Polymer film, and preparation method therefor and use thereof

Abstract

The present application provides a polymer film, and a preparation method therefor and the use thereof. The polymer film comprises the following components in percentages by mass: 90-99.9% of a main-body polymer and 0.1-10% of a carbon nanocomposite material modified by a magnetic material and a polymer. In the present application, by using the carbon nanocomposite material modified by a magnetic material and a polymer, the thermal conductivity of the polymer film is improved, and in particular, the thermal conductivity of the polymer film in the thickness direction is improved. A composite current collector prepared by using the polymer film provided in the present application as a base film has relatively good conductivity and a relatively low hole defect rate.

Description

A polymer film and its preparation method and application

[0001] This application claims priority to the Chinese patent application number 202310672421.8 filed with the China Patent Office on June 8, 2023. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of polymer materials, and specifically relates to a polymer film and a preparation method and application thereof. Background Art

[0003] At present, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. The preparation process of the composite current collector is usually: a layer of metal (aluminum, copper, etc.) material is deposited on a polymer film (such as polypropylene, polyester, etc.) by physical vapor deposition (PVD) method. The prepared surface metallized film with a certain conductivity is the composite current collector. Compared with traditional current collectors, composite current collectors based on polymer films have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0004] CN113795954A discloses a composite current collector, a battery and an electronic device using the composite current collector. The composite current collector comprises a polymer film layer and a metal layer provided on at least one surface of the polymer film layer. A first coating layer is provided between the polymer film layer and the metal layer, and a second coating layer is provided between the first coating layer and the metal layer. The bonding force between the first coating layer and the second coating layer is greater than the bonding force between the second coating layer and the metal layer, and greater than the bonding force between the first coating layer and the polymer film layer, thereby effectively improving the bonding force between the metal layer and the polymer film layer. Although the composite current collector provided by this technical solution has good bonding force between the metal layer and the polymer film layer, the thermal conductivity of the polymer film layer is poor, and the electrical conductivity of the composite current collector prepared thereby is poor.

[0005] CN114361463A discloses a method for preparing a composite current collector. The method comprises the following steps: combining two layers of conductive metal foil with a polymer film to form a laminated material comprising an upper metal foil layer, a middle polymer film layer, and a lower metal foil layer; then heating the laminated material in an oven to melt the middle polymer film layer; and during the heating process, the upper and lower metal foil layers are tightly bonded to the molten polymer film layer through hot pressing. After the laminated material is removed from the oven, it is cooled and shaped, and finally, both the upper and lower metal foil layers of the cooled and shaped laminated material are thinned to obtain a composite current collector. The polymer film layer used in this technical solution has poor thermal conductivity, and the resulting composite current collector has poor electrical conductivity.

[0006] In the related art, in the process of preparing composite current collectors using traditional polymer films as base films, there are the following problems: the thermal conductivity of the polymer film is relatively poor, especially the thermal conductivity in the thickness direction, resulting in the heat generated by atomic deposition in the process of preparing composite current collectors using physical vapor deposition with it as the base film. It cannot be quickly conducted to the cooling surface of the main roller along the thickness direction, that is, rapid heat exchange between the polymer film and the main roller cannot be achieved, thereby causing hole defects in the prepared composite current collector, and ultimately resulting in poor conductivity of the prepared composite current collector.

[0007] Therefore, in order to address the above-mentioned problems of traditional polymer membranes and to prepare high-performance composite current collectors, how to provide a polymer membrane with good thermal conductivity, especially good thermal conductivity in the thickness direction, has become a technical problem that needs to be solved urgently.

[0008] Summary of the Invention

[0009] 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.

[0010] To address the shortcomings of related technologies, the present application aims to provide a polymer film, its preparation method, and its application. The present application utilizes a magnetic material-polymer modified carbon nanocomposite material to improve the thermal conductivity of the polymer film, particularly in the thickness direction. The composite current collector prepared using the polymer film provided herein as a base film exhibits good electrical conductivity and a low void defect rate.

[0011] To achieve this goal, this application adopts the following technical solutions:

[0012] In a first aspect, an embodiment of the present application provides a polymer film, wherein the polymer film comprises the following components in percentage by weight: 90-99.9% of a host polymer and 0.1-10% of a magnetic material-polymer modified carbon nanocomposite material;

[0013] The raw materials for preparing the magnetic material-polymer modified carbon nanocomposite material include the following components: carbon nanomaterial, polymer and magnetic material precursor;

[0014] The mass ratio of the carbon nanomaterial, polymer and magnetic material precursor is (2-5): (70-200): (40-85);

[0015] The magnetic material-polymer modified carbon nanocomposite material is prepared by the following method, which comprises the following steps:

[0016] (S1) preparing carbon oxide nanomaterials;

[0017] (S2) After uniformly mixing the oxidized carbon nanomaterial and solvent A, a weakly alkaline substance and a magnetic material precursor are added thereto, mixed uniformly, and reacted to obtain a magnetic material-modified carbon nanomaterial;

[0018] (S3) dispersing the magnetic material-modified carbon nanomaterial in solvent B, acidifying it, and then adding a polymer thereto to react to obtain the magnetic material-polymer-modified carbon nanocomposite material;

[0019] The solvent A includes an alcohol solvent;

[0020] The solvent B is selected from any one of water, ether or ethanol, or a combination of at least two thereof.

[0021] In the examples of this application, the use of a magnetic material-polymer modified carbon nanocomposite material improves the thermal conductivity of the polymer film, particularly in the thickness direction. Composite current collectors prepared using the polymer film provided in the examples of this application as a base film exhibit good electrical conductivity and a low void defect rate.

[0022] In the embodiments of the present application, a magnetic material-polymer modified carbon nanocomposite material is introduced into a polymer film. On the one hand, the orientation of the magnetic material molecules in the composite material in a magnetic field is utilized, and a magnetic field is applied during the preparation of the polymer film to achieve regular arrangement of the magnetic material-polymer modified carbon nanocomposite material in the thickness direction of the polymer film, thereby achieving improved thermal conductivity in the thickness direction; on the other hand, the polymer molecules in the magnetic material-polymer modified carbon nanocomposite material are utilized to achieve good compatibility between the magnetic material-polymer modified carbon nanocomposite material and the main polymer, thereby reducing the problem of poor thermal conductivity caused by interface resistance.

[0023] In the embodiments of the present application, the magnetic material and polymer in the magnetic material-polymer modified carbon nanocomposite are grafted onto the carbon nanomaterial via chemical bonds. Furthermore, through a specific preparation method, the magnetic material in the magnetic material-polymer modified carbon nanocomposite is grafted onto both ends of the carbon nanomaterial. During the film formation process, due to the action of the magnetic field, the magnetic material-polymer modified carbon nanocomposite will be uniformly and regularly arranged in the thickness direction of the polymer film, thereby promoting the thermal conductivity of the polymer film in the thickness direction; the polymer grafted onto the carbon nanomaterial is used to improve the compatibility of the carbon nanomaterial and the main polymer, thereby reducing the problem of poor thermal conductivity caused by the interfacial resistance between the two. The improvement in compatibility between the two can moderately increase the amount of carbon nanomaterial added to the polymer film, thereby further promoting the improvement of thermal conductivity. In addition, the polymer molecules grafted onto the carbon nanomaterial can promote the improvement of the adhesion between the metal layer and the polymer film in the composite current collector. The reason is that the polymer molecules grafted onto the carbon nanomaterial can play a bridging role. On the one hand, they can be entangled with the main polymer molecules, and on the other hand, the oxygen-containing functional groups in the molecules can interact with the metal atoms. The two together promote the improvement of the adhesion between the metal layer and the polymer film.

[0024] In the embodiments of the present application, by controlling the content of the magnetic material-polymer-modified carbon nanocomposite in the polymer film within a specific range, the resulting polymer film exhibits good thermal conductivity and good mechanical properties. If the content of the magnetic material-polymer-modified carbon nanocomposite in the polymer film is too low, the improvement in thermal conductivity through the thickness of the polymer film is not significant. If the content of the magnetic material-polymer-modified carbon nanocomposite in the polymer film is too high, the carbon nanomaterial is prone to agglomeration, forming defects, which in turn leads to poor mechanical properties of the polymer film.

[0025] In the embodiments of the present application, the use of magnetic material-polymer modified carbon nanocomposite materials can replace the functions of anti-blocking agents and lubricants, so that additives such as anti-blocking agents and lubricants can be omitted in the formulation of the polymer film.

[0026] In an embodiment of the present application, the mass percentage of the main polymer in the polymer film can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 99.9%, etc.

[0027] The mass percentage of the magnetic material-polymer modified carbon nanocomposite material in the polymer film can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0028] In the embodiment of the present application, the mass ratio of the carbon nanomaterial, the polymer and the magnetic material precursor can be 2:70:40, 2:100:40, 2:150:40, 2:200:40, 2:70:50, 2:70:85, 2:100:50, 2:100:85, 2:200:50, 2:200:85, 4:70:40, 4:100:40, 4:150:40, 4:200:40, :200:40, 4:70:50, 4:70:85, 4:100:50, 4:100:85, 4:200:50, 4:200:85, 4:70:40, 5:100:40, 5:150:40, 5:200:40, 5:70:50, 5:70:85, 5:100:50, 5:100:85, 5:200:50 or 5:200:85, etc.

[0029] The magnetic material precursor includes any one of an iron source, a neodymium source, a boron source, an aluminum source, a nickel source, a cobalt source, a chromium source, and a samarium source, or a combination of at least two of the sources.

[0030] It should be noted that there is no special restriction on the sources of the iron source, neodymium source, boron source, aluminum source, nickel source, cobalt source, chromium source, and samarium source in the embodiments of the present application, as long as they can be used as ferroferric oxide (Fe3O4), ferrous oxide (Fe2O3), neodymium iron boron (Nd2Fe 14 B), aluminum nickel cobalt (AlNiCo), iron chromium cobalt (FeCrCo) or samarium cobalt (SmCo) sources, illustratively including:

[0031] The iron source includes FeCl3 . 6H2O; the neodymium source includes NdCl3; the boron source includes H3BO3; the aluminum source includes AlCl3 and / or Al2(SO4)3; the nickel source includes NiCl2 and / or NiSO4; the cobalt source includes CoCl2 . 6H2O and / or CoSO4·7H2O; the chromium source includes CrCl2 and / or Cr2(SO4)3; the samarium source includes at least one of SmCl3, Sm2(SO4)3 or Sm(NO3)3.

[0032] The following are optional technical solutions for the embodiments of the present application, but are not intended to limit the technical solutions provided in the present application. Through the following optional technical solutions, the objectives and beneficial effects of the present application can be better achieved and realized.

[0033] As an optional technical solution of the embodiment of the present application, the magnetic material in the magnetic material-polymer modified carbon nanocomposite material is selected from ferroferric oxide (Fe3O4), ferrous oxide (Fe2O3), neodymium iron boron (Nd2Fe 14B), any one or a combination of at least two of aluminum nickel cobalt (AlNiCo), iron chromium cobalt (FeCrCo) or samarium cobalt (SmCo);

[0034] In one embodiment, the polymer in the magnetic material-polymer modified carbon nanocomposite material is selected from any one of polyvinyl alcohol, polyethylene glycol, polyacrylic acid or polysiloxane, or a combination of at least two thereof.

[0035] In one embodiment, the carbon nanomaterial in the magnetic material-polymer modified carbon nanocomposite material is selected from any one of graphene, carbon nanotubes, carbon nanofibers or nanodiamonds, or a combination of at least two thereof.

[0036] As an optional technical solution of an embodiment of the present application, the main polymer is selected from any one or a combination of at least two of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene (PE), polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), polyphenylene oxide (PPO), polystyrene (PS) or polyimide (PI).

[0037] As an optional technical solution of an embodiment of the present application, the thickness of the polymer film is ≥1μm (for example, it can be 1μm, 2μm, 5μm, 7μm, 10μm, 12μm, 15μm, 18μm, 20μm, 24μm, 27μm or 30μm, etc.), preferably 2~20μm.

[0038] The thinner the polymer film, the more it can promote the improvement of the energy density of the composite current collector, but the production difficulty must be taken into account at the same time. Since the thinner the polymer film, the greater the production difficulty and the lower the yield rate, in the embodiment of the present application, the thickness of the polymer film is controlled to be ≥1μm, which can not only prepare a polymer film with excellent performance, but also take into account the production process of the polymer film, so that it has a higher yield rate.

[0039] As an optional technical solution of the embodiment of the present application, the method for preparing the carbon oxide nanomaterial in step (S1) is to use a modified Hummers method for preparation;

[0040] The method for preparing carbon oxide nanomaterials using the modified Hummers method comprises the following steps:

[0041] The carbon nanomaterial and sodium nitrate are added to a reactor, and concentrated sulfuric acid is slowly added thereto under ice-water bath conditions and stirred for 20 to 40 minutes, and then potassium permanganate is slowly added thereto and stirred for 20 to 30 hours, and then the ice-water bath is removed and stirred at 30 to 40°C for 20 to 28 hours, and then potassium permanganate is slowly added thereto under ice-water bath conditions for about 24 hours. After the addition is completed, the ice-water bath is removed and stirred at 30 to 40°C for 20 to 28 hours; then cooled to room temperature, and then added thereto in sequence. Add ice water and hydrogen peroxide, stir for 8 to 12 hours, cool to room temperature, ultrasonicate for 3 to 5 hours at a power of 350 to 450 W, and then filter. The obtained filter cake is first filtered and washed 10 times with the prepared dilute hydrochloric acid (analytical grade hydrochloric acid: water = 4:1, volume ratio), and then the obtained filter cake is dispersed with water to obtain a solution. Finally, the solution is placed in a centrifuge and washed with water at a high speed of 13,000 rpm until the filtrate is neutral to remove residual metal ions and acidic small molecule impurities, and then dried to obtain carbon oxide nanomaterials.

[0042] It should be noted that the amount of each component used in the preparation of carbon oxide nanomaterials using the modified Hummers method can be based on the amount disclosed in the prior art; the hydrochloric acid used is analytical grade.

[0043] As an optional technical solution of an embodiment of the present application, the solvent A is selected from any one of ethylene glycol, diethylene glycol, glycerol or 1,4-butanediol, or a combination of at least two thereof.

[0044] The mixing method in step (S2) includes ultrasonic dispersion, and the ultrasonic power is 400-600W, for example, 400W, 420W, 440W, 460W, 480W, 500W, 520W, 540W, 560W, 580W or 600W.

[0045] In one embodiment, the weak alkaline substance in step (S2) includes any one or a combination of at least two of sodium acrylate, sodium acetate, sodium citrate, sodium tartrate or sodium benzoate.

[0046] In one embodiment, the weight amount of the alkaline substance added in step (S2) is 140 to 180 parts, for example, 140 parts, 145 parts, 150 parts, 155 parts, 160 parts, 165 parts, 170 parts, 175 parts or 180 parts.

[0047] In one embodiment, the reaction temperature in step (S2) is 180-320°C, for example, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C or 320°C, etc.

[0048] In one embodiment, the reaction time of step (S2) is 25 to 35 hours, for example, it can be 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours or 35 hours.

[0049] In one embodiment, after the reaction in step (S2), a post-treatment step is further included, and the post-treatment method includes centrifugation, washing, and drying.

[0050] As an optional technical solution of an embodiment of the present application, the pH of the acidified system in step (S3) is 2.5 to 3.5, for example, it can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4 or 3.5, etc.

[0051] In one embodiment, the temperature of adding the polymer is 60-80°C, for example, 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C.

[0052] In one embodiment, the reaction in step (S3) is carried out under ultrasonic water bath conditions.

[0053] In one embodiment, the reaction temperature in step (S3) is 50-80°C, for example, 50°C, 52°C, 55°C, 57°C, 60°C, 63°C, 65°C, 68°C, 70°C, 72°C, 75°C, 77°C or 80°C, etc.

[0054] In one embodiment, the reaction time of step (S3) is 4 to 8 hours, for example, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours.

[0055] In one embodiment, the reaction in step (S3) further includes a post-treatment step, and the post-treatment method includes purification.

[0056] In one embodiment, the purification comprises filtering and washing.

[0057] The preparation method of the magnetic material-polymer modified carbon nanocomposite material specifically comprises the following steps:

[0058] (S1) Prepare carbon oxide nanomaterials by using the improved Hummers method: add carbon nanomaterials and sodium nitrate to a reactor, slowly add concentrated sulfuric acid in a water bath while stirring continuously for 20 to 40 minutes; then slowly add potassium permanganate to the reactor and stir, the addition and stirring time is 20 to 30 hours; remove the ice-water bath, stir at 30 to 40°C for 20 to 28 hours, then add potassium permanganate in an ice bath again, ensuring that the addition time is about 24 hours, remove the ice bath, stir at 30 to 40°C for 20 to 28 hours; then cool The mixture is cooled to room temperature, ice water is added, and then 30% by weight hydrogen peroxide is added, stirred for 8 to 12 hours, cooled to room temperature, ultrasonicated at a power of 350 to 450 W for 3 to 5 hours, and then filtered; the obtained filter cake is first filtered and washed 10 times with the prepared (analytical grade hydrochloric acid: water = 4:1, volume ratio), and then the obtained filter cake is dispersed with water and placed in a centrifuge for high-speed centrifugation at 13,000 rpm and washed until the filtrate is neutral to remove residual metal ions and acidic small molecular impurities; and finally dried to obtain the carbon oxide nanomaterial.

[0059] (S2) preparing a carbon nanomaterial modified with a magnetic material: adding the oxidized carbon nanomaterial prepared in step (S1) to solvent A and performing ultrasonic dispersion treatment (ultrasonic power of 400 to 600 W) to form a suspension; then, adding a weak alkaline substance and a magnetic material precursor to the suspension, mixing them evenly, transferring the mixture to an autoclave, and reacting them at 180 to 320° C. for 25 to 35 hours; finally, placing the solution in a high-speed centrifuge, centrifuging it at 8000 rpm, and washing it twice with ethanol and deionized water alternately. After washing, drying the mixture to obtain a carbon nanomaterial modified with a magnetic material;

[0060] (S3) preparing a magnetic material-polymer modified carbon nanocomposite material: using ultrasound (ultrasonic power of 400-600W) to disperse the magnetic material modified carbon nanomaterial prepared in step (S2) in solvent B to obtain a magnetic material modified carbon nanomaterial dispersion with a concentration of 0.8-1.4g / L; using sulfuric acid, adjusting the pH of the mixed solution to 2.5-3.5, then heating it to 70°C, and adding a polymer thereto, stirring until it is completely dissolved, and after complete dissolution, placing the mixed solution in a 50-80°C ultrasonic water bath and reacting for 4-8h; then, filtering the above reaction solution through a 0.22μm microporous membrane, and the substance retained on the membrane surface is the unpurified magnetic material-polymer modified carbon nanocomposite material, and finally washing the magnetic material-polymer modified carbon nanocomposite material on the filter membrane surface with 60°C deionized water until the total organic carbon (TOC) content in the aluminum liquid is 0, so as to completely remove the residual polymer, thereby obtaining a purified magnetic material-polymer modified carbon nanocomposite material.

[0061] In a second aspect, an embodiment of the present application provides a method for preparing the polymer film according to the first aspect, the method comprising the following steps:

[0062] (1) mixing a main polymer and a magnetic material-polymer modified carbon nanocomposite material, melting, filtering, and extruding to obtain a molten material;

[0063] (2) casting the molten material obtained in step (1) onto a casting roll, cooling and forming the molten material, longitudinally stretching, transversely stretching, and heat treating the molten material to obtain the polymer film;

[0064] Step (1) and step (2) are both carried out in the presence of a magnetic field;

[0065] The direction of the magnetic field is parallel to the thickness direction of the polymer film.

[0066] In an embodiment of the present application, by preparing a polymer film under the action of a magnetic field and further controlling the direction of the magnetic field to be parallel to the thickness direction of the polymer film, the magnetic material-polymer modified carbon nanocomposite material can be regularly arranged in the thickness direction of the polymer film, thereby achieving an improvement in thermal conductivity in the thickness direction.

[0067] In the embodiment of the present application, by setting up magnetic fields at the two process positions of melt extrusion and casting (the molten material obtained in step (1) is cast onto a casting roller and cooled to form), it is possible to ensure that the magnetic material-polymer modified carbon nanocomposite material is regularly arranged along the thickness direction of the polymer film when the polymer film is formed; the reason for setting up magnetic fields at the process positions of longitudinal stretching, transverse stretching and heat treatment is to maintain the regular arrangement of the magnetic material-polymer modified carbon nanocomposite material and prevent the regular arrangement structure of the magnetic material-polymer modified carbon nanocomposite material from being destroyed during the stretching and heat treatment process, thereby affecting the thermal conductivity of the polymer film.

[0068] As an optional technical solution of an embodiment of the present application, the strength of the magnetic field is 0.1~2.0T, for example, it can be 0.1T, 0.2T, 0.4T, 0.6T, 0.8T, 1.0T, 1.2T, 1.4T, 1.6T, 1.8T or 2.0T, etc.

[0069] In the embodiments of the present application, by controlling the magnetic field intensity within a specific range, the magnetic material-polymer-modified carbon nanocomposite can be both regularly arranged and uniformly distributed within the polymer film, thereby producing a polymer film with improved thermal conductivity. If the magnetic field intensity is too low, the regular arrangement of the magnetic material-polymer-modified carbon nanocomposite in the thickness direction of the polymer film is poor, resulting in limited improvement in the thermal conductivity of the polymer film. If the magnetic field intensity is too high, the magnetic material-polymer-modified carbon nanocomposite will be enriched on both surfaces of the film due to the strong magnetic field, resulting in uneven distribution through the thickness direction, which in turn leads to poor thermal conductivity of the polymer film.

[0070] As an optional technical solution of the embodiment of the present application, the melting temperature is T m -(T m +50)℃, for example, it can be T m 、(T m +10)℃、(T m +20)℃、(T m +30)℃、(T m +40)℃ or (T m +50)℃, etc. Among them, T m is the melting temperature of the main polymer, the same below.

[0071] In one embodiment, the filtering method includes filtering through a filter with a filter mesh of 10 μm.

[0072] It should be noted that, in the examples of the present application, melting and extrusion are carried out in a twin-screw extruder.

[0073] As an optional technical solution of the embodiment of the present application, the cooling molding method is molding through water cooling treatment.

[0074] In one embodiment, the cooling molding temperature is 15-60°C, for example, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C.

[0075] In one embodiment, the preheating temperature for longitudinal stretching is Tg-(Tg+40)°C, for example, Tg°C, (Tg+10)°C, (Tg+20)°C, (Tg+30)°C, or (Tg+40)°C, etc., wherein Tg is the glass transition temperature of the main polymer, the same below.

[0076] In one embodiment, the stretching temperature of the longitudinal stretching is (Tg+10)-(Tg+50)°C, for example, it can be (Tg+10)°C, (Tg+20)°C, (Tg+30)°C, (Tg+40)°C or (Tg+50)°C.

[0077] In one embodiment, the longitudinal stretching ratio is 2-5 times, for example, 2, 3, 4 or 5.

[0078] In one embodiment, the longitudinal stretching further includes a post-processing step.

[0079] In one embodiment, the post-treatment method includes cooling to room temperature.

[0080] In one embodiment, the preheating temperature for transverse stretching is Tg-(Tg+40)°C, for example, it can be Tg°C, (Tg+10)°C, (Tg+20)°C, (Tg+30)°C or (Tg+40)°C.

[0081] In one embodiment, the stretching temperature of the transverse stretching is (Tg+10)-(Tg+50)°C, for example, it can be (Tg+10)°C, (Tg+20)°C, (Tg+30)°C, (Tg+40)°C or (Tg+50)°C.

[0082] In one embodiment, the stretching ratio of the transverse stretching is 2-5 times, for example, 2, 3, 4, 5, etc.

[0083] In one embodiment, the heat setting temperature for transverse stretching is (Tg+20)-(Tg+60)°C, for example, it can be (Tg+20)°C, (Tg+30)°C, (Tg+40)°C, (Tg+50)°C or (Tg+60)°C.

[0084] In one embodiment, the heat treatment temperature is Tg-(Tg+50)°C, for example, it can be Tg°C, (Tg+10)°C, (Tg+20)°C, (Tg+30)°C, (Tg+40)°C or (Tg+50)°C.

[0085] The purpose of heat treatment is to eliminate the internal stress of the membrane and improve the thermal stability of the membrane.

[0086] In one embodiment, the heat treatment further includes a post-treatment step.

[0087] In one embodiment, the post-processing method includes: after air cooling in the platform area, the film enters the winding system through the traction system to be wound up.

[0088] In one embodiment, the winding tension is 20-30 N / m, for example, it can be 20 N / m, 21 N / m, 22 N / m, 23 N / m, 24 N / m, 25 N / m, 26 N / m, 27 N / m, 28 N / m, 29 N / m or 30 N / m, etc.

[0089] In the embodiment of the present application, the method for preparing the polymer film specifically includes the following steps:

[0090] (1) The main polymer and the magnetic material-polymer modified carbon nanocomposite are placed in a twin-screw extruder and extruded at T m -(T m +50) ° C, filtered through a filter with a filter mesh of 10 μm, and extruded through an extruder die to obtain a molten material;

[0091] (2) casting the molten material obtained in step (1) onto a casting roll, cooling the molten material with water at 15-60° C., stretching the molten material longitudinally and transversely, and then heat treating the molten material at Tg-(Tg+50)° C. The molten material is passed through a traction system into a winding system, and winding the film under a winding tension of 20-30 N / m to obtain the polymer film;

[0092] Step (1) and step (2) are both carried out in the presence of a magnetic field;

[0093] The direction of the magnetic field is parallel to the thickness direction of the polymer film, and the intensity of the magnetic field is 1.0-2.0T.

[0094] Wherein, longitudinal stretching: preheating temperature is Tg-(Tg+40)℃, stretching temperature is (Tg+10)-(Tg+50)℃; longitudinal stretching ratio is 2-5, and then cooled to room temperature;

[0095] Transverse stretching: preheating temperature is Tg-(Tg+40)℃, stretching temperature is (Tg+10)-(Tg+50)℃; heat setting temperature is Tg+20)-(Tg+60)℃, and transverse stretching ratio is 2-5.

[0096] In a third aspect, an embodiment of the present application further provides a composite current collector, the composite current collector comprising a metal layer and a polymer film layer;

[0097] The polymer film layer is the polymer film as described in the first aspect.

[0098] In one embodiment, the metal layer material is selected from at least one of copper, aluminum, silver, gold, and nickel and / or at least one of an alloy formed by at least two of copper, aluminum, silver, gold, and nickel, and is further preferably any one of copper, aluminum, or a copper-aluminum alloy.

[0099] In one embodiment, the composite current collector includes a first protective layer, a first metal layer, a polymer film layer, a second metal layer, and a second protective layer stacked in sequence;

[0100] The polymer film layer is the polymer film as described in the first aspect.

[0101] The polymer film provided in the first aspect of the embodiment of the present application serves as a carrier and a supporting layer of the composite current collector.

[0102] The first metal layer and the second metal layer are used for conducting electricity, and the first protective layer and the second protective layer are used for preventing the first metal layer and the second metal layer from being chemically corroded or physically damaged.

[0103] As an optional technical solution of an embodiment of the present application, the materials of the first metal layer and the second metal layer are each independently selected from at least one of copper, aluminum, silver, gold, nickel and / or at least one of an alloy formed by at least two metals of copper, aluminum, silver, gold, nickel, and further preferably any one of copper, aluminum or copper-aluminum alloy.

[0104] In one embodiment, the thickness of the first metal layer and the second metal layer are independently selected from 500-2000 nm (for example, 500 nm, 700 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm or 2000 nm, etc.), and more preferably 700-1500 nm.

[0105] In an embodiment of the present application, the first metal layer and the second metal layer are each independently prepared by physical vapor deposition (such as resistance heating vacuum evaporation, electron beam heating vacuum evaporation, laser heating vacuum evaporation, magnetron sputtering, etc.), electroplating or chemical plating, or a combination of at least two of them, preferably physical vapor deposition.

[0106] In one embodiment, the materials of the first protective layer and the second protective layer are independently selected from any one or a combination of at least two of aluminum oxide, nickel oxide, chromium oxide, cobalt oxide, copper oxide, copper chromium oxide, formate-copper complex, nickel-chromium alloy, graphite, carbon nano-quantum dots, carbon nanotubes, carbon nanofibers and graphene.

[0107] In one embodiment, the thickness of the first protective layer and the second protective layer are each independently selected from 10-150nm (for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm or 150nm, etc.), and more preferably 20-100nm.

[0108] In one embodiment, the thickness of the first protection layer and the second protection layer is less than or equal to one tenth of the thickness of the first metal layer and the thickness of the second metal layer.

[0109] In the embodiments of the present application, the preparation methods of the first protective layer and the second protective layer each independently include any one of physical vapor deposition, chemical vapor deposition, in-situ forming, and coating, or a combination of at least two thereof. Among these, the physical vapor deposition method is preferably vacuum evaporation and magnetron sputtering; the chemical vapor deposition method is preferably atmospheric pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition; the in-situ forming method is preferably a method of forming a metal oxide passivation layer in situ on the surface of the metal layer; and the coating method is preferably die coating, blade coating, or extrusion coating.

[0110] In a fourth aspect, an embodiment of the present application provides a battery, comprising the composite current collector as described in the third aspect.

[0111] Compared with the related art, this application has the following beneficial effects:

[0112] (1) In the present application, a magnetic material-polymer modified carbon nanocomposite material is used as a raw material for preparing a polymer film, and the content of the magnetic material-polymer modified carbon nanocomposite material in the polymer film is controlled within a specific range. At the same time, the preparation method of the polymer film is adjusted. The polymer film prepared under a specific magnetic field strength has good thermal conductivity, high mechanical strength, suitable surface roughness, and no defects on the surface of the polymer film. Its thermal conductivity is 0.60~7.13W / m / K, its tensile strength is 223~355MPa, and its surface roughness is 91~118nm.

[0113] (2) In this application, a polymer membrane with excellent performance is prepared by designing the raw materials and preparation methods for the polymer membrane. The composite current collector prepared by using the polymer membrane as the base membrane has no holes and low square resistance. The bonding force between the polymer membrane and the metal layer is large, with a square resistance of 31 to 33 mΩ and a bonding force of 1.3 to 2.5 N / cm.

[0114] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0116] FIG1 is a schematic structural diagram of graphene oxide provided in Preparation Example 1;

[0117] FIG2 is a schematic structural diagram of the composite current collector provided in Application Example 1;

[0118] Among them, 1 is the first protective layer, 2 is the first metal layer, 3 is the polymer film layer, 4 is the second metal layer, and 5 is the second protective layer. DETAILED DESCRIPTION

[0119] The technical solution of the present application will be further described below with reference to the accompanying drawings and through specific implementation methods. Those skilled in the art should understand that the embodiments are only for the purpose of helping to understand the present application and should not be regarded as specific limitations of the present application.

[0120] The sources of some components in the following preparation examples, embodiments and comparative examples are as follows:

[0121] Polyvinyl alcohol: weight average molecular weight 30000Da, purchased from Sinopharm Reagent Group;

[0122] Polyethylene glycol: weight average molecular weight is 8000Da, purchased from Jiangsu Santuo New Materials Co., Ltd.

[0123] Polydimethylsiloxane: viscosity 20 cS (25°C), purchased from KCC Beauty, South Korea;

[0124] Graphene: 0.5 μm sheet diameter, purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.

[0125] Carbon nanotubes: diameter less than 2 nm, length 0.5 μm, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0126] Carbon nanofibers: diameter: 50 nm, length: 1 μm, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0127] Polyethylene terephthalate: weight average molecular weight of 30,000, molecular weight distribution of 2.0, purchased from Sinopec Yizheng Chemical Fiber Co., Ltd.

[0128] Polyethylene naphthalate: weight average molecular weight 30,000, molecular weight distribution 2.0, purchased from Sinopec Yizheng Chemical Fiber Co., Ltd.

[0129] Polypropylene: melt index of 3.2 g / 10 min (230° C. / 2.16 kg), molecular weight distribution index of 4.6, isotacticity of 97%, purchased from Korea Petrochemical.

[0130] The raw materials used in the following preparation examples, such as sulfuric acid, potassium permanganate, hydrochloric acid, hydrogen peroxide, ferric chloride hexahydrate, ethylene glycol, ethanol, diethylene glycol, sodium acrylate, sodium acetate, neodymium chloride, boric acid, chromium chloride, and cobalt chloride, were all of analytical grade and purchased from Sinopharm Reagent Group.

[0131] Preparation Example 1

[0132] This preparation example provides an iron oxide-polyvinyl alcohol modified graphene composite material and a preparation method thereof, and the preparation method is as follows:

[0133] (S1) Preparation of graphene oxide using the improved Hummers method:

[0134] 300g of graphite and 1500g of sodium nitrate were added to a 100L reactor, and 7L of concentrated sulfuric acid was slowly added under ice-water bath conditions while stirring continuously for 30min. Then, 900g of potassium permanganate was slowly added to the reactor and stirred. The addition and stirring time was 24h. The ice-water bath was removed, and the mixture was stirred at 35°C for 24h. Then, 900g of potassium permanganate was added under ice-water bath conditions, ensuring that the addition time was about 24h. The ice bath was removed, and the mixture was stirred at 35°C for 24h. Then, the mixture was cooled to room temperature, 40L of ice water was added, and the mixture was stirred for 24h. 300 mL of 30% by mass hydrogen peroxide was added, stirred for 10 hours, cooled to room temperature, ultrasonicated for 4 hours, and then filtered; the filter cake was first filtered and washed 10 times with a prepared hydrochloric acid solution, where the hydrochloric acid solution was prepared by mixing analytically pure hydrochloric acid with water in a volume ratio of 4:1, and then the filter cake was dispersed with water; finally, the solution was placed in a centrifuge and washed with water at a high speed of 13,000 rpm until the filtrate was neutral to remove residual metal ions and acidic small molecule impurities, and finally dried to obtain graphene oxide (GO).

[0135] (S2) Preparation of iron oxide-modified graphene: 100 mL of ethylene glycol and 900 mL of diethylene glycol were stirred and mixed uniformly. After mixing uniformly, 4 g of graphene oxide prepared in step (S1) was added and ultrasonic dispersion treatment (ultrasonic power of 500 W) was performed to form a suspension; then, 10 g of sodium acrylate, 150 g of sodium acetate and 55 g of FeCl3 were added to the suspension. . 6H2O, stirred for 1 hour; after the stirring was completed, the resulting suspension was transferred to an autoclave and reacted at 200°C for 30 hours; finally, the solution was placed in a high-speed centrifuge and centrifuged at 8000 rpm, and finally washed twice alternately with ethanol and deionized water. After washing, it was dried to obtain iron oxide-modified graphene.

[0136] (S3) Preparation of iron oxide-polyvinyl alcohol-modified graphene: The iron oxide-modified graphene prepared in step (S2) is dispersed in pure water using ultrasound (ultrasonic power of 500 W) to obtain an iron oxide-modified graphene dispersion with a concentration of 1 g / L, and the pH of the mixed solution is adjusted to 3 using sulfuric acid; then, 10 L of the above solution is taken, heated to 70°C, and 20 g of polyvinyl alcohol is added to the solution, and stirred at 5000 rpm until completely dissolved. After complete dissolution, the mixed solution is placed in a 60°C ultrasonic water bath and reacted for 6 hours; then, the above reaction solution is filtered through a 0.22 μm microporous membrane, and the substance retained on the membrane surface is the unpurified iron oxide-polyvinyl alcohol-modified graphene. Finally, the iron oxide-polyvinyl alcohol-modified graphene on the filter membrane surface is washed with 60°C deionized water until the total organic carbon (TOC) content in the filtrate is 0, so as to completely remove the residual polymer and obtain purified iron oxide-polyvinyl alcohol-modified graphene.

[0137] Regarding the theoretical explanation of the grafting of iron oxide onto both ends of graphene and polyvinyl alcohol onto the graphene surface: Graphene oxide as shown in FIG1 can be obtained by treating graphene using the improved Hummers method as described above (as described in “D.C. Marcano, D.V. Kosynkin, J.M. Berglin, a. Sinitskii, Z.Z. Sun, a. Slesarev, L.B. Alemany, W. Lu, and J.M. Tour, “Improved Synthesis of Graphene Oxide,” ACS Nano, vol. 4, no. 8, pp. 4806–4814, 2010.”). As shown in Figure 1, carboxyl groups are distributed on the edges of graphene oxide, and hydroxyl and epoxy groups are distributed on the surface. Among them, the carboxyl groups distributed on the edges of graphene oxide sheets can combine with iron salts to react to form iron oxide-modified graphene, while the epoxy groups distributed on the graphene sheets can condense with the hydroxyl groups of polyvinyl alcohol under acidic conditions, thereby obtaining iron oxide-polyvinyl alcohol-modified graphene with the edges modified by magnetic iron oxide and the surface modified by polyvinyl alcohol.

[0138] Preparation Example 2

[0139] This preparation example provides an iron oxide-polyvinyl alcohol modified carbon nanotube composite material and a preparation method thereof. The only difference from Preparation Example 1 is that graphite is replaced by carbon nanotubes, and other conditions are the same as Preparation Example 1.

[0140] Preparation Example 3

[0141] This preparation example provides an iron oxide-polyvinyl alcohol modified carbon nanofiber composite material and a preparation method thereof. The only difference from Preparation Example 1 is that graphite is replaced by carbon nanofiber, and other conditions are the same as Preparation Example 1.

[0142] Preparation Example 4

[0143] This preparation example provides a neodymium iron boron-polyvinyl alcohol modified graphene composite material and a preparation method thereof, which differs from Preparation Example 1 in that:

[0144] (S2) Preparation of NdFeB-modified graphene: 100 mL of ethylene glycol and 900 mL of diethylene glycol were stirred and mixed uniformly. After mixing uniformly, 4 g of graphene oxide prepared in step (S1) was added and ultrasonic dispersion treatment (ultrasonic power of 500 W) was performed to form a suspension. Then, 10 g of sodium acrylate, 150 g of sodium acetate and 30 g of FeCl3 were added to the suspension. . 6H2O, 25gNdCl3, 20gH3BO3, and stirring for 2h; after stirring, the resulting suspension was transferred to an autoclave and reacted at 300℃ for 30h. After the reaction was completed, the solution was placed in a high-speed centrifuge at 8000rpm, then washed twice with ethanol and deionized water alternately, and dried, and finally placed in a vacuum oven at 600℃ for 12h for thermal reduction reaction to obtain NdFeB-modified graphene;

[0145] The other steps are the same as those in Preparation Example 1.

[0146] Preparation Example 5

[0147] This preparation example provides an iron-chromium-cobalt-polyvinyl alcohol modified graphene composite material and a preparation method thereof, which differs from Preparation Example 1 in that:

[0148] (2) Preparation of Fe-Cr-Co modified graphene: 100 mL of ethylene glycol and 900 mL of diethylene glycol were stirred and mixed uniformly. After mixing uniformly, 4 g of graphene oxide prepared in step (S1) was added and ultrasonic dispersion treatment (ultrasonic power of 500 W) was performed to form a suspension. Then, 10 g of sodium acrylate, 150 g of sodium acetate and 25 g of FeCl3 were added to the suspension. . 6H2O, 20gCoCl2 . 6H2O, 22gCrCl2, and stirred for 2h, then the resulting suspension was transferred to an autoclave and reacted at 250℃ for 30h. After the reaction was completed, the solution was placed in a centrifuge and centrifuged at 8000rpm to obtain iron-chromium-cobalt oxide-modified graphene, which was then washed twice with ethanol and deionized water alternately and dried, and finally placed in a vacuum oven at 500℃ for 10h for thermal reduction reaction to obtain iron-chromium-cobalt modified graphene;

[0149] The other steps are the same as those in Preparation Example 1.

[0150] Preparation Example 6

[0151] This preparation example provides an iron oxide-polyethylene glycol modified graphene composite material and a preparation method thereof. The only difference from Preparation Example 1 is that polyvinyl alcohol is replaced by polyethylene glycol, and other conditions are the same as those in Preparation Example 1.

[0152] Preparation Example 7

[0153] This preparation example provides an iron oxide-polydimethylsiloxane-modified graphene composite material and a preparation method thereof. The only difference from Preparation Example 1 is that polyvinyl alcohol is replaced with polydimethylsiloxane, and other conditions are the same as those in Preparation Example 1.

[0154] Preparation Example 8

[0155] This preparation example provides an iron oxide-modified graphene composite material and a preparation method thereof. The only difference from Preparation Example 1 is that step (S3) is not performed, and other conditions are the same as those in Preparation Example 1.

[0156] Preparation Example 9

[0157] This preparation example provides a polyvinyl alcohol-modified graphene composite material and a preparation method thereof. The only difference from Preparation Example 1 is that step (S2) is not performed, and other conditions are the same as those in Preparation Example 1.

[0158] Example 1

[0159] This embodiment provides a polymer film and a preparation method thereof. The polymer film includes the following components in parts by weight: 99.9 parts of polyethylene terephthalate and 0.1 parts of the iron oxide-polyvinyl alcohol modified graphene composite material provided in Preparation Example 1.

[0160] The preparation method of the above polymer film is as follows:

[0161] (1) placing the components of the polymer film in a twin-screw extruder, melting them at 280°C, filtering them through a filter with a 10 μm filter screen, and extruding them through the die head of the extruder to obtain a molten material. The die head temperature was 280°C.

[0162] (2) casting the molten material obtained in step (1) onto a casting roll, cooling the molten material with water at 25° C. to form the molten material, stretching the molten material longitudinally and transversely, and then heat treating the molten material at 130° C.;

[0163] (3) The product heat-treated in step (2) enters the winding system through the traction system, and is wound under a winding tension of 30 N / m to obtain a polymer film with a thickness of 6 μm;

[0164] Step (1) and step (2) are both carried out in the presence of a magnetic field;

[0165] The direction of the magnetic field is parallel to the thickness direction of the polymer film, and the intensity of the magnetic field is 0.1T.

[0166] Among them, longitudinal stretching: preheating temperature is 90℃, stretching temperature is 110℃; longitudinal stretching ratio is 3 times, and then cooled to room temperature;

[0167] Transverse stretching: preheating temperature is 90℃, stretching temperature is 120℃, heat setting temperature is 140℃, and transverse stretching ratio is 3 times.

[0168] Example 2

[0169] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 95.0 parts of polyethylene terephthalate and 5.0 parts of the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1. Other conditions are the same as those in Example 1.

[0170] Example 3

[0171] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 90.0 parts of polyethylene terephthalate and 10.0 parts of the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1. Other conditions are the same as those in Example 1.

[0172] Example 4

[0173] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the intensity of the magnetic field is 1.0 T, and other conditions are the same as those in Example 1.

[0174] Example 5

[0175] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the intensity of the magnetic field is 2.0 T, and other conditions are the same as those in Example 1.

[0176] Example 6

[0177] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 5 is that the polymer film includes the following components in parts by weight: 90.0 parts of polyethylene terephthalate and 10.0 parts of the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1. Other conditions are the same as those in Example 5.

[0178] Example 7

[0179] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the iron oxide-polyvinyl alcohol-modified carbon nanotube composite material provided in Preparation Example 2. Other conditions are the same as those in Example 6.

[0180] Example 8

[0181] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the iron oxide-polyvinyl alcohol-modified carbon nanofiber composite material provided in Preparation Example 3. Other conditions are the same as those in Example 6.

[0182] Example 9

[0183] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the neodymium iron boron-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 4. Other conditions are the same as those in Example 6.

[0184] Example 10

[0185] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the iron chromium cobalt-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 5, and other conditions are the same as Example 6.

[0186] Example 11

[0187] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the iron oxide-polyethylene glycol-modified graphene composite material provided in Preparation Example 6, and other conditions are the same as Example 6.

[0188] Example 12

[0189] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1 is replaced by the iron oxide-polydimethylsiloxane-modified graphene composite material provided in Preparation Example 7. Other conditions are the same as those in Example 6.

[0190] Example 13

[0191] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 6 is that polyethylene terephthalate is replaced by polyethylene naphthalate, and other conditions are the same as those in Example 6.

[0192] Example 14

[0193] This embodiment provides a polymer film and a preparation method thereof. The polymer film includes the following components in parts by weight: 90 parts of polypropylene and 10 parts of the iron oxide-polyvinyl alcohol modified graphene composite material provided in Preparation Example 1.

[0194] The preparation method of the above polymer film is as follows:

[0195] (1) The components of the polymer film were placed in a twin-screw extruder, melted at 240°C, filtered through a filter with a 10 μm filter screen, and extruded through the die head of the extruder to obtain a molten material. The die head temperature was 250°C.

[0196] (2) casting the molten material obtained in step (1) onto a casting roll, cooling the molten material with water at 25° C. to form the molten material, stretching the molten material longitudinally and transversely, and then heat treating the molten material at 130° C.;

[0197] (3) The product heat-treated in step (2) enters the winding system through the traction system, and is wound under a winding tension of 30 N / m to obtain a polymer film with a thickness of 6 μm;

[0198] Step (1) and step (2) are both carried out in the presence of a magnetic field;

[0199] The direction of the magnetic field is parallel to the thickness direction of the polymer film, and the intensity of the magnetic field is 2.0T.

[0200] Among them, longitudinal stretching: preheating temperature is 130℃, stretching temperature is 140℃; longitudinal stretching ratio is 7 times, and then cooled to room temperature;

[0201] Transverse stretching: preheating temperature is 132℃, stretching temperature is 155℃, heat setting temperature is 160℃, and transverse stretching ratio is 6 times.

[0202] Example 15

[0203] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the intensity of the magnetic field is 0.05 T, and other conditions are the same as those in Example 1.

[0204] Example 16

[0205] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the intensity of the magnetic field is 2.1 T, and other conditions are the same as those in Example 1.

[0206] Example 17

[0207] This embodiment provides a polymer film and a preparation method thereof. The only difference from Example 1 is that both step (1) and step (2) are not performed in the presence of a magnetic field. Other conditions are the same as those in Example 1.

[0208] Comparative Example 1

[0209] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film does not contain the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1, the weight portion of polyethylene terephthalate is 100 parts, and other conditions are the same as Example 1.

[0210] Comparative Example 2

[0211] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 99.95 parts of polyethylene terephthalate and 0.05 parts of the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1. Other conditions are the same as those in Example 1.

[0212] Comparative Example 3

[0213] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 89 parts of polyethylene terephthalate and 11 parts of the iron oxide-polyvinyl alcohol-modified graphene composite material provided in Preparation Example 1. Other conditions are the same as those in Example 1.

[0214] Comparative Example 4

[0215] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 99.9 parts of polyethylene terephthalate, 0.01 parts of iron oxide, 0.01 parts of polyvinyl alcohol, and 0.08 parts of graphene. Other conditions are the same as those in Example 1.

[0216] Comparative Example 5

[0217] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 99.9 parts of polyethylene terephthalate and 0.1 parts of the iron oxide-modified graphene composite material provided in Preparation Example 8. Other conditions are the same as those in Example 1.

[0218] Comparative Example 6

[0219] This comparative example provides a polymer film and a preparation method thereof. The only difference from Example 1 is that the polymer film includes the following components in parts by weight: 99.9 parts of polyethylene terephthalate and 0.1 parts of polyvinyl alcohol-modified graphene provided in Preparation Example 9. Other conditions are the same as those in Example 1.

[0220] Application Example 1

[0221] This application example provides a composite current collector and a preparation method thereof. The structural schematic diagram of the composite current collector is shown in FIG2 , comprising a first protective layer 1, a first metal layer 2, a polymer film layer 3, a second metal layer 4, and a second protective layer 5 stacked in sequence;

[0222] The polymer film layer 3 is the polymer film provided in Example 1.

[0223] The preparation method of the composite current collector is as follows:

[0224] (1) The polymer film layer 3 provided in Example 1, which had undergone surface cleaning, was placed in a vacuum evaporation chamber. High-purity aluminum wire (with a purity greater than 99.99%) in the metal evaporation chamber was melted and evaporated at a high temperature of 1300° C. The evaporated metal atoms were passed through a cooling system in the vacuum coating chamber and deposited on both surfaces of the polymer film layer 3 to form an aluminum metal conductive layer with a thickness of 1 μm, thereby obtaining a first metal layer 2, a polymer film layer 3, and a second metal layer 4 stacked in sequence.

[0225] (2) 1.5 g of carbon nanotubes were uniformly dispersed in 998.5 g of nitrogen methyl pyrrolidone (NMP) solution by ultrasonic dispersion to prepare a coating solution with a solid content of 0.15 wt.%, and then the coating solution was uniformly coated on the surface of the aluminum metal conductive layer on both sides of the polymer film layer 3 by a die coating process. The coating thickness was 60 μm, and finally dried at 100° C. to obtain the composite current collector.

[0226] Application Example 2-17

[0227] Application Examples 2-17 respectively provide a composite current collector and a preparation method thereof. The difference from Application Example 1 is that the polymer film provided in Example 1 is replaced by the polymer films provided in Examples 2-17 in sequence, and other conditions are the same as those in Application Example 1.

[0228] Comparative Application Examples 1-6

[0229] Comparative Application Examples 1-6 respectively provide a composite current collector and a preparation method thereof. The difference from Application Example 1 is that the polymer film provided in Example 1 is replaced by the polymer films provided in Comparative Examples 1-6 in sequence, and other conditions are the same as those in Application Example 1.

[0230] As previously mentioned, the purpose of preparing a polymer film with enhanced thermal conductivity in the thickness direction in this application is to improve the thermal conductivity of the polymer film, and then use this polymer film as a substrate to prepare a composite current collector with low defectivity and high electrical conductivity. Therefore, this application characterizes the thermal conductivity of the polymer film prepared above, the number of holes per unit area, and the square resistance of the composite current collector. In addition, key indicators such as the tensile strength, surface roughness and number of surface defects of the polymer film, and the adhesion between the base film and the metal layer of the composite current collector are characterized as follows:

[0231] The properties of the polymer films provided in the above examples and comparative examples were tested. The specific testing methods are as follows. The test results are detailed in Table 1 below:

[0232] ① Thermal conductivity: The thermal conductivity of the polymer film prepared above was tested according to the standard ISO 22007-3:2008.

[0233] ②Tensile strength: The tensile strength of the polymer film prepared above was tested according to the standard GB / T 1040.3-2006.

[0234] ③ Surface roughness: The surface roughness of the polymer film prepared above was tested according to the standard GB / T 31227-2014.

[0235] ④ Number of surface defects: The polymer film prepared as described above was placed on the EPVISION plastic film surface defect visual online detection system to count the number of surface defects per unit area of ​​the polymer film.

[0236] Table 1

[0237] As can be seen from the contents of Table 1, in this application, by using a magnetic material-polymer modified carbon nanocomposite material as a raw material for preparing a polymer film, and controlling the content of the magnetic material-polymer modified carbon nanocomposite material in the polymer film within a specific range, and adjusting the preparation method of the polymer film, the polymer film prepared under a specific magnetic field strength has good thermal conductivity, high mechanical strength, suitable surface roughness, and no defects on the surface of the polymer film. Its thermal conductivity is 0.60~7.13W / m / K, its tensile strength is 223~355MPa, and its surface roughness is 91~118nm.

[0238] Compared with Example 1, if the polymer film does not contain magnetic material-polymer modified carbon nanocomposite material (Comparative Example 1), the thermal conductivity of the prepared polymer film is poor and the thermal conductivity is low; if the content of magnetic material-polymer modified carbon nanocomposite material in the polymer film is too low (Comparative Example 2), the thermal conductivity of the prepared polymer film is also poor and the thermal conductivity is also low; if the content of magnetic material-polymer modified carbon nanocomposite material in the polymer film is too high (Comparative Example 3), the prepared polymer film has a large number of surface defects and poor mechanical properties.

[0239] Compared with Example 1, if the magnetic field intensity in the preparation of the polymer film is low (Example 15), the thermal conductivity of the prepared polymer film is poor and the thermal conductivity is low; if the magnetic field intensity in the preparation of the polymer film is high (Example 16), the number of surface defects of the prepared polymer film is large and the mechanical properties are poor; if the polymer film is not prepared under the action of a magnetic field (Example 17), the thermal conductivity of the prepared polymer film is poor and the thermal conductivity is low.

[0240] Compared with Example 1, if magnetic materials, polymers and carbon nanomaterials are directly used as components for preparing the polymer film, and the magnetic materials and polymers are not grafted onto the carbon nanomaterials (Comparative Example 4), the thermal conductivity of the prepared polymer film is poor and the thermal conductivity is low; if the carbon nanocomposite material modified by the magnetic material is used as the component for preparing the polymer film (Comparative Example 5), the number of surface defects of the prepared polymer film is large; if the polymer film does not contain magnetic materials, and the polymer-modified carbon nanocomposite material is used as the component for preparing the polymer film (Comparative Example 6), the thermal conductivity of the prepared polymer film is poor and the thermal conductivity is low.

[0241] From the above content, it can be seen that in this application, by using a magnetic material-polymer modified carbon nanocomposite material as a raw material for preparing a polymer film, and controlling the content of the magnetic material-polymer modified carbon nanocomposite material in the polymer film within a specific range, and at the same time adjusting the preparation method of the polymer film, the polymer film prepared under a specific magnetic field strength has good thermal conductivity, high mechanical strength, suitable surface roughness, and no defects on the surface of the polymer film.

[0242] The properties of the polymer films provided in the above application examples and comparative application examples were tested. The specific test methods are as follows. The test results are detailed in Table 2 below:

[0243] ① Number of hole defects per unit area of ​​composite current collector: The prepared composite current collector sample is placed in a surface quality detection system (micro-visual charge-coupled device CCD), its surface is scanned, and then the optical signal is converted into an electrical signal and transmitted to a computer to count the number of hole defects per unit area of ​​the composite current collector with a pore size less than 100 μm (it is generally required that the finished product cannot have holes larger than 100 μm).

[0244] ② Square resistance: Place the prepared composite current collector sample on the sample stage and use a four-probe square resistance meter to test the square resistance of the sample.

[0245] ③ The adhesion between the polymer film and the metal layer in the composite current collector: a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the composite current collector was adhered on the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the composite current collector. Then, a 1.3×10 5 N / m 2 , hot pressing at 120℃ for 10s, cooling to room temperature, cutting into 150mm×15mm strips, and finally fixing the ethylene acrylic acid copolymer film of the sample strip on the upper fixture of the tensile machine, and the rest on the lower fixture. After fixing, the two are peeled off at an angle of 180° and a speed of 100mm / min to test the peeling force, that is, the adhesion between the polymer film and the metal layer.

[0246] Table 2

[0247] It can be seen from the contents of the above table that in this application, a polymer membrane with excellent performance was prepared by designing the raw materials and preparation methods for the polymer membrane. The composite current collector prepared using the polymer membrane as the base membrane has no holes and a low square resistance. The bonding force between the polymer membrane and the metal layer is large, with a square resistance of 31 to 33 mΩ and a bonding force of 1.3 to 2.5 N / cm.

[0248] Compared with Application Example 1, if the polymer film does not contain magnetic material-polymer modified carbon nanocomposite material, the composite current collector prepared from the polymer film has a larger number of holes per unit area, a larger square resistance, and a lower bonding force between the polymer film and the metal layer (Comparative Application Example 1); if the content of magnetic material-polymer modified carbon nanocomposite material in the polymer film is too low, the composite current collector prepared from the polymer film has a larger number of holes per unit area, a larger square resistance, and a lower bonding force between the polymer film and the metal layer (Comparative Application Example 2); if the content of magnetic material-polymer modified carbon nanocomposite material in the polymer film is too high, the bonding force between the polymer film and the metal layer in the composite current collector prepared from the polymer film is lower (Comparative Application Example 3).

[0249] Compared with Application Example 1, if the magnetic field intensity in the preparation of the polymer film is low, the number of holes per unit area of ​​the composite current collector prepared from the polymer film is large, the square resistance is large, and the bonding force between the polymer film and the metal layer is low (Application Example 15); if the magnetic field intensity in the preparation of the polymer film is high, the bonding force between the polymer film and the metal layer in the composite current collector prepared from the polymer film is low (Application Example 16); if the polymer film is not prepared under the action of a magnetic field, the number of holes per unit area of ​​the composite current collector prepared from the polymer film is large, and the square resistance is large (Application Example 17).

[0250] Compared with Application Example 1, if magnetic materials, polymers and carbon nanomaterials are directly used as components for preparing polymer films, the magnetic materials and polymers are not grafted onto the carbon nanomaterials, and the composite current collector prepared from the polymer film has a larger number of pores per unit area, a larger square resistance, and a lower adhesion between the polymer film and the metal layer (Comparative Application Example 4); if a carbon nanocomposite material modified by a magnetic material is used as a component for preparing a polymer film, the adhesion between the polymer film and the metal layer in the composite current collector prepared from the polymer film is lower (Comparative Application Example 5); if the polymer film does not contain magnetic materials, and a polymer-modified carbon nanocomposite material is used as a component for preparing a polymer film, the composite current collector prepared from the polymer film has a larger number of pores per unit area and a larger square resistance (Comparative Application Example 6).

[0251] In summary, in this application, a polymer membrane with excellent performance was prepared by designing the raw materials and preparation methods for the polymer membrane. The composite current collector prepared using the polymer membrane as the base membrane has no holes, low square resistance, and strong adhesion between the polymer membrane and the metal layer.

[0252] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed process flow of the present application, the present application is not limited to the above-mentioned detailed process flow, which does not mean that the present application must rely on the above-mentioned detailed process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A polymer film, comprising the following components in percentage by weight: 90-99.9% of a main polymer and 0.1-10% of a magnetic material-polymer modified carbon nanocomposite material; The raw materials for preparing the magnetic material-polymer modified carbon nanocomposite material include the following components: carbon nanomaterial, polymer and magnetic material precursor; The mass ratio of the carbon nanomaterial, the polymer and the magnetic material precursor is (2-5): (70-200): (40-85); The magnetic material precursor includes any one of an iron source, a neodymium source, a boron source, an aluminum source, a nickel source, a cobalt source, a chromium source, and a samarium source, or a combination of at least two thereof; The magnetic material-polymer modified carbon nanocomposite material is prepared by the following method, which comprises the following steps: (S1) preparing carbon oxide nanomaterials; (S2) after uniformly mixing the oxidized carbon nanomaterial and the solvent A, adding a weakly alkaline substance and a magnetic material precursor thereto, uniformly mixing, and reacting to obtain a carbon nanomaterial modified with a magnetic material; (S3) dispersing the carbon nanomaterial modified by the magnetic material in solvent B, acidifying it, and then adding a polymer thereto to react to obtain the magnetic material-polymer modified carbon nanocomposite material; The solvent A comprises an alcohol solvent; The solvent B is selected from any one of water, ether or ethanol, or a combination of at least two thereof; The weak alkaline substance in step (S2) includes any one of sodium acrylate, sodium acetate, sodium citrate, sodium tartrate or sodium benzoate, or a combination of at least two thereof.

2. The polymer film according to claim 1, wherein The polymer in the magnetic material-polymer modified carbon nanocomposite material is selected from any one of polyvinyl alcohol, polyethylene glycol, polyacrylic acid or polysiloxane, or a combination of at least two thereof.

3. The polymer film according to claim 1 or 2, wherein The carbon nanomaterial in the magnetic material-polymer modified carbon nanocomposite material is selected from any one of graphene, carbon nanotube, carbon nanofiber or nanodiamond or a combination of at least two thereof.

4. The polymer film according to any one of claims 1 to 3, wherein The magnetic material in the magnetic material-polymer modified carbon nanocomposite material is selected from any one of ferroferric oxide, ferrous oxide, neodymium iron boron, aluminum nickel cobalt, iron chromium cobalt or samarium cobalt, or a combination of at least two thereof.

5. The polymer film according to any one of claims 1 to 4, wherein The main polymer is selected from any one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene oxide, polystyrene or polyimide, or a combination of at least two thereof. 6 . The polymer film according to claim 1 , wherein the thickness of the polymer film is ≥ 1 μm.

7. A method for preparing a polymer film according to any one of claims 1 to 6, wherein: The preparation method comprises the following steps: (1) mixing a main polymer and a magnetic material-polymer modified carbon nanocomposite material, melting, filtering, and extruding to obtain a molten material; (2) casting the molten material obtained in step (1) onto a casting roll, cooling and forming the molten material, and performing longitudinal stretching, transverse stretching, and heat treatment to obtain the polymer film; Step (1) and step (2) are both performed in the presence of a magnetic field; The direction of the magnetic field is parallel to the thickness direction of the polymer film.

8. The preparation method according to claim 7, wherein: The intensity of the magnetic field is 0.1-2.0T.

9. A composite current collector, comprising a metal layer and a polymer film layer; the polymer film layer is the polymer film according to any one of claims 1 to 6. 10 . A battery comprising the composite current collector according to claim 9 .

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