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

Abstract

The invention 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 formation and heat treatment, and the dielectric film 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 a polyimide polymer and a precursor polyamide acid of the polyimide polymer; the additive is selected from one or more inorganic fillers of aluminum oxide, boehmite and silicon carbide. Compared with the prior art, the invention has the advantages of uniform thickness, strong breakdown resistance and high dielectric strength.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage material preparation, and relates to a dielectric film for high-temperature energy storage and a preparation method and device thereof. Background Art

[0002] In recent years, dielectric capacitors have become an important part of modern power systems. Their advantages are that they have intrinsic extremely fast charging and discharging capabilities and ultra-high power density, all-solid-state structure, high operating voltage, and low loss. However, the common problem of film capacitors based on various dielectric electrolyte materials is that their energy density is low, which seriously hinders the development of manufacturing technology for high-power and large-capacity capacitors.

[0003] Therefore, in practical applications, in order to avoid occupying too much volume in integrated circuits, there is a demand for improving energy storage performance. In particular, for scenarios such as pulse power systems, hybrid vehicles, oil and gas energy exploration and mining, and efficient use of clean energy such as wind energy, higher high-temperature resistant energy storage performance requirements are further proposed. Taking the commonly used commercial capacitor film, biaxially oriented polypropylene (BOPP), as an example, its operating temperature is usually around 70°C, and the maximum is generally not more than 105°C. For film capacitors made of BOPP material, the internal leakage current of the dielectric will increase exponentially at higher temperatures and high electric fields, causing a sharp drop in charging and discharging efficiency and energy storage density, while generating a large amount of Joule heat, exacerbating the performance degradation. Domestic and foreign researchers have developed polymers with high glass transition temperatures as dielectric film materials for organic film capacitors, such as polyimide (PI), polyetherimide (PEI), etc., which have improved high-temperature energy storage performance. However, the thickness of these dielectric films for high-temperature energy storage is generally greater than 10μm, which cannot meet the thin layer requirements of dielectric films.

[0004] The application of various new polymers in dielectric capacitors is often limited by film manufacturing technology. How to manufacture large, ultra-thin, continuous and uniform high-quality dielectric films is an important technical issue in the development of dielectric capacitors for high-temperature energy storage. The current commercial BOPP film can be as thin as 2.2μm, using a process of melt extrusion combined with biaxial stretching, and the equipment cost is relatively high. Previously, patent CN115093590A disclosed a film for high-temperature electrostatic energy storage and its preparation method and application. The film uses an ultrasonic spraying process, which is simple and widely applicable, and is suitable for large-scale industrial production of high-quality ultra-thin polymer-based dielectric films. However, the concentration of the polymer applicable to this process is 0.01-0.05g / mL, so a large amount of organic solvent is required for dilution, which increases the pollution to the environment. Therefore, it is particularly important to develop a more environmentally friendly and low-cost new high-temperature energy storage high-quality, large-area ultra-thin dielectric film preparation process.

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

[0006] Patent CN116178782A discloses a method for preparing a high-filler ultra-thin polytetrafluoroethylene-based composite dielectric substrate, wherein 51-75% of ceramic powder, 15-25% of polytetrafluoroethylene emulsion, 1-13% of fiber, and 8-19% of deionized water are mixed and stirred by weight to obtain a composite slurry, and then a flocculant accounting for 5-15% of the weight ratio of the composite slurry is added, stirred for 15-30 minutes, and the water is filtered to obtain a dough-like high-filler PTFE composite wet material, and the high-filler PTFE composite wet material is subjected to normal temperature calendering, supercritical drying, atomization spraying of impregnating agent, high pressure calendering technology, and high-temperature drying to prepare a high-filler ultra-thin PTFE-based composite dielectric substrate. However, the preparation process of this patent is relatively complicated, cumbersome, and costly. Summary of the invention

[0007] The purpose of the present invention is to overcome at least one defect of the above-mentioned prior art and to provide a dielectric film for high-temperature energy storage and a preparation method and device thereof. The present invention has uniform thickness, strong breakdown resistance and high dielectric strength.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide a dielectric film for high-temperature energy storage, which is prepared by supercritical spraying film formation 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 which is a 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 polyimide, fluorinated polyimide and polyetherimide.

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

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

[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 film for high temperature energy storage, the method comprising the following steps:

[0018] S1, slurry prefabrication, mixing a high temperature resistant polymer and a solvent to obtain a spray slurry;

[0019] S2, supercritical spraying, adding spray slurry and additives, introducing carbon dioxide as a diluent and mixing with the spray slurry in a supercritical state, and spraying the polymer slurry having a gas-liquid mixture mixed in a supercritical state onto the surface of the substrate to form a wet film;

[0020] S3, post-treatment, subjecting the wet film to gradient heating treatment, removing the solvent as much as possible and completing 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° C. and the mixing time is 0.5-2 h.

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

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

[0025] Furthermore, when preparing the multi-layer wet film in step S3, the wet film sprayed on the front layer is subjected to a heating treatment at 50-80° C. for 0.5-2 h before the rear layer is sprayed, and the wet film sprayed on the last layer is subjected to a gradient heating treatment.

[0026] One of the technical solutions of the present invention is to provide a device for preparing a dielectric film for high-temperature energy storage, which adopts the method described above to perform slurry prefabrication and supercritical spraying, and includes a diluent pressure vessel, a spray slurry mixing vessel, an additive storage vessel, a supercritical dilution mixing vessel, a buffer vessel, a regulating valve and a spray gun.

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

[0028] The supercritical dilution mixing container is connected to the diluent pressure container, the spray slurry mixing container and the additive storage container, and the spray slurry, the additive and the diluent are mixed to obtain the polymer slurry.

[0029] The supercritical dilution mixing container is connected to a buffer container, the buffer container is connected to a regulating valve, the regulating valve is connected to a spray gun. Under a specified saturation pressure, according to a program set in the device, the opening size of the regulating valve is controlled to allow the polymer slurry to be transported outward in a supercritical state at a certain pressure and temperature, diffused at a certain angle and arc through the diffusion nozzle of the spray gun, and scattered on 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 a soluble precursor thereof with a high glass transition temperature, which has great application potential in the field of high temperature energy storage, and the wide band gap of the polymer and the addition of additive fillers can provide higher breakdown strength;

[0032] (2) The present invention also uses a supercritical spraying process, utilizing the gas-like diffusivity, liquid-like density and solubility in a supercritical state, while also having the characteristics of low viscosity and low surface tension;

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

[0034] (4) The present invention is easy to implement, simple to operate, has good applicability and high efficiency, and is suitable for large-scale, low-cost industrial production of high-quality ultra-thin polymer-based dielectric films, while the equipment cost is greatly reduced compared to a complete set of biaxial stretching equipment; and the film prepared by the present invention has uniform thickness, strong breakdown resistance and high dielectric strength, and therefore has excellent high-temperature energy storage performance and good reliability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Description of the markings in the figure:

[0037] 1—diluent pressure vessel, 2—spray slurry mixing container, 3—additive storage container, 4—supercritical dilution mixing container, 5—buffer container, 6—regulating valve, 7—diffusion nozzle, 8—substrate, 9—wet film. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0039] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0040] A device for preparing a dielectric film 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 container 1 stores diluent liquid, the spray slurry mixing container 2 uses a magnetic stirring tank to mix the high temperature resistant polymer and the solvent to obtain the spray slurry, and the additive storage container 3 stores the additive.

[0042] The supercritical dilution mixing container 4 is a high-pressure magnetic stirring tank, which 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.

[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, by controlling the opening size of the regulating valve 6, the polymer slurry is transported outward in a supercritical state at a certain pressure and temperature, and diffuses at a certain angle and arc through the diffusion nozzle of the spray gun 7, and scatters on the substrate 8 to form a wet film 9.

[0044] Embodiment 1:

[0045] A dielectric film for high-temperature energy storage and a preparation method thereof, using the above device for slurry prefabrication and supercritical spraying, the specific steps are as follows:

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

[0047] S2, supercritical spraying, adding the spray slurry and the aluminum oxide powder from the additive storage container 3 into the supercritical dilution mixing container 4 at a mass ratio of 99:1, introducing carbon dioxide as a diluent from the diluent pressure container 1, controlling the conditions, the temperature is 36° C., the pressure is 7.6 MPa, and the spray slurry is mixed with the supercritical state for 3 hours, and the polymer slurry with a gas-liquid mixture mixed into a supercritical state is sprayed onto the surface of a 15 cm×20 cm aluminum foil by operating the regulating valve 6 and the spray gun 7 to form a wet film 9;

[0048] S3, post-treatment, subjecting the wet film 9 to gradient heating treatment, 60°C, 1h, 100°C, 1h, 150°C, 1h, 210°C, 1h, 260°C, 1h to remove the solvent as much as possible and complete thermal imidization to obtain a PI dielectric film for high-temperature energy storage.

[0049] Embodiment 2:

[0050] A dielectric film for high-temperature energy storage and a preparation method thereof are basically the same as those in Example 1, except that in step S3, the single-layer spraying is replaced by double-layer spraying, the single-layer sprayed wet film 9 is heated at 60° C. for 1 h, and then step S2 is repeated to spray the second layer with the previous wet film 9 as the substrate, and then gradient heating is performed to obtain a double-layer PI dielectric film for high-temperature energy storage.

[0051] Embodiment 3:

[0052] A dielectric film for high-temperature energy storage and a preparation method thereof are basically the same as those in Example 2, except that in step S3, the double-layer spraying is replaced by a three-layer spraying, the double-layer sprayed wet film 9 is heated at 60° C. for 1 h, and then step S2 is repeated to spray the third layer with the previous wet film 9 as the substrate, and then gradient heating is performed to obtain a three-layer PI dielectric film for high-temperature energy storage.

[0053] Embodiment 4:

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

[0055] Embodiment 5:

[0056] A dielectric film for high-temperature energy storage and a preparation method thereof 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 spray slurry instead of a PI precursor polyamic acid solution.

[0057] Embodiment 6:

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

[0059] Embodiment 7:

[0060] A dielectric film for high-temperature energy storage and a preparation method thereof 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 film for high-temperature energy storage and a preparation method thereof are substantially the same as those of embodiments 1 to 7, except that no additive powder is added in step S2.

[0063] Comparative Examples 8 to 14:

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

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

[0066] Compared with comparative examples 1 to 7, the breakdown field strength of examples 1 to 7 at 150° C. is increased by 5-8%, and the dielectric loss is reduced by 10-15%;

[0067] The thickness range of Examples 1 to 7 is reduced by 10-15% compared with Comparative Examples 8 to 14. For the post-processing time, the surface of the examples is flat under the same post-processing time, while the surface of the comparative examples has black impurities. Even if the time of each gradient heating treatment is increased to 3 hours, the surfaces of Comparative Examples 8, 9, 11, 13 and 14 still have wrinkles and have not reached a flat state.

[0068] After testing, the embodiment of the present invention is easy to implement, simple to operate, has good applicability and high efficiency, and is suitable for large-scale, low-cost industrial production of high-quality ultra-thin polymer-based dielectric films, while the equipment cost is greatly reduced compared to a complete set of biaxial stretching equipment; and the film prepared by the embodiment of the present invention has uniform thickness, strong breakdown resistance and high dielectric strength, and therefore has excellent high-temperature energy storage performance and good reliability.

[0069] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the scope of protection of the present invention.

Claims

1. A dielectric film for high temperature energy storage, characterized in that: The dielectric film is prepared by supercritical spraying film formation and heat treatment, and includes 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 which is a precursor of polyimide polymers; The additive is selected from one or more inorganic fillers selected from alumina, boehmite, and silicon carbide.

2. A dielectric film for high temperature energy storage according to claim 1, characterized in that: The polyimide polymer is selected from one or more of polyimide, fluorinated polyimide and polyetherimide.

3. The dielectric film for high temperature energy storage according to claim 1, characterized in that: The solvent is selected from one or more of N,N'-dimethylacetamide, N-methylpyrrolidone, and N,N'-dimethylformamide.

4. A method for preparing a dielectric film for high temperature energy storage according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1, slurry prefabrication, mixing a high temperature resistant polymer and a solvent to obtain a spray slurry; S2, supercritical spraying, adding spray slurry and additives, introducing carbon dioxide as a diluent and mixing it with the spray slurry in a supercritical state, and spraying the mixed polymer slurry onto the surface of the substrate (8) to form a wet film (9); S3, post-processing, subjecting the wet film (9) to gradient heating treatment to obtain a dielectric film for high-temperature energy storage.

5. The method for preparing a dielectric film for high temperature energy storage according to claim 4, characterized in that: In step S2, the substrate (8) includes aluminum foil, copper foil, glass sheet or polymer film.

6. The method for preparing a dielectric film for high temperature energy storage according to claim 4, characterized in that: The mixing temperature in step S1 is 20-40° C. and the mixing time is 0.5-2 h.

7. The method for preparing a dielectric film for high temperature energy storage according to claim 4, characterized in that: The mixing temperature in step S2 is 32-40° C., the pressure is 7.4-8.4 MPa, and the mixing time is 2-5 h.

8. The method for preparing a dielectric film for high temperature energy storage according to claim 4, characterized in that: The minimum temperature of the gradient heating treatment in step S3 is 50-80°C, the maximum temperature is 200-350°C, the gradient temperature difference is 20-80°C, and the time for each treatment is 0.5-2h.

9. The method for preparing a dielectric film for high temperature energy storage according to claim 4, characterized in that: When preparing the multi-layer wet film (9) in step S3, the wet film (9) sprayed on the front layer is subjected to a heating treatment at 50-80°C for 0.5-2h before the rear layer is sprayed, and the wet film (9) sprayed on the last layer is subjected to a gradient heating treatment.

10. A device for preparing a dielectric film for high-temperature energy storage, characterized in that: The device adopts the method as claimed in claim 4 to perform slurry prefabrication and supercritical spraying, comprising a diluent pressure container (1), a spray slurry mixing container (2), an additive storage container (3), a supercritical dilution mixing container (4), a buffer container (5), a regulating valve (6) and a spray gun (7). The diluent pressure container (1) stores diluent liquid, the spray slurry mixing container (2) mixes the high temperature resistant polymer and the solvent to obtain the spray slurry, and the additive storage container (3) stores the additive. 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, the additive and the diluent are mixed to obtain a polymer slurry. The supercritical dilution mixing container (4) is connected to a buffer container (5), the buffer container (5) is connected to a regulating valve (6), the regulating valve (6) is connected to a spray gun (7), and the polymer slurry is transported outward in a supercritical state through the regulating valve (6), diffused through the diffusion nozzle of the spray gun (7), and scattered on the substrate (8) to form a wet film (9).

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