Preparation method and application of uiO-66-CDs / PEI composite dielectric film

Abstract

The application discloses a kind of preparation methods and applications of UiO-66-CDs / PEI composite dielectric film, characteristics are as follows: including the following steps: amino-functionalized metal organic framework UiO-66-NH2 is mixed with carbon quantum dots CDs, and the obtained UiO-66-CDs are synthesized by chemical bonding method, UiO-66-CDs and PEI polymer are blended, and then electrospinning and hot-pressing are carried out to form film, to obtain UiO-66-CDs / PEI composite dielectric film, wherein the mass of UiO-66-CDs is 0.5-1.5% of the mass of the composite dielectric film;Advantages are that MOFs and polymer substrate interface defects can be improved, trap energy levels and interface thermal conductivity are also improved, and the dielectric properties, energy storage performance and high-temperature stability of the composite dielectric film are improved.

Description

Technical Field

[0001] This invention belongs to the field of dielectric capacitor technology, specifically relating to a method for preparing a UiO-66-CDs / PEI composite dielectric thin film and its application. Background Technology

[0002] Dielectric capacitors are widely used in power regulation, electric propulsion systems, aerospace equipment, and pulsed power electronics platforms. In these applications, dielectric materials typically need to achieve long-term stable operation under high-temperature and high-electric-field conditions. However, under the coupling effect of high temperature and high electric field, polymer dielectric materials are prone to significant electro-thermal coupling failure, becoming a key factor limiting their service reliability and energy density improvement. Under high-temperature conditions, a strong electric field significantly enhances carrier injection, field emission, and thermally activated transition behavior, leading to a significant increase in the conductivity loss of the polymer dielectric. Simultaneously, the increased molecular chain segment vibration and phonon fluctuations caused by temperature rise easily lead to heat accumulation in localized areas, further inducing structural instability. This mutually reinforcing electrical and thermal degradation process causes polymer dielectric materials to exhibit problems such as decreased breakdown strength, reduced energy storage density, and decreased energy efficiency under high-temperature and high-electric-field conditions, severely restricting their application under extreme conditions.

[0003] Polyetherimide (PEI), a typical aromatic high-temperature polymer, is widely used in high-temperature dielectric systems due to its high glass transition temperature and good thermomechanical stability. However, PEI inherently lacks deep-level trap structures that can effectively suppress the injection and migration of thermally activated charge carriers, and also lacks effective interfacial barriers to block charge transport. Under high temperature and strong electric field conditions, charge carriers in PEI tend to form continuous transport channels, thereby accelerating the electro-thermal coupling degradation process and limiting further improvements in its dielectric and energy storage properties.

[0004] To improve the stability of polymer dielectric materials under high-temperature and strong electric field conditions, existing technologies commonly employ the method of introducing inorganic fillers into the polymer matrix. By constructing an interface structure between the polymer and the filler, localized trap levels and interface barriers can be introduced to a certain extent, thereby suppressing carrier injection and reducing thermally activated conductivity losses. Among these, wide-bandgap ceramic fillers are considered helpful in improving the electrical stability of polymer dielectric materials under high-temperature conditions due to their carrier scattering effect and interface-induced trapping effect. However, traditional inorganic fillers typically have rigid lattice structures with limited electronic structure modulation capabilities, and the interface modulation effect introduced in composite dielectric systems often manifests as single trap level characteristics. Such single-trap structures are difficult to effectively suppress the thermally activated migration process of carriers under high-temperature and strong electric field conditions, and still cannot block the formation of continuous conductive channels. Furthermore, the interaction between traditional inorganic fillers and the polymer matrix is ​​usually dominated by physical interactions or weak interactions, and the interface lacks a stable covalent coupling structure, limiting the synergistic modulation capability of carrier transport and heat conduction in the interface region. Under high-temperature conditions, the interfacial thermal diffusion efficiency is limited, which is not conducive to the rapid conduction and release of heat, thus affecting the dielectric stability and long-term reliability of composite dielectric materials.

[0005] Against this backdrop, metal-organic frameworks (MOFs) with designable organic ligands and tunable electronic structures have gradually attracted attention. By controlling the structure of organic ligands and the composition of the framework, MOFs are expected to introduce specific interfacial electronic modulation effects in composite media, providing new insights for improving carrier transport behavior. However, in existing MOF-based polymer composite media systems, MOF fillers are typically still dispersed non-covalently within the polymer matrix, and their interfacial interaction mechanism is mainly characterized by single-level trap modulation. Furthermore, their interfacial thermal conductivity is limited, making it difficult to achieve synergistic optimization of charge transport and thermal diffusion under high-temperature and high-electric-field conditions. Therefore, current technologies still struggle to simultaneously achieve multi-level carrier trap modulation and efficient interfacial thermal conductivity regulation in polymer dielectric materials, especially under extreme operating conditions such as high-temperature and high-electric-field conditions, making it difficult to balance breakdown strength, energy density, and energy efficiency. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing UiO-66-CDs / PEI composite dielectric films that can improve the interface defects between MOFs and polymer substrates, improve the trap energy level and interfacial thermal conductivity, and enhance dielectric properties, energy storage performance and high-temperature stability, as well as their applications.

[0007] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a method for preparing a UiO-66-CDs / PEI composite dielectric film, comprising the following steps: mixing an amino-functionalized metal-organic framework UiO-66-NH2 with carbon quantum dots CDs to synthesize UiO-66-CDs through chemical bonding; blending UiO-66-CDs with PEI polymer; and then electrospinning and hot-pressing to form a film to obtain a UiO-66-CDs / PEI composite dielectric film. Alternatively, carboxyl-rich CDs are grafted onto the surface of amino-containing UiO-66-NH2 via an amidation reaction to obtain UiO-66-CDs; and UiO-66-CDs and PEI are heat-treated to form a stable interface, constructing a cross-linked coupling structure. The two-level traps at the interface between UiO-66-CDs and the PEI substrate trap electrons, and covalently coupled vibrations promote phonon transport.

[0008] Further, the preparation method of the amino-functionalized metal-organic framework UiO-66-NH2 is as follows: a zirconium chloride solution with a concentration of 0.5-1.5 wt.% dissolved in N,N-dimethylformamide and a 2-aminoterephthalic acid solution with a concentration of 0.5-1 wt.% dissolved in N,N-dimethylformamide are mixed and stirred for 20-40 min, then acetic acid is added, and then the mixture is placed in a reaction vessel and reacted at 100-140℃ for 10-14 h. The reaction product is centrifuged, washed, and dried at 50-70℃ to obtain the amino-functionalized metal-organic framework UiO-66-NH2, wherein the volume ratio of zirconium chloride solution, 2-aminoterephthalic acid solution and acetic acid is (4-6):(4-6):1.

[0009] Further, the preparation method of the amino-functionalized metal-organic framework UiO-66-NH2 is as follows: A zirconium chloride solution with a concentration of 1 wt.% dissolved in N,N-dimethylformamide and a 2-aminoterephthalic acid solution with a concentration of 0.7 wt.% dissolved in N,N-dimethylformamide are mixed and stirred for 30 min. Acetic acid is then added, and the mixture is placed in a reaction vessel and reacted at 120℃ for 12 h. The reaction product is then centrifuged, washed, and dried at 60℃ to obtain the amino-functionalized metal-organic framework UiO-66-NH2, wherein the volume ratio of zirconium chloride solution, 2-aminoterephthalic acid solution, and acetic acid is 5:5:1.

[0010] Furthermore, the carbon quantum dots (CDs) are prepared by aldol reaction. The preparation method is as follows: Sodium hydroxide powder is dissolved in acetaldehyde at a mass-volume ratio of 2-5 g: 10 mL and stirred for 1-3 h. Dilute hydrochloric acid is added to adjust the pH value to neutral. The mixture is allowed to stand until a precipitate is formed. The precipitate is collected, washed by centrifugation, and dried at 50-70 °C to obtain carbon quantum dots (CDs).

[0011] Further, UiO-66-NH2 was dissolved in N,N-dimethylformamide to obtain a UiO-66-NH2 solution. Carbon quantum dots (CDs), 2-aminoterephthalic acid, and N-hydroxysuccinimide were dissolved in N,N-dimethylformamide to obtain a mixed solution. The UiO-66-NH2 solution and the mixed solution were mixed in an equal volume ratio and stirred at 70–90 °C for 10–14 h. The reaction product was centrifuged, washed, and dried at 50–70 °C to obtain UiO-66-CDs.

[0012] Furthermore, the mass ratio of UiO-66-NH2, carbon quantum dots CDs, 2-aminoterephthalic acid and N-hydroxysuccinimide is 3:10:30:33.

[0013] Further, UiO-66-CDs were added to DMF for ultrasonic dispersion, followed by the addition of polyetherimide (PEI) particles. The mixture was stirred at 70–90°C for 1–3 h to obtain a homogeneous solution. The solution was then electrospun into nanofibers, which were attached to the surface of conductive glass. The nanofibers were then placed in a vacuum vulcanizing machine and subjected to gradient heating at a pressure of 10–20 MPa. Finally, the mixture was hot-pressed at 100–200°C for 2–4 h to obtain a UiO-66-CDs / PEI composite dielectric film. The mass of UiO-66-CDs was 0.5–1.5% of the mass of the composite dielectric film.

[0014] Furthermore, the gradient heating is performed by hot pressing at 100℃, 150℃, and 200℃ for 1 hour each.

[0015] The present invention also provides the application of the UiO-66-CDs / PEI composite dielectric film prepared by the above method in the preparation of high-temperature dielectric capacitors and power electronics.

[0016] Compared with the prior art, the advantages of the present invention are as follows: The present invention discloses a method for preparing UiO-66-CDs / PEI composite dielectric films and their applications. The method involves chemically bonding carboxyl-rich carbon dots (CDs) with amino-functionalized metal-organic frameworks UiO-66-NH2 through an amidation reaction to form UiO-66-CDs composite fillers. This structure has a bi-level trap structure, which can suppress charge migration, reduce conductivity loss, and improve breakdown field strength.

[0017] UiO-66-CDs were introduced into a polyetherimide (PEI) polymer substrate at different ratios, and after heat treatment, an interface-stable composite dielectric film was formed. During this process, a cross-linked coupling structure was established between the UiO-66-CDs filler and the PEI molecular chains, forming a synergistically regulated interface system. This cross-linked structure can simultaneously regulate carrier transport behavior and interfacial thermal conduction, achieving synergistic management of electron and phonon transport, thereby improving the thermal conductivity of the film and significantly optimizing its energy storage performance under high-temperature conditions. The resulting composite dielectric film exhibits excellent breakdown stability, dielectric properties, and energy storage characteristics under high-temperature, strong electric field coupling environments, making it suitable for applications such as high-temperature dielectric capacitors and power electronics.

[0018] In summary, this invention provides a method for preparing a UiO-66-CDs / PEI composite dielectric film and its application. By constructing a UiO-66-CDs filler system with tunable electronic structure, stable interfacial coupling, and good thermal conductivity, the overall performance of polymer dielectric materials under extreme environments is significantly improved. This results in a composite dielectric film with excellent breakdown resistance, dielectric properties, and high-temperature stability. The method is simple, environmentally friendly, and has wide applicability. Attached Figure Description

[0019] Figure 1 The preparation flow chart for the UiO-66-CDs modification process; Figure 2 The images show the morphology of UiO-66-CDs before and after modification, where (a) is a SEM microstructure image, (b) is a TEM microstructure image, and (c) is a TEM high-resolution image. Figure 3 The functional group structure, potential and adsorption properties of UiO-66-CDs before and after modification are characterized, where (a) is the XPS spectrum of C 1s, (b) is the XPS spectrum of N 1s, (c) is the XPS spectrum of O 1s, (d) is the characterization of FI-IR spectrum, (f) is the particle size and zeta potential, and (g) is the adsorption properties. Figure 4 This is a flowchart illustrating the preparation process of the UiO-66-CDs / PEI composite dielectric thin film. Figure 5 The cross-sectional morphology and phase characterization of the UiO-66-CDs / PEI composite dielectric film are shown in (a) SEM cross-sectional morphology, (b) XRD pattern characterization, and (c) FT-IR pattern characterization. Figure 6 Analysis of the energy level structure (a) and electron transport mechanism (b) of UiO-66-CDs / PEI composite dielectric thin film; Figure 7The figures show (a) temperature change curves and (b) infrared images of UiO-66-CDs / PEI and PEI composite dielectric films on a 100-degree heating stage, (c) comparison of out-of-plane thermal conductivity, and (d) comparison of simulated heat flow. Figure 8 The following are the comparisons of (a) high-temperature performance, (b) fast charge / discharge rate, (c) cycle stability, and (d) regional stability of the UiO-66-CDs / PEI composite dielectric film. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] Polyetherimide (PEI) was purchased from Shanghai Sanaifu New Materials Co., Ltd.; N,N-dimethylformamide (AR, 99.5%, DMF), sodium hydroxide (AR, 99.5%), zirconium chloride, acetaldehyde, 2-aminoterephthalic acid (EDC, ≥98%), and N-hydroxysuccinimide (NHS, ≥98%) were purchased from Aladdin. I. Specific Implementation Methods A UiO-66-CDs / PEI composite dielectric film is formed by adding surface-modified UiO-66-CDs to a PEI polymer substrate in different proportions. The surface-modified UiO-66-CDs are formed by chemical bonding between UiO66-NH2 and CDs.

[0023] Example 1: A UiO-66-CDs / PEI composite dielectric thin film, the preparation method steps are as follows: Step 1: Preparation of amino-functionalized metal-organic frameworks (MOFs), as detailed below: 233.04 mg of zirconium chloride powder was added to 25 mL of DMF solvent to obtain a zirconium chloride solution. 166.13 mg of 2-aminoterephthalic acid powder was added to 25 mL of DMF solvent to obtain a 2-aminoterephthalic acid solution. The zirconium chloride solution and the 2-aminoterephthalic acid solution were mixed and stirred for 30 min, and then 5 mL of acetic acid was added. The mixture was then placed in a reaction vessel and reacted at 120 °C for 12 h. The reaction product was centrifuged, washed, and dried at 60 °C to obtain an amino-functionalized metal-organic framework, denoted as UiO-66-NH2.

[0024] Step 2: Prepare carbon quantum dots, as detailed below: 300g of sodium hydroxide powder was mixed with 1000mL of acetaldehyde and stirred for 2 hours. Dilute hydrochloric acid was added to adjust the pH to neutral. The mixture was allowed to stand until a precipitate was formed. The precipitate was collected, washed by centrifugation, and dried at 60°C to obtain carbon quantum dots, denoted as CDs.

[0025] Step 3: Prepare UiO-66-CDs, as detailed below: Take 30 mg UiO-66-NH2 and add it to 40 mL DMF solvent. Take 100 mg CDs, 300 mg EDC and 330 mg NHS and add them to 40 mL DMF. Mix the two solutions and stir at 80 °C for 12 h. The reaction product is centrifuged, washed and dried at 60 °C to obtain UiO-66-CDs.

[0026] Step 4: Blend UiO-66-CDs and PEI polymer, then electrospin and hot-press to form a film, as detailed below: 0.0063 g of UiO-66-CDs was added to 5 mL of DMF and ultrasonically dispersed. Then, 1.25 g of PEI particles were added, and the mixture was stirred at 80 °C for 2 h to obtain a homogeneous solution. The solution was then electrospun into nanofibers, which were attached to the surface of conductive glass. The nanofibers were placed in a vacuum vulcanizing machine and subjected to gradient heating at a pressure of 15 MPa. The nanofibers were then hot-pressed at 100 °C, 150 °C, and 200 °C for 1 h each to obtain a UiO-66-CDs / PEI composite dielectric film, denoted as 0.5 wt.% UiO-66-CDs / PEI, which is the mass of UiO-66-CDs divided by the mass of the composite dielectric film (i.e., the sum of the masses of UiO-66-CDs and PEI particles, excluding DMF solvent evaporation by weight), approximately 0.5%.

[0027] Example 2 is the same as Example 1 above, except that in step 4, 0.0126g of UiO-66-CDs is added to 5mL of LDMF for ultrasonic dispersion, and then 1.25g of PEI particles are added. The mixture is stirred at 80°C for 2 hours to obtain a uniform mixed solution. The mixed solution is then electrospun into nanofibers, which are attached to the surface of conductive glass. The nanofibers are placed in a vacuum vulcanizing machine and subjected to gradient heating at a pressure of 15MPa. The nanofibers are then hot-pressed at 100°C, 150°C, and 200°C for 1 hour each to obtain a UiO-66-CDs / PEI composite dielectric film, denoted as 1.0wt.% UiO-66-CDs / PEI.

[0028] Example 3 is the same as Example 1 above, except that in step 4, 0.0190g of UiO-66-CDs is added to 5mL of LDMF for ultrasonic dispersion, and then 1.25g of PEI particles are added. The mixture is stirred at 80℃ for 2 hours to obtain a uniform mixed solution. The mixed solution is then electrospun into nanofibers, which are attached to the surface of conductive glass. The nanofibers are placed in a vacuum vulcanizing machine and subjected to gradient heating at a pressure of 15MPa. The nanofibers are then hot-pressed at 100℃, 150℃, and 200℃ for 1 hour each to obtain a UiO-66-CDs / PEI composite dielectric film, denoted as 1.5wt.% UiO-66-CDs / PEI.

[0029] Comparative Example 1: 1.25g of PEI particles were added to 5mL of DMF and ultrasonically dispersed. The mixture was stirred at 80℃ for 2h to obtain a uniform mixed solution. The mixed solution was then electrospun into nanofibers, which were attached to the surface of conductive glass. The nanofibers were placed in a vacuum vulcanizing machine and subjected to gradient heating at a pressure of 15MPa. The nanofibers were then hot-pressed at 100℃, 150℃, and 200℃ for 1h each to obtain a PEI dielectric film.

[0030] II. Analysis of Experimental Results Figure 1 This is a flowchart illustrating the preparation process of UiO-66-CDs modification. First, using zirconium chloride and 2-aminoterephthalic acid as precursors, amino-functionalized UiO-66-NH2 was prepared via a solvothermal reaction in N,N-dimethylformamide solvent. Subsequently, through an amidation reaction between the carboxyl groups on the carbon dots (CDs) surface and the amino groups on the UiO-66-NH2 surface, the CDs were chemically bonded to the surface of the UiO-66 framework, ultimately obtaining surface-modified UiO-66-CDs. This preparation process achieved a stable covalent connection between CDs and UiO-66-NH2, providing a structural basis for subsequent interface control.

[0031] Figure 2 These are SEM and TEM images of the microstructure of UiO-66-CDs. Figure 2 (a) The scanning electron microscope (SEM) image shows that UiO-66-CDs exhibit a regular octahedral morphology with a particle size of approximately 300 nm. Figure 2 (b) Transmission electron microscopy (TEM) images further confirmed the integrity of the regular octahedral structure. Figure 2In the high-resolution TEM image (c), CD lattice fringes distributed on the surface of UiO-66-CDs can be clearly observed, with an interplanar spacing of approximately 0.21 nm, while no obvious lattice fringes were observed in the bulk region of UiO-66-NH2. This result indicates that CDs were successfully loaded onto the surface of UiO-66-NH2 without disrupting the overall morphology and structure of the UiO-66 framework.

[0032] Figure 3 Characterization of the functional group structure of UiO-66-CDs, as well as its potential and adsorption properties. Figure 3 X-ray photoelectron spectroscopy (XPS) of (a)-(c) shows clear signals for each element in UiO-66-CDs, indicating stable material composition and structure. Compared to UiO-66-NH2, a new –CONH– characteristic peak appears in the C1s level of UiO-66-CDs, while the C–N component and carbonyl signals are enhanced, indicating that CDs are covalently bonded to UiO-66-NH2 via amide bonds. The shift of the N 1s level towards higher binding energy reflects a change in the electronic environment around the nitrogen atom, indicating a significant interfacial charge rearrangement between the UiO-66-NH2 framework and CDs. The cooperative shift of the C 1s and O 1s levels further confirms the modulation of the interfacial electronic structure. Figure 3 (d) FTIR spectroscopy results show that UiO-66-CDs are at approximately 1659 cm⁻¹. -1 A new characteristic absorption peak of amide bond appeared at the position, and the –NH stretching vibration peak changed significantly, further verifying the covalent amidation reaction between CDs and UiO-66-NH2. Figure 3 The particle size statistics of (e) are consistent with the SEM morphology, and the deta potential test results show that the surface charge state of UiO-66-CDs has changed significantly compared with UiO-66-NH2, indicating that CDs were successfully introduced and effectively controlled the surface properties of the material. Figure 3 The nitrogen adsorption data in (f) show that pore accessibility and surface structure were modulated without compromising the integrity of the framework. These structural and electronic characteristics lay the foundation for subsequent charge and thermal transport modulation in composite dielectrics.

[0033] Figure 4This is a flowchart illustrating the preparation process of the UiO-66-CDs / PEI composite dielectric film. UiO-66-CDs are dispersed in a solvent and thoroughly mixed with PEI polymer. The composite film is then prepared by electrospinning and gradient hot pressing. During the heat treatment, the residual carboxyl groups on the surface of UiO-66-CDs can further react with the amino groups in the PEI molecular chain, thereby constructing a stable cross-linked structure between the filler and the polymer, forming a three-phase cross-linked network composed of UiO-66-CDs, PEI, and their interfacial regions.

[0034] Figure 5 Cross-sectional morphology and phase characterization of UiO-66-CDs / PEI composite dielectric thin film. Figure 5 (a) is a cross-sectional scanning electron microscope (SEM) image of the UiO-66-CDs / PEI composite dielectric film. It can be seen that the overall structure of the composite film is dense and continuous, with no obvious delamination or macroscopic defects observed, indicating that UiO-66-CDs are uniformly distributed in the PEI matrix and form a stable interfacial bond with the polymer matrix during hot pressing. This dense cross-sectional morphology is beneficial for maintaining the structural integrity of the material under high temperature and strong electric field conditions. Figure 5(b) shows the XRD patterns of composite films with different UiO-66-CDs contents. Gradually increasing characteristic diffraction peaks can be observed at approximately 7.27° and 8.45°, corresponding to the characteristic crystal planes of UiO-66. The intensity of the characteristic peaks increases with increasing UiO-66-CDs content, indicating that UiO-66-CDs have been successfully introduced into the PEI matrix, and the crystal structure remains stable during composite film preparation and gradient heating hot pressing. Figure 5 (c) shows the FTIR spectrum of the composite film. Compared to the pure PEI film, the composite film exhibits higher FTIR spectra at approximately 3500 cm⁻¹. -1 The weakening of the –NH stretching vibration peak indicates that during the gradient heating and hot pressing process, the amino groups in PEI react with the carboxyl groups on the surface of UiO-66-CDs to form a stable interfacial cross-linked structure. This cross-linking enhances the interfacial bonding between UiO-66-CDs and PEI and contributes to the construction of the cross-linked network.

[0035] Figure 6 Analysis of the energy level structure and electron transport mechanism of UiO-66-CDs / PEI composite dielectric thin films. Figure 6 (a) The energy level structure diagram shows that the lowest unoccupied molecular orbital (LUMO) energy level of CDs is significantly lower than that of UiO-66-NH2 and PEI, thus forming a deep-level electronic trap at the UiO-66-CDs / PEI interface. Therefore, it can be analyzed that... Figure 6(b) Electron transport mechanism: Under the action of an applied electric field, electrons injected by the electrodes are preferentially captured and localized at the interface by the deep energy levels of CDs, forming a stable deep trap region. This process not only raises the electron injection barrier but also suppresses the continuous injection of subsequent electrons through the Coulomb repulsion effect. Furthermore, the migration of electrons from the deep energy levels of CDs to UiO-66-NH2 or PEI requires overcoming a large energy difference, forming a multi-level energy barrier structure along the transport path, thus effectively suppressing thermally activated transitions under high-temperature conditions. In contrast, the UiO-66-NH2 / PEI interface only provides a single, shallow trap energy level, offering limited resistance to carrier migration at high temperatures.

[0036] Figure 7 Analysis of out-of-plane thermal conductivity and phonon transport mechanism of UiO-66-CDs / PEI and PEI composite dielectric films.

[0037] Figure 7(a) shows the temperature rise curves of the 1.0 wt.% UiO-66-CDs / PEI composite film and the pure PEI film under a heating stage of 100 ℃. It can be seen that, compared with the pure PEI film, the 1.0 wt.% UiO-66-CDs / PEI composite film can reach the same temperature as the heating stage in a shorter time, indicating that it has a better thermal response capability. Figure 7 (b) Infrared thermal imaging results of the two films during the heating process are presented. When the surface temperature reaches a steady state, the overall temperature distribution of the 1.0 wt.% UiO-66-CDs / PEI composite film is basically consistent with the heating stage temperature, while the pure PEI film still has local low-temperature regions, indicating that its thermal conductivity is limited. The above phenomena show that the out-of-plane thermal conductivity of the composite film is significantly enhanced after the introduction of UiO-66-CDs. To further quantitatively verify the above results, the out-of-plane thermal conductivity of the two films was tested, and the results are as follows: Figure 7 As shown in (c), the out-of-plane thermal conductivity of the 1.0 wt.% UiO-66-CDs / PEI composite film is nearly twice that of the pure PEI composite film, further confirming the effectiveness of UiO-66-CDs in improving the thermal transport performance of composite films. Figure 7 (d) The heat flow distribution of the two films during the thermal conduction process was simulated. It was found that continuous heat conduction channels were preferentially formed in the 1.0 wt.% UiO-66-CDs / PEI composite film, while the heat flow distribution in the pure PEI film was relatively dispersed. This is mainly attributed to the stable cross-linking structure formed between UiO-66-CDs and the PEI matrix after CDs interface modification, which effectively reduced the interfacial thermal resistance and thus optimized the interfacial phonon transport.

[0038] Figure 8Analysis of high-temperature energy storage performance and cycle stability of UiO-66-CDs / PEI and PEI composite dielectric films. Figure 8 (a) shows that the dielectric, breakdown and energy storage properties of the 1.0 wt.% UiO-66-CDs / PEI composite film at 200 °C are superior to those of the pure PEI film. Figure 8 (b) indicates that at 200 °C and 400 MV·m -1 Under these conditions, the UiO-66-CDs / PEI film can reach 90% of its saturation energy density within 17.8 μs, demonstrating excellent fast charge and discharge capabilities. Figure 8 (c) In high-temperature long-cycle testing, the UiO-66-CDs / PEI film maintained an energy efficiency greater than 90% and an energy density stable at 3.62 J·cm² after more than 50,000 charge-discharge cycles at 200℃. -3 It exhibits significantly better cycle stability than pure PEI. Furthermore, Figure 8 (d) The energy storage performance test results in different regions show that the UiO-66-CDs / PEI composite film has good spatial consistency, indicating that its internal electric and thermal fields are uniformly distributed. The comparison with existing high-temperature dielectric materials further demonstrates that the UiO-66-CDs / PEI composite dielectric film can achieve high energy density and energy efficiency at both 150 ℃ and 200 ℃, showcasing the significant technical advantages of achieving electron-phonon synergistic regulation through MOF interface modification and cross-linked network construction in high-temperature energy storage applications.

[0039] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A method for preparing a UiO-66-CDs / PEI composite dielectric thin film, characterized in that... Includes the following steps: UiO-66-CDs were synthesized by chemical bonding of amino-functionalized metal-organic framework UiO-66-NH2 with carbon quantum dots CDs. UiO-66-CDs were then blended with PEI polymer, followed by electrospinning and hot pressing to form a film, resulting in a UiO-66-CDs / PEI composite dielectric film.

2. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 1, characterized in that... The preparation method of the amino-functionalized metal-organic framework UiO-66-NH2 is as follows: A zirconium chloride solution with a concentration of 0.5-1.5 wt.% dissolved in N,N-dimethylformamide and a 2-aminoterephthalic acid solution with a concentration of 0.5-1 wt.% dissolved in N,N-dimethylformamide are mixed and stirred for 20-40 min. Then acetic acid is added, and the mixture is placed in a reaction vessel and reacted at 100-140℃ for 10-14 h. The reaction product is centrifuged, washed, and dried at 50-70℃ to obtain the amino-functionalized metal-organic framework UiO-66-NH2, wherein the volume ratio of zirconium chloride solution, 2-aminoterephthalic acid solution and acetic acid is (4-6):(4-6):

1.

3. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 2, characterized in that... The preparation method of the amino-functionalized metal-organic framework UiO-66-NH2 is as follows: A zirconium chloride solution with a concentration of 1 wt.% dissolved in N,N-dimethylformamide and a 2-aminoterephthalic acid solution with a concentration of 0.7 wt.% dissolved in N,N-dimethylformamide are mixed and stirred for 30 min. Acetic acid is then added, and the mixture is placed in a reaction vessel and reacted at 120℃ for 12 h. The reaction product is centrifuged, washed, and dried at 60℃ to obtain the amino-functionalized metal-organic framework UiO-66-NH2, wherein the volume ratio of zirconium chloride solution, 2-aminoterephthalic acid solution, and acetic acid is 5:5:

1.

4. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 2, characterized in that... The carbon quantum dots (CDs) are prepared by aldol reaction. The preparation method is as follows: Sodium hydroxide powder is dissolved in acetaldehyde at a mass-volume ratio of 2-5 g: 10 mL and stirred for 1-3 h. Dilute hydrochloric acid is added to adjust the pH to neutral. The mixture is allowed to stand until a precipitate is formed. The precipitate is collected, washed by centrifugation, and dried at 50-70 °C to obtain carbon quantum dots (CDs).

5. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 4, characterized in that: UiO-66-NH2 was dissolved in N,N-dimethylformamide to obtain a UiO-66-NH2 solution. Carbon quantum dots (CDs), 2-aminoterephthalic acid, and N-hydroxysuccinimide were dissolved in N,N-dimethylformamide to obtain a mixed solution. The UiO-66-NH2 solution and the mixed solution were mixed in an equal volume ratio and stirred at 70–90 °C for 10–14 h. The reaction product was centrifuged, washed, and dried at 50–70 °C to obtain UiO-66-CDs.

6. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 5, characterized in that: The mass ratio of UiO-66-NH2, carbon quantum dots (CDs), 2-aminoterephthalic acid, and N-hydroxysuccinimide is 3:10:30:

33.

7. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 6, characterized in that: UiO-66-CDs were added to DMF and ultrasonically dispersed, followed by the addition of polyetherimide particles. The mixture was stirred at 70–90°C for 1–3 hours to obtain a homogeneous solution. The solution was then electrospun into nanofibers, which were attached to the surface of conductive glass. The nanofibers were then placed in a vacuum vulcanizing machine and subjected to a gradient temperature increase at 10–20 MPa. Finally, the mixture was hot-pressed at 100–200°C for 2–4 hours to obtain a UiO-66-CDs / PEI composite dielectric film. The mass of UiO-66-CDs was 0.5–1.5% of the mass of the composite dielectric film.

8. The method for preparing a UiO-66-CDs / PEI composite dielectric thin film according to claim 7, characterized in that: The gradient heating is performed by hot pressing at 100℃, 150℃, and 200℃ for 1 hour each.

9. The application of a UiO-66-CDs / PEI composite dielectric film prepared by any one of claims 1-8 in the preparation of high-temperature dielectric capacitors and power electronics.

Images