Aramid battery separator and method and apparatus for making same

Abstract

This invention discloses an aramid battery separator and its preparation method and apparatus. The apparatus includes two opposing liquid inlet units, a collector, and a booster. The collector is a motor-driven collecting plate. Each liquid inlet unit includes a liquid inlet plate and a liquid inlet delivery pipe. The liquid inlet plate includes a liquid distribution plate and a mesh surface covering the liquid distribution plate. The liquid inlet delivery pipe is connected to the liquid distribution plate. The booster drives the liquid inlet units to move, causing the mesh surfaces of the two liquid inlet units to reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces generate filaments. The collecting plate passes between the two mesh surfaces to collect the fine fibers. Ultrafine aramid fiber bundles are prepared using the above apparatus. These ultrafine aramid fiber bundles are then subjected to biaxial stretching and heat setting to obtain the aramid battery separator. The aramid separator prepared by this invention has a smaller fiber diameter and a larger specific surface area, which can significantly improve the interfacial bonding strength of the fibers within the aramid separator, effectively enhancing the mechanical strength and dielectric properties of the aramid separator.

Description

Technical Field

[0001] This invention belongs to the field of new materials, and specifically relates to an aramid battery separator and its preparation method. Background Technology

[0002] A lithium-ion battery is a rechargeable battery that primarily functions by the movement of lithium ions between the positive and negative electrodes. During charging and discharging, Li... + Intercalation and deintercalation back and forth between the two electrodes: During charging, Li + Lithium is extracted from the positive electrode, inserted into the negative electrode via the electrolyte, and the negative electrode is in a lithium-rich state; the process is reversed during discharge. The battery separator, a layer of material between the positive and negative electrodes, is a crucial component of the battery, directly impacting its safety and cost. Its main functions are to isolate the positive and negative electrodes, preventing electrons from freely passing through while allowing ions in the electrolyte to freely pass between them. While the separator effectively reduces the risk of short circuits, it also increases the battery's internal resistance. The separator itself does not participate in electrochemical reactions, but its structure and performance directly influence the overall performance of the lithium battery.

[0003] The performance of the separator has a significant impact on battery performance, providing a migration channel for lithium ions while isolating the positive and negative electrodes. Battery 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, the localized high temperature causes the separator to shrink, leading to safety issues such as short circuits. Furthermore, polyolefin separators have relatively low wettability to the electrolyte, which also prevents 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 membranes. Currently, meta-aramid materials for membranes 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 membrane strength, making it unsuitable for large-scale applications. Therefore, there is an urgent need to develop a technology for preparing 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 an aramid separator for lithium batteries.

[0006] Another object of the present invention is to provide an aramid separator for lithium batteries that is efficiently prepared by the method described above.

[0007] Another object of the present invention is to provide an apparatus for preparing an aramid separator for lithium batteries by the method described above.

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

[0009] An apparatus for preparing fine fibers includes two oppositely arranged liquid inlet units, a collector, and a booster. The collector is a motor-driven collecting plate. Each liquid inlet unit includes a liquid inlet plate and a liquid inlet delivery pipe. The liquid inlet plate includes a liquid distribution plate with a plurality of liquid inlet holes and a mesh surface covering the liquid distribution plate. The liquid inlet delivery pipe is connected to the liquid distribution plate. The booster drives the liquid inlet units to move, causing the mesh surfaces of the two liquid inlet units to reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces are drawn together. Each time the distance between the two mesh surfaces reaches or approaches its maximum, the collecting plate passes between the two mesh surfaces to collect the fine fibers.

[0010] Preferably, the mesh surface is a mesh blanket or a grid.

[0011] Preferably, the collector consists of two or more collecting plates that rotate around the motor spindle, and the collecting plates can rotate at a certain angle.

[0012] A method for preparing an aramid battery separator includes the following steps:

[0013] (1) Preparation of aramid polymer solution;

[0014] (2) Preparation of ultrafine aramid fiber bundles: The aramid polymer dispersion obtained by diluting the aramid polymer solution in step (1) is introduced into the liquid inlet unit of the above device. The booster is turned on to make the two mesh surfaces come into close contact and then separate, generating countless fine filaments between the two mesh surfaces. The collecting plate collects the aramid filaments through the gap between the two plates. When the collecting plate moves away, the booster drives the two mesh surfaces to come into close contact again and then separate and draw the filaments. The collecting plate collects the aramid filaments through the gap between the two mesh surfaces again. This cycle is repeated to collect oriented ultrafine aramid fiber bundles.

[0015] (3) A aramid battery separator is prepared by biaxial stretching and heat setting of ultrafine aramid fiber bundles.

[0016] Preferably, the concentration of the aramid polymer dispersion in step (2) is 5-30% by mass.

[0017] The liquid inlet plate in step (2) is square and made of stainless steel, chrome-plated alloy, or plastic for the surface layer; the size of the liquid inlet plate can also be adjusted according to actual production. The size of the collection plate can be adjusted according to the distance between the two liquid inlet plates.

[0018] Preferably, the maximum distance between the mesh surfaces of the two liquid inlet units is 5 to 100 cm; the liquid inlet speed is 0.1 to 50 mL / min; and the collecting plate rotates a certain angle in the same direction after each time it leaves the gap between the two mesh surfaces.

[0019] Preferably, the liquid inlet temperature in step (2) is 20-130°C, more preferably 50-130°C.

[0020] Preferably, (1) the preparation of the aramid polymer solution is: a neutral aramid polymer solution is prepared by polymerizing m-phenylenediamine and isophthaloyl chloride in an organic solvent under low temperature and protective atmosphere conditions; the molar ratio of m-phenylenediamine to isophthaloyl chloride is 100:(85-120); isophthaloyl chloride is added in 2-5 batches.

[0021] Preferably, the concentration of the aramid polymer dispersion in step (2) is 10-25% by mass, the maximum distance between the two mesh surfaces is 15-50 cm, the rotation angle of the collecting plate is 30-90 degrees, the liquid feeding speed is 10-40 mL / min, and the aramid polymer dispersion is also subjected to vacuum defoaming pretreatment.

[0022] Preferably, the ultrafine aramid fiber bundle in step (3) is pretreated as follows before stretching: first, the solvent is evaporated at 50-200°C, and then it is washed with water and dried; the solvent evaporation temperature is more preferably 70-140°C.

[0023] Preferably, the bidirectional stretching in step (3) specifically involves a transverse stretching of 1.3-3.0 times and a longitudinal stretching of 1.3-3.0 times; the heat setting temperature is 260-330℃ and the time is 1-60 min.

[0024] Preferably, the water used for washing in step (3) is deionized water or ultrapure water.

[0025] 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 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.

[0026] 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.

[0027] An aramid separator for lithium batteries is prepared by the above method.

[0028] The aramid membrane can be used in the preparation of lithium batteries, lithium-sulfur batteries, electrical insulation materials, adsorption and filtration materials, flexible electronic device substrates, etc.

[0029] 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.

[0030] The present invention has the following advantages and effects compared with the prior art:

[0031] (1) This invention obtains multilayered aramid separators of different thicknesses by changing the spatial position of the receiving plate and the number of times it passes through the receiving plate in the molding device. These separators exhibit excellent liquid absorption, porosity, temperature resistance, mechanical properties, and electrochemical performance, significantly improving the safe application of lithium batteries. The prepared aramid separators contain interwoven aramid fine fibers (less than 5 μm), with intersecting gaps between fibers (as shown in the attached diagram). Figure 3 and 4 The unique microporous structure, with a larger specific surface area, not only increases porosity but also provides space for more electrolyte, significantly improving electrolyte absorption and ionic conductivity. The interwoven aramid fibers significantly improve the interfacial bonding strength within the aramid membrane, effectively enhancing its mechanical strength and electrochemical performance. This prevents short circuits caused by punctures or lithium dendrites, improving the safety of lithium batteries. Furthermore, the excellent electrolyte adsorption and retention capabilities of the lithium battery separator effectively reduce interfacial resistance, optimize electrical performance, and extend battery life.

[0032] (2) By changing the distance between the upper and lower plates and the liquid flow rate, this invention can easily obtain aramid membranes of different diameters, and effectively control the porosity of the aramid membrane. The amide groups in the meta-aramid macromolecules are connected to each other by meta-phenyl groups. Their covalent bonds do not have a conjugation effect, and their internal rotation energy is relatively lower than that of para-aromatic polyamide fibers. The macromolecular chains exhibit a flexible structure and can withstand a certain amount of external force. When the polymer molecules are stretched, the chemical bond length increases and the bond angle increases, which promotes the straightening and alignment of the aramid polymer molecular chains, thereby achieving controllable and adjustable diameter of aramid single fibers, and thus regulating the microporous structure of the aramid membrane.

[0033] (3) The aramid membrane prepared by the present invention has a smaller diameter and a larger specific surface area, which can significantly improve the interfacial bonding strength of the fibers in the aramid membrane, effectively enhance the mechanical strength and dielectric properties of the aramid membrane, and can be widely used in the field of high-end battery membrane new materials.

[0034] (4) The aramid membrane preparation method of this invention can effectively realize solvent recovery and reuse. Not only is the preparation operation simple and convenient, but it also has higher production efficiency than the current conventional preparation methods, making it suitable for continuous industrial production. It has wide applications in new energy batteries, filtration and separation, functional textiles, flexible circuit boards and other fields.

[0035] (5) After longitudinal and transverse stretching, residual stress is eliminated, 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.

[0036] (6) 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

[0037] Figure 1 This is a flowchart illustrating the preparation process of the aramid separator of this invention.

[0038] Figure 2 This is a schematic diagram of an aramid diaphragm forming device.

[0039] Figure 3 This is a surface electron microscope image of the aramid membrane prepared in Example 4.

[0040] Figure 4 This is a surface electron microscope image of the aramid membrane prepared in Example 5. Detailed Implementation

[0041] 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.

[0042] The starting materials used in the preparation method of this invention can be purchased from the market or prepared according to existing technical methods.

[0043] like Figure 2 As shown, the apparatus for preparing the aramid diaphragm according to this embodiment includes: first-fourth collecting plates 1-4, upper liquid inlet plate 5, lower liquid inlet plate 6, booster 7, upper liquid inlet conveying pipe 8, liquid distribution plate of upper liquid inlet plate 9, mesh grid of upper liquid inlet plate 10, mesh grid of lower liquid inlet plate 11, liquid distribution plate of lower liquid inlet plate 12, motor 13, rotary shifter 14, upper feed main pipe 15, and lower feed main pipe 16.

[0044] Example 1

[0045] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0046] (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.

[0047] (2) Preparation of aramid membrane: The neutral aramid polymer solution obtained in step (1) is diluted to an appropriate concentration of aramid polymer dispersion and then defoamed under vacuum. The solution is then transported to the upper inlet delivery pipe 8 and the lower inlet delivery pipe. Figure 2 On the upper inlet plate 5 and lower inlet plate 6 of the device, the booster 7 is opened, raising the lower inlet plate 6 so that it comes into close contact with the upper inlet plate 5 and then separates. Due to the rough surface of the mesh of the upper and lower inlet plates, countless fine filaments are generated in the upper and lower inlet plates under the action of surface tension. At this time, the first collecting plate 1 passes through the gap between the upper and lower inlet plates and collects the aramid fibers on its surface. After the first collecting plate 1 moves away from the upper and lower inlet plates, the first collecting plate 1 automatically rotates 90 degrees clockwise (maintaining this position until the first collecting plate 1 passes through again). After passing through and leaving the upper and lower inlet plates, the booster 7 continues to work, lifting the lower inlet plate 6, which then separates from the upper inlet plate 5 after close contact. At this time, the first collecting plate 2 passes through the gap between the upper and lower inlet plates and collects the aramid fibers on the surface of the second collecting plate 2. After the second collecting plate 2 leaves the upper and lower inlet plates, it automatically rotates 90 degrees clockwise (maintaining this position until the second collecting plate 2 passes through and leaves the upper and lower collecting plates again), and so on, so that the aramid filaments form a warp and weft interwoven fiber web on the collecting plate. The upper and lower inlet plates in step (2) are square with a side length of 30mm and are made of stainless steel for the surface layer; the size of the upper and lower inlet plates can also be adjusted according to actual production. The collecting plate is made of stainless steel.

[0048] The concentration of the aramid polymer dispersion is 5% by mass; the size of the collecting plate is adjusted according to the distance between the upper and lower inlet plates; the distance between the upper and lower inlet plates can be adjusted to 5cm; the inlet rate is 10mL / min under the condition of inlet temperature of 20℃.

[0049] (3) Stretching and shaping of aramid membrane: The aramid membrane obtained from the collection plate in step (2) is treated at a certain temperature for a period of time. After the solvent has fully evaporated, it is washed with water and dried. Finally, it is stretched longitudinally and laterally on a biaxial stretching machine and then heat-shaped in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0050] The solvent evaporation temperature is 50℃ for 1 minute, the washing water is deionized water, and the process is accompanied by ultrasonic treatment with an ultrasonic power of 200W, a temperature of 30℃, and a time of 60 minutes; the biaxial stretching specifically involves a transverse stretching of 1.3 times and a longitudinal stretching of 1.3 times; the heat setting temperature is 260℃ for 60 minutes.

[0051] Example 2

[0052] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0053] (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.

[0054] (2) Preparation of aramid membrane: Refer to Example 1.

[0055] The concentration of the aramid polymer dispersion is 13% by mass; the size of the collecting plate is adjusted according to the distance between the upper and lower plates; the distance between the upper and lower plates can be adjusted to 20cm; the inlet rate is 20mL / min under the condition of an inlet temperature of 50℃.

[0056] (3) Stretching and shaping of aramid membrane: The aramid membrane obtained from the collection plate in step (2) is treated at a certain temperature for a period of time. After the solvent has fully evaporated, it is washed with water and dried. Finally, it is stretched longitudinally and laterally on a biaxial stretching machine and then heat-shaped in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0057] The solvent evaporation temperature is 200℃ for 1 min; the water used for washing is deionized water, and the washing process is accompanied by ultrasonic treatment with an ultrasonic power of 500W, a temperature of 50℃, and a time of 10 min; the biaxial stretching specifically involves a transverse stretching of 1.5 times and a longitudinal stretching of 1.5 times; the heat setting temperature is 280℃ for 30 min.

[0058] Example 3

[0059] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0060] (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 0.5 h, and after the heat treatment, calcium oxide was added for neutralization to prepare a neutral aramid polymer solution.

[0061] (2) Preparation of aramid membrane: Refer to Example 1.

[0062] The concentration of the aramid polymer dispersion is 20% by mass; the size of the collecting plate is adjusted according to the distance between the upper and lower plates; the distance between the upper and lower plates can be adjusted to 50cm; the inlet rate is 50mL / min under the condition of an inlet temperature of 100℃.

[0063] (3) Stretching and shaping of aramid membrane: The aramid membrane obtained from the collection plate in step (2) is treated at a certain temperature for a period of time. After the solvent has fully evaporated, it is washed with water and dried. Finally, it is stretched longitudinally and laterally on a biaxial stretching machine and then heat-shaped in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0064] The solvent evaporation temperature is 150℃ for 1 min; the water used for washing is deionized water, and the washing process is accompanied by ultrasonic treatment with an ultrasonic power of 800W, a temperature of 60℃, and a time of 30 min; the biaxial stretching specifically involves a transverse stretching of 2.0 times and a longitudinal stretching of 2.0 times; the heat setting temperature is 300℃ for 10 min.

[0065] Example 4

[0066] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0067] (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.

[0068] (2) Preparation of aramid membrane: Refer to Example 1.

[0069] The concentration of the aramid polymer dispersion is 28% by mass; the size of the collecting plate is adjusted according to the distance between the upper and lower plates; the distance between the upper and lower plates can be adjusted to 40cm; the inlet rate is 40mL / min under the condition of an inlet temperature of 130℃.

[0070] (3) Stretching and shaping of aramid membrane: The aramid membrane obtained from the collection plate in step (2) is treated at a certain temperature for a period of time. After the solvent has fully evaporated, it is washed with water and dried. Finally, it is stretched longitudinally and laterally on a biaxial stretching machine and then heat-shaped in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0071] The solvent evaporation temperature is 130℃ for 1 min; the water used for washing is deionized water, and the process is accompanied by ultrasonic treatment with an ultrasonic power of 1500W, a temperature of 90℃, and a time of 10 min; the biaxial stretching specifically involves a transverse stretching of 2.3 times and a longitudinal stretching of 2.3 times; the heat setting temperature is 330℃ for 1 min.

[0072] Example 5

[0073] An aramid separator for lithium batteries and its preparation method, comprising the following steps:

[0074] (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.

[0075] (2) Preparation of aramid membrane: Refer to Example 1.

[0076] The concentration of the aramid polymer dispersion is 22% by mass. The size of the collecting plate is adjusted according to the distance between the upper and lower plates; the distance between the upper and lower plates can be adjusted to 40cm; the inlet rate is 35mL / min under the condition of an inlet temperature of 90℃.

[0077] (3) Stretching and shaping of aramid membrane: The aramid membrane obtained from the collection plate in step (2) is treated at a certain temperature for a period of time. After the solvent has fully evaporated, it is washed with water and dried. Finally, it is stretched longitudinally and laterally on a biaxial stretching machine and then heat-shaped in a high-temperature oven to finally prepare a high-performance aramid membrane.

[0078] The solvent evaporation temperature is 110℃ for 1 min; the water used for washing is deionized water, and the process is accompanied by ultrasonic treatment with an ultrasonic power of 1200W, a temperature of 60℃, and a time of 20 min; the biaxial stretching specifically involves a transverse stretching of 3.0 times and a longitudinal stretching of 3.0 times; the heat setting temperature is 310℃ for 2 min.

[0079] Compare with Example 1

[0080] 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.

[0081] Compare with Example 2

[0082] In step (3) of Example 3, the longitudinal stretch ratio was 2.5, and the other membrane-making processes remained unchanged. Finally, the membrane products were tested for various indicators, and the results are listed in Table 1.

[0083] Compare with Example 3

[0084] In Example 3, the collection plate in step (2) was replaced with nylon material, while the rest of the membrane manufacturing process remained unchanged. Finally, the membrane product was tested for various indicators, and the results are listed in Table 1.

[0085] 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.

[0086] 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, the diaphragm is treated at 250℃ for 24 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... oThis 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.

[0087] Table 1. Detection data of the high-performance aramid membranes prepared in the examples.

[0088]

[0089]

[0090] 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. (By) Figure 3 and 4 It is known that the aramid fibers used in this invention have an average diameter of less than 5 μm, which can effectively increase the bonding effect between the aramid fibers during the forming process. The microporous structure formed by the interlacing of fine aramid fibers enables the aramid separator of this invention to effectively unify the thickness, porosity, and mechanical properties of battery separator materials. In summary, the technology of this invention prepares a thin and high-strength aramid separator, synergistically achieving an organic unity of the porosity, thickness, and mechanical properties of the aramid separator, ensuring the safe use of high-performance batteries.

[0091] 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 an aramid separator for lithium batteries, characterized in that, Includes the following steps: (1) Preparation of aramid polymer solution: a 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); isophthaloyl chloride is added in 2-5 batches; (2) Preparation of ultrafine aramid fiber bundles: The aramid polymer dispersion obtained by diluting the aramid polymer solution in step (1) is introduced into the liquid inlet unit of the device for preparing fine fibers. The booster is turned on so that the first and second mesh surfaces are in close contact and then separated, generating countless fine filaments between the two mesh surfaces. The collector collects the aramid filaments through the gap between the two mesh surfaces. When the collector leaves, the two mesh surfaces are in close contact again under the drive of the booster and then separated and drawn. The collector collects the aramid filaments through the gap between the two mesh surfaces again. This cycle is repeated to collect oriented ultrafine aramid fiber bundles. (3) A aramid separator for lithium batteries is prepared by biaxial stretching and heat setting of ultrafine aramid fiber bundles; The apparatus for preparing fine fibers includes a liquid inlet unit, a collector, and a booster. The collector is a motor-driven collection plate. The liquid inlet unit includes a liquid inlet plate and a liquid inlet delivery pipe. The liquid inlet plate includes a liquid distribution plate with several liquid inlet holes and a first mesh surface covering the liquid distribution plate. The liquid inlet delivery pipe is connected to the liquid distribution plate. A docking plate covered with a second mesh surface is provided opposite the first mesh surface of the liquid inlet plate. The booster drives the liquid inlet plate and / or the docking plate to move, so that the first mesh surface and the second mesh surface reciprocate between close contact and a distance of more than 5 cm. After contact and separation, the two mesh surfaces generate filaments without breaking. The collection plate passes through the space between the two mesh surfaces to collect the fine fibers.

2. The preparation method according to claim 1, characterized in that, The first and second mesh surfaces are mesh blankets or mesh grids; the liquid inlet plate and the docking plate are horizontally arranged.

3. The preparation method according to claim 2, characterized in that, The collector consists of two or more collecting plates that rotate around the motor spindle, and each collecting plate can rotate at a certain angle; the docking plate is located below the liquid inlet plate, and the booster drives the docking plate to move up and down.

4. The method according to claim 1, 2, or 3, characterized in that, The concentration of the aramid polymer dispersion in step (2) is 5-30% by mass; the maximum distance between the first and second mesh surfaces is 5-100 cm; the liquid feeding speed is 0.1-50 mL / min; the temperature of the aramid polymer dispersion entering the liquid feeding unit is 20-130℃; and the collecting plate rotates a certain angle in the same direction after each time it leaves the gap between the two mesh surfaces.

5. The method according to claim 4, characterized in that, The concentration of the aramid polymer dispersion in step (2) is 10-25% by mass, the maximum distance between the first and second mesh surfaces is 15-50 cm, the angle of rotation of the collecting plate is 30-90 degrees each time, the liquid feeding speed is 10-40 mL / min, and the aramid polymer dispersion is also subjected to vacuum defoaming pretreatment.

6. The method according to claim 1, 2, or 3, characterized in that, Before stretching, the ultrafine aramid fiber bundles in step (3) are pretreated as follows: the ultrafine aramid fiber bundles collected in step (2) are successively replaced and washed with water in an extractant and water; the extractant is an aqueous solution or alcoholic solution of one or more of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, ethylene glycol, glycerol, and acetone; the extraction process is accompanied by ultrasonic treatment.

7. The method according to claim 6, characterized in that, Step (3) specifically involves biaxial stretching of 1.1-3.0 times in the transverse direction and 1.1-3.0 times in the longitudinal direction; the heat setting temperature is 260-330℃, and the time is 1-60 min; the extraction solution is N,N-dimethylacetamide or a mixed solution of N,N-dimethylacetamide, ethylene glycol, and water; the ultrasonic treatment conditions are 200-1500W power, 30±10℃ temperature, and 1-30 min time; the water washing conditions are 30-90℃ temperature and 1-60 min time.

8. The method according to claim 1, 2, or 3, characterized in that, 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 to obtain a reaction solution; as the reaction proceeds, the temperature of the reaction solution gradually increases. 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.

9. The aramid separator for lithium batteries prepared by the method according to any one of claims 1-8.

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