KR20160054937A - Separator and preparation method thereof - Google Patents

Abstract

A porous polymer substrate, and a porous coating layer formed on at least one side of the porous polymer substrate, wherein the porous coating layer is composed of inorganic particles and a binder polymer fiber.

Description

SEPARATOR AND PREPARATION METHOD THEREOF [0002]

More particularly, the present invention relates to a separator having improved air permeability and a method for producing the same.

Recently, interest in energy storage technology is increasing. Efforts to research and develop electrochemical cauterization are becoming more and more evident as the applications of cell phones, camcorders, notebook PCs, and even electric automobiles are expanded. Electrochemical devices have attracted the greatest attention in this respect, among which the development of rechargeable secondary batteries capable of being charged and discharged has become a focus of attention. In recent years, in order to improve capacity density and specific energy in developing such batteries, Research and development on the design of new batteries is under way.

Among the currently applied rechargeable batteries, the lithium secondary battery developed in the early 1990s has a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution It is attracting attention as an advantage.

Such electrochemical devices are produced in many companies, but their stability characteristics are different from each other. It is very important to evaluate the stability and stability of such an electrochemical device. The most important consideration is that the electrochemical device should not injure the user in case of malfunction. For this purpose, the safety standard strictly regulates the ignition and fuming in the electrochemical device.

In the safety characteristics of the electrochemical device, there is a high possibility that the electrochemical device is overheated and thermal explosion occurs or an explosion occurs when the separator is penetrated. Particularly, a polyolefin-based porous substrate commonly used as a separator of an electrochemical device exhibits extreme heat shrinkage behavior at a temperature of 100 DEG C or more due to characteristics of the manufacturing process including material properties and elongation, . ≪ / RTI >

In order to solve the safety problem of such an electrochemical device, an organic / inorganic composite separator in which a porous coating layer is formed by coating a mixture of inorganic particles and a binder polymer on at least one surface of a polyolefin-based porous substrate having a plurality of pores has been proposed

At this time, in manufacturing such an organic / inorganic composite separator, a porous coating layer of inorganic particles is formed by applying a binder dissolved in a solvent.

However, since the binder dissolved in the solvent penetrates into the pores of the polyolefin-based porous substrate, the pores are blocked to increase the resistance of the electrochemical device. As a result, the problem of deteriorating the performance of the electrochemical device still occurs.

The present invention provides a porous polymer base material and a porous coating layer formed on at least one surface of the porous polymer base material, wherein the porous coating layer is composed of inorganic particles and a binder polymer fiber, Disclosed is a separator wherein the impregnation in the base material is basically blocked at the time of coating on the surface of the base material and the increase in the ventilation time is minimized.

Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

According to an aspect of the present invention, there is provided a porous polymer substrate comprising: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises a separator comprising inorganic particles and a binder polymer fiber / RTI >

The average diameter of the binder polymer fibers may be larger than the average pore diameter of the porous substrate.

The average diameter of the binder polymer fibers may be 20 nm or more.

The binder polymer fiber may be selected from the group consisting of cellulose, polyvinylidene fluoride-cohexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, poly But are not limited to, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide Polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl, Alcohol( a polymer selected from the group consisting of cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose, or a mixture of two or more thereof May be formed of a mixture.

The porous polymer substrate may be a porous polymer film substrate or a porous polymer nonwoven substrate.

The porous polymeric film substrate may be formed of at least one polymer selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene.

The porous polymer substrate may be formed of a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, polyetheretherketone, polyetheretherketone, polyetheretherketone, a polymer selected from the group consisting of polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide and polyethylene naphthalene, or a mixture of two or more thereof .

The inorganic particles may be 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 weight ratio of the inorganic particles and the binder polymer fibers may be 50:50 to 99: 1.

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

According to another aspect of the present invention, there is provided a method for producing a binder polymer fiber, comprising the steps of: preparing a binder polymer fiber; dispersing the binder polymer fiber and the inorganic particles in a solvent to prepare a coating solution; And the solution is coated on at least one side of the porous polymer substrate to form a porous coating layer.

The average diameter of the binder polymer fibers may be larger than the pore diameter of the porous polymer base material.

The present invention is advantageous in that the binder polymer prevents impregnation in the porous substrate by coating the porous coating layer comprising the binder polymer and inorganic particles in the form of fibers with the porous substrate.

Further, since the porous base material is not impregnated with the polymeric binder, the problem of blocking the pores and causing an increase in resistance is solved.

In addition, by having an optimized range of the diameter of the binder polymer fibers, there is an advantage of minimizing an increase in the ventilation time of the separator.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, It is not interpreted.
1 is a flowchart of a separator manufacturing method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. The terms and words used in the specification and claims should not be construed to be limited to ordinary or dictionary terms, and the inventor should properly define the concept of the term to describe its own invention in the best way possible. It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention, and not all of the technical ideas of the present invention are described. Therefore, It should be understood that various equivalents and modifications may be present.

According to an aspect of the present invention, there is provided a separator comprising a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises inorganic particles and binder polymer fibers.

The porous polymer base material of the present invention may be a porous polymeric film base or a porous polymer nonwoven base.

The porous polymeric film substrate may be a porous polymeric film made of a polyolefin such as polyethylene or polypropylene. The polyolefin porous polymeric film substrate exhibits a shutdown function at a temperature of, for example, 80 to 130 ° C.

At this time, the polyolefin porous polymer film may be made of a polyolefin-based polymer such as polyethylene, polypropylene, polybutylene or polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, .

In addition, the porous polymeric film substrate may be produced by molding various polymeric materials such as polyester in addition to polyolefin. In addition, the porous polymeric film substrate may have a structure in which two or more film layers are laminated, and each film layer may be formed of a polymer such as polyolefin, polyester, or the like, It is possible.

In addition, the porous polymer film base and the porous nonwoven base material may be formed of a material selected from the group consisting of polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, Polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene, polyetherketone, polyetherketone, polyetherketone, And the like may be used alone or in the form of a mixture thereof.

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 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, or 10 or more, inorganic particles having lithium ion-transporting ability, or a mixture thereof.

Nonlimiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x Ti _1-x ) O ₃ (PZT, 0 <x <1), Pb _1-x La _x Zr _1-y Ti _y O _{3 (PLZT, 0 <x <} 1, 0 <y <1), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, 0 <x <1), Wherein the metal oxide selected from the group consisting of hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ Inorganic particles such as one or a mixture of two or more of them exhibit a high dielectric constant property with a dielectric constant of 100 or more. In addition, piezoelectricity, in which charge is generated when a certain pressure is applied and tension is generated, It is possible to prevent internal short-circuiting of both electrodes due to an external impact, thereby improving the safety of the electrochemical device.

As the inorganic particles, inorganic particles having a lithium ion transferring ability, that is, inorganic particles containing a lithium element but having a function of transferring lithium ions without storing lithium can be used. Non-limiting examples of 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, including (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 _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5) such as Li _3.25 Ge _0.25 P _0.75 S ₄ ), Li ₃ lithium nitride such as _{N (Li x N y, 0} <x <4, 0 <y <2), Li 3 PO 4 SiS 2 family, such as _{-Li 2 S-SiS 2 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 high- When the inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

The binder polymer used in the present invention solves the problem that the binder dissolved in the conventional solvent penetrates into the pores of the substrate when the binder is dissolved in the conventional solvent to increase the resistance of the pores by blocking the pores, Therefore, there is an advantage of maintaining a balance between adhesion and swelling property at high temperature.

Therefore, the average diameter of the binder polymer fibers is preferably larger than the average pore diameter of the porous substrate, more specifically 20 nm or more, more preferably 20 nm to 50 nm or less, and when it is less than 20 nm, There is a problem that the fibers are impregnated into the porous polymer substrate to increase resistance.

The binder polymer applicable to the present invention is preferably a polymer having a glass transition temperature (T _g ) of -200 to 200 ° C. This is because the mechanical properties such as flexibility and elasticity of the finally formed porous coating layer This can be improved.

Such binder polymer fibers may be selected from the group consisting of cellulose, polyvinylidene fluoride-cohexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, poly But are not limited to, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide Polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl, egg one of the polymers selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or carboxyl methyl cellulose, or two of them Or more.

In the porous coating layer, the inorganic particles are charged and bound to each other by the binder polymer fibers in contact with each other, thereby forming an interstitial volume between the inorganic particles, The interstitial volume becomes void and forms pores.

That is, the binder polymer fibers attach the inorganic particles to each other so that the inorganic particles can remain bonded to each other. For example, the binder polymer fibers connect and fix the inorganic particles. In addition, the pores of the porous coating layer are pores formed by interstitial volume between inorganic particles as void spaces, and the pores of the porous coating layer are formed of inorganic materials substantially closed in a packed structure (closed packed or densely packed) It is the space defined by the particles. A path through which lithium ions necessary for operating the battery through the pores of the porous coating layer can be provided.

The weight ratio of the inorganic particles contained in the porous coating layer to the binder polymer fibers is in the range of 50:50 to 99: 1, and preferably 70:30 to 95: 5. When the inorganic material content ratio of the binder polymer fibers is less than 50:50, improvement of the thermal stability of the separator is deteriorated due to an increase of the polymer content and interstitial volume formed between the inorganic particles is not sufficiently formed, There is a problem that the pore size and porosity decrease. When the content of the inorganic particles exceeds 99 parts by weight, there is a problem that the fillerability of the porous coating layer is weakened because the content of the binder polymer is relatively small.

The separator of the present invention may further comprise other additives in addition to the above-mentioned binder polymer fibers and inorganic particles as the porous coating layer component.

According to another aspect of the present invention, there is provided a secondary battery including the above-described separator, wherein the secondary battery of the present invention may include a cathode, an anode, and a separator interposed therebetween.

The cathode or anode used in the present invention may include an electrode current collector and an electrode active material layer, wherein the electrode current collector is made of stainless steel; aluminum; nickel; titanium; Fired carbon; Copper; Stainless steel surface-treated with carbon, nickel, titanium or silver, aluminum-cadmium alloy, or the like can be used.

At this time, the electrode active material layer used for the cathode is composed of LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCoPO ₄ , LiFePO ₄ , LiNiMnCoO _2, and LiNi _{1 -x-yz} Co _x M _y M2 _z O ₂ X, y and z are independently selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg and Mo, 0? X <0.5, 0? Y <0.5, 0? Z <0.5, 0 <x + y + z? 1).

In addition, the electrode active material layer used for the anode may be made of natural graphite, artificial graphite, a carbonaceous material, a lithium-containing titanium composite oxide (LTO), metals such as Si, Sn, Li, Zn, Mg, Cd, Ce, ); An alloy composed of the metal (Me); An oxide of the metal (Me) (MeOx); And a composite of the metal (Me) and carbon, and the like.

At this time, the cathode and the anode use an electrode composition including an electrode active material, a binder, a solvent, and optionally a conductive material to form an electrode active material layer on the current collector. At this time, the method of forming the electrode active material layer may be a method of directly coating the electrode active material composition on the collector, or a method of coating the electrode active material composition on a separate support and drying, As shown in FIG. Here, the support may be any as long as it can support the active material layer. Specific examples thereof include a mylar film, a polyethylene terephthalate (PET) film, and the like.

The binder, conductive material, and solvent may be those conventionally used in the production of lithium secondary batteries.

Specifically, the binder may include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate ) And mixtures thereof can be used. Examples of the conductive material include carbon black or acetylene black, and examples of the solvent include acetone and N-methylpyrrolidone.

According to still another aspect of the present invention, there is provided a method of manufacturing a separator as described above.

FIG. 1 is a flowchart illustrating a method of manufacturing a separator according to an embodiment of the present invention. Referring to FIG. 1, a binder polymer fiber is manufactured (S10), a coating solution is prepared (S20), and a porous coating layer is formed (S30).

The step (S10) of producing the binder polymer fiber is a step of extracting the binder polymer raw material into a long and thin fiber form.

At this time, the binder polymer raw material may be selected from the group consisting of cellulose, polyvinylidene fluoride-cohexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, Polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide (polyvinylpyrrolidone), polyvinylacetate polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethyl Polyvinyl alcohol One of the polymers selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan or carboxyl methyl cellulose, or 2 Or more.

The step (S20) of preparing the coating solution is a step of dispersing the binder polymer fibers and the inorganic particles prepared in the above step in a solvent to prepare a coating solution for coating the porous polymer base material.

In addition, it is preferable that the solvent does not dissolve the binder polymer fiber to be used and has a low boiling point. This is to maintain the fiber form to prevent penetration into the pores of the substrate and then to facilitate solvent removal, and non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride ( methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, have.

The step of forming the porous coating layer (S30) is a step of selectively coating and drying the coating solution in which the binder polymer fibers and the inorganic particles are dispersed, on both or only one side of the porous polymer substrate to form a porous coating layer. May be used without limitation, and examples of the coating method include various coating methods such as a dip coating, a die coating, a roll coating, a comma coating, Method can be used.

The porous polymer base material used in the step (S30) of forming the porous coating layer uses a base material having a pore diameter smaller than the average diameter of the binder polymer fibers. This is because the binder polymer fibers penetrate the pores of the porous polymer base material to increase the resistance .

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims (12)

And a porous coating layer formed on at least one surface of the porous polymer substrate,
Wherein the porous coating layer comprises an inorganic particle and a binder polymer fiber. The method according to claim 1,
Wherein the average diameter of the binder polymer fibers is larger than the average pore diameter of the porous substrate. The method according to claim 1,
Wherein the average diameter of the binder polymer fibers is 20 nm or more. The method according to claim 1,
The binder polymer fiber may be selected from the group consisting of cellulose, polyvinylidene fluoride-cohexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, poly But are not limited to, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide Polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinyl, Alcohol( a polymer selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose, or a mixture of two or more thereof Wherein the separator is formed of a mixture. The method according to claim 1,
Wherein the porous polymer base material is a porous polymeric film base or a porous polymer nonwoven base base. 6. The method of claim 5,
Wherein the porous polymeric film substrate is formed of at least one polymer selected from the group consisting of polyethylene, polypropylene, polybutylene, and polypentene. The method according to claim 1,
The porous polymer substrate may be formed of a material selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, Polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, polyetheretherketone, polyetheretherketone, polyetheretherketone, a polymer selected from the group consisting of polyphenylene oxide, cyclic olefin copolymer, polyphenylenesulfide, and polyethylenenaphthalene, or a mixture of two or more thereof . 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 weight ratio of the inorganic particles to the binder polymer fibers is 50:50 to 99: 1. A secondary battery comprising the separator according to any one of claims 1 to 9. Preparing a binder polymer fiber;
Dispersing the binder polymer fibers and the inorganic particles in a solvent to prepare a coating solution; And
And coating the at least one side of the porous polymer substrate with the coating solution to form a porous coating layer. 12. The method of claim 11,
Wherein the average diameter of the binder polymer fibers is larger than the pore diameter of the porous polymer base material.

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