WO2020226370A1 - Separator for electrochemical device, and electrochemical device comprising same - Google Patents

Abstract

The present invention relates to a separator for an electrochemical device and an electrochemical device comprising same. The separator includes a porous polymer substrate and a heat-resistant coating layer disposed on at least one surface of the porous polymer substrate, and the heat-resistant coating layer is a porous polymer membrane having pores formed thereon, and includes polyvinylpyrrolidone and a PVDF-based polymer.

Description

Separator for electrochemical device and electrochemical device including the same

This application claims priority based on Korean Patent Application No. 10-2019-0054535 filed on May 9, 2019 and Korean Patent Application No. 10-2020-0051771 filed on April 28, 2020. The present invention relates to a separator for an electrochemical device and an electrochemical device including the same.

Recently, great attention has been paid to securing its safety in the field of electrochemical devices. Particularly, a secondary battery such as a lithium secondary battery has an electrode assembly including a positive electrode, a negative electrode, and a separator, and the electrode assembly may be manufactured in a structure in which a separator is interposed between the positive electrode and the negative electrode.

Electrochemical devices as described above are produced by many companies, but their safety characteristics are different. It is very important to evaluate the safety of these electrochemical devices and ensure safety. The most important consideration is that if an electrochemical device malfunctions, it must not injure the user, and for this purpose, the safety standards strictly regulate ignition and smoke in the electrochemical device. In terms of the safety characteristics of an electrochemical device, there is a high concern that an explosion may occur when the electrochemical device is overheated, causing thermal runaway or penetrating the separator. In particular, polyolefin-based porous polymer substrates, which are commonly used as separators for electrochemical devices, exhibit extreme heat shrinkage behavior at a temperature of 100 degrees Celsius (℃) or higher due to material properties and manufacturing process characteristics including stretching. There is a problem that causes a short circuit between the and the cathode.

In order to solve the safety problem of such an electrochemical device, an electrode in which a porous coating layer is formed by coating a mixture of an excessive amount of inorganic particles and a binder resin on at least one surface of a porous polymer substrate having a plurality of pores has been proposed. Since the inorganic particles contained in the porous coating layer have excellent heat resistance, even when the electrochemical device is overheated, insulation between the anode and the cathode is maintained to prevent a short circuit.

The preparation of such a porous coating layer includes preparing a polymer solution by mixing a polymer resin with a solvent, adding inorganic particles to the polymer solution and dispersing the inorganic particles uniformly in a slurry, and controlling the inorganic particles to a predetermined size. It goes through a number of process steps such as milling. In this process, it takes a lot of time to disperse and pulverize the inorganic particles, which causes the process to be delayed.

Accordingly, development of a separation membrane having a high process efficiency and a level similar to that of a separation membrane containing inorganic particles is required.

An object of the present invention is to provide a method of manufacturing a separator with high process efficiency. In addition, another object of the present invention is to provide a separator that is thin and has high heat resistance. Other objects and advantages of the present invention will be understood by the following description. In addition, it will be easily understood that the objects and advantages of the present invention can be realized by means or methods described in the claims, and combinations thereof.

The present invention was derived to solve the above-described technical problem. A first aspect of the present invention relates to a separator for an electrochemical device, wherein the separator includes a porous polymer substrate; A heat-resistant coating layer formed on at least one surface of the porous polymer substrate, wherein the heat-resistant coating layer includes a resin composition including a PVDF-based polymer and a polyvinylpyrrolidone (PVP)-based polymer, and the resin composition is 100 wt%. The content of the PVP-based polymer is included in a ratio of 5 wt% to 40 wt%, the PVP-based polymer has a molecular weight (Mw) of 900,000 g/mol or more, and the resin composition has a loading amount of 1 g/cm ² on the surface of the porous polymer substrate. It is above, and the air permeability is less than 900s/100cc.

A second aspect of the present invention is that in the first aspect, the heat-resistant coating layer has a thickness of 0.5 μm to 5.0 μm.

A third aspect of the present invention according to at least one of the first to second aspects, wherein the heat-resistant coating layer comprises a resin composition comprising a PVDF-based polymer and a polyvinylpyrrolidone-based polymer, and a heat-resistant coating layer Of the resin composition, 90 wt% or more, preferably 99 wt% or more is included.

The fourth aspect of the present invention according to at least any one of the first to third aspects, wherein the PVDF-based polymer comprises vinylidene fluoride homopolymer (PVDF), PVDF-HFP, PVDF-CTFE, or two or more of them. It includes a mixture.

The fifth aspect of the present invention is according to at least one of the first to fourth aspects, wherein the PVP-based polymer is a homopolymer of N-vinylpyrrolidone, an additional copolymer capable of free radical copolymerization with N-vinylpyrrolidone. A copolymer with monomers or at least one of them is included, and the copolymer is at least 60 wt% of the content of N-vinylpyrrolidone.

In the sixth aspect of the present invention, in the fifth aspect, the comonomer includes acrylamide, a derivative of acrylamide, an acrylic ester, a derivative of an acrylic ester, or two or more of them.

A seventh aspect of the present invention is that according to at least one of the first to sixth aspects, the PVP-based polymer has a glass transition temperature (Tg) of 150°C or higher.

An eighth aspect of the present invention is that in at least one of the first to seventh aspects, the PVP-based polymer has a melting temperature (Tm) of 380°C or higher.

In a ninth aspect of the present invention, according to at least one of the first to eighth aspects, the PVP-based polymer has a packing density of 0.1 g/m ³ to 0.6 g/m ³ .

A tenth aspect of the present invention is 0.2g / m ³ to about 0.5g / m ³ is the density (packing density) of the PVP-based polymer according to the ninth aspect.

An eleventh aspect of the present invention relates to a method of manufacturing a separator having the above-described characteristics, wherein the method comprises preparing a polymer solution including a resin composition and a dispersion medium containing a PVDF-based polymer and a PVP-based polymer, and the polymer The solution is applied to the surface of the porous polymer substrate and then dried under humidified conditions, and the dispersion medium includes a solvent and a non-solvent for the resin composition, and the resin composition in the polymer solution is contained in a concentration of less than 20 wt%.

In a twelfth aspect of the present invention, in the eleventh aspect, the dispersion medium contains 20 mol% or less of a non-solvent relative to 100 mol% of the dispersion medium.

The separation membrane according to the present invention is provided with a heat-resistant layer containing polyvinylpyrrolidone, and thus has a thin thickness and excellent heat-resistant stability. In addition, since the process of dispersing and pulverizing inorganic particles is omitted in the method of manufacturing a separator according to the present invention, the time required for manufacturing is shortened, thereby improving process efficiency.

The following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical spirit of the present invention together with the content of the above-described invention, so the present invention is limited to the matters described in such drawings. It is not intended to be limited and interpreted.

1 shows a SEM image of the surface of the separator prepared in Example 1.

Hereinafter, the present invention will be described in detail. The terms or words used in this 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. Therefore, the configurations described in the embodiments described in the present specification and shown in the drawings are only one embodiment of the present invention and do not represent all the technical ideas of the present invention, and thus various alternatives that can be substituted for them at the time of application It should be understood that there may be equivalents and variations.

In the entire specification of the present application, when a certain part "includes" a certain constituent element, it means that other constituent elements may be further included instead of excluding other constituent elements unless otherwise stated.

In addition, the terms "about" and "substantially" used throughout the specification of the present application are used as a meaning at or close to the numerical value when a manufacturing and material tolerance inherent to the stated meaning is presented to aid understanding of the present application. In order to prevent unreasonable use by unscrupulous infringers of the stated disclosures, either exact or absolute figures are used.

In the entire specification of the present application, the description of "A and/or B" means "A or B or both".

Certain terms used in the detailed description of the invention that follow are for convenience and are not limiting. The words “right”, “left”, “top” and “bottom” indicate directions in the drawings to which reference is made. The words'inwardly' and'outwardly' refer to a direction towards or away from the geometric center of a specified device, system and members, respectively. 'Forward','rear','upward','downward' and related words and phrases represent positions and orientations in the drawings to which reference is made, and should not be limited. These terms include the words listed above, their derivatives and words of similar meaning.

The present invention relates to a separator for an electrochemical device and an electrochemical device including the same.

In one embodiment of the present invention, the electrochemical device is a device that converts chemical energy into electrical energy by an electrochemical reaction, and is a concept including a primary battery and a secondary battery, and the secondary battery is charged Over-discharge is possible and is a concept encompassing lithium ion batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. The separator for an electrochemical device according to an aspect of the present invention serves as an insulating film that electrically insulates electrodes having opposite polarities in the electrochemical device, and includes, for example, a unit cell including an anode, a cathode, and a separator. cell).

Next, the configuration of the separator according to the present invention will be described in more detail.

In one embodiment of the present invention, the separator comprises a porous polymer substrate and a heat resistant coating layer disposed on at least one surface of the porous polymer substrate, and the heat resistant coating layer is a porous polymer membrane having pores, and polyvinylpyrroly Includes money and PVDF-based polymers.

The porous polymer substrate refers to a substrate having a plurality of pores formed therein as an ion-conducting barrier that passes ions while blocking electrical contact between a cathode and an anode. The pores are interconnected with each other, so that gas or liquid can pass from one side of the substrate to the other side. As the material constituting such a porous polymer substrate, either an organic material or an inorganic material having electrical insulation can be used. In particular, from the viewpoint of imparting a shutdown function to the substrate, it is preferable to use a thermoplastic resin as a constituent material of the substrate. Here, the shutdown function refers to a function of preventing the thermal runaway of the battery by blocking the movement of ions by dissolving the thermoplastic resin and closing the pores of the porous substrate when the battery temperature is increased. As the thermoplastic resin, a thermoplastic resin having a melting point of less than 200°C is suitable, and polyolefin is particularly preferred.

In addition, polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene It may further include at least any one of. The porous polymer substrate may be a non-woven fabric or a porous polymer film, or a laminate of two or more of them, but is not particularly limited thereto.

Specifically, the porous polymer substrate is any one of the following a) to e).

a) a porous film formed by melting/extruding a polymer resin,

b) a multilayer film in which two or more layers of the porous film of a) are stacked,

c) a nonwoven web produced by integrating filaments obtained by melting/spinning a polymer resin,

d) a multilayer film in which two or more layers of the nonwoven web of c) are stacked,

e) A porous composite membrane having a multilayer structure comprising two or more of the above a) to d).

In the present invention, the porous polymer substrate preferably has a thickness of 3 μm to 12 μm or 5 μm to 12 μm. When the thickness thereof is less than the above value, the function of the conductive barrier is not sufficient. On the other hand, when it exceeds the above range (ie, when it is too thick), the resistance of the separator may increase excessively.

In one embodiment of the present invention, the weight average molecular weight (Mw, g/mol) of the polyolefin may be 100,000 to 5 million. When the weight average molecular weight is less than 100,000, it may become difficult to secure sufficient mechanical properties. In addition, when it is larger than 5 million, the shutdown characteristics may deteriorate or molding may become difficult. In addition, the strength of the protrusion of the porous polymer substrate may be 300 gf or more from the viewpoint of improving the manufacturing yield.

In the present specification, the molecular weight (Mw) means a weight average molecular weight. In one embodiment of the present invention, the molecular weight (Mw) may be measured using gel permeation chromatography (GPC). For example, 200 mg of a polymer resin for molecular weight measurement can be diluted in a solvent such as 200 ml Tetrahydrofuran (THF) to prepare a sample of about 1000 ppm, and measured through an RI detector at 1 ml/min flow using an Agilent 1200 series GPC device. .

The piercing strength of a porous substrate refers to the maximum piercing load (gf) measured by performing a piercing test under the conditions of a needle tip radius of curvature of 0.5 mm and a piercing speed of 2 mm/sec using a Kato tech KES-G5 handy compression tester.

In a specific embodiment of the present invention, the porous polymer substrate can be used as long as it is a planar porous polymer substrate used in an electrochemical device, for example, has high ion permeability and mechanical strength, and a pore diameter is generally 10 nm to An insulating thin film having a thickness of 100 nm and generally 5 μm to 12 μm may be used.

In the present invention, the heat-resistant coating layer may be formed on at least one surface of the porous polymer substrate and includes polyvinylpyrrolidone and PVDF-based polymer.

The heat-resistant coating layer is a porous membrane having a plurality of fine pores. In the heat-resistant coating layer, these micropores have a structure connected to one or more adjacent pores, and have a porous structure through which gas or liquid can pass from one surface to the other surface.

In one embodiment of the present invention, the fine pores of the heat-resistant coating layer may be derived by humidification phase separation of the binder resin performed during the production of the heat-resistant coating layer, as described later. In one embodiment of the present invention, pores of various sizes ranging from several nanometers to tens of micrometers in diameter may be formed in the heat-resistant coating layer. The size of the pores may be calculated from shape analysis through SEM images. If the size of the pores is too small, the pores are likely to be clogged due to the expansion of the binder resin in the heat-resistant coating layer, and if the pore size is excessively large, the function as an insulating film is difficult and self-discharge characteristics deteriorate after manufacturing a secondary battery. Therefore, it is desirable to control it to an appropriate size in consideration of these points. These pore diameters can be controlled in an appropriate range by appropriately selecting and controlling temperature, humidity, solvent, non-solvent component, etc. in the raw material for the heat-resistant coating layer and the humidification phase separation process described later.

In one embodiment of the present invention, the porosity of the heat-resistant coating layer is preferably 30% to 80%. If the porosity is 30% or more, it is advantageous in terms of permeability of lithium ions, and if the porosity is 80% or less, the surface opening ratio is not too high, which is suitable for securing the adhesion between the separator and the electrode. Meanwhile, in one embodiment of the present invention, the air permeability of the separator is 900s/100cc or less, preferably 500s/100cc or less.

On the other hand, in the present invention, the porosity and size of the pores are measured using BEL JAPAN's BELSORP (BET equipment) using an adsorption gas such as nitrogen, or a mercury intrusion porosimetry or capillary flow measurement method It can be measured in the same way as (capillary flow porosimetry). Alternatively, in one embodiment of the present invention, the porosity may be calculated from the theoretical density of the coating layer by measuring the thickness and weight of the obtained coating layer.

The term "permeability" as used herein refers to the time for 100 cc of air to permeate through the separator, and as a unit thereof, seconds/100 cc are used herein, and can be used interchangeably with permeability. And is usually expressed as a Gurely value.

In one embodiment of the present invention, the thickness of the heat-resistant coating layer is preferably 0.5 μm to 5.0 μm on one side of the porous polymer substrate. The thickness may be preferably 0.7㎛ or more, 1㎛ or more, or 1.5㎛ or more when considering mechanical properties or adhesion, and the adhesion to the electrode within the above numerical range is excellent, and as a result, the cell strength of the battery is Is increased. On the other hand, if the thickness is 5.0 μm or less, it is advantageous in terms of cycle characteristics and resistance characteristics of the battery.

The heat-resistant coating layer includes a resin composition containing a PVDF-based polymer and a polyvinylpyrrolidone-based polymer, and the resin composition is 90 wt% or more, preferably 99 wt% or more, or 99.9 wt% of 100 wt% of the heat-resistant coating layer. % Or more.

PVDF polymer

In one embodiment of the present invention, the PVDF-based polymer may be included in a range of 60 wt% to 95 wt% relative to 100 wt% of the resin composition. As will be described later, the heat-resistant coating layer may form pores by inducing phase separation of the PVDF-based binder while the polymer solution for forming the heat-resistant coating layer is solidified under humidified conditions. At this time, when the content of the PVDF-based binder resin is small in the resin composition, the binder resin component capable of phase separation is not sufficient, and thus pores are not formed at a desired level in terms of the size and porosity of the pores.

In one embodiment of the present invention, the PVDF-based polymer has a molecular weight (Mw) of 10,000 to 1 million, preferably 150,000 to 500,000.

In one embodiment of the present invention, the PVDF-based polymer may include a homopolymer of vinylidene fluoride (ie, polyvinylidene fluoride), a copolymer of vinylidene fluoride and a monomer copolymerizable therewith, or a mixture thereof. have. In one embodiment of the present invention, as the monomer, for example, a fluorinated monomer and/or a chlorine-based monomer may be used. Non-limiting examples of the fluorinated monomers include vinyl fluoride; Trifluoroethylene (TrFE); Chlorofluoroethylene (CTFE); 1,2-difluoroethylene; Tetrafluoroethylene (TFE); Hexafluoropropylene (HFP); Perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE), and perfluoro (propyl vinyl) ether (PPVE); Perfluoro(1,3-dioxole); And perfluoro (2,2-dimethyl-1,3-dioxole) (PDD), and one or more of them may be included.

In one embodiment of the present invention, when the PVDF-based polymer includes a copolymer of vinylidene fluoride and a monomer capable of copolymerization therewith, the substitution ratio of the monomer in the copolymer may be 0.1 wt% to 25 wt%. Preferably, the substitution rate of the monomer may be 8 wt% to 20 wt%.

In one embodiment of the present invention, the PVDF-based polymer comprises vinylidene fluoride homopolymer (PVDF), PVDF-HFP, PVDF-CTFE, PVDF-CTFE, PVDF-TFE, PVDF-TrFE, or two or more of them. It can be a mixture.

In a specific embodiment of the present invention, the PVDF-based polymer may include PVDF-HFP. In addition, the PVDF-based polymer may further include one or more of PVDF-CTFE, PVDF-FEP, and PVDF-TFE together with PVDF-HFP. Here, the PVDF-HFP may have a molecular weight (Mw) of 10,000 to 1 million, preferably 150,000 to 500,000. In addition, the substitution rate of HFP in the PVDF-HFP may be 0.1wt% to 25wt%, preferably 8wt% to 80wt%.

Polyvinylpyrrolidone polymer

In the present invention, the polyvinylpyrrolidone (PVP)-based polymer refers to a polymer polymer containing N-vinylpyrrolidone as a monomer. The polyvinylpyrrolidone-based polymer may include a single copolymer of N-vinylpyrrolidone, a copolymer of N-vinylpyrrolidone and additional comonomers capable of free radical copolymerization, or at least one of them.

Meanwhile, in a specific embodiment of the present invention, in the case of using a copolymer with comonomers as the polyvinylpyrrolidone-based polymer, N-vinyl among them in terms of improving the electrochemical properties intended in the present invention It is preferable that it is 60 wt% or more, 70 wt% or more, or 80 wt% or more of the content of pyrrolidone.

In one embodiment of the present invention, the comonomer is, for example, acrylic acid and substituted acrylic acid, and salts, esters and amides thereof (wherein the substituent on the carbon atom is at the position 2 or 3 of acrylic acid, and independently of each other C 1 to C 20 alkyl, -CN, selected from the group consisting of COOH), methacrylic acid, ethacrylic acid, acrylamide, methacrylamide, N,N-dimethylacrylamide and N,N-dimethylmethacrylamide And one or more of them.

In addition, in addition to the aforementioned monomers, further suitable comonomers are amides of acrylic acid and derivatives thereof such as ethacrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-butylacrylamide, Nt -Butylacrylamide, N-octylacrylamide, Nt-octylacrylamide, N-octadecylacrylamide, N-phenylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-isopropylmethacryl Amide, N-dodecylmethacrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N-[3-(dimethylamino)propyl]acrylamide, N-[3-(dimethylamino)butyl] Methacrylamide, N-[8-(dimethylamino)octyl]methacrylamide, N-[12-(dimethylamino)dodecyl]methacrylamide, N-[3-(diethylamino)propyl]methacrylamide , N-[3-(diethylamino)propyl]acrylamide, unsaturated sulfonic acids such as acrylamidopropanesulfonic acid; It is 3-cyanoacrylic acid.

The esters of acrylic acid and derivatives thereof are, for example, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, Methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, stearyl (Meth)acrylate, 2,3-dihydroxypropyl acrylate, 2,3-dihydroxypropyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate Rate, 2-hydroxyethyl ethacrylate, 2-methoxyethyl acrylate, 2-methoxyethyl methacrylate, 2-methoxyethyl ethacrylate, 2-ethoxyethyl methacrylate, 2- Ethoxyethyl ethacrylate, hydroxypropyl methacrylate, glyceryl monoacrylate, glyceryl monomethacrylate, polyalkylene glycol (meth)acrylate, N,N-dimethylaminomethyl (meth)acrylate , N,N-diethylaminomethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminobutyl ( Meth)acrylate, N,N-diethylaminobutyl (meth)acrylate, N,N-dimethylaminohexyl (meth)acrylate, N,N-dimethylaminooctyl (meth)acrylate, N,N-dimethyl It is aminododecyl (meth)acrylate.

Other suitable comonomers are vinyl and allyl esters of linear, branched, or carbocyclic carboxylic acids having 1 to 40 carbon atoms, such as vinyl acetate, vinyl propionate, and valences thereof. Decomposition products such as vinyl alcohol, vinyl or allyl halides, preferably vinyl chloride and allyl chloride, vinyl ethers, preferably methyl, ethyl, butyl or dodecyl vinyl ether, vinylformamide, N-vinyl-N-methylacet Amide, vinylamine; Methyl vinyl ketone; Vinyllactam, preferably vinylpyrrolidone, vinylcaprolactam and vinylpiperidone, vinyl- or allyl-substituted heterocyclic compounds, preferably vinylpyridine, vinyloxazoline and allylpyridine, and vinylfuran and allyl alcohol to be. Also suitable is N-vinylimidazole of the following formula (1).

[Formula 1]

At this time, R ⁹ to R ¹¹ are each independently hydrogen, alkyl or phenyl having 1 to 4 carbon atoms. Examples are 1-vinylimidazole, 1-vinyl-2-methylvinylimidazole, 3-methyl-1-vinylimidazolium chloride and 3-methyl-1-vinylimidazolium methylsulfate.

In other embodiments, the additional suitable comonomer may be diallylamine of formula (II).

[Formula 2]

At this time, R ¹² is an alkyl having 1- to 24 carbon atoms, for example diallyldimethylammonium chloride.

Other further suitable comonomers are maleic acid, fumaric acid, maleic anhydride and half-esters and half-amides and imides thereof, maleimide, crotonic acid, itaconic acid, vinyl ethers (e.g. methyl, ethyl, butyl or Dodecyl vinyl ether), vinylidene chloride, and hydrocarbons having at least one carbon-carbon double bond, preferably styrene, alpha-methylstyrene, tert-butylstyrene, styrenesulfonic acid and salts thereof, butadiene, isoprene, cyclohexa Diene, ethylene, propylene, 1-butene, 2-butene, isobutylene, and vinyl toluene.

Among these, preferred are acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, maleic anhydride, and half-esters thereof, and half-amides and imides, methyl acrylate, methyl methacrylate, ethyl acrylate, Ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, t-butyl acrylate, t-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, ste Aryl acrylate, stearyl methacrylate, Nt-butylacrylamide, N-octylacrylamide, Nt-octylacrylamide, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-2-hydroxy Ethyl methacrylate, 3-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, alkylene glycol (meth)acrylate, styrene, unsaturated sulfonic acids and salts thereof, such as, for example, acrylamidopropanesulfonic acid And styrenesulfonic acid, vinylpyrrolidone, vinylcaprolactam, vinyl ether (eg: methyl, ethyl, butyl or dodecyl vinyl ether), vinylformamide, N-vinyl-N-methylacetamide, vinylamine, 1 -Vinylimidazole, 1-vinyl-2-methylimidazole, N,N-dimethylaminomethyl methacrylate and N-[3-(dimethyl-amino)propyl]methacrylamide; 3-methyl-1-vinylimidazolium chloride, 3-methyl-1-vinylimidazolium methylsulfate, N,N-dimethylaminoethyl methacrylate, N-isopropyl-methacrylamide, methyl chloride 4 N-[3-(dimethylamino)propyl]methacrylamide, VCAp, VI, 1-vinyl-3-methylimidazolium salts such as chloride and methylsulfate (QVI), VAC, (meth)acrylamide , Dimethylaminoethyl (meth)acrylate and dimethylaminoethyl (meth)acrylamide and their quaternized analogs, diallyldimethylammonium chloride, vinyl alcohol (by hydrolysis from vinyl acetate after polymerization), VFA, vinylamine (By hydrolysis from VFA after polymerization reaction), dimethylaminopropyl (meth)acrylate, dimethylaminopropyl (meth)acrylamide, (meth)acrylic acid, vinyl piperidone, N,N-dimethyl (meth)acrylamide , tert-butyl (meth)acrylamide, N-tert-octyl (meth)acrylamide, stearyl (meth)acrylamide, methyl, ethyl, butyl, tert-butyl (meth)acrylate, 2,3-dihydro Roxypropyl (meth)acrylate, N-isopropylacrylamide, vinyl propionate, 1-vinyl-2-methylimidazole, vinylpyridine, ester of (meth)acrylic acid or ether of allyl alcohol and at the end of the chain Ether of polyethylene oxide or propylene oxide or poly(ethylene oxide copropylene oxide) having a total of 2 to 200 EO or PO units or EO/PO units having a methoxy group or a hydroxy group, methyl vinyl ether, hydroxyethyl (meth )Acrylate, hydroxypropyl (meth)acrylate, vinyllactam, vinyloxazoline, such as vinyloxazoline, vinylmethyloxazoline, vinylethyloxazoline, acrylamidopropanesulfonic acid, allyl alcohol.

Further suitable comonomers are polyfunctional monomers such as triallylamine, trivinyl ether, divinylethyleneurea, 3-vinyl-N-vinylpyrrolidone, 4-vinyl-N-vinylpyrrolidone, 5-vinyl- N-vinylpyrrolidone, pentaerythritol triallyl ether, methylenebisacrylamide, butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, allyl methacrylate, divinylbenzene, ethylene glycol dimetha Acrylate, triethylene glycol dimethacrylate and triethylene glycol divinyl ether.

Very particularly preferred comonomers are N-vinylcaprolactam (VCAp), N-vinyl-imidazole (VI), 1-vinyl-3-methylimidazolium salt (QVI), for example methyl chloride or dimethyl sulfate. Salts obtainable by quaternization, vinyl acetate, (meth)acryl-amide, dimethylaminoethyl (meth)acrylate and dimethylaminoethyl-(meth)acrylamide and their quaternized analogs, diallyldimethylammonium chloride.

Meanwhile, in a specific embodiment of the present invention, when considering the aspect of improving adhesion, the comonomer preferably contains at least one of acrylamide and derivatives thereof, acrylic esters and derivatives thereof. In one embodiment of the present invention, the polyvinylpyrrolidone polymer is It may be included in the range of 5wt% to 50wt%, or 5wt% to 40wt% relative to 100wt% of the resin composition.

In the present invention, when considering the aspect of heat resistance stability of the separator, the PVP-based polymer preferably has a Tg of 150°C or higher and a Tm of 380°C or higher.

On the other hand, the molecular weight (Mw) of the PVP-based polymer is 900,000 (g/mol) or more. When the above numerical range is satisfied, heat resistance similar to that of the heat-resistant layer containing inorganic material may be exhibited, and since it does not contain inorganic material particles, process efficiency may be improved and a thin film of the separator may be realized.

On the other hand, in one embodiment of the present invention, the heat-resistant coating layer is preferably 1 g / cm ² or more in the loading amount of the resin composition. The loading amount represents the weight per unit area of the resin composition contained in the heat-resistant coating layer coated on both sides of the porous polymer substrate. If the loading amount is less than the above-described range, the content of the polymer material included in the heat-resistant coating layer is insufficient, so that the shrinkage rate characteristics and adhesion characteristics of the separator are deteriorated.

On the other hand, in one embodiment of the present invention, the density (packing density) of the PVP-based polymer in the heat-resistant coating layer is 0.1 g/m ³ to 0.7 g/m ³ , preferably 0.2 g/m ³ to 0.5 g/ m ³ . When the density of PVP satisfies the above range, heat resistance is improved and the phase separation behavior of the PVDF-based polymer is not hindered.

In the present specification, the density (packing density) of the PVP-based polymer can be calculated by the following (Equation 1).

(Equation 1)

PVP polymer density (g/m ³⁾ = (PVP content in heat-resistant coating layer) X {(weight per unit area of separator-weight per unit area of porous polymer substrate)/(thickness of separator-thickness of porous polymer substrate)}

Next, a method of manufacturing a separator according to the present invention will be described. The separator according to the present invention can be prepared by preparing a polymer solution containing the resin composition and then applying it on a porous polymer substrate and solidifying the polymer solution to form a heat-resistant coating layer integrally on the porous polymer substrate. I can.

Specifically, first, a polymer solution is prepared by introducing a resin composition containing a PVDF-based polymer and a PVP-based polymer into a dispersion medium. The dispersion medium may include a solvent and a non-solvent for the resin composition.

In one embodiment of the present invention, the solvent may be a polar amide solvent such as acetone, methyl ethyl ketone, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, dimethylformamide, etc., and at least one of them You can select and use appropriately.

In addition, in one embodiment of the present invention, the non-solvent is methanol, ethanol, propanol, isopropyl alcohol (IPA), isopropanol, butanol, sec-butanol, amyl alcohol, 2-ethyl-1-hexanol , Cyclohexanol, phenol (50° C.), ethylene glycol, 1,3-butanediol, 1,4 butanediol, glycerin, diacetone alcohol, formic acid, acetic acid, propionic acid, glycol ether, diethylene glycol, triethylene glycol, Hexamethylene glycol, polyethylene glycol 400, 2,2-thiodiethanol, gammabutylrolactone, ethyl acetate, butylamine, cyclhexamine analine, ethylenediamine, pyridine, morpholine, 2-aminoaniline, diethanolamine, triethanolamine, aminoethylethanloamine, 2-hydroxyethylmorpholine, 2-amino-2-methyl-1-propanol, and the like are exemplified, and one or more of them may be appropriately selected and used.

The non-solvent in the dispersion medium is preferably contained in a ratio of 30 mol% or less, preferably 25 mol% or less, and more preferably 20 mol% or less with respect to 100 mol% of the dispersion medium. If the content of the non-solvent exceeds the above range, there is a problem that the phase separation does not proceed effectively, so that the pores do not develop and the adhesion properties are deteriorated.

Meanwhile, in one embodiment of the present invention, it is preferable that the resin composition in the polymer solution has a concentration of less than 20 wt%, preferably less than 15 wt%. If it exceeds the above range, the resin composition precipitates and phase separation does not proceed effectively.

Next, the polymer solution is applied on a porous polymer substrate and allowed to stand for a predetermined time under humidified conditions to solidify (dry) the polymer solution. In one embodiment of the present invention, the humidification condition is about 40% to 80% relative humidity. Further, in the present invention, the solidification of the polymer solution may be performed in a range of about 10 degrees Celsius (℃) to 70 degrees Celsius. At this time, phase separation of the PVDF-based polymer in the polymer solution is induced. In the process of phase separation, the solvent moves to the surface of the heat-resistant coating layer, and as the solvent moves, the PVDF-based polymer moves to the surface of the heat-resistant coating layer, thereby increasing the content of the PVDF-based polymer on the surface of the heat-resistant coating layer.

In one embodiment of the present invention, the polymer solution may be applied by a conventional coating method such as a Meyer bar, a die coater, a reverse roll coater, and a gravure coater.

Meanwhile, the present invention provides a secondary battery including the separator. The battery includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, and the separator includes the binder resin composition according to the present invention.

In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer including a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material may include a layered compound such as lithium manganese composite oxide (LiMn ₂ O ₄ , LiMnO _2, etc.), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as formula Li _1+x Mn _2-x O ₄ (wherein x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, A lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 wherein} part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ It may contain one or a mixture of two or more.

In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer including a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The negative electrode includes carbon such as lithium metal oxide, non-graphitized carbon, and graphite-based carbon as a negative electrode active material; Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1), Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me' : Al, B, P, Si, elements of groups 1, 2 and 3 of the periodic table, halogen, metal complex oxides such as 0<x≦1;1≦y≦3;1≦z≦8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ and Metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; It may include one or a mixture of two or more selected from among titanium oxides.

In a specific embodiment of the present invention, the conductive material is, for example, graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivative It may be any one selected from the group consisting of, or a mixture of two or more conductive materials among them. More specifically, natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, carbon fiber, carbon nanotube, It may be one selected from the group consisting of aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials.

The current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Surface-treated carbon, nickel, titanium, silver, or the like may be used.

As the binder resin used for the electrode, a polymer commonly used for electrodes in the art may be used. Non-limiting examples of such a binder resin include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate. , Polyetylexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene -co-vinyl acetate), polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl Flulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, flulan, and carboxyl methyl cellulose Can be, but is not limited thereto.

The electrode assembly prepared as described above may be charged in an appropriate case and an electrolyte may be injected to manufacture a battery. In one embodiment of the present invention, the electrolyte is a salt having a structure such as A+B-, wherein 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 ion 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), an ester-based compound, and some dissolved or dissociated in an organic solvent including a mixture of at least one selected among them, but are not limited thereto.

In addition, the present invention provides a battery module including a battery including the electrode assembly as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include a power tool that is powered by an omniscient motor and moves; Electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); Electric golf cart; Power storage systems, etc., but are not limited thereto.

Hereinafter, examples will be described in detail to illustrate the present invention in detail. However, the embodiments according to the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Example

Preparation of separator

A resin composition was prepared according to the composition of the following [Table 1]. Acetone and isopropyl alcohol (IPA) were mixed to prepare a dispersion medium, and a polymer solution was prepared by adding a resin composition including PVP and PVDF-HFP of each of Examples and Comparative Examples thereto. The PVDF-HFP had a molecular weight (Mw) of 300,000, and a substitution rate of 15 wt%. The polymer solution was coated on a porous polymer substrate (thickness 9㎛, porosity 32vol%, molecular weight 500,000 polyethylene) by a dip coating method, and humidified phase separation was induced at a relative humidity (RH) of 60% and at room temperature. . A separator was manufactured in this way.

	Resin composition		Dispersion medium		Resin composition concentration (wt%)	PVP molecular weight (Mw, g/mol)
	PVP(wt%)	PVDF-HFP (wt%)	IPA concentration (mol%)	Acetone concentration (mol%)
Example 1	40	60	20	80	15	900,000
Implementation 2	40	60	20	80	15	3,000,000
Comparative Example 1	40	60	20	80	15	50,000
Comparative Example 2	40	60	20	80	15	500,000
Example 3	40	60	20	80	15	900,000
Comparative Example 3	40	60	20	80	15	900,000
Comparative Example 4	40	60	20	80	15	900,000
Example 4	20	80	20	80	15	900,000
Comparative Example 5	60	40	20	80	15	900,000
Example 5	40	60	10	90	15	900,000
Comparative Example 6	40	60	25	75	15	900,000
Comparative Example 7	40	60	30	70	15	900,000
Example 6	40	60	20	80	10	900,000
Example 7	15	85	20	80	15	900,000
Comparative Example 8	40	60	20	80	20	900,000
Comparative Example 9	40	60	20	80	25	900,000

	Coating layer thickness (㎛)	Loading amount (g/cm 2 )	PVP density in heat-resistant coating layer (g/m 3 )	Air permeability (s/100cc)	Heat shrinkage (%, 150℃)(TD/MD)	Electrode adhesion (gf/25mm)
Example 1	1㎛/1㎛	1.0	0.50	280	29/25	57
Example 2	1㎛/1㎛	1.0	0.50	381	20/18	46
Comparative Example 1	1㎛/1㎛	1.0	0.50	93	67/63	60
Comparative Example 2	1㎛/1㎛	1.0	0.50	160	52/49	62
Example 3	1㎛/1㎛	2.0	0.50	433	19/15	84
Comparative Example 3	1㎛/1㎛	0.8	0.50	221	38/34	31
Comparative Example 4	1㎛/1㎛	0.5	0.50	130	57/55	13
Example 4	1㎛/1㎛	1.0	0.2	250	37/32	95
Comparative Example 5	1㎛/1㎛	1.0	0.6	986	24/21	51
Example 5	1㎛/1㎛	1.0	0.50	300	28/24	51
Comparative Example 6	1㎛/1㎛	1.0	0.50	1024	15/10	17
Comparative Example 7	1㎛/1㎛	1.0	0.50	3365	15/9	10
Example 6	1㎛/1㎛	1.0	0.50	279	29/27	60
Example 7	1㎛/1㎛	1.0	0.1	181	51/47	103
Comparative Example 8	3㎛/3㎛	1.0	0.50	-	-	-
Comparative Example 9	3㎛/3㎛	1.0	0.50	-	-	-

As confirmed in Table 2, the separator according to the Example showed superior results in terms of air permeability, electrode adhesion, and heat shrinkage compared to the comparative example.

Experimental method

1) loading amount

It shows the weight per unit area of the resin composition contained in the heat-resistant coating layer coated on both sides of the porous polymer substrate.

2) Air permeability

The air permeability meter (manufacturer: Asahi Seiko, product name: EG01-55-1MR) was used to measure the time (sec) it took for 100 cc of air to pass through the separator at a constant pressure (0.05 MPa). The average was recorded by measuring a total of 3 points at each 1 point on the left/middle/right of the sample.

If it is more than 2000s/100cc, it may cause a decrease in battery power and cycle characteristics.

3) Heat shrinkage rate

The separation membrane prepared in each Example and Comparative Example was cut into a size of 5cm x 5cm, and then the degree of shrinkage after holding at 150°C for 30 minutes was calculated in the TD and MD directions.

Heat contraction rate (%) = [(length before contraction-length after contraction) / length before contraction] X 100

4) Electrode adhesion

The separator prepared in each Example and Comparative Example was cut into 100 mm (length) x 25 mm (width) and laminated with a cathode by hot press at 60°C, 6.5 MPa, 1s, and then UTM equipment (Instron) was used. Then, peeling was performed at an angle of 180 degrees at a speed of 300 mm/min, and the strength at this time was measured. It is desirable to secure at least 50g/25mm.

The negative electrode was prepared as follows. A negative electrode slurry was prepared by mixing 66.1 wt% artificial graphite (coal tar pitch), 26.9 wt% natural graphite, 1.5 wt% SiO, 1.5 wt% carbon black, 3 wt% SBR binder, and 1 wt% CMC. This was applied to a copper foil at a loading amount of 495mg/25cm ² , dried in a vacuum oven at 100° C. for 10 hours or longer, and a negative electrode (total thickness of 159.6 μm) was prepared using a roll-type press.

Claims (12)

1. Porous polymer substrate; A heat-resistant coating layer formed on at least one surface of the porous polymer substrate, wherein the heat-resistant coating layer includes a resin composition containing a PVDF-based polymer and a polyvinylpyrrolidone (PVP)-based polymer, and 100 wt% of the resin composition The PVP-based polymer content is included in a ratio of 5 wt% to 40 wt%, and the PVP-based polymer has a molecular weight (Mw) of 900,000 g/mol or more, and the resin composition has a loading amount of 1 g/cm on the surface of the porous polymer substrate. ² or more, and the air permeability is 900s/100cc or less for an electrochemical device.
2. The method of claim 1,

   The heat-resistant coating layer is a separator for an electrochemical device having a thickness of 0.5 μm to 5.0 μm.
3. The method of claim 1,

   The heat-resistant coating layer includes a resin composition including a PVDF-based polymer and a polyvinylpyrrolidone-based polymer, and the resin composition in the heat-resistant coating layer is 90 wt% or more, preferably 99 wt% or more. Separation membrane for chemical devices.
4. The method of claim 1,

   The PVDF-based polymer is a separator for an electrochemical device comprising a vinylidene fluoride homopolymer (PVDF), PVDF-HFP, PVDF-CTFE, or a mixture containing two or more of them.
5. The method of claim 1,

   The PVP-based polymer includes a homopolymer of N-vinylpyrrolidone, a copolymer of N-vinylpyrrolidone and additional comonomers capable of free radical copolymerization, or at least one of them, and the copolymer is N- A separator for an electrochemical device that is 60wt% or more of the content of vinyl pyrrolidone.
6. The method of claim 5,

   The comonomer is an acrylamide, an acrylamide derivative, an acrylic acid ester, an acrylic acid ester derivative, or a separator for an electrochemical device comprising two or more of them.
7. The method of claim 1,

   The PVDF-based polymer includes PVDF-HFP, and its molecular weight (Mw) is 10,000 to 1 million. A separator for an electrochemical device.
8. The method of claim 1,

   The PVDF-based polymer includes PVDF-HFP, wherein the HFP has a substitution rate of 0.1wt% to 25wt%. A separator for an electrochemical device.
9. The method of claim 1,

   A separator for an electrochemical device that has a packing density of 0.1g/m ³ to 0.6g/m ³ of a PVP-based polymer.
10. The method of claim 9,

    A separator for an electrochemical device that has a packing density of 0.2g/m ³ to 0.5g/m ³ of the PVP-based polymer.
11. A method of manufacturing the separator according to claim 1, wherein the method comprises preparing a polymer solution containing a resin composition and a dispersion medium containing a PVDF-based polymer and a PVP-based polymer, and applying the polymer solution to the surface of a porous polymer substrate. After drying under humidified conditions, the dispersion medium comprises a solvent and a non-solvent for the resin composition, and the resin composition in the polymer solution is contained in a concentration of less than 20wt% of a separator for an electrochemical device.
12. The method of claim 11,

    The dispersion medium is a method of manufacturing a separator containing less than 20 mol% of a non-solvent relative to 100 mol% of the dispersion medium.

Images