A high-strength and high-ionic-conductivity semi-solid aramid separator and a preparation method thereof

Abstract

The application relates to the field of lithium ion battery diaphragms and specifically discloses a semi-solid aramid diaphragm with high strength and high ion conductivity and a preparation method thereof. The preparation method of the semi-solid aramid diaphragm with high strength and high ion conductivity comprises the following steps: S1. preparing para-aramid; S2. preparing a para-aramid diaphragm coating solution: blending the para-aramid and epichlorohydrin, stirring at a temperature of 28-35 DEG C for 15-18 h, extracting after removing the solvent, drying to obtain modified para-aramid, then blending and dispersing the modified para-aramid and cellulose nanocrystals in a composite solvent, uniformly stirring to obtain the para-aramid diaphragm coating solution; and S3. preparing a para-aramid diaphragm: coating, coagulation bath, infrared curing, heat pressing enhancement, and obtaining the aramid diaphragm with a tensile strength of greater than or equal to 180 MPa. The application effectively improves the solubility of the para-aramid in a polar solvent, maintains the electrochemical stability, and effectively improves the tensile strength.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion battery separators, and in particular to a semi-solid aramid separator with high strength and high ionic conductivity and a method for preparing the same. Background Technology

[0002] In today's era of rapid technological advancement, electronic devices are constantly being updated and replaced. From smartphones to tablets, from laptops to wearable devices, people are placing increasingly higher demands on the performance and battery life of electronic devices. Lithium-ion batteries, as a type of rechargeable battery, exhibit significant advantages such as high energy density, long cycle life, and low self-discharge rate due to their unique working principle based on the movement of lithium ions between the positive and negative electrodes. Furthermore, because they do not contain heavy metals such as cadmium and mercury, they possess excellent environmental friendliness and high efficiency, making them the mainstream power source for modern electronic devices. They play a crucial role in the field of electronic devices, greatly promoting their development. This allows for thinner and lighter designs, making them more portable; longer battery life, meeting the needs of users in various scenarios; and more stable performance, providing reliable protection for people's lives and work. Moreover, lithium-ion batteries have broad application prospects in electric vehicles, energy storage systems, and other fields, making significant contributions to promoting the development of green energy.

[0003] In the field of lithium-ion batteries, various types of separators are commonly used to meet battery performance requirements. Polyolefin-based (PE / PP) separators are a common type, utilizing the properties of polyolefin materials, such as good chemical stability and mechanical properties, to achieve the separator's function. In practical applications, polyolefin-based separators are manufactured using specific processes to create films with microporous structures, allowing lithium ions to pass through while isolating the positive and negative electrodes to prevent short circuits. Aramid composite separators are used in batteries due to the high strength and high-temperature resistance of aramid materials. Aramid composite separators typically combine aramid fibers with other materials to form separators with unique properties. Different preparation methods, such as coating and impregnation, can be used to uniformly distribute the aramid material in the separator to improve its performance. Inorganic solid electrolyte membranes rely on their special solid electrolyte properties to meet battery requirements. These separators utilize the ion conduction characteristics of inorganic materials to achieve rapid lithium ion transport. Inorganic solid electrolyte membranes typically have high ionic conductivity and good thermal stability, which can improve battery safety and performance to a certain extent. These separators play important roles in batteries, such as isolating the positive and negative electrodes and allowing lithium ions to pass through. They are an indispensable component of lithium-ion batteries.

[0004] However, existing separators have significant drawbacks. Polyolefin-based separators, due to their low melting points (PE below 140℃ and PP below 170℃), are prone to deformation or even melting during battery operation when temperatures rise, resulting in insufficient thermal stability and impacting battery safety and performance. Inorganic solid-state electrolyte membranes, while possessing good thermal stability and conductivity, suffer from excessively high interfacial impedance, leading to significant energy loss during charging and discharging, reducing charging and discharging efficiency, and affecting overall battery performance. While para-aramid membranes in aramid composite separators offer advantages such as high temperature resistance, good self-extinguishing properties, and electrolyte affinity, their high molecular chain rigidity and strong intermolecular hydrogen bonding result in poor dispersion in polar solvents (such as DMAC and NMP). This makes the separator surface prone to localized agglomeration or cracking, and also increases the viscosity of the coating slurry, making it difficult to form a uniform porous structure through slot coating or impregnation processes. Therefore, these defects in para-aramid separators significantly reduce their mechanical strength, making them unable to meet the high-performance requirements of modern electronic devices. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a semi-solid aramid membrane with high strength and high ionic conductivity, and a method for preparing the same.

[0006] In a first aspect, this application provides a method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity, comprising the following steps:

[0007] S1. Preparation of para-aramid fibers;

[0008] S2. Preparation of para-aramid membrane coating solution: Para-aramid obtained in S1 and epichlorohydrin are blended in a weight ratio of 20:(10-15), stirred at 28-35℃ for 15-18h, the solvent is removed, extracted and dried to obtain modified para-aramid. Then, the modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent in a weight ratio of 100:(1-5), and stirred evenly to obtain para-aramid membrane coating solution.

[0009] S3. Preparation of para-aramid membrane: The para-aramid membrane coating solution is coated at a speed of 15-20 m / min. After coating, the membrane is subjected to coagulation bath, infrared curing, and hot pressing to enhance its properties, thereby obtaining the aramid membrane.

[0010] By employing the above technical solution, this application first prepared para-aramid, and then used epichlorohydrin to blend with para-aramid, forming a stable intermolecular connection and enhancing the crosslinking density of the molecular chains. A three-dimensional crosslinking network was formed between the molecular chains of para-aramid, inhibiting molecular chain slippage and effectively improving the tensile strength of the film formed after para-aramid coating. Furthermore, this application added cellulose nanofibers to the system, which have nanoscale size and high aspect ratio, forming a rigid network structure with para-aramid. Through hydrogen bonding and mechanical interlocking, they effectively share the stress borne by the aramid molecular chains, significantly improving the tensile strength of the aramid membrane. Cellulose nanofibers also have a high specific surface area and abundant surface hydroxyl groups. The active hydroxyl groups can form strong interfacial interactions with the aramid molecular chains, which can act as a dispersant to promote the uniform distribution of modified para-aramid in the composite solvent, and can also improve the adhesion between the para-aramid membrane coating liquid and the substrate (such as lithium battery membrane).

[0011] After obtaining the para-aramid membrane coating solution, this application coats the membrane at a certain coating speed. After coating, a coagulation bath is applied to induce the precipitation of aramid molecular chains, forming a porous structure. Infrared curing is then performed to promote the crystallization of aramid molecular chains and the bonding between the coating and the base film. Finally, hot pressing is performed to enhance the coating density and mechanical strength, resulting in an aramid membrane with a tensile strength of not less than 180 MPa. Therefore, this application effectively improves the solubility of para-aramid in polar solvents, maintains electrochemical stability, and effectively enhances tensile strength.

[0012] Preferably, the specific steps for preparing para-aramid in step S1 are as follows:

[0013] Terephthaloyl chloride, p-phenylenediamine and 2,5-diaminophenol in a molar ratio of 10:(6-8):(2-4) were co-dispersed in a composite solvent, the solvent was removed, and the mixture was extracted and dried to obtain para-aramid.

[0014] By adopting the above technical solution, this application utilizes 2,5-diaminophenol to partially replace p-phenylenediamine. The hydroxyl groups of 2,5-diaminophenol disrupt the hydrogen bonds between the molecular chains of para-aramid, reducing crystallinity and thereby increasing the solubility of para-aramid in the coating solution. This improves the compatibility between the polymer and the solvent, enhances the dispersion effect in polar solvents, reduces the possibility of local agglomeration or cracks on the membrane surface, reduces the viscosity of the coating solution, and promotes the formation of a uniform porous structure in the aramid membrane, thus improving the tensile strength of the aramid membrane. At the same time, the membrane maintains electrochemical stability, has a small electrolyte contact angle, and a high electrolyte absorption rate, thereby also improving the cycle life of the battery.

[0015] Furthermore, this application strictly controls the molar ratio of p-phenylenediamine and 2,5-diaminophenol. If the amount of 2,5-diaminophenol added is too small, it will not be able to effectively improve the solubility of para-aramid. If the amount of 2,5-diaminophenol added is too large, it will cause the benzene ring conjugated structure of the aramid main chain to be distorted, and the tensile strength will be damaged.

[0016] Preferably, the molar ratio of terephthaloyl chloride, p-phenylenediamine, and 2,5-diaminophenol is 10:7:3.

[0017] By adopting the above technical solution, this application further controls the molar ratio of terephthaloyl chloride, p-phenylenediamine and 2,5-diaminophenol to 10:7:3, which can maximize the solubility of para-aramid with almost no impact on the tensile strength of aramid film.

[0018] Preferably, in S2, the weight ratio of para-aramid and epichlorohydrin obtained in S1 is 20:13.

[0019] By adopting the above technical solution, this application strictly controls the weight ratio of para-aramid and epichlorohydrin, further strengthening the stability of the intermolecular connection formed between the two, inhibiting molecular chain slippage, and effectively improving the tensile strength of the film formed after para-aramid coating.

[0020] Preferably, in step S2, the modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent at a weight ratio of 100:(2-3).

[0021] By adopting the above technical solution, this application strictly controls the weight ratio of modified para-aramid to cellulose nanofibers. If the amount of cellulose nanofibers is too small, the tensile strength of the separator cannot be effectively improved. If the amount of cellulose nanofibers is too large, the degree of internal aggregation will increase sharply, which will not only reduce the tensile strength of the separator, but also cause the conductivity of the aramid separator to surge, reducing the battery's service life.

[0022] Preferably, in step S3, the infrared light wavelength used for infrared curing is 2.5-4 μm.

[0023] Preferably, in step S3, the infrared light power density used for infrared curing is 1-3 kW / m². 2 Irradiation distance: 10-20cm.

[0024] Preferably, in step S3, infrared curing is performed using staged heating, specifically: first, the temperature is raised to 60-80℃ and processed for 30-60 seconds, and finally the temperature is raised to 100-120℃ and maintained for 60-180 seconds.

[0025] Preferably, in step S3, the temperature for hot pressing is 100-120°C and the pressure is 0.5-1.0 MPa.

[0026] Secondly, this application provides an aramid membrane prepared by the above-mentioned method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity, having a tensile strength ≥180MPa.

[0027] By adopting the above technical solution, this application utilizes the blending reaction of epichlorohydrin and para-aramid to enhance the cross-linking density of molecular chains, form a three-dimensional cross-linking network to inhibit molecular chain slippage, add cellulose nanofibers to share stress, consume crack propagation energy, improve interfacial bonding strength and material density, and then through coating, coagulation bath, infrared curing and hot pressing reinforcement steps, an aramid membrane with a tensile strength of not less than 180 MPa can be obtained, thus improving the strength of the aramid membrane.

[0028] In summary, this application has the following beneficial technical effects:

[0029] 1. This application utilizes the blending reaction of epichlorohydrin and para-aramid to form stable intermolecular connections, enhance the crosslinking density of molecular chains, form a three-dimensional crosslinking network between molecular chains, inhibit molecular chain slippage, and improve the tensile strength of the film formed after aramid coating.

[0030] 2. This application incorporates cellulose nanofibers as nano-reinforcements to share the stress borne by the aramid molecular chains. Through pull-out and bridging effects, it consumes crack propagation energy, forms amide bonds with the amino groups at the ends of the aramid molecular chains to enhance interfacial bonding strength, occupies the free volume between the aramid molecular chains to increase material density, and comprehensively improves the strength of the aramid membrane.

[0031] 3. This application involves coating at a certain coating speed, followed by a coagulation bath to induce the precipitation of aramid molecular chains to form a porous structure, infrared curing to promote the crystallization of aramid molecular chains and the bonding between the coating and the base film, and hot pressing to enhance the density and mechanical strength of the coating, thereby obtaining an aramid membrane with a tensile strength of not less than 180 MPa. Detailed Implementation

[0032] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0033] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity includes the following steps:

[0034] S1. Preparation of para-aramid fibers;

[0035] S2. Preparation of para-aramid membrane coating solution: Para-aramid obtained in S1 and epichlorohydrin are blended in a weight ratio of 20:(10-15), stirred at 28-35℃ for 15-18h, the solvent is removed, extracted and dried to obtain modified para-aramid. Then, the modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent in a weight ratio of 100:(1-5), and stirred evenly to obtain para-aramid membrane coating solution.

[0036] S3. Preparation of para-aramid membrane: The para-aramid membrane coating solution is coated at a speed of 15-20 m / min. After coating, the membrane is subjected to coagulation bath, infrared curing, and hot pressing to enhance its properties, thereby obtaining the aramid membrane.

[0037] In a preferred embodiment of this application, the specific steps for preparing para-aramid in step S1 are as follows:

[0038] Terephthaloyl chloride, p-phenylenediamine and 2,5-diaminophenol in a molar ratio of 10:(6-8):(2-4) were co-dispersed in a composite solvent, the solvent was removed, and the mixture was extracted and dried to obtain para-aramid.

[0039] In a preferred embodiment of this application, the molar ratio of terephthaloyl chloride, p-phenylenediamine, and 2,5-diaminophenol is 10:7:3.

[0040] In a preferred embodiment of this application, in step S2, the weight ratio of para-aramid and epichlorohydrin obtained in step S1 is 20:13.

[0041] In a preferred embodiment of this application, in step S2, modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent at a weight ratio of 100:(2-3).

[0042] In a preferred embodiment of this application, in step S3, the infrared light wavelength used for infrared curing is 2.5-4 μm.

[0043] In a preferred embodiment of this application, in step S3, the infrared light power density used for infrared curing is 1-3 kW / m². 2 Irradiation distance: 10-20cm.

[0044] In a preferred embodiment of this application, in step S3, infrared curing is performed by staged heating, specifically: first, the temperature is raised to 60-80°C and processed for 30-60 seconds, and finally the temperature is raised to 100-120°C and maintained for 60-180 seconds.

[0045] In a preferred embodiment of this application, in step S3, the temperature of the hot-pressing enhancement is 100-120°C and the pressure is 0.5-1.0 MPa.

[0046] Example 1

[0047] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity includes the following steps:

[0048] S1. Preparation of para-aramid: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 15:85 and stirred evenly to obtain a composite solvent. Then, 10 mol of p-phenylenediamine was added to it and stirred until completely dissolved. The mixture was then cooled to -10℃. Finally, 10 mol of terephthaloyl chloride was added in three portions and stirred at 1000 r / min. When the viscosity of the system increased sharply, the cooling was stopped and the reaction was allowed to continue at room temperature for 2 h. Finally, calcium hydroxide was added to adjust the pH of the system to 7. The system was degassed using a vacuum pump, and a large amount of ethanol was added to remove the solvent. The mixture was then dried to obtain para-aramid.

[0049] S2. Preparation of para-aramid membrane coating solution: Under nitrogen protection, 40g of sodium hydride and 15L of anhydrous dimethyl sulfoxide were mixed and reacted at 70℃ for 40min. Then the temperature was lowered to 30℃, and 200g of para-aramid was slowly added. The mixture was mechanically stirred at room temperature for 2 days. Then 100g of epichlorohydrin was slowly added dropwise through a constant pressure low liquid funnel and stirred at 35℃ for 15h. Then a large amount of anhydrous ethanol was added to remove the solvent and excess reactants. The solid product was extracted for 24h and then vacuum dried at 60℃ for 24h to obtain modified para-aramid. Then 100g of modified para-aramid and 1g of cellulose nanofibers were mixed and dispersed in 1.68L of composite solvent obtained in S1 and stirred for 5h to obtain para-aramid membrane coating solution.

[0050] S3. Preparation of para-aramid membrane: A precision coating machine was used to coat the para-aramid membrane coating solution from S2 onto a porous PE substrate at a coating speed of 20 m / min. The wet film thickness was controlled at 30 μm. The coated composite membrane was then immersed in a coagulation bath (water and DMSO at a volume ratio of 4:1) and treated at 30°C for 20 min, followed by infrared curing at an infrared wavelength of 2.5 μm and an infrared power density of 3 kW / m². 2 The irradiation distance was 10cm, the infrared curing temperature was 90℃, the time was 165s, and the film was soaked in deionized water for 8min to remove residual solvent. Then it was dried and shaped with hot air at 80℃, and then hot-pressed at 100℃ and 1.0MPa pressure of hot roller for 30s to obtain aramid membrane.

[0051] Example 2

[0052] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity includes the following steps:

[0053] S1. Preparation of para-aramid: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 15:85 and stirred evenly to obtain a composite solvent. Then, 10 mol of p-phenylenediamine was added to it and stirred until completely dissolved. The mixture was then cooled to -10℃. Finally, 10 mol of terephthaloyl chloride was added in three portions and stirred at 1000 r / min. When the viscosity of the system increased sharply, the cooling was stopped and the reaction was allowed to continue at room temperature for 2 h. Finally, calcium hydroxide was added to adjust the pH of the system to 7. The system was degassed using a vacuum pump, and a large amount of ethanol was added to remove the solvent. The mixture was then dried to obtain para-aramid.

[0054] S2. Preparation of para-aramid membrane coating solution: Under nitrogen protection, 40g of sodium hydride and 15L of anhydrous dimethyl sulfoxide were mixed and reacted at 70℃ for 40min. Then the temperature was lowered to 30℃, and 200g of para-aramid was slowly added. The mixture was mechanically stirred at room temperature for 2 days. Then 150g of epichlorohydrin was slowly added dropwise through a constant pressure low liquid funnel and stirred at 35℃ for 15h. Then a large amount of anhydrous ethanol was added to remove the solvent and excess reactants. The solid product was extracted for 24h and then vacuum dried at 60℃ for 24h to obtain modified para-aramid. Then 100g of modified para-aramid and 5g of cellulose nanofibers were mixed and dispersed in 1.75L of composite solvent obtained in S1 and stirred for 5h to obtain para-aramid membrane coating solution.

[0055] S3. Preparation of para-aramid membrane: A precision coating machine was used to coat the para-aramid membrane coating solution from S2 onto a porous PE substrate at a coating speed of 15 m / min. The wet film thickness was controlled at 30 μm. The coated composite membrane was then immersed in a coagulation bath (water and DMSO in a 4:1 volume ratio) and treated at 30°C for 20 min, followed by infrared curing at a wavelength of 4 μm and an infrared power density of 1 kW / m². 2 The irradiation distance was 20cm, the infrared curing temperature was 90℃, the time was 165s, and the film was soaked in deionized water for 8min to remove residual solvent. Then it was dried and shaped with hot air at 80℃, and then hot-pressed at 120℃ and 0.5MPa pressure of hot roller for 30s to obtain aramid membrane.

[0056] Example 3

[0057] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 1 in that the preparation method of S1 is different, specifically:

[0058] S1. Preparation of para-aramid: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 15:85 and stirred evenly to obtain a composite solvent. Then, 8 mol of p-phenylenediamine and 2 mol of 2,5-diaminophenol were added to it and stirred until completely dissolved. The mixture was then cooled to -10℃. Finally, 10 mol of terephthaloyl chloride was added in three portions and stirred at 1000 r / min. When the viscosity of the system increased sharply, the cooling was stopped and the reaction was allowed to continue at room temperature for 2 h. Finally, calcium hydroxide was added to adjust the pH of the system to 7, and the system was degassed using a vacuum pump. A large amount of ethanol was added to remove the solvent, and the mixture was dried to obtain para-aramid.

[0059] Example 4

[0060] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 1 in that the preparation method of S1 is different, specifically:

[0061] S1. Preparation of para-aramid: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 15:85 and stirred evenly to obtain a composite solvent. Then, 7 mol of p-phenylenediamine and 3 mol of 2,5-diaminophenol were added to it and stirred until completely dissolved. The mixture was then cooled to -10℃. Finally, 10 mol of terephthaloyl chloride was added in three portions and stirred at 1000 r / min. When the viscosity of the system increased sharply, the cooling was stopped and the system was allowed to continue reacting at room temperature for 2 h. Finally, calcium hydroxide was added to adjust the pH of the system to 7. The system was degassed using a vacuum pump, and a large amount of ethanol was added to remove the solvent. The mixture was then dried to obtain para-aramid.

[0062] Example 5

[0063] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 1 in that the preparation method of S1 is different, specifically:

[0064] S1. Preparation of para-aramid: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 15:85 and stirred evenly to obtain a composite solvent. Then, 6 mol of p-phenylenediamine and 4 mol of 2,5-diaminophenol were added to it and stirred until completely dissolved. The mixture was then cooled to -10℃. Finally, 10 mol of terephthaloyl chloride was added in three portions and stirred at 1000 r / min. When the viscosity of the system increased sharply, the cooling was stopped and the system was allowed to continue reacting at room temperature for 2 h. Finally, calcium hydroxide was added to adjust the pH of the system to 7. The system was degassed using a vacuum pump, and a large amount of ethanol was added to remove the solvent. The mixture was then dried to obtain para-aramid.

[0065] Example 6

[0066] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 4 in that, in S2, the amount of epichlorohydrin used is 115g, while the rest are the same as in Example 4.

[0067] Example 7

[0068] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 4 in that, in S2, the amount of epichlorohydrin used is 130g, while the rest are the same as in Example 4.

[0069] Example 8

[0070] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 4 in that, in S2, the amount of epichlorohydrin used is 145g, while the rest are the same as in Example 4.

[0071] Example 9

[0072] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 7 in that, in S2, the amount of cellulose nanofibers used is 2g, while the rest are the same as in Example 7.

[0073] Example 10

[0074] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity, which differs from Example 7 in that the amount of cellulose nanofibers used in S2 is 3g, while the rest is the same as in Example 7.

[0075] Example 11

[0076] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 1 in that, in S3, infrared curing is performed using staged heating: first, the temperature is raised to 80°C and treated for 30 seconds, and finally the temperature is raised to 100°C and maintained for 180 seconds. The rest is the same as in Example 1.

[0077] Example 12

[0078] A method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity differs from Example 1 in that, in S3, infrared curing is performed using staged heating: first, the temperature is raised to 60°C and treated for 60 seconds, and finally the temperature is raised to 120°C and maintained for 60 seconds. The rest is the same as in Example 1.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that S2 specifically involves:

[0081] 101g of para-aramid obtained in S1 was dispersed in 1.68L of composite solvent obtained in S1, and the mixture was stirred for 5h to obtain a para-aramid membrane coating solution.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that in S2, specifically: under nitrogen protection, 40g of sodium hydride and 15L of anhydrous dimethyl sulfoxide are mixed and reacted at 70°C for 40min. Then, the temperature is lowered to 30°C, and 200g of para-aramid is slowly added. The mixture is mechanically stirred at room temperature for 2 days. Then, 100g of epichlorohydrin is slowly added dropwise using a constant pressure low-pressure funnel, and the mixture is stirred at 35°C for 15h. Subsequently, a large amount of anhydrous ethanol is added to remove the solvent and excess reactants. The solid product is extracted for 24h and then vacuum dried at 60°C for 24h to obtain modified para-aramid. Then, 100g of modified para-aramid is dispersed in 1.68L of the composite solvent obtained in S1 and stirred for 5h to obtain the para-aramid membrane coating solution.

[0084] Comparative Example 3

[0085] The difference from Example 1 is that S2 specifically involves:

[0086] 100g of para-aramid and 1g of cellulose nanofibers obtained in S1 were dispersed in 1.68L of composite solvent obtained in S1, and the mixture was stirred for 5h to obtain a para-aramid membrane coating solution.

[0087] Comparative Example 4

[0088] The difference from Example 1 is that the amount of cellulose nanocrystals used in S2 is 0.5g, while the rest is the same as in Example 1.

[0089] Comparative Example 5

[0090] The difference from Example 1 is that the amount of cellulose nanocrystals used in S2 is 7g, while the rest is the same as in Example 1.

[0091] Comparative Example 6

[0092] The difference from Example 1 is that infrared curing in S3 is removed and replaced with ordinary curing (drying at 90°C for 300s), while the rest is the same as Example 1.

[0093] Comparative Example 7

[0094] The difference from Example 1 is that the hot-pressing enhancement in S3 is removed, while the rest is the same as Example 1.

[0095] Performance testing

[0096] 1. The composite diaphragms obtained in the examples and comparative examples were cut into rectangular paper pieces with a specification of 20mm×50mm. Tensile strength tests were performed using a servo high and low temperature tensile testing machine with a tensile speed of 5mm / min and a gravity sensor specification of 500kN. The tensile strength was measured and the results were recorded in Table 1.

[0097] 2. Assemble the CR2032 button cell in the order of positive electrode active material, electrolyte, separator, and lithium sheet. Then, use a battery packaging machine to press the battery tightly and let it stand for more than 12 hours until the battery is fully balanced. Then, perform a discharge capacity test on the battery testing system to test the discharge capacity of the sample at 3C.

[0098] 3. Assemble the CR2032 button cell in the order of positive electrode active material, electrolyte, separator, and lithium sheet. Then, press the battery tightly with a battery packaging machine and let it stand for more than 12 hours until the battery is fully balanced. Then, perform charge-discharge cycle tests on the battery testing system with a constant current rate of 1C and a charge-discharge cutoff voltage of 2.5-3.8V. Record the battery capacity retention rate after 100 cycles in Table 1.

[0099] Table 1 Performance Test Table

[0100] Example 1 183 114 82.5 Example 2 190 111 80.5 Example 3 198 119 84.0 Example 4 203 125 86.5 Example 5 197 120 84.0 Example 6 202 125 86.5 Example 7 209 128 87.0 Example 8 205 126 86.5 Example 9 214 126 86.5 Example 10 215 124 85.5 Example 11 192 117 83.5 Example 12 194 115 83.0 Comparative Example 1 104 96 70.5 Comparative Example 2 138 101 74.0 Comparative Example 3 144 90 68.5 Comparative Example 4 168 119 83.5 Comparative Example 5 172 103 76.5 Comparative Example 6 169 110 82.0 Comparative Example 7 166 115 82.5

[0101] Data Analysis:

[0102] As can be seen from Table 1, the tensile strength of the aramid separators obtained in Examples 1-2 of this application is 183-190 MPa, the discharge capacity of the lithium-ion batteries at 3C is 111-114 mAh, and the battery capacity retention rate after 100 cycles at 1C is 80.5-82.5%. It can be seen that this application effectively improves the solubility of para-aramid in polar solvents, maintains electrochemical stability, and effectively improves tensile strength.

[0103] In Examples 3-5, this application changed the raw materials for preparing para-aramid. The results showed that the tensile strength of the aramid separator was improved, and the discharge capacity of the lithium-ion battery at 3C and the capacity retention rate after 100 cycles at 1C were significantly improved. In particular, the tensile strength of the aramid separator in Example 4 reached 203 MPa, the discharge capacity of the lithium-ion battery at 3C reached 125 mAh, and the capacity retention rate after 100 cycles at 1C reached 86.5%. Therefore, this application utilizes 2,5-diaminophenol to partially replace p-phenylenediamine. The hydroxyl groups of diaminophenol disrupt the hydrogen bonds between the molecular chains of para-aramid, reducing its crystallinity and thus increasing the solubility of para-aramid in the coating solution. This improves the compatibility of the polymer with the solvent, enhances dispersion in polar solvents, reduces the possibility of local agglomeration or cracks on the membrane surface, lowers the viscosity of the coating solution, and promotes the formation of a uniform porous structure in the aramid membrane. This, in turn, improves the tensile strength of the aramid membrane. At the same time, the membrane maintains electrochemical stability, has a small electrolyte contact angle, and a high electrolyte absorption rate, thereby also improving the cycle life of the battery.

[0104] In Examples 6-8, this application changed the amount of epichlorohydrin in S2. The results showed that the tensile strength of the aramid membrane in Example 7 was improved, and the discharge capacity of the lithium-ion battery at 3C and the capacity retention rate of the battery after 100 cycles at 1C were significantly improved. It can be seen that this application strictly controls the weight ratio of para-aramid and epichlorohydrin, which can further enhance the stability of the intermolecular connection formed between the two, inhibit molecular chain slippage, and effectively improve the tensile strength of the film formed after para-aramid coating.

[0105] In Examples 9-10, this application changed the amount of cellulose nanofibers in S2. The results showed that the tensile strength of the aramid membrane was greatly improved. It can be seen that this application strictly controlled the weight ratio of modified para-aramid to cellulose nanofibers, which can further optimize the electrical properties and tensile strength of the aramid membrane.

[0106] In Examples 11-12, this application changed the heating method during infrared curing in S3. The results showed that the tensile strength of the aramid separator was improved, and the discharge capacity of the lithium-ion battery at 3C and the capacity retention rate of the battery after 100 cycles at 1C were significantly improved. It can be seen that the staged heating of this application can improve the coating density, mechanical strength and electrical performance.

[0107] In Comparative Examples 1-3, this application removed cellulose nanofibers and / or epichlorohydrin modification. The results showed a significant decrease in the tensile strength of the aramid membrane, and a decrease in the discharge capacity of the lithium-ion battery at 3C and the capacity retention rate of the battery after 100 cycles at 1C. It is evident that this application utilizes the blending reaction of epichlorohydrin and para-aramid to form stable intermolecular connections, enhancing the crosslinking density of the molecular chains and forming a three-dimensional crosslinking network between the molecular chains of para-aramid. This inhibits molecular chain slippage and effectively improves the tensile strength of the film formed after coating with para-aramid. The cellulose nanofibers of this application have nanoscale size and high aspect ratio, forming a rigid network structure with para-aramid. Through hydrogen bonding and mechanical interlocking, they effectively share the stress borne by the aramid molecular chains, significantly improving the tensile strength of the aramid separator. The cellulose nanofibers also have a high specific surface area and abundant surface hydroxyl groups. The active hydroxyl groups can form strong interfacial interactions with the aramid molecular chains, which can act as a dispersant to promote the uniform distribution of modified para-aramid in the composite solvent, and can also improve the adhesion between the para-aramid separator coating liquid and the substrate (such as lithium battery separator).

[0108] In Comparative Example 4, this application reduced the amount of cellulose nanofibers in S2, and the results showed that the tensile strength of the aramid separator was significantly reduced. In Comparative Example 5, this application increased the amount of cellulose nanofibers in S2, and the results showed that the tensile strength of the aramid separator was significantly reduced. The discharge capacity of the lithium-ion battery at 3C and the capacity retention rate of the battery after 100 cycles at 1C also decreased. It can be seen that if the amount of cellulose nanofibers is too small, it cannot effectively improve the tensile strength of the separator. If the amount of cellulose nanofibers is too large, it will lead to a sharp increase in the degree of internal aggregation, which will not only lead to a decrease in the tensile strength of the separator, but also cause a surge in the conductivity of the aramid separator, reducing the battery's service life.

[0109] In Comparative Example 6, the infrared curing in S3 was removed and replaced with ordinary curing. In Comparative Example 7, the hot-pressing enhancement in S3 was removed. The results showed that the tensile strength of the aramid membrane was significantly reduced. It can be seen that infrared curing can promote the crystallization of aramid molecular chains and the bonding between the coating and the base film interface, while hot-pressing enhancement can improve the density and mechanical strength of the coating, resulting in an aramid membrane with a tensile strength ≥180MPa.

[0110] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method of making a semi-solid aramid separator membrane with high strength and high ionic conductivity, characterized in that, Includes the following steps: S1. Preparation of para-aramid fibers; S2. Preparation of para-aramid membrane coating solution: Para-aramid obtained in S1 and epichlorohydrin are blended in a weight ratio of 20:(10-15), stirred at 28-35℃ for 15-18h, the solvent is removed, extracted and dried to obtain modified para-aramid. Then, the modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent in a weight ratio of 100:(1-5), and stirred evenly to obtain para-aramid membrane coating solution. S3. Preparation of para-aramid membrane: The para-aramid membrane coating solution is coated at a speed of 15-20 m / min. After coating, the membrane is subjected to coagulation bath, infrared curing, and hot pressing to enhance its properties, thereby obtaining the aramid membrane.

2. The method of claim 1, wherein the semi-solid aramid membrane has high strength and high ionic conductivity. The specific steps for preparing para-aramid in S1 are as follows: Terephthaloyl chloride, p-phenylenediamine and 2,5-diaminophenol in a molar ratio of 10:(6-8):(2-4) were co-dispersed in a composite solvent, the solvent was removed, and the mixture was extracted and dried to obtain para-aramid.

3. The method of claim 2, wherein the semi-solid aramid membrane has high strength and high ionic conductivity, and is characterized by, The molar ratio of terephthaloyl chloride, p-phenylenediamine, and 2,5-diaminophenol is 10:7:

3.

4. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, In step S2, the weight ratio of para-aramid and epichlorohydrin obtained in step S1 is 20:

13.

5. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, In S2, modified para-aramid and cellulose nanofibers are blended and dispersed in a composite solvent at a weight ratio of 100:(2-3).

6. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, In S3, the infrared light wavelength used for infrared curing is 2.5-4μm.

7. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, The infrared light power density used for infrared curing in the S3 is 1-3 kW / m 2 , and the irradiation distance is 10-20 cm.

8. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, In S3, infrared curing is performed using staged heating, specifically: first, the temperature is raised to 60-80℃ and processed for 30-60 seconds, and finally the temperature is raised to 100-120℃ and maintained for 60-180 seconds.

9. The method for preparing a semi-solid aramid membrane with high strength and high ionic conductivity according to claim 1, characterized in that, In S3, the temperature for hot pressing is 100-120℃ and the pressure is 0.5-1.0MPa.

10. An aramid separator obtained by the method for preparing a semi-solid aramid separator with high strength and high ionic conductivity as described in any one of claims 1-9, characterized in that, Tensile strength ≥180MPa.