High-safety aramid diaphragm and preparation method and application thereof

Abstract

The application discloses a kind of high safety aramid film and its preparation method and application, including the following steps: (1) preparation aramid polymer solution;(2) aramid polymer dispersion solution obtained by diluting aramid polymer solution is uniformly coated on the collection plate, then dry treatment, after solvent is fully volatilized, it is washed with water, accompanied by ultrasonic treatment in the process of washing with water, further dry treatment, finally after two-way stretching, heat setting is carried out again, and finally high safety aramid film is obtained.The application overcomes the technical problems that the film made by conventional method is brittle and easy to break, and the mechanical strength and pore structure of the prepared film are further improved, so that it can work in high temperature environment for a long time.

Description

Technical Field

[0001] This invention belongs to the field of new materials, and specifically relates to a high-safety aramid membrane, its preparation method, and its application. Background Technology

[0002] In recent years, lithium batteries have gained immense popularity due to their superior performance, including long battery life and high cycle life. However, this popularity has also amplified some negative aspects. Under conditions such as overcharging, over-discharging, rapid charging and discharging, short circuits, mechanical abuse, and high-temperature thermal shock, dangerous internal side reactions can easily occur, generating heat and directly damaging the passivation film on the positive and negative electrode surfaces. Furthermore, the organic solvents used in lithium batteries are flammable and have low flash points. Unsafe practices leading to thermal runaway can easily ignite these low-flash-point flammable liquid components, causing the battery to boil. When a battery cracks, and the ambient humidity is high, moisture and oxygen in the air can easily react violently with the lithium-intercalated carbon negative electrode, releasing a large amount of heat and potentially causing the battery to burn. Lithium battery safety is one of the most pressing concerns in the industry and a critical issue that the new energy sector urgently needs to address. The lithium battery industry is continuously exploring and developing new battery separator materials with high temperature resistance, high mechanical properties, and good wettability.

[0003] The performance of the separator has a significant impact on battery performance. Currently, commercially available separators are generally made of PE (polyethylene) and PP (polypropylene), and are classified into single-layer PE / PP films and three-layer PP / PE films, as shown in Chinese patents 201010578194.5 and 201310303894.7. However, lithium-ion batteries made of polyolefins are increasingly failing to meet practical needs, limiting the application and development of lithium-ion batteries. In particular, during high-power charging and discharging, lithium-ion batteries experience separator shrinkage due to localized overheating, leading to safety issues such as short circuits. Furthermore, polyolefin separators have relatively low wettability to electrolytes, which also hinders the efficient directional movement of lithium ions within the separator, limiting the electrochemical performance of lithium-ion batteries. Therefore, there is an urgent need to develop high-performance battery separator materials and their key manufacturing technologies.

[0004] Aramid, as a high-temperature resistant specialty polymer material, is widely used in industry. It possesses extremely high thermal stability (up to 400℃), excellent self-extinguishing properties, and good wettability to electrolytes, making it a promising candidate material for high-performance separators. Currently, meta-aramid materials for separators are mainly prepared via electrospinning, as illustrated in Chinese patents 201910686373.1, 201811529222.7, and 201810835751.3. However, electrospinning itself has limitations, such as low efficiency, high cost, and relatively low separator strength, making it unsuitable for large-scale applications. Some researchers have also used high-temperature resistant materials such as aramid to coat the surface of polyolefin substrates to improve their temperature resistance, as illustrated in Chinese patents 201821819348.3, 202110431425.8, and 202210268442.9. However, these methods undoubtedly increase the number of manufacturing steps required for battery separators. Therefore, it is urgent to develop a technology for the efficient preparation of highly safe aramid membranes that is suitable for large-scale production. Summary of the Invention

[0005] The primary objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a method for preparing a highly safe aramid membrane.

[0006] Another object of the present invention is to provide a highly safe aramid membrane that can be efficiently prepared by the method described above.

[0007] Another object of the present invention is to provide the application of the aramid separator for lithium batteries.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing a high-safety aramid membrane includes the following steps:

[0010] (1) Preparation of aramid polymer solution;

[0011] (2) The aramid polymer solution is diluted to obtain an aramid polymer dispersion, which is then uniformly coated onto a collection plate and dried. After the solvent has fully evaporated, it is washed with water, accompanied by ultrasonic treatment during the water washing process. It is then further dried, and finally subjected to biaxial stretching and heat setting to obtain a high-safety aramid membrane.

[0012] Preferably, the concentration of the aramid polymer dispersion in step (2) is 5-30% by mass.

[0013] Preferably, the concentration of the aramid polymer dispersion in step (2) is 10-25% by mass.

[0014] Preferably, the bidirectional stretching in step (2) is specifically a transverse stretching of 1.3-4.0 times and a longitudinal stretching of 1.3-4.0 times, more preferably a transverse stretching of 1.5-3.0 times and a longitudinal stretching of 1.5-4.0 times; the heat setting temperature is 280-330℃ and the time is 1-30min.

[0015] Preferably, the ultrasonic treatment in step (2) has a power of 200-1500W, a temperature of 30-90℃, and a time of 5-60min. The collecting plate is made of stainless steel.

[0016] Preferably, the temperature of the first drying in step (2) is 50 to 200°C, and the aramid polymer dispersion is also subjected to vacuum defoaming pretreatment.

[0017] Preferably, the temperature of the first drying in step (2) is 70-140°C; the coating is applied by scraping or spin coating, and the coating thickness is 20-200 μm.

[0018] Preferably, step (1) preparation of aramid polymer solution: neutral aramid polymer solution is prepared by polymerization reaction of m-phenylenediamine and isophthaloyl chloride in an organic solvent at low temperature and under a protective atmosphere; the molar ratio of m-phenylenediamine and isophthaloyl chloride is 100:(85-120), more preferably 100:(100-110).

[0019] Preferably, in step (1) the preparation of aramid polymer: under low temperature and nitrogen protection atmosphere, the cosolvent and m-phenylenediamine are dissolved in N,N-dimethylacetamide, and then isophthaloyl chloride is added in 2-5 portions to obtain a reaction solution; as the reaction proceeds, the temperature of the reaction solution gradually increases, and after heat preservation treatment, an alkaline agent is added for neutralization to prepare a neutral aramid polymer solution.

[0020] Preferably, the co-solvent is one or more of lithium bromide, lithium chloride, calcium chloride, and calcium bromide; the heat preservation treatment is performed at 40-80°C for 0.5-12 hours; and the alkaline agent is one or more of calcium oxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, sodium hydroxide, and organic amines.

[0021] The aramid membrane can be used in the preparation of lithium batteries, lithium-sulfur batteries, electrical insulation materials, adsorption and filtration materials, and flexible electronic device substrates.

[0022] The method and apparatus for preparing aramid membranes described above are also applicable to membrane formation from other raw materials, such as para-aramid, polyacrylonitrile, viscose, spandex and other synthetic fiber polymers.

[0023] The present invention has the following advantages and effects compared with the prior art:

[0024] (1) The aramid polymer dispersion is extruded through a die onto a collection plate, and then subjected to simple heat treatment in an oven to promote full evaporation of the solvent. Then, ice water is quickly added for washing, accompanied by ultrasonic treatment. During the rapid temperature drop, the molecular chains shrink rapidly, causing the distance between the aramid polymer molecular chains to increase, thus generating initial micro-defects. After further longitudinal and transverse stretching on a biaxial stretching machine, an ideal pore structure is obtained. Finally, a high-safety aramid battery separator that can work in a high-temperature environment for a long time is prepared by heat setting in a high-temperature oven.

[0025] (2) After longitudinal and transverse stretching, further heat setting eliminates residual stress, and the molecular chains or crystals are arranged in an orderly manner along the planar direction. The orientation structure of the macromolecules is fixed under tension or relaxation. Under tension, the fiber interface is also tightly bonded, overcoming the technical difficulties of brittle and easily broken membranes produced by conventional methods. The mechanical strength and pore structure are further improved. This technical solution further expands the industrialization process and application scope of aramid membranes.

[0026] (3) The efficient preparation technology of aramid membrane of the present invention can also increase its functionalization and performance by adding functional units (such as functional nanoparticles, conductive polymers, thermally conductive fillers, etc.) to aramid polymers. This is of great significance for the diversified application of aramid membranes in various fields such as battery membranes, reinforcing materials, textile materials, electrically insulating nanopaper, flexible electronic devices, and adsorption filter media. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the preparation process of the aramid separator of this invention.

[0028] Figure 2 This is a surface electron microscope image of the aramid membrane prepared in Example 4.

[0029] Figure 3 This is a surface electron microscope image of the aramid membrane prepared in Example 5. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field. Test methods in the following embodiments that do not specify specific experimental conditions are generally performed under conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are all commercially available.

[0031] The starting materials used in the preparation method of this invention can be purchased from the market or prepared according to existing technical methods.

[0032] Example 1

[0033] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0034] (1) Preparation of aramid polymer: Under nitrogen protection at 15°C, an appropriate amount of co-solvent lithium bromide and m-phenylenediamine were dissolved in N,N-dimethylacetamide, wherein the molar ratio of m-phenylenediamine to isophthaloyl chloride was 100:85; then isophthaloyl chloride was added in one batch to obtain a reaction solution; as the reaction proceeded, the reaction solution was kept at 50°C for 12 h, and after the heat treatment, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0035] (2) Preparation of aramid membrane: The aramid polymer dispersion obtained in step (1) is diluted to a suitable concentration and then vacuum defoamed. Then it is transferred to a collection plate by a scraping device and placed in an oven for a certain period of time. After the solvent has fully evaporated, it is washed with ice water. During the washing process, ultrasonic treatment is carried out. Then it is further dried. Finally, it is stretched longitudinally and transversely on a biaxial stretching machine and then heat-set in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0036] The concentration of the aramid polymer dispersion is 5% by mass; the coating device is a coating rod with a die length of 200 mm and a coating thickness of 20 μm; the collecting plate is made of stainless steel; the oven temperature is 50℃ and the time is 60 min. Ultrapure water is used for washing, and the ultrasonic power during the process is 200 W, the temperature is 30℃, and the time is 60 min; the biaxial stretching specifically involves longitudinal stretching of 1.1 times and transverse stretching of 1.3 times; the heat setting temperature is 280℃ and the time is 30 min.

[0037] Example 2

[0038] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0039] (1) Preparation of aramid polymer: Under nitrogen protection at 10°C, an appropriate amount of cosolvent lithium chloride and m-phenylenediamine were dissolved in N,N-dimethylacetamide, wherein the molar ratio of m-phenylenediamine to isophthaloyl chloride was 100:115; then isophthaloyl chloride was added in two portions to obtain a reaction solution; as the reaction proceeded, the reaction solution was kept at 60°C for 8 hours, and after the heat treatment, calcium hydroxide was added for neutralization to prepare a neutral aramid polymer solution.

[0040] (2) Preparation of aramid membrane: The aramid polymer dispersion obtained in step (1) is diluted to a suitable concentration and then vacuum defoamed. Then it is transferred to a collection plate by a scraping device and placed in an oven for a certain period of time. After the solvent has fully evaporated, it is washed with ice water. During the washing process, ultrasonic treatment is carried out. Then it is further dried. Finally, it is stretched longitudinally and transversely on a biaxial stretching machine and then heat-set in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0041] The concentration of the aramid polymer dispersion is 13% by mass; the coating device is a coating rod with a die length of 200 mm and a coating thickness of 90 μm; the collecting plate is made of nylon; the oven temperature is 80℃ for 30 min; the washing water is ultrapure water, and the ultrasonic power during the process is 500 W, the temperature is 90℃, and the time is 10 min; the biaxial stretching specifically involves longitudinal stretching of 1.5 times and transverse stretching of 1.3 times; the heat setting temperature is 280℃ for 30 min.

[0042] Example 3

[0043] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0044] (1) Preparation of aramid polymer: Lithium chloride and m-phenylenediamine were dissolved in N,N-dimethylacetamide under nitrogen protection at 5°C, with a molar ratio of m-phenylenediamine to isophthaloyl chloride of 100:104; then isophthaloyl chloride was added in three portions to obtain a reaction solution; as the reaction proceeded, the reaction solution was kept at 80°C for 4 hours, and after the heat treatment, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0045] (2) Preparation of aramid membrane: The aramid polymer dispersion obtained in step (1) is diluted to a suitable concentration and then vacuum defoamed. Then it is transferred to a collection plate by a scraping device and placed in an oven for a certain period of time. After the solvent has fully evaporated, it is washed with ice water. During the washing process, ultrasonic treatment is carried out. Then it is further dried. Finally, it is stretched longitudinally and transversely on a biaxial stretching machine and then heat-set in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0046] The concentration of the aramid polymer dispersion is 20% by mass; the coating device is a coating rod with a die length of 200 mm and a coating thickness of 160 μm; the collecting plate is made of glass; the oven temperature is 120℃ for 20 min; the washing water is ultrapure water; the ultrasonic power during the process is 800 W, the temperature is 50℃, and the time is 30 min; the biaxial stretching specifically involves longitudinal stretching of 2.1 times and transverse stretching of 1.7 times; the heat setting temperature is 300℃ for 10 min.

[0047] Example 4

[0048] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0049] (1) Preparation of aramid polymer: Lithium chloride and m-phenylenediamine were dissolved in N,N-dimethylacetamide under nitrogen protection at 8°C, with a molar ratio of m-phenylenediamine to isophthaloyl chloride of 100:120; then isophthaloyl chloride was added in 5 portions to obtain a reaction solution; as the reaction proceeded, the reaction solution was kept at 70°C for 8 hours, and after the heat treatment, calcium hydroxide was added for neutralization to prepare a neutral aramid polymer solution.

[0050] (2) Preparation of aramid membrane: The aramid polymer dispersion obtained in step (1) is diluted to a suitable concentration and then vacuum defoamed. Then it is transferred to a collection plate by a scraping device and placed in an oven for a certain period of time. After the solvent has fully evaporated, it is washed with ice water. During the washing process, ultrasonic treatment is carried out. Then it is further dried. Finally, it is stretched longitudinally and transversely on a biaxial stretching machine and then heat-set in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0051] The concentration of the aramid polymer dispersion is 28% by mass; the coating device is a coating rod with a die length of 200 mm and a coating thickness of 200 μm; the collecting plate is made of stainless steel; the oven temperature is 150℃ for 5 min; the washing water is ultrapure water; the ultrasonic power during the process is 1500 W, the temperature is 40℃, and the time is 5 min; the biaxial stretching specifically involves longitudinal stretching of 2.8 times and transverse stretching of 2.0 times; the heat setting temperature is 330℃ for 1 min.

[0052] Example 5

[0053] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0054] (1) Preparation of aramid polymer: Lithium chloride and m-phenylenediamine were dissolved in N,N-dimethylacetamide under nitrogen protection at 7°C, with a molar ratio of m-phenylenediamine to isophthaloyl chloride of 100:102; then isophthaloyl chloride was added in two portions to obtain a reaction solution; as the reaction proceeded, the reaction solution was kept at 60°C for 5 hours, and after the heat treatment, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0055] (2) Preparation of aramid membrane: The aramid polymer dispersion obtained in step (1) is diluted to a suitable concentration and then vacuum defoamed. Then it is transferred to a collection plate by a scraping device and placed in an oven for a certain period of time. After the solvent has fully evaporated, it is washed with ice water. During the washing process, ultrasonic treatment is carried out. Then it is further dried. Finally, it is stretched longitudinally and transversely on a biaxial stretching machine and heat-set in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0056] The concentration of the aramid polymer dispersion is 20% by mass; the coating device is a coating rod with a die length of 200 mm and a coating thickness of 150 μm; the collecting plate is made of stainless steel; the oven temperature is 110℃ for 10 min; the washing water is ultrapure water; the ultrasonic power during the process is 1200 W, the temperature is 60℃, and the time is 10 min; the biaxial stretching specifically involves longitudinal stretching of 3.5 times and transverse stretching of 2.8 times; the heat setting temperature is 295℃ for 5 min.

[0057] Compare with Example 1

[0058] The aramid polymer dispersion obtained in step (2) of Example 3 was used to prepare a film by electrospinning, and then various indicators were tested. The results are listed in Table 1.

[0059] Compare with Example 2

[0060] In Example 3, step (2) involved solvent evaporation in an oven, which was replaced by a coagulation bath for 20 minutes to displace the solvent. The coagulation bath was prepared according to the mass fraction of dimethylacetamide: glycerol: water = 40:30:30. After coagulation, the membrane was air-dried and then stretched longitudinally and laterally to obtain a diaphragm. Finally, the diaphragm product was tested for various indicators, and the results are listed in Table 1.

[0061] The performance testing reference standards for the aramid separator involved in the embodiments of the present invention are as follows, and the test results are listed in Table 1.

[0062] Test methods: Thickness is specified according to GB / T 20628.2-2006; tensile strength and elongation at break are tested according to GB / T29627.2-2013 using the strip specimen method; moisture content is determined according to GB / T 29627.2-2013; for heat shrinkage rate, the diaphragm is treated at 200℃ for 12 hours, and the percentage change in area after shrinkage is recorded by photographing and recording the results. The formula is: (A0-A) / A0×100, where A... o This refers to the initial area of ​​the diaphragm, where A is the final area of ​​the diaphragm after heat treatment. The liquid absorption rate is determined as follows: a circular diaphragm with a diameter of 18 mm is immersed in lithium hexafluorophosphide electrolyte for 4 hours, and the mass after immersion is measured. Liquid absorption rate = [(M1-M0) / M0]×100; where M0 and M1 are the masses of the diaphragm before and after immersion in the electrolyte, in grams; puncture resistance is determined according to ASTM F1306-90; porosity is tested using the n-butanol absorption method: a circular diaphragm with a diameter of 18 mm is immersed in n-butanol solution for 4 hours, and the mass after immersion is measured. The porosity is calculated using the formula: porosity = [(M1-M0) / ρV]×100, where M0 and M1 are the masses of the diaphragm before and after immersion in n-butanol, in grams; ρ is the density of n-butanol, 0.81 g / cm³. 3 V represents the volume of the diaphragm, in cm³.3 Ion conductivity was calculated by measuring the bulk impedance of the simulated battery. Ion conductivity = L / (R×A), where L is the thickness of the separator; A is the effective contact area of ​​the separator; and R is the bulk resistance of the separator (Ω). Battery assembly: In an argon-filled glove box, button batteries were assembled in the following order: positive electrode shell / stainless steel sheet / separator / stainless steel sheet / negative electrode shell. After sealing, the batteries were left to stand for 12 hours before testing. Battery cycle performance was tested by constant current charging and discharging at a current density of 0.5C for 100 cycles, with a voltage range of 3.0V to 4.2V. The capacity retention rate (%) was calculated by dividing the capacity after 100 cycles by the capacity of the first test.

[0063] Table 1. Detection data of the high-performance aramid membranes prepared in the examples.

[0064]

[0065] As shown in Table 1, the high-performance aramid separator described in this invention outperforms lithium battery separators prepared by electrospinning in all aspects. The aramid separator prepared by this invention exhibits excellent puncture resistance, effectively preventing short circuits caused by separator punctures. Furthermore, improving the puncture resistance of the separator helps reduce the deformation of the separator pores, thus promoting the lithium... + Uniform flow of the fluid. Temperature resistance performance shows that the prepared separator has a shrinkage rate of less than 2% at 200℃, ensuring the safety of lithium batteries. Figure 2 and Figure 3 It is known that the aramid separator used in this invention has an average pore size of less than 1 μm, which effectively allows ions to pass through while possessing good ionic conductivity. This enables the aramid separator of this invention to effectively unify the temperature resistance and mechanical properties of battery separator materials, ensuring the safe use of high-performance lithium batteries.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-safety aramid separator, characterized in that, Includes the following steps: (1) Preparation of aramid polymer solution; (2) The aramid polymer solution was diluted to obtain an aramid polymer dispersion, which was then uniformly coated onto a collection plate and placed in an oven for drying. After the solvent was fully evaporated, ice water was quickly added for washing. During the washing process, ultrasonic treatment was carried out, followed by further drying. Finally, the membrane was biaxially stretched and then heat-set to obtain a high-safety aramid membrane. Step (1) Preparation of aramid polymer solution: Neutral aramid polymer solution is prepared by polymerization reaction of m-phenylenediamine and isophthaloyl chloride in an organic solvent at low temperature and under a protective atmosphere; the molar ratio of m-phenylenediamine to isophthaloyl chloride is 100:(85~120). Step (1) Preparation of aramid polymer: Under low temperature and nitrogen protection atmosphere, the cosolvent and m-phenylenediamine are dissolved in N,N-dimethylacetamide, and then isophthaloyl chloride is added in 2-5 portions to obtain a reaction solution; as the reaction proceeds, the temperature of the reaction solution gradually increases, and after heat preservation treatment, an alkaline agent is added for neutralization to prepare a neutral aramid polymer solution; The co-solvent is one or more of lithium bromide, lithium chloride, calcium chloride, and calcium bromide; the heat preservation treatment is performed at 40-80°C for 0.5-12 hours; the alkaline agent is one or more of calcium oxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, sodium hydroxide, and organic amine.

2. The preparation method according to claim 1, characterized in that, The concentration of the aramid polymer dispersion in step (2) is 5-30% by mass; the biaxial stretching specifically refers to a transverse stretching of 1.3-4.0 times and a longitudinal stretching of 1.3-4.0 times.

3. The preparation method according to claim 2, characterized in that, The concentration of the aramid polymer dispersion in step (2) is 10-25% by mass; the biaxial stretching specifically refers to a transverse stretching of 1.5-3.0 times and a longitudinal stretching of 1.5-4.0 times.

4. The preparation method according to claim 1, 2, or 3, characterized in that, The heat setting temperature in step (2) is 280-330℃, and the time is 1-30 min; the ultrasonic treatment power is 200-1500W, the temperature is 30-90℃, and the time is 5-60 min.

5. The preparation method according to claim 1, 2, or 3, characterized in that, The temperature of the first drying in step (2) is 50-200℃, and the aramid polymer dispersion is also pretreated by vacuum defoaming.

6. The preparation method according to claim 5, characterized in that, Step (2) The temperature for the first drying is 70-140℃; the coating is applied by scraping or spin coating, and the coating thickness is 20-200µm.

7. The high-safety aramid membrane prepared by the method according to any one of claims 1-6.

8. The high-safety aramid separator of claim 7 is used in the preparation of lithium batteries, lithium-sulfur batteries, electrical insulation materials, adsorption and filtration materials, and flexible electronic device substrates.

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