JPH07307154A - Hydrogen storage electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To increase the maximum discharge capacity and decrease the cycle number reaching the maximum discharge capacity by continuously orienting conductive metal powder in parallel or almost in parallel in the cross section structure of a hydrogen storage electrode to form a micro current collector. CONSTITUTION:10-30g of conductive metal powder (flaky copper powder) whose mean major axis is 45-100mum and mean minor axis is 1-20mum is mixed with 100g of hydrogen storage alloy powder pulverized in 45mum or less. The mixed powder is filled in a mold, then press-molded at 100Mpa to form a 30mmX40 mmX0.6mm sheet. A sheet-shaped hydrogen storage electrode with cross section structure in which the conductive metal powder is arranged (oriented) in a continuously contacted state in the parallel or almost parallel direction to an electrode surface (in the vertical or almost vertical direction to the press molding direction) is obtained. In this cross section structure, the conductive metal powder is capable of efficiently collecting current from the hydrogen storage alloy powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element storage electrode used for a negative electrode of a nickel-metal hydride battery and a method for producing the same.

[0002]

2. Description of the Related Art Hydrogen storage alloys have the property of being able to absorb and release 1000 times or more of the volume of hydrogen, and are used as hydrogen storage materials, separation / purification materials, and hydrogen transportation. It is expected to be useful as a medium.

Conventionally, Ni-Cd batteries have been widely used as secondary batteries. However, due to the fact that Cd has toxicity and the battery capacity is small, other secondary batteries can be used. Substitution is progressing rapidly. The hydrogen storage alloy is used in a secondary battery called nickel-metal hydride battery that uses nickel for the positive electrode and hydrogen storage alloy for the negative electrode.

However, many problems remain to be solved in applying the hydrogen storage alloy to the secondary battery, and one of them is improvement of the discharge capacity of the battery.

The hydrogen storage alloy has a catalytic ability for decomposing hydrogen molecules into hydrogen atoms on its surface. Therefore, if the surface area is increased, that is, if the powder is made into a fine powder, the catalytic ability can be improved. Are known. This is
By using a fine powder of the hydrogen storage alloy, it is meant that the catalytic ability is improved along with the increase of the specific surface area, and the discharge capacity of the nickel-metal hydride battery is improved. However, when the hydrogen storage alloy is a fine powder, the number of alloy powders increases, the number of contacts between the alloy powders increases, and as a result, the conductivity decreases and the internal resistance of the hydrogen storage electrode increases. There are drawbacks such as a low initial discharge capacity of the battery and a large number of cycles until reaching the maximum discharge capacity.

Further, since the insulating resin is used as the binder when forming the hydrogen-absorbing alloy powder into a sheet-shaped hydrogen-absorbing electrode, the binder resin lowers the conductivity between the particles of the hydrogen-absorbing alloy powder. ing. Therefore,
In order to improve the conductivity between the hydrogen storage alloy powder particles and reduce the internal resistance, powdered carbon as a conductive material,
A large amount of copper, nickel, etc. are added. For example, by adding 3 g of copper powder powder to 1 g of hydrogen storage alloy powder, as shown in FIG. 1 (B), a sheet-shaped hydrogen storage electrode having a cross-sectional structure in which the periphery of alloy powder particles is covered with copper powder. Is generally performed to improve the discharge capacity of the secondary battery, but satisfactory results have not been obtained.

The method of plating the hydrogen storage alloy powder with a conductive metal such as copper or nickel improves the conductivity of the electrode,
Since it also improves the discharge capacity of the battery, it is useful in improving the performance of the battery. However, this method
The cost of processing the plating waste liquid is high; if the hydrogen-absorbing alloy powder is plated over the entire surface, hydrogen gas cannot flow in and out, and the battery reaction will not occur, so it is necessary to perform porous plating by a special method. It is not common because of the high cost.

In order to improve the drawbacks of the plating method, Japanese Patent Laid-Open No. 9504/1993 proposes a dry method of coating the hydrogen storage alloy powder with copper powder and cuprous oxide powder. This method is safe and has a simple manufacturing process, and the secondary battery using the obtained copper powder-coated hydrogen storage alloy is said to have a large maximum discharge capacity. However, the cuprous oxide powder used in this method exhibits its characteristics after being reduced to copper by charging, so that the initial discharge capacity of the battery is low and the number of cycles to reach the maximum discharge capacity is large. Further, since the powder formed by granulation is spherical, it is difficult to form a sheet-shaped negative electrode by pressure molding, and a negative electrode must be prepared using a resin as a binder. Therefore, there is a problem that the resistance of the sheet-shaped negative electrode is high, and the discharge capacity is not significantly improved.

Further, according to JP-A-4-262367, by mixing the hydrogen storage alloy powder and the flake nickel powder, the surface of the hydrogen storage alloy powder is easily covered with the flake nickel powder, and the particles It is said that the conductivity is improved. However, in this case, since the shape of each powder particle is different, it is difficult to uniformly mix the two powders by an operation of simply mixing the two powders, and the flake nickel powder encloses the hydrogen storage alloy powder. Is
Practically difficult. Moreover, the method described in this publication has an essential problem that the discharge capacity of the secondary battery is not significantly improved because the negative electrode is formed by using the resin as the binder.

[0010]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a method capable of producing an electrode for a secondary battery safely and at low cost.

The present invention also provides a hydrogen storage electrode capable of forming a secondary battery having a large maximum discharge capacity and a small number of cycles for reaching the maximum discharge capacity.
To aim.

[0012]

Means for Solving the Problem In the process of conducting various studies on means for improving the conductivity of the hydrogen storage electrode, the present inventor decided to continuously contact the conductive metal powder in the hydrogen storage electrode. In the case of orienting to, it is possible to form a thin hydrogen storage electrode excellent in workability only by pressure molding without using a resin, and as a result, the conductivity of the hydrogen storage electrode is significantly improved. As a result, it was found that a secondary battery having a large maximum discharge capacity and a small number of cycles reaching the maximum discharge capacity can be formed.

That is, the present invention provides the following hydrogen storage electrode and a method for producing the same: 100 parts by weight of hydrogen storage alloy powder having a particle diameter of 1.45 μm or less and an average major axis of 4
5 to 100 μm and 10 to 30 parts by weight of a conductive metal powder having an average minor axis of 1 to 20 μm, and the major axis direction surface of the conductive metal powder is parallel or nearly parallel to the electrode surface in the electrode. A hydrogen storage electrode, which is characterized by forming a network in continuous contact.

Hydrogen storage alloy powder 10 of 2.45 μm or less
0 parts by weight and 10 to 30 parts by weight of a conductive metal powder having an average major axis of 45 to 100 μm and an average minor axis of 1 to 20 μm were filled in a mold and roller-compressed at least once. After that, the method for producing a hydrogen storage electrode is characterized by performing pressure molding.

In the method of the present invention, in order to enhance the conductivity of the hydrogen storage electrode, the hydrogen storage alloy powder and the conductive metal powder are mixed, and the conductive metal powder is continuously contacted and oriented to form a conductive network. In order to form the above, the mixed powder is filled in a mold, compressed by a roller, and then pressure-molded.

The hydrogen storage alloy used in the present invention is not particularly limited, and is a LaNi ₅ type alloy represented by an AB ₅ type composition formula, MmNi ₅ (Mm means Misch metal which is a mixture of rare earth alloys). Alloys, Ti-Mn alloys,
La Zr group represented by the composition formula of AB ₂ - Beth phase alloy;; Ti-Cr alloy, Zr-Mn based alloy, Ti-Fe based alloy, Ti-Ni based alloys, and the like, and these improved; more Any alloy that forms a metal hydride by contact with hydrogen may be used. The hydrogen storage alloy powder is used after being pulverized to a powder of 45 μm or less. Particle size of hydrogen storage alloy powder is 45μ
When it is at most m, the dispersion of the conductive metal powder will proceed efficiently, and good battery characteristics will be obtained when the formed hydrogen storage electrode is incorporated into a battery.

The conductive metal powder used in the present invention is copper (Cu) or nickel (N) which has been conventionally used as a conductive metal powder in nickel-metal hydride batteries.
i), a single powder of cobalt (Co) or these two
Mixed powder consisting of at least one kind, and any one of these
Any compound powder or the like in which any one or more of the other is plated may be used. The powder is a powder having a major axis and a minor axis, and is preferably in the shape of, for example, flaky powder, dendritic powder, fibrous powder, acicular powder or the like. Specifically, the average particle diameter of the major axis is about 45 to 100 μm, the minor axis is about 1 to 20 μm, and about 1/5 to 1/50 of the major axis (particularly preferably 1/10 to 1/1). A powder of about 20) is suitable. When the major axis of the conductive metal powder is less than 45 μm or the minor axis is 20 μm or more, it becomes smaller than the hydrogen storage alloy powder, and therefore, the number of hydrogen storage alloy powders interposed between the conductive metal powders exceeds two. The conductive metal powders may not be in direct contact with each other, and many conductive metal powder particles are required. In this case, the number of contacts increases, that is, the contact resistance increases, so that the conductivity decreases, and there is not much difference from the conventional copper powder used conventionally. On the other hand, when the major axis of the conductive metal powder exceeds 100 μm or more or the minor axis is less than 1 μm, segregation or bending due to the difference in shape and size when mixed with the hydrogen storage alloy powder, It aggregates in a round shape, a continuous contact orientation state cannot be obtained, and it is difficult to obtain the target cross-sectional structure.

Conventionally, the conductive metal powder is generally used by adding it in the range of 5 to 300% by weight based on 100 parts by weight of the hydrogen storage alloy powder. According to the method of the present invention,
It may be added in an amount of 10 to 30 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. When the content of the conductive metal powder is less than 10 parts by weight, continuous contact between the conductive metal powders becomes insufficient and the conductive network is not sufficiently formed. In this case, the number of hydrogen storage alloy powders existing between the network layers formed of the conductive metal powder exceeds 5 particles, the discharge capacity of the battery is not sufficiently improved, and the maximum discharge capacity is not achieved. The number of cycles to reach to increases, and the characteristics further vary. On the other hand, when the amount of the conductive metal powder is more than 30 parts by weight, no remarkable improvement in the orientation due to the addition is observed, and the conductive metal powder surrounds the hydrogen storage alloy powder, Since the smooth absorption and desorption of hydrogen gas is hindered, neither the increase of the maximum discharge capacity nor the effect of reducing the number of cycles until reaching the maximum discharge capacity is achieved. Moreover, the manufacturing cost of the hydrogen storage electrode increases. That is, by setting the blending amount of the conductive metal powder to 100 parts by weight of the hydrogen storage alloy powder to be 10 to 30 parts by weight, a cross-sectional structure oriented so that the conductive metal powder particles are continuously contacted in the electrode is formed. This facilitates the operation, which is advantageous in terms of battery characteristics and economics.

When manufacturing the hydrogen storage alloy electrode according to the present invention, first, the hydrogen storage alloy powder and the conductive metal powder are mixed. Hydrogen storage alloy powder and conductive metal powder are
Since it is easily oxidized, it is preferable to add an antioxidant or a rust preventive which is commonly used in the field of powder metallurgy to coat the powder surface when mixing in air. This coating formation prevents oxidation of both powders, improves dispersibility of both powders, and improves orientation of the conductive metal powder in the electrode. As an antioxidant or rust preventive,
Known higher fatty acids such as stearic acid and oleic acid and salts thereof may be used. As an antioxidant or a rust preventive agent, the effect of a liquid oil is particularly remarkable,
Even solid fats and oils can obtain the same effects as liquid fats and oils if they are dissolved in a solvent. Liquid fats and oils or fats and oils dissolved in a solvent rapidly coat the powders when mixing two types of powders, and exert an antioxidant or rust preventive effect from the initial stage of mixing, so that mixing in air is possible. Become. Further, since the hydrogen storage alloy powder coated with oil and fat and the conductive metal powder have lubricity, the particles in the mixed powder are likely to slip with each other and move easily. As a result, the conductive metal powders are substantially aligned (orientated) in a certain direction parallel to the electrode surface due to the synergistic effect of the filling by roll compression and the shape characteristic due to the difference between the long diameter and the short diameter.

When the brittle and hard hydrogen-absorbing alloy powder and the softer conductive metal powder are mixed by using a Raikai machine or the like, the hydrogen-absorbing alloy powder is further finely pulverized. In addition, the conductive metal powders that are overlapped or agglomerated are easily dispersed into particles one by one.
As the mixer used for mixing the hydrogen storage alloy powder and the conductive metal powder, a mixer generally used in the field of powder metallurgy can be used as it is. More specifically, for example,
Examples thereof include a reiki machine, a ball mill, a vibration mill, and an attritor. Particularly, in order to keep the number of stacked hydrogen storage alloy powders existing between conductive networks within 5 particles, the hydrogen storage alloy powders and conductive metal powders that are overlapped or agglomerated during the mixing operation are Since it is necessary to efficiently disperse the particles into individual particles, it is preferable to use a mechanofusion type mixer (for example, a product manufactured by Hosokawa Micron Co., Ltd. is commercially available) that can apply a shearing force to the powder. The operating conditions of the mechanofusion type mixer are not particularly limited, but are usually about 300 to 900 rpm.
The mixing time may be about 120 to 5 minutes.

Since the hydrogen storage alloy powder and the conductive metal powder are easily oxidized, it is preferable to carry out in a non-oxidizing gas atmosphere such as argon gas or nitrogen gas. However, as described above, when an antioxidant or a rust preventive agent is used, they can be mixed in the air. The size, composition, etc. of the hydrogen storage alloy powder and the conductive metal powder to be used may be appropriately selected within the above range according to desired characteristics.

Next, the mixed powder prepared as described above is put into a mold, compressed by a roller and filled, and then pressure-molded to form a sheet-shaped hydrogen storage electrode. In this process, the soft conductive metal powder and the hard hydrogen-absorbing alloy powder come into strong contact with each other under pressure. Then, as shown in FIG. 1 (A), the conductive metal powder is continuously contacted in a direction parallel or substantially parallel to the electrode surface (in other words, a method perpendicular or substantially perpendicular to the molding pressure direction). Thus, a sheet-shaped hydrogen storage electrode having an aligned (orientated) cross-sectional structure is obtained. With this cross-sectional structure, the conductive metal powder can efficiently collect current from the hydrogen storage alloy powder. Further, since the conductive metal powder does not densely coat the circumference of the hydrogen storage alloy powder, hydrogen can easily enter and leave the hydrogen storage alloy powder. Further, since the conductive metal powder is continuously oriented, it becomes a micro-current collector and exerts an effect of lowering the internal resistance of the hydrogen storage electrode.

In the filling by the above roller compression, the larger the major axis of the conductive metal powder, the easier it becomes to be aligned (orientate) in parallel with the electrode surface of the hydrogen storage electrode. That is, in the state where the hydrogen storage alloy and the conductive metal powder are simply mixed, the conductive metal powder is oriented in an irregular direction. However, the metal powder having one side longer than the other side is compressed at least once (more preferably a plurality of times) by a roller moving from one end to the other end in a state of being filled in the mold. For example, the copper powder having a major axis of 50 μm, although initially oriented in the vertical direction in the mixed powder in the mold, gradually changes its orientation in the horizontal direction and is then arranged parallel or substantially parallel to the electrode surface. The orientation characteristic of the conductive metal powder due to the roller compression becomes more remarkable as the major axis is larger than the minor axis. If the major axis of the conductive metal powder is as small as the dimension of the hydrogen storage alloy powder, even if the mixed powder is compressed by the roller, the hydrogen storage alloy powder will disturb the conductive metal powder and the conductive metal powder will be deposited on the electrode surface. A substantially parallel and continuously oriented cross-sectional structure is not obtained. In the above roller compression step, the size and the quantitative ratio of the hydrogen storage alloy powder and the conductive metal powder in the mixed powder satisfy the requirements of the present invention, and both powders are uniformly dispersed and mixed. If the above two conditions are satisfied, the mixed powder is compressed by a roller to form a conductive network in which the conductive metal powder is continuously arranged in parallel or substantially parallel to the electrode surface. Thus, a layer is formed in which the number of stacked hydrogen storage alloy powders within the network is 5 or less. If there is segregation in the mixed powder, the conductive metal powder will not be favorably oriented, and the number of hydrogen storage alloy powders stacked will exceed 5,
The desired purpose of improving discharge capacity is not achieved.

In the above-mentioned roller compression, if necessary, half of the required amount of the mixed powder is charged while being roller-compressed into a mold having a shape corresponding to a predetermined electrode shape, and then,
A current collector (for example, a metal mesh) may be placed and the remaining mixed powder may be charged while being roller-compressed.

Next, the mixed powder filled in the die is pressure-molded into a sheet-shaped hydrogen storage electrode. The pressure during molding is not particularly limited, but is usually 5 to 500M.
Pa, and more preferably 100 to 300 MPa
It is a degree.

Thus, as shown in FIG. 1 (A), the surfaces of the conductive metal powder particles in the major axis direction are in continuous contact with each other in parallel with the electrode surface, and these serve as a micro-current collector. As a result, a sheet-shaped hydrogen storage electrode exhibiting good characteristics can be obtained.

[0027]

According to the present invention, a hydrogen storage electrode having a unique sectional structure can be manufactured at low cost by a simple process. The obtained hydrogen storage electrode was nickel-
The discharge capacity of the metal hydride battery can be significantly increased, the number of cycles to reach the maximum discharge capacity can be significantly reduced, and the life of the battery can be extended.

[0028]

EXAMPLES Next, the features of the present invention will be described in more detail by showing examples and comparative examples.

Example 1 Hydrogen storage alloy powder (MmNi
_3.65 Co _0.7 Al _0.65 : However, Mm represents misch metal, which is a mixture of rare earth metals), and the average major axis is 49.3 μm (the average minor axis is 1/1 of the major axis).
The mixing amount of the flaky copper powder (in the range of 0 to 1/20) is 1
The amount was changed from 0 g to 30 g, blended, and mixed by a mechanofusion device at 800 rpm for 10 minutes.

Next, 1.2 g of each of the obtained three kinds of mixed powders was put into a mold (30 mm × 40 mm × 2 mm), a pressure of about 2 MPa was applied by a roller, and the powder was packed while being compressed. Place the copper-plated nickel wire mesh, which is the last item, and finally, 1.2g of the remaining mixed powder with a roller for about 2MP
The pressure of a was applied and filling was performed while compressing.

Next, the three types of mold fillings obtained as described above were each pressure-molded at 100 MPa, and 30 mm ×
A 40 mm × 0.6 mm sheet-shaped compact was obtained.

This sheet-shaped molded body was wrapped with a non-woven fabric made of polyamide as a separator to form a negative electrode, a sintered nickel oxide electrode as a positive electrode, and a 6N potassium hydroxide solution was used as an electrolytic solution to assemble an open-type battery. This open battery was installed in a constant temperature bath at a temperature of 20 ° C., and an experiment was repeated 200 cycles of charging / discharging with the following operations (a) to (c) as one cycle, and the maximum discharge capacity of the open battery and the The number of cycles to reach it was measured. (B) Charge the battery with a charging current of 400 mA for 3 hours. → (b)
Pause for 0.5 hours. → (c) Discharge at a discharge current of 200 mA until the voltage drops to 0.8 V.

Table 1 shows the relationship between the blending amount (parts by weight) of the flaky copper powder in the mixed powder and the discharge capacity. In addition, as a result of observing a cross section of each of the prepared electrode samples with a microscope, the number of stacked hydrogen storage alloy powders between the conductive networks was 5 or less in any of the samples (Sample No. 1 to No. 1).
6).

Example 2 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
The average major axis is 10.0 to 120.0 with respect to 100 g of the alloy.
Various flaky copper powders varied in the range of μm (the average of the minor axis is in the range of 1/10 to 1/20 of the average major axis) 2
0g blended, 800r by mechanofusion device
Mix for 10 minutes at pm.

Using each of the resulting mixed powders,
A sheet-shaped negative electrode was prepared in the same manner as in Example 1, a battery was assembled, and the maximum discharge capacity and the number of cycles until reaching it were measured.

The results are shown in Table 1. Shown as 7-10. As a result of observing the cross section of the prepared sample with a microscope, the number of stacked hydrogen storage alloy powders between the conductive networks was 5 or less in any sample.

Comparative Example 1 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
Flake-shaped copper powder having an average particle size of 25.1 μm was mixed with 100 g of the alloy in the range of 5 to 50 g. Then, according to the conventional method, PTFE resin was added to each mixed powder at a ratio of 5% by weight and mixed well to form a gum-like sheet, which was wrapped in a nickel wire mesh and pressed at a pressure of 20 MPa to 30 × 40 ×× 0. ．
A 6 mm sheet was created. This sheet was wrapped with a nylon separator to prepare a hydrogen storage electrode. Using this hydrogen storage electrode as a negative electrode, a battery was assembled in the same manner as in Example 1, and the maximum discharge capacity of the battery and the number of cycles until reaching it were measured. When the cross section of the hydrogen storage electrode was observed with a microscope, no conductive network was formed and the flaky copper powder was not in parallel and continuous contact.

The results are shown in Table 1. Shown as 11 to 18.

[0039]

[Table 1]

As is clear from the results shown in Table 1, when the hydrogen storage electrode according to the present invention is used, the maximum discharge capacity of the battery is high and the number of cycles until reaching the maximum discharge capacity is small. it is obvious. On the other hand, the sample No. In Nos. 11 to 18, the maximum battery capacity is low, and the number of cycles to reach the maximum discharge capacity is not satisfactory.

Example 3 MmNi _3.65 Co _0.7 Al ground to 45 μm or less
_With respect to 100 g of _0.65 alloy, flake nickel powder having an average major axis of 50.4 μm (the average of the minor axis is in the range of 1/10 to 1/20 of the average major axis) was added in the range of 10 to 30 g. A sheet-shaped negative electrode was prepared in the same manner as in Example 1 except that a nickel wire net was used as the current collector and the molding pressure was set to 200 MPa, and the battery was assembled. And the number of cycles to reach it was measured.

The results are shown in Table 2 (Sample Nos. 19 to 2).
3). In addition, according to cross-sectional observation with a microscope, the number of stacked hydrogen-absorbing alloy powders between the conductive networks was 5 or less in any sample.

Example 4 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
The average major axis is 11.2 to 111 μm with respect to 100 g of the alloy.
20 g of flaky nickel powder (average of minor axis is in the range of 1/10 to 1/20 of average major axis) varied in the range of 1 by a mechanofusion device at a rotation speed of 800 rpm.
Mix for 0 minutes.

Then, a sheet electrode was prepared in the same manner as in Example 3, a battery was assembled, and its maximum discharge capacity and the number of cycles until reaching it were measured. The results are shown in Table 2. Shown as 24-27. In all the samples, the number of stacked hydrogen-absorbing alloy powders between the conductive networks was 5 or less.

[0045]

[Table 2]

As is clear from the results shown in Table 2, the hydrogen storage electrode of the present invention using nickel as the conductive metal powder also increases the maximum discharge capacity of the battery and reaches the maximum discharge capacity. It is clear that the number of cycles is reduced.

Example 5 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
Flake-shaped copper powder having an average major axis of 49.3 μm with respect to 100 g of the alloy (the average of the minor axis is 1/10 to 1/20 of the average major axis).
And a flaky nickel powder having an average major axis of 50.4 μm (the average of the minor axis is 1/10 to 1/2 of the average major axis).
(In the range of 0) was mixed in the range of 10 to 30 g in a weight ratio of 25/75 to 75/25, and the mixture was mixed for 10 minutes at a rotation speed of 700 rpm by a mechanofusion device. Similarly, a sheet-shaped negative electrode was prepared, a battery was assembled, and its maximum discharge capacity and the number of cycles until reaching it were measured.

Table 3 shows the results. Shown as 28-34. As a result of observing the cross section of the created sample with a microscope,
In all the samples, the number of stacked hydrogen storage alloy powders between the conductive networks was 5 or less.

[0049]

[Table 3]

Example 6 A composite powder of copper and nickel having an average major axis of 60.0 μm and an average minor axis of 3 μm (the ratio of the two is 25/75 to 75 /
25 range) was made with a ball mill and mixed with 100 g of MmNi _3.65 Co _0.7 Al _0.65 alloy pulverized to 45 μm or less in the range of 10 to 30 g, and mixed by a mechanofusion device at a rotation speed of 700 rpm for 10 minutes,
A sheet-like negative electrode was prepared in the same manner as in Example 1, a battery was assembled, and the maximum discharge capacity of the battery and the number of cycles until reaching it were measured.

Table 4 shows the results. Shown as 35-41. As a result of observing the cross section of the created sample with a microscope,
In all the samples, the number of stacked hydrogen storage alloy powders between the conductive networks was 5 or less.

[0052]

[Table 4]

Example 7 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
With respect to 100 g of the alloy, 20 g of electrolytic copper powder having an average major axis of 100 μm and an average minor axis of 11 μm {branched copper powder having short major axis (short thickness) with well-developed branches having long major axis) was blended. , Rotation speed 500r by mechanofusion device
After mixing at pm for 10 minutes, a sheet-shaped negative electrode was prepared in the same manner as in Example 1, a battery was assembled, and the maximum discharge capacity of the battery and the number of cycles until reaching it were measured.

The results are shown in Table 5 as sample No. Shown as 42-43. As a result of observing the cross section of the created sample with a microscope,
In all the samples, the number of stacked hydrogen storage alloy powders between the conductive networks was 5 or less.

[0055]

[Table 5]

Example 8 MmNi _3.65 Co _0.7 Al _0.65 ground to 45 μm or less
Flake-shaped cobalt powder having an average major axis of 45.1 μm with respect to 100 g of the alloy (the average of the minor axes is 1/10 to 1/1 of the average major axis).
10 g (in the range of 20) and mixed by a mechanofusion device at a rotation speed of 500 rpm for 10 minutes, and then a sheet-shaped negative electrode was prepared in the same manner as in Example 1, a battery was assembled, and the maximum discharge capacity of the battery and The number of cycles to reach it was measured.

The results are shown in Table 6. Shown as 44.
As a result of observing the cross section of the prepared sample with a microscope, the number of stacked hydrogen-absorbing alloy powders between the conductive networks was 5
It was within the number.

[0058]

[Table 6]

Test Example 1 The results of comparing the charge and discharge characteristics of the batteries of Example 3 according to the present invention in which 20% by weight of flaky copper powder was mixed in the ratio of 20% by weight and Comparative Example 13 according to the conventional method are shown in FIG. Shown in.

As is apparent from FIG. 2, the hydrogen storage electrode of the present invention has a smaller number of cycles until reaching the maximum discharge capacity, a larger maximum discharge capacity, and 200 cycles as compared with the conventional hydrogen storage electrode. It can be seen that there is little deterioration in the discharge capacity up to.

From the above results, the battery using the hydrogen storage electrode obtained by the method of the present invention has a higher maximum discharge capacity than the battery using the hydrogen storage electrode by the conventional method, and the cycle reaching the maximum discharge capacity. It can be seen that the number of times is as small as about 1/3, and the amount of the conductive metal powder mixed is also small.

The hydrogen storage electrode obtained by the method of the present invention is
For example, when used in a nickel-metal hydride battery,
It is clear that a battery having a high discharge capacity and a small number of cycles reaching the maximum discharge capacity can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional structure of a hydrogen storage electrode according to the method of the present invention (A).
FIG. 3 is a schematic diagram showing a cross-sectional structure (B) of a hydrogen storage electrode according to a conventional method and FIG.

2 is a graph showing charge / discharge characteristics of batteries using the hydrogen storage electrodes obtained in Example 3 and Comparative Example 13. FIG.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Miyamura 1-831 Midorigaoka, Ikeda City, Osaka Prefecture Industrial Technology Institute, Osaka Institute of Industrial Technology (72) Inventor Nobuhiro Kuriyama 1-8 Midorigaoka, Ikeda City, Osaka Prefecture No. 31 Industrial Technology Institute Osaka Industrial Technology Research Institute (72) Inventor Sai Uehara 1-8-31 Midorigaoka, Ikeda City, Osaka Prefecture Industrial Technology Institute Osaka Industrial Technology Research Institute (72) Inventor Hiroshi Yoshinaga Yamashina, Kyoto Prefecture 20 Nishinoyama-Nakashinmachi, Nishino-ku, Fukuda Metal Foil & Powder Industry Co., Ltd. (72) Inventor Hidaka ▼ Kensuke Nishinoyama Naka-Omimachi, 20 Yamanashi Ward, Kyoto City, Kyoto Prefecture (72) Inventor Yoshio Kodaira 20 Nakanomachi, Nishinoyama, Yamashina-ku, Kyoto City, Kyoto Prefecture Fukuda Metal Foil & Powder Co., Ltd.

Claims (2)

[Claims] 1. A conductive metal powder comprising 100 parts by weight of a hydrogen storage alloy powder having a diameter of 45 μm or less and 10 to 30 parts by weight of a conductive metal powder having an average major axis of 45 to 100 μm and an average minor axis of 1 to 20 μm. A hydrogen storage electrode, characterized in that the major axis surface of the conductive metal powder forms a continuous network in the electrode in parallel or near parallel to the electrode surface. 2. A mixed powder comprising 100 parts by weight of a hydrogen storage alloy powder having a diameter of 45 μm or less, and 10 to 30 parts by weight of a conductive metal powder having an average major axis of 45 to 100 μm and an average minor axis of 1 to 20 μm. A method for producing a hydrogen storage electrode, comprising: filling a metal mold with a roller, compressing the roller at least once, and then pressure molding.