Lithium ion battery composite diaphragm with high safety and high ionic conductivity and preparation method of lithium ion battery composite diaphragm

Abstract

The invention provides a lithium ion battery composite membrane with high safety and high ionic conductivity and a preparation method thereof.The lithium ion battery composite membrane comprises a base membrane and a functional coating compounded on the surface of at least one side of the base membrane, and the functional coating comprises, by weight, 60-85% of a high-temperature-resistant polymer matrix, 1-5% of a binder, 1-5% of an antioxidant and 1-5% of a lubricant. And 15-40% of sulfobetaine functionalized inorganic nanoparticles. The high-temperature-resistant polymer matrix and the sulfobetaine functionalized inorganic nanoparticles form a synergistic effect, so that the high-temperature thermal shrinkage of the diaphragm can be effectively inhibited, the short-circuit risk of the battery caused by diaphragm melting can be greatly reduced, and the use reliability is improved. Meanwhile, the zwitterionic groups on the surfaces of the sulfobetaine functionalized inorganic nanoparticles are extremely high in hydrophilicity, so that the infiltration speed of the diaphragm on electrolyte can be increased, the electrolyte retention capability can be enhanced, a continuous micro-nano ion transmission channel can be constructed in the coating, and the lithium ion migration efficiency can be improved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically to a high-safety, high-ionic-conductivity lithium-ion battery composite separator and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, and environmental friendliness, have been widely used in portable electronic devices, electric vehicles, and energy storage systems. As a key component of lithium-ion batteries, the separator's core function is to separate the positive and negative electrodes to prevent short circuits, while ensuring that lithium ions can migrate freely.

[0003] Currently, commercially available lithium-ion battery separators are mainly made of polyolefin materials (such as polyethylene (PE) and polypropylene (PP)). These materials possess excellent mechanical properties and chemical stability. However, polyolefin materials suffer from insufficient thermal stability. When the battery temperature rises to near their melting point (approximately 135°C for PE and 165°C for PP), they are prone to thermal shrinkage or even melting, leading to direct contact between the positive and negative electrodes and potentially causing safety hazards (such as fire or explosion). Furthermore, polyolefin separators have low surface energy, and their wettability and electrolyte retention capabilities need improvement. This characteristic reduces the battery's ionic conductivity and affects cycle performance.

[0004] To improve the performance of polyolefin separators, researchers have explored various modification strategies, including surface coating, blending modification, and electrospinning composites. For example, coating the surface of a polyolefin separator with inorganic particles such as Al2O3 and SiO2 can improve its thermal stability and wettability, but insufficient adhesion between the coating and the base film may lead to detachment. Using high-temperature resistant polymers (such as polyimide (PI) and polyethersulfone (PES)) to prepare separators or composite separators can significantly enhance thermal stability; however, pure PI separators are expensive, and their flexibility and processing performance still need optimization. Therefore, developing novel separators that combine high safety, high ionic conductivity, and suitable mechanical properties is of great significance for promoting the development of lithium-ion battery technology. Summary of the Invention

[0005] To address the problems of insufficient thermal stability and poor electrolyte wettability in existing lithium-ion battery separators, as well as the high cost, mechanical properties, or processability of some high-temperature resistant separators, this invention provides a lithium-ion battery composite separator with high safety, high ionic conductivity, and good mechanical properties, and its preparation method. The separator prepared by this invention can improve battery safety while enhancing the battery's electrochemical performance.

[0006] The technical solution provided by this invention: A high-safety, high-ionic-conductivity lithium-ion battery composite separator, comprising a base film and a functional coating laminated on at least one surface of the base film, wherein the functional coating comprises the following components by weight percentage:

[0007] High-temperature resistant polymer matrix: 60-85%;

[0008] Sulfonate betaine-functionalized inorganic nanoparticles: 15-40%.

[0009] Furthermore, the high-temperature resistant polymer matrix is ​​selected from one of polyimide, polyetheretherketone, polyethersulfone, and polyphenylene sulfide.

[0010] Furthermore, the sulfonate betaine-functionalized inorganic nanoparticles are inorganic nanoparticles with sulfonate betaine groups grafted onto their surface, and the chemical structure of the sulfonate betaine groups is -N. + (CH3)2(CH2) n SO3⁻, where n is an integer from 1 to 6.

[0011] Furthermore, the inorganic nanoparticles are selected from one of silicon dioxide, aluminum oxide, and titanium oxide, and the D50 of the inorganic nanoparticles is 50-200 nm.

[0012] Furthermore, the base film is one of PP, PE, PP / PE / PP, PE / PP / PE, PET, PI, and cellulose film.

[0013] Furthermore, the thickness of the functional coating is 1-10 μm, and the peel strength between the functional coating and the base film is ≥0.5 N / cm.

[0014] Another technical solution provided by this invention: a method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator, comprising the following steps:

[0015] (1) Preparation of sulfonate betaine functionalized inorganic nanoparticles

[0016] Inorganic nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane was added. The mixture was reacted at 60-80℃ for 4-8 hours, filtered, washed, and dried to obtain amino-modified inorganic nanoparticles. The amino-modified inorganic nanoparticles were then dispersed in N,N-dimethylformamide, and sulfonate betaine monomer was added. The mixture was reacted at 80-100℃ for 6-12 hours, filtered, washed, and vacuum dried to obtain sulfonate betaine-functionalized inorganic nanoparticles.

[0017] (2) Preparation of functional coating slurry

[0018] Dissolve the high-temperature resistant polymer matrix in an organic solvent and stir for 1-3 hours until completely dissolved. Then add the sulfonate betaine functionalized inorganic nanoparticles obtained in step (1), and after ultrasonic dispersion for 20-60 minutes, mechanically stir for 1-2 hours to form a uniformly dispersed slurry.

[0019] (3) Coating and drying

[0020] The slurry prepared in step (2) is coated on at least one side of the base film, dried at 60-80℃ for 5-30 min, and then dried at 100-120℃ for 1-10 min to obtain a lithium-ion battery composite separator with high safety and high ionic conductivity.

[0021] Furthermore, in step (1), the mass ratio of the inorganic nanoparticles to 3-aminopropyltriethoxysilane is 1:0.1-0.2, and the mass ratio of the sulfonate betaine monomer to the inorganic nanoparticles is 0.3-0.4:1.

[0022] Furthermore, the organic solvent in step (2) is selected from N,N-dimethylformamide, N-methylpyrrolidone or a mixture thereof, and the mass concentration of the high-temperature resistant polymer matrix in the organic solvent is 5-15 wt%.

[0023] Furthermore, the coating method described in step (3) is one of gravure coating, extrusion coating, wire rod coating, or scraping coating.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The high-safety, high-ionic-conductivity lithium-ion battery composite separator prepared in this invention utilizes a thermally stable high-temperature polymer matrix combined with functionalized nanoparticles to create a synergistic effect, effectively suppressing thermal shrinkage of the separator at high temperatures. This results in superior performance compared to traditional separators, fundamentally reducing the risk of short circuits and significantly improving battery reliability. Simultaneously, the zwitterionic groups (-N) on the surface of the sulfonate betaine functionalized inorganic nanoparticles... + (CH3)2(CH2) n SO3⁻ has extremely strong hydrophilicity, which can not only accelerate the wetting speed of the diaphragm to the electrolyte and enhance the liquid retention capacity, but also build continuous micro-nano-level ion transport channels inside the coating, effectively improving the lithium ion migration efficiency. This successfully solves the core pain points of poor electrolyte wetting and insufficient ionic conductivity in traditional diaphragm electrolytes.

[0026] Furthermore, the composite separator prepared by this invention possesses excellent mechanical properties, interfacial stability, and promising industrialization prospects. The polyolefin substrate layer provides reliable mechanical support, while the functional coating bonds tightly to the substrate through physical or chemical interactions. This optimizes key performance characteristics while ensuring the tensile strength and flexibility of the separator, meeting the mechanical requirements for battery assembly and use. The sulfonate betaine groups stabilize the electrode / electrolyte interface, suppress side reactions, and improve the long-cycle stability of the battery. Moreover, the preparation process is based on mature coating and drying technologies, requiring simple equipment with controllable costs. It eliminates the need for specialized and complex equipment, facilitating large-scale continuous production and demonstrating significant industrial application value. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, specific implementation examples are provided below to further illustrate the technical solutions of this invention. However, the specific details of the embodiments are only for illustrating this invention and do not represent all technical methods under the concept of this invention. Therefore, they should not be construed as limiting the overall technical solution of this invention.

[0028] It should be noted that, unless otherwise specified, the experimental methods used in the examples are conventional methods, and the materials and reagents used in the examples are commercially available unless otherwise specified.

[0029] Example 1

[0030] A method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator includes the following steps:

[0031] Step 1: Preparation of sulfonate betaine-functionalized inorganic nanoparticles: Inorganic silica nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane was added, wherein the mass ratio of inorganic nanoparticles to 3-aminopropyltriethoxysilane was 1:0.1. The reaction was carried out at 60℃ for 4 h, and the mixture was filtered, washed, and dried to obtain amino-modified silica particles. The amino-modified silica particles were then dispersed in N,N-dimethylformamide, and sulfonate betaine monomer was added, wherein the mass ratio of sulfonate betaine monomer to inorganic nanoparticles was 0.3:1. The reaction was carried out at 80℃ for 6 h, and the mixture was filtered, washed, and vacuum dried to obtain sulfonate betaine-functionalized silica particles.

[0032] Step 2: Preparation of functional coating slurry: Dissolve the high-temperature resistant polymer polyimide in the organic solvent NMP, stir for 1.5 h until completely dissolved, add sulfonate betaine functionalized silica particles, ultrasonically disperse for 25 min and mechanically stir for 1.5 h to form a uniformly dispersed slurry.

[0033] Step 3: Coating and drying: The slurry prepared in step 2 is coated on one side of a 12µm PP base film, dried at 60℃ for 10 min, and then dried at 100℃ for 3 min to obtain a high-safety, high-ionic-conductivity lithium-ion battery composite separator.

[0034] The components of the above-mentioned functional coating are composed of the following weight percentages: 65% high-temperature resistant polymer polyimide and 35% sulfonate betaine functionalized silica particles; wherein the concentration of the high-temperature resistant polymer polyimide in the organic solvent NMP is 10%.

[0035] Example 2

[0036] A method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator includes the following steps:

[0037] Step 1: Preparation of sulfonate betaine-functionalized inorganic nanoparticles: Inorganic alumina nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane was added, wherein the mass ratio of inorganic nanoparticles to 3-aminopropyltriethoxysilane was 1:0.12. The reaction was carried out at 70℃ for 5 h, and the mixture was filtered, washed, and dried to obtain amino-modified alumina particles. The amino-modified alumina particles were dispersed in N,N-dimethylformamide, and sulfonate betaine monomer was added, wherein the mass ratio of sulfonate betaine monomer to inorganic nanoparticles was 0.35:1. The reaction was carried out at 90℃ for 7 h, and the mixture was filtered, washed, and vacuum dried to obtain sulfonate betaine-functionalized alumina particles.

[0038] Step 2: Preparation of functional coating slurry: Dissolve the high-temperature resistant polymer polyphenylene sulfide in the organic solvent NMP, stir for 2 hours until completely dissolved, add sulfonate betaine functionalized alumina particles, ultrasonically disperse for 30 minutes and mechanically stir for 2 hours to form a uniformly dispersed slurry.

[0039] Step 3: Coating and drying: The slurry prepared in step 2 is coated on one side of a 12µm PE base film, dried at 70℃ for 6 min, and then dried at 105℃ for 2 min to obtain a high-safety, high-ionic-conductivity lithium-ion battery composite separator.

[0040] The components of the above-mentioned functional coating are composed of the following weight percentages: 70% high-temperature resistant polymer polyphenylene sulfide and 30% sulfonic acid betaine functionalized alumina particles; wherein the concentration of the high-temperature resistant polymer polyphenylene sulfide in the organic solvent NMP is 12%.

[0041] Example 3

[0042] A method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator includes the following steps:

[0043] Step 1: Preparation of sulfonate betaine-functionalized inorganic nanoparticles: Inorganic titanium dioxide nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane was added, wherein the mass ratio of inorganic nanoparticles to 3-aminopropyltriethoxysilane was 1:0.16. The reaction was carried out at 75℃ for 4.5 h, filtered, washed, and dried to obtain amino-modified titanium dioxide particles; The amino-modified titanium dioxide particles were dispersed in N,N-dimethylformamide, and sulfonate betaine monomer was added, wherein the mass ratio of sulfonate betaine monomer to inorganic nanoparticles was 0.38:1. The reaction was carried out at 85℃ for 7.5 h, filtered, washed, and vacuum dried to obtain sulfonate betaine-functionalized titanium dioxide particles.

[0044] Step 2: Preparation of functional coating slurry: Dissolve the high-temperature resistant polymer polyether ether ketone in the organic solvent N,N-dimethylformamide, stir for 1.5h until completely dissolved, add sulfonate betaine functionalized titanium dioxide particles, ultrasonically disperse for 25min and mechanically stir for 1h to form a uniformly dispersed slurry.

[0045] Step 3: Coating and drying: The slurry prepared in step 2 is coated on one side of a 12µm PP / PE / PP base film, dried at 65℃ for 7 min, and then dried at 110℃ for 4 min to obtain a high-safety, high-ionic-conductivity lithium-ion battery composite separator.

[0046] The components of the above-mentioned functional coating are composed of the following weight percentages: 75% high-temperature resistant polymer polyether ether ketone and 25% sulfonate betaine functionalized titanium dioxide particles; wherein the concentration of the high-temperature resistant polymer polyether ether ketone in the organic solvent N,N-dimethylformamide is 13%.

[0047] Comparative Example 1

[0048] The difference from Example 1 is that the inorganic particles are unmodified silicon dioxide.

[0049] Comparative Example 2

[0050] The difference from Example 1 is that the inorganic particles are unmodified silica, and no high-temperature resistant polymer is added to the system.

[0051] Performance testing

[0052] The coating peel strength, ionic conductivity, thermal shrinkage rate, and air permeability increment of the diaphragms in the examples and comparative examples were measured, and the results are shown in Table 1.

[0053] Table 1 Performance Test Results

[0054]

[0055] 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 alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-safety, high-ionic-conductivity composite separator for lithium-ion batteries, characterized in that, The substrate includes a base film and a functional coating laminated to at least one surface of the base film, the functional coating comprising the following components by weight percentage: High-temperature resistant polymer matrix: 60-85%; Sulfonate betaine-functionalized inorganic nanoparticles: 15-40%.

2. The high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 1, characterized in that, The high-temperature resistant polymer matrix is ​​selected from one of polyimide, polyetheretherketone, polyethersulfone, and polyphenylene sulfide.

3. The high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 1 is characterized in that, The sulfonate betaine-functionalized inorganic nanoparticles are inorganic nanoparticles with sulfonate betaine groups grafted onto their surface, and the chemical structure of the sulfonate betaine groups is -N. + (CH3)2(CH2) n SO3⁻, where n is an integer from 1 to 6.

4. The high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 3 is characterized in that, The inorganic nanoparticles are selected from one of silicon dioxide, aluminum oxide, and titanium oxide, and the D50 of the inorganic nanoparticles is 50-200 nm.

5. The high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 1 is characterized in that, The base film is one of PP, PE, PP / PE / PP, PE / PP / PE, PET, PI, and cellulose film.

6. The high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 1 is characterized in that, The thickness of the functional coating is 1-10 μm, and the peel strength between the functional coating and the base film is ≥0.5 N / cm.

7. A method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of sulfonate betaine functionalized inorganic nanoparticles Inorganic nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane was added. The mixture was reacted at 60-80℃ for 4-8 hours, filtered, washed, and dried to obtain amino-modified inorganic nanoparticles. The amino-modified inorganic nanoparticles were then dispersed in N,N-dimethylformamide, and sulfonate betaine monomer was added. The mixture was reacted at 80-100℃ for 6-12 hours, filtered, washed, and vacuum dried to obtain sulfonate betaine functionalized inorganic nanoparticles. (2) Preparation of functional coating slurry Dissolve the high-temperature resistant polymer matrix in an organic solvent and stir for 1-3 hours until completely dissolved. Then add the sulfonate betaine functionalized inorganic nanoparticles obtained in step (1), and after ultrasonic dispersion for 20-60 minutes, mechanically stir for 1-2 hours to form a uniformly dispersed slurry. (3) Coating and drying The slurry prepared in step (2) is coated on at least one side of the base film, dried at 60-80℃ for 5-30 min, and then dried at 100-120℃ for 1-10 min to obtain a lithium-ion battery composite separator with high safety and high ionic conductivity.

8. The method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 7, characterized in that, In step (1), the mass ratio of inorganic nanoparticles to 3-aminopropyltriethoxysilane is 1:0.1-0.2, and the mass ratio of sulfonate betaine monomer to inorganic nanoparticles is 0.3-0.4:

1.

9. The method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 7, characterized in that, The organic solvent in step (2) is selected from N,N-dimethylformamide, N-methylpyrrolidone or a mixture thereof, and the mass concentration of the high-temperature resistant polymer matrix in the organic solvent is 5-15 wt%.

10. The method for preparing a high-safety, high-ionic-conductivity lithium-ion battery composite separator according to claim 7, characterized in that, The coating method described in step (3) is one of gravure coating, extrusion coating, wire rod coating, or scraping coating.

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