A film capacitor with high breakdown strength and its preparation method and application

Abstract

The present invention belongs to the technical field of circuit element preparation, and specifically relates to a film capacitor with high breakdown strength, a preparation method and application thereof. The film capacitor comprises a polymer dielectric and a nanosheet doped in the polymer dielectric; the nanosheet is oriented in a horizontal direction in the film capacitor. The film capacitor provided by the present invention has excellent breakdown strength. The polymer film capacitor doped with nanosheets provided by the present invention, the nanosheets are oriented in a horizontal direction in the film capacitor, perpendicular to the direction of applying an external electric field, and can effectively block the conductive path along the direction of the external electric field, thereby improving the breakdown strength of the film capacitor.

Description

Technical Field

[0001] The present invention belongs to the technical field of circuit element preparation, and in particular relates to a film capacitor with high breakdown strength and a preparation method and application thereof. Background Art

[0002] As one of the most basic circuit components in the circuit, capacitors have long been the focus of research by scientists in the electrical field. In recent years, with the rapid development of electronic technology and the electrical industry, people have put forward higher and higher requirements on the reliability and insulation performance of capacitors, and the research on capacitors with better performance is imminent.

[0003] According to the difference of dielectric between the plates, capacitors can be divided into three categories: organic polymer capacitors, inorganic dielectric capacitors, and electrolytic capacitors. Among them, the capacitor with organic polymer as dielectric material - polymer film capacitor, is a capacitor structure formed by overlapping metal film with polymer films such as polypropylene, polycarbonate, and polyimide from both ends and winding. Polymer film capacitors have the advantages of light weight, low cost, higher reliability, non-polarity, high insulation impedance, and low loss. At present, they have been widely used in electric vehicles, aerospace, wind power, photovoltaics, lighting, and railway locomotives. In photovoltaic power generation, wind power generation, vehicle brake control systems, aerospace, and electric vehicle inverter systems, polymer film capacitors are one of the most important components.

[0004] PVDF is a chain polymer polymerized from the gaseous monomer of vinylidene fluoride. Common PVDF binary copolymers include P(VDF-TrFE), P(VDF-TFE), P(VDF-CTFE) and P(VDF-HFP). Compared with PVDF, these binary copolymers have better dielectric constants. For example, the dielectric constant of P(VDF-CTFE) is 10-12, the dielectric constant of P(VDF-HFP) is 10-14, and the dielectric constant of P(VDF-BTFE) is 13. Film materials of these binary copolymers can be obtained by preparation processes such as solution casting or melt co-extrusion. Compared with the breakdown field strength of PVDF polymer of about 350MV / m, these binary random copolymers have a breakdown field strength of 400MV / m. Although the existing technology can further improve the breakdown field strength, it will increase the hysteresis loss by 40%, which is not suitable for polymer film capacitors. Therefore, how to improve the breakdown field strength of polymer film capacitors without increasing the hysteresis loss has become one of the difficulties. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art such as how to improve the breakdown strength of polymer film capacitors without increasing hysteresis loss, thereby providing a film capacitor with high breakdown strength and its preparation method and application.

[0006] To this end, the present invention provides the following technical solutions.

[0007] The present invention provides a thin film capacitor with high breakdown strength, comprising a polymer dielectric and nanosheets doped in the polymer; the nanosheets are oriented in a horizontal direction in the thin film capacitor.

[0008] The nanosheets are oriented in a horizontal direction in the thin film capacitor, and the angle between the nanosheets and the horizontal direction is not higher than 10°.

[0009] The nanosheet is at least one of a boron nitride nanosheet, an aluminum oxide nanosheet, a magnesium oxide nanosheet, a molybdenum oxide nanosheet and a silicon oxide nanosheet;

[0010] Preferably, the nanosheets are boron nitride nanosheets;

[0011] Preferably, the parameters of the nanosheets are: lateral size 0.5-5 μm, and thickness less than 10 nm.

[0012] Furthermore, the doping amount of the nanosheets in the thin film capacitor is not higher than 15% in volume fraction;

[0013] Preferably, the doping amount of the nanosheets in the thin film capacitor is 4.5-7.5% in volume fraction;

[0014] Preferably, the doping amount of the nanosheets in the thin film capacitor is 6% in volume fraction, wherein the doping amount refers to the percentage of the nanosheets in the total volume of the nanosheets and the polymer dielectric.

[0015] The polymer dielectric is a homopolymer and / or copolymer containing vinylidene fluoride;

[0016] Preferably, the polymer dielectric includes at least one of PVDF, P(VDF-TrFE), P(VDF-TFE), P(VDF-CTFE), P(VDF-HFP), P(VDF-TrFE-CFE) and P(VDF-TrFE-CTFE).

[0017] The present invention also provides a method for preparing a thin film capacitor with high breakdown strength, comprising: orienting the nanosheets in the thin film capacitor along a horizontal direction.

[0018] Furthermore, the nanosheets are oriented in the horizontal direction in the thin film capacitor by stretching, electric field induction or spin coating;

[0019] Preferably, the angle between the oriented nanosheets and the horizontal is no greater than 10°;

[0020] Preferably, the process of orienting the nanosheets in the thin film capacitor in a horizontal direction further includes a heating step;

[0021] Preferably, the heating temperature is lower than the melting point of the polymer dielectric;

[0022] Preferably, the difference between the heating temperature and the melting point of the polymer dielectric in the film capacitor is 5-10°C.

[0023] The preparation method comprises the following steps:

[0024] (1) preparing a solution containing a polymer dielectric;

[0025] (2) mixing the nanosheets with the solution obtained in step (1) so that the nanosheets are uniformly dispersed in the solution;

[0026] (3) Preparation of polymer film capacitors doped with nanosheets;

[0027] (4) Orienting the nanosheets in the thin film capacitor along a horizontal direction so that the angle between the oriented nanosheets and the horizontal direction is no greater than 10°.

[0028] The step (3) is to prepare a polymer film capacitor doped with nanosheets by a tape casting method;

[0029] Preferably, when preparing the thin film capacitor, the solvent used is at least one of N,N-dimethylformamide, N-methylpyrrolidone and toluene.

[0030] Furthermore, when the polymer dielectric in the film capacitor is P(VDF-HFP), in step (3) when preparing a polymer film capacitor doped with nanosheets, the drying process includes: drying the cast film in a natural convection oven at 40°C for 6 hours, and then placing it in a vacuum oven at 40°C for further drying for 12 hours. After taking it out, it is placed in a natural convection oven at 200°C for 5 minutes, and immediately placed in ice water after drying, and the film is peeled off from the glass plate, and then dried in a vacuum oven at 40°C overnight to obtain a film capacitor.

[0031] When the polymer dielectric in the film capacitor is P(VDF-TrFE-CFE), step (3) in preparing the polymer film capacitor doped with nanosheets, the drying process includes: drying the cast film in a natural convection oven at 80°C for 12 hours, and then peeling the film from the glass plate. In order to remove the residual solvent, it is placed in a vacuum oven at 110°C overnight to completely remove impurities.

[0032] In addition, the present invention also provides an application of the above-mentioned film capacitor or the film capacitor prepared by the above-mentioned preparation method in photovoltaic power generation, wind power generation, vehicle braking control system, aerospace or electric vehicles.

[0033] The technical solution of the present invention has the following advantages:

[0034] 1. The film capacitor with high breakdown strength provided by the present invention comprises a polymer dielectric and a nanosheet doped in the polymer dielectric; the nanosheet is oriented in a horizontal direction in the film capacitor; the film capacitor provided by the present invention has excellent breakdown strength. The polymer film capacitor doped with nanosheets provided by the present invention, the nanosheet is oriented in a horizontal direction in the film capacitor, perpendicular to the direction of applying an external electric field, can effectively block the conductive path along the direction of the external electric field, thereby improving the breakdown strength of the film capacitor.

[0035] 2. The film capacitor with high breakdown strength provided by the present invention dopes the polymer dielectric with nanosheets with high insulation strength such as boron nitride, aluminum oxide, magnesium oxide, molybdenum oxide, silicon oxide, etc., so that these high-insulation nanosheets are oriented in the horizontal direction in the polymer film capacitor, which can significantly improve the breakdown strength of the film capacitor. By controlling the doping concentration of the nanosheets in the film capacitor, the breakdown strength of the film capacitor can be optimized, especially when the doping concentration of the nanosheets is 6%, the breakdown strength of the film capacitor is optimal, about 652MV / m, an increase of 45%.

[0036] 3. The method for preparing a thin film capacitor with high breakdown strength provided by the present invention makes the nanosheets in the thin film capacitor tend to be oriented in a horizontal direction, thereby improving the breakdown strength of the thin film capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 is a SEM image of the thin film capacitor of Example 1 of the present invention;

[0039] Figure 2 is the Weibull distribution of the breakdown strength of the 1P (VDF-HFP) / BNNS film capacitors in Examples 1 to 7 of the present invention and the comparative example;

[0040] Figure 3This is the variation law of the Weibull breakdown strength of the P(VDF-HFP) / BNNS film capacitor in Examples 1-7 of the present invention and Comparative Example 1 with the volume proportion of boron nitride nanosheets. DETAILED DESCRIPTION

[0041] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0042] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0043] The raw materials used in the following examples are:

[0044] The ratio of VDF to HFP in the P(VDF-HFP) polymer was 90:10 and was purchased from PolyK Technologies.

[0045] The ratio of VDF, TrFE and CFE in P(VDF-TrFE-CFE) powder is 60.4 / 30.5 / 9.1, which was purchased from PIEZOTECH, France.

[0046] N,N-Dimethylformamide, anhydrous grade, was purchased from Sigma-Aldrich.

[0047] Aluminum oxide nanosheets, magnesium oxide nanosheets, molybdenum oxide nanosheets and silicon oxide nanosheets can be obtained commercially; boron nitride nanosheets can be prepared by the following method:

[0048] (1) Dispersing 2 g of boron nitride powder in 300 mL of DMF solvent under vigorous stirring to obtain a boron nitride powder dispersion; wherein the particle size of the boron nitride powder is not more than 10 μm and its particle size D90 is 9.5 μm, the purity is 99.5%, and the density is 2.290 g / cm 3 ;

[0049] (2) subjecting the boron nitride powder dispersion to a Qsonica, Q700 Sonicator treatment to obtain an ultrasonic dispersion, wherein the amplitude of the Qsonica treatment is 70% and the time is 24 h;

[0050] (3) centrifuging the ultrasonic dispersion three times in sequence, collecting the supernatant after the third centrifugation to obtain a first supernatant, wherein the speed of each centrifugation is 1000 rpm and the duration is 40 min;

[0051] (4) centrifuging the first supernatant again, collecting the precipitate and the supernatant respectively, to obtain a first precipitate and a second supernatant, wherein the centrifugal speed is 6000 rpm and the duration is 40 min;

[0052] (5) centrifuging the second supernatant to collect the precipitate to obtain a second precipitate, wherein the centrifugal speed is 10000 rpm and the duration is 40 min;

[0053] (6) The first precipitate is placed in a vacuum oven at 70°C and dried for 24 hours to completely remove impurities, thereby obtaining about 200 mg of a first boron nitride nanosheet, i.e., a large-sized boron nitride nanosheet; the second precipitate is placed in a vacuum oven at 70°C and dried for 24 hours to completely remove impurities, thereby obtaining about 100 mg of a second boron nitride nanosheet, i.e., a small-sized boron nitride nanosheet.

[0054] The lateral size of the small-sized boron nitride nanosheets is 0.5-1 μm and the thickness is 2-5 nm; the lateral size of the large-sized boron nitride nanosheets is 1-5 μm and the thickness is 5-8 nm.

[0055] Example 1

[0056] The present embodiment provides a thin film capacitor with high breakdown strength, which includes a P (VDF-HFP) polymer dielectric and boron nitride nanosheets (boron nitride nanosheets are referred to as BNNS) doped in the polymer dielectric; wherein, in terms of volume fraction, the doping amount of BNNS in the thin film capacitor is 6%, the size of BNNS is 1-5μm, the thickness is 5-8nm, and after the nanosheets are horizontally oriented, the angle between them and the horizontal is less than 10°.

[0057] The method for preparing the above-mentioned film capacitor with high breakdown strength comprises the following steps:

[0058] (1) 500 mg of P(VDF-HFP) polymer film was cut into small pieces and dissolved in 10 ml of DMF to obtain a 50 mg / mL solution. The solution was stirred vigorously overnight.

[0059] (2) Disperse BNNS uniformly in the solution obtained in step (1) and stir vigorously.

[0060] (3) The mixed solution obtained in step (2) is subjected to tip ultrasonic treatment for 30 minutes with an amplitude of 60%, and then a film is laid. The mixed solution is evenly dropped on a clean glass. The cast film is dried in a natural convection oven at 40°C for 6 hours, and then dried in a vacuum oven at 40°C for 12 hours, and then dried in a natural convection oven at 200°C for 5 minutes. After drying, it is immediately placed in ice water, the film is peeled off from the glass plate, and then dried in a vacuum oven at 40°C overnight to obtain a polymer film capacitor doped with nanosheets.

[0061] (4) The thin film capacitor obtained in step (3) has the following specifications: 10 cm in length and 5 cm in width. The thin film capacitor is stretched and mounted in a fixture and pressed tightly. One side of the stretching machine is set to move 20 mm at a rate of 0.125 mm / s and the other side is set to move 60 mm at a rate of 0.375 mm / s. After the stretching is completed, the capacitor is taken out and the stretching multiple is 300%. It is ensured that the angle between the nanosheet and the horizontal is less than 10 degrees after the nanosheet is horizontally oriented. Thus, a horizontally oriented P(VDF-HFP) / BNNS thin film capacitor is obtained.

[0062] Example 2

[0063] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 1.5%.

[0064] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0065] Example 3

[0066] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 3%.

[0067] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0068] Example 4

[0069] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 4.5%.

[0070] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0071] Example 5

[0072] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 7.5%.

[0073] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0074] Example 6

[0075] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 9%.

[0076] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0077] Example 7

[0078] This embodiment provides a thin film capacitor with high breakdown strength, which is different from Embodiment 1 in that, in terms of volume fraction, the doping amount of BNNS is 10.5%.

[0079] The preparation method of the above-mentioned film capacitor with high breakdown strength is the same as that of Example 1.

[0080] Example 8

[0081] The present embodiment provides a thin film capacitor with high breakdown strength, comprising a P (VDF-TrFE-CFE) polymer dielectric and Al2O3 nanosheets doped in the polymer dielectric; wherein, in terms of volume fraction, the doping amount of the Al2O3 nanosheets in the film is 6%, the size of the Al2O3 nanosheets is 1-5 μm, the thickness is 5-8 nm, and after the nanosheets are horizontally oriented, the angle between them and the horizontal is less than 10°.

[0082] The method for preparing the above-mentioned film capacitor with high breakdown strength comprises the following steps:

[0083] (1) 500 mg of P(VDF-TrFE-CFE) polymer film was cut into small pieces, dissolved in 10 ml of DMF to obtain a 50 mg / mL solution, and stirred vigorously overnight.

[0084] (2) Disperse Al2O3 nanosheets uniformly in the solution obtained in step (1) and stir vigorously.

[0085] (3) The mixed solution obtained in step (2) was subjected to tip ultrasonic treatment for 30 min at an amplitude of 60%, and then the film was spread, and the mixed solution was evenly dropped on a clean glass, and the cast film was dried in a natural convection oven at 80°C for 12 h, and then the film was peeled off from the glass plate. In order to remove the residual solvent, P(VDF-TrFE-CFE) / Al2O3 was placed in a vacuum oven at 110°C overnight to completely remove impurities, and a P(VDF-TrFE-CFE) / Al2O3 thin film capacitor doped with nanosheets was obtained.

[0086] (4) The film capacitor obtained in step (3) is made into a specification of: 10 cm in length and 5 cm in width, and the P(VDF-TrFE-CFE) / Al2O3 film capacitor is stretched to ensure that the nanosheets are oriented horizontally and the angle between them and the horizontal is less than 10°, that is, a horizontally oriented P(VDF-TrFE-CFE) / Al2O3 film capacitor is obtained.

[0087] Comparative Example 1

[0088] This comparative example provides a thin film capacitor, which includes a P (VDF-HFP) polymer dielectric and BNNS doped in the polymer dielectric; wherein the doping amount of BNNS in the thin film capacitor is 6%, the size of the BNNS is 1-5 μm, and the thickness is 5-8 nm.

[0089] The method for preparing the above-mentioned film capacitor comprises the following steps:

[0090] (1) 500 mg of P(VDF-HFP) polymer film was cut into small pieces and dissolved in 10 ml of DMF to obtain a 50 mg / mL solution. The solution was stirred vigorously overnight.

[0091] (2) Disperse BNNS uniformly in the solution obtained in step (1) and stir vigorously.

[0092] (3) The mixed solution obtained in step (2) is subjected to tip ultrasonic treatment for 30 minutes with an amplitude of 60%, and then a film is laid. The mixed solution is evenly dropped on a clean glass. The cast film is dried in a natural convection oven at 40°C for 6 hours, then dried in a vacuum oven at 40°C for 12 hours, and then dried in a natural convection oven at 200°C for 5 minutes. After drying, it is immediately placed in ice water, the film is peeled off from the glass plate, and then dried in a vacuum oven at 40°C overnight to obtain a film capacitor.

[0093] Test example

[0094] This test example provides performance tests of the film capacitors provided in the embodiments and comparative examples, as follows:

[0095] (1) Figure 1 This is the SEM spectrum of the film capacitor of Example 1. Figure 1 It can be seen that the BNNS in the P(VDF-HFP) / BNNS film capacitor has been oriented in the horizontal direction.

[0096] (2) Using P(VDF-HFP) polymer film capacitor as a control group, the breakdown strength of the film capacitors of Examples 1-7 and Comparative Example 1 was measured. The results are shown in Figure 2 and Figure 3The breakdown strength was tested by an amplifier (TREK 610C) at a linear voltage boost rate of 500 V / s and a limiting current of 5 mA, and the experimental data were analyzed using two-parameter Weibull statistics; the expression of the two-parameter Weibull distribution is:

[0097] P(E)=1-exp(-(E / α) β )

[0098] Where P(E) is the cumulative probability of electrical failure; E is the measured breakdown electric field strength; the scale parameter α is the electric field strength at which the sample has a 63% probability of breakdown, also known as the characteristic breakdown strength; the shape parameter β evaluates the dispersion of the data, and a higher value of β indicates a higher reliability of the dielectric.

[0099] The electrical breakdown strength of polymer film capacitors was examined using two-parameter Weibull statistics.

[0100] from Figure 2 It can be seen that compared with comparative example 1, the breakdown strength of the film capacitors in Examples 1-7 of the present invention is significantly improved after the nanosheets are horizontally oriented. By controlling the doping concentration of the nanosheets in the film capacitor, the breakdown strength of the film capacitor can be optimized. In particular, when the BNNS doping amount is 6%, the breakdown strength of the film capacitor is optimal, about 667MV / m. Compared with the blank experiment, the breakdown strength of the film capacitor of the present invention is improved by about 48%. Among them, Figure 3 The first point in the curve corresponds to a BNNS doping amount of 0, which is a blank experiment. The difference between the blank experiment and Example 1 is that BNNS is not doped, and the rest is the same as Example 1.

[0101] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a film capacitor with high breakdown strength, characterized in that: include: The nanosheets are oriented in the horizontal direction in the thin film capacitor by stretching, electric field induction or spin coating; The angle between the oriented nanosheets and the horizontal is no higher than 10°; The process of orienting the nanosheets in a horizontal direction in the thin film capacitor also includes a heating step; The heating temperature is lower than the melting point of the polymer dielectric; The parameters of the nanosheets are: lateral size 0.5-5 μm, thickness less than 10 nm; In units of volume fraction, the doping amount of the nanosheets in the film capacitor is 1.5%-15%; The difference between the heating temperature and the melting point of the polymer dielectric in the film capacitor is 5-10°C.

2. The preparation method according to claim 1, characterized in that: The following steps are involved: (1) preparing a solution containing a polymer dielectric; (2) mixing the nanosheets with the solution obtained in step (1) so that the nanosheets are uniformly dispersed in the solution; (3) Preparation of polymer film capacitors doped with nanosheets; (4) Orienting the nanosheets in the thin film capacitor along a horizontal direction so that the angle between the oriented nanosheets and the horizontal direction is no greater than 10°.

3. The preparation method according to claim 2, characterized in that: The step (3) is to prepare a polymer film capacitor doped with nanosheets by a tape casting method; When preparing the film capacitor, the solvent used is at least one of N,N-dimethylformamide, N-methylpyrrolidone and toluene.

4. The preparation method according to claim 1, characterized in that: The nanosheet is at least one of a boron nitride nanosheet, an aluminum oxide nanosheet, a magnesium oxide nanosheet, a molybdenum oxide nanosheet and a silicon oxide nanosheet.

5. The preparation method according to claim 1 or 2, characterized in that: The polymer dielectric is a homopolymer and / or copolymer containing vinylidene fluoride.

6. A film capacitor prepared by the preparation method according to any one of claims 1 to 5.

7. Application of the film capacitor prepared by the preparation method according to any one of claims 1 to 5 in photovoltaic power generation, wind power generation, vehicle braking control system, aerospace or electric vehicles.

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