Film capacitor and preparation method thereof

Abstract

The present invention relates to the technical field of dielectric composite films, and specifically to a thin film capacitor and a preparation method thereof, wherein the preparation method of the thin film capacitor comprises the following steps: Step 1: preparing a 3-5 μm double-layer dielectric film, wherein the components of the upper film include polypropylene with a mass fraction of not less than 70%, and the components of the lower film include polyvinylidene fluoride with a mass fraction of 40-60%, and polypropylene with a mass fraction of not less than 20%; Step 2: evaporating metal on the upper film to form a metallized film; Step 3: winding the metallized film into shape and then leading out the electrodes to obtain a thin film capacitor. The thin film capacitor prepared by the preparation method disclosed in the present invention has an energy storage density of up to 6.2 J / cm 3 The charging and discharging efficiency is close to that of pure polypropylene film and can meet industrial needs.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitors, and in particular to a thin film capacitor and a preparation method thereof. Background Art

[0002] Common materials for the base film of film capacitors include polypropylene (PP) and polyvinylidene fluoride (PVDF). However, the dielectric constant of PP material is relatively low, resulting in low energy storage density of the produced film capacitors. PVDF has a high dielectric constant. The existing technology has used a method of blending polypropylene (PP) and polyvinylidene fluoride (PVDF) to improve the energy storage density of film materials. However, the charge and discharge efficiency of the blended film cannot meet industrial needs. Therefore, how to maintain high charge and discharge efficiency while improving energy density is an urgent problem that needs to be solved. Summary of the Invention

[0003] The present invention aims to solve the above technical problems.

[0004] One object of the present invention is to provide a method for preparing a thin film capacitor, wherein the upper film is mainly composed of a polypropylene component with high breakdown strength, which is used for evaporating metal to form a metallized film, and the lower film is mainly composed of a polyvinylidene fluoride component with a high dielectric constant. The energy storage density of the thin film material is improved by compounding the upper film and the lower film, and by adjusting the ratio of the components in the upper film and the lower film, it is ensured that the energy density of the thin film capacitor is improved while maintaining high charging and discharging efficiency.

[0005] The present invention provides a method for preparing a thin film capacitor, which is characterized by comprising the following steps:

[0006] Step 1: preparing a 3-5 μm double-layer dielectric film, wherein the upper film comprises not less than 70% by mass of polypropylene, and the lower film comprises 40-60% by mass of polyvinylidene fluoride and not less than 20% by mass of polypropylene;

[0007] Step 2: Vapor-depositing metal on the upper film to form a metallized film;

[0008] Step 3: Wind the metallized film into shape and then lead out the electrodes to obtain a film capacitor.

[0009] According to an embodiment of the present disclosure, the components of the lower film in step one further include inorganic nanoparticles with a mass fraction of no more than 30%.

[0010] According to an embodiment of the present disclosure, the inorganic nanoparticles are selected from one or more of boron nitride, aluminum oxide, silicon dioxide, and barium titanate.

[0011] According to an embodiment of the present disclosure, in step 1, polyvinylidene fluoride, polypropylene and inorganic nanoparticles are mixed to form a coating which is applied to the surface of the upper film and then dried to form a 3-5 μm double-layer dielectric film.

[0012] According to an embodiment of the present disclosure, the components of the upper film in step one further include graft-modified polypropylene with a mass fraction not greater than 30%.

[0013] According to an embodiment of the present disclosure, the monomer used for the graft modification is a methacrylic acid monomer or a maleic anhydride monomer.

[0014] According to an embodiment of the present disclosure, the methacrylic acid monomer is selected from methyl methacrylate or trifluoroethyl methacrylate.

[0015] According to an embodiment of the present disclosure, the components of the upper film in step one further include polyvinylidene fluoride with a mass fraction not greater than 20%.

[0016] According to an embodiment of the present disclosure, in the step 1, the polypropylene, the graft-modified polypropylene and the polyvinylidene fluoride are mixed and then biaxially stretched to obtain the upper film.

[0017] The present invention also provides a thin film capacitor prepared by the method for preparing a thin film capacitor as described in any one of the above.

[0018] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0019] The reagents and raw materials used in the present invention are commercially available.

[0020] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0021] The method for preparing a thin film capacitor provided by an embodiment of the present invention includes the following steps: Step 1: preparing a 3-5 μm double-layer dielectric film, wherein the components of the upper film include polypropylene with a mass fraction of not less than 70%, and the components of the lower film include polyvinylidene fluoride with a mass fraction of 40-60%, and polypropylene with a mass fraction of not less than 20%; Step 2: evaporating metal on the upper film to form a metallized film; Step 3: winding the metallized film into shape and then leading out the electrodes to obtain a thin film capacitor. The thin film capacitor prepared by the preparation method disclosed in the present invention has an energy storage density of up to 6.2 J / cm 3 The charging and discharging efficiency is close to that of pure polypropylene film and can meet industrial needs.

[0022] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are specifically listed below. DETAILED DESCRIPTION

[0023] The present invention is further illustrated below by way of examples, but it is to be understood that these specific examples will not limit the scope of the present invention in any way. It should be noted that, unless otherwise specified, the raw materials used in the following examples are all commercially available products, and their quality meets national standards.

[0024] The sources of chemicals or testing methods used in the embodiments and comparative examples of the present invention are as follows and will not be repeated in the embodiments.

[0025] Energy storage density and charge-discharge efficiency: The DE curve is calculated using the Sawyer-Tower circuit method. This involves connecting a standard capacitor Co in parallel with a test capacitor (where the standard capacitor's capacitance is significantly greater than the test capacitor), connecting it to an oscilloscope, and applying an AC voltage (triangular or sine wave) to the sample. The DE curve is then plotted against the voltage across the test capacitor and the standard capacitor Co. Measuring the DE curve provides a simple and intuitive representation of the charge and discharge energy density of a dielectric material, and the charge-discharge efficiency parameter is calculated through integration.

[0026] The present invention provides a method for preparing a thin film capacitor, comprising the following steps:

[0027] Step 1: preparing a 3-5 μm double-layer dielectric film, wherein the upper film comprises not less than 70% by mass of polypropylene, and the lower film comprises 40-60% by mass of polyvinylidene fluoride and not less than 20% by mass of polypropylene;

[0028] Step 2: Vapor-depositing metal on the upper film to form a metallized film;

[0029] Step 3: Wind the metallized film into shape and then lead out the electrodes to obtain a film capacitor.

[0030] According to an embodiment of the present disclosure, the components of the lower film in step one further include inorganic nanoparticles with a mass fraction of no more than 30%.

[0031] According to an embodiment of the present disclosure, the inorganic nanoparticles are selected from one or more of boron nitride, aluminum oxide, silicon dioxide, and barium titanate.

[0032] According to an embodiment of the present disclosure, in step 1, polyvinylidene fluoride, polypropylene and inorganic nanoparticles are mixed to form a coating which is applied to the surface of the upper film and then dried to form a 3-5 μm double-layer dielectric film.

[0033] According to an embodiment of the present disclosure, the components of the upper film in step one further include graft-modified polypropylene with a mass fraction not greater than 30%.

[0034] According to an embodiment of the present disclosure, the monomer used for the graft modification is a methacrylic acid monomer or a maleic anhydride monomer.

[0035] According to an embodiment of the present disclosure, the methacrylic acid monomer is selected from methyl methacrylate or trifluoroethyl methacrylate.

[0036] According to an embodiment of the present disclosure, the components of the upper film in step one further include polyvinylidene fluoride with a mass fraction not greater than 20%.

[0037] According to an embodiment of the present disclosure, in the step 1, the polypropylene, the graft-modified polypropylene and the polyvinylidene fluoride are mixed and then biaxially stretched to obtain the upper film.

[0038] The present invention also provides a thin film capacitor prepared by the method for preparing a thin film capacitor as described in any one of the above.

[0039] The present invention is described in detail below through specific examples.

[0040] Example 1

[0041] Pure polypropylene (ungrafted) was melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3μm upper film. Polyvinylidene fluoride and polypropylene were weighed in a mass ratio of 4:6, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to the upper film after surface treatment (corona treatment or plasma treatment) to a thickness of 1μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a winding process. After winding, the film capacitor was heat treated, gold sprayed, and the electrodes were extracted.

[0042] Example 2

[0043] Pure polypropylene (ungrafted) and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:3. These were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3 μm upper film. Polyvinylidene fluoride and polypropylene were weighed in a mass ratio of 4:6, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a surface-treated (corona or plasma) upper film to a thickness of 1 μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a coiling process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0044] Example 3

[0045] Pure polypropylene (ungrafted) and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:3. These were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3 μm upper film. Polyvinylidene fluoride, polypropylene, and barium titanate were weighed in a mass ratio of 4:3:3, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a surface-treated (corona or plasma) upper film to a thickness of 1 μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0046] Example 4

[0047] Pure polypropylene (ungrafted) and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:3. These were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3 μm upper film. Polyvinylidene fluoride and polypropylene were weighed in a mass ratio of 6:4, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a surface-treated (corona or plasma) upper film to a thickness of 1 μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a coiling process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0048] Example 5

[0049] Pure polypropylene (ungrafted), polypropylene modified with methacrylic acid monomer, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1.5:0.5. These materials were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 4 μm upper film. Polyvinylidene fluoride and polypropylene were weighed in a mass ratio of 4:6, dissolved, mixed, and stirred uniformly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to the upper film, which had been surface-treated (corona or plasma treatment), to a thickness of 1.5 μm, and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0050] Example 6

[0051] Pure polypropylene (ungrafted), polypropylene modified with methacrylic acid monomer, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1.5:0.5. These materials were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 4 μm upper film. Polyvinylidene fluoride, polypropylene, and barium titanate were weighed in a mass ratio of 4:3:3, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a 2 μm thickness onto the surface-treated (corona or plasma) upper film and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0052] Example 7

[0053] Pure polypropylene (ungrafted), polypropylene modified with methacrylic acid monomer, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:2:1. These materials were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 5 μm upper film. Polyvinylidene fluoride, polypropylene, and barium titanate were weighed in a mass ratio of 5.5:2.5:2, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a surface-treated (corona or plasma) upper film to a thickness of 1 μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0054] Example 8

[0055] Pure polypropylene (ungrafted), polypropylene modified with methacrylic acid monomer, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 7:1:2. These materials were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3 μm upper film. Polyvinylidene fluoride, polypropylene, and barium titanate were weighed in a mass ratio of 6:2:3, dissolved, mixed, and stirred evenly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a 1 μm thickness on the upper film after surface treatment (corona treatment or plasma treatment) and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat treated, gold sprayed, and electrodes were extracted.

[0056] Example 9

[0057] Pure polypropylene (ungrafted), polypropylene modified with methacrylic acid monomer, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 8:1.5:0.5. These materials were melted at 250°C, filtered, and extruded through a die. After cooling and solidification at 95°C, a 1 mm cast sheet was obtained. This sheet was then biaxially stretched to produce a 3 μm upper film. Polyvinylidene fluoride and polypropylene were weighed in a mass ratio of 6:4, dissolved, mixed, and stirred uniformly. The mixture was ball-milled and filtered to produce a coating solution. The coating solution was applied to a surface-treated (corona or plasma) upper film to a thickness of 1 μm and dried in an oven to produce a double-layer dielectric film. A zinc-aluminum alloy electrode was deposited on the opposite side of the upper film from the lower film using a vapor deposition device. The resulting metallized film was then wound using a roll-to-roll process. After winding, the film capacitor was heat-treated, gold-sprayed, and electrodes were extracted.

[0058] The energy storage density and energy storage efficiency of the thin films of Examples 1-9 of the present invention were evaluated under an electric field of 450 MV / m. The specific evaluation results are shown in the following table.

[0059]

[0060]

[0061] As can be seen from the table above, the energy storage density of the double-layer dielectric film of the film capacitor prepared by the preparation method disclosed in the present invention is as high as 6.2 J / cm 3 The charging and discharging efficiency is close to that of pure polypropylene film and can meet industrial needs.

[0062] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, utilize the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a thin film capacitor, characterized in that: The steps include: Step 1: preparing a 3-5 μm double-layer dielectric film, wherein the upper film comprises at least 70% by mass of polypropylene, and the lower film comprises at least 40-60% by mass of polyvinylidene fluoride and at least 20% by mass of polypropylene; Step 2: Vapor-depositing metal on the upper film to form a metallized film; Step 3: Winding the metallized film into shape and then leading out the electrodes to obtain a film capacitor; Wherein, the components of the upper film in the step 1 further include graft-modified polypropylene with a mass fraction not greater than 30%; the monomer used for the graft modification is methacrylic acid monomer or maleic anhydride monomer.

2. The method for preparing a thin film capacitor according to claim 1, wherein: The components of the lower film in step 1 also include inorganic nanoparticles with a mass fraction of no more than 30%.

3. The method for preparing a thin film capacitor according to claim 2, wherein: The inorganic nanoparticles are selected from one or more of boron nitride, aluminum oxide, silicon dioxide, and barium titanate.

4. The method for preparing a thin film capacitor according to claim 2 or 3, wherein: In the step 1, polyvinylidene fluoride, polypropylene and inorganic nanoparticles are mixed to form a coating which is coated on the surface of the upper film and then dried to form a 3-5 μm double-layer dielectric film.

5. The method for preparing a thin film capacitor according to claim 1, wherein: The methacrylic acid monomer is selected from methyl methacrylate or trifluoroethyl methacrylate.

6. The method for preparing a thin film capacitor according to claim 1, wherein: The components of the upper film in step 1 also include polyvinylidene fluoride with a mass fraction not greater than 20%.

7. The method for preparing a thin film capacitor according to claim 6, wherein: In the step 1, the polypropylene, graft-modified polypropylene and polyvinylidene fluoride are mixed and then biaxially stretched to obtain the upper film.

8. A thin film capacitor prepared by the method for preparing a thin film capacitor according to any one of claims 1 to 6.

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