JP3462682B2 - Method for producing hydrogen storage alloy powder - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, nickel-
The present invention relates to a method for producing a hydrogen storage alloy powder used as a material for an electrode (negative electrode) of a hydrogen secondary battery.

[0002]

2. Description of the Related Art A hydrogen storage alloy electrode which serves as a negative electrode of a nickel-hydrogen secondary battery is obtained by adding a binder to a hydrogen storage alloy powder obtained by crushing a hydrogen storage alloy lump and molding the powder into an electrode shape. Made by. As the hydrogen storage alloy, an AB ₅ type or AB ₂ type rare earth-based hydrogen storage alloy, for example, an Mm-Ni-based or Zr-Ni-based hydrogen storage alloy containing La is used. By the way, in the nickel-hydrogen secondary battery, in order to improve the activity of the hydrogen storage alloy, a surface treatment is carried out by immersing the hydrogen storage alloy powder in an acidic aqueous solution such as hydrochloric acid for a predetermined time. By this surface treatment, the oxide film formed on the surface of the alloy particles is removed, the rare earth elements (La, etc.) are dissolved, and a metal surface such as nickel is exposed on the surface of the particles. The catalytic activity is improved.

However, in the conventional surface modification method, the pH of the treatment liquid rapidly rises during the treatment, so that the elution rate of the metal from the surface of the alloy particles varies depending on the location, and the uniform surface modification is performed. It was difficult to measure the quality. Further, the metal becomes a hydroxide and is deposited on the surface to form a thick layer, so that not only the activity cannot be sufficiently improved, but also the hydrogen gas absorption capacity of the hydrogen storage alloy is lowered. It was

Therefore, the applicant has proposed a method of modifying the surface of the hydrogen storage alloy particles with an acidic treatment liquid having a buffering action (JP-A-8-185856). According to this method, since the pH is kept substantially constant by the buffering action of the treatment liquid, the surface modification of the hydrogen-absorbing alloy particles is performed uniformly, and the precipitation of hydroxide is suppressed, so that the hydrogen-absorbing alloy particles are suppressed more than before. High activity and gas absorption capacity are obtained.

[0005]

However, it has been found that the surface modification method proposed by the applicant has not yet obtained the high activity that should be obtained by exposing the metal surface. As a result of intensive research, the inventors of the present invention have clarified the cause thereof and completed the present invention as follows. That is,
When the hydrogen storage alloy particles are surface-treated with an acidic treatment liquid having a buffering action, as shown in FIG. 4, from the surface of the hydrogen storage alloy particles (1), a constituent element (La) in a metal state or an oxide state (La) is formed. , Ni, Mn, etc.) are evenly eluted in the treatment liquid (3), and the desired activity cannot be obtained due to the elution of nickel that should contribute to the activity improvement.

[0006]

Means for Solving the Problems] Therefore, in the present invention, as the processing liquid to be used for surface modification of the hydrogen storage alloy particles, the first and having a buffering action containing nickel ions
An acidic treatment liquid whose pH is adjusted to 4.1 to 5 is adopted. That is, in the production of the hydrogen storage alloy powder, after crushing the hydrogen storage alloy powder to prepare the hydrogen storage alloy powder, the initial pH of the hydrogen storage alloy powder containing nickel ions and having a buffering action is 4 Surface treatment with an acid treatment liquid adjusted to 0.1 to 5 is performed.

As described above, in the surface treatment of hydrogen storage alloy particles using an acidic treatment liquid containing nickel ions and having a buffering action, the acid coating of the treatment liquid removes the oxide film on the surface of the particles. At the same time, the dissolution of the rare earth element exposes a metal surface such as nickel on the particle surface. At this time, the buffering action of the treatment liquid keeps the pH of the treatment liquid substantially constant, uniformizes the surface modification, and suppresses the precipitation of hydroxide. Here, the treatment liquid contains nickel ions in advance,
Since the amount of nickel ions that can be present in the treatment liquid is limited, the elution of nickel from the particle surface is suppressed.
As a result, a nickel-enriched layer is formed on the surface layer of the hydrogen storage alloy particles, and for example, in the surface layer within a depth of 10 nm, the relative ratio of nickel to all constituent elements is 75.
It becomes a high value of atm% or more. Nickel in the surface layer portion of the hydrogen storage alloy particles contributes to the electrochemical hydrogen absorption / dissociation reaction on the surface of the particle in terms of both conductivity and catalytic activity.

A treatment liquid having a pH of less than 1 may corrode the inside of the alloy particles, and a treatment liquid having a pH of more than 5 may not provide a high surface modification effect.

The treatment liquid is an acidic solution having a buffering action and an additive containing nickel is added, and the concentration of the additive is preferably set to 0.001 mol / l or more. If the concentration of the additive is less than 0.001 mol / l, nickel elution cannot be suppressed with high effect. However, when the concentration of the additive exceeds 0.01 mol / l, the effect is saturated. Therefore, the concentration of the additive is preferably 0.001 mol / l to 0.01 mol / l.

[0010]

According to the present invention, a hydrogen storage alloy powder and a hydrogen storage alloy electrode exhibiting high activity and gas absorption ability can be obtained by forming a nickel-enriched layer.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. The hydrogen-absorbing alloy powder according to the present invention is, as described below, subjected to surface treatment with an acidic treatment liquid containing nickel ions and having a buffering action, and as a result of the surface treatment, the hydrogen-absorbing alloy particles are The relative ratio of nickel to all the constituent elements is 75 atm% or more in the surface layer portion within a depth of 10 nm. Here, the hydrogen storage alloy particles include AB ₅ type rare earth hydrogen storage alloys, AB ₂ type non-rare earth hydrogen storage alloys,
For example, MmNi _3.3 CoMn _0.5 Al _0.2 , ZrNi _1.2 V
_{It is formed of 0.2} Mn _0.6 , ZrLa _0.05 Ni _1.2 V _0.2 Mn _{0.6, and the} like.

FIG. 3 shows a structure of a nickel-hydrogen secondary battery using the above hydrogen storage alloy powder as a negative electrode material. The positive electrode (11), the negative electrode (12), the separator (13) and the positive electrode lead ( 14), negative lead (15), positive external terminal (16), negative can
(17), the sealing lid (18) and the like constitute a nickel-hydrogen secondary battery having a sealed structure. The positive electrode (11) and the negative electrode (12) are housed in a negative electrode can (17) in a spirally wound state via a separator (13), and the positive electrode (11) is a positive electrode lead (1).
4) to the sealing lid (18) and the negative electrode (12) to the negative electrode lead (15).
It is connected to the negative electrode can (17) via. An insulating packing (20) is attached to the joint between the negative electrode can (17) and the sealing lid (18) to seal the battery. Positive external terminal (1
A coil spring (19) is provided between 6) and the sealing lid (18). The coil spring (19) is compressed when the internal pressure of the battery rises abnormally, and releases the gas inside the battery to the atmosphere.

In the manufacture of the above nickel-hydrogen secondary battery, as shown in FIG. 1, first, an ingot of a hydrogen storage alloy having a predetermined composition is prepared, and then the particle size is 5 μm.
To 500 μm to produce a hydrogen storage alloy powder
(Process P1). Next, the hydrogen storage alloy powder is immersed in an acidic treatment liquid containing nickel ions and having a buffering action, and stirred for about 20 minutes to subject the hydrogen storage alloy particles to a surface treatment. As the solution having a buffering action, a solution obtained by dissolving a weak acid and a salt of the weak acid in a molar ratio of 1: 9 to 9: 1,
For example, a combination of citric acid and citrate, a combination of phosphoric acid and phosphate, a combination of malic acid and malate, a combination of phthalic acid and phthalate, a combination of oxalic acid and oxalate, etc. can be adopted. Therefore, sodium, potassium, lithium or the like can be used as the cation of the salt. It is desirable to adjust the pH of the treatment liquid to 1-5. Then, metallic nickel, nickel chloride, nickel iodide, or the like is added to these acidic solutions to contain nickel ions. It is desirable to set the concentration of the additive to 0.001 mol / l or more. Then, the hydrogen storage alloy powder is washed with water and dried to obtain the surface-treated alloy powder according to the present invention.

After that, the nickel-hydrogen secondary battery shown in FIG. 3 is assembled (process P3). First, the hydrogen storage alloy powder obtained through the process P2 and an aqueous solution of a binder such as PTFE are mixed to prepare a paste, and the paste is applied to both sides of a nickel-plated base made of punching metal. After being applied and dried at room temperature, it is cut into a predetermined size to prepare a hydrogen storage alloy electrode. Then, using the hydrogen storage alloy electrode as a negative electrode, a positive electrode dominant nickel-hydrogen battery (for example, battery capacity 1000 mAh) having a structure shown in FIG. 3 is manufactured. A sintered nickel electrode can be used as the positive electrode, an alkali-resistant nonwoven fabric can be used as the separator, and a 30 wt% potassium hydroxide aqueous solution can be used as the electrolytic solution.

Surface treatment of the above hydrogen storage alloy powder (process P
In 2), the pH of the treatment liquid is kept substantially constant by its buffering action, so that the surface modification of the hydrogen-absorbing alloy particles is performed uniformly, and the precipitation of hydroxide is suppressed, so that it is better than before. High activity and gas absorption capacity are obtained.

As shown in FIG. 2, hydrogen storage alloy particles (1)
Although rare earth elements such as La as well as metals such as Ni and Mn are eluted from the surface of the treatment solution, the treatment solution (2) contains nickel ions in advance, and nickel ions that may be present in the treatment solution are present. Since the amount of nickel is limited, the elution of nickel from the particle surface is suppressed. By elution of the rare earth element, a metal surface appears on the surface of the hydrogen storage alloy particles (1), and the elution of nickel from the particle surface is suppressed as described above, and the surface layer of the hydrogen storage alloy particles is rich in nickel. Since the converted layer is formed, the electrochemical catalytic activity and the gas absorption capacity of the hydrogen storage alloy can be improved.

FIG. 5 and FIG. 6 show the results of experiments conducted to confirm the effects of the present invention. In the experiment, a hydrogen storage alloy powder having a composition of MmNi _3.3 CoMn _0.5 Al _0.2 was used, and 50 g of the hydrogen storage alloy powder was immersed in each treatment liquid (100 ml) shown in FIG. 5, stirred for 20 minutes, and washed with water. And dried. Next, a test electrode was prepared using each hydrogen storage alloy powder after the treatment, and a test cell having the test electrode as a negative electrode was assembled. Then, charge and discharge were repeated using the test cell to measure the discharge capacity.

FIG. 5 shows 1 obtained during repeated charging and discharging.
It represents the discharge capacity at the cycle, the maximum discharge capacity, and the ratio (%) of the discharge capacity at the first cycle to the maximum capacity, that is, the initial activation rate.

In Experiment Nos. 1 to 3, a solution of citric acid and sodium citrate was used as an acidic solution having a buffering action, and nickel chloride, nickel iodide, or nickel metal was added as an additive in three kinds of treatments. Surface treatment was performed with the liquid. The concentration of each additive was 0.1M (mo
l / l). On the other hand, in Experiment No. 4, a treatment liquid in which no additive is added to the acidic solution having a buffer action is used. In any of Experiment Nos. 1 to 4, there was no great change in the pH before and after the treatment due to the buffering effect of the treatment solution, but the initial activation rates obtained in Experiment Nos. 1 to 3 were obtained in Experiment No. 4. The value obtained by using the additive is apparent. On the other hand, Experiment Nos. 5 and 6 use an acidic solution having no buffering action, and show a low initial activation rate regardless of whether or not the additive is added. In this case, the pH is greatly increased before and after the treatment.

Experiment Nos. 7 and 8 used a solution of phosphoric acid and sodium phosphate as an acidic solution having a buffer action. In Experiment No. 7 in which nickel chloride was added as an additive, the additive was added. A high initial activation rate is obtained as compared to the case of Experiment No. 8 in which no addition was made. Further, in Experiment Nos. 9 and 10, a solution of malic acid and sodium malate was used as the acidic solution having a buffering action. In Experiment No. 9 in which nickel chloride was added as an additive, the additive was added. A high initial activation rate is obtained as compared with the case of Experiment No. 10 which did not exist. Therefore, it is proved that the acidic solution having a buffering effect is not limited to the solution of citric acid and sodium citrate, but the solution of phosphoric acid and sodium phosphate and the solution of malic acid and sodium malate are also effective.

Further, in Experiment Nos. 11 to 13, the concentration of the additive (nickel chloride) to be added to the solution of citric acid and sodium citrate was changed to 0.001M, 0.01M and 0.1M. , The concentration of additives is 0.001M
In contrast, a higher initial activation rate was obtained than in the conventional example of Experiment No. 4, but a sufficiently high initial activation rate was obtained by increasing the concentration to 0.01M. But,
Even if the concentration is increased to 0.1 M, the initial activation rate does not increase any more, and it is saturated. Therefore, it can be said that the concentration of the additive is preferably in the range of 0.001M to 0.01M.

FIG. 6 is a transmission electron microscope-quantitative analyzer (TEM-EDX) used to measure the depth of each hydrogen storage alloy particle from the surface to a depth of 5 nm, 10 nm, and the nickel ratio at the particle center (bulk). It represents the result of measuring (the proportion of nickel in all elements, atm%). The experiment number 1 corresponding to the present invention is the experiment number 4 corresponding to the conventional example.
Compared with Nos. 5 and 5, the nickel ratio was high at both the depths of 5 nm and 10 nm, and it is clear that the elution of nickel is suppressed by the surface treatment using the treatment liquid of the present invention. At the center of the hydrogen storage alloy particles, a value corresponding to the original nickel ratio of the hydrogen storage alloy was obtained.

Also, in Experiment No. 7 corresponding to the present invention, the depth is 5 nm as compared with Experiment No. 8 corresponding to the conventional example.
And the nickel ratio at 10 nm is large, and it is clear that the elution of nickel is suppressed. Further, it is apparent that the elution of nickel is also suppressed in Experiment No. 11 corresponding to the present invention.

From the above results, the hydrogen storage alloy particles have a depth of 10 n from the surface by the surface treatment using the acidic treatment liquid containing nickel ions and having a buffering action.
The nickel ratio becomes 75 atm% or more in the surface layer portion within m, which proves that the initial activity and gas absorption capacity of the hydrogen storage alloy electrode are improved.

The above description of the embodiments is for explaining the present invention and should not be construed as limiting the invention described in the claims or reducing the scope.
Further, it goes without saying that the configuration of each part of the present invention is not limited to the above-described embodiment, and various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a process drawing showing a method for producing a hydrogen storage alloy electrode according to the present invention.

FIG. 2 is a diagram illustrating the action of an acidic treatment liquid containing nickel ions.

FIG. 3 is a cross-sectional view of a nickel-hydrogen secondary battery.

FIG. 4 is a diagram for explaining the action of an acidic treatment liquid that does not contain nickel ions.

FIG. 5 is a chart showing the results of an experiment conducted to confirm the effect of the present invention.

FIG. 6 is another diagram of the same as above.

[Explanation of symbols]

(1) Hydrogen storage alloy particles (2) Treatment liquid (11) Positive electrode (12) Negative electrode (13) Separator

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kozo Nogami, 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Denki Co., Ltd. (72) Ikuro Yonezu 2-chome, Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-10-12233 (JP, A) Hei 8-291391 (JP, A) International publication 95/023435 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22F 1/00 B22F 5/00 H01M 4/24 H01M 4 / 26 H01M 4/38

Claims (3)

(57) [Claims] 1. A hydrogen storage alloy powder is produced by crushing a lump of hydrogen storage alloy, and the initial pH of the hydrogen storage alloy powder containing nickel ions and having a buffering action is 4.
A method for producing a hydrogen storage alloy powder, which comprises subjecting a surface treatment with an acidic treatment liquid adjusted to 1 to 5 . 2. A treatment liquid, an acidic solution having a buffering action, a liquid obtained by adding an additive containing nickel, the concentration of the additive is set to more than 0.001mol / l 請
The method for producing a hydrogen storage alloy powder according to claim 1 . 3. A buffered acidic solution is malic acid.
The solution according to claim 2, which is a solution of maltate and malate.
Method for producing hydrogen storage alloy powder of.