High-performance lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a high-performance lithium battery diaphragm and a preparation method thereof.The high-performance lithium battery diaphragm comprises a base membrane and a coating on the base membrane, the coating comprises a photoinitiator, a dispersing agent, a cross-linking agent and filler, and the preparation method of the high-performance lithium battery diaphragm comprises the steps that the base membrane is coated with slurry, drying and pretreatment are conducted, and the high-performance lithium battery diaphragm is obtained. The pretreatment comprises the step of irradiating for at least 2 minutes under an ultraviolet lamp. The photoinitiator, the dispersing agent, the cross-linking agent and the filler are introduced into the slurry disclosed by the invention, so that the diaphragm prepared from the slurry disclosed by the invention has relatively good needling strength, heat resistance, ionic conductivity and peel strength and relatively high diaphragm rupture temperature. In addition, the preparation method is simple, high in production efficiency and suitable for continuous production.

Description

Technical Field

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

[0002] The separator separates the positive and negative electrodes, preventing battery short circuits while allowing lithium ions to pass through. With the rapid development of lithium batteries, the performance requirements for lithium battery separators are becoming increasingly stringent. Currently, polyolefin separators are the most commonly used lithium battery separators in the industry. While polyolefin separators offer excellent chemical stability and high mechanical strength, they tend to shrink at high temperatures, which can cause battery short circuits and lead to safety accidents.

[0003] Currently, the most common approach to addressing separator heat resistance is to apply a ceramic coating to the base film. However, this approach suffers from issues such as multiple coatings, high processing costs, poor adhesion, and easy powder shedding, making it unsuitable for mass production. Therefore, there is a need to develop a high-performance lithium battery separator that can be produced continuously. Summary of the Invention

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

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned high-performance lithium battery separator.

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

[0007] A high-performance lithium battery separator, comprising: a base film and a coating on the base film, wherein the coating comprises: a photoinitiator, a dispersant, a crosslinking agent and a filler, wherein the ratio of the photoinitiator, the dispersant, the crosslinking agent and the filler is (0.03-3): (1-1.8): (30-60): (40-70) by mass;

[0008] The photoinitiator is one or a mixture of benzoin photoinitiators, α-hydroxyacetophenone photoinitiators, α-aminoacetophenone photoinitiators, acylphosphine oxide photoinitiators, benzophenone photoinitiators, thioxanthone photoinitiators and anthraquinone photoinitiators;

[0009] The filler is at least one of silicon dioxide, zirconium dioxide, titanium dioxide, aluminum oxide, boehmite and magnesium oxide;

[0010] The crosslinking agent is one or a mixture of tripropylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

[0011] In the above technical solution, the cross-linking agent is preferably pentaerythritol tetraacrylate.

[0012] In the above technical solution, the dispersant is at least one of a polyester dispersant, a polyether dispersant, a polyacrylate dispersant and an amide dispersant.

[0013] In the above technical solution, the thickness of the coating is 1 to 3 μm.

[0014] In the above technical solution, the coating is obtained by coating with a slurry, which includes: the photoinitiator, the solvent, the dispersant, the cross-linking agent and the filler, and the solvent is one or a mixture of several of methanol, ethanol, acetone, butanone, ethyl acetate, butyl acetate, toluene, xylene and dichloromethane.

[0015] In the above technical solution, the method for obtaining the base film includes: adding polyolefin and white oil to the extruder through the feeding system, melting them into a uniform melt in the barrel of the extruder, extruding the uniform melt through the T-die of the extruder to obtain a transparent melt cast sheet, casting the transparent melt cast sheet onto a shaping roller and rapidly cooling it to obtain a cast sheet, stretching the cast sheet for the first time, extracting it, stretching it for the second time, and heat treating it to obtain the base film, wherein, in terms of mass, the ratio of polyolefin to white oil is (10-30): (70-90), the first stretching includes: first stretching longitudinally once and then stretching transversely once, and the second stretching includes: stretching transversely once.

[0016] In the method for obtaining a base film, the temperature of the barrel (melting) is 170 to 230°C.

[0017] In the method for obtaining the base film, the temperature of the sizing roll is 10 to 25°C.

[0018] In the method for obtaining the base film, the extrusion amount of the T-die is 100 to 700 kg per hour.

[0019] In the method for obtaining the base film, the molecular weight of the polyolefin is 600,000 to 4,000,000.

[0020] In the method for obtaining the base film, at least one of dichloromethane, methanol and ethanol is used for extraction, and the extraction temperature is 15 to 25°C.

[0021] In the method for obtaining the base film, the temperature of the heat treatment is 80 to 125°C.

[0022] In the method for obtaining the base film, the first stretching includes: longitudinal stretching once at 80-120° C. (stretching 6-10 times), and transverse stretching once at 105-130° C. (stretching 6-12 times).

[0023] In the method for obtaining the base film, the second stretching includes: stretching in the transverse direction once at 125-135° C. (stretching 1.2-1.5 times).

[0024] The preparation method of the high-performance lithium battery separator includes: coating the slurry on the base film, drying, and pre-treating to obtain the high-performance lithium battery separator, wherein the pre-treatment includes: irradiating under ultraviolet light for at least 2 minutes.

[0025] In the above technical solution, the energy of the UV lamp is 900~2800mJ / cm 2 .

[0026] In the above technical solution, the drying temperature is 50-90°C.

[0027] In the above technical solution, the coating method is one of dipping, blade coating and roller coating.

[0028] A slurry comprising: a photoinitiator, a solvent, a dispersant, a crosslinking agent and a filler, wherein the ratio of the photoinitiator, the solvent, the dispersant, the crosslinking agent and the filler is (0.03-3): (97-99.7): (1-1.8): (30-60): (40-70) by mass;

[0029] The photoinitiator is one or a mixture of benzoin photoinitiators, α-hydroxyacetophenone photoinitiators, α-aminoacetophenone photoinitiators, acylphosphine oxide photoinitiators, benzophenone photoinitiators, thioxanthone photoinitiators and anthraquinone photoinitiators;

[0030] The filler is at least one of silicon dioxide, zirconium dioxide, titanium dioxide, aluminum oxide, boehmite and magnesium oxide;

[0031] The crosslinking agent is one or a mixture of tripropylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

[0032] In the above technical solution, the solvent is one or a mixture of methanol, ethanol, acetone, butanone, ethyl acetate, butyl acetate, toluene, xylene and dichloromethane.

[0033] In the above technical solution, the dispersant is at least one of a polyester dispersant, a polyether dispersant, a polyacrylate dispersant and an amide dispersant.

[0034] The method for preparing the above-mentioned slurry includes: mixing a first system and a second system until they are uniform to obtain a slurry, wherein the first system includes: a photoinitiator and a solvent; the second system includes: a dispersant, a cross-linking agent and a filler, and the ratio of the photoinitiator, the solvent, the dispersant, the cross-linking agent and the filler is (0.03-3): (97-99.7): (1-1.8): (30-60): (40-70) by mass.

[0035] In the above technical solution, the method for obtaining the first system includes: mixing the photoinitiator and the solvent, and stirring them at room temperature until they are uniform, to obtain the first system.

[0036] In the above technical solution, the method for obtaining the second system includes: mixing the dispersant and the cross-linking agent, stirring at room temperature until uniform, then adding the filler, and stirring until uniform to obtain the second system.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The slurry of the present invention incorporates a photoinitiator, dispersant, crosslinker, and filler. The resulting separator exhibits excellent needle puncture strength, heat resistance, ionic conductivity, peel strength, and a high membrane rupture temperature. Furthermore, the preparation method of the present invention is simple, highly efficient, and suitable for continuous production. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below with reference to specific embodiments.

[0040] Tetraethyl Michler's ketone: purity 99%, solid powder;

[0041] 2,4,6-Trimethylbenzoyldiphenylphosphine oxide: purity 98%, solid powder.

[0042] 2-Benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone: purity 98%, solid powder.

[0043] Benzophenone: purity 99%, solid powder.

[0044] 2-Ethylanthraquinone: purity 97%, solid powder.

[0045] Trimethylolpropane triacrylate: purity 99%, colorless and transparent liquid.

[0046] Pentaerythritol tetraacrylate: purity 99%, colorless and transparent liquid.

[0047] Polyacrylamide: M w =300000.

[0048] Thickness: The test was carried out using a Mahr thickness gauge (C1216).

[0049] Needle puncture strength at 200°C: The test was performed using a Shimadzu intelligent electronic tensile testing machine AGS-50N. A 100 mm long and 100 mm wide diaphragm was cut as a sample. The temperature of the Shimadzu intelligent electronic tensile testing machine was set to 200°C to obtain the needle puncture strength at this temperature.

[0050] Membrane rupture temperature: The instrument used is Q400 from TA of the United States. Cut a diaphragm of 8mm*4.5mm and put it into the instrument. The tensile force is set to 0.03N and the heating rate is set to 5℃ / min. The membrane rupture temperature is measured under these parameters.

[0051] Ionic conductivity: Tested in accordance with GB / T36363-2018 (test temperature 25°C, relative humidity 60 RH%).

[0052] Peel strength: Cut a 150mm*30mm diaphragm sample, adhere a 100mm*25mm 3M tape to the coated side of the diaphragm and press it firmly. Clamp the sample and 3M tape at both ends of a tensile testing machine and peel the sample at a speed of 100mm / min and 180° to measure the peel strength.

[0053] In the following examples and comparative examples, a method for obtaining a base film (the thickness of the base film is 9 μm) comprises: adding polyolefin (polyethylene) and white oil to a twin-screw extruder via a feeding system, wherein the temperature of the barrel, T-die, and each heating section of the twin-screw extruder is 185° C., melting the polyolefin (polyethylene) and white oil into a uniform melt in the barrel of the twin-screw extruder, extruding the uniform melt through the T-die of the twin-screw extruder to obtain a transparent melt cast sheet, casting the transparent melt cast sheet onto a shaping roller at a temperature of 20° C. and rapidly cooling the cast sheet to obtain a cast sheet, stretching the cast sheet for the first time, and rolling the cast sheet at 20° C. The film was extracted in dichloromethane at 0°C for 10 minutes to extract the white oil, and then stretched for a second time and heat treated at 100°C for 30 seconds to obtain a base film, wherein the ratio of polyolefin to white oil was 23:77 by mass, and the first stretching included: first longitudinal stretching once at 100°C (stretching 9 times), and then transverse stretching once at 120°C (stretching 10 times), and the second stretching included: transverse stretching once at 134°C (stretching 1.3 times), the extrusion capacity of the T-die head was 300 kg per hour, and the molecular weight of the polyolefin was 1 million.

[0054] Example 1 (for comparison)

[0055] A method for preparing a diaphragm comprises: mixing a photoinitiator and a solvent, stirring the mixture at a speed of 800 r / min for 30 minutes at room temperature until the mixture is uniform, obtaining a slurry, coating the slurry on a base film by dip coating at a coating speed of 30 m / min, drying the mixture in an oven at 70°C for 3 minutes, and performing pretreatment to obtain the diaphragm, wherein the pretreatment comprises irradiating the mixture under an ultraviolet lamp (365 nm LED ultraviolet lamp) for 4 minutes, wherein the energy of the ultraviolet lamp is 2800 mJ / cm 2 The photoinitiator is a benzophenone photoinitiator (tetraethyl Michler's ketone), the solvent is ethanol, and the ratio of the photoinitiator to the solvent is 1:99 by mass.

[0056] Example 2 (for comparison)

[0057] A method for preparing a diaphragm comprises: mixing a photoinitiator and a solvent, stirring the mixture at a speed of 800 r / min for 30 minutes at room temperature until uniform, obtaining a slurry, coating the slurry on both sides of a base film at a coating speed of 10 m / min by roller coating, drying the mixture in an oven at 70°C for 8 minutes, and performing pretreatment to obtain the diaphragm, wherein the pretreatment comprises: irradiating the mixture under an ultraviolet lamp (mercury lamp) for 10 minutes, wherein the energy of the ultraviolet lamp is 900 mJ / cm 2 The photoinitiator is an acylphosphine oxide photoinitiator (2,4,6-trimethylbenzoyldiphenylphosphine oxide), and the solvent is butyl acetate. The ratio of the photoinitiator to the solvent is 1.5:98.5 in parts by mass.

[0058] Example 3 (for comparison)

[0059] A method for preparing a diaphragm comprises: mixing a photoinitiator and a solvent, stirring the mixture at a speed of 800 r / min for 30 minutes at room temperature until uniform, obtaining a slurry, coating the slurry on both sides of a base film at a coating speed of 60 m / min by roller coating, drying the mixture in an oven at 70°C for 1 minute, and performing pretreatment to obtain the diaphragm, wherein the pretreatment comprises: irradiating the mixture under an ultraviolet lamp (mercury lamp) for 2 minutes, wherein the energy of the ultraviolet lamp is 2200 mJ / cm 2 The photoinitiator is a mixture of an α-aminoacetophenone photoinitiator (2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone) and a benzophenone photoinitiator (benzophenone). The solvent is methanol. The ratio of 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone (photoinitiator 369), benzophenone, and solvent is 0.5:1:98.5 in parts by mass.

[0060] Example 4

[0061] A method for preparing a high-performance lithium battery separator comprises: coating a slurry on a single side of a base film at a coating speed of 60 m / min by roller coating, drying in an oven at 70°C for 1 min, and pre-treating to obtain a coating on the base film to obtain a high-performance lithium battery separator. The pre-treatment comprises: irradiating under an ultraviolet lamp (365 nm LED ultraviolet lamp) for 2 min, the energy of the ultraviolet lamp being 2200 mJ / cm 2 .

[0062] The preparation method of the above-mentioned slurry includes: mixing the first system and the second system until they are uniform to obtain a slurry, the first system includes: a photoinitiator and a solvent, and the second system includes: a dispersant, a cross-linking agent and a filler. The ratio of the photoinitiator, the solvent, the dispersant, the cross-linking agent and the filler is 1:99:1:30:40 by mass, the photoinitiator is an anthraquinone photoinitiator (2-ethyl anthraquinone), the filler is titanium dioxide, the solvent is methanol, the dispersant is an amide dispersant (polyacrylamide), and the cross-linking agent is trimethylolpropane triacrylate.

[0063] The method for obtaining the first system includes: mixing a photoinitiator and a solvent, and stirring the mixture at a rotation speed of 800 r / min for 30 minutes at room temperature until the mixture is uniform, thereby obtaining the first system.

[0064] The method for obtaining the second system includes: mixing the dispersant and the crosslinking agent, stirring at a speed of 600 r / min for 10 minutes at room temperature until uniform, then adding filler, and stirring at a speed of 800 r / min for 10 minutes at room temperature until uniform, to obtain the second system.

[0065] Example 5

[0066] A method for preparing a high-performance lithium battery separator is basically the same as that of Example 4, except that "trimethylolpropane triacrylate" is replaced by "pentaerythritol tetraacrylate".

[0067] Example 6 (for comparison)

[0068] A method for preparing a diaphragm comprises: applying the first system of Example 4 to a base film at a coating speed of 60 m / min by dip coating to form a first coating layer on both sides of the base film, then applying the second system of Example 4 to each first coating layer by roller coating at a coating speed of 60 m / min, drying in an oven at 70° C. for 1 minute, pre-treating, forming a second coating layer on each first coating layer (the two second coating layers have the same thickness), and obtaining a diaphragm (the diaphragm has a layered structure, comprising, from top to bottom, the second coating layer, the first coating layer, the base film, the first coating layer, and the second coating layer), wherein the pre-treatment comprises: irradiating under an ultraviolet lamp (a 365 nm LED ultraviolet lamp) for 2 minutes, the energy of the ultraviolet lamp being 2200 mJ / cm 2 .

[0069] Comparative Example 1

[0070] A method for preparing a diaphragm is substantially the same as that of Example 4, except that no crosslinking agent (trimethylolpropane triacrylate) is added.

[0071] Comparative Example 2

[0072] A method for preparing a diaphragm is substantially the same as that of Example 6, except that no crosslinking agent (trimethylolpropane triacrylate) is added.

[0073] Comparative Example 3

[0074] A method for preparing a diaphragm comprises: coating a slurry on a single side of a base film at a coating speed of 60 m / min by roller coating, drying in an oven at 70°C for 1 min, and pre-treating the diaphragm, wherein the pre-treatment comprises irradiating the diaphragm with an ultraviolet lamp (365 nm LED ultraviolet lamp) for 2 min, wherein the energy of the ultraviolet lamp is 2200 mJ / cm 2 .

[0075] The preparation method of the above-mentioned slurry includes: mixing methanol, a dispersant, a cross-linking agent and a filler until uniform to obtain a slurry, wherein the ratio of methanol, dispersant, cross-linking agent and filler is 99:1:30:40 by mass, the filler is titanium dioxide, the dispersant is an amide dispersant (polyacrylamide), and the cross-linking agent is trimethylolpropane triacrylate.

[0076] The test results of the diaphragms prepared in Examples 1 to 6 and Comparative Examples 1 to 3 are as follows:

[0077]

[0078] In Example 6, a first coating layer containing a photoinitiator was first formed, followed by a second coating layer formed on top of the first coating layer. The resulting membrane exhibited comparable peel strength to that of Examples 4 and 5, but exhibited poor heat resistance. Comparing Example 4 with Comparative Example 1 reveals that the addition of a crosslinker increased the crosslink density of the base film and coating layer, improving various performance characteristics. In Comparative Example 3, no photoinitiator was added to the slurry, resulting in a membrane with poor performance. This further demonstrates that the crosslinking reaction between the photoinitiator and crosslinker after exposure to light enhances membrane performance.

[0079] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A high-performance lithium battery separator, characterized in that: include: The base film and the coating on the base film include: a photoinitiator, a dispersant, a crosslinking agent and a filler, wherein the ratio of the photoinitiator, the dispersant, the crosslinking agent and the filler is (0.03-3): (1-1.8): (30-60): (40-70) by weight; The photoinitiator is one or a mixture of benzoin photoinitiators, α-hydroxyacetophenone photoinitiators, α-aminoacetophenone photoinitiators, acylphosphine oxide photoinitiators, benzophenone photoinitiators, thioxanthone photoinitiators and anthraquinone photoinitiators; The filler is at least one of silicon dioxide, zirconium dioxide, titanium dioxide, aluminum oxide, boehmite and magnesium oxide; The crosslinking agent is one or a mixture of tripropylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

2. The high-performance lithium battery separator according to claim 1, characterized in that The dispersant is at least one of a polyester dispersant, a polyether dispersant, a polyacrylate dispersant and an amide dispersant.

3. The high-performance lithium battery separator according to claim 1, characterized in that The thickness of the coating is 1 to 3 μm.

4. The high-performance lithium battery separator according to claim 1, characterized in that The method for obtaining a base film comprises: melting polyolefin and white oil into a uniform melt in an extruder, extruding the uniform melt through a T-die of the extruder to obtain a transparent melt cast sheet, casting the transparent melt cast sheet onto a shaping roller and rapidly cooling it to obtain a cast sheet, stretching the cast sheet for the first time, extracting it, stretching it for the second time, and heat treating it to obtain a base film, wherein the ratio of the polyolefin to the white oil is (10-30):(70-90) by mass, the first stretching comprises: first stretching longitudinally once and then stretching transversely once, and the second stretching comprises: stretching transversely once.

5. A slurry, characterized in that: include: The photoinitiator, solvent, dispersant, crosslinking agent and filler are calculated by weight, and the ratio of the photoinitiator, solvent, dispersant, crosslinking agent and filler is (0.03-3): (97-99.7): (1-1.8): (30-60): (40-70). The photoinitiator is one or a mixture of benzoin photoinitiators, α-hydroxyacetophenone photoinitiators, α-aminoacetophenone photoinitiators, acylphosphine oxide photoinitiators, benzophenone photoinitiators, thioxanthone photoinitiators and anthraquinone photoinitiators; The filler is at least one of silicon dioxide, zirconium dioxide, titanium dioxide, aluminum oxide, boehmite and magnesium oxide; The crosslinking agent is one or a mixture of tripropylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

6. The slurry according to claim 5, characterized in that The dispersant is at least one of polyester dispersants, polyether dispersants, polyacrylate dispersants and amide dispersants, and the solvent is one of methanol, ethanol, acetone, butanone, ethyl acetate, butyl acetate, toluene, xylene and dichloromethane or a mixture of several thereof.

7. The method for preparing the slurry according to claim 5, characterized in that: include: The first system and the second system are mixed until uniform to obtain a slurry, wherein the first system includes: a photoinitiator and a solvent; the second system includes: a dispersant, a cross-linking agent and a filler, and the ratio of the photoinitiator, the solvent, the dispersant, the cross-linking agent and the filler is (0.03-3): (97-99.7): (1-1.8): (30-60): (40-70) by mass.

8. A method for preparing a high-performance lithium battery separator, characterized in that: include: The slurry according to claim 5 is coated on the base film and dried. Pretreatment is performed to obtain a high-performance lithium battery separator, wherein the pretreatment includes irradiation under ultraviolet light.

9. The use of crosslinking agents in the crosslinking reaction after photoinitiator illumination to improve the puncture strength, heat resistance, ionic conductivity, peel strength or membrane rupture temperature of the membrane.

10. The use according to claim 9, characterized in that The crosslinking agent is one or a mixture of tripropylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and pentaerythritol tetraacrylate.

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