JP3191270B2 - Method for producing hydrogen storage electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode made of a hydrogen storage alloy used for a negative electrode of an alkaline storage battery or the like.

[0002]

2. Description of the Related Art A hydrogen storage electrode uses a hydrogen storage alloy capable of reversibly storing and releasing hydrogen as an electrode. The electrochemical oxidation-reduction reaction of the hydrogen is used as a negative electrode of an alkaline storage battery. It is used for electromotive reaction. The hydrogen storage alloy used for the hydrogen storage electrode includes LaNi ₅ ,
In some cases, the constituent elements of intermetallic compounds such as ZrNi ₂ or TiNi in the s phase are replaced with other metals to improve the performance as a hydrogen storage electrode.

[0003] Conventional methods of manufacturing a hydrogen storage electrode using these hydrogen storage alloys include the following.

[0004] One is a method in which a powder of a hydrogen storage alloy is held on an alkali-resistant conductive support such as punched metal or foamed nickel with a binder such as a fluororesin. The electrode manufactured by this method is called a plastic bonded type electrode. The other is a method of sintering a powder of a hydrogen storage alloy. The electrode manufactured by this method is called a sintered electrode.

[0005] The plastic bonded electrode can be produced by a method in which a powder of a hydrogen storage alloy is made into a paste, and the paste is applied or filled on a conductive support, and then dried and pressed. It is excellent in that electrodes can be manufactured at high speed by a simple manufacturing apparatus.

However, since the plastic bonded electrode cannot increase the density of the hydrogen storage alloy higher than a certain level as compared with a sintered electrode described later, when the electrode volume is the same, There is a disadvantage that the discharge capacity is reduced. The main causes are the following two.

First, in a plastic bonded electrode, the mechanical binding force of the hydrogen storage alloy powder is obtained by a binder, and the smaller the amount of the binder, the higher the mechanical strength of the hydrogen storage electrode. descend. On the other hand, when a battery is manufactured by handling a hydrogen storage electrode, it is necessary to increase the mechanical strength of the electrode so that the hydrogen storage alloy powder does not fall off or peel off. Therefore, in order to obtain a practically strong mechanical electrode having such a level that does not hinder the production of the battery, the electrode does not contribute to the charge / discharge reaction of the hydrogen storage electrode. It is necessary to increase the amount of the agent to some extent and to reduce the amount of the hydrogen storage alloy.

Second, when the plastic bonded electrode is pressurized in a temperature range from room temperature to several hundreds of degrees Celsius so that the binder is not deteriorated, the packing density of the hydrogen storage alloy powder becomes several t / cm ^2. However, even if the pressing force is further increased to about 20 kg / cm ² , the packing density of the hydrogen storage alloy powder hardly increases further. The cause is as follows. That is, after the pressure exceeds several t / cm ² , a bridge structure is formed between the hydrogen storage alloy powders. Since the hydrogen storage alloy powder has a remarkably high yield stress near room temperature, it is difficult to break this bridge structure even if the pressing force is set higher than this, and the packing density of the hydrogen storage alloy powder must be increased. Becomes difficult.

On the other hand, the sintered electrode has a high mechanical strength without using a binder which does not participate in the charge / discharge reaction of the electrode since the hydrogen storage alloy is sintered and bonded. Therefore, if sintering is sufficiently advanced, a hydrogen storage alloy having a high mechanical strength and a high packing density of the hydrogen storage alloy can be obtained. Further, since this electrode has high electron conductivity between the hydrogen storage alloys, it is superior to the plastic bonded electrode in that the electrode has a small polarization.

However, in the case of sintered electrodes, for example,
As described in No. 58-40828, a long sintering process at high temperature is required, such as sintering at 950 ° C for 30 minutes or 850 ° C for 5 hours, and hydrogen storage is required. There is an inconvenience that productivity in the electrode manufacturing process is significantly reduced.

[0011] Therefore, there has been a demand for a method capable of producing a hydrogen storage electrode having a high packing density of the hydrogen storage alloy and a high mechanical strength in a short time.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for supporting fine particles of a molten hydrogen storage alloy on a support.
Of hydrogen storage electrode that forms the layer by spraying
Method, among other things, to remove the fine particles of the molten hydrogen storage alloy.
The means for spraying the support to form that layer is thermal spraying.
Manufacturing method of the hydrogen storage electrode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Thermal spraying is a technique in which a material is melted to form fine particles in a liquid state, and the melted fine particles are blown forward to form a film on the material.

In the present invention, a hydrogen storage electrode is manufactured by spraying fine particles of a molten hydrogen storage alloy on a support to form a layer thereof. One of these means
Therefore, thermal spraying using wire or powder can be used.
You. Also, instead of going through a wire or powder state,
Spray deposition that sprays metal materials directly into droplets
Can also be used as one of these means.

According to this method, a hydrogen storage alloy layer having a porosity of about several to 10% can be obtained by appropriately selecting the conditions such as the feed rate of the thermal spray material and the thermal spray distance. This porosity is a low value comparable to the porosity obtained by sintering the hydrogen storage alloy powder. In addition, the thermal spray layer has a layer structure called lamella, in which particles on the liquid collide with the surface and extend flat, and the hydrogen storage alloys are directly bonded to each other. Without using an agent, it has a high packing density of a hydrogen storage alloy as high as that of a sintered hydrogen storage electrode, and high mechanical strength enough to withstand battery assembly.

Further, according to the method of manufacturing a hydrogen storage electrode by thermal spraying, the hydrogen storage electrode can be manufactured immediately by only a simple process of spraying a droplet of a molten alloy onto a support to form a sprayed layer. The time required for manufacturing the hydrogen storage electrode is significantly reduced as compared with the conventional manufacturing method in which the hydrogen storage alloy powder is molded and then sintered at a high temperature for a long time.

The sprayed layer of the hydrogen-absorbing alloy thus obtained works well as a hydrogen-absorbing electrode of a battery.

Since there are various phenomena peculiar to the thermal spraying method, the following various means can be selected in consideration of the phenomena and the characteristics of the hydrogen storage alloy.

First, the thermal spraying method includes various methods such as a gas melting method, an arc method, a flame method, a plasma method, and an explosion method according to the form of a heat source and a material. Hydrogen storage alloys contain metal elements that are easily oxidized, such as rare earth elements and the titanium group of the periodic table. To avoid a change in the alloy composition, a method of preventing such oxidation is recommended. It is desirable to choose from the law. Specifically, a reduced pressure plasma spraying method using argon gas in a reduced pressure chamber is suitable. According to this method, oxidation of the hydrogen storage alloy can be prevented, and a sprayed layer having a thickness of several millimeters can be obtained, and the thickness of the hydrogen storage alloy electrode can be increased as compared with the normal pressure method. .

If the support of the thermal spray layer is a conductor such as metal or carbon which can withstand the electrolyte of the battery, an integrated product of the thermal spray layer and the support formed by thermal spraying is directly used as a hydrogen storage electrode for a battery. Can be used. Further, when plastic or metal is used for the support, if the support is removed by dissolution or decomposition, a sprayed layer of the hydrogen storage alloy remains, which can be used as a hydrogen storage electrode. If the surface of these supports is roughened in advance by sandblasting or the like, the adhesion of the sprayed layer is improved.

Further, in the hydrogen storage alloy of the thermal sprayed layer, the molten liquid droplets are quenched, so that the crystal of the metal structure has large distortion. In this case, the equilibrium hydrogen pressure of the hydrogen storage alloy-
The slope of the flat portion of the hydrogen storage amount-isothermal diagram (PTC characteristic) increases, and the change in the equilibrium potential with the progress of charge and discharge of the hydrogen storage electrode increases. Therefore, when it is desired to reduce the change in the equilibrium potential, the hydrogen storage alloy obtained by thermal spraying may be heat-treated. In this case, it is economically advantageous to use a hydrogen storage alloy that has not been heat-treated in advance as a material for thermal spraying. This is because, because distortion occurs due to thermal spraying, even if the hydrogen storage alloy is heat-treated in advance to remove crystal distortion, the treatment is useless.

Since the thermal sprayed layer has a large surface roughness, when this hydrogen storage electrode is used for a negative electrode of a sealed battery, the gas absorption performance is improved. However, when the surface roughness is extremely large and the protrusions on the surface penetrate the separator to cause an internal short circuit of the battery, it is desirable to process the surface to be smooth. In addition, above and below, we focus on thermal spraying
As described, the essence of the present invention is that molten hydrogen
The occlusion alloy is made into fine droplets and sprayed on the support
Producing hydrogen storage electrodes by means of deposition
Use spray deposition instead of thermal spraying
Needless to say, the same effect can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described by way of preferred embodiments. [Hydrogen storage electrode (A)] (Example according to the manufacturing method of the present invention) A hydrogen storage alloy powder was produced as follows.

That is, the molar ratio of La _0.8 Ce _0.2 Ni _3.8 Co
La, Ce, Ni, C so that the composition is _0.7 Al _0.3 Mn _0.2
o, Al and Mn were charged into a high-frequency melting furnace and melted. Next, this melt was poured into a water-cooled copper mold and solidified. The ingot was roughly pulverized with a jaw crusher and then finely pulverized with an alumina ball mill. Then, classification was performed to obtain a hydrogen storage alloy powder having a particle size of 45 μm or less.

Next, using the hydrogen storage alloy powder as a material,
Using a Ni plate having a thickness of 0.06 mm, whose surface was roughened by sandblasting, as a support, thermal spraying was performed with argon plasma in a chamber in an argon atmosphere at a reduced pressure of 5 × 10 ³ Pa. Thermal spraying, the thickness of the sprayed layer is about 0.15 mm on each side of the support
It was done on both sides so that The time required for thermal spraying was 10 minutes. Then, this support is cut, and the size of the supporting portion of the hydrogen storage alloy is about 0.4 mm in thickness and about 16 in width.
A hydrogen storage electrode (A) having a height of about 57 mm and a height of about 57 mm according to the production method of the present invention was obtained. As for the electrode, a lead plate made of a Ni plate was attached to a Ni plate as a support at the end of the electrode that did not support the hydrogen storage alloy, and current was collected.

The weight of the hydrogen storage alloy contained in one electrode was about 1.7 g.

In addition, 100 mg of the alloy powder classified to have a particle size of 45 μm or less and 400 mg of electrolytic copper powder were mixed and pressed to form an electrode for evaluating the capacity of the alloy. The battery was charged at a current of 15 mA for 2.5 hours, and was repeatedly charged and discharged to 0.7 V with reference to the mercury oxide electrode potential. The discharge capacity was determined to be about 0.32 Ah per gram of the alloy. .

Therefore, one hydrogen storage alloy electrode has:
A hydrogen storage alloy having a discharge capacity of about 0.65 Ah is included.

Since the electrode had high mechanical strength, no loss of the hydrogen storage alloy was observed when cutting the electrode or assembling the battery. [Hydrogen storage electrode (B)] (Comparative Example by Conventional Manufacturing Method) Same as that used for the support for thermal spraying of hydrogen storage electrode (A)
On both sides of the Ni plate, the same hydrogen storage alloy powder as that used for the material for spraying the hydrogen storage electrode (A) was pressed and pressed under vacuum.
Sintered at 950 ° C for 30 minutes. The obtained sintered body was cut into the same dimensions as the hydrogen storage electrode (A) to produce a hydrogen storage electrode (B) by a conventional manufacturing method.

The weight of the hydrogen storage alloy contained in one electrode was about 1.7 g. Therefore, one hydrogen storage alloy electrode contains a hydrogen storage alloy having a discharge capacity of about 0.65 Ah.

Since the electrode had high mechanical strength, no loss of the hydrogen storage alloy was observed when cutting the electrode or assembling the battery. [Hydrogen storage electrode (C)] (Comparative example by conventional production method) 100 parts by weight of the same hydrogen storage alloy powder as used for the material for thermal spraying of hydrogen storage electrode (A) and 1.5 parts by weight of furnace black as a conductive auxiliary agent And an aqueous solution in which polyvinyl alcohol was dissolved in an amount of 3 parts by weight (corresponding to 100 parts by weight of the hydrogen storage alloy powder) as a binder was added and kneaded to prepare a paste-like mixture. Then, this paste-like mixture is applied to both sides of the same Ni plate as that used for the thermal spray support of the hydrogen storage electrode (A), dried, and then dried at about 5 ton /
Pressed at a pressure of ² cm ² , cut into the same dimensions as the hydrogen storage electrode (A),
Was made.

The weight of the hydrogen storage alloy contained in one hydrogen storage electrode was about 1.0 g. Therefore, one hydrogen storage alloy electrode contains a hydrogen storage alloy having a discharge capacity of about 0.32 Ah. [Hydrogen storage electrode (D)] (Comparative example by conventional manufacturing method) The amount of polyvinyl alcohol as a binder used in the paste mixture of the hydrogen storage electrode (C) was set to 0.5 part by weight, and the other components were hydrogen storage. A hydrogen storage electrode (D) was manufactured in the same manner as the electrode (C) by a conventional manufacturing method.

The weight of the hydrogen storage alloy contained in one hydrogen storage electrode was about 1.2 g. Therefore, one hydrogen storage alloy electrode contains a hydrogen storage alloy having a discharge capacity of about 0.38 Ah. Since the amount of the binder is small in this electrode, the carried amount of the hydrogen storage alloy per volume of the electrode is larger than that of the hydrogen storage electrode (C), but the electrode is cut because the strength of the active material layer is small. During the handling of the electrodes, the falling of the hydrogen storage alloy powder was remarkable. Therefore, even if an attempt is made to assemble a complete battery using the hydrogen storage electrode (C),
The battery could not be assembled because internal short-circuiting of the battery due to the dropped hydrogen storage alloy powder occurred frequently.

Therefore, an open nickel metal hydride storage battery was manufactured using one of the hydrogen storage electrodes (A), (B) and (C) as the negative electrode.

Each of these batteries has a size of about
Using two known sintered nickel hydroxide electrodes of 0.85 mm, width of about 17 mm and height of about 58 mm, the total amount of nickel hydroxide and the additive cobalt hydroxide contained in these two positive plates is It is about 2.9 g, and the theoretical capacity assuming that the reaction follows a one-electron process is about 0.84 Ah. For the negative electrodes of these batteries, one negative electrode plate was sandwiched between the two positive electrode plates with a separator interposed therebetween. Therefore,
The discharge capacity of any of these batteries is limited by the discharge capacity of the negative electrode.

As the separator, a non-woven fabric made of nylon was used. The electrode group thus configured was housed in a rectangular battery container to form an open nickel / metal hydride storage battery. The electrolyte used was 7 M KOH to which 20 g / l of LiOH had been added.

In these batteries, a hydrogen storage electrode (A),
A battery using (B) and (C) as the negative electrode,
The batteries are referred to as (a), (a), and (c), respectively.

At 25 ° C., these three types of batteries were
Charging for 1.2 hours at 1A current, terminal voltage of 1.0V at 1A current
The charge / discharge cycle of discharging until was reached was repeated 10 times. Table 1 shows the discharge capacity at the tenth cycle.

[0039]

[Table 1] The amount of the hydrogen storage alloy supported on the hydrogen storage electrode (A) manufactured by the method of the present invention is about twice that of the hydrogen storage electrode (C) manufactured by the conventional plastic bonded method. This is almost the same as the hydrogen storage electrode (B) manufactured by the conventional sintering method, which requires a long time to manufacture. Therefore, since the discharge of the battery was limited by the capacity of the negative electrode, the discharge capacity of the battery (A) was about twice as large as that of the battery (C), and was almost the same value as the battery (A).

In the above embodiment, the description has been given of the case of the hydrogen storage alloy in which a part of the component elements of the LaNi ₅ alloy is replaced by another specific element. However, the effect of the present invention is not limited to the TiNi alloy and the Laves alloy. A similar effect can be obtained for a phase alloy.

[0041]

According to the present invention, a hydrogen storage electrode having a high packing density of a hydrogen storage alloy and a high mechanical strength is provided.
Can be manufactured in a short time.

Claims (2)

(57) [Claims] 1. A support comprising fine particles of a molten hydrogen storage alloy.
Spraying to form that layer
Method of manufacturing storage electrode. 2. The support is made of fine particles of the molten hydrogen storage alloy.
That the means of spraying to form that layer is thermal spraying
The method for producing a hydrogen storage electrode according to claim 1, wherein: