JP2966493B2 - Manufacturing method of hydrogen storage alloy electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hydrogen storage alloy electrode used for a negative electrode of a metal-hydrogen alkaline storage battery.

2. Description of the Related Art In recent years, a metal-hydrogen alkaline storage battery capable of achieving a higher energy density than a nickel-cadmium battery has attracted attention as a new alkaline storage battery replacing the nickel-cadmium battery.

Here, a hydrogen storage alloy is used as the negative electrode of the battery. Then, as a method for producing this alloy, a crucible is filled with an alloy material, the molten material is melted to form a molten metal, and then the molten metal is ejected from a nozzle under an inert atmosphere to produce an alloy powder (so-called alloy powder). , Gas atomizing method) and then subjecting the alloy powder to an alkali treatment.

However, in the above-mentioned conventional manufacturing method, the reaction rate in the alkali treatment is low, and thus the porosity of the hydroxide layer generated in this treatment is large. For this reason, the hydrogen storage alloy easily comes into contact with the electrolytic solution or oxygen, and the alloy is corroded, and the cycle characteristics deteriorate. In addition, since the surface area of the hydrogen storage alloy powder is small, initial activation is poor. In addition, a high-concentration solution is used as an alkaline solution for the alkali treatment in order to speed up the treatment, but in this case, water washing is indispensable after the treatment. For this reason, there has been a problem that the manufacturing process becomes complicated.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for manufacturing a hydrogen storage alloy electrode that can solve the above-described disadvantages.

Means for Solving the Problems In order to achieve the above object, the present invention provides a melting step of melting a hydrogen storage alloy material to produce a molten metal, and quenching while jetting the molten metal to produce a hydrogen storage alloy powder. In the method for producing a hydrogen storage alloy electrode having an ejection step, at least one of the melting step and the ejection step includes:
It is characterized in that it is performed in an atmosphere containing water vapor.

Action According to the above production method, the molten hydrogen storage alloy reacts with water molecules to form a hydroxide layer on the surface of the alloy. In this case, the molten hydrogen storage alloy is quenched,
The reaction rate between the alloy and water molecules is significantly higher than in the case of performing the alkali treatment, and the porosity is smaller than that of the hydroxide layer obtained by the alkali treatment. As a result, it becomes difficult for the hydrogen storage alloy to come into contact with the electrolytic solution or oxygen, so that corrosion of the hydrogen storage alloy can be suppressed.

Further, according to the above manufacturing method, the water molecules are dissolved in the molten hydrogen storage alloy, and the water molecules are rapidly vaporized when the molten hydrogen storage alloy is cooled. A large number of pores will result. Therefore, the specific surface area of the hydrogen-absorbing alloy powder is dramatically increased, so that the initial activation of the battery is facilitated. Since the surface of the pores is also covered with a hydroxide layer having the same structure as described above, it is possible to suppress corrosion of the hydrogen storage alloy.

In addition, since an alkaline solution is not used, a washing step is not required, and the manufacturing process can be simplified.

Embodiment An embodiment of the present invention will be described below with reference to FIG. 1 and FIG.

[Example I]

FIG. 1 is a cross-sectional view of a cylindrical nickel-hydrogen alkaline storage battery using a hydrogen storage alloy electrode manufactured according to the present invention, and shows a positive electrode 1 made of sintered nickel, a negative electrode 2 containing a hydrogen storage alloy, An electrode group 4 including a separator 3 interposed between the positive and negative electrodes 1 and 2 is spirally wound. The electrode group 4 is disposed in an outer can 6 that also serves as a negative electrode terminal. The outer can 6 and the negative electrode 2 are connected by a negative electrode conductive tab 5. A sealing body 8 is attached to the upper opening of the outer can 6 via a packing 7,
A coil spring 9 is provided inside the sealing body 8. The coil spring 9 is configured such that when the internal pressure inside the battery rises abnormally, it is pressed in the direction of arrow A and the gas inside is released to the atmosphere. The sealing body 8 and the positive electrode 1 are connected by a positive electrode conductive tab 10.

Here, the cylindrical nickel-hydrogen alkaline storage battery having the above structure was produced as follows.

First, commercially available Mm (mixture of misch metal: rare earth element), Ni, Co, Mn, and Al are weighed so that the element ratio is 1: 3.2: 1: 0.6: 0.2, and then the sealed ultra-high pressure resistant type. It is melted in a high-frequency melting furnace (inert gas atmosphere) to create molten metal. The temperature at this time was 1400 ° C (the melting point of the alloy was 1350 ° C).
° C). Thereafter, the molten metal, under the following conditions, is ejected from the nozzle by a gas atomizing method, by further cooling, to prepare a hydrogen-absorbing alloy powder represented by MmNi _3.2 CoMn _0.6 Al _0.2.

The alloy powder thus produced is hereinafter referred to as (a ₁ ) powder.

・ Conditions Outside air temperature: Room temperature (25 ° C) Pressure: Atmospheric pressure Outside atmosphere: Mixed atmosphere of inert gas such as Ar and water vapor (flowing at high speed) Water vapor amount: Humidity 70-90% (at room temperature) Cooling Speed: 10 ⁴ to 10 ⁵ ° C./sec.After this, the hydrogen storage alloy powder
5 wt% of FE (polytetrafluoroethylene) powder is added and kneaded to prepare a paste. Further, this paste is pressed against both surfaces of a current collector made of punching metal to form a negative electrode 2.
Was prepared.

Next, the negative electrode 2 and a sintered nickel positive electrode 1 having a sufficiently larger capacity than the negative electrode 2 were wound via a separator 3 made of a non-woven fabric to produce an electrode group 4. Thereafter, the electrode group 4 is inserted into the outer can 6 and further 30% by weight.
Is injected into the outer can 6, and then the outer can 6
Was sealed to produce a cylindrical nickel-hydrogen storage battery. The theoretical capacity of the battery thus manufactured is 1000 mAh.

The battery fabricated in this manner is hereinafter referred to as (A ₁ ) battery.

(Example II)

The atmosphere in the melting furnace is an atmosphere containing steam (steam pressure 1.
1 GPa and a pressurized atmosphere), and an alloy powder and a battery were prepared in the same manner as in Example I, except that the jetting atmosphere was as shown below.

The alloy powder and the battery thus manufactured are hereinafter referred to as (a ₂ ) powder and (A ₂ ) battery, respectively.

・ Conditions Ambient temperature: room temperature (25 ° C.) Pressure: Atmospheric pressure Atmosphere: Inert gas such as Ar (flowing at high speed) [Example III] An atmosphere in the melting furnace containing steam (steam pressure 1) .
An alloy powder and a battery were produced in the same manner as in Example I except that the pressure was changed to 1 GPa).

The alloy powder and the battery thus manufactured are hereinafter referred to as (a ₃ ) powder and (A ₃ ) battery, respectively.

[Comparative Example I]

When the molten metal of the hydrogen storage alloy is jetted from the nozzle, the external atmosphere is made only of an inert gas such as Ar,
In the same manner as in the above, an alloy powder and a battery were produced.

The alloy powder and the battery thus manufactured are hereinafter referred to as (x ₁ ) powder and (X ₁ ) battery, respectively.

[Comparative Example II] When the molten metal of the hydrogen storage alloy was ejected from the nozzle, the external atmosphere was made only of an inert gas such as Ar, and the hydrogen storage alloy powder thus produced was subjected to alkali treatment. In the same manner as in I, an alloy powder and a battery were produced.

The alloy powder and the battery thus manufactured are hereinafter referred to as (x ₂ ) powder and (X ₂ ) battery, respectively.

[Experiment I]

Said by the manufacturing method of the present invention (a ₁₎ a powder ~ (a ₃₎ powder, and (x ₁₎ powder by the manufacturing method of the comparative example, since the measured and average particle diameter and specific surface area (x ₂₎ powder, The results are shown in Table 1 below. The average particle size (particle size distribution) was measured by a centrifugal sedimentation method, and the specific surface area was measured by a mercury intrusion method.

As shown in Table 1, the average particle size, by the manufacturing method of the present invention (a ₁₎ a powder ~ (a ₂₎ according to the production method of the powder of Comparative Example (x ₁₎ powder, (x ₂₎ powder Although there is no difference observed between the, in the specific surface area, (a ₁₎ a powder ~ (a ₂₎
It is recognized that the powder is larger than the (x ₁ ) powder and the (x ₂ ) powder, and particularly that the (a ₂ ) powder and the (a ₃ ) powder are significantly larger.

This is because water molecules are dissolved in the molten hydrogen storage alloy, and when the molten hydrogen storage alloy is further cooled and decompressed, the water molecules are rapidly vaporized, so that many pores are generated inside and outside the hydrogen storage alloy. It depends on the reason. In particular, (a ₂ ) powder, (a ₃ )
The reason why the specific surface area of the powder is remarkably large is that, in the case of (a ₁ ) powder, the squirting process is performed in a steam atmosphere or the like, and pores are formed only near the surface of the hydrogen storage alloy powder,
In the case of (a ₂ ) powder and (a ₂ ) powder, since the melting process is in a steam atmosphere, it is considered that pores are formed deep in the alloy.

(Experiment II)

The batteries (A ₁ ) to (A ₃ ) using the electrodes manufactured by the manufacturing method of the present invention described above, and the batteries (X ₁ ) and (X ₂ ) using the electrodes manufactured by the manufacturing method of the comparative example In FIG. 2, the relationship between the battery capacity and the number of charge / discharge cycles was examined, and the results are shown in FIG. The experimental conditions were 2.0C
After charging the battery for 38 minutes, the battery voltage is 1.
The condition is to discharge until reaching 0V.

As is apparent from FIG. 2, the (A ₁ ) battery of the present invention
(A ₃₎ batteries, (X ₁₎ battery of Comparative Example, (X ₂₎ than the batteries, large initial battery capacity, it is observed that also extends and cycle life, in particular (A ₂₎ cell , (A ₃ ) batteries.

This is because, as shown in Experiment I above, the specific surface area of the hydrogen storage alloy powder used for the batteries (A ₁ ) to (A ₃ ) of the present invention is large, so that the initial activation becomes easy and at the same time, The reduced porosity of the hydroxide layer makes it difficult for the hydrogen storage alloy and the electrolyte to come into contact with each other, so that corrosion of the hydrogen storage alloy can be suppressed.

[Other Matters] In the above example, the hydrogen storage alloy powder was produced by the gas atomization method, but it has been confirmed that the water atomization method has the same effect.

In the above embodiment, the steam pressure in the melting furnace is set to be equal to or higher than the saturated steam pressure, but may be equal to or lower than the saturated steam pressure. However, the surface area of the alloy increases when the pressure is set to be equal to or higher than the saturated water vapor pressure.

In the above embodiment, a cylindrical storage battery is used, but the present invention can of course be applied to a flat storage battery.

Effects of the Invention As described above, according to the present invention, the porosity of the hydroxide layer generated on the surface of the hydrogen storage alloy powder is reduced, so that the hydrogen storage alloy and the electrolyte or oxygen are hardly in contact with each other, Corrosion of the hydrogen storage alloy can be suppressed. As a result, cycle characteristics can be significantly improved.

Further, since a large number of pores are formed inside and outside the hydrogen storage alloy, the specific surface area of the hydrogen storage alloy powder is dramatically increased, and initial activation of the battery using the alloy becomes easy. As a result, the discharge capacity increases from the initial charge / discharge cycle.

In addition, since the washing step is not required, the manufacturing steps can be simplified and the manufacturing cost of the battery can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical nickel-hydrogen alkaline storage battery using the electrode of the present invention, and FIG. 2 shows (A ₁ ) to (A ₂ ) batteries using the electrode manufactured by the manufacturing method of the present invention. (X ₁ ) battery using the electrode manufactured by the manufacturing method of the comparative example,
6 is a graph showing cycle characteristics of (X ₂ ) batteries. 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-22310 (JP, A) JP-A-1-309937 (JP, A) JP-A-3-223408 (JP, A) JP-A-2- 306541 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/24-4/26 H01M 4/38 B22F 9/08 C22C 19/00

Claims (1)

(57) [Claims] 1. A method for manufacturing a hydrogen storage alloy electrode, comprising: a melting step of melting a hydrogen storage alloy material to produce a molten metal; and a jetting step of jetting the molten metal to rapidly cool the molten metal to produce a hydrogen storage alloy powder. A method for producing a hydrogen storage alloy electrode, wherein at least one of the melting step and the jetting step is performed in an atmosphere containing water vapor.