KR20210049554A - Separator for lithium secandary battery, and lithium secandary battery containing the same - Google Patents

Abstract

Provided are a separator for a lithium secondary battery including a metal ion adsorption layer, and a lithium secondary battery including the same. According to the present invention, the separator for a lithium secondary battery comprises: a porous polymer substrate having a plurality of pores; and a metal ion adsorption layer positioned on at least one surface of the porous polymer substrate and comprising a binder polymer, and a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of coordinating with a metal cation to adsorb the metal cation.

Description

Separator for lithium secondary battery and lithium secondary battery including the same {SEPARATOR FOR LITHIUM SECANDARY BATTERY, AND LITHIUM SECANDARY BATTERY CONTAINING THE SAME}

The present invention relates to a separator for a lithium secondary battery and a lithium secondary battery including the same, and to a separator for a lithium secondary battery that effectively adsorbs metal ions to improve battery performance, and to a lithium secondary battery including the same.

Recently, interest in energy storage technology is increasing. As the fields of application to mobile phones, camcorders, notebook PCs, and even electric vehicles are expanded, efforts for research and development of electrochemical devices are increasingly being materialized. Electrochemical devices are the field that is receiving the most attention in this respect, and the development of secondary batteries capable of charging and discharging among them is the focus of interest, and recently, in developing such batteries, new electrodes have been developed to improve capacity density and specific energy. It is proceeding with research and development on the design of the battery and the battery.

Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has the advantage of having a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. It is in the limelight. However, as the energy density of the lithium secondary battery has recently increased, it is difficult to secure electrode assembly stability due to an increase in the charging voltage.

In particular, positive electrode active materials used during high voltage charging and high temperature charging/discharging, for example, transition metals such as Ni and Mn, are eluted as ions, increasing the rate of deterioration of the electrode assembly of the lithium secondary battery, causing degradation of the electrode assembly. I can make it.

Accordingly, the problem to be solved by the present invention is to provide a separator for a lithium secondary battery that improves battery performance by effectively adsorbing metal ions eluted from a positive electrode active material.

Another problem to be solved by the present invention is to provide a lithium secondary battery having the separator for the lithium secondary battery.

In order to solve the above problems, according to an aspect of the present invention, a separator for a lithium secondary battery of the following embodiment is provided.

According to the first embodiment, a porous polymer substrate having a plurality of pores, and

A binder polymer positioned on at least one surface of the porous polymer substrate; And a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of adsorbing metal cations by coordinating with metal cations.

According to the second embodiment, in the first embodiment,

The crosslinked polymer may be a result of polymerization of a chelating group having two or more heterocyclic amines, a chelating monomer having one or more carbon-carbon double bonds, and a crosslinking agent having two or more carbon-carbon double bonds.

According to the third embodiment, in the first embodiment or the second embodiment,

The chelating group C1 to C5 alkyl or halogen substituted or unsubstituted bipyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted terpyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted Phenanthroline group, or two or more of these.

According to the fourth embodiment, in any one of the first to third embodiments,

The content of the crosslinked polymer may be 1 to 80 parts by weight based on 100 parts by weight of the binder polymer in the metal ion adsorption layer.

According to the fifth embodiment, in any one of the first to fourth embodiments,

As a result of XPS element analysis, the metal ion adsorption layer may have a nitrogen element ratio of 0.5% or more.

According to a sixth embodiment,

A composition for a coating layer by dissolving a binder polymer, a chelating group having two or more heterocyclic amines, a chelating monomer having one or more carbon-carbon double bonds, a crosslinking agent having two or more carbon-carbon double bonds, and an initiator in a solvent Preparing to;

Applying the composition for a coating layer on at least one surface of a porous polymer substrate having a plurality of pores; And

There is provided a method of manufacturing a separator for a lithium secondary battery comprising a step of forming a metal ion adsorption layer by performing a polymerization reaction between the chelating monomer and a crosslinking agent while drying the applied coating layer composition.

According to the seventh embodiment, in the sixth embodiment,

The chelating group C1 to C5 alkyl or halogen substituted or unsubstituted bipyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted terpyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted Phenanthroline group, or two or more of these.

According to the eighth embodiment, in the sixth embodiment or the seventh embodiment,

The chelating monomer is 4-methyl-4'-vinyl-2,2'-bipyridine, 5-vinyl-2,2'-bipyridine, 4-vinyl-2,2'-bipyridine, 3-vinyl- 2,2'-bipyridine, or two or more of these may be included.

According to the ninth embodiment, in any one of the sixth to eighth embodiments,

The crosslinking agent may be a polymerizable compound having two or more (meth)acrylate residues in the molecule.

According to the tenth embodiment, in any one of the sixth to ninth embodiments,

The crosslinking agent is hexanediol di(meth)acrylate, trimethylolpropane trioxyethyl di(meth)acrylate, alkylene glycol di(meth)acrylate, dialkylene glycol di(meth)acrylate, trialkylene glycol Di(meth)acrylate, dicyclopentenyl di(meth)acrylate, dicyclopentenyloxyethyl di(meth)acrylate, neopentyl glycol di(meth)acrylate, dipentaerythritol hexa di(meth) Acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, or two or more of these may be included.

According to the eleventh embodiment, in the sixth to tenth embodiments,

The crosslinking agent is 3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane triacrylate, tetraethyleneglycol di Acrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, or two or more of these may be included.

According to the twelfth embodiment, in the sixth to eleventh embodiments,

The molar ratio of the crosslinking agent and the chelating monomer may be 1:1 to 4:1.

According to the thirteenth embodiment, in the sixth to twelfth embodiments,

The binder polymer is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, Polybutylacrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co -vinyl acetate), polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl Fluran (cyanoethylpullulan), cyanoethylpolyvinylalcohol (cyanoethylpolyvinylalcohol), cyanoethylcellulose (cyanoethylcellulose), cyanoethylsucrose (cyanoethylsucrose), flulan (pullulan), carboxyl methyl cellulose (carboxyl methyl cellulose), or these Two or more of them may be included.

According to a fourteenth embodiment,

In a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, a lithium secondary battery is provided, wherein the separator is a separator according to any one of the first to fifth embodiments.

The separator for a lithium secondary battery according to an embodiment of the present invention comprises a metal ion adsorption layer on a porous polymer substrate in the form of a crosslinked polymer in which the chelating monomer is crosslinked with a crosslinking agent and is not dissolved in the electrolyte. Under conditions, it is possible to adsorb the metal cations by coordinating with the metal cations eluted from the anode stably.

The separator for a lithium secondary battery according to an embodiment of the present invention is, in particular, when a positive electrode active material used during high voltage charging and high temperature charging/discharging, for example, a transition metal such as Ni, Mn, is eluted as a cation, By preventing the eluted metal cations from being transferred to the negative electrode by adsorbing the eluted metal cations by the chelating group of the crosslinked polymer included in the metal ion adsorption layer, the lithium secondary battery equipped with the separator significantly reduces the rate of degeneration by the eluted cations Thus, the capacity and cycle performance of the lithium secondary battery can be greatly improved.

Hereinafter, the present invention will be described in detail. The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The separator according to an aspect of the present invention,

A porous polymer substrate having a plurality of pores, and

A binder polymer positioned on at least one surface of the porous polymer substrate; And a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of adsorbing metal cations by coordinating bonds with metal cations.

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

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

At this time, the polyolefin porous polymer film is a high-density polyethylene, linear low-density polyethylene, low-density polyethylene, polyethylene such as ultra-high molecular weight polyethylene, polyolefin-based polymers such as polypropylene, polybutylene, polypentene, etc. It can be formed with.

In addition, the porous polymer film substrate may be manufactured by molding into a film shape using various polymers such as polyester in addition to polyolefin. In addition, the porous polymer film substrate may be formed in a structure in which two or more film layers are stacked, and each film layer may be formed of a polymer such as polyolefin or polyester described above alone or a mixture of two or more of them. have.

In addition, the porous polymer film substrate and the porous nonwoven fabric substrate include polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, in addition to the polyolefin-based materials described above. ), polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene And the like may be formed of a polymer alone or a mixture of them, respectively.

The thickness of the porous polymer substrate is not particularly limited, but specifically 1 to 100 μm, more specifically 5 to 50 μm, and the pore size and porosity present in the porous polymer substrate are also not particularly limited, but each 0.01 to 50 It is preferably in the range of μm and 10 to 95%.

The separator for a lithium secondary battery of the present invention is located on at least one surface of the porous polymer substrate, and includes a binder polymer; And a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of adsorbing metal cations by coordinating bonds with metal cations.

In the metal ion adsorption layer of the separator of the present invention, the chelating group, that is, the ligand contained in the crosslinked polymer, is a metal cation eluted by coordinating with the metal cation eluted from the positive electrode when the separator is later used in a lithium secondary battery. It can play a role of adsorbing.

According to an embodiment of the present invention, the crosslinking polymer is a chelating group having two or more heterocyclic amines, a chelating monomer having one or more carbon-carbon double bonds, and a crosslinking agent having two or more carbon-carbon double bonds. It may be a result of the polymerization reaction of.

Therefore, in the separation membrane according to an embodiment of the present invention, the chelating group is included in the form of a functional group of a monomer and is not simply physically mixed in the metal ion adsorption layer, but a crosslinking agent and a chelating monomer are crosslinked through a polymerization reaction. It is contained in polymer.

If the chelating monomer is present in a monomolecular state that is not crosslinked, it is dissolved by the electrolyte when the electrolyte is injected after assembly of the electrode assembly, and the metal cations cannot be adsorbed.

However, in one embodiment of the present invention, since the chelating monomer is present in the form of a crosslinked polymer by crosslinking with a crosslinking agent, it is not dissolved by the electrolyte even under the condition impregnated with the electrolyte, and it is possible to continuously and stably adsorb metal cations. have.

As a result, the separator for a lithium secondary battery according to an embodiment of the present invention, in particular, when a positive electrode active material used during high voltage charging and high temperature charging/discharging, for example, transition metals such as Ni and Mn, is eluted as a cation, By preventing the eluted metal cations from being transferred to the negative electrode by adsorbing the eluted metal cations by the chelating group of the crosslinked polymer included in the metal ion adsorption layer of the separator, the lithium secondary battery provided with the separator has a rate of degradation due to the eluted cations. Remarkably reduced, the capacity and cycle performance of the lithium secondary battery can be greatly improved.

The chelating group may include bipyridine unsubstituted or substituted with C1 to C5 alkyl or halogen, phenanthroline unsubstituted or substituted with C1 to C5 alkyl or halogen, or two or more of them.

In one embodiment of the present invention, as the binder polymer, a polymer commonly used in forming a porous coating layer in the art may be used. In particular, a polymer having a glass transition temperature (T _g ) of -200 to 200°C may be used, because it is possible to improve mechanical properties such as flexibility and elasticity of the finally formed porous coating layer. Such a binder polymer faithfully plays a role of maintaining the bonding without dissolving in the electrolytic solution in the coating layer a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of adsorbing metal cations by coordinating with metal cations. You can do it.

In addition, the binder polymer does not necessarily have ion conduction capability, but when a polymer having ion conduction capability is used, the performance of the lithium secondary battery may be further improved. Therefore, as the binder polymer, one having a high dielectric constant as possible may be used. In fact, since the degree of dissociation of the salt in the electrolyte depends on the dielectric constant of the solvent of the electrolyte, the higher the dielectric constant of the binder polymer, the higher the degree of dissociation of the salt in the electrolyte. The dielectric constant of such a binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and in particular may be 10 or more.

In addition to the above-described functions, the binder polymer may have a characteristic capable of exhibiting a high degree of swelling by gelling when impregnated with a liquid electrolyte. Accordingly, the solubility index of the binder polymer, that is, the Hildebrand solubility parameter, is in the range of 15 to 45 MPa ^1/2 or 15 to 25 MPa ^1/2 and 30 to 45 MPa ^1/2 . Therefore, hydrophilic polymers having a large number of polar groups may be used more than hydrophobic polymers such as polyolefins. This is because, when the solubility index is less than ^{15 MPa 1/2 and exceeds 45 MPa 1/2} , it may be difficult to swell by a conventional liquid electrolyte for batteries.

Non-limiting examples of such binder polymers include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polymethylmethacrylic. Polymethylmethacrylate, polybutylacrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate aerial Polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate ), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, flulan, carboxyl methyl cellulose cellulose), or two or more of them, but is not limited thereto.

According to an embodiment of the present invention, the content of the crosslinked polymer may be 1 to 80 parts by weight, or 30 to 70 parts by weight, or 33 to 67 parts by weight based on 100 parts by weight of the binder polymer in the metal ion adsorption layer. When the content of the crosslinked polymer satisfies this range, the chelating effect can be maximized at a level that does not impair the adhesion ability of the binder polymer to the coating layer.

As a result of XPS element analysis, the metal ion adsorption layer may have a nitrogen element ratio of 0.5% or more, specifically, a nitrogen element ratio of 0.5% or more, and a nitrogen element ratio of 0.7 to 1.8%. When the metal ion adsorption layer has a nitrogen element ratio within this range, the metal ion kelite effect by nitrogen atoms can be enhanced.

At this time, the nitrogen element ratio of the metal ion adsorption layer is an intensity scan method according to binding energy using a K-alpha X-ray photoelectron spectrometer (XPS) system (thermos fisher scientific) equipment. Can be measured.

A method of manufacturing a separator according to an aspect of the present invention,

A composition for a coating layer by dissolving a binder polymer, a chelating group having two or more heterocyclic amines, a chelating monomer having one or more carbon-carbon double bonds, a crosslinking agent having two or more carbon-carbon double bonds, and an initiator in a solvent Preparing to;

Applying the composition for a coating layer on at least one surface of a porous polymer substrate having a plurality of pores; And

And forming a metal ion adsorption layer by performing a polymerization reaction between the chelating monomer and a crosslinking agent while drying the applied coating layer composition. Hereinafter, we will look at each step.

First, a binder polymer, a chelating group having two or more heterocyclic amines, and a chelating monomer having one or more carbon-carbon double bonds, a crosslinking agent having two or more carbon-carbon double bonds, and an initiator are dissolved in a solvent to obtain a coating layer. Prepare a composition for use.

As described above, the chelating group is a C1 to C5 alkyl or a halogen-substituted or unsubstituted bipyridine group, a C1 to C5 alkyl or halogen-substituted or unsubstituted terpyridine group, a C1 to C5 alkyl or halogen It may contain a substituted or unsubstituted phenanthroline group, or two or more of them.

The chelating monomer may be applied without limitation as long as it is a chelating group having two or more heterocyclic amines and a compound having one or more carbon-carbon double bonds, and specifically, a bipyridine group, a terpyridine It may be a compound containing a group, a phenanthroline group, and the like and having a double bond (vinyl group, etc.). At this time, a chelating group having two or more heterocyclic amines such as a bipyridine group, a terpyridine group, and a phenanthroline group may be substituted or unsubstituted with C1 to C5 alkyl or halogen.

According to an embodiment of the present invention, the chelating monomer is 4-methyl-4'-vinyl-2,2'-bipyridine (4-Methyl-4'-vinyl-2,2'-bipyridine (MVBipy)) , 5-vinyl-2,2'-bipyridine, 4-vinyl-2,2'-bipyridine, 3-vinyl-2,2'-bipyridine, and the like, but are not limited thereto.

The crosslinking agent having two or more carbon-carbon double bonds may be a polymerizable compound having two or more (meth)acrylate residues in a molecule.

According to an embodiment of the present invention, the crosslinking agent is hexanediol di(meth)acrylate, trimethylolpropane trioxyethyl di(meth)acrylate, alkylene glycol di(meth)acrylate, dialkylene glycol di. (Meth)acrylate, trialkylene glycol di(meth)acrylate, dicyclopentenyl di(meth)acrylate, dicyclopentenyloxyethyl di(meth)acrylate, neopentyl glycol di(meth)acrylate , Dipentaerythritol hexa di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, or two or more of these may be included.

In addition, as the crosslinking agent, 3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane triacrylate, tetra Ethylene glycol diacrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, or two or more of these may be included.

As the initiator, at least one selected from the group of initiators consisting of persulfate-based initiators, azo-based initiators, hydrogen peroxide and ascorbic acid may be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na2S2O8), potassium persulfate (K2S2O8), and ammonium persulfate ((NH4)2S2O8), and the like, and Azo-based Examples of initiators include 2, 2-azobis-(2-amidinopropane) dihydrochloride (2, 2-azobis(2-amidinopropane) dihydrochloride), 2, 2-azobis-(N, N-dimethylene) isobu Tyramide dihydrochloride (2,2-azobis-(N, N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoyl azo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis [2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride), 4,4-azobis-( 4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)) and the like, but are not limited thereto.

The initiator may be included in a concentration of about 0.001 to about 0.5% by weight based on the composition for the coating layer. When the concentration of the initiator satisfies this range, polymerization between the chelating monomer and the crosslinking agent may occur smoothly, and when mixed with other polymers, the chemical bond of the crosslinked polymer may not be broken, which is advantageous.

The solvent used at this time has a solubility index similar to that of the binder polymer, chelating monomer, and crosslinking agent to be used, and preferably has a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, cyclohexane, a mixed solvent of methanol and benzene, or these It may be used as a mixture of two or more of them.

According to an embodiment of the present invention, the solvent may be appropriately selected and applied depending on the object to be dissolved. For example, acetone, N-methyl-2-pyrrolidone, etc. may be used as a solvent for dissolving the binder polymer, and a mixed solvent of methanol and benzene may be used as a solvent for dissolving the chelating monomer. In addition, a mixed solvent of methanol and benzene may be used as a solvent for dissolving the crosslinking agent. In this case, in the case of a mixed solvent of methanol and benzene, the volume ratio may be 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5.

According to an embodiment of the present invention, a binder polymer solution is prepared by dissolving the binder polymer in a first solvent, and a chelating monomer solution is prepared by dissolving the chelating monomer in a second solvent, and the crosslinking agent is used as a third solution. By dissolving in a solvent, each crosslinking agent solution can be prepared. In addition, in the case of mixing the prepared solution, a chelating monomer solution and a crosslinking agent solution may be sequentially added to the binder polymer solution, and the addition method may be introduced in small portions using a pipette or the like. The reason for this small amount is that the degree of polymerization of the chelating monomer can be maximized by controlling the crosslinking rate. Thereafter, an initiator may be added to a solution obtained by mixing the binder polymer solution, the chelating monomer solution, and the crosslinking agent solution to prepare a coating layer composition.

According to an embodiment of the present invention, the concentration of the binder polymer solution may be 1 to 15% by weight, the concentration of the chelating monomer solution may be 1 to 20% by weight, and the concentration of the crosslinking agent solution is 1 to 15% by weight. It may be 20% by weight.

In the coating layer composition, the molar ratio of the crosslinking agent and the chelating monomer is 1:1 to 4:1, or 1:1 to 3.5:1, or 1.02:1 to 3.06:1, or 1:1 to 2.04:1 days I can. When the molar ratio satisfies this range, adsorption properties for metal ions may be improved, and the effect of chelating metal ions in the coating layer may be maximized due to improvement in the degree of polymerization of the chelating monomer.

According to an embodiment of the present invention, in the composition for a coating layer, the content of the crosslinking agent may be 15 to 60 parts by weight, or 15 to 35 parts by weight, based on 100 parts by weight of the binder polymer, and the content of the chelating monomer is It may be 8 to 20 parts by weight, or 8 to 15 parts by weight. When the content of the crosslinking agent and the content of the chelating monomer satisfy these ranges, the metal ion chelating effect in the coating layer may be maximized due to the improvement in the degree of polymerization of the chelating monomer.

Next, the composition for a coating layer is applied on at least one surface of a porous polymer substrate having a plurality of pores.

The method of coating the composition for the coating layer on the porous polymer substrate is not particularly limited, but it is preferable to use a slot coating or dip coating method. In the slot coating, the composition supplied through the slot die is applied to the entire surface of the substrate, and the thickness of the coating layer can be adjusted according to the flow rate supplied from the metering pump. In addition, dip coating is a method of coating by immersing a substrate in a tank containing the composition, and the thickness of the coating layer can be adjusted according to the concentration of the composition and the speed of removing the substrate from the composition tank. Through it, the amount of coating on the substrate can be adjusted.

Next, while drying the applied coating layer composition, a metal ion adsorption layer is formed by performing a polymerization reaction between the chelating monomer and a crosslinking agent.

By drying the porous polymer substrate coated with the composition for the coating layer using a dryer such as an oven or a conveyor dryer, a polymerization reaction between the chelating monomer and the crosslinking agent contained in the composition for the coating layer can be carried out, thereby forming a crosslinking agent through a crosslinking reaction. .

In this case, the drying temperature may be 60 to 100 °C, or 60 to 80 °C, and the drying time may be 12 to 24 hours, or 12 to 18 hours.

According to an embodiment of the present invention, the applied composition for a coating layer may be dried to undergo a crosslinking reaction, and then washed with a solvent, and then further dried again. In this case, the additional drying temperature may be 60 to 120 °C, or 60 to 100 °C, and the additional drying time may be 12 to 36 hours, or 18 to 36 hours. The reason why drying is not performed once, but proceeds twice, is to remove the solution washed with residues after the thermal crosslinking reaction.

An electrochemical device according to an aspect of the present invention includes an anode, a cathode, and a separator interposed between the anode and the cathode, and the separator is a separator according to an embodiment of the present invention described above.

Such an electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor devices. Particularly, among the secondary batteries, 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 preferred.

The positive electrode and the negative electrode to be applied together with the separator of the present invention are not particularly limited, and an electrode active material may be prepared in a form bound to an electrode current collector according to a conventional method known in the art. As a non-limiting example of the positive electrode active material among the electrode active materials, a conventional positive electrode active material that can be used for the positive electrode of a conventional electrochemical device may be used, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use one 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 the negative electrode of a conventional electrochemical device may be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorption materials such as graphite or other carbons are preferable. Non-limiting examples of the positive electrode current collector include aluminum, nickel, or a foil manufactured by a combination thereof, and non-limiting examples of the negative electrode current collector include copper, gold, nickel, or a copper alloy, or a combination thereof. And foils that are manufactured.

The electrolyte that can be used in the electrochemical device of the present invention is a salt having a structure such as ^{A +} B ^{- , where A +} contains an ion consisting of an alkali metal cation such as Li ⁺ , Na ⁺ , K ^{+ or a combination thereof, 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 ) ₃ ^- A salt containing an anion or a combination thereof such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl Carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (g -Butyrolactone) or dissolved or dissociated in an organic solvent consisting of a mixture thereof, but is not limited thereto.

The electrolyte injection may be performed at an appropriate step in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it can be applied before assembling the battery or in the final step of assembling the battery.

Hereinafter, examples will be described in detail in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in 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 describe the present invention to those of ordinary skill in the art.

Example 1

As a binder polymer, 6 g of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) 10.0 μmoL (weight average molecular weight: 600,000) was dissolved in 94 g of acetone as a solvent to prepare a binder polymer solution having a concentration of 6% by weight.

As a chelating monomer, 5.0mmoL (0.98g) of 4-methyl-4'-vinyl-2,2'-bipyridine (4-Methyl-4'-vinyl-2,2'-bipyridine (MVBipy)) was added to methanol and benzene. Was added to 5 mL of a mixed solvent (volume ratio of 1:1), and stirred with a magnetic bar until the chelating monomer was sufficiently dissolved to prepare a chelating monomer solution.

The chelating monomer solution prepared in the binder polymer solution was added in small portions with a pipette and stirred.

Thereafter, ethylene glycol dimethacrylate 5.10 mmoL (1.01 g) as a crosslinking agent was pipetted into the mixed solution of the binder polymer solution and the chelating monomer solution, followed by stirring until a uniform solution was observed.

To the obtained solution, 0.3 mmoL of AIBN (Azobisisobutyronitrile) was added as an initiator and stirred to prepare a composition for a coating layer.

Under the conditions of 35% humidity and room temperature (25°C), the composition for the coating layer was coated with a slurry bar on one side of a porous polyethylene film substrate (thickness 9㎛, resistance 0.66 ohm, air permeability 142 sec/100cc) as a porous polymer substrate, and convection After drying at 60℃ for 18hr using a convection oven and crosslinking reaction, after washing with a mixed solvent of methanol and benzene (volume ratio 1:1), vacuum drying at 80℃ for 24hr, porous polyethylene film A separator having a metal ion adsorption layer on one side of the substrate was prepared. At this time, the thickness of the metal ion adsorption layer was 3 µm.

_{96.7 parts by weight of Li[Ni 0.6} Mn _0.2 Co _0.2 ]O ₂ functioning as a positive electrode active material, 1.3 parts by weight of graphite functioning as a conductive agent, and 2.0 parts by weight of polyvinylidene fluoride (PVdF) functioning as a binder are mixed, A positive electrode mixture was prepared. A positive electrode mixture slurry was prepared by dispersing the obtained positive electrode mixture in 1-methyl-2-pyrrolidone serving as a solvent. This slurry was coated, dried, and pressed on both sides of an aluminum foil having a thickness of 20 μm, respectively, to prepare a positive electrode.

By mixing 97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) functioning as a negative electrode active material, 1.2 parts by weight of styrene-butadiene rubber (SBR) functioning as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC) , A negative electrode mixture was prepared. A negative electrode mixture slurry was prepared by dispersing this negative electrode mixture in ion-exchanged water serving as a solvent. This slurry was coated on both sides of a copper foil having a thickness of 20 μm, dried, and pressed to prepare a negative electrode.

In an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a composition of 3:3:4 (volume ratio), LiPF ₆ was dissolved to a concentration of 1.0M to obtain a non-aqueous electrolyte. Was prepared.

A separator-electrode composite was prepared by laminating the separator so that the separator was interposed between the positive electrode and the negative electrode prepared above, so that at least one of the active material layers of the positive electrode and the negative electrode was interviewed with the porous coating layer of the separator. After storing the separator-electrode composite in a pouch, the electrolyte was injected to prepare a secondary battery.

Example 2

A separator and a secondary battery having the same were prepared in the same manner as in Example 1, except that 10.20 mmoL (2.02 g) of ethylene glycol dimethacrylate was used as a crosslinking agent.

Example 3

A separator and a secondary battery having the same were prepared in the same manner as in Example 1, except that ethylene glycol dimethacrylate 15.30 mmoL (3.03 g) was used as a crosslinking agent.

Comparative Example 1

As a binder polymer, 6 g of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) 10.0 μmoL (weight average molecular weight: 600,000) was dissolved in 94 g of acetone as a solvent to prepare a binder polymer solution having a concentration of 6% by weight.

Under conditions of 35% humidity and room temperature (25° C.), the binder polymer solution was coated with a slurry bar on one side of a porous polyethylene film substrate, which is a porous polymer substrate, and dried at room temperature (25° C.) for 10 minutes to prepare a separator. In addition, a secondary battery including this separator was manufactured in the same manner as in Example 1.

Evaluation results

(1) XPS elemental analysis and evaluation

For the separation membranes of Examples 1 to 3 and Comparative Example 1, analysis was performed using the K-Alpha (model name) XPS equipment of ThermoFisher Scientific. The X-ray source used had an energy of monochromated Al Ka, 1486.6 eV. Survay scan spectrum conditions were a binding energy range of -10 to 1350 eV, a dwell time of 10 ms with a step of 1 eV, a pass energy of 200 eV (CAE mode), and a number of scans of 20 scans. As a result of the evaluation, the element content in the metal ion adsorption layer of the separators of Examples 1 to 3 and Comparative Example 1 was analyzed, and the results are shown in Table 1.

(2) Ni ion absorption amount evaluation

Element content analysis was performed using Perkin Elmer's ICP-OES OPTIMA 7300DV equipment. The test method is as follows. The results are shown in Table 1 below.

1) The secondary batteries of Examples 1 to 3 and Comparative Example 1 were charged to SOC 30 at a 0.1 C-rate at room temperature, respectively, and aged for 3 days, and then gas was removed. Thereafter, the secondary battery was decomposed to separate the secondary battery after charging and discharging a total of 100 cycles by charging up to a voltage of 4.3 V at a current density of 0.33 C-rate and discharging to 2.5 V at the same current density. A metal ion adsorption layer sample was prepared by separating the metal ion adsorption layer from the porous polymer substrate of the separated membrane using a razor blade. About 0.05 g of the prepared metal ion adsorption layer sample was aliquoted into a platinum crucible and the weight was accurately measured.

2) 1 mL of concentrated sulfuric acid and 1 mL of phosphoric acid were sequentially added to the sample, and then well shaken to mix.

3) The sample was dissolved by heating the sample on a hot plate. (After the first heating at 370° C., the second heating at 540° C.).

4) The sample was dissolved while shaking while heating. (Add 0.5 mL of concentrated sulfuric acid to prevent phosphoric acid from hardening.)

5) When the sample was clearly dissolved, 1 drop of hydrofluoric acid was added, sealed, and well shaken to mix.

6) The sample was allowed to stand at room temperature for about 3 hours to dissolve.

7) About 1 mL of boric acid water was added, 0.1 mL of Sc was added as an internal standard and diluted with 10 mL of ultrapure water.

8) The diluted resultant was filtered to measure ICP (Inductively Coupled Plasma Spectrometer).

Molar ratio of crosslinking agent and chelating monomer XPS Elemental Analysis-Elemental Ratio (%) Ni ion adsorption amount (ppm) Carbon element ratio (%) Fluorine element ratio (%) Hydrogen element ratio (%) Nitrogen element ratio (%) Example 1 1.02:1 65.9 26.3 1.7 1.8 170 Example 2 2.04:1 64.9 26.2 1.6 1.1 210 Example 3 3.06:1 64.6 26.4 1.6 0.7 100 Comparative Example 1 - 65.9 26.5 1.8 0.2 40

Referring to Table 1, it was confirmed that the separator of Examples 1 to 3 of the present invention significantly improved the Ni ion adsorption performance, which is a kind of transition metal eluted from the positive electrode active material, compared to the separator of Comparative Example 1. As a result, in the lithium secondary battery employing the separators of Examples 1 to 3 of the present invention, the rate of degeneration by the eluted cations is significantly reduced, and the capacity and cycle performance of the lithium secondary battery are expected to be greatly improved.

Claims (14)

A porous polymer substrate having a plurality of pores, and
A binder polymer positioned on at least one surface of the porous polymer substrate; And a crosslinked polymer containing a chelating group having two or more heterocyclic amines capable of adsorbing metal cations by coordinating with metal cations. The method of claim 1,
The crosslinked polymer is characterized in that it is a result of polymerization of a chelating group having two or more heterocyclic amines and a chelating monomer having one or more carbon-carbon double bonds and a crosslinking agent having two or more carbon-carbon double bonds. A separator for lithium secondary batteries. The method of claim 1,
The chelating group C1 to C5 alkyl or halogen substituted or unsubstituted bipyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted terpyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted A separator for a lithium secondary battery, comprising a phenanthroline group, or two or more of them. The method of claim 1,
A separator for a lithium secondary battery, wherein the content of the crosslinked polymer is 1 to 80 parts by weight based on 100 parts by weight of the binder polymer in the metal ion adsorption layer. The method of claim 1,
A separator for a lithium secondary battery, wherein the metal ion adsorption layer has a nitrogen element ratio of 0.5% or more as a result of XPS element analysis. A composition for a coating layer by dissolving a binder polymer, a chelating group having two or more heterocyclic amines, a chelating monomer having one or more carbon-carbon double bonds, a crosslinking agent having two or more carbon-carbon double bonds, and an initiator in a solvent Preparing for it;
Applying the composition for a coating layer on at least one surface of a porous polymer substrate having a plurality of pores; And
The method for producing a separator for a lithium secondary battery according to claim 1, comprising: forming a metal ion adsorption layer by performing a polymerization reaction between the chelating monomer and a crosslinking agent while drying the applied coating layer composition. The method of claim 6,
The chelating group C1 to C5 alkyl or halogen substituted or unsubstituted bipyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted terpyridine group, C1 to C5 alkyl or halogen substituted or unsubstituted A method for producing a separator for a lithium secondary battery, comprising a phenanthroline group, or two or more of them. The method of claim 6,
The chelating monomer is 4-methyl-4'-vinyl-2,2'-bipyridine, 5-vinyl-2,2'-bipyridine, 4-vinyl-2,2'-bipyridine, 3-vinyl- 2,2'-bipyridine, or a method for producing a separator for a lithium secondary battery comprising two or more of these. The method of claim 6,
The method for producing a separator for a lithium secondary battery, characterized in that the crosslinking agent is a polymerizable compound having two or more (meth)acrylate residues in a molecule. The method of claim 9,
The crosslinking agent is hexanediol di(meth)acrylate, trimethylolpropane trioxyethyl di(meth)acrylate, alkylene glycol di(meth)acrylate, dialkylene glycol di(meth)acrylate, trialkylene glycol Di(meth)acrylate, dicyclopentenyl di(meth)acrylate, dicyclopentenyloxyethyl di(meth)acrylate, neopentyl glycol di(meth)acrylate, dipentaerythritol hexa di(meth) An acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, or a method for producing a separator for a lithium secondary battery comprising two or more of them. The method of claim 9,
The crosslinking agent is 3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane triacrylate, tetraethyleneglycol di A method for producing a separator for a lithium secondary battery, comprising acrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, or two or more of them. The method of claim 6,
The method of manufacturing a separator for a lithium secondary battery, characterized in that the molar ratio of the crosslinking agent and the chelating monomer is 1:1 to 4:1. The method of claim 6,
The binder polymer is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, Polybutylacrylate, polybutylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co -vinyl acetate), polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl Fluran (cyanoethylpullulan), cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, flulan, carboxyl methyl cellulose, or these Method for producing a separator for a lithium secondary battery, characterized in that it comprises two or more of. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, wherein the separator is the separator according to any one of claims 1 to 5.