A modified aramid separator coating slurry, a battery separator, and a method of making the same

Abstract

The present application relates to the technical field of lithium ion battery separator preparation, and particularly relates to a modified aramid fiber separator coating slurry, a battery separator and a preparation method thereof, the preparation method of the modified aramid fiber separator coating slurry is as follows: under the protection of inert gas, a cosolvent is dissolved into a polymerization solvent to obtain a solvent-cosolvent mixed system; p-phenylenediamine is added into the solvent-cosolvent mixed system to be dissolved to obtain a mixed solution; p-phenylenediamine is added into the mixed solution in batches, and a polymerization reaction is carried out by controlling the temperature of the system; and the modified aramid fiber separator coating slurry is obtained after the polymerization reaction is completed; and the preparation method further adds a third monomer to participate in the polymerization reaction, and the third monomer is at least one of an amine type third monomer and an acyl chloride type third monomer. The modified aramid fiber separator coating slurry can be used to prepare a battery separator with heat resistance and air permeability, and the process is simple.

Description

TECHNICAL FIELD

[0001] The present application relates to a modified aramid separator coating slurry, a battery separator and a preparation method thereof, and belongs to the technical field of battery separator preparation. BACKGROUND

[0002] Lithium ion batteries have high specific energy, high cycle life, small volume, light weight, no memory effect, no pollution and other characteristics, and are the replacement products of mainstream nickel-cadmium and hydrogen-nickel batteries. They have great potential in the development direction of energy storage equipment, and have rapidly developed into a new generation of energy storage power supply. They can be used in power support in the fields of information technology, electric vehicles and hybrid electric vehicles, aerospace, etc. As one of the key inner components of lithium ion batteries, the separator plays a crucial role in the performance of lithium ion batteries. The capacity, cycle performance, safety performance, etc. of the battery are closely related to the performance of the separator.

[0003] Traditional separator materials are polyolefin separators, such as polyethylene PE, polypropylene PP and composite separators of the two. However, polyolefin separators have poor wettability with electrolyte due to the large difference in polarity between them and the electrolyte, poor thermal stability at high temperatures, and are prone to shrinkage, which causes instability in the size of the separator, easily causing short circuits between electrodes, leading to thermal runaway of the battery, and finally causing fire, explosion and other safety problems. Therefore, technical personnel are looking for new heat-resistant materials to be coated on the surface of PE and PP separator materials to improve the temperature resistance of the separator.

[0004] Aramid is an aromatic polyamide fiber with high strength, high modulus, and excellent properties such as high temperature resistance and flame resistance. The commonly used aramid includes poly-m-phenylene isophthalamide (aramid 1313), poly-p-phenylene terephthalamide (aramid 1414, aramid II) and heterocyclic aramid (aramid III). Among them, aramid 1414 is a high-temperature-resistant fiber variety that has been developed early, widely applied, produced in large quantities and developed rapidly. It has excellent high-temperature resistance and corrosion resistance, and coating it on the separator can significantly improve the heat resistance of the separator. However, aramid-coated separators have high density, resulting in poor air permeability of the separator. Chinese patent application CN118943660A discloses an aramid coating slurry, a separator and a preparation method and application thereof. The patent proposes adding ceramic as a pore-forming agent to the aramid stock solution to improve the air permeability of the separator. The problem with this method is that the ceramic is difficult to disperse in the stock solution, the dispersion period is long and the dispersion is uneven, affecting the performance of the separator.

[0005] Therefore, it is necessary to prepare a new aramid coating slurry to enable aramid-coated separators to have excellent thermal performance and air permeability. SUMMARY

[0006] The present application provides a modified aramid membrane coating slurry, a battery separator and a preparation method thereof to solve the problems of poor dispersibility and long dispersion period of the existing ceramic aramid membrane coating slurry.

[0007] The technical scheme for solving the above technical problems is as follows: a preparation method of a modified aramid membrane coating slurry, the preparation method being:

[0008] S1, dissolving a cosolvent into a polymerization solvent under the protection of an inert gas to obtain a solvent-cosolvent mixed system;

[0009] S2, adding p-phenylenediamine to the solvent-cosolvent mixed system to obtain a mixed solution;

[0010] S3, adding p-phthaloyl chloride to the mixed solution in batches to control the temperature of the system to perform a polymerization reaction, and obtaining the modified aramid membrane coating slurry after the polymerization reaction is completed;

[0011] The preparation method further adds a third monomer to participate in the polymerization reaction, and the third monomer is at least one of an amine type third monomer and an acyl chloride type third monomer; when the amine type third monomer is used, the amine type third monomer is added in step S2; when the acyl chloride type third monomer is used, the acyl chloride type third monomer is added in batches in step S3;

[0012] The amine type third monomer is at least one of 2-chloro-p-phenylenediamine, aniline and piperazine;

[0013] The acyl chloride type third monomer is at least one of benzoyl chloride, 4-chlorobenzoyl chloride and p-methylbenzoyl chloride.

[0014] Further, the cosolvent is at least one of calcium chloride and lithium chloride; and the polymerization solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

[0015] Further, the addition amount of the cosolvent is 3%-8% of the mass of the polymerization solvent.

[0016] Further, the total amount of the p-phenylenediamine and the amine type third monomer in the solvent-cosolvent mixed system is 0.1-0.5 mol / L.

[0017] Further, the molar ratio of the p-phenylenediamine to the amine type third monomer is (4-9):1.

[0018] Further, the molar ratio of the p-phthaloyl chloride to the acyl chloride type third monomer is (4-9):1.

[0019] Further, the ratio of the total moles of terephthaloyl chloride and acyl chloride third monomer to the total moles of p-phenylenediamine and amine third monomer is (0.9-1.1):1.

[0020] The application further discloses a modified aramid membrane coating slurry prepared by the preparation method.

[0021] The application further discloses a preparation method of the battery membrane, which comprises the following steps: uniformly coating the modified aramid membrane coating slurry on two surfaces of a base film, and then performing water washing and drying after solidification and curing in a coagulation bath to obtain the battery membrane.

[0022] The application further discloses a battery membrane prepared by the preparation method.

[0023] The application has the following beneficial effects:

[0024] The application prepares the p-aramid coating slurry by a polymerization method, adjusts solvents, cosolvents and added third monomers to directly form nanoparticles in the slurry by copolymerization in the polymerization process, and replaces inorganic ceramic particles to improve the air permeability of the coated membrane.

[0025] The preparation method of the modified aramid membrane coating slurry disclosed by the application uses p-phenylenediamine and terephthaloyl chloride as polymerization monomers, prepares p-aramid stock solution by low-temperature solution polycondensation, adds third monomers to replace the positions of p-benzene for copolymerization modification, thereby destroying the regularity of the molecular chain of p-aramid, converting the rigid rod-like structure of the molecular chain into a spiral shape, increasing the flexibility, adjusting the dosages of polymerization solvents and cosolvents to realize the dissolution of p-aramid in solvents, and polymerizing to form part of nanoparticles as pore-forming agents under the synergistic action of these process conditions, thereby preparing the modified aramid coated battery membrane with heat resistance and air permeability, and having wide application prospects in the field of battery membranes.

[0026] The method prepares the aramid membrane coating slurry by the one-pot method, has the advantages of simple process, time saving and high efficiency, and the prepared membrane has excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The figure is a micro-morphology diagram of the modified aramid coated battery membrane of Example 1.

[0028] Figure 2 The figure is a micro-morphology diagram of the pure aramid coated battery membrane of Comparative Example 1.

[0029] Figure 3 Micrograph of ceramic / aramid coated battery separator for Comparative Example 2. DETAILED DESCRIPTION

[0030] The specific embodiments of the present application will be described in detail below. The present application can be implemented in many different ways than described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, so the present application is not limited to the specific embodiments disclosed.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used is for the purpose of describing the specific embodiments only and not for limiting the application.

[0032] A preparation method of a modified aramid separator coating slurry, the preparation method is:

[0033] S1, dissolving a cosolvent into a polymerization solvent under the protection of inert gas to obtain a solvent-cosolvent mixed system;

[0034] S2, dissolving p-phenylenediamine into the solvent-cosolvent mixed system to obtain a mixed solution;

[0035] S3, adding p-phenyl dichloride into the mixed solution in batches, controlling the temperature of the system to carry out polymerization reaction, and obtaining the modified aramid separator coating slurry after the polymerization reaction is completed;

[0036] A third monomer is also added in the preparation method to participate in the polymerization reaction, the third monomer is at least one of an amine type third monomer and an acyl chloride type third monomer; when the amine type third monomer is used, the amine type third monomer is added in step S2; when the acyl chloride type third monomer is used, the acyl chloride type third monomer is added in step S3 in batches;

[0037] The amine type third monomer is at least one of 2-chloro-p-phenylenediamine, aniline, and piperazine;

[0038] The acyl chloride type third monomer is at least one of benzoyl chloride, 4-chlorobenzoyl chloride, and p-methyl benzoyl chloride.

[0039] Specifically, the cosolvent is at least one of calcium chloride and lithium chloride; and the polymerization solvent is at least one of N-methyl pyrrolidone and N,N-dimethylacetamide.

[0040] Specifically, the addition amount of the cosolvent is 3%-8% of the mass of the polymerization solvent.

[0041] Specifically, the total amount of the p-phenylenediamine and the amine type third monomer in the solvent-cosolvent mixed system is 0.1-0.5 mol / L.

[0042] Specifically, the molar ratio of the p-phenylenediamine to the amine third monomer is (4-9):1.

[0043] Specifically, the molar ratio of the terephthaloyl chloride to the acyl chloride third monomer is (4-9):1.

[0044] Specifically, the ratio of the total moles of the terephthaloyl chloride and the acyl chloride third monomer to the total moles of the p-phenylenediamine and the amine third monomer is (0.9-1.1):1.

[0045] More specifically, the polymerization reaction is low-temperature polymerization, and the reaction temperature is -10-0℃, and -5℃ is used in the embodiment of the present application.

[0046] A modified aramid membrane coating slurry is prepared by the preparation method of the present application.

[0047] A preparation method of a battery separator, which comprises the following steps: uniformly coating the modified aramid membrane coating slurry of the present application on both sides of a base film, and then washing and drying the base film after solidification and curing in a coagulation bath to obtain a battery separator.

[0048] Specifically, the base film is a polyolefin base film, and the thickness of the polyolefin base film is 5-40μm.

[0049] More specifically, the polyolefin base film is selected from a polyethylene film, a polypropylene film, or a polypropylene / polyethylene / polypropylene composite film.

[0050] More specifically, in the embodiment of the present application, the coagulation bath is an aqueous solution of a polymerization solvent, the mass concentration of the polymerization solvent in the coagulation bath is 40%, and the temperature of the coagulation bath is 30℃.

[0051] A battery separator is prepared by the preparation method of the present application.

[0052] Embodiment 1

[0053] A preparation method of a modified aramid membrane coating slurry and a battery separator, which comprises the following steps:

[0054] (1) 10g of anhydrous CaCl2 is weighed, NMP is added to 200g, and the mixture is heated and stirred to dissolve under N2 protection to obtain an NMP-CaCl2 mixed system;

[0055] (2) The NMP-CaCl2 mixed system is cooled to 20℃, and 3.9796g of p-phenylenediamine and 0.3522g of piperazine (the molar ratio of p-phenylenediamine to piperazine is 9:1) are accurately added and stirred to dissolve under N2 protection to obtain a mixed solution of 0.2mol / L;

[0056] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to the total moles of p-phenylenediamine and piperazine is 1.007:1) is added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Wislicenus phenomenon, to obtain a modified aramid separator coating slurry;

[0057] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method, the coated separator is immersed in a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery separator is obtained.

[0058] Example 2

[0059] A preparation method of a modified aramid separator coating slurry and a battery separator, specifically comprising the following steps:

[0060] (1) 10 g of anhydrous CaCl2 is weighed, NMP is added to 200 g, and the mixture is dissolved by heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0061] (2) The above-mentioned NMP-CaCl2 mixed system is cooled to 20°C, and 3.9796 g of p-phenylenediamine and 0.5830 g of 2-chloro-p-phenylenediamine (the molar ratio of p-phenylenediamine to 2-chloro-p-phenylenediamine is 9:1) are accurately added, and the mixture is dissolved by stirring under N2 protection to obtain a 0.2 mol / L mixed solution;

[0062] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to the total moles of p-phenylenediamine and 2-chloro-p-phenylenediamine is 1.007:1) is added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Wislicenus phenomenon, to obtain a modified aramid separator coating slurry;

[0063] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method, the coated separator is immersed in a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery separator is obtained.

[0064] Example 3

[0065] A preparation method of a modified aramid separator coating slurry and a battery separator, specifically comprising the following steps:

[0066] (1) 10 g of anhydrous CaCl2 is weighed, NMP is added to 200 g, and the mixture is dissolved by heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0067] (2) The NMP-CaCl2 mixed system is cooled to 20°C, and 3.9796 g of p-phenylenediamine and 0.7616 g of aniline (the molar ratio of p-phenylenediamine to aniline is 8:2) are accurately added and dissolved under stirring in N2 protection to obtain a mixed solution of 0.2 mol / L;

[0068] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to the total moles of p-phenylenediamine and aniline is 1.007:1) is added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Weissenberg phenomenon to obtain a modified aramid separator coating slurry;

[0069] (4) A polypropylene / polyethylene / polypropylene composite film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method, and the coated separator is immersed in a coagulation bath for solidification and molding, and a modified aramid coated battery separator is obtained after drying.

[0070] Example 4

[0071] A preparation method of a modified aramid separator coating slurry and a battery separator, specifically comprising the following steps:

[0072] (1) 10 g of anhydrous CaCl2 is weighed, NMP is added to 200 g, and the mixture is dissolved under heating and stirring in N2 protection to obtain an NMP-CaCl2 mixed system;

[0073] (2) The NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added and dissolved under stirring in N2 protection to obtain a mixed solution of 0.2 mol / L;

[0074] (3) The mixed solution in step (2) is cooled to -5°C, and 7.5236 g of terephthaloyl chloride and 0.5788 g of benzoyl chloride (the molar ratio of terephthaloyl chloride to benzoyl chloride is 9:1, and the total moles of terephthaloyl chloride and benzoyl chloride to the moles of p-phenylenediamine is 1.007:1) are added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Weissenberg phenomenon to obtain a modified aramid separator coating slurry;

[0075] (4) A polyethylene base film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method, and the coated separator is immersed in a coagulation bath for solidification and molding, and a modified aramid coated battery separator is obtained after drying.

[0076] Example 5

[0077] A modified aramid membrane coating slurry and a preparation method of a battery separator, specifically comprising the following steps:

[0078] (1) Take 10 g of anhydrous CaCl2, add NMP to 200 g, and dissolve under heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0079] (2) The above NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added and dissolved under stirring under N2 protection to obtain a mixed solution of 0.2 mol / L;

[0080] (3) The mixed solution in step (2) is cooled to -5°C, and 7.5236 g of terephthaloyl chloride and 0.7206 g of 4-chlorobenzoyl chloride (molar ratio of terephthaloyl chloride to 4-chlorobenzoyl chloride is 9:1, and the total molar number of terephthaloyl chloride and 4-chlorobenzoyl chloride to the molar number of p-phenylenediamine is 1.007:1) are added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Weissenberg phenomenon to obtain a modified aramid membrane coating slurry;

[0081] (4) Select a polyvinyl film with a thickness of 12 μm, and coat the above-mentioned modified aramid membrane coating slurry on both sides of the base film by using a wire roller coating method, immerse the coated separator into a coagulation bath for solidification and molding, and obtain a modified aramid coated battery separator after drying.

[0082] Example 6

[0083] A modified aramid membrane coating slurry and a preparation method of a battery separator, specifically comprising the following steps:

[0084] (1) Take 10 g of anhydrous CaCl2, add NMP to 200 g, and dissolve under heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0085] (2) The above NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added and dissolved under stirring under N2 protection to obtain a mixed solution of 0.2 mol / L;

[0086] (3) The mixed solution in step (2) is cooled to -5°C, and 7.5236 g of terephthaloyl chloride and 0.7206 g of 4-chlorobenzoyl chloride (molar ratio of terephthaloyl chloride to 4-chlorobenzoyl chloride is 9:1, and the total molar number of terephthaloyl chloride and 4-chlorobenzoyl chloride to the molar number of p-phenylenediamine is 1.007:1) are added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Weissenberg phenomenon to obtain a modified aramid membrane coating slurry;

[0087] (4) Select a polyethylene base film with a thickness of 9 μm, use a wire roller coating method to coat the above-mentioned modified aramid membrane coating slurry on both sides of the base film, immerse the coated membrane into a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery membrane is obtained.

[0088] Example 7

[0089] A preparation method of a modified aramid membrane coating slurry and a battery membrane, specifically comprising the following steps:

[0090] (1) Take 10 g of anhydrous LiCl, add DMAc to 200 g, and heat and stir to dissolve under N2 protection to obtain a DMAc-LiCl mixed system;

[0091] (2) The above-mentioned NMP-LiCl mixed system is cooled to 20°C, and 3.9796 g of p-phenylenediamine and 0.3522 g of aniline (molar ratio of p-phenylenediamine to aniline is 9:1) are accurately added, and stirred to dissolve under N2 protection to obtain a mixed solution of 0.2 mol / L;

[0092] (3) The mixed solution in step (2) is cooled to -5°C, and 7.5236 g of terephthaloyl chloride and 0.5788 g of benzoyl chloride (molar ratio of terephthaloyl chloride to benzoyl chloride is 9:1, molar ratio of acyl chloride monomer to amine monomer is 1.007:1) are added in batches under stirring conditions, and low-temperature solution polymerization is started under N2 protection and strong stirring conditions, and the reaction is stopped after the appearance of the Wissberg phenomenon to obtain a modified aramid membrane coating slurry;

[0093] (4) Select a polyethylene base film with a thickness of 9 μm, use a wire roller coating method to coat the above-mentioned modified aramid membrane coating slurry on both sides of the base film, immerse the coated membrane into a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery membrane is obtained.

[0094] Example 8

[0095] A preparation method of a modified aramid membrane coating slurry and a battery membrane, specifically comprising the following steps:

[0096] (1) Take 14 g of anhydrous CaCl2, add NMP to 200 g, and heat and stir to dissolve under N2 protection to obtain an NMP-CaCl2 mixed system;

[0097] (2) The above-mentioned NMP-CaCl2 mixed system is cooled to 20°C, and 6.9210 g of p-phenylenediamine, 0.7450 g of aniline, and 1.1406 g of 2-chloro-p-phenylenediamine (molar ratio of the three is 8:1:1) are accurately added, and stirred to dissolve under N2 protection to obtain a mixed solution of 0.4 mol / L;

[0098] (3) The mixed solution in step (2) is cooled to -5°C, and 16.3553 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to amine monomer is 1.007:1) is added in batches under stirring. Low-temperature solution polymerization is started under N2 protection and strong stirring, and the reaction is stopped after the appearance of the Wissberg phenomenon. A modified aramid separator coating slurry is obtained;

[0099] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method. The coated separator is immersed in a coagulation bath for solidification and molding. After drying, a modified aramid coated battery separator is obtained.

[0100] Comparative Example 1

[0101] The difference between Comparative Example 1 and Example 1 is that a pure separator coating slurry is prepared without adding amine third monomers or acyl chloride third monomers. The specific implementation method is as follows:

[0102] (1) 10 g of anhydrous CaCl2 is weighed, and NMP is added to 200 g. The mixture is dissolved by heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0103] (2) The above-mentioned NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added. The mixture is dissolved by stirring under N2 protection to obtain a 0.2 mol / L mixed solution;

[0104] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to p-phenylenediamine is 1.007:1) is added in batches under stirring. Low-temperature solution polymerization is started under N2 protection and strong stirring, and the reaction is stopped after the appearance of the Wissberg phenomenon. An aramid separator coating slurry is obtained;

[0105] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned aramid slurry is coated on both sides of the base film by using a wire roller coating method. The coated separator is immersed in a coagulation bath for solidification and molding. After drying, an aramid coated battery separator is obtained.

[0106] Comparative Example 2

[0107] Comparative Example 2 adds inorganic ceramic particles on the basis of Comparative Example 1 to improve the air permeability of the aramid coated separator. The specific implementation method is as follows:

[0108] (1) 10 g of anhydrous CaCl2 is weighed, and NMP is added to 200 g. The mixture is dissolved by heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system with a mass fraction of 5%;

[0109] (2) The NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added and dissolved under stirring in N2 protection to obtain a 0.2 mol / L mixed solution;

[0110] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to p-phenylenediamine is 1.007:1) is added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Wislicenus phenomenon to obtain an aramid separator coating slurry;

[0111] (4) 2% of nano-sized alumina by mass fraction is added to the aramid slurry in step (3), and stirring is performed for 120 min using a high-speed dispersion emulsifier to obtain a ceramic / aramid separator coating slurry;

[0112] (4) A polyethylene film with a thickness of 9 μm is selected, and the ceramic / aramid separator coating slurry is coated on both sides of the base film in a line roller coating manner, the coated separator is immersed in a coagulation bath for solidification and forming, and a ceramic / aramid coated battery separator is obtained after drying.

[0113] Comparative Example 3

[0114] The difference between the present comparative example 3 and Example 1 is that the proportion of the amount of the auxiliary solvent is increased when preparing the separator coating slurry, and in the present comparative example 3, the amount of the auxiliary solvent added is 10% of the mass of the polymerization solvent. The specific preparation process is as follows:

[0115] (1) 20 g of anhydrous CaCl2 is weighed, NMP is added to 200 g, and stirring and dissolution are performed under heating in N2 protection to obtain an NMP-CaCl2 mixed system;

[0116] (2) The NMP-CaCl2 mixed system is cooled to 20°C, and 3.9796 g of p-phenylenediamine and 0.3522 g of piperazine (the molar ratio of p-phenylenediamine to piperazine is 9:1) are accurately added and dissolved under stirring in N2 protection to obtain a 0.2 mol / L mixed solution;

[0117] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to p-phenylenediamine and piperazine is 1.007:1) is added in batches under stirring, and low-temperature solution polymerization is started under N2 protection and strong stirring until the reaction is stopped after the appearance of the Wislicenus phenomenon to obtain a modified aramid separator coating slurry;

[0118] (4) Select a polyethylene film with a thickness of 9 μm, use a wire roller coating method to coat the above-mentioned modified aramid separator coating slurry on both sides of the base film, immerse the coated separator into a coagulation bath for solidification and molding, and obtain a modified aramid coated battery separator after drying.

[0119] Comparative Example 4

[0120] The difference between Comparative Example 4 and Example 1 is that when preparing the pure separator coating slurry, the proportion of the amount of the cosolvent is reduced. In Comparative Example 3, the amount of the cosolvent added is 2% of the mass of the polymerization solvent. The specific preparation process is as follows:

[0121] (1) Take 4 g of anhydrous CaCl2, add NMP to 200 g, and heat and stir to dissolve under N2 protection to obtain an NMP-CaCl2 mixed system;

[0122] (2) Cool the above-mentioned NMP-CaCl2 mixed system to 20°C, accurately add 3.9796 g of p-phenylenediamine and 0.3522 g of piperazine (the molar ratio of p-phenylenediamine to piperazine is 9:1), and stir to dissolve under N2 protection to obtain a mixed solution of 0.2 mol / L;

[0123] (3) Cool the mixed solution in step (2) to -5°C, and add 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to p-phenylenediamine and piperazine is 1.007:1) in batches under stirring conditions. Start the low-temperature solution polymerization under N2 protection and strong stirring conditions, and stop the reaction after the appearance of the Wissbergh phenomenon to obtain a modified aramid separator coating slurry;

[0124] It is found in the experiment that the modified aramid separator coating slurry prepared in this comparative example 4 has a high viscosity and cannot be uniformly coated on the base film.

[0125] Comparative Example 5

[0126] The difference between Comparative Example 5 and Example 1 is that the proportion of piperazine is increased and the proportion of p-phenylenediamine is reduced in step (2). The specific preparation process is as follows:

[0127] (1) Take 10 g of anhydrous CaCl2, add NMP to 200 g, and heat and stir to dissolve under N2 protection to obtain an NMP-CaCl2 mixed system;

[0128] (2) Cool the above-mentioned NMP-CaCl2 mixed system to 20°C, accurately add 0.4326 g of p-phenylenediamine and 3.1009 g of piperazine (the molar ratio of p-phenylenediamine to piperazine is 1:9), and stir to dissolve under N2 protection to obtain a mixed solution of 0.2 mol / L;

[0129] (3) The mixed solution in step (2) is cooled to -5°C, and 8.3595 g of terephthaloyl chloride (the molar ratio of terephthaloyl chloride to the total moles of p-phenylenediamine and piperazine is 1.007:1) is added in batches under stirring conditions. The low-temperature solution polymerization is started under N2 protection and strong stirring, and the reaction is stopped after the appearance of the Wislicenus phenomenon, to obtain a modified aramid separator coating slurry;

[0130] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method. The coated separator is immersed in a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery separator is obtained.

[0131] Comparative Example 6

[0132] The difference between this comparative example 6 and example 4 is that the proportion of benzoyl chloride is increased and the proportion of terephthaloyl chloride is reduced in step (2). The specific preparation process is as follows:

[0133] (1) 10 g of anhydrous CaCl2 is weighed, NMP is added to 200 g, and the mixture is dissolved by heating and stirring under N2 protection to obtain an NMP-CaCl2 mixed system;

[0134] (2) The above-mentioned NMP-CaCl2 mixed system is cooled to 20°C, and 4.4218 g of p-phenylenediamine is accurately added and dissolved by stirring under N2 protection to obtain a 0.2 mol / L mixed solution;

[0135] (3) The mixed solution in step (2) is cooled to -5°C, and 0.8178 g of terephthaloyl chloride and 5.0958 g of benzoyl chloride (the molar ratio of terephthaloyl chloride to benzoyl chloride is 1:9, and the total molar ratio of terephthaloyl chloride and benzoyl chloride to the moles of p-phenylenediamine is 1.007:1) are added in batches under stirring conditions. The low-temperature solution polymerization is started under N2 protection and strong stirring, and the reaction is stopped after the appearance of the Wislicenus phenomenon, to obtain a modified aramid separator coating slurry;

[0136] (4) A polyethylene film with a thickness of 9 μm is selected, and the above-mentioned modified aramid separator coating slurry is coated on both sides of the base film by using a wire roller coating method. The coated separator is immersed in a coagulation bath for solidification and molding, and after drying, a modified aramid coated battery separator is obtained.

[0137] For the products in each example and comparative example, the thickness of the separator is tested by a thickness measuring instrument, the air permeability of the separator is tested by an air permeability detector, and the heat shrinkage rate of the separator is calculated by using an oven and a ruler. The test indicators are summarized in Table 1 below.

[0138] Table 1 Battery separator performance test data

[0139]

[0140] From the above data, it can be seen that the modified aramid coated battery separator prepared by the preparation method of the present application in Examples 1-8 has excellent air permeability and heat resistance. Compared with Comparative Example 1, the air permeability value of the modified aramid coated separator is lower than that of the pure aramid coated separator, indicating that the air permeability is improved, which proves that the nanoparticles generated by the polymerization of the modified aramid can effectively improve the air permeability, and at the same time, the problem of long dispersion period of the post-added inorganic ceramic in Comparative Example 2 is avoided. The air permeability value of the modified aramid coated separator prepared by the method of the present application reaches 140.3 s / 100cc (Example 7), which is better than 269.6 s / 100cc of Comparative Example 2, because the uniformity of the nanoparticles generated by polymerization in the slurry is better than that of the post-added inorganic ceramic particles.

[0141] From the comparison of the data of Comparative Example 3 and Example 1, it can be seen that if the amount of the cosolvent is too much, it will cause the air permeability of the separator to decrease, because the solubility of the para-aramid in the solvent increases, the degree of polymerization increases, and the compactness of the coated separator increases.

[0142] From the comparison of the experimental conditions of Comparative Example 4 and Example 1, it can be seen that if the amount of the cosolvent is too small, the prepared modified aramid separator coating slurry is too thick, and the coating operation on the base film cannot be realized, because the solubility of the para-aramid in the solvent decreases, and the flowability becomes poor.

[0143] From the comparison of the data of Comparative Example 5 and Example 1, and Comparative Example 6 and Example 4, it can be seen that if the proportion of the third monomer is increased, the heat resistance of the separator decreases, therefore, by using the proportion of the third monomer defined in the present application, the separator can have good air permeability and excellent heat resistance at the same time.

[0144] In summary, the present application discloses a modified aramid separator coating slurry, a battery separator and a preparation method thereof, by introducing a low-reactivity third monomer into the aramid polymerization for copolymerization modification, and adjusting the polymerization solvent and the cosolvent, part of the nanoparticles formed in the polymerization process of the para-aramid are used as pore-forming agents for the separator coating slurry, and a modified aramid coated separator with heat resistance and air permeability is prepared. The method of the present application prepares the aramid separator coating slurry by "one-pot method", which has the advantages of simple process, time-saving and high efficiency, and the prepared separator has excellent performance.

[0145] The technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not exhaustively listed, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0146] For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application, the protection scope of the present application is subject to the appended claims.

Claims

1. A method of preparing a battery separator, characterized by, The preparation method of the battery separator comprises the following steps: uniformly coating a modified aramid separator coating slurry on both sides of a base film, then washing and drying after solidification and curing in a coagulation bath to obtain the battery separator. The preparation method of the modified aramid separator coating slurry comprises the following steps: S1. Dissolving a cosolvent into a polymerization solvent to obtain a solvent-cosolvent mixed system under the protection of inert gas; S2. Dissolving p-phenylenediamine into the solvent-cosolvent mixed system to obtain a mixed solution; S3. Adding p-phenylenediamine into the mixed solution in batches, controlling the temperature of the system to perform a polymerization reaction, and obtaining the modified aramid separator coating slurry after the polymerization reaction is completed; The preparation method further comprises adding a third monomer to participate in the polymerization reaction, wherein the third monomer is an amine third monomer; and the amine third monomer is added in step S2. The amine third monomer is 2-chloro-p-phenylenediamine or aniline. The addition amount of the cosolvent is 3%-8% of the mass of the polymerization solvent. The molar ratio of the p-phenylenediamine, aniline and 2-chloro-p-phenylenediamine is 8:1:

1.

2. The method of claim 1, wherein the battery separator is prepared by the steps of: The cosolvent is at least one of calcium chloride and lithium chloride; and the polymerization solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

3. The method of claim 1, wherein the battery separator is prepared by the steps of: The total amount of the p-phenylenediamine and the amine third monomer in the solvent-cosolvent mixed system is 0.1-0.5 mol / L.

4. A battery separator characterized by, The battery separator is prepared according to the preparation method in any one of claims 1-3.

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