Block copolymerized polyimide dielectric film for high-temperature-resistant film capacitor and preparation method of block copolymerized polyimide dielectric film

Abstract

The invention discloses a block copolymerized polyimide film and application thereof in a capacitor, and belongs to the technical field of dielectric polymer materials and film capacitors. A molecular chain in the copolymer is formed by alternately connecting flexible soft chain segments and rigid hard chain segments, and the soft chain segments and the hard chain segments are incompatible in thermodynamics and can be driven in the polymer to form a nano-scale microphase separation structure. A fluorine-containing electron withdrawing group and a sulfone-containing large dipole moment group are introduced into a hard chain segment, so that a nano microphase separation interface is formed in the polymer and can be used as a deep energy level trap, and the electron forbidden band width of the material is synergistically widened. The design inhibits carrier generation and migration under high temperature and high electric field, and improves the breakdown field strength and dielectric constant of the material. The block copolymer film has high static energy storage density, excellent charge and discharge efficiency and cycling stability exceeding 100,000 times, and is suitable for high-temperature-resistant and high-energy-density film capacitors and electrical insulating materials.

Description

Technical Field

[0001] This invention relates to the field of thin-film capacitor technology, specifically to a block copolymer film that can improve the upper limit of the operating temperature and energy density of capacitor devices. This polyimide film is prepared using a two-step polycondensation method and includes soft and hard segments, which synergize the physical properties of each segment, exhibiting good high-temperature stability and high breakdown strength. Background Technology

[0002] Film capacitors are devices based on metallized polymer dielectric films. Due to their good stability, high withstand voltage, low loss, long lifespan, excellent frequency characteristics, and non-polarity, they are widely used in many fields. Currently, most film capacitors on the market are based on biaxially oriented polypropylene (BOPP) films, with an operating temperature range typically from -40℃ to 80℃. With the rapid development of modern power electronics technology, especially in demanding applications such as hybrid electric vehicles, aerospace, and deep-earth exploration, there is an urgent need for film capacitors that can operate stably in high-temperature environments and possess high energy density. Simultaneously improving the dielectric constant and breakdown field strength of the material while maintaining excellent thermal stability is a technological challenge in developing next-generation high-performance polymer dielectric materials.

[0003] Among numerous polymer materials, high-temperature resistant aromatic polymers, represented by polyimide (PI), have been extensively studied due to their excellent thermal stability. However, traditional PI materials contain a large number of conjugated structures in their molecular backbone, leading to strong intramolecular and intermolecular charge transfer (CT) effects. While this effect imparts heat resistance to the material, its negative impact is also significant, resulting in a narrower electronic bandgap (E0). gThe inherent defects, such as high leakage current, are particularly pronounced under high temperature and high electric field conditions. This fundamental limitation restricts the breakdown field strength of the film, thus affecting its electrostatic energy storage density. To overcome this technical bottleneck, various modification strategies have been explored in existing technologies. For example, a common method is to improve the breakdown strength of the composite material by adding inorganic fillers such as boron nitride nanosheets (Composit. Sci. Tech. 2022, 229, 109681) or barium titanate nanoparticles (Compos. Part A: Appl. Sci. Manuf. 2024, 186, 108405) to the polyimide matrix. However, inorganic nanofillers are prone to agglomeration and are difficult to uniformly disperse in the polymer matrix. Another approach is to use polymer blending or random copolymerization. However, simple physical blending or random copolymerization with disordered chain segments often fails to construct a regular and ordered microstructure, leading to phase separation of the components. Moreover, the performance advantages of each component cannot be fully synergistically utilized, resulting in limited improvement on the overall performance of the material. Therefore, this invention starts from the molecular level and constructs a regular microstructure to simultaneously solve the contradiction between the insufficient intrinsic insulation properties and low dielectric constant of polyimide, providing an effective technical solution to improve the high-temperature energy storage performance of polymer films. Summary of the Invention

[0004] The purpose of this invention is to improve the energy density and high-temperature resistance of thin-film capacitors. Addressing the problem of poor breakdown strength of existing polyimide (PI) films due to insufficient intrinsic insulation properties under high temperature and high electric field conditions, a block copolymer film derived from PI was designed and prepared. This film can synergistically improve the dielectric constant and breakdown field strength at high temperatures by combining the physical properties of the two blocks.

[0005] To achieve the above objectives, the present invention provides a block copolymer polyimide dielectric material, which is composed of at least one flexible soft segment and at least one rigid hard segment alternately connected; the soft segment and the hard segment are thermodynamically incompatible and can drive the formation of a nanoscale microphase separation structure within the polymer.

[0006] As a preferred option, the synthesis scheme of block copolymer materials is as follows: Figure 1 As shown. The soft segment is polymerized from a first diamine monomer and a first dianhydride monomer, designed to provide processability and mechanical flexibility of the polymer. Specifically, the first diamine monomer is 4,4'-oxodiphenylamine (ODA), the first dianhydride monomer is bisphenol A dianhydride (BPADA), and the synthesized soft segment is named BO.

[0007] As a preferred embodiment, the hard segment is polymerized from a second diamine monomer and a second dianhydride monomer, serving as the core functional unit to provide high electrical insulation and high polarizability. Specifically, the second diamine monomer is 4,4'-diaminodiphenyl sulfone (DDS), and the second dianhydride monomer is 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA). The synthesized hard segment chain is named DF.

[0008] Furthermore, the hard segment is characterized by containing a hexafluoroisopropene group (-CF3) as a strong electron-withdrawing group, which is used to broaden the electronic band gap of the material and suppress carrier transport; at the same time, it contains a sulfone group (-SO2-) as a large dipole moment group, which is used to enhance the polarization ability and dielectric constant of the material.

[0009] In one specific embodiment, the molar ratio of the soft segment (BO) to the hard segment (DF) molecules can be 2:1, 1:1, or 1:2, with the optimal overall dielectric energy storage performance achieved when the molar ratio is 1:1 (sample name BO1-DF1). Scanning electron microscope images of thin film samples with different block ratios are shown below. Figure 1 It can be seen that the samples exhibit different micro-phase separation characteristics.

[0010] Compared with the prior art, the present invention, through the above technical solution, achieves at least the following beneficial effects:

[0011] (1) Achieving a synergistic improvement in dielectric properties and a significant increase in energy storage density. The block copolymer of this invention utilizes the microphase separation of soft and hard segments, simultaneously achieving a high dielectric constant ( Figure 1 ) and penetration strength ( Figure 2 The synchronous efficiency was significantly improved. At a high temperature of 150°C, the optimal embodiment (BO1-DF1) achieved a high efficiency of 6.0 J / cm³. 3 The discharge energy storage density and 90% charge / discharge efficiency, such as Figure 5 As shown, the energy storage density is increased by 218% compared to the pure soft segment homopolymer control group.

[0012] (2) The insulation performance and breakdown field strength of the material are significantly enhanced. The material of this invention exhibits extremely high breakdown field strength at 150°C, with the characteristic breakdown field strength of the optimal embodiment reaching 621 kV / mm (see...). Figure 4 The breakdown strength (354kV / mm) of the control group was improved by 75%. At the same time, its leakage current density was reduced by an order of magnitude compared with the control group, demonstrating superior insulation performance.

[0013] (3) The performance enhancement mechanism is clear. The excellent dielectric properties of the preferred sample of this invention are due to a dual synergistic mechanism. On the one hand, the introduction of functional hard segments effectively broadens the overall electronic bandgap of the material (the optical bandgap can reach 3.12 eV), suppressing the generation of charge carriers from the source; on the other hand, the nano-interface formed by microphase separation acts as a physical deep-level trap, effectively capturing and restricting the migration of charge carriers, thereby hindering the formation of electrical breakdown channels.

[0014] (4) Excellent overall performance, meeting the application requirements under harsh conditions. The polymer thin film material of the present invention not only has outstanding capacitive energy storage performance, but also has excellent thermal stability, with no significant mass loss in air below 300°C, and excellent cycle stability. After 100,000 charge-discharge cycles at 150°C and 200kV / mm electric field strength, the energy storage capacity has no significant decay, meeting the long-term service requirements of power electronic devices in harsh environments. Attached Figure Description

[0015] Appendix Figure 1 Soft and hard block molecular structures and methods for preparing block copolymer polyimides.

[0016] Appendix Figure 2 Scanning electron microscope images of different thin film samples. (a) Pure soft block polymer film; (b) Film with a soft-to-hard block ratio of 2:1; (c) Film with a soft-to-hard block ratio of 1:1; (d) Film with a soft-to-hard block ratio of 1:2.

[0017] Appendix Figure 3 Figures showing the test results of dielectric constant and dielectric loss of soft and hard segment block copolymer polyimides in Examples 1 to 3 and comparative examples of the present invention.

[0018] Appendix Figure 4 The breakdown strength test results of soft and hard segment block copolymer polyimides of the present invention in Examples 1 to 3 and comparative examples are shown in the figure.

[0019] Appendix Figure 5 Figures showing the test results of energy density and energy storage efficiency of soft and hard segment block copolymer polyimides in Examples 1 to 3 and comparative examples of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be described in more detail below with reference to embodiments. However, it should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention in any way. Any equivalent substitutions or modifications made in accordance with the ideas and teachings of the present invention should be covered within the protection scope of the present invention. Example 1

[0021] Raw materials used in the examples: 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA), 4,4'-(4,4'-isopropylidene diphenoxy) bis(phthalic anhydride) (BPADA), 4,4'-oxodiphenylamine (ODA), 4,4'-diaminodiphenyl sulfone (DDS) and N-methylpyrrolidone (NMP) solvent.

[0022] This embodiment describes the synthesis process of a block copolymer polyimide (named BO1-DF1) with a soft-hard segment molar ratio of 1:1.

[0023] (1) Preparation of monomer solutions: ODA, BPADA, 6FDA and DDS monomers were dissolved in NMP and prepared into solutions with a concentration of 150 mg / mL under continuous stirring. -1 The stock solution.

[0024] (2) Synthesis of polyamic acid (PAA) oligomers: Under nitrogen protection, 0.94 mL of BPADA solution was added dropwise to 0.40 mL of ODA solution, and the mixture was stirred vigorously at room temperature for 6 hours to obtain an amino-terminated soft segment BO oligomer solution. Simultaneously, in another reaction flask, 0.89 mL of 6FDA solution was added dropwise to 0.45 mL of DDS solution, and the mixture was stirred vigorously for 6 hours under the same conditions to obtain an anhydride-terminated hard segment DF oligomer solution.

[0025] (3) Block copolymerization: Freshly prepared PAA oligomer solutions of BO and DF were mixed and stirred for 18 hours under nitrogen protection to obtain a yellow, viscous PAA block copolymer precursor solution.

[0026] (4) Casting and Thermal Imidization: The precursor solution was uniformly cast onto a clean glass plate. First, it was dried in a vacuum oven at 40°C for 24 hours to remove most of the solvent. Then, thermal imidization was performed using a stepped heating process, i.e., heating at 150°C, 200°C, and 250°C for 1 hour each. After cooling to room temperature, the formed film was carefully peeled off from the glass substrate to obtain the BO1-DF1 block copolymer polyimide film.

[0027] Example 2: The block copolymer polyimide BO2-DF1 was prepared according to the general steps of Example 1, except that the amount of monomer solution was adjusted so that the molar ratio of soft segment (BO) to hard segment (DF) was 2:1.

[0028] Example 3: The block copolymer polyimide BO1-DF2 was prepared according to the general steps of Example 1, except that the amount of monomer solution was adjusted so that the molar ratio of soft segment (BO) to hard segment (DF) was 1:2.

[0029] Comparative Example 1: Preparation of Homopolymer Polyimide BO To compare performance, a homopolymer with pure soft segments (named BO) was synthesized using conventional methods. The monomer molar ratio of BPADA and ODA was maintained at 1:1 during the polymerization reaction, and the remaining steps were carried out according to the general procedure of Example 1.

[0030] The dielectric properties and electrostatic energy storage properties of the thin film were tested.

[0031] In summary, the above embodiments are only for illustrating the relevant principles and implementation methods, and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention without departing from the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A block copolymeric polyimide dielectric material characterized by, The block copolymer is composed of at least one flexible soft segment and at least one rigid hard segment connected alternately; and the soft segment and the hard segment are incompatible in thermodynamics and can drive the formation of a nano-scale micro-phase separation structure inside the polymer.

2. The dielectric material of claim 1, wherein, The soft segment is polymerized from a first diamine monomer and a first dianhydride monomer.

3. The block co-polyimide dielectric material of claim 2, wherein, The first diamine monomer is 4,4'-oxydianiline (ODA), and the first dianhydride monomer is 4,4'-(4,4'-isopropylidene diphenyloxy) bis(phthalic anhydride) (BPADA).

4. The block co-polyimide dielectric material of claim 1, wherein, The hard segment is polymerized from a second dianhydride monomer containing an electron-withdrawing group and a second diamine monomer containing a large dipole moment group.

5. The block co-polyimide dielectric material of claim 4, wherein, The second dianhydride monomer is 4,4'-(hexafluoroisopropylidene) diphenyl dicarboxylic anhydride (6FDA), and the second diamine monomer is 4,4'-diaminodiphenyl sulfone (DDS).

6. The block co-polyimide dielectric material of claim 1, wherein, The optimized molar ratio of the soft segment to the hard segment is 1:

1.

7. The block copolymer polyimide dielectric material according to claims 1-7, which is applied in the field of thin film capacitors and electrical insulation materials.

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