measuring plate (5), ensuring that the distance between the measuring plate (5) and the battery cell (100) is equal to the reserved gap. Charge and discharge the battery cell (100). When the SOC of the battery cell (100) is a preset value b, measure the displacement a of the measuring plate (5) and the force F of the measuring plate (5). Repeat the above steps to obtain the displacement a1, a2...an and the force F1, F2...Fn corresponding to the reserved gaps t1, t2...tn. S4. Based on the values ​​of the n reserved gaps and the displacement, calculate n expansion deformation amounts ΔS, and plot the curve of the force value and the expansion deformation amount. The slope of the curve is the expansion stiffness of the battery cell (100). In step S3, the displacement of the measuring plate (5) is measured by the third displacement sensor (6), and the force value of the measuring plate (5) is measured by the pressure sensor (7). The device in step S3 also includes a stabilizing plate (8), a pushing plate (9), and a connecting rod (10). The connecting rod (10) passes through the threaded hole of the stabilizing plate (8), and the external thread of the connecting rod (10) is matched with the threaded hole. One end of the connecting rod (10) is connected to the pushing plate (9), and the pressure sensor (7) is sandwiched between the measuring plate (5) and the pushing plate (9). The device in step S3 also includes a rolling plate, with multiple rollers disposed below the rolling plate, and the battery cell (100) is placed on the rolling plate; In step S4, the expansion deformation ΔS is the sum of the reserved gap and the displacement.

2. The cell bulge stiffness test method of claim 1, wherein, The charging and discharging process of the battery cell (100) in steps S1 and S3 satisfies the following: the initial SOC and charge / discharge rate of the battery cell (100) are the same in different measurement processes.

3. The cell bulge stiffness test method of claim 2, wherein, The initial SOC of the battery cell (100) is 0.

4. The cell bulge stiffness test method of claim 1, wherein, b≥90%。 5. The cell expansion stiffness testing method according to claim 1, characterized in that, Step S1 includes: placing the battery cell (100) vertically, placing a first displacement sensor (1) and a second displacement sensor (2) on both sides of the battery cell (100) respectively, charging and discharging the battery cell (100), and summing the maximum displacement values ​​of the sidewalls of the battery cell (100) measured by the first displacement sensor (1) and the second displacement sensor (2) to obtain the free expansion deformation amount t0.

6. The cell expansion stiffness testing method according to claim 5, characterized in that, The test end of the first displacement sensor (1) and the test end of the second displacement sensor (2) are located on the same horizontal line.

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