A dry-process high-temperature resistant lithium battery separator and its preparation method

Abstract

This invention discloses a dry-process high-temperature resistant lithium battery separator and its preparation method, relating to the field of lithium battery separator technology. The specific preparation method involves first activating and crosslinking polypropylene, polyimide, PP-b-PI block copolymer, and crosslinking agent BIBP under nitrogen protection to obtain a polypropylene-polyimide matrix; after melting, adding pre-sintered ZrO2@Al2O3 core-shell filler, hydroxylated boron nitride, and zinc borate, followed by bi-stage screw extrusion, ultrasonic orientation, nitrogen annealing, and rapid cooling with cold rollers to obtain a mixed melt; then, through warm stretching and hot air circulation heat treatment, a hard, elastic, crystalline base film is prepared; further, through stretching, thermal relaxation, and heat setting, a microporous base film is obtained; after slitting, plasma activation is performed, and an epoxy silane and tetraethyl orthosilicate / polybenzimidazole aerogel precursor is sprayed on, followed by pre-curing and heat shrink curing to form a nano-closed-pore coating; finally, electrostatic elimination and winding are performed to obtain the finished product. The lithium battery separator prepared by this invention exhibits excellent high-temperature resistance and low thermal shrinkage.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, specifically to a dry-process high-temperature resistant lithium battery separator and its preparation method. Background Technology

[0002] In modern battery technology, lithium batteries, with their advantages of high energy density and long cycle life, have been widely used in electric vehicles, energy storage systems, and other fields. Among these, the lithium battery separator, as one of the key internal components, plays an indispensable role. The main function of the separator is to separate the positive and negative electrodes of the battery, preventing short circuits caused by contact between the electrodes. Simultaneously, it must also allow electrolyte ions to pass through. Its performance directly determines the battery's interface structure, internal resistance, and other characteristics, profoundly impacting the battery's capacity, cycle life, and safety performance.

[0003] Currently, the energy density of commercial lithium-ion batteries has significantly improved, reaching 300 Wh / kg, and is expected to increase further. However, as people continue to pursue higher battery energy density, battery safety issues are becoming increasingly prominent. Traditional lithium battery separators, especially the widely used polyolefin separators, have significant shortcomings in high-temperature resistance. Their thermal stability is poor, and their pore structure is not uniform enough. When the battery operates in a high-temperature environment, or when heat accumulates inside the battery for various reasons, the polyolefin separator is prone to shrinkage. This shrinkage disrupts the structural stability of the battery's internal structure, shortening the distance between the originally separated positive and negative electrodes, or even causing them to come into direct contact, leading to an internal short circuit. Once a short circuit occurs, a large amount of heat will rapidly be generated inside the battery, triggering thermal runaway. In severe cases, this can lead to dangerous situations such as battery fire and explosion, greatly limiting the application of lithium batteries in high-temperature environments, such as high-temperature industrial environments and outdoor energy storage under extreme weather conditions. Summary of the Invention

[0004] The purpose of this invention is to provide a dry-process high-temperature resistant lithium battery separator and its preparation method, thereby solving the technical problem of poor high-temperature resistance of lithium battery separators mentioned in the background art. The lithium battery separator prepared by this invention has excellent high-temperature resistance.

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

[0006] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0007] a) Polypropylene, polyimide, PP-b-PI block copolymer and crosslinking agent BIBP are activated and then crosslinked under nitrogen protection to obtain a polypropylene-polyimide matrix with an interpenetrating network;

[0008] b) After melting the polypropylene-polyimide matrix, add pre-sintered ZrO2@Al2O3 core-shell filler, hydroxylated boron nitride and zinc borate, and then extrude it through a two-stage screw extruder with ultrasonic orientation. Subsequently, nitrogen annealing and cold roll quenching are performed sequentially to obtain a mixed melt.

[0009] c) The mixed melt is stretched once under warm conditions, and then subjected to hot air circulation heat treatment to obtain a hard elastic crystalline base film.

[0010] d) The hard elastic crystalline base film is subjected to warm stretching, hot air stretching, thermal relaxation and heat setting in sequence to lock the microporous structure and obtain a microporous base film.

[0011] e) After the microporous base membrane is slit, it is first activated by plasma, then sprayed with epoxy silane, followed by microfluidic spraying of tetraethyl orthosilicate / polybenzimidazole aerogel precursor, and then pre-cured and heat-shrinked cured in sequence to form a nano-closed-pore aerogel coating, thus obtaining the nascent lithium battery separator.

[0012] f) After electrostatic elimination by ion wind, the nascent lithium battery separator is wound up to obtain a dry-process high-temperature resistant lithium battery separator.

[0013] In this invention, the polymer matrix of the diaphragm is first modified to improve its high-temperature resistance. During the modification process, polyimide (PI), with its rigid aromatic ring structure and high glass transition temperature, complements the properties of polypropylene (PP) molecular chains. The PP-b-PI block copolymer effectively eliminates phase separation and constructs interfacial bridges through the compatibility of PP segments with the matrix and the bonding between PI segments and PI particles. A crosslinking agent triggers a covalent crosslinking reaction between PP and PI under specific temperature conditions, forming a stable interpenetrating network structure. This network synergistically inhibits high-temperature failure through two types of chemical interactions: covalent bonds significantly inhibit molecular chain deentanglement, increasing the material's thermal decomposition temperature; and the aromatic heterocyclic skeleton of PI efficiently absorbs thermal vibration energy, improving the material's elastic modulus retention at high temperatures. Ultimately, this improves the diaphragm's high-temperature resistance, thereby reducing the diaphragm's thermal shrinkage rate and enhancing its dimensional stability.

[0014] Secondly, the pre-sintered ZrO2@Al2O3 core-shell filler and hydroxylated boron nitride significantly improve the high-temperature resistance of the membrane by constructing a thermal defense network. In the pre-sintered ZrO2@Al2O3 core-shell structure, the ultra-high melting point of the alumina core forms a robust rigid framework, providing structural support. After pre-sintering, the zirconium oxide shell tightly encapsulates the alumina core through a stable Al-O-Zr covalent interface. The ZrO2 crystal clusters protruding on its surface are embedded in the interlayer gaps of the hydroxylated boron nitride during melt extrusion, forming a stable mechanical anchoring structure and strengthening the interfacial bonding between the two fillers. After surface modification, the ultra-large aspect ratio plate-like structure of the hydroxylated boron nitride is oriented during processing to form a multilayer barrier. Its surface hydroxyl groups chemically bond with the BO-Al bonds on the surface of the core-shell filler, forming a "rigid-flexible interlocking" composite network. The intercalation structure of ZrO2 clusters and BN sheets hinders interfacial separation caused by thermal expansion. The interfacial phonon scattering mechanism reduces the peak thermal conductivity. The interfacial interaction between hydroxylated boron nitride and ZrO2 significantly scatters thermal vibration energy, reducing heat transfer. The bidirectional stress dissipation function balances internal and external stresses. The hydroxylated boron nitride sheets absorb lateral expansion stress through their own deformation, while the core-shell filler resists longitudinal deformation with its rigid framework. Through this structural design, a stable thermal protection system is ultimately formed, ensuring that the membrane micropores maintain structural integrity in extreme temperature fields.

[0015] Finally, the tetraethyl orthosilicate / polybenzimidazole aerogel undergoes a sol-gel phase transition during thermosetting, forming a nanoscale closed-pore structure on the substrate surface. The air filled within this closed-pore structure has an extremely low thermal conductivity, and the closed-pore structure confines the air within independent micro-spaces, preventing free flow and creating an effective thermal barrier. This structure significantly blocks heat transfer paths via air convection and heat conduction, drastically reducing the efficiency of heat transfer from the coating surface to the substrate. Furthermore, during coating preparation, plasma activation treatment generates numerous hydroxyl groups on the substrate surface. These hydroxyl groups undergo a condensation reaction with the siloxane ends of the epoxysilane KH-560, forming strong Si-O-Si covalent bonds. Simultaneously, the epoxy groups of KH-560 undergo a ring-opening reaction with the imidazole rings of polybenzimidazole during the curing stage, generating CN bonds, significantly improving the interfacial adhesion between the coating and the substrate and preventing coating detachment.

[0016] This invention, through the above synergistic effects, significantly improves the high-temperature resistance of lithium battery separators, thereby reducing the heat recovery rate of the separators and maintaining the stability of separator performance in extreme environments. Figure 1 The image shows a SEM image of the dry-process high-temperature resistant lithium battery separator prepared according to the present invention. The electron microscope image shows that the surface of the prepared lithium battery separator exhibits a stretched porous structure.

[0017] Preferably, in step a), the mass ratio of polypropylene, polyimide, and PP-b-PI block copolymer is 100:4-8:2-5.

[0018] Preferably, in step a), the crosslinking temperature is 185–195°C and the crosslinking time is 20–30 min.

[0019] Preferably, in step b), the preparation method of the pre-sintered ZrO2@Al2O3 core-shell filler is as follows:

[0020] First, ammonium polyacrylate was dissolved in deionized water, and Al2O3 powder was added and ultrasonically dispersed to obtain a dispersion. ZrOCl2·8H2O and Y(NO3)3·6H2O were added to deionized water and stirred to dissolve, resulting in a mixed solution. The pH of the dispersion was adjusted to 4.5±0.1, and then the mixed solution was added dropwise to the dispersion. The mixture was heated and stirred in a water bath to promote the hydrolysis of ZrOCl2, forming a ZrO(OH)2 coating layer on the surface of Al2O3. After washing and drying, the dried product was placed in a muffle furnace and sintered at a higher temperature to obtain a pre-sintered ZrO2@Al2O3 core-shell filler.

[0021] In this invention, pre-sintered ZrO2@Al2O3 is used instead of ordinary ZrO2@Al2O3. High-temperature sintering allows for complete crystallization of ZrO2, resulting in a highly crystalline tetragonal ZrO2. Al2O3 also undergoes a phase transformation, strengthening into a corundum structure. Simultaneously, high-energy Al-O-Zr covalent bonds are formed at the interface, improving the bonding stability between the two. Furthermore, regarding the enhancement of the filler-polymer interfacial bonding strength, unsintered fillers are only bonded to the PP matrix by van der Waals forces, leading to easy interfacial delamination at high temperatures. Pre-sintering, however, increases the mechanical interlocking area by forming a nanoscale rough surface, thereby improving the bonding effect between the two.

[0022] Preferably, in step b), the method for preparing hydroxylated boron nitride includes the following steps:

[0023] Boron nitride was added to concentrated nitric acid and heated to carry out an oxidation reaction. After the reaction was completed, the mixture was cooled, and then deionized water was added for ultrasonic treatment. After centrifugation, washing, and drying, hydroxylated boron nitride was obtained.

[0024] Preferably, in step c), the first stretching temperature is 60-80°C.

[0025] Preferably, in step d), the temperature for warm stretching is 70–85°C; and the temperature for hot air stretching is 110–120°C.

[0026] Preferably, in step d), the heat setting process involves first treating at 150–160°C for 10–15 seconds, and then treating at 130–140°C for 20–30 seconds.

[0027] Preferably, in step e), the tetraethyl orthosilicate / polybenzimidazole aerogel precursor also contains nanocellulose, wherein the amount of nanocellulose added is 0.4 to 0.6% of the mass of the tetraethyl orthosilicate / polybenzimidazole aerogel precursor.

[0028] In the technical solution of this invention, the research team discovered through in-depth research that the tetraethyl orthosilicate / polybenzimidazole aerogel precursor preferentially gels at the edge of ZrO2@Al2O3 filler, forming microcracks. The capillary effect at the crack edge causes uneven electrolyte wetting, resulting in increased electrochemical impedance and thus reduced battery rate performance. Further research revealed that the microcracks are caused by a dielectric field distortion effect between the pre-sintered ZrO2@Al2O3 filler and the polymer matrix. During plasma treatment, the electric field intensity on the surface of the high dielectric constant filler is significantly enhanced, while the electric field intensity in the low dielectric matrix region is attenuated, forming a strong electric field gradient. This distortion causes the tetraethyl orthosilicate / polybenzimidazole aerogel precursor to accelerate hydrolysis and condensation at the filler edge, forming a dense gel shell. The gelation reaction in the matrix region is delayed, and the volume shrinkage during solidification exerts a tensile effect on the dense area, ultimately forming radial stress cracks at the interface. To further address the aforementioned technical problems, this invention adds nanocellulose to the tetraethyl orthosilicate / polybenzimidazole aerogel precursor. The hydroxyl groups on the cellulose surface form a hydrogen bond network with the Si-OH hydrolysis products of tetraethyl orthosilicate, increasing the precursor viscosity and triggering a shear thickening effect. This inhibits the flow and accumulation of the precursor into the electric field distortion region during spraying. Furthermore, the cellulose nanofibers permeate the gel system, forming a skeletal structure that slows the condensation reaction rate through bonding, uniformly disperses curing shrinkage stress, and eliminates interfacial strain gradients. This prevents the formation of microcracks at the edges of the ZrO2@Al2O3 filler in the tetraethyl orthosilicate / polybenzimidazole aerogel precursor, thereby improving the battery rate performance.

[0029] A dry-process high-temperature resistant lithium battery separator is prepared by the method described in the preceding claims.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. By leveraging the complementary properties of polyimide and polypropylene, the interfacial bridging effect of PP-b-PI block copolymer, and the covalent cross-linked interpenetrating network triggered by cross-linking agent, the thermal decomposition temperature and high-temperature elastic modulus retention rate of the material are significantly improved, the thermal shrinkage rate is reduced, and the dimensional stability and high-temperature resistance of the diaphragm are effectively enhanced.

[0032] 2. The pre-sintered ZrO2@Al2O3 core-shell filler achieves complete crystallization of ZrO2 and phase transformation strengthening of Al2O3 through high-temperature sintering, and enhances structural stability through Al-O-Zr covalent bonds; it forms a "rigid-flexible interlocking" composite network with hydroxylated boron nitride, which hinders thermal expansion separation through mechanical anchoring, reduces heat transfer through interfacial phonon scattering, and balances internal and external stresses through bidirectional stress dissipation, ensuring the integrity of the membrane microporous structure under extreme temperatures.

[0033] 3. The nano-closed-pore structure significantly reduces the thermal conductivity by blocking air, forming a highly efficient thermal insulation barrier; plasma activation and the interaction with epoxy silane form Si-O-Si and CN covalent bonds, which significantly improves the interfacial bonding between the coating and the substrate, prevents the coating from falling off at high temperatures, and enhances the high-temperature protection effect.

[0034] 4. Adding nanocellulose to the aerogel precursor inhibits the enrichment of the precursor in the electric field distortion region through the hydrogen bond network. The framework structure delays the condensation reaction, uniformly disperses the curing shrinkage stress, eliminates interfacial microcracks, solves the problem of uneven electrolyte wetting, and effectively improves the rate performance of the battery. Attached Figure Description

[0035] Figure 1 This is a SEM image of the surface of the dry-process high-temperature resistant lithium battery separator prepared according to the present invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0037] Example 1

[0038] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0039] Step 1: Weigh the raw materials according to the mass ratio of 100g polypropylene, 7g polyimide, and 4g PP-b-PI block copolymer, then add 1.0g of crosslinking agent BIBP, and put all the raw materials into the reactor. Purge the reactor with nitrogen until the oxygen content is ≤0.5%, and perform activation treatment under nitrogen protection: control the temperature at 170℃±2℃, the stirring speed at 200r / min, and continue for 5min; then raise the temperature to 190℃, maintain the stirring speed at 200r / min and carry out the crosslinking reaction for 25min, so that PP and PI form an interpenetrating network structure to obtain the polypropylene-polyimide matrix.

[0040] Step 2: Dissolve 3.5g of ammonium polyacrylate in 700mL of deionized water and stir until completely dissolved. Add 70g of nano-α-Al₂O₃ powder (50nm particle size) and ultrasonically disperse at 500W for 30min to obtain a dispersion. Separately, dissolve 30g of ZrOCl₂·8H₂O and 2.68g of Y(NO₃)₃·6H₂O in 300mL of deionized water and stir until completely dissolved to obtain a mixed solution. Adjust the pH of the dispersion to 4.5±0.1 with hydrochloric acid. Add the mixed solution dropwise to the dispersion at a stirring rate of 300r / min. After the addition is complete, place the mixture in a 90℃ water bath and stir for 1.5h to promote the hydrolysis of ZrOCl₂ to form a ZrO(OH)₂ coating layer. After the reaction is complete, wash the product three times with a mixture of ethanol / deionized water (volume ratio 1:1) by centrifugation and dry at 120℃ for 24h. The dried product was placed in a muffle furnace and heated to 600℃ at a rate of 5℃ / min and held for 2 hours to remove organic matter. Then, the temperature was increased to 1200℃ at a rate of 10℃ / min and held for 2 hours. Finally, the product was cooled with the furnace at a rate of ≤3℃ / min to obtain the pre-sintered ZrO2@Al2O3 core-shell packing.

[0041] Weigh 10g of boron nitride sheets (aspect ratio ≥100, thickness ≤10nm), add to 500mL of concentrated nitric acid (68% concentration), and stir in an 80℃ water bath for 6h (stirring rate 300r / min). The NO2 gas generated by the reaction is absorbed and treated by alkaline solution (5% NaOH solution). After the reaction is complete, allow to cool naturally to 25℃, slowly add 500mL of deionized water (volume ratio of 1:1 to the reaction liquid), and sonicate at 400W power and 20kHz frequency for 1h. Centrifuge the mixture (10000r / min, 15min), collect the solid product, wash with deionized water until the pH of the filtrate is 7.0±0.2, wash three times with anhydrous ethanol, and finally dehydrate in a vacuum drying oven at 120℃ for 2h to obtain hydroxylated boron nitride.

[0042] Take 100g of polypropylene-polyimide matrix and heat it to 250℃ in a melting device until it is completely melted. Add 4g of pre-sintered ZrO2@Al2O3 core-shell filler (particle size ≤50nm), 1.33g of hydroxylated boron nitride (BN) sheets (aspect ratio ≥100), and 1.5g of zinc borate to the molten matrix, and stir for 10min to ensure uniform dispersion of the filler. Feed the mixture into a two-stage screw extruder: first-stage temperature 190℃, rotation speed 200 r / min, and shear rate 800s. -1 Simultaneously, 20kHz ultrasonic-assisted directional BN was applied; the second-order temperature was 240℃, the rotation speed was 250r / min, and the shear rate was 1000s. -1Immediately after extrusion, nitrogen annealing is performed: the mixture is held at 160℃ in a nitrogen atmosphere for 2 minutes, and then transferred to a -60℃ metal roller for rapid cooling with a contact time of 0.5s and a cooling rate of 80℃ / s to obtain a mixed melt.

[0043] Step 3: Place the mixed melt in a stretching device and perform a warm stretching at 70℃: stretching ratio 3.5×, stretching rate 10mm / s, to form a crystalline structure perpendicular to the extrusion direction. After stretching, send the film material into a hot air circulating furnace, control the furnace temperature at 125℃, and heat treat for 5 minutes to obtain a hard elastic crystalline base film.

[0044] Step 4: Process the hard elastic crystalline base film sequentially: First, perform warm stretching at 80℃ with a stretching ratio of 100%; then, perform hot air stretching in a hot air environment at 115℃ with a stretching ratio of 105%, and hold it on a heating wheel at 130℃ for 25 seconds; then, perform thermal relaxation treatment with a relaxation rate of 18±2%; finally, perform multi-stage heat setting: first, treat at 155℃ for 12 seconds, and then treat at 135℃ for 25 seconds to obtain a microporous base film.

[0045] Step 5: Weigh 8g of polybenzimidazole powder and add it to 400mL of NMP. Stir at 80℃ for 2h to obtain a polybenzimidazole solution. Measure 70mL of tetraethyl orthosilicate and 70mL of anhydrous ethanol, mix them evenly to reduce viscosity, and then add the mixture to the above polybenzimidazole solution. Perform high-speed shear emulsification to obtain a tetraethyl orthosilicate / polybenzimidazole aerogel precursor. Add 0.55g of nanocellulose to 100g of the precursor and stir evenly to obtain the precursor spraying liquid.

[0046] After the microporous membrane was slit, it was first activated by plasma: DBD treatment was used with an argon / oxygen volume ratio of 98:2 and a power density of 0.8 W / cm³. 2 The processing time was 15 seconds. Then, epoxy silane KH-560 was sprayed (15g per square meter of base film), and allowed to stand for 2 minutes to cure. Next, a precursor coating liquid was sprayed using microfluidic technology at a spraying pressure of 0.4 MPa. After spraying, it was pre-cured at 80℃ for 10 minutes, then heated to 200℃ for heat shrink curing for 5 minutes to form a nano-closed-pore aerogel coating with a pore size ≤100nm, thus obtaining the nascent lithium battery separator.

[0047] Step 6: Eliminate static electricity on the nascent lithium battery separator using an ionizer: wind speed 5 m / s, ensuring 100% coverage of the membrane surface, and controlling the ambient humidity at 40–50% RH. Then, rewind to obtain the dry-process high-temperature resistant lithium battery separator.

[0048] Example 2

[0049] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0050] Step 1: Weigh the raw materials according to the mass ratio of 100g polypropylene, 5g polyimide, and 3g PP-b-PI block copolymer, then add 1.0g of crosslinking agent BIBP, and put all the raw materials into the reactor. Purge the reactor with nitrogen until the oxygen content is ≤0.5%, and perform activation treatment under nitrogen protection: control the temperature at 170℃±2℃, the stirring speed at 200r / min, and continue for 5min; then raise the temperature to 190℃, maintain the stirring speed at 200r / min and carry out the crosslinking reaction for 25min, so that PP and PI form an interpenetrating network structure to obtain the polypropylene-polyimide matrix.

[0051] Step 2: Dissolve 3.5g of ammonium polyacrylate in 700mL of deionized water and stir until completely dissolved. Add 70g of nano-α-Al₂O₃ powder (50nm particle size) and ultrasonically disperse at 500W for 30min to obtain a dispersion. Separately, dissolve 30g of ZrOCl₂·8H₂O and 2.68g of Y(NO₃)₃·6H₂O in 300mL of deionized water and stir until completely dissolved to obtain a mixed solution. Adjust the pH of the dispersion to 4.5±0.1 with hydrochloric acid. Add the mixed solution dropwise to the dispersion at a stirring rate of 300r / min. After the addition is complete, place the mixture in a 90℃ water bath and stir for 1.5h to promote the hydrolysis of ZrOCl₂ to form a ZrO(OH)₂ coating layer. After the reaction is complete, wash the product three times with a mixture of ethanol / deionized water (volume ratio 1:1) by centrifugation and dry at 120℃ for 24h. The dried product was placed in a muffle furnace and heated to 600℃ at a rate of 5℃ / min and held for 2 hours to remove organic matter. Then, the temperature was increased to 1200℃ at a rate of 10℃ / min and held for 2 hours. Finally, the product was cooled with the furnace at a rate of ≤3℃ / min to obtain the pre-sintered ZrO2@Al2O3 core-shell packing.

[0052] Weigh 10g of boron nitride sheets (aspect ratio ≥100, thickness ≤10nm), add to 500mL of concentrated nitric acid (68% concentration), and stir in an 80℃ water bath for 6h (stirring rate 300r / min). The NO2 gas generated by the reaction is absorbed and treated by alkaline solution (5% NaOH solution). After the reaction is complete, allow to cool naturally to 25℃, slowly add 500mL of deionized water (volume ratio of 1:1 to the reaction liquid), and sonicate at 400W power and 20kHz frequency for 1h. Centrifuge the mixture (10000r / min, 15min), collect the solid product, wash with deionized water until the pH of the filtrate is 7.0±0.2, wash three times with anhydrous ethanol, and finally dehydrate in a vacuum drying oven at 120℃ for 2h to obtain hydroxylated boron nitride.

[0053] Take 100g of polypropylene-polyimide matrix and heat it to 250℃ in a melting device until it is completely melted. Add 4g of pre-sintered ZrO2@Al2O3 core-shell filler (particle size ≤50nm), 1.33g of hydroxylated boron nitride (BN) sheets (aspect ratio ≥100), and 1.5g of zinc borate to the molten matrix, and stir for 10min to ensure uniform dispersion of the filler. Feed the mixture into a two-stage screw extruder: first-stage temperature 190℃, rotation speed 200 r / min, and shear rate 800s. -1 Simultaneously, 20kHz ultrasonic-assisted directional BN was applied; the second-order temperature was 240℃, the rotation speed was 250r / min, and the shear rate was 1000s. -1 Immediately after extrusion, nitrogen annealing is performed: the mixture is held at 160℃ in a nitrogen atmosphere for 2 minutes, and then transferred to a -60℃ metal roller for rapid cooling with a contact time of 0.5s and a cooling rate of 80℃ / s to obtain a mixed melt.

[0054] Step 3: Place the mixed melt in a stretching device and perform a warm stretching at 70℃: stretching ratio 3.5×, stretching rate 10mm / s, to form a crystalline structure perpendicular to the extrusion direction. After stretching, send the film material into a hot air circulating furnace, control the furnace temperature at 125℃, and heat treat for 5 minutes to obtain a hard elastic crystalline base film.

[0055] Step 4: Process the hard elastic crystalline base film sequentially: First, perform warm stretching at 80℃ with a stretching ratio of 100%; then, perform hot air stretching in a hot air environment at 115℃ with a stretching ratio of 105%, and hold it on a heating wheel at 130℃ for 25 seconds; then, perform thermal relaxation treatment with a relaxation rate of 18±2%; finally, perform multi-stage heat setting: first, treat at 155℃ for 12 seconds, and then treat at 135℃ for 25 seconds to obtain a microporous base film.

[0056] Step 5: Weigh 8g of polybenzimidazole powder and add it to 400mL of NMP. Stir at 80℃ for 2h to obtain a polybenzimidazole solution. Measure 70mL of tetraethyl orthosilicate and 70mL of anhydrous ethanol, mix them evenly to reduce viscosity, and then add the mixture to the above polybenzimidazole solution. Perform high-speed shear emulsification to obtain a tetraethyl orthosilicate / polybenzimidazole aerogel precursor. Add 0.45g of nanocellulose to 100g of the precursor and stir evenly to obtain the precursor spraying liquid.

[0057] After the microporous membrane was slit, it was first activated by plasma: DBD treatment was used with an argon / oxygen volume ratio of 98:2 and a power density of 0.8 W / cm³. 2The processing time was 15 seconds. Then, epoxy silane KH-560 was sprayed (15g per square meter of base film), and allowed to stand for 2 minutes to cure. Next, a precursor coating liquid was sprayed using microfluidic technology at a spraying pressure of 0.4 MPa. After spraying, it was pre-cured at 80℃ for 10 minutes, then heated to 200℃ for heat shrink curing for 5 minutes to form a nano-closed-pore aerogel coating with a pore size ≤100nm, thus obtaining the nascent lithium battery separator.

[0058] Step 6: Eliminate static electricity on the nascent lithium battery separator using an ionizer: wind speed 5 m / s, ensuring 100% coverage of the membrane surface, and controlling the ambient humidity at 40–50% RH. Then, rewind to obtain the dry-process high-temperature resistant lithium battery separator.

[0059] Example 3

[0060] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0061] Step 1: Weigh the raw materials according to the mass ratio of 100g polypropylene, 6g polyimide, and 3.5g PP-b-PI block copolymer, then add 1.0g crosslinking agent BIBP, and put all the raw materials into the reactor. Purge the reactor with nitrogen until the oxygen content is ≤0.5%, and perform activation treatment under nitrogen protection: control the temperature at 170℃±2℃, the stirring speed at 200r / min, and continue for 5min; then raise the temperature to 190℃, maintain the stirring speed at 200r / min, and carry out the crosslinking reaction for 25min, so that PP and PI form an interpenetrating network structure to obtain the polypropylene-polyimide matrix.

[0062] Step 2: Dissolve 3.5g of ammonium polyacrylate in 700mL of deionized water and stir until completely dissolved. Add 70g of nano-α-Al₂O₃ powder (50nm particle size) and ultrasonically disperse at 500W for 30min to obtain a dispersion. Separately, dissolve 30g of ZrOCl₂·8H₂O and 2.68g of Y(NO₃)₃·6H₂O in 300mL of deionized water and stir until completely dissolved to obtain a mixed solution. Adjust the pH of the dispersion to 4.5±0.1 with hydrochloric acid. Add the mixed solution dropwise to the dispersion at a stirring rate of 300r / min. After the addition is complete, place the mixture in a 90℃ water bath and stir for 1.5h to promote the hydrolysis of ZrOCl₂ to form a ZrO(OH)₂ coating layer. After the reaction is complete, wash the product three times with a mixture of ethanol / deionized water (volume ratio 1:1) by centrifugation and dry at 120℃ for 24h. The dried product was placed in a muffle furnace and heated to 600℃ at a rate of 5℃ / min and held for 2 hours to remove organic matter. Then, the temperature was increased to 1200℃ at a rate of 10℃ / min and held for 2 hours. Finally, the product was cooled with the furnace at a rate of ≤3℃ / min to obtain the pre-sintered ZrO2@Al2O3 core-shell packing.

[0063] Weigh 10g of boron nitride sheets (aspect ratio ≥100, thickness ≤10nm), add to 500mL of concentrated nitric acid (68% concentration), and stir in an 80℃ water bath for 6h (stirring rate 300r / min). The NO2 gas generated by the reaction is absorbed and treated by alkaline solution (5% NaOH solution). After the reaction is complete, allow to cool naturally to 25℃, slowly add 500mL of deionized water (volume ratio of 1:1 to the reaction liquid), and sonicate at 400W power and 20kHz frequency for 1h. Centrifuge the mixture (10000r / min, 15min), collect the solid product, wash with deionized water until the pH of the filtrate is 7.0±0.2, wash three times with anhydrous ethanol, and finally dehydrate in a vacuum drying oven at 120℃ for 2h to obtain hydroxylated boron nitride.

[0064] Take 100g of polypropylene-polyimide matrix and heat it to 250℃ in a melting device until it is completely melted. Add 4g of pre-sintered ZrO2@Al2O3 core-shell filler (particle size ≤50nm), 1.33g of hydroxylated boron nitride (BN) sheets (aspect ratio ≥100), and 1.5g of zinc borate to the molten matrix, and stir for 10min to ensure uniform dispersion of the filler. Feed the mixture into a two-stage screw extruder: first-stage temperature 190℃, rotation speed 200 r / min, and shear rate 800s. -1 Simultaneously, 20kHz ultrasonic-assisted directional BN was applied; the second-order temperature was 240℃, the rotation speed was 250r / min, and the shear rate was 1000s. -1 Immediately after extrusion, nitrogen annealing is performed: the mixture is held at 160℃ in a nitrogen atmosphere for 2 minutes, and then transferred to a -60℃ metal roller for rapid cooling with a contact time of 0.5s and a cooling rate of 80℃ / s to obtain a mixed melt.

[0065] Step 3: Place the mixed melt in a stretching device and perform a warm stretching at 70℃: stretching ratio 3.5×, stretching rate 10mm / s, to form a crystalline structure perpendicular to the extrusion direction. After stretching, send the film material into a hot air circulating furnace, control the furnace temperature at 125℃, and heat treat for 5 minutes to obtain a hard elastic crystalline base film.

[0066] Step 4: Process the hard elastic crystalline base film sequentially: First, perform warm stretching at 80℃ with a stretching ratio of 100%; then, perform hot air stretching in a hot air environment at 115℃ with a stretching ratio of 105%, and hold it on a heating wheel at 130℃ for 25 seconds; then, perform thermal relaxation treatment with a relaxation rate of 18±2%; finally, perform multi-stage heat setting: first, treat at 155℃ for 12 seconds, and then treat at 135℃ for 25 seconds to obtain a microporous base film.

[0067] Step 5: Weigh 8g of polybenzimidazole powder and add it to 400mL of NMP. Stir at 80℃ for 2h to obtain a polybenzimidazole solution. Measure 70mL of tetraethyl orthosilicate and 70mL of anhydrous ethanol, mix them evenly to reduce viscosity, and then add the mixture to the above polybenzimidazole solution. Perform high-speed shear emulsification to obtain a tetraethyl orthosilicate / polybenzimidazole aerogel precursor. Add 0.5g of nanocellulose to 100g of the precursor and stir evenly to obtain the precursor spraying liquid.

[0068] After the microporous membrane was slit, it was first activated by plasma: DBD treatment was used with an argon / oxygen volume ratio of 98:2 and a power density of 0.8 W / cm³. 2 The processing time was 15 seconds. Then, epoxy silane KH-560 was sprayed (15g per square meter of base film), and allowed to stand for 2 minutes to cure. Next, a precursor coating liquid was sprayed using microfluidic technology at a spraying pressure of 0.4 MPa. After spraying, it was pre-cured at 80℃ for 10 minutes, then heated to 200℃ for heat shrink curing for 5 minutes to form a nano-closed-pore aerogel coating with a pore size ≤100nm, thus obtaining the nascent lithium battery separator.

[0069] Step 6: Eliminate static electricity on the nascent lithium battery separator using an ionizer: wind speed 5 m / s, ensuring 100% coverage of the membrane surface, and controlling the ambient humidity at 40–50% RH. Then, rewind to obtain the dry-process high-temperature resistant lithium battery separator.

[0070] Example 4

[0071] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0072] Step 1: Weigh the raw materials according to the mass ratio of 100g polypropylene, 8g polyimide, and 5g PP-b-PI block copolymer, then add 1.0g of crosslinking agent BIBP, and put all the raw materials into the reactor. Purge the reactor with nitrogen until the oxygen content is ≤0.5%, and perform activation treatment under nitrogen protection: control the temperature at 170℃±2℃, the stirring speed at 200r / min, and continue for 5min; then raise the temperature to 195℃, maintain the stirring speed at 200r / min and carry out the crosslinking reaction for 30min, so that PP and PI form an interpenetrating network structure to obtain the polypropylene-polyimide matrix.

[0073] Step 2: Dissolve 3.5g of ammonium polyacrylate in 700mL of deionized water and stir until completely dissolved. Add 70g of nano-α-Al₂O₃ powder (50nm particle size) and ultrasonically disperse at 500W for 30min to obtain a dispersion. Separately, dissolve 30g of ZrOCl₂·8H₂O and 2.68g of Y(NO₃)₃·6H₂O in 300mL of deionized water and stir until completely dissolved to obtain a mixed solution. Adjust the pH of the dispersion to 4.5±0.1 with hydrochloric acid. Add the mixed solution dropwise to the dispersion at a stirring rate of 300r / min. After the addition is complete, place the mixture in a 90℃ water bath and stir for 1.5h to promote the hydrolysis of ZrOCl₂ to form a ZrO(OH)₂ coating layer. After the reaction is complete, wash the product three times with a mixture of ethanol / deionized water (volume ratio 1:1) by centrifugation and dry at 120℃ for 24h. The dried product was placed in a muffle furnace and heated to 600℃ at a rate of 5℃ / min and held for 2 hours to remove organic matter. Then, the temperature was increased to 1200℃ at a rate of 10℃ / min and held for 2 hours. Finally, the product was cooled with the furnace at a rate of ≤3℃ / min to obtain the pre-sintered ZrO2@Al2O3 core-shell packing.

[0074] Weigh 10g of boron nitride sheets (aspect ratio ≥100, thickness ≤10nm), add to 500mL of concentrated nitric acid (68% concentration), and stir in an 80℃ water bath for 6h (stirring rate 300r / min). The NO2 gas generated by the reaction is absorbed and treated by alkaline solution (5% NaOH solution). After the reaction is complete, allow to cool naturally to 25℃, slowly add 500mL of deionized water (volume ratio of 1:1 to the reaction liquid), and sonicate at 400W power and 20kHz frequency for 1h. Centrifuge the mixture (10000r / min, 15min), collect the solid product, wash with deionized water until the pH of the filtrate is 7.0±0.2, wash three times with anhydrous ethanol, and finally dehydrate in a vacuum drying oven at 120℃ for 2h to obtain hydroxylated boron nitride.

[0075] Take 100g of polypropylene-polyimide matrix and heat it to 250℃ in a melting device until it is completely melted. Add 4g of pre-sintered ZrO2@Al2O3 core-shell filler (particle size ≤50nm), 1.33g of hydroxylated boron nitride (BN) sheets (aspect ratio ≥100), and 1.5g of zinc borate to the molten matrix, and stir for 10min to ensure uniform dispersion of the filler. Feed the mixture into a two-stage screw extruder: first-stage temperature 190℃, rotation speed 200 r / min, and shear rate 800s. -1 Simultaneously, 20kHz ultrasonic-assisted directional BN was applied; the second-order temperature was 240℃, the rotation speed was 250r / min, and the shear rate was 1000s. -1Immediately after extrusion, nitrogen annealing is performed: the mixture is held at 160℃ in a nitrogen atmosphere for 2 minutes, and then transferred to a -60℃ metal roller for rapid cooling with a contact time of 0.5s and a cooling rate of 80℃ / s to obtain a mixed melt.

[0076] Step 3: Place the mixed melt in a stretching device and perform a warm stretching at 80℃: stretching ratio 3.5×, stretching rate 10mm / s, to form a crystalline structure perpendicular to the extrusion direction. After stretching, send the film material into a hot air circulating furnace, control the furnace temperature at 125℃, and heat treat for 5 minutes to obtain a hard elastic crystalline base film.

[0077] Step 4: Process the hard elastic crystalline base film sequentially: First, perform warm stretching at 85℃ with a stretching ratio of 100%; then, perform hot air stretching in a hot air environment at 120℃ with a stretching ratio of 105%, and hold it on a heating wheel at 130℃ for 25 seconds; then, perform thermal relaxation treatment with a relaxation rate of 18±2%; finally, perform multi-stage heat setting: first, treat at 160℃ for 15 seconds, and then treat at 140℃ for 30 seconds to obtain a microporous base film.

[0078] Step 5: Weigh 8g of polybenzimidazole powder and add it to 400mL of NMP. Stir at 80℃ for 2h to obtain a polybenzimidazole solution. Measure 70mL of tetraethyl orthosilicate and 70mL of anhydrous ethanol, mix them evenly to reduce viscosity, and then add the mixture to the above polybenzimidazole solution. Perform high-speed shear emulsification to obtain a tetraethyl orthosilicate / polybenzimidazole aerogel precursor. Add 0.6g of nanocellulose to 100g of the precursor and stir evenly to obtain the precursor spraying liquid.

[0079] After the microporous membrane was slit, it was first activated by plasma: DBD treatment was used with an argon / oxygen volume ratio of 98:2 and a power density of 0.8 W / cm³. 2 The processing time was 15 seconds. Then, epoxy silane KH-560 was sprayed (15g per square meter of base film), and allowed to stand for 2 minutes to cure. Next, a precursor coating liquid was sprayed using microfluidic technology at a spraying pressure of 0.4 MPa. After spraying, it was pre-cured at 80℃ for 10 minutes, then heated to 200℃ for heat shrink curing for 5 minutes to form a nano-closed-pore aerogel coating with a pore size ≤100nm, thus obtaining the nascent lithium battery separator.

[0080] Step 6: Eliminate static electricity on the nascent lithium battery separator using an ionizer: wind speed 5 m / s, ensuring 100% coverage of the membrane surface, and controlling the ambient humidity at 40–50% RH. Then, rewind to obtain the dry-process high-temperature resistant lithium battery separator.

[0081] Example 5

[0082] A method for preparing a dry-process high-temperature resistant lithium battery separator includes the following steps:

[0083] Step 1: Weigh the raw materials according to the mass ratio of 100g polypropylene, 4g polyimide, and 2g PP-b-PI block copolymer, then add 1.0g of crosslinking agent BIBP, and put all the raw materials into the reactor. Purge the reactor with nitrogen until the oxygen content is ≤0.5%, and perform activation treatment under nitrogen protection: control the temperature at 170℃±2℃, the stirring speed at 200r / min, and continue for 5min; then raise the temperature to 185℃, maintain the stirring speed at 200r / min and carry out the crosslinking reaction for 20min, so that PP and PI form an interpenetrating network structure to obtain the polypropylene-polyimide matrix.

[0084] Step 2: Dissolve 3.5g of ammonium polyacrylate in 700mL of deionized water and stir until completely dissolved. Add 70g of nano-α-Al₂O₃ powder (50nm particle size) and ultrasonically disperse at 500W for 30min to obtain a dispersion. Separately, dissolve 30g of ZrOCl₂·8H₂O and 2.68g of Y(NO₃)₃·6H₂O in 300mL of deionized water and stir until completely dissolved to obtain a mixed solution. Adjust the pH of the dispersion to 4.5±0.1 with hydrochloric acid. Add the mixed solution dropwise to the dispersion at a stirring rate of 300r / min. After the addition is complete, place the mixture in a 90℃ water bath and stir for 1.5h to promote the hydrolysis of ZrOCl₂ to form a ZrO(OH)₂ coating layer. After the reaction is complete, wash the product three times with a mixture of ethanol / deionized water (volume ratio 1:1) by centrifugation and dry at 120℃ for 24h. The dried product was placed in a muffle furnace and heated to 600℃ at a rate of 5℃ / min and held for 2 hours to remove organic matter. Then, the temperature was increased to 1200℃ at a rate of 10℃ / min and held for 2 hours. Finally, the product was cooled with the furnace at a rate of ≤3℃ / min to obtain the pre-sintered ZrO2@Al2O3 core-shell packing.

[0085] Weigh 10g of boron nitride sheets (aspect ratio ≥100, thickness ≤10nm), add to 500mL of concentrated nitric acid (68% concentration), and stir in an 80℃ water bath for 6h (stirring rate 300r / min). The NO2 gas generated by the reaction is absorbed and treated by alkaline solution (5% NaOH solution). After the reaction is complete, allow to cool naturally to 25℃, slowly add 500mL of deionized water (volume ratio of 1:1 to the reaction liquid), and sonicate at 400W power and 20kHz frequency for 1h. Centrifuge the mixture (10000r / min, 15min), collect the solid product, wash with deionized water until the pH of the filtrate is 7.0±0.2, wash three times with anhydrous ethanol, and finally dehydrate in a vacuum drying oven at 120℃ for 2h to obtain hydroxylated boron nitride.

[0086] Take 100g of polypropylene-polyimide matrix and heat it to 250℃ in a melting device until it is completely melted. Add 4g of pre-sintered ZrO2@Al2O3 core-shell filler (particle size ≤50nm), 1.33g of hydroxylated boron nitride (BN) sheets (aspect ratio ≥100), and 1.5g of zinc borate to the molten matrix, and stir for 10min to ensure uniform dispersion of the filler. Feed the mixture into a two-stage screw extruder: first-stage temperature 190℃, rotation speed 200 r / min, and shear rate 800s. -1 Simultaneously, 20kHz ultrasonic-assisted directional BN was applied; the second-order temperature was 240℃, the rotation speed was 250r / min, and the shear rate was 1000s. -1 Immediately after extrusion, nitrogen annealing is performed: the mixture is held at 160℃ in a nitrogen atmosphere for 2 minutes, and then transferred to a -60℃ metal roller for rapid cooling with a contact time of 0.5s and a cooling rate of 80℃ / s to obtain a mixed melt.

[0087] Step 3: Place the mixed melt in a stretching device and perform a warm stretching at 60℃: stretching ratio 3.5×, stretching rate 10mm / s, to form a crystalline structure perpendicular to the extrusion direction. After stretching, send the film material into a hot air circulating furnace, control the furnace temperature at 125℃, and heat treat for 5 minutes to obtain a hard elastic crystalline base film.

[0088] Step 4: Process the hard elastic crystalline base film sequentially: First, perform warm stretching at 70℃ with a stretching ratio of 100%; then, perform hot air stretching in a hot air environment at 110℃ with a stretching ratio of 105%, and hold it on a heating wheel at 130℃ for 25 seconds; then, perform thermal relaxation treatment with a relaxation rate of 18±2%; finally, perform multi-stage heat setting: first, treat at 150℃ for 10 seconds, and then treat at 130℃ for 20 seconds to obtain a microporous base film.

[0089] Step 5: Weigh 8g of polybenzimidazole powder and add it to 400mL of NMP. Stir at 80℃ for 2h to obtain a polybenzimidazole solution. Measure 70mL of tetraethyl orthosilicate and 70mL of anhydrous ethanol, mix them evenly to reduce viscosity, and then add the mixture to the above polybenzimidazole solution. Perform high-speed shear emulsification to obtain a tetraethyl orthosilicate / polybenzimidazole aerogel precursor. Add 0.4g of nanocellulose to 100g of the precursor and stir evenly to obtain the precursor spraying liquid.

[0090] After the microporous membrane was slit, it was first activated by plasma: DBD treatment was used with an argon / oxygen volume ratio of 98:2 and a power density of 0.8 W / cm³. 2The processing time was 15 seconds. Then, epoxy silane KH-560 was sprayed (15g per square meter of base film), and allowed to stand for 2 minutes to cure. Next, a precursor coating liquid was sprayed using microfluidic technology at a spraying pressure of 0.4 MPa. After spraying, it was pre-cured at 80℃ for 10 minutes, then heated to 200℃ for heat shrink curing for 5 minutes to form a nano-closed-pore aerogel coating with a pore size ≤100nm, thus obtaining the nascent lithium battery separator.

[0091] Step 6: Eliminate static electricity on the nascent lithium battery separator using an ionizer: wind speed 5 m / s, ensuring 100% coverage of the membrane surface, and controlling the ambient humidity at 40–50% RH. Then, rewind to obtain the dry-process high-temperature resistant lithium battery separator.

[0092] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that in step 1, the polypropylene is not modified, that is, the polypropylene-polyimide matrix is ​​replaced with ordinary polypropylene matrix.

[0093] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that step 2 is omitted, that is, the pre-sintered ZrO2@Al2O3 core-shell filler and hydroxylated boron nitride are not doped in the polypropylene-polyimide matrix.

[0094] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that in step 2, the pre-sintered ZrO2@Al2O3 core-shell filler is replaced with ordinary ZrO2@Al2O3 core-shell filler.

[0095] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that step 5 is omitted, that is, a nano-closed-pore aerogel coating is not deposited on the microporous base membrane.

[0096] Comparative Example 5: The difference between Comparative Example 4 and Example 1 is that in step 5, the precursor spraying liquid does not contain nanocellulose.

[0097] Performance testing:

[0098] 1. Heat Shrinkage Rate Test: Following GB / T 36363-2018 "Polyolefin Separators for Lithium-ion Batteries" standard, the separator was cut into 100mm × 100mm square samples. These samples were placed in a 200℃ oven for 1 hour, and after cooling to room temperature, the longitudinal and transverse length changes were measured. The heat shrinkage rate was calculated using the formula "Heat Shrinkage Rate = (Initial Length - Length After Treatment) / Initial Length × 100%". The average of three parallel tests was taken. The test results are shown in Table 1.

[0099] 2. Thermal decomposition temperature test: Thermogravimetric analysis (TGA) was used. Under a nitrogen atmosphere (flow rate 50 mL / min), approximately 5 mg of diaphragm sample was heated from room temperature to 600 °C at a rate of 10 °C / min. The temperature at which the sample mass loss was 5% was recorded as the thermal decomposition temperature. The average value of two parallel tests was taken. The test results are shown in Table 1.

[0100] 3. Tensile Strength Test: According to GB / T 21302-2007 "Polyolefin Separators for Lithium-ion Batteries", the separator was cut into strips 150 mm long and 15 mm wide. A universal testing machine was used to test the tensile strength at a tensile rate of 50 mm / min. The maximum load at break was recorded. Tensile strength was calculated using the formula "Tensile Strength = Maximum Load / Specimen Width × Specimen Thickness", and the average of five parallel tests was taken. The test results are shown in Table 1.

[0101] 4. Battery Rate Performance Test: CR2032 coin cells (positive electrode: LiCoO2, negative electrode: metallic Li) were assembled using a separator. The electrolyte was 1 mol / L LiPF6 / EC+DMC+EMC, volume ratio 1:1:1. Using a battery testing system at 25℃, the cells were charged to 4.2V at 0.2C, and then discharged to 3.0V at 0.5C, 1C, 2C, and 5C rates. The ratio of the 5C discharge capacity to the 0.5C discharge capacity was recorded as the rate performance retention rate. The average value of the three battery tests was taken. The test results are shown in Table 1.

[0102] Table 1:

[0103]

[0104] 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 dry-process high-temperature resistant lithium battery separator, characterized in that, Includes the following steps: a) Polypropylene, polyimide, PP-b-PI block copolymer and crosslinking agent BIBP are activated and then crosslinked under nitrogen protection to obtain a polypropylene-polyimide matrix with an interpenetrating network; b) After melting the polypropylene-polyimide matrix, add pre-sintered ZrO2@Al2O3 core-shell filler, hydroxylated boron nitride and zinc borate, and then extrude it through a two-stage screw extruder with ultrasonic orientation. Subsequently, nitrogen annealing and cold roll quenching are performed sequentially to obtain a mixed melt. c) The mixed melt is stretched once under warm conditions, and then subjected to hot air circulation heat treatment to obtain a hard elastic crystalline base film; d) The hard elastic crystalline base film is subjected to warm stretching, hot air stretching, thermal relaxation and heat setting in sequence to lock the microporous structure and obtain a microporous base film. e) After the microporous base membrane is slit, it is first activated by plasma, then sprayed with epoxy silane, followed by microfluidic spraying of tetraethyl orthosilicate / polybenzimidazole aerogel precursor, and then pre-cured and heat-shrinked cured in sequence to form a nano-closed-pore aerogel coating, thus obtaining the nascent lithium battery separator. f) After electrostatic elimination by ion wind, the nascent lithium battery separator is wound up to obtain a dry-process high-temperature resistant lithium battery separator.

2. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step a), the mass ratio of polypropylene, polyimide, and PP-b-PI block copolymer is 100:4-8:2-5.

3. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step a), the crosslinking temperature is 185–195°C and the crosslinking time is 20–30 min.

4. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step b), the preparation method of the pre-sintered ZrO2@Al2O3 core-shell filler is as follows: First, ammonium polyacrylate was dissolved in deionized water, and Al2O3 powder was added and ultrasonically dispersed to obtain a dispersion. ZrOCl2·8H2O and Y(NO3)3·6H2O were added to deionized water and stirred to dissolve, resulting in a mixed solution. The pH of the dispersion was adjusted to 4.5±0.1, and then the mixed solution was added dropwise to the dispersion. The mixture was heated and stirred in a water bath to promote the hydrolysis of ZrOCl2, forming a ZrO(OH)2 coating layer on the surface of Al2O3. After washing and drying, the dried product was placed in a muffle furnace and sintered at a higher temperature to obtain a pre-sintered ZrO2@Al2O3 core-shell filler.

5. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step b), the preparation method of hydroxylated boron nitride includes the following steps: Boron nitride was added to concentrated nitric acid and heated to carry out an oxidation reaction. After the reaction was completed, the mixture was cooled, and then deionized water was added for ultrasonic treatment. After centrifugation, washing, and drying, hydroxylated boron nitride was obtained.

6. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step c), the first stretching temperature is 60-80℃.

7. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step d), the temperature for warm stretching is 70–85°C; the temperature for hot air stretching is 110–120°C.

8. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step d), the heat setting process involves first treating at 150–160°C for 10–15 seconds, and then treating at 130–140°C for 20–30 seconds.

9. The method for preparing a dry-process high-temperature resistant lithium battery separator according to claim 1, characterized in that, In step e), nanocellulose is also added to the tetraethyl orthosilicate / polybenzimidazole aerogel precursor, and the amount of nanocellulose added is 0.4 to 0.6% of the mass of the tetraethyl orthosilicate / polybenzimidazole aerogel precursor.

10. A dry-process high-temperature resistant lithium battery separator, characterized in that, Prepared by the method described in any one of claims 1-9 above.

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