Composite film and preparation method and application thereof

Abstract

The invention relates to the field of thin film capacitors, and discloses a composite thin film and a preparation method and application thereof. The composite film is formed by thermal crosslinking of a high-temperature dielectric material and a piezoelectric ferroelectric polymer. Wherein the high-temperature dielectric material is polyimide or polyetherimide; the piezoelectric ferroelectric polymer is selected from cyanoethyl cellulose or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P (VDF-TrFE-CFE)), polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P (VDF-TrFE)), and the piezoelectric ferroelectric polymer is selected from polyvinylidene fluoride-trifluoroethylene (P (VDF-TrFE)) and polyvinylidene fluoride-trifluoroethylene (P (VDF-TrFE)); wherein the mass ratio of the high-temperature dielectric material to the piezoelectric ferroelectric polymer is 1: (0.00036-0.1). When the composite film is applied to a film capacitor, the effects of high dielectric constant and high breakdown strength, and improvement of thermal stability, thermal conductivity and energy storage performance can be achieved.

Description

Technical Field

[0001] The invention relates to the field of film capacitors, and in particular to a composite film and a preparation method and application thereof. Background Art

[0002] Polymer dielectric materials have the characteristics of high breakdown strength, light weight, and easy processing, and have become a hot topic of research and are widely used in dielectric capacitors. However, ordinary polymer dielectrics can no longer meet the increasingly urgent needs, especially in the aerospace field, new energy vehicle industry, and high-temperature environments such as oil exploration. High-temperature resistant dielectric materials have become a hot topic for researchers.

[0003] Polyimide (PI) is a widely used high-temperature polymer dielectric material. Its molecular chain has a thermally stable rigid imide ring. After thermal cross-linking, the polyimide film has excellent properties such as chemical resistance, ultra-high Tg and thermal stability.

[0004] On the one hand, the rigid conjugated structure on the PI main chain brings good thermal stability to these polymers, but the restricted dipole motion makes the dielectric constant of these polymers low, which limits their application in the field of high dielectric materials. And compared with batteries, its energy density is low and can no longer meet the corresponding needs. To achieve this goal, compounding with other high dielectric materials is a simple and easy method. However, the aggregation and voids of fillers in the composite material will cause a serious decrease in the breakdown strength, thereby reducing its energy storage performance. Therefore, a composite film is needed to solve the problem that both dielectric constant and breakdown strength cannot be taken into account. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art that high temperature resistant polymer materials cannot have both high dielectric constant and high breakdown strength, have poor thermal stability and thermal conductivity, and have low energy storage density, and to provide a composite film and a preparation method and application thereof.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composite film, characterized in that the composite film is formed by thermally cross-linking a high-temperature dielectric material and a piezoelectric ferroelectric polymer;

[0007] Wherein, the high temperature dielectric material is polyimide or polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene P (VDF-TrFE-CFE), polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P (VDF-TrFE));

[0008] Wherein, the mass ratio of the high temperature dielectric material to the piezoelectric ferroelectric polymer is 1:0.00036-0.1.

[0009] A second aspect of the present invention provides a method for preparing a composite film, characterized in that the method comprises:

[0010] (1) mixing a high temperature dielectric material and a piezoelectric ferroelectric polymer to obtain a polymer mixed solution;

[0011] (2) subjecting the polymer mixed solution in step (1) to a film-forming process to obtain the composite film;

[0012] Wherein, the high temperature dielectric material is polyamic acid or polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose or P(VDF-TrFE-CFE), polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)).

[0013] The third aspect of the present invention provides use of the composite film described in the first aspect of the present invention in a film capacitor.

[0014] Through the above technical solution, the present invention can achieve the following effects:

[0015] 1. The present invention incorporates two new organic particles to prepare a PI or PEI-based all-organic high-temperature dielectric nanocomposite film material, and the dielectric constant and energy storage performance of the composite material can be significantly improved by regulating the filler component.

[0016] 2. The material used in the present invention has good flexibility and can maintain the stability of the material under different bending conditions compared to common ceramic materials.

[0017] 3. The polymer used in the present invention and the incorporated organic nanoparticles are both ecologically and environmentally friendly materials, which can be applied in bio-related aspects.

[0018] 4. The dielectric film prepared in the present invention has good thermal stability and thermal conductivity, and can maintain good energy storage performance under high temperature conditions.

[0019] 5. The materials used in the present invention are simple to prepare and have good repeatability and performance stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) is the fabrication process of CEC / PI composite film, (b) SEM image of CEC / PI-0.5 cross section, and (c) transmission electron microscopy (TEM) image of CEC / PI-0.5 nanoparticles.

[0021] Figure 2 are the (a) dielectric constant and (b) loss of PI and CEC / PI nanocomposite films;

[0022] Figure 3 (a)-(b) breakdown circuit of PI and CEC / PI nanocomposite films at room temperature, (c) energy density and efficiency;

[0023] Figure 4 (a)-(b) breakdown circuit of PI and CEC / PI nanocomposite films at high temperature, (c) energy density and efficiency;

[0024] Figure 5 (a) is the preparation process flow chart of Terpolymer / PI nanocomposite film and (b) SEM and (c) TEM images;

[0025] Figure 6 are the (a) dielectric constant and (b) loss of PI and Terpolymer / PI nanocomposite films;

[0026] Figure 7 is the breakdown strength and energy density of PI and Terpolymer / PI nanocomposite films at room temperature and elevated temperature;

[0027] Figure 8 are the (a) dielectric constant and (b) loss of PI and CEC / PEI nanocomposite films;

[0028] Fig. 9 (a)-(b) breakdown circuits of PEI and CEC / PEI composite films at room temperature, (c) energy density and efficiency;

[0029] Fig.10 (a)-(b) breakdown circuits of PEI and CEC / PEI composite films at high temperatures, and (c) energy density and efficiency;

[0030] Fig.11 are the (a) dielectric constant and (b) loss of PEI and Terpolymer / PEI nanocomposite films;

[0031] Fig.12 are the (a) energy density and (b) efficiency of PEI and Terpolymer / PEI composite films at room temperature;

[0032] Fig.13 It is a flow chart for the preparation of all-organic polymer-based composite nanomaterials. DETAILED DESCRIPTION

[0033] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0034] As mentioned above, the first aspect of the present invention provides a composite film, characterized in that the composite film is formed by thermally cross-linking a high-temperature dielectric material and a piezoelectric ferroelectric polymer;

[0035] Wherein, the high temperature dielectric material is polyimide or polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose or P(VDF-TrFE-CFE);

[0036] The mass ratio of the high temperature dielectric material to the piezoelectric ferroelectric polymer is 1:0.00036-0.1, which can improve the dielectric constant and breakdown strength of the prepared composite film, thereby improving the energy storage density.

[0037] In some embodiments of the present invention, preferably, the high temperature dielectric material is polyimide (PI); and the piezoelectric ferroelectric polymer is cyanoethyl cellulose (CEC).

[0038] In some embodiments of the present invention, preferably, the mass ratio of the polyimide to the cyanoethyl cellulose is 1:0.00036-0.1, for example, it can be 1:0.0015, 1:0.0018, 1:0.0021, 1:0.0024, 1:0.0027, 1:0.0030, 1:0.0033, 1:0.0036, 1:0.0039, 1:0.0042, 1:0.0045, 1:0.0054, 1:0.0063, 1:0.0072, 1:0.0081, 1:0.0090, 1:0.010, 1:0.015, 1:0.018, 1:0.028, 1:0.038, 1:0.1, and any range composed of any two of the above values ​​and any value in any range.

[0039] This mass ratio can enable the prepared composite film to achieve an increase in dielectric constant and energy storage density, thereby increasing the energy storage density.

[0040] In some embodiments of the present invention, preferably, the high temperature dielectric material is polyimide; and the piezoelectric ferroelectric polymer is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene.

[0041] In some embodiments of the present invention, preferably, the mass ratio of the polyimide to polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene is 1:0.0018-0.1, for example, it can be 1:0.003, 1:0.006, 1:0.009, 1:0.012, 1:0.015, 1:0.018, 1:0.021, 1:0.024, 1:0.027, 1:0.037, 1:0.1, and any range composed of any two of the above values ​​and any value in any range.

[0042] In some embodiments of the present invention, preferably, the high temperature dielectric material is polyetherimide; and the piezoelectric ferroelectric polymer is cyanoethyl cellulose.

[0043] In some embodiments of the present invention, preferably, the mass ratio of the polyetherimide to the cyanoethyl cellulose is 1:0.001-0.1, for example, it can be 1:0.001, 1:0.002, 1:0.003, 1:0.004, 1:0.005, 1:0.1, any range consisting of any two of the above values ​​and any value in any range.

[0044] In some embodiments of the present invention, preferably, the high temperature dielectric material is polyetherimide (PEI); the piezoelectric ferroelectric polymer is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene P (VDF-TrFE-CFE). P (VDF-TrFE-CFE) can also be called Terpolymer.

[0045] In some embodiments of the present invention, preferably, the mass ratio of the polyetherimide to P(VDF-TrFE-CFE) is 1:0.002-0.1, for example, 1:0.002, 1:0.004, 1:0.006, 1:0.008, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.1, and any range consisting of any two of the above values ​​and any value in any range. This mass ratio can improve the dielectric constant and energy storage density of the prepared composite film, thereby improving the energy storage density.

[0046] In some embodiments of the present invention, preferably, the dielectric constant of the composite film is 3.5-4.5.

[0047] In some embodiments of the present invention, preferably, the thickness of the composite film is 10-30 μm.

[0048] In some embodiments of the present invention, preferably, the weight average molecular weight of the polyimide is 50,000-80,000.

[0049] In some embodiments of the present invention, preferably, the weight average molecular weight of the polyetherimide is 40,000-60,000, and the melt index is 9 g / 10 min.

[0050] In some embodiments of the present invention, preferably, the weight average molecular weight of the cyanoethyl cellulose is 100-800, wherein each 1 mol of the cellulose molecule contains 2.6 mol of cyanoethyl groups.

[0051] In some embodiments of the present invention, preferably, the weight average molecular weight of P(VDF-TrFE-CFE) is 400000-600000, and the molar content of each structural unit is polyvinylidene fluoride (VDF): trifluoroethylene (TrFE): chlorofluoroethylene (CFE) = 40-80: 10-50: 7.2, for example, it can be 40.3: 10.7: 7.2, 43.4: 13.6: 7.2, 47.8: 17.1: 7. .2, 51.9:21.3:7.2, 55.6:25.4:7.2, 57.7:29.3:7.2, 59.2:33.6:7.2, 63.5:37.8:7.2, 67.8:40.9:7.2, 71.6:43.2:7.2, 75.1:47.3:7.2, 79.5:48.2:7.2, and any range consisting of any two of the above values ​​and any value in any range.

[0052] A second aspect of the present invention provides a method for preparing a composite film, characterized in that the method comprises:

[0053] (1) mixing a high temperature dielectric material and a piezoelectric ferroelectric polymer to obtain a polymer mixed solution;

[0054] (2) subjecting the polymer mixed solution in step (1) to a film-forming process to obtain the composite film;

[0055] Wherein, the high temperature dielectric material is polyamic acid or polyetherimide; and the piezoelectric ferroelectric polymer is cyanoethyl cellulose or P(VDF-TrFE-CFE).

[0056] In the present invention, the preparation process of the composite film is as follows Figure 5 (a) shown.

[0057] In some embodiments of the present invention, preferably, in step (1), the high temperature dielectric material is polyamic acid, the piezoelectric ferroelectric polymer is cyanoethyl cellulose, and the mass ratio of the polyamic acid to the cyanoethyl cellulose is 1:0.00036-0.1, for example, it can be 1:0.0015, 1:0.0018, 1:0.0021, 1:0.0024, 1:0.0027, 1:0.0030, 1:0.0033, 1:0.0036, 1:0.0039, 1:0.0042, 1:0.0045, 1:0.0054, 1:0.0063, 1:0.0072, 1:0.0081, 1:0.0090, 1:0.010, 1:0.015, 1:0.018, any range composed of any two of the above values ​​and any value in any range.

[0058] In some embodiments of the present invention, preferably, the high-temperature dielectric material is polyetherimide, the piezoelectric ferroelectric polymer is P(VDF-TrFE-CFE), and the mass ratio of polyetherimide to P(VDF-TrFE-CFE) is 1:0.002-0.05, for example, it can be 1:0.002, 1:0.004, 1:0.006, 1:0.008, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, and any range composed of any two of the above values ​​and any value in any range.

[0059] In some embodiments of the present invention, preferably, in step (1), the mixing method includes stirring and / or ultrasonic treatment.

[0060] In some embodiments of the present invention, preferably, the mixing temperature is 20-80°C.

[0061] In some embodiments of the present invention, preferably, in step (2), the film forming process comprises drying and heat treatment.

[0062] In some embodiments of the present invention, preferably, the drying temperature is 50-100°C.

[0063] In some embodiments of the present invention, preferably, the heat treatment temperature is 80-400° C. and the time is 18-30 h.

[0064] The third aspect of the present invention provides use of the composite film described in the first aspect of the present invention in a film capacitor.

[0065] The present invention will be described in detail below through examples. In the following examples, the raw material of polyamic acid solution (PAA) is a commercial product of Jiangsu Changzhou Teyue Plastic Co., Ltd.; the raw material of cyanoethyl cellulose (CEC) is a commercial product of Aladdin; the raw material of polyetherimide (PEI) is a commercial product of Maclean; the raw material of Terpolymer is a commercial product of Piezo Tech. Inc., France with the brand name RTFS.

[0066] Example 1

[0067] In the first step, 1.5 g of 20 wt% PAA solution was dissolved in N,N-dimethylformamide (DMF) solution, and the mixed solution was magnetically stirred at 25°C, wherein the weight average molecular weight of the PAA was 80,000 g / mol. After filtration, a PAA / DMF mixed solution was obtained. Then, 0.00054 g of CEC was added to the mixed solution, and after two hours of magnetic stirring and two hours of ultrasonic treatment at 25°C, a polymer mixed solution was obtained, wherein the weight average molecular weight of the CEC was 800 g / mol.

[0068] In the second step, the polymer mixed solution obtained in the first step was poured onto a smooth glass plate. The solvent was dried in a drying oven at 60°C, and heat treated at 200°C for 24 hours to undergo thermal crosslinking. The resulting nanocomposite film was designated as CEC / PI-1. The thickness of the composite film was 20 μm. The preparation process of the composite film is as follows: Figure 1 (a) shows; the scanning electron microscope image of the cross section of the composite film is shown in Figure 1 (b) shows; the transmission electron microscope (TEM) image of the composite film nanoparticles is shown as Figure 1 (c) as shown.

[0069] Example 2

[0070] In the first step, 1.5 g of 20 wt% PAA solution was dissolved in N,N-dimethylformamide (DMF) solution, and the mixed solution was magnetically stirred at 25° C., wherein the weight average molecular weight of the PAA was 80,000 g / mol. Then 0.0027 g of Terpolymer powder was added to the mixed solution, and the mixture was ultrasonically treated in a 60° C. water bath and then magnetically stirred to obtain a polymer mixed solution, wherein the weight average molecular weight of the Terpolymer was 600,000 g / mol, and the molar content of each structural unit was VDF:TrFE:CFE=59.2 / 33.6 / 7.2.

[0071] In the second step, the polymer mixed solution obtained in the first step was poured onto a smooth glass plate. The solvent was dried in a drying oven at 60°C and heat-treated at 300°C for 24 hours to undergo a thermal crosslinking reaction. The resulting nanocomposite film was designated Terpolymer / PI-1. The thickness of the composite film was 20 μm.

[0072] Preparation flow chart of Terpolymer / PI nanocomposite film and SEM and TEM images are shown in Figure 2. Figure 5 shown.

[0073] Example 3

[0074] In the first step, 0.2 g of PEI particles are added to N-methylpyrrolidone (NMP), and the obtained mixed solution is subjected to magnetic stirring at 25° C. to obtain a PEI / NMP mixed solution, wherein the weight average molecular weight of the polyetherimide is 60,000 and the melt index is 9 g / 10 minutes. Then 0.0002 g of cyanoethyl cellulose is added to the mixed solution to prepare a CEC / PEI solution. The solution is heated and stirred at 60° C. to fully dissolve the solution.

[0075] In the second step, the CEC / PEI solution obtained in the first step was dropped onto a smooth glass plate. The solvent was dried in a drying oven at 80°C, and then heated to 150°C and subjected to thermal crosslinking reaction in a vacuum drying oven at 200°C. The obtained nanocomposite film was recorded as CEC / PEI-1. The thickness of the composite film was 20 μm.

[0076] Example 4

[0077] In the first step, 0.2 g of PEI particles are added to N-methylpyrrolidone (NMP), and the obtained mixed solution is subjected to magnetic stirring at 25° C. to obtain a PEI / NMP mixed solution, wherein the weight average molecular weight of the polyetherimide is 60,000 and the melt index is 9 g / 10 minutes. Then 0.002 g of Terpolymer is added to the mixed solution to prepare a Terpolymer / PEI solution. The mixture is heated and stirred at 60° C. to fully dissolve the solution.

[0078] In the second step, the Terpolymer / PEI solution obtained in the first step was dropped onto a smooth glass plate. The solvent was dried in a drying oven at 80°C, and then heated to 150°C and subjected to thermal crosslinking reaction in a vacuum drying oven at 200°C. The obtained nanocomposite film was designated as Terpolymer / PEI-1. The thickness of the composite film was 20 μm.

[0079] Example 5

[0080] A composite film was prepared according to the method of Example 2, except that in the first step, 0.0027 g of Terpolymer powder was added. The obtained nanocomposite film was recorded as Terpolymer / PI-2.

[0081] Comparative Example 1

[0082] A film was prepared according to the method of Example 1, except that CEC was not added in the first step. The obtained film was recorded as PI.

[0083] Comparative Example 2

[0084] A film was prepared according to the method of Example 3, except that CEC was not added in the first step. The obtained film was recorded as PEI.

[0085] Test Example 1

[0086] At 25° C., the dielectric constant and energy storage density of the films prepared in Examples 1-13 and Comparative Examples 1 and 2 were tested using an LCR meter and a ferroelectric tester, respectively. The test results are shown in Table 1.

[0087] Table 1

[0088] film Dielectric constant Energy storage density (at room temperature) Example 1 3.78 <![CDATA[6.74J / cm 3 ]]> Example 2 3.51 <![CDATA[9.8J / cm 3 ]]> Example 5 4.27 <![CDATA[9.9J / cm 3 ]]> Comparative Example 1 3.41 <![CDATA[5.99J / cm 3 ]]>

[0089] Table 1

[0090] film Dielectric constant Energy storage density (at room temperature) Example 3 3.64 <![CDATA[10.04J / cm 3 ]]> Example 4 3.62 <![CDATA[7.56J / cm 3 ]]> Comparative Example 2 3.45 <![CDATA[6.99J / cm 3 ]]>

[0091] Figure 2 The dielectric constants and losses of PI and CEC / PI-1 all-organic composite films were compared to illustrate the effect of CEC on the dielectric constant of PI. From the data, it can be seen that the dielectric constant of the composite film CEC / PI-1 is higher than that of pure PI. The dielectric constant of pure PI is 3.41, and at a frequency of 1kHz, the dielectric constant of the composite film doped with CEC is 3.78. The dielectric constant of CEC / PI-1 is 10.85% higher than that of pure PI. From the data, it can be seen that the dielectric constant of the film has been improved after the addition of CEC.

[0092] like Figure 6 As shown in Figure 2, the addition of Terpolymer significantly increases the dielectric constant of PI film. 3 At Hz, the dielectric constants of Terpolymer / PI-1 and Terpolymer / PI-2 are 3.51 and 4.27, respectively, which are significantly higher than the dielectric constant of pure PI. The dielectric loss of Terpolymer / PI composite film is slightly higher than that of PI film, and increases with the increase of Terpolymer mass content. The above results show that Terpolymer / PI composite film has excellent frequency stability, which is beneficial to improve the electric displacement and breakdown electric field strength.

[0093] Figure 8 The dielectric constants and losses of PEI and CEC / PEI all-organic composite films were compared, and the effect of CEC on the dielectric constant of PEI was explained. From the data, it can be seen that the dielectric constant of the blended film is higher than that of pure PEI. The dielectric constant of pure PEI is 3.45, and the dielectric constant of the composite film doped with CEC is 3.64 at a frequency of 1kHz. The data shows that the dielectric constant has been improved after adding an appropriate amount of CEC.

[0094] Fig.11 The dielectric constants and losses of PEI and Terpolymer / PEI all-organic composite films were compared, and the effect of Terpolymer on the dielectric constant of PEI was explained. From the data, it can be seen that the dielectric constant of the blended film is higher than that of pure PEI. At a frequency of 1kHz, the dielectric constant of the Terpolymer / PEI composite film is 3.62. The data shows that the dielectric constant is improved after adding an appropriate amount of Terpolymer.

[0095] Test Example 2

[0096] At 25° C., the breakdown strength of the films prepared in Examples 1-5 and Comparative Examples 1 and 2 were tested using a ferroelectric tester. The test results are shown in Table 2.

[0097] Table 2

[0098]

[0099]

[0100] Table 2

[0101] film Breakdown strength (MV / m) (at 25°C) Example 3 580 Example 4 550 Comparative Example 2 500

[0102] Figure 3 The breakdown strength of PI and CEC / PI all-organic composite films at room temperature was compared. The breakdown electric field of CEC / PI-1 increased from 500 MV / m to 520 MV / m at room temperature. The energy storage density increased from 5.99 J / cm 3 Increased to 6.74 J / cm 3 . Figure 4 The breakdown strength of PI and CEC / PI all-organic composite films at high temperatures was compared. The latter increased from 250 MV / m to 450 MV / m at 150 °C, and its energy density increased from 1.73 J / cm 3 Increased to 5.11 J / cm 3 .

[0103] Figure 7The breakdown strength and energy density of PI and Terpolymer / PI nanocomposite films at room temperature and high temperature. The energy density and charge-discharge efficiency of the prepared Terpolymer / PI composite material are significantly improved compared with pure PI. At room temperature, under an electric field of 500MV / m, the energy density of Terpolymer / PI-1 can reach 9.8J / cm 3 ; The energy density of Terpolymer / PI-2 can reach 9.9J / cm 3

[0104] Fig. 9 The breakdown strength of room temperature PEI and CEC / PEI all-organic composite films was compared. From the data graph, it can be found that doping with CEC can increase the polarization value of the composite material, and the breakdown electric field of the pure film can reach up to 500MV / m at room temperature. The breakdown strength of CEC / PEI-1 at room temperature is 580MV / m, and the energy density corresponding to it reaches 10.04J / cm 3 , compared with pure PEI (6.99 J / cm 3 ) has improved.

[0105] Fig.10 The breakdown circuit, energy density and efficiency of PEI and CEC / PEI composite films under high temperature environment. The energy density of PEI reaches 4.51J / cm at 450MV / m 3 , and the charge and discharge efficiency remains above 90%. The breakdown strength of CEC / PEI-1 at 150°C is 480MV / m, and the energy density corresponding to it reaches 6.84J / cm 3 ,

[0106] Fig.12 The breakdown strength and energy density of PEI and Terpolymer / PEI nanocomposite films at room temperature. The energy density and charge-discharge efficiency of the prepared Terpolymer / PEI composite material are significantly improved compared with pure PEI. At room temperature, under an electric field of 550MV / m, its energy density can reach 7.56J / cm 3 , the charge and discharge efficiency is greater than 90%.

[0107] Test Example 3

[0108] Under high temperature conditions of 150° C., a ferroelectric tester was used to test the breakdown strength and energy storage density of the films prepared in Examples 1-12 and Comparative Examples 1 and 2, respectively. The test results are shown in Table 3.

[0109] Table 3

[0110]

[0111] Table 3

[0112] film Breakdown strength (MV / m) <![CDATA[Energy storage density (J / cm 3 )]]> Example 3 480 6.84 Comparative Example 2 450 4.51

[0113] It can be seen from the results in Tables 1-3 that compared with the PI or PEI films of the comparative examples, the composite films prepared by the embodiments of the technical solution of the present invention have better beneficial effects in terms of dielectric constant, energy storage density at room temperature, and breakdown strength, reflecting excellent energy storage performance.

[0114] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A composite film, It is characterized in that The composite film is formed by thermal cross-linking of a high-temperature dielectric material and a piezoelectric ferroelectric polymer; Wherein, the high temperature dielectric material is polyimide or polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, polyvinylidene fluoride and polyvinylidene fluoride-trifluoroethylene; Wherein, the mass ratio of the high temperature dielectric material to the piezoelectric ferroelectric polymer is 1:0.00036-0.

1.

2. The composite film according to claim 1, in, The high temperature dielectric material is polyimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose; Wherein, the mass ratio of the polyimide to cyanoethyl cellulose is 1:0.00036-0.

1.

3. The composite film according to claim 1, in, The high temperature dielectric material is polyimide; the piezoelectric ferroelectric polymer is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene; Wherein, the mass ratio of the polyimide to polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene is 1:0.0018-0.

1.

4. The composite film according to claim 1, in, The high temperature dielectric material is polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose; Wherein, the mass ratio of the polyetherimide to cyanoethyl cellulose is 1:0.001-0.

1.

5. The composite film according to claim 1, in, The high temperature dielectric material is polyetherimide; the piezoelectric ferroelectric polymer is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene; Wherein, the mass ratio of the polyetherimide to polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene is 1: 0.002-0.1。 6. The composite film according to any one of claims 1 to 5, in, The dielectric constant of the composite film is 3.5-4.5; And / or, the composite film has a thickness of 10-30 μm.

7. The composite film according to any one of claims 1 to 6, in, The weight average molecular weight of the polyimide is 50000-80000; And / or, the weight average molecular weight of the polyetherimide is 40000-60000; And / or, the weight average molecular weight of the cyanoethyl cellulose is 100-800; wherein each 1 mol of the cellulose molecule contains 2.6 mol of cyanoethyl groups; And / or, the weight average molecular weight of polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene is 400,000-600,000, and the molar content of each structural unit is polyvinylidene fluoride:trifluoroethylene:chlorofluoroethylene=40-80:10-50:7.

2.

8. A method for preparing a composite film, It is characterized in that The method includes: (1) mixing a high temperature dielectric material and a piezoelectric ferroelectric polymer to obtain a polymer mixed solution; (2) subjecting the polymer mixed solution in step (1) to a film-forming process to obtain the composite film; Wherein, the high temperature dielectric material is polyamic acid or polyetherimide; the piezoelectric ferroelectric polymer is cyanoethyl cellulose or polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, polyvinylidene fluoride and polyvinylidene fluoride-trifluoroethylene.

9. The method according to claim 8, in, In step (1), the high temperature dielectric material is polyamic acid, the piezoelectric ferroelectric polymer is cyanoethyl cellulose, and the mass ratio of the polyamic acid to the cyanoethyl cellulose is 1:0.00036-0.1; And / or, the high temperature dielectric material is polyetherimide, the piezoelectric ferroelectric polymer is polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene, and the mass ratio of polyetherimide to polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene is 1:0.002-0.

1. Preferably, in step (1), the mixing method includes stirring and / or ultrasonic treatment; Preferably, the mixing temperature is 20-80°C. Preferably, in step (2), the film forming process comprises drying and heat treatment; Preferably, the drying temperature is 50-100°C; Preferably, the heat treatment is carried out at a temperature of 80-400°C and for a time of 18-30 hours.

10. Use of the composite film according to any one of claims 1 to 7 in a film capacitor.

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