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

Abstract

The invention provides a normal-pressure drying preparation method and application of polyimide aerogel powder, and the method comprises the following steps: taking aromatic diamine and aromatic dianhydride as monomers, dissolving the monomers in an organic solvent, and carrying out condensation polymerization to generate a polyamide acid solution; the preparation method comprises the following steps: introducing metal ions into a polyamide acid solution, constructing a cross-linked network among molecular chains by a cross-linking agent, and preparing a polyimide solution through chemical imidization reaction; a polyimide solution is directly injected into absolute ethyl alcohol to shorten the gel aging time, rapid solvent exchange is carried out, the production cycle of the polyimide aerogel is remarkably shortened, and the obtained suspension is filtered and dried at normal pressure to prepare polyimide aerogel powder. The polyimide aerogel powder can be used for preparing functional slurry, a high-performance battery diaphragm is processed through a coating process, and the battery performance is remarkably improved. According to the invention, the slurry and the industrial spraying production technology are combined, the batch preparation of the large-area composite battery diaphragm can be realized, and the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer composite materials and batteries, and relates to a normal pressure drying preparation method of polyimide aerogel powder and application thereof. Background Art

[0002] With the rapid development of new energy vehicles and energy storage materials, society's demand for high-performance batteries is also expanding. Lithium metal batteries are considered to be one of the representatives of high-performance batteries because of their high theoretical capacity and high energy density. However, the heat accumulation problem generated during high-rate charging and discharging and long-term cycling always poses a safety hazard. As the core protective component inside the battery, the performance of the diaphragm directly determines the battery's safety, ion transfer efficiency, cycle life and other performance. The current mainstream commercial polyolefin diaphragms have a significant shortcoming and a low heat deformation temperature. Coating modification can improve the thermal stability and mechanical strength of the diaphragm, improve electrolyte wettability, and increase functionality. Combined with the characteristics of polyimide aerogel, it can improve the performance of battery diaphragms to a certain extent as a coating material.

[0003] Traditional bulk polyimide and polyimide separator materials suffer from insufficient electrolyte adsorption capacity due to their low specific surface area and porosity. Furthermore, their existing pore structures are difficult to match the process requirements of separator coating slurry systems, limiting their direct application. In contrast, aerogel, an ultra-lightweight, highly porous nanoporous material, has demonstrated unique advantages in energy, environmental protection, aerospace, and other fields due to its low density, high specific surface area, and excellent thermal insulation properties. In particular, polyimide aerogel, by combining the porous properties of aerogel with the high heat resistance, mechanical strength, and chemical stability of polyimide, has become a research hotspot for the next generation of high-performance functional materials. However, existing polyimide aerogel preparation technologies face significant bottlenecks: while the currently mainstream supercritical drying and freeze-drying processes can effectively remove solvents and construct a porous network, they are subject to high equipment complexity, high energy consumption, and high costs, severely restricting the material's large-scale production. Furthermore, existing aerogel product forms are mostly limited to bulk or thin films, and their preparation and molding methods significantly limit the expansion of commercial applications.

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

[0005] Purpose of the Invention: To address the problems and shortcomings of the prior art, the present invention provides a method for preparing polyimide aerogel powder by atmospheric drying and its application. This method optimizes the solvent exchange process to improve efficiency and shorten aging time, and combines it with an atmospheric drying process to successfully prepare polyimide aerogel powder. This process ensures that the powder forms a three-dimensional porous network structure with uniform pore distribution and structural integrity, resulting in excellent workability. Based on these characteristics, the polyimide aerogel powder can be used to formulate functional slurries and is suitable for coating and preparing lithium 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 drying at normal pressure, the method comprising the following steps:

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

[0008] (2) adding a metal salt and a cross-linking agent to the polyamic acid prepolymer solution in sequence to achieve molecular chain cross-linking, and then adding a catalyst and a water scavenger to carry out a chemical imidization reaction to obtain a 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, which is then filtered and dried at normal pressure to obtain a polyimide aerogel powder.

[0010] The present invention accelerates solvent exchange efficiency, shortens aging time, and achieves an increase in solvent exchange rate. A polyimide aerogel powder with a nanoporous microstructure can be obtained through a normal pressure drying process. This presents 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-phenyl ether)phenyl-1,4-diazabutadiene (DAB), p-phenylenediamine, benzyldiamine, 4,4'-diaminodiphenyl ether or 4,4'-diaminodiphenyl sulfide, preferably 1,4-bis(4-amino-phenyl 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 anhydride, pyromellitic anhydride, 4,4'-oxydiphthalic anhydride or biphenyltetracarboxylic anhydride, 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 to the dianhydride monomer in step (1) is 1:1-1:1.5, 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 embodiment, 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 embodiment, in step (2), the molar ratio of the metal salt to the aromatic diamine monomer is 1:(0.5-3).

[0019] In one embodiment, in step (2), the coordination chemical reaction time is 1-3 hours, preferably 2 hours.

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

[0021] Furthermore, in one embodiment, 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 cross-linking agent includes at least one of triphenyl phosphate, triethyl phosphate, ammonium tripolyphosphate, ammonium orthophosphate or ammonium polyphosphate, preferably an ammonium polyphosphate cross-linking 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, and 3-aminopropyltriethoxysilane is selected.

[0024] In one embodiment, in step (2), the molar ratio of the cross-linking 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 water scavenger is preferably acetic anhydride.

[0028] Furthermore, in one embodiment, the molar ratio of the catalyst, the water scavenger and the 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 embodiment, 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-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 the drying time is 4-12 hours.

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

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

[0038] Powder density is 0.4-0.5g / cm 3 , and / or

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

[0040] The third aspect of the present invention is to provide a coating slurry for a battery separator, wherein the coating slurry contains any of the polyimide aerogel powders described above.

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

[0042] Mixing the dispersant with the organic solvent II and stirring to form a uniform dispersed solution;

[0043] Adding polyimide aerogel powder to the dispersion solution and continuously stirring to obtain a primary dispersion slurry;

[0044] Adding the primary dispersed slurry into the grinding preparation for grinding, controlling the particle size distribution, and obtaining the grinding slurry;

[0045] Add a binder to the polishing slurry and stir to obtain a coating slurry.

[0046] In one embodiment, the mass ratio of the 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, polyvinyl pyrrolidone, and sodium lauryl 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 min, preferably 10 min.

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

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

[0055] The fifth aspect of the present invention is to provide a use of the above-mentioned 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 the coating slurry as described above or prepared by the method described above.

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

[0058] The battery separator is laid flat on aluminum foil, and organic solvent III is applied to the separator surface through an atomizing spray device for wetting treatment;

[0059] The coating slurry containing polyimide aerogel powder is injected into an atomizing spray device, and the wetted diaphragm is evenly sprayed under the same pressure condition;

[0060] The battery separator sprayed on one side is transferred to a blast drying device, and the organic solvent III is completely volatilized under certain temperature conditions to obtain a dry film coated on one side;

[0061] The dry film is turned over and the above steps are repeated to finally obtain a composite diaphragm coated with 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 1-5s, preferably 1s.

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

[0067] Furthermore, in one embodiment, the spraying time is 1-5s.

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

[0069] Furthermore, in one embodiment, 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] a cation transfer number of 0.45, and / or

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

[0075] 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 diaphragm is used for high-rate cycling conditions at 20C, stably cycles for more than 1500 cycles, and retains 93.3% of its capacity.

[0078] The seventh aspect of the present invention is to provide a use of the polyimide aerogel powder as described above, or the coating slurry as described above, or the polyimide aerogel composite membrane as described above, which is applied to the field of batteries. Preferably, the battery includes a lithium / sodium metal battery.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] 1. The present invention uses a chemical imidization method to obtain polyimide, and obtains polyimide aerogel powder after solvent exchange and atmospheric pressure drying. The traditional polyimide aerogel preparation requires high-temperature carbonization, freeze drying or supercritical drying process, which has high energy consumption, strict equipment requirements, and low solvent recovery rate. This invention can significantly reduce production costs and is suitable for continuous

[0081] 2. The present invention significantly shortens the production cycle of polyimide aerogel by reducing aging time and rapidly exchanging solvents. After filtration and drying, polyimide aerogel powder is obtained. Compared to traditional block or film-shaped polyimides, polyimide aerogel powder has excellent processability. Composite membranes can be produced through coating processes such as spraying or blade coating a polyimide aerogel powder slurry.

[0082] 3. The three-dimensional continuous porous network structure based on polyimide aerogel has the characteristics of high porosity, high temperature resistance, and lightweight. By introducing metal ions to regulate the aerogel pore structure, the safety of the battery separator and its electrochemical properties such as ion migration number can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 The figure is a process flow chart for the preparation and coating of the polyimide gel powder of the present invention.

[0084] Figure 2 The following are photos of the finished product of the polyimide aerogel powder in Example 1 and multi-magnification scanning electron microscope photos.

[0085] Figure 3 This is a BET specific surface area test curve of the polyimide aerogel powder in Example 1.

[0086] Figure 4 The flowchart of the preparation of Celgard membrane coated with polyimide aerogel powder in Example 1.

[0087] Figure 5 This is a photo of the Celgard membrane with a large area of ​​polyimide aerogel powder coated with the slurry prepared from the polyimide aerogel powder in Example 1 and sprayed thereon.

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

[0089] Figure 7 This is a scanning electron microscope photograph of the Celgard membrane coated with polyimide aerogel powder in Example 1 and its pore size distribution diagram.

[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 not coated with polyimide aerogel powder in Comparative Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2 were tested.

[0091] Figure 10 The interface impedance diagrams are for the Celgard membrane coated with polyimide aerogel powder in Example 1, the Celgard membrane coated with polyimide aerogel powder in Comparative Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2.

[0092] Figure 11 Nyquist plots and ionic conductivity test results of a stainless steel symmetrical cell assembled with a Celgard membrane coated with polyimide aerogel powder in Example 1, a Celgard membrane coated with polyimide aerogel powder in Comparative Example 1, and a Celgard membrane coated with Al2O3 in Comparative Example 2.

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

[0094] Figure 13 Long cycle test of lithium metal batteries at a rate of 20C using the Celgard diaphragm coated with polyimide aerogel powder in Example 1, the Celgrd diaphragm coated with polyimide aerogel powder in Comparative Example 1, and the Celgard diaphragm coated with Al2O3 in Comparative Example 2. DETAILED DESCRIPTION

[0095] The present invention provides a method for preparing polyimide aerogel powder by drying at normal pressure and its application. The method uses aromatic diamine and aromatic dianhydride as monomers, dissolves them in an organic solvent, and generates a polyamic acid solution through a condensation reaction; introduces metal ions and a cross-linking agent into the polyamic acid solution to construct a cross-linked network between molecular chains, and obtains a polyimide solution through a chemical imidization reaction; directly injects the polyimide solution into anhydrous ethanol to shorten the gel aging time, conducts rapid solvent exchange, and significantly shortens the production cycle of the polyimide aerogel; the obtained suspension is filtered and dried at normal pressure to obtain polyimide aerogel powder. The polyimide aerogel powder can be used to prepare functional slurry and processed into high-performance battery separators through a coating process, significantly improving battery performance. The present invention combines slurry with industrialized spray production technology to achieve batch preparation of large-area composite battery separators, and has broad application prospects.

[0096] like Figure 1 The following is a process flow chart for the preparation and coating of the polyimide gel powder of the present invention. The main technical steps include: preparation of polyimide, synthesis of polyimide aerogel powder, preparation of a polyimide aerogel powder composite slurry, and preparation of a polyimide aerogel powder composite separator. The key technology of this invention lies in eliminating aging time after polyimide preparation, directly performing rapid solvent exchange, and replacing high-cost drying techniques with atmospheric pressure drying. This improves efficiency while reducing energy costs, making it more compatible with the transportation and processing requirements of industrial production, and demonstrating significant industrial application value in fields such as lithium battery separator materials.

[0097] Among them, such as Figure 4 The figure shows a flow chart for preparing the polyimide aerogel powder-coated Celgard separator of the present invention. The spray-coated battery separator forms a sandwich structure, with a base film in the middle and polyimide aerogel powder coatings on both sides. This makes it suitable for large-scale production and cutting using existing technology.

[0098] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0099] Unless otherwise specified, the sources of the reagents used in the examples of the present invention can be purchased from the market.

[0100] The present invention provides a characterization test result diagram of Example 1. The other embodiments all adopt the same characterization test method. Those skilled in the art can directly and unambiguously determine the content of the embodiments of the present invention through the characterization test method provided by the present invention, which will not be elaborated here.

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

[0102] (1) Under inert gas, 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 amount 0.0064 mol, divided into 1.00 g, 1.00 g, and 0.86 g, respectively) was added in three batches with 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 10 wt% was obtained.

[0103] (2) 0.6 g (2.57 mmol) of zirconium tetrachloride was added to the polyamic acid solution obtained in step (2), and the reaction was carried out for 2 h until the solution turned brown. Subsequently, 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate was added (stirred for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane was added (reacted for 0.5 h), and finally 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride were added dropwise, and stirring was continued 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 accounts for 20 parts, and stirred at 300 rpm for 12 hours to perform solvent exchange. The resulting light brown suspension was filtered and dried at atmospheric pressure to obtain a yellow-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 is added as an organic solvent, and the solid content is 5 wt%.

[0107] (1) Under inert gas, 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 amount 0.0064 mol, divided into 1.00 g, 1.00 g, and 0.86 g, respectively) was added in three batches with 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 5 wt% was obtained.

[0108] (2) 0.6 g (2.57 mmol) of zirconium tetrachloride was added to the polyamic acid solution obtained in step (2), and the reaction was carried out for 2 h until the solution turned brown. Subsequently, 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate was added (stirred for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane was added (reacted for 0.5 h), and finally 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride were added dropwise, and stirring was continued 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 accounts for 20 parts, and stirred at 300 rpm for 12 hours to perform solvent exchange. The resulting light brown suspension was filtered and dried at atmospheric pressure to obtain a yellow-brown aerogel powder.

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

[0111] The difference from Example 1 is that the solvent exchange in step (3) is not stirred.

[0112] (1) Under inert gas, 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 amount 0.0064 mol, divided into 1.00 g, 1.00 g, and 0.86 g, respectively) was added in three batches with 15 min intervals. After reacting for 2 h, a yellow polyamic acid solution with a solid content of 10 wt% was obtained.

[0113] (2) 0.6 g (2.57 mmol) of zirconium tetrachloride was added to the polyamic acid solution obtained in step (2), and the reaction was carried out for 2 h until the solution turned brown. Subsequently, 5.00 g of N,N-dimethylacetamide solution containing 1.00 g (0.007 mmol) of ammonium polyphosphate was added (stirred for 0.5 h), 1.42 g (9.5 mmol) of 3-aminopropyltriethoxysilane was added (reacted for 0.5 h), and finally 5.18 g (0.0465 mol) of triethylamine and 5.23 g (0.0465 mol) of acetic anhydride were added dropwise, and stirring was continued 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 accounts for 20 parts, and the solvent exchange was carried out without stirring for 12 hours. The resulting light brown suspension was filtered and dried at normal pressure to obtain a yellow-brown aerogel powder.

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

[0116] like Figure 2 The polyimide aerogel powder 1# prepared in Example 1 is shown in the macroscopic scale ( Figure 2 a) It is a yellow-brown fine powder, which is loosely piled in the container and has no obvious agglomeration after drying. Figure 2 The microstructural characterization shown in Figure b reveals the morphology of polyimide aerogel powder #1 particles at low magnification, and also reveals a porous structure. This demonstrates that the atmospheric pressure drying process successfully avoids the structural collapse 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 graph shows the specific surface area test curve of the polyimide aerogel powder 1# in Example 1. The porosity of the powder was characterized by BET test, and the results revealed that its specific surface area was approximately 154.0 m 2 / g, which is consistent with the microstructural characteristics observed by scanning electron microscopy, and further confirms the existence of a large number of evenly distributed pores inside the polyimide aerogel powder.

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

[0119] This example is intended to use the polyimide aerogel powder 1# prepared in Example 1 to prepare a coating slurry, which is further used to prepare a double-sided polyimide aerogel composite separator 1#.

[0120] (a) 35 parts by mass of anhydrous ethanol and 0.35 parts of polyacrylic acid were mixed (900 rpm, 30 min), 7 parts of the polyimide aerogel powder 1# prepared in Example 1 were added, and the mixture was stirred for 2 h. After grinding for 10 min, 2 parts of phenolic resin were added, and stirring was continued for 30 min to prepare a uniform polyimide aerogel coating slurry 1#.

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

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

[0123] This example is intended to use the polyimide aerogel powder 2# prepared in Example 2 to prepare a coating slurry, which is further used to prepare a double-sided polyimide aerogel composite separator 2#. The preparation method is the same as that of Example 4.

[0124] (a) 35 parts by mass of anhydrous ethanol and 0.35 parts of polyacrylic acid were mixed (900 rpm, 30 min), 7 parts of polyimide aerogel powder 2# prepared in Example 2 were added, and the mixture was stirred for 2 h. After grinding for 10 min, 2 parts of phenolic resin were added, and stirring was continued for 30 min to prepare a uniform polyimide aerogel coating slurry 2#.

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

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

[0127] This example is intended to use the polyimide aerogel powder 3# prepared in Example 3 to prepare a coating slurry, which is further used to prepare a double-sided polyimide aerogel composite separator 3#. The preparation method is the same as that of Example 6.

[0128] (a) 35 parts by mass of anhydrous ethanol and 0.35 parts of polyacrylic acid were mixed (900 rpm, 30 min), 7 parts of polyimide aerogel powder 3# prepared in Example 3 were added, and the mixture was stirred for 2 h. After grinding for 10 min, 2 parts of phenolic resin were added, and stirring was continued for 30 min to prepare a uniform polyimide aerogel coating slurry 3#.

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

[0130] Example 7: Polyimide aerogel powder coated polyethylene diaphragm 4#

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

[0132] (a) 35 parts by mass of anhydrous ethanol and 0.35 parts of polyacrylic acid were mixed (900 rpm, 30 min), 7 parts of the polyimide aerogel powder 1# prepared in Example 1 were added, and the mixture was stirred for 2 h. After grinding for 10 min, 2 parts of phenolic resin were added, and stirring was continued for 30 min to prepare a uniform polyimide aerogel coating slurry 4#.

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

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

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

[0136] 2.70g (0.0265mol) of aluminum oxide (Al2O3) was weighed and dispersed in 12.31g (0.124mol) of N-methylpyrrolidone (NMP) with stirring at 400rpm for 2h. 0.45g (0.0045mmol) of polyvinylidene fluoride (PVDF) binder was added and stirred for 12h until the viscosity was uniform and the binder was completely dissolved. The slurry was evenly coated on one side of a 16μm commercial polypropylene (PP) separator. After drying at 60°C for 12h to set the membrane, the same process was repeated on the other side to produce a double-sided Al2O3@PP composite separator.

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

[0138] The assembly process of the button battery is as follows: the Celgard diaphragm coated with polyimide aerogel powder in Example 1, the Celgard diaphragm not coated with polyimide gel in Comparative Example 1, and the Celgard diaphragm coated with Al2O3 in Comparative Example 2 are cut into discs with a diameter of 19 mm as diaphragms, and then CR2032 button batteries (LiFePO4|diaphragm|Li) are respectively installed on the battery testing system. The battery performance of the polyimide aerogel composite diaphragm prepared in Example 1 is studied at 25°C and in the potential range of 2.4 to 4.2V; wherein, the positive electrode active material is composed of LiFePO4, conductive carbon black Super P and PVDF binder in a mass ratio of 8:1:1, and the active material loading is about 2.2 mg / cm 2 ; The working electrolyte is LB-124 lithium salt electrolyte system; all battery assemblies are completed in an inert atmosphere glove box, where the ambient atmosphere is argon.

[0139] like Figure 5 The figure shows the polyimide aerogel powder slurry and coating process in Example 1. Figure 5 The slurry in a is yellow, homogeneous and viscous. This feature not only ensures the continuity of the spraying process, but also 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 light yellow and has a uniform and smooth surface.

[0140] like Figure 6 The following is the Fourier transform infrared spectrum of Celgard membrane coated with polyimide aerogel powder in Example 1 and Celgard membrane coated with polyimide aerogel powder and polyimide aerogel powder in Comparative Example 1. -1 , 1721cm -1 and 1377cm -1 The vibrations are attributed to the characteristic peaks of C=O, C=N and benzene ring in polyimide, proving the successful synthesis of polyimide aerogel.

[0141] like Figure 7 Shown are scanning electron microscope images of the Celgard membrane coated with polyimide aerogel powder in Example 1 and its pore size distribution diagram. It can be seen that the nano-multi-structure of the aerogel can be retained by coating the polyimide aerogel powder into a slurry on the membrane surface, and the pore size of the membrane is approximately 145 nm as analyzed by the pore size statistics software ImageJ.

[0142] like Figure 8 、 9The electrolyte affinity test is shown for the Celgard membrane coated with polyimide aerogel powder in Example 1, the Celgard membrane not coated with polyimide aerogel powder in Comparative Example 1, and the Celgard membrane coated with Al2O3 in Comparative Example 2. 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 the minimum contact angle being 0°. The higher affinity facilitates rapid wetting of the membrane. At the same time, the Gibbs binding energy of the membrane is calculated by combining the surface tension of the electrolyte with the following formula:

[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 gas-liquid interface and solid-liquid interface; 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 Celgard diaphragm coated with polyimide aerogel powder in Example 1 is shown, the Celgard diaphragm coated with polyimide aerogel powder in Comparative Example 1 and the Celgard diaphragm coated with Al2O3 in Comparative Example 2. The interface impedance test of the diaphragm is obtained by assembling Li|diaphragm|Li battery and performing electrochemical impedance spectroscopy test. In the figure, the Celgard diaphragm coated with polyimide aerogel powder in Example 1 has improved absorption capacity of electrolyte due to its porous structure characteristics, which significantly reduces the interface impedance of the diaphragm (157Ω).

[0147] like Figure 11Shown are the Nyquist plots and ionic conductivity test results of a stainless steel symmetric cell assembled from a Celgard membrane coated with polyimide aerogel powder (Example 1), a Celgard membrane coated with polyimide aerogel powder (Comparative Example 1), and a Celgard membrane coated with Al2O3 (Comparative Example 2). Electrochemical impedance spectroscopy (EIS) testing of the stainless steel / membrane / stainless steel symmetric cell reveals significant differences in bulk resistance between Example 1, Comparative Example 1, and Comparative Example 2. Calculations show that Example 1 exhibits lower interfacial impedance than the two comparative examples, which increases its ionic conductivity to 0.67 mS / cm, demonstrating the improved performance of the polyimide aerogel powder coating on the membrane.

[0148] like Figure 12 The Celgard membrane coated with polyimide aerogel powder in Example 1, the Celgard membrane not coated with polyimide aerogel powder in Comparative Example 2, and the Celgard membrane coated with Al2O3 in Comparative Example 2 were assembled into lithium symmetric batteries. The lithium ion migration number of the membrane was determined by electrochemical resistance spectrum analysis and constant voltage polarization test combined with the following formula:

[0149]

[0150] where R o and R S are the interface resistance before and after constant potential polarization, I o and I S are the initial current and steady-state current respectively. Calculation shows that due to the introduction of metal ion coordination, the powder coating membrane of Example 1 can selectively conduct lithium ions and adsorb anions in the electrolyte, which increases the lithium ion transfer number of the separator of Example 1 to 0.45. According to the above formula, a high anion transfer number will shorten the start time of nucleation of lithium dendrites on the metal anode, thereby promoting the growth of lithium dendrites. Therefore, reducing the anion transfer number or increasing the Li + Transfer number (t Li + ), which is of great significance for inhibiting lithium dendrites.

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

[0152] It should be noted that other embodiments may also use the same method as in embodiments 1 and 4 to perform product performance testing, and obtain similar technical effects as in embodiment 1, which will not be described in detail in this application.

[0153] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing polyimide aerogel powder by drying at normal pressure, characterized in that: The following steps are involved: (1) Under the protection of an inert atmosphere, an aromatic diamine monomer is dissolved in a reaction solvent, and a dianhydride monomer is added in an ice-water bath to carry out a polycondensation reaction to obtain a polyamic acid prepolymer solution; (2) adding a metal salt and a cross-linking agent to the polyamic acid prepolymer solution in sequence to achieve molecular chain cross-linking, and then adding a catalyst and a water scavenger to carry out a chemical imidization reaction to obtain a polyimide solution; (3) The polyimide solution is directly injected into the continuously stirred organic solvent I to perform solvent exchange to obtain a polyimide aerogel particle suspension, which is then filtered and dried at normal pressure to obtain a polyimide aerogel powder.

2. The method for preparing polyimide aerogel powder by drying at normal pressure according to claim 1, wherein: The aromatic diamine monomer in step (1) comprises at least one of 1,4-bis(4-amino-phenyl ether)phenyl-1,4-diazabutadiene (DAB), p-phenylenediamine, benzyldiamine, 4,4'-diaminodiphenyl ether or 4,4'-diaminodiphenyl sulfide; and / or The dianhydride monomer in step (1) is an aromatic dianhydride monomer including at least one of 4,4'-(hexafluoroisopropylene)diphthalic anhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride or 4,4'-oxydiphthalic anhydride; and / or The reaction solvent in step (1) comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide or N-methylpyrrolidone; and / or The molar ratio of the aromatic diamine monomer to the dianhydride monomer in step (1) is 1:1-1:1.5; and / or The mass concentration of the polyamic acid prepolymer solution in step (1) is 3%-15%; and / or The polycondensation reaction time in step (1) is 1-3 hours; In the step (2), the metal salt comprises at least one of zirconium chloride, titanium chloride, tin chloride, chromium chloride or aluminum chloride; and / or In the step (2), the molar ratio of the metal salt to the aromatic diamine monomer is 1:(0.5-3); and / or In the step (2), the chemical cross-linking reaction time is 1-3 hours; and / or In the step (2), the cross-linking agent includes a flame retardant cross-linking agent and / or a silane coupling agent, wherein the flame retardant cross-linking agent includes at least one of triphenyl phosphate, triethyl phosphate, ammonium tripolyphosphate, ammonium orthophosphate or ammonium polyphosphate cross-linking agent; the silane coupling agent includes at least one of 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane cross-linking agent, γ-mercaptopropyltrimethoxysilane or vinyltriethoxysilane; and / or In the step (2), the molar ratio of the cross-linking agent to the aromatic diamine monomer is 1:(0.5-3); and / or In the step (2), the cross-linking time is 10-50 min; and / or In the step (2), the catalyst comprises at least one of pyridine, tributylphosphine or triethylamine; and / or The dehydrating agent comprises at least one of acetic anhydride, propionic anhydride, trifluoroacetic anhydride, benzoic anhydride, thionyl chloride or N,N'-dicyclohexylcarbodiimide; and / or In the step (2), the molar ratio of the catalyst, the water scavenger and the aromatic diamine monomer is 8:8:(0.5-3); and / or In the step (2), the chemical imidization reaction time is 20-40 minutes.

3. The method for preparing polyimide aerogel powder by drying at normal pressure according to claim 1, wherein: In step (3), the organic solvent I comprises at least one of methanol, anhydrous ethanol, acetone, cyclohexane or n-hexane; and / or The volume ratio of the organic solvent I to the polyimide solution is (20-30):1; and / or The stirring speed of the organic solvent I is 300-800 rpm; and / or The injection speed of the polyimide solution is 5 mL / min-20 mL / min; and / or The solvent exchange time is 12-24h; and / or The drying parameters are 30-40° C. under normal pressure and time of 4-12 hours.

4. A polyimide aerogel powder, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 3.

5. The polyimide aerogel powder according to claim 4, characterized in that: The polyimide aerogel powder has the following characteristics: Powder density is 0.4-0.5g / cm 3 , and / or The specific surface area of ​​the powder is about 150-160m 2 / g.

6. A coating slurry for battery separator, characterized in that: The coating slurry contains a polyimide aerogel powder as claimed in claim 4 or 5.

7. The method for preparing the coating slurry according to claim 6, characterized in that: The following steps are involved: Mixing the dispersant with the organic solvent II and stirring to form a dispersed solution; Adding the polyimide aerogel powder to the dispersed solution and continuously stirring to obtain a primary dispersed slurry; The primary dispersed slurry is added to the grinding equipment for grinding, and the particle size distribution is controlled to obtain the grinding slurry; adding a binder to the grinding slurry and stirring to obtain a coating slurry; Preferably, 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 of methanol, ethanol, acetone or n-hexane; and / or The dispersant comprises at least one of polyacrylic acid, polyvinyl pyrrolidone or sodium lauryl 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 minutes; and / or The polyimide aerogel powder is stirred for 1-3 hours after addition; and / or The grinding time is 5-15 min; and / or The binder comprises at least one of phenolic resin, polymethyl acrylate or polyvinylidene fluoride; and / or The stirring time after the binder is added is 20-40 minutes.

8. A polyimide aerogel composite diaphragm, characterized in that: The battery separator is obtained by coating the coating slurry prepared by the method according to claim 6 or claim 7, wherein the battery separator includes a polypropylene separator, a polyethylene separator or a polyimide fiber membrane.

9. The polyimide aerogel composite diaphragm according to claim 8, characterized in that: The polyimide aerogel composite diaphragm has the following characteristics: The average pore size is 145 nm, and / or The average film thickness is 26-42 μm, and / or a cation transfer number of 0.45, and / or Interface impedance is 140-160Ω, and / or Ionic conductivity is 0.67 mS / cm, and / or The electrolyte contact angle of the polyimide aerogel composite membrane is ≤6.6°, preferably 0°, and / or The polyimide aerogel composite diaphragm is used for high-rate cycling conditions at 20C, stably cycles for more than 1500 cycles, and retains 93.3% of its capacity.

10. Use of the polyimide aerogel powder according to claim 4 or 5, or the coating slurry according to claim 6, or the polyimide aerogel composite separator according to claim 8 or 9 in the field of batteries, preferably, the battery comprises a lithium / sodium metal battery.

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