Multilayer composite film and current collector prepared from same

Abstract

The present application relates to the technical field of current collectors, and specifically relates to a multilayer composite film and a current collector prepared from same. The present application provides a preparation method for the multilayer composite film. The multilayer composite film comprises a layer X, a layer Y and a layer Z from top to bottom; the layer X and the layer Z are made of polyimide, and the polyimide is a polycondensation reactant of carboxylic acid anhydride and diamine; and the material of the layer Y is any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenyl ether, polyester, polystyrene and derivatives thereof. The polyimide prepared in the present application solves the problems of low solubility and poor processability of conventional fully aromatic polyimides, and a composite current collector is prepared by using heat resistance and improved surface polarity of polyimides, thereby improving the bonding force between a composite current collector film and a metal layer, and improving the tensile strength of a finished product.

Description

A multilayer composite film and current collector prepared therefrom Technical Field

[0001] The present application relates to the technical field of current collectors, and specifically to a multilayer composite film and a current collector prepared therefrom. Background Art

[0002] In recent years, the gradual implementation of my country's "Carbon Peaking and Carbon Neutrality" policy has promoted the development of new energy vehicles. Lithium batteries, due to their high energy density, long cycle life, stable operating voltage, and environmental friendliness, are currently one of the most widely commercialized energy products.

[0003] The composite current collector is the carrier of the active material of the lithium battery. The preparation process of the composite current collector is usually: using the physical vapor deposition method to deposit a layer of metal materials such as aluminum or copper on a polymer film (such as polypropylene, polyethylene, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polyester, polyimide, etc. base film), and then continue to deposit a certain thickness of metal layer through chemical electroplating. The surface metallized film with a certain conductivity is prepared, which is the composite current collector. Compared with traditional current collectors, the composite current collector has the advantages of low cost, light weight and good internal insulation.

[0004] In view of the production cost and product performance of composite current collectors, polymer films such as polyester films or polypropylene films are currently mostly used as the base film of composite current collectors. However, the polyester film used in traditional packaging is directly used to prepare composite current collectors, which has the problem of poor resistance to electrolyte corrosion, resulting in significant performance degradation during the battery charge and discharge cycle; and the polypropylene film has a low surface tension, resulting in poor adhesion between it and the metal layer, and the two are easy to separate, resulting in poor product performance. In addition, the thermal dimensional stability of polyolefin films is poor, and thermal shrinkage will occur when the battery temperature rises, which will lead to a large-area short circuit in the battery and trigger thermal runaway. The existing technology usually uses the corona method to improve the problem of using polypropylene film as the base film of composite current collector, but the improvement ability of this method is limited.

[0005] Therefore, in order to solve the above problems, improve the bonding force between the composite current collector film and the metal layer, and improve the tensile strength, the present application provides a multilayer composite film and a current collector prepared therefrom. Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The purpose of this application is to provide a multilayer composite film and a current collector prepared therefrom to solve the problems raised in the above background technology.

[0008] In order to solve the above technical problems, the present application provides the following technical solutions: a multi-layer composite film and a current collector prepared therefrom. The multi-layer composite film is composed of an X layer, a Y layer, and a Z layer from top to bottom; the material of the X and Z layers is polyimide, and the glass transition temperature of the polyimide is between 100-220°C, preferably 120-190°C. If the glass transition temperature is too high, the solubility of the polyimide is low, and the processability is poor. The subsequent heat-sealing temperature with the Y layer is too high, which may cause the Y layer material to melt and decompose; if the glass transition temperature is too low, the tensile strength of the polyimide is poor, which affects the mechanical properties of the composite film. The molecular weight distribution of the polyimide molecule is between 5000-4w, preferably 1w-3w. If the molecular weight is too high, the solubility of the polyimide is poor, the melting temperature is high, and the melt viscosity is large, resulting in harsh molding process conditions. If the molecular weight distribution is too low, the mechanical properties of the film are reduced, affecting the overall performance.

[0009] The Y layer material is any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polyester, polystyrene and derivatives thereof.

[0010] The polyimide is a condensation reaction product of a carboxylic anhydride and a diamine. More optimally, the diamine is any one or more of 1,6-hexanediamine, 4,4'-methylenedianiline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenylmethane.

[0011] The carboxylic anhydride is any one or more of 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride;

[0012] More optimally, the molar ratio of the carboxylic anhydride to the diamine is 1:1.

[0013] Preferably, the multi-layer composite film satisfies at least one of the following conditions: the thicknesses of the X layer and the Z layer may be the same or different;

[0014] The thickness of the X layer d1 and the thickness of the Y layer d2 satisfy d1 / d2<55%, preferably d1 / d2<45%; the thickness of the Z layer d3 and the thickness of the Y layer d2 satisfy d3 / d2<55%, preferably d3 / d2<45%; the thickness of the multilayer composite film is 2-20μm.

[0015] A method for preparing a multilayer composite film comprises the following steps: stacking layer X, layer Y, and layer Z from top to bottom, heating and pressing, to obtain a multilayer composite film. Preferably, the method for preparing layer X or layer Z comprises the following steps:

[0016] S1: Preparation of polyamic acid solution:

[0017] Take diamine and solvent, stir evenly, add carboxylic anhydride in batches, and stir for 10-14 hours in an ice bath under nitrogen protection to obtain a polyamic acid solution;

[0018] S2: Preparation of polyamic acid gel film:

[0019] The polyamic acid solution is vacuumed, defoamed, cast, and pre-dried to obtain a polyamic acid gel film; S3: stretching-imidization:

[0020] The polyamic acid gel film is longitudinally stretched at 155-160° C., and then transversely stretched. After the stretching is completed, the temperature is increased to perform imidization treatment to obtain an X layer or a Z layer;

[0021] More optimally, the preparation method of the Y layer includes:

[0022] The polymer material is stirred evenly, melted at 200-260° C., filtered, and extruded to obtain a molten material; the molten material is cast, cooled at 10-60° C., and formed; longitudinal stretching and transverse stretching are performed, wherein the preheating temperature for longitudinal stretching is 110-135° C., the stretching temperature is 140-150° C., and the stretching ratio is 6-8 times; the preheating temperature for transverse stretching is 120-140° C., the stretching temperature is 150-160° C., the heat setting temperature is 165-170° C., and the stretching ratio is 5-7 times; then, heat treatment is performed at 125-135° C. to obtain a film; the film is cooled and rolled up with a rolling tension of 20-30 N / m to obtain a Y layer.

[0023] The polymer material is any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polyester, and polystyrene;

[0024] More optimally, the heating and pressing temperature is 200-260° C., the pressure is 0.2-0.8 MPa, and the time is 20-60 s.

[0025] More optimally, in S2, the film is pre-dried, heated to 60-80°C, kept warm for 1-3 hours, then heated to 120-140°C, kept warm for 1-3 hours, and the pre-drying heating rate is 2-5°C / min; in S3, the imidization temperature is 300-500°C, and the aspect ratio of stretching is 1.1-1.3.

[0026] A composite current collector, comprising, from top to bottom, an anti-oxidation layer, a metal layer, a multi-layer composite film layer, a metal layer, and an anti-oxidation layer;

[0027] The thickness of the metal layer is 1-3 μm;

[0028] The material of the metal layer is any one of copper alloy and copper;

[0029] The metal layer is prepared by one or more methods such as physical vapor deposition (including but not limited to electron beam heating vacuum evaporation, laser heating vacuum evaporation, magnetron sputtering, etc.), chemical vapor deposition, electroplating, chemical plating, etc.;

[0030] The material of the anti-oxidation layer is prepared by reacting, combining or cross-linking any one or more substances among chromic anhydride passivation agent, benzotriazoles, and silane coupling agents or their hydrolyzates with copper.

[0031] More optimally, the preparation method of the composite current collector is: clean and dry the surface of the multilayer composite film; use one or more of physical vapor deposition, chemical vapor deposition, electroplating, and chemical plating to form a metal layer on the surface of the multilayer composite film to obtain a current collector; immerse the current collector in a mixed solution of any one or more solvents of chromic anhydride passivator, benzotriazole or silane coupling agent, with a solution concentration of 0.5-3g / L and a residence time of 10-30s. After washing with water, dry in an oven at 45-75°C to finally obtain a composite current collector.

[0032] Compared with the prior art, the beneficial effects achieved by this application are:

[0033] (1) The present application proposes a method for preparing a multilayer composite film, wherein the multilayer composite film comprises an X layer, a Y layer, and a Z layer from top to bottom; the materials of the X layer and the Z layer are polyimide, which is a condensation reaction product of a carboxylic anhydride and a diamine; the material of the Y layer is any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polyester, polystyrene, and their derivatives. The polyimide prepared in the present application solves the low solubility and poor processability of traditional fully aromatic polyimides, and utilizes the heat resistance and surface polarity of polyimide to prepare a composite current collector, thereby solving the problem of poor adhesion between the composite current collector base film and the metal layer, improving the adhesion between the composite current collector film and the metal layer, and improving the tensile strength of the finished product.

[0034] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings:

[0036] FIG1 is a schematic structural diagram of a multilayer composite membrane of the present application;

[0037] FIG2 is a schematic structural diagram of the composite current collector of the present application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] There is no special restriction on the purchase manufacturers of all raw materials involved in this application, and examples include: polypropylene can be purchased from Aladdin with product number P110851.

[0040] Example 1: A method for preparing a multilayer composite film and a composite current collector thereof, comprising the following steps: Step 1: Preparation of a Y-layer polypropylene film:

[0041] Polypropylene was melted at 260°C, filtered through a 10-micron filter, and extruded to obtain a molten material; the molten material was cast onto a casting roll and cooled at 30°C to form a film; the film was preheated at 130°C and then longitudinally stretched at 150°C; the film was preheated at 130°C and then transversely stretched at 150°C, and then heat-set at 170°C with a longitudinal and transverse stretch ratio of 1.2:1. The film was then heat-treated at 130°C to obtain a film; the film was cooled and rolled up with a rolling tension of 25 N / m to obtain a Y-layer polypropylene film;

[0042] Step 2: Preparation of X layers of polyimide film: S1: Preparation of polyamic acid solution:

[0043] 1,6-hexanediamine was added to an organic solvent, N-methylpyrrolidone, and stirred uniformly to form a solution having a mass fraction of 20% hexanediamine. 3,3',4,4'-benzophenonetetracarboxylic dianhydride was then added in batches, with the molar ratio of 1,6-hexanediamine to 3,3',4,4'-benzophenonetetracarboxylic dianhydride being 1:1. The mixture was stirred in an ice bath under nitrogen protection for 12 hours to carry out a polycondensation reaction to obtain a polyamic acid solution.

[0044] S2: The polyamic acid solution was vacuum defoamed for 3.5 hours; the defoamed polyamic acid solution was cast through the slit of a casting nozzle onto a stainless steel circulating belt running below it, and evenly coated with a scraper to form a film; then pre-dried, the room temperature was raised to 80°C, the temperature was kept for 2 hours, and then the temperature was raised to 120°C, the temperature was kept for 2 hours, and the heating rate was 2°C / min to obtain a polyamic acid gel film;

[0045] After being peeled off from the steel belt of the casting machine, the polyamic acid gel film is directly fed into a stretching machine, heated to 155°C by preheating rollers for longitudinal stretching, followed by transverse stretching to achieve an aspect ratio of 1.2:1. After stretching, the film enters an imidization furnace and is imidized at 300°C. The biaxially stretched and imidized film is cooled, trimmed, and rolled to obtain an X layer.

[0046] The preparation of the Z layer polyimide film is the same as that of the X layer. Step 3: Preparation of multilayer composite film:

[0047] Layers X, Y, and Z are stacked from top to bottom and heat-pressed to obtain a multilayer composite film comprising, from top to bottom, a polyimide film, a polypropylene film, and a polyimide film; wherein the thickness of the polypropylene film in the prepared composite film is 6 μm, and the thickness of the polyimide film is 3 μm; the heat-pressing temperature is 240° C., the heat-pressing pressure is 0.4 MPa, and the heat-sealing time is 30 seconds;

[0048] Step 4: Preparation of composite current collector: S1: Preparation of metal layer:

[0049] The surface of the multilayer composite film prepared above was cleaned and dried, and then placed in a vacuum evaporation chamber. High-purity copper wire (purity greater than 99.99%) was melted and evaporated at a high temperature of 1600°C in the metal evaporation chamber. The evaporated metal atoms passed through the cooling system in the vacuum coating chamber and were deposited on both surfaces of the composite film, forming a metal conductive layer with a thickness of 1 micron.

[0050] S2: Preparation of anti-oxidation layer:

[0051] The prepared composite current collector was passed through an aqueous solution of BTA with a concentration of 2 g / L, left for 20 seconds and washed with water, and then dried in an oven at 75° C. to obtain a composite current collector.

[0052] Example 2: The preparation method of the polyamic acid solution in step 2 S1 is different, and the rest is the same as Example 1: Preparation of polyamic acid solution:

[0053] 1,6-hexanediamine is added to an organic solvent, N-methylpyrrolidone, to form a solution with a mass fraction of 1,6-hexanediamine of 20%, and the mixture is stirred evenly. Then, 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride is added in batches, and the molar ratio of 1,6-hexanediamine to 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride is 1:1. The mixture is stirred for 12 hours in an ice bath under nitrogen protection to carry out a polycondensation reaction to obtain a polyamic acid solution.

[0054] Example 3: The preparation method of the polyamic acid solution in step 2 S1 is different, and the rest is the same as Example 1: Preparation of polyamic acid solution:

[0055] 1,6-hexanediamine and 4,4'-methylenedianiline were added to an organic solvent, N-methylpyrrolidone, and stirred evenly. Then, 3,3',4,4'-benzophenonetetracarboxylic dianhydride was added in batches. The molar ratio of 1,6-hexanediamine, 4,4'-methylenedianiline, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride was 0.5:0.5:1. The mixture was stirred for 12 hours in an ice bath under nitrogen protection to carry out a polycondensation reaction to obtain a polyamic acid solution.

[0056] Example 4: The preparation method of the polyamic acid solution in step 2 S1 is different, and the rest is the same as Example 3: Preparation of polyamic acid solution:

[0057] 1,6-hexanediamine and 4,4'-methylenedianiline are added to an organic solvent, N-methylpyrrolidone, and stirred evenly. Then, 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride is added in batches. The molar ratio of 1,6-hexanediamine, 4,4'-methylenedianiline, and 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride is 0.5:0.5:1. The mixture is stirred for 12 hours in an ice bath under nitrogen protection to carry out a polycondensation reaction to obtain a polyamic acid solution.

[0058] Example 5: The pre-drying temperature during the polyimide film formation in step 2 S1 is 130°C, and the rest is the same as in Example 3:

[0059] S2: The polyamic acid solution is vacuum-defoamed for 3.5 hours; the defoamed polyamic acid solution is cast through the gap of the casting nozzle onto a stainless steel circulating belt running below it, and is evenly coated with a scraper to form a film; then pre-drying is performed, the room temperature is raised to 80°C, the temperature is kept for 2 hours, and then the temperature is raised to 130°C and the temperature is kept for 2 hours at a heating rate of 2°C / min to obtain a polyamic acid gel film.

[0060] Example 6: The pre-drying temperature during the polyimide film formation in step 2 S1 is 140°C, and the rest is the same as in Example 3:

[0061] S2: The polyamic acid solution is vacuum-defoamed for 3.5 hours; the defoamed polyamic acid solution is cast through the gap of the casting nozzle onto a stainless steel circulating belt running below it, and is evenly coated with a scraper to form a film; then pre-drying is performed, the room temperature is raised to 80°C, the temperature is kept for 2 hours, and then the temperature is raised to 140°C and the temperature is kept for 2 hours at a heating rate of 2°C / min to obtain a polyamic acid gel film.

[0062] Example 7: The heating rate during the polyimide film formation in step 2 S1 is 4°C / min, and the rest is the same as in Example 5:

[0063] S2: The polyamic acid solution is vacuum-defoamed for 3.5 hours; the defoamed polyamic acid solution is cast through the gap of the casting nozzle onto a stainless steel circulating belt running below it, and is evenly coated with a scraper to form a film; then pre-drying is performed, the room temperature is raised to 80°C, the temperature is kept for 2 hours, and then the temperature is raised to 140°C and the temperature is kept for 2 hours at a heating rate of 4°C / min to obtain a polyamic acid gel film.

[0064] Example 8: The temperature during imidization of the polyimide in step 2 S1 is 450° C., and the rest is the same as in Example 5:

[0065] After being peeled off from the steel belt of the casting machine, the polyamic acid gel film is directly fed into a stretching machine, heated to 155°C by preheating rollers for longitudinal stretching, followed by transverse stretching to achieve an aspect ratio of 1.2:1. After stretching, the film enters an imidization furnace and is imidized at 450°C. The biaxially stretched and imidized film is cooled, trimmed, and wound to obtain the X layer.

[0066] Example 9: The temperature during imidization of the polyimide in step 2 S1 is 500° C., and the rest is the same as in Example 5:

[0067] The polyamic acid gel film is peeled off from the steel belt of the casting machine and directly enters the stretching machine. It is heated to 155°C by preheating rollers for longitudinal stretching, and then transverse stretching to achieve an aspect ratio of 1.2:1. After stretching, it enters the imidization furnace and is then imidized at 500°C. The biaxially stretched and imidized film is cooled, trimmed, and wound to obtain the X layer.

[0068] Example 10: The temperature of heating and pressing in step 3 is 220°C, and the rest is the same as in Example 8: Step 3: Preparation of multilayer composite film:

[0069] Layer X, layer Y, and layer Z are stacked from top to bottom and heat-pressed to obtain a multilayer composite film consisting of a polyimide film, a polypropylene film, and a polyimide film from top to bottom; the thickness of the single polypropylene film in the prepared composite film is 6 μm, and the thickness of the polyimide film is 3 μm; the heating and pressing temperature is 220° C., the heating and pressing pressure is 0.4 MPa, and the heat sealing time is 30 s.

[0070] Example 11: The temperature of heating and pressing in step 3 is 260°C, and the rest is the same as Example 8: Step 3: Preparation of a multilayer composite film: Layer X, layer Y, and layer Z are stacked from top to bottom and heated and pressed to obtain a multilayer composite film comprising a polyimide film, a polypropylene film, and a polyimide film from top to bottom; wherein the thickness of each layer of the polypropylene film in the prepared composite film is 6 μm, and the thickness of the polyimide film is 3 μm; the temperature of the heating and pressing is 260°C, the pressure of the heating and pressing is 0.4 MPa, and the heat sealing time is 30 s.

[0071] Example 12: The thickness of the polyimide film in step 3 is 2 μm, and the rest is the same as Example 8. Example 13: The thickness of the polyimide film in step 3 is 4 μm, and the rest is the same as Example 8. Example 14: The thickness of the polyimide film in step 3 is 5 μm, and the rest is the same as Example 8.

[0072] Comparative Example 1: After the polypropylene film is prepared, it is directly used to prepare a composite current collector. The preparation method of the composite current collector includes the following steps:

[0073] Step 1: Preparation of polypropylene film:

[0074] Polypropylene was melted at 260°C, filtered, and extruded to obtain a molten material; the molten material was cast onto a casting roll and cooled to form a film; the film was longitudinally and transversely stretched at 150°C, and heat-treated at 130°C to obtain a film; the film was cooled and wound at a winding tension of 25 N / m to obtain a polypropylene film;

[0075] Step 2: Preparation of composite current collector:

[0076] S1: Preparation of metal layer:

[0077] The surface of the prepared polypropylene film is cleaned and dried, and then placed in a vacuum evaporation chamber. High-purity copper wire (purity greater than 99.99%) is melted and evaporated at a high temperature of 1600°C in the metal evaporation chamber. The evaporated metal atoms pass through the cooling system in the vacuum coating chamber and are deposited on both surfaces of the composite film, forming a metal conductive layer with a thickness of 1 micron.

[0078] S2: Preparation of anti-oxidation layer:

[0079] The prepared composite current collector was passed through a 2 g / L BTA solution, left for 20 seconds, washed with water, and then dried in an oven at 75° C. to obtain a composite current collector.

[0080] Comparative Example 2: The pre-drying temperature during polyimide film formation in step 2 S1 is 160°C, and the rest is the same as in Example 3:

[0081] S2: The polyamic acid solution is vacuum-defoamed for 3.5 hours; the defoamed polyamic acid solution is cast through the gap of the casting nozzle onto a stainless steel circulating belt running below it, and is evenly coated with a scraper to form a film; then pre-drying is performed, the room temperature is raised to 80°C, the temperature is kept for 2 hours, and then the temperature is raised to 160°C and the temperature is kept for 2 hours at a heating rate of 2°C / min to obtain a polyamic acid gel film.

[0082] Comparative Example 3: The imidization temperature during polyimide film formation in step 2 S2 is 600° C., and the rest is the same as in Example 3:

[0083] S2: The polyamic acid gel film is peeled off from the steel belt of the casting machine and directly enters the stretching machine. The temperature is raised to 155°C by a preheating roller for longitudinal stretching, and then transverse stretching is performed to make the aspect ratio of the stretching 1.2:1. After the stretching is completed, it enters the imidization furnace and is then imidized at a temperature of 600°C. The biaxially stretched and imidized film is cooled, trimmed, and wound to obtain the X layer.

[0084] experiment

[0085] The multilayer composite films and composite current collectors prepared in Examples 1-14 and Comparative Examples 1-3 were subjected to performance testing. The surface tension of the multilayer composite films was tested in accordance with GB / T 14216-2008. The adhesion between the multilayer composite film and the metal layer in the composite current collector was tested: a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the composite current collector was adhered above the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel 0903, 50 μm thick) was covered above the composite current collector. The films were then hot-pressed at 1.3 × 10⁵ N / m² and 120°C for 10 seconds, cooled to room temperature, and cut into 150 mm × 15 mm strips. Finally, the ethylene acrylic acid copolymer film of the sample strip was fixed to the upper fixture of a tensile testing machine, and the remaining portion was fixed to the lower fixture. After being fixed, the two strips were peeled at an angle of 180° and a speed of 100 mm / min to test the peel strength. The tensile strength test was carried out according to the national standard GB / T 1040.3-2006. The data are all in the MD direction. The obtained data are as follows:

[0086] Conclusion: Comparing the data of Examples 1-4 in the above table, it can be seen that the monomers of carboxylic anhydride and dianhydride have a certain influence on the properties of polyimide and composite film.

[0087] By comparing Examples 5 and 7 in the above table, it can be seen that different heating rates have a certain impact on the film properties. When the heating rate is low, the solvent volatilization rate is slow, the monomers have enough time to react with each other to form polymers with large molecular weight, and the impact of the solvent volatilization on the film surface can be reduced; when the heating rate is too fast, a large number of unreacted small molecules remain in the film and are deposited on the film surface in the form of solid particles, resulting in an increase in the surface roughness of the film, but at the same time, it will cause the rigid structure in the molecular structure of the film to become less and the molecular chain to become shorter, thereby causing the tensile strength of the film to decrease.

[0088] From Examples 5, 8-9, and Comparative Example 3, it can be seen that the imidization temperature should be selected as 450°C. When the temperature is 400°C, the imidization reaction of the film may not be complete. When the imidization temperature reaches 500°C, the film performance is similar to that at 450°C. When the temperature is greater than 500°C, the tensile properties of the film will be reduced, and too high a temperature will cause film damage.

[0089] It can be seen from Examples 8, 10-11 that when the heat-sealing temperature is relatively low, the bonding between the layers of the composite film is not strong, and when the heat-sealing temperature is too high, the middle layer will be damaged, which will affect the performance of the composite film.

[0090] It can be seen from Examples 8, 12-14 that reducing the thickness of the PI layer will increase the adhesion between the metal layer and the composite film, but wrinkles will appear on the surface. Increasing the thickness of the PI layer will increase the tensile strength of the composite film, but its compatibility with the intermediate layer will deteriorate, and the surface tension and bonding strength of the material will also deteriorate.

[0091] It can be seen from Comparative Example 1 that, compared with the single-layer PP film, the use of the composite film improves the overall tensile strength, surface tension and bonding strength with the metal layer.

[0092] Finally, it should be noted that the above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A multilayer composite film, comprising, from top to bottom, an X layer, a Y layer, and a Z layer; the X and Z layers are made of polyimide, having a molecular weight of 5000-4w and a glass transition temperature of 100-220°C; the Y layer is made of any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polyester, and polystyrene.

2. A multilayer composite film according to claim 1, wherein: The polyimide is a condensation product of carboxylic anhydride and diamine; The diamine is any one or more of 1,6-hexanediamine, 4,4'-methylenedianiline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenyl ether, and 4,4'-diaminodiphenylmethane; The carboxylic anhydride is any one or more of 5-[2,5-(dioxytetrahydrofuranyl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, pyromellitic dianhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

3. A multi-layer composite film according to claim 2, wherein: The molar ratio of the carboxylic anhydride to the diamine is 1:

1.

4. A multi-layer composite film according to claim 3, wherein: The multi-layer composite film satisfies at least one of the following conditions: The thickness of the X layer and the Z layer may be the same or different; The thickness d1 of the X layer and the thickness d2 of the Y layer satisfy d1 / d2<55%; the thickness d3 of the Z layer and the thickness d2 of the Y layer satisfy d3 / d2<55%; the thickness of the multilayer composite film is 2-20 μm.

5. The method for preparing a multilayer composite film according to any one of claims 1 to 4, comprising the following steps: The X layer, the Y layer, and the Z layer are stacked from top to bottom, heated and pressed to obtain a multilayer composite film.

6. [Corrected 23.12.2024 in accordance with Rule 26] A method for preparing a multilayer composite film according to claim 5, wherein: The preparation method of the X layer or the Z layer comprises the following steps: S1: Preparation of polyamic acid solution: Take diamine and solvent, stir evenly, add carboxylic anhydride in batches, and stir for 10-14 hours in an ice bath under nitrogen protection to obtain a polyamic acid solution; S2: Preparation of polyamic acid gel film: The polyamic acid solution is subjected to vacuum defoaming, casting, and pre-drying to obtain a polyamic acid gel film; S3: stretching-imidization: The polyamic acid gel film is longitudinally stretched at 155-160° C. and then transversely stretched. After the stretching is completed, the film is heated and imidized to obtain an X layer or a Z layer.

7. The method for preparing a multi-layer composite film according to claim 5, wherein: The preparation method of the Y layer comprises: A polymer material is mixed and uniformly melted at 200-260° C., filtered, and extruded to obtain a molten material; the molten material is cast, cooled at 10-60° C., and formed; longitudinal stretching and transverse stretching are performed, with the longitudinal stretching temperature being 140-150° C., the transverse stretching temperature being 150-160° C., and the heat setting temperature being 165-170° C.; and heat treatment is then performed at 125-135° C. to obtain a film; the film is cooled and rolled up, with the rolling tension being 20-30 N / m, to obtain a Y layer. The polymer material is any one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polyester, and polystyrene.

8. The method for preparing a multi-layer composite film according to claim 5, wherein: The heating and pressing process is performed at a temperature of 200-260° C., a pressure of 0.2-0.8 MPa, and a time of 20-60 seconds.

9. The method for preparing a multi-layer composite film according to claim 6, wherein: In S2, the film is pre-dried by heating to 60-80°C, keeping the temperature for 1-3 hours, then heating to 120-140°C, keeping the temperature for 1-3 hours, and the pre-drying heating rate is 2-5°C / min; in S3, the imidization temperature is 300-500°C, and the aspect ratio of the stretching is 1.1-1.

3.

10. A composite current collector comprising, from top to bottom, an anti-oxidation layer, a metal layer, a multi-layer composite film layer, a metal layer, and an anti-oxidation layer; the multi-layer composite film layer is the multi-layer composite film according to any one of claims 1 to 4 or a multi-layer composite film prepared by the preparation method according to any one of claims 5 to 9, and satisfies at least one of the following conditions: The thickness of the metal layer is 1-3 μm; The material of the metal layer is any one of copper alloy and copper; The metal layer is prepared by one or more methods including physical vapor deposition, chemical vapor deposition, electroplating, and chemical plating; The material of the anti-oxidation layer is prepared by reacting, combining or cross-linking any one or more substances among chromic anhydride passivation agent, benzotriazoles, and silane coupling agents or their hydrolyzates with copper.

11. A composite current collector according to claim 10, wherein: The preparation method of the composite current collector comprises: cleaning and drying the surface of the multilayer composite film; forming a metal layer on the surface of the multilayer composite film by one or more of physical vapor deposition, chemical vapor deposition, electroplating, and chemical plating to obtain the current collector; The current collector is immersed in a mixed solution of any one or more solvents of a chromic anhydride passivator, a benzotriazole or a silane coupling agent, with a solution concentration of 0.5-3 g / L and a residence time of 10-30 s. After washing with water, it is dried in an oven at 45-75° C. to finally obtain a composite current collector.

Images