JP3433008B2 - Method for producing hydrogen storage alloy for alkaline storage battery - 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 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-hydrogen storage battery using a hydrogen storage alloy as a negative electrode active material, the battery performance depends on the superiority or inferiority of the activity of the hydrogen storage alloy. Therefore, in this type of storage battery, pulverized and finely divided hydrogen storage alloy powder is used. This is because if the fine hydrogen storage alloy powder is used, the reaction area involved in the electrochemical reaction is increased and the packing density in the electrode substrate is increased, so that high energy density can be easily achieved.

However, the 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 reduces the electrical conductivity of the alloy as well as the electrochemical reactivity. Therefore,
Conventionally, various methods have been proposed for recovering the electrochemical activity of alloys.

One of them is an acid treatment method in which the surface of the hydrogen storage alloy is surface-treated with an acidic aqueous solution (JP-A-4-17905).
5, JP-A-7-73878, and JP-A 7-1.
53460 gazette). This acid treatment method is characterized in that the treatment operation is simple and the effect of removing an oxide film and the like is excellent, and by applying this method, the electrochemical activity of the hydrogen storage alloy can be relatively easily restored. However, even with this method, high rate discharge characteristics and cycle characteristics cannot be sufficiently improved. Therefore, further improvement is expected.

[0005]

DISCLOSURE OF THE INVENTION The present invention establishes treatment conditions capable of further enhancing the high rate discharge characteristics and cycle characteristics of a hydrogen storage alloy electrode in an acid treatment method of surface treating a hydrogen storage alloy with an acidic solution. The purpose is to do.

[0006]

Means for Solving the Problems As a result of intensive studies on the acid treatment method for hydrogen storage alloys, the present inventors have found that the electrochemical activity of the hydrogen storage alloy is remarkable by incorporating metal ions in the acid treatment liquid. The present invention having the following constitution was completed.

A first aspect of the present invention, the initial pH value 0.
5 to 3.0 in acid solution with metal ions or bismuth
Acid treatment solution containing ON (hereinafter referred to as metal ion-containing acid treatment solution)
Surface treatment of the hydrogen storage alloy with
In the region of 6, the metal ion or bismuth ion
A method for producing a hydrogen storage alloy for an alkaline storage battery, wherein the hydrogen storage alloy is deposited on the surface of the hydrogen storage alloy .

A second aspect of the present invention is the method for producing a hydrogen storage alloy for alkaline storage batteries according to the first aspect , wherein the metal ion is at least one selected from the group consisting of nickel ion and cobalt ion. It is characterized by being selected.

A third aspect of the present invention is the above-mentioned first or first aspect .
In the method for producing a hydrogen storage alloy for alkaline storage batteries according to the second aspect, the metal ion-containing acid treatment liquid further has a pH of 4
Substances added to exert Oite pH buffering action in the range 6 of
It is characterized by being added .

[0010] A fourth aspect of the present invention is the manufacturing method of the third aspect of the <br/> for alkaline storage battery hydrogen storage alloy, before
Aluminum ion is a substance that exerts a pH buffering effect.
And characterized in that.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the contents of the method for producing a hydrogen storage alloy of the present invention will be described by comparing and examining the electrochemical characteristics of the hydrogen storage alloy to which the method of the present invention is applied and the hydrogen storage alloy to which the conventional method is applied. To clarify.

(Preparation of Hydrogen Storage Alloy Powder) Commercially available misch metal (Mm; mixture of rare earth elements such as La, Ce, Nd, Pr), nickel (Ni), cobalt (Co),
Aluminum (Al), and manganese (Mn) and a raw material, 1 each elementary ratio: 3.4: 0.8: 0.2 were mixed so that 0.6 ratio of the composition formula using a high frequency melting furnace MmNi _3.4 Co _0.8 Al _{0 .} were prepared of ₂ Mn _0.6 hydrogen storage alloy ingot. 1000 ℃ ・ 1 for this alloy ingot
Annealing treatment was performed for 0 hours.

Ball crushing was performed by using 1 liter of water for 1 kg of the alloy ingot and the alloy ingot had an average particle size of 5
The hydrogen storage alloy was 0 μm. This alloy is designated as alloy A.

(Acid treatment) Five kinds of hydrochloric acid solutions having an initial pH of 0.5, 1, 2, 3, 4 were prepared, and 1% by weight of nickel hydroxide was dissolved in each hydrochloric acid solution to remove nickel ions. A hydrochloric acid solution containing the same (a metal ion-containing acid treatment solution) was prepared. On the other hand, add hydrochloric acid solution with an initial pH of 4
One of cobalt hydroxide, copper hydroxide, and bismuth hydroxide was dissolved in each of them by 1% by weight to prepare four kinds of metal ion-containing acid treatment solutions having different dissolved metal ions and the like . Furthermore, a metal ion-containing acid treatment liquid was prepared by dissolving 1% by weight of nickel hydroxide and 1% by weight of aluminum hydroxide in a hydrochloric acid solution having an initial pH of 1. Note that in the following,
"," Means bismuth ions
Has been done.

Table 1 shows a list of the treatment solutions prepared above. The initial pH means the pH of the treatment liquid before treating the hydrogen storage alloy.

Next, surface treatment was performed on the alloy A using each of the treatment solutions described above. The surface treatment was performed by adding an equal weight of the treatment liquid to Alloy A and stirring the mixture with a stirring mixer until the pH of the treatment liquid reached 7. The alloy after the acid treatment was washed with purified water and dried, and used in the following experiments. As shown in Table 1, No. 1 was surface-treated with the metal ion-containing acid treatment liquid according to the present invention. 1 to 9.

On the other hand, as a comparative example, an alloy surface-treated with a hydrochloric acid solution containing no metal ions and having an initial pH of 1 (No. 1).
1), an alloy which is not subjected to any acid treatment (No. 12), and an alloy which is plated with 3 wt% of nickel on the alloy A by an electrolytic plating method and is not surface-treated with an acid treatment solution (N.
o. 10) was prepared separately. This nickel-plated alloy is for verifying the effect of metal ions.

For the sake of convenience, in the following description, alloy No. No. 10 and 12 are also "treated alloys"
Include in.

(Experiment) Using each of the above treated alloys as a negative electrode active material, a test cell and a nickel-hydrogen storage battery were prepared by the following method, and the electrochemical characteristics (high rate discharge characteristics and cycle characteristics) of each treated alloy were prepared. Was measured. Then, based on the measurement results, the relationship between the difference in the treatment liquid and the electrochemical characteristics was clarified.

<Method for Measuring High Rate Discharge Characteristics> A test cell for measuring high rate discharge characteristics was prepared 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 were added and kneaded to prepare an alloy paste. This alloy paste was wrapped in 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 sufficiently larger capacity than this electrode were placed in a container, and an excessive amount of potassium hydroxide was added as an electrolytic solution, and then the container was closed. To make a test cell.

Using this test cell, the battery was charged at a current value of 50 mA per gram of hydrogen storage alloy (50 mA / g-alloy) for 8 hours, and after resting for 1 hour, the discharge end voltage was at a current value of 200 mA / g-alloy. The battery was discharged until it reached 1.0 V, and the discharge capacity (CH) at this time was measured. After this, discharge 1
After resting for a while to recover the voltage of the test cell,
Discharge was performed at a current value of 0 mA / g-alloy until the discharge end voltage reached 1.0 V, and the discharge capacity (CL) at this time was measured. Using CH and CL, the electrochemical activity (%) of each treated alloy was calculated according to Equation 1, and this value was taken as the high rate discharge characteristic value.

[0022]

[Equation 1]   High rate discharge characteristic value (% activity) = CH / (CH + CL) × 100 ...

<Measuring method of cycle characteristics> The cycle characteristics were measured using a nickel-hydrogen storage battery. nickel·
The method for manufacturing the hydrogen storage battery is as follows. Alloy powder,
Polytetrafluoroethylene powder is added as a binder in an amount of 5 wt% with respect to the weight of the alloy, and the mixture is kneaded to prepare an alloy paste. This paste is applied to both sides of a collector made of punching metal and then pressed to prepare 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 via a separator to form a spirally wound electrode body, which is then inserted into an outer can. A 30 wt% potassium hydroxide aqueous solution is poured into the outer can to seal the outer can. In this way
A cylindrical nickel-hydrogen storage battery with a theoretical capacity of 1000 mAh was produced.

First, for the nickel-hydrogen storage battery,
After charging for 16 hours at 100mA and resting for 1 hour, 20
The activation treatment was performed by repeating a cycle of discharging at 0 mA until the discharge end voltage became 1.0 V and then resting for 1 hour at room temperature for 3 cycles. Charge the storage battery after this activation treatment at 1500 mA for 48 minutes, and
After resting for 1 hour, the discharge end voltage is 1.0 at 1500 mA.
The cycle of discharging until reaching V and further resting for 1 hour was repeated, and the number of cycles until the discharge capacity reached 500 mAh or less was measured. The cycle characteristics of each alloy were evaluated using the number of cycles as the cycle characteristic value (battery life value).

The results for various alloys are shown in Table 1 together with alloy treatment conditions. Further, FIG. 1 schematically shows a change in solution pH when a hydrogen storage alloy is treated with a metal ion-containing acid treatment liquid (for example, No. 9).

[0026]

[Table 1]

The following is clear from Table 1. No. 1 surface-treated with the metal ion-containing acid treatment liquid according to the present invention.
Alloy Nos. 1 to 9 are comparative examples. Compared with Nos. 10 to 11, both high rate discharge characteristics and cycle characteristics were excellent. However, No. As is clear from the comparison of Nos. 1 to 5, No. No. 5 is No. The battery characteristics were remarkably deteriorated as compared with Nos. 1 to 4. From this, the initial pH of the treatment liquid needs to be 3 or less. Moreover, the initial pH was the same, and only the kinds of metal ions were different. 2, N
o. From the comparison of the results of 6 to 9, it was found that the treatment liquid containing nickel ions or cobalt ions had better battery characteristics than the treatment liquid containing copper ions or bismuth ions. Further, No. 1 containing nickel ion and aluminum ion. In 9, even better results were obtained. Therefore, nickel ions and cobalt ions are preferably used as the metal ions contained in the treatment liquid. Further, it is more preferable to use aluminum ions in combination with other metal ions.

The above results will be examined in more detail. No. No surface treatment with the treatment liquid was performed. 12 and No. 12 surface-treated with an acidic treatment liquid containing no metal ion. Comparison with No. 11, and No. 11 No. 11 in which this acidic treatment liquid contained metal ions. 2, No. From the comparison with Nos. 6 to 9, when the alloy is surface-treated with the acidic treatment liquid, the electrochemical characteristics are improved, but when the metal is dissolved in the acidic treatment liquid, the electrochemical characteristics are more remarkably improved. I understand. On the other hand, N
o. No. 12 and nickel plated No. From the comparison with No. 10, it is understood that even if the metal layer is formed on the alloy surface by the plating method, the battery characteristics are hardly improved.

As shown in FIG. 1, when the hydrogen storage alloy is washed with a strong acid (initially pH 0.5), the pH of the treatment liquid rises as the surface treatment progresses. With this in mind, consider the above results.

When the alloy is surface-treated with an acidic treatment liquid, alloy components (rare earth elements, nickel, cobalt, etc., or their oxides) are treated in the treatment liquid pH range of 0.5 to 4.
(Hydroxide) reacts with hydrogen ions in the treatment solution and is eluted into the treatment solution, but the solubility and elution rate of each component of the alloy are not uniform, so this elution forms irregularities on the alloy surface,
The specific surface area of the alloy increases, and nickel or cobalt isolation layers appear on the surface of the alloy due to elution of metal oxides.

On the other hand, when the reaction between the alloy components and hydrogen ions proceeds and the pH of the treatment liquid rises to the pH range of 4 to 6, the solubility of the metal decreases. Therefore, nickel ions, cobalt ions, etc. dissolved in the treatment liquid are re-precipitated and deposited mainly on the convex portions (isolated layer portion) of the alloy. By this deposition / deposition,
The thickness of the metal isolation layer on the alloy surface increases. As a result, the high rate discharge characteristics and cycle characteristics of the hydrogen storage alloy are improved. This is because the more the irregularities are, the larger the specific surface area of the alloy is and the larger the electrochemical reaction area is, so that the oxygen gas absorption performance (cycle characteristics) and the high rate discharge characteristics are improved. In addition, the metal isolation layer (nickel layer, cobalt layer) on the surface of the alloy is rich in catalytic properties for gas absorption reaction and discharge reaction, so that electrode characteristics are further improved.

Here, the metal ion-containing acid treatment solution according to the present invention is a metal ion such as cobalt or nickel.
Since There has been added, compared with the case of surface treatment with an acidic solution of metal ions is not added, the greater the amount of precipitation of the metal ions in pH4~6 zone. Therefore, the unevenness of the alloy surface becomes large, and the thickness of the metal isolation layer (catalyst layer) becomes even thicker. As a result, the high rate discharge characteristic and the cycle characteristic can be more remarkably improved.

It should be noted that, in the above description, No. 1 using the method of directly plating the surface of the alloy with metal. 10 and No. This is supported by 12 comparison results. That is, even if the plating method is used, a metal layer can be formed on the alloy surface, but since the metal uniformly adheres to the alloy surface by the plating method, it acts rather to reduce the unevenness of the metal surface. Therefore, it is considered that there is no effect of improving the high rate discharge characteristics and the cycle characteristics.

Further, alloy No. No. 1 surface-treated with an acid treatment liquid containing nickel ions and aluminum ions was used. The reason why the best result was obtained in No. 9 is considered to be as follows. That is, since aluminum ions have a pH buffering ability in the pH range of 4 to 6, the pH of the acid treatment solution is set to 4 to 4.
It works to keep it in the range of 6 for a long time. Therefore, as a result of more metal ions in the treatment liquid being deposited and adhering to the surface of the alloy, the electrochemical characteristics of the alloy are improved.

[0035]

As is apparent from the above, according to the method of the present invention for surface-treating a hydrogen storage alloy using an acid treatment liquid containing metal ions, the pH of the treatment liquid due to the reaction between hydrogen ions and alloy components is During the ascending process, the surface of the hydrogen storage alloy is modified so that the electrochemical reaction can be suitably performed. Therefore, when the method of the present invention is applied to the hydrogen storage alloy for alkaline storage batteries, high rate discharge characteristics and cycle characteristics can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a graph showing a pH rise curve of an acid treatment liquid in surface treatment.

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-7-73878 (JP, A) JP-A-7-153460 (JP, A) JP-A-7-320731 (JP, A) JP-A-7- 326353 (JP, A) JP-A-4-110403 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/38 H01M 4/24-4/26

Claims (4)

(57) [Claims] [Claim 1] initial pH value is 0.5 to 3.0 San溶
Acid treatment by adding metal ions or bismuth ions to the solution
Surface treatment of hydrogen storage alloy using liquid, pH range of 4-6
The metal ion or bismuth ion in the hydrogen
A method for producing a hydrogen storage alloy for an alkaline storage battery, which comprises depositing on a surface of the storage alloy . 2. The method for producing a hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the metal ions are selected from the group consisting of nickel ions and cobalt ions. 3. The metal ion or bismuth ion
The pH of the added acid treatment liquid is within the range of 4 to 6.
A substance which exerts an H-buffering action is added.
Alternatively, the method for producing a hydrogen storage alloy for alkaline storage batteries according to the item 2. 4. The metal ion or bismuth ion
The method for producing a hydrogen storage alloy for alkaline storage batteries according to claim 3, wherein the added acid treatment liquid contains aluminum ions as a substance exhibiting a buffering action within a pH range of 4 to 6.