A method for testing a coated separator for lithium batteries for dusting

Abstract

This invention discloses a method for testing the powder shedding of coated separators for lithium batteries. The method involves first using a spectrophotometer to perform a baseline test on foam cotton, then selecting a color fastness meter as the friction testing instrument. After attaching the foam cotton to a counterweight friction head, the sample is subjected to a friction test. Following the friction test, the foam cotton is removed, and the foam cotton after the friction test is tested again using a spectrophotometer. The powder shedding rate is calculated based on the measured brightness, red-green, and yellow-blue values. The friction test in this invention's coated separator powder shedding test method utilizes a color fastness meter. Without altering the structure of existing color fastness meters, using softer foam cotton attached to a metal friction head effectively avoids damage to the coating caused by the back-and-forth friction of the metal friction head in existing tests, accurately characterizing the actual powder shedding situation. Using a spectrophotometer to characterize powder shedding through L, A, and B values ​​provides more accurate test results.

Description

Technical Field

[0001] This invention relates to the field of separator manufacturing technology, and specifically to a method for testing powder shedding from coated separators used in lithium batteries. Background Technology

[0002] In the field of battery manufacturing technology, lithium-ion batteries are widely used due to their high energy density, long lifespan, and good environmental performance. The performance of lithium-ion batteries is closely related to the separator inside the battery. The separator is an indispensable inner component of lithium-ion batteries, its main function being to prevent physical contact between the positive and negative electrodes while allowing lithium ions to pass through. To further improve the performance of lithium-ion batteries, researchers have developed coated separators, which involve coating the separator surface with one or more layers of coatings with special functions. These coatings can improve the mechanical strength, thermal stability, chemical stability, and electrochemical performance of the separator.

[0003] In the field of lithium battery technology, the problem of powder shedding from coated separators is an important research topic. Powder shedding refers to the phenomenon where the coating detaches from the separator surface when subjected to friction, impact, or other external forces. Powder shedding leads to a decline in coating performance, affecting the overall performance and safety of lithium batteries. Therefore, accurately assessing the powder shedding rate of coated separators is crucial for controlling lithium battery quality. Existing solutions: Current methods for testing powder shedding from coated separators typically rely on visual inspection or simple friction tests. Friction tests directly use a metal head as the friction head. During the back-and-forth friction of the separator sample, the metal head rubs off the PCS (Polymer coating separator) surface layer, while simultaneously damaging the CCS (Ceramic coating separator) inorganic coating, thus failing to accurately characterize the powder shedding of the PCS coating layer. Overall, existing methods for testing powder shedding from coated separators are simple to operate, highly subjective, and have low accuracy, failing to meet the needs of large-scale separator quality control. Therefore, developing a highly accurate, efficient, and widely adaptable method for testing powder shedding from coated separators has become an urgent problem to be solved in the field of lithium battery coated separators. Summary of the Invention

[0004] The purpose of this invention is to provide a method for testing the powder shedding of coated separators for lithium batteries, thereby solving the technical problems of high subjectivity and low accuracy in existing methods for testing the powder shedding of coated separators.

[0005] The present invention adopts the following technical solution: a method for testing powder shedding from a coated separator used in lithium batteries, comprising the following steps:

[0006] S1. Foam Cotton Reference Value Test: Cut the foam cotton into standard foam cotton and carrier foam cotton. Take one standard foam cotton as a standard sample. Completely cover the bottom of the standard sample with double-sided tape and stick it on top of a carrier foam cotton. Use a spectrophotometer to detect the luminance value L of the standard sample with the carrier foam cotton attached. R Red-green value A R Yellow-blue value B R ;

[0007] S2. Preparation of samples for friction-induced powder shedding: The lithium battery to be tested is cut into separator samples of the same size using a coated separator as test samples;

[0008] S3. Preparation of test conditions for color fastness tester:

[0009] (1) A color fastness meter was selected as the friction test instrument;

[0010] (2) Take a standard foam cotton and use double-sided tape to stick it to the counterweight friction head of the color fastness tester;

[0011] (3) Place the test sample on the test platform of the color fastness tester, clamp the front and back of the test sample with clamps respectively, and stick the excess part of the diaphragm to the front and back sides of the test platform below the clamps.

[0012] S4. Sample Testing and Characterization: Set the number of friction experiments and use a counterweight friction head with standard foam cotton to conduct friction experiments on the test sample.

[0013] S5. After the friction test, remove the standard foam cotton. Place the standard foam cotton with the friction test side facing up and the carrier foam cotton on the bottom side. Use a spectrophotometer to measure the brightness value L of the standard foam cotton after the friction test. s Red-green value A s Yellow-blue value B s ;

[0014] S6. Calculate the powder shedding rate of the test sample using the following formula:

[0015]

[0016] In step S3, before placing the test sample on the test platform of the color fastness meter, a lint-free paper is first covered on the test platform of the color fastness meter, and the lint-free paper is fixed around its edges with tape. The lint-free paper adheres to the test platform, and its surface is flat and wrinkle-free. The tape surface is also flat. Then, the test sample is placed on the lint-free paper. Before fixing the test sample, paper tape is first pasted on the front and back sides of the test platform under the fixture, and then double-sided tape is pasted on the surface of the paper tape. After the test sample is clamped by the fixture, the excess part of the diaphragm is pasted on the double-sided tape on the front and back sides of the test platform.

[0017] The paper tape is larger than the double-sided tape. The width of the paper tape is 10–30 mm (e.g., 10 mm, 12 mm, 15 mm, 18 mm, 20 mm, 22 mm, 25 mm, 28 mm, 30 mm), and the length is 250–500 mm (e.g., 250 mm, 280 mm, 300 mm, 350 mm, 380 mm, 400 mm, 450 mm, 480 mm, 5 mm). 00mm); the width of the double-sided tape pasted on the paper tape is 10-30mm (for example, it can be 10mm, 12mm, 15mm, 18mm, 20mm, 22mm, 25mm, 28mm, 30mm), and the length is 250-400mm (for example, it can be 250mm, 280mm, 300mm, 350mm, 380mm, 400mm, 450mm, 480mm, 500mm).

[0018] Step S3, step (2) specifically involves: attaching double-sided tape to the counterweight friction head, placing the standard foam cotton on the counterweight friction head with tweezers, and clamping it tightly with tweezers to ensure the standard foam cotton adheres closely to the counterweight friction head.

[0019] In step S5, after the friction test, the standard foam cotton is removed from the counterweight friction head using tweezers.

[0020] The foam cotton is black foam cotton, and the hardness of the foam cotton is Shore hardness of 10 to 50 (for example, it can be 10, 15, 20, 25, 30, 35, 40, 45, 50); the foam cotton material is one of XPE, EPE, EVA, and polystyrene foam cotton.

[0021] The thickness of the foam cotton is 2–100 mm (e.g., it can be 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm); the standard size of the foam cotton is 20–50 mm × 20–50 mm (e.g., it can be 20 mm × 20 mm, 30 mm × 20 mm, 40 mm × 20 mm, 50 mm × 20 mm, 30 mm × 30 mm, or 40 mm × 30 mm). 50mm×30mm, 40mm×40mm, 50mm×40mm, 50mm×50mm); the carrier foam cotton size is 40~100mm×40~100mm (for example, it can be 40mm×40mm, 50mm×40mm, 60mm×40mm, 70mm×40mm, 80mm×40mm, 90mm×40mm, 100mm×40mm, 50mm×50mm, 60mm×50mm, 70mm×50mm, 80mm×50mm, 90mm×50mm, 100mm×40mm, 50mm×50mm, 60mm×50mm, 70mm×50mm, 80mm×50mm, 90mm×50mm, 100mm×30mm, 40mm×40mm, 50mm×4 ... The sample sizes are 50mm×50mm, 60mm×60mm, 70mm×60mm, 80mm×60mm, 90mm×60mm, 100mm×60mm, 70mm×70mm, 80mm×70mm, 90mm×70mm, 100mm×70mm, 80mm×80mm, 90mm×80mm, 100mm×80mm, 90mm×90mm, 100mm×90mm, 100mm×100mm; the diaphragm sample size is 10~35mm×200~300mm (for example, it can be...). 10mm×200mm, 15mm×200mm, 20mm×200mm, 25mm×200mm, 30mm×200mm, 35mm×200mm, 10mm×250mm, 15mm×250mm, 20mm×250mm, 25mm×250mm, 30mm×250mm, 35mm×250mm, 10mm×300mm, 15mm×300mm, 20mm×300mm, 25mm×300mm, 30mm×300mm, 35mm×300mm).

[0022] In step S4, the number of friction tests is 1 to 10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 times); the friction speed is 20-40 cycles / min (e.g., 20, 25, 30, 35, or 40 cycles / min); and the counterweight of the friction head is 1-4N (e.g., 1N, 2N, 3N, or 4N).

[0023] The ambient temperature of the spectrophotometer is 15-35℃ (e.g., 15℃, 20℃, 25℃, 30℃, 35℃) and the humidity is 10-50% (e.g., 10%, 20%, 30%, 40%, 50%).

[0024] The lithium battery coating membrane to be tested is suitable for aqueous multilayer membranes, ceramic-coated membranes, aqueous mixed-coated membranes, oil-based multilayer coated membranes, and oil-based mixed-coated membranes; more preferably, the lithium battery coating membrane to be tested is suitable for aqueous multilayer adhesive-coated membranes, ceramic mixed-coated membranes, ceramic multilayer coated membranes, aqueous mixed-coated membranes, oil-based multilayer adhesive-coated membranes, and oil-based mixed-coated membranes; even more preferably, the lithium battery coating membrane to be tested is suitable for aqueous multilayer adhesive-coated membranes, ceramic mixed-coated membranes, ceramic multilayer coated membranes, aqueous mixed-coated membranes, oil-based multilayer PVDF / PMMA coated membranes, oil-based multilayer aramid coated membranes, and oil-based mixed-coated membranes.

[0025] The lithium battery coated separators to be tested are suitable for aqueous multilayer coated separators, ceramic multilayer coated separators, oil-based multilayer PVDF / PMMA coated separators, and oil-based multilayer aramid coated separators.

[0026] The beneficial effects of this invention are:

[0027] (1) The friction test in the coating separator powder shedding test method adopted in this invention is carried out using a color fastness meter. Without changing the structure of the existing color fastness meter, a softer foam cotton is pasted on the metal friction head, which can effectively avoid the damage to the coating during the back-and-forth friction of the metal friction head in the existing test, and can accurately characterize the actual situation of coating powder shedding; the coating of lithium battery coated separator is relatively thin, with an inorganic coating thickness of about 1-4μm and an adhesive layer of 0.5-1.5μm. The foam cotton is soft and can protect the coating from damage. In addition, the foam cotton has a porous structure and a certain roughness, which can effectively attach the peeled powder to the black foam cotton, making the powder shedding rate characterization more accurate;

[0028] (2) High accuracy: The spectrophotometer is used to characterize the powder shedding by using L, A, and B values. L represents the degree of powder shedding on the black foam cotton, which is characterized by whiteness and is the only variable of powder shedding. A and B are standard values, which are quantitative and can accurately assess the color change and surface performance of the object. Compared with manual visual inspection or simple friction test, the test results of this invention are more accurate and avoid the influence of human factors.

[0029] (3) Wide range of applications: The test method provided by this invention can meet the quality control requirements of different coating specifications, different coating series and mixed coating series coated diaphragms, and has a wide range of applications.

[0030] Overall, this invention can improve the accuracy of diaphragm powder shedding rate testing, and can quickly and accurately assess the manufacturing level of the diaphragm in the production process, avoiding a series of problems such as product scrapping and abnormal customer use caused by diaphragm powder shedding.

[0031] Preferably, since both the inorganic coating and adhesive layer of the lithium battery separator are white coatings, and black foam cotton is used, the black and white color contrast is more obvious, and the powder shedding characterization is more accurate.

[0032] Preferably, the two ends of the diaphragm are fixed by paper tape and double-sided tape. Paper tape is easy to tear and does not leave adhesive residue on the equipment. One side of the double-sided tape is pasted on the paper tape, and the other side is used to paste the sample. If the double-sided tape is damaged, the paper tape can be torn off and replaced at the same time. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a spectrophotometer;

[0034] Figure 2 yes Figure 1 Top view;

[0035] Figure 3 This is a schematic diagram of a color fastness tester;

[0036] Figure 4 yes Figure 3 Side view of the test platform of the color fastness tester.

[0037] In the diagram: 1-Spectrophotometer, 1.1-Black light shield, 1.2-Projection target cover, 1.3-Display screen, 1.4-Sample placement stage, 1.5-Groove, 2-Color fastness meter, 2.1-Test platform, 2.2-Clamp, 2.3-Counterweight friction head, 2.4-Rubbing cycle setting panel, 2.5-Start button, 2.6-Stop button, 2.7-Power button, 3-Test sample. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0039] This embodiment provides a method for testing powder shedding from a coated separator used in lithium batteries. The specific steps are as follows:

[0040] S1. Foam Cotton Reference Value Test: Black EVA foam cotton with a thickness of 3mm and a Shore hardness of 20 is selected as the powder carrier. The foam cotton is cut into standard foam cotton and carrier foam cotton. The standard foam cotton is 20mm × 20mm in size, and the carrier foam cotton is 45mm × 45mm in size. A standard foam cotton is attached to a carrier foam cotton using 3M double-sided tape, ensuring the standard foam cotton completely covers the tape. The standard foam cotton is placed on the sample testing stage of the spectrophotometer and secured with a black light shield before testing. The brightness, red-green, and yellow-blue values ​​of the standard sample are read from the spectrophotometer's display screen and recorded as L. R A R B R ;

[0041] S2. Preparation of samples for friction-induced powder shedding: The lithium battery to be tested is cut into separator samples of the same size using a coated separator as test samples. In this embodiment, the test sample size is 20mm×250mm. The coated separator type is water-based multilayer adhesive 8+1.5+0.5, where 1.5 is a boehmite layer with a coating thickness of 1.5 micrometers, and 0.5 is a PCS adhesive layer with an adhesive thickness of 0.5 micrometers.

[0042] S3. Preparation of test conditions for color fastness tester:

[0043] (1) Select a color fastness meter as the friction test instrument. Cover the test platform of the color fastness meter with lint-free paper and fix the lint-free paper around its perimeter with tape. The lint-free paper should be flat and wrinkle-free, and the tape should be flat. First, paste 250mm×25mm paper tape on the front and back sides of the test platform under the fixture of the color fastness meter, and then paste 250mm×20mm double-sided tape on the paper tape. The paper tape is larger than the double-sided tape. The paper tape is easy to tear and does not leave adhesive residue on the equipment. One side of the double-sided tape is pasted on the paper tape, and the other side is used to paste the sample. If the double-sided tape is damaged, the paper tape can be torn off and replaced at the same time. Since the double-sided tape is pasted on the paper tape, the double-sided tape is required to be smaller than the paper tape. The main function of the paper tape is to leave no adhesive residue when it is torn off the equipment.

[0044] (2) Select a 2N counterweight for the color fastness tester's counterweight friction head, attach double-sided tape to the counterweight friction head, use tweezers to take a standard foam cotton and attach it to the counterweight friction head, and use tweezers to clamp it so that the standard foam cotton is tightly attached to the counterweight friction head; a new standard foam cotton needs to be replaced for each sample test.

[0045] (3) Place the test sample on the test platform of the color fastness tester, clamp the front and back of the test sample with clamps respectively, and stick the excess part of the diaphragm to the double-sided tape on the front and back sides of the test platform under the clamps.

[0046] S4. Sample testing and characterization: The test sample was subjected to friction test using a counterweight friction head with standard foam cotton. The number of friction tests was set to 5, and the friction speed was 30 cycles / min.

[0047] S5. After the friction test, remove the standard foam cotton with tweezers. Place the standard foam cotton with the friction test side facing up and the carrier foam cotton attached to the bottom side. Place it on the sample test stage of the spectrophotometer and secure it with a black light shield. Read the brightness, red-green, and yellow-blue values ​​of the standard foam cotton after the friction test through the spectrophotometer's display screen, and record them as Ls, As, and Bs, respectively. The carrier foam cotton is placed on the spectrophotometer stage as the carrier for the spectrophotometer. A new carrier foam cotton can be replaced after each test; if it is not damaged, it does not need to be replaced.

[0048] The spectrophotometer, placed in an environment of 25℃ and 40% humidity, can read the brightness, red-green, and yellow-blue values ​​of the sample to be tested, denoted by L, A, and B, respectively.

[0049] L—brightness, ranging from 0 to 100. The higher the L value, the brighter the color; the lower the L value, the darker the color.

[0050] A—Red-green, a positive value indicates an increase in red content, and a negative value indicates an increase in green content;

[0051] B—Yellowish-blue, a positive value indicates an increase in yellow content, and a negative value indicates an increase in blue content.

[0052] S6. Calculate the powder shedding rate of the test sample using the following formula:

[0053]

[0054] Following the above method, the powder shedding rate of the five test samples is shown in the table below:

[0055]

[0056] Test Sample 1 18.78 0.05 0.15 1.21 Test Sample 2 18.77 0.07 0.14 1.20 Test sample 3 19.11 0.06 0.10 1.55 Test sample 4 18.78 0.05 0.11 1.22 Test sample 5 18.82 0.05 0.16 1.25

[0057] In other embodiments of the present invention, the number of friction tests and the counterweight of the counterweight friction head can be flexibly selected according to actual needs. The number of friction tests is usually less than 10, and the counterweight of the counterweight friction head is usually 1-4N.

[0058] In other embodiments of the present invention, foam cotton of other colors can also be used, as long as there is a significant color difference with the diaphragm sample to be tested; the material, hardness, and thickness of the foam cotton can be selected according to actual needs; the size of the standard foam cotton and the carrier foam cotton can also be flexibly cut according to actual needs.

Claims

1. A method for testing powder shedding from a coated separator used in lithium batteries, characterized in that, It includes the following steps: S1. Foam Cotton Reference Value Test: Cut the foam cotton into standard foam cotton and carrier foam cotton. Take one standard foam cotton as a standard sample. Completely cover the bottom of the standard sample with double-sided tape and stick it on top of a carrier foam cotton. Use a spectrophotometer to detect the luminance value L of the standard sample with the carrier foam cotton attached. R Red-green value A R Yellow-blue value B R ; S2. Preparation of samples for friction-induced powder shedding: The lithium battery to be tested is cut into separator samples of the same size using a coated separator as test samples; S3. Preparation of test conditions for color fastness tester: (1) A color fastness meter was selected as the friction test instrument; (2) Take a standard foam cotton and use double-sided tape to stick it to the counterweight friction head of the color fastness tester; (3) Place the test sample on the test platform of the color fastness tester, clamp the front and back of the test sample with clamps respectively, and stick the excess part of the diaphragm to the front and back sides of the test platform below the clamps. S4. Sample Testing and Characterization: Set the number of friction experiments and use a counterweight friction head with standard foam cotton to conduct friction experiments on the test sample. S5. After the friction test, remove the standard foam cotton. Place the standard foam cotton with the friction test side facing up and the carrier foam cotton on the bottom side. Use a spectrophotometer to measure the brightness value L of the standard foam cotton after the friction test. s Red-green value A s Yellow-blue value B s ; S6. Calculate the powder shedding rate of the test sample using the following formula:

2. The method for testing powder shedding from coated separators for lithium batteries according to claim 1, characterized in that: In step S3, before placing the test sample on the test platform of the color fastness meter, a lint-free paper is first covered on the test platform of the color fastness meter, and the lint-free paper is fixed around its edges with tape. The lint-free paper adheres to the test platform, and its surface is flat and wrinkle-free. The tape surface is also flat. Then, the test sample is placed on the lint-free paper. Before fixing the test sample, paper tape is first pasted on the front and back sides of the test platform under the fixture, and then double-sided tape is pasted on the surface of the paper tape. After the test sample is clamped by the fixture, the excess part of the diaphragm is pasted on the double-sided tape on the front and back sides of the test platform.

3. The method for testing powder shedding from coated separators for lithium batteries according to claim 2, characterized in that: The paper tape is larger than the double-sided tape. The width of the paper tape is 10-30mm and the length is 250-500mm. The width of the double-sided tape pasted on the paper tape is 10-30mm and the length is 250-400mm.

4. The method for testing powder shedding from coated separators for lithium batteries according to claim 1, characterized in that: Step S3, step (2) specifically involves: attaching double-sided tape to the counterweight friction head, placing the standard foam cotton on the counterweight friction head with tweezers, and clamping it tightly with tweezers to ensure the standard foam cotton adheres closely to the counterweight friction head.

5. The method for testing powder shedding from a coated separator for lithium batteries according to claim 1, characterized in that: In step S5, after the friction test, the standard foam cotton is removed from the counterweight friction head using tweezers.

6. The method for testing powder shedding from coated separators for lithium batteries according to claim 1, characterized in that: The foam cotton is black foam cotton, and the hardness of the foam cotton is Shore hardness 10-50; the foam cotton material is one of XPE, EPE, EVA, and polystyrene foam cotton.

7. The method for testing powder shedding from coated separators for lithium batteries according to claim 1, characterized in that: The thickness of the foam cotton is 2-100mm; the size of the standard foam cotton is 20-50mm × 20-50mm; the size of the carrier foam cotton is 40-100mm × 40-100mm; and the size of the diaphragm sample is 10-35mm × 200-300mm.

8. The method for testing powder shedding from a coated separator for lithium batteries according to claim 1, characterized in that: In step S4, the number of friction tests is 1 to 10; the friction speed is 20-40 cycles / min; and the counterweight of the counterweight friction head is 1-4N.

9. The method for testing powder shedding from a coated separator for lithium batteries according to claim 1, characterized in that: The ambient temperature of the spectrophotometer is 15-35℃, and the humidity is 10-50%.

10. The method for testing powder shedding from a coated separator for lithium batteries according to claim 1, characterized in that: The lithium battery coated separator to be tested is suitable for aqueous multilayer separators, ceramic coated separators, aqueous mixed-coating separators, oil-based multilayer coated separators, and oil-based mixed-coating separators.

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