JP3500031B2 - Hydrogen storage alloy electrode and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of a metal-hydride storage battery such as an alkaline storage battery, and more particularly to a hydrogen storage alloy electrode excellent in initial activity.

[0002]

2. Description of the Related Art A metal-hydride storage battery such as a Ni-MH battery using a hydrogen storage alloy that stores and releases hydrogen reversibly as a negative electrode is known. The hydrogen storage alloy electrode is formed by mixing hydrogen storage alloy powder with a binder to form a paste, applying the paste to a collector such as punching metal, foam metal, or nickel mesh, and then performing sintering or drying. It is produced by A conductive material such as nickel powder may be mixed with the paste as needed.

[0003]

It is desirable that the metal-hydride storage battery maintain a high capacity from the beginning of the charge / discharge cycle to a long period of time. However, the hydrogen storage alloy electrode, which is the negative electrode of the storage battery, generally does not have sufficient hydrogen storage capacity in the initial stage. This is because the gas is adsorbed on the particle surface of the hydrogen storage alloy powder used for the hydrogen storage alloy electrode,
This is because a dense oxide film is likely to be formed. When an oxide film or the like is formed, a desired hydrogen storage capacity cannot be obtained, so it was necessary to perform an initial activation treatment to activate the particle surface of the hydrogen storage alloy powder.

JP-A-5-28989 (H01M 4 /
In 24), the hydrogen storage alloy particles are mixed with nickel fine powder of a conductive metal having a small particle size in a mortar to adhere nickel to the surface of the hydrogen storage alloy particles to increase the capacity of the hydrogen storage alloy. ing. However, since the oxide film is formed on the surface of the hydrogen storage alloy particles as described above, the conductive metal particles (44) attached as shown in FIG.
An oxide film (46) or the like may remain between the hydrogen storage alloy particles (42) and the hydrogen storage alloy particles (42).

An object of the present invention is to provide a hydrogen storage alloy electrode having excellent initial charge / discharge characteristics.

[0006]

In order to solve the above-mentioned problems, a hydrogen storage alloy electrode of the present invention is provided with conductive metal particles (40) on the surface of hydrogen storage alloy particles (40) containing Zr, Ni, V and Mn. A hydrogen storage alloy electrode (44) in which a hydrogen storage alloy powder (40) made by adhering 44) by a mechanochemical method in a reducing atmosphere containing carbon monoxide is integrated with a current collector. The oxygen concentration is 0.5% or less.
It is desirable that the conductive metal particles (44) contain at least one metal selected from the group consisting of Ni (nickel), Co (cobalt) and Cu (copper).

The hydrogen storage alloy powder (40) constituting the hydrogen storage alloy electrode is obtained by mixing the hydrogen storage alloy particles (42) and the conductive metal particles (44) and stirring in a reducing atmosphere containing carbon monoxide. Can be obtained by Further, the hydrogen storage alloy electrode can be manufactured by integrating the hydrogen storage alloy powder (40) having the conductive metal particles (44) attached to the surface of the particles with the current collector. It is desirable to stir the hydrogen storage alloy particles (42) and the conductive metal particles (44) by a mechanochemical method. Regarding the mechanochemical method,
More on this later. As the reducing atmosphere may include an atmosphere containing carbon monoxide. The method of integrating the current collector and the hydrogen storage alloy powder (40) is not particularly limited, and examples thereof include a method of mixing the binder and the hydrogen storage alloy powder and applying the mixture to the current collector. be able to.

[0008]

[Operation and effect] By stirring the hydrogen storage alloy particles and the conductive metal particles in a reducing atmosphere containing carbon monoxide , the oxide film and the like existing on the surface of the hydrogen storage alloy particles are removed, and the hydrogen storage alloy particles are removed. The surface of is activated.
Since the conductive metal particles adhere to the active surface of the hydrogen storage alloy particles from which the oxide film and the like have been removed, surface modification of the hydrogen storage alloy particles can be effectively performed. Further, the conductive metal particles directly adhere to the surface of the hydrogen storage alloy particles, whereby the conductivity of the hydrogen storage alloy powder can be dramatically improved.

When a hydrogen storage alloy powder, which has been effectively surface-modified, is integrated with a current collector to produce a hydrogen storage alloy electrode, the obtained hydrogen storage alloy electrode is excellent from the beginning of the charge / discharge cycle. Since it has excellent charge and discharge characteristics, it is possible to achieve improvement in the performance of the metal-hydride storage battery. Further, the hydrogen-absorbing alloy electrode, since the initial activity is high because it is made of hydrogen-absorbing alloy powder in which the conductive metal particles are directly attached to the surface of the hydrogen-absorbing alloy particles, it is possible to omit the conventional initial activation treatment or It can be simplified.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION When preparing the hydrogen storage alloy particles (42), the preparation method is not particularly limited,
Various methods can be used. For example, the cast alloy may be heat-treated and then crushed, or prepared by an atomizing method. The average particle size of the hydrogen storage alloy particles is 30μ
It is desirable that the thickness is adjusted to m to 80 μm.

The conductive metal particles (44) have an average particle size of about 10
It is desirable to use the one prepared so as to have a thickness of μm or less. When the average particle size is larger than 10 μm, the particle size of the hydrogen-absorbing alloy powder (40) to which the conductive metal particles are adhered is also large, and the number of contact points between the particles is reduced when the electrode is manufactured, and the conductivity is reduced. This is because the improvement effect is weakened. In addition, since the conductive metal does not store hydrogen, if the ratio of the conductive metal in the hydrogen storage alloy electrode is large, the capacity is reduced.

The hydrogen storage alloy particles (42) and the conductive metal particles (44) thus prepared are mixed and then stirred in a reducing atmosphere. The mixing may be performed in a reducing atmosphere. As the reducing gas contained in the reducing atmosphere, and the like carbon monoxide gas. It may be mixed with an inert gas such as argon gas to carbon monoxide gas. The hydrogen storage alloy particles (42) and the conductive metal particles (44) can be stirred by a mechanochemical method or the like. As a mechanochemical method, a mechanical alloying method can be mentioned. An example of the mechanical alloying processing device (50) is shown in FIGS. The device (50) comprises two ceramic-made cylindrical pots (54) (54) equidistant from the center of the turntable (52), and when the turntable rotates, the cylindrical pot Rotates about the direction opposite to that of the turntable. Inside the cylindrical pot (54),
As shown in FIG. 4, a predetermined amount of hydrogen storage alloy particles (42), conductive metal particles (44), and ceramic balls (56) are housed, and the atmosphere inside the pot is a reducing atmosphere. Has become. When the turntable (52) and the cylindrical pot (54) are respectively rotated in opposite directions, the hydrogen storage alloy particles (42) and the conductive metal particles (44) contained in the pot are agitated together with the ceramic balls. It is possible to obtain the hydrogen storage alloy powder (40) in which the hydrogen storage alloy particles are reduced and the surface is activated, and the conductive metal particles are directly attached to the activated surface of the hydrogen storage alloy particles. The rotation speed of the cylindrical pot is preferably 50 rpm to 200 rpm.

[0013]

Example A hydrogen storage alloy electrode was produced by the following method, and a charge / discharge cycle was performed to measure and compare the activation degree. Sample No. 1 Zr, Ni, V and Mn were weighed in a predetermined molar ratio, melted in an arc melting furnace in an argon atmosphere, and then allowed to cool naturally to have a composition of ZrNi1.1V0.2Mn0.7. An AB2 type hydrogen storage alloy was produced. The produced hydrogen storage alloy ingot was roughly crushed into 1 cm squares, crushed to 100 μm or less by a crushing mill in an air atmosphere, and then classified using a sieve so that the average particle size was 50 μm. When the oxygen concentration of the obtained hydrogen storage alloy powder was measured,
It was 0.6%.

50 g of the above hydrogen storage alloy powder and 2 g of Ni powder having an average particle size of 0.5 μm were mechanically alloyed by using the mechanochemical treatment device (50) shown in FIGS. 3 and 4. The mechanical alloying processing conditions are as follows. -Pot volume: 250 ml-Atmosphere inside the pot: Hydrogen gas-Ceramics balls: Diameter 5 mm, 50 pieces-Pot rotation speed: 80 rpm-Processing time: 20 hours

By carrying out the above treatment, as shown in FIG. 1, conductive metal particles are formed on the surface of the hydrogen storage alloy particles (42).
Hydrogen storage alloy powder (4) with Ni powder directly attached (4
0) was obtained. The oxygen concentration of the hydrogen storage alloy powder (40) was measured and found to be 0.08% (see Table 1). After mixing 0.5 g of the above hydrogen storage alloy powder with 0.1 g of the binder polytetrafluoroethylene (PTFE), the mixture was filled in a current collector (porous nickel foam) and pressurized at 1.2 ton / cm ^2. It was molded to prepare a disk-shaped hydrogen storage alloy electrode having a diameter of 20 mm (test sample No. 1).

[0016]

[Table 1]

For comparison with test sample No. 2, the same hydrogen storage alloy powder as sample No. 1 was prepared by mixing the hydrogen storage alloy particles in the pot without mixing the Ni powder and stirring the mixture. A hydrogen storage alloy electrode was produced by the method described above.

Sample No. 3 and Sample No. 4 Mechanical alloying treatment time was 5 hours, sample N
Same conditions as o.1 (No.3), same conditions as test No.2 (No.4)
Then, hydrogen storage alloy electrodes were prepared respectively. The oxygen concentration of each hydrogen storage alloy powder was measured, and the results were as shown in Table 1.

Test No. 5 and Test No. 6 Under the same conditions as Test No. 1 (No. 5) and Test No. 1, the inside of the pot of the mechanical alloying treatment was made an inert argon gas atmosphere which was not a reducing gas. Under the same conditions as in No. 2 (No. 6), hydrogen storage alloy electrodes were produced. The oxygen concentration of each hydrogen storage alloy powder did not change because no reduction was performed (see Table 1).

Sample No. 7 to Sample No. 10 The average particle size of the Ni powder, which is the conductive metal particle, is 0.2 μm.
m (No. 7), 2 μm (No. 8), 5 μm (No. 9), 12 μm
Instead of (No. 10), a hydrogen storage alloy electrode was produced under the same conditions as in Test No. 1. The oxygen concentration of the hydrogen storage alloy powder is also shown in Table 1.

Test No. 11 and Test No. 12 Conductive metal particles were converted from Ni powder to Cu powder (No. 11), C
In place of the powder (No. 12), a hydrogen storage alloy electrode was produced under the same conditions as the sample No. 1.

The composition of the hydrogen storage alloys of sample No. 13 and sample No. 14 is MmNi3.2Co1.0Mn0.6.
In place of Al0.2, a hydrogen storage alloy electrode was produced under the same conditions (No. 13) as the test No. 1 and the same conditions (No. 14) as the test No. 2. The method for producing the hydrogen storage alloy is also the same.

Test No. 15 and Test No. 16 The hydrogen storage alloy was replaced with MgNi1.9Mn0.1, and the same conditions as Test No. 1 (No. 15) and Test No. 2 were used. A hydrogen storage alloy electrode was produced under the same conditions (No. 16). In addition,
The manufacturing method of the hydrogen storage alloy is also the same.

Test No. 17 to Test No. 21 The hydrogen storage alloy electrodes were prepared under the same conditions as in Test No. 1 by changing the atmosphere in the pot of the mechanical alloying treatment to the atmosphere shown in Table 2. For Test No. 20, Cu powder was used as the conductive metal particles.

[0025]

[Table 2]

[Assembly of Test Cell] A test cell (1) was assembled using the obtained hydrogen storage alloy electrodes (Sample No. 1 to Sample No. 21) as a negative electrode (2). As shown in FIG. 5, the test cell (1) comprises a cylindrical polypropylene closed container (11) with an upper lid (1
From 2), a hydrogen storage alloy electrode as the negative electrode (2), a cylindrical sintered nickel electrode as the positive electrode (3), and a plate-shaped sintered nickel electrode as the reference electrode (35) are suspended. It is supported.
The top lid (12) has a pressure gauge (15) and a relief valve (1
It has a relief tube (14) consisting of 6). The container (1) is filled with a 30 wt% potassium hydroxide aqueous solution (L). The positive electrode (3) is an electrode having an electrochemical capacity sufficiently larger than that of the negative electrode hydrogen storage alloy electrode,
It is supported by a positive electrode lead (31) penetrating the (12).
Further, the negative electrode (2) is supported by a negative electrode lead (21) penetrating the upper lid (12) so as to be vertically positioned substantially in the center of the positive electrode cylinder. The other ends of the positive electrode lead (31) and the negative electrode lead (21) are respectively connected to the positive electrode terminal (32) and the negative electrode terminal (22) at the upper part of the upper lid.
It is connected to the. The relief pipe (14) is provided to prevent the internal pressure of the container from rising above a predetermined pressure, and the internal pressure of the container is kept constant by adjusting the relief valve (16).

[Charge / Discharge Cycle Test (Unipolar Test)] Each test electrode was used as the negative electrode of the test cell having the above-mentioned constitution, and it was charged at 50 mA / g for 8 hours at room temperature and then left for 1 hour.
Perform a charge / discharge cycle in which the discharge resting voltage is 0.9 V at mA / g and the resting step is 1 cycle.
The discharge capacity (mAh / g) was measured. The results are shown in Tables 1 and 2. In this test, the maximum capacity is the maximum discharge capacity value after 100 charge / discharge cycles, and the activation degree is the value obtained by dividing the first cycle discharge capacity by the maximum capacity. Is.

Regarding Test Samples No. 1 to No. 6, referring to Table 1, Test Samples No. 1 to No. 4 which have been subjected to the reduction treatment are Test Samples No. 5 and No. which have not been subjected to the reduction treatment. It can be seen that the degree of activation is higher than that of No. 6. Especially, the test No. 1 and No. 2 which have a long reduction treatment time, compared with the test No. 3 and No. 4,
The degree of activation is high in each case. In addition, test No. 1 and N in which conductive metal particles were attached to the surface of the hydrogen storage alloy particles
o. 3 and No. It can be seen that the sample No. 5 has higher activation degree than the samples No. 2, No. 4 and No. 6 without conductive metal at the same oxygen concentration. In other words, test No. 1 and No. 3 which were subjected to reduction treatment and conductive metal particles were attached
Has a much higher degree of activation than the others.

Similarly, for the test Nos. 7 to 10, Table 1
With reference to, it can be seen that the conductive metal particles attached to the surface of the hydrogen storage alloy particles have a higher degree of activation as the average particle diameter is smaller. This is because when the average particle size of the conductive metal particles increases, the number of points of contact between the particles decreases and the electric resistance increases. As described above, when the average particle diameter of the conductive metal particles is about 12 μm, the activation degree is greatly reduced, so that it is preferable to use particles having a particle size of about 10 μm or less.

Regarding test Nos. 11 and 12, when the conductive metal particles were replaced with Cu powder and Co powder, the degree of activation was inferior to the case where Ni powder was used, but the activity was higher than the others. It can be seen that it has a degree of chemical conversion.

Regarding Test Nos. 13 to 16, even if the composition components of the hydrogen storage alloy were changed, the degree of activation was similarly improved by stirring with the conductive metal particles in a reducing atmosphere. I understand.

Regarding Test Nos. 17 to 21, referring to Table 2, the higher the concentration of the reducing gas in the reducing atmosphere, the higher the degree of activation and the sufficient surface modification of the hydrogen storage alloy particles. I know that it will be done.

As described above, by stirring the hydrogen storage alloy particles with the conductive metal particles in the reducing atmosphere, the surface modification of the hydrogen storage alloy particles can be effectively performed, and the obtained hydrogen is obtained. A metal-hydroxide storage battery having a hydrogen storage alloy electrode using a storage alloy powder as a negative electrode has a high degree of activation and can realize a high capacity from the beginning of a charge / discharge cycle.

[Brief description of drawings]

FIG. 1 is a sectional view of a hydrogen storage alloy powder of the present invention.

FIG. 2 is a cross-sectional view of a conventional hydrogen storage alloy powder.

FIG. 3 is an explanatory diagram of a mechanochemical treatment device.

FIG. 4 is a sectional view of a cylindrical pot.

FIG. 5 is a perspective view in which a part of a test cell is cross-sectioned.

[Explanation of symbols]

(40) Hydrogen storage alloy powder (42) Hydrogen storage alloy particles (44) Conductive metal particles

─────────────────────────────────────────────────── ─── 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 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-9-199121 (JP, A) Hei 6-145850 (JP, A) JP 6-124705 (JP, A) JP 7-29571 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4 / 38 H01M 4/24-4/26

Claims (3)

(57) [Claims] 1. Conductive metal particles (44) are formed on the surface of hydrogen storage alloy particles (42) containing Zr, Ni, V and Mn with carbon monoxide.
A hydrogen storage alloy electrode (40) having a hydrogen storage alloy powder (40) attached by a mechanochemical method in a reducing atmosphere and a current collector, wherein the hydrogen storage alloy powder (40) has an oxygen concentration of 0. A hydrogen storage alloy electrode, which is 5% or less. 2. The conductive metal particle (44) according to claim 1, wherein the conductive metal particle (44) contains at least one metal selected from the group consisting of Ni (nickel), Co (cobalt) and Cu (copper). Hydrogen storage alloy electrode. 3. Hydrogen storage alloy particles (42) and conductive metal particles
Hydrogen storage alloy powder (40) with conductive metal particles (44) adhered to the surface by mixing (44) with the mechanochemical method and stirring
A method for preparing a hydrogen storage alloy electrode by integrating the hydrogen storage alloy powder (40) with a current collector, comprising the hydrogen storage alloy particles (42) and conductive metal particles (44). A method for producing a hydrogen storage alloy electrode, wherein stirring is performed in a reducing atmosphere containing carbon monoxide .