JPH1079249A - Manufacture of hydrogen storage alloy for electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent charging efficiency in the initial stage from being deteriorated, by specifying a pH value in the treatment of hydrogen storage alloy in acidic solution. SOLUTION: Hydrogen storage alloy is immersed into acidic solution whose initial pH value is 2 or less. Therefore, a layer of oxide on the alloy surface is removed, rare earth elements of Mn, Al having the high ionization tendency in alloy are dissolved, a number of active parts having many Ni compounds appear on the front surface side, and dissolved ion is deposit on the surface of alloy. When pH of acidic solution reaches the specified value in the range of 3 to 5, alloy is taken out and washed in water, and ion deposited on the surface is removed. When alloy is immersed into acidic solution having a pH value equal to a predetermined value, oxide remaining on the alloy front surface is dissolved, a number of active parts having many Ni compounds appear on the alloy front surface. As a result, hydrogen gas is sufficiently absorbed to alloy from the initial stage, and charging efficiency is improved.

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 for an electrode used as a negative electrode material for a sealed nickel-hydrogen secondary battery, and more particularly to a method for manufacturing a sealed nickel-hydrogen secondary battery in the early stage of using the same. It is characterized in that the negative electrode is activated to improve the charging efficiency at the time of initial charging.

[0002]

2. Description of the Related Art Conventionally, secondary batteries such as nickel-cadmium storage batteries and lead storage batteries have been widely used as secondary batteries, but in recent years, with the development of mobile devices such as mobile phones and notebook computers, high capacity batteries have been developed. And high performance batteries have been required. Therefore, a sealed nickel-hydrogen secondary battery having a high energy density and excellent safety has attracted attention, and research and development thereof have been performed.

[0003] Here, a sealed nickel-hydrogen secondary battery is a secondary battery that utilizes a hydrogen storage / release reaction of a hydrogen storage alloy, and generally includes a negative electrode made of a hydrogen storage alloy, a nickel positive electrode, and an alkali positive electrode. The hydrogen storage alloy used for the negative electrode is composed of a mixture of rare earth elements (lanthanum, cerium, praseodymium, neodymium, etc.).
m) and CuCa composed of metal elements such as Ni, Mn, and Al
AB ₅ type hydrogen storage alloys having _five structures are widely used.

[0004] However, in the above-mentioned hydrogen storage alloy, an oxide or hydroxide layer is formed on the surface by natural oxidation or the like, and the hydrogen gas in the hydrogen storage alloy is formed by the oxide or hydroxide layer. There has been a problem that the absorption capacity is reduced, and in the initial stage of using such a hydrogen storage alloy for the negative electrode, the hydrogen gas is not sufficiently absorbed, and the charging efficiency is reduced.

In recent years, for example, as disclosed in JP-A-6-88150, an oxide or hydroxide formed on the surface of a hydrogen storage alloy is immersed in an acidic solution. Methods have been proposed for removing layers of objects.

Here, when the hydrogen storage alloy is immersed in the acidic solution as described above, the oxide and hydroxide layers formed on the surface of the hydrogen storage alloy are removed to some extent, and the surface of the hydrogen storage alloy is removed. At the same time as this reaction, ions and the like dissolved in the acidic solution are adsorbed on the surface of the hydrogen storage alloy, and as the pH in the acidic solution rises, ions and the like are generated as described above. Precipitates in the form of oxides and the like on the surface of the hydrogen storage alloy, thereby reducing active sites on the surface of the hydrogen storage alloy.In the initial stage of using this hydrogen storage alloy for the negative electrode, hydrogen gas is still sufficiently absorbed. However, there is a problem that the charging efficiency is reduced.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in a hydrogen storage alloy used for a negative electrode of a sealed nickel-hydrogen secondary battery. An object of the present invention is to provide a method for producing a hydrogen storage alloy for an electrode, in which hydrogen gas is sufficiently absorbed from the initial stage of using a negative electrode as a negative electrode and the initial charging efficiency does not decrease.

[0008]

In the method for producing a hydrogen storage alloy for an electrode according to the present invention, in order to solve the above-mentioned problems, the hydrogen storage alloy is immersed in an acidic solution having an initial pH value of 2 or less. When the pH value of the acidic solution reaches a predetermined pH value in the range of 3 to 5, after removing the ions attached to the hydrogen storage alloy, the hydrogen storage alloy is brought into the predetermined pH value. Immerse in an acidic solution of the same pH value,
Thereafter, the hydrogen storage alloy was washed with water and dried.

Here, when the hydrogen storage alloy is immersed in an acidic solution having an initial pH value of 2 or less as in the present invention, the oxide and hydroxide layers on the surface of the hydrogen storage alloy are removed and In the hydrogen storage alloy, the highly ionizable rare earth elements, Mn, Al, and the like in the hydrogen storage alloy are dissolved, and many active sites having a composition with a large amount of Ni components appear on the surface side, while the dissolved ions form the hydrogen storage alloy. It adheres to the surface or is partially formed as an oxide on the surface of the hydrogen storage alloy.

[0010] When the pH value of the acidic solution reaches a predetermined pH value in the range of 3 to 5, water is added to the acidic solution, or the hydrogen absorbing alloy is taken out and washed with water, for example. When the ions adhering to the surface of the alloy are removed, and then this hydrogen storage alloy is immersed in an acidic solution having the same pH value as the above-mentioned predetermined pH value, oxides and the like remaining on the surface of the hydrogen storage alloy are removed. Is dissolved and N
It is considered that many active sites having a composition with a large amount of the i component appear on the surface of the hydrogen storage alloy.

[0011] Since many active sites having a composition containing a large amount of Ni components appear on the surface of the hydrogen storage alloy as described above, the hydrogen storage alloy can be used for the negative electrode from the beginning.
Hydrogen gas is sufficiently absorbed by the hydrogen storage alloy, and the initial charging efficiency is improved.

Here, the pH value of the initial acidic solution in which the hydrogen storage alloy is immersed is adjusted to be 2 or less. If the pH value is larger than 2, rare-earth elements, Mn, and Al in the hydrogen storage alloy are used. This is because it is not possible to sufficiently dissolve the compound and the like, and many active sites having a composition containing a large amount of Ni components cannot appear on the surface of the hydrogen storage alloy. Ni and the like in the storage alloy are also dissolved and active sites are reduced, and the surface state of the hydrogen storage alloy is deteriorated. Therefore, the pH value of the initial acidic solution is preferably in the range of 1 to 1.5. I do.

The reason why the pH value of the acidic solution is set in the range of 3 to 5 when removing the ions attached to the surface of the hydrogen storage alloy is that when the pH value is lower than 3, the hydrogen storage alloy While the removal of oxide and hydroxide layers on the surface of the alloy and the dissolution of rare earth elements, Mn, Al and the like in the hydrogen storage alloy are not sufficiently performed, the dissolution occurs when the pH is higher than 5. This is because a large amount of the ions adhere to the surface of the hydrogen storage alloy and form oxides and the like, which cannot be sufficiently removed by the next treatment. The pH value of the acidic solution at the time of removing the adhered ions is adjusted to a range of 3 to 4.

Further, as described above, the hydrogen-absorbing alloy from which ions have been removed at a predetermined pH value is replaced with the same p value as this pH value.
The immersion in the acidic solution having an H value is such that when immersed in an acidic solution having a pH value lower than a predetermined pH value, the rare earth element, Mn, and A in the hydrogen storage alloy as described above are used.
1 and the like are dissolved, the ions and the like adhere to the surface of the hydrogen storage alloy and active sites on the surface of the hydrogen storage alloy decrease, while immersing in an acidic solution having a pH value higher than a predetermined pH value, This is because oxides and the like remaining on the surface of the hydrogen storage alloy cannot be sufficiently removed, and active sites having a composition containing a large amount of Ni components appearing on the surface of the hydrogen storage alloy decrease.

[0015]

EXAMPLES Hereinafter, a method for producing a hydrogen storage alloy for an electrode according to an example of the present invention will be specifically described,
Comparative examples show that the initial charging efficiency is improved when the hydrogen storage alloy for an electrode manufactured by the method of the embodiment of the present invention is used. The method for producing a hydrogen storage alloy for an electrode according to the present invention is not particularly limited to those described in the following examples, but can be carried out by appropriately changing the scope of the invention without changing its gist.

(Embodiments 1 to 5) In these embodiments, a misch metal (Mm) containing at least one of La, Ce, Pr and Sm, Ni, Co, Al and Mn are used.
MnNi _3.2 Co _1.0 Al _0.2 Mn _0.6 were weighed and mixed so as to have a composition ratio, and these were alloyed using an arc melting furnace, and then mechanically pulverized to obtain a hydrogen storage alloy powder.

In these examples, the above hydrogen storage alloy powder was placed in a hydrochloric acid acidic solution (primary treatment solution) having an initial pH of 1.0 at a weight ratio of hydrogen storage alloy: primary treatment solution = 1. : 2 and when the pH of the primary treatment solution reaches a predetermined pH value in the range of 2.0 to 5.0 as shown in Table 1 below, the primary treatment solution is added to each of the primary treatment solutions. After adding 10 times the weight of water to dilute each primary treatment solution and diffuse ions dissolved in the primary treatment solution, immediately take out the hydrogen storage alloy powder,
Each hydrogen storage alloy powder was washed twice with 10 times the weight of water, and further washed with alcohol, and then each hydrogen storage alloy powder was dried.

Thereafter, each of the dried hydrogen storage alloy powders is put into a hydrochloric acid acidic solution (secondary treatment solution) having the same pH as the predetermined pH at the time of adding the water, by weight ratio of the hydrogen storage alloy: secondary. Treatment solutions = 1: 2 were added, and the reaction was terminated when the pH of the secondary treatment solutions reached 7, and then 10 times the weight of water was added to each secondary treatment solution. After the addition, the hydrogen-absorbing alloy powder was taken out from each of the secondary treatment solutions, and each hydrogen-absorbing alloy powder was washed twice with 10 times the weight of water, and further washed with alcohol. Was dried. Then, classify each of the above hydrogen storage alloy powders,
As shown in Table 1 below, each hydrogen storage alloy powder having an average particle size of about 80 μm was obtained, and this was used as a negative electrode material of a sealed nickel-hydrogen secondary battery.

Then, 0.5% by weight of polyethylene oxide and water are added to each of the above hydrogen storage alloy powders to prepare slurries, and each of the slurries is applied to a current collector made of punching metal. Was cut into a predetermined size to produce each hydrogen storage alloy electrode using the hydrogen storage alloy of Examples 1 to 5.

On the other hand, a positive electrode is prepared by adding an aqueous solution containing methylcellulose to nickel hydroxide powder to form a paste, filling the paste in a nickel foam metal, drying the paste, and molding it into a predetermined size. It was used.

Then, as shown in FIG.
A separator 3 made of a non-woven nylon fabric is interposed between the battery and the negative electrode 2. The separator 3 is wound in a spiral shape and accommodated in the battery can 4.
The positive electrode 1 is connected to the positive electrode external terminal 6 through the positive electrode lead 5 by injecting an alkaline electrolyte of KOH, attaching the positive electrode external terminal 6 to the battery can 4 via the insulating packing 8 and sealing the positive electrode 1. The negative electrode 2 is connected to the battery can 4 via the negative electrode lead 7.
To produce sealed nickel-hydrogen secondary batteries each having a capacity of 1000 mAh.

Comparative Examples 1 to 7 In Comparative Example 1, MmNi _3.2 C was used in the same manner as in Examples 1 to 5 described above.
o _1.0 Al _0.2 Mn _0.6 The alloyed alloy having a composition ratio of _0.6 was mechanically pulverized to obtain a hydrogen storage alloy powder, and the hydrogen storage alloy powder was classified, as shown in Table 1 below. The hydrogen storage alloy powder having an average particle size of about 80 μm was used for the negative electrode material, and the surface treatment with the acidic solution was not performed.

In Comparative Example 2, MmN
After mechanically pulverizing the alloyed alloy to have a composition ratio of i _3.2 Co _1.0 Al _0.2 Mn _0.6 , the hydrogen storage alloy powder was initially acidified with a hydrochloric acid solution having a pH of 1.0 (primary treatment solution). When the pH of the acidic solution reaches 7, the hydrogen-absorbing alloy powder is taken out, and the hydrogen-absorbing alloy powder is washed twice with water as described above, and further washed with alcohol. The occlusion alloy powder is dried and classified, and as shown in Table 1 below, a hydrogen occlusion alloy powder having an average particle size of about 80 μm is used for the negative electrode material, and the surface treatment with the secondary treatment solution is not performed. I did it.

In Comparative Examples 3 to 5, M
MNI _3.2 Co _1.0 Al _0.2 was mechanically pulverized one obtained by alloying to obtain the composition ratio of Mn _0.6, initial pH of the hydrogen-absorbing alloy powder of 1.0 hydrochloric acid solution (primary process solution) Immersed in, as shown in Table 1 below,
In Comparative Example 3, when the pH of the primary treatment solution became 2.0, in Comparative Example 4, when the pH of the primary treatment solution became 2.5, and in Comparative Example 5, the primary treatment solution became pH 6.0. At this point, water was added to this primary treatment solution to dilute it, and the hydrogen storage alloy powder was immediately taken out, and each hydrogen storage alloy powder was removed as described above. Washed twice with water, further washed with alcohol and dried. Thereafter, each hydrogen storage alloy powder was immersed in a secondary treatment solution having the same pH value as that at the time when water was added, and thereafter, in the same manner as in the above example, the following table was used. As shown in FIG. 1, each hydrogen storage alloy powder having an average particle size of about 80 μm was obtained and used as a negative electrode material.

In Comparative Examples 6 and 7, the hydrogen-absorbing alloy powder was immersed in a primary treatment solution having an initial pH of 1.0 as described above. When the pH of the solution reaches 4.0, water is added to the primary treatment solution to dilute the solution, and the hydrogen storage alloy powder is immediately taken out. Washed twice with water as above, then washed with alcohol and dried. Then, as shown in Table 1 below, the hydrogen storage alloy powder was immersed in a secondary treatment solution having a pH different from pH 4.0 at the time when water was added. Is immersed in a secondary processing solution having a pH of 3.0 in Comparative Example 6, and then in a secondary processing solution having a pH of 5.0 in Comparative Example 6. As shown, the average particle size is 80
Each hydrogen storage alloy powder having a size of about μm was obtained, and this was used as a negative electrode material.

Then, Comparative Examples 1 to 5 prepared as described above were used.
Each sealed nickel-hydrogen secondary battery was produced in the same manner as in the above example, using each hydrogen storage alloy powder of No. 5.

Next, in each of the initial sealed nickel-hydrogen secondary batteries produced using the hydrogen storage alloy powders of Examples 1 to 5 and Comparative Examples 1 to 4, a hole was formed in the bottom of each battery can. Then, the pressure sensor was connected, and the amount of pressure rise (atm) inside each battery when charged at a constant current of 500 mA (0.5 C) for 30 minutes was examined. The results are shown in Table 1 below. It should be noted that the lower the rise in internal pressure of the battery when charged in this way, the more efficiently hydrogen is absorbed by the hydrogen storage alloy, and the higher the charging efficiency.

[0028]

[Table 1]

As a result, Example 1 in which the primary processing solution and the secondary processing solution were used to satisfy the conditions of the present invention.
The sealed nickel-hydrogen secondary batteries using the hydrogen storage alloys of Nos. 1 to 5 were those using the hydrogen storage alloy of Comparative Example 1 in which these treatments were not performed and those in which the treatment with the secondary treatment solution was not performed. In the case where the hydrogen storage alloy of Example 2 was used or the pH value when water was added to the primary treatment solution was 3
Comparative Examples treated with a pH outside the range of ~ 5, those using the hydrogen storage alloys of 3-5, and Comparative Examples treated with a secondary treatment solution having a pH different from the pH value when water was added in the primary treatment The increase in the internal pressure of the battery was lower than that using the hydrogen storage alloy of No. 6, 7, and hydrogen was efficiently absorbed by the hydrogen storage alloy, and the charging efficiency was high.

(Examples 6 to 9 and Comparative Examples 8 and 9) In Examples 6 to 9 and Comparative Examples 8 and 9, the pH of the hydrochloric acid solution (primary treatment solution) in which the hydrogen storage alloy powder was initially immersed was used.
H was changed from that of Examples 1 to 5 above, and a primary treatment solution having an initial pH of 0.5 was used.

In Examples 6 to 9, the hydrogen storage alloy powder was immersed in the primary treatment solution, and the pH of the primary treatment solution was 3.0 to 5.0 as shown in Table 2 below.
Water was added at the time when the pH reached a predetermined value in the range described above, and thereafter, the same treatment as in Examples 1 to 5 was performed to obtain each hydrogen storage alloy powder, and this was used as a negative electrode material. A sealed nickel-hydrogen secondary battery was produced.

On the other hand, in Comparative Example 8, the hydrogen-absorbing alloy powder was immersed in the primary treatment solution.
As in the case of the above, when the pH of the acidic solution reached 7, the hydrogen storage alloy powder was taken out and treated, so that the surface treatment with the secondary treatment liquid was not performed. Then, a sealed nickel-hydrogen secondary battery was manufactured using the hydrogen storage alloy powder as a negative electrode material.

In Comparative Example 9, the hydrogen storage alloy powder was immersed in the primary treatment solution.
As in the case of the above, when the pH of the primary treatment solution became 2.5, water was added to dilute the solution.
Each of the hydrogen storage alloy powders was obtained in the same manner as in the case of the above, and these were used as a negative electrode material to produce a sealed nickel-hydrogen secondary battery.

Each of the sealed nickel-hydrogen secondary batteries produced using the hydrogen-absorbing alloy powders of Examples 6 to 9 and Comparative Examples 8 and 9 was prepared in the same manner as described above. The internal pressure rise (atm) was examined, and the results are shown in Table 2 below.

[0035]

[Table 2]

As a result, in the same manner as described above, the sealed nickel alloy using the hydrogen storage alloy of Examples 6 to 9 which was treated with the primary treatment solution and the secondary treatment solution so as to satisfy the conditions of the present invention. The hydrogen secondary battery uses the hydrogen storage alloy of Comparative Example 8 in which the treatment with the secondary treatment solution is not performed, and the pH value when water is added to the primary treatment solution is lower than 3 to 5. As compared with the case of using the treated hydrogen storage alloy of Comparative Example 9, the rise of the internal pressure of the battery was lower, and hydrogen was efficiently absorbed by the hydrogen storage alloy, and the charging efficiency was higher.

(Examples 10 to 13 and Comparative Examples 10 and 1
1) In Examples 10 to 13 and Comparative Examples 10 and 11, the pH of the hydrochloric acid acidic solution (primary treatment solution) in which the hydrogen storage alloy powder was initially immersed was changed from that in Examples 1 to 5, The primary treatment solution having a pH of 1.5 was used.

Also in Examples 10 to 13, the hydrogen storage alloy powder was immersed in the primary treatment solution, and the pH of the primary treatment solution was 3.0 to 3.0 as shown in Table 3 below.
When a predetermined pH value in the range of 5.0 was reached, water was added. Thereafter, the same treatment as in Examples 1 to 5 was performed to obtain each hydrogen storage alloy powder, and this was used as a negative electrode material. To produce a sealed nickel-hydrogen secondary battery.

On the other hand, in Comparative Example 10, the hydrogen-absorbing alloy powder was immersed in the primary treatment solution, and when the pH of the acidic solution reached 7 as in Comparative Example 2, the hydrogen-absorbing alloy powder was absorbed. The alloy powder was taken out and treated, and the surface treatment with the secondary treatment liquid was not performed. Then, using this hydrogen storage alloy powder as a negative electrode material, a sealed nickel-
A hydrogen secondary battery was manufactured.

In Comparative Example 11, the hydrogen-absorbing alloy powder was immersed in the primary treatment solution, and, as in Comparative Example 4, when the pH of the primary treatment solution reached 2.5. Water was added for dilution, and then, Examples 1 to
Each of the hydrogen-absorbing alloy powders was obtained by performing the same treatment as in the case of No. 5, and a sealed nickel-hydrogen secondary battery was produced using these powders as the negative electrode material.

Examples 10 to 13 and Comparative Example 1
With respect to the initial sealed nickel-hydrogen secondary batteries prepared using each of the hydrogen storage alloy powders Nos. 0 and 11 as well, the amount of pressure rise (atm) inside each battery was examined in the same manner as described above. Are shown in Table 3 below.

[0042]

[Table 3]

As a result, similarly to the above case, the sealed nickel using the hydrogen storage alloy of Examples 10 to 13 was treated with the primary treatment solution and the secondary treatment solution so as to satisfy the conditions of the present invention. A hydrogen secondary battery using the hydrogen storage alloy of Comparative Example 10 in which the treatment with the secondary treatment solution was not performed, or a pH value when water was added to the primary treatment solution.
Example 11 treated at a pH lower than the range of 3 to 5
The increase in internal pressure of the battery was lower than that using the hydrogen storage alloy, and hydrogen was efficiently absorbed by the hydrogen storage alloy, resulting in higher charging efficiency.

(Examples 14 to 17 and Comparative Examples 12 to 1)
4) In Examples 14 to 17 and Comparative Examples 12 to 14, the pH of the hydrochloric acid acidic solution (primary treatment solution) in which the hydrogen storage alloy powder was initially immersed was changed from that of Examples 1 to 5, In Examples 14 to 17 and Comparative Examples 10 and 11, the primary treatment solution having an initial pH of 1.5 was used.
In 4, the primary treatment solution having an initial pH of 2.5 was used.

In Examples 14 to 17, the hydrogen storage alloy powder was immersed in the primary treatment solution, and the pH of the primary treatment solution was 3.0 to 3.0 as shown in Table 4 below.
When a predetermined pH value in the range of 5.0 was reached, water was added. Thereafter, the same treatment as in Examples 1 to 5 was performed to obtain each hydrogen storage alloy powder, and this was used as a negative electrode material. To produce a sealed nickel-hydrogen secondary battery.

On the other hand, in Comparative Example 12, the hydrogen-absorbing alloy powder was immersed in the primary treatment solution, and when the pH of the acidic solution reached 7 as in Comparative Example 2, the hydrogen-absorbing alloy powder was absorbed. The alloy powder was taken out and treated, and the surface treatment with the secondary treatment liquid was not performed. Then, using this hydrogen storage alloy powder as a negative electrode material, a sealed nickel-
A hydrogen secondary battery was manufactured.

In Comparative Example 13, the hydrogen-absorbing alloy powder was immersed in the primary treatment solution, and when the pH of the primary treatment solution reached 2.5, as in Comparative Example 4. Water was added for dilution, and then, Examples 1 to
Each of the hydrogen-absorbing alloy powders was obtained by performing the same treatment as in the case of No. 5, and a sealed nickel-hydrogen secondary battery was produced using these powders as the negative electrode material.

In Comparative Example 14, as described above, the hydrogen storage alloy powder was immersed in the 2.5 primary treatment solution whose initial pH was higher than 2, and the pH of the primary treatment solution became 4.0. At the time, water was added, and thereafter, the same treatment as in Example 3 was performed to obtain each hydrogen storage alloy powder, and these were used as a negative electrode material to produce a sealed nickel-hydrogen secondary battery. .

Examples 14 to 17 and Comparative Example 12
In each of the initial sealed nickel-hydrogen secondary batteries produced using each of the hydrogen storage alloy powders of Nos. 1 to 14, the pressure rise amount (atm) inside each battery was examined in the same manner as in the above case. The results are shown in Table 4 below.

[0050]

[Table 4]

As a result, in the same manner as described above, the sealed nickel alloy using the hydrogen storage alloy of Examples 14 to 17 which was treated with the primary treatment solution and the secondary treatment solution so as to satisfy the conditions of the present invention. The hydrogen secondary battery used the hydrogen storage alloy of Comparative Example 12 in which the treatment with the secondary treatment solution was not performed, or the pH at the time of adding water to the primary treatment solution.
Comparative Example 13 treated with a pH lower than the range of 3 to 5
Using a hydrogen storage alloy, and an initial pH of 2
Comparative Example 1 treated with a higher pH 2.5 primary treatment solution
The increase in the internal pressure of the battery was lower than that of the battery using the hydrogen storage alloy of No. 4, and the hydrogen was efficiently absorbed by the hydrogen storage alloy, and the charging efficiency was high.

[0052]

As described above in detail, in the method for producing a hydrogen storage alloy for an electrode according to the present invention, the hydrogen storage alloy is immersed in an acidic solution having an initial pH value of 2 or less, and the pH value of the acidic solution is reduced. When the pH reaches a predetermined pH value in the range of 3 to 5, the ions adhering to the hydrogen storage alloy are removed, and then the hydrogen storage alloy is subjected to the same p as the predetermined pH value.
The hydrogen storage alloy was immersed in an acidic solution having an H value, and then the hydrogen storage alloy was washed with water and dried, so that the oxide and hydroxide layers on the surface of the hydrogen storage alloy were removed and the surface of the hydrogen storage alloy was removed. Many active sites having a composition containing a large amount of Ni components have come to appear.

As a result, when the hydrogen storage alloy obtained by the method of the present invention is used as a negative electrode material of a sealed nickel-hydrogen secondary battery, hydrogen is sufficiently stored in the hydrogen storage alloy from the initial charging. Thus, a sealed nickel-hydrogen secondary battery having good charging efficiency from the time of initial charging can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing the internal structure of a sealed nickel-hydrogen secondary battery using a hydrogen storage alloy produced in each of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Mamoru Kimoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kozo Nogami 2-chome Keihanhondori, Moriguchi-shi, Osaka No. 5-5 Sanyo Electric Co., Ltd. (72) Inventor Ikuro Yonezu 2-5-5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio Keihanhondori, Moriguchi City, Osaka 2-5-5 Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A hydrogen storage alloy is immersed in an acidic solution having an initial pH value of 2 or less, and when the pH value of the acidic solution reaches a predetermined pH value within a range of 3 to 5, the hydrogen storage alloy is absorbed. After removing the ions attached to the alloy, this hydrogen storage alloy is immersed in an acidic solution having the same pH value as the above-mentioned predetermined pH value,
Thereafter, the method for producing a hydrogen storage alloy for an electrode is characterized in that the hydrogen storage alloy is washed with water and dried. 2. The method for producing a hydrogen storage alloy for an electrode according to claim 1, wherein the pH value of the initial acidic solution in which the hydrogen storage alloy is immersed is in the range of 1 to 1.5. For manufacturing hydrogen storage alloys for automobiles. 3. The method for producing a hydrogen storage alloy for an electrode according to claim 1, wherein the pH value of the initial acidic solution in which the hydrogen storage alloy is immersed is within a range of 3 to 4.
A method for producing a hydrogen storage alloy for an electrode, comprising removing ions adhering to the hydrogen storage alloy when the value reaches a value.