Composite aluminum foil film and method for manufacturing the same

Abstract

The application discloses a kind of composite aluminum foil film, by substrate layer and the metal aluminum foil adhered to the two sides of substrate layer are constituted, wherein, the metal aluminum foil is by 5-15 μm first thickness of metal aluminum foil is rolled and stretched into 3-8 μm second thickness of metal aluminum foil on the two sides of the substrate layer, the outside of the metal aluminum foil is attached with a layer of rolling protection film, the metal aluminum foil and rolling protection film are uniformly distributed with position corresponding hole.This application further discloses a kind of preparation above-mentioned composite aluminum foil film method.The composite aluminum foil film of the application uses first thickness of metal aluminum foil as initial raw material, after being bonded with substrate layer, it is rolled and stretched to become second thickness, and then it is not necessary to carry out composite operation again, both can obtain thinner metal aluminum foil, and can guarantee conductivity and strength.

Description

Technical Field

[0001] This invention relates to current collectors used for conduction in lithium-ion batteries, and more specifically, to a composite aluminum foil film that can be used as a positive electrode current collector in lithium-ion batteries and a method for preparing the same. Background Technology

[0002] With the continuous development of energy storage and conversion technologies, lithium-ion batteries are increasingly widely used in electric vehicles, mobile devices, and other fields. The positive electrode current collector is a crucial component of lithium-ion batteries, and its performance significantly impacts the battery's electrochemical performance and safety. Traditionally, positive electrode current collectors are mostly aluminum foil, while negative electrode current collectors are mostly copper foil. However, due to the high density, low strength, and susceptibility to puncture of metal foil, composite materials have been explored as positive electrode current collectors. Composite materials are composed of various materials and possess excellent mechanical properties, electrochemical properties, and stability. Among them, composite aluminum foil film is a composite material with broad application prospects.

[0003] CN 112201389 B discloses a conductive film for use as a positive electrode current collector in lithium batteries, comprising an aluminum layer, an intermediate reinforcement layer, and a polymer film layer. The intermediate reinforcement layer is disposed on both sides of the polymer film layer, and the aluminum layer is disposed on the outer side of the intermediate reinforcement layer. In this prior art, the thickness of the aluminum layer is 100-3000 nm, the thickness of the polymer film layer is 3-15 μm, and the thickness of the intermediate reinforcement layer is 10-100 nm. The process used includes, but is not limited to, vapor deposition, magnetron sputtering, or a combination of two processes. This prior art requires forming intermediate reinforcement layers on both sides of the polymer film layer, and then forming an aluminum layer on the outer side of each intermediate reinforcement layer, requiring at least four deposition operations. Existing deposition equipment can typically achieve a deposition thickness of only a few hundred nanometers in a single vapor deposition operation, and magnetron sputtering can achieve even thinner layers. To achieve a deposition thickness of 1000 nm or greater, repeated vapor deposition is required, making the process extremely cumbersome and complex. In addition, the thinner the polymer film, the easier it is for wrinkles to appear when the film is wound. Repeated winding and multiple evaporation processes on both sides result in high wrinkle rate, scrap rate and cost.

[0004] CN 114695900 B discloses a composite current collector, comprising a first aluminum foil layer, a PET layer, and a second aluminum foil layer stacked sequentially. Both the first and second aluminum foil layers are fixedly connected to the PET layer. The upper surface of the first aluminum foil layer has several first grooves, and the lower surface of the second aluminum foil layer has several second grooves. This prior art employs a thicker aluminum foil structure to obtain the grooves.

[0005] Then, the aluminum and copper foils used as current collectors are mainly for conductivity and do not participate in the active reaction. Therefore, one way to improve the energy density of batteries at present is to reduce the mass ratio of the current collector: on the one hand, by using composite metal foil films with lower density, and on the other hand, by reducing the thickness of the metal layer. Therefore, using thicker aluminum foil is not advisable at present. However, the complex process and high cost also limit the application of coating technology on composite metal foil films. In addition, the metal layer formed by evaporation or sputtering is too thin and not dense enough, and its conductivity is far inferior to that of pure metal foil. Especially for aluminum foil, since an oxide layer is easily formed on its surface, the conductivity will be greatly reduced if an oxide layer is formed when the substrate is too thin. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a composite aluminum foil film and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0007] To address the aforementioned technical problems, this application proposes a composite aluminum foil film, comprising a substrate layer and metal aluminum foils adhered to both sides of the substrate layer. The metal aluminum foils are formed by rolling and stretching a first-thickness metal aluminum foil of 5-15 μm to a second-thickness metal aluminum foil of 3-8 μm on both sides of the substrate layer. A rolling protective film is attached to the outer side of the metal aluminum foils, and the metal aluminum foils and the rolling protective film have uniformly distributed holes at corresponding positions.

[0008] Preferably, the end of the hole extends into half the thickness of the substrate layer.

[0009] This application also proposes a method for preparing a composite aluminum foil film, comprising the following steps: providing a substrate layer, and bonding a metal aluminum foil with a first thickness of 5-15 μm to both sides of the substrate layer; attaching a rolling protective film to the outside of the metal aluminum foil; placing the film layer with the rolling protective film attached between at least one pair of rolling rollers, and rolling the metal aluminum foil from the first thickness to a second thickness of 3-8 μm by the pressure of the rolling rollers; placing the rolled film layer between a pair of die rollers with protrusions, and uniformly forming corresponding holes on the metal aluminum foil and the rolling protective film by the protrusions on the die rollers.

[0010] Preferably, the tip of the spike penetrates half the thickness of the substrate layer.

[0011] Preferably, the method further includes the following step: heating the film layer before it is rolled by the rolling roller.

[0012] Preferably, the method further includes the following steps: while the film layer is being rolled by the rolling roller, the two sides of the film layer are laterally clamped and stretched along the axial direction of the rolling roller.

[0013] Preferably, the method further includes the step of heating and annealing the film layer before forming the pores.

[0014] The composite aluminum foil film of this application uses a first-thickness aluminum foil of 5-15μm as the initial raw material. After bonding and laminating it with the substrate layer, it is rolled and stretched to make it a second-thickness film. After that, no further lamination is required. This method can obtain a thinner aluminum foil while ensuring conductivity and strength. Attached Figure Description

[0015] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0016] Figure 1 The image shown is a cross-sectional view of a composite aluminum foil film according to a specific embodiment of this application. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0018] Compared to copper foil used for the negative electrode current collector in lithium-ion batteries, aluminum foil has slightly lower strength and density, generally requiring a greater thickness to ensure conductivity. Existing aluminum-plated films produced through processes like vapor deposition often struggle to achieve the minimum thickness required for conductivity, necessitating repeated deposition processes. This process is complex, prone to wrinkling, resulting in low yields and high costs. Furthermore, vapor-deposited aluminum layers have poor adhesion and are easily detached, generally limiting their use to food packaging materials. Current lithium-ion batteries typically use aluminum foil obtained through aluminum rolling as the positive electrode current collector. Due to inherent strength limitations, the thickness of this aluminum foil is difficult to reduce, otherwise it easily tears during handling. Even when combining aluminum foil with plastic films, excessively thin aluminum foil is unsuitable for this process.

[0019] In view of this, this application proposes a composite aluminum foil film, such as Figure 1 As shown, the composite aluminum foil film consists of a substrate layer 1 and metallic aluminum foil 2 adhered to both sides of the substrate layer 1. The substrate layer 1 can be made of a plastic film made of materials such as polyolefins or polyester. In a preferred embodiment, the substrate layer 1 is preferably made of polyester film. The metallic aluminum foil 2 can be bonded to both sides of the substrate layer 1 using an adhesive (not shown in the figure), preferably a polyurethane adhesive with good high-temperature resistance.

[0020] Furthermore, the aluminum foil 2 in the composite aluminum foil film of this application is composed of a first-thickness aluminum foil of 5-15 μm, which is rolled and stretched to a second-thickness aluminum foil of 3-8 μm on both sides of the substrate layer 1. That is, the aluminum foil 2 of this application initially has a first thickness, which becomes the final second thickness after being rolled and stretched on both sides of the substrate layer 1. Since the material strength of aluminum is not very good, directly using a second-thickness aluminum foil of 3-8 μm is expensive and difficult to perform bonding and other composite operations. Therefore, this application uses a first-thickness aluminum foil of 5-15 μm as the initial raw material, which is bonded and composited with the substrate layer 1, and then rolled and stretched to become the second thickness. After that, no further composite operation is required, which can obtain a thinner aluminum foil while ensuring conductivity and strength.

[0021] For example, the aluminum foil 2 used is rolled from aluminum with an aluminum content of more than 98%, and existing finished aluminum foil products with a thickness of 5-15μm sold on the market can be selected as the initial raw material for the first thickness.

[0022] Furthermore, as shown in the figure, a rolling protective film 3 is also attached to the outer side of the aluminum foil 2 to protect the surface of the aluminum foil 2 from scratches and tears during the rolling and stretching process. The rolling protective film 3 can be made of plastic film made of materials such as polyolefin, polyester, and nylon. In a preferred embodiment, the rolling protective film 3 is preferably made of nylon film with excellent strength and self-lubricating properties, preferably with a thickness of 8-10 μm.

[0023] Furthermore, the aluminum foil 2 and the rolled protective film 3 are also uniformly distributed with corresponding holes 4. These holes 4 are evenly distributed on both sides of the composite aluminum foil film, and are all tapered holes with large openings and small ends, as shown in the figure. In a preferred embodiment, the end of the hole 4 extends into approximately half the thickness of the substrate layer 1. Of course, it is difficult to precisely extend into half the thickness of the substrate layer 1. From a cost perspective, it is preferable that the end of the hole 4 extends into 1 / 3 to 2 / 3 of the thickness of the substrate layer 1.

[0024] The holes 4 formed on the aluminum foil 2 are used to increase the contact area between the aluminum foil 2 and the positive electrode material, improve the adhesion between the positive electrode material and the aluminum foil 2, and prevent them from separating, thus increasing internal resistance. The holes 4 on both sides of the composite aluminum foil film shown in the figure are not through holes; this is to prevent leakage of the slurry during subsequent coating of the positive electrode material. Later, during cell compaction, these holes 4 can be enlarged by the positive electrode material, thereby increasing the contact area with the positive electrode material. In the event of a short circuit and overheating of the cell, the substrate layer 1 melts and blocks these holes 4, preventing the current from continuing to increase and reducing the risk of battery combustion and explosion.

[0025] After the aluminum foil 2 is rolled and stretched, the rolling protective film 3 still needs to be retained on the surface of the aluminum foil 2. This is to protect the aluminum foil 2 when the holes 4 are formed subsequently, so as to avoid the formation of large tear edges in the holes of the aluminum foil 2, thereby improving the consistency of the holes 4. Afterwards, the rolling protective film 3 can continue to protect the metal surface until it is necessary to remove it.

[0026] To further improve the consistency of the current collector, after forming the holes 4, a corrosive liquid can be sprayed or coated onto the surface of the rolled protective film 3 to corrode the edges of the aluminum foil 2 squeezed into the holes 4, thereby removing the edge burrs formed during the hole formation process. Simultaneously, corroding away a portion of the aluminum foil can further reduce the weight of the composite aluminum foil film, which is beneficial for improving the energy density of the lithium battery.

[0027] In a preferred embodiment, the maximum opening diameter of the hole 4 on the aluminum foil 2 is 20-30 μm, and the center distance between adjacent holes 4 is 50-100 μm.

[0028] Furthermore, this application also proposes a method for preparing the above-mentioned composite aluminum foil film, comprising the following steps.

[0029] First, a substrate layer 1 is provided, for example, a substrate layer 1 made of PET, the initial thickness of which is 10-20 μm. Then, a metal aluminum foil 2 with a first thickness of 5-15 μm is bonded to both sides of the substrate layer 1.

[0030] Subsequently, a rolled protective film 3, such as a thin film of 8-10 μm thickness made of nylon, is attached to the outside of the aluminum foil 2.

[0031] Then, the film layer with the rolled protective film 3 attached is placed between at least one pair of rolling rollers, and the aluminum foil 2 is rolled from a first thickness to a second thickness of 3-8 μm by the pressure of the rolling rollers. Rolling the aluminum foil 2 from the first thickness to the second thickness only requires controlling the gap between the rolling rollers. Of course, considering the large elastic deformation capacity of the plastic in the film layer, the gap between the rolling rollers should be slightly smaller than the thickness of the film layer after reduction. In addition, thinning the film layer by pure extrusion can easily damage the film layer structure. Therefore, the rolled protective film 3 in contact with the rolling rollers is made of nylon to improve sliding properties and avoid crushing. After rolling and stretching, the thickness of the substrate layer 1 changes from 10-20 μm to about 6-12 μm.

[0032] Furthermore, it is preferable to heat the film layer before it is rolled by the rolling rollers to increase the ductility of the plastic film and improve the efficiency of rolling and thinning. At the same time, the rebound of the heated plastic film will be reduced, which is beneficial to maintaining the thickness of the stretched film layer. In a preferred embodiment, the film layer can be heated by infrared heating, and the preferred heating temperature of the film layer is 150-170°C.

[0033] Alternatively, while the film layer is being rolled by the rolling rollers, its two sides can be laterally clamped and stretched along the axial direction of the rolling rollers. That is, the film layer is longitudinally extended by the rolling rollers, while simultaneously being laterally stretched by clamping the two sides in the width direction, thus accelerating the material thinning process. Because the stretching of the aluminum foil is involved, the entire film layer needs to be clamped tightly during clamping and stretching, and the speed of lateral stretching must be controlled to avoid inconsistent stretching ratios between film layers.

[0034] Next, the rolled film is placed between a pair of die rollers with protrusions, and holes 4 are uniformly formed on the aluminum foil 2 and the rolled protective film 3 by the protrusions on the die rollers.

[0035] If stress exists during the rolling of the membrane layer when creating the holes, the membrane layer with excessive stress will displace and shrink after perforation, causing the holes to close when the protrusions move out. To avoid this problem, it is preferable to heat and anneal the membrane layer before forming the holes 4 to minimize stress in the membrane layer. The preferred annealing temperature is 130-150°C, and the annealing time is 5-15 minutes.

[0036] After annealing to release stress, if a small amount of stress remains, it can be released by creating holes through puncture, thus preventing the composite aluminum foil film from becoming twisted and uneven. Although a small amount of stress may deform the holes, by setting the appropriate hole size and center distance as described above, it is possible to prevent the holes from closing completely.

[0037] Furthermore, after forming the holes 4, a corrosive liquid can be sprayed or coated onto the surface of the rolled protective film 3 to corrode the edges of the aluminum foil 2 extruded into the holes 4, thereby removing the edge burrs formed during the hole formation process. Finally, the foil is rinsed with water to remove the corrosive liquid, then dried, trimmed, and rolled up.

[0038] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0039] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A method for preparing a composite aluminum foil film, comprising the following steps: providing a substrate layer, and bonding a metal aluminum foil with an initial thickness of 5-15µm to both sides of the substrate layer; attaching a rolling protective film to the outer side of the metal aluminum foil; placing the film layer with the rolling protective film attached between at least one pair of rolling rollers, and rolling the metal aluminum foil from the first thickness to a second thickness of 3-8µm by the pressure of the rolling rollers; placing the rolled film layer between a pair of die rollers with protrusions, and uniformly forming corresponding holes on the metal aluminum foil and the rolling protective film by the protrusions on the die rollers, wherein the formed holes are conical holes with a large opening and a small end, and the end of the hole extends into 1 / 3-1 / 2 of the thickness of the substrate layer.

2. The method as described in claim 1, characterized in that, The rolling protective film remains on the surface of the aluminum foil during the puncture process to protect the aluminum foil and prevent the holes from forming tear edges.

3. The method of claim 1 further includes the following step: heating the film layer before it is rolled by the rolling roller.

4. The method of claim 1 further includes the following steps: while the film layer is being rolled by the rolling roller, the two sides of the film layer are laterally clamped and stretched along the axial direction of the rolling roller.

5. The method of claim 1, further comprising the step of: heating and annealing the film layer before forming the pores.

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