Lithium ion battery diaphragm testing method and testing device

Abstract

The invention provides a lithium ion battery diaphragm testing method and device, and the method comprises the steps: applying a tensile stress to a diaphragm at a preset strain rate, and stopping applying the tensile stress to the diaphragm under the condition that the tensile stress reaches a preset tensile stress; applying a compression load to the diaphragm in a tensile state under the condition that the application of the tensile stress to the diaphragm is stopped; under the condition that a compression load is applied to the diaphragm, monitoring a test current between a positive plate and a negative plate which are arranged on two sides of the diaphragm in real time; and collecting data of the compression load and the test current, establishing an association relationship between the compression load and the test current, and determining the coupling breakdown strength of the diaphragm according to a data abrupt change point of the test current in the association relationship. According to the method, the effect of the compression load is considered, and meanwhile, the effect of the tensile stress is combined, so that the electrode particle breakdown resistance of the lithium ion battery diaphragm can be more intuitively represented, and the safety and reliability of the diaphragm in an actual battery can be better evaluated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery separator testing method and testing device. BACKGROUND

[0002] In a lithium ion battery, the separator is between the positive and negative plates, physically isolating the two plates to prevent internal short circuit of the battery, while at the same time allowing lithium ions in the electrolyte to pass through the micropores of the separator itself to reach the positive and negative poles to complete the lithium extraction process during battery charging and discharging cycles. Therefore, once the separator is mechanically broken, damaged or broken, it will directly cause internal short circuit of the battery, causing the local temperature of the short circuit area to rise sharply, and even possibly causing thermal runaway. In the related art, for the possible mechanical breakdown, a breakdown test of the separator is performed before the battery is shipped, but the test method in the related art does not consider the tensile stress acting on the separator in the actual battery, and the reliability is poor. SUMMARY

[0003] Embodiments of the present application provide a lithium ion battery separator testing method and testing device to solve the problem of poor reliability of lithium ion battery separator strength testing in the related art.

[0004] To solve the above problems, the technical solutions provided by the present application are as follows:

[0005] In a first aspect, the present application provides a lithium ion battery separator testing method, one side of the separator is provided with a positive plate, and the other side is provided with a negative plate, and the testing method comprises:

[0006] applying a tensile stress to the separator at a preset strain rate, and stopping applying the tensile stress to the separator when the tensile stress reaches a preset tensile stress;

[0007] applying a compression load to the separator in a tensile state while stopping applying the tensile stress to the separator;

[0008] monitoring the test current between the positive plate and the negative plate in real time while applying the compression load to the separator;

[0009] collecting data of the compression load and the test current, establishing a correlation between the compression load and the test current, and determining the coupling breakdown strength of the separator according to a data mutation point of the test current in the correlation.

[0010] In an embodiment, the applying a tensile stress to the separator at a preset strain rate comprises:

[0011] applying a tensile stress to the separator at a strain rate of 0.01% to 0.05% per second.

[0012] In an embodiment, the stopping the applying of the tensile stress to the separator upon the tensile stress reaching a preset tensile stress comprises:

[0013] stopping the applying of the tensile stress to the separator upon the preset tensile stress reaching 50% to 90% of the yield strength of the separator material.

[0014] In an embodiment, the stopping the applying of the tensile stress to the separator upon the tensile stress reaching a preset tensile stress comprises:

[0015] stopping the applying of the tensile stress to the separator upon the preset tensile stress reaching 50Mpa to 150Mpa.

[0016] In an embodiment, the applying of the tensile stress to the separator at a preset strain rate, and stopping the applying of the tensile stress to the separator upon the tensile stress reaching a preset tensile stress comprises:

[0017] applying of the tensile stress to the separator at a strain rate of 0.032% / s, and stopping the applying of the tensile stress to the separator upon the tensile stress reaching 100Mpa.

[0018] In an embodiment, the applying of the compression load to the separator in the tensile state upon the stopping of the applying of the tensile stress to the separator comprises:

[0019] applying of the compression load to the separator in the tensile state at a loading rate of 0.5kgf / s to 5kgf / s in synchronization with the stopping of the applying of the tensile stress to the separator.

[0020] In an embodiment, the applying of the compression load to the separator in the tensile state upon the stopping of the applying of the tensile stress to the separator comprises:

[0021] applying of the compression load to the separator in the tensile state at a loading rate of 1kgf / s in synchronization with the stopping of the applying of the tensile stress to the separator.

[0022] In an embodiment, the real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet comprises:

[0023] applying a voltage of 1mV to 10mV between the positive electrode sheet and the negative electrode sheet, and scanning the current of the loop to obtain the test current.

[0024] In an embodiment, the real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet comprises:

[0025] A voltage of 5 mV is applied between the positive electrode sheet and the negative electrode sheet, and a current of a loop is scanned to obtain the test current.

[0026] In an embodiment, the collecting data of the compression load and the test current, and establishing a correlation between the compression load and the test current comprises:

[0027] The data of the compression load and the test current are aligned by time axis synchronization to obtain the correlation between the compression load and the test current.

[0028] In an embodiment, the determining the coupling breakdown strength of the separator according to a data mutation point of the test current in the correlation comprises:

[0029] In the case that the test current lasts more than a first threshold value, the compression load corresponding to the first time when the test current lasts more than the first threshold value is determined as the coupling breakdown strength; or

[0030] A first derivative of the test current with respect to the compression load is calculated, and when the first derivative exceeds a preset slope threshold value, the corresponding compression load is determined as the coupling breakdown strength.

[0031] In a second aspect, the present application provides a testing device for a lithium ion battery separator, comprising:

[0032] A support module configured to place a separator to be tested, one side of the separator being provided with a positive electrode sheet and the other side being provided with a negative electrode sheet, the length of the separator being greater than the length of the positive electrode sheet or the negative electrode sheet;

[0033] A stretching module configured to fix both ends of the separator and apply a tensile stress to the separator at a preset strain rate, and stop applying the tensile stress to the separator when the tensile stress reaches a preset tensile stress;

[0034] A compression module configured to apply a compression load to the stack of positive electrode sheet-separator-negative electrode sheet when the tensile stress is stopped;

[0035] A monitoring module configured to monitor a test current between the positive electrode sheet and the negative electrode sheet in real time when the compression load is applied to the separator;

[0036] A control module configured to collect data of the compression load and the test current, establish a correlation between the compression load and the test current, and determine the coupling breakdown strength of the separator according to a data mutation point of the test current in the correlation.

[0037] In an embodiment, the stretching module is configured to:

[0038] applying a tensile stress to the separator at a strain rate of 0.032% / s, and stopping the tensile stress to the separator when the tensile stress reaches 100 MPa.

[0039] In an embodiment, the compression module is configured to:

[0040] synchronously with the action of stopping the tensile stress to the separator, applying a compression load to the separator in the tensile state at a loading rate of 1 kgf / s.

[0041] In an embodiment, the monitoring module is configured to:

[0042] applying a voltage of 5 mV between the positive electrode sheet and the negative electrode sheet, and scanning the current of the loop to obtain a test current.

[0043] In an embodiment, the control module is configured to:

[0044] collecting data of the compression load and the test current, synchronously aligning the data of the compression load and the test current through a time axis to obtain a correlation between the compression load and the test current, and determining the coupling breakdown strength of the separator according to a data mutation point of the test current in the correlation.

[0045] The embodiments of the present application provide a lithium ion battery separator testing method and testing device. The testing method comprises the following steps: applying a tensile stress to a separator at a preset strain rate, and stopping the tensile stress to the separator when the tensile stress reaches a preset tensile stress; applying a compression load to the separator in a tensile state when the tensile stress to the separator is stopped; monitoring a test current between positive electrode sheets and negative electrode sheets arranged on two sides of the separator in real time when the compression load is applied to the separator; collecting data of the compression load and the test current, establishing a correlation between the compression load and the test current, and determining a coupling breakdown strength of the separator according to a data mutation point of the test current in the correlation. Through the above scheme, the performance of the lithium ion battery separator in resisting electrode particle breakdown can be more intuitively represented by considering the effect of the compression load and combining the effect of the tensile stress, and the safety and reliability of the separator in an actual battery can be better evaluated. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0047] ATTACHMENTFigure 1 Schematic diagram of the stress on the separator during the winding process of the battery cell in the embodiment of the present application;

[0048] Attachment Figure 2 This is a schematic diagram of the steps of the lithium-ion battery separator testing method in an embodiment of the present application;

[0049] Attachment Figure 3 Schematic diagram of the loading of tensile stress and compressive load in the embodiment of the present application;

[0050] Attachment Figure 4 This is a graph of measured data of the lithium-ion battery separator testing method in the embodiment of this application;

[0051] Attachment Figure 5 The scanning electron microscope images of the indentation of the diaphragm under different test methods at different magnifications in the embodiment of the present application are shown;

[0052] Attachment Figure 6 This is a schematic structural diagram of an optional lithium-ion battery separator testing device in an embodiment of the present application.

[0053] Description of reference numerals in the figures:

[0054] 100. Testing device for lithium-ion battery separator; 200. Separator; 300. Positive electrode sheet; 400. Negative electrode sheet; 110. Support module; 120. Tensile module; 130. Compression module; 140. Monitoring module; 150. Control module. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0056] In lithium-ion batteries, the diaphragm is located between the positive and negative plates, physically isolating the two plates to prevent internal short circuits in the battery. At the same time, during the battery charge and discharge cycle, it allows lithium ions in the electrolyte to pass through the micropores of the diaphragm itself to reach the positive and negative electrodes to complete the lithium insertion and extraction process. It can be seen that once the diaphragm is mechanically broken down, damaged, or broken, it will directly lead to an internal short circuit in the battery, causing the local temperature in the short circuit area to rise sharply, and may even cause thermal runaway. Targetedly, for possible mechanical breakdown, the diaphragm will be subjected to breakdown tests before leaving the factory, such as ASTM (American Society of Testing Materials) standard tests and mixed breakdown strength tests.

[0057] ReferenceFigure 1 The figure shown is a schematic diagram of the stress on the diaphragm during the winding process of the battery cell. After the positive and negative plates and diaphragms are released by their respective unwinding mechanisms, they are stacked into a positive electrode sheet-diaphragm-negative electrode sheet-diaphragm stack via guide wheels, and then the stack is wound into a cylindrical battery cell by the winding mechanism. In order to ensure that the positive and negative electrode sheets and diaphragms can fit tightly together, a certain tensile stress is applied to the stack before entering the winding mechanism, so that radial hoop stress exists in the wound battery cell. It is this deliberate application of hoop stress that causes the diaphragm in the stack to be subjected to tensile stress before entering the winding mechanism. Figure 1 As shown in the enlarged diagram in the lower right corner. Moreover, after the stack is wound into a battery cell, the diaphragm begins to be compressed under the action of the hoop stress. Figure 1 As shown in the enlarged schematic diagram on the upper right, the diaphragm is now subjected to the coupling of tensile and compressive stresses, especially the compressive stress. During the charge and discharge process of the battery, the compressive stress will be further accumulated and increased due to the expansion of the volume of the electrode active material.

[0058] It can be seen that both compressive stress and tensile stress have an important influence in the failure analysis of lithium-ion batteries, but the testing methods in related technologies do not consider the tensile stress that the diaphragm is subjected to in actual batteries.

[0059] Reference Figure 2 According to the first aspect of the present application, a method for testing a lithium-ion battery separator is provided, wherein a positive electrode sheet is provided on one side of the separator and a negative electrode sheet is provided on the other side to form a laminated structure. The testing method comprises:

[0060] S10: applying tensile stress to the diaphragm at a preset strain rate, and stopping applying the tensile stress to the diaphragm when the tensile stress reaches the preset tensile stress.

[0061] Reference Figure 3 As shown, during the period from 0 to t1, tensile stress will continue to be applied to the diaphragm. When the tensile stress reaches the value P, the stretching will stop. During the subsequent period from t1 to t2, the diaphragm will be in a certain tensile state, and the tensile stress it is subjected to will gradually decrease.

[0062] Specifically, in some embodiments of the present application, the step of applying tensile stress to the diaphragm at a preset strain rate includes applying tensile stress to the diaphragm at a strain rate of 0.01% / s to 0.05% / s. It should be noted that when the strain rate is less than 0.01% / s, the test time may be too long, which is inconsistent with the efficiency of the actual production line and reduces the reliability of the test results. When the strain rate is greater than 0.05% / s, it may cause local stress concentration, thereby causing non-uniform deformation of the diaphragm, deviating from the actual working conditions and also reducing the reliability of the test results.

[0063] In some embodiments of the present application, the step of stopping applying the tensile stress to the separator when the tensile stress reaches a preset tensile stress can comprise: stopping applying the tensile stress to the separator when the preset tensile stress reaches 50% to 90% of the yield strength of the material of the separator. It should be noted that the yield strength refers to the critical stress value at which the material of the separator transitions from elastic deformation to plastic deformation. Therefore, the preset tensile stress is set to be no more than 90% of the yield strength of the material of the separator to prevent the tensile stress from approaching the yield strength and causing damage to the microstructure of the separator, resulting in distorted test results. The preset tensile stress is set to be no less than 50% of the yield strength of the material of the separator to ensure that the tensile stress is sufficient to simulate the mechanical constraints in the battery manufacturing process and avoid overly lenient test conditions.

[0064] In some embodiments of the present application, the step of stopping applying the tensile stress to the separator when the tensile stress reaches a preset tensile stress can also comprise: stopping applying the tensile stress to the separator when the preset tensile stress reaches 50Mpa to 150Mpa. When the preset tensile stress is less than 50Mpa, the separator can not be sufficiently stretched, resulting in a deviation from the actual working condition and a false high evaluation of the puncture strength of the separator in the final test results. When the preset tensile stress is greater than 150Mpa, the separator can be damaged before the actual puncture test, which will also interfere with the determination of the coupled puncture strength of the separator.

[0065] Based on the foregoing embodiments, the step S10 can specifically be: applying a tensile stress to the separator at a strain rate of 0.032% / s, and stopping applying the tensile stress to the separator when the tensile stress reaches 100Mpa. Through this setting, the working condition of the separator during actual production and use can be effectively simulated, which is conducive to improving the accuracy of the coupled puncture strength test of the separator.

[0066] S20: Apply a compression load to the separator in the stretched state while stopping applying the tensile stress to the separator.

[0067] Referring to Figure 3 As shown in FIG. 2, the compression load is applied to the separator at the same time as the tensile stress is stopped being applied to the separator at t1. The compression load changes linearly from t1 to t2. When the compression load reaches M, the compression load is maintained for a period of time (from t2 to t3), and then the compression load is unloaded.

[0068] Specifically, in some embodiments of the present application, step S20 can specifically include: synchronously with the action of stopping the stretching stress applied to the diaphragm, applying a compression load to the diaphragm in the stretched state at a loading rate of 0.5 kgf / s to 5 kgf / s. It should be noted that the loading rate of 0.5 kgf / s can simulate the stress state of the diaphragm in the low-speed extrusion scene such as the slow deformation of the battery pack, and the loading rate of 5 kgf / s can simulate the stress state of the diaphragm in the mechanical impact scene such as an accident.

[0069] More specifically, in some embodiments of the present application, step S20 is specifically: synchronously with the action of stopping the stretching stress applied to the diaphragm, applying a compression load to the diaphragm in the stretched state at a loading rate of 1 kgf / s. At this loading rate, the coupling breakdown strength of the diaphragm measured can have good data stability.

[0070] S30: Real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet under the condition of applying a compression load to the diaphragm.

[0071] Specifically, in some embodiments of the present application, the step of real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet includes: applying a voltage of 1 mV to 10 mV between the positive electrode sheet and the negative electrode sheet, and scanning the current of the loop to obtain the test current. It should be noted that setting the voltage value to be no less than 1 mV can avoid the current signal in the test loop being too weak to be covered by the noise of the device, thereby avoiding missing the event of the diaphragm being broken down; setting the voltage value to be no more than 10 mV can avoid local electronic conduction caused by a higher voltage to produce a "pseudo breakdown signal", and can also avoid the stress change of the diaphragm caused by the electrostatic adsorption effect.

[0072] Optionally, in some embodiments of the present application, the step of real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet includes: applying a voltage of 5 mV between the positive electrode sheet and the negative electrode sheet, and scanning the current of the loop to obtain the test current.

[0073] S40: Collecting data of the compression load and the test current, establishing the correlation between the compression load and the test current, and determining the coupling breakdown strength of the diaphragm according to the data mutation point of the test current in the correlation.

[0074] Specifically, in some embodiments of the present application, the step of collecting data of the compression load and the test current, and establishing the correlation between the compression load and the test current includes: synchronously aligning the data of the compression load and the test current through the time axis to obtain the correlation between the compression load and the test current.

[0075] Reference Figure 4As shown, in some embodiments of the present application, by obtaining the change curve of the compression load-time relationship and the change curve of the test current-time relationship, the change curve of the test current-compression load relationship can be derived.

[0076] On this basis, the step of determining the coupling breakdown strength of the diaphragm according to the data mutation point of the test current in the correlation relationship comprises: in the case that the test current continuously exceeds the first threshold value, determining the compression load corresponding to the first time when the test current continuously exceeds the first threshold value as the coupling breakdown strength. Specifically, the step of measuring the coupling breakdown strength by threshold method can be:

[0077] Calculate the baseline mean of the current in the i-f curve, that is, the average value of the current in the stable section before the diaphragm is broken down;

[0078] Set the first threshold value as 3 times the standard deviation of the baseline mean;

[0079] The compression load corresponding to the first time when the test current continuously exceeds the first threshold value is the breakdown strength.

[0080] Optionally, in some embodiments of the present application, the coupling breakdown strength can also be obtained by dynamic slope. Specifically, it can include: smoothing the i-f curve, calculating the first derivative of the test current with respect to the compression load, and determining the corresponding compression load as the coupling breakdown strength when the first derivative exceeds a preset slope threshold (such as 10 ma / kgf).

[0081] In combination with the above embodiments, the test method of the lithium ion battery diaphragm of the present application can more intuitively represent the performance of the diaphragm in resisting electrode particle breakdown, and can better evaluate the safety and reliability of the diaphragm in the actual battery.

[0082] Reference Figure 5 As shown, according to the second aspect of the present application, a test device 100 of a lithium ion battery diaphragm is provided to implement the test method of any of the preceding embodiments. The test device comprises a support module 110, a stretching module 120, a compression module 130, a monitoring module 140 and a control module 150.

[0083] Specifically, the support module 110 is configured to place the diaphragm 200 to be tested. One side of the diaphragm 200 is provided with a positive electrode sheet 300, and the other side is provided with a negative electrode sheet 400. The length of the diaphragm 200 is greater than the length of the positive electrode sheet 300 or the negative electrode sheet 400. Optionally, in some specific examples, the support module 110 can include a height-adjustable pad iron.

[0084] The stretching module 120 is configured to fix both ends of the separator 200 and apply a tensile stress to the separator 200 at a preset strain rate, and stop applying the tensile stress to the separator 200 when the tensile stress reaches a preset tensile stress. Optionally, in some specific examples, the stretching module 120 can include a precision stretcher configured to apply a tensile stress to the separator 200 at a strain rate of 0.032% / s, and stop applying the tensile stress to the separator 200 when the tensile stress reaches 100 MPa.

[0085] The compression module 130 is configured to apply a compression load to the stack of the positive plate 300-separator 200-negative plate 400 when the tensile stress applied to the separator 200 is stopped. Optionally, in some specific examples, the compression module 130 is configured to apply a compression load to the separator 200 in a stretched state at a loading rate of 1 kgf / s, synchronously with the action of stopping the tensile stress applied to the separator 200. The compression module 130 can include a ball indenter connected to a force sensor, and the diameter of the ball indenter can be 0.5 inches, so as to simulate the size of the electrode particles, and facilitate the improvement of the accuracy of the test data.

[0086] The monitoring module 140 is configured to monitor the test current between the positive plate 300 and the negative plate 400 in real time when the compression load is applied to the separator 200. Optionally, in some specific examples, the monitoring module 140 can include an electrochemical workstation configured to apply a voltage of 5 mV between the positive plate 300 and the negative plate 400, and scan the current of the loop to obtain the test current.

[0087] The control module 150 is configured to collect the data of the compression load and the test current, establish the correlation between the compression load and the test current, and determine the coupling breakdown strength of the separator 200 according to the data mutation point of the test current in the correlation. Optionally, in some specific examples, the control module 150 is configured to collect the data of the compression load and the test current, align the data of the compression load and the test current on the time axis synchronously, obtain the correlation between the compression load and the test current, and determine the coupling breakdown strength of the separator 200 according to the data mutation point of the test current in the correlation.

[0088] According to the foregoing lithium ion battery separator 200 test method and test device, the present application is further verified. Specifically, Celgard 2325PP-PE-PP three-layer composite separator 200 is used as the research object of this verification experiment. The positive and negative plates are respectively selected as the electrode plates without flattening using LiMn2O4 and MCMB graphite as the active material. The positive plate 300 and the negative plate 400 are respectively cut into 15 mm x 30 mm for standby. The separator 200 is cut into a 20 mm x 50 mm strip for standby, and the 50 mm long side is required to be parallel to the stretching direction.

[0089] After the membrane 200 is fixed on the precision tensile tester, the center of the gauge length of the membrane 200 is adjusted to be below the position of the ball indenter, and the positive and negative plates are placed on the membrane 200 respectively. It should be noted that the electrode plate below the membrane 200 is directly placed on the pad iron, and the height is carefully adjusted to ensure that the electrode plate below the membrane 200 is in close contact with the membrane 200 while not significantly compressing the membrane 200.

[0090] Subsequently, the working electrode and the counter electrode of the electrochemical workstation are connected to the positive plate 300 and the negative plate 400 in the stack respectively. In order to ensure that no short circuit occurs between the two electrodes, a large piece of membrane 200 with a test window only in the indenter area is used to insulate and separate the two electrodes.

[0091] After the preparation work is completed, the tensile tester is started to load the membrane 200 to 100 MPa, and then the indenter is immediately driven to press the stack. At the same time, the electrochemical workstation is started to apply a voltage of 5 mV to the positive and negative electrodes and scan the current in the loop. The compression force on the indenter is loaded linearly from 0 kgf to 100 kgf, and then held for 10 s before unloading quickly. After the i-t / f-t curves obtained in the experiment are derived, the i-f curves are derived to find the coupling breakdown strength value of the membrane 200. Five membrane 200 samples complete the above test, and the coupling breakdown strength of Celgard 2325 membrane 200 under the coupling effect of 100 MPa tensile stress is 72±11 kgf;

[0092] In order to compare with the test method of the present application, a plurality of membrane 200 samples are tested for mixed breakdown strength. Only the positive and negative electrode-membrane 200 stack is compressed (to 100 kgf), and the current between the two electrodes is monitored. It is found that in multiple mixed breakdown experiments, the current does not change significantly, so the mixed breakdown strength of the 2325 membrane 200 is >100 kgf.

[0093] The indentations formed in the membrane 200 after the test method of the present application and the mixed breakdown method are imaged under a scanning electron microscope (Zeiss Ultra plus type). Referring to FIG. 6, a typical set of indentation SEM images is shown. Figure 6

[0094] Figure 6 (a), (c) and (e) are images of the indentations at different magnifications corresponding to the mixed breakdown test method (i.e. without tensile stress). As can be seen from the figures, the membrane 200 is still intact and has no cracks, notches or cracks, etc., only "meteor crater" like indentations formed by electrode particles pressing into the membrane 200, and particles remaining on the surface of the membrane 200. As can be seen from the EDX map embedded in (c), the particles are electrode particles. Figure 6

[0095] ​​Figure 6 (b), (d) and (f) are SEM images of the indentation left after the test method of the present application at different magnifications. In sharp contrast to the case without tensile stress, there is a clear 0.8 mm long crack in the middle of the indentation caused by the test method of the present application, and the crack direction is perpendicular to the tensile direction indicated by the arrow, and the crack can be seen from Figure 6 (f) The large magnification image shows that there are clear grain slip shear tracks around the crack, which indicates that the crack is indeed caused by the breakdown of the electrode particles.

[0096] From the above comparison, it can be seen that the tensile stress inside the separator 200 has a significant negative impact on the breakdown resistance of the separator 200, and the presence of tensile stress greatly accelerates the process of the separator 200 being broken down by particles, which can greatly reduce the breakdown strength of the separator 200. Therefore, the test method of the lithium ion battery separator 200 of the present application can more comprehensively and reasonably evaluate the safety and reliability of the separator 200.

[0097] In summary, although the preferred embodiments of the present application have been disclosed as above, the above preferred embodiments are not intended to limit the present application, and those skilled in the art can make various modifications and decorations without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application is defined by the scope of the claims.

Claims

1. A lithium-ion battery separator testing method, characterized in that: The separator is provided with a positive electrode sheet on one side and a negative electrode sheet on the other side. The testing method includes: applying a tensile stress to the diaphragm at a preset strain rate, and stopping applying the tensile stress to the diaphragm when the tensile stress reaches the preset tensile stress; applying a compressive load to the diaphragm in a stretched state while stopping applying the tensile stress to the diaphragm; When a compressive load is applied to the diaphragm, a test current between the positive electrode sheet and the negative electrode sheet is monitored in real time; The data of the compression load and the test current are collected, a correlation relationship between the compression load and the test current is established, and the coupling breakdown strength of the diaphragm is determined according to a data mutation point of the test current in the correlation relationship.

2. The testing method according to claim 1, wherein: Applying tensile stress to the diaphragm at a preset strain rate includes: A tensile stress was applied to the separator at a strain rate of 0.01% / s to 0.05% / s.

3. The testing method according to claim 1, wherein: The step of stopping applying the tensile stress to the diaphragm when the tensile stress reaches a preset tensile stress comprises: When the preset tensile stress reaches 50% to 90% of the yield strength of the diaphragm material, the application of the tensile stress to the diaphragm is stopped.

4. The testing method according to claim 1, wherein: The step of stopping applying the tensile stress to the diaphragm when the tensile stress reaches a preset tensile stress comprises: When the preset tensile stress reaches 50 MPa to 150 MPa, the application of the tensile stress to the diaphragm is stopped.

5. The testing method according to claim 1, wherein: Applying tensile stress to the diaphragm at a preset strain rate and stopping applying tensile stress to the diaphragm when the tensile stress reaches the preset tensile stress includes: A tensile stress was applied to the diaphragm at a strain rate of 0.032% / s, and the application of the tensile stress to the diaphragm was stopped when the tensile stress reached 100 MPa.

6. The testing method according to claim 1, wherein: The step of applying a compressive load to the diaphragm in a stretched state while stopping applying the tensile stress to the diaphragm comprises: Synchronously with the stopping of the application of the tensile stress to the diaphragm, a compressive load is applied to the diaphragm in the tensile state at a loading rate of 0.5 kgf / s to 5 kgf / s.

7. The testing method according to claim 6, characterized in that: The step of applying a compressive load to the diaphragm in a stretched state while stopping applying the tensile stress to the diaphragm comprises: Synchronously with the cessation of the application of the tensile stress to the diaphragm, a compressive load was applied to the diaphragm in the tensile state at a loading rate of 1 kgf / s.

8. The testing method according to claim 1, wherein: The real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet includes: A voltage of 1 mV to 10 mV is applied between the positive electrode sheet and the negative electrode sheet, and the current of the loop is scanned to obtain the test current.

9. The testing method according to claim 8, characterized in that: The real-time monitoring of the test current between the positive electrode sheet and the negative electrode sheet includes: A voltage of 5 mV is applied between the positive electrode sheet and the negative electrode sheet, and the current of the loop is scanned to obtain the test current.

10. The testing method according to claim 1, wherein: The collecting data of the compression load and the test current and establishing a correlation between the compression load and the test current includes: The correlation between the compression load and the test current is obtained by synchronously aligning the data of the compression load and the test current on a time axis.

11. The testing method according to claim 1, wherein: Determining the coupling breakdown strength of the diaphragm according to the data mutation point of the test current in the association relationship includes: In a case where the test current continuously exceeds a first threshold, determining the compression load corresponding to when the test current continuously exceeds the first threshold for the first time as the coupling breakdown strength; or A first-order derivative of the test current with respect to the compressive load is calculated, and when the first-order derivative exceeds a preset slope threshold, the corresponding compressive load is determined to be the coupling breakdown strength.

12. A testing device for lithium-ion battery separator, characterized in that: include: A support module is configured to place a diaphragm to be tested, wherein one side of the diaphragm is provided with a positive electrode sheet, and the other side is provided with a negative electrode sheet, and the length of the diaphragm is greater than the length of the positive electrode sheet or the negative electrode sheet; a stretching module, configured to fix both ends of the diaphragm and apply a tensile stress to the diaphragm at a preset strain rate, and stop applying the tensile stress to the diaphragm when the tensile stress reaches the preset tensile stress; a compression module configured to apply a compressive load to the stack of positive electrode sheet-separator-negative electrode sheet while ceasing to apply tensile stress to the separator; a monitoring module configured to monitor in real time a test current between the positive electrode sheet and the negative electrode sheet when a compressive load is applied to the diaphragm; as well as The control module is configured to collect data of the compression load and the test current, establish a correlation between the compression load and the test current, and determine the coupling breakdown strength of the diaphragm according to a data mutation point of the test current in the correlation.

13. The testing device according to claim 12, characterized in that: The stretching module is configured as follows: A tensile stress was applied to the diaphragm at a strain rate of 0.032% / s, and the application of the tensile stress to the diaphragm was stopped when the tensile stress reached 100 MPa.

14. The testing device according to claim 13, characterized in that: The compression module is configured as follows: Synchronously with the cessation of the application of the tensile stress to the diaphragm, a compressive load was applied to the diaphragm in the tensile state at a loading rate of 1 kgf / s.

15. The testing device according to claim 14, characterized in that: The monitoring module is configured as follows: A voltage of 5 mV is applied between the positive electrode sheet and the negative electrode sheet, and the current of the loop is scanned to obtain a test current.

16. The testing device according to claim 15, characterized in that The control module is configured as follows: Collect the data of the compression load and the test current, synchronize the data of the compression load and the test current through the time axis to obtain the correlation relationship between the compression load and the test current, and determine the coupling breakdown strength of the diaphragm according to the data mutation point of the test current in the correlation relationship.

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