KR101662638B1 - Separator having binder layer, electrochemical device comprising the separator, and method of preparing the separator - Google Patents

Abstract

The present invention relates to a separator having a binder layer, an electrochemical device including the separator, and a process for producing the separator. According to an aspect of the present invention, there is provided a porous substrate comprising a porous substrate, a porous coating layer, and a binder layer, wherein the binder present in the porous coating layer and the binder layer comprises two or more poly (oxyalkylene) units having a difference in content of hexafluoropropylene (HFP) There is provided a separator comprising a vinylidene fluoride (PVDF) homopolymer or polyvinylidene fluoride-co-hexafluoropropylene (P (VDF-HFP)) based copolymer. According to another aspect of the present invention, there is provided a method for forming a binder solution, comprising the steps of forming a binder solution, forming a slurry, and forming a porous coating layer, wherein the binder in the binder solution comprises two or more PVDF single copolymers Or a P (VDF-HFP) based copolymer is provided. The separation membrane produced according to an aspect of the present invention may be formed by additionally forming a binder layer comprising a binder having a high adhesive strength by drying a porous coating layer including a binder without separately forming a binder layer in a manufacturing process, The binder layer formed in this manner has excellent adhesion at the time of bonding with the electrode and exhibits an effect of suppressing the increase in resistance at the interface with the electrode, thereby improving the cycle characteristics.

Description

TECHNICAL FIELD The present invention relates to a separator having a binder layer, an electrochemical device including the separator, and a separator having a separator having a separator,

The present invention relates to a separator having a binder layer, an electrochemical device including the separator, and a process for producing the separator.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, laptops and even electric vehicles are expanded, efforts for research and development of electrochemical devices are becoming more and more specified. The electrochemical device is one of the most remarkable fields in this respect, and the development of a rechargeable secondary battery has become a focus of attention.

BACKGROUND OF THE INVENTION [0002] Electrochemical devices have been developed by continuous research as electrode active materials whose various performances, particularly those with significantly improved power. Among the currently applied secondary batteries, the lithium secondary batteries developed in the early 1990's are attracting attention because they have higher operating voltage and higher energy density than conventional batteries such as Ni-MH. However, there is a fear that the lithium secondary battery may generate an explosion due to a heat generation phenomenon depending on the use environment.

In order to solve the safety problem of such a secondary battery, it is necessary to increase the coupling force between the porous coating layer and the electrode of the separation membrane, particularly, the separation membrane to strengthen the safety due to the strong integration of the separation membrane and the electrode, There is still a demand for a binder which suppresses an increase in interfacial resistance and improves air permeability, and a separator using the same.

Accordingly, it is an object of the present invention to provide a membrane electrode assembly which is improved in safety due to strong integration of a separator and an electrode by raising the bonding force between the porous coating layer and the electrode of the separator and increases the interfacial resistance of the separator and the electrode due to the electrode side reaction And a binder for improving the air permeability.

According to an aspect of the present invention, there is provided a porous substrate having a plurality of pores; A plurality of inorganic particles formed on at least one surface of the porous substrate or at least one surface of the porous substrate and a porous region of the porous substrate; A porous coating layer comprising two or more compounds of the following formula (1) and a binder containing a compound of the following formula (2) in which the difference in the content of hexafluoropropylene (HFP) is 3% by weight or more; And a binder layer comprising a compound represented by the following general formula (1) and a compound represented by the following general formula (2), wherein the content of the compound of the general formula (2) in the total of the porous coating layer and the binder layer / Content of the compound of formula (2))) is more than 10% but less than 99%, and the fraction of the compound of formula (2) in the binder layer is 50 to 99%

In this formula,

VDF refers to vinylidene fluoride, HFP refers to hexafluoropropylene, a, b, c, and d are percent by weight,

a + b = 100, c + d = 100, b? 0, d> 0, d-b?

According to another aspect of the present invention, there is provided a method for producing a binder solution, which comprises dissolving a binder containing at least two compounds of the above formula (1) and a compound of the above formula (2) in a content of at least 3% by weight in hexafluoropropylene (HFP) ; Adding inorganic particles to the binder solution and stirring to form a slurry in which the inorganic particles are dispersed; And applying the slurry to at least one side of the porous substrate having pores and drying to form at least one surface of the porous substrate or at least one surface of the porous substrate and a region of the pores of the porous substrate, Of the compound represented by the general formula (2) / (content of the compound of the general formula (1) + content of the compound of the general formula (2)) is 50 to 99% as the total amount of the compound Wherein a fraction of the compound of formula (2) in the binder in the binder solution is more than 10% but less than 99%.

According to another aspect of the present invention, there is provided an electrochemical device including the separator, a lithium secondary battery.

The separation membrane produced according to an aspect of the present invention may be formed by additionally forming a binder layer comprising a binder having a high adhesive strength by drying a porous coating layer including a binder without separately forming a binder layer in a manufacturing process, The binder layer formed in this manner has excellent adhesion at the time of bonding with the electrode and exhibits an effect of suppressing the increase in resistance at the interface with the electrode, thereby improving the cycle characteristics.

The accompanying drawings illustrate preferred embodiments of the invention and are not to be construed as limiting the scope of the invention.
1 is a schematic cross-sectional view of a separation membrane comprising a porous substrate, a porous coating layer, and a binder layer prepared according to one embodiment of the present invention.
2 is a schematic flow diagram of a method of manufacturing a separation membrane according to another embodiment of the present invention.
3 is a SEM photograph of the surface of the separation membrane produced according to Example 1 of the present invention.
4 is an SEM photograph of a cross-section of a separation membrane produced according to Example 1 of the present invention.

Hereinafter, the present invention will be described in detail. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor may designate the concept of a term appropriately in order to describe its own invention in the best way possible. It should be interpreted as meaning and concept consistent with the technical idea of the present invention. Therefore, it is to be understood that the present invention may be embodied in many other specific forms such as those described in the following embodiments, It should be understood that variations can be made.

1 is a schematic cross-sectional view of a separation membrane comprising a porous substrate, a porous coating layer, and a binder layer prepared according to one embodiment of the present invention.

Referring to FIG. 1, a separation membrane according to one aspect of the present invention includes a porous substrate having a plurality of pores; A plurality of inorganic particles formed on at least one surface of the porous substrate or at least one surface of the porous substrate and a porous region of the porous substrate; A porous coating layer including a binder for connecting and fixing the porous coating layer; And a binder layer formed on the porous coating layer. Since the binder layer according to the present invention is porous, the ionic conductivity of the separator is improved, and particularly, the binder layer is excellent in adhesion to electrodes. Further, the binder layer functions as an electrode adhesion layer which facilitates adhesion of the electrode with the porous coating layer when assembling the battery such as an electrode assembly.

The porous substrate may be any porous substrate that is typically used in an electrochemical device. Porous substrates include, but are not limited to, polyethylene, polypropylene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, ), Polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, and the like. ), A polymer selected from the group consisting of polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide, and polyethylenenaphthalene. Or a mixture of two or more thereof Or the generated polymer may be those of a multi-film, a woven or non-woven fabric, but are not limited to.

The thickness of the porous substrate is not particularly limited, but may be about 5 to about 50 탆, and the pore size and porosity present in the porous substrate are also not particularly limited, but are about 0.01 to about 50 탆 and about 10 to about 95 탆, %. ≪ / RTI >

In the porous coating layer, the binder is a mixture of two or more compounds of the following formula (1) (hereinafter also referred to as a first binder) having a difference in the content of hexafluoropropylene (HFP) of not less than about 3 wt% , Also referred to as a second binder):

Formula 1

(2)

In this formula,

VDF refers to vinylidene fluoride, HFP refers to hexafluoropropylene, a, b, c, and d are percent by weight,

a + b = 100, c + d = 100, b? 0, d> 0, d-b?

Alternatively, the binder may comprise at least two polyvinylidene fluoride (PVDF) homopolymers or polyvinylidene fluoride-co-poly (vinylidene fluoride) copolymers having a difference in content of hexafluoropropylene (HFP) Hexafluoropropylene (P (VDF-HFP)) based copolymer.

The two or more compounds of the binder is a copolymer having a difference in the content of hexafluoropropylene (HFP) of about 3% by weight or more, which is PVDF _HFP HFP content of _high - PVDF _HFP HFP content of _low ≫ = 3 wt% (where PVDF _{HFP high} is a PVDF polymer having a relatively _high HFP content and PVDF _{HFP low} is a PVDF polymer having a relatively _low HFP content). That is, PVDF _{HFP high} indicates a compound of Formula 2 having a relatively high HFP content as described above, and PVDF _{HFP low} may represent a compound of formula (I) wherein the HFP content is relatively low.

Also, the fraction of the compound of formula (2) (content of compound of formula (2) / content of compound of formula (1) + content of compound of formula (2)) may be greater than about 10% to less than about 99%, or 30 to 90% . Alternatively, the fraction of the compound of formula 2 is PVDF _{HFP High} fraction (PVDF _{HFP high} content / (PVDF _{HFP high} + PVDF _{HFP low} ))).

If the fraction of the compound of formula (2) (fraction of PVDF _{HFP high} ) does not fall within the above-mentioned range, the finally produced binder layer may cause a problem that the adhesive force with the electrode is lowered. When the proportion of the compound of formula (2) is less than 10%, the content of the binder of the compound of formula (1) increases and the melting point (Mp) of the binder increases due to the low HFP content. Can be disadvantageous. On the contrary, when the proportion of the compound of formula (2) is 99% or more, it is difficult to obtain the porous binder layer at the outermost part of the porous coating layer, thereby decreasing the ionic conductivity of the separation membrane and deteriorating the characteristics of the battery.

The two or more compounds of Formula 1 and the compound of Formula 2 may be about 3 to about 50 parts by weight, or about 5 to about 30 parts by weight, based on 100 parts by weight of the inorganic particles. When the amount of the two or more compounds is less than 3 parts by weight based on 100 parts by weight of the inorganic particles, the amount of the binder is too small to effectively form the binder layer itself, and the inorganic particles are connected and fixed, It becomes difficult to fully exert the role of fixing. On the other hand, when the amount exceeds 50 parts by weight, the binder layer is formed too thick and the pores in the porous coating layer are clogged, resulting in increased air permeability, which may adversely affect battery performance.

Alternatively, according to one embodiment of the present invention, the porous coating layer may further comprise a dispersing agent.

The dispersing agent may be one or a mixture of two or more selected from the group consisting of acrylic copolymers. This dispersant exhibits a function as an excellent dispersing agent for improving the dispersibility of an inorganic substance. In addition, the dispersant has a function as a binder having an excellent function as the dispersant and an adhesive force.

This dispersant contains a polar group, and by having such a polar group, it can interact with the surface of the inorganic material to increase the dispersibility of the inorganic material. In addition, the dispersant can control the physical properties thereof easily, and it is possible to improve the dispersibility and the balance of the adhesive force, thereby contributing to the stability of the separator including the separator and the electrochemical device using the separator.

The acrylic copolymer may be a copolymer containing at least one functional group selected from the group consisting of an OH group, a COOH group, a CN group, an amine group and an amide group.

The acrylic copolymer may be a copolymer containing at least one first functional group and at least one second functional group. Here, the first functional group may be selected from the group consisting of an OH group and a COOH group, and the second functional group may be selected from the group consisting of an amine group and an amide group. At this time, when a polymer having OH group or COOH group alone is used, there is a problem that the adhesive force is increased but the dispersing ability is lowered and the coating does not uniformly occur. On the other hand, when a polymer having an amine group and / or an amide group is used alone, there is still a concern that the dispersing ability is increased but the adhesion with the porous separator substrate may be low. Therefore, by using a copolymer containing at least one functional group selected from the group consisting of OH group and COOH group and at least one functional group selected from the group consisting of an amine group and an amide group as a second functional group as the first functional group, It is possible to uniformly coat the coating layer with improved dispersibility and thus to prevent the coating layer from being desorbed and to provide electrochemical stability.

The acrylic copolymer may have a repeating unit derived from a monomer having a first functional group and a repeating unit derived from a monomer having a second functional group.

Nonlimiting examples of the monomer having the first functional group include (meth) acrylic acid, 2- (meth) acryloyloxyacetic acid, 3- (meth) acryloyloxypropyl acid, 4- (meth) acryloyloxy (Meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, (Meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyleneglycol (meth) acrylate, 6-hydroxyhexyl It may be more than one kind.

Examples of the monomer having the second functional group include at least one of an amine group and an amide group in the side chain. Non-limiting examples of the monomer include 2 - (((butoxyamino) carbonyl) oxy) ethyl (meth) (Meth) acrylate, 3- (dimethylamino) ethyl (meth) acrylate, 2- (dimethylamino) ethyl (Meth) acrylamido-2-methyl-1-propanesulfonic acid, (meth) acrylamido (meth) acrylate, (Meth) acrylamidoethyl chloride, N- (meth) acryloylamido-ethoxyethanol, 3- (meth) acryloylamino-1-propanol, N- (butoxymethyl) (Meth) acrylamide, N-tert-butyl (meth) acrylamide, diacetone (meth) acrylamide, (Meth) acrylamide, N-phenyl (meth) acrylamide, N- (tris (hydroxymethyl) methyl) (Meth) acrylamide, NN '- (1,3-phenylene) dimaleimide, NN' Di-hydroxyethylene) bisacrylamide, N, N'-ethylene bis (meth) acrylamide and N-vinylpyrrolidinone.

Examples of such acrylic copolymers include ethyl acrylate-acrylic acid-N, N-dimethyl acrylamide copolymer, ethyl acrylate-2- (dimethylamino) ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N, N -Diethyl acrylamide copolymer, and ethyl acrylate-2- (diethylamino) ethyl acrylate copolymer.

In addition to the above-mentioned binders, additional binders may be further added to the binders for enhancing the binding property between the inorganic particles and improving the durability of the porous coating layer. Such additional binders include, but are not limited to, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-co-vinyl acetate, co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, Cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer acrylonitrile-styrene-butadiene copolymer, polyimide, Each may be used alone or by mixing two or more of them be used.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to about 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having ion transfer ability are used, the ion conductivity in the electrochemical device can be increased to improve the performance.

When inorganic particles having a high dielectric constant are used as the inorganic particles, dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte is also increased, and ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may comprise high-permittivity inorganic particles having a dielectric constant of at least about 5, such as at least about 10, inorganic particles having lithium ion transport capability, or mixtures thereof. Non-limiting examples of a dielectric constant of about 5 or more inorganic particles is _{BaTiO 3, Pb (Zr, Ti} ) O 3 (PZT), Pb 1 - x La x Zr 1 - y Ti y O 3 (PLZT), PB (Mg ₃ Nb _2/3 ) O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _{2 ,} SiC Or mixtures thereof.

In particular, above a _{BaTiO 3, Pb (Zr, Ti} ) O 3 (PZT), Pb 1 - x La x Zr 1 - y Ti y O 3 (PLZT), PB (Mg 3 Nb 2/3) O 3 -PbTiO ₃ (PMN-PT) and hafnia, and a charge is generated when (HfO ₂₎ and that of the inorganic particles not only exhibit a dielectric constant of about 100 or more high dielectric constant characteristics, is applied by tension or compression to a predetermined pressure and a potential difference between both sides of By providing the piezoelectricity to be generated, it is possible to prevent the internal short-circuit of both electrodes due to the external impact, thereby improving the safety of the electrochemical device. Further, when the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

The inorganic particles having the lithium ion transferring ability refer to inorganic particles that contain a lithium element but do not store lithium but have a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability exist in the particle structure It is possible to transfer and move lithium ions due to a kind of defect, so that the lithium ion conductivity in the battery is improved, thereby improving the performance of the battery. Examples of the inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y < (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O ₅ as such (LiAlTiP) _x O _y series glass (0 <x <4, 0 <y <13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2, 0 <y <3 ), Li _{3 .25} Ge _{0 .25} P _{0 .75} S ₄ Lithium, such as germanium Mani help thiophosphate lithium nitro, such as _{(Li x Ge y P z S} w, 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5), Li 3 N fluoride _{(Li x N y, 0 <} x <4, 0 <y <2), Li 3 PO 4 -Li 2 S-SiS 2 SiS 2 family, such as _{glass (Li x Si y S z} , 0 <x <3 , 0 <y <2, 0 <z <4), LiI-Li 2 SP 2 S 5 , etc., such as P ₂ S ₅ based _{glass (Li x P y S z} , 0 <x <3, 0 <y <3, 0 < z < 7), or a mixture thereof.

The inorganic particle size is not limited, but may be as low as possible, preferably from about 0.01 to about 10 microns, or from about 0.05 to about 1.0 microns, for coating layer formation and proper porosity of uniform thickness. When the size of the inorganic particles satisfies the above range, the dispersibility is improved, the physical properties of the separator can be easily controlled, the thickness of the porous coating layer is increased, and the mechanical properties are deteriorated or excessively large, The problem of an internal short circuit can be prevented.

The composition ratio of the inorganic particles and the binder in the porous coating layer may be, for example, about 50:50 to about 99: 1, or about 60:40 to about 95: 5. The thickness of the porous coating layer composed of the inorganic particles and the binder is not particularly limited, but may be in the range of about 0.01 to about 20 mu m. Also, the pore size and porosity are not particularly limited, but the pore size may range from about 0.01 to about 5 탆, and the porosity may range from about 5 to about 75%.

As the component of the porous coating layer, in addition to the above-mentioned inorganic particles and polymers, other additives commonly used in the art may be further included.

The binder layer is present as a binder layer at the outermost portion of the porous coating layer, and includes the compound of Formula 1 and the compound of Formula 2 (or dispersant, if necessary). As described above with respect to the porous coating layer, the compound of formula (2) is a compound containing a hexafluoropropylene (HFP) content of 3 wt% or more higher than that of the compound of formula (1). In the binder layer, the compound of formula (2) is present in a relatively larger amount than the compound of formula (1). That is, the fraction of the compound of Formula 2 in the binder layer is about 50 to about 99%.

According to another aspect of the present invention, there is provided an electrochemical device, such as a lithium secondary battery, having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

2 is a schematic flow diagram of a method of manufacturing a separation membrane according to another embodiment of the present invention. Referring to FIG. 2, there is provided a method for producing a separation membrane according to another aspect of the present invention, which comprises forming a binder solution (S1), forming a slurry (S2), and forming a porous coating layer (S3).

In the step S1, the binder solution is formed by dissolving the binder in the solvent. Further, the binder solution may further include a dispersant.

Binders and dispersants may be used as described above with respect to the separator herein. For example, the binder includes two or more compounds of the above formula (1) and a compound of the above formula (2) in which the difference in the content of hexafluoropropylene (HFP) is not less than 3% by weight.

In addition, the fraction of the compound of Formula 2 may be greater than about 10% to less than about 99%, or 30 to 90%. The two or more compounds of Formula 1 and the compound of Formula 2 may be about 3 to about 50 parts by weight, or about 5 to about 30 parts by weight, based on 100 parts by weight of the inorganic particles.

Further, as the binder constituting the porous coating layer, in addition to the above-mentioned binder, further binders may be further mixed for enhancing the binding property between inorganic particles and improving the durability of the porous coating layer. Can be used as described. Further, the binder may further contain the compound of the above-described formula (3) in addition to the above-mentioned binder

As the solvent, the solubility index is similar to the binder to be used, and it is preferable that the solvent has a low boiling point. This is because the mixing can be made uniform and then the solvent can be easily removed. Particularly, the solvent is preferably a polar solvent having a boiling point of less than 100 캜. However, it is not preferable in the case of a non-polar solvent because there is a fear of lowering the dispersibility.

Non-limiting examples of the solvent include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N- methyl-2-pyrrolidone (NMP), cyclohexane, water, and the like.

The solvent includes about 50 to about 90 parts by weight based on 100 parts by weight of the total amount of the solid and the solvent, that is, 100 parts by weight of the total amount of the inorganic substance, the solid mixture of the two binders and the dispersant, and the solvent (e.g., polar solvent). When the amount of the solvent is less than 50 parts by weight based on 100 parts by weight of the total amount of the solid and the solvent, the coating property is deteriorated due to the increase in viscosity and the difficulty in forming the binder layer and the difficulty of thinning are present. On the other hand, Degradation and increased manufacturing costs.

In step S2, inorganic particles are added to the binder solution formed in step S1 and stirred to form a slurry in which the inorganic particles are dispersed.

After the inorganic particles are added to the binder solution, the inorganic particles can be crushed. Wherein the crushing time is suitably from about 1 to about 20 hours, and the particle size of the crushed inorganic particles may be from about 0.01 to about 3 microns. As the crushing method, a conventional method can be used, and in particular, a milling method such as a ball mill method can be used.

The inorganic particles can be used as previously described herein for the separator.

In step S3, the slurry formed in step S2 is applied to at least one surface of the porous substrate to form a porous coating layer.

The porous substrate can be used as described above with respect to the separator herein.

As a method for coating a slurry in which inorganic particles are dispersed on a porous substrate, a conventional coating method known in the art may be used. For example, a dip coating, a die coating, a roll coating, a comma (comma) coating, or a combination thereof. Further, the porous coating layer can be selectively formed on both or only one side of the porous substrate.

The coating process is preferably carried out in a certain range of humidity, and the humidity range thereof may be about 10% or more, preferably 15% or more, more preferably 20% or more. This is because when the humidity during the coating process falls within the above-mentioned range, the coating process of the slurry is smooth, and then the slurry is dried to form the porous coating layer, so that two or more polyvinylidene fluoride (PVDF) (HFP) component in the homopolymer or polyvinylidene fluoride-co-hexafluoropropylene (P (VDF-HFP)) based copolymer was found to be affected by the distribution of the HFP component in the coating layer depending on the content of the hexafluoropropylene This can be advantageous.

Specifically, the compound of Formula 1 (first binder) and the compound of Formula 2 (second binder), which are dissolved in the coating layer (slurry) after the slurry is coated and dried, And have different phase transition characteristics due to the vapor-induced phase separation phenomenon. In general, the phase transition rate by non-solvent (for example, water or vapor) has a low phase separation rate under the same non-solvent as the HFP content is high, and the amount of non-solvent required for phase separation is relatively high Much needed. As a result, the first binder having a low HFP content is uniformly distributed throughout the thickness of the finally formed porous coating layer because the phase transition occurs due to the relatively small amount of non-solvent and the speed is high, and the second binder having a relatively high HFP content The binder is present in the outermost portion of the porous coating layer more than the first binder because the amount of the non-solvent necessary for the phase separation is large and the speed is relatively slow. Thus, according to one embodiment of the present invention, a structurally stable porous coating layer and a binder layer having an excellent adhesive force to the electrode are formed on the porous coating layer. When the difference in content of the HFP component in the two or more kinds of copolymers is at least 3% by weight or more, the binder has a distribution tendency as described above.

The drying can be carried out by a method known in the art and can be carried out batchwise or continuously using an oven or a heating chamber in a temperature range considering the vapor pressure of the solvent used. The drying almost removes the solvent present in the slurry, which is preferably as early as possible in consideration of productivity and the like, and can be carried out for a time of 1 minute or less, preferably 30 seconds or less.

As described above, the separation membrane of the present invention produced by the above-described production method can be used as a separation membrane of an electrochemical device. That is, a separation membrane according to an embodiment of the present invention may be useful as a separation membrane interposed between an anode and a cathode.

The electrochemical device includes all devices that perform an electrochemical reaction. Specific examples of the electrochemical device include a capacitor such as a primary cell, a secondary cell, a fuel cell, a solar cell, or a supercapacitor. Particularly, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the above secondary batteries is preferable.

The electrochemical device may be manufactured by a conventional method known in the art, and examples thereof may be manufactured by assembling the positive electrode and the negative electrode with the separator interposed therebetween, and then injecting an electrolyte solution.

The electrode to be applied together with the separator according to an embodiment of the present invention is not particularly limited, and the electrode active material may be bound to the current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use a lithium composite oxide. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of an electrochemical device can be used. In particular, lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, Lithium-adsorbing materials such as graphite or other carbon-based materials and the like are preferable. Non-limiting examples of the positive electrode current collector include aluminum, nickel, or a foil produced by a combination of these. Non-limiting examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy or a combination thereof Foil and so on.

The electrolytic solution which can be used in one embodiment of the present invention is a salt having a structure such as A ⁺ B ^- , wherein A ⁺ includes ions consisting of alkali metal cations such as Li ⁺ , Na ⁺ , K ⁺ B ^- is _{^{PF 6 -, BF 4 -,}} Cl -, Br -, I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, _{C (CF 2 SO 2) 3} - anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), di (DMP), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone butyrolactone), or a mixture thereof, but the present invention is not limited thereto.

The electrolyte may be injected at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

As a process for applying the separation membrane according to an embodiment of the present invention, a lamination, stacking and folding process of a separation membrane and an electrode can be performed in addition to a general winding process. Particularly, when the separator of the present invention is applied to the lamination step in the above process, the effect of improving the thermal stability of the electrochemical device becomes remarkable. This is due to the fact that the heat shrinkage of the separator is more severely affected by the cells produced by the lamination and folding process than the cell produced by the general winding process. Further, when the separator of the present invention is applied to a lamination and stacking process, the binder having a crosslinked structure can be easily assembled at a higher temperature due to excellent thermal stability and adhesive property.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the above-described embodiments. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

Preparation of dispersant

As shown in the following Table 1, each component was added according to each content (molar part) to prepare a dispersant.

Monomer
Kinds The first dispersant The second dispersant Third dispersant DMAAM 35 30 28 DMAEA - - 35 AN 15 15 15 EA 30 54 30 BA 10 - - IBA 10 - - AA - One - HBA - - 2

In Table 1, DMAAm is N, N-dimethylacrylamide, DMAEA is N, N-dimethylaminoethyl acrylate, AN is acrylonitrile, EA is ethyl acrylate, BA is n-butyl acrlate, IBA is isobutyl acrlate, AA is acrylic acid, HBA is hydrolyzed, Hydroxybutyl acrlate. &Lt; / RTI &gt;

Example  One

Hexafluoropropylene (Kynar LBG2, HFP (hereinafter referred to as "first binder")) was added to 100 parts by weight of Al ₂ O ₃ (Japanese light metal, particle size d50 0.4 μm) 5 parts by weight), 15 parts by weight of polyvinylidene fluoride-hexafluoropropylene (Kynar 2500, HFP 18% by weight) as a compound of the formula 2 (hereinafter referred to as a second binder) 1 part by weight of the third dispersant of Table 1 was mixed, and acetone was added as a solvent to form a slurry. The total amount of solids of the first binder, second binder, dispersant and inorganic particles was 20 parts by weight. The slurry was sufficiently dispersed in a ball mill for 5 hours.

The dispersed slurry was coated on both surfaces of a polyolefin (PO) based separator (Celgard 2320) at a humidity of 20% or more using a dip coater. After coating, the thickness of the coating layer can be varied from 2 to 10 mu m. The solvent in the coating layer was dried to volatilize in 30 seconds to finally prepare a separator (see FIGS. 3 and 4).

94 wt% of LiCoO ₂ as a positive electrode active material, 3 wt% of carbon black as a conductive material, and 3 wt% of PVdF as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry Respectively. The positive electrode mixture slurry was applied to an aluminum (Al) thin film as a positive electrode current collector having a thickness of about 20 탆, which was a positive current collector, and dried to prepare a positive electrode.

A negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive material to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 탆 and dried to prepare a negative electrode.

The positive electrode, negative electrode and separator prepared by the above-described method were assembled using a stacking method. The assembled battery was charged with ethylene carbonate / propylene carbonate / diethyl carbonate (LiPF ₆ ) dissolved in 1 M of lithium hexafluorophosphate (EC / PC / DEC = 30: 20: 50% by weight) was injected to prepare a lithium secondary battery.

Example  2

A separator and a lithium secondary battery were produced in the same manner as in Example 1 except that 10 parts by weight of polyvinylidene fluoride-hexafluoropropylene (Solef 21510, HFP 15 wt%) was used as a second binder .

Example  3

Hexafluoropropylene (Kynar 2850, HFP 5-7 wt%) and polyvinylidene fluoride-hexafluoropropylene (Solef 11010, HFP 10-12 wt%) as the first binder and the second binder, respectively, %) Was used as a negative electrode active material, a separator and a lithium secondary battery were produced.

Example  4

(Kynar 2751, HFP 13 wt%) and polyvinylidene fluoride-hexafluoropropylene (Kynar 2500, HFP 17 wt%) were used as the first binder and the second binder, respectively, , A separator and a lithium secondary battery were produced in the same manner as in Example 1.

Example  5 and 6

A separator and a lithium secondary battery were prepared in the same manner as in Example 1 except that the first dispersant and the second dispersant in Table 1 were used as dispersants, respectively.

Comparative Example  One

19 parts by weight of polyvinylidene fluoride-hexafluoropropylene (Kynar LBG2, HFP 5% by weight) as a sole binder and 1 part by weight of the third dispersant of Table 1 as a dispersant were used. A separator and a lithium secondary battery were fabricated by the same method.

Comparative Example  2

A separator and a lithium secondary battery were produced in the same manner as in Comparative Example 1, except that the third dispersant in Table 1 was not used as a dispersant.

Comparative Example  3

Except that 19 parts by weight of polyvinylidene fluoride-hexafluoropropylene (Kynar, HFP 17 wt%) as a sole binder and 1 part by weight of cyanoethylfuran as a dispersing agent were used To prepare a separator and a lithium secondary battery.

Comparative Example  4

Hexafluoropropylene (Solef 11010, HFP 10 to 12 wt%) and polyvinylidene fluoride-hexafluoropropylene (Kynar 2800, HFP 10 to 12 wt%) as the first binder and the second binder, respectively, as polyvinylidene fluoride- %) Was used as a negative electrode active material, a separator and a lithium secondary battery were produced.

Membrane and cell properties

Permeability of membrane

The separation membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were cut into 50 mm × 50 mm to prepare samples. Then, the time (in seconds) required for 100 ml of air to completely pass through the prepared samples was measured. The air permeability was evaluated by the time (s) taken for the separation membrane to pass completely through 100 ml of air.

Separator Heat shrinkage

With respect to the separation membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 4, after separating membranes were kept at 150 ° C for 1 hour, the separation membrane heat exports in the stretching direction were measured.

Evaluation of adhesion between porous coating layer and substrate

After the separation membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were fixed on a glass plate using a double-sided tape, a tape (3M transparent tape) was tightly bonded to the exposed porous coating layer, After cutting to 100 mm, the force (gf / 15 mm) required to desorb the bonded membranes at a rate of 100 mm / min was measured using a tensile strength measuring instrument.

Evaluation of the adhesion between the electrode adhesive layer (separator-separator)

Two sheets of the separator prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were laminated and laminated at a speed of 100 DEG C and 100 mm / min using a laminator, cut into a width of 15 mm and a length of 100 mm, (Gf / 25 mm) required for desorbing the bonded membranes at a rate of 100 mm / min was measured using a tensile strength measuring apparatus.

Evaluation of Resistance of Membrane

The separation membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 4 were sufficiently wetted with an electrolyte solution (EC / EMC = 1: 2 by volume ratio, 1 mole LiPH ₆ ), and coin cells were produced using only such separation membranes. The prepared coin cell was allowed to stand at room temperature for 1 day, and the resistance of the separator was measured and evaluated by an impedance measurement method.

The results of the air permeability, heat shrinkage, adhesion and membrane resistance are shown in Table 2 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Membrane Thickness (㎛) 28 28 28 28 28 28 28 28 28 28 Membrane ventilation rate (sec / 100ml) 1010 910 1100 1320 1210 1230 930 880 2030 1420 Coating layer loading (g / m ² ) 18.1 17.8 17.6 17.6 17.5 17.8 16.5 15.1 18.1 15.7 Separator 150 캜 Heat shrinkage (%) 16 17 18 18 18 16 25 41 18 26 Adhesion (gf / 15 mm) between the porous coating layer and the substrate 210 150 180 220 180 174 88 42 220 170 Adhesive force between electrode adhesive layers (gf / 25 mm) 120 85 95 105 101 108 45 40 80 58 Membrane resistance
(ohm) 1.7 1.5 1.7 1.8 1.6 1.7 1.6 1.7 2.4 2.0

Claims (25)

A porous substrate having a plurality of pores;
A plurality of inorganic particles formed on at least one surface of the porous substrate or at least one surface of the porous substrate and a porous region of the porous substrate; A porous coating layer comprising two or more compounds of the following formula (1) and a binder containing a compound of the following formula (2) in which the difference in the content of hexafluoropropylene (HFP) is 3% by weight or more; And
And a binder layer comprising a compound of the following formula (1) and a compound of the following formula (2)
(The content of the compound of the formula 2 / the content of the compound of the formula 1 + the content of the compound of the formula 2) in the entirety of the porous coating layer and the binder layer is more than 10% and less than 99%
The proportion of the compound of the formula (2) in the binder layer is 50 to 99%
Membrane:
Formula 1

(2)

In this formula,
VDF refers to vinylidene fluoride, HFP refers to hexafluoropropylene, a, b, c, and d are percent by weight,
a + b = 100, c + d = 100, b? 0, d> 0, db? The method according to claim 1,
And the fraction of the compound of the general formula (2) in the whole of the porous coating layer and the binder layer is 30 to 90%. The method according to claim 1,
Wherein the porous coating layer further comprises a dispersing agent. The method of claim 3,
Wherein the dispersing agent is one or a mixture of two or more selected from the group consisting of acrylic copolymers. The method of claim 3,
Wherein the content of the dispersant is 0.5 to 5 parts by weight based on 100 parts by weight of the inorganic particles. 5. The method of claim 4,
Wherein the acrylic copolymer is a copolymer comprising at least one functional group selected from the group consisting of an OH group, a COOH group, a CN group, an amine group and an amide group. The method according to claim 1,
Wherein the porous substrate is selected from the group consisting of polyethylene, polypropylene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, poly Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyetheretherketone, polyetherketone, polyetherketone, polyetherketone, A polymer selected from the group consisting of polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide and polyethylenenaphthalene, or a polymer selected from the group consisting of Tombs formed by a mixture of two or more A caption or a multilayer thereof, a woven fabric or a nonwoven fabric. The method according to claim 1,
Wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof. The method according to claim 1,
Wherein the content of the binder is 3 to 50 parts by weight based on 100 parts by weight of the inorganic particles. 10. An electrochemical device comprising a separator according to any one of claims 1 to 9 interposed between an anode and a cathode and between the anode and the cathode. 11. The method of claim 10,
Wherein the electrochemical device is a lithium secondary battery. Forming a binder solution in a polar solvent by dissolving a binder comprising at least two compounds of the following formula (1) and a compound of the following formula (2) in which the difference in the content of hexafluoropropylene (HFP) is not less than 3% by weight;
Adding inorganic particles to the binder solution and stirring to form a slurry in which the inorganic particles are dispersed; And
Applying the slurry to at least one surface of the porous substrate having pores; And
Drying the slurry applied to at least one side of the porous substrate,
As the drying step proceeds, a porous coating layer and a binder layer are sequentially formed in the thickness direction from the porous substrate,
The content of the compound of the general formula (2) / the content of the compound of the general formula (1) + the content of the compound of the general formula (2)) in the whole of the porous coating layer and the binder layer is 50 to 99%
Wherein the porous coating layer is present on at least one surface of the porous substrate or at least one surface of the porous substrate and a region of the pores of the porous substrate,
A method for producing a separator having a fraction of the compound of the formula (2) in the binder solution of more than 10% but less than 99%
Formula 1

(2)

In this formula,
VDF refers to vinylidene fluoride, HFP refers to hexafluoropropylene, a, b, c, and d are percent by weight,
a + b = 100, c + d = 100, b? 0, d> 0, db? 13. The method of claim 12,
Wherein a fraction of the compound of formula (2) in the binder in the binder solution is 30 to 90%. 13. The method of claim 12,
Wherein the binder solution further comprises a dispersing agent. 15. The method of claim 14,
Wherein the dispersant is a mixture of at least one selected from the group consisting of acrylic copolymers. 15. The method of claim 14,
Wherein the content of the dispersing agent is 0.5 to 5 parts by weight based on 100 parts by weight of the inorganic material. 16. The method of claim 15,
Wherein the acrylic copolymer is a copolymer comprising at least one functional group selected from the group consisting of an OH group, a COOH group, a CN group, an amine group and an amide group. 13. The method of claim 12,
Wherein the porous substrate is selected from the group consisting of polyethylene, polypropylene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, poly Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyetheretherketone, polyetherketone, polyetherketone, polyetherketone, A polymer selected from the group consisting of polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide and polyethylenenaphthalene, or a polymer selected from the group consisting of Tombs formed by a mixture of two or more Captioned film or a multilayer thereof, woven fabric or nonwoven fabric. 13. The method of claim 12,
Wherein the inorganic particles are selected from the group consisting of inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transporting ability, and mixtures thereof. 13. The method of claim 12,
Wherein the content of the binder is 3 to 50 parts by weight based on 100 parts by weight of the inorganic particles. 13. The method of claim 12,
Wherein the polar solvent has a boiling point of less than 100 占 폚. 13. The method of claim 12,
Wherein the polar solvent is selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone wherein the solvent is a mixture of at least one member selected from the group consisting of pyrrolidone, NMP, cyclohexane and water. 13. The method of claim 12,
Wherein the polar solvent is 50 to 90 parts by weight based on 100 parts by weight of the total amount of the inorganic substance, the binder, the dispersant and the polar solvent. 13. The method of claim 12,
Wherein the slurry is applied at a humidity of 10% or more. A separation membrane produced by the method for producing a separation membrane according to any one of claims 12 to 24.

Images