JP2002329497A - Binder for negative electrode of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for a negative electrode of a secondary battery, which permits providing a negative electrode for a nickel hydrogen secondary battery good in adhesion of a negative electrode mix to a current collector and excellent in electrolyte resistance and providing a secondary battery excellent in cycle properties upon assembly of the battery. SOLUTION: The binder for a negative electrode of a nickel-hydrogen secondary battery is composed of a copolymer latex obtained by emulsion- polymerizing 100 pts.wt. in total of a monomer mixture composed of 20-60 wt.% of an aliphatic conjugated diene monomer, 1-10 wt.% of an ethylenically unsaturated carboxylic acid monomer and 30-79 wt.% of any other monomer copolymerizable therewith in the presence of a 4-methylcyclohexene and 1- methylcyclohexene and having an unsaturated bond in its ring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a binder for a negative electrode of a nickel hydride secondary battery.

[0002]

2. Description of the Related Art Compared with nickel-cadmium secondary batteries of the same size, nickel-hydrogen secondary batteries are environmentally clean in that they do not use cadmium, and have a large discharge capacity and can drive electronic equipment for a longer time. It has excellent features that are possible. Also, when compared with lithium ion secondary batteries, nickel-metal hydride secondary batteries are inferior in weight energy density, but have substantially the same volume energy density and can be supplied at low cost. It is becoming increasingly important as a drive power supply.

A nickel-hydrogen secondary battery is composed of a positive electrode using a nickel compound as a positive electrode active material and a negative electrode mainly comprising a hydrogen storage alloy capable of reversibly storing and releasing hydrogen as a negative electrode active material at a low pressure. It is configured.

The following methods have been proposed as methods for producing the negative electrode of this nickel-metal hydride secondary battery. (1) A method in which a hydrogen storage alloy powder is sintered together with a conductive powder to form an electrode. (2) A method in which a hydrogen storage alloy powder is filled into a three-dimensional metal porous body without using a binder to form an electrode. (3) A method in which the hydrogen storage alloy powder is held on a conductive support by a binder to form an electrode. Among these methods, the sintering method (1) has a disadvantage in that the surface of the hydrogen storage alloy is oxidized during sintering and becomes nonconductive, the conductivity of the electrode is reduced, and the discharge voltage is lowered. In addition, the method (2) has a problem that the battery capacity cannot be sufficiently increased because the three-dimensional porous metal body is expensive and a portion that does not contribute to the electrode capacity increases. Among the above, the method (3) using a binder is a method for producing a negative electrode which is excellent in electrode performance, production workability and cost.

[0005] In the method (3) using a binder, first, a hydrogen storage alloy powder having a predetermined particle size, a conductive agent powder having a predetermined particle size, a predetermined amount of an aqueous solution of a thickener, a binder, and other additives are added. The whole is kneaded to prepare a mixture slurry. Thereafter, the mixture slurry is applied to a conductive support, dried, and further adjusted by rolling, for example, to a predetermined thickness, and cut into a predetermined shape to carry the mixture containing the hydrogen storage alloy powder. A nickel-hydrogen secondary battery negative electrode (hydrogen storage alloy electrode) is manufactured. In this,
The binder has a significant effect on the performance of the final electrode.

Conventionally, a fluorine-based polymer such as polyvinylidene fluoride (PVDF) has been used as the binder. However, instead of the fluorine-based polymer, a styrene-butadiene-based copolymer latex (hereinafter, referred to as a latex) is used.
(Referred to as a copolymer latex), the self-discharge of the secondary battery during standing is suppressed, and a decrease in the open voltage is suppressed (Japanese Patent Laid-Open No. Hei 10-247492).
It is known in the art that copolymer latex exhibits excellent performance.

[0007]

In the manufacture of a negative electrode for a nickel-metal hydride secondary battery, in the case of manufacturing an electrode by holding a hydrogen storage alloy powder on a conductive support with a binder,
It is necessary to hold the hydrogen storage alloy powder firmly on the conductive support. Copolymer latex shows superior adhesion performance to negative electrode materials such as hydrogen storage alloy powder, conductive agent powder and current collector compared to conventional fluoropolymers, but recent advances in battery manufacturing technology and peripheral materials In view of the above, it has been expected that the performance of the negative electrode of a nickel-metal hydride secondary battery will be improved by further improving the performance of the copolymer latex.

[0008]

As a result of intensive studies to solve the above problems, it has been found that the above problems can be solved by using a specific copolymer latex as a binder, and the present invention has been completed. Reached. That is,
The present invention is an aliphatic conjugated diene monomer 20 to 60% by weight,
A total of 100 parts by weight of a monomer composed of 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 30 to 79% by weight of another monomer copolymerizable therewith is mixed with cyclopentene, cyclohexene, cycloheptene, 4- Nickel comprising a copolymer latex obtained by emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon having one unsaturated bond in the ring selected from methylcyclohexene and 1-methylcyclohexene It is intended to provide a binder for a negative electrode of a hydrogen secondary battery.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The copolymer latex in the present invention is obtained by emulsion polymerization of an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer and another monomer copolymerizable therewith. It is.

As the aliphatic conjugated diene monomer, 1, 1
3-butadiene, 2-methyl-1,3-butadiene,
2,3-dimethyl-1,3-butadiene, 2-chloro-
Examples thereof include 1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and one or more kinds can be used. Particularly, 1,3-butadiene is preferred.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Two or more types can be used.

Other monomers copolymerizable therewith include aromatic vinyl monomers, vinyl cyanide monomers,
Examples thereof include an unsaturated carboxylic acid alkyl ester monomer, an unsaturated monomer containing a hydroxyalkyl group, and an unsaturated carboxylic acid amide monomer, and one or more of these can be used.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, methyl α-methylstyrene,
Vinyl toluene and divinyl benzene, and the like,
One or more kinds can be used. Particularly, styrene is preferred.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like, and one or more of them can be used. Particularly, acrylonitrile and methacrylonitrile are preferred.

The unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl Examples include itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate, and one or more of them can be used. Particularly, methyl methacrylate is preferred.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
Hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate,
Di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl)
Maleate, 2-hydroxyethyl methyl fumarate and the like can be mentioned, and one kind or two or more kinds can be used. Particularly, β-hydroxyethyl acrylate is preferable.

The unsaturated carboxylic acid amide monomers include:
Acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,
N-dimethylacrylamide and the like can be mentioned, and one or more kinds can be used. Acrylamide is particularly preferred.

Further, in addition to the above-mentioned monomers, any of the monomers used in ordinary emulsion polymerization, such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride and vinylidene chloride, can be used.

The polymerizable monomer composition includes 20 to 60% by weight of an aliphatic conjugated diene monomer, 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, and another monomer copolymerizable therewith. 30-79% by weight.

When the amount of the aliphatic conjugated diene monomer is less than 20% by weight, when a mixture paste containing the copolymer latex of the present invention as a binder is applied to a current collector, the mixture between the mixture paste and the current collector may be reduced. If the adhesion exceeds 60% by weight, sufficient adhesiveness cannot be obtained, and when the mixture paste is applied to the current collector to produce a battery negative electrode, a problem that the electrolytic solution resistance is lowered is not preferable. Preferably it is 30 to 55% by weight.

If the amount of the ethylenically unsaturated carboxylic acid monomer is less than 1% by weight, the stability of the copolymer latex itself and the mixture paste containing the copolymer latex as a binder may be inferior. If it exceeds, the viscosity of the latex increases, which may cause a problem in handling the copolymer latex itself, which is not preferable.
Preferably it is 1 to 7% by weight.

When the amount of the other copolymerizable monomer is less than 30% by weight, the mixture paste containing the copolymer latex of the present invention as a binder is applied to a current collector to produce an electrolyte resistant solution when a battery negative electrode is manufactured. If it exceeds 79% by weight, the adhesiveness between the hydrogen storage alloy, the conductive agent, and the current collector is poor when the mixture paste is applied to the current collector, which is not preferable. Preferably it is 38 to 69% by weight.

In the present invention, when the above monomer is subjected to emulsion polymerization, a cyclic unsaturated compound having one unsaturated bond in a ring selected from cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene is used. It is necessary to carry out the emulsion polymerization in the presence of a saturated hydrocarbon emulsion polymerization. The proportion of the unsaturated hydrocarbon used is not particularly limited, but is 0.1 to 50 parts by weight based on 100 parts by weight of the total amount of the monomers. If the amount is less than 0.1 part by weight, the effect of the present invention is insufficient, and if it exceeds 50 parts by weight, the amount of the compound remaining as an unreacted substance also relatively increases, and the energy required for the recovery is greatly increased. Is not preferred. Preferably it is 0.5 to 30 parts by weight.

In the present invention, if necessary, a conventionally known chain transfer agent, for example, n-hexyl mercaptan,
n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, alkyl mercaptans such as n-stearyl mercaptan, xanthogen compounds such as dimethyl xanthogen disulfide, diisopropyl xanthogen disulfide, α-methyl styrene dimer, terpinolene And thiuram-based compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, 2,6-di-t-butyl-4-methylphenol, phenolic compounds such as styrenated phenol, and allyl alcohol. Allyl compounds, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide, α-benzyloxystyrene, α-benzyloxy One or two kinds of vinyl ethers such as acrylonitrile and α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, α-benzyloxystyrene, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, etc. The above can also be used. The use amount of these chain transfer agents is not limited at all, and can be appropriately adjusted according to the performance required for the copolymer latex.
It is 0.05 to 10 parts by weight with respect to 0 parts by weight.

In the present invention, a usual emulsifier is used when the copolymer latex is obtained by emulsion polymerization. Examples of the emulsifier include anionic surfactants such as sulfates of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates and sulfates of nonionic surfactants. Alternatively, one or more nonionic surfactants such as alkyl ester type, alkyl phenyl ether type, and alkyl ether type of polyethylene glycol are used.

In the present invention, water-soluble initiators such as potassium persulfate, ammonium persulfate and sodium persulfate, redox initiators, and oil-soluble initiators such as benzoyl peroxide can be used as the polymerization initiator.

In the polymerization of the copolymer latex,
The method for adding the monomer and other components is not particularly limited, and a batch addition method, a split addition method,
Any of the continuous addition methods can be employed, and in the present invention, any of single-stage polymerization, two-stage polymerization, and multi-stage polymerization can be employed.

The number average particle size of the copolymer latex is not particularly limited, but is preferably 50 to 250 n.
m, preferably 70-200 nm.

In producing a negative electrode for a nickel-metal hydride secondary battery, the hydrogen storage alloy used together with the binder of the present invention can be used without any particular limitation as long as it is used for a nickel-metal hydride secondary battery. Specific examples of the hydrogen storage alloy include LaNi _5- based alloy and MmNi _5- based alloy (MmNi-based alloy).
Is an abbreviation for misch metal), ZrNi ₂ alloy, TiNi alloy and the like. These hydrogen storage alloys reduce costs, prevent oxidation, prevent pulverization, improve cycle life, improve corrosion resistance, improve alkali corrosion resistance, improve initial capacity, suppress gas generation, reduce hydrogen dissociation equilibrium pressure, increase capacity, and extend service life. For the purpose, a part of the main alloy component metal may be replaced with another metal atom, or one or a mixture of two or more may be used in combination with a technique such as surface treatment of the alloy. As the shape of the hydrogen storage alloy, a powder having an average particle diameter of about 10 to 50 μm, which is usually pulverized mechanically or finely divided by storing and releasing hydrogen gas, is used.

In the production of a negative electrode for a nickel-metal hydride secondary battery, a mixture of other conductive agents, current collectors, thickeners, water repellents, and other additives used together with the binder of the present invention.
The negative electrode material can be used without any particular limitation as long as it is used for a nickel-hydrogen secondary battery.

The method for applying the negative electrode mixture slurry comprising the copolymer latex, the hydrogen storage alloy powder, the conductive agent powder, the thickener, the water repellent, and other additives according to the present invention to the current collector is performed by a reverse roll method. Method, comma bar method, gravure method, air knife method and any other coater head can be used, and drying methods include standing drying, blast drying equipment, hot air drying equipment, infrared heating equipment, far infrared heating equipment, etc. Can be used.

Further, a positive electrode active material, a positive electrode binder, a current collector, a separator, an electrolytic solution, a terminal, and the like, which are used when a nickel-metal hydride secondary battery is manufactured using the negative electrode prepared by using the binder of the present invention. Existing insulators, battery containers, and the like can be used without any particular limitation. Also, the final battery form can be used for both cylindrical nickel-metal hydride secondary batteries and prismatic nickel-metal hydride secondary batteries without limitation. Further, the copolymer latex of the present invention can be used as a binder for a positive electrode.

[0034]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless the gist of the present invention is changed. In the examples,
Parts and percentages indicating percentages are based on weight. The evaluation of various physical properties in the examples was based on the following methods.

[0035]Number average particle size measurement  The number average particle size of the copolymer latex is determined by the dynamic light scattering method.
Measured. In addition, at the time of measurement, LPA-3000 /
3100 (manufactured by Otsuka Electronics) was used.

[0036]Preparation of copolymer latex  In a pressure-resistant polymerization reactor, 125 parts of pure water and dodecylbenze
0.8 parts of sodium sulfonate, potassium persulfate 1.
After charging 2 parts and stirring thoroughly, each of the first stages shown in Table 1
Monomer and 6 parts of cyclohexene, α-methylstyrene
0.3 part of dimer, 0.2 part of t-dodecyl mercaptan
Was added to initiate polymerization at 75 ° C. Polymerization after 1.5 hours
Keep the temperature down to 70 ° C and keep each single dose in the second stage shown in Table 1.
Body and 4 parts of cyclohexene, potassium persulfate 0.5
Parts and 10 parts of pure water were continuously added over 2 hours.
Thereafter, each monomer in the third stage shown in Table 1 and 5 parts of pure water were added for 4 hours.
Was added continuously. Further raise the temperature to 73 ° C
After 5 hours, the polymerization was terminated. Then, copolymerization
The body latex is adjusted to pH 7 with aqueous sodium hydroxide solution.
After that, unreacted monomer and other low boiling point by steam distillation
The compound was removed to obtain a copolymer latex (a). Ma
In addition, except that the conditions shown in Table 1 were changed,
In the same manner as in (a), the copolymer latex (b)
To (g). Incidentally, copolymer latex (a),
(B) and (g) are copolymer latexes obtained by three-stage polymerization.
(C), (d), (e) and (f) are obtained by two-stage polymerization
Created.

[0037]Preparation of mixture slurry  100 parts of hydrogen storage alloy powder LaNi4.5Al0.5 and conductive carbon
Carboxymethyl as thickener using 5 parts of nickel
2 parts by weight of cellulose, 5 parts of copolymer latex (a)
And an appropriate amount of water so that the total solid content is 50%.
A mixture slurry for a negative electrode of Example 1 described in Table 1 was prepared.
Was. Similarly, the copolymer latex described in Table 1
Compositions for battery electrodes of Examples 2 to 3 using (b) to (c)
Using the copolymer latex (d) to (g)
The mixture slurries of Comparative Examples 1 to 4 were prepared.

[ Examples 1 to 3 and Comparative Examples 1 to 4] Each of the mixture slurries was used as a current collector to a thickness of 15 μm and an aperture ratio of 38%.
, And dried at 120 ° C. for 5 minutes, and compression-molded with a hot press to produce negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 4, respectively. The details of these evaluations are as follows. Table 1 shows the evaluation results.

[0039]Binding  From the mixture layer to the current collector using a knife on the surface of the negative electrode
Cut in depth to reach depth at 2mm intervals
I made six cuts in the grid. In this notch
Apply adhesive tape and peel off immediately to remove active material.
The degree of drop was visually judged from 5 points (no dropout) to 1 point (complete
Was dropped off).

[0040]Electrolyte resistance  In the same manner as above, insert the negative electrode
For 12 hours in 40 ° C electrolyte consisting of 1 KOH and 1N LiOH
Take it out by soaking it, and visually check the state of the negative electrode surface for 5 points (change
1) (completely dropped out) from 1).

[0041]Cycle  Each of the negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 4 was
Non-sintered nickel positive electrode using nickel hydroxide powder
And non-woven fabric of sulfonated polypropylene
And wound it into a wound body.
The rotating body is housed in a cylindrical battery can that also serves as the negative electrode terminal,
And the negative and positive terminals and the positive terminal are connected by lead terminals.
Filled the pond with an electrolyte consisting of 7N KOH and 1N LiOH
After that, the battery cover with the positive terminal is
First, a cylindrical battery was prepared. Charge / discharge at charge / discharge rate 0.2C
Is repeated 10 times to perform the activation process, and then a constant current of 1C
And 1. Charge for 5 hours, pause for 1 hour, constant current of 1C
Repeat the charge / discharge cycle to discharge to 1.0 V at
Count the number of cycles when the volume reaches 60% of the initial
Was.

[0042]

[Table 1]

[0043]

By using the copolymer latex of the present invention as a binder for a negative electrode of a nickel metal hydride secondary battery, a nickel hydride having good adhesion of a negative electrode mixture to a current collector and excellent electrolytic solution resistance is obtained. A secondary battery negative electrode is obtained, and a secondary battery having excellent cycleability can be obtained when assembled into a battery.

Continued on the front page F term (reference) 4J011 AA05 KA14 5H050 AA07 BA14 CA03 CB16 DA03 DA11 EA28 GA11 HA01

Claims (1)

[Claims] 1. An aliphatic conjugated diene monomer of 20 to 60% by weight and an ethylenically unsaturated carboxylic acid monomer of 1 to 10% by weight.
And a total of 100 parts by weight of a monomer comprising 30 to 79% by weight of another monomer copolymerizable therewith, in a ring selected from cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene A binder for a negative electrode of a nickel-hydrogen secondary battery, comprising a copolymer latex obtained by emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon having one unsaturated bond.