JP2628013B2 - Conductive material for hydrogen storage alloy electrode and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive material blended in a hydrogen storage alloy electrode incorporated as a negative electrode in an alkaline secondary battery such as a nickel-hydrogen secondary battery and a method for producing the same. The present invention relates to a conductive material for a hydrogen-absorbing alloy electrode which has excellent dispersibility in a slurry used in the production of an electrode and contributes to improvement of a rapid discharge characteristic of a battery, and a method for producing the same.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery using a hydrogen storage alloy as a negative electrode, an electrode having a current collector supporting nickel hydroxide as a positive electrode active material as a positive electrode, and an alkaline aqueous solution as an electrolytic solution has a high capacity. It is attracting attention as a battery. As the hydrogen storage alloy electrode used in this battery, for example, a hydrogen storage alloy powder was mixed with a binder powder such as polytetrafluoroethylene powder, polyethylene powder, and polypropylene powder, and the mixture was formed into a sheet. Further, there are known collectors such as a conductive mesh sheet and a punched metal sheet having a desired porosity, which are coated or filled with a hydrogen storage alloy powder, and the like.

[0003] Of these electrodes, the latter is generally manufactured as follows. First, a slurry of the hydrogen storage alloy powder is prepared as follows. For example, in a thickener aqueous solution 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, hydrogen having a predetermined particle size A predetermined amount of the storage alloy powder is dispersed. At this time, for example, polytetrafluoroethylene powder, polyethylene powder, etc., in order to strengthen the mutual binding of the alloy powders in the hydrogen storage alloy layer carried on the current collector and to prevent them from peeling off from the current collector. , Polypropylene powder, polyvinylidene fluoride powder, or a binder powder such as cobalt powder, copper powder, carbon powder, etc. An appropriate amount of such conductive material powder is blended.

[0004] A current collector such as a punched nickel sheet or a nickel net is immersed in the slurry thus prepared, and the current collector is pulled up at a predetermined speed to fill the current collector with the slurry. Apply. Then, after drying the slurry carried on the current collector, by performing a rolling process at a predetermined pressure on the whole, while controlling the thickness of the dried slurry layer to a predetermined thickness,
It is held in close contact with the current collector to form a target hydrogen storage alloy electrode.

[0005] When polytetrafluoroethylene powder or polyvinylidene fluoride powder is used as the binder powder, the above-mentioned rolling treatment is followed by firing at a temperature of about 150 to 210 ° C in a nitrogen atmosphere, for example. Therefore, a measure is taken to soften and bind these binders. By the way, it is known that a battery having a negative electrode of a hydrogen storage alloy electrode manufactured using a slurry in which carbonyl nickel powder having a predetermined particle size is blended as a conductive material is suppressed from increasing in internal battery pressure during overcharge. (See Japanese Patent Application Laid-Open No. 3-179664).

The carbonyl nickel powder proposed here is produced by pyrolyzing nickel carbonyl and has a three-dimensionally branched chain structure such as a structure of carbon black. It contains carbon as a residue at the time of decomposition.
Those commercially available from NCO under trade names such as Type 210 and Type 205 can be cited as typical examples.

[0007]

However, the above-mentioned carbonyl nickel powder is poor in dispersibility in a slurry and, at the same time, has a property that it is very easily aggregated. Therefore, when the whole slurry is subjected to a stirring treatment for the purpose of uniformly dispersing the slurry after being blended into the slurry, the carbonyl nickel powders are associated with each other, and as a result, secondary aggregation occurs to cause a larger diameter. The slurry is dispersed in the slurry in a state of being granulated.

When the current collector is immersed in the slurry in such a state to form a slurry layer on the surface thereof, a secondary aggregate of carbonyl nickel powder having a diameter of about 0.1 to 1 mm is formed on the surface of the slurry layer. And appear in a state of being distributed in large numbers as pill-shaped projections. Thereafter, when the slurry layer and the current collector are subjected to a predetermined rolling treatment, the pill-shaped projections are flattened, and the slurry layer after rolling has a large number of circular spots having metallic luster distributed therein. To be observed.

When such an electrode is incorporated in a battery as a negative electrode, the obtained battery tends to have a deteriorated battery characteristic such as a rapid discharge characteristic. Further, when carbonyl nickel powder is used as the conductive material, even if the theoretical core amount calculated based on the premise that the dispersibility in the slurry is good and secondary aggregation does not occur, the actual production process In the case of, due to secondary agglomeration, apparent reduction is caused in the hydrogen storage alloy layer, so that the actual current collecting ability is not exhibited.

[0010] Therefore, in order to allow the electrode to exhibit an appropriate current collecting ability, an excess amount of carbonyl nickel powder more than a necessary amount must be added to the slurry. The present invention solves the above-mentioned problem when conventional carbonyl nickel powder is used as a conductive material, has excellent dispersibility in slurry, and has the above-mentioned pill-shaped projections on a slurry layer formed on the surface of a current collector. It is an object of the present invention to provide a conductive material for a hydrogen-absorbing alloy electrode which can contribute to improvement of battery performance such as rapid discharge characteristics of a battery without being expressed as a battery, and a method of manufacturing the same.

[0011]

In order to achieve the above object, in the present invention, a carbonyl nickel powder is used.
Carbonyl nickel powder refined by applying mechanical external force
There, an average particle diameter 2~8μm when measured by a laser diffraction particle size measurement method, and a bulk density of 0.4～1.0G /
hydrogen storage alloy electrode for the conductive material, characterized in that it consists of carbon sulfonyl nickel powder is cm ³ is provided, also, tertiary
A method for producing a conductive material for a hydrogen-absorbing alloy electrode is provided, wherein a mechanical external force is applied to carbonyl nickel powder having a chain structure branched in the original direction to make the carbonyl nickel powder finer. You.

[0012] The conductive material of the present invention is produced by subjecting carbonyl nickel powder to a process described later. This conductive material first has an average particle size in the range of 2 to 8 μm as measured by a laser diffraction type particle size measuring method. That is, for example, a surfactant such as a neutral detergent
This conductive material is put into a dispersion liquid in which the weight% is added, and the conductive material is usually dispersed by ultrasonic waves of 30 to 60 MHz, and after 20 seconds, the turbidity of the dispersion liquid when irradiated with laser light is measured. The particle size is calculated from the time change.

In the case where the conductive material has a particle size of more than 8 μm, the dispersibility in the slurry is poor and secondary aggregation is likely to occur. Therefore, when the slurry layer is formed, the above-mentioned appearance of the ball-shaped projections is sufficiently prevented. Can not do it. In addition, even if the particle size is smaller than 2 μm, the effect of preventing the appearance of the ball-shaped projections not only reaches saturation, but also the use of externally unnecessary mechanical force on the carbonyl nickel powder at the time of manufacturing described later. This is because it is uneconomical.

Further, the bulk density of this conductive material is 0.4 to 1.0 g /
It is in the range of cm ^3. In the case of the conductive material of the present invention, when the carbonyl nickel powder is subjected to the processing described below, the obtained carbonyl nickel powder has a complicated three-dimensional structure broken before the processing, and therefore, has a finer grain size. It is believed that the individual granules are reagglomerated and granulated, so to speak, as a result of which the resulting powder has a higher density than the original carbonyl nickel powder. .

Therefore, the above bulk density is considered to be a factor indicating the re-agglomeration or granulation state of the powder in the finely divided state. The material is 3 of the original carbonyl nickel powder
It means that it is an aggregate of carbonyl nickel powder having a chain shape smaller than the chain shape of the three-dimensional structure. In other words, the dense body has few voids, and therefore is a powder that hardly causes further aggregation and has improved dispersibility in slurry.

From the above, the bulk density is 0.4 g / cm ³
Smaller particles have poor dispersibility in the slurry and still have a property of easily agglomerating. Therefore, it is not possible to prevent the appearance of the ball-shaped projections during the formation of the slurry layer. Further, those having a bulk density of more than 1.0 g / cm ³ are effective in preventing the appearance of pill-shaped projections, but are likely to settle in the slurry and hinder uniform slurry preparation. Become.

The cohesive force of the carbonyl nickel powder and
A comparison of the cohesive force of a material that has once been made finer and then re-agglomerated (the conductive material of the present invention) is stronger in the former than in the latter. That is, the conductive material of the present invention is easily decomposed when a force higher than the force required for the above-mentioned aggregation is applied, and restores the state before the aggregation, that is, the state in which the carbonyl nickel powder is finely divided.

The conductive material of the present invention can be manufactured as follows. That is, first, carbonyl nickel powder is prepared as a raw material. For example, Ty manufactured by INCO
pe210, Type205, and the like. The particle size of the carbonyl nickel powder is usually 9 to 18 μm when measured by a laser diffraction type particle size measuring method.

Next, a mechanical external force is applied to the carbonyl nickel powder. Specifically, the carbonyl nickel powder is supplied to a rotary drum mixer, a V-blender, a chopper mill,
After throwing into a normal crushing and mixing machine such as a jet mill,
These pulverizers and mixers may be operated. A force such as, for example, a shearing force acts on the supplied carbonyl nickel powder. At that time, the secondary aggregation occurs at first due to the mutual association of the carbonyl nickel powder, and then the secondary aggregate and the initial carbonyl nickel powder are pulverized by the action of further force, respectively, and the carbonyl nickel powder is three-dimensional. The chain shape of the structure is destroyed and the particles are refined. At the same time, between the finely divided carbonyl nickel powders, an agglomeration action is effected to promote agglomeration and become the conductive material of the present invention.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) Production of Conductive Material 1000 g of Type 210 (trade name, carbonyl nickel powder manufactured by INCO) was put into a chopper mill (Spartan Luzer RMO-2H type, manufactured by Fuji Paudal Co., Ltd.) and operated at 5000 rpm for 3 minutes. .

The particle size, bulk density, specific surface area,
The sieve passage time was measured based on the following specifications. For comparison, the same measurement was performed for Type 210. Particle size: Powder is dispersed in a mixed solution of water and a neutral detergent by applying ultrasonic vibration. After pretreatment, Laser Micron sizer 7000S (laser diffraction type particle size analyzer manufactured by Seishin Enterprise Co., Ltd.) Measured using

Bulk density: Measured using IH-2000 (bulk density measuring device manufactured by Seishin Enterprise Co., Ltd.). Specific surface area: Measured by the BET method. Sieve passing time: Place the powder on a 40 mesh (Tyler) electric sieve and measure the time required for 99% of the powder to pass.

The results are shown in Table 1.

[0024]

[Table 1] In addition, the conductive material of the present invention and Type 21 before sieving were used.
Scanning electron micrographs (magnification: 75) of 0 are shown in FIGS.

From the scanning electron micrograph, immediately after the grain refinement, the conductive material of the present invention appears to have a larger overall particle size due to agglomeration, but this is due to the granulated carbonyl nickel powder having a smaller particle size. Is apparent from the measured particle size after the dispersion operation. Further, when the sieving operation is performed, it can be seen that the above-mentioned granulated product is refined and passed through the 40-mesh sieve in a short time.

(2) Production of Hydrogen Storage Alloy Electrode First, the composition: MmNi _3.3 Co _1.0 M
n _0.4 Al _0.3 (and only, Mm is the representative of the Mi Sshumetaru) was melted a hydrogen storage alloy represented by, and the hydrogen-absorbing alloy powder of 150 mesh or less by grinding the ingot (Tyler sieve).

Next, an aqueous solution of a thickener 250 obtained by dissolving 1% by weight of carboxymethyl cellulose in ion-exchanged water is used.
Then, 1000 g of the hydrogen-absorbing alloy powder, 150 g of the conductive material produced from (1), and 30 g of polyvinylidene fluoride powder having an average particle diameter of 3 μm were added to the mixture, and the whole was sufficiently stirred to prepare a slurry (1). For comparison, a slurry (2) containing 150 g of Type 210 as it was as a conductive material was prepared.

A perforated nickel sheet having a thickness of 0.07 mm and a porosity of 38% (hole diameter of 1.5 mm) was dipped into these slurries, pulled up, dried in the air, and dried in air.
After rolling at a pressure of n / cm ² , the whole was baked for 1 hour in a nitrogen atmosphere at 170 ° C. to produce two negative electrode sheets (hydrogen storage alloy electrodes). The number of protrusions on the surface of each sheet was measured with a microscope to calculate the number per 100 cm ² .

The negative electrode sheet using the slurry (1) has a thickness of 0.1
The number was 5 pieces / 100 cm ² , and 200 pieces / 100 cm ² in the negative electrode sheet using the slurry (2). (3) Production of battery A sponge-like nickel sheet having a thickness of 1.1 mm and a porosity of 94% is provided with 93% by weight of Ni (OH) ₂ powder, 3% by weight of Ni powder,
An active material mixture prepared by adding a 1% aqueous carboxymethylcellulose solution to a mixed powder consisting of 4% by weight of oO powder was filled, dried at 100 ° C. for 2 hours, and then rolled at a pressure of 5 ton / cm ² to form a positive electrode. A sheet was manufactured. The filling amount of the active material mixture was 3.6 g.

A nylon separator is arranged between the positive electrode sheet and the above-mentioned negative electrode sheet, and the whole is spirally wound to form a power generating element having a diameter of about 13 mm. Two sealed cylindrical batteries each having a rated capacity of 1100 mAh were manufactured by placing them in a 0.2 mm cylindrical container, injecting a KOH aqueous solution having a specific gravity of 1.37, and closing the lid.

Next, these batteries were charged at 20 ° C. for 3 hours.
The discharge capacity was measured under the condition of C. The discharge capacity of the battery incorporating the negative electrode sheet using the slurry (1) is 98
0 mAh, and the discharge capacity of the battery incorporating the negative electrode sheet using the slurry (2) was 900 mAh.

[0032]

As is apparent from the above description, the hydrogen storage alloy electrode produced by using the slurry containing the conductive material of the present invention hardly shows hair ball-shaped projections.
Also, the rapid discharge characteristics of a battery incorporating the electrode as a negative electrode have been greatly improved. This is an effect obtained by applying mechanical external force to commercially available carbonyl nickel powder to make it finer, and at the same time, to use the granulated powder as the conductive material.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing a grain shape of a conductive material of the present invention before sieving.

FIG. 2 is a scanning electron micrograph showing the particle shape of a conventional carbonyl nickel powder.

Claims (2)

(57) [Claims] 1. A mechanical external force is applied to carbonyl nickel powder.
In addition, finely divided carbonyl nickel powder having an average particle size of 2 to 8 as measured by a laser diffraction type particle size measuring method.
A conductive material for a hydrogen storage alloy electrode, comprising carbonyl nickel powder having a thickness of 0.4 μm and a bulk density of 0.4 to 1.0 g / cm ³ . 2. A hydrogen-absorbing alloy characterized in that the carbonyl nickel powder is refined by applying a mechanical external force to the carbonyl nickel powder having a chain structure branched in a three-dimensional direction. A method for producing a conductive material for an electrode.