JP3198896B2 - Nickel-metal hydride battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen storage battery using a hydrogen storage alloy which can electrochemically store and release hydrogen as an active material, and more particularly to an improvement in hydrogen storage alloy powder.

[0002]

2. Description of the Related Art A hydrogen storage alloy capable of storing and releasing a large amount of hydrogen as an active material has attracted attention as an electrode material having a high energy density, and is being applied to nickel-hydrogen storage batteries. The hydrogen storage alloy here is generally CaCu ₅
A part of Ni of MmNi ₅ system alloy having a crystal structure of the type Co, Al, has been used to replace an element such as Mn.

[0003] It is considered that such a hydrogen storage alloy gradually becomes finer and oxidizes and deteriorates as the battery is charged and discharged. As a method of improving the cycle life of the hydrogen storage alloy, there is a method of increasing the amount of cobalt in the alloy. It is believed that cobalt in the alloy is effective in suppressing the expansion and contraction of the crystal lattice due to the storage and release of hydrogen.

As a method for improving the cycle life of a hydrogen storage alloy, Japanese Patent Application Laid-Open No. Hei 5-314971 discloses that the specific surface area of a hydrogen storage alloy by the BET method is 0.04 to 0.12.
m ² / g, and JP-A-4-137361 discloses that the specific surface area of the hydrogen storage alloy by the BET method is 0.1 to
It has been respectively proposed to be 10 m ² / g.

[0005]

According to such a conventionally proposed method, the cycle life characteristics are improved by increasing the amount of cobalt in the alloy, but the discharge characteristics of the battery are degraded. There was a point. In addition, since cobalt is a high-cost material, there is also a problem that increasing the amount of cobalt in the hydrogen storage alloy increases the cost of the alloy.

When the hydrogen storage alloy is made to have a specific surface area as proposed in Japanese Patent Application Laid-Open No. Hei 5-314971, it is effective in improving the life characteristics, but the discharge characteristics of the battery are remarkably deteriorated.

Japanese Patent Application Laid-Open No. 4-137361 does not disclose a detailed relationship between the amount of cobalt in the hydrogen storage alloy and the BET specific surface area. In particular, a hydrogen storage alloy having a small amount of cobalt has been proposed. It is not clear whether the specific surface area is effective.

Furthermore, these conventional techniques do not disclose the particle size of the hydrogen storage alloy powder and the relationship between the particle size and the specific surface area.

The present invention solves such a problem, and uses a hydrogen storage alloy having a small amount of cobalt to improve its cycle life and to provide a low-cost nickel-hydrogen storage battery having excellent discharge characteristics as a battery. The purpose is to provide.

[0010]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a positive electrode mainly composed of nickel oxide and a hydrogen storage capable of electrochemically storing and releasing hydrogen as an active material. In a nickel-metal hydride storage battery including a negative electrode having an alloy powder as a main constituent material, a separator, and an alkaline electrolyte, the hydrogen storage alloy powder has a CaCu ₅ type crystal structure including a rare earth element and cobalt, the cobalt content is less 5 wt%, specific surface area by BET method of 0.3 m ² / g or more 0.7 m ² / g or less, average particle size is obtained by a 5 to 60 m.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION It is considered that the amount of cobalt in a multiplexed hydrogen storage alloy powder affects the fragility of the hydrogen storage alloy. By adopting a configuration as in the present invention, even in a hydrogen storage alloy having a small cobalt content, oxidation and deterioration of the alloy powder due to charging and discharging of the battery can be suppressed, the cycle life of the alloy powder is improved, and the discharge characteristics are improved. An excellent, low-cost nickel-metal hydride storage battery can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings and embodiments.

Using a commercially available metal such as Mm, Ni, Co, Al, and Mn as a raw material, a hydrogen storage alloy was prepared by heating and melting in a high-frequency melting furnace in an argon atmosphere. The composition is represented by the general formula: MmNi _4.0 Mn _0.4 Al _0.3 Co
_It was prepared to be _0.4 .

Next, in order to homogenize the hydrogen storage alloy, heat treatment was performed at 1050 ° C. for 6 hours in an argon atmosphere. After coarsely pulverizing the obtained alloy lump, it was finely pulverized by a wet ball mill to prepare fine powders having various average particle diameters. Next, this fine powder was stirred in an aqueous potassium hydroxide solution, washed with water and dried to obtain a hydrogen storage alloy powder. The average particle size was adjusted by changing the pulverization time by a wet ball mill. Further, the specific surface area was adjusted by changing the processing temperature, the processing time, and the concentration of the aqueous potassium hydroxide solution during the stirring treatment in the aqueous potassium hydroxide solution.

The specific surface area of the powder was measured by a BET method using nitrogen gas, and the average particle diameter was measured by using a laser diffraction type particle size distribution analyzer.

Water was added to these hydrogen-absorbing alloy powders to form a paste, filled in a porous nickel foam, dried, pressurized, and cut into predetermined dimensions to prepare a hydrogen-absorbing alloy electrode.
This is combined with a known foamed nickel-type positive electrode and a separator formed by sulfonating a polypropylene non-woven fabric to form a spiral electrode group and insert it into a metal case, and then have a specific gravity of 1.30.
After injecting a predetermined amount of potassium hydroxide aqueous solution as an electrolytic solution, the case is sealed, and each has an AA size and a battery capacity of 10
A nickel-metal hydride storage battery of 00 mAh was formed.

A cycle life test was performed using each of the above batteries. Charge and discharge conditions are 45 ° C atmosphere, 1C
After charging for 1.5 hours at 1 mA, 1 Cm to the final voltage of 1.0 V
A discharge was performed. The specific surface area and the discharge capacity of the hydrogen storage alloy powder having the respective average particle diameters according to the BET method were 1 / the initial values.
FIG. 1 shows the relationship with the number of cycles until the capacity reaches 2.

As is clear from FIG. 1, for powders of the same particle size, the cycle life was improved by the sample whose specific surface area was reduced by the BET method, and the effect was obtained when it was 0.7 m ² / g or less. I understand. In addition, when the specific surface area was the same, the life characteristics were improved as the average particle size was larger.

Similarly, a discharge characteristic test was performed using the above-mentioned battery. The charge and discharge conditions were as follows: an atmosphere at 20 ° C., charging at 1 CmA for 1.5 hours, and a final voltage at 20 ° C. and 0 ° C.
Discharge was performed at 1 CmA to 0 V. BE of hydrogen storage alloy
FIG. 2 shows the relationship between the specific surface area by the T method and the discharge capacity ratio of 0 ° C. to 20 ° C. of each battery.

As is apparent from FIG. 2, in the case of powders having the same particle size, the sample having a small specific surface area exhibited a decrease in discharge characteristics, and it was found that the discharge characteristics were effective at 0.3 m ² / g or more. . Also, when the specific surface area is the same, the larger the average particle size, the lower the discharge characteristics, but the average particle size is 60 μm.
If it was below, there was no problem in actual specifications.

As described above, the content of cobalt in the hydrogen storage alloy powder is 5 wt% or less, the specific surface area by the BET method is 0.3 m ² / g or more and 0.7 m ² / g or less, and the average particle diameter is 5 wt% or less. By setting the thickness to μ60 μm, a low-cost nickel-hydrogen storage battery having a long cycle life and excellent discharge characteristics can be provided.

In this embodiment, the hydrogen storage alloy is Mm
Although Ni _4.0 Mn _0.4 Al _0.3 Co _0.4 was used, it had a CaCu ₅ type crystal structure containing a rare earth element and cobalt, had a cobalt content of 5 wt% or less, and had a specific surface area of 0.3 m ² / BET method. It goes without saying that almost the same effect can be obtained by using any type of hydrogen storage alloy as long as the powder has a particle size of at least 0.7 m ² / g and an average particle diameter of 5 to 60 μm.

[0023]

As described above, according to the present invention, a positive electrode mainly composed of nickel oxide and a hydrogen storage alloy powder capable of electrochemically storing and releasing hydrogen as an active material are mainly constituted. In a nickel-hydrogen storage battery composed of a negative electrode as a material, a separator, and an alkaline electrolyte, the hydrogen storage alloy powder used contains a rare earth element, cobalt containing Ca.
It has a Cu ₅ type crystal structure with a cobalt content of 5 wt%
Hereinafter, when the specific surface area by the BET method is 0.3 m ² / g or more and 0.7 m ² / g or less and the average particle diameter is 5 to 60 μm, both cycle life and discharge characteristics are excellent.
A low-cost nickel-metal hydride storage battery can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the BET specific surface area and the cycle life of a negative electrode hydrogen storage alloy powder of a sealed nickel-metal hydride storage battery according to an example of the present invention.

FIG. 2 is a diagram showing a relationship between a BET specific surface area of a negative electrode hydrogen storage alloy powder of the storage battery and a discharge capacity ratio of 0 ° C. to 20 ° C.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hideo Kamiya 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-137361 (JP, A) JP-A-5- 314971 (JP, A) JP-A-7-73880 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/38 H01M 10/30

Claims (1)

(57) [Claims] A positive electrode mainly composed of nickel oxide; a negative electrode mainly composed of a hydrogen storage alloy powder capable of electrochemically storing and releasing hydrogen as an active material; a separator; a nickel-metal hydride battery composed of an electrolytic solution, wherein the hydrogen storage alloy powder has a crystal structure of CaCu ₅ type include rare earth elements and cobalt, less 5 wt% content of cobalt in the alloy, BET A nickel-hydrogen storage battery having a specific surface area of 0.3 m ² / g or more and 0.7 m ² / g or less and an average particle diameter of 5 to 60 μm by a method.