Integrated preparation method of composite lithium battery diaphragm

Abstract

The invention discloses an integrated preparation method of a composite lithium battery diaphragm, and belongs to the technical field of lithium battery diaphragms.The integrated preparation method comprises the following steps that one or two faces of a base film precursor are coated with slurry, drying and shaping are conducted after transverse stretching, and the composite lithium battery diaphragm is obtained; the slurry is prepared from the following raw materials in parts by weight: 0.1-1 part of a dispersing agent, 2-10 parts of an adhesive, 0.1-1 part of a wetting agent, 0.2-10 parts of a thickening agent, 100 parts of a solvent and 20-45 parts of modified inorganic filler, continuous and synchronous production of the composite diaphragm is realized through the integrated design of base diaphragm production and coating processing, the production process is simplified, the cost is saved, and the production efficiency is improved. Meanwhile, the thermal stability of the composite diaphragm can be greatly improved, so that the thermal shrinkage of the diaphragm is reduced to about 1 / 10 of the original thermal shrinkage; the adhesive has good release force and liquid absorption rate, and has good application prospects and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery separators, and in particular relates to an integrated preparation method for a composite lithium battery separator. Background Art

[0002] Lithium-ion battery separators are a crucial component of lithium batteries. They are the insulating layer that separates the positive and negative electrode materials in the battery and provide a channel for the migration of lithium ions. The matrix of lithium battery separators is thermoplastic materials such as high molecular weight polyethylene and polypropylene, which causes the separators to shrink and break easily when the battery is at high temperature, seriously affecting the application safety of the battery.

[0003] To address this problem, the industry currently mainly improves the heat resistance and stability of polyolefin diaphragms by coating the surface of polyolefin diaphragms with micron-sized rigid ceramic particles. However, this requires the configuration of corresponding slitting machines (for the convenience of transportation and adaptation of the coating width) and coating machines; the factory workshop needs to be equipped with a transit warehouse and a flow of people and goods channel to transfer film vehicles and packaging auxiliary materials for the coating of heat-resistant materials in the later stage, which increases the equipment cost by about 30%; at the same time, the post-processing of slitting, transportation and coating also increases the labor, energy consumption and maintenance costs of the products. In addition, polyolefin diaphragms need to be left idle for a long time during the slitting, transportation and coating process. Due to the relaxation phenomenon of plastic materials, deformations of varying degrees will occur, which will deteriorate the flatness of the membrane surface, causing serious quality problems such as coating omissions and cell winding misalignment, affecting the yield of the finished diaphragm products. Summary of the invention

[0004] The purpose of the present invention is to provide an integrated preparation method for a composite lithium battery separator to solve the problems of high production cost and low finished product yield of existing lithium battery separators.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

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

[0007] S1, mixing and extruding ultra-high molecular weight polyethylene, a pore-forming agent, a nucleating agent and an antioxidant to obtain a melt, casting the melt and cooling it to obtain a crystalline cast sheet, stretching and extracting the crystalline cast sheet to obtain a dry film, stretching, shrinking and heat-setting the dry film to obtain a base film precursor;

[0008] S2. Coat the slurry on one or both sides of the base film precursor, stretch it transversely, and then dry and shape it to obtain a composite lithium battery separator.

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

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

[0011] Further, the modified inorganic filler is prepared by the following steps:

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

[0013] Further, the amphiphilic silane coupling agent is prepared by the following steps:

[0014] Add dodecyldimethylhydroxyethylammonium chloride to the flask, evacuate with a double-row tube and then fill with high-purity argon, repeat three times, then add THF, heat to 40°C, add isocyanatepropyltriethoxysilane and triethylamine, heat to reflux for 8 hours, then remove THF by rotary evaporation;

[0015] The usage ratio of dodecyldimethylhydroxyethylammonium chloride, THF, isocyanatepropyltriethoxysilane and triethylamine is 2.5 mmol:10 mL:3.0 mmol:3.0 mmol.

[0016] Furthermore, the inorganic filler includes a mixture of one or more of clay, talc, 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 a mixture of one or more of perfluoropolyether alcohol, perfluoropropyl perfluorovinyl ether, polyhexafluoropropylene oxide monomethanol, and polyethylene glycol octanoate.

[0018] Furthermore, the adhesive is a mixture of one or more of dimethyl phthalate, polyvinylidene fluoride, polymethyl methacrylate, polypropylene, polyisophenylene phthalamide, polyacrylic acid emulsion, polypropylene alcohol, polyacrylonitrile and polyvinyl pyrrolidone.

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

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

[0021] Furthermore, the solvent is composed of ultrapure water and an organic solvent in a mass ratio of 100:0.2-10. Preferably, the solvent is composed of ultrapure water and an organic solvent in a mass ratio of 100:1-8.

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

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

[0024] Furthermore, the 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 compound mixture of pimelic acid and calcium stearate, and the mass ratio of pimelic acid to calcium stearate is (0.8-3.8):(1.2-4.2).

[0026] Furthermore, the pore-forming agent is a mixture of one or more of white oil, DOP (dioctyl phthalate), DOTP (dioctyl terephthalate), DBP (dibutyl phthalate) and DEHP (diethylhexyl phthalate), preferably a compound mixture of white oil and DOTP, and the compound ratio is (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 basement membrane precursor preparation steps are specifically as follows:

[0029] Step a, adding ultra-high molecular weight polyethylene and a nucleating agent to an extruder by means of a loss-in-weight scale, with a flow rate accuracy of less than 3‰, stirring and mixing an antioxidant and a pore-forming agent at a temperature of 90 to 130° C. and a stirring speed of 40 to 60 rpm for 30 to 60 minutes, injecting the mixture into the extruder by means of a plunger pump, with a flow rate accuracy of the plunger pump of less than 5‰, and then melt-extruding to obtain a melt;

[0030] Step b, passing the melt through a melt line and a T-die head for melt casting, and applying the melt on a shaping roller for cooling to form a crystal casting sheet;

[0031] Step c, performing bidirectional synchronous stretching or longitudinal stretching and first transverse stretching on the crystallized cast sheet to obtain a thinned oil film;

[0032] Step d, pulling the thinned oil film through an extraction roller, immersing it in an extraction liquid for extraction, and after the extraction is completed, pulling it along a hot roller to a drying room for drying to obtain a dry film;

[0033] Step e: stretch the dry film transversely for a second time, shrink it, and heat-set it to obtain a base film precursor.

[0034] First, the raw materials are added to the extruder in a quantitative and proportioned manner. Under the dual effects of high-temperature heating of the barrel and shearing of the screw, the components are melted and mixed to obtain a uniform thermodynamic single-phase melt. In this process, the molten high-molecular polyethylene and the pore-forming agent undergo solid-liquid phase separation during the quenching process, and the polyethylene molecules agglomerate and crystallize to form a crystalline cast sheet. In this process, the crystalline cast sheet slips and collapses after being stretched at a multiple under heating conditions, oriented along the stress direction to form fibrous crystal bundles, and holes are formed in the gaps. At the same time, the cast sheet is thinned synchronously to form a thinned oil film. Then, extraction is performed. In this process, due to the better compatibility of the pore-forming agent in the extractant, the pore-forming agent in the film is extracted, and the extractant is dried and volatilized in a drying room. The volume space occupied by the pore-forming agent in the film is replaced to form pores to obtain a dry film. The dry film is stretched transversely for the second time to obtain a base film precursor. During the secondary transverse stretching process, a small ratio of stretching is performed, and 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, and further improve 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, has 15 heating zones, a screw speed of 100-240 rpm, and a screw aspect ratio of 56-68.

[0036] Furthermore, in step b, the heating temperature of the melt line 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 melt casting is 200 ～ 240℃.

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

[0039] Furthermore, the method of simultaneous biaxial stretching or longitudinal stretching and first transverse stretching in step c is a combination of one or more of roller stretching, chain clip stretching, needle punching stretching and roller stretching.

[0040] Furthermore, the stretching ratios of the simultaneous biaxial stretching or longitudinal stretching and the first transverse stretching in step c are both 5 ～ 15 times.

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

[0042] Further, in step d, the extractant is a mixed solution 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 trifluoromethanesulfonyl and N-butyl-N-methylpyrrolidone trifluoromethanesulfonyl, preferably dichloromethane with a concentration of >99.8%.

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

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

[0045] Furthermore, the second transverse stretching method in step e is a combination of one or more of roller stretching, chain clip 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 1.2-2 times.

[0047] Furthermore, the secondary horizontal stretching and shrinking in step e is heating and shrinking at a temperature of 120 to 140° C. at a speed of 0.5 to 5% / s, and the heating and shrinking ratio is 5 to 25%.

[0048] Furthermore, in step e, the temperature of the secondary transverse drawing heat setting is 120-140° C., and the heat setting time is 5-50 seconds.

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

[0050] Step (1), weighing raw materials according to the formula and mixing them evenly to obtain slurry, coating the base film precursor with the slurry through a coating device to obtain a coated diaphragm;

[0051] Step (2), the coated separator is pulled by rollers for a third time and dried to form a composite lithium battery separator.

[0052] Furthermore, the coating device in step (1) is a combination of one or more of a gravure roller coating device, a wire rod coating device, a slit coating device, a spray coating device, a dot coating device and an electrostatic spinning coating device.

[0053] Furthermore, in step (1), the coating amount of the slurry is 0.5 to 30 g / m 2 .

[0054] Furthermore, in step (2), the two sides of the separator are clamped by chain clips or needles for the third time to be stretched, specifically, at 80-140° C. and at a speed of 2-30% / s to 0.85-1.15 times.

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

[0056] Beneficial effects of the present invention:

[0057] 1. The present invention provides an integrated preparation method for a composite lithium-ion battery separator. The method realizes continuous and synchronous production of the composite separator through the integrated design of base film production and coating processing, simplifies the production process, saves about 30% of the coating equipment investment, and saves the labor, processing, energy consumption and maintenance costs of cutting, transporting and coating. At the same time, the composite separator can greatly improve its thermal stability, reducing the thermal shrinkage of the separator to about 1 / 10 of the original; it has good peeling force and liquid absorption rate, and has good application prospects and economic benefits.

[0058] 2. In the process of preparing the base film precursor, the present invention performs a second transverse stretching after extraction, and performs a small ratio stretching during the secondary transverse stretching process. 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, and further improve the elastic modulus and thermal stability of the film.

[0059] 3. The present invention utilizes an adhesive and a modified inorganic filler to prepare a slurry, which is applied to the surface of a base film precursor, so that the adhesive entrains the inorganic filler and uniformly adheres to the surface of the base film, so as to improve the thermal stability of the diaphragm and the adhesion to the electrode, wherein the modified inorganic filler is modified by an amphiphilic silane coupling agent, and the surface content is a hydrophobic alkyl long chain and a hydrophilic quaternary ammonium salt group, and the hydrophobic long chain alkyl fixes the inorganic filler to the surface of the base film precursor through hydrophobic interaction, which, on the one hand, makes the film have good thermal stability, and on the other hand, improves the adhesion between the coating and the base film precursor, and the hydrophilic group is exposed to the environment, which is beneficial to improve the affinity between the diaphragm and the polar organic electrolyte and improve the liquid absorption rate of the diaphragm. The improvement of the liquid absorption rate can provide more ion transmission pathways, thereby improving the lithium ion transmission capacity, thereby improving the electrochemical performance of the battery. DETAILED DESCRIPTION

[0060] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

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

[0063] Coating device: Shanghai Fosait Functional Equipment Co., Ltd.

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

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

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

[0067] Ultra-high molecular weight polyethylene: Korea Petrochemical Corporation;

[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 SE, industrial grade;

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

[0073] Dichloromethane: concentration ≥99.99%, Shandong Luxi Chemical.

[0074] Clay, talc, 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, methyl ether, ethyl 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 monomethanol, polyethylene glycol octanoate: Zhejiang Huanxin Fluoro Materials Co., Ltd., industrial grade;

[0077] Dimethyl phthalate, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene, 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), dipolyhydroxystearate: 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] The modified inorganic filler is prepared by the following steps:

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

[0083] The amphiphilic silane coupling agent is prepared by the following steps:

[0084] Add 25 mmol of dodecyldimethylhydroxyethylammonium chloride to the flask, evacuate with a double-row tube and then fill with high-purity argon, repeat three times, then add 100 mL of THF, raise the temperature to 40°C, add 30 mmol of isocyanatepropyltriethoxysilane and 30 mmol of triethylamine, raise the temperature to reflux for 8 hours, and then remove THF by rotary evaporation.

[0085] Preparation Example 2

[0086] The modified inorganic filler is prepared by the following steps:

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

[0088] The amphiphilic silane coupling agent is prepared by the following steps:

[0089] Add 25 mmol of dodecyldimethylhydroxyethylammonium chloride to the flask, evacuate with a double-row tube and then fill with high-purity argon, repeat three times, then add 100 mL of THF, raise the temperature to 40°C, add 30 mmol of isocyanatepropyltriethoxysilane and 30 mmol of triethylamine, raise the temperature to reflux for 8 hours, and then remove THF by rotary evaporation.

[0090] Example 1

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

[0092] Step a, according to the raw material ratio in Table 1, ultra-high molecular weight polyethylene and nucleating agent are quantitatively added into the extruder through a weight loss scale, the flow accuracy is less than 3‰, the antioxidant and the pore-forming agent are stirred and mixed at a temperature of 90°C and a stirring speed of 40rpm for 30min, injected into the extruder through a plunger pump, the flow accuracy of the plunger pump is less than 5‰, and then melt-extruded, the heating temperature of the extruder is 160-200°C, the extruder is a co-rotating twin-screw extruder, 15 heating zones, the screw speed is 100rpm, and the screw aspect ratio is 56, to obtain a melt;

[0093] Step b, passing the melt through a 170° C. melt line and a T-die head for melt casting, wherein the temperature of the melt during melt casting is 200° C., and applying the melt to a 10° C. shaping roller for cooling to form a crystalline casting sheet with a thickness of 1.4 mm;

[0094] Step c, performing bidirectional synchronous stretching and first transverse stretching on the crystallized cast sheet, with the stretching ratio being 5 times, to obtain a thinned oil film;

[0095] Step d, pulling the thinned oil film through an extraction roller, immersing it in dichloromethane for extraction, the extraction time is 60 seconds, the extraction temperature is 15°C, after the extraction is completed, pulling it along the hot roller to a drying room for drying, the drying temperature is 40°C, and the drying time is 10 seconds to obtain a dry film;

[0096] Step e, stretching the dry film to 1.2 times at a speed of 2% / s at 120° C. (second transverse stretching), heating and shrinking at a speed of 0.5% / s at a temperature of 120° C., with a heating shrinkage ratio of 5% (shrinkage), and heat-setting at 120° C. for 5 seconds to obtain a base film precursor;

[0097] According to the raw material ratio in Table 1, weigh the raw materials and mix them evenly to obtain slurry. The base film precursor is coated with the slurry through a coating device. The coating amount of the slurry is 10g / m 2 , obtaining a coated separator; the coated separator was pulled by a roller and stretched to 0.85 times at a speed of 2% / s at 80°C, and the heat treatment time at 80°C was 20s to obtain a composite lithium battery separator.

[0098] In step c, the bidirectional synchronous stretching is performed at 100° C. at a speed of 10% / s; and the 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 comprises the following steps:

[0101] Step a, according to the raw material ratio in Table 1, ultra-high molecular weight polyethylene and nucleating agent are quantitatively added into the extruder through a weight loss scale, the flow rate accuracy is less than 3‰, the antioxidant and the pore-forming agent are stirred and mixed at a temperature of 110°C and a stirring speed of 50rpm for 40min, injected into the extruder through a plunger pump, the flow rate accuracy of the plunger pump is less than 5‰, and then melt-extruded, the heating temperature of the extruder is 180°C, the extruder is a co-rotating twin-screw extruder, 15 heating zones, the screw speed is 140rpm, and the screw aspect ratio is 57, to obtain a melt;

[0102] Step b, passing the melt through a 190° C. melt line and a T-die head for melt casting, wherein the temperature of the melt during melt casting is 230° C., and applying the melt to a 20° C. shaping roller for cooling to form a crystalline casting sheet with a thickness of 1.4 mm;

[0103] Step c, longitudinally stretching the crystallized cast sheet and performing a first transverse stretching, both at a stretching ratio of 10 times, to obtain a thinned oil film;

[0104] Step d, pulling the thinned oil film through an extraction roller, immersing it in dichloromethane for extraction, the extraction time is 140s, the extraction temperature is 20°C, after the extraction is completed, pulling it along the hot roller to dry it in a drying room, the drying temperature is 60°C, and the drying time is 20s to obtain a dry film;

[0105] Step e, stretching the dry film to 1.7 times at a speed of 10% / s at 130° C. (second transverse stretching), heating and shrinking at a speed of 2% / s at a temperature of 130° C., with a heating shrinkage ratio of 10% (shrinkage), and heat-setting at 130° C. for 20 seconds to obtain a base film precursor;

[0106] According to the raw material ratio in Table 1, weigh the raw materials and mix them evenly to obtain slurry. The base film precursor is coated with the slurry through a coating device. The coating amount of the slurry is 10g / m 2, obtaining a coated separator; the coated separator was pulled by a roller and stretched to 1 times at a speed of 10% / s at 120°C, and heat treated at 110°C for 80s to obtain a composite lithium battery separator.

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

[0108] Example 3

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

[0110] Step a, according to the raw material ratio in Table 1, ultra-high molecular weight polyethylene and nucleating agent are quantitatively added into the extruder through a weight loss scale, the flow accuracy is less than 3‰, the antioxidant and the pore-forming agent are stirred and mixed at a temperature of 130°C and a stirring speed of 60rpm for 60min, injected into the extruder through a plunger pump, the flow accuracy of the plunger pump is less than 5‰, and then melt-extruded, the heating temperature of the extruder is 200°C, the extruder is a co-rotating twin-screw extruder, 15 heating zones, the screw speed is 240rpm, and the screw aspect ratio is 68, to obtain a melt;

[0111] Step b, passing the melt through a 210° C. melt line and a T-die head for melt casting, wherein the temperature of the melt during melt casting is 240° C., and applying the melt to a 30° C. shaping roller for cooling to form a crystalline casting sheet with a thickness of 1.4 mm;

[0112] Step c, performing bidirectional synchronous stretching and first transverse stretching on the crystallized cast sheet, with the stretching ratio being 15 times, to obtain a thinned oil film;

[0113] Step d, pulling the thinned oil film through an extraction roller, immersing it in dichloromethane for extraction, the extraction time is 240s, the extraction temperature is 25°C, after the extraction is completed, pulling it along the hot roller to a drying room for drying, the drying temperature is 110°C, and the drying time is 40s to obtain a dry film;

[0114] Step e, stretching the dry film to 2 times at 140° C. at a speed of 30% / s (second transverse stretching), heating and shrinking at a temperature of 140° C. at a speed of 5% / s, with a heating shrinkage ratio of 25% (shrinkage), and heat-setting at 140° C. for 50 seconds to obtain a base film precursor;

[0115] According to the raw material ratio in Table 1, weigh the raw materials and mix them evenly to obtain slurry. The base film precursor is coated with the slurry through a coating device. The coating amount of the slurry is 10g / m 2 , obtaining a coated separator; the coated separator was pulled by a roller and stretched to 1.15 times at a speed of 30% / s at 140°C, and the heat treatment time at 140°C was 100s to obtain a composite lithium battery separator.

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

[0128] The dry film is coated with slurry through a coating device, and the slurry coating amount is 10g / m 2 , to obtain a coated diaphragm; the coated diaphragm is pulled by a roller and stretched to 1.1 times at a speed of 10% / s at 120°C, and heat treated at 90°C for 80s to obtain a composite lithium battery diaphragm. The dry film preparation process is the same as step ad of Example 1, and the slurry preparation process is the same as step e of 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 aluminum oxide, and the remaining raw materials and preparation process are the same as Example 1.

[0131] Comparative Example 3

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

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

[0134] The test methods for thickness, gram weight and needle puncture strength are all based on the national standard "Polyolefin separator for lithium-ion batteries" (GB / T36363-2018);

[0135] The peeling force test method is as follows: take a double-sided tape with an adhesive force of more than 800N / m and a length of 60mm (tape width 20mm), paste the double-sided tape on a steel plate cleaned with alcohol (steel plate size 100mm*20mm*0.5mm), and roll it with a 2kg roller for 3 times to ensure that there are no bubbles between the tape and the steel plate; then cut the composite diaphragm into 25mm*200mm strips, paste the composite diaphragm strips on the tape, and continue to roll it with a roller for 3 times; finally, clamp the steel plate and the tape in the upper and lower clamps of the stretching machine respectively, stretch them at a speed of 5mm / s, and test the peeling force;

[0136] The liquid absorption rate test method is as follows: 1,3-dioxolane and 1,2-dimethoxyethane are prepared into a mixed solution at a volume ratio of 1:1, the composite lithium battery separator is weighed and immersed in the solvent, and taken out after soaking at 25°C for 1-8 minutes, and the surface is wiped dry to remove excess solvent, and the mass after soaking is weighed respectively. According to the formula, liquid absorption rate (%) = (A1-A0) / A0×100%, 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 imager; then fold the sample with A4 paper and clamp it into a metal tray with Teflon glue on the bottom, place it in a 130℃ oven for 1 hour, and take it out and cool it to room temperature after completion; finally, use an imager to test the MD and TD lengths and calculate the heat shrinkage. Heat shrinkage calculation formula: 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] Observe the data recorded in Table 1. It can be seen from the test results of Example 1, Example 2 and Example 5 compared with Comparative Example 3 that the inorganic filler coating can greatly improve the thermal stability of the diaphragm, and reduce the thermal shrinkage of the diaphragm to about 1 / 10 of the original; it can be seen from the test results of Example 1 and Comparative Example 1 that a second lateral stretching of the dry film is beneficial to improving the thermal stability. It can be seen from the test results of Example 1 and Comparative Example 2 that modification of the inorganic filler is beneficial to improving the peeling force, thermal stability and liquid absorption rate of the diaphragm.

[0142] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

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

Claims

1. An integrated preparation method for a composite lithium battery separator, characterized in that: The following steps are involved: S1, mixing and extruding ultra-high molecular weight polyethylene, a pore-forming agent, a nucleating agent and an antioxidant to obtain a melt, casting the melt and cooling it to obtain a crystalline cast sheet, stretching and extracting the crystalline cast sheet to obtain a dry film, stretching, shrinking and heat-setting the dry film to obtain a base film precursor; S2, coating the slurry on one or both sides of the base film precursor, stretching it transversely and drying it to obtain a composite lithium battery separator; The slurry comprises the following raw materials in parts by weight: 0.1 to 1 part of a dispersant, 2 to 10 parts of an adhesive, 0.1 to 1 part of a wetting agent, 0.2 to 10 parts of a thickener, and 100 parts of a solvent.

2. The integrated preparation method of a composite lithium battery separator according to claim 1, characterized in that: The slurry also includes 20 to 45 parts of modified inorganic filler.

3. The integrated preparation method of a composite lithium battery separator according to claim 2, characterized in that: The modified inorganic filler is prepared by the following steps: Add the amphiphilic silane coupling agent to anhydrous ethanol, mix well to obtain a modified liquid, add the inorganic filler to the ethanol aqueous solution, ultrasonically disperse for 2 hours, then add the modified liquid, stir and react for 6-8 hours, and finally place in an oven and dry at 60°C to constant weight.

4. The integrated preparation method of a composite lithium battery separator according to claim 3, characterized in that: The amount of the amphiphilic silane coupling agent used is 2-5% of the mass of the inorganic filler.

5. The integrated preparation method of a composite lithium battery separator according to claim 3, characterized in that: The amphiphilic silane coupling agent is prepared by the following steps: Add dodecyldimethylhydroxyethylammonium chloride to the flask, evacuate and then fill with high-purity argon, repeat three times, then add THF, raise the temperature to 40°C, add isocyanatepropyltriethoxysilane and triethylamine, raise the temperature to reflux and react for 8 hours, then remove THF by rotary evaporation.

6. The integrated preparation method of a composite lithium battery separator according to claim 5, characterized in that: The usage ratio of dodecyldimethylhydroxyethylammonium chloride, THF, isocyanatepropyltriethoxysilane and triethylamine is 2.5mmol:10mL:3.0mmol:3.0mmol.

7. The integrated preparation method of a composite lithium battery separator according to claim 3, characterized in that: The inorganic filler includes a mixture of one or more of clay, talc, mica powder, asbestos powder, coal ore powder, sepiolite powder, attapulgite, ultrafine calcium carbonate, nano calcium, montmorillonite, alumina and boehmite.

8. The integrated preparation method of a composite lithium battery separator according to claim 1, characterized in that: The mass ratio of ultra-high molecular weight polyethylene, pore former, nucleating agent and antioxidant is (20-30): (70-80): (0.5-5): (0.01-0.1).

9. The integrated preparation method of a composite lithium battery separator according to claim 1, characterized in that: The specific operations of dry film stretching and retraction are as follows: The dry film is stretched to 1.2 to 2 times at a speed of 2 to 30% / s at 120 to 140° C., and then heated and shrunk at a speed of 0.5 to 5% / s at a temperature of 120 to 140° C., and the heating and shrinking ratio is 5 to 25%.

10. The integrated preparation method of a composite lithium battery separator according to claim 1, characterized in that: The heat setting temperature is 120-140°C, and the heat setting time is 5-50s.

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