Flexible composite dielectric and method of making and energy storage applications thereof

Abstract

The application provides a flexible composite dielectric and a preparation method and energy storage application thereof, and the preparation method comprises the following steps: weighing polyvinylidene fluoride (PVDF), barium titanate (BTO) and graphene quantum dots (GQDs) and adding them into a beaker; taking N,N-dimethylformamide (DMF) solution and dropping it into the beaker, then placing the beaker on a magnetic stirrer, sealing the beaker with a preservative film, and stirring to obtain a uniform mixed solution; placing polyethylene terephthalate (PET) in a table type film applicator, dropping the mixed solution on the flexible substrate PET for reaction, drying, and obtaining a flexible composite dielectric graphene quantum dots / barium titanate / polyvinylidene fluoride (GQDs / BTO / PVDF) film. In the case that the graphene quantum dot addition amount is only 0.5wt%, the dielectric constant is increased to 460, which is much higher than the current reported results (only about dozens).

Description

Technical Field

[0001] This invention relates to the field of dielectric capacitors, and particularly to a flexible composite dielectric, its preparation method, and its energy storage applications. Background Technology

[0002] Faced with the new global energy landscape and the rapid development of new energy sources, the research and development of energy materials with high energy density, high energy efficiency, and good high-temperature stability is urgently needed. Dielectric capacitors have been widely studied due to their long service life, good temperature stability, and high power density, but their energy density is limited. Flexible composite dielectrics are attracting increasing attention in the new energy field due to their stable dielectric properties, excellent power density, and charge / discharge efficiency. However, due to the mismatch between the polymer matrix and the dielectric ceramic filler interface, it is difficult to simultaneously improve the relative dielectric constant and breakdown strength of dielectric composite materials.

[0003] In the traditional inorganic filler BTO / PVDF system, due to the critical effect of dielectric constant, when the breakdown strength of the dielectric is increased, its relative dielectric constant often decreases. Therefore, there is an urgent need for a method that can simultaneously improve the breakdown strength and dielectric constant, or maintain the breakdown strength and increase the dielectric constant.

[0004] Therefore, based on the researched BaTiO3 / PVDF dielectric composite material system, this invention improves the dielectric constant of the composite dielectric material, as well as the energy storage density and energy storage efficiency, by adding graphene quantum dots (GQDs). The invention studies and prepares a flexible composite dielectric with excellent properties of high dielectric constant and high energy efficiency, which has good application prospects in the field of energy storage devices. Summary of the Invention

[0005] This invention provides a flexible composite dielectric, its preparation method, and its energy storage application, with the aim of solving the aforementioned problems in the background technology.

[0006] To achieve the above objectives, based on the percolation threshold theory—adding conductive fillers (at concentrations below the percolation threshold) to polymer nanocomposites can significantly enhance the relative permittivity of the composite material—the dielectric properties of the flexible composite dielectric were improved by studying the contents of barium titanate (BTO) and graphene quantum dots (GQDs). By controlling the BTO content (0-20 wt%), the results showed that the BTO-10 wt% composition yielded the highest relative permittivity (298.3 at 1 kHz), while the sample with added GQDs-NH2 (0.5 wt%) exhibited the best dielectric properties, reaching a relative permittivity of 2553.3 at 1 kHz and an energy efficiency of 79.04%. Compared with other similar composite dielectric material systems, the composite dielectric GQDs / BaTiO3 / PVDF prepared in this invention exhibits both higher dielectric constant and energy efficiency.

[0007] An embodiment of the present invention provides a method for preparing a flexible composite dielectric, comprising the following steps:

[0008] S1. Weigh the matrix, filler, and dielectric modifier and add them to a beaker;

[0009] S2. Add N,N-dimethylformamide (DMF) solution dropwise into a beaker, place it on a magnetic stirrer, seal the beaker with plastic wrap, and stir to obtain a homogeneous mixed solution;

[0010] S3. Place the polyethylene terephthalate (PET) substrate in a benchtop spin coater, drop the mixed solution onto the PET substrate to react, and dry to obtain a flexible composite dielectric;

[0011] Furthermore, the matrix is ​​polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)), or vinylidene fluoride-trifluoroethylene-chlorofluoroethylene copolymer (P(VDF-CTFE-TrFE)), and the filler is barium titanate (BTO) or Ba. 0.85 Ca 0.15 Zr 0.10 Ti 0.90 O3(BCZT), with graphene quantum dots (GQDs) or carbon quantum dots (CQDs) as dielectric modifiers.

[0012] Furthermore, the matrix is ​​0.5g, the filler is 0-2g, and the dielectric modifier is 0.05g.

[0013] Furthermore, the stirring temperature is 25–60°C, and the stirring speed is 60–120 r / min.

[0014] Furthermore, the spin coating speed is 1000-3000 r / min, and the spin coating time is 1-2 minutes.

[0015] Furthermore, the drying temperature is 60–80°C, and the drying time is 12–24 hours.

[0016] Based on a general inventive concept, the present invention also provides a flexible composite electrolyte obtained by the above preparation method, wherein the flexible composite electrolyte is a thin film of graphene quantum dots / barium titanate / polyvinylidene fluoride (GQDs / BTO / PVDF).

[0017] Furthermore, the flexible composite dielectric has a breakdown field strength of 50–75 kV / mm and an energy storage density of 0.29–1.00 J / cm³. 3 The energy storage efficiency is 79.04%–90.04%.

[0018] Furthermore, the thickness of the flexible composite dielectric is 34.16–94.16 μm.

[0019] The present invention also provides a flexible composite dielectric obtained by the above preparation method or the application of the above flexible composite dielectric in the field of energy storage.

[0020] The above-described solution of the present invention has the following beneficial effects:

[0021] This invention achieves a dielectric constant of 460 with only 0.5 wt% graphene quantum dots, significantly higher than current reported results (only around tens). Graphene quantum dots, as semiconductor materials, exhibit a significant percolation effect after being dispersed and filled into BTO / PVDF, greatly enhancing the polymer's dielectric constant. The dielectric constant is improved based on percolation theory: when conductive fillers are added to the polymer matrix, near the percolation threshold, the free charge at the insulator-conductor interface increases, leading to Maxwell-Wagner-Sillars (MWS) polarization and a significant increase in the dielectric constant. Furthermore, the effective dielectric constant of the percolation system is inversely proportional to the difference between the percolation threshold and the filler content. When the filler content approaches the percolation threshold, the corresponding composite dielectric material will possess an extremely high dielectric constant. However, when the filler content exceeds the percolation threshold, the composite material will transform from an insulator to a conductor. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The dielectric constant of the sample containing only PVDF in the embodiments of the present invention is the theoretical simulation result (pure PVDF).

[0024] Figure 2 The dielectric constant of the sample containing only BTO in the embodiments of the present invention (10wt% BTO / PVDF) is the theoretical simulation result.

[0025] Figure 3 The theoretical simulation results of the dielectric constant of the sample with added BTO and GQDs in this embodiment of the invention (9.5wt% BTO - 0.05wt% GQDs / PVDF). Detailed Implementation

[0026] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0027] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Flexible composite dielectrics are gaining increasing attention in the new energy field due to their stable dielectric properties, excellent power density, and charge / discharge efficiency. However, due to the mismatch between the polymer matrix and the dielectric ceramic filler interface, it is difficult to simultaneously improve the relative permittivity and breakdown strength of dielectric composite materials. In the traditional inorganic filler BTO / PVDF system, because of the critical effect of the dielectric constant, increasing the breakdown strength of the dielectric often leads to a decrease in its relative permittivity. Therefore, there is an urgent need for a method that can simultaneously improve the breakdown strength and dielectric constant, or maintain the breakdown strength while increasing the dielectric constant.

[0030] To address the existing problems, embodiments of the present invention provide a method for preparing a flexible composite dielectric, comprising the following steps:

[0031] S1. Weigh the matrix, filler, and dielectric modifier and add them to a beaker;

[0032] S2. Add N,N-dimethylformamide (DMF) solution dropwise into a beaker, place it on a magnetic stirrer, seal the beaker with plastic wrap, and stir to obtain a homogeneous mixed solution;

[0033] S3. Place the polyethylene terephthalate (PET) substrate in a benchtop spin coater, add the mixed solution dropwise onto the PET substrate to react, and dry to obtain a flexible composite dielectric;

[0034] Furthermore, the matrix is ​​polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)), or vinylidene fluoride-trifluoroethylene-chlorofluoroethylene copolymer (P(VDF-CTFE-TrFE)), and the filler is barium titanate (BTO) or Ba. 0.85 Ca 0.15 Zr 0.10 Ti 0.90 O3(BCZT), with graphene quantum dots (GQDs) or carbon quantum dots (CQDs) as dielectric modifiers.

[0035] Furthermore, the matrix is ​​0.5g, the filler is 0-2g, and the dielectric modifier is 0.05g.

[0036] Furthermore, the stirring temperature is 25–60°C, and the stirring rate is 60–120 r / min.

[0037] Furthermore, the spin coating speed is 1000-3000 r / min, and the spin coating time is 1-2 minutes.

[0038] Furthermore, the drying temperature is 60–80°C, and the drying time is 12–24 hours.

[0039] Based on a general inventive concept, the present invention also provides a flexible composite electrolyte obtained by the above preparation method, wherein the flexible composite electrolyte is a thin film of graphene quantum dots / barium titanate / polyvinylidene fluoride (GQDs / BTO / PVDF).

[0040] Furthermore, the flexible composite dielectric has a breakdown field strength of 50–75 kV / mm and an energy storage density of 0.29–1.00 J / cm³. 3 The energy storage efficiency is 79.04%–90.04%.

[0041] Furthermore, the thickness of the flexible composite dielectric is 34.16–94.16 μm.

[0042] The present invention also provides a flexible composite dielectric obtained by the above preparation method or the application of the above flexible composite dielectric in the field of energy storage.

[0043] In this embodiment, a flexible PET conductive substrate is used as the base.

[0044] Example

[0045] A method for preparing a flexible composite dielectric includes the following steps:

[0046] S1. Weigh out the corresponding masses (see Table 1 for specific ratios) of polyvinylidene fluoride (PVDF), barium titanate (BTO), and graphene quantum dots (GQDs) using an electronic balance and add them to a beaker;

[0047] S2. Use a dropper to draw N,N-dimethylformamide (DMF) solution and add it to a beaker. Note that when the specified mass is almost reached, the dropping frequency should be slowed down. Then place the beaker on a magnetic stirrer, seal the mouth of the beaker with plastic wrap, and set the heating temperature and stirring frequency to stir and obtain a uniform mixed solution.

[0048] S3. Place the polyethylene terephthalate (PET) substrate in a benchtop spin coater, set the spin speed and spin coat time, drop the mixed solution onto the PET substrate to react, and then place it in an oven at 60°C for 24 hours to obtain a flexible composite dielectric graphene quantum dot / barium titanate / polyvinylidene fluoride (GQDs / BTO / PVDF) film.

[0049] Table 1

[0050]

[0051] Table 2 E of Example 1 and Comparative Example 2 b U e Performance Comparison Analysis with η

[0052]

[0053] As shown in Table 2, the dielectric constant of the sample with added GQDs increased from 11 (comparative example 1 containing only PVDF) and 556 (comparative example 2 containing PVDF and BTO) to 1306 (example 1 containing PVDF, BTO and GQDs) at 100Hz.

[0054] Due to the high power density of the flexible composite dielectric, the flexible composite dielectric obtained in the above embodiments can be applied to pulse power devices, hybrid power systems, laser electromagnetic guns, and the stored energy can be used for electrocaloric effect refrigeration, replacing the traditional air compression refrigeration mode.

[0055] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A flexible composite dielectric for dielectric energy storage, characterized in that, Its preparation method includes the following steps: S1. Weigh 0.5g of polyvinylidene fluoride, 0.95g of barium titanate, and 0.05g of graphene quantum dots and add them to a beaker; S2. Add N,N-dimethylformamide solution dropwise into a beaker, place it on a magnetic stirrer, seal the beaker with plastic wrap, and stir at 25~60℃ and 60~120r / min to obtain a homogeneous mixed solution; S3. Place the polyethylene terephthalate substrate in a benchtop spin coater, drop the mixed solution onto the PET substrate and spin coat it at a speed of 1000~3000 r / min for 1-2 minutes, then dry it at 60~80℃ for 12~24 h to obtain a flexible composite dielectric. The flexible composite dielectric is a thin film of graphene quantum dots / barium titanate / polyvinylidene fluoride; The breakdown field strength of the composite dielectric is 75 kV / mm, the energy storage density is 0.2851 J / cm3, and the energy storage efficiency is 79.04%.

2. The flexible composite dielectric according to claim 1, characterized in that, The thickness of the flexible composite dielectric is 94.16 μm.

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