Dielectric film based on dielectric graphene coating modification

Abstract

The invention discloses a dielectric film based on dielectric graphene coating modification, and belongs to the technical field of films. The core is a composite structure of a'graphene core-double-layer dielectric shell layer 'core-shell filler and a polymer matrix, the oxygen content of the graphene core is 5-8 at%, the sheet diameter is 50-200 nm, and the high polarization characteristic is reserved; the inner layer of the double-layer shell layer is a high-dielectric oxide, the outer layer is a high-insulation oxide, and the total thickness is 3-10nm; a core-shell filler is prepared through a sol-gel + ALD fine trimming process, and the core-shell filler is compounded with matrixes such as PVDF / PI and the like to form a film with the filling amount of 2-8 wt%; according to the design, electron tunneling is blocked, electric field distortion is corrected, and performance synergy is achieved, wherein the dielectric constant is larger than or equal to 21.5, the breakdown strength is larger than or equal to 402 kV / mm, the dielectric loss is smaller than or equal to 0.017, the tensile strength is larger than or equal to 56.9 MPa, and the energy density is 12-15 J / cm < 3 >. The contradiction between dielectric enhancement and loss and breakdown strength of a traditional composite material is solved, the method is suitable for high-density energy storage devices, flexible electronic devices and the like, and the technology is compatible with large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of thin film technology, and particularly relates to dielectric thin films based on dielectric graphene coating modification. Background Technology

[0002] As a core component of electronic devices, dielectric films rely heavily on dielectric constant (ε) and breakdown strength (Eb) to determine the energy density and reliability of these devices. In applications such as embedded capacitors and energy storage modules for electric vehicles, traditional dielectric materials face insurmountable performance contradictions: polymer matrices (such as polyvinylidene fluoride (PVDF) and polyimide (PI), while possessing high breakdown strength (typically 200-300 kV / mm) and excellent flexibility, generally have dielectric constants below 10, failing to meet the demands of high-density energy storage; while inorganic ceramic fillers (such as barium titanate (BT) and magnesium oxide (MgO), although significantly improving the dielectric constant, lead to increased material brittleness, a sharp drop in breakdown strength, and deteriorated processing performance at high filler concentrations. Graphene, as a two-dimensional carbon nanomaterial, offers a new pathway for dielectric modification due to its ultra-high theoretical dielectric constant and conductivity. However, existing graphene / polymer composite systems suffer from fatal flaws: the strong π-π interactions between graphene sheets easily lead to aggregation, forming a conductive network that causes a surge in dielectric loss; simultaneously, the dielectric property mismatch between graphene and the polymer matrix generates localized electric field concentration, significantly reducing breakdown strength. For example, the dielectric loss of unmodified graphene / PVDF composites typically exceeds 0.1 kV / mm, and the breakdown strength is less than 200 kV / mm, failing to meet practical application requirements. To address the aforementioned issues, existing technologies attempt to improve the dispersibility of graphene through surface functionalization, such as coating graphene with iron-containing MOF materials or grafting barium titanate onto graphene oxide. While these methods can improve dielectric properties, they still suffer from poor coating uniformity and insufficient synergy between dielectric and mechanical properties. Particularly under high-frequency operating conditions, interfacial polarization relaxation leads to increased dielectric loss and poor performance, limiting its applications. Therefore, developing a dielectric thin film that combines high dielectric constant, high breakdown strength, and low loss has become a pressing technical challenge in this field. Summary of the Invention

[0003] To address the problems in the prior art, the present invention proposes the following technical solution: A dielectric film based on dielectric graphene coating modification, wherein the dielectric film is composed of a core-shell structured dielectric graphene filler and a polymer matrix, and the core-shell structure is a "graphene core-double dielectric shell", comprising: Graphene core: oxygen content of 5-8 at%, retaining 92-95% of the π-electron conjugated structure, sheet diameter of 50-200 nm, and specific surface area of ​​500-800 m².2 / g; Double dielectric shell: Total thickness 3-10 nm, inner layer is high dielectric oxide with dielectric constant ε=10-300 and thickness 2-5 nm; outer layer is high insulating oxide with a bandgap width of [missing information]. >8eV, with a thickness of 1-5nm; Core-shell filler: 2-8 wt% by mass and 0.5-2 vol% by volume in dielectric thin films. Polymer matrix: selected from PVDF, PI, PET or PEEK; The dielectric film has a dielectric constant (1kHz) ≥21.5, a breakdown strength ≥402kV / mm, a dielectric loss (1kHz) ≤0.017, and a tensile strength ≥56.9MPa. As a preferred embodiment of the above technical solution, the preparation process of the graphene core includes the following steps: preparation of graphene oxide: natural graphite powder is mixed with concentrated sulfuric acid, potassium permanganate is added under ice bath conditions for oxidation, followed by hydrothermal reaction, hydrogen peroxide reduction, centrifugation and washing until pH=7.0±0.1, and then freeze-drying to obtain graphene oxide. Ethylene glycol modification: Graphene oxide was dispersed in DMF, ethylene glycol was added, and the reaction was carried out at 80±1℃ for 4.0 h under nitrogen protection. After centrifugation, washing and vacuum drying, the modified graphene oxide was obtained. Reduction treatment: The modified graphene oxide was dispersed in deionized water, hydrazine hydrate was added, and the reaction was carried out at 90±1℃ for 3.0h. After centrifugation, washing and vacuum drying, the graphene core was obtained. As a preferred embodiment of the above technical solution, the material combination of the double dielectric shell is selected from any of the following: Inner layer: MgO, BaTiO3 or TiO2; outer layer: Al2O3, ZrO2 or SiO2. Inner layer: MgO, outer layer: SiO2; Inner layer: BaTiO3, outer layer: ZrO2; Inner layer: SiO2, outer layer: Al2O3. As a preferred embodiment of the above technical solution, the preparation process of the core-shell filler includes two steps: sol-gel coating of the initial layer and ALD finishing. Sol-gel coating primary layer: Graphene cores are dispersed in an ethanol-water mixed solvent, a metal source and KH550 silane coupling agent are added, the pH is adjusted to 8-9, and the reaction is carried out at 60-80℃ for 3.0-4.0h. After centrifugation, washing and vacuum drying, the primary coated graphene is obtained. ALD refinement: The initially coated graphene is placed in an atomic layer deposition system, using trimethylaluminum, zirconium tetrachloride or tetraethyl orthosilicate as precursors, and deposited 50-200 times at 200-250℃ at a deposition rate of 0.05±0.005nm / cycle. After cooling, the core-shell filler is obtained. As a preferred embodiment of the above technical solution, the core-shell filler has a mass fraction of 5-6 wt%, the total thickness of the double dielectric shell is 6 nm, wherein the inner layer thickness is 3 nm and the outer layer thickness is 3 nm, and the corresponding dielectric film dielectric constant (1 kHz) is ≥28.5, the breakdown strength is ≥425 kV / mm, and the dielectric loss (1 kHz) is ≤0.014. As a preferred embodiment of the above technical solution, the preparation process includes the following steps: Preparation of blend: The core-shell filler was added to the solvent solution of the polymer matrix, ultrasonically dispersed for 30 min, stirred for 3.0 h under nitrogen protection, and vacuum degassed for 30 min to obtain the blend; Casting film: The blend solution was cast onto a plasma-treated glass plate at a speed of 8±0.5 cm / min, the film thickness was 200±10 μm, and the film was pre-dried at 80±1℃ for 4.0 h to obtain a wet film; Hot pressing curing: Set the hot pressing parameters according to the polymer matrix type: PVDF matrix: 160-180℃, 5-10MPa, 1.5h; PI matrix: 300±1℃, 10±0.5MPa, 2.0h; PET matrix: 130±1℃, 5±0.5MPa, 1.0h; PEEK matrix: 280±1℃, 10±0.5MPa, 2.0h. After cooling, peel off and cut the dielectric film to obtain a thickness of 50-150μm and a thickness uniformity of ±5%. As a preferred embodiment of the above technical solution, the dielectric thin film is used in high-density energy storage devices, flexible electronic devices, or high-frequency dielectric devices, with an energy density of 12-15 J / cm². 3 Bending resistance (radius 5mm) >1000 times, filler dispersion stability >6 months, sedimentation rate. As a preferred embodiment of the above technical solution, the interfacial energy between the core-shell filler and the polymer matrix is ​​≤10mJ / m. 2 Interface defect state density ≤10 12 cm -3 Interfacial shear strength ≥15MPa.

[0004] The beneficial effects of this invention are as follows: 1. By synergistically coating an inner layer of high-dielectric oxide (MgO / BaTiO3 / TiO2) and an outer layer of high-insulating oxide (Al2O3 / ZrO2 / SiO2), the high polarization characteristics of the graphene core are utilized to improve the dielectric constant, while the outer insulating shell blocks electron tunneling (when the shell thickness is ≥3nm, the tunneling probability T<10).-10 Meanwhile, the local electric field distortion coefficient was corrected (reduced from 125 to 0.9), achieving synergistic optimization of "high dielectric constant - high breakdown strength - low dielectric loss", breaking through the problem that "dielectric enhancement and loss, breakdown strength cannot be achieved simultaneously" in traditional graphene / polymer composite materials. 2. By controlling the nuclear oxygen content of graphene at 5-8 at%, 92-95% of the π-electron conjugated structure is retained to maintain the high polarization basis, while forming 0.5-1.0 electrons / nm. 2 The high hydroxyl density provides ample adhesion sites for uniform shell coating; simultaneously, it limits the flake diameter to 50-200 nm (specific surface area 500-800 nm). 2 / g), to avoid aggregation problems caused by insufficient specific surface area due to excessively small flake size or excessively large flake size. 3. Initial coating of the inner high-dielectric oxide layer is achieved via the sol-gel method, followed by atomic layer deposition (ALD) to prepare the outer insulating shell. The deposition rate is precisely controlled at 0.05±0.005 nm / cycle to ensure a uniform total shell thickness of 3-10 nm (thickness accuracy ±0.1 nm) and a low surface roughness. The bridging effect of KH550 silane coupling agent ensures that the interfacial energy between the core-shell filler and the polymer matrix is ​​≤10 mJ / m². 2 The interface defect state density decreased to 10 12 cm -3 The interfacial shear strength is ≥15MPa, which significantly improves the mechanical properties of the composite material and avoids the performance degradation problem caused by uneven shell and weak interfacial bonding in traditional coating processes. Detailed Implementation

[0005] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0006] The underlying logic of this technical solution is based on the "interface polarization synergistic insulation barrier effect of core-shell structure", and its microscopic mechanism and quantification principle are as follows: 1. Quantification mechanism of interfacial polarization-enhanced dielectric constant Dual interface polarization: graphene core (high conductivity σ≈10) 4 S / m) and dielectric shell (low conductivity σ≈10) -14 The first interface is formed by S / m, and the shell and the polymer matrix (σ≈10) form the first interface. -16 S / m) forms a second interface, and both types of interfaces satisfy the "high σ-low σ" polarization condition; Polarization intensity calculation: According to the Maxwell-Wagner-Sillars (MWS) polarization model, the formula for interface polarization intensity is: The meanings of each letter are as follows: Interfacial polarization intensity (unit: C / m) 2 ); Vacuum dielectric constant (dielectric constant under vacuum conditions, value is 8.85 × 10⁻⁶) -12 F / m (constant) The relative permittivity of a material (dimensionless, a core parameter characterizing the dielectric properties of a material). External electric field strength (unit: V / m); Formula for calculating the effective dielectric constant of core-shell structure: The meanings of each letter are as follows: Effective relative permittivity of core-shell structure; : The relative permittivity of the polymer matrix; Volume fraction of core-shell packing material (range 0-1); : Relative permittivity (dimensionless) of core-shell packing material; when =5wt% =80、 When =8, The calculated value is approximately 28, which closely matches the measured value. Polarization relaxation control: The shell thickness of 3-10nm is matched with the Debye relaxation length (5-15nm) to ensure that the polarization relaxation is synchronized with the electric field frequency in the 1kHz-1MHz frequency band, thus avoiding the increase of dielectric loss.

[0007] 2. Electronic mechanisms by which insulating shells suppress conductive pathways Electron tunneling blocking: Band gap of dielectric oxide shell >5 eV (MgO: 7.8 eV, Al2O3: 8.8 eV, SiO2: 8.9 eV), far exceeding the thermal excitation energy of electrons (≈0.026 eV at room temperature). The electron tunneling probability formula is: The meanings of each letter are as follows: Electron tunneling probability (representing the probability of an electron crossing a potential barrier); Dielectric shell thickness (unit: m); Electron rest mass (constant, value 9.11 × 10⁻⁶) -31 kg); : Bandgap width of dielectric shell (unit: J, 1eV=1.6×10⁻⁶) -19 J); Kinetic energy of electrons (unit: J); Reduced Planck constant (a constant with a value of 1.05 × 10⁻⁶) -34 J.s. , (where Planck's constant is used). when When ≥3nm, T -10 It can completely block electron tunneling between graphene sheets; Local electric field distortion correction: Local electric field distortion coefficients without graphene coating In the core-shell structure Combined with the insulating buffering effect of the shell, the final electric field distortion coefficient is reduced to 0.9, avoiding the concentration of breakdown field strength.

[0008] 3. Molecular mechanism of double-shell optimization of interfacial compatibility The role of the inner high dielectric oxide: There are a large number of hydroxyl groups (-OH) on the surface of MgO / BaTiO3 / TiO2, which form hydrogen bonds with the hydroxyl groups on the surface of the graphene core (bond energy ≈20-30kJ / mol), ensuring the bonding strength between the shell and the core (interfacial shear strength >15MPa). The role of the outer low-roughness oxide layer: After Al2O3 / SiO2 is deposited by ALD, the surface roughness is 5 nm. The interfacial energy with the polymer matrix (PVDF / PI) is calculated using the Young-Dupré equation. The meanings of each letter are as follows: Interfacial energy between solid (core-shell packing material) and liquid (polymer matrix) (unit: mJ / m) 2 ); Surface energy of solids and vacuum (unit: mJ / m) 2 ); Surface energy of liquids and vacuum (unit: mJ / m²) 2 ); : Contact angle of a liquid on a solid surface (characterizing the degree of wetting between a liquid and a solid). when At °, J / m2 It has the best interface compatibility; The bridging effect of silane coupling agents: The amino group (-NH2) of KH550 undergoes a condensation reaction with the hydroxyl group of the inner metal hydroxide (-NH2+-OH→-NH-O-+H2O), while the alkoxy group (-OCH3) at the other end hydrolyzes to generate a hydroxyl group, which forms a covalent bond with the polymer matrix, further reducing the interfacial defect state density (from 10). 15 cm -3 Reduced to 1012cm -3 ).

[0009] 4. Quantum chemical principles for graphene core parameter design Oxygen content control: An oxygen content of 5-8 at% corresponds to a hydroxyl group density of 0.5-1.0 hydroxyl groups / nm on the graphene surface. 2 This density provides sufficient shell attachment sites (per 1 nm). 2 Graphene requires only 0.3 hydroxyl groups to achieve uniform coating, while retaining its π-electron conjugated structure (reduction degree 92-95%), ensuring a high dielectric polarization basis; if the oxygen content >8 at%, the π-electron conjugated structure is destroyed, and the graphene conductivity drops to 10. 2 Below S / m, the polarization contribution decreases significantly; Graphene core specific surface area is controlled at 500-800 nm by using a 50-200 nm diameter. 2 / g, according to the "area effect" of dielectric polarization, the polarization intensity P (C / m) 2 ) and specific surface area S (m 2 / g) shows a linear positive correlation; if the flake size is too small (<50nm), the specific surface area is insufficient (m 2 / g), if the flake size is too large (>200nm), van der Waals forces will dominate and lead to aggregation (aggregation energy >50kJ / mol).

[0010] Core parameter limitations 1. Graphene core: Oxygen content 5-8 at% (hydroxyl density 0.5-1.0 hydroxyl groups / nm) 2 ), retaining 92-95% π-conjugated structure; flake diameter 50-200 nm (specific surface area 500-800 m² / g), 2 / g), to avoid aggregation (aggregation energy <50kJ / mol).

[0011] 2. Dielectric shell: Double-layer structure (inner high dielectric + outer insulating layer), total thickness 3-10nm (matching Debye relaxation length 5-15nm); inner layer =10 -300 Thickness 2-5nm (contributes 80% of dielectric gain); outer layer >8eV, thickness 1-5nm (electron tunneling probability T)-10 ).

[0012] 3. Core-shell filler content: 2-8 wt% (volume fraction 0.5-2 vol%), optimal 5-6 wt%. >28, breakdown strength >420kV / mm); 2wt% is the dielectric enhancement threshold, and 8wt% is the agglomeration critical value.

[0013] 4. Key process parameters: Graphene pretreatment: ethylene glycol modification (interlayer spacing increased from 0.34nm to 0.52nm) + hydrazine hydrate reduction (reduction potential -1.16V); Sol-gel coating: pH 8-9, temperature 60-80℃ (hydrolysis rate 10) -4 mol / (L・s), gel porosity <5%) ALD finishing: Temperature 200-250℃, trimethylaluminum precursor (deposition rate 0.05nm / cycle, thickness accuracy ±0.1nm); Hot pressing film formation: PVDF matrix 160-180℃, 5-10MPa (β crystal content increased from 30% to 70%).

[0014] General preparation process 1. Preparation of dielectric graphene core-shell filler (1) Graphene core pretreatment Raw materials: natural graphite powder (purity 99.95%, particle size 50μm), concentrated sulfuric acid (98wt%), potassium permanganate, ethylene glycol (99.9wt%), hydrazine hydrate (50wt% aqueous solution), deionized water (resistivity 18.2MΩ・cm); step: a. Preparation of graphene oxide: Add 20 ml of concentrated sulfuric acid to a 500 ml three-necked flask, add 1.000 g of graphite powder in an ice bath at 0-5 °C, and add 3.000 g of potassium permanganate in three portions (10 min apart); react at 35 ± 1 °C for 2.0 h, add 50 ml of deionized water and react at 90 °C for 15 min; add 30 wt% hydrogen peroxide dropwise until colorless, centrifuge and wash (8000 r / min, 20 min / time) until pH = 7.0 ± 0.1, and freeze-dry at -50 °C for 24 h (yield ≈ 85%). b. Ethylene glycol modification: 0.500g graphene oxide was dispersed in 20.0ml DMF and sonicated for 30min (300W, 40kHz); 0.200g ethylene glycol was added, and the mixture was reacted at 80±1℃ for 4.0h under nitrogen protection (50ml / min); the mixture was centrifuged and washed 3 times, and then vacuum dried at 60℃ for 8h. c. Reduction treatment: Disperse in 50ml of deionized water, add 1.000g of hydrazine hydrate, react at 90±1℃ for 3.0h; centrifuge and wash 3 times, vacuum dry at 60℃ for 12h to obtain hydroxylated graphene (oxygen content 5-8at%, sheet diameter 50-200nm).

[0015] (2) Sol-gel coating of the primary layer Raw materials: hydroxylated graphene, metal source (magnesium chloride hexahydrate / tetrabutyl titanate / barium nitrate + titanium chloride), KH550 (98%), ethanol-water mixed solvent (volume ratio 1:1), ammonia (25wt%). step: a. Dispersion: 0.500g of hydroxylated graphene was added to 50.0ml of ethanol-water and sonicated for 30min (300W, 40kHz) to form a dispersion of 10.0mg / ml; b. Metal source hydrolysis: Select the metal source according to the target inner layer (MgO: 1.000g magnesium chloride hexahydrate; TiO2: 1.200g tetrabutyl titanate; BaTiO3: 0.800g barium nitrate + 0.600g titanium chloride), and stir for 30min (500r / min). c. Coupling and gelation: Add 0.300g KH550, adjust pH to 8.5±0.1 with ammonia, and react at 70±1℃ for 3.0h; d. Post-processing: Centrifuge (10000r / min, 30min), wash 3 times, vacuum dry at 60℃ for 8h to obtain initially coated graphene (shell thickness 2-5nm).

[0016] (3) ALD Refinement Equipment: Atomic Layer Deposition System (ALD, model GEMStar-6); Raw materials: precursor (trimethylaluminum / zirconium tetrachloride / tetraethyl orthosilicate), reaction gas (oxygen / ozone), carrier gas (nitrogen 99.999%). step: a. Sample loading: 0.300g of initially coated graphene is spread on a 5cm substrate. 2 Quartz boat, placed into the reaction chamber; b. Vacuuming: Pressure drops to 1.0 × 10⁻⁶ -3 Below MPa, keep warm at 220±5℃ for 30 minutes; c. Deposition: Select the precursor according to the outer layer (Al2O3: trimethylaluminum; ZrO2: zirconium tetrachloride; SiO2: tetraethyl orthosilicate), parameters: precursor pulse 0.10s, purge 10.0s, reaction gas pulse 0.20s, cycle 50-200 times (0.05±0.005nm / cycle). d. Cooling: Cool to room temperature at 5℃ / min to obtain core-shell filler (total shell thickness 3-10nm).

[0017] 2. Preparation of dielectric thin films (1) Preparation of blend solution Raw materials: core-shell filler (self-made), polymer matrix (PVDF / PI / PET / PEEK), solvent (NMP / DMF / m-cresol); step: a. Polymer dissolution: Select a solvent according to the matrix, stir at 75±1℃ for 3.0h to form an 18wt% (PVDF / PET) or 15wt% (PI / PEEK) solution; b. Packing material dispersion: Weigh 2-8 wt% of the core-shell packing material, add it to the solution, sonicate for 30 min (300 W), and stir for 3.0 h (500 r / min) under nitrogen protection. c. Degassing: -0.09MPa vacuum, 60±1℃ for 30min.

[0018] (2) Casting film Equipment: Automatic casting machine (model FY-200); Steps: Casting speed 8±0.5cm / min, film thickness 200±10μm, cast on plasma-treated glass plate (roughness <0.1nm); pre-dry at 80±1℃ for 4.0h to obtain wet film (thickness 80-120μm).

[0019] (3) Hot pressing curing / post-treatment Equipment: Flat plate hot press (model SFM-20); step: a. Hot pressing: Parameters are set according to the matrix (PVDF: 170±1℃, 8±0.5MPa, 1.5h; PI: 300±1℃, 10±0.5MPa, 2.0h; PET: 130±1℃, 5±0.5MPa, 1.0h; PEEK: 280±1℃, 10±0.5MPa, 2.0h). b. Cooling: Reduce temperature to room temperature at 5℃ / min; c. Peeling and cutting: Cut into 10.0mm×10.0mm (dielectric test) or 20.0mm×5.0mm (mechanical test), with a thickness of 50-150μm (uniformity ±5%).

[0020] Example 1: MgO-Al2O3 double-shell (6nm) / PVDF film (5wt% filler) parameter: Graphene core: oxygen content 6 at%, sheet diameter 100 nm; Core-shell packing material: 3nm inner layer of MgO (1.000g magnesium chloride hexahydrate, reacted at 70℃ for 3h) + 3nm outer layer of Al2O3 (ALD cycled 60 times). Thin film preparation: 0.400g core-shell filler + 7.600g 18wt% PVDF / NMP solution, casting speed 8cm / min, hot pressing at 170℃ and 8MPa for 1.5h to obtain a 100μm thick film; Performance testing: Dielectric constant (1kHz) 28.5, breakdown strength 442kV / mm, dielectric loss 0.011, tensile strength 63.8MPa.

[0021] Example 2: TiO2-Al2O3 bilayer shell (8nm) / PI film (5wt% filler) parameter: Graphene core: oxygen content 7 at%, sheet diameter 150 nm; Core-shell packing: TiO2 inner layer 4nm (1.200g tetrabutyl titanate, reaction at 75℃ for 3.5h) + Al2O3 outer layer 4nm (ALD cycle 80 times). Thin film preparation: 0.300g core-shell filler + 5.700g 15wt% polyamic acid / DMF solution, casting speed 7cm / min, thermal imidization (80℃ / 2h→120℃ / 1h→200℃ / 1h→300℃ / 1h) to obtain an 80μm thick PI film; Performance testing: Dielectric constant (1kHz) 25.3, breakdown strength 418kV / mm, dielectric loss 0.013, tensile strength 79.2MPa.

[0022] Example 3: BaTiO3-Al2O3 bilayer shell (6nm) / PVDF film (6wt% filler) parameter: Graphene core: oxygen content 6 at%, sheet diameter 120 nm; Core-shell packing material: BaTiO3 inner layer 3nm (0.800g barium nitrate + 0.600g titanium chloride, reacted at 70℃ for 3h) + Al2O3 outer layer 3nm (ALD cycled 60 times). Thin film preparation: 0.500g core-shell filler + 7.833g 18wt% PVDF / NMP solution, casting speed 9cm / min, hot pressing at 175℃ and 9MPa for 1.5h to obtain a 95μm thick film; Performance testing: Dielectric constant (1kHz) 32.1, breakdown strength 425kV / mm, dielectric loss 0.014, tensile strength 61.5MPa.

[0023] Example 4: ZrO2-Al2O3 double shell (10nm) / PEEK film (5wt% filler) parameter: Graphene core: oxygen content 8 at%, sheet diameter 200 nm; Core-shell packing: 5nm ZrO2 inner layer (1.500g zirconium tetrachloride, reacted at 80℃ for 4h) + 5nm Al2O3 outer layer (ALD cycled 100 times); Thin film preparation: 0.250g core-shell filler + 4.750g 15wt% PEEK / m-cresol solution, casting speed 6cm / min, hot pressing at 280℃ and 10MPa for 2h to obtain a 120μm thick film; Performance testing: Dielectric constant (1kHz) 23.7, breakdown strength 468kV / mm, dielectric loss 0.010, tensile strength 85.6MPa.

[0024] Example 5: MgO-SiO2 double-shell (3nm) / PET film (8wt% filler) parameter: Graphene core: oxygen content 5 at%, sheet diameter 50 nm; Core-shell packing material: 2nm inner layer of MgO (1.000g magnesium chloride hexahydrate, reacted at 60℃ for 2h) + 1nm outer layer of SiO2 (ALD cycled 20 times, tetraethyl orthosilicate precursor); Thin film preparation: 0.400g core-shell filler + 4.600g 15wt% PET / DMF solution, casting speed 10cm / min, hot pressing at 130℃ and 5MPa for 1h to obtain a 60μm thick film; Performance testing: Dielectric constant (1kHz) 29.8, breakdown strength 402kV / mm, dielectric loss 0.015, tensile strength 58.3MPa.

[0025] Example 6: TiO2 monolayer shell (6nm) / PVDF film (5wt% filler) parameter: Graphene core: oxygen content 6 at%, sheet diameter 100 nm; Core-shell filler: TiO2 monolayer shell 6nm (1.200g tetrabutyl titanate, reaction at 70℃ for 4h, without ALD finishing). Thin film preparation: Same as in Example 1 (blending solution, casting, and hot pressing parameters are the same); Performance testing: Dielectric constant (1kHz) 26.7, breakdown strength 385kV / mm, dielectric loss 0.016, tensile strength 59.7MPa.

[0026] Example 7: BaTiO3-ZrO2 bilayer shell (6nm) / PI film (filler 2wt%) parameter: Graphene core: oxygen content 7 at%, sheet diameter 150 nm; Core-shell packing: BaTiO3 inner layer 3nm + ZrO2 outer layer 3nm (ALD cycle 60 times, zirconium tetrachloride precursor); Thin film preparation: 0.100g core-shell filler + 4.900g 15wt% polyamic acid / DMF solution, casting and thermal imidization are the same as in Example 2; Performance testing: Dielectric constant (1kHz) 18.2, breakdown strength 475kV / mm, dielectric loss 0.009, tensile strength 76.4MPa.

[0027] Example 8: MgO-Al2O3 bilayer shell (6nm) / PVDF film (8wt% filler) parameter: Graphene core: oxygen content 6 at%, sheet diameter 100 nm; Core-shell packing: Same as in Example 1 (MgO-Al2O3 double shell 6nm). Thin film preparation: 0.667g core-shell filler + 7.333g 18wt% PVDF / NMP solution, casting and hot pressing are the same as in Example 1; Performance testing: Dielectric constant (1kHz) 31.3, breakdown strength 398kV / mm, dielectric loss 0.017, tensile strength 56.9MPa.

[0028] Example 9: SiO2-Al2O3 bilayer shell (6nm) / PEEK film (5wt% filler) parameter: Graphene core: oxygen content 7 at%, sheet diameter 120 nm; Core-shell filler: SiO2 inner layer 3nm (1.000g tetraethyl orthosilicate, reacted at 70℃ for 3h) + Al2O3 outer layer 3nm (ALD cycle 60 times). Thin film preparation: 0.250g core-shell filler + 4.750g 15wt% PEEK / m-cresol solution, casting and hot pressing are the same as in Example 4; Performance testing: Dielectric constant (1kHz) 21.5, breakdown strength 482kV / mm, dielectric loss 0.008, tensile strength 88.3MPa.

[0029] Comparative Example 1: Uncoated graphene / PVDF film Difference parameters: Graphene: Unmodified (without ethylene glycol modification), oxygen content 3 at%; Preparation: 0.400g unmodified graphene + 7.600g 18wt% PVDF / NMP solution, sonicated for 30min, stirred for 3h (without nitrogen protection), cast and hot-pressed as in Example 1; Performance testing: Dielectric constant (1kHz) 58.7, breakdown strength 185kV / mm, dielectric loss 0.123, tensile strength 44.2MPa; Conclusion: Uncoated graphene is prone to agglomeration to form a conductive network, resulting in a surge in dielectric loss and a sharp drop in breakdown strength.

[0030] Comparative Example 2: Single-layer MgO shell (without ALD finishing) / PVDF film Difference parameters: Core-shell packing material: 6nm MgO monolayer shell (1.000g magnesium chloride hexahydrate, reacted at 70℃ for 5h, without ALD refinement); Preparation: Same as in Example 1; Performance testing: Dielectric constant (1kHz) 27.3, breakdown strength 326kV / mm, dielectric loss 0.028, tensile strength 52.6MPa; Conclusion: The monolayer sol-gel coating has poor uniformity (roughness > 1.2 nm), insufficient insulation barrier, and decreased breakdown strength and compatibility.

[0031] Comparative Example 3: Core-shell filler content 10wt% / PVDF film Difference parameters: Filler content: 10wt% (0.889g core-shell filler + 7.111g 18wt% PVDF / NMP solution); Preparation: Same as in Example 1; Performance testing: Dielectric constant (1kHz) 33.5, breakdown strength 298kV / mm, dielectric loss 0.035, tensile strength 49.8MPa; Conclusion: When the filler content exceeds the 8wt% agglomeration critical value, the electric field concentration intensifies, and the breakdown strength is significantly reduced.

[0032] Comparative Example 4: Pure Al2O3 shell (without MgO inner layer) / PVDF thin film Difference parameters: Core-shell filler: Pure Al2O3 shell 6nm (ALD cycle 120 times, no sol-gel inner layer); Preparation: Same as in Example 1; Performance testing: Dielectric constant (1kHz) 16.8, breakdown strength 453kV / mm, dielectric loss 0.009, tensile strength 62.1MPa; Conclusion: Without a high-dielectric inner layer, the dielectric gain is insufficient and cannot meet the requirements of high-density energy storage.

[0033] Comparative Example 5: Graphene nuclear oxygen content 10 at% / PVDF film Difference parameters: Graphene core: oxygen content 10 at% (during reduction, 0.500 g of hydrated hydrazine was used, and the reaction time was 2 h); Preparation: Same as in Example 1; Performance testing: Dielectric constant (1kHz) 22.4, breakdown strength 438kV / mm, dielectric loss 0.012, tensile strength 60.3MPa; Conclusion: Excessive oxygen content disrupts the π-conjugated structure, reduces the conductivity of graphene, and weakens its polarization contribution.

[0034] The following is a summary table of the performance of the examples and comparative examples: The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A dielectric thin film based on dielectric graphene coating modification, characterized in that, The dielectric film is composed of a core-shell structured dielectric graphene filler and a polymer matrix, wherein the core-shell structure is a "graphene core-double dielectric shell" comprising: Graphene core: oxygen content of 5-8 at%, retaining 92-95% of the π-electron conjugated structure, sheet diameter of 50-200 nm, and specific surface area of ​​500-800 m². 2 / g; Double dielectric shell: Total thickness 3-10 nm, inner layer is high dielectric oxide with dielectric constant ε=10-300 and thickness 2-5 nm; outer layer is high insulating oxide with a bandgap width of [missing information]. >8eV, with a thickness of 1-5nm; Core-shell filler: 2-8 wt% by mass and 0.5-2 vol% by volume in dielectric thin films. Polymer matrix: selected from PVDF, PI, PET or PEEK; The dielectric film has a dielectric constant (1kHz) ≥21.5, a breakdown strength ≥402kV / mm, a dielectric loss (1kHz) ≤0.017, and a tensile strength ≥56.9MPa.

2. The dielectric thin film according to claim 1, characterized in that, The preparation process of the graphene core includes the following steps: Preparation of graphene oxide: Natural graphite powder was mixed with concentrated sulfuric acid, and potassium permanganate was added under ice bath conditions for oxidation. After hydrothermal reaction, reduction with hydrogen peroxide, centrifugation and washing until pH=7.0±0.1, graphene oxide was obtained by freeze drying. Ethylene glycol modification: Graphene oxide was dispersed in DMF, ethylene glycol was added, and the reaction was carried out at 80±1℃ for 4.0 h under nitrogen protection. After centrifugation, washing and vacuum drying, the modified graphene oxide was obtained. Reduction treatment: The modified graphene oxide was dispersed in deionized water, hydrazine hydrate was added, and the reaction was carried out at 90±1℃ for 3.0h. After centrifugation, washing and vacuum drying, the graphene core was obtained.

3. The dielectric thin film according to claim 1, characterized in that, The material combination of the double dielectric shell is selected from any of the following: Inner layer: MgO, BaTiO3 or TiO2; outer layer: Al2O3, ZrO2 or SiO2. Inner layer: MgO, outer layer: SiO2; Inner layer: BaTiO3, outer layer: ZrO2; Inner layer: SiO2, outer layer: Al2O3.

4. The dielectric thin film according to claim 1, characterized in that, The preparation process of the core-shell filler includes two steps: sol-gel coating of the initial layer and ALD finishing. Sol-gel coating primary layer: Graphene cores are dispersed in an ethanol-water mixed solvent, a metal source and KH550 silane coupling agent are added, the pH is adjusted to 8-9, and the reaction is carried out at 60-80℃ for 3.0-4.0h. After centrifugation, washing and vacuum drying, the primary coated graphene is obtained. ALD refinement: The initially coated graphene is placed in an atomic layer deposition system, using trimethylaluminum, zirconium tetrachloride or tetraethyl orthosilicate as precursors, and deposited 50-200 times at 200-250℃ at a deposition rate of 0.05±0.005nm / cycle. After cooling, the core-shell filler is obtained.

5. The dielectric thin film according to claim 1, characterized in that, The core-shell filler has a mass fraction of 5-6 wt%, and the total thickness of the double dielectric shell is 6 nm, with the inner layer thickness being 3 nm and the outer layer thickness being 3 nm. The corresponding dielectric film has a dielectric constant (1 kHz) ≥ 28.5, a breakdown strength ≥ 425 kV / mm, and a dielectric loss (1 kHz) ≤ 0.

014.

6. The dielectric thin film according to claim 1, characterized in that, The preparation process includes the following steps: Preparation of blend: The core-shell filler was added to the solvent solution of the polymer matrix, ultrasonically dispersed for 30 min, stirred for 3.0 h under nitrogen protection, and vacuum degassed for 30 min to obtain the blend; Casting film: The blend solution was cast onto a plasma-treated glass plate at a speed of 8±0.5 cm / min, the film thickness was 200±10 μm, and the film was pre-dried at 80±1℃ for 4.0 h to obtain a wet film; Hot pressing curing: Set the hot pressing parameters according to the polymer matrix type: PVDF matrix: 160-180℃, 5-10MPa, 1.5h; PI matrix: 300±1℃, 10±0.5MPa, 2.0h; PET matrix: 130±1℃, 5±0.5MPa, 1.0h; PEEK matrix: 280±1℃, 10±0.5MPa, 2.0h. After cooling, peel off and cut the dielectric film to obtain a thickness of 50-150μm and a thickness uniformity of ±5%.

7. The dielectric thin film according to any one of claims 1-6, characterized in that, The dielectric thin film is used in high-density energy storage devices, flexible electronic devices, or high-frequency dielectric devices, with an energy density of 12-15 J / cm². 3 Bending resistance (radius 5mm) >1000 times, filler dispersion stability >6 months, sedimentation rate.

8. The dielectric thin film according to claim 1, characterized in that, The interfacial energy between the core-shell filler and the polymer matrix is ​​≤10mJ / m 2 Interface defect state density ≤10 12 cm -3 Interfacial shear strength ≥15MPa.

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