Method for testing thermal shrinkage rate of battery diaphragm

Abstract

The invention belongs to the technical field of battery diaphragm detection, and discloses a method for testing the thermal shrinkage rate of a battery diaphragm, which comprises the following steps: preparing a substrate; a diaphragm with the length larger than the set length is taken, the first end of the diaphragm is fixed to the base plate, and a heavy object with the set weight is hung at the second end of the diaphragm; fixing the set position, between the first end and the second end, of the diaphragm on the substrate, and enabling the length, between the two fixed ends, of the diaphragm to be the set length; taking down the weight hung at the second end of the diaphragm; placing the substrate and the diaphragm in an environment with a set temperature for a set time; and measuring the minimum width of the baked diaphragm, and obtaining the thermal shrinkage rate of the diaphragm according to the minimum width of the baked diaphragm and the width of the diaphragm before baking. The method for testing the thermal shrinkage rate of the battery diaphragm provided by the invention can truly simulate the state of the diaphragm in a battery cell, characterize the shrinkage state of the diaphragm after a drying process, and truly measure the shrinkage rate of the diaphragm.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separator detection, and in particular to a method for testing the thermal shrinkage rate of a battery separator. Background Art

[0002] Lithium-ion battery separator is one of the key components in the internal structure of lithium-ion battery. The performance of the separator determines the interface structure and internal resistance of the battery, and directly affects the battery's capacity, cycle and safety. The main function of lithium-ion battery separator is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and causing a short circuit. In addition, it should ensure the normal passage of electrolyte ions. Since the electrolyte is usually an organic solvent system, the separator material must also be resistant to dissolution and corrosion by organic solvents. Generally, a high-strength thin-film polyolefin porous membrane is used. The performance requirement for the separator is generally that the thermal shrinkage rate of the separator is small, otherwise it will cause a short circuit, which will lead to safety problems such as thermal runaway of the battery. Therefore, it is of great significance to test the thermal shrinkage of the separator before production.

[0003] The existing test method for the thermal shrinkage rate of the diaphragm is to print a rectangular frame on the diaphragm, sandwich the diaphragm between A4 paper, and place it at a certain temperature for a certain period of time, then measure the length and width of the rectangular frame again, and calculate the shrinkage rate of the length and width of the diaphragm based on the measurement results. The existing test method for the thermal shrinkage rate of the diaphragm cannot accurately characterize the actual thermal shrinkage rate of the diaphragm in the battery cell. Summary of the invention

[0004] The purpose of the present invention is to provide a test method for the thermal shrinkage rate of a battery diaphragm, which can truly simulate the state of the diaphragm in the battery cell, characterize the shrinkage state of the diaphragm after the drying process, and truly measure the shrinkage rate of the diaphragm.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] The test method for thermal shrinkage of battery separators includes:

[0007] Prepare substrate;

[0008] Take a diaphragm with a length greater than a set length, fix the first end of the diaphragm on the substrate, and hang a weight of a set weight on the second end of the diaphragm;

[0009] Fixing the diaphragm at a set position between the first end and the second end on the substrate so that the length of the diaphragm between the two fixed ends is the set length;

[0010] Remove the weight hanging on the second end of the diaphragm;

[0011] placing the substrate and the diaphragm in an environment of a set temperature for a set time;

[0012] The minimum width of the diaphragm after baking is measured, and the thermal shrinkage rate of the diaphragm is obtained based on the minimum width of the diaphragm after baking and the width of the diaphragm before baking.

[0013] Beneficial effects of the present invention:

[0014] The test method for the thermal shrinkage rate of a battery diaphragm provided by the present invention can simulate the fixation of the two ends of the R angle of a battery cell diaphragm in reality by fixing the two fixed ends; by applying a weight of a set weight in the length direction of the diaphragm, it can simulate the tensile force applied to the diaphragm during the process of being wound into a battery cell; the set length between the two fixed ends of the diaphragm is the inner diameter length of the battery cell, simulating the actual cut-off length of the diaphragm in the battery cell; thereby, the state of the diaphragm in the battery cell can be truly simulated, the shrinkage state of the diaphragm after the drying process can be characterized, and the shrinkage rate of the diaphragm can be truly measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic flow chart of a method for testing thermal shrinkage of a battery separator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0017] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0019] In the description of this embodiment, the terms "upper", "lower", "right", etc., directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0020] The diaphragm is one of the key components in the internal structure of lithium-ion batteries. The performance of the diaphragm determines the interface structure and internal resistance of the battery, and directly affects the battery's capacity, cycle and safety. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and causing a short circuit. In addition, it should ensure the normal passage of electrolyte ions. Since the electrolyte is usually an organic solvent system, the diaphragm material must also be resistant to dissolution and corrosion by organic solvents. Generally, a high-strength thin-film polyolefin porous membrane is used. The performance requirements for the diaphragm are generally that the thermal shrinkage rate of the diaphragm is small, otherwise it will cause a short circuit, which will lead to safety problems such as thermal runaway of the battery. Therefore, it is of great significance to test the thermal shrinkage of the diaphragm before production.

[0021] The existing test method for the thermal shrinkage rate of the diaphragm is to print a rectangular frame on the diaphragm, sandwich the diaphragm between A4 paper, and place it at a certain temperature for a certain period of time, then measure the length and width of the rectangular frame again, and calculate the shrinkage rate of the length and width of the diaphragm based on the measurement results. The existing test method for the thermal shrinkage rate of the diaphragm cannot accurately characterize the actual thermal shrinkage rate of the diaphragm in the battery cell.

[0022] like Figure 1 As shown, based on the above problems, an embodiment of the present invention provides a method for testing the thermal shrinkage rate of a battery separator, comprising the following steps:

[0023] S1. Prepare a substrate.

[0024] The substrate needs to be made of high temperature resistant material to avoid deformation after being placed in the oven. Optionally, the substrate can be made of a wooden board, a metal board, or a ceramic board. In this embodiment, the substrate is made of a wooden board, which can avoid deformation after being placed in the oven and will not overheat, so as to avoid burns to the experimenter when taking it out of the oven.

[0025] It should also be noted that the substrate must be clean, flat, and non-deformed so that the diaphragm can be flat and non-deformed after being fixed on it, thereby improving the accuracy of the test results.

[0026] S2. Take a diaphragm whose length is greater than a set length, fix the first end of the diaphragm on a substrate, and hang a weight of a set weight on the second end of the diaphragm.

[0027] In this embodiment, the length is set to 170 mm, which is the half length of the innermost diameter of the L194F130A battery cell. Of course, the set length is not limited to this embodiment, but depends on the battery cell model. In this embodiment, a diaphragm with a length greater than 170 mm is used.

[0028] The first end of the diaphragm is fixed on the substrate by pasting a first double-sided adhesive tape on the substrate and pasting the first end of the diaphragm on the first double-sided adhesive tape. It should be noted that the junction between the diaphragm and the first double-sided adhesive tape needs to be pasted flat. In the above manner, both the firmness of the diaphragm fixation and the flatness of the diaphragm after fixation can be ensured.

[0029] Furthermore, after the first end of the diaphragm is pasted on the first double-sided tape, the upper surface of the first end of the diaphragm is covered with a high temperature protection layer. It should be noted that the edge of the high temperature protection layer facing the second end of the diaphragm needs to be flush with the edge of the first double-sided tape facing the second end of the diaphragm to ensure the accuracy of the actual test length of the diaphragm. By covering the upper surface of the first end of the diaphragm with a high temperature protection layer, the first end of the diaphragm can be prevented from shrinking and deforming during the oven baking process, thereby avoiding shrinkage and deformation that affects the actual measurement length range of the diaphragm, and ensuring the accuracy of the test results. Optionally, the high temperature protection layer can be a high temperature tape, which can not only prevent high temperatures, but also be convenient to cover on the diaphragm.

[0030] By hanging a weight of a set weight on the second end of the diaphragm, the tensile force on the diaphragm during winding into a battery cell can be simulated. Optionally, the set weight of the weight hung on the second end of the diaphragm is 110g. Of course, the set weight is not limited to this and is determined specifically according to the model of the battery cell.

[0031] S3. Fix the diaphragm on the substrate at a set position between the first end and the second end, so that the length of the diaphragm between the two fixed ends is the set length.

[0032] By fixing the two fixed ends, it is possible to simulate the fixation of the battery cell diaphragm at both ends of the R angle in reality.

[0033] Specifically, a second double-sided tape is pasted on the substrate so that the distance between the edge of the first double-sided tape facing the second double-sided tape and the edge of the second double-sided tape facing the first double-sided tape is the above-mentioned set length; the position corresponding to the diaphragm and the second double-sided tape is pasted on the second double-sided tape. It should be noted that the junction between the diaphragm and the second double-sided tape needs to be pasted flat. In the above manner, both the firmness of the diaphragm fixation and the flatness of the diaphragm after fixation can be guaranteed. It should also be noted that during the posting process, the diaphragm needs to maintain the tension of the set weight, that is, the second end of the diaphragm needs to be hung with a weight of the set weight.

[0034] Furthermore, after the diaphragm is pasted on the second double-sided tape, the upper surface of the position where the diaphragm is pasted on the second double-sided tape is covered with a high temperature protection layer. It should be noted that the edge of the high temperature protection layer facing the first end of the diaphragm needs to be flush with the edge of the second double-sided tape facing the first end of the diaphragm to ensure the accuracy of the actual test length of the diaphragm. By covering the high temperature protection layer at the position corresponding to the diaphragm and the second double-sided tape, it is possible to avoid shrinkage deformation of the fixed position of the diaphragm during the oven baking process, thereby avoiding shrinkage deformation that affects the actual measurement length range of the diaphragm and ensuring the accuracy of the test results. Optionally, the high temperature protection layer can be a high temperature tape, which can not only prevent high temperatures, but also be convenient to cover on the diaphragm.

[0035] S4. Remove the weight hanging on the second end of the diaphragm.

[0036] At this point the diaphragm has been secured under the tension of the weight, so the weight can be removed.

[0037] S5. Place the substrate and the diaphragm in an environment with a set temperature for a set time.

[0038] Optionally, the set temperature ranges from 60°C to 100°C. For example, the set temperature may be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C. Optionally, the set time ranges from 8h to 10h. For example, the set time may be 8h, 8.5h, 9h, 9.5h, or 10h. Optionally, the substrate and the diaphragm may be placed in the oven together.

[0039] S6. Measure the minimum width of the diaphragm after baking, and calculate the thermal shrinkage rate of the diaphragm based on the minimum width of the diaphragm after baking and the width of the diaphragm before baking. At the same time, observe the curling of the diaphragm and take photos to record.

[0040] Thermal shrinkage ratio of the separator = (width of the separator before shrinkage - minimum width of the separator after shrinkage) / width of the separator before shrinkage.

[0041] The above steps can be repeated, with the set temperature of the oven being a variable and the other conditions being unchanged, to obtain the thermal shrinkage rate of the diaphragm at different baking temperatures.

[0042] The test method for the thermal shrinkage rate of the battery diaphragm provided in the embodiment of the present invention can simulate the fixation of the battery cell diaphragm at the two ends of the R angle in reality by fixing the two fixed ends; by applying a weight of a set weight in the length direction of the diaphragm, it can simulate the tensile force applied to the diaphragm in the process of being wound into a battery cell; the set length between the two fixed ends of the diaphragm is the inner diameter length of the battery cell, simulating the actual cut-off length of the diaphragm in the battery cell; thereby, the state of the diaphragm in the battery cell can be truly simulated, the shrinkage state of the diaphragm after the drying process can be characterized, and the shrinkage rate of the diaphragm can be truly measured.

[0043] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for testing thermal shrinkage of battery separators, characterized in that: include: Prepare substrate; Take a diaphragm with a length greater than a set length, fix the first end of the diaphragm on the substrate, and hang a weight of a set weight on the second end of the diaphragm; Fixing the diaphragm at a set position between the first end and the second end on the substrate so that the length of the diaphragm between the two fixed ends is the set length; Remove the weight hanging on the second end of the diaphragm; placing the substrate and the diaphragm in an environment of a set temperature for a set time; The minimum width of the diaphragm after baking is measured, and the thermal shrinkage rate of the diaphragm is obtained based on the minimum width of the diaphragm after baking and the width of the diaphragm before baking.

2. The method for testing thermal shrinkage of a battery separator according to claim 1, characterized in that: Fixing the first end of the diaphragm on the substrate specifically includes: pasting a first double-sided adhesive tape on the substrate, and pasting the first end of the diaphragm on the first double-sided adhesive tape.

3. The method for testing thermal shrinkage of battery separator according to claim 2, characterized in that: After the first end of the diaphragm is adhered to the first double-sided tape, the upper surface of the first end of the diaphragm is covered with a high-temperature protection layer, and the edge of the high-temperature protection layer toward the second end of the diaphragm must be flush with the edge of the first double-sided tape toward the second end of the diaphragm.

4. The method for testing thermal shrinkage of battery separator according to claim 1, characterized in that: The set weight is equal to the tensile force to which the diaphragm is subjected during the process of being wound into a battery core.

5. The method for testing thermal shrinkage of battery separator according to claim 1, characterized in that: The diaphragm is fixed at a set position between the first end and the second end on the substrate so that the length of the diaphragm between the two fixed ends is the set length. Specifically, the second double-sided tape is pasted on the substrate so that the distance between the edge of the first double-sided tape facing the second double-sided tape and the edge of the second double-sided tape facing the first double-sided tape is the above-mentioned set length; the position corresponding to the diaphragm and the second double-sided tape is pasted on the second double-sided tape.

6. The method for testing thermal shrinkage of a battery separator according to claim 5, characterized in that: After the diaphragm is attached to the second double-sided tape, the upper surface of the diaphragm where the diaphragm is attached to the second double-sided tape is covered with a high-temperature protection layer, and the edge of the high-temperature protection layer facing the first end of the diaphragm must be flush with the edge of the second double-sided tape facing the first end of the diaphragm.

7. The method for testing thermal shrinkage of a battery separator according to claim 3 or 6, characterized in that: The high temperature protection layer is a high temperature adhesive tape.

8. The method for testing thermal shrinkage of battery separator according to claim 1, characterized in that: The set temperature ranges from 60°C to 100°C.

9. The method for testing thermal shrinkage of battery separator according to claim 1, characterized in that: The setting time ranges from 8h to 10h.

10. The method for testing thermal shrinkage of battery separator according to claim 1, characterized in that: The substrate is a wooden board.

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