JPH10241692A - Hydrogen-storage electrode binder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow to firing risk, lessen effect on electrode active materials, maintain high conductivity, and enhance the binding property with collecting material by specifying a glass transition point and the containing amount of toluene insoluble portion, and constituting of an aqueous dispersing body of a copolymer, containing a functional group in a polymer. SOLUTION: In a copolymer used as a hydrogen-storage electrode binder, a toluene insoluble portion is 20 to 100 percentage by weight, a glass transition point is 5 deg. or less, a functional group such as a carboxyl group, an acid anhydride group, a glycidyl group, or an amino group is required. As the aqueous dispersing body of the copolymers, a styrene-isoprene copolymer, polyorganosiloxane polymer polyvinylidene fluoride polymer, and the like are cited, and the same can be synthesized by a normal emulsion polymerization method. By the binder formed thereof, it is possible to obtain a hydrogen storage alloy electrode for a nickel hydrogen secondary battery, which has a high binding property with the collecting material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for a secondary battery electrode having excellent binding properties, charge / discharge cycle properties, storage characteristics, and safety. More specifically, the present invention relates to a binder composition for a hydrogen storage electrode in which a hydrogen storage alloy is held on a current collector.

[0002]

2. Description of the Related Art In recent years, technological progress in the electronics industry has been remarkable, and demands for high energy density, safety, and the like have also been increasing in battery technology. Nickel / hydrogen batteries have attracted attention as batteries with high energy density per unit volume and excellent safety because they do not contain pollutants. Nickel / hydrogen batteries use a hydrogen storage alloy as the active material of the negative electrode, which freely releases hydrogen ions with heat generation and heat absorption in a hydrogen atmosphere. The ease of absorbing and releasing hydrogen ions leads to higher capacity and longer life. Nickel / hydrogen batteries have already been put to practical use because they are capable of rapid charge / discharge, are resistant to overcharge and overdischarge, and have excellent performance in terms of high capacity, small size, and light weight. In nickel / hydrogen batteries, a polymer binder is used for the purpose of fixing the active material to the current collector, and the performance required for this binder is that the binding between the active material and the current collector is good,
Examples of the method include freely moving hydrogen ions in the electrolytic solution with as little resistance as possible, and preventing volume change due to the electrolytic solution and charge / discharge. For example, conventionally, as binders for hydrogen storage alloys, fluorine-based polymers such as polytetrafluoroethylene and polyvinylidene fluoride have been known, but these fluorine-based polymers have poor binding properties with a current collector, and have a poor charge / discharge cycle. There is a problem that the active material is easily peeled off by repeating the above. In order to solve such a problem, attempts have been made to use, for example, SEBS (styrene-ethylenebutylene-styrene block copolymer) which is a thermoplastic elastomer. In addition, since an organic solvent such as toluene is used, there is a problem in that there is a high risk of ignition in a mixing process with a hydrogen storage alloy in an industrial scale manufacturing process. Attempts have been made to use emulsions of aqueous styrene-butadiene copolymers, but since the binder encloses the entire active material,
There is a problem that charge / discharge efficiency is poor and adhesion to a current collector is insufficient.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a nickel / hydrogen secondary battery using a hydrogen storage alloy as an electrode active material, in an aqueous system having no danger of ignition in the mixing process of the hydrogen storage alloy and the binder. An object of the present invention is to achieve long life and high capacity by using a binder that has little influence on a substance, maintains high conductivity, and has excellent binding properties with a current collector.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a polymer having a glass transition point of 5 ° C. or less, a toluene insoluble content of 20 to 100% by weight, and a polymer containing a functional group. An object of the present invention is to provide a binder for a hydrogen storage electrode, comprising a water-based dispersion of a polymer.

Hereinafter, the present invention will be described in detail. The copolymer used in the present invention has a toluene-insoluble content of 20 to 100% by weight, preferably 30 to 90% by weight, particularly preferably 5 to 90% by weight.
0 to 85% by weight. In the present invention, the toluene-insoluble content is adjusted to pH with 0.5N ammonia water or 0.5N hydrochloric acid.
The aqueous dispersion of the copolymer having a solid content of 50% by weight adjusted to 8 was added to 1
After drying at 20 ° C. for 1 hour to form a film, the dried film is put in a container such as an Erlenmeyer flask together with 100 parts by weight of toluene of the polymer, shaken for 3 hours, and then filtered through a 200 mesh filter to remove insoluble matter. And collected at 120 ° C
After drying for 1 hour, the weight of the insoluble matter is measured, and the gel amount is determined by the following equation. Gel amount = (weight of toluene-insoluble matter / weight before immersion) × 10
If the toluene-insoluble content of the 0 (%) copolymer is less than 20% by weight, a polymer flow occurs when the electrode is formed and heated and dried, so that the electrode active material is excessively covered. In addition, the durability of potassium hydroxide, which is an electrolytic solution, is poor, and the hydrogen storage alloy is detached from the current collector.
The glass transition point (Tg) of the copolymer used in the present invention is 5
It is below ° C. When the Tg exceeds 5 ° C., the polymer film obtained from the copolymer has poor flexibility and tackiness and poor adhesion of the active material to the current collector. In the present invention, the copolymer is used as an aqueous dispersion. The average particle size of the copolymer particles dispersed in the aqueous dispersion is 0.05 to 5 μm.
m is preferably, more preferably 0.1 to 2 μm, and desirably smaller than 1/3 of the electrode active material. The copolymer used in the present invention needs to have a functional group such as a carboxy group, an acid anhydride group, a glycidyl group, and an amino group.
%, Preferably determined by pyrolysis gas chromatography. When the functional group is less than 0.1%, the binder performance and chemical resistance of the copolymer are inferior, while 10%
Exceeding the water resistance and storage stability are undesirably poor.

The aqueous dispersion of the copolymer that can be used in the present invention includes styrene-isoprene copolymer,
Examples thereof include polyorganosiloxane polymers and polyvinylidene fluoride polymers. Aqueous dispersions of these copolymers can be synthesized by a usual emulsion polymerization method. Styrene-isoprene copolymer is isoprene 30
% Or more, 30 to 60% by weight of styrene, and 0.1 to 10% by weight of a functional monomer described below by emulsion polymerization.
The polyorganosiloxane-based polymer is obtained by co-condensing a polyorganosiloxane-based polymer with an organosiloxane, if necessary, in the presence of an aqueous dispersion of the polyorganosiloxane-based polymer, an alkyl acrylate, a functional monomer described below. And other monomer components copolymerizable therewith by emulsion polymerization. In addition, acrylates include, for example, methyl (meth) acrylate, (meth)
Ethyl acrylate, n-propyl (meth) acrylate,
I-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth)
N-Amyl acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-hexyl (meth) acrylate, octyl (meth) acrylate, (meth)
Examples thereof include i-nonyl acrylate, decyl (meth) acrylate, hydroshimethyl (meth) acrylate, and hydroxyethyl (meth) acrylate. Examples of monomers copolymerizable with the alkyl acrylate and the functional monomer include α-methylstyrene, divinylbenzene, and ethylene glycol dimethacrylate.

[0007] The polyvinylidene fluoride polymer is
(B) a polymer obtained by polymerizing a monomer comprising 50 to 80% by weight of vinylidene fluoride, 20 to 50% by weight of propylene hexafluoride and 0 to 30% by weight of a copolymerizable monomer; A) a fluoropolymer obtained by polymerizing a monomer comprising 50 to 80% by weight of vinylidene fluoride, 20 to 50% by weight of propylene hexafluoride and 0 to 30% by weight of a copolymerizable monomer; ) 40 to 100% by weight of alkyl acrylate and other copolymerizable monomer 0
And a composite polymer obtained by compounding an acrylic polymer obtained by polymerizing a monomer of 60 to 60% by weight. The polyvinylidene fluoride-based polymer can be synthesized preferably by the method described in JP-A-7-258499, and the polyorganosiloxane-based polymer can be synthesized preferably by the method described in JP-A-4-261454.

In the present invention, examples of the functional monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, (meth) acrylic acid, itaconic acid, fumaric acid, and maleic acid; (meth) acrylamide, N-methylolacrylamide Alkyl amides of ethylenically unsaturated carboxylic acids such as vinyl acetate; vinyl carboxylate esters such as vinyl acetate and vinyl propionate; acid anhydrides, monoalkyl esters, monoamides of ethylenically unsaturated dicarboxylic acids; aminoethyl acrylate, dimethylamino Aminoalkyl esters of ethylenically unsaturated carboxylic acids such as ethyl acrylate and butylaminoethyl acrylate; ethylene compounds such as aminoethylacrylamide, dimethylaminomethylmethacrylamide, methylaminopropylmethacrylamide (Meth) acrylonitrile, alpha-chloro acrylonitrile vinyl cyanide compounds such as; aminoalkyl amides of unsaturated carboxylic acids and unsaturated aliphatic glycidyl esters such as glycidyl (meth) acrylate. These can be used alone or in combination of two or more.
It is essential in terms of binding strength. These functional monomers are used in an amount of 0.1 to 10% by weight, preferably 2 to 10% by weight, based on the total amount of all monomer components used for producing the copolymer.
%, More preferably 3 to 10% by weight.

In the present invention, a battery electrode composition containing an aqueous dispersion of a copolymer as a binder may optionally contain a thickener as an additive in an amount of 1 to 100 parts by weight of the copolymer.
200 parts by weight may be used. Examples of the water-soluble thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein and the like. The solids content of the aqueous dispersion of the copolymer is usually 20 to 65% by weight, preferably 35 to 60% by weight.

The binder for a hydrogen storage electrode of the present invention is mixed with a hydrogen storage alloy powder to form a composition for a battery electrode, and the composition for a battery electrode is applied to a current collector and dried to obtain a hydrogen storage electrode. Can be manufactured. The hydrogen storage alloy powder used in the present invention is obtained by replacing a part of Ni with Mn, Al, Co or the like based on MmNi5.
Here, Mm represents a misch metal which is a mixture of rare earth elements. The shape of the powder is a powder that has passed through 100 mesh, and the particle diameter is about 3 to 400 μm. The binder for a hydrogen storage electrode of the present invention is compounded in a solid content of 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the hydrogen storage alloy powder. If the amount of the binder for a hydrogen storage electrode is less than 0.1 part by weight, good adhesive strength cannot be obtained, and if it exceeds 20 parts by weight, the overvoltage increases significantly and adversely affects battery characteristics. The composition for a battery electrode is composed of a hydrogen storage alloy powder, a binder for a hydrogen storage electrode, and a water-soluble thickener as required.
Dispersants such as sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, and sodium polyacrylate; additives such as nonionic and anionic surfactants as latex stabilizers; and for the purpose of imparting electrode conductivity Carbon may be added.

In order to form a hydrogen storage electrode, the composition for a battery electrode is preferably applied in the form of a slurry to a current collector, heated and dried. The current collector is a core plate made of a metal such as nickel and having a thickness of 40 to 80 μm, and is preferably porous. At this time, the opening ratio of the metal core plate is usually 30 to 60%. At this time, if necessary, it may be molded together with the current collector material, or alternatively, it may be used by being applied to a current collector base material such as Ni mesh or punched Ni. As a method of applying the composition for a battery electrode, any coater head such as a reverse roll method, a comma bar method, a gravure method, and an air knife method can be used, and the drying methods include standing drying, blast drying, and hot air drying. , An infrared heater, a far infrared heater and the like can be used. The drying temperature is usually 150 ° C.

When assembling a nickel-metal hydride battery using the battery electrode obtained as described above, potassium hydroxide of 5N or more is used as an electrolyte, and a positive electrode material NiOO
H, a hydrogen storage alloy is used for the negative electrode. Further, if necessary, a battery is configured using components such as a separator, a current collector, a terminal, and an insulating plate. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, and, if necessary, a paper type battery having a single-layer or multiple-layer separator,
Alternatively, examples include a positive electrode, a negative electrode, and, if necessary, a cylindrical battery in which a separator is wound in a roll shape. The battery electrode manufactured using the binder for a hydrogen storage electrode of the present invention can be suitably used for OA equipment, portable AV equipment, and the like.

[0013]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these embodiments. Measurement method (1) Toluene gel amount measurement; latex adjusted to pH 8 with 0.5N ammonia water and 0.5N hydrochloric acid was used for 120
After drying at ℃ for 1 hour to form a film, 1% of the polymer weight
After immersing in 00 parts by weight of toluene and shaking for 3 hours, 200
The mixture was filtered through a mesh filter to collect insolubles, and 12
After drying at 0 ° C. for 1 hour, the weight of the insoluble matter was measured, and the gel amount was determined by the following equation. Gel amount = (weight of toluene-insoluble matter / weight before immersion) × 10
0 (%) (2) Measurement of glass transition point: Using the film prepared in (1), the glass transition point was determined using a Seiko Denshi Kogyo KK (differential scanning calorimeter). (3) Measurement of average particle diameter: The particle diameter was measured using a laser particle size analysis system LPA-3000s / 3100 manufactured by Otsuka Electronics Co., Ltd.

Example 1 An autoclave equipped with a stirrer was charged with 70 parts of ion-exchanged water and 0.3 part of potassium persulfate, and the gas phase was replaced with nitrogen gas for 15 minutes, and the temperature was raised to 80 ° C. On the other hand, the components shown in Table 1 and 0.2 parts by weight of the emulsifier dodecylbenzenesulfonic acid were mixed in a separate container and added dropwise to the autoclave over 15 hours. During the dropwise addition, the reaction was carried out at 80 ° C. After the completion of the dropwise addition, the mixture was further stirred at 85 ° C. for 5 hours to terminate the reaction. After cooling to 25 ° C., the pH was adjusted to 7 with potassium hydroxide, then steam was introduced to remove residual monomers, and then concentrated to obtain an aqueous dispersion of a copolymer.

Examples 2 and 4 (1) Vinylphenylmethyldimethoxysilane (VpM
(DMS) 1.5 parts and octamethylcyclotetrasiloxane (D4) 98.5 parts were mixed, and this was mixed with α-olefin sulfonic acid (RCH ＝ CH (CH 2) nSO 3 Na).
About 75 wt%, RCH2CH (OH) (CH2) mSO
2.0 parts of a mixture of 3Na (about 25% by weight) was placed in 300 parts of distilled water in which 2.0 parts were dissolved, and the mixture was stirred for 3 minutes with a homomixer to emulsify and disperse. This mixed solution was transferred to a separable flask equipped with a condenser, a nitrogen inlet and a stirrer, heated at 90 ° C. for 6 hours while stirring and mixing, and then heated at 5 ° C. for 2 hours.
The condensation was completed by cooling for 4 hours. The obtained aqueous dispersion of organopolysiloxane was neutralized to a sodium carbonate aqueous solution pH of 7. (2) A separable flask equipped with a condenser, a nitrogen inlet, and a stirrer was charged with 100 parts by weight (solid content) of an aqueous dispersion of an organopolysiloxane, 70 parts of ion-exchanged water, and 0.3 part of ammonium persulfate. The phase was replaced with nitrogen gas for 15 minutes, and the temperature was raised to 80 ° C. (3) Separately, 21 parts by weight of styrene, 71 parts by weight of n-butyl acrylate and 8 parts by weight of glycidyl methacrylate were mixed in a separate container, and added dropwise to the aqueous organopolysiloxane dispersion of (2) over 3 hours. During the dropwise addition, the reaction was carried out at 80 ° C. while introducing nitrogen gas. After the completion of the dropwise addition, the mixture was further stirred at 85 ° C. for 2 hours to terminate the reaction. Then cool to 25 ° C, adjust to pH 7 with aqueous ammonia,
An aqueous dispersion of a styrene acrylic-modified silicone polymer was obtained.

Example 3 (1) An autoclave equipped with an electromagnetic stirrer and having an internal volume of about 6 liters was sufficiently replaced with nitrogen gas, and then 2.5 liters of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier were used. And heated to 60 ° C. while stirring at 350 rpm. Next, a mixed gas consisting of 44.2% by weight of vinylidene fluoride monomer (VdF) and 55.8% by weight of propylene hexafluoride monomer (HFP) was charged to 20 kg / cm 2 G, and diisopropyl par as a polymerization initiator was charged. 25 g of a Freon 113 solution containing 20% by weight of oxydicarbonate was injected with nitrogen gas to initiate polymerization. As the pressure drops as the polymerization proceeds, V
A mixed gas consisting of 60.2% by weight of dF and 39.8% by weight of HFP was sequentially injected, and the reaction was continued while maintaining the pressure at 20 kg / cm 2 G. Since the polymerization rate decreases with the reaction time, after 3 hours, the same amount of the polymerization initiator as above was again injected with nitrogen gas, and the reaction was further continued for 3 hours. Next, the system was cooled and the stirring was stopped, and then the unreacted monomer was released to stop the reaction, thereby obtaining a water body of the fluoropolymer. (2) After the inside of the separable flask having a capacity of 7 liters was replaced with nitrogen, 150 parts of the obtained fluoropolymer aqueous dispersion was converted to solids and 2- (1-allyl) -4-
Nonylphenoxy polyethylene glycol sulfate ammonium (3 parts) was added, and the temperature was raised to 75 ° C. Next, the monomer mixture (and optionally water) was added and stirred at 75 ° C. for 30 minutes. After adding 0.5 part of sodium persulfate thereto and polymerizing at 85 to 95 ° C. for 2 hours, the reaction was stopped by cooling to obtain an aqueous dispersion of a polyvinyldenfluoride-based polymer.

Comparative Examples 1 and 3 A polymer aqueous dispersion was obtained in the same manner as in Example 1 except that the composition of the monomer component was changed as shown in Table 2. Comparative Example 2 An aqueous dispersion of a styrene acrylic-modified silicone polymer was prepared in the same manner as in Example 4 except that the amount of the organopolysiloxane used and the composition of the monomer components were changed as shown in Table 2. Obtained.

[0018]

[0019] The abbreviations of the monomers in Tables 1 and 2 indicate the following compounds. D4 = octamethylcyclotetrasiloxane VpMDMS = vinylphenylmethyldimethoxysilane VdF = vinylidene fluoride HFP = propylene hexafluoride ST = styrene IP = isoprene GMA = glycidyl methacrylate nBA = n-butyl acrylate MMA = methyl methacrylate AA = acrylic acid IA = Itaconic acid NMAM = N-methylolacrylamide

Test Example Hydrogen storage alloy powder having an average particle diameter of 170 μm (La 0.99 wt%, Ni 3.41 wt%, Co 1.20 wt%, Mn 0.10 wt%, Al 0.29 wt%) and Example 1 ~ 6 and Comparative Examples 1 ~
1 part by weight of the binder for the battery electrode prepared in 3 and 1 part by weight of a polyvinyl alcohol aqueous solution as a thickener in solid content were added and mixed well to prepare a composition for a battery electrode, and the obtained battery electrode was used. The following tests were performed. The results are shown in Tables 3 and 4. (1) Binding property with Ni mesh; Using a 1 mm thick Ni mesh as a base material, the obtained composition for a battery electrode was applied with an applicator at a thickness of 400 g / m 2,
The resultant was dried at 20 ° C. for 20 minutes and pressure-bonded to obtain a 200 μm thick battery electrode. An adhesive tape was attached to the obtained battery electrode, and after peeling off, the condition of the coating film attached to the adhesive surface was evaluated. For example, when the coating film hardly adheres to the adhesive surface, 5 points,
One point is when the coating film on the entire adhesive surface is peeled off. (2) Conductivity measurement method: A battery electrode composition was applied to a 100 μm PET film at a thickness of 400 g / m 2,
The coating was dried at 50 ° C. × 20 minutes and pressed to obtain a coating film having a thickness of 200 μm. The resistance was measured by a four-terminal method. (3) Electrolytic solution resistance: The battery electrode obtained in the above (1) was immersed in an electrolytic solution 6NKOH for 24 hours. 5 points when there is no change and 1 point when completely peeled. (4) Battery characteristics: Nickel oxide as positive electrode, battery electrode obtained in (1) above as negative electrode, 0.9 cm × 5.5 cm
And a Ni lead wire was welded to each, and a 6N aqueous potassium hydroxide solution was used as an electrolyte to combine with a separator to assemble a battery. The cycle of charging the battery to 2.0 V and discharging it to 1.0 V at 10 mA was repeated, and the capacity retention was measured. The cell charged to 2.0 V was stored at 70 ° C. for 30 days, and the storage stability was measured.

[0021]

[0022]

Examples 1 to 4 in Table 1 show the polymers falling within the scope of the present invention, and Table 2 shows the compositions of the polymers outside the scope of the present invention, toluene gel, Tg, and average particle diameter. As is evident from Table 3, when the polymer of the present invention is used, the binding property, the conductivity, and the resistance to the electrolytic solution are balanced, and the cycle characteristics of battery characteristics, storage characteristics, and safety are excellent. On the other hand, Comparative Examples 1 and 2 are examples of a polymer having a high Tg, and have low binding power and low flexibility and are inferior in battery characteristics. Comparative Example 3
Is an example of a polymer into which a monomer having a functional group is not introduced, and is inferior in binding properties, electrolyte resistance, and battery characteristics.

[0024]

According to the binder for a hydrogen storage electrode of the present invention, in a battery using a hydrogen storage alloy as an electrode active material, mainly in a nickel-hydrogen secondary battery, excellent electrolyte resistance and high conductivity are maintained. In addition, a hydrogen storage alloy electrode having a high binding property with the current collector can be obtained. In addition, since water is used as a dispersion medium, the process of forming an electrode is also facilitated. Further, the hydrogen storage alloy electrode using the binder of the present invention provides a nickel-hydrogen secondary battery having excellent charge / discharge cycle characteristics.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasumasa Takeuchi 2-11-24 Tsukiji, Chuo-ku, Tokyo Inside Nippon Gosei Rubber Co., Ltd.

Claims (1)

[Claims] A binder for a hydrogen storage electrode, comprising a water-based dispersion of a copolymer having a glass transition point of 5 ° C. or lower, a toluene insoluble content of 20 to 100% by weight, and a functional group in a polymer. .