阅读说明：本技术 一种锂离子电池隔膜及其制备方法 (lithium ion battery diaphragm and preparation method thereof ) 是由 丁盛巍 刘婵 侯敏 曹辉 于 2019-08-30 设计创作，主要内容包括：本发明提出一种锂离子电池隔膜,包括基膜,还包括聚偏氟乙烯PVDF共聚物混合涂层,所述混合涂层由PVDF1和PVDF2两种共聚物浆料混合而成；其中PVDF1和PVDF2在混合浆料中所占PVDF质量比是PVDF1为70％-95％,PVDF2为5％-30％。本发明还提出了一种制备上述锂离子电池隔膜的方法。本发明提出的锂离子电池隔膜及其制备方法,通过不同HFP占比的合理配比,既改善了电池的粘结力,降低PVDF使用量,降低工艺条件,提升了效率,透气增加小,而且通过PVDF共聚物溶胀性,提高保液性,提高离子电导率,降低电池内部游离态电解液,提升安全性。(The invention provides a lithium ion battery diaphragm, which comprises a base film and a polyvinylidene fluoride PVDF copolymer mixed coating, wherein the mixed coating is formed by mixing two copolymer slurries of PVDF1 and PVDF 2; wherein the mass ratio of PVDF1 to PVDF2 in the mixed slurry is 70-95% of PVDF1 and 5-30% of PVDF 2. The invention also provides a method for preparing the lithium ion battery diaphragm. According to the lithium ion battery diaphragm and the preparation method thereof, the reasonable proportion of different HFP accounts is adopted, so that the cohesive force of the battery is improved, the usage amount of PVDF is reduced, the process conditions are reduced, the efficiency is improved, the ventilation is increased slightly, and the liquid retention property, the ionic conductivity and the free electrolyte in the battery are improved and the safety is improved through the swelling property of the PVDF copolymer.)

1. the lithium ion battery diaphragm comprises a base film and is characterized by also comprising a polyvinylidene fluoride PVDF copolymer mixed coating, wherein the mixed coating is formed by mixing two copolymer slurries of PVDF1 and PVDF 2; wherein the mass ratio of PVDF1 to PVDF2 in the mixed slurry is 70-95% of PVDF1 and 5-30% of PVDF 2.

2. the lithium ion battery separator according to claim 1, wherein said PVDF1 is a vinylidene fluoride copolymer PVDF-HFP, wherein hexafluoropropylene HFP is present in a ratio of 4% to 8%; PVDF2 is vinylidene fluoride copolymer PVDF-HFP, wherein the proportion of hexafluoropropylene HFP is 13% -18%.

3. The lithium ion battery separator according to claim 1, wherein the coating comprises PVDF1 and PVDF2 copolymer mixed slurry, dispersant, thickener, binder, etc.; wherein, the solid content in the slurry is 5 to 15 percent of mixed slurry of PVDF1 and PVDF 2; 1 to 10 percent of binder, 0.5 to 5 percent of dispersant and 0.5 to 3 percent of thickener.

4. the lithium ion battery separator according to claim 3, wherein the dispersant is at least one of silicates, alkali metal phosphates, triethylhexylphosphoric acid modified polyether polymers, fatty alcohols, sodium polyethylene glycol alkyl aryl ether sulfonate, alkylphenol polyvinyl ether, polyoxyethylene alkyl phenol ether, and sodium polyacrylate.

5. the lithium ion battery separator of claim 3, wherein the thickener is at least one of sodium carboxymethylcellulose, polyallyl alcohol, polyvinyl alcohol, polyethylene glycol, povidone, and carboxymethylcellulose.

6. The lithium ion battery separator according to claim 3, wherein the binder is at least one of polyacrylate, polyethylacrylate, polybutylacrylate, and alpha-cyanoacrylate.

7. The lithium ion battery separator according to claim 1, wherein the base film is at least one of a polyethylene base film, a polypropylene base film, a polyethylene ceramic film, and a polypropylene ceramic film.

8. The lithium ion battery separator according to claim 1, wherein the polyvinylidene fluoride PVDF copolymer hybrid coating is a single-sided or double-sided coating, and the coating thickness is 1-10 um.

9. the lithium ion battery separator according to claim 1, wherein the base film has a thickness of 5-30 um.

10. A method of making the lithium ion battery separator of any of claims 1-9, comprising the steps of:

(a) preparing polyvinylidene fluoride PVDF copolymer mixed coating slurry;

(b) spraying or rolling polyvinylidene fluoride PVDF copolymer mixed slurry on at least one surface of the battery diaphragm; the coating thickness is 1-5um, and the coating amount is 0.3-0.8g per square meter per surface;

(c) Drying at 30-60 deg.C.

11. The method for preparing a lithium ion battery separator according to claim 10, wherein the preparation of the polyvinylidene fluoride (PVDF) copolymer hybrid coating slurry in the step (a) comprises the following steps:

(1) Preparing polyvinylidene fluoride PVDF copolymer mixed slurry: two PVDF copolymers were weighed in mass ratios: 70-95% of PVDF1 and 5-30% of PVDF 2;

(2) Preparing a thickening agent: adding a thickening agent into deionized water to prepare a thickening agent solution with solid content of about 10%;

(3) Preparing PVDF slurry: adding a dispersing agent into deionized water, adding polyvinylidene fluoride PVDF copolymer mixed slurry, stirring at a high speed for dispersing for 2 hours, and uniformly dispersing;

(4) adding the prepared thickening agent and the binder and stirring uniformly.

Technical Field

The invention relates to the technical field of lithium ion battery manufacturing, in particular to a lithium ion battery diaphragm and a preparation method thereof.

Background

With the popularization of electric vehicles, safety issues are receiving more and more attention, and a lithium ion battery separator, which is one of four main materials, is one of main components affecting battery safety. The diaphragm has the main function of isolating the positive electrode from the negative electrode, so that internal short circuit caused by direct contact of the positive electrode and the negative electrode is avoided, and ions can pass through the diaphragm in the charging and discharging process to form current. The performance of the separator thus determines the condition of the internal interface of the battery, internal resistance, self-discharge, etc., directly affecting the capacity, cycle and safety of the battery. When thermal runaway occurs in the battery, the liquid electrolyte is easy to decompose and burn, and the thermal runaway can be assisted.

At present, the membrane is usually treated by functional coating, and although the performance and safety of polyolefin base membrane are greatly improved, the method still cannot meet the requirement of higher and higher energy density, especially the safety requirement on the ternary power battery. The existing Polyvinylidene fluoride (PVDF) coating is mainly divided into two types, oil coating and water coating. The oily system uses a large amount of chemical solvents, has large environmental pollution and complex technology, and is coated by a water-based system in China. However, compared with oil coating, water coating has a less good bonding effect, high hot pressing condition requirements and low efficiency. If the viscosity is increased, the amount of PVDF used is increased, the cost of use is high, and the permeation of the separator is increased, which may result in an increase in internal resistance, which may affect cycle and battery safety.

PVDF used in existing waterborne coatings is made from copolymerization of vinylidene fluoride (VDF) and Hexafluoropropylene (HFP). Among them, the hexafluoropropylene HFP has different proportions, and the formed PVDF-HFP has different crystallinity and different melting points, so that the PVDF-HFP has different hot-pressing conditions and hot-pressing effects, and has different swelling coefficients in the electrolyte, thereby affecting the ionic conductivity in the electrolyte. And Hexafluoropropylene (HFP) is now commonly used in a fixed proportion. Therefore, the amount of use, the hot-pressing effect, and the influence in the battery cannot be obtained at the same time.

Disclosure of Invention

In order to solve the problems of poor cohesiveness, large dosage and influence on battery performance in the water-based coating process in the prior art, the invention provides a lithium ion battery diaphragm, which comprises a base film and a polyvinylidene fluoride PVDF copolymer mixed coating, wherein the mixed coating is formed by mixing two copolymer slurries of PVDF1 and PVDF 2; wherein the mass ratio of the PVDF1 to the PVDF2 in the mixed slurry is 70-95 percent of the PVDF1 and 5-30 percent of the PVDF 2.

Wherein the PVDF1 is vinylidene fluoride copolymer PVDF-HFP, wherein the proportion of hexafluoropropylene HFP is 4% -8%; PVDF2 is vinylidene fluoride copolymer PVDF-HFP, wherein the proportion of hexafluoropropylene HFP is 13% -18%.

Wherein the solid content of the slurry of the coating is 5-35%, and the coating comprises PVDF1 and PVDF2 copolymer mixed slurry, a dispersant, a thickening agent, a binder and the like; wherein, the mixed slurry of PVDF1 and PVDF2 is 5% -15%, the binder is 1% -10%, the dispersant is 0.5% -5%, and the thickener is 0.5% -3%.

The dispersing agent is at least one of silicates, alkali metal phosphates, styrene-maleic anhydride, triethyl hexyl phosphoric acid modified polyether polymer, fatty alcohols, polyethylene glycol alkyl aryl ether sodium sulfonate, alkylphenol polyvinyl ether, polyoxyethylene alkyl phenol ether and sodium polyacrylate.

Wherein the thickener is at least one of sodium carboxymethylcellulose, polyallyl alcohol, polyvinyl alcohol, polyethylene glycol, povidone and carboxymethylcellulose.

Wherein the binder is at least one of polyacrylate, polyethylacrylate, styrene butadiene rubber, polyvinyl alcohol, polybutyl acrylate and alpha-cyanoacrylate.

the base film is at least one of a polyethylene base film, a polypropylene base film, a polyethylene ceramic film and a polypropylene ceramic film.

The polyvinylidene fluoride PVDF copolymer mixed coating is a single-side or double-side coating, and the thickness of the coating is 1-10 um.

Wherein, the thickness of the base film is 5-30 um.

The invention also provides a method for preparing the lithium ion battery diaphragm, which comprises the following steps:

(a) Preparing polyvinylidene fluoride PVDF copolymer mixed coating slurry;

(b) Spraying or rolling polyvinylidene fluoride PVDF copolymer mixed slurry on at least one surface of the battery diaphragm; the coating thickness is 1-5um, and the coating amount is 0.3-0.8g/m²A/side;

(c) drying at 30-60 deg.C.

wherein, the preparation of the polyvinylidene fluoride PVDF copolymer mixed coating slurry in the step (a) comprises the following steps:

(1) Preparing polyvinylidene fluoride PVDF copolymer mixed slurry: two PVDF copolymers were weighed in mass ratios: 70-95% of PVDF1 and 5-30% of PVDF 2;

(2) Preparing a thickening agent: adding a thickening agent into deionized water to prepare a thickening agent solution with solid content of about 10%;

(3) Preparing PVDF slurry: adding a dispersing agent into deionized water, adding polyvinylidene fluoride PVDF copolymer mixed slurry, stirring at a high speed for dispersing for 2 hours, and uniformly dispersing;

(4) Adding the prepared thickening agent and the binder and stirring uniformly.

According to the lithium ion battery diaphragm and the preparation method thereof, the PVDF1 has small swelling, stable structure and low swelling ratio by reasonable proportion of different HFP ratios, and can keep viscosity and stable structure in the internal reaction of the battery; the PVDF2 has high viscosity and swelling capacity at a low temperature during hot pressing, has high ionic conductivity after absorbing the electrolyte, can reduce the free electrolyte in the battery, form gel electrolyte and improve the safety of the battery. The bonding force of the battery is improved, the usage amount of PVDF is reduced, the process conditions are reduced, the efficiency is improved, the ventilation is increased slightly, and through the swelling property of the PVDF copolymer, the liquid retention property is improved, the ionic conductivity is improved, the free electrolyte in the battery is reduced, and the safety is improved.

Detailed Description

The present invention is further described by the following specific examples, which are only for illustrating the present invention and are not intended to limit the scope of the present invention.

The invention provides a lithium ion battery diaphragm which comprises a base film, wherein a polyvinylidene fluoride PVDF copolymer mixed coating is coated on the base film. The polyvinylidene fluoride PVDF copolymer mixed coating is formed by mixing two copolymer slurries of PVDF1 and PVDF 2; wherein the mass ratio of the PVDF1 to the PVDF2 in the PVDF of the mixed slurry is 70-95 percent of the PVDF1 and 5-30 percent of the PVDF 2. PVDF1 is vinylidene fluoride copolymer PVDF-HFP, wherein the proportion of hexafluoropropylene HFP is 4% -8%; PVDF2 is vinylidene fluoride copolymer PVDF-HFP, wherein the proportion of hexafluoropropylene HFP is 13% -18%. The base film is at least one of a polyethylene base film, a polypropylene base film, a polyethylene ceramic film and a polypropylene ceramic film. The thickness of the base film is 5-30 um.

The solid content of the polyvinylidene fluoride PVDF copolymer mixed coating is 5-35%, and the polyvinylidene fluoride PVDF copolymer mixed coating comprises PVDF1 and PVDF2 copolymer mixed slurry, a dispersing agent, a thickening agent, a binder and the like. Wherein, the mixed slurry of PVDF1 and PVDF2 is 5% -15%, the binder is 1% -10%, the dispersant is 0.5% -5%, and the thickener is 0.5% -3%. The dispersing agent is at least one of silicate, alkali metal phosphate, triethyl hexyl phosphoric acid modified polyether polymer, fatty alcohol, polyethylene glycol alkyl aryl ether sodium sulfonate, alkylphenol polyoxyethylene, polyoxyethylene alkyl phenol ether and sodium polyacrylate. The thickener is at least one of sodium carboxymethylcellulose, polyallyl alcohol, polyvinyl alcohol, polyethylene glycol, polyvidone and carboxymethyl cellulose. The binder is at least one of polyacrylate, polyethylacrylate, polybutyl acrylate and alpha-cyano acrylate. The polyvinylidene fluoride PVDF copolymer mixed coating is a single-side or double-side coating, and the thickness of the coating is 1-10 um.

The preparation method of the lithium ion battery diaphragm comprises the following steps:

(a) Preparing polyvinylidene fluoride PVDF copolymer mixed coating slurry;

(b) spraying or rolling polyvinylidene fluoride PVDF copolymer mixed slurry on at least one surface of the battery diaphragm; the coating thickness is 1-5um, and the coating amount is 0.3-0.8g/m²A/side;

(c) drying at 30-60 deg.C.

Wherein, the preparation of the polyvinylidene fluoride PVDF copolymer mixed coating slurry in the step (a) comprises the following steps:

(1) preparing polyvinylidene fluoride PVDF copolymer mixed slurry: two PVDF copolymers were weighed in mass ratios: 70-95% of PVDF1 and 5-30% of PVDF 2;

(2) preparing a thickening agent: adding a thickening agent into deionized water to prepare a thickening agent solution with solid content of about 10%;

(3) Preparing PVDF slurry: adding a dispersing agent into deionized water, adding polyvinylidene fluoride PVDF copolymer mixed slurry, stirring at a high speed for dispersing for 2 hours, and uniformly dispersing;

(4) adding the prepared thickening agent and the binder and stirring uniformly.

The following are specific examples of the lithium ion battery separator of the present invention. The specific proportions and parameters in the following examples are adjusted according to actual conditions.