A para-aramid lithium battery separator and its preparation method

Abstract

This application relates to the technical field of battery materials, and in particular to a para-aramid lithium battery separator and its preparation method. A para-aramid lithium battery separator includes a para-aramid slurry and a base film. The para-aramid slurry is coated on both sides of the base film to form a para-aramid coating. The para-aramid slurry includes the following raw materials in parts by weight: 20-40 parts of modified para-aramid polymer solution, 10-20 parts of nano-ceramic composite powder, and 10-18 parts of solvent. The nano-ceramic composite powder includes the following raw materials in parts by weight: 50-100 parts of nano-alumina, 8-12 parts of nano-zirconia, 0.3-0.8 parts of yttrium trioxide, 1-5 parts of magnesium nitrate hexahydrate, 0.1-1 parts of polyacrylic acid, 1-2 parts of ammonia, 1-3 parts of coupling agent, and 20-30 parts of silicon dioxide. This application, by adding nano-ceramic composite powder to the para-aramid slurry, enables the para-aramid separator to have better thermal stability and reduces the phenomenon of thermal shrinkage of the separator at high temperatures.

Description

Technical Field

[0001] This application relates to the technical field of battery materials, and in particular to a para-aramid lithium battery separator and its preparation method. Background Technology

[0002] In lithium-ion batteries, the separator is a crucial component, playing a vital role in isolating the positive and negative electrodes to prevent short circuits while ensuring smooth lithium-ion transport. Its performance directly determines the battery's safety, cycle life, and energy density. While traditional polyolefin separators possess certain mechanical properties, they are prone to rapid thermal shrinkage at high temperatures, which can lead to short circuits between the positive and negative electrodes and trigger thermal runaway. Para-aramid fibers, due to their high modulus, chemical resistance, and excellent high-temperature resistance, are considered ideal materials for high-safety lithium-ion battery separators. However, existing para-aramid lithium battery separators still face several technical bottlenecks in practical applications: First, insufficient thermal stability. Although aramid itself has excellent heat resistance, the separators made from it still suffer from high longitudinal thermal shrinkage under high-temperature conditions, failing to fully meet the stability requirements under high-power discharge or abnormal operating conditions. Second, mechanical property defects. The separator has poor tensile strength and is prone to breakage due to mechanical stress during battery assembly and charge-discharge cycles, affecting the integrity of the battery structure. Third, material solubility problems. Para-aramid molecules have strong hydrogen bonding, resulting in extremely poor solubility in conventional polar solvents, making its processing and preparation difficult. Therefore, overcoming the problems of insufficient thermal stability, mechanical property defects, and poor solubility of para-aramid lithium battery separators has become a key issue that urgently needs to be addressed in the current development of lithium-ion battery separator technology. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a para-aramid lithium battery separator and its preparation method.

[0004] In a first aspect, this application provides a para-aramid lithium battery separator, employing the following technical solution: A para-aramid lithium battery separator includes a para-aramid slurry and a base film. The para-aramid slurry is coated on both sides of the base film to form a para-aramid coating. The para-aramid slurry includes the following raw materials in parts by weight: 20-40 parts of modified para-aramid polymer liquid, 10-20 parts of nano-ceramic composite material powder, and 10-18 parts of solvent. The nano-ceramic composite material powder comprises the following raw materials in parts by weight: 50-100 parts of nano-alumina, 8-12 parts of nano-zirconia, 0.3-0.8 parts of yttrium trioxide, 1-5 parts of magnesium nitrate hexahydrate, 0.1-1 parts of polyacrylic acid, 1-2 parts of ammonia, 1-3 parts of coupling agent, and 20-30 parts of silicon dioxide.

[0005] By adopting the above technical solution, the raw materials are improved in this application by adding nano-ceramic composite material powder. The nano-ceramic composite material powder can be uniformly dispersed in the para-aramid slurry, further enhancing the bonding force between the para-aramid slurry and the base film, extending the strength and structural stability of the base film, thereby further improving the tensile strength, heat resistance, density and structural stability of the diaphragm.

[0006] Furthermore, the preparation method of the nano-ceramic composite material powder includes the following steps: Nano-zirconia, magnesium nitrate hexahydrate, polyacrylic acid, and yttrium oxide were mixed, and then nano-alumina was added and mixed again. Ammonia water was added and mixed, centrifuged, and dried to obtain powder. The powder is calcined once to obtain the powder material; The powder is calcined a second time; After the powder was calcined twice, it was mixed with silica and a coupling agent, centrifuged, and dried to obtain nano-ceramic composite material powder.

[0007] By adopting the above technical solution, this application uses nano-alumina and nano-zirconia as the main raw materials, and then mixes them with yttrium oxide, magnesium nitrate hexahydrate, polyacrylic acid and ammonia to prepare a mixture. The prepared mixture is then mixed with silicon dioxide under the action of a coupling agent, centrifuged and dried to prepare nano-ceramic composite material powder containing nano-alumina, nano-zirconia and silicon dioxide, thereby further improving the tensile strength, heat resistance, density and structural stability of the diaphragm.

[0008] Furthermore, when calcining the powder once, the calcination temperature is 1100-1400℃ and the calcination time is 1-3 hours.

[0009] Furthermore, when the powder is calcined a second time, the calcination temperature is 1500-1700℃ and the calcination time is 1.5-3.5 hours.

[0010] Furthermore, before the powder is calcined a second time, the powder is placed at 180-220MPa for 5-15 minutes and then pre-calcined at 1000-1200℃ for 0.5-1.5 hours.

[0011] Furthermore, the nano-ceramic composite material powder also includes 5-10 parts by weight of composite nano solid material.

[0012] Furthermore, the composite nano-solid material comprises the following raw materials in parts by weight: 15-20 parts of tetraethyl orthosilicate, 6-13 parts of ethanol, 1-5 parts of hydrochloric acid, and 0.1-1 parts of zirconium oxychloride.

[0013] By adopting the above technical solution, this application improves the raw materials by adding composite nano-solid materials. The added composite nano-solid materials can be uniformly dispersed in the para-aramid slurry, thereby further improving the heat resistance, tensile strength, density and structural stability of the diaphragm.

[0014] Furthermore, the preparation method of the composite nano-solid material includes the following steps: mixing tetraethyl orthosilicate, a first portion of ethanol, and hydrochloric acid; adding zirconium oxychloride and a second portion of ethanol; drying; and pulverizing to obtain the composite nano-solid material.

[0015] By adopting the above technical solution, this application uses tetraethyl orthosilicate and zirconium oxychloride as raw materials to prepare a composite nano-solid material containing zirconium dioxide and silicon dioxide. The prepared composite nano-solid material can be uniformly dispersed in para-aramid slurry, thereby further improving the heat resistance, mechanical strength, density and structural stability of the diaphragm.

[0016] Furthermore, the mass ratio of the first part of ethanol to the second part of ethanol is (5-10):(1-3).

[0017] Furthermore, the preparation method of the modified para-aramid polymer solution includes the following steps: Terephthaloyl chloride, p-phenylenediamine and a third monomer in a molar ratio of 10:(3-7):(3-7) were co-dispersed in a composite solvent and reacted to obtain a modified para-aramid polymer solution.

[0018] Furthermore, the third monomer comprises 4,4'-diaminodiphenyl ether and diamine adipate; the molar ratio of 4,4'-diaminodiphenyl ether and diamine adipate is (6-7):(3-4).

[0019] Furthermore, the composite solvent includes a 1-butyl-3-methylimidazolium chloride ionic liquid; the volume percentage of the 1-butyl-3-methylimidazolium chloride ionic liquid is 13-18% of the total volume of the composite solvent.

[0020] By adopting the above technical solution, this application uses terephthaloyl chloride, p-phenylenediamine and a third monomer to prepare a modified para-aramid polymer solution. The third monomer includes 4,4'-diaminodiphenyl ether, which can reduce the reaction rate and avoid excessive aggregation of high molecular weight segments of para-aramid. Meanwhile, 4,4'-diaminodiphenyl ether can disrupt the regularity of the para-aramid molecular chain. The ether bonds (-O-) in its molecule disrupt the completely para-symmetrical structure of the para-aramid backbone. Compared with the rigid p-phenylenediamine-terephthaloyl chloride segments of pure para-aramid, the flexibility of the ether bonds causes local twisting of the molecular chain, reducing the regularity of the molecular chain arrangement. At the same time, the introduction of 4,4'-diaminodiphenyl ether makes the hydrogen bond distribution uneven, reduces the hydrogen bond density per unit volume, and weakens the intermolecular forces. Furthermore, when 4,4'-diaminodiphenyl ether is added to the system, the crystallinity of para-aramid decreases and the crystal region size shrinks, making it easier for the solvent to penetrate into the interior of para-aramid. After modification with 4,4'-diaminodiphenyl ether, the proportion of amorphous regions of the para-aramid polymer increases, and solvent molecules can diffuse in smoothly, forming a solvation layer and gradually dissolving the para-aramid. The ether bonds of 4,4'-diaminodiphenyl ether generate dipole-dipole interactions with the carbonyl groups in the composite solvent, significantly increasing the binding energy and improving the compatibility between the polymer and the solvent. Overall, 4,4'-diaminodiphenyl ether significantly improves the solubility of para-aramid fibers in composite solvents through a triple mechanism: disrupting molecular chain regularity, reducing crystallinity, and enhancing solvent interactions.

[0021] This application incorporates adipic acid diamine into the third monomer, introducing a flexible amide bond monomer, which breaks the regularity of the para-aramid molecular chain, improves its solubility in composite solvents, and maintains the mechanical strength of the battery separator.

[0022] The preparation method of this application effectively improves the solubility of para-aramid in polar solvents by copolymerizing and modifying the ether-bonded third monomer, while maintaining electrochemical stability. At the same time, the application of the ionic liquid complex solvent system effectively destroys the original intermolecular hydrogen bond network of para-aramid, reduces crystallinity, and utilizes the stacking effect to generate competition, thereby increasing the molecular chain spacing of para-aramid and providing channels for solvent molecule penetration. Therefore, the prepared separator does not affect the battery's discharge capacity, and the battery's cycle life is also guaranteed.

[0023] Secondly, this application provides a method for preparing a para-aramid lithium battery separator, employing the following technical solution: A method for preparing a para-aramid lithium battery separator, comprising the following steps: Weigh out each ingredient according to the formula; Modified para-aramid polymer liquid, nano-ceramic composite material powder, and solvent are mixed to obtain para-aramid slurry. The para-aramid slurry is then coated on both sides of the base film. After coagulation, washing, and drying, the para-aramid lithium battery separator is obtained.

[0024] In summary, this application includes at least one of the following beneficial technical effects: This application discloses a para-aramid lithium battery separator and its preparation method. In this application, by improving the raw materials of the para-aramid slurry and adding nano-ceramic composite material powder to the para-aramid slurry, the para-aramid separator has better thermal stability, reducing the phenomenon of thermal shrinkage of the separator at high temperature, thereby improving the electrochemical stability of the lithium battery. At the same time, the separator prepared by this application will not affect the discharge capacity and cycle life of the battery. Detailed Implementation

[0025] The technical solutions of this application are further illustrated by specific embodiments below. These specific embodiments do not represent a limitation on the scope of protection of this application. Any non-essential modifications and adjustments made by others based on the concept of this application still fall within the scope of protection of this application.

[0026] All raw materials involved in this application are commercially available products, among which, Nano-alumina, 99.9% purity, purchased from Aladdin; Nano-zirconia, 99.95% purity, purchased from Wuxi Tuoboda Titanium Dioxide Products Co., Ltd. Polyacrylic acid, purchased from Sinopharm Chemical Reagent Co., Ltd.; The present application will be further described in detail below with reference to embodiments and comparative examples.

[0027] Preparation Example 1: The preparation method of nano-ceramic composite powder includes the following steps: (1) Preparation of composite nanomaterials: 18 kg of tetraethyl orthosilicate, 7 kg of ethanol, and 3 kg of hydrochloric acid were mixed to obtain a mixed solution. The mixed solution was heated and refluxed at 65°C for 2 hours. Then, 0.5 kg of zirconium oxychloride and 1.5 kg of ethanol were added and mixed. The mixture was heated and refluxed for another 2 hours, then dried and pulverized to obtain a composite nano-solid material.

[0028] (2) Preparation of nano-ceramic composite powder: Mix 10 kg of nano-zirconia, 3 kg of magnesium nitrate hexahydrate, 0.5 kg of polyacrylic acid, and 0.5 kg of yttrium oxide, then add 75 kg of nano-alumina and mix. Stir the mixture while slowly adding 1.5 kg of ammonia water dropwise, and monitor the pH value in real time with a pH meter to maintain the pH at 9-10. After the addition is complete, continue stirring for 2 hours, centrifuge, and dry at 50°C for 20 minutes to obtain powder. The dried powder was calcined at 1280℃ for 2 hours to obtain the powder material. After the powder was held under pressure at 200 MPa for 10 minutes, it was pre-calcined at 1100℃ for 1 hour, then heated to 1600℃ at 100℃ / min and calcined again at 1600℃ for 2.5 hours to obtain the powder after secondary calcination. 25 kg of silica, 50 L of water, and 200 L of ethanol were mixed to obtain a silica emulsion. After the powder was calcined twice, it was mixed with silica emulsion and 2 kg of silane coupling agent KH-570, centrifuged, dried, and then 7 kg of composite nano solid material was added and mixed to obtain nano ceramic composite material powder.

[0029] Preparation Example 2: The preparation method of nano-ceramic composite powder includes the following steps: (1) Preparation of composite nanomaterials: 15 kg of tetraethyl orthosilicate, 5 kg of ethanol, and 1 kg of hydrochloric acid were mixed to obtain a mixed solution. The mixed solution was heated and refluxed at 65°C for 2 hours. Then, 0.1 kg of zirconium oxychloride and 1 kg of ethanol were added and mixed. The mixture was heated and refluxed for another 2 hours, then dried and pulverized to obtain a composite nano-solid material.

[0030] (2) Preparation of nano-ceramic composite powder: Mix 8 kg of nano-zirconia, 1 kg of magnesium nitrate hexahydrate, 0.1 kg of polyacrylic acid, and 0.3 kg of yttrium oxide, then add 50 kg of nano-alumina and mix. Stir the mixture while slowly adding 1 kg of ammonia water dropwise, and monitor the pH value in real time with a pH meter to maintain the pH at 9-10. After the addition is complete, continue stirring for 2 hours, centrifuge, and dry at 50°C for 20 minutes to obtain powder. The dried powder was calcined at 1280℃ for 2 hours to obtain the powder material. After the powder was held under pressure at 200 MPa for 10 minutes, it was pre-calcined at 1100℃ for 1 hour, then heated to 1600℃ at 100℃ / min and calcined again at 1600℃ for 2.5 hours to obtain the powder after secondary calcination. 20 kg of silica, 40 L of water, and 120 L of ethanol were mixed to obtain a silica emulsion. After the powder was calcined twice, it was mixed with silica emulsion and 1 kg of silane coupling agent KH-570, centrifuged, dried, and then 5 kg of composite nano solid material was added and mixed to obtain nano ceramic composite material powder.

[0031] Preparation Example 3: The preparation method of nano-ceramic composite powder includes the following steps: (1) Preparation of composite nanomaterials: 20 kg of tetraethyl orthosilicate, 10 kg of ethanol, and 5 kg of hydrochloric acid were mixed to obtain a mixed solution. The mixed solution was heated and refluxed at 65°C for 2 hours. Then, 1 kg of zirconium oxychloride and 3 kg of ethanol were added and mixed. The mixture was heated and refluxed for another 2 hours, dried, and pulverized to obtain a composite nano-solid material.

[0032] (2) Preparation of nano-ceramic composite powder: 12 kg of nano-zirconia, 5 kg of magnesium nitrate hexahydrate, 1 kg of polyacrylic acid, and 0.8 kg of yttrium oxide were mixed together, and then 100 kg of nano-alumina was added and mixed. The mixture was stirred while 2 kg of ammonia water was slowly added dropwise. The pH value was monitored in real time with a pH meter and maintained at 9-10. After the addition was completed, the mixture was stirred for 2 hours, centrifuged, and dried at 50°C for 20 minutes to obtain powder. The dried powder was calcined at 1280℃ for 2 hours to obtain the powder material. After the powder was held under pressure at 200 MPa for 10 minutes, it was pre-calcined at 1100℃ for 1 hour, then heated to 1600℃ at 100℃ / min and calcined again at 1600℃ for 2.5 hours to obtain the powder after secondary calcination. 30 kg of silica, 60 L of water, and 240 L of ethanol were mixed to obtain a silica emulsion. After the powder was calcined twice, it was mixed with silica emulsion and 3 kg of silane coupling agent KH-570, centrifuged, dried, and then 10 kg of composite nano solid material was added and mixed to obtain nano ceramic composite material powder.

[0033] Example 1: A method for preparing a para-aramid lithium battery separator, comprising the following steps: S1. Preparation of modified para-aramid polymer solution: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 13:87 and stirred until homogeneous to obtain a composite solvent. Then, 7 mol of the third monomer (6 mol of 4,4'-diaminodiphenyl ether and 1 mol of adipate diamine) was added to the composite solvent and completely dissolved. Then, 3 mol of p-phenylenediamine was added and stirred until completely dissolved. The mixture was then cooled to -10°C. 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. After degassing with a vacuum pump, the modified para-aramid polymer solution was obtained.

[0034] S2. Preparation of para-aramid slurry: 30 kg of modified para-aramid polymer solution and 15 kg of nano-ceramic composite powder were mixed and stirred at 500 r / min for 30 min. Then, 14 kg of solvent (a composite of dimethylformamide and potassium chloride with a mass ratio of 1:0.5) was added and stirred at 500 r / min for 90 min to adjust the viscosity of the system to 2000 mPa·s. The mixture was then passed through a 350 mesh filter to obtain para-aramid slurry. The nano-ceramic composite powder was prepared according to Preparation Example 1.

[0035] S3. Preparation of battery separator: The para-aramid slurry was uniformly coated onto both sides of the base membrane using a coating machine. The membrane was then cured in a coagulation bath using an immersion-reverse method, washed with deionized water, and dried to obtain the para-aramid lithium battery separator.

[0036] Example 2: A method for preparing a para-aramid lithium battery separator, comprising the following steps: S1. Preparation of modified para-aramid polymer solution: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 13:87 and stirred until homogeneous to obtain a composite solvent. Then, 7 mol of the third monomer (6 mol of 4,4'-diaminodiphenyl ether and 1 mol of adipate diamine) was added to the composite solvent and completely dissolved. Then, 3 mol of p-phenylenediamine was added and stirred until completely dissolved. The mixture was then cooled to -10°C. 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. After degassing with a vacuum pump, the modified para-aramid polymer solution was obtained.

[0037] S2. Preparation of para-aramid slurry: 20 kg of modified para-aramid polymer solution and 10 kg of nano-ceramic composite powder were mixed and stirred at 500 r / min for 30 min. Then, 10 kg of solvent (a composite of dimethylformamide and potassium chloride with a mass ratio of 1:0.5) was added and stirred at 500 r / min for 90 min to adjust the viscosity of the system to 2000 mPa·s. The mixture was then passed through a 350 mesh filter to obtain para-aramid slurry. The nano-ceramic composite powder was prepared in Preparation Example 2.

[0038] S3. Preparation of battery separator: The para-aramid slurry was uniformly coated onto both sides of the base membrane using a coating machine. The membrane was then cured in a coagulation bath using an immersion-reverse method, washed with deionized water, and dried to obtain the para-aramid lithium battery separator.

[0039] Example 3: A method for preparing a para-aramid lithium battery separator, comprising the following steps: S1. Preparation of modified para-aramid polymer solution: Under nitrogen protection, 1-butyl-3-methylimidazolium chloride ionic liquid and DMAC were mixed at a volume ratio of 13:87 and stirred until homogeneous to obtain a composite solvent. Then, 7 mol of the third monomer (6 mol of 4,4'-diaminodiphenyl ether and 1 mol of adipate diamine) was added to the composite solvent and completely dissolved. Then, 3 mol of p-phenylenediamine was added and stirred until completely dissolved. The mixture was then cooled to -10°C. 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. After degassing with a vacuum pump, the modified para-aramid polymer solution was obtained.

[0040] S2. Preparation of para-aramid slurry: 40 kg of modified para-aramid polymer solution and 20 kg of nano-ceramic composite powder were mixed and stirred at 500 r / min for 30 min. Then, 18 kg of solvent (a composite of dimethylformamide and potassium chloride with a mass ratio of 1:0.5) was added and stirred at 500 r / min for 90 min to adjust the viscosity of the system to 2000 mPa·s. The mixture was then passed through a 350 mesh filter to obtain para-aramid slurry. The nano-ceramic composite powder was prepared in Preparation Example 3.

[0041] S3. Preparation of battery separator: The para-aramid slurry was uniformly coated onto both sides of the base membrane using a coating machine. The membrane was then cured in a coagulation bath using an immersion-reverse method, washed with deionized water, and dried to obtain the para-aramid lithium battery separator.

[0042] Example 4: The difference from Example 1 is that the nano-ceramic composite powder was prepared in Example 2.

[0043] Example 5: The difference from Example 1 is that the nano-ceramic composite powder was prepared by Example 3.

[0044] Example 6: The difference from Example 1 is that the amount of nano-ceramic composite material powder added is 10 kg when preparing the para-aramid slurry.

[0045] Example 7: The difference from Example 1 is that the amount of nano-ceramic composite material powder added is 20 kg when preparing the para-aramid slurry.

[0046] Example 8: The difference from Example 1 is that the amount of composite nano solid material added is 5 kg when preparing nano-ceramic composite powder.

[0047] Example 9: The difference from Example 1 is that the amount of composite nano solid material added is 10 kg when preparing nano-ceramic composite powder.

[0048] Comparative Example 1: The difference from Example 1 is that no nano-ceramic composite material powder is added when preparing the para-aramid slurry.

[0049] Comparative Example 2: The difference from Example 1 is that the amount of nano-ceramic composite material powder added is 9 kg when preparing the para-aramid slurry.

[0050] Comparative Example 3: The difference from Example 1 is that the amount of nano-ceramic composite material powder added is 21 kg when preparing the para-aramid slurry.

[0051] Comparative Example 4: The difference from Example 1 is that no composite nanomaterials are added when preparing nano-ceramic composite powder.

[0052] Comparative Example 5: The difference from Example 1 is that the amount of composite nano solid material added is 4 kg when preparing nano-ceramic composite powder.

[0053] Comparative Example 6: The difference from Example 1 is that the amount of composite nano solid material added is 11 kg when preparing nano-ceramic composite powder.

[0054] Performance testing: 1. Tensile strength: The diaphragm samples 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 to detect their tensile strength.

[0055] 2. Heat shrinkage rate test: The diaphragm samples obtained in the examples and comparative examples were heat-treated in an oven at 130°C for 60 minutes, and the change in diaphragm area before and after heat treatment was measured.

[0056] 3. Discharge capacity: The separators obtained in the examples and comparative examples were assembled into CR2032 button batteries in the order of positive electrode active material, electrolyte, separator, and lithium sheet. The batteries were then pressed together using a battery packaging machine and left to stand for more than 12 hours until the batteries were fully balanced. The discharge capacity of the samples was then tested on a battery testing system to test the discharge capacity at 3C.

[0057] 4. Battery capacity retention rate: The separators obtained in the examples and comparative examples were assembled into CR2032 button batteries in the order of positive electrode active material, electrolyte, separator, and lithium sheet. The batteries were then pressed together using a battery packaging machine and left to stand for more than 12 hours until the batteries were fully balanced. After that, charge-discharge cycle tests were performed on a battery testing system with a constant current rate of 1C and a charge-discharge cutoff voltage of 2.5-3.8V. The battery capacity retention rate was recorded after 100 cycles.

[0058] Table 1 Performance Test Table As shown in Table 1, the para-aramid lithium battery separator prepared in this application has good thermal stability, reducing the thermal shrinkage of the separator at high temperatures and thus improving the electrochemical stability of the lithium battery. Secondly, this application effectively improves the solubility of para-aramid in polar solvents by copolymerizing and combining it with an ether-bonded third monomer, while maintaining electrochemical stability. The separator prepared in this application does not affect the discharge capacity of the battery, and the battery cycle life is also guaranteed.

[0059] Based on the test results of Example 1 and Comparative Example 1, it can be seen that the tensile strength and thermal shrinkage rate of Example 1 are better than those of Comparative Example 1. This indicates that the addition of nano-ceramic composite material powder in this application effectively improves the thermal stability of the separator and effectively reduces the thermal shrinkage of the separator at high temperatures, thereby improving the electrochemical stability of the lithium battery. At the same time, the prepared separator does not affect the discharge capacity and capacity retention rate of the battery.

[0060] Based on the test results of Examples 1, 6, 7, Comparative Examples 2 and 3, it can be seen that the amount of nano-ceramic composite material powder added during the preparation of para-aramid slurry affects the tensile strength and thermal shrinkage rate of the diaphragm. Furthermore, the tensile strength and thermal shrinkage rate of the diaphragm are optimal when the amount of nano-ceramic composite material powder added is 10-20 kg.

[0061] As can be seen from Example 1 and Comparative Example 4, the tensile strength and thermal shrinkage rate of Example 1 are better than those of Comparative Example 4, indicating that the addition of composite nano-solid materials in this application effectively improves the thermal stability of the separator and effectively reduces the thermal shrinkage of the separator at high temperatures, thereby improving the electrochemical stability of the lithium battery; at the same time, the prepared separator does not affect the discharge capacity and capacity retention rate of the battery.

[0062] Based on the test results of Examples 1, 8, 9, Comparative Examples 5 and 6, it can be seen that the amount of composite nano-solid material added during the preparation of nano-ceramic composite powder affects the tensile strength and thermal shrinkage rate of the diaphragm. Furthermore, the tensile strength and thermal shrinkage rate of the diaphragm are optimal when the amount of composite nano-solid material added is 5-10 kg.

Claims

1. A para-aramid lithium battery separator, characterized in that: The product includes a para-aramid slurry and a base film. The para-aramid slurry is coated on both sides of the base film to form a para-aramid coating. The para-aramid slurry includes the following raw materials in parts by weight: 20-40 parts of modified para-aramid polymer liquid, 10-20 parts of nano-ceramic composite material powder, and 10-18 parts of solvent. The nano-ceramic composite material powder comprises the following raw materials in parts by weight: 50-100 parts of nano-alumina, 8-12 parts of nano-zirconia, 0.3-0.8 parts of yttrium trioxide, 1-5 parts of magnesium nitrate hexahydrate, 0.1-1 parts of polyacrylic acid, 1-2 parts of ammonia, 1-3 parts of coupling agent, and 20-30 parts of silicon dioxide; The preparation method of the nano-ceramic composite material powder includes the following steps: Nano-zirconia, magnesium nitrate hexahydrate, polyacrylic acid, and yttrium oxide were mixed, and then nano-alumina was added and mixed again. Ammonia water was added and mixed, centrifuged, and dried to obtain powder. The powder is calcined once to obtain the powder material; The powder is calcined a second time; After the powder was calcined twice, it was mixed with silica and coupling agent, centrifuged and dried to obtain nano-ceramic composite material powder. When the powder is calcined once, the calcination temperature is 1100-1400℃ and the calcination time is 1-3 hours; When the powder is calcined a second time, the calcination temperature is 1500-1700℃ and the calcination time is 1.5-3.5 hours. Before the powder is calcined a second time, it is placed at 180-220MPa for 5-15 minutes and then pre-calcined at 1000-1200℃ for 0.5-1.5 hours.

2. The para-aramid lithium battery separator according to claim 1, characterized in that: The nano-ceramic composite material powder also includes 5-10 parts by weight of composite nano solid materials.

3. The para-aramid lithium battery separator according to claim 2, characterized in that: The composite nanomaterial comprises the following raw materials in parts by weight: 15-20 parts of tetraethyl orthosilicate, 6-13 parts of ethanol, 1-5 parts of hydrochloric acid, and 0.1-1 parts of zirconium oxychloride.

4. The para-aramid lithium battery separator according to claim 3, characterized in that: The preparation method of the composite nano-solid material is as follows: Tetraethyl orthosilicate, a first portion of ethanol, and hydrochloric acid are mixed, zirconium oxychloride and a second portion of ethanol are added and mixed, and then dried to obtain the composite nano-solid material.

5. The para-aramid lithium battery separator according to claim 4, characterized in that: The mass ratio of the first part of ethanol to the second part of ethanol is (5-10):(1-3).

6. The para-aramid lithium battery separator according to claim 1, characterized in that: The preparation method of the modified para-aramid polymer liquid is as follows: terephthaloyl chloride, p-phenylenediamine and a third monomer in a molar ratio of 10:(3-7):(3-7) are co-dispersed in a composite solvent and reacted to obtain the modified para-aramid polymer liquid. The third monomer comprises 4,4'-diaminodiphenyl ether and adipate diamine; the molar ratio of 4,4'-diaminodiphenyl ether and adipate diamine is (6-7):(3-4). The composite solvent includes a chlorinated (1-butyl-3-methylimidazolium) ionic liquid; the volume percentage of the chlorinated (1-butyl-3-methylimidazolium) ionic liquid is 13-18% of the total volume of the composite solvent.

7. A method for preparing the para-aramid lithium battery separator according to any one of claims 1-6, characterized in that: The preparation method steps are as follows: Weigh out each ingredient according to the formula; Modified para-aramid polymer liquid, nano-ceramic composite material powder, and solvent are mixed to obtain para-aramid slurry. The para-aramid slurry is then coated on both sides of the base film. After coagulation, washing, and drying, the para-aramid lithium battery separator is obtained.

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