A four-layer polyvinylidene fluoride / barium titanate composite film and a preparation method thereof

Abstract

The application discloses a four-layer structure polyvinylidene fluoride / barium titanate composite film and a preparation method thereof. The method comprises the following steps: dissolving PVDF in DMF to obtain a PVDF solution; uniformly dispersing 100 nm, 200 nm and 500 nm BaTiO3 nanoparticles in the DMF respectively to obtain solutions X1, X2 and X3; casting the PVDF solution and then vacuum drying to form a PVDF layer; casting the solution X1 on the PVDF layer and then vacuum drying; casting the solutions X2 and X3 on the formed composite layer in sequence and then vacuum drying; removing the DMF in the composite, heating at 197-203 DEG C, quenching in water for 3-6 min, and finally vacuum drying at 56-62 DEG C for 13-17 h to obtain the four-layer structure polyvinylidene fluoride / barium titanate composite film, which has high breakdown field strength, high energy storage density and high energy storage efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of energy storage polymer dielectric materials, and particularly relates to a four-layer structure polyvinylidene fluoride / barium titanate composite film and a preparation method. BACKGROUND

[0002] As a core device in the field of high-energy pulse power technology, a dielectric capacitor has the characteristics of high power density, high working voltage, wide working temperature range and long service life, and is widely used in many fields such as electric vehicles, smart grids, aerospace and medical devices. However, compared with energy storage devices such as batteries and supercapacitors, the energy storage density of the dielectric capacitor is relatively low, which cannot meet the development requirements of lightweight, miniaturization and integration of today's electronic systems. The dielectric material is the most important component of the dielectric capacitor. To improve the energy storage density of the dielectric material, the dielectric constant and the breakdown field strength must be improved at the same time.

[0003] Polymer dielectric materials include polyvinylidene fluoride (PVDF), polyimide (PI), epoxy resin and the like, and have the advantages of strong flexibility, high breakdown field strength, small volume and light weight. However, the dielectric constant is very low, which is difficult to meet the actual application requirements.

[0004] Among polymer dielectric materials, PVDF has a relatively high dielectric constant while having a high breakdown field strength, and therefore is widely used in the current field of energy storage polymer dielectric materials. At present, ceramic fillers such as barium titanate (BaTiO3), strontium titanate (SrTiO3) and lead zirconate titanate (PbZrTiO3) with high dielectric constant are added to the polymer matrix PVDF to prepare a composite film material, which can improve the dielectric constant to further improve the energy storage density of the PVDF-based composite film material. However, the introduction of a large amount of ceramic fillers can improve the dielectric constant while reducing the breakdown field strength of the composite film material and introducing a high leakage current, so that the improvement of the energy storage density is limited. To balance the high breakdown field strength and high dielectric constant in the PVDF-based composite film material, a sandwich structure composite film material is designed, in which a pure PVDF layer serves as an insulating layer to provide a high breakdown field strength, and a PVDF layer containing ceramic fillers serves as a polarization layer to provide a high dielectric constant. The insulating layer and the polarization layer in the sandwich structure composite film material complement each other in performance, which can synergistically improve the breakdown field strength and the dielectric constant, and significantly improve the energy storage density. However, the dielectric constant at the interface between different layers in the sandwich structure composite film material is quite different, which leads to uneven local electric field distribution, so that the improvement of the breakdown field strength and the energy storage density of the composite film material is still not ideal. SUMMARY

[0005] The present application aims at overcoming the defects in the prior art, and provides a four-layer structure polyvinylidene fluoride / barium titanate composite film and a preparation method thereof.

[0006] To achieve the above object, the present application adopts the following technical scheme:

[0007] A four-layer structure polyvinylidene fluoride / barium titanate composite film, wherein the composite film comprises, from bottom to top, a PVDF layer, a 100 nm BaTiO3 nanoparticle / PVDF composite layer, a 200 nm BaTiO3 nanoparticle / PVDF composite layer and a 500 nm BaTiO3 nanoparticle / PVDF composite layer.

[0008] Preferably, the total thickness of the composite film is 16-24 μm.

[0009] A preparation method of a four-layer structure polyvinylidene fluoride / barium titanate composite film, comprising the following steps:

[0010] S1, dissolving PVDF in DMF to obtain a PVDF solution;

[0011] dispersing 100 nm BaTiO3 nanoparticles and PVDF uniformly in DMF to obtain a mixed solution X1, dispersing 200 nm BaTiO3 nanoparticles and PVDF uniformly in DMF to obtain a mixed solution X2, and dispersing 500 nm BaTiO3 nanoparticles and PVDF uniformly in DMF to obtain a mixed solution X3;

[0012] wherein the three different specifications of BaTiO3 nanoparticles each account for 1-9% of the volume of the corresponding PVDF;

[0013] S2, casting the PVDF solution on a glass plate, and then vacuum drying to form a PVDF layer on the glass plate;

[0014] casting the mixed solution X1 on the PVDF layer, and then vacuum drying to form a 100 nm BaTiO3 nanoparticle / PVDF composite layer on the PVDF layer;

[0015] casting the mixed solution X2 on the 100 nm BaTiO3 nanoparticle / PVDF composite layer, and then vacuum drying to form a 200 nm BaTiO3 nanoparticle / PVDF composite layer on the 100 nm BaTiO3 nanoparticle / PVDF composite layer;

[0016] The mixed solution X3 is cast on the 200 nm BaTiO3 nanoparticle / PVDF composite layer, and finally vacuum dried to form a 500 nm BaTiO3 nanoparticle / PVDF composite layer on the 200 nm BaTiO3 nanoparticle / PVDF composite layer, thereby obtaining a composite;

[0017] S3, after removing DMF in the composite, heating at 197-203°C, then quenching in water for 3-6 min, and finally vacuum drying at 56-62°C for 13-17 h, to obtain a four-layer structure polyvinylidene fluoride / barium titanate composite film.

[0018] Preferably, the PVDF solution in S1 is obtained by the following process:

[0019] The PVDF is dispersed in DMF, followed by ultrasonic treatment for 2.5-5 h, and then magnetic stirring at a speed of 390-440 r / min and a temperature of 35-55°C for 10.5-11 h, to obtain a PVDF solution.

[0020] Preferably, in S1, the 100 nm BaTiO3 nanoparticles, 200 nm BaTiO3 nanoparticles and 500 nm BaTiO3 nanoparticles and the corresponding PVDF are respectively ultrasonically treated in DMF for 4.5-8 h, and then magnetically stirred at a speed of 420-480 r / min and a temperature of 45-65°C for 13.5-15 h, to obtain the mixed solution X1, the mixed solution X2 and the mixed solution X3.

[0021] Preferably, the casting operation in S2 is performed at a speed of 12-16 mm / s and a height of 4-6 μm at 182-195°C.

[0022] Preferably, the vacuum drying in S2 is performed at 78-84°C.

[0023] Further, the vacuum drying time of the PVDF layer in S2 is 5-8 min, the vacuum drying time of the 100 nm BaTiO3 nanoparticle / PVDF composite layer is 10-13 min, the vacuum drying time of the 200 nm BaTiO3 nanoparticle / PVDF composite layer is 13-16 min, and the vacuum drying time of the 500 nm BaTiO3 nanoparticle / PVDF composite layer is 16-19 min.

[0024] Preferably, the composite in S3 is vacuum dried at 56-62°C for 11-14 h.

[0025] Preferably, after removing DMF in the composite in S3, heating at 197-203°C for 7-10 min, and then quenching in water at 0°C.

[0026] Compared with the prior art, the application has the following beneficial technical effects:

[0027] The application discloses a preparation method of a four-layer structure polyvinylidene fluoride / barium titanate composite film, and the four-layer gradient structure PVDF-based composite film material is prepared by adopting a solution blending method to prepare a pure PVDF solution and different particle size BaTiO3 NPs / PVDF mixed solutions, and then through a laminated flow casting method, wherein the pure PVDF layer, the 100nm BaTiO3 NPs / PVDF composite layer, the 200nm BaTiO3 NPs / PVDF composite layer and the 500nm BaTiO3 NPs / PVDF composite layer are sequentially arranged from bottom to top. In the past, the local electric field distribution at the interface between different layers in the sandwich structure composite film material composed of an insulation layer and a polarization layer limits the improvement of the breakdown field strength and the energy storage density of the composite film material, while the four-layer gradient structure composite film material can break through the limitation of regulating the energy storage performance of the sandwich structure composite film material. The pure PVDF layer is used as the insulation layer to improve the breakdown field strength, the BaTiO3 NPs / PVDF composite layer is used as the polarization layer to improve the dielectric constant, the volume concentration of ceramic fillers in each layer is designed to be the same, the particle size is sequentially reduced from top to bottom to construct a gradient structure, the interface blocking effect is formed, and the electric tree breakdown is blocked layer by layer, so that the electric field distribution is optimized, and the defects of low breakdown field strength, low energy storage density and poor energy storage efficiency caused by the local electric field concentration of most composite film materials are effectively overcome. The four-layer gradient structure PVDF-based composite film material can improve the dielectric constant while uniformly distributing the local electric field, improving the breakdown field strength, and significantly improving the effective energy storage density (up to 19.91 J / cm 3 ) and the energy storage efficiency (up to 72.39%).The energy storage density of a commercial biaxially oriented polypropylene (BOPP) composite film material is only 2 J / cm 3 BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a sectional SEM image of the four-layer gradient structure PVDF-based composite film material of the application with the content of BaTiO3 NPs of different particle sizes being 7vol%.

[0029] Figure 2 It is a dielectric spectrum of the four-layer gradient structure PVDF-based composite film material prepared in Example 1 of the application.

[0030] Figure 3The electric hysteresis loop diagram of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 1 of the present application;

[0031] Figure 4 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 2 of the present application;

[0032] Figure 5 The electric hysteresis loop diagram of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 2 of the present application;

[0033] Figure 6 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 3 of the present application;

[0034] Figure 7 The electric hysteresis loop diagram of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 3 of the present application;

[0035] Figure 8 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 4 of the present application;

[0036] Figure 9 The electric hysteresis loop diagram of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 4 of the present application;

[0037] Figure 10 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 5 of the present application;

[0038] Figure 11 The electric hysteresis loop diagram of the four-layer gradient structure PVDF-based composite film material prepared in Embodiment 5 of the present application. DETAILED DESCRIPTION

[0039] The present application will be further described in conjunction with specific embodiments, which are intended to explain but not to limit the present application.

[0040] The present application is a preparation method of a four-layer gradient structure PVDF-based (PVDF / BaTiO3) composite film material with high energy storage density. Pure PVDF solution and different particle size BaTiO3 NPs / PVDF mixed solution are prepared by solution blending method, and then are prepared by laminated casting method. The four-layer gradient structure is from bottom to top in order of pure PVDF layer, 100 nm (small particle size) BaTiO3 NPs / PVDF composite layer, 200 nm (medium particle size) BaTiO3 NPs / PVDF composite layer and 500 nm (large particle size) BaTiO3 NPs / PVDF composite layer.

[0041] Specifically, the following steps are included:

[0042] (1) PVDF is dispersed in solvent DMF, ultrasonic 2.5-5h, magnetic stirring at 390-440r / min and 35-55℃ for 10.5-11h to prepare pure PVDF solution A; 100nm BaTiO3 NPs (barium titanate nanoparticles), 200nm BaTiO3 NPs and 500nm BaTiO3 NPs with different contents (1vol%-9vol%, volume ratio of BaTiO3 NPs and PVDF) are respectively dispersed in solvent DMF with PVDF, ultrasonic 4.5-8h, magnetic stirring at 420-480r / min and 45-65℃ for 13.5-15h to prepare 100nm BaTiO3 NPs / PVDF mixed solution X1, 200nm BaTiO3 NPs / PVDF mixed solution X2 and 500nm BaTiO3 NPs / PVDF mixed solution X3.

[0043] (2) Set the temperature of the casting machine to 182-195℃, adjust the doctor blade speed to 12-16mm / s, and control the doctor blade height to 4-6μm. Solution A is first cast on a glass plate, and vacuum dried at 78-84℃ for 5-8min in a vacuum drying box to complete the film forming process; mixed solution X1 is secondly cast on the glass plate (PVDF layer) on which the first film forming is completed, and vacuum dried at 78-84℃ for 10-13min in a vacuum drying box to form a film; mixed solution X2 is thirdly cast on the glass plate (100nm BaTiO3 nanoparticle / PVDF composite layer) on which the second film forming is completed, and vacuum dried at 78-84℃ for 13-16min in a vacuum drying box to form a film; mixed solution X3 is fourthly cast on the glass plate (200nm BaTiO3 nanoparticle / PVDF composite layer) on which the third film forming is completed, and vacuum dried at 78-84℃ for 16-19min in a vacuum drying box to form a 500nm BaTiO3 nanoparticle / PVDF composite layer; finally, the four-layer gradient structure PVDF-based composite film material is vacuum dried at 56-62℃ for 11-14h to volatilize the solvent.

[0044] (3) The above prepared composite film material is heated at 197-203℃ for 7-10min and immediately quenched in ice water at 0℃ for 3-6min, and finally vacuum dried at 56-62℃ for 13-17h in a vacuum drying box, and then taken off from the glass plate to obtain a four-layer gradient structure PVDF-based composite film material with a total thickness of 16-24μm.

[0045] Performance test:

[0046] The four-layer gradient structure PVDF-based composite film material prepared in an embodiment is subjected to cross-section SEM test;

[0047] The prepared film sample is cut into a rectangle of 12 mm x 15 mm, and then a derived film is prepared, a gold electrode with a diameter of 4 mm is plated, and then the dielectric property is tested at room temperature;

[0048] The prepared film sample is cut into a rectangle of 12 mm x 15 mm, and then a derived film is prepared, a gold electrode with a diameter of 2 mm is plated, and then the ferroelectric property is tested at room temperature, and the energy storage performance, the total energy storage density (U), the effective energy storage density (U e ) and the energy storage efficiency (η) are calculated.

[0049]

[0050]

[0051]

[0052] wherein P max represents the maximum polarization intensity, P r represents the residual polarization intensity, E represents the electric field intensity, and P represents the polarization intensity.

[0053] Example 1

[0054] In this embodiment, a four-layer gradient structure PVDF-based composite film material is prepared by using a solution blending method and a laminated casting method, wherein from bottom to top, there are a pure PVDF layer, a 100 nm BaTiO3 NP / PVDF composite layer, a 200 nm BaTiO3 NP / PVDF composite layer and a 500 nm BaTiO3 NP / PVDF composite layer. The composite film material can be simplified as an LMSPX model, wherein L represents the 500 nm BaTiO3 NP / PVDF composite layer, M represents the 200 nm BaTiO3 NP / PVDF composite layer, S represents the 100 nm BaTiO3 NP / PVDF composite layer, P represents the pure PVDF layer, and X represents the volume fraction of BaTiO3 NPs with different particle sizes. In this example, the four-layer gradient structure composite film material can be simplified as an LMSP1 model, wherein the content of BaTiO3 NPs with different particle sizes is 1 vol%.

[0055] The preparation method of the four-layer gradient structure PVDF-based composite film material, comprising the following steps:

[0056] (1) 1.2g PVDF was dispersed in 10ml DMF solvent, ultrasonic for 4.5h, magnetic stirring for 10.5h at 420r / min and 45℃, to prepare pure PVDF solution A; 0.0338g 100nm BaTiO3 NPs, 200nm BaTiO3 NPs and 500nm BaTiO3 NPs were respectively dispersed in 10ml DMF solvent with 1.2g PVDF, ultrasonic for 7.5h, magnetic stirring for 14.5h at 450r / min and 55℃, to prepare 100nm BaTiO3 NPs / PVDF mixed solution X1, 200nm BaTiO3 NPs / PVDF mixed solution X2 and 500nm BaTiO3 NPs / PVDF mixed solution X3.

[0057] (2) The temperature of the casting machine was set to 193℃, the speed of the doctor blade was adjusted to 14mm / s, and the height of the doctor blade was controlled to 5μm. Solution A was first cast on a glass plate, and then vacuum dried at 82℃ for 7min to form a film. Mixed solution X1 was secondly cast on the glass plate with the first film, and then vacuum dried at 82℃ for 12min to form a film. Mixed solution X2 was thirdly cast on the glass plate with the second film, and then vacuum dried at 82℃ for 15min to form a film. Mixed solution X3 was fourthly cast on the glass plate with the third film, and then vacuum dried at 82℃ for 18min to form a film. Finally, the four-layer gradient structure PVDF-based composite film material was vacuum dried at 62℃ for 13h to volatilize the solvent.

[0058] (3) The prepared composite film material was heated at 202℃ for 10min, and then immediately quenched in ice water at 0℃ for 6min. Finally, the material was vacuum dried at 62℃ for 16h in a vacuum drying oven, and then peeled off from the glass plate to obtain the four-layer gradient structure PVDF-based composite film material LMSP1.

[0059] (4) The prepared film sample was cut into a rectangle of 12mm×15mm, and then made into a film sample with a diameter of 4mm. The dielectric properties of the film sample were tested at room temperature. Figure 2 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material LMSP1 of this embodiment is shown in the figure. As can be seen from the figure, the dielectric constant of the composite film material LMSP1 prepared in this embodiment gradually decreases and the dielectric loss gradually increases with the increase of frequency. When the frequency is 10kHz, the dielectric constant of the composite film material LMSP1 prepared in this embodiment is 9.53, and the dielectric loss is 0.0258.

[0060] (9) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, and a film sample was prepared, a gold electrode with a diameter of 2 mm was plated, and then the ferroelectric performance test was carried out at room temperature, and the energy storage performance was calculated. Figure 3 The effective energy storage density of the four-layer gradient structure PVDF-based composite film material LMSP1 of the present example at a breakdown field strength of 480 MV / m was 14.10 J / cm 3 , and the energy storage efficiency was 80.96%. Table 1 shows the energy storage performance of the four-layer gradient structure PVDF-based composite film material LMSP1 of the present example at room temperature.

[0061] Example 2:

[0062] The four-layer gradient structure PVDF-based composite film material of the present example was prepared by solution blending and laminated casting method, wherein from bottom to top, it was pure PVDF layer, 100 nm BaTiO3 NPs / PVDF composite layer, 200 nm BaTiO3 NPs / PVDF composite layer and 500 nm BaTiO3 NPs / PVDF composite layer. The composite film material can be simplified as LMSPX model, wherein L represents 500 nm BaTiO3 NPs / PVDF composite layer, M represents 200 nm BaTiO3 NPs / PVDF composite layer, S represents 100 nm BaTiO3 NPs / PVDF composite layer, P represents pure PVDF layer, and X represents the volume fraction of BaTiO3 NPs with different particle sizes. In the present example, the four-layer gradient structure composite film material can be simplified as LMSP3 model, wherein the content of BaTiO3 NPs with different particle sizes is 3 vol%.

[0063] The preparation method of the four-layer gradient structure PVDF-based composite film material described above comprises the following steps:

[0064] (1) 1.2 g PVDF was dispersed in 10 ml DMF solvent, ultrasonic for 4.5 h, magnetic stirring at 420 r / min and 45℃ for 10.5 h to prepare pure PVDF solution A; 0.1014 g 100 nm BaTiO3 NPs, 200 nm BaTiO3 NPs and 500 nm BaTiO3 NPs were respectively dispersed in 10 ml DMF solvent with 1.2 g PVDF, ultrasonic for 7.5 h, magnetic stirring at 450 r / min and 55℃ for 14.5 h to prepare 100 nm BaTiO3 NPs / PVDF mixed solution X1, 200 nm BaTiO3 NPs / PVDF mixed solution X2 and 500 nm BaTiO3 NPs / PVDF mixed solution X3.

[0065] (2) The temperature of the casting machine was set to 193℃, the speed of the doctor blade was adjusted to 14 mm / s, and the height of the doctor blade was controlled to 5 μm. Solution A was first cast on a glass plate and vacuum dried at 82℃ for 7 min to form a film; mixed solution X1 was secondly cast on the glass plate on which the first film was formed, and vacuum dried at 82℃ for 12 min to form a film; mixed solution X2 was thirdly cast on the glass plate on which the second film was formed, and vacuum dried at 82℃ for 15 min to form a film; mixed solution X3 was fourthly cast on the glass plate on which the third film was formed, and vacuum dried at 82℃ for 18 min to form a film; finally, the four-layer gradient structure PVDF-based composite film material was vacuum dried at 62℃ for 13 h to volatilize the solvent.

[0066] (3) The above prepared composite film material was heated at 202℃ for 10 min and immediately quenched in ice water at 0℃ for 6 min, and finally vacuum dried at 62℃ for 16 h in a vacuum drying box. The four-layer gradient structure PVDF-based composite film material LMSP3 was obtained by peeling off from the glass plate.

[0067] (4) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, then a film was made, a gold electrode with a diameter of 4 mm was plated, and then the dielectric properties were tested at room temperature. Figure 4 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material LMSP3 of this embodiment is shown in the figure. It can be seen from the figure that the dielectric constant of the composite film material LMSP3 prepared in this embodiment gradually decreases and the dielectric loss gradually increases with the increase of frequency. When the frequency is 10 kHz, the dielectric constant of the composite film material LMSP3 prepared in this embodiment is 10.59, and the dielectric loss is 0.0266.

[0068] (9) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, and then a film was made, a gold electrode with a diameter of 2 mm was plated, and then the ferroelectric performance test was carried out at room temperature, and the energy storage performance was calculated. Figure 5 The effective energy storage density of the four-layer gradient structure PVDF-based composite film material LMSP3 of the present example at a breakdown field strength of 500 MV / m was 16.81 J / cm 3 , and the energy storage efficiency was 79.71%. Table 1 shows the energy storage performance of the four-layer gradient structure PVDF-based composite film material LMSP3 of the present example at room temperature.

[0069] Example 3:

[0070] The four-layer gradient structure PVDF-based composite film material of the present example was prepared by solution blending and laminated casting method, wherein from bottom to top, it was pure PVDF layer, 100 nm BaTiO3 NPs / PVDF composite layer, 200 nm BaTiO3 NPs / PVDF composite layer and 500 nm BaTiO3 NPs / PVDF composite layer. The composite film material can be simplified as LMSPX model, wherein L represents 500 nm BaTiO3 NPs / PVDF composite layer, M represents 200 nm BaTiO3 NPs / PVDF composite layer, S represents 100 nm BaTiO3 NPs / PVDF composite layer, P represents pure PVDF layer, and X represents the volume fraction of BaTiO3 NPs with different particle sizes. In the present example, the four-layer gradient structure composite film material can be simplified as LMSP5 model, wherein the content of BaTiO3 NPs with different particle sizes is 5 vol%.

[0071] The preparation method of the above-mentioned four-layer gradient structure PVDF-based composite film material, comprising the following steps:

[0072] (1) 1.2 g PVDF was dispersed in 10 ml DMF solvent, ultrasonic for 4.5 h, magnetic stirring at 420 r / min and 45℃ for 10.5 h to prepare pure PVDF solution A; 0.1690 g 100 nm BaTiO3 NPs, 200 nm BaTiO3 NPs and 500 nm BaTiO3 NPs were respectively dispersed in 10 ml DMF solvent with 1.2 g PVDF, ultrasonic for 7.5 h, magnetic stirring at 450 r / min and 55℃ for 14.5 h to prepare 100 nm BaTiO3 NPs / PVDF mixed solution X1, 200 nm BaTiO3 NPs / PVDF mixed solution X2 and 500 nm BaTiO3 NPs / PVDF mixed solution X3.

[0073] (2) The temperature of the casting machine was set to 193℃, the speed of the doctor blade was adjusted to 14 mm / s, and the height of the doctor blade was controlled to 5 μm. Solution A was first cast on a glass plate and vacuum dried at 82℃ for 7 min to form a film; mixed solution X1 was secondly cast on the glass plate on which the first film was formed, and vacuum dried at 82℃ for 12 min to form a film; mixed solution X2 was thirdly cast on the glass plate on which the second film was formed, and vacuum dried at 82℃ for 15 min to form a film; mixed solution X3 was fourthly cast on the glass plate on which the third film was formed, and vacuum dried at 82℃ for 18 min to form a film; finally, the four-layer gradient structure PVDF-based composite film material was vacuum dried at 62℃ for 13 h to volatilize the solvent.

[0074] (3) The prepared composite film material was heated at 202℃ for 10 min and immediately quenched in ice water at 0℃ for 6 min, and finally vacuum dried at 62℃ for 16 h in a vacuum drying box. The four-layer gradient structure PVDF-based composite film material LMSP5 was obtained by peeling off from the glass plate.

[0075] (4) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, then a film sample was prepared, a gold electrode with a diameter of 4 mm was plated, and then the dielectric properties were tested at room temperature. Figure 6 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material LMSP5 of this embodiment is shown in the figure. It can be seen from the figure that the dielectric constant of the composite film material LMSP5 prepared in this embodiment gradually decreases and the dielectric loss gradually increases with the increase of frequency. When the frequency is 10 kHz, the dielectric constant of the composite film material LMSP5 prepared in this embodiment is 11.81, and the dielectric loss is 0.0285.

[0076] (9) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, and then a film was made, a gold electrode with a diameter of 2 mm was plated, and then the ferroelectric performance test was carried out at room temperature, and the energy storage performance was calculated. Figure 7 The effective energy storage density of the four-layer gradient structure PVDF-based composite film material LMSP5 of the present example at a breakdown field strength of 540 MV / m was 19.40 J / cm 3 , and the energy storage efficiency was 72.79%. Table 1 shows the energy storage performance of the four-layer gradient structure PVDF-based composite film material LMSP5 of the present example at room temperature.

[0077] Example 4:

[0078] The four-layer gradient structure PVDF-based composite film material of the present example was prepared by solution blending method and laminated casting method, wherein from bottom to top, it was pure PVDF layer, 100 nm BaTiO3 NPs / PVDF composite layer, 200 nm BaTiO3 NPs / PVDF composite layer and 500 nm BaTiO3 NPs / PVDF composite layer. The composite film material can be simplified as LMSPX model, wherein L represents 500 nm BaTiO3 NPs / PVDF composite layer, M represents 200 nm BaTiO3 NPs / PVDF composite layer, S represents 100 nm BaTiO3 NPs / PVDF composite layer, P represents pure PVDF layer, and X represents the volume fraction of BaTiO3 NPs with different particle sizes. In the present example, the four-layer gradient structure composite film material can be simplified as LMSP7 model, wherein the content of BaTiO3 NPs with different particle sizes is 7 vol%.

[0079] The preparation method of the above-mentioned four-layer gradient structure PVDF-based composite film material, comprising the following steps:

[0080] (1) 1.2 g of PVDF was dispersed in 10 ml of DMF solvent, sonicated for 4.5 h, and magnetically stirred for 10.5 h at a speed of 420 r / min and a temperature of 45 °C to obtain pure PVDF solution A; 0.2366 g of 100 nm BaTiO3 NPs, 200 nm BaTiO3 NPs and 500 nm BaTiO3 NPs were dispersed with 1.2 g of PVDF in 10 ml of DMF solvent, sonicated for 7.5 h, and magnetically stirred for 14.5 h at a speed of 450 r / min and a temperature of 55 °C to obtain 100 nm BaTiO3 NPs / PVDF mixed solution X1, 200 nm BaTiO3 NPs / PVDF mixed solution X2 and 500 nm BaTiO3 NPs / PVDF mixed solution X3.

[0081] (2) Set the casting machine temperature to 193℃, adjust the doctor blade speed to 14mm / s, and control the doctor blade height to 5μm. First, cast solution A on a glass plate and vacuum dry it at 82℃ for 7 minutes to form a film. Second, cast mixed solution X1 on the glass plate after the first film formation and vacuum dry it at 82℃ for 12 minutes to form a film. Third, cast mixed solution X2 on the glass plate after the second film formation and vacuum dry it at 82℃ for 15 minutes to form a film. Fourth, cast mixed solution X3 on the glass plate after the third film formation and vacuum dry it at 82℃ for 18 minutes to form a film. Finally, vacuum dry the four-layer gradient PVDF-based composite film material at 62℃ for 13 hours to allow the solvent to evaporate.

[0082] (3) The composite film material prepared above was heated at 202℃ for 10 min and immediately placed in 0℃ ice water for 6 min. Finally, it was placed in a vacuum drying oven and vacuum dried at 62℃ for 16 h. It was then peeled off from the glass plate to obtain the four-layer gradient structure PVDF-based composite film material LMSP7.

[0083] (4) The prepared four-layer gradient structure PVDF-based composite thin film material LMSP7 was subjected to cross-sectional SEM testing, such as... Figure 1 As shown in the figure, the composite thin film material obtained in this embodiment exhibits a distinct four-layer structure with good interface bonding and no structural defects, and a total thickness of approximately 20 μm. From bottom to top, the layers are a pure PVDF layer, a 100 nm BaTiO3 NPs / PVDF composite layer, a 200 nm BaTiO3 NPs / PVDF composite layer, and a 500 nm BaTiO3 NPs / PVDF composite layer, each with a thickness of approximately 5 μm.

[0084] (5) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, then a derived film was prepared, a gold electrode with a diameter of 4 mm was plated, and then the dielectric properties were tested at room temperature. Figure 8 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material LMSP7 of the present example is shown in the figure. As can be seen from the figure, the dielectric constant of the composite film material LMSP7 prepared in the present example gradually decreases and the dielectric loss gradually increases with the increase of frequency. When the frequency is 10 kHz, the dielectric constant of the composite film material LMSP7 prepared in the present example is 12.86, and the dielectric loss is 0.0309.

[0085] (6) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, then a derived film was prepared, a gold electrode with a diameter of 2 mm was plated, and then the ferroelectric performance test was carried out at room temperature, and the energy storage performance was calculated. Figure 9 The electric hysteresis loop of the four-layer gradient structure PVDF-based composite film material LMSP7 of the present example at room temperature is shown in the figure. Based on the electric hysteresis loop, the effective energy storage density of the four-layer gradient structure PVDF-based composite film material LMSP7 of the present example at a breakdown field strength of 520 MV / m is 19.91 J / cm 3 , and the energy storage efficiency is 72.39%. Table 1 shows the energy storage performance of the four-layer gradient structure PVDF-based composite film material LMSP7 of the present example at room temperature.

[0086] Example 5:

[0087] The four-layer gradient structure PVDF-based composite film material of the present example was prepared by solution blending method and laminated casting method, wherein from bottom to top, it is pure PVDF layer, 100 nm BaTiO3 NPs / PVDF composite layer, 200 nm BaTiO3 NPs / PVDF composite layer and 500 nm BaTiO3 NPs / PVDF composite layer. The composite film material can be simplified as LMSPX model, wherein L represents 500 nm BaTiO3 NPs / PVDF composite layer, M represents 200 nm BaTiO3 NPs / PVDF composite layer, S represents 100 nm BaTiO3 NPs / PVDF composite layer, P represents pure PVDF layer, and X represents the volume fraction of BaTiO3 NPs with different particle sizes. In the present example, the four-layer gradient structure composite film material can be simplified as LMSP9 model, wherein the content of BaTiO3 NPs with different particle sizes is 9 vol%.

[0088] The preparation method of the above-mentioned four-layer gradient structure PVDF-based composite film material comprises the following steps:

[0089] (1) 1.2 g PVDF was dispersed in 10 ml DMF solvent, ultrasonic for 4.5 h, magnetic stirring at 420 r / min and 45℃ for 10.5 h to prepare pure PVDF solution A; 0.3042 g 100 nm BaTiO3 NPs, 200 nm BaTiO3 NPs and 500 nm BaTiO3 NPs were respectively dispersed in 10 ml DMF solvent with 1.2 g PVDF, ultrasonic for 7.5 h, magnetic stirring at 450 r / min and 55℃ for 14.5 h to prepare 100 nm BaTiO3 NPs / PVDF mixed solution X1, 200 nm BaTiO3 NPs / PVDF mixed solution X2 and 500 nm BaTiO3 NPs / PVDF mixed solution X3.

[0090] (2) The temperature of the casting machine was set to 193℃, the speed of the doctor blade was adjusted to 14 mm / s, and the height of the doctor blade was controlled to 5 μm. Solution A was first cast on a glass plate and vacuum dried at 82℃ for 7 min to form a film; mixed solution X1 was secondly cast on the glass plate on which the first film was formed, and vacuum dried at 82℃ for 12 min to form a film; mixed solution X2 was thirdly cast on the glass plate on which the second film was formed, and vacuum dried at 82℃ for 15 min to form a film; mixed solution X3 was fourthly cast on the glass plate on which the third film was formed, and vacuum dried at 82℃ for 18 min to form a film; finally, the four-layer gradient structure PVDF-based composite film material was vacuum dried at 62℃ for 13 h to volatilize the solvent.

[0091] (3) The prepared composite film material was heated at 202℃ for 10 min and immediately quenched in ice water at 0℃ for 6 min, and finally vacuum dried at 62℃ for 16 h in a vacuum drying box. The film was removed from the glass plate to obtain the four-layer gradient structure PVDF-based composite film material LMSP9.

[0092] (4) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, then a film was made, a gold electrode with a diameter of 4 mm was plated, and then the dielectric properties were tested at room temperature. Figure 10 The dielectric spectrum of the four-layer gradient structure PVDF-based composite film material LMSP9 of this embodiment is shown in the figure. It can be seen from the figure that the dielectric constant of the composite film material LMSP9 prepared in this embodiment gradually decreases and the dielectric loss gradually increases with the increase of frequency. When the frequency is 10 kHz, the dielectric constant of the composite film material LMSP9 prepared in this embodiment is 13.84, and the dielectric loss is 0.0336.

[0093] (5) The prepared film sample was cut into a rectangle of 12 mm x 15 mm, and then a film was prepared, a gold electrode with a diameter of 2 mm was plated, and then a ferroelectric performance test was carried out at room temperature, and the energy storage performance was calculated. Figure 11 The effective energy storage density of the four-layer gradient structure PVDF-based composite film material LMSP9 of the present embodiment at a breakdown field strength of 450 MV / m is 16.85 J / cm 3 , and the energy storage efficiency is 68.92%. Table 1 shows the energy storage performance of the four-layer gradient structure PVDF-based composite film material LMSP9 of the present embodiment at room temperature.

[0094] Table 1 Energy storage performance of four-layer gradient structure PVDF-based composite film material at room temperature

[0095]

[0096] As can be seen from Table 1, the four-layer gradient structure composite film material has an energy storage density of 14.10-19.91 J / cm 3 at room temperature, and the four-layer gradient structure PVDF-based composite film material with a content of 7 vol% of BaTiO3 NPs of different particle sizes has the best comprehensive energy storage performance. At a breakdown field strength of 520 MV / m, based on the hysteresis loop calculation, an effective energy storage density of 19.91 J / cm 3 and an energy storage efficiency of 72.39% are obtained at room temperature. Through the above embodiments, it can be found that the four-layer gradient structure composite film material designed by the present application, in which the particle size of the ceramic filler BaTiO3 NPs decreases from top to bottom, can block the electrical treeing layer by layer, thereby optimizing the electric field distribution and effectively overcoming the shortcomings of low breakdown field strength, low energy storage density and poor energy storage efficiency caused by local electric field concentration in most composite film materials. The energy storage density of the commercialized biaxially oriented polypropylene (BOPP) composite film material is only 2 J / cm 3 at 640 MV / m. The four-layer gradient structure PVDF-based composite film material prepared by the present application has high energy storage density and is expected to replace BOPP to prepare film capacitors and be widely used in new energy electric vehicles, smart grids and high-energy pulse weapons.

Claims

1. A four-layered polyvinylidene fluoride / barium titanate composite film, characterized by, The composite film comprises, from bottom to top, a PVDF layer, a 100 nm BaTiO3 nanoparticle / PVDF composite layer, a 200 nm BaTiO3 nanoparticle / PVDF composite layer, and a 500 nm BaTiO3 nanoparticle / PVDF composite layer.

2. The four-layer structure polyvinylidene fluoride / barium titanate composite film according to claim 1, characterized in that, The total thickness of the composite film is 16-24 μm.

3. A method for preparing a four-layered polyvinylidene fluoride / barium titanate composite film, characterized by, The method comprises the following steps: S1, dissolving PVDF in DMF to obtain a PVDF solution; 100 nm BaTiO3 nanoparticles and PVDF are uniformly dispersed in DMF to obtain a mixed solution X1, 200 nm BaTiO3 nanoparticles and PVDF are uniformly dispersed in DMF to obtain a mixed solution X2, and 500 nm BaTiO3 nanoparticles and PVDF are uniformly dispersed in DMF to obtain a mixed solution X3; The three different specifications of BaTiO3 nanoparticles each account for 1-9% of the corresponding PVDF volume; S2, casting the PVDF solution on a glass plate, followed by vacuum drying to form a PVDF layer on the glass plate; The mixed solution X1 is cast on the PVDF layer, followed by vacuum drying to form a 100 nm BaTiO3 nanoparticle / PVDF composite layer on the PVDF layer; The mixed solution X2 is cast on the 100 nm BaTiO3 nanoparticle / PVDF composite layer, followed by vacuum drying to form a 200 nm BaTiO3 nanoparticle / PVDF composite layer on the 100 nm BaTiO3 nanoparticle / PVDF composite layer; The mixed solution X3 is cast on the 200 nm BaTiO3 nanoparticle / PVDF composite layer, followed by vacuum drying to form a 500 nm BaTiO3 nanoparticle / PVDF composite layer on the 200 nm BaTiO3 nanoparticle / PVDF composite layer, thereby obtaining a composite; S3, removing the DMF in the composite, heating at 197-203 ℃, quenching in water for 3-6 min, and finally vacuum drying at 56-62 ℃ for 13-17 h to obtain a four-layer polyvinylidene fluoride / barium titanate composite film.

4. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, The PVDF solution in S1 is obtained as follows: PVDF is dispersed in DMF, followed by ultrasonic treatment for 2.5-5 h, and then magnetic stirring at a speed of 390-440 r / min and a temperature of 35-55 ℃ for 10.5-11 h to obtain the PVDF solution.

5. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, The 100 nm BaTiO3 nanoparticles, 200 nm BaTiO3 nanoparticles, and 500 nm BaTiO3 nanoparticles in S1 are each ultrasonically treated with the corresponding PVDF in DMF for 4.5-8 h, and then magnetically stirred at a speed of 420-480 r / min and a temperature of 45-65 ℃ for 13.5-15 h to obtain the mixed solution X1, the mixed solution X2, and the mixed solution X3.

6. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, The casting operation in S2 is performed at a speed of 12-16 mm / s and a height of 4-6 μm at 182-195 ℃.

7. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, The vacuum drying in S2 is all carried out at 78-84 ℃.

8. The method for preparing a four-layer polyvinylidene fluoride / barium titanate composite film according to claim 7, characterized in that, The vacuum drying time of the PVDF layer in S2 is 5-8 min, the vacuum drying time of the 100 nm BaTiO3 nanoparticle / PVDF composite layer is 10-13 min, the vacuum drying time of the 200 nm BaTiO3 nanoparticle / PVDF composite layer is 13-16 min, and the vacuum drying time of the 500 nm BaTiO3 nanoparticle / PVDF composite layer is 16-19 min.

9. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, S3 removes the DMF in the composite by vacuum drying at 56-62 ℃ for 11-14 h.

10. The method for preparing the four-layer polyvinylidene fluoride / barium titanate composite film according to claim 3, characterized in that, After removing the DMF in the composite, S3 heats at 197-203 ℃ for 7-10 min, and then quenches in water at 0 ℃.

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