Polypropylene-based energy storage dielectric material, and preparation method and application thereof

Abstract

The application discloses a polypropylene-based energy storage dielectric material and a preparation method and application thereof. The preparation method comprises the following steps: after a polypropylene substrate and a (meth) acrylic acid fluorine-containing ester monomer are pre-swollen in a solvent, polymerization reaction is carried out through an initiator, and post-treatment is carried out on a grafted polymer to obtain a (meth) acrylic acid fluorine-containing ester functionalized polypropylene. The application adopts a suspension polymerization method, introduces a fluorine-containing group into a polypropylene structure to induce electron cloud distribution, promotes crystalline domain aggregation to improve crystallinity, adjusts dielectric constant, loss factor, leakage current and breakdown electric field of a polymer material, so that energy storage density and efficiency of a polymer dielectric are controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thin film capacitors, in particular to a polypropylene-based energy storage dielectric material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of ultra-high voltage transmission, electromagnetic equipment, new energy vehicles, national defense and military industry, the demand for pulse capacitor dielectric polymer film is increasing year by year.

[0003] Among the dielectric polymer materials for energy storage, high-dielectric polymer represented by polyvinylidene fluoride (PVDF) will cause high energy loss due to the strong coupling-induced dipole polarization relaxation of ferroelectric phase; glassy polymer represented by styrene-methyl methacrylate copolymer (MS) exhibits high energy loss due to dipole polarization relaxation, and is difficult to process into film; special engineering plastic polymer represented by polyaryletherketone (PAEK) is difficult to be widely applied due to its high cost.

[0004] Polypropylene (PP) is one of the general synthetic materials, which is widely used in power electronics, capacitors, high-voltage transmission, automobiles, biomedicine and other fields. Compared with other general plastics, it has the advantages of low dielectric loss, high dielectric strength, good processability and low price. The most advanced commercial polymer dielectric is biaxially oriented polypropylene (BOPP) film, which has a low dielectric constant (~ 2.2) and a maximum discharge energy density of about 4 J / cm3, resulting in the inability to meet the growing demand for high energy storage capacitors in many fields. Therefore, it is urgent to develop a new PP-based polymer with higher energy density, better mechanical properties and better processability to replace BOPP. Weak breakdown strength and low dielectric constant are the bottleneck of PP-based polymer energy storage performance, and the current solution is mainly doping coating and grafting modification. Doping and coating inorganic nanoparticles in PP can improve the dielectric constant and breakdown strength to some extent, but the interface polarization between the doped particles and the coating layer leads to high dielectric and energy loss, and the improvement effect of doping and coating is limited. In addition, due to the good compatibility and dispersion of grafted compounds in the polymer matrix, chemical grafting can effectively overcome the shortcomings of doping and coating. In theory, the introduction of polar groups can improve the energy storage density by increasing the dielectric constant. However, the introduction of polar groups will destroy the regularity of PP, resulting in a significant decrease in breakdown strength, which limits the increase of energy storage density. That is, the dielectric material cannot meet the characteristics of high energy storage density and high discharge efficiency (low loss) at the same time. In addition, the existing PP-based modified polymers cannot realize large-scale production and processing.

[0005] In summary, no matter PVDF-based polymer with high dielectric constant or BOPP with high breakdown electric field, or glassy polymer and special engineering plastic polymer, there are insurmountable shortcomings as high energy storage dielectric. Therefore, it is of great significance to develop polymer dielectric material with "double high" characteristics and large-scale production and processing. SUMMARY

[0006] In view of the above technical problems, the present application provides a polypropylene-based energy storage dielectric material and a preparation method and application thereof, so as to improve the energy storage density of polymer dielectric and reduce the loss.

[0007] To achieve the above-mentioned object, the technical scheme adopted by the present application is as follows:

[0008] On the one hand, the present application provides a preparation method of polypropylene-based energy storage dielectric material, comprising the following steps:

[0009] Polymerizing polypropylene, (meth) acrylic acid fluorine-containing ester monomer and initiator in a suspension system.

[0010] In the technical scheme of the present application, the polymerization reaction is heterogeneous polymerization.

[0011] In the technical scheme of the present application, the (meth) acrylic acid fluorine-containing ester monomer is selected from any one or several of methacrylic acid fluorine-containing ester monomer and acrylic acid fluorine-containing ester monomer, and is preferably one or several of the following monomers: (meth) acrylic acid trifluoroethyl ester, (meth) acrylic acid trifluoropentyl ester, (meth) acrylic acid pentafluorobenzyl ester, (meth) acrylic acid pentafluorophenyl ester, (meth) acrylic acid pentafluoropropyl ester, (meth) acrylic acid heptafluorobutyl ester, (meth) acrylic acid heptafluoroisobutyl ester, (meth) acrylic acid tridecafluorooctyl ester.

[0012] In the technical scheme of the present application, the initiator is selected from any one or several of oil-soluble initiator and water-soluble initiator; wherein the oil-soluble initiator is selected from at least one of azo initiator and peroxide initiator; the azo initiator can be listed as azobisisobutyronitrile, azobisisoheptyl nitrile, azobisisopentyl nitrile, azobiscyclohexyl methyl nitrile and azobisdimethyl isobutyrate initiator; the peroxide initiator can be listed as dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, etc.; the water-soluble initiator can be listed as persulfate, redox initiation system, azobisdimethylformamide hydrochloride, azobisdimethylimidazole hydrochloride, azobisdimethylimidazole and azobis-dicyanopentanoic acid, etc.

[0013] As a preferred embodiment, the solvent of the suspension system is selected from any one or several of an oily solvent and an aqueous solvent; the oily solvent can be exemplified by chlorobenzene, o-dichlorobenzene, toluene, xylene, acetonitrile, etc.; the aqueous solvent can be exemplified by deionized water, ultrapure water, tap water, etc.

[0014] In the technical solution of the present application, the use amount of the polypropylene and the (meth)acrylic acid fluorine-containing ester monomer is not particularly limited, and the mass ratio is preferably 1:0.1-0.5;

[0015] In some specific embodiments, the polypropylene is polypropylene granules, polypropylene powder, etc.

[0016] As a preferred embodiment, the mass of the initiator is 1%-10% of the mass of the polypropylene;

[0017] Preferably, the temperature of the polymerization reaction is 70-90°C;

[0018] Preferably, the time of the polymerization reaction is 1-8h.

[0019] As a preferred embodiment, the polymerization reaction includes a pre-swelling operation before the polymerization reaction;

[0020] In some specific embodiments, the pre-swelling is achieved by vigorous stirring at 70-90°C for 1-2h; the pre-swelling can increase the volume of the polymer, which is beneficial to the full reaction.

[0021] In some specific embodiments, the polymerization reaction is carried out in an inert atmosphere.

[0022] In some specific embodiments, the preparation method further includes a post-treatment; the post-treatment includes suction filtration, washing, and drying;

[0023] In some specific embodiments, the solvent for the washing is acetone, and more preferably anhydrous acetone.

[0024] In another aspect, the present application provides a polypropylene-based energy storage dielectric material obtained by the above preparation method.

[0025] In another aspect, the present application provides a polypropylene-based energy storage dielectric film, which is prepared from the above polypropylene-based energy storage dielectric material.

[0026] As a preferred embodiment, the polypropylene-based energy storage dielectric film is prepared from a solution of the above polypropylene-based energy storage dielectric material on a substrate by a hot-pressing fusion method or a flow extrusion method;

[0027] Preferably, the temperature of the hot-pressing fusion method or the flow extrusion method is 200-250°C;

[0028] Preferably, the solvent in the solution of the polypropylene-based energy storage dielectric material is selected from any one or several of an oily solvent and an aqueous solvent;

[0029] Preferably, the preparation further comprises annealing;

[0030] Preferably, the temperature of the annealing is 100-140℃;

[0031] Preferably, the time of the annealing is 24-72h;

[0032] In another aspect, the present application provides the use of the above-mentioned polypropylene-based energy storage dielectric material and the above-mentioned polypropylene-based energy storage dielectric film in the preparation of a thin film capacitor.

[0033] The above technical solution has the following advantages or beneficial effects:

[0034] The polypropylene-based energy storage dielectric material provided by the present application is prepared by using a suspension polymerization method, and a polypropylene substrate and a (methyl) acrylic acid fluorine-containing ester monomer are prepared under the action of an initiator. The polypropylene-based energy storage dielectric material prepared by the present application induces electron cloud distribution by introducing a fluorine-containing group into the polypropylene structure, promotes crystalline domain aggregation to improve crystallinity, adjusts the dielectric constant and breakdown electric field of the polymer material, and thus manipulates the energy storage density and efficiency of the polymer dielectric. The preparation method provided by the present application uses suspension polymerization, the reaction is controllable, the operation is simple, the practicability is strong, and the method is easy to industrialize, replicate and popularize. The type and molecular weight of the monomer can be changed according to actual needs, and various polymers can be prepared. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The main chemical reactions occurring in the preparation of the polypropylene-based energy storage dielectric material PP-g-TFEMA in Examples 1-3 of the present application.

[0036] Figure 2 The FT-IR spectrum of TFEMA2 in Example 1 of the present application.

[0037] Figure 3 The DSC spectrum of TFEMA2 in Example 1 of the present application after 48 hours of annealing. 1 H NMR spectrum.

[0038] Figure 4 The DSC spectrum of TFEMA2 in Application Example 2 of the present application after 48 hours of annealing.

[0039] Figure 5 The graph of the dielectric constant of the polymer film measured in Application Example 3 of the present application versus frequency.

[0040] Figure 6Weibull distribution plot of the polymer film measured in Example 3 of the present application.

[0041] Figure 7 Energy storage performance plot of the polymer film measured in Example 3 of the present application. DETAILED DESCRIPTION

[0042] The following examples are merely exemplary of some of the applications of the present application and therefore are not intended to limit the scope of the application being claimed. The following detailed description is not intended to limit the scope of the application as claimed. Various embodiments of the application can be derived from the embodiments of the application, without resorting to creating inventive labor, and all of these embodiments fall within the scope of the present application.

[0043] In the present application, all the equipment and raw materials, etc. can be purchased from the market or commonly used in the industry, unless otherwise specified. The methods in the following examples are all conventional methods in the art, unless otherwise specified.

[0044] Example 1 Polypropylene-based energy storage dielectric material: poly(propylene-trifluoroethyl methacrylate) polymer

[0045] 100 g of polypropylene (pellets, purchased from Zhongyuan Petrochemical, product number YY12251321A) was dispersed in 4 kg of water;

[0046] 10 g of trifluoroethyl methacrylate (TFEMA) and 4 g of dibenzoyl peroxide (BPO) were dispersed in 86 g of dimethylbenzene;

[0047] The above two solutions were transferred to a reaction kettle (under a nitrogen atmosphere throughout, oxygen and moisture were removed by an uninterrupted vacuum-nitrogen circulation process in advance), and after being heated to 80°C, the system was stirred vigorously for 1 hour to complete the pre-swelling; after the temperature of the system was stabilized, the continuous reaction was carried out for 4 hours to obtain the crude product of PP-g-TFEMA;

[0048] The filter cake was filtered and washed with excess anhydrous acetone; then the poly(propylene-trifluoroethyl methacrylate) polymer (PP-g-TFEMA polypropylene-based energy storage dielectric material, TFEMA2) was collected after drying overnight in a vacuum oven at 50°C.

[0049] In this example, the main chemical reaction process of the polymerization reaction is as shown in Figure 1 .

[0050] In this example, the FT-IR spectrum of PP-g-TFEMA is as shown in Figure 2 .

[0051] In this embodiment, the molar ratio of TFEMA unit to PP unit in PP-g-TFEMA is 9:250 according to the experimental characterization, and the polymer has a molecular weight of 1.5 x 105. 1 The H NMR spectrum is shown in Figure 3 .

[0052] Example 2 Polypropylene-based energy storage dielectric material: poly(propylene-trifluoroethyl methacrylate) polymer

[0053] 100 g of polypropylene (pellets, purchased from Zhongyuan Petrochemical, product number YY12251321A) was dispersed in 4 kg of water;

[0054] 20 g of trifluoroethyl methacrylate (TFEMA) and 4 g of dibenzoyl peroxide (BPO) were dispersed in 86 g of dimethylbenzene;

[0055] The above two solutions were transferred to a reaction kettle (under a nitrogen atmosphere throughout, and oxygen and moisture were removed by an uninterrupted vacuum-nitrogen circulation process in advance), and after being heated to 80°C, they were stirred vigorously for 1 hour to complete the pre-swelling. After the temperature of the system was stabilized, continuous reaction was carried out for 4 hours to obtain a crude product of PP-g-TFEMA;

[0056] After filtration, the filter cake was washed with excess anhydrous acetone; then, after drying overnight in a vacuum oven at 50°C, poly(propylene-trifluoroethyl methacrylate) polymer (PP-g-TFEMA polypropylene-based energy storage dielectric material) was collected.

[0057] Example 3

[0058] 100 g of polypropylene (pellets, purchased from Zhongyuan Petrochemical, product number YY12251321A) was dispersed in 4 kg of water;

[0059] 30 g of trifluoroethyl methacrylate (TFEMA) and 4 g of dibenzoyl peroxide (BPO) were dispersed in 86 g of dimethylbenzene;

[0060] The above two solutions were transferred to a reaction kettle (under a nitrogen atmosphere throughout, and oxygen and moisture were removed by an uninterrupted vacuum-nitrogen circulation process in advance), and after being heated to 80°C, they were stirred vigorously for 1 hour to complete the pre-swelling. After the temperature of the system was stabilized, continuous reaction was carried out for 4 hours to obtain a crude product of PP-g-TFEMA;

[0061] After filtration, the filter cake was washed with excess anhydrous acetone; then, after drying overnight in a vacuum oven at 50°C, PP-g-TFEMA polypropylene-based energy storage dielectric material was collected.

[0062] Application Example 1: Preparation of a polymer film

[0063] The polymer PP-g-TFEMA prepared in Examples 1-3 and polypropylene (pellets, product number YY12251321A) purchased from Zhongyuan Petrochemical were respectively used to prepare films using a screw extruder. The preparation process was as follows: after the raw materials were cleaned to remove impurities, 1 kg of PP-g-TFEMA resin or 1 kg of polypropylene (PP) resin was added to the screw extruder, and the temperature was maintained at 200-250°C to obtain a film sample with a thickness of 10 μm; a low-temperature ion sputtering method was used to spray gold circular electrodes with a thickness of 50 nm on both sides of the polymer film for subsequent dielectric and energy storage performance tests.

[0064] Application Example 2: Processing of polymer films by heat treatment

[0065] The PP-g-TFEMA film and the PP film prepared in Application Example 1 were subjected to annealing heat treatment at a temperature of 140°C for 48 h.

[0066] The DSC spectrum of the TFEMA2 film in Example 1 after annealing is shown in Figure 4 .

[0067] Application Example 3: Electrical performance characterization

[0068] The polymer film samples in Application Example 2 were subjected to electrical performance characterization using an impedance analyzer, a ferroelectric analyzer, a film voltage resistance tester, and other equipment, and the test results are shown in Figures 5 to 7 . As can be seen from Figure 5 , compared with PP (dielectric constant 2.4), the dielectric constant of the TFEMA2 polymer (dielectric constant 2.8) after the introduction of TFEMA has been improved to a certain extent. As can be seen from Figure 6 , after the introduction of TFEMA, the breakdown electric field has been greatly improved from 694 MV / m to 895 MV / m. Figure 7 The discharge energy density and efficiency of the PP film annealed for 48 h (PP-48) and the TFEMA2 film annealed for 48 h (TFEMA2-48) are compared, and it can be seen that by optimizing the substituent group, the comprehensive electrical performance of the polymer can be regulated. The discharge energy density of the TFEMA2 film annealed for 48 h reaches 8.2 J cm -3 , and the efficiency exceeds 90%, which is significantly better than that of the PP film.

[0069] In summary, the dielectric constant and breakdown electric field of the polypropylene-based energy storage dielectric material prepared in the present application have been significantly improved.

[0070] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A polypropylene-based energy storage dielectric film, characterized by, The polypropylene-based energy storage dielectric film is prepared by a hot-pressing melt method or a casting extrusion method from a solution of a polypropylene-based energy storage dielectric material on a substrate; the preparation further comprises annealing; the annealing temperature is 100-140 ℃; the annealing time is 24-72 h; The preparation method of the polypropylene-based energy storage dielectric material comprises the following steps: Polypropylene, a (meth)acrylic fluorine-containing ester monomer and an initiator are subjected to a polymerization reaction in a suspension system.

2. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The (meth)acrylic fluorine-containing ester monomer is selected from any one or several of a methacrylic fluorine-containing ester monomer and an acrylic fluorine-containing ester monomer.

3. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The initiator is selected from any one or several of an oil-soluble initiator and a water-soluble initiator.

4. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The mass ratio of the polypropylene to the (meth)acrylic fluorine-containing ester monomer is 1:0.1-0.

5.

5. The polypropylene-based energy storage dielectric film of claim 1, wherein, The mass of the initiator is 1%-10% of the mass of the polypropylene.

6. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The polymerization reaction temperature is 70-90 ℃.

7. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The polymerization reaction time is 1-8 h.

8. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The pre-swelling operation is included before the polymerization reaction.

9. The polypropylene-based energy-storing dielectric film of claim 8, wherein, The pre-swelling is achieved by vigorous stirring at 70-90 ℃ for 1-2 h.

10. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The temperature of the hot-pressing melt method or the casting extrusion method is 200-250 ℃.

11. The polypropylene-based energy-storing dielectric film of claim 1, wherein, The solvent in the solution of the polypropylene-based energy storage dielectric material is selected from any one or several of an oily solvent and an aqueous solvent.

12. Use of the polypropylene-based energy storage dielectric film of claim 1 in the preparation of a thin-film capacitor.

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