JPH09259875A - Manufacture of hydrogen absorbing alloy electrode, and metal hydroxide storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep strength to suppress the reduction in discharge capacity by holding a prescribed starting material mixture by an active material support body, and sintering it at a specified temperature to form an electrode in the formation of the electrode having a hydrogen storage alloy containing Mn. SOLUTION: A paste (e.g. polyethylene oxide), and Ni or one or more Ni compounds preferably selected from NiO, Ni(NO3 )2 , NiCO3 and Ni(OH)2 or a Ni-contained alloy, preferably NiMn alloy or Ni-Fe alloy, are mixed to a hydrogen storage alloy containing Mn [e.g. MnNi3.4 Co0.8 Mn0.6 Al0.2 (Mn is a mixture of rare earth metal)] to manufacture a mixture. This mixture is held by an active material support body (e.g. a metallic porous core boy plated with Ni), and then sintered at 680-780 deg.C to from an electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hydrogen storage alloy electrode using a hydrogen storage alloy which electrochemically stores and releases hydrogen as a negative electrode material, and more particularly to a method for manufacturing a sintered hydrogen storage alloy electrode. The present invention relates to an improved method and a metal hydride storage battery using a sintered hydrogen storage alloy electrode.

[0002]

2. Description of the Related Art Recent advances in electronics technology have been remarkable and will continue to accelerate. Along with this, portable and cordless electronic devices have been developed, and at the same time, there has been a strong demand for the development of small, lightweight, high-energy-density, high-performance secondary batteries as power supplies for these devices. Therefore, a metal hydride storage battery using a hydrogen storage alloy for the negative electrode has recently attracted particular attention as a clean power source having a higher capacity, higher density, and a higher capacity than nickel cadmium storage batteries, lead storage batteries, and the like.

By the way, as a hydrogen storage alloy electrode for an alkaline storage battery, a slurry is prepared by mixing a hydrogen storage alloy with polyethylene oxide, polyvinyl alcohol or the like as a binder, and then forming the slurry into a conductive core such as punching metal. A so-called non-sintered hydrogen storage alloy electrode, which is manufactured by applying it to the body, is generally used.

However, in these non-sintered hydrogen storage alloy electrodes, in order to hold the hydrogen storage alloy in the conductive core, the above-mentioned sizing agent is used between the hydrogen storage alloy particles and in the hydrogen storage alloy. And the conductive core must be interposed. However, since the above-mentioned paste is insulative, a decrease in discharge capacity cannot be avoided.

Therefore, as a solution to this problem, the method of manufacturing the electrode may be changed from the non-sintering method to the sintering method.
It is proposed in Japanese Patent No. 12766. In this publication,
Hydrogen storage alloys with Co, Ni, TiN as sintering aids
After mixing powders such as i _X , and then press-molding the mixed powder with the metal perforated plate placed at the center, the mixed powder is sintered at a temperature of 800 ° C or 950 ° C in a vacuum or an inert atmosphere. By doing so, a method for obtaining an electrode having a high strength as a sintered body is disclosed.

[0006]

However, the above-mentioned C
When powders such as o, Ni, and TiNi _x are mixed with a hydrogen storage alloy containing Mn and then sintered, Mn in the hydrogen storage alloy flows out from the alloy, so that the composition of the alloy is significantly different from the desired composition. There has been a problem that the discharge capacity of the electrode deviates, and the discharge capacity at the time of high rate discharge is reduced.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a hydrogen storage alloy electrode which suppresses a decrease in discharge capacity while sufficiently maintaining the strength of the electrode. Is the subject of.

[0008]

A method of manufacturing a hydrogen storage alloy electrode according to the present invention is a method for preparing a mixture by mixing a hydrogen storage alloy containing Mn with a sizing agent and metallic Ni or a Ni compound or an alloy containing Ni. And a step of obtaining the electrode by holding the mixture on an active material support and then sintering the mixture at a temperature of 680 ° C. or higher and 780 ° C. or lower in an inert atmosphere, a reducing atmosphere or a vacuum. It is characterized by that.

[0009]

When a mixture of a hydrogen storage alloy containing Mn and metallic Ni or a Ni compound or an alloy containing Ni is sintered at a high temperature, Mn in the hydrogen storage alloy easily flows out from the alloy, and the composition of the alloy becomes Significant deviations from the desired composition. Then, as a result of examining the temperature condition for sintering, 680
It was found that a hydrogen storage alloy having excellent electrode characteristics can be obtained by heat treatment in a relatively low temperature range of ˜780 ° C. This is because Ni was not sufficiently sintered under the heat treatment temperature condition of 670 ° C. or lower, and the hydrogen storage alloy was significantly detached from the electrode. Or, when the metal reacts with the active material support metal, especially Mn in the hydrogen storage alloy flows out from the alloy, the composition of the hydrogen storage alloy is deviated, and as a result, the discharge capacity, especially the discharge capacity at high rate discharge It is thought that this will lead to a decrease in

In addition, added metal Ni, Ni compound, N
The mixing ratio of the alloy containing i is preferably 4 wt% or more and 20 wt% or less of Ni with respect to the hydrogen storage alloy in terms of metal amount. If this is less than 4% by weight,
The amount of the hydrogen storage alloy dropped from the electrode core was remarkable, which was an insufficient amount to hold the hydrogen storage alloy on the electrode.
This is because if the content exceeds 0% by weight, the retention of the hydrogen storage alloy is limited, but the electrochemical capacity as an electrode decreases.

[0011]

【Example】

(Example 1) Mm (mixture of rare earth elements): Ni: C
Each metal element of o: Mn: Al is 1: 3.4: 0.8:
A commercially available metal element was weighed so that the ratio was 0.6: 0.2, and a composition formula MmNi _3.4 C was obtained by an Ar atomizing method.
A hydrogen storage alloy ingot represented by o _0.8 Mn _0.6 Al _0.2 was prepared.

Next, this alloy ingot is made to have an average particle size of about 80 μm.
Mechanically crushed to 150μm or more, 25μ
Those having a particle size of m or less were removed by passing through a mesh to prepare a hydrogen storage alloy powder. [Preparation of Sintered Hydrogen Storage Alloy Electrode] 10% by weight of metal Ni powder with respect to the hydrogen storage alloy powder containing Mn
And about 1% by weight of polyethylene oxide are mixed, and an appropriate amount of water is slurried, and the slurry is applied to a nickel-plated metal open-core core as an active material support. After drying, 10% compression was performed to increase the packing density, and then reduction heat treatment was performed in hydrogen and argon mixed gas (hydrogen 4 vol%) for 3 hours at 720 ° C. to produce a sintered hydrogen storage alloy electrode, Called A.

[0013] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 2 An electrode B of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 680 ° C.

[0015] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 3 An electrode C of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 690 ° C.

[0017] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 4 An electrode D of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 700 ° C.

[0019] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 5 An electrode E of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 710 ° C.

[0021] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 6 An electrode F of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 730 ° C.

[0023] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

(Example 7) An electrode G of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 740 ° C.

[0025] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 8 An electrode H of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 750 ° C.

[0027] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

(Example 9) An electrode I of the present invention was prepared in the same manner as in Example 1 except that the heat treatment temperature was 760 ° C.

[0029] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

(Example 10) An electrode J of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was changed to 770 ° C.

[0031] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Example 11 An electrode K of the present invention was produced in the same manner as in Example 1 except that the heat treatment temperature was 780 ° C.

[0033] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

Comparative Example 1 A comparative electrode W was prepared in the same manner as in Example 1 except that the heat treatment was not performed.

Comparative Example 2 A comparative electrode X was prepared in the same manner as in Example 1 except that the heat treatment temperature was 790 ° C.

[0036] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.4 Al} 0.2
Therefore, outflow of Mn was observed with respect to the initial composition.

Comparative Example 3 A comparative electrode Y was prepared in the same manner as in Example 1 except that the heat treatment temperature was 800 ° C.

[0038] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.3 Al} 0.2
Therefore, outflow of Mn was observed with respect to the initial composition.

(Comparative Example 4) A comparative electrode Z was prepared in the same manner as in Example 1 except that the heat treatment temperature was 670 ° C.

[0040] The composition was the hydrogen storage alloy elemental analysis after the heat _{treatment, MmNi 3.4 Co 0.8 Mn 0.6 Al} 0.2
It was found that there was almost no change from that before the heat treatment.

[Experiment 1] In this experiment, the internal resistance, discharge capacity and operating voltage of the electrode A of the present invention and the comparative electrodes W and X were measured and compared.

Using the electrode A of the present invention and the comparative electrodes W and X, the following test cell was prepared.

Using the electrodes A, W and X as negative electrodes,
A known sintered Ni positive electrode having a sufficient discharge capacity with respect to the negative electrode capacity was placed on both sides of the negative electrode via a separator and then inserted into an outer can to have a nominal capacity of 1000 mA.
A nickel-metal hydride storage battery of AA size was manufactured.

After that, charge and discharge is carried out at room temperature under the following conditions:
Cycles were performed to stabilize the characteristics.

Charging is performed at a current value of 0.1 C (100 mA) for 12 hours, and then discharging is performed at a current value of 0.2 C (200 mA) until the final voltage reaches 0.8V. However, the rest time from discharging to the next charging was 1 hour.

Measurement of Internal Resistance Table 1 below shows the results of measuring the internal resistance of the AA size nickel-metal hydride storage battery under an alternating current method of 1 kHz.

Measurement of discharge capacity and operating voltage 12 at a current value of 0.1 C (100 mA) at room temperature
After charging for 1 hour, resting for 1 hour, then 0.2C (200
discharge at a current value of mA) until the final voltage becomes 1.0 V, and the discharge capacity at that time is measured.
The battery voltage (operating voltage) during discharging was measured, and the results are also shown in Table 1 below.

[0048]

[Table 1]

As is clear from Table 1, the electrode A of the present invention is
It is understood that is superior to the reference electrode X in the characteristics of discharge capacity and internal resistance. Further, it can be seen that the electrode A of the present invention is superior to the comparative electrode W in characteristics of internal resistance and operating voltage while maintaining the same discharge capacity.

This is 680 to 78 in the electrode A of the present invention.
Since sintering is performed in the temperature range of 0 ° C., Mn is
It is considered that the reduction of the discharge capacity and the increase of the internal resistance due to the elution of Al from the alloy were prevented and the operating voltage was increased because the sizing agent was removed.

[Experiment 2] In this experiment, electrodes A to A of the present invention were used.
The discharge capacities per 1 g of the hydrogen storage alloy were measured and compared for K and the comparative electrodes X to Z.

The following test cells were prepared using the electrodes A to K of the present invention and the comparative electrodes X to Z.

The electrodes A to K and the comparative electrodes X to Z (the hydrogen storage alloy amount was set to 1.0 g in each case).
Is used as a negative electrode, and a nickel hydroxide electrode having a sufficiently large capacity with respect to the expected capacity of the negative electrode is combined as a counter electrode, and a specific gravity of 1 containing potassium hydroxide and sodium hydroxide and lithium hydroxide is mainly used. A liquid-rich type test cell was prepared by sufficiently using the electrolytic solution of 0.30.

After that, charge and discharge is carried out at room temperature under the following conditions:
The result of measuring the discharge capacity after cycling is shown in FIG.
In addition, the data shown in FIG. 1 is a comparison for each maximum value.

Charging was carried out at a current value of 30 mA for 12 hours, then rested for 1 hour, and discharging was carried out at a current value of 60 mA until the final voltage reached 1.0V.

As is apparent from FIG. 1, the heat treatment temperature is 68.
Good characteristics are obtained at 0 to 780 ° C, and it is understood that when the temperature exceeds 780 ° C, the discharge capacity of the hydrogen storage alloy is remarkably reduced. In particular, the heat treatment is preferably performed in the range of 680 to 750 ° C, more preferably 710 to 730 ° C.

When the temperature was 670 ° C. or lower, the alloy was severely detached from the electrode, and measurement could not be performed.

From the above, as in the electrode of the present invention, 68
It is important to sinter at a temperature of 0 ° C or higher and 780 ° C or lower.

[Experiment 3] In this experiment, with respect to the electrode A of the present invention and the comparative electrode X, the same test cell as in [Experiment 2] was prepared and the discharge curves were compared.

Then, the result of measuring the relationship between the discharge capacity and the battery voltage under the following conditions at room temperature is shown in FIG.

Charging was carried out at a current value of 30 mA for 12 hours, then rested for 1 hour, and discharging was carried out at a current value of 60 mA until the final voltage reached 1.0V.

As is apparent from FIG. 2, the discharge capacity of the electrode A of the present invention is larger than that of the reference electrode X.

In this example, metallic Ni powder was used.
However, not limited to these, in an inert atmosphere or a reducing atmosphere
Any material that can be converted to metallic Ni by heat treatment in
For example, instead of metallic Ni powder, NiO, Ni (N
O_Three)_Two, NiCO_ThreeOr Ni (OH)_Two Using
Can be. In addition, NiO, Ni (NO_Three)_Two, NiCO _Three
And Ni (OH)_Two At least one selected from
You may use the above.

Also, instead of the metallic Ni powder, Ni--Mn is used.
Alloys or Ni-Fe alloys may be used.

In this embodiment, the heat treatment is carried out in a mixed gas of hydrogen and argon in an inert atmosphere or a reducing atmosphere. However, hydrogen gas or argon gas may be used alone,
Moreover, you may heat-process in a vacuum.

[0066]

As is apparent from the above, according to the production method of the present invention, a sintered hydrogen storage alloy in which the reduction of the discharge capacity is suppressed while the electrode strength is sufficiently maintained by a very simple method. An electrode is obtained and its industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between heat treatment temperature and discharge capacity.

FIG. 2 is a diagram showing a comparison of discharge curves of an electrode A of the present invention and a comparative electrode X.

Claims (5)

[Claims] 1. A method for producing a hydrogen storage alloy electrode comprising a hydrogen storage alloy containing Mn, wherein a hydrogen storage alloy containing Mn is mixed with a sizing agent and metal Ni or a Ni compound or an alloy containing Ni. To obtain a mixture, and after holding the mixture on an active material support, 680
And a step of obtaining an electrode by sintering at a temperature of 750 ° C. or higher and 780 ° C. or lower. 2. NiO, Ni as the Ni compound
(NO_Three)_Two, NiCO _ThreeAnd Ni (OH)_Two Select from
A contract characterized by using at least one kind of exposed
The method for producing a hydrogen storage alloy electrode according to claim 1. 3. The alloy containing Ni is Ni--
The method for producing a hydrogen storage alloy electrode according to claim 1, wherein a Mn alloy or a Ni-Fe alloy is used. 4. The mixing ratio of the metallic Ni or the Ni compound or the alloy containing Ni is calculated in terms of the metallic Ni amount.
The method for producing a hydrogen storage alloy electrode according to claim 1, wherein the content is 4% by weight or more and 20% by weight or less with respect to the hydrogen storage alloy containing Mn. 5. A metal hydride storage battery, wherein the hydrogen storage alloy electrode produced by the production method of claim 1 is used as a negative electrode.