Normal pressure drying preparation method of polyimide aerogel powder and application thereof

Abstract

This invention provides a method for preparing polyimide aerogel powder by atmospheric pressure drying and its application. The method uses aromatic diamine and aromatic dianhydride as monomers, dissolving them in an organic solvent and reacting them via polycondensation to generate a polyamic acid solution. Metal ions and crosslinking agents are introduced into the polyamic acid solution to construct a crosslinked network between molecular chains, and a polyimide solution is obtained through a chemical imidization reaction. The polyimide solution is then directly injected into anhydrous ethanol to shorten the gel aging time and facilitate rapid solvent exchange, significantly shortening the production cycle of the polyimide aerogel. The resulting suspension is filtered and dried at atmospheric pressure to obtain polyimide aerogel powder. This polyimide aerogel powder can be used to formulate functional slurries and processed into high-performance battery separators through coating processes, significantly improving battery performance. This invention combines slurry preparation with industrialized spray coating technology, enabling the mass production of large-area composite battery separators, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials and battery technology, and relates to a method for preparing polyimide aerogel powder by atmospheric pressure drying and its application. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage materials, the demand for high-performance batteries is constantly expanding. Lithium metal batteries, due to their high theoretical capacity and high energy density, are considered one of the representatives of high-performance batteries. However, the heat accumulation generated during high-rate charging and discharging and long-term cycling always poses safety hazards. As a core protective component inside the battery, the performance of the separator directly determines the battery's safety, ion transport efficiency, and cycle life. Currently, mainstream commercial polyolefin separators have significant shortcomings, such as low heat distortion temperature. Coating modification can improve the thermal stability and mechanical strength of the separator, improve electrolyte wettability, and increase functionality. Combining the properties of polyimide aerogel, it can be used as a coating material to improve the performance of battery separators to a certain extent.

[0003] Traditional bulk polyimide and polyimide membrane materials suffer from insufficient electrolyte adsorption capacity due to their low specific surface area and porosity. Furthermore, the existing pore structure is difficult to match the process requirements of membrane coating slurry systems, limiting their direct application. In contrast, aerogels, as ultralight, high-porosity nanoporous materials, have demonstrated unique advantages in energy, environmental protection, and aerospace fields due to their low density, high specific surface area, and excellent thermal insulation properties. Of particular note is that polyimide aerogels, by combining the porous properties of aerogels with the high heat resistance, mechanical strength, and chemical stability of polyimide materials, have become a research hotspot for next-generation high-performance functional materials. However, existing polyimide aerogel preparation technologies face significant bottlenecks: while mainstream supercritical drying and freeze-drying processes can effectively remove solvents and construct porous networks, they suffer from high equipment complexity, high energy consumption, and high costs, severely restricting the large-scale production of materials. More importantly, existing aerogel products are mostly limited to bulk or thin film forms, and their preparation processes and molding methods greatly limit the expansion of commercial applications.

[0004] Therefore, it is crucial to design a polyimide aerogel powder that can maintain its porous structure stability and significantly shorten aging time through atmospheric pressure drying without requiring complex drying processes. Such a material could not only be directly applied as a functional coating material to slurry systems, for example, significantly improving electrolyte wettability and thermal safety of batteries through composite membrane processing, but also provide innovative solutions for the industrial upgrading of battery separator coating materials, possessing significant application value. Summary of the Invention

[0005] Objective: To address the problems and shortcomings of existing technologies, this invention provides a method for preparing polyimide aerogel powder by atmospheric pressure drying and its application. This method improves efficiency and shortens aging time through optimized solvent exchange processes, combined with atmospheric pressure drying, to successfully prepare polyimide aerogel powder. This process ensures the formation of a three-dimensional porous network structure with uniform pore distribution and structural integrity, resulting in powder with excellent processability. Based on these characteristics, this polyimide aerogel powder can be used to formulate functional slurries and is suitable for coating and preparing lithium-ion battery composite separators, significantly improving battery safety and electrochemical performance.

[0006] The first aspect of the present invention is to provide a method for preparing polyimide aerogel powder by atmospheric pressure drying, the method comprising the following steps:

[0007] (1) Under an inert atmosphere, the aromatic diamine monomer is dissolved in the reaction solvent, and the dianhydride monomer is added under ice-water bath conditions to carry out a polycondensation reaction to obtain a polyamic acid prepolymer solution.

[0008] (2) Metal salt and crosslinking agent are added sequentially to polyamic acid prepolymer solution to achieve molecular chain crosslinking, and then catalyst and dehydrating agent are added to carry out chemical imidization reaction to obtain polyimide solution;

[0009] (3) The polyimide solution is directly injected into the continuously stirred organic solvent I to reduce the aging time and perform rapid solvent exchange to obtain a polyimide aerogel particle suspension. After filtration and drying at normal pressure, polyimide aerogel powder is obtained.

[0010] This invention accelerates solvent exchange efficiency, shortens aging time, and improves the solvent exchange rate. A polyimide aerogel powder with a nanoporous microstructure can be obtained through an atmospheric pressure drying process. This invention represents a highly promising method for the large-scale preparation of polyimide aerogel powder.

[0011] In one embodiment, the aromatic diamine monomer in step (1) includes at least one of 1,4-bis(4-amino-phenylene ether)phenyl-1,4-diazabutadiene (DAB), p-phenylenediamine, biphenylenediamine, 4,4'-diaminodiphenyl ether or 4,4'-diaminodiphenyl sulfide, preferably 1,4-bis(4-amino-phenylene ether)phenyl-1,4-diazabutadiene.

[0012] In one embodiment, the dianhydride monomer in step (1) is an aromatic dianhydride monomer, including at least one of hexafluorodianhydride, pyromellitic dianhydride, pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride or biphenyltetracarboxylic acid dianhydride, preferably hexafluorodianhydride.

[0013] In one embodiment, the reaction solvent in step (1) is at least one of N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone, preferably N,N-dimethylacetamide.

[0014] In one embodiment, the molar ratio of the aromatic diamine monomer and the dianhydride monomer in step (1) is 1:1 to 1:1.5, preferably 1:1.1.

[0015] In one embodiment, the mass concentration of the polyamic acid prepolymer solution in step (1) is 3%-15%, preferably 7%-12%, and more preferably 10%.

[0016] In one implementation, the polycondensation reaction time in step (1) is 1-3 hours, preferably 2 hours.

[0017] In one embodiment, in step (2), the metal salt includes at least one of zirconium chloride, titanium chloride, tin chloride, chromium chloride, or aluminum chloride, preferably zirconium chloride.

[0018] In one implementation, in step (2), the molar ratio of the metal salt to the aromatic diamine monomer is 1:(0.5-3).

[0019] In one embodiment, step (2) is performed with a coordination chemical reaction time of 1-3 hours, preferably 2 hours.

[0020] In one implementation, in step (2), the crosslinking agent includes a flame-retardant crosslinking agent and / or a silane coupling agent.

[0021] Furthermore, in one implementation, in step (2), the flame retardant crosslinking agent is an ammonium phosphate crosslinking agent.

[0022] Furthermore, in one embodiment, in step (2), the ammonium phosphate crosslinking agent includes at least one of triphenyl phosphate, triethyl phosphate, ammonium tripolyphosphate, ammonium orthophosphate, or ammonium polyphosphate, preferably an ammonium polyphosphate crosslinking agent.

[0023] In one embodiment, the silane coupling agent in step (2) includes at least one of 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, and vinyltriethoxysilane, with 3-aminopropyltriethoxysilane being selected.

[0024] In one embodiment, in step (2), the molar ratio of the crosslinking agent to the aromatic diamine monomer is 1:(0.5-3), preferably 1:1.1.

[0025] In one embodiment, in step (2), the catalyst includes at least one of pyridine, tributylphosphine, and triethylamine.

[0026] In one embodiment, in step (2), the dehydrating agent includes at least one of acetic anhydride, propionic anhydride, trifluoroacetic anhydride, benzoic anhydride, thionyl chloride, and N,N'-dicyclohexylcarbodiimide.

[0027] Furthermore, in one embodiment, the catalyst is preferably triethylamine, and the dehydrating agent is preferably acetic anhydride.

[0028] Furthermore, in one embodiment, the molar ratio of the catalyst, dehydrating agent, and aromatic diamine monomer is 8:8:(0.5-3), preferably 8:8:1.

[0029] Furthermore, in one embodiment, the imidization reaction time is 20-40 min, preferably 30 min.

[0030] In one implementation, in step (3), the organic solvent I includes at least one of methanol, ethanol, acetone, cyclohexane or n-hexane, preferably anhydrous ethanol.

[0031] Furthermore, in one embodiment, the volume ratio of the organic solvent I to the polyimide solution is (20-30):1, preferably 20:1.

[0032] Furthermore, in one embodiment, the stirring speed of the organic solvent I is 300-800 rpm.

[0033] Furthermore, in one embodiment, the injection rate of the polyimide solution is 5 mL / min to 20 mL / min.

[0034] Furthermore, in one embodiment, the solvent exchange time is 12-24 hours, preferably 12 hours.

[0035] Furthermore, in one embodiment, the drying parameters are 30-40°C under normal pressure and a drying time of 4-12 hours.

[0036] A second aspect of the present invention is to provide a polyimide aerogel powder prepared by any of the methods described above.

[0037] In one embodiment, the polyimide aerogel powder has the following characteristics:

[0038] The powder density is 0.4-0.5 g / cm³. 3 , and / or

[0039] The specific surface area of ​​the powder is approximately 150-160 m².2 / g.

[0040] A third aspect of the present invention is to provide a coating slurry for a battery separator, the coating slurry containing a polyimide aerogel powder as described above.

[0041] A fourth aspect of the present invention is to provide a method for preparing the above-described coating slurry for a battery separator, comprising the following steps:

[0042] The dispersant is mixed with organic solvent II and stirred to form a uniform dispersion solution;

[0043] Polyimide aerogel powder was added to the dispersion solution and stirred continuously to obtain a primary dispersion slurry;

[0044] The primary dispersion slurry is added to a grinding mill for grinding, and the particle size distribution is controlled to obtain a grinding slurry;

[0045] A binder is added to the grinding slurry, and the mixture is stirred to obtain the final coating slurry.

[0046] In one embodiment, the mass ratio of organic solvent II: polyimide aerogel powder: dispersant: binder is 35:7:(0.2-0.8):2, preferably 35:7:0.35:2.

[0047] In one embodiment, the organic solvent II includes at least one of methanol, ethanol, acetone, cyclohexane, and n-hexane, preferably anhydrous ethanol.

[0048] In one embodiment, the stirring speed of the slurry is 500-1000 rpm.

[0049] In one embodiment, the dispersant includes at least one of polyacrylic acid, polyvinylpyrrolidone, and sodium dodecyl sulfate, preferably polyacrylic acid.

[0050] In one embodiment, the stirring time after the dispersant is added is 20-40 minutes, preferably 30 minutes.

[0051] In one embodiment, the polyimide aerogel powder is stirred for 1-3 hours after being added.

[0052] In one embodiment, the grinding time is 5-15 minutes, preferably 10 minutes.

[0053] In one embodiment, the adhesive includes at least one of phenolic resin, polymethyl methacrylate, and polyvinylidene fluoride, preferably phenolic resin.

[0054] In one embodiment, the mixing time after the adhesive is added is 20-40 minutes, preferably 30 minutes.

[0055] The fifth aspect of this invention is to provide an application of the above-described technical method and the polyimide aerogel coating slurry prepared therefrom, including but not limited to the field of battery separators.

[0056] A sixth aspect of the present invention is to provide a polyimide aerogel composite separator obtained by coating a battery separator with a coating slurry prepared as described above or by the methods described above.

[0057] In one embodiment, the method of coating a battery separator with a coating slurry includes the following steps:

[0058] The battery separator is laid flat on aluminum foil, and organic solvent III is applied to the surface of the separator for wetting treatment by atomizing spraying device.

[0059] The above-mentioned coating slurry containing polyimide aerogel powder is injected into an atomizing spraying device and uniformly sprayed onto the wetted diaphragm under the same pressure conditions.

[0060] The battery separator with single-sided spraying is transferred to a blower drying device, and the organic solvent III is completely evaporated under certain temperature conditions to obtain a single-sided coated dry film.

[0061] The dry film is flipped over and the above steps are repeated to finally obtain a composite membrane with a polyimide aerogel coating on both sides.

[0062] Furthermore, in one embodiment, the battery separator includes a lithium / sodium metal battery separator.

[0063] Furthermore, in one embodiment, the battery separator includes a polypropylene separator, a polyethylene separator, or a polyimide fiber membrane.

[0064] Furthermore, in one embodiment, the organic solvent III includes at least one of methanol, ethanol, acetone, and n-hexane, preferably anhydrous ethanol.

[0065] Furthermore, in one embodiment, the spraying time is 1-5 seconds, preferably 1 second.

[0066] Furthermore, in one embodiment, the pressure of the air pump is 0.3-0.4 MPa.

[0067] Furthermore, in one implementation, the spraying time is 1-5 seconds.

[0068] Furthermore, in one embodiment, the hot air drying temperature is 30-60°C.

[0069] Furthermore, in one implementation, the drying time is 3-12 hours.

[0070] In one embodiment, the polyimide aerogel composite membrane has the following characteristics:

[0071] The average pore size is 145 nm, and / or

[0072] The average film thickness is 26-42 μm, and / or

[0073] The cation transference number is 0.45, and / or

[0074] The interface impedance is 140-160Ω, and / or

[0075] The ionic conductivity is 0.67 mS / cm, and / or

[0076] The electrolyte contact angle of the polyimide aerogel composite membrane is ≤6.6°, preferably 0°, and / or

[0077] The polyimide aerogel composite membrane, when used under high-rate cycling conditions at 20°C, can stably cycle for more than 1500 cycles with a capacity retention of 93.3%.

[0078] A seventh aspect of the present invention is to provide the use of the polyimide aerogel powder as described above, or the coating slurry as described above, or the polyimide aerogel composite separator as described above, in the field of batteries, preferably, the battery comprising a lithium / sodium metal battery.

[0079] Compared with the prior art, the beneficial effects of the present invention are:

[0080] 1. This invention uses chemical imidization to obtain polyimide, followed by solvent exchange and atmospheric pressure drying to obtain polyimide aerogel powder. Traditional polyimide aerogel preparation requires high-temperature carbonization, freeze-drying, or supercritical drying processes, which are energy-intensive, require demanding equipment, and have low solvent recovery rates. This invention significantly reduces production costs and is suitable for continuous production.

[0081] 2. In this invention, the production cycle of polyimide aerogel is significantly shortened by reducing aging time and accelerating solvent exchange. After filtration and drying, polyimide aerogel powder is obtained. Compared with traditional block and film forms of polyimide, polyimide aerogel powder has excellent processability. Composite membranes can be prepared by coating processes such as spraying or scraping polyimide aerogel powder slurry.

[0082] 3. Based on the three-dimensional continuous porous network structure of polyimide aerogel, it has the characteristics of high porosity, high temperature resistance and lightweight. By introducing metal ions to regulate the pore structure of aerogel, the safety and electrochemical performance of battery separators, such as ion transference number, can be significantly improved. Attached Figure Description

[0083] Figure 1 This is a process flow diagram of the preparation and coating of polyimide gel powder according to the present invention.

[0084] Figure 2 The images show the finished polyimide aerogel powder product from Example 1, along with a multi-magnification scanning electron microscope photograph.

[0085] Figure 3 The graph shows the BET specific surface area test curve of the polyimide aerogel powder in Example 1.

[0086] Figure 4 This is a flowchart illustrating the preparation process of the Celgard membrane coated with polyimide aerogel powder in Example 1.

[0087] Figure 5 Photographs of the slurry prepared from the polyimide aerogel powder in Example 1 and the Celgard diaphragm with a large area of ​​polyimide aerogel powder sprayed onto it.

[0088] Figure 6 The Celgard membrane coated with polyimide aerogel powder is shown in Example 1. The Fourier transform infrared spectra of the Celgard membrane coated with polyimide aerogel powder and the polyimide aerogel powder are shown in Comparative Example 1.

[0089] Figure 7 Scanning electron microscope (SEM) image of the Celgard membrane coated with polyimide aerogel powder in Example 1 and its pore size distribution.

[0090] Figure 8 , 9 The Gibbs binding energy and electrolyte contact angle of the Celgard membrane coated with polyimide aerogel powder in Example 1, the Celgard membrane without polyimide aerogel powder in Comparative Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2 were tested.

[0091] Figure 10 The images show the interfacial impedance diagrams of the Celgard membrane coated with polyimide aerogel powder in Example 1, and the Celgard membrane coated with polyimide aerogel powder in Comparative Example 1 and Al2O3 in Comparative Example 2.

[0092] Figure 11 The Nyquist plot and ionic conductivity test results of the stainless steel symmetric cell assembled with the Celgard membrane coated with polyimide aerogel powder in Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2 are shown in Example 1.

[0093] Figure 12 Example 1 shows the Celgard membrane coated with polyimide aerogel powder, and Comparative Example 1 shows the lithium-ion transference number test results of the Celgard membrane coated with polyimide aerogel powder and the Celgard membrane coated with Al2O3 in Comparative Example 2.

[0094] Figure 13 Example 1 shows a Celgard separator coated with polyimide aerogel powder. Comparative Example 1 shows a Celgard separator coated with polyimide aerogel powder, and Comparative Example 2 shows a Celgard separator coated with Al2O3. The lithium metal batteries were subjected to long-cycle testing at a rate of 20C. Detailed Implementation

[0095] This invention provides a method for preparing polyimide aerogel powder by atmospheric pressure drying and its application. The method uses aromatic diamine and aromatic dianhydride as monomers, dissolving them in an organic solvent and reacting them via polycondensation to generate a polyamic acid solution. Metal ions and crosslinking agents are introduced into the polyamic acid solution to construct a crosslinked network between molecular chains, and a polyimide solution is obtained through a chemical imidization reaction. The polyimide solution is then directly injected into anhydrous ethanol to shorten the gel aging time and facilitate rapid solvent exchange, significantly shortening the production cycle of the polyimide aerogel. The resulting suspension is filtered and dried at atmospheric pressure to obtain polyimide aerogel powder. This polyimide aerogel powder can be used to formulate functional slurries and processed into high-performance battery separators through coating processes, significantly improving battery performance. This invention combines slurry preparation with industrialized spray coating technology, enabling the mass production of large-area composite battery separators, and has broad application prospects.

[0096] like Figure 1 The diagram shows the process flow for the preparation and coating of the polyimide aerogel powder of this invention. The main technologies include four steps: preparation of polyimide, synthesis of polyimide aerogel powder, preparation of polyimide aerogel powder composite slurry, and composite membrane of polyimide aerogel powder. The key technology of this invention lies in eliminating the aging time after polyimide preparation, directly performing rapid solvent exchange, and replacing high-cost drying technology with atmospheric pressure drying, thereby improving efficiency and reducing energy consumption costs. This better meets the transportation and processing requirements of industrial production, demonstrating significant industrial application value in fields such as lithium battery separator materials.

[0097] Among them, such as Figure 4 The diagram shows the preparation process of the Celgard separator coated with polyimide aerogel powder according to the present invention. The battery separator after spraying has a sandwich composite structure, with a base film in the middle and polyimide aerogel powder coatings on both sides, which is suitable for large-scale production and cutting by large machinery under existing technology.

[0098] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0099] Unless otherwise specified, all reagents used in the embodiments of this invention can be purchased commercially.

[0100] The present invention provides a figure showing the characterization test results of Embodiment 1. Other embodiments all use the same characterization test method. Those skilled in the art can directly and without doubt determine the content of the embodiments of the present invention through the characterization test method provided by the present invention, and will not be described in detail here.

[0101] Example 1: Preparation of polyimide aerogel powder #1

[0102] (1) Under inert gas protection, 2.45 g (5.8 mmol) of aromatic diamine monomer DAB and 47.79 g (0.549 mol) of N,N-dimethylacetamide were added to a three-necked flask placed in an ice-water bath and stirred at 300 rpm until dissolved. Hexafluorodianhydride (total 0.0064 mol, in portions of 1.00 g, 1.00 g, and 0.86 g) was added in three batches at 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 10 wt% was obtained.

[0103] (2) Add 0.6 g (2.57 mmol) of zirconium tetrachloride to the polyamic acid solution obtained in step (2) and react for 2 h until the solution turns brown. Then add 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate (stir for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane (react for 0.5 h), and finally add 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride dropwise, and continue stirring for 0.5 h to complete the chemical imidization.

[0104] (3) The polyimide solution obtained in step (3) was injected into anhydrous ethanol at a volume ratio of 1:20, wherein the volume of anhydrous ethanol accounted for 20 parts. The mixture was stirred at 300 rpm for 12 h to perform solvent exchange. The resulting light brown suspension was filtered and dried under normal pressure to obtain a yellowish-brown aerogel powder.

[0105] Example 2: Preparation of polyimide aerogel powder #2

[0106] The difference from Example 1 is that in step (1), 100.89 g (1.16 mol) of N,N-dimethylacetamide was added as an organic solvent, with a solid content of 5 wt%.

[0107] (1) Under inert gas protection, 2.45 g (5.8 mmol) of aromatic diamine monomer DAB and 100.89 g (1.16 mol) of N,N-dimethylacetamide were added to a three-necked flask placed in an ice-water bath and stirred at 300 rpm until dissolved. Hexafluorodianhydride (total 0.0064 mol, in portions of 1.00 g, 1.00 g, and 0.86 g) was added in three batches at 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 5 wt% was obtained.

[0108] (2) Add 0.6 g (2.57 mmol) of zirconium tetrachloride to the polyamic acid solution obtained in step (2) and react for 2 h until the solution turns brown. Then add 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate (stir for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane (react for 0.5 h), and finally add 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride dropwise, and continue stirring for 0.5 h to complete the chemical imidization.

[0109] (3) The polyimide solution obtained in step (3) was injected into anhydrous ethanol at a volume ratio of 20:1, wherein the volume of anhydrous ethanol accounted for 20 parts. The mixture was stirred at 300 rpm for 12 hours to perform solvent exchange. The resulting light brown suspension was filtered and dried under normal pressure to obtain a yellowish-brown aerogel powder.

[0110] Example 3: Preparation of polyimide aerogel powder #3

[0111] The difference from Example 1 is that no stirring is performed during solvent exchange in step (3).

[0112] (1) Under inert gas protection, 2.45 g (5.8 mmol) of aromatic diamine monomer DAB and 47.79 g (0.549 mol) of N,N-dimethylacetamide were added to a three-necked flask placed in an ice-water bath and stirred at 300 rpm until dissolved. Hexafluorodianhydride (total 0.0064 mol, in portions of 1.00 g, 1.00 g, and 0.86 g) was added in three batches at 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 10 wt% was obtained.

[0113] (2) Add 0.6 g (2.57 mmol) of zirconium tetrachloride to the polyamic acid solution obtained in step (2) and react for 2 h until the solution turns brown. Then add 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate (stir for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane (react for 0.5 h), and finally add 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride dropwise, and continue stirring for 0.5 h to complete the chemical imidization.

[0114] (3) The polyimide solution obtained in step (3) was injected into anhydrous ethanol at a volume ratio of 20:1, wherein the volume of anhydrous ethanol was 20 parts. Solvent exchange was carried out for 12 hours without stirring. The resulting light brown suspension was filtered and dried under normal pressure to obtain a yellowish-brown aerogel powder.

[0115] Test Example 1: Characteristic Test of Polyimide Aerogel Powder

[0116] like Figure 2 The image shows the polyimide aerogel powder 1# prepared in Example 1 on a macroscopic scale. Figure 2 a) It is a yellowish-brown fine powder, loosely piled in a container, and does not show obvious agglomeration after drying. Figure 2 The microstructure characterization shown in b reveals the morphology of polyimide aerogel powder particle #1 at low magnification, and also indicates that the powder possesses a porous structure. This demonstrates that the atmospheric pressure drying process successfully avoids the structural collapse problem encountered in conventional drying processes, overcomes the limitations of traditional aerogel drying, and reduces energy consumption, providing an innovative solution for the large-scale preparation of high-performance aerogel powders.

[0117] like Figure 3 The figure shows the specific surface area curve of polyimide aerogel powder #1 in Example 1. The porosity of the powder was characterized by BET testing, revealing a specific surface area of ​​approximately 154.0 m². 2 / g, this value corroborates the microstructural features observed by scanning electron microscopy, further confirming that there are a large number of uniformly distributed pores inside the polyimide aerogel powder.

[0118] Example 4: Celgard membrane 1# coated with polyimide aerogel powder 1#

[0119] This embodiment aims to use the polyimide aerogel powder 1# prepared in Example 1 to prepare a coating slurry, and further use it to prepare a double-sided polyimide aerogel composite membrane 1#.

[0120] (a) Mix 35 parts by weight of anhydrous ethanol with 0.35 parts of polyacrylic acid (900 rpm, 30 min), add 7 parts of polyimide aerogel powder 1# prepared in Example 1 and stir for 2 h. After grinding for 10 min, add 2 parts of phenolic resin and continue stirring for 30 min to obtain uniform polyimide aerogel coating slurry 1#.

[0121] (b) A 16μm polypropylene diaphragm was laid flat on an aluminum foil and pre-sprayed with anhydrous ethanol to wet the surface. The coating slurry 1# was sprayed using a spraying device (single-sided contact time 1s). After the solvent evaporated, the coating was repeated on the reverse side to prepare a double-sided polyimide aerogel composite diaphragm 1#.

[0122] Example 5: Celgard membrane #2 coated with polyimide aerogel powder #2

[0123] This embodiment aims to use the polyimide aerogel powder 2# prepared in Example 2 to prepare a coating slurry, and further use it to prepare a double-sided polyimide aerogel composite membrane 2#. The preparation method is the same as in Example 4.

[0124] (a) Mix 35 parts by weight of anhydrous ethanol with 0.35 parts of polyacrylic acid (900 rpm, 30 min), add 7 parts of polyimide aerogel powder 2# prepared in Example 2 and stir for 2 h. After grinding for 10 min, add 2 parts of phenolic resin and continue stirring for 30 min to obtain uniform polyimide aerogel coating slurry 2#.

[0125] (b) A 16μm polypropylene diaphragm was laid flat on an aluminum foil and pre-sprayed with anhydrous ethanol to wet the surface. A coating slurry 2# was sprayed using a spraying device (single-sided contact time 1s). After the solvent evaporated, the coating was repeated on the reverse side to prepare a double-sided polyimide aerogel composite diaphragm 2#.

[0126] Example 6: Celgard membrane #3 coated with polyimide aerogel powder #3

[0127] This embodiment aims to use the polyimide aerogel powder 3# prepared in Example 3 to prepare a coating slurry, and further use it to prepare a double-sided polyimide aerogel composite membrane 3#. The preparation method is the same as in Example 6.

[0128] (a) Mix 35 parts by weight of anhydrous ethanol with 0.35 parts of polyacrylic acid (900 rpm, 30 min), add 7 parts of polyimide aerogel powder 3# prepared in Example 3 and stir for 2 h. After grinding for 10 min, add 2 parts of phenolic resin and continue stirring for 30 min to obtain uniform polyimide aerogel coating slurry 3#.

[0129] (b) A 16μm polypropylene diaphragm was laid flat on an aluminum foil and pre-sprayed with anhydrous ethanol to wet the surface. The coating slurry 3# was sprayed using a spraying device (single-sided contact time 1s). After the solvent evaporated, the coating was repeated on the reverse side to prepare a double-sided polyimide aerogel composite diaphragm 3#.

[0130] Example 7: Polyethylene diaphragm #4 coated with polyimide aerogel powder

[0131] The difference from Example 4 is that the sprayed separator is a polyethylene separator. This example aims to explore the applicability of the coating slurry containing polyimide aerogel powder prepared according to the present invention for different battery separators.

[0132] (a) Mix 35 parts by weight of anhydrous ethanol with 0.35 parts of polyacrylic acid (900 rpm, 30 min), add 7 parts of polyimide aerogel powder 1# prepared in Example 1 and stir for 2 h. After grinding for 10 min, add 2 parts of phenolic resin and continue stirring for 30 min to obtain uniform polyimide aerogel coating slurry 4#.

[0133] (b) The polyethylene diaphragm was laid flat on the aluminum foil and pre-sprayed with anhydrous ethanol to wet the surface. The coating slurry 4# was sprayed using a spraying device (single-sided contact time 1s). After the solvent evaporated, the coating was repeated on the reverse side to prepare the double-sided polyimide aerogel composite diaphragm 4#.

[0134] Comparative Example 1: Celgard membrane without polyimide aerogel powder coating

[0135] Comparative Example 2: Celgard membrane coated with Al2O3

[0136] Weigh 2.70 g (0.0265 mol) of alumina (Al2O3) and disperse it in 12.31 g (0.124 mol) of N-methylpyrrolidone (NMP). Stir at 400 rpm for 2 h. Add 0.45 g (0.0045 mmol) of polyvinylidene fluoride (PVDF) binder and continue stirring for 12 h until the system viscosity is uniform and the binder is completely dissolved. Coat the slurry evenly onto one side of a 16 μm commercial polypropylene (PP) membrane. After drying at 60 °C for 12 h, repeat the same steps to coat the other side, thus obtaining a double-sided coated Al2O3@PP composite membrane.

[0137] Test Example 2: Structural Characterization and Performance Testing of Polyimide Aerogel Powder-Coated Separators

[0138] The assembly process of the button cell was as follows: Celgard separators coated with polyimide aerogel powder (Example 1), Celgard separators without polyimide aerogel coating (Comparative Example 1), and Celgard separators coated with Al2O3 (Comparative Example 2) were cut into 19mm diameter discs and used as separators. Then, CR2032 button cells (LiFePO4|separator|Li) were installed on a battery testing system. The battery performance of the polyimide aerogel composite separator prepared in Example 1 was studied at 25°C and within a potential range of 2.4–4.2V. The positive electrode active material was composed of LiFePO4, conductive carbon black Super P, and PVDF binder in a mass ratio of 8:1:1, with an active material loading of approximately 2.2 mg / cm³. 2 The working electrolyte is the LB-124 lithium salt electrolyte system; all battery assembly is completed in an inert atmosphere glove box, where the ambient atmosphere is argon.

[0139] like Figure 5 The diagram shown illustrates the polyimide aerogel powder slurry and coating process in Example 1. Figure 5 The slurry in part a is yellow, homogeneous, and viscous. This characteristic ensures the continuity of the spraying process and avoids sedimentation and stratification during the coating process, which helps to achieve uniform and smooth coating of the diaphragm. Figure 5 Figure b shows a Celgard diaphragm coated with polyimide aerogel powder over a large area. The coated diaphragm is pale yellow and has a uniform and smooth surface.

[0140] like Figure 6 The image shows the Celgard membrane coated with polyimide aerogel powder in Example 1. Comparative Example 1 shows the Fourier transform infrared (FTIR) spectra of the Celgard membrane coated with polyimide aerogel powder and the polyimide aerogel powder. The spectrum is located at 1782 cm⁻¹. -1 1721cm -1 And 1377cm -1 The vibrations were attributed to the characteristic peaks of C=O, C=N and benzene ring in polyimide, respectively, confirming the successful synthesis of polyimide aerogel.

[0141] like Figure 7 The image shown is a scanning electron microscope image and pore size distribution diagram of the Celgard membrane coated with polyimide aerogel powder in Example 1. It can be seen that the nanostructure of the aerogel can be retained by preparing the polyimide aerogel powder into a slurry and coating it on the surface of the membrane. The pore size of the membrane is about 145 nm according to the pore size statistics software ImageJ.

[0142] like Figure 8 , 9The figures shown are the Celgard membrane coated with polyimide aerogel powder in Example 1, the Celgard membrane without polyimide aerogel powder in Comparative Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2, and their electrolyte affinity tests. Figure 9 The test results show that the porous structure of the polyimide aerogel and the introduction of metal salts improve the electrolyte affinity of the composite membrane, with a minimum contact angle of 0°. This higher affinity facilitates rapid wetting of the membrane. Simultaneously, the Gibbs binding energy of the membrane is calculated using the following formula, taking into account the surface tension of the electrolyte:

[0143] ΔG=γ l-s γ l-g ―γ s-g

[0144] ΔG=W a =-γ l-g (1+cosθ)

[0145] Where γ l-s γ l-g γ s-g Represents the surface tension between liquid-solid, liquid-gas, and solid-gas phases; θ represents the contact angle between the gas-liquid interface and the solid-liquid interface; by Figure 8 The calculation results show that the Gibbs binding energy of the Celgard membrane coated with polyimide aerogel powder is reduced to -63mN / m, achieving a more beneficial electrolyte-membrane interface.

[0146] like Figure 10 The figure shows the Celgard membrane coated with polyimide aerogel powder in Example 1. Comparative Example 1 shows the Celgard membrane coated with polyimide aerogel powder, and Comparative Example 2 shows the Celgard membrane coated with Al2O3. The interfacial impedance of the membranes was obtained by electrochemical impedance spectroscopy test after assembling a Li|membrane|Li battery. In the figure, the Celgard membrane coated with polyimide aerogel powder in Example 1 has a significantly reduced interfacial impedance (157Ω) due to its improved absorption capacity of electrolyte by its porous structure.

[0147] like Figure 11The figures show the Celgard separator coated with polyimide aerogel powder in Example 1, and the Nyquist plot and ionic conductivity test results of stainless steel symmetric cells assembled from the Celgard separator coated with polyimide aerogel powder in Comparative Example 1 and the Celgard separator coated with Al2O3 in Comparative Example 2. Electrochemical impedance spectroscopy tests of the stainless steel|separator|stainless steel symmetric cell showed significant differences in bulk resistance among Example 1, Comparative Example 1, and Comparative Example 2. Calculations revealed that Example 1 exhibited a lower interfacial impedance compared to the two comparative examples, resulting in an increased ionic conductivity of 0.67 mS / cm, demonstrating the improving effect of the polyimide aerogel powder coating on the separator performance.

[0148] like Figure 12 The image shows a Celgard separator coated with polyimide aerogel powder in Example 1. A Celgard separator without polyimide aerogel powder coating, and a Celgard separator coated with Al2O3 in Comparative Example 2 were assembled into lithium-ion symmetric batteries. The lithium-ion transference number of the separators was determined by electrochemical resistance spectroscopy and constant voltage polarization testing combined with the following formula:

[0149]

[0150] Where R o and R S These are the interface resistances before and after constant potential polarization, I o and I S The initial current and steady-state current are respectively used. Calculations show that, due to the introduction of metal ion coordination, the powder-coated film of Example 1 can selectively conduct lithium ions and adsorb anions in the electrolyte, increasing the lithium-ion transference number of the separator in Example 1 to 0.45. According to the above formula, a high anion transference number shortens the nucleation start time of lithium dendrites on the metal anode, thereby promoting lithium dendrite growth. Therefore, reducing the anion transference number or increasing the Li... + Transition number (t) Li + This is of great significance for suppressing lithium dendrites.

[0151] like Figure 13The diagram shows the Celgard separator coated with polyimide aerogel powder in Example 1. Comparative Example 1 shows the long-term cycling tests of lithium metal batteries with Celgard separators coated with polyimide aerogel powder and Celgard separators coated with Al2O3 in Comparative Example 2, both at a high rate of 20C. It can be seen that the lithium metal battery assembled with the Celgard separator coated with polyimide aerogel powder in Example 1 can achieve stable 1500 charge-discharge cycles. After 1500 cycles, the capacity retention rate reaches 93.3%. In contrast, the lithium metal battery assembled with the Celgard separator coated with Al2O3 in Comparative Example 2 experiences capacity decay to below 80% after 698 cycles.

[0152] It should be noted that other embodiments can also use the same method as embodiments 1 and 4 to perform product performance testing, and have also achieved similar technical effects as embodiment 1. This application will not repeat the details here.

[0153] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing polyimide aerogel powder by atmospheric pressure drying, characterized in that, Includes the following steps: (1) Under an inert atmosphere, the aromatic diamine monomer is dissolved in the reaction solvent, and the dianhydride monomer is added under ice-water bath conditions to carry out a polycondensation reaction to obtain a polyamic acid prepolymer solution. (2) Metal salt and crosslinking agent are added sequentially to the polyamic acid prepolymer solution to achieve molecular chain crosslinking, and then a catalyst and dehydrating agent are added to carry out chemical imidization reaction to obtain polyimide solution; (3) The polyimide solution is directly injected into an organic solvent I under continuous stirring to perform solvent exchange, thereby obtaining a polyimide aerogel particle suspension. After filtration and drying under normal pressure, polyimide aerogel powder is obtained. The organic solvent I includes at least one of methanol, anhydrous ethanol, acetone, cyclohexane or n-hexane. The stirring speed of the organic solvent I is 300-800 rpm, and the injection speed of the polyimide solution is 5 mL / min-20 mL / min; The polyimide aerogel powder has the following properties: The powder density is 0.4-0.5 g / cm³. 3 , and / or The specific surface area of ​​the powder is 150-160 m². 2 / g.

2. The method for preparing polyimide aerogel powder by atmospheric pressure drying according to claim 1, characterized in that, In step (1), the aromatic diamine monomer includes at least one of 1,4-bis(4-amino-phenylene ether)phenyl-1,4-diazabutadiene (DAB), p-phenylenediamine, biphenylenediamine, 4,4'-diaminodiphenyl ether, or 4,4'-diaminodiphenyl sulfide; and / or In step (1), the dianhydride monomer is an aromatic dianhydride monomer including at least one of 4,4'-(hexafluoroisopropene)phthalic anhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, or 4,4'-oxobisphthalic anhydride; and / or The reaction solvent in step (1) includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone; and / or In step (1), the molar ratio of the aromatic diamine monomer to the dianhydride monomer is 1:1 to 1:1.5; and / or In step (1), the mass concentration of the polyamic acid prepolymer solution is 3%-15%; and / or The polycondensation reaction time in step (1) is 1-3 h.

3. The method for preparing polyimide aerogel powder by atmospheric pressure drying according to claim 1, characterized in that, In step (2), the metal salt includes at least one of zirconium chloride, titanium chloride, tin chloride, chromium chloride, or aluminum chloride; and / or In step (2), the molar ratio of the metal salt to the aromatic diamine monomer is 1:(0.5-3); and / or In step (2), the chemical cross-linking reaction time is 1-3 h; and / or In step (2), the crosslinking agent includes a flame-retardant crosslinking agent and / or a silane coupling agent, wherein the flame-retardant crosslinking agent includes at least one of triphenyl phosphate, triethyl phosphate, ammonium tripolyphosphate, ammonium orthophosphate, or ammonium polyphosphate; the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, or vinyltriethoxysilane; and / or In step (2), the molar ratio of the crosslinking agent to the aromatic diamine monomer is 1:(0.5-3); and / or In step (2), the crosslinking time is 10-50 min; and / or In step (2), the catalyst includes at least one of pyridine, tributylphosphine, or triethylamine; and / or The dehydrating agent includes at least one of acetic anhydride, propionic anhydride, trifluoroacetic anhydride, benzoic anhydride, thionyl chloride, or N,N'-dicyclohexylcarbodiimide; and / or In step (2), the molar ratio of catalyst, dehydrating agent, and aromatic diamine monomer is 8:8:(0.5-3); and / or In step (2), the chemical imidization reaction time is 20-40 min.

4. The method for preparing polyimide aerogel powder by atmospheric pressure drying according to claim 1, characterized in that, In step (3), the volume ratio of the organic solvent I to the polyimide solution is (20-30):

1.

5. The method for preparing polyimide aerogel powder by atmospheric pressure drying according to claim 1, characterized in that, In step (3), the solvent exchange time is 12-24 h.

6. The method for preparing polyimide aerogel powder by atmospheric pressure drying according to claim 1, characterized in that, In step (3), the drying parameters are 30-40 °C under normal pressure and 4-12 h.

7. A polyimide aerogel powder, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

8. A coating slurry for battery separators, characterized in that, The coating slurry contains a polyimide aerogel powder as described in claim 7.

9. A method for preparing the coating slurry as described in claim 8, characterized in that, Includes the following steps: The dispersant is mixed with organic solvent II and stirred to form a dispersion solution; The polyimide aerogel powder was added to the dispersion solution and stirred continuously to obtain a primary dispersion slurry; The primary dispersion slurry is added to a grinding equipment for grinding, and the particle size distribution is controlled to obtain a ground slurry; Add a binder to the grinding slurry and stir to obtain a coating slurry.

10. The method according to claim 9, characterized in that, The mass ratio of the organic solvent II, polyimide aerogel powder, dispersant, and binder is 35:7:(0.2-0.8):2; and / or The organic solvent II includes at least one selected from methanol, ethanol, acetone, or n-hexane; and / or The dispersant comprises at least one of polyacrylic acid, polyvinylpyrrolidone, or sodium dodecyl sulfate; and / or The stirring speed of the slurry is 500-1000 rpm; and / or The stirring time after the dispersant is added is 20-40 min; and / or The polyimide aerogel powder is added and stirred for 1-3 hours; and / or The grinding time is 5-15 min; and / or The adhesive comprises at least one of phenolic resin, polymethyl methacrylate, or polyvinylidene fluoride; and / or The mixing time after adding the adhesive is 20-40 minutes.

11. A polyimide aerogel composite membrane, characterized in that, The battery separator is obtained by coating a battery separator with a coating slurry prepared by the method of claim 8 or claim 9 or 10, wherein the battery separator comprises a polypropylene separator, a polyethylene separator, or a polyimide fiber membrane.

12. The polyimide aerogel composite membrane according to claim 11, characterized in that, The polyimide aerogel composite membrane has the following characteristics: The average pore size is 145 nm, and / or The average film thickness is 26-42 μm, and / or The cation transference number is 0.45, and / or The interface impedance is 140-160 Ω, and / or The ionic conductivity is 0.67 mS / cm, and / or The electrolyte contact angle of the polyimide aerogel composite membrane is ≤6.6°, and / or The polyimide aerogel composite membrane, when used under high-rate cycling conditions at 20°C, can stably cycle for more than 1500 cycles with a capacity retention of 93.3%.

13. The polyimide aerogel composite membrane according to claim 12, characterized in that, The electrolyte contact angle of the polyimide aerogel composite membrane is 0°.

14. Use of a polyimide aerogel powder as described in claim 7, or a coating slurry as described in claim 8, or a polyimide aerogel composite separator as described in any one of claims 11-13, in the field of batteries.

15. The use according to claim 14, characterized in that, The battery includes a lithium / sodium metal battery.

Images