JP2013069671A - Composition for forming nickel hydrogen secondary battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for forming a nickel hydrogen secondary battery electrode which improves battery performance by having superior dispersibility of a raw material compounded in the composition and furthermore can form a mixture layer having high flexibility.SOLUTION: A composition for forming a nickel hydrogen secondary battery electrode contains: a nitrogen-containing acrylic emulsion binder (C); an ampholytic resin type dispersant (D) formed by neutralizing at least a part of a carboxyl group in a copolymer prepared by copolymerizing the following monomers; and an aqueous liquid medium (E). An ethylenically unsaturated monomer having an aromatic ring (d1): 5 to 70 wt.%. An ethylenically unsaturated monomer having the carboxyl group (d2): 15 to 60 wt.%. An ethylenically unsaturated monomer having an amino group (d3): 1 to 80 wt.%. A different monomer from monomers (d1) to (d3): 0 to 79 wt.%.(where the total amount of the monomers (d1) to (d3) is 100 wt.%).

Description

  The present invention relates to a composition for forming a nickel metal hydride secondary battery electrode.

  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. In addition, in a large-sized secondary battery for use in automobiles or the like, it is desired to realize a large-sized secondary battery instead of a conventional lead storage battery.

  In order to meet such demands, development of secondary batteries such as lithium ion secondary batteries and nickel metal hydride secondary batteries, for example, development of composite inks used for forming electrodes has been actively conducted.

  The composite ink is required to have an appropriate fluidity so that it can be applied to the surface of the metal foil serving as a current collector. Furthermore, in order to form a composite material layer whose surface is as flat as possible and has a uniform thickness, the composite ink is required to have an appropriate viscosity.

  After the formation of the composite material layer formed from the composite material ink, the metal foil as the base material is cut into pieces of a desired size and shape or punched out in order to adjust the shape of the electrode. Therefore, the composite material layer is required to have hardness that does not damage and softness that does not crack or peel off by cutting or punching.

In preparation of the composite ink, it is important to uniformly disperse the active material and the conductive auxiliary agent in order to obtain good battery characteristics. For example, a nickel-metal hydride battery positive electrode generally uses an aqueous slurry in which a cobalt compound is added as a conductive additive. It is considered that the cobalt compound is easily dispersed uniformly in the mixture ink by stirring or the like. Further, it is known that the cobalt compound is once eluted in the alkaline electrolyte and then reprecipitated on the surface of nickel hydroxide by a charging reaction to form a dense conductive network.
On the other hand, when carbon is added to a water-based composite ink as a conductive additive, it is considered that a network formation by elution / reprecipitation such as a cobalt compound cannot be expected. Furthermore, since hydrophobic carbon is difficult to disperse uniformly in water, it needs to be devised. For example, as in Patent Document 1, a device such as the use of a carbon black dispersion using a cellulose-based water-soluble resin as a dispersant for a composite ink has been devised.

  The dispersant is added to the composite ink as an aid for uniformly dispersing the active material and the conductive aid in the medium. When the dispersant functions, a part of the dispersant is adsorbed on the active material and the conductive additive, but the non-adsorbed is dissolved in the aqueous liquid medium. When the dispersing agent is uniformly dispersed among the active material, the conductive auxiliary agent, and the solvent, even distribution of the active material and the conductive auxiliary agent can be realized even when the composite material layer is formed. When the composite ink contains a binder, the dispersant that does not contribute to the dispersion is taken into the binder forming the composite layer, but the distribution of the dispersant is biased due to the poor compatibility between the dispersant and the binder. When it occurs, when the composite material layer is formed, the active material, the conductive auxiliary agent, and the binder are easily dispersed. At this time, the formation of the conductive network becomes insufficient, and the utilization factor is likely to decrease, and electrode deterioration is likely to occur. In order to produce a uniform composite, the compatibility between the dispersant and the binder is important.

Japanese Patent No. 3856074

  However, in Patent Document 1, since a cellulose-based water-soluble resin is used, the nickel-hydrogen secondary battery electrode that is alkaline is resistant to the electrolytic solution, but is blended as a binder with an active material and a conductive auxiliary agent. The compatibility with the binder was poor. Therefore, there has been a problem that the battery performance is lowered due to insufficient dispersibility between the raw materials (active material, conductive additive and binder) blended in the composition.

  It is an object of the present invention to provide a composition for forming a nickel-hydrogen secondary battery electrode capable of forming a composite material layer with improved battery performance and higher flexibility due to excellent dispersibility of raw materials blended in the composition. To do.

The present invention is an amphoteric resin type dispersion obtained by neutralizing at least a part of a carboxyl group in a copolymer obtained by copolymerizing a nitrogen-containing acrylic emulsion type binder (C) and the following monomer with a basic compound. It is a composition for nickel-hydrogen secondary battery electrode formation containing an agent (D) and an aqueous liquid medium (E).
Ethylenically unsaturated monomer having an aromatic ring (d1): 5 to 70% by weight
Ethylenically unsaturated monomer having a carboxyl group (d2): 15 to 60% by weight
Ethylenically unsaturated monomer having an amino group (d3): 1 to 80% by weight
Other monomers (d4) other than (d1) to (d3): 0 to 79% by weight
(However, the total of (d1) to (d4) is 100% by weight)

In the present invention, the use of the amphoteric resin type dispersant having a specific monomer composition improves the dispersibility of the carbon material which is an active material or a conductive aid. Furthermore, by using a nitrogen-containing emulsion type binder, compatibility with the amphoteric resin type dispersant was good, and battery performance could be improved. And the composite material layer formed from the composite material ink containing an amphoteric resin type dispersing agent and a nitrogen-containing emulsion type binder is excellent in flexibility.
Next, when the composition for forming a nickel metal hydride secondary battery electrode of the present invention was blended with the primer composition for forming the base layer of the electrode, the battery performance was improved by improving the dispersibility of the conductive auxiliary agent, Furthermore, the surprising effect that the flexibility of the underlayer was improved was obtained.

  According to the present invention, the battery performance can be improved by forming the active material and the conductive auxiliary agent in the primer composition as well as the composite ink, thereby improving the battery performance and forming a more flexible composite layer or base layer. The composition for forming a nickel metal hydride secondary battery electrode could be provided.

The electrode for a secondary battery can be obtained by various methods.
For example, on the surface of a current collector such as a metal foil,
(1) an ink-like composition containing an active material and a liquid medium (hereinafter referred to as composite ink),
(2) a mixed ink containing an active material, a conductive additive and a liquid medium;
(3) a mixed ink containing an active material, a binder and a liquid medium;
(4) A mixed ink containing an active material, a conductive additive, a binder, and a liquid medium,
It can be used to form a composite layer and obtain an electrode.

  Alternatively, on the surface of the current collector of the metal foil, a primer composition containing a conductive additive and a liquid medium is used to form a base layer, and the above-described mixed inks (1) to (1) to ( An electrode can also be obtained by forming a composite layer using 4) or other composite inks.

In any case, the battery performance is affected by the dispersion state of the active material and the conductive additive and the compatibility between the dispersant and the binder.
The amphoteric resin type dispersing agent (D) relaxes the aggregation of the active material and functions as a dispersing agent for the carbon material that is a conductive additive.
Therefore, the composition for forming a nickel metal hydride secondary battery electrode of the present invention can be used as a mixed ink that requires an active material or a primer composition that does not require an active material.
First, the amphoteric resin type dispersant (D) in the present invention will be described.
The amphoteric resin type dispersant (D) in the present invention comprises an ethylenically unsaturated monomer (d1) having an aromatic ring, an ethylenically unsaturated monomer (d2) having a carboxyl group, and an ethylene having an amino group. Is obtained by neutralizing at least a part of the carboxyl group in the copolymer containing the basic unsaturated monomer (d3) as an essential component with a basic compound.
The amphoteric resin dispersant (D) of the present invention is excellent in dispersibility of the carbon material which is an active material and a conductive additive, and further has good compatibility with the nitrogen-containing emulsion binder, thereby improving battery performance. it can.

First, the ethylenically unsaturated monomer (d1) having an aromatic ring will be described.
Examples of the ethylenically unsaturated monomer (d1) having an aromatic ring used in the present invention include styrene, α-methylstyrene, and benzyl (meth) acrylate.

Next, the ethylenically unsaturated compound (d2) having a carboxyl group will be described.
The monomer (d2) used in the present invention is, as a carboxyl group-containing unsaturated compound, maleic acid, fumaric acid, itaconic acid, citraconic acid, or an alkyl or alkenyl monoester thereof, phthalic acid β- (meth) Acryloxyethyl monoester, isophthalic acid β- (meth) acryloxyethyl monoester, terephthalic acid β- (meth) acryloxyethyl monoester, succinic acid β- (meth) acryloxyethyl monoester, acrylic acid, methacrylic acid And crotonic acid, cinnamic acid, and the like. In particular, methacrylic acid and acrylic acid are preferable.

Next, the ethylenically unsaturated monomer (d3) having an amino group will be described.
The ethylenically unsaturated monomer (d3) having an amino group used in the present invention includes dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, methylethylaminoethyl (meth) acrylate, dimethylaminostyrene, diethylamino Examples include styrene.

Next, the monomer (d4) other than (d1) to (d3) will be described.
Examples of (meth) acrylate compounds include alkyl (meth) acrylates and alkylene glycol (meth) acrylates.

  More specifically, examples of the alkyl-based (meth) acrylate include alkyl (meth) acrylate having 1 to 22 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth) acrylate. ) When there is an acrylate and the purpose is to adjust the polarity, an alkyl group-containing acrylate having an alkyl group having 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, or a corresponding methacrylate is preferable.

Examples of the alkylene glycol (meth) acrylate include diethylene glycol mono (meth) acrylate and polyethylene glycol mono (meth) acrylate, which are monoacrylates having a hydroxyl group at the terminal and having a polyoxyalkylene chain, or corresponding monometas. Acrylate, etc.
Methoxyethylene glycol (meth) acrylate, methoxydiethylene glycol (meth) acrylate, etc., monoacrylate having an alkoxy group at the terminal and having a polyoxyalkylene chain or the corresponding monomethacrylate,
There are polyoxyalkylene-based acrylates having a phenoxy or aryloxy group at the terminal, such as phenoxyethylene glycol (meth) acrylate, or corresponding methacrylates.

  Examples of hydroxyl-containing unsaturated compounds other than the above include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, glycerol mono (meth) acrylate, 4-hydroxyvinylbenzene And so on.

As nitrogen-containing unsaturated compounds, monoalkylol (meth) acrylamides such as (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl- (meth) acrylamide,
Examples thereof include acrylamide-type unsaturated compounds such as N, N-di (methylol) acrylamide, N-methylol-N-methoxymethyl (meth) acrylamide, and dialalkylol (meth) acrylamide such as N, N-di (methoxymethyl) acrylamide. .

Furthermore, as other unsaturated compounds, perfluoromethylmethyl (meth) acrylate, perfluoroethylmethyl (meth) acrylate, 2-perfluorobutylethyl (meth) acrylate, 2-perfluorohexylethyl (meth) acrylate, etc. Perfluoroalkyl alkyl (meth) acrylates having a C 1-20 perfluoroalkyl group;
Perfluoroalkyl such as perfluorobutylethylene, perfluorohexylethylene, perfluorooctylethylene, perfluorodecylethylene, and perfluoroalkyl group-containing vinyl monomers such as alkylene, vinyltrichlorosilane, vinyltris (βmethoxyethoxy) silane, vinyl Examples thereof include silanol group-containing vinyl compounds such as triethoxysilane and γ- (meth) acryloxypropyltrimethoxysilane and derivatives thereof, and a plurality of them can be used from these groups.

  Examples of the fatty acid vinyl compound include vinyl acetate, vinyl butyrate, vinyl propionate, vinyl hexanoate, vinyl caprylate, vinyl laurate, vinyl palmitate, and vinyl stearate.

  Examples of the alkyl vinyl ether compound include butyl vinyl ether and ethyl vinyl ether.

  Examples of the α-olefin compound include 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and the like.

  Examples of vinyl compounds include allyl compounds such as allyl acetate, allyl alcohol, allylbenzene, and allyl cyanide, vinyl cyanide, vinylcyclohexane, vinyl methyl ketone, styrene, α-methylstyrene, 2-methylstyrene, and chlorostyrene. Can be mentioned.

  Examples of the ethynyl compound include acetylene, ethynylbenzene, ethynyltoluene, 1-ethynyl-1-cyclohexanol and the like. These can be used alone or in combination of two or more.

The ratio of the monomers constituting the copolymer in the amphoteric resin type dispersant (D) used in the present invention is such that the total of the monomers (d1) to (d4) is 100% by weight,
5 to 70% by weight of ethylenically unsaturated monomer (d1) having an aromatic ring,
15 to 60% by weight of ethylenically unsaturated monomer (d2) having a carboxyl group,
1 to 80% by weight of ethylenically unsaturated monomer (d3) having an amino group,
The other monomer (d4) other than (d1) to (d3) is 0 to 79% by weight.
Preferably, (d1): 20 to 70% by weight, (d2): 15 to 45% by weight, (d3): 1 to 70% by weight, (d4): 0 to 50% by weight.
More preferably, they are (d1): 30-70 weight%, (d2): 15-35 weight%, (d3): 1-40 weight%, (d4): 0-40 weight%.

  An active ring (A) or a carbon material, which will be described later, includes an aromatic ring derived from an ethylenically unsaturated monomer (d1) having an aromatic ring and an amino group derived from an ethylenically unsaturated monomer (d3) having an amino group. Presumed to be the main adsorption site to (B).

The ethylenically unsaturated monomer (d2) having a carboxyl group has a function of dissolving or dispersing a neutralized copolymer in an aqueous liquid medium.
Then, the active material (A) or the carbon material (B) is adsorbed via an aromatic ring or an amino group, neutralized, and the charge repulsion of the ionized carboxyl group, the active material (A) or the carbon material. It is considered that the dispersion state of (B) in the aqueous liquid medium can be kept stable.

The molecular weight of the copolymer obtained by copolymerizing the monomers (d1) to (d4) is not particularly limited, but the viscosity of the amphoteric resin dispersant (D) in a 20% aqueous solution of a nonvolatile content is preferably 5 to 100. 000 mPa · s, more preferably 10 to 50,000 mPa · s. When the viscosity of the amphoteric resin dispersant (D) is lower than the predetermined range and the molecular weight of the amphoteric resin dispersant (D) is higher than the predetermined range and the molecular weight of the amphoteric resin dispersant (D) is too high, the electrode active material There is a possibility of causing poor dispersion of (A) or the carbon material (B) which is a conductive additive.
In addition, the viscosity in this invention is the value measured on 25 degreeC conditions using the B-type viscosity meter.

The copolymer is obtained by copolymerizing a carboxyl group-containing unsaturated compound (d2), and it is preferable that the constituent ratio of the monomer having an anionic functional group in the copolymer is represented by the acid value as follows. That is, the acid value of the copolymer used is preferably in the range of 50 mgKOH / g to 400 mgKOH / g, and the acid value is preferably in the range of 80 mgKOH / g to 300 mgKOH / g.
When the acid value of the copolymer used in the present invention is lower than the above range, the dispersion stability of the dispersion tends to decrease and the viscosity tends to increase. Moreover, when the acid value of the copolymer used in the present invention is higher than the above range, the adhesion of the copolymer to the pigment surface tends to decrease, and the storage stability of the dispersion tends to decrease.
The acid value of the copolymer in the present invention is a value obtained by converting the measured acid value (mgKOH / g) into a nonvolatile content in accordance with the potentiometric titration method of JIS K 0070.

The amphoteric resin dispersant (D) can be obtained by various production methods.
For example, the monomers (d1) to (d4) are polymerized in an organic solvent that can be azeotroped with water. Thereafter, an aqueous liquid medium represented by water and a neutralizing agent are added to neutralize at least a part of the carboxyl groups, the azeotropic solvent is distilled off, and an aqueous solution of the amphoteric resin type dispersant (D) or An aqueous dispersion can be obtained.
As the organic solvent at the time of polymerization, any solvent that azeotropes with water may be used, but those having high solubility in the copolymer are preferable, and ethanol, 1-propanol, 2-propanol, and 1-butanol are preferable. Preferably 1-butanol.

Alternatively, it is copolymerized in a hydrophilic organic solvent, neutralized by adding water and an amine to make it aqueous, and as described above, the hydrophilic organic solvent is not distilled off, and an aqueous liquid medium containing the hydrophilic organic solvent and water In addition, a solution in which the amphoteric resin dispersant (D) is dissolved or dispersed can be obtained.
In this case, the hydrophilic organic solvent used is preferably one having high solubility in the copolymer, preferably glycol ethers, diols, more preferably (poly) alkylene glycol monoalkyl ethers having 3 to 6 carbon atoms. Alkanediols are good.

The following are mentioned as a neutralizing agent used for neutralization of a copolymer.
For example, inorganic alkaline agents such as ammonia water, various organic amines such as dimethylaminoethanol, diethanolamine, and triethanolamine, alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide, organic acids and mineral acids Etc. can be used. The copolymer as described above is dispersed or dissolved in an aqueous liquid medium.

  Next, the nitrogen-containing acrylic emulsion type binder (C) will be described. The binder in the present invention is used for binding particles such as a conductive additive and other active materials, and for adhesion to a metal current collector. Examples of the binder form include a water-soluble type, an emulsion type, and a hydrosol type. Among these, an emulsion type is preferable from the viewpoint of adhesion to the metal current collector. The emulsion type here means a state in which the binder is not dissolved in the aqueous liquid solvent but is dispersed in the form of particles in the aqueous liquid solvent.

  The compatibility with the dispersant will be described. The dispersant contains amino groups in the copolymer. This amino group and the nitrogen-containing component in the binder are thought to contribute greatly to the compatibility. The present inventors have created a binder using a nitrogen atom-containing component, so that when the composite ink or primer composition is applied to a metal foil to form a composite layer, the compatibility between the dispersant and the binder is achieved. Therefore, it was found that the dispersant was uniformly incorporated in the binder forming the continuous layer of the composite material layer and the underlayer without unevenness, and as a result, the battery characteristics were improved. The nitrogen atom-containing component here refers to at least one of an ethylenically unsaturated monomer, an emulsifier, and an initiator of the binder synthesis material.

  Examples of the nitrogen-containing ethylenically unsaturated monomer include maleimide, N-vinylpyrrolidone, (meth) acrylic ethylenically unsaturated monomer primary amine, secondary amine, tertiary amine, and quaternary ammonium salt, And (meth) acrylamide. Specifically, N-cyclohexylmaleimide, N-phenylmaleimide, N-acryloylmorpholine, N, N- (dimethylamino) ethyl (meth) acrylate, N, N- (dimethylamino) propyl (meth) acrylate, 3- (3-pyridinyl) propyl (meth) acrylate, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-methyl (meth) acrylamide, N-isopropylacrylamide, N-ethyl ( And (meth) acrylamide and N-hexyl (meth) acrylamide. Among these, N-acryloylmorpholine, maleimide, and N-isopropylacrylamide are preferable from the viewpoint of ease of synthesis. These at least one nitrogen-containing ethylenically unsaturated monomer and other ethylenically unsaturated monomers can be used in combination.

  As the ethylenically unsaturated monomer that can be used in combination with the nitrogen-containing ethylenically unsaturated monomer, a known monomer can be used. For example, alkyl (meth) acrylate, alkylene glycol ( Examples include meth) acrylate and styrene.

The nitrogen-containing _{emulsifiers, RNH 2 · HCl, RNH 2} · CH 3 long chain primary amine salts such as COOH,
Quaternary ammonium salts such as alkyltrimethylammonium salt, dialkyldimethylammonium salt, alkyldimethylbenzylammonium salt,
Heterocyclic amines such as alkylimidazolines, 1-hydroxyethyl-2-alkylimidazolines, 1-acetylaminoethyl-2-alkylimidazolines, 2-alkyl-4-methyl-4-hydroxymethyloxazolines,
Examples thereof include amine derivatives such as polyoxyethylene alkylamine, N-alkylpropylenediamine, N-alkylpolyethylenepolyamine, N-alkylpolyethylenepolyamine dimethyl sulfate, alkylbiguanide, and long-chain amine oxide. These at least one nitrogen-containing emulsifier and other emulsifiers can be used in combination.

  As an emulsifier that can be used in combination with a nitrogen-containing emulsifier, a known emulsifier can be used, and examples thereof include an anionic emulsifier and a nonionic emulsifier.

  As the nitrogen-containing initiator, 2,2′-azobis (2-amidinopropane) dihydrochloride (V-50 manufactured by Wako), 2,2′azobis (N, N′-dimethyleneisobutylamidine) dihydrochloride (VA−) 044). These at least one nitrogen-containing initiator and other initiators can be used in combination.

  As the initiator that can be used in combination with the nitrogen-containing initiator, a known initiator can be used, and examples thereof include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate.

  The nitrogen-containing acrylic emulsion type binder (C) can be prepared by using at least one of a nitrogen-containing ethylenically unsaturated monomer, an emulsifier, and an initiator. Among these, an ethylenically unsaturated monomer is preferable because it has a high ratio as a component constituting the binder and can introduce many nitrogen atoms. In that case, a nitrogen-containing ethylenically unsaturated monomer and the above-mentioned known emulsifier and initiator not containing nitrogen can be used in combination.

  The nitrogen-containing acrylic emulsion binder (C) can be obtained by copolymerizing a nitrogen-containing ethylenically unsaturated monomer and another ethylenically unsaturated monomer. The amount of the nitrogen-containing ethylenically unsaturated monomer is preferably from 0.1 to 20% by weight, more preferably from 0.5 to 10% by weight, based on the total amount of the ethylenically unsaturated monomer. If it is less than 0.1% by weight, there is a concern that the effect of improving the compatibility with the dispersant is not sufficiently exhibited. When the amount is more than 20% by weight, the dispersion stability is lowered, and there is a concern that the dispersion stability may be lowered during preparation of the composite ink.

  The nitrogen-containing acrylic emulsion-type binder (C) can be prepared by a polymerization method such as emulsion polymerization, suspension polymerization, miniemulsion polymerization, or dispersion polymerization. Among these, emulsion polymerization is preferable from the viewpoint of easy progress of the polymerization reaction.

  The ratio of the non-volatile content of the nitrogen-containing acrylic emulsion binder (C) to the total non-volatile content of the composite ink is preferably 0.1 to 15% by weight, and more preferably 1 to 10% by weight.

<Composite ink>
As described above, the nickel-hydrogen secondary battery electrode forming composition of the present invention can be used for a composite ink and also for a primer composition. Therefore, a description will be given of a composite ink that essentially includes an active material, which is one of the preferred embodiments of the composition for forming a nickel metal hydride secondary battery of the present invention. The composite ink includes a positive electrode composite ink or a negative electrode composite ink. The composite ink includes an electrode active material (A), a nitrogen-containing acrylic emulsion binder (C), and an amphoteric resin dispersant (D). The carbon material (B) which consists of an aqueous liquid medium (E) and is further a conductive support agent depending on the case can be used.

As a positive electrode active material for a nickel metal hydride secondary battery or a hydrogen storage alloy for a negative electrode, conventionally known materials can be appropriately selected. For example, the positive electrode active material is a nickel compound such as nickel hydroxide or nickel oxyhydroxide. As the kind of nickel hydroxide, a cobalt coated product obtained by coating nickel hydroxide with cobalt hydroxide or cobalt oxyhydroxide is more preferable. By coating the surface of nickel hydroxide with cobalt, the conductivity of nickel hydroxide can be further increased. Hydrogen storage alloy used as a negative electrode composition (F) is, for example, LaNi ₅ and MmNix (misch metal; a mixture of rare earth metals, x = from 4.7 to 5.2) is AB ₅ type, such as. In the former, a material in which a part of Ni is replaced with Cu, Al, Co, Si or the like, or a material in which a part of La is replaced with Nd or Zr has been developed. The latter material is generally used at present, and inexpensive Mm is used for the rare earth, and a part of Ni is replaced with Co, Mn, Al, or the like. In _{addition, TiNi, Ti 2 AB / A} 2 B types such as Ni (titanium-based), there are _two systems or ZrV AB ₂ type, such as _2-based ZrNi.

  The sizes of the electrode active material (A) and the electrode composition (F) are preferably in the range of 0.05 to 100 μm, more preferably in the range of 0.1 to 50 μm. And it is preferable that the dispersed particle size of the electrode active material (A) and electrode composition (F) in compound ink is 0.5-20 micrometers. The dispersed particle size referred to here is a particle size (D50) that is 50% when the volume ratio of the particles is integrated from the fine particle size distribution in the volume particle size distribution. A particle size distribution meter such as a dynamic light scattering type particle size distribution meter ("Microtrack UPA" manufactured by Nikkiso Co., Ltd.).

Next, the carbon material (B) which is a conductive support agent will be described.
The composite ink for forming a secondary battery electrode of the present invention preferably contains a carbon material (B) in order to further increase the conductivity of the formed electrode.
The carbon material (B) is not particularly limited as long as it is a carbon material having conductivity, but graphite, carbon black, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon fiber), fullerene, etc. It can be used alone or in combination of two or more. Carbon black is preferred from the viewpoints of conductivity, availability, and cost.

  Carbon black is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reactor, especially ketjen black using ethylene heavy oil as a raw material. Channel black that has been rapidly cooled and precipitated, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material, and particularly various types such as acetylene black using acetylene gas as a raw material, or 2 More than one type can be used in combination. Ordinarily oxidized carbon black, hollow carbon and the like can also be used.

  The oxidation treatment of carbon is performed by treating carbon at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc. This is a treatment for directly introducing (covalently bonding) an oxygen-containing polar functional group to the carbon surface, and is generally performed to improve the dispersibility of carbon. However, since it is common for the conductivity of carbon to fall, so that the introduction amount of a functional group increases, it is preferable to use the carbon which has not been oxidized.

As the specific surface area of carbon black increases, the number of contact points between the carbon black particles increases, which is advantageous in reducing the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the amount of nitrogen adsorbed is 20 m ² / g or more and 1500 m ² / g or less, preferably 50 m ² / g or more and 1500 m ² / g or less, more preferably 100 m ^2. / G or more and 1500 m ² / g or less are desirable. 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 of more than 1500 m ² / g may be difficult to obtain from commercially available materials. is there.

  Moreover, the particle size of carbon black is preferably 0.005 to 1 μm, and particularly preferably 0.01 to 0.2 μm in terms of primary particle size. However, the primary particle diameter here is an average of about 20 to 50 particle diameters measured with an electron microscope or the like.

It is desirable that the dispersed particle size in the composite ink of the carbon material (B), which is a conductive additive, be refined to 0.03 μm or more and 5 μm or less. It may be difficult to produce a composition having a dispersed particle size of the carbon material as the conductive aid of less than 0.03 μm. In addition, when a composition having a dispersed particle size of the carbon material as the conductive auxiliary agent exceeding 2 μm is used, there may be problems such as variations in the material distribution of the composite coating film and variations in the resistance distribution of the electrodes. .
The dispersed particle size referred to here is a particle size (D50) that is 50% when the volume ratio of the particles is integrated from the fine particle size distribution in the volume particle size distribution. A particle size distribution meter such as a dynamic light scattering type particle size distribution meter ("Microtrack UPA" manufactured by Nikkiso Co., Ltd.).

  Examples of commercially available carbon black include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Furnace Black), Printex L and the like (Degussa Co., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205, etc. (manufactured by Colombian, furnace black), # 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3030B, # 3030B # 3350B, # 3400B, # 5400B etc. (Mitsubishi Chemical Co., Furnace Black), MONARCH1400, 1300, 900, VulcanXC- 2R, BlackPearls2000, etc. (Cabot, Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS Examples of graphite such as -100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black) include natural graphite such as artificial graphite, flaky graphite, massive graphite, and earthy graphite, but are not limited thereto. Instead, two or more types may be used in combination.

  As the conductive carbon fibers, those obtained by firing from petroleum-derived raw materials are preferable, but those obtained by firing from plant-derived raw materials can also be used. For example, VGCF manufactured by Showa Denko Co., Ltd. manufactured with petroleum-derived raw materials can be mentioned.

Next, the aqueous liquid medium (E) will be described.
As the aqueous liquid medium (E) used in the present invention, it is preferable to use water, but if necessary, for example, a liquid medium compatible with water in order to improve the coating property to the current collector. May be used.
Liquid media compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters , Ethers, nitriles and the like, and may be used as long as they are compatible with water.

  Furthermore, a film forming aid, an antifoaming agent, a leveling agent, a preservative, a pH adjuster, a viscosity adjuster, and the like can be blended in the composite ink as necessary.

The viscosity of the composite ink is preferably 100 mPa · s or more and 30,000 mPa · s or less in a nonvolatile content range of 30 to 90% by weight, depending on the coating method.
It is preferable that the active material (A) or the electrode composition (F) is contained as much as possible within the viscosity range that can be applied. Specifically, the proportion of the active material (A) or the electrode composition (F) in the non-volatile content of the composite ink is preferably 80% by weight or more and 99% by weight or less.
Moreover, it is preferable that the ratio of the amphoteric resin type dispersant (D) in the non-volatile content of the composite ink is 0.1 to 15% by weight.
When the carbon material (B) is included, the proportion of the carbon material (B) in the non-volatile content of the composite ink is preferably 0.1 to 15% by weight.

The composite ink of the present invention can be obtained by various methods.
However, the use of the carbon material (B) is arbitrary.
For example, in the case of a mixture ink for positive electrode,
(4-1) An aqueous dispersion of an active material containing an active material (A), an amphoteric resin type dispersant (D), and an aqueous liquid medium (E) is obtained, and the carbon material (B) and A nitrogen-containing acrylic emulsion binder (C) can be added to obtain a composite ink.
The carbon material (B) and the nitrogen-containing acrylic emulsion binder (C) can be added simultaneously, or after the carbon material (B) is added, the binder may be added, or vice versa.
(4-2) Obtaining an aqueous dispersion of the conductive additive containing the carbon material (B), the amphoteric resin type dispersant (D) and the aqueous liquid medium (E), and adding the active material (A) to the aqueous dispersion A nitrogen-containing acrylic emulsion binder (C) can be added to obtain a composite ink.
The active material (A) and the binder can be added simultaneously, or after adding the active material (A), the nitrogen-containing acrylic emulsion type binder (C) may be added, or vice versa.
(4-3) An aqueous dispersion of the active material containing the active material (A), the amphoteric resin type dispersant (D), the nitrogen-containing acrylic emulsion type binder (C), and the aqueous liquid medium (E) is obtained, and the aqueous A carbon material (B) can be added to the dispersion to obtain a mixed ink.
(4-4) Obtaining an aqueous dispersion of a conductive additive containing a carbon material (B), an amphoteric resin type dispersant (D), a nitrogen-containing acrylic emulsion type binder (C), and an aqueous liquid medium (E), An active material (A) can be added to the aqueous dispersion to obtain a composite ink.
(4-5) The active material (A), the carbon material (B), the amphoteric resin type dispersant (D), the nitrogen-containing acrylic emulsion type binder (C), and the aqueous liquid medium (E) are mixed almost simultaneously. Ink can be obtained.
In the case of the negative electrode mixture ink, the active material (A) in the above example may be replaced with the electrode composition (F).

(Disperser / Mixer)
As an apparatus used for obtaining the composite ink, a disperser or a mixer which is 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, or “fillmix” manufactured by PRIMIX; paint conditioner (manufactured by Red Devil), ball mill, sand mill Media type dispersers such as “Dynomill” manufactured by Shinmaru Enterprises, Inc., Attritor, Pearl Mill (“DCP Mill” manufactured by Eirich), or Coball Mill; Media-less dispersers such as “Starburst” manufactured by Machine, “Nanomizer” manufactured by Nanomizer, etc., “Claire SS-5” manufactured by M Technique, or “MICROS” manufactured by Nara Machinery; or other roll mills, etc. Although The present invention is not limited to these. 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. As the media, it is preferable to use glass beads, ceramic beads such as 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. In the case of a positive electrode active material or a hydrogen storage alloy for a negative electrode, which tends to break or crush particles due to a strong impact, a medialess disperser such as a roll mill or a homogenizer is preferable to a media disperser.

<Primer composition>
The composition for forming a nickel metal hydride secondary battery electrode of the present invention can also be used as a primer composition. Here, the primer composition is preferably used for forming an underlayer of the electrode.
The primer composition contains a conductive additive (B), a nitrogen-containing acrylic emulsion type binder (C), an amphoteric resin type dispersant (D), and an aqueous liquid medium (E). About each component, it is the same as that of the case of compound ink.

  The proportion of the carbon material (B) in the total nonvolatile content of the composition used for the underlayer is preferably 5% by weight to 95% by weight, more preferably 10% by weight to 90% by weight. If the carbon material (B) as a conductive auxiliary agent is small, the conductivity of the underlayer may not be maintained. On the other hand, if the carbon material (B) as a conductive auxiliary agent is too much, the resistance of the coating film decreases. There is a case. Moreover, although the appropriate viscosity of a primer composition is based on the coating method, generally it is preferable to set it as 10 mPa * s or more and 30,000 mPa * s or less.

<Electrode>
An electrode for a nickel-hydrogen secondary battery can be obtained by coating and drying the composite material ink of the present invention on a current collector to form a composite material layer.
Alternatively, a primer composition containing the composition for forming a nickel metal hydride secondary battery electrode of the present invention is coated on a current collector and dried to form a base layer, and a composite layer is formed on the base layer. By forming, an electrode for a nickel metal hydride secondary battery can be obtained. In addition, the composite material layer provided on a base layer may be formed using the above-described composite material inks (1) to (4) of the present invention, or may be formed using other composite material inks.

(Current collector)
The material and shape of the current collector used for the electrode for the nickel hydride secondary battery are not particularly limited, and conventionally known ones can be appropriately selected. For example, examples of the material for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. In general, foil on a flat plate is used as the shape, but the surface is roughened, porous foam, perforated foil, and mesh current collector. Can also be used. When providing a base layer on the electrode for a nickel metal hydride secondary battery, it is preferable to use a flat foil-shaped current collector.

There is no restriction | limiting in particular as a method of apply | coating mixed-material ink on a collector, A well-known method can be used.
Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method. As drying methods, standing drying, blower dryer, hot air dryer, infrared heater, far infrared heater and the like can be used, but are not particularly limited thereto.
Moreover, you may perform the rolling process by a lithographic press, a calender roll, etc. after application | coating. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less. When the underlayer is provided, the total thickness of the underlayer and the composite layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

<Ni-MH secondary battery>
A nickel metal hydride secondary battery can be obtained by using the above electrode for at least one of a positive electrode and a negative electrode. Furthermore, a well-known electrolyte solution, a separator, etc. can be used suitably.

  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 obtained by subjecting them to a hydrophilic treatment.

  The structure of the nickel metal hydride secondary battery using the composition for forming a nickel metal hydride secondary battery of the present invention is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator provided as necessary, and a paper Various shapes can be formed according to the purpose of use, such as a mold, a cylinder, a button, and a laminated mold.

  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, “part” represents “part by weight”.

(Dispersant synthesis example 1)
A reaction vessel equipped with a gas introduction tube, a thermometer, a condenser, and a stirrer was charged with 200.0 parts of n-butanol and replaced with nitrogen gas. The inside of the reaction vessel was heated to 110 ° C., and a mixture of 100.0 parts of styrene, 60.0 parts of acrylic acid, 40.0 parts of dimethylaminoethyl methacrylate, and 12.0 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) The polymerization reaction was carried out dropwise over 2 hours. After completion of the dropwise addition, the mixture was further reacted at 110 ° C. for 3 hours, 0.6 parts of V-601 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the reaction was further continued at 110 ° C. for 1 hour to obtain a copolymer (1) solution. Got. The weight average molecular weight of the copolymer (1) was about 10,000, and the acid value was 219.1 (mgKOH / g).
Further, after cooling to room temperature, 74.2 parts of dimethylaminoethanol was added for neutralization. This is the amount that neutralizes 100% of acrylic acid. Furthermore, after adding 400 parts of water and making it aqueous, it heated to 100 degreeC, butanol was azeotroped with water, and butanol was distilled off.
Dilution with water gave an aqueous solution or dispersion of an amphoteric resin dispersant (1) with a nonvolatile content of 20%. Moreover, the viscosity of the aqueous solution of the amphoteric resin type dispersant (1) having a nonvolatile content of 20% was 40 mPa · s.

(Dispersant Synthesis Examples 2 to 12)
The compounding compositions shown in Table 1 were synthesized in the same manner as in Synthesis Example 1 to obtain dispersants of Synthesis Examples 2-12.

The contents of the abbreviations in Table 1 are shown below.
St: Styrene AA: Acrylic acid BzMA: Benzyl methacrylate DM: Dimethylaminoethyl methacrylate BMA: Butyl methacrylate

(Carbon material dispersion for nickel metal hydride secondary battery electrodes)
10 parts of acetylene black (DENKA BLACK HS-100) as a carbon material which is a conductive additive, and 10 parts of an aqueous solution or aqueous dispersion of the amphoteric resin type dispersant (1) described in Synthesis Example (1) Part) and 80 parts of water were mixed in a mixer, and further dispersed in a sand mill to obtain a carbon material dispersion (1) for nickel-hydrogen secondary battery electrodes.

[Carbon material dispersion]
Using the dispersant shown in Table 1, carbon material dispersions (2) to (12) for nickel metal hydride secondary battery electrodes were formed in the same manner as the carbon material dispersion (1) for nickel metal hydride secondary battery electrodes. Obtained.

<Binder Synthesis Example 13>
As nitrogen-containing monomer, 5.0 parts of N-acryloylmorpholine, as other monomers, 53 parts of methyl methacrylate, 40.5 parts of butyl acrylate, 1.5 parts of acrylic acid, anionic emulsifier as emulsifier Hytenol NF-08 (an anionic emulsifier manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and a mixture of 53.1 parts of ion-exchanged water were emulsified with a blade to create a monomer pre-emulsion 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. Subsequently, 0.2 parts of Haitenol NF-08 as an emulsifier is added to the reaction vessel, and the monomer pre-emulsion is continuously dropped from a dropping tank over 5 hours, using 0.3 part of ammonium persulfate, Emulsion polymerization was performed at 60 ° C. over 6 hours.

After completion of the dropwise addition, the mixture was kept at 60 ° 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 nitrogen-containing acrylic emulsion binder. There was no aggregate remaining on the filter cloth, and the polymerization stability was good.
A part of the emulsion after filtration was measured, dried at 150 ° C. for 20 minutes, and the nonvolatile content concentration was determined to be 40.0%. The emulsion had a pH of 2.0 and a viscosity of 10 mPa · s.

<Binder synthesis examples 14 to 18>
By the composition shown in Table 2, it synthesize | combined by the method similar to binder synthesis example 13, and the binder of the synthesis examples 14-18 was obtained.

The contents of the abbreviations in Table 2 are shown below.
ACMO: N-acryloylmorpholine NIPAAm: N-isopropylacrylamide MMA: methyl methacrylate BA: butyl acrylate

(Compatibility of dispersant and binder)
The compatibility between the dispersant and the binder was evaluated as follows. 25 parts of dispersant (5 parts as nonvolatile content) and 12.5 parts of binder (5 parts as nonvolatile content) are mixed, applied to a 50 μm PET film, dried at 100 ° C. for 3 minutes, Produced. The thickness of the resin layer of the obtained film was 3 μm. The degree of compatibility of the obtained film was determined by visual judgment. The evaluation criteria are shown below.
Y: "No abnormality"
Δ: “Slightly cloudy”
×: “Opaque or aggregated”

<Nickel metal secondary battery positive electrode ink>, <Positive electrode>, <Coin-type battery>
[Example 1]
Nickel hydroxide coated with cobalt hydroxide as the positive electrode active material (CZ, Tanaka Chemical Laboratory (manufactured)) for 50 parts of carbon material dispersion for secondary battery electrode (1) (5 parts as acetylene black nonvolatile content) ) 45 parts, 12.5 parts of the binder synthesized in Synthesis Example 13 and 50 parts of water were mixed to prepare a mixture ink for a secondary battery electrode for a positive electrode. The dispersity of the composite ink was determined in the same manner as the dispersity of the carbon material dispersion described above.
Then, the positive electrode secondary battery electrode composite ink was applied onto a 30 μm-thick nickel-plated steel plate, which is a foil-shaped current collector, using a doctor blade, and then dried by heating. Furthermore, the rolling process by a roll press was performed and the positive electrode with a thickness of 85 micrometers was obtained. The obtained positive electrode was not cracked or peeled off.

(Electrode adhesion)
Using the knife, the incision from the surface of the electrode to the depth reaching the current collector was cut into 6 grids in the vertical and horizontal directions at intervals of 2 mm. An adhesive tape was applied to the cut and immediately peeled off, and the degree of the active material falling off was determined by visual judgment. The evaluation criteria are shown below.
○: “No peeling (good)”
○ △: “Slightly peeled (no problem in practical use)”
Δ: “About half peel (cannot be used)”
×: “Peel off at most parts (cannot be used)”

[Examples 2 to 12], [Comparative Examples 1 to 5]
As shown in Table 3, except that the combination of the carbon material dispersion for the secondary battery electrode and the binder synthesis example was changed, the mixture ink for the positive electrode secondary battery electrode and the positive electrode were obtained in the same manner as in Example 1. Evaluation was performed in the same manner.

[Example 13]
45 parts of non-cobalt-coated nickel hydroxide as the positive electrode active material (ZD, manufactured by Tanaka Chemical Research Co., Ltd.), 50 parts of the carbon material dispersion (1) for the secondary battery electrode as the conductive material, and Synthesis Example 13 as the binder 12.5 parts of the polymer emulsion obtained in the above 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.

[Example 14]
In the same manner as in Example 1, a mixed ink for a positive electrode secondary battery electrode was prepared, dip-coated on foamed nickel serving as a current collector, dried by heating under reduced pressure, and adjusted to a thickness of 200 μm. Furthermore, the rolling process by a roll press was performed and the positive electrode from which thickness becomes 150 micrometers was produced. The obtained positive electrode was not cracked or peeled off.

[Example 15], [Comparative Example 6]
In the same manner as in Example 1 except that the dispersant shown in Table 3 was used instead of the carbon material dispersion for the secondary battery electrode and the combination of the binder synthesis example was changed, and a mixture ink for the positive electrode secondary battery electrode, and A positive electrode was obtained and evaluated in the same manner.

<Preparation of negative electrode for positive electrode evaluation>
45 parts of a misch metal nickel alloy (AB5 alloy) powder as a hydrogen storage alloy, 2.0 parts of acetylene black (DENKA BLACK HS-100) as a conductive material, 5.0 parts of a binder (polytetrafluoro) Ethylene 30-J: Mitsui DuPont Fluoro Chemical Co., Ltd., 60% aqueous dispersion) and 1.5 parts of carboxymethylcellulose were kneaded to prepare a negative electrode mixture ink. The composite ink was applied to a nickel-plated punching metal as a current collector, dried at 80 ° C., adjusted in thickness with a roll press, and then cut into a predetermined size to produce a negative electrode.

  Next, the obtained positive electrode and negative electrode are punched out to a predetermined size, and a coin-type battery comprising a separator (porous polypropylene nonwoven fabric) inserted between the positive electrode and the negative electrode and an electrolyte 6N potassium hydroxide is produced. did. After the coin-type battery was manufactured, predetermined battery characteristics were evaluated.

(Charge / discharge storage characteristics)
About the obtained coin-type battery, charging / discharging measurement was performed using the charging / discharging apparatus (SM-8 by Hokuto Denko).
The battery was charged to 100% of the calculated battery capacity at a charging current of 0.2C. Thereafter, constant current discharge was performed at a discharge current of 0.2 C until a discharge end voltage of 0.8 V was reached. These charge / discharge cycles are defined as one cycle, and 5 cycles of charge / discharge are repeated, and the discharge capacity at the fifth cycle is defined as the initial discharge capacity. (The initial discharge capacity is assumed to be 100% maintenance rate).

Next, after charging with a charging current of 1 C, constant current discharging is performed with a discharging current of 1 C until the discharge end voltage reaches 0.8 V, and 500 cycles of charging and discharging are performed with these charging and discharging cycles as one cycle. Repeatedly, the capacity retention rate was calculated (the closer to 100%, the better).
Capacity maintenance rate = (discharge capacity after 500 cycles) / (initial discharge capacity)
○: “Capacity maintenance rate is 95% or more (particularly excellent)”
○ △: “Capacity maintenance rate is 90% or more and less than 95% (good)”
Δ: “Capacity maintenance rate is 85% or more and less than 90% (no problem in practical use)”
×: “Capacity maintenance rate is less than 85%.

<Nickel-metal secondary battery negative electrode ink>, <Negative electrode>, <Coin-type battery>
[Example 16]
Binder 12 synthesized in Synthesis Example 15 with respect to 50 parts of carbon material dispersion (1) for secondary battery electrode (5 parts as acetylene black nonvolatile content), 45 parts of hydrogen storage alloy as negative electrode composition (F) .5 parts and 50 parts of water were mixed to produce a negative electrode material ink for a secondary battery electrode. The dispersity of the composite ink was determined in the same manner as the dispersity of the carbon material dispersion described above.
The negative electrode secondary battery electrode composite ink was applied onto a nickel-plated steel plate having a thickness of 30 μm, which is a foil-like current collector, using a doctor blade, and then dried by heating. Furthermore, the rolling process by roll press was performed and the 100-micrometer-thick negative electrode was obtained. The resulting negative electrode was not cracked or peeled off.

  Next, the positive electrode obtained in Example 1 and the negative electrode obtained in Example 15 were punched out to a predetermined size, and a separator (porous polypropylene nonwoven fabric) inserted between the positive electrode and the negative electrode, and an electrolyte 6N A coin-type battery made of potassium hydroxide was produced. A predetermined battery characteristic evaluation was performed after producing a coin type battery.

[Example 17] [Comparative Examples 7 to 9]
As shown in Table 3, except for changing the combination of the carbon material dispersion for the secondary battery electrode and the binder synthesis example, a mixture ink for the negative electrode secondary battery electrode and the negative electrode were obtained in the same manner as in Example 15, Evaluation was performed in the same manner.

As shown in Table 3, when the nickel-metal hydride secondary battery electrode forming composite ink of the present invention is used, the carbon material or the active material, which is a conductive auxiliary agent, is uniformly dispersed in the composite ink. It is considered that the flexibility and adhesion of the electrode are balanced, and the charge / discharge storage characteristics are improved also in the battery characteristics.
As for this, when the carbon material or active material, which is a conductive auxiliary agent, is not sufficiently dispersed in the mixture ink, a uniform conductive network as an electrode is not formed. It is considered that resistance distribution due to mechanical aggregation occurs, and current concentration occurs when used as a battery, so that deterioration is accelerated.
Moreover, when the dispersion control of the carbon material or the active material which is the conductive auxiliary agent is insufficient, the electrode adhesion tends to be insufficient. In particular, when the dispersion control of the carbon material that is a conductive additive is insufficient, the tendency is remarkable.
Furthermore, it is thought that by improving the compatibility between the dispersant and the binder, inhibition of the battery reaction derived from the dispersant is suppressed in the composite layer, and the battery characteristics are improved. As in Comparative Example 5, even when the dispersion state of the carbon material or the active material, which is a conductive additive, is good, if the compatibility between the dispersant and the binder is low, the binder layer in the continuous layer in the composite layer Thus, the distribution of the dispersant is biased, the resistance is locally increased, the electrode is deteriorated, and the durability of the battery is finally lowered.
On the other hand, as in Comparative Example 1, it is considered that the battery characteristics are deteriorated even though the compatibility is good due to the decrease in the adhesion of the electrodes. Therefore, in order to improve battery characteristics, it is considered necessary to satisfy both electrode adhesion and compatibility. Although there is a correlation between the compatibility and the battery characteristics, it is considered necessary to ensure the adhesion of the electrodes as a precondition.
Therefore, in the case where the mixed ink for forming the nickel metal hydride secondary battery electrode of the present invention is used, the carbon material or the active material as the conductive auxiliary agent is uniformly dispersed in the mixed ink, and further, the dispersant and the binder It is considered that the good compatibility of these materials has made it possible to reduce the inhibition of the battery reaction of the dispersant and to improve it.

[Example 18]
Secondary battery electrode primer composition by mixing 12.5 parts of binder synthesized in Synthesis Example 13 with 10 parts of carbon material dispersion for secondary battery electrode (1) (1 part as acetylene black nonvolatile content) A product was obtained, and the degree of dispersion was measured with a grind gauge.
Then, this primer composition was applied onto a nickel-plated steel plate having a thickness of 30 μm to be a foil-shaped current collector using a doctor blade, followed by drying by heating to form an undercoat layer having a thickness of 8 μm. .
Subsequently, after applying the mixture ink for nickel-metal hydride secondary battery positive electrode of Example 5 on the said foundation layer, it dried under reduced pressure, obtained the positive electrode similarly to Example 5, and evaluated it similarly.

[Example 19, comparative example 10]
A primer composition for a secondary battery electrode was obtained and evaluated in the same manner as in Example 17 except that the carbon material dispersion shown in Table 4 was used.
Subsequently, after applying the mixture ink for secondary battery positive electrode shown in Table 4 on the said base layer, it dried under reduced pressure heating, obtained the positive electrode similarly to Example 5, and evaluated it similarly.

  As shown in Table 4, when the composition for forming a nickel metal hydride secondary battery electrode of the present invention is used for the underlayer, it is even better than the evaluation results of Example 5 in which the underlayer is not used. I understand that. This is presumably because the composition for forming a nickel metal hydride secondary battery electrode of the present invention made the adhesion portion between the current collector and the composite material layer more uniform and strong. However, in Comparative Example 10, the dispersion state of the composition for forming the nickel hydrogen secondary battery electrode for the underlayer is insufficient, and even when the electrode is used, the result is inferior to the evaluation result of Example 5. there were. This is presumably because the state of close contact between the current collector and the composite material layer was inadequate, resulting in a non-uniform state as an electrode as compared with the case where the base layer was not used.

Claims (9)

An amphoteric resin dispersant (D) obtained by neutralizing at least a part of a carboxyl group in a copolymer obtained by copolymerizing a nitrogen-containing acrylic emulsion binder (C) and the following monomers with a basic compound: And an aqueous liquid medium (E), a composition for forming a nickel metal hydride secondary battery electrode.
Ethylenically unsaturated monomer having an aromatic ring (d1): 5 to 70% by weight
Ethylenically unsaturated monomer having a carboxyl group (d2): 15 to 60% by weight
Ethylenically unsaturated monomer having an amino group (d3): 1 to 80% by weight
Other monomers (d4) other than (d1) to (d3): 0 to 79% by weight
(However, the total of (d1) to (d4) is 100% by weight)   A mixed ink for a nickel-hydrogen secondary battery electrode, comprising the electrode active material (A) and the composition for forming a nickel-hydrogen secondary battery electrode according to claim 1.   The mixed ink for nickel-metal hydride secondary battery electrodes according to claim 2, wherein the electrode active material (A) is nickel hydroxide.   4. The nickel hydride secondary battery electrode composite ink according to claim 3, wherein the nickel hydroxide is coated with cobalt hydroxide.   A nickel-hydrogen secondary battery electrode composite ink comprising the nickel-hydrogen secondary battery electrode forming composition according to claim 1 and a hydrogen storage alloy as the electrode composition (F).   A primer composition for a nickel metal hydride secondary battery positive electrode, comprising the carbon material (B) as a conductive additive and the composition for forming a nickel metal hydride secondary battery electrode according to claim 1.   An electrode for a nickel metal hydride secondary battery comprising a base material and a composite material layer formed from the composite material ink for a nickel metal hydride secondary battery electrode according to claim 2.   The electrode for a nickel metal hydride secondary battery according to claim 7, wherein the base material is foamed nickel or a nickel plated steel sheet.   It forms from the base material formed from the base material, the primer composition for nickel-hydrogen secondary battery positive electrodes of Claim 6, and the mixture ink for nickel-hydrogen secondary battery electrodes in any one of Claims 2-5. An electrode for a nickel metal hydride secondary battery comprising a composite material layer.