A polyester film for a composite aluminum foil film and a method for manufacturing the same

Abstract

The application discloses a polyester film for a composite aluminum foil film, which is used as a base material layer of the composite aluminum foil film, and two sides of the base material layer are bonded with metal aluminum foils, the metal aluminum foils are composed of metal aluminum foils with a first thickness of 5-15 mu m and are rolled and stretched into metal aluminum foils with a second thickness of 3-8 mu m on two sides of the base material layer; wherein the polyester film is prepared from the following components by weight: polyisobutylene succinimide 10-20 parts by weight, tetrabutyl titanate 1-3 parts by weight, 1,4-dimethoxybenzene 3-5 parts by weight, cyano acrylate 5-10 parts by weight, nano-modified montmorillonite particles 2-4 parts by weight, and PET chip 1000-2000 parts by weight. After various treatments for preparing the composite aluminum foil film, the polyester film of the application can maintain a uniform thickness and will not be damaged and stress curled and other defects due to the preparation treatment of the composite aluminum foil film.

Description

Technical Field

[0001] This invention relates to the manufacturing technology of current collectors in lithium-ion batteries, and more particularly to the manufacturing technology of composite aluminum foil films that can be used as positive electrode current collectors in lithium-ion batteries, and especially to a polyester film for composite aluminum foil films and its preparation method. Background Technology

[0002] In lithium-ion batteries, aluminum foil is commonly used as the positive electrode current collector, while copper foil is commonly used as the negative electrode current collector. To improve battery energy density, composite current collectors, consisting of a plastic film and a metal layer, have emerged, such as composite aluminum current collectors used as the positive electrode and composite copper current collectors used as the negative electrode. The metal layer in these composite current collectors can be formed by bonding metal foil to the plastic film, or by vapor deposition or sputtering. Metal foil has excellent conductivity but requires a relatively thick layer; sputtered and vapor-deposited metal layers are thinner, have poorer conductivity, require multiple deposition processes, have high process requirements, and repeated deposition of plastic films easily leads to wrinkles, resulting in low yield and high cost.

[0003] For example, 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 a plurality of first grooves, and the lower surface of the second aluminum foil layer has a plurality of second grooves. This prior art employs a relatively thick aluminum foil structure to obtain the grooves.

[0004] 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 this stage 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 this stage. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a polyester film for composite aluminum foil film and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0006] To address the aforementioned technical problems, this application proposes a polyester film for use as a substrate layer of the composite aluminum foil film. Metal aluminum foil is adhered to both sides of the substrate layer of the composite aluminum foil film. The metal aluminum foil is composed of a first-thickness metal aluminum foil of 5-15 μm rolled and stretched to a second-thickness metal aluminum foil of 3-8 μm on both sides of the substrate layer. The polyester film is prepared from the following components in parts by weight: 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, 2-4 parts by weight of nano-modified montmorillonite particles, and 1000-2000 parts by weight of PET chips.

[0007] This application also proposes a method for preparing the aforementioned polyester film, comprising the following steps: adding 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, 2-4 parts by weight of nano-modified montmorillonite particles, and 1000-2000 parts by weight of PET chips to a high-speed mixer for pre-dispersion mixing at a speed of 1500-2000 rpm for 30-60 minutes to form a mixture; then the mixture is fed into a vented twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270℃-280℃; the material is processed in the extruder... After melting, the material is filtered and extruded into thick sheets. The thickness and profile of the sheets can be adjusted by the extrusion rate of the extruder, the speed of the casting roller, and the opening of the die. The sheets are preheated at 50°C to 90°C and then placed in an infrared heating zone at 300°C to 500°C. They are then longitudinally stretched at a linear speed of 40 to 150 m / min, with a longitudinal stretching ratio of 4.0, to obtain stretched sheets. The stretched sheets are then preheated at 90°C to 120°C and transversely stretched at 100°C to 160°C, with a transverse stretching ratio of 3.8. After being shaped at 160°C to 240°C and then cooled at 100°C to 50°C, the polyester film is obtained.

[0008] Preferably, the preparation method further includes the step of preparing the nano-modified montmorillonite particles: adding 10-20 parts by weight of nano-montmorillonite to 100-200 parts by weight of polyvinyl alcohol aqueous solution, stirring continuously for 60-120 minutes to fully disperse; then lyophilizing the dispersion mixture to obtain a surface-modified solid particle mixture; adding the obtained solid particle mixture to clean water for multiple washing and filtration to obtain a dispersion free of soluble substances; lyophilizing the dispersion mixture again, and screening to obtain particles with a particle size of 10-20 nm, which are the nano-modified montmorillonite particles.

[0009] Preferably, the solid content of the dispersion is 20-40 wt%.

[0010] Preferably, the polyvinyl alcohol content in the polyvinyl alcohol aqueous solution is 10wt%-15wt%.

[0011] Preferably, the particle size of the nano-modified montmorillonite particles is 10-20 nm.

[0012] The polyester film of this application can maintain a uniform thickness after various treatments in the preparation of composite aluminum foil film, and will not suffer from defects such as damage or stress curling due to the preparation process of composite aluminum foil film. Attached Figure Description

[0013] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0014] 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

[0015] 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.

[0016] Existing lithium batteries generally use aluminum foil obtained by rolling aluminum as the positive electrode current collector. Due to the inherent strength limitations of the material, it is difficult to reduce the thickness of the aluminum foil used, otherwise it will easily tear during operation. Even when aluminum foil is laminated with plastic film, it is impossible to use aluminum foil that is too thin for the lamination process.

[0017] 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 polyolefin or polyester. In a preferred embodiment, the substrate layer 1 is preferably made of polyester film. The metallic aluminum foil 2 can be adhered to both sides of the substrate layer 1 using an adhesive.

[0018] Furthermore, the aluminum foil 2 in the composite aluminum foil film of this application can be composed of a first-thickness aluminum foil of 5-15 μm, rolled and stretched on both sides of the substrate layer 1 to a second-thickness aluminum foil of 3-8 μm. That is, the aluminum foil 2 of this application initially has a first thickness, and becomes the final second thickness after being attached to both sides of the substrate layer 1 and rolled and stretched. 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, bonds it to the substrate layer 1, and then performs a rolling and stretching operation to make it the second thickness. After that, no further composite operation is needed, which can obtain a thinner aluminum foil while ensuring conductivity and strength.

[0019] 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.

[0020] 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 also 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.

[0021] In the preparation of the composite aluminum foil film of this application, an adhesive can first be coated on both sides of a substrate layer 1 with an initial thickness of 10-20 μm, and then a metal aluminum foil 2 of the first thickness can be bonded to the surface of the substrate layer 1. Afterwards, a lubricant such as machine oil or silicone grease can be coated on the outside of the metal aluminum foil 2, and then a rolling protective film 3, for example, made of nylon and with a thickness of 8-10 μm, can be attached to the surface of the oiled metal aluminum foil 2. The application of machine lubricant increases the adhesion of the rolling protective film 3 to the metal aluminum foil 2, and simultaneously reduces friction during subsequent rolling and stretching processes, preventing film rupture.

[0022] 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. Thinning the film layer by pure extrusion can easily damage the film layer structure; therefore, the rolled protective film 3, which is in contact with the rolling rollers, is made of nylon to improve sliding properties and prevent tearing. Additionally, applying lubricating oil can further reduce the friction between the film layer and the rolling rollers during rolling. After rolling and stretching, the thickness of the substrate layer 1 changes from 10-20 μm to approximately 6-12 μm.

[0023] Alternatively, the film layer can be heated before being rolled by the rolling rollers to increase the ductility of the plastic film and improve the efficiency of rolling and thinning. Simultaneously, the rebound of the heated plastic film will decrease, which helps maintain the thickness of the stretched film layer. In a preferred embodiment, the film layer can be heated using infrared heating, with a preferred heating temperature of 150-170°C.

[0024] Alternatively, while the film layer is being rolled by the rollers, its two sides can be stretched outwards. This means the film layer is longitudinally extended by the rollers, while simultaneously being stretched laterally along its width using a clamping device, 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 stretching, and the speed of lateral stretching must be controlled to avoid inconsistent stretching ratios between film layers.

[0025] In addition, after the film layer is rolled and stretched, in order to prevent the film layer from rebounding due to stress, it can be further heated and annealed to eliminate the stress in the film layer. The preferred annealing temperature is 130-150℃, and the annealing time is 5-15 minutes.

[0026] Finally, the protective film 3 of the annealed film layer is removed, the lubricating oil on the outer surface of the aluminum foil 2 is removed with a cleaning agent, and then the film is rinsed with water, dried, trimmed, and rolled up to obtain the composite aluminum foil film of this application.

[0027] Based on the description of the structure and preparation process of the composite aluminum foil film of this application, this application further proposes a polyester film suitable for the composite aluminum foil film of this application, wherein the polyester film serves as the substrate layer 1 of the composite aluminum foil film. The substrate layer 1 prepared from the polyester film of this application not only possesses excellent mechanical properties, but can also withstand the heating, rolling, stretching, and annealing treatments of the composite aluminum foil film of this application, and maintains a uniform thickness after treatment, without suffering defects such as damage or stress curling due to the preparation process of the composite aluminum foil film.

[0028] Specifically, this application proposes a polyester film for use as a substrate layer 1 of the composite aluminum foil film. Metal aluminum foil 2 is adhered to both sides of the substrate layer. The metal aluminum foil 2 can be composed of a first-thickness metal aluminum foil of 5-15 μm rolled and stretched to a second-thickness metal aluminum foil of 3-8 μm on both sides of the substrate layer. The polyester film is prepared from the following components in parts by weight: 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, 2-4 parts by weight of nano-modified montmorillonite particles, and 1000-2000 parts by weight of PET chips.

[0029] In one specific embodiment of this application, 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, 2-4 parts by weight of nano-modified montmorillonite particles, and 1000-2000 parts by weight of PET chips can be added to a high-speed mixer for pre-dispersion and mixing at 1500-2000 rpm for 30-60 minutes to form a mixture.

[0030] The mixture is then fed into a vented twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270℃~280℃.

[0031] After the material is melted in the extruder, it is filtered and extruded into thick sheets. The thickness and profile of the sheets can be adjusted by the extruder output, the casting roller speed, and the die opening.

[0032] The above-mentioned thick sheet is preheated at a temperature of 50℃~90℃, then placed in an infrared heating zone of 300℃~500℃, and longitudinally stretched at a linear speed of 40~150m / min with a longitudinal stretching ratio of 4.0 to obtain a stretched sheet.

[0033] The stretched sheet is preheated at 90°C to 120°C, then transversely stretched at 100°C to 160°C with a transverse stretch ratio of 3.8. It is then shaped at 160°C to 240°C and cooled at 100°C to 50°C to obtain the polyester film described in this application.

[0034] To facilitate the uniform dispersion of nano-montmorillonite in the organic components of the polyester film, surface modification treatment is required for the nano-montmorillonite. The specific steps are as follows: 10-20 parts by weight of nano-montmorillonite are added to 100-200 parts by weight of a polyvinyl alcohol aqueous solution, and the mixture is continuously stirred for 60-120 minutes to achieve full dispersion; then, the dispersion mixture is lyophilized by spray drying to obtain a mixture of surface-modified solid particles; the obtained solid particle mixture is washed and filtered multiple times in clean water to obtain a dispersion with a solid content of 20-40 wt% free of soluble substances; the dispersion is then lyophilized by spray drying again, and particles with a particle size of 10-20 nm are obtained by screening, which are the nano-modified montmorillonite particles. The polyvinyl alcohol content in the polyvinyl alcohol aqueous solution is 10 wt%-15 wt%.

[0035] Examples 1-5

[0036] Polyester films for the substrate layer of composite aluminum foil films were prepared according to the raw material weight ratios in the table below.

[0037] Example 1 Example 2 Example 3 Example 4 Example 5 Polyisobutylene succinimide 10 12 15 18 20 Tetrabutyl titanate 1.0 1.5 2.0 2.5 3.0 1,4-Dimethoxybenzene 3.0 3.5 4.0 4.5 5.0 cyanoacrylate 5.0 6.0 7.5 9.0 10.0 Nano-modified montmorillonite particles 2.0 2.5 3.0 3.5 4.0 PET 1000 1200 1500 1800 2000 Polyester film thickness (μm) 10 12 15 18 20

[0038] Comparative Examples 6-10

[0039] Following the same method as in the above embodiments, polyester films for comparison were prepared according to the raw material weight ratios in the table below.

[0040]

[0041]

[0042] The performance parameters of each prepared polyester film were tested, and a 15μm thick film made from pure PET without any added components was compared. Examples 1-5, Comparative Examples 6-10, and the pure PET film used as the substrate layer of this application were subjected to processes such as bonding aluminum foil, rolling, and stretching. The performance of the final composite aluminum foil film was then examined. Tests showed that the polyester films of Examples 1-5 maintained uniform thickness after all the processes involved in preparing the composite aluminum foil film, and no defects such as damage or stress curling were observed due to the composite aluminum foil film preparation process. However, Comparative Examples 6-10 and the pure PET film, which did not undergo the preparation process, both showed varying degrees of damage and curling.

[0043] 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.

[0044] 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 polyester film for use as a substrate layer of a composite aluminum foil film, wherein metal aluminum foil is adhered to both sides of the substrate layer of the composite aluminum foil film, the metal aluminum foil being composed of metal aluminum foil of a first thickness of 5-15µm rolled and stretched to a second thickness of 3-8µm on both sides of the substrate layer; characterized in that, The polyester film is prepared from the following components in parts by weight: 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, dispersed in polyvinyl alcohol aqueous solution, lyophilized by spraying, washed and filtered, lyophilized by spraying again, and sieved to obtain 2-4 parts by weight of nano-modified montmorillonite particles with a particle size of 10-20 nm, and 1000-2000 parts by weight of PET chips.

2. The method for preparing the polyester film according to claim 1, comprising the following steps: adding 10-20 parts by weight of polyisobutylene succinimide, 1-3 parts by weight of tetrabutyl titanate, 3-5 parts by weight of 1,4-dimethoxybenzene, 5-10 parts by weight of cyanoacrylate, 2-4 parts by weight of nano-modified montmorillonite particles, and 1000-2000 parts by weight of PET chips to a high-speed mixer for pre-dispersion mixing at a speed of 1500-2000 rpm. Mix at rpm for 30-60 minutes to form a mixture; then the mixture enters a vented twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270℃-280℃; after the material melts in the extruder, it is filtered and extruded into a thick sheet; the thickness and profile of the thick sheet can be adjusted by the extrusion rate of the extruder, the speed of the casting roller, and the die opening; the above thick sheet is preheated at 50℃-90℃ and then placed in an infrared heating zone at 300℃-500℃, and longitudinally stretched at a linear speed of 40-150 m / min with a longitudinal stretching ratio of 4.0 to obtain a stretched sheet; the stretched sheet is preheated at 90℃-120℃ and transversely stretched at 100℃-160℃ with a transverse stretching ratio of 3.8; then it is shaped at 160℃-240℃ and cooled at 100℃-50℃ to obtain the polyester film.

3. The preparation method according to claim 2 further includes the step of preparing the nano-modified montmorillonite particles: adding 10-20 parts by weight of nano-montmorillonite to 100-200 parts by weight of polyvinyl alcohol aqueous solution, stirring continuously for 60-120 minutes to fully disperse; then lyophilizing the dispersion mixture to obtain a surface-modified solid particle mixture; adding the obtained solid particle mixture to water for multiple washing and filtration to obtain a dispersion free of soluble substances; lyophilizing the dispersion mixture again, and screening to obtain particles with a particle size of 10-20 nm, which are the nano-modified montmorillonite particles.

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