A lattice-doped boehmite / polyimide composite fiber slurry and its preparation method

Abstract

This invention discloses a lattice-doped boehmite / polyimide composite fiber slurry and its preparation method. The battery separator includes a base film and a coating on the base film. The coating includes lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants, and adhesives. The lattice-doped boehmite / polyimide composite fibers include carboxyl-activated polyimide nanofibers and lithium-doped lattice-modified boehmite nanocrystals loaded on the surface of the carboxyl-activated polyimide nanofibers. The functional additive is polyvinylpyrrolidone. The lithium-doped lattice-modified boehmite nanocrystals are uniformly and stably attached to the surface of the carboxyl-activated polyimide nanofibers, providing a continuous and stable interfacial channel for subsequent lithium-ion conduction, balancing mechanical integrity and electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically relating to a lattice-doped boehmite / polyimide composite fiber slurry and its preparation method. Background Technology

[0002] Lithium-ion batteries are the core power source for new energy vehicles and energy storage systems, and their safety and electrochemical performance have attracted much attention. The separator, as one of the key components of the battery, mainly functions to isolate the positive and negative electrodes, prevent short circuits, and allow lithium ions to pass through. Its performance directly affects the battery's rate performance, cycle life, and safety characteristics.

[0003] Currently, commercial lithium-ion batteries mainly use polyolefin microporous membranes, but these membranes have inherent defects such as poor thermal stability and poor electrolyte wettability. To solve these problems, researchers have widely adopted ceramic coating modification technology, which involves coating the base membrane surface with a slurry containing inorganic nanoparticles such as alumina and boehmite, utilizing their excellent thermal and chemical stability to improve the membrane's high-temperature shrinkage resistance. However, existing improvements are usually based on simple physical composites, and ceramic particles are prone to agglomeration, leading to poor slurry stability, uneven coating thickness, and increased local defects, making it difficult to meet industrial coating requirements. Furthermore, conventional ceramic powders lack intrinsic lithium-ion conductivity, and introducing ceramics into the coating can easily increase membrane impedance and reduce ionic conductivity. Patent CN 113725554 A discloses a polyimide / magnesium oxide composite lithium-ion battery membrane and its preparation method, which uses an ion exchange method to introduce Mg onto polyamic acid fibers. 2+ Metal ions, after subsequent heat treatment, simultaneously achieve the imidization of polyamic acid and the formation of MgO nanoparticles. However, the magnesium salt ion exchange process has poor controllability and is prone to causing local pore blockage. Utility model patent CN 213026385 U discloses a multifunctional double-sided heterogeneous Janus separator for lithium-ion batteries. This double-sided heterogeneous Janus separator is composed of a polyolefin single-sided inorganic coating separator layer, an adhesive layer, and a high-temperature resistant polymer nanofiber membrane layer arranged sequentially. While this improves thermal dimensional stability, the multi-layer composite increases interfacial impedance, and the heterogeneous interface reduces the uniformity of ion transport. Invention patent CN 116315437 A discloses a modified composite separator and its preparation method. The coating of the modified composite separator is composed of a mixture of high-temperature resistant polymer nanofibers and inorganic particles. Although it retains the high-temperature resistance advantage of inorganic particles, the simple physical mixing of nanofibers and inorganic particles easily leads to uneven pore distribution, still increasing separator impedance and reducing ionic conductivity. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a battery separator.

[0005] Another object of the present invention is to provide a lattice-doped boehmite / polyimide composite fiber slurry.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] A battery separator includes: a base film and a coating on the base film, the coating comprising: lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants, and adhesives, wherein the ratio of lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants, and adhesives by mass parts is (5~20):(1.9~2.1):(0.4~0.6):(0.15~0.2), wherein the lattice-doped boehmite / polyimide composite fibers comprise: carboxyl-activated polyimide (PI-COOH) nanofibers and lithium-doped lattice-modified boehmite nanocrystals loaded on the surface of the carboxyl-activated polyimide (PI-COOH) nanofibers; the functional additive is polyvinylpyrrolidone (PVP).

[0008] In the above technical solution, the loading of lithium-doped lattice-modified boehmite nanocrystals in the lattice-doped boehmite / polyimide composite fiber is 30~45wt%.

[0009] In the above technical solution, the thickness of the coating (single-sided coating) is 1~5μm.

[0010] In the above technical solution, the dispersant is sodium carboxymethyl cellulose (CMC-Na), and the adhesive is polyacrylic acid or epoxy resin.

[0011] In the above technical solution, the preferred ratio of lattice-doped boehmite / polyimide composite fiber, functional additives, dispersant and adhesive by mass parts is (16~18):(1.9~2.1):(0.4~0.6):(0.15~0.2).

[0012] In the above technical solution, the method for obtaining lattice-doped boehmite / polyimide composite fibers includes: immersing carboxyl-activated polyimide (PI-COOH) nanofibers in a lattice-doped boehmite precursor solution, stirring at room temperature for 1.5-2.5 h until homogeneous, and then hydrothermally reacting at 170-190℃ (stirring at 600-1000 r / min) for 22-26 h to form lithium-doped lattice-modified boehmite nanocrystals, and then... Boehmite nanocrystals were loaded onto the surface of carboxyl-activated polyimide (PI-COOH) nanofibers, cooled to room temperature, washed, and dried (at 55-65°C for 11-13 hours) to obtain lattice-doped boehmite / polyimide composite fibers. The lattice-doped boehmite precursor solution included: an aluminum source, a lithium source, urea, and a second solvent. The ratio of aluminum source, lithium source, and urea by mass was (3.70-3.80):(0.069-0.138):1.80.

[0013] In the method for obtaining lattice-doped boehmite / polyimide composite fibers, carboxyl-activated polyimide (PI-COOH) nanofibers (1cm*1cm in size) are immersed in a lattice-doped boehmite precursor solution. The ratio of the mass fraction of the carboxyl-activated polyimide (PI-COOH) nanofibers to the volume fraction of the lattice-doped boehmite precursor solution is 1:(90~110), where the mass fraction is in g and the volume fraction is in mL.

[0014] In the method for obtaining lattice-doped boehmite / polyimide composite fibers, the second solvent is water, and the ratio of the volume fraction of the second solvent to the mass fraction of urea is (75~85):1.80, where the mass fraction is in g and the volume fraction is in mL.

[0015] In the method for obtaining lattice-doped boehmite / polyimide composite fibers, the aluminum source is aluminum nitrate nonahydrate (Al(NO3)3·9H2O), and the lithium source is lithium nitrate (LiNO3).

[0016] In the above technical solution, the method for obtaining carboxyl-activated polyimide (PI-COOH) nanofibers includes: soaking polyimide (PI) nanofibers in an alkaline solution for 25-35 min, washing with water, then soaking in an acidic solution for 15-25 min, washing with water, and drying (drying at 55-65℃ for 11-13 h) to obtain carboxyl-activated polyimide (PI-COOH) nanofibers, wherein the alkaline solution includes potassium hydroxide, and the acidic solution is an aqueous solution of acetic acid.

[0017] In the above technical solution, the concentration of potassium hydroxide in the alkaline solution is 0.95~1.05 mol / L, and the concentration of CH3COOH in the acetic acid aqueous solution is 0.45~0.55 mol / L.

[0018] In the above technical solution, the method for obtaining an alkaline solution includes: mixing anhydrous ethanol and a third solvent until homogeneous, adding potassium hydroxide (powder), mixing until homogeneous, and obtaining an alkaline solution. In the alkaline solution, the ratio of anhydrous ethanol to the third solvent by volume is 1:(0.95~1.05), and the third solvent is water.

[0019] In the above technical solution, the method for preparing polyimide (PI) nanofibers includes: mixing 4,4'-diaminodiphenyl ether (ODA), N,N-dimethylformamide (DMF) and pyromellitic dianhydride (PMDA), stirring at 0~5℃ for 22~26h to obtain a spinning solution, electrospinning the spinning solution at an ambient temperature of 40~50℃ to obtain nanofibers, and thermally imidizing the nanofibers to obtain polyimide (PI) nanofibers. The ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) by mass is (7.09~7.11):(7.89~7.91).

[0020] In the above technical solution, thermal imidization includes: first holding at 75~85℃ for 0.9~1.1 hours, then holding at 145~155℃ for 0.9~1.1 hours, then holding at 245~255℃ for 0.9~1.1 hours, and finally holding at 295~305℃ for 0.4~0.6 hours.

[0021] In the above technical solution, the ratio of the mass fraction of 4,4'-diaminodiphenyl ether (ODA) to the volume fraction of N,N-dimethylformamide (DMF) is (7.09~7.11):(50~60), where the mass fraction is in g and the volume fraction is in mL.

[0022] In the above technical solution, the spinning solution is drawn into the syringe and then electrospinning is performed. The electrospinning rate is 0.8~1.2 mL / h, the distance between the receiver and the metal needle of the syringe is 13~17 cm, and the electrospinning voltage is 17~19 kV.

[0023] In the above technical solution, the method for obtaining the lattice-doped boehmite precursor solution includes: mixing an aluminum source and a second solvent until homogeneous, adding a lithium source and mixing until homogeneous, adding urea and mixing until homogeneous, adjusting the pH to 4.0~5.0, and obtaining the lattice-doped boehmite precursor solution.

[0024] The above-mentioned method for preparing the battery separator includes: coating a lattice-doped boehmite / polyimide composite fiber slurry onto a base film on one or both sides, drying it, obtaining a coating on the base film, and obtaining the battery separator. The lattice-doped boehmite / polyimide composite fiber slurry includes: lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants, adhesives, and a first solvent.

[0025] A method for preparing a lattice-doped boehmite / polyimide composite fiber slurry includes: mixing lattice-doped boehmite / polyimide composite fibers, an aqueous solution containing functional additives, an aqueous solution containing dispersants, an adhesive, and a first solvent until homogeneous to obtain the lattice-doped boehmite / polyimide composite fiber slurry, wherein, by mass parts, the ratio of functional additives in the aqueous solution containing functional additives, dispersants in the aqueous solution containing dispersants, adhesive, and the first solvent is (5~20):(1.9~2.1):(0.4~0.6):(0.15~0.2):(80~85).

[0026] In the above technical solution, the method for preparing lattice-doped boehmite / polyimide composite fiber slurry includes: mixing the lattice-doped boehmite / polyimide composite fiber and a first solvent until uniform, adding an aqueous solution containing functional additives, mixing until uniform, adding an aqueous solution containing dispersant and an adhesive, mixing until uniform, filtering, and obtaining the slurry.

[0027] In the above technical solution, the content of functional additives in the aqueous solution containing functional additives is 9~11wt%.

[0028] In the above technical solution, the content of dispersant in the aqueous solution containing dispersant is 1~3wt%.

[0029] In the above technical solution, the first solvent is water.

[0030] In the above technical solution, the preferred ratio of lattice-doped boehmite / polyimide composite fiber, functional additive in aqueous solution containing functional additive, dispersant in aqueous solution containing dispersant, adhesive and first solvent by mass parts is (16~18):(1.9~2.1):(0.4~0.6):(0.15~0.2):(80~85).

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. Addressing the technical challenges of traditional polyimide (PI) nanofiber-ceramic particle composites, where the interface relies solely on physical adsorption and van der Waals forces, resulting in loose bonding, easy peeling, and interface defects that degrade the mechanical and conductive properties of the membrane, this invention innovatively introduces carboxyl (-COOH) active sites onto the surface of the polyimide nanofibers to provide stable chemical bonding anchoring sites. Specifically, by surface modification of the polyimide nanofibers, carboxyl active groups are directionally introduced. These carboxyl active groups interact with Al in the lattice-doped boehmite precursor solution. 3+ and Li + Coordination complexes occur, forming "molecular anchor points." In the early stages of the hydrothermal reaction, Al... 3+ Preferential hydrolysis at the molecular anchor site to form boehmite, while Li + Lithium-doped lattice-modified boehmite nanocrystals are formed by entering the boehmite lattice and growing heterogeneously on the surface of carboxyl-activated polyimide (PI-COOH) nanofibers. These nanocrystals are firmly bonded to the PI-COOH nanofibers via Al-OC chemical bonds. This design fundamentally solves the core problem of weak interfacial bonding when polyimide (PI) nanofibers are combined with ceramic particles, enabling the lithium-doped lattice-modified boehmite nanocrystals to uniformly and stably adhere to the surface of the PI-COOH nanofibers. This provides a continuous and stable interfacial channel for subsequent lithium-ion conduction, balancing mechanical integrity and electrochemical performance.

[0033] 2. Boehmite (γ-AlOOH), as an inert ceramic material, inherently lacks lithium-ion conductivity and can only be used as a mechanical reinforcing phase in traditional applications, limiting its use in lithium-ion conduction-related fields. This invention overcomes this technical limitation by enabling lithium-ion conduction... + The Li was precisely introduced into the boehmite crystal structure in the form of lattice doping, enabling Li... + Replacing part of the Al in the boehmite lattice 3+ The octahedral coordination sites (or filling the interstitial spaces of the lattice) are used to compensate for lattice distortion and adjust charge balance (such as by introducing oxygen vacancies and hydroxyl defects) to enable Li + It can exist stably in the boehmite lattice and achieve rapid migration. This enables boehmite to have lithium-ion conductivity, achieving the dual functions of "mechanical enhancement + lithium-ion conduction" without the need for additional lithium-ion conducting media, significantly improving the lithium-ion conduction efficiency and structural stability of the separator.

[0034] 3. This invention employs a one-step hydrothermal method, directly placing carboxyl-activated polyimide (PI-COOH) nanofibers into a lattice-doped boehmite precursor solution containing lithium and aluminum sources. Under hydrothermal conditions, in-situ growth of lithium-doped lattice-modified boehmite nanocrystals on the surface of carboxyl-activated polyimide (PI-COOH) nanofibers is achieved. This solves the pain points of poor stability of traditional slurries, easy detachment of ceramic phases, and cumbersome processes, providing a convenient and efficient technical path for the large-scale preparation of subsequent composite films, electrode materials, and other products, while ensuring the consistency of the final product's performance. Attached Figure Description

[0035] Figure 1 SEM image of polyimide (PI) nanofibers. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0037] The raw material information involved in the examples and comparative examples is as follows:

[0038]

[0039] In the following examples, the base film is a wet-process PE film with a thickness of 7 μm and an air permeability of 160 Sec / 100 mL (base films of other thicknesses and air permeability values ​​are also acceptable, as are other types of base films).

[0040] Shrinkage rate: The battery separator was cut into 4cm × 6cm pieces, and its length and width were measured after heat treatment in a 200℃ oven for 1 hour. The shrinkage rates in the longitudinal direction (MD) and transverse direction (TD) were obtained respectively. Longitudinal (MD) shrinkage rate = (Length of battery separator before heat treatment - Length of battery separator after heat treatment) / Length of battery separator before heat treatment * 100%; Transverse (TD) shrinkage rate = (Width of battery separator before heat treatment - Width of battery separator after heat treatment) / Width of battery separator before heat treatment * 100%.

[0041] Ionic conductivity: The ionic conductivity test method was performed according to Chapter 6, Section 6.6.2 of GB / T 36363-2018. The test environment was: temperature (23±2)℃ and relative humidity (50±10)%.

[0042] Liquid absorption rate and liquid retention rate: Cut a 50mm×50mm battery separator as a sample, weigh the cut sample and record the mass as m1. Immerse the weighed battery separator in electrolyte at 25℃ for 30 minutes, remove it, wipe off the free electrolyte on the surface of the battery separator, weigh the dried battery separator and record the mass as m2; let it stand for 1 hour, weigh it again and record the mass as m3; calculate the liquid absorption rate and liquid retention rate according to the following formulas: Liquid absorption rate (%) = (m2-m1) / m1×100%; Liquid retention rate (%) = (m3-m1) / m1×100%.

[0043] Peel strength: Prepare a standard-sized sample of the battery separator (10-25mm wide, 150mm long). Attach the sample to the coated surface using 3M transparent tape, leaving a sufficient peel margin (at least 20mm). Apply pressure evenly to the sample three times using a standard roller. Secure both ends of the sample to the upper and lower clamps, with the peel direction at 180°. ° Use a stretching machine to tear one end of the 3M transparent tape to obtain the peel strength.

[0044] Examples 1-4

[0045] A method for preparing a slurry (lattice-doped boehmite / polyimide composite fiber slurry) includes: adding lattice-doped boehmite / polyimide composite fibers to a first solvent at room temperature, stirring at 450 r / min for 30 min until homogeneous, adding an aqueous solution containing functional additives, stirring at 10000 r / min for 30 min until homogeneous, adding an aqueous solution containing a dispersant and an adhesive, and stirring at 3000... The mixture was stirred at a speed of r / min for 30 minutes until homogeneous. It was then filtered through a 200-mesh sieve to obtain a slurry. The first solvent was deionized water, the functional additive was polyvinylpyrrolidone (PVP), the dispersant was sodium carboxymethyl cellulose (CMC-Na), and the adhesive was polyacrylic acid (weight average molecular weight 450,000, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.). The functional additive content in the aqueous solution was 10 wt%, and the dispersant content in the aqueous solution was 2 wt%. The ratio of lattice-doped boehmite / polyimide composite fiber, functional additive in the aqueous solution, dispersant in the aqueous solution, adhesive, and first solvent, by mass parts, was X (the value of X is shown in Table 1).

[0046] The method for obtaining lattice-doped boehmite / polyimide composite fibers includes: immersing 1g of carboxyl-activated polyimide (PI-COOH) nanofibers (film) with a size of 1cm*1cm in 100mL of lattice-doped boehmite precursor solution, magnetically stirring at 600r / min for 2h at room temperature, transferring to a reaction vessel, and hydrothermally reacting at 180℃ with stirring (600r / min) for 24h to form lithium-doped lattice-modified boehmite nanocrystals (Al in the lattice-doped boehmite precursor solution). 3+ Hydrolysis forms boehmite, and the lattice is doped with Li in the boehmite precursor solution. + In-situ doping of boehmite lattice was used to form lithium-doped lattice-modified boehmite nanocrystals, which were then loaded onto the surface of carboxyl-activated polyimide (PI-COOH) nanofibers. The mixture was cooled to room temperature, washed (rinsed three times with deionized water, then three times with anhydrous ethanol), and dried at 60°C for 12 h to obtain lattice-doped boehmite / polyimide composite fibers. The loading of lithium-doped lattice-modified boehmite nanocrystals in the lattice-doped boehmite / polyimide composite fibers was 40 wt%.

[0047] The method for obtaining the lattice-doped boehmite precursor solution includes: mixing an aluminum source (aluminum nitrate nonahydrate) and a second solvent, magnetically stirring at 600 r / min for 30 min at room temperature until homogeneous, adding a lithium source (lithium nitrate), magnetically stirring at 600 r / min for 30 min at room temperature until homogeneous, adding urea, magnetically stirring at 600 r / min for 30 min at room temperature until homogeneous, adjusting the pH to 4.5 with 0.1 mol / L dilute nitric acid to obtain the lattice-doped boehmite precursor solution. The ratio of aluminum source, lithium source and urea by mass is 3.75:0.105:1.80. The second solvent is deionized water, and the volume fraction of the second solvent to the mass fraction of urea is 80:1.80. The units of mass fraction are g and the units of volume fraction are mL.

[0048] The method for obtaining carboxyl-activated polyimide (PI-COOH) nanofibers includes: soaking polyimide (PI) nanofibers in an alkaline solution at room temperature for 30 min, rinsing three times with deionized water, then soaking in an acidic solution for 20 min, rinsing three times with deionized water, and drying at 60℃ for 12 h to obtain carboxyl-activated polyimide (PI-COOH) nanofibers. The method for obtaining the alkaline solution includes: mixing anhydrous ethanol and a third solvent (deionized water) until homogeneous, adding potassium hydroxide (powder), and mixing until homogeneous to obtain the alkaline solution. The concentration of potassium hydroxide in the alkaline solution is 1 mol / L, and by volume, it contains no... The ratio of water-ethanol to the third solvent is 1:1. The acidic solution is an aqueous solution of acetic acid, and the concentration of CH3COOH in the aqueous solution of acetic acid is 0.5 mol / L. The method for preparing polyimide (PI) nanofibers includes: mixing 4,4'-diaminodiphenyl ether (ODA), N,N-dimethylformamide (DMF), and pyromellitic dianhydride (PMDA), stirring in an ice-water bath at 0°C for 24 h to obtain a spinning solution, and performing electrospinning on the spinning solution at an ambient temperature of 45°C (the ambient temperature inside the electrospinning apparatus is 45°C). (The spinning solution is drawn into a syringe before electrospinning, and the electrospinning rate is 1...) The electrospinning rate was mL / h, the distance between the roller receiver and the metal needle of the syringe was 15 cm, and the voltage of electrospinning was 18 kV. Nanofibers were obtained, and the nanofibers were thermally imidized to obtain polyimide (PI) nanofibers. The mass ratio of 4,4'-diaminodiphenyl ether (ODA) to pyromellitic dianhydride (PMDA) was 7.1:7.9, and the mass ratio of 4,4'-diaminodiphenyl ether (ODA) to the volume ratio of N,N-dimethylformamide (DMF) was 7.1:55. The mass part is in g and the volume part is in mL. The thermal imidization included: first holding at 80℃ for 1 hour, then holding at 150℃ for 1 hour, then holding at 250℃ for 1 hour, and finally holding at 300℃ for 0.5 hours.

[0049] Table 1

[0050]

[0051] Comparative Example 1

[0052] A method for preparing a slurry is basically the same as that in Example 3, except that no lithium source (lithium nitrate) is added when preparing the lattice-doped boehmite precursor solution.

[0053] Comparative Example 2

[0054] A method for preparing a slurry includes: adding lithium-doped lattice-modified boehmite nanocrystals and carboxyl-activated polyimide (PI-COOH) nanofibers prepared in Example 3 to a first solvent at room temperature, stirring at 450 r / min for 30 min until homogeneous, adding an aqueous solution containing functional additives, stirring at 10000 r / min for 30 min until homogeneous, adding an aqueous solution containing a dispersant and an adhesive, and stirring at 3000... Stir at a speed of r / min for 30 minutes until homogeneous, filter through a 200-mesh sieve to obtain a slurry. The first solvent is deionized water. The aqueous solution containing functional additives is the same as the aqueous solution containing functional additives in Example 3. The aqueous solution containing dispersant is the same as the aqueous solution containing dispersant in Example 3. The adhesive is the same as the adhesive in Example 3. By mass parts, the ratio of lithium-doped lattice modified boehmite nanocrystals, carboxyl-activated polyimide (PI-COOH) nanofibers, functional additives in the aqueous solution containing functional additives, dispersant in the aqueous solution containing dispersant, adhesive and first solvent is 10:5:2:0.5:0.2:80.

[0055] The method for preparing lithium-doped lattice-modified boehmite nanocrystals includes: transferring the lattice-doped boehmite precursor solution obtained in Example 3 to a reaction vessel, hydrothermally reacting it at 180°C with stirring (600 r / min) for 24 h, cooling it to room temperature, washing it (rinsing it 3 times with deionized water and then rinsing it 3 times with anhydrous ethanol), and drying it at 60°C for 12 h to obtain lithium-doped lattice-modified boehmite nanocrystals.

[0056] Comparative Example 3

[0057] A method for preparing the slurry is basically the same as in Example 3, except that the "lattice-doped boehmite / polyimide composite fiber" is replaced with "carboxyl-activated polyimide (PI-COOH) nanofibers". The preparation method of carboxyl-activated polyimide (PI-COOH) nanofibers is the same as in Example 3.

[0058] Comparative Example 4

[0059] A method for preparing the slurry is basically the same as in Example 3, except that the "lattice-doped boehmite / polyimide composite fiber" is replaced with "lithium-doped lattice-modified boehmite nanocrystals". The preparation method of the lithium-doped lattice-modified boehmite nanocrystals is the same as in Comparative Example 2.

[0060] Comparative Example 5

[0061] A method for preparing the slurry is essentially the same as in Example 3, except that "polyvinylpyrrolidone (PVP)" is replaced with "polyethylene glycol". The number average molecular weight of polyethylene glycol is 10,000.

[0062] Examples 5-8 and Comparative Examples 6-10

[0063] A method for preparing a battery separator includes: applying a slurry to both sides of a base film using a roller coating method (coating speed of 15 m / min), drying at 60°C for 5 min, and obtaining a coating layer (coating thickness of 2 μm on one side) on the base film to obtain the battery separator. The slurry is one of the slurries prepared in Examples 1-4 and Comparative Examples 1-5.

[0064] Table 2

[0065]

[0066] The battery separators prepared in Examples 5-8 and Comparative Examples 6-10 are shown in Table 3.

[0067] Table 3

[0068]

[0069] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A battery separator, characterized in that, include: The base film and the coating on the base film, the coating comprising: lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants and adhesives, wherein the ratio of lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants and adhesives by mass parts is (5~20):(1.9~2.1):(0.4~0.6):(0.15~0.2), wherein the lattice-doped boehmite / polyimide composite fibers comprise: carboxyl-activated polyimide nanofibers and lithium-doped lattice-modified boehmite nanocrystals loaded on the surface of the carboxyl-activated polyimide nanofibers; the functional additive is polyvinylpyrrolidone.

2. The battery separator according to claim 1, characterized in that, The coating thickness is 1~5μm.

3. The battery separator according to claim 1, characterized in that, The dispersant is sodium carboxymethyl cellulose, and the adhesive is polyacrylic acid or epoxy resin.

4. The battery separator according to claim 1, characterized in that, A method for obtaining lattice-doped boehmite / polyimide composite fibers includes: immersing carboxyl-activated polyimide nanofibers in a lattice-doped boehmite precursor solution, stirring at room temperature until homogeneous, and then hydrothermally reacting at 170-190°C under stirring conditions for 22-26 hours to form lithium-doped lattice-modified boehmite nanocrystals. The lithium-doped lattice-modified boehmite nanocrystals are then loaded onto the surface of the carboxyl-activated polyimide nanofibers. The mixture is cooled to room temperature, washed, and dried to obtain lattice-doped boehmite / polyimide composite fibers. The lattice-doped boehmite precursor solution comprises: an aluminum source, a lithium source, urea, and a second solvent. The ratio of the aluminum source, lithium source, and urea by mass is (3.70-3.80):(0.069-0.138):1.

80.

5. The battery separator according to claim 4, characterized in that, The method for obtaining carboxyl-activated polyimide nanofibers includes: soaking polyimide nanofibers in an alkaline solution for 25-35 minutes, washing with water, then soaking them in an acidic solution for 15-25 minutes, washing with water, and drying to obtain carboxyl-activated polyimide nanofibers. The alkaline solution includes potassium hydroxide, and the acidic solution is an aqueous solution of acetic acid.

6. The battery separator according to claim 5, characterized in that, The method for preparing polyimide nanofibers includes: mixing 4,4'-diaminodiphenyl ether, N,N-dimethylformamide and pyromellitic dianhydride, stirring at 0~5℃ for 22~26h to obtain a spinning solution, electrospinning the spinning solution at an ambient temperature of 40~50℃ to obtain nanofibers, and thermally imidizing the nanofibers to obtain polyimide nanofibers. The ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride by mass is (7.09~7.11):(7.89~7.91).

7. The method for preparing a battery separator according to any one of claims 1 to 6, characterized in that, include: A lattice-doped boehmite / polyimide composite fiber slurry is coated on one or both sides of a base film, dried, and a coating is obtained on the base film to obtain a battery separator. The lattice-doped boehmite / polyimide composite fiber slurry includes: lattice-doped boehmite / polyimide composite fibers, functional additives, dispersants, adhesives, and a first solvent.

8. A method for preparing lattice-doped boehmite / polyimide composite fiber slurry, characterized in that, include: Lattice-doped boehmite / polyimide composite fibers, an aqueous solution containing functional additives, an aqueous solution containing dispersant, an adhesive, and a first solvent are mixed until homogeneous to obtain a lattice-doped boehmite / polyimide composite fiber slurry. The ratio of functional additives, dispersant, adhesive, and first solvent in the aqueous solution containing functional additives, by mass parts, is (5~20):(1.9~2.1):(0.4~0.6):(0.15~0.2):(80~85).

9. The method according to claim 8, characterized in that, The content of functional additives in the aqueous solution is 9-11 wt%.

10. The method according to claim 8, characterized in that, The content of dispersant in the aqueous solution is 1~3wt%.

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