High-strength separator for fast-charging lithium ion batteries and preparation method thereof

Abstract

The application discloses a high-strength diaphragm for fast-charging lithium ion batteries and a preparation method thereof, and belongs to the technical field of battery diaphragms. Zirconium-doped boehmite and dopamine are coated to obtain polydopamine-coated zirconium-doped boehmite, which is then compounded with mercapto mesoporous nano-silicon dioxide to form nano-enhanced particles. Then, the nano-enhanced particles, nano-cellulose whiskers, an adhesive, deionized water, a silane coupling agent KH-550, a wetting agent, polyvinylidene fluoride and N,N-dimethylformamide are mixed to prepare a composite slurry. Through a coating and heat curing process, the high-strength diaphragm for fast-charging lithium ion batteries is obtained. The high-thermal-stability, high-mechanical-strength, good electrolyte affinity and excellent ionic conductivity are realized, and the safety and electrochemical performance of the diaphragm in a fast-charging scenario are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a high-strength separator for fast-charging lithium-ion batteries and its preparation method. Background Technology

[0002] As one of the four key materials of a battery, the lithium-ion battery separator is an insulating film with a specific porous structure. The main materials are polyolefins and modified types such as ceramic coating and polymer composites. Its core function is to physically isolate the positive and negative electrodes to prevent short circuits and to provide a transport channel for lithium ions. Its porous structure, pore size and distribution directly affect the battery performance.

[0003] As a key component of core energy storage devices in the new energy field, the separator, although not directly involved in electrochemical reactions, plays a decisive role in battery safety, cycle life, and charge / discharge efficiency. However, with the increasing demand for charging speed from products such as electric vehicles and fast-charging mobile phones, high-rate fast charging technology brings multiple stringent challenges to the separator: insufficient lithium-ion transport rate under high current can easily lead to concentration polarization and lithium dendrite precipitation; high temperatures caused by rapid heat generation can easily cause traditional polyolefin separators to shrink and melt, leading to short circuits; lithium dendrite growth may puncture separators with insufficient mechanical strength; and insufficient hydrophilicity and liquid retention capacity of the separator will further aggravate the transmission resistance and lead to battery performance degradation. Therefore, high-performance separators for fast charging scenarios must possess high ionic conductivity (suitable porosity, uniform pore size distribution, and good connectivity), excellent thermal stability (dimensional stability at 80-150℃), high mechanical strength and puncture resistance, good electrolyte wettability and liquid retention capacity, and stable chemical compatibility.

[0004] Chinese invention patent application CN118198653A discloses a secondary battery separator coating slurry, a composite separator, and a preparation method. The secondary battery separator coating slurry uses nanofiber cellulose whisker material with high wettability, high heat resistance, and lightweight, as well as high-adhesion, low-cost PMMA material, which combines the performance advantages of both materials. In the structure of this composite separator, the flexible three-dimensional network skeleton is mainly composed of nanofiber whisker material. However, under fast charging conditions, lithium dendrites grow vigorously, rapidly, and with high hardness, making it difficult to provide sufficient rigid support. They are easily pierced by sharp dendrites, leading to internal short circuits, high-temperature thermal runaway, and even serious safety accidents such as fires and explosions. Summary of the Invention

[0005] The purpose of this invention is to provide a high-strength separator for fast-charging lithium-ion batteries and its preparation method. Thiol-based mesoporous nano-silica is prepared by template method combined with surface modification. Reinforcing units with zirconium-doped boehmite as the core and polydopamine as the interface layer are obtained by hydrothermal synthesis and interface coating. The two are combined into nano-reinforcing particles, which work synergistically with nanocellulose whisker framework to achieve a multifunctional composite coating with high thermal stability, high mechanical strength, good electrolyte affinity and excellent ionic conductivity, significantly improving the safety and electrochemical performance of the separator in fast-charging scenarios.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a high-strength separator for fast-charging lithium-ion batteries includes the following steps:

[0008] Step 1: Zirconium-doped boehmite was prepared by co-precipitation, then coated with polydopamine, and then combined with mercapto-based mesoporous silica nanoparticles synthesized by template method to obtain nano-reinforced particles.

[0009] Step 2: Mix nano-reinforcing particles, nano-cellulose whiskers, binder, deionized water, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride and N,N-dimethylformamide to prepare a composite slurry; coat the composite slurry on the surface of a polyolefin separator and heat-cur it to obtain a high-strength separator for fast-charging lithium-ion batteries.

[0010] Furthermore, the specific preparation steps of the nano-reinforcing particles are as follows:

[0011] Tris(hydroxymethyl)aminomethane was added to deionized water and stirred for 30-40 min. Then, mercapto-based mesoporous silica nanoparticles were added and sonicated for 15-30 min. Next, polydopamine-coated zirconium-doped boehmite was added and stirred at room temperature for 6-8 h. After centrifugation for 15-30 min, the mixture was filtered. The filter cake was washed 3-5 times alternately with deionized water and anhydrous ethanol and then vacuum dried to constant weight to obtain nano-reinforced particles.

[0012] Furthermore, the ratio of tris(hydroxymethyl)aminomethane, deionized water, mercapto-mesoporous nano-silica, and polydopamine-coated zirconium-doped boehmite is 7.2-12.6 g: 600-1000 mL: 12-15 g: 6-8 g.

[0013] Furthermore, the specific preparation steps of thiol-based mesoporous silica nanoparticles are as follows:

[0014] Hexadecyltrimethylammonium bromide and triethanolamine were dissolved in deionized water, and sodium salicylate was added. The mixture was stirred at 80-90℃ and 500-600 rpm until the solid was completely dissolved. Tetraethyl orthosilicate was added dropwise and stirred for 2-3 hours. Then, silane coupling agent KH590 was added dropwise and stirred for another 2-3 hours to obtain a milky white solution. The solution was centrifuged at 3500-4000 rpm, and the solid was collected. The solid was washed alternately with anhydrous ethanol and deionized water 3-5 times and dried under vacuum to constant weight to obtain mercapto-based mesoporous silica nanoparticles.

[0015] Furthermore, the ratio of hexadecyltrimethylammonium bromide, triethanolamine, deionized water, sodium salicylate, tetraethyl orthosilicate, and silane coupling agent KH590 is 3.64-6.68g: 5.44-10.22g: 160-300mL: 2.4-4.5g: 32-36g: 8-15g.

[0016] Furthermore, the specific preparation steps for polydopamine-coated zirconium-doped boehmite are as follows:

[0017] Zirconium-doped boehmite was added to Tris buffer solution (10 mM, pH 8.5), sonicated for 20-30 min, dopamine was added, stirred in the dark for 12-15 h, centrifuged for 15-30 min, filtered, and the product was washed with deionized water and anhydrous ethanol alternately 3-5 times, and dried under vacuum to constant weight to obtain polydopamine-coated zirconium-doped boehmite.

[0018] Furthermore, the ratio of zirconium-doped boehmite, Tris buffer solution, and dopamine is 1 g: 1 L: 1 g.

[0019] Furthermore, the specific preparation steps for zirconium-doped boehmite are as follows:

[0020] Add water-soluble zirconium salt and water-soluble aluminum salt to deionized water and stir until completely dissolved. Adjust the pH to 10 with sodium hydroxide solution and stir magnetically for 30-40 min. Transfer to a polytetrafluoroethylene reactor and react at 150-160℃ for 24-30 h. Centrifuge at 8000-9000 rpm for 15-30 min, filter, and wash the filter cake alternately with ethanol and deionized water 3-5 times. Vacuum dry to constant weight to obtain zircon-doped boehmite.

[0021] Furthermore, the ratio of water-soluble zirconium salt and water-soluble aluminum salt to deionized water is 4.3-8.2g: 33.76-65.42g: 1-1.5L.

[0022] Furthermore, the water-soluble zirconium salt is either zirconium nitrate or zirconium sulfate.

[0023] Furthermore, the water-soluble aluminum salt is either aluminum nitrate or aluminum sulfate.

[0024] Furthermore, the specific preparation steps for the high-strength separator used in fast-charging lithium-ion batteries are as follows:

[0025] Nano-reinforcing particles, nano-cellulose whiskers, binder, and deionized water are mixed and stirred at 2000-3000 rpm rotation and 20-30 rpm revolution for 30-40 minutes. Then, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride, and N,N-dimethylformamide are added, and the mixture is stirred at 600-800 rpm rotation and 20-30 rpm revolution for 60-70 minutes to obtain a composite slurry. The slurry is then uniformly coated onto the surface of a polyolefin separator substrate using a gravure roller coating process. After thermosetting at 150-160℃ for 30-40 minutes, a high-strength separator for fast-charging lithium-ion batteries is obtained.

[0026] Furthermore, the adhesive is either sodium polyacrylate or sodium carboxymethyl cellulose.

[0027] Furthermore, the ratio of the amounts of nano-reinforcing particles, nanocellulose whiskers, binder, deionized water, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride, and N,N-dimethylformamide is 15-20g: 15-20g: 3-5g: 30-50mL: 2-3g: 0.3-0.5g: 8-10g: 30-50mL.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention develops a fast-charging lithium-ion battery separator with excellent comprehensive performance through multi-level composite and synergistic design; the nano-reinforcing particles composed of zirconium-doped boehmite and mercapto-based mesoporous silica covalently linked with polydopamine combine the rigid support of boehmite with the efficient electrolyte wetting and storage capacity of mesoporous silica to construct multi-level ion transport channels, significantly improving ion conductivity to meet the requirements of fast charging, and forming a flexible three-dimensional skeleton with nanocellulose whiskers to ensure the high thermal stability and mechanical strength of the separator.

[0030] By using a gravure roller coating process to firmly bond functional particles with a fiber skeleton, the resulting separator exhibits excellent thermal dimensional stability, puncture resistance, low interfacial impedance, and outstanding electrolyte retention, fundamentally and simultaneously improving the fast-charging performance, cycle life, and safety of lithium-ion batteries.

[0031] 2. The nano-reinforcing particles in this invention creatively construct a "core-bridge-shell" composite structure. Zirconium-doped boehmite serves as a rigid core, providing excellent thermal stability and puncture resistance. Simultaneously, polydopamine is used as a highly adhesive "molecular bridge" to firmly coat the surface of mesoporous mercapto silica. This synergistically endows the membrane with a "rigid-flexible" mechanical reinforcement, preventing lithium dendrite puncture while ensuring overall flexibility. The synergistic high-speed ion channels significantly improve ionic conductivity to meet fast charging requirements. Through the excellent interfacial compatibility of polydopamine, the bonding force between the nanoparticles and the fiber matrix is ​​enhanced, reducing interfacial impedance and ensuring the structural integrity and electrochemical stability of the membrane during long-term cycling. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments in the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: A method for preparing a high-strength separator for fast-charging lithium-ion batteries, comprising the following steps:

[0034] S1: Dissolve 3.64 g cetyltrimethylammonium bromide and 5.44 g triethanolamine in 160 mL of deionized water, then add 2.4 g sodium salicylate. Stir at 80 °C and 500 rpm until the solid is completely dissolved. Add 32 g tetraethyl orthosilicate dropwise and stir for 2 h. Then add 8 g silane coupling agent KH590 dropwise and continue stirring for 2 h to obtain a milky white solution. Centrifuge at 3500 rpm to collect the solid. Wash the solid three times alternately with anhydrous ethanol and deionized water. Dry under vacuum at 120 °C for 12 h to obtain mercapto-mesoporous nano-silica with an average particle size of 150 nm.

[0035] Using micelles formed by CTAB as templates, tetraethyl orthosilicate is hydrolyzed and condensed under the action of triethanolamine and sodium salicylate to form a dendritic silica / CTAB composite material. The silane coupling agent KH590 is covalently grafted onto the silanol groups on the surface of the composite material to introduce thiol functional groups. The template and impurities are then removed by washing to obtain thiol-based mesoporous nano silica.

[0036] S2: Add 4.3g of zirconium nitrate and 33.76g of aluminum nitrate to 1L of deionized water, stir until completely dissolved, adjust the pH to 10 with sodium hydroxide solution, stir magnetically for 30min, transfer to a polytetrafluoroethylene reactor, react at 150℃ for 24h, centrifuge at 8000rpm for 15min, filter, wash the filter cake three times alternately with ethanol and deionized water, and vacuum dry to constant weight to obtain zirconium-doped boehmite powder with an average particle size of 80nm.

[0037] An aluminum-zirconium mixed hydroxide precursor was obtained under alkaline conditions via co-precipitation. Under high temperature and pressure, the precursor underwent a dissolution-recrystallization process, which directionally generated a crystalline boehmite main framework. Zirconium ions were doped into the boehmite lattice through heterovalent substitution, forming a zirconium-doped boehmite material.

[0038] S3: Add 4g of zirconium-doped boehmite powder to 4L of Tris buffer solution (10 mM, pH 8.5), sonicate for 20min, add 4g of dopamine, stir in the dark for 12h, centrifuge for 15min, filter, wash the product with deionized water and anhydrous ethanol three times alternately, and vacuum dry to constant weight to obtain polydopamine-coated zirconium-doped boehmite.

[0039] In Tris buffer, dopamine undergoes oxidative self-polymerization to generate a polydopamine layer with an average thickness of 30 nm, which is then coated on the zircon-doped boehmite surface.

[0040] S4: Add 7.2g of tris(hydroxymethyl)aminomethane to 600mL of deionized water and stir for 30min. Then add 12g of mercapto-mesoporous nano silica and sonicate for 15min. Then add 6g of polydopamine-coated zirconium-doped boehmite and stir at room temperature for 6h. Centrifuge for 15min and filter. Wash the filter cake three times alternately with deionized water and anhydrous ethanol and vacuum dry to constant weight to obtain nano-reinforced particles.

[0041] In Tris buffer, the active groups on the surface of zirconium-doped boehmite are coated with polydopamine and covalently react with the thiol groups on the surface of modified dendritic silica. At the same time, hydrogen bonds, coordination bonds and the inherent strong adhesion of polydopamine are used to make them composite, thus obtaining nano-reinforced particles.

[0042] S5: Mix 15g of nano-reinforcing particles, 15g of nano-cellulose whiskers, 3g of sodium polyacrylate and 30mL of deionized water, and stir at 2000rpm for 30min. Then add 2g of silane coupling agent KH-550, 0.3g of wetting agent, 8g of polyvinylidene fluoride and 30mL of N,N-dimethylformamide, and stir at 600rpm for 60min to obtain a composite slurry. Use a gravure roller coating process to uniformly coat the slurry onto the surface of a polyolefin separator. After heat curing at 150℃ for 30min, a high-strength separator for fast-charging lithium-ion batteries is obtained.

[0043] Example 2: A method for preparing a high-strength separator for fast-charging lithium-ion batteries, comprising the following steps:

[0044] S1: Dissolve 5.16g hexadecyltrimethylammonium bromide and 7.83g triethanolamine in 230mL of deionized water, then add 3.45g sodium salicylate. Stir at 85℃ and 550rpm until the solid is completely dissolved. Add 34g tetraethyl orthosilicate dropwise and stir for 2.5h. Then add 11.5g silane coupling agent KH590 dropwise and continue stirring for 2.5h to obtain a milky white solution. Centrifuge at 3750rpm to collect the solid. Wash the solid four times alternately with anhydrous ethanol and deionized water. Dry under vacuum at 125℃ for 14h to obtain mercapto-mesoporous nano-silica with an average particle size of 150nm.

[0045] S2: Add 6.25g zirconium nitrate and 49.59g aluminum nitrate to 1.25L deionized water, stir until completely dissolved, adjust the pH to 10 with sodium hydroxide solution, stir magnetically for 35min, transfer to a polytetrafluoroethylene reactor, react at 155℃ for 27h, centrifuge at 8500rpm for 22.5min, filter, wash the filter cake alternately with ethanol and deionized water 4 times, and vacuum dry to constant weight to obtain zirconium-doped boehmite powder with an average particle size of 80nm.

[0046] S3: Add 6g of zirconium-doped boehmite powder to 6L of Tris buffer solution (10 mM, pH 8.5), sonicate for 25min, add 6g of dopamine, stir in the dark for 13.5h, centrifuge for 22.5min, filter, wash the precipitate with deionized water and anhydrous ethanol alternately 4 times, and vacuum dry to constant weight to obtain polydopamine-coated zirconium-doped boehmite.

[0047] S4: Add 9.9g of tris(hydroxymethyl)aminomethane to 800mL of deionized water and stir for 35min. Then add 13.5g of mercapto-mesoporous nano-silica and sonicate for 22.5min. Then add 7g of polydopamine-coated zirconium-doped boehmite and stir at room temperature for 7h. Centrifuge for 22.5min and filter. Wash the filter cake with deionized water and anhydrous ethanol alternately 4 times and vacuum dry to constant weight to obtain nano-reinforced particles.

[0048] S5: Mix 17.5g of nano-reinforcing particles, 17.5g of nano-cellulose whiskers, 4g of sodium polyacrylate and 40mL of deionized water, and stir at 2500rpm for 35min. Then add 2.5g of silane coupling agent KH-550, 0.4g of wetting agent, 9g of polyvinylidene fluoride and 40mL of N,N-dimethylformamide, and stir at 700rpm for 65min to obtain a composite slurry. Use a gravure roller coating process to uniformly coat the slurry onto the surface of a polyolefin separator substrate. After heat curing at 155℃ for 35min, a high-strength separator for fast-charging lithium-ion batteries is obtained.

[0049] Example 3: A method for preparing a high-strength separator for fast-charging lithium-ion batteries, comprising the following steps:

[0050] S1: Dissolve 6.68g of hexadecyltrimethylammonium bromide and 10.22g of triethanolamine in 300mL of deionized water, then add 4.5g of sodium salicylate. Stir at 90℃ and 600rpm until the solid is completely dissolved. Add 36g of tetraethyl orthosilicate dropwise and stir for 3h. Then add 15g of silane coupling agent KH590 dropwise and continue stirring for 3h to obtain a milky white solution. Centrifuge at 4000rpm to collect the solid. Wash the solid alternately with anhydrous ethanol and deionized water 5 times and vacuum dry at 130℃ for 16h to obtain mercapto-mesoporous nano-silica with an average particle size of 150nm.

[0051] S2: Add 8.2g zirconium nitrate and 65.42g aluminum nitrate to 1.5L of deionized water, stir until completely dissolved, adjust the pH to 10 with sodium hydroxide solution, stir magnetically for 40min, transfer to a polytetrafluoroethylene reactor, react at 160℃ for 30h, centrifuge at 9000rpm for 30min, filter, wash the filter cake alternately with ethanol and deionized water 5 times, and vacuum dry to constant weight to obtain zirconium-doped boehmite powder with an average particle size of 80nm.

[0052] S3: Add 8g of zirconium-doped boehmite powder to 8L of Tris buffer solution (10 mM, pH 8.5), sonicate for 30min, add 8g of dopamine, stir in the dark for 15h, centrifuge for 30min, filter, wash the product with deionized water and anhydrous ethanol alternately 5 times, and vacuum dry to constant weight to obtain polydopamine-coated zirconium-doped boehmite.

[0053] S4: Add 12.6g of tris(hydroxymethyl)aminomethane to 1000mL of deionized water and stir for 40min. Then add 15g of mercapto-mesoporous nano-silica and sonicate for 30min. Then add 8g of polydopamine-coated zirconium-doped boehmite and stir at room temperature for 8h. Centrifuge for 30min and filter. Wash the filter cake alternately with deionized water and anhydrous ethanol 5 times and vacuum dry to constant weight to obtain nano-reinforced particles.

[0054] S5: Mix 20g of nano-reinforcing particles, 20g of nano-cellulose whiskers, 5g of sodium polyacrylate and 50mL of deionized water, and stir at 3000rpm and 30rpm for 40min. Then add 3g of silane coupling agent KH-550, 0.5g of wetting agent, 10g of polyvinylidene fluoride and 50mL of N,N-dimethylformamide, and stir at 800rpm and 30rpm for 70min to obtain a composite slurry. Use a gravure roller coating process to uniformly coat the slurry onto the surface of a polyolefin separator substrate. After heat curing at 160℃ for 40min, a high-strength separator for fast-charging lithium-ion batteries is obtained.

[0055] Example 4: This example provides a method for preparing a high-strength separator for fast-charging lithium-ion batteries. The difference from Example 1 is that zirconium sulfate and aluminum sulfate are used instead of zirconium nitrate and aluminum nitrate in step S2 to prepare a high-strength separator for fast-charging lithium-ion batteries.

[0056] Example 5: This example provides a method for preparing a high-strength separator for fast-charging lithium-ion batteries. The difference from Example 1 is that sodium carboxymethyl cellulose is used instead of sodium polyacrylate in step S5 to prepare a high-strength separator for fast-charging lithium-ion batteries.

[0057] In Examples 1-5, the polyolefin membrane substrate thickness was 20 μm, the wet coating thickness was 3-5 μm, and the dry coating thickness was 0.8-1.2 μm. The wetting agent was selected from Dongguan Caihua Plastics Technology Co., Ltd., brand BYKET3004 (Germany). The nanocellulose whiskers were selected from Beijing Deco Island Gold Technology Co., Ltd., model CNWS-50, with a diameter of 12±2 nm and a length of 200±20 nm. The remaining raw materials were commercially available products.

[0058] Comparative Example 1: The difference from Example 1 is that steps S2, S3 and S4 are omitted, and in step S5, mercapto-based mesoporous silica nanoparticles are used instead of nano-reinforcing particles. The remaining steps remain unchanged, and a high-strength separator for fast-charging lithium-ion batteries is prepared.

[0059] Comparative Example 2: The difference from Example 1 is that steps S1 and S4 are omitted, and in step S5, polydopamine-coated zirconium-doped boehmite prepared in step S3 is used instead of nano-reinforcing particles. The remaining steps remain unchanged, and a high-strength separator for fast-charging lithium-ion batteries is prepared.

[0060] Comparative Example 3: The difference from Example 1 is that step S2 is omitted, and in step S3, boehmite is used instead of zircon-doped boehmite for dopamine coating. The remaining steps remain unchanged, and a high-strength separator for fast-charging lithium-ion batteries is prepared.

[0061] The following performance tests were performed on the high-strength separators for fast-charging lithium-ion batteries prepared in Examples 1-5 and Comparative Examples 1-3:

[0062] Heat shrinkage rate: Referring to GB / T36363-2018 "Polyolefin separator for lithium-ion batteries", the separator was cut into 100mm×100mm samples, kept in a forced-air drying oven at 150℃ for 1h, and after cooling, the dimensional change was measured and the heat shrinkage rate in the MD and TD directions was calculated.

[0063] Puncture strength: Referring to GB / T36363-2018 "Polyolefin separator for lithium-ion batteries", a universal testing machine was used with a spherical needle with a diameter of 1.0 mm and a puncture speed of 100 mm / min. The result was the average of three tests.

[0064] Liquid absorption rate: Referring to GB / T36363-2018 "Polyolefin separators for lithium-ion batteries", the separator was immersed in 1M LiPF6 / EC:EMC:DMC (1:1:1, v / v / v) electrolyte in an argon glove box at 25℃ for 4 hours. The liquid absorption rate was calculated by mass change. The calculation formula is: Liquid absorption rate = (mass after immersion - mass before immersion) / mass before immersion × 100%;

[0065] Ionic conductivity: Refer to electrochemical impedance spectroscopy. Assemble a symmetrical cell consisting of an SS|separator|SS electrode (SS being stainless steel), inject the same electrolyte as described above, and allow it to stand for 2 hours to ensure full wetting. Perform EIS testing using an electrochemical workstation at 25°C, a frequency range of 1 MHz to 0.1 Hz, and a perturbation voltage of 10 mV. Obtain the bulk resistance (R_b) by fitting the Nyquist plot, and calculate the ionic conductivity (σ) using the formula σ = d / (R_b × A), where d is the average thickness of the separator and A is the effective area of ​​the stainless steel electrode.

[0066] The results are shown in Table 1:

[0067] Table 1. Performance Test Results of High-Strength Separator for Fast-Charging Lithium-ion Batteries

[0068]

[0069] As can be seen from Table 1, the high-strength separators for fast-charging lithium-ion batteries prepared in Examples 1-5 are significantly better than those in Comparative Examples 1-3. The nano-reinforcing particles are composed of zirconium-doped boehmite as the core, polydopamine as the interface layer, and dendritic nano-silica with active thiol groups. They work synergistically with the nano-cellulose whisker framework to achieve a breakthrough in the comprehensive performance of the separator in terms of puncture strength, thermal dimensional stability, liquid absorption rate, and ionic conductivity, thus meeting the stringent requirements of fast-charging batteries for high safety and high power.

[0070] The significant increase in thermal shrinkage and puncture strength in Comparative Example 1 may be due to the absence of polydopamine-coated zirconium-doped boehmite. The membrane coating loses its rigid support framework. Polydopamine can not only enhance the interfacial bonding strength through its strong adhesion, but more importantly, it can form covalent bonds with mercapto-mesoporous silica to build a stable structure. Its absence makes the coating more prone to shrinkage under thermal stress. At the same time, when subjected to puncture, the stress cannot be effectively dispersed through the rigid core, ultimately resulting in a simultaneous decrease in thermal stability and mechanical strength.

[0071] The significantly increased liquid absorption rate and ionic conductivity in Comparative Example 2 may be due to the lack of thiol-based mesoporous nano-silica. The high specific surface area and well-developed mesoporous network of dendritic thiol-based mesoporous silica constitute the main channels for electrolyte storage and ion transport. Its abundant thiol functional groups can also enhance electrolyte wettability through polarity. At the same time, the decrease in puncture strength also indicates that mesoporous silica, as a reinforcing phase, makes an important contribution to the mechanical properties of the coating through mechanical interlocking with the polymer matrix.

[0072] The degradation of thermal shrinkage and puncture strength in Comparative Example 3 may be due to the presence of undoped boehmite. Zirconium ions enter the boehmite lattice through heterovalent doping, resulting in significant lattice distortion and pinning effects. This can increase the activation energy of the phase transition of the material, inhibit grain growth and coarsening at high temperatures, and thus improve its thermal stability. Zirconium doping can also enhance the intrinsic modulus and hardness of boehmite, enabling the "core" structure to more effectively resist deformation and disperse stress when subjected to external forces.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a high-strength separator for fast-charging lithium-ion batteries, characterized in that, Includes the following steps: Step 1: Zirconium-doped boehmite was prepared by co-precipitation, then coated with polydopamine, and then combined with mercapto-based mesoporous silica nanoparticles synthesized by template method to obtain nano-reinforced particles. Step 2: Mix nano-reinforcing particles, nano-cellulose whiskers, binder, deionized water, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride and N,N-dimethylformamide to prepare a composite slurry; coat the composite slurry on the surface of a polyolefin separator and heat-cur it to obtain a high-strength separator for fast-charging lithium-ion batteries. The ratio of the following components is as follows: nano-reinforcing particles, nanocellulose whiskers, binder, deionized water, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride, and N,N-dimethylformamide. The specific preparation steps for the nano-reinforced particles are as follows: Tris(hydroxymethyl)aminomethane was added to deionized water and stirred for 30-40 min. Then, mercapto-based mesoporous silica nanoparticles were added and sonicated for 15-30 min. Next, polydopamine-coated zirconium-doped boehmite was added and stirred at room temperature for 6-8 h. After centrifugation for 15-30 min, the mixture was filtered. The filter cake was washed 3-5 times alternately with deionized water and anhydrous ethanol and then vacuum dried to constant weight to obtain nano-reinforced particles.

2. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 1, characterized in that, The ratio of the amounts of tris(hydroxymethyl)aminomethane, deionized water, mercapto-based mesoporous nano-silica, and polydopamine-coated zirconium-doped boehmite is 7.2-12.6 g: 600-1000 mL: 12-15 g: 6-8 g.

3. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 2, characterized in that, The specific preparation steps for the thiol-based mesoporous silica nanoparticles are as follows: Hexadecyltrimethylammonium bromide and triethanolamine were dissolved in deionized water, and sodium salicylate was added. The mixture was stirred at 80-90℃ and 500-600 rpm until the solid was completely dissolved. Tetraethyl orthosilicate was added dropwise and stirred for 2-3 hours. Then, silane coupling agent KH590 was added dropwise and stirred for another 2-3 hours to obtain a milky white solution. The solution was centrifuged at 3500-4000 rpm, and the solid was collected. The solid was washed alternately with anhydrous ethanol and deionized water 3-5 times and dried under vacuum to constant weight to obtain mercapto-based mesoporous silica nanoparticles. The ratio of hexadecyltrimethylammonium bromide, triethanolamine, deionized water, sodium salicylate, tetraethyl orthosilicate, and silane coupling agent KH590 is 3.64-6.68g: 5.44-10.22g: 160-300mL: 2.4-4.5g: 32-36g: 8-15g.

4. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 2, characterized in that, The specific preparation steps for polydopamine-coated zirconium-doped boehmite are as follows: Zirconium-doped boehmite was added to Tris buffer solution, sonicated for 20-30 min, dopamine was added, stirred in the dark for 12-15 h, centrifuged for 15-30 min, filtered, and the product was washed with deionized water and anhydrous ethanol alternately 3-5 times, and vacuum dried to constant weight to obtain polydopamine-coated zirconium-doped boehmite. The ratio of zirconium-doped boehmite, Tris buffer solution, and dopamine is 1g:1L:1g.

5. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 4, characterized in that, The specific preparation steps for the zircon-doped boehmite are as follows: Add water-soluble zirconium salt and water-soluble aluminum salt to deionized water and stir until completely dissolved. Adjust the pH to 10 with sodium hydroxide solution and stir magnetically for 30-40 min. Transfer to a polytetrafluoroethylene reactor and react at 150-160℃ for 24-30 h. Centrifuge at 8000-9000 rpm for 15-30 min, filter, and wash the filter cake alternately with ethanol and deionized water 3-5 times. Vacuum dry to constant weight to obtain zircon-doped boehmite.

6. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 5, characterized in that, The ratio of water-soluble zirconium salt, water-soluble aluminum salt, and deionized water is 4.3-8.2g: 33.76-65.42g: 1-1.5L; The water-soluble zirconium salt is either zirconium nitrate or zirconium sulfate; The water-soluble aluminum salt is either aluminum nitrate or aluminum sulfate.

7. The method for preparing a high-strength separator for fast-charging lithium-ion batteries according to claim 1, characterized in that, The specific preparation steps for the high-strength separator used in the fast-charging lithium-ion battery are as follows: Nano-reinforcing particles, nano-cellulose whiskers, binder, and deionized water are mixed and stirred at 2000-3000 rpm rotation and 20-30 rpm revolution for 30-40 minutes. Then, silane coupling agent KH-550, wetting agent, polyvinylidene fluoride, and N,N-dimethylformamide are added, and the mixture is stirred at 600-800 rpm rotation and 20-30 rpm revolution for 60-70 minutes to obtain a composite slurry. The slurry is then uniformly coated onto the surface of a polyolefin separator substrate using a gravure roller coating process. After thermosetting at 150-160℃ for 30-40 minutes, a high-strength separator for fast-charging lithium-ion batteries is obtained. The adhesive is either sodium polyacrylate or sodium carboxymethyl cellulose.

8. A high-strength separator for fast-charging lithium-ion batteries, prepared by the method for preparing a high-strength separator for fast-charging lithium-ion batteries according to any one of claims 1-7.

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