JPH09320577A - Manufacture of hydrogen absorbing alloy electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a hydrogen absorbing alloy electrode which can easily be manufactured at low cost and has enhanced electric characteristics by improving a hydrogen absorbing alloy electrode manufacturing method that requires a troublesome job of preparing a plate by addition of a binder to hydrogen absorbing alloy powder in addition to a thickener and that causes an increase in the cost of manufacture. SOLUTION: A slurry in the form of a paste, composed chiefly of hydrogen absorbing alloy powders and prepared by adding a conductive agent and at least an aqueous solution of polyvinyl alcohol as a consistency imparting agent to the powders and kneading them together, is applied to a conductive substrate and is heat treated at 120 to 200 deg.C for one to five minutes after drying and pressurization, so that a condensate of the polyvinyl alcohol works as a binding agent. Therefore, an electrode can be obtained in which the hydrogen absorbing alloy does not undergo thermal deterioration so that its electric characteristic is enhanced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art A hydrogen storage electrode used as a negative electrode of a nickel-hydrogen storage battery is generally manufactured as follows. That is, MmNi ₅ or a part of Ni is replaced with Co, Al, M
Mainly consists of MmNi-based hydrogen storage alloy powder substituted with n or the like, and a conductive agent powder such as cobalt, copper, nickel or carbon, and a paste form for coating the hydrogen storage alloy powder on the conductive substrate. In order to do so, as a thickener, polyvinyl alcohol, methyl cellulose, polyethylene oxide, at least one kind of water-soluble synthetic resin powder such as carboxymethyl cellulose is kneaded with a thickener aqueous solution dissolved in water to form a paste slurry, In addition to this, the polytetrafluoroethylene powder, the polypropylene powder, the polyvinylidene fluoride powder as a binder that prevents the alloy powder coated on the conductive substrate from peeling and firmly bonds the alloy powders to each other. To prepare a slurry in which at least one kind of water-insoluble binder powder such as This is applied to a conductive substrate to form a slurry layer, which is then dried and pressure-molded to a predetermined thickness, and then heated to a temperature at which the surface of the binder powder melts at least in a heating furnace. 150-2 for rides
It was heated at 10 ° C. for several hours to bond the particles of the hydrogen-absorbing alloy powder to each other to manufacture a hydrogen-absorbing alloy electrode without dropping of the alloy powder.

[0003]

The above-mentioned conventional method for manufacturing a hydrogen storage alloy electrode requires a complicated work of adding a water-insoluble binder powder separately from the thickener and uniformly kneading. In addition, the production cost is increased, and further, in order to prevent the coating of the hydrogen storage alloy coating from peeling off from the conductive substrate, a long heat treatment for several hours is required. In addition to the above, the heating for a long time causes thermal deterioration of the hydrogen alloy powder, which significantly deteriorates the hydrogen storage characteristics, which inevitably causes a reduction in the discharge capacity of the storage battery using this as an anode. It was

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems all at once, can be manufactured easily and at low cost, and can firmly obtain alloy powder mutual binding and peel off the adhered material. The present invention provides a method for producing a hydrogen storage alloy electrode having an increased discharge capacity without thermal deterioration of the hydrogen storage alloy, which is mainly composed of hydrogen storage alloy powder, and a conductive agent powder and at least polyvinyl alcohol added thereto. After a paste-like slurry obtained by kneading a thickener aqueous solution in which is dissolved in water is applied to a conductive substrate to form a slurry layer, which is dried and pressure-molded to a predetermined thickness, 120- 1 at 200 ° C
The heat treatment is performed for 5 minutes.

[0005]

As described above, according to the present invention, since the use of the water-insoluble binder, which has been conventionally required for manufacturing the hydrogen storage alloy electrode, is eliminated, the electrode manufacturing work is easy and the manufacturing cost is reduced. Bring In addition, polyvinyl alcohol was originally
It acts as a thickening agent, imparts a thickening agent to the slurry, and serves not only for application to a conductive substrate, but also at 120 ° C to 20 ° C.
Polyvinyl alcohol is condensed by heating in the range of 0 ° C., and the condensate is a water-insoluble and strong bond that causes strong bonding between the hydrogen storage alloy powder particles and strong bonding to the conductive substrate. Serves as an agent, dropping of alloy powder,
A stable and robust battery with no peeling of the adherend and improved discharge characteristics is provided.

[0006]

Next, an embodiment of the present invention will be described. The type of alloy of the hydrogen storage alloy powder, which is the main raw material for producing the electrode of the present invention, can be appropriately selected from all conventionally known types such as MmNi type and LaNi type. As the conductive agent added to this, at least one selected from conventionally known metal powders such as cobalt powder, copper powder, and nickel powder, and carbon powder is selected and used. The amount of addition is 0.5 to 2 by weight ratio with respect to the hydrogen storage alloy powder.
The range is 0%. Further, at least polyvinyl alcohol (PVA) is indispensable as a thickening agent, and if necessary, as another water-soluble thickening agent, a known thickening agent such as methyl cellulose, carboxymethyl cellulose, or polyethylene oxide can be used. At least one kind may be used in combination, and at least 0.5 to 10 wt. %, Added and dissolved to prepare a thickener aqueous solution. Thus, the hydrogen storage alloy powder is mainly used, and the conductive agent powder and the thickener aqueous solution containing at least PVA are mixed and kneaded to prepare a paste slurry. Next, this is applied to a conductive substrate to form a slurry layer thereof. As the conductive substrate, a non-perforated metal foil, a non-perforated thin metal sheet, a perforated punching metal sheet, a wire mesh sheet, or a three-dimensional micro-perforated metal sheet such as foam metal is selectively used. In the case of a non-porous conductive substrate, a coating work is performed to apply the slurry to both sides with a uniform thickness, and in the case of a porous conductive substrate, the slurry is filled in a large number of holes and both sides are filled. A coating operation is performed to form a slurry layer having a uniform thickness. Then, the slurry-coated conductive positive electrode plate is heated at a temperature of 100 ° C. or lower to evaporate water to dry the slurry layer, and then pressure-formed to a uniform thickness through a pair of pressure rollers. Then, after obtaining the dry-filled substrate, according to the present invention, it is introduced into a heating furnace such as an electric furnace, and as it is, or under an inert gas atmosphere in which nitrogen gas, argon gas, etc. are introduced, or inside Of the hydrogen-absorbing alloy of the present invention by heating at a temperature of 120 to 200 ° C. for a short time of only 1 to 5 minutes under a vacuum reduced pressure in which the air of the above is removed by suction, and then rapidly cooling to room temperature and then discharging from a heating furnace. An electrode is obtained.

The reason for heating at 120 ° C. or higher is to bond the polyvinyl alcohol in the hydrogen storage alloy coating layer to form a water-insoluble and binding strong condensate. 20
If the temperature exceeds 0 ° C, the alloy powder particles will be deteriorated by heat, which is not preferable. Further, the reason for limiting the time to 1 to 5 minutes is that at least 1 minute is required to produce the condensation product of polyvinyl alcohol at the above heating temperature, while if it exceeds 5 minutes, the alloy powder is This is because heat deterioration deteriorates the hydrogen storage characteristics and the like. Usually, since a long strip-shaped sheet is used as the conductive substrate, a large number of electrode plates can be selectively obtained by cutting into a predetermined electrode plate size after the above heat treatment.

[0008]

EXAMPLES Next, specific examples 1 to 6 of the present invention will be described together with comparative examples 1 to 3 and a conventional example. Example 1 A hydrogen storage alloy having a composition of MmNi _3.3 Co _0.9 Al _0.3 Mn _0.4 (Mm is misch metal) was crushed to obtain an average particle size of 60.
A powder having a size of μm was prepared, and 100 parts by weight of this powder was kneaded with 10 parts by weight of nickel powder as a conductive agent and 20 parts by weight of a 5% aqueous solution of polyvinyl alcohol as a thickening agent to prepare a slurry. This slurry was punched into a nickel sheet (opening diameter 1.5 mm, opening ratio 38%, thickness 0.07).
(mm) opening and apply it on both sides to form a slurry layer, then heat at 80 ° C. to remove water and dry, and further roll with a pair of rolls at a pressing force of ² ton / cm ^2. Then, a negative electrode plate having a total thickness of 0.4 mm is formed, and then heat treatment is performed in air at a temperature of 120 to 200 ° C. for 1 to 5 minutes in a heating furnace to give a hydrogen storage alloy electrode of Example 1 shown in Table 1 below. Was manufactured. Examples 2 to 6 A hydrogen storage alloy having a composition of MmNi _3.3 Co _0.9 Al _0.3 Mn _0.4 (Mm is misch metal) was crushed to obtain an average particle size of 60.
As a conductive agent, 10 parts by weight of nickel powder, 9 parts by weight of a 10% aqueous solution of polyvinyl alcohol and 10 parts by weight of a 0.5% aqueous solution of carboxymethyl cellulose were kneaded with 100 parts by weight of this powder. To prepare a slurry. A punching nickel sheet (opening diameter 1.5 mm, opening ratio 38%, thickness 0.
(07 mm) opening and apply it on both sides to form a slurry layer, then heat at 80 ° C. to remove water and dry, and further roll with a pair of rolls at a pressing force of ² ton / cm ^2. Then, after making a negative electrode plate having a total thickness of 0.4 mm, it is heated at a temperature of 120 to 200 ° C. for 1 to 1
Example 2 shown in Table 1 below after heat treatment in air for 5 minutes
~ 6 hydrogen storage alloy electrodes were produced.

Comparative Examples 1 to 6 For comparison, the same negative electrode plate as described above was used at a temperature of 1
Heat treatment was carried out under conditions deviating from one or both of 20 to 200 ° C. and 1 to 5 minutes to manufacture hydrogen storage alloy electrodes of Comparative Examples 1 to 6 shown in Table 1.

Conventional Example On the other hand, as a conventional example, a hydrogen storage alloy electrode was manufactured by the following manufacturing method. Using the same hydrogen storage alloy powder as that used in the production of Examples 1 to 5, with respect to 100 parts by weight of this powder, 10 parts by weight of nickel powder as a conductive agent and 0.5% of carboxymethylcellulose as a thickening agent. A slurry was prepared by kneading 10 parts by weight of the aqueous solution and 2 parts by weight of polyvinylidene fluoride powder as a binder. This slurry was filled in the openings of a punching nickel sheet and applied on both sides thereof, then heated at 80 ° C., and further rolled at a pressing force of ² ton / cm ² to obtain an overall thickness of 0.
After making a negative electrode plate of 4 mm, the temperature is 170 ° C. in a heating furnace.
A hydrogen storage alloy electrode was manufactured by performing heat treatment in nitrogen for 60 minutes.

The hydrogen storage electrodes of Examples 1 to 6, Comparative Examples 1 to 6 and the conventional example were subjected to a unipolar test by the following method, and the discharge capacity per gram of the hydrogen storage alloy after being sufficiently activated. Was measured. The monopolar test was performed as follows. That is, 30 wt. % Potassium hydroxide aqueous solution as an electrolytic solution, using metallic nickel as a counter electrode, a mercury oxide electrode as a reference electrode, and a hydrogen storage alloy electrode prepared as described above as a working electrode, in a container filled with the electrolytic solution. Put these in 3
The battery was charged at 0 mA / g, left for 15 hours, and then discharged until the hydrogen storage alloy potential became −750 mV (vs. Hg / HgO). Then, after charging / discharging at 70 mA / g for several cycles until the capacity became stable, the discharge capacity was measured. Further, these electrodes were immersed in an electrolytic solution, and the appearance at that time was examined for the presence or absence of peeling of the coating. The results are shown in Table 1 below.

[0012]

[Table 1]

As is apparent from Table 1 above, the conventional example is
No peeling of the coated material occurs, but the discharge capacities are those of Examples 1 to 6
It is lower than. This proves that the storage characteristics of the hydrogen storage alloy are thermally deteriorated. In Comparative Examples 1 to 6, as is clear from comparison with Examples 1 to 6, when the heat treatment is not carried out, the condensation of polyvinyl alcohol does not occur when the heating temperature is lower than 120 ° C., and accordingly Since it has only a weak binding force, it causes peeling of the adhered material and is not practical as a negative electrode. On the other hand, the heating temperature is 20
If the heating time exceeds 5 minutes, even if the heating temperature exceeds 0 ° C. or the heating temperature exceeds 200 ° C. and 120 ° C. or more, the coating material does not peel off, but the discharge capacity is 120 to 200.
Example 1 of the present invention, which is a heat treatment condition at 1 ° C for 1 to 5 minutes
It is significantly lower than that of No. 5.

In the production of the electrodes of Examples 1 to 6 above, polyvinyl alcohol serves as a thickening agent in the preparation of the paste, and also serves as a binder under the above heat treatment conditions. Since it is not necessary to add a binder separately, peeling of the adhered material is prevented, and compared with an electrode obtained by using a conventional binder and heating at high temperature for a long time, a hydrogen storage alloy Since it does not cause thermal deterioration and maintains good hydrogen storage characteristics, it provides a hydrogen storage alloy electrode with improved discharge capacity.

[0015]

As described above, according to the present invention, in addition to using polyvinyl alcohol as a thickener for forming a hydrogen storage alloy into a paste-like slurry, 120
The hydrogen storage alloy powder particles are firmly bound to each other by a heat treatment of heating at a heating temperature of ~ 200 ° C for 1 to 5 minutes, and
The adhered material prevents the hydrogen storage alloy applied to the conductive substrate from peeling off, resulting in a hydrogen storage alloy electrode that is stable and robust and has improved electrical characteristics. Since they are not used together, an electrode that is easy to manufacture and has a low manufacturing cost can be obtained.

Claims (1)

[Claims] 1. A paste-like slurry obtained by kneading a hydrogen-absorbing alloy powder as a main component, and a conductive agent powder added to the powder and a thickener aqueous solution in which at least polyvinyl alcohol is dissolved in water are kneaded on a conductive substrate. After coating and forming a slurry layer, drying and press-molding to a predetermined thickness, 120-2
A method for producing a hydrogen storage alloy electrode, which comprises heat treatment at 00 ° C. for 1 to 5 minutes.