A double-layer structure polymer-based composite material for dielectric energy storage and a preparation method thereof

Abstract

The application discloses a double-layer structure polymer-based composite material for dielectric energy storage and a preparation method thereof, relates to a composite material for dielectric energy storage and a preparation method thereof. The application solves the problems of low relative dielectric constant, low breakdown field strength and low energy storage efficiency of the polymer-based composite material in the prior art, and the low discharge energy storage density and energy storage efficiency of the polymer-based composite material. The material is a double-layer structure polymer-based composite material composed of a PEI-based composite material film and a PVDF-based composite material film, has a discharge energy storage density U dis ≥ 20 J / cm 3 , and an energy storage efficiency η > 70%. The method comprises the following steps: 1. preparing one-dimensional and two-dimensional sheet-shaped fillers; 2. preparing PEI-based composite material solution and PVDF-based composite material solution; and 3. preparing the double-layer structure polymer-based composite material. The application discloses the double-layer structure polymer-based composite material for dielectric energy storage and the preparation method thereof.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite material for dielectric energy storage and a preparation method thereof. BACKGROUND

[0002] In recent years, dielectric capacitors play a crucial role in advanced electronic power systems and energy storage devices due to their fast charge-discharge characteristics and excellent power density. Polymer-based dielectric capacitors are favored by researchers due to their high electronic resistance, low mass, structural stability, and good flexibility; however, compared with batteries and supercapacitors, the lower discharge energy storage density limits the widespread application of polymer-based dielectric capacitors in the energy storage device market. To improve the discharge energy storage density (U dis ) of polymer-based dielectric capacitors, it is necessary to improve the breakdown strength (E b ) and the relative dielectric constant (ε r ) of the dielectric component. where ε0 is the vacuum permittivity, i.e. 8.85 x 10 -12 F m -1 ). In this context, filling the polymer matrix with two-dimensional dielectric materials such as boron nitride nanosheets (BNNS), Ca2Nb3O 10 , Mxene and montmorillonite (MMT) is an effective method to enhance the tortuosity of the conduction path under a large electric field, thereby improving the E b of the composite material. Unfortunately, commonly used two-dimensional materials such as BNNS have a relatively low ε r (~3-4), which is not conducive to improving the ε r of the composite material, and their small size (~100 nm) is not conducive to fully exerting the blocking effect of two-dimensional materials on space charge, resulting in no significant improvement in the overall ε r and E b of the composite material after introducing these common two-dimensional materials, ultimately leading to a relatively low U dis . In addition, widely used single polymer matrix materials such as PVDF, PVDF-HFP and P(VDF-TrFE-CTFE) have a very low energy storage efficiency (η) of about 60%, which means a large amount of energy is lost and converted into heat, which is harmful to long-term operation. Therefore, developing dielectric energy storage materials with high U dis and η is still a daunting challenge. SUMMARY

[0003] The present application solves the problem of low relative dielectric constant, low breakdown field strength and low energy storage efficiency of polymer-based composite materials in the prior art, which leads to low discharge energy storage density and low energy storage efficiency, and further provides a double-layer structure polymer-based composite material for dielectric energy storage with high discharge energy storage density and high energy storage efficiency and a preparation method thereof.

[0004] A double-layer structure polymer-based composite material for dielectric energy storage, which is a double-layer structure polymer-based composite material composed of a PEI-based composite material film and a PVDF-based composite material film;

[0005] The PEI-based composite material film is prepared from a PEI-based polymer and a two-dimensional sheet-shaped filler; and the PVDF-based composite material film is prepared from a PVDF-based polymer and a two-dimensional sheet-shaped filler.

[0006] The PEI-based polymer is one or a combination of several of polyetherimide, polyimide and vulcanized polyetherimide.

[0007] The PVDF-based polymer is one or a combination of several of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and terpolymer P(VDF-TrFE-CTFE).

[0008] The two-dimensional sheet-shaped filler is one or a combination of several of Na 0.5 Bi 4.5 Ti4O 15 , Bi4Ti3O 12 and SrBi2Ta2O9.

[0009] The two-dimensional sheet-shaped filler has a sheet diameter of 0.5-5 μm; the two-dimensional sheet-shaped filler in the PEI-based composite material film accounts for 0.1-2.0% of the mass of the PEI-based polymer; and the two-dimensional sheet-shaped filler in the PVDF-based composite material film accounts for 0.1-2.0% of the mass of the PVDF-based polymer.

[0010] The double-layer structure polymer-based composite material for dielectric energy storage has a discharge energy storage density U dis ≥ 20 J / cm 3 and an energy storage efficiency η > 70%.

[0011] A preparation method of a double-layer structure polymer-based composite material for dielectric energy storage, which is performed according to the following steps:

[0012] I. Preparation of a two-dimensional sheet-shaped filler:

[0013] The raw materials are weighed according to the stoichiometric ratio of the chemical formula of the two-dimensional sheet-shaped filler, and NaCl is weighed according to a mass ratio of raw materials to molten salt of 1:(1.5-15); the raw materials and NaCl are ball-milled to obtain a mixture, the mixture is calcined at a temperature of 800-1050°C for 1-8 h, and finally washed and dried to obtain the two-dimensional sheet-shaped filler.

[0014] The two-dimensional sheet-shaped filler has a sheet diameter of 0.5-5 μm.0.5 Bi 4.5 Ti4O 15 Bi4Ti3O 12 and one or a combination of several of SrBi2Ta2O9;

[0015] II. Preparation of PEI-based composite solutions and PVDF-based composite solutions:

[0016] PEI-based composite material solutions and PVDF-based composite material solutions were prepared using PEI-based polymers, PVDF-based polymers, two-dimensional sheet fillers, and N-methylpyrrolidone, respectively.

[0017] The PEI-based polymer is one or a combination of several of polyetherimide, polyimide and sulfurized polyetherimide;

[0018] The PVDF-based polymer is one or a combination of several of the following: polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and terpolymer P (VDF-TrFE-CTFE);

[0019] The two-dimensional sheet filler in the PEI-based composite material solution accounts for 0.1% to 2.0% of the PEI-based polymer mass; the two-dimensional sheet filler in the PVDF-based composite material solution accounts for 0.1% to 2.0% of the PVDF-based polymer mass.

[0020] III. Preparation of bilayer polymer-based composite materials:

[0021] A PEI-based composite material solution is cast onto a substrate and vacuum dried to obtain a PEI-based composite material film. Then, a PVDF-based composite material solution is cast onto the PEI-based composite material film and vacuum dried. Finally, the resulting bilayer polymer-based composite material is removed from the substrate, thus completing the preparation method of the bilayer polymer-based composite material for dielectric energy storage.

[0022] Principle: This invention selects two PVDF-based polymers with different energy storage characteristics (high ε) r ) and PEI-based polymers (high E b Using PVDF-based polymers and PEI-based polymers as the matrix and two-dimensional sheet-like fillers as powder fillers, a polymer-based composite material with both high discharge energy density and high energy storage efficiency was invented through a double-layer structure design. Specifically, appropriate amounts of high ε-coefficient polymers were introduced into PVDF-based polymers and PEI-based polymers. r Two-dimensional sheet-like packing. On the one hand, two-dimensional sheet-like packing has a high ε... r It can improve the ε of composite materials r, on the other hand, two-dimensional sheet-shaped fillers can fully exert their blocking effect on the space charge applied on the surface as two-dimensional materials, and can effectively block the charge from passing along the direction perpendicular to the plane, thereby improving the E b of the composite material. In addition, the two improved composite materials are compounded together by a layer-by-layer stacking process, a large number of electronic deep traps are formed at the interface by utilizing the interface effect, the charge is bound to pass, thereby improving the breakdown resistance of the material, and the E b of the double-layer structure polymer-based composite material is further improved, thereby improving the discharge energy storage density U dis and optimizing the efficiency.

[0023] Advantages of the present application:

[0024] The present application is based on the synergistic regulation strategy of the blocking effect of two-dimensional materials on space charge and the binding effect of double-layer structure interface on charge, and a polymer-based composite material with high discharge energy storage density and high energy storage efficiency is prepared, the discharge energy storage density U dis ≥ 20 J / cm 3 , the energy storage efficiency η is greater than 70%, and the comprehensive energy storage performance is better than most of the currently reported polymer-based composite materials. In addition, under the conditions of an electric resistance R of 300 Ω and an electric field of 3000 kV / cm, the discharge rate t 0.9 of the double-layer structure polymer-based composite material for dielectric energy storage is less than or equal to 50 ns, the power density P D is greater than 50 MW / cm 3 .

[0025] The preparation process of the present application is simple and efficient, which is conducive to industrialized mass production, and provides a design and preparation idea for the continued research and development of polymer-based energy storage capacitors with high energy storage density, excellent energy storage stability and a wide practical temperature range. At the same time, the polymer-based capacitor as an energy storage element shows great application potential in the integration, lightness and miniaturization applications of pulse power devices. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a micro-morphology diagram of the two-dimensional sheet-shaped Na 0.5 Bi 4.5 Ti4O 15 filler prepared in step one of the embodiment;

[0027] Figure 2 is a breakdown field strength hysteresis loop diagram, (a) P(VDF-HFP) film and NBT-P(VDF-HFP) film, (b) PEI film and NBT-PEI film;

[0028] Figure 3The topography and element energy distribution of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example One, (a) cross-section microtopography, (b) energy distribution of characteristic element F of NBT-P(VDF-HFP) film, (c) energy distribution of characteristic element O of NBT-PEI film;

[0029] Figure 4 The electric hysteresis loop of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example One under the breakdown field strength;

[0030] Figure 5 The charge-discharge rate diagram of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example One;

[0031] Figure 6 The electric hysteresis loop of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example Two under the breakdown field strength;

[0032] Figure 7 The electric hysteresis loop of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example Three under the breakdown field strength. DETAILED DESCRIPTION

[0033] The technical solution of the present application is not limited to the following specific embodiments, but also includes any combination between the specific embodiments.

[0034] Specific embodiment one: the double-layer structure polymer-based composite material for dielectric energy storage of the present embodiment is a double-layer structure polymer-based composite material composed of a PEI-based composite material film and a PVDF-based composite material film;

[0035] The PEI-based composite material film is prepared from a PEI-based polymer and a two-dimensional sheet-shaped filler; the PVDF-based composite material film is prepared from a PVDF-based polymer and a two-dimensional sheet-shaped filler;

[0036] The PEI-based polymer is one or a combination of several of polyetherimide, polyimide and vulcanized polyetherimide;

[0037] The PVDF-based polymer is one or a combination of several of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and terpolymer P(VDF-TrFE-CTFE);

[0038] The two-dimensional sheet-shaped filler is one or a combination of several of Na 0.5 Bi 4.5 Ti4O 15 , Bi4Ti3O 12 and SrBi2Ta2O9;

[0039] The thickness of the two-dimensional sheet filler is 0.5-5 μm; the two-dimensional sheet filler accounts for 0.1-2.0% of the mass of the PEI-based polymer in the PEI-based composite film; and the two-dimensional sheet filler accounts for 0.1-2.0% of the mass of the PVDF-based polymer in the PVDF-based composite film.

[0040] The discharge energy storage density U of the double-layer structure polymer-based composite for dielectric energy storage dis ≥20 J / cm 3 , and the energy storage efficiency η is >70%.

[0041] The specific embodiment has the following advantages:

[0042] The specific embodiment is based on a synergistic regulation strategy of two-dimensional materials for space charge blocking effect and double-layer structure interface effect for charge binding, and a polymer-based composite with high discharge energy storage density and high energy storage efficiency is prepared, the discharge energy storage density U of the double-layer structure polymer-based composite for dielectric energy storage dis ≥20 J / cm 3 , the energy storage efficiency η is >70%, and the comprehensive energy storage performance is better than most of the polymer-based composites reported at present. In addition, under the conditions of an electrical resistance R of 300 Ω and an electric field of 3000 kV / cm, the discharge rate t of the double-layer structure polymer-based composite for dielectric energy storage 0.9 ≤50 ns, and the power density P D is greater than 50 MW / cm 3 .

[0043] The specific embodiment has a simple and efficient preparation process, is conducive to industrialized mass production, and provides a design and preparation idea for the continued research and development of polymer-based energy storage capacitors with high energy storage density, excellent energy storage stability, and a relatively wide practical temperature range. At the same time, the polymer-based capacitor as an energy storage element shows great application potential in the integration, lightness, and miniaturization applications of pulse power devices.

[0044] Specific embodiment two: The difference between this embodiment and specific embodiment one is that the thickness ratio of the PEI-based composite film to the PVDF-based composite film is 1:(0.2-3.0); the thickness of the two-dimensional sheet filler is 1-2 μm; the two-dimensional sheet filler accounts for 0.25-1.0% of the mass of the PEI-based polymer in the PEI-based composite film; and the two-dimensional sheet filler accounts for 0.25-1.0% of the mass of the PVDF-based polymer in the PVDF-based composite film. The rest is the same as specific embodiment one.

[0045] Specific embodiment three: A preparation method of a double-layer structure polymer-based composite for dielectric energy storage, which is completed according to the following steps:

[0046] Preparation of the two-dimensional sheet-shaped filler:

[0047] According to the stoichiometric ratio of the chemical formula of the two-dimensional sheet-shaped filler, the raw materials are weighed, and NaCl is weighed according to the mass ratio of raw materials to molten salt of 1:(1.5-15); the raw materials and NaCl are ball-milled to obtain a mixture, the mixture is calcined at a temperature of 800-1050℃ for 1-8h, and finally washed and dried to obtain the two-dimensional sheet-shaped filler;

[0048] The sheet diameter of the two-dimensional sheet-shaped filler is 0.5-5μm; the two-dimensional sheet-shaped filler is Na 0.5 Bi 4.5 Ti4O 15 , Bi4Ti3O 12 , and SrBi2Ta2O9, or a combination of several thereof;

[0049] II. Preparation of PEI-based composite solution and PVDF-based composite solution:

[0050] PEI-based composite solution and PVDF-based composite solution are prepared by using PEI-based polymer, PVDF-based polymer, two-dimensional sheet-shaped filler, and N-methyl pyrrolidone, respectively;

[0051] The PEI-based polymer is one or a combination of several of polyetherimide, polyimide, and vulcanized polyetherimide;

[0052] The PVDF-based polymer is one or a combination of several of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and terpolymer P(VDF-TrFE-CTFE);

[0053] The two-dimensional sheet-shaped filler in the PEI-based composite solution accounts for 0.1%-2.0% of the mass of the PEI-based polymer; the two-dimensional sheet-shaped filler in the PVDF-based composite solution accounts for 0.1%-2.0% of the PVDF-based polymer;

[0054] III. Preparation of double-layer structure polymer-based composite:

[0055] The PEI-based composite solution is cast on a substrate and vacuum dried to obtain a PEI-based composite film, then the PVDF-based composite solution is cast on the PEI-based composite film and vacuum dried, and finally the formed double-layer structure polymer-based composite is removed from the substrate, thus completing the preparation method of the double-layer structure polymer-based composite for dielectric energy storage.

[0056] In the third step of the embodiment, since the PEI-based polymer is a thermosetting polymer and is insoluble in the PVDF-based composite material solution, the PVDF-based composite material solution is cast on the PEI-based composite material film as a top film, and the PEI-based composite material film is used as a bottom film.

[0057] The fourth embodiment is different from the third embodiment in that the purity of the raw materials and NaCl in the first step is ≥ 99.0%. The other steps are the same as those in the third embodiment.

[0058] The fifth embodiment is different from the third or fourth embodiment in that the ball milling in the first step is specifically performed as follows: using ethanol as a ball milling medium, the ball milling is performed at a rotation speed of 800 r / min to 1200 r / min for 12 h to 24 h. The other steps are the same as those in the third or fourth embodiment.

[0059] The sixth embodiment is different from the third to fifth embodiments in that the concentration of the PEI-based polymer in the PEI-based composite material solution in the second step is 0.1 g / mL to 0.2 g / mL, and the concentration of the PVDF-based polymer in the PVDF-based composite material solution in the second step is 0.1 g / mL to 0.2 g / mL. The other steps are the same as those in the third to fifth embodiments.

[0060] The seventh embodiment is different from the third to sixth embodiments in that the PEI-based composite material solution and the PVDF-based composite material solution are prepared by using the PEI-based polymer, the PVDF-based polymer, the two-dimensional sheet-shaped filler, and N-methyl pyrrolidone, and the preparation is specifically performed as follows:

[0061] ①The PEI-based polymer is added to N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a PEI-based polymer solution;

[0062] ②The PVDF-based polymer is added to N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a PVDF-based polymer solution;

[0063] ③The two-dimensional sheet-shaped filler is added to N-methyl pyrrolidone and ultrasonically dispersed at a power of 500 W to 700 W for 10 min to 20 min to obtain a two-dimensional sheet-shaped filler dispersion liquid;

[0064] (4) mixing the PEI-based polymer solution with the two-dimensional sheet-shaped filler dispersion liquid at a rotation speed of 1000 r / min to 1500 r / min for 10 h to 14 h to obtain a PEI-based composite material solution; mixing the PVDF-based polymer solution with the two-dimensional sheet-shaped filler dispersion liquid at a rotation speed of 1000 r / min to 1500 r / min for 10 h to 14 h to obtain a PVDF-based composite material solution. The other steps are the same as those in Embodiment 3 to 6.

[0065] The purpose of the ultrasonic dispersion in step (3) of the present embodiment is to separate the two-dimensional sheet-shaped filler sufficiently and avoid agglomeration.

[0066] Embodiment 8: The present embodiment is different from any one of Embodiments 3 to 7 in that the casting in step (3) is performed by using a casting machine at a casting speed of 2 cm / s to 4 cm / s. The other steps are the same as those in Embodiments 3 to 7.

[0067] Embodiment 9: The present embodiment is different from any one of Embodiments 3 to 8 in that the two-dimensional sheet-shaped filler in step (1) has a sheet diameter of 1 μm to 2 μm; the two-dimensional sheet-shaped filler in the PEI-based composite material solution in step (2) accounts for 0.25% to 1.0% of the mass of the PEI-based polymer; the two-dimensional sheet-shaped filler in the PVDF-based composite material solution in step (2) accounts for 0.25% to 1.0% of the mass of the PVDF-based polymer; and the thickness ratio of the PEI-based composite material film to the PVDF-based composite material film in step (3) is 1:(0.2 to 3.0). The other steps are the same as those in Embodiments 3 to 8.

[0068] Embodiment 10: The present embodiment is different from any one of Embodiments 3 to 9 in that the double-layer structured polymer-based composite material prepared in step (3) has a thickness of 7 μm to 10 μm. The other steps are the same as those in Embodiments 3 to 9.

[0069] The beneficial effects of the present application are verified by the following examples:

[0070] Example 1:

[0071] A preparation method of a double-layer structured polymer-based composite material for dielectric energy storage is performed according to the following steps:

[0072] (1) two-dimensional sheet-shaped Na 0.5 Bi 4.5 Ti4O 15 Preparation of the filler:

[0073] According to Na 0.5 Bi 4.5 Ti4O 15The two-dimensional flaky Na 0.5 Bi 4.5 Ti4O 15 filler is prepared by the following steps: taking Na2CO3, Bi2O3 and TiO2 as raw materials, taking NaCl according to the mass ratio of raw materials to molten salt as 1:15; mixing the raw materials and NaCl by ball milling under the condition of 900 r / min for 24 h, taking the mixture, calcining the mixture under the condition of 850 ℃ for 1 h, and finally washing and drying to obtain the two-dimensional flaky Na 0.5 Bi 4.5 Ti4O 15 filler.

[0074] The two-dimensional flaky Na 0.5 Bi 4.5 Ti4O 15 filler has a flake diameter of 1 μm to 2 μm.

[0075] II. Preparation of NBT-PEI solution and NBT-P(VDF-HFP) solution:

[0076] ①Polyetherimide is added into N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a PEI solution;

[0077] ②Polyvinylidene hexafluoropropylene is added into N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a P(VDF-HFP) solution;

[0078] ③The two-dimensional flaky Na 0.5 Bi 4.5 Ti4O 15 filler is added into N-methyl pyrrolidone and ultrasonically dispersed for 20 min to obtain a two-dimensional flaky NBT dispersion;

[0079] ④The PEI solution is mixed with the two-dimensional flaky NBT dispersion under the condition of 1500 r / min for 12 h to obtain a NBT-PEI solution; the P(VDF-HFP) solution is mixed with the two-dimensional flaky NBT dispersion under the condition of 1500 r / min for 12 h to obtain a NBT-P(VDF-HFP) solution;

[0080] The concentration of polyetherimide in the NBT-PEI solution is 0.16 g / mL; the concentration of polyvinylidene hexafluoropropylene in the NBT-P(VDF-HFP) solution is 0.16 g / mL; the two-dimensional flaky Na 0.5 Bi 4.5 Ti4O 15 filler accounts for 0.75% of the mass of polyetherimide; the two-dimensional flaky Na 0.5 Bi 4.5 Ti4O15 The filler accounts for 0.75% of the mass of polyvinylidene fluoride-hexafluoropropylene;

[0081] III. Preparation of bilayer NBT-PEI / NBT-P (VDF-HFP) composite material:

[0082] Under the condition of a casting speed of 3 cm / s, NBT-PEI solution was cast onto a glass substrate using a casting machine, and then vacuum dried at a temperature of 70°C for 12 h to obtain an NBT-PEI film. Then, under the condition of a casting speed of 3 cm / s, NBT-P (VDF-HFP) solution was cast onto the NBT-PEI film using a casting machine, and then vacuum dried at a temperature of 70°C for 12 h. Finally, the bilayer structure NBT-PEI / NBT-P (VDF-HFP) composite material formed was removed from the substrate, which is a bilayer structure polymer-based composite material for dielectric energy storage.

[0083] The purity of Na2CO3 mentioned in step one is 99.5%; the purity of Bi2O3 mentioned in step one is ≥99.9%; the purity of TiO2 mentioned in step one is ≥99.0%; and the purity of NaCl mentioned in step one is ≥99.5%.

[0084] The bilayer polymer-based composite material for dielectric energy storage prepared above is a bilayer polymer-based composite material with a thickness of 8 μm composed of an NBT-PEI film and an NBT-P (VDF-HFP) film; the thickness ratio of the NBT-PEI film to the NBT-P (VDF-HFP) film is 0.7:0.3.

[0085] The two-dimensional sheet-like Na 0.5 Bi 4.5 Ti4O 15 The filler has a sheet diameter of 1 μm to 2 μm; the two-dimensional sheet-like Na in the NBT-PEI film 0.5 Bi 4.5 Ti4O 15 The filler accounts for 0.75% of the mass of polyetherimide; the two-dimensional sheet-like Na in the NBT-P(VDF-HFP) film. 0.5 Bi 4.5 Ti4O 15 The filler accounts for 0.75% of the mass of polyvinylidene fluoride-hexafluoropropylene;

[0086] The bilayer polymer matrix composite material for dielectric energy storage prepared in Example 1 was covered with Au electrodes of 2 mm diameter on both sides for measuring its electrical properties: the breakdown electric field E of the bilayer polymer matrix composite material for dielectric energy storage. b It is 8283 kV / cm, and the discharge energy storage density Udis = 25.0 J / cm 3 , the discharge rate t of the double-layer structure polymer-based composite material for dielectric energy storage is 46.6 ns, the power density P is 62.2 MW / cm 0.9 D 3 .

[0087] Figure 1 The micro-morphology of the two-dimensional sheet-like Na 0.5 Bi 4.5 Ti4O 15 filler prepared in step one of the embodiment is shown in the figure. As can be seen from the figure, the two-dimensional sheet-like NBT prepared by the molten salt method has a regular shape and a size of about 1 μm to 2 μm.

[0088] The PEI film, P(VDF-HFP) film, NBT-PEI film and NBT-P(VDF-HFP) film were respectively prepared on a substrate by the casting method of step three of the embodiment, and the thickness of the PEI film, P(VDF-HFP) film, NBT-PEI film and NBT-P(VDF-HFP) film was 8 μm, and Au electrodes with a diameter of 2 mm were covered on both sides of the films for measuring the electrical properties.

[0089] Figure 2 The figure is the hysteresis loop at the breakdown field strength, (a) P(VDF-HFP) film and NBT-P(VDF-HFP) film, (b) PEI film and NBT-PEI film. As can be seen from the figure, after the introduction of the two-dimensional sheet-like NBT, the breakdown field strength E b of the NBT-P(VDF-HFP) film is increased from 4986 kV / cm to 6084 kV / cm. The breakdown field strength E b of the NBT-PEI film is increased from 5467 kV / cm to 7484 kV / cm. Moreover, due to the higher ε r of the two-dimensional sheet-like NBT, the polarization strength of the NBT-PEI film and NBT-P(VDF-HFP) film at the same field strength is also increased. This all indicates that the two-dimensional sheet-like NBT plays an important role in improving the E b and polarization strength of the composite material. Therefore, the energy storage density is calculated by the following formula:

[0090]

[0091] wherein U dis is the discharge energy storage density, unit J / cm 3 ; U tot is the total energy storage density, unit J / cm 3 ; η is the energy storage efficiency; P​​max Pmax is the maximum polarization strength, unit μC / cm 2 Pmax is the maximum polarization strength, unit μC / cm r Pmax is the maximum polarization strength, unit μC / cm 2 E is the applied electric field, unit kV / cm. It can be calculated that the discharge energy storage density U dis of NBT-P(VDF-HFP) film is increased from 9.8 J / cm 3 to 15.5 J / cm 3 , and the energy storage efficiency η is increased from 60.7% to 62.4%; the discharge energy storage density U dis of NBT-PEI film is increased from 8.2 J / cm 3 to 16.7 J / cm 3 , and the energy storage efficiency η is increased from 90.1% to 92.3%; all of which show that the introduction of NBT plays an important role in improving the overall energy storage performance of the composite material.

[0092] Figure 3 Figure 2 is a morphology and element energy distribution diagram of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example 1, (a) cross-sectional micro-morphology diagram, (b) energy distribution diagram of characteristic element F of NBT-P(VDF-HFP) film, (c) energy distribution diagram of characteristic element O of NBT-PEI film. From Figure 3 (a) can be seen that NBT-P(VDF-HFP) and NBT-PEI are respectively located in the upper and lower layers of the figure in the double-layer composite material, and the two-layer composite material is tightly combined without voids. Figure 3 (b) and (c) can be seen that the characteristic element F representing the NBT-P(VDF-HFP) layer and the characteristic element O representing the NBT-PEI are uniformly dispersed in each layer, proving that the entire double-layer structure is uniform in quality, providing a basis for its superior energy storage performance.

[0093] Figure 4 Figure 3 is the electric hysteresis loop of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example 1 under the breakdown field strength; from the figure, it can be seen that the breakdown field strength E b of the double-layer structure NBT-PEI / NBT-P(VDF-HFP) composite material is 8283 kV / cm, and it can be calculated that the discharge energy storage density U dis is 25.0 J / cm 3 , and the energy storage efficiency η is 81.2%.

[0094] Figure 5 Figure 4 is the charge and discharge rate diagram of the double-layer structure polymer-based composite material for dielectric energy storage prepared in Example 1; from the figure, it can be seen that under the condition of resistance R being 300 Ω and electric field being 3000 kV / cm, the discharge rate t 0.9was 46.6 ns, and the power density P D was 62.2 MW / cm 3 .

[0095] Example Two: This example is different from Example One in that the thickness ratio of the NBT-PEI film to the NBT-P(VDF-HFP) film was 0.5:0.5. Otherwise, it is the same as Example One.

[0096] The double-layer structured polymer-based composite material for dielectric energy storage prepared in Example Two was covered with Au electrodes with a diameter of 2 mm on both sides for measuring electrical properties: Figure 6 is the hysteresis loop of the double-layer structured polymer-based composite material for dielectric energy storage prepared in Example Two under a breakdown field strength; the breakdown electric field E b was 7791 kV / cm, and the discharge energy storage density U dis = 23.6 J / cm 3 , and the energy storage efficiency η = 76.1%.

[0097] Example Three: This example is different from Example One in that the thickness ratio of the NBT-PEI film to the NBT-P(VDF-HFP) film was 0.3:0.7. Otherwise, it is the same as Example One.

[0098] The double-layer structured polymer-based composite material for dielectric energy storage prepared in Example Three was covered with Au electrodes with a diameter of 2 mm on both sides for measuring electrical properties: Figure 7 is the hysteresis loop of the double-layer structured polymer-based composite material for dielectric energy storage prepared in Example Three under a breakdown field strength; the breakdown electric field E b was 7082 kV / cm, and the discharge energy storage density U dis = 21.5 J / cm 3 , and the energy storage efficiency η = 73.4%.

Claims

1. A double-layered structure polymer-based composite for dielectric energy storage, characterized in that It is a double-layer structure polymer-based composite material composed of a PEI-based composite material film and a PVDF-based composite material film; the thickness of the double-layer structure polymer-based composite material is 7 μm-10 μm; the thickness ratio of the PEI-based composite material film to the PVDF-based composite material film is 1:(0.2-3.0); The PEI-based composite material film is prepared from a PEI-based polymer and a two-dimensional sheet-shaped filler; and the PVDF-based composite material film is prepared from a PVDF-based polymer and a two-dimensional sheet-shaped filler; The PEI-based polymer is one or a combination of several of polyetherimide, polyimide and vulcanized polyetherimide; The PVDF-based polymer is one or a combination of several of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and terpolymer P(VDF-TrFE-CTFE); The two-dimensional sheet-like filler is Na 0.5 Bi 4.5 Ti4O 15 , Bi4Ti3O 12 and SrBi2Ta2O9; The two-dimensional sheet-shaped filler has a sheet diameter of 0.5 µm-5 µm; the two-dimensional sheet-shaped filler accounts for 0.1 %-2.0 % of the mass of the PEI-based polymer in the PEI-based composite material film; and the two-dimensional sheet-shaped filler accounts for 0.1 %-2.0 % of the mass of the PVDF-based polymer in the PVDF-based composite material film; The discharge energy storage density of the double-layer structure polymer-based composite material for dielectric energy storage U dis ≥20 J / cm 3 , energy storage efficiency The thickness ratio of the PEI-based composite material film to the PVDF-based composite material film is 1:(0.2-3.0); the two-dimensional sheet-shaped filler has a sheet diameter of 1 µm-2 µm; the two-dimensional sheet-shaped filler accounts for 0.25 %-1.0 % of the mass of the PEI-based polymer in the PEI-based composite material film; and the two-dimensional sheet-shaped filler accounts for 0.25 %-1.0 % of the mass of the PVDF-based polymer in the PVDF-based composite material film. >70 %; under the condition that the resistance R is 300 Ω and the electric field is 3000 kV / cm, the discharge rate t of the double-layer structure polymer-based composite material for dielectric energy storage 0.9 ≤50 ns, power density P D >50 MW / cm 3 .

2. A double layer structured polymer matrix composite for dielectric energy storage according to claim 1, characterized in that It is carried out in the following steps:

3. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 1 wherein Preparation of a two-dimensional sheet-shaped filler: The raw materials are weighed according to the stoichiometric ratio of the chemical formula of the two-dimensional sheet-shaped filler, and NaCl is weighed according to a mass ratio of raw materials to molten salt of 1:(1.5-15); the raw materials and NaCl are ball-milled and mixed to obtain a mixture, the mixture is calcined at a temperature of 800 ℃-1050 ℃ for 1 h-8 h, and finally washed and dried to obtain the two-dimensional sheet-shaped filler; Preparation of PEI-based composite material solution and PVDF-based composite material solution: The two-dimensional sheet-shaped filler has a sheet diameter of 0.5 µm to 5 µm; the two-dimensional sheet-shaped filler is Na 0.5 Bi 4.5 Ti4O 15 , Bi4Ti3O 12 and SrBi2Ta2O9, or a combination of several thereof; PEI-based composite material solution and PVDF-based composite material solution are respectively prepared by using PEI-based polymer, PVDF-based polymer, two-dimensional sheet-shaped filler and N-methyl pyrrolidone; The PEI-based polymer is one or a combination of several of polyetherimide, polyimide and vulcanized polyetherimide; The PVDF-based polymer is one or a combination of several of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene and terpolymer P(VDF-TrFE-CTFE); The two-dimensional sheet-shaped filler accounts for 0.1 %-2.0 % of the mass of the PEI-based polymer in the PEI-based composite material solution; and the two-dimensional sheet-shaped filler accounts for 0.1 %-2.0 % of the mass of the PVDF-based polymer in the PVDF-based composite material solution; Preparation of a double-layer structure polymer-based composite material: ​ The PEI-based composite solution is cast on a substrate and vacuum dried to obtain a PEI-based composite film, then the PVDF-based composite solution is cast on the PEI-based composite film and vacuum dried, and finally the formed double-layer structure polymer-based composite is removed from the substrate, i.e. the preparation method of the double-layer structure polymer-based composite for dielectric energy storage is completed.

4. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein The purity of the raw material and NaCl in step one is all ≥ 99.0%.

5. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein The ball milling mixing in step one is specifically performed by the following steps: taking ethanol as the ball milling medium, under the condition that the rotating speed is 800 r / min-1200 r / min, ball milling mixing for 12 h-24 h.

6. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein The concentration of the PEI-based polymer in the PEI-based composite solution in step two is 0.1 g / mL-0.2 g / mL; the concentration of the PVDF-based polymer in the PVDF-based composite solution in step two is 0.1 g / mL-0.2 g / mL.

7. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein the said process is characterized by The PEI-based composite solution and the PVDF-based composite solution are respectively prepared by using the PEI-based polymer, the PVDF-based polymer, the two-dimensional sheet-shaped filler and N-methyl pyrrolidone in step two, which is specifically performed by the following steps: ①The PEI-based polymer is added into N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a PEI-based polymer solution; ②The PVDF-based polymer is added into N-methyl pyrrolidone and stirred until the particles are completely dissolved to obtain a PVDF-based polymer solution; ③The two-dimensional sheet-shaped filler is added into N-methyl pyrrolidone and ultrasonically dispersed for 10 min-20 min under the condition that the power is 500 W-700 W to obtain a two-dimensional sheet-shaped filler dispersion liquid; ④The PEI-based polymer solution and the two-dimensional sheet-shaped filler dispersion liquid are mixed for 10 h-14 h under the condition that the rotating speed is 1000 r / min-1500 r / min to obtain a PEI-based composite solution; the PVDF-based polymer solution and the two-dimensional sheet-shaped filler dispersion liquid are mixed for 10 h-14 h under the condition that the rotating speed is 1000 r / min-1500 r / min to obtain a PVDF-based composite solution.

8. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein The casting in step three is specifically performed by using a casting machine under the condition that the casting speed is 2 cm / s-4 cm / s.

9. A process for the preparation of a double layer structured polymer matrix composite for dielectric energy storage as claimed in claim 3, wherein The flake diameter of the two-dimensional sheet-shaped filler in step one is 1 µm-2 µm; the two-dimensional sheet-shaped filler accounts for 0.25 %-1.0 % of the mass of the PEI-based polymer in the PEI-based composite solution in step two; the two-dimensional sheet-shaped filler accounts for 0.25 %-1.0 % of the mass of the PVDF-based polymer in the PVDF-based composite solution in step two.

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