Sepiolite coating diaphragm with multilevel structure and preparation method of sepiolite coating diaphragm

Abstract

The invention provides a multistage-structure sepiolite coating diaphragm and a preparation method thereof, the multistage-structure sepiolite coating diaphragm comprises a base membrane and a composite coating, the composite coating is coated on the surface of one side or two sides of the base membrane, and the composite coating is coated on the surface of the other side or two sides of the base membrane. The composite coating is composed of the following components in percentage by mass: 15-25% of modified sepiolite, 5-8% of a conductive polymer, 5-8% of a lithium salt dispersion liquid, 5-8% of a binder and the balance of deionized water, and the modified sepiolite is an ammonia water assisted silane grafting-metal ion chelating-mesoporous silica coated modified product. The composite material has a'one-dimensional fiber-nanoparticle-mesoporous shell layer 'three-stage interwoven structure. The one-dimensional sepiolite fiber provides a macroscopic transmission path, the surface-chelated nanoparticles reduce an ion migration energy barrier, and the mesoporous silica shell layer realizes rapid transmission of lithium ions. And meanwhile, by combining the pre-dispersion design of the lithium salt and the synergistic effect of the conductive polymer, the conductivity of the lithium ions is further improved.

Description

Technical Field

[0001] This invention relates to the field of battery separator technology, specifically a multi-level sepiolite-coated separator and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in many fields such as new energy vehicles and portable electronic devices due to their significant advantages such as high energy density and long cycle life. As one of the core components of lithium-ion batteries, the separator's main functions are to separate the positive and negative electrodes, prevent short circuits, and ensure the transport of lithium ions. Its performance has a direct impact on the battery's safety and cycle stability.

[0003] Currently, commercial lithium-ion battery separators are mainly polyolefin-based membranes. However, polyolefin-based membranes suffer from drawbacks such as poor thermal stability, inadequate wettability, and low ionic conductivity, which to some extent limits the development of high-energy-density lithium-ion batteries. To address these issues, surface treatment of the base membrane is typically performed using coating modification methods. By coating the base membrane surface with materials such as inorganic particles and conductive polymers, the thermal stability and ion transport performance of the separator can be effectively improved.

[0004] Sepiolite, a natural one-dimensional nanofiber mineral, possesses a unique layered channel structure, high specific surface area, and good thermal stability, making it an ideal inorganic filler for membrane coating. However, the presence of numerous hydroxyl groups on the sepiolite surface leads to agglomeration and poor compatibility with organic base membranes and electrolytes. Direct coating can result in insufficient coating adhesion and increased ion transport resistance. Existing technologies often employ silane coupling agents to modify sepiolite, but single silane modification cannot simultaneously address both agglomeration and ion transport efficiency issues. Some patents use ammonia-assisted silane grafting modification, which accelerates the grafting reaction, but the modified sepiolite still retains a single-fiber structure with limited ion transport pathways and lacks synergistic effects with lithium ions, making it difficult to further improve the electrochemical performance of the membrane.

[0005] Therefore, developing a sepiolite-coated separator with a special microstructure that combines high ionic conductivity and high thermal stability is of great significance for promoting the performance upgrade of lithium-ion batteries. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a multi-level sepiolite-coated diaphragm and its preparation method. By constructing a modified sepiolite with a three-level interwoven structure of "one-dimensional fiber-nanoparticle-mesoporous shell", and synergistically combining it with conductive polymer and lithium salt dispersion, the technical problems of high ion transport resistance, insufficient thermal stability and poor coating adhesion of traditional coated diaphragms are solved.

[0007] The technical solution provided by this invention is a multi-level structured sepiolite-coated diaphragm, comprising a base membrane and a composite coating. The composite coating is coated on one or both sides of the base membrane. The composite coating is composed of the following components by mass percentage: 15-25% modified sepiolite, 5-8% conductive polymer, 5-8% lithium salt dispersion, 5-8% binder, and the balance being deionized water. The modified sepiolite is an ammonia-assisted silane grafting-metal ion chelation-mesoporous silica-coated modified product, which has a three-level interwoven structure of "one-dimensional fiber-nanoparticle-mesoporous shell".

[0008] Furthermore, the base membrane is a composite membrane of polyethylene, polypropylene, or polyolefin; the thickness of the base membrane is 8-30 μm, the porosity is 35-50%, and the thickness of the composite coating is 1-5 μm.

[0009] Furthermore, the one-dimensional fiber has a diameter of 10–50 nm, the metal ion chelated nanoparticles loaded on the fiber surface have a size of 50–200 nm, the mesoporous silica shell has a thickness of 10–30 nm and a mesopore diameter of 2–5 nm, the overall porosity is 40–60%, and the metal ion is Zr. 4+ Ti 4+ At least one of them.

[0010] Furthermore, the conductive polymer is at least one of polythiophene, polypyrrole, polycarbazole, or a derivative of polyaniline.

[0011] Furthermore, the lithium salt dispersion is a mixture of lithium bis(trifluoromethanesulfonate)imine, ethylene carbonate, and dimethyl carbonate, with a mass ratio of 1:4:6 for each component.

[0012] Furthermore, the adhesive is at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, and sodium carboxymethyl cellulose.

[0013] Another technical solution provided by the present invention: a method for preparing a multi-level structure sepiolite-coated diaphragm, comprising the following steps:

[0014] (1) Preparation of modified sepiolite: sepiolite was ultrasonically dispersed to form a suspension. After adjusting the pH to 9.5-10.5 with ammonia, γ-glycidoxypropyltrimethoxysilane was added and grafted at 70°C for 3 h. Then, a zirconium / titanium metal ion salt solution containing sodium citrate chelating agent was added dropwise and stirred at 70°C for 1.5 h. Subsequently, tetraethyl orthosilicate was added dropwise and stirred at 70°C for 4 h. The product was filtered, washed, dried, ground and sieved to obtain modified sepiolite.

[0015] (2) Preparation of composite coating slurry: Modified sepiolite, conductive polymer, lithium salt dispersion, binder and deionized water are mixed in proportion and dispersed in aqueous solution at a speed of 1000-2000 r / min for 30-60 min to obtain composite coating slurry;

[0016] (3) Coating and drying: The composite coating slurry obtained in step (2) is coated onto the surface of the base film using a micro-gravure coating method at a coating speed of 80-100 m / min. Then, it is pre-dried at 70-80℃ for 10-20 s and then vacuum-dried at 80-90℃ for 2-10 s to obtain a multi-level structure sepiolite coated diaphragm.

[0017] Furthermore, the mass ratio of each component in step (1) is: γ-glycidyl etheroxypropyltrimethoxysilane: zirconium / titanium metal ion salt: tetraethyl orthosilicate: sepiolite = (0.05-0.1):(0.05-0.1):(0.125-0.2):1; the chelating agent sodium citrate is 50%–150% of the mass of zirconium / titanium metal ion salt.

[0018] Furthermore, the vacuum degree of the vacuum drying in step (3) is -0.08-0.1 MPa.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention achieves a comprehensive improvement in lithium-ion battery performance by constructing a modified sepiolite-coated separator with a three-tiered interwoven structure of "one-dimensional fiber-nanoparticle-mesoporous shell". This structure forms a three-dimensional interconnected ion transport channel: one-dimensional sepiolite fibers provide a macroscopic transport path, chelated nanoparticles on their surface lower the ion migration barrier, and the mesoporous silica shell enables rapid and selective lithium-ion transport. Simultaneously, the synergistic effect of lithium salt pre-dispersion design and conductive polymer further improves ionic conductivity. Furthermore, the modified sepiolite mesoporous silica coating forms a stable supporting framework, maintaining structural integrity under high-temperature conditions; the high specific surface area and mesoporous structure of the modified sepiolite enhance electrolyte adsorption capacity, optimize battery cycle performance, and significantly improve ion transport efficiency, thermal stability, and cycle performance.

[0021] The preparation process employed in this invention is characterized by its green and efficient nature: an aqueous dispersion system, mild reaction conditions, and low energy consumption, perfectly aligning with environmentally friendly principles. Its raw materials are widely available, allowing for effective cost control and diverse application scenarios. The coated separator prepared by this invention possesses high ionic conductivity, high thermal stability, excellent wettability, and cycle stability, making it compatible with various battery systems such as ternary lithium batteries and lithium iron phosphate batteries. It is particularly suitable for new energy vehicles, energy storage power stations, and other fields, demonstrating significant industrial application value and broad market prospects. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] In the following examples, the lithium salt dispersion is a mixture of lithium bis(trifluoromethanesulfonate)imine, ethylene carbonate, and dimethyl carbonate, with a mass ratio of 1:4:6.

[0025] Example 1

[0026] A method for preparing a multi-level sepiolite-coated diaphragm includes the following steps:

[0027] Step 1: Preparation of modified sepiolite: Sepiolite was ultrasonically dispersed to form a suspension. After adjusting the pH to 9.5-10.5 with ammonia, γ-glycidoxypropyltrimethoxysilane was added, and the grafting reaction was carried out at 70℃ for 3 hours. Then, a zirconium metal ion salt solution containing sodium citrate chelating agent was added dropwise, and the mixture was stirred at 70℃ for 1.5 hours. Subsequently, tetraethyl orthosilicate was added dropwise, and the mixture was stirred at 70℃ for 4 hours. The product was filtered, washed, dried, ground, and sieved to obtain modified sepiolite.

[0028] Step 2: Preparation of composite coating slurry: Modified sepiolite, conductive polymer polythiophene, lithium salt dispersion, binder polyvinylidene fluoride-hexafluoropropylene copolymer and deionized water are mixed in proportion and dispersed in aqueous solution at a speed of 1500 r / min for 35 min to obtain composite coating slurry.

[0029] Step 3: Coating and drying: The composite coating slurry obtained in step 2 is coated onto the surface of a 12µm PP base film using a microgravure coating method at a coating speed of 80m / min. Then, it is pre-dried at 75℃ for 12s and then vacuum-dried at 80℃ for 4s with a vacuum degree of -0.09Mpa to obtain a multi-level structure sepiolite coated diaphragm.

[0030] In step 1, the mass ratio of the core reaction components is: γ-glycidyl etheroxypropyltrimethoxysilane: zirconium metal ion salt: tetraethyl orthosilicate: sepiolite = 0.06:0.06:0.14:1; and the chelating agent sodium citrate accounts for 80% of the mass of zirconium metal ion salt.

[0031] The composite coating slurry consists of the following components by mass percentage: 18% modified sepiolite, 5.5% conductive polymer polythiophene, 6% lithium salt dispersion, 5.4% binder polyvinylidene fluoride-hexafluoropropylene copolymer, and the balance being deionized water.

[0032] Example 2

[0033] A method for preparing a multi-level sepiolite-coated diaphragm includes the following steps:

[0034] Step 1: Preparation of modified sepiolite: Sepiolite was ultrasonically dispersed to form a suspension. After adjusting the pH to 9.5-10.5 with ammonia, γ-glycidoxypropyltrimethoxysilane was added, and the grafting reaction was carried out at 70℃ for 3 hours. Then, a titanium metal ion salt solution containing sodium citrate chelating agent was added dropwise, and the mixture was stirred at 70℃ for 1.5 hours. Subsequently, tetraethyl orthosilicate was added dropwise, and the mixture was stirred at 70℃ for 4 hours. The product was filtered, washed, dried, ground, and sieved to obtain modified sepiolite.

[0035] Step 2: Prepare composite coating slurry: Mix modified sepiolite, conductive polymer polypyrrole, lithium salt dispersion, binder polyacrylic acid and deionized water in proportion, and disperse in aqueous solution at a speed of 1300 r / min for 40 min to obtain composite coating slurry.

[0036] Step 3: Coating and drying: The composite coating slurry obtained in step 2 is coated onto the surface of a 12µm PP / PE / PP base film using a microgravure coating method at a coating speed of 85m / min. Then, it is pre-dried at 80℃ for 10s and then vacuum-dried at 85℃ for 3s with a vacuum degree of -0.12MPa to obtain a multi-level structure sepiolite coated diaphragm.

[0037] In step 1, the mass ratio of the core reaction components is: γ-glycidyl etheroxypropyltrimethoxysilane: titanium metal ion salt: tetraethyl orthosilicate: sepiolite = 0.05:0.05:0.126:1; and the chelating agent sodium citrate is 120% of the mass of titanium metal ion salt.

[0038] The composite coating slurry consists of the following components by mass percentage: 18% modified sepiolite, 5.8% conductive polymer polypyrrole, 6.2% lithium salt dispersion, 5.5% binder polyacrylic acid, and the balance being deionized water.

[0039] Example 3

[0040] A method for preparing a multi-level sepiolite-coated diaphragm includes the following steps:

[0041] Step 1: Preparation of modified sepiolite: Sepiolite was ultrasonically dispersed to form a suspension. After adjusting the pH to 9.5-10.5 with ammonia, γ-glycidoxypropyltrimethoxysilane was added, and the grafting reaction was carried out at 70℃ for 3 hours. Then, a titanium metal ion salt solution containing sodium citrate chelating agent was added dropwise, and the mixture was stirred at 70℃ for 1.5 hours. Subsequently, tetraethyl orthosilicate was added dropwise, and the mixture was stirred at 70℃ for 4 hours. The product was filtered, washed, dried, ground, and sieved to obtain modified sepiolite.

[0042] Step 2: Preparation of composite coating slurry: Modified sepiolite, conductive polymer polycarbazole, lithium salt dispersion, binder sodium carboxymethyl cellulose and deionized water are mixed in proportion and dispersed in aqueous solution at a speed of 1600 r / min for 45 min to obtain composite coating slurry.

[0043] Step 3: Coating and drying: The composite coating slurry obtained in step 2 is coated onto the surface of a 12µm PE base film using a microgravure coating method at a coating speed of 90m / min. Then, it is pre-dried at 75℃ for 15s and then vacuum-dried at 85℃ for 4s with a vacuum degree of -0.15MPa to obtain a multi-level structure sepiolite coated diaphragm.

[0044] In step 1, the mass ratio of the core reaction components is: γ-glycidyl etheroxypropyltrimethoxysilane: titanium metal ion salt: tetraethyl orthosilicate: sepiolite = 0.058:0.058:0.128:1; and the chelating agent sodium citrate is 130% of the mass of titanium metal ion salt.

[0045] The composite coating slurry consists of the following components by mass percentage: 19% modified sepiolite, 6.1% conductive polymer polycarbazole, 5.8% lithium salt dispersion, 6% sodium carboxymethyl cellulose binder, and the balance being deionized water.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that it is unmodified sepiolite.

[0048] Comparative Example 2

[0049] Commercially available 12+2 ceramic alumina coated PP separator.

[0050] Performance testing

[0051] The 180° peel strength, ion conductivity, thermal shrinkage rate (150℃ / 1h), and air permeability increment of the membranes in the examples and comparative examples were measured, and the results are shown in Table 1. The data indicate that the coated membrane prepared in this invention possesses characteristics such as high ion conductivity, high thermal stability, excellent wettability, and cycling stability.

[0052] Table 1 Performance Test Results

[0053]

[0054] 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 multi-level sepiolite-coated diaphragm, comprising a base membrane and a composite coating, wherein the composite coating is coated on one or both sides of the base membrane, characterized in that, The composite coating is composed of the following components by mass percentage: 15-25% modified sepiolite, 5-8% conductive polymer, 5-8% lithium salt dispersion, 5-8% binder, and the balance being deionized water. The modified sepiolite is an ammonia-assisted silane grafting-metal ion chelation-mesoporous silica coating modified product, which has a three-level interwoven structure of "one-dimensional fiber-nanoparticle-mesoporous shell".

2. The multi-level structure sepiolite-coated diaphragm according to claim 1, characterized in that, The base membrane is a composite membrane of polyethylene, polypropylene, or polyolefin; the thickness of the base membrane is 8-30 μm, the porosity is 35-50%, and the thickness of the composite coating is 1-5 μm.

3. The multi-level structure sepiolite-coated diaphragm according to claim 1, characterized in that, The one-dimensional fiber has a diameter of 10–50 nm, the metal ion chelated nanoparticles loaded on the fiber surface have a size of 50–200 nm, the mesoporous silica shell has a thickness of 10–30 nm and a mesopore diameter of 2–5 nm, the overall porosity is 40–60%, and the metal ion is Zr. 4+ Ti 4+ At least one of them.

4. The multi-level structure sepiolite-coated diaphragm according to claim 1, characterized in that, The conductive polymer is at least one of polythiophene, polypyrrole, polycarbazole, or a derivative of polyaniline.

5. The multi-level structure sepiolite-coated diaphragm according to claim 1, characterized in that, The lithium salt dispersion is a mixture of lithium bis(trifluoromethanesulfonate)imine, ethylene carbonate, and dimethyl carbonate, with a mass ratio of 1:4:

6.

6. The multi-level structure sepiolite-coated diaphragm according to claim 1, characterized in that, The adhesive is at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylic acid, and sodium carboxymethyl cellulose.

7. A method for preparing a multi-level sepiolite-coated diaphragm according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of modified sepiolite: The sepiolite was ultrasonically dispersed to form a suspension. After adjusting the pH to 9.5-10.5 with ammonia, γ-glycidoxypropyltrimethoxysilane was added and the grafting reaction was carried out at 70°C for 3 hours. Then, a zirconium / titanium metal ion salt solution containing sodium citrate chelating agent was added dropwise and stirred at 70°C for 1.5 hours. Then, tetraethyl orthosilicate was added dropwise, and the mixture was stirred at 70°C for 4 hours. The product was filtered, washed, dried, ground, and sieved to obtain modified sepiolite. (2) Preparation of composite coating slurry: Modified sepiolite, conductive polymer, lithium salt dispersion, binder and deionized water are mixed in proportion and dispersed in aqueous solution at a speed of 1000-2000 r / min for 30-60 min to obtain composite coating slurry; (3) Coating and drying: The composite coating slurry obtained in step (2) is coated onto the surface of the base film using a micro-gravure coating method at a coating speed of 80-100 m / min. Then, it is pre-dried at 70-80℃ for 10-20 s and then vacuum-dried at 80-90℃ for 2-10 s to obtain a multi-level structure sepiolite coated diaphragm.

8. The method for preparing a multi-level structure sepiolite-coated diaphragm according to claim 7, characterized in that, The mass ratio of each component in step (1) is: γ-glycidyl oxypropyltrimethoxysilane: zirconium / titanium metal ion salt: tetraethyl orthosilicate: sepiolite = (0.05-0.1):(0.05-0.1):(0.125-0.2):1; the chelating agent sodium citrate is 50%–150% of the mass of zirconium / titanium metal ion salt.

9. The method for preparing a multi-level structure sepiolite-coated diaphragm according to claim 7, characterized in that, The vacuum degree of vacuum drying in step (3) is -0.08-0.1 MPa.

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