JP3290895B2 - Hydrogen storage alloy powder for nickel-metal hydride batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen absorbing alloy powder, and in particular to AB ₅ -type hydrogen absorbing alloy powder for the negative electrode material for a nickel-hydrogen battery.

[0002]

In recent years, nickel-hydrogen battery is attracting attention as a secondary battery in place of nickel-cadmium battery, a hydrogen absorbing alloy powder therefor have been studied, among others AB ₅
Hydrogen storage alloy powders are used with excellent characteristics as negative electrode materials for batteries. This is, for example, Ce50
%, La 25%, Nd 15%, remaining Pr, etc., and a mixture of a misch metal Mm and a nickel alloy containing, for example, Mn, Al, Co, or the like.
Is the type of intermetallic compounds such as _{1.0 Ni (5-x-y} -z) Mn x Al y Co z. Conventionally, this has been pulverized by various methods such as pulverization of a cast material, pulverization of a rapidly solidified thin ribbon brought into contact with a rotating drum, and atomization of an inert gas such as argon.

[0003]

Among the various powdering methods described above, the method of pulverizing a cast material does not have a uniform composition of each powder particle due to segregation of the material and the like, and the performance when used in a secondary battery is reduced. Is inferior to powders obtained by gas atomization or crushing of rapidly solidified ribbons. Since the powder obtained by the gas atomization method has a spherical particle shape, the packing density when incorporated into a battery electrode is superior to that obtained by pulverizing a cast material or a quenched ribbon, and has the same hydrogen storage capacity. Even when a powder having characteristics is used for the electrode, the energy density of the electrode can be increased, a battery with a large capacity can be manufactured, and it is more suitable for mass production than the quenched ribbon method. Also has the advantage that it can be advantageously manufactured.

[0004] However, the fact that the particles are spherical
There is a technical problem in maintaining electrical contact when filling into the battery electrode, if the contact is incomplete, the packing density is high,
There is a problem that the merit of the atomized powder, which can exhibit stable characteristics without segregation, cannot be sufficiently exhibited. A solution to this problem is to mix the atomized powder with the powder obtained by the casting and pulverizing method to combine the advantages of the atomized powder with a high packing density and the advantages of the cast and pulverized powder with stable electrical contact. It is possible to make it. However, when powders having different production methods are mixed as described above, the disadvantage of cast ground powder that segregation is large and characteristics are not stable remains, and an economical and effective solution has been desired.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively developed and as a result, the hydrogen storage atomized alloy powder is classified with a desired particle size, and the coarse particles remaining on the sieve after the classification are obtained. The powder of the particle size is pulverized and mixed with the powder of the fine particle size passed through a sieve to improve the electrical contact in the electrode, which is a problem peculiar to the spherical powder, while maintaining the stable characteristics of the atomized powder, and to reduce the cost. It has been found that a hydrogen storage alloy powder can be provided which can also obtain a special merit.

The gist of the invention is as follows: (1) In a hydrogen storage alloy powder for a nickel-metal hydride battery,
Nickel-metal hydride, characterized in that gas atomized powder is classified at 50 to 300 μm, and a gas atomized powder obtained by pulverizing a powder coarser than the classification particle size into a powder having a classification particle size or less and a gas atomizing powder having a classification particle size or less are mixed. Hydrogen storage alloy powder for batteries. (2) The hydrogen storage alloy powder for a nickel-metal hydride battery according to the above (1), wherein the gas atomized pulverized powder and the gas atomized powder are heat-treated. (3) The hydrogen storage alloy powder for a nickel-metal hydride battery according to the above (1), wherein the powdered gas atomized powder and the gas atomized powder are heat-treated and then surface-treated with an acid or alkali solution.

Hereinafter, the present invention will be described in detail. Usually, the particle size to be sieved varies depending on the electrode design of the battery.
Since it is about 00μ, the maximum diameter of the atomized powder that can be used without pulverization is 300μ. From the economical viewpoint, it is advantageous to reduce the powder to be pulverized as much as possible. If the sieving is too large, the packing density tends to decrease. Therefore, it is appropriate that the minimum sieving diameter in sieving is about 50 μm.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, a fine powder that has passed through a sieve is a powder that exhibits the advantages of gas atomization, that is, a spherical shape, a high packing density, low segregation, and stable characteristics. In addition, the powder obtained by grinding the coarse powder remaining in the sieve becomes irregularly shaped like the cast ground powder,
By mixing with the spherical powder, it plays a role of effectively improving the electrical contact of the spherical powder. Here, since the ground powder is originally a powder manufactured by gas atomization which is a quenching method, the advantage of exhibiting stable characteristics with less segregation is exhibited as it is, and when the cast ground powder and the atomized powder are mixed. There are no such instability factors.

Further, since the remaining coarse powder of the atomized powder is crushed and used, it cannot be used in the process of making an electrode using the conventional atomized powder, and is used as a return for re-dissolution or disposal. Coarse powder can be used at the same time, which has a great economic effect. As described above, after sieving the atomized powder, the coarse powder is crushed and mixed with the powder that has passed through the sieving, so that a high packing density and stable electrical contact can be achieved at the same time, and it is cost-effective. It has become possible to further enhance the advantages of the gas atomized powder.

[0010]

【Example】

(Example _{1) Mm 1.0 Ni 3.4 Co 0.8} Mn 0.6 Al
A metal raw material blended to form _0.2 is placed in an alumina crucible, melted in an induction melting furnace, a 1500 ° C molten metal is dropped through an alumina nozzle having a diameter of 3 mm, and a gas atomized powder is produced by blowing argon gas onto the molten metal. did. This powder was classified with a sieve having an opening of 150 μm, and divided into a fine powder passed through the sieve and a coarse powder remaining in the sieve. The weight ratio of the powder remaining in the sieve to the powder passed through the sieve was 25:75. The coarse powder remaining in the sieve is stored in an agate pot together with a powder of agate having the same weight as the powder and having a diameter of 10 mm and pure water having a volume five times the powder volume.
Grinding treatment was performed for 30 minutes with a planetary ball mill. All of the pulverized powders passed through a sieve with a mesh size of 150 μm and were pulverized well. The pulverized powder and the previously sieved fine powder were put into a V-type mixer and mixed.

The mixed powder A according to the present invention shown in Table 1 was mixed with 50
The packing density was measured by measuring 0 g, setting the volume in a tap filling machine, and tapping 100 times. For comparison, a fine gas atomized powder (no pulverization) B passed through a 150 μm aperture, a powder C that was pulverized from a gas atomized powder remaining in a sieve and passed through a 150 μm aperture, and melted and cast in a small induction melting furnace And then finely pulverized with a planetary ball mill, and then cast and pulverized powder D passing through an opening of 150 μm.
Was also measured for packing density. Further, in order to measure the electrochemical properties of these powders, Ni powder (0.5 and 2 g) having a particle size of 3 μm as a conductive agent was added to 1 g of the mixed powder,
PTFE (polytetrafluoroethylene) as binder
0.2 g of the powder was mixed, pressed with a die having a diameter of 20 mm into a coin shape, and sandwiched between Ni meshes, and a Ni conductive plate was spot-welded to produce a negative electrode. This negative electrode is commercially available N
The battery was mounted in a Teflon cell together with a NiOOH / NiOH positive electrode (capacity: 1400 mAh) taken out of the iCd battery, immersed in a 6N KOH solution, and sealed with 5 atm of argon gas to measure the discharge capacity of the test battery.

[0012]

[Table 1]

Example 2 An argon gas atomized hydrogen storage alloy powder produced in the same manner as in Example 1 was
The mixture was classified with a 00μ sieve and divided into a fine powder passed through the sieve and a coarse powder remaining in the sieve. The weight ratio of the powder remaining in the sieve to the powder passed through the sieve was 20:80. Store each powder in a mild steel container at 700 ° C
After the heat treatment was performed in an argon gas atmosphere for 5 hours, the coarse powder was pulverized under the same conditions as in Example 1 to prepare a pulverized powder passing through a mesh of 200 μm. The pulverized powder and the previously sieved fine powder were put into a V-type mixer and mixed.
The mixed powder A according to the present invention shown in Table 2 and a gas atomized fine powder (no pulverization) B having passed through a mesh 200 μm subjected to the same heat treatment as above as a comparative material and a gas atomized powder remaining in the sieve were pulverized and pulverized. A test battery was prepared under the same conditions as in Example 1 for powder C that passed through a 200 μ sieve, and cast and ground powder D that passed through an opening of 200 μ that was melted and cast in a small induction melting furnace and then finely ground with a planetary ball mill. And the discharge capacity was measured.

[0014]

[Table 2]

Example 3 An argon gas atomized hydrogen storage alloy powder produced in the same manner as in Example 1 was
The mixture was classified with a 00μ sieve and divided into a fine powder passed through the sieve and a coarse powder remaining in the sieve. The weight ratio of the powder remaining in the sieve to the powder passed through the sieve was 30:70. Store each powder in a mild steel container at 700 ° C
After performing a heat treatment in an argon gas atmosphere for 5 hours, the coarse powder was pulverized under the same conditions as in Example 1 to prepare a pulverized powder passing through a mesh of 100 μm. The pulverized powder and the previously sieved fine powder were put into a V-type mixer and mixed.
Further, the mixed powder and a hydrochloric acid solution 5 times the volume of the powder adjusted to pH = 1.0 were put into a beaker together with pH = 6.
The surface treatment was performed while stirring until the mixture reached 5. The mixed powder A according to the present invention shown in Table 3 after the surface treatment, the heat-treated as described above, the finely divided gas atomized powder (no pulverization) B having passed through an opening of 100 μm, and the gas atomized powder remaining on the sieve were subjected to the same surface treatment. Powder C, which has been crushed and passed through a sieve with an opening of 100μ, is further melted in a small induction melting furnace.
Aperture 100 finely pulverized with a planetary ball mill after casting
A test battery was manufactured under the same conditions as in Example 1 for the cast and ground powder D passing through μ, and the discharge capacity was measured.

[0016]

[Table 3]

In Example 1, the packing density of the powder A of the present invention is as high as that of the gas atomized fine powder B having a spherical shape, and is at least 15% higher than that of the gas atomized powder C or the cast and ground powder D. It showed a high density.
Further, in any of the cases of Examples 1 to 3, the powder of the present invention has an extremely good discharge capacity equivalent to that when a large amount of Ni powder is added even in an electrode in which the amount of Ni powder as a conductive agent is reduced. The discharge capacity is equivalent to the case where a large amount of Ni powder is added to the spherical gas atomized fine powder.

On the other hand, the gas atomized fine powder B as the comparative material shows a good discharge capacity when the amount of the Ni powder as the conductive agent is large, but when the amount of the Ni powder is reduced, the electric contact decreases and the discharge capacity also decreases. I do. Although the gas atomized powder C and the cast and ground powder D have good electrical contact even when the amount of Ni powder is reduced, the discharge capacity shows the same discharge capacity as the case where the amount of Ni powder is large, but the cast and ground powder is gas atomized powder. There is a structural non-uniformity as compared with that of the gas atomized powder, and the value is lower than that of the gas atomized powder. As described above, according to the present invention, it was possible to improve the discharge capacity in a situation where electrical contact, which was a problem of the spherical powder, was disadvantageous while maintaining an extremely high packing density equivalent to that of the spherical gas atomized powder.

[0019]

As described above, it is an object of the present invention to provide an extremely economically advantageous production method while using the atomized powder mixed according to the present invention to achieve extremely stable characteristics.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadayuki Maruo 3007 one-letter Nakajima character in Shima, Himeji City, Hyogo Prefecture Inside Sanyo Special Steel Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) B22F 9 / 08 B22F 1/00 H01M 4/38

Claims (3)

(57) [Claims] In a hydrogen storage alloy powder for a nickel-metal hydride battery, a gas atomized powder is classified at 50 to 300 μm, and a powder coarser than the classified particle size is pulverized into a powder having a size smaller than the classified particle size. A hydrogen storage alloy powder for a nickel-metal hydride battery, wherein the powder is mixed with a gas atomized powder. 2. The hydrogen storage alloy powder for a nickel metal hydride battery according to claim 1, wherein the gas atomized powder and the gas atomized powder are heat-treated. 3. The hydrogen-absorbing alloy powder for a nickel-metal hydride battery according to claim 1, wherein the gas-atomized powder and the gas-atomized powder are heat-treated and then surface-treated with an acid or alkali solution.