Dot coating roller, separator, and adhesive coating device
The dot coating roller with a hexagonal honeycomb structure addresses uneven adhesive application in lithium-ion battery separators, achieving cost-effective, uniform coating and high adhesion while reducing internal resistance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- HEBEI GELLEC NEW ENERGY MATERIAL SCI&TECHNOLOY CO LTD
- Filing Date
- 2024-12-04
- Publication Date
- 2026-06-25
AI Technical Summary
Conventional adhesive coating methods for lithium-ion battery separators result in uneven adhesive application, high coating amounts, and low adhesive strength, leading to increased internal resistance and reduced electrochemical performance.
A dot coating roller with a hexagonal honeycomb structure and adjustable gap design is used to apply adhesive in a controlled, uniform manner, forming hexagonal coating points on the separator surface, reducing the coating amount to 0.3 g/m² while maintaining high adhesive strength.
The solution achieves uniform adhesive distribution, lowers production costs, and reduces internal resistance by controlling the coverage rate, ensuring high adhesion to the positive electrode sheet without compromising electrochemical performance.
Smart Images
Figure 2026521001000001_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of batteries, and specifically relates to a dot coating roller, a separator, and an adhesive coating device.
Background Art
[0002] Lithium-ion batteries have characteristics such as high voltage, high specific energy, and high cycle efficiency, and are widely used in various fields of production and life. Among them, the separator, as an indispensable part of the battery, plays an important role in the safety and electrical performance of the battery.
[0003] Currently, polyolefin-based microporous membranes have advantages such as stable chemical and electrochemical properties and high mechanical strength, and thus have become the mainstream as LIBs (lithium-ion battery) separators. However, due to the inherent low melting point and anisotropy of polyolefin-based materials, they are likely to melt and shrink at high temperatures, resulting in battery short-circuiting and irreversible damage to the battery. Furthermore, in the battery manufacturing process, problems such as the electrode sheet and the separator not adhering firmly or the battery cell being too soft still remain. As a basic and effective method to solve these problems, a functional coating with adhesive properties is added based on the original separator to adhere the positive electrode, negative electrode, and separator, improving the hardness of the battery cell and the safety and electrochemical performance of the battery. However, conventional coatings often have a high coating rate and a large coating amount, resulting in an increase in the internal resistance of the battery and a decrease in electrochemical performance. Therefore, it is necessary to appropriately control the coating rate of the coating so that the coated separator has both high adhesive strength and excellent electrochemical properties.
[0004] In invention patent disclosure number CN107876313A, a method for coating a battery separator is disclosed. The coating method involves spraying a slurry onto the separator surface using a spray coating device, and then scraping off excess slurry using a scraping device to make it flat and allowing it to dry. This method reduces the amount of coating compared to the conventional concave roller coating method, but the size of the coating points becomes uneven, resulting in reduced consistency of the adhesive strength of the electrode sheet after hot pressing. In utility model patent authorization number CN204307779U, a new type of adhesive coating device is provided. On the outer surface of the adhesive coating roller, multiple convex ridges are formed at intervals along the axial direction of the adhesive coating roller. When the separator moves, the adhesive coating roller rotates, thereby forming a spaced-out strip-like adhesive coating layer on the separator. The strip-like adhesive coating layer is applied more uniformly, but the amount of coating is also larger. The invention patent with publication number CN113363672A provides a spray-coated separator, which includes a base film, an inorganic coating applied to one side of the base film, and an organic particle dot coating spray-coated to both the coating side and the base film side. The spray coating points are approximately circular, and the amount of adhesive applied to a single layer is 0.7 g / m². 2 As a result, the amount of adhesive applied is still large, the adhesive strength is <1.2 N / m, the adhesive force is low, and the adhesive application points are irregularly distributed. Therefore, conventional techniques do not adequately solve problems such as poor adhesion of battery separators and uneven adhesive application. [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] This invention has been made in view of the shortcomings of the prior art, and aims to provide a dot coating roller.
[0006] Another object of the present invention is to provide a separator.
[0007] Another object of the present invention is to provide an adhesive application apparatus.
[0008] Another object of the present invention is to provide an adhesive application method for separators that improves the safety performance of the separator by achieving the following characteristics without affecting the electrochemical performance of the separator: uniform size of application points on the separator surface, arrangement of application points in an array, low application amount, controllable coverage, and high adhesion. [Means for solving the problem]
[0009] The object of the present invention is achieved by the following technical solutions.
[0010] A dot coating roller comprising a cylindrical cavity, wherein a plurality of protrusions are formed on the surface of the cylindrical cavity such that lines connecting the protrusions on the surface of the cylindrical cavity can form an arc-shaped honeycomb structure, the protrusions are arranged in a hexagonal structure and located at the corners of the hexagonal structure, and the regular hexagons are bent along the curvature of the surface of the cylindrical cavity to form the hexagonal structure in which the arc surface is hexagonal.
[0011] In the above technical solution, the same projection is placed at the vertices of the hexagonal structure formed by connecting the three vertices.
[0012] In the above technical solution, the side lengths of the regular hexagon are 850 to 1000 μm.
[0013] In the above technical solution, the diameter of each of the protrusions is 300 to 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] The separator includes a base film on which multiple coating points are formed on its surface. The coating points are arranged in a hexagonal pattern, and because the coating points are located at the corners of the hexagon, the lines connecting the coating points can form a honeycomb structure on the surface of the base film. When calculated by area, the coverage rate of the coating points on the surface of the base film is 5-10%.
[0016] In the above-described technical solution for the separator, the same coating point is placed at the vertex angles of the hexagon formed by connecting the three vertex angles of each other.
[0017] In the above technical solution, the hexagon is a regular hexagon.
[0018] An adhesive application apparatus, comprising the dot application roller.
[0019] A method for applying adhesive to a separator, wherein the application is performed using the adhesive application apparatus. [Effects of the Invention]
[0020] Compared to conventional technology, the beneficial effects of the present invention are as follows: 1. The protrusions of the dot coating roller of the present invention are distributed in a hexagonal structure, and the coating points of the separator obtained by coating are uniformly arranged in a hexagonal shape. Compared to spray coating, the coating points of the present invention are more uniform in size and have a more regular shape. 2. By using the dot coating roller of the present invention, compared to roller coating / spray coating processes, the coating amount can be significantly reduced, production costs can be lowered, and the coverage rate can be controlled to 10% or less, with a single-sided coating amount of 0.3 g / m². 2 This is less than the limit, avoiding the problem of increased breathability after applying adhesive to the base film, and reducing the internal resistance of the battery. 3. Using the dot coating roller of the present invention, assuming low coating amount and coverage, the resulting separator exhibits high adhesive strength to the hot-pressed positive electrode sheet and high viscosity consistency. 4. The adhesive coating apparatus of the present invention allows for adjustment of the coverage rate of the coating points on the surface of the base film.
Brief Description of the Drawings
[0021] [Figure 1] It is a schematic diagram of the protrusions of the dot coating roller of Example 1. [Figure 2] It is a schematic diagram of the protrusions of the dot coating roller of Comparative Example 1. [Figure 3] It is a schematic diagram of the protrusions of the dot coating roller of Comparative Example 2. [Figure 4] It is a schematic diagram of the protrusions of the dot coating roller of Comparative Example 3. [Figure 5] It is a schematic diagram of the protrusions of the dot coating roller of Comparative Example 4. [Figure 6] It is a schematic diagram of the adhesive coating device. [Figure 7] It is a scanning electron microscope image of the coating points of the separator manufactured in Example 4. [Figure 8] It is a scanning electron microscope image of the coating points of the separator manufactured in Comparative Example 3. [Figure 9] It is an adhesive force test curve of the separator manufactured in Example 4 and the separator manufactured in Comparative Example 6. [Figure 10] It is an electron microscope image of the coating points of the separator manufactured in Comparative Example 6.
Modes for Carrying Out the Invention
[0022] The technical solution of the present invention will be further described below in conjunction with specific examples.
[0023] The information on the raw materials according to the following examples is as follows. For the organic polymer, one or a mixture of multiple kinds of polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene copolymer, and polyvinylidene fluoride - trifluoroethylene copolymer is selected. For the dispersant, cationic ammonium salt and quaternary ammonium salt are selected. The thickener is selected from one or more of carboxymethyl cellulose and hydroxyethyl cellulose. For the adhesive, one or more of the following will be selected: polyvinyl alcohol, polyvinyl butyral, acrylic acid, or styrene-butadiene rubber.
[0024] The equipment and its model number information for the following embodiment are as follows: Regarding the heat press machine, it is not limited to a specific model number; it just needs to be able to heat up to 80°C and reach a pressure of 1000 kg. Regarding electronic tensile testing machines, they are not limited to a specific model number of the equipment, but are required to be able to stably record tensile force values during the tensile process, and have an effective tensile distance of ≥25 mm.
[0025] The base film used is a microporous membrane made from at least one of the following: polyethylene, polypropylene, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyimide, polyetherimide, polysulfone, polyethersulfone, polyamide, polyphenylene ether, and polyphenylene sulfide.
[0026] In the following examples, the base film is a PE base film with a thickness of 9 μm. However, base films of other thicknesses may also be used. The organic polymer is a polyvinylidene fluoride-hexafluoropropylene copolymer, selected for its melting point of 148-155°C and melt index of 3-8. The dispersant has a density of 1.06 kg / m³. 2 A polyacrylate-based aqueous polymer is selected and used. The adhesive is an aqueous adhesive with a viscosity of 7300-9300 mPas and a solids content of 15%. The thickener is sodium carboxymethylcellulose, a pale yellow powder with a viscosity of 400-800 cP (tested to dissolve in water at 2% at 25°C).
[0027] In the following examples, the coating slurry is always a PVDF slurry. The method for producing the PVDF slurry involves weighing out 0.18 kg of dispersant, adding it to 19 L of pure water, stirring for 10 minutes until homogeneous, then adding 5.2 kg of polyvinylidene fluoride-hexafluoropropylene copolymer (powder), stirring for 1 hour under vacuum until homogeneous, then sequentially adding 9.8 kg of thickener and 2.1 kg of adhesive, stirring for 10 minutes until homogeneous, and finally sand polishing for 5 minutes to obtain a uniform PVDF slurry. The viscosity of the PVDF slurry is approximately 300 mPa.s, the solid content is approximately 17%, and the particle size D50 is approximately 6.0 μm.
[0028] In the following example of a separator manufacturing method, an adhesive coating device is used to coat one or both sides of a base film to form multiple coating points on the surface of the base film, and then the separator is obtained by drying it in an oven at 60°C. The coating speed is 120 m / min. Regarding coverage, for any size test area, the total area of all coated points was defined as the percentage of the test area occupied, and this was tested using a Keyence microscope. Regarding the adhesive strength of the hot-pressed positive electrode sheet, the separator was cut to a size of 25*150mm, the positive electrode sheet was also 25*150mm, the heat press machine temperature was adjusted to 80°C, the pressure was 1000KG, the separator and positive electrode sheet were preheated for 1 second in the heat press machine, and then hot-pressed for 1 second. The adhesive strength of the hot-pressed positive electrode sheet was tested using an electronic tensile tester. The tensile distance of the electronic tensile tester was 50mm, the speed of the electronic tensile tester was 300mm / min, and the separator and positive electrode sheet were separated until the degree of peel was 180°. The adhesive strength of the hot-pressed positive electrode sheet = peel force divided by the tensile distance of the electronic tensile tester. The peel force is the average value of the force collected by the electronic tensile tester during the peeling process of the separator and positive electrode sheet. The adhesive strength of a hot-pressed positive electrode sheet is calculated based on data for tensile distances of 10 to 40 mm; that is, the adhesive strength of the hot-pressed positive electrode sheet = the peel force at a tensile distance of 10 to 40 mm divided by 30 mm.
[0029] In the following embodiment, the diameter of the cylindrical cavity is 128 mm.
[0030] In the following example, distance is the distance between the center points of the two objects. Examples 1-4
[0031] The dot coating roller includes a cylindrical cavity, and as shown in Figure 1, multiple protrusions are formed on the surface of the cylindrical cavity such that lines connecting the protrusions on the surface of the cylindrical cavity can form an arc-shaped honeycomb structure. The protrusions are arranged in a hexagonal structure and located at the corners of the hexagonal structure, where a regular hexagon is bent along the surface curvature of the cylindrical cavity to form a hexagonal structure with an arc surface. In a hexagonal structure where three vertices are connected, the same protrusions are provided at the connected vertices. The side length of the regular hexagon is 1000 μm, and the diameter of each protrusion is 450 μm.
[0032] As shown in Figure 6, the adhesive application apparatus includes a slurry tank 1 and the aforementioned dot application roller 2. The base film passes over the over roller and back roller, the slurry tank is filled with PVDF slurry, the dot application roller is positioned below the base film 3, and the dot application roller 2 is used to apply the PVDF slurry to the base film after it has passed the back roller. A scraper 4 is provided on one side of the dot application roller 2 to remove excess PVDF slurry. The dot application roller is mounted on a slide rail via a slider, and the size of the gap between the base film and the dot application roller can be adjusted by adjusting the position of the dot application roller 2 on the slide rail, thereby adjusting the coverage rate (the smaller the gap between the base film and the dot application roller, the higher the coverage rate).
[0033] Using the adhesive application apparatus described above, a separator is obtained by applying the adhesive to one side of a base film. The obtained separator includes the base film, and multiple application points are formed on the surface of the base film such that the lines connecting the application points can form a honeycomb structure on the surface of the base film. The application points are arranged in a hexagon, the hexagon is a regular hexagon, the application points are located at the corners of the hexagon, and the same application points are placed at the vertices where the hexagons formed by connecting three vertices are connected to each other.
[0034] By adjusting the size of the gap between the base film and the dot coating roller, the coverage rates can be achieved as 5.2%, 7.1%, 8.4%, and 9.8%, respectively. Table 1 [Table 1]
[0035] Table 1 shows the adhesive application data for the separators manufactured in Examples 1-4. From Table 1, it was found that as the coverage rate increased, the thickness of the application points tended to increase slightly, and the diameter of the application points tended to increase. As the distance between the roller and the film surface decreased, the diameter of the application points tended to increase, and the amount of adhesive applied also increased.
[0036] As shown in Figure 7, scanning electron microscope images of the coated points of the separator manufactured in Example 4 revealed that the coated points were circular and had a regular shape. Example 5
[0037] Using the same adhesive application apparatus (including the dot application roller) as in Example 1, a base film was coated on both sides (one side was coated first, then the other side) to obtain a separator. Comparative Example 1
[0038] The adhesive application apparatus is basically the same as that of Example 1, except that the diameter of the protrusions on the dot application roller of Comparative Example 1 is 500 μm (as shown in Figure 2).
[0039] A separator was obtained by applying the adhesive to one side of the base film using the adhesive application apparatus of Comparative Example 1. Comparative Example 2
[0040] The adhesive application apparatus is basically the same as that of Example 1, except that the diameter of the protrusions on the dot application roller in Comparative Example 2 is 250 μm (as shown in Figure 3).
[0041] A separator was obtained by applying the adhesive to one side of the base film using the adhesive application apparatus of Comparative Example 2. Comparative Example 3
[0042] The dot coating roller includes a cylindrical cavity, and as shown in Figure 4, a plurality of protrusions are formed on the surface of the cylindrical cavity, the protrusions are arranged in a quadrilateral structure (matrix arrangement), the protrusions are located at the corners of the quadrilateral structure, the regular quadrilateral is bent along the surface curvature of the cylindrical cavity so that the arc surface forms the quadrilateral structure, where the distance along the surface of the cylindrical cavity is 1100 μm between the center points of any two adjacent protrusions along the circumferential direction on the surface of the cylindrical cavity, the distance between any two adjacent protrusions along the axial direction on the surface of the cylindrical cavity (i.e., the distance between the center points) is 1100 μm, and the diameter of each protrusion is 450 μm.
[0043] As shown in Figure 6, the adhesive application apparatus is basically the same as that of Example 1, the only difference being the use of the dot application roller of Comparative Example 3 (as shown in Figure 3).
[0044] A separator was obtained by applying the adhesive to one side of the base film using the adhesive application apparatus of Comparative Example 3. As shown in Figure 8, in the microscopic image of the application points of the separator produced in Comparative Example 3, it can be observed that all application points are circular, uniform in size, have a regular shape, and are uniformly arranged. Comparative Example 4
[0045] The dot coating roller includes a cylindrical cavity, and as shown in Figure 5, multiple protrusions are formed on the surface of the cylindrical cavity, the protrusions are arranged repeatedly according to a composite structure, each composite structure includes one quadrilateral structure and one triangular structure (the quadrilateral and triangular structures do not overlap), one protrusion is placed at each corner of the quadrilateral and triangular structures, each protrusion has a diameter of 450 μm, one quadrilateral structure is placed on each side of each triangular structure, the quadrilateral structures on both sides of each triangular structure are arranged symmetrically, a regular quadrilateral is bent according to the surface of the cylindrical cavity so that the arc surface forms a quadrilateral structure, the side length of the regular quadrilateral is d1 μm, and an isosceles triangle is bent according to the surface of the cylindrical cavity so that the arc surface forms a triangular structure, the height of the isosceles triangle is d2 μm, and the base length of the isosceles triangle is d3. In the quadrilateral structure, one layer of projections aligned along the axial direction of the cylindrical cavity is collinear with the projection located at the base of the triangular structure, and another layer of projections aligned laterally within the quadrilateral structure is collinear with the projection located at the vertex corner of the triangular structure. The distance d5 between the edges of the quadrilateral structures on both sides of each triangular structure, furthest from the projection along the axial direction of the cylindrical cavity, was 7050 μm, and the length L along the circumferential surface of the cylindrical cavity, between the edges adjacent to the two nearest projections of adjacent composite structures, was 200 μm. In one group of composite structures, the distance between the projections of the quadrilateral and triangular structures that are close to each other was d4, with d1 and d2 both being 1100 μm, d3 being 2200 μm, and d4 being 1100 μm.
[0046] As shown in Figure 6, the adhesive application apparatus is basically the same as that of Example 1, the only difference being the use of the dot application roller of Comparative Example 4 (as shown in Figure 3).
[0047] A separator was obtained by applying the adhesive to one side of the base film using the adhesive application apparatus of Comparative Example 4. Comparative Example 5
[0048] The separator was obtained by applying it to one side of a base film using a conventional roller coating process (using a coating machine from Shenzhen Xinjia Tuo Automation Technology Co., Ltd.). Comparative Example 6
[0049] The separator was obtained by applying it to one side of a base film using a conventional spray coating process (using a coating machine from Shenzhen Xinjia Tuo Automation Technology Co., Ltd.). As shown in Figure 10, the electron microscope image of the coating points of the separator showed that the spray coating points were irregularly and randomly distributed.
[0050] Table 2 shows comparative data of the separators produced in Examples 1-5 and the separators produced in Comparative Examples 1-6 (the coverage rate of Comparative Example 5 in the table is 100%, representing full coverage). Table 2 [Table 2]
[0051] The separator manufactured in Comparative Example 1 showed a significantly increased coverage rate, increased coating amount, and increased cost. The separator manufactured in Comparative Example 2 showed a significantly decreased coverage rate and reduced coating amount, but the adhesive strength of the hot-pressed positive electrode sheet also decreased significantly. The separator manufactured in Comparative Example 3 showed a significantly increased coverage rate, increased coating amount, and increased cost. The separator manufactured in Comparative Example 4 had a coverage rate similar to Examples 4 and 5, but was still higher than the examples, had a larger coating amount than Example 4, and increased manufacturing cost. The separator manufactured in Comparative Example 5 (coated with a conventional gravure roller) had a large coating amount, a higher increase in air permeability, and a larger internal resistance of the battery. Figure 9 shows the adhesive strength test curves of the separator manufactured in Example 4 and the separator manufactured in Comparative Example 6. In Figure 9, the horizontal axis is tensile distance, and the vertical axis is peel force (force collected by an electronic tensile testing machine during the process of peeling the separator from the positive electrode sheet). The adhesive strength of the hot-pressed positive electrode sheet of the separator manufactured in Comparative Example 6 (manufactured using a conventional spray coating process) was not significantly different from that of the Examples, but the coating amount and coverage rate were much larger than those of the Examples. As can be seen from Figure 9, the adhesive strength test curve of the separator manufactured in Example 4 (the film of the present invention in Figure 9) showed regular vertical fluctuations, the range of fluctuation was basically the same, and there was no significant difference in the critical value of the curve, indicating that the coating points were regularly distributed. This indicates that the adhesive force between the separator and the positive electrode sheet manufactured in Example 4 was relatively uniform. On the other hand, during the test process of the separator manufactured in Comparative Example 6 (the conventional spray-coated film in Figure 9), the adhesive strength test curve showed a large range of fluctuation and fluctuated irregularly, indicating that the adhesive force between the separator and the positive electrode sheet manufactured in Comparative Example 6 was non-uniform. As can be seen from the comparison of the data in Table 1 and Table 2, the adhesive application apparatus using the dot application roller of the present invention can effectively control the coverage rate and reduce the amount of adhesive applied, while still ensuring adhesion between the separator and the electrode sheet (adhesion strength of the hot-pressed positive electrode sheet) despite the reduced amount of adhesive applied.
[0052] The present invention has been described above as an example. Any simple modification, alteration, or other equivalent substitution that a person skilled in the art can make without expending creative effort is included within the scope of protection of the present invention, without departing from the core of the invention. [Explanation of Symbols]
[0053] 1 slurry tank 2. Dot application roller 3 Base film 4. Scraper
Claims
1. A dot coating roller comprising a cylindrical cavity, wherein a plurality of protrusions are formed on the surface of the cylindrical cavity such that lines connecting the protrusions on the surface of the cylindrical cavity can form an arc-shaped honeycomb structure, the protrusions are arranged in a hexagonal structure and located at the corners of the hexagonal structure, and the regular hexagons are bent along the curvature of the surface of the cylindrical cavity to form the hexagonal structure in which the arc surface is hexagonal.
2. The dot coating roller according to claim 1, characterized in that the same projection is arranged at the vertex angles of the hexagonal structure formed by connecting three vertex angles.
3. The dot coating roller according to claim 1, characterized in that the side length of the regular hexagon is 850 to 1000 μm.
4. The dot coating roller according to claim 1, characterized in that the diameter of each of the aforementioned protrusions is 300 to 450 μm.
5. The dot coating roller according to claim 1, characterized in that the size of the gap between the dot coating roller and the base film to be coated is adjustable.
6. A separator comprising a base film having a plurality of coating points formed on its surface, wherein the coating points are arranged in a hexagon and located at the corners of the hexagon so that the lines connecting the coating points can form a honeycomb structure on the surface of the base film, and the coating points on the surface of the base film cover 5 to 10% of the surface area when calculated by area.
7. The separator according to claim 6, characterized in that the same coating point is placed at the vertex angles of the hexagon formed by connecting the three vertex angles of each other.
8. The separator according to claim 6, characterized in that the hexagon is a regular hexagon.
9. An adhesive application apparatus comprising a dot application roller according to any one of claims 1 to 5.
10. A method for applying adhesive to a separator, wherein the application is performed using the adhesive application apparatus described in claim 9.