Dot-coating patterned roller, separator and adhesive-coating device

Abstract

A dot-coating patterned roller, a separator and an adhesive-coating device. The dot-coating patterned roller comprises: a cylindrical cavity, wherein a plurality of bumps are formed on the surface of the cylindrical cavity, and the bumps are arranged in the form of a hexagonal structure, and are located at the corners of the hexagonal structure, such that after the bumps on the surface of the cylindrical cavity are connected with lines, the connecting lines can form an arc-shaped honeycombed structure by means of enclosure; and the hexagonal structure refers to a curved-surface hexagon formed by means of bending a regular hexagon along the surface curvature of the cylindrical cavity. The separator comprises a base film, wherein a plurality of coated dots are formed on the surface of the base film, and the coated dots are arranged in the form of a hexagon, and are located at the corners of the hexagon, such that after the coated dots are connected with lines, the connecting lines can form a honeycombed structure on the surface of the base film by means of enclosure. The bumps on the dot-coating patterned roller are distributed in the form of a hexagonal structure, and the coated dots on the separator obtained by means of coating are uniformly distributed in the form of a hexagon; and compared with spray coating, coated dots of the present invention have more uniform sizes and more regular shapes.

Description

Dot coating roller, diaphragm and adhesive application device Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a dot coating roller, a separator, and an adhesive coating device. Background Technology

[0002] Lithium-ion batteries are characterized by high voltage, high specific energy, and high cycle efficiency, and are widely used in various fields of production and daily life. Among them, the separator, as an indispensable part of the battery, plays an important role in the battery's safety and electrical performance.

[0003] Currently, polyolefin microporous membranes dominate the LIB (lithium-ion battery) separator market due to their stable chemical and electrochemical properties and high mechanical strength. However, the inherent low melting point and anisotropy of polyolefin materials make them prone to melting and shrinkage at high temperatures, causing short circuits and irreversible damage to the battery. Furthermore, during battery manufacturing, issues such as poor adhesion between the electrodes and the separator, and a soft cell remain. A fundamental and effective solution is to add a functional coating with adhesive properties to the original separator, which acts as a bond between the positive and negative electrodes and the separator, increasing the cell's rigidity and thus improving battery safety and electrochemical performance. However, existing coatings often have high coverage and large coating amounts, which can lead to increased internal resistance and decreased electrochemical performance. Therefore, it is necessary to rationally control the coating coverage to ensure that the coated separator possesses both high adhesion and excellent electrochemical performance.

[0004] The invention patent with publication number CN107876313 A discloses a battery separator coating method. The coating method involves spraying slurry onto the separator surface using a spraying device, scraping off excess slurry with a scraping device, and then drying. This method reduces the coating amount compared to the traditional concave roller coating method, but the coating point size is uneven, and the adhesion of the electrode sheets after hot pressing is poor. The utility model patent with authorization announcement number CN204307779U provides a novel adhesive coating device. The outer circumferential surface of the adhesive coating roller of this device has multiple raised strips spaced apart along the axial direction of the adhesive coating roller. When the separator moves, it drives the adhesive coating roller to rotate, thereby forming a spaced strip-shaped adhesive layer on the separator. Although the strip-shaped adhesive layer provides more uniform coating, the coating amount is also larger. The invention patent with publication number CN113363672A provides a spray-coated separator, which includes a base film, an inorganic coating coated on one side of the base film, and an organic particulate dot coating sprayed on the coating side and the base film side. Its spray points are approximately circular, but its single-layer adhesive application rate is 0.7 g / m². 2 The amount of adhesive applied is still relatively large, the bonding strength is <1.2 N / m, the adhesion is weak, and the adhesive application points are irregularly distributed. Therefore, the existing technology has not been able to effectively solve the problems of poor adhesion and uneven adhesive application in battery separators. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a dot coating roller.

[0006] Another object of the present invention is to provide a diaphragm.

[0007] Another object of the present invention is to provide an adhesive application apparatus.

[0008] Another objective of this invention is to provide a coating method for a diaphragm, which, without affecting the electrochemical performance of the diaphragm, achieves uniform coating point size on the diaphragm surface, arrayed coating point positions, low coating amount, controllable coverage, and high adhesion, thereby improving the safety performance of the diaphragm.

[0009] The objective of this invention is achieved through the following technical solution.

[0010] A dot-coating roller includes: a cylindrical cavity, on the surface of which a plurality of protrusions are formed, the protrusions being arranged in a hexagonal structure, the protrusions being located at the corners of the hexagonal structure, so that when the protrusions are connected on the surface of the cylindrical cavity, the connecting line can form an arc-shaped honeycomb structure, wherein the regular hexagons are bent along the arc of the surface of the cylindrical cavity to form an arc-shaped hexagon, which is the hexagonal structure.

[0011] In the above technical solution, the three hexagonal structures with their vertices connected are provided with the same protrusion at their vertices.

[0012] In the above technical solution, the side length of the regular hexagon is 850-1000 μm.

[0013] In the above technical solution, the diameter of each of the protrusions is 300-450 μm.

[0014] In the above technical solution, the size of the gap between the dot coating roller and the base film to be coated is adjustable.

[0015] A diaphragm includes: a base membrane, on the surface of which a plurality of coating dots are formed, the coating dots being arranged in a hexagonal pattern and located at the corners of the hexagons, such that when the coating dots are connected, the lines can form a honeycomb structure on the surface of the base membrane, wherein the coverage of the coating dots on the surface of the base membrane is 5 to 10% by area.

[0016] In the above-mentioned diaphragm technical solution, the same coating point is provided on the vertices of the three interconnected hexagons.

[0017] In the above-mentioned diaphragm technical solution, the hexagon is a regular hexagon.

[0018] An adhesive application apparatus, comprising: the dot-coating roller.

[0019] A method for applying adhesive to a diaphragm includes: applying adhesive using the adhesive application device.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. The protrusions of the dot coating roller of the present invention are distributed in a hexagonal structure, and the coating dots of the coated diaphragm are evenly arranged in hexagons. Compared with spraying, the coating dots of the present invention are uniform in size and regular in shape.

[0022] 2. The dot-coating roller of this invention significantly reduces the coating amount compared to roller coating / spray coating processes, thereby lowering production costs. The coverage rate can be controlled to below 10%, and the coating amount on a single side can be less than 0.3 g / m². 2 This avoids the problem of increased air permeability after the base film is coated with adhesive, and reduces the internal resistance of the battery;

[0023] 3. The diaphragm obtained by using the dot-coating roller of the present invention has high hot-pressed positive electrode bonding strength and higher viscosity consistency under the premise of lower coating amount and coverage.

[0024] 4. The coating device of the present invention allows for adjustable coverage of the coating points on the base film surface. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the raised dots on the dot coating roller in Example 1;

[0026] Figure 2 is a schematic diagram of the protrusions on the dot coating roller in Comparative Example 1;

[0027] Figure 3 is a schematic diagram of the protrusions on the dot coating roller in Comparative Example 2;

[0028] Figure 4 is a schematic diagram of the protrusions on the dot coating roller in Comparative Example 3;

[0029] Figure 5 is a schematic diagram of the dot-coating roller protrusions in Comparative Example 4;

[0030] Figure 6 is a schematic diagram of the adhesive application device;

[0031] Figure 7 is a scanning electron microscope image of the coating points of the diaphragm prepared in Example 4;

[0032] Figure 8 is a microscope image of the coating points of the diaphragm prepared in Comparative Example 3;

[0033] Figure 9 shows the adhesion test curves of the diaphragm prepared in Example 4 and the diaphragm prepared in Comparative Example 6;

[0034] Figure 10 is an electron microscope image of the coating points of the diaphragm prepared in Comparative Example 6.

[0035] Among them, 1: slurry tank, 2: dot coating roller, 3: base film, 4: doctor blade. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] The raw material information involved in the following examples is as follows:

[0038] Organic polymers: One or a mixture of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polyvinylidene fluoride-trifluoroethylene copolymer are selected;

[0039] Dispersants: cationic ammonium salts and quaternary ammonium salts are selected;

[0040] Thickener: One or more of carboxymethyl cellulose and hydroxyethyl cellulose are selected;

[0041] Adhesive: One or more of polyvinyl alcohol, polyvinyl butyral, acrylic acid or styrene-butadiene rubber are selected;

[0042] The instruments and their model information involved in the following embodiments are as follows:

[0043] Hot press: Any press capable of heating up to 80℃ and achieving a pressure of 1000Kg is acceptable, regardless of the specific model.

[0044] Electronic tensile testing machine: capable of stably recording tensile force values ​​during the tensile process, with an effective tensile distance ≥25mm, regardless of the specific model of the equipment;

[0045] The base membrane used is a microporous membrane prepared from at least one of polyethylene, polypropylene, polyethylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyimide, polyetherimide, polysulfone, polyethersulfone, polyamide, polyphenylene ether, and polyphenylene sulfide.

[0046] In the following examples, the base film is a 9μm thick PE base film. It should be noted that base films of other thicknesses can also be used. The organic polymer selected is a polyvinylidene fluoride-hexafluoropropylene copolymer with a melting point of 148-155℃ and a melt index of 3-8. The dispersant is a water-based polyacrylate polymer with a density of 1.06 kg / m³. 2 The adhesive used is a water-based adhesive with a viscosity of 7300-9300 mPa·s and a solid content of 15%; the thickener is sodium carboxymethyl cellulose, a light yellow powder with a viscosity of 400-800 cP (2% soluble in water at 25℃).

[0047] In the following examples, the coating slurry used is PVDF slurry. The preparation method of PVDF slurry includes: weighing 0.18 kg of dispersant and adding it to 19 L of pure water, stirring for 10 min until uniform, then adding 5.2 kg of polyvinylidene fluoride-hexafluoropropylene copolymer (powder), stirring under vacuum for 1 h until uniform, then adding 9.8 kg of thickener and 2.1 kg of binder in sequence, stirring for 10 min until uniform, and sand milling for 5 min to obtain a uniform PVDF slurry. The viscosity of the PVDF slurry is about 300 mPa·s, the solid content is about 17%, and the particle size D50 is about 6.0 μm.

[0048] The method for preparing the diaphragm in the following embodiments is as follows: a coating device is used to coat the base membrane on one side / double side, forming multiple coating points on the surface of the base membrane, and then the membrane is dried in an oven at 60°C to obtain the diaphragm. The coating speed is 120 m / min.

[0049] Coverage: The percentage of the sum of the areas of all coated points within the test area at any size, measured using a Keyence microscope.

[0050] Hot-pressed positive electrode bonding strength: The separator and positive electrode are cut to a size of 25*150mm and 25*150mm respectively. The temperature of the hot press is set to 80℃ and the pressure to 1000KG. The separator and positive electrode are preheated for 1 second and then hot-pressed for 1 second. The bonding strength of the hot-pressed positive electrode is tested using an electronic tensile testing machine. The separator and positive electrode are peeled until the tensile distance of the electronic tensile testing machine is 50mm. The speed of the electronic tensile testing machine is 300mm / min and the peel angle is 180°. The bonding strength of the hot-pressed positive electrode is calculated as the peel force divided by the tensile distance of the electronic tensile testing machine. The peel force is the average value of the force collected by the electronic tensile testing machine during the peeling process of the separator and positive electrode. The bonding strength of the hot-pressed positive electrode is calculated based on the data between 10 and 40mm, that is, the bonding strength of the hot-pressed positive electrode is calculated as the peel force between 10 and 40mm divided by 30mm.

[0051] In the following embodiments, the diameter of the cylindrical cavity is 128 mm.

[0052] In the following examples, the distance is the distance between the center points of the two objects.

[0053] Examples 1-4

[0054] A dot-coating roller includes: a cylindrical cavity, on the surface of which multiple protrusions are formed, as shown in Figure 1. The protrusions are arranged in a hexagonal structure, with the protrusions located at the corners of the hexagonal structure, so that the lines connecting the protrusions on the surface of the cylindrical cavity can form an arc-shaped honeycomb structure. The regular hexagons are curved along the surface arc of the cylindrical cavity to form an arc-shaped hexagonal structure. The three vertices of the hexagonal structure are connected and have the same protrusion at their vertices. The side length of the regular hexagon is 1000 μm, and the diameter of each protrusion is 450 μm.

[0055] As shown in Figure 6, a coating device includes: a slurry tank 1 and the aforementioned dotting roller 2. The base film passes through the feed roller and the back roller. The slurry tank contains PVDF slurry. The dotting roller 2 is located below the base film 3 and is used to coat the base film that has passed through the back roller. A scraper 4 is provided on one side of the dotting roller 2 to remove excess PVDF slurry. The dotting roller is mounted on a slide rail via a slider, and the position of the dotting roller 2 on the slide rail can be adjusted to adjust the size of the gap between the base film and the dotting roller, thereby adjusting the coverage (the smaller the gap between the base film and the dotting roller, the greater the coverage).

[0056] The above-mentioned coating device is used to coat a single side of the base film to obtain a diaphragm. The obtained diaphragm includes: a base film, on which multiple coating points are formed. The coating points are arranged in a hexagonal pattern, and the hexagons are regular hexagons. The coating points are located at the corners of the hexagons so that when the lines connecting the coating points are connected, the lines can form a honeycomb structure on the surface of the base film. The same coating point is provided at the corners of the hexagons with three connected vertices.

[0057] By adjusting the gap between the base film and the dot-coating roller, coverage rates of 5.2%, 7.1%, 8.4%, and 9.8% were achieved, respectively.

[0058] Table 1

[0059] Table 1 shows the coating data for the diaphragms prepared in Examples 1-4. As can be seen from Table 1, with the increase in coverage, the thickness of the coating points shows a slight upward trend, while the diameter of the coating points shows an increasing trend. Because the distance between the roller and the membrane surface becomes closer, the diameter of the coating points also tends to increase, leading to an increase in the coating amount.

[0060] Figure 7 shows a scanning electron microscope image of the coating spots on the membrane prepared in Example 4. It can be seen that the coating spots are circular and have a regular shape.

[0061] Example 5

[0062] Using the same coating device (the same dot coating roller) as in Example 1, double-sided coating was performed on the base film to obtain a diaphragm (one side was coated first, then the other side was coated).

[0063] Comparative Example 1

[0064] A glue-applying device is basically the same as the glue-applying device of Example 1, except that the diameter of the bumps on the dot-coating roller in Comparative Example 1 is 500 μm (as shown in Figure 2).

[0065] The base membrane was coated on one side using the coating device of Comparative Example 1 to obtain a diaphragm.

[0066] Comparative Example 2

[0067] A glue-applying device is basically the same as the glue-applying device of Example 1, except that the diameter of the bumps on the dot-coating roller in Comparative Example 2 is 250 μm (as shown in Figure 3).

[0068] The base membrane was coated on one side using the coating device of Comparative Example 2 to obtain a diaphragm.

[0069] Comparative Example 3

[0070] A dot-coating roller includes: a cylindrical cavity, on the surface of which multiple protrusions are formed, as shown in Figure 4. The protrusions are arranged in a quadrilateral structure (matrix arrangement), with the protrusions located at the corners of the quadrilateral structure. The quadrilaterals are curved along the surface arc of the cylindrical cavity to form an arc surface quadrilateral structure. The length of the center point of any two adjacent protrusions along the circumferential direction of the cylindrical cavity surface is 1100 μm, the distance between any two adjacent protrusions along the axial direction of the cylindrical cavity surface (i.e., the distance between the center points) is 1100 μm, and the diameter of each protrusion is 450 μm.

[0071] As shown in Figure 6, a glue coating device is basically the same as the glue coating device in Example 1, except that it uses the dot coating roller of Comparative Example 3.

[0072] The base membrane was coated on one side using the coating device of Comparative Example 3 to obtain a diaphragm. A microscopic image of the coating spots on the diaphragm prepared in Comparative Example 3 is shown in Figure 8. It can be observed that all coating spots are circular, uniform in size, regular in shape, and evenly arranged.

[0073] Comparative Example 4

[0074] A dot-coating roller includes: a cylindrical cavity with multiple protrusions formed on its surface, as shown in Figure 5. The protrusions are arranged in a repeating composite structure, each composite structure including a quadrilateral structure and a triangular structure (the quadrilateral and triangular structures do not overlap). A protrusion is provided at each corner of the quadrilateral and triangular structures. The diameter of each protrusion is 450 μm. A quadrilateral structure is provided on each side of each triangular structure, and the quadrilateral structures on both sides of each triangular structure are symmetrically arranged. A regular quadrilateral is curved along the surface arc of the cylindrical cavity to form an arc surface, with a side length of d1 μm. An isosceles triangle is curved along the surface arc of the cylindrical cavity to form an arc surface, with a height of d2 μm. The base of the triangle is d3. In the quadrilateral structure, the protrusions arranged along the axial direction of the cylindrical cavity are on the same straight line as the protrusions on the base of the triangle. In the quadrilateral structure, the protrusions arranged laterally are on the same straight line as the protrusions at the apex of the triangle. The distance d5 between the edges of the farthest protrusions on both sides of each triangle along the axial direction of the cylindrical cavity is 7050μm. The length L along the circumference of the cylindrical cavity is 200μm for the edges of the two closest protrusions of adjacent composite structures. The distance d4 between the protrusions of the quadrilateral and triangular structures in a set of composite structures is d4. d1 and d2 are both 1100μm, d3 is 2200μm, and d4 is 1100μm.

[0075] As shown in Figure 6, a glue coating device is basically the same as the glue coating device in Example 1, except that it uses the dot coating roller of Comparative Example 4.

[0076] The base membrane was coated on one side using the coating device of Comparative Example 4 to obtain a diaphragm.

[0077] Comparative Example 5

[0078] A diaphragm is obtained by coating a base film on one side using a conventional roller coating process (using a coating machine from Shenzhen Xinjiatuo Automation Technology Co., Ltd.).

[0079] Comparative Example 6

[0080] A diaphragm is obtained by coating a base film on one side using a conventional spraying process (using a coating machine from Shenzhen Xinjiatuo Automation Technology Co., Ltd.). The electron microscope image of the coating points of the diaphragm is shown in Figure 10. The spraying points are irregular and randomly distributed.

[0081] Table 2 shows the comparative data of the diaphragms prepared in Examples 1-5 and the diaphragms prepared in Comparative Examples 1-6 (in the table, the coverage rate of Comparative Example 5 is 100%, which represents full-surface coating).

[0082] Table 2

[0083] The membrane prepared in Comparative Example 1 showed a significantly increased coverage and coating amount, leading to increased cost. The membrane prepared in Comparative Example 2 showed a significantly decreased coverage and coating amount, but the bonding strength of the hot-pressed positive electrode sheet also decreased significantly. The membrane prepared in Comparative Example 3 showed a significantly increased coverage and coating amount, resulting in increased cost. The membrane prepared in Comparative Example 4 had a coverage similar to Examples 4-5, but still greater, and a larger coating amount than Example 4, increasing production cost. The membrane prepared in Comparative Example 5 (coated by a conventional gravure roller) had a large coating amount, higher air permeability, and higher internal resistance of the battery. Figure 9 shows the adhesion test curves of the membranes prepared in Example 4 and Comparative Example 6. The horizontal axis of Figure 9 represents the tensile distance, and the vertical axis represents the peeling force (when peeling the membrane and the positive electrode sheet). The bonding strength of the hot-pressed positive electrode sheet of the diaphragm prepared in Comparative Example 6 (prepared by conventional spraying process) is not much different from that of the Example, but the coating amount and coverage are much greater than those of the Example. As can be seen from Figure 9, the bonding force test curve of the diaphragm prepared in Example 4 (the membrane of the present invention in Figure 9) shows regular up and down fluctuations, and the fluctuation range is basically similar with little difference in the critical value of the curve, indicating that the coating points are regularly distributed. The bonding force between the diaphragm prepared in Example 4 and the positive electrode sheet is relatively uniform. However, the bonding force test curve of the diaphragm prepared in Comparative Example 6 (the conventional sprayed membrane in Figure 9) fluctuates greatly and irregularly during the test, indicating that the bonding force between the diaphragm prepared in Comparative Example 6 and the positive electrode sheet is not uniform. The comparison of the data in Tables 1 and 2 shows that the coating device using the dot-coating roller of the present invention can effectively control the coverage and reduce the coating amount. While reducing the coating amount, it ensures the adhesion between the diaphragm and the electrode sheet (bonding strength of the hot-pressed positive electrode sheet).

[0084] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A dot-coating roller, comprising: A cylindrical cavity has multiple protrusions formed on its surface. The protrusions are arranged in a hexagonal structure and located at the corners of the hexagonal structure, so that the lines connecting the protrusions on the surface of the cylindrical cavity can form an arc-shaped honeycomb structure. The hexagonal structure is formed by bending regular hexagons along the curvature of the surface of the cylindrical cavity to form an arc-shaped hexagon.

2. The dotting roller according to claim 1, characterized in that, The three hexagonal structures connected at their vertices have the same protrusion at each of their interconnected vertices.

3. The dotting roller according to claim 1, characterized in that, The side length of the regular hexagon is 850–1000 μm.

4. The dotting roller according to claim 1, characterized in that, The diameter of each of the protrusions is 300–450 μm.

5. The dotting roller according to claim 1, characterized in that, The gap between the dot coating roller and the base film to be coated is adjustable.

6. A diaphragm, comprising: The base film has multiple coating points formed on its surface. The coating points are arranged in a hexagonal pattern and located at the corners of the hexagons, so that when the coating points are connected, the lines can form a honeycomb structure on the surface of the base film. The coverage rate of the coating points on the base film surface is 5 to 10% by area.

7. The diaphragm according to claim 6, characterized in that, The same coating point is provided at the vertices of the three interconnected hexagons.

8. The diaphragm according to claim 6, characterized in that, The hexagon is a regular hexagon.

9. An adhesive applicator, comprising: The dot-coating roller according to any one of claims 1 to 5.

10. A method for coating a diaphragm with adhesive, comprising: The coating is performed using the coating apparatus described in claim 9.

Images