Preparation method of high-strength low-breathability para-aramid base film

Abstract

The invention relates to the technical field of battery diaphragms, and provides a preparation method of a high-strength low-air-permeability para-aramid-based membrane, and the high-strength low-air-permeability para-aramid-based membrane comprises a crosslinking product of a component A and a component B, the component A is para-aramid fiber; the component B is an amide high polymer except for para-aramid; the amide high polymer comprises one or more of polyethyleneimine, polyamideimide, nylon 66 and meta-aramid fiber. According to the technical scheme, the problem that the air permeability value, the ionic conductivity and the heat resistance of the aramid-based membrane in the prior art are difficult to consider at the same time is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of battery separators, in particular to a preparation method of a high-strength low-air-permeability para-aramid-based film. BACKGROUND

[0002] In recent years, lithium ion batteries are widely used in various fields. The separator is a key component of a lithium ion battery, which can prevent direct contact between the cathode and the anode to prevent short circuit of the battery, and allow ions in the electrolyte to pass through to form a loop. At present, the commonly used separator is mainly a polyolefin separator, such as PP and PE, which has high strength and good chemical stability, but the thermal stability is poor at high temperature, and the performance is significantly reduced. The existing solution is mainly to prepare a coated composite film, and para-aramid is coated on the polyolefin-based film to improve the heat resistance of the base film. However, there are few reports on aramid-based films.

[0003] Para-aramid (PPTA) is a material with high strength, high modulus, stability and chemical corrosion resistance, which can be used as a dual-purpose material for military and civilian use. The para-aramid-based film prepared by using para-aramid has the problems of high air permeability and low ion conductivity, and it is difficult to balance the heat resistance, which cannot meet the use requirements of lithium ion batteries.

[0004] The patent application with the publication number CN119764747A obtains a porous para-aramid separator by exchanging the solute in the proton solution with the aramid nanofiber gel dispersed with a proton donor. This method not only consumes a long time in the preparation process, but also sacrifices part of the heat resistance, thereby sacrificing part of the heat resistance.

[0005] The patent application with the publication number CN119161572A introduces a third monomer as a flexible unit into the para-aramid chain by block copolymerization modification, thereby improving the overall performance of the aramid-based film, and obtaining a modified para-aramid-based film with excellent heat resistance, high film breaking temperature and porous structure. However, from the performance, it can be seen that the introduction of the flexible unit significantly reduces the heat resistance of the aramid-based film.

[0006] Therefore, it is necessary to obtain an aramid-based film with excellent heat resistance, high air permeability and high ion conductivity. SUMMARY

[0007] The application provides a preparation method of a high-strength low-air-permeability para-aramid-based film, which solves the problem that the air permeability and ion conductivity of the aramid-based film in the related art are difficult to balance with the heat resistance.

[0008] The technical solutions of the present application are as follows: The present application provides a high-strength low-air-permeability p-aramid-based film, which comprises a crosslinked product of component A and component B. The component A is p-aramid. The component B is an amide-based polymer other than p-aramid.

[0009] As a further technical solution, the amide-based polymer comprises one or more of polyethyleneimine, polyamide-imide, nylon 66, and m-aramid.

[0010] As a further technical solution, the high-strength low-air-permeability p-aramid-based film has a thickness of 14-16 μm and an air permeability of 500-6500 s / 100 mL.

[0011] As a further technical solution, the p-aramid is obtained by polymerization of p-phenylenediamine and terephthaloyl chloride.

[0012] As a further technical solution, the molar ratio of the p-phenylenediamine to the terephthaloyl chloride is 1:1-1.1, for example, it can be 1:1, 1:006, 1:1.02, 1:1.04, 1:1.06, 1:1.08, or 1:1.1.

[0013] As a further technical solution, the mass ratio of the component A to the component B is 1:0.01-1.

[0014] The present application also provides a preparation method of a high-strength low-air-permeability p-aramid-based film, which is used for preparing the high-strength low-air-permeability p-aramid-based film and comprises the following steps: S1, stirring and mixing N-methyl pyrrolidone and a cosolvent to obtain an N-methyl pyrrolidone salt solution; S2, stirring and mixing the N-methyl pyrrolidone salt solution and p-phenylenediamine, adding terephthaloyl chloride for further mixing, and standing to obtain a PPTA gel block; S3, mixing the PPTA gel block and the NMP salt solution to obtain a coating stock solution; S4, mixing an amide-based polymer and an NMP salt solution to obtain a mixture; S5, blending the coating stock solution and the mixture, coating to form a film, extracting, and drying to obtain an aramid-based film.

[0015] As a further technical solution, in step S1, the temperature of the stirring and mixing is 60-150℃, for example, it can be 60℃, 80℃, 100℃, 120℃, 140℃, 150℃; the stirring speed is 300-500r / min, for example, it can be 300r / min, 350r / min, 400r / min, 450r / min, 500r / min; the stirring time is 30-120min, for example, it can be 30min, 60min, 80min, 100min, 120min. The cosolvent includes one or more of CaCl2, AlCl3, and LiCl.

[0016] As a further technical solution, in step S1, the mass of the cosolvent is 3%-10% of the mass of the N-methylpyrrolidone.

[0017] As a further technical solution, in step S2, the stirring and mixing speed is 300-500r / min, and the time is 20-60min. The continued mixing speed is 300-500r / min, and the time is 1-20min.

[0018] As a further technical solution, in step S5, the standing time is 5-60min.

[0019] As a further technical solution, in step S2, in step S2, the molar volume ratio of the p-phenylenediamine to the N-methylpyrrolidone in the N-methylpyrrolidone salt solution is 0.1-0.3mol / L, for example, it can be 0.1mol / L, 0.15mol / L, 0.2mol / L, 0.25mol / L, or 0.3mol / L.

[0020] As a further technical solution, in step S3, the mass ratio of the PPTA gel block to the NMP salt solution is 1:1-3.

[0021] As a further technical solution, in step S4, the mass of the amide-based polymer is 1%-5% of the mass of the NMP salt solution.

[0022] As a further technical solution, in step S4, the mixing temperature is 30-80℃, and the speed is 300-500r / min.

[0023] As a further technical solution, in step S5, in step S5, the blending time is 25-35min, and the speed is 300-500r / min.

[0024] As a further technical solution, in step S5, the extraction time is 30-60min.

[0025] As a further technical solution, in step S5, the drying includes vacuum hot-press drying.

[0026] As a further technical solution, in step S5, the temperature of the vacuum hot pressing drying is 50~100℃, the vacuum pressure is 0.2~1.0MPa, and the heating time is 1~5min.

[0027] The present invention also proposes a lithium-ion battery containing the high-strength, low-permeability para-aramid film described above or the high-strength, low-permeability para-aramid film prepared by the aforementioned method.

[0028] The working principle and beneficial effects of this invention are as follows: In this invention, para-aramid fibers are physically blended with amide polymers. This allows the amide bonds on PPTA and the amide bonds on the amide polymers to interact through hydrogen bonding, forming a physical cross-linked network. This enhances interfacial bonding, reduces the interaction forces between aramid fibers, and decreases its own cross-linking, resulting in a porous structure where aramid fibers and amide polymer fibers interweave. This significantly improves the air permeability, ionic conductivity, and flexibility of the aramid-based membrane while retaining the heat resistance of para-aramid.

[0029] By physically crosslinking para-aramid with amide polymers, pores formed by interwoven fibers are generated on the base film, enhancing interfacial bonding. While maintaining high tensile strength, the air permeability of the aramid base film is significantly reduced, the ionic conductivity of the aramid base film is increased, and the high heat resistance of the aramid base film is well maintained. Attached Figure Description

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a SEM image of the aramid-based film prepared in Example 1 of the present invention.

[0032] Figure 2 This is a SEM image of the aramid-based film prepared in Example 2 of the present invention.

[0033] Figure 3 This is a SEM image of the aramid-based film prepared in Example 4 of the present invention.

[0034] Figure 4 This is a SEM image of the pure para-aramid-based film prepared in Comparative Example 3 of this invention. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] In the following examples and comparative examples, the weight-average molecular weight of PPTA was 18,000; the type of PEI was ULTEM 1000; the type of PAI was Solvay 5030; the type of meta-aramid was Zhongfeitiantu AR-6; and the type of nylon 66 was Invista U48202.

[0037] Example 1 A method for preparing a high-strength, low-permeability aramid-based film includes the following steps: S1. Weigh 300g of NMP solution, add 18g of CaCl2 to it, stir at 130℃ for 1h, and wait for CaCl2 to completely dissolve to obtain N-methylpyrrolidone salt solution. S2. Add 6.4884 g of p-phenylenediamine to the solution and stir for 30 min until completely dissolved; S3. Add 12.1812g of terephthaloyl chloride to the solution, stir for 5 minutes, then remove and stir at room temperature for 30 minutes until the solution gels. S4. Dilute the prepared para-aramid gel block according to the mass ratio of NMP:PPTA=2:1. After dilution, perform vacuum degassing to obtain the coating stock solution. S5. Prepare a 5% PEI solution by adding 3.0g of PEI to 60g of NMP salt solution (the preparation of NMP salt solution is the same as the preparation of N-methylpyrrolidone salt solution in step S1), heating and stirring at 50℃ and 400r / min until the PEI is completely dissolved. S6. Weigh 60g of the coating stock solution, add 2.2135g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform the coating film preparation. S7. Place the above mixed solution on the mold and coat it into a film using a bidirectional coating method. After standing for 1 minute, extract it in water and let it stand for 20 minutes to remove the solvent NMP. S8. After extraction, the base membrane is vacuum hot-pressed and dried at a temperature of 80℃, a vacuum pressure of 0.8MPa, and a pressing time of 5min. After drying, an aramid-based membrane is obtained. The SEM image of the aramid-based membrane is shown below. Figure 1 As shown.

[0038] Example 2 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of the coating stock solution, add 3.320g of PEI solution, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a coating process; the SEM image of the final aramid-based film is shown below. Figure 2 As shown.

[0039] Example 3 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of coating stock solution, add 4.427g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a scraping coating to form a film.

[0040] Example 4 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of the coating stock solution, add 6.6405g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a coating process; the SEM image of the final aramid-based film is shown below. Figure 3 As shown.

[0041] Example 5 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of coating stock solution, add 7.7472g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a scraping coating to form a film.

[0042] Example 6 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of coating stock solution, add 8.854g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a scraping coating to form a film.

[0043] Example 7 The difference between this embodiment and Embodiment 1 lies only in the preparation method of the high-strength, low-permeability aramid-based film. Step S6 is as follows: Weigh 60g of coating stock solution, add 9.9607g of PEI solution to it, stir for 30min at a speed of 500r / min, and after the solution is mixed evenly, perform a scraping coating to form a film.

[0044] Example 8 The only difference between this embodiment and embodiment 5 is that PEI is replaced with PAI.

[0045] Example 9 The only difference between this embodiment and Embodiment 5 is that PEI is replaced with meta-aramid.

[0046] Example 10 The only difference between this embodiment and embodiment 5 is that PEI is replaced with Nylon 66.

[0047] Comparative Example 1 A method for preparing a high-strength, low-permeability aramid-based film includes the following steps: S1. The aramid mixed stock solution obtained in step S6 of Example 5 is coated on a PE base film (model: SG12, source: Hebei Jinli New Energy Technology Co., Ltd.) with a coating thickness of 1μm. After standing for 1min, it is placed in water for extraction. S2. After extraction, the base membrane is dried by vacuum hot pressing at a temperature of 80°C, a vacuum pressure of 0.8 MPa, and a pressing time of 5 min. After drying the water, a composite membrane is obtained.

[0048] Comparative Example 2 A method for preparing a high-strength, low-permeability aramid-based film includes the following steps: S1. The PEI solution prepared in step S5 of Example 1 is coated and filmed, extracted, and dried to serve as the base film of PEI. S2. The coating stock solution obtained in step S4 of Example 1 is directly coated onto the PEI base film with a coating thickness of 1 μm. After standing for 1 min, it is placed in water for extraction. S3. After extraction, the base membrane is dried by vacuum hot pressing at a temperature of 80°C, a vacuum pressure of 0.8 MPa, and a pressing time of 5 min. After drying the water, a composite membrane is obtained.

[0049] Comparative Example 3 A method for preparing a high-strength, low-permeability aramid-based film includes the following steps: S1. Weigh 300g of NMP solution, add 18g of CaCl2 to it, stir at 130℃ for 1h, and wait for CaCl2 to completely dissolve to obtain N-methylpyrrolidone salt solution. S2. Add 6.4884 g of p-phenylenediamine to the solution and stir for 30 min until completely dissolved; S3. Add 12.1812g of terephthaloyl chloride to the solution, stir for 5 minutes, then remove and stir at room temperature for 30 minutes until the solution gels. S4. Dilute the prepared para-aramid gel block according to the mass ratio of NMP:PPTA=2:1. After dilution, perform vacuum degassing to obtain the coating stock solution. S5. Place the above-mentioned coating stock solution on the mold, and coat the film by bidirectional coating method. After standing for 1 minute, place it in water for extraction. After standing for 20 minutes, remove the solvent NMP completely. S6. After extraction, the base film was vacuum hot-pressed and dried at 80℃, with a vacuum pressure of 0.8MPa and a hot-pressing time of 5min. After drying, a pure para-aramid base film was obtained. The SEM image of the final pure para-aramid base film is shown below. Figure 4 As shown.

[0050] Experimental Example The membranes prepared in Examples 1-10 and Comparative Examples 1-2 were subjected to the following tests: Air permeability: The diaphragm is placed in the test head of an air permeability meter with a suitable test range to test the air permeability. The average value of three test results is taken as the air permeability of the diaphragm. Tensile strength: Refer to GB / T36363-2018, use a sample base film with a width of (15±0.1) mm, an initial distance between the clamps of (100±5) mm, and a test speed of (250±10) mm / min; Shrinkage rate: Cut three 100mm×100mm square diaphragms in the longitudinal direction of the sample and mark them in the longitudinal and transverse directions. After measuring the length in the longitudinal and transverse directions with a length measuring instrument, sandwich the diaphragm between two sheets of quantitative filter paper, press it with a stainless steel plate, and place it flat on the middle of the stainless steel plate in the middle of the forced-air drying oven. Keep it at 250℃ for 2 hours. After heating, wait for the diaphragm to return to room temperature, and measure the marked lengths in the longitudinal and transverse directions again to calculate its heat shrinkage rate. Membrane rupture temperature: The instrument used was a TA Q400 from the United States. A membrane measuring 8mm × 4.5mm was cut and placed into the instrument. The tensile force was set to 0.03N and the heating rate was set to 5℃ / min. The membrane rupture temperature was obtained under these test conditions. Ionic conductivity (test temperature 25℃, relative humidity 60%): Cut four diaphragms that match the resistance test mold. Immerse the diaphragms in an electrolyte solution with a concentration of 1.0 mol / L lithium hexaphosphate (LiPF6), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 ratio, keeping the solution sealed, for 2 hours. Inject the electrolyte solution into the resistance test mold, then place one diaphragm layer at a time and test its AC impedance resistance, recording it as R1, R2, R3, and R4 respectively. After the measurement, perform linear fitting with the number of diaphragm layers as the x-axis and the diaphragm resistance as the y-axis. The results are shown in Table 1 below.

[0051] Table 1 Performance Test Results

[0052] As can be seen from the data in Examples 1-6, with the successful doping of PEI, the air permeability of the aramid-based film is significantly reduced, while its ionic conductivity is significantly increased, approaching that of conventional PE-based films. Simultaneously, the porous structure formed by the interweaving of PPTA and PEI fibers can be clearly observed in the SEM images. Although the successful doping of PEI slightly reduces the tensile strength of the aramid-based film, the data on film rupture temperature and thermal shrinkage show that its heat resistance is not significantly reduced due to PEI doping, maintaining the high heat resistance of the aramid-based film. Furthermore, as shown in Examples 6-7, when the PEI doping amount exceeds a certain proportion, although the thermal permeability further decreases, the overall performance of the base film—tensile strength and heat resistance—significantly decreases. Therefore, the doping ratio in Example 5 allows for the preparation of an aramid-based film with excellent overall performance.

[0053] Table 2 Performance Test Results

[0054] As can be seen from the data in Examples 5 and 7-10, using other amide polymers through physical crosslinking can also significantly improve the ionic conductivity of aramid-based films. However, compared to PEI-doped aramid-based films, the tensile strength decreases more significantly. When using PAI and Nylon 66 for doping, other properties are basically similar to those of PEI-doped films. When using meta-aramid, since it is also an aramid, hydrogen bonds are more easily formed during physical crosslinking, resulting in a more significant decrease in air permeability and higher ionic conductivity. However, meta-aramid has poorer heat resistance, leading to a significant decrease in the rupture temperature of the aramid-based film after doping. Therefore, in summary, using PEI for physical doping can produce aramid-based films with excellent overall performance.

[0055] As can be seen from the data in Comparative Example 1, the PE base film itself has high tensile strength and low air permeability, but its heat resistance is poor. After coating the PE base film with a composite solution of para-aramid and PEI, the air permeability of the base film increases. This may be because the interwoven fibers, when coated on the surface, cause some pores to be blocked. Although the heat resistance is improved, when the heat shrinkage test is conducted at 250℃, the base film is relatively brittle and easily breaks after drying for 1 hour, and has lost the performance of the base film itself. This is because the heat resistance of PE itself is poor. Although coating can improve the heat resistance, the structure and properties of PE itself have not changed, and it is impossible to maintain the excellent performance of the base film at high temperatures.

[0056] As can be seen from the data in Comparative Example 2, coating the PEI base film with para-aramid results in a lower tensile strength of the composite separator. This is because the PEI base film itself has low tensile strength, and coating with para-aramid does not affect the mechanical properties of the base film, only improving its heat resistance, which is essentially the same as coating the PE base film with para-aramid. The structure and properties of PEI itself remain unchanged; therefore, the composite separator cannot maintain superior separator performance at high temperatures like the composite separator prepared by physically blending para-aramid and PEI.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, low-permeability para-aramid-based film, characterized in that, The components include the cross-linked products of component A and component B; Component A is para-aramid; Component B is an amide polymer other than para-aramid.

2. The high-strength, low-permeability para-aramid-based membrane according to claim 1, characterized in that, The amide polymers include one or more of polyethyleneimine, polyamideimine, nylon 66, and meta-aramid.

3. The high-strength, low-permeability para-aramid-based membrane according to claim 1, characterized in that, The high-strength, low-permeability para-aramid-based film has a thickness of 14~16μm and a permeability of 500~6500s / 100mL.

4. The high-strength, low-permeability para-aramid-based membrane according to claim 1, characterized in that, The para-aramid was obtained by polymerizing p-phenylenediamine and terephthaloyl chloride.

5. A high-strength, low-permeability para-aramid-based membrane according to claim 4, characterized in that, The molar ratio of p-phenylenediamine to terephthaloyl chloride is 1:1 to 1.

1.

6. The high-strength, low-permeability para-aramid-based membrane according to claim 1, characterized in that, The mass ratio of component A to component B is 1:0.01~1.

7. A method for preparing a high-strength, low-permeability para-aramid-based film, used to prepare the high-strength, low-permeability para-aramid-based film according to any one of claims 4 to 6, characterized in that, Includes the following steps: S1. Take N-methylpyrrolidone and a co-solvent and stir to mix them to obtain an N-methylpyrrolidone salt solution; S2. Stir and mix the N-methylpyrrolidone salt solution and p-phenylenediamine, add terephthaloyl chloride and continue mixing, let stand, and obtain PPTA gel block; S3. Mix the PPTA gel block and NMP salt solution to obtain the coating stock solution; S4. Mix the amide polymer and NMP salt solution to obtain a mixture; S5. The coating stock solution and the mixture are blended, coated with a film, extracted, and dried to obtain an aramid-based film.

8. The method for preparing a high-strength, low-permeability para-aramid-based film according to claim 7, characterized in that, In step S1, the stirring and mixing temperature is 60~150℃, the rotation speed is 300~500r / min, and the time is 30~120min; The co-solvent includes one or more of CaCl2, AlCl3, and LiCl; In step S1, the mass of the co-solvent is 3% to 10% of the mass of the N-methylpyrrolidone; In step S4, the mixing temperature is 30~80℃ and the rotation speed is 300~500r / min; In step S2, the stirring speed is 300~500 r / min and the time is 20~60 min; The mixing speed is 300~500 r / min, and the time is 1~20 min; In step S2, the molar volume ratio of p-phenylenediamine to N-methylpyrrolidone in the N-methylpyrrolidone salt solution is 0.1~0.3 mol / L; In step S3, the mass ratio of the PPTA gel block to the NMP salt solution is 1:1~3; In step S4, the mass of the amide polymer is 1% to 5% of the mass of the NMP salt solution; In step S4, the mixing temperature is 30~80℃ and the rotation speed is 300~500r / min.

9. The method for preparing a high-strength, low-permeability para-aramid-based film according to claim 7, characterized in that, In step S5, the blending time is 25-35 min and the rotation speed is 300-500 r / min; The drying process includes vacuum hot-press drying.

10. A lithium-ion battery, characterized in that, The high-strength, low-permeability para-aramid-based membrane according to any one of claims 1 to 6, or the high-strength, low-permeability para-aramid-based membrane prepared by the preparation method according to any one of claims 7 to 9.

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