WO2019156172A1 - Lithium ion secondary battery, lithium ion secondary battery negative electrode structure, and production method for lithium ion secondary battery - Google Patents

Abstract

The present invention is a lithium ion secondary battery that comprises: a negative electrode that has a negative electrode active material layer; a positive electrode; a separator that is arranged between the negative electrode and the positive electrode; and an adhesive layer that is arranged between the separator and at least one of the negative electrode and the positive electrode and adheres the separator and the electrode(s). The adhesive layer contains 30–55 volume% of at least one type of resin selected from the group that consists of polyvinylidene fluoride/hexafluoropropylene copolymers and acrylic resins. The density of the negative electrode active material layer is 1.50–1.70 g/cm3. The present invention makes it possible to provide a lithium ion secondary battery that has favorable rapid charging properties, favorable adhesion between a separator and an electrode, and a high energy density.

Description

Lithium ion secondary battery, negative electrode structure for lithium ion secondary battery, and method for producing lithium ion secondary battery

The present invention relates to a lithium ion secondary battery, a negative electrode structure for a lithium ion secondary battery, and a method for producing a lithium ion secondary battery.

Lithium ion secondary batteries are used as large stationary power sources for power storage, power sources for electric vehicles, and the like, and in recent years, research on miniaturization and thinning of batteries has been progressing. Generally, a lithium ion secondary battery includes both electrodes (a positive electrode and a negative electrode) in which an electrode active material layer is formed on the surface of a metal foil, and a separator disposed between both electrodes. The separator plays a role of preventing a short circuit between both electrodes and holding an electrolytic solution.
A lithium ion secondary battery is manufactured by preparing a positive electrode and a negative electrode, which are constituent members thereof, and a separator or the like provided therebetween, and hot-pressing them. At this time, the separator is displaced from a fixed position. In some cases, there may be a manufacturing defect such as a partial lift from the electrode.
From such a viewpoint, a technique is known in which an adhesive layer is provided between each electrode and the separator to improve the adhesion between each electrode and the separator, thereby preventing the above-described manufacturing problems.
For example, Patent Document 1 discloses a technique for manufacturing a lithium ion secondary battery by providing an electrode adhesive layer on a separator made of a porous polymer substrate.

Special table 2016-522553 gazette

However, when the adhesive layer is used, the adhesion between the electrode and the separator is improved, and it is possible to prevent problems related to poor adhesion such as floating of the separator when manufacturing a lithium ion secondary battery. The rapid chargeability of lithium ion secondary batteries tends to deteriorate.
Therefore, an object of the present invention is to provide a lithium ion secondary battery that has both good adhesion and rapid chargeability between the electrode and the separator and has high energy density.

As a result of intensive studies, the inventors have provided an adhesive layer that is disposed between at least one of the negative electrode and the positive electrode and the separator, and adheres the separator and the electrode, and the density of the negative electrode active material layer is within a specific range. As a result, the inventors have found that the above problems can be solved, and have completed the following present invention. The gist of the present invention is the following [1] to [10].
[1] A negative electrode having a negative electrode active material layer, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and disposed between at least one of the negative electrode and the positive electrode and the separator, An adhesive layer for adhering the electrode, wherein the adhesive layer contains 30 to 55% by volume of at least one resin selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin, A lithium ion secondary battery in which the density of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ .
[2] The lithium ion secondary battery according to [1], wherein the adhesive layer is disposed between the negative electrode and the separator.
[3] The lithium ion secondary battery according to the above [1] or [2], wherein the adhesive layer contains a urea resin.
[4] The lithium ion secondary battery according to any one of [1] to [3], wherein the adhesive layer is an insulating layer containing insulating fine particles.
[5] The lithium ion secondary battery according to any one of [1] to [4], wherein the adhesive layer contains 30 to 55% by volume of a polyvinylidene fluoride-hexafluoropropylene copolymer.
[6] The lithium ion secondary battery according to any one of [1] to [5], wherein the adhesive layer has a thickness of 1 to 10 μm.
[7] A negative electrode having a negative electrode active material layer and an adhesive layer, wherein the adhesive layer contains 30 to 55% by volume of at least one resin selected from a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin. A negative electrode structure for a lithium ion secondary battery, wherein the negative electrode active material layer has a density of 1.50 to 1.70 g / cm ³ .
[8] A step of forming the adhesive layer on one surface selected from the separator and the electrode, a step of bonding the other selected from the separator and the electrode, and the adhesive layer by hot pressing; A method for producing a lithium ion secondary battery according to any one of the above [1] to [6].
[9] The lithium ion secondary battery according to [8], including a step of forming an adhesive layer on the negative electrode active material layer of the negative electrode, and a step of bonding the separator and the adhesive layer by hot pressing. Manufacturing method.
[10] The method for producing a lithium ion secondary battery according to the above [8] or [9], wherein the temperature of the hot press is 60 to 120 ° C. and the pressure is 0.2 to 2.0 MPa.

According to the present invention, it is possible to provide a lithium ion secondary battery that has both good adhesion and rapid chargeability between the electrode and the separator and high energy density.

It is a schematic sectional drawing which shows one Embodiment of the lithium ion secondary battery of this invention.

<Lithium ion secondary battery>
Hereinafter, the lithium ion secondary battery of the present invention will be described in detail.
FIG. 1 is a schematic cross-sectional view showing an embodiment of the lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 includes a negative electrode 11, a positive electrode 12, a separator 13 disposed between the negative electrode 11 and the positive electrode 12, and an adhesive layer 14 disposed between the separator 13 and the negative electrode 11.
The negative electrode 11 includes a negative electrode current collector 11a and a negative electrode active material layer 11b laminated on the negative electrode current collector 11a. Similarly, the positive electrode 12 has a positive electrode current collector 12a and a positive electrode current collector 12a. And a positive electrode active material layer 12b laminated thereon. An adhesive layer 14 is provided between the negative electrode active material layer 11b and the separator 13 so as to be in contact with both, and the two are adhered to each other. In FIG. 1, the adhesive layer 14 is provided between the negative electrode active material layer 11 b and the separator 13, but may be provided between the positive electrode active material layer 12 b and the separator 13. The adhesive layer 14 may be provided between both the negative electrode active material layer 11b and the separator 13 and between the positive electrode active material layer 12b and the separator 13, but is preferably provided on either one. The adhesive layer improves the adhesion between the electrode and the separator, and it is possible to prevent problems such as floating of the separator when assembling a lithium ion secondary battery.

[Adhesive layer]
The adhesive layer used in the lithium ion secondary battery of the present invention is disposed between at least one of the negative electrode and the positive electrode and the separator, and adheres the separator and the electrode.
The adhesive layer is preferably disposed between the negative electrode and the separator from the viewpoint of improving the adhesion between the electrode and the separator. This is because the surface area of the negative electrode active material layer constituting the negative electrode is generally larger than the surface area of the positive electrode active material layer, and the area where the adhesive layer can be formed is larger in the negative electrode.
The adhesive layer is made of at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and an acrylic resin (hereinafter also referred to as a specific resin) in an amount of 30 to 55 on the basis of the total amount of the adhesive layer. Contains by volume. As the specific resin, it is preferable to use a polyvinylidene fluoride-hexafluoropropylene copolymer from the viewpoint of further improving the adhesion between the electrode and the separator.
When the content of the specific resin is less than 30% by volume, the adhesion between the electrode and the separator is lowered, and when the content of the specific resin exceeds 55% by volume, the quick chargeability of the lithium ion secondary battery is deteriorated. . From the viewpoint of improving the adhesion between the electrode and the separator and increasing the quick chargeability, the content of the specific resin in the adhesive layer is preferably 32 to 48% by volume, and preferably 35 to 45% by volume. Is more preferable.

As an acrylic resin, for example, a homopolymer of (meth) acrylate monomer, a copolymer of two or more (meth) acrylate monomers, a (meth) acrylate monomer, and these can be copolymerized Examples thereof include copolymers with other vinyl monomers. In the specification, (meth) acrylic acid is a generic term for acrylic acid and methacrylic acid.
Examples of the (meth) acrylate monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl (meth) acrylate. , Isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, phenyl (meth) acrylate, isobornyl (meth) acrylate, (meth) Examples include cyclohexyl acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentadienyl (meth) acrylate, and dihydrodicyclopentadienyl (meth) acrylate.
Examples of other vinyl monomers copolymerizable with the (meth) acrylic acid ester monomer include acrylic acid, methacrylic acid, styrene, methylstyrene, vinyl acetate, acrylonitrile, itaconic acid, maleic acid and the like.
Among acrylic resins, polymethyl acrylate, polymethyl methacrylate, and the like can be suitably used.

The adhesive layer preferably contains a urea resin from the viewpoint of improving the adhesion between the electrode and the separator. The urea resin is a synthetic resin obtained by reacting urea with formaldehyde. The content of urea resin in the adhesive layer is preferably 5 to 70% by volume, more preferably 10 to 65% by volume, and further preferably 25 to 35% by volume based on the total amount of the adhesive layer. . Compared to the specific resin, urea resin has a low degree of decrease in rapid chargeability even when the content is increased. Therefore, the content is relatively increased to improve adhesiveness while maintaining rapid chargeability. it can. When the urea resin is used, the total amount of the urea resin in the adhesive layer and insulating fine particles described later is preferably 70% by volume or less, and preferably 65% by volume or less based on the total amount of the adhesive layer.

The adhesive layer may contain other resins other than the specific resin and urea resin as long as the effects of the present invention are not hindered. Other resins include fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), and polyether nitrile. (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber, poly (meth) acrylic acid, carboxymethylcellulose, hydroxyethylcellulose, and polyvinyl alcohol. These may be used individually by 1 type and 2 or more types may be used together. In addition, carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.
The content of the other resin in the adhesive layer is preferably 10% by volume or less, more preferably 5% by volume or less, and still more preferably 0% by volume.

The adhesive layer preferably further contains insulating fine particles to form an insulating layer. By containing the insulating fine particles, the adhesive layer also functions as an insulating layer, and it is possible to effectively prevent a short circuit between the positive electrode and the negative electrode.
The insulating fine particles are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles. Specific organic particles include, for example, polymethyl methacrylate, styrene-acrylic acid copolymer, acrylonitrile resin, polyamide resin, polyimide resin, poly (2-acrylamido-2-methylpropanesulfonic acid lithium), polyacetal resin, Examples thereof include particles composed of an organic compound such as an epoxy resin, a polyester resin, a phenol resin, and a melamine resin. Inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), potassium fluoride, fluorine And particles composed of inorganic compounds such as lithium fluoride, clay, zeolite, and calcium carbonate. The inorganic particles may be particles composed of a known composite oxide such as niobium-tantalum composite oxide or magnesium-tantalum composite oxide.
The insulating fine particles may be particles in which each of the above materials is used alone or in combination of two or more. The insulating fine particles may be fine particles containing both an inorganic compound and an organic compound. For example, inorganic-organic composite particles in which the surface of particles made of an organic compound is coated with an inorganic oxide may be used.
Among these, inorganic particles are preferable, and alumina particles and boehmite particles are particularly preferable.

The average particle diameter of the insulating fine particles is not particularly limited as long as it is smaller than the thickness of the adhesive layer, and is, for example, 0.001 to 1 μm, preferably 0.05 to 0.8 μm, more preferably 0.1 to 0.6 μm. is there.
The average particle diameter means the particle diameter (D50) at a volume integration of 50% in the particle size distribution of the insulating fine particles obtained by the laser diffraction / scattering method.
Further, the insulating fine particles may be used alone as an average particle diameter within the above range, or may be used by mixing two kinds of insulating fine particles having different average particle diameters.

When the urea resin is not contained in the adhesive layer, the content of the insulating fine particles contained in the adhesive layer is preferably 45 to 70% by volume, and 52 to 68% by volume based on the total amount of the adhesive layer. More preferably, the content is 55 to 65% by volume.
Further, when the urea resin is contained in the adhesive layer, the content of the insulating fine particles contained in the adhesive layer is preferably 20 to 65% by volume, and preferably 20 to 60% by volume based on the total amount of the adhesive layer. More preferably, it is more preferably 25 to 35% by volume.

The thickness of the adhesive layer is not particularly limited, but is preferably 1 to 10 μm. By setting the thickness of the insulating layer to 10 μm or less, quick chargeability is improved. Moreover, the adhesiveness of an electrode and a separator improves by setting it as 1 micrometer or more. From the viewpoint of quick chargeability and adhesiveness, the thickness of the adhesive layer is more preferably 1.5 to 8.5 μm, and further preferably 3 to 7 μm.

(Negative electrode)
The negative electrode in the lithium ion secondary battery of the present invention has a negative electrode active material layer, preferably a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector. The negative electrode active material layer typically includes a negative electrode active material and a negative electrode binder. The density of the negative electrode active material layer is 1.50 to 1.70 g / cc. When the density of the negative electrode active material layer is less than 1.50 g / cc, the energy density of the lithium ion secondary battery is lowered. When the density of the negative electrode active material layer exceeds 1.70 g / cc, the quick chargeability deteriorates. The density of the negative electrode active material layer is preferably 1.53 to 1.60 g / cc from the viewpoint of improving both energy density and rapid chargeability.

The method for adjusting the density of the negative electrode active material layer is not particularly limited, and can be adjusted, for example, by adjusting the type, blending amount, average particle size, and the like of the negative electrode active material. Further, the negative electrode having the negative electrode current collector on which the negative electrode active material layer is formed is sandwiched between two flat jigs, and the entire surface of the negative electrode active material layer is uniformly pressed in the thickness direction. it can. For example, the density of the negative electrode active material layer can be adjusted by a method of pressing the negative electrode with a roll press or the like.

The density of the negative electrode active material layer can be measured as follows. First, a plurality of measurement samples are prepared by punching out the negative electrode with a predetermined size (for example, a diameter of 16 mm). The mass of each measurement sample is weighed with a precision balance, and the mass is measured. By subtracting the mass of the negative electrode current collector measured in advance from the measurement result, the mass of the negative electrode active material layer in the measurement sample can be calculated. Further, the thickness of the negative electrode active material layer is measured by a known method such as observing a cross-section processed measurement sample with an SEM. Based on the following formula (1), the density of the negative electrode active material layer can be calculated from the average value of each measured value.
Density of negative electrode active material layer (g / cc) = mass of negative electrode active material layer (g) / [(thickness of negative electrode active material layer (cm) × punched negative electrode area (cm ² )) (1)

Examples of the negative electrode active material used in the negative electrode active material layer include carbon materials such as graphite and hard carbon, composites of tin compounds and silicon and carbon, lithium, and the like. Among these, carbon materials are preferable, and graphite is preferable. More preferred.
The negative electrode active material is not particularly limited, but the average particle diameter is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. The average particle diameter of the negative electrode active material means a particle diameter (D50) at a volume integration of 50% in the particle size distribution of the negative electrode active material obtained by a laser diffraction / scattering method.
The content of the negative electrode active material in the negative electrode active material layer is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the negative electrode active material layer.

The negative electrode active material layer may contain a conductive additive. As the conductive auxiliary agent, a material having higher conductivity than the negative electrode active material is used, and specific examples include carbon materials such as ketjen black, acetylene black, carbon nanotube, and rod-like carbon.
When the negative electrode active material layer contains a conductive additive, the conductive auxiliary agent content is preferably 1 to 30% by mass, preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferable.

The negative electrode active material layer is preferably configured by binding a negative electrode active material, or a negative electrode active material and a conductive auxiliary agent with a negative electrode binder. Specific examples of the negative electrode binder include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA). ), Acrylic resin such as polymethyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) , Polyacrylonitrile (PAN), acrylonitrile butadiene rubber, styrene butadiene rubber, poly (meth) acrylic acid, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. These binders may be used individually by 1 type, and 2 or more types may be used together. In addition, carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.
The content of the negative electrode binder in the negative electrode active material layer is preferably 1.5 to 40% by mass, more preferably 2.0 to 25% by mass, based on the total amount of the negative electrode active material layer.
The thickness of the negative electrode active material layer is not particularly limited, but is preferably 10 to 200 μm, and more preferably 50 to 150 μm.

Examples of the material constituting the negative electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum or copper is preferable, and copper is more preferable. The negative electrode current collector is generally made of a metal foil, and the thickness thereof is not particularly limited, but is preferably 1 to 50 μm.

(Positive electrode)
The positive electrode in the lithium ion secondary battery of the present invention has a positive electrode active material layer, and preferably has a positive electrode current collector and a positive electrode active material layer laminated on the positive electrode current collector. The positive electrode active material layer typically includes a positive electrode active material and a positive electrode binder.
Examples of the positive electrode active material include a metal acid lithium compound. Examples of the metal acid lithium compound include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ). Alternatively, olivine type lithium iron phosphate (LiFePO ₄ ) may be used. Further, a metal using a plurality of metals other than lithium may be used, and an NCM (nickel cobalt manganese) -based oxide, an NCA (nickel cobalt aluminum-based) oxide or the like called a ternary system may be used.

The average particle size of the positive electrode active material is not particularly limited, but is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. In addition, the average particle diameter of a positive electrode active material means the particle size (D50) by 50% of volume integration in the particle size distribution of the positive electrode active material calculated | required by the laser diffraction / scattering method. The content of the positive electrode active material in the positive electrode active material layer is preferably 50 to 99% by mass, more preferably 60 to 95% by mass, based on the total amount of the positive electrode active material layer.
The positive electrode active material layer may contain a conductive additive. As the conductive auxiliary agent, a material having higher conductivity than the positive electrode active material is used, and specific examples thereof include carbon materials such as ketjen black, acetylene black, carbon nanotube, and rod-like carbon.
In the case where the positive electrode active material layer contains a conductive additive, the conductive auxiliary agent content is preferably 0.5 to 30% by mass, based on the total amount of the positive electrode active material layer, and is 1 to 25% by mass. More preferred is 1.5 to 10% by mass.
Although it does not restrict | limit especially as a binder for positive electrodes, The thing similar to what was demonstrated as a binder for negative electrodes can be used.
The material for the positive electrode current collector is the same as the compound used for the negative electrode current collector, but preferably aluminum or copper, more preferably aluminum. The positive electrode current collector is generally made of a metal foil, and the thickness thereof is not particularly limited, but is preferably 1 to 50 μm.

(Separator)
The lithium ion secondary battery of this invention is equipped with the separator arrange | positioned between a negative electrode and a positive electrode. The short circuit between the positive electrode and the negative electrode is effectively prevented by the separator. The separator may hold an electrolyte described later.
Examples of the separator include a porous polymer film, a nonwoven fabric, and glass fiber. Among these, a porous polymer film is preferable. Examples of the porous polymer film include olefin-based porous films such as ethylene-based porous films.

(Electrolytes)
The lithium ion secondary battery of the present invention includes an electrolyte. The electrolyte is not particularly limited, and a known electrolyte used in a lithium ion secondary battery may be used. As the electrolyte, for example, an electrolytic solution is used.
Examples of the electrolytic solution include an electrolytic solution containing an organic solvent and an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, and tetrohydra. Examples thereof include polar solvents such as furan, 2-methyltetrahydrofuran, dioxolane, and methyl acetate, or a mixture of two or more of these solvents. Examples of the electrolyte salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ CO ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ). ₂ and lithium-containing salts such as LiN (COCF ₂ CF ₃ ) ₂ , lithium bisoxalate borate (LiB (C ₂ O ₄ ) _{2. In} addition, organic acid lithium salt-boron trifluoride complex, LiBH _And a complex such as a complex hydride such as _4. These salts or complexes may be used alone or in a mixture of two or more.
The electrolyte may be a gel electrolyte that further includes a polymer compound in the electrolyte solution. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacrylic polymer such as poly (meth) methyl acrylate. The gel electrolyte may be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode. For example, the electrolyte solution is filled in a battery cell in which the negative electrode, the positive electrode, and the separator described above are housed. In addition, for example, the electrolyte may be applied on the negative electrode or the positive electrode and disposed between the negative electrode and the positive electrode.

The lithium ion secondary battery may have a multilayer structure in which a plurality of negative electrodes and positive electrodes are stacked. In this case, the negative electrode and the positive electrode may be provided alternately along the stacking direction. The separator may be disposed between each negative electrode and each positive electrode, and the adhesive layer may be provided at least at one place between the negative electrode and the separator and between the positive electrode and the separator. It is preferable to provide an adhesive layer.

<Method for producing lithium ion secondary battery>
Although the manufacturing method of the lithium ion secondary battery of this invention is not specifically limited, It is preferable to prepare a negative electrode, a positive electrode, and a separator, and to include the process (1) and process (2) mentioned later.

(Manufacture of negative electrode)
The negative electrode can be obtained by applying the composition for negative electrode active material layer to one or both surfaces of the negative electrode current collector and drying it. The applied negative electrode active material layer composition is dried to form a negative electrode active material layer. The composition for negative electrode active material layers is a slurry containing at least one solvent selected from a negative electrode active material, a negative electrode binder, an organic solvent, and water.
The negative electrode active material layer may be formed by applying the composition for negative electrode active material layer onto a substrate other than the negative electrode current collector and drying it. As a base material other than the negative electrode current collector, a known release sheet may be mentioned. The negative electrode active material layer formed on the substrate may be peeled off from the substrate and transferred onto the negative electrode current collector.
The negative electrode active material layer formed on the negative electrode current collector or the substrate is preferably pressure-pressed. It is possible to adjust the density of the negative electrode active material by pressing with pressure.
(Manufacture of positive electrode)
The positive electrode can be produced by the same method as the production of the negative electrode described above. That is, in manufacturing the negative electrode, the negative electrode can be read as the positive electrode.

The method for producing a lithium ion secondary battery of the present invention preferably includes the following steps (1) and (2).
Step (1) is a step of forming an adhesive layer on one surface selected from the separator and the electrode. Step (2) is a step in which the other selected from the separator and the electrode is bonded to the adhesive layer formed in step (1) by hot pressing to obtain a laminate. Here, an electrode means either a positive electrode or a negative electrode.
Among them, the step (1) is preferably a step of forming an adhesive layer on the surface of the negative electrode, and the step (2) is a step of bonding the separator and the adhesive layer formed in the step (1) by hot pressing. It is preferable that it is the process of making it.

(Process (1))
Step (1) is a step of forming an adhesive layer on one surface selected from the separator and the electrode. An adhesive layer may be formed on one or both surfaces of the separator to form a separator structure for a lithium ion secondary battery including the separator and the adhesive layer. In addition, a positive electrode structure for a lithium ion secondary battery having a positive electrode and an adhesive layer formed by forming an adhesive layer on the surface of the electrode, specifically on the surface of the negative electrode active material layer or the positive electrode active material layer, or the negative electrode It is good also as a negative electrode structure for lithium ion secondary batteries provided with a contact bonding layer.
Among them, when assembling a lithium ion secondary battery, it is possible to obtain an electrode structure for a lithium ion secondary battery including an electrode and an adhesive layer from the viewpoint of preventing problems such as floating of the separator and improving workability. Preferably, it is more preferable to obtain a negative electrode structure for a lithium ion secondary battery comprising a negative electrode having a negative electrode active material layer and an adhesive layer.
The adhesive layer is formed using the adhesive layer composition. The adhesive layer composition includes at least one resin selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin, and, if necessary, a urea resin, other resins, insulating fine particles, a solvent, etc. It is a slurry-like composition containing this. The adhesive layer can be formed by applying the composition for the adhesive layer on the surface of the separator, the negative electrode active material layer, or the positive electrode active material layer and drying it.
The method for applying the adhesive layer composition is not particularly limited, and examples thereof include a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, and a screen printing method. Among these, the bar coating method or the gravure coating method is preferable from the viewpoint of uniformly applying the adhesive composition and improving the adhesion between the electrode and the separator.
The drying temperature is not particularly limited, but is, for example, 40 to 120 ° C., preferably 50 to 90 ° C. Further, the drying time is not particularly limited, but is, for example, 1 to 10 minutes.

(Process (2))
Step (2) is a step in which the other selected from the separator and the electrode is bonded to the adhesive layer formed in step (1) by hot pressing to obtain a laminate. In the step (2), when an adhesive layer is formed on the separator in the step (1), the adhesive layer on the separator and the electrode are bonded by hot pressing, and the step (1) is applied on the electrode. When the adhesive layer is formed, the adhesive layer on the electrode and the separator are bonded by hot pressing. By the step (2), the electrode and the separator are adhered by the adhesive layer, and the adhesion failure of the separator is effectively prevented.
In addition, when manufacturing a lithium-ion secondary battery having a multilayer structure in which a plurality of negative electrodes and positive electrodes are laminated, a plurality of structures obtained in the step (1) are prepared and overlapped with a plurality of other members. What is necessary is just to heat press. For example, when a negative electrode structure for a lithium ion secondary battery is obtained by the step (1), a plurality of negative electrode structures for a lithium ion secondary battery, a plurality of separators, and a plurality of positive electrodes are prepared. And superposition so as to be disposed between the positive electrode and the positive electrode, followed by hot pressing.
The temperature of the hot press is preferably 60 to 120 ° C, more preferably 70 to 100 ° C. The pressure at the time of hot pressing is preferably 0.2 to 2 MPa, more preferably 0.2 to 1 MPa, and further preferably 0.3 to 0.7 MPa. By hot pressing under such conditions, the adhesion between the electrode and the separator can be improved.
After the step (2), if necessary, the positive electrode, the negative electrode, or the separator is laminated on the laminate obtained in the step (2) and hot-pressed again. A lithium ion secondary battery may be obtained.
The lithium ion secondary battery produced through the steps (1) and (2) is usually used in a battery cell. The battery cell may be any of a square shape, a cylindrical shape, a lamination method and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The obtained lithium ion secondary battery was evaluated by the following evaluation methods.
(Adhesive strength)
A separator (polyethylene porous film) was placed on the adhesive layer side of the electrode having the adhesive layer produced in the examples and comparative examples, and 1 using a flat plate hot press machine at 80 ° C. and 0.6 MPa. The laminate was obtained by pressing for a minute.
A double-sided tape was affixed to a SUS plate, and a laminate cut out to 2 cm × 5 cm was stuck on the SUS plate so that the electrode and the double-sided tape overlapped.
Pull the separator 2cm at a speed of 50mm / min in the direction of peeling horizontally in the long side direction of the laminate with a digital force gauge ((ZTS-5N), manufacturer: IMADA Co., Ltd.), and the average force Was the adhesive strength. The adhesive strength was classified and evaluated as follows.
A: Adhesive strength is 2 N / m or more B: Adhesive force is 1 N / m or more and less than 2 N / m C: Adhesive strength is 0.5 N / m or more and less than 1 N / m D: Adhesive force is less than 0.5 N / m

(Rapid chargeability)
The lithium ion secondary batteries produced in the examples and comparative examples were charged and discharged under the following conditions.
(1) A constant current charge of 10 mA was performed, and then the current was reduced as soon as 4.2 V was reached, and a constant voltage charge was completed when the charge reached 0.5 mA, and the charge capacity was calculated.
(2) A constant current charge of 250 mA was performed, the current was reduced as soon as 4.2 V was reached, and a constant voltage charge was completed when the charge reached 0.5 mA, and the charge capacity was calculated.
The charge capacity ratio was calculated as follows, and classified and evaluated as follows.
(Charge capacity ratio,%) = 100 × ((1) charge capacity) ÷ ((2) charge capacity)
A: 75% or more B: 60% or more, less than 75% C: 50% or more, less than 60% D: less than 50%

(Energy density)
The lithium ion secondary batteries produced in the examples and comparative examples were charged and discharged under the following conditions, the discharge capacity was calculated, and the energy density was determined by the following formula (1) using the discharge capacity.
A constant current charge of 10 mA was performed, and then the current was decreased as soon as 4.2 V was reached, and the constant voltage charge was completed when the charge reached 0.5 mA. Thereafter, a constant current discharge of 10 mA was performed, and when discharging was performed to 2.5 V, a discharge was completed, and a discharge capacity was calculated.
In addition, the area and thickness of each positive electrode, negative electrode, and separator are as follows.
Positive electrode: 20 cm ² , 100 μm
Negative electrode: 20 cm ² , thickness is as described in Table 1 Separator: 20 cm ² , 15 μm
(Energy density) = (discharge capacity) / (total volume of positive electrode, negative electrode, separator) (1)
The obtained energy density was evaluated according to the following evaluation criteria.
A: 181 mAh / cm ³ or more
B: 177 mAh / cm ³ or more, less than 181 mAh / cm ³ C: 173 mAh / cm ³ or more, less than 177 mAh / cm ³ D: less than 173 mAh / cm ³

[Example 1]
(Preparation of positive electrode)
100 parts by mass of Li (Ni—Co—Al) O ₂ (NCA oxide) having an average particle diameter of 10 μm as a positive electrode active material, 4 parts by mass of acetylene black as a conductive additive, and polyvinylidene fluoride as an electrode binder 4 parts by mass of (PVDF) and N-methylpyrrolidone (NMP) as a solvent were mixed. This obtained the composition for positive electrode active material layers adjusted to solid content concentration 60 mass%. This composition for positive electrode active material layer was applied to both surfaces of a 15 μm thick aluminum foil as a positive electrode current collector, pre-dried and then vacuum dried at 120 ° C. Thereafter, the positive electrode current collector coated with the composition for the positive electrode active material layer on both sides is pressure-pressed at 400 kN / m, punched out to 100 mm × 200 mm square of electrode dimensions, and the positive electrode having the positive electrode active material layer on both sides It was. Among the dimensions, the area where the positive electrode active material was applied was 100 mm × 180 mm.

(Preparation of negative electrode)
100 parts by mass of graphite (average particle diameter 10 μm) as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, 1.5 parts by mass of sodium salt of carboxymethyl cellulose (CMC), and water as a solvent are mixed. Thus, a negative electrode active material layer composition adjusted to a solid content of 50% by mass was obtained. This composition for negative electrode active material layers was applied to both sides of a 15 μm-thick copper foil as a negative electrode current collector, and dried at 100 ° C. under vacuum. Then, the negative electrode collector which apply | coated the composition for negative electrode active material layers on both surfaces was press-pressed by the linear pressure of 500 kN / m, and it was set as the negative electrode. The density of the negative electrode active material layer was 1.55 g / cc. In addition, the dimension of the negative electrode was 110 mm × 210 mm, and the area on which the negative electrode active material layer was applied was 110 mm × 190 mm.

(Preparation of electrolyte)
LiPF ₆ as an electrolyte salt is dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 (EC: DEC) so as to be 1 mol / liter. Prepared.

(Production of electrode having adhesive layer)
Polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) powder while applying moderate shearing force to 60 parts by volume of alumina particles (product name: AHP200, average particle size 0.4 μm) as insulating fine particles Was mixed to obtain a mixture. The above mixture was mixed with NMP so that the solid content concentration was 30% by mass, gently stirred with a stirrer for 30 minutes, and filtered with a filter having an aperture of 80 μm to obtain an adhesive layer composition. The viscosity of the composition was 1800 mPa · s under the conditions of a B-type viscometer, 60 rpm, and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of the negative electrode active material layer with a bar coater. A coating film formed by applying the composition is dried at 60 ° C., thereby forming an adhesive layer on the surface of the negative electrode active material layer, and having the adhesive layer (that is, a negative electrode structure for a lithium ion secondary battery) Got. The thickness of the adhesive layer was measured and found to be 4 μm.

(Manufacture of lithium ion secondary batteries)
Ten negative electrodes having the adhesive layer obtained above, nine positive electrodes, and 18 separators were laminated to obtain a temporary laminate. Here, the negative electrode and the positive electrode were alternately disposed, and a separator was disposed between each negative electrode and the positive electrode. As the separator, a polyethylene porous film was used. Using a flat plate type hot press machine, the temporary laminate was pressed for 1 minute at 80 ° C. and 0.6 MPa to obtain a laminate.
The ends of the exposed portions of the positive electrode current collectors of the positive electrodes were joined together by ultrasonic fusion, and terminal tabs that protruded to the outside were joined. Similarly, the ends of the exposed portions of the negative electrode current collector of each negative electrode were joined together by ultrasonic fusion, and the terminal tabs protruding to the outside were joined.
Next, the laminate was sandwiched between aluminum laminate films, the terminal tabs were projected to the outside, and the three sides were sealed by laminating. A laminate-type cell was manufactured by injecting the electrolytic solution obtained above from one side left without being sealed and vacuum-sealing.

[Example 2]
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that 68 parts by volume of alumina particles and 32 parts by volume of PVDF-HFP powder were used to produce an electrode having an adhesive layer.

[Example 3]
A lithium ion secondary battery was obtained in the same manner as in Example 1, except that 52 parts by volume of alumina particles and 48 parts by volume of PVdF-HFP powder were used for producing an electrode having an adhesive layer.

[Example 4]
The production of the positive electrode, the production of the negative electrode, and the adjustment of the electrolyte solution were performed in the same manner as in Example 1. The production of the electrode having the adhesive layer and the production of the lithium ion secondary battery were performed as follows. Obtained.
(Production of electrode having adhesive layer)
Polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) powder while applying moderate shearing force to 60 parts by volume of alumina particles (product name: AHP200, average particle size 0.4 μm) as insulating fine particles Was mixed to obtain a mixture. The above mixture was mixed with NMP so that the solid content concentration was 30% by mass, gently stirred with a stirrer for 30 minutes, and filtered with a filter having an aperture of 80 μm to obtain an adhesive layer composition. The viscosity of the composition was 1800 mPa · s under the conditions of a B-type viscometer, 60 rpm, and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of the positive electrode active material layer with a bar coater. A coating film formed by applying the composition is dried at 60 ° C., thereby forming an adhesive layer on the surface of the positive electrode active material layer, and having the adhesive layer (that is, a positive electrode structure for a lithium ion secondary battery) Got. The thickness of the adhesive layer was measured and found to be 4 μm.
(Manufacture of lithium ion secondary batteries)
Ten sheets of the negative electrode obtained above, nine positive electrodes having an adhesive layer, and 18 separators were laminated to obtain a temporary laminate. Here, the negative electrode and the positive electrode were alternately disposed, and a separator was disposed between each negative electrode and the positive electrode. As the separator, a polyethylene porous film was used. Using a flat plate type hot press machine, the temporary laminate was pressed for 1 minute at 80 ° C. and 0.6 MPa to obtain a laminate.
The ends of the exposed portions of the positive electrode current collectors of the positive electrodes were joined together by ultrasonic fusion, and terminal tabs that protruded to the outside were joined. Similarly, the ends of the exposed portions of the negative electrode current collector of each negative electrode were joined together by ultrasonic fusion, and the terminal tabs protruding to the outside were joined.
Next, the laminate was sandwiched between aluminum laminate films, the terminal tabs were projected to the outside, and the three sides were sealed by laminating. A laminate-type cell was manufactured by injecting the electrolytic solution obtained above from one side left without being sealed and vacuum-sealing.

[Example 5]
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that the production of the electrode having the adhesive layer was changed as follows.
(Production of electrode having adhesive layer)
Polyvinylidene fluoride hexafluoropropylene (PVDF-HFP) powder while applying moderate shear force to 30 parts by volume of alumina particles (product name: AHP200, average particle size 0.4 μm) as insulating fine particles 40 parts by volume and 30 parts by volume of polymethylurea ("Pergopack M6" manufactured by AlmaVale) were mixed to obtain a mixture. The above mixture was mixed with NMP so that the solid content concentration was 30% by mass, gently stirred with a stirrer for 30 minutes, and filtered with a filter having an aperture of 80 μm to obtain an adhesive layer composition. The viscosity of the composition was 1800 mPa · s under the conditions of a B-type viscometer, 60 rpm, and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of the negative electrode active material layer with a bar coater. A coating film formed by applying the composition is dried at 60 ° C., thereby forming an adhesive layer on the surface of the negative electrode active material layer, and having the adhesive layer (that is, a negative electrode structure for a lithium ion secondary battery) Got. The thickness of the adhesive layer was measured and found to be 4 μm.

[Example 6]
In the production of the negative electrode, a lithium ion secondary battery was obtained in the same manner as in Example 1 except that the pressure of the pressure press was 600 kN / m and the density of the negative electrode active material layer was 1.62 g / cc. .

[Comparative Example 1]
In the production of the negative electrode, a lithium ion secondary battery was obtained in the same manner as in Example 1, except that the pressure of the pressure press was 200 kN / m and the density of the negative electrode active material layer was 1.4 g / cc. .

[Comparative Example 2]
In the production of the negative electrode, a lithium ion secondary battery was obtained in the same manner as in Example 1, except that the pressure of the pressure press was 800 kN / m and the density of the negative electrode active material layer was 1.72 g / cc. .

[Comparative Example 3]
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that 80 parts by volume of alumina particles and 20 parts by volume of PVDF-HFP were used for producing an electrode having an adhesive layer.

[Comparative Example 4]
A lithium ion secondary battery was obtained in the same manner as in Example 1 except that 40 parts by volume of alumina particles and 60 parts by volume of PVDF-HFP were used for producing an electrode having an adhesive layer.

As shown in Examples 1 to 6 above, the lithium ion secondary battery containing 30 to 55% by volume of a specific resin and having a negative electrode active material layer density of 1.55 to 1.70 g / cm ³ is: Adhesive strength, quick chargeability, and energy density were all good. On the other hand, when the content of the specific resin is out of the range of 30 to 55% by volume or the density of the negative electrode active material is out of the range of 1.55 to 1.70 g / cm ³ , the adhesive strength, rapid chargeability, and The result was inferior in the physical property balance of energy density.

DESCRIPTION OF SYMBOLS 10 Lithium ion secondary battery 11 Negative electrode 11a Negative electrode collector 11b Negative electrode active material layer 12 Positive electrode 12a Positive electrode collector 12b Positive electrode active material layer 13 Separator 14 Adhesive layer

Claims (10)

A negative electrode having a negative electrode active material layer;
A positive electrode;
A separator disposed between the negative electrode and the positive electrode;
An electrode disposed between at least one of the negative electrode and the positive electrode and a separator, and an adhesive layer for bonding the separator and the electrode;
The adhesive layer contains 30 to 55% by volume of at least one resin selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin;
A lithium ion secondary battery in which the density of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ . The lithium ion secondary battery according to claim 1, wherein the adhesive layer is disposed between the negative electrode and the separator. The lithium ion secondary battery according to claim 1 or 2, wherein the adhesive layer contains a urea resin. The lithium ion secondary battery according to any one of claims 1 to 3, wherein the adhesive layer is an insulating layer containing insulating fine particles. The lithium ion secondary battery according to any one of claims 1 to 4, wherein the adhesive layer contains 30 to 55% by volume of a polyvinylidene fluoride-hexafluoropropylene copolymer. 6. The lithium ion secondary battery according to claim 1, wherein the adhesive layer has a thickness of 1 to 10 μm. A negative electrode having a negative electrode active material layer, and an adhesive layer, wherein the adhesive layer contains 30 to 55% by volume of at least one resin selected from a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin,
A negative electrode structure for a lithium ion secondary battery, wherein the density of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ . Forming the adhesive layer on one surface selected from the separator and the electrode;
The method for producing a lithium ion secondary battery according to any one of claims 1 to 6, further comprising a step of bonding the other selected from the separator and the electrode and the adhesive layer by hot pressing. Forming an adhesive layer on the negative electrode active material layer of the negative electrode;
The manufacturing method of the lithium ion secondary battery of Claim 8 provided with the process of adhere | attaching the said separator and the said contact bonding layer by hot press. 10. The method for producing a lithium ion secondary battery according to claim 8, wherein the temperature of the hot press is 60 to 120 ° C. and the pressure is 0.2 to 2.0 MPa.

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