JPH01231272A - Gelatinizer for gel-state anode for alkaline battery - Google Patents

Abstract

PURPOSE:To make it possible to eliminate spinnability, and to obtain high thickening in an alkaline electrolyte and the stable dispersibility of a powder- state anode active material by using the gelatinizer composed of a water absorptive resin having a sulfone group. CONSTITUTION:A water absorptive resin having a sulfone group is used as a gelatinizer. This, as it has a high dissociative high polymer electrolyte, causes the thickening in an alkaline electrolyte to become higher, the lowering of the thickening to be reduced even if a polyvalent metal ion exists, and the elapse stability of a gel to be improved. And the elapsed setting of a powder- state anode active material having a large specific gravity is small, a stable battery characteristic is given for a long time, and a battery having a long life is obtained. Moreover a filling workability into a battery is improved since spinnability is unshown with a bridge structure existed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a gelling agent for a gelled cathode of an alkaline battery.

[Prior Art] Conventionally, gelling agents for gelatinous materials used in alkaline batteries include carboxymethyl cellulose, sodium polyacrylate, cross-linked sodium polyacrylate, and saponified starch-acrylonitrile copolymers. Weakly decomposable water-soluble resins or crosslinked water-swellable resins have been used.

[Problems to be Solved by the Invention] However, when a powdered cathode active material (for example, zinc powder) is dispersed using these as a gelling agent, a good gel state with almost no stringiness is created in the initial stage. However, over time, it decomposes in the alkaline electrolyte and its viscosity decreases, resulting in a sticky gel with high stringiness. In addition, the viscosity of water-soluble resins such as carboxymethyl cellulose and sodium polyacrylate changes relatively sharply with temperature. As a result, the dispersion stability of the powdered cathode active material with a large specific gravity is impaired and sedimentation occurs.
Problems arise in that the internal resistance of the battery increases and the discharge performance deteriorates.

In addition, the above-mentioned weakly dissociable gelling agent having a carboxyl group progresses to insolubilization of the cathode active material such as zinc contained in the gelled cathode due to ionic crosslinking, and its thickening property decreases over time. Therefore, there is a problem that the long-term dispersion stability of the cathode active material is poor.

[Means for Solving the Problems] The present inventors have discovered a method that has no stringiness, exhibits high viscosity in alkaline electrolytes, and has stable dispersibility of powdered cathode active materials such as zinc dust. As a result of extensive research into a gelling agent for a gelled cathode of an alkaline battery that can maintain the internal resistance and discharge performance of the battery well over a long period of time, the present invention has been arrived at. That is, the present invention is a gelling agent for a gelled cathode of an alkaline battery, which is made of a water-absorbing resin having a sulfone group.

In the present invention, the water-absorbing resin having a sulfone group includes (1) a vinyl monomer having a sulfone group (A>, a copolymerizable crosslinking agent (B) and, if necessary, a nonionic vinyl monomer (D)). (2) a vinyl monomer having a sulfone group (A), a copolymerizable crosslinking agent (
B), a water-absorbing resin obtained by polymerizing a vinyl monomer (C) having a carboxyl group and, if necessary, a nonionic vinyl monomer (C), which may be neutralized or partially neutralized with an alkali compound. Examples include.

Examples of the vinyl monomer (A) having a sulfonic group include aliphatic or aromatic vinylsulfonic acids [vinylsulfonic acid, (meth)allylsulfonic acid, vinyltoluenesulfonic acid, styrenesulfonic acid, etc., (meth)acrylic acid] Examples include sulfonic acid [sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, etc.], (meth)acrylamidosulfonic acid [2-acrylamido-2-methylpropanesulfonic acid, etc.].

As the vinyl monomer (C) having a carboxyl group,
For example, unsaturated mono- or polycarboxylic acids [(meth)acrylic acid (refers to acrylic acid and/or methacrylic acid. The same description will be used hereinafter), crotonic acid, sorbic acid, maleic acid, itaconic acid, cinnamic acid, etc. and their anhydrides [such as maleic anhydride].

These vinyl monomers having sulfonic groups and/or carboxyl groups may be used as water-soluble salts. These salts include alkali metal salts (storium, potassium, lithium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), ammonium salts and amine salts (alkyl amine salts such as methylamine, trimethylamine, etc.). salts; salts of alkanolamines such as triethanolamine and jetanolamine) and two or more thereof. Preferred among these are sodium and potassium salts.

The above vinyl monomers having a sulfone group and/or a carboxyl group may be used alone or in combination of two or more.

The copolymerizable crosslinking agent (B) includes (1) a compound having at least two polymerizable double bonds and (2) a compound having one polymerizable double bond and a sulfonic group and/or a carboxyl group. Examples include compounds having at least one reactive group.

Examples of the compound (1) include N,N-methylenebis(meth)acrylamide, polyols [ethylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, etc.] ) Acrylic acid ester, divinylbenzene, divinyltoluene, tetraallyloxyethane, diallyl phthalate, diallylazibe-1.

Examples of compounds (2) include ethylenically unsaturated compounds containing groups reactive with sulfone groups and/or carboxyl groups, such as hydroxyl groups, epoxy groups, amine groups, and quaternary ammonium bases. For example, unsaturated compounds containing hydroxyl groups [N-methylol (
meth)acrylamide, etc., epoxy group-containing unsaturated compounds [such as methacrylate] and quaternary ammonium J, base-containing unsaturated compounds [(meth)acryloyloxyethyltrimethylammonium chloride, trimethylaminopropyl(meth)acrylate, etc.] ) acrylamide chloride, etc.].

Among the copolymerizable crosslinking agents (13), preferred are (1)
Among these compounds, particularly preferred are N,N-methylenebisacrylamide, ethylene glycol diacrylate-1, trimethylolpropane triacrylate. A polymer (D) can be used in combination, for example, hydroxyethyl (meth)acrylate).
Examples include hydroxypropyl (meth)acrylate, (meth)acrylamide, and vinylpyrrolidone.

In the water absorbent resin of the present invention, the amount of the vinyl monomer (A) having a sulfone group is determined by the amount of the vinyl monomer (A) having the required absorption performance, viscosity
Although it varies depending on conditions such as the strength of the gel, (A)
, ([3), based on the total weight of (C) and (D), it is usually 30% or more, preferably 50% or more.

If the amount of (A) is less than 30%, alkaline n! 1? α
The thickening properties of the cathode active material and its stability over time are reduced, and as a result, the long-term dispersion stability of the cathode active material is also reduced.

The amount of the vinyl monomer (C) having a carboxyl group used together if necessary is (A), (B), <C> and ('')
), usually 70% or less, preferably 50% or less, based on the total weight of

In the present invention, the amount of the copolymerizable crosslinking agent (B) is (A),
Usually 0 for the total weight of (B), (C) and (D)
．． 0.01-10%, preferably 0.1-5%. If the content of the copolymerizable crosslinking agent is less than 0.01%, the resulting resin will have a low gel strength when absorbed with an alkaline electrolyte and will become sol-like.
Shows stringability. Furthermore, the dispersion stability of the cathode active material is also poor.

On the other hand, if it exceeds 10% by weight, the gel strength will be too high and the viscosity will decrease.

In addition, nonionic vinyl monomer (D
) is usually 30% or less, preferably 10% or less, based on the total weight of (A), (B), (C) and (D).

A vinyl monomer having a sulfonic group (A), a copolymerizable crosslinking agent (U3), and a vinyl monomer having a carboxyl group (C) and/or a nonionic vinyl monomer (D) used together if necessary. The polymerization method may be a conventionally known method, such as a method in which an aqueous solution or dispersion of these is polymerized using a radical polymerization initiator,
Examples include a reverse phase suspension polymerization method using an organic solvent and a conventional method of irradiating with radiation, electron beams, ultraviolet rays, etc.

In the present invention, if necessary, an alkali compound can be added to neutralize the acid groups to partially form an alkali base.

Alkali compounds include alkali metal hydroxides (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.)
, alkali metal carbonates (sodium carbonate, sodium bicarbonate), amine compounds, ammonium compounds, and two or more thereof. Preferred among these are sodium hydroxide, potassium hydroxide and sodium bicarbonate.

The degree of neutralization is usually 90 mol% or less, preferably 50 to 80 mol% of the sulfonic acid groups and/or carboxylic acid groups. If the degree of neutralization of the sulfonic acid groups and/or the carbonic acid groups exceeds 90 mol %, the resulting resin will have a high degree of concavity, which poses a safety problem for human skin.

By further crosslinking with a compound that has at least two groups that react with the functional groups in the polymer, a resin with higher gel strength and thickening properties and superior viscosity and stability of the cathode active material is produced. can do.

Examples of such compounds include compounds having at least two groups reactive with sulfonic groups and/or carboxyl groups such as epoxy groups, hydroxyl groups, isocyanate groups, and quaternary ammonium groups, and polyvalent metal compounds capable of forming ionic crosslinks. can be given.

Next, the polymer is dried and pulverized by a conventional method, and if necessary, the particle size is adjusted to a desired size to obtain the gelling agent of the present invention.

The shape of the gelling agent is not particularly limited, and may be powdery, granular,
It may be in any shape such as flakes or fibers. Preferably, it is in the form of a fine powder with a particle size of 200 microns or less.

A method for creating a gelled cathode using the gelling agent of the present invention and applying it to an alkaline battery includes (1) an alkaline electrolyte (for example, 30 to 40% potassium hydroxide, water and, if necessary, zinc oxide, etc.); (2) A method in which a gelling agent and powdered zinc are added simultaneously or separately to a gelling agent (composed of Examples of methods include adding a curing agent and powdered zinc into the battery and then injecting an alkaline electrolyte to form a gel cathode. applied in the following manner.

The amount of the gelling agent added is usually 0.5 to 10%, preferably 1 to 5%, based on the total weight of the alkaline electrolyte and the gelling agent. If the amount added is less than 0.5%, the viscosity of the gelled cathode will be insufficient and the zinc dust will settle over time, and there is a risk of leakage. In addition, the internal resistance changes significantly over time. On the other hand, if it exceeds 10%, the viscosity becomes too high, leading to the entrapment of air bubbles, a decrease in the workability of filling into the battery, and an increase in internal resistance.

[Example] The present invention will be further explained below with reference to Examples, but the present invention is not limited thereto. Note that parts in the examples are parts by weight.

Example 1 60 parts of acrylic acid, 115 parts of 2-acrylamido-2-methylpropanesulfonic acid, 1 part of N,N-methylenebisacrylamide, and 525 parts of water were charged into an airtight container that can be opened and closed, and the liquid temperature was lowered under a nitrogen atmosphere. The temperature was set at 10°C (u
When 1 part of a 10.5% N aqueous ammonium persulfate solution and 1 part of a 0.5% sodium bisulfite aqueous solution were added and polymerized, it became gel-like with heat generation. Eight hours after the start of polymerization, the closed reaction vessel was opened, and the produced gel-like hydrous crosslinked polymer was taken out. After cutting this gel-like water-containing cross-linked polymer into pieces, a 30% thorium hydroxide aqueous solution 1
38 parts of the polymer was added to neutralize the mixture, and the mixture was roughly and uniformly kneaded to convert about 75 mol % of the acid groups in the polymer into lithium salt.

This neutralized gel was dried with a drum dryer heated to 150° C., and then ground to a particle size of 100 mesh or less to obtain the gelling agent (a) of the present invention.

Example 2 The gelling agent (b) of the present invention was obtained in exactly the same manner as in Example 1 except that 116 parts of sulfopropyl methacrylate was used in place of 115 parts of 2-acrylamido-2-methylpropanesulfonic acid. Ta.

Example 3 In Example 1, 160 parts of acrylic, 115 parts of 2-acrylamido-2-methylpropanesulfonic acid, N.

30 parts of acrylic acid, 2-acrylamide-2- in place of 1 part of N-methylenebisacrylamide and 525 parts of water
A gelling agent (c) of the present invention was obtained in exactly the same manner except that 201 parts of methylpropanesulfonic acid, 0.8 parts of tetraallyloxyethane and 693 parts of water were used.

Example 4 In Example 3, 287 parts of 2-acrylamido-2-methylpropanesulfonic acid and 860 parts of water were used in place of 30 parts of acrylic acid, 2-acrylamido-2-methyl, 1 part of methylpropanesulfone M2O, and 693 parts of water. The gelling agent (d) of the present invention was obtained in exactly the same manner except for using the same method.

<Evaluation method> The amounts of the gelling agents (a), (b), (c) or (d) obtained in Examples 1 to 4 shown in Table 1 were added to a 40% potassium hydroxide aqueous solution and mixed. A gel electrolyte solution of 11 and 8 was prepared, and 1 part 8 of zinc powder (average particle size 200 microns) was added to this gel electrolyte solution, and the mixture was stirred and mixed uniformly to obtain a gel material. This gel-like substance is stored in a cylindrical container (height 1001Illll).
I, diameter 50+nn+) was sealed and stored at room temperature for a month, and the settling height of the zinc powder was measured.

Immediately after assembling a battery by filling the same gel-like substance as above into the hollow space in the separator of an alkaline manganese battery and after storing it at room temperature for 2 months (20°C
) was measured. These results are shown in Table 1.

For comparison, as a gelling agent, Calbonxymethylcellulose (Daiichi Kogyo Seiyaku 01) and Fine Gum IIES were used.
S), when using sodium polyacrylate (manufactured by Toagosei Co., Ltd., Aron A-20P), and when using cross-linked sodium polyacrylate-based water absorbent resin (Steel Chemical Industry Co., Ltd. (manufactured by Toagosei Co., Ltd., Aqua Keep 10SH)). The evaluation results when used are also listed in Table 1 as Examples 5 to 7.

[Effects of the Invention] By using the gelling agent for the gelled cathode of an alkaline battery of the present invention, the following effects are achieved.

(1) It has good thickening properties and gel stability over time even when added in small amounts.

Conventional water-soluble resins or cross-linked water-swellable resins consisting of carboxyl groups are weakly dissociable polymer electrolytes, so they have poor viscosity in alkaline electrolytes containing large amounts of potassium hydroxide, etc. If polyvalent metal ions exist, the insolubilization of the resin will proceed due to ionic crosslinking, further reducing the viscosity increasing property.Therefore, the stability of the gel over time will be poor.

However, since the water-absorbing resin having a sulfone group in the present invention is a strongly dissociable polymer electrolyte, it has a high viscosity increase in an alkaline electrolyte, and even in the presence of polyvalent ions, the viscosity decreases only slightly. , excellent gel stability over time.

(2) A good dispersion state of the powdered cathode active material (for example, zinc powder) can be maintained for a long period of time.

As mentioned above, the gelling agent of the present invention has a high viscosity increasing property for an alkaline electrolyte containing a cathode active material, and also has excellent gel stability over time. There is little sedimentation. Therefore, a battery with stable battery characteristics over a long period of time and a long life can be obtained.

(3) There is no stringiness in the gel-like cathode state.

Since the gelling agent of the present invention has a crosslinked structure, it does not exhibit stringiness. Therefore, the workability of filling the battery into the battery is good.

(4) Little change in viscosity due to temperature.

Since the gelling agent of the present invention has a crosslinked structure, its viscosity changes less with temperature than non-crosslinked water-soluble resins such as carboxymethyl cellulose and sodium polyacrylate. Therefore, it exhibits stable battery characteristics in a wide range of temperature environments.

(5) Since the gelling agent of the present invention strongly retains the alkaline electrolyte for a long time, there is little increase in resistance due to drying.

(6) Internal resistance is small and its change over time is also small.

(7) No leakage even after long-term storage.

Because of the above effects, the gelling agent for gelled cathodes of the present invention can be used not only for cylindrical alkaline manganese batteries, but also for button-shaped alkaline manganese batteries, silver oxide batteries, mercury batteries, nickel batteries, etc. It can also be applied to other primary and secondary alkaline batteries as required.

1-nininini 1

Claims (1)

[Scope of Claims] 1. A gelling agent for a gelled cathode of an alkaline battery, which is made of a water-absorbing resin having a sulfone group. 2. The water absorbent resin having a sulfone group contains a vinyl monomer (A) having a sulfone group, a copolymerizable crosslinking agent (B), and, if necessary, other anionic vinyl monomers (C).
The gelling agent according to claim 1, which is a water-absorbing resin obtained by polymerizing and/or a nonionic vinyl monomer (D) and which may be neutralized or partially neutralized with an alkali compound. 3. The content of the vinyl monomer (A) having a sulfone group is 30% or more based on the total weight of (A), (B), (C) and (D). gelling agent.