A polyimide dielectric film, its preparation method and application

Abstract

The application discloses a kind of polyimide dielectric film and its preparation method and application, belong to material field.The material will PDA be dissolved in solvent after adding cesium fluoride, then stirring 20~35min in oxygen-free environment, finally under the condition of stirring, reaction is carried out for 18~20h at 75~85 ℃, reaction mixture is filtered, finally obtained FPDA;After FPDA is dissolved in solvent, then under the condition of-5~5 ℃, diphenyl ether dianhydride is added in batches and stirred for 8~10h, to obtain polyamide acid PAA solution, solution is dropped on glass substrate and is treated by thermal imidization reaction, after reaction, glass substrate is placed in deionized water and film is stripped, and film with thickness of 1~20 μm is obtained.The product prepared by the application has lower leakage current loss, higher glass transition temperature and charge-discharge efficiency, and has overall excellent energy storage characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials, in particular to a polyimide dielectric film and a preparation method and application thereof. BACKGROUND

[0002] Nowadays, the power grid is continuously promoting the construction of new power systems, and is constantly developing towards digitization and intelligentization, so higher requirements are put forward for energy storage applications. Thin film capacitor is an important energy storage element, in order to obtain greater capacity and better performance, it is urgent to improve the energy storage density and charge-discharge efficiency of the capacitor. At present, the dielectric of thin film capacitor usually adopts polymer type, however, these ordinary polymer dielectrics are prone to produce excessive leakage current in the environment exceeding 100℃, resulting in the decline of energy storage characteristics, and it is difficult to work for a long time in extreme high temperature conditions.

[0003] The current mainstream solution includes improving molecular structure, blending modification, covalent crosslinking, etc. Molecular structure design is to add strong polar dipole groups to the main chain or side chain of linear polymer to improve the glass transition temperature, but the main chain containing a large number of such structures will cause the leakage current of the material to increase significantly at high temperature, resulting in the decline of charge-discharge efficiency; the blending strategy is to mix the polymer dielectric with molecular semiconductors or another polymer into nanocomposites in a certain proportion to improve the dielectric constant of the original dielectric, however, the chemical bond and dielectric property of the two mixed materials often differ, and it is difficult to have good compatibility, resulting in local electric field distortion between the interface of the filler and the polymer, and the breakdown strength and maximum discharge energy density of the material decrease; the crosslinking method is to fix the polymer chain through the network formed by covalent bond to improve the breakdown strength and discharge efficiency of the dielectric, since the crosslinking conditions of the polymer dielectric and the manufacturing conditions of the thin film capacitor often differ, and the change of crosslinking degree is not easy to control, the cost is that it will adversely affect the energy storage characteristics of the capacitor at high temperature. As can be seen, these methods are difficult to simultaneously consider multiple material properties such as high energy storage density, high charge-discharge efficiency and high glass transition temperature, and often one performance is improved at the expense of other performances. Therefore, it is expected to find a polymer dielectric material with high dielectric constant and low dielectric loss under extreme high temperature working conditions.

[0004] Polyimide (PI) as a kind of polymer with excellent mechanical properties, stable chemical properties, the effect of intramolecular benzene ring and imide ring makes it have very high glass transition temperature, so it is considered to be a potential dielectric material. But the unique aromatic structure of PI makes it very difficult to achieve both high temperature resistance and high energy density: on the one hand, PI can work continuously at high temperature above 200 DEG C. This is because its unique aromatic structure endows the material with much stronger thermal stability than other polymers; on the other hand, the discharge energy density of PI at 200 DEG C is about 0.26 J / cm-3, and the energy loss reaches nearly 60%. The reason is that the aromatic structure of traditional PI will produce a large leakage current when the electronic shift is intensified under high temperature and strong electric field, thereby reducing its discharge energy density.

[0005] Therefore, in order to obtain PI with better energy storage properties, the structure thereof needs to be improved. SUMMARY

[0006] In view of the above defects, the aromatic structure in the PI is innovatively modified by fluorine in the application, which forms an internal electric field induced electron migration in the PI molecular chain, affects the electron distribution and hinders the movement of the electron to suppress the formation of leakage current. While ensuring the high heat resistance of PI, the problem of excessive leakage current is alleviated, and the discharge density and charge-discharge efficiency are improved.

[0007] The object of the application can be achieved by the following technical solutions:

[0008] A preparation method of a polyimide dielectric film, the method comprising the following steps:

[0009] (1) 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene PDA and 1,4-dioxane are dissolved in a solvent, then cesium fluoride is added, and then stirred in an oxygen-free environment for 20-35 min, and finally reacted at a temperature of 75-85 DEG C and under stirring conditions for 18-20 h. The reaction mixture is filtered, and finally fluorine-modified 4,4'-(((9H-fluorene-9,9-diyl)bis(4,1-phenylene))bis(oxy))diphenylamine FPDA is obtained;

[0010] (2) FPDA is dissolved in a solvent, then diphenyl ether dianhydride is added in batches under the condition of-5-5 DEG C and stirred for 8-10 h, so as to obtain a polyamide acid PAA solution. The solution is dropped on a glass substrate and subjected to thermal imidization reaction treatment. After the reaction is completed, the glass substrate is placed in deionized water to peel off the film, and a film PI-FP with a thickness of 1-20 μm is obtained.

[0011] In the technical scheme of the present application: the mass ratio of 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene PDA, 1,4-dioxane and cesium fluoride in step (1) is 3-4: 35-47: 1.5-2.5.

[0012] In the technical scheme of the present application: the solvent used in step (1) and step (2) is methylpyrrolidone.

[0013] In the technical scheme of the present application: the heat imine reaction treatment condition in step (2) is 55-65℃ for 0.5-1.5h, 110-130℃ for 1-3h, 190-210℃ for 1-3h, 240-260℃ for 0.5-1.5h, and 300-320℃ for 0.5-1.5h.

[0014] In the technical scheme of the present application: the FPDA doping mass fraction in the thin film PI-FP in step (2) is 1-10%wt.

[0015] A kind of polyimide dielectric film, which is prepared by the above method.

[0016] In the technical scheme of the present application, the film prepared by the above method is applied as a capacitor material.

[0017] The beneficial effects of the present application are:

[0018] (1) The present application prepares fluorine-modified polyimide (PI-FP), which can inhibit electron flow transmission, while maintaining the high heat resistance of the original PI, has lower leakage current loss, higher glass transition temperature and charge and discharge efficiency, and has overall excellent energy storage characteristics.

[0019] (2) The present application proposes a fluorine modification electron sensing shift strategy based on the aromatic structure of PI from the overall structure of the molecule. First, the introduction of fluorine-modified fluorene diamine can improve the spatial structure of PI and increase the molecular chain spacing, thereby increasing the glass transition temperature and polarization capacity of the material; second, the fluorine-modified fluorene diamine can regulate the energy band structure of the PI polymer molecule, the difference between the polymer molecular orbital energy gap is large, so the energy required for electronic excitation increases, and the movement of electrons is inhibited, thereby reducing the leakage current density; the large difference between the molecular orbital energy gap and the blocked electronic excitation greatly reduces the energy loss, ultimately leading to a charge and discharge efficiency of PI-FP material of nearly 90%.

[0020] (3) The polymer dielectric film capacitor material prepared by the present application can work stably under extreme high temperature working conditions of 200℃, and has overall excellent energy storage performance: the glass transition temperature rises to 264.07℃; under an electric field intensity of 200MV / m, the leakage current density is reduced from 7.1×10 -7 A / cm2 decreased to 2.8 x 10 -8 A / cm 2 , and the charge-discharge efficiency reached 82.32%, which was improved by 927.83% compared with PI; the discharge energy density was increased to 5.324 J / cm 3 . BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The infrared spectra of PDA and FPDA are characterized.

[0022] Figure 2 The maximum discharge energy density and volume resistivity of PI and PI-FP are compared.

[0023] Figure 3 The D-E loop test results of PI at 200℃ are shown.

[0024] Figure 4 The D-E loop test results of PI-FP at 200℃ are shown.

[0025] Figure 5 The discharge energy density and charge-discharge efficiency of PI and PI-FP at 200℃ are shown. DETAILED DESCRIPTION

[0026] The application will be further described below in conjunction with examples, but the scope of protection of the application is not limited thereto:

[0027] Example 1

[0028] 3.218 g of 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene (PDA) was dissolved in 42.0 mL of 1,4-dioxane in methylpyrrolidone solution at room temperature, 1.914 g of cesium fluoride (CsF) was added, stirred for 30 min under N2 atmosphere, and then heated to 80℃ and stirred for 20 h. After cooling to room temperature, the reaction mixture was filtered, and finally fluorine-modified 4,4'-(((9H-fluorene-9,9-diyl)bis(4,1-phenylene))bis(oxy))diphenylamine (FPDA) was obtained,

[0029] Preparation flow of PI-FP filmFPDA was dissolved in N-methylpyrrolidone (NMP) solution and stirred for 2 h. Diphenyl ether dianhydride was added in 8 portions at 0 °C and stirred for 10 h to obtain a homogeneous polyamic acid (PAA) solution. The solution was dropped on a clean glass substrate and treated by thermal imidization with a temperature gradient of 60 °C / 1 h, 120 °C / 1 h, 200 °C / 2 h, 250 °C / 1 h, 300 °C / 1 h. After cooling to room temperature, the glass substrate was placed in deionized water to peel off the film, obtaining a polymer film PI-FP containing FPDA doped at a mass fraction of 5 wt%, with a thickness of about 10 μιη.

[0030] Example 2

[0031] Other conditions are the same as in Example 1, except that the FPDA doped mass fraction in the polymer film PI-FP is 1% wt.

[0032] Example 3

[0033] Other conditions are the same as in Example 1, except that the FPDA doped mass fraction in the polymer film PI-FP is 3% wt.

[0034] Example 4

[0035] Other conditions are the same as in Example 1, except that the FPDA doped mass fraction in the polymer film PI-FP is 7% wt.

[0036] Example 5

[0037] Other conditions are the same as in Example 1, except that the FPDA doped mass fraction in the polymer film PI-FP is 9% wt.

[0038] Comparative Example 1

[0039] Preparation flow of PI film 4,4'-diaminodiphenyl ether was dissolved in N-methylpyrrolidone (NMP) solution and stirred for 2 h. Diphenyl ether dianhydride was added in 6 portions at 0 °C and stirred for 8 h to obtain a homogeneous polyamic acid (PAA) solution, with a molar ratio of 4,4'-diaminodiphenyl ether and diphenyl ether dianhydride of 1:20. The solution was dropped on a clean glass substrate and treated by thermal imidization with a temperature gradient of 60 °C for 1 h, 120 °C for 2 h, 200 °C for 2 h, 250 °C for 1 h, 310 °C for 1 h. After cooling to room temperature, the glass substrate was placed in deionized water to peel off the film, obtaining a film without FPDA, with a thickness of about 10 μιη.

[0040] Determination of breakdown strength:

[0041] The sample was immersed in silicone oil and the breakdown strength was tested using a digital temperature control version. The voltage was gradually increased using a voltage transformer with a gradient of 2000 V / s.

[0042] Table 1

[0043] Film breakdown field strength (MV / m) Example 1 724.4 Example 2 607.3 Example 3 649.2 Example 4 687.8 Example 5 662.1 Comparative Example 1 317.8

[0044] From the above table, it can be seen that adjusting the mass fraction of FPDA doped in the PI-FP composite film has a significant effect on the breakdown field strength thereof, because within a certain range, the breakdown field strength of the film is directly proportional to the mass fraction of FPDA doped. Beyond this range, the breakdown field strength of the film begins to decrease.

[0045] Other performance tests (the following are based on Comparative Example 1 and Example 1)

[0046] Infrared spectroscopy characterization:

[0047] Fourier transform infrared spectra in the range of 500-3500 cm -1 were recorded by a Nicolet iS50 spectrometer. X-ray diffraction (XRD) tests were performed on the polymer film by a Panalytical B.V. diffractometer to determine the amorphous peak in the range of 5-70°. As shown in Figure 1 , the stretching vibration peak at 1331 cm -1 corresponds to the C-F bond. In PDA, the stretching vibration peak between 3200-3500 cm -1 contains both -OH and -NH2 groups. After fluorine substitution, the stretching vibration peak between 3200-3500 cm -1 in FPDA becomes more sharp, indicating that the large and wide stretching vibration peak of -OH disappears due to fluorine substitution, leaving only the stretching vibration peak of -NH2. This confirms the success of fluorine substitution.

[0048] The dielectric performance test results of the present application are as follows:

[0049] Using a DSC3+ calorimeter, according to differential scanning calorimetry (DSC), in a nitrogen environment at 25-300℃, the heating or cooling rate is set to 10℃ / min. The dielectric constant and dielectric loss of the sample are measured by a Concept 80 broadband dielectric spectrometer, with a test frequency range of 100-10 6 Hz, a voltage of 0.5kV, and a temperature of 200℃. As shown in Figure 2 , the volume resistivity of PI-FP is increased from 1.21×10 14 Ω·cm 2 to 9.23×10 14 Ω·cm 2 , an increase of 673.95%. At 200℃, the maximum discharge energy density of PI-FP is increased from the original 0.371 J / cm 2The breakdown voltage of PI film was increased from 322.9 MV / m to 684.4 MV / m, which was increased by 124% at most. 2 The breakdown voltage of PI film was increased from 322.9 MV / m to 684.4 MV / m, which was increased by 124% at most.

[0050] The charge and discharge energy storage characteristics of the thin film capacitor were as follows:

[0051] The single-pole displacement-electric field (D-E) loop was measured by PK-FERRO20B ferroelectric tester at a frequency of 100 Hz. The thin film sample was immersed in silicone oil, and the breakdown strength was tested by controlling the temperature of the digital hot plate equipped with a thermocouple. The voltage transformer was used to apply voltage at a ramp rate of 200 V / s. The energy storage performance of PI and PI-FP at high temperature was evaluated by D-E loop method. As shown in Figure 3 and Figure 4 The breakdown voltage of PI film was increased from 322.9 MV / m to 684.4 MV / m, which was increased by 124% at most. The PI derivative coated with fluorine-containing diamine showed a narrower D-E loop and a lower residual polarization. Among them, the energy storage performance of PI-FP at high temperature was significantly enhanced, which was higher than that of PI, and had a smaller residual polarization. As shown in Figure 5 Preparation flow of PI-FP film Preparation flow of PI film Film breakdown field strength (MV / m) Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 The energy loss of PI dielectric thin film increased sharply to 1.09 J / cm 3 at a breakdown field strength of only 350 MV / m; while the energy loss of PI-FP thin film was smaller, which was only 0.57 J / cm 3 at an electric field strength of 600 MV / m. This is because the FPDA coating makes the molecular orbital spacing larger and inhibits the process of charge excitation and transmission, which leads to an efficiency of nearly 90%.

Claims

1. A method for producing a polyimide dielectric film, characterized by: The method comprises the following steps: (1) dissolving 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene PDA and 1,4-dioxane in a solvent, then adding cesium fluoride, stirring for 20-35 min in an oxygen-free environment, and finally reacting at a temperature of 75-85°C under stirring for 18-20 h. The reaction mixture is filtered to obtain fluorine-modified 4,4'-(((9H-fluorene-9,9-diyl)bis(4,1-phenylene))bis(oxy))diphenylamine FPDA; (2) dissolving FPDA in a solvent, then adding diphenyl ether dianhydride in batches under the condition of -5-5°C and stirring for 8-10 h to obtain a polyamic acid PAA solution. The solution is dropped on a glass substrate and treated by thermal imidization reaction. After the reaction, the glass substrate is placed in deionized water to peel off the film, and a film PI-FP with a thickness of 1-20 μm is obtained.

2. The method of claim 1, wherein: The mass ratio of 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene PDA, 1,4-dioxane and cesium fluoride in step (1) is 3-4:35-47:1.5-2.

5.

3. The method for preparing the polyimide dielectric film according to claim 1, characterized in that: The solvent used in steps (1) and (2) is methylpyrrolidone.

4. The method of claim 1, wherein: The thermal imidization reaction treatment in step (2) is carried out at 55-65°C for 0.5-1.5 h, at 110-130°C for 1-3 h, at 190-210°C for 1-3 h, at 240-260°C for 0.5-1.5 h, and at 300-320°C for 0.5-1.5 h.

5. The method of claim 1, wherein: The FPDA doping mass fraction in the film PI-FP in step (2) is 1-10% wt.

6. A polyimide dielectric film characterized by comprising: The film is prepared by any one of the methods of claims 1-5.

7. The use of the film prepared by the method of claim 1 as a capacitor material.

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