Polymer films and methods for making the same, composite current collectors and methods for making the same

Abstract

This application relates to the field of battery technology, and discloses a polymer film and its preparation method, a composite current collector and its preparation method. The polymer film includes: a first polymer and a modified polymer, wherein the first polymer includes polypropylene; the modified polymer includes at least one selected from polyvinyl butyral, polyethylene terephthalate, polyimide, and polyamide. It has strong surface adhesion.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to polymer films and their preparation methods, and composite current collectors and their preparation methods. Background Technology

[0002] As lithium-ion battery technology continues to advance towards higher energy density, lighter weight, and higher safety, composite current collectors have become a key component for improving the performance of next-generation lithium-ion batteries. Compared with traditional pure metal current collectors (copper foil, aluminum foil), composite current collectors have a "sandwich" structure, using a polymer material as the support film and a conductive metal layer on the outer layer of the support film, which has significant technological advantages. Replacing some of the metal with low-density polymers can effectively improve the overall mass energy density of the battery; under thermal runaway conditions, polymers have a "fusible link" effect, which can physically cut off the internal short-circuit current path, thereby improving the intrinsic safety of lithium-ion batteries.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect of this application, a polymer film is provided, comprising: a first polymer and a modified polymer, wherein the first polymer comprises polypropylene; and the modified polymer comprises at least one selected from polyvinyl butyral, polyethylene terephthalate, polyimide, and polyamide.

[0005] In some embodiments, the mass ratio of the first polymer to the modified polymer is (6~9): (1~4).

[0006] In a second aspect of this application, a method for preparing the polymer film proposed in this application is provided, comprising: melt-blending 1 to 4 parts by mass of a modified polymer, 6 to 9 parts by mass of a first polymer, and 0.5 to 1 parts by mass of a compatibilizer to obtain a first blend; performing a melt casting process on the first blend to obtain a second mixture; and performing a film-forming process on the second mixture to obtain the polymer film.

[0007] In some embodiments, at least one of the following conditions is met: the compatibilizer includes at least one of maleic anhydride-grafted polypropylene, styrene-ethylene-styrene block copolymer with maleic anhydride graft, and styrene-butene-styrene block copolymer with maleic anhydride graft; the acetal degree of the modified polymer is 65wt%~85wt%; the intrinsic viscosity of the polyethylene terephthalate is 0.50dL / g~1.00dL / g; the polyimide includes one or more of aromatic polyimide, semi-aromatic polyimide, and aliphatic polyimide; the polyamide (according to the number of repeating units) includes one or more of polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide 6 / 66, and polyamide 66 / 610; and the melt blending temperature is 175°C~205°C.

[0008] In some embodiments, at least one of the following conditions is met: the temperature of the melting and casting process is 175°C to 205°C; the cooling temperature of the melting and casting process is 15°C to 30°C; and the temperature of the film-forming process is 150°C to 170°C.

[0009] In some embodiments, the method further includes: performing a heat setting treatment on the polymer film at a temperature of 155°C to 175°C; and / or performing a preheating treatment on the second mixture at a temperature of 135°C to 155°C.

[0010] In a third aspect of this application, a composite current collector is provided, comprising: a support membrane, the support membrane comprising the polymer membrane proposed in this application; and a metal layer disposed on at least one side of the support layer, the metal layer comprising aluminum or copper.

[0011] In some embodiments, at least one of the following conditions is met: the thickness of the metal layer is 1 μm to 2 μm; the thickness of the support film is 4 μm to 8 μm.

[0012] In a fourth aspect of this application, a method for preparing the composite current collector proposed in this application is provided, comprising: performing physical vapor deposition on at least one side of the polymer film proposed in this application to obtain a first composite film; and performing electroplating on the first composite film to obtain the composite current collector.

[0013] In some embodiments, at least one of the following conditions is met: the deposition thickness of the physical vapor deposition treatment is 50 nm to 100 nm; the deposition thickness of the electroplating treatment is 1 μm to 2 μm.

[0014] The beneficial effects of the technical solution proposed in this application include at least the following: The polymer membrane of this application modifies the polypropylene in the first polymer, polypropylene, by incorporating a highly polar modified polymer. This increases the polar groups on the surface of the polymer membrane, creating conditions for hydrogen bonding and strong van der Waals forces between the polymer membrane surface and the metal, thereby modifying the polymer membrane surface. Therefore, by combining the polymer membrane of this application with a metal, a composite current collector with high adhesion to the metal interface can be prepared. Detailed Implementation

[0015] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0016] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0017] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0018] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0021] Among related technologies, polymer materials with potential as composite current collector support films include the following categories: polyethylene terephthalate (PET), polyimide (PI), and polypropylene (PP). However, PET suffers from swelling in lithium-ion battery electrolytes, leading to reduced battery life. PI has high preparation costs and has not been widely studied. PP has the advantages of low cost and stable chemical properties.

[0022] However, polypropylene is a highly nonpolar saturated hydrocarbon polymer. Films made of polypropylene have extremely low surface energy and poor interfacial adhesion with metal coatings. This weak interfacial bond leads to coating peeling and a sharp increase in interfacial impedance during battery rolling, winding, and long-term cycling, ultimately causing performance degradation or even failure of lithium-ion batteries. Therefore, enhancing the adhesion of the PP support film surface to the metal layer is a key issue in improving the performance of composite current collectors containing PP support films.

[0023] In a first aspect of this application, a polymer film is provided, comprising: a first polymer and a modified polymer, wherein the first polymer comprises polypropylene; and the modified polymer comprises at least one selected from polyvinyl butyral, polyethylene terephthalate, polyimide, and polyamide.

[0024] The polymer membrane of this application modifies the polypropylene in the first polymer, polypropylene, by incorporating a highly polar modified polymer. This increases the polar groups on the surface of the polymer membrane, creating conditions for hydrogen bonding and strong van der Waals forces between the polymer membrane surface and the metal, thereby modifying the polymer membrane surface. Therefore, by combining the polymer membrane of this application with a metal, a composite current collector with high adhesion to the metal interface can be prepared.

[0025] In some embodiments, the mass ratio of the first polymer to the modified polymer is (6~9):(1~4). Therefore, the polar groups in the modified polymer can effectively improve the surface group distribution of the polymer film, thereby significantly enhancing the surface adhesion of the polymer film.

[0026] In a second aspect of this application, a method for preparing the polymer film proposed in this application is provided, comprising: melt-blending 1 to 4 parts by mass of a modified polymer, 6 to 9 parts by mass of a first polymer, and 0.5 to 1 parts by mass of a compatibilizer to obtain a first blend; performing a melt casting process on the first blend to obtain a second mixture; and performing a film-forming process on the second mixture to obtain the polymer film.

[0027] The modified polymer and the first polymer, with the assistance of a compatibilizer, are melt-blended to achieve physicochemical mixing of their molecular weights, resulting in a first blend. During the blending process, the melts of the modified polymer and the first polymer undergo strong shearing and thermodynamic coupling, experiencing melting, droplet breakage, and physical diffusion and entanglement between the two phases. The compatibilizer plays an in-situ compatibilizing role, causing the active polar groups on the compatibilizer chain to react in situ with the polar functional groups on the modified polymer chain, anchoring the interface through covalent bonds. Simultaneously, the nonpolar polyolefin backbone of the compatibilizer undergoes co-crystallization and molecular chain entanglement with the first polymer. This synergistic mechanism of "chemical anchoring and physical interpenetration" effectively reduces interfacial tension and inhibits thermodynamic aggregation of the dispersed phase in the molten state, thereby constructing a more uniform and stable nano / micron-scale multiphase dispersion. A second blend is further obtained through melt casting and prepared into a cast sheet suitable for film stretching. The second blend is then subjected to film-forming treatment to obtain the polymer film of this application. Thus, the modified polymer is thoroughly mixed with the first polymer, polypropylene, to form a polymer film with uniform composition, stable structure, and significantly improved surface polarity.

[0028] In some embodiments, at least one of the following conditions is met: the compatibilizer includes at least one of maleic anhydride-grafted polypropylene, styrene-ethylene-styrene block copolymer maleic anhydride graft, and styrene-butene-styrene block copolymer maleic anhydride graft; the acetal degree of the modified polymer is 65wt%~85wt%; and the melt blending temperature is 175℃~205℃.

[0029] The aforementioned compatibilizer can significantly improve the compatibility between the first polymer (PP) and the highly polar modified polymer, and induce a certain degree of cross-linking, thereby enhancing interfacial adhesion. The modified polymer, with its acetal content within the aforementioned range, exhibits good processing fluidity, allowing for effective mixing with the molecular chains of the first polymer and reducing interfacial tension between the two phases. The aforementioned melt blending temperature effectively promotes the mixing and dispersion of the first and modified polymers and facilitates the compatibilizer reaction. Therefore, this contributes to improving the mechanical properties of the prepared polymer film and significantly enhancing the adhesion of the polymer film surface.

[0030] In some embodiments, at least one of the following conditions is met: the intrinsic viscosity of the polyethylene terephthalate is 0.50 dL / g to 1.00 dL / g; the polyimide includes one or more of aromatic polyimide, semi-aromatic polyimide, and aliphatic polyimide; the polyamide (according to the number of repeating units) includes one or more of polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide 6 / 66, and polyamide 66 / 610.

[0031] In some embodiments, at least one of the following conditions is met: the temperature of the melting and casting process is 175°C to 205°C; the cooling temperature of the melting and casting process is 15°C to 30°C; and the temperature of the film-forming process is 150°C to 170°C.

[0032] In some embodiments, the film-forming process includes a biaxial stretching film-forming process.

[0033] The casting process under the aforementioned conditions results in a more uniform morphology of the two-phase mixture compared to the first blend, further reducing uneven distribution such as molecular agglomeration. The film-forming process under these conditions promotes uniform plasticization of the prepared polymer film, resulting in a smooth and fine surface. This, in turn, improves the flatness and quality of the prepared polymer film.

[0034] In some embodiments, the method further includes: performing a heat setting treatment on the polymer film at a temperature of 155°C to 175°C; and / or performing a preheating treatment on the second mixture at a temperature of 135°C to 155°C.

[0035] Heat setting can release accumulated stress in the polymer film, which helps improve the stability of the polymer film structure and reduce film dimensional shrinkage. Preheating can soften the second mixture, which helps improve the thickness uniformity of the prepared polymer film. Therefore, it is beneficial to improve the surface quality and overall performance stability of the prepared polymer film.

[0036] In a third aspect of this application, a composite current collector is provided, comprising: a support membrane, the support membrane comprising the polymer membrane proposed in this application; and a metal layer disposed on at least one side of the support layer, the metal layer comprising aluminum or copper.

[0037] Composite current collectors use polymer films as the supporting membrane, and the polymer film combined with metal forms a composite structure, achieving multiple synergistic effects. Among these, the relatively lightweight polymer film significantly reduces the weight of the current collector and helps improve the energy density of lithium-ion batteries. The flexible polymer film can buffer the expansion stress generated during lithium-ion battery operation and uniformly distribute the current. Furthermore, the polymer film has a melting-breaking function to prevent thermal runaway. Therefore, it provides key material support for high-safety, high-energy-density, and long-life power batteries and energy storage systems.

[0038] In some embodiments, at least one of the following conditions is met: the thickness of the metal layer is 1 μm to 2 μm; the thickness of the support film is 4 μm to 8 μm. Therefore, the composite current collector exhibits good conductivity and bending resistance, which is beneficial for improving the structural stability of the composite current collector.

[0039] In a fourth aspect of this application, a method for preparing the composite current collector proposed in this application is provided, comprising: performing physical vapor deposition on at least one side of the polymer film proposed in this application to obtain a first composite film; and performing electroplating on the first composite film to obtain the composite current collector.

[0040] The method of this application uses physical vapor deposition to deposit a first metal layer on the surface of a polymer film, which is dense and continuous and forms a tight bond with the polymer film. Further electroplating is then performed on the deposited first metal layer to form a composite current collector metal layer of appropriate thickness. Therefore, the metal layer of the composite current collector has strong adhesion to the supporting film, effectively reducing the failure of the composite current collector and the resulting lithium-ion battery failure caused by metal layer separation and poor interfacial bonding.

[0041] In some embodiments, at least one of the following conditions is met: the deposition thickness of the physical vapor deposition treatment is 50 nm to 100 nm; the deposition thickness of the electroplating treatment is 1 μm to 2 μm. Thus, a composite current collector with a tightly bonded structure, excellent conductivity, and a tightly bonded interface with the polymer film can be prepared.

[0042] In some embodiments, the physical vapor deposition includes at least one of magnetron sputtering and electroplating.

[0043] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0044] Example 1 The preparation of polymer films includes the following steps: Step (1): By weight, mix 1 part polyvinyl butyral, 9 parts polypropylene, and 0.5 parts maleic anhydride-grafted polypropylene evenly, and then melt-blend them using a twin-screw extruder. After melt extrusion, water-cooled stranding, and pelletizing, the first blend particles are obtained. The process parameters are as follows: the melt extrusion channel temperatures are 75℃, 120℃, 150℃, 170℃, 180℃, 185℃, 190℃, 195℃, 200℃, and 205℃, and the die temperature is 200℃; the screw speed is 150 RPM, the feeding speed is 1.5 RPM, and the cooling water temperature is 25℃. Step (2): The first blend particles obtained in step (1) are subjected to melting and casting treatment, including feeding them into a twin-screw extruder for casting, followed by melt extrusion, cooling by cooling rollers, and winding to obtain a second blend casting sheet; the process parameters are as follows: the melt extrusion channel temperatures are 75℃, 120℃, 150℃, 170℃, 180℃, 185℃, 190℃, 195℃, 200℃, and 205℃ in sequence, and the die temperature is 200℃; the screw speed is 150RPM, the feeding speed is 1.5RPM, and a vacuum is drawn; the cooling roller temperature is 25℃; the thickness of the resulting casting sheet is 150μm and the width is 200mm; Step (3): Cut the second mixture casting obtained in step (2) into 95mm×95mm castings for film preparation. Use a high-temperature biaxial stretching machine to perform synchronous biaxial stretching to obtain a polymer film. The process parameters are: longitudinal stretching temperature 155℃, stretching ratio 5; transverse stretching temperature 155℃, stretching ratio 5, stretching rate 10mm / s; polymer film thickness is 5μm.

[0045] It also includes: preheating the second mixture at a temperature of 150°C for 3 minutes; and heat-setting the polymer film at a temperature of 160°C for 3 minutes.

[0046] The preparation of composite current collectors includes the following steps: Step (4): Cut the polymer film obtained in step (3) into 100mm×100mm pieces, attach them to a 6-inch silicon wafer with PI tape, and perform physical vapor deposition (PVD) on the polymer film surface to deposit metallic copper, obtaining a first composite film with a metal layer covering the polymer film surface. The deposition thickness of the PVA is 90nm. The process parameters are: cavity vacuum degree less than 1×10 -7 Torr, the process gas is argon, the magnetron sputtering power is 50W, the metal deposition rate is 1.0 Å / s, and the coating time is 15 min; Step (5): The first composite film obtained in step (4) is electroplated. The first composite film is pasted onto a titanium plate as a cathode and a copper sheet is used as an anode. Water electroplating is performed to obtain a composite current collector. The process parameters are: current density of 1A / dm 2 The electroplating time was 5 minutes, and the deposition thickness of the electroplating treatment was 1 μm.

[0047] Example 2 Example 2 is the same as Example 1, except that it uses 2 parts by mass of polyvinyl butyral and 8 parts by mass of polypropylene.

[0048] Example 3 Example 3 is the same as Example 1, except that it uses 4 parts by mass of polyvinyl butyral and 6 parts by mass of polypropylene.

[0049] Comparative Example 1 Comparative Example 1 is the same as Example 1, except that only isotactic polypropylene was used to prepare the support membrane.

[0050] Test method: 1. Adhesion force test of composite current collector was performed in accordance with GB / T 2791-1995 "Test method for peel strength of adhesives T-type flexible materials".

[0051] 2. The tensile strength of the composite current collector was tested in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets".

[0052] Test results: See Table 1.

[0053] Table 1

[0054] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of the indicated feature.

[0055] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0056] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0057] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A polymer film, characterized in that, include: A first polymer and a modified polymer, wherein the first polymer comprises polypropylene; The modified polymer includes at least one of polyvinyl butyral, polyethylene terephthalate, polyimide, and polyamide.

2. The polymer film according to claim 1, characterized in that, The mass ratio of the first polymer to the modified polymer is (6~9): (1~4).

3. A method for preparing the polymer film according to claim 1 or 2, characterized in that, include: 1 to 4 parts by mass of the modified polymer, 6 to 9 parts by mass of the first polymer, and 0.5 to 1 part by mass of the compatibilizer are melt-blended to obtain the first blend. The first blend is subjected to melting and casting to obtain a second mixture; The second mixture is subjected to a film-forming process to obtain the polymer film.

4. The method according to claim 3, characterized in that, At least one of the following conditions must be met: The compatibilizer includes at least one of maleic anhydride-grafted polypropylene, styrene-ethylene-styrene block copolymer maleic anhydride graft, and styrene-butene-styrene block copolymer maleic anhydride graft. In the modified polymer, the degree of acetalization of polyvinyl butyral is 65wt%~85wt%; The intrinsic viscosity of the polyethylene terephthalate is 0.50 dL / g to 1.00 dL / g; The polyimide includes one or more of aromatic polyimides, semi-aromatic polyimides, and aliphatic polyimides; The polyamide includes one or more of polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, polyamide 6 / 66, and polyamide 66 / 610; The temperature of the melt blending treatment is 175℃~205℃.

5. The method according to claim 3, characterized in that, At least one of the following conditions must be met: The temperature of the melting and casting process is 175℃~205℃; The cooling temperature for the melting and casting process is 15℃~30℃; The film-forming process is carried out at a temperature of 150℃~170℃.

6. The method according to any one of claims 3 to 5, characterized in that, Also includes: The polymer film is subjected to heat setting treatment at a temperature of 155°C to 175°C; and / or, The second mixture is preheated at a temperature of 135°C to 155°C.

7. A composite current collector, characterized in that, include: A support membrane, wherein the support membrane comprises the polymer membrane according to claim 1 or 2; A metal layer is disposed on at least one side of the support layer, the metal layer comprising aluminum or copper.

8. The composite current collector according to claim 7, characterized in that, At least one of the following conditions must be met: The thickness of the metal layer is 1μm~2μm; The thickness of the support membrane is 4μm to 8μm.

9. A method for preparing the composite current collector according to claim 7 or 8, characterized in that, include: At least one side of the polymer film according to claim 1 or 2 is subjected to physical vapor deposition to obtain a first composite film; The first composite film is subjected to electroplating to obtain the composite current collector.

10. The method according to claim 9, characterized in that, At least one of the following conditions must be met: The deposition thickness of the physical vapor deposition process is 50 nm to 100 nm. The deposition thickness of the electroplating treatment is 1μm~2μm.

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