Preparing method of flame retardant polyimide aerogel and polyimide aerogel prepared using the same

Abstract

The present invention relates to a method for manufacturing a flame-retardant polyimide aerogel and a polyimide aerogel manufactured using the same, and has the effect of providing a polyimide aerogel having high porosity and improved flame-retardant properties.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a flame-retardant polyimide aerogel and a polyimide aerogel manufactured using the same. Background Technology

[0003] Since the discovery of aerogels in the 1930s, various studies have been conducted on them. Among them, silica aerogel, the most common form, is an ultra-lightweight new material with excellent physical properties and has wide-ranging potential applications in energy, environment, electrical and electronic, space, and medical fields, such as aerospace, building insulation, medical equipment for organ storage and transportation, drug delivery media, catalyst carriers, and electrical insulating films with low dielectric constant.

[0004] However, to manufacture silica aerogels with excellent physical properties, micropores must not be destroyed; to prevent this, a drying method using supercritical carbon dioxide is employed. Nevertheless, this supercritical drying method has disadvantages, including the risk of safety accidents due to the high pressure and temperature required, difficulties in continuous processing caused by autoclave size limitations, and high production costs.

[0005] To address these issues, research is being conducted on manufacturing aerogels using various raw materials, and in particular, various studies have been attempted on manufacturing aerogels using polymers.

[0006] Meanwhile, polyimide resin is an advanced chemical material that is in the spotlight in fields requiring high heat resistance, low insulation, and high strength. It has a chemical structure that does not decompose even at high temperatures of over 400°C, and is thin and highly flexible, so it is widely used as a core material in industries such as aerospace, IT, automotive, semiconductor, and display.

[0007] In order to manufacture aerogels using polyimide resin, a polyimide aerogel having a very high porosity (80% or 90% or more, see Comparative Examples 1-4 of the present invention) can be manufactured by using a high internal phase emulsion (HIPE), but in this case, there was a problem in that the flame retardant properties inherent to the polyimide material were reduced due to the large surface area.

[0008] Accordingly, the inventors developed a method for manufacturing a polyimide aerogel compounded with a flame-retardant filler using a high internal phase pickering emulsion (HIPPE) to improve the flame retardancy of the polyimide aerogel, and a polyimide aerogel manufactured using the same, and confirmed the performance to complete the present invention. Prior art literature

[0010] Korean Patent Publication No. 10-2139544 (Published July 21, 2020) The problem to be solved

[0011] The objective of the present invention is to provide a method for manufacturing a flame-retardant polyimide aerogel and a polyimide aerogel manufactured using the same.

[0012] Another objective of the present invention is to provide a polyimide aerogel that maintains high porosity while improving flame retardant properties and mechanical properties, manufactured using a high internal phase emulsion process.

[0013] Another objective of the present invention is to provide a polyimide aerogel that can be used as an insulating material / flame retardant between battery cells or as a separator within a battery cell, a method for manufacturing the same, and a battery comprising said polyimide aerogel.

[0014] The problems that the present invention aims to solve are not limited to the problem(s) mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0016] To achieve the above objective, the present invention provides a method for manufacturing a polyimide aerogel, comprising the steps of: mixing a flame retardant into an aqueous polyamic acid solution; preparing an oil-in-water emulsion containing the mixed solution; and removing the solvent from the emulsion and performing an imidization reaction.

[0017] The above-mentioned polyamic acid aqueous solution may be a mixture of a polyamic acid obtained by polymerizing a diamine monomer and a dianhydride monomer in an organic solvent and a water-soluble agent in an aqueous solution.

[0018] The above-mentioned polyamic acid aqueous solution may be obtained by polymerizing a diamine monomer, a dianhydride monomer, and an aqueous catalyst in an aqueous solution.

[0019] The content of the flame retardant may be 20 to 250 phr relative to the polyimide.

[0020] The above flame retardant may be an inorganic flame retardant and may be one or more combinations selected from aluminum hydroxide, aluminum oxide hydroxide (AlOOH, Boehmite), magnesium hydroxide, cerium oxide, antimony trioxide, antimony pentoxide, silicon oxide, zinc tartaric acid, molybdates, guanidine salts, zinc borate, and zirconium.

[0021] The above flame retardants are phosphorus-based flame retardants, including aluminum dialkylphosphinate, triphenyl phosphate [TPP], triaryl phosphate [TAP], aromatic phosphate esters, 2-ethylhexyldiphenyl phosphate [EHDPP], triethyl phosphate [TEP], tricresyl phosphate [TCP], tributyl phosphate [TBP], tri-iso-butyl phosphate [TiBP], tris(2-butoxyethyl)phosphate [TBEP], tris(2-ethylhexyl)phosphate [TEHP], ammonium polyphosphate [APP], and red phosphorus (CG-P). It may be one or more combinations selected from isopropylphenyl diphenyl phosphate (IPPP), cresyl diphenyl phosphate, resorcinol diphenyl phosphate, tris(chloropropyl)phosphate (TCPP), tris(2-chloroethyl)phosphate (TCEP), tris(1,3-dichloro-2-propyl)phosphate (TDCP), halogen-containing condensed phosphate esters, aromatic condensed phosphate esters, and polyphosphates.

[0022] The flame retardant may be a brominated flame retardant, such as tetrabromobisphenol A (TBBA), decabromodiphenyl oxide (DBDPO), hexabromocyclododecane (HBCD), octabromodiphenyl oxide (OBDPO), bistribromophenoxyethane (BTBPE), tribromophenol (TBP), ethylenebistetrabromophthalimide, TBA polycarbonate oligomer, brominated polystyrene, TBA epoxy oligomer, TBA-bis(2,3-dibromopropyl ether), ethylenebispentabromodiphenyl, polybromophenyl oxide, brominated aromatic triadine, and hexabromobenzene; a chlorinated flame retardant, such as one or a combination of two or more selected from chlorinated paraffin, perchlorocyclopentadecane, and chlorened acid.

[0023] The flame retardant may be one or more combinations selected from carbon nanoparticles (CNT), graphene, boron nitride nanotubes (BNNT), graphene oxide, and reduced graphene oxide.

[0024] The above emulsion may be a Pickering emulsion.

[0025] In addition, the present invention provides a polyimide aerogel prepared by the method described above.

[0026] The above polyimide aerogel may have a 15% weight loss temperature in thermogravimetric analysis (TGA) of 500°C or higher.

[0027] In addition, the present invention provides a battery comprising a polyimide aerogel manufactured by the method described above. Effects of the invention

[0029] According to the present invention, there is an effect of providing a method for manufacturing a flame-retardant polyimide aerogel and a polyimide aerogel manufactured using the same.

[0030] In addition, according to the present invention, there is an effect of providing a polyimide aerogel having high porosity while having improved flame retardant properties and mechanical properties.

[0031] In addition, the flame-retardant polyimide aerogel according to the present invention is used as an insulating material / flame retardant between battery cells or as a separator within a battery cell, thereby suppressing the occurrence of fire caused by the battery and, in particular, having the effect of preventing battery chain explosions.

[0032] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0034] FIG. 1 is a process flowchart of a method for manufacturing a flame-retardant polyimide aerogel according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing the manufacturing process of a flame-retardant polyimide aerogel according to one embodiment of the present invention and an image of an actual sample thereof. FIG. 3a shows a polyamic acid salt (PMDA-m-TB + DMEA) prepared according to one embodiment (Comparative Example 1) of the present invention. 1 Figure 3b shows the H-NMR data and the measured molecular weight. FIG. 4 shows a cross-sectional view and enlarged view of a high internal phase Pickering emulsion (HIPPE) according to one embodiment of the present invention, a cross-sectional view and enlarged view of a polyamic acid aerogel from which a solvent has been removed from the emulsion, and a cross-sectional view and enlarged view of a polyimide aerogel from which the same has been imidized. FIG. 5 is a photograph of a flame-retardant polyimide aerogel sample according to one embodiment of the present invention (comparative example, Examples 1-5). FIG. 6 shows a method for evaluating flame retardancy in one embodiment of the present invention (comparative example, Examples 1-5). Figure 7 is a photograph showing the flame retardancy evaluation results of a flame-retardant polyimide aerogel according to one embodiment of the present invention (comparative example, Examples 1-5). FIG. 8 is a graph showing the thermogravimetric analysis results of a flame-retardant polyimide aerogel according to one embodiment of the present invention (comparative example, Examples 1-3). FIG. 9 is a graph showing the thermogravimetric analysis results of flame-retardant polyimide aerogel according to one embodiment (Examples 2, 4, and 5) of the present invention. FIG. 10 is a graph showing the compressive strength evaluation results of a flame-retardant polyimide aerogel according to one embodiment of the present invention (comparative example, Examples 1-3). FIG. 11 is a graph showing the compressive strength evaluation results of flame-retardant polyimide aerogel according to one embodiment of the present invention (Examples 2, 4, and 5). FIG. 12 shows a scanning electron microscope (SEM) image of a flame-retardant polyimide aerogel according to one embodiment of the present invention (comparative example, Examples 1-5). FIG. 13 shows (a) a battery cell in which a flame-retardant polyimide aerogel according to one embodiment of the present invention can be used, (b) a battery module formed by stacking the battery cell, and a battery pack formed by adding a system to an assembly of the battery modules, and (c) a schematic diagram of battery chain explosion and prevention thereof. Specific details for implementing the invention

[0035] It should be noted that in the following description, only the parts necessary for understanding the embodiments of the present invention are described, and the description of other parts will be omitted to the extent that it does not detract from the gist of the present invention.

[0036] The terms and words used in the specification and claims described below should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely preferred embodiments of the invention and do not represent all aspects of the technical spirit of the invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0037] The present invention will be described in detail below.

[0039] Method for manufacturing polyimide aerogel

[0040] The present invention provides a method for manufacturing a polyimide aerogel, comprising the steps of: mixing a flame retardant into an aqueous polyamic acid solution; preparing an oil-in-water emulsion containing the mixed solution; and removing the solvent from the emulsion and performing an imidization reaction.

[0041] FIG. 1 is a process flowchart of a method for manufacturing a polyimide aerogel according to one embodiment of the present invention. The following description will be explained with reference to FIG. 1.

[0043] First, a flame retardant is mixed into an aqueous polyamic acid solution (S10).

[0044] The polyamic acid aqueous solution of this step may be an aqueous solution containing polyamic acid or polyamic acid salt.

[0045] The above-mentioned polyamic acid aqueous solution may be prepared by mixing a polyamic acid obtained by polymerizing a diamine monomer and a dianhydride monomer in an organic solvent with a water-soluble agent in an aqueous solution.

[0046] Specifically, the preparation of the above-mentioned polyamic acid aqueous solution may include: a step of polymerizing a diamine monomer and a dianhydride monomer in an organic solvent to form a polyamic acid; b step of precipitating and drying the formed polyamic acid to produce polyamic acid particles; and c step of mixing the polyamic acid particles and a water-soluble agent into an aqueous solution.

[0047] In step a above, the organic solvent may be a polar aprotic solvent, for example, NMP, DMF, and DMAc.

[0048] In step a above, the diamine monomer is, as a non-limiting example, 4,4'-diaminodiphenyl ether (ODA), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), paraphenylenediamine (pPDA), metaphenylenediamine (mPDA), 3,5-diaminobenzoic acid (or DABA), diaminodiphenyl ether such as 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (methylenediamine), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, bis(4-aminophenyl)sulfide, 4,4'-diaminobenzanilide, 3,3'-dichlorobenzidine, 3,3'-dimethylbenzidine (or o-tolidine), 2,2'-dimethylbenzidine (or m-tolidine), 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-Diaminobenzophenone, 4,4'-Diaminobenzophenone, 3,3'-Diamino-4,4'-Dichlorobenzophenone, 3,3'-Diamino-4,4'-Dimethoxybenzophenone, 3,3'-Diaminodiphenylmethane, 3,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylmethane, 2,2-Bis(3-aminophenyl)propane, 2,2-Bis(4-aminophenyl)propane, 2,2-Bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-Bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-Diaminodiphenylsulfoxide, 3,4'-Diaminodiphenylsulfoxide, It may be 4,4'-diaminodiphenylsulfoxide or a mixture thereof.

[0049] In step a above, the dianhydride monomer may be, as a non-limiting example, pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (DSDA), 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride (6-FDA), or a mixture thereof.

[0050] In the step of precipitating the polyamic acid in step b above, any solvent that has poor solubility with polyamic acid may be used as a precipitating agent. For example, it may be a protic solvent or an aprotic solvent. Non-limiting examples of protic solvents may be water, methanol, ethanol, isopropyl alcohol, or mixtures thereof, and non-limiting examples of aprotic solvents may be acetone, TMF, methyl ethyl keton (MEK), acetonitrile (MeCN), or mixtures thereof.

[0051] The drying step of step b above can be performed at a vacuum temperature of 20°C to 60°C for 6 hours or more.

[0052] In the step of mixing the polyamic acid particles and the water-soluble agent of step c into an aqueous solution, the water-soluble agent may be an amine-based water-soluble agent or an imidazole-based water-soluble agent.

[0053] 상기 아민계 수용화제는 비제한적인 예로, 2-Dimethylaminoethanol(DMEA), N,N-Diethylethanolamine(DEEA), 3-Dimethylaminopropanol, Diethanolamine (DEA), 3-Diethylamino-1-propanol, NMethyldiethanolamine(MDEA), Triethanol amine(TEOA), Diethanolisopropylamine, Diethanolisopropanolamine(DEIPA), N,N-Dimethylisopropanolamine, 1-[Ethyl(2-hydroxyethyl)amino)]-2-propanol, Triisopropanolamine, N-(2-hydroxyethyl)-N-(2-hydroxypropyl)methylamine, 3-[2-hydroxyethyl(methyl)amino]propane-1,2-diol, 3-[ethyl(2-hydroxyethyl)amino]propane-1,2-diol, 2-(Diethylamino)propanol, 1-[methyl(propyl)amino]propan-2-ol, N,N-Diethyl-2-hydroxypropylamine, 1-(ethylmethylamino)-2-propanol, 2-(Dimethylamino)-2-methyl-1-propanol (DMAMP-80), 3-Dimethylamino-1-propanol, 4-Dimethylamino-1-butanol, 1-(dimethylamino)-2-methyl-2-propanol, 1-(Dipropylamino)-2-propanol, 2-(Buthylmethylamino)ethanol, 2-(Dipropylamino)ethanol, 2-[Methyl(2-methylpropyl)amino]ethanol, 2-[sec-Butyl(methyl)amino]ethanol, 2-(Isopropylpropylamino)Ethanol,1-[(2-Hydroxyethyl)propylamino]-2-propanol, 1-[Butyl(methyl)amino]propan-2-ol, N-Propyl Diethanolamine, Ethylamine, Diethylamine, Propylamine, Dipropylamine, Butylamine, Pentylamine, Hexylamine, Cyclohexylamine, N-ethyl-N-methyl-2-propanamine, Diethylisopropylamine, N,N-diisopropylamine(DIPA), Nethyl-N-methyl-1,2-ethanediamine, N,N-dimethylhexylamine, 또는 N,N-dimethylethylamine일 수 있다.,

[0054] 상기 이미다졸계 수용화제는 비제한적인 예로, 1,2-Dimethylimidazole, Imidazole, 2-methylimidazole, 1-Methylimidazole, 2-Ethylimidazole, 4(5)-Methylimidazole, 2-Ethyl-4-methylimidazole, 2,2-imidazole, Benzimidazole, 1-Benzyl-2-methylimidazole, 2-Methyl-1-pyrroline, Pyrazole, 2-ethyl-4-ethyl imidazole, 2-methyl-4-ethyl imidazole, 1-methyl-4-ethyl imidazole, 1-methylpyrrolidine, 5-methylbenzimidazole, Isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, 4-n-propylpyridine, 또는 2-Ethyl-4-methy-1H-limidazole-1-propanenitrile일 수 있다.

[0055] In addition, the above water-soluble agent may be in a range of 0.5 to 1.5 times equivalents relative to 1 equivalent of a carboxyl group in the polyamic acid. Below this range, there is a problem that the formation of polyamic acid (salt) is not easy, and above this range, there is a problem of inefficiency.

[0056] In the step of mixing the polyamic acid particles and the water-soluble agent of step c above into an aqueous solution, the aqueous solution is a solution containing water, preferably water, distilled water, or purified water, but is not limited thereto.

[0057] In step c above, a polyamic acid solution can be formed by mixing polyamic acid particles and a water-soluble agent into an aqueous solution and stirring. The stirring time varies depending on 1) the polyamic acid solid content, 2) the type of water-soluble agent, and 3) the polyamic acid molecular structure, but in most cases, the entire solution can be soluble within 48 hours.

[0058] In addition, the above-mentioned aqueous polyamic acid solution may be prepared by polymerizing a mixture of a diamine monomer, a dianhydride monomer, and an aqueous catalyst in an aqueous solution. As one example, the process may involve the steps of adding a water-soluble agent and an aqueous catalyst, which is an organic base acting as a catalyst, to water containing a diamine monomer and stirring, adding a dianhydride monomer to react and polymerizing the polyamic acid (polyamic acid or polyamic acid salt), and cooling.

[0059] The above-mentioned aqueous catalyst may be an imidol-based water-soluble agent, and non-limiting examples of imidol-based water-soluble agents are as described above.

[0060] In addition, the above aqueous catalyst may be a pyridine derivative compound having at least one electron donor group and may be represented by the following chemical formula 1 or chemical formula 2.

[0061] [Chemical Formula 1]

[0062]

[0063] In the above chemical formula 1, at least one of R1 to R3 is an alkylamine group having 1 to 4 carbon atoms, a hydroxyl group, an alkoxy group having 1 to 4 carbon atoms, a thiol group, a thiol ether group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a heterocyclic group.

[0064] Examples of aqueous catalysts represented by the above chemical formula 1 may be 4-(methylamino)pyridine, 4-(dimethylamino)pyridine, 2-hydroxypyridine, 4-hydroxypyridine, 4-methoxypyridine, 2-methoxypyridine, 2,6-dimethoxypyridine, 2-ethoxypyridine, 4-mercaptopyridine, 2-mercaptopyridine, 4-(methylthio)pyridine, 2-(methylthio)pyridine), 4-methylpyridine, 2-methylpyridine, 4-ethylpyridine, 2-ethylpyridine, 4-propylpyridine, 2,4,6-trimethylpyridine, 4-piperidinopyridine, 4-mornopolinopyridine, or 4-pyrrolidinopyridine.

[0065] [Chemical Formula 2]

[0066]

[0067] In the above chemical formula 2, at least one of R4 and R5 is a monoalkylamino group having 1 to 4 carbon atoms, a dialkylamino group having 1 to 4 carbon atoms, a piperidino group, a morpholino group, or a pyrrolidino group.

[0068] Examples of aqueous catalysts represented by the above chemical formula 2 may be 4-dimethylaminopyridine, 2-dimethylaminopyridine, 4-methylaminopyridine, 4-piperidinopyridine, 4-mornopolinopyridine, or 4-pyrrolidinopyridine.

[0069] The above aqueous catalyst may be in a range of 0.5 to 1.5 equivalents relative to 1 equivalent of a carboxyl group in the polyamic acid. Below this range, there is a problem that the formation of polyamic acid (salt) is not easy, and above this range, there is a problem of inefficiency.

[0070] In addition, the above-mentioned aqueous catalyst may have a polydentate structure in which two or more tertiary amines are linked to an aliphatic or aromatic hydrocarbon, and may include at least one of the compounds of the following chemical formulas 3 to 6.

[0071] [Chemical Formula 3]

[0072]

[0073] [Chemical Formula 4]

[0074]

[0075] [Chemical Formula 5]

[0076]

[0077] [Chemical Formula 6]

[0078]

[0079] In the above formulas 3, 4, 5, and 6, R1 to R6 are each independently an alkyl group having 1 to 4 carbon atoms, and A1 to A3 are each independently oxygen, a carbonyl group, an alkyl carbonyl group, an alkyl group, an alkylene group, or an alkylidene group. The alkylene group or alkylidene group may be substituted or unsubstituted with at least one substituent. The substituent may be, for example, an alkyl group, an alkenyl group, or an alkynyl group, but is not limited thereto. The alkyl group, alkenyl group, or alkynyl group may be straight-chain, branched-chain, or cyclic, and may have a carbon number within the range of 1 to 30 or within the range of 1 to 10 carbon atoms. The lower limit of the carbon number may be 1, 2, 3, or 4, and the upper limit may be 30, 25, 20, 15, 10, or 8 or less.

[0080] The above aqueous catalyst may be within a range of 0.5 to 2.0 equivalents relative to 1 equivalent of a carboxyl group in the polyamic acid. Below this range, there is a problem that the formation of polyamic acid (salt) is not easy, and above this range, there is a problem of inefficiency.

[0081] The flame retardant mixed into the polyamic acid aqueous solution in this step may be one or a mixture of two or more of inorganic flame retardants, phosphorus-based flame retardants, halogen-based flame retardants (bromine-based flame retardants, chlorine-based flame retardants, etc.), and carbon-based flame retardants. In addition, the particle size of the flame retardant particles may be an average of 10 nm to 100 µm.

[0082] The flame retardant may be 20 to 250 phr with respect to the polyimide, and preferably 50 to 200 phr with respect to the polyimide. Within the above range, flame retardancy (or heat resistance) and / or mechanical properties are improved as the amount of flame retardant added increases (Figs. 8-9, 10-11, Table 5). However, below the above range, there is a problem of insufficient flame retardancy, and above the above range, there is a problem of inefficiency in that flame retardancy does not improve as much as the amount of flame retardant added increases.

[0083] The above inorganic flame retardant may be one or a combination of two or more selected from aluminum hydroxide, aluminum oxide hydroxide (AlOOH, Boehmite), magnesium hydroxide, cerium oxide, antimony trioxide, antimony pentoxide, silicon oxide, zinc tartaric acid, molybdates, guanidine salts, zinc borate, and zirconium.

[0084] The above phosphorus-based flame retardants include aluminum dialkylphosphinate, triphenyl phosphate [TPP], triaryl phosphate [TAP], aromatic phosphate esters, 2-ethylhexyldiphenyl phosphate [EHDPP], triethyl phosphate [TEP], tricresyl phosphate [TCP], tributyl phosphate [TBP], tri-iso-butyl phosphate [TiBP], tris(2-butoxyethyl)phosphate [TBEP], tris(2-ethylhexyl)phosphate [TEHP], ammonium polyphosphate [APP], and red phosphorus (CG-P). It may be one or more combinations selected from isopropylphenyl diphenyl phosphate (IPPP), cresyl diphenyl phosphate, resorcinol diphenyl phosphate, tris(chloropropyl)phosphate (TCPP), tris(2-chloroethyl)phosphate (TCEP), tris(1,3-dichloro-2-propyl)phosphate (TDCP), halogen-containing condensed phosphate esters, aromatic condensed phosphate esters, and polyphosphates.

[0085] The above phosphorus-based flame retardant may preferably be a phosphorus flame retardant represented by the following chemical formula 1.

[0086] [Chemical Formula 7]

[0087]

[0088] In the above chemical formula 7, R' and R" are each C 1-10 It is an alkyl group, and n is an integer from 1 to 10.

[0089] In addition, the phosphorus-based flame retardant may preferably be a hydrophilic phosphorus flame retardant represented by Chemical Formula 7. This may be a phosphorus flame retardant represented by Chemical Formula 7 that has been surface-modified with a hydrophilic material, specifically a surface-modified with polyethylene oxide (PEO).

[0090] The above halogen-based flame retardant may be a combination of one or more of tetrabromobisphenol A (TBBA), decabromodiphenyl oxide (DBDPO), hexabromocyclododecane (HBCD), octabromodiphenyl oxide (OBDPO), bistribromophenoxyethane (BTBPE), tribromophenol (TBP), ethylenebistetrabromophthalimide, TBA polycarbonate oligomer, brominated polystyrene, TBA epoxy oligomer, TBA-bis(2,3-dibromopropyl ether), ethylenebispentabromodiphenyl, polybromophenyl oxide, brominated aromatic triadine, and hexabromobenzene as a brominated flame retardant, or a combination of one or more selected from chlorinated paraffin, perchlorocyclopentadecane, and chlorened acid as a chlorinated flame retardant.

[0091] The above carbon-based flame retardant may be one or more combinations selected from carbon nanoparticles (CNT), graphene, boron nitride nanotubes (BNNT), graphene oxide, and reduced graphene oxide.

[0092] The step of mixing a flame retardant into the polyamic acid aqueous solution of this step may involve adding the flame retardant to the polyamic acid aqueous solution prepared as described above and stirring to prepare a mixed solution. The stirring may be performed until the flame retardant is sufficiently mixed into the polyamic acid aqueous solution.

[0094] Next, an oil-in-water emulsion containing the mixed solution prepared in S10 is prepared (S20).

[0095] The above oil-in-water emulsion may comprise an aqueous polyamic acid solution containing a flame retardant as the continuous phase and an organic solvent that does not mix with water as the dispersed phase.

[0096] The above organic solvent may be a cyclohexane-based organic solvent, an alkane-based organic solvent, a toluene-based organic solvent, a benzene-based organic solvent, or other water-insoluble organic solvent.

[0097] An oil-in-water emulsion can be prepared by adding the organic solvent to an aqueous polyamic acid solution containing the flame retardant and emulsifying it. This can preferably be prepared as a High Internal Phase Pickering Emulsion (HIPPE). A High Internal Phase Pickering Emulsion is a Pickering emulsion stabilized by solid particles at the interface, and refers to an emulsion system in which the volume of dispersed droplets is 74 volume% or more of the total emulsion. Such a highly dispersed Pickering emulsion has a very high specific surface area relative to volume compared to ordinary emulsions, making it useful. Furthermore, by using the High Internal Phase Pickering Emulsion as a template, it is possible to fabricate various porous materials, which can be utilized in various industrial fields such as filters, sensors, adsorbents, and catalyst supports.

[0098] Accordingly, the organic solvent constituting the internal phase may be 74 to 99.99% (v / v) of the total mixed solution, and preferably 80 to 99.99% (v / v). At this time, the aqueous solution containing the flame retardant, which is the external phase, may be 0.01 to 26% (v / v), and preferably 0.01 to 20% (v / v).

[0099] The above emulsion requires strong energy, and methods commonly used in the technical field of the present invention can be used, and energy can be supplied using a homogenizer, but is not limited thereto.

[0101] Finally, the solvent of the emulsion prepared in S20 is removed and imidization is performed (S30).

[0102] Before the above step, the prepared oil-in-water emulsion may be placed in a mold and then cast to make the surface flat.

[0103] The step of removing the solvent from the emulsion can be performed by rapidly cooling the prepared oil-in-water emulsion, pre-freezing it, and freeze-drying it to remove the aqueous solution of the continuous phase (external phase) and the organic solvent of the dispersed phase (internal phase). The rapid cooling can be performed in a liquid nitrogen atmosphere and can be performed for 5 minutes or more.

[0104] The temperature during the above preliminary freezing may be -30°C to -5°C, preferably -5°C to -20°C, more preferably -5°C to -15°C, and most preferably close to -10°C. The above preliminary freezing may be performed for at least one hour.

[0105] The temperature during freeze-drying above may be -60°C to -5°C, preferably -55°C to -15°C, more preferably -50°C to -30°C, and most preferably a temperature close to -40°C. The freeze-drying time may be 1 hour to 48 hours, preferably 6 hours to 36 hours, and more preferably 8 hours to 24 hours.

[0106] The vacuum level during the above freeze-drying is 10 -6 It can be from torr to 1 torr, preferably 10 -5 torr to 10 -3 It can be torr, and more preferably 10 4 It can be a pressure close to torr.

[0107] The above imidization step includes the heat treatment step, and a polyimide aerogel can be formed by thermally imidizing.

[0108] The above heat treatment temperature may be 100°C to 400°C, and preferably 120°C to 350°C.

[0109] The above heat treatment can be performed in a convection oven or a vacuum oven, and can be performed while slowly increasing the temperature. The above heat treatment can be performed for 10 to 300 minutes, preferably for 50 to 250 minutes, and more preferably for 100 to 200 minutes.

[0111] Polyimide Aerogel

[0112] The present invention provides a polyimide aerogel manufactured by the above-described method.

[0113] The above polyimide aerogel is 0.001 g / cm³ 3 Up to 1.0 g / cm³ 3 It can have a density of, specifically 0.01 g / cm³ 3Up to 0.7 g / cm² 3 It can have a density of, more specifically, 0.01 g / cm³ 3 Up to 0.6 g / cm 3 It can have a density of.

[0114] The above polyimide aerogel can have a porosity of 80% or more, specifically 90% or more, and more specifically 90% to 99.9%.

[0115] The above polyimide aerogel may have a pore size of 0.001 to 100 μm, and specifically, may have a pore size of 0.01 to 50 μm.

[0116] The above polyimide aerogel has excellent flame retardancy and may have a 15% weight loss temperature in thermogravimetric analysis of 500°C or higher, preferably 600°C or higher (Figs. 8, 9).

[0117] The above polyimide aerogel has excellent mechanical properties and may have a Young's modulus of 15 to 55 (kPa) (Fig. 10, Fig. 11, Table 5).

[0119] Battery containing polyimide aerogel

[0120] The present invention provides a battery comprising a polyimide aerogel manufactured by the above-described method.

[0121] The above battery may be a secondary battery, and in particular, may be a secondary battery for electric vehicles.

[0122] The above secondary battery may be used in information and communication devices, electric vehicles, or energy storage devices.

[0123] In particular, with the recent rise in interest regarding the commercialization of electric vehicles, efforts to ensure the safety of batteries used in electric vehicles are increasing. Batteries, which serve as the power source for electric vehicles, pose a high risk of fire and a very high risk of secondary explosions.

[0124] The battery separator prevents physical contact between the positive and negative active materials inside the battery and simultaneously acts as a channel for ions to pass through (Fig. 13a).

[0125] Meanwhile, to increase battery performance, battery cells are made and stacked for use, and if a problem occurs in one cell and it explodes and causes a fire, it triggers a chain of explosions (Fig. 13b).

[0126] Accordingly, the polyimide aerogel according to the present invention has excellent flame retardancy (Figs. 8 and 9), so when used as a battery separator, it can delay a short circuit (a short circuit is when the negative and positive electrodes that need to be separated are connected by a conductor such as metal, which is highly likely to lead to ignition) that may occur when the battery is exposed to external impact or fire, and can prevent thermal runaway. In addition, by using the polyimide aerogel according to the present invention as a flame retardant between battery cells, it is possible to prevent battery chain explosions caused by a fire spreading from a thermally runaway cell to another cell (Fig. 13c). Furthermore, the polyimide aerogel according to the present invention has excellent mechanical properties (Figs. 10, 11, and Table 5), so when used as a battery separator, it can withstand defects caused by dendrite formation, thereby improving battery operation stability.

[0128] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0130] Comparative Example 1

[0131] [Reaction Equation]

[0132]

[0133] The reaction for the synthesis of polyimide aerogel can be represented by the above reaction equation. The specific manufacturing method is as follows.

[0134] (1) Polyamic acid was prepared by polymerizing PMDA (3.3835 g, 0.0115 mol) and DMBZ (m-TB) (2.4332 g, 0.0115 mol) in Dimethylacetamide (DMAc) (52.3503 g, 55.6918 ml, 90 wt% to solid). The polymerized polyamic acid was precipitated in acetone and ground with a mixer to effectively remove internal organic solvents. The precipitate was filtered and washed with acetone three times to obtain a purified polyamic acid precipitate, which was then vacuum dried at 40°C for more than 12 hours to prepare polyamic acid particles. The polyamic acid particles were placed in distilled water along with DMEA equivalent to twice the amount of polyamic acid and stirred for 5 hours to prepare an aqueous polyamic acid solution.

[0135] (2) Cyclohexane was added to the above polyamic acid aqueous solution as an organic solvent (80% (v / v) of the total solution) [20 ml of polyamic acid aqueous solution and 80 ml of organic solvent (cyclohexane) per 100 ml of emulsion] and emulsified using a homogenizer at a rotation speed of 5,000 to 25,000 rpm for 8 to 10 minutes. The prepared emulsion was placed in a silicone mold and cast to make the surface flat.

[0136] (3) After that, the polyamic acid aerogel was prepared by rapidly cooling it in a liquid nitrogen atmosphere (at least 5 minutes), then pre-freezing it at -40°C for at least 2 hours until it was completely frozen inside the emulsion, and then freeze-drying it at -10°C for at least 12 hours to remove the organic solvent, which is the continuous phase, and the water, which is the dispersed phase.

[0137] Polyimide (PI) aerogels were prepared by thermally imidizing dried polyamic acid foam in a vacuum oven at 120, 180, 250, 300, and 350°C for 30 minutes each.

[0139] Comparative Example 2

[0140] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that BPDA and pPDA were used instead of PMDA and DMBZ(m-TB) in step (1) of Comparative Example 1.

[0142] Comparative Example 3

[0143] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that BPDA and MDA were used instead of PMDA and DMBZ(m-TB) in step (1) of Comparative Example 1.

[0145] Comparative Example 4

[0146] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that 6FDA and m-TB were used instead of PMDA and DMBZ(m-TB) in step (1) of Comparative Example 1.

[0148] Comparative Example 5 (Aqueous Polymerization)

[0149] Except for performing step (1) of Comparative Example 1 as follows, it was performed in the same manner as Comparative Example 1.

[0150] 63.7 g of distilled water was added as a solvent to a nitrogen-filled reactor equipped with a temperature controller. To this, 1.0814 g (0.0094 mol) of p-phenylenediamine (pPDA) and 2.5 equivalents of 4-dimethylaminopyridine relative to the carboxyl group were added, and the mixture was dissolved using a mechanical stirrer at 25°C for 1 hour. Subsequently, 2.9422 g (0.01 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) was added, and the polymerization reaction was carried out by stirring the mixture at 70°C for 18 hours to prepare an aqueous polyamic acid solution. An emulsion was prepared using the aqueous polyamic acid solution obtained by the above water-based polymerization as the external phase and cyclohexane as the internal phase (the preparation of the emulsion was the same as in Comparative Example 1).

[0152] FIG. 3a shows the aqueous solution of the polyamic acid (PMDA-m-TB + DMEA) prepared in Comparative Example 1 above. 1 As H-NMR data, it was confirmed that the polyimide aerogel was successfully synthesized into the desired structure. Figure 3b shows the molecular weight results obtained using size-exclusion chromatography (SEC), and Table 1 shows the number average molecular weight (Mn), weight average molecular weight (Mw), and polydispersity index (Mw / Mn) obtained using the size-exclusion chromatography data.

[0153] Number average molecular weight (Mn) Weight-average molecular weight (Mw) Multivariance (Mw / Mn) W-PAAS 17440 35485 2.05

[0154] The physical properties of the polyimide aerogels prepared in Comparative Examples 1 to 4 above were summarized and presented in Table 2.

[0155] Mn(kg mol -1 ) / Ð Foam density (g / cm³) 3 ) Bulk density (g / cm³) 3 ) Porosity (%) Pore ​​size (㎛) Td 5wt%(℃) Residue (wt%) Comparative Example 1 23.0 / 2.46 0.014 1.50 99.0 0.01~45 467.7 13.20 Comparative Example 2 8.4 / 2.20 0.010 1.76 99.4 0.01~25 568.7 1.88 Comparative Example 3 - 0.058 - 92.8 - 544.0 58.2 Comparative Example 4 16.8 / 2.46 0.019 1.71 98.9 - 548.4 0.91 Comparative Example 5 28.0 / 1.54 0.015 1.51 99.1 0.01~50 475.5 11.5

[0156] * Residue: Weight ratio of carbides remaining after TGA experiment

[0158] Example 1

[0159] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that 50 phr of AlOOH powder (Boehmite, provided by LG chem) was added as a flame retardant filler to the polyamic acid aqueous solution prepared in step (1) of Comparative Example 1.

[0161] Example 2

[0162] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that 100 phr of AlOOH powder (Boehmite, provided by LG chem) was added as a flame retardant filler to the polyamic acid aqueous solution prepared in step (1) of Comparative Example 1.

[0164] Example 3

[0165] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that 200 phr of AlOOH powder (Boehmite, provided by LG chem) was added as a flame retardant filler to the polyamic acid aqueous solution prepared in step (1) of Comparative Example 1.

[0167] Example 4

[0168] The above Comparative Example 1 was performed in the same manner as Comparative Example 1, except that 100 phr of Mg(OH)2 powder (sigma aldrich 310093) was added as a flame retardant filler to the polyamic acid aqueous solution prepared in step (1) of Comparative Example 1.

[0170] Example 5

[0171] The procedure was carried out in the same manner as Comparative Example 1, except that 100 phr of water-soluble phosphorus flame retardant powder was added as a flame retardant filler to the polyamic acid aqueous solution prepared in step (1) of Comparative Example 1. The water-soluble phosphorus flame retardant powder is a phosphorus flame retardant having the structural formula of Chemical Formula 8 [Universal Chemtech Co., Ltd. Aluminum phosphinate-based flame retardant OMP-800] surface modified with a polyethylene oxide (PEO) polymer.

[0172] [Chemical Formula 8]

[0173]

[0175] The types and amounts of flame retardants added to Comparative Example 1 and Examples 1-5 are summarized in Table 3.

[0176] AlOOH Mg(OH)2 Phosphorus-based flame retardant Comparative Example 1 - - - Example 1 50 phr - - Example 2 100 phr - - Example 3 200 phr - - Example 4 - 100 phr - Example 5 - - 100 phr

[0178] Experimental Example 1

[0179] The morphology of the polyimide aerogels of Comparative Example 1 and Examples 1-5 was observed.

[0180] Referring to Figure 5, it was confirmed that the foam was well molded / processed into a stable structure without defects, even with the addition of flame-retardant fillers and various amounts of them.

[0182] Experimental Example 2

[0183] The flame retardant properties of the polyimide aerogels of Comparative Example 1 and Examples 1-5 were evaluated. As shown in Fig. 6, the polyimide aerogels of Comparative Example and Examples 1-5 were heated with a gas torch for 30 seconds (the distance between the torch and the sample was set to 10 cm; see Fig. 6), and the results are shown in Fig. 7.

[0184] Referring to Fig. 7, the flame retardant properties of the comparative example were very low. When the same amount of AlOOH, Mg(OH)2, and phosphorus-based flame retardant (Examples 2, 4, 5) was added, AlOOH showed the best flame retardant properties, and it was confirmed that the flame retardant properties improved as the AlOOH content increased (Examples 1, 2, 3).

[0186] Experimental Example 3

[0187] Thermogravimetric analysis was performed to evaluate the thermal properties of the polyimide aerogels of Comparative Example 1 and Examples 1-5. First, thermogravimetric analysis was performed according to the flame retardant content of Comparative Example and Examples 1-3, and the results are shown in Fig. 8. Next, thermogravimetric analysis was performed according to the type of flame retardant of Examples 2, 4-5, and the results are shown in Fig. 9. In addition, the thermogravimetric analysis results (Td, 15 wt%) of Examples 1-5 are shown in Table 4.

[0188] The specific method for the above thermogravimetric measurement is as follows. In accordance with the JIS K 7120 (1987) standard, the sample mass was 2.5 to 3.5 mg, the measurement temperature was 40 ℃ to 850 ℃, and the heating rate was 10 ℃ / min. The temperature at which the sample weight decreased by 15% by weight was set as the 15% weight loss temperature. However, nitrogen was used as the inlet gas for the measurement, and the flow rate was set to 200 ml / min.

[0189] Referring to Figure 8, it was confirmed that thermal stability improves with increasing AlOOH content.

[0190] Referring to Figure 9, it was confirmed that AlOOH exhibits superior thermal stability compared to Mg(OH)2 or phosphorus-based flame retardants at the same content.

[0191] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Td, 15 wt% (℃) 546.54 555.98 582.78 597.26 396.70 431.21

[0193] Experimental Example 4

[0194] To verify the mechanical properties, the compressive strength of the polyimide aerogels of Comparative Example 1 and Examples 1-5 was evaluated. First, the compressive strength according to the flame retardant content of Comparative Example 1 and Examples 1-3 was measured, and the resulting stress-strain curve is shown in Fig. 10. Next, the compressive strength according to the type of flame retardant of Examples 2 and 4-5 was measured, and the resulting stress-strain curve is shown in Fig. 11.

[0195] Specifically, the compressive strength was measured using a Universal Testing Machine with a 2 × 2 × 1 (W × L × H, cm) rectangular prism specimen at a maximum load of 1000 N at a speed of 1 mm per minute. The stress-strain curve was plotted based on the results of the compressive strength test (Figs. 10, 11), and Young's modulus was calculated based on this and presented in Table 5.

[0196] Referring to Figure 10, it was confirmed that mechanical properties (Young's modulus) increased with increasing AlOOH content.

[0197] Referring to Figure 11, mechanical properties differ depending on the type of flame retardant added, and the mechanical properties of phosphorus-based flame retardants were the highest, followed by Mg(OH)2 and AlOOH.

[0198] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Example 5 Young's modulus (kPa) 18.2 19.66 20.82 23.15 36.07 51.49

[0200] Experimental Example 5

[0201] The porous structure and the shape of the flame-retardant filler were confirmed through scanning electron microscope (SEM) image analysis of the polyimide aerogels of Comparative Example 1 and Examples 1-5.

[0202] As a result of the SEM analysis in Fig. 12, an open cell structure was observed, the pore size was 20 μm or less, the porosity was 98% or more, and it was confirmed that flame-retardant fillers were added between the porous bodies and exposed on the surface. Therefore, it can be seen that the polyimide aerogel according to the present invention exhibits excellent thermal insulation properties due to its high porosity, and that flame-retardant properties are improved because the flame-retardant is exposed on the surface.

[0204] Although specific embodiments regarding a method for manufacturing a flame-retardant polyimide aerogel according to one embodiment of the present invention and a polyimide aerogel manufactured using the same have been described so far, it is obvious that various modifications are possible within the scope of the present invention.

[0205] Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

[0206] That is, the aforementioned embodiments should be understood as exemplary in all respects and not limiting, and the scope of the invention is defined by the claims set forth below rather than by the detailed description, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the invention.

Claims

Claim 1 A method for manufacturing a polyimide aerogel, comprising the steps of: mixing a flame retardant into an aqueous polyamic acid solution; preparing a Pickering emulsion containing the mixed solution; and removing the solvent from the emulsion and performing an imidization reaction, wherein the flame retardant is one or more selected from the group consisting of aluminum oxide hydroxide (AlOOH), magnesium hydroxide (Mg(OH)2), and aluminum dialkylphosphinate, the content of the flame retardant is 50 to 200 phr relative to the polyimide, and the manufactured polyimide aerogel has a pore size of 20 μm or less and a porosity of 98% or more, and a 15% weight loss temperature of thermogravimetric analysis (TGA) of 582.78°C or more. Claim 2 A method for manufacturing a polyimide aerogel according to claim 1, wherein the polyamic acid aqueous solution is a mixture of a polyamic acid obtained by polymerizing a diamine monomer and a dianhydride monomer in an organic solvent and a water-soluble agent in an aqueous solution. Claim 3 A method for manufacturing a polyimide aerogel according to claim 1, wherein the polyamic acid aqueous solution is polymerized by mixing a diamine monomer, a dianhydride monomer, and an aqueous catalyst in an aqueous solution. Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 Polyimide aerogel manufactured by the method of claim 1. Claim 11 A polyimide aerogel according to claim 10, characterized in that the 15% weight loss temperature of thermogravimetric analysis (TGA) is 582.78°C or higher. Claim 12 A battery comprising the polyimide aerogel of claim 10.

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