Sandwich structure composite material containing negative dielectric layer and preparation method and application thereof

Abstract

The application belongs to the technical field of polymer-based capacitor, and relates to the preparation of composite material, a sandwich structure composite material containing a negative dielectric layer and a preparation method and application thereof. The sandwich structure is a three-layer laminated structure closely adhered, which is composed of a first positive dielectric layer, an intermediate negative dielectric layer and a second positive dielectric layer in sequence. The material of the first positive dielectric layer and the second positive dielectric layer is a composite material of polyvinylidene fluoride and boron nitride. The intermediate negative dielectric layer is a composite material of polyvinylidene fluoride and multi-walled carbon nanotubes. The content of boron nitride in the composite material of polyvinylidene fluoride and boron nitride is 5-25wt%. The content of multi-walled carbon nanotubes in the composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is 2-40wt%. The sandwich structure composite material containing a negative dielectric layer provided by the application can maintain low dielectric loss while maintaining high energy density.

Description

Technical Field

[0001] This invention relates to the field of polymer-based capacitor technology, specifically to the preparation of composite materials, and to sandwich-structured composite materials containing a negative dielectric layer, their preparation methods, and applications. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Polymer-based capacitors offer advantages such as high power density, long cycle life, and high safety. However, the limiting factor for their application is their relatively low energy storage density and high dielectric loss. To address these issues, the inventors have designed sandwich-structured composite materials. These materials combine the strengths of each layer to compensate for their weaknesses, achieving a synergistic effect that significantly improves energy storage density while maintaining low dielectric loss, thus meeting various performance requirements. However, the inventors' research has revealed that current three-layer dielectric composite materials, which are composed of stacked positive dielectric materials with different properties, still suffer from insufficient energy density and high losses, severely restricting their practical application. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a sandwich-structured composite material containing a negative dielectric layer, its preparation method, and its application. The sandwich-structured composite material containing a negative dielectric layer provided by the present invention can maintain low dielectric loss while maintaining high energy density.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] On the one hand, a sandwich structure composite material containing a negative dielectric layer, wherein the sandwich structure is a tightly fitted three-layer structure, consisting of a first positive dielectric layer, an intermediate negative dielectric layer and a second positive dielectric layer in sequence. The first and second positive dielectric layers are made of a composite material of polyvinylidene fluoride and boron nitride, and the intermediate negative dielectric layer is made of a composite material of polyvinylidene fluoride and multi-walled carbon nanotubes. The content of boron nitride in the polyvinylidene fluoride and boron nitride composite material is 5-25 wt%, and the content of multi-walled carbon nanotubes in the polyvinylidene fluoride and multi-walled carbon nanotube composite material is 2-40 wt%.

[0007] This invention introduces a negative dielectric layer with a negative dielectric constant into a three-layer structure material to prepare a "positive-negative-positive" sandwich structure composite material. Through the synergistic effect of "positive-negative" dielectrics and strong polarization, the sandwich structure composite material maintains both high energy density and low dielectric loss.

[0008] On the other hand, a method for preparing the above-mentioned sandwich structure composite material containing a negative dielectric layer involves first cold pressing a composite material of polyvinylidene fluoride and boron nitride to form a first positive dielectric layer, then laying a composite material of polyvinylidene fluoride and multi-walled carbon nanotubes on the surface of the first positive dielectric layer, performing a second cold pressing to obtain a double-layer composite material containing an intermediate negative dielectric layer, then laying a composite material of polyvinylidene fluoride and boron nitride on the surface of the intermediate negative dielectric layer of the double-layer composite material, and finally hot pressing to obtain the final product.

[0009] Thirdly, the application of the aforementioned sandwich-structured composite material containing a negative dielectric layer in polymer-based capacitors.

[0010] The beneficial effects of this invention are as follows:

[0011] 1. This invention introduces a single-layer negative dielectric composite material into a composite material to construct a "positive-negative-positive" sandwich structure composite material, which is prepared by a layer-by-layer hot pressing method. By adjusting the dielectric constant and thickness ratio between the positive and negative dielectric layers, and utilizing the synergistic effect of positive and negative dielectrics between the positive and negative dielectric layers, as well as the macroscopic interface polarization between layers and the microscopic interface polarization within layers, high energy density performance is achieved while maintaining low dielectric loss.

[0012] 2. Experiments show that this invention successfully prepared a "positive-negative-positive" sandwich-structured dielectric composite material using a hot-pressing method. The discharge energy density of this sandwich-structured composite material reaches as high as 22.3 J / cm². 3 At the same time, it can maintain a low dielectric loss of 0.02 (10kHz).

[0013] 3. Experiments show that the present invention successfully prepared a "positive-negative-positive" sandwich structure dielectric composite material using hot pressing molding method. The dielectric constant is as high as 432 (10kHz), which is 2700% higher than that of single-layer material. The loss factor can also be maintained at a low level of 0.06. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 The diagram shows the process flow chart (a, b), morphology diagram (c), and elemental distribution diagram (d) of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material prepared in the embodiments of the present invention.

[0016] Figure 2The images show the characterization of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material prepared in the embodiments of the present invention. a is the XRD pattern and b is the Fourier transform infrared pattern.

[0017] Figure 3 Different BN contents prepared in the embodiments of the present invention

[0018] The dielectric constant dispersion curves and dielectric loss dispersion curves of PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite materials are shown in Figure 1. (a) is the dielectric constant dispersion curve of the 5-12-5 sample, (b) is the dielectric constant dispersion curve of the 15-12-15 sample, (c) is the dielectric constant dispersion curve of the 25-12-25 sample, and (d) is a summary graph of the dielectric constants of the three samples.

[0019] Figure 4 Different MWCNT contents prepared in the embodiments of the present invention

[0020] The dielectric constant dispersion curves and dielectric loss dispersion curves of PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite materials; (a) is the dielectric constant dispersion curve of the 15-2-15 sample, (b) is the dielectric constant dispersion curve of the 15-12-15 sample, (c) is the dielectric constant dispersion curve of the 15-40-15 sample, and (d) is a summary graph of the dielectric constants of the three samples.

[0021] Figure 5 The breakdown strength diagrams (a, b) and the breakdown strength bar charts (c, d) of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material in the embodiments of the present invention are shown.

[0022] Figure 6 The images show the discharge energy density diagrams (a, b, c, d) and charge-discharge efficiency diagrams (d, f) of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material in the embodiments of the present invention. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] Given the problems of low energy density and dielectric loss in existing three-layer dielectric composite materials, this invention proposes a sandwich-structured composite material containing a negative dielectric layer, its preparation method, and its application.

[0026] In a typical embodiment of the present invention, a sandwich structure composite material containing a negative dielectric layer is provided. The sandwich structure is a tightly fitted three-layer structure, consisting of a first positive dielectric layer, a middle negative dielectric layer, and a second positive dielectric layer. The first and second positive dielectric layers are made of a composite material of polyvinylidene fluoride and boron nitride, and the middle negative dielectric layer is made of a composite material of polyvinylidene fluoride and multi-walled carbon nanotubes. The content of boron nitride in the polyvinylidene fluoride and boron nitride composite material is 5-25 wt%, and the content of multi-walled carbon nanotubes in the polyvinylidene fluoride and multi-walled carbon nanotube composite material is 2-40 wt%.

[0027] Studies have shown that the content of boron nitride affects the dielectric constant of sandwich-structured composite materials; as the content of boron nitride increases, the dielectric constant first increases and then decreases. Therefore, in order to further improve the dielectric constant of sandwich-structured composite materials, in some embodiments, the content of boron nitride in the composite material of polyvinylidene fluoride and boron nitride is 10–20 wt%, preferably 14–17 wt%.

[0028] Studies have shown that the content of multi-walled carbon nanotubes affects the dielectric constant of sandwich-structured composite materials; the dielectric constant increases with increasing multi-walled carbon nanotube content. Therefore, to further improve the dielectric constant of sandwich-structured composite materials, in some embodiments, the content of multi-walled carbon nanotubes in the composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is 30–40 wt%, preferably 35–40 wt%.

[0029] In some embodiments, the relative thickness ratio of the first positive dielectric layer, the intermediate negative dielectric layer, and the second positive dielectric layer is 1:0.1–20:0.8–1.2. When the relative thickness ratio of the first positive dielectric layer, the intermediate negative dielectric layer, and the second positive dielectric layer is 1:0.1–1.0:0.9–1.1, especially 1:0.4–0.6:0.9–1.1, it has a higher discharge energy density and lower dielectric loss. When the relative thickness ratio of the first positive dielectric layer, the intermediate negative dielectric layer, and the second positive dielectric layer is 1:15–20:0.9–1.1, especially 1:18–20:0.9–1.1, it has a higher dielectric constant and a lower loss factor.

[0030] The boron nitride content in the materials of the first and second positive dielectric layers can be the same or different. In some embodiments, the boron nitride content in the materials of the first and second positive dielectric layers is the same.

[0031] Another embodiment of the present invention provides a method for preparing the above-mentioned sandwich structure composite material containing a negative dielectric layer. The method involves first cold pressing a composite material of polyvinylidene fluoride and boron nitride to form a first positive dielectric layer, then laying a composite material of polyvinylidene fluoride and multi-walled carbon nanotubes on the surface of the first positive dielectric layer, and then performing a second cold pressing to obtain a double-layer composite material containing an intermediate negative dielectric layer. Finally, a composite material of polyvinylidene fluoride and boron nitride is laid on the surface of the intermediate negative dielectric layer of the double-layer composite material, and then hot pressing is performed to obtain the final product.

[0032] In some embodiments, the hot pressing process conditions are: pressure of 15-25 MPa, temperature of 150-170°C, and time of 25-35 min.

[0033] Both the first cold pressing and the second cold pressing are methods of applying pressure to the material at room temperature (15-30°C). In some embodiments, the pressure of the first cold pressing is 1.5-2.5 MPa and the time is 1-3 min.

[0034] The composite material of polyvinylidene fluoride and boron nitride is obtained by ball milling polyvinylidene fluoride and boron nitride.

[0035] The composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is obtained by ball milling polyvinylidene fluoride and multi-walled carbon nanotubes.

[0036] In some embodiments, the pressure of the second cold pressing is 1.5 to 2.5 MPa, and the time is 1 to 3 minutes.

[0037] A third embodiment of the present invention provides an application of the above-mentioned sandwich structure composite material containing a negative dielectric layer in a polymer-based capacitor.

[0038] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0039] Example 1

[0040] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0041] Step 1: Fabrication of the positive dielectric layer

[0042] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were removed and set aside for use as a PVDF / BN composite material. The boron nitride content was 5 wt%.

[0043] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0044] Step 2: Fabrication of the intermediate negative dielectric layer

[0045] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 40 wt%.

[0046] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0047] Step 3: Preparation of the three-layer composite material

[0048] Weigh 0.2g of the PVDF / BN composite powder from the first step and evenly spread it on the negative dielectric layer of the bilayer material, then hot-press it. The hot-pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material of this invention, with a diameter of 25mm and a thickness of approximately 1.5±0.02mm. The preparation process is as follows... Figure 1 As shown in (a, b).

[0049] Figure 1 (c) and (d) are cross-sectional scanning electron microscopy (SEM) images and elemental distribution maps (EDS) of the sandwich-structured composite material. From... Figure 1In (c), it can be clearly seen that the three layers of material are tightly hot-pressed together without obvious cracks or voids. The three-layer composite material has good interfacial adhesion, which helps to improve the breakdown strength and dielectric constant of the composite material. Figure 1 As shown, the PVDF / BN positive dielectric layer is located in the outer layer, and the PVDF / MWCNTs negative dielectric layer is located in the middle layer. The BN sheets are uniformly distributed in the outer layer, indicating that the uniform distribution of BN sheets in the outer layer material is beneficial to improving BDS.

[0050] Figure 2 In the image, (a) is the XRD pattern of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material, and (b) is the Fourier transform infrared (FTIR) image of the sandwich structure composite material. From... Figure 2 As can be seen, no impurity peaks appeared in the XRD pattern and no extra absorption peaks appeared in the FT-IR, indicating that the sandwich structure composite material was successfully prepared in this embodiment without any impurities.

[0051] The BN content and layer thickness ratio of this embodiment were adjusted, and performance tests were conducted. The results are as follows:

[0052] Figure 3 The dielectric constant and dielectric loss dispersion curves of PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich composite materials with different BN contents and layer thickness ratios are shown. It can be seen that the dielectric constant gradually increases as the layer thickness ratio of the sandwich composite material decreases from 1:1:1 to 1:20:1. When the filler content in the negative dielectric layer of PVDF / MWCNTs remains constant, the dielectric constant of the composite material first increases and then decreases as the BN content increases from 5wt% to 25wt%. Specifically, when the layer thickness ratio remains constant at 1:20:1, the dielectric constant of the 15-40-15 composite material is as high as 432, and the dielectric loss is approximately 0.06.

[0053] Figure 4 The dielectric constant and dielectric loss dispersion curves of PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich composite materials with different MWCNT contents and layer thickness ratios are shown. As the layer thickness ratio decreases, or with the MWCNT content increasing from 2 wt% to 40 wt%, the dielectric constant of the three-layer composite material gradually increases, with the optimal sample being 15-40-15, exhibiting a dielectric constant as high as 432. When the intermediate layer is a positive dielectric layer, the intermediate layer of sample 15-2-15 changes from a negative dielectric layer to a positive dielectric layer, and the dielectric constant decreases to 191. Therefore, introducing a negative dielectric layer as an intermediate layer can improve the dielectric constant of the material.

[0054] Figure 5The breakdown strength diagram of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich composite material shows that when the layer thickness ratio is 1:0.5:1, the breakdown field strength of sample 15-12-15 is 22.3kV / mm, which is significantly improved compared with the "positive-positive-positive" composite material and composite materials with other filler contents.

[0055] Figure 6 The diagram shows the discharge energy density of the PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich composite material, and (d, f) represents the charge-discharge efficiency of the sandwich composite material. Compared to pure PVDF monolayer materials and "positive-positive-positive" composite materials, the three-layer composite material containing a negative dielectric layer exhibits the highest discharge energy density, at 23.4 J / cm². 3 It also exhibits high charge-discharge efficiency. Therefore, the synergistic effect of the positive and negative dielectric constant layers and the sandwich structure play a crucial role in achieving high discharge energy density.

[0056] Example 2:

[0057] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0058] Step 1: Fabrication of the positive dielectric layer

[0059] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were removed and set aside for use as a PVDF / BN composite material. The boron nitride mass percentage was 15 wt%.

[0060] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0061] Step 2: Fabrication of the intermediate negative dielectric layer

[0062] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 40 wt%.

[0063] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0064] Step 3: Preparation of the three-layer composite material

[0065] Weigh 0.2g of the PVDF / BN composite powder from step one and evenly spread it on the negative dielectric layer of the bilayer material, then hot-press it. The hot-pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields a PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material with a diameter of 25mm and a thickness of approximately 1.5±0.02mm.

[0066] Example 3:

[0067] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0068] Step 1: Fabrication of the positive dielectric layer

[0069] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were taken out for use as PVDF / BN composite material. The mass percentage of boron nitride was 25 wt%.

[0070] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0071] Step 2: Fabrication of the intermediate negative dielectric layer

[0072] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 40 wt%.

[0073] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0074] Step 3: Preparation of the three-layer composite material

[0075] Weigh 0.2g of the PVDF / BN composite powder from step one and evenly spread it on the negative dielectric layer of the bilayer material, then hot-press it. The hot-pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields a PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material with a diameter of 25mm and a thickness of approximately 1.5±0.02mm.

[0076] Example 4:

[0077] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0078] Step 1: Fabrication of the positive dielectric layer

[0079] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were removed and set aside for use as a PVDF / BN composite material. The boron nitride mass percentage was 15 wt%.

[0080] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0081] Step 2: Fabrication of the intermediate negative dielectric layer

[0082] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 2 wt%.

[0083] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0084] Step 3: Preparation of the three-layer composite material

[0085] Weigh 0.2g of the PVDF / BN composite powder from step one and evenly spread it on the negative dielectric layer of the bilayer material, then hot-press it. The hot-pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields a PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material with a diameter of 25mm and a thickness of approximately 1.5±0.02mm.

[0086] Example 5:

[0087] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0088] Step 1: Fabrication of the positive dielectric layer

[0089] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were removed and set aside for use as a PVDF / BN composite material. The boron nitride mass percentage was 15 wt%.

[0090] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0091] Step 2: Fabrication of the intermediate negative dielectric layer

[0092] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 12 wt%.

[0093] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0094] Step 3: Preparation of the three-layer composite material

[0095] Weigh 0.2g of the PVDF / BN composite powder from step one and evenly spread it on the negative dielectric layer of the bilayer material, then hot-press it. The hot-pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields a PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material with a diameter of 25mm and a thickness of approximately 1.5±0.02mm.

[0096] Example 6:

[0097] The preparation method of a sandwich-structured composite material containing a negative dielectric layer specifically includes the following steps:

[0098] Step 1: Fabrication of the positive dielectric layer

[0099] A certain amount of polyvinylidene fluoride (PVDF) and boron nitride (BN) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were evenly mixed, they were removed and set aside for use as a PVDF / BN composite material. The boron nitride mass percentage was 15 wt%.

[0100] 0.2g of PVDF / BN composite material was weighed and uniformly spread in a hot press for cold pressing. The cold pressing process was as follows: pressure 1MPa, holding time 2min. A circular PVDF / BN positive dielectric layer with a diameter of 25mm and a thickness of approximately 0.5±0.02mm was obtained.

[0101] Step 2: Fabrication of the intermediate negative dielectric layer

[0102] A certain amount of polyvinylidene fluoride (PVDF) and multi-walled carbon nanotube (MWCNT) powders were weighed and placed in a ball mill and ball-milled for 10 minutes. After the powders were mixed evenly, they were taken out for use as PVDF / MWCNTs composite materials. The mass percentage of multi-walled carbon nanotubes was 40 wt%.

[0103] 0.2g of PVDF / MWCNTs composite material was weighed and uniformly spread on the lower positive dielectric layer, then cold-pressed. The cold-pressing process was carried out at a pressure of 2MPa and a holding time of 2min. A circular PVDF / BN-PVDF / MWCNTs bilayer composite material with a diameter of 25mm and a bilayer material thickness of approximately 1±0.02mm was obtained.

[0104] Step 3: Preparation of the three-layer composite material

[0105] Weigh 0.2g of the PVDF / BN composite powder from step one and evenly spread it on the negative dielectric layer of the double-layer material for hot pressing. The hot pressing process is as follows: pressure 20MPa, temperature 160℃, time 30min. This yields a PVDF / BN-PVDF / MWCNTs-PVDF / BN sandwich structure composite material with a diameter of 25mm and a thickness of 1.5±0.02mm.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sandwich-structured composite material containing a negative dielectric layer, characterized in that, The sandwich structure is a tightly fitted three-layer structure, consisting of a first positive dielectric layer, a middle negative dielectric layer, and a second positive dielectric layer. The first and second positive dielectric layers are made of a composite material of polyvinylidene fluoride (PVDF) and boron nitride (BN). The middle negative dielectric layer is a composite material of PVDF and multi-walled carbon nanotubes (MWC). The PVDF-BN composite material contains 5–25 wt% boron nitride, and the PVDF-MWC composite material contains 2–40 wt% MWC MWC. The relative thickness ratio of the first positive dielectric layer, the intermediate negative dielectric layer, and the second positive dielectric layer is 1:0.4~0.6:0.9~1.1, or the relative thickness ratio is 1:15~20:0.9~1.

1.

2. The sandwich-structured composite material containing a negative dielectric layer as described in claim 1, characterized in that, The boron nitride content in the composite material of polyvinylidene fluoride and boron nitride is 10~20 wt%.

3. The sandwich-structured composite material containing a negative dielectric layer as described in claim 2, characterized in that, The boron nitride content in the composite material of polyvinylidene fluoride and boron nitride is 14~17 wt%.

4. The sandwich-structured composite material containing a negative dielectric layer as described in claim 1, characterized in that, The content of multi-walled carbon nanotubes in the composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is 30~40 wt%.

5. The sandwich-structured composite material containing a negative dielectric layer as described in claim 4, characterized in that, The content of multi-walled carbon nanotubes in the composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is 35~40 wt%.

6. The sandwich-structured composite material containing a negative dielectric layer as described in claim 1, characterized in that, The relative thickness ratio of the first positive dielectric layer, the intermediate negative dielectric layer, and the second positive dielectric layer is 1:18~20:0.9~1.

1.

7. The sandwich-structured composite material containing a negative dielectric layer as described in claim 1, characterized in that, The first and second positive dielectric layers contain the same amount of boron nitride.

8. A method for preparing a sandwich-structured composite material containing a negative dielectric layer as described in any one of claims 1 to 7, characterized in that, A first positive dielectric layer is formed by first cold pressing of a composite material of polyvinylidene fluoride and boron nitride. A composite material of polyvinylidene fluoride and multi-walled carbon nanotubes is then laid on the surface of the first positive dielectric layer. A second cold pressing is then performed to obtain a double-layer composite material containing an intermediate negative dielectric layer. A composite material of polyvinylidene fluoride and boron nitride is then laid on the surface of the intermediate negative dielectric layer of the double-layer composite material. Finally, a hot pressing is performed to obtain the final product.

9. The method for preparing the sandwich-structured composite material containing a negative dielectric layer as described in claim 8, characterized in that, The hot pressing process conditions are: pressure of 15~25 MPa, temperature of 150~170 ℃, and time of 25~35 min.

10. The method for preparing the sandwich-structured composite material containing a negative dielectric layer as described in claim 8, characterized in that, The pressure for the first cold pressing is 1.5~2.5 MPa, and the time is 1~3 min.

11. The method for preparing the sandwich-structured composite material containing a negative dielectric layer as described in claim 8, characterized in that, The second cold pressing process involves a pressure of 1.5~2.5 MPa and a time of 1~3 min.

12. The application of a sandwich-structured composite material containing a negative dielectric layer as described in any one of claims 1 to 7 in a polymer-based capacitor.

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