JPH1197002A - Hydrogen storage alloy electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy electrode for an alkaline storage battery, which can accomplish objects for making its conductivity high and its capacity higher by enhancing the filling density of particles made of hydrogen storage alloys, and concurrently securing electrical contact between each hydrogen storage alloy particle and a current collector, and among the respective hydrogen particle them selves. SOLUTION: Thirty % to 80% hydrogen storage alloy powder 10 by volume is composed of hydrogen storage alloy particles 14 and 16 in a spherical or non-spherical shape each less than 30 μm in grain size, and the remaining part is composed of hydrogen storage alloy particles in a non-spherical shape each equal to or more than 30 μm but less than 100 μm in grain size. The hydrogen storage alloy particles 18 less than 30 μm in grain size are formed out of at least 3% the whole of the hydrogen storage alloy powder 10 by volume, which is composed of the hydrogen storage alloy particles 14, so as to be combined with a current collector 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of an alkaline storage battery.

[0002]

2. Description of the Related Art As alkaline storage batteries using a hydrogen storage alloy as a negative electrode, metal-hydride storage batteries such as nickel-hydride storage batteries are known. The hydrogen storage alloy electrode has excellent characteristics such that the energy density per unit volume and unit weight is high and the capacity can be increased. As shown in FIG. 2, the hydrogen storage alloy electrode (30) is formed by bonding a hydrogen storage alloy powder (32) and a current collector (34). The hydrogen storage alloy is prepared by mechanically pulverizing an ingot of the hydrogen storage alloy into a powder or preparing the powder in advance by a gas atomizing method or the like. As the current collector (34), a plate-shaped Ni base is used. Generally, the hydrogen storage alloy powder (32) is mixed with a binder and applied to the Ni base, or by sintering. An electrode is made.

[0003]

Conventionally, a hydrogen storage alloy powder having a relatively uniform particle size has been used for a hydrogen storage alloy electrode. Therefore, as shown in FIG. There is a problem that a large gap (36) is present in the device. As a result, the packing density of the hydrogen storage alloy is reduced,
Further, sufficient electrical contact between the hydrogen storage alloy, the current collector and the hydrogen storage alloy could not be achieved.

[0004] It is an object of the present invention to improve the packing density of the hydrogen storage alloy particles and to secure electrical contact between the hydrogen storage alloy particles, the current collector, and the hydrogen storage alloy particles.
An object of the present invention is to provide a hydrogen storage alloy electrode for an alkaline storage battery, which can enhance conductivity and achieve high capacity.

[0005]

According to the present invention, there is provided a hydrogen storage alloy electrode for an alkaline storage battery according to the present invention.
Is 30% to 80% by volume of the hydrogen storage alloy powder (10)
Consists of spherical or non-spherical hydrogen storage alloy particles (14) (16) having a particle size of 30 μm or less, and the rest is non-spherical and has a particle size of 30 μm.
The hydrogen storage alloy particles (18) having a particle diameter of 30 μm or less are formed of hydrogen storage alloy particles (18) having a particle diameter of at least 3% by volume or more. It is formed by joining a hydrogen storage alloy powder (10) as an alloy particle (14) to a current collector (20). Current collector (20)
As a porous body such as foamed nickel, metal fiber sintered body, etc.
It is desirable to use (22) and fill the porous body (22) with the hydrogen storage alloy powder (10) to form a hydrogen storage alloy electrode.

[0006] In the present invention, the term "spherical" means a shape of a round particle having an outwardly convex curved surface, and includes not only a sphere and an ellipsoid but also particles having a similar form. Shall be included. Spherical hydrogen storage alloy particles can be prepared by an atomizing method. The ratio of the major axis to the minor axis (major axis / minor axis) of the spherical hydrogen storage alloy particles (14) is desirably 1.2 or less as shown in Example 3 described later.

In the present invention, “non-spherical” means
It refers to particles that are not spherical, and typically refers to the shape of particles that have angular portions. Non-spherical hydrogen storage alloy particles can be prepared by mechanically pulverizing or hydrogenating a hydrogen storage alloy ingot.

[0008] The spherical hydrogen storage alloy particles (14) contain at least Ni in the composition and are 50 nm from the surface of the particles.
The amount of Ni remaining in the central portion exceeding the thickness of
It is desirable that the ratio of the residual amount of Ni in the thickness portion within 50 nm from the surface of the particle is 1.5 or more.
In order to increase the residual ratio of Ni on the particle surface, the particles may be subjected to an acid treatment or the like.

[0009]

[Function and Effect] By incorporating spherical hydrogen storage alloy particles (14) having a particle diameter of 30 μm or less, the degree of filling of the electrode with the hydrogen storage alloy can be increased. In addition, even if the non-spherical hydrogen storage alloy particles are finely pulverized with the charge / discharge cycle, the spherical hydrogen storage alloy particles have high mechanical strength and are hardly pulverized. State can be maintained. Further, when the spherical hydrogen storage alloy particles are prepared by the atomizing method, the particles are rapidly cooled, so that systematically uniform particles can be obtained, and the progress of pulverization can be suppressed.

[0010] When the Ni-containing spherical hydrogen storage alloy particles (14) are subjected to an acid treatment or the like to increase the residual ratio of Ni on the particle surfaces, the conductivity between the alloy particles can be further increased.

When an electrode obtained by bonding the hydrogen storage alloy powder of the present invention to a current collector is used as a negative electrode of an alkaline storage battery, the degree of filling of the electrode with the hydrogen storage alloy powder is high, so that a high capacity can be achieved. Further, even if the non-spherical hydrogen storage alloy powder is pulverized, the conductivity is maintained by the spherical hydrogen storage alloy powder which is hard to be pulverized, whereby the high-rate discharge characteristics can be improved, and the low-temperature discharge characteristics can be further improved.

If a porous body (22) such as foamed nickel is used as the current collector (20), the conductivity between the hydrogen storage alloy powder and the current collector can be further increased.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The composition of a hydrogen storage alloy to which the present invention is applied is not particularly limited. In addition, as shown in the following Examples, when performing an acid treatment, it is desirable that nickel is included in the composition. The spherical hydrogen storage alloy powder can be produced by an atomizing method. The non-spherical hydrogen storage alloy powder can be produced by various methods such as a casting method and a roll quenching method. When the hydrogen storage alloy is manufactured in an ingot state, the ingot may be mechanically pulverized to prepare a powder. In addition, the obtained hydrogen storage alloy powder can be separated for each desired particle size by sieving using a sieve or the like.

[0014]

Example 1 <Preparation of powder> The composition was MmNi _3.2 Co _1.0 Mn _0.6 Al
_The raw materials were mixed so as to be _0.2 and melted in an arc melting furnace, and spherical hydrogen storage alloy powder and non-spherical hydrogen storage alloy powder were prepared under the following conditions. The spherical hydrogen storage alloy powder was produced by a gas atomizing method. The non-spherical hydrogen storage alloy powder was produced by mechanically pulverizing an ingot obtained by casting.

<Sieving of Powder> Each of the obtained hydrogen storage alloy powders was sieved. Incidentally, the "maximum particle size", when sieving using a sieve of a predetermined roughness, means the largest particle diameter passed through the sieve,
"Minimum particle size" shall mean the smallest particle diameter that has not passed through a sieve of predetermined roughness. The spherical hydrogen storage alloy powder was sieved so that the maximum particle size became 10 μm to 50 μm, and the maximum particle size was 10 μm and 20 μm.
m, a hydrogen storage alloy powder of 30 μm as an invention example, a maximum particle size of 40 μm, a hydrogen storage alloy powder of 50 μm as a comparative example, according to the maximum particle size of the spherical hydrogen storage alloy powder,
The non-spherical hydrogen storage alloy powder was also sieved.

<Preparation of Test Electrode> The sieved spherical hydrogen storage alloy powder and the non-spherical hydrogen storage alloy powder were mixed at a volume percentage shown in Table 1 to prepare a test electrode.

[0017]

[Table 1]

The test electrode was used for 800 g of the mixed powder.
160 g of a 5% aqueous solution of polyethylene oxide was added and applied to both sides of a Ni-plated 0.8 mm thick punching metal. When the electrode packing density of each test electrode was measured, as shown in Table 1, the values of Invention Examples 1 to 3 were higher than Comparative Examples 101 and 102. This is because the spherical and non-spherical hydrogen storage alloy particles having a small particle size filled the voids formed between the non-spherical hydrogen storage alloy particles having a large particle size.

<Preparation of Test Battery> Each of the prepared test electrodes is rolled using a hydraulic press and wound together with a known sintered nickel electrode through an alkali-resistant separator to form a spiral electrode body. Produced. Each of the electrode bodies was inserted into a battery can, and an alkaline aqueous solution to which 1 M lithium hydroxide was added with respect to a 6 M aqueous solution of potassium hydroxide to improve the utilization rate of the positive electrode active material was added to the battery can. A test battery was prepared by injecting the solution into the sample.

<Charge / Discharge Cycle Test> The prepared test battery was charged at 1000 mA × 1.2 hours and discharged at:
The charge / discharge cycle was repeated under the conditions of 1000 mA (cut voltage = 1.0 V), and the number of charge / discharge cycles until the initial activation (discharge capacity stabilization cycle number) and the charge / discharge cycle life were measured. The “number of stable discharge capacity cycles” is the number of cycles required until the discharge capacity at the time of the 1A charge / discharge cycle of the battery reaches a stable state, and the “charge / discharge cycle life”
Was evaluated by the number of cycles when the discharge capacity was lower than 500 mAh. Table 1 shows the results.

Referring to Table 1, the batteries using Inventive Examples 1 to 3 as the negative electrodes have a cycle life improved by 10% or more as compared with the batteries using Comparative Examples 101 and 102.
It can be seen that the number of cycles required for activation is also reduced. This is because, as the maximum particle size of the hydrogen storage alloy powder increases, the contact between the hydrogen storage alloy particles tends to be point contact, and the conductivity decreases. In addition,
Inventive Example 1, in which the maximum particle size of the spherical hydrogen storage alloy particles is 10 μm, has a shorter cycle life than Inventive Example 2, so that the maximum particle size of the spherical hydrogen storage alloy particles is 10 μm.
It can be seen that the effect of improving the cycle life is difficult to obtain even if it is smaller. Therefore, it is desirable that the spherical hydrogen storage alloy particles have a particle size of 10 μm or more.

Example 2 Next, the electrode packing density and the cycle life were measured in the same manner as in Example 1 except that the ratio of the spherical hydrogen storage alloy powder contained in the hydrogen storage alloy powder having a particle size of 30 μm or less was changed. . Table 2 shows the results.

[0023]

[Table 2]

Referring to Table 2, the more the spherical hydrogen storage alloy powder is contained in the hydrogen storage alloy powder having a particle diameter of 30 μm or less, the higher the packing density of the electrode and the longer the cycle life. This is because the spherical hydrogen storage alloy particles having a small particle diameter are prepared by the atomizing method, so that the cooling rate at the time of particle preparation is high and the structure is homogeneous, while the casting has a low cooling rate. This is because it is difficult to be homogeneously organized. In addition, the hydrogen storage alloy particles prepared by the atomization method have sufficient mechanical strength even if the particle size is small, while the hydrogen storage alloy powder produced by casting is mechanically pulverized. This is because sufficient mechanical strength cannot be obtained if the particle size is reduced because of the preparation. According to Example 2, when a larger amount of the spherical hydrogen storage alloy powder is included in the hydrogen storage alloy powder having a particle size of 30 μm or less, the packing density of the manufactured electrode can be increased, and the battery life can be improved. It can be seen that the improvement of the above can be achieved.

Example 3 Particles having different ratios of the major axis to the minor axis (major axis / minor axis) of the spherical hydrogen-absorbing alloy particles were produced, and a test electrode was produced from the hydrogen-absorbing alloy powder containing the obtained particles. Note that the hydrogen storage alloy powder has a particle diameter of 30 μm having a different major axis / minor axis ratio.
m of spherical hydrogen storage alloy powder having a particle size of 25% by volume or less.
Non-spherical hydrogen storage alloy powder of 25 μm or less, 25% by volume, particle size 3
50% by volume of a non-spherical hydrogen storage alloy powder of 0 to 100 μm was mixed and used. A test battery was prepared using the test electrode, and the electrode packing density and the charge / discharge cycle life were measured in the same manner as in Example 1. Table 3 shows the results.

[0026]

[Table 3]

Referring to Table 3, the more the hydrogen-absorbing alloy particles having a ratio of major axis / minor axis of 1.2 or less, that is, the shape closer to a true sphere, are used as the spherical hydrogen-absorbing alloy particles, the higher the packing density of the electrode is. It was found that the charge and discharge cycle life could be improved.

Example 4 With respect to the hydrogen-absorbing alloy powder used in Invention Example 3, only the spherical hydrogen-absorbing alloy powder was subjected to a surface treatment with an acidic aqueous solution having a different pH. The conditions other than the surface treatment were the same as those of Inventive Example 3, a test electrode was prepared in the same manner as in Example 1, and a test battery was assembled in the same manner.
The surface treatment was an acid treatment, which was performed by using hydrochloric acid as an acidic aqueous solution and immersing the spherical hydrogen storage alloy powder in hydrochloric acid. Regarding the spherical hydrogen-absorbing alloy particles subjected to the acid treatment, the amount of nickel present in the portion within 50 nm from the particle surface and the amount of nickel remaining in the central portion exceeding 50 nm from the particle surface were respectively determined by XPS (XP
Line photoelectron spectroscopy analyzer) to determine the ratio of nickel abundance (surface abundance / internal abundance)
The results as shown in Table 4 were obtained. It should be noted that Inventive Example 3 not subjected to the acid treatment is shown in Table 4 as a reference example.

[0029]

[Table 4]

Referring to Table 4, it can be seen that by performing the acid treatment, the rare-earth oxide on the particle surface is eluted, and the particle surface is in a nickel-rich state. In addition, when the acid treatment was performed using an acidic aqueous solution having a strong acidity, the nickel content ratio on the particle surface was higher.

Next, the packing densities of the fabricated test electrodes were measured, and all were 4.8 g / cm ^3.
Met. A charge / discharge cycle test was performed on the fabricated test battery in the same manner as in Example 1, and the cycle life and the number of cycles of stable discharge capacity were measured. Table 4 shows the results. Also, to measure the high rate discharge characteristics of each battery,
The discharge capacity at the time of 4A discharge was measured. The results are shown in Table 4. Referring to Table 4, although the charge-discharge cycle life and the number of discharge stable cycles are hardly changed by mixing the acid-treated spherical hydrogen storage alloy powder,
It can be seen that the discharge capacity at the time of 4A discharge is increased by performing the acid treatment, and that the high-rate discharge characteristics are improved.
The high-rate discharge characteristics have been improved because the spherical hydrogen storage alloy particles, whose conductivity has been increased by the acid treatment, serve as a conductive path between the non-spherical hydrogen storage alloy particles having a large particle size to improve the conductivity between the particles. It is because it raised.

Embodiment 5 This embodiment is an embodiment (invention examples 14 and 15) in which an electrode is manufactured by sintering. Inventive Examples 14 and 15 include 25% by volume of a spherical hydrogen storage alloy powder having a particle size of 30 μm or less, 25% by volume of a non-spherical hydrogen storage alloy powder having a particle size of 30 μm or less, and a non-spherical hydrogen storage alloy powder having a remaining particle size of 30 μm or less and 100 μm or less. Spherical hydrogen storage alloy powder was used. The spherical hydrogen storage alloy powder of Inventive Example 14 was subjected to the acid treatment at pH 1 shown in Example 4. For comparison, a test electrode (Comparative Example 108) was manufactured by sintering a hydrogen storage alloy powder (non-spherical) having a maximum particle size of 100 μm obtained by mechanically pulverizing a hydrogen storage alloy prepared by a casting method. Further, a test electrode (Comparative Example 109) was prepared by sintering a hydrogen storage alloy powder (spherical) having a maximum particle size of 100 μm prepared by an atomizing method.

The sintering temperature of each hydrogen storage alloy powder was set to a temperature necessary for the electrode to obtain a predetermined strength. Table 5 shows the sintering temperatures.

[0034]

[Table 5]

Referring to Table 5, it can be seen that the sintering temperatures of the test electrodes of Invention Examples 14 and 15 were lower than those of Comparative Examples 108 and 109. The sintering temperatures of Invention Examples 14 and 15 could be set lower than that of Comparative Example 109 because spherical hydrogen storage alloy particles produced by the atomization method were included. During the production of the alloy, it is subjected to rapid cooling from the outside of the particles, and since the proportion of nickel having a relatively high melting point is higher than that of the cast alloy, the temperature required for sintering can be lowered. In addition, the sintering temperature of Invention Examples 14 and 15 could be set lower than that of Comparative Example 108 because Comparative Example 108 in which all were spherical powders.
This is because the hydrogen storage alloy particles are in point contact with each other, and the sintering temperature must be increased to obtain a predetermined strength.

The charge / discharge cycle life and the discharge capacity at the time of 4A discharge were measured for the produced test electrodes. Table 5 shows the results. For reference, Table 5 also shows the measurement results of the test electrodes (Invention Example 3 and Invention Example 12) manufactured using the binder. Comparing Inventive Examples 14 and 15, and Inventive Reference Examples 3 and 12, the electrode produced by sintering can increase the discharge capacity at the time of 4A discharge, and can improve the high rate discharge characteristics of the battery. Recognize. The reason for this is that sintering can sufficiently achieve electrical bonding between the hydrogen-absorbing alloy particles as compared with the case where a binder is used.
In addition, comparing Inventive Examples 14 and 15 with Comparative Examples 108 and 109, both the charge / discharge cycle life and the discharge capacity at the time of 4A discharge are improved. This is because the sintering temperature of the hydrogen storage alloy electrode of the invention example could be set lower than that of the comparative example, and when the sintering temperature was high, the alloy structure was re-segregated,
This is to cause a decrease in the charge / discharge cycle. In addition, comparing Inventive Example 14 and Inventive Example 15, since Inventive Example 14 includes a spherical hydrogen-absorbing alloy powder whose surface was enriched with nickel by acid treatment, as shown in Example 4, the high-rate discharge was performed. It can be seen that the characteristics have been improved.

Embodiment 6 This is an embodiment using foamed nickel as the current collector. As the hydrogen storage alloy powder, 25% by volume of a spherical hydrogen storage alloy powder having a particle size of 30 μm or less, 25% by volume of a non-spherical hydrogen storage alloy powder having a particle size of 30 μm or less, and 1% of the remaining particle size exceeding 30 μm.
A non-spherical hydrogen storage alloy powder having a size of 00 μm or less was used. The spherical hydrogen storage alloy powder of Inventive Example 16 had a pH
1 is being treated with acid.

The test electrode was used for 800 g of the mixed powder.
It was prepared by adding 160 g of a 5% aqueous solution of polyethylene oxide and applying the foamed metal. The charge / discharge cycle life and the discharge capacity at the time of 4A discharge were measured for the produced test electrode. Table 6 shows the results. In addition, the said invention example 12 and invention example 3 are shown together with Table 6 for reference.

[0039]

[Table 6]

Referring to Table 6, it can be seen that the electrode using nickel foam has a higher discharge capacity than the electrode using punching metal. This is because the porous portion of the foamed nickel is also filled with the hydrogen storage alloy particles, and the conductivity is improved. Inventive Example 16 and Inventive Example 17
Compared with the above, by using the spherical hydrogen storage alloy powder enriched with nickel on the surface by acid treatment, the conductivity between the hydrogen storage alloy powder and the foamed nickel is further increased, and the high rate discharge characteristics can be improved. You can see that

Example 7 Next, the hydrogen storage alloy powder used had a particle size of 30%.
The electrode filling density, charge / discharge cycle life, and discharge capacity at the time of 1C discharge were measured by changing the ratio of the hydrogen storage alloy powder having a particle diameter of 30 μm or less, and the desirable content of the hydrogen storage alloy powder having a particle diameter of 30 μm or less was determined. . In addition, 1/2 of the amount of the hydrogen storage alloy powder having a particle diameter of 30 μm or less is defined as a spherical hydrogen storage alloy powder. Table 7 shows the content of each hydrogen storage alloy powder and the measurement results.

[0042]

[Table 7]

Referring to Table 7, it can be seen that when the hydrogen storage alloy powder having a particle size of 30 μm or less falls below 30% by volume, the electrode packing density decreases, and as a result, the discharge capacity decreases. Also, when the hydrogen storage alloy powder having a particle diameter of 30 μm or less exceeds 80% by volume, the cycle life is reduced. This is considered to be because the surface area of the alloy particles involved in the reaction was increased by increasing the content of the hydrogen storage alloy powder having a particle size of 30 μm or less, and the particles were easily oxidized accordingly. From the above results,
In order to obtain an electrode having a high electrode packing density, a high cycle life and a high discharge capacity, the proportion of the hydrogen storage alloy powder having a particle size of 30 μm or less is desirably 30% by volume or more and 80% by volume or less.

As can be seen from the above-described embodiments, the hydrogen storage alloy electrode of the present invention can increase the packing density of the hydrogen storage alloy powder as compared with the conventional hydrogen storage alloy electrode, thereby achieving a higher capacity. Can be achieved, and the cycle life is longer, and additionally the number of cycles required for activation can be reduced.

In particular, the spherical hydrogen storage alloy particles are subjected to an acid treatment, the electrodes are produced by sintering the hydrogen storage alloy powder, and a porous material such as foamed nickel is used as a current collector. Thereby, the cycle life and the discharge capacity can be further improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a hydrogen storage alloy electrode of the present invention.

FIG. 2 is an explanatory view showing a conventional hydrogen storage alloy electrode.

[Explanation of symbols]

(10) Hydrogen storage alloy powder (14) Spherical hydrogen storage alloy particles with a particle size of 30 μm or less (16) Non-spherical hydrogen storage alloy particles with a particle size of 30 μm or less (18) Non-spherical hydrogen storage with a particle size of more than 30 μm and 100 μm or less Alloy particles (20) Current collector (25) Hydrogen storage alloy electrode

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Kikuko Kato 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Teruhiko Imoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Yasushi Kuroda 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Pref. Sanyo Electric Co., Ltd. (72) Shin Fujitani 2 5-5-5 Sanyo Electric Co., Ltd. (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (5)

[Claims] 1. A hydrogen storage alloy electrode for an alkaline storage battery formed by joining a hydrogen storage alloy powder (10) and a current collector (20), wherein the hydrogen storage alloy powder (30) is 30% by volume to 80% by volume. But,
Hydrogen storage alloy particles having a spherical or non-spherical particle size of 30 μm or less
(14) (16), the remainder being non-spherical hydrogen storage alloy particles (18) having a particle size of more than 30 μm and not more than 100 μm, wherein the hydrogen storage alloy particles having a particle size of 30 μm or less are hydrogen storage alloy powder ( A hydrogen-absorbing alloy electrode for an alkaline storage battery, characterized in that at least 3% by volume or more of the entirety of (10) is spherical hydrogen-absorbing alloy particles (14). 2. The hydrogen storage alloy electrode for an alkaline storage battery according to claim 1, wherein the spherical hydrogen storage alloy particles (14) are particles prepared by an atomizing method. 3. The hydrogen storage alloy electrode for an alkaline storage battery according to claim 1, wherein the ratio of the major axis to the minor axis of the spherical hydrogen storage alloy particles (14) is 1.2 or less. 4. The spherical hydrogen-absorbing alloy particles (14) contain at least Ni in the composition and have a thickness of 50 nm from the particle surface with respect to the amount of Ni remaining in a central portion exceeding a thickness of 50 nm from the particle surface. The hydrogen storage alloy electrode for an alkaline storage battery according to any one of claims 1 to 3, wherein the ratio of the remaining amount of Ni in a thickness portion within the range is 1.5 or more. 5. The current collector (20) is a porous body (22), and the porous body (22) is filled with a hydrogen storage alloy powder (10). A hydrogen storage alloy electrode for an alkaline storage battery according to any one of the above.