UV cross-linked high-performance battery diaphragm and preparation method thereof

Abstract

The invention discloses a UV cross-linked high-performance battery diaphragm and a preparation method thereof.The preparation method comprises the steps that at least one face of a base membrane is coated with UV coating liquid, drying and ultraviolet lamp irradiation are conducted after the UV coating liquid is coated every time, the UV cross-linked high-performance battery diaphragm is obtained after all coating is completed, and the UV coating liquid comprises a substance A, a photoinitiator and a solvent, and the substance A is a monomer and / or an oligomer. According to the invention, polymerization of the monomer and / or oligomer is initiated by ultraviolet radiation to form a cross-linked structure, so that the heat resistance and mechanical properties of the diaphragm are improved, the probability of rupture or damage of the diaphragm is reduced, and the application range of the diaphragm in a high-temperature environment is widened. While the air permeability of the diaphragm is guaranteed, the heat resistance and the mechanical property of the diaphragm are greatly improved, and meanwhile, the ionic conductivity of the diaphragm is also improved. In addition, the adhesive property is better than that of a ceramic coating film, and the risk that the coating falls off is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery separators, and in particular relates to a UV-crosslinked high-performance battery separator and a preparation method thereof. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in various fields. The separator is a key component of lithium-ion batteries, preventing direct contact between the cathode and anode, thus preventing battery short circuits, while allowing ions in the electrolyte to pass through, forming a circuit. Currently, polyolefin separators are commonly used, which offer excellent chemical stability and thermal closure. However, polyolefin separators suffer from poor thermal stability at high temperatures and weak mechanical strength, making them prone to failure. Furthermore, polyolefin separators suffer from insufficient ionic conductivity, which severely impacts the performance of lithium-ion batteries and makes them difficult to meet current usage requirements.

[0003] To this day, existing technologies still face difficult problems in improving diaphragm performance, and no effective solution has been found. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing a UV-crosslinked high-performance battery separator.

[0005] Another object of the present invention is to provide a UV cross-linked high-performance battery separator.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A method for preparing a UV-crosslinked high-performance battery separator comprises: coating a UV coating liquid on at least one side of a base film, drying after each coating of the UV coating liquid, irradiating with an ultraviolet lamp, and obtaining a UV-crosslinked high-performance battery separator after all coatings are completed, wherein the UV coating liquid comprises: a substance A, a photoinitiator, and a solvent, the substance A is a monomer and / or an oligomer, and the monomer is isobornyl acrylate, isobornyl methacrylate, N,N-dimethylacrylamide, dicyclopentadiene acrylate, acryloylmorpholine, lauryl acrylate, lauryl methacrylate, isodecyl acrylate, ethoxyethoxyethyl acrylate The present invention relates to a mixture of one or more of substance A, tripropylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate; the oligomer is a mixture of one or more of aliphatic polyurethane acrylate, aromatic polyurethane acrylate and epoxy acrylate; and the ratio of substance A, photoinitiator and solvent is (5-30): (0.03-2.0): (70-95) by mass.

[0008] In the above technical solution, the photoinitiator is a hydrogen abstraction initiator or a cleavage initiator. The hydrogen abstraction initiator is one or a mixture of 2-isopropylthioxanthone (ITX), 2,4-diethylthioxanthone, benzophenone, 2-ethylanthraquinone, and tetraethyl Michler's ketone. The cleavage initiator is one or a mixture of α-hydroxyacetophenone, α-aminoacetophenone, acylphosphine oxide, and oxime ester initiators. The hydrogen abstraction initiator is preferably used.

[0009] In the above technical solution, the solvent is one or a mixture of methanol, ethanol, isopropanol, benzene, toluene, xylene, acetone, butanone, ether, propylene oxide, methyl acetate, ethyl acetate, butyl acetate, and ethylene glycol methyl ether.

[0010] In the above technical solution, substance A is preferably a mixture of monomers and oligomers.

[0011] In the above technical solution, the ratio of monomer to oligomer is (1-6):(1-6) in parts by mass.

[0012] In the above technical solution, the monomers are trimethylolpropane triacrylate and isobornyl acrylate, and the ratio of trimethylolpropane triacrylate to isobornyl acrylate is (1-3):(1-5) in parts by mass.

[0013] In the above technical solution, the method for obtaining the UV coating liquid includes: mixing the substance A, the photoinitiator and the solvent until they are uniform to obtain the UV coating liquid.

[0014] In the method for obtaining the UV coating liquid, the A substance, the photoinitiator and the solvent are mixed and stirred until uniform to obtain the UV coating liquid. The stirring self-rotation speed is 600-1000 r / min, the stirring revolution speed is 30-50 r / min, and the stirring time is 30-40 min.

[0015] In the above technical solution, the coating method is blade coating, and the coating speed is 30-50 m / min.

[0016] In the above technical solution, the wavelength of the ultraviolet lamp is 365-395 nm, the energy of the ultraviolet lamp is 500-1100 mJ / cm 2 , and the ultraviolet lamp irradiation time is 5-10 s.

[0017] In the above technical solution, the wavelength of the ultraviolet lamp is preferably 380-390 nm.

[0018] In the above technical solution, the drying temperature is 40-80℃.

[0019] A UV-crosslinked high-performance battery separator comprises a base film, a coating layer formed on one side or both sides of the base film, and the coating layer comprises a crosslinked structure formed after UV curing of an A substance initiated by a photoinitiator, the A substance is a monomer and / or an oligomer, the monomer is one or a mixture of several of isobornyl acrylate, isobornyl methacrylate, N,N-dimethyl acrylamide, dicyclopentadiene acrylate, acryloyl morpholine, lauryl acrylate, lauryl methacrylate, isodecyl acrylate, ethoxyethoxyethyl acrylate, tripropylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate, and the oligomer is one or a mixture of several of aliphatic polyurethane acrylate, aromatic polyurethane acrylate, and epoxy acrylate.

[0020] In the technical solution of the UV-crosslinked high-performance battery separator, the ratio of the A substance to the photoinitiator is (5-30):(0.03-2.0) by mass fraction.

[0021] In the technical solution of the UV-crosslinked high-performance battery separator, the A substance is a mixture of a monomer and an oligomer.

[0022] In the technical solution of the UV-crosslinked high-performance battery separator, the ratio of the monomer to the oligomer is (1-6):(1-6) by mass fraction.

[0023] In the technical scheme of the UV-crosslinked high-performance battery separator, the monomers are trimethylolpropane triacrylate and isobornyl acrylate, and the mass ratio of the trimethylolpropane triacrylate to the isobornyl acrylate is (1-3) : (1-5).

[0024] Application of the aliphatic polyurethane acrylate, trimethylolpropane triacrylate and isobornyl acrylate in synergistically improving the heat resistance, mechanical properties and / or ionic conductivity of the separator.

[0025] The application improves the heat resistance and mechanical properties of the separator by initiating polymerization of the monomers and / or oligomers to form a crosslinked structure through ultraviolet irradiation, reduces the probability of rupture or damage of the separator, and widens the application of the separator in a high-temperature environment. Compared with other methods, the application not only greatly improves the heat resistance and mechanical properties of the separator while ensuring the air permeability of the separator, but also improves the ionic conductivity of the separator. In addition, the adhesion performance is better than that of a ceramic coating film, reducing the risk of coating falling off. DETAILED DESCRIPTION

[0026] The technical scheme of the application will be further described below in combination with specific examples.

[0027] In the following examples, the base film is a 9-micron PE film. It should be noted that other base films can also be used.

[0028] Needle puncture strength: cut a 100mm*96mm separator as a sample, and place the sample flat between the two clamps of an electronic tensile testing machine; set the test temperature to room temperature and 200 DEG C respectively, and use a puncture clamp (provided with the electronic tensile testing machine) to perform needle puncture test to obtain the needle puncture strength at room temperature and the hot needle puncture strength at 200 DEG C respectively.

[0029] Film breaking temperature: use a Q400 from TA, USA, cut a 8mm*4.5mm separator, place it in the instrument, set the tensile force to 0.03N, and set the heating rate to 5 DEG C / min, and obtain the film breaking temperature under the test conditions.

[0030] 200 DEG C film breaking time: prepare a 80mm diameter glass culture dish, place a 100mm*100mm separator flat on the glass culture dish, fix it with a rubber band so that the separator is flat and has no wrinkles, place it in a preheated 200 DEG C oven, start timing, and stop timing immediately when the separator breaks, and record the time data at this moment as the 200 DEG C film breaking time.

[0031] Peeling force: take a 150mm*30mm separator as a sample, paste a 100mm*25mm 3M tape on the coating side of the separator and press it flat, clamp the sample and the 3M tape at both ends of a tensile testing machine, peel at a speed of 100mm / min and at an angle of 180 DEG to obtain the peeling force.

[0032] The tensile strength, ionic conductivity (test temperature 25℃, relative humidity value 60%), and shrinkage of the separator are tested according to GB / T36363-2018.

[0033] Isobornyl acrylate: Guangzhou Kuntai New Material Co., Ltd.

[0034] 2,4,6-trimethylbenzoyl-diphenylphosphine oxide: Shanghai Yinchang New Material Co., Ltd.

[0035] Trimethylolpropane triacrylate: Guangzhou Kuntai New Material Co., Ltd.

[0036] Examples 1-6

[0037] A preparation method of a UV-crosslinked high-performance battery separator, comprising: using a doctor blade to coat a UV coating liquid on one side of a base film at a coating speed of 40 m / min, drying in an oven at 70℃ for 1 min, irradiating with a UV lamp for 6 s, using a doctor blade to coat a UV coating liquid on the other side of the base film at a coating speed of 40 m / min, drying in an oven at 70℃ for 1 min, and irradiating with a UV lamp for 6 s, to obtain a high-performance battery separator, wherein the wavelength of the UV lamp is 385 nm, the energy of the UV lamp is 800 mJ / cm 2 , the UV coating liquid comprises: A substance, a photoinitiator, and a solvent, the A substance is an oligomer (aliphatic polyurethane acrylate, specifically IPDI-based polyurethane acrylate, Shanghai Yinchang New Material Co., Ltd. YC2117), the photoinitiator is X, and the solvent is ethanol, and the ratio of the A substance, the photoinitiator, and the solvent is Y by mass fraction.

[0038] The method for obtaining the above-mentioned UV coating liquid comprises: mixing the A substance, the photoinitiator, and the solvent, and stirring until uniform, to obtain the UV coating liquid, the self-rotation speed of the stirring is 800 r / min, the revolution speed is 40 r / min, and the stirring time is 35 min.

[0039] X and Y are shown in Table 1. By changing X and Y, the high-performance battery separators of Examples 1-6 are obtained.

[0040] Table 1

[0041]

[0042]

[0043] Examples 7-11

[0044] A method for preparing a UV-crosslinked high-performance battery separator, comprising: coating a UV coating liquid on one side of a base film by using a doctor blade method at a coating speed of 40 m / min, drying in an oven at 70 DEG C for 1 min, irradiating with a UV lamp for 6 s, coating the UV coating liquid on the other side of the base film by using the doctor blade method at a coating speed of 40 m / min, drying in the oven at 70 DEG C for 1 min, and irradiating with the UV lamp for 6 s, to obtain the high-performance battery separator, wherein the wavelength of the UV lamp is 385 nm, and the energy of the UV lamp is 800 mJ / cm 2 The UV coating liquid comprises: an A substance, a photoinitiator, and a solvent, the A substance is M, the photoinitiator is 2-isopropylthioxanthone (ITX), and the solvent is ethanol, and the ratio of the A substance, the photoinitiator, and the solvent is N in mass fraction.

[0045] The method for obtaining the UV coating liquid comprises: mixing the A substance, the photoinitiator, and the solvent, and stirring until uniform, to obtain the UV coating liquid, the stirring rotation speed is 800 r / min, the revolution speed is 40 r / min, and the stirring time is 35 min.

[0046] M and N are shown in Table 2. The high-performance battery separators of Examples 7-11 are obtained by changing M and N.

[0047] Table 2

[0048]

[0049] Example 12

[0050] A method for preparing a UV-crosslinked high-performance battery separator, which is basically the same as that of Example 11, except that the wavelength of the UV lamp in Example 12 is 365 nm.

[0051] Comparative Example 1

[0052] A method for preparing a ceramic coating film, comprising the following steps:

[0053] Step 1, mixing water and polyacrylamide (M w = 300000) at a rotation speed of 1000 r / min for 10 min until uniform; adding boehmite and stirring at a rotation speed of 1000 r / min for 30 min until uniform; sand milling the above solution to a particle size D90 = 1.5 μm using a sand mill, and adding carboxymethyl cellulose (CMC) solution after sand milling and stirring at a rotation speed of 1200 r / min for 10 min until uniform; adding acrylic resin (polyacrylic acid, M w = 200000) and silane coupling agent (glycidyl ether propyl trimethoxysilane) and stirring at a rotation speed of 1300 r / min for 10 min until uniform; removing magnetic substances by electromagnetic filtration at 3.5 kV, to obtain a coating slurry,

[0054] The ratio of water, polyacrylamide, boehmite, carboxymethyl cellulose (CMC), acrylic resin and silane coupling agent in the carboxymethyl cellulose (CMC) solution is 60.8:1:33:0.15:5:0.05 by mass, and the concentration of carboxymethyl cellulose (CMC) in the carboxymethyl cellulose (CMC) solution is 5wt%;

[0055] Step 2: The coating slurry obtained in step 1 is placed in a coating liquid tank, and the coating slurry is evenly coated on both sides of the PE film by roller coating at a coating speed of 60 m / min, and dried in an oven at 80°C for 1 min to obtain a ceramic coating film.

[0056] The test data of the base film and the high-performance battery separators prepared in Examples 1 to 6 are as follows:

[0057]

[0058]

[0059] The data from Examples 1-4 show that UV treatment significantly improves the heat resistance, mechanical properties, and ionic conductivity of PE films. In Examples 1-3, increasing the ITX ratio leads to improved performance in high-performance battery separators. However, as the ITX ratio continues to increase, the high-performance battery separator prepared in Example 4 shows minimal improvement in heat resistance, while its mechanical properties and ionic conductivity begin to decline. Combining Examples 3, 5, and 6, it can be seen that UV coating solutions containing hydrogen abstraction initiators offer superior performance to those prepared using pyrolysis initiators, with ITX providing the best results.

[0060] The test data of the high-performance battery separators prepared in Examples 7 to 12 and the ceramic coating membrane prepared in Comparative Example 1 are as follows:

[0061]

[0062]

[0063] When the A substance is only an oligomer (aliphatic polyurethane acrylate), the heat resistance and mechanical properties of the separator are improved due to the cross-linking of the aliphatic polyurethane acrylate with a bifunctional group, but the air permeability value also increases. For example, the high-performance battery separator prepared in Example 7 has a relatively high air permeability because a relatively large amount of oligomer is added, which results in good performance of the separator. When the A substance is only a monomer (isobornyl acrylate), the thermal shrinkage performance is improved due to the rigidity of the monomer, and the air permeability increases less due to the non-cross-linking of the monofunctional group. When the A substance is a mixture of a monomer and an oligomer, the performance of the separator can be improved with less increase in air permeability. Further, when trimethylolpropane triacrylate with a trifunctional group is introduced into the oligomer, the heat resistance, mechanical properties, and ionic conductivity of the separator are all at the best level, and the air permeability does not increase significantly. Compared with the ceramic-coated film, the high-performance battery separator prepared in Example 11 has a larger advantage in performance. As can be seen from Example 11 and Example 12, the performance of the separator obtained by irradiation with a 385 nm ultraviolet lamp is better than that obtained by irradiation with a 365 nm ultraviolet lamp.

[0064] The above describes the present application by way of examples, and it should be noted that any simple modification, change or equivalent replacement that does not deviate from the core of the present application and can be made by those skilled in the art without creative effort falls within the scope of the present application.

Claims

1. A UV coating liquid, characterized in that, include: A substance A, a photoinitiator and a solvent, wherein substance A is a monomer and / or an oligomer, wherein the monomer is one or a mixture of isobornyl acrylate, isobornyl methacrylate, N,N-dimethylacrylamide, dicyclopentadiene acrylate, acryloylmorpholine, lauryl acrylate, lauryl methacrylate, isodecyl acrylate, ethoxyethoxyethyl acrylate, tripropylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate, and the oligomer is one or a mixture of aliphatic polyurethane acrylate, aromatic polyurethane acrylate and epoxy acrylate. The ratio of substance A, photoinitiator and solvent is (5-30):(0.03-2.0):(70-95) in parts by mass.

2. The UV coating liquid according to claim 1, characterized in that The photoinitiator is a hydrogen abstraction type initiator or a cleavage type initiator.

3. The UV coating liquid according to claim 2, characterized in that The hydrogen abstraction initiator is one or a mixture of 2-isopropylthioxanthone, 2,4-diethylthioxanthone, benzophenone, 2-ethylanthraquinone and tetraethyl Michler's ketone; the cleavage initiator is one or a mixture of α-hydroxyacetophenone, α-aminoacetophenone, acylphosphine oxide and oxime ester initiators.

4. The method for preparing the UV coating liquid according to claim 1, characterized in that: include: The substance A, the photoinitiator and the solvent are mixed until uniform to obtain a UV coating liquid.

5. A method for preparing a UV cross-linked high-performance battery separator, characterized in that: include: The UV coating liquid according to claim 3 is coated on at least one side of the base film, and is dried after each coating of the UV coating liquid and irradiated with ultraviolet light. After all coatings are completed, a UV-crosslinked high-performance battery separator is obtained.

6. The preparation method according to claim 5, characterized in that The wavelength of the UV lamp is 365-395nm, and the energy of the UV lamp is 500-1100mJ / cm 2 , the UV lamp irradiation time is 5 to 10 seconds.

7. A UV cross-linked high-performance battery separator, comprising: A base film, having a coating formed on one or both sides of the base film, characterized in that the coating comprises: a cross-linked structure formed by UV curing of substance A initiated by a photoinitiator, substance A is a monomer and / or oligomer, the monomer is one or a mixture of isobornyl acrylate, isobornyl methacrylate, N,N-dimethylacrylamide, dicyclopentadiene acrylate, acryloylmorpholine, lauryl acrylate, lauryl methacrylate, isodecyl acrylate, ethoxyethoxyethyl acrylate, tripropylene glycol diacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate, and the oligomer is one or a mixture of aliphatic polyurethane acrylate, aromatic polyurethane acrylate and epoxy acrylate.

8. The application of aliphatic polyurethane acrylate, trimethylolpropane triacrylate and isobornyl acrylate to synergistically improve the heat resistance of the diaphragm.

9. Application of aliphatic polyurethane acrylate, trimethylolpropane triacrylate and isobornyl acrylate to synergistically improve the mechanical properties of the diaphragm.

10. Application of aliphatic polyurethane acrylate, trimethylolpropane triacrylate and isobornyl acrylate to synergistically improve the ionic conductivity of the separator.

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