JP5696826B2 - Binder composition for electrode, slurry composition for electrode, electrode and battery - Google Patents

Description

  The present invention relates to an electrode used for forming an electrode used for an electrochemical element such as a lithium ion secondary battery or an electric double layer capacitor (hereinafter sometimes collectively referred to as “electrochemical element electrode”). The present invention relates to a binder composition for an electrode, a slurry composition for an electrode using the binder composition for an electrode, an electrode, and a battery.

  Utilizing the small size, light weight, high energy density, and the ability to repeatedly charge and discharge, electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors are rapidly expanding their demand. ing. Lithium ion secondary batteries have a relatively high energy density and are therefore used in fields such as mobile phones and notebook personal computers. In addition, since the electric double layer capacitor can be rapidly charged and discharged, it is used as a memory backup compact power source for personal computers and the like. Furthermore, the electric double layer capacitor is expected to be applied as a large power source for electric vehicles. Also, with the aim of achieving both high energy density and charge / discharge speed, a hybrid capacitor that uses a Faraday reaction electrode for one of the positive electrode and the negative electrode and a non-Faraday reaction electrode for the other has been developed. In addition, redox capacitors that utilize the oxidation-reduction reaction (pseudo electric double layer capacitance) on the surface of metal oxides or conductive polymers are also attracting attention due to their large capacity. With the expansion and development of applications, these electrochemical elements are required to further improve characteristics such as low resistance, high capacity, and improved mechanical characteristics. Under such circumstances, in order to improve the performance of the electrochemical element, various improvements have been made on the material forming the electrochemical element electrode.

  The production of the electrochemical device electrode is performed by applying an electrode slurry composition containing an electrode binder composition and an electrode active material, which is an aqueous dispersion of polymer particles, onto a current collector to form an electrode active material layer. After drying, it is performed by performing pressure treatment such as a roll press (Patent Document 1).

  In recent years, it has been desired to improve the productivity of electrochemical device electrodes by increasing the speed of the production process of electrochemical device electrodes and increasing the roll length of the current collector used in the electrochemical device electrodes. It is becoming.

JP 2008-135262 A

  However, in the conventional method, if the manufacturing process of the electrochemical device electrode is accelerated or the roll length of the current collector is increased, it is possible to stably produce a battery having a smooth electrode active material layer and a high capacity retention rate. It was difficult.

  Therefore, the present invention has been made in view of the above problems, and a battery having a high capacity retention rate can be stably manufactured even when the manufacturing process is speeded up or the current collector roll length is increased. It aims at providing the binder composition for electrodes, the slurry composition for electrodes using this binder composition for electrodes, an electrode, and a battery.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the polymer particle aqueous dispersion contains coarse particles or aggregates having a size that can be visually recognized. It has been found that the above problem can be solved by doing so. That is, when the electrode active material layer is formed on the current collector using the slurry containing the coarse particles or aggregates, the smoothness of the electrode active material layer may be deteriorated and the battery capacity may be reduced. Furthermore, when the electrode active material layer is subjected to pressure treatment, coarse particles or aggregates adhere to an apparatus such as a roll, the apparatus is contaminated, and the coarse particles or aggregates attached to the roll or the like are It was found that the material reattached to the material layer, the smoothness of the electrode active material layer was deteriorated, and the battery capacity was reduced.

  As a result of further intensive studies, the present inventors have found that the binder composition for an electrode has a concentration of coarse particles and / or aggregates having a sphere volume equivalent diameter of not less than a specific particle diameter measured by the Coulter method being a predetermined concentration or less. It was found that a battery having a high capacity retention rate can be stably provided even when the manufacturing process is speeded up and the current collector roll length is increased.

That is, this invention which solves the said subject contains the following matters as a summary.
(1) A binder composition for an electrode in which the sphere volume equivalent diameter of particles measured by the Coulter method is 3 μm or more, and the concentration of coarse particles and / or aggregates is 2000 ppm or less.
(2) A slurry composition for an electrode comprising the battery binder composition described in (1) above and an electrode active material.
(3) An electrode obtained by applying the slurry composition for an electrode according to (2) above to a current collector and drying it.
(4) A battery using the electrode according to (3) above.
(5) The electrode binder composition and electrode slurry composition comprising the electrode active material as described in (1) above are applied to at least one side of the current collector at a rate of 3 m / min or more and dried by heating. Forming a layer;
And a step of pressing the electrode active material layer at 3 m / min or more.

  The binder composition for an electrode of the present invention comprises coarse particles and / or aggregates (hereinafter sometimes referred to as “coarse particles etc.”) having a sphere volume equivalent diameter of 3 μm or more as measured by the Coulter method. Since the concentration is 2000 ppm or less, a smooth thin electrode active material layer can be formed even if the manufacturing process of the electrochemical element electrode is accelerated or the roll length of the current collector is increased. In addition, since coarse particles hardly adhere to an apparatus such as a roll, the apparatus is prevented from being contaminated, and a smooth electrode active material layer can be formed at a high speed. Therefore, the battery using the electrode binder composition of the present invention is less likely to generate a battery having a reduced battery capacity and capacity retention rate in a cycle test, compared to a battery using a conventional electrode binder composition. High productivity.

<Binder composition for electrode>
The binder composition for an electrode of the present invention has a particle volume equivalent diameter measured by a Coulter method of 3 μm or more, and the concentration of coarse particles and the like is 2000 ppm or less, preferably 1500 ppm or less, particularly preferably 1000 ppm or less. In particular, the concentration of coarse particles having a sphere volume equivalent diameter of 11 μm or more is preferably 500 ppm or less. When the number of coarse particles is small, the occurrence frequency of defective defects such as coating defects (coating unevenness) and roll stains associated with press working accompanying the production of electrochemical element electrodes is reduced, and productivity is improved. In addition, the probability of occurrence of a battery in which the battery capacity of the manufactured battery and the capacity maintenance rate in a cycle test are reduced is reduced.

  Coarse particles and the like are a general term for fine solidified substances generated in the process of producing a binder dispersion. These are mainly generated in the polymerization reaction step of the polymerization composition, but may be generated in a subsequent step such as a step of removing residual monomer during pH adjustment. These are removed as necessary to obtain an electrode binder composition.

  The equivalent spherical volume diameter of coarse particles or the like can be measured by the Coulter method. In addition, the guide regarding the particle size distribution measurement using the Coulter principle (pore electrical resistance method) is described in the international standard ISO13319 “Electrical sensing zone method”.

  The sphere volume equivalent diameter of coarse particles or the like is measured by directly measuring the volume (three-dimensional) of each particle by the Coulter method (electric detection zone method). The concentration of coarse particles and the like is measured by preparing the following measurement solution. First, the binder dispersion is filtered through a # 325 mesh wire mesh, and about 1.0 g is precisely weighed into a 200 ml volumetric flask. Next, the solution is made up with Isoton (ISOTON-II: electrolyte solution: manufactured by Beckman-Coulter) to obtain a measurement solution. The measurement solution is measured three times for each sample with MuItizer 3 (aperture size 100 μm, suction amount 2000 μm) manufactured by Beckman Coulter, and the average value is defined as the concentration of coarse particles and the like. The number of decomposition channels is divided into 32, the measurement particle size range is 3 to 67 μm, and the concentration of coarse particles in the binder dispersion is expressed in terms of ppm concentration from the measurement result and the solid content concentration of the initial sample. .

  The binder composition for an electrode of the present invention is a compound capable of binding an electrode active material and a conductive material, which will be described later, to each other, and a solution in which binder (polymer) particles having binding force are dissolved or dispersed in water. Alternatively, a dispersion liquid (hereinafter, these may be collectively referred to as “binder dispersion liquid”) is filtered.

(Binder dispersion)
The binder dispersion is usually an aqueous dispersion of polymer particles, for example, a diene polymer particle aqueous dispersion, an acrylic polymer particle aqueous dispersion, a fluorine polymer particle aqueous dispersion, a silicon polymer particle. Examples thereof include an aqueous dispersion. A diene polymer particle aqueous dispersion or an acrylic polymer particle aqueous dispersion is preferred because of its excellent binding properties to the electrode active material and the strength and flexibility of the resulting electrode.

  The diene polymer particle aqueous dispersion is an aqueous dispersion of a polymer containing monomer units formed by polymerizing a conjugated diene such as butadiene or isoprene. The proportion of monomer units obtained by polymerizing conjugated diene in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Examples of the diene polymer include homopolymers of conjugated dienes such as polybutadiene and polyisoprene; and copolymers with monomers copolymerizable with conjugated dienes. Examples of the copolymerizable monomer include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene, chlorostyrene, Styrene monomers such as vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene; olefins such as ethylene and propylene Halogen-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; methyl vinyl Vinyl ketones such as ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocycle-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole; acrylic acid such as methyl acrylate and methyl methacrylate Ester and / or methacrylic acid ester compounds; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid Etc.

  The acrylic polymer particle aqueous dispersion is an aqueous dispersion of a polymer containing monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester. The proportion of monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Examples of the acrylic polymer include homopolymers of acrylic acid esters and / or methacrylic acid esters, and copolymers with monomers copolymerizable therewith. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; two or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate. -Carboxylic acid ester having a carbon double bond; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, vinyl benzoate methyl, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, Styrene monomers such as divinylbenzene; Amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropane sulfonic acid; α, β-defect such as acrylonitrile and methacrylonitrile Japanese nitrile compounds; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate Vinyl esters such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; N-vinyl pyrrolidone, Heterocycle-containing vinyl compounds such as vinylpyridine and vinylimidazole; and hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate.

  As the binder dispersion for the positive electrode, an aqueous dispersion of acrylic polymer particles that is a dispersion of a saturated polymer having no unsaturated bond in the polymer main chain is preferable because of excellent oxidation resistance during charging. Moreover, as a binder dispersion liquid for negative electrodes, since it is excellent in reduction resistance and a strong binding force is obtained, a diene polymer particle aqueous dispersion is preferable.

  The binder dispersion can be produced, for example, by emulsion polymerization of the monomer in water. The number average particle diameter of the binder particles in the binder dispersion is preferably 50 to 500 nm, and more preferably 70 to 400 nm. When the number average particle diameter of the binder particles is within this range, the strength and flexibility of the obtained electrode are good.

  The glass transition temperature (Tg) of the polymer in the binder dispersion is appropriately selected according to the purpose of use, but is usually −100 ° C. to + 100 ° C., preferably −80 ° C. to + 50 ° C., more preferably −50 ° C. It is the range of ~ + 30 degreeC. When the Tg of the polymer is within this range, characteristics such as flexibility, binding and winding properties of the electrode, and adhesion between the electrode active material layer and the current collector layer are highly balanced, which is preferable.

  The solid concentration of the binder dispersion is usually 15 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. When the solid content concentration is within this range, the workability in producing the electrode slurry composition is good.

(Production of binder composition for electrodes)
The binder composition of the present invention can be efficiently obtained by subjecting a binder dispersion produced by emulsion polymerization of the above monomers in water to filtration using a stainless steel wire mesh or a filtration filter. .

  In the filtration treatment method using a filtration filter, the details of the type and structure of the filtration filter are not particularly limited, and any filtration filter may be used as long as it can remove foreign matters that do not pass through a pore size of 5 to 50 μm. A system for removing coarse particles and the like using these filtration filters is not particularly limited, and is not particularly limited as long as no major problem occurs in filtration.

  Examples of materials for these filtration filters include paper, cloth, cellulose acetate polymer, polysulfone, polyethersulfone, polyacrylonitrile, polyether, fluoropolymer (polyvinylidene fluoride, tetrafluoroethylene), polyamide, polyimide, polyethylene , Polypropylene, stainless steel, ceramic and the like. The form is a flat membrane, a cartridge membrane, a hollow fiber membrane and the like, and is not particularly limited. In order to perform filtration with the cartridge filtration filter, it is particularly preferable to use a housing in which the cartridge filtration filter is mounted.

  Many of these filtration filters are commercially available from various companies. For example, in the case of a cartridge type polyolefin-based composite fiber, a Chisso CP filter (various sizes such as CP-10 (10 μm), CP-25 (25 μm), CP-50 (50 μm)) (this is Chisso Filter Co., Ltd.) If it is made of polypropylene, Micro Syria filter cartridge EX type (various sizes) (above, manufactured by Loki Techno), Microwind IIHP series filter cartridge (various sizes) (above, manufactured by Sumitomo 3M Ltd.) If it is made of tetrafluoroethylene, there is a micro-serial filter cartridge BO type (various sizes) (above, manufactured by Loki Techno).

  When using these filtration filters, there are no particular limitations on the method of use, and it is sufficient that coarse particles and the like can be removed without clogging. However, in general, the above filtration filter is effective without requiring an installation area by being mounted on a housing. The size and shape of the housing are not particularly limited, and may be a circular shape, a square shape, or a single filter loading type, and two or more filters may be loaded at a time. Furthermore, it is possible to greatly increase the filtration filter area by connecting two or more filters. Furthermore, a flat membrane type can also be used in the present invention. Specifically, a filtration filter is installed on the receiving part, a device serving as a liquid storage part is fixed thereon, and the filter mounting part is fastened with a fastening member so as not to leak the filtrate. At this time, packing is installed in the filter installation part to prevent liquid leakage.

  Next, in carrying out the filtration of the binder dispersion used in the present invention, there is no limitation on the pressure for feeding, but generally coarse particles and the like are removed by passing through a filtration filter under pressure or reduced pressure. It is preferable. In particular, pressurization is often carried out by feeding the binder dispersion with a pump or the like, but it is also preferable to place the binder dispersion at a higher position than the filtration filter and filter it with natural pressure (pressure by its own weight). Furthermore, it is also preferable to apply a pressure to the binder dispersion with a gas. In this case, the tank in which the binder dispersion is present is preferably a closed system. In the case of applying pressure with a pump at the time of liquid delivery, pressurization with its own weight or even pressurization with gas, especially if the filtration filter is damaged or clogged and the performance is not deteriorated. It is not limited. From the viewpoint of the life and processing speed of the filter, it is more preferable to preliminarily filter the aggregates in the binder dispersion with a wire mesh of 150 mesh or the like and then perform the filter filtration treatment.

  Since the binder composition for an electrode of the present invention has few coarse particles and the like, it can be used as a binder composition for a porous film used as a protective film for a secondary battery electrode in addition to the binder composition for a secondary battery electrode. Can be used.

<Slurry composition for electrodes>
The electrode slurry composition of the present invention contains the electrode binder composition and an electrode active material.

(Electrode active material)
The electrode active material used in the present invention is a substance that transfers electrons in an electrode for an electrochemical element. Specifically, the active material for lithium ion secondary batteries, the active material for electric double layer capacitors, etc. are mainly mentioned.

Examples of the active material for a lithium ion secondary battery include a positive electrode and a negative electrode. Specifically, as an electrode active material (positive electrode active material) used for the positive electrode of the electrode for a lithium ion secondary battery, lithium-containing materials such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO _4, etc. Composite metal oxides; transition metal sulfides such as TiS ₂ , TiS ₃ , amorphous MoS ₃ ; Cu ₂ V ₂ O ₃ , amorphous V ₂ O · P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , Examples include transition metal oxides such as V ₆ O ₁₃ . Furthermore, conductive polymers such as polyacetylene and poly-p-phenylene are listed. Preferred is a lithium-containing composite metal oxide.

  Specific examples of the electrode active material (negative electrode active material) used for the negative electrode of a lithium ion secondary battery electrode include amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon fibers. Carbonaceous material; conductive polymer such as polyacene. Crystalline carbonaceous materials such as graphite, natural graphite, and mesocarbon microbeads (MCMB) are preferable.

  The shape of the electrode active material used for the electrode for a lithium ion secondary battery is preferably a granulated particle. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.

  The volume average particle diameter of the electrode active material used for the electrode for a lithium ion secondary battery is usually 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 20 μm for both the positive electrode and the negative electrode.

The tap density of the electrode active material used for the electrode for the lithium ion secondary battery is not particularly limited, but preferably 2 g / cm ³ or more for the positive electrode and 0.6 g / cm ³ or more for the negative electrode.

  As the electrode active material used for the electric double layer capacitor electrode, a carbon allotrope is usually used. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite, and these powders or fibers can be used. A preferred electrode active material is activated carbon, and specific examples include activated carbon made from phenol resin, rayon, acrylonitrile resin, pitch, coconut shell, and the like.

  The volume average particle diameter of the electrode active material used for the electric double layer capacitor electrode is usually 0.1 to 100 μm, preferably 1 to 50 μm, and more preferably 5 to 20 μm.

The specific surface area of the electrode active material used in the electrode for an electric double layer capacitor, ^{30 m} 2 / g or more, preferably 500~5,000m ² / g, and more preferably are from 1,000~3,000m ² / g preferable. Since the density of the obtained electrode active material layer tends to decrease as the specific surface area of the electrode active material increases, an electrode active material layer having a desired density can be obtained by appropriately selecting the electrode active material.

  These electrode active materials can be used individually or in combination of 2 or more types according to the kind of electrochemical element.

  The total amount of the electrode binder composition and the electrode active material in the electrode slurry composition is preferably 10 to 90 parts by mass, more preferably 30 to 80 parts by mass, with respect to 100 parts by mass of the electrode slurry composition. Part. Moreover, the usage-amount of the electrode active material in the slurry composition for electrodes is preferably 5 to 80 parts by mass and more preferably 10 to 60 parts by mass with respect to 100 parts by mass of the slurry composition for electrodes. When the total amount of each component and the usage amount of the electrode active material are within this range, the viscosity of the resulting slurry composition for an electrode is optimized, and the coating can be performed smoothly.

  The amount of the electrode binder composition used in the electrode slurry composition is usually 0.1 to 10 parts by mass, preferably 0.5 to 8 parts by mass, based on 100 parts by mass of the electrode active material. More preferably, it is 0.7-1.2 mass part. When the amount used is within this range, the strength and flexibility of the obtained electrode will be good.

(Thickener)
The slurry composition for electrodes of the present invention may contain a thickener. Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches.

  As for the compounding quantity of a thickener, 0.5-1.5 mass parts is preferable with respect to 100 mass parts of electrode active materials. When the blending amount of the thickener is within this range, the coating property and the adhesion with the current collector are good. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”.

(Conductive material)
The slurry composition for an electrode of the present invention may contain a conductive material. As the conductive material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. By using a conductive material, the electrical contact between the electrode active materials can be improved, and the discharge rate characteristics can be improved when used in a non-aqueous electrolyte secondary battery. The usage-amount of a electrically conductive material is 0-20 mass parts normally with respect to 100 mass parts of active materials, Preferably it is 1-10 mass parts.

(Production of slurry composition for electrode)
The slurry composition for electrodes is obtained by mixing the binder composition for electrodes, an active material, a thickener used as necessary, and a conductive material.

   The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

<Electrode>
The electrode of the present invention is an electrode having an electrode active material layer and a current collector formed by applying and drying the slurry composition for an electrode of the present invention. The method for producing the electrode of the present invention is not particularly limited. For example, the electrode slurry composition is applied to at least one surface, preferably both surfaces of the current collector at a speed of 3 m / min or more, and dried by heating and drying. This is a method of forming a material layer.

  The method for applying the electrode slurry composition to the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a comma direct coating, a slide die coating, and a brush coating method. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C. The active material layer may be formed by repeating application and drying a plurality of times.

  Subsequently, it is preferable to reduce the porosity of the electrode active material layer by performing pressure treatment such as press working at a speed of 3 m / min or more. The preferable range of the porosity is 5% to 15%, more preferably 7% to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, there are problems that it is difficult to obtain a high volume capacity or that the electrode active material layer is easily peeled off from the current collector. Further, when a curable polymer is used, it is preferably cured.

  The press working is performed using, for example, a roll press or a sheet press using a metal roll, an elastic roll, or a heating roll. In the present invention, the pressing temperature may be performed at room temperature or may be performed as long as the temperature is lower than the temperature for drying the coating film of the active material layer. As a guide, it is 15 to 35 ° C.).

  Press processing (roll press) by a roll press machine is preferable because a long sheet-like negative electrode plate can be continuously pressed. When performing the roll press, either a stereotaxic press or a constant pressure press may be performed. The line speed of the press is usually 5 to 50 m / min. When the pressure of the roll press is managed by linear pressure, the pressure is adjusted according to the diameter of the pressure roll, but the linear pressure is usually 0.5 kgf / cm to 1 tf / cm.

Also, pressing by the sheet pressing machine normally when performing (sheet ^{press), 4903~73550N / cm 2 (500~7500kgf} / cm 2), preferably ^{29420~49033N / cm 2 (3000~5000kgf / cm} 2) Adjust the pressure to the range of. If the pressing pressure is too small, it is difficult to obtain the homogeneity of the active material layer. If the pressing pressure is too large, the electrode plate itself including the current collector may be damaged. The active material layer may have a predetermined thickness by a single press, or may be pressed several times for the purpose of improving homogeneity.

  The thickness of the electrode active material layer of the electrode of the invention is usually 5 μm or more and 300 μm or less, preferably 30 μm or more and 250 μm or less.

(Current collector)
The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material. However, a metal material is preferable because it has heat resistance. For example, iron, copper, aluminum Nickel, stainless steel, titanium, tantalum, gold, platinum and the like.

  The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength with the electrode active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the electrode active material layer.

<Battery>
The battery of the present invention comprises the electrode of the present invention as at least one of a positive electrode and a negative electrode. Applicable batteries include manganese batteries, alkaline batteries, nickel-based primary batteries, silver oxide batteries, air zinc batteries, lead storage batteries, lithium ion secondary batteries, nickel metal hydride secondary batteries, nickel cadmium batteries, alkaline storage batteries, solar batteries, fuel A battery etc. are mentioned. Among these, a lithium ion secondary battery is preferable. Hereinafter, the case where it uses for a lithium ion secondary battery is demonstrated.

  A method for producing a lithium ion secondary battery is a method in which a negative electrode and a positive electrode are overlapped via a separator, and this is wound according to the shape of the battery, folded into a battery container, and an electrolyte is injected into the battery container to seal it. To do. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

(Electrolyte)
The electrolytic solution used in the present invention is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used individually or in mixture of 2 or more types. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity decreases, and the charging characteristics and discharging characteristics of the battery decrease.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used individually or in mixture of 2 or more types. Moreover, it is also possible to use the electrolyte solution by containing an additive. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte such as LiI and Li ₃ N.

(Separator)
As the separator, known ones such as a microporous film or non-woven fabric made of polyolefin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing inorganic ceramic powder; For example, polyolefin (polyethylene, polypropylene, polybutene, polyvinyl chloride), and microporous membranes made of resins such as mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide , A microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, or a woven polyolefin-based fiber, or a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like.

  The thickness of a separator is 0.5-40 micrometers normally, Preferably it is 1-30 micrometers, More preferably, it is 1-10 micrometers. Within this range, the resistance due to the separator in the battery is reduced, and the workability during battery production is excellent.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard.

  In the examples and comparative examples, charge / discharge cycle characteristics, charge / discharge rate characteristics (load characteristics), and roll press workability determination were performed as follows.

<Charge / discharge cycle characteristics>
Using the laminated cell batteries obtained in the following examples and comparative examples, charging was performed at a constant current until the voltage became 4.2 V by a constant current constant voltage charging method of 0.1 C at 25 ° C., and then a constant voltage. And a charge / discharge cycle in which the battery was discharged to 3.0 V with a constant current of 0.1 C. The charge / discharge cycle was performed up to 100 cycles, and the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity was defined as the capacity maintenance rate, and the determination was made based on the probability of occurrence of a battery with this capacity maintenance rate of 80% or less. The discharge capacity at the 50th cycle was defined as the battery capacity.

<Charge / discharge rate characteristics (load characteristics)>
Except for changing the measurement condition to a constant current amount of 2.0 C, the discharge capacity at the 50th cycle at each constant current amount was measured in the same manner as the measurement of charge / discharge cycle characteristics. The ratio of the discharge capacity under the above conditions with respect to the battery capacity was calculated as a percentage to obtain the charge / discharge rate characteristics, and the determination was made based on the probability of occurrence of the battery that was less than 70%.

<Roll press workability judgment>
The roll surface after rolling the electrode active material layer with a roll press was visually confirmed and determined as follows.
A: No adhesion of electrode active material layer or the like on the roll surface, and mirror surface of the roll surface B: No adhesion of electrode active material layer or the like on the roll surface C: Adhesion of electrode active material layer or the like on the roll surface, or roll Cloudiness on the surface D: Adhesion of electrode active material, etc. on the roll surface, or cloudiness on the roll surface, or peeling in part of the electrode active material layer

Example 1
(Manufacture of negative electrode)
In a 5 MPa pressure autoclave with a stirrer, 47 parts of styrene, 49 parts of 1,3-butadiene, 2 parts of methacrylic acid, 2 parts of acrylic acid, 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water, t- After 0.3 parts of dedecyl mercaptan and 1 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred, the polymerization was started by heating to 45 ° C. When the reaction rate reaches 96.0%, the reaction is stopped by cooling to obtain a diene polymer particle aqueous dispersion (diene binder dispersion) having a glass transition temperature of -15 ° C. and a number average particle diameter of 100 nm. It was.

  The obtained diene binder dispersion was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution, and then the unreacted monomers were removed by heating under reduced pressure. Then, while further adjusting the solid content concentration with ion-exchanged water, the mixture was filtered through a 200 mesh (mesh size: about 77 μm) stainless steel wire mesh to obtain a negative electrode binder composition having a solid content concentration of 40%.

  A 1% aqueous solution was prepared using carboxymethylcellulose (“Daicel 2200” manufactured by Daicel Chemical Industries, Ltd.) having a 1% aqueous solution viscosity of 2000 mPa · s. Into a planetary mixer with a disper, 100 parts of artificial graphite having an average particle size of 25 μm was added, 100 parts of the above aqueous solution was added thereto, and the solid content concentration was adjusted to 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. . Next, after adjusting the solid content concentration to 50% with ion-exchanged water, the mixture was further mixed at 25 ° C. for 15 minutes. Next, 2.5 parts of the above binder composition for negative electrode (solid content concentration 40%) was added, mixed for another 10 minutes, and then defoamed under reduced pressure to obtain an electrode slurry composition.

  The electrode slurry composition was applied on both sides with a comma direct coating at a speed of 3 m / min on a copper foil having a thickness of 20 μm so that the film thickness after drying was about 100 μm. The electrode active material layer was obtained by drying for 1 minute and heat treatment at 120 ° C. for 2 minutes. The electrode active material layer was rolled with a roll press at a speed of 3 m / min to obtain a negative electrode having a thickness of 170 μm and a density of 1.7 g / cc.

(Manufacture of positive electrode)
Polyvinylidene fluoride was added as a binder composition to 100 parts of LiMn ₂ O ₄ having a spinel structure as a positive electrode active material so that the solid content equivalent amount was 2 parts, and further 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added. In addition, it was mixed with a planetary mixer to obtain a positive electrode slurry composition. This positive electrode slurry composition was applied to an aluminum foil having a thickness of 18 μm, dried at 150 ° C. for 3 hours, and then roll pressed to obtain a positive electrode having an active material layer thickness of 100 μm.

A battery container was prepared using a laminate film in which both surfaces of an aluminum sheet were coated with a resin made of polypropylene. Next, using the positive electrode and the negative electrode, the active material layer was removed from each end, and the Ni tab was welded to the positive electrode and the Cu tab was welded to the negative electrode to form a positive electrode and a negative electrode. The obtained positive electrode and negative electrode were wound with a separator made of a polyethylene microporous membrane so that the active material layer surfaces of both electrodes were opposed, and wound and stored in the battery container. Subsequently, an electrolytic solution in which LiPF ₆ was dissolved to a concentration of 1 mol / liter was injected into a mixed solvent (volume ratio at 25 ° C .: 1: 2) in which ethylene carbonate and diethyl carbonate were mixed. . Next, the laminate film was sealed to produce a laminate cell type lithium ion secondary battery. 100 such laminated cell type lithium ion secondary batteries were produced. Table 1 shows the evaluation results of the performance of this battery.

(Example 2)
Except that the aqueous diene polymer particle dispersion (diene binder dispersion) in Example 1 was filtered using a 200-mesh stainless steel mesh and a 400-mesh stainless steel mesh (mesh size: about 43 μm). In the same manner as in Example 1, a negative electrode binder composition was obtained, a laminated cell type lithium ion secondary battery was produced, and performance was evaluated. The results are shown in Table 1.

(Example 3)
Except that the diene polymer particle aqueous dispersion (diene binder dispersion) in Example 1 was filtered using a 200 mesh stainless steel wire mesh and a polypropylene cartridge filter (filtration accuracy: 25 μm). In the same manner as in Example 1, a negative electrode binder composition was obtained, a laminated cell type lithium ion secondary battery was produced, and performance was evaluated. The results are shown in Table 1.

Example 4
The diene polymer particle aqueous dispersion (diene binder dispersion) in Example 1 was used using a 200 mesh stainless steel wire mesh, a polypropylene cartridge filter (filtration accuracy 25 μm), and a polypropylene cartridge filter (filtration accuracy 10 μm). A negative electrode binder composition was obtained in the same manner as in Example 1 except that filtration was performed, and a laminated cell type lithium ion secondary battery was produced, and performance was evaluated. The results are shown in Table 1.

(Example 5)
In a 5 MPa pressure autoclave with a stirrer, 80 parts of n-butyl acrylate, 15 parts of acrylonitrile, 3 parts of methacrylic acid, 1 part of acrylic acid, 1 part of allyl glycidyl ether, 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water, polymerization started After adding 1.2 parts of potassium persulfate as an agent and stirring sufficiently, the mixture was heated to 60 ° C. to initiate polymerization. When the reaction rate reached 80%, 3 parts of an aqueous solution of potassium persulfate (3% aqueous solution) was further added and heated to 70 ° C. When the reaction rate reaches 97.0%, the reaction is stopped by cooling to obtain an acrylic polymer particle aqueous dispersion (acrylic binder dispersion) having a glass transition temperature of -35 ° C. and a number average particle diameter of 250 nm. It was.

  The obtained acrylic binder dispersion was adjusted to pH 8 by adding a 5% aqueous sodium hydroxide solution, and then the unreacted monomer was removed by heating under reduced pressure. Then, while further adjusting the solid content concentration with ion-exchanged water, filtration was performed using a 100 mesh (mesh approximately 154 μm) and 325 mesh (mesh approximately 44 μm) stainless steel wire mesh, for a negative electrode having a solid content concentration of 40%. A binder composition was obtained. A laminated cell type lithium ion secondary battery was produced and performance was evaluated in the same manner as in Example 1 except that this negative electrode binder composition was used. The results are shown in Table 1.

(Comparative Example 1)
A negative electrode binder composition was obtained in the same manner as in Example 1 except that the stainless steel wire mesh in Example 1 was changed from 200 mesh to 100 mesh (mesh size: about 154 μm). A secondary battery was prepared and performance was evaluated. The results are shown in Table 1.

(Comparative Example 2)
A negative electrode binder composition was obtained in the same manner as in Example 5 except that the stainless steel wire mesh in Example 5 was filtered only with 100 mesh (mesh size: about 154 μm), and a laminated cell type lithium ion secondary battery was obtained. Fabricated and evaluated for performance. The results are shown in Table 1.

As can be seen from Table 1, in the laminated cell type lithium ion secondary batteries of Examples 1 to 5, the roll press workability of the electrodes is higher than in the laminated cell type lithium ion secondary batteries of Comparative Examples 1 and 2. The probability of occurrence of a battery having a good capacity retention rate in charge / discharge cycle characteristics and a battery having reduced charge / discharge rate characteristics was low.

Claims (2)

A step of producing a diene polymer particle aqueous dispersion or an acrylic polymer particle aqueous dispersion by emulsion polymerization of a monomer,
The diene polymer particle aqueous dispersion or acrylic polymer particle aqueous dispersion is filtered using a stainless steel wire mesh and a cartridge filtration filter, and the diene polymer particle aqueous dispersion or acrylic polymer is filtered. Binder composition for electrodes in which the concentration of coarse particles and / or aggregates, which are finely-agglomerated particles having a sphere volume equivalent diameter of 3 μm or more, measured by the Coulter method generated during the production of the particle aqueous dispersion is 370 to 2000 ppm Obtaining a product,
The electrode binder composition, the electrode slurry composition comprising an electrode active material is applied to at least one side of the current collector at 3 m / min or more, and heated and dried to form an electrode active material layer, and the electrode The manufacturing method of the electrode which has the process of pressing an active material layer at 3 m / min or more. A battery comprising an electrode obtained by the production method according to claim 1.