Preparation method of high-peel-strength ultrathin lithium battery diaphragm

Abstract

The invention relates to the technical field of battery diaphragms, and provides a preparation method of a high-peel-strength ultrathin lithium battery diaphragm. The high-peel-strength ultrathin lithium battery diaphragm comprises a base membrane and a coating arranged on one side or two sides of the base membrane, the coating is prepared from slurry, and the slurry is prepared from the following components in parts by weight: 20 to 40 parts of aluminum oxide, 40 to 80 parts of water, 0.3 to 0.5 part of a binding agent, 0.05 to 0.1 part of a dispersing agent, 0.5 to 1 part of a thickening agent and 0.05 to 0.1 part of a wetting agent; the binder comprises an emulsion type polyacrylate binder and a solution type sulfobutyl-beta-cyclodextrin binder in a mass ratio of 10: (1-5). According to the technical scheme, the problems of insufficient lightness and thinness and relatively low peel strength of the lithium battery diaphragm in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a method for preparing an ultra-thin lithium battery separator with high peel strength. Background Art

[0002] With the rapid progress of modern society and the significant improvement in the quality of life, people have put forward increasingly stringent requirements for the performance of energy storage devices, especially lithium-ion batteries. These requirements not only reflect the pace of scientific and technological progress, but also reflect consumers' urgent need for efficient, safe and reliable energy solutions. Specifically, the performance improvement of lithium-ion batteries mainly focuses on three aspects: fast charging capability, cycle stability, and safety and reliability. In order to improve these performances, functional coatings are usually applied on one or both sides of polyolefin separators. However, the coatings have low peel strength and are easy to fall off, which is not conducive to the stability and safety of the internal structure of the battery. At the same time, the coating of lithium battery separators is developing towards a trend of being lighter and thinner.

[0003] To this end, lithium battery separator and coating technologies are constantly innovating, and there is a need to obtain lithium battery separators that are lighter and thinner and have higher coating peel strength. Summary of the invention

[0004] The present invention provides a method for preparing an ultra-thin lithium battery separator with high peel strength, which solves the problems of insufficient thinness and low peel strength of the lithium battery separator coating in the related art.

[0005] The technical solution of the present invention is as follows: The present invention provides an ultra-thin lithium battery separator with high peel strength, comprising a base film and a coating arranged on one side or both sides of the base film, wherein the coating is prepared from a slurry; The slurry comprises the following components in parts by weight: 20-40 parts of aluminum oxide, 40-80 parts of water, 0.3-0.5 parts of a binder, 0.05-0.1 parts of a dispersant, 0.5-1 parts of a thickener, and 0.05-0.1 parts of a wetting agent; The binder comprises an emulsion type polyacrylate binder and a solution type sulfobutyl-β-cyclodextrin binder in a mass ratio of 10:1-5.

[0006] As a further technical solution, the particle size D50 of the emulsion type polyacrylate binder is 100-200 nm, and the solid content is 40%-50%; the solid content of the solution type sulfobutyl-β-cyclodextrin binder is 60%-70%.

[0007] As a further technical solution, the particle size D50 of the aluminum oxide is 0.2-0.3 μm, D90 is 0.6-0.7 μm, D99 is 0.9-1.0 μm, and the specific surface area is 10-15 m 2 / g.

[0008] In the present invention, the particle size D50 is 0.2-0.3 μm, D90 is 0.6-0.7 μm, D99 is 0.9-1.0 μm, and the specific surface area is 10-15 m 2 / g of alumina is paired with an emulsion-type polyacrylate binder with a particle size D50 of 100~200nm. Due to their small size, the latex particles of the small-particle emulsion can more delicately fit the microscopic undulations and depressions on the surface of the large specific surface area ceramic powder, achieving a closer physical contact. The numerous small-particle latex particles are like fine "tentacles" that can penetrate into every corner and active site on the surface of the alumina powder, thereby increasing the effective bonding contact area. In terms of chemical interactions, the high dispersibility of the small-particle emulsion makes it easier for its functional groups to chemically bond or intermolecularly interact with the corresponding active sites on the surface of the ceramic powder. As the number of latex particles per unit weight increases, the number of functional groups also increases accordingly, further strengthening the chemical interaction with the surface of the alumina powder. This multi-directional, multi-level close physical contact and chemical interaction work synergistically, making the bond between the small-particle emulsion polyacrylate binder and the small-particle, large-specific-surface-area alumina powder stronger. At the same time, combined with the solution-type sulfobutyl-β-cyclodextrin binder, the coating peel strength of the lithium battery separator is significantly improved, and the ionic conductivity and heat resistance of the lithium battery separator are also improved.

[0009] As a further technical solution, the dispersant includes one or more of ammonium polyacrylate, polyacrylic acid, and sodium polyacrylate; The thickener includes a carboxymethyl cellulose solution; the solid content of the thickener is 1% to 5%; The wetting agents include acetylenic diols and small molecule modified polysiloxane polymers.

[0010] As a further technical solution, the method for preparing the slurry comprises the following steps: S1. First, a dispersant, water and alumina are mixed to obtain a mixture; S2. Add the remaining components of the slurry into the mixture and mix them to obtain a slurry.

[0011] As a further technical solution, in step S1, the mixing time is 20-40 min, the rotation speed is 1500-3000 r / min, and the revolution speed is 20-60 r / min; In step S2, the mixing is performed under a vacuum environment of 0.06-0.08 kPa, the rotation speed of the mixing is 2000-4000 r / min, the revolution speed is 20-60 r / min, the ultrasonic frequency is 5-8 kHz, and the mixing time is 20-40 min.

[0012] As a further technical solution, the alumina is 4-methoxybenzoic acid modified alumina.

[0013] As a further technical solution, the preparation method of the 4-methoxybenzoic acid modified alumina comprises the following steps: 4-methoxybenzoic acid is dissolved, mixed with alumina, and dried to obtain 4-methoxybenzoic acid-modified alumina.

[0014] As a further technical solution, the mass ratio of the 4-methoxybenzoic acid to the alumina is 0.04~0.08:1.

[0015] In the present invention, 4-methoxybenzoic acid is used to perform surface modification treatment on aluminum oxide, thereby further improving the ion conductivity of the lithium battery separator.

[0016] The present invention also provides a method for preparing a high peel strength ultra-thin lithium battery separator, comprising the following steps: The slurry is coated on one side or both sides of the base film and dried to obtain a lithium battery separator.

[0017] As a further technical solution, the coating speed is 80-120 m / min; The drying temperature is 80-100° C. and the drying time is 20-30 seconds.

[0018] As a further technical solution, the thickness of the coating is 1 μm.

[0019] In the present invention, the thickness of the coating is only 1 μm, making the diaphragm thinner and lighter. The reduction in the thickness of the diaphragm can reduce the overall volume and weight of the battery, thereby increasing the energy density per unit volume and per unit weight. This is crucial for electric vehicles, portable electronic devices, and other applications that require lightweight and high energy density. The thinner diaphragm can also reduce the migration distance of lithium ions inside the battery, thereby reducing internal resistance. The thinner diaphragm can effectively promote the migration of lithium ions, thereby reducing the deposition of lithium metal on the negative electrode, reducing the risk of "lithium dendrites" in lithium batteries, and increasing battery life.

[0020] The working principle and beneficial effects of the present invention are: In the present invention, aluminum oxide is used as the main active material of the coating, and an emulsion-type polyacrylate binder and a solution-type sulfobutyl-β-cyclodextrin binder are added for synergy, so that when the diaphragm is subjected to external force, the coating and the base film can maintain good bonding and are not easily peeled off. By optimizing the raw material formula of the surface coating of the lithium battery diaphragm, a lighter and thinner coating is achieved, and at the same time, the peeling strength of the coating of the lithium battery diaphragm is significantly improved. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the following examples and comparative examples, alumina was purchased from Suzhou Jinyi New Material Technology Co., Ltd.; The emulsion polyacrylate binder was purchased from Suzhou Derby New Energy Technology Co., Ltd.; The solvent in the solution-type sulfobutyl-β-cyclodextrin binder and the solution-type carboxymethyl-β-cyclodextrin binder is water; Alkyne diol and small molecule modified polysiloxane polymer were purchased from Hunan Yueyang Kaimen Waterborne Additive Co., Ltd.; The thickener is CMC solution; Ammonium polyacrylate was purchased from Shanghai Sunray Polymer Materials Technology Co., Ltd.

[0023] Example 1 An ultra-thin lithium battery separator with high peel strength comprises a base film and a coating arranged on one side of the base film, wherein the coating is prepared from a slurry; The slurry includes the following components in parts by weight: alumina (particle size D50 is 0.225 μm, D90 is 0.678 μm, D99 is 0.998 μm, specific surface area is 13.15 m 2 / g) 20 parts, water 79.1 parts, binder 0.3 parts, ammonium polyacrylate 0.05 parts, thickener (solid content 1%) 0.5 parts, acetylene glycol and small molecule modified polysiloxane polymer 0.05 parts; The binder is an emulsion type polyacrylate binder (particle size D50 is 175nm, solid content is 45%) and a solution type sulfobutyl-β-cyclodextrin binder (solid content is 60%) in a mass ratio of 10:3; The method for preparing the slurry comprises the following steps: S1. First, ammonium polyacrylate, water and aluminum oxide were mixed in a double planetary mixer XFZH-30L at a rotation speed of 1500 r / min and a revolution speed of 20 r / min for 20 min to obtain a mixture; S2. Add the remaining components of the slurry to the mixture, and mix for 20 min at a rotation speed of 2000 r / min, a revolution speed of 20 r / min, and an ultrasonic frequency of 5 kHz in a vacuum environment of 0.06 kPa to obtain a slurry; A method for preparing an ultra-thin lithium battery separator with high peel strength comprises the following steps: The slurry was coated on one side of a PE film having a thickness of 7 μm at a coating speed of 80 m / min, and dried at 80° C. for 30 s to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 1 μm.

[0024] Example 2 An ultra-thin lithium battery separator with high peel strength comprises a base film and a coating arranged on one side of the base film, wherein the coating is prepared from a slurry; The slurry includes the following components in parts by weight: alumina (particle size D50 is 0.279 μm, D90 is 0.696 μm, D99 is 0.988 μm, specific surface area is 13.5 m 2 / g) 30 parts, water 68.7 parts, binder 0.4 parts, ammonium polyacrylate 0.075 parts, thickener (solid content 3%) 0.75 parts, acetylene glycol and small molecule modified polysiloxane polymer 0.075 parts; The binder is an emulsion type polyacrylate binder (particle size D50 is 170nm, solid content is 45%) and a solution type sulfobutyl-β-cyclodextrin binder (solid content is 60%) in a mass ratio of 10:5; The method for preparing the slurry comprises the following steps: S1. First, ammonium polyacrylate, water and aluminum oxide were mixed in a double planetary mixer XFZH-30L at a rotation speed of 2000 r / min and a revolution speed of 40 r / min for 30 min to obtain a mixture; S2. Add the remaining components of the slurry to the mixture, and mix for 30 min at a rotation speed of 3000 r / min, a revolution speed of 40 r / min, and an ultrasonic frequency of 5 kHz in a vacuum environment of 0.07 kPa to obtain a slurry; A method for preparing an ultra-thin lithium battery separator with high peel strength comprises the following steps: The slurry was coated on one side of a PE film having a thickness of 7 μm at a coating speed of 100 m / min, and dried at 90° C. for 25 seconds to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 1 μm.

[0025] Example 3 An ultra-thin lithium battery separator with high peel strength comprises a base film and a coating arranged on one side of the base film, wherein the coating is prepared from a slurry; The slurry includes the following components in parts by weight: alumina (particle size D50 is 0.253 μm, D90 is 0.642 μm, D99 is 0.955 μm, specific surface area is 14.7 m 2 / g) 40 parts, water 58.3 parts, binder 0.5 parts, ammonium polyacrylate 0.1 parts, thickener (solid content 5%) 1 part, acetylene glycol and small molecule modified polysiloxane polymer 0.1 parts; The binder is an emulsion type polyacrylate binder (particle size D50 is 152nm, solid content is 47.6%) and a solution type sulfobutyl-β-cyclodextrin binder (solid content is 70%) in a mass ratio of 10:1; The method for preparing the slurry comprises the following steps: S1. First, ammonium polyacrylate, water and aluminum oxide were mixed in a double planetary mixer XFZH-30L at a rotation speed of 3000 r / min and a revolution speed of 60 r / min for 40 min to obtain a mixture; S2. Add the remaining components of the slurry to the mixture, and mix for 40 min at a rotation speed of 4000 r / min, a revolution speed of 60 r / min, and an ultrasonic frequency of 5 kHz in a vacuum environment of 0.08 kPa to obtain a slurry; A method for preparing an ultra-thin lithium battery separator with high peel strength comprises the following steps: The slurry was coated on one side of a PE film having a thickness of 7 μm at a coating speed of 120 m / min, and dried at 100° C. for 20 seconds to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 2 μm.

[0026] Example 4 The difference between this embodiment and embodiment 1 is that the aluminum oxide is also subjected to benzoic acid modification treatment, and the modification treatment method comprises the following steps: 0.04 g of benzoic acid was dissolved in 5 mL of ethanol, mixed with 1 g of alumina, and dried to obtain benzoic acid-modified alumina.

[0027] Example 5 The difference between this embodiment and embodiment 1 is that the aluminum oxide is also modified by 4-methoxybenzoic acid, and the modification method comprises the following steps: 0.04 g of 4-methoxybenzoic acid was dissolved in 5 mL of ethanol, mixed with 1 g of alumina, and dried to obtain 4-methoxybenzoic acid-modified alumina.

[0028] Example 6 The difference between this embodiment and embodiment 1 is that the aluminum oxide is also modified by 4-methoxybenzoic acid, and the modification method comprises the following steps: 0.08 g of 4-methoxybenzoic acid was dissolved in 5 mL of ethanol, mixed with 1 g of alumina, and dried to obtain 4-methoxybenzoic acid-modified alumina.

[0029] Example 7 The difference between this embodiment and embodiment 1 is that the aluminum oxide (particle size D50 is 0.225 μm, D90 is 0.678 μm, D99 is 0.998 μm, and specific surface area is 13.15 m 2 / g) was replaced by alumina (particle size D50 is 0.289μm, D90 is 0.682μm, D99 is 0.948μm, specific surface area is 14.1m 2 / g); The emulsion type polyacrylate binder (particle size D50 is 175 nm, solid content is 45%) is replaced by the emulsion type polyacrylate binder (particle size D50 is 325 nm, solid content is 45%).

[0030] Example 8 The difference between this embodiment and embodiment 1 is that the aluminum oxide (particle size D50 is 0.225 μm, D90 is 0.678 μm, D99 is 0.998 μm, and specific surface area is 13.15 m 2 / g) was replaced by alumina (particle size D50 is 0.587μm, D90 is 1.315μm, D99 is 2.325μm, specific surface area is 5.8m 2 / g).

[0031] Comparative Example 1 The difference between this comparative example and Example 7 is that the solution-type sulfobutyl-β-cyclodextrin binder is replaced by a solution-type polyacrylate binder (Tg is 180° C.).

[0032] Comparative Example 2 The difference between this comparative example and Example 7 is that the solution-type sulfobutyl-β-cyclodextrin binder is replaced by a solution-type carboxymethyl-β-cyclodextrin binder.

[0033] Comparative Example 3 The only difference between this comparative example and Example 7 is that the binder is an emulsion-type polyacrylate binder (particle size D50 is 325 nm, solid content is 45%).

[0034] Comparative Example 4 The difference between this comparative example and Example 7 is that the binder is a solution-type sulfobutyl-β-cyclodextrin binder (solid content is 60%).

[0035] The lithium battery separators prepared in Examples 1 to 8 and Comparative Examples 1 to 4 were tested as follows: Air permeability and ionic conductivity test: Tested in accordance with standard GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries".

[0036] Shrinkage test: After covering the upper and lower parts of the lithium battery separator with a piece of A4 paper, place it in an oven at 130°C for 1 hour, and then measure the transverse (TD) shrinkage and longitudinal (MD) shrinkage of the lithium battery separator.

[0037] Liquid absorption rate and liquid retention rate test: Cut 3 diaphragm samples with an area of ​​50mm×50mm. For diaphragms with a width of less than 50mm, cut 3 full-width diaphragm samples with a length of 50mm, with the side length accurate to 1mm; Weigh the cut sample and record it as m 1 , soak the weighed diaphragm in the electrolyte for 30 minutes; spread a layer of clean industrial wipe paper (area greater than 150mm×150mm) on a flat table, take out the sample, quickly place it on the industrial wipe paper, and use another piece of industrial wipe paper to gently press and wipe the free electrolyte on the surface of the diaphragm until the granular electrolyte is no longer visible to the naked eye; weigh the mass of the sample after wiping dry m 2 , then leave it for one hour and weigh it, record it as m 3 .

[0038] The liquid absorption rate and liquid retention rate of the diaphragm are calculated according to the following formulas: Liquid absorption rate = [(m 2 -m 1 ) / m 1 ]×100%; Liquid retention rate = [(m 3 -m 1 ) / m 1 ]×100%; Where: m 1 is the weight of the diaphragm after cutting, in grams (g); m 2 is the weight of the diaphragm after soaking, in grams (g); m 3 The weight of the diaphragm after being soaked and left for 1 hour, in grams (g); Take the average value of 3 parallel sample tests and retain the calculation result to one decimal place.

[0039] Peel strength test: Cut 3 samples with a width of 15 mm along the longitudinal direction of the diaphragm, stick the cut samples on a glass slide with double-sided tape, fold the free end of the sample 180° after sticking, peel off the adhesive surface about 10~20 mm by hand, and test the peel strength using a tensile testing machine.

[0040] The results are shown in Tables 1 to 3 below.

[0041] Table 1 Diaphragm performance test results

[0042] Table 2 Test results of membrane ion conductivity

[0043] Table 3 Test results of membrane peel strength performance

[0044] Compared with Comparative Examples 1 to 4, the coating peel strength of the lithium battery separator prepared in Example 7 is higher, indicating that the composite use of aluminum oxide, emulsion-type polyacrylate binder and solution-type sulfobutyl-β-cyclodextrin binder achieves a lighter and thinner coating, while significantly improving the peel strength of the lithium battery separator coating.

[0045] Compared with Examples 7 and 8, the coating peel strength, membrane liquid absorption rate, liquid retention rate and ion conductivity of the lithium battery separator prepared in Example 1 are higher, and the shrinkage rate of the lithium battery separator is lower, indicating that the particle size D50 is 0.2-0.3 μm, D90 is 0.6-0.7 μm, D99 is 0.9-1.0 μm, and the specific surface area is 10-15 m 2 / g of aluminum oxide is combined with an emulsion-type polyacrylate binder with a particle size D50 of 100~200nm, and a solution-type sulfobutyl-β-cyclodextrin binder, which improves the coating peeling strength of the lithium battery separator and also improves the ionic conductivity, heat resistance and other properties of the lithium battery separator.

[0046] Compared with Example 1 and Example 4, the lithium battery separators prepared in Examples 5 and 6 use 4-methoxybenzoic acid to perform surface modification treatment on aluminum oxide, thereby further improving the ionic conductivity of the lithium battery separator.

[0047] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A high peel strength ultra-thin lithium battery separator, characterized in that: It comprises a base film and a coating arranged on one side or both sides of the base film, wherein the coating is prepared from a slurry; The slurry comprises the following components in parts by weight: 20-40 parts of aluminum oxide, 40-80 parts of water, 0.3-0.5 parts of a binder, 0.05-0.1 parts of a dispersant, 0.5-1 parts of a thickener, and 0.05-0.1 parts of a wetting agent; The binder comprises an emulsion type polyacrylate binder and a solution type sulfobutyl-β-cyclodextrin binder in a mass ratio of 10:1-5.

2. The high peel strength ultra-thin lithium battery separator according to claim 1, characterized in that: The particle size D50 of the emulsion type polyacrylate binder is 100-200 nm, and the solid content is 40%-50%; the solid content of the solution type sulfobutyl-β-cyclodextrin binder is 60%-70%.

3. The high peel strength ultra-thin lithium battery separator according to claim 1, characterized in that: The particle size D50 of the alumina is 0.2-0.3 μm, D90 is 0.6-0.7 μm, D99 is 0.9-1.0 μm, and the specific surface area is 10-15 m 2 / g.

4. The high peel strength ultra-thin lithium battery separator according to claim 1, characterized in that: The dispersant includes one or more of ammonium polyacrylate, polyacrylic acid, and sodium polyacrylate; The thickener includes a carboxymethyl cellulose solution; the solid content of the thickener is 1% to 5%; The wetting agents include acetylenic diols and small molecule modified polysiloxane polymers.

5. The high peel strength ultra-thin lithium battery separator according to claim 1, characterized in that: The preparation method of the slurry comprises the following steps: S1. First, a dispersant, water and alumina are mixed to obtain a mixture; S2. Add the remaining components of the slurry into the mixture and mix them to obtain a slurry.

6. The high peel strength ultra-thin lithium battery separator according to claim 5, characterized in that: In step S1, the mixing time is 20-40 min, the rotation speed is 1500-3000 r / min, and the revolution speed is 20-60 r / min; In step S2, the mixing is performed under a vacuum environment of 0.06-0.08 kPa, the rotation speed of the mixing is 2000-4000 r / min, the revolution speed is 20-60 r / min, the ultrasonic frequency is 5-8 kHz, and the mixing time is 20-40 min.

7. The high peel strength ultra-thin lithium battery separator according to claim 5, characterized in that: The alumina is 4-methoxybenzoic acid modified alumina.

8. The high peel strength ultra-thin lithium battery separator according to claim 7, characterized in that: The preparation method of the 4-methoxybenzoic acid modified alumina comprises the following steps: 4-methoxybenzoic acid is dissolved, mixed with alumina, and dried to obtain 4-methoxybenzoic acid-modified alumina.

9. The high peel strength ultra-thin lithium battery separator according to claim 8, characterized in that: The mass ratio of the 4-methoxybenzoic acid to the aluminum oxide is 0.04-0.08:

1.

10. The method for preparing a high peel strength ultra-thin lithium battery separator according to any one of claims 1 to 9, characterized in that: The following steps are involved: The slurry is coated on one side or both sides of the base film and dried to obtain a lithium battery separator.

Images