Composite dielectric material as well as preparation method and application of in-situ generated core-shell structure nanofiller of composite dielectric material

Abstract

The invention discloses a composite dielectric material and a preparation method and application of in-situ generated core-shell structure nanofiller of the composite dielectric material, and belongs to the technical field of advanced functional high polymer materials.The method comprises the steps that a polymer matrix, a soluble filler precursor and a shell layer substance are dissolved in a solvent and stirred till a homogeneous precursor solution is formed; after the solvent is removed, a solid pre-complex is formed; the preparation method comprises the following steps: performing in-situ conversion on a soluble filler precursor into an insoluble nano filler core through heat treatment, and coating the surface of the nano filler core with a shell substance to form an in-situ generated core-shell structure nano filler, and dispersing the core-shell structure nano filler in a polymer matrix to obtain the composite dielectric material. The filler precursor is converted into an insoluble nano filler core in situ in a polymer matrix, and is spontaneously coated by a shell layer substance to form the core-shell structure nano filler with extremely uniform dispersion. The problem of agglomeration of the nanofiller is fundamentally solved, and the high-performance composite dielectric material with super-uniform dispersion and excellent comprehensive performance is obtained.

Description

Technical Field

[0001] This invention belongs to the field of advanced functional polymer materials technology, specifically relating to the preparation method and application of composite dielectric materials and their in-situ generated core-shell structured nanofillers. Background Technology

[0002] Introducing nanofillers with excellent dielectric, heat resistance, or thermal conductivity properties into a polymer matrix is ​​a common strategy for preparing high-performance composite dielectric materials. However, the success of this strategy largely depends on the dispersion state of the nanofillers in the polymer matrix. Traditional preparation methods, namely the non-in-situ method of "synthesizing the filler first and then melt-blending," face a deep-rooted problem: due to their extremely high specific surface energy, nanoparticles are prone to secondary aggregation, forming micron-sized aggregates.

[0003] These agglomerates not only fail to effectively utilize the size effect of nanomaterials, but also become stress concentration points and sources of electric field distortion within the material, severely weakening the mechanical and electrical insulation properties of the composite material. In the fabrication of capacitor films, these agglomerates often lead to film rupture during biaxial stretching, making industrial production difficult. Although surface modification and high-intensity shearing can improve dispersion to some extent, fundamentally eliminating secondary agglomeration and achieving truly molecular-level uniform dispersion of nanofillers in the matrix remains a significant challenge.

[0004] Therefore, there is an urgent need to develop a novel method for preparing composite materials that can bypass the inherent defects of traditional blending methods, ensure the ultimate dispersion of nanofillers from the source, and thus fully unleash the performance potential of nanocomposite materials. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing composite dielectric materials and their in-situ generated core-shell structured nanofillers, as well as their applications, so as to solve the technical problem of easy agglomeration of nanofillers in the existing composite dielectric material preparation methods.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a composite dielectric material with in-situ generated core-shell structured nanofillers, comprising: dissolving a polymer matrix, a soluble filler precursor, and a shell material together in a solvent and stirring until a homogeneous precursor solution is formed; removing the solvent from the homogeneous precursor solution to form a solid precomposite; and subjecting the solid precomposite to heat treatment to transform the soluble filler precursor into an insoluble nanofiller core in situ, while the shell material coats the surface of the nanofiller core, forming an in-situ generated core-shell structured nanofiller and dispersing it in the polymer matrix to obtain the composite dielectric material.

[0007] Preferably, the polymer matrix is ​​a thermoplastic polymer selected from at least one of polypropylene, polyetherimide, polycarbonate and polyvinylidene fluoride; The soluble filler precursor is a soluble polybenzoxazole precursor, a soluble phenolic resin, or a polyacrylonitrile. When the soluble filler precursor is polyamic acid, the polyamic acid is converted in situ into the polyimide nanofiller core during the heat treatment process. When the polymer matrix is ​​polypropylene, the solvent is decahydronaphthalene; When the polymer matrix is ​​polyetherimide, polycarbonate or polyvinylidene fluoride, the solvent is N,N-dimethylformamide or N-methylpyrrolidone.

[0008] Preferably, the shell material is an ionic liquid or a surfactant; The ionic liquid is at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate; The surfactant is at least one of polyoxyethylene-polyoxypropylene block copolymer, sorbitan monooleate, and polyethylene glycol monostearate.

[0009] Preferably, the mass ratio of polymer matrix, soluble filler precursor and shell material is (80-99):(1-20):(0.1-5); the stirring time is 12-48 h.

[0010] Preferably, the method for removing solvent from the homogeneous precursor solution includes: forming a film by solution casting, scraping or spraying; and drying at 60-100°C for 6-24 h.

[0011] Preferably, the heat treatment conditions include: under nitrogen protection, heat treatment is carried out according to the following procedure: from room temperature to 130-170°C at a rate of 2-10°C / min and held for 0.5-2 h, then at a rate of 2-10°C / min to 230-300°C and held for 1-4 h, and then naturally cooled to room temperature.

[0012] The present invention also discloses a composite dielectric material, which is prepared by the above-mentioned method for preparing composite dielectric materials with in-situ core-shell structured nanofillers.

[0013] Preferably, the composite dielectric material comprises a polymer matrix and in-situ generated core-shell structured nanofillers dispersed in the polymer matrix, wherein the average particle size of the core-shell structured nanofillers is less than 100 nm.

[0014] The present invention also discloses a dielectric thin film, which is a composite dielectric material prepared by the above-mentioned method for preparing a composite dielectric material containing an in-situ generated core-shell structured nanofiller.

[0015] The present invention also discloses a thin-film capacitor comprising the above-described dielectric thin film.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing composite dielectric materials with in-situ core-shell structured nanofillers. First, a molecularly homogeneous precursor system is constructed. Then, through solvent removal and heat treatment, the in-situ generation and uniform dispersion of the core-shell structured nanofillers are achieved. Instead of blending pre-synthesized nanofillers with polymers, the core-shell structured nanofillers are generated in-situ within a molecularly homogeneous precursor system, avoiding nanofiller agglomeration. This effectively prevents nanofiller agglomeration and achieves molecularly homogeneous dispersion, thereby improving the dielectric properties and thermal stability of the composite dielectric material. The in-situ generation strategy fundamentally solves the problem of nanofiller agglomeration in traditional methods, achieving molecularly homogeneous dispersion of the nanofillers in the polymer matrix. This results in a denser filler-matrix interface with fewer defects, which is beneficial for charge management and stress transfer. This method allows the size effect of the nanofillers to be fully utilized, thereby improving the dielectric properties and heat resistance of the composite dielectric material and avoiding performance degradation caused by agglomeration. Furthermore, thermoplastic polymers are polymers that soften and melt when heated, and solidify upon cooling, a process that can be repeated. They typically possess good processability and mechanical properties. Selecting a specific thermoplastic polymer as the matrix ensures good flowability and plasticity of the composite material during processing, while simultaneously imparting the required dielectric properties, mechanical strength, and heat resistance. Polypropylene, polyetherimide, polycarbonate, and polyvinylidene fluoride are common, high-performance dielectric materials, each with different dielectric constants, loss tangents, breakdown strengths, and temperature resistances, which can be selected based on specific application requirements. Polypropylene exhibits low dielectric loss and high breakdown strength; polyetherimide, on the other hand, possesses excellent high-temperature resistance and mechanical strength. The soluble filler precursor is polyamic acid, a soluble polymer, commonly used as a precursor for polyimide. Polyimide is a high-performance polymer with excellent heat resistance, mechanical strength, and electrical insulation. Polyamic acid was chosen as the soluble filler precursor due to its excellent solubility in solvents, ensuring thorough mixing with the polymer matrix and shell material in the homogeneous precursor solution. During subsequent heat treatment, polyamic acid is converted in situ into insoluble polyimide via a dehydration cyclization reaction, forming the nanofiller core. This in-situ conversion mechanism ensures uniform dispersion of the nanofiller in the polymer matrix and avoids the problem of pre-fabricated nanofiller agglomeration. Polyimide, as the core material, provides a high dielectric constant and excellent heat resistance, thereby improving the overall performance of the composite dielectric material. Solvent selection is crucial for dissolving the polymer matrix and soluble filler precursor. When the polymer matrix is ​​polypropylene, decahydronaphthalene serves as an excellent solvent, effectively dissolving polypropylene to form a homogeneous solution. This ensures thorough mixing of the polymer matrix, soluble filler precursor, and shell material in solution, laying the foundation for the subsequent formation of a homogeneous precursor solution. When the polymer matrix is ​​polyetherimide, N,N-dimethylformamide or N-methylpyrrolidone are commonly used, highly efficient solvents. These solvents can fully dissolve polyetherimide, ensuring that all components are uniformly dispersed when preparing homogeneous precursor solutions, avoiding phase separation or precipitation, thereby guaranteeing the macroscopic uniformity and microstructural consistency of the final composite material.

[0017] Furthermore, ionic liquids are a class of salts that are liquid at or near room temperature, typically composed of organic cations and inorganic or organic anions. They possess high ionic conductivity, low vapor pressure, good thermal stability, and the ability to dissolve a variety of substances. In this application, ionic liquids serve as shell materials; their unique polar properties and good fluidity help provide a stable microenvironment during the formation of the nanofiller core, promoting uniform shell coating. In addition, the interfacial interaction between the ionic liquid, the polymer matrix, and the nanofiller core helps improve the dispersibility of the nanofiller in the polymer matrix and reduces agglomeration. Surfactants are molecules with both hydrophilic and lipophilic groups, capable of reducing liquid surface tension and forming an adsorption layer at the interface. In this application, surfactants serve as shell materials; their amphiphilic structure allows them to adsorb onto the surface of the nanofiller core, forming a stable protective layer that effectively prevents agglomeration of the nanofiller during formation and dispersion. By selecting appropriate surfactants, the surface properties of the nanofiller core can be controlled, enhancing its compatibility with the polymer matrix, thereby achieving uniform dispersion of the nanofiller in the polymer matrix.

[0018] Furthermore, by precisely controlling the mass ratio of the polymer matrix, soluble filler precursor, and shell material, it is possible to ensure that each component exists in the optimal proportion. This allows for the full conversion of the soluble filler precursor and the complete encapsulation of the nanofiller core by the shell material during heat treatment, effectively avoiding core-shell structure defects or uneven filler dispersion caused by improper component ratios. Simultaneously, the stirring time of 12-48 hours greatly promotes the uniform dissolution and mixing of each component in the solvent, forming a highly homogeneous homogeneous precursor solution, laying the foundation for the subsequent formation of the solid pre-composite. This precise proportioning and thorough mixing work synergistically to ensure highly uniform dispersion of the in-situ generated core-shell nanofiller in the polymer matrix, significantly improving the dielectric stability, breakdown strength, and service life of the composite dielectric material, overcoming the performance fluctuation problems caused by component inhomogeneity and insufficient mixing in traditional methods.

[0019] Furthermore, removing the solvent from the homogeneous precursor solution aims to effectively separate the solvent, allowing the polymer matrix, soluble filler precursor, and shell material to solidify and tightly bond, forming a solid pre-composite with a specific shape and strength. This process is crucial for ensuring the smooth progress of subsequent heat treatment and the formation of uniformly dispersed core-shell structured nanofillers. During film formation, any of the following methods can be used: solution casting, blade coating, or spray coating. Solution casting involves directly pouring the homogeneous precursor solution onto a flat substrate, forming a thin film through natural solvent evaporation or auxiliary heating. This method is simple and yields a smooth film surface. Blade coating uses a blade or scraper to uniformly coat the homogeneous precursor solution onto the substrate, forming a wet film with controllable thickness, which is then cured by solvent evaporation. This method allows for precise control of film thickness and improves film uniformity. Spray coating atomizes the homogeneous precursor solution and sprays it onto the substrate surface to form a uniform thin film. This method is suitable for coating substrates with complex shapes and enables rapid film formation. A drying temperature of 60-100℃ is designed to provide sufficient heat energy to accelerate solvent evaporation while avoiding excessively high temperatures that could lead to undesirable degradation or phase separation of the polymer matrix or precursor. A drying time of 6-24 hours ensures that the solvent is fully and thoroughly removed from the precomposite, minimizing the impact of residual solvent on subsequent heat treatment and the final material properties.

[0020] Furthermore, nitrogen effectively isolates the material from oxygen in the air, preventing oxidation or thermal degradation of the polymer matrix, soluble filler precursor, and shell material under high-temperature conditions, thus ensuring the chemical stability and structural integrity of the material during the conversion process. The heat treatment procedure first raises the temperature from room temperature to 130-170°C at a rate of 2-10°C / min and holds it for 0.5-2 hours. This relatively gentle heating rate helps the solid pre-composite to be heated uniformly, avoiding internal stress accumulation due to rapid heating. Subsequently, a temperature of 230-300°C is usually sufficient to drive the complete chemical conversion of the precursor, and a holding time of 1-4 hours ensures the full progress of the conversion reaction and promotes the formation of a stable and dense coating layer on the surface of the newly formed nanofiller core. After the high-temperature holding is completed, the material is cooled to room temperature naturally. Natural cooling is a slow cooling process that can effectively avoid internal stress caused by thermal shock during rapid cooling of materials, thereby preventing cracking, deformation or microstructural defects in composite materials. It helps to maintain the integrity and stability of the macroscopic morphology and microstructure of the final composite dielectric material.

[0021] This invention discloses a composite dielectric material comprising a polymer matrix and in-situ generated core-shell structured nanofillers dispersed within the polymer matrix. The core-shell structured nanofillers consist of a nanofiller core and a shell material coating the surface of the core. The nanofiller core is formed in-situ from a soluble filler precursor during heat treatment. Because the core-shell structured nanofillers are generated in-situ within the polymer matrix, the components are uniformly mixed at the molecular level, fundamentally avoiding secondary agglomeration of nanoparticles and achieving a uniform dispersion effect that is difficult to achieve with traditional methods. Simultaneously, the in-situ generation process helps form a denser filler-matrix interface with fewer defects, which is beneficial for stress transfer and charge management. This extreme dispersibility allows the size effect of the nanofillers to be fully utilized, more effectively improving the dielectric properties and heat resistance of the material while avoiding performance degradation caused by agglomeration.

[0022] Furthermore, controlling the average particle size of the nanofiller to below 100 nm is crucial to ensuring its uniform dispersion within the polymer matrix. When the nanofiller size is too large, it is prone to agglomeration in the polymer matrix, forming macroscopic defects that reduce the dielectric breakdown strength of the composite material and increase dielectric loss. By precisely controlling the average particle size of the nanofiller at the nanoscale, the interfacial area between the filler and the polymer matrix can be significantly increased, optimizing interfacial interactions and thus improving the overall dielectric properties of the composite material. Achieving this small particle size typically requires fine-tuning the reaction conditions during the in-situ conversion process, adjusting the concentration of the soluble filler precursor, reaction temperature, reaction time, and the coating conditions of the shell material to promote the formation of uniform and fine nanocores and ensure effective coating by the shell material.

[0023] This invention discloses a dielectric thin film. In traditional dielectric thin film preparation, the nanofiller is prone to agglomeration during blending with the polymer matrix, leading to uneven filler dispersion. This not only affects the stability of dielectric properties but may also cause localized electric field concentration, reducing breakdown field strength and lifespan. This invention uses an in-situ generation method to prepare a dielectric thin film from a composite dielectric material, achieving molecular-level uniform dispersion of the core-shell structured nanofiller within the polymer matrix, fundamentally avoiding the problem of secondary agglomeration of the nanofiller. The core-shell structured nanofiller in this dielectric thin film consists of a nanofiller core and a shell material covering its surface. The core is formed by the in-situ transformation of a soluble filler precursor into insoluble nanoparticles during heat treatment, while the shell material spontaneously coats the core surface during the transformation, forming a stable interface structure. This structural design not only significantly improves the compatibility between the filler and the matrix but also optimizes the charge transport path and stress distribution, effectively suppressing the generation of interface defects. The prepared dielectric film has an ultra-uniform filler dispersion, excellent dielectric strength and thermal stability, which can give full play to the size effect of nanofillers and avoid performance degradation caused by agglomeration, thereby meeting the stringent requirements of high-performance film capacitors for dielectric materials.

[0024] This invention discloses a thin-film capacitor comprising the aforementioned dielectric film. A thin-film capacitor is an important electronic component whose primary function is to store electrical energy in an electric field. It typically consists of two conductive electrodes and a dielectric layer sandwiched between them. In thin-film capacitors, these layers are fabricated to an extremely thin thickness, typically on the nanometer to micrometer scale, enabling the capacitor to achieve high capacitance density and compact device size. By integrating the aforementioned dielectric film into the thin-film capacitor, the excellent dielectric properties of the dielectric film can be directly utilized, thereby achieving efficient energy storage. Since the dielectric film is prepared from a composite dielectric material with in-situ generated core-shell nanofillers, the internal core-shell nanofillers effectively improve the dielectric constant and breakdown strength of the material. When used as the dielectric layer of a thin-film capacitor, it significantly enhances the energy density and power density of the capacitor while maintaining good operational stability. This integration method allows high-performance materials to be transformed into practical application devices, providing a key energy storage solution for miniaturized, highly integrated electronic devices. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the preparation process of the composite dielectric material disclosed in this invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0029] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0030] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0031] In this invention, unless otherwise specified, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply a shortened representation of these numerical combinations.

[0032] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0033] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0034] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0035] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0036] The method for preparing the composite dielectric material disclosed in this invention includes the following steps: 1) Construction of a homogeneous precursor solution: The polymer matrix, one or more soluble filler precursors, and a shell material are dissolved together in one or more co-solvents to form a completely homogeneous, molecularly mixed precursor solution. The mass ratio of the polymer matrix, soluble filler precursor, and shell material is (80-99):(1-20):(0.1-5); the stirring and dissolution time is 12-48 h.

[0037] 2) Formation of a solid precomplex: A film is formed by solution casting, scraping, or spraying, and the solvent is slowly removed. It is then dried at 60-100℃ for 6-24 hours. Because the components are "locked in" at the molecular level, a highly uniform mixing state is maintained even during solvent evaporation, forming a solid precomplex.

[0038] 3) In-situ transformation and core-shell formation: The solid precomposite is subjected to specific treatment (usually heat treatment, with conditions including: under nitrogen protection, heat treatment according to the following procedure: from room temperature to 130-170℃ at a rate of 2-10℃ / min and hold for 0.5-2 h, then heat to 230-300℃ at a rate of 2-10℃ / min and hold for 1-4 h, followed by natural cooling to room temperature). During this treatment, the soluble filler precursor undergoes irreversible chemical transformation (such as dehydration cyclization, crosslinking, etc.), generating an in-situ insoluble and infusible nanofiller core. Simultaneously, the shell material, pre-uniformly dispersed around it, spontaneously coats the surface of the newly generated nanofiller core due to the principle of energy minimization or specific intermolecular interactions, thus forming an in-situ generated core-shell structured nanofiller dispersed in the polymer matrix.

[0039] The selection of components and process details of the method of the present invention are as follows: Polymer matrix: The polymer should be selected that can form a co-solution with the filler precursor and shell material in a specific solvent. For high-temperature applications, polymers with good heat resistance, such as polyetherimide (PEI), are preferred. For general-purpose capacitors, polypropylene (PP) and polyvinylidene fluoride (PVDF) can also be selected, but a suitable solvent system needs to be chosen (e.g., the high-temperature solvent decahydronaphthalene is used for PP).

[0040] Soluble filler precursors: The key is to select a soluble substance that can be transformed into the target high-performance filler in subsequent processing. A typical example is polyamic acid (PAA), which is soluble in strongly polar solvents such as N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP), and is transformed in situ into high-performance, insoluble and infusible polyimide (PI) through a dehydration cyclization reaction at high temperatures (>200℃). PI has excellent heat resistance and dielectric properties.

[0041] Soluble filler precursors also include, but are not limited to: Soluble polybenzoxazole precursor (polyhydroxyamide): can be dehydrated and cyclized under heat treatment to generate high-modulus, high-heat-resistant polybenzoxazole (PBO) nanofillers in situ.

[0042] Soluble phenolic resins (such as linear phenolic resins): can undergo cross-linking and curing under heat treatment to generate cross-linked phenolic resin nanofillers in situ, or carbonize at higher temperatures to generate nano-carbon fillers.

[0043] Polyacrylonitrile (PAN): Soluble in solvents such as DMF, it can undergo cyclization and graphitization under heat treatment, generating in-situ graphene-like or turbine-layered carbon nanofillers.

[0044] These precursors all meet the technical characteristics of being soluble and capable of in-situ conversion in this invention, providing a variety of feasible technical paths for those skilled in the art to select according to the required filler performance.

[0045] Shell material: Used to coat the core during in-situ formation and improve the interfacial interaction between the final core-shell filler and the matrix. Suitable choices include ionic liquids (ILs) or specific surfactants. Ionic liquids are ideal for forming functional shells due to their unique polarity and interaction with a variety of polymers. The shell material is either an ionic liquid or a surfactant; the ionic liquid is at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate; the surfactant is at least one of polyoxyethylene-polyoxypropylene block copolymer (Pluronic F-127), sorbitan monooleate (Span 80), and polyethylene glycol (400) monostearate.

[0046] Solvent: Must be able to dissolve all three components simultaneously. For example, when the matrix is ​​PEI and the precursor is PAA, NMP or DMF are good co-solvents. When the polymer matrix is ​​polypropylene, the solvent is decahydronaphthalene; when the polymer matrix is ​​polyetherimide, polycarbonate, or polyvinylidene fluoride, the solvent is N,N-dimethylformamide or N-methylpyrrolidone.

[0047] In-situ conversion: Primarily achieved through heat treatment (iminolation). The temperature and time procedures for heat treatment need precise control to ensure complete conversion of PAA to PI while avoiding degradation of the matrix polymer. The filler precursor is a soluble polymer precursor that transforms into an insoluble nanofiller core during heat treatment through dehydration cyclization, crosslinking, or pyrolysis reactions.

[0048] The beneficial effects of this invention are as follows: 1. Extreme dispersibility: Since the filler core is generated in situ in a molecular-level mixed state, the problem of secondary agglomeration of nanoparticles is fundamentally avoided, achieving a uniform dispersion effect that is difficult to achieve with traditional methods.

[0049] 2. Excellent interfacial bonding: The in-situ generation process helps to form a tighter filler-matrix interface with fewer defects, which is beneficial for stress transfer and charge management.

[0050] 3. Maximizing performance: The extreme dispersibility allows the size effect of nanofillers to be fully utilized, which can more effectively improve the overall properties of materials such as dielectric and heat resistance, while avoiding performance degradation caused by agglomeration.

[0051] 4. Process integration potential: This method integrates filler synthesis with composite material preparation, providing the possibility for developing integrated thin film manufacturing processes.

[0052] Figure 1 This is a schematic diagram of the preparation process of the composite dielectric material disclosed in this invention. As shown in the diagram, the preparation process of the composite dielectric material consists of three steps: dissolving the polymer matrix, soluble filler precursor, and shell material together in a solvent and stirring until a homogeneous precursor solution is formed; removing the solvent from the homogeneous precursor solution to form a solid pre-composite; and subjecting the solid pre-composite to heat treatment, causing the soluble filler precursor to transform in situ into an insoluble nanofiller core, while the shell material coats the surface of the nanofiller core, forming an in-situ generated core-shell structured nanofiller that is dispersed in the polymer matrix, thus obtaining the composite dielectric material. This method effectively solves the problems of easy agglomeration and uneven dispersion of nanofillers in traditional methods by controlling the formation and coating of fillers at the molecular level, thereby obtaining a composite dielectric material with uniform dispersion and excellent comprehensive performance.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] Example 1 Preparation of in-situ generated PI@IL / PEI composite materials (low filler content) 1) Preparation of precursor solution: In a clean, dry beaker, 9.4 g of polyetherimide (PEI) particles were dissolved in 100 mL of N-methylpyrrolidone (NMP), and the solution was heated and stirred until completely dissolved. After cooling to room temperature, 0.5 g of polyamic acid (PAA, prepared from pyromellitic dianhydride and diaminodiphenyl ether, a 15% solids NMP solution) and 0.1 g of the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) were added. The mixture was stirred continuously for 24 h to ensure that all components were mixed evenly, forming a transparent, viscous, homogeneous precursor solution.

[0055] 2) Preparation of pre-composite membrane: The above precursor solution was uniformly cast onto a clean glass plate, and the thickness was controlled by a doctor blade. The glass plate was placed in a vacuum oven at 80°C and dried for 12 hours to slowly remove most of the NMP solvent, resulting in a solid pre-composite membrane.

[0056] 3) In-situ transformation: The glass plate with the pre-composite film was placed in a temperature-controlled muffle furnace. Under nitrogen protection, the heat treatment was carried out according to the following procedure: the temperature was increased from room temperature to 150°C at a rate of 5°C / min and held for 1 hour, then increased to 250°C at a rate of 5°C / min and held for 2 hours, and finally cooled naturally to room temperature. During this process, PAA was transformed in-situ into PI nanocores and coated with [EMIM][BF4].

[0057] 4) Final material acquisition: The heat-treated film is carefully peeled off from the glass plate, which is the PEI composite dielectric material film containing about 5 wt% in-situ generated PI@IL core-shell filler.

[0058] Example 2 Preparation of in-situ generated PI@IL / PEI composite materials (high filler content) All steps of Example 1 were repeated, except that in step 1, “Precursor Solution Preparation,” the amounts of each component were adjusted to: 8.9 g PEI, 1.0 g PAA, and 0.1 g [EMIM][BF4]. The final product was a PEI composite dielectric film containing approximately 10 wt% in-situ generated PI@IL core-shell filler.

[0059] Example 3 Preparation using different shell materials All steps of Example 1 were repeated, except that in step 1, “Precursor Solution Preparation”, 0.1 g of ionic liquid [EMIM][BF4] was replaced with 0.1 g of surfactant Pluronic F-127. The final product was a PEI composite dielectric film containing approximately 5 wt% in-situ generated PI@F-127 core-shell filler.

[0060] Example 4 Preparation of different ionic liquids All steps of Example 1 were repeated, except that in step 1, “Precursor Solution Preparation”, 0.1 g of the ionic liquid [EMIM][BF4] was replaced with 0.1 g of the ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM][PF6]), which has a long-chain alkyl group. The final product was a PEI composite dielectric film containing approximately 5 wt% in-situ generated PI@[OMIM][PF6] core-shell filler.

[0061] Example 5 Preparation using polypropylene matrix 1) Preparation of precursor solution: In a high-pressure reactor, 9.4 g of random copolymer polypropylene (PP) particles, 0.5 g of PAA (solid powder), and 0.1 g of ionic liquid [OMIM][PF6] were added to 100 mL of decahydronaphthalene solvent. The reactor was sealed, heated to 160 °C under nitrogen protection, and stirred vigorously until all components were completely dissolved to form a homogeneous solution.

[0062] 2) Pre-composite and in-situ conversion: While maintaining a high temperature, the solution was rapidly cast onto a preheated metal plate. After rapid solvent evaporation, a solid pre-composite film was formed. Subsequently, the film was transferred to a muffle furnace and, under nitrogen protection, heated to 250°C at a rate of 5°C / min and held for 2 hours for in-situ conversion. The final product was a PP composite dielectric material containing in-situ generated PI@[OMIM][PF6] core-shell filler.

[0063] Example 6 Preparation using polyvinylidene fluoride body and block copolymer shell Precursor solution preparation: In a clean, dry beaker, 92 g of polyvinylidene fluoride (PVDF) powder was dissolved in 1000 mL of N,N-dimethylformamide (DMF) and stirred at 60 °C until completely dissolved. After cooling to room temperature, 7 g of polyamic acid (PAA, solid powder) and 1 g of surfactant Pluronic F-127 were added. The mixture was mechanically stirred continuously at room temperature for 36 h to form a homogeneous precursor solution.

[0064] Preparation of pre-composite film: The above solution was coated onto a glass plate at 80°C by a blade coating method, and then dried in a vacuum oven at 70°C for 20 hours to obtain a solid pre-composite film.

[0065] In-situ conversion: A glass plate with a pre-composite film was placed in a muffle furnace and heated to 160°C at a rate of 8°C / min under nitrogen protection and held for 1.5 h. Then, the temperature was increased to 280°C at a rate of 8°C / min and held for 1.5 h, followed by natural cooling. The final product was a PVDF composite dielectric material containing in-situ generated PI@F-127 core-shell filler.

[0066] Example 7 Preparation using polycarbonate matrix and different ionic liquids Precursor solution preparation: 97 g of polycarbonate (PC) particles were dissolved in 1000 mL of N-methylpyrrolidone (NMP) and stirred at 120 °C. After cooling, 2.5 g of PAA (solid powder) and 0.5 g of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) were added. The mixture was stirred continuously for 48 h to form a homogeneous precursor solution.

[0067] Preparation of pre-composite membrane: The solution was cast onto a glass plate and dried in a vacuum oven at 60°C for 24 hours to obtain a solid pre-composite membrane.

[0068] In-situ conversion: The pre-composite membrane was heated to 130℃ at a rate of 10℃ / min and held for 2 hours under nitrogen protection, then heated to 230℃ at a rate of 10℃ / min and held for 4 hours, and finally cooled naturally. The final product was a PC composite dielectric material containing in-situ generated PI@[BMIM][PF6] core-shell filler.

[0069] Example 8 Preparation using high-content fillers and different surfactants Precursor solution preparation: In a clean, dry beaker, 85 g of polyetherimide (PEI) particles were dissolved in 1000 mL of NMP and heated with stirring until dissolved. After cooling, 14 g of PAA (solid powder) and 1 g of surfactant sorbitan monooleate (Span 80) were added. The mixture was stirred continuously for 12 h to form a homogeneous precursor solution.

[0070] Preparation of pre-composite film: The solution was sprayed onto a metal substrate and dried in a vacuum oven at 100°C for 6 hours to obtain a solid pre-composite film.

[0071] In-situ conversion: The pre-composite membrane was heated to 170℃ at a rate of 2℃ / min and held for 0.5h under nitrogen protection, then heated to 300℃ at a rate of 2℃ / min and held for 1h, and finally cooled naturally. The final product was a PEI composite dielectric material containing approximately 15wt% in-situ generated PI@Span80 core-shell filler.

[0072] Example 9 Precursor solution preparation: In a clean, dry beaker, 9.8 g of PEI particles were dissolved in 100 mL of NMP and heated with stirring until completely dissolved. After cooling to room temperature, 0.1 g of soluble polybenzoxazole precursor (solid powder) and 0.1 g of surfactant polyethylene glycol monostearate were added. The mixture was stirred continuously for 24 h to form a homogeneous precursor solution (mass ratio 98:1:0.1, filler 1 wt%).

[0073] Pre-composite membrane preparation: The precursor solution was cast onto a clean glass plate, the thickness was controlled by a scraper, and the plate was dried in a vacuum oven at 80°C for 12 hours to obtain a solid pre-composite membrane.

[0074] In-situ conversion: The pre-composite membrane was placed in a muffle furnace and heated to 150°C at a rate of 5°C / min for 1 hour under nitrogen protection, then heated to 250°C at a rate of 5°C / min for 2 hours, and naturally cooled to room temperature. The soluble polybenzoxazole precursor was in-situ converted into a nano-core, which was then coated with polyethylene glycol monostearate. The membrane was peeled off to obtain a PEI composite dielectric film containing 1 wt% in-situ generated polybenzoxazole@polyethylene glycol monostearate core-shell filler.

[0075] Example 10 Precursor solution preparation: In a clean, dry beaker, 7.5 g of PEI particles were dissolved in 100 mL of NMP and heated with stirring until completely dissolved. After cooling to room temperature, 2.0 g of soluble phenolic resin (solid powder) and 0.5 g of ionic liquid [EMIM][BF4] were added. Stirring was continued for 24 h to form a homogeneous precursor solution (mass ratio 75:20:5, filler 20 wt%, shell 5 wt%).

[0076] Preparation of pre-composite membrane: The precursor solution was coated onto a glass plate and dried in a vacuum oven at 90°C for 18 hours to obtain a solid pre-composite membrane.

[0077] In-situ conversion: The pre-composite membrane was placed in a muffle furnace and heated to 150°C at a rate of 5°C / min for 1 hour under nitrogen protection, then heated to 280°C at a rate of 5°C / min for 3 hours, and naturally cooled to room temperature. Soluble phenolic resin was in-situ converted into a nano-core, which was then coated with [EMIM][BF4]. The film was peeled off to obtain a PEI composite dielectric film containing 20 wt% in-situ generated phenolic resin@[EMIM][BF4] core-shell filler.

[0078] Example 11 Precursor solution preparation: In a clean, dry beaker, 9.0 g of PVDF powder was dissolved in 100 mL of DMF and stirred at 60 °C until completely dissolved. After cooling to room temperature, 1.0 g of polyacrylonitrile (solid powder) and 0.2 g of surfactant Pluronic F-127 were added. The mixture was stirred continuously for 30 h to form a homogeneous precursor solution (mass ratio 90:10:2).

[0079] Preparation of pre-composite film: The precursor solution was sprayed onto the metal substrate and dried in a vacuum oven at 80°C for 15 hours to obtain a solid pre-composite film.

[0080] In-situ conversion: The pre-composite membrane was placed in a muffle furnace and heated to 160℃ at a rate of 6℃ / min for 1.5 h under nitrogen protection, then heated to 260℃ at a rate of 6℃ / min for 2.5 h, and naturally cooled to room temperature. Polyacrylonitrile was in-situ converted into a nano-core, which was then coated with Pluronic F-127. The membrane was peeled off to obtain a PVDF composite dielectric film containing 10 wt% in-situ generated polyacrylonitrile@Pluronic F-127 core-shell filler.

[0081] Example 12 Precursor solution preparation: In a high-pressure reactor, 9.5 g of PP particles, 0.4 g of polyacrylonitrile (solid powder) and 0.1 g of ionic liquid [OMIM][PF6] were added to 100 mL of decahydronaphthalene. Under nitrogen protection, the mixture was stirred vigorously at 160 °C until completely dissolved to form a homogeneous solution (mass ratio 95:4:1).

[0082] Pre-composite and in-situ conversion: The solution was rapidly cast onto a preheated metal plate at high temperature. After solvent evaporation, a pre-composite film was formed and transferred to a muffle furnace. Under nitrogen protection, the temperature was increased to 250℃ at a rate of 5℃ / min and held for 2 hours, followed by natural cooling. A PP composite dielectric material containing 4wt% in-situ generated polyacrylonitrile@[OMIM][PF6] core-shell filler was obtained.

[0083] Performance testing To verify the beneficial effects of the preparation method disclosed in this invention, the materials or films prepared in the above embodiments and comparative examples were characterized in terms of performance.

[0084] Comparative Example 1 Pure polymer matrix thin film 9.4 g of PEI particles from Example 1 were dissolved in 100 mL of NMP without adding any other components. Subsequently, film formation and heat treatment were performed according to steps 2) and 3) of Example 1 (the heat treatment procedure was only for removing residual solvent and eliminating thermal history, and did not involve chemical reactions) to obtain a pure PEI film.

[0085] Comparative Example 2 Traditional physical blending method for preparing composite materials First, 0.5 g of PAA (solid powder) was pre-converted into insoluble polyimide (PI) nanoparticles using the same heat treatment procedure as in Example 1. Then, the 0.5 g PI nanoparticles, 0.1 g of ionic liquid [EMIM][BF4], and 9.4 g of PEI particles were mechanically mixed and melt-blended and granulated at 320°C using a twin-screw extruder.

[0086] Test methods Processing performance (biaxial tensile strength): The composite material particles were cast into sheets by casting, and then subjected to a 5×5 tensile test on a biaxial tensile tester in the laboratory. The tensile process was observed to see if it was smooth and whether there were any holes or fractures. The film formation was recorded.

[0087] Dielectric property testing: Circular aluminum electrodes are vapor-deposited on the surface of the thin film, and the dielectric constant and dielectric loss are tested at 1 kHz frequency and 150 °C using a broadband dielectric spectrometer (such as Novocontrol Concept 80).

[0088] Breakdown performance test: A DC withstand voltage tester was used to conduct a breakdown test on the thin film sample at a high temperature of 150℃. The data were statistically analyzed using the Weibull distribution to obtain the characteristic breakdown field strength.

[0089] Energy storage performance calculation: based on the formula Calculate the theoretical energy storage density at 150℃.

[0090] Among them, U e ε is the energy storage density; ε0 is the vacuum permittivity; ε r E is the relative permittivity; b To break through the field strength.

[0091] Test Results

[0092] Results Analysis Improved Electrical Performance: Comparing Example 1 and Comparative Example 1 (pure PEI matrix), it can be seen that by generating PI@IL core-shell filler in situ, the dielectric constant of the composite material increased from 3.2 to 3.8, while the breakdown field strength also increased from 450 MV / m to 480 MV / m. This indicates that the method of the present invention not only improves the dielectric constant but also effectively suppresses electric field concentration and improves insulation performance due to the formation of a tight, defect-free interface. Ultimately, the energy storage density was significantly improved (from 2.9 J / cm³). 3 Up to 3.7 J / cm 3 ).

[0093] Universality of the method: Examples 5-11 demonstrate that the method of the present invention has good applicability to different polymer matrices (PP, PVDF, PEI) and different filler precursors (polyamic acid, polybenzoxazole precursor, phenolic resin, polyacrylonitrile). Regardless of the combination used, it can prepare composite materials with uniform dispersion and excellent performance, proving that the technical solution of the present invention has broad universality and industrial application value.

[0094] In summary, this invention relates to a composite dielectric material and its preparation method and application of in-situ generated core-shell structured nanofillers. This method avoids the traditional "synthesis followed by blending" process. Its core lies in: firstly, dissolving the polymer matrix, soluble filler precursor, and shell material together to form a molecularly uniform homogeneous precursor solution; then removing the solvent to form a solid pre-composite; finally, through heat treatment or other methods, the filler precursor is in-situ transformed into an insoluble nanofiller core within the polymer matrix, which is then spontaneously coated by the shell material, forming a highly uniformly dispersed core-shell structured nanofiller. For example, polyamic acid can be used as a precursor, in-situ transformed into a polyimide nanocore within a polyetherimide matrix, and then coated by an ionic liquid. This method fundamentally solves the problem of nanofiller agglomeration, aiming to prepare high-performance composite dielectric materials with ultra-uniform dispersion and excellent comprehensive performance.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite dielectric material with in-situ generated core-shell structured nanofillers, characterized in that, include: The polymer matrix, soluble filler precursor, and shell material are dissolved together in a solvent and stirred until a homogeneous precursor solution is formed. After removing the solvent from the homogeneous precursor solution, a solid precomplex is formed; The solid precomposite is heat-treated to transform the soluble filler precursor into an insoluble nanofiller core in situ. At the same time, the shell material coats the surface of the nanofiller core, forming an in-situ generated core-shell structured nanofiller that is dispersed in the polymer matrix to obtain a composite dielectric material.

2. The method for preparing composite dielectric materials with in-situ generated core-shell structured nanofillers according to claim 1, characterized in that, The polymer matrix is ​​a thermoplastic polymer selected from at least one of polypropylene, polyetherimide, polycarbonate and polyvinylidene fluoride; The soluble filler precursor is a soluble polybenzoxazole precursor, a soluble phenolic resin, or a polyacrylonitrile. When the soluble filler precursor is polyamic acid, the polyamic acid is converted in situ into the polyimide nanofiller core during the heat treatment process. When the polymer matrix is ​​polypropylene, the solvent is decahydronaphthalene; When the polymer matrix is ​​polyetherimide, polycarbonate or polyvinylidene fluoride, the solvent is N,N-dimethylformamide or N-methylpyrrolidone.

3. The method for preparing composite dielectric materials with in-situ generated core-shell structured nanofillers according to claim 1, characterized in that, The shell material is an ionic liquid or a surfactant; The ionic liquid is at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-octyl-3-methylimidazolium hexafluorophosphate; The surfactant is at least one of polyoxyethylene-polyoxypropylene block copolymer, sorbitan monooleate, and polyethylene glycol monostearate.

4. The method for preparing composite dielectric materials with in-situ generated core-shell structured nanofillers according to claim 1, characterized in that, The mass ratio of the polymer matrix, soluble filler precursor, and shell material is (80-99):(1-20):(0.1-5); the stirring time is 12-48 h.

5. The method for preparing composite dielectric materials with in-situ generated core-shell structured nanofillers according to claim 1, characterized in that, Methods for removing solvent from homogeneous precursor solutions include: forming a film by solution casting, scraping, or spraying; and drying at 60-100℃ for 6-24 h.

6. The method for preparing composite dielectric materials with in-situ generated core-shell structured nanofillers according to claim 1, characterized in that, The heat treatment conditions include: under nitrogen protection, heat treatment is carried out according to the following procedure: from room temperature to 130-170℃ at a rate of 2-10℃ / min and held for 0.5-2 h, then at a rate of 2-10℃ / min to 230-300℃ and held for 1-4 h, and then naturally cooled to room temperature.

7. A composite dielectric material, characterized in that, The composite dielectric material was prepared by the method for in-situ generation of core-shell structured nanofillers as described in any one of claims 1-6.

8. The composite dielectric material according to claim 7, characterized in that, The composite dielectric material comprises a polymer matrix and in-situ generated core-shell structured nanofillers dispersed in the polymer matrix, wherein the average particle size of the core-shell structured nanofillers is less than 100 nm.

9. A dielectric thin film, characterized in that, The composite dielectric material is prepared by the method of preparing the in-situ generated core-shell structured nanofiller as described in any one of claims 1-6.

10. A thin-film capacitor, characterized in that, It includes the dielectric thin film of claim 9.

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