JP3069767B2 - Hydrogen storage alloy electrode - Google Patents

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 electrode, and more particularly, to a hydrogen storage alloy electrode capable of suppressing an increase in battery internal pressure and overheating of a battery during overcharge, thereby increasing charging efficiency.

[0002]

2. Description of the Related Art Nickel-hydrogen secondary batteries, which have attracted attention as high-capacity batteries, operate on hydrogen as a negative electrode active material and collect hydrogen-absorbing alloy capable of electrochemically absorbing and releasing hydrogen. A separator having electrical insulation and liquid retention properties between a negative electrode supported on a conductive substrate functioning as a body and a positive electrode supported on a conductive substrate with nickel hydroxide operating as a positive electrode active material. To form an electrode group, and house the electrode group in a conductive bottomed can,
Here, a predetermined alkaline electrolyte is injected and then the whole is sealed.

The hydrogen storage alloy electrode incorporated in this battery is generally manufactured as follows. First,
A slurry of the hydrogen storage alloy powder is prepared as follows. For example, an aqueous solution of a thickener obtained by dissolving a predetermined amount of one or more of a thickener such as methylcellulose, carboxymethylcellulose, polyethylene oxide, and polyvinyl alcohol in ion-exchanged water or distilled water is mixed with hydrogen having a predetermined particle size. A predetermined amount of the storage alloy powder is dispersed. At this time, in order to strengthen the mutual bonding of each alloy powder in the hydrogen storage alloy powder layer supported on the conductive substrate and to prevent them from peeling off from the conductive substrate, for example, polytetrafluoroethylene powder Binder powder such as polyethylene powder, polypropylene powder, polyvinylidene fluoride powder, and cobalt powder, copper powder, etc. in order to increase the conductivity of the above-mentioned hydrogen storage alloy powder layer and improve the current collecting ability as a negative electrode. And a conductive material powder such as carbon powder are blended in an appropriate amount.

[0004] A conductive substrate such as a punched nickel sheet or a nickel net is immersed in the slurry thus prepared, and the conductive substrate is pulled up at a predetermined speed to fill the conductive substrate with the slurry. Apply. Next, after drying the slurry filled or coated on the conductive substrate, the whole is subjected to a rolling treatment at a predetermined pressure to control the thickness of the dried slurry layer to a predetermined thickness and to make the conductive layer a conductive slurry. The substrate is held in close contact with the substrate to form a target hydrogen storage alloy electrode.

[0005] Incidentally, 150 to 210 ° C. in the case of using the port re vinylidene fluoride powder as a binder powder, following the rolling process described above, for example in a nitrogen atmosphere
A measure is taken to soften and bind these binders by baking at about the same temperature.

[0006]

SUMMARY OF THE INVENTION By the way, nickel
In a hydrogen secondary battery, oxygen gas is generated from the positive electrode during charging. When the battery reaction proceeds normally, the generated oxygen gas reacts with hydrogen stored in the negative electrode and is reduced to water. When the reduction of oxygen gas to water does not proceed smoothly, the internal pressure of the battery is increased due to the sealed structure, and the temperature of the battery is increased because the reaction between oxygen gas and hydrogen is an exothermic reaction. . This phenomenon appears remarkably during overcharging.

As the internal pressure of the battery increases, the battery may be ruptured. To prevent this, an internal pressure valve is provided in the battery or a buffer space is provided in the battery. However, such a measure is not so preferable because it complicates the battery structure as a whole and increases the size. In addition, when the battery temperature rises, the temperature rises considerably at the end of charging, so that the hydrogen absorbing alloy electrode has a poor hydrogen acceptability, which eventually leads to a reduction in charging efficiency.

The present invention provides a hydrogen storage alloy electrode that can solve the above-mentioned problems in a nickel-hydrogen secondary battery, suppresses an increase in battery internal pressure, and suppresses a rise in battery temperature. Aim.

[0009]

In order to achieve the above object, according to the present invention, a hydrogen absorbing alloy powder layer is supported on a conductive substrate, and the surface of the hydrogen absorbing alloy powder layer is
There is provided a hydrogen storage alloy electrode characterized by being coated with a nickel powder having a three-dimensional chain structure having a Fisher size of 3.0 μm or less.

[0010] In particular, a nickel powder covering the surface of the hydrogen storage alloy powder layer by 80% or more is provided as a preferred example.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydrogen storage alloy electrode according to the present invention is conventionally known except that the surface of a hydrogen storage alloy powder layer supported on a conductive substrate is coated with nickel powder described later. It does not differ from the structure of the hydrogen storage alloy electrode used. Here, the nickel powder covering the surface of the hydrogen storage alloy powder layer is a Fisher size (Fisher size).
size) is 3.0 μm or less.

This nickel powder functions as a catalyst for promoting the reaction between oxygen gas and hydrogen. In other words, this nickel powder reduces the oxygen gas generated at the positive electrode and reaches the surface of the hydrogen storage alloy electrode to water by rapidly reacting on the electrode surface with the hydrogen stored in the hydrogen storage alloy. Thus, the rise in battery internal pressure is suppressed. This nickel powder is made of nickel carbonyl vapor (Ni (C
O) ₄ ) is a powder produced by pyrolysis and having a three-dimensional chain structure such as a structure of carbon black, for example, a powder commercially available from INCO as Filamentary Nickel Powder.

The Fisher size is an index for indicating the particle size of the agglomerated powder, and is defined by JIS H2116.
Refers to the specific surface area diameter measured by the method specified in 1979, using a Fischer air permeation apparatus, and the following formula: Dm = 6 × 10 ⁴ / ρ · Sw (where Dm is the particle size (μm) of the powder to be measured) , Ρ are calculated and defined based on the true density (g / cm ³ ) of the powder to be measured, and Sw is the specific surface area (cm ² / g) of the powder to be measured.

The smaller the value, the larger the specific surface area of the powder, which means that the surface activity of the powder is increased. In the present invention, a nickel powder having a Fisher size of 3.0 μm or less is used. If the size of the fisher is larger than 3.0 μm, the surface activity does not show enough for the reaction between oxygen gas and hydrogen, and the effect of suppressing the rise in battery internal pressure and the rise in battery temperature during charging is reduced. Become. The preferred Fisher size is
0.8 to 3.0 μm.

The hydrogen storage alloy electrode of the present invention can be manufactured as follows. First, by a known method,
A hydrogen storage alloy powder layer is supported on a conductive substrate. on the other hand,
A nickel powder having a predetermined Fisher size is prepared by mixing water, ethanol, polyvinyl alcohol, carboxymethylcellulose, methylcellulose, sodium polyacrylate, polyethylene oxide, polyethylene powder, and DN.
A suspension of the nickel powder is prepared by dispersing a predetermined amount in a dispersion medium containing at least one selected from the group consisting of aqueous solution A, gelatin, and polyethylene glycol.

Next, the above-mentioned hydrogen storage alloy electrode is immersed in the above suspension, or a predetermined amount of the suspension is applied to the surface of the hydrogen storage alloy electrode. Thereafter, the treated electrode is dried and further rolled to obtain the electrode of the present invention. In the process of immersion or coating, the individual powder constituting the entire surface of the hydrogen storage alloy powder layer or the powder layer comes into contact with the suspension, and after drying, the nickel powder becomes the hydrogen storage alloy powder layer or the individual powder. To cover the surface.

In this case, since the nickel powder has a three-dimensional chain structure as described above, the coating is not formed as a dense film, but has a porous structure in which the nickel powders are entangled with each other. Become. Therefore, the electrolytic solution can penetrate into the hydrogen storage alloy powder layer through the nickel powder coating, so that the battery reaction is not inhibited.

The nickel powder preferably covers 80% or more of the surface of the hydrogen storage alloy powder layer. If the coating surface area is less than 80%, the catalytic activity for reducing oxygen gas to water is insufficient, and the action of suppressing an increase in battery internal pressure and a rise in battery temperature is reduced. Therefore, when preparing the above-described suspension, it is preferable to adjust the dispersion concentration of the nickel powder so that the nickel powder can cover the surface of the hydrogen storage alloy powder by 80% or more.

[0019]

EXAMPLES Examples 1 to 7 and Comparative Examples 1 to 4 Composition: MmNi _3.3 Co _0.4 Al _0.3 Mn _0.4 (Mm is a misch metal) hydrogen storage alloy was pulverized to an average particle size of 60 μm.
m powder, 100 parts by weight of this powder, 10 parts by weight of nickel powder having an average particle diameter of 0.8 μm, 2 parts by weight of polyvinylidene fluoride powder having an average particle diameter of 3 μm, and a 0.5% aqueous solution of carboxymethyl cellulose as a conductive material. A slurry was prepared by kneading 0.1 part by weight.

This slurry was applied to both sides of a punched nickel sheet (opening diameter 1.5 mm, opening ratio 38%, thickness 0.07 mm), dried at room temperature for 120 minutes, and further pressed at a pressure of 2 mm.
After being roll-rolled at ton / cm ² to form a negative electrode plate having a thickness of 0.4 mm, a heat treatment was performed at 160 to 200 ° C. for 2 hours in a vacuum heating furnace. The weight of the hydrogen storage alloy powder layer supported on the negative electrode plate was 7.0 g.

On the other hand, a nickel powder having a Fisher size shown in Table 1 was dispersed in water to prepare a suspension having the indicated dispersion concentration. Then, the above-mentioned negative electrode plate was immersed in each suspension, taken out, dried at a temperature of 50 ° C. for 30 minutes, and further roll-rolled at a pressure of ² ton / cm ² to produce various hydrogen storage alloy electrodes.

The weight of each hydrogen-absorbing alloy electrode was measured, and the weight before suspension immersion was subtracted from the value to determine the weight of the attached nickel powder. Further, the thickness of the hydrogen storage alloy electrode before and after the nickel powder was attached was measured with a micrometer, and the thickness of the attached nickel powder layer was measured from the difference.

[0023]

(Equation 1)

Based on the above, the area ratio (%) of the nickel powder covering the surface of the hydrogen storage alloy powder layer was calculated. Further, 40.5 parts by weight of an aqueous solution of carboxymethyl cellulose having a concentration of 1.2% by weight and 8 parts by weight of cobalt monoxide powder having a particle size of about 5 μm was added to 100 parts by weight of spherical nickel hydroxide powder having a particle size distribution of 1 to 40 μm. An active material paste was prepared by kneading, filled in a sponge-like nickel plate having a porosity of 96%, dried at a temperature of 80 ° C. for 120 minutes, and then roll-rolled at a pressure of ² ton / cm ² to obtain a 0.6 mm-thick material. A nickel plate was manufactured.

A nylon separator is interposed between each of the above-mentioned hydrogen storage alloy electrodes and the nickel electrode plate, and then wound to form an electrode plate group, which is formed of a nickel-plated stainless steel cylinder. The container was housed in a can, and a predetermined alkaline electrolyte was injected into the container and sealed, thereby assembling a cylindrical nickel-hydrogen secondary battery having an AA size and a rated capacity of 1100 mAh.

With respect to these batteries, battery internal pressure and battery temperature were measured according to the following specifications. Battery internal pressure: Attach a pressure gauge to the bottom of the battery,
The battery was charged at 1100 mAh for 4.5 hours at ℃, and the internal pressure of the battery was measured. Battery temperature: Thermocouple attached outside battery, 1100mA
Charge for 4.5 hours with h and measure the temperature at that time.

Table 1 summarizes the above results.

[0028]

[Table 1]

The following is clear from the results in Table 1. 1) In the battery in which the surface of the hydrogen storage alloy powder layer was not coated with nickel powder (Comparative Example 1), both the battery internal pressure and the battery temperature were lower than those of the battery in which the hydrogen storage alloy electrode of the example was incorporated. It has risen significantly. That is, the effect of coating with nickel powder is obvious.

2) However, as is apparent from Examples 1 to 3 and Comparative Example 2, even if the surface of the electrode is coated with 100% nickel powder, the internal pressure of the battery increases as the nickel powder becomes larger. The battery temperature is rising, and it can be seen that the Fisher size of the nickel powder should be 3.0 μm or less in order to optimize these characteristics.

3) Examples 1, 4 and 5 and Comparative Example 3
As is clear from comparison of No. 4 , hydrogen absorption and
It can be seen that when the ratio of covering the surface of the gold electrode becomes smaller than 80%, the battery internal pressure starts to increase and the battery temperature also starts to increase.

[0032]

As is apparent from the above description, the hydrogen storage alloy electrode of the present invention suppresses both the rise in battery internal pressure and the rise in battery temperature during charging of a battery incorporating the same. This means that the surface of the hydrogen storage alloy powder layer is coated with nickel powder having a Fisher size of 3.0 μm or less, and the reaction between oxygen gas generated during charging by the catalytic action of the nickel powder and hydrogen stored by the hydrogen storage alloy is performed. This is because oxygen gas can be reduced to water by promotion.

Claims (2)

(57) [Claims] 1. A hydrogen storage alloy powder layer is supported on a conductive substrate, and the surface of the hydrogen storage alloy powder layer is made of nickel powder having a three-dimensional chain structure with a Fisher size of 3.0 μm or less. A hydrogen storage alloy electrode characterized by being coated. Wherein said nickel powder, the hydrogen absorbing alloy powder layer of hydrogen storage alloy electrode according to claim 1 which covers 80% of the surface of the.