Polyimide separator, and preparation method therefor and use thereof

Abstract

The present invention belongs to the field of polymer materials, and discloses a polyimide separator, and a preparation method therefor and the use thereof. The preparation method for a polyimide separator comprises the following steps: (1) adding a diamine monomer and a dianhydride monomer to a solvent, and reacting same to obtain a polyamic-acid-containing solution; (2) adding a monomer containing an amide group to the polyamic-acid-containing solution, and reacting same to obtain a slurry; and (3) subjecting the slurry to a phase inversion method to obtain a polyimide separator. A monomer containing an amide group is added to the preparation of the polyimide separator to improve the structure, thereby improving the electrolyte wettability and electrolyte absorption rate of the separator, and further improving the rate performance of a battery; and the tensile strength and the puncture resistance are also significantly enhanced.

Description

Polyimide membranes, their preparation methods and applications Technical Field

[0001] This invention relates to polyimide separators, their preparation methods, and applications, belonging to the field of polymer materials. Background Technology

[0002] With the rapid development of high-power equipment such as new energy electric vehicles and large-scale energy storage systems, high-capacity, high-energy-density power and energy storage lithium-ion batteries have experienced explosive growth in recent years. However, the frequent spontaneous combustion and explosion incidents of new energy electric vehicles in recent years have raised serious concerns and questions about the safety of power lithium-ion batteries. One of the core reasons is that the performance of existing lithium battery separators cannot meet the application requirements of high-energy-density batteries. The separator plays two main roles in lithium-ion batteries: firstly, the separator material needs to have good insulation and a certain mechanical strength to prevent direct contact between the positive and negative electrodes within the battery and effectively prevent short circuits caused by punctures from burrs, dendrites, etc. Secondly, it must ensure that there are no significant dimensional changes under sudden high-temperature conditions, thus ensuring battery safety.

[0003] Most lithium-ion battery separators are made of polyolefin microporous membranes based on polypropylene (PP) and polyethylene (PE). Their low melting points (PP 165℃, PE 135℃) and softening temperatures make the batteries prone to thermal runaway due to separator shrinkage, especially under overcharging, over-discharging, and high-power charging and discharging conditions, which can lead to battery fires or explosions. Furthermore, PP and PE are non-polar polymers with poor electrolyte wettability, resulting in high internal resistance. Combined with their low porosity (approximately 40%) and low electrolyte absorption, this severely limits the battery's high-rate performance and makes it difficult to meet the needs of high-current, rapid charging and discharging. Although modification of traditional polyolefin separators can improve their heat resistance and wettability, it cannot solve the current problems faced by separators or meet the market demand for high-performance separators.

[0004] Currently, polyimide separators have high thermal stability and mechanical properties, and have gradually become the main research direction for battery separator materials. However, their low wettability and electrolyte absorption rate can reduce the rate performance of the battery. In addition, lithium dendrites can puncture the separator, causing short circuits in the battery. In severe cases, this can lead to safety accidents such as battery explosion and fire. Summary of the Invention

[0005] To address the aforementioned issues, a polyimide separator, its preparation method, and its applications are provided. In the preparation of this polyimide separator, monomers containing amide groups are added to improve its structure, thereby enhancing the electrolyte wettability and electrolyte absorption rate. This facilitates the efficient, stable, and rapid migration of lithium ions, thus improving the battery's rate performance. Furthermore, the tensile strength is significantly increased, thereby improving the separator's puncture resistance and preventing short circuits caused by lithium dendrites piercing the separator.

[0006] According to one aspect of the present invention, a method for preparing a polyimide separator is provided, comprising the following steps:

[0007] (1) Add diamine monomers and dianhydride monomers to a solvent and react to obtain a solution containing polyamic acid;

[0008] (2) Add a monomer with an amide group to the polyamic acid-containing solution, and after reaction, a slurry is obtained;

[0009] (3) The slurry is subjected to phase inversion to obtain a polyimide membrane.

[0010] In step (1), the amine monomer undergoes a nucleophilic attack reaction with the acid anhydride to obtain polyamic acid, with the following reaction structure:

[0011] In step (2), after polyamic acid and monomers containing amide groups are uniformly mixed, the reaction structure is as follows. During this process, the C=O group of polyamic acid and the NH group of monomers containing amide groups generate hydrogen bonding forces, which enables the monomers containing amide groups to be uniformly dispersed. At the same time, the monomers containing amide groups themselves will also generate forces through hydrogen bonding.

[0012] The structural diagram of polyamic acid is shown below:

[0013] In the polyamic acid structural formula, n refers to the number of repeating units in the polymer, and Ar and R are as follows:

[0014] The sample prepared in step (3) is formed by phase inversion and then baked to obtain polyimide.

[0015] Optionally, the molar ratio of the diamine monomer to the dianhydride monomer is 1:1; and the monomer containing the amide group accounts for 10%-50% of the weight percentage of the polyamic acid.

[0016] The content of the monomer containing the amide group affects the wettability and absorption rate of the diaphragm to the electrolyte, as well as its mechanical strength. Within the above range, as the amount of amide group increases, the contact angle becomes smaller, the wettability and absorption rate of the electrolyte become better, and the tensile strength and modulus become higher.

[0017] If the monomer containing amide groups accounts for less than 10% by weight of polyamic acid, there is no significant difference in electrolyte wettability and absorption rate compared to when no amide groups are added. If it is greater than 50%, although it is beneficial to the electrolyte absorption rate, its mechanical strength will decrease.

[0018] Optionally, the monomer containing the amide group is selected from at least one of benzoylaniline, methyl 2-acetaminophen, 2-benzoylacetaniline, and oxaloylaniline, preferably benzoylaniline.

[0019] The aforementioned monomers containing amide groups possess hydrogen bonding capabilities, which can enhance the overall structural strength when added within a specific range. Furthermore, the amide groups can improve the absorption of the electrolyte, facilitating lithium-ion transfer within the separator and thus improving battery performance.

[0020] Optionally, in step (2), a curing accelerator is added along with the monomer containing an amide group, wherein the molar ratio of the curing accelerator to the diamine monomer is 2-3:1.

[0021] Optionally, the curing accelerator is selected from at least one of triethylamine, benzimidazole, 1-methylimidazole, quinoline, 1,8-diazabicycloundec-7-ene, imidazole, pyridine, and 3-methylpyridine.

[0022] After adding the curing accelerator, the reaction in step (2) is carried out by thermal imidization and chemical imidization. The curing accelerator acts as an affinity agent to attack the carbon atoms on the carboxyl groups in polyamic acid, transferring hydrogen atoms to the carboxyl groups and promoting the catalytic mechanism of cyclization and dehydration, thereby improving the performance of the obtained membrane, reducing the reaction time, and saving production costs. If the amount of the above curing accelerator is too small, the improvement of the reaction promotion will not be obvious. If the amount is too large, it will increase the cost and reduce the molecular weight.

[0023] Optionally, the reaction temperature in step (1) is 20-25℃, and the reaction time is 60-80 min. In step (1), if the reaction temperature is too high, the molecular weight will decrease, which is not conducive to improving the mechanical strength of the membrane. If the reaction temperature is too low or the time is too short, the reaction will be insufficient, the molecular weight of the membrane will decrease, and thus affect the performance of the membrane. Optionally, inert gas is introduced for protection in both steps (1) and (2), and the inert gas includes nitrogen, argon, helium, neon, krypton, and xenon.

[0024] Optionally, the solvent is selected from polar solvents, low-boiling-point solvents, or low-water-absorbing solvents.

[0025] Optionally, the solvent is selected from at least one of dimethylacetamide (DMAc), m-cresol, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), chloroform, 3-methoxy-N,N-dimethylpropionamide, and γ-butyrolactone (GBL).

[0026] Optionally, the reaction temperature in step (2) is 60℃-100℃, and the reaction time is at least 6h. In step (2), if the reaction temperature is too high or the reaction time is too long, the production time will be increased and the product will be degraded. If the reaction temperature is too low or the reaction time is too short, it will not be conducive to promoting the catalytic mechanism of cyclization dehydration.

[0027] Optionally, the diamine monomer is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,5-diaminobenzoic acid, 4,4-diaminodiphenylmethane, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-diphenyl]-4,4'-diyl)bis(4-aminobenzamide), 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzoylaniline, 3,3'-dihydroxybenzidine, and 9,9-bis(4-aminophenyl)fluorene;

[0028] The dianhydride monomer is selected from at least one of pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 3,3,4,4-diphenylsulfone tetracarboxylic anhydride, and hexafluorodianhydride.

[0029] Optionally, the phase inversion method in step (3) is as follows: after the slurry is cooled to room temperature, a certain amount of solvent is added for dilution and continuous stirring is performed. Then, the diluted slurry is coated onto the substrate, and the substrate is immersed in a mixed solution of water and ethanol to obtain the polyimide membrane by phase inversion. Finally, the membrane is removed from the substrate and dried by heating.

[0030] Optionally, the substrate may be a glass substrate, a polytetrafluoroethylene (PTFE) substrate, a stainless steel substrate, or other suitable substrate.

[0031] Optionally, the coating method may be spin coating, bar coating, doctor blade coating, roller coating, gravure coating, or other suitable coating methods.

[0032] Optionally, the thickness of the polyimide membrane is 5-30 μm, preferably 10-15 μm.

[0033] For example, the thickness of the polyimide membrane can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, or any value in between.

[0034] According to another aspect of the present invention, a polyimide separator prepared by the method described in any one of the preceding claims is provided.

[0035] According to another aspect of the present invention, the application of the polyimide separator prepared by the method described in any one of the above claims in a battery is provided.

[0036] The beneficial effects of the present invention include, but are not limited to:

[0037] 1. The method for preparing the polyimide separator of the present invention uses simple and readily available raw materials, is convenient to operate, is suitable for industrial production and processing, and produces a separator with good consistency, which can be used in lithium batteries for a long time and extend the battery's service life.

[0038] 2. The polyimide separator prepared by reacting monomers containing amide groups with polyamic acid in this invention can improve the structure of the polyimide separator, thereby enhancing the wettability and absorption rate of the separator to the electrolyte, promoting the rapid migration of lithium ions in the battery, and improving the rate performance of the battery; in addition, the improvement of the structure can also improve the mechanical strength of the separator and enhance its puncture resistance.

[0039] 3. Compared with the membrane without amide-containing monomers, the polyimide membrane of the present invention has a significantly reduced contact angle. The more amide-containing monomers are added, the more significant the reduction in contact angle, which can be reduced to a minimum of 9°, and the electrolyte absorption rate is increased by 50-90%. Detailed Implementation

[0040] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0041] Unless otherwise specified, the raw materials used in the embodiments of this invention were all purchased through commercial channels.

[0042] Unless otherwise specified, the methods used in the embodiments of the present invention are conventional methods in the prior art.

[0043] Example 1

[0044] This embodiment relates to a method for preparing a polyimide separator, comprising the following steps:

[0045] (1) Under nitrogen atmosphere, 26.8g of 4,4'-diaminodiphenyl ether and 317g of DMAc were added to a 500ml three-necked flask and stirred at 22℃ for 30min. After the 4,4'-diaminodiphenyl ether was completely dissolved, 29.19g of pyromellitic dianhydride was added and the reaction was continued at 22℃ for 60min to obtain a solution containing polyamic acid.

[0046] (2) Add 43.21g of quinoline and benzoylaniline of 0%, 10%, 30% and 50% by weight of polyamic acid to a solution containing polyamic acid and stir until dissolved (the sample codes are OP-B0%, OP-B10%, OP-B30% and OP-B50%, respectively). Raise the temperature to 60℃ and stir for 6h to obtain slurry.

[0047] (3) Cool the above four slurries to room temperature, add 94g of DMAc and stir continuously for 30min to dilute. Then, coat the diluted OP-B0%, OP-B10%, OP-B30% and OP-B50% slurries onto the glass plate respectively. Immerse the substrate in a mixed solution of water and ethanol (water / ethanol volume ratio = 3 / 7) for 15min. Then peel the film off the glass and bake it in a vacuum oven at 180℃ for 60min to obtain the polyimide membrane.

[0048] The performance tests of the four types of diaphragms are shown in Table 1.

[0049] Table 1

[0050] As shown in Table 1, the electrolyte absorption rate of the samples (OP-B10%, OP-B30%, and OP-B50%) prepared with monomers containing amide groups increased by 52.29%-89.90%, and the contact angle decreased significantly. This indicates that the polyimide membranes prepared with monomers containing amide groups can effectively increase the wettability of the electrolyte, and their mechanical strength is also superior to that of membranes without monomers containing amide groups.

[0051] Example 2

[0052] This embodiment relates to a method for preparing a polyimide separator, comprising the following steps:

[0053] (1) Under nitrogen atmosphere, 14.47 g of p-phenylenediamine and 305 g of DMAc were added to a 500 ml three-necked flask and stirred at 22 °C for 30 min. After the p-phenylenediamine was completely dissolved, 39.38 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride was added and the mixture was stirred at 22 °C for 60 min to obtain a solution containing polyamic acid.

[0054] (2) Add 43.21g of quinoline and benzoylaniline of 0%, 10%, 30% and 50% by weight of polyamic acid to a solution containing polyamic acid and stir until dissolved (the sample codes are PB-B0%, PB-B10%, PB-B30% and PB-B50%, respectively). Raise the temperature to 60℃ and stir for 6 hours to obtain a slurry.

[0055] (3) Cool the above four slurries to room temperature, add 90g of DMAc and stir continuously for 30min to dilute. Then, coat the diluted slurries of PB-B0%, PB-B10%, PB-B30% and PB-B50% onto the glass plate. Immerse the substrate in a mixed solution of water and ethanol (volume ratio of water / ethanol = 3 / 7) for 15min. Then peel the film off the glass and bake it in a vacuum oven at 180℃ for 60min to obtain the polyimide membrane.

[0056] The performance tests of the four types of diaphragms are shown in Table 2.

[0057] Table 2

[0058] As shown in Table 2, the electrolyte absorption rate of the samples (PB-B10%, PB-B30%, and PB-B50%) prepared with monomers containing amide groups increased by 55.60%-97.56%, and the contact angle decreased significantly. This indicates that the polyimide membranes prepared with monomers containing amide groups can effectively increase the wettability of the electrolyte, and their mechanical strength is also superior to that of membranes without monomers containing amide groups.

[0059] Example 3

[0060] This embodiment relates to a method for preparing a polyimide separator, comprising the following steps:

[0061] (1) Under nitrogen atmosphere, 14.47 g of 3,3'-dihydroxybenzidine and 204.3 g of DMAc were added to a 500 ml three-necked flask and stirred at 20 °C for 30 min. After the 3,3'-dihydroxybenzidine was completely dissolved, 21.56 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride was added and stirred at 20 °C for 80 min to obtain a solution containing polyamic acid.

[0062] (2) Add 17.29g of quinoline and 2-benzoylacetanilide, which account for 0%, 10%, 30% and 50% of the weight of polyamic acid, to a solution containing polyamic acid and stir until dissolved (the sample codes are HT-2B0%, HT-2B10%, HT-2B30% and HT-2B50%, respectively). Raise the temperature to 90℃ and stir for 6h to obtain a slurry.

[0063] (3) Cool the above four slurries to room temperature, add 96g of DMAc and stir continuously for 30min to dilute. Then, coat the diluted slurries of HT-2B0%, HT-2B10%, HT-2B30% and HT-2B50% onto the glass plate. Immerse the substrate in a mixed solution of water and ethanol (volume ratio of water / ethanol = 3 / 7) for 15min. Then peel the film off the glass and bake it in a vacuum oven at 180℃ for 60min to obtain the polyimide membrane.

[0064] The performance tests of the four types of diaphragms are shown in Table 3.

[0065] Table 3

[0066] As shown in Table 3, the electrolyte absorption rate of the samples (HT-2B10%, HT-2B30%, and HT-2B50%) prepared with monomers containing amide groups increased by 55.55%-109.59%, and the contact angle decreased significantly. This indicates that the polyimide membranes prepared with monomers containing amide groups can effectively increase the wettability of the electrolyte, and their mechanical strength is also superior to that of membranes without monomers containing amide groups.

[0067] Example 4

[0068] This embodiment relates to a method for preparing a polyimide separator, comprising the following steps:

[0069] (1) Under nitrogen atmosphere, 23.31 g of 9,9-bis(4-aminophenyl)fluorene and 249.3 g of DMAc were added to a 500 ml three-necked flask and stirred at 25 °C for 30 min. After the 9,9-bis(4-aminophenyl)fluorene was completely dissolved, 20.76 g of 4,4'-oxobisphthalic anhydride was added and the reaction was stirred at 25 °C for 60 min to obtain a solution containing polyamic acid.

[0070] (2) Add 25.93g of quinoline and 0%, 10%, 30% and 50% oxaloyl aniline by weight of polyamic acid to a solution containing polyamic acid and stir until dissolved (the sample codes are FO-OX0%, FO-OX10%, FO-OX30% and FO-OX50%, respectively). Raise the temperature to 100℃ and stir for 6h to obtain a slurry.

[0071] (3) Cool the above four slurries to room temperature, add 118g of DMAc and stir continuously for 30min to dilute. Then, coat the diluted slurries of FO-OX0%, FO-OX10%, FO-OX30% and FO-OX50% onto the glass plate. Immerse the substrate in a mixed solution of water and ethanol (volume ratio of water / ethanol = 3 / 7) for 15min. Then peel the film off the glass and bake it in a vacuum oven at 180℃ for 60min to obtain the polyimide membrane.

[0072] The performance tests of the four types of diaphragms are shown in Table 4.

[0073] Table 4

[0074] As shown in Table 4, the electrolyte absorption rate of the samples (FO-OX10%, FO-OX30%, and FO-OX50%) prepared with monomers containing amide groups increased by 30.20%-76.73%, and the contact angle decreased significantly. This indicates that the polyimide membranes prepared with monomers containing amide groups can effectively increase the wettability of the electrolyte, and their mechanical strength is also superior to that of membranes without monomers containing amide groups.

[0075] As shown in the data from Examples 1-4 above, the mechanical strength gradually increases with the number of monomers containing amide groups. This is because the C=O and NH functional groups in the amide groups interact, thereby reinforcing the mechanical strength of the membrane. Furthermore, the increase in the number of monomers containing amide groups also improves the wettability of the electrolyte, thus increasing its electrolyte absorption rate. This indicates that amide groups can attract electrolyte groups to form ion-transfer sites. Therefore, the more monomers containing amide groups there are, the more positive harmonic effects they can create in the polyimide structure, enhancing its overall properties.

[0076] The above description is merely an embodiment of the present invention, and the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing a polyimide separator, characterized by, Includes the following steps: (1) Add diamine monomers and dianhydride monomers to a solvent and react to obtain a solution containing polyamic acid; (2) Add a monomer with an amide group to the polyamic acid-containing solution, and after reaction, a slurry is obtained; (3) The slurry is subjected to phase inversion to obtain a polyimide membrane.

2. The production method according to claim 1, characterized by, The molar ratio of the diamine monomer to the dianhydride monomer is 1:1; The monomer containing amide groups accounts for 10%-50% of the weight percentage of the polyamic acid.

3. The preparation method according to claim 1, characterized in that, The monomer containing the amide group is selected from at least one of benzoylaniline, methyl 2-acetaminoacetate, 2-benzoylacetaniline, and oxaloylaniline.

4. The method of claim 1, wherein, In step (2), a curing accelerator is added along with the monomer containing an amide group. The molar ratio of the curing accelerator to the diamine monomer is 2-3:

1.

5. The preparation method according to claim 4, characterized in that, The curing accelerator is selected from at least one of triethylamine, benzimidazole, 1-methylimidazole, quinoline, 1,8-diazabicycloundec-7-ene, imidazole, pyridine, and 3-methylpyridine.

6. The method of claim 1, wherein, The reaction temperature in step (1) is 20-25℃ and the reaction time is 60-80min.

7. The preparation method according to claim 1, characterized in that, The reaction temperature in step (2) is 60-100℃ and the reaction time is 6h.

8. The method of claim 1, wherein, The diamine monomer is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, 3,5-diaminobenzoic acid, 4,4-diaminodiphenylmethane, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-dibiphenyl]-4,4'-diyl)bis(4-aminobenzamide), 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminobenzoylaniline, 3,3'-dihydroxybenzidine, and 9,9-bis(4-aminophenyl)fluorene; The dianhydride monomer is selected from at least one of pyromellitic dianhydride, 4,4'-oxobisphthalic anhydride, 3,3',4,4'-biphenyltetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, 3,3,4,4-diphenylsulfone tetracarboxylic anhydride, and hexafluorodianhydride.

9. The polyimide membrane prepared by the method of any one of claims 1-8.

10. The application of the polyimide separator prepared by the method of any one of claims 1-8 in a battery.

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