KR20210033327A - Electrode assembly comprising free-standing separator for secondary batteries and Secondary batteries comprising the same - Google Patents

Abstract

The present invention is to provide an electrode assembly including a free-standing separator for a secondary battery excellent in both adhesion and air permeability and a secondary battery including the same and relates to a laminated electrode assembly including a positive electrode, a negative electrode, and a free-standing separator interposed between the positive electrode and the negative electrode. The free-standing separator includes: a free-standing porous membrane including inorganic particles and a binder; and hot-melt non-woven fabric layers located on both sides of the free-standing porous membrane. In the free-standing porous membrane, inorganic particles are substantially in contact with each other to form an interstitial volume. The interstitial volume between the inorganic particles forms pores of the free-standing porous membrane. The hot-melt non-woven fabric layer is formed that a hot-melt non-woven fabric sheet composed of polyester, polyamide, ethylene-vinyl acetate, or filaments containing two or more thereof starts to melt at a temperature of 50°C or more and less than 90°C, which is a lamination process temperature. The free-standing separator for a secondary battery on both sides of the hot-melt non-woven layer has air permeability in the range of 10 sec/100 cc to 500 sec/100 cc.

Description

[Electrode assembly comprising free-standing separator for secondary batteries and secondary batteries comprising the same}

The present invention relates to an electrode assembly including a free-standing separator for a secondary battery and a secondary battery including the same.

Recently, among electrochemical devices, interest in energy storage technology is increasing. As the field of application to mobile phones, camcorders, notebooks, and even electric vehicles is expanded, efforts for research and development of batteries are increasingly being materialized. Electrochemical devices are the field that attracts the most attention in this respect, and among them, the development of a secondary battery capable of charging and discharging has become a focus of interest.

Lithium secondary batteries are currently being produced by many companies because they have the advantage of higher operating voltage and higher energy density than conventional batteries of Ni-MH using an aqueous electrolyte solution, but their safety characteristics are showing different aspects. Particularly, a problem has been pointed out that the separator causes an internal short circuit due to its damage and causes an explosion. In the case of a lithium secondary battery using a polyolefin-based material as the material for the separator, the polyolefin-based material has a melting point of 200°C or less, And/or it has been found that when the battery rises to a high temperature due to external stimulation, the separator shrinks or melts, resulting in a short circuit between both electrodes.

As part of an effort in the art to solve this problem, a freestanding separator made of a sheet type using a mixture containing inorganic particles and a polymeric binder has been proposed. However, such a freestanding separator does not use a porous polymer substrate such as a polyolefin-based film or a nonwoven fabric, and thus relatively many binder polymers tend to be used, thereby reducing air permeability and increasing battery resistance. In addition, although a relatively large amount of binder polymer is used compared to a separator in which a porous polymer substrate such as a polyolefin film or a nonwoven fabric is used, the binder polymer is present in a position for binding between inorganic particles rather than on the surface of the separator. There was a tendency that the adhesion to the electrode was insufficient.

Accordingly, an object of the present invention is to provide an electrode assembly comprising a freestanding separator composed of inorganic particles and a binder, and comprising a freestanding separator for a secondary battery having excellent air permeability and electrode adhesion.

In addition, in the present invention, it is another object to provide a secondary battery including the electrode assembly as described above.

According to an aspect of the present invention, in the first aspect of the present invention, it relates to a laminated electrode assembly comprising an anode, a cathode, and a freestanding separator interposed between the anode and the cathode, wherein the freestanding separator is an inorganic material. A free-standing porous membrane containing particles and a binder; And a hot-melt nonwoven fabric layer positioned on both sides of the freestanding porous membrane, wherein inorganic particles in the freestanding porous membrane substantially contact each other to form an interstitial volume, and between the inorganic particles The interstitial volume of the freestanding porous membrane forms pores, and the hot-melt non-woven fabric layer is a hot-melt non-woven fabric sheet composed of filaments containing polyester, polyamide, ethylene-vinyl acetate, or two or more thereof. Laminated electrode assembly, characterized in that it is formed by starting to melt at a temperature less than, and the freestanding separator for secondary batteries having the hot-melt nonwoven fabric layer on both sides has an air permeability in the range of 10 sec/100 cc to 500 sec/100 cc. Is provided.

According to a second aspect of the present invention, in the first aspect, a laminated electrode assembly is provided, wherein the hot-melt nonwoven sheet has an air permeability in the range of 0.1 sec/100 cc to 10 sec/100 cc.

According to a third aspect of the present invention, in the first aspect or the second aspect, a laminated electrode assembly is provided ^{, wherein the hot-melt nonwoven sheet has a basis weight of 15 to 100 g/m 2.}

According to a fourth aspect of the present invention, in any one of the first to third aspects, a laminated electrode assembly is provided, wherein the hot-melt nonwoven sheet has a thickness in the range of 5 to 150 μm.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the hot-melt nonwoven sheet has a negative electrode and a positive electrode adhesion in the range of 50 gf/25 mm or more. An assembly is provided.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, the binder is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoropropylene. Polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyetylexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinyl p Rolidone (polyvinylpyrrolidone), polyvinyl acetate (polyvinylacetate), ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide (polyethylene oxide), polyarylate (polyarylate) An electrode assembly is provided.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the inorganic particles have a D50 of 0.02 to 1 μm, and a laminated electrode assembly is provided. do.

According to another aspect of the present invention, in the eighth aspect of the present invention, (S1) a binder resin is dissolved in a solvent to prepare a binder composition, and inorganic particles are added thereto to prepare a composition for forming a freestanding porous film. Steps, (S2) coating and drying the composition for forming the freestanding porous film on a release paper, (S3) removing the release paper from the dried freestanding porous film, and (S4) the hot melt nonwoven fabric according to item 1 And laminating at a temperature in the range of 60 to 70° C. and a pressure in the range of 1 MPa to 100 MPa by placing on both sides of the dried freestanding porous membrane and interposed between the anode and the cathode. A method of manufacturing the laminated electrode assembly according to claim 1 is provided.

According to a ninth aspect of the present invention, there is provided a secondary battery comprising the laminated electrode assembly described in any one of the first to seventh aspects of the present invention.

According to another aspect of the present invention, according to the tenth aspect of the present invention, as a hot-melt nonwoven sheet, having a air permeability in the range of 0.1 sec/100 cc to 10 sec/100 cc, and a negative electrode in the range of 50 gf/25 mm or more, and There is provided a hot-melt nonwoven fabric sheet for a component of a lithium secondary battery, characterized in that it starts to melt at a temperature of 50°C or more and less than 90°C.

The free-standing separator for a secondary battery according to the present invention includes a free-standing porous membrane including inorganic particles and a binder; And a hot-melt nonwoven fabric layer positioned on both sides of the freestanding porous membrane, wherein interstitial volumes are formed on the freestanding porous membrane, and a thermoplastic resin is spun on both sides of the freestanding porous membrane to form an intersection. A film-formed hot melt nonwoven fabric layer is formed, and it is characterized by having excellent air permeability.

In addition, the free-standing separator for a secondary battery according to the present invention includes a hot-melt non-woven fabric layer, and the hot-melt non-woven fabric layer is melted during lamination of the electrode-separator-electrode, thereby forming stronger electrode adhesion between the porous film and the electrode.

In addition, the free-standing separator for a secondary battery according to the present invention may have excellent heat resistance as it is used as an inorganic particle without a polyolefin-based polymer substrate as a main component.

As described above, the freestanding separator for secondary batteries and the hot-melt nonwoven fabric sheet having excellent air permeability, electrode adhesion and heat resistance are used as components of the secondary battery electrode assembly, so that the final manufactured secondary battery exhibits superiority in terms of battery cycle life characteristics. do.

1A and 1B are images of filaments constituting the hot-melt nonwoven fabric layer, respectively, by disassembling the electrode assembly laminated in Example 1, and before and after lamination, respectively.
2A and 2B are images of filaments constituting the hot-melt nonwoven fabric layer, respectively, by disassembling the electrode assembly laminated in Example 2, and before and after lamination, respectively.

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 on the basis of the principle that there is. Therefore, the configuration described in the embodiments described in the present specification is only the most preferred embodiment of the present invention, and does not represent all the technical spirit of the present invention, and various equivalents that can replace them at the time of application It should be understood that there may be variations and variations.

According to an aspect of the present invention, it relates to a laminated electrode assembly comprising an anode, a cathode, and a freestanding separator interposed between the anode and the cathode, wherein the freestanding separator comprises inorganic particles and a binder. Porous membrane; And a hot-melt nonwoven fabric layer positioned on both sides of the freestanding porous membrane, wherein inorganic particles in the freestanding porous membrane substantially contact each other to form an interstitial volume, and between the inorganic particles The interstitial volume of the freestanding porous membrane forms pores, and the hot-melt non-woven fabric layer is a hot-melt non-woven fabric sheet composed of filaments containing polyester, polyamide, ethylene-vinyl acetate, or two or more thereof, which is a lamination process temperature of 50. It is formed by starting to melt at a temperature of not less than ℃ 90 ℃, characterized in that the free-standing separator for secondary batteries having the hot-melt nonwoven fabric layer on both sides has an air permeability in the range of 10 sec / 100 cc to 500 sec / 100 cc. A laminated electrode assembly is provided.

In the present specification, the term "free standing" is understood to refer to a property that can exist in a continuous form without an additional separate support or description.

In the present specification, the term "free-standing porous membrane" may exist in a continuous form without an additional separate support or substrate, and an interstitial volume is formed in a state in which inorganic particles are substantially in contact with each other. , It is understood that the interstitial volume between the inorganic particles refers to a free-standing membrane having porosity to form pores and allow the electrolyte or lithium ions to pass therethrough.

In the present specification, the term "permeability" refers to the time for 100cc of air to permeate to an object for measuring air permeability such as a separator, and can use seconds/100cc as its unit, and can be used interchangeably with permeability. Can be, and is usually expressed as a Gurely value or the like. In a specific embodiment of the present invention, the air permeability is measured according to JIS P8117. In addition, the air permeability P1 measured in the object having the thickness T1 can be converted to the permeability P2 when the thickness of the object is set to 20 μm by the formula: P2=(P1Х20)/T1.

In the present specification, the "melting point" refers to an endothermic peak at a certain temperature when observed while increasing the temperature from -30°C to 200°C at a constant rate of 10°C using differential scanning calorimetry (DSC). The temperature at this time is called the melting point.

According to a specific embodiment of the present invention, the inorganic particles used in the freestanding porous membrane are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as the oxidation and/or reduction reaction does not occur in ^{the operating voltage range (eg, 0 to 5 V based on Li/Li +) of the applied electrochemical device.} Particularly, when inorganic particles having a high dielectric constant are used as inorganic particles, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte.

For the above reasons, the inorganic particles may include high-k inorganic particles having a dielectric constant of 5 or more or 10 or more. Non-limiting examples of inorganic particles greater than a dielectric constant of 5 is _{BaTiO 3, Pb (Zr x,} Ti 1-x) O 3 (PZT, where, 0 <x <1 _{Im), Pb 1 - x La x} Zr 1 - _y Ti _y O ₃ (PLZT, where 0<x<1, 0<y<1), (1-x)Pb(Mg _1/3 Nb _2/3 )O _{3 - x} PbTiO ₃ (PMN-PT , Where 0<x<1), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC and It may be any one inorganic particle selected from the group consisting of _{TiO 2 or a mixture of two or more of them.}

In addition, as the inorganic particles, inorganic particles having a lithium ion transfer capability, that is, inorganic particles having a function of moving lithium ions without storing lithium but containing a lithium element may be used. Non-limiting examples of inorganic particles having a lithium ion transfer ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x <2, 0 <y <3), Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 <x <2, 0 <y <1, 0 <z <3), 14 Li ₂ O-9Al ₂ O ₃ -38 TiO ₂ -39P ₂ (LiAlTiP) _x O _y series glass such as O ₅ (0 <x <4, 0 <y <13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 <x <2, 0 <y <3) , Li _3.25 Ge _0.25 P _0.75 S ₄ lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 <x <4, 0 <y <1, 0 <z <1, 0 <w <5 ), Li ₃ N, such as lithium nitride (Li _x N _y , 0 <x <4, 0 <y <2), Li ₃ PO ₄ -Li ₂ S-SiS ₂ SiS ₂ series glass (Li _x Si _{P 2} S ₅ series glass such as _y S _z , 0 <x <3, 0 <y <2, 0 <z <4), LiI-Li ₂ SP ₂ S _{5 (Li x} P _y S _z , 0 <x <3, 0 <y <3, 0 <z <7) or mixtures of two or more thereof.

The size of the inorganic particles is not particularly limited, but D50 may be in the range of 0.01 to 5 µm, or in the range of 0.02 to 3 µm, or in the range of 0.03 to 1 µm. When the size of the inorganic particles satisfies the above range, it is easy to control the structure and physical properties of the separator due to appropriate dispersibility, and the thickness of the separator is appropriate to prevent phenomena such as mechanical property deterioration, and also appropriate pore size. Occurs.

In the present specification, "Dn" means a particle diameter at n% of the cumulative particle volume distribution according to the particle diameter. That is, D50 is the particle diameter at 50% of the cumulative particle volume distribution according to the particle diameter, D90 is the particle diameter at 90% of the cumulative particle volume distribution according to the particle diameter, and D10 is 10% of the cumulative particle volume distribution according to the particle diameter. It is the particle size at the point. The Dn can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Malvern MASTERSIZER 3000) to measure the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam. Calculate the distribution. D10, D50, and D90 can be measured by calculating the particle diameters at the points at 10%, 50%, and 90% of the cumulative particle volume distribution according to the particle diameter in the measuring device.

According to a specific embodiment of the present invention, the binder used for the freestanding porous membrane is not particularly limited as long as it is electrochemically stable, which is commonly used in the art.

According to a specific embodiment of the present invention, non-limiting examples of the binder include polyvinylidene fluoride, polyvinylidene fluoride-hexafluoro propylene, and polyvinylidene fluoride- Trichloroethylene (polyvinylidene fluoride-co-trichloro ethylene), polyvinylidene fluoride-co-chlorotrifluoro ethylene, polymethyl methacrylate, polyacrylonitrile ), polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate (cellulose acetate butyrate), cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose ), pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyimide, or a mixture of two or more thereof.

In the freestanding porous membrane, the binder attaches the inorganic particles to each other so that the inorganic particles are bound to each other, so that the binder may connect and fix the inorganic particles. The inorganic particles of the freestanding porous membrane may form an interstitial volume in a state in which they are substantially in contact with each other, and in this case, the interstitial volume is a structure filled with inorganic particles (closed packed or densely packed). It means a space defined by inorganic particles that are in contact with each other. The interstitial volume between the inorganic particles becomes an empty space to form pores of the freestanding porous membrane.

According to a specific embodiment of the present invention, the freestanding porous membrane may have a thickness in the range of 1 to 150 µm, a thickness in the range of 3 to 50 µm, or a thickness in the range of 5 to 20 µm. If the freestanding porous membrane has a thickness thinner than the lower limit, a fracture problem may occur due to a decrease in strength, and if the freestanding porous membrane has a thickness greater than the upper limit, a problem may occur in that the cycle characteristics of the battery decrease due to an increase in resistance. Because.

According to a specific embodiment of the present invention, the freestanding porous membrane may contain a binder in a range of 10 to 70 parts by weight or 20 to 60 parts by weight or an amount of 30 to 50 parts by weight based on 100 parts by weight of inorganic particles. . When the binder is included in an amount within the above range, the problem that the binder is contained less than the lower limit, making it impossible to manufacture a freestanding porous membrane, and the problem that the resistance increases due to the reduction of pores due to the amount of the binder more than the upper limit, are avoided. Can be.

The freestanding separator for a secondary battery according to the present invention includes a hot-melt nonwoven fabric layer attached to both sides of the freestanding porous membrane.

The hot-melt nonwoven layer is a lamine consisting of filaments containing polyester, polyamide, ethylene-vinyl acetate, or two or more thereof starting to melt at a temperature of 50° C. or more and less than 90° C. It may be made from a sheet. The hot-melt non-woven fabric layer is a hot-melt non-woven fabric sheet prepared from a filament containing polyester, polyamide, ethylene-vinyl acetate, or two or more thereof starting to melt at a temperature of 50° C. or more and less than 90° C. or 55° C. to 85° C. May be formed by placing on both sides of the freestanding porous membrane, interposing between the anode and the cathode, and laminating. In this case, the lamination process may be performed at a temperature of 65 to 75°C, for example, 70°C.

In the present specification, the term'substantially' is intended to mean that the present invention includes an embodiment containing an additive in a trace amount or trace amount that does not significantly affect the intended effect of the present invention or an aspect containing unintended impurities.

Specific examples of polyesters having a melting point of 50° C. or more and less than 90° C. that can be used in the present invention are prepared from terephthalic acid or isophthalic acid and 1,4-butadiene, but tackifying resin, plasticizing oil, or both are further added thereto. It may include a compound capable of controlling the melting point or a mixture of two or more of these compounds.

Specific examples of polyamides having a melting point of 50° C. or more and less than 90° C. usable in the present invention include oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, Suberic acid, Azelaic acid, undecanedioic acid, dodecanedioic acid, Brassylic acid, Thapsic acid, Japanic straight-chain diacids such as acid, Phellogenic acid, or Equisetolic acid, phthalic acid, isophthalic acid, terephthalic acid, diphenic acid, aromatic diacids such as 2,6-naphthalenedicarboxylic acid, or β-propiolactam, γ-buty Lactam family such as lolactam, δ-valerolactam, or ε-caprolactam, and methanediamine, ethylenediamine, 1,3-diaminopropane, putrescine, cadaverine, hexa Methylenediamine, 1,2-diaminopropine, 1,4-diazacycloheptane, PPD (para-phenylenediamine), 1,4-diazacycloheptane, o-xylylenediamine (o- xylylenediamine), m-xylylenediamine, p-xylylenediamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, dimethyl-4-phenylenediamine, 4,4 '- diaminobiphenyl, a compound prepared by reacting a diamine such as 1,8-diaminonaphthalene, or a mixture of two or more of these compounds.

Specific examples of ethylene-vinyl acetate having a melting point of 50° C. or more and less than 90° C. that can be used in the present invention include an ethylene-vinyl acetate-based compound containing 18 parts by weight or more and less than 40 parts by weight of vinyl acetate, or two or more thereof. Mixtures are mentioned.

According to a specific embodiment of the present invention, the hot-melt nonwoven sheet may have ^{a basis weight of 0.2 to 150 g/m 2} or a basis weight of 15 to 100 g/m ² . When the hot-melt nonwoven layer has a basis weight less than the lower limit, the intersection point between the spun filaments of the spun thermoplastic resin is reduced or the strength of the nonwoven fabric is reduced due to its thin thickness. There are many cross points between the filaments of the thermoplastic resin, and the opening ratio is lowered, resulting in a problem that the air permeability is lowered or the thickness is increased.

According to a specific embodiment of the present invention, the hot-melt nonwoven sheet may have ^{a density of 0.01 to 0.9 g/cm 3} or a density of 0.05 to 0.6 g/cm ³ . When the hot-melt non-woven fabric sheet has a density within the above range, the hot-melt non-woven fabric layer (adhesive layer) finally formed while maintaining a desirable strength may have an appropriate range of air permeability and thickness, and may exhibit adhesive strength.

According to a specific embodiment of the present invention, the hot melt nonwoven sheet has excellent air permeability for use as a lithium secondary battery electrode assembly component, and the air permeability performed on the hot melt nonwoven sheet alone is 10 s/100 cc or less or 0.1 To 10 s/100 cc. The air permeability was measured according to JIS P8117.

According to a specific embodiment of the present invention, the hot-melt non-woven fabric layer finally formed on the laminated electrode assembly has excellent adhesion for use as a component of the lithium secondary battery electrode assembly, and the hot-melt non-woven fabric layer is 50 gf/25 mm or more or 50 gf/25 mm to 1000 gf/25 mm or 350 gf/25 mm to 1000 gf/25 mnm. The adhesion is a 180° peel test, by interposing a hot-melt nonwoven fabric sheet between the negative electrode for a secondary battery and a freestanding separator for a secondary battery, hot pressing at a temperature of 70° C. and a pressure of 1,000 kgf for 1 second, and then using a texture analyzer. This is a measurement value obtained by measuring the force (gf) applied until the free-standing separator for secondary batteries is pulled off from the negative electrode by pulling the free-standing separator for secondary batteries at a peeling rate of 300 mm/min.

According to a specific embodiment of the present invention, the filaments forming the hot-melt nonwoven sheet have a diameter in the range of 10 µm to 100 µm or a diameter in the range of 20 µm to 80 µm, or a diameter in the range of 40 µm to 60 µm. do. When the filament has a diameter in the range, the strength is weak in the filament having a diameter smaller than the lower limit, so that the lamination process is not easily performed. As the thickness of the nonwoven fabric becomes thick in the filament or is compressed after lamination, the thickness of the filament becomes thick and the pores are lowered can be avoided.

According to a specific embodiment of the present invention, the pores formed in the hot-melt nonwoven sheet are characterized by having a diameter in the range of 100 μm to 5000 μm. When the pores have pores in a diameter range, a problem in that air permeability decreases due to pores having a diameter smaller than the lower limit value and a problem in that the strength of the nonwoven fabric is weakened due to pores having a diameter larger than the upper limit value can be avoided.

According to a specific embodiment of the present invention, the hot-melt nonwoven sheet may have a thickness in the range of 5 to 150 µm or a thickness in the range of 50 to 120 µm. When the hot-melt non-woven sheet has a thickness in the above range, the hot-melt non-woven sheet has a thickness less than the lower limit, so that it has weak strength, and the hot-melt non-woven sheet is broken during the lamination process and has a thickness greater than the upper limit. When the pores are blocked, the air permeability decreases, the resistance increases, and the overall thickness of the separator increases, making it difficult to apply to an actual product can be avoided.

Hereinafter, a method of manufacturing a free-standing separator for a secondary battery according to the present invention will be described. For each material material used in the manufacture of a freestanding separator for a secondary battery, refer to the above description.

According to a specific embodiment of the present invention, the method of manufacturing a freestanding separator for a secondary battery of the present invention includes (S1) dissolving a binder resin in a solvent to prepare a binder composition, and adding inorganic particles thereto to prepare a freestanding porous membrane. Preparing a composition for formation, (S2) coating and drying the composition for forming the freestanding porous film on a release paper, (S3) removing the release paper from the dried freestanding porous film, and (S4) It characterized in that it comprises the step of forming a hot-melt nonwoven fabric layer by spinning polyester, polyamide, ethylene-vinyl acetate, or two or more molten resins thereof on the dried freestanding porous film.

(S1) First, a binder resin is dissolved in a solvent to prepare a binder composition, and inorganic particles are added thereto to prepare a composition for forming a free-standing porous film.

The solvent may be a component capable of dissolving the binder resin used. As such a solvent, for example, polar amide solvents such as acetone, methyl ethyl ketone, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide can be appropriately selected and used.

In one embodiment of the present invention, the binder composition may be appropriately adjusted so that the concentration of the solid content excluding the solvent is within the range of about 5% to 15% by weight. For example, the concentration of the binder composition may be about 10% by weight.

Inorganic particles are added to the binder composition and mixed to prepare a composition for forming a freestanding porous film. The mixing may be performed using an appropriate mixing device such as a homomixer, and the mixing time when mixing using such a mixing device may be controlled to a level in which the input components have a uniform dispersed phase. The mixing may be performed, for example, for about 10 minutes to 1 hour. In the composition obtained after mixing, the concentration of the solid content excluding the solvent may be included in an amount of about 10% by weight or less.

(S2) Then, the composition for forming the free-standing porous film is coated and dried on a release paper.

A composition for forming a free-standing porous film is applied to a release paper such as a terephthalate film and formed into a sheet form.

The application of the composition may be performed by a conventional coating method such as a Meyer bar, a die coater, a reverse roll coater, and a gravure coater.

(S3) Then, the release paper is removed from the dried freestanding porous membrane.

(S4) Next, the hot-melt nonwoven fabric sheet was positioned on both sides of the freestanding porosity, interposed between the positive electrode and the negative electrode, and laminated by hot pressing to prepare an electrode assembly.

The lamination may be performed at a temperature in the range of 60 to 70° C. and a pressure in the range of 1 MPa to 100 MPa. When the lamination temperature is lower than the lower limit, the hot-melt nonwoven sheet does not melt, so that the cathode-separator-anode is not bound, and when the lamination temperature is higher than the upper limit, the pores of the hot-melt nonwoven sheet are blocked. In addition, when the lamination pressure is lower than the lower limit, adhesion to the negative electrode and/or the positive electrode decreases, and when the lamination pressure is higher than the upper limit, the filaments constituting the hot-melt nonwoven fabric layer are compressed and the pores are blocked.

According to a specific embodiment of the present invention, the hot-melt nonwoven layer is interposed between the positive electrode and the negative electrode after spinning polyester, polyamide, ethylene-vinyl acetate, or two or more molten resins thereof on the dried freestanding porous film. After that, it may be formed by lamination, or a hot-melt nonwoven fabric sheet may be placed on both sides of the dried freestanding porous membrane and then interposed between the anode and the cathode, followed by lamination.

의 고온의 공기에 의해 연신시키고 컨베이어 벨트상에 적층하여 부직포층으로 수득될 수 있다. 이 때, 폴리에스테르, 폴리아미드, 에틸렌-비닐 아세테이트 또는 이들의 2 이상은 익스트루더 설비로부터 상기 프리스탠딩 다공성 막의 일 면과 다른 면에 방사될 수 있다.According to a specific embodiment of the present invention, the hot melt nonwoven fabric layer may be a spunbond nonwoven fabric. For this, for example, a pilot spunbond facility of Reicofil is used, and the nozzle is 500mm wide, 28HPI (Hole per Inch), and the hole size is 0.25mm by using a detent. Ester, polyamide, ethylene-vinyl acetate, or two or more thereof are melted and spun from an extruder facility, and filaments spun through a plurality of spinnerets are sprayed from both sides of the nozzle.

It can be obtained as a nonwoven layer by stretching it with hot air and laminating on a conveyor belt. In this case, polyester, polyamide, ethylene-vinyl acetate, or two or more thereof may be radiated from an extruder facility to one side and the other side of the freestanding porous membrane.

According to another aspect of the present invention, there is provided a secondary battery including the free-standing separator for secondary batteries. The secondary battery includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, and the separator is a free-standing separator for a secondary battery having the above-described characteristics.

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 layered compounds such as lithium manganese composite oxide (LiMn 2} O ₄ , LiMnO _2, etc.), lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or compounds 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 , LiFe ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O _7; Lithium nickel oxide represented by the formula LiNi _{1 - x} M _x O ₂ (here, M = Co, Mn, Al, Cu, Fe, Mg, B and Ga, and x = 0.01 ~ 0.3); Formula LiMn _{2 - x} M _x O ₂ (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 ~ 0.1), Li _a Ni _x Co _y Mn _z O ₂ (0.5<a< 1.5, 0<x,y,z<1, x+y+z=1) or Li ₂ Mn ₃ MO ₈ (where M = Fe, Co, Ni, Cu or Zn) ; _{LiMn 2} O _{4 in} which Li in the formula is partially 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, summer black, denka black, aluminum powder, nickel powder, It may be one selected from the group consisting of 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 a chemical change in 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 on the surface.

As the binder resin, a polymer commonly used in electrodes in the art may be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate ( 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 , Cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, flulan, and carboxyl methyl cellulose ), and the like, but are not limited thereto.

The electrode assembly prepared as described above may be charged into an appropriate case and an electrolyte may be injected to manufacture a battery.

In the present invention, the electrolyte 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 ) _{A salt containing an ion or a combination thereof such as 3} ^- is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone ), ester-based compounds, and one or more dissolved or dissociated in an organic solvent including a mixture of at least one selected among them, but is 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 omnipotent 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 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 One

Freestanding Fabrication of porous membrane

A binder composition was prepared by dissolving 7.5 parts by weight of a ^{binder resin (PVdF, weight average molecular weight 1 x 10 6} , Solvay) based on 100 parts by weight of the solvent n-methylpyrrolidone (manufacturer: Daejeonghwa Geum). Here, a composition for forming a freestanding porous film was prepared by adding ^{AlO(OH) (Sasol, BET 100m 2} /g) having an average particle diameter (D50) of 0.07 µm.

The composition was mixed for 30 minutes using a homomixer (Dispermat LC, VMA).

After the mixing process, the obtained composition was uniformly dispersed in each component using a horizontal mill (Mini-cer, Netzsch).

Next, the obtained composition was applied to a release paper (terephthalate film) to a thickness of about 0.4 mm by a bar coating method, and placed in an oven heated to 90° C. for 2 hours. Thereafter, the release paper was removed from the dried result, and a free standing porous membrane having a thickness of 15 μm was obtained.

Fabrication of electrode assembly

As a hot-melt nonwoven sheet, as a polyether sulfone material, a hot-melt nonwoven sheet having a melting point of 80 to 95°C, a basis weight of 15 to 60 g/m ² , and a thickness of 175 μm measured by DSC (manufacturer name: JCC, product name: W90, air permeability 3 s/100 or less) and placed on both sides of the freestanding porous membrane.

For the preparation of the negative electrode, a negative electrode active material (graphite), a conductive material (acetylene black), a thickener (CMC, weight average molecular weight of 1.3 million), and a styrene-butadiene binder were added to 95.7% by weight, 1% by weight, 1.1% by weight and 2.2% by weight, respectively. The mixture was mixed so as to be a weight% to prepare an anode slurry. The negative electrode slurry was coated on a copper (Cu) thin film of a negative electrode current collector having a thickness of 10 μm, dried to prepare a negative electrode, and then roll pressed to prepare a negative electrode.

For the production of the positive electrode, 95.7% by weight, 1% by weight, 1.1% by weight, and 2.2% by weight _{of lithium cobalt oxide (LiCoO 2) as a positive electrode active material, a conductive material (acetylene black), and polyvinylidene fluoride (PVdF) as a binder in distilled water, respectively.} %, thereby preparing a positive electrode slurry. The positive electrode slurry was coated on an aluminum (Cu) thin film of a positive electrode current collector having a thickness of 10 μm, dried to prepare a positive electrode, and then roll press to prepare a positive electrode.

An electrode assembly was prepared by interposing a freestanding porous membrane on both sides of a hot-melt nonwoven fabric sheet between the positive electrode and the negative electrode, hot pressing for 1 second at a temperature of 70° C. and a pressure of 100 MPa for 1 second.

Example 2

In order to prepare a hot melt nonwoven fabric layer, a hot melt nonwoven fabric having a melting point of 60 to 85°C, a basis weight of 15 to 100 g/m ² , and a thickness of 160 μm as an ethylene vinyl acetate material as an ethylene vinyl acetate material ( An electrode assembly was manufactured in the same manner as in Example 1, except that the manufacturer name: JCC, product name: W80, air permeability 3 s/100 or less) was used.

Comparative example One

An electrode assembly was manufactured in the same manner as in Example 1, except that the hot-melt nonwoven layer was not formed.

Comparative example 2

In order to prepare a hot melt nonwoven fabric layer, a hot melt nonwoven fabric having a melting point of 90 to 100°C, a basis weight of 15 to 150 g/m ² , and a thickness of 160 μm as a polyamide material as a polyamide material (manufacturer Name: JCC, product name: W95, air permeability 3 s/100 or less) was prepared in the same manner as in Example 1, to prepare a freestanding porous membrane having a hot-melt nonwoven fabric layer formed thereon.

Comparative example 3:

2-ethylhexyl acrylate (EHA): 2-hydroxyethyl acrylate (HEA) = 90:10, and 2 parts by weight of an isocyanate curing agent were added to obtain a resin composition having a weight average molecular weight of 600,000. The resin composition was coated on both sides of the freestanding porous membrane prepared in the same manner as in Example 1 to a thickness of 5 μm by a bar coating method, and dried at 130° C. for 2 minutes.

Evaluation example

The adhesive layer thickness, air permeability, negative electrode adhesion, and electrolyte impregnation properties of the freestanding separators prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated by the following methods, and the results are summarized in Table 1 below. .

(1) ventilation

In Examples 1 and 2 and Comparative Examples 1 and 2, only the anode and the cathode were removed and air permeability was measured. The air permeability was measured according to JIS P8117.

(2) cathode adhesion

As a 180° peeling test of the separator, the free-standing separator for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 3, respectively, was hot-pressed for 1 second at a temperature of 70° C. and a pressure of 1,000 kgf on the negative electrode for a secondary battery. I did.

Thereafter, the free-standing separator for secondary batteries was pulled at a peeling rate of 300 mm/min using a texture analyzer, and the force (gf) applied until the free-standing separator for secondary batteries fell from the negative electrode was measured.

(3) Rate of dimensional change after impregnation with electrolyte

A free-standing separator for secondary batteries having a width x length x thickness of 10 cm x 10 cm x 0.002 cm was prepared.

In addition, an electrolyte solution was prepared by dissolving _{lithium hexafluoro phosphate (LiPF 6} ) at 1.0 M as a lithium salt in an organic solvent in which dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate components were mixed at a volume ratio of 50:30:20.

The electrolyte was impregnated with a free-standing separator for a secondary battery for 60 minutes. The freestanding separator for a secondary battery taken out from the electrolyte was immediately measured for width x length x thickness without a drying procedure. The dimensional change rate was calculated as [(length of the separator before impregnation-length of the separator after impregnation)/length of the separator before impregnation] x 100.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Layer thickness for adhesion (㎛) 175 (hot melt nonwoven fabric layer) 160
(Hot Melt Nonwoven Fabric Layer) none 160
(Hot Melt Nonwoven Fabric Layer) 5
(Adhesive film layer) Air permeability of the freestanding porous membrane with hot melt adhesion layer/adhesive layer applied on both sides
(s/100cc) 340 340 340 340 1,000 or more Cathode adhesion (gf/25mm) 350 or more 50 Not attached Not attached 100 Dimensional change rate after impregnation of electrolyte (%) 0.8% One% One% One% 0.8%

(4) filament change

By disassembling the electrode assembly laminated in each of Examples 1 and 2, before and after lamination, filaments constituting the hot-melt nonwoven layer were photographed with a microscope, respectively, and FIGS. 1A and 1B, and FIGS. 2A and 2B. It was made into.

Looking at the changes before and after lamination of the hot melt nonwoven fabric layer of the electrode assembly of Example 1 from FIGS. 1A and 1B, it was confirmed that the hot melt nonwoven fabric layer of Example 1 was formed of a filament having a slightly increased diameter than before lamination. Looking at the changes before and after lamination of the hot-melt nonwoven fabric layer of the electrode assembly of Example 2 from FIGS. 2A and 2B, it was confirmed that the hot-melt nonwoven fabric layer of Example 2 was formed of a filament having a slightly increased diameter than before lamination.

As in Comparative Example 1, when there was no hot-melt nonwoven fabric layer or adhesive layer, no adhesion to the electrode was observed.

The hot-melt nonwoven fabric sheet of Comparative Example 2 did not melt the hot-melt nonwoven fabric even after the lamination process, so no significant change occurred in the filaments constituting the hot-melt nonwoven fabric, and no significant change occurred in the thickness of the hot-melt nonwoven fabric layer. In addition, adhesion (adhesion) between the separator and the electrode was not expressed even after the lamination process.

In Comparative Example 3, a polymer adhesive layer was used to adhere between the separator and the electrode, but the measured value was 1,000 s/100 cc or more because there was no ventilation.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (10)

It relates to a laminated electrode assembly comprising an anode, a cathode, and a freestanding separator interposed between the anode and the cathode,
The free-standing separator may include a free-standing porous membrane including inorganic particles and a binder; And a hot-melt nonwoven fabric layer positioned on both sides of the freestanding porous membrane,
In the freestanding porous membrane, inorganic particles form an interstitial volume in a state in which they are substantially in contact with each other, and the interstitial volume between the inorganic particles forms pores of the freestanding porous membrane,
The hot-melt non-woven fabric layer is formed by starting to melt at a temperature of 50° C. or more and less than 90° C., a hot-melt non-woven fabric sheet composed of filaments containing polyester, polyamide, ethylene-vinyl acetate, or two or more thereof,
Laminated electrode assembly, characterized in that the free-standing separator for secondary batteries having the hot-melt nonwoven layer on both sides has an air permeability in the range of 10 sec/100 cc to 500 sec/100 cc.
The method of claim 1,
The laminated electrode assembly, characterized in that the hot-melt nonwoven sheet has an air permeability in the range of 0.1 sec/100 cc to 10 sec/100 cc.
The method of claim 1,
Laminated electrode assembly, characterized in that the hot-melt nonwoven sheet has ^{a basis weight of 0.2 ~ 150 g / m 2.}
The method of claim 1,
Laminated electrode assembly, characterized in that the hot-melt nonwoven sheet has a thickness in the range of 5 to 150 ㎛.
The method of claim 1,
The hot-melt nonwoven sheet is a laminated electrode assembly, characterized in that having a negative electrode and positive electrode adhesion of 50 gf/25 mm or more.
The method of claim 1,
The binder is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethylmethacrylate, polyethylhexyl Acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer (polyethylene-co-vinyl) acetate), polyethylene oxide, polyarylate, or two or more of these.
The method of claim 1,
The inorganic particles are laminated electrode assembly, characterized in that the D50 has an average particle diameter in the range of 0.02 to 1 ㎛.
(S1) preparing a binder composition by dissolving a binder resin in a solvent, and preparing a composition for forming a free-standing porous film by adding inorganic particles thereto,
(S2) coating and drying the composition for forming the freestanding porous film on a release paper,
(S3) removing the release paper from the dried freestanding porous membrane, and
(S4) Laminated at a temperature in the range of 60 to 70 °C and a pressure in the range of 1 MPa to 100 MPa by placing the hot melt nonwoven fabric according to item 1 on both sides of the dried freestanding porous membrane and interposed between the anode and the cathode. Step; The method of manufacturing the laminated electrode assembly according to claim 1, characterized in that it comprises.
A secondary battery comprising the laminated electrode assembly according to any one of claims 1 to 7.
As a hot melt nonwoven sheet,
It has an air permeability in the range of 0.1 sec/100 cc to 10 sec/100 cc,
It has negative and positive adhesion in the range of 50 gf/25 mm or more,
It begins to melt at a temperature of 50 ℃ or more and less than 90 ℃,
Hot-melt nonwoven sheet for lithium secondary battery components.

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