Low-filling high-energy-storage flexible dielectric material and preparation method thereof

Abstract

The invention discloses a low-filling high-energy-storage flexible dielectric material. The low-filling high-energy-storage flexible dielectric material is prepared from gt; 98.00 wt% of a polymer matrix and lt; and 2wt% of boron nitride quantum dots. The preparation method comprises the following steps: introducing the boron nitride quantum dots into a polymer monomer or a polymer solution or polymer particles, uniformly mixing, and preparing the composite film through a spin coating, blade coating or mould pressing process. The wide-band-gap boron nitride quantum dots construct a large number of deep traps in the polymer, and electrons are effectively captured; the nano coulomb blocking effect further hinders carrier transmission, and the breakdown strength of the medium is remarkably improved. Finally, under extremely low filling amount, the dielectric material with relatively high energy storage density and efficiency is obtained, the service life of the polymer dielectric material is greatly prolonged, the cycling stability of the polymer dielectric material is greatly improved, and the strength, the flexibility and the heat-conducting property of the polymer dielectric material are also synchronously improved. The preparation method is simple in process, low in cost and high in designability, and can be widely applied to thin-film capacitors and embedded devices.

Description

Technical Field

[0001] The invention belongs to the field of polymer energy storage dielectrics and discloses a low-filling high-energy storage flexible dielectric material and a preparation method thereof. Background Art

[0002] Polymer-based dielectric materials are considered to be potential candidates for the preparation of dielectric capacitors due to their inherent resistance to breakdown, low loss, flexibility, light weight and excellent processing properties. With the development of miniaturization, lightweight and integration of electronic devices, it is urgent to develop polymer dielectric materials with higher energy storage density, higher charge and discharge efficiency, and longer cycle stability to meet the requirements of various extreme working conditions. For example, the accumulation of space charge in dielectric materials under high fields can cause local discharge and leakage current. The high integration of electronic devices is inevitably accompanied by high power loss and heat accumulation, which seriously affects the energy storage characteristics and service life of dielectric capacitors. Adding wide-bandgap, high-thermal conductivity nanofillers (such as boron nitride BN, Al2O3, SiO2) to the polymer matrix can effectively suppress leakage current and enhance the dielectric energy storage characteristics and thermal conductivity. However, the compatibility between traditional nanofillers and polymer matrices is poor, and high filling amount of fillers can also cause defects inside the polymer, reduce the flexibility and mechanical strength of the material, and deteriorate the energy storage density and electrical properties of the dielectric material. Therefore, the development of flexible polymer dielectric materials with ultra-low filling content, high breakdown strength, high energy storage density and high thermal conductivity is of great significance for achieving high thermal stability and long life of electrical equipment.

[0003] In order to achieve the above objectives, commonly used methods are to modify the filler interface, design multi-scale molecular structures, and design composite multilayer membrane structures. Cha Junwei et al. introduced a boron nitride nanosheet (BNNS) layer on the outside of PI to prepare a BNNS / PI composite film. At room temperature, the breakdown strength of the BNNS / PI composite film can reach up to 591 kV / mm, which is 43% higher than that of pure PI (448 kV / mm), and the energy storage density is twice that of pure PI. Pan Zhongbin et al. introduced a core-shell structured BNNS@Al2O3 nanofiller into PEI. When the filler content was 3 vol%, the energy storage density of BNNS@Al2O3 / PEI (12.45 J / cm 3 ) is 3.6 times that of pure PEI. These strategies have improved the breakdown strength and energy storage density of the medium to a certain extent, but the preparation process is relatively complex and the filler filling amount is large, which inevitably introduces defects. It is difficult to take into account the contradictory relationship between the dielectric constant and breakdown strength of the material, the breakdown strength and thermal conductivity, and the flexibility and strength of the polymer itself, and the energy storage density and efficiency have been limited. Summary of the invention

[0004] The object of the present invention is to provide a low-filling high-energy storage flexible dielectric material and a preparation method thereof.

[0005] The technical solution provided by the present invention to solve the above problems is: a low-filling, high-energy storage flexible dielectric material, composed of a polymer matrix and boron nitride quantum dots, wherein the amount of boron nitride quantum dots accounts for <2wt% (preferably, the amount accounts for 0.04wt%).

[0006] Furthermore, the polymer is one or more of thermoplastic polyethylene, polypropylene, polybutylene, polyvinyl alcohol, polymethyl methacrylate, polystyrene, polyetheretherketone, polyvinylidene fluoride and copolymers thereof, and thermosetting polyimide, epoxy resin, polyurethane and polyetherimide.

[0007] A method for preparing a low-filling high-energy storage flexible dielectric material, the steps are as follows:

[0008] S1. In situ generation of boron nitride quantum dots by solvothermal method, ion intercalation method or microwave irradiation method;

[0009] S2, compounding the polymer monomer or polymer solution or polymer particles with the boron nitride quantum dots, and mixing them evenly by ultrasound or banburying;

[0010] S3. Prepare the composite film by spin coating, blade coating or molding process.

[0011] The present invention has the following beneficial effects:

[0012] (1) The preparation process is simple. Boron nitride quantum dots that are well dispersed in different organic solvents are synthesized by a simple solvothermal method. The polymer is introduced in situ to achieve uniform dispersion of the two.

[0013] (2) Good flexibility and high strength. The breakdown and energy storage performance can be significantly improved at extremely low filling amounts, while maintaining the flexibility of the polymer matrix.

[0014] (3) Taking into account energy storage density, efficiency and thermal conductivity. The Coulomb blockade effect of boron nitride quantum dots can effectively capture electrons and hinder carrier transport, which is beneficial to the improvement of breakdown strength and energy storage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the TEM image of the BNQDs / PI composite film in Example 1 ( Figure 1 (a)) and digital photographs ( Figure 1 (b));

[0016] Figure 2 is the simultaneous thermal analysis curve of BNQDs / PI in Examples 1-3;

[0017] Figure 3 is the dielectric property curve of BNQDs / PI in Examples 1-3;

[0018] Figure 4 is the Weibull distribution diagram of the breakdown strength of BNQDs / PI in Examples 1-3;

[0019] Figure 5 is the energy storage performance curve of BNQDs / PI in Examples 1-3;

[0020] Figure 6 is the cycling performance diagram of BNQDs / PI in Example 2;

[0021] Figure 7 is the thermal conductivity of BNQDs / PI in Examples 1-3. DETAILED DESCRIPTION

[0022] In order to demonstrate the essential features and significant improvements of the present invention, the following examples are used to further illustrate the implementation methods and effects.

[0023] Embodiment one:

[0024] Boron nitride quantum dots / polyimide (BNQDs / PI) composite dielectric material, wherein the content of BNQDs is 0.02wt%.

[0025] Prepare the BNQDs / PI dielectric film as follows:

[0026] S1. Ultrasonic disperse BNNS in N,N-dimethylacetamide (DMAc), then transfer to a hydrothermal autoclave, place in an oven at 180°C for 12 h, cool naturally to room temperature, and filter using a 0.2 μm filter to obtain a BNQDs dispersion.

[0027] S2. Ultrasonic disperse the BNQDs dispersion in S1 in 6 ml DMAc according to the mass fraction of BNQDs.

[0028] S3. Add 0.5 g of 4,4'-diaminodiphenyl ether to the dispersion obtained in S2 and stir until completely dissolved, then add 1.1 g of hexafluorodianhydride and stir at room temperature for 12 h to obtain a PAA precursor solution.

[0029] S4. Place the PAA solution in S3 on a clean glass plate and apply it by scraping with a coating machine.

[0030] S5. Place the coated glass plate in a muffle furnace and gradually increase the temperature to perform thermal imidization treatment to obtain a BNQDs / PI dielectric thin film material.

[0031] Embodiment 2

[0032] The difference from Example 1 is that the content of BNQDs is 0.04 wt %.

[0033] Embodiment 3

[0034] The difference from Example 1 is that the content of BNQDs is 0.06 wt %.

[0035] The TEM electron microscope image of the BNQDs / PI composite film in Example 1 is as follows: Figure 1 As shown in (a), its cross section is dense and has no holes. The digital image of BNQDs / PI is shown in Figure 1 (b) shows the excellent flexibility of the composite film.

[0036] The TGA curves of the BNQDs / PI composite films in Examples 1-3 are as follows: Figure 2 As shown, the temperature at which the 0.06wt% BNQDs / PI material loses 5wt% is 523°C, while that of PI is 510°C, and the thermal stability of the composite material is significantly improved.

[0037] The dielectric properties of the materials in Examples 1-3 were tested. The dielectric constant and loss of the composite materials varied with frequency. Figure 3 As shown. At the same frequency, the dielectric constant of the composite material increases with the increase of BNQDs content ( Figure 3 (a)). The dielectric constant of 0.06wt% BNQDs / PI film is 2.68, which is 25% higher than that of pure PI. This is due to the interfacial polarization between BNQDs and PI matrix. Figure 3 (b) It can be seen that due to the Coulomb blockade effect of BNQDs and the existence of deep traps, the dielectric loss of the composite material is lower than that of PI and maintained at a low value.

[0038] The materials in Examples 1-3 were tested for their breakdown properties. Figure 4 As shown in the figure, after adding BNQDs, the breakdown performance of the composite material is significantly improved. When the BNQDs content is 0.04wt%, the breakdown strength of the composite material is as high as 614.3kV / mm, which is significantly higher than that of pure PI (392.3kV / mm) by 222kV / mm, indicating that a significant improvement in breakdown strength can be achieved with extremely low BNQDs content.

[0039] The energy storage performance of the polymer composite dielectric materials of Examples 1-3 is as follows: Figure 5 As shown in Figure 2, at room temperature, the energy storage density of 0.04wt% BNQDs / PI at 650kV / mm is as high as 5.38J / cm 3 (η>90%), which is 3.2 times that of pure PI.

[0040] The cycling performance of the polymer composite dielectric material of Example 2 is as follows: Figure 6As shown in the figure, at room temperature, the energy storage density and efficiency of the 0.04wt% BNQDs / PI film did not decrease after 15,000 cycles, while pure PI showed breakdown failure after nearly 7,000 charge and discharge cycles. In contrast, the 0.04wt% BNQDs / PI film has a longer cycle life.

[0041] The thermal conductivity of the materials of Examples 1-3 was tested. The thermal conductivity of 0.04wt% BNQDs / PI was 21.8% higher than that of pure PI ( Figure 7 ).

[0042] Embodiment 4:

[0043] Boron nitride quantum dots / polyvinylidene fluoride (BNQDs / PVDF) composite dielectric materials, wherein the mass fraction of the boron nitride quantum dots is 0.02wt%, 0.04wt%, and 0.06wt%.

[0044] Prepare the BNQDs / PVDF dielectric film as follows:

[0045] S1. Boron nitride nanosheets (BNNS) were ultrasonically dispersed in N,N-dimethylformamide (DMF), then transferred to a hydrothermal autoclave, placed in an oven at 180°C for 12 h, naturally cooled to room temperature, taken out, and filtered using a 0.2 μm filter to obtain a BNQDs dispersion.

[0046] S2. Ultrasonic disperse the BNQDs dispersion in S1 in 6 ml of DMF according to the mass fraction of BNQDs.

[0047] S3. Add 0.5 g of PVDF particles to the dispersion obtained in S2 and stir at 70° C. until completely dissolved.

[0048] S4. Place the composite solution in S3 on a clean glass plate and apply it by scraping with a coating machine.

[0049] S5. The film obtained in S4 is placed in a vacuum drying oven and dried at 80° C. for 2 h to remove the solvent, and then heated to 200° C. for heat treatment for 5 min to obtain a BNQDs / PVDF dielectric film material.

[0050] The dielectric properties of the material in Example 4 were tested, and the dielectric constant of the 0.06wt% BNQDs / PVDF film was 8.9, which is 1.2 times that of pure PVDF.

[0051] According to the test, the breakdown strength of the polymer composite dielectric material of this embodiment is 526 kV / mm, which is 45% higher than that of pure PVDF (363 kV / mm).

[0052] The energy storage performance of the polymer composite dielectric material of this embodiment is tested. At room temperature, the energy storage density of 0.04wt% BNQDs / PVDF at 540kV / mm is as high as 8.7J / cm 3 (η>75%), which is 2.5 times that of pure PVDF.

[0053] Of course, the above embodiments of the present invention are only examples for illustrating the present invention, and are not intended to limit the specific implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above examples. It is impossible to give detailed examples of all implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A low-filling high-energy storage flexible dielectric material, characterized in that: It consists of a polymer matrix and boron nitride quantum dots, wherein the amount of the boron nitride quantum dots is less than 2wt% (preferably, the amount is 0.04wt%).

2. The low-filling high-energy storage flexible dielectric material according to claim 1, characterized in that: The polymer is one or more of thermoplastic polyethylene, polypropylene, polybutylene, polyvinyl alcohol, polymethyl methacrylate, polystyrene, polyetheretherketone, polyvinylidene fluoride and copolymers thereof, and thermosetting polyimide, epoxy resin, polyurethane and polyetherimide.

3. A method for preparing a low-filling, high-energy storage flexible dielectric material as claimed in claim 1 or 2, characterized in that: Here are the steps: S1. In situ generation of boron nitride quantum dots by solvothermal method, ion intercalation method or microwave irradiation method; S2, compounding the polymer monomer or polymer solution or polymer particles with the boron nitride quantum dots, and mixing them evenly by ultrasound or banburying; S3. Prepare the composite film by spin coating, blade coating or molding process.

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