WO2017016373A1 - Aramid fiber polymer coated lithium ion battery membrane and preparation method therefor - Google Patents

Abstract

An aramid fiber polymer coated lithium ion battery membrane and a preparation method therefor. The aramid fiber polymer coated lithium ion battery membrane comprises a lithium ion battery base membrane and a coating coated on a single side or both sides of the base membrane, the thickness of the coating being 0.5 to 4 microns. An aramid fiber polymer is used in an aramid fiber slurry. A membrane obtained by pre-solidification in the environment of greater than 90% has good mechanical performance and high temperature resistance. Moreover, the membrane has an opening pore structure, such that the electrolyte wettability thereof is greatly promoted. In addition, the preparation method has the characteristics such as being environmentally friendly, low in cost, simple in process, and convenient for continuous production.

Description

[Correction according to Rule 26 21.07.2016] Aramid polymer coated lithium ion battery separator and preparation method thereof Technical field

The invention relates to a lithium ion battery separator, in particular to a composite lithium ion battery separator and a preparation method thereof, and belongs to the technical field of batteries.

Background technique

Lithium-ion batteries are widely used as power sources for various mobile devices because of their high energy density, high operating voltage, no memory effect, and long cycle life. Lithium-ion batteries usually include a positive electrode, a negative electrode, a separator, and an electrolyte. The separator acts as a barrier between the positive and negative electrodes and plays a vital role in the performance of the lithium-ion battery. Therefore, the safety of the lithium ion battery is improved by improving the performance of the separator. Research on sex, usability and craftsmanship has received more and more attention. Currently, the separator used in lithium ion batteries is generally a polyolefin porous film having a melting point of less than 170 °C. When the battery temperature rises due to internal or external factors, the diaphragm will shrink or melt and cause hole breakage, causing the battery to be short-circuited due to contact between the positive and negative terminals of the battery, causing accidents such as battery burning and explosion.

When preparing aramid-coated lithium ion battery separator, the organic solvent such as DMAC, DMF, NMP, DMSO or the like is directly used to dissolve the aramid fiber to prepare the aramid solution, and then the pore former is added to obtain the aramid pulp. The coated film is solidified by the immersion coagulating liquid, and finally washed and dried to obtain an aramid-coated lithium ion battery separator. The method still has the following problems: First, the aramid fiber needs to be heated and dissolved, and the process may cause partial aramid fiber to decompose, resulting in poor heat resistance and mechanical properties; second, the method is subject to the thermodynamic state of the slurry and the slurry. The mass transfer dynamics between the feed and the coagulating liquid are co-ordinated, the influencing factors are complex, and the pore structure is difficult to control. Third, the coating consists of a dense skin layer and a loose porous sub-layer, and the dense skin layer The formation hinders the migration of lithium ions and affects the wetting property of the electrolyte and the membrane. Fourth, the composition of the coagulating liquid varies widely, and most of them are high-concentration organic solutions, causing cost pressure and causing problems such as recycling and environmental pollution.

Summary of the invention

The invention aims to overcome the defects of the prior art and provides an aramid polymer coated lithium ion battery separator, which has the advantages of small pollution, low cost, simple process, large-scale continuous production, and can maintain the original Based on the excellent heat resistance and mechanical properties of the aramid coated separator, it further enhances the wettability of the electrolyte.

The present invention also provides a method of preparing such an aramid polymer coated lithium ion battery separator.

The technical problem of the present invention is solved by the following technical solutions:

An aramid polymer coated lithium ion battery separator comprising a base film and a coating applied to one or both sides of the base film, the coating being coated, pre-solidified, and immersed in water by an aramid slurry After drying, the improvement is that the composition of the aramid pulp and its mass fraction are:

The solvent A is one of NMP, DMSO, DMF or DMAC, and the solvent B is one or more of ethyl acetate, isopropanol, dichloromethane or triethyl phosphate; the aramid The aramid content in the polymer is 10-20% by mass.

In the above lithium ion battery separator, the aramid polymer is a para-position of a molecular weight of 5,000 to 100,000 or One or two of meta-aramid polymers.

In the above lithium ion battery separator, the emulsifier is one or more of polyethylene oxide, polyethylene glycol, polyvinyl alcohol, sodium polyacrylate or polyacrylamide.

In the above lithium ion battery separator, the coating has a thickness of 0.5 to 4 μm.

In the above lithium ion battery separator, the adhesive is a vinylpyrrolidone and a vinyl acetate (PVP-VA) copolymer adhesive.

In the above lithium ion battery separator, the base film of the lithium ion battery is a polyethylene film having a thickness of 5-40 μm and a porosity of 30-80%, a polypropylene base film or a polypropylene/polyethylene/polypropylene composite base film, and a polyacyl group. One of an imide base film, a polyvinylidene fluoride film, a polyethylene nonwoven fabric base film, a polypropylene nonwoven fabric base film, and a polyimide nonwoven fabric base film.

A method for preparing the above-mentioned aramid polymer coated lithium ion battery separator, which is prepared according to the following steps:

a certain proportion of emulsifier is added to the solvent A, stirred until the emulsifier powder is completely dissolved, to obtain an emulsifier solution I;

b. adding a formula amount of the above emulsifier solution to the aramid polymer solution, and stirring to obtain a solution II;

c. adding a formula amount of polymer adhesive, solvent B to solution II, and stirring uniformly to obtain an aramid slurry;

d. coating aramid slurry on the surface of the corona treated lithium battery base film to prepare a coating film;

e. pre-solidifying the coating film in an environment having a relative humidity of 90% or more;

f. Washed and dried to obtain the finished product.

In the above preparation method, the pre-solidification condition in the step e is a humidity of 95% or more, and the pre-solidification time 3-15s.

In the above preparation method, the coating method in the step f is one of gravure coating, slit coating, dip coating or spray coating.

The lithium ion battery separator prepared by the invention has the following advantages compared with the prior art:

1. The aramid fiber slurry is directly used to prepare the aramid pulp instead of the aramid fiber solution, thereby avoiding the problem of decomposition of the aramid fiber caused by the heating and dissolution process.

2. The aramid polymer used does not contain an inorganic salt cosolvent, which avoids the adverse effects of inorganic ion residue on battery performance.

3. The viscosity of the aramid polymer itself is smaller than that of the aramid fiber solution, and the wettability to the base film is good, the use amount of the low melting point emulsifier can be reduced, and the high temperature resistance of the coating can be improved.

4. The introduction of a high-humidity environment enhances the influence of the pre-solidification process on the solidification rate of the cortex, and avoids the formation of a dense skin layer, so that the separator of the present invention has an open pore structure, which greatly improves the wettability of the electrolyte.

5. The combination of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymerization adhesive and pure water coagulation bath improves the adhesion of the coating under water and reduces the amount of organic solvent used. The preparation method of the invention membrane has the characteristics of environmental friendliness, low cost, simple process and convenient continuous production. .

DRAWINGS

Figure 1 is a topographical view of a first embodiment of the present invention;

Figure 2 is a comparative surface topography;

3 is a topographical view of a high power microscope according to Embodiment 1 of the present invention;

Figure 4 is a comparison of the contact angle wetting curves of aramid.

detailed description

The aramid polymer coated lithium ion battery separator of the invention comprises a base film and a coating coated on one side or both sides of the base film, for the existing coating slurry (that is, using aramid short fiber or pulp)粕 heating and dissolution method) to improve, directly using aramid polymer to prepare coating slurry, the process can be completed by mechanical stirring at room temperature, on the basis of saving energy, reducing solvent evaporation, avoiding heating The problem of decomposition of the aramid fiber can maintain the excellent mechanical properties and heat resistance of the aramid fiber to the utmost extent. At the same time, the viscosity of the aramid polymer itself is smaller than that of the aramid fiber solution, and the wettability to the base film is good, the use amount of the low melting point emulsifier can be reduced, and the high temperature resistance of the coating can be improved.

In addition, the composition difference between the polymer solution of the present invention and the aramid fiber solution leads to a change in the thermodynamic state of the final slurry, and a dense non-porous structure is formed according to the conventional coating process, and therefore, the aramid polymer is coated. The preparation method of the coated lithium ion battery separator has also been correspondingly improved, and the improvement point is mainly reflected in the environmental control of the interval from the coating to the water washing. The introduction of high-humidity environment enhances the influence of pre-solidification process on the solidification rate of cortex, avoids the loss of a large amount of solvent on the surface layer of aramid coating when water is encountered, and the formation of dense skin layer caused by the rapid increase of aramid concentration, creating the surface and inner layer. The open pore structure with the same structure increases the transport channel of lithium ions and improves the wettability between the separator and the electrolyte.

Several specific embodiments of the invention are provided below:

Example 1:

Weigh 2kg of DMAC, add 0.1kg of sodium polyacrylate, stir until completely dissolved, add 4.4kg of meta-aramid polymer to the above solution, the aramid content is 10%, the molecular weight of aramid is 80,000-100,000, stirring After homogenization, 3.35 kg of isopropanol and 0.05 kg of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymer adhesive were sequentially added while stirring, and the aramid pulp was uniformly dispersed; 16 μm was selected. The thickness of the corona polypropylene base film, the porosity was 42%, and the aramid slurry was applied to one side of the base film by gravure coating, and the coating rate was 15 m/min. Pre-solidified in a 90% humidity environment for 10s, washed for 10s, and dried in a three-stage oven. The oven temperatures are 55°C, 60°C, 70°C, respectively. After drying, the aramid polymer coated lithium ion battery is obtained. Diaphragm. The aramid polymer coated lithium ion battery separator had a thickness of 20 μm and a coating thickness of 4 μm.

Example 2:

Weigh 2.85kg of DMF, add 0.05kg of polyvinyl alcohol powder, stir until completely dissolved, add 5kg of para-aramid polymer to the above solution, the aramid content is 13.75%, and the molecular weight of aramid is 4-7 million. After stirring evenly, 2 kg of isopropanol and 0.05 kg of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymer adhesive were sequentially added with stirring to uniformly disperse the aramid pulp; corona polymerization with a thickness of 22 μm was selected. The imide base film had a porosity of 44%, and the aramid slurry was applied to both sides of the base film by dip coating, and the coating rate was 5 m/min. Pre-solidified in a 95% humidity environment for 15s, washed for 15s, and dried in a three-stage oven. The oven temperatures are 45°C, 50°C, 60°C, respectively. After drying, the aramid polymer coated lithium ion battery is obtained. Diaphragm. The aramid polymer coated lithium ion battery separator had a thickness of 26 μm and each coating thickness was 2 μm.

Example 3:

Weigh 1.45kg of DMSO, add 0.05kg of polyacrylamide, stir until completely dissolved, add 7.5kg of para-aramid polymer to the above solution, the active ingredient of aramid is 12.5%, and the molecular weight of aramid is 1-3 million. After stirring evenly, 0.8 kg of ethyl acetate and 0.2 kg of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymeric adhesive were added while stirring, and the aramid pulp was uniformly dispersed; a polycondensation of 32 μm thickness was selected. The propylene-based film had a porosity of 60%, and the aramid slurry was applied to one side of the base film by gravure coating at a coating rate of 30 m/min. Pre-solidified in a 95% humidity environment for 5 s, washed 15s, using a three-stage oven for drying, the oven temperature of each stage is 60 ° C, 65 ° C, 55 ° C, after drying to obtain aramid polymer coated lithium ion battery separator. The aramid polymer coated lithium ion battery separator had a thickness of 35 μm and a coating thickness of 3 μm.

Example 4

Weigh 2.3kg of DMF, add 0.05kg of polyethylene glycol, stir until completely dissolved, add 6kg of meta-aramid polymer to the above solution, the active ingredient of aramid is 20%, and the molecular weight of aramid is 0.5-20,000. After stirring evenly, 1.5 kg of dichloromethane and 0.15 kg of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymer adhesive were sequentially added while stirring, and the aramid pulp was uniformly dispersed to obtain a thickness of 5 μm. The polyethylene base film had a porosity of 30%, and the aramid slurry was applied to both sides of the base film by a slit coating method at a coating rate of 30 m/min. Pre-solidified for 3s in a 95% humidity environment, washed for 15s, and dried in a three-stage oven. The oven temperatures are 60°C, 60°C, and 55°C, respectively. After drying, the aramid polymer coated lithium ion battery is obtained. Diaphragm. The aramid polymer coated lithium ion battery separator had a thickness of 6 μm and each side coating layer had a thickness of 0.5 μm.

Example 5

Weigh 3.0kg of DMAC, add 0.75kg of polyethylene oxide, stir until completely dissolved, add 4.8kg of para-aramid polymer to the above solution, the active ingredient of aramid is 15%, and the molecular weight of aramid is 80,000-100,000. After stirring evenly, add 1.25 kg of triethyl phosphate and 0.2 kg of vinylpyrrolidone and vinyl acetate (PVP-VA) copolymer adhesive while stirring, and uniformly disperse to obtain aramid pulp; select 40 μm thick poly The propylene non-woven base film had a porosity of 80%, and the aramid slurry was applied to both sides of the base film by spray coating, and the coating rate was 30 m/min. Pre-solidified in a 95% humidity environment for 15s, washed for 15s, and dried in a three-stage oven. The oven temperatures are 60°C, 65°C, 55°C, respectively. After drying, the aramid polymer coated lithium ion battery is obtained. Diaphragm. The aramid polymer coated lithium ion The thickness of the battery separator was 48 μm, and the thickness of each surface coating was 4 μm.

Comparative example:

a. Weigh 0.5kg of co-solvent LiCl into 6kg of the first solvent DMAC, stir until completely dissolved, slowly and uniformly add 0.05kg of dispersing agent polyoxyethylene powder with a molecular weight of 10 million to 1 million, stir at low speed until dispersed. The agent is completely dissolved, adding 0.44kg of meta-aramid chopped fiber with a molecular weight of 80-100,000, heated in a boiling water bath and stirred until completely dissolved, to obtain a meta-aramid fiber solution I;

b. Take the second solvent, isopropanol, 3.3kg, add 0.1kg of sodium polyacrylate, and disperse for 40min, then add 0.05kg of the adhesive vinylpyrrolidone and vinyl acetate to the above aramid solution, and disperse evenly to make the aromatic Polyester slurry

c. A corona polypropylene base film having a thickness of 16 μm was selected, and the porosity was 42%. The aramid slurry was applied to one side of the base film by gravure coating, and the coating rate was 15 m/min. Pre-solidified in a 90% humidity environment for 10s, washed for 10s, and dried in a three-stage oven. The oven temperatures are 55°C, 60°C, 70°C, respectively. After drying, the aramid polymer coated lithium ion battery is obtained. Diaphragm. The aramid polymer coated lithium ion battery separator had a thickness of 20 μm and a coating thickness of 4 μm.

The performance test data of the aramid polymer coated lithium ion battery separators obtained in the examples and the comparative examples are shown in Table 1 below:

Example	Breathable sec/100cc	Heat shrinkage 150°C*1h/%	Longitudinal tensile strength kg/cm 2
Example 1	310	0.5	1860
Example 2	325	0.5	1825
Example 3	299	0.5	1780
Example 4	280	0.5	1860
Example 5	300	0.5	1800

Comparative example

370

1

1760

It can be seen from the data in Table 1 that the gas permeability, heat shrinkage and tensile strength properties of the separator obtained in Example 1 are better than the comparative examples. The good gas permeability indicates that the open pore structure is favorable for providing more lithium ion channels, heat shrinkage performance and The good tensile strength indicates that the use of aramid fiber solution does result in a decrease in performance due to decomposition of the aramid fiber.

The ionic polymer-coated lithium ion battery separator obtained in Example 1 and Comparative Example was subjected to SEM, and the morphology was observed by 1000-fold magnification. The open pore structure of Example 1 was clearly observed by electron micrograph comparison.

4, the aramid-coated lithium ion battery separator of Example 1 and the comparative example, the wetting angle change curve of the electrolyte over time was found to be comparatively found that the aramid coating of Example 1 had a smaller wetting angle and contact. The angle changes faster with time, indicating that the open-porous structure of the aramid-coated membrane has better wettability and faster liquid absorption rate.

Claims (9)

1. An aramid polymer coated lithium ion battery separator comprising a base film and a coating applied to one or both sides of the base film, the coating being coated, pre-solidified, and immersed in water by an aramid slurry Obtained after drying, characterized in that

   The composition of the aramid pulp and its mass parts are:

   

   The solvent A is one of NMP, DMSO, DMF or DMAC, and the solvent B is one or more of ethyl acetate, isopropanol, dichloromethane or triethyl phosphate; the aramid The aramid content in the polymer is 10-20% by mass.
2. The lithium ion battery separator according to claim 1, wherein the aramid polymer is one or both of a para or meta-aramid polymer having a molecular weight of 5,000 to 100,000.
3. The lithium ion battery separator according to claim 2, wherein the emulsifier is one or more of polyethylene oxide, polyethylene glycol, polyvinyl alcohol, sodium polyacrylate or polyacrylamide.
4. The lithium ion battery separator according to claim 3, wherein the coating has a thickness of 0.5 to 4 μm.
5. The lithium ion battery separator according to claim 4, wherein the adhesive is a vinylpyrrolidone and a vinyl acetate (PVP-VA) copolymer adhesive.
6. The lithium ion battery separator according to claim 5, wherein the base film of the lithium ion battery is a polyethylene film, a polypropylene base film or a polypropylene/poly layer having a thickness of 5 to 40 μm and a porosity of 30 to 80%. One of an ethylene/polypropylene composite base film, a polyimide base film, a polyvinylidene fluoride film, a polyethylene nonwoven base film, a polypropylene nonwoven base film, and a polyimide nonwoven base film Kind.
7. A method of preparing an aramid polymer coated lithium ion battery separator according to any one of claims 1 to 6, wherein the preparation is carried out according to the following steps: a. adding a proportion of the emulsifier to the solvent A , stirring until the emulsifier powder is completely dissolved, to obtain an emulsifier solution I;

   b. adding a formula amount of the above emulsifier solution to the aramid polymer solution, and stirring to obtain a solution II;

   c. adding a formula amount of polymer adhesive, solvent B to solution II, and stirring uniformly to obtain an aramid slurry;

   d. coating aramid slurry on the surface of the corona treated lithium battery base film to prepare a coating film;

   e. pre-solidifying the coating film in an environment having a relative humidity of 90% or more;

   f. Washed and dried to obtain the finished product.
8. The method for preparing a lithium ion battery separator according to claim 7, wherein the pre-solidification conditions in the step e are a humidity of 95% or more and a pre-solidification time of 3-15 s.
9. The method for preparing a lithium ion battery separator according to claim 8, wherein the coating method in the step f is in gravure coating, slit coating, dip coating or spray coating. One.

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