Dielectric film for high-temperature energy storage and preparation method and device thereof

Abstract

The application relates to a dielectric film for high-temperature energy storage and a preparation method and device thereof, the dielectric film is prepared through supercritical spraying film forming and heat treatment, and comprises the following components in parts by weight: 5-30 parts of a high-temperature-resistant polymer, 0.1-5 parts of an additive and 60-95 parts of a solvent; the high-temperature-resistant polymer is selected from one or more of polyimide polymers and a precursor polyamide acid of the polyimide polymers; the additive is selected from one or more inorganic fillers of aluminum oxide, boehmite and silicon carbide. Compared with the prior art, the application has the advantages of uniform thickness, strong breakdown resistance, high dielectric strength and the like.

Description

Technical Field

[0001] This invention belongs to the field of energy storage material preparation technology, and relates to a dielectric thin film for high-temperature energy storage and its preparation method and apparatus. Background Technology

[0002] In recent years, dielectric capacitors have become an important component of modern power systems. Their advantages lie in their inherently fast charging and discharging capabilities, ultra-high power density, all-solid-state structure, high operating voltage, and low loss. However, a common drawback of film capacitors based on various dielectric electrolyte materials is their relatively low energy density, which seriously hinders the development of manufacturing technology for high-power, high-capacity capacitors.

[0003] Therefore, in practical applications, there is a need to improve energy storage performance to avoid occupying excessive space in integrated circuits. This is especially true for applications such as pulse power systems, hybrid vehicles, oil and gas exploration and extraction, and the efficient utilization of clean energy sources like wind power, which further necessitates higher high-temperature energy storage performance. Taking biaxially oriented polypropylene (BOPP), a commonly used commercial capacitor film, as an example, its operating temperature is typically around 70℃, generally not exceeding 105℃. For BOPP film capacitors, the leakage current inside the dielectric increases exponentially under higher temperatures and electric fields, causing a sharp decrease in charge / discharge efficiency and energy density, while also generating a large amount of Joule heat, exacerbating the performance degradation. Researchers at home and abroad have developed dielectric film materials for organic film capacitors using polymers with high glass transition temperatures, such as polyimide (PI) and polyetherimide (PEI), which have improved high-temperature energy storage performance. However, the thickness of these high-temperature energy storage dielectric films is generally greater than 10μm, which cannot meet the requirement for thinner dielectric films.

[0004] The application of various novel polymers in dielectric capacitors is often limited by thin-film manufacturing technology. How to manufacture large-scale, ultra-thin, continuous, and uniform high-quality dielectric films is a crucial technical issue in the development of dielectric capacitors for high-temperature energy storage. Currently, commercially available BOPP films can be as thin as 2.2 μm, employing a melt extrusion combined with biaxial stretching process, which results in high equipment costs. Previously, patent CN115093590A disclosed a high-temperature electrostatic energy storage film, its preparation method, and its application. This film uses an ultrasonic spraying process, which is simple, widely applicable, and suitable for the large-scale industrial production of high-quality ultra-thin polymer-based dielectric films. However, this process is suitable for polymer concentrations of 0.01-0.05 g / mL, thus requiring large amounts of organic solvents for dilution, increasing environmental pollution. Therefore, developing a more environmentally friendly and low-cost process for preparing novel high-quality, large-area ultra-thin dielectric films for high-temperature energy storage is particularly important.

[0005] Patent CN116487819A discloses a composite membrane, its preparation method, and its application. The composite membrane comprises a porous substrate and a heat-resistant coating disposed on one or both sides of the porous substrate. The heat-resistant coating contains heat-resistant polymer particles, inorganic fillers, and auxiliary binders. The heat-resistant polymer particles contain a heat-resistant resin with an average particle size of 10-200 nm and a glass transition temperature of Ts+40℃ or higher. However, the composite membrane of this patent has relatively uneven thickness and uneven distribution of fillers in the membrane material, resulting in performance defects in the membrane.

[0006] Patent CN116178782A discloses a method for preparing a high-filler ultrathin polytetrafluoroethylene (PTFE) composite dielectric substrate. The method involves mixing 51-75% ceramic powder, 15-25% PTFE emulsion, 1-13% fiber, and 8-19% deionized water by weight to obtain a composite slurry. Then, 5-15% flocculant is added to the slurry, and the mixture is stirred for 15-30 minutes. After filtration, a dough-like high-filler PTFE composite wet material is obtained. This wet material is then subjected to room-temperature calendering, supercritical drying, atomized spraying of a wetting agent, high-pressure calendering, and high-temperature drying to produce a high-filler ultrathin PTFE-based composite dielectric substrate. However, the preparation process of this patent is relatively complex, cumbersome, and costly. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a dielectric thin film for high-temperature energy storage, as well as a method and apparatus for its preparation. This invention has uniform thickness, strong breakdown resistance, and high dielectric strength.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide a dielectric thin film for high-temperature energy storage, which is prepared by supercritical spraying and heat treatment, and comprises the following components in parts by weight:

[0010] 5-30 parts of high-temperature resistant polymer, 0.1-5 parts of additives, and 60-95 parts of solvent;

[0011] The high-temperature resistant polymer is selected from one or more of polyimide polymers and polyamic acid, the precursor of polyimide polymers;

[0012] The additive is selected from one or more inorganic fillers selected from alumina, boehmite, and silicon carbide.

[0013] Furthermore, the polyimide polymer is selected from one or more of polyimides, fluorinated polyimides, and polyetherimides.

[0014] As a preferred technical solution, the high-temperature resistant polymer is selected from polyimide, fluorinated polyimide, polyetherimide, or polyamic acid, which is a precursor of one or more polyimide polymers.

[0015] The glass transition temperature of the high-temperature resistant polymer is not less than 150°C, and its band gap is not less than 3eV.

[0016] Furthermore, the solvent is selected from one or more of N,N'-dimethylacetamide, N-methylpyrrolidone, and N,N'-dimethylformamide.

[0017] One of the technical solutions of the present invention is to provide a method for preparing the dielectric thin film for high-temperature energy storage, the method comprising the following steps:

[0018] S1. Slurry pre-preparation: High-temperature resistant polymer and solvent are mixed to obtain spray slurry;

[0019] S2, supercritical spraying, add spraying slurry and additives, introduce carbon dioxide as a diluent and mix with the spraying slurry in a supercritical state, spray the supercritical polymer slurry with gas-liquid mixture onto the surface of the substrate to form a wet film.

[0020] S3. Post-processing: The wet film is subjected to gradient heating to remove solvent as much as possible and complete thermal imidization to obtain a dielectric film for high-temperature energy storage.

[0021] Furthermore, in step S2, the substrate includes aluminum foil, copper foil, glass sheet, or polymer film.

[0022] Furthermore, the mixing temperature in step S1 is 20-40℃, and the time is 0.5-2h.

[0023] Furthermore, in step S2, the mixing temperature is 32-40℃, the pressure is 7.4-8.4MPa, and the time is 2-5h.

[0024] Furthermore, in step S3, the minimum temperature of the gradient heating treatment is 50-80℃, the maximum temperature is 200-350℃, the gradient temperature difference is 20-80℃, and the time for each step is 0.5-2h.

[0025] Furthermore, in step S3, when preparing the multilayer wet film, the wet film of the first layer is heat-treated at 50-80℃ for 0.5-2h before the second layer is sprayed, and the wet film of the last layer is subjected to gradient heat treatment.

[0026] One of the technical solutions of the present invention is to provide an apparatus for preparing a dielectric thin film for high-temperature energy storage. This apparatus employs the method described above for slurry pre-preparation and supercritical spraying, and includes a diluent pressure vessel, a slurry mixing vessel, an additive storage vessel, a supercritical dilution mixing vessel, a buffer vessel, regulating valves, and a spray gun.

[0027] The diluent pressure vessel stores liquid diluent; the spray slurry mixing vessel mixes the high-temperature resistant polymer and solvent to obtain the spray slurry; and the additive storage container stores additives.

[0028] The supercritical dilution mixing vessel connects the diluent pressure vessel, the spray slurry mixing vessel, and the additive storage vessel, and mixes the spray slurry, additives, and diluent to obtain a polymer slurry.

[0029] The supercritical dilution mixing container is connected to a buffer container, which is connected to a regulating valve, which is connected to a spray gun. Under a specified saturation pressure, according to the program set in the device, the polymer slurry is transported outward in a supercritical state at a certain pressure and temperature by controlling the opening size of the regulating valve. It diffuses at a certain angle and arc through the diffusion nozzle of the spray gun and falls onto the substrate to form a wet film.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention uses a soluble high-temperature resistant polymer or its soluble precursor with a high glass transition temperature, which shows great application potential in the field of high-temperature energy storage. Furthermore, the wide band gap of the polymer and the addition of additives and fillers can provide higher breakdown strength.

[0032] (2) The present invention employs a supercritical spraying process, which utilizes the gas-like diffusivity, liquid-like density and solubility in the supercritical state, while also possessing the characteristics of low viscosity and low surface tension.

[0033] (3) This invention uses supercritical carbon dioxide, which is stable, safe and non-toxic, as a diluent to control the viscosity and mixing uniformity of the slurry to improve film-forming performance and reduce defects. At the same time, it reduces the baking after dilution of a large amount of organic solvent, saves energy for high-temperature solvent removal and reduces pollution from a large amount of diluent.

[0034] (4) The present invention is easy to implement, simple to operate, has good applicability and high efficiency. It is suitable for large-scale, low-cost industrial production of high-quality ultrathin polymer-based dielectric films, while the equipment cost is much lower than that of a complete set of biaxial stretching equipment. Furthermore, the film prepared by the present invention has uniform thickness, strong breakdown resistance and high dielectric strength, thus exhibiting excellent high-temperature energy storage performance and good reliability. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the apparatus for preparing a dielectric thin film for high-temperature energy storage in an embodiment of the present invention.

[0036] Explanation of markings in the diagram:

[0037] 1—Diluent pressure vessel, 2—Spray slurry mixing vessel, 3—Additive storage vessel, 4—Supercritical dilution mixing vessel, 5—Buffer vessel, 6—Regulating valve, 7—Diffusion nozzle, 8—Substrate, 9—Wet film. Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0039] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0040] An apparatus for preparing dielectric thin films for high-temperature energy storage, such as... Figure 1 As shown, it includes a diluent pressure vessel 1, a spray slurry mixing vessel 2, an additive storage vessel 3, a supercritical dilution mixing vessel 4, a buffer vessel 5, a regulating valve 6, and a spray gun 7.

[0041] The diluent pressure vessel 1 stores the diluent liquid; the spray slurry mixing vessel 2 is a magnetic stirring tank used to mix the high-temperature resistant polymer and solvent to obtain the spray slurry; and the additive storage vessel 3 stores the additives.

[0042] The supercritical dilution mixing vessel 4 is a high-pressure magnetic stirring tank, connected to the diluent pressure vessel 1, the spray slurry mixing vessel 2, and the additive storage vessel 3. The spray slurry, additives, and diluent are mixed to obtain a polymer slurry.

[0043] The supercritical dilution mixing container 4 is connected to the buffer container 5, the buffer container 5 is connected to the regulating valve 6, and the regulating valve 6 is connected to the spray gun 7. Under the specified saturation pressure, according to the program set in the device, the polymer slurry is transported outward in a supercritical state under a certain pressure and temperature by controlling the opening size of the regulating valve 6. It diffuses at a certain angle and arc through the diffusion nozzle of the spray gun 7 and falls onto the substrate 8 to form a wet film 9.

[0044] Example 1:

[0045] A dielectric thin film for high-temperature energy storage and its preparation method are disclosed, which involves slurry pre-preparation and supercritical spraying using the aforementioned apparatus. The specific steps are as follows:

[0046] S1. Slurry preparation: Polyamic acid, a precursor of polyimide (PI), and N-methylpyrrolidone are mixed in a spray slurry mixing container 2 at 25°C for 1 hour to obtain a uniform polyamic acid solution with a solid content of 20% as the spray slurry.

[0047] S2. Supercritical spraying: The spraying slurry and alumina powder from the additive storage container 3 are added to the supercritical dilution mixing container 4 at a mass ratio of 99:1. Carbon dioxide from the diluent pressure container 1 is introduced as a diluent. The conditions are controlled at a temperature of 36°C and a pressure of 7.6 MPa. The mixture is mixed with the spraying slurry in a supercritical state for 3 hours. By operating the regulating valve 6 and the spray gun 7, the polymer slurry with gas-liquid mixture in a supercritical state is sprayed onto the surface of a 15cm×20cm aluminum foil to form a wet film 9.

[0048] S3. Post-treatment: The wet film 9 is subjected to gradient heating treatment at 60℃ for 1 hour, 100℃ for 1 hour, 150℃ for 1 hour, 210℃ for 1 hour, and 260℃ for 1 hour to remove the solvent as much as possible and complete the thermal imidization to obtain a PI dielectric film for high-temperature energy storage.

[0049] Example 2:

[0050] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 1, except that in step S3, single-layer spraying is replaced by double-layer spraying. The wet film 9 of single-layer spraying is subjected to heat treatment at 60°C for 1 hour. Then, step S2 is repeated to apply the second layer of spraying with the previous wet film 9 as the substrate, and then gradient heat treatment is performed to obtain a double-layer PI dielectric thin film for high-temperature energy storage.

[0051] Example 3:

[0052] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 2, except that the double-layer spraying in step S3 is replaced by triple-layer spraying. The wet film 9 of the double-layer spraying is subjected to heat treatment at 60°C for 1 hour. Then, step S2 is repeated to apply the third layer spraying with the previous wet film 9 as the substrate, and then gradient heat treatment is performed to obtain a three-layer PI dielectric thin film for high-temperature energy storage.

[0053] Example 4:

[0054] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 1, except that a polyamic acid solution with a solid content of 15% is used as the spraying slurry in step S1 instead of a solution with a solid content of 20%.

[0055] Example 5:

[0056] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 1, except that in step S1, a polyetherimide (PEI) precursor polyamic acid solution with a solid content of 20% is used as the spraying slurry instead of a PI precursor polyamic acid solution.

[0057] Example 6:

[0058] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 1, except that the mass ratio of the spraying slurry and alumina powder in step S2 is 99.5:0.5 instead of 99:1.

[0059] Example 7:

[0060] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Example 1, except that boehmite powder is used in step S2 instead of alumina powder.

[0061] Comparative Examples 1 to 7:

[0062] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Examples 1 to 7, except that no additive powder is added in step S2.

[0063] Comparative Examples 8 to 14:

[0064] A dielectric thin film for high-temperature energy storage and its preparation method are basically the same as those in Examples 1 to 7, except that carbon dioxide is not introduced directly in step S2.

[0065] Compared with Examples 1 to 3, each additional wet film layer 9 increases the breakdown field strength at 150°C by 5-10% and reduces the dielectric loss by 10-20%.

[0066] Compared with Comparative Examples 1 to 7, Examples 1 to 7 show a 5-8% increase in breakdown field strength and a 10-15% decrease in dielectric loss at 150°C.

[0067] Compared with Comparative Examples 8 to 14, Examples 1 to 7 showed a 10-15% reduction in thickness variation. Regarding post-processing time, the surfaces of the Examples were smooth at the same time, while the surfaces of the Comparative Examples had black impurities. Even with the gradient heating treatment time increased to 3 hours each time, the surfaces of Comparative Examples 8, 9, 11, 13 and 14 still had wrinkles and did not achieve a smooth state.

[0068] After testing, the embodiments of the present invention are convenient to implement, simple to operate, have good applicability, and high efficiency. They are suitable for large-scale, low-cost industrial production of high-quality ultrathin polymer-based dielectric films, while the equipment cost is significantly lower than that of a complete set of biaxial stretching equipment. Furthermore, the films prepared using the embodiments of the present invention have uniform thickness, strong breakdown resistance, and high dielectric strength, thus exhibiting excellent high-temperature energy storage performance and good reliability.

[0069] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a dielectric thin film for high-temperature energy storage, characterized in that, The dielectric thin film is prepared by supercritical spraying and heat treatment, and comprises the following components in parts by weight: 5-30 parts of high-temperature resistant polymer, 0.1-5 parts of additives, and 60-95 parts of solvent; The high-temperature resistant polymer is selected from one or more of polyimide polymers and polyamic acid, the precursor of polyimide polymers; The additive is selected from one or more inorganic fillers selected from alumina, boehmite, and silicon carbide; The solvent is selected from one or more of N,N'-dimethylacetamide, N-methylpyrrolidone, and N,N'-dimethylformamide; The method includes the following steps: S1. Slurry pre-preparation: High-temperature resistant polymer and solvent are mixed to obtain spray slurry; S2, supercritical spraying, add spraying slurry and additives, introduce carbon dioxide as a diluent and mix with the spraying slurry in a supercritical state, spray the polymer slurry with gas-liquid mixture in a supercritical state onto the surface of the substrate (8) to form a wet film (9). S3. Post-processing: The wet film (9) is subjected to gradient heating to remove the solvent as much as possible and complete thermal imidization to obtain a dielectric film for high-temperature energy storage. The mixing temperature in step S1 is 20-40 ℃, and the time is 0.5-2 h; In step S2, the temperature of the carbon dioxide introduced is 32-40 ℃, the pressure is 7.4-8.4 MPa, and the mixing time is 2-5 h; In step S3, the minimum temperature of the gradient heating treatment is 50-80 ℃, the maximum temperature is 200-350 ℃, the gradient temperature difference is 20-80 ℃, and the time for each step is 0.5-2 h. In step S3, when preparing the multilayer wet film (9), the wet film (9) of the first layer is heat-treated at 50-80 °C for 0.5-2 h before the second layer is sprayed, and the wet film (9) of the last layer is subjected to gradient heat treatment.

2. The method for preparing a dielectric thin film for high-temperature energy storage according to claim 1, characterized in that, The polyimide polymer is selected from one or more of polyimides, fluorinated polyimides, and polyetherimides.

3. The method for preparing a dielectric thin film for high-temperature energy storage according to claim 1, characterized in that, In step S2, the substrate (8) includes aluminum foil, copper foil, glass sheet or polymer film.

4. An apparatus for preparing a dielectric thin film for high-temperature energy storage, characterized in that, The device employs the method described in claim 1 for slurry pre-preparation and supercritical spraying, including a diluent pressure vessel (1), a spray slurry mixing vessel (2), an additive storage vessel (3), a supercritical dilution mixing vessel (4), a buffer vessel (5), a regulating valve (6), and a spray gun (7). The diluent pressure vessel (1) stores diluent liquid; the spray slurry mixing container (2) mixes the high-temperature resistant polymer and solvent to obtain the spray slurry; and the additive storage container (3) stores additives. The supercritical dilution mixing container (4) is connected to the diluent pressure container (1), the spray slurry mixing container (2), and the additive storage container (3), and the spray slurry, additives, and diluent are mixed to obtain a polymer slurry. The supercritical dilution mixing container (4) is connected to a buffer container (5), which is connected to a regulating valve (6), which is connected to a spray gun (7). By regulating the valve (6), the polymer slurry is transported outward in a supercritical state, and diffused through the diffusion nozzle of the spray gun (7), and scattered onto the substrate (8) to form a wet film (9).

Images