JPH08171909A - Manufacture of hydrogen storage alloy electrode containing a'b'o3 compound - Google Patents

Abstract

PURPOSE: To provide the manufacture of a hydrogen storing alloy electrode containing a A'B'O3 compound, which is used as the negative electrode of an alkali battery, has a long charging/discharging cyclic life, and can efficiently remove oxygen generated by a positive electrode. CONSTITUTION: Slurry is prepared, which contains 100 parts of hydrogen storing alloy by weight formed out of only an AB5 phase, 0.5 to 5 parts of provskite type conductive oxide by weight represented by A'B'O3 , and 0.1 to 5 parts of binder by weight. Slurry thus obtained is coated on the surface of a conductive support body, then dried, and bonded with pressure thereafter, or a sheet is formed out of the aforesaid slurry, the sheet thus obtained is bonded with pressure on the surface of the conductive support body thereafter, and then dried, or after a hydrogen storing alloy electrode containing no A' B'O3 has been formed, slurry containing A'B'O3 compounds and binder is coated over the surface of the aforesaid electrode, and then dried. In this case, in the aforesaid formulas, A represents Mm, B represents at least one kind of chemical selected out of Al, Co, Mn and Ni, A' represents at least one kind of chemical selected out of Mm, Ca and Sr, and B' represents Co or Mn.

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 electrode used as a negative electrode of an alkaline battery, and more particularly, to a charging device capable of efficiently converting oxygen gas generated from the positive electrode during overcharge into water. The present invention relates to a method for manufacturing a hydrogen storage alloy electrode having a long discharge cycle life.

[0002]

2. Description of the Related Art Since the discovery of hydrogen storage alloys capable of storing and releasing hydrogen, their applications have been expanded to heat pumps and batteries, as well as simple means for storing hydrogen. In particular, alkaline storage batteries using a hydrogen storage alloy as a negative electrode have almost reached the practical range, and the hydrogen storage alloys used have been improved one after another.

That is, the LaNi ₅ alloy initially studied (see Japanese Patent Application Laid-Open No. 51-13934) has the advantage of having a large hydrogen storage capacity, while the La metal is expensive and also stores hydrogen. It has a drawback that it is easily pulverized by repeated discharge and is easily corroded by an alkaline solution or an acid solution. Therefore, when the above hydrogen storage alloy is used as an electrode of an alkaline storage battery, the electric capacity is high in the initial stage, but when the charge / discharge cycle is repeated about 50 times, the electric capacity becomes half or less, and it is necessary to use it for a long period of time. There was a drawback that you couldn't.

The drawback is that a part of La is replaced by Ce, P
By substituting r, Nd and other rare earth elements,
And / or by substituting a part of Ni with a metal such as Co, Al or Mn (see, for example, JP-A-53-53).
No. 4918, No. 54-64014, No. 60-
250558, 61-91862, and 6
No. 1-233969).

Although these alloys have a slightly reduced hydrogen storage capacity as compared with the LaNi ₅ alloy, they are corrosive to alkaline solutions and acid solutions and the cycle life of charging / discharging of alkaline storage batteries is improved. However, the above alloys
From an industrial point of view, since the charge / discharge cycle life is still short, it is hard to say that it has sufficient practical value.

This drawback can be improved by using a hydrogen storage alloy containing no intermetallic compound phase other than the AB ₅ phase (Japanese Patent Application No. 5-257846), but it can be said that the charge / discharge cycle is still sufficient. It wasn't something. However,
Here, A is La or a mixture of two or more rare earth elements containing at least La, and B is Al, Co, Cr,
It is at least one element selected from Fe, Mn, Ni, Ti, V, Zn and Zr. That is, in actual use, overcharge is often performed, and in this case, the oxygen gas generated from the positive electrode increases the internal pressure of the battery, which causes the battery to lose its function and oxidize the alloy. The negative electrode deteriorates.

Therefore, in order to improve such a defect, a carbon powder layer is formed on the surface of a hydrogen storage alloy electrode which is a negative electrode (Japanese Patent Laid-Open No. 63-195960), or a fibrous oxygen gas having conductivity. Forming a consumer layer
No. 335,014) is proposed. However, in the former case, there is a drawback that the negative electrode is cracked together with the carbon powder layer applied to the surface while the charge / discharge cycle is repeated. On the other hand, in the latter case, there is no drawback as described above, but in order to obtain sufficient performance, it is necessary to further carry a catalyst such as palladium on the surface of the electrically conductive fiber, which is complicated. In addition, there is a drawback that the manufacturing cost becomes high.

[0008]

Therefore, as a result of further studies by the present inventors, in order to more simply and conveniently improve the above-mentioned inconvenience due to overcharging, the hydrogen storage alloy near the surface of the hydrogen storage alloy electrode was found to be , It is difficult to store hydrogen because it is oxidized, and therefore, the function of consuming oxygen generated from the positive electrode by reacting hydrogen with oxygen is poor, and such a drawback is that at least the surface of the hydrogen storage alloy has a conductive property. It has been found that the presence of a perovskite-type A′B′O ₃ oxide, which has a property and which has a catalytic activity of decomposing oxygen molecules into atomic oxygen, can be improved, and has reached the present invention.

Therefore, a first object of the present invention is to provide a method for producing a hydrogen storage alloy electrode having a long charge / discharge cycle life, which is used as a negative electrode of an alkaline battery. A second object of the present invention is to provide a method for producing a hydrogen storage alloy electrode for a negative electrode of an alkaline battery, which can efficiently eliminate oxygen generated in the positive electrode.

[0010]

The above-mentioned various objects of the present invention are as follows: 100 parts by weight of a hydrogen storage alloy containing only the AB ₅ phase;
After preparing a slurry containing 0.5 to 5 parts by weight of a perovskite-type conductive oxide represented by A'B'O ₃ and 0.1 to 5 parts by weight of a binder, the obtained slurry is made conductive. It is applied on the surface of the support and dried and then pressure-bonded, or the slurry is molded into a sheet and then the sheet is pressure-bonded to the surface of the conductive support and dried, or hydrogen absorption consisting of only the AB ₅ phase is carried out. 100 parts by weight of alloy and 0.
0.5 to 5 parts by weight of a perovskite type conductive oxide represented by A′B′O ₃ is formed on the surface of the hydrogen storage alloy electrode having a layer containing 1 to 5 parts by weight on the surface of the conductive support. A slurry containing 0.5 to 5 parts by weight of a binder was added to A '.
B′O ₃ is applied so as to cover 20 to 80% of the surface of the hydrogen storage alloy electrode, and then dried.
It was achieved by a method of manufacturing a hydrogen storage alloy electrode having an A′B′O ₃ compound. However, in the above formula, A is Mm and B is at least 1 selected from Al, Co, Mn and Ni.
A'is at least one selected from Mm, Ca and Sr, and B'is Co or Mn.

Mm is CaCu_FiveHas a type crystal structure
LaNi_FiveCe, Pr, Nd and some of La of the alloy
Misch metal, which is a metal substituted with other rare earth elements
It is a mixture of rare earth elements. Mm is like
For example, Ce 45% by weight, La 30% by weight, Nd 5% by weight,
And 20% by weight of other rare earth elements. In the present invention
AB to use_FiveA hydrogen storage alloy consisting of only phases will be described later.
As you can see, AB _FiveHydrogen containing no intermetallic compound phases other than phases
It is an occlusion alloy.

The perovskite type conductive oxide represented by A'B'O ₃ used in the present invention has conductivity and acts as a catalyst when decomposing oxygen molecules into oxygen atoms. Specific examples of A'B'O ₃ include Mm
CoO ₃ , MmMnO _{3 and the} like can be mentioned, but especially A ′
Is preferably Mm _1-y (Ca, Sr) _y . However, y is a molar ratio of 0 ≦ y ≦ 0.5.

The hydrogen storage alloy consisting of only the AB ₅ phase used in the manufacturing method of the present invention prevents corrosion by an alkali or acid solution when used as a battery electrode and prolongs the cycle life. A _x B in stoichiometry
It is an alloy represented by _5.0 (x is a rational number in the range of 0.95 ≤ x ≤ 1.00), and its alloy structure does not include an intermetallic compound phase other than the AB ₅ phase.

When producing an alloy having such a composition, the above-mentioned metal elements are weighed and mixed so as to have this composition, and the produced hydrogen storage alloy contains carbon in the range of 30 to 500 ppm. Therefore, it is necessary to add carbon. By adding a small amount of carbon in this way, precipitation of other intermetallic compounds such as A ₂ B ₇ phase and AB ₂ phase can be suppressed, and only the AB ₅ phase can be precipitated.

That is, when the alloy is melted and then cooled to be solidified, the alloy is generally solidified in the descending order of the melting points. However, in the case of producing the hydrogen storage alloy of the present invention, the AB ₅ phase and the A ₂ B phase are used.
_{The 7th} phase, the AB ₂ phase, the AB ₃ phase, the AB phase, and the A ₃ B phase are solidified in this order. Therefore, as for the alloy structure, first, the AB ₅ phase forms crystal grains, and other intermetallic compounds are present in the crystal grain boundaries, but the added carbon precipitates in the grain boundaries during solidification of the AB ₅ phase. However, the precipitation of other intermetallic compounds such as A ₂ B ₇ phase and AB ₂ phase is suppressed.

The crystal grains of the AB ₅ phase are formed by melting the molten metal containing a minute amount of the above-mentioned carbon, which becomes uniform, at 4 to 100 ° C.
It is obtained by cooling at a cooling rate of / sec. Examples of the cooling method include a method of casting in a water-cooled mold. Such an alloy structure forms extremely fine crystal grains of an intermetallic compound. In other words, since the obtained particles are fine, the gaps between the particles are small, and as a result, the grain boundaries can be made small, so that the corrosion resistance to an alkali solution or an acid solution is high. From the viewpoint of facilitating mixing, stirring, etc., it is preferable to use the above hydrogen storage alloy in powder form. The average particle size of the hydrogen storage alloy powder used is appropriately determined, but is usually 20 to 100 μm.

A perovskite type conductive oxide represented by A'B'O ₃ (referred to as a conductive oxide) is A'B'O _3.
It can be obtained by mixing an aqueous solution of a salt capable of constituting the above and calcining the obtained precipitate. Examples of the salt include calcium carbonate, strontium carbonate, cobalt carbonate, manganese carbonate and the like. The obtained conductive oxide is preferably pulverized and used in the form of fine powder in order to uniformly disperse it in the hydrogen storage alloy electrode. The average particle diameter of the preferred conductive oxide powder is usually
It is 0.5 to 10 μm. As the binder, a known water-soluble resin having a binding property such as polyvinyl alcohol and methyl cellulose can be appropriately used.

In the preparation of the slurry when A'B'O ₃ is used together with the hydrogen storage alloy, the perovskite type conductive oxide represented by A'B'O ₃ is stored in the hydrogen storage alloy containing only the AB ₅ phase. It is used in an amount of 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, based on 100 parts by weight of the alloy. If it is 0.5 parts by weight or less, an electrode capable of efficiently eliminating oxygen cannot be manufactured, and if it is 5 parts by weight or more, not only becomes uneconomical, but also reduces the hydrogen storage capacity of the hydrogen storage alloy, and Performance decreases. The binder is
From the viewpoint of improving moldability when manufacturing the electrode, AB
_For 100 parts by weight of hydrogen storage alloy consisting of only ₅ phases,
It is used in an amount of 0.1 to 5 parts by weight, preferably 0.5 to 1.5 parts by weight. If it is less than 0.1 parts by weight, the manufacturability of the electrode will be reduced, and if it is more than 5 parts by weight, the hydrogen storage alloy will be covered with the insulating film, so the hydrogen storage capacity will be reduced.
The obtained electrode performance deteriorates.

In the first manufacturing method of the present invention, AB
100 parts by weight of hydrogen storage alloy consisting of only ₅ phases, A'B '
After preparing a slurry containing 2 parts by weight of a perovskite type conductive oxide represented by O ₃ and 0.82 parts by weight of a binder, the obtained slurry was applied on the surface of the conductive support and dried. A'B'O by post pressure bonding
A hydrogen storage alloy electrode having ₃ compounds is manufactured.

In the second production method of the present invention, the above slurry is formed into a sheet, and then the sheet is pressure-bonded to the surface of the conductive support and dried to form A'B'O.
A hydrogen storage alloy electrode having ₃ compounds is manufactured. When molding the slurry into a sheet shape, a known molding method such as a pressure molding method can be used. The thickness of the sheet to be molded may be appropriately determined according to the type of electrode to be manufactured. Further, as a means for pressing the sheet onto the surface of the conductive support, a known pressure bonding method or the like can be used.

In the third production method of the present invention, for example, a slurry containing 100 parts by weight of a hydrogen storage alloy consisting only of AB ₅ phase and 0.75 parts by weight of a binder is coated on the surface of the conductive support, Crimp after drying, or
The slurry is molded into a sheet shape, and then the sheet is pressure-bonded to the surface of the conductive support and dried, and the hydrogen storage alloy electrode surface provided with the layer containing the hydrogen storage alloy and the binder, for example, 2 parts by weight of a perovskite type conductive oxide represented by A'B'O ₃ and a binder of 0.
A hydrogen storage alloy electrode having an A′B′O ₃ compound is manufactured by applying a slurry containing 06 parts by weight and then drying. In this case, it is preferable to coat the slurry so that A′B′O ₃ covers 20 to 80% of the surface of the hydrogen storage alloy electrode. Below 20%, when the manufactured electrode is used as an alkaline battery electrode,
The internal pressure of the battery cannot be reduced. If it is 80% or more, the electrode performance deteriorates.

As the conductive support (current collector) used in the production method of the present invention, a known conductive support used in alkaline batteries can be used, but it is easy to put it in a battery container. From this viewpoint, it is preferable to use a fibrous material. Examples of the fibrous conductive support include Ni fibrous support. In the production method of the present invention, when the slurry is applied on the surface of the conductive support or the hydrogen storage alloy electrode, dried and then pressure-bonded, known coating, drying and pressure-bonding means can be used.

[0023]

The method for producing a hydrogen storage alloy electrode having an A'B'O ₃ compound according to the present invention comprises mixing a conductive oxide represented by A'B'O ₃ and a hydrogen storage alloy in a specific ratio. Coating the slurry on the surface of the conductive support, drying it, or pressing it, or
After molding the slurry into a sheet shape, the sheet is pressed onto the surface of the conductive support and dried, or the conductive oxide represented by A′B′O ₃ is formed on the surface of the hydrogen storage alloy electrode. Since it can be produced only by coating and drying a slurry containing a, it is extremely simple.

Since the hydrogen storage alloy electrode obtained by the manufacturing method of the present invention uses a hydrogen storage alloy containing no intermetallic compound phase other than the AB ₅ phase, it has high corrosion resistance and decomposes oxygen molecules. Since it has an oxide represented by A′B′O ₃ having catalytic activity and can efficiently eliminate oxygen gas, it is particularly suitable for a negative electrode for alkaline storage batteries.

[0025]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Examples 1 to 4 La (purity 99% or higher), Ce (purity 99% or higher), P
r (purity 99% or higher), Nd (purity 99% or higher), Ni
(Purity of 99% or more), Co (Purity of 99% or less), Al
Each metal element consisting of (purity of 99% or more) and Mn was weighed and mixed so as to have a composition as shown in Table 1. Carbon was added to the obtained mixture so as to be 50 ppm. Then, this mixture was melted by a high frequency melting method under an argon atmosphere and cast in a water-cooled mold.
A hydrogen storage alloy having a composition as shown in (Examples 1 to 1
4) was produced.

[0026]

[Table 1]

When casting in a water-cooled mold, the cooling rate was controlled by setting the casting thickness to 5 to 20 mm. When the obtained alloy was subjected to X-ray diffraction, a peak of only the AB ₅ phase was observed, and it was confirmed that the alloy was a hydrogen storage alloy consisting of only the AB ₅ phase. The obtained alloy was pulverized into powder having an average particle size of 30 μm. The Mm oxide, calcium carbonate, strontium carbonate, cobalt carbonate and manganese carbonate used in Example 1 were replaced with Mm _0.8 Ca _0.1 Sr _0.1 Co _0.5 Mn _0.5 O.
After mixing so as to have a stoichiometric ratio of ₃ , the mixture was baked at 900 ° C. and pulverized to obtain a conductive oxide powder represented by A′B′O ₃ having an average particle diameter of 4 μm.

With respect to 15 g of the obtained hydrogen storage alloy powder,
0.3 g of the conductive oxide powder and an aqueous solution of 3% by weight of polyvinyl alcohol were mixed at a ratio of 4.1 g to form a slurry. The obtained slurry is applied to a fibrous Ni support and dried, and then pressure-molded into a sheet having a thickness of 0.5 to 1.0 mm, and then a lead wire is attached to form four types of sheet. A negative electrode was made.

As the positive electrode, a porous Ni sintered body was impregnated with Ni (OH) ₂ , and this was subjected to chemical conversion treatment to obtain Ni.
An OOH electrode was prepared so that it would not be affected. Each of the sheet-shaped negative electrodes and positive electrodes thus produced was wound around a separator made of a polyolefin non-woven fabric, filled in a cylindrical container, and a 6 mol / liter KOH aqueous solution was injected as an electrolytic solution. After that, the cans were sealed and four types of sealed nickel-hydrogen secondary batteries (alkaline storage batteries) having a nominal capacity of 2,400 milliamperes / hour were manufactured.

Each of the obtained batteries was subjected to 5 at a current of 720 mA.
After charging for an hour, the battery voltage is 1.0 at a current of 480mA.
The charge and discharge of discharging to V was repeated, the number of cycles until 60% of the initial capacity was measured, and the charge and discharge cycle life at 20 ° C. was examined. In addition, the internal pressure of the battery was measured after 10 charge / discharge cycles. The results are shown in Table 2.

[0031]

[Table 2]

Examples 5-8. Four types of alkaline storage batteries (Examples 5 to 8) were performed in exactly the same manner as in Examples 1 to 4 except that the following hydrogen storage alloy electrodes were used instead of the hydrogen storage alloy electrodes used in Examples 1 to 4. Example 1 to 4
The charge / discharge cycle life and the battery internal pressure were measured in exactly the same manner as. The results are shown in Table 2.

Preparation of Hydrogen Storage Alloy Electrode A fibrous Ni support was coated with a slurry prepared by mixing 15 g of the hydrogen storage alloy powder used in Examples 1 to 4 with an aqueous solution of 3% by weight of polyvinyl alcohol at a ratio of 3.8 g. And dry
A slurry obtained by mixing 0.3 g of the conductive oxide used in Example 1 with an aqueous solution of 3% by weight of polyvinyl alcohol in a proportion of 0.3 g was applied to the pressure-bonded electrode surface and dried,
Four types of hydrogen storage alloy electrodes having A′B′O ₃ compound were obtained.

Comparative Examples 1-4. A ′ used in Examples 1 to 4
Four types of alkaline storage batteries (Comparative Examples 1 to 4) were prepared in the same manner as in Examples 1 to 4 except that the conductive oxide powder represented by B′O ₃ was not used, and the charge / discharge cycle was performed. The life and the battery internal pressure were measured. The results are shown in Table 2.

Comparative Example 5. An alkaline storage battery was prepared in exactly the same manner as in Example 5, except that 0.1 g of carbon fiber was used instead of 0.1 g of the conductive oxide used in the electrode of Example 5, and the charge / discharge cycle life and battery internal pressure were changed. Was measured. The results are shown in Table 2.

As shown in Table 2, it is understood that in the case of the embodiment, the charge / discharge cycle life is long and the internal pressure of the battery is low as compared with the case of the comparative example. The results show that the negative electrode used in the examples improved the battery life.

Claims (3)

[Claims] 1. A hydrogen storage alloy 100 consisting of only the AB ₅ phase.
Parts by weight, 0.5 to 5 parts by weight of a perovskite type conductive oxide represented by A'B'O ₃ , and a binder of 0.1 to 5 parts by weight.
A hydrogen storage alloy having an A′B′O ₃ compound, characterized in that after preparing a slurry containing 5 parts by weight, the obtained slurry is applied on the surface of a conductive support, dried and then pressure-bonded. Manufacturing method of electrode; provided that in the above formula, A is Mm; B
Is at least one selected from Al, Co, Mn and Ni; A ′ is at least one selected from Mm, Ca and Sr; B ′ is Co or Mn. 2. A hydrogen storage alloy 100 consisting of only the AB ₅ phase.
Parts by weight, 0.5 to 5 parts by weight of a perovskite type conductive oxide represented by A'B'O ₃ , and a binder of 0.1 to 5 parts by weight.
After preparing a slurry containing 5 parts by weight, the obtained slurry is formed into a sheet, and then the sheet is pressure-bonded to the surface of the conductive support and dried.
Method for producing hydrogen storage alloy electrode having B′O ₃ compound;
However, in the above formula, A is Mm; B is Al, Co, Mn and N
at least one selected from i; A ′ is Mm,
At least one selected from Ca and Sr; B'is C
o or Mn. 3. A hydrogen storage alloy 100 consisting of only the AB ₅ phase.
The hydrogen-absorbing alloy electrode surface formed by providing a layer containing 0.1 to 5 parts by weight parts by weight and the binder a conductive support surface, a perovskite-type conductive oxide represented by A'B'O ₃ 0. After applying a slurry containing 5 to 5 parts by weight of a binder and 0.5 to 5 parts by weight of a binder so that A'B'O ₃ covers 20 to 80% of the surface of the hydrogen storage alloy electrode,
A method for producing a hydrogen storage alloy electrode having an A′B′O ₃ compound, characterized by drying; wherein A is M
m; B is at least one selected from Al, Co, Mn and Ni; A ′ is at least one selected from Mm, Ca and Sr; B ′ is Co or Mn.