A low-moisture coated film and a method for making the same

Abstract

The application discloses a kind of low water content coating film and preparation method thereof, belong to lithium ion battery technical technical field.The coating film includes base film, ceramic coating, the ceramic coating is by ceramic slurry coating in the surface of one side or both sides of base film, after drying is obtained;The composition of ceramic slurry includes: granular boehmite 40-55 parts, linear boehmite 10-20 parts, carbonized wood 10-20 parts, modified ethylene vinyl tri (beta-methoxy ethoxy) silane 0.1-1 part, adhesive 0.1-0.6 part, sodium carboxymethyl cellulose 0.1-1 part, dispersing agent 0.1-4 parts, wetting agent 0.1-6 parts, deionized water 45-70 parts according to mass ratio.The coating film has the characteristics of low water content, strong anti-puncture performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a low-water-content coating film and its preparation method. Background Technology

[0002] Currently, the separators used in lithium-ion batteries are primarily microporous polyolefin films, such as polyethylene, polypropylene, or composites of different polyolefins. While polyolefin separators possess good mechanical strength and chemical stability at room temperature, they exhibit high thermal shrinkage at high temperatures. This leads to rapid generation of significant heat at the contact between the positive and negative electrodes. When the temperature exceeds a certain limit, the separator dissolves, causing a large-area short circuit and generating high pressure inside the battery, potentially leading to combustion or explosion. Single-layer polyolefin separators pose a significant risk of battery short circuits. From a safety perspective, coated separators offer superior performance characteristics for lithium batteries, including tensile strength, puncture resistance, permeability, wettability, chemical stability, thermal stability, and overall safety.

[0003] Currently, coating materials are mainly organic and inorganic. Inorganic materials include alumina, silica, boehmite, and barium sulfate; organic materials include polyvinylidene fluoride (PVDF), para-aramid, polyethylene terephthalate (PET), and polymethyl methacrylate (PMMA). Ceramic composite separators, due to their excellent heat resistance and safety, are seeing a year-on-year increase in their application as coated separators. They consist of a base membrane coated with a specially processed ceramic slurry, which, after bonding, forms a stable ceramic composite separator. However, ceramic-coated separators still suffer from high moisture content, leading to increased internal pressure, poor discharge performance, and negatively impacting battery performance.

[0004] Chinese patent CN111312967A discloses a ceramic coating slurry and its preparation method, a lithium battery separator, and a lithium battery separator formed by coating a base film with a lithium battery. By using chemical means to increase the thickening effect of the thickener while reducing the amount used, the air permeability and shrinkage rate are reduced, while the peel strength and voltage resistance of the coating film are increased, thus improving the overall performance of the separator. However, due to problems such as excessive water content and weak puncture resistance of the ceramic coating film, the battery life is limited. Summary of the Invention

[0005] The purpose of this invention is to provide a low-moisture-content coating film and its preparation method, so as to solve the problems of high moisture content and weak puncture resistance of existing coating films.

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

[0007] A low-moisture-content coated film includes a base film and a ceramic coating, wherein the ceramic coating is obtained by coating a ceramic coating slurry onto one or both surfaces of the base film and then drying it.

[0008] Preferably, the ceramic coating comprises, by mass ratio: 40-55 parts granular boehmite, 10-20 parts linear boehmite, 10-20 parts carbonized wood, 0.1-1 parts modified vinyltris(β-methoxyethoxy)silane, 0.1-0.6 parts adhesive, 0.1-1 parts sodium carboxymethyl cellulose, 0.1-4 parts dispersant, 0.1-6 parts wetting agent, and 45-70 parts deionized water.

[0009] Preferably, carbonized wood is prepared by the following steps: crushing the wood, passing it through a 100-200 mesh sieve, mixing the crushed wood with a 5wt% potassium hydroxide solution, filtering, reacting the filter cake at 500-800℃ under a nitrogen atmosphere for 3-6 hours, then immersing it in a 1wt% hydrochloric acid solution for 1-2 hours, adjusting the pH to 7, filtering, and drying to obtain carbonized wood.

[0010] Preferably, the wood includes any one or more of poplar, linden, pine and balsa wood.

[0011] Preferably, the ratio of pulverized wood to 5wt% potassium hydroxide solution is 1-3g:50-100mL.

[0012] Preferably, the adhesive comprises any one or more of silicone-modified acrylate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyacrylic acid, polyvinyl ether, styrene-butadiene rubber, styrene-acrylic rubber, and polymethyl methacrylate.

[0013] Preferably, the dispersant is any one or more of N,N-dimethylaminopropylamine, polyethylenepolyamine, octadecylaminopropylamine, sodium polyacrylate, ammonium polyacrylate, ethylene oxide, and propylene oxide copolymers.

[0014] Preferably, the wetting agent is any one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, and polyether-modified polysiloxane.

[0015] Preferably, the modified vinyltris(β-methoxyethoxy)silane is prepared by the following steps:

[0016] Vinyltris(β-methoxyethoxy)silane, 1H,1H,2H,2H-perfluorododecylthiol, and benzoin dimethyl ether were added to tetrahydrofuran to form a mixed solution. The resulting mixed solution was then irradiated with a UV lamp at room temperature. The UV lamp had a wavelength of 365 nm, a power of 100 W, and a light intensity of 4500 μW / cm². 2 After stirring for 15-30 minutes, the mixture is rotary evaporated under vacuum at 40-60℃ to obtain a crude product. The crude product is then added to petroleum ether, filtered, and dried to obtain modified vinyltris(β-methoxyethoxy)silane.

[0017] Preferably, the mass ratio of vinyltris(β-methoxyethoxy)silane, 1H,1H,2H,2H-perfluorododecylthiol and benzoin dimethyl ether is 1:1.5-2:0.01-0.02.

[0018] A method for preparing a low-water-content coated film includes the following steps:

[0019] (1) Granular boehmite, linear boehmite, modified vinyltris(β-methoxyethoxy)silane, carbonized wood, adhesive, sodium carboxymethyl cellulose, dispersant and wetting agent are added to deionized water in sequence and mixed and stirred to obtain ceramic slurry;

[0020] (2) The obtained ceramic slurry is coated on one or both sides of the base film with a coating thickness of 2-5 μm and dried to obtain a low water content coated film.

[0021] Preferably, the stirring speed is 300-500 r / min and the stirring time is 30-50 min.

[0022] Preferably, the porosity of the base membrane is 40-65%, and the thickness of the base membrane is 3-20 μm.

[0023] Preferably, the coating method includes any one of gravure roller coating, wire rod coating, dip coating, and spray coating.

[0024] Preferably, the coating speed is 60-120 m / min, the drying temperature is 40-80℃, and the drying time is 0.5-3 h.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention provides a low-moisture-content coated membrane and its preparation method. Granular boehmite, linear boehmite, carbonized wood, modified vinyltris(β-methoxyethoxy)silane, adhesive, sodium carboxymethyl cellulose, dispersant, wetting agent, and deionized water are mixed and stirred to obtain a ceramic slurry. This ceramic slurry is then used to coat a base membrane, which is dried to obtain the coated membrane. The resulting coated membrane exhibits good puncture resistance, low moisture content, and low thermal shrinkage, meeting the requirements of lithium-ion battery processes for separators.

[0027] 2. The ceramic slurry provided by this invention uses a mixture of linear and granular boehmite. Since linear boehmite has better electrochemical performance than granular boehmite, while granular boehmite has better thermal shrinkage and puncture resistance, mixing them in a certain proportion makes the overall performance of boehmite in the membrane more excellent. Carbonized wood has extremely strong stability, and its internal hydrophilic groups are reorganized, lowering the hygroscopic equilibrium point and maintaining a stable low water content state, which helps to prevent the accumulation and diffusion of moisture in the membrane. After the boehmite and carbonized wood are mixed, the high porosity of the carbonized wood can also form a three-dimensional network structure when the boehmite combines with the base membrane, thereby improving the conduction speed during lithium-ion recharge and discharge and effectively reducing the formation of lithium dendrites.

[0028] 3. In this invention, vinyltris(β-methoxyethoxy)silane undergoes a click reaction with 1H,1H,2H,2H-perfluorododecylthiol to obtain modified vinyltris(β-methoxyethoxy)silane. By introducing a long-chain fluorinated group, it has strong hydrophobic properties, which helps to reduce the retention of moisture on the membrane surface and synergistically maintain a low moisture content with carbonized wood. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of 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.

[0030] The sources and compositions of some of the raw materials in the following examples and comparative examples are as follows:

[0031] Granular boehmite has a particle size of 350 nm, while linear boehmite has a particle size of 300 nm and a length of 500 nm.

[0032] The average molecular weight of sodium carboxymethyl cellulose is 100,000-200,000.

[0033] The polyether-modified polydimethylsiloxane is sourced from Shanghai Manhai Gaoschmit Chemical Co., Ltd., and its model number is FlussigS-3330.

[0034] The polymethyl methacrylate is sourced from Dongguan Baojia Plastics Co., Ltd., and its model number is I RD-70.

[0035] Sodium polyacrylate is sourced from Renqiu Pengyu Chemical Co., Ltd.

[0036] Example 1

[0037] This embodiment provides a modified vinyltris(β-methoxyethoxy)silane, prepared through the following steps:

[0038] 1.2 g of vinyltris(β-methoxyethoxy)silane, 1.8 g of 1H,1H,2H,2H-perfluorododecylthiol, and 0.012 g of benzoin dimethyl ether were added to 30 mL of tetrahydrofuran to form a mixed solution. The resulting mixed solution was then irradiated with a UV lamp at room temperature. The UV lamp had a wavelength of 365 nm, a power of 100 W, and a light intensity of 4500 μW / cm². 2 After stirring for 15 minutes, the mixture was rotary evaporated under vacuum at 40°C to obtain a crude product. The crude product was then added to 20 mL of petroleum ether, filtered, and dried to obtain modified vinyltris(β-methoxyethoxy)silane.

[0039] Example 2

[0040] This embodiment provides a modified vinyltris(β-methoxyethoxy)silane, prepared through the following steps:

[0041] 1.2 g of vinyltris(β-methoxyethoxy)silane, 2.4 g of 1H,1H,2H,2H-perfluorododecylthiol, and 0.024 g of benzoin dimethyl ether were added to 30 mL of tetrahydrofuran to form a mixed solution. The resulting mixed solution was then irradiated with a UV lamp at room temperature. The UV lamp had a wavelength of 365 nm, a power of 100 W, and a light intensity of 4500 μW / cm². 2 After stirring for 30 minutes, the mixture was rotary evaporated under vacuum at 60°C to obtain a crude product. The crude product was then added to 20 mL of petroleum ether, filtered, and dried to obtain modified vinyltris(β-methoxyethoxy)silane.

[0042] Example 3

[0043] This embodiment provides a carbonized wood, which is produced through the following steps:

[0044] 1g of balsa wood was crushed and passed through a 100-mesh sieve. The crushed balsa wood was mixed with 50mL of 5wt% potassium hydroxide solution. The filter cake was reacted at 500℃ under a nitrogen atmosphere for 3 hours. Then it was soaked in 1wt% hydrochloric acid solution for 1 hour to adjust the pH to 7. After filtration and drying, carbonized wood was obtained.

[0045] Example 4

[0046] This embodiment provides a carbonized wood, which is produced through the following steps:

[0047] 3g of balsa wood was crushed and passed through a 200-mesh sieve. The crushed balsa wood was mixed with 100mL of 5wt% potassium hydroxide solution, filtered, and the filter cake was reacted at 800℃ under a nitrogen atmosphere for 6 hours. Then it was soaked in 1wt% hydrochloric acid solution for 2 hours, the pH was adjusted to 7, filtered, and dried to obtain carbonized wood.

[0048] Example 5

[0049] This embodiment provides a method for preparing a low-water-content coated film, including the following steps:

[0050] (1) 20 parts of granular boehmite, 5 parts of linear boehmite, 0.5 parts of carbonized wood from Example 4, 0.05 parts of modified vinyltris(β-methoxyethoxy)silane from Example 2, 0.05 parts of polymethyl methacrylate, 0.05 parts of sodium carboxymethyl cellulose, 0.05 parts of sodium polyacrylate, and 0.05 parts of polyether-modified polydimethylsiloxane were added sequentially to 22.5 parts of deionized water and mixed. The stirring speed was 300 r / min and the stirring time was 30 min to obtain ceramic slurry.

[0051] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 40% by gravure roller coating. The base film thickness was 3μm, the coating speed was 60m / min, the coating thickness was 2μm, the drying temperature was 40℃, and the drying time was 0.5h to obtain a low water content coated film.

[0052] Example 6

[0053] This embodiment provides a method for preparing a low-water-content coated film, including the following steps:

[0054] (1) 27.5 parts of granular boehmite, 10 parts of linear boehmite, 10 parts of carbonized wood from Example 4, 0.5 parts of modified vinyltris(β-methoxyethoxy)silane from Example 1, 0.3 parts of polymethyl methacrylate emulsion, 0.5 parts of sodium carboxymethyl cellulose, 2 parts of sodium polyacrylate, and 3 parts of polyether-modified polydimethylsiloxane were added sequentially to 35 parts of deionized water and mixed. The stirring speed was 500 r / min and the stirring time was 50 min to obtain a ceramic slurry.

[0055] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 65% by gravure roller coating. The base film thickness was 20 μm, the coating speed was 120 m / min, the coating thickness was 5 μm, the drying temperature was 80℃, and the drying time was 3 h to obtain a low water content coated membrane.

[0056] Example 7

[0057] This embodiment provides a method for preparing a low-water-content coated film, including the following steps:

[0058] (1) 25 parts of granular boehmite, 8 parts of linear boehmite, 7 parts of carbonized wood from Example 3, 0.3 parts of modified vinyltris(β-methoxyethoxy)silane from Example 1, 0.1 parts of polymethyl methacrylate, 0.3 parts of sodium carboxymethyl cellulose, 0.4 parts of sodium polyacrylate, and 0.6 parts of polyether-modified polydimethylsiloxane were added sequentially to 30 parts of deionized water and mixed. The stirring speed was 400 r / min and the stirring time was 38 min to obtain ceramic slurry.

[0059] (2) The obtained ceramic slurry was coated on one side of a polyethylene microporous membrane with a porosity of 55% by gravure roller coating. The base film thickness was 8μm, the coating speed was 80m / min, the coating thickness was 3.6μm, the drying temperature was 60℃, and the drying time was 1h to obtain a low water content coated membrane.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a low-water-content coated film, comprising the following steps:

[0062] Based on Example 7, the carbonized wood in Example 7 was removed, and the remaining raw materials and preparation methods were the same as in Example 7.

[0063] Comparative Example 2

[0064] This comparative example describes a method for preparing a low-water-content coated film, comprising the following steps:

[0065] Based on Example 7, the modified vinyltris(β-methoxyethoxy)silane in Example 7 was removed, and the remaining raw materials and preparation methods were the same as in Example 7.

[0066] Comparative Example 3

[0067] This comparative example describes a method for preparing a low-water-content coated film, comprising the following steps:

[0068] Based on Example 7, the modified vinyltris(β-methoxyethoxy)silane in Example 7 was replaced with vinyltris(β-methoxyethoxy)silane, and the remaining raw materials and preparation methods were the same as in Example 7.

[0069] Comparative Example 4

[0070] This comparative example describes a method for preparing a low-water-content coated film, comprising the following steps:

[0071] Based on Example 7, all linear boehmite in Example 7 was replaced with granular boehmite, and the remaining raw materials and preparation methods were the same as in Example 7.

[0072] Comparative Example 5

[0073] This comparative example describes a method for preparing a low-water-content coated film, comprising the following steps:

[0074] Based on Example 7, all granular boehmite in Example 7 was replaced with linear boehmite, and the remaining raw materials and preparation methods were the same as in Example 7.

[0075] Performance tests were conducted on Examples 5-7 and Comparative Examples 1-5. Puncture measurements were performed on the low-moisture-content coated membrane samples according to GB / T 36363 / 2018 standard. A 100mm × 100mm sample was prepared with the length in the MD direction, with 11 sheets of A4 paper sandwiched between the top and bottom of the membrane. The sample was placed in an oven at 150℃ for 30 minutes and then removed. The sample size was L, and the heat shrinkage rate was (100-L)%. 1.2g of composite membrane was prepared under conditions where the dew point was less than -40℃. The membrane was baked at 120℃ for 5 minutes, and the moisture content was tested using the Karl Fischer method. Ionic conductivity was tested using a conductivity meter.

[0076] The results are shown in Table 1:

[0077] Table 1

[0078]

[0079]

[0080] As shown in Table 1, compared to Comparative Examples 1-3, the moisture content of Examples 5-7 is below 400 ppm. The synergistic effect of carbonized wood and modified vinyltris(β-methoxyethoxy)silane results in a lower moisture content in the coating film of this invention. The heat shrinkage rate (MD) at 150℃ in Examples 5-7 is less than 2%, indicating improved heat resistance. The puncture strength of Examples 5-7 is above 700 gf, suggesting that carbonized wood and modified vinyltris(β-methoxyethoxy)silane also enhance interfacial strength. The ionic conductivity of Example 7 is higher than that of Comparative Example 1, which has an ionic conductivity of only 0.328 mS / cm, indicating that carbonized wood promotes ion transport in the membrane. Compared to Examples 5-7, the moisture content obtained in Comparative Examples 4-5 is relatively higher.

[0081] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0082] 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 low-moisture-content coating film, characterized in that, It includes a base film and a ceramic coating, wherein the ceramic coating is obtained by coating a ceramic slurry onto one or both surfaces of the base film and then drying it; The ceramic slurry comprises, by mass ratio: 40-55 parts granular boehmite, 10-20 parts linear boehmite, 10-20 parts carbonized wood, 0.1-1 parts modified vinyltris(β-methoxyethoxy)silane, 0.1-0.6 parts adhesive, 0.1-1 parts sodium carboxymethyl cellulose, 0.1-4 parts dispersant, 0.1-6 parts wetting agent, and 45-70 parts deionized water; The modified vinyltris(β-methoxyethoxy)silane is prepared by the following steps: Vinyltris(β-methoxyethoxy)silane, 1H,1H,2H,2H-perfluorododecylthiol and benzoin dimethyl ether were added to tetrahydrofuran to form a mixed solution. The resulting mixed solution was irradiated with a UV lamp at room temperature and stirred for 15-30 min. Then, it was rotary evaporated under vacuum at 40-60 °C to obtain a crude product. The crude product was added to petroleum ether, filtered, and dried to obtain modified vinyltris(β-methoxyethoxy)silane.

2. The low-moisture-content coating film according to claim 1, characterized in that, The carbonized wood is produced through the following steps: The wood is crushed and passed through a 100-200 mesh sieve. The crushed wood is mixed with a 5wt% potassium hydroxide solution, filtered, and the filter cake is reacted at 500-800℃ under a nitrogen atmosphere for 3-6 hours. Then it is immersed in a 1wt% hydrochloric acid solution for 1-2 hours, the pH is adjusted to 7, filtered, and dried to obtain carbonized wood.

3. The low-moisture-content coating film according to claim 2, characterized in that, The ratio of the pulverized wood to 5wt% potassium hydroxide solution is 1-3g:50-100mL.

4. The low-moisture-content coating film according to claim 1, characterized in that, The adhesive includes any one or more of the following: silicone-modified acrylate, ethylene-vinyl acetate copolymer, polyvinyl alcohol, polyacrylic acid, polyvinyl ether, styrene-butadiene rubber, styrene-acrylic rubber, and polymethyl methacrylate.

5. The low-moisture-content coating film according to claim 1, characterized in that, The dispersant is any one or more of N,N-dimethylaminopropylamine, polyethylenepolyamine, octadecylaminopropylamine, sodium polyacrylate, ammonium polyacrylate, ethylene oxide, and propylene oxide copolymers.

6. The low-moisture-content coating film according to claim 1, characterized in that, The wetting agent is any one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, and polyether-modified polysiloxane.

7. The low-moisture-content coating film according to claim 1, characterized in that, The mass ratio of vinyltris(β-methoxyethoxy)silane, 1H,1H,2H,2H-perfluorododecylthiol and benzoin dimethyl ether is 1:1.5-2:0.01-0.

02.

8. The low-moisture-content coating film according to claim 1, characterized in that, The base membrane is a polyolefin microporous membrane.

9. The method for preparing a low-water-content coated film according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Granular boehmite, linear boehmite, modified vinyltris(β-methoxyethoxy)silane, carbonized wood, adhesive, sodium carboxymethyl cellulose, dispersant and wetting agent are added to deionized water in sequence and mixed. The stirring speed is 300-500 r / min and the stirring time is 30-50 min to obtain ceramic slurry. (2) The obtained ceramic slurry is coated on one or both sides of the base film with a coating thickness of 2-5 μm and dried to obtain a low water content coated film.

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