A method for preparing a lithium battery separator

Abstract

This invention relates to a method for preparing a lithium battery separator, comprising the following steps: mixing and stirring polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and a solvent to induce swelling of the mixture, followed by plasticization to obtain a homogeneous mixture; cooling and shaping the homogeneous mixture into a cast sheet to obtain a cast sheet; allowing the cast sheet to stand at 30-50°C for 24-48 hours in the dark to obtain an oil film; simultaneously stretching the oil film bidirectionally, followed by extraction with an extractant and a photoinitiator, wherein the weight ratio of the extractant to the photoinitiator is (90.0-99.9):(0.1-10.0); stretching the extracted film laterally, followed by UV curing for 2-30 seconds; and heat-setting the cured film to obtain the lithium battery separator. The separator prepared by this method exhibits both good puncture resistance and adhesion.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, and specifically relates to a method for preparing a lithium battery separator. Background Technology

[0002] The separator is a key component of lithium-ion batteries because it provides a physical barrier between the positive and negative electrodes to prevent short circuits. The separator also serves as the electrolyte reservoir for ion transport during battery charge-discharge cycles. The performance of lithium-ion batteries is largely influenced by the separator material and structure. The separator must possess chemical and electrochemical stability against the electrolyte and electrode materials in the lithium-ion battery. Similarly, it has high mechanical performance requirements, such as tensile strength and puncture strength in the longitudinal (MD) and transverse (TD) directions. Polyolefin (PE) separators are currently the most common separator product. Although PE separators are now commercially available, their pore-closure and rupture temperatures are very close. While the separator can close its micropores near the melting point of PE in a timely manner, this process can cause excessive shrinkage and deformation, even leading to rupture, posing a significant safety hazard.

[0003] To address the above issues, current methods primarily involve surface coating modification, surface grafting modification, and blending modification to improve the puncture strength and heat shrinkage properties of the membrane. Industrially, an adhesive (such as PVDF-HFP) is used to coat the membrane surface with inorganic materials, ultimately producing a composite membrane. After coating, the membrane's thermal stability is significantly improved, and other properties are also relatively good. While this modification method imparts high thermal stability to the PE membrane, the process requires an adhesive, and the membrane needs to be immersed in the electrolyte environment for extended periods. This makes the surface coating material extremely prone to detachment, affecting the overall membrane performance. Furthermore, during the bonding process, the low polarity of PE results in poor adhesion, necessitating further modification.

[0004] Therefore, in order to solve the above problems, it is of great significance to prepare a diaphragm with high mechanical properties and good adhesion. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a lithium battery separator, which produces a separator with good puncture resistance and adhesion.

[0006] In a first aspect, the present invention provides a method for preparing a lithium battery separator, comprising the following steps:

[0007] Step 1: Mix and stir polyethylene with a viscosity-average molecular weight of 500,000-1,000,000, ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 2,000,000-4,000,000, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent to cause the mixture to swell, and then plasticize to obtain a homogeneous mixture. The weight ratio of the polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent is (15-20):(1-5):(5-10):(0.2-1):(1-5):(60-85).

[0008] Step 2: The homogeneous mixture is cooled and shaped into a casting to obtain a casting sheet. The casting sheet is then placed in the dark at 30-50°C for 24-48 hours to obtain an oil film.

[0009] Step 3: The oil film is subjected to bidirectional synchronous stretching, and then extracted with an extractant and a photoinitiator, wherein the weight ratio of the extractant to the photoinitiator is (90.0-99.9):(0.1-10.0);

[0010] Step 4: Stretch the extracted film laterally and then cure it under ultraviolet light for 2-30 seconds.

[0011] Step 5: Heat-set the cured film to obtain the lithium battery separator.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. Currently, the introduction of cross-linked structures into membranes is mainly achieved through irradiation. This method easily leads to a decrease in membrane molecular weight, resulting in a reduction in strength. This invention introduces hydrogenated polybutadiene, which has good compatibility with olefins, into the system, effectively introducing double bonds and increasing the cross-linked structure in the amorphous region, thereby effectively improving membrane puncture strength.

[0014] 2. By selecting the best antioxidants, the negative impact of antioxidants on the subsequent crosslinking process can be reduced.

[0015] 3. By introducing photoinitiators through the extraction process, the loss of initiators and double bonds generated during the extrusion process is reduced. At the same time, the negative impact of photoinitiators on the interior of the membrane skeleton is reduced, so that the free radicals generated by photoinitiation can only form cross-linked structures on the surface and amorphous parts, thereby improving the membrane strength.

[0016] 4. By controlling the light exposure time, some double bond structures remain on the film surface, which improves the adhesion performance of the film during subsequent coating modification. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the method for preparing the lithium battery separator according to the present invention. Detailed Implementation

[0018] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0019] The first method of the present invention provides a method for preparing a lithium battery separator, comprising the following steps:

[0020] Step 1: Mix and stir polyethylene with a viscosity-average molecular weight of 500,000-1,000,000, ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 2,000,000-4,000,000, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent to induce swelling of the mixture, followed by plasticization to obtain a homogeneous mixture. The weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent is (15-20):(1-5):(5-10):(0.2-1):(1-5):(60-85). In this step, polyethylene is a conventional raw material for preparing lithium battery separators, and its molecular weight can specifically be 500,000, 600,000, or 700,000. The molecular weights of polyethylene can be 10,000, 800,000, 900,000, 1,000,000, or a mixture of the above-mentioned molecular weights; the molecular weights of ultra-high molecular weight polyethylene can be 2,000,000, 2,300,000, 2,500,000, 2,700,000, 3,000,000, 3,300,000, 3,500,000, 4,000,000, or a mixture of the above-mentioned molecular weights; the specific weight ratios of polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent can be 15:1:5:1:5:73, 20:5:10:0.2:1:63.8, 17:3:5:0.5:2:72.5, and 15:1:5:0.2:1:77.8.

[0021] Step 2: The homogeneous mixture is cooled and shaped into a casting to obtain a casting sheet. The casting sheet is then placed in the dark at 30-50℃ for 24-48 hours to obtain an oil film. The specific standing temperature can be 30℃, 35℃, 40℃, 45℃, or 50℃, and the standing time can be 24 hours, 30 hours, 35 hours, 40 hours, 45 hours, or 48 hours.

[0022] Step 3: The oil film is subjected to bidirectional synchronous stretching, and then extracted with an extractant and a photoinitiator. The weight ratio of the extractant to the photoinitiator is (90.0-99.9):(0.1-10.0), and the specific weight ratio can be 90:10, 95:5, 97:3, 98:2, or 99.9:0.1.

[0023] Step 4: Stretch the extracted film laterally and then cure it under ultraviolet light for 2-30 seconds. The specific curing time can be 2 seconds, 3 seconds, 5 seconds, 6 seconds, 10 seconds, 15 seconds, 25 seconds, or 30 seconds.

[0024] Step 5: Heat-set the cured film to obtain the lithium battery separator.

[0025] In the method described in this invention, the ultra-high molecular weight polyethylene (UHMWPE) and polypropylene (PP) components provide high puncture strength; hydrogenated polybutadiene, as a crosslinkable component and providing double bond moieties, lays the foundation for subsequent crosslinking structures and improved adhesion strength; the hindered amine moieties not only have a certain antioxidant degradation effect but also have a minimal impact on subsequent crosslinking. The light-protected settling step serves to perfect the phase separation process and allow the hydrogenated polybutadiene to gradually migrate to the surface. The extraction step removes the solvent while introducing a photoinitiator. Its advantage is that the photoinitiator mainly adheres to the surface of the extraction membrane, with very little penetration into the backbone. This reduces the impact of the generated free radicals on the PE and PP within the membrane backbone during subsequent UV initiation of free radicals. The extractant used in the extraction is a conventional industrial extractant, such as dichloromethane. This application does not specifically limit the type of extractant; those skilled in the art can choose according to the actual situation. The purpose of UV curing is to partially cure and crosslink the hydrogenated polybutadiene. By controlling the curing time, only a portion of the hydrogenated polybutadiene is cured. At this time, the amorphous region of the resulting film has a certain crosslinked structure, which improves the strength of the amorphous region. At the same time, a certain number of double bonds are retained on the film surface for subsequent coating, bonding or other modifications.

[0026] In this invention, no specific limitation is made to the solvent. Any solvent can be used to dissolve polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant and hydrogenated polydibutylene to form a homogeneous substance. Those skilled in the art can select the solvent based on common technical knowledge in the field. Preferably, white oil can be used.

[0027] In this invention, the step of mixing polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polydibutylene, and solvent in step one is a conventional technical operation in the art. No specific limitation is made on the specific mixing method. Those skilled in the art can select and adjust the stirring time and speed according to actual conditions and conventional technical knowledge. Rapid mixing can be achieved under high-speed stirring. The mixing temperature can be 50-100℃, more specifically 50℃, 65℃, 70℃, 75℃, 80℃, 90℃, or 100℃. The stirring time can be 12-24 hours, such as 12 hours, 15 hours, 18 hours, 21 hours, or 24 hours. The plasticizing process is also a conventional technical operation in the art, and this invention does not impose any special limitations. Preferably, plasticizing can be carried out in a twin-screw extruder at a plasticizing temperature of 150-220℃, more specifically 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, or 220℃.

[0028] In this invention, the molecular weights of polypropylene and hydrogenated polybutadiene are not specifically limited. The viscosity-average molecular weight of the polypropylene is 500,000 to 1,000,000, specifically 500,000, 600,000, 700,000, 800,000, 900,000, and 1,000,000, and can be a mixture of polypropylenes with different molecular weights. The weight-average molecular weight of the hydrogenated polybutadiene is 1,000 to 4,000, specifically 1,000, 1,500, 2,000, 2,500, 3,000, 3,500, and 4,000.

[0029] In this invention, the casting sheet cooling and shaping process described in step two is a conventional technical operation in the field, and this invention does not impose specific limitations. Preferably, the temperature of the quenching roller during the casting sheet cooling and shaping process is 10-50℃. More preferably, the temperature of the quenching roller can be 10℃, 20℃, 30℃, 40℃, or 50℃. The thickness of the casting sheet can be determined according to the actual situation, such as 2000μm-3000μm, and more specifically, 2000μm, 2200μm, 2350μm, 2500μm, or 3000μm.

[0030] In this invention, biaxial stretching in step three is a conventional technical operation in the field. This invention does not specifically limit the operating conditions. Those skilled in the art can select appropriate operating conditions according to the actual situation. Preferably, the temperature for biaxial stretching is 100℃-135℃, specifically 100℃, 110℃, 120℃, 130℃, or 135℃, and the stretching ratio is 5-10 times, specifically 5 times, 6 times, 7 times, 8 times, 9 times, or 10 times.

[0031] In this invention, when extracting the oil film in step three, the photoinitiator is a commonly used type of photoinitiator in the art, such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator 819), or 1-hydroxycyclohexylphenyl ketone (photoinitiator 184). The extraction temperature is 20-50℃, specifically 20℃, 30℃, 40℃, or 50℃, and the extraction time is 2-10 minutes, specifically 2 minutes, 5 minutes, 7 minutes, or 10 minutes.

[0032] In this invention, the transverse stretching in step four is a conventional technical operation in the field. This invention does not specifically limit the operating conditions. Those skilled in the art can select appropriate operating conditions according to the actual situation. Preferably, the transverse stretching ratio is 1.1-1.6 times, specifically 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, or 1.6 times, and the temperature is 110℃-150℃, specifically 110℃, 120℃, 130℃, 140℃, or 150℃.

[0033] In this invention, the ultraviolet wavelength range in step four is 280nm-400nm, specifically 280nm, 290nm, 310nm, 330nm, 350nm, 370nm, 390nm, and 400nm.

[0034] In this invention, the heat setting in step five is a conventional technical operation in the field. This invention does not specifically limit the operating conditions. Those skilled in the art can select appropriate operating conditions according to the actual situation. Preferably, the heat setting temperature is 110℃-150℃, specifically 110℃, 120℃, 130℃, 140℃, or 150℃, and the time is 10-40 minutes, specifically 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, or 40 minutes. The final thickness of the lithium battery separator is 10μm-20μm, such as 10μm, 12μm, 15μm, 17μm, or 20μm.

[0035] The diaphragm prepared by this method can be used directly or coated with inorganic materials to improve its performance. The specific coating method is a conventional preparation method in this field and is not specifically limited in this application.

[0036] The present invention will be further described below with reference to the embodiments, but the scope of the present invention is not limited to these embodiments.

[0037] Example 1

[0038] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0039] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0040] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0041] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0042] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0043] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0044] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0045] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 2 seconds.

[0046] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0047] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0048] Example 2

[0049] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0050] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0051] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0052] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0053] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0054] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0055] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0056] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 6 seconds.

[0057] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0058] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0059] Example 3

[0060] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0061] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0062] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0063] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0064] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0065] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0066] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0067] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 30 seconds.

[0068] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0069] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0070] Example 4

[0071] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0072] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0073] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0074] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0075] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0076] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 98:2; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0077] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0078] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 6 seconds.

[0079] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0080] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0081] Example 5

[0082] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0083] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0084] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0085] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0086] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0087] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 90:10; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0088] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0089] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 6 seconds.

[0090] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0091] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0092] Comparative Example 1

[0093] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0094] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0095] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0096] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0097] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0098] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 90:10; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0099] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0100] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 200 seconds.

[0101] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0102] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0103] Comparative Example 2

[0104] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0105] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0106] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0107] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0108] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0109] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0110] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0111] Step 7: Heat-set the film obtained in Step 6. The heat-setting temperature is 130℃. The time is 2 minutes.

[0112] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0113] Comparative Example 3

[0114] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0115] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0116] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0117] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0118] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0119] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 80:20; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0120] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0121] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 6 seconds.

[0122] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0123] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0124] Comparative Example 4

[0125] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0126] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is 1010; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (1010), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0127] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0128] Step 3: Place the obtained casting at 40°C in the dark for 30 hours.

[0129] Step 4: Perform bidirectional synchronous stretching on the oil film obtained in Step 3. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0130] Step 5: Extract the oil film obtained in Step 4. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0131] Step Six: The membrane obtained in Step Five is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0132] Step 7: Curing the film obtained in Step 6 by ultraviolet irradiation. The ultraviolet wavelength range is 365nm, and the curing time is 6 seconds.

[0133] Step 8: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0134] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0135] Comparative Example 5

[0136] Step 1: Polyethylene, ultra-high molecular weight polyethylene polypropylene, antioxidant, hydrogenated polybutadiene, and white oil are stirred at high speed at 85°C for 24 hours to induce swelling. The mixture is then plasticized in a twin-screw extruder at 210°C to obtain a homogeneous mixture.

[0137] The polyethylene has a viscosity-average molecular weight of 800,000, and the ultra-high molecular weight polyethylene has a molecular weight of 2 million; the polypropylene has a weight-average molecular weight of 600,000; the antioxidant is a hindered amine; the hydrogenated polybutadiene has a weight-average molecular weight of 3,000; the weight ratio of polyethylene, ultra-high molecular weight polyethylene, polypropylene, antioxidant (hindered amine), hydrogenated polybutadiene, and white oil is 14:2:1:0.5:3.5:79.

[0138] Step 2: The obtained homogeneous blend is shaped into a casting sheet by a casting cooling process; the temperature of the quenching roller is 10℃.

[0139] Step 3: Perform bidirectional synchronous stretching on the oil film obtained in Step 2. The stretching temperature is 130℃, and the stretching ratio is 8 times.

[0140] Step 4: Extract the oil film obtained in Step 3. The extractant is a mixture of dichloromethane and photoinitiator (TPO) in a weight ratio of 95:5; the extraction temperature is 25°C and the extraction time is 5 minutes.

[0141] Step 5: The membrane obtained in Step 4 is subjected to transverse stretching. The stretching ratio is 1.2 times, and the temperature is 130℃.

[0142] Step Six: Curing the film obtained in Step Five by UV irradiation. The UV wavelength range is 365nm, and the curing time is 6 seconds.

[0143] Step 7: Heat-set the film obtained in Step 7. The heat-setting temperature is 130℃. The time is 2 minutes.

[0144] Step Nine: Coating. Polyacrylate derivatives, polyethylene oxide, and silica (with a D50 of 1.0 μm) were selected as the inorganic ceramic powder. Butanol was used as the dispersant, and hydroxyethyl cellulose as the thickener. First, deionized water, dispersant, thickener, and silica were mixed in a weight ratio of 70:0.3:0.2:29 to prepare a dispersion. Then, the polyacrylate derivative, polyethylene oxide, and dispersion were mixed uniformly in a weight ratio of 1:0.3:99 to obtain a ceramic slurry with a viscosity of 30 cP. After preparing the ceramic slurry, it was coated onto one surface of the resulting film using a gravure roller coating method. The coating speed was 30 m / min, the drying temperature was 50 °C, the drying time was 20 min, and the coating thickness was 3 μm, resulting in a lithium-ion ceramic separator.

[0145] The diaphragms prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to performance tests. "Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the tensile strength of the diaphragms was tested according to GB / T 1040.3-2006 test standard. The puncture strength of the diaphragms was tested according to GB / T10004-2008 standard."

[0146] Adhesion strength: Cut a 40mm×100mm sample, fix the ceramic diaphragm on both sides to the fixed clamp and the movable clamp respectively with tape, and stretch it in the opposite direction at 180° to peel the ceramic layer and the substrate film. The greater the tensile force required, the higher the peel strength of the ceramic diaphragm, which means the higher the adhesion strength.

[0147] The performance tests are shown in the table below:

[0148]

[0149]

[0150] As shown in the table above, based on Example 2 and Comparative Example 2, under the same conditions, the difference lies in the presence or absence of ultraviolet (UV) light irradiation. It can be seen that under UV irradiation, the tensile strength and needle penetration strength are significantly greater than those of the un-irradiated sample. Simultaneously, due to the lack of UV crosslinking, a crosslinking network is not formed, resulting in a sticky film surface, ultimately affecting the bonding strength. Based on Example 2 and Comparative Example 4, the difference lies in the choice of antioxidant. It can be found that hindered amine antioxidants have less impact on UV-induced free radicals, leading to higher crosslinking efficiency and thus higher strength. Based on Example 2 and Comparative Example 5, the difference lies in whether the oil film is allowed to stand in the dark. It can be seen that the mechanical strength and bonding strength after standing are greater than those of the un-standing sample. The migration of small molecules after standing reduces skeletal defects and allows them to accumulate on the film surface, ultimately resulting in a more significant strength increase during light irradiation. The tensile strength, puncture strength, and adhesive strength data of the diaphragms obtained from the above embodiments and comparative examples show that it is necessary to control the appropriate ultraviolet irradiation time during the preparation process so that the diaphragm has both good tensile strength, puncture strength, and good adhesive strength.

[0151] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for producing a lithium battery separator, characterized by, Includes the following steps: Step 1: Mix and stir polyethylene with a viscosity-average molecular weight of 500,000-1,000,000, ultra-high molecular weight polyethylene with a viscosity-average molecular weight of 2,000,000-4,000,000, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent to cause the mixture to swell, and then plasticize to obtain a homogeneous mixture. The weight ratio of the polyethylene, ultra-high molecular weight polyethylene, polypropylene, hindered amine antioxidant, hydrogenated polybutadiene, and solvent is (15-20):(1-5):(5-10):(0.2-1):(1-5):(60-85). Step 2: The homogeneous mixture is cooled and shaped into a casting to obtain a casting sheet. The casting sheet is then placed in the dark at 30-50°C for 24-48 hours to obtain an oil film. Step 3: The oil film is subjected to bidirectional synchronous stretching, and then extracted with an extractant and a photoinitiator, wherein the weight ratio of the extractant to the photoinitiator is (90.0-99.9):(0.1-10.0); Step 4: Stretch the extracted film laterally and then cure it under ultraviolet light for 2-30 seconds. Step 5: Heat-set the cured film to obtain the lithium battery separator.

2. The method of producing a lithium battery separator according to claim 1, characterized by, The solvent is white oil.

3. The method of claim 1, wherein the polymeric material is a polyolefin. In step one, the swelling temperature is 50-100℃ and the plasticizing temperature is 150-220℃.

4. The method of claim 1, wherein the polymeric material is a polyolefin. The polypropylene has a viscosity-average molecular weight of 500,000 to 1,000,000, and the hydrogenated polybutadiene has a weight-average molecular weight of 1,000 to 4,000.

5. The method of claim 1, wherein the polymeric material is a polyolefin. In step two, the temperature of the quenching roller during the cooling and shaping process of the cast sheet is 10-50℃, and the thickness of the cast sheet is 2000μm-3000μm.

6. The method of claim 1, wherein the polymeric material is a polyolefin. In step three, the temperature for biaxial stretching is 100℃-135℃, and the stretching ratio is 5-10 times.

7. The method for preparing the lithium battery separator according to claim 1, characterized in that, In step three, the extraction temperature is 20-50℃ and the extraction time is 2-10 minutes.

8. The method for preparing a lithium battery separator according to claim 1, characterized in that, In step four, the transverse stretching ratio is 1.1-1.6 times, and the temperature is 110℃-150℃.

9. The method for preparing a lithium battery separator according to claim 1, characterized in that, In step four, the ultraviolet wavelength range is 280nm-400nm.

10. The method for preparing a lithium battery separator according to claim 1, characterized in that, In step five, the heat setting temperature is 110℃-150℃, and the time is 10-40 minutes, resulting in a lithium battery separator thickness of 10μm-20μm.

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