JPH1074510A - Manufacture of hydrogen absorbing alloy for alkali storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish the activating condition of a hydrogen absorbing alloy for an alkali storage battery for reducing the initial charge inner pressure of the battery of hydrogen absorbing alloy electrode and providing excellent high-efficiency discharge characteristic, low-temperature discharge characteristic and cycle characteristic. SOLUTION: A hydrogen absorbing alloy is dipped in metal ion containing acidic treatment liquid with an initial pH of 0.5-3.0 for cleaning. At a when the treatment liquid pH is increased to be 4-5, metal ion containing alkali solution is put in the treatment liquid so that the treatment liquid pH can be increased to be at least 7 at a time for alloy activation.

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 alkaline storage battery, and more particularly to an improvement in an acid treatment method for a hydrogen storage alloy.

[0002]

2. Description of the Related Art In a nickel-metal hydride storage battery using a hydrogen storage alloy as a negative electrode active material, the battery performance is affected by the degree of activity of the hydrogen storage alloy. For this reason, in this type of storage battery, hydrogen storage alloy powder that has been pulverized and refined is used. When the hydrogen storage alloy powder is fine, the reaction area involved in the electrochemical reaction increases, and the packing density of the electrode substrate increases, so that high energy density can be easily achieved.

However, a hydrogen storage alloy is an extremely active substance, and is oxidized during pulverization or storage to form an oxide film on the surface. This oxide film lowers the electrical conductivity of the alloy and deteriorates the electrochemical reactivity. For this reason, various methods for restoring the electrochemical activity of the alloy have been proposed and implemented.

One of the methods is an acid treatment method in which the surface of a hydrogen storage alloy is surface-treated with an acidic aqueous solution (Japanese Patent Laid-Open No. Hei 4-17905).
No. 5, JP-A-7-73878, JP-A 7-1
No. 53460). This acid treatment method is characterized in that the treatment operation is simple and the effect of removing an oxide film or the like is excellent. Therefore, if this method is applied, the electrochemical activity of the hydrogen storage alloy can be easily recovered. However, although the conventional acid treatment method can improve the low-temperature discharge characteristics and cycle characteristics of the hydrogen storage alloy electrode, it has a problem in that the internal pressure of the battery during the initial charge of the battery is increased.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an acid treatment method for treating a hydrogen storage alloy with an acidic solution, in which the initial charge internal pressure of an alkaline storage battery using a hydrogen storage alloy as a negative electrode active material can be reduced and the temperature can be reduced. An object of the present invention is to establish alloy processing conditions that can improve discharge characteristics, high-rate discharge characteristics, and cycle characteristics.

[0006]

To solve the above-mentioned problems, the present invention has the following arrangement. In the method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 1, the hydrogen storage alloy is immersed in an acidic treatment liquid having an initial pH of 0.5 to 3.0, and the pH of the treatment liquid in which the hydrogen storage alloy is immersed is adjusted. The method is characterized in that an alloy activation treatment step is performed in which an alkaline solution is added to the treatment liquid before the treatment liquid rises to 5, thereby accelerating the rise of the treatment liquid pH.

According to a second aspect of the present invention, there is provided the method for producing a hydrogen storage alloy for an alkaline storage battery according to the first aspect, wherein the pH of the treatment liquid in which the hydrogen storage alloy is immersed is 4 or more and less than 5, and the alkali solution is introduced. It is characterized by performing.

According to a third aspect of the present invention, there is provided a method for producing a hydrogen storage alloy for an alkaline storage battery according to the first or second aspect,
The acidic treatment liquid contains metal ions.

The invention according to claim 4 is the invention according to claim 1, 2 or 3.
The method for producing a hydrogen storage alloy for an alkaline storage battery according to the above, wherein the alkaline solution contains metal ions.

According to a fifth aspect of the present invention, there is provided a method for producing a hydrogen storage alloy for an alkaline storage battery according to the third or fourth aspect,
The metal ions are selected from one or more of the group consisting of nickel, cobalt and aluminum.

The invention according to claim 6 is the invention according to claims 1, 2, 3, 4
Alternatively, in the method for producing a hydrogen storage alloy for an alkaline storage battery according to 5, the pH of the treatment liquid in which the hydrogen storage alloy is immersed is adjusted to 7 to 12 by introducing the alkali solution.

According to a seventh aspect of the present invention, there is provided a method for producing a hydrogen storage alloy for an alkaline storage battery according to the third or fourth aspect,
When the acidic treatment liquid and / or the alkali solution contains metal ions, the pH of the treatment liquid is set to 12 or more from the introduction of the alkali solution.

The invention of claim 8 is the invention of claim 3, 4, or 7.
In the method for producing a hydrogen storage alloy for an alkaline storage battery as described above, a solution having a temperature of 65 ° C. or higher is used as the acidic treatment liquid and / or the alkaline solution.

According to a ninth aspect of the present invention, in the method for producing a hydrogen storage alloy for an alkaline storage battery according to any one of the third, fourth, seventh, or eighth aspects, the temperature of the processing solution into which the alkaline solution is charged is set to 65 ° C. or higher. It is characterized by the following.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an alloy processing method for cleaning the surface of an alloy with an acidic solution to enhance the electrochemical characteristics of the hydrogen storage alloy. It is characterized by rapidly raising the pH and by dissolving the metal in this treatment solution. Hereinafter, the significance of the configuration of the present invention will be clarified, and embodiments of the present invention will be described.

When the hydrogen storage alloy is immersed in a strong acid and washed (surface treatment), the electrochemical reactivity of the alloy increases. The reason is considered as follows. When the hydrogen storage alloy is immersed in a strongly acidic treatment liquid, the alloy components (rare earth elements, nickel, cobalt, etc.,
Or their oxides and hydroxides) react with the hydrogen ions in the processing solution and elute into the processing solution, and the pH of the processing solution gradually increases with the reaction, but the solubility and elution rate of the alloy components are not uniform. Therefore, as a result of this elution, irregularities are formed on the alloy surface, and the specific surface area of the alloy increases. In addition, since an isolated layer of nickel or cobalt appears on the surface of the alloy due to elution of the metal oxide or the like, low-temperature discharge characteristics and cycle characteristics of the hydrogen storage alloy are improved.

However, the rise in the pH of the processing solution does not stop at 4, but rises above 4, and the solubility of the alloy component becomes pH
Due to the dependence, when the pH of the treatment liquid rises to around 5, the rare earth elements and the like dissolved in the treatment liquid in the pH range of 0.5 to 4 become hydroxides, precipitate again, and deposit on the alloy surface. In this case, since the rate of pH rise from pH 5 to near neutrality is slow, a dense layer made of a hydroxide such as a rare earth element is formed on the alloy surface. Since this dense layer inhibits the oxygen consuming reaction of the hydrogen storage alloy, the internal pressure characteristics of the battery deteriorate.

Here, in the alloy activation treatment method of the present invention, an alkali is added during the acid treatment. Therefore, the metal ions such as the rare earth elements once eluted in the acidic treatment liquid are forcibly and rapidly reacted by the added alkali (hydroxide ions) to become hydroxides, and are deposited on the alloy surface. If the deposited layer is formed by such a rapid reaction, the layer becomes porous, so that the oxygen consumption reaction is not hindered, and the hydroxide layer acts rather to catalyze the oxygen consumption reaction. That is, according to the alloy activation treatment method of the present invention, it is possible to form a hydrogen storage alloy that has excellent low-temperature discharge characteristics, high-rate discharge characteristics, and cycle characteristics, and does not cause an increase in battery internal pressure.

In the alloy activation treatment method of the present invention having such an effect, an acid solution having an initial pH value of 0.5 to 3.0 is used as the acid treatment solution, and the pH of the acid treatment solution is adjusted to 0.5 to 3.0.
Before the pH reaches 5, more preferably at a pH of 4 or more and less than 5, an alkali solution is charged. It is difficult to obtain an acidic treatment liquid having an initial pH value of less than 0.5. On the other hand, an acid treatment liquid having an initial pH value of more than 3.0 can sufficiently remove an oxide film, a hydroxide film, and the like on the alloy surface. , And a sufficient acid treatment effect cannot be obtained. In addition, when an alkaline solution is added at a stage when the pH of the acidic treatment liquid exceeds 5, formation of a dense hydroxide layer cannot be sufficiently prevented. On the other hand, when an alkali is added at a stage of less than pH 4, the acid treatment effect is reduced.

In the acid treatment method of the present invention, the acidic treatment solution and / or the alkali solution preferably contains metal ions. Thereby, it is possible to form a hydrogen storage alloy having more excellent electrochemical characteristics (oxygen consumption characteristics, high-rate discharge characteristics, and the like). The reason is that when metal ions other than the metal derived from the alloy are present in the processing liquid, the metal is precipitated in the process of increasing the pH of the processing liquid, and the alloy surface is made into a metal-rich shape (properties) with more irregularities. Because.

Examples of the metal ions include ions of nickel, cobalt, aluminum, copper, bismuth and the like, and among them, one or more selected from the group consisting of nickel ions, cobalt ions and aluminum ions are preferable. It is considered that nickel, cobalt, and aluminum are particularly preferable because these metals are excellent in conductivity and have a catalytic action on the oxygen consumption reaction on the surface of the alloy. Also, nickel, cobalt, and aluminum are usually part of the alloy component,
It is considered that there is almost no adverse effect on the battery reaction.

The above-mentioned metal ions are contained in either one of the acidic treatment solution and the alkaline solution, or both the acidic treatment solution and the alkaline solution. However, when it is contained in either one of the solutions, it is effective to dissolve it in the acidic treatment liquid from the viewpoint of high rate discharge characteristics,
In addition, since the high-rate discharge characteristics can be further enhanced,
More preferably, it is contained in both the acidic treatment solution and the alkali solution.

As a method for containing metal ions in an acidic treatment solution or the like, a metal (element) may be directly dissolved in an acidic treatment solution or the like, but usually a metal compound is used. Specifically, for example, a metal salt is used for an acidic treatment solution, and a metal hydroxide is used for an alkali solution. The concentration of metal ions to be dissolved in the acidic treatment liquid or the like is not particularly limited, and may be generally 1% to 5% by weight (weight of the metal salt) with respect to the acidic treatment liquid or the like. If the amount is less than 1% by weight, it is difficult to obtain a sufficient effect.
This is because dissolution of more than weight% is not easy. In addition, it is also preferable that the acidic treatment liquid or the like is dissolved at a high concentration by heating. This will be described later.

In the alloy activation treatment method of the present invention, the surface of the alloy is treated with a strong acid to form a state suitable for an electrochemical reaction, and the alkali treatment is performed for the purpose of terminating the alloy treatment without deteriorating this state. I do. Therefore, the pH of the processing solution after the introduction of the alkaline solution has a great effect on the electrochemical properties of the alloy. In order to obtain a sufficient effect by adding an alkali, in the case of a combination of an acidic treatment solution containing no metal ion and an alkali solution containing no metal ion, preferably, the treatment solution p is introduced by adding an alkali solution.
H is adjusted to 7 to pH12. Within this range, both the initial charging internal pressure and the high rate discharge characteristics can be improved.

On the other hand, when metal ions are contained in the acidic treatment liquid and / or the alkaline solution, the pH is more preferably adjusted to 12 or more. Under conditions in which metals other than alloy-derived metals are dissolved in the treatment liquid, if the pH of the treatment liquid is adjusted to pH 12 or higher by adding an alkaline solution, the high-rate discharge characteristics are further improved without lowering the initial charge internal pressure characteristics. be able to. The details will be clarified in Examples described later.

Further, in the alloy activation treatment method of the present invention, it is preferable that the temperature of the treatment liquid after the introduction of the alkaline solution is set to 65 ° C. or higher. When the temperature of the processing solution is set to 65 ° C. or higher, the reaction rate between a metal such as a rare earth element eluted in the processing solution and the added alkali (hydroxide ion) increases, and more favorable porous hydroxylation is performed. This is because the material layer is formed on the alloy surface. Furthermore, in the alloy activation treatment method of the present invention, it is preferable to use a metal-containing acidic treatment solution and / or an alkali solution heated to 65 ° C. or higher. 6
An acidic treatment liquid or the like heated to 5 ° C. or more can dissolve more metal ions, and thus can enhance the effect of modifying the alloy surface. In particular, since the solubility of metal ions in an alkaline solution is small, it is more effective to promote dissolution by heating. In addition, since a pre-heated solution is used, the metals (metals such as rare earth elements and metals dissolved in an acidic processing solution) and alkalis (and metals dissolved in an acidic processing solution) and alkali (and alkali solution) in the processing solution are immediately mixed with the alkali solution. This is because the reaction with the metal can proceed.

When the hydrogen-absorbing alloy is immersed and washed in an acidic treatment liquid, the temperature of the treatment liquid rises to about 30 to 35 ° C. due to heat of chemical reaction or the like. Need to apply heat from Further, at normal atmospheric pressure, the temperature of the processing solution cannot be increased to 100 ° C. or higher, and there is no need for this. Therefore, the temperature is generally increased to 65 ° C. or higher and lower than 100 ° C. In this case, it is not preferable to boil the treatment liquid because evaporation of the liquid occurs.

As the acid component of the acid treatment solution according to the present invention, for example, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, phosphoric acid, etc. can be used. As the alkaline component of the alkaline solution, potassium hydroxide, lithium hydroxide, water Sodium oxide and the like can be used.

The alloy activation treatment method of the present invention is applicable to various kinds of hydrogen storage alloys for alkaline storage batteries, and is applicable to, for example, hydrogen storage alloys of rare earth type, titanium type, zirconium type and magnesium type.

[0030]

EXAMPLES The contents of the present invention will be described in detail based on examples (experiments).

[First Example (When No Metal Ion is Contained)] The content of the production method of the present invention is clarified by comparing an acid treatment method with alkali addition and a conventional acid treatment method without alkali addition. I do. (Preparation of hydrogen storage alloy powder) Commercially available misch metal (M
m; a mixture of rare earth elements such as La, Ce, Nd and Pr), nickel (Ni), cobalt (Co), aluminum (Al) and manganese (Mn) as raw materials, each having an element ratio of 1: 3.4: 0.8. : 0.2: 0.6 and the composition formula MmNi using a high frequency melting furnace.
_3.4 to prepare a hydrogen-absorbing alloy ingot of Co _0.8 Al _{0. 2} Mn _0.6. This alloy ingot was annealed at 1000 ° C. for 10 hours. 1 kg of this alloy ingot is water 1
Liter and pulverized with a ball mill, average particle size 50 μm
Was prepared.

(Alloy activating treatment) The acidic treatment liquid (without addition of metal ions) has an initial pH of 0.5, 1, 2, and 3
The following aqueous hydrochloric acid solutions were prepared. A 10 N aqueous potassium hydroxide solution was prepared as an alkaline solution (without addition of metal ions). Next, the alloy powder and the hydrochloric acid aqueous solution are put into a stirring mixer at a weight ratio of 1: 1 and stirred while monitoring the pH of the processing solution. When the pH of the processing solution reaches a predetermined value, a predetermined amount of water is added. An aqueous solution of potassium oxide was added. Stirring was further continued. When the pH value of the treatment liquid was stabilized, the stirring was stopped and the alloy was taken out. This alloy was washed with purified water and dried to obtain treated alloys A1 to A12. These operations were all performed at room temperature (about 25 ° C.).

Here, the predetermined value of the pH of the processing solution is pH 2 shown in "Processing pH at the time of adding alkali" in Table 1.
4, 5, and 7, and the predetermined amount of the aqueous solution of potassium hydroxide refers to the pH 6, 7, 10, 12, 12 shown in “Processing pH after alkali addition” in Table 1 after the addition of the alkali solution.
It refers to the amount of aqueous potassium hydroxide solution that can be adjusted to 15. The alloys A1 to A12 treated under such conditions are listed in Table 1 below. In the above description, the pH of the treatment liquid after the addition was adjusted by changing the amount of the 10 N aqueous potassium hydroxide solution. However, the treatment liquid after the introduction without changing the amount of the injection liquid by using a solution having a different alkali strength. The pH may be adjusted. The point is that the amount of hydroxide ions that is equal to or higher than the hydrogen ion concentration of the processing solution when the alkali is charged may be charged.

On the other hand, as a conventional treatment method in which alkali is not charged, the hydrogen storage alloy powder is subjected to an acid treatment using an aqueous hydrochloric acid solution having an initial pH of 1 (X2 in Table 1). A surface treated with an alkaline solution (potassium hydroxide solution) having a pH of 15 (X3 in Table 1) and a hydrogen absorbing alloy powder without any acid treatment (X1 in Table 1) were prepared as control products.

(Battery Chemical Characteristics Test of Treated Alloys) In order to evaluate the initial charge internal pressure characteristics and the high rate discharge characteristics of the treated alloys, a test cell and a nickel-hydrogen battery were prepared using the treated alloys as negative electrode active materials. Storage batteries were prepared, and the initial charging internal pressure characteristics and the high-rate discharge characteristics of each of the treated alloys were examined by the following methods using the storage batteries.

<Method of Measuring Initial Charging Internal Pressure Characteristics> Initial charging internal pressure characteristics were measured using a nickel-hydrogen storage battery.
The method for producing the nickel-metal hydride storage battery is as follows. A polytetrafluoroethylene powder as a binder is added to the alloy powder in an amount of 5 wt% based on the weight of the alloy, and the mixture is kneaded to prepare an alloy paste. This paste is applied to both surfaces of a current collector made of punching metal, and then pressed to produce a hydrogen storage alloy electrode. Next, this electrode (negative electrode) and a known sintered nickel electrode (positive electrode) having a smaller capacity than this electrode are wound through a separator to form a spiral electrode body.
Insert into the outer can. A 30 wt% aqueous solution of potassium hydroxide was injected into the outer can, the outer can was sealed, and the theoretical capacity was 10%.
A nickel-metal hydride storage battery of 00 mAh is formed.

The above nickel-hydrogen storage battery is 1000
The battery was charged for 60 minutes at mA, and the internal pressure of the battery at this time was measured.

<Method of Measuring High Rate Discharge Characteristics> The high rate discharge characteristics were measured using a test cell. The method for producing the test cell is as follows. To 1 g of each alloy powder, 1.2 g of carbonyl nickel as a conductive agent and 0.2 g of polytetrafluoroethylene powder as a binder are added and kneaded to prepare an alloy paste. This alloy paste is wrapped in a nickel mesh and pressed to produce a hydrogen storage alloy electrode (negative electrode). This hydrogen storage alloy electrode and a known sintered nickel electrode (positive electrode) having a capacity sufficiently larger than this electrode are arranged in a container, and after excessively adding potassium hydroxide as an electrolyte, the container is sealed. Test cell.

The test cell was charged at a current value of 50 mA per 1 g of the hydrogen storage alloy (50 mA / g-alloy) for 8 hours, paused for 1 hour, and then discharged at a current value of 200 mA / g-alloy. Discharge until reaching 1.0 V, and measure the discharge capacity (CH) at this time. After this, discharge
After resting for a period of time and restoring the test cell voltage,
Discharge is performed at a current value of 0 mA / g-alloy until the discharge end voltage reaches 1.0 V, and the discharge capacity (CL) at this time is measured. Using CH and CL, the electrochemical activity (%) of each treated alloy is calculated according to Equation 1, and this value is used as a high-rate discharge characteristic value.

[0040]

## EQU1 ## High-rate discharge characteristic value (activity%) = CH / (CH + CL) .times.100

The test results are shown in Table 1 together with the processing conditions for each alloy. Further, the initial pH of the acid treatment solution is set to 1 (constant).
A5, A2, and A6 that were activated under the conditions that the pH at the time of alkali introduction was changed to 2 or 4 or 5, and the pH of the treatment liquid after alkali introduction was added to be 7 (constant) and the alkali solution was added. FIG. 1 is a graph showing the relationship between the pH of the treatment liquid when the alkali is charged and the initial charge characteristics and the high-rate discharge characteristics of the battery.
(Constant), the pH at the time of alkali addition is set to 4 (constant),
And the pH of the processing solution after the addition of the alkali is adjusted to pH 6 and p, respectively.
The results of A7, A2, A8, A9, and A10 activated under the conditions of changing to H7, pH10, pH12, and pH15 are shown in relation to the pH of the treatment liquid after alkali addition and the initial charge characteristics and high-rate discharge characteristics of the battery. A graph is shown in FIG.

[0042]

[Table 1]

(Relationship between Differences in Processing Conditions and Electrochemical Properties-I) X1 in Table 1 (no acid treatment)
And X2 (conventional acid treatment method without adding alkali), it can be seen that when acid treatment is performed on the hydrogen storage alloy, high-rate discharge characteristics are improved, but initial charge internal pressure characteristics are deteriorated. Also, from the results of X2 and A1 to A12 (alkali charging acid treatment method), it can be seen that initial charging internal pressure characteristics can be improved by adding alkali to the treatment liquid during the acid treatment. This will be described in more detail.

The pH of the alkaline solution was set to 4 (constant), the pH of the treating solution after the alkaline solution was set to 7, and the initial pH of the acidic treating solution was 0.5, 1, 2, and 3.
In 4, the initial pH of the acidic treatment liquid is 0.5, 1, 2,
3, the initial charging internal pressure is 2.
It was 8 kg / cm ³ and did not change at all. On the other hand, it was recognized that the high-rate discharge characteristic value tended to decrease as the initial pH of the acidic treatment liquid increased. In addition, the initial pH was set to 1, and the pH at the time of adding alkali was 2 (A5), 4 (A2), 5 (A2).
(A6), and the pH of the treatment liquid after the introduction of the alkali is 7
In the comparison of A5, A2, and A6 with (constant) (see FIG. 1), compared to the case where the pH at the time of adding alkali was 2 and 4,
The initial charging internal pressure was higher when the pH was 5 when the alkali was charged. Further, A1 was adjusted to pH 7 when the alkali was charged.
1 and A12, the initial charging internal pressure was even higher. From these results, the initial pH value of the acidic treatment solution was set to 0.5 to 3,
It is preferable to carry out alkali addition before the pH value of the treatment liquid rises to 5, and it is more preferable to carry out alkali addition at a stage of pH 4 or more and less than 5.

On the other hand, the initial pH of the acidic treatment liquid was set at 1 (constant), the pH at the time of alkali addition was set at 4 (constant), and the pH of the treatment liquid after alkali addition was set at pH 6 (A7), p
H7 (A2), pH10 (A8), pH12 (A9),
In FIG. 2 showing the results of A2 and A7 to 10 when the pH was 15 (A10), the pH of the treatment liquid after the addition of the alkali was pH6.
Although the high-rate discharge characteristics hardly changed even when it changed to １２12, the initial internal pressure of battery charging increased when the pH of the processing solution after the alkali was charged was 6 or less or exceeded 12. From this result, it is preferable to add an alkaline solution so that the pH of the processing solution is 7 to 12.

From a comparison between X1 not subjected to any acid treatment or the like and X3 treated only with an alkali solution, it is found that neither the initial charge internal pressure characteristic nor the high-rate discharge characteristic is improved at all by the alkali treatment alone. . This means that the above effects can be obtained for the first time when an alkaline solution is introduced during the acid treatment.

[Second embodiment (in the case of containing metal ions)] In the second embodiment, a case where metal ions are contained in the treatment liquid will be described. The specific contents of the second embodiment are the same as those of the first embodiment except that the treatment liquid contains metal ions. Therefore, only the points different from the first embodiment will be described below.

First, four types of hydrochloric acid aqueous solutions having different initial pHs and a 10 N aqueous solution of potassium hydroxide were prepared, and these solutions were used as an acidic treatment solution containing no metal ions and an alkaline solution. A predetermined metal ion was dissolved to prepare a metal ion-containing acidic treatment solution and a metal ion-containing alkali solution, respectively. Specifically, chlorides of nickel, cobalt, copper, bismuth, and aluminum are used, and one of these metal chlorides is added to the aqueous hydrochloric acid solution for 5 hours.
By dissolving the resulting solution in an amount of 5% by weight, five types of acidic treatment solutions containing metal ions were prepared. On the other hand, one of these metal hydroxides is dissolved in the aqueous potassium hydroxide solution to a saturation concentration (room temperature; about 25 ° C.) to prepare five kinds of alkali solutions containing metal ions. (See Tables 2 and 3).

Using each of the above acidic treatment solutions and each alkali solution, the pH of the treatment solution when the alkali was introduced was set to 4, the pH of the treatment solution after the introduction of the alkali was set to 7 (all in common), and other treatment conditions were changed. , B1 to B8 (using an acidic treatment solution containing metal ions), C1 to C8 (using an alkali solution containing metal ions), and D1 to D12 (both containing metal ions) were prepared (see Tables 2 and 3). .

Further, the treatment liquid p
In order to examine the extent to which H should be increased, treated alloys E1 to E3 were prepared by changing the pH after alkali addition to 10, 12, and 15.

Further, in order to investigate the effect of the temperature of the processing solution on the electrochemical properties of the alloy, the temperature of the processing solution obtained by combining the nickel-containing acidic processing solution and the nickel-containing alkali solution was heated to 65 ° C. Other than the above, D2
F1 was prepared under the same conditions as in (room temperature operation) (see Table 3).

The electrochemical properties of each of the above treated alloys were examined in the same manner as in the first embodiment. The results are listed in Tables 2 and 3 together with the processing conditions.

[0053]

[Table 2]

[0054]

[Table 3]

(Relationship Between Differences in Processing Conditions and Electrochemical Characteristics-II) First, the initial internal pressure value of A1 to A4 (Table 1) of the first embodiment, which does not contain metal ions, is 2.8 kg / c.
to which the m ^2, and only the acidic treating solution was contained Ni ions B1 to B4 (Table 2), Ni only in an alkaline solution
C1 to C4 containing ions (Table 2), Ni was added to both liquids.
The initial internal pressure values of D1 to D4 (Table 3) containing ions are all 2.0 Kg / cm ^2. Therefore, when metals other than alloys are dissolved in the treatment liquid, the initial charging internal pressure characteristics are improved. You can see.

On the other hand, the high-rate discharge characteristics were also remarkably improved by the presence of metals other than those derived from alloys. However, as is apparent from FIG. It was not uniform like the internal pressure characteristics and varied depending on the processing conditions. That is, the high-rate discharge characteristics have a large improvement degree, and both liquids contain Ni ions.gtoreq. [Ni
Ion-containing acidic treatment liquid]> [Ni-ion-containing alkaline solution]> [No Ni-ion added].

From the above results, when a metal other than the metal derived from the alloy (added from outside) is dissolved in the treatment solution in which the hydrogen storage alloy is immersed, the initial charge internal pressure characteristics and the high rate discharge characteristics are further improved. It can be seen that the degree of improvement in the high-rate discharge characteristics differs depending on which solution can be used and which solution contains metal ions. For this reason, when metal ions are contained in only one of the solutions, the metal ions are preferably contained in the acidic treatment solution, and more preferably in both the acidic treatment solution and the alkali solution.

Next, the relationship between the types of metal ions and the electrochemical characteristics will be described. FIG. 4 is a graph showing the results of B2 and B5 to B8, C2 and C5 to C8 (other conditions are common) in which the types of metal ions are changed. FIG.
Also, the degree of improvement of the high-rate discharge characteristics was [Ni-acid-containing acidic treatment liquid]> [Ni-ion-containing alkaline solution], and showed the same tendency as described above. On the other hand, in relation to the type of metal, Al ≧ Ni = Co> Cu = Bi was approximately satisfied. For this reason, Al, Ni, and Co are preferably used as the metal ions, and Al is more preferably used.

As the metal ion, preferably, Al, Ni,
The conclusion that the use of Co, and more preferably the use of Al, is concluded is that both liquids contain D2 containing metal ions.
And D5 to D12 (other conditions are common). That is, Ni-Ni (D2), Co-Ni (D
5), Al-Co (D8), Ni-Co (D9), Ni
In the combination of -Al ((D12)), better high-rate discharge characteristics were obtained (see Table 3).

FIG. 5 shows the relationship between the pH of the processing solution after alkali addition and the high-rate discharge characteristics when metal ions are contained in both the acidic processing solution and the alkaline solution. FIG. 5 is a graph of E1 to E3 and X4 in Table 3. As is apparent from FIG. 5, the pH of the treatment liquid is preferably raised to 7 or more, more preferably to 12 or more, depending on the amount of the alkaline solution charged.

Further, F1 at a processing liquid temperature of 65 ° C .;
From the comparison with D2 treated at room temperature, F1 was better than D2.
It can be seen that the high rate discharge characteristics are more excellent. As described above, F1 and D2 differ only in the processing liquid temperature, and the difference between the high-rate discharge characteristics of the two is the processing liquid temperature. That is, when the temperature of the treatment liquid is set to 65 ° C. or higher, the high-rate discharge characteristics can be further improved.

[0062]

According to the alloy activation treatment method of the present invention, the acid treatment is continued as it is at a pH of 0.5 to 4 at which the acid effectively acts on the alloy surface, and the acid treatment effect is reduced and the alloy surface is reduced. PH 4-5 at which a dense hydroxide layer begins to form
In the step, the alkaline solution is added to the treatment liquid to raise the pH of the treatment liquid to a neutral or alkaline side at once. With this configuration, it is possible to prevent a dense hydroxide layer of a rare earth element or the like from being formed on the surface of the alloy. Hydrogen storage alloy for alkaline storage batteries.

Further, in such an alloy activation treatment method, when a metal ion such as aluminum, cobalt, nickel or the like is contained in an acidic treatment solution and / or an alkaline solution, these metals are increased during the process of increasing the pH of the treatment solution. Precipitates on the alloy surface to modify the alloy surface into a shape (or property) more suitable for electrochemical reactions. Therefore, electrochemical characteristics such as initial charge internal pressure characteristics, low-temperature discharge characteristics, high-rate discharge characteristics, and cycle characteristics of the battery can be further improved.

Therefore, if an alkaline storage battery is formed using a hydrogen storage alloy to which the method for producing a hydrogen storage alloy of the present invention is applied, a high performance secondary battery which has never been obtained before can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the pH of a processing solution when an alkali is charged, the initial charge internal pressure of a battery, and a high-rate discharge characteristic value.

FIG. 2 is a graph showing the relationship between the pH of a processing solution after alkali addition, the initial charge internal pressure of a battery, and a high-rate discharge characteristic value.

FIG. 3 is a graph showing the effectiveness (high-rate discharge characteristics) of the alloy activation treatment method of the present invention in which metal ions are contained in the treatment liquid.

FIG. 4 is a graph showing the relationship between the type of metal ions contained in the treatment liquid and the high-rate discharge characteristics.

FIG. 5 is a graph showing the relationship between the pH of a treatment solution after the introduction of a metal ion-containing alkali solution and high-rate discharge characteristics.

Claims (9)

[Claims] 1. A hydrogen storage alloy having an initial pH of 0.5 to 3.
0, and before the pH of the treatment solution in which the hydrogen storage alloy is immersed rises to 5, an alkaline solution is added to the treatment solution to accelerate the increase in the pH of the treatment solution. A method for producing a hydrogen storage alloy for an alkaline storage battery, comprising an alloy activation treatment step. 2. The pH of a treatment liquid in which a hydrogen storage alloy is immersed.
The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the alkali solution is charged when the temperature is 4 or more and less than 5. 3. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the acidic treatment liquid contains metal ions. 4. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the alkaline solution contains metal ions. 5. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 3, wherein the metal ion is at least one selected from the group consisting of nickel, cobalt, and aluminum. 6. The alkaline storage battery according to claim 1, wherein the pH of the treatment liquid in which the hydrogen storage alloy is immersed is adjusted to 7 to 12 by introducing the alkaline solution. For manufacturing hydrogen storage alloys for automobiles. 7. The alkali according to claim 3, wherein when the acidic treatment liquid and / or the alkali solution contains metal ions, the pH of the treatment liquid is adjusted to 12 or more by adding the alkali solution. A method for producing a hydrogen storage alloy for a storage battery. 8. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 3, wherein a solution having a temperature of 65 ° C. or more is used as the acidic treatment liquid and / or the alkaline solution. 9. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 3, wherein the temperature of the treatment liquid into which the alkaline solution has been introduced is set to 65 ° C. or higher.