JP3414148B2 - Hydrogen storage alloy powder and hydrogen storage electrode for Ni-H secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to nickel-hydrogen (Ni
-H) A hydrogen storage alloy powder and a hydrogen storage electrode suitable for a secondary battery.

[0002]

2. Description of the Related Art Hydrogen has attracted attention as a clean fuel that can replace fossil fuels due to global environmental problems such as air pollution and global warming caused by fossil fuels. This is because hydrogen uses water as a raw material, combustion products are water, and
This is because it is a material that can be applied to an energy conversion system for heat and power.

A hydrogen storage alloy is known as a material for storing hydrogen, and has been applied and developed to hydrogen storage, heat pumps, actuators and the like. in recent years,
Using a hydrogen storage alloy for the negative electrode, charging and discharging hydrogen
A Ni-H secondary battery, which is an alkaline secondary battery for discharging, has been put into practical use.

An electrode using a hydrogen storage alloy is formed by forming a hydrogen storage alloy powder into a paste together with a small amount of a binder (organic binder), and rolling the alloy powder paste onto an electrode substrate (current collector) made of a porous metal. It is generally produced by pressing it into a sheet using a machine.

Compared with the Ni-Cd secondary battery, which has been the mainstream of conventional small alkaline secondary batteries, the Ni-H secondary battery can increase the battery capacity and energy density, and makes the device portable and even more portable. It is easy to meet the needs for higher capacity due to the miniaturization. Furthermore, due to the pollution and resource problems of Cd, the demand for Ni-H secondary batteries has increased significantly in the last few years, and their application to electric vehicles is being put to practical use.

The major alloy systems that have been investigated as hydrogen storage alloys for Ni-H secondary batteries are Mg-based alloys, such as LaNi ₅ and MmNi ₅
Examples thereof include B ₅ type rare earth type, AB ₂ type Laves phase type represented by ZrV _{2 and the} like, AB / A ₂ B type (titanium type) represented by TiNi and Ti ₂ Ni. AB ₅ type and AB ₂ type hydrogen storage alloys are being put to practical use. It is generally said that the AB ₅ type is superior in terms of high rate discharge characteristics and initial activation, and the AB ₂ type is superior in terms of capacity per unit weight.

It has been several years since the mass production of Ni-H secondary batteries has started, and their capacities have been increasing. However, the demand for higher capacities from equipment manufacturers and the recent high capacity lithium ion batteries have been increasing. With the advent of, the need for higher capacity Ni-H secondary batteries is increasing.

As a means for increasing the capacity, increasing the filling rate of the hydrogen storage alloy per electrode having a limited volume directly leads to the capacity improvement. From this viewpoint, it has been proposed, for example, in Japanese Patent Laid-Open No. 3-116655 to improve the filling rate of the alloy into the negative electrode by using a spherical hydrogen storage alloy. Such a spherical hydrogen storage alloy powder can be produced by a gas atomizing method, a rotating electrode method, or the like.

Further, as described in JP-A-8-17433, in a sintered electrode in which a hydrogen storage alloy is sintered without using an organic binder, the packing density is 5.3 to 5.
It can be increased to 8 g / ml. However, it is not easy to manufacture a hydrogen storage electrode without using a binder, and there is a problem that the production cost increases.

[0010]

As described above, when spherical powder of hydrogen storage alloy is used, an electrode having a high filling rate can be manufactured, but it has been found that there is a problem in the manufacturing process. That is, because of the spherical shape, the contact between the alloys becomes point contact, and the contact area is small, so there is little friction. Therefore, slippage occurs in the process of pressing the alloy powder paste onto the substrate by the roll rolling machine during the electrode manufacturing process, and the rolling does not proceed smoothly.

As shown in FIG. 1 (a), the irregularly-shaped crushed powder obtained by crushing a cast hydrogen storage alloy (ingot) does not slip between the powders, so that the rolling proceeds smoothly, It is possible to form a pressure-bonding paste having a uniform thickness and packing density.

On the other hand, if spherical powder is used, the result shown in FIG.
As shown in (b), the rolling rolls do not bite well due to the slippage of the powder, causing slackness and widening, and the situation constantly changes.Therefore, the thickness of the paste pressed onto the substrate is uneven. And alloy powder sparse / dense change (change in filling rate)
Occurs.

Therefore, the thickness of the electrode and the filling rate of the alloy become non-uniform, which makes it difficult to stably manufacture an electrode of a predetermined quality. As a result, the obtained electrode was used as a negative electrode for Ni-
There are problems that a predetermined capacity cannot be obtained when the H secondary battery is constructed, an internal pressure rises during charging, and high rate discharge characteristics at low temperatures are poor.

JP-A-7-105943 and JP-A-8-
45505 discloses that the contact area of the alloy is increased by mixing pulverized powder with spherical powder of hydrogen storage alloy or by partially sintering the spherical powder for the purpose of improving high rate discharge characteristics. Has been done. However, by such means as mixing with pulverized powder or partial sintering, the filling rate of the alloy is reduced as compared with the case where spherical powder is used as it is, so there is a limit to improving the capacity of the battery.

An object of the present invention is to stabilize a high-capacity Ni-H secondary battery, which does not have the above-mentioned problems, by using a spherical powdery hydrogen-absorbing alloy capable of being highly filled, and to increase the production cost. It is to provide a hydrogen storage alloy powder and a hydrogen storage electrode that can be produced without performing the above.

[0016]

The present inventors defined the particle size distribution of spherical hydrogen-absorbing alloy powders, in particular, coexisting coarse particles considerably larger than the average diameter in an amount within a certain range, and the particles were also constant. Higher filling can be achieved by making more than a certain amount,
Moreover, they have found that even with spherical powder, slippage during rolling is suppressed, and a hydrogen storage electrode having a high packing density can be stably manufactured, and the present invention has been accomplished.

In the present invention, the average diameter is 5 μm or more.
the average diameter in the particle size distribution + 30μ
wherein the ratio of the above powder m is 5% or more and 30% or less, the following proportions of powder diameter 20μm is 5% or more, moth
It is a substantially spherical hydrogen storage alloy powder for a Ni-H secondary battery manufactured by a atomizing method or a rotating electrode method . In the present invention, the ratio in the particle size distribution of the hydrogen storage alloy powder is the volume ratio. This particle size distribution is measured by a laser diffraction type particle size distribution meter.

The present invention is also an electrode made of this hydrogen-absorbing alloy powder and an organic polymer binder, which is manufactured by rolling and has a packing density of 5.0 g / min.
Also provided is a hydrogen storage electrode for a Ni-H secondary battery, which is characterized by having a cm ³ or more.

The "substantially spherical" hydrogen storage alloy powder means a spherical or substantially spherical shape, for example,
The powder produced by the gas atomizing method or the rotating electrode method corresponds to this. Generally, in such powder, the ratio (aspect ratio) of the maximum value and the minimum value of the powder particle diameter is 2 or less,
It is preferably 1.5 or less.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy powder of the present invention defines the average diameter and particle size distribution as described above. Therefore, since the hydrogen storage alloy can be applied regardless of the type of hydrogen storage alloy, the hydrogen storage alloy to be used may be any hydrogen storage alloy conventionally known or developed in the future. The presently preferred hydrogen storage alloy is the AB ₅ type or AB ₂ type hydrogen storage alloy which is now in practical use.

As described above, the hydrogen-absorbing alloy powder of the present invention is a substantially spherical spherical powder. Therefore, from the molten hydrogen-absorbing alloy, for example, a gas atomizing method (eg, argon gas atomizing method) or a rotating electrode method is used. Can be manufactured by. Spherical powder produced by another method may be used as long as it is substantially spherical powder in the above-mentioned sense. Further, the produced alloy powder may be classified, and the classified powder may be appropriately mixed and used to obtain a desired particle size distribution, or spherical powders of two or more lots may be appropriately mixed.

Since spherical powder generally undergoes rapid solidification,
The quenching strain may remain, and if necessary, the spherical powder may be heat-treated after solidification to relax the quenching strain. In addition, various chemical treatment methods (eg, acid and / or alkali treatment) of the hydrogen storage alloy powder have been proposed for the purpose of improving the initial activation characteristics, and such treatment may be performed if desired. You can also

The hydrogen-absorbing alloy powder of the present invention is substantially spherical and has an average diameter of 5 μm or more and 50 μm or less, and the ratio of the powder having the average diameter + 30 μm or more in its particle size distribution is 5% or more, 30% or more. Below, the proportion of powder having a diameter of 20 μm or less is 5% or more. The spherical powder having such an average diameter and particle size distribution has a tap density, as will be shown later in Examples.
(Indicator of maximum packing density of powder) is high, it is possible to perform high packing from the beginning, it is hard to slip during rolling in the manufacturing process of electrodes, and it can be rolled smoothly like crushed powder with irregular shape, so high filling after rolling. It is possible to obtain an electrode having a uniform filling rate and a uniform thickness while maintaining the density, which enables high capacity and stabilizes product quality.

When the average diameter of the spherical alloy powder is larger than 50 μm, the number of contact points between the alloys becomes smaller, so that the powders slip each other during roll rolling, resulting in uneven rolling.
Problems such as the inability to obtain a predetermined capacity may occur. If the average diameter is smaller than 5 μm, the alloy becomes too fine and the specific surface area becomes large, so that the alloy is easily oxidized during overcharging, the life of the battery is deteriorated rapidly, and the cost of the raw material powder also increases.

In the present invention, in addition to the above definition of the average diameter, the particle size distribution is also defined. This is because the above problem cannot be solved only by the average diameter. Therefore, in the present invention, 5 to 30% of the powder having the average diameter + 30 μm or more (coarse particles larger than the average diameter by 30 μm or more) is present, and 5% or more of the powder (fine particles) having the diameter of 20 μm or less is present.

In general, it is said that the packing rate of the powder is improved when the particle size distribution of the spherical powder is rather wide rather than extremely narrow. The present inventor has found that the spherical powder can be highly filled by allowing the coarse particles to exist to some extent. However, in the present invention, not only the filling rate is improved, but by defining the particle size distribution as described above, slippage does not easily occur when rolling the paste of spherical powder, an unexpected result is obtained. .

The ratio of coarse particles having an average diameter of 30 μm or more is 30
If it exceeds%, even if the filling rate is further improved, the contact points between the alloys are decreased, the powder becomes slippery during roll rolling, and there is a high possibility that the electrode cannot be successfully manufactured. When the difference in particle diameter from the average diameter of the coarse particles is set to less than 30 μm, the advantage of improving the filling rate of the spherical powder with respect to the irregularly ground powder may not be sufficiently obtained. On the other hand, if the ratio of the powder having the average diameter + 30 μm or more is less than 5%, a sufficient effect of improving the filling rate cannot be obtained. The average diameter +30 μm
The ratio of the above powder is preferably 10 to 20%.

If the proportion of powder of 20 μm or less is less than 5%,
After all, the powder becomes slippery during roll rolling, which increases the possibility that the electrode cannot be manufactured well. The proportion of powder of 20 μm or less is preferably 10% or more, whereby the effect of preventing slippage during rolling becomes more remarkable.

If the average diameter and particle size distribution deviate from the ranges specified in the present invention, not only the phenomenon that the alloy slips during roll rolling in the production of electrodes but also the effect of increasing the amount of alloy filled in the electrode is small and sufficient. The effect of high capacity cannot be obtained. In the present invention, the average diameter of the particle size distribution +
If the ratio of the coarse powder of 30 μm or more and the ratio of the fine powder of 20 μm or less are within the above range, the above effect can be obtained, so that the overall particle size distribution is not particularly limited.

From the substantially spherical hydrogen-absorbing alloy powder of the present invention, a hydrogen-absorbing electrode can be produced by a conventional method using an organic polymer binder as a binder. Ni-H
Since the electrolyte of the secondary battery is an alkaline aqueous solution (eg, potassium hydroxide aqueous solution), an alkali-resistant organic polymer material is used as the binder. Examples of suitable binders are polyvinyl alcohol, polyethylene oxide,
Organic polymers such as carboxymethyl cellulose and polytetrafluoroethylene.

Hydrogen storage alloy powder is mixed with a solution of an organic polymer binder to form a paste. This paste is applied to an electrode substrate serving as a current collector and dried. The substrate is generally made of a porous metal (usually nickel metal or nickel-plated iron) such as plain weave wire mesh, expanded metal, punching metal, foam metal, and fibrous metal. To increase the packing density of the hydrogen storage alloy, after coating and drying,
An electrode is obtained by rolling with a rolling mill and pressing the hydrogen storage alloy powder onto the substrate.

Although the hydrogen-absorbing alloy powder of the present invention is a spherical powder, it does not cause slippage during rolling, so that the original high filling property can be maintained as it is, and the filling of the electrode containing the binder can be performed. Density (excluding substrate)
Is 5.0 g / cm ³ or more, preferably 5.5 g / cm ³ or more,
As a binder-containing electrode, it is possible to manufacture an electrode having a high packing density. As a result, the hydrogen storage amount is larger than that of the hydrogen storage electrode of the same volume produced by using the irregularly-shaped pulverized powder, so that a high capacity Ni-H secondary battery can be produced.

[0033]

EXAMPLES The effects of the present invention will be illustrated by the following examples. In the examples,% other than those relating to the particle size distribution is% by weight unless otherwise specified. % Related to particle size distribution is
As described above, it is the volume ratio.

The hydrogen storage alloy powders used in the examples are shown in Table 1.
AB ₅ type alloy (alloy A) and AB ₂ having the composition shown in
It is a type alloy (alloy B). In the table, Mm is La: 27%, Ce:
Rare earth metal mixed alloy containing 48%, Pr: 7%, Nd: 17%
(Misch Metal).

[0035]

[Table 1]

Example 1 Using the composition of AB ₅ type alloy A shown in Table 1, a substantially spherical hydrogen storage alloy powder was produced by an Ar gas atomizing method. By changing the conditions, hydrogen storage alloy powders having different average diameters are produced, and as they are or by appropriately mixing them, or by classifying them appropriately after mixing, various atomized particles having different average diameters and particle size distributions. A spherical powder (also called atomized powder) was prepared.

As a conventional hydrogen-absorbing alloy powder, a hydrogen-absorbing alloy powder (crushed powder) obtained by crushing a cast ingot of the same composition by a ball mill, and atomized powder and crushed powder are mixed as described in JP-A-7-105943. The mixed powder (mixed weight ratio of atomized powder: crushed powder = 7: 3) and the atomized powder were heat-treated (1000 ° C. × 4 hours) and partially sintered as described in JP-A-8-45505. A part of the sintered powder that was crushed later was also manufactured.

Table 2 shows the average diameter of the obtained hydrogen storage alloy powder, the ratio of the powder having the average diameter +30 μm or more and the diameter of 20 μm or less, and the tap density. The average diameter and proportion were calculated from the integrated 50% diameter (average diameter) and particle size distribution measured by a laser diffraction particle size distribution analyzer.

The tap density is an index of the closest packing density obtained by compressing the alloy powder by tapping a cylinder uniformly filled with the alloy powder and dividing the weight of the alloy powder at that time by its occupied volume. Is the value.
In this embodiment, cylinder volume: 100 cc, stroke: 40
mm, tapping: The measurement was performed under the condition of 800 times (2 times / second).

Each alloy powder was used after being heat-treated at 900 ° C. for 4 hours. Add 5% polyvinyl alcohol aqueous solution of binder in the same ratio to each alloy powder and knead,
A hydrogen storage alloy powder paste was prepared. This paste was applied on both sides of punching metal (nickel plating) to a constant thickness, dried, and then rolled by a roll mill to produce a hydrogen storage electrode. Here, in each electrode, the volume occupied by the dry alloy paste excluding the punching metal of the electrode substrate is 1 cm ³ by making the roll interval constant.
Was manufactured to have a constant thickness. The packing density (excluding punching metal of the substrate) of the obtained electrode was measured and is also shown in Table 2.

This electrode was used as a negative electrode, combined with a commercially available sintered nickel positive electrode having a larger capacity than the negative electrode via a polyamide non-woven fabric, and inserted into a container to give 6N- as an electrolytic solution.
A KOH aqueous solution was injected to form a negative electrode capacity regulated Ni-H secondary battery.

The capacity of this battery was calculated from the alloy filling rate of the electrode and the electrode capacity of the alloy (about 320 mAh / g for alloy A).
After performing 110% overcharge at a current of a time rate, discharging was performed to a terminal voltage of 0.9 V at a current of a similar rate for 3 hours, and the discharge capacity at that time was measured. The results are also shown in Table 2. In addition,
The 3-hour rate current means a current value at which a predetermined capacity is charged or discharged in 3 hours.

[0043]

[Table 2]

As can be seen from Table 2, Test No. using spherical powder having the average diameter and particle size distribution specified in the present invention.
It is understood that the tap densities of Nos. 1, 3, 4, 6, 7, 9, and 11 are higher than those of the crushed powder of Test No. 13 which is a conventional example, and high filling is possible. In addition, the packing density of the electrode after it was made into a paste and rolled after coating was high, and an electrode having a packing density of 5.0 g / cm ³ or more could be formed. In particular,
Even if the tap density is extremely high as in Test Nos. 1, 3, 5, and 6, it retains a high packing density after rolling, which suppresses slippage during rolling and has a high packing property of alloy powder. Indicates that it is maintained during rolling.
Due to the high packing density, the battery capacity was also significantly higher than Test No. 13 using ground powder.

On the other hand, in the comparative example in which the average diameter or the particle size distribution was out of the range of the present invention even when the spherical powder was used,
As in Test Nos. 2 and 10, even when the tap density was very high, the packing density of the electrode was significantly reduced, and was about the same as the conventional example. This is because in Test No.2, the content of coarse particles with the average diameter +30 μm or more is too large, and in Test No.10, the average diameter is too large. Is considered to have significantly decreased. Further, in Test Nos. 2 and 10, gas was generated during charging. It is considered that this phenomenon also occurred due to insufficient contact between the alloy particles due to the above-described slippage during rolling. In addition, in the present invention example, such gas generation was not observed.

In Test Nos. 5 and 8, the particle size distribution was inappropriate, the tap density was too low, and high packing density and capacity were not obtained. In Test No. 12, the average diameter was too small to contain coarse particles, so that a sufficient packing density could not be obtained.

Further, in the conventional example of Test No. 14 using a mixed powder of spherical atomized powder and crushed powder and Test No. 15 using the atomized powder partially sintered by heat treatment to crush, Although a higher packing density was obtained than Test No. 13 using only pulverized powder, both the packing density and the battery performance were inferior to the inventive examples using only spherical powder, and the hydrogen storage of the present invention was It can be seen that the alloy powder is superior to these conventional hydrogen storage alloy powders.

Example 2 A hydrogen storage alloy powder and a hydrogen storage electrode were prepared in the same manner as in Example 1 except that the AB ₂ type alloy B shown in Table 1 was used, and the same test as in Example 1 was conducted. did. The test results are shown in Table 3.

[0049]

[Table 3]

Since the AB ₂ type alloy having a high capacity was used, the battery capacity was generally higher than that in Example 1. However, even if the alloy composition was different, the same tendency as in Example 1 was observed. Recognize.

That is, in the example of the present invention, both the tap density and the packing density of the electrode are higher than the case where the pulverized powder of the conventional example is used, and the packing density is 5.0 g / cm ³ or more (excluding the substrate). A high capacity electrode was obtained. On the other hand, when the average diameter or the particle size distribution was out of the range of the present invention, the packing density of the electrode was low and the electrode capacity was reduced even if the tap density was high. Further, in the conventional example, a mixed powder of atomized powder and pulverized powder or a part of the powder of atomized powder was higher in packing density than the pulverized powder, but the packing density was still higher than that of the example of the present invention. And the battery performance was inferior.

[0052]

As described above, according to the present invention, by adjusting the average diameter and the particle size distribution within a certain range, the high filling property of the spherical hydrogen-absorbing alloy powder can be utilized while the electrode is manufactured. The problems peculiar to spherical alloy powder (decrease in packing density due to defects during roll rolling) can be overcome, and the packing density excluding the substrate part of the electrode is 5.0 g / cm ³ or more, preferably 5.5 g / cm Higher than ³ and high capacity electrodes can be manufactured. In addition, if there is no problem during rolling, it is possible to manufacture an electrode having a uniform thickness and packing density, so that there is no variation in quality and the product yield improves.

According to the present invention, a spherical hydrogen storage alloy powder capable of being highly filled can be used to stably manufacture a hydrogen storage electrode having a high capacity without causing a problem, thereby increasing the capacity of a Ni-H secondary battery. Can be realized.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a state of roll rolling in which a paste of hydrogen storage alloy powder is pressure-bonded to a substrate. FIG. 1 (a) shows a case where irregularly-shaped pulverized powder is used, and FIG. 1 (b) shows Defects due to slippage when spherical powder is used are shown.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noriyuki Noriyuki 4-533 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd. (72) Koichi Kamishiro 4-5 Kitahama, Chuo-ku, Osaka City No. 33 Sumitomo Metal Industries Co., Ltd. (56) Reference JP-A-7-73880 (JP, A) JP-A-1-132049 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) H01M 4/24 H01M 4/38

Claims (2)

(57) [Claims] 1. An average diameter of 5 μm or more and 50 μm or less,
A gas atomizer characterized in that the volume ratio of the powder having the average diameter + 30 μm or more in the particle size distribution is 5% or more and 30% or less, and the volume ratio of the powder having a diameter of 20 μm or less is 5% or more.
A substantially spherical hydrogen storage alloy powder for a Ni-H secondary battery, which is produced by the Izu method or the rotating electrode method . 2. An electrode comprising the hydrogen storage alloy powder according to claim 1 and an organic polymer binder, which is manufactured by rolling and has a packing density of 5.0 g / cm, excluding the substrate.
^A hydrogen storage electrode for a Ni-H secondary battery, which is characterized by having ³ or more.