JPH0652855A - Hydrogen storage alloy electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve reaction activity of the surface of a hydrogen storage alloy, maintain high discharging capacity for a long duration, and improve the durability and storage property of the alloy by mixing powder of the hydrogen storage alloy and powder of another metal by a mill in sealed condition. CONSTITUTION:A powder mixed by a mill is prepared by pulverizing and mixing a mixed powder of a hydrogen storage alloy powder and a powder of at least one of other metals by a mill apparatus in sealed condition. The mixed-by-mill powder is directly press-formed on a net or a porous plate made of a metal. In this case, a viscosity increasing agent is added to the mixed-by-mill powder in a prescribed ratio and the mixed-by-mill powder is press-formed on a conductive substrate and then heating treatment at highest 1100 deg.C is carried out. Consequently, the surface of the hydrogen absorbing alloy is coated with other metals without being oxidized. As a result, with no decrease of the reaction activity of the surface of the hydrogen storage alloy, the high discharging capacity is maintained for a long duration and at the same time hydrogen absorbing alloy electrodes with high durability and excellent storage property are easily obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode used for a negative electrode of a secondary battery or the like and a method for producing the same.

[0002]

2. Description of the Related Art A nickel-hydrogen battery using a hydrogen storage alloy for the negative electrode, nickel oxide for the positive electrode, and an alkaline aqueous solution for the electrolytic solution has been developed as a secondary battery with high energy density and no pollution. ing. As the hydrogen storage alloy used for the negative electrode, LaNi ₅ , MmNi ₅ (M
m: misch metal) based rare earth / nickel based AB ₅ type alloy, Ti ₂ Ni and TiNi based titanium / nickel based alloy, represented by the composition formula of AB ₂ and has a Laves phase Alloys based on alloys are used.

Generally, as a method of manufacturing an electrode using a hydrogen storage alloy, a hydrogen storage alloy ingot is simply crushed by a mill device in air, and this hydrogen storage alloy powder is mixed with a thickener and a binder in water as a medium. As a paste, fill or apply it to a metal porous body or plate,
A paste-type manufacturing method of drying is adopted. In addition, a sintering type manufacturing method is also performed in which the hydrogen storage alloy powder is sintered together with a metal net.

[0004]

However, the hydrogen storage alloy powder obtained by the conventional method has a relatively low activity, and the hydrogen storage alloy electrode produced by using the powder has a relatively low discharge capacity. For this reason, it is necessary to repeat charging and discharging a number of times until the maximum discharge capacity is exhibited. Further, the hydrogen storage alloy powder has a problem that the discharge capacity decreases when it is stored for a long period of time. Such a problem is mainly when crushing the hydrogen storage alloy ingot by a mill device, and further on the surface of the powder particles during storage after the hydrogen storage alloy powder is manufactured,
It is considered that a stable oxide film of La, Ti, Zr, etc., which are the constituent elements, is generated and this inhibits the electrode reaction.

Further, since the conventional paste-type electrode plate manufacturing method uses an organic polymer such as a thickener and a binder, it covers the surface of the hydrogen storage alloy. Therefore, there is a problem that the reaction activity on the surface of the hydrogen storage alloy is further reduced. In particular, carboxymethyl cellulose (CMC) used when preparing a paste using water as a medium
Thickeners such as have high hydrophilicity and water retention and have an effect of uniformly wetting the surface of the hydrogen storage alloy, so that CMC adhered to the surface reduces and absorbs oxygen gas in the negative electrode (hydrogen storage alloy electrode). Prevents reaction or absorption of hydrogen gas. As a result, the internal pressure of the battery rises during overcharging. further,
In such a paste-type manufacturing method, there is also a problem that the filling amount of the hydrogen storage alloy must be reduced by the amount of the thickening agent, the binder, etc. contained.

On the other hand, the sintering type manufacturing method can suppress the volume occupation of components other than the active material as much as possible. However, since a heat treatment of about 1100 ° C. is required under vacuum or in a reducing atmosphere, the electrode manufacturing equipment becomes complicated. Further, during the heat treatment at high temperature, the surface of the hydrogen storage alloy is contaminated by oxidation or the like. Due to this surface contamination, the reaction activity of the surface of the hydrogen storage alloy is reduced.

The present invention has been made in view of the above points, and it is possible to improve the reaction activity of the surface of a hydrogen storage alloy, maintain a high discharge capacity for a long period of time, and further, have excellent durability and storability. It is an object of the present invention to provide an electrode and a method for manufacturing a hydrogen storage alloy electrode that can easily obtain the electrode.

[0008]

According to the present invention, there is provided a step of mixing a hydrogen storage alloy powder and a powder of at least one other metal to obtain a mixed powder, and pulverizing and mixing the mixed powder in a closed mill device. A method for producing a hydrogen storage alloy electrode, comprising the steps of producing a mill mixed powder by performing the above, and a step of obtaining a hydrogen storage alloy using the mill mixed powder.

Further, according to the present invention, a step of mixing a hydrogen storage alloy powder and a powder of at least one other metal to obtain a mixed powder, and pulverizing and mixing the mixed powder in a closed mill device for milling A method for producing a hydrogen storage alloy electrode, comprising: a step of producing a mixed powder; and a step of directly press-molding the mill mixed powder on a conductive substrate to obtain a hydrogen storage alloy.

Further, the present invention comprises a conductive substrate and a mixed powder which is directly pressure-molded on the conductive substrate and which is obtained by mixing the hydrogen storage alloy powder and the powder of at least one other metal. Then, the mixed powder is obtained by crushing and mixing in a closed mill device to provide a hydrogen storage alloy electrode.

The hydrogen storage alloy used in the present invention includes rare earth / nickel AB ₅ type alloys, titanium / nickel alloys, zirconium / nickel alloys, zirconium-based Laves phase alloys, and Zr- having the following composition formula: V
A -Ni pseudo-secondary Laves phase-based alloy or the like can be used.

[0012] _{Zr 1-a Ti a (V} 0.33 + x Ni 0.67-xb A b) in _{2 + c} equation, 0 ≦ a ≦ 0.7, -0.05 <x <0.07,0 <b ≦
0.4, 0 ≦ c ≦ 1, A = Fe, Co, Mn The hydrogen storage alloy powder may have an average particle size of about 1 μm, or may be a coarse particle having an average particle size of about 1 to several mm. It may be. Oxidation of the hydrogen storage alloy in the pulverization step can be further suppressed by using coarse particles, so that a hydrogen storage alloy electrode with further improved activity can be obtained.

Other metals include copper, nickel,
Cobalt, aluminum, silver, palladium, gold, platinum,
Tin, antimony, etc. can be used. The metal may be in the form of powder having an average particle diameter of about 0.1 μm or coarse particles having an average particle diameter of about 1 to several mm.

As the closed mill device used in the present invention, a stainless steel ball mill, an attritor or the like can be used.

As the binder to be added to the mill mixed powder, polytetrafluoroethylene powder, polyvinylidene fluoride powder or the like can be used. Further, the amount of the binder added to the mill mixed powder is preferably 1.5% by weight or less. This is because when the amount of the binder exceeds 1.5% by weight, the filling amount of the alloy powder in the electrode plate becomes small.

In the present invention, a metal net, a perforated plate, a foam metal material or the like can be used as the conductive substrate.

In the present invention, in order to improve the strength of the hydrogen storage alloy electrode obtained, it is preferable to carry out a heat treatment at 1100 ° C. or lower after the pressure molding. This is because when the heating temperature exceeds 1100 ° C., the metal coated on the surface of the hydrogen storage alloy diffuses into the inside, or remarkable oxidation due to impure oxygen in the system occurs.

[0018]

In the present invention, the oxide film formed on the surface of the hydrogen storage alloy powder particles is broken or peeled by the mechanical impact of the mill mixing when the mixed powder is mill-mixed by the mill device. At this time, since the added powder particles of the metal are strongly pressed against the hydrogen storage alloy powder particles, at least a part of the surface of the hydrogen storage alloy powder particles is coated with the metal instead of the oxide film. The mill mixed powder thus obtained is
Since the metal is coated on at least a part of the surface, the hydrogen storage alloy is prevented from being oxidized. Therefore, long-term storage is possible. Further, the hydrogen storage alloy electrode obtained by using the mill-mixed powder shows a high discharge capacity in a few charge / discharge cycles. It should be noted that coarse particles of the hydrogen storage alloy having an average particle diameter of about 1 to several mm have a smaller surface area than the powder, and thus are less likely to be oxidized by air. Therefore, a highly active milled mixed powder can be obtained.

Further, in the present invention, since the mill mixing is performed in a closed system, not in an open system performed in a mortar or the like, the hydrogen storage alloy is formed while the oxide film is peeled off from the hydrogen storage alloy powder particles and coated with the metal. Oxidation of powder particles can be suppressed. Therefore, the activity of the hydrogen storage alloy powder particle surface can be improved. Therefore, the hydrogen storage alloy electrode using this mill mixed powder exhibits a high discharge capacity. Further, by performing the mill mixing in a closed system, the amount of oxidation of the hydrogen storage alloy powder can be controlled.

Generally, hydrogen storage alloys have high hardness,
Poor property of crimping to other materials by pressure (crimpability). Therefore, it is difficult to produce an electrode sheet by pressure-molding only a non-treated hydrogen storage alloy powder on a conductive substrate. Therefore, in the conventional sintering-type manufacturing method, it is necessary to perform pressure molding and heat treatment at about 1100 ° C.

On the other hand, as described above, the hydrogen storage alloy particles whose surface is coated with a highly malleable metal have a good pressure-bonding property. Therefore, by directly press-molding the hydrogen-absorbing alloy particles, an electrode sheet having a considerably high strength is obtained. be able to. Even in this case, it is preferable to perform a heat treatment in order to further increase the strength of the electrode sheet, but particles whose surface is covered with a metal and whose particle size is small have a high surface energy, so that the alloy can be used even at a relatively low temperature. Bonding between particles occurs sufficiently. Further, by performing hot press treatment, an electrode sheet having high strength can be produced more effectively.

The heat treatment at a temperature of 1100 ° C. or lower reduces the oxidation rate, so that the oxidation contamination of the surface of the hydrogen storage alloy can be suppressed. Also, metal oxides such as nickel oxide and copper oxide are easily electrochemically reduced in an alkaline electrolyte, so even if oxidative contamination of the surface occurs, the original elemental metal is charged when the electrode is charged. Return to. Therefore,
In particular, the hydrogen storage alloy powder covered with nickel, copper, etc.
Little decrease in reaction activity due to oxidative contamination during heating. However, heating at a temperature higher than 1100 ° C. is not preferable because the coating metal such as nickel and copper on the surface becomes a diffusion alloy inside.

Further, a binder polymer powder such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) or polyvinylidene fluoride (PDVF) is mixed in advance with the hydrogen storage alloy powder, and this mixed powder is pressure-molded. Also by doing so, the strength of the electrode sheet can be increased. At this time, if pulverization and mixing using a mill device is adopted, since the pressure-bonding property of the mixed powder is high, sufficient strength can be obtained even with the addition of a small amount of 1.5 wt% or less, so that the volume occupation by the binder is prevented. It can be kept low.

[0024]

EXAMPLES Examples of the present invention will be specifically described below.

Example 1 Zr _0.9 Ti _0.1 (V which is a Laves phase alloy containing Zr
_0.33 Ni _0.51 Co _0.08 Mn _0.08 ) _2.4 alloy ingots crushed to an average particle size of about 1 mm in advance, 20 g of hydrogen storage alloy powder, and 2.8 g of nickel powder having an average particle size of 0.3 μm are mixed and mixed powder Then, the mixed powder was mill-mixed for 1 hour in air with a stainless ball mill to prepare a mill mixed powder of hydrogen storage alloy and nickel. This mill mixed powder had a particle size of 63 μm or less, and at least a part of the surface of the hydrogen storage alloy was covered with nickel.

0.3g of polytetrafluoroethylene powder was added and mixed to 0.97g of this mill mixed powder, and then this was filled in a porous nickel plate and the pressure was 3t / cm ^2.
Then, a disk-shaped hydrogen storage alloy electrode (Example 1) having a diameter of 20 mm was produced by pressure molding.

Example 2 A mill mixed powder of a hydrogen storage alloy and nickel was prepared in the same manner as in Example 1 except that the mill mixing time was 5 hours. Using this mill mixed powder, a hydrogen storage alloy electrode (Example 2) was prepared in the same manner as in Example 1.

Example 3 20 g of hydrogen storage alloy powder used in Example 1,
A mixed powder was obtained by mixing with 2.8 g of copper powder having an average particle size of 0.8 to 1.2 μm, and the mixed powder was mill-mixed for 1 hour in air with a stainless ball mill to obtain a hydrogen storage alloy and copper. The mill mixed powder of This mill-mixed powder had an average particle size of 63 μm, and at least a part of the surface of the hydrogen storage alloy was covered with copper. Using this mill mixed powder, a hydrogen storage alloy electrode (Example 3) was produced in the same manner as in Example 1.

Example 4 A mill mixed powder of a hydrogen storage alloy and copper was produced in the same manner as in Example 1 except that the time of mill mixing was 5 hours.
Using this mill mixed powder, a hydrogen storage alloy electrode (Example 4) was produced in the same manner as in Example 1.

Conventional Example 1 20 g of the hydrogen storage alloy powder used in Example 1 was milled in a stainless ball mill in air for 1 hour to prepare a hydrogen storage alloy powder having an average particle size of 63 μm or less. 2.8 g of 0.2 μm nickel powder
Was mixed, put in a styrene bottle, and shaken in the bottle to prepare a mixed powder of hydrogen storage alloy and nickel. Using this mixed powder, a hydrogen storage alloy electrode (conventional example) was produced in the same manner as in Example 1.

Comparative Examples 1 to 4 Mill mixed powders were produced in the same manner as in Examples 1 to 4 except that a mortar was used instead of the ball mill for pulverization and mixing. Using this mixed powder, hydrogen storage alloy electrodes (Comparative Examples 1 to 4) were produced in the same manner as in Example 1.

With respect to the obtained hydrogen storage alloy electrodes of Examples 1 to 4, Comparative Examples 1 to 4 and Conventional Example 1, the maximum discharge capacity, and the relationship between the number of cycles and the discharge capacity were examined. The results are shown in FIGS. 1 and 2. The maximum discharge capacity was determined by attaching a lead wire to a hydrogen storage alloy electrode as a negative electrode, immersing this in a 30 wt% -potassium hydroxide electrolyte, arranging a nickel plate as a counter electrode to form a cell, and , Was measured by repeating charge and discharge at a current of 70 mA per gram of hydrogen storage alloy. The discharge end potential at this time is −
The charging time was 0.75 V vs. Hg / HgO and 1.3 times the discharging time.

As is apparent from FIGS. 1 and 2, the hydrogen storage alloy electrodes obtained by the method of the present invention (Examples 1 to 1)
All of 4) had a discharge capacity significantly higher than that of the hydrogen storage alloy electrode (conventional example 1) obtained by the conventional method. Further, in the hydrogen storage alloy electrode of the conventional example, it took 40 cycles or more to reach the maximum discharge capacity, whereas the hydrogen storage alloy electrodes of Examples 1 to 4
Maximum discharge capacity was reached in less than 10 cycles.

Further, as can be seen from FIG. 1, the hydrogen storage alloy electrodes of Examples 1 and 2 reach the maximum discharge capacity in a smaller number of cycles than the hydrogen storage alloy electrodes of Comparative Examples 1 and 2, and have a large discharge capacity. The capacity is indicated. Similarly, as can be seen from FIG. 2, the hydrogen storage alloy electrodes of Examples 3 and 4 reach the maximum discharge capacity in a smaller number of cycles and have a larger discharge capacity than the hydrogen storage alloy electrodes of Comparative Examples 3 and 4. Indicated.

As is clear from the above, the hydrogen storage alloy powder obtained by the method of the present invention has the oxide film on its surface removed during mill mixing, and instead is coated with another metal such as copper or nickel. Therefore, the activity of the hydrogen storage alloy is remarkably improved.

Therefore, the hydrogen storage alloy electrode of the present invention using this mill mixed powder has a large discharge capacity from the beginning as compared with the conventional hydrogen storage alloy electrode, and the number of charge / discharge cycles required to reach the maximum discharge capacity is increased. It can be significantly reduced.
In addition, in this example, it can be seen that when the mill mixing time is long, the activity of the hydrogen storage alloy is improved and the discharge capacity is increased.

Further, in the same manner as in the above embodiment, the hydrogen storage alloy powder was mixed with cobalt powder alone, cobalt powder and nickel powder, cobalt powder and copper powder, and nickel powder,
Cobalt powder and copper powder were respectively added and mixed to obtain a mixed powder, and the mixed powder was mill-mixed to prepare four types of mill mixed powders, each of which was used to manufacture a hydrogen storage alloy electrode. When the maximum discharge capacity and the charge / discharge cycle were examined in the same manner as in FIG.
The result was the same as that shown in.

Further, the hydrogen storage alloy electrodes obtained in Examples 1 to 4, Comparative Examples 1 to 4 and Conventional Example 1 were used as negative electrodes, and known paste type nickel electrodes (capacity 1300 mAh) were used.
g ^-1 ) is used as a positive electrode, and a separator is further combined to
Each A-size battery was manufactured. In this case, in the negative electrode, each mixed powder and polytetrafluoroethylene powder were kneaded at a weight ratio of 99.5: 0.5, and the mixture was rolled to form a sheet. It was produced by further rolling together and cutting into a predetermined size.

For these batteries, 0.2C (260
The charge / discharge cycle was repeated at a current of mA). At this time, charging is designed capacity (1300 mAhg ^{-1 of} nickel pole capacity)
And the final discharge voltage was 1.00V. At this time, the relationship between the number of cycles at the initial charge / discharge repetition of each battery and the battery discharge capacity was examined. The results are shown in FIGS. 3 and 4.

As is clear from FIGS. 3 and 4, the batteries using the hydrogen storage alloy electrodes of Examples 1 to 4 had a large initial discharge capacity, and the designed capacity was 1300 within 20 cycles.
The discharge capacity of mAhg ^-1 was reached. On the other hand, the battery using the hydrogen storage alloy electrode of Conventional Example 1 shows an extremely slow increase in the discharge capacity with the number of charge / discharge cycles, and shows only a slight discharge capacity of about 100 mAhg ⁻¹ even after repeating about 40 cycles. There wasn't.

Further, the batteries using the hydrogen storage alloy electrodes of Comparative Examples 1 to 4 had a larger initial discharge capacity than the batteries using the hydrogen storage alloy electrode of Conventional Example 1, but the hydrogen of Examples 1 to 4 was used. The discharge capacity was much smaller than that of the battery using the occlusion alloy electrode, and the design capacity of 1300 mAhg ^-1 was not reached.

As a hydrogen storage alloy, Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Fe _0.08 Mn) which is a Laves phase alloy.
_0.08 ) Using _2.4 , a battery was manufactured in the same manner as above, and the relationship between the number of cycles at the initial charging / discharging cycle and the battery discharge capacity was examined. As a result, the initial discharge capacity was large, and the battery was designed within 20 cycles. It was confirmed that the discharge capacity of 1300 mAhg ^-1 was reached.

Example 5 Mm _4.0 Co which is a misch metal-nickel alloy
20 g of hydrogen storage alloy powder obtained by crushing an ingot of _0.5 Al _0.5 alloy to an average particle size of about 1 mm and an average particle size of 0.
2.8 g of 2 μm nickel powder was mixed to obtain a mixed powder, and the mixed powder was mill-mixed for 1 hour in the air by a stainless ball mill to prepare a mill mixed powder of hydrogen storage alloy and nickel.

0.3 g of polytetrafluoroethylene powder was added to and mixed with 0.97 g of this mill mixed powder, and then this was filled in a porous nickel plate and the pressure was 3 t / cm ^2.
Was pressed and formed into a disk-shaped hydrogen storage alloy electrode (Example 5) having a diameter of 20 mm.

Example 6 20 g of the hydrogen storage alloy powder used in Example 5,
1 g of nickel powder having an average particle diameter of 0.2 μm and 1.8 g of cobalt powder having an average particle diameter of 1.2 to 1.5 μm are mixed to obtain a mixed powder, and the mixed powder is in air by a stainless ball mill. The mixture was mill-mixed for 1 hour to prepare a mill-mixed powder of hydrogen storage alloy, nickel, and cobalt. Using this mill mixed powder, a hydrogen storage alloy electrode (Example 6) was produced in the same manner as in Example 1.

Conventional Example 2 The hydrogen-absorbing alloy powder used in Example 5 having an average particle size of about 1 mm was milled in a ball mill for 1 hour in air to obtain a hydrogen-absorbing alloy powder having an average particle size of 63 μm or less. 2.8 nickel powder with an average particle size of 0.2 μm was added to this.
g was added, and this was put in a styrene bottle and shaken in the bottle to prepare a mixed powder of a hydrogen storage alloy and nickel. Using this mixed powder, a hydrogen storage alloy electrode (conventional example 2) was produced in the same manner as in Example 1.

With respect to the obtained hydrogen storage alloy electrodes of Examples 5 and 6 and Conventional Example 2, the relationship between the maximum discharge capacity, the number of cycles and the discharge capacity was examined by the same method as described above. The result is as shown in FIG.

As is apparent from FIG. 5, the hydrogen storage alloy electrodes (Examples 5 and 6) obtained by the method of the present invention have a discharge capacity of 250 to 260 mAhg ⁻¹ , whereas The hydrogen storage alloy electrode (conventional example 2) obtained by the conventional method had a discharge capacity of 230 mAhg ^−1, which was considerably low.

Furthermore, copper powder alone, copper powder and nickel powder, cobalt powder and copper powder, and nickel powder, cobalt powder and copper powder were added and mixed to the hydrogen storage alloy powder in the same manner as in the above-mentioned embodiment. Obtained mixed powder, prepared four kinds of mill mixed powder by mill-mixing the mixed powder, and examined the maximum discharge capacity and charge / discharge cycle in the same manner as above for the hydrogen storage alloy electrode manufactured using each. As a result, it was the same as the result shown in FIG.

According to the method of the present invention, the hydrogen-absorbing alloy powder and the other metal powder are mill-mixed, and the surface of the hydrogen-absorbing alloy powder particles is pressure-bonded with the metal. Is good. Therefore, when the hydrogen storage alloy electrode is manufactured using this mill mixed powder, the initial activity can be maintained even if the mill mixed powder is stored for a long period of time. Therefore, even if the hydrogen-absorbing alloy electrode was produced using the mill-mixed powder after long-term storage, its discharge capacity was equivalent to that of the hydrogen-absorbing alloy electrode produced immediately after the mill-mixed powder was produced. Is.
Hereinafter, examples performed to clarify this will be described.

Example 7 MmNi _4.0 Co _0.5 Al used in Example 5
An alloy ingot of _0.5 is crushed by a crusher and the average particle size is about 1
Coarse grains of 0 mm were obtained. To 20 g of the coarse particles, 2.8 g of various metal powders having an average particle size of 0.3 mm shown in Table 1 below was added, and this was mill-mixed in a stainless ball mill for 5 hours in the air to obtain a hydrogen storage alloy and the following table. A mill mixed powder with the metal shown in 1 was prepared. This mill mixed powder has an average particle size of 63
The thickness was not more than μm, and at least a part of the surface of the hydrogen storage alloy was covered with a metal.

To 0.97 g of this mill mixed powder, 0.3 g of polytetrafluoroethylene powder was added and mixed, and then this was filled in a porous nickel plate and the pressure was 3 t / cm ^2.
Disc-shaped hydrogen storage alloy electrode with a diameter of 20 mm (Test Nos. 1, 2, 5, 6, 9, 10, 13 to 26)
Was produced.

Comparative Example 5 20 g of the hydrogen storage alloy coarse particles used in Example 7 were milled in a stainless ball mill for 5 hours in air to obtain a hydrogen storage alloy powder having an average particle size of 63 μm or less. This hydrogen storage alloy powder and 2.8 g of various metal powders having an average particle size of 0.3 mm shown in Table 1 below were put in a styrene bottle and shaken in the bottle for 5 hours to prepare mixed powders. did. Using these mixed powders, hydrogen storage alloy electrodes (Test No. 3, 4, 7,
8, 11, 12) was produced.

A lead wire was attached to the hydrogen storage alloy electrodes of Example 7 and Comparative Example 5, immersed in a 30 wt% potassium hydroxide electrolytic solution, and a nickel plate was combined as a counter electrode to form a cell. In this cell, hydrogen storage alloy 1g
The charging / discharging was carried out 3 times with a current of 70 mA. At this time, the discharge end potential is -0.75 V vs Hg / HgO,
The charging time was 1.3 times the discharging time. The discharge capacity was measured for each charge / discharge cycle. The results are also shown in Table 1 below.

Further, in order to examine the preservability of the mill mixed powder, after leaving the mill mixed powder of Example 7 and the mixed powder of Comparative Example 5 in the air for 5 months, hydrogen was respectively treated in the same manner as above. An occlusion alloy electrode was produced and the discharge capacity at each charge / discharge cycle was measured. The results are also shown in Table 1 below. In Table 1, the "standing time" means the time during which the hydrogen storage alloy is left in the air until the hydrogen storage alloy electrode is manufactured and the hydrogen storage alloy electrode is first charged.

[0056]

[Table 1] As is clear from Table 1, the hydrogen storage alloy electrode obtained by the method of the present invention had a large discharge capacity.
Moreover, the hydrogen storage alloy electrode produced by using the mill mixed powder after being left for a long time also had a large discharge capacity (see Test Nos. 1 to 12). Therefore, it was confirmed that the preservability thereof was extremely good (Test Nos. 1, 2; 5,6; 9,10; 13,14; 15,16; 17,18; 19,20). The same 21,22; the same 23,2
4; ibid. 25, 26). As a result, the mill-mixed powder can be stored as it is for a long period of time, and the hydrogen storage alloy electrode can be manufactured stably and satisfactorily. Furthermore, the hydrogen storage alloy electrode can be stored for a long time.

On the other hand, the hydrogen storage alloy electrode obtained by the conventional method had a significantly reduced discharge capacity after 5 months and was found to have no storability (Test No.
3, 4; ibid. 7, 8; ibid., 11, 12).

In mill mixing, the above hydrogen-absorbing alloy powder having an average particle diameter of 10 mm was used in place of the hydrogen-absorbing alloy powder having an average particle diameter of 10 mm, the above-mentioned various metals were added, and the mixture was mill mixed to prepare a mill mixed powder. After being left standing for 5 months, a hydrogen storage alloy electrode was produced using this, and the discharge capacity was measured in the same manner as above. The results are shown in Table 2.

[0059]

[Table 2] As is clear from Table 2, the hydrogen storage alloy electrode obtained by using the hydrogen storage alloy powder having a large average particle size had a large discharge capacity. It is considered that this is because so-called coarse particles having a large average particle size have a relatively small surface area and are less susceptible to oxidation.

In the above examples, an alloy based on MmNi was used as the hydrogen storage alloy, but TiNi,
Titanium-nickel alloy based on TiNi, Zr
It was confirmed that similar effects were obtained also with an alloy such as a Laves phase alloy based on.

Example 8 Zr _0.9 Ti _0.1 which is a typical alloy having a Laves phase
(V _0.33 Ni _0.51 Co _0.08 Mn _0.08 ) _{2.4 The} alloy powder obtained by previously pulverizing the alloy to an average particle size of about 63 μm and nickel powder are stirred and mixed at a weight ratio of 96: 4, and then this is air-mixed with a stainless ball mill. The mixture was pulverized and mixed in the mixture for 5 hours to prepare a mixed powder. Next, a net made of nickel was cut into a circular shape having an outer diameter of 20 mm to obtain a core. 1 g of the mixed powder was pressure-molded on the core body at a pressure of 3 t / cm ² to prepare a hydrogen storage alloy electrode sheet of Example 8 having an outer diameter of 20 mm.

Examples 9 to 11 In the same manner as in Example 8, the mixed powder was pressure-molded on the core body.
In addition to this, 350 ° C x 3 under exhaust by rotary pump
The hydrogen storage alloy electrode sheets of Examples 9 to 11 were produced by individually performing three types of heat treatments for 1 hour, 600 ° C. × 3 hours, or 1100 ° C. × 3 hours.

Example 12 In the same manner as in Example 8, the mixed powder was pressure-molded on the core.
This was hot-pressed at 350 ° C. under exhaust from a rotary pump to prepare a hydrogen storage alloy electrode sheet of Example 12.

Example 13 A mixed powder was prepared in the same manner as in Example 8. A PTFE dispersion and a CMC dispersion were added to this mixed powder to prepare a paste. This paste was applied to the core used in Example 8, dried, and then pressure-molded in the same manner as in Example 8 to prepare a hydrogen storage alloy electrode sheet of Example 13.

Comparative Example 6 Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Co _0.08 Mn _0.08 )
2.4g of alloy powder made by crushing _2.4 alloy in advance to an average particle size of 63μm is pressure-molded at a pressure of 3t / cm ^{2 on} a core made of a nickel net that has been cut into a circular shape with an outer diameter of 20mm. A hydrogen storage alloy electrode sheet of Comparative Example 6 was produced.

Comparative Examples 7 to 9 In the same manner as in Comparative Example 6, alloy powder was pressure-molded on the core body.
In addition to this, 350 ° C x 3 under exhaust by rotary pump
Time, 600 ° C. × 3 hours, or 1100 ° C. × 3 hours were individually applied to the three types of heat treatments to produce hydrogen storage alloy electrode sheets of Comparative Examples 7 to 9.

Comparative Example 10 Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Co _0.08 Mn _0.08 )
_An alloy powder prepared by previously pulverizing the _2.4 alloy to an average particle size of about 63 μm and a nickel powder were stirred and mixed at a weight ratio of 96: 4 to prepare a mixed powder. Then, in the same manner as in Comparative Example 6, the mixed powder was pressure-molded on the core to prepare a hydrogen storage alloy electrode sheet of Comparative Example 10.

Comparative Examples 11 to 13 In the same manner as in Comparative Example 10, the mixed powder was pressure-molded on the core body. In addition, 350 ° C under exhaust by rotary pump
The hydrogen storage alloy electrode sheets of Comparative Examples 11 to 13 were produced by individually performing three types of heat treatments of × 3 hours, 600 ° C × 3 hours, or 1100 ° C × 3 hours.

The obtained Examples 8 to 13 and Comparative Examples 6 to
Regarding the hydrogen storage alloy electrode sheet of No. 13, the maximum discharge capacity, the number of cycles until the capacity decreased by 10%, and the state (durability) of the electrode were examined. The results are shown in Table 3 below. The maximum discharge capacity was determined by attaching a lead wire to a hydrogen-absorbing alloy electrode sheet, immersing the lead wire in a 30 wt% -potassium hydroxide electrolyte solution, arranging a nickel plate as a counter electrode to form a cell, and then using hydrogen. 70m per 1g of storage alloy
It was measured by repeating charge and discharge at a current of A. The discharge end potential at this time is -0.75 V vs Hg / HgO,
The charging time was 1.3 times the discharging time. All electrodes showed the behavior that the discharge capacity increased at first and then gradually decreased.

[0070]

[Table 3] As is clear from Table 3, in the hydrogen storage alloy electrode sheets (Examples 8 to 13) obtained by the method of the present invention, there is almost no drop of the alloy from the electrodes due to charge and discharge, and the capacity decrease of 10% is 200. It did not occur even in a cycle, and the discharge capacity was large. In the thirteenth embodiment,
Since the hydrogen storage alloy was formed into a paste, the durability was excellent, but the discharge capacity was small.

On the other hand, in the case where the core was pressure-molded by using only the hydrogen-absorbing alloy powder (Comparative Examples 6 to 9), the alloy dropped off remarkably due to charge and discharge, and therefore the discharge capacity was small. In addition, the one obtained by press-molding the core body using the mixed powder obtained by simply mixing the nickel powder with the hydrogen-absorbing alloy powder (Comparative Examples 10 to 13) has a large amount of alloy falling off due to charge and discharge, and therefore the discharge capacity is small. It was Among these, those subjected to the heat treatment at 1100 ° C. (Comparative Examples 9 and 13) had a small discharge capacity of the alloy from the electrodes due to charge and discharge, but had a small discharge capacity.

Example 14 Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Co _0.08 Mn _0.08 )
_{2.4 The} alloy powder obtained by pulverizing the alloy to an average particle size of 63 μm and nickel powder are mixed by stirring at a weight ratio of 96: 4, and then this is pulverized and mixed in the air for 5 hours in a stainless ball mill to obtain a mixed powder. Was produced. Next, the PTFE powder was mixed with this mixed powder by stirring at 1.5% by weight. Next, use a net made of nickel with an outer diameter of 20 mm.
Was cut into a circular shape to obtain a core. Powder 1 on this core
g was pressure-molded at a pressure of 3 t / cm ² to prepare a hydrogen storage alloy electrode sheet of Example 14.

Example 15 A hydrogen storage alloy electrode sheet of Example 15 was prepared in the same manner as in Example 14 except that the amount of PTFE powder mixed was 3% by weight.

Example 16 The same hydrogen storage alloy electrode sheet as in Example 14 was applied under reduced pressure to 20.
The hydrogen storage alloy electrode sheet of Example 16 was produced by performing a heat treatment at 0 ° C. for 2 hours.

Comparative Example 14 Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Co _0.08 Mn _0.08 )
1.5% by weight of PTFE powder was agitated and mixed with 1 g of alloy powder obtained by previously pulverizing _2.4 alloy to an average particle size of about 63 μm to prepare a mixed powder. Next, this mixed powder was pressure-molded at a pressure of 3 t / cm ² to a core body made of a nickel net previously cut into a circular shape having an outer diameter of 20 mm to prepare a hydrogen storage alloy electrode sheet of Comparative Example 14.

Comparative Example 15 A hydrogen storage alloy electrode sheet of Comparative Example 15 was prepared in the same manner as Comparative Example 14 except that the mixing amount of PTFE powder was 3% by weight.

Comparative Example 16 Zr _0.9 Ti _0.1 (V _0.33 Ni _0.51 Co _0.08 Mn _0.08 )
_{2.4 The} alloy powder is pulverized in advance to an average particle size of 63 μm and the nickel powder is stirred and mixed at a weight ratio of 96: 4 to prepare a mixed powder, and PT is added to this mixed powder.
The FE powder was mixed by stirring at 1.5% by weight. In the same manner as in Comparative Example 14, the mixed powder was pressure-molded on the core to prepare a hydrogen storage alloy electrode sheet of Comparative Example 16.

Comparative Example 17 A hydrogen storage alloy electrode sheet of Comparative Example 17 was prepared in the same manner as Comparative Example 16 except that the mixing amount of PTFE powder was 3% by weight.

Obtained Examples 14 to 16 and Comparative Example 1
With respect to the hydrogen storage alloy electrode sheets of Nos. 4 to 17, the maximum discharge capacity, the number of cycles until the capacity decreased by 10%, and the state of the electrode (durability) were examined as described above. The results are shown in Table 4 below. All electrodes showed the behavior that the discharge capacity increased at first and then gradually decreased.

[0080]

[Table 4] As is clear from Table 4, the hydrogen-absorbing alloy electrode sheets (Examples 14 to 16) obtained by the method of the present invention show almost no fall of the alloy from the electrodes due to charge / discharge and 10%.
The capacity was not decreased even after 200 cycles, and the discharge capacity was large.

On the other hand, in the case where the core was pressure-molded using only the hydrogen-absorbing alloy powder (Comparative Examples 14 and 15), the alloy dropped off due to charge and discharge, and therefore the discharge capacity was small. Also, the one obtained by press-molding the core body using the mixed powder obtained by simply mixing the nickel powder with the hydrogen-absorbing alloy powder (Comparative Example 16) had a large amount of the alloy falling off due to charge and discharge, and therefore the discharge capacity was small. 3% by weight of PTF in powder mixture
A mixture of E and a core body which is pressure-molded (Comparative Example 1)
In 7), the durability was good, but the discharge capacity was small.

In the above examples, nickel powder was used as the powder to be mixed with the hydrogen storage alloy powder, but it was confirmed that the same effect can be obtained by using copper powder. It was also confirmed that the same effect can be obtained by using polyvinylidene fluoride powder instead of PTFE powder.

The electrode obtained by the method of the present invention was combined with the nickel hydroxide positive electrode obtained by the conventional paste-type production method to prepare an AA size sealed nickel-hydrogen battery, and its characteristics were examined. It was confirmed that the same effect as that of this example was obtained. It was also confirmed that a hydrogen storage alloy electrode sheet using another Laves phase alloy containing Zr or an alloy based on MmNi ₅ can achieve the same effect as this example.

[0084]

As described above, according to the method for producing a hydrogen storage alloy electrode of the present invention, the hydrogen storage alloy powder and the other metal powder are mill-mixed in a closed system, so that the surface of the hydrogen storage alloy powder is oxidized. Without being coated with other metals. Therefore, it is possible to easily obtain a hydrogen storage alloy electrode which can maintain a high discharge capacity for a long period of time without lowering the reaction activity of the surface of the hydrogen storage alloy and which is excellent in durability and storability.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between discharge capacity and charge / discharge cycle for hydrogen storage alloy electrodes.

FIG. 2 is a graph showing the relationship between discharge capacity and charge / discharge cycle for hydrogen storage alloy electrodes.

FIG. 3 is a graph showing the relationship between the discharge capacity and the charge / discharge cycle of a battery using a hydrogen storage alloy electrode.

FIG. 4 is a graph showing the relationship between discharge capacity and charge / discharge cycle for a battery using a hydrogen storage alloy electrode.

FIG. 5 is a graph showing the relationship between discharge capacity and charge / discharge cycle for hydrogen storage alloy electrodes.

Claims (5)

[Claims] 1. A step of mixing a hydrogen storage alloy powder and a powder of at least one other metal to obtain a mixed powder, and pulverizing and mixing the mixed powder in a closed mill device to prepare a mill mixed powder. And a step of obtaining a hydrogen storage alloy electrode by using the mill mixed powder, the method of manufacturing a hydrogen storage alloy electrode. 2. A step of mixing a hydrogen storage alloy powder and a powder of at least one other metal to obtain a mixed powder, and pulverizing and mixing the mixed powder in a closed mill device to prepare a mill mixed powder. And a step of directly press-molding the mill-mixed powder onto a metal net or a porous plate to obtain a hydrogen-absorbing alloy electrode. 3. The method for producing a hydrogen storage alloy electrode according to claim 1, wherein a thickener is mixed with the mill mixed powder at a predetermined ratio. 4. The method for producing a hydrogen storage alloy electrode according to claim 2, wherein after the milled mixed powder is pressure-molded on the conductive substrate, heat treatment at 1100 ° C. or lower is performed. 5. A conductive substrate, and a mixed powder which is directly pressure-molded on the conductive substrate and is formed by mixing a hydrogen storage alloy powder and a powder of at least one other metal. The powder is a hydrogen storage alloy electrode obtained by pulverizing and mixing in a closed mill device.