A lithium battery separator and a method of making the same

Abstract

This invention provides a lithium-ion battery separator and its preparation method. The preparation method includes the following steps: melamine and terephthalaldehyde react in dimethyl sulfoxide to obtain SNW-1COF; SNW-1COF reacts with propylene-1,3-sulfonyl lactone in acetonitrile to obtain propylene-based SCOF; polyarylene ether benzimidazole, 2-mercapto-5-fluorobenzimidazole, triethylamine, and propylene-based SCOF react in a third solvent to obtain a casting solution; the casting solution is applied to a substrate, and the solvent in the casting solution is removed to obtain the lithium-ion battery separator. This invention improves the mechanical properties of the separator, such as thermal shrinkage, tensile strength, and puncture strength, as well as its electrical properties, such as wettability and ionic conductivity, by forming a covalent crosslinked network through the reaction of an OPBI matrix with propylene-based SCOF.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a lithium battery separator and its preparation method. Background Technology

[0002] Lithium-ion battery separators have numerous interconnected micropores that allow electrolyte ions to pass freely and form a charging and discharging circuit. When the battery is overcharged or the temperature rises, the separator separates the positive and negative electrodes through its pore-closing function to prevent them from directly contacting each other and short-circuiting. This helps to block current conduction and prevent the battery from overheating or even exploding. Therefore, it is necessary to improve the electrical performance of the separator to increase energy efficiency, and also to improve its mechanical properties to reduce the probability of short circuits caused by separator damage.

[0003] Currently, lithium-ion battery separators are mainly made of polyolefin materials. These materials suffer from poor thermal stability and poor wettability with electrolytes, making them unsuitable for high-performance and safer battery systems. Furthermore, batteries assembled with polyolefin separators experience severe lithium dendrite growth during service, which can easily puncture the separator and compromise battery safety. Patent application CN202411403565.4 discloses a lithium-ion battery separator containing modified halloysite nanotubes. This separator uses polybenzimidazole (OPBI) as a matrix and dops it with sulfonated lithium halloysite nanotubes (sHNT-Li). Compared to polyolefin separators, this separator shows improvements in heat resistance and electrical performance, but its mechanical properties still need further improvement. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a lithium battery separator and its preparation method. The lithium battery separator exhibits excellent electrical properties and improvements in thermal stability and mechanical strength, thereby enhancing battery safety.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

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

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

[0008] S2: Mix SNW-1COF, propenyl-1,3-sulfonyl lactone and a second solvent (acetonitrile), heat to react SNW-1COF with propenyl-1,3-sulfonyl lactone, separate and dry to obtain a white solid product propenyl SCOF;

[0009] S3: Mix polyarylene ether benzimidazole, 2-mercapto-5-fluorobenzimidazole, triethylamine, propenyl SCOF and a third solvent (NMP), and heat to react 2-mercapto-5-fluorobenzimidazole with propenyl SCOF to obtain a casting solution;

[0010] S4: Apply the casting solution to the substrate and remove the solvent from the casting solution to obtain the lithium battery separator.

[0011] The reaction mechanism of this invention is as follows: Under triethylamine catalysis, the thiol group (-SH) of 2-mercapto-5-fluorobenzimidazole is first deprotonated to generate a thiolate anion (RS). - Subsequently, the sulfonyl group attacks the double bond of the SCOF group via nucleophilic addition, forming a carbon-sulfur bond and generating a carbanion intermediate. Due to the electron-withdrawing effect of the sulfonyl lactone group, the β-carbon atom of the double bond becomes the main site for nucleophilic attack. Following the Markovnikov rule, the reaction is ultimately completed via proton transfer. Triethylamine is regenerated and maintains the catalytic cycle, eliminating the need for a metal catalyst and achieving highly efficient and atom-economical thiol-olefin addition.

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

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

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

[0015] Further, in step S2, by mass parts, SNW-1COF is 6 to 10 parts and propylene-1,3-sulfonyl lactone is 18 to 70 parts.

[0016] Furthermore, in step S2, the heating temperature is 80~90℃ and the reaction time is 24~30h.

[0017] Further, in 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, and then the solid product is washed with anhydrous acetone. Subsequently, the solid product is vacuum dried at 60~80℃ for 20~26h to obtain propylene-based SCOF.

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

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

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

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

[0022] Further, in step S3, polyarylene ether benzimidazole powder, 2-mercapto-5-fluorobenzimidazole, triethylamine solution and NMP are mixed to form a first solution, and propylene-based 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 undergo an addition reaction with at least a portion of the propylene-based SCOF, thereby obtaining a casting solution.

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

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

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

[0026] 1. This invention uses polyarylene ether benzimidazole as the main matrix of 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 short-circuit risk during battery thermal runaway.

[0027] 2. In the lithium battery separator provided by the present invention, the introduction of sulfonyl lactone groups enhances the separator's wettability to the electrolyte. At the same time, the ion channels constructed through the thiol-ene crosslinking reaction improve the ion conductivity, which benefits from the continuous ion transport path provided by SCOF nanoparticles.

[0028] 3. In the lithium battery separator provided by the present invention, propylene-based SCOF nanoparticles and OPBI matrix form a reinforcing phase through chemical bonding, which improves tensile strength and puncture strength, and has excellent flexibility, thus meeting the relevant standard requirements for lithium battery production.

[0029] 4. In the lithium battery separator provided by the present invention, the sulfonic acid groups promote uniform lithium deposition by electrostatically adsorbing lithium ions, which makes the battery assembled by the composite membrane more stable in cycle and effectively inhibits the growth of lithium dendrites. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example

[0032] Example 1

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

[0034] S1: Weigh 12g of melamine and 40g of terephthalaldehyde according to the mass fraction and add them to 500mL of dimethyl sulfoxide solution. Disperse the mixture by ultrasound at room temperature. The frequency of ultrasound treatment is 40kHz, the power is 300W, and the time is 30min. Then, heat the mixture under nitrogen protection at 150℃ for 60h. After the reaction is completed, cool it to room temperature. Take the solid mixture after the reaction and wash it with acetone, DMF and tetrahydrofuran. Then purify it with methanol solvent through a Soxhlet extractor. Collect the purified solid product and place it in a vacuum oven to dry at 60℃ for 11h to obtain a light yellow powder SNW-1COF.

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

[0036] S3: Take 10g of polyarylene ether benzimidazole powder, 0.3g of 2-mercapto-5-fluorobenzimidazole and 2g of triethylamine, dissolve them in 100mL of NMP solution, and stir at 80℃ for 20h to obtain OPBI solution; take 0.8g of propylene-based SCOF nanoparticles, dissolve them in 40mL of NMP, and ultrasonically disperse them for 1.5h to obtain SCOF solution; pour the uniformly dispersed SCOF solution into OPBI solution, and magnetically stir at 80℃ for 12h to finally obtain a uniformly dispersed casting solution;

[0037] S4: Let the casting solution stand at room temperature for 20 hours to remove bubbles, then scrape it onto a clean glass plate with a stainless steel scraper. Immerse the glass plate in an anhydrous methanol bath for 10 minutes, remove it and air dry at room temperature for 1 hour. Transfer it to a vacuum oven and dry at 50°C for 2 hours. Then raise the temperature to 120°C and dry for 4 hours to obtain a transparent and flexible lithium-ion separator.

[0038] Example 2

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

[0040] S1: Weigh 13g of melamine and 50g of terephthalaldehyde according to the mass fraction and add them to 650mL of dimethyl sulfoxide solution. Disperse the mixture by ultrasonication at room temperature. The ultrasonic treatment frequency is 40kHz, the power is 300W, and the time is 33min. Then, heat the mixture under nitrogen protection at 160℃ for 70h. After the reaction is completed, cool it to room temperature and wash it with acetone, DMF and tetrahydrofuran. Then purify it with methanol solvent through a Soxhlet extractor. Collect the purified solid product and place it in a vacuum oven to dry at 60℃ for 12h to obtain a light yellow powder SNW-1COF.

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

[0042] S3: Take 13g of polyarylene ether benzimidazole powder, 0.5g of 2-mercapto-5-fluorobenzimidazole and 3g of triethylamine, dissolve them in 120mL of NMP solution, and stir at 83℃ for 23h to obtain OPBI solution; take 1.5g of propylene-based SCOF nanoparticles, dissolve them in 37mL of NMP, and ultrasonically disperse them for 1.3h to obtain SCOF solution; pour the uniformly dispersed SCOF solution into OPBI solution, and magnetically stir at 83℃ for 15h to finally obtain a uniformly dispersed casting solution;

[0043] S4: Let the casting solution stand at room temperature for 22 hours to remove bubbles, then scrape it onto a clean glass plate with a stainless steel scraper. Immerse the glass plate in an anhydrous methanol bath for 10 minutes, remove it and air dry at room temperature for 1.3 hours. Transfer it to a vacuum oven and dry at 50°C for 2.3 hours. Then raise the temperature to 120°C and dry for 5 hours to obtain a transparent and flexible lithium-ion separator.

[0044] Example 3

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

[0046] S1: Weigh 14g of melamine and 60g of terephthalaldehyde according to the mass fraction and add them to 800mL of dimethyl sulfoxide solution. Disperse the mixture by ultrasonication at room temperature. The ultrasonic treatment frequency is 40kHz, the power is 300W, and the time is 36min. Then, heat the mixture under nitrogen protection at a reaction temperature of 170℃ for 80h. After the reaction is completed, cool the mixture to room temperature and wash it with acetone, DMF and tetrahydrofuran. Then purify it with methanol solvent through a Soxhlet extractor. Collect the purified solid product and place it in a vacuum oven to dry at 60℃ for 11h to obtain a light yellow powder SNW-1COF.

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

[0048] S3: Take 16g of polyarylene ether benzimidazole powder, 0.7g of 2-mercapto-5-fluorobenzimidazole and 3.5g of triethylamine, dissolve them in 140mL of NMP solution, and stir at 87℃ for 20h to obtain OPBI solution; take 2.2g of propylene-based SCOF nanoparticles, dissolve them in 42mL of NMP, and ultrasonically disperse them for 1.6h to obtain SCOF solution; pour the uniformly dispersed SCOF solution into OPBI solution, and magnetically stir at 86℃ for 18h to finally obtain a uniformly dispersed casting solution;

[0049] S4: Let the casting solution stand at room temperature for 24 hours to remove bubbles, then scrape it onto a clean glass plate with a stainless steel scraper. Immerse the glass plate in an anhydrous methanol bath for 16 minutes, remove it and air dry at room temperature for 1.6 hours. Transfer it to a vacuum oven and dry at 62°C for 2 hours. Then raise the temperature to 120°C and dry for 6 hours to obtain a transparent and flexible lithium-ion separator.

[0050] Example 4

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

[0052] S1: Weigh 15g of melamine and 75g of terephthalaldehyde according to the mass fraction and add them to 1000mL of dimethyl sulfoxide solution. Disperse the mixture by ultrasonication at room temperature. The ultrasonic treatment frequency is 40kHz, the power is 300W, and the time is 40min. Then, heat the mixture under nitrogen protection at a reaction temperature of 180℃ for 90h. After the reaction is completed, cool the mixture to room temperature and wash it with acetone, DMF, and tetrahydrofuran. Then purify it with methanol solvent through a Soxhlet extractor. Collect the purified solid product and place it in a vacuum oven to dry at 60℃ for 14h to obtain a light yellow powder SNW-1COF.

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

[0054] S3: Take 20g of polyarylene ether benzimidazole powder, 0.9g of 2-mercapto-5-fluorobenzimidazole and 2g of triethylamine, dissolve them in 150mL of NMP solution, and stir at 90℃ for 30h to obtain OPBI solution; take 3g of propylene-based SCOF nanoparticles, dissolve them in 50mL of NMP, and ultrasonically disperse them for 2h to obtain SCOF solution; pour the uniformly dispersed SCOF solution into OPBI solution, and magnetically stir at 90℃ for 20h to finally obtain a uniformly dispersed casting solution;

[0055] S4: Let the casting solution stand at room temperature for 26 hours to remove bubbles, then scrape it onto a clean glass plate with a stainless steel scraper. Immerse the glass plate in an anhydrous methanol bath for 20 minutes, remove it and air dry at room temperature for 2 hours. Transfer it to a vacuum oven and dry at 70°C for 3 hours. Then raise the temperature to 120°C and dry 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, which is prepared according to Example 1, except that 2-mercapto-5-fluorobenzimidazole is not added in step S3, and the amount of polyarylene ether benzimidazole powder is 10.3g.

[0058] Comparative Example 2

[0059] This comparative example provides a lithium battery separator, the preparation method of which is as follows:

[0060] S1: Take 10g of polyarylene ether benzimidazole powder, dissolve it in 100mL of NMP solution, stir at 80℃ for 20h to obtain OPBI solution, and magnetically stir OPBI at 80℃ for 12h to use as casting solution.

[0061] S2: Let the casting solution stand at room temperature for 20 hours to remove bubbles, then use a stainless steel scraper to coat it onto a clean glass plate. Immerse the glass plate in an anhydrous methanol bath for 10 minutes, remove it, and air dry at room temperature for 1 hour. Transfer it to a vacuum oven and dry at 50°C for 2 hours. Then raise the temperature to 120°C and dry for 4 hours to obtain a transparent and flexible lithium-ion separator.

[0062] The performance of Examples 1-4 and Comparative Examples 1-2 was tested below, and the test results are shown in Table 1.

[0063] Thickness: Test according to the method in standard GB / T6672-2001.

[0064] Porosity test: Immerse the dried composite membrane in n-butanol for 2 hours and calculate its porosity P. The calculation formula is P=(W1-W O ) / ρ b V b *100%, where W1 is the weight of the membrane after immersion, W O ρ is the weight of the dried composite membrane. b V is the density of n-butanol. b This is the volume of the dried composite membrane. Cut all the membranes into rectangles 2cm long and 1cm wide, measure the thickness, and 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 by the static drop method of a contact angle meter to obtain the electrolyte wettability of the diaphragm.

[0066] Liquid absorption rate: The liquid absorption rate of the composite membrane is tested by weighing method. First, the weight of the composite membrane before immersion in electrolyte is weighed. After immersion in electrolyte for 2 hours, the weight of the composite membrane after immersion in 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 membrane sample, place the membrane flat on one of the quantitative filter papers on the stainless steel plate in the middle of the blower-type constant temperature chamber, press it down with another quantitative filter paper, close the constant temperature chamber door, start the time, keep it at 150℃ for 1 hour, after heating, take out the membrane, wait for the membrane to return to room temperature, measure the longitudinal and transverse marking lengths, thermal shrinkage rate = (membrane area before heating - membrane area after heating) / membrane area before heating * 100%.

[0068] Tensile strength and puncture strength shall be tested in accordance with the relevant provisions in GB / T36363-2018.

[0069] Ionic conductivity: The ionic conductivity (σ) of the electrolyte-permeable membrane in a two-electrode system between the SS electrodes using a CHI660E electrochemical workstation was measured using EIS. This was achieved by sandwiching the membrane / electrolyte system between the symmetrical SS electrodes at an AC amplitude of 10 mV, 1-10... 5 Tested within a frequency range 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); and S is the film area cut during the experiment (cm²). 2 ).

[0070] Cyclic performance test

[0071] Preparation of lithium metal batteries: 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 2wt.% fluoroethylene carbonate (FEC) added as an additive. First, lithium iron phosphate, Super P conductive agent, and PVDF binder were mixed at a mass ratio of 80:10:10, and an appropriate amount of NMP was added to prepare a slurry. The slurry was uniformly coated onto aluminum foil, vacuum dried at 80℃ for 12 hours, and then cut into 14mm diameter discs as the positive electrode. A 50μm thick lithium metal foil was used as the negative electrode, cut into 16mm diameter discs. The batteries were assembled in an Ar atmosphere glove box in the following sequence: negative electrode (lithium metal) → separator → positive electrode → injection of 40μL electrolyte → encapsulation in a CR2032 battery case. After assembly, the batteries were allowed to stand at room temperature for 12 hours to ensure complete electrolyte wetting of the electrodes and separator.

[0072] The constant current charge-discharge specific capacity of lithium-ion batteries was evaluated using the Blue Battery Detection System. The evaluation was conducted at a rate of 0.5 C and a voltage range of 2.7-4.2V. The coulombic efficiency of the battery was tested after 200 charge-discharge cycles.

[0073] Table 1

[0074] Group Thickness (μm) Porosity (%) Contact angle (°) Liquid absorption rate (%) Heat shrinkage rate (150℃, 1h) Tensile strength (MPa) Puncture intensity (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

[0075] According to the experimental results shown in Table 1, compared with the comparative example, using OPBI as the matrix and forming a covalent cross-linked network with propylene-based SCOF can improve the mechanical properties of lithium battery separators in terms of thermal shrinkage, tensile strength, and puncture strength. At the same time, the increase in separator thickness is slightly greater than the increase in mechanical properties. Therefore, the improvement in physical properties is not simply caused by the increase in separator thickness. In addition, the lithium battery separator also shows significant improvement in wettability, ionic conductivity, and cycle stability. As the proportion of propylene-based SCOF gradually increases, the above-mentioned electrical properties also show an improving trend.

[0076] Finally, it should be noted that the above description 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 foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lithium battery separator, characterized in that, Includes the following steps: S1: Melamine, terephthalaldehyde and dimethyl sulfoxide are mixed and heated to react melamine and terephthalaldehyde. After separation and drying, a pale yellow solid product SNW-1COF is obtained; wherein, by mass parts, melamine is 12-15 parts and terephthalaldehyde is 40-75 parts. S2: SNW-1COF, propylene-1,3-sulfonyl lactone, and acetonitrile are mixed and heated to react SNW-1COF with propylene-1,3-sulfonyl lactone. After separation and drying, a white solid product, propylene-SCOF, is obtained. The mass fractions of SNW-1COF are 6-10 parts and propylene-1,3-sulfonyl lactone are 18-70 parts. S3: Mix polyaryl ether benzimidazole, 2-mercapto-5-fluorobenzimidazole, triethylamine, propenyl SCOF and NMP, and heat to react 2-mercapto-5-fluorobenzimidazole with propenyl SCOF at a temperature of 80-90°C for 12-20 hours to obtain a casting solution; wherein, by mass fraction, polyaryl ether benzimidazole is 10-20 parts, 2-mercapto-5-fluorobenzimidazole is 0.3-0.9 parts, triethylamine is 2-4 parts, and propenyl SCOF is 0.8-3 parts; S4: Apply the casting solution to the substrate, immerse it in anhydrous methanol, then remove and dry it to obtain the lithium battery separator.

2. The method for preparing a lithium battery separator according to claim 1, characterized in that: In step S1, the heating temperature is 150~180℃ and the reaction time is 60~90h.

3. The method for preparing a lithium battery separator according to claim 1, characterized in that: Furthermore, in step S2, the heating temperature is 80~90℃ and the reaction time is 24~30h.

4. The method for preparing a lithium battery separator according to claim 1, characterized in that: In step S3, polyarylene ether benzimidazole powder, 2-mercapto-5-fluorobenzimidazole, triethylamine solution and NMP are mixed to form a first solution. Propylene 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 to undergo an addition reaction with propenyl SCOF, thus obtaining a casting solution.

5. The method for preparing a lithium battery separator according to claim 1, characterized in that: In step S4, the soaking time in anhydrous methanol is 10-20 minutes.

6. A lithium battery separator, characterized in that: It is prepared by the method described in any one of claims 1 to 5.