JPH06267536A - Hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To prevent the deterioration owing to the oxidization in the storing condition, by making 20% or more of the surface of an active material compound in a water soluble binder, so as to reduce the feeding speed of the oxygen in the air. CONSTITUTION:In a hydrogen storage alloy electrode 3 made by applying an active material compound mainly of a hydrogen storage alloy powder to a conductive core, the oxygen in the air is fed to the powder in the storing condition, so as to promote oxidizing deterioration of the hydrogen storage alloy. In this case, by covering 20% or more of the surface of the active material compound with a membrane which consists of a water soluble binder, the feeding speed of the oxygen from the air to the hydrogen storage alloy powder in the active material compound is reduced. As a result, an electrode 3 in which the oxidizing deterioration of the hydrogen storage alloy powder in the storing condition can be suppressed can be obtained. Furthermore, when the membrane is installed to an alkaline battery, it is dissolved in the electrolyte solution, and the electric property can be exercised in a good condition.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hydrogen storage alloy electrode.

[0002]

2. Description of the Related Art In recent years, electronic devices have become more portable and cordless due to higher integration of electronic components and advances in packaging technology. Along with this, there is an increasing demand for higher capacity secondary batteries for driving the electronic devices.

In order to meet the demand for higher capacity, a nickel-hydrogen secondary battery using a hydrogen storage alloy for the negative electrode has been developed with a battery capacity up to about twice that of the nickel-cadmium secondary battery. . Further, the nickel-hydrogen secondary battery is excellent in large-current discharge characteristics and low-temperature discharge characteristics than the nickel-cadmium secondary battery, is effective in environmental protection because it does not contain cadmium, compatibility with nickel-cadmium secondary battery It has advantages such as having.

The hydrogen storage alloy electrode incorporated in the above nickel hydride secondary battery or the like is usually manufactured as follows. First, the hydrogen storage alloy powder is kneaded with a conductive material, a binder, water and the like to prepare an active material paste. After applying this active material paste to the conductive core, drying, pressing,
Cut. Thus, a hydrogen storage alloy electrode in which the conductive core is coated with an active material mixture containing hydrogen storage alloy powder as a main component is manufactured.

By the way, the hydrogen storage alloy powder is easily oxidized and deteriorated by reacting with oxygen in the air to form an oxide film. The hydrogen storage alloy electrode containing the hydrogen storage alloy powder that has been oxidized and deteriorated as described above has a reduced ratio of effective hydrogen storage alloy powder. There is a problem that the polarization is increased to lower the battery voltage.

From the above, in order to suppress the oxidative deterioration of the hydrogen storage alloy powder during the production of the hydrogen storage alloy electrode, the contact time with the air in the wet state of the hydrogen storage alloy powder is shortened. The production line is set up to do so. Particularly in the drying process of the active material paste in which the oxidative deterioration of the hydrogen-absorbing alloy powder is apt to proceed, the time to be in a high temperature state is shortened, or drying is performed in an inert gas atmosphere such as nitrogen gas or argon gas or in vacuum. Etc. are taken.

However, the hydrogen storage alloy electrode is
There is a problem that even during storage before the battery is assembled, the hydrogen storage alloy powder progresses oxidative deterioration due to contact with air.

In order to solve the above-mentioned problems, the hydrogen storage alloy electrodes are stored in a storage room at low temperature and low humidity, in an inert gas atmosphere or in a vacuum, or the hydrogen storage alloy electrodes are individually stored. There is a measure to seal it. However, these measures are essential because they require complicated operations such as controlling the atmosphere each time the hydrogen storage alloy electrode is taken in and out, which impedes mass productivity and increases storage costs. It has not been resolved.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the conventional problems, and an object thereof is to provide a hydrogen storage alloy electrode in which oxidative deterioration of the hydrogen storage alloy powder during storage is suppressed. It is a thing.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a hydrogen storage alloy electrode in which a conductive core is coated with an active material mixture containing hydrogen storage alloy powder as a main component, and 20% or more of the surface of the active material mixture is used. Is a hydrogen storage alloy electrode, characterized in that: is covered with a thin film of a water-soluble binder.

Examples of the conductive core include a perforated metal plate such as punched metal; a metal net; and a metal porous body having a three-dimensional porous structure such as foamed metal such as Celmet (trade name of Sumitomo Electric Industries, Ltd.). To be

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. . For example, the general formula XY _5-a Z _a
(However, X is a rare earth element containing La, Y is Ni, Z is C
o, Mn, Al, Fe, Ti, Cu, Zn, Zr, C
at least one element selected from r, V and B, and a is 0
≦ a <2.0) is used.
Specifically, LaNi ₅ , MmNi ₅ , LmNi ₅ (L
m; lanthanum-enriched misch metal), and some of these Nis as Co, Mn, Al, Fe, Ti, Cu, Z
Examples thereof include multi-element type ones substituted with elements such as n, Zr, Cr, V and B.

Examples of the water-soluble binder forming the thin film include polyacrylic acid salts such as sodium polyacrylate and potassium polyacrylate, water-soluble polymers such as carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA). Can be mentioned. Among these,
From the viewpoint of promptly dissolving the thin film in an alkaline electrolyte to improve the electrode performance when incorporated in an alkaline battery, polyacrylate or carboxymethyl cellulose is preferable.

The reason for limiting the lower limit of the ratio of the surface of the active material mixture coated with the thin film is that if the ratio is less than 20%, the oxidative deterioration of the hydrogen storage alloy powder during storage can be sufficiently suppressed. It will be difficult. Further, the lower limit of the ratio is 20 from the viewpoint of more sufficiently suppressing the oxidative deterioration.
It is desirable to set it as%. The upper limit of the above ratio is 8 from the viewpoint of sufficiently exhibiting electrode performance from the initial stage of battery assembly.
It is desirable to set it to 0%. In the active material, in addition to the hydrogen storage alloy powder and the water-soluble binder, a water-insoluble binder, a conductive material powder, etc. may be blended, if necessary.

Examples of the water-insoluble binder include fluororesins such as polytetrafluoroethylene (PTFE). The mixing ratio of such a binder is
It is desirable that the amount is in the range of 0.1 to 5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder.

Examples of the conductive material powder include carbon black, graphite and acetylene black. The mixing ratio of the conductive material powder is preferably in the range of 0.1 to 4 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. A more preferable mixing ratio of the conductive powder is 0.1 to 2 with respect to 100 parts by weight of the hydrogen storage alloy powder.
The range is parts by weight.

The hydrogen storage alloy electrode described above can be manufactured, for example, by the following method. First, the hydrogen storage alloy powder is kneaded with a water-soluble binder and water to prepare an active material paste. Then, after coating the active material paste on the conductive core, by drying, pressing and cutting,
A hydrogen storage alloy electrode in which 20% or more of the surface of the active material mixture is covered with a thin film composed of the water-soluble binder is manufactured.

[0018]

In the hydrogen storage alloy electrode in which the conductive core is coated with the active material mixture containing hydrogen storage alloy powder as a main component, oxygen in the air is supplied to the hydrogen storage alloy powder during storage and the hydrogen storage alloy powder is stored. The oxidative deterioration of the alloy powder progresses. In particular, when stored under high temperature and high humidity, the oxygen supply rate becomes maximum, and oxidative deterioration of the hydrogen storage alloy powder progresses remarkably.

According to the present invention, 20% of the surface of the active material mixture is
By coating the above with a thin film made of a water-soluble binder, the supply rate of oxygen from the air to the hydrogen storage alloy powder in the active material mixture is reduced. As a result, it is possible to obtain a hydrogen storage alloy electrode in which oxidative deterioration of the hydrogen storage alloy powder during storage is suppressed. Also, since the thin film dissolves in the alkaline electrolyte when incorporated in an alkaline battery, the electrode performance can be exhibited well.

[0020]

EXAMPLES Examples of the present invention will be described in detail below. Example 1

First, lanthanum-enriched misch metal (L
m), nickel, cobalt, manganese, and aluminum were weighed and mixed so that the composition was LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3, and then melted and cooled in a high-frequency induction furnace to prepare a hydrogen storage alloy ingot. Subsequently, this ingot was heat-treated in an electric furnace and then pulverized to obtain a hydrogen storage alloy powder having an average particle size of 50 μm. After mixing 1% by weight of carbon black, 1.5% by weight of PTFE, and 0.2% by weight of sodium polyacrylate with the hydrogen storage alloy powder,
While stirring, water was added until a paste was formed to prepare a negative electrode active material paste. The surface of the active material mixture coated with a thin film made of sodium polyacrylate is uniformly coated with both surfaces of a punched metal having a thickness of 80 μm, dried, and pressed. A hydrogen storage alloy electrode having a ratio (coverage) of 34% was prepared. The coverage was determined by observing the surface of the active material mixture with a microscope and measuring the area of the polysodium acrylate thin film using an image analyzer installed in the microscope. Examples 2 to 4 and Comparative Example 1

The blending amount of sodium polyacrylate is shown in Table 1 below.
In addition, the negative electrode active material paste was prepared by suppressing the change in the paste viscosity due to the change in the compounding amount within a range not impairing the coatability by adjusting the addition amount of water and the stirring time. Except for this, the same procedure as in Example 1 was performed. Thereby, a hydrogen storage alloy electrode having the coverage shown in Table 1 was produced.

The obtained hydrogen storage alloy electrodes of Examples 1 to 4 and Comparative Example 1 were stored for 30 days in a thermo-hygrostat controlled to a humidity of 50% and a temperature of 30 ° C., and then described below (1). ) And (2) were tested. (1) Characteristic test using a unipolar evaluation test cell

First, each hydrogen storage alloy electrode is sandwiched between two large-capacity nickel electrodes via a separator made of polypropylene, and these are immersed in an alkaline electrolyte contained in a case, as shown in FIG. A test cell for unipolar evaluation was assembled. That is, this test cell includes the case 1 having an open top. An alkaline electrolyte 2 is contained in the case 1. In this alkaline electrolyte solution 2, a hydrogen storage alloy electrode 3 is vertically held between two nickel electrodes 4 with a separator 5 interposed therebetween and immersed therein. A pressing plate 6 is provided on each side of the two nickel electrodes 4.
Are arranged and fixed by bolts 7 and nuts 8, respectively. The hydrogen storage alloy electrode 3 is led out by a negative electrode lead 9, and the two nickel electrodes 4 are led out by a positive electrode lead 10.

Next, these test cells were set to 0.3 CmA.
After being overcharged at 1 A, the capacity and average operating voltage of the hydrogen storage alloy electrode were measured by discharging at 1 A. The results are also shown in Table 1 below. (2) Characteristic test with battery model cell

First, each hydrogen storage alloy electrode was wound together with a nickel electrode via a polypropylene separator to prepare an electrode group. After inserting each of these electrode groups into an AA size space of a container equipped with a pressure detector, an alkaline electrolyte is injected into this space, and the space is sealed, as shown in FIG.
A model cell of a battery as shown in Fig. 3 was assembled. That is, this model cell includes a container including the container body 11 and the lid 12. A space 13 having the same inner diameter and height as an AA size battery can is formed in the center of the container body 11, and an electrode group 14 is housed in the space 13 and further an alkaline electrolyte is stored therein. It has been infused. The lid 1
The numeral 2 serves as a sealing plate, and a pressure detector 15 is attached so that the internal pressure of the space 13 can be detected. On the container body 11, the lid 12 is airtightly fixed by a bolt 18 and a nut 19 via a rubber sheet 16 and an O-ring 17. The electrode group 1
The negative electrode lead 20 from the hydrogen storage alloy electrode 4 and the positive electrode lead 21 from the nickel electrode of the same electrode group 14 are led out through between the rubber sheet 16 and the O-ring 17, respectively.

Next, these model cells are set to 0.1 Cm.
The battery was charged to 150% with A and then discharged to 0.8 V with 1A. Subsequently, the battery was charged at 1 CmA for 300% time, and the maximum internal pressure of the model cell was measured. The results are also shown in Table 1 below.

[0028]

[Table 1]

As is apparent from Table 1, the hydrogen storage alloy electrodes of Examples 1 to 4 have a larger electrode capacity than the hydrogen storage alloy electrodes of Comparative Example 1. This is because 20% or more of the surface of the active material mixture was covered with a thin film made of sodium polyacrylate, so that the oxidative deterioration of the hydrogen storage alloy powder during storage in the constant temperature and humidity chamber was suppressed. This is due to the fact.

In the hydrogen storage alloy electrode of Example 4, the thin film made of sodium polyacrylate remained without being dissolved in the alkaline electrolyte during both characteristic tests, and thus the remaining thin film became a resistance component and averaged operation. The maximum internal pressure of the model cell is increased by lowering the voltage and decreasing the reaction area with oxygen gas during overcharge. Therefore, it is understood that the electrode performance is not sufficiently exhibited at the initial stage of charge / discharge. However, when the charge / discharge cycle is repeated thereafter, the thin film is melted / peeled by the expansion / contraction of the hydrogen storage alloy powder, and the electrode performance is sufficiently exhibited.

In the above examples, the coverage was controlled by changing the blending amount of the water-soluble binder sodium polyacrylate. However, the blending amount of other components in the negative electrode active material paste, the drying conditions, It is also possible to control the coverage by changing the press conditions and the like.

[0032]

As described in detail above, according to the present invention, it is possible to provide a hydrogen storage alloy electrode in which the oxidative deterioration of the hydrogen storage alloy powder during storage is suppressed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a test cell for unipolar evaluation used in an example.

FIG. 2 is a cross-sectional view showing a model cell of a battery used in an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Case, 2 ... Alkaline electrolyte solution, 3 ... Hydrogen storage alloy electrode, 4 ... Nickel electrode, 5 ... Separator, 11 ... Container main body, 12 ... Lid body, 14 ... Electrode group, 15 ... Pressure detector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masafumi Fujiwara 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research and Development Center (72) Inventor Kazuta Takeno 3-chome Minami-Shinagawa, Shinagawa-ku, Tokyo No. 4-10 Toshiba Battery Co., Ltd. (72) Inventor Yuji Sato No. 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated, Toshiba Research and Development Center

Claims (1)

[Claims] 1. A hydrogen storage alloy electrode having a conductive core coated with an active material mixture containing hydrogen storage alloy powder as a main component, wherein 20% or more of the surface of the active material mixture is composed of a water-soluble binder. A hydrogen storage alloy electrode characterized by being covered with a thin film.