JPH0589877A - Manufacture of negative electrode of hydrogen storage alloy - Google Patents

Abstract

PURPOSE:To prevent a three-dimensional mesh structure from being ruptured by powder of hydrogen storage alloy having edges with acute angle. CONSTITUTION:A powder 1 of hydrogen storage alloy and an organic binder are kneaded together to form a paste, and a three-dimensional mesh structure 2 consisting of foaming nickel is filled with this paste to accomplish a material to neg. electrode. This material is compressed across the thickness. Furnace carbon black 3 is added to the paste. In case 4.0g/cm<3> is exceeded by the filling density when the three-dimensional mesh structure 2 is filled with the hydrogen storage alloy 1, an organic binder is used as an organic binder which is a water solution containing polyvinyl alcohol 0.2-2.0% by weight of the paste, and thereto a furnace carbon black 0.1-1.0% by weight of the paste is added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hydrogen storage alloy negative electrode used in, for example, a negative electrode of an alkaline storage battery.

[0002]

2. Description of the Related Art A negative electrode using a hydrogen-absorbing alloy powder can be increased in energy density, and thus research and development thereof has been advanced in recent years. When manufacturing a conventional hydrogen storage alloy negative electrode, a negative electrode material is first formed and this negative electrode material is compressed in the thickness direction to manufacture a hydrogen storage alloy negative electrode. As a method of forming the negative electrode material, a method of forming a negative electrode material by applying a paste prepared by kneading a hydrogen storage alloy with an organic binder on a nickel porous plate, and a three-dimensional mesh shape such as a foamed nickel porous body or felt. There is a method of forming a negative electrode material by filling a paste in which a hydrogen absorbing alloy powder is kneaded with an organic binder such as a polyvinyl alcohol (PVA) aqueous solution in the structure. Compressing the negative electrode material in the thickness direction is
This is because the energy density of the negative electrode is increased by increasing the packing density of the hydrogen storage alloy powder. However, when compressing the negative electrode material using the nickel porous plate, if the compression is too strong, there is a problem that the paste is easily separated from the nickel porous plate. Further, in the negative electrode manufactured in this manner, there is a problem that the paste is easily peeled off from the nickel porous plate due to the absorption and desorption of hydrogen accompanying charge and discharge. Therefore, as a technique to prevent peeling of the paste,
As disclosed in Japanese Patent Laid-Open No. 63-110552, a technique of adding carbon fiber to the paste to improve the strength of the paste has been studied. However, in the negative electrode in which the paste is applied to the nickel porous plate, there is a limit in increasing the degree of adhesion between the nickel porous plate and the paste. Therefore, it is hard to say that it is appropriate to use the nickel perforated plate when manufacturing the hydrogen storage alloy negative electrode.

On the other hand, in the hydrogen storage alloy negative electrode in which the paste is filled in the three-dimensional mesh structure, the peeling of the paste caused by compression and discharge hardly occurs. However, as shown in FIG. 6, when the hydrogen storage alloy powder 1 is formed by mechanical crushing or hydrogenating crushing, unlike the nickel hydroxide powder having a nearly spherical shape, an acute angle portion (edge) 1a is formed on the outer periphery of the powder 1. Is formed. Therefore, when the negative electrode material is strongly compressed or the negative electrode is wound, the edge 1a ruptures the three-dimensional network structure 2 which is a holder of the hydrogen storage alloy powder 1 and cracks 2a occur in the negative electrode. There was a problem to do. Various techniques have been studied in order to solve such problems. For example, JP-A-60-77357
The publication discloses a technique for improving the strength of a three-dimensional network structure by depositing a metal thin film on the surface of the three-dimensional network structure.

[0004]

However, even if the metal thin film is vapor-deposited on the surface of the three-dimensional network structure to improve the strength, it is not possible to sufficiently increase the strength of the three-dimensional network structure. There is. For example, the packing density of the hydrogen storage alloy powder should be 4.0 g / cm ³ to increase the energy density.
When the negative electrode material was compressed or the negative electrode was wound as described above, breakage occurred even in the three-dimensional network structure whose strength was improved by the metal thin film. As described above, it was not possible to obtain a hydrogen storage alloy negative electrode that can be practically used with the conventional technique.

An object of the present invention is to provide a method for producing a hydrogen storage alloy negative electrode in which cracks are less likely to occur.

[0006]

According to a first aspect of the present invention, a negative electrode material having a three-dimensional network structure filled with a paste prepared by kneading a hydrogen storage alloy powder and an organic binder is compressed in the thickness direction. A method of manufacturing a storage alloy negative electrode is targeted. In the present invention, furnace carbon is added to the paste used.

According to the second aspect of the present invention, an aqueous solution of polyvinyl alcohol having a weight ratio to the paste weight of 0.2% to 2.0% is used as the organic binder, and the weight ratio of the furnace carbon to the paste weight is 0.1. %
It is above 1.0%.

[0008]

When the furnace carbon is added to the paste as in the first aspect of the invention, the furnace carbon enters between the hydrogen storage alloy powder and the three-dimensional network structure. Furnace-based carbon has a well-developed structure, that is, the carbon particles are close to spherical and the three-dimensional connection of the carbon particles is large, so that the carbon has a large lubricating effect. Therefore, even if the negative electrode material is strongly compressed, the furnace-based carbon has a lubricating effect, so that the edge portion of the hydrogen-absorbing alloy powder is prevented from breaking the three-dimensional network structure.

When a predetermined amount of the aqueous solution of polyvinyl alcohol is used as the organic binder as in the second aspect of the present invention, when the furnace carbon is used, the molecules of the polyvinyl alcohol are bonded to each other by the furnace carbon, and the binder is stronger. Acts as. Further, when the amounts of the polyvinyl alcohol and the furnace carbon added are as in the invention of claim 2, breakage of the three-dimensional network structure can be significantly suppressed. If the weight ratio of polyvinyl alcohol to the paste weight is less than 0.2%, it will not function as an organic binder. 2.0% again
When it exceeds, the weight ratio of the hydrogen storage alloy powder to the paste weight becomes small, and the energy density of the negative electrode decreases. If the weight ratio of the furnace carbon to the paste is less than 0.1%, the lubricating action cannot be sufficiently achieved. Further, even if it exceeds 2.0%, there is almost no difference in the effect of suppressing the breakage of the three-dimensional network structure, and since the weight ratio of the hydrogen storage alloy powder to the paste weight becomes small, the energy density of the negative electrode is reduced. Since it decreases, it is not necessary to increase the amount of furnace carbon any more.

[0010]

EXAMPLES Examples of a method for producing a hydrogen storage alloy negative electrode of the present invention will be described in detail below with reference to the drawings.

First, a paste prepared by kneading a hydrogen storage alloy powder crushed in a mortar, an organic binder composed of an aqueous solution of polyvinyl alcohol (PVA), and furnace carbon is filled in a three-dimensional network structure composed of a foamed nickel porous body. To form a negative electrode material. Next, after drying this negative electrode material, it was compressed in the thickness direction to increase the packing density of the hydrogen storage alloy powder to manufacture a hydrogen storage alloy negative electrode. The hydrogen storage alloy used had an average particle size of 440 to 200 mesh, nickel foam had an average porosity of 95%, and the branch portion of the nickel foam had an average thickness of 100 μm. The thickness of the nickel foam was 1.0 mm. As for the carbon of the furnace type, Cabot Co.
The product sold under the product number P-2000 was used. The carbon had an average particle size of about 200 Å.

FIG. 1 is a diagram schematically showing a cross section of a hydrogen storage alloy negative electrode manufactured by the method of the embodiment of the present invention. In FIG. 1, 1 is a hydrogen storage alloy powder, and this hydrogen storage alloy powder 1 has an acute edge 1a. Reference numeral 2 is a three-dimensional mesh structure composed of a foamed nickel porous body, and reference numeral 3 is furnace carbon. Even if the negative electrode material filled with the paste is strongly compressed, the pressing force of the edge 1a of the hydrogen-absorbing alloy powder 1 against the three-dimensional network structure 2 is suppressed by the lubricity of the carbon 3 of the furnace system, and the three-dimensional network The structural body 2 is less likely to be broken.

Next, the above-mentioned negative electrode material formed by the conventional method and the method of the present invention is gradually compressed so that the packing density of the hydrogen storage alloy powder is changed to produce a hydrogen storage alloy negative electrode, and the three-dimensional mesh is formed by compression. The area ratio of cracks generated in the structural body to the entire negative electrode was determined. FIG. 2 is a diagram showing the relationship between the packing density of hydrogen storage alloy powder and the area ratio of cracks to the entire negative electrode. In FIG. 2, the curve a is polyvinyl alcohol having a weight ratio of 1% with respect to the weight of the paste and 0.
The characteristics of the negative electrode manufactured by the method of the present invention in which a paste containing 5% of furnace carbon and hydrogen storage alloy powder is filled in a foamed nickel porous body are shown. A curve b shows the characteristics of the negative electrode manufactured by the conventional method in which a substrate obtained by vapor-depositing nickel on a foamed nickel porous body is filled with polyvinyl alcohol having a weight ratio of 1% with respect to the paste weight and a hydrogen storage alloy powder. The curve c shows the characteristics of the negative electrode in which the foamed nickel porous body is filled with polyvinyl alcohol having a weight ratio of 1% with respect to the paste weight and the hydrogen storage alloy powder. It should be noted that the negative electrodes produced by various methods all use a foamed nickel porous body having the same shape and size (20 × 20 × 1.0 mm). From this figure, when the negative electrode is manufactured by the method of the present invention, even if the negative electrode material is compressed to increase the packing density of the hydrogen-absorbing alloy powder, cracks are generated in the three-dimensional network structure as compared with the conventional method. I find it difficult. In particular, it can be seen that when compressed at a packing density of more than 4.0 g / cm ³ , the conventional method causes a large amount of cracks, whereas the method of the present invention makes it difficult to cause a crack.

Next, various negative electrode materials having different weight ratios of the furnace carbon to the paste were formed, and the various negative electrode materials were compressed so that the packing density of the hydrogen storage alloy powder was changed, and the area ratio of the cracks generated in the negative electrode. Was measured.
As the three-dimensional mesh structure used to form the negative electrode material, the same foamed nickel porous body as that used in the test of FIG. 2 was used, and the binder was polyvinyl alcohol with a weight ratio of 1% to the weight of the paste. And the carbon described above with reference to FIG. 1 was used. FIG. 3 is a diagram showing the relationship between the weight ratio of the furnace carbon and the crack generation area ratio. In FIG. 3, curves d, e, and f represent the packing densities of the hydrogen storage alloy powders of 3.8 g / cm ³ and 4.0 g / cm, respectively.
It is a curve showing the characteristics when compressed to ³ , 4.2 g / cm ³ . From this figure, when the weight ratio of the furnace-based carbon is set to 0.1% or more, the generation of cracks in the negative electrode can be suppressed even if the hydrogen storage alloy powder is compressed to a packing density of 4.0 g / cm or more. I understand. Further, it can be seen that even if the weight ratio of the furnace-based carbon exceeds 1.0%, the crack occurrence rate does not change significantly.

Next, various pastes having different weight ratios of furnace carbon were filled in the same foamed nickel porous body as used in the test of FIG. 2 to form various negative electrode materials, and each negative electrode material was formed in the thickness direction. Then, the packing density at which the hydrogen-absorbing alloy powder could be packed to the maximum was measured. Incidentally, 1% by weight of polyvinyl alcohol is added as a binder to each paste. FIG. 4 is a diagram showing the relationship between the weight ratio of the furnace-based carbon and the packing density of the hydrogen storage alloy powder. From this figure, it can be seen that when the weight ratio of the furnace-based carbon exceeds 1%, the packing density of the hydrogen storage alloy powder sharply decreases.

Next, various pastes having different weight ratios of polyvinyl alcohol were filled in the same foamed nickel porous body as that used in the test of FIG. 2 to form various negative electrode materials, and various negative electrode materials were formed in the thickness direction. It was compressed at 1000 kg / cm ² and the relationship between the weight ratio of polyvinyl alcohol and the area ratio of cracks generated in the negative electrode was measured. In addition, 0.5 wt% of furnace carbon is added to each paste. FIG. 5 is a diagram showing the measurement results. From this figure, it can be seen that even if the weight ratio of polyvinyl alcohol exceeds 2%, the crack generation area ratio does not change significantly. still,
When the weight ratio of polyvinyl alcohol is less than 0.2%, it does not substantially serve as a binder. Then 1% by weight
Each negative electrode produced by the method of the present invention in which the packing density of the hydrogen-absorbing alloy powder is variously changed by using the paste containing polyvinyl alcohol and 0.5% by weight of the furnace-based carbon and the conventional method in which the furnace-based carbon is not added Each negative electrode produced by changing the packing density of the hydrogen-absorbing alloy powder by the method described above and each of the negative electrodes produced through the separator are wound together with the sintered positive electrode to produce a battery. The short-circuit occurrence rate was measured. Table 1 is a table showing the measurement results. In Table 1, g represents the short circuit occurrence rate (%) of the battery using the negative electrode manufactured by the method of the present invention, and h
Indicates the occurrence rate of short circuit (%) of the battery using the negative electrode manufactured by the conventional method.

[0017]

[Table 1]

From this table, when the negative electrode material is compressed at a pressure at which the hydrogen storage alloy powder packing density is particularly 4.0 g / cm ³ to 4.2 g / cm ³ , the negative electrode produced by the method of the present invention is used. It can be seen that in the battery used, the short-circuit occurrence rate is greatly reduced to 1/3 to 1/5 as compared with the battery using the negative electrode manufactured by the conventional method.

[0019]

According to the invention of claim 1, in the paste,
Since the furnace-based carbon is added, the three-dimensional network structure does not break. For this reason, there is an advantage that it is possible to obtain a negative electrode in which cracks are unlikely to occur and which has a high energy density.

According to the second aspect of the invention, there is an advantage that a stronger binder can be obtained and the breakage of the three-dimensional network structure can be surely suppressed.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross-sectional structure of a hydrogen storage alloy negative electrode manufactured by the method of the present invention.

FIG. 2 is a diagram showing the relationship between the packing density of hydrogen storage alloy powder and the area ratio of cracks with respect to the entire negative electrode.

FIG. 3 is a diagram showing a relationship between a weight ratio of furnace carbon and a crack generation rate.

FIG. 4 is a diagram showing a relationship between a weight ratio of furnace carbon and a packing density of hydrogen storage alloy powder.

FIG. 5 is a diagram showing the relationship between the weight ratio of polyvinyl alcohol and the incidence of cracks generated in the negative electrode.

FIG. 6 is an enlarged schematic view showing a cross section of a hydrogen storage alloy negative electrode manufactured by a conventional method.

[Explanation of symbols]

1 ... Hydrogen storage alloy powder, 2 ... Three-dimensional mesh structure, 3 ...
Furnace type carbon.

Claims (2)

[Claims] 1. A negative electrode material is formed by filling a paste prepared by kneading a hydrogen storage alloy powder and an organic binder into a three-dimensional network structure, and compressing the negative electrode material in the thickness direction to produce a hydrogen storage alloy negative electrode. A method for producing a hydrogen storage alloy negative electrode, characterized in that furnace carbon is added to the paste. 2. The paste contains an aqueous solution of polyvinyl alcohol having a weight ratio to the paste weight of 0.2% or more and 2.0% or less and the organic binder, and the weight ratio to the paste weight is 0.1% or more and 1% or more. The furnace type carbon is contained in an amount of 0.0% or less.
The method for producing the hydrogen storage alloy negative electrode according to 1.