An asymmetric sandwich structure PVDF-based composite film and a preparation method thereof

Abstract

The application provides an asymmetric sandwich structure PVDF-based composite film and a preparation method thereof, the composite film comprises a BT / PVDF composite layer, a P(VDF-HFP) polymer layer and a BN / PVDF composite layer connected in sequence, the BT / PVDF composite layer is a polyvinylidene fluoride-based composite layer doped with barium titanate nanoparticles, and the BN / PVDF composite layer is a polyvinylidene fluoride-based composite layer doped with two-dimensional boron nitride nanosheets. Through macroscopic design of the laminated structure of the composite film, the application realizes a substantial increase of the breakdown field and the energy storage density of the composite film, and effectively overcomes the defects of low breakdown strength, low effective energy storage density and poor energy storage efficiency of most existing materials due to the interface effect.

Description

Technical Field

[0001] This invention belongs to the field of polymer energy storage, specifically an asymmetric sandwich structure PVDF-based high energy density composite thin film material and its preparation method. Background Technology

[0002] With the rapid development of modern science and technology, energy and environmental issues are becoming increasingly prominent, and energy storage technology will play an important role in social transformation. Dielectric capacitors, with their long lifespan, good stability, and significantly higher power density and breakdown field strength compared to any other energy storage device, have attracted widespread attention in the field of advanced energy storage materials. Currently, mainstream commercial dielectric capacitors, such as biaxially oriented polypropylene film (BOPP), have low energy density (~2 J-cm). -3 This significantly limits the miniaturization of devices and their application in pulsed applications. For example, in the inverter system of hybrid electric vehicles, dielectric capacitors account for more than 30% of the volume. In other words, for every doubling of the energy density of a dielectric capacitor, its volume can be halved. Therefore, developing new materials with ultra-high energy density to replace BOPP is a current hot research direction.

[0003] Traditional polymer dielectric materials such as polyimide (PI), polyvinylidene fluoride (PVDF), and epoxy resin have advantages such as small size and ease of processing, but their low dielectric constant makes them difficult to meet practical application requirements. To further improve the energy density of polymer materials, nano-ceramic particles with high dielectric constants have been selected as fillers and added to the polymer matrix, thus forming ceramic / polymer composites. On the one hand, selecting ceramics with high dielectric constants as fillers can effectively improve the dielectric constant of the composite material; on the other hand, the polymer matrix retains its high breakdown field strength, thereby achieving a significant increase in energy storage density. Currently, the ceramic fillers commonly used in the preparation of PVDF-based composites mainly include barium titanate (BaTiO3, BT), titanium dioxide (TiO2), and lead zirconate titanate (PbZrTiO3). However, with the development of ceramic / polymer energy storage composites, researchers have found that although the addition of ceramics can effectively improve the dielectric constant of the polymer, it also reduces its breakdown field strength and introduces higher leakage conductivity. Therefore, the method of simply blending ceramics with polymers to prepare composites can no longer meet the demand for higher energy storage densities. Therefore, researchers have attempted to introduce layered structure design into the preparation of ceramic / polymer composites, adding ceramic nanoparticles to the top and bottom layers to increase the dielectric constant, while the middle layer is a pure polymer layer to maintain a high breakdown electric field. This layered structure can effectively combine the advantages of each layer, achieving both high dielectric constant and high breakdown field strength. Furthermore, by controlling the thickness relationship between the three layers, the energy storage density can be significantly improved. Thus, the design of the micro / macro structure of materials by introducing inorganic ceramic fillers to enhance polymer energy storage density has attracted considerable attention.

[0004] Most current technologies for fabricating sandwich-structured composite films employ a paired structure, where the outer layer is a composite layer doped with ceramic filler, and the middle layer is a pure polymer layer with high breakdown strength, or vice versa. This method primarily achieves high energy density by increasing the dielectric constant of the composite film. However, this structure suffers from severe interface effects, numerous defects, limited improvement in material breakdown strength, and energy storage efficiency far from meeting application requirements. For example, using sodium niobate (NN) nanosheets as a ceramic filler incorporated into polyvinylidene fluoride (PVDF) polymer to form a composite film, with this composite film layer as the outer layer and the pure PVDF layer as the middle layer, results in a breakdown electric field strength of 400 MV·m. -1 The energy storage density is 13.5 J·cm³. -3 The energy storage efficiency is 66.9%. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects in the prior art and provide an asymmetric sandwich structure PVDF-based composite film and its preparation method. This asymmetric sandwich structure composite film has an ultra-high breakdown electric field and an ultra-high energy density.

[0006] This invention is achieved through the following technical solution: An asymmetric sandwich structure PVDF-based composite film, comprising a BT / PVDF composite layer, a P(VDF-HFP) polymer layer and a BN / PVDF composite layer connected in sequence, wherein the BT / PVDF composite layer is a polyvinylidene fluoride composite layer doped with barium titanate nanoparticles, and the BN / PVDF composite layer is a polyvinylidene fluoride composite layer doped with two-dimensional boron nitride nanosheets.

[0007] Preferably, the volume fraction of the two-dimensional boron nitride nanosheets in the BN / PVDF composite layer is 1% to 7%.

[0008] Preferably, the energy storage density of the composite film is between 17.31 and 22.72 J·cm at room temperature. -3 between.

[0009] The method for preparing the asymmetric sandwich structure PVDF-based composite thin film includes the following steps: Two-dimensional boron nitride nanosheets and polymer PVDF powder were dispersed in DMF to obtain suspension C. The obtained suspension C was then cast onto a substrate to form a BN / PVDF composite layer. P(VDF-HFP) powder was dispersed in DMF to obtain solution B. The obtained solution B was then cast onto the BN / PVDF composite layer to form a P(VDF-HFP) polymer layer by a casting method. BaTiO3 nanoparticles and polymer PVDF powder were dispersed in DMF to obtain suspension A. The obtained suspension A was then cast onto a P(VDF-HFP) polymer layer to form a BT / PVDF composite layer.

[0010] Preferably, the preparation method of the two-dimensional boron nitride nanosheets includes: adding hexagonal boron nitride powder to an isopropanol solution, sonicating for 1-2 h, stirring for 30-60 min, and repeating 3-5 times; and then stirring the resulting suspension at 3000-4000 r·min. -1 Centrifuge for 6-15 min, filter the supernatant, and dry the precipitate to obtain two-dimensional boron nitride nanosheets.

[0011] Preferably, two-dimensional boron nitride nanosheets and polymer PVDF powder are dispersed in DMF. Specifically, two-dimensional boron nitride nanosheets are added to DMF, and the mixture is stirred and sonicated alternately several times. Then, polymer PVDF powder is added, and the mixture is stirred and sonicated alternately several times to obtain suspension C.

[0012] Preferably, BaTiO3 nanoparticles and polymer PVDF powder are dispersed in DMF. Specifically, BaTiO3 nanoparticles are added to DMF, and the mixture is stirred and sonicated alternately several times. Then, polymer PVDF powder is added, and the mixture is stirred and sonicated alternately several times to obtain suspension A.

[0013] Preferably, during casting, the casting machine temperature is set to 185~195 ℃ and the scraper height is 8~15 μm.

[0014] Preferably, after casting to form a BT / PVDF composite layer, a preliminary sample of an asymmetric sandwich structure composite film is obtained. The preliminary sample of the asymmetric sandwich structure composite film is heated and held at 195~205 ℃ for 5-10 min and then quenched in ice water to obtain the asymmetric sandwich structure composite film.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention relates to an asymmetric sandwich structure PVDF-based composite thin film comprising three layers: a first layer is a dielectric guiding layer doped with barium titanate (BaTiO3) nanoparticles; a second layer is a breakdown buffer layer composed of P(VDF-HFP); and a third layer is a breakdown cutoff layer doped with two-dimensional boron nitride (BN) nanosheets. The first layer contains ultra-high dielectric constant BaTiO3 nanoparticles, which can concentrate and guide the growth of the breakdown tree; the second layer is a pure polymer layer used to dissipate the energy of the breakdown tree; and the third layer contains ultra-high insulating two-dimensional BN nanosheets, which can cut off the breakdown tree. Through macroscopic design of the composite thin film stack structure, a significant improvement in the breakdown electric field and energy storage density is achieved, effectively overcoming the shortcomings of most existing materials, such as low breakdown strength, low effective energy storage density, and poor energy storage efficiency due to interface effects. It can be rapidly charged and discharged and exhibits excellent cycle stability. The composite thin film of this invention has excellent energy storage characteristics, with a breakdown electric field as high as 720 MV·m at room temperature. -1 The optimal effective energy storage density can reach 22.7 J·cm³. -3 The energy storage efficiency at this point is 77.84%, which is expected to replace commercially available biaxially oriented polypropylene film materials to meet the application needs of extreme high-pressure fields such as laser pulse weapons.

[0016] The present invention uses a multiple solution casting method to prepare the composite film, which is simple in preparation process.

[0017] Furthermore, the preparation method of the two-dimensional boron nitride nanosheets of the present invention is simple to operate, low in cost, and does not easily generate impurities. It is a simple and rapid laboratory method for preparing pure phase BN nanosheets.

[0018] Furthermore, this invention involves quenching the product. Since the Curie temperature of PVDF is around 140 degrees Celsius, quenching increases the content of the polar phase (β phase) inside the PVDF, thereby improving the polarization intensity of the composite film and thus increasing its energy density. Secondly, quenching increases the density of the composite film and reduces defects (such as pores), further increasing its breakdown field strength and thus its energy density. Without quenching, the content of the polar phase inside the composite film will be low, leading to low polarization intensity. Simultaneously, the internal solvent and pores may not be completely removed, resulting in defects within the composite film and a low breakdown field strength. This would cause the energy density of the composite film to be lower than that of the quenched sample. Attached Figure Description

[0019] Figure 1 XRD pattern of nano-BaTiO3 powder; Figure 2 XRD pattern of two-dimensional BN nanosheets; Figure 3SEM image of nano-BaTiO3 powder; Figure 4 SEM image of two-dimensional BN nanosheets; Figure 5 The dielectric spectrum of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 1; Figure 6 Hysteresis loop of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 1 (test frequency: 10 Hz). Figure 7 The dielectric spectrum of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 2; Figure 8 Hysteresis loop of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 2 (test frequency: 10 Hz). Figure 9 The dielectric spectrum of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 3; Figure 10 Hysteresis loop of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 3 (test frequency: 10 Hz). Figure 11 The dielectric spectrum of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 4; Figure 12 Hysteresis loop of the asymmetric sandwich structure PVDF-based high energy density composite thin film material prepared in Example 4 (test frequency: 10 Hz). Detailed Implementation

[0020] To further understand the present invention, the present invention will be described below with reference to embodiments. These descriptions are only for further explaining the features and advantages of the present invention and are not intended to limit the claims of the present invention.

[0021] This invention relates to an asymmetric sandwich structure PVDF-based high energy density composite thin film, comprising a first layer, a second layer, and a third layer connected in sequence. The first layer is a dielectric guiding layer doped with barium titanate nanoparticles, i.e., a BT / PVDF composite layer. The second layer is a breakdown buffer layer composed of P(VDF-HFP), i.e., a P(VDF-HFP) polymer layer. The third layer is a breakdown stop layer doped with two-dimensional boron nitride nanosheets, i.e., a BN / PVDF composite layer. The volume fraction of the two-dimensional BN nanosheets in the third layer is 1% to 7%.

[0022] The BT / PVDF composite layer is prepared by dispersing BaTiO3 nanoparticles and polymer PVDF powder in DMF solvent via a casting method; the P(VDF-HFP) polymer layer is prepared by dispersing P(VDF-HFP) powder in DMF solvent via a casting method; and the BN / PVDF composite layer is prepared by dispersing two-dimensional boron nitride nanosheets with different contents and polymer PVDF powder in DMF solvent via a casting method. This asymmetric sandwich structure high energy density composite thin film material exhibits an energy density of 17.31–22.72 J·cm⁻¹ at room temperature. -3 between.

[0023] The method for preparing the asymmetric sandwich structure PVDF-based high energy density composite thin film of the present invention includes the following steps: (1) Add hexagonal boron nitride powder (purity >99.8%) to a 50 vol% isopropanol solution, sonicate for 1-2 h, then stir for 30-60 min, repeat 3-5 times to obtain a BN suspension. Further, heat the suspension at 3000-4000 r·min -1 Centrifuge for 6-15 min, filter the supernatant, and collect two-dimensional BN nanosheets by drying, for example, incubating at 80 ℃ for 12-18 h. (2) Add BaTiO3 nanoparticles to DMF solvent, stir at 60 °C for 2 h, sonicate for 30 min, repeat 6-9 times to obtain a uniformly dispersed and stable suspension. Add PVDF solid powder to the uniform suspension at a certain volume ratio, stir at 60 °C for 2 h, sonicate for 30 min, repeat 6-9 times to obtain a uniform suspension A of BaTiO3 / PVDF DMF blend. Separately, disperse P(VDF-HFP) powder in DMF solvent, dissolve by magnetic stirring at 60 °C for 12-18 h to obtain a pure polymer DMF solution B of P(VDF-HFP). Add the two-dimensional BN nanosheets obtained in step (1) to DMF solvent, stir at 60 °C for 2 h, and rotate at 450-600 r·min. -1 The mixture was sonicated for 30 minutes, alternating between sonication and so on, for a total of 6-9 times to obtain a uniformly dispersed and stable suspension. PVDF solid powder was then added to the uniform suspension at a certain volume ratio, and the mixture was stirred at 60 °C for 2 hours at a speed of 450-600 r·min. -1 The mixture of two-dimensional BN nanosheets and PVDF was sonicated for 30 min, and repeated 6-9 times to obtain a uniform suspension C of DMF blended with BN nanosheets and PVDF. (3) Set the casting machine temperature to 185~195 ℃, adjust the height of the scraper to 8 μm, cast the suspension C obtained in step (2) once, vacuum dry at 80 ℃ for 30 min to form a film, then adjust the height of the scraper to 11 μm, cast the solution B obtained in step (2) on the glass plate of the first film formation a second time, vacuum dry at 80 ℃ for 30 min to form a film, then adjust the height of the scraper to 15 μm, cast the suspension A obtained in step (2) on the glass plate of the second film formation a third time, vacuum dry at 80 ℃ for 30 min to form a film, and finally, vacuum dry the sandwich structure composite film obtained at 60 ℃ for 12~18 h to obtain a preliminary sample; (4) The preliminary sample of the prepared asymmetric sandwich structure composite film was heated at 195~205 °C for 5-10 min and then immediately placed in ice water for quenching to obtain a dense asymmetric sandwich structure composite film.

[0024] X-ray diffraction (XRD) was performed on BaTiO3 nanoparticles; XRD was performed on two-dimensional BN nanosheets; SEM was performed on BaTiO3 nanoparticles; SEM was performed on two-dimensional BN nanosheets.

[0025] The prepared sample was cut into a 10 mm × 15 mm rectangle to form a diffracted film, and a gold electrode with a diameter of 6 mm was deposited on it. Then, its dielectric properties were tested at room temperature.

[0026] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a gold electrode with a diameter of 2 mm was deposited on it. Then, its ferroelectric properties were tested at 10 Hz at room temperature, and its energy storage characteristics were calculated, including the energy storage density. W 1) and energy loss density ( W The calculation formula for 2) is: (2) (3) in W 1 and W 2 represents energy storage density and energy loss density, respectively. P max Indicates the maximum polarization intensity. P r Indicates the remanent polarization intensity. E Indicates electric field strength. P This indicates the polarization intensity.

[0027] The following examples provide a clearer understanding of the invention, but are not intended to limit the scope of the invention.

[0028] Example 1: This embodiment prepares a set of asymmetric sandwich-structured PVDF-based high-energy-density composite films using a solution layer-by-layer casting process. The composite films can be simplified to the BPBNX model, where B represents the first layer (BT / PVDF composite layer), P represents the second layer (P(VDF-HFP) pure polymer layer), and BNX represents the third layer (BN / PVDF composite layer), where X represents the volume fraction of two-dimensional BN nanosheets in the third layer. In this example, the asymmetric sandwich-structured composite film can be simplified to the BPBN1 model, where the first layer is a BT / PVDF composite layer with a 1% volume fraction of BT nanoparticles, the second layer is a P(VDF-HFP) pure polymer layer, and the third layer is a BN / PVDF composite layer with a 1% volume fraction of two-dimensional BN nanosheets.

[0029] The above-mentioned method for preparing PVDF high energy density composite thin film materials with asymmetric sandwich structure includes the following steps: (1) Add 1 g of hexagonal boron nitride powder to 100 ml of 50 vol% isopropanol solution, sonicate for 2 h, then stir for 60 min, repeat 3 times to obtain a BN suspension. Further, heat the suspension at 3600 r·min -1 Centrifuge for 10 min, filter the supernatant, and collect the two-dimensional BN nanosheets by drying.

[0030] (2) Take 0.041 g of BaTiO3 nanoparticles and add them to 10 ml of DMF solvent. Stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniform suspension A of BaTiO3 / PVDF DMF blend. Separately, take 1 g of P(VDF-HFP) powder and disperse it in 10 ml of DMF solvent. Dissolve it by magnetic stirring at 60 ℃ for 12 h to obtain a pure polymer DMF solution B of P(VDF-HFP). Take 0.015 g of the two-dimensional BN nanosheets obtained in step (1), add them to 10 ml of DMF solvent, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. The process was repeated 6 times, alternating between the two-dimensional BN nanosheets and PVDF in DMF to obtain a uniform suspension C.

[0031] (3) Set the casting machine temperature to 190 ℃, adjust the height of the scraper to 8 μm, cast the suspension C obtained in step (2) once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 11 μm, cast the solution B obtained in step (2) on the glass plate that formed the film once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 15 μm, cast the suspension A obtained in step (2) on the glass plate that formed the film twice, and vacuum dry it at 80 ℃ for 30 min to form a film. Finally, vacuum dry the sandwich structure composite film obtained at 60 ℃ for 18 h to obtain a preliminary sample.

[0032] (4) The prepared sandwich structure composite film preliminary sample was heated at 200 °C for 8 min and then immediately placed in ice water for quenching to obtain dense asymmetric sandwich structure composite film BPBN1.

[0033] X-ray diffraction tests were performed on the BaTiO3 nanoparticles, and the results are as follows: Figure 1 As shown. By Figure 1 The XRD pattern shows that the BaTiO3 nanoceramic powder used in this embodiment has a pure perovskite structure.

[0034] X-ray diffraction tests were performed on the two-dimensional BN nanosheets, and the results are as follows: Figure 2 As shown. By Figure 2 The XRD pattern shows that the two-dimensional BN nanosheets prepared in this embodiment have a hexagonal structure.

[0035] SEM analysis of BaTiO3 nanoparticles yielded the following results: Figure 3 As shown. By Figure 3 The SEM images show that the BaTiO3 nanoceramic powder used in this embodiment consists of uniformly sized nanospheres with a particle size of approximately 100 nm.

[0036] The two-dimensional BN nanosheets were subjected to SEM testing, and the results are as follows: Figure 4 As shown. By Figure 4 The SEM images show that the two-dimensional BN nanosheets prepared in this embodiment are smooth nanosheets with a diameter of about 300 nm and a thickness of about 20 nm.

[0037] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 6 mm diameter gold electrode was deposited on it. The dielectric properties were then tested at room temperature, and the results are as follows: Figure 5 As shown, the dielectric constant of the composite film prepared in this embodiment gradually decreases while the dielectric loss gradually increases with increasing frequency. When the frequency is 10 kHz, the dielectric constant of the composite film prepared in this embodiment is 11.935 and the dielectric loss is 0.045.

[0038] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 2 mm diameter gold electrode was deposited on it. Its ferroelectric properties were then tested at 10 Hz at room temperature, and its energy storage characteristics were calculated. Figure 6 The figure shows the hysteresis loop of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment, measured at room temperature. Based on the hysteresis loop, the energy storage characteristics can be calculated, and the effective energy storage density of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment is at an electric field strength of 620 MV·m. -1 The peak efficiency reached 19.42 J·cm -3 Table 1 shows the energy storage characteristics of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment at room temperature.

[0039] Example 2: This embodiment prepares a set of asymmetric sandwich-structured PVDF high-energy-density composite thin film materials using a solution layer-by-layer casting process. The composite thin film can be simplified to a BPBNX model, where B represents the first layer of BT / PVDF composite layer, P represents the second layer of P(VDF-HFP) pure polymer layer, and BNX represents the third layer of BN / PVDF composite layer, where X represents the volume fraction of two-dimensional BN nanosheets in the third layer. In this example, the asymmetric sandwich-structured composite thin film can be simplified to a BPBN3 model, where the first layer is a BT / PVDF composite layer with a 1% volume fraction of BT nanoparticles, the second layer is a P(VDF-HFP) pure polymer layer, and the third layer is a BN / PVDF composite layer with a 3% volume fraction of two-dimensional BN nanosheets.

[0040] The above-mentioned method for preparing PVDF high energy density composite thin film materials with asymmetric sandwich structure includes the following steps: (1) Add 1 g of hexagonal boron nitride powder to 100 ml of 50 vol% isopropanol solution, sonicate for 2 h, then stir for 60 min, repeat 3 times to obtain a BN suspension. Further, heat the suspension at 3600 r·min -1 Centrifuge for 10 min, filter the supernatant, and collect the two-dimensional BN nanosheets by drying.

[0041] (2) Take 0.041 g of BaTiO3 nanoparticles and add them to 10 ml of DMF solvent. Stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniform suspension A of BaTiO3 / PVDF DMF blend. Separately, take 1 g of P(VDF-HFP) powder and disperse it in 10 ml of DMF solvent. Dissolve it by magnetic stirring at 60 ℃ for 12 h to obtain a pure polymer DMF solution B of P(VDF-HFP). Take 0.046 g of the two-dimensional BN nanosheets obtained in step (1), add them to 10 ml of DMF solvent, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. The process was repeated 6 times, alternating between the two-dimensional BN nanosheets and PVDF in DMF to obtain a uniform suspension C.

[0042] (3) Set the casting machine temperature to 190 ℃, adjust the height of the scraper to 8 μm, cast the solution C obtained in step (2) once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 11 μm, cast the solution B obtained in step (2) on the glass plate that formed the film once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 15 μm, cast the suspension A obtained in step (2) on the glass plate that formed the film twice, and vacuum dry it at 80 ℃ for 30 min to form a film. Finally, vacuum dry the sandwich structure composite film obtained at 60 ℃ for 18 h to obtain a preliminary sample.

[0043] (4) The prepared sandwich structure composite film preliminary sample was heated at 200 °C for 8 min and then immediately placed in ice water for quenching to obtain dense asymmetric sandwich structure composite film BPBN1.

[0044] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 6 mm diameter gold electrode was deposited. Dielectric properties were then tested at room temperature. Figure 7 As shown, the dielectric constant of the composite film prepared in this embodiment gradually decreases while the dielectric loss gradually increases with increasing frequency. When the frequency is 10 kHz, the dielectric constant of the composite film prepared in this embodiment is 10.939 and the dielectric loss is 0.037.

[0045] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 2 mm diameter gold electrode was deposited on it. Its ferroelectric properties were then tested at 10 Hz at room temperature, and its energy storage characteristics were calculated. Figure 8 The figure shows the hysteresis loop of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment, measured at room temperature. Based on the hysteresis loop, the energy storage characteristics can be calculated, and the effective energy storage density of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment is at an electric field strength of 660 MV·m. -1 Up to 20.88 J·cm -3 Table 1 shows the energy storage characteristics of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment at room temperature.

[0046] Example 3: This embodiment prepares a set of asymmetric sandwich-structured PVDF high-energy-density composite thin film materials using a solution layer-by-layer casting process. The composite thin film can be simplified to a BPBNX model, where B represents the first layer of BT / PVDF composite layer, P represents the second layer of P(VDF-HFP) pure polymer layer, and BNX represents the third layer of BN / PVDF composite layer, where X represents the volume fraction of two-dimensional BN nanosheets in the third layer. In this example, the asymmetric sandwich-structured composite thin film can be simplified to a BPBN5 model, where the first layer is a BT / PVDF composite layer with a 1% volume fraction of BT nanoparticles, the second layer is a P(VDF-HFP) pure polymer layer, and the third layer is a BN / PVDF composite layer with a 5% volume fraction of two-dimensional BN nanosheets.

[0047] The above-mentioned method for preparing PVDF high energy density composite thin film materials with asymmetric sandwich structure includes the following steps: (1) Add 1 g of hexagonal boron nitride (BN) powder to 100 ml of 50 vol% isopropanol solution, sonicate for 2 h, then stir for 60 min, repeat 3 times to obtain a BN suspension. Further, heat the suspension at 3600 r·min -1 Centrifuge for 10 min, filter the supernatant, and collect the two-dimensional BN nanosheets by drying.

[0048] (2) Take 0.041 g of BaTiO3 nanoparticles and add them to 10 ml of DMF solvent. Stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniform suspension A of BaTiO3 / PVDF DMF blend. Separately, take 1 g of P(VDF-HFP) powder and disperse it in 10 ml of DMF solvent. Dissolve it by magnetic stirring at 60 ℃ for 12 h to obtain a pure polymer DMF solution B of P(VDF-HFP). Take 0.077 g of the two-dimensional BN nanosheets obtained in step (1), add them to 10 ml of DMF solvent, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. The process was repeated 6 times, alternating between the two-dimensional BN nanosheets and PVDF in DMF to obtain a uniform suspension C.

[0049] (3) Set the casting machine temperature to 190 ℃, adjust the height of the scraper to 8 μm, cast the suspension C obtained in step (2) once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 11 μm, cast the solution B obtained in step (2) on the glass plate that formed the film once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 15 μm, cast the suspension A obtained in step (2) on the glass plate that formed the film twice, and vacuum dry it at 80 ℃ for 30 min to form a film. Finally, vacuum dry the sandwich structure composite film obtained at 60 ℃ for 18 h to obtain a preliminary sample.

[0050] (4) The prepared sandwich structure composite film preliminary sample was heated at 200 °C for 8 min and then immediately placed in ice water for quenching to obtain dense asymmetric sandwich structure composite film BPBN5.

[0051] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 6 mm diameter gold electrode was deposited. Dielectric properties were then tested at room temperature. Figure 9 As shown, the dielectric constant of the composite film prepared in this embodiment gradually decreases while the dielectric loss gradually increases with increasing frequency. When the frequency is 10 kHz, the dielectric constant of the composite film prepared in this embodiment is 8.801 and the dielectric loss is 0.022.

[0052] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 2 mm diameter gold electrode was deposited on it. Its ferroelectric properties were then tested at 10 Hz at room temperature, and its energy storage characteristics were calculated. Figure 10 The figure shows the hysteresis loop of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment, measured at room temperature. Based on the hysteresis loop, the energy storage characteristics can be calculated, and the effective energy storage density of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment is at an electric field strength of 720 MV·m. -1 Up to 22.72 J·cm -3 Table 1 shows the energy storage characteristics of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment at room temperature.

[0053] Example 4: This embodiment prepares a set of asymmetric sandwich-structured PVDF high-energy-density composite thin film materials using a solution layer-by-layer casting process. The composite thin film can be simplified to the BPBNX model, where B represents the first layer of BT / PVDF composite layer, P represents the second layer of P(VDF-HFP) pure polymer layer, and BNX represents the third layer of BN / PVDF composite layer, where X represents the volume fraction of two-dimensional BN nanosheets in the third layer. In this example, the asymmetric sandwich-structured composite thin film can be simplified to the BPBN7 model, where the first layer is a BT / PVDF composite layer with a 1% volume fraction of BT nanoparticles, the second layer is a P(VDF-HFP) pure polymer layer, and the third layer is a BN / PVDF composite layer with a 7% volume fraction of two-dimensional BN nanosheets.

[0054] The above-mentioned method for preparing PVDF high energy density composite thin film materials with asymmetric sandwich structure includes the following steps: (1) Add 1 g of hexagonal boron nitride powder to 100 ml of 50 vol% isopropanol solution, sonicate for 2 h, then stir for 60 min, repeat 3 times to obtain a BN suspension. Further, heat the suspension at 3600 r·min -1 Centrifuge for 10 min, filter the supernatant, and collect the two-dimensional BN nanosheets by drying.

[0055] (2) Take 0.041 g of BaTiO3 nanoparticles and add them to 10 ml of DMF solvent. Stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniform suspension A of BaTiO3 / PVDF DMF blend. Separately, take 1 g of P(VDF-HFP) powder and disperse it in 10 ml of DMF solvent. Dissolve it by magnetic stirring at 60 ℃ for 12 h to obtain a pure polymer DMF solution B of P(VDF-HFP). Take 0.108 g of the two-dimensional BN nanosheets obtained in step (1), add them to 10 ml of DMF solvent, stir at 60 ℃ for 2 h and sonicate for 30 min. Repeat this process 6 times to obtain a uniformly dispersed and stable suspension. Add 1 g of PVDF solid powder to the uniform suspension, stir at 60 ℃ for 2 h and sonicate for 30 min. The process was repeated 6 times, alternating between the two-dimensional BN nanosheets and PVDF in DMF to obtain a uniform suspension C.

[0056] (3) Set the casting machine temperature to 190 ℃, adjust the height of the scraper to 8 μm, cast the suspension C obtained in step (2) once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 11 μm, cast the solution B obtained in step (2) on the glass plate that formed the film once, and vacuum dry it at 80 ℃ for 30 min to form a film. Then, adjust the height of the scraper to 15 μm, cast the suspension A obtained in step (2) on the glass plate that formed the film twice, and vacuum dry it at 80 ℃ for 30 min to form a film. Finally, vacuum dry the sandwich structure composite film obtained at 60 ℃ for 18 h to obtain a preliminary sample.

[0057] (4) The prepared sandwich structure composite film preliminary sample was heated at 200 °C for 8 min and then immediately placed in ice water for quenching to obtain dense asymmetric sandwich structure composite film BPBN7.

[0058] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 6 mm diameter gold electrode was deposited. Dielectric properties were then tested at room temperature. Figure 11 As shown, the dielectric constant of the composite film prepared in this embodiment gradually decreases while the dielectric loss gradually increases with increasing frequency. When the frequency is 10 kHz, the dielectric constant of the composite film prepared in this embodiment is 7.254 and the dielectric loss is 0.038.

[0059] The prepared sample was cut into 10 mm × 15 mm rectangles to form a diffracted film, and a 2 mm diameter gold electrode was deposited on it. Its ferroelectric properties were then tested at 10 Hz at room temperature, and its energy storage characteristics were calculated. Figure 12 The figure shows the hysteresis loop of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment, measured at room temperature. Based on the hysteresis loop, the energy storage characteristics can be calculated, and the effective energy storage density of the asymmetric sandwich-structured PVDF high energy density composite thin film material prepared in this embodiment is at an electric field strength of 660 MV·m. -1 The temperature reached as high as 17.31 J·cm. -3 Table 1 shows the energy storage characteristics of the asymmetric sandwich structure PVDF high energy density composite thin film material prepared in this embodiment at room temperature.

[0060] Table 1. Energy storage characteristics of PVDF-based high energy density composite thin film materials with asymmetric sandwich structure at room temperature in the examples.

[0061] Table 1 shows that when the volume fraction of two-dimensional BN nanosheets in the third layer is 5%, the PVDF-based high energy density composite thin film material with this asymmetric sandwich structure achieves the best overall energy storage characteristics. The breakdown electric field strength reaches 720 MV·m. -1 The highest effective energy storage density is 22.72 J·cm³. -3 The energy storage efficiency reaches as high as 77.84%. Through the above examples, it can be seen that the macroscopic design of the composite thin film material with a multilayer structure effectively overcomes the shortcomings of most existing materials, such as low material breakdown strength, low effective energy storage density, and poor energy storage efficiency due to interface effects. The prepared asymmetric sandwich structure high energy density composite thin film material is expected to replace commercially available biaxially oriented polypropylene (BOPP) in the preparation of thin film capacitors (640 MV·m). -1 The energy storage density under the electric field strength is only 2 J·cm -3 (Approximately), to improve the withstand voltage and energy density of film capacitors, enabling them to meet the application requirements of extreme high-voltage fields such as laser pulse weapons.

[0062] The above-described embodiments provide a clearer understanding of the present invention, but are not intended to limit the scope of the invention.

Claims

1. An asymmetric sandwich structure PVDF-based composite thin film, characterized in that, The composite film comprises a BT / PVDF composite layer, a P(VDF-HFP) polymer layer, and a BN / PVDF composite layer connected in sequence. The BT / PVDF composite layer is a polyvinylidene fluoride composite layer doped with barium titanate nanoparticles, and the BN / PVDF composite layer is a polyvinylidene fluoride composite layer doped with two-dimensional boron nitride nanosheets. The volume fraction of the two-dimensional boron nitride nanosheets in the BN / PVDF composite layer is 5%.

2. The asymmetric sandwich structure PVDF-based composite film according to claim 1, characterized in that, At room temperature, the energy storage density of the composite film is 22.72 J·cm⁻¹. -3 .

3. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to any one of claims 1-2, characterized in that, Includes the following steps: Two-dimensional boron nitride nanosheets and polymer PVDF powder were dispersed in DMF to obtain suspension C. The obtained suspension C was then cast onto a substrate to form a BN / PVDF composite layer. P(VDF-HFP) powder was dispersed in DMF to obtain solution B. The obtained solution B was then cast onto the BN / PVDF composite layer to form a P(VDF-HFP) polymer layer by a casting method. BaTiO3 nanoparticles and polymer PVDF powder were dispersed in DMF to obtain suspension A. The obtained suspension A was then cast onto a P(VDF-HFP) polymer layer to form a BT / PVDF composite layer.

4. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to claim 3, characterized in that, The preparation method of the two-dimensional boron nitride nanosheets includes: adding hexagonal boron nitride powder into an isopropanol solution, sonicating for 1-2 h, stirring for 30-60 min, and repeating 3-5 times; and then stirring the resulting suspension at 3000-4000 r·min. -1 Centrifuge for 6-15 min, filter the supernatant, and dry the precipitate to obtain two-dimensional boron nitride nanosheets.

5. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to claim 3, characterized in that, Two-dimensional boron nitride nanosheets and polymer PVDF powder are dispersed in DMF. Specifically, two-dimensional boron nitride nanosheets are added to DMF, and the mixture is stirred and sonicated alternately several times. Then, polymer PVDF powder is added, and the mixture is stirred and sonicated alternately several times to obtain suspension C.

6. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to claim 3, characterized in that, BaTiO3 nanoparticles and polymer PVDF powder are dispersed in DMF. Specifically, BaTiO3 nanoparticles are added to DMF, and the mixture is stirred and sonicated alternately several times. Then, polymer PVDF powder is added, and the mixture is stirred and sonicated alternately several times to obtain suspension A.

7. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to claim 3, characterized in that, During casting, the casting machine temperature was set to 185~195 ℃ and the scraper height was set to 8~15 μm.

8. The method for preparing the asymmetric sandwich structure PVDF-based composite thin film according to claim 3, characterized in that, After casting to form a BT / PVDF composite layer, a preliminary sample of an asymmetric sandwich structure composite film is obtained. The preliminary sample of the asymmetric sandwich structure composite film is heated and held at 195~205 ℃ for 5-10 min and then quenched in ice water to obtain the asymmetric sandwich structure composite film.

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