JPH06283171A - Hydrogen storage alloy powder - Google Patents

Abstract

PURPOSE:To reduce the inner pressure at the time of charging, and to extend charging/ discharging cycle life by specifying accumulation of powder corresponding to a biaxial average diameter R when the particle diameter is expressed with R. CONSTITUTION:The particle diameter of hydrogen storage alloy powder is expressed with biaxial average diameter R. The cumulative particle. size distribution of the hydrogen storage alloy powder is as follows. Accumulation of powder when R is no more than 10mum is 0%. Accumulation of powder when R is no more than 20mum is no more than 5%, and accumulation of powder when R is no more than 30mum is 5-12%. Accumulation of powder when R is no more than 5mum is 20-30%, and accumulation of powder when R is no more than 100mum is 60-80%, while accumulation of powder when R is no more than 300mum is 95-100%. Since powder of R of no more than 10mum is not contained, no material causing oxidation or granulation of each component is not contained, thus achieving intrinsic performance. The inner pressure increase at the time of charging battery is reduced, while the charging/discharging cycle is elongated. When R falls outside the abovementioned accumulation range, rapid discharging characteristic is degraded, while the life is shortened, and the inner pressure is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy powder, and more particularly to a hydrogen storage alloy powder for a hydrogen storage alloy electrode incorporated in a nickel-hydrogen secondary battery, which is used for charging the assembled battery. The present invention relates to a hydrogen storage alloy powder that is effective for reducing internal pressure, improving rapid discharge characteristics of batteries, and extending battery life.

[0002]

2. Description of the Related Art With the progress of miniaturization, weight reduction, and cordlessness of various electric / electronic devices, there is an increasing demand for miniaturization, weight reduction, and high capacity of batteries used as power sources for the electric and electronic devices. Recently, as a high capacity battery to meet this demand,
Nickel-hydrogen secondary batteries are drawing attention.

This nickel-hydrogen secondary battery operates by using hydrogen as a negative electrode active material, and has a negative electrode formed by carrying a hydrogen storage alloy capable of reversibly storing and releasing hydrogen on a conductive base material. Usually, it is configured by arranging a nickel hydroxide, which operates as a positive electrode active material, on a conductive base material and a positive electrode, which are placed in an alkaline electrolyte. Here, the above-mentioned negative electrode is usually manufactured as follows.

That is, first, a hydrogen storage alloy having a predetermined composition is melted, and then the ingot is crushed to produce a hydrogen storage alloy powder having a predetermined particle size. Then, a predetermined amount of the hydrogen storage alloy powder is dispersed in a solution prepared by dissolving a thickening agent such as methyl cellulose, carboxymethyl cellulose or ethylene oxide in ion exchange water to prepare a slurry. A conductive base material such as a punched nickel sheet is immersed in this slurry and the conductive base material is pulled up to adhere the slurry to the surface of the conductive base material, and then the attached slurry is dried and rolled. A hydrogen storage alloy powder layer having a desired thickness is supported on a conductive base material.

[0005]

By the way, nickel-
In the hydrogen secondary battery, the potential at which the charge reaction of the hydrogen storage alloy takes place is a value close to the electrolysis potential of water that constitutes the alkaline electrolyte. Therefore, at the end of the charging operation, the gas pressure of hydrogen gas generated by the electrolysis of water is added to increase the internal pressure of the battery. In order to suppress this increase in internal pressure, it is possible to reduce the capacity to a certain extent by increasing the capacity of the negative electrode, but such a measure leads to an increase in the size of the battery, a reduction in the size of the battery, and a higher battery. It is not preferable in terms of energy density.

Further, the nickel-hydrogen secondary battery, like other secondary batteries such as nickel-cadmium secondary battery, eventually decreases its battery capacity in the course of repeated charging / discharging, and finally becomes. Life is exhausted. For example, in the case of a nickel-cadmium secondary battery, according to the JIS standard relating to it, it is determined that the battery life is exhausted when the capacity becomes 60% or less of the rating, and during that time, 500 or more charge / discharge cycles are performed. Is required to be able to be repeated.

In the case of the conventionally known nickel-hydrogen secondary battery, the charge / discharge cycle until the battery capacity reaches about 80% of the rating is about 300 to 350 times, which is about 60% of the rating. Charge-discharge cycle up to 350-4
It is about 00 times. Conversely, if the charge and discharge are repeated the number of times described above, the battery capacity will drop to about 80% and 60% of the rating, and the service life of the battery will be exhausted after 300 to 400 charge and discharge cycles. It means that it will end up.

For these reasons, there is a demand for the development of nickel-hydrogen secondary batteries having a longer service life. INDUSTRIAL APPLICABILITY The present invention can meet the above-mentioned demands, the internal pressure at the time of charging is reduced, the charge / discharge cycle life is extended, and the hydrogen suitable for producing a nickel-hydrogen secondary battery having excellent rapid discharge characteristics is also provided. An object is to provide a hydrogen storage alloy powder for a storage alloy electrode.

[0009]

The present inventor has found that nickel-
In solving the above problems in the hydrogen secondary battery,
When the influence of the particle size of the hydrogen storage alloy electrode as the negative electrode, especially the hydrogen storage alloy powder used for it was investigated,
When the other battery constituents are the same, it was found that the battery internal pressure and the number of charge / discharge cycles depend on the particle size distribution of the alloy powder, and based on this finding, the hydrogen storage alloy powder of the present invention is suitable. I found the fact that there is.

That is, the hydrogen storage alloy powder of the present invention is
A hydrogen storage alloy powder used for a hydrogen storage alloy electrode for a nickel-hydrogen secondary battery, the particle size of which is a biaxial average diameter R
When expressed by, the accumulation of the powder having R of 10 μm or less is 0.
%, R is 20 μm or less, the cumulative amount of powder is 5% or less, R
Of powder having a particle size of 30 μm or less is 5 to 12%, and R is 5
The accumulation of powder having a size of 0 μm or less is 20 to 30%, and R is 10
The cumulative amount of powder having a size of 0 μm or less is 60 to 80%, and R is 30.
The accumulation of powders of 0 μm or less is characterized by having a cumulative particle size distribution of 95-100%.

The most characteristic feature of the hydrogen storage alloy powder of the present invention is that it does not contain powder having R of 10 μm or less. The powder having R of 10 μm or less contains a large amount of substances that are easily pulverized, such as oxides of the respective components forming the hydrogen storage alloy and alloys having a composition that largely deviates from the target composition. Therefore, the powder having R of 10 μm or less does not exhibit the original performance as a hydrogen storage alloy, but also dissolves in an alkaline electrolyte to form a hydroxide. And
It is considered that these hydroxides cover the active surface of the other hydrogen storage alloy, and as a result, the activity of the hydrogen storage alloy electrode is impaired.

Therefore, in the electrode made of the hydrogen storage alloy powder from which the powder having R of 10 μm or less is removed,
Since the above-mentioned inconvenience factors are eliminated, the original performance as a hydrogen storage alloy is secured, and as a result, it is considered that the internal pressure rise of the battery is reduced and the cycle life is extended. Further, in the hydrogen storage alloy of the present invention, when the cumulative particle size distribution deviates from the above value, particularly when the accumulation of the powder having R of 30 μm or less deviates from the above value, the reason is not understood, but the increase in the battery internal pressure However, the cycle life is shortened and the rapid discharge characteristics are deteriorated.

The hydrogen storage alloy powder of the present invention is obtained by smelting an alloy having a desired composition and mechanically crushing the ingot with an ordinary crusher such as a ball mill, an edge runner, a rod mill or a disc mill. After classifying the obtained powders, the powders of the respective classifications can be mixed to produce the above-mentioned cumulative particle size distribution.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION By the arc melting method, composition: MmNi _3.3.
A hydrogen storage alloy represented by Co _1.0 Mn _0.4 Al _0.3 (where Mm represents misch metal) was melted, and the ingot was crushed by a ball mill. After classifying the obtained powder, three kinds of alloy powders A, B and C having a cumulative particle size distribution as shown in FIG. 1 were manufactured. In the figure, powder A is the powder of the present invention, powder B contains fine powder having R of 10 μm or less, and powder C does not contain powder having R of 30 μm or less.

The biaxial average diameter R is a value measured using Microtrac (manufactured by Nikkiso Co., Ltd.). For each 100 parts by weight of ion-exchanged water, the above-mentioned alloy powder 400
A slurry comprising 1 part by weight of carboxymethyl cellulose and 1 part by weight of carboxymethyl cellulose was prepared.
Immerse a punching nickel sheet with a porosity of 38% (hole diameter 1.5 mm), pull it up, and then dry it in the air, and
A negative electrode sheet having a thickness of 0.4 mm was manufactured by rolling at a pressure of ton / cm ² .

On the other hand, a sponge-like nickel sheet having a thickness of 1.6 mm and a porosity of 96% was coated with 93% by weight of Ni (OH) ₂ powder.
To a mixed powder consisting of 3% by weight of Ni powder and 4% by weight of CoO powder 1.
A positive electrode sheet was manufactured by filling an active material mixture prepared by adding a 2% aqueous carboxymethylcellulose solution, drying the mixture at 80 ° C. for 2 hours, and rolling it at a pressure of ² ton / cm ² . The filling amount of the active material mixture was 4.4 g.

A nylon separator is arranged between the positive electrode sheet and the negative electrode sheet, and the whole is spirally wound to form an electrode plate group having a diameter of 13 mm, which is made of steel and has an inner diameter of 13.2 mm. Stored in a cylindrical container with a specific gravity of 1.
After injecting 38 KOH aqueous solution, the lid was closed and three types of sealed cylindrical batteries were manufactured. Each of these batteries was charged under the following specifications and the internal pressure of the battery was measured.

Charging: 1 C, 4.5 hours, temperature: 20 ° C. In addition, a charge / discharge cycle test was conducted with the following specifications, and the number of cycles until the ratings reached 80% and 60% was measured. Charge: 1C, -V control, temperature: 20 ° C. Discharge: 1C, end voltage of discharge 1.0V, temperature: 20 ° C.

Further, a rapid discharge test at 20 ° C. was conducted. That is, it was charged at 0.2 ° C. for 7.5 hours at 20 ° C., and then discharged at 3 ° C. to 1.0 V at 20 ° C., and the 3C / 0.2C discharge capacity ratio was measured. The above results are collectively shown in Table 1.

[0020]

[Table 1]

[0021]

As is apparent from the above description, the nickel-hydrogen secondary battery in which the negative electrode using the hydrogen storage alloy powder of the present invention is incorporated has a low battery internal pressure during charging and a long cycle life. Also, the rapid discharge characteristics are excellent.

[Brief description of drawings]

FIG. 1 is a graph showing a cumulative particle size distribution of hydrogen storage alloy powder.

Claims (1)

[Claims] 1. A hydrogen storage alloy powder for use in a hydrogen storage alloy electrode for a nickel-hydrogen secondary battery, wherein R is 10 μm or less when the particle diameter is expressed by a biaxial average diameter R. Is 0%, the accumulation of the powder having R of 20 μm or less is 5% or less, and the accumulation of the powder having R of 30 μm or less is 5%.
12%, accumulation of powder having R of 50 μm or less is 20 to 3
0%, accumulation of powder having R of 100 μm or less is 60 to 8
0%, accumulation of powder with R less than 300 μm is 95-1
Hydrogen storage alloy powder having a cumulative particle size distribution of 00%.