Water-based ceramic slurry binder for ceramic-coated polyolefin separators

Abstract

The application discloses a kind of water-based ceramic slurry adhesives for ceramic-coated polyolefin separators, and relates to the technical field of polyolefin separators.The adhesives prepared by the preparation method provided by the application can promote the uniform dispersion of inorganic ceramic particles in the ceramic slurry, and the excellent adhesion of the adhesives can firmly bond the inorganic ceramic particles to the separators, preventing the phenomenon of powder falling during production, transportation and use, thereby ensuring the improvement effect of the thermal stability of the inorganic ceramic particles on the separators.

Description

Technical fields:

[0001] This invention relates to the field of polyolefin membrane technology, and more specifically to an aqueous ceramic slurry adhesive for ceramic-coated polyolefin membranes. Background technology:

[0002] In the structure of a lithium-ion battery, the separator is one of the key internal components. The performance of the separator determines the battery's interface structure, internal resistance, and other factors, directly affecting the battery's capacity, cycle life, and safety performance. The main function of the separator is to separate the positive and negative electrodes, preventing short circuits caused by contact between the electrodes. It also allows electrolyte ions to pass through. For lithium-ion batteries, since the electrolyte is an organic solvent system, separator materials resistant to organic solvents are required, typically high-strength, thin-film polyolefin porous membranes.

[0003] Because polyolefin materials have low melting points, they are prone to shrinkage or even melting at high temperatures, causing contact between the positive and negative electrodes and resulting in a short circuit in the lithium battery. To improve the thermal stability of polyolefin separators, adhesives are commonly used in the field to coat the surface of the polyolefin separator with a layer of inorganic ceramic to prepare a ceramic-coated polyolefin separator. However, the commonly used adhesive, polyvinylidene fluoride (PVDF), requires the use of the oily solvent N-methylpyrrolidone. N-methylpyrrolidone is an organic solvent, which can affect the production environment and human health. Furthermore, N-methylpyrrolidone has a high boiling point, making it impossible to quickly obtain a ceramic coating through heat curing. Summary of the Invention:

[0004] The technical problem to be solved by the present invention is to provide an aqueous ceramic slurry adhesive for ceramic-coated polyolefin diaphragms. This adhesive can promote the uniform dispersion of inorganic ceramic particles in the ceramic slurry and use its adhesiveness to firmly bond the inorganic ceramic particles to the diaphragm, preventing powder shedding during production, transportation and use, thereby ensuring the improvement effect of inorganic ceramic particles on the thermal stability of the diaphragm.

[0005] The technical problem to be solved by this invention is achieved by the following technical solution:

[0006] The first objective of this invention is to provide a method for preparing an adhesive, comprising the following steps:

[0007] (1) Add allyl dihexyl chlorosilane and ethanol to toluene, heat the reaction until allyl dihexyl chlorosilane reacts completely, and recover the unreacted ethanol by vacuum distillation to obtain an allyl (ethoxy) dihexyl silane solution.

[0008] (2) Add an azo initiator dropwise to an allyl (ethoxy)dihexylsilane solution. After the addition is complete, heat the reaction. After the reaction is complete, recover toluene by vacuum distillation to obtain the adhesive.

[0009] Preferably, the number-average molecular weight of the adhesive is 3000-4000. If the molecular weight is too small, it will affect the adhesion of the inorganic ceramic particles to the diaphragm; if the molecular weight is too large, it will affect the uniformity of dispersion of the inorganic ceramic particles in the ceramic slurry, making it impossible for the inorganic ceramic particles to adhere evenly to the diaphragm.

[0010] Preferably, the molar ratio of allyl dihexylchlorosilane to ethanol is 1:(1.2-1.5). Under conditions of excess ethanol, allyl dihexylchlorosilane is allowed to react completely, converting the chlorine substituent in the allyl dihexylchlorosilane structure to an ethoxy group.

[0011] Preferably, the azo initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

[0012] Preferably, the amount of the azo initiator is 0.5-1% of the weight of allyldihexylchlorosilane. Other oil-soluble initiators, such as organic peroxide initiators, may also be used.

[0013] The preparation principle of the adhesive of the present invention is as follows: allyl dihexylchlorosilane undergoes a substitution reaction with ethanol to obtain allyl (ethoxy) dihexylsilane, and polyallyl (ethoxy) dihexylsilane is obtained by polymerization reaction using allyl (ethoxy) dihexylsilane as a monomer. Polyallyl (ethoxy) dihexylsilane is then used as an adhesive.

[0014] A second object of the present invention is to provide an adhesive obtained by the aforementioned preparation method.

[0015] A third object of the present invention is to provide an aqueous ceramic slurry comprising the aforementioned binder, inorganic ceramic particles, and water.

[0016] The ethoxy group in the molecular structure of the adhesive prepared by this invention will hydrolyze in water to form hydrophilic silanol groups. Therefore, water can be used as a solvent for preparing ceramic slurry. Furthermore, its unique three-dimensional network structure can be used to promote the uniform dispersion of inorganic ceramic particles in water and prevent the inorganic ceramic particles from agglomerating and settling.

[0017] This invention uses water as a solvent to prepare water-based ceramic slurry, which not only solves the problems of increased cost and environmental pollution caused by solvent evaporation during curing when using organic solvents to prepare ceramic slurry, but also solves the problem that resin-based binders cannot adhere a sufficient amount of inorganic ceramic particles to the diaphragm due to poor adhesion, thus failing to significantly improve its thermal stability.

[0018] Preferably, the inorganic ceramic particles are at least one selected from alumina, boehmite, silicon dioxide, and titanium dioxide. Appropriate amounts of transition metal oxides or rare earth metal oxides such as cerium dioxide and zirconium dioxide may also be added.

[0019] Preferably, the amount of adhesive used is 10-15% of the weight of the inorganic ceramic particles. If the amount of adhesive used is too small, there will be too few inorganic ceramic particles bonded to the diaphragm, which will not achieve the technical effect of significantly improving the thermal stability of the diaphragm; if the amount of adhesive used is too large, the ceramic coating will contain too much binder, which is also not conducive to improving the thermal stability of the diaphragm.

[0020] A fourth objective of this invention is to provide the application of the aforementioned aqueous ceramic slurry in ceramic-coated polyolefin membranes.

[0021] The beneficial effects of this invention are: This invention provides a method for preparing an aqueous ceramic slurry adhesive for ceramic-coated polyolefin diaphragms. The adhesive obtained by this preparation method can promote the uniform dispersion of inorganic ceramic particles in the ceramic slurry, and utilize the excellent adhesion of the adhesive to firmly bond the inorganic ceramic particles to the diaphragm, preventing powder shedding during production, transportation and use, thereby ensuring the improvement effect of inorganic ceramic particles on the thermal stability of the diaphragm. Detailed implementation method:

[0022] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0023] The raw materials used in the embodiments and comparative examples of this invention are described below:

[0024] The PE membrane has a thickness of 20μm, an air permeability of 200sec / 100mL, and a porosity of 40%.

[0025] The D50 particle size of alumina is 0.5–1.0 μm, and the specific surface area is 4–8 m². 2 / g.

[0026] Example 1

[0027] The method for preparing the adhesive in this embodiment includes the following steps:

[0028] (1) Add allyl dihexyl chlorosilane and ethanol in a molar ratio of 1:1.2 to toluene, heat to 80°C and keep warm until allyl dihexyl chlorosilane reacts completely. Distill under reduced pressure to recover unreacted ethanol and obtain an allyl (ethoxy) dihexyl silane solution.

[0029] (2) Add dimethyl azobisisobutyrate dropwise to the allyl(ethoxy)dihexylsilane solution prepared in step (1). The amount of dimethyl azobisisobutyrate is 0.5% of the weight of allyldihexylchlorosilane. After the addition is complete, heat to 80°C to react. After the reaction is complete, distill under reduced pressure to recover toluene and obtain polyallyl(ethoxy)dihexylsilane with a number average molecular weight of 3300.

[0030] Example 2

[0031] (1) Add allyl dihexyl chlorosilane and ethanol in a molar ratio of 1:1.5 to toluene, heat to 80°C and keep warm until allyl dihexyl chlorosilane reacts completely. Distill under reduced pressure to recover unreacted ethanol and obtain an allyl (ethoxy) dihexyl silane solution.

[0032] (2) Add dimethyl azobisisobutyrate dropwise to the allyl(ethoxy)dihexylsilane solution prepared in step (1). The amount of dimethyl azobisisobutyrate is 1% of the weight of allyldihexylchlorosilane. After the addition is complete, heat to 80°C to react. After the reaction is complete, distill under reduced pressure to recover toluene and obtain polyallyl(ethoxy)dihexylsilane with a number average molecular weight of 3500.

[0033] Example 3

[0034] (1) Add allyl dihexyl chlorosilane and ethanol in a molar ratio of 1:1.5 to toluene, heat to 80°C and keep warm until allyl dihexyl chlorosilane reacts completely. Distill under reduced pressure to recover unreacted ethanol and obtain an allyl (ethoxy) dihexyl silane solution.

[0035] (2) Add azobisisobutyronitrile dropwise to the allyl(ethoxy)dihexylsilane solution prepared in step (1). The amount of azobisisobutyronitrile is 1% of the weight of allyldihexylchlorosilane. After the dropwise addition is complete, heat to 80°C to react. After the reaction is complete, distill under reduced pressure to recover toluene and obtain polyallyl(ethoxy)dihexylsilane with a number average molecular weight of 4000.

[0036] Application Example 1

[0037] Add 30g of alumina and 3g of polyallyl(ethoxy)dihexylsilane prepared in Example 1 to 100g of water as a binder, mix evenly to obtain an aqueous ceramic slurry; then coat the aqueous ceramic slurry evenly onto the PE membrane, and cure at 110℃ to form a ceramic coating with a thickness of 4μm, to obtain a ceramic-coated polyolefin membrane.

[0038] Application Example 2

[0039] Add 30g of alumina and 4.5g of polyallyl(ethoxy)dihexylsilane prepared in Example 1 to 100g of water as a binder, mix evenly to obtain an aqueous ceramic slurry; then coat the aqueous ceramic slurry evenly onto the PE membrane, and cure at 110℃ to form a ceramic coating with a thickness of 4μm, to obtain a ceramic-coated polyolefin membrane.

[0040] Application Example 3

[0041] Add 30g of alumina and 4.5g of polyallyl(ethoxy)dihexylsilane prepared in Example 2 to 100g of water as a binder, mix evenly to obtain an aqueous ceramic slurry; then coat the aqueous ceramic slurry evenly onto the PE membrane, and cure at 110°C to form a ceramic coating with a thickness of 4μm, thus obtaining a ceramic-coated polyolefin membrane.

[0042] Application Example 4

[0043] Add 30g of alumina and 4.5g of polyallyl(ethoxy)dihexylsilane prepared in Example 3 to 100g of water as a binder, mix evenly to obtain an aqueous ceramic slurry; then coat the aqueous ceramic slurry evenly onto the PE membrane, and cure at 110°C to form a ceramic coating with a thickness of 4μm, thus obtaining a ceramic-coated polyolefin membrane.

[0044] Application Comparative Example 1

[0045] The method for preparing ceramic-coated polyolefin membranes using Comparative Example 1 is the same as that used in Application Example 4, except that the polyallyl(ethoxy)dihexylsilane added as a binder in Application Example 4 is replaced with the same mass of sodium carboxymethyl cellulose.

[0046] Application Comparative Example 2

[0047] The method for preparing ceramic-coated polyolefin membranes using Comparative Example 2 is the same as that used in Application Example 4, except that the polyallyl(ethoxy)dihexylsilane added as an adhesive in Application Example 4 is replaced with the same mass of acrylic resin, and the method for preparing the acrylic resin is the same as that used in Example 1 of Patent CN 113583532A.

[0048] Application Comparative Example 3

[0049] Add 30g of alumina and 4.5g of polyvinylidene fluoride as binders to 100g of N-methylpyrrolidone and mix evenly to obtain an oily ceramic slurry. Then, coat the oily ceramic slurry evenly onto a PE membrane and let it stand at 55℃ for 30 minutes. Then, immerse the membrane in room temperature water until the liquid film is completely solidified, wash with water, and dry to obtain a ceramic-coated polyolefin membrane with a ceramic coating thickness of 4μm.

[0050] The peel strength of the ceramic coatings in Application Examples 1-4 and Application Comparative Examples 1-3 was tested according to the standard GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". The results are shown in Table 1.

[0051] Table 1 Peel strength of ceramic coating

[0052] Peeling strength (N / m) Application Example 1 63 Application Example 2 75 Application Example 3 84 Application Example 4 80 Application Comparative Example 1 46 Application Comparative Example 2 53 Application Comparative Example 3 59

[0053] As can be seen from the data in Table 1, compared with sodium carboxymethyl cellulose, acrylic resin and polyvinylidene fluoride commonly used in the field, the adhesive prepared by the present invention has excellent bonding performance, which can achieve firm bonding of inorganic ceramic particles on the diaphragm, so that the inorganic ceramic particles can effectively play their role in improving the thermal stability of the diaphragm; at the same time, the adhesive prepared by the present invention can also use water as a solvent for preparing ceramic slurry, which improves the environmental protection and safety of ceramic slurry, reduces solvent costs and simplifies the curing process of ceramic coating.

[0054] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an adhesive, characterized in that, Includes the following steps: (1) Add allyl dihexyl chlorosilane and ethanol to toluene, heat the reaction until allyl dihexyl chlorosilane reacts completely, and recover the unreacted ethanol by vacuum distillation to obtain an allyl (ethoxy) dihexyl silane solution. (2) Add an azo initiator dropwise to an allyl (ethoxy)dihexylsilane solution. After the addition is complete, heat the reaction. After the reaction is complete, recover toluene by vacuum distillation to obtain the adhesive. The number average molecular weight of the adhesive is 3000~4000.

2. The preparation method according to claim 1, characterized in that: The molar ratio of allyl dihexylchlorosilane to ethanol is 1: (1.2~1.5).

3. The preparation method according to claim 1, characterized in that: The azo initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, and dimethyl azobisisobutyrate.

4. The preparation method according to claim 3, characterized in that: The amount of the azo initiator is 0.5 to 1% of the weight of allyldihexylchlorosilane.

5. The adhesive obtained by the preparation method according to any one of claims 1 to 4.

6. An aqueous ceramic slurry comprising the binder of claim 5, inorganic ceramic particles, and water.

7. The aqueous ceramic slurry according to claim 6, characterized in that: The inorganic ceramic particles are at least one of alumina, boehmite, silicon dioxide, and titanium dioxide.

8. The aqueous ceramic slurry according to claim 7, characterized in that: The amount of adhesive used is 10-15% of the weight of the inorganic ceramic particles.

9. The application of the aqueous ceramic slurry according to any one of claims 6 to 8 in ceramic-coated polyolefin membranes.