Lithium battery diaphragm and preparation method thereof

Abstract

The invention provides a lithium battery diaphragm and a preparation method thereof, and the preparation method comprises the following steps: carrying out a reaction on melamine and terephthalaldehyde in dimethyl sulfoxide to obtain SNW-1COF; the preparation method comprises the following steps: enabling SNW-1COF to react with allyl-1, 3-sultone in acetonitrile, so as to obtain allyl SCOF; the polyarylether benzimidazole, the 2-sulfydryl-5-fluorobenzimidazole, triethylamine and allyl SCOF are subjected to a reaction in a third solvent, and a membrane casting solution is obtained; and applying the membrane casting solution to a base material, and removing the solvent in the membrane casting solution to obtain the lithium battery diaphragm. According to the invention, the OPBI matrix and the propenyl SCOF react to form a covalent cross-linked network, so that the mechanical properties of the diaphragm in the aspects of thermal shrinkage rate, tensile strength, puncture strength and the like and the electrical properties in the aspects of wettability and ionic conductivity are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium battery separator and a preparation method thereof. Background Art

[0002] Lithium battery separators have a large number of tortuous micropores that can ensure the free passage of electrolyte ions to form a charge and discharge circuit. When the battery is overcharged or the temperature rises, the separator separates the positive and negative electrodes of the battery through its closed-pore function to prevent them from direct contact and short circuit, thereby blocking current conduction and preventing the battery from overheating or even explosion. Therefore, on the one hand, it is necessary to improve the electrical properties of the separator and improve energy efficiency. On the other hand, it is also necessary to improve the mechanical properties of the separator and reduce the probability of battery short circuit due to separator damage.

[0003] Currently, lithium-ion battery separators are mainly made of polyolefin materials. Due to poor thermal stability and poor wettability with electrolytes, this type of material cannot meet the requirements of high-performance and safer battery systems. In addition, batteries assembled with polyolefin separators experience severe lithium dendrite growth during service, which can easily pierce the separator and affect battery safety. Patent document CN202411403565.4 discloses a lithium-ion battery separator containing modified halloysite nanotubes. The separator is made of polybenzimidazole (OPBI) as a matrix and is doped with sulfonated lithiated halloysite nanotubes (sHNT-Li). Compared with polyolefin separators, the separator has improved heat resistance and electrical properties, but the mechanical properties of the separator still need to be improved. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a lithium battery separator and a preparation method thereof. The lithium battery separator has good electrical properties and is improved in thermal stability, mechanical strength, etc., which can improve the safety of the battery.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A lithium battery separator, the preparation method of which comprises the following steps:

[0007] S1: Melamine, terephthalaldehyde, and the first solvent (dimethyl sulfoxide) are mixed and heated to react with the melamine and terephthalaldehyde. After separation and drying, a light yellow solid product SNW-1COF is obtained;

[0008] S2: SNW-1COF, propenyl-1,3-sultone, and a second solvent (acetonitrile) are mixed and heated to react with propenyl-1,3-sultone. The white solid product, propenyl SCOF, is obtained after separation and drying.

[0009] S3: mixing poly(arylene ether benzimidazole), 2-mercapto-5-fluorobenzimidazole, triethylamine, propenyl SCOF, and a third solvent (NMP), and heating to allow 2-mercapto-5-fluorobenzimidazole to react with propenyl SCOF to obtain a casting solution;

[0010] S4: applying the casting solution to the substrate and removing the solvent in the casting solution to obtain a lithium battery separator.

[0011] The reaction mechanism of the present invention is as follows: under the catalysis of triethylamine, the thiol group (-SH) of 2-mercapto-5-fluorobenzimidazole is first deprotonated to generate a thiol anion (RS - ), followed by nucleophilic addition to the double bond of the propenyl SCOF, forming a carbon-sulfur bond and generating a carbanion intermediate. Due to the electron-withdrawing effect of the sultone group, the β-carbon atom of the double bond becomes the primary site of nucleophilic attack. Following the Markovnikov rule, the reaction is ultimately completed by proton transfer, with triethylamine regenerated and the catalytic cycle maintained. This eliminates the need for metal catalysts, achieving efficient and atom-economical thiol-ene addition.

[0012] Furthermore, in step S1, the amount of melamine is 12 to 15 parts by mass, and the amount of terephthalaldehyde is 40 to 75 parts by mass.

[0013] Furthermore, in the step S1, the heating reaction temperature is 150-180° C., and the reaction time is 60-90 h.

[0014] Furthermore, in step S1, the separation and drying steps are performed as follows: the solid mixture after the reaction is washed with acetone, DMF, and tetrahydrofuran, and then purified by a Soxhlet extractor with methanol solvent. The purified remaining solid product is collected and vacuum dried at 50-70°C for 11-14 hours to obtain SNW-1COF.

[0015] Furthermore, in the step S2, the amount of SNW-1COF is 6 to 10 parts by mass, and the amount of propenyl-1,3-sultone is 18 to 70 parts by mass.

[0016] Furthermore, in the step S2, the temperature of the heating reaction is 80-90° C., and the reaction time is 24-30 hours.

[0017] Furthermore, in the step S2, the separation and drying steps are performed as follows: the mixture after the reaction is completed is centrifuged to separate the solid product, the solid product is then washed with anhydrous acetone, and then the solid product is vacuum dried at 60-80° C. for 20-26 hours to obtain propenyl SCOF.

[0018] Furthermore, in the steps S1 and S2, the heating reactions are both carried out under a protective gas atmosphere.

[0019] Furthermore, the protective gas is one of nitrogen or argon.

[0020] Furthermore, in the step S3, the amount of polyarylether benzimidazole is 10-20 parts, the amount of 2-mercapto-5-fluorobenzimidazole is 0.3-0.9 parts, the amount of triethylamine is 2-4 parts, and the amount of propenyl SCOF is 0.8-3 parts, in parts by mass.

[0021] Furthermore, in the step S3, the reaction temperature is 80-90° C., and the reaction time is 12-20 h.

[0022] Furthermore, in the S3 step, polyarylether benzimidazole powder, 2-mercapto-5-fluorobenzimidazole, triethylamine solution and NMP are mixed to form a first solution, and propenyl SCOF nanoparticles are mixed with NMP to form a second solution. The first solution and the second solution are then mixed and heated to allow at least a portion of the 2-mercapto-5-fluorobenzimidazole to react with at least a portion of the propenyl SCOF to obtain a casting solution.

[0023] Furthermore, in the step S4, the operation of removing the solvent in the casting solution is as follows: the substrate applied with the casting solution is immersed in anhydrous methanol for 10 to 20 minutes, and then taken out and dried to obtain a lithium battery separator.

[0024] Furthermore, in the step S4, the drying process is performed as follows: first air-drying at room temperature for 1 to 2 hours, then vacuum drying at 50 to 70°C for 2 to 3 hours, and finally vacuum drying at 120°C for 4 to 7 hours to obtain a lithium battery separator.

[0025] The application of the present invention has the following beneficial effects:

[0026] 1. The present invention uses polyarylether benzimidazole as the main matrix of the lithium battery separator. The 2-mercapto-5-fluorobenzimidazole dispersed in the main matrix reacts with propenyl SCOF to form a covalent cross-linked network, constructing a high-temperature resistant skeleton structure with excellent dimensional stability at high temperatures, which can effectively avoid the risk of short circuit during thermal runaway of the battery.

[0027] 2. In the lithium battery separator provided by the present invention, the introduction of sultone groups enhances the membrane's wettability to the electrolyte. At the same time, the ion channels constructed through the thiol-ene cross-linking reaction improve the ionic conductivity, which is due to the continuous ion transmission path provided by the SCOF nanoparticles.

[0028] 3. In the lithium battery separator provided by the present invention, the propylene-based SCOF nanoparticles and the OPBI matrix are chemically bonded to form a reinforcing phase, which improves the tensile strength and puncture strength, and has excellent flexibility, which can meet the relevant standard requirements for lithium battery production.

[0029] 4. In the lithium battery separator provided by the present invention, the sulfonic acid group promotes uniform lithium deposition by electrostatically adsorbing lithium ions, thereby improving the cycle stability of the battery assembled with the composite membrane and effectively inhibiting the growth of lithium dendrites. DETAILED DESCRIPTION

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Example

[0032] Example 1

[0033] This embodiment provides a lithium battery separator, and the preparation method thereof is as follows:

[0034] S1: 12 g of melamine and 40 g of terephthalaldehyde were weighed by mass and added to 500 mL of dimethyl sulfoxide solution. The mixture was ultrasonically dispersed at room temperature at a frequency of 40 kHz, a power of 300 W, and a time of 30 min. The mixture was then heated under nitrogen at a temperature of 150°C for 60 h. After the reaction was completed, the mixture was cooled to room temperature. The solid mixture was washed with acetone, DMF, and tetrahydrofuran, and then purified by Soxhlet extraction with methanol. The remaining solid product was collected and dried in a vacuum oven at 60°C for 11 h to obtain SNW-1COF as a light yellow powder.

[0035] S2: 6 g of SNW-1COF and 18 g of propenyl-1,3-sultone were added to 1000 mL of acetonitrile solution, stirred continuously under nitrogen protection, and heated at 80°C for 24 h. After the reaction, the mixture was cooled to room temperature and then centrifuged at 3000 rpm for 10 min. The white precipitate was collected and washed several times with dry acetone. The precipitate was then placed in a vacuum oven and dried at 60°C for 20 h to obtain a white solid product, propenyl SCOF.

[0036] S3: 10 g of poly(arylene ether benzimidazole) powder, 0.3 g of 2-mercapto-5-fluorobenzimidazole, and 2 g of triethylamine were dissolved in 100 mL of NMP solution and stirred at 80°C for 20 h to obtain an OPBI solution; 0.8 g of propylene-based SCOF nanoparticles were dissolved in 40 mL of NMP and ultrasonically dispersed for 1.5 h to obtain a SCOF solution; the uniformly dispersed SCOF solution was poured into the OPBI solution and magnetically stirred at 80°C for 12 h to obtain a uniformly dispersed casting solution;

[0037] S4: The casting solution was allowed to stand at room temperature for 20 hours to degas, and then applied to a clean glass plate with a stainless steel scraper. The glass plate was immersed in an anhydrous methanol bath for 10 minutes. After being taken out of the immersion, it was air-dried at room temperature for 1 hour, transferred to a vacuum oven, dried at 50°C for 2 hours, and then heated to 120°C and dried for 4 hours to obtain a transparent and flexible lithium-ion separator.

[0038] Example 2

[0039] This embodiment provides a lithium battery separator, and the preparation method thereof is as follows:

[0040] S1: 13 g of melamine and 50 g of terephthalaldehyde were weighed by mass and added to 650 mL of dimethyl sulfoxide solution. Ultrasonic dispersion was performed at room temperature at a frequency of 40 kHz, a power of 300 W, and a time of 33 min. The mixture was then heated under nitrogen at a temperature of 160°C for 70 h. After the reaction was completed, the mixture was cooled to room temperature and washed with acetone, DMF, and tetrahydrofuran. The mixture was then purified by Soxhlet extraction with methanol solvent. The remaining solid product was collected and dried in a vacuum oven at 60°C for 12 h to obtain SNW-1COF as a light yellow powder.

[0041] S2: 7.5 g of SNW-1COF and 35 g of propenyl-1,3-sultone were added to 1300 mL of acetonitrile solution, and the mixture was stirred continuously under nitrogen protection. The mixture was heated at 85°C for 27 h. After the reaction, the mixture was cooled to room temperature and then centrifuged at 3250 rpm for 12 min. The white precipitate was collected and washed several times with dry acetone. The white precipitate was then placed in a vacuum oven and dried at 66°C for 22 h to obtain a white solid product, propenyl SCOF.

[0042] S3: 13 g of poly(arylene ether benzimidazole) powder, 0.5 g of 2-mercapto-5-fluorobenzimidazole, and 3 g of triethylamine were dissolved in 120 mL of NMP solution and stirred at 83 °C for 23 h to obtain an OPBI solution; 1.5 g of propylene-based SCOF nanoparticles were dissolved in 37 mL of NMP and ultrasonically dispersed for 1.3 h to obtain a SCOF solution; the uniformly dispersed SCOF solution was poured into the OPBI solution and magnetically stirred at 83 °C for 15 h to obtain a uniformly dispersed casting solution;

[0043] S4: The casting solution was allowed to stand at room temperature for 22 hours to degas, and then applied to a clean glass plate with a stainless steel scraper. The glass plate was immersed in an anhydrous methanol bath for 10 minutes. After being taken out of the immersion, it was air-dried at room temperature for 1.3 hours, transferred to a vacuum oven, dried at 50°C for 2.3 hours, and then heated to 120°C and dried for 5 hours to obtain a transparent and flexible lithium-ion separator.

[0044] Example 3

[0045] This embodiment provides a lithium battery separator, and the preparation method thereof is as follows:

[0046] S1: 14 g of melamine and 60 g of terephthalaldehyde were weighed by mass and added to 800 mL of dimethyl sulfoxide solution. Ultrasonic dispersion was performed at room temperature at a frequency of 40 kHz, a power of 300 W, and a time of 36 min. The mixture was then heated under nitrogen at a temperature of 170°C for 80 h. After the reaction was completed, the mixture was cooled to room temperature and washed with acetone, DMF, and tetrahydrofuran. The mixture was then purified by Soxhlet extraction with methanol solvent. The remaining solid product was collected and dried in a vacuum oven at 60°C for 11 h to obtain SNW-1COF as a light yellow powder.

[0047] S2: 9 g of SNW-1COF and 50 g of propenyl-1,3-sultone were added to 1000 mL of acetonitrile solution, stirred continuously under nitrogen protection, and heated at 90°C for 28 h. After the reaction, the mixture was cooled to room temperature and then centrifuged at 3600 rpm for 14 min. The white precipitate was collected and washed several times with dry acetone. The precipitate was then placed in a vacuum oven and dried at 72°C for 24 h to obtain a white solid product, propenyl SCOF.

[0048] S3: 16 g of poly(arylene ether benzimidazole) powder, 0.7 g of 2-mercapto-5-fluorobenzimidazole, and 3.5 g of triethylamine were dissolved in 140 mL of NMP solution and stirred at 87°C for 20 h to obtain an OPBI solution; 2.2 g of propylene-based SCOF nanoparticles were dissolved in 42 mL of NMP and ultrasonically dispersed for 1.6 h to obtain a SCOF solution; the uniformly dispersed SCOF solution was poured into the OPBI solution and magnetically stirred at 86°C for 18 h to obtain a uniformly dispersed casting solution;

[0049] S4: The casting solution was allowed to stand at room temperature for 24 hours to degas, and then applied to a clean glass plate with a stainless steel scraper. The glass plate was immersed in an anhydrous methanol bath for 16 minutes. After being taken out of the immersion, it was air-dried at room temperature for 1.6 hours, transferred to a vacuum oven, dried at 62°C for 2 hours, and then heated to 120°C and dried for 6 hours to obtain a transparent and flexible lithium-ion separator.

[0050] Example 4

[0051] This embodiment provides a lithium battery separator, and the preparation method thereof is as follows:

[0052] S1: 15 g of melamine and 75 g of terephthalaldehyde were weighed by mass and added to 1000 mL of dimethyl sulfoxide solution. Ultrasonic dispersion was performed at room temperature at a frequency of 40 kHz, a power of 300 W, and a time of 40 min. The mixture was then heated under nitrogen at a temperature of 180°C for 90 h. After the reaction was completed, the mixture was cooled to room temperature and washed with acetone, DMF, and tetrahydrofuran. The mixture was then purified by Soxhlet extraction with methanol solvent. The remaining solid product was collected and dried in a vacuum oven at 60°C for 14 h to obtain SNW-1COF as a light yellow powder.

[0053] S2: 10 g of SNW-1COF and 70 g of propenyl-1,3-sultone were added to 2000 mL of acetonitrile solution, and the mixture was stirred continuously under nitrogen protection. The mixture was heated at 90°C for 30 h. After the reaction, the mixture was cooled to room temperature and then centrifuged at 4000 rpm for 15 min. The white precipitate was collected and washed several times with dry acetone. The precipitate was then placed in a vacuum oven and dried at 80°C for 26 h to obtain a white solid product, propenyl SCOF.

[0054] S3: 20 g of poly(arylene ether benzimidazole) powder, 0.9 g of 2-mercapto-5-fluorobenzimidazole, and 2 g of triethylamine were dissolved in 150 mL of NMP solution and stirred at 90°C for 30 h to obtain an OPBI solution; 3 g of propylene-based SCOF nanoparticles were dissolved in 50 mL of NMP and ultrasonically dispersed for 2 h to obtain a SCOF solution; the uniformly dispersed SCOF solution was poured into the OPBI solution and magnetically stirred at 90°C for 20 h to obtain a uniformly dispersed casting solution;

[0055] S4: The casting solution was allowed to stand at room temperature for 26 hours to degas, and then applied to a clean glass plate with a stainless steel scraper. The glass plate was immersed in an anhydrous methanol bath for 20 minutes. After being taken out of the immersion, it was air-dried at room temperature for 2 hours, transferred to a vacuum oven, dried at 70°C for 3 hours, and then heated to 120°C and dried for 7 hours to obtain a transparent and flexible lithium-ion separator.

[0056] Comparative Example 1

[0057] This comparative example provides a lithium battery separator, and its preparation method is the same as that of Example 1, except that 2-mercapto-5-fluorobenzimidazole is not added in step S3, and the amount of polyarylether benzimidazole powder is 10.3 g.

[0058] Comparative Example 2

[0059] This comparative example provides a lithium battery separator, and its preparation method is as follows:

[0060] S1: 10 g of poly(arylene ether benzimidazole) powder was dissolved in 100 mL of NMP solution and stirred at 80 °C for 20 h to obtain OPBI solution. OPBI was magnetically stirred at 80 °C for 12 h and used as a casting solution.

[0061] S2: The casting solution was allowed to stand at room temperature for 20 hours to degas, and then applied to a clean glass plate with a stainless steel scraper. The glass plate was immersed in an anhydrous methanol bath for 10 minutes. After being taken out of the immersion, it was air-dried at room temperature for 1 hour, transferred to a vacuum oven, dried at 50°C for 2 hours, and then heated to 120°C and dried for 4 hours to obtain a transparent and flexible lithium-ion separator.

[0062] The performance tests of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0063] Thickness: The test refers to the method in standard GB / T6672-2001.

[0064] Porosity test: The dried composite membrane was immersed in n-butanol for 2 hours, and its porosity P was calculated as follows: P = (W1-W O ) / ρ b V b *100%, where W1 is the weight of the membrane after immersion, W O is the weight of the dry composite film, ρ b is the density of n-butanol, V b is the volume of the dried composite membrane. All the membranes were cut into rectangles with a length of 2 cm and a width of 1 cm, and the thickness was measured to calculate the volume.

[0065] Contact angle: 20 μL of electrolyte was dropped onto the surface of a circular diaphragm with a diameter of 17 mm using a pipette, and the surface wetting was recorded. The contact angle (CA) of the diaphragm at room temperature was recorded using the sessile drop method using a contact angle meter to obtain the electrolyte wettability of the diaphragm.

[0066] Liquid absorption rate: The weighing method is used to test the liquid absorption rate of the composite membrane. First, the weight of the composite membrane before being immersed in the electrolyte is weighed. After it is immersed in the electrolyte for 2 hours, the weight of the composite membrane after being immersed in the electrolyte is weighed. The liquid absorption rate of the membrane is calculated by comparing the weight change of the composite membrane before and after immersion. The specific calculation formula is X=(m-m0) / m0*100%.

[0067] Thermal stability: Take a 10cm×10cm composite film sample and place it flat on one of the quantitative filter papers on the stainless steel plate in the middle of a blast thermostatic chamber. Press it down with another piece of quantitative filter paper, close the thermostatic chamber door, start counting the time, and keep it at 150°C for 1 hour. After heating, take out the film and measure the longitudinal and transverse marked lengths after the film returns to room temperature. Thermal shrinkage rate = (film area before heating - film area after heating) / film area before heating * 100%.

[0068] The tensile strength and puncture strength are tested in accordance with the relevant provisions of GB / T36363-2018.

[0069] Ionic conductivity: The ionic conductivity (σ) of the membrane impregnated with electrolyte was measured by EIS using a CHI660E electrochemical workstation in a two-electrode system between SS. The membrane / electrolyte system was sandwiched between SS symmetrical electrodes at an AC amplitude of 10 mV and a 1-10 5 The test is conducted at a frequency of Hz. The formula for calculating ionic conductivity is: σ (mScm -1 ) = d / (Rb*S), where d is the film thickness (μm); R is the film resistance (Ω); S is the film area cut during the test (cm 2 ).

[0070] Cyclic performance test

[0071] Lithium metal batteries were prepared: lithium iron phosphate (LiFePO4) was selected as the positive electrode material, and high-purity lithium metal was used as the negative electrode. The electrolyte consisted of 1M LiPF6 dissolved in EC / DMC / EMC (1:1:1, volume ratio), with 2 wt.% fluoroethylene carbonate (FEC) added as an additive. First, lithium iron phosphate, Super P conductive agent, and PVDF binder were mixed in a mass ratio of 80:10:10, and an appropriate amount of NMP was added to prepare a slurry. The slurry was evenly coated on aluminum foil, vacuum-dried at 80°C for 12 hours, and then cut into 14 mm diameter discs for use as the positive electrode. The negative electrode used was 50 μm thick lithium metal foil, cut into 16 mm diameter discs. The battery was assembled in an Ar atmosphere glove box in the following order: negative electrode (lithium metal) → separator → positive electrode → injection of 40 μL of electrolyte → packaging in a CR2032 battery case. After assembly, the battery was allowed to stand at room temperature for 12 hours to ensure complete electrolyte penetration of the electrodes and separator.

[0072] The constant current charge and discharge specific capacity of lithium-ion batteries was evaluated using the Blue Power Battery Testing System at a rate of 0.5 C and a voltage range of 2.7-4.2 V. The coulombic efficiency of the battery was tested when the charge and discharge cycle was 200 times.

[0073] Table 1 Group Thickness (μm) Porosity (%) Contact angle (°) Liquid absorption rate (%) Thermal shrinkage (150℃, 1h) Tensile strength (MPa) Puncture strength (N / μm) Ionic conductivity (σ) Coulomb efficiency after 200 cycles (% Example 1 24 60 12.9 308 0.04% 17.3 0.68 1.28 99 Example 2 26 65 9.8 352 0.03% 20.8 0.75 1.47 99 Example 3 26 68 7.5 380 0.02% 24.7 0.82 1.53 99 Example 4 27 72 5.9 428 0.01% 29.5 0.91 1.76 99 Comparative Example 1 24 55 15.3 308 0.08% 12.4 0.52 0.97 95 Comparative Example 2 25 43 18.8 275 1% 5.7 0.39 0.392 90

[0074] According to the experimental results shown in Table 1, compared with the comparative example, using OPBI as the matrix, by forming a covalent cross-linked network with propylene SCOF, the mechanical properties of the lithium battery separator in terms of thermal shrinkage, tensile strength and puncture strength can be improved. At the same time, the thickness of the separator is slightly increased. Compared with the increase in the thickness of the separator, the increase in its mechanical properties is significantly higher. Therefore, the improvement in the physical properties is not simply caused by the increase in the thickness of the separator, and the lithium battery separator also has obvious improvements in wettability, ionic conductivity and cycle stability. As the proportion of propylene SCOF added gradually increases, the above-mentioned electrical properties also tend to improve.

[0075] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a lithium battery separator, characterized in that: The following steps are involved: S1: Melamine, terephthalaldehyde, and dimethyl sulfoxide are mixed and heated to react with melamine and terephthalaldehyde, followed by separation and drying to obtain a light yellow solid product, SNW-1COF; S2: SNW-1COF, propenyl-1,3-sultone, and acetonitrile are mixed and heated to react with propenyl-1,3-sultone, followed by separation and drying to obtain a white solid product, propenyl SCOF; S3: mixing poly(arylene ether benzimidazole), 2-mercapto-5-fluorobenzimidazole, triethylamine, propenyl SCOF, and NMP, and heating to allow 2-mercapto-5-fluorobenzimidazole to react with propenyl SCOF to obtain a casting solution; S4: applying the casting solution to the substrate and removing the solvent in the casting solution to obtain a lithium battery separator.

2. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S1, the amount of melamine is 12 to 15 parts by mass, and the amount of terephthalaldehyde is 40 to 75 parts by mass.

3. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S1, the heating reaction temperature is 150-180° C., and the reaction time is 60-90 h.

4. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S2, the amount of SNW-1COF is 6 to 10 parts by mass, and the amount of propenyl-1,3-sultone is 18 to 70 parts by mass.

5. The method for preparing a lithium battery separator according to claim 1, wherein: Furthermore, in the step S2, the heating reaction temperature is 80-90° C., and the reaction time is 24-30 h.

6. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S3, the amount of polyarylether benzimidazole is 10-20 parts, the amount of 2-mercapto-5-fluorobenzimidazole is 0.3-0.9 parts, the amount of triethylamine is 2-4 parts, and the amount of propenyl SCOF is 0.8-3 parts, in parts by mass.

7. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S3, poly(arylene ether benzimidazole) powder, 2-mercapto-5-fluorobenzimidazole, triethylamine solution and NMP are mixed to form a first solution, and propenyl SCOF nanoparticles are mixed with NMP to form a second solution. The first solution and the second solution are then mixed and heated to allow 2-mercapto-5-fluorobenzimidazole and propenyl SCOF to undergo an addition reaction to obtain a casting solution.

8. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S3, the reaction temperature is 80-90° C., and the reaction time is 12-20 h.

9. The method for preparing a lithium battery separator according to claim 1, wherein: In the step S4, the operation of removing the solvent in the casting solution is as follows: the substrate coated with the casting solution is immersed in anhydrous methanol for 10 to 20 minutes, and then taken out and dried to obtain a lithium battery separator.

10. A lithium battery separator, characterized in that: Prepared by the method according to any one of claims 1 to 9.