TW201939803A - 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 manufacturing 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 manufacturing a lithium ion secondary battery.

Lithium-ion secondary batteries are used as power sources for large-scale stationary power storage, electric vehicles, and the like. In recent years, research into miniaturization and thinning of batteries is being developed. Lithium-ion secondary batteries generally include two electrodes (a positive electrode and a negative electrode) in which an electrode active material layer is formed on a surface of a metal foil, and a separator disposed between the two electrodes. The spacer plays a role of preventing a short circuit between the two electrodes or maintaining an electrolyte.
Lithium-ion secondary batteries are manufactured by preparing the positive and negative electrodes as the constituent members, the spacers and the like provided therebetween, and hot-pressing them, but there are cases where the spacers are shifted from their fixed positions. In some cases, manufacturing abnormalities such as partial floating of the electrode may occur.
From such a viewpoint, a technique is known in which an adhesive layer is provided between each electrode and the spacer to improve the adhesion between each electrode and the spacer, and to prevent the above manufacturing abnormality.
For example, Patent Document 1 discloses a technology for producing a lithium ion secondary battery by providing an electrode adhesive layer on a spacer made of a porous polymer substrate.
Prior art literature patent literature

Patent Document 1: Japanese Patent Publication No. 2016-522553

[Problems to be Solved by the Invention]

However, in the case of using an adhesive layer, although the adhesion between the electrode and the spacer is improved, it is possible to prevent abnormalities related to poor adhesion such as the floating of the spacer when manufacturing a lithium ion secondary battery, but there are lithium ion secondary The tendency of the battery to deteriorate quickly.
Therefore, an object of the present invention is to provide a lithium ion secondary battery that has good adhesion and fast chargeability between an electrode and a separator, and high energy density.
[Technical means to solve the problem]

The present inventors conducted painstaking research, and found that, by setting at least any one electrode and a separator disposed between the negative electrode and the positive electrode so that the separator and the electrode are bonded to each other, and setting the density of the negative electrode active material layer The above-mentioned problems can be solved for a specific range, and the following inventions have been completed. The gist of the present invention is the following [1] to [10].
[1] A lithium ion secondary battery including: 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 an adhesive layer disposed at least between the negative electrode and the positive electrode The spacer and the electrode are bonded between any one of the electrodes and the spacer; the bonding layer contains at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer and acrylic resin 30 to 55 The volume percentage of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ .
[2] The lithium ion secondary battery according to the above [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 the above [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 the above [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 the above [1] to [5], wherein a thickness of the adhesive layer is 1 to 10 μm.
[7] 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, wherein the adhesive layer is selected from a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin. The density of the at least one resin is 30 to 55% by volume, and the density of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ .
[8] A method for manufacturing a lithium ion secondary battery according to any one of the above [1] to [6], comprising the steps of forming on a surface selected from one of the spacer and the electrode The step of bonding the layer, and the step of bonding the other selected from the spacer and the electrode to the bonding layer by hot pressing.
[9] The method for manufacturing a lithium ion secondary battery according to the above [8], comprising the steps of: forming a bonding layer on the negative electrode active material layer of the negative electrode; and hot-pressing the separator with the separator. The above-mentioned adjoining steps are followed by steps.
[10] The method for manufacturing a lithium ion secondary battery according to the above [8] or [9], wherein the temperature of the hot pressing is 60 to 120 ° C and the pressure is 0.2 to 2.0 MPa.
[Effect of the invention]

According to the present invention, it is possible to provide a lithium ion secondary battery having good adhesion and fast chargeability between an electrode and a separator, and high energy density.

＜ 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 a lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 includes a negative electrode 11, a positive electrode 12, a spacer 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. The positive electrode 12 also includes a positive electrode current collector 12a and a positive electrode laminated on the positive electrode current collector 12a. Active material layer 12b. An adhesive layer 14 is provided between the negative electrode active material layer 11 b and the separator 13 so as to be in contact with both, and the two are adhered. In FIG. 1, the adhesion 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 next layer 14 may be provided between the negative electrode active material layer 11 b and the separator 13 and between the positive electrode active material layer 12 b and the separator 13, but it is preferably provided on one of them. With this bonding layer, the adhesion between the electrode and the separator is improved, and abnormalities such as floating of the separator can be prevented when the lithium ion secondary battery is assembled.

[Next layer]
The adhesive layer used in the lithium ion secondary battery of the present invention is arranged between at least any one of the negative electrode and the positive electrode and the separator, so that the separator is connected to the electrode.
From the viewpoint of improving the adhesion between the electrode and the separator, the adhesive layer is preferably disposed between the negative electrode and the separator. The reason is that the surface area of the negative electrode active material layer that normally constitutes the negative electrode is larger than that of the positive electrode active material layer, and the area that the negative electrode can form an adhesive layer is larger.
The next layer contains at least one resin (hereinafter also referred to as a specific resin) selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and acrylic resin based on the total amount of the adhesive layer. 30 ~ 55% by volume. As the specific resin, a polyvinylidene fluoride-hexafluoropropylene copolymer is preferably used from the viewpoint of further improving the adhesion between the electrode and the separator.
If the content of the specific resin is less than 30% by volume, the adhesion between the electrode and the separator is reduced. If the content of the specific resin exceeds 55% by volume, the rapid chargeability of the lithium ion secondary battery is deteriorated. From the viewpoint of improving the adhesion between the electrode and the spacer and improving the fast chargeability, the content of the specific resin in the adhesive layer is preferably 32 to 48% by volume, and more preferably 35 to 45% by volume.

Examples of the acrylic resin include a homopolymer of a (meth) acrylate monomer, a copolymer of two or more kinds of (meth) acrylate monomers, a (meth) acrylate monomer, and a copolymer with which Copolymers of other vinyl monomers, etc. In addition, in this specification, (meth) acrylic acid means the general term of acrylic acid and methacrylic acid.
Examples of the (meth) acrylate monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and (methyl) N-butyl acrylate, isobutyl (meth) acrylate, tertiary butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, (meth) Phenyl acrylate, isoamyl (meth) acrylate, cyclohexyl (meth) acrylate, tertiary butyl cyclohexyl (meth) acrylate, dicyclopentadiene (meth) acrylate, and (formyl) Group) dihydrodicyclopentadiene acrylate and the like.
Examples of other vinyl monomers that can be copolymerized with the (meth) acrylate monomer include acrylic acid, methacrylic acid, styrene, methylstyrene, vinyl acetate, acrylonitrile, itaconic acid, and malay. Acid etc.
Among the acrylic resins, polymethyl acrylate, polymethyl methacrylate, and the like can be suitably used.

From the viewpoint of improving the adhesion between the electrode and the separator, the adhesive layer preferably contains a urea resin. Urea resin is a synthetic resin obtained by reacting urea with formaldehyde. The content of the urea resin in the adhesive layer is preferably 5 to 70% by volume, more preferably 10 to 65% by volume, and even more preferably 25 to 35% by volume based on the total amount of the adhesive layer. Compared with the above-mentioned specific resin, the urea resin has a lower degree of lowering the fast chargeability even if the content is increased. Therefore, the urea resin can be relatively increased in content to improve adhesion and maintain fast chargeability. When a urea resin is used, the total amount of the urea resin in the adhesive layer and the following insulating fine particles is based on the total amount of the adhesive layer, preferably 70% by volume or less, and more preferably 65% by volume or less.

The adhesive layer may contain other resins other than the above-mentioned specific resin and urea resin so long as the effect of the present invention is not hindered. Examples of other resins include fluorine-containing resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyimide (PA), and polyvinyl chloride. Ethylene (PVC), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber, poly (methyl) ) Acrylic acid, carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. These may be used individually by 1 type, and may use 2 or more types together. In addition, carboxymethyl cellulose and the like can be used in the form of a salt such as a sodium salt.
The content of other resins in the subsequent layer is preferably 10% by volume or less, more preferably 5% by volume or less, and even more preferably 0% by volume.

The adhesive layer is preferably an insulating layer further containing insulating fine particles. By containing insulating fine particles, the adhesive layer can also function as an insulating layer, which can 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 examples of the organic particles include polymethyl methacrylate, styrene-acrylic copolymer, acrylonitrile resin, polyimide resin, polyimide resin, and poly (2-acrylamidamine-2-methyl). Lithium propane sulfonate), polyacetal resin, epoxy resin, polyester resin, phenol resin, melamine resin and other organic compounds. Examples of the inorganic particles include silicon dioxide, silicon nitride, aluminum oxide, boehmite, titanium oxide, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide ( Nb ₂ O ₅ ) , and tantalum oxide. ( Ta ₂ O ₅ ) , potassium fluoride, lithium fluoride, clay, zeolite, calcium carbonate and other inorganic compounds. The inorganic particles may be particles composed of a known composite oxide such as a niobium-tantalum composite oxide or a magnesium-tantalum composite oxide.
The insulating fine particles may be particles in which one kind of each of the above materials is used alone, or two or more kinds of particles may be used in combination. The insulating fine particles may be fine particles containing both inorganic compounds and organic compounds. For example, it may be an inorganic-organic composite particle obtained by coating an inorganic oxide on the surface of a particle composed of an organic compound.
Among these, inorganic particles are preferred, and among them, alumina particles and boehmite particles are preferred.

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, and more preferably 0.1 to 0.6 μm.
The average particle size means the particle size distribution (D50) when the volume of the insulating fine particles obtained by the laser diffraction-scattering method is 50% by volume.
In addition, as the insulating fine particles, one type of insulating fine particles having an average particle diameter in the above range may be used alone, or two types of insulating fine particles having different average particle diameters may be used in combination.

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

The thickness of the adhesion 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, the fast chargeability is improved. Moreover, by making it 1 micrometer or more, the adhesiveness of an electrode and a spacer improves. From the viewpoints of such fast 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. Typically, the negative electrode active material layer contains 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. If 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 becomes low. When the density of the negative electrode active material layer exceeds 1.70 g / cc, the fast chargeability is deteriorated. From the viewpoint of making both energy density and fast chargeability good, the density of the negative electrode active material layer is preferably 1.53 to 1.60 g / cc.

The method of adjusting the density of the negative electrode active material layer is not particularly limited, and it can be adjusted by, for example, adjusting the type, blending amount, average particle size, and the like of the negative electrode active material. Alternatively, a negative electrode having a negative electrode current collector having a negative electrode active material layer formed therebetween may be used to sandwich the negative electrode active material layer between two flat jigs and press the entire surface of the negative electrode active material layer uniformly in the thickness direction. Method to adjust. For example, the density of the negative electrode active material layer can be adjusted by a method of pressing the negative electrode with a roller press or the like.

The density of the negative electrode active material layer can be measured in the following manner. First, prepare a plurality of measurement samples obtained by punching a negative electrode with a specific size (for example, a diameter of 16 mm). The weight of each measurement sample is measured with a precision balance to determine the quality. The mass of the negative electrode current collector previously measured is subtracted from the measurement result, thereby calculating the mass of the negative electrode active material layer in the measurement sample. In addition, the thickness of the negative electrode active material layer is measured by a known method such as observing a measurement sample obtained by cross-section processing with an SEM. Based on the average value of each measured value, the density of the negative electrode active material layer can be calculated based on the following formula (1).
Density of the negative electrode active material layer (g / cc) = mass of the negative electrode active material layer (g) / [(thickness of the negative electrode active material layer (cm) × the area of the negative electrode punched (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, a complex of a tin compound and silicon and carbon, and lithium. Among these, a carbon material is preferred, and more preferably graphite.
The negative electrode active material is not particularly limited, and its average particle diameter is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. In addition, the average particle diameter of the negative electrode active material means a particle diameter (D50) when the volume of the negative electrode active material obtained by the laser diffraction scattering method is 50% by volume.
The content of the negative electrode active material in the negative electrode active material layer is based on the total amount of the negative electrode active material layer, preferably 50 to 98.5% by mass, and more preferably 60 to 98% by mass.

The negative electrode active material layer may contain a conductive auxiliary agent. As the conductive auxiliary agent, a material having higher conductivity than the above-mentioned negative electrode active material is used. Specific examples include carbon materials such as Ketjenblack, acetylene black, carbon nanotubes, and rod-shaped carbon.
When the negative electrode active material layer contains a conductive auxiliary agent, the content of the conductive auxiliary agent is based on the total amount of the negative electrode active material layer, preferably 1 to 30% by mass, and more preferably 2 to 25% by mass.

The negative electrode active material layer is preferably constituted by a negative electrode active material, or a negative electrode active material and a conductive auxiliary agent bonded together with a negative electrode binder. Specific examples of the binder for the negative electrode include fluorine-containing resins such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polytetrafluoroethylene (PTFE), Acrylic resins such as polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl acetate, polyimide (PI), polyimide (PA), polyvinyl chloride (PVC), polyether Nitrile (PEN), polyethylene (PE), polypropylene (PP), polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber, poly (meth) acrylic acid, carboxymethyl fiber Cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. These adhesives may be used individually by 1 type, and may use 2 or more types together. In addition, carboxymethyl cellulose and the like can be used in the form of a salt such as a sodium salt.
The content of the binder for the negative electrode in the negative electrode active material layer is based on the total amount of the negative electrode active material layer, preferably 1.5 to 40% by mass, and more preferably 2.0 to 25% by mass.
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 preferred, and copper is more preferred. The negative electrode current collector is usually made of a metal foil, and its thickness 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, preferably a positive electrode current collector and a positive electrode active material layer laminated on the positive electrode current collector. Typically, the positive electrode active material layer contains a positive electrode active material and a binder for a positive electrode.
Examples of the positive electrode active material include a lithium metal acid compound. Examples of the lithium metal acid compound include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ). It may also be olivine-type lithium iron phosphate (LiFePO ₄ ). Furthermore, a variety of metals other than lithium may be used, and NCM (nickel-cobalt-manganese) -based oxides, NCA (nickel-cobalt-aluminum-based) -based oxides, which are called ternary systems, may also be used.

The average particle diameter 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 the positive electrode active material means a particle diameter (D50) when the volume of the positive electrode active material obtained by the laser diffraction-scattering method is 50% by volume. The content of the positive electrode active material in the positive electrode active material layer is based on the total amount of the positive electrode active material layer, preferably 50 to 99% by mass, and more preferably 60 to 95% by mass.
The positive electrode active material layer may contain a conductive auxiliary agent. As the conductive auxiliary agent, a material having higher conductivity than the above-mentioned positive electrode active material is used. Specific examples include carbon materials such as Ketjen Black, acetylene black, carbon nanotubes, and rod-shaped carbon.
When the positive electrode active material layer contains a conductive additive, the content of the conductive additive is based on the total amount of the positive electrode active material layer, preferably 0.5 to 30% by mass, more preferably 1 to 25% by mass, and even more preferably It is 1.5 to 10% by mass.
It does not specifically limit as a binder for positive electrodes, The thing similar to the binder demonstrated as the binder for negative electrodes can be used.
The material used as the positive electrode current collector is the same as the compound used in the negative electrode current collector described above, and aluminum or copper is preferably used, and aluminum is more preferably used. The positive electrode current collector is usually made of a metal foil, and its thickness is not particularly limited, but is preferably 1 to 50 μm.

(Spacer)
The lithium ion secondary battery of the present invention includes a spacer disposed between the negative electrode and the positive electrode. The separator effectively prevents a short circuit between the positive electrode and the negative electrode. In addition, the separator may hold the electrolyte described below.
Examples of the spacer include a porous polymer film, a nonwoven fabric, and glass fiber. Among these, a porous polymer film is preferred. Examples of the porous polymer film include an olefin-based porous film such as an ethylene-based porous film.

(Electrolyte)
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 organic solvent and an electrolytic solution containing an electrolyte salt. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, cyclobutylammonium, dimethylmethylene, acetonitrile, dimethylformamide, and dimethylformamide. Polar solvents such as ethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, methyl acetate, or two A mixture 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 , and LiN (COCF ₃ ) ₂ and lithium-containing salts such as LiN (COCF ₂ CF ₃ ) ₂ and lithium bisoxalate borate (LiB (C ₂ O ₄ ) ₂ ). In addition, examples include complexes such as lithium organic acid salts-boron trifluoride complexes, and complex hydrides such as LiBH ₄ . These salts or complexes may be used alone or as a mixture of two or more.
The electrolyte may be a gel electrolyte containing a polymer compound in the electrolyte. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride, and a polyacrylic polymer such as poly (meth) acrylate. Moreover, a gel-like electrolyte can also be used as a separator.
The electrolyte may be disposed between the negative electrode and the positive electrode. For example, the electrolyte liquid is filled in a battery cell in which the negative electrode, the positive electrode, and the separator are housed. The electrolyte may be applied to, for example, the negative electrode or the positive electrode, and may be disposed between the negative electrode and the positive electrode.

The lithium ion secondary battery may have a multilayer structure in which a negative electrode and a positive electrode are laminated in multiple layers. In this case, the negative electrodes and the positive electrodes may be alternately disposed along the stacking direction. In addition, the separator only needs to be arranged between each negative electrode and each positive electrode, and the bonding layer may be provided at least one place between the negative electrode and the separator, and between the positive electrode and the separator, and it is more preferable to be disposed between multiple negative electrodes. Adhesive layers are provided between the spacers.

＜ Manufacturing method of lithium ion secondary battery ＞
The manufacturing method of the lithium ion secondary battery of the present invention is not particularly limited, and it is preferable to prepare a negative electrode, a positive electrode, and a separator, and include the following steps (1) and (2).

(Manufacturing of negative electrode)
The negative electrode can be obtained by applying a composition for a negative electrode active material layer on one surface or both surfaces of a negative electrode current collector and drying the composition. The coated negative electrode active material layer composition is dried to form a negative electrode active material layer. The composition for a negative electrode active material layer is a slurry state containing a negative electrode active material, a negative electrode binder, and at least one solvent selected from an organic solvent and water.
The negative electrode active material layer may be formed by applying the composition for a negative electrode active material layer to a substrate other than the negative electrode current collector and drying it. Examples of the base material other than the negative electrode current collector include well-known release sheets. The negative electrode active material layer formed on the substrate may be peeled from the substrate and transferred to the negative electrode current collector.
The negative electrode active material layer formed on the negative electrode current collector or the substrate is preferably pressurized. By performing pressurization, the density of the negative electrode active material can be adjusted.
(Manufacturing of positive electrode)
The positive electrode can be manufactured by the same method as the above-mentioned manufacturing of the negative electrode. That is, in the production of the above-mentioned negative electrode, the negative electrode may be replaced with a positive electrode.

The manufacturing method of the 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 a surface selected from one of a spacer and an electrode. Step (2) is a step of obtaining another laminated body by bonding the other one selected from the spacer and the electrode to the adhesive layer formed in step (1) by hot pressing. Here, the electrode means any one of a positive electrode and a negative electrode.
Among them, step (1) is preferably a step of forming an adhesive layer on the surface of the negative electrode, and step (2) is preferably a step of attaching the spacer to the adhesive layer formed in step (1) by hot pressing.

(step 1))
Step (1) is a step of forming an adhesive layer on a surface selected from one of a spacer and an electrode. The adhesive layer may be formed on one surface 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, an adhesive layer can be formed on the surface of the electrode, specifically, on the surface of the negative electrode active material layer or the positive electrode active material layer, to form a positive electrode structure for a lithium ion secondary battery including the positive electrode and the adhesive layer, or A negative electrode structure for a lithium ion secondary battery including a negative electrode and an adhesive layer.
Among them, from the viewpoint of preventing abnormalities such as floating of the spacer when assembling a lithium ion secondary battery and improving workability, it is preferable to obtain an electrode structure for a lithium ion secondary battery having an electrode and an adhesive layer, more preferably To obtain a negative electrode structure for a lithium ion secondary battery including a negative electrode having a negative electrode active material layer and an adhesive layer.
The adhesive layer is formed using the composition for adhesive layers. The composition for the subsequent layer is a paste-like composition containing at least one resin selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin, and a urea resin as required, and others Resin, insulating fine particles, solvent, etc. The adhesive layer can be formed by applying the composition for an adhesive layer on the surface of a separator, a negative electrode active material layer, or a positive electrode active material layer and drying it.
The method for applying the composition for an adhesive layer 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, a rod coating method or a gravure coating method is preferable from the viewpoint of uniformly coating the adhesive composition and improving the adhesion between the electrode and the separator.
The drying temperature is not particularly limited, and is, for example, 40 to 120 ° C, and preferably 50 to 90 ° C. The drying time is not particularly limited, and is, for example, 1 to 10 minutes.

(Step (2))
Step (2) is a step of obtaining another laminated body by bonding the other one selected from the spacer and the electrode to the adhesive layer formed in step (1) by hot pressing. When a bonding layer is formed on the spacer in step (1), step (2) is a step of bonding the bonding layer on the spacer to the electrode by hot pressing, and on the electrode in step (1) In the case where an adhesive layer is formed, step (2) is a step of adhering the adhesive layer and the spacer on the electrode by hot pressing. In step (2), the electrode and the spacer are adhered by using an adhesive layer, thereby effectively preventing poor adhesion of the spacer.
In the case of manufacturing a lithium-ion secondary battery having a multilayer structure in which a negative electrode and a positive electrode are respectively laminated, as long as a plurality of structures obtained in step (1) are prepared, and a plurality of other members are overlapped and hot-pressed, can. For example, when a negative electrode structure for a lithium ion secondary battery is obtained in step (1), a plurality of negative electrode structures for a lithium ion secondary battery, a plurality of separators, and a plurality of positive electrodes may be prepared so that the separator The method of arranging between the negative electrode and the positive electrode may suffice for such overlapping hot pressing.
The temperature of the hot pressing is preferably 60 to 120 ° C, and more preferably 70 to 100 ° C. The pressure during hot pressing is preferably 0.2 to 2 MPa, more preferably 0.2 to 1 MPa, and even more preferably 0.3 to 0.7 MPa. By performing hot pressing under such conditions, the adhesion between the electrode and the spacer can be made good.
After step (2), a positive electrode, a negative electrode, or a separator may be laminated on the layered body obtained in step (2) as needed, and then hot pressing and the like are performed again, and hot pressing is performed multiple times to obtain a lithium ion secondary battery.
The lithium ion secondary battery produced through steps (1) and (2) is usually housed in a battery cell and used. The battery cells may be square, cylindrical, laminated, or the like.
Examples

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

The obtained lithium ion secondary battery was evaluated by the following evaluation method.
(Then force)
The spacer (polyethylene porous film) was superimposed on the adhesive layer side of the electrode having an adhesive layer produced in the examples and comparative examples, and pressed using a flat-plate heat press at 80 ° C and 0.6 MPa for 1 minute. A laminated body was obtained.
A double-sided tape was stuck on the SUS board, and a laminated body cut into a size of 2 cm × 5 cm was attached on the SUS board so that the electrodes and the double-sided tape overlap.
Using a digital dynamometer ((ZTS-5N), manufacturer: made by IMADA Co., Ltd.), the spacer was peeled horizontally from the long side of the laminate, and stretched at a speed of 50 cm / min by 2 cm Length, the average force is taken as the adhesion force. The following forces were classified and evaluated as follows.
A: Adhesion force is 2 N / m or more
B: Adhesion force is 1 N / m or more and less than 2 N / m
C: Adhesion force is 0.5 N / m or more and less than 1 N / m
D: Adhesion force is less than 0.5 N / m

(Fast charging)
The lithium ion secondary batteries produced in the examples and comparative examples were charged and discharged under the following conditions.
(1) Perform constant current charging at 10 mA, and then gradually reduce the current when it reaches 4.2 V. Perform constant voltage charging at the time when charging becomes 0.5 mA, and calculate the charging capacitance.
(2) Perform constant current charging at 250 mA, and then gradually reduce the current when it reaches 4.2 V, and perform constant voltage charging at the time when charging becomes 0.5 mA, and calculate the charging capacitance.
The charging capacitance ratio was calculated by the following, and it was classified and evaluated as follows.
(Charging capacitor ratio,%) = 100 × ((1) charging capacitor) ÷ ((2) charging capacitor)
A: 75% or more
B: Above 60% and less than 75%
C: 50% or more and 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, and the discharge capacitance was calculated. Using this discharge capacitance, the energy density was obtained by the following formula (1).
Charge at a constant current of 10 mA, and then gradually reduce the current when it reaches 4.2 V, and charge at a constant voltage at the end of charging at the time when it becomes 0.5 mA. Thereafter, a constant current discharge of 10 mA was performed, and the discharge was completed at the time point when the discharge reached 2.5 V, and the discharge capacitance was calculated.
The areas and thicknesses of the respective positive electrodes, negative electrodes, and separators are as follows.
Positive electrode: 20 cm ² , 100 μm
Negative electrode: 20 cm ² , thickness as described in Table 1 Spacer: 20 cm ² , 15 μm
(Energy density) = (Discharge capacitance) ÷ (Total volume of positive electrode, negative electrode, and 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 and less than 181 mAh / cm ³
C: 173 mAh / cm ³ or more and less than 177 mAh / cm ³
D: less than 173 mAh / cm ³

[Example 1]
(Production of positive electrode)
100 parts by mass of Li (Ni-Co-Al) O ₂ (NCA-based 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 auxiliary agent, and a polymer as an electrode binder 4 parts by mass of vinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) as a solvent were mixed. Thereby, the composition for positive electrode active material layers whose solid content concentration was adjusted to 60% by mass was obtained. This composition for a positive electrode active material layer was coated on both sides of an aluminum foil having a thickness of 15 μm as a positive electrode current collector, pre-dried, and 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 was press-pressed at 400 kN / m, and then pressed to a size of 100 mm × 200 mm square of the electrode size to produce positive electrode activity on both sides. Positive electrode of the material layer. In this size, the area coated with the positive electrode active material was 100 mm × 180 mm.

(Production of negative electrode)
100 parts by mass of graphite (average particle size: 10 μm) as a negative electrode active material, 1.5 parts by mass of a styrene butadiene rubber as a binder, 1.5 parts by mass of a sodium salt of carboxymethyl cellulose (CMC), and a solvent Water was mixed to obtain a composition for a negative electrode active material layer whose solid content was adjusted to 50% by mass. This negative electrode active material layer composition was coated on both sides of a copper foil having a thickness of 15 μm as a negative electrode current collector, and vacuum-dried at 100 ° C. Thereafter, the negative electrode current collector coated with the composition for a negative electrode active material layer on both sides was press-pressed at a linear pressure of 500 kN / m to prepare a negative electrode. The density of the negative electrode active material layer was 1.55 g / cc. Furthermore, the size of the negative electrode was 110 mm × 210 mm, and in this size, the area coated with the negative electrode active material layer was 110 mm × 190 mm.

(Preparation of electrolyte)
Dissolve LiPF ₆ as an electrolyte salt in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of 3: 7 (EC: DEC) to 1 mol / liter. To prepare an electrolyte.

(Production of electrode with adhesive layer)
A moderate amount of shear force was applied to 60 parts by volume of alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name: AHP200, average particle size 0.4 μm) as insulating fine particles, and polyvinylidene fluoride hexafluoropropylene was mixed on the side. (PVDF-HFP) 40 parts by volume of powder to obtain a mixture. The above mixture was mixed into NMP so that the solid content concentration became 30% by mass, and the mixture was stably stirred for 30 minutes with a stirrer, and filtered with a filter having a mesh of 80 μm to obtain a composition for an adhesive layer. The viscosity of the composition was 1800 mPa · s under a B-type viscometer at 60 rpm and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of a negative electrode active material layer using a bar coater. The coating film formed by applying the composition was dried at 60 ° C., and a bonding layer was formed on the surface of the negative electrode active material layer to obtain a negative electrode having a bonding layer (that is, a negative electrode structure for a lithium ion secondary battery). When the thickness of the adhesion layer was measured, it was 4 micrometers.

(Manufacture of lithium-ion secondary batteries)
10 negative electrodes, 9 positive electrodes, and 18 separators each having the adhesive layer obtained in the above were laminated to obtain a pre-laminated body. Here, the negative electrodes and the positive electrodes are alternately arranged, and a separator is disposed between each of the negative electrodes and the positive electrodes. As the spacer, a polyethylene porous film was used. Using a flat-plate hot press, the pre-laminated body was pressed at 80 ° C. and 0.6 MPa for 1 minute to obtain a laminated body.
The ends of the exposed portions of the positive electrode current collectors of the respective positive electrodes are collected, joined by ultrasonic welding, and the tabs protruding to the outside are joined. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes are brought together, and are joined by ultrasonic welding, and the terminal sheet protruding to the outside is joined.
Next, the laminated body is sandwiched by an aluminum laminate film, the terminal plate is protruded to the outside, and three sides are sealed by lamination. The electrolytic solution obtained above was injected from the remaining unsealed side and vacuum-sealed to manufacture a laminated battery.

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

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

[Example 4]
Production of the positive electrode, production of the negative electrode, and adjustment of the electrolytic solution were performed in the same manner as in Example 1, and an electrode having an adhesive layer was produced in the following manner to produce a lithium ion secondary battery to obtain a lithium ion secondary battery.
(Production of electrode with adhesive layer)
A moderate amount of shear force was applied to 60 parts by volume of alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name: AHP200, average particle size 0.4 μm) as insulating fine particles, while polyvinylidene fluoride hexafluoropropylene was mixed (PVDF-HFP) 40 parts by volume of powder to obtain a mixture. The above mixture was mixed into NMP so that the solid content concentration became 30% by mass, and the mixture was stably stirred for 30 minutes with a stirrer, and filtered with a filter having a mesh of 80 μm to obtain a composition for an adhesive layer. The viscosity of the composition was 1800 mPa · s under a B-type viscometer at 60 rpm and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of a positive electrode active material layer using a bar coater. The coating film formed by applying the composition was dried at 60 ° C., and a bonding layer was formed on the surface of the positive electrode active material layer to obtain a positive electrode having a bonding layer (that is, a positive electrode structure for a lithium ion secondary battery). When the thickness of the adhesion layer was measured, it was 4 micrometers.
(Manufacture of lithium-ion secondary batteries)
10 pre-laminated bodies were obtained by laminating 10 negative electrodes obtained above, 9 positive electrodes having an adhesive layer, and 18 separators. Here, the negative electrodes and the positive electrodes are alternately arranged, and a separator is disposed between each of the negative electrodes and the positive electrodes. As the spacer, a polyethylene porous film was used. Using a flat-plate hot press, the pre-laminated body was pressed at 80 ° C. and 0.6 MPa for 1 minute to obtain a laminated body.
The ends of the exposed portions of the positive electrode current collectors of the respective positive electrodes were collected, and joined by ultrasonic welding, and the terminal tabs protruding to the outside were joined. Similarly, the ends of the exposed portions of the negative electrode current collectors of the respective negative electrodes are brought together, and are joined by ultrasonic welding, and the terminal sheet protruding to the outside is joined.
Next, the laminated body is sandwiched by an aluminum laminate film, the terminal plate is protruded to the outside, and three sides are sealed by lamination. The electrolytic solution obtained above was injected from the remaining unsealed side and vacuum-sealed to manufacture a laminated battery.

[Example 5]
An ion secondary battery was obtained in the same manner as in Example 1 except that the production of the electrode having an adhesive layer was changed in the following manner.
(Production of electrode with adhesive layer)
A moderate amount of shear force was applied to 30 parts by volume of alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name: AHP200, average particle size 0.4 μm) as insulating fine particles, and polyvinylidene fluoride hexafluoropropylene was mixed on the side. (PVDF-HFP) 40 parts by volume of powder and 30 parts by volume of polymethylurea ("Pergopak M6" manufactured by Albemarle) to obtain a mixture. The above mixture was mixed into NMP so that the solid content concentration became 30% by mass, and the mixture was stably stirred for 30 minutes with a stirrer, and filtered with a filter having a mesh of 80 μm to obtain a composition for an adhesive layer. The viscosity of the composition was 1800 MPa · s under a B-type viscometer at 60 rpm and 25 ° C.
The obtained composition for an adhesive layer was applied to the entire surface of a negative electrode active material layer using a bar coater. The coating film formed by applying the composition was dried at 60 ° C., and a bonding layer was formed on the surface of the negative electrode active material layer to obtain a negative electrode having a bonding layer (that is, a negative electrode structure for a lithium ion secondary battery). When the thickness of the adhesion layer was measured, it was 4 micrometers.

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

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

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

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

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

[Table 1]

As shown in Examples 1 to 6 above, a lithium ion secondary battery containing 30 to 55% by volume of a specific resin and a density of the negative electrode active material layer of 1.55 to 1.70 g / cm ³ , its adhesion, fast chargeability, and The energy density is good. On the other hand, when the content of the specific resin is not in the range of 30 to 55% by volume, or the density of the negative electrode active material is not in the range of 1.55 to 1.70 g / cm ³ , the adhesive force, fast chargeability, and The result of poor physical balance of energy density.

10‧‧‧ Lithium-ion secondary battery

11‧‧‧ Negative

11a‧‧‧Negative current collector

11b‧‧‧Negative electrode active material layer

12‧‧‧Positive

12a‧‧‧Positive collector

12b‧‧‧Positive electrode active material layer

13‧‧‧ spacer

14‧‧‧ Adjacent layer

FIG. 1 is a schematic cross-sectional view showing an embodiment of a lithium ion secondary battery of the present invention.

Claims (10)

A lithium ion secondary battery comprising: 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 an adhesive layer disposed at least one of the negative electrode and the positive electrode The spacer and the electrode are bonded between the electrode and the spacer; the bonding 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. 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. The lithium ion secondary battery according to any one of claims 1 to 5, wherein the thickness of the adhesive layer is 1 to 10 μm. 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, wherein the adhesive layer contains at least one selected from a polyvinylidene fluoride-hexafluoropropylene copolymer and an acrylic resin. The resin is 30 to 55% by volume, and the density of the negative electrode active material layer is 1.50 to 1.70 g / cm ³ . A method for manufacturing a lithium ion secondary battery according to any one of claims 1 to 6, comprising the steps of: forming the above-mentioned adhesive layer on a surface selected from one of the spacer and the electrode; and The step of bonding the other one selected from the spacer and the electrode to the adhesive layer by hot pressing. The method for manufacturing a lithium ion secondary battery according to claim 8, comprising the steps of: forming a bonding layer on the negative electrode active material layer of the negative electrode; and The step of bonding the spacer and the adhesive layer by hot pressing. The method for manufacturing a lithium ion secondary battery according to claim 8 or 9, wherein the temperature of the hot pressing is 60 to 120 ° C and the pressure is 0.2 to 2.0 MPa.