JPH05151967A - Electrode of hydrogen occluding alloy - Google Patents

Abstract

PURPOSE:To provide an electrode of hydrogen occluding alloy, with which the high rate discharging characteristics and low temperature discharging characteristics of the battery are enhanced to a great extent by activating the hydrogen occluding alloy from the beginning of operating cycles. CONSTITUTION:An electrode is made of a hydrogen occluding alloy containing cobalt or nickel, wherein the inter-metal compound phase with cobalt or nickel concentrated exists without forming solid solution with the parent phase.

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 made of a hydrogen storage alloy containing cobalt or nickel.

[0002]

2. Description of the Related Art Lead-acid batteries and nickel-cadmium batteries have been conventionally used as storage batteries. However, in recent years, since it is possible to have a lighter weight and a higher capacity than these batteries, an electrode provided with a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, which is a negative electrode active material, particularly under normal pressure. Is used as the negative electrode, and a metal oxide having a metal oxide such as nickel hydroxide as the positive electrode active material is used as the positive electrode.
Hydrogen alkaline storage batteries are receiving attention.

However, the above-mentioned metal-hydrogen alkaline storage battery has a problem that the initial capacity becomes small because hydrogen cannot be sufficiently absorbed and released during charging at the beginning of the charge / discharge cycle of the battery. Therefore, conventionally, hydrogen storage alloys have been subjected to chemical conversion treatment such that cracks are formed on the surface of the hydrogen storage alloys by absorbing and releasing hydrogen and repeating expansion and contraction of the alloy volume before shipping the batteries. Have been proposed.

[0004]

However, in the above method, the activation cannot be sufficiently achieved, and as a result, the high rate discharge characteristics and the low temperature discharge characteristics at the beginning of the charge / discharge cycle are dramatically improved. There was a problem that it was not possible. The present invention has been made in view of the present situation, and can activate the hydrogen storage alloy from the beginning of the cycle to dramatically improve the high rate discharge characteristics and the low temperature discharge characteristics of the battery using the same. An object is to provide a hydrogen storage alloy electrode.

[0005]

In order to achieve the above object, the present invention provides a hydrogen storage alloy electrode comprising a hydrogen storage alloy containing cobalt or nickel, wherein at least cobalt or nickel is contained in the hydrogen storage alloy. It is characterized in that the intermetallic compound phase as one component is present without forming a solid solution with the matrix phase.

[0006]

As described above, if an intermetallic compound phase that does not form a solid solution with the parent phase exists in the hydrogen storage alloy, the crystal structure of the alloy is distorted, so that the crystal lattice expands during hydrogen storage. , Large internal stress occurs. Therefore, many cracks are generated in the hydrogen storage alloy to form a new active surface, so that the reaction surface area of the hydrogen storage alloy becomes large. As a result, activation of the alloy proceeds from the beginning of the charge / discharge cycle.

In addition, if cracks occur in the alloy, nickel or cobalt will be present on the new active surface. In this case, nickel or cobalt has a large catalytic action to promote the hydrogen storage / release reaction. As a result, the discharge characteristics are improved even at low temperatures at which hydrogen storage / release reactions are unlikely to occur.

[0008]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. [Example 1] An example of a method for producing a hydrogen storage alloy electrode according to the present invention will be described below.

First, commercially available Mm (mixture of rare earth elements, which is a misch metal), Ni, Co, Mn, Al and Mo in an element ratio of 1: 3.4: 0.8: 0.4: 0. ．
After weighing so that the ratio becomes 4: 0.09, it is melted in a high-frequency melting furnace to prepare a molten metal. Next, by cooling the molten metal, MmNi _3.4 Co _0.8 Mn
A hydrogen storage alloy ingot represented by _0.4 Al _0.4 Mo _0.09 was prepared. Next, the hydrogen-storing alloy ingot was pulverized to have a particle size of 50 μm or less, and then the hydrogen-storing alloy powder (1 g) was mixed with PTFE (polytetrafluoroethylene, 0.2 g) as a binder. , Nickel powder (0.8 g) as a conductive agent were added and kneaded, and the mixture was wrapped in a nickel mesh to apply pressure.

The electrode thus prepared is described below (A
₁ ) It is called an electrode. Example 2 A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that B was used in place of Mo as a raw material of the hydrogen storage alloy (that is, the hydrogen storage alloy was MmNi.
_3.4 Co _0.8 Mn _0.4 Al _0.4 B _0.09 ).

The electrode thus produced is described below (A
₂ ) Referred to as an electrode. [Example 3] A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that Ta was used instead of Mo as a raw material for the hydrogen storage alloy (that is, the hydrogen storage alloy was MmNi.
_3.4 Co _0.8 Mn _0.4 Al _0.4 Ta _0.09 ).

The electrode produced in this manner is described below (A
₃ ) It is called an electrode. As a raw material of Comparative Example 1 a hydrogen storage alloy, other using no Mo is A battery was fabricated in the same manner as in Example 1 (i.e., the hydrogen storage alloy _MmNi 3.4 _Co 0.8 Mn
_0.4 Al _0.4 ).

The electrode thus manufactured is hereinafter referred to as (X) electrode. [Experiment 1] The initial discharge rate characteristics of the (A ₁ ) electrode to (A ₃ ) electrode of the present invention and the (X) electrode of the comparative example were examined, and the results are shown in Table 1 below. In the experiment, a 30% KOH solution was used as an electrolytic solution and a sintered nickel positive electrode was used as a counter electrode. The experimental condition is 50 mA.
50 mA / g and 20 after charging for 8 hours at a current of / g
The conditions were such that each was discharged at a current of 0 mA / g, and the experiment temperature was two temperatures of 25 ° C and -10 ° C. Then, the evaluation of the experiment was performed by setting the discharge capacity when discharged at 50 mA / g to C ₁ and the discharge capacity when discharged at 200 mA / g to C _2, and C ₂ / C ₁ × 100 (%)
It was performed by calculating [discharge capacity ratio].

[0014]

[Table 1] As is clear from Table 1 above, the (X) electrode of the comparative example has a discharge capacity ratio of 70% at 25 ° C.
In the (A ₁ ) electrode to (A ₃ ) electrode of the present invention, the discharge capacity ratio at 25 ° C. is 87 to 92%, and it is recognized that the discharge capacity ratio is high.

Further, as is clear from Table 1, in the (X) electrode of the comparative example, the discharge capacity ratio at -10 ° C was 30%, which was significantly lower than the discharge capacity ratio at 25 ° C. On the other hand, in the (A ₁ ) electrode to (A ₃ ) electrode of the present invention, the discharge capacity ratio at −10 ° C. is 76 to 80%, and
It is recognized that the discharge capacity ratio at 5 ° C. is not so much decreased.

Therefore, the (A ₁ ) electrodes to (A ₃ ) of the present invention are used.
Experiments 2 to 4 described below were conducted in order to investigate the reason why the electrode has better discharge rate characteristics than the (X) electrode of the comparative example. [Experiment 2] The hydrogen storage alloys of the (A ₁ ) electrode and the (A ₂ ) electrode of the present invention were examined by the X-ray diffraction method, and the results are shown in FIGS. 1 and 2.

As is apparent from FIG. 1, in the hydrogen storage alloy of the (A ₁ ) electrode, μ-Co-Ni-Mo (CoMo ₂
It is recognized that an intermetallic compound phase represented by Ni) has newly appeared. Also, as is clear from FIG.
In the hydrogen storage alloy of the (A ₂ ) electrode, it is recognized that an intermetallic compound phase represented by MmCo ₄ B has newly appeared.

Although not shown in the figure, in the hydrogen storage alloy of the (X) electrode of the comparative example, μ-Co-Ni-Mo and MmCo were used.
_{4 B} is make sure that does not appear. Further, it has been confirmed by experiments that the intermetallic compound phase in the case of using Ta as the additive element [(A ₃ ) electrode] is Ni ₃ Ta, CoTa ₂ . [Experiment 3] Electron reflection images of the hydrogen storage alloys of the (A ₁ ) electrode and the (A ₂ ) electrode were examined (see FIGS. 3 and 4 respectively).
Shown in Fig.), A site different from the matrix (μ-Co-Ni-M
o, EPMA-in the site where MmCo ₄ B exists)
Since the quantitative analysis by ZAF was performed, those results are shown in FIG. 5 and FIG. 6, respectively. It should be noted that in FIG. 5, the portion indicated by the line segment AB in FIG. 3 and in FIG. 6 the line segment A ′ in FIG.
The site indicated by -B 'was examined.

As is clear from FIGS. 5 and 6, it is confirmed that the amounts of Mo and B are large in the part different from the matrix phase, and that the amount of Co is also increased accordingly. .. [Experiment 4] After the above (A ₁ ) electrode was charged and discharged for one cycle, the hydrogen storage alloy of the (A ₁ ) electrode was observed with an electron microscope (SE).
M) and X-ray, the results are shown in FIGS. 7 and 8, respectively. The charging / discharging conditions are the same as those shown in Experiment 1 above.

As is clear from FIGS. 7 and 8, it is recognized that a large number of cracks are formed in the hydrogen storage alloy in the Mo-rich portion (white portion in FIG. 8). Similarly, after charging and discharging the (A ₃ ) electrode for one cycle,
The hydrogen storage alloy of the (A ₃ ) electrode was examined by an electron microscope and X-ray, and the results are shown in FIGS. 9 and 10, respectively.

As is apparent from FIGS. 9 and 10, Ta
It can be seen that a large number of cracks in the hydrogen storage alloy are generated in a portion with a large amount (white portion in FIG. 10). [Summary of Experiments 2 to 4] As is clear from Experiment 4, it is recognized that in the electrode of the present invention, a crack is generated at a site where a large amount of Mo or the like is present. And such M
As is clear from Experiment 2 and Experiment 3, a large amount of Co is present at the site where a large amount of o and the like are present. Therefore, in the electrode of the present invention, a crack is generated from the beginning of the charge / discharge cycle in the portion where a large amount of Co is present.

As described above, if a large number of cracks are generated from the beginning of the charge / discharge cycle, the reaction area of the hydrogen storage alloy increases (that is, a new active surface is generated), so that the high rate discharge characteristic is higher than that at the beginning of the charge / discharge cycle. improves. In addition, if a large number of cracks are generated in a portion where a large amount of Co is present, the catalytic action of Co improves the discharge characteristics at low temperatures. In the above examples, the case where a large amount of Co is present in the intermetallic compound phase different from the parent phase has been described, but the same effect is obtained when a large amount of Ni is present in the intermetallic compound phase. This will be clarified in the second embodiment described below.

(Second Example) [Example 1] A hydrogen storage alloy electrode was prepared in the same manner as in Example 1 except that Zr was used in place of Mo as the raw material of the hydrogen storage alloy (that is, hydrogen). Storage alloy is MmNi
_3.4 Co _0.8 Mn _0.4 Al _0.4 Zr _0.09 ).

The electrode thus prepared is
₁ ) It is called an electrode. In this case, Co ₂ Zr is generated as an intermetallic compound phase in the hydrogen storage alloy. Example 2 A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that Ti was used instead of Mo as a raw material of the hydrogen storage alloy (that is, the hydrogen storage alloy was MmNi.
_3.4 Co _0.8 Mn _0.4 Al _0.4 Ti _0.09 ).

The electrode thus prepared is
₂ ) Referred to as an electrode. In this case, Ni ₄ Ti ₃ is produced as an intermetallic compound phase in the hydrogen storage alloy. [Example 3] A hydrogen storage alloy electrode was produced in the same manner as in Example 1 except that W was used instead of Mo as a raw material of the hydrogen storage alloy (that is, the hydrogen storage alloy was MmNi.
_3.4 Co _0.8 Mn _0.4 Al _0.4 W _0.09 ).

The electrode thus prepared is
₃ ) It is called an electrode. In this case, W-Co is generated as an intermetallic compound phase in the hydrogen storage alloy. [Experiment] The initial discharge rate characteristics of the (B ₁ ) electrode to (B ₃ ) electrode of the present invention were examined, and the results are shown in Table 2 below. The experimental conditions and the evaluation of the experiment are the same as those of the experiment 1 of the first embodiment.

[0027]

[Table 2] As is clear from Table 2 above, the (B ₁ ) electrode of the present invention
In the (B ₃ ) electrode, the discharge capacity ratio at 25 ° C. was 77 to 93.
%, And it is recognized that the discharge capacity ratio is high as in the case of the (A ₁ ) electrode to (A ₃ ) electrode of the first embodiment. Further, as is clear from Table 2, (B ₁ ) of the present invention
In the electrode to (B ₃ ) electrode, the discharge capacity ratio at −10 ° C. is 6
It is 5 to 81%, and it is recognized that the discharge capacity ratio at 25 ° C. does not decrease so much. [Other Matters] The hydrogen storage alloy of the parent phase is not limited to the ones shown in the above examples, and the present invention can be applied to any hydrogen storage alloy containing Ni or Co. is there. The intermetallic compound phase is not limited to those shown in the above-mentioned examples, and, for example, N in the case of using Nb as an additional element
It has also been confirmed by experiments that b ₅ Ni and the like are present. The intermetallic compound phase is not limited to the one in which cobalt or nickel is concentrated, and it has been confirmed by experiments that at least cobalt or nickel is one component. The hydrogen storage alloy electrode of the present invention can be used for a cylindrical storage battery or a flat storage battery.

[0028]

As described above, according to the present invention, a large number of cracks are generated in the hydrogen storage alloy from the beginning of the charge / discharge cycle, so that a new active surface is generated and the reaction surface area of the hydrogen storage alloy is increased. .. As a result, the activation of the alloy proceeds from the beginning of the charge / discharge cycle, and the high rate discharge characteristics are improved from the beginning.

In addition, since a large amount of nickel or cobalt, which has a large catalytic action, is present on the new active surface, it has an excellent effect that the discharge characteristics are improved even at a low temperature at which hydrogen absorption / desorption reaction hardly occurs. Play.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of a hydrogen storage alloy of an (A ₁ ) electrode.

FIG. 2 is an X-ray diffraction diagram of the hydrogen storage alloy of the (A ₂ ) electrode.

FIG. 3 is a photograph showing an electron reflection image of the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 4 is a photograph showing an electron reflection image of the hydrogen storage alloy of the (A ₂ ) electrode.

FIG. 5: EPMA in hydrogen storage alloy of (A ₁ ) electrode
It is a graph which shows the quantitative analysis by ZAF.

FIG. 6 EPMA in hydrogen storage alloy of (A ₂ ) electrode
It is a graph which shows the quantitative analysis by ZAF.

FIG. 7 is an electron micrograph of the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 8 is an X-ray photograph of the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 9 is an electron micrograph of the hydrogen storage alloy of the (A ₃ ) electrode.

FIG. 10 is an X-ray photograph of the hydrogen storage alloy of the (A ₃ ) electrode.

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[Procedure amendment]

[Submission date] December 16, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of a hydrogen storage alloy of an (A ₁ ) electrode.

FIG. 2 is an X-ray diffraction diagram of the hydrogen storage alloy of the (A ₂ ) electrode.

FIG. 3 is a photograph showing an electron reflection image of the metal composition in the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 4 is a photograph showing an electron reflection image of the metal composition in the hydrogen storage alloy of the (A ₂ ) electrode.

FIG. 5: EPMA in hydrogen storage alloy of (A ₁ ) electrode
It is a graph which shows the quantitative analysis by ZAF.

FIG. 6 EPMA in hydrogen storage alloy of (A ₂ ) electrode
It is a graph which shows the quantitative analysis by ZAF.

FIG. 7 is an electron micrograph of the metal composition of the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 8 is an X-ray photograph of the hydrogen storage alloy of the (A ₁ ) electrode.

FIG. 9 is an electron micrograph of the metal composition of the hydrogen storage alloy of the (A ₃ ) electrode.

FIG. 10 is an X-ray photograph of the hydrogen storage alloy of the (A ₃ ) electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikiro Tadokoro, 2-18 Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. (72) Inventor Nobuhiro Furukawa 2-18, Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. Within

Claims (2)

[Claims] 1. A hydrogen storage alloy electrode made of a hydrogen storage alloy containing cobalt or nickel, wherein an intermetallic compound phase in which at least cobalt or nickel is one component is solid-dissolved in the mother phase in the hydrogen storage alloy. A hydrogen storage alloy electrode characterized by being present without a hydrogen storage alloy electrode. 2. The hydrogen storage alloy electrode according to claim 1, wherein the intermetallic compound phase has a structure in which cobalt or nickel is concentrated.