KR102278447B1 - Winding type electrode assembly for rechargeable lithium battery and rechargeable lithium battery including the same - Google Patents

Abstract

a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator includes a porous membrane and an adhesive layer formed on at least one surface of the porous membrane, the adhesive layer comprising fluorine-based polymer-containing microparticles and a binder A wound-up electrode assembly for a lithium secondary battery comprising the same and a lithium secondary battery including the same are provided.

Description

Wind-up electrode assembly for a lithium secondary battery and a lithium secondary battery including the same {WINDING TYPE ELECTRODE ASSEMBLY FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME}

It relates to a wound-type electrode assembly for a lithium secondary battery and a lithium secondary battery including the same.

A fluorine-based polymer such as polyvinylidene fluoride (PVDF) is widely used as a matrix polymer of a gel electrolyte of a lithium secondary battery. For example, a technique for forming a porous layer made of a fluorine-based polymer on the surface of a separator is known, which is formed, for example, by the following method.

In the first method, a slurry is prepared by dissolving a fluorine-based polymer in an organic solvent such as N-methylpyrrolidone, dimethylacetamide, or acetone. Next, the slurry is applied to a separator or an electrode, and then the fluorine-based polymer is phase-separated using a poor solvent such as water, methanol, tripropylene glycol, or the like to form a porous coating layer of the fluorine-based polymer. In the second method, a heating slurry is prepared by dissolving a fluorine-based polymer in a heating electrolyte using dimethyl carbonate, propylene carbonate, ethylene carbonate, or the like as a solvent. Next, the heating slurry is applied to a separator or an electrode to form a coating layer. Then, by cooling the coating layer, the fluorine-based polymer is gelled to form a porous layer swollen by the electrolyte solution.

However, the separator in which the porous layer is formed on the surface by the method described above has a problem in that it is difficult to handle in the manufacturing process because it has poor sliding properties and is easy to generate static electricity as compared to the separator in which the porous layer is not formed. Specifically, when a wound electrode assembly is manufactured, there is a problem in that the strip-shaped positive electrode, the negative electrode, and the separator have poor mutual sliding properties when stacked, so that the wound electrode assembly is distorted. When the wound type electrode assembly is distorted, it may be difficult to accommodate it in the case, and there is a problem in that the cycle life of the battery is not sufficient due to the distortion of the wound type electrode assembly.

One embodiment is to provide a wound-up electrode assembly for a lithium secondary battery that is easy to handle during manufacture by using a separator with less slippage, suppresses distortion of the wound-type electrode assembly, and improves cycle life characteristics of the battery will be.

Another embodiment is to provide a lithium secondary battery including the wound-type electrode assembly for the lithium secondary battery.

One embodiment is a positive electrode; cathode; and a separator disposed between the positive electrode and the negative electrode, wherein the separator includes a porous membrane and an adhesive layer formed on at least one surface of the porous membrane, wherein the adhesive layer is a lithium secondary containing fluorine-based polymer-containing microparticles and a binder Provided is a wound-type electrode assembly for a battery.

The binder may be included in an amount smaller than that of the fluorine-based polymer-containing microparticles.

The volume ratio of the fluorine-based polymer-containing microparticles and the binder may be 1.5:1 to 20:1.

The fluorine-based polymer-containing microparticles may be spherical particles.

The fluorine-based polymer-containing fine particles may include a fluorine-based polymer and fine particles complexed with a resin different from the fluorine-based polymer, and the resin different from the fluorine-based polymer may include an acrylic resin.

The fluorine-based polymer contained in the fluorine-based polymer-containing microparticles may include polyvinylidene fluoride.

The binder may include a polyolefin resin.

The adhesive layer may further include inorganic particles.

The negative electrode may include a negative electrode active material layer including a negative electrode active material and a binder, the binder may include fluorine-based polymer-containing fine particles, and the adhesive layer of the separator may bind to the negative electrode active material layer.

The binder may further include fine particles of an elastomeric polymer.

Another embodiment provides a lithium secondary battery including the wound-type electrode assembly.

The details of other implementations are included in the detailed description below.

By using the separator with less slipping, it is easy to handle during manufacture, and it is possible to suppress the distortion of the wound-type electrode assembly and improve the cycle life characteristics of the battery.

1 is a cross-sectional view showing a schematic configuration of a wound-up electrode assembly for a lithium secondary battery according to an embodiment.
2 is a cross-sectional view illustrating a schematic configuration of an electrode laminate for a lithium secondary battery according to an exemplary embodiment.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

Hereinafter, a lithium secondary battery according to an embodiment will be described with reference to FIGS. 1 and 2 .

1 is a cross-sectional view illustrating a schematic configuration of a wound-up electrode assembly for a lithium secondary battery according to an embodiment, and FIG. 2 is a cross-sectional view illustrating a schematic configuration of an electrode stack for a lithium secondary battery according to an embodiment.

1 and 2 , the lithium secondary battery includes a wound-type electrode assembly 100 , a non-aqueous electrolyte, and a packaging material. The wound electrode assembly 100 is obtained by winding an electrode stack 100a in which a negative electrode 10, a separator 20, a positive electrode 30, and a separator 20 are sequentially stacked in the longitudinal direction and compressed in the B direction. will be. The negative electrode 10 , the separator 20 , and the positive electrode 30 may be a band-shaped negative electrode, a belt-shaped separator, and a belt-shaped positive electrode, respectively.

Hereinafter, the said separator is demonstrated.

The separator 20 may include a porous film 20c and an adhesive layer 20a formed on at least one surface of the porous film 20c, for example, on both surfaces.

The porous membrane 20c is not particularly limited, and, for example, a porous membrane or a nonwoven fabric exhibiting excellent high-rate discharge performance may be used alone or in combination.

In addition, as the resin constituting the porous membrane 20c, for example, polyolefin resin, polyester resin, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinyl Lidenfluoride-perfluorovinyl ether copolymer, vinylidenefluoride-tetrafluoroethylene copolymer, vinylidenefluoride-trifluoroethylene copolymer, vinylidenefluoride-fluoroethylene copolymer, vinylidene fluoride Ride-hexafluoroacetone copolymer, vinylidenefluoride-ethylene copolymer, vinylidenefluoride-propylene copolymer, vinylidenefluoride-trifluoropropylene copolymer, vinylidenefluoride-tetrafluoroethylene-hexa A fluoropropylene copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, etc. are mentioned. Examples of the polyolefin-based resin include polyethylene and polypropylene, and examples of the polyester-based resin include polyethylene terephthalate and polybutylene terephthalate.

The adhesive layer 20a may include fluorine-based polymer-containing microparticles 20b-1 and a binder 20b-2, and may include the separator 20 and the negative electrode 10, or the separator 20 and The positive electrode 30 may be bound.

The fluorine-based polymer-containing microparticles 20b-1 may be microparticles containing a fluorine-based polymer, and specifically, fine particles complexed with a fluorine-based polymer and a resin different from the fluorine-based polymer may be used.

The resin different from the fluorine-based polymer may include an acrylic resin. That is, as examples of the fluorine-based polymer-containing fine particles, fine particles in which a fluorine-based polymer and an acrylic resin are complexed may be used, but the present invention is not limited thereto. The complex may have an inter-penetrating network polymer (IPN) type structure.

The fluorine-based polymer contained in the fluorine-based polymer-containing microparticles 20b-1 may be polyvinylidene fluoride (PVDF) or a copolymer including polyvinylidene fluoride (PVDF). As the copolymer containing PVDF, vinylidene fluoride (VDF)-hexafluoropropylene (HFP) copolymer, vinylidene fluoride (VDF)-tetrafluoroethylene (TFE) copolymer, vinylidene fluoride ( VDF)-tetrafluoroethylene (TFE)-hexafluoropropylene (HFP) copolymer and the like may be used alone or in combination of two or more.

The particle size (diameter when the fine particles are regarded as spherical) of the fluorine-based polymer-containing fine particles 20b-1 is not particularly limited, and may be any value as long as it can be dispersed in the negative electrode active material layer 10a. For example, the average particle diameter (arithmetic mean value of the particle diameter) of the fluorine-based polymer-containing microparticles may be 80 nm to 500 nm. The average particle diameter of the fluorine-based polymer-containing fine particles may be measured, for example, by laser diffractometry. Specifically, the particle size distribution of the fluorine-based polymer-containing fine particles is measured by a laser diffraction method, and the arithmetic mean value of the particle size may be calculated according to the particle size distribution.

The fluorine-based polymer-containing microparticles (20b-1) are, for example, prepared by emulsion polymerization of a fluorine-based polymer-inducing monomer, or by suspension polymerization of a fluorine-based polymer-inducing monomer, followed by suspension polymerization. ) can be prepared by pulverizing. Examples of the monomer for inducing the fluorine-based polymer may include vinylidene fluoride (VDF).

The fluorine-based polymer-containing microparticles 20b-1 may be spherical particles. The spherical fluorine-based polymer-containing microparticles may be formed by, for example, the emulsion polymerization method. In addition, the shape and structure of the fluorine-based polymer-containing microparticles may be confirmed by, for example, a scanning electron microscope (SEM).

The binder 20b-2 may support the fluorine-based polymer-containing microparticles 20b-1 in the adhesive layer 20a.

The content occupied by the binder 20b-2 in the adhesive layer 20a may be smaller than the content occupied by the fluorine-based polymer-containing microparticles 20b-1 on a volume basis. For example, the volume ratio of the fluorine-based polymer-containing microparticles and the binder may be 1.5:1 to 20:1, and 2:1 to 20:1.

The binder 20b-2 may use a polyolefin resin. Examples of the polyolefin resin include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, and ionomers thereof.

The binder 20b-2 may further include fine particles of an elastomeric polymer.

Examples of the elastomer-based polymer include styrene-butadiene rubber, butadiene rubber, nitrile butadiene rubber, natural rubber, isoprene rubber, ethylene-propylene-diene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, acrylic acid ester, and methacrylic acid ester. A copolymer, a partially hydride or fully hydride of these, an acrylic acid ester type copolymer, etc. are mentioned. Each of these may be modified with a monomer having a polar functional group, such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, and a hydroxyl group, in order to improve binding properties.

The adhesive layer 20a may further include a thickener to impart a viscosity suitable for application.

As the thickener, a water-soluble polymer may be used, for example, a cellulose-based polymer, a polyacrylic acid-based polymer, polyvinyl alcohol, polyethylene oxide, and the like. Examples of the cellulose-based polymer include metal salts or ammonium salts of carboxymethyl cellulose (CMC), cellulose derivatives such as methyl cellulose, ethyl cellulose, and hydroxyalkyl cellulose. Other examples include polyvinylpyrrolidone (PVP), starch, starch phosphate, casein, various modified starches, chitin, and chitosan derivatives. These thickeners can be used individually or in combination of 2 or more types, respectively. Among them, the cellulose-based polymer may be used, and specifically, an alkali metal salt of carboxymethyl cellulose may be used.

The content ratio of the thickener and the binder is not particularly limited.

In addition, the adhesive layer 20a may further include inorganic particles for porosity control or thermal stability. The inorganic particles may be ceramic particles, specifically, metal oxide particles. Examples of the metal oxide particles include fine particles such as alumina, boehmite, titania, zirconia, magnesia, zinc oxide, aluminum hydroxide, and magnesium hydroxide. The average particle diameter of the inorganic particles may be 1/2 or less of the thickness of the adhesive layer. The average particle diameter of the inorganic particles is, for example, 50% of the volume cumulatively measured by a laser diffraction method or the like, and represents a D50 value. The content of the inorganic particles is not particularly limited, and may be, for example, 70% by weight or less based on the total amount of the adhesive layer 20a.

The separator 20 may be manufactured by the following method. Dispersing and dissolving the material of the adhesive layer 20a in water to prepare an adhesive layer mixture slurry, that is, an aqueous slurry, and then applying the mixture slurry to at least one surface of the porous membrane 20c to form an application layer, and then By drying the application layer, the adhesive layer 20a can be formed.

Hereinafter, the negative electrode will be described.

The negative electrode 10 includes a negative electrode current collector 10b, and a negative electrode active material layer 10a formed on the negative electrode current collector 10b. The negative electrode 10 may be an aqueous negative electrode.

The anode active material layer 10a may include an anode active material and a binder, and may further include a thickener.

The negative active material is not particularly limited as long as it is a lithium-containing alloy or a material capable of reversibly occluding and releasing lithium, for example, lithium (Li), indium (In), tin (Sn), aluminum (Al), silicon Metals such as (Si), alloys and oxides thereof, _{transition metal oxides such as Li 4 /3} Ti _{5 /3} O ₄ , SnO, artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, artificial graphite coated Natural graphite, non-graphitizable carbon, graphite carbon fiber, resin calcined carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin calcined carbon, polyacene , and carbon materials such as pitch-based carbon fibers. These negative electrode active materials may be used independently and 2 or more types may be used together. Among them, a graphite-based material can be used as the main material.

The binder binds negative electrode active materials to each other. The binder may include fluorine-based polymer-containing microparticles.

The fluorine-based polymer-containing microparticles may be dispersed in water to form latex. Therefore, water may be used as a solvent of the slurry for forming the negative electrode active material layer 10a.

The fluorine-based polymer-containing microparticles are the same as the fluorine-based polymer-containing microparticles 20b-1 included in the above-described adhesive layer of the separator, and a description thereof will be omitted herein.

The binder may further include fine particles of an elastomeric polymer. The fine particles of the elastomeric polymer are the same as the fine particles of the elastomeric polymer included in the adhesive layer of the separator, and a description thereof will be omitted herein.

The thickener may adjust the negative electrode mixture slurry to a viscosity suitable for application, and may function as a binder in the negative electrode active material layer 10a. The thickener is the same as the thickener included in the adhesive layer of the separator, and a description thereof will be omitted herein.

The content ratio of the thickener and the binder is not particularly limited, and any ratio applicable to the negative active material layer of the lithium secondary battery may be used.

The negative electrode current collector 10b may be any conductor as long as it is a conductor, and for example, copper, stainless steel, nickel-plated steel, or the like may be used. A negative terminal is connected to the negative electrode current collector 10b.

The negative electrode 10 may be manufactured by the following method. The above-mentioned material of the negative electrode active material layer is dispersed in water to form a negative electrode mixture slurry, that is, an aqueous slurry, and the negative electrode mixture slurry is applied on a current collector to form an application layer, and then the application layer is dried. For example, in the negative electrode mixture slurry, fluorine-based polymer-containing particles and elastomeric polymer particles are dispersed in the negative electrode active material layer 10a. Next, the dried coating layer may be rolled together with the negative electrode current collector 10b to manufacture the negative electrode 10 .

Hereinafter, the anode will be described.

The positive electrode 30 includes a positive electrode current collector 30b and a positive electrode active material layer 30a formed on the positive electrode current collector 30b.

The positive active material layer 30a may include at least a positive active material, and may further include a conductive agent and a binder.

The positive active material is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions, and for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide , lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, vanadium oxide, and the like. These positive electrode active materials may be used alone or in combination of two or more. Specifically, among them, a lithium metal oxide having a layered rock salt structure may be used.

The lithium metal oxide having the layered rock salt structure is, for example, Li _{1 -xyz} Ni _x Co _y Al _z O ₂ or Li _{1 -xy- z} Ni _x Co _y Mn _z O ₂ (0<x<1, 0 and <y<1 and 0<z<1, and x+y+z<1).

The conductive agent may include, for example, carbon black such as Ketjenblack and acetylene black, natural graphite, and artificial graphite, but is not particularly limited as long as it is intended to increase the conductivity of the positive electrode.

The binder binds the positive electrode active materials to each other and at the same time binds the positive active material to the positive electrode current collector 30b. The type of the binder is not particularly limited, and any binder used for the positive electrode active material layer of a conventional lithium secondary battery may be used. For example, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride Ride-trifluoroethylene copolymer, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, cellulose nitrate, etc. can be heard

The positive electrode current collector 30b may be any conductor as long as it is a conductor, and may be, for example, aluminum, stainless steel, or nickel-plated steel. A positive terminal is connected to the positive electrode current collector 30b.

The positive electrode 30 may be manufactured by the following method. A positive electrode mixture slurry is prepared by dispersing the material of the positive electrode active material layer in an organic solvent or water, the positive electrode mixture slurry is applied on a current collector to form an application layer, and then the application layer is dried. Then, the positive electrode 30 can be manufactured by rolling the dried coating layer together with the positive electrode current collector 30b.

Hereinafter, the non-aqueous electrolyte will be described.

As the non-aqueous electrolyte, the same non-aqueous electrolyte that can be used in a lithium secondary battery may be used without particular limitation. Specifically, the non-aqueous electrolyte has a composition in which an electrolyte salt is contained in a non-aqueous solvent.

The electrolyte salt is, for example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF _{6 -x} (CnF _{2n +1} ) _x (1<x<6, n=1 or 2), LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , an inorganic ion salt containing one of lithium, sodium, or potassium such as KSCN; LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ), LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H _{7 )} ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, (C _{2 )} and organic ionic salts such as H ₅ ) ₄ N-phthalate, lithium stearyl sulfonate, lithium octyl sulfonate, and lithium dodecylbenzenesulfonate, and these ionic compounds may be used alone or in combination of two or more.

The concentration of the electrolyte salt is not particularly limited, and may be used, for example, in a concentration of 0.8 to 1.5 mol/L.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain esters such as methyl formate, methyl acetate, and methyl butyric acid; tetrahydrofuran or a derivative thereof; ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, and methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or a derivative thereof; Ethylene sulfide, sulfolane, sultone or a derivative thereof may be used alone or as a mixture of two or more, but is not limited thereto.

The non-aqueous electrolyte may be impregnated in the separator 20 .

A well-known conductive support agent, an additive, etc. can be added suitably to each electrode mentioned above.

The exterior material may be, for example, an aluminum laminate.

Hereinafter, the manufacturing method of a lithium secondary battery is demonstrated.

The electrode stack 100a may be formed by sequentially stacking the negative electrode 10 , the separator 20 , the positive electrode 30 , and the separator 20 . Accordingly, since the separator 20 is disposed on one surface of the electrode stack 100a and the cathode 10 is disposed on the back side of the electrode stack 100a, when the electrode stack 100a is wound, the surface of the portion where the electrode stack 100a is located, that is, , the back side of the other part of the electrode stack 100a, that is, the negative electrode 10, is in contact with the separator 20 . As a result, the wound electrode assembly 100 may be manufactured. Next, the flat wound electrode assembly 100 is manufactured by pressing the wound electrode assembly 100 , and then the flat wound electrode assembly 100 is inserted into an exterior body, for example, a laminate film together with a non-aqueous electrolyte. and sealing the exterior body, a lithium secondary battery can be produced. When sealing the exterior body, a terminal conducting to each current collector is protruded to the outside of the exterior body.

Hereinafter, specific embodiments of the present invention are presented. However, the examples described below are only for specifically illustrating or explaining the present invention, and the present invention is not limited thereto. In addition, since the content not described here can be sufficiently technically inferred by a person skilled in the art, the description thereof will be omitted.

Example One

(anode manufacturing)

LiCoO ₂ , carbon black, and polyvinylidene fluoride were dissolved and dispersed in N-methylpyrrolidone at a solid weight ratio of 96:2:2 to prepare a positive electrode mixture slurry. Then, the positive electrode mixture slurry was applied to both surfaces of an aluminum foil current collector having a thickness of 12 μm and dried. A positive electrode active material layer was prepared by rolling the dried coating layer. The total thickness of the current collector and the positive electrode active material layer was 120 μm. Then, an aluminum lead wire was welded to the electrode end to prepare a positive electrode.

(Cathode Manufacturing)

Graphite, an aqueous dispersion of carboxy-modified styrene-butadiene rubber particles as a binder, and an aqueous dispersion of fluorine-based polymer-containing microparticles complexed by polymerizing an acrylic resin in an aqueous dispersion of polyvinylidene fluoride (PVDF) as a binder (Arkema Aquatec ARC) ), and a sodium salt of carboxymethyl cellulose as a thickener was dissolved and dispersed in water at a weight ratio of solid content of 97:1:1:1 to prepare a negative electrode mixture slurry. At this time, it was confirmed that the average particle diameter of the fluorine-based polymer-containing microparticles was measured by laser diffraction method to be 300 nm, and as a result of observing the fluorine-based polymer-containing microparticles with a scanning electron microscope (SEM), it was confirmed that they were spherical particles. Then, the negative electrode mixture slurry was applied to both surfaces of a copper foil current collector having a thickness of 10 μm, and then dried. The applied layer after drying was rolled to form a negative electrode active material layer. In this case, the total thickness of the current collector and the anode active material layer was 120 μm. Then, a negative electrode was manufactured by welding a nickel lead wire to the end.

(Separator Manufacturing)

Aqueous dispersion of fluorine-based polymer-containing microparticles (Arkema's Aquatec ARC) complexed by polymerizing an acrylic resin in an aqueous dispersion of polyvinylidene fluoride (PVDF), sodium salt of carboxymethyl cellulose as a thickener, and polyethylene ionomer microparticles as a binder An aqueous dispersion (Soken Chemical Co., 　SX-130H) was dissolved and dispersed in water at a solid weight ratio of 95:1:4 to prepare an adhesive layer mixture slurry. Next, the adhesive layer mixture slurry was applied and dried on both sides of a porous polyethylene film having a thickness of 12 μm to prepare a separator having an adhesive layer having a thickness of 3 μm on both sides. At this time, the volume ratio of the fluorine-based polymer-containing microparticles to the aqueous dispersion of the polyethylene ionomer microparticles was 18:1.

(Manufacture of wound electrode assembly)

Using the negative electrode, the separator, and the positive electrode prepared above, the negative electrode, the separator, the positive electrode and the separator were sequentially laminated, and the laminate was wound in the longitudinal direction using a wick having a diameter of 3 cm. After fixing the end to the tape, the wick was removed, and the cylindrical wound-type electrode assembly was sandwiched between two metal plates with a thickness of 3 cm and held for 3 seconds to prepare a flat wound-type electrode assembly.

(Lithium secondary battery production)

The wound-type electrode assembly was pressure-sealed together with an electrolyte so that two lead wires went out to a laminate film made of three layers of polypropylene/aluminum/nylon, thereby manufacturing a lithium secondary battery. _{As the electrolyte, 1M LiPF 6} dissolved in a solvent in which ethylene carbonate and ethylmethyl carbonate were mixed in a volume ratio of 3:7 was used. The lithium secondary battery was placed between two metal plates having a thickness of 3 cm heated to 80° C. and maintained for 5 minutes.

Example 2

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode mixture slurry during the preparation of the negative electrode and the adhesive layer mixture slurry during the preparation of the separator were respectively prepared as follows.

Graphite, an aqueous dispersion of carboxy-modified styrene-butadiene rubber fine particles as a binder, and a sodium salt of carboxymethyl cellulose as a thickener were dissolved and dispersed in water at a solid weight ratio of 97:2:1 to prepare a negative electrode mixture slurry.

Aqueous dispersion of fluorine-based polymer-containing microparticles complexed by polymerizing acrylic resin in PVDF water dispersion (Arkema's Aquatec ARC), sodium salt of carboxymethyl cellulose as a thickener, and an aqueous dispersion of polyethylene ionomer microparticles as a binder (Soken Chemical, SX-130H) was dissolved and dispersed in water at a solid weight ratio of 89:1:10 to prepare an adhesive layer mixture slurry. At this time, the volume ratio of the fluorine-based polymer-containing microparticles to the aqueous dispersion of the polyethylene ionomer microparticles was 7:1.

Example 3

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the adhesive layer mixture slurry was prepared as follows when the separator was manufactured.

Alumina powder with an average particle diameter of 0.5 μm as inorganic particles, an aqueous dispersion of fluorine-based polymer-containing fine particles complexed by polymerizing acrylic resin in a PVDF aqueous dispersion (Arkema Aquatec ARC), sodium salt of carboxymethyl cellulose as a thickener, and as a binder An aqueous dispersion of polyethylene ionomer microparticles (Soken Chemical, 　SX-130H) was dissolved and dispersed in water at a solid weight ratio of 62:27:1:10 to prepare an adhesive layer mixture slurry. At this time, the volume ratio of the fluorine-based polymer-containing microparticles to the aqueous dispersion of the polyethylene ionomer microparticles was 2:1. In addition, the average particle diameter of the alumina powder is a volume cumulative 50% (D50) value measured by laser diffraction method.

comparative example One

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the separator was manufactured as follows.

A solution of polyvinylidene fluoride (PVDF) dissolved in N-methylpyrrolidone is applied to both sides of a porous polyethylene film having a thickness of 12 μm, and the film coated with the solution is immersed in water and then dried, both sides of the film A mesh-shaped porous adhesive layer was formed. At this time, the thickness of the adhesive layer was 3㎛.

comparative example 2

A lithium secondary battery was manufactured in the same manner as in Example 2, except that crosslinked polystyrene fine particles were used instead of the aqueous dispersion of fluorine-based polymer-containing fine particles complexed by polymerizing an acrylic resin in the PVDF aqueous dispersion during the manufacture of the separator.

Rating 1: winding type Thickness increase rate of electrode assembly

For the wound-up electrode assemblies prepared in Examples 1 to 3 and Comparative Examples 1 and 2, the stability of the shape was evaluated by measuring the thickness increase rate before and after standing for 48 hours. The results are shown in Table 1 below.

The smaller the thickness increase rate, the smaller the distortion of the wound-type electrode assembly, and thus the better shape stability. The thickness increase rate is calculated by dividing the thickness increase amount of the electrode assembly before and after standing for 48 hours by the thickness of the electrode assembly before standing for 48 hours.

Evaluation 2: Cycle Life Characteristics

The lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were charged with a constant current to 4.4V at 1/10CA of the design capacity (1CA is a discharge rate for 1 hour), and then 1/20CA was Constant voltage charging was performed until After that, constant current discharge was performed to 3.0V with 1/2CA. The capacity at this time was determined as the initial discharge capacity, and a battery for life evaluation was manufactured.

The manufactured battery was subjected to a cycle test in which the charging process of constant current charging of 0.5CA and 4.4V, the charging process of constant voltage charging up to 0.05CA, and the discharging process of constant current discharge of 0.5CA and 3.0V were repeated, and the initial discharge capacity after 100 cycles The reduction rate of the discharge capacity was calculated for , and the results are shown in Table 1 below.

In Table 1 below, the capacity retention rate (%) is calculated by dividing the discharge capacity after 100 cycles by the initial discharge capacity.

separator cathode Thickness increase rate (%) Capacity retention rate (%) adhesive layer Inorganic particles in the adhesive layer Fluoropolymer-containing fine particles/volume ratio of binder Fluorine polymer-containing microparticles Example 1 Fluoropolymer-containing fine particles free 18 contain 5 91 Example 2 Fluorine polymer-containing microparticles free 7 free 7 90 Example 3 Fluoropolymer-containing fine particles contain 2 contain 6 92 Comparative Example 1 Reticulated fluorine-based polymer free 18 contain 10 85 Comparative Example 2 crosslinked polystyrene fine particles free 0 free 6 85

Referring to Table 1, it can be seen that Examples 1 to 3 in which the fluorinated polymer-containing microparticles were used when forming the separator adhesive layer had a small thickness increase rate and excellent cycle life characteristics. In addition, it can be seen that the cycle life characteristics of Example 3, which further included inorganic particles when forming the separator adhesive layer, were further improved.

It can be seen that Comparative Example 1 uses a fluorine-based polymer having a mesh-like structure rather than a particle shape, and thus shape stability after manufacturing the flat wound-type electrode assembly is reduced. In other words, it can be seen that the shape of the wound electrode assembly of Comparative Example 1 is greatly distorted. In addition, the separator of Comparative Example 1 had poor slipperiness, and when the wound-type electrode assembly was manufactured in a flat shape, the contact portion between the electrode stacks did not slide well. As a result, it was found that the wound-type electrode assembly was distorted. It seems that the cycle life characteristics are deteriorated because the distance between them is not stable.

It can be seen that the cycle life characteristics of Comparative Example 3 in which crosslinked polystyrene fine particles were used instead of the fluorine-based polymer-containing fine particles also deteriorated.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also presented. It is within the scope of the invention.

100: wound electrode assembly
100a: electrode laminate
10: cathode
10a: anode active material layer
10b: negative electrode current collector
20: separator
20a: adhesive layer
20b-1: Fluorine-based polymer-containing microparticles
20b-2: binder
20c: porous membrane
30: positive electrode
30a: positive electrode active material layer
30b: positive electrode current collector

Claims (15)

anode;
cathode; and
a separator disposed between the positive electrode and the negative electrode;
The separator includes a porous membrane and an adhesive layer formed on at least one surface of the porous membrane,
The adhesive layer includes fluorine-based polymer-containing microparticles and a binder,
The binder is a wound-up electrode assembly for a lithium secondary battery comprising a polyolefin resin. According to claim 1,
The binder is a wound-up electrode assembly for a lithium secondary battery that is included in a smaller content than the fluorine-based polymer-containing microparticles. According to claim 1,
The volume ratio of the fluorine-based polymer-containing microparticles and the binder is 1.5:1 to 20:1 wound-up electrode assembly for a lithium secondary battery. According to claim 1,
The fluorine-containing polymer-containing fine particles are spherical particles wound-up electrode assembly for a lithium secondary battery. According to claim 1,
The fluorine-based polymer-containing microparticles are a fluorine-based polymer and a wound-up electrode assembly for a lithium secondary battery comprising microparticles complexed with a resin different from the fluorine-based polymer. 6. The method of claim 5,
The wound-type electrode assembly for a lithium secondary battery comprising a resin different from the fluorine-based polymer is an acrylic resin. According to claim 1,
The fluorine-based polymer contained in the fluorine-based polymer-containing microparticles is a wound-up electrode assembly for a lithium secondary battery comprising polyvinylidene fluoride. delete According to claim 1,
The adhesive layer is a wound-up electrode assembly for a lithium secondary battery further comprising inorganic particles. According to claim 1,
The negative electrode includes a negative electrode active material layer comprising a negative electrode active material and a binder,
The binder includes fluorine-based polymer-containing microparticles,
The adhesive layer of the separator is a wound-up electrode assembly for a lithium secondary battery that binds to the anode active material layer. 11. The method of claim 10,
The fluorine-based polymer-containing microparticles are a fluorine-based polymer and a wound-up electrode assembly for a lithium secondary battery comprising microparticles complexed with a resin different from the fluorine-based polymer. 12. The method of claim 11,
The wound-type electrode assembly for a lithium secondary battery comprising a resin different from the fluorine-based polymer is an acrylic resin. 11. The method of claim 10,
The fluorine-based polymer contained in the fluorine-based polymer-containing microparticles is a wound-up electrode assembly for a lithium secondary battery comprising polyvinylidene fluoride. 11. The method of claim 10,
The binder is a wound-up electrode assembly for a lithium secondary battery further comprising fine particles of an elastomeric polymer. A lithium secondary battery comprising the wound electrode assembly of any one of claims 1 to 7 and 9 to 14.

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