Composite conductive film and method for manufacturing the same
By forming a composite conductive film with asymmetrical contour differences on the surface of the support layer, the adhesion problem of the film during the winding process is solved, enabling efficient roll-to-roll production and maintaining the energy density of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2024-12-31
- Publication Date
- 2026-07-24
AI Technical Summary
Existing composite current collectors have excessively smooth film surfaces after coating preparation, which makes them prone to sticking during the winding process, affecting subsequent processing. Furthermore, existing methods increase production costs or reduce the energy density of lithium-ion batteries.
An asymmetric contour difference is formed on the surface of the support layer. Through laser etching and controlled evaporation processes, an asymmetric conductive layer structure is formed on the support layer. This ensures that there is a cavity for gas containment when the two composite conductive films are in contact, reducing the vacuum level and preventing adhesion.
In roll-to-roll production, a gas-containing cavity is formed between the two composite conductive films, which improves the film adhesion problem, increases the yield, and maintains the energy density of lithium-ion batteries without adding extra processes.
Smart Images
Figure CN119786622B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of current collector technology, and more specifically, relates to a composite conductive film and its preparation method. Background Technology
[0002] The safety of lithium-ion batteries has always been a concern for end users. While lithium-ion batteries are generally safe, they can pose a fire or explosion hazard if used, charged improperly, or damaged, especially as the specific energy density of current lithium batteries approaches their theoretical limits. Many methods have been proposed in the prior art to improve the safety performance of lithium-ion batteries, such as using intrinsically safe electrode materials (e.g., lithium iron phosphate instead of ternary cathode materials), adding flame-retardant electrolytes (e.g., solid-state or non-flammable electrolytes), or using thermally stable separators. However, most of these methods involve additional manufacturing processes and / or require the use of additional materials, which not only increases production costs but also reduces the energy density of lithium-ion batteries.
[0003] Metal-plastic film current collectors (composite current collectors) can effectively ensure the safety of lithium-ion batteries under mechanical abuse without sacrificing their energy density. Therefore, more and more lithium battery manufacturers are beginning to explore the use of composite current collectors to replace pure metal films as current collectors for lithium-ion batteries. Compared to metal current collectors, metal-plastic film composite current collectors are lighter, lower in cost, and offer better safety performance.
[0004] Current technologies for preparing composite current collectors involve obtaining a metal coating on a polymer substrate film through magnetron sputtering, vapor deposition, or electroless plating, followed by drying and anti-oxidation treatment to achieve a sandwich structure of "metal layer-polymer layer-metal layer". Currently, after coating preparation, the composite current collector requires film winding, especially for double-sided coated current collectors. Because the film surface is too smooth and flat, vacuum caking occurs under winding tension, causing the film to stick together during unwinding, resulting in coating detachment or even film breakage. Furthermore, adhesion can cause film vibration during subsequent unwinding, affecting subsequent processing.
[0005] Therefore, there is an urgent need to design a composite conductive film to avoid film adhesion during the unwinding process and improve the yield. Summary of the Invention
[0006] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a composite conductive film and its preparation method, wherein the support layer has different surface contours to form air-accommodating cavities, thereby improving the film adhesion problem during roll-to-roll processing.
[0007] To achieve the above objectives, according to one aspect of the present invention, a composite conductive film is provided, comprising a support layer 1 having two surfaces in the thickness direction; and a conductive layer 2 formed on at least one surface of the support layer 1; wherein the two surfaces of the formed composite conductive film have different profiles in the thickness direction, so as to form a gas-containing cavity 3 after the two composite conductive films come into contact.
[0008] Based on the above technical solution, the difference in contour morphology creates a gas-containing cavity when the two composite conductive films come into contact, thus improving the film adhesion problem.
[0009] Preferably, the composite conductive film has two surfaces with different contour units on the thickness direction, and the difference is not less than 0.5 μm.
[0010] Based on the above technical solution, due to the difference in the average width of the surface contours, when the two contour surfaces come into contact after winding, one side has a wider average width of contour unit, thus leaving gaps to retain air, thereby reducing the vacuum degree after film bonding and improving the adhesion of the film surface.
[0011] Preferably, the composite conductive film has different surface roughness Rz on its two surfaces in the thickness direction.
[0012] Based on the above technical solution, surfaces with different roughness can increase the voids in the mating surface and can also increase the adhesion of related active materials in the subsequent electrode to a certain extent.
[0013] Preferably, the composite conductive film has two surfaces in the thickness direction with different average widths Rsm of contour units and different surface roughness Rz.
[0014] Based on the above technical solution, the gap in the mating surface can be further increased; preferably, the surface with a larger roughness is set on the side with a larger average width of the surface profile, so that the gap formed by the profile unit can be coordinated to reserve more air retention space and reduce the vacuum degree after the film is wound and laminated.
[0015] Preferably, the average width of the contour unit on one surface of the composite conductive film in the thickness direction is Rsm1, which ranges from 2 to 8 μm; the average width of the contour unit on the other surface is Rsm2, which ranges from 0.2 to 2 μm.
[0016] Preferably, the roughness Rz1 of one surface of the composite conductive film in the thickness direction is 0.01-0.4 times the thickness of the corresponding composite conductive film, and the roughness Rz2 of the other surface is 0.1-0.6 times Rz1.
[0017] Preferably, the thickness of the support layer 1 is set to 3-50 μm, and its material is a polymer material or graphite film with a surface roughness of 0.5 μm or more.
[0018] Preferably, the thickness of the conductive layer 2 is 0.05-3μm, and its material is one or a combination of gold, silver, copper, aluminum, nickel, and chromium.
[0019] According to another aspect of the present invention, a method for preparing a composite conductive film is provided:
[0020] When a conductive layer 2 is set on one side of a support layer 1, a support layer 1 with an appropriate average width of surface contour units is selected, and the average width of contour units on the surface of the conductive layer 2 is controlled according to the average width of contour units on the surface of the support layer 1; when a conductive layer 2 is set on both sides of a support layer 1, the average width of contour units forming differences on the surfaces of the conductive layers 2 on both sides is controlled.
[0021] Preferably, when a conductive layer 2 is provided on one side of the support layer 1, the support layer 1 is treated with laser etching. Laser etching can effectively depict two asymmetrical surfaces on the support layer 1. Based on this, metal layer deposition, magnetron deposition, etc. can be performed to obtain a composite conductive film surface determined by the surface morphology of the support layer 1.
[0022] Preferably, when the conductive layer 2 is provided on both sides of the support layer 1, the conductive layer 2 is plated on both sides in at least one of the following ways to form a different surface profile: increasing the target temperature after evaporation; increasing the target temperature after evaporation; or reducing the speed of the support layer; or reducing the distance between the support layer and the target; or using laser etching to process the support layer.
[0023] Based on the above technical solution, by adjusting the evaporation power to increase the temperature of the vapor deposition target, the energy of the particles can be increased, which is beneficial to crystal growth. Furthermore, some crystals forming the conductive layer recrystallize due to the high temperature, resulting in larger crystal sizes and fewer small crystals formed by the particles deposited on the surface of the support layer. Consequently, the surface contours will have larger spacing and greater surface roughness. Lower vehicle speeds result in a greater number of high-temperature particles per unit time, thus increasing the overall thermal energy and forming larger, more columnar crystals, which are easier to form with larger contour spacing and surface roughness. Reducing the distance between the support layer and the target can also increase the energy of the particles deposited on the surface of the support layer to a certain extent, thereby increasing the energy and temperature of the particles.
[0024] Furthermore, the conductive layer 2 is formed based on the deposition of metal particles. The different energy of the target particles deposited on the surface of the support layer 1 results in different crystal sizes.
[0025] Based on the above technical solution, by controlling the energy difference of target particles deposited on the surface of the support layer, the crystal size formed by the deposition of metal particles can be controlled, which manifests as differences in surface profile units. When metal particles with higher energy are deposited on the surface of the support layer, the crystals tend to aggregate to form relatively larger crystal sizes, thus having larger gaps between profile units and gaps for air retention after winding.
[0026] In summary, compared with the prior art, the composite conductive film provided by the present invention has the following advantages:
[0027] 1. The composite conductive film proposed in this invention forms a gas-containing cavity between two wound composite conductive films after contact during roll-to-roll manufacturing. This invention achieves an asymmetrical conductive layer structure through asymmetric support layer contour differences, resulting in a gas-containing cavity when the two composite conductive films are bonded together, thus improving the film adhesion problem during roll-to-roll processing.
[0028] 2. This invention can achieve asymmetrical composite conductive film surface morphology through various means. For example, by controlling the surface morphology differences of the support layer, asymmetrical conductive film morphology differences can be obtained. Laser etching can effectively depict two asymmetrical surfaces on the support layer. Based on this, metal layer deposition, magnetron sputtering, or other methods can be performed to obtain a composite conductive film surface determined by the surface morphology of the support layer. This invention can create various unique asymmetrical structures in the support layer, such as trenches and wavy structures, and the area of the asymmetrical structure is controllable. By controlling the size of the laser-etched area, the utilization of the gas-containing cavity can be maximized.
[0029] 3. This invention can control the grain size of the conductive layer in different regions by using different methods of forming the conductive layer. By stacking grains of different sizes, an asymmetric structure on the surface of the composite conductive film can also be achieved. When high-energy metal particles are deposited on the surface of the support layer, the crystals tend to aggregate to form relatively larger crystal sizes, thus having larger profile unit gaps and air retention gaps after winding. Therefore, the film adhesion problem in roll-to-roll production processes can be solved without adding extra steps. Attached Figure Description
[0030] Figure 1 This is a schematic diagram of the support layer structure of the composite conductive film;
[0031] Figure 2 This is a schematic diagram of a composite conductive film with two conductive layers.
[0032] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:
[0033] 1-Support layer; 2-Conductive layer; 3-Cavity. Detailed Implementation
[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0035] Please see Figure 1 and Figure 2 The present invention provides a composite conductive film, including a support layer 1 having two surfaces in the thickness direction; and a conductive layer 2 formed on at least one surface of the support layer 1; the two surfaces of the formed composite conductive film have different profiles in the thickness direction to achieve the formation of a gas-containing cavity 3 after the two composite conductive films come into contact.
[0036] Based on the above technical solution, the difference in contour morphology creates a gas-containing cavity when the two composite conductive films come into contact, thus improving the film adhesion problem.
[0037] Specifically, the composite conductive film has two surfaces with different contour units in the thickness direction, with an average width Rsm that is not less than 0.5 μm.
[0038] Based on the above technical solution, due to the difference in the average width of the surface contours, when the two contour surfaces come into contact after winding, one side has a wider average width of contour unit, thus leaving gaps to retain air, thereby reducing the vacuum degree after film bonding and improving the adhesion of the film surface.
[0039] Specifically, the composite conductive film has different surface roughness Rz on its two surfaces in the thickness direction.
[0040] Based on the above technical solution, surfaces with different roughness can increase the voids in the mating surface and can also increase the adhesion of related active materials in the subsequent electrode to a certain extent.
[0041] Specifically, the composite conductive film has two surfaces with different average widths Rsm of contour cells and different surface roughness Rz in the thickness direction.
[0042] Based on the above technical solution, the gap in the mating surface can be further increased; preferably, the surface with a larger roughness is set on the side with a larger average width of the surface profile, so that the gap formed by the profile unit can be coordinated to reserve more air retention space and reduce the vacuum degree after the film is wound and laminated.
[0043] Specifically, the average width of the contour unit on one surface of the composite conductive film in the thickness direction is Rsm1, which ranges from 2 to 8 μm; the average width of the contour unit on the other surface is Rsm2, which ranges from 0.2 to 2 μm.
[0044] Specifically, the roughness Rz1 of one surface of the composite conductive film in the thickness direction is 0.01-0.4 times the thickness of the corresponding composite conductive film, and the roughness Rz2 of the other surface is 0.1-0.6 times Rz1.
[0045] Specifically, the thickness of the support layer 1 is set to 3-50μm, and its material is a polymer material or graphite film with a surface roughness of 0.5μm or more.
[0046] Specifically, the thickness of conductive layer 2 is 0.05-3μm, and its material is one or a combination of gold, silver, copper, aluminum, nickel, and chromium.
[0047] This embodiment also provides a method for preparing a composite conductive film:
[0048] When a conductive layer 2 is set on one side of a support layer 1, a support layer 1 with an appropriate average width of surface contour units is selected, and the average width of the contour units on the surface of the conductive layer 2 is controlled according to the average width of the contour units on the surface of the support layer 1.
[0049] When conductive layers 2 are provided on both sides of the support layer 1, the average width of the contour units formed on the surfaces of the conductive layers 2 on both sides is controlled to be different.
[0050] Specifically, when a conductive layer 2 is set on one side of the support layer 1, the support layer 1 is treated with laser etching. Laser etching can effectively depict two asymmetrical surfaces on the support layer 1. Based on this, metal layer deposition, magnetron deposition, etc. can be performed to obtain a composite conductive film surface determined by the surface morphology of the support layer 1.
[0051] Specifically, when the conductive layer 2 is provided on both sides of the support layer 1, the conductive layer 2 is plated on both sides in at least one of the following ways to form a different surface profile: increasing the target temperature after evaporation; increasing the target temperature after evaporation; or reducing the speed of the support layer; or reducing the distance between the support layer and the target; or using laser etching to process the support layer.
[0052] Furthermore, the conductive layer 2 is formed based on the deposition of metal particles. The different energy of the target particles deposited on the surface of the support layer 1 results in different crystal sizes.
[0053] The relevant vapor deposition process and equipment are existing and well-known technologies. Those skilled in the art can adapt the relevant process parameters by combining the above-mentioned contents of this application.
[0054] Of course, it can also be applied to other coating methods, such as sputtering. By adjusting the energy (radio frequency power RF) of the bombardment target particles, a larger crystal size can be obtained, thereby achieving a larger profile cell spacing and roughness.
[0055] For a single-sided conductive layer, the material of the support layer affects its surface roughness. For example, when the support layer is a polymer substrate, it has relatively high flatness (0.05-0.1 μm), thus allowing for larger contour spacing and roughness during the conductive layer formation process. Support layer materials can include polyamide (PA), polyethylene terephthalate (PET), polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), acrylonitrile butadiene styrene copolymers (ABS), and polybutylene terephthalate (PP). It contains at least one of the following: terephthalat (PBT), poly-p-phenylene terephthamide (PPA), polyformaldehyde (POM), phenolic resin, polypropylene (PPE), polytetrafluoroethylene (PTFE), and polycarbonate (PC).
[0056] For high-temperature resistant substrates, such as graphite films, their relatively large surface roughness and wide profile allow for vapor deposition using conventional processes. Furthermore, since the surface roughness of commercially available pressed graphite films is generally above 0.5 μm (and the thickness of the graphite film is much greater than the thickness of the conductive layer, typically above 20 μm), and preferably above 2 μm, a low-speed process can be employed to rapidly form the conductive layer. The surface particles of the conductive layer aggregate to form larger crystal sizes, resulting in wider profile unit spacing.
[0057] Comparative Example
[0058] Evaporation is performed according to normal process, with a 6μm support layer selected. The machine speed is set to 4.5-6.5m / s for adaptability, and the wire (aluminum wire) feeding speed is set to 300-600mm / min in combination with the machine speed. During this process, the current and voltage are controlled to make the evaporation boat bright (generally controlled to be orange-yellow). The sheet resistance of the plated aluminum layer is 38-42mΩ / □, and the thickness is about 1μm.
[0059] Preparation Example 1
[0060] The difference from the comparative example is that a 30μm graphite film was selected as the support layer, and an aluminum layer of about 1μm was deposited on one side.
[0061] Preparation Example 2
[0062] The difference from preparation one is that one side is vapor-deposited at normal vehicle speed, while the other side is depressed at a reduced vehicle speed of 1.5-2.5 m / s, and an aluminum layer of about 1 μm thickness is vapor-deposited on both sides.
[0063] Preparation Example 3
[0064] The difference from the comparative example is that the evaporation distance was reduced by 20 mm, while the other conditions remained basically unchanged, resulting in the formation of an aluminum layer of about 1 μm.
[0065] Adhesion test: Samples were taken from the roll using a blade-cutting method to test the adhesion between two bonded films. When testing the bonded film, sample preparation followed the adhesion test method: a layer of ethylene-acrylic acid copolymer film was placed on both the top and bottom of the sample to be tested, and then subjected to a 1.3 × 10⁵ N / m... 2 The sample was hot-pressed at 120℃ for 10 seconds (or fixed with double-sided tape), cooled to room temperature, and used as the traction fixing part of the tensile testing machine. It was then cut into strips of 150mm × 15mm. Finally, the ethylene-acrylic acid copolymer film of the sample strips was fixed to the upper and lower clamps of the tensile testing machine, respectively. After fixing, the two layers were peeled at an angle of 180° and a speed of 50mm / min, and the maximum value of the separation of the two layers of film was recorded.
[0066] The comparative example is 1.3N / 15mm;
[0067] Example 1 shows a thickness of 0.2 N / 15 mm. Due to the high surface roughness of the graphite film, after coating a single-sided aluminum layer, the aluminum layer surface is relatively smooth due to the relatively fast coating speed, making it easier to separate the two thin films.
[0068] Example 2 shows a coating with a thickness of 0.5 N / 15 mm. The coating surfaces formed after coating at different speeds on both sides have significantly different profiles. The side with slower speed has larger crystal size and more aggregated crystals, resulting in a larger profile unit spacing on one side, thus causing the difference in profiles between the two sides.
[0069] Preparation Example 3 is 0.8N / 15mm; due to the reduction in evaporation distance, the heat of the evaporated aluminum vapor is increased, so the crystal size of the aluminum layer formed after coating is relatively larger. Small crystals are easy to recrystallize and aggregate to form large crystals at high temperature, thus having a larger profile unit spacing, which can improve the adhesion problem to a certain extent.
[0070] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A composite conductive film current collector, characterized in that: The composite conductive film includes a support layer (1) having two surfaces in the thickness direction; and a conductive layer (2) formed on at least one surface of the support layer (1); the two surfaces of the composite conductive film have different profile morphologies in the thickness direction to achieve the formation of a gas-containing cavity (3) after the two composite conductive films come into contact; the conductive layer structure is an asymmetric conductive layer structure; the two surfaces of the composite conductive film have different average widths Rsm of the profile units in the thickness direction, and the difference is not less than 0.5 μm; or the two surfaces of the composite conductive film have different surface roughnesses Rz in the thickness direction; or the two surfaces of the composite conductive film have different average widths Rsm of the profile units and different surface roughnesses Rz in the thickness direction; the roughness Rz1 of one surface of the composite conductive film in the thickness direction is 0.01-0.4 times the thickness of its corresponding composite conductive film, and the roughness Rz2 of the other surface is 0.1-0.6 times Rz1; The method for preparing the composite conductive film current collector includes, when a conductive layer (2) is set on one side of the support layer (1), laser etching is used to process the support layer (1). Laser etching can effectively depict two asymmetrical surfaces on the support layer (1). When a conductive layer (2) is set on both sides of the support layer (1), at least one of the following methods is used to double-sidedly deposit the conductive layer (2) to form different surface profiles: increasing the target temperature after evaporation; or reducing the speed of the support layer; or reducing the distance between the support layer and the target; or laser etching is used to process the support layer.
2. The composite conductive film current collector as described in claim 1, characterized in that: The average width of the contour unit on one surface of the composite conductive film in the thickness direction is Rsm1, which ranges from 2 to 8 μm; the average width of the contour unit on the other surface is Rsm2, which ranges from 0.2 to 2 μm.
3. The composite conductive film current collector as described in claim 1, characterized in that: The thickness of the support layer (1) is set to 3-50 μm, and its material is a polymer material or graphite film with a surface roughness of 0.5 μm or more.
4. The composite conductive film current collector as described in claim 1, characterized in that: The conductive layer (2) has a thickness of 0.05-3μm and is made of one or a combination of gold, silver, copper, aluminum, nickel and chromium.
5. A method for preparing a composite conductive film current collector as described in any one of claims 1-4, characterized in that: When a conductive layer (2) is set on one side of a support layer (1), a support layer (1) with an appropriate average width of surface contour units is selected, and the average width of the contour units on the surface of the conductive layer (2) is controlled according to the average width of the contour units on the surface of the support layer (1). When a conductive layer (2) is provided on both sides of a support layer (1), the average width of the contour unit formed on the surfaces of the conductive layers (2) on both sides is controlled to be different.
6. The method for preparing a composite conductive film current collector as described in claim 5, characterized in that: When a conductive layer (2) is provided on both sides of a support layer (1), the conductive layer (2) is plated on both sides in at least one of the following ways to form a different surface profile: increasing the target temperature after evaporation; or reducing the speed of the support layer; or reducing the distance between the support layer and the target; or using laser etching to process the support layer.