Diaphragm coating, preparation method thereof and diaphragm

Abstract

The invention relates to the technical field of battery diaphragms, and provides a diaphragm coating, a preparation method thereof and a diaphragm. The diaphragm coating comprises the following components in parts by weight: 25-36 parts of hydrated aluminum silicate, 4-14 parts of cellulose acetate butyrate, 12.5-24 parts of polymethyl methacrylate, 11-15 parts of polyvinylidene fluoride, 1-3 parts of a dispersing agent, 6-10 parts of an adhesive and 100 parts of a solvent. Through the technical scheme, the problem of poor puncture resistance of the diaphragm obtained by the diaphragm coating in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators. Specifically, it relates to a separator coating, a preparation method thereof, and a separator. Background Art

[0002] With the rapid development of lithium-ion battery technology, the performance requirements for lithium-ion battery separators are increasing day by day. As a key component of lithium-ion batteries, lithium-ion battery separators play a role in separating the positive and negative electrodes, preventing short circuits, and allowing lithium ions to pass through freely. Traditional lithium-ion battery separators are mainly made of polymer materials such as polyethylene and polypropylene. The separators composed of these materials basically meet the safety requirements during normal use. However, when the battery works under high temperature or abusive conditions, due to certain limitations of these materials in terms of puncture resistance, the separator may rupture, resulting in a decline in battery performance or even safety accidents.

[0003] In order to improve the performance of lithium-ion battery separators, researchers have developed various coated separator technologies. By coating one or more functional coatings on the surface of traditional separators, the puncture resistance or ion conductivity of the separators can be improved to a certain extent. However, in order to improve the mechanical strength of the current lithium-ion battery separator coatings, some nano-inorganic particles, such as alumina nano-particles, are added. These nano-particles are extremely easy to agglomerate and are unevenly dispersed in the coating, resulting in limited improvement in the puncture resistance of lithium-ion battery separators. In addition, the coating material cost of the existing coated separators is relatively high, and the coating process is relatively complex, which also limits their popularization in practical applications. Summary of the Invention

[0004] The present invention provides a separator coating, a preparation method thereof, and a separator, which solve the problem of poor puncture resistance of the separator obtained from the separator coating in the related art.

[0005] The technical solution of the present invention is as follows: The present invention provides a separator coating, comprising the following components in parts by weight: 25 - 36 parts of hydrated aluminum silicate, 4 - 14 parts of cellulose acetate butyrate, 12.5 - 24 parts of polymethyl methacrylate, 11 - 15 parts of polyvinylidene fluoride, 1 - 3 parts of dispersant, 6 - 10 parts of binder, and 100 parts of solvent.

[0006] As a further technical solution, the weight ratio of the hydrated aluminum silicate to the cellulose acetate butyrate is 3 - 5:1.

[0007] When the weight ratio of hydrated aluminum silicate to cellulose acetate butyrate is 3 - 5:1, the puncture resistance of the separator can be further improved. When the weight ratio of hydrated aluminum silicate to cellulose acetate butyrate < 3:1, the supporting ability of the separator coating is insufficient, resulting in a decrease in puncture resistance. When the weight ratio of hydrated aluminum silicate to cellulose acetate butyrate > 5:1, the internal stability of the separator coating is limited, affecting the puncture resistance of the separator.

[0008] As a further technical solution, the hydrated aluminum silicate is hydrated aluminum silicate compounded with ethylene bisstearamide.

[0009] As a further technical solution, the raw materials of the hydrated aluminum silicate compounded with ethylene bisstearamide include hydrated aluminum silicate and ethylene bisstearamide, and the weight ratio of the hydrated aluminum silicate to the ethylene bisstearamide is 40:3 - 6.

[0010] In the present invention, the hydrated aluminum silicate is compounded with ethylene bisstearamide. While ensuring that the separator has good puncture resistance, the hydrated aluminum silicate can maintain a stable structure at high temperatures, reduce the thermal shrinkage or rupture of the separator, and enable the separator to have good heat resistance.

[0011] When the weight ratio of hydrated aluminum silicate to ethylene bisstearamide is 40:3 - 6, the heat resistance of the separator can be further improved. When the weight ratio of hydrated aluminum silicate to ethylene bisstearamide < 20:3, the thermal stability of the separator decreases. When the weight ratio of hydrated aluminum silicate to ethylene bisstearamide > 40:3, the processing performance of the hydrated aluminum silicate compounded with ethylene bisstearamide itself becomes poor, and its dispersibility in the separator coating system decreases, thereby reducing the heat resistance of the separator.

[0012] As a further technical solution, the dispersant is one or two of sodium lauryl polyoxyethylene ether sulfate and polyacrylamide.

[0013] In the separator coating system, there are various components such as hydrated aluminum silicate, cellulose acetate butyrate, polymethyl methacrylate, and polyvinylidene fluoride. The dispersant can adsorb on the surfaces of these components, reduce the surface tension between the components, make them evenly dispersed in the solvent, form a stable dispersion system, and thus ensure the uniformity of the separator coating.

[0014] As a further technical solution, the binder is one or more of sodium carboxymethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0015] The binder can bond the components in the separator coating to a certain extent, form a tight overall structure, so that these components can interact synergistically in the coating, enhance the cohesive strength of the coating, and prevent the coating from delaminating and peeling off during use.

[0016] As a further technical solution, the solvent is one or more of N-methylpyrrolidone, acetone, ethanol, and dimethylformamide.

[0017] As a further technical solution, the thickness of the separator coating is 2-4 μm.

[0018] The present invention also provides a method for preparing the separator coating, comprising the following steps: S1. Mix hydrated aluminum silicate, cellulose acetate butyrate, polymethyl methacrylate, polyvinylidene fluoride, and a binder, stir once, add a solvent with a volume fraction of 50%-60%, and stir twice to obtain a first mixed solution; S2. After adding the remaining solvent to the first mixed solution, add a dispersant and stir to obtain a mixed slurry; S3. After coating the mixed slurry, dry it to obtain the separator coating.

[0019] As a further technical solution, during the first stirring, the stirring speed is 100-200 r / min, and the stirring time is 15-25 min; during the second stirring, the stirring speed is 900-1000 r / min, and the stirring time is 50-80 min.

[0020] As a further technical solution, in step S2, during the stirring, the stirring speed is 600-700 r / min, and the stirring time is 30-40 min.

[0021] In the present invention, during the first stirring, a stirring speed of 100-200 r / min is adopted to gently contact and disperse hydrated aluminum silicate, cellulose acetate butyrate, polymethyl methacrylate, polyvinylidene fluoride, and the binder in the initial stage, avoiding the occurrence of local high concentration; during the second stirring, a stirring speed of 900-1000 r / min is adopted to enable the solvent to fully penetrate into each component, and under the action of the dispersant, a uniform and stable mixed slurry is formed, thereby ensuring the consistency of the performance of the final separator coating.

[0022] As a further technical solution, in step S3, during the coating, a doctor blade coating method is specifically adopted.

[0023] When using the doctor blade coating method for coating, the coating thickness can be precisely controlled, and the separator coating is uniformly distributed on the surface of the base film.

[0024] As a further technical solution, in step S3, during the drying, the temperature is 60-80 °C.

[0025] The present invention also provides a method for preparing the separator coating, comprising the following steps: A1. After melting the ethylene bisstearamide, add the hydrated aluminum silicate, mix evenly, cool, and pulverize to obtain the hydrated aluminum silicate of the composite ethylene bisstearamide; A2. Mix the hydrated aluminum silicate of the composite ethylene bisstearamide, cellulose acetate butyrate, polymethyl methacrylate, polyvinylidene fluoride, and sodium carboxymethyl cellulose, stir once, add a solvent with a volume fraction of 50% - 60%, and stir twice to obtain a first mixed solution; A3. After adding the remaining solvent to the first mixed solution, add a dispersant and stir to obtain a mixed slurry; A4. After coating the mixed slurry, dry it to obtain a separator coating.

[0026] As a further technical solution, during melting, the temperature is 150 - 160 °C; when mixing evenly, the stirring speed is 500 - 700 r / min, and the time is 1 - 2 h.

[0027] The present invention also provides a separator, including the separator coating described above or the separator coating prepared by the preparation method described above.

[0028] As a further technical solution, it further includes a base film, the base film is one of a polypropylene film and a polyethylene film, and the thickness of the base film is 8 - 10 μm.

[0029] The working principle and beneficial effects of the present invention are as follows: 1. In the present invention, using hydrated aluminum silicate as the main material, in combination with cellulose acetate butyrate, polymethyl methacrylate, polyvinylidene fluoride, as well as a dispersant and a binder, a uniform and dense separator coating is formed, and it has good ionic conductivity, without affecting the free passage of lithium ions in the lithium battery.

[0030] 2. Polymethyl methacrylate and polyvinylidene fluoride in the separator coating have good electrolyte wettability, and together with the binder, they make the separator coating and the base film have good adhesion. Hydrated aluminum silicate and cellulose acetate butyrate have a synergistic effect. When used in combination, they promote the connection and internal stability of the separator coating, improve the strength and toughness of the separator coating, and enable the separator to well resist the puncture of sharp substances such as lithium dendrites.

[0031] 3. In the present invention, using low-cost hydrated aluminum silicate and polymethyl methacrylate as separator coating materials reduces the preparation cost of the coated separator. Specific Embodiments

[0032] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0033] In the following examples and comparative examples, the dispersant is sodium lauryl polyoxyethylene ether sulfate, with an active ingredient content of 99% and a CAS number of 9004-82-4; the binder is sodium carboxymethyl cellulose, with an active ingredient content of 99% and a CAS number of 9004-32-4; the base film is a polyethylene film, and the model of polyethylene is LL0220K; aluminum silicate hydrate, with an average particle size of 1.5 μm; the model of cellulose acetate butyrate is CAB-551-0.2; the model of polymethyl methacrylate is HFI-7; the model of polyvinylidene fluoride is PVDF2850-02; the model of ethylene bisstearamide is P130.

[0034] Example 1 A separator coating includes the following components in parts by weight: 25 parts of aluminum silicate hydrate, 4 parts of cellulose acetate butyrate, 12.5 parts of polymethyl methacrylate, 11 parts of polyvinylidene fluoride, 1 part of sodium lauryl polyoxyethylene ether sulfate, 6 parts of sodium carboxymethyl cellulose, and 100 parts of N-methylpyrrolidone; A method for preparing a separator including the above separator coating includes the following steps: S1. Mix 25 parts of aluminum silicate hydrate, 4 parts of cellulose acetate butyrate, 12.5 parts of polymethyl methacrylate, 11 parts of polyvinylidene fluoride, and 6 parts of sodium carboxymethyl cellulose, stir at a stirring speed of 100 r / min for 25 min, then add N-methylpyrrolidone with a volume fraction of 50%, and stir at a stirring speed of 900 r / min for 80 min to obtain a first mixed solution; S2. After adding the remaining N-methylpyrrolidone to the first mixed solution, add 1 part of sodium lauryl polyoxyethylene ether sulfate, and stir at a stirring speed of 600 r / min for 40 min to obtain a mixed slurry; S3. Coat the mixed slurry on the upper and lower surfaces of a 10-μm-thick polyethylene film by the doctor blade coating method, and dry at 60 °C to obtain a separator with separator coatings coated on the upper and lower surfaces of the polyethylene film. The thickness of the separator coatings on the upper and lower surfaces of the polyethylene film is 2 μm.

[0035] Example 2 A separator coating includes the following components in parts by weight: 26 parts of aluminum silicate hydrate, 10 parts of cellulose acetate butyrate, 18 parts of polymethyl methacrylate, 13 parts of polyvinylidene fluoride, 2 parts of sodium lauryl polyoxyethylene ether sulfate, 8 parts of sodium carboxymethyl cellulose, 100 parts of N-methylpyrrolidone; A method for preparing a separator including the above separator coating, comprising the following steps: S1. Mix 26 parts of aluminum silicate hydrate, 10 parts of cellulose acetate butyrate, 18 parts of polymethyl methacrylate, 13 parts of polyvinylidene fluoride, and 8 parts of sodium carboxymethyl cellulose, stir for 20 min at a stirring speed of 150 r / min, then add N-methylpyrrolidone with a volume fraction of 55%, and stir for 65 min at a stirring speed of 950 r / min to obtain a first mixed solution; S2. After adding the remaining N-methylpyrrolidone to the first mixed solution, add 2 parts of sodium lauryl polyoxyethylene ether sulfate, and stir for 35 min at a stirring speed of 650 r / min to obtain a mixed slurry; S3. Coat the mixed slurry on the upper and lower surfaces of a polyethylene film with a thickness of 9 μm by a doctor blade coating method, and dry at 70 °C to obtain a separator with separator coatings coated on the upper and lower surfaces of the polyethylene film. The thickness of the separator coatings on the upper and lower surfaces of the polyethylene film is 3 μm.

[0036] Example 3 A separator coating, comprising the following components in parts by weight: 36 parts of aluminum silicate hydrate, 14 parts of cellulose acetate butyrate, 24 parts of polymethyl methacrylate, 15 parts of polyvinylidene fluoride, 3 parts of sodium lauryl polyoxyethylene ether sulfate, 10 parts of sodium carboxymethyl cellulose, 100 parts of N-methylpyrrolidone; A method for preparing a separator including the above separator coating, comprising the following steps: S1. Mix 36 parts of aluminum silicate hydrate, 14 parts of cellulose acetate butyrate, 24 parts of polymethyl methacrylate, 15 parts of polyvinylidene fluoride, and 10 parts of sodium carboxymethyl cellulose, stir for 15 min at a stirring speed of 200 r / min, then add N-methylpyrrolidone with a volume fraction of 60%, and stir for 50 min at a stirring speed of 1000 r / min to obtain a first mixed solution; S2. After adding the remaining N-methylpyrrolidone to the first mixed solution, add 3 parts of sodium lauryl polyoxyethylene ether sulfate, and stir for 30 min at a stirring speed of 700 r / min to obtain a mixed slurry; S3. Coat the mixed slurry on the upper and lower surfaces of a polyethylene film with a thickness of 8 μm by a doctor blade coating method, and dry at 80 °C to obtain a separator with separator coatings coated on the upper and lower surfaces of the polyethylene film. The thickness of the separator coatings on the upper and lower surfaces of the polyethylene film is 4 μm.

[0037] Example 4 The difference between this example and Example 2 is only that in this example, 32 parts of hydrated aluminum silicate and 4 parts of cellulose acetate butyrate are added.

[0038] Example 5 The difference between this example and Example 2 is only that in this example, 27 parts of hydrated aluminum silicate and 9 parts of cellulose acetate butyrate are added.

[0039] Example 6 The difference between this example and Example 2 is only that in this example, 30 parts of hydrated aluminum silicate and 6 parts of cellulose acetate butyrate are added.

[0040] Example 7 The difference between this example and Example 6 is only that in this example, 30 parts of hydrated aluminum silicate are replaced with 30 parts of hydrated aluminum silicate of compound ethylene bisstearamide; The preparation method of the separator including the above separator coating includes the following steps: A1. After melting 1 part of ethylene bisstearamide at 155 °C, add 40 parts of hydrated aluminum silicate, stir at a stirring speed of 500 r / min for 2 h, mix evenly, cool, and pulverize to obtain hydrated aluminum silicate of compound ethylene bisstearamide; A2. Mix 30 parts of the above hydrated aluminum silicate of compound ethylene bisstearamide, 10 parts of cellulose acetate butyrate, 18 parts of polymethyl methacrylate, 13 parts of polyvinylidene fluoride, and 8 parts of sodium carboxymethyl cellulose, stir at a stirring speed of 150 r / min for 20 min, then add N-methylpyrrolidone with a volume fraction of 55%, and stir at a stirring speed of 950 r / min for 65 min to obtain a first mixed solution; A3. After adding the remaining N-methylpyrrolidone to the first mixed solution, add sodium lauryl polyoxyethylene ether sulfate, and stir at a stirring speed of 650 r / min for 35 min to obtain a mixed slurry; A4. Coat the mixed slurry on the upper and lower surfaces of a 9-μm-thick polyethylene film by the doctor blade coating method, and dry at 70 °C to obtain a separator with separator coatings coated on the upper and lower surfaces of the polyethylene film. The thickness of the separator coatings on the upper and lower surfaces of the polyethylene film is 3 μm.

[0041] Example 8 The difference between this example and Example 7 is only that in this example, 7 parts of ethylene bisstearamide are added in step A1.

[0042] Example 9 The difference between this example and Example 7 is only that in this example, 3 parts of ethylene bisstearamide are added in step A1.

[0043] Example 10 The difference between this example and Example 7 is only that in this example, 6 parts of ethylene bisstearamide are added in step A1.

[0044] Example 11 The difference between this example and Example 2 is only that in this example, in step S3, the mixed slurry is coated on the upper surface of a polyethylene film with a thickness of 9 μm by the doctor blade coating method and dried at 70°C to obtain a separator with a separator coating on the upper surface of the polyethylene film, and the thickness of the separator coating on the upper surface of the polyethylene film is 3 μm.

[0045] Example 12 The difference between this example and Example 2 is only that in this example, in step S3, the mixed slurry is coated on the lower surface of a polyethylene film with a thickness of 9 μm by the doctor blade coating method and dried at 70°C to obtain a separator with a separator coating on the lower surface of the polyethylene film, and the thickness of the separator coating on the lower surface of the polyethylene film is 3 μm.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is only that in this comparative example, cellulose acetate butyrate is not added, and 29 parts of hydrated aluminum silicate are added.

[0047] Comparative Example 2 The difference between this comparative example and Example 1 is only that in this comparative example, hydrated aluminum silicate is not added, and 29 parts of cellulose acetate butyrate are added.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is only that in this comparative example, hydrated aluminum silicate is replaced with an equal amount of alumina powder.

[0049] Comparative Example 4 The difference between this comparative example and Example 1 is only that in this comparative example, neither hydrated aluminum silicate nor cellulose acetate butyrate is added.

[0050] Experimental Example 1 Puncture Resistance Test The separators prepared in Examples 1 to 6, Examples 11 to 12 and Comparative Examples 1 to 4 were subjected to a puncture strength test according to the method in GB / T 36363-2018 "Polyolefin Separators for Lithium-Ion Batteries", where the puncture rate was 100 mm / min, and the test results are shown in Table 1 below: Table 1 Puncture Strength Test Results of Separators

[0051] As can be seen from Table 1, compared with Comparative Examples 1-4, the puncture strength of the diaphragms obtained in Examples 1-6 is > 13 N, indicating that aluminum silicate hydrate and cellulose acetate butyrate have a synergistic effect and can improve the puncture resistance of the diaphragm. Among them, compared with Examples 2 and 4, the puncture strength of the diaphragms obtained in Examples 5-6 is further improved, indicating that when the weight ratio of aluminum silicate hydrate to cellulose acetate butyrate is 3-5:1, the puncture resistance of the diaphragm can be further improved.

[0052] Experimental Example 2 Heat resistance The diaphragms prepared in Examples 6-10 were measured for the transverse (TD) and longitudinal (MD) thermal shrinkage rates according to the method in GB / T 36363-2018 "Polyolefin Diaphragms for Lithium-Ion Batteries". Among them, the size of the diaphragm specimen was 100 mm × 100 mm, and the test results of the transverse and longitudinal thermal shrinkage rates were the averages of 3 specimens. The test results are shown in Table 2 below: Table 2 Test results of diaphragm thermal shrinkage rate

[0053] As can be seen from Table 2, compared with Example 6, the thermal shrinkage rate of the diaphragms obtained in Examples 7-10 is reduced, indicating that when the aluminum silicate hydrate is the aluminum silicate hydrate compounded with ethylene bisstearamide, the heat resistance of the diaphragm can be improved. Among them, compared with Examples 7-8, the thermal shrinkage rate of the diaphragms obtained in Examples 9-10 is reduced, indicating that when the weight ratio of aluminum silicate hydrate to ethylene bisstearamide is 40:3-6, the heat resistance of the diaphragm can be further improved.

[0054] Experimental Example 3 The following performance tests were carried out on the diaphragm prepared in Example 1: ① Adhesion: After the diaphragm obtained in Example 1 was superimposed with the positive electrode sheet, it was thermally pressed at 3 MPa and 90 °C for 60 s to bond the diaphragm and the positive electrode sheet. The adhesion between the diaphragm and the positive electrode sheet was measured by a peel tester, where the specimen width was 30 mm and the peel speed was 30 mm / min; ② Tensile strength: The diaphragm obtained in Example 1 was tested for the transverse (TD) and longitudinal (MD) tensile strength according to the method in GB / T 36363-2018 "Polyolefin Diaphragms for Lithium-Ion Batteries". Among them, the specimen was a Type 2 specimen with a width of 15 mm, and the test speed was 250 mm / min.

[0055] The test results are shown in Table 3 below: Table 3 Test results of adhesion and tensile strength

[0056] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A diaphragm coating, characterized in that: The composition comprises the following components in parts by weight: 25-36 parts of hydrated aluminum silicate, 4-14 parts of cellulose acetate butyrate, 12.5-24 parts of polymethyl methacrylate, 11-15 parts of polyvinylidene fluoride, 1-3 parts of dispersant, 6-10 parts of binder, and 100 parts of solvent.

2. A diaphragm coating according to claim 1, characterized in that: The weight ratio of the hydrated aluminum silicate to the cellulose acetate butyrate is 3-5:

1.

3. A diaphragm coating according to claim 1, characterized in that: The hydrated aluminum silicate is hydrated aluminum silicate of composite ethylene bisstearic acid amide.

4. A diaphragm coating according to claim 3, characterized in that: The raw materials of the hydrated aluminum silicate of the composite ethylene bis stearic acid amide include hydrated aluminum silicate and ethylene bis stearic acid amide, and the weight ratio of the hydrated aluminum silicate to the ethylene bis stearic acid amide is 40:3-6.

5. A diaphragm coating according to claim 1, characterized in that: The dispersant is one or both of sodium lauryl alcohol polyoxyethylene ether sulfate and polyacrylamide; and / or The binder is one or more of sodium carboxymethyl cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose; and / or The solvent is one or more of N-methylpyrrolidone, acetone, ethanol and dimethylformamide.

6. A diaphragm coating according to claim 1, characterized in that: The thickness of the diaphragm coating is 2-4 μm.

7. The method for preparing a diaphragm coating according to claim 1, characterized in that: The following steps are involved: S1, mixing hydrated aluminum silicate, cellulose acetate butyrate, polymethyl methacrylate, polyvinylidene fluoride and a binder, stirring once, adding 50% to 60% by volume of a solvent, stirring a second time, to obtain a first mixed solution; S2, adding the remaining solvent to the first mixed solution, adding a dispersant, and stirring to obtain a mixed slurry; S3, coating the mixed slurry and drying it to obtain a diaphragm coating.

8. The method for preparing a diaphragm coating according to claim 7, characterized in that: During the first stirring, the stirring speed is 100-200 r / min, and the stirring time is 15-25 min; during the second stirring, the stirring speed is 900-1000 r / min, and the stirring time is 50-80 min.

9. A diaphragm, comprising a diaphragm coating according to any one of claims 1 to 6 or a diaphragm coating prepared by the preparation method according to any one of claims 7 to 8.

10. A diaphragm according to claim 9, characterized in that: It also includes a base film, which is one of a polypropylene film and a polyethylene film, and has a thickness of 8-10 μm.

Images