Preparation method of high-peeling-strength ultra-thin lithium battery diaphragm

Abstract

This invention relates to the field of battery separator technology and proposes a method for preparing a high peel strength ultrathin lithium battery separator. The high peel strength ultrathin lithium battery separator includes a base film and a coating disposed on one or both sides of the base film. The coating is prepared from a slurry, which includes the following components in parts by weight: 20-40 parts alumina, 40-80 parts water, 0.3-0.5 parts binder, 0.05-0.1 parts dispersant, 0.5-1 parts thickener, and 0.05-0.1 parts wetting agent. The binder includes an emulsion-type polyacrylate binder and a solution-type sulfobutyl-β-cyclodextrin binder with a mass ratio of 10:1-5. This technical solution solves the problems of insufficient thinness and low peel strength in related lithium battery separators.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, and more specifically, to a method for preparing an ultrathin lithium battery separator with high peel strength. Background Technology

[0002] With the rapid progress of modern society and the significant improvement in living standards, people have placed increasingly stringent demands on the performance of energy storage devices, especially lithium-ion batteries. These demands not only reflect the pace of 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. To improve these performances, functional coatings are usually applied to one or both sides of the polyolefin separator. However, these coatings suffer from low peel strength and are prone to detachment, which is detrimental to the stability and safety of the battery's internal structure. At the same time, the coatings on lithium battery separators are trending towards thinner and lighter designs.

[0003] Therefore, lithium battery separator and coating technologies are constantly being innovated, and there is a need to obtain thinner lithium battery separators with higher coating peel strength. Summary of the Invention

[0004] This invention proposes a method for preparing an ultrathin lithium battery separator with high peel strength, which solves the problems of insufficient thinness and low peel strength of lithium battery separator coatings in related technologies.

[0005] The technical solution of the present invention is as follows:

[0006] This invention proposes a high peel strength ultrathin lithium battery separator, comprising a base film and a coating disposed on one or both sides of the base film, wherein the coating is prepared from a slurry;

[0007] The slurry comprises the following components in parts by weight: 20-40 parts alumina, 40-80 parts water, 0.3-0.5 parts binder, 0.05-0.1 parts dispersant, 0.5-1 parts thickener, and 0.05-0.1 parts wetting agent;

[0008] The binder includes an emulsion-type polyacrylate binder and a solution-type sulfobutyl-β-cyclodextrin binder with a mass ratio of 10:1 to 5.

[0009] As a further technical solution, the emulsion-type polyacrylate binder has a particle size D50 of 100~200nm and a solid content of 40%~50%; the solution-type sulfobutyl-β-cyclodextrin binder has a solid content of 60%~70%.

[0010] As a further technical solution, the alumina has a particle size D50 of 0.2~0.3μm, a D90 of 0.6~0.7μm, a D99 of 0.9~1.0μm, and a specific surface area of ​​10~15m². 2 / g.

[0011] In this invention, particle sizes D50 are 0.2~0.3μm, D90 is 0.6~0.7μm, D99 is 0.9~1.0μm, and the specific surface area is 10~15m². 2 Alumina per gram, combined with an emulsion-type polyacrylate binder with a particle size D50 of 100-200 nm, allows the small-particle-size emulsion to more precisely adhere to the microscopic undulations and depressions on the surface of ceramic powders with large specific surface areas, achieving a closer physical contact. The numerous small-particle latex particles act like fine "tentacles," penetrating every corner and active site on the alumina powder surface, thus increasing the effective bonding contact area. Regarding chemical interactions, the high dispersibility of the small-particle-size emulsion makes it easier for its functional groups to chemically bond or form intermolecular forces with the corresponding active sites on the ceramic powder surface. 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 alumina powder surface. This multi-directional, multi-layered close physical contact and chemical interaction synergistic effect makes the bond between the small-particle-size emulsion-type polyacrylate binder and the small-particle-size alumina powder with a large specific surface area more solid. At the same time, the combination with the solution-type sulfobutyl-β-cyclodextrin binder significantly improves the coating peel strength of the lithium battery separator, as well as the ionic conductivity and heat resistance of the lithium battery separator.

[0012] As a further technical solution, the dispersant includes one or more of ammonium polyacrylate, polyacrylic acid, and sodium polyacrylate;

[0013] The thickener comprises a carboxymethyl cellulose solution; the solid content of the thickener is 1% to 5%.

[0014] The wetting agent includes acetylenic diol and small molecule modified polysiloxane polymer.

[0015] As a further technical solution, the method for preparing the slurry includes the following steps:

[0016] S1. First, mix the dispersant, water, and alumina to obtain a mixture;

[0017] S2. Add the remaining components of the slurry to the mixture and mix to obtain the slurry.

[0018] 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;

[0019] In step S2, the mixing is carried out in a vacuum environment of 0.06~0.08kPa, the rotation speed of the mixing is 2000~4000r / min, the revolution speed is 20~60r / min, the ultrasonic frequency is 5~8kHz, and the mixing time is 20~40min.

[0020] As a further technical solution, the alumina is 4-methoxybenzoic acid modified alumina.

[0021] As a further technical solution, the preparation method of the 4-methoxybenzoic acid modified alumina includes the following steps:

[0022] 4-Methoxybenzoic acid was dissolved and mixed with aluminum oxide, then dried to obtain 4-methoxybenzoic acid-modified aluminum oxide.

[0023] As a further technical solution, the mass ratio of 4-methoxybenzoic acid to alumina is 0.04~0.08:1.

[0024] In this invention, 4-methoxybenzoic acid is used to modify the surface of alumina, which further improves the ionic conductivity of the lithium battery separator.

[0025] This invention also proposes a method for preparing a high peel strength ultrathin lithium battery separator, comprising the following steps:

[0026] The slurry is coated on one or both sides of the base film and dried to obtain a lithium battery separator.

[0027] As a further technical solution, the coating speed is 80~120m / min;

[0028] The drying temperature is 80~100℃ and the time is 20~30s.

[0029] As a further technical solution, the thickness of the coating is 1 μm.

[0030] In this invention, the coating thickness of only 1 μm allows for a thinner and lighter separator. Reduced separator thickness lowers the overall volume and weight of the battery, thereby increasing the energy density per unit volume and weight. This is crucial for electric vehicles, portable electronic devices, and other applications requiring lightweight construction and high energy density. The thinner separator also reduces the migration distance of lithium ions within the battery, thus lowering internal resistance. Furthermore, the thinner separator effectively promotes lithium ion migration, reducing lithium metal deposition on the negative electrode, mitigating the risk of lithium dendrite formation, and improving battery life.

[0031] The working principle and beneficial effects of this invention are as follows:

[0032] In this invention, alumina is used as the main active material for the coating, and emulsion-type polyacrylate binder and solution-type sulfobutyl-β-cyclodextrin binder are added synergistically to ensure that the coating and the base film can maintain good adhesion when the separator is subjected to external force, and it is not easy to peel off. By optimizing the raw material formula of the lithium battery separator surface coating, a thinner coating is achieved, while significantly improving the coating peel strength of the lithium battery separator. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] In the following examples and comparative examples, alumina was purchased from Suzhou Jinyi New Material Technology Co., Ltd.;

[0035] The emulsion-type polyacrylate adhesive was purchased from Suzhou Derby New Energy Technology Co., Ltd.

[0036] The solvent in both solution-type sulfobutyl-β-cyclodextrin binders and solution-type carboxymethyl-β-cyclodextrin binders is water.

[0037] The acetylenic diol and small molecule modified polysiloxane polymer were purchased from Hunan Yueyang Kaimen Waterborne Additives Co., Ltd.

[0038] The thickener is a CMC solution;

[0039] Ammonium polyacrylate was purchased from Shanghai Sanrui Polymer Materials Technology Co., Ltd.

[0040] Example 1

[0041] A high peel strength ultrathin lithium battery separator includes a base film and a coating disposed on one side of the base film, the coating being prepared from a slurry;

[0042] The slurry comprises the following components in parts by weight: alumina (particle size D50 0.225 μm, D90 0.678 μm, D99 0.998 μm, specific surface area 13.15 m²). 2 20 parts ( / g), 79.1 parts water, 0.3 parts binder, 0.05 parts ammonium polyacrylate, 0.5 parts thickener (1% solid content), and 0.05 parts acetylenic diol and small molecule modified polysiloxane polymer;

[0043] The binders are an emulsion-type polyacrylate binder (particle size D50 of 175 nm and solid content of 45%) with a mass ratio of 10:3 and a solution-type sulfobutyl-β-cyclodextrin binder (solid content of 60%).

[0044] The method for preparing the slurry includes the following steps:

[0045] S1. First, mix ammonium polyacrylate, water, and alumina 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 minutes to obtain a mixture.

[0046] S2. Add the remaining components of the slurry to the mixture, and mix for 20 minutes in a vacuum environment of 0.06 kPa with a rotation speed of 2000 r / min, a revolution speed of 20 r / min, and an ultrasonic frequency of 5 kHz to obtain the slurry.

[0047] A method for preparing a high-peel-strength ultrathin lithium-ion battery separator includes the following steps:

[0048] A slurry was coated on one side of a PE film with a thickness of 7 μm at a coating speed of 80 m / min, and dried at 80℃ for 30 s to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 1 μm.

[0049] Example 2

[0050] A high peel strength ultrathin lithium battery separator includes a base film and a coating disposed on one side of the base film, the coating being prepared from a slurry;

[0051] The slurry comprises the following components in parts by weight: alumina (particle size D50 0.279 μm, D90 0.696 μm, D99 0.988 μm, specific surface area 13.5 m²). 2 30 parts ( / g), 68.7 parts water, 0.4 parts binder, 0.075 parts ammonium polyacrylate, 0.75 parts thickener (solid content 3%), and 0.075 parts acetylenic diol and small molecule modified polysiloxane polymer;

[0052] The binders are an emulsion-type polyacrylate binder (particle size D50 of 170 nm and solid content of 45%) with a mass ratio of 10:5 and a solution-type sulfobutyl-β-cyclodextrin binder (solid content of 60%).

[0053] The method for preparing the slurry includes the following steps:

[0054] S1. First, mix ammonium polyacrylate, water, and alumina 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 minutes to obtain a mixture.

[0055] S2. Add the remaining components of the slurry to the mixture, and mix for 30 minutes in a vacuum environment of 0.07 kPa with a rotation speed of 3000 r / min, a revolution speed of 40 r / min, and an ultrasonic frequency of 5 kHz to obtain the slurry.

[0056] A method for preparing a high-peel-strength ultrathin lithium-ion battery separator includes the following steps:

[0057] A slurry was coated on one side of a PE film with a thickness of 7 μm at a coating speed of 100 m / min and dried at 90 °C for 25 s to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 1 μm.

[0058] Example 3

[0059] A high peel strength ultrathin lithium battery separator includes a base film and a coating disposed on one side of the base film, the coating being prepared from a slurry;

[0060] The slurry comprises the following components in parts by weight: alumina (particle size D50 0.253 μm, D90 0.642 μm, D99 0.955 μm, specific surface area 14.7 m²). 2 40 parts ( / g), 58.3 parts water, 0.5 parts binder, 0.1 parts ammonium polyacrylate, 1 part thickener (solid content 5%), and 0.1 parts acetylenic diol and small molecule modified polysiloxane polymer;

[0061] The binders are an emulsion-type polyacrylate binder (particle size D50 of 152 nm and solid content of 47.6%) with a mass ratio of 10:1 and a solution-type sulfobutyl-β-cyclodextrin binder (solid content of 70%).

[0062] The method for preparing the slurry includes the following steps:

[0063] S1. First, mix ammonium polyacrylate, water, and alumina 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 minutes to obtain a mixture.

[0064] S2. Add the remaining components of the slurry to the mixture, and mix for 40 minutes in a vacuum environment of 0.08 kPa with a rotation speed of 4000 r / min, a revolution speed of 60 r / min, and an ultrasonic frequency of 5 kHz to obtain the slurry.

[0065] A method for preparing a high-peel-strength ultrathin lithium-ion battery separator includes the following steps:

[0066] A slurry was coated on one side of a PE film with a thickness of 7 μm at a coating speed of 120 m / min and dried at 100 °C for 20 s to obtain a lithium battery separator; the coating thickness of the lithium battery separator was 2 μm.

[0067] Example 4

[0068] The only difference between this embodiment and Embodiment 1 is that the alumina has undergone benzoic acid modification treatment. The modification treatment method includes the following steps:

[0069] 0.04 g of benzoic acid was dissolved in 5 mL of ethanol and then mixed with 1 g of aluminum oxide. The mixture was dried to obtain benzoic acid-modified aluminum oxide.

[0070] Example 5

[0071] The only difference between this embodiment and Example 1 is that the alumina has undergone 4-methoxybenzoic acid modification treatment. The modification treatment method includes the following steps:

[0072] 0.04 g of 4-methoxybenzoic acid was dissolved in 5 mL of ethanol and then mixed with 1 g of aluminum oxide. The mixture was dried to obtain 4-methoxybenzoic acid-modified aluminum oxide.

[0073] Example 6

[0074] The only difference between this embodiment and Example 1 is that the alumina has undergone 4-methoxybenzoic acid modification treatment. The modification treatment method includes the following steps:

[0075] 0.08 g of 4-methoxybenzoic acid was dissolved in 5 mL of ethanol and then mixed with 1 g of aluminum oxide. The mixture was dried to obtain 4-methoxybenzoic acid-modified aluminum oxide.

[0076] Example 7

[0077] The only difference between this embodiment and Example 1 is that the alumina (particle size D50 is 0.225 μm, D90 is 0.678 μm, D99 is 0.998 μm, and specific surface area is 13.15 m²) is used. 2 The particle size distribution ( / g) was replaced with alumina (particle size D50 0.289 μm, D90 0.682 μm, D99 0.948 μm, specific surface area 14.1 m²). 2 / g);

[0078] Replace the emulsion-type polyacrylate binder (particle size D50 of 175 nm, solid content of 45%) with an emulsion-type polyacrylate binder (particle size D50 of 325 nm, solid content of 45%).

[0079] Example 8

[0080] The only difference between this embodiment and Example 1 is that the alumina (particle size D50 is 0.225 μm, D90 is 0.678 μm, D99 is 0.998 μm, and specific surface area is 13.15 m²) is used. 2 The particle size distribution ( / g) was replaced with alumina (particle size D50 is 0.587μm, D90 is 1.315μm, D99 is 2.325μm, specific surface area is 5.8m²). 2 / g).

[0081] Comparative Example 1

[0082] The only difference between this comparative example and Example 7 is that the solution-type sulfobutyl-β-cyclodextrin binder is replaced with a solution-type polyacrylate binder (Tg is 180°C).

[0083] Comparative Example 2

[0084] The only difference between this comparative example and Example 7 is that the solution-type sulfobutyl-β-cyclodextrin binder is replaced with a solution-type carboxymethyl-β-cyclodextrin binder.

[0085] Comparative Example 3

[0086] The only difference between this comparative example and Example 7 is that the binder is an emulsion-type polyacrylate binder (particle size D50 is 325nm, solid content is 45%).

[0087] Comparative Example 4

[0088] The only difference between this comparative example and Example 7 is that the binder is a solution-type sulfobutyl-β-cyclodextrin binder (solid content is 60%).

[0089] The lithium battery separators prepared in Examples 1-8 and Comparative Examples 1-4 were subjected to the following tests:

[0090] Air permeability and ionic conductivity tests: Tested according to standard GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries".

[0091] Shrinkage test: After covering the top and bottom of the lithium battery separator with a sheet of A4 paper, place it in an oven at 130°C for 1 hour, and then measure the transverse (TD) shrinkage rate and longitudinal (MD) shrinkage rate of the lithium battery separator.

[0092] Liquid absorption rate and liquid retention rate tests:

[0093] Cut three diaphragm samples with an area of ​​50mm×50mm. For diaphragms with a width of <50mm, cut three full-width diaphragm samples with a length of 50mm, with the side length accurate to 1mm.

[0094] Weigh the cut sample and record it as m1. Immerse the weighed diaphragm in the electrolyte for 30 minutes. Lay a clean industrial wiping paper (area greater than 150mm×150mm) on a flat table. Take out the sample and quickly place it on the industrial wiping paper. Use another industrial wiping paper to gently press and wipe the free electrolyte on the surface of the diaphragm until no particulate electrolyte is visible to the naked eye. Weigh the dried sample as m2, then let it stand for one hour, weigh it again, and record it as m3.

[0095] The diaphragm liquid absorption rate and liquid retention rate are calculated according to the following formulas:

[0096] Liquid absorption rate = [(m2-m1) / m1] × 100%;

[0097] Liquid retention rate = [(m3-m1) / m1]×100%;

[0098] In the formula:

[0099] m1 is the weight of the cut diaphragm in grams (g).

[0100] m2 is the weight of the diaphragm after soaking, in grams (g).

[0101] m3 is the weight of the diaphragm after soaking and standing for 1 hour, in grams (g).

[0102] Take the average value of 3 parallel sample tests, and keep the result to one decimal place.

[0103] Peel strength test: Cut three 15mm wide samples from the diaphragm along the longitudinal direction. Attach the cut samples to a glass slide using double-sided tape. After attaching, fold the free end of the sample 180° and peel off about 10-20mm of the adhesive surface by hand. Test the peel strength using a tensile testing machine.

[0104] The results are shown in Tables 1-3 below.

[0105] Table 1. Test results of diaphragm performance

[0106]

[0107] Table 2. Test results of membrane ionic conductivity

[0108]

[0109] Table 3. Test results of diaphragm peel strength performance

[0110]

[0111] Compared with Comparative Examples 1-4, the lithium battery separator prepared in Example 7 has a higher coating peel strength, indicating that the combined use of alumina, emulsion-type polyacrylate binder and solution-type sulfobutyl-β-cyclodextrin binder achieves a thinner coating and significantly improves the peel strength of the lithium battery separator coating.

[0112] Compared with Examples 7-8, the lithium battery separator prepared in Example 1 has higher coating peel strength, separator liquid absorption rate, liquid retention rate, and ionic conductivity, and lower shrinkage rate. This indicates that the particle size used is D50 of 0.2-0.3 μm, D90 of 0.6-0.7 μm, D99 of 0.9-1.0 μm, and specific surface area of ​​10-15 m². 2 The combination of alumina per g with an emulsion-type polyacrylate binder with a particle size D50 of 100~200nm, along with a solution-type sulfobutyl-β-cyclodextrin binder, improves the coating peel strength of the lithium battery separator, as well as the ionic conductivity, heat resistance, and other properties of the lithium battery separator.

[0113] Compared with Examples 1 and 4, the lithium battery separators prepared in Examples 5 and 6 were further improved by surface modification of alumina with 4-methoxybenzoic acid.

[0114] The above are merely 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 within the protection scope of the present invention.

Claims

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

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

3. The high peel strength ultrathin lithium battery separator according to claim 1, characterized in that, The alumina has a particle size of D50 of 0.2~0.3μm, D90 of 0.6~0.7μm, D99 of 0.9~1.0μm, and a specific surface area of ​​10~15m². 2 / g.

4. The high peel strength ultrathin 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 comprises a carboxymethyl cellulose solution; the solid content of the thickener is 1% to 5%. The wetting agent includes acetylenic diol and small molecule modified polysiloxane polymer.

5. The high peel strength ultrathin lithium battery separator according to claim 1, characterized in that, The method for preparing the slurry includes the following steps: S1. First, mix the dispersant, water, and alumina to obtain a mixture; S2. Add the remaining components of the slurry to the mixture and mix to obtain the slurry.

6. The high peel strength ultrathin 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 carried out in a vacuum environment of 0.06~0.08kPa, the rotation speed of the mixing is 2000~4000r / min, the revolution speed is 20~60r / min, the ultrasonic frequency is 5~8kHz, and the mixing time is 20~40min.

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

8. The high peel strength ultrathin lithium battery separator according to claim 7, characterized in that, The preparation method of the 4-methoxybenzoic acid modified alumina includes the following steps: 4-Methoxybenzoic acid was dissolved and mixed with aluminum oxide, then dried to obtain 4-methoxybenzoic acid-modified aluminum oxide.

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

1.

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

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