WO2003056047A1

WO2003056047A1 - Hydrogen-occluding alloy, powder of hydrogen-occluding alloy, processes for producing these, and negative electrode for nickel-hydrogen secondary battery

Info

Publication number: WO2003056047A1
Application number: PCT/JP2002/013607
Authority: WO
Inventors: Kiyofumi Takamaru; Hiroki Hayashi; Hideaki Ikeda
Original assignee: Santoku Corporation
Priority date: 2001-12-27
Filing date: 2002-12-26
Publication date: 2003-07-10
Also published as: AU2002360049A1; JPWO2003056047A1; JP4685353B2

Abstract

A hydrogen-occluding alloy which is reduced in cobalt content, has a satisfactory balance among activity, corrosion resistance, and life characteristics, and has excellent suitability for recycling. The hydrogen-occluding alloy has a composition represented by the formula (1), is constituted substantially of a single phase, and has an average crystal grain diameter of 15 µm or smaller and a major axis/minor axis ratio in each crystal of 3 or higher. RNiaCobAlcMndMe (1) (R is any of rare earth elements including yttrium, etc.; M is magnesium, iron, copper, zirconium, etc.; and 3.30<a≤5.15, 0.10≤b≤0.50, 0.15≤c<0.35, 0.10≤d≤0.45, 0≤e≤0.50, 5.10≤a+b+c+d+e≤5.50, and 0.1≤c/d≤5.0.)

Description

Hydrogen storage alloys, hydrogen storage alloy powders, their production methods, and negative electrodes for nickel hydrogen secondary batteries

INDUSTRIAL APPLICABILITY The present invention is useful as an electrode material for nickel-metal hydride secondary batteries and the like.In particular, when used as a negative electrode material for secondary batteries, a hydrogen storage alloy having a good balance of good activity, corrosion resistance and life characteristics is provided. The present invention relates to the powder, a method for producing the powder, and a negative electrode for a Huckel hydrogen secondary battery.

Background art

At present, attention has been focused on a metal oxide monohydrogen battery in which the hydrogen negative electrode is made of a hydrogen storage alloy. Such batteries inherently have a high energy density, are excellent in volumetric efficiency, can operate safely, and are excellent in characteristics and reliability. The AB ₅ M7] containing storage alloy is mainly used as a negative electrode material of the battery, usually, in order to improve the characteristics of the battery, high hydrogen storage capacity, a variety of such low pressures, corrosion resistance, plateau flatness Characteristics are required. Since some of these properties are contradictory, research has been conducted on improving one property without sacrificing the other property, and some of them have been put to practical use.

In terms of improving the corrosion resistance of the hydrogen storage alloy, which is a factor that improves the cycle characteristics of batteries, the method of adding cobalt is effective and has been put to practical use. However, cobalt is a very expensive metal, which increases the price of the alloy. Therefore, technology to maintain the corrosion resistance of the alloy while reducing the amount of cobalt added is being developed. For example, a method of using a large number of other additive elements together with cobalt is being studied. However, this method has a new problem that the number of elements constituting the alloy increases, which makes it difficult to recycle the battery and increases the cost of recycling. Attempts have been made to increase the ratio of B-site components mainly composed of Ni to A-site components mainly composed of rare earth elements. According to this method, it is difficult to homogenize the alloy structure, and the inclination of the blast plateau in the PCT curve becomes too large, and the tendency toward multi-stage blast plateau is high, so that the battery capacity is reduced and the internal pressure characteristics of the battery are reduced. Problems such as lowering occur. In terms of improving the activity of the hydrogen storage alloy, which is a factor that improves the activity of the battery, attempts have been made to apply a surface treatment to the alloy with an acid or alkali and to increase the proportion of the A-site component to the alloy. Have been. The activity is contradictory to the aforementioned corrosion resistance Therefore, these methods for improving the activity have a problem that the corrosion resistance is reduced at the same time.

Recently, nickel-metal hydride secondary batteries have come to be used for batteries that require high-rate discharge, such as power tool applications, and there is a need for further improvement in the properties of the hydrogen storage alloy used for these batteries.

Disclosure of the invention

An object of the present invention is to be useful as an electrode material of a nickel-hydrogen secondary battery, and by using it as a negative electrode material, it is possible to use a small amount of cobalt, to have an activity such as initial activity, high-rate discharge characteristics, corrosion resistance, and life. An object of the present invention is to provide a hydrogen storage alloy having excellent characteristics in a well-balanced manner and excellent recyclability, a powder thereof, a method for producing the same, and a negative electrode for a nickel-metal hydride secondary battery using the hydrogen storage alloy powder.

The present inventors have conducted intensive studies on the correlation between the composition and structure of the alloy and the corrosion resistance and activity in order to solve the above-mentioned problems. As a result, the B-site component of the alloy is set to a specific range, and the B-site The inventors have found that the above problems can be solved by setting the amounts of A1 and Mn in the components to a specific range, and completed the present invention.

That is, according to the present invention, it has a composition represented by the formula (1), is substantially a single phase, has an average crystallite diameter of 15 μηι or less, and each crystal has a short diameter (D1). A hydrogen storage alloy having a ratio (D1 / D2) of 3 or more to the diameter (D2) is used.

RN i _a C o _b A l ₀ Mn _d M _e

(Wherein, R represents a rare earth element including yttrium or a mixed element thereof, M represents' Mg, Fe, Cu, Zr, Ti, Mo, W, B or a mixture thereof. A represents 3.30 <a≤ 5.15, b is 0.10≤b≤0.50 _N c is 0.15≤c <0.35, d is 0.10≤d≤0.45, e is 0≤e≤0.50, 5.10≤a + b + c + d + e≤5.50, And the abundance ratio c / d of Al and Mn is from 0 to 5.0. ') According to the present invention, the average crystal grain size of the crystal having the composition represented by the formula (1) is included. Provided is a hydrogen storage alloy powder having a diameter (D1ZD2) of 3 or more, which is 15 μπι or less, a ratio of a major axis (D1) to a minor axis D2) of 3 or more, and a particle diameter of ΙΟμπι or greater.

Furthermore, according to the present invention, after melting the alloy raw material having the composition represented by the formula (1), the alloy melt was cooled and solidified to obtain a piece having an average thickness of 0.05 to 0.5 mm. The above-mentioned method for producing a hydrogen storage alloy in which a piece is heat-treated at 900 to 1100 ° C. for 30 minutes to 10 hours, and the method for producing a hydrogen storage alloy powder in which a pulverizing step is performed. Further, according to the present invention, there is provided a negative electrode for a nickel hydrogen secondary battery including the above-mentioned hydrogen storage alloy powder and a conductive material as a negative electrode material.

Preferred embodiments of the invention

Hereinafter, the present invention will be described in detail.

The hydrogen storage alloy of the present invention has a composition represented by the above formula (1). R in the formula (1) represents a rare earth element containing yttrium or a mixed element of two or more thereof. Specifically, for example, one or two selected from the group consisting of La, Ce, Pr and Nd from the viewpoint of improving corrosion resistance when used as a negative electrode active material of a nickel hydrogen secondary battery. It is desirable that the force includes at least one kind or at least one kind selected from the group consisting of La, Ce, Pr and Nd. In this case, the ratio of each rare earth element is preferably 40 to 100% by mass of La, 0 to 50% by mass of Ce, 0 to 50% by mass of Pr, and 0 to 50% by mass of Nd.

A in the formula (1), which indicates the amount of Ni, is 3.30 to a≤5.15, preferably 3.90 a 4.75. B indicating the amount of Co is 0.10≤b≤0.50, preferably 0.20≤b≤0.50. If b exceeds 0.50, the alloy price increases, and if it is less than 0.10, a decrease in corrosion resistance is inevitable. C indicating the amount of A1 is 0.15 ≦ c ≦ 0.35, preferably 0.20 ≦ c ≦ 0.30. D indicating the amount of Mn is 0.10≤d≤0.45, preferably 0.20≤d≤0.30. Also, cZd indicating the abundance ratio of A1 and Mn is 0: !! to 5.0, preferably 0.3 to 1.0. If cZd is out of the above range, a desired alloy cannot be obtained. M in the formula (1) is an additive element for adjusting the hydrogen storage properties of the alloy, and represents Mg, Fe, Cu, Zr, Ti, Mo, W, B, or a mixture of two or more thereof. E, which indicates the amount of M, is 0 ≤ e ≤ 0.50. If e exceeds 0.50, it may not be possible to improve properties corresponding to the added amount, and recycling may be difficult.

In the alloy of the present invention, the value of a + b + c + d + e indicating the B-site element ratio is 5.10 to 5.50, preferably 5.20 to 5.40. If this value is less than 5.10, it becomes difficult to obtain a desired alloy structure, and if it exceeds 5.50, a decrease in capacity when used as a battery material is inevitable.

The hydrogen storage alloy structure of the present invention is substantially single-phase in order to obtain the desired effects of the present invention. The fact that the alloy structure is substantially a single phase means that when there is a phase peak derived from a phase other than the desired phase by X-ray diffraction, the peak having the highest peak intensity is derived from the desired phase. It means that the value is within 5% of the peak intensity.

The hydrogen storage alloy of the present invention has a crystal structure, and the average crystal grain size of the contained crystals is 15 111 or less, preferably 10 m or less, particularly preferably 1 to 10 m, and D1ZD2 Is 3 or more, preferably 10 or more, particularly preferably 10 to 40. If the average crystal grain size exceeds 15 μπι, it is difficult to obtain a desired activity when used for a negative electrode for a secondary battery. If the D1 / D2 force is less than S3, it is difficult to obtain the desired corrosion resistance.

In the present invention, D1 is the major axis of the crystal, and the major axis means the maximum value in the longitudinal direction of the crystal grain, and D2 is the minor axis of the crystal, and the minor axis is a line indicating the major axis. The line is divided into five equal parts, and the four straight lines perpendicular to the line indicating the major axis mean the average value of the lengths of the lines cut by the ends of the crystal grains. In the present invention, the average crystal grain size means an average value of the minor axis.

The method for producing the hydrogen storage alloy of the present invention is not particularly limited as long as the composition and crystal of the obtained alloy can be controlled as described above, but the following production method of the present invention is preferable. In the method for producing a hydrogen storage alloy of the present invention, an alloy raw material having a composition represented by the above formula (1) is melted, and then the alloy melt is cooled and solidified to obtain a piece having a specific average thickness. It is characterized in that the piece is heat-treated under specific conditions.

In the production method of the present invention, the alloy raw material having the composition represented by the above formula (1) is not particularly limited as long as the obtained alloy composition is a mixture of a metal or an alloy satisfying the formula (1). In general, a mixture of metals having the composition represented by the formula (1) or a mother alloy having a desired composition prepared in advance can be used. The alloy melt of the alloy raw material can be obtained, for example, by a known method such as high-frequency melting in an inert gas atmosphere using an alumina tube.

Next, in the production method of the present invention, the above-mentioned alloy melt is solidified by cooling to obtain a piece having an average thickness of 0.05 to 0.5 mm. At this time, if the cooling rate is high, the crystal grain size becomes finer, and if the cooling speed is slow, the crystal grain size becomes coarse. Since the crystal grain size is not uniform during the preparation of the piece, ripening treatment is performed under specific conditions in a later step. Therefore, it is not preferable that the cooling rate at the time of producing the piece is too slow, because the crystal sizing diameter becomes large during the heat treatment described below. Conversely, if the cooling rate is too high, the crystals are finely dispersed and the dispersed state is improved, but it is not preferable because the control of the heat treatment conditions becomes difficult or the productivity is reduced. In addition, when the cooling rate is further increased to become amorphous, it is not preferable because it is difficult to precipitate desired crystal grains even if heat treatment is performed thereafter.

From the above points, it is preferable that the above-mentioned piece production is performed by a strip casting method using a single roll or a twin roll, a centrifugal production method, a rotating disk production method, or the like which can obtain a suitable cooling rate. The cooling conditions are usually about 10 to 3000 ° C./sec, preferably 10 to 500 ° C./sec, and more preferably 10 to 200 ° C./sec. The thickness of the obtained piece is controlled in the range of 0.05 to 0.5 mm in order to eliminate the variation of the crystal grain size in the cross-sectional direction of the piece and to make the crystal grain size after heat treatment described later uniform. There is a need. In this case, columnar crystals grow in the thickness direction of the obtained piece by rubbing the cooling method. In single-sided cooling such as single roll strip casting, the crystal grain size on the surface that comes into contact with the cooling medium is the smallest, and the crystal grain size increases toward the opposite surface. In double-sided cooling, such as twin roll strip casting, the crystal grain size on the surface in contact with the cooling medium is small, and the crystal grain size increases toward the center of the piece.と If the thickness of the piece exceeds 0.5 mm, the difference in grain size between the portion with a small crystal grain size and the portion with a large crystal grain size becomes too large, making it difficult to obtain the desired structure by the heat treatment described below. . Next, in the production method of the present invention, a desired hydrogen storage alloy can be obtained by subjecting the obtained piece to a specific heat treatment. In general, the higher the heat treatment temperature and the longer the heat treatment time, the smaller the grain size difference of each crystal in the piece can be. However, the crystal grain size becomes too large and the desired characteristics cannot be obtained. There is fear. Therefore, in the production method of the present invention, it is necessary to set the ripening treatment conditions at 900 to: L100 ° C for 30 minutes to 10 hours.

The hydrogen storage alloy powder of the present invention has a composition represented by the above formula (1), the average crystal grain size of the included crystals is 15 m or less, preferably 10 m or less, and D1 / D2 of each crystal is It is an alloy powder having a particle size of 10 m or more, preferably 3 or more, preferably 10 or more. Here, the meaning of each configuration is the same as the above-described hydrogen storage alloy of the present invention.

When the hydrogen storage alloy powder of the present invention is used as a negative electrode for a secondary battery, it may contain another alloy powder, and the average particle size of the alloy powder containing the hydrogen storage alloy powder of the present invention is as follows: 5 to; 100 μπι is preferred. Further, the composition of the alloy powder other than the hydrogen storage alloy of the present invention is preferably all compositions represented by the formula (1). However, the cZd value in equation (1) does not need to be satisfied! / ,.

When used as the secondary battery negative electrode, the alloy powder containing the hydrogen storage alloy powder of the present invention has a crystal grain size of preferably 5 m or more, and more preferably 5 to 50 μπι, particularly when used as an electrode. It is preferable that the crystal grain size is 1/2 or less of the average particle size of the alloy powder used.

When such a hydrogen storage alloy powder is used as an electrode material, for example, for the purpose of further improving various electrode characteristics, the surface is covered with plating or a high-molecular polymer, or a solution of an acid, alkaline solution, or the like. A publicly known treatment such as a surface treatment can be performed.

In order to produce the hydrogen storage alloy powder of the present invention, for example, After production, it can be obtained by the production method of the present invention or the like in which the obtained heat-treated pieces are ground.

The step of pulverizing the piece after the heat treatment is not particularly limited as long as the alloy oxidation does not proceed during the pulverization of the piece and a specific particle size can be obtained, and a known method can be used. For example, a wet pulverization method using low oxygen water, a dry pulverization method such as a pin mill or a disk mill, a hydrogen pulverization method using hydrogen gas, and the like are preferable.

The negative electrode for a nickel-hydrogen secondary battery of the present invention is not particularly limited as long as it contains the hydrogen storage alloy powder of the present invention and a conductive material as negative electrode materials. May contain other materials to achieve other purposes.

In order to prepare the negative electrode for a nickel-metal hydride secondary battery of the present invention, for example, an alloy powder containing the hydrogen-absorbing alloy of the present invention ground to a specific particle size and a conductive material are used. A negative electrode can be obtained by mixing and molding with an auxiliary agent and the like. The conductive material, the binder, the conductive auxiliary agent and the like used at this time are not particularly limited, and known materials can be used.

Since the hydrogen storage alloy and the powder thereof of the present invention have a specific composition and a specific structure, they are useful as an electrode material for a nickel-metal hydride secondary battery. Discharge characteristics, corrosion resistance, and life characteristics are well-balanced, and these characteristics can be obtained with a small amount of Co, and recyclability can be considered. Further, according to the production method of the present invention, such a hydrogen storage alloy and its powder can be industrially easily obtained.

The negative electrode for a nickel-metal hydride secondary battery of the present invention uses the hydrogen-absorbing alloy powder of the present invention as an active material, so that the effect obtained when the negative electrode for a secondary battery is obtained is obtained, and the utility is rich. Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited thereto.

Examples 1-1 to 1-5 and Comparative Examples 1-1 to: 1-2

Rare earth metals having the atomic ratios shown in Table 1 (Examples 1-1 to 1-4 used misch metal manufactured by Santoku Co., Ltd.) as the A site, and Ni, Co, Mn when the A site was 1. A raw material metal or an alloy was blended so that the atomic ratio of Al, Al and X of ABx became the values shown in Table 1, and were subjected to high frequency melting in an argon atmosphere using an alumina tube to prepare an alloy melt. Next, the obtained alloy melt is continuously supplied to a single roll via a tundish, A 0.2 mm thick piece was prepared by rapid cooling at a cooling rate of 100 ° C / sec by the lip casting method. Next, the obtained piece was heat-treated in an argon gas atmosphere under the conditions shown in Table 1 to prepare a hydrogen storage alloy.

The composition of the obtained hydrogen storage alloy was quantitatively analyzed by X-ray fluorescence analysis (SMX-10, manufactured by Rigaku Denki Kogyo). As a result, it was confirmed that the composition was the same as the composition. Also, the alloy structure was observed with a scanning electron microscope, and it was confirmed by X-ray diffraction whether or not the alloy was substantially a single phase. Furthermore, the average crystal grain size, D1 and D2 were measured from the alloy structure observed with a scanning electron microscope. Table 1 shows the results.

table 1

Examples 2-l to 2-5 and Comparative examples 2-1 to 2-2

Examples 1-1 to 1-5 or Comparative Example 1- :! The hydrogen storage alloys prepared in Steps 1 to 2 were mechanically pulverized to prepare hydrogen storage alloy powders having an average particle diameter of 60 m or less.

The composition of the obtained hydrogen-absorbing alloy powder was quantitatively analyzed by X-ray fluorescence analysis (SMX-10, manufactured by Rigaku Denki Kogyo), and as a result, Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1 It was confirmed that the composition was the same as the composition of the hydrogen storage alloy prepared in -2. Table 2 shows the results of the measurements performed in the same manner as in Examples 1-1 to L-5.

Table 2

Example 3-1 to 3-5 and Comparative Example 3-1 to 3-2

1.2 g of each of the hydrogen storage alloy powders prepared in Examples 2-1 to 2-5 or Comparative Examples 2-1 to 2-2 were weighed, and carbonyl carbon lg as a conductive material and a fluororesin powder as a binder were weighed. The mixture was mixed with 0.2 g to prepare fibrous materials. The obtained whisker-like material was wrapped in a nickel mesh and pressed under a pressure of 2.8 ton // cm ^{2 to} produce a negative electrode for a nickel-metal hydride secondary battery. Each electrode was subjected to a charge / discharge test in a pressurized vessel at 5 atm in 30% KOH to evaluate the initial activity, high rate discharge characteristics and corrosion resistance shown below. Table 3 shows the results. The initial activity was carried out for 10 cycles at a discharge current of 0.2 C, and the discharge capacity at the third cycle was evaluated with respect to the discharge capacity at the tenth cycle.

As for the high rate discharge characteristics, the capacity at the time of discharging at 1 C at the 11th cycle was measured, and the ratio of the value at this time to the discharge capacity at the 10th cycle was evaluated.

With respect to the corrosion resistance, after the 12th cycle, the battery was discharged at a discharge current of 0.2 C, and the capacity retention ratio at the 600th cycle with respect to the discharge capacity at the 10th cycle was Hffi. Table 3

Initial activity High rate discharge Corrosion resistance (%) Characteristics (%) (%) Example 3-1 96.6 93.3 95.6 Example 3-2 95.0 92.5 96.8 Example 3-3 97.5 94.1 96.2 Example 3-4 97.9 95.0 96.6 Example 3-5 95.7 93.2 94.2 Comparative example 3-1 89.4 84.2 95.5 Comparative example 3-2 96.2 82.2 82.2

Claims

The scope of the claims

1.has a composition represented by the formula (1), is substantially a single phase, and has an average crystal grain size of 15 m or less, and the major axis (D1) and minor axis (D2) of each crystal Hydrogen storage alloy with a ratio (D1ZD2) of 3 or more.

RN i _a C o _b A 1 ₀ Mn _d M _e (1)

(In the formula, R represents a rare earth element or a mixture elements including Ittoriumu, M is Mg, Fe, Cu _N Zr, shows Ti, Mo, W, B or mixtures thereof. A is 3.30 <a≤5.15 B tt 0.10≤b≤0.50 _% c is 0.15≤c <0.35, d is 0.10≤d 0.45, e is 0≤e 0.50, 5.10 ≤a + b + c + d + e≤5.50, and Al and存在 Mn abundance c / d is 0:! ~ 5.0.)

2. Having the composition represented by the formula (1), the average crystal grain size of the contained crystals is 15 m or less, and the ratio of the major axis (D1) to the minor axis (D2) of each crystal (D1 / D2 ) Is 3 or more and the particle diameter is 10 μm or more.

3. After melting the alloy raw material having the composition represented by the formula (1), the alloy melt is cooled and solidified to obtain a piece having an average thickness of 0.05 to 0.5 mm. L100. The method for producing a hydrogen storage alloy according to claim 1, wherein the heat treatment is performed at 30 minutes to 10 hours at C.

4. After melting the alloy raw material having the composition represented by the formula (1), the alloy melt is cooled and solidified to obtain a piece having an average thickness of 0.05 to 0.5 mm. The method for producing a hydrogen storage alloy powder according to claim 2, wherein the powder is heat-treated at 1100 ° C for 30 minutes to 10 hours and then pulverized.

5. A negative electrode for a nickel-metal hydride secondary battery, comprising the hydrogen storage alloy powder of claim 2 and a conductive material as a negative electrode material.