ECI-based composite current collectors, their preparation methods and applications

Abstract

This application relates to an ECI-based composite current collector, its preparation method, and its application. The preparation method of the composite current collector includes: mixing a polymer, a first flame retardant, and a compatibilizer, followed by granulation to prepare composite granules; sequentially melt-extruding and casting the composite granules into a film, and sequentially subjecting the cast film to a first stretching, a first shaping, a second stretching, and a second shaping to prepare a polymer base film; the direction of the first stretching is perpendicular to the direction of the second stretching, the temperature of the second stretching is higher than the temperature of the first stretching, and the temperature of the second shaping is higher than the temperature of the first shaping; a copper layer is prepared on at least one side of the polymer base film, and a flame retardant layer is prepared on at least one side of the obtained current collector intermediate to obtain the composite current collector. This application constructs an environmentally controllable ECI suppression safety management system, which improves the flame retardant safety performance of the composite current collector while retaining excellent mechanical strength and flexibility, effectively improving the thermal safety performance of lithium batteries.

Description

Technical Field

[0001] This application relates to the field of current collector technology, and in particular to ECI-based composite current collectors, their preparation methods, and applications. Background Technology

[0002] Lithium-ion batteries are mainly composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Copper foil is the core current collector for the negative electrode, and its conductivity and structural stability directly affect the energy density, cycle life, and safety of the lithium-ion battery. Currently, rolled copper foil or electrolytic copper foil is commonly used as the negative electrode current collector. However, these pure copper current collectors have several inherent drawbacks: First, pure copper has a high density, which increases the overall weight of the battery and is detrimental to improving energy density. Second, the market price of copper raw materials is high, making it difficult to reduce battery production costs. Third, pure copper lacks flame retardant and thermal runaway protection capabilities; in the event of thermal runaway, it cannot quickly cut off the conductive circuit, easily causing safety hazards such as cell fires and explosions.

[0003] To address the aforementioned problems with pure copper foil, sandwich-structured composite current collectors formed by combining a polymer base film with a metallic copper layer have become the mainstream alternative research and development direction in the industry. However, existing composite current collectors still have significant shortcomings. Under battery thermal runaway conditions, the internal polymer base film is highly susceptible to continuous combustion, making it difficult to effectively prevent the spread of fire. The industry often achieves flame-retardant modification by doping flame-retardant components into the base film; however, traditional blending and doping methods significantly reduce the core mechanical properties of the composite current collector, such as mechanical strength and flexibility, making it difficult to simultaneously achieve flame-retardant safety performance and overall structural stability.

[0004] In summary, there is an urgent need to optimize and improve the existing technical solutions. Summary of the Invention

[0005] Based on this, this application provides a method for preparing and applying an ECI-based composite current collector that can possess both flame-retardant and mechanical properties.

[0006] The technical solution to the above-mentioned technical problems in this application is as follows.

[0007] The first aspect of this application provides a method for preparing an ECI-based composite current collector, comprising the following steps:

[0008] A mixture is prepared by mixing the polymer, the first flame retardant, and the compatibilizer;

[0009] The mixture is granulated to prepare composite granules;

[0010] The composite granules are sequentially melt-extruded and cast into a film to prepare a cast film preform.

[0011] The cast preform is subjected to a first stretching, a first shaping, a second stretching, and a second shaping in sequence to prepare a polymer base film; the direction of the first stretching is perpendicular to the direction of the second stretching, the temperature of the second stretching is higher than the temperature of the first stretching, and the temperature of the second shaping is higher than the temperature of the first shaping.

[0012] A copper layer is prepared on at least one side of the polymer base film to obtain a current collector intermediate;

[0013] A flame-retardant layer is prepared on at least one side of the current collector intermediate to obtain the composite current collector.

[0014] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0015] (1) The polymeric material includes at least one of polypropylene and polyethylene terephthalate;

[0016] (2) The first flame retardant includes triphenyl phosphate;

[0017] (3) The compatibilizer includes at least one of polypropylene grafted with maleic anhydride and polyester grafted with glycidyl methacrylate;

[0018] (4) The preparation of the mixture also includes the addition of at least one of an antioxidant and a lubricant.

[0019] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0020] (1) The temperature difference between the second stretching and the first stretching is 5℃~40℃;

[0021] (2) The temperature of the first shaping is greater than the temperature of the first stretching, and the difference between the temperature of the first shaping and the temperature of the first stretching is 10℃~50℃;

[0022] (3) The second shaping temperature is greater than the second stretching temperature, and the difference between the second shaping temperature and the second stretching temperature is 60℃~110℃.

[0023] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0024] (1) The temperature of the first stretching is 90℃~110℃;

[0025] (2) The temperature of the second stretching is 110℃~130℃;

[0026] (3) The first shaping temperature is 120℃~140℃;

[0027] (4) The second shaping temperature is 200℃~230℃;

[0028] (5) The stretching ratio of the first stretch is 3 to 4 times;

[0029] (6) The stretching ratio of the second stretch is 3 to 4 times;

[0030] (7) Before performing the first stretching, the process includes: preheating the cast film, wherein the temperature of the first preheating is lower than the temperature of the first stretching; optionally, the temperature of the first preheating is 80°C to 100°C.

[0031] (8) Before performing the second stretching, the process includes: preheating the first stretched cast film in a second temperature lower than the temperature of the second stretching; optionally, the temperature of the first preheating is 100°C to 120°C.

[0032] (9) The thickness of the polymer base film is 12 μm to 16 μm.

[0033] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0034] (1) The granulation includes: granulation using a co-rotating twin-screw extruder, wherein the temperature of the extruder feeding section is 180℃~200℃, the temperature of the melting section is 240℃~260℃, the temperature of the homogenization section is 250℃~265℃, and the die temperature is 255℃~265℃; the screw speed is controlled at 200rpm~300rpm, and the vacuum degree is ≤-0.09MPa;

[0035] (2) The temperature of the melt extrusion is 250℃~265℃;

[0036] (3) The thickness of the cast film is 150 μm to 250 μm.

[0037] In some embodiments, the method for preparing the composite current collector includes preparing the copper layer as follows:

[0038] A copper seed layer is deposited on at least one side of the polymer base film using magnetron sputtering;

[0039] Electroplating is performed on the side of the copper seed layer away from the polymer base film to form an electroplated copper layer.

[0040] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0041] (1) The thickness of the copper seed layer is 20 nm to 70 nm;

[0042] (2) The electroplating solution used for the electroplating, by mass concentration, comprises the following components: copper sulfate 30 g / L~50 g / L, sulfuric acid 100 g / L~150 g / L, hydrochloric acid 0.01 g / L~0.06 g / L, sodium chloride 0.01 g / L~0.08 g / L, polyethylene glycol 2 g / L~10 g / L, polyethyleneimine 1 g / L~5 g / L, sodium dithiopropane sulfonate 3 g / L~10 g / L, mercaptobenzimidazole 0.01 g / L~0.06 g / L, collagen 0.01 g / L~0.06 g / L, diamond 0.01 g / L~0.05 g / L, polyethylene glycol alkylphenyl ether 10 g / L~20 g / L, and propynyl ethoxy ether 3 g / L~10 g / L;

[0043] (3) The thickness of the electroplated copper layer is 0.8 μm to 1.2 μm;

[0044] (4) Before preparing the copper layer, the method further includes: subjecting the polymer base film to corona treatment.

[0045] In some embodiments, the method for preparing the composite current collector satisfies at least one of the following conditions:

[0046] (1) The preparation of the flame-retardant layer includes:

[0047] An emulsion is prepared by mixing water-based acrylic resin, a second flame retardant, a silane coupling agent, an antifoaming agent, and water.

[0048] The emulsion is applied to at least one side of the current collector intermediate and cured to form the flame retardant layer;

[0049] (2) Before preparing a flame-retardant layer on at least one side of the current collector intermediate, the method further includes: subjecting the current collector intermediate to plasma treatment;

[0050] (3) The thickness of the flame retardant layer is 0.5 μm to 1 μm.

[0051] The second aspect of this application provides an ECI-based composite current collector, which is prepared using the above-described method for preparing an ECI-based composite current collector.

[0052] The third aspect of this application provides the application of the above-mentioned ECI-based composite current collector in the preparation of lithium batteries.

[0053] The method for preparing the ECI-based composite current collector of this application involves first granulating, melt extruding, and casting a mixture containing a polymer, a first flame retardant, and a compatibilizer in sequence. Then, the resulting cast film is subjected to a first stretching, a first shaping, a second stretching, and a second shaping, wherein the direction of the first stretching is perpendicular to the direction of the second stretching. By in-situ doping the flame retardant into the polymer base film and controlling the temperature of the second stretching to be higher than that of the first stretching, and controlling the temperature of the second shaping to be higher than that of the first shaping, the flame retardant properties of the composite current collector can be improved while ensuring that its mechanical strength, flexibility, and other mechanical properties remain largely unaffected. Furthermore, a copper layer is prepared on at least one side of the polymer base film, and a flame retardant layer is prepared on at least one side of the prepared current collector intermediate. This multi-faceted approach ensures that the prepared composite current collector possesses both flame retardant and mechanical properties. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 A schematic diagram of the structure of a composite current collector provided in one embodiment.

[0056] Figure label:

[0057] 10: Polymer base film; 20: Copper layer; 21: Copper seed layer; 22: Electroplated copper layer; 30: Flame retardant layer. Detailed Implementation

[0058] The present application will be further described in detail below with reference to the embodiments and examples. It should be understood that these embodiments and examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive.

[0059] It should also be understood that this application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various alterations or modifications without departing from the spirit of this application, and the resulting equivalent forms also fall within the protection scope of this application. For example, features described or illustrated as part of one embodiment can be combined in a suitable manner in another embodiment to produce new embodiments. Furthermore, numerous specific details are set forth in the following description to provide a fuller understanding of this application; it should be understood that this application can be implemented without one or more of these details.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for descriptive purposes only and is not intended to be limiting of the application.

[0061] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0062] In this application, the terms "multiple", "various", "multiple times", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0063] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0064] In this document, the term "suitable" as used in "suitable combination", "suitable method", "any suitable method", etc., refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0065] In this document, terms such as "preferred," "better," "more suitable," and "ideal" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0066] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0067] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0068] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0069] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0070] In this application, when numerical intervals (i.e., numerical ranges) are mentioned, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include numerical interval types such as percentage intervals, ratio intervals, and proportion intervals.

[0071] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0072] In this application, the terms "room temperature" or "normal temperature" generally refer to 4℃ to 35℃, for example, 20℃ ± 5℃. In some embodiments of this application, "room temperature" or "normal temperature" refers to 10℃ to 30℃. In some embodiments of this application, "room temperature" or "normal temperature" refers to 20℃ to 30℃.

[0073] In this application, if the unit of a data range is only followed by the right endpoint, it indicates that the units of the left and right endpoints are the same. For example, 3~5 h means that the units of the left endpoint "3" and the right endpoint "5" are both h (hours).

[0074] All references to documents mentioned in this application are incorporated herein by reference as if each document were individually incorporated by reference. Unless they conflict with the inventive purpose and / or technical solution of this application, all cited documents are incorporated herein by reference in their entirety and for all purposes. When citing documents in this application, the definitions of relevant technical features, terms, nouns, phrases, etc., are also incorporated herein by reference. When citing documents in this application, examples and preferred embodiments of the cited technical features may also be incorporated herein by reference, but only to the extent that they enable the implementation of this application. It should be understood that when the cited content conflicts with the description in this application, this application shall prevail or modifications shall be made adaptably to the description in this application.

[0075] The mass or weight of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship of mass or weight between the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass or weight mentioned in the embodiments of this application can be units known in the chemical industry, such as μg, mg, g, and kg.

[0076] It is understood that the ECI in this application refers to the Environment Controlled Inhibition (ECI) safety management system. This system is an environmentally responsive safety control technology developed for lithium-ion battery composite current collectors. Through material adaptation, structural and process optimization, the composite current collectors maintain good mechanical strength and flexibility while possessing safety characteristics such as controllable flame retardancy, thermal circuit breaking, and inhibition of thermal runaway propagation.

[0077] One embodiment of this application provides a method for preparing an ECI-based composite current collector, comprising the following steps:

[0078] Step S100: Mix the polymer, the first flame retardant and the compatibilizer to prepare a mixture.

[0079] In some examples, in step S100, the polymer comprises at least one of polypropylene (PP) and polyethylene terephthalate (PET). Optionally, the polymer comprises both polypropylene and polyethylene terephthalate. Further, the mass ratio of polyethylene terephthalate to polypropylene is 7:3 to 9:1. It is understood that the mass ratio of polyethylene terephthalate to polypropylene includes, but is not limited to, 7:3, 8:2, and 9:1. The polymer, as a matrix resin, provides mechanical strength and flexibility, balancing toughness and processability.

[0080] In some examples, in step S100, the polymer is dried. Optionally, polyethylene terephthalate is vacuum dried at 150°C to 160°C for 4 to 6 hours, so that the moisture content is ≤50 ppm. Optionally, polypropylene is hot-air dried at 80°C to 90°C for 2 to 3 hours.

[0081] In some of these examples, in step S100, the first flame retardant includes triphenyl phosphate (TPP). It is understood that the types of triphenyl phosphate include, but are not limited to, Albemarle Phosflex TPP, Daihachi TPP, and those with a particle size ≤5 μm.

[0082] In some examples, in step S100, the mass of the first flame retardant accounts for 8 wt% to 12 wt% of the total mass of the mixture. It is understood that the percentage of the first flame retardant in the total mass of the mixture includes, but is not limited to, 8 wt%, 9 wt%, 10 wt%, 11 wt%, and 12 wt%. In-situ doping of the flame retardant ensures its uniform dispersion within the matrix, providing a gas-phase flame retardant effect that is long-lasting and free from migration or precipitation issues. By controlling the doping content of the flame retardant in the mixture, both mechanical strength and flame retardant effect are balanced, avoiding excessively high doping that would negatively impact mechanical strength, while insufficient doping would result in inadequate flame retardant performance.

[0083] In some examples, in step S100, the compatibilizer includes at least one of polypropylene grafted maleic anhydride (PP-g-MAH) and polyester grafted glycidyl methacrylate (PET-g-GMA). This improves the interfacial compatibility between the polymer and the combustion promoter, thereby enhancing dispersibility.

[0084] In some examples, step S100, in preparing the mixture, further includes adding an antioxidant. Optionally, the antioxidant includes at least one of antioxidant 1010 and antioxidant 168. Adding an antioxidant can reduce the risk of resin degradation during high-temperature processing.

[0085] In some examples, step S100, during the preparation of the mixture, further includes the addition of a lubricant. Optionally, the lubricant includes at least one of EBS and silicone. Adding a lubricant can improve processing fluidity and reduce die buildup.

[0086] In some of these examples, in step S100, the mixture comprises, by mass parts: 85-92 parts of polymer, 8-15 parts of first flame retardant, 1-3 parts of compatibilizer, 0.2-0.5 parts of antioxidant, and 0.3-0.8 parts of lubricant.

[0087] In some examples, in step S100, the polymer, the first flame retardant, the compatibilizer, the antioxidant, and the lubricant are added to a high-speed mixer and mixed at 60°C to 80°C for 5 to 10 minutes. This improves the uniformity of dispersion.

[0088] Step S200: Granulate the mixture to prepare composite granules.

[0089] In some examples, step S200, granulation includes: granulation using a co-rotating twin-screw extruder, wherein the extruder feeding section temperature is 180℃~200℃, the melting section temperature is 240℃~260℃, the homogenization section temperature is 250℃~265℃, and the die temperature is 255℃~265℃; the screw speed is controlled at 200rpm~300rpm, and the vacuum degree is ≤-0.09MPa; optionally, the vacuum degree is -0.095MPa~-0.09MPa. This ensures complete melting and removal of small molecule volatiles. After melt blending, the mixture is water-cooled, drawn into strands, air-dried, and pelletized to obtain a polymer composite granule with in-situ flame retardant doping.

[0090] Step S300: The composite granules are sequentially melt-extruded and cast into a film to prepare a cast film preform.

[0091] In some of these examples, in step S300, the temperature of the melt extrusion is 250°C to 265°C.

[0092] In some of these examples, in step S300, the thickness of the cast preform is 150 μm to 250 μm.

[0093] Understandably, in some examples, in step S300, the composite granules are added to a single-screw extruder, the die width matches the target product (e.g., 600mm~1200mm), and the melt is flowed from the die lip to the quench roll (temperature 20℃~40℃) after passing through a metering pump and a filter (20μm~40μm), and is rapidly cooled to form an amorphous cast preform.

[0094] Step S400: The cast film is subjected to first stretching, first shaping, second stretching and second shaping in sequence to prepare a polymer base film; the direction of the first stretching is perpendicular to the direction of the second stretching, the temperature of the second stretching is greater than the temperature of the first stretching, and the temperature of the second shaping is greater than the temperature of the first shaping.

[0095] It is understandable that in some examples, in step S400, the first stretching is longitudinal stretching and the second stretching is transverse stretching. By controlling the temperature of the second stretching to be higher than the temperature of the first stretching, and by controlling the temperature of the second shaping to be higher than the temperature of the first shaping, it is possible to improve the flame retardant properties of the composite current collector while ensuring that its mechanical strength, flexibility, and other mechanical properties remain largely unaffected.

[0096] In some examples, in step S400, the temperature difference between the second stretching and the first stretching is 5°C to 40°C. It is understood that the temperature difference between the second stretching and the first stretching includes, but is not limited to, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C.

[0097] In some of these examples, in step S400, the temperature of the first shaping is greater than the temperature of the first stretching, and the temperature of the second shaping is greater than the temperature of the second stretching.

[0098] In some examples, in step S400, the temperature difference between the first shaping and the first stretching is 10°C to 50°C. It is understood that the temperature difference between the first shaping and the first stretching includes, but is not limited to, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C.

[0099] In some examples, in step S400, the temperature difference between the second shaping and the second stretching is 60°C to 110°C. It is understood that the temperature difference between the second shaping and the second stretching includes, but is not limited to, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, and 110°C.

[0100] In some examples, in step S400, the temperature of the first stretching is 90℃~110℃. It can be understood that the temperature of the first stretching includes, but is not limited to, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, and 110℃; in some examples, it can be any two of these point values ​​forming a range, the same applies below.

[0101] In some of these examples, in step S400, the stretching ratio of the first stretch is 3 to 4 times.

[0102] In some examples, in step S400, the first shaping temperature is 120℃~140℃. It can be understood that the first shaping temperature includes, but is not limited to, 120℃, 122℃, 124℃, 126℃, 128℃, 130℃, 132℃, 134℃, 136℃, 138℃, and 140℃.

[0103] In some examples, step S400, before the first stretching, includes: preheating the cast film to a temperature lower than the first stretching temperature. Optionally, the first preheating temperature is 80°C to 100°C. It is understood that the first preheating temperature includes, but is not limited to, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C, and 100°C.

[0104] In some examples, in step S400, the temperature of the second stretching is 110°C to 130°C. It is understood that the temperature of the second stretching includes, but is not limited to, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, 122°C, 124°C, 126°C, 128°C, and 130°C.

[0105] In some of these examples, in step S400, the stretching ratio of the second stretch is 3 to 4 times.

[0106] In some examples, in step S400, the second shaping temperature is 200℃~230℃. It is understood that the second shaping temperature includes, but is not limited to, 200℃, 202℃, 204℃, 206℃, 208℃, 210℃, 212℃, 214℃, 216℃, 218℃, 220℃, 222℃, 224℃, 226℃, 228℃, and 230℃. By controlling the second shaping temperature, the polymer crystallizes and shapes, improving dimensional stability.

[0107] In some examples, before performing the second stretching in step S400, the process includes: subjecting the first-stretched cast film to a second preheating, wherein the preheating temperature is lower than the second stretching temperature. Optionally, the second preheating temperature is 100℃~120℃. It is understood that the second preheating temperature includes, but is not limited to, 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, and 120℃.

[0108] In some of these examples, in step S400, the thickness of the polymer base film is 12 μm to 16 μm.

[0109] Step S500: Prepare a copper layer on at least one side of the polymer base film to obtain a current collector intermediate.

[0110] It is understandable that a copper layer can be prepared on one side of the polymer base film, or on both sides of the polymer base film.

[0111] In some of these examples, in step S500, the copper layer comprises a copper seed layer and an electroplated copper layer disposed sequentially.

[0112] In some of these examples, step S500, preparing the copper layer includes:

[0113] Step S510: Deposit a copper seed layer on at least one side of the polymer base film using magnetron sputtering.

[0114] Optionally, in step S510, the vacuum level of magnetron sputtering is ≤5×10⁻⁶. -3 Pa; furthermore, the vacuum degree of magnetron sputtering is 1×10⁻⁶. -3 Pa~5×10 -3 Pa; the target material is a copper target with a purity of ≥99.99%; the process gas is Ar with a flow rate of 50 sccm~100 sccm; the sputtering power is 5 kW~10 kW.

[0115] In some examples, in step S510, the thickness of the copper seed layer is 20 nm to 70 nm to ensure continuous conductivity.

[0116] Step S520: Electroplating is performed on the side of the copper seed layer away from the polymer base film to form an electroplated copper layer.

[0117] In some of these examples, in step S520, the thickness of the electroplated copper layer is 0.8 μm to 1.2 μm.

[0118] In some of these examples, in step S520, the electroplating solution used for electroplating includes copper ions, sulfuric acid, chloride ions, inhibitors, accelerators, twinning promoters, and leveling agents.

[0119] Optionally, the inhibitor includes at least one of polyethylene glycol (PEG) and polyethyleneimine (PEI). Further, the weight-average molecular weight (MW) of the polyethylene glycol is 4000. Further, in the electroplating solution, the mass concentration of polyethylene glycol is 2 g / L to 10 g / L; the mass concentration of polyethyleneimine is 1 g / L to 5 g / L. Optionally, the inhibitor includes both polyethylene glycol and polyethyleneimine. The combination of polyethylene glycol and polyethyleneimine can refine the grain size and improve the density of the coating.

[0120] Optionally, the accelerator includes at least one of sodium polydisulfide dipropane sulfonate (SPS) and mercaptobenzimidazole (MBI). Further, in the electroplating solution, the mass concentration of sodium polydisulfide dipropane sulfonate is 3 g / L to 10 g / L; the mass concentration of mercaptobenzimidazole is 0.01 g / L to 0.06 g / L. Optionally, the accelerator includes sodium polydisulfide dipropane sulfonate and mercaptobenzimidazole. The combination of sodium polydisulfide dipropane sulfonate and mercaptobenzimidazole maintains a dynamic balance, reduces overpotential while inhibiting pinholes in the plating layer, and improves current efficiency.

[0121] Optionally, the twinning promoter includes at least one of collagen and diamond. Further, in the electroplating solution, the mass concentration of collagen is 0.01 g / L to 0.06 g / L; the mass concentration of diamond is 0.01 g / L to 0.05 g / L. Optionally, the twinning promoter includes collagen and diamond. The combination of collagen and diamond, with collagen regulating the grain growth direction and nanodiamond acting as a heterogeneous nucleation site, effectively induces an increase in the proportion of nanotwinned structures.

[0122] Optionally, the leveling agent includes at least one of polyethylene glycol alkylphenyl ether (JGB) and propargyl alcohol ethoxy ether (PME). Further, in the electroplating solution, the mass concentration of polyethylene glycol alkylphenyl ether is 10 g / L to 20 g / L; the mass concentration of propargyl alcohol ethoxy ether is 3 g / L to 10 g / L. Optionally, the leveling agent includes polyethylene glycol alkylphenyl ether and propargyl alcohol ethoxy ether. The combination of polyethylene glycol alkylphenyl ether and propargyl alcohol ethoxy ether synergistically adsorbs in the high-current region, effectively improving the smoothness of the coating and reducing the smoothness (Rz) to below 0.8 μm.

[0123] Optionally, the source of copper ions includes copper sulfate; further, the mass concentration of copper sulfate is 30 g / L to 50 g / L; alternatively, the source of copper ions also includes copper aminosulfonate. The combination of copper aminosulfonate and copper sulfate can refine the grain structure and improve the coating's ductility. Further, the mass concentration of copper aminosulfonate is 5 g / L to 10 g / L. By controlling the mass concentrations of copper sulfate and copper aminosulfonate, a balance is struck between current efficiency and deposition rate, thus improving the electroplating effect.

[0124] Optionally, the sources of chloride ions include hydrochloric acid and sodium chloride. The combination of hydrochloric acid and sodium chloride improves the stability of chloride ion concentration while reducing the cost of chloride supply. Further, in the electroplating solution, the mass concentration of hydrochloric acid is 0.01 g / L to 0.06 g / L; the mass concentration of sodium chloride is 0.01 g / L to 0.08 g / L.

[0125] Optionally, the mass concentration of sulfuric acid is 100 g / L to 150 g / L. By controlling the mass concentration of sulfuric acid, the conductivity of the electroplating solution is improved, while the Cu content is inhibited. 2+ Hydrolysis maintains the stability of the electroplating solution and improves the electroplating effect.

[0126] In some examples, in step S520, the electroplating solution used for electroplating, by mass concentration, comprises the following components: copper sulfate 30 g / L~50 g / L, sulfuric acid 100 g / L~150 g / L, hydrochloric acid 0.01 g / L~0.06 g / L, sodium chloride 0.01 g / L~0.08 g / L, polyethylene glycol 2 g / L~10 g / L, polyethyleneimine 1 g / L~5 g / L, sodium dithiopropane sulfonate 3 g / L~10 g / L, mercaptobenzimidazole 0.01 g / L~0.06 g / L, collagen 0.01 g / L~0.06 g / L, diamond 0.01 g / L~0.05 g / L, polyethylene glycol alkylphenyl ether 10 g / L~20 g / L, and propynyl ethoxy ether 3 g / L~10 g / L. Furthermore, the electroplating solution used for electroplating, based on mass concentration, also includes copper sulfamate at concentrations of 5 g / L to 10 g / L.

[0127] In some of these examples, in step S520, the pH of the electroplating solution is 1 to 4.

[0128] In some examples, during step S520, the stirring speed is 50 rpm to 100 rpm during electroplating; it can be understood that magnetic stirring or ultrasonic assistance is used to prevent the sedimentation of nanoparticles.

[0129] In some of these examples, in step S520, the electroplating temperature is 25°C to 30°C.

[0130] In some of these examples, in step S520, the electroplating current density is 1.5 A / dm². 2 ~2.5A / dm 2 .

[0131] It is understandable that after electroplating, deionized water is used for rinsing and hot air drying (temperature ≤60℃).

[0132] In some examples, step S500, before preparing the copper layer, further includes subjecting the polymer base film to corona treatment. Corona treatment of the polymer base film activates the surface and introduces polar groups, effectively improving the adhesion between the subsequent copper layer or flame-retardant layer and the polymer base film, thus preventing peeling and other problems. In some examples, the surface dyne value of the polymer base film after corona treatment is ≥42 mN / m.

[0133] It is understandable that after corona treatment, the thickness is measured using lasers or X-rays to control thickness uniformity.

[0134] Understandably, in some examples, in step S500, after corona treatment or thickness measurement, winding is performed. Optionally, the winding tension is controlled at 50 N / m to 100 N / m; this avoids wrinkling and deformation of the film roll.

[0135] Step S600: Prepare a flame-retardant layer on at least one side of the current collector intermediate to obtain a composite current collector.

[0136] The above-mentioned method for preparing the composite current collector involves first granulating, melt extruding, and casting a mixture containing a polymer, a first flame retardant, and a compatibilizer sequentially. Then, the resulting cast film is subjected to a first stretching, a first shaping, a second stretching, and a second shaping, with the direction of the first stretching perpendicular to the direction of the second stretching. By in-situ incorporating the flame retardant into the polymer base film and controlling the temperature of the second stretching to be higher than that of the first stretching, and controlling the temperature of the second shaping to be higher than that of the first shaping, the flame retardant properties of the composite current collector can be improved while ensuring that its mechanical strength, flexibility, and other mechanical properties remain largely unaffected. Furthermore, a copper layer is prepared on at least one side of the polymer base film, and a flame retardant layer is prepared on at least one side of the prepared current collector intermediate. This multi-faceted approach ensures that the prepared composite current collector possesses both flame retardant and mechanical properties. Preparing a flame retardant layer on the outer side of the copper layer (the side furthest from the polymer base film) directly covers the surface of the copper layer, providing more direct flame retardant protection and rapidly inhibiting thermal diffusion of the copper layer. Simultaneously, the reduced exposed copper surface area results in better oxidation resistance and corrosion resistance.

[0137] It is understood that a flame-retardant layer can be prepared on one side of the current collector intermediate, or on both sides of the current collector intermediate. In some examples, a copper layer is prepared on one side of the polymer base film, and a flame-retardant layer is prepared on the side of the copper layer away from the polymer base film; the composite current collector prepared in this case includes a polymer base film, a copper layer, and a flame-retardant layer stacked sequentially. In other examples, a copper layer is prepared on one side of the polymer base film, and a flame-retardant layer is prepared on the side of the polymer base film away from the copper layer; the composite current collector prepared in this case includes a flame-retardant layer, a polymer base film, and a copper layer stacked sequentially. In still other examples, a copper layer is prepared on one side of the polymer base film, and a flame-retardant layer is prepared on both the side of the copper layer away from the polymer base film and the side of the polymer base film away from the copper layer; the composite current collector prepared in this case includes a flame-retardant layer, a polymer base film, a copper layer, and a flame-retardant layer stacked sequentially. In other examples, copper layers are prepared on both sides of the polymer base film, and a flame-retardant layer is prepared on one or two copper layers away from the polymer base film; the composite current collector prepared in this case includes copper layers, polymer base film, copper layers and flame-retardant layer stacked in sequence, or the composite current collector includes flame-retardant layer, copper layer, polymer base film, copper layer and flame-retardant layer stacked in sequence.

[0138] In some of these examples, at least one flame-retardant layer is disposed on the side of the copper layer away from the polymer base film.

[0139] Optionally, in step S500, copper layers are prepared on both sides of the polymer base film; in step S600, a flame-retardant layer is prepared on the side of one of the copper layers away from the polymer base film. This allows the prepared composite current collector to possess conductivity, flame retardancy, and mechanical properties.

[0140] In some of these examples, step S600 includes:

[0141] An emulsion is prepared by mixing water-based acrylic resin, a second flame retardant, a silane coupling agent, an antifoaming agent, and water.

[0142] The emulsion is placed on at least one side of the current collector intermediate obtained in step S500 and cured to form a flame-retardant layer.

[0143] In some of these examples, in step S600, the emulsion contains, by mass percentage, 30% to 40% waterborne acrylic resin, 15% to 20% second flame retardant, 0.5% to 1% silane coupling agent, 0.1% to 0.3% defoamer, and the balance water.

[0144] It is understood that waterborne acrylic resins are used as film-forming agents and binders, including but not limited to BASF Joncryl 1982, Dow Primal AC-261, or Wanhua A-1160.

[0145] In some of these examples, in step S600, the second flame retardant comprises triphenyl phosphate. It is understood that in some of these examples, the second flame retardant is the same as the first flame retardant.

[0146] In some examples, in step S600, the silane coupling agent is of a type including, but not limited to, Nanjing Shuguang KH-550 or Dow Corning Z-6020. The silane coupling agent can improve the adhesion between the flame-retardant layer and the polymer base film.

[0147] In some of these examples, in step S600, the defoamer is of a type including, but not limited to, BYK-024.

[0148] In some of these examples, step S600, the preparation of the emulsion includes:

[0149] The silane coupling agent is premixed with a portion of water, and then stirred for the first time to form a silane coupling agent hydrolysate; optionally, the first stirring is performed for 10 min to 15 min.

[0150] The second flame retardant is added to the remaining water, and the mixture is stirred to form a suspension; optionally, the stirring speed is 1000 rpm to 1500 rpm and the stirring time is 15 min to 25 min.

[0151] Add water-based acrylic resin to the suspension, stir a third time, then add silane coupling agent hydrolysate, stir a fourth time, and then add defoamer; optionally, the stirring speed of the third stirring is 500 rpm to 800 rpm and the time is 15 min to 25 min; the stirring time of the fourth stirring is 10 min to 20 min.

[0152] It is understandable that after the raw materials are mixed to obtain an emulsion, the aggregated particles are removed by filtration; the pH value is controlled between 7.0 and 8.5 to ensure the stability of the acrylic resin emulsion.

[0153] In some examples, in step S600, the coating thickness of the emulsion is 1 μm to 2 μm, and the speed is 10 m / min to 20 m / min; a microgravure coating method is used.

[0154] In some of these examples, step S600 includes curing: pre-baking at 80°C to 90°C for 1 to 2 minutes, followed by curing at 120°C to 130°C for 2 to 3 minutes.

[0155] In some of these examples, in step S600, the thickness of the flame-retardant layer is 0.5 μm to 1 μm.

[0156] In some examples, step S600, before preparing the flame-retardant layer on at least one side of the current collector intermediate, further includes: plasma treatment of the current collector intermediate. This can improve the adhesion between the subsequent flame-retardant layer and the current collector intermediate. Optionally, the plasma treatment power is 5kW~10kW, and the treatment time is 30s~60s. The surface roughness Ra of the plasma-treated intermediate is 0.2μm~0.5μm.

[0157] One embodiment of this application provides an ECI-based composite current collector, which is prepared using the above-described method for preparing composite current collectors.

[0158] The ECI-based composite current collector provided in this application has the following advantages:

[0159] (1) Compared with traditional copper foil, the composite current collector provided in this application is lighter, reducing the weight by about 56% to 60%, resulting in a decrease in the overall weight of the lithium battery by about 8% to 10%, which corresponds to an increase in battery energy density of 10% to 11%.

[0160] (2) Compared with traditional copper foil, the cost of the composite current collector provided in this application is significantly reduced, and the material cost is reduced by more than 60%.

[0161] (3) The composite current collector provided in this application can effectively reduce the risk of thermal runaway. On the one hand, the copper layer of the composite current collector is thinner, the burr size is smaller, and because the polymer material layer is an insulating material, it will have a circuit breaking effect, so the possibility of puncturing the separator is low, which can effectively reduce the risk of battery spontaneous combustion.

[0162] (4) The composite current collector provided in this application contains flame retardant material and has self-extinguishing function. By adding TPP flame retardant material to the polymer material layer, the oxygen content can be reduced during the material combustion process, thus playing a self-extinguishing function and reducing the probability of thermal runaway.

[0163] One embodiment of this application provides the application of the above-described ECI-based composite current collector in the preparation of lithium batteries.

[0164] Another embodiment of this application provides a lithium battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is located between the positive electrode and the negative electrode; the negative electrode includes the above-mentioned ECI-based composite current collector.

[0165] The lithium battery provided in this application includes the aforementioned composite current collector, which can effectively improve the safety protection performance, structural stability, and cycle life of the lithium battery.

[0166] The present application will be described in further detail below with reference to specific embodiments, but the embodiments of the present application are not limited thereto.

[0167] Example 1

[0168] (1) Add 88 parts of high molecular weight polymer (polyethylene terephthalate and polypropylene in a mass ratio of 8:2), 10 parts of first flame retardant (TPP), 1 part of compatibilizer, 0.5 parts of antioxidant and 0.5 parts of lubricant to a high-speed mixer and mix at 80°C for 5 min to prepare a mixture;

[0169] (2) Granulation: Composite granules are prepared using a co-rotating twin-screw extruder; wherein, the temperature of the extruder feeding section is 200℃, the temperature of the melting section is 250℃, the temperature of the homogenization section is 250℃, the die temperature is 260℃, the screw speed is controlled at 200rpm, and the vacuum degree is ≤-0.09MPa;

[0170] (3) Melt extrusion and casting film formation: The composite granules are added to a single screw extruder and the extrusion temperature is 250℃. After passing through a metering pump and a filter, the melt is cast from the die lip to the quenching roller (temperature 20℃~40℃) and rapidly cooled to form an amorphous cast film with a thickness of 200 μm.

[0171] (4) Preparation of polymer base film: The cast film is subjected to first preheating, first stretching (longitudinal stretching), first shaping, second preheating, second stretching (transverse stretching) and second shaping to prepare a polymer base film with a thickness of 15 μm; the temperature of the first preheating is 90℃, the temperature of the first stretching is 100℃, the stretching ratio of the first stretching is 3 times, and the temperature of the first shaping is 130℃; the temperature of the second preheating is 110℃, the temperature of the second stretching is 120℃, the stretching ratio of the second stretching is 3 times, and the temperature of the second shaping is 210℃; the temperature difference between the second stretching temperature and the first stretching temperature is 20℃, the temperature difference between the first shaping temperature and the first stretching temperature is 30℃, and the temperature difference between the second shaping temperature and the second stretching temperature is 90℃;

[0172] (5) The polymer base film was subjected to corona treatment. After corona treatment, the surface dyne value of the polymer base film was 42 mN / m.

[0173] (6) Copper seed layers were deposited on both sides of the polymer base film by magnetron sputtering with a sputtering power of 5kW and a thickness of 50nm;

[0174] (7) Preparation of electroplated copper layer: Copper electroplating was carried out at room temperature using copper electroplating solution to obtain current collector intermediate; the copper electroplating solution, by mass concentration, consisted of: copper sulfate 40 g / L, copper aminosulfonate 5 g / L, sulfuric acid 130 g / L, hydrochloric acid 0.03 g / L, sodium chloride 0.05 g / L, polyethylene glycol 8 g / L, polyethyleneimine 2 g / L, sodium polydithiopropane sulfonate 6 g / L, mercaptobenzimidazole 0.02 g / L, collagen 0.02 g / L, diamond 0.01 g / L, polyethylene glycol alkylphenyl ether 15 g / L and propynyl alcohol ethoxy ether 5 g / L; the thickness of the electroplated copper layer was 1 μm;

[0175] (8) Remove the surface oil stains of the current collector intermediate and perform plasma treatment with a power of 5kW and a treatment time of 30s;

[0176] (7) Preparation of flame retardant layer: by mass percentage, waterborne acrylic resin 30%, flame retardant (TPP) 15%, silane coupling agent (KH-550) 0.5%, defoamer (BYK-024) 0.1% and the balance water; mix silane coupling agent and part of water (10% of the total mass of water) and stir for 10 min to form silane coupling agent hydrolysate; add flame retardant to the remaining water and stir for 15 min with a high-speed disperser (1000 rpm) to form suspension; under continuous stirring, add waterborne acrylic resin emulsion to suspension and stir at 500 rpm for 20 min, then add silane coupling agent hydrolysate and stir for 10 min, then add defoamer and stir for 10 min, and finally filter with a 200 mesh filter to obtain emulsion; place the emulsion on both sides of the current collector intermediate, pre-bake at 80℃ for 1 min, and then cure at 120℃ for 3 min to form flame retardant layer with a thickness of 0.5 μm.

[0177] Example 2

[0178] The difference from Example 1 is that in step (4), the temperature of the first stretching is 90°C and the temperature of the second stretching is 130°C; the temperature difference between the second stretching and the first stretching is 30°C, the temperature difference between the first shaping and the first stretching is 40°C, and the temperature difference between the second shaping and the second stretching is 80°C.

[0179] Example 3

[0180] The difference from Example 1 is that in step (4), the first shaping temperature is 120°C and the second shaping temperature is 230°C; the difference between the first shaping temperature and the first stretching temperature is 20°C and the difference between the second shaping temperature and the second stretching temperature is 110°C.

[0181] Example 4

[0182] The difference from Example 1 is that in step (4), the temperature of the first stretching is 110°C; the temperature of the second stretching is 10°C different from the temperature of the first stretching; and the temperature of the first shaping is 20°C different from the temperature of the first stretching.

[0183] Comparative Example 1

[0184] The difference from Example 1 is that in step (4), the temperature of the first stretching and the second stretching are both 120°C, and the temperature of the first shaping and the second shaping are both 210°C.

[0185] Comparative Example 2

[0186] The difference from Example 1 is that in step (4), the temperature of the first stretching is 120°C and the temperature of the first shaping is 210°C; the temperature of the second stretching is 100°C and the temperature of the second shaping is 130°C.

[0187] Performance testing

[0188] Peel strength test: The adhesion between the coating and the polymer base film is evaluated according to GB / T 2790-1995 (180° peel method).

[0189] UL94 V-0 vertical flammability test: The flame retardancy rating of the composite current collectors prepared in each embodiment and comparative example was evaluated according to the UL94-2021 vertical flammability standard.

[0190] Shear resistance test: The conductivity uniformity of the composite current collectors prepared in each embodiment and comparative example was evaluated according to GB / T 15519-2018 (four-probe method).

[0191] Thermal break test: The thermal runaway simulation method at 180℃ / 30min was used to record whether the composite current collector prepared in each embodiment and comparative example melted and the time of circuit break.

[0192] The test results are shown in Table 1.

[0193] Table 1

[0194]

[0195] As shown in Table 1, this application achieves a UL94 V-0 flame retardant rating, high peel strength, low sheet resistance, and rapid thermal breakage in all embodiments through a composite design of a base film incorporating flame retardants, specific differentiated biaxial stretching and shaping, and a surface flame retardant layer. Comparative Example 1 did not employ differentiated biaxial stretching and shaping (single-temperature biaxial stretching and shaping), and although Comparative Example 2 did employ differentiated biaxial stretching and shaping, it did not meet the requirements that the second stretching temperature was higher than the first stretching temperature, or the second shaping temperature was higher than the first shaping temperature. The flame retardant rating of Comparative Examples 1 and 2 was only V-2, with low peel strength, high sheet resistance, and failure to break the circuit due to thermal runaway. This demonstrates that this application, through a composite design of a base film incorporating flame retardants, specific differentiated biaxial stretching and shaping, and a surface flame retardant layer, effectively improves the flame retardant safety, interfacial adhesion, electrical conductivity stability, and thermal protection capability of the composite current collector, balancing high safety with mechanical / electrical performance.

[0196] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0197] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing an ECI-based composite current collector, characterized in that, Includes the following steps: A mixture is prepared by mixing the polymer, the first flame retardant, and the compatibilizer; The mixture is granulated to prepare composite granules; The composite granules are sequentially melt-extruded and cast into a film to prepare a cast film preform. The cast preform is subjected to a first stretching, a first shaping, a second stretching, and a second shaping in sequence to prepare a polymer base film; the direction of the first stretching is perpendicular to the direction of the second stretching, the temperature of the second stretching is higher than the temperature of the first stretching, and the temperature of the second shaping is higher than the temperature of the first shaping. A copper layer is prepared on at least one side of the polymer base film to obtain a current collector intermediate; A flame-retardant layer is prepared on at least one side of the current collector intermediate to obtain the composite current collector.

2. The method for preparing the composite current collector as described in claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The polymeric material includes at least one of polypropylene and polyethylene terephthalate; (2) The first flame retardant includes triphenyl phosphate; (3) The compatibilizer includes at least one of polypropylene grafted with maleic anhydride and polyester grafted with glycidyl methacrylate; (4) The preparation of the mixture also includes the addition of at least one of an antioxidant and a lubricant.

3. The method for preparing the composite current collector as described in claim 2, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The temperature difference between the second stretching and the first stretching is 5℃~40℃; (2) The temperature of the first shaping is greater than the temperature of the first stretching, and the difference between the temperature of the first shaping and the temperature of the first stretching is 10℃~50℃; (3) The second shaping temperature is greater than the second stretching temperature, and the difference between the second shaping temperature and the second stretching temperature is 60℃~110℃.

4. The method for preparing the composite current collector as described in claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The temperature of the first stretching is 90℃~110℃; (2) The temperature of the second stretching is 110℃~130℃; (3) The first shaping temperature is 120℃~140℃; (4) The second shaping temperature is 200℃~230℃; (5) The stretching ratio of the first stretch is 3 to 4 times; (6) The stretching ratio of the second stretch is 3 to 4 times; (7) Before performing the first stretching, the process includes: preheating the cast film, wherein the temperature of the first preheating is lower than the temperature of the first stretching; optionally, the temperature of the first preheating is 80°C to 100°C. (8) Before performing the second stretching, the process includes: preheating the first stretched cast film in a second temperature lower than the temperature of the second stretching; optionally, the temperature of the first preheating is 100°C to 120°C. (9) The thickness of the polymer base film is 12 μm to 16 μm.

5. The method for preparing the composite current collector according to any one of claims 1 to 4, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The granulation includes: granulation using a co-rotating twin-screw extruder, wherein the temperature of the extruder feeding section is 180℃~200℃, the temperature of the melting section is 240℃~260℃, the temperature of the homogenization section is 250℃~265℃, and the die temperature is 255℃~265℃; the screw speed is controlled at 200rpm~300rpm, and the vacuum degree is ≤-0.09MPa; (2) The temperature of the melt extrusion is 250℃~265℃; (3) The thickness of the cast film is 150 μm to 250 μm.

6. The method for preparing the composite current collector according to any one of claims 1 to 4, characterized in that, The preparation of the copper layer includes: A copper seed layer is deposited on at least one side of the polymer base film using magnetron sputtering; Electroplating is performed on the side of the copper seed layer away from the polymer base film to form an electroplated copper layer.

7. The method for preparing the composite current collector as described in claim 6, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The thickness of the copper seed layer is 20 nm to 70 nm; (2) The electroplating solution used for the electroplating, by mass concentration, comprises the following components: copper sulfate 30 g / L~50 g / L, sulfuric acid 100 g / L~150 g / L, hydrochloric acid 0.01 g / L~0.06 g / L, sodium chloride 0.01 g / L~0.08 g / L, polyethylene glycol 2 g / L~10 g / L, polyethyleneimine 1 g / L~5 g / L, sodium dithiodipropane sulfonate 3 g / L~10 g / L, mercaptobenzimidazole 0.01 g / L~0.06 g / L, collagen 0.01 g / L~0.06 g / L, diamond 0.01 g / L~0.05 g / L, polyethylene glycol alkylphenyl ether 10 g / L~20 g / L, and propynyl ethoxy ether 3 g / L~10 g / L; (3) The thickness of the electroplated copper layer is 0.8 μm to 1.2 μm; (4) Before preparing the copper layer, the method further includes: subjecting the polymer base film to corona treatment.

8. The method for preparing the composite current collector according to any one of claims 1 to 4, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The preparation of the flame-retardant layer includes: An emulsion is prepared by mixing water-based acrylic resin, a second flame retardant, a silane coupling agent, an antifoaming agent, and water. The emulsion is applied to at least one side of the current collector intermediate and cured to form the flame retardant layer; (2) Before preparing a flame-retardant layer on at least one side of the current collector intermediate, the method further includes: subjecting the current collector intermediate to plasma treatment; (3) The thickness of the flame retardant layer is 0.5 μm to 1 μm.

9. A composite current collector based on ECI, characterized in that, It is prepared by the method for preparing ECI-based composite current collectors as described in any one of claims 1 to 8.

10. The application of the ECI-based composite current collector as described in claim 9 in the preparation of lithium batteries.

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