JP3432870B2 - Method for producing metal hydride electrode - Google Patents

Description

Detailed Description of the Invention

[0001]

2. Description of the Related Art Lead-acid batteries and nickel-cadmium batteries have been widely used as storage batteries. However, in recent years, since it is possible to have a lighter weight and a higher capacity than these batteries, a negative electrode is a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, which is a negative electrode active material, at normal pressure. And a metal oxide having a metal oxide such as nickel hydroxide as a positive electrode active material is used as a positive electrode.
Hydrogen alkaline storage batteries are receiving attention.

Conventionally, in order to improve the battery characteristics of this metal-hydrogen alkaline storage battery, a hydrogen storage alloy having various surface modification treatments has been used as a negative electrode material. For example, in Japanese Examined Patent Publication No. 4-79474, the surface of the hydrogen storage alloy is treated with an alkaline aqueous solution. According to this method, a nickel-rich layer is formed on the surface of the hydrogen storage alloy by performing the alkali treatment.

Since nickel serves as a catalyst for the reduction reaction of oxygen, a nickel-rich layer is formed on the surface of the hydrogen storage alloy, so that the oxygen gas released from the positive electrode during overcharge is smoothly absorbed on the alloy surface. As a result, the increase in battery internal pressure is suppressed, and the charge / discharge cycle characteristics are improved. Further, JP-A-3-98259 discloses a method of surface-treating a hydrogen storage alloy with heated water at 60 ° C. or higher. Also in the hydrogen storage alloy treated by this method, a nickel-rich layer is formed on the surface, and the charge / discharge cycle characteristics are improved in the same manner as above.

However, these surface-treated alloys are excellent in oxygen gas absorption ability, and thus are excellent in charge / discharge cycle life. However, since hydroxide is formed on the surface of the hydrogen storage alloy, the hydrogen storage alloy is formed. There is a problem that the contact resistance between them is large and the activation is poor, and especially the high rate charge / discharge characteristics and the low temperature discharge characteristics at the beginning of the charge / discharge cycle are poor. like this,
The following methods have been proposed as methods for improving the high rate discharge characteristics at the initial stage of the charge / discharge cycle and the low temperature discharge characteristics. Method disclosed in JP-A-3-152868 In this method, a dense oxygen film that inhibits the initial activation of the alloy is removed by acid treatment, and then alkali treatment is performed to achieve high rate charge / discharge. It is disclosed that a metal hydride electrode having excellent gas absorption ability can be realized. Method disclosed in JP-A-5-135797 In this method, by treating the negative electrode with an alkaline aqueous solution to which a soluble hydride such as sodium borohydride, which is a reducing agent, is treated, the activation is excellent and the battery internal pressure rises. It is disclosed that an electrode in which is suppressed can be realized. As described above, it is considered that the reason why the activity is improved by adding the reducing agent is that the hydrogen generated from the reducing agent is partially occluded in the hydrogen.

[0005]

However, even with the above processing method, the following problems occur. Problems of the method disclosed in JP-A-3-152868. When this treatment method is used, when the acid treatment is followed by the alkali treatment, the activity is lowered as compared with the case of only the acid treatment, and low temperature discharge is performed. There is a problem that the characteristics are not sufficient and further improvement is necessary. Problems of the method disclosed in Japanese Patent Laid-Open No. 135797/1993 Even in this method, the activity is not sufficiently improved and further improvement is desired.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing a metal hydride electrode having a long charge / discharge cycle life and high activity.

[0007]

In order to achieve the above object, in the present invention, in a method for producing a metal hydride electrode using a hydrogen storage alloy as a negative electrode material, a nonuniform strain is 3.5.
PH value of 0.5 to 10 for hydrogen storage alloys of 10 ⁻³ or less
The method is characterized by having a step of performing surface treatment with an aqueous solution obtained by adding a reducing agent to the acidic aqueous solution of 6.0.

Further, the step of performing the surface treatment with the acidic aqueous solution is performed when the hydrogen storage alloy ingot is pulverized. Further, the step of performing the surface treatment with the acidic aqueous solution is performed on the hydrogen storage alloy powder before producing the electrode. Further, the surface treatment with the acidic aqueous solution is performed on the electrode.

[0009]

By carrying out the manufacturing including the steps as described above, the following operations occur. When the hydrogen storage alloy is surface-treated with an acidic aqueous solution having a pH value of 0.5 to 6.0, the surface of the hydrogen storage alloy dissolves while generating hydrogen. Hydrogen generated by the melting of this alloy is again stored in the hydrogen storage alloy. When hydrogen is absorbed by the hydrogen storage alloy, a crack is generated in the metal, a new active surface is generated, and the activity of the alloy is improved. As described above, when the activity of the alloy is improved, the high rate discharge characteristic and the low temperature discharge characteristic are improved.

Further, the hydrogen generated from the reducing agent is also absorbed, and this hydrogen is also absorbed by the alloy. In the case of the present invention, hydrogen is generated from the alloy and the reducing agent, and moreover, since the reducing agent is added to the acidic solution, hydrogen is easily generated from the reducing agent. Therefore, a large amount of hydrogen is generated, the hydrogen is easily absorbed in the alloy, and the activity of the alloy is increased.

Since the hydrogen storage alloy of the present invention has a non-uniform strain of 3.5 × 10 ⁻³ or less, it has excellent crystallinity and does not cause large cracks even when subjected to acid treatment. Further, even when the charge / discharge cycle is advanced, pulverization does not proceed too much, and the discharge cycle life is not shortened. Further, the components of the other alloys have a higher solubility in the acidic region than nickel, which is the main component of the hydrogen storage alloy, and are selectively dissolved by immersion in acid, and the surface of the hydrogen storage alloy is rich in nickel. A layer is formed. Since nickel serves as a catalyst for absorbing oxygen gas in the hydrogen storage alloy, absorption of oxygen gas during overcharging proceeds smoothly in this nickel-rich layer, and increase in battery internal pressure is suppressed. The suppression of the rise in battery internal pressure is effective in preventing leakage from the safety valve and improving the charge / discharge cycle life.

The above-mentioned non-uniform strain is a value defined as follows. This is one of the causes of the phenomenon that the Debye ring becomes broad when it is measured with a Laue camera or the like, and it is defined by the following formula 1.

[0013]

[Equation 1]

[0014]

EXAMPLES Examples according to an example of the present invention will be described below. (Example 1) [Production method of electrohydrogen storage alloy electrode] First, a hydrogen storage alloy powder for an electrode was produced as follows.

Commercially available misch metal Mm (La, Ce,
A mixture of rare earth elements such as Nd and Pr), Ni, Co, and Mn are used, and the element ratio is Mm: Ni: Co: Al: Mn.
Were weighed and mixed so that the ratio was 1: 3.4: 0.8: 0.2: 0.6. Next, this mixture is melted in a high-frequency melting furnace under an argon-inert atmosphere and cooled to obtain Mm.
A hydrogen storage alloy ingot represented by Ni _3.4 Co _0.8 Al _0.2 Mn _0.6 was produced. The non-uniform strain of the hydrogen storage alloy at this time is 5.4 × 10 ⁻³ , and this hydrogen storage alloy ingot is hereinafter referred to as hydrogen storage alloy ingot (M ₁ ).

Next, the hydrogen-absorbing alloy ingot (M ₁ ) is annealed in an inert gas at 1000 ° C. for 8 hours.
The non-uniform strain of the hydrogen storage alloy ingot after the annealing treatment is 2.5 × 10 ⁻³ , and this hydrogen storage alloy powder is hereinafter referred to as hydrogen storage alloy ingot (M ₂ ). This hydrogen-absorbing alloy ingot (M ₂ ) was once treated with an inert gas to a particle size of 500
Average particle size of 150 μm using a ball mill in a solution in which 0.3% of sodium borohydride as a reducing agent is dissolved in hydrochloric acid having a pH of 1.0
It was crushed to the following. After pulverization, it was thoroughly washed with ion-exchanged water and dried to prepare a hydrogen storage alloy powder for electrodes. The processing temperature during pulverization is room temperature.

5% by weight of polytetrafluoroethylene powder as a binder was added to the hydrogen storage alloy powder for an electrode thus prepared and kneaded to prepare a paste. This paste was pressure-bonded to both sides of a current collector made of punching metal and then pressed to produce a metal hydride electrode. [Assembly of Battery] The metal hydride electrode produced as described above and a known sintered nickel electrode were wound with a separator made of a non-woven fabric interposed therebetween to produce an electrode group. This electrode group was inserted into an outer can, and a 30 wt% potassium hydroxide aqueous solution was further poured into the outer can, and then the outer can was sealed to produce a cylindrical nickel-hydrogen storage battery having a theoretical capacity of 1000 mAh. .

The battery produced in this manner is described below (A
₁ ) Called battery. (Example 2) The above hydrogen storage alloy ingot (M ₂ ) was pulverized in an inert gas so that the average particle diameter was 150 μm or less, and the pulverized hydrogen storage alloy was treated with hydrochloric acid having a pH of 1.0. On the other hand, it was immersed in a solution in which sodium borohydride was dissolved by 0.3% for 20 minutes, then sufficiently washed with ion-exchanged water and dried to prepare a hydrogen storage alloy powder for electrodes. An electrode and a battery were produced in the same manner as in Example 1 using the hydrogen storage alloy powder for an electrode thus produced.

The battery produced in this manner is described below (A ₂ )
It is called a battery. (Comparative Example 1) pH as a treatment solution used when pulverizing an alloy
= 1.0 for sodium borohydride against hydrochloric acid of 1.0.
A hydrogen storage alloy powder for an electrode was prepared in the same manner as in Example 1 except that a 0.3% sodium borohydride aqueous solution was used instead of the 3% dissolved solution. Using the above, an electrode and a battery were produced in the same manner as in Example 1 above.

The battery thus manufactured is hereinafter referred to as a (X ₁ ) battery. (Comparative Example 2) As a treatment solution used when pulverizing an alloy, p
Hydrogen storage for electrodes was carried out in the same manner as in Example 1 except that hydrochloric acid having a pH of 1 was used in place of a solution prepared by dissolving 0.3% of sodium borohydride in hydrochloric acid having a H of 1.0. An alloy powder was prepared, and an electrode and a battery were prepared in the same manner as in Example 1 using the hydrogen storage alloy powder for an electrode.

The battery thus produced is hereinafter referred to as a (X ₂ ) battery. (Comparative Example 3) A hydrogen storage alloy powder for electrodes was prepared in the same manner as in Example 1 except that the hydrogen storage alloy powder (M ₁ ) was not annealed. Using the above, an electrode and a battery were prepared in the same manner as in Example 1 above.

The battery thus manufactured is hereinafter referred to as (X ₃ ). (Comparative Example 4) The hydrogen-absorbing alloy powder (M ₁ ) was not annealed, and sodium borohydride was added to hydrochloric acid having a pH of 1.0 as a treatment solution to be used for pulverizing the alloy. A hydrogen storage alloy powder for an electrode was prepared in the same manner as in Example 1 except that a 0.3% sodium borohydride aqueous solution was used instead of the 0.3% dissolved solution. An electrode and a battery were prepared using the powder in the same manner as in Example 1 above. The battery thus manufactured is hereinafter referred to as (X ₄ ) battery. (Comparative Example 5) The hydrogen-absorbing alloy powder (M ₁ ) was not annealed, and sodium borohydride was added to hydrochloric acid having a pH of 1.0 as a treatment solution to be used for pulverizing the alloy. A hydrogen storage alloy powder for electrodes was prepared in the same manner as in Example 1 except that hydrochloric acid having a pH of 1 was used in place of the 0.3% dissolved solution, and the hydrogen storage alloy powder for electrodes was used. An electrode and a battery were prepared in the same manner as in Example 1 above. The battery thus produced is hereinafter referred to as (X ₅ ) battery. (Comparative Example 6) In the immersion treatment of the alloy after crushing, as a treatment solution, 0.3% of sodium borohydride was dissolved in hydrochloric acid having a pH of 1.0, instead of 0.3%. %
An electrode hydrogen storage alloy powder was prepared in the same manner as in Example 2 except that an aqueous sodium borohydride solution was used, and the electrode hydrogen storage alloy powder was used in the same manner as in Example 1 above to prepare an electrode and a battery. Was prepared.

The battery produced in this way is described below (X ₆ )
It is called a battery. (Comparative Example 7) Instead of a solution prepared by dissolving 0.3% of sodium borohydride in hydrochloric acid having a pH value of 1.0 as a treatment solution for dipping the alloy after grinding, pH =
An electrode hydrogen storage alloy powder was prepared in the same manner as in Example 2 except that 1.0 hydrogen chloride was used, and the electrode and battery were prepared in the same manner as in Example 1 using the hydrogen storage alloy powder for electrode. Was prepared.

The battery thus produced is hereinafter referred to as a (X ₇ ) battery. (Comparative Example 8) The hydrogen storage alloy ingot (M ₂ ) was crushed in an inert gas so that the average particle size was 150 μm or less, and the crushed hydrogen storage alloy was used as it was as a hydrogen storage alloy for electrodes. Using the hydrogen storage alloy powder for electrodes, electrodes and batteries were prepared in the same manner as in Example 1 above.

The battery thus produced is described below.
(X ₈₎ is referred to as a battery. Regarding the above batteries, the non-uniform strain of the hydrogen storage alloy and the surface treatment method of the alloy are listed, which is shown in Table 1 below.

[0026]

[Table 1]

(Experiment 1) (A ₁ ) of the above embodiment,
High rate discharge characteristics, low temperature discharge characteristics and charge / discharge cycle life were examined using the (A ₂ ) battery and the (X ₁ ) to (X ₈ ) batteries of Comparative Examples. The results are shown in Tables 2 to 2 below. 4 shows.
Prior to the experiment, each battery was activated by the following method.

Each battery was charged at 100 mA for 16 hours,
After resting for 1 hour, discharging was performed at 200 mA until the voltage became 1.0 V, and resting for 1 hour was repeated 3 cycles at room temperature. The conditions for each of the experiments carried out on the cells thus activated are shown below. [High Rate Discharge Characteristic] At room temperature, the battery was charged at 100 mA for 16 hours, rested for 1 hour, then discharged at 4000 mA to 1.0 V, and the discharge capacity of each battery was measured. [Low-temperature discharge characteristics] Charged at 100 mA for 16 hours at room temperature, rested at -10 ° C for 3 hours, and then at -10 ° C, 100
The battery was discharged at 0 mA to 1.0 V, and the discharge capacity of each battery was measured. [Charge / Discharge Cycle Characteristics] At room temperature, the battery was charged at 1500 mA for 48 minutes, rested for 1 hour, and then at 1500 mA for 1.
Discharge until it reaches 0 V, and then perform a charge-discharge cycle of resting for 1 hour until the battery capacity reaches 500 mAh.
Repeatedly, the number of cycles was examined.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

The high rate discharge characteristics, the low temperature discharge characteristics and the charge / discharge cycle life of (A ₁ ), (A ₂ )
The battery showed excellent characteristics. Further, the short charging / discharging cycle life of the (X ₃ ) battery which has been subjected to the same surface treatment has a large non-uniform strain, which causes excessive pulverization at the time of hydrogen absorption and deterioration of the alloy due to oxidation. It is considered that the charging and discharging cycle characteristics progressed and the charging and discharging cycle characteristics deteriorated. (Experiment 2) The relationship between the pH value of the solution in which the reducing agent is dissolved and the high rate discharge characteristics was investigated, and the results are shown in FIG.

The experimental conditions of this experiment are as follows. Hydrogen storage alloy (M ₂ ) (non-uniform strain 2.5 × 10
^-3 ) The pH value of the solution in which sodium borohydride is dissolved at the time of preparing the treatment solution used for pulverization is from 0 to p
The electrode was changed to H = 9.0, the same as in Example 1 above,
A battery was prepared, and an experiment was performed under the same conditions as the measurement of the high rate charge / discharge characteristics in Experiment 1 above.

The solution in which sodium borohydride was used in this experiment was hydrochloric acid at 0 ≦ pH <7, and pH = 7.
Pure water was used, and a potassium hydroxide solution was used when 7 <pH ≦ 9, and 0.3% of sodium borohydride was dissolved in each solution. As is clear from FIG. 1, good high rate discharge characteristics were obtained when a treatment solution in which a reducing agent was dissolved in a solution having a pH value of 0.5 to 6.0 was used. (Experiment 3) The relationship between the pH value of the solution in which the reducing agent is dissolved and the charge / discharge cycle life was examined. The results are shown in FIG.

The experimental conditions for this experiment are as follows. As in Experiment 2 above, the pH value of the solution in which sodium borohydride is dissolved ranges from pH = 0 to pH = 9.
An electrode and a battery were manufactured by changing to 0, and the experiment was performed under the same conditions as the measurement of the charge / discharge cycle life in Experiment 1 above.
As is clear from FIG. 2, when the treatment solution prepared by dissolving the reducing agent in the solution having the pH value of 0.5 to 6.0 was used, good charge / discharge cycle life was obtained. (Experiment 4) From the experimental results of the charge-discharge cycle characteristics of Experiment 1 above, the (X ₃ ) battery was tested in spite of the fact that the surface-treated hydrogen storage alloy was used as the electrode material. The result was that the charge / discharge cycle life was shorter than that of the example battery.

It was thought that this might be due to the difference in the non-uniform strain of the hydrogen storage alloy, and the relationship between the magnitude of the non-uniform strain and the charge / discharge cycle life was investigated. The results are shown in FIG. The conditions of this experiment are as shown below. Using hydrogen storage alloys having different non-uniform strains, the same surface treatment, electrodes and batteries as in Example 1 were prepared, and experiments were conducted under the same conditions as the measurement of charge / discharge cycle characteristics in Experiment 1 above.

The non-uniform strain of the alloy was adjusted by the cooling rate during the alloy preparation and the annealing treatment. As is clear from FIG. 3, good values were obtained for alloys with a non-uniform strain of 3.5 × 10 ⁻³ or less. (Other matters) Regarding the type of reducing agent, similar effects can be obtained by using potassium borohydride, lithium aluminum hydride, sodium hypophosphite, potassium hypophosphite, formalin, etc. in addition to sodium borohydride. Has been confirmed by experiments. Regarding the type and pH of acid In the above examples, hydrochloric acid was used as the acid, but boric acid,
Even if other acids such as phosphoric acid and hydrofluoric acid are used, the pH is 0.5 to
It was confirmed experimentally that the same effect was obtained in the range of 6.0. Regarding the composition of the hydrogen storage alloy, if the hydrogen equilibrium pressure is about the same, it is considered that hydrogen storage will be performed similarly to the alloy used in this example. The composition is not limited to. Further, although the rare earth metal-based hydrogen storage alloy is used in the above-mentioned examples, the same effect is recognized in the titanium-based hydrogen storage alloy. In the above examples, the case of crushing the hydrogen-absorbing alloy ingot, or the case of performing the surface treatment on the hydrogen-absorbing alloy after crushing, the electrode was produced using the hydrogen-absorbing alloy without surface treatment. It has been confirmed by experiments that the same effect can be obtained by treating the hydrogen storage alloy after the electrode is manufactured.

[0038]

As described above, according to the present invention,
A large amount of hydrogen is generated from the hydrogen storage alloy and the reducing agent by performing the surface treatment with an acidic aqueous solution containing a reducing agent, and the hydrogen storage alloy also stores a large amount of hydrogen accordingly. The activity of the alloy was improved, and the high rate discharge characteristics and the low temperature discharge characteristics at the beginning of the charge / discharge cycle were improved. Further, since the hydrogen storage alloy used as the electrode material has a non-uniform strain of 3.5 × 10 ⁻³ or less, even if the charge / discharge cycle is repeated, pulverization does not proceed and the charge / discharge cycle life is shortened. We were able to extend the service life.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a pH value of a treatment solution and a high rate discharge characteristic.

FIG. 2 is a graph showing the relationship between the pH value of the treatment solution and the charge / discharge cycle life.

FIG. 3 is a graph showing the relationship between non-uniform strain and charge / discharge cycle life.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-132048 (JP, A) JP-A-4-121960 (JP, A) JP-A-3-152868 (JP, A) JP-A-5- 135797 (JP, A) JP-A-5-114403 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38

Claims (4)

(57) [Claims] 1. A method for producing a metal hydride electrode using a hydrogen storage alloy as a negative electrode material, wherein a pH value is 0.5 to 6 for a hydrogen storage alloy having a nonuniform strain of 3.5 × 10 ⁻³ or less. A method for producing a metal hydride storage battery electrode, comprising a step of performing a surface treatment with an aqueous solution obtained by adding a reducing agent to an acidic aqueous solution of 0.0. 2. The method for producing a metal hydride electrode according to claim 1, wherein the step of performing the surface treatment with the acidic aqueous solution is performed when the hydrogen storage alloy ingot is pulverized. 3. The method for producing a metal hydride electrode according to claim 1, wherein the step of performing the surface treatment with the acidic aqueous solution is performed on the hydrogen storage alloy powder before the electrode is produced. 4. The method for producing a metal hydride electrode according to claim 1, wherein the surface treatment with the acidic aqueous solution is performed on the electrode.