JP2014035900A - Primer composition, nickel hydrogen secondary battery positive electrode, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a primer composition for a positive electrode used in a nickel hydrogen secondary battery that is good in output characteristics and cycle life, and also suppressed in influence on cycle characteristics.SOLUTION: A primer composition according to one embodiment of the present invention is used for a nickel hydrogen secondary battery positive electrode including a two-dimensional structure collector, and contains leaf-shaped graphite particles (A) having an average particle size of 1-50 μm, carbon blacks (B) having an average particle size of 0.01-0.3 μm, and an aqueous resin (C).

Description

  The present invention relates to a primer composition, a nickel-hydrogen secondary battery positive electrode, and a method for producing the same.

  In recent years, small portable electronic devices such as digital cameras and mobile phones have been widely used. These electronic devices have always been required to minimize the volume and reduce the weight, and the batteries to be mounted are also required to be small, light, and have a large capacity. On the other hand, in a large-sized secondary battery mounted on a bus, a truck, or the like, it is desired to realize a large-sized secondary battery that is lightweight and has high output performance instead of a conventional lead-acid battery.

  In order to meet such demands, development of non-aqueous secondary batteries such as alkaline secondary batteries such as nickel metal hydride secondary batteries and lithium ion batteries has been actively conducted. And improvement of an electrode is examined in order to implement | achieve performance enhancement of a battery.

  Incidentally, nickel hydride secondary batteries used in substations, automobiles, trains, and the like are required to have higher output, higher voltage, and higher capacity than those used in conventional dry batteries and portable devices. Therefore, it is necessary to use a large one. When a nickel metal hydride secondary battery is mounted on a vehicle, regenerative power generated during braking can be stored in the mounted nickel metal hydride secondary battery and used as a power source for the vehicle. Therefore, the operation energy efficiency of the vehicle can be increased. Here, when charging the regenerative power to the nickel metal hydride secondary battery, it is necessary to rapidly charge with a large current. On the other hand, when driving a vehicle using a nickel metal hydride secondary battery, it is necessary to rapidly discharge with a large current.

  Generally, in a positive electrode of an alkaline storage battery such as a nickel metal hydride battery, a porous base material such as foamed nickel is used as a current collector. This is filled with nickel hydroxide powder having a surface coated with cobalt hydroxide or cobalt oxyhydroxide, or nickel hydroxide powder added with a cobalt compound such as cobalt hydroxide or cobalt oxide. Cobalt hydroxide, cobalt oxide, and the like change to cobalt oxyhydroxide during charging, exhibit high electrical conductivity, and form a dense conductive network between the nickel hydroxide particles. Thereby, a high utilization factor is obtained. On the other hand, since the foamed nickel or cobalt compound is used as the electrode material, it is difficult to reduce the cost. The utilization rate is the ratio of the actual discharge capacity to the theoretical capacity of the battery.

  An electrode using a material other than foamed nickel as a base material is also disclosed. For example, Patent Document 1 discloses an alkaline secondary battery in which a mixture containing nickel hydroxide surface-coated with α-type cobalt hydroxide, a conductive additive, and a binder is supported on a two-dimensional structure current collector. A nickel positive electrode is disclosed.

  Patent Document 2 includes an active material, a binder, and a conductive auxiliary agent in a smooth nickel substrate that is a two-dimensional structure current collector, instead of filling a mixture of foamed porous nickel that is a porous porous substrate. A technique for applying a composite ink is disclosed.

JP 2000-77068 A JP 2010-108821 A

When a two-dimensional structure current collector is used as a base material, a nickel network that expands three-dimensionally like foamed nickel wraps nickel hydroxide and cannot be fixed by mechanical adhesion. That is, since only the chemical adhesion by the binder holds the contact between the active material and the substrate, the active material holding power is weak. This is because the organic polymer constituting the binder gradually oxidizes and deteriorates due to the charge / discharge cycle, and the base material and the composite material peel off due to a decrease in adhesion. As a result, there is a problem that electron conduction becomes difficult between the peeled active material and the base material, and the utilization rate is lowered.
Moreover, since the use of cobalt hydroxide was essential, there was a problem that cost reduction was difficult.

  An object of the present invention is to provide a primer composition for a positive electrode for a nickel-metal hydride secondary battery that has good output characteristics and cycle life, and that has no influence on the cycle characteristics.

  A primer composition according to an aspect of the present invention includes a two-dimensional structure current collector, and is used for a nickel metal hydride secondary battery positive electrode in which a main component of an active material supported on the two-dimensional structure current collector is not cobalt hydroxide. And containing foliar graphite particles (A) having an average particle diameter of 1 to 50 μm, carbon black (B) having an average particle diameter of 0.01 to 0.3 μm, and an aqueous resin (C). It is a feature.

  According to the present invention, it is possible to provide a primer composition for a positive electrode for a nickel-metal hydride secondary battery, which has good output characteristics and cycle life, and has suppressed influence on cycle characteristics.

One example of test results of charge / discharge cycle characteristics of a nickel-metal hydride battery using an electrode using the positive electrode primer composition of the present invention and an electrode composed of only a base material and a composite layer without using the primer composition. Show.

  The primer composition for a nickel metal hydride secondary battery positive electrode according to the present invention can form a base layer by being applied to a two-dimensional structure current collector. And the composite ink coated on the underlayer can constitute a composite layer. It is preferable to manufacture a nickel metal hydride secondary battery using the nickel metal hydride secondary battery positive electrode thus obtained. In the present invention, the two-dimensional structure current collector is also referred to as a foil-shaped current collector.

  The primer composition for positive electrode of the present invention comprises foliar graphite particles (A) having an average particle diameter of 1 to 50 μm, carbon black (B) having an average particle diameter of 0.01 to 0.3 μm, and an aqueous resin (C). It is preferable to contain.

  In general, the graphite particles have a leaf shape, a spherical shape, a soil shape, and the like. In the present invention, the graphite particles preferably have a leaf shape having a smooth particle surface from the viewpoint of the conductivity of the underlayer.

  The foliar graphite particles (A) preferably have an average particle size of 1 to 50 μm, more preferably an average particle size of 3 to 40 μm. In the present invention, the average particle diameter means a mixture of particles, water, and a dispersion using a dynamic light scattering particle size distribution meter (“Microtrac UPA” manufactured by Nikkiso Co., Ltd.). In the particle size distribution, it means the particle diameter (D50) that is 50% when the volume ratio of the particles is accumulated from the fine particle diameter.

  The foliar graphite particles (A) can be obtained, for example, by pulverizing massive natural graphite or by performing delamination along the cleavage plane of the intercalation compound of natural graphite. In the case of pulverization, for example, foliar graphite can be obtained by a dry pulverization method using a ball mill or the like.

  The foliar graphite particles (A) can also be obtained by a method utilizing the cleavage plane of the intercalation compound. Specifically, for example, an intercalation compound of graphite and sulfuric acid obtained by treating natural graphite with a mixed acid of sulfuric acid and nitric acid, or graphite and sulfuric acid obtained by electrically oxidizing natural graphite in sulfuric acid. The expanded graphite obtained by heating and expanding the intercalation compound or the like can be obtained by a method of peeling the cleavage plane of the crystal structure. In the expanded graphite, since the interlayer of the cleavage plane is spread, delamination is easily performed along the cleavage plane, and a smooth particle surface, that is, foliar graphite particles can be obtained.

  The foliar graphite particles (A) are manufactured by Chuetsu Graphite Co., Ltd. CX-3000, FBF, BF, CBR, SSC-3000, SSC-600, SSC-3, SSC, CX-600, CPF-8, CPF-3. CPB-6S, CPB-3, 96E, 96L, 96L-3, 90L-3, CPC, S-87, K-3, CF-80, CF-48, CF-32, CP-150, CP-100 CP, HF-80, HF-48, HF-32, SC-120, SC-80, SC-60, SC-32, manufactured by Fuji Graphite Industry Co., Ltd., UF-2, CBF-1, CBF- 3, CPF-3, 96L, COP, FAC-1, FAC-2, FGB, CSP-2, CF-2, SNO-20, SNO-10, SNO-5, SNE-20 manufactured by SEC Carbon Co., Ltd. , SNE-10, SNE-5, Japan CSSP, CSPE, CSP, CP, CB-150, CB-100, ACP, ACB-150, SP-10, SP-20, J-SP, SP-270, HOP, CMX, UP -5, UP-10, UP-20, Z-5F, CNP-7, CNP-15, CNP-35, Z-100, Z + 80, Z-25, Z-50, X- 10, X-20.

  Carbon black (B) plays the role which improves the electroconductivity of a base layer by entering into the clearance gap which the particle group of a foliar graphite particle (A) forms. The contribution of carbon black (B) to the improvement in conductivity is presumed that not all of carbon black (B) enters the gap, but the conductivity improves if a part of the carbon black (B) enters.

  Carbon black (B) is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reaction furnace, especially ketjen black using ethylene heavy oil as a raw material. Preference is given to channel black that has been rapidly cooled and deposited on the bottom of the steel, thermal black obtained by periodically repeating combustion and thermal decomposition using a gas as a raw material, and particularly acetylene black using an acetylene gas as a raw material. Ordinarily oxidized carbon black, hollow carbon and the like can also be used. Carbon black (B) can be used alone or in combination of two or more.

The average primary particle size of carbon black (B) is preferably 0.01 to 0.3 μm. Here, the average primary particle diameter is obtained by averaging the numerical values of 10 to 50 particles from an image appropriately enlarged 10,000 to 100,000 times using a transmission electron microscope (TEM). Furthermore, the larger the specific surface area of the carbon black (B), the more contact points between the carbon black particles, which is advantageous in reducing the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the adsorption amount of nitrogen is preferably 20 m ² / g or more and 1500 m ² / g or less, more preferably 50 m ² / g or more and 1500 m ² / g or less, and 100 m ² / g. More preferably, it is 1500 m ² / g or less. If carbon black having a specific surface area of less than 20 m ² / g is used, it may be difficult to obtain sufficient conductivity, and carbon black exceeding 1500 m ² / g is difficult to obtain in the market.

  Examples of commercially available carbon blacks include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Ltd., Furnace Black), Printex L, etc. (Degussa Co., Ltd., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205, etc. # 3030B, # 3230B, # 3350B, # 3400B, # 5400B etc. (Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900 , VulcanXC-72R, BlackPearls2000, etc. (Cabot Corporation, Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (Akzo Corporation) Manufactured), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black) and the like, but are not limited to these, and are used in combination of two or more. Also good.

  When the water-based resin (C) binds the foliar graphite particles (A) and the carbon black (B) and further forms a base layer, the base layer and the current collector, and the composite material layer and the base layer are in close contact with each other. Use for.

Examples of the water-based resin (C) include acrylic resin, polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, silicon resin, fluorine resin, carboxymethyl cellulose, and the like. Examples thereof include cellulose resins, synthetic rubbers such as styrene-butadiene rubber and fluorine rubber, conductive resins such as polyaniline and polyacetylene, and polymer compounds containing fluorine atoms such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene. Further, a modified product, a mixture, or a copolymer of these resins may be used. These water-based resins can be used alone or in combination.
Examples of the water-based resin include a water-soluble type, an emulsion type, and a hydrosol type, and can be appropriately selected.

  The ratio of using the foliar graphite particles (A) and the carbon black (B) is such that the ratio of the graphite particles (A) is 60 to 99 wt% in the total 100 wt% of the foliar graphite particles (A) and the carbon black (B). % Is preferable, and 65 to 95% by weight is more preferable. Moreover, 1 to 40 weight% is preferable and, as for the ratio of carbon black (B), 5-35 weight% is more preferable. When the graphite particles (A) and the carbon black (B) are appropriately present in the underlayer, the adhesion between the current collector and the composite layer can be further improved, and the conductivity can be further improved.

The underlayer is formed by manufacturing a primer composition containing foliar graphite particles (A), carbon black (B), and an aqueous resin (C), and then applying and drying the primer composition on a current collector. It is preferable.
The production of the primer composition will be described. First, the foliar graphite particles (A) are preferably used after being preliminarily mixed with a solvent and a dispersant to produce a dispersion. Carbon black (B) is also preferably used after being produced as a dispersion in the same manner as foliar graphite particles (A). And a primer composition can be obtained by mixing a foliar graphite particle (A) dispersion, a carbon black (B) dispersion, and an aqueous resin (C). The dispersant is preferably a cellulose resin, an acrylic resin, a styrene / acrylic resin, a polyester resin, a urethane resin, a surfactant, or the like.

  For the dispersion and mixing, a disperser or a mixer usually used for pigment dispersion or the like can be used. For example, mixers such as dispersers, homomixers, or planetary mixers; homogenizers such as “CLEARMIX” manufactured by M Technique Co., Ltd. or “FILMIX” manufactured by PRIMIX; paint conditioner (manufactured by Red Devil Co., Ltd.) , Ball mills, sand mills (Shinmaru Enterprises Co., Ltd. “Dino Mill” etc.), attritors, pearl mills (Eirich Co. Ltd. “DCP Mill” etc.), or media type dispersers such as Coball Mills; wet jet mills (Genus "Genus PY" manufactured by Co., Ltd., "Starburst" manufactured by Sugino Machine Co., Ltd., "Nanomizer" manufactured by Nanomizer Co., Ltd.), "Claire SS-5" manufactured by M Technique Co., Ltd., or Nara Machinery Co., Ltd. ) Medialess dispersers such as "MICROS" manufactured by; or Other roll mill of, but not limited thereto. Moreover, as the disperser, it is preferable to use a disperser that has been subjected to a metal contamination prevention treatment from the disperser.

  For example, when using a media-type disperser, a disperser in which the agitator and vessel are made of a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. Is preferably used. And as a medium, it is preferable to use ceramic beads, such as glass beads, zirconia beads, or alumina beads. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination.

  The primer composition can further contain a film forming aid, an antifoaming agent, a leveling agent, a dispersant, an antiseptic, a pH adjuster, a viscosity adjuster, and the like as required.

  What is necessary is just to adjust the viscosity of a primer composition suitably with the coating method, and it is preferable to set it as 10 mPa * s or more and 30,000 mPa * s or less.

  Examples of the coating of the underlayer include a die coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen coating method, and an electrostatic coating method. In addition, for drying, devices such as a blower dryer, a hot air dryer, an infrared heater, and a far infrared heater can be used, but are not particularly limited thereto. For example, it may be left to dry.

The thickness of the underlayer is preferably from 0.1 to 20 μm, more preferably from 0.5 to 10 μm, and more preferably from 1 to 8 μm. Basis weight of the base layer is preferably ^{0.0001~0.01g / cm 2, 0.0005~0.005g / cm} 2 is more preferable.

The foil-like current collector is made of a base material obtained by thinly striking a metal, has a smooth surface and end face, and does not have irregularities or hole processing due to a porous body structure. Therefore, the shape is greatly different from the punched plate having the porous body structure with the uneven nickel foam and the hole processing.
The material for the foil-like current collector is preferably nickel from the viewpoint of resistance to alkaline electrolyte. From the viewpoint of cost, it is preferable that the surface of the iron material is nickel-plated to prevent corrosion due to the electrolytic solution.
A flat foil with a smooth surface is used for the foil current collector in order to apply the primer composition. 10-70 micrometers is preferable and, as for the thickness of an electrical power collector, 15-60 micrometers is more preferable. When the total thickness of the foil-shaped current collector is 10 μm or more, the strength of the current collector itself is further improved, and the electrode is less likely to be damaged during coating and pressing. In addition, when the total thickness of the foil-like current collector is 70 μm or less, it is easy to make the current collector itself appropriate in strength, and it becomes easier to wind the current collector during coating.

  The thickness of the nickel plating is preferably 0.1 to 5 μm, and more preferably 0.5 to 4 μm. When the thickness of the nickel plating is 0.1 μm or more, corrosion due to the electrolytic solution hardly occurs. Further, when the thickness of the nickel plating is 5 μm or less, it is advantageous in terms of cost.

  A composite material layer can be formed by applying the composite material ink to the base layer formed on the current collector. The composite ink preferably contains an active material, a conductive material, and a polymer emulsion (D).

As an active material, a well-known thing can be used as a positive electrode active material for nickel-hydrogen secondary batteries. Examples thereof include nickel compounds such as nickel hydroxide and nickel oxyhydroxide. As the kind of nickel hydroxide, cobalt coated nickel hydroxide in which the surface of nickel hydroxide is coated with at least one of cobalt hydroxide and cobalt oxyhydroxide is more preferable. Moreover, what mixed and mixed nickel hydroxide, cobalt hydroxide, cobalt oxide, etc. can also be used.
In the present invention, the desired conductivity can be obtained without a cobalt coat, so that the cost is easily reduced. However, the use of cobalt-coated nickel hydroxide does not hinder the use with higher conductivity.

  The particle diameter of the active material is preferably 0.5 to 100 μm, more preferably 1 to 50 μm, and further preferably 3 to 40 μm.

  The proportion of the active material in the total nonvolatile content of the composite ink is preferably 80 to 98% by weight, more preferably 85 to 95% by weight.

  The polymer emulsion (D) is used for binding the active materials to each other and the active material with the base layer when forming the composite material layer.

  The acrylic emulsion is, for example, 1 to 5% by weight of a first monomer (d-1) containing a hydratable functional group and 20 to 60% by weight of a second monomer (d-2) containing an aromatic ring. And 35% to 79% by weight of a third monomer (d-3) not containing a hydratable functional group and an aromatic ring, and having a glass transition temperature of −40 to 20 ° C. synthesized by emulsion polymerization. An emulsion is preferred. By containing this emulsion in the composite material layer, the conductivity of the positive electrode is further improved, and the charge / discharge cycle characteristics are further improved.

  The monomer (d-1) containing a hydratable functional group is a monomer containing a hydrophilic functional group. For example, hydroxyethyl acrylate (homopolymer glass transition temperature Tg = −15 ° C., hereinafter the same), hydroxypropyl acrylate (Tg = −7 ° C.), hydroxybutyl acrylate (Tg = −80 ° C.), hydroxy methacrylate Hydroxy group-containing monomers such as ethyl (Tg = 55 ° C.), hydroxypropyl methacrylate (Tg = 26 ° C.), hydroxybutyl methacrylate (Tg = −40 ° C.), acrylamide (Tg = 153 ° C.), methacrylamide (Tg = 77 ° C), diacetone acrylamide (Tg = 77 ° C), N-isopropylacrylamide (Tg = 134 ° C), N-methylacrylamide (Tg = 130 ° C), N-methylmethacrylamide (Tg = 65 ° C), N, N-dimethylacrylamide (Tg = 119 ° C.), N-ethyl alcohol Rilamide (Tg = 100 ° C.), N, N-diethylacrylamide (Tg = 81 ° C.), N-butylacrylamide (Tg = 46 ° C.), hydroxyethylacrylamide (Tg = 98 ° C.), acryloylmorpholine (Tg = 145 ° C.) Amide group-containing monomers such as glycidyl methacrylate (Tg = 41 ° C.), glycidyl group-containing monomers such as glycidyl acrylate (Tg = 10 ° C.), and the like. Of these, amide group-containing monomers are particularly preferred.

  The amount of the monomer (d-1) containing a hydratable functional group is preferably 1 to 5% by weight, and more preferably 2 to 4% by weight. If it is 1% by weight or more, chemical stability is further improved due to the effect of hydration with water molecules. Moreover, when it becomes 5 weight% or less, the stability at the time of emulsion polymerization will increase more. That is, the fluidity of the emulsion increases and the emulsion tends to hardly aggregate.

  The aromatic ring-containing monomer (d-2) will be described. By using the aromatic ring-containing monomer (d-2), it is possible to reduce the amount of, for example, an alkyl acrylate ester that is easily hydrolyzed in an alkaline solution, so that the alkali resistance can be further improved. Furthermore, the adhesion to the current collector can be further improved by controlling the glass transition point of the emulsion within an appropriate range.

  The amount of the aromatic ring-containing monomer (d-2) used is preferably 20 to 60% by weight, more preferably 25 to 55% by weight, based on all monomers. When it is 20% by weight or more, the alkali resistance of the polymer is further improved. Moreover, if it is 60 weight% or less, the adhesiveness to a current collection material will improve more.

  Examples of the aromatic ring-containing monomer (d-2) include styrene (glass transition temperature of homopolymer Tg = 100 ° C., the same applies hereinafter), α-methylstyrene (Tg = 168 ° C.), benzyl methacrylate (Tg = 54 ° C.), and the like. Can be mentioned.

The other monomer (d-3) will be described.
The other monomer (d-3) in the present embodiment is a radical polymerizable monomer other than the monomer (d-1) containing a hydratable functional group and the aromatic ring-containing monomer (d-2). .

Other monomers include, for example, methyl methacrylate (Tg = 100 ° C.), ethyl methacrylate (Tg = 65 ° C.), butyl methacrylate (Tg = 20 ° C.), isobutyl methacrylate (Tg = 67 ° C.), methacrylic acid Methacrylic acid esters such as tertiary butyl (Tg = 107 ° C.), 2-ethylhexyl methacrylate (Tg = −10 ° C.), cyclohexyl methacrylate (Tg = 66 ° C.);
Methyl acrylate (homopolymer glass transition temperature Tg = −8 ° C., hereinafter the same), ethyl acrylate (Tg = −20 ° C.), butyl acrylate (Tg = −45 ° C.), 2-ethylhexyl acrylate, etc. Acrylic acid esters of Tg = −55 ° C .;
Etc.

  The other monomer (d-3) is preferably selected as appropriate so that the theoretical glass transition temperature Tg of the polymer is -40 to 20 ° C. The range of the theoretical glass transition temperature Tg of the polymer is more preferably −35 to 15 ° C.

The theoretical glass transition temperature Tg of the polymer of the emulsion in the present embodiment is derived from the following formula [I].
1 / Tg
= [(W1 / Tg1) + (W2 / Tg2) + ... + (Wn / Tgn)] / 100
... [I]
However,
W1:% by weight of monomer 1,
Tg1: glass transition temperature (K) of a homopolymer that can be formed only from monomer 1;
W2:% by weight of monomer 2,
Tg2: glass transition temperature (K) of a homopolymer that can be formed from monomer 2 only,
Wn:% by weight of monomer n,
Tgn: glass transition temperature (K) of a homopolymer that can be formed only from monomer n,
(W1 + W2 + ... + Wn = 100)

  In addition, when using what has a radically polymerizable unsaturated group as an emulsifier when superposing | polymerizing a radically polymerizable unsaturated monomer in an aqueous medium, identification of the structure of a radically polymerizable unsaturated monomer and a copolymer In the calculation of Tg, an emulsifier having a radically polymerizable unsaturated group is not included in the monomer.

In the present embodiment, it is important that the polymer emulsion (D) is copolymerized by emulsion polymerization. During copolymerization, it is preferable to use an emulsifier from the viewpoint of polymerization stability.
The emulsifier is preferably 0.1 part by weight or more and 5 parts by weight or less, and more preferably 1 part by weight or more and 3 parts by weight or less with respect to 100 parts by weight of the total amount of monomers used. When the amount of the emulsifier is 0.1 parts by weight or more, the polymerization stability is further improved. Moreover, when the amount of the emulsifier is 5 parts by weight or less, the alkali resistance of the secondary battery electrode is further improved.

  In the present embodiment, an anionic emulsifier or a nonionic emulsifier can be used alone or in combination as an emulsifier. The emulsifier may be a reactive emulsifier having a radical polymerizable functional group or a non-reactive emulsifier having no radical polymerizable functional group. Or both can be used together.

  Of the emulsifiers used in the present embodiment, the reactive emulsifier is an anionic or nonionic emulsifier having one or more unsaturated double bonds capable of radical polymerization in the molecule. For example, sulfosuccinic acid ester type (for example, Latemul S-120P, S-180A, Sanyo Kasei Co., Ltd. Eleminol JS-2, etc. manufactured by Kao Corporation), alkylphenol ether type (commercially available products, Dai-Ichi Kogyo Seiyaku Co., Ltd. Aqualon KH-10, RN-20, etc.).

Among the emulsifiers used in the present embodiment, as a non-reactive emulsifier,
Anionic non-reactive emulsifiers such as polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene alkyl ether sulfate,
Polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether; polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether and polyoxyethylene oleyl ether; And polyoxypolycyclic phenyl ethers such as oxyethylene distyrenated phenyl ether; and nonionic non-reactive emulsifiers such as polyoxyethylene sorbitan fatty acid ester.

  Specifically, as anionic non-reactive emulsifiers, hightenol NF-08 [repetition number of ethylene oxide units (hereinafter referred to as “number of EO units”): 8], NF-17 (number of EO units: 17) [Above, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], Eleminol CLS-20 (EO unit number: 10), Eleminol ES-12 (EO unit number: 6), ES-30 (EO unit number: 15), ES- 70 (number of EO units: 35) [Sanyo Chemical Industries, Ltd.] and the like.

Nonionic non-reactive emulsifiers include Emulgen 1108 (EO unit number: 8), 1118S-70 (EO unit number: 18), 1135S-70 (EO unit number: 35), 1150S-70 (EO unit number: 50). ) [Above, manufactured by Kao Corporation].
Said non-reactive emulsifier may be used independently and can also be used together multiple types.
In addition, a conventionally well-known thing can be used as a reactive emulsifier among emulsifiers.

  Examples of the radical polymerization initiator that can be used in the present embodiment include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate.

  The amount of the polymerization initiator used is preferably 0.1 to 1 part by weight and more preferably 0.2 to 0.8 part by weight based on 100 parts by weight of the total amount of monomers used for emulsion polymerization. When the amount is 0.1 parts by weight or more, the polymerization stability is further improved. Moreover, when it becomes 1 weight part or less, water resistance will improve more.

  It is also preferable to use a redox initiator in which a peroxide-based initiator and a reducing agent are combined. As the redox initiator, a combination of a peroxide-based initiator and a reducing agent is preferable. Examples of the peroxide initiator include perbutyl H (tertiary butyl hydroperoxide), perbutyl O (tertiary butyl peroxy-2-ethylhexanoate), cumene hydroperoxide, and p-menthane hydroperoxide. . Examples of the reducing agent include Erbit N (sodium ascorbate), L-ascorbic acid (vitamin C), sodium sulfite, sodium hydrogen sulfite, sodium pyrosulfite (SMBS), and sodium hyposulfite (hydrosulfite).

  It is preferable that the composite ink further contains a conductive material. Examples thereof include nickel powder, copper powder, cobalt oxide, cobalt hydroxide, and carbon. Examples of carbon include acetylene black, ketjen black, furnace black, carbon fiber, and fullerenes. Acetylene black and furnace black are preferred. Since the particle diameter of the conductive material is large, it is preferable to use the conductive material by dispersing it in the range of 0.1 to 50 μm in advance using water or a dispersion resin. As the dispersion resin, an acrylic water-soluble resin, a styrene / acrylic water-soluble resin, a water-soluble polyester resin, an aqueous urethane resin, and the like are preferable.

  The compound ink is preferably blended in an amount of 0.05 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the active material. If the amount is less than 0.05 parts by weight, the binding force between the active material and the undercoat layer is reduced, and as a result, the contact between the active material and the substrate is not maintained, and the utilization factor of the positive electrode may be reduced. Moreover, when it exceeds 20 weight part, the ratio of the active material which occupies for material ink will fall, and the energy density of an electrode will fall easily. Furthermore, the electrical resistance of the electrode may be increased by increasing the proportion of the polymer that is difficult to conduct electricity.

  A film forming aid, an antifoaming agent, a leveling agent, a dispersant, a preservative, a pH adjusting agent, a viscosity adjusting agent, and the like can be further added to the composite ink as necessary.

  The viscosity of the composite ink can be appropriately selected depending on the coating method, but is preferably 100 mPa · s or more and 30,000 mPa · s or less.

The composite material layer can be formed by applying and drying a composite ink on the base layer. 1-500 micrometers is preferable and, as for the thickness of a compound-material layer, 10-300 micrometers is more preferable. Basis weight of the mixture layer is preferably ^{0.001~0.1g / cm 2, 0.005~0.05g / cm} 2 is more preferable.

  In the nickel metal hydride secondary battery positive electrode, the electrode layer may be pressed by a lithographic press, a calender roll, or the like after a composite layer is formed on the base layer. Thereby, the adhesiveness of a base layer and a compound material layer improves more.

(Disperser / Mixer)
For mixing the active material and the polymer emulsion (D) when producing the composite ink, the same disperser and mixer as in the production of the primer composition can be used.

  The nickel metal hydride secondary battery preferably includes a nickel metal hydride secondary battery positive electrode, a negative electrode, an electrolytic solution of the present invention, and a separator provided as necessary. The shape of the battery can be various shapes according to the purpose of use, such as a paper type, a cylindrical type, a coin type, a button type, or a laminated type.

  Examples of the electrolytic solution include an aqueous potassium hydroxide solution and an aqueous potassium hydroxide solution obtained by adding sodium hydroxide or lithium hydroxide.

Examples of the separator include, but are not limited to, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyamide nonwoven fabric, and those subjected to hydrophilic treatment.
The nickel metal hydride secondary battery provided with the nickel metal hydride secondary battery positive electrode of the present invention can be preferably used for applications such as substations, buses, trucks, and trains.

  EXAMPLES The present invention will be described more specifically with reference to the following examples. However, the following examples do not limit the scope of rights of the present invention. In the examples and comparative examples, “parts” represents “parts by weight”.

(Graphite particle dispersion (1))
10 parts of graphite flake CPB-3 (manufactured by Chuetsu Graphite Co., Ltd., particle diameter 18 μm) as graphite particles (A), and water-soluble acrylic resin Jonkrill 96J (manufactured by BASF Corp., nonvolatile content 34%) as a dispersant 5.9 parts and 84.1 parts of water were mixed in a mixer and dispersed for 1 hour using a homomixer to obtain a graphite particle dispersion (1).

(Carbon black dispersion)
10 parts of acetylene black (Denka Black HS-100) as carbon black (B), 5.9 parts of water-soluble acrylic resin Jonkrill 96J and 84.1 parts of water as a dispersant are mixed in a mixer, and further mixed with a sand mill. And dispersion for 5 hours to obtain a carbon black (a) dispersion. In addition, when the particle diameter was measured using Microtrac UPA, the particle diameter (D50) was 0.3 μm.

<Primer composition production example 1>
1. carboxymethylcellulose, a water-soluble cellulose resin, as a binder with respect to 90 parts of a graphite particle dispersion (1) containing 10% by weight of graphite particles and 10 parts of a carbon black (a) dispersion containing 10% by weight of carbon black. 5 parts and 50 parts of water were mixed to obtain a primer composition.

<Primer Composition Production Examples 2 to 10>
As shown in Table 1, a primer composition was obtained in the same manner as in Production Example 1 except that the type and amount of raw materials were changed.

The contents of the abbreviations in Table 1 are described below.
CPB-3: foliated graphite (manufactured by Chuetsu Graphite Co., Ltd., particle size 18 μm)
-FBF: foliated graphite (manufactured by Chuetsu Graphite Co., Ltd., particle size 8 μm)
CNP-15: foliated graphite (manufactured by Ito Graphite Co., Ltd., average particle size 15 μm)
Z-100: foliated graphite (manufactured by Ito Graphite Co., Ltd., average particle size 60 μm)
SG-BH8: Spherical graphite (manufactured by Ito Graphite Co., Ltd., average particle size 8 μm)
Carbon black (a): acetylene black, Denka black HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.)
Carbon black (f): Furnace black, Super-PLi (manufactured by TIMCAL)
・ CMC: Carboxymethylcellulose (manufactured by Daicel Finechem Co., Ltd.)
W-168: acrylic emulsion resin (manufactured by Toyochem Co., Ltd.)

<Polymer emulsion synthesis example 1>
3.0 parts of 2-hydroxyethyl acrylate as the hydratable functional group-containing monomer (d-1), 50 parts of styrene as the second monomer (d-2) containing an aromatic ring, and acrylic as the monomer (d-3) A mixture of 47 parts of 2-ethylhexyl acid, 1.4 parts of Eleminol CLS-20 (Reactive emulsifier manufactured by Sanyo Chemical Industries Co., Ltd.) and 53.1 parts of ion-exchanged water as an emulsifier is emulsified with a blade, and monomer A pre-emulsion was created and placed in a dropping tank.

  A reaction vessel is a 2 L four-necked flask equipped with a reflux condenser, a stirrer, a thermometer, a nitrogen inlet tube, and a raw material inlet, and 89.4 parts of ion-exchanged water is introduced into the reaction vessel while introducing nitrogen. The liquid temperature was warmed to 60 ° C. while stirring. Next, 0.1 part of CLS-20 as an emulsifier was added to the reaction vessel, and the monomer pre-emulsion was continuously dropped from a dropping tank over 5 hours, and 0.6 part of ammonium persulfate was used at 70 ° C. For 5 hours.

After completion of dropping, the mixture was kept at 70 ° C. for 3 hours for aging. Thereafter, cooling was started, the temperature was lowered to 50 ° C., and the mixture was filtered through a 180 mesh polyester filter cloth to obtain a polymer emulsion containing a binder resin composition. There was no aggregate remaining on the filter cloth, and the polymerization stability was good.
A part of the emulsion after filtration was weighed, dried at 150 ° C. for 20 minutes, and the nonvolatile content concentration was determined to be 40.0% by weight. The emulsion had a pH of 2.0 and a viscosity of 10 mPa · s.
Using a Microtrac UPA (Leeds & Northrup), the D50 particle size at pH 2.0 was measured by a dynamic light scattering method, which was 190 nm.
The theoretical glass transition temperature Tg of the polymer determined from the monomer is 6 ° C.

<Polymer emulsion synthesis examples 2 to 8>
As shown in Table 2, a polymer emulsion was obtained in the same manner as in Synthesis Example 1 except that the type and amount of the raw material were changed.

Hereinafter, the contents of the abbreviations in Table 2 are described.
2HEMA: 2-hydroxyethyl acrylate GMA: glycidyl methacrylate DEAA: N, N-diethylacrylamide St: styrene BzMA: benzyl methacrylate 2EHA: 2-ethylhexyl acrylate MMA: methyl methacrylate

<Composite ink>
45 parts of nickel hydroxide CZ (cobalt coated product, manufactured by Tanaka Chemical Research Co., Ltd.) as a positive electrode active material, 50 parts of carbon black (a) dispersion as a conductive material, and polymer emulsion obtained in Synthesis Example 1 as a binder 12.5 parts and 10 parts of ion-exchanged water were mixed to prepare a positive electrode mixture ink. The viscosity at that time was 4000 mPa · s.

[Example 1]
The primer composition obtained in Production Example 1 was applied onto a 30 μm thick nickel-plated steel plate as a current collector using a doctor blade, and then heated and dried in a reduced pressure atmosphere to obtain a 5 μm thick underlayer. It was. The basis weight of the underlayer was 0.0015 g / cm ² . Furthermore, the nickel hydride secondary battery positive electrode mixture ink was applied onto the underlayer and then dried by heating. Furthermore, the press process was performed with the roll press machine, and the positive electrode with a thickness of 85 micrometers was obtained. The basis weight of the composite material layer was 0.015 g / cm ² .

<Preparation of negative electrode for nickel metal hydride secondary battery>
As a negative electrode active material, 100 parts of a hydrogen storage alloy, 50 parts of carbon black (a) dispersion, and 12.5 parts of the binder resin composition obtained in Synthesis Example 1 were kneaded with a disper to produce a composite ink for a negative electrode. . The viscosity at that time was 6000 mPa · s. After coating the ink mixture on a nickel-plated steel plate, which is a current collector, using a doctor blade, drying at 100 ° C, adjusting the thickness with a roll press, and cutting the negative electrode to a predetermined size Produced.

(Battery assembly)
The positive electrode prepared earlier was punched to a diameter of 15.9 mm, the negative electrode was punched to a diameter of 16.1 mm, a hydrophilized polypropylene as a separator was punched to 23 mm, the mixture layers were opposed to each other through the separator, and an electrolyte solution (potassium hydroxide) 4.8 normal + 1.2 standard sodium hydroxide) was satisfied, and a two-pole sealed metal cell was assembled. After the cell assembly, a predetermined battery characteristic evaluation was performed.

(Charge / discharge cycle characteristics test)
About the test battery produced as mentioned above, the charging / discharging cycle test was done and the transition of the charging / discharging characteristic by cycling progress was measured. In this charge / discharge cycle test, the activation charge / discharge was performed first, and then the 3C-3C charge / discharge cycle was performed. The test conditions in activation charge / discharge and 3C-3C charge / discharge are as follows.

(Activated charge / discharge)
Charging: Constant current 0.2C (charging to 100% of rated capacity) 5-cycle discharging: Constant current 0.2C (discharging final voltage 0.8V) 5-cycle charging: Constant current 0.5C (up to 100% of rated charging capacity) Charge) 5-cycle discharge: constant current 0.5 C (discharge end voltage 0.8 V) 5-cycle charge: constant current 1.0 C (charge to 100% of rated charge capacity) 30-cycle discharge: constant current 1.0 C (discharge end) Voltage 0.8V) 30 cycles (charge / discharge)
Charging: Constant current 3.0C (charge to 100% of rated charge capacity)
Discharge: constant current 3.0C (discharge end voltage 1.0V)

The charge / discharge cycle characteristic test was evaluated based on the utilization rate after 2000 cycles of charge / discharge. FIG. 1 shows the results of a charge / discharge cycle characteristic test for Example 1 and Comparative Example 1 as an example. The utilization rate is expressed by the following formula.
Utilization rate (%) = discharge capacity (mAh) / theoretical battery capacity (mAh) × 100
80 to 100%: very good (◎)
60 to 80%: Good (◯)
50-60%: relatively good (△)
-50%: Defect (x)

(Rapid charge / discharge characteristics test)
In the rapid charge / discharge characteristic test, activation charge / discharge was first performed, and then a 10C-10C charge / discharge cycle was performed. The test conditions in activation charge / discharge and 10C-10C high-speed charge / discharge are as follows.

(Activated charge / discharge)
Charging: Constant current 0.2C (charging up to 100% of the rated charging capacity) 5-cycle discharging: Constant current 0.2C (discharging end voltage 0.8V) 5-cycle charging: Constant current 0.5C (100% of the rated charging capacity) 5 cycle discharge: constant current 0.5C (discharge end voltage 0.8V) 5 cycle charge: constant current 1.0C (charge to 100% of rated charge capacity) 30 cycle discharge: constant current 1.0C (discharge) 30-cycle charge: constant current 3.0C (charge to 100% of rated charge capacity) 50-cycle discharge: constant current 3.0C (discharge final voltage 0.8V) 50 cycles (charge / discharge)
Charging: Constant current 10.0C (charging to 100% of rated charging capacity)
Charging: Constant current 10.0C (end-of-discharge voltage 1.0V)

The high-speed charge / discharge characteristic test was evaluated based on the utilization rate after 500 cycles of charge / discharge.
80 to 100%: very good (◎)
60 to 80%: Good (◯)
50-60%: relatively good (△)
-50%: Defect (x)

[Examples 2 to 13], [Comparative Examples 1 to 5]
As shown in Table 3, a nickel-hydrogen secondary battery positive electrode was obtained in the same manner as in Example 1 except that the combination of the primer composition production example and the polymer emulsion synthesis example for the positive electrode was changed. Evaluated.

[Example 14]
45 parts of nickel hydroxide ZD (non-cobalt coated product, manufactured by Tanaka Chemical Research Co., Ltd.) as positive electrode active material, 50 parts of carbon black (a) dispersion as conductive material, polymer obtained in Synthesis Example 1 as binder 12.5 parts of emulsion and 10 parts of ion-exchanged water were mixed to prepare a positive electrode mixture ink. The viscosity at that time was 4000 mPa · s. Thereafter, in the same manner as in Example 1, a nickel metal hydride secondary battery positive electrode was obtained and evaluated in the same manner as in Example 1.

  As shown in Table 3 and FIG. 1, when the nickel-metal hydride secondary battery positive electrode of the present invention is used, the surface of the base layer formed is smooth, so that the contact resistance with the composite layer decreases, and the battery charge is excellent. It is considered that the discharge storage characteristics can be obtained.

  In particular, in Examples 1 to 3, since the electrolytic solution resistance of the polymer emulsion is good, the electrolytic solution resistance of the formed electrode is improved, and the charge / discharge cycle characteristics and the high-speed charge / discharge characteristics are considered to be very excellent. .

  Furthermore, in Example 14, even when nickel hydroxide ZD, which is a non-cobalt-coated product, is used, it is considered that charge / discharge cycle characteristics and high-speed charge / discharge characteristics are good due to the effect of reducing the contact resistance of the underlayer.

  On the other hand, in Comparative Example 1, since the nickel hydride secondary battery positive electrode was formed without using the primer composition, the positive electrode had low conductivity, and sufficient charge / discharge cycle characteristics and high-speed charge / discharge were not obtained. It is done.

  Moreover, in Comparative Example 2, since the particle size of the foliar graphite particles used is large, the graphite particles cannot be sufficiently dispersed, the surface smoothness of the resulting underlayer cannot be maintained, and the adhesion is deteriorated. It is considered that sufficient battery charge / discharge characteristics and high-speed charge / discharge cannot be obtained.

  In addition, as shown in Comparative Example 3, when graphite particles other than foliar graphite are used, the smoothness of the surface of the underlying layer to be formed cannot be maintained, and the adhesion is deteriorated, resulting in sufficient battery charge / discharge characteristics. In addition, it is considered that high-speed charge / discharge characteristics cannot be obtained.

  Moreover, in Comparative Example 4, since the primer composition was prepared without using graphite particles, the surface of the obtained underlayer was rough, so that the electrical resistance with the composite layer is considered to increase.

  Furthermore, in Comparative Example 5, since the primer composition was prepared without using carbon black, voids were generated between the graphite particles of the obtained underlayer, the adhesion was low, and the conductive network was not sufficient. As a result, it is considered that battery charge / discharge characteristics and high-speed charge / discharge are reduced.

Claims (10)

A primer composition for a nickel metal hydride secondary battery positive electrode provided with a two-dimensional structure current collector,
Foliated graphite particles (A) having an average particle diameter of 1 to 50 μm,
Carbon black (B) having an average particle diameter of 0.01 to 0.3 μm;
A primer composition comprising an aqueous resin (C).   Among the total 100% by weight of foliar graphite particles (A) and carbon black (B), the proportion of foliar graphite particles (A) is 60 to 99% by weight and the proportion of carbon black (B) is 1 to 40% by weight. The primer composition according to claim 1. An underlayer composed of the primer composition according to claim 1 or 2,
A two-dimensional structure current collector made of a nickel-plated steel plate and having the underlayer formed thereon;
A nickel-metal hydride secondary battery positive electrode comprising: a composite material layer formed on the underlayer.   The nickel-hydrogen secondary battery positive electrode according to claim 3, wherein a thickness of the underlayer is 0.1 to 20 μm. The composite layer is
A polymer emulsion (D) obtained by emulsion polymerization;
Active material,
The nickel metal hydride secondary battery positive electrode according to claim 3, comprising a conductive material.   The nickel-hydrogen secondary battery positive electrode according to claim 5, wherein the active material is nickel hydroxide.   The nickel-hydride secondary battery positive electrode according to claim 6, wherein the surface of the nickel hydroxide is coated with at least one of cobalt oxyhydroxide and cobalt hydroxide.   The nickel-hydrogen secondary battery positive electrode according to claim 5, wherein the polymer emulsion (D) is an acrylic polymer emulsion having a glass transition temperature of -40 to 20 ° C. The polymer emulsion (D)
1 to 5% by weight of a first monomer (d-1) containing a hydratable functional group;
20 to 60% by weight of the second monomer (d-2) containing an aromatic ring;
9. The monomer group containing 35% to 79% by weight of a third monomer (d-3) that does not contain a hydratable functional group and an aromatic ring, and is obtained by emulsion polymerization. Nickel metal hydride secondary battery positive electrode. Forming a primer layer by coating the primer composition on the two-dimensional structure current collector;
A step of forming a composite material layer by coating a polymer emulsion (D) obtained by emulsion polymerization, an active material, and a composite ink containing a conductive material on the base layer,
In the primer composition,
Foliated graphite particles (A) having an average particle diameter of 1 to 50 μm,
Carbon black (B) having an average particle diameter of 0.01 to 0.3 μm;
An aqueous resin (C),
The basis weight of the base layer is 0.0001 to 0.01 g / cm ² ,
A method for producing a positive electrode for a nickel metal hydride battery, characterized in that the basis weight of the composite layer is 0.001 to 0.1 g / cm ² .

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