An integrated preparation method for composite lithium battery separators

Abstract

This invention discloses an integrated preparation method for a composite lithium battery separator, belonging to the field of lithium battery separator technology. The method includes the following steps: coating a slurry onto one or both sides of a base film precursor, stretching it laterally, and then drying and shaping it to obtain the composite lithium battery separator. The slurry comprises the following raw materials by weight: 0.1-1 parts dispersant, 2-10 parts binder, 0.1-1 parts wetting agent, 0.2-10 parts thickener, and 100 parts solvent. The slurry also includes 20-45 parts modified inorganic filler. This invention achieves continuous and synchronous production of the composite separator through the integrated design of base film production and coating processing, simplifying the production process and saving costs. Simultaneously, the composite separator can significantly improve its thermal stability, reducing thermal shrinkage to approximately 1 / 10 of its original value. With good peel strength and liquid absorption rate, it has good application prospects and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery separator technology, specifically relating to an integrated preparation method for a composite lithium battery separator. Background Technology

[0002] The separator in a lithium-ion battery is a crucial component, serving as an insulating layer that separates the positive and negative electrode materials while providing a pathway for lithium ion migration. The separator substrate is typically made of thermoplastic materials such as polyethylene and polypropylene, which makes it prone to shrinkage and rupture at high battery temperatures, severely impacting battery safety.

[0003] To address this issue, the industry currently primarily improves the heat resistance and stability of polyolefin separators by coating the surface with micron-sized rigid ceramic particles. However, this requires the configuration of corresponding slitting machines (for easy transport and to accommodate coating widths) and coating machines. The factory workshop needs to be equipped with transit warehouses and personnel / material flow channels to transfer film carts and packaging materials for subsequent heat-resistant material coating processing, increasing equipment costs by approximately 30%. Furthermore, the post-processing of slitting, transporting, and coating also increases labor, energy consumption, and maintenance costs. In addition, polyolefin separators require prolonged periods of inactivity during slitting, transporting, and coating. Due to the relaxation phenomenon of plastic materials, varying degrees of deformation occur, leading to poor membrane surface flatness and causing serious quality problems such as incomplete coating and misalignment of the battery cells, thus affecting the yield of finished separator products. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated preparation method for composite lithium battery separators, which solves the problems of high production cost and low yield of existing lithium battery separators.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] An integrated preparation method for a composite lithium battery separator includes the following steps:

[0007] S1. Mix and extrude ultra-high molecular weight polyethylene, pore-forming agent, nucleating agent and antioxidant to obtain melt. After casting and cooling the melt, obtain crystalline cast sheet. Stretch and extract the crystalline cast sheet to obtain dry film. Stretch, shrink and heat set the dry film to obtain base film precursor.

[0008] S2. The slurry is coated on one or both sides of the base film precursor, stretched laterally, and then dried and shaped to obtain a composite lithium battery separator.

[0009] Further, the slurry comprises the following raw materials in parts by weight: 0.1 to 1 part dispersant, 2 to 10 parts binder, 0.1 to 1 part wetting agent, 0.2 to 10 parts thickener, and 100 parts solvent.

[0010] Furthermore, the slurry also includes 20 to 45 parts of modified inorganic filler.

[0011] Furthermore, the modified inorganic filler is prepared through the following steps:

[0012] Add the amphiphilic silane coupling agent to anhydrous ethanol and mix well to obtain a modified solution. Add the inorganic filler to the ethanol aqueous solution and ultrasonically disperse for 2 hours. Then add the modified solution and stir for 6-8 hours. Finally, place it in an oven and dry at 60°C to constant weight. The amount of amphiphilic silane coupling agent is 2-5% of the mass of the inorganic filler.

[0013] Furthermore, the amphiphilic silane coupling agent is prepared through the following steps:

[0014] Add dodecyl dimethyl hydroxyethyl ammonium chloride to the flask, evacuate using a double-row tube, and then purge with high-purity argon. Repeat this process three times. Then add THF, heat to 40°C, add propyltriethoxysilane isocyanate and triethylamine, and reflux for 8 hours. Finally, remove THF by rotary evaporation.

[0015] The ratio of dodecyl dimethyl hydroxyethyl ammonium chloride, THF, propyltriethoxysilane isocyanate, and triethylamine is 2.5 mmol: 10 mL: 3.0 mmol: 3.0 mmol.

[0016] Furthermore, the inorganic filler includes one or more of the following: clay, talc powder, mica powder, asbestos powder, coal ore powder, sepiolite powder, attapulgite, ultrafine calcium carbonate, nano-calcium, montmorillonite, alumina, and boehmite, preferably a mixture of one or both of alumina and boehmite.

[0017] Furthermore, the dispersant is one or a mixture of perfluoropolyether alcohol, perfluoropropyl perfluorovinyl ether, polyhexafluoropropylene oxide monoethanol, and polyethylene glycol octanoate.

[0018] Furthermore, the adhesive is one or more of the following: dimethyl phthalate, polyvinylidene fluoride, polymethyl methacrylate, polypropylene ester, polyisophthalamide, polyacrylic acid emulsion, polyacrylamide, polyacrylonitrile, and polyvinylpyrrolidone.

[0019] Furthermore, the wetting agent is one or a mixture of alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and dihydroxystearate.

[0020] Furthermore, the thickener is one or more mixtures of sodium carboxymethyl cellulose, sodium hydroxyethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxymethyl starch, and acrylate.

[0021] Further, the solvent is composed of ultrapure water and organic solvent in a mass ratio of 100:0.2 to 10, preferably, the solvent is composed of ultrapure water and organic solvent in a mass ratio of 100:1 to 8.

[0022] Furthermore, the organic solvent is one or more of anhydrous ethanol, isopropanol, n-propanol, dimethyl ether, diethyl ether, propyl ether, ethyl acetate, acetone, dimethylformamide, and dimethyl sulfoxide, with acetone being preferred.

[0023] Furthermore, the mass ratio of ultra-high molecular weight polyethylene, pore-forming agent, nucleating agent and antioxidant is (20-30): (70-80): (0.5-5): (0.01-0.1).

[0024] Furthermore, ultra-high molecular weight polyethylene has a weight-average molecular weight of 600,000 to 4,000,000 and a melt index of 0.1 to 0.5 g / 10 min.

[0025] Furthermore, the nucleating agent is a mixture of pimelic acid and calcium stearate, with a mass ratio of pimelic acid to calcium stearate of (0.8–3.8):(1.2–4.2).

[0026] Further, the pore-forming agent is one or a mixture of several of the following: white oil, DOP (dioctyl phthalate), DOTP (dioctyl terephthalate), DBP (dibutyl phthalate) and DEHP (diethylhexyl phthalate), preferably a mixture of white oil and DOTP, with a mixing ratio of (6-8):(2-4).

[0027] Furthermore, the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010).

[0028] Furthermore, the preparation steps of the base film precursor are as follows:

[0029] Step a: Add ultra-high molecular weight polyethylene and nucleating agent to the extruder in a quantitative manner using a loss-in-weight balance, with a flow rate accuracy of <3‰. Mix antioxidant and pore-forming agent at a temperature of 90-130℃ and a stirring speed of 40-60rpm for 30-60min. Inject the mixture into the extruder through a plunger pump, with a plunger pump flow rate accuracy of <5‰. Then, melt extrude to obtain the melt.

[0030] Step b: The melt is cast through a melt pipeline and a T-die, and then applied to a shaping roller for cooling to form a crystalline casting sheet.

[0031] Step c: Perform bidirectional synchronous stretching or longitudinal stretching and first transverse stretching on the crystalline casting to obtain a thin oil film;

[0032] Step d: The thin oil film is pulled by the extraction roller and immersed in the extraction solution for extraction. After extraction, it is pulled by the hot roller to the drying room for drying to obtain a dry film.

[0033] Step e: Perform a second lateral stretching of the dry film, shrink it, and heat set it to obtain the base film precursor.

[0034] First, the raw materials are quantitatively and proportionally added to the extruder. Under the dual action of high-temperature heating in the barrel and shearing by the screw, the components are melted and mixed to obtain a homogeneous thermodynamic single-phase melt. During this process, the molten polyethylene and pore-forming agent undergo solid-liquid phase separation during rapid cooling, and the polyethylene molecules aggregate and crystallize to form crystalline wafers. In this process, the crystalline wafers undergo slippage and collapse under heating conditions through proportional stretching, oriented along the stress direction to form fibrous crystal bundles, with gaps forming pores. Simultaneously, the wafers are thinned to form a thin oil film. Extraction is then performed. During this process, due to the better compatibility of the pore-forming agent in the extractant, the pore-forming agent in the film is extracted. The extractant is then dried and volatilized in an oven, and the volume space occupied by the pore-forming agent in the film is replaced, forming pores, resulting in a dry film. The dry film is then subjected to a second transverse stretching to obtain the base film precursor. During the secondary transverse stretching process, a small-ratio stretching is performed. Through the dual effects of heating and orientation, the crystallinity of the film is further improved, the microporous structure of the film is solidified, and the dimensional stability is enhanced. In addition, heating and shrinking can eliminate the internal stress generated during the stretching process, further improving the elastic modulus and thermal stability of the film.

[0035] Furthermore, in step a, the heating temperature of the extruder is 160–200°C, the extruder is a co-rotating twin-screw extruder with 15 heating zones, the screw speed is 100–240 rpm, and the screw length-to-diameter ratio is 56–68.

[0036] Furthermore, in step b, the heating temperature of the melt pipeline and the T-die is 170–210°C, and the temperature of the shaping roller is 10–30°C.

[0037] Furthermore, in step b, the temperature of the melt during the melt flow delay is 200°C. ～ 240℃.

[0038] Furthermore, the thickness of the crystalline casting obtained in step b is 0.8–2.0 mm.

[0039] Furthermore, in step c, the synchronous bidirectional stretching or longitudinal stretching and the first transverse stretching are performed by one or more of the following combined stretching methods: roller stretching, chain clamp stretching, needle punching stretching, and roller rolling stretching.

[0040] Furthermore, in step c, the stretching ratio of the simultaneous bidirectional stretching or longitudinal stretching and the first transverse stretching is 5. ～ 15 times.

[0041] Further, in step c, the bidirectional synchronous stretching is performed at 100-130°C at a speed of 10-150% / s; the longitudinal stretching is performed at 90-110°C at a speed of 25-250% / s; and the first transverse stretching is performed at 110-130°C at a speed of 10-150% / s.

[0042] Further, in step d, the extractant is a mixture of one or more of dichloromethane, dichloroethane, ethanol, acetone, N-butyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidone bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidone trifluoromethanethioyl and N-butyl-N-methylpyrrolidone trifluoromethanethioyl, preferably dichloromethane with a concentration > 99.8%.

[0043] Further, in step d, the extraction time is 60 minutes. ～ 240s, extraction temperature 15 ～ 25℃.

[0044] Furthermore, in step d, the film drying temperature is 40°C. ～ 110℃, drying time 10 ～ 40s.

[0045] Furthermore, the second transverse stretching method in step e is one or more of the following combined stretching methods: roller stretching, chain clamp stretching, needle punching stretching, and roller rolling stretching.

[0046] Furthermore, in step e, the second transverse stretching is performed at 120–140°C at a speed of 2–30% / s to stretch to 1.2–2 times the original length.

[0047] Furthermore, in step e, the secondary horizontal stretching and retraction is performed by heating and retracting at a temperature of 120–140°C at a rate of 0.5–5% / s, with a heating and retraction ratio of 5–25%.

[0048] Furthermore, in step e, the temperature for the secondary horizontal stretching heat setting is 120–140°C, and the heat setting time is 5–50 seconds.

[0049] Furthermore, the specific steps for preparing the composite lithium battery separator are as follows:

[0050] Step (1): Weigh the raw materials according to the formula and mix them evenly to obtain a slurry. Apply the slurry to the base film precursor through a coating device to obtain a coated diaphragm.

[0051] Step (2): The coated separator is pulled by the roller for a third horizontal stretch and dried to obtain the composite lithium battery separator.

[0052] Further, in step (1), the coating device is one or more of the following combinations: gravure roller coating device, wire bar coating device, slot coating device, spraying device, dot coating and electrospinning coating device.

[0053] Furthermore, in step (1), the amount of slurry applied is 0.5–30 g / m². 2 .

[0054] Furthermore, in step (2), the third transverse stretching is performed by clamping the two sides of the diaphragm with chain clips or needles, specifically at 80-140°C and stretching at a speed of 2-30% / s to 0.85-1.15 times.

[0055] Furthermore, in step (2), the heat setting temperature is 80–140°C and the heat treatment time is 20–100 s.

[0056] The beneficial effects of this invention are:

[0057] 1. This invention provides an integrated preparation method for composite lithium-ion battery separators. This method integrates base film production and coating processing, enabling continuous and synchronized production of the composite separator. This simplifies the production process, saves approximately 30% of the investment in coating equipment, and also reduces labor, processing, energy consumption, and maintenance costs associated with slitting, transporting, and coating. Furthermore, the composite separator significantly improves its thermal stability, reducing thermal shrinkage to approximately 1 / 10 of its original value. With excellent peel strength and liquid absorption rate, it demonstrates promising application prospects and economic benefits.

[0058] 2. In the preparation of the base film precursor, the present invention performs a second transverse stretching after extraction. During the second transverse stretching, a small-ratio stretching is performed. Through the dual effects of heating and orientation, the crystallinity of the film is further improved, the microporous structure of the film is solidified, and the dimensional stability is enhanced. In addition, heating and shrinking can eliminate the internal stress generated during the stretching process, further improving the elastic modulus and thermal stability of the film.

[0059] 3. This invention utilizes an adhesive and modified inorganic filler to prepare a slurry, which is then coated onto the surface of a base membrane precursor. This allows the adhesive to uniformly adhere the inorganic filler to the base membrane surface, thereby improving the thermal stability of the separator and its adhesion to the electrodes. The modified inorganic filler is obtained by modifying an amphiphilic silane coupling agent, and its surface contains hydrophobic alkyl long chains and hydrophilic quaternary ammonium salt groups. The hydrophobic long-chain alkyl groups fix the inorganic filler to the surface of the base membrane precursor through hydrophobic interactions, which on the one hand gives the membrane good thermal stability, and on the other hand enhances the adhesion between the coating and the base membrane precursor. The hydrophilic groups are exposed to the environment, which helps to improve the affinity between the separator and the polar organic electrolyte, and increases the liquid absorption rate of the separator. The increased liquid absorption rate can provide more ion transport pathways, thereby improving the lithium ion transport capacity and thus improving the electrochemical performance of the battery. Detailed Implementation

[0060] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0061] The relevant equipment used in the specific embodiments of the present invention is as follows:

[0062] Feeding, extrusion, stretching, extraction, and heat setting equipment: Shibaura Corporation, Japan;

[0063] Coating equipment: Shanghai Forsatech Intelligent Equipment Co., Ltd.;

[0064] Vacuum drying oven: DHG-1000A-L type, Shanghai Binglin Electronic Technology Co., Ltd.;

[0065] Stretching machine: HY-0508, Shanghai Hengyi Precision Instruments Co., Ltd.;

[0066] The relevant materials used in the specific embodiments of this invention are as follows:

[0067] Ultra-high molecular weight polyethylene: Daehan Oil & Chemical Co., Ltd., South Korea;

[0068] White oil: Zhejiang Zhengxin Chemical Co., Ltd., industrial grade;

[0069] DOP (dioctyl phthalate), DOTP (dioctyl terephthalate), DBP (dibutyl phthalate) and DEHP (diethylhexyl phthalate): Shandong Shengfan Chemical Co., Ltd., industrial grade;

[0070] Pimelic acid and calcium stearate: Shanghai Kaiyin Chemical Co., Ltd., analytical grade;

[0071] Antioxidant: BASF AG, industrial grade;

[0072] 2-[[tris(hydroxymethyl)methyl]amino]ethanesulfonic acid, sodium 2-amino-1-naphthalenesulfonate, γ-aminopropyltriethoxysilane, 1,1,3-trimethylcyclohexenone, dimethyl succinate, dimethyl glutarate, dimethyl adipate, and N-methylpyrrolidone, etc.: Shanghai Yuanyang New Material Technology Co., Ltd., industrial grade;

[0073] Dichloromethane: Concentration ≥ 99.99%, Shandong Luxi Chemical Co., Ltd.

[0074] Clay, talc powder, mica powder, asbestos powder, coal ore powder, sepiolite powder, attapulgite, ultrafine calcium carbonate, nano calcium, montmorillonite, alumina and boehmite: Tianma Aluminum Co., Ltd., industrial grade;

[0075] Ethanol, isopropanol, n-propanol, dimethyl ether, diethyl ether, propyl ether, ethyl acetate, acetone, dimethylformamide and dimethyl sulfoxide: Shanghai Denuo Chemical Co., Ltd., industrial grade;

[0076] Perfluoropolyether alcohol (PFPE-OH), perfluoropropyl perfluorovinyl ether (PPVE), polyhexafluoropropylene oxide monoethanol, polyethylene glycol octanoate: Zhejiang Huanxin Fluorine Materials Co., Ltd., industrial grade;

[0077] Dimethyl phthalate, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene ester, poly(p-phenylene isophthalamide): Suzhou Tetrafluoro New Materials Co., Ltd., industrial grade;

[0078] Alkyl polyoxyethylene ether, alkylphenol polyoxyethylene ether (APEO), fatty alcohol polyoxyethylene ether (AEO), dihydroxy stearate: Qingdao Enze Chemical Co., Ltd., industrial grade;

[0079] Sodium carboxymethyl cellulose (CMC), sodium hydroxyethyl cellulose, sodium hydroxypropyl methyl cellulose, sodium hydroxymethyl starch, acrylate: Shanghai Kaiyin Chemical Co., Ltd., industrial grade.

[0080] Preparation Example 1

[0081] Modified inorganic fillers are prepared through the following steps:

[0082] Add 2g of amphiphilic silane coupling agent to 50mL of anhydrous ethanol and mix well to obtain a modified solution. Add 100g of alumina to 1L of 70wt% ethanol aqueous solution and ultrasonically disperse for 2h. Then add the modified solution and stir for 6h. Finally, place in an oven and dry at 60℃ to constant weight.

[0083] Amphiphilic silane coupling agents are prepared by the following steps:

[0084] Add 25 mmol of dodecyl dimethyl hydroxyethyl ammonium chloride to the flask, evacuate using a double-row tube, and then purge with high-purity argon. Repeat this process three times. Then add 100 mL of THF, heat to 40 °C, add 30 mmol of propyltriethoxysilane isocyanate and 30 mmol of triethylamine, and reflux for 8 hours. Finally, remove the THF by rotary evaporation.

[0085] Preparation Example 2

[0086] Modified inorganic fillers are prepared through the following steps:

[0087] Add 5g of amphiphilic silane coupling agent to 50mL of anhydrous ethanol and mix well to obtain a modified solution. Add 100g of boehmite to 1L of 70wt% ethanol aqueous solution and sonicate for 2h. Then add the modified solution and stir for 8h. Finally, place in an oven and dry at 60℃ to constant weight.

[0088] Amphiphilic silane coupling agents are prepared by the following steps:

[0089] Add 25 mmol of dodecyl dimethyl hydroxyethyl ammonium chloride to the flask, evacuate using a double-row tube, and then purge with high-purity argon. Repeat this process three times. Then add 100 mL of THF, heat to 40 °C, add 30 mmol of propyltriethoxysilane isocyanate and 30 mmol of triethylamine, and reflux for 8 hours. Finally, remove the THF by rotary evaporation.

[0090] Example 1

[0091] An integrated preparation method for a composite lithium battery separator includes the following steps:

[0092] Step a: According to the raw material ratio in Table 1, add ultra-high molecular weight polyethylene and nucleating agent to the extruder quantitatively using a loss-in-weight balance with a flow rate accuracy of <3‰. Mix the antioxidant and pore-forming agent at 90℃ and 40rpm for 30min, and inject them into the extruder through a plunger pump with a flow rate accuracy of <5‰. Then, perform melt extrusion. The heating temperature of the extruder is 160-200℃. The extruder is a co-rotating twin-screw extruder with 15 heating zones, a screw speed of 100rpm, and a screw length-to-diameter ratio of 56 to obtain the melt.

[0093] Step b: The melt is cast through a 170°C melt pipeline and a T-die. The temperature of the melt during casting is 200°C. It is then placed on a 10°C setting roller for cooling and forming a 1.4mm thick crystalline casting sheet.

[0094] Step c: Perform bidirectional synchronous stretching and first transverse stretching on the crystalline casting, with a stretching ratio of 5 times for both, to obtain a thin oil film;

[0095] Step d: The thin oil film is pulled by the extraction roller and immersed in dichloromethane for extraction. The extraction time is 60s and the extraction temperature is 15℃. After extraction, it is pulled by the hot roller to the drying room for drying. The drying temperature is 40℃ and the drying time is 10s to obtain a dry film.

[0096] Step e: Stretch the dry film to 1.2 times its original size at 120°C at a speed of 2% / s (second transverse stretching), heat and shrink it at 120°C at a speed of 0.5% / s, the shrinkage ratio is 5% (shrinkage), and heat set at 120°C for 5s to obtain the base film precursor.

[0097] Weigh the raw materials according to the proportions in Table 1 and mix them evenly to obtain a slurry. Apply the slurry to the base film precursor using a coating device. The coating amount of the slurry is 10 g / m³. 2 The coated separator is obtained; the coated separator is stretched to 0.85 times its original size at 80°C at a speed of 2% / s by roller traction, and the heat treatment time at 80°C is 20s to obtain a composite lithium battery separator.

[0098] In step c, bidirectional synchronous stretching is performed at 100°C at a speed of 10% / s; longitudinal stretching is performed at 90°C at a speed of 25% / s.

[0099] Example 2

[0100] An integrated preparation method for a composite lithium battery separator includes the following steps:

[0101] Step a: According to the raw material ratio in Table 1, add ultra-high molecular weight polyethylene and nucleating agent to the extruder quantitatively using a loss-in-weight balance with a flow rate accuracy of <3‰. Mix the antioxidant and pore-forming agent at 110℃ and 50rpm for 40min, and inject them into the extruder through a plunger pump with a flow rate accuracy of <5‰. Then, perform melt extrusion. The heating temperature of the extruder is 180℃. The extruder is a co-rotating twin-screw extruder with 15 heating zones, a screw speed of 140rpm, and a screw length-to-diameter ratio of 57 to obtain the melt.

[0102] Step b: The melt is cast through a 190°C melt pipeline and a T-die. The temperature of the melt during casting is 230°C. It is then placed on a 20°C setting roller for cooling and forming a 1.4mm thick crystalline casting sheet.

[0103] Step c: The crystalline casting is subjected to longitudinal stretching and first transverse stretching, both with a stretching ratio of 10 times, to obtain a thin oil film;

[0104] Step d: The thin oil film is pulled by the extraction roller and immersed in dichloromethane for extraction. The extraction time is 140s and the extraction temperature is 20℃. After extraction, it is pulled by the hot roller to the drying room for drying. The drying temperature is 60℃ and the drying time is 20s to obtain a dry film.

[0105] Step e: Stretch the dry film to 1.7 times its original size at 130°C at a speed of 10% / s (second transverse stretching), heat it back at 130°C at a speed of 2% / s, the heat shrinkage ratio is 10% (shrinkage), and heat set at 130°C for 20s to obtain the base film precursor.

[0106] Weigh the raw materials according to the proportions in Table 1 and mix them evenly to obtain a slurry. Apply the slurry to the base film precursor using a coating device. The coating amount of the slurry is 10 g / m³. 2The coated separator is obtained; the coated separator is stretched to 1 times its original size at 10% / s by roller traction at 120℃, and then heat-treated at 110℃ for 80s to obtain a composite lithium battery separator.

[0107] In step c, the longitudinal stretching is performed at 100°C and a speed of 150% / s; the first transverse stretching is performed at 120°C and a speed of 140% / s.

[0108] Example 3

[0109] An integrated preparation method for a composite lithium battery separator includes the following steps:

[0110] Step a: According to the raw material ratio in Table 1, add ultra-high molecular weight polyethylene and nucleating agent to the extruder quantitatively using a loss-in-weight balance with a flow rate accuracy of <3‰. Mix the antioxidant and pore-forming agent at 130℃ and 60rpm for 60min, and inject them into the extruder through a plunger pump with a flow rate accuracy of <5‰. Then, perform melt extrusion. The heating temperature of the extruder is 200℃. The extruder is a co-rotating twin-screw extruder with 15 heating zones, a screw speed of 240rpm, and a screw length-to-diameter ratio of 68 to obtain the melt.

[0111] Step b: The melt is cast through a 210°C melt pipeline and a T-die. The temperature of the melt during casting is 240°C. It is then placed on a 30°C setting roller for cooling and forming a 1.4mm thick crystalline casting sheet.

[0112] Step c: Perform bidirectional synchronous stretching and first transverse stretching on the crystalline casting, with a stretching ratio of 15 times for both, to obtain a thin oil film;

[0113] Step d: The thin oil film is pulled by the extraction roller and immersed in dichloromethane for extraction. The extraction time is 240s and the extraction temperature is 25℃. After extraction, it is pulled by the hot roller to the drying room for drying. The drying temperature is 110℃ and the drying time is 40s to obtain a dry film.

[0114] Step e: Stretch the dry film to twice its original size at 140°C at a speed of 30% / s (second transverse stretching), heat and shrink it at 140°C at a speed of 5% / s, the shrinkage ratio is 25% (shrinkage), and heat set at 140°C for 50s to obtain the base film precursor.

[0115] Weigh the raw materials according to the proportions in Table 1 and mix them evenly to obtain a slurry. Apply the slurry to the base film precursor using a coating device. The coating amount of the slurry is 10 g / m³. 2 The coated separator is obtained; the coated separator is stretched to 1.15 times its original size at 140℃ and a speed of 30% / s by roller traction, and the heat treatment time at 140℃ is 100s to obtain a composite lithium battery separator.

[0116] In step c, bidirectional synchronous stretching is performed at 130°C and a stretching speed of 150% / s; the first transverse stretching is performed at 130°C and a stretching speed of 150% / s.

[0117] Example 4

[0118] An integrated preparation method for a composite lithium battery separator, except that the raw material system is shown in Table 1, the other raw materials and preparation methods are the same as in Example 3.

[0119] Example 5

[0120] An integrated preparation method for a composite lithium battery separator, except that the raw material system is shown in Table 1, the other raw materials and preparation methods are the same as in Example 1.

[0121] Example 6

[0122] An integrated preparation method for a composite lithium battery separator, except that the raw material system is shown in Table 1, the other raw materials and preparation methods are the same as in Example 3.

[0123] Table 1. Content of each raw material component in Examples 1-6

[0124]

[0125]

[0126] Comparative Example 1

[0127] An integrated preparation method for a composite lithium battery separator includes the following steps:

[0128] The dry film is coated with a slurry using a coating device, with a slurry coating amount of 10 g / m². 2 The coated separator is obtained; the coated separator is stretched to 1.1 times its original size at 10% / s by roller traction at 120°C, and then heat-treated at 90°C for 80s to obtain a composite lithium battery separator. The dry film preparation process is the same as step ad in Example 1, and the slurry preparation process is the same as step e in Example 1.

[0129] Comparative Example 2

[0130] An integrated preparation method for a composite lithium battery separator, compared with Example 1, only the modified inorganic filler in Example 1 is replaced with an equal mass of alumina, while the other raw materials and preparation process are the same as in Example 1.

[0131] Comparative Example 3

[0132] This comparative example is a base film precursor, and the specific preparation process is the same as in Example 1.

[0133] The composite lithium battery separators obtained in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests, including thickness, basis weight, liquid absorption rate, needle penetration strength, peel strength, and heat shrinkage performance. The specific test methods are as follows:

[0134] The thickness, basis weight and needle penetration strength test methods are all in accordance with the national standard "Polyolefin Separator for Lithium-ion Batteries" (GB / T36363-2018);

[0135] The peel strength test method is as follows: Take a 60mm long double-sided tape (20mm wide) with an adhesion strength > 800N / m, and stick the double-sided tape onto a steel plate (steel plate size 100mm*20mm*0.5mm) that has been cleaned with alcohol. Roll it three times with a 2kg roller to ensure that there are no air bubbles between the tape and the steel plate. Then, cut the composite diaphragm into strips of 25mm*200mm, stick the composite diaphragm strips onto the tape, and continue to roll it three times with a roller. Finally, clamp the steel plate and the tape into the upper and lower fixtures of the stretching machine, and stretch them at a speed of 5mm / s to test the peel strength.

[0136] The liquid absorption rate test method is as follows: Prepare a mixed solution by mixing 1,3-dioxolane and 1,2-dimethoxyethane at a volume ratio of 1:1. Weigh the composite lithium battery separator and immerse it in the solvent. After soaking at 25°C for 1-8 minutes, remove it, wipe the surface dry to remove excess solvent, and weigh the mass after soaking. The liquid absorption rate (%) is calculated according to the formula: Liquid absorption rate (%) = (A1-A0) / A0×100%, where A is the mass before soaking (g) and A1 is the mass after soaking (g).

[0137] The heat shrinkage test method is as follows: First, cut the composite diaphragm into 60mm*40mm samples and test its initial MD and TD lengths under an imaging instrument; then, fold the samples with A4 paper, clamp them, and place them in a metal tray with Teflon adhesive on the bottom, and place them in a 130℃ oven for 1 hour. After completion, remove them and cool them to room temperature; finally, use an imaging instrument to test the MD and TD lengths again and calculate the heat shrinkage. The heat shrinkage calculation formula is: Heat shrinkage = (L0-L1) / L0*100%; where L0 is the initial MD / TD length, and L1 is the MD / TD length after heat drying;

[0138] The results are shown in Table 2:

[0139] Table 2

[0140]

[0141] Observing the data recorded in Table 1, the test results of Examples 1, 2, and 5 compared with Comparative Example 3 show that the inorganic filler coating can greatly improve the thermal stability of the diaphragm, reducing the thermal shrinkage of the diaphragm to about 1 / 10 of the original. The test results of Examples 1 and Comparative Example 1 show that performing a second transverse stretch on the dry film is beneficial to improving thermal stability. The test results of Examples 1 and Comparative Example 2 show that modifying the inorganic filler is beneficial to improving the peel force, thermal stability, and liquid absorption rate of the diaphragm.

[0142] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0143] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for integrated production of composite lithium battery separators, characterized in that, The method comprises the following steps: S1, mixing, extruding, obtaining a melt, casting and cooling to obtain a crystalline casting sheet, stretching, extracting, obtaining a dry film, stretching, shrinking, heat setting to obtain a base film precursor; S2, coating the slurry on one side or both sides of the base film precursor, transversely stretching, drying and setting to obtain a composite lithium battery separator; The slurry comprises the following raw materials by weight: 0.1-1 part of a dispersing agent, 2-10 parts of a bonding agent, 0.1-1 part of a wetting agent, 0.2-10 parts of a thickening agent, and 100 parts of a solvent; The slurry further comprises 20-45 parts of a modified inorganic filler; The modified inorganic filler is prepared by the following steps: The amphiphilic silane coupling agent is prepared by the following steps: The amphiphilic silane coupling agent is prepared by the following steps: The dry film is stretched and shrunk according to the following steps: The dry film is stretched at a speed of 2-30% per second to 1.2-2 times at a temperature of 120-140℃, and then shrunk at a speed of 0.5-5% per second at a temperature of 120-140℃, and the shrinkage rate is 5-25%. The modified inorganic filler is modified by the amphiphilic silane coupling agent, and the surface contains hydrophobic alkyl long chains and hydrophilic quaternary ammonium salt groups. The amount of the amphiphilic silane coupling agent is 2-5% of the mass of the inorganic filler.

2. The method of claim 1, wherein the method further comprises the step of: The amount ratio of dodecyl dimethyl hydroxyethyl ammonium chloride, THF, propyl triethoxy silane isocyanate, and triethylamine is 2.5 mmol:10 mL:3.0 mmol:3.0 mmol.

3. The method of claim 1, wherein the method further comprises the step of: The inorganic filler comprises a mixture of one or more of the following: clay, talc powder, mica powder, asbestos powder, coal mine stone powder, sepiolite powder, attapulgite, ultra-fine calcium carbonate, nano calcium, montmorillonite, alumina, and boehmite. ​ 4. The method of claim 1, wherein the method further comprises the step of: The mass ratio of the ultra-high molecular weight polyethylene, the pore-forming agent, the nucleating agent, and the antioxidant is (20-30):(70-80):(0.5-5):(0.01-0.1). ​ 5. The method of claim 1, wherein the method further comprises the step of: The heat setting temperature is 120-140℃, and the heat setting time is 5-50 seconds. ​ 6. The method of claim 1, wherein the method further comprises: ​

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