Polyvinylidene fluoride-based ferroelectric polymer films, methods of making and use thereof

Abstract

The application relates to the field of polymer films, and discloses a polyvinylidene fluoride-based ferroelectric polymer film and a preparation method and application thereof. The method comprises the following steps: (1) mixing modified carbon nanotubes with 1,3-dioxolane to obtain a mixed solution a; (2) mixing a polyvinylidene fluoride-based ferroelectric polymer with 1,3-dioxolane to obtain a mixed solution b; (3) mixing the mixed solution a and the mixed solution b to obtain a mixed solution c, and performing spin coating and heat treatment on the mixed solution c in sequence to obtain a film; and (4) performing hot pressing treatment on the film obtained in the step (3), and then stretching. The method disclosed by the application uses a more green solvent which is small in toxicity and more environmentally-friendly, has strong process operability, is easy to be industrialized, and the prepared polyvinylidene fluoride-based ferroelectric polymer film has excellent electrical properties and physical mechanical properties, and can be very well applied to thin film capacitors.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer films, in particular to a polyvinylidene fluoride-based ferroelectric polymer film and a preparation method and application thereof. BACKGROUND

[0002] With the increasing demand for energy and the rapid consumption of fossil fuels, it has become increasingly urgent to improve energy use efficiency, and both the industry and academia are actively seeking new energy storage methods. Capacitors, as a new generation of energy storage devices, have been widely used in electric vehicles, intelligent equipment, medicine and other industries due to their fast energy release speed, high reliability, good flexibility and cycle stability. At present, the ferroelectric dielectric material for energy storage is mainly based on barium titanate ceramics. This material has high dielectric constant, good thermal stability and rigidity, and strong energy storage capacity. However, its high density and dielectric loss, brittle material and complex processing technology limit its large-scale application. In contrast, polyvinylidene fluoride and its copolymers, as the dielectric layer of thin film capacitors, have the advantages of good flexibility, light weight, and easy processing into complex shaped devices. These unique properties have made them applied to many high-tech fields. However, single piezoelectric polymer or piezoelectric ceramic materials cannot meet the growing technical requirements, so the preparation and research of new ferroelectric polymer films containing nano fillers have become the focus of recent research.

[0003] For nano-ferroelectric polymer composites, the crystal form of the ferroelectric polymer is a key factor determining the ferroelectric response. The formation and content of the beta crystal form are not only related to the chemical structure of the polymer itself, but also have important relevance to the preparation and processing technology of the film material. At present, most researchers use melt blending to form films or solution blending to cast films. The melt hot pressing method is mainly a simple mechanical blending without strong shearing action, which cannot completely solve the problem of nanotube agglomeration. The use of mixers and extruders for extrusion processing causes the destruction of carbon nanotube structures and polymer molecular chains at high temperature and high shear, and the process control is complex. Solution casting film can obtain a polymer film with high beta content by controlling the evaporation rate of the solvent, but the polymer film has high porosity, is easy to break, and is highly brittle, which seriously affects the electrical and mechanical properties.

[0004] In addition, the solution blending method for preparing polymer films usually uses toxic DMF or DMSO solvents, which poses a great safety hazard to the health of the staff preparing the film. SUMMARY

[0005] The purpose of the present application is to overcome the problems of the prior art, such as the need to further improve the performance of polyvinylidene fluoride-based ferroelectric polymer films and the toxicity of organic solvents used, and to provide a polyvinylidene fluoride-based ferroelectric polymer film and a preparation method and application thereof.

[0006] The polyvinylidene fluoride-based ferroelectric polymer film material prepared in the present research is dissolved using an environmentally friendly solvent, functionalized carbon nanotubes are added to the polyvinylidene fluoride copolymer by a solution method, and a polymer film is prepared by a spin coating method. The polymer film is processed by heat pressing and stretching to control the formation of the polar crystal β phase. The surface functionalization of the carbon nanotubes promotes the interface interaction between the matrix and the carbon nanotubes, solves the problem of agglomeration, and the carbon nanotubes act as nucleating agents to induce and promote the formation of the polar β crystal phase during the heat pressing and stretching process, so that the polymer film has good mechanical strength and electrical properties.

[0007] To achieve the above-mentioned purpose, in one aspect, the present application provides a preparation method of a polyvinylidene fluoride-based ferroelectric polymer film, which comprises the following steps:

[0008] (1) mixing modified carbon nanotubes and 1,3-dioxolane to obtain a mixed solution a;

[0009] (2) mixing a polyvinylidene fluoride-based ferroelectric polymer and 1,3-dioxolane to obtain a mixed solution b;

[0010] (3) mixing the mixed solution a and the mixed solution b to obtain a mixed solution c, and sequentially performing spin coating and heat treatment on the mixed solution c to obtain a thin film;

[0011] (4) performing heat pressing treatment and stretching on the thin film obtained in step (3);

[0012] The polyvinylidene fluoride-based ferroelectric polymer is selected from one or two or more of polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer and polyvinylidene fluoride-hexafluoropropylene copolymer;

[0013] The proportion of the modified carbon nanotubes is 2-10 parts by weight based on the total weight of the polyvinylidene fluoride-based ferroelectric polymer and the modified carbon nanotubes.

[0014] Preferably, the modified carbon nanotubes are selected from one or two or more of hydroxylated modified carbon nanotubes, carboxylated modified carbon nanotubes and aminated modified carbon nanotubes.

[0015] Preferably, the modified carbon nanotubes have an outer diameter of 1-5 nm and a length of 5-10 um.

[0016] Preferably, the heat pressing treatment has a temperature of 100-150℃, a pressure of 80-150 MPa and a time of 3-15 minutes.

[0017] Preferably, the stretching has a temperature of 60-150℃.

[0018] Preferably, the stretching ratio of the stretching is 1-8.

[0019] Preferably, in step (3), the conditions of the heat treatment include: the temperature of the heat treatment is 50-120℃, and the time of the heat treatment is 4-16 hours.

[0020] Preferably, the rotation speed of the spin coating is 800-2500 rpm.

[0021] The second aspect of the present application provides a polyvinylidene fluoride-based ferroelectric polymer film obtained by the above preparation method.

[0022] The third aspect of the present application can also provide an application of the polyvinylidene fluoride-based ferroelectric polymer film in a thin film capacitor.

[0023] The beneficial effects of the present application are:

[0024] (1) The present application adds carbon nanotubes with surface functionalization in the polyvinylidene fluoride ferroelectric polymer. Carboxyl, hydroxyl, or amino groups will interact with carbon-hydrogen groups at the interface, not only reducing filler agglomeration, but also improving the interfacial strength between the nanofiller and the polymer matrix, inducing the transition of α to β crystal conformation. Moreover, the carbon nanotubes are uniformly distributed, which induces the positive arrangement of the polymer matrix dipole during the subsequent stretching process; it also improves heat dissipation and quickly releases the excess heat generated by the loss tangent, thereby reducing the dielectric loss while improving the piezoelectric performance of the ferroelectric polymer film material without losing mechanical strength.

[0025] (2) The method of the present application does not use solvents commonly used in solution blending methods, such as DMF or DMSO, which are toxic solvents. Instead, a more environmentally friendly green solvent, 1,3-dioxolane, is used. The solvent used is less toxic and safer, and can quickly dissolve the polyvinylidene fluoride-based ferroelectric polymer at the same time. The boiling point of the solvent is low, and the evaporation rate is controllable, which can avoid more holes in the finally prepared ferroelectric polymer film, which is beneficial to improve the mechanical properties of the prepared ferroelectric polymer film, and also conducive to the generation of β crystal form in the ferroelectric polymer film;

[0026] (3) The heat pressing treatment of the spin-coated polyvinylidene fluoride-based ferroelectric polymer film in the method of the present application helps to reduce the hole defects of the spin-coated polyvinylidene fluoride-based ferroelectric polymer film, improve the density of the polyvinylidene fluoride-based ferroelectric polymer film, and make the prepared polyvinylidene fluoride-based ferroelectric polymer film better applied in thin film capacitors. At the same time, the processing technology of heat pressing treatment in the method of the present application can further promote the formation of β crystal form in the ferroelectric polymer film. Through this preparation process, the polyvinylidene fluoride-based ferroelectric polymer film has excellent physical and mechanical properties and electrical properties at the same time;

[0027] (4) The method further comprises stretching the polymer film after the hot-pressing treatment, which promotes the oriented arrangement and accumulation of the dipoles in the ferroelectric polymer film, so that the piezoelectric performance, dielectric constant, energy storage density and dielectric strength of the ferroelectric polymer film are greatly improved;

[0028] (5) The method uses a chemically modified polyvinylidene fluoride-based ferroelectric polymer as the raw material to prepare the ferroelectric polymer film, and due to the presence of structural units such as trifluoroethylene, tetrafluoroethylene or hexafluoropropylene in the raw material, it is easier to generate the β crystal form during the preparation of the polymer film. The content of the β crystal form in the polyvinylidene fluoride-based ferroelectric polymer film obtained during the subsequent hot-pressing and stretching preparation process is higher, thereby ensuring the excellent electrical performance of the polymer film.

[0029] (6) The method has simple preparation process, no pollution of toxic reagents in the preparation process, and is very suitable for industrialization and has great industrial value. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0031] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood to include values approximately near these ranges and values within these ranges. For ranges with endpoints, the endpoints are included in the range. For ranges without endpoints, the range extends to the endpoints of the nearest lower and upper ranges. For ranges with endpoints, the endpoints are included in the range. For ranges without endpoints, the range extends to the endpoints of the nearest lower and upper ranges. The endpoints of the ranges and the individual values are combinable to create one or more new ranges or points. These new ranges are to be considered disclosed within this document.

[0032] In this document, the polyvinylidene fluoride-based ferroelectric polymer refers to a copolymer containing a polyvinylidene fluoride structural unit in the material, which is selected from one or more than two of polyvinylidene fluoride-tetrafluoroethylene copolymer and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0033] In this document, the modified carbon nanotube refers to the surface of the carbon nanotube being modified by a chemical method, so that corresponding functional groups are generated on the surface of the carbon nanotube. The hydroxylated modified carbon nanotube refers to the surface of the carbon nanotube generating hydroxyl groups after modification. The carboxylated modified carbon nanotube refers to the surface of the carbon nanotube generating carboxyl groups after modification. The aminated modified carbon nanotube refers to the surface of the carbon nanotube generating amino groups after modification.

[0034] In this document, the outer diameter of the modified carbon nanotube refers to the diameter of the outermost layer of the modified carbon nanotube.

[0035] The application provides a preparation method of a polyvinylidene fluoride-based ferroelectric polymer film, and the preparation method comprises the following steps:

[0036] (1) mixing modified carbon nanotubes and 1,3-dioxolane to obtain a mixed solution a;

[0037] (2) mixing polyvinylidene fluoride-based ferroelectric polymer and 1,3-dioxolane to obtain a mixed solution b;

[0038] (3) mixing the mixed solution a and the mixed solution b to obtain a mixed solution c, and sequentially performing spin coating and heat treatment on the mixed solution c to obtain a film;

[0039] (4) performing heat pressing treatment and stretching on the film obtained in the step (3).

[0040] In the method, a specific solvent 1,3-dioxolane is used as a solvent, the solvent is less toxic and safer, and the solvent 1,3-dioxolane has higher solubility for the polyvinylidene fluoride-based ferroelectric polymer, the boiling point of the solvent is low, the evaporation rate of the solvent after spin coating is controllable, and more holes in the finally prepared polyvinylidene fluoride-based ferroelectric polymer film are avoided, which is beneficial to the improvement of the mechanical properties of the polyvinylidene fluoride-based ferroelectric polymer film and the generation of the beta crystal form.

[0041] In the method, the addition amount of the modified carbon nanotubes needs to be controlled, too much of the modified carbon nanotubes will increase the electric conduction loss of the polymer film and reduce the breakdown strength, which will affect the subsequent application of the material, and will also cause the modified carbon nanotubes to be unable to uniformly disperse in the ferroelectric polymer, in order to make the prepared polyvinylidene fluoride-based ferroelectric polymer film have better performance, in the application, the proportion of the modified carbon nanotubes is 2-10 parts by weight, based on the total weight of the polyvinylidene fluoride-based ferroelectric polymer and the modified carbon nanotubes. Specifically, the proportion of the modified carbon nanotubes can be 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight or 10 parts by weight.

[0042] In a preferred embodiment, the proportion of the modified carbon nanotubes is 2-7 parts by weight, further preferably 5-6 parts by weight, and more preferably 5 parts by weight, based on the total weight of the polyvinylidene fluoride-based ferroelectric polymer and the modified carbon nanotubes.

[0043] In the method, the modified carbon nanotubes are selected from one or two or more of hydroxylated modified carbon nanotubes, carboxylated modified carbon nanotubes and aminated modified carbon nanotubes.

[0044] In a preferred embodiment, the modified carbon nanotube is selected from one of a hydroxylated modified carbon nanotube, a carboxylated modified carbon nanotube and an aminated modified carbon nanotube.

[0045] In a more preferred embodiment, the modified carbon nanotube is a hydroxylated modified carbon nanotube.

[0046] In the method of the present application, in order to improve the dispersibility of the modified carbon nanotube in the polymer matrix, the outer diameter of the modified carbon nanotube is limited to 1-5 nm and the length of the modified carbon nanotube is limited to 5-10 um.

[0047] In the method of the present application, the nanofiller of the surface-modified carbon nanotube is added to the vinylidene fluoride ferroelectric polymer. The carboxyl, hydroxyl or amino groups on the surface of the modified carbon nanotube can interact with the carbon-hydrogen groups at the interface, which not only reduces the agglomeration of the filler, but also improves the interface strength between the nanofiller and the polymer matrix, and induces the transition of the α crystal structure to the β crystal structure. Moreover, the modified carbon nanotube is more uniformly distributed in the polymer matrix, which can induce the positive arrangement of the polymer matrix dipole during the subsequent stretching process. In addition, the modified carbon nanotube can improve the heat dissipation and the rapid release of the excess heat generated by the loss tangent, thereby reducing the dielectric loss and improving the piezoelectric performance of the ferroelectric polymer film without sacrificing the mechanical strength.

[0048] In a specific embodiment, the polyvinylidene fluoride-based ferroelectric polymer is selected from one or more of a polyvinylidene fluoride-trifluoroethylene copolymer, a polyvinylidene fluoride-tetrafluoroethylene copolymer and a polyvinylidene fluoride-hexafluoropropylene copolymer.

[0049] In a preferred embodiment, the polyvinylidene fluoride-based ferroelectric polymer is selected from one of a polyvinylidene fluoride-trifluoroethylene copolymer, a polyvinylidene fluoride-tetrafluoroethylene copolymer and a polyvinylidene fluoride-hexafluoropropylene copolymer.

[0050] In a further preferred embodiment, the polyvinylidene fluoride-based ferroelectric polymer is selected from a polyvinylidene fluoride-trifluoroethylene copolymer or a polyvinylidene fluoride-tetrafluoroethylene copolymer.

[0051] In a more preferred embodiment, the polyvinylidene fluoride-based ferroelectric polymer is a polyvinylidene fluoride-trifluoroethylene copolymer.

[0052] In a specific embodiment, the polyvinylidene fluoride-trifluoroethylene copolymer has a molecular weight of 150-550, preferably 200-500, and further preferably 280-350; the polyvinylidene fluoride-tetrafluoroethylene copolymer has a molecular weight of 150-600, preferably 200-500, and further preferably 300-400; and the polyvinylidene fluoride-hexafluoropropylene copolymer has a molecular weight of 200-600, preferably 250-500, and further preferably 300-400.

[0053] In the method of the present application, the polyvinylidene fluoride-trifluoroethylene copolymer contains vinylidene fluoride and trifluoroethylene structural units, and the content of the trifluoroethylene structural units is 10-30%, preferably 12-28%, and further preferably 18-25%, based on the weight of the polyvinylidene fluoride-trifluoroethylene copolymer.

[0054] The polyvinylidene fluoride-tetrafluoroethylene copolymer contains vinylidene fluoride and tetrafluoroethylene structural units, and the content of the tetrafluoroethylene structural units is 7-30%, preferably 13-25%, and further preferably 18-23%, based on the weight of the polyvinylidene fluoride-tetrafluoroethylene copolymer.

[0055] The polyvinylidene fluoride-hexafluoropropylene copolymer contains vinylidene fluoride and hexafluoropropylene structural units, and the content of the hexafluoropropylene structural units is 5-25%, preferably 8-23%, and further preferably 10-20%, based on the weight of the polyvinylidene fluoride-hexafluoropropylene copolymer.

[0056] In the method of the present application, the modified polyvinylidene fluoride-based ferroelectric polymer is used as the raw material for preparing the polymer film. Due to the presence of the trifluoroethylene, tetrafluoroethylene or hexafluoropropylene structural units in the polymer raw material, it is easier to generate the β crystal form during the preparation of the polymer film, thereby improving the electrical properties of the polyvinylidene fluoride-based ferroelectric polymer film prepared.

[0057] In the method of the present application, the modified polyvinylidene fluoride-based ferroelectric polymer is used as the raw material for preparing the polymer film, and the modified carbon nanotube is added as the nanofiller. By controlling the amounts of the two, the content of the β crystal form in the polyvinylidene fluoride-based ferroelectric polymer film prepared is higher, and thus the electrical properties of the polyvinylidene fluoride-based ferroelectric polymer film obtained are more superior.

[0058] In the method of the present application, the modified carbon nanotube is a commercially available product, and the polyvinylidene fluoride-based ferroelectric polymer can be a conventional commercially available product or a product prepared according to a conventional method, and the source of the raw material is not limited.

[0059] In a specific embodiment, the mixed solution a obtained by mixing the modified carbon nanotubes and 1,3-dioxolane is a suspension, and the modified carbon nanotubes are uniformly dispersed in the solvent 1,3-dioxolane.

[0060] In a specific embodiment, after mixing the polyvinylidene fluoride-based ferroelectric polymer and 1,3-dioxolane, the solution is uniformly mixed by magnetic stirring to obtain the mixed solution b, the stirring temperature is 30-50℃, and the stirring time is 6-10h.

[0061] In a specific embodiment, after mixing the mixed solution a and the mixed solution b, the solution is uniformly mixed by magnetic stirring to obtain the mixed solution c, the stirring temperature is 30-50℃, and the stirring time is 6-10h.

[0062] In the method described in the present application, in step (3), the product after spin coating is subjected to heat treatment to remove the solvent 1,3-dioxolane, and the heat treatment conditions include: the heat treatment temperature is 50-120℃, and the heat treatment time is 4-16h. Specifically, the heat treatment temperature can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃ or 120℃; and the heat treatment time can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or 16h.

[0063] In a preferred embodiment, in step (3), the heat treatment conditions include: the heat treatment temperature is 60-100℃, and the heat treatment time is 8-12h.

[0064] In a preferred embodiment, in step (3), in order to obtain the required polyvinylidene fluoride-based ferroelectric polymer film, the mixed solution c is first divided into several groups of mixed solutions with the same volume, and then the divided mixed solutions are sequentially subjected to several times of spin coating-heat treatment with the same spin coating and heat treatment operations and process parameters to obtain several groups of polyvinylidene fluoride-based ferroelectric polymer films with the same properties, and then the several groups of polyvinylidene fluoride-based ferroelectric polymer films are stacked and subjected to heat pressing treatment and then stretched.

[0065] In a further preferred embodiment, the number of spin coating-heat treatment is 8-10 times, and specifically, the number of spin coating-heat treatment can be 8 times, 9 times or 10 times.

[0066] In the method described in the present application, the rotation speed during spin coating is 800-2500rpm, preferably 1500-2000rpm. Specifically, it can be 800rpm, 1000rpm, 1500rpm, 1600rpm, 1700rpm, 1800rpm, 1900rpm, 2000rpm or 2500rpm.

[0067] In specific embodiments, the hot-pressing treatment is performed at a temperature of 100-150℃, a pressure of 80-150MPa, and for a time of 3-15min. Specifically, the hot-pressing treatment can be performed at a temperature of 100℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, or 150℃; a pressure of 80MPa, 90MPa, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, or 150MPa; and for a time of 3min, 5min, 8min, 10min, 11min, 12min, 13min, 14min, or 15min.

[0068] In preferred embodiments, the hot-pressing treatment is performed at a temperature of 115-135℃, a pressure of 100-120MPa, and for a time of 5-10min.

[0069] In specific embodiments, the polyvinylidene fluoride-based ferroelectric polymer film after spin coating can be subjected to hot-pressing treatment using a high-temperature vulcanizing machine, and cooling treatment is further required for demolding after the hot-pressing treatment.

[0070] In the method of the present application, the hot-pressing treatment of the polyvinylidene fluoride-based ferroelectric polymer film after spin coating can reduce the number and size of pores in the obtained polyvinylidene fluoride-based ferroelectric polymer film, improve the density of the polyvinylidene fluoride-based ferroelectric polymer film, and promote the formation of β crystal in the ferroelectric polymer film, so that the prepared polymer film is rich in more β crystal, thereby improving the electrical properties of the polymer film, and the polyvinylidene fluoride-based ferroelectric polymer film has excellent physical and mechanical properties and electrical properties.

[0071] In the method of the present application, the polyvinylidene fluoride-based ferroelectric polymer film after hot-pressing treatment is also subjected to stretching treatment, and the stretching can also promote the conversion of α crystal to β crystal in the film, thereby improving the electrical properties of the polyvinylidene fluoride-based ferroelectric polymer film.

[0072] In specific embodiments, the stretching is performed at a temperature of 60-150℃, preferably 80-120℃. Specifically, the stretching can be performed at a temperature of 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, or 150℃.

[0073] In specific embodiments, the stretching is performed at a stretching ratio of 1-8, preferably 1-4. Specifically, the stretching can be performed at a ratio of 1, 2, 3, 4, 5, 6, 7, or 8.

[0074] In the method, the stretching is longitudinal stretching.

[0075] In the method, by selecting a suitable polyvinylidene fluoride-based ferroelectric polymer as a raw material, adding modified carbon nanotubes as nanofillers to improve the ferroelectric and piezoelectric properties of the polyvinylidene fluoride-based ferroelectric polymer film, and by heat pressing and stretching the spin-coated film, the content of the beta crystal form in the polyvinylidene fluoride-based ferroelectric polymer film is further improved by selecting a suitable raw material and an additive and matching the preparation process, so as to further improve the electrical properties of the material, and at the same time, the physical defects of the polymer film caused by internal pores are reduced, so that the prepared polymer film is more dense and has good physical and mechanical properties.

[0076] The application further provides a polyvinylidene fluoride-based ferroelectric polymer film prepared by the preparation method.

[0077] In the method, the thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.1-0.3 mm.

[0078] The application further provides an application of the polyvinylidene fluoride-based ferroelectric polymer film in a thin film capacitor.

[0079] The application will be described in detail below through examples, but the protection scope of the application is not limited thereto.

[0080] In the following examples and comparative examples, the carboxylated modified carbon nanotubes, the hydroxylated modified carbon nanotubes and the aminated modified carbon nanotubes are purchased from Shanghai Aladdin Biochem Technology Co., Ltd., the butanone is purchased from Shandong Fengcang Chemical Co., Ltd., and the 1,3-dioxolane is purchased from Shanghai Aladdin Biochem Technology Co., Ltd.

[0081] Example 1

[0082] (1) 0.5 g of carboxylated modified carbon nanotubes (with an outer diameter of 1-5 nm and a length of 5-10 um) and 50 g of 1,3-dioxolane were weighed and mixed, and after ultrasonic dispersion, a mixed solution a was obtained;

[0083] (2) 9.5 g of polyvinylidene fluoride-trifluoroethylene copolymer (with a molecular weight of 320,000 and a content of trifluoroethylene structural units of 18%) and 100 g of 1,3-dioxolane were weighed and mixed, and then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45 DEG C under magnetic stirring for 8 h to obtain a mixed solution b;

[0084] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45℃ for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 8 groups, then using a spin coater to spin coat the 8 groups of equally divided solutions on a quartz substrate at a rotation speed of 1500rpm, then placing the spin-coated product on a hot table for heat treatment, the heat treatment temperature being 60℃ and the heat treatment time being 12h, and then cooling and demolding after the heat treatment to obtain 8 pieces of film;

[0085] (4) stacking the 8 pieces of film obtained in step (3) and then performing hot pressing treatment on a high-temperature vulcanizing machine, the hot pressing treatment conditions being a temperature of 125℃, a pressure of 100MPa and a time of 10min, then cooling and demolding to obtain a hot-pressed film, and then placing the hot-pressed film on a high-temperature stretching device for uniaxial stretching, the stretching temperature being 80℃ and the stretching ratio being 4, and finally obtaining a polyvinylidene fluoride-based ferroelectric polymer film;

[0086] The total weight of the polyvinylidene fluoride-trifluoroethylene copolymer and the carboxyl-modified carbon nanotubes is 100 parts by weight, and the carboxyl-modified carbon nanotubes account for 5 parts by weight. The thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.3mm.

[0087] Example 2

[0088] (1) 0.2 grams of hydroxyl-modified carbon nanotubes (outer diameter of 1-5nm, length of 5-10um) were mixed with 50 grams of 1,3-dioxolane, and after ultrasonic dispersion, a mixed solution a was obtained;

[0089] (2) 9.8 grams of polyvinylidene fluoride-tetrafluoroethylene copolymer (molecular weight of 350,000, content of tetrafluoroethylene structural unit of 20%) were mixed with 100 grams of 1,3-dioxolane, and then magnetically stirred at a temperature of 45℃ for 8h to fully dissolve the polyvinylidene fluoride-based ferroelectric polymer in 1,3-dioxolane to obtain a mixed solution b;

[0090] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45℃ for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 10 groups, then using a spin coater to spin coat the 10 groups of equally divided solutions on a quartz substrate at a rotation speed of 1800rpm, then placing the spin-coated product on a hot table for heat treatment, the heat treatment temperature being 80℃ and the heat treatment time being 9h, and then cooling and demolding after the heat treatment to obtain 10 pieces of film;

[0091] (4) stacking the 10 films obtained in step (3) and performing hot-pressing treatment on a high-temperature vulcanizing machine, the hot-pressing treatment being performed at 135℃, the pressure of the hot-pressing treatment being 120 MPa, the time of the hot-pressing treatment being 5 min, then cooling and demolding to obtain the hot-pressed film, and then placing the hot-pressed film on a high-temperature stretching device to perform uniaxial stretching, the stretching temperature being 100℃, the stretching ratio being 1, and then obtaining the polyvinylidene fluoride-based ferroelectric polymer film after the stretching is completed;

[0092] The total weight of the polyvinylidene fluoride-tetrafluoroethylene copolymer and the hydroxyl-modified carbon nanotubes is 100 parts by weight, and the proportion of the hydroxyl-modified carbon nanotubes is 2 parts by weight. The thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.3 mm.

[0093] Example 3

[0094] (1) 0.7 grams of amino-modified carbon nanotubes (outer diameter of 1-5 nm, length of 5-10 um) were mixed with 50 grams of 1,3-dioxolane, and an ultrasonic dispersion was obtained to obtain a mixed solution a;

[0095] (2) 9.3 grams of polyvinylidene fluoride-hexafluoropropylene copolymer (molecular weight of 300,000, content of hexafluoropropylene structural unit of 15%) were mixed with 100 grams of 1,3-dioxolane, and then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45℃ for 8h by magnetic stirring to obtain a mixed solution b;

[0096] (3) The mixed solution a and the mixed solution b were mixed, and then the solution was uniformly mixed by magnetic stirring at a temperature of 45℃ for 8h to obtain a mixed solution c. The mixed solution c was filtered and equally divided into 9 groups, and then the 9 groups of equally divided solutions were spin-coated on a quartz substrate using a spin coater at a speed of 2000 rpm. Then the spin-coated product was placed on a hot stage for heat treatment, the heat treatment being performed at a temperature of 100℃ for 8h, and then the heat treatment was cooled and demolded to obtain 9 films;

[0097] (4) The 9 films obtained in step (3) were stacked and hot-pressed on a high-temperature vulcanizing machine, the hot-pressing treatment being performed at 120℃, the pressure of the hot-pressing treatment being 110 MPa, the time of the hot-pressing treatment being 8 min, then cooling and demolding to obtain the hot-pressed film, and then placing the hot-pressed film on a high-temperature stretching device to perform uniaxial stretching, the stretching temperature being 90℃, the stretching ratio being 2, and then obtaining the polyvinylidene fluoride-based ferroelectric polymer film after the stretching is completed;

[0098] The total weight of the polyvinylidene fluoride-hexafluoropropylene copolymer and the amino-modified carbon nanotubes is 100 parts by weight, and the amino-modified carbon nanotubes account for 7 parts by weight; the thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.3 mm.

[0099] Example 4

[0100] (1) 0.3 grams of hydroxyl-modified carbon nanotubes (outer diameter of 1-5 nm, length of 5-10 um) were weighed and mixed with 50 grams of 1,3-dioxolane, and after ultrasonic dispersion, a mixed solution a was obtained;

[0101] (2) 9.7 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight of 320,000, content of trifluoroethylene structural unit of 18%) were weighed and mixed with 100 grams of 1,3-dioxolane, and then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45°C for 8h to obtain a mixed solution b;

[0102] (3) The mixed solution a and the mixed solution b were mixed, and then the solution was uniformly mixed at a temperature of 45°C for 8h to obtain a mixed solution c. The mixed solution c was filtered and equally divided into 8 groups, and then the 8 groups of equally divided solutions were spin-coated on a quartz substrate using a spin coater at a speed of 1800 rpm. Then the spin-coated product was placed on a hot stage for heat treatment at a temperature of 60°C for 12h, and then cooled and demolded to obtain 8 thin films;

[0103] (4) The 8 thin films obtained in step (3) were stacked and heat pressed on a high-temperature vulcanizing machine under the conditions of a temperature of 115°C, a pressure of 100 MPa, and a time of 10 min, and then cooled and demolded to obtain a heat-pressed thin film. Then the heat-pressed thin film was placed on a high-temperature stretching device for uniaxial stretching at a temperature of 80°C and a stretching ratio of 4, and then cooled and demolded to obtain a polyvinylidene fluoride-based ferroelectric polymer film;

[0104] The total weight of the polyvinylidene fluoride-trifluoroethylene copolymer and the hydroxyl-modified carbon nanotubes is 100 parts by weight, and the hydroxyl-modified carbon nanotubes account for 3 parts by weight; the thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.3 mm.

[0105] Example 5

[0106] (1) 0.4 grams of carboxyl-modified carbon nanotubes (outer diameter of 1-5 nm, length of 5-10 um) were weighed and mixed with 50 grams of L1,3-dioxolane, and after ultrasonic dispersion, a mixed solution a was obtained;

[0107] (2) 9.6 g of polyvinylidene fluoride-tetrafluoroethylene copolymer (molecular weight 350,000, content of tetrafluoroethylene structural unit 20%) was weighed and mixed with 100 g of 1,3-dioxolane, and then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at 45°C under magnetic stirring for 8 h to obtain a mixed solution b;

[0108] (3) The mixed solution a and the mixed solution b were mixed, and then the solution was uniformly mixed at 45°C under magnetic stirring for 8 h to obtain a mixed solution c. The mixed solution c was filtered and then equally divided into 9 groups. The 9 groups of equally divided solutions were spin-coated on a quartz substrate using a spin coater at a speed of 1500 rpm. The spin-coated product was then placed on a hot stage for heat treatment at a temperature of 60°C for 12 h. After heat treatment, cooling and demolding were performed to obtain 9 films;

[0109] (4) The 9 films obtained in step (3) were stacked and heat pressed on a high-temperature vulcanizing machine under the conditions of 120°C, 100 MPa and 10 min. Cooling and demolding were then performed to obtain a heat-treated film. The heat-treated film was then placed on a high-temperature stretching device for uniaxial stretching at a temperature of 80°C and a stretching ratio of 4. Finally, a polyvinylidene fluoride-based ferroelectric polymer film was obtained.

[0110] The total weight of the polyvinylidene fluoride-tetrafluoroethylene copolymer and the carboxyl-modified carbon nanotubes was 100 parts by weight. The carboxyl-modified carbon nanotubes accounted for 4 parts by weight. The thickness of the polyvinylidene fluoride-based ferroelectric polymer film was 0.3 mm.

[0111] Example 6

[0112] (1) 0.6 g of carboxyl-modified carbon nanotubes (outer diameter 1-5 nm, length 5-10 um) was weighed and mixed with 50 g of L1,3-dioxolane. After ultrasonic dispersion, a mixed solution a was obtained.

[0113] (2) 9.4 g of polyvinylidene fluoride-hexafluoropropylene copolymer (molecular weight 300,000, content of hexafluoropropylene structural unit 15%) was weighed and mixed with 100 g of 1,3-dioxolane. Then, the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at 45°C under magnetic stirring for 8 h to obtain a mixed solution b.

[0114] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45℃ for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 10 groups, then using a spin coater to spin coat the 10 groups of equally divided solutions on a quartz substrate at a rotation speed of 1800rpm, then placing the spin-coated product on a hot table for heat treatment, the heat treatment temperature being 60℃ and the heat treatment time being 12h, and then cooling and demolding after the heat treatment to obtain 10 pieces of thin film;

[0115] (4) stacking the 10 pieces of thin film obtained in step (3) and then performing hot pressing treatment on a high-temperature vulcanizing machine, the hot pressing treatment conditions being a temperature of 120℃, a pressure of 100MPa and a time of 10min, then cooling and demolding to obtain a hot-pressed thin film, then placing the hot-pressed thin film on a high-temperature stretching device for uniaxial stretching, the stretching temperature being 80℃ and the stretching ratio being 4, and finally obtaining a polyvinylidene fluoride-based ferroelectric polymer film;

[0116] The total weight of the polyvinylidene hexafluoropropylene copolymer and the carboxyl-modified carbon nanotubes is 100 parts by weight, and the carboxyl-modified carbon nanotubes account for 6 parts by weight. The thickness of the polyvinylidene fluoride-based ferroelectric polymer film is 0.3mm.

[0117] Comparative Example 1

[0118] (1) 0.5 grams of carbon nanotubes (unmodified, outer diameter of 1-5nm, length of 5-10um) were mixed with 50 grams of L1,3-dioxolane, and after ultrasonic dispersion, a mixed solution a was obtained;

[0119] (2) 9.5 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight of 320,000, content of trifluoroethylene structural unit of 18%) were mixed with 100 grams of 1,3-dioxolane, and then magnetically stirred at a temperature of 45℃ for 8h to fully dissolve the polyvinylidene fluoride-based ferroelectric polymer in 1,3-dioxolane to obtain a mixed solution b;

[0120] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45℃ for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 10 groups, then using a spin coater to spin coat the 10 groups of equally divided solutions on a quartz substrate at a rotation speed of 1800rpm, then placing the spin-coated product on a hot table for heat treatment, the heat treatment temperature being 60℃ and the heat treatment time being 12h, and then cooling and demolding after the heat treatment to obtain 10 pieces of thin film;

[0121] (4) stacking the 8 pieces of the film obtained in step (3) and performing hot-pressing treatment on a high-temperature vulcanizing machine, the hot-pressing treatment being performed at a temperature of 125°C, a pressure of 100 MPa, and for a time of 10 min, and then cooling and demolding to obtain a hot-pressed film, and then placing the hot-pressed film on a high-temperature stretching device to perform uniaxial stretching at a temperature of 80°C and a stretching ratio of 4, to obtain a polymer film after the stretching is completed;

[0122] The total weight of the polyvinylidene fluoride-trifluoroethylene copolymer and the unmodified carbon nanotubes is 100 parts by weight, and the proportion of the unmodified carbon nanotubes is 5 parts by weight; the thickness of the polymer film is 0.3 mm.

[0123] Comparative Example 2

[0124] (1) 10 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight 320,000, content of trifluoroethylene structural unit 18%) and 100 grams of 1,3-dioxolane were mixed, and then the polyvinylidene fluoride ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45°C under magnetic stirring for 8 h to obtain a mixed solution b;

[0125] (2) The mixed solution b was filtered and then equally divided into 8 groups, and then the 8 groups of solutions were spin-coated on a quartz substrate using a spin coater at a speed of 1500 rpm, and then the spin-coated product was placed on a hot stage for heat treatment at a temperature of 60°C for a time of 12 h, and then cooled and demolded to obtain 8 pieces of film;

[0126] (3) The 8 pieces of film obtained in step (2) were stacked and then hot-pressed on a high-temperature vulcanizing machine, the hot-pressing treatment being performed at a temperature of 125°C, a pressure of 100 MPa, and for a time of 10 min, and then cooled and demolded to obtain a hot-pressed film, and then the hot-pressed film was placed on a high-temperature stretching device to perform uniaxial stretching at a temperature of 80°C and a stretching ratio of 4, to obtain a polymer film after the stretching was completed.

[0127] The thickness of the polymer film is 0.3 mm.

[0128] Comparative Example 3

[0129] (1) 1.1 grams of carboxyl-modified carbon nanotubes (outer diameter 1-5 nm, length 5-10 um) and 50 grams of L1,3-dioxolane were mixed and ultrasonically dispersed to obtain a mixed solution a;

[0130] (2) 8.9 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight of 320,000, content of trifluoroethylene structural unit of 18%) was weighed and mixed with 100 grams of 1,3-dioxolane, and then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45°C under magnetic stirring for 8 hours to obtain a mixed solution b;

[0131] (3) The mixed solution a and the mixed solution b were mixed, and then the solution was uniformly mixed at a temperature of 45°C under magnetic stirring for 8 hours to obtain a mixed solution c. The mixed solution c was filtered and equally divided into 8 groups. The equally divided 8 groups of solutions were spin-coated on a quartz substrate using a spin coater at a speed of 1500 rpm. Then the spin-coated product was placed on a hot stage for heat treatment at a temperature of 60°C for 12 hours. After heat treatment, cooling and demolding were performed to obtain 8 films;

[0132] (4) The 8 films obtained in step (3) were stacked and heat pressed by a high temperature vulcanizing machine. The heat pressing conditions were a temperature of 125°C, a pressure of 100 MPa, and a time of 10 minutes. Then cooling and demolding were performed to obtain a heat-pressed film. Then the heat-pressed film was placed on a high-temperature stretching device for unidirectional stretching at a temperature of 80°C with a stretching ratio of 4. After completion, a polymer film was obtained.

[0133] The total weight of the polyvinylidene fluoride-trifluoroethylene copolymer and the carboxyl-modified carbon nanotube was 100 parts by weight. The carboxyl-modified carbon nanotube accounted for 11 parts by weight. The thickness of the polymer film was 0.3 mm.

[0134] Comparative Example 4

[0135] (1) 0.5 grams of carboxyl-modified carbon nanotubes (outer diameter of 1-5 nm, length of 5-10 um) were weighed and mixed with 50 grams of 1,3-dioxolane. After ultrasonic dispersion, a mixed solution a was obtained.

[0136] (2) 9.5 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight of 320,000, content of trifluoroethylene structural unit of 18%) was weighed and mixed with 100 grams of 1,3-dioxolane. Then the polyvinylidene fluoride-based ferroelectric polymer was fully dissolved in 1,3-dioxolane at a temperature of 45°C under magnetic stirring for 8 hours to obtain a mixed solution b.

[0137] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45°C for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 8 groups, then using a spin coater to spin coat the 8 groups of equally divided solutions on a quartz substrate at a rotation speed of 1500 rpm, then placing the spin-coated product on a hot table for heat treatment at a temperature of 60°C for 12h, and then cooling and demolding after the heat treatment to obtain 8 pieces of thin film;

[0138] (4) stacking the 8 pieces of thin film obtained in step (3) and then performing hot pressing treatment by a high-temperature vulcanizing machine, the hot pressing treatment being performed at a temperature of 125°C, a pressure of 100 MPa, and for a time of 10 min, and then cooling and demolding to obtain a polymer film after the hot pressing treatment.

[0139] The thickness of the polymer film is 0.3 mm.

[0140] Comparative Example 5

[0141] (1) mixing 0.5 grams of carboxyl-modified carbon nanotubes (outer diameter of 1-5 nm, length of 5-10 um) with 50 grams of butanone, and then ultrasonic dispersion to obtain a mixed solution a;

[0142] (2) mixing 9.5 grams of polyvinylidene fluoride-trifluoroethylene copolymer (molecular weight of 320,000, content of trifluoroethylene structural unit of 18%) with 100 grams of butanone, and then magnetically stirring at a temperature of 45°C for 8h to fully dissolve the polyvinylidene fluoride-based ferroelectric polymer in 1,3-dioxolane to obtain a mixed solution b;

[0143] (3) mixing the mixed solution a and the mixed solution b, then magnetically stirring at a temperature of 45°C for 8h to mix the solution uniformly to obtain a mixed solution c, filtering the mixed solution c and then equally dividing the filtered solution into 8 groups, then using a spin coater to spin coat the 8 groups of equally divided solutions on a quartz substrate at a rotation speed of 1500 rpm, then placing the spin-coated product on a hot table for heat treatment at a temperature of 60°C for 12h, and then cooling and demolding after the heat treatment to obtain 8 pieces of thin film;

[0144] (4) stacking the 8 pieces of thin film obtained in step (3) and then performing hot pressing treatment by a high-temperature vulcanizing machine, the hot pressing treatment being performed at a temperature of 125°C, a pressure of 100 MPa, and for a time of 10 min, and then cooling and demolding to obtain a polymer film after the hot pressing treatment, then placing the polymer film after the heat treatment on a high-temperature stretching device for uniaxial stretching at a temperature of 80°C and a stretching ratio of 4, and then obtaining a polymer film after the stretching is completed;

[0145] The total weight of the polyvinylidene fluoride-trifluoroethylene copolymer and the carboxyl-modified carbon nanotube is 100 parts by weight, and the carboxyl-modified carbon nanotube accounts for 5 parts by weight; the thickness of the polymer film is 0.3 mm.

[0146] Test Example

[0147] Test Example 1

[0148] The electrical properties and physical and mechanical properties of the products obtained in Test Examples 1-6 and Comparative Examples 1-5 are shown in Table 1.

[0149] Tensile strength test: the test was performed according to the method described in GB / T 1040-2006 "Test method for tensile properties of plastics", and the test results are shown in Table 1;

[0150] Flexural modulus: the test was performed according to the method described in JB / T 6544-93 "Test method for tensile and flexural properties of plastics", and the test results are shown in Table 1;

[0151] Dielectric strength test: the test was performed according to the method described in standard GB / T 1408-2006 "Test method for electrical strength of insulating materials", and the test results are shown in Table 1;

[0152] Dielectric constant and dielectric loss test: the test was performed according to the method described in standard GB / T 1409-2006 "Recommended method for the determination of permittivity and dissipation factor of electrical insulating materials at power frequencies, audio frequencies and high frequencies (including meter wave length)", and the test results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] As can be seen from the results in Table 1, the polyvinylidene fluoride-based ferroelectric polymer film prepared by the method described in the present application has excellent electrical properties, the dielectric constant and dielectric strength are obviously improved, the dielectric loss does not increase obviously, and the mechanical properties are excellent, which shows that the polyvinylidene fluoride-based ferroelectric polymer film prepared by the present application can be well applied to thin film capacitors and has great industrial application prospects.

[0157] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed in the present application and fall within the protection scope of the present application.

Claims

1. A method for preparing a polyvinylidene fluoride-based ferroelectric polymer film, characterized by, The method comprises the following steps: (1) mixing modified carbon nanotubes with 1,3-dioxolane to obtain a mixed solution a; (2) mixing polyvinylidene fluoride-based ferroelectric polymer with 1,3-dioxolane to obtain a mixed solution b; (3) mixing the mixed solution a and the mixed solution b to obtain a mixed solution c, and then performing spin coating and heat treatment on the mixed solution c to obtain a thin film; (4) performing hot pressing treatment on the thin film obtained in step (3), and then performing stretching; The polyvinylidene fluoride-based ferroelectric polymer is selected from one or more of polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer and polyvinylidene fluoride-hexafluoropropylene copolymer; The total weight of the polyvinylidene fluoride-based ferroelectric polymer and the modified carbon nanotubes is 100 parts by weight, and the proportion of the modified carbon nanotubes is 2-10 parts by weight; The modified carbon nanotubes are selected from one or more of hydroxylated modified carbon nanotubes, carboxylated modified carbon nanotubes and aminated modified carbon nanotubes; the polyvinylidene fluoride-trifluoroethylene copolymer contains vinylidene fluoride and trifluoroethylene structural units, and the content of the trifluoroethylene structural units is 10-30% based on the weight of the polyvinylidene fluoride-trifluoroethylene copolymer; the polyvinylidene fluoride-tetrafluoroethylene copolymer contains vinylidene fluoride and tetrafluoroethylene structural units, and the content of the tetrafluoroethylene structural units is 7-30% based on the weight of the polyvinylidene fluoride-tetrafluoroethylene copolymer; the polyvinylidene fluoride-hexafluoropropylene copolymer contains vinylidene fluoride and hexafluoropropylene structural units, and the content of the hexafluoropropylene structural units is 5-25% based on the weight of the polyvinylidene fluoride-hexafluoropropylene copolymer.

2. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1, characterized in that, The modified carbon nanotubes have an outer diameter of 1-5 nm and a length of 5-10 um.

3. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1, characterized in that, The hot pressing treatment has a temperature of 100-150°C, a pressure of 80-150 MPa and a time of 3-15 min.

4. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1, characterized in that, The stretching has a temperature of 60-150°C.

5. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1 or 4, characterized in that, The stretching has a stretching ratio of 1-8.

6. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1, characterized in that, In step (3), the heat treatment has a temperature of 50-120°C and a time of 4-16 h.

7. The method for preparing the polyvinylidene fluoride ferroelectric polymer film according to claim 1, characterized in that, The spin coating has a rotation speed of 800-2500 rpm.

8. A polyvinylidene fluoride-based ferroelectric polymer film prepared by the method of any one of claims 1-7.

9. Use of the polyvinylidene fluoride-based ferroelectric polymer film of claim 8 in a thin film capacitor.

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