KR20120097238A - Separator and preparation method of separator thereof - Google Patents

Abstract

PURPOSE: A separator for a secondary battery is provided to have improved mechanical properties because a polymer binder is cross-linked, and to have excellent shut down function because a cross-linked binder polymer does not limit a function of thermoplastic particles. CONSTITUTION: A separator comprises a porous substrate having many porous substrate, a first polymer binder having a functional group, respectively crosslinked to each other, inside the porous substrate; and a mixture of a second polymer binder having a functional group coated on the porous substrate and a thermoplastic micro powder having low melting point lower than a melting point or a decomposition point of the porous substrate. The second polymer binder is crosslinked with a first polymer binder. The separator additionally comprises inorganic particle inside the porous substrate.

Description

Separator and manufacturing method of the separator {SEPARATOR AND PREPARATION METHOD OF SEPARATOR THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for secondary batteries and a manufacturing method thereof, and to a separator having enhanced heat resistance and a shutdown function.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. The electrochemical device is the most attracting field in this respect, and the development of a secondary battery capable of charging and discharging has been the focus of attention, and in recent years in the development of such a battery in order to improve the capacity density and specific energy The research and development of the design of the battery is progressing.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has advantages such as higher operating voltage and higher energy density than conventional batteries such as Ni-MH, Ni-Cd and sulfuric acid-lead batteries using an aqueous electrolyte solution . However, such a lithium ion battery has safety problems such as ignition and explosion when using an organic electrolytic solution, and it is disadvantageous in that it is difficult to manufacture. Recently, the lithium ion polymer battery has been considered as one of the next generation batteries by improving the weakness of the lithium ion battery, but the capacity of the battery is still relatively lower than that of the lithium ion battery, and the discharge capacity is improved due to insufficient discharge capacity at low temperatures. This is urgently needed.

Such electrochemical devices are produced in many companies, but their safety characteristics are different. It is very important to evaluate the safety and safety of such an electrochemical device. The most important consideration is that an electrochemical device should not cause injury to the user in case of malfunction. For this purpose, safety standards strictly regulate the ignition and smoke in the electrochemical device. In the safety characteristics of the electrochemical device, there is a high possibility that an explosion occurs when the electrochemical device is overheated to cause thermal runaway or the separator penetrates. In particular, polyolefin-based porous substrates commonly used as separators for electrochemical devices exhibit extreme heat shrinkage behavior at temperatures of 100 degrees or more due to material characteristics and manufacturing process characteristics including stretching, and thus, a short circuit between the anode and the cathode. There is a problem that causes.

In order to overcome this problem, Korean Unexamined Patent Publication No. 2010-0113030 discloses a nonwoven fabric incorporating thermoplastic fine powder, and achieves stability of an electrochemical device by implementing a heat resistance improvement and a shutdown function. However, the nonwoven fabric is weak in mechanical properties, there is still a problem of the possibility of breaking or stretching the nonwoven fabric during the process.

Accordingly, an object of the present invention is to provide a separator having excellent mechanical properties and heat resistance, a shutdown function, and a method of manufacturing a separator having improved workability.

In order to solve the above problems, the present invention is a planar porous substrate having a plurality of pores; A first polymer binder positioned inside the porous substrate and having functional groups and crosslinked with each other; And a mixture of a second polymer binder having a functional group coated on the porous substrate and a thermoplastic fine powder having a melting point lower than a melting point or a decomposition point of the porous substrate, wherein the second polymer binder is the crosslinked first polymer. A separator is provided, which is crosslinked with a binder. In addition, the separator of the present invention may further include an inorganic material inside the porous substrate.

The porous substrate is not particularly limited in its kind, but a nonwoven substrate may be used. The nonwoven substrate may be formed of a microfiber having an average thickness of 0.5 to 10 μm, and pores having a pore diameter of 0.1 to 70 μm in total pores. It is preferable to include 50% or more based on the number.

In addition, it is preferable that the melting point or decomposition point of such a nonwoven substrate is 200 ° C. or more, and the nonwoven substrate is polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide , Polyphenylene sulfide, and polyethylene naphthalene. It is preferable that the thickness of the said nonwoven fabric base material is 9-30 micrometers.

The average particle diameter of the thermoplastic fine powder may be used to 0.1 to 10 um, the melting point of the thermoplastic fine powder is preferably 80 to 150 ℃. In addition, the thermoplastic fine powder may be made of polyvinylidene fluoride, polyethylene, polystyrene, and the like.

In addition, the first binder polymer and the second binder polymer of the present invention, independently of each other, (a) a first monomer unit containing at least one or more of an amine group or an amide group in the side chain and (b) 1 to carbon atoms It may be used a copolymer comprising a second monomer unit of (meth) acrylate having an alkyl group of 14, the content of the first monomer unit is 10 to 80 mol% based on the entire copolymer, the second The content of monomer units is preferably 20 to 90 mol%.

Examples of the first monomer unit include 2-(((butoxyamino) carbonyl) oxy) ethyl (meth) acrylate, 2- (diethylamino) ethyl (meth) acrylate, 2- (dimethylamino) ethyl ( Metha) acrylate, 3- (diethylamino) propyl (meth) acrylate, 3- (dimethylamino) propyl (meth) acrylate, methyl 2-acetoamido (meth) acrylate, 2- (meth) acrylic Amidoglycolic acid, 2- (meth) acrylamido-2-methyl-1-propanesulfonic acid, (3- (meth) acrylamidopropyl) trimethyl ammonium chloride, N- (meth) acryloyl amido- Ethoxyethanol, 3- (meth) acryloyl amino-1-propanol, N- (butoxymethyl) (meth) acrylamide, N-tert-butyl (meth) acrylamide, diacetone (meth) acrylamide , N, N-dimethyl (meth) acrylamide, N- (isobutoxymethyl) acrylamide, N- (isopropyl) (meth) acrylamide, (meth) acrylamide, N -Phenyl (meth) acrylamide, N- (tris (hydroxymethyl) methyl) (meth) acrylamide, N-N '-(1,3-phenylene) dimaleimide, N-N'-(1, 4-phenylene) dimaleimide, N-N '-(1,2-dihydroxyethylene) bisacrylamide, N-N'-ethylenebis (meth) acrylamide and N-vinylpyrrolidinone can be used. The second monomer unit may be (methyl) methacrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth ) Acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate and tetradecyl (meth) acrylate, etc. Can be used.

In addition, the copolymer may further include (c) a third monomer unit including a cyano group, and the content of the third monomer unit is preferably 5 to 50 mol% based on the entire copolymer.

It is preferable to use an average particle diameter of the inorganic particles is 0.01 to 10 um.

The present invention comprises the steps of: impregnating a first polymer binder solution containing a first polymer binder having a functional group and a crosslinking agent into a planar porous substrate having a plurality of pores, and then heating the first polymer binder to crosslink with each other; And a second polymer binder solution in which the second polymer binder having a functional group and the thermoplastic fine powder having a melting point lower than the melting point or the decomposition point of the porous substrate are mixed with the crosslinked first polymer binder. After impregnation, it provides a method for producing a separator comprising the step of heating the second polymer binder to crosslink with the crosslinked first polymer binder. The first polymer binder solution and the second polymer binder solution may further include inorganic particles.

The separator of the present invention is suitable for an electrochemical device including a separator interposed between a positive electrode, a negative electrode, and the positive electrode and the negative electrode, and may be particularly used in a lithium secondary battery.

The secondary battery separator of the present invention including the thermoplastic particles and the crosslinkable polymer binder has excellent mechanical properties by crosslinking the polymer binder and excellent shutdown performance since the crosslinked binder polymer does not limit the function of the thermoplastic particles.

In addition, the present invention can prevent the detachment of the thermoplastic particles or the inorganic particles and improve the workability by using a crosslinkable polymer binder having excellent affinity.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments of the invention and, together with the description of the invention, It should not be construed as limited.
1 is an SEM photograph of the surface of the separator of Example 1. FIG.
2 is a SEM photograph of the surface of the separator of Comparative Example 1. FIG.
3 is an SEM photograph of the surface of the separator of Comparative Example 2. FIG.
4 is a SEM photograph of the surface of the separator of Comparative Example 3.
5 is a graph of MD tensile strength.
6 is a graph of TD tensile strength.
7 is a graph showing resistance to temperature of the separators of Example 1 and Comparative Examples 1 and 3;
8 is a graph illustrating a charge / discharge test for a lithium secondary battery.

Hereinafter, the present invention will be described in detail with reference to the drawings. The 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 appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

The separator of the present invention is a planar porous substrate having a plurality of pores; A first polymer binder positioned inside the porous substrate and having functional groups and crosslinked with each other; And a mixture of a second polymer binder having a functional group coated on the porous substrate and a thermoplastic fine powder having a melting point lower than a melting point or a decomposition point of the porous substrate, wherein the second polymer binder is the crosslinked first polymer. It is characterized by crosslinking with a binder.

The porous substrate used in the present invention is not particularly limited in its kind, and both membranes and nonwoven fabrics may be used. For example, a polymer binder may be formed to form crosslinks in the porous substrate, such as a nonwoven substrate. It is preferable to use one having a pore size and porosity as large as possible. After impregnating the first polymer binder having a functional group inside the porous substrate, the first polymer binder is crosslinked with each other using a crosslinking agent. The first polymer binder located inside the porous substrate has a crosslinked structure by crosslinking, and since the crosslinked structure itself has excellent mechanical properties, it contributes to improving mechanical properties of the entire porous substrate.

In addition, the second binder polymer serves to help the thermoplastic fine powder to be attached to the porous substrate. In particular, the second binder polymer is crosslinked with the crosslinked first polymer binder, and the second binder polymer does not crosslink with each other. Since the crosslinking agent does not easily occur between the first polymer binders because the crosslinking agent is not additionally used when the second binder polymer is applied, the existing crosslinking agent used for the crosslinking of the first polymer binder with the first polymer binder This is because crosslinking with the second polymer binder occurs.

The thermoplastic fine powder is used to impart a shutdown function to the separator. The thermoplastic fine powder having a melting point lower than the melting point or decomposition point of the porous substrate is melted when the separator is heated to a predetermined temperature or more, thereby causing pores of the porous substrate. This prevents the transfer of ions and prevents the electrochemical reaction from further evaporating. In particular, when the polymer binders used for adhesion of the thermoplastic micropowder are crosslinked with each other to surround and cure the thermoplastic micropowder, the shutdown function is limited. The micropowder of the present invention is the second polymer binder and the first polymer binder. While the crosslinking of the liver firmly adheres to the porous substrate, the second polymer binder does not cross-link, and thus does not limit the shutdown function since the fine powder does not prevent the fine powder from penetrating into the pores by melting.

In addition, the separator of the present invention may include inorganic particles inside the porous substrate for improving heat resistance, etc. The polymer binder used in the present invention has excellent affinity with the inorganic particles, thereby preventing the inorganic particles from being detached. Therefore, the separator of this invention is excellent in workability.

As the porous substrate used in the present invention, a nonwoven fabric may be used. In the case of the nonwoven fabric, the fibers are irregularly connected, and the fibers are connected to each other by the crosslinking of the first polymer binder of the present invention. Since it improves the mechanical properties of the nonwoven fabric, the mechanical properties are weak, reducing the possibility of breakage or stretching of the nonwoven fabric during the process. Such a nonwoven substrate is preferably formed of a microfiber having an average thickness of 0.5 to 10 um, and using a pore having a long diameter of 0.1 to 70 um based on the total number of pores by 50% or more. The melting point or decomposition point of the nonwoven fabric base may be 200 ℃ or more, and the nonwoven substrate may be polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide , Polyphenylene sulfide, polyethylene naphthalene or the like is preferably used. In addition, it is preferable that the thickness of the said nonwoven fabric base material is 9-30 micrometers.

Preferably, the thermoplastic fine powder of the present invention is smaller than the average particle diameter of the pores present in the porous substrate, which fills the pores, and fills the pores of the nonwoven substrate and the remaining thermoplastic fine powder may be located on the surface of the porous substrate. . The average particle diameter of the thermoplastic fine powders according to the present invention is not limited as long as the above object can be achieved, for example, 0.1 to 10 um. In addition, the thermoplastic fine powder has a melting point lower than the melting point or decomposition point of the porous substrate. Accordingly, when the electrochemical device is overheated, the thermoplastic fine powder may be melted to express a shutdown effect that prevents the pores of the pores, thereby suppressing the progress of the electrochemical reaction. In the present invention, the 'decomposition point' is to be understood as a term in place of the melting point when the polymer is made of a thermosetting polymer that decomposes before melting. Thus, the thermoplastic fine powder is melted first before the nonwoven substrate is melted or decomposed. It is preferable that melting | fusing point of such a thermoplastic fine powder is 80-150 degreeC. Examples of the thermoplastic fine powder include, but are not limited to, fine powder made of polyvinylidene fluoride, polyethylene, polystyrene, or the like.

The first polymer binder and the second polymer binder (a) a (meth) acrylate having a first monomer unit containing at least one or more of an amine group or an amide group in the side chain and (b) an alkyl group having 1 to 14 carbon atoms. It is characterized in that the copolymer comprising a second monomer unit. Such a copolymer may be represented by (first monomer unit) _m − (second monomer unit) _n (0 <m <1, 0 <n <1), which includes a first monomer unit and a second monomer unit If it is a copolymer, the form of all copolymers, such as a random copolymer and a block copolymer, is included. The first monomer unit and the second monomer unit included in the copolymer impart high adhesion between the thermoplastic fine powder, the inorganic particles, and the porous substrate.

The first monomer unit containing at least one of an amine group or an amide group in the side chain may be 2-(((butoxyamino) carbonyl) oxy) ethyl (meth) acrylate, 2- (diethylamino) ethyl ( Meth) acrylate, 2- (dimethylamino) ethyl (meth) acrylate, 3- (diethylamino) propyl (meth) acrylate, 3- (dimethylamino) propyl (meth) acrylate, methyl 2-acetoami Degree (meth) acrylate, 2- (meth) acrylamidoglycolic acid, 2- (meth) acrylamido-2-methyl-1-propanesulfonic acid, (3- (meth) acrylamidopropyl) trimethyl ammonium Chloride, N- (meth) acryloylamido-ethoxyethanol, 3- (meth) acryloyl amino-1-propanol, N- (butoxymethyl) (meth) acrylamide, N-tert-butyl (Meth) acrylamide, diacetone (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N- (isobutoxymethyl) acrylamide, N- (Isopropyl) (meth) acrylamide, (meth) acrylamide, N-phenyl (meth) acrylamide, N- (tris (hydroxymethyl) methyl) (meth) acrylamide, N-N '-(1, 3-phenylene) dimaleimide, N-N '-(1,4-phenylene) dimaleimide, N-N'-(1,2-dihydroxyethylene) bisacrylamide, N-N'- Ethylene bis (meth) acrylamide, N-vinylpyrrolidinone, etc. can be used individually or 2 or more types can be used, respectively. It is preferable that the above-mentioned first monomer unit is an acrylic monomer unit.

Further, as the second monomer unit of (meth) acrylate having an alkyl group having 1 to 14 carbon atoms, (methyl) methacrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl ( Meta) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2 -Ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, tetradecyl (meth) acrylate, etc. These may be used alone or in combination of two or more thereof. When the number of carbon atoms contained in the alkyl group of the second monomer unit exceeds 14, since the alkyl group becomes too long and the nonpolarity becomes large, the adhesion may be reduced.

In the separator of the present invention, the content of the first monomer unit is preferably 10 to 80 mol%, more preferably 15 to 80 mol% based on the entire copolymer. If the content is less than 10 mol%, the adhesion may be lowered, and if the content is more than 80 mol%, the electrical resistance may be excessively high as the adhesion strength is excessively increased. On the other hand, the content of the second monomer unit is preferably 20 to 90 mol% based on the entire copolymer. If the content is less than 20 mol%, the adhesion may be lowered. If the content is more than 90 mol%, the adhesion may be lowered as the content of the first monomer unit is lowered.

In the separator of the present invention, it is preferable that the copolymer further comprises (c) a third monomer unit containing a cyano group, wherein the third monomer unit is ethyl cis- (beta-cyano) (meth) Acrylate, (meth) acrylonitrile, 2- (vinyloxy) ethanenitrile, 2- (vinyloxy) propanenitrile, cyanomethyl (meth) acrylate, cyanoethyl (meth) acrylate, cyanopropyl ( Meth) acrylate, etc. are mentioned. The content of the preferred third monomer unit is 5 to 50 mol% based on the entire copolymer.

In the separator of the present invention, the copolymer is preferably crosslinked with each other by the crosslinkable functional group by including a monomer unit having a crosslinkable functional group. As a crosslinkable functional group, a hydroxyl group, a primary amine group, a secondary amine group, an acidic group, an epoxy group, an oxetane group, an imidazole group, an oxazoline group, etc. can be illustrated, For example, the monomer which has such a crosslinkable functional group is mentioned. For example, 1 to 20 mol% may be further copolymerized, and then crosslinking agents such as an isocyanate compound, an epoxy compound, an oxetane compound, an aziridine compound, and a metal chelating agent may be added to crosslink the copolymers with each other.

In addition to this, the copolymer described above may further include other monomer units within the scope of not impairing the object of the present invention. For example, in order to improve the ion conductivity of the separator, alkoxy diethylene glycol (meth) acrylic acid ester having 1 to 8 carbon atoms, alkoxy triethylene glycol (meth) acrylic acid ester, alkoxy tetraethylene glycol (meth) acrylic acid ester, phenoxy (Meth) acrylic acid alkylene oxide adducts such as diethylene glycol (meth) acrylic acid esters, alkoxy dipropylene glycol (meth) acrylic acid esters, alkoxy tripropylene glycol (meth) acrylic acid esters, phenoxy dipropylene glycol (meth) acrylic acid esters And the like can be further copolymerized.

As the binder polymer, it will be apparent to those skilled in the art that a binder polymer may be used in combination with the above-described copolymer without departing from the object of the present invention.

In the separator of the present invention, the inorganic particles to be used are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and / or reduction reactions do not occur in the operating voltage range (for example, 0 to 5 V on the basis of Li / Li ⁺ ) of the applied electrochemical device. In particular, in the case of using the inorganic particles having the ion transport ability, it is possible to improve the performance by increasing the ion conductivity in the electrochemical device.

In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the dissociation degree of the electrolyte salt such as lithium salt in the liquid electrolyte.

For the above reasons, the inorganic particles preferably include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, inorganic particles having a lithium ion transfer ability, or a mixture thereof.

Non-limiting examples of inorganic particles having a dielectric constant greater than or equal to BaTiO ₃ , Pb (Zr _x Ti _{1 -x} ) O ₃ (PZT, where 0 <x <1), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, where, 0 <x <1, 0 <y <1 Im), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, where 0 < x <1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO ₂ Etc. can be used individually or in mixture of 2 or more types, respectively.

In particular, BaTiO ₃ , Pb (Zr _x Ti _{1- x} ) O ₃ (PZT, where 0 <x <1), Pb _{1 - x} La _x Zr _{1 -y} Ti _y O ₃ (PLZT, where 0 < x <1, 0 <y < 1 Im), (1-x) Pb (Mg 1/3 Nb 2/3) O 3 -xPbTiO 3 (PMN-PT, where 0 <x <1), hafnia (HfO Inorganic particles such as ₂ ) not only exhibit high dielectric constant characteristics of dielectric constant above 100, but also have piezoelectricity in which electric charges are generated when a tension or tension is applied under a constant pressure, thereby causing a potential difference between both surfaces. The internal short circuit of the positive electrode can be prevented from occurring, and the safety of the electrochemical device can be improved. In addition, synergistic effects of the high dielectric constant inorganic particles and the inorganic particles having lithium ion transfer ability may be doubled.

In the present invention, the inorganic particles having a lithium ion transferring ability refer to inorganic particles containing a lithium element but not lithium and having a function of transferring lithium ions. The inorganic particles having lithium ion transferring ability are contained in the particle structure Since lithium ions can be transferred and transferred due to a kind of defect present, the lithium ion conductivity in the battery is improved, thereby improving battery performance. Non-limiting examples of the inorganic particles having a lithium ion transfer capacity is lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3) , Lithium aluminum titanium phosphate (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 (LiAlTiP) _x O _y series glass such as ₂ O ₅ (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 germanium thiophosphate 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, etc. SiS ₂ series glass (Li _x Si _y S _z , 0 <x <3) such as Ride (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS _2, etc. , 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S ₅ There is 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 as such.

In the separator of the present invention, the inorganic particle size of the porous coating layer is not limited, but is preferably in the range of 0.01 to 10um as possible. If it is less than 0.01 um, the dispersibility is lowered, so it is not easy to control the physical properties of the separator, and if it exceeds 10 um, mechanical properties may be reduced.

The separator of the present invention can be manufactured through the following process.

First, after impregnating the first polymer binder solution in which the first polymer binder having a functional group and the crosslinking agent is mixed into a planar porous substrate having a plurality of pores, the first polymer binder is crosslinked with each other. Such crosslinking may cause UV crosslinking by photoinitiator or the like or by heating.

The first polymer binder solution is a mixture of a polymer binder having a functional group and a crosslinking agent in an organic solvent. The first polymer binder is impregnated into the porous substrate by impregnation, and crosslinking is generated between the first polymers using a crosslinking agent. Since the first polymer binder has excellent affinity with the porous substrate, the mechanical properties of the porous substrate are improved by bonding between the porous substrate and the crosslinked structure by crosslinking of the first polymer binder.

As such a crosslinking agent, the kind is not limited, but a crosslinking agent such as an isocyanate compound, an epoxy compound, an oxetane compound, an aziridine compound or a metal chelating agent can be used.

Thereafter, a second polymer binder solution having a second polymer binder having a functional group and a thermoplastic fine powder having a melting point lower than the melting point or the decomposition point of the porous substrate is mixed with the porous polymer including the crosslinked first polymer binder. After impregnation of the substrate, the second polymer binder is allowed to crosslink with the crosslinked first polymer binder.

The second polymer binder solution is used by mixing a polymer having a functional group and a thermoplastic fine powder having a melting point lower than the melting point or decomposition point of the porous substrate in an organic solvent. The porous base material is impregnated in the second polymer binder solution, and then crosslinked with the second polymer binder through UV irradiation or heating. Since the second polymer binder solution does not include a crosslinking agent, crosslinking occurs due to the crosslinking agent remaining after crosslinking of the first polymer binder of the porous substrate included in the first polymer binder solution. Since these remaining crosslinking agents are mainly involved in the crosslinking of the site of the functional group of the first polymer binder, the functional group of the newly impregnated second polymer binder is crosslinked with the functional group of the first polymer semi-inder, and the second binder polymer itself Crosslinking between functional groups is not easy. The second polymer binder is shown to surround the whole or part of the thermoplastic fine powder according to the amount of use thereof. In the case where the curable polymer is enclosed in the thermoplastic fine powder and trapped, the shutdown function may be limited because the movement is limited even when the thermoplastic fine powder is melted due to high temperature. In the separator of the present invention, the second polymer binder has almost no crosslinking therebetween. Since it is not produced, the shutdown function of the thermoplastic fine powder is not limited.

In addition, in order to improve physical properties of the separator of the present invention, the first polymer binder solution or the second polymer binder solution may further include inorganic particles.

The separator of the present invention prepared as described above may be used as a separator of an electrochemical device. That is, the separator of the present invention can be usefully used as the separator interposed between the positive electrode and the negative electrode. Electrochemical devices include all devices that undergo an electrochemical reaction, and specific examples include capacitors such as all kinds of primary, secondary cells, fuel cells, solar cells, or supercapacitor elements. 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 is preferable.

The electrochemical device may be manufactured according to conventional methods known in the art, and for example, may be manufactured by injecting an electrolyte after assembling the separator described above between an anode and a cathode. .

The electrode to be used together with the separator of the present invention is not particularly limited, and the electrode active material may be bound to an electrode current collector according to a conventional method known in the art. Non-limiting examples of the positive electrode active material of the electrode active material may be a conventional positive electrode active material that can be used for the positive electrode of the conventional electrochemical device, in particular lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide or combinations thereof It is preferable to use one lithium composite oxide. Non-limiting examples of the negative electrode active material may be a conventional negative electrode active material that can be used for the negative electrode of the conventional electrochemical device, in particular lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, Lithium adsorbents such as graphite or other carbons are preferred. Non-limiting examples of the positive electrode current collector is a foil made by aluminum, nickel or a combination thereof, and non-limiting examples of the negative electrode current collector by copper, gold, nickel or copper alloy or a combination thereof Foils produced.

Electrolyte that may be used in the present invention is A ⁺ B ^- A salt of the structure, such as, A ⁺ is Li ^+, Na ^+, K ⁺ comprises an alkaline metal cation or an ion composed of a combination thereof, such as, and 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 ) Salts containing ions consisting of anions such as ₃ ^- or combinations thereof include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethylcarbonate (EMC), gamma butyrolactone or mixtures thereof Some are dissolved or dissociated in an organic solvent, but are not limited thereto.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the battery assembly or at the end of battery assembly.

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 embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example

Preparation of Polymer Binders

NN-dimethylacrylamide (N, N-dimethylacrylamide) 40 parts by weight, acrylonitrile (20 parts by weight), 36 parts by weight of ethyl acrylate (ethyl acrylate) and 8 parts by weight of acrylic acid polymerized polymer A binder was prepared.

Example  1.second coated Separator

Primary coating

A 3 wt% acetone solution was prepared by dissolving the prepared polymer binder and the crosslinking agent, N, N, N ', N'-tetraglycidylethylenediamine in acetone. In addition, a polyethylene terephthalate nonwoven fabric having an average thickness of about 3 μm and having a thickness of 14 μm in excess of 50% of pores having a long diameter of less than 70 μm was prepared.

The nonwoven fabric was coated by dip coating using the 2 wt% acetone solution. After coating it was cured at 80 ° C. for 1 day. The thickness of the primary coated nonwoven was 15 um.

Secondary coating

PVdF latex and the prepared polymeric binder were mixed in a weight ratio of 2: 1 and dissolved in acetone to prepare a 6% by weight acetone solution. The primary coated nonwoven was recoated by dip coating using the 6 wt% acetone solution. After coating it was cured at 80 ° C. for 1 day. The thickness of the primary coated nonwoven was 18 um.

Comparative example  1. Nonwoven

Polyethylene terephthalate nonwoven fabric having an average thickness of about 3 μm and having a thickness of 14 μm with more than 50% of pores having a long diameter of less than 70 μm was prepared.

Comparative example  2. Primary coating Separator

A 3 wt% acetone solution was prepared by dissolving the prepared polymer binder and the crosslinking agent, N, N, N ', N'-tetraglycidylethylenediamine in acetone. In addition, a polyethylene terephthalate nonwoven fabric having an average thickness of about 3 μm and having a thickness of 14 μm in excess of 50% of pores having a long diameter of less than 70 μm was prepared.

The nonwoven fabric was coated by dip coating using the 2 wt% acetone solution. After coating it was cured at 80 ° C. for 1 day. The thickness of the primary coated nonwoven was 15 um.

Comparative example  3. Thermoplastic fine powder coating Separator

The PVdF latex is mixed with the polymer binder prepared in a weight ratio of 2: 1, and N, N, N ', N'-tetraglycidylethylenediamine as a crosslinking agent is added. Dissolved in acetone to prepare a 6% by weight acetone solution. In addition, a polyethylene terephthalate nonwoven fabric having an average thickness of about 3 μm and having a thickness of 14 μm in excess of 50% of pores having a long diameter of less than 70 μm was prepared.

The nonwoven fabric was coated by dip coating using the 6 wt% acetone solution. After coating it was cured at 80 ° C. for 1 day. The thickness of the coated nonwoven was 18 um.

Test Example  One. SEM  Picture

SEM pictures of Example 1 and Comparative Examples 1-3 were taken and shown in FIGS. 1-4. Figure 2 shows the surface of the non-coated non-woven fabric because the microfibers are not connected to each other in a state vulnerable to deformation when a physical force is applied, when the first coating, the polymeric binder is located inside the nonwoven fabric as shown in FIG. It was found that the microfibers are bonded by crosslinking to improve mechanical strength.

Comparing FIG. 1 showing Example 1 with FIG. 4 showing Comparative Example 3, in FIG. 1, the form of the microfibers can be confirmed by bonding between the secondary coated polymer binder and the primary coated crosslinked polymer binder. 4, it was found that the thermoplastic fine powder uniformly covered the entire nonwoven fabric by the randomly crosslinked polymer binder, and thus it was impossible to confirm the form of the microfiber.

Test Example  2. Tensile Strength Measurement

The separators of Example 1 and Comparative Examples 1-3 were prepared in a specimen of 15 mm X 10 cm to measure the tensile strength at a measuring speed of 50 mm / min is shown in Table 1 below, the tensile strength test graph is shown in Figure 5 and 6 is shown.

Value load
(gf) Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 MD 1754.46 1106.42 1537.95 1724.86 TD 473.49 207.53 326.15 455.73

Table 1 and Figures 5 and 6, it can be seen that the tensile strength of Example 1 was the highest, MD 60%, TD 127% compared to the nonwoven fabric of Comparative Example 1 was found to be improved.

Test Example  3. Measurement of resistance change with temperature

    The separators prepared in Example 1 and Comparative Examples 1 and 3 were shown in FIG. 7 by measuring the resistance while gradually increasing the temperature from room temperature.

In the separator of Example 1, it turned out that resistance increases rapidly in the vicinity of 140 degreeC. However, in the case of the separator using only the nonwoven fabric, which is the case of Comparative Example 1, the resistance is constant, and in the case of Comparative Example 3 in which the shutdown function is limited by the crosslinked binder polymer, although the thermoplastic fine powder is used, there is no rapid increase in the resistance. I noticed that the shutdown function did not work properly.

Test Example  4. of lithium secondary battery Charging and discharging  Test

Fabrication of Lithium Secondary Battery

N-methyl-2pyrrolidone (NMP), which is a solvent, is made of carbon powder as a negative electrode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as 96% by weight, 3% by weight, and 1% by weight as a conductive material, respectively. ) To prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper thin film, which is a negative electrode current collector having a thickness of 10 um, and dried, followed by roll press, to prepare a negative electrode.

A cathode mixture slurry was prepared by adding 92 wt% of lithium cobalt composite oxide as a cathode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of PVdF as a binder to N-methyl-2pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was applied to an aluminum thin film of a positive electrode current collector having a thickness of 20 μm, dried, and roll-pressed to prepare a positive electrode.

The HOSEN CR2016 coin cell was manufactured using the prepared negative electrode and positive electrode, and the separators prepared in Examples 1 and Comparative Examples 1-3, and the electrolyte (EC / EMC = 1/2 volume ratio, LiPF ₆ 1) was assembled into the assembled battery. Mole) was injected to prepare a battery.

Charge / discharge test

The charge and discharge test results of the manufactured lithium secondary battery are shown in FIG. 8.

The battery using the separators of Example 1 and Comparative Example 3 was normally charged and discharged, but the battery using the separators of Comparative Example 1 and Comparative Example 2 is very large pores of the non-woven fabric, the fine short is generated to charge and discharge normally It can be seen that.

Claims (25)

Planar porous substrates having a plurality of pores;
A first polymer binder positioned inside the porous substrate and having functional groups and crosslinked with each other; And
A mixture of a second polymer binder having a functional group coated on the porous substrate and a thermoplastic fine powder having a melting point lower than a melting point or a decomposition point of the porous substrate,
And the second polymer binder is crosslinked with the crosslinked first polymer binder. The method of claim 1,
Separator, characterized in that the inside of the porous substrate further comprises inorganic particles. The method of claim 1,
The porous substrate is a separator, characterized in that the non-woven substrate. The method of claim 3,
The nonwoven substrate is formed of a microfiber having an average thickness of 0.5 to 10 um, the separator characterized in that it comprises 50% or more of the pores having a long diameter of 0.1 to 70 um based on the total number of pores. The method of claim 3,
The melting point or decomposition point of the nonwoven fabric base material is a separator, characterized in that 200 ℃ or more. The method of claim 3,
The nonwoven substrate is any one polymer selected from the group consisting of polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene Or a separator formed from a mixture of two or more of them. The method of claim 3,
The thickness of the nonwoven substrate is a separator, characterized in that 9 to 30um. The method of claim 1,
The average particle diameter of the thermoplastic fine powder is a separator, characterized in that 0.1 to 10um. The method of claim 1,
The melting point of the thermoplastic fine powder is a separator, characterized in that 80 to 150 ℃. The method of claim 1,
The thermoplastic fine powder is a separator, characterized in that formed of any one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride, polyethylene and polystyrene. The method of claim 1,
The first binder polymer and the second binder polymer have, independently of each other, (a) a first monomer unit containing at least one or more of an amine group or an amide group in a side chain, and (b) an alkyl group having 1 to 14 carbon atoms. A copolymer comprising a second monomer unit of (meth) acrylate. The method of claim 11,
The content of the first monomer unit is 10 to 80 mol% based on the total copolymer, the separator characterized in that the content of the second monomer unit is 20 to 90 mol%. The method of claim 11,
The first monomer unit is 2-(((butoxyamino) carbonyl) oxy) ethyl (meth) acrylate, 2- (diethylamino) ethyl (meth) acrylate, 2- (dimethylamino) ethyl (meth ) Acrylate, 3- (diethylamino) propyl (meth) acrylate, 3- (dimethylamino) propyl (meth) acrylate, methyl 2-acetoamido (meth) acrylate, 2- (meth) acrylamide Dogglycolic acid, 2- (meth) acrylamido-2-methyl-1-propanesulfonic acid, (3- (meth) acrylamidopropyl) trimethyl ammonium chloride, N- (meth) acryloyl amido-e Methoxyethanol, 3- (meth) acryloyl amino-1-propanol, N- (butoxymethyl) (meth) acrylamide, N-tert-butyl (meth) acrylamide, diacetone (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N- (isobutoxymethyl) acrylamide, N- (isopropyl) (meth) acrylamide, (meth) acrylamide, N- Nyl (meth) acrylamide, N- (tris (hydroxymethyl) methyl) (meth) acrylamide, N-N '-(1,3-phenylene) dimaleimide, N-N'-(1,4 -Phenylene) dimaleimide, N-N '-(1,2-dihydroxyethylene) bisacrylamide, N-N'-ethylenebis (meth) acrylamide and N-vinylpyrrolidinone At least one selected. The method of claim 11,
The second monomer unit is (methyl) methacrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl ( Meth) acrylate, sec-butyl (meth) acrylate, pentyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, And at least one selected from the group consisting of isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate and tetradecyl (meth) acrylate. The method of claim 11,
The copolymer further comprises (c) a third monomer unit comprising a cyano group. 16. The method of claim 15,
The content of the third monomer unit is a separator, characterized in that 5 to 50 mol% based on the entire copolymer. The method of claim 2,
The average particle diameter of the inorganic particles is a separator, characterized in that 0.01 to 10um. Impregnating a first polymer binder solution having a first polymer binder having a functional group and a crosslinking agent on a planar porous substrate having a plurality of pores, thereby allowing the first polymer binder to crosslink with each other; And
Impregnating a second polymer binder solution comprising a second polymer binder having a functional group and a thermoplastic fine powder having a melting point lower than the melting point or the decomposition point of the porous substrate into the porous substrate having the crosslinked first polymer binder. After the step of allowing the second polymer binder to crosslink with the crosslinked first polymer binder. 19. The method of claim 18,
The first polymer binder solution is a method for producing a separator, characterized in that it further comprises inorganic particles. 19. The method of claim 18,
The second polymer binder solution is a method for producing a separator, characterized in that it further comprises inorganic particles. 19. The method of claim 18,
The porous substrate is formed of a microfiber having an average thickness of 0.5 to 10 um, the method of manufacturing a separator, characterized in that the non-woven substrate containing at least 50% of the pores having a long diameter of 0.1 to 70 um based on the total number of pores . The method of claim 18,
The first binder polymer and the second binder polymer have, independently of each other, (a) a first monomer unit containing at least one or more of an amine group or an amide group in a side chain, and (b) an alkyl group having 1 to 14 carbon atoms. It is a copolymer containing the 2nd monomeric unit of (meth) acrylate, The manufacturing method of the separator characterized by the above-mentioned. The method of claim 22,
The copolymer further comprises (c) a third monomer unit containing a cyano group. In the electrochemical device comprising an anode, a cathode, a separator interposed between the anode and the cathode,
The separator is an electrochemical device, characterized in that the separator of any one of claims 1 to 17. 25. The method of claim 24,
The electrochemical device is an electrochemical device, characterized in that the lithium secondary battery.

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