JP2002184398A - Slurry for preparing positive electrode of nickel-metal hydride battery, positive electrode of nickel-metal hydride battery, and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: Nickel comprising (A) nickel hydroxide, (B) at least one selected from a water-soluble cellulose derivative and a water-soluble natural polysaccharide, and (C) a water-soluble polyol. Slurry for making positive electrode of hydrogen battery. According to the present invention, a nickel hydroxide slurry having excellent viscosity stability over time can be obtained for preparing a positive electrode of a nickel-metal hydride battery, and as a result, a positive electrode of a nickel-metal hydride battery having excellent coating film uniformity can be obtained. Therefore, a nickel-metal hydride battery that is stable in quality can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode used as a positive electrode of an alkaline storage battery, and more particularly to a positive electrode of a nickel-metal hydride battery using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen. The present invention relates to a slurry, a positive electrode of a nickel-metal hydride battery, and a method of manufacturing the same.

[0002]

2. Description of the Related Art
Nickel-cadmium and lead storage batteries are used as storage batteries, that is, secondary batteries. However, in recent years,
With the spread of mobile phones and portable personal computers, as well as the increasing environmental pollution of automobiles and the growing interest in electric vehicles, the development of batteries that are lighter, have higher capacities, and have higher energy densities than these batteries has been desired. . Therefore, a so-called nickel-metal hydride battery, a so-called nickel-metal hydride battery, using a hydrogen storage alloy in combination with a nickel hydroxide positive electrode as a negative electrode and a hydrogen storage alloy capable of storing and releasing hydrogen at around normal temperature has attracted attention. I have.

[0003] The positive electrode of this nickel-metal hydride battery is a slurry in which an active material mainly composed of nickel hydroxide is dispersed in water, and the slurry mainly contains conductive foam such as foamed nickel, fiber nickel, and nickel sintered plate. It is obtained by immersing the support or applying it to a conductive support and drying. At this time, it is common practice to add a water-soluble polymer as a thickener in order to improve the stability and applicability of the slurry. Therefore, the slurry for preparing a positive electrode of a nickel-metal hydride battery includes at least an active material mainly composed of nickel hydroxide, water, and a water-soluble polymer. Nickel hydroxide is sparingly soluble in water but slightly soluble in water and shows alkalinity. On the other hand, it is known that a water-soluble polymer is reduced in molecular weight, that is, depolymerized in an alkaline aqueous solution, resulting in a decrease in viscosity.

[0004] As described above, at the time of manufacturing a positive electrode of a nickel-metal hydride battery, at least the viscosity of the slurry for the positive electrode decreases with time, causing a problem that the coating characteristics on the conductive support fluctuate.

[0005] The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a slurry for preparing a positive electrode of a nickel-metal hydride battery having excellent viscosity stability over time, a positive electrode of a nickel-metal hydride battery including the same, and a method for producing the same.

[0006]

Means for Solving the Problems and Embodiments of the Invention The present inventors have conducted intensive studies to achieve the above object, and as a result, among various water-soluble polymers, water-soluble polyols have been particularly used. In this case, it was found that the viscosity stability in the nickel hydroxide slurry was improved, and that a good aqueous slurry could be obtained, and that the obtained slurry was stable over time in coatability to the positive electrode.

That is, the present invention is characterized in that it comprises (I) (A) nickel hydroxide, (B) at least one selected from water-soluble cellulose derivatives and water-soluble natural polysaccharides, and (C) a water-soluble polyol. The slurry for preparing a positive electrode of a nickel-metal hydride battery according to (I), wherein the component (II) and the component (B) have a 1% by weight aqueous solution at 20 ° C. having a viscosity of 200 mPa · s or more. The positive electrode for a nickel-metal hydride battery according to (I) or (II), wherein the slurry for preparing a positive electrode for a battery and the water-soluble cellulose derivative of the component (III) (B) are hydroxyalkylalkylcellulose or alkylcellulose. The preparation slurry, wherein the water-soluble polyol (IV) or (C) is a polyhydric alcohol or polyhydric alcohol having three or more hydroxyl groups in one molecule. The slurry for preparing a positive electrode of a nickel-metal hydride battery according to any one of (I) to (III), (V) (A) nickel hydroxide, (B) a water-soluble cellulose derivative, (C) a positive electrode of a nickel-metal hydride battery characterized by containing at least one selected from water-soluble natural polysaccharides, (C) a water-soluble polyol, and (VI) nickel according to any one of (I) to (IV) above. A method for producing a positive electrode for a nickel-metal hydride battery, comprising immersing a conductive support in a slurry for preparing a positive electrode of a hydrogen battery or applying the slurry to the surface of the conductive support, followed by drying.

Hereinafter, the present invention will be described in more detail. The nickel hydroxide as the component (A) of the present invention is not particularly limited, and any known commercially available nickel hydroxide may be used. be able to.

The water-soluble cellulose derivative and the water-soluble natural polysaccharide of the component (B) of the present invention are not particularly limited, but the viscosity of a 1% by weight aqueous solution at 20 ° C. is 2%.
It is more preferably at least 00 mPa · s, particularly preferably at least 500 mPa · s. When the viscosity is less than 200 mPa · s, a slurry for preparing a positive electrode of a nickel-metal hydride battery having excellent operability in application or immersion on a conductive support is prepared without precipitation of nickel hydroxide having a high specific gravity even if a small amount is added. May not be possible.

Further, from the viewpoint that the electrochemical reaction of the battery is not hindered, a high-purity product containing a small amount of impurities derived from the production process of the water-soluble cellulose derivative and the water-soluble natural polysaccharide and the raw material pulp is required. More preferred.

Examples of the water-soluble cellulose derivative include hydroxyalkylalkylcellulose, alkylcellulose and carboxyalkylcellulose. Specific examples of the hydroxyalkylalkylcellulose include hydroxypropylmethylcellulose, hydroxyethylmethylcellulose and hydroxyethylethylcellulose. And the like. Examples of the alkyl cellulose include methyl cellulose and the like, and examples of the carboxyalkyl cellulose include carboxymethyl cellulose. These cellulose derivatives have excellent solubility in water used as a dispersion medium, and have the property that these cellulose derivative aqueous solutions are gelled by heating. It is preferable as a thickener for a slurry for preparing a positive electrode of a nickel-metal hydride battery, since it has a characteristic that a change in shape that occurs during drying after dipping in a slurry for application or application is small.

The water-soluble natural polysaccharides include, for example, xanthan gum, welan gum, gellan gum, ramzan gum, curdlan and the like. These water-soluble natural polysaccharides have a non-Newtonian viscous behavior in an aqueous solution, and when the conductive support is immersed in the slurry, the aqueous solution flows when the slurry is applied, but thereafter, the liquid flows due to the structural viscosity. Is stopped, and there is a characteristic that the change in the shape of the coating film is reduced.

The addition amount of the water-soluble cellulose derivative and the water-soluble natural polysaccharide is 0.1 to 2.0% by weight, preferably 0.2 to 1.5% by weight based on nickel hydroxide. If the amount is less than 0.1% by weight, sufficient viscosity cannot be exhibited, and a slurry having good coatability may not be obtained. On the other hand, when the content exceeds 2.0% by weight, the conductivity of the electrode is reduced, and the water-soluble cellulose derivative or the water-soluble natural polysaccharide coats nickel hydroxide to inhibit the electrochemical reaction in the battery, and the battery and In some cases, the capacity of the electrode cannot be sufficiently increased.

The water-soluble polyol of the component (C) of the present invention is preferably a polyhydric alcohol or a polyhydric alkanolamine having three or more hydroxyl groups in one molecule. Specifically, for example, glycerin, pentaerythritol, sorbitol, xylitol, diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine and the like can be mentioned, and polyhydric alcohols are particularly preferable.

The amount of the water-soluble polyol to be added is as described in the above (B).
0.1 to 3% by weight, preferably 0.5 to 2% by weight
% By weight. If the amount is less than 0.1% by weight, the effect of suppressing the decomposition of the binder of the component (B) may be insufficient, and 3
If the amount is more than 10% by weight, the binding effect of the binder may be impaired.

[0016] The positive electrode of the nickel-metal hydride battery of the present invention is prepared by preparing a slurry containing at least one water-soluble polyol selected from nickel hydroxide, a water-soluble cellulose derivative and a water-soluble natural polysaccharide. It can be produced by immersing the body or applying the slurry to the surface of the conductive support and drying.

Specifically, first, a 0.5 to 5% by weight aqueous solution of the water-soluble cellulose derivative of the component (B) is prepared, and a predetermined amount of a water-soluble polyol is added thereto and dissolved. The aqueous solution is added to a predetermined amount of nickel hydroxide.
Then, if necessary, water is added to prepare a slurry having an appropriate viscosity, and the obtained slurry is applied to the surface of the conductive support with a blade or the like, or the conductive support is immersed in the slurry. Thus, the slurry can be supported on the surface of the conductive support, dried, and optionally pressurized to produce the slurry.

In this case, the slurry is prepared by adding a predetermined amount of a water-soluble cellulose derivative or the like as a powder to a predetermined amount of nickel hydroxide and mixing the mixture, and then adding an appropriate amount of water as a dispersion medium so as to have an appropriate viscosity. The mixture can be also prepared by stirring and mixing, further adding a predetermined amount of a water-soluble polyol, and stirring and mixing.

Here, the conductive support can be appropriately selected from known ones. Examples thereof include foamed nickel, fiber nickel, nickel sintered plate, punching metal, expanded metal and the like. Since an alkaline solution is used as the electrolyte, at least the surface of the conductive support is preferably a nickel surface having excellent contact resistance.

[0020]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Hydroxypropyl methylcellulose having a 1.0% by weight aqueous solution viscosity of 4,620 mPa · s at 20 ° C. (90SH, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to nickel hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.). -100,0
00) and an aqueous solution prepared by adding the same amount of glycerin as hydroxypropylmethylcellulose contained in this aqueous solution to nickel hydroxide, wherein the amount of hydroxypropylmethylcellulose is 0.5% relative to nickel hydroxide. % By weight, and an appropriate amount of water was further added to prepare a kneaded slurry.

Also, after using foamed nickel as a conductive support and immersing it in the slurry prepared above,
By pulling up, a nickel hydroxide-containing slurry was applied to the surface of the nickel foam, dried, and pressed to obtain a positive electrode.

The slurry prepared in this way is
C., and the viscosity was measured over time with an E-type viscometer, and the viscosity retention with respect to the initial viscosity was calculated according to the following equation.
It was shown to. In addition, the weight of the electrode prepared using the slurry in each of the days to be left is measured, and the amount of the slurry applied to the electrode is calculated as a coating rate with respect to the initial applied amount according to the following equation,
The results are shown in Table 1. Viscosity maintenance rate (% by weight) = (measured viscosity / initial viscosity) × 10
0: Shown by A in the table. Coating rate (% by weight) = (coating amount / initial coating amount) × 100:
Indicated by B in the table.

Example 2 As a water-soluble polymer, 20 ° C.
Of a 1.0% by weight aqueous solution at 15,800 m
A slurry and a positive electrode were prepared in exactly the same manner as in Example 1, except that a 1.5% by weight aqueous solution of hydroxypropylmethylcellulose (SHV-P, manufactured by Shin-Etsu Chemical Co., Ltd.) having a Pa · s was used.

Comparative Example 1 Except that glycerin was not added,
A slurry and a positive electrode were prepared in exactly the same manner as in Example 1.

Comparative Example 2 Except that glycerin was not added,
A slurry and a positive electrode were prepared in exactly the same manner as in Example 2.

[0027]

[Table 1]

From the results shown in Table 1, it is clear that the slurries of the present invention shown in the examples are stable over time and the coating amount on the conductive support is stable.

[0029]

According to the present invention, a nickel hydroxide slurry having excellent viscosity stability over time can be obtained for preparing a positive electrode of a nickel-metal hydride battery. As a result, a positive electrode of a nickel-metal hydride battery having excellent coating film uniformity can be obtained. Is obtained,
A nickel-metal hydride battery that is stable in quality can be manufactured.

Claims (6)

[Claims] 1. A positive electrode for a nickel-metal hydride battery comprising (A) nickel hydroxide, (B) at least one selected from a water-soluble cellulose derivative and a water-soluble natural polysaccharide, and (C) a water-soluble polyol. For slurry. 2. Component (B) is 1% by weight at 20 ° C.
The slurry for preparing a positive electrode of a nickel-metal hydride battery according to claim 1, wherein the viscosity of the aqueous solution is 200 mPa · s or more. 3. The slurry for preparing a positive electrode for a nickel-metal hydride battery according to claim 1, wherein the water-soluble cellulose derivative as the component (B) is hydroxyalkylalkylcellulose or alkylcellulose. 4. The water-soluble polyol as the component (C) is a polyhydric alcohol or a polyhydric alkanolamine having three or more hydroxyl groups in one molecule.
4. The slurry for preparing a positive electrode for a nickel-metal hydride battery according to any one of items 3 to 3. 5. A positive electrode of a nickel-metal hydride battery comprising (A) nickel hydroxide, (B) at least one selected from a water-soluble cellulose derivative and a water-soluble natural polysaccharide, and (C) a water-soluble polyol. 6. A conductive support is immersed in the slurry for preparing a positive electrode of a nickel-metal hydride battery according to claim 1, or the slurry is applied to the surface of the conductive support and dried. A method for producing a positive electrode for a nickel-metal hydride battery.