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

Abstract

The invention discloses a polypropylene-based energy storage dielectric material as well as a preparation method and application thereof. The preparation method comprises the following steps: pre-swelling a polypropylene substrate and a (methyl) acrylic acid fluorine-containing ester monomer in a solvent, then carrying out polymerization reaction through an initiator, and carrying out post-treatment on a graft polymer to obtain the (methyl) acrylic acid fluorine-containing ester functionalized polypropylene. A suspension polymerization method is adopted, a fluorine-containing group is introduced to a polypropylene structure to induce electron cloud distribution, crystal domain aggregation is promoted, the crystallinity is improved, and the dielectric constant, the loss factor, the leakage current and the breakdown electric field of a polymer material are adjusted, so that the energy storage density and the efficiency of a polymer dielectric medium are controlled.

Description

Technical Field

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

[0002] With the rapid development of ultra-high voltage power transmission, electromagnetic equipment, new energy vehicles, national defense and military industries, the demand for pulse capacitor dielectric polymer films has increased year by year.

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

[0004] As one of the general synthetic materials, polypropylene (PP) 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. Due to its low dielectric constant (~2.2), its maximum discharge energy density is about 4J / cm3, which cannot 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 bottlenecks of the energy storage performance of PP-based polymers. The current solutions are mainly doping, coating and grafting modification. Doping and coating of inorganic nanoparticles in PP can improve the dielectric constant and breakdown strength to a certain extent, but the improvement effect of doping and coating is limited due to the interfacial polarization between the doped particles and the coating, which leads to undesirable high dielectric and energy losses. In addition, chemical grafting can effectively overcome the shortcomings of doping and coating due to the good compatibility and dispersibility of the grafted compound in the polymer matrix. Theoretically, the introduction of polar groups can improve 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 in energy storage density. In other words, dielectric materials cannot simultaneously meet the characteristics of high energy storage density and high discharge efficiency (low loss). In addition, existing PP-based modified polymers cannot be mass-produced and processed.

[0005] In summary, whether it is PVDF-based polymers with high dielectric constants or BOPP with high breakdown electric fields, or glassy polymers and special engineering plastic polymers, they all have insurmountable shortcomings when used as high energy storage dielectrics. Therefore, it is of great significance to develop polymer dielectric materials with "double high" characteristics and capable of large-scale production and processing. Summary of the invention

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

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] In one aspect, the present invention provides a method for preparing a polypropylene-based energy storage dielectric material, comprising the following steps:

[0009] Polypropylene, (meth)acrylic acid fluorinated ester monomer and initiator are polymerized in a suspension system.

[0010] In the technical solution of the present invention, the polymerization reaction is heterogeneous polymerization.

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

[0012] In the technical scheme of the present invention, the initiator is selected from any one or more of oil-soluble initiators and water-soluble initiators; wherein the oil-soluble initiator is selected from at least one of an azo initiator and a peroxide initiator; the azo initiator may include initiators such as azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile and dimethyl azobisisobutyrate; the peroxide initiator may include diisopropylbenzene peroxide, benzoyl peroxide, di-tert-butyl peroxide, etc.; the water-soluble initiator may include persulfate, redox initiation system, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisobutylimidazoline and azobiscyanovaleric acid, etc.

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

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

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

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

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

[0018] Preferably, the polymerization reaction time is 1 to 8 hours.

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

[0020] In some specific embodiments, the pre-swelling is achieved by vigorously stirring at 70-90° C. for 1-2 hours; the volume of the polymer can be increased by pre-swelling, which is beneficial for sufficient reaction.

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

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

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

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

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

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

[0027] Preferably, the temperature of the hot pressing and melting method or the cast 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 more of an oily solvent and an aqueous solvent;

[0029] Preferably, the preparation further comprises annealing;

[0030] Preferably, the annealing temperature is 100-140°C;

[0031] Preferably, the annealing time is 24 to 72 hours;

[0032] In another aspect, the present invention provides 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 film capacitors.

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

[0034] The polypropylene-based energy storage dielectric material provided by the present invention is prepared by a suspension polymerization method using a polypropylene substrate and a (meth)acrylic acid fluorinated ester monomer under the action of an initiator. The polypropylene-based energy storage dielectric material prepared by the present invention induces electron cloud distribution by introducing fluorinated groups into the polypropylene structure, promotes crystallization domain aggregation to improve crystallinity, and adjusts the dielectric constant and breakdown electric field of the polymer material, thereby manipulating the energy storage density and efficiency of the polymer dielectric. The preparation method provided by the present invention adopts suspension polymerization, has a controllable reaction, is simple to operate, has strong practicality, is easy to replicate and promote industrially, and can prepare a variety of polymers by changing the type and molecular weight of monomers according to actual needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the main chemical reaction occurring during the preparation of the polypropylene-based energy storage dielectric material PP-g-TFEMA in Examples 1-3 of the present invention.

[0036] Figure 2 This is the FT-IR spectrum of TFEMA2 in Example 1 of the present invention.

[0037] Figure 3 is the TFEMA2 in Example 1 of the present invention 1 H NMR spectrum.

[0038] Figure 4 This is the DSC spectrum of TFEMA2 in Application Example 2 of the present invention after annealing for 48 hours.

[0039] Figure 5 This is a graph showing the variation of the dielectric constant of the polymer film with frequency measured in Application Example 3 of the present invention.

[0040] Figure 6This is the Weibull distribution diagram of the polymer film measured in Application Example 3 of the present invention.

[0041] Figure 7 This is a diagram of the energy storage performance of the polymer film measured in Application Example 3 of the present invention. DETAILED DESCRIPTION

[0042] The following embodiments are only some embodiments of the present invention, rather than all embodiments. Therefore, the detailed description in the embodiments of the present invention provided below is not intended to limit the scope of the present invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the protection scope of the present invention.

[0043] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments 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 (granules, purchased from Zhongyuan Petrochemical, product number YY12251321A) was dispersed in 4 kg of water;

[0046] Disperse 10 g of trifluoroethyl methacrylate (TFEMA) and 4 g of dibenzoyl peroxide (BPO) in 86 g of xylene;

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

[0048] Filter and wash the filter cake with excess anhydrous acetone; then dry overnight in a vacuum oven at 50°C and collect to obtain poly(propylene-trifluoroethyl methacrylate) polymer (PP-g-TFEMA polypropylene-based energy storage dielectric material, TFEMA2).

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

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

[0051] In this embodiment, according to experimental characterization, the molar ratio of TFEMA unit to PP unit in PP-g-TFEMA is 9:250. 1 H NMR spectrum Figure 3 shown.

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

[0053] 100 g of polypropylene (granules, 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 xylene;

[0055] The above two solutions were transferred to a reactor (nitrogen atmosphere throughout the process, and oxygen and moisture were removed in advance through an uninterrupted vacuum-nitrogen filling cycle process), heated to 80°C and vigorously stirred for 1 hour to complete pre-swelling; after the system temperature stabilized, the reaction was continued for 4 hours to obtain a crude PP-g-TFEMA product;

[0056] The filter cake was filtered and washed with excess anhydrous acetone; it was then dried overnight at 50° C. in a vacuum oven and collected to obtain poly(propylene-trifluoroethyl methacrylate) polymer (PP-g-TFEMA polypropylene-based energy storage dielectric material).

[0057] Example 3

[0058] Disperse 100 g of Zhongyuan Petrochemical polypropylene (granules, purchased from Zhongyuan Petrochemical, product number YY12251321A) 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 xylene;

[0060] The above two solutions were transferred to a reactor (nitrogen atmosphere throughout the process, and oxygen and moisture were removed in advance through an uninterrupted vacuum-nitrogen filling cycle process), heated to 80°C and vigorously stirred for 1 hour to complete pre-swelling; after the system temperature stabilized, the reaction was continued for 4 hours to obtain a crude PP-g-TFEMA product;

[0061] The filter cake was filtered and washed with excess anhydrous acetone; it was then dried overnight at 50° C. in a vacuum oven and collected to obtain the PP-g-TFEMA polypropylene-based energy storage dielectric material.

[0062] Application Example 1: Preparation of polymer film

[0063] The polymer PP-g-TFEMA prepared in Examples 1-3 and polypropylene (granules, product number YY12251321A) purchased from Zhongyuan Petrochemical were respectively used to prepare films using screw extruders. The preparation process is as follows: After cleaning and removing impurities from the raw materials, 1 kg of PP-g-TFEMA resin or 1 kg of polypropylene granules (PP) resin was added to the screw extruder, and the temperature range was maintained between 200 and 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, in preparation for subsequent dielectric and energy storage performance tests of the polymer film.

[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 an annealing heat treatment at a temperature of 140° C. for 48 hours.

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

[0067] Application Example 3: Electrical Performance Characterization

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

[0070] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a polypropylene-based energy storage dielectric material, characterized in that: The following steps are involved: Polypropylene, (meth)acrylic acid fluorinated ester monomer and initiator are polymerized in a suspension system.

2. The preparation method according to claim 1, characterized in that: The (meth)acrylic acid fluorinated ester monomer is selected from any one or more of methacrylic acid fluorinated ester monomers and acrylic acid fluorinated ester monomers; Preferably, the initiator is selected from any one or more of oil-soluble initiators and water-soluble initiators.

3. The preparation method according to claim 1, characterized in that: The mass ratio of the polypropylene to the (meth)acrylic acid fluorinated ester monomer is 1:0.1-0.5; Preferably, the mass of the initiator is 1% to 10% of the mass of the polypropylene.

4. The preparation method according to claim 1, characterized in that: The polymerization reaction temperature is 70-90°C; Preferably, the polymerization reaction time is 1 to 8 hours.

5. The preparation method according to claim 1, characterized in that: The polymerization reaction includes a pre-swelling operation; Preferably, the pre-swelling is achieved by vigorously stirring at 70-90° C. for 1-2 hours.

6. A polypropylene-based energy storage dielectric material obtained by the preparation method according to any one of claims 1 to 5.

7. A polypropylene-based energy storage dielectric film, characterized in that: The polypropylene-based energy storage dielectric film is prepared from the polypropylene-based energy storage dielectric material described in claim 6.

8. The polypropylene-based energy storage dielectric film according to claim 7, characterized in that: The polypropylene-based energy storage dielectric film is prepared by a solution of the polypropylene-based energy storage dielectric material on a substrate by a hot pressing melting method or a casting extrusion method; Preferably, the temperature of the hot pressing and melting method or the cast extrusion method is 200-250°C; Preferably, the solvent in the solution of the polypropylene-based energy storage dielectric material is selected from any one or more of an oily solvent and an aqueous solvent.

9. The polypropylene-based energy storage dielectric film according to claim 7, characterized in that: The preparation further comprises annealing; Preferably, the annealing temperature is 100-140°C; Preferably, the annealing time is 24 to 72 hours.

10. Use of the polypropylene-based energy storage dielectric material according to claim 6 or the polypropylene-based energy storage dielectric film according to claim 7 in the preparation of film capacitors.

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