Polyimide diaphragm as well as preparation method and application thereof

Abstract

The invention provides a polyimide diaphragm and a preparation method and application thereof.According to the polyimide diaphragm, through introduction of a BMIM structural unit, the thermal stability, electrolyte wettability and lithium ion conduction performance of the diaphragm are improved, meanwhile, the original mechanical strength of polyimide is kept, and the diaphragm can keep a stable structure in a high-temperature environment; the method is further applied to manufacturing of the lithium ion battery to ensure the safety of the battery; the preparation method is easy to operate and low in experimental environment requirement, the polyimide nanofiber membrane obtained through the electrostatic spinning process has high porosity and a three-dimensional zigzag pore structure, infiltration of an electrolyte is facilitated, direct perforation and passing of lithium dendrites are blocked, the permeation speed and retention amount of the electrolyte in the diaphragm can be increased, and the service life of the diaphragm is prolonged. The transmission efficiency of lithium ions is improved, so that the charge-discharge efficiency and the power density of the battery are improved; and in the long-term cycle process of the battery, expansion and shrinkage of an electrode material can be borne, and the cycle life of the battery is ensured.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a polyimide separator, its preparation method, and its application. Background Technology

[0002] In practical applications of lithium-ion batteries, the separator, as a key component, has a crucial impact on battery safety, charge / discharge efficiency, and cycle life. Currently, traditional polyolefin separators (such as polypropylene and polyethylene separators) have some significant drawbacks. First, their thermal stability is poor; they are prone to shrinkage and deformation at high temperatures, often leading to direct contact between the positive and negative electrodes, causing short circuits and seriously threatening battery safety. Second, traditional separators have poor electrolyte wettability, making it difficult for the electrolyte to fully penetrate the separator, thus affecting lithium-ion transport efficiency and reducing battery charge / discharge efficiency and power density. Furthermore, traditional separators have limited mechanical strength; during battery charge / discharge, the expansion and contraction of the electrode materials can easily damage the separator, further affecting the battery's cycle life.

[0003] While ordinary polyimide separators possess good thermal stability and mechanical strength, their lithium-ion conductivity still needs improvement. The chemical properties of their surface make their compatibility with the electrolyte less than ideal, and they are prone to interfacial reactions upon contact with the electrolyte, hindering lithium-ion migration within the separator and limiting the overall battery performance. Therefore, developing a separator with good thermal stability, high electrolyte wettability, high lithium-ion conductivity, and high mechanical strength is a pressing technical challenge in the current lithium-ion battery field. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a polyimide separator.

[0005] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned polyimide separator.

[0006] Another technical problem to be solved by the present invention is to provide the application of the above-mentioned polyimide separator.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A polyimide membrane, specifically a BMIM-based polyimide nanofiber membrane, has the structure shown in Formula I: Formula I, Where Ar is: .

[0008] Preferably, in the above-mentioned polyimide separator, Ar is: .

[0009] Preferably, in the above-mentioned polyimide separator, Ar is: .

[0010] Preferably, the above-mentioned polyimide membrane has a three-dimensional tortuous pore structure and a porosity ≥75%.

[0011] The above-mentioned method for preparing the polyimide membrane involves synthesizing a diamine monomer containing 1-butyl-3-methylimidazolium (BMIM), followed by low-temperature polymerization to obtain a polyamic acid solution, and then electrospinning to obtain the polyimide membrane. The reaction equation is as follows: .

[0012] Preferably, the preparation method of the above-mentioned polyimide separator includes the following specific steps: (1) Nucleophilic substitution reaction An acetonitrile solution of 1,4-dibromobutane was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol, K₂CO₃, and acetonitrile, using the mixed solution as the solvent. 1-5 ml of solvent was added per millimol of monomer. The reaction was carried out at 80-85 °C for 6-10 h. After the reaction, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine-containing monomer. (2) Ionization reaction and anion exchange reaction The bromodiamine monomer and 1-butylimidazole were added to a 100 ml round-bottom flask, and DMF (N,N-dimethylformamide) was added as a solvent. The reaction was carried out at 140-160 °C under a nitrogen atmosphere for 5-15 h. After the reaction was completed, a 0.5-1 M lithium perchlorate aqueous solution was added. After the reaction was completed, the mixture was extracted with dichloromethane and dried with magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain the diamine monomer containing 1-butyl-3-methylimidazole (BMIM). (3) Low-temperature polycondensation The diamine monomer prepared above was fully dissolved in a three-necked flask containing DMF solvent under mechanical stirring. The reaction system was placed in an ice-water bath for reaction, and the dianhydride monomer was added to the reaction system in batches. After stirring thoroughly for 3-6 hours, a light yellow, transparent, viscous polyamic acid (PAA) spinning solution was obtained. (4) Electrospinning and thermal imidization PAA nanofiber membranes were prepared by electrospinning a PAA spinning solution placed in a 20-30ml syringe. Specific parameters were set as follows: ambient temperature 22-25℃, ambient humidity 20-40%, spinning voltage 20-22kV, syringe advance speed 0.6-0.8ml / h, aluminum foil was used as the receiving substrate and adhered tightly to the receiving roller, the distance between the receiving roller and the syringe was 15-18cm, and the roller rotation speed was 430-450r / min. After continuous spinning for 10-12h, a white PAA nanofiber membrane was obtained. The PAA nanofiber membrane underwent thermal imidization under programmed temperature control with stretching forces at both ends. The specific temperature control process was as follows: the temperature was increased from room temperature to 100-110℃ over 0.5-1h and held for 2-3h to ensure complete solvent removal; then, the temperature was increased to 300-320℃ over 1-2h and held for 1-2h to ensure complete imidization, ultimately yielding a yellow PI nanofiber membrane.

[0013] Preferably, in the above-mentioned method for preparing the polyimide membrane, the molar ratio of 4,4'-bis(N,N-dimethylamino)diphenylmethanol:1,4-dibromobutane:K2CO3 in step (1) is 1:1-1.2:3-4.

[0014] Preferably, in the above-mentioned method for preparing the polyimide membrane, in step (3), 3-5 ml of DMF solvent is added per millimolar of diamine monomer.

[0015] Preferably, in the above-mentioned method for preparing the polyimide membrane, the molar ratio of dianhydride monomer to diamine monomer in step (3) is 1:1.

[0016] The above-mentioned polyimide separator is used in the manufacture of lithium-ion batteries.

[0017] Beneficial effects: The polyimide separator, through the introduction of BMIM (1-butyl-3-methylimidazolium) structural units, improves the separator's thermal stability, electrolyte wettability, and lithium-ion conductivity, while maintaining the original mechanical strength of polyimide. This allows the separator to maintain a stable structure at high temperatures, thus ensuring battery safety in lithium-ion battery manufacturing. Its preparation method employs a low-temperature polycondensation polymerization method, which is simple to operate and has low requirements for the experimental environment. The polyimide nanofiber membrane obtained through electrospinning has high porosity and a three-dimensional tortuous pore structure, which facilitates electrolyte wetting and prevents direct penetration of lithium dendrites. This increases the electrolyte penetration rate and retention in the separator, improves lithium-ion transport efficiency, and thus enhances the battery's charge / discharge efficiency and power density. Furthermore, during long-term battery cycling, it can withstand the expansion and contraction of electrode materials, ensuring the battery's cycle life. Specifically: (1) Good thermal stability: The modified polyimide separator has excellent thermal stability and can maintain a stable structure in high temperature environment. It is not easy to shrink and deform, which effectively avoids the problem of short circuit between positive and negative electrodes caused by high temperature and improves the safety performance of battery.

[0018] (2) High electrolyte wettability: BMIM-modified polyimide has good polarity and solubility, which can significantly improve the surface properties of the polyimide membrane, making it more compatible with the electrolyte. The modified membrane can quickly absorb the electrolyte and distribute it evenly inside the membrane, improving the electrolyte penetration rate and retention, and providing a good channel for lithium ion transport.

[0019] (3) High lithium-ion conductivity: The BMIM structure and its introduction of anions help to build a continuous lithium-ion conduction channel, reduce the transmission resistance of lithium ions in the separator, thereby improving the lithium-ion conductivity and enhancing the battery's charge and discharge efficiency and power density.

[0020] (4) Excellent mechanical strength and unique microstructure: Polyimide itself has high mechanical strength. The introduction of BMIM does not weaken its mechanical properties. On the contrary, it enhances the flexibility and tensile strength of the separator to a certain extent. During the charging and discharging process of the battery, the modified separator can withstand the expansion and contraction of the electrode materials and is not easy to break or be damaged, thus ensuring the cycle life of the battery.

[0021] (5) A methylimidazolium structure was introduced into the diamine monomer, and a diamine monomer with a para-anion was obtained through anion exchange reaction. The ether bond of this diamine monomer can effectively increase the electrospinnability of polyamic acid. By electrospinning technology, a nanofiber network structure with high specific surface area and high porosity can be prepared. This structure not only provides a large number of ion transport channels, but also effectively adsorbs electrolyte and reduces interfacial impedance. Attached Figure Description

[0022] Figure 1 The 1H NMR spectrum of the bromodiamine-containing monomer obtained in Example 1; Figure 2 The 1H NMR spectrum of the diamine monomer containing 1-butyl-3-methylimidazolium (BMIM) obtained in Example 1; Figure 3 The image shows the 1H NMR spectrum of the polyamic acid (PAA) obtained in Example 1. Figure 4 This is a scanning electron microscope image of the polyimide membrane obtained in Example 1. Detailed Implementation

[0023] The polyimide separator of the present invention, its preparation method, and its application are described in detail below with reference to embodiments and accompanying drawings.

[0024] Example 1 A polyimide separator has the following structure: .

[0025] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K₂CO₃ (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer, the 1H NMR spectrum of which is shown in [reference needed]. Figure 1 .

[0026] (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the sample was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM). Its 1H NMR spectrum is shown in [Figure number missing]. Figure 2 .

[0027] (3) 22.6 g and 0.046 mol of the diamine monomer prepared above were fully dissolved in a dry three-necked flask containing 230 ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 10.0 g and 0.046 mol of pyromellitic dianhydride (PMDA) were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20 ml of DMF solvent. After stirring thoroughly for 3 h, a pale yellow, transparent, viscous polyamic acid (PAA) spinning solution was obtained. The 1H NMR spectrum of polyamic acid is shown in [reference needed]. Figure 3 .

[0028] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization. Finally, a yellow PI nanofiber membrane (polyimide membrane) was obtained. The scanning electron microscope image is shown below. Figure 4 As shown, the diaphragm has a three-dimensional porous structure.

[0029] Example 2 A polyimide separator has the following structure: .

[0030] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (5.8 mmol, 1.24 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (19.2 mmol, 2.7 g), and 24 mL of acetonitrile. The reaction was carried out at 85 °C for 10 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 160 °C under a nitrogen atmosphere for 5 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0031] (3) 22.6g and 0.046mol of the diamine monomer prepared above were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. Then the three-necked flask was placed in an ice-water bath for reaction. 14.3g and 0.046mol of OPDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 6 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0032] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 30ml syringe. The specific parameters were set as follows: ambient temperature was 22℃, ambient humidity was 20%, spinning voltage was 22kV, syringe advance speed was 0.6ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 15cm, the roller speed was 430r / min, and after continuous spinning for 12h, a white PAA nanofiber membrane was obtained. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 110℃ for 1h and held for 2h to ensure complete removal of the solvent, and then raised to 320℃ for 1h and held for 1h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0033] Example 3 A polyimide separator has the following structure: .

[0034] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (5.3 mmol, 1.14 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K₂CO₃ (16.8 mmol, 2.3 g), and 24 mL of acetonitrile. The reaction was carried out at 83 °C for 8 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 150 °C under a nitrogen atmosphere for 10 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0035] (3) 22.6g and 0.046mol of the prepared diamine monomer were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 14.8g and 0.046mol of BTDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 6 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0036] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 25ml syringe. The specific parameters were set as follows: ambient temperature was 23℃, ambient humidity was 30%, spinning voltage was 21kV, syringe advance speed was 0.7ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 16cm, the roller speed was 440r / min, and spinning was continued for 11h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 105℃ in 0.8h and held for 2.5h to ensure complete removal of the solvent, and then raised to 310℃ in 1.5h and held for 1h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0037] Example 4 A polyimide separator has the following structure: .

[0038] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0039] (3) 22.6g and 0.046mol of the diamine monomer prepared above were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. Then the three-necked flask was placed in an ice-water bath for reaction. 20.4g and 0.046mol of 6FDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 3h, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0040] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0041] Example 5 A polyimide separator has the following structure: .

[0042] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0043] (3) 22.6g and 0.046 mol of the prepared diamine monomer were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 13.5g and 0.046mol of BPDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 3 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0044] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0045] Example 6 A polyimide separator has the following structure: .

[0046] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0047] (3) 22.6g and 0.046mol of the prepared diamine monomer were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 12.3g and 0.046mol of NTDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 3 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0048] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0049] Example 7 A polyimide separator has the following structure: .

[0050] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0051] (3) 22.6g and 0.046 mol of the prepared diamine monomer were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 10.3g and 0.046mol of PMDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 3 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0052] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0053] Example 8 A polyimide separator has the following structure: .

[0054] The above-mentioned polyimide membrane is obtained by the following preparation method: (1) 1,4-Dibromobutane (4.8 mmol, 1.04 g) was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol (4.8 mmol, 1.3 g), K2CO3 (14.4 mmol, 1.99 g), and 24 mL of acetonitrile. The reaction was carried out at 80 °C for 6 h. After the reaction was completed, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine monomer. (2) A 100 mL round-bottom flask was filled with a bromodiamine monomer (2.64 mmol, 0.92 g), 1-butylimidazole (5.28 mmol, 0.655 g), and 5 mL of N,N-dimethylformamide (DMF). The reaction was carried out at 140 °C under a nitrogen atmosphere for 15 h. The reaction was monitored by TLC. Anion exchange was performed using lithium perchlorate. After the reaction was completed, the mixture was extracted with dichloromethane and dried over magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain a diamine monomer containing 1-butyl-3-methylimidazole (BMIM).

[0055] (3) 22.6g and 0.046mol of the prepared diamine monomer were fully dissolved in a dry three-necked flask containing 230ml of DMF solvent under mechanical stirring. The three-necked flask was then placed in an ice-water bath for reaction. 16.4g and 0.046mol of DSDA were weighed and added to the reaction system in batches. After the last batch was added, the residual PMDA at the feed port of the three-necked flask was rinsed with 20ml of DMF solvent. After stirring for 3 hours, a light yellow transparent viscous polyamic acid (PAA) spinning solution was obtained.

[0056] (4) PAA nanofiber membranes were prepared by electrospinning the PAA spinning solution placed in a 20ml syringe. The specific parameters were set as follows: ambient temperature was 25℃, ambient humidity was 40%, spinning voltage was 20kV, syringe advance speed was 0.8ml / h, aluminum foil was used as the receiving substrate and was attached tightly to the receiving roller, the distance between the receiving roller and the syringe was 18cm, the roller speed was 450r / min, and spinning was continued for 10h to obtain a white PAA nanofiber membrane. The PAA nanofiber membrane was subjected to thermal imidization under programmed temperature control under the action of stretching force at both ends. The specific temperature control process was as follows: the temperature was raised from room temperature to 100℃ in 0.5h and held for 3h to ensure complete removal of the solvent, and then raised to 300℃ in 2h and held for 2h to ensure complete imidization, finally obtaining a yellow PI nanofiber membrane.

[0057] Example 9 The polyimide membranes obtained in the above embodiments were tested for thermal stability, porosity, and ionic conductivity.

[0058] Thermal stability test: Thermogravimetric analysis was used to characterize the mass change of the obtained diaphragm under gradually increasing temperature. The sample was vacuum dried at 100℃ and then tested in air atmosphere. The temperature range was set from room temperature to 800℃, and the heating rate was 5℃ / min. -1 .

[0059] Porosity test: Cut the diaphragm into 3... A 3 cm square sample was weighed and soaked in n-butanol for 2 hours. After wiping off the n-butanol from the diaphragm surface with filter paper, it was weighed again. The porosity was calculated using the following formula: Porosity = (W a / ρ a ) / ( W a / ρ a + W b / ρ b In the formula, W a and ρ a W represents the weight and density of n-butanol, respectively. b and ρ bThis represents the dry weight and density of the diaphragm, with weight measured in grams (g) and density in g / cm³. 3 .

[0060] Ionic conductivity testing: Characterization was performed using a CHI660 electrochemical workstation with a frequency range of 0.01-105 Hz and an amplitude voltage of 5 mV. The ionic conductivity of the membrane was calculated using the following formula: Ionic conductivity = d / R b In the formula ×S, d represents the thickness of the diaphragm, and R b S represents the volumetric internal resistance of the assembled membrane battery, where S represents the membrane area, thickness is in μm, volumetric internal resistance is in Ω, and area is in cm². 2 .

[0061] The test results are shown in Table 1.

[0062] Table 1

[0063] As shown in Table 1, the obtained polyimide membranes exhibit good thermal stability (their 5% mass decomposition temperatures are all greater than 380℃), large porosity (>75%), and high ionic conductivity (>0.7 mS / cm). -1 These advantages help improve the safety of the separator, promote the rapid migration of lithium ions at high current densities, and significantly improve the rate performance of the battery.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention. The construction steps of the structure of the present invention are not in any particular order. All improvements and modifications, such as structural modifications, made by those skilled in the art based on the method of the present invention or based on the method are considered to be within the scope of protection of the present invention.

Claims

1. A polyimide separator, characterized in that: It has the structure shown in Equation I: Formula I, Where Ar is: 。 2. The polyimide separator according to claim 1, characterized in that: The Ar is: 。 3. The polyimide separator according to claim 1, characterized in that: The Ar is: 。 4. The polyimide separator according to claim 1, characterized in that: It has a three-dimensional tortuous pore structure with a porosity of ≥75%.

5. A method for preparing the polyimide separator according to any one of claims 1-4, characterized in that: A diamine monomer containing 1-butyl-3-methylimidazolium was synthesized, and then a polyamic acid solution was obtained by low-temperature polymerization. The polyimide membrane was then obtained by electrospinning.

6. The method for preparing the polyimide separator according to claim 5, characterized in that: The specific steps are as follows: (1) Nucleophilic substitution reaction An acetonitrile solution of 1,4-dibromobutane was added dropwise to a mixed solution of 4,4'-bis(N,N-dimethylamino)diphenylmethanol, K₂CO₃, and acetonitrile, using the mixed solution as the solvent. 1-5 ml of solvent was added per millimol of monomer. The reaction was carried out at 80-85 °C for 6-10 h. After the reaction, the product was extracted with dichloromethane and water. The organic phases were combined and dried over anhydrous sodium sulfate. The product was purified by rotary evaporation and column chromatography to obtain a bromodiamine-containing monomer. (2) Ionization reaction and anion exchange reaction The bromine-containing diamine monomer and 1-butylimidazole were added to a round-bottom flask, and DMF was added as a solvent. The reaction was carried out at 140-160℃ under a nitrogen atmosphere for 5-15 h. After the reaction was completed, a 0.5-1 M lithium perchlorate aqueous solution was added. After the reaction was completed, the mixture was extracted with dichloromethane and dried with magnesium sulfate. Finally, the dichloromethane was removed by rotary evaporation to obtain the diamine monomer containing 1-butyl-3-methylimidazole. (3) Low-temperature polycondensation The diamine monomer prepared above was fully dissolved in a three-necked flask containing DMF solvent under mechanical stirring. The reaction system was placed in an ice-water bath for reaction, and the dianhydride monomer was added to the reaction system in batches. After stirring thoroughly for 3-6 hours, a light yellow, transparent, viscous PAA spinning solution was obtained. (4) Electrospinning and thermal imidization PAA nanofiber membranes were prepared by electrospinning a PAA spinning solution placed in a 20-30ml syringe. Specific parameters were set as follows: ambient temperature 22-25℃, ambient humidity 20-40%, spinning voltage 20-22kV, syringe advance speed 0.6-0.8ml / h, aluminum foil was used as the receiving substrate and adhered tightly to the receiving roller, the distance between the receiving roller and the syringe was 15-18cm, and the roller rotation speed was 430-450r / min. After continuous spinning for 10-12h, a white PAA nanofiber membrane was obtained. The PAA nanofiber membrane underwent thermal imidization under programmed temperature control with stretching forces at both ends. The specific temperature control process was as follows: the temperature was increased from room temperature to 100-110℃ over 0.5-1h and held for 2-3h to ensure complete solvent removal; then, the temperature was increased to 300-320℃ over 1-2h and held for 1-2h to ensure complete imidization, ultimately yielding a yellow PI nanofiber membrane.

7. The method for preparing the polyimide separator according to claim 6, characterized in that: In step (1), the molar ratio of 4,4'-bis(N,N-dimethylamino)diphenylmethanol:1,4-dibromobutane:K2CO3 is 1:1-1.2:3-4.

8. The method for preparing the polyimide separator according to claim 6, characterized in that: In step (3), 3-5 ml of DMF solvent is added for every millimole of diamine monomer.

9. The method for preparing the polyimide separator according to claim 6, characterized in that: In step (3), the molar ratio of dianhydride monomer to diamine monomer is 1:

1.

10. The use of the polyimide separator according to any one of claims 1-4 in the manufacture of lithium-ion batteries.

Images