High-temperature-resistant water-soluble aramid fiber coating diaphragm and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant water-soluble aramid coating diaphragm and a preparation method thereof, and belongs to the technical field of battery diaphragms. The diaphragm is obtained by coating the surface of a base membrane with water-soluble aramid fiber slurry and performing cross-linking and drying, the base membrane is a PE / PVA composite membrane; the water-soluble aramid fiber slurry is prepared from the following raw materials in parts by mass: 10 to 20 parts of modified aramid fiber polymer, 40 to 80 parts of deionized water, 3 to 6 parts of cosolvent and 5 to 8 parts of multi-epoxy group cross-linking agent; the modified aramid fiber polymer is obtained by carrying out polymerization reaction on 1, 4-phenylenediamine-2-sulfonic acid and 2, 6-dipicolinic acid. The hydrophilic property of the polymer is improved by the pyridine ring and sulfonic acid introduced into the modified aramid polymer, the prepared water-based slurry is more environment-friendly, the reaction of the multi-epoxy group cross-linking agent and the polyvinyl alcohol of the PE / PVA composite diaphragm under the heating condition is promoted through the sulfonic group, a cross-linked network is formed, and the binding force of the coating and the base membrane is enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separator, and particularly relates to a high-temperature-resistant water-soluble aramid coating separator and a preparation method thereof. BACKGROUND

[0002] In the structure of a lithium battery, a separator plays a role of electronic insulation to prevent the positive and negative electrodes from directly contacting each other, and the porous structure of the separator can allow lithium ions in an electrolyte to pass freely under certain conditions and prevent electrons from passing through, which plays a crucial role in the performance of the battery.

[0003] The commonly used commercial separator in the market is a polyolefin microporous film, which has good mechanical properties and electrochemical stability, but cannot maintain dimensional stability at high temperatures, resulting in internal short circuit and safety risks of the battery. In addition, the generation of lithium dendrites during operation will cause puncture damage to the separator, which will eventually also lead to the occurrence of internal short circuit of the battery.

[0004] In order to improve the mechanical strength and temperature resistance of the separator, coating the surface of the separator is the most effective measure at present. The main coating materials include special alumina, boehmite, aramid, polyvinylidene fluoride (PVDF), PMMA, etc. Compared with inorganic materials as coating materials, the temperature resistance and puncture resistance of aramid coating are better, and the coating thickness is lower, so the aramid-coated separator is more lightweight than the inorganic material-coated separator. However, the use of N,N-dimethylacetamide organic solvent is required for aramid coating, and the treatment of the solvent has environmental pollution risks, and the adhesion of the aramid coating to the polyolefin-based film needs to be improved. The existing aramid coating is prone to coating peeling, and the comprehensive performance of the separator is difficult to guarantee. SUMMARY

[0005] The application provides a high-temperature-resistant water-soluble aramid coating separator and a preparation method thereof, which can solve the problem of weak adhesion between the coating and the base film in the prior art.

[0006] The object of the application can be achieved by the following technical solutions.

[0007] A high-temperature-resistant water-soluble aramid coating separator, which is obtained by coating a water-soluble aramid slurry on the surface of a base film, cross-linking and drying to form a coating

[0008] The base film is a PE / PVA composite separator.

[0009] The water-soluble aramid slurry comprises the following raw materials in parts by mass:

[0010] 10-20 parts of modified aramid polymer, 40-80 parts of deionized water, 3-6 parts of cosolvent, and 5-8 parts of multi-epoxy crosslinking agent.

[0011] The modified aramid polymer is obtained by polymerization reaction of 1,4-phenylenediamine-2-sulfonic acid and 2,6-pyridine dicarboxylic acid.

[0012] The coating slurry of the aramid coating on the conventional separator is obtained by dissolving p-aramid or m-aramid in an organic solvent (DMAC, NMP), the binding force between the coating and the base film is insufficient, and due to the obvious difference in thermal stability between the coating and the base film, the base film and the coating will cause the coating to fall off due to the difference in thermal shrinkage in the case of battery temperature rise, and the aramid in the slurry needs an organic solvent to be dissolved, the amount of organic solvent is large, and the environmental hazards caused by the flow of solvent into the environment in the subsequent treatment are large.

[0013] The modified aramid polymer is obtained by polymerization reaction of 1,4-phenylenediamine-2-sulfonic acid and 2,6-pyridine dicarboxylic acid, the pyridine ring and the sulfonic acid group are introduced into the structure of the modified aramid polymer, the pyridine ring and the sulfonic acid group can form hydrogen bonds with water molecules, improve the hydrophilicity, and make the modified aramid polymer have solubility in water, the slurry prepared by using the modified aramid polymer as the main solvent is deionized water, which is more environmentally friendly. In addition, the sulfonic acid group can promote the ring-opening crosslinking of the epoxy group in the multi-epoxy crosslinking agent, and the residual carboxylic acid group can also react with the hydroxyl group of polyvinyl alcohol in the base film to form a crosslinked network on the contact surface of the coating and the base film, thereby enhancing the binding force and improving the temperature resistance.

[0014] Further, the PE / PVA composite separator has a thickness of 15-20 μm, and the coating has a thickness of 1-2 μm.

[0015] Further, the PE / PVA composite separator is prepared as follows:

[0016] Step one, polyvinyl alcohol is dissolved in deionized water, sodium dodecyl sulfate is added and stirred to obtain an impregnating solution;

[0017] Step two, the PE microporous membrane is washed with anhydrous ethanol and dried, then soaked in the impregnating solution for 20-40 min, taken out and blown with nitrogen to remove the residual liquid on the surface, and vacuum dried to obtain the PE / PVA composite separator.

[0018] The PE microporous membrane has a certain hydrophobicity, and the electrolyte has poor wettability as a separator. The PE microporous membrane is impregnated with polyvinyl alcohol, the hydroxyl group of the polyvinyl alcohol is rich, the surface of the composite separator after impregnation has more hydroxyl groups, the hydrophilicity is improved, the electrolyte has better wettability, and accordingly, the electrochemical performance of the battery is improved.

[0019] Further, the mass-volume ratio of the polyvinyl alcohol and deionized water is 2-5 g / L. The concentration of polyvinyl alcohol should not be too high, and the polyvinyl alcohol invades the micropores of the PE microporous membrane at a high concentration, resulting in a small pore size, increased lithium ion transmission resistance, and affected rate performance of the battery. The appropriate concentration of polyvinyl alcohol can improve the microporous structure after impregnation, avoid lithium dendrite puncture, and improve the mechanical properties of the separator.

[0020] Further, the mass concentration of sodium dodecyl sulfonate in the impregnating solution is 0.1-0.3 wt%. Sodium dodecyl sulfonate can reduce the surface tension of the PE membrane, so that PVA uniformly penetrates into the inside of the PE micropore.

[0021] Further, the modified aramid polymer is prepared as follows:

[0022] Step 1, stir 2,6-pyridine dicarboxylic acid in water, add 1,4-benzenediamine-2-sulfonic acid, adjust the pH to 7.2-7.5, and stir for 3-5 h;

[0023] Step 2, move into the reaction kettle, continue to stir under the nitrogen atmosphere at 200-230℃ and 1.5-2.0 MPa for 2-3 h, and react at normal pressure for 1-1.5 h. After cooling and precipitation, filter and dry to obtain a prepolymer;

[0024] Step 3, crush the prepolymer and add it into a solid-phase polymerization kettle, stir and react at 9-12 Pa and 200-240℃ for 2-3 h, and then cool and decompress to normal temperature and pressure. The modified aramid polymer is obtained by discharging.

[0025] Further, the molar ratio of 1,4-benzenediamine-2-sulfonic acid to 2,6-pyridine dicarboxylic acid is 1.2-1.5:1.

[0026] Further, the cosolvent is one of ethanol and acetone.

[0027] Further, the multi-epoxy crosslinking agent is at least one of polyethylene glycol diglycidyl ether and glycerol triglycidyl ether. The compound containing multi-epoxy groups is used as a crosslinking agent, and the epoxy groups are ring-opened and crosslinked with polyvinyl alcohol under the catalysis of sulfonic acid groups.

[0028] The application also provides a preparation method of a high-temperature-resistant water-soluble aramid coating separator, which comprises the following steps:

[0029] S1, uniformly mix the modified aramid polymer, deionized water, cosolvent and multi-epoxy crosslinking agent in proportion to obtain a water-soluble aramid slurry;

[0030] S2, coat the water-soluble aramid slurry on the surface of the PE / PVA composite separator and heat and crosslink;

[0031] S3, after crosslinking, drying to form a coating layer, a high-temperature-resistant water-soluble aramid coating separator is obtained.

[0032] Further, the heating crosslinking is arranged as follows:

[0033] The temperature is raised to 110-130 DEG C, and the crosslinking reaction is kept constant for 10-15 min, and then the temperature is raised to 140-150 DEG C, and the crosslinking reaction is kept constant for 5-10 min. At 110-130 DEG C, the epoxy groups open ring and react with the hydroxyl groups of polyvinyl alcohol, and at 140-150 DEG C, the residual carboxylic acid groups in the modified aramid polymer react with the hydroxyl groups of polyvinyl alcohol, and gradually crosslink under heating conditions.

[0034] The beneficial effects of the present application are:

[0035] (1) The modified aramid polymer prepared by polymerization of 1,4-benzenediamine-2-sulfonic acid and 2,6-pyridine dicarboxylic acid is used as the main component of the coating layer, and the introduction of the pyridine ring and the sulfonic acid improves the hydrophilicity of the polymer, enabling the polymer to be dissolved in water-based solvents, and the prepared water-based slurry is more environmentally friendly.

[0036] (2) While ensuring that the modified aramid polymer has a rigid skeleton, the sulfonic acid groups in the modified aramid polymer promote the reaction between the multi-epoxy crosslinking agent and the polyvinyl alcohol of the PE / PVA composite separator under heating conditions, forming a crosslinking network, enhancing the bonding force between the coating layer and the base film, and improving the thermal stability.

[0037] (3) The PE / PVA composite separator prepared by impregnating polyvinyl alcohol into a PE microporous film is used as the base film, and the polyvinyl alcohol improves the microporous structure while enhancing the mechanical properties of the base film. The hydroxyl groups of the base film and the sulfonic acid groups introduced by the modified aramid polymer can both improve the hydrophilicity of the separator, and the electrolyte wettability is better. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] Example 1

[0040] A high-temperature-resistant water-soluble aramid coating separator, the separator is obtained by coating water-soluble aramid slurry on the surface of a base film, and then forming a coating layer after crosslinking and drying.

[0041] The water-soluble aramid slurry includes the following raw materials in mass fractions:

[0042] Modified aramid polymer 15 parts, deionized water 60 parts, ethanol 3 parts and polyethylene glycol diglycidyl ether 5 parts.

[0043] The preparation of PE / PVA composite separator is as follows:

[0044] Step one, polyvinyl alcohol is dissolved in deionized water with a concentration of 2g / L, sodium dodecyl sulfonate is added and stirred to mix evenly to obtain an impregnating solution, the mass concentration of sodium dodecyl sulfonate in the impregnating solution is 0.1wt%.

[0045] Step two, PE microporous membrane (thickness 15μm, porosity 45%) is washed with anhydrous ethanol and dried, then soaked in the impregnating solution for 30min, removed and nitrogen blown to remove the surface residual liquid, vacuum dried to obtain PE / PVA composite separator with a thickness of 16μm.

[0046] The preparation of modified aramid polymer is as follows:

[0047] Step 1, 2,6-pyridine dicarboxylic acid is added to water and stirred to dissolve, with a concentration of 3g / L, 1,4-benzenediamine-2-sulfonic acid is added, ammonia is used to adjust the pH to 7.3, and stirred to react for 3-5h, wherein the molar ratio of 1,4-benzenediamine-2-sulfonic acid to 2,6-pyridine dicarboxylic acid is 1.2:1.

[0048] Step 2, move into the reaction kettle, continue to stir to react under nitrogen atmosphere at 210℃ and 1.5MPa for 2.5h, and react at normal pressure for 1h, then cool and precipitate, filter and dry to obtain the prepolymer.

[0049] Step 3, crush the prepolymer and add it into the solid-phase polymerization kettle, stir to react at 230℃ under 10Pa for 2h, then cool and reduce the pressure to normal temperature and pressure, and discharge to obtain the modified aramid polymer.

[0050] The preparation of water-soluble aramid coating separator is as follows:

[0051] S1, mix the modified aramid polymer, deionized water, ethanol and polyethylene glycol diglycidyl ether in proportion to obtain water-soluble aramid slurry.

[0052] S2, coat the water-soluble aramid slurry on one side of the PE / PVA composite separator, heat to 110-130℃ for crosslinking reaction for 10-15min, then heat to 140-150℃ for crosslinking reaction for 5-10min.

[0053] S3, after the crosslinking reaction is completed, dry to form a coating, the thickness of the coating is 1.5μm, and the water-soluble aramid coating separator with high temperature resistance is obtained.

[0054] Example 2

[0055] The difference from Example 1 is only that the molar ratio of 1,4-phenylenediamine-2-sulfonic acid to 2,6-pyridinedicarboxylic acid is adjusted to 1.4:1 when preparing the modified aramid polymer, and other conditions and preparation steps are the same as those of Example 1.

[0056] Example 3

[0057] The difference from Example 1 is only that the molar ratio of 1,4-phenylenediamine-2-sulfonic acid to 2,6-pyridinedicarboxylic acid is adjusted to 1.5:1 when preparing the modified aramid polymer, and other conditions and preparation steps are the same as those of Example 1.

[0058] Example 4

[0059] The difference from Example 2 is only that the concentration of polyvinyl alcohol dissolved in deionized water is adjusted to 4.5 g / L when preparing the PE / PVA composite separator, and other conditions and preparation steps are the same as those of Example 2.

[0060] Example 5

[0061] The difference from Example 1 is only that the concentration of polyvinyl alcohol dissolved in deionized water is adjusted to 5 g / L when preparing the PE / PVA composite separator, and other conditions and preparation steps are the same as those of Example 2.

[0062] Examples 6-9

[0063] The difference from Example 1 is only that the mass fraction of raw materials of the water-soluble aramid slurry is different. The specific raw material ratio is shown in Table 1.

[0064] Table 1

[0065]

[0066] Comparative Example 1

[0067] The difference from Example 1 is only that the PE microporous membrane is used to replace the PE / PVA composite separator in this comparative example, and other conditions and preparation steps are the same as those of Example 1.

[0068] Comparative Example 2

[0069] The difference from Example 1 is only that polyethylene glycol diglycidyl ether is not added when preparing the water-soluble aramid coating separator in this comparative example, and other conditions and preparation steps are the same as those of Example 1.

[0070] Comparative Example 3

[0071] The difference from Example 1 is only that 1,4-phenylenediamine-2-sulfonic acid is replaced by p-phenylenediamine in this comparative example.

[0072] A high-temperature-resistant aramid coating separator, the separator is obtained by coating aramid slurry on the surface of a base film, washing with water and drying to form a coating. The base film is a PE / PVA composite separator.

[0073] The aramid slurry includes the following raw materials by mass fraction:

[0074] Modified aramid polymer 15 parts, deionized water 30 parts, dimethylacetamide 30 parts, ethanol 3 parts and polyethylene glycol diglycidyl ether 5 parts.

[0075] The preparation of the PE / PVA composite separator is as follows:

[0076] Step one, dissolve polyvinyl alcohol in deionized water with a concentration of 2 g / L, add sodium dodecyl sulfonate and stir to mix evenly to obtain an impregnating solution, and the mass concentration of sodium dodecyl sulfonate in the impregnating solution is 0.1 wt%.

[0077] Step two, the PE microporous membrane (thickness 15 μm, porosity 45%) is washed with anhydrous ethanol and dried, soaked in the impregnating solution for 30 min, removed and nitrogen blown to remove the surface residual liquid, and vacuum dried to obtain a PE / PVA composite separator with a thickness of 16 μm.

[0078] The preparation of the modified aramid polymer is as follows:

[0079] Step 1, add 2,6-pyridine dicarboxylic acid to water and stir to dissolve, with a concentration of 3 g / L, add p-phenylenediamine, adjust the pH to 7.3 with ammonia water, and stir to react for 3-5 h, wherein the molar ratio of p-phenylenediamine to 2,6-pyridine dicarboxylic acid is 1.2:1.

[0080] Step 2, move into the reaction kettle, continue to stir to react under a nitrogen atmosphere at 210℃ and 1.5 MPa for 2.5 h, and react at normal pressure for 1 h, filter and dry to obtain a prepolymer.

[0081] Step 3, crush the prepolymer and add it to a solid-phase polymerization kettle, stir to react at 10 Pa and 230℃ for 2 h, cool and reduce the pressure to normal temperature and pressure, and discharge to obtain a modified aramid polymer.

[0082] The preparation of the aramid coating separator is as follows:

[0083] S1, mix the modified aramid polymer, deionized water, dimethylacetamide, ethanol and polyethylene glycol diglycidyl ether in proportion to obtain an aramid slurry.

[0084] S2, coat the aramid slurry on one side of the PE / PVA composite separator, heat to 110-130℃ and keep the temperature constant for 10-15 min, and then heat to 140-150℃ and keep the temperature constant for 5-10 min.

[0085] S3, after washing with water, dry to form a coating, and the coating thickness is 1.5 μm, to obtain a high-temperature-resistant aramid coating separator.

[0086] The performance tests were carried out on the separators obtained in Examples 1-9 and Comparative Examples 1-3, and the specific tests were as follows:

[0087] The thermal shrinkage, puncture strength and air permeability were detected according to the standard GB / T 36363-2018 Polyolefin Separator for Lithium Ion Battery. The peeling strength of the coating layer and the base film was detected by a mechanical testing machine.

[0088] Liquid absorption rate detection: The prepared separator was cut into a 2 cm disc, dried in a vacuum drying oven, weighed, and recorded as M0. The disc was immersed in electrolyte (solute LiPF6, solute mass fraction 20%, solvent EC+DMC+DEC, mass ratio 4:2:4) for 12 h, the surface residual liquid was absorbed by filter paper, weighed and recorded as M1, and the liquid absorption rate = (M1-M0) / M0x100%.

[0089] The results are shown in Table 2:

[0090] Table 2

[0091]

[0092]

[0093] As can be seen from Table 2, in Examples 1-3, the increase in the molar amount of 1,4-phenylenediamine-2-sulfonic acid relative to 2,6-pyridinedicarboxylic acid is more conducive to promoting the forward progress of the modified aramid polymer polycondensation reaction, the degree of polymerization is higher, and the heat resistance of the coated separator is better, but excessive addition will increase the residual reactants and the content of small molecular substances in the modified aramid polymer, and the thermal stability will also decrease. In Examples 4 and 5, the concentration of polyvinyl alcohol in the preparation of PE / PVA composite separator is adjusted based on Example 2. The increase in the concentration of polyvinyl alcohol increases the hydroxyl groups on the PE microporous membrane, and the crosslinking reaction with the coating layer is more sufficient, and the peeling strength is improved. When the concentration of polyvinyl alcohol is under the conditions of Example 5, too high a concentration will cause polyvinyl alcohol to block the micropores of the PE microporous membrane, and the air permeability will decrease. In Examples 6-9, the raw material ratio of the slurry is adjusted, and the comprehensive performance of Example 8 is the best. It can be known from Comparative Examples 1, 2, 3 and Example 1 that in the absence of PVA to provide hydroxyl groups, the absence of polyethylene glycol diglycidyl ether to provide epoxy groups, and the absence of modified aramid polymer to provide sulfonic acid groups, the crosslinking reaction between the coating layer and the base film lacks key participating groups, resulting in weakened adhesion and reduced peeling strength.

[0094] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is not intended to exclude myriad other embodiments of the present application that other inventors can develop based on the same general inventive concepts embodied by the described embodiments. That is, although the present application is described in terms of particular embodiments and illustrative figures, it should be apparent that the scope of the present application is not limited to these specific embodiments.

[0095] While the embodiments of the application have been shown and described herein, it will be understood by those skilled in the art that many changes, modifications, substitutions and alterations to these embodiments can be made without departing from the principles and spirits of the application, and it is intended that the scope of the application be limited solely by the scope of the appended claims and the equivalents thereof.

Claims

1. A high temperature resistant water-soluble aramid coating diaphragm, characterized in that: The diaphragm is obtained by coating a water-soluble aramid slurry on the surface of a base film, cross-linking, and drying to form a coating; The base film is a PE / PVA composite diaphragm; The water-soluble aramid slurry comprises the following raw materials in parts by mass: 10-20 parts of modified aramid polymer, 40-80 parts of deionized water, 3-6 parts of cosolvent and 5-8 parts of polyepoxy crosslinking agent; The modified aramid polymer is obtained by polymerization reaction of 1,4-phenylenediamine-2-sulfonic acid and 2,6-pyridinedicarboxylic acid.

2. The high temperature resistant water-soluble aramid coating diaphragm according to claim 1, characterized in that: The thickness of the PE / PVA composite diaphragm is 15-20 μm, and the thickness of the coating is 1-2 μm.

3. The high temperature resistant water-soluble aramid coating diaphragm according to claim 1, characterized in that: The preparation of the PE / PVA composite membrane is as follows: Step 1: dissolving polyvinyl alcohol in deionized water, adding sodium lauryl sulfate and stirring to obtain an impregnation solution; Step 2: The PE microporous membrane is washed with anhydrous ethanol and then dried, and then immersed in the impregnation liquid for 20-40 minutes. After being taken out, the residual liquid on the surface is purged with nitrogen and vacuum dried to obtain a PE / PVA composite membrane.

4. The high temperature resistant water-soluble aramid coating diaphragm according to claim 3, characterized in that: The mass volume ratio of the polyvinyl alcohol to deionized water is 2-5 g / L.

5. The high temperature resistant water-soluble aramid coating diaphragm according to claim 3, characterized in that: The mass concentration of the sodium lauryl sulfate in the impregnation solution is 0.1-0.3 wt %.

6. The high temperature resistant water-soluble aramid coating diaphragm according to claim 1, characterized in that: The preparation of the modified aramid polymer is as follows: Step 1: Add 2,6-pyridinedicarboxylic acid to water and stir, add 1,4-phenylenediamine-2-sulfonic acid, adjust the pH to 7.2-7.5, and stir to react for 3-5 hours; Step 2: transfer the mixture into a reactor, continue stirring and reacting at 200-230°C and 1.5-2.0 MPa under nitrogen atmosphere for 2-3 hours, then react at normal pressure for 1-1.5 hours, cool and precipitate, filter and dry to obtain a prepolymer; Step 3: crush the prepolymer and add it into a solid phase polymerization reactor, heat it to 200-240° C. at 9-12 Pa, stir and react for 2-3 hours, cool it down and reduce the pressure to room temperature and pressure, and discharge the material to obtain a modified aramid polymer.

7. The high temperature resistant water-soluble aramid coating diaphragm according to claim 6, characterized in that: The molar ratio of the 1,4-phenylenediamine-2-sulfonic acid to the 2,6-pyridinedicarboxylic acid is 1.2-1.5:

1.

8. The high temperature resistant water-soluble aramid coating diaphragm according to claim 1, characterized in that: The cosolvent is one of ethanol and acetone; The polyepoxy crosslinking agent is at least one of polyethylene glycol diglycidyl ether and glycerol triglycidyl ether.

9. A method for preparing a high temperature resistant water-soluble aramid coating diaphragm according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. uniformly mixing the modified aramid polymer, deionized water, a cosolvent and a polyepoxy crosslinking agent in proportion to obtain a water-soluble aramid slurry; S2, coating the water-soluble aramid slurry on the surface of the PE / PVA composite diaphragm and heating to cross-link; S3. After cross-linking is completed, the coating is dried to obtain a high-temperature resistant water-soluble aramid coating diaphragm.

10. The method for preparing a high-temperature resistant water-soluble aramid coating diaphragm according to claim 9, characterized in that: The heating cross-linking is set up as follows: The temperature was raised to 110-130°C and cross-linked for 10-15 minutes, and then the temperature was raised to 140-150°C and cross-linked for 5-10 minutes.

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