JP2003313601A - Hydrogen storage alloy, its production process and electrode for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy which comprises a bcc phase having a high hydrogen storage capacity as a main phase and is suitable as an electrode for a secondary battery, and its production method. <P>SOLUTION: The hydrogen storage alloy is composed of a Ti-Cr alloy base metal 1 having the phase (bcc phase) of a body-centered cubic crystal structure as the main phase and Ni-containing regions (Ni-deposited phases 2 and Ti-Ni alloy regions 3) formed in a dispersed manner on the surface of the Ti-Cr alloy base metal 1. This can inhibit the generation of a Laves phase, even when subjecting the surface of the Ti-Cr alloy base metal 1 to a heat treatment for forming the Ti-Ni alloy regions 3 having catalytic activities, thereby the high hydrogen storage capacity can be maintained. <P>COPYRIGHT: (C)2004,JPO

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 capable of storing and releasing hydrogen, and particularly to a hydrogen storage alloy of body-centered cubic (bcc) crystal structure type having a theoretically high capacity. The present invention relates to a hydrogen storage alloy and the like which has an excellent hydrogen absorption / desorption amount in a specific pressure range and a temperature range and has a high hydrogen storage amount per unit weight and a highly practical industrial production capable of highly efficient industrial production.

[0002]

2. Description of the Related Art At present, there is a concern about acid rain caused by NOx (nitrogen oxide), which is increased by the use of fossil fuels, and global warming due to CO _2. These environmental destructions are serious problems. Is coming. Among them, the practical application of hydrogen energy as clean energy has been attracting worldwide attention. Hydrogen is an inexhaustible constituent element of water on the earth, and not only can it be created using various primary energies, but it is also a by-product of water, so there is no concern of environmental damage. Further, it has excellent characteristics such as being relatively easy to store as compared with electric power.

Therefore, in recent years, research and development of hydrogen storage alloys as a storage and transportation medium for these hydrogens and studies for their practical use have been actively carried out. These hydrogen storage alloys are metals and alloys that can absorb and release hydrogen under appropriate conditions. By using this alloy, it becomes possible to store hydrogen at a low pressure and at a high density as compared with a conventional hydrogen gas cylinder. The volume density thereof is almost equal to or higher than that of liquid hydrogen or solid hydrogen, and the handling safety is remarkably excellent.

LaNi is one of these hydrogen storage alloys._Five
AB such as_FiveType alloy or TiMn ₂AB such as₂Pattern
Gold has been put to practical use. However, its hydrogen storage capacity is at most
It is around 1.4 mass%, for example, WE-NET (country
Water such as fuel cells advocated by the International Energy Network)
Target performance of hydrogen storage alloy used for elementary storage 100 ℃ or less
Can't reach 3 mass%. In recent years, for example,
For example, JP-A-10-110225 and JP-A-10-12
1180 and Japanese Patent Laid-Open No. 2000-345273.
The number of hydrogen storage sites is large and
The theoretical amount of hydrogen that can be stored per unit weight of gold is about 4
mass%, (H / M = 2, H: occluded hydrogen atom, M: total
Very large body-centered cubic structure (hereinafter “bc”)
Called "phase c", "bcc type" or "bcc")
Ti-Cr type alloys with
Many studies have begun.

In order to obtain a Ti-Cr binary alloy containing the bcc phase as the main phase, it is effective to heat the alloy in a temperature range where the bcc phase is produced and then rapidly cool it, for example, in water.
In this Ti-Cr binary alloy, the mixing ratio that allows hydrogen storage and release at a practical temperature and pressure is 40≤Cr (at%) ≤60. However, the alloy of 40 ≦ Cr (at%) ≦ 60 is
As can be seen from the -Cr binary system phase diagram, the melting point of the alloy and C
14 type crystal structure (βTiCr ₂ / Laves phase) or C
The width of the temperature region in which the bcc phase is generated, which is between the temperature in which the 15-type crystal structure (αTiCr ₂ / Laves phase) is generated, is extremely small. Therefore, another C14 type or C15 type Laves phase different from the bcc phase is formed in the alloy in a considerable amount, and it is difficult to obtain an alloy having the bcc phase as the main phase.

[0006]

By the way, when a hydrogen storage alloy is used as an electrode for a secondary battery, it is necessary to contain Ni which functions as a catalyst in the hydrogen storage alloy. However, a hydrogen storage alloy containing Ni, such as Ti-C
The r-Ni-based alloy not only has a lower hydrogen storage amount per unit weight than the bcc single-phase Ti-Cr-based alloy, but also recharges a secondary battery in a strongly alkaline electrolyte such as 6N KOH. There is a problem that it does not operate as a working electrode. In view of such a problem, Japanese Patent Laid-Open No. 2001-273891 proposes to remove Ni from the basic composition constituting the hydrogen storage alloy and to form a Ti—Ni based alloy phase on the surface layer portion of the hydrogen storage alloy particles. ing. However, in the method disclosed in Japanese Patent Laid-Open No. 2001-273891,
In order to form a Ti-Ni-based alloy phase on the surface layer of the hydrogen storage alloy particles, a long time, specifically, 600 to 700 ° C. is used for 6 hours.
Since heating is performed for a time, the Laves phase appears in the hydrogen storage alloy. Then, as described above, when the Laves phase appears, the hydrogen storage amount decreases. Therefore, the present invention has been made in view of the above problems, and provides a hydrogen storage alloy, which has a bcc phase having a high hydrogen storage capacity as a main phase, and is suitable as an electrode for a secondary battery, a method for producing the same, and the like. The task is to do.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the present inventor has conducted various studies for containing Ni without reducing the bcc phase of a Ti—Cr alloy base material. As a result, it was found that the bcc phase can be used as the main phase while suppressing the appearance of the Laves phase by discretely forming the Ni-containing regions on the surface of the Ti-Cr alloy base material. That is, according to the present invention, a Ti—Cr based alloy base material having a phase (bcc phase) having a body-centered cubic crystal structure as a main phase and Ni formed discretely on the surface of the Ti—Cr based alloy base material. Provided is a hydrogen storage alloy having a containing region. Here, in the present specification,
“Discretely” does not mean that the Ni-containing region exists so as to cover the entire surface of the Ti—Cr based alloy base material, but Ti—C.
This means that Ni-containing regions are scattered on the surface of the r-based alloy base material. The Ni-containing region means a region containing Ni element in some form. In the hydrogen storage alloy of the present invention, the Ni-containing regions discretely formed on the surface of the Ti-Cr alloy base material are entirely or partially made of Ti-N.
The i-based alloy region may be used, and the Ni-containing region may have a diameter of 5 μm or less (not including 0).

Further, the present invention is a hydrogen storage alloy composed of a Ti-Cr alloy base material having a phase (bcc phase) having a body-centered cubic crystal structure as a main phase, which is a Ti-Cr alloy base material. On the surface, Ti-Cr alloy phase and Ti having catalytic ability
And a Ni-based alloy phase. In the hydrogen storage alloy of the present invention, Ti
It is desirable that the composition of the -Cr alloy base material be as follows. High bcc by adjusting the composition to the following range
It has a phase-forming ability and is in a cast state (hereinafter referred to as "as ca" as appropriate.
st)) or heat treatment after casting and simple cooling to obtain a bcc phase single phase alloy containing almost no harmful Laves phase such as C14 type and C15 type. Moreover, the obtained bcc phase is Ti-Cr
It is maintained even after the heat treatment for diffusing Ni deposited on the surface of the base alloy base material. _{Ti (100-abcd) Cr a} X b X 'c Ni d where 20 ≦ a (at%) ≦ 80,0 ≦ b (at%) ≦ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W And at least one element of Al

Further, according to the hydrogen storage alloy of the present invention, it is possible to make the above Ti—Cr alloy base material into a single phase structure of a phase (bcc phase) having a body-centered cubic crystal structure.

Furthermore, the present invention provides a method for producing a hydrogen storage alloy having the following characteristics, which is suitable for obtaining the hydrogen storage alloy having the above characteristics. That is, in the method for producing a hydrogen storage alloy of the present invention, the step (a) of obtaining the Ti—Cr based alloy base material and the Ni on the surface of the Ti—Cr based alloy base material obtained in the step (a) are dispersed in a discrete manner. A step (b) of depositing on
And a step (c) of diffusing Ni deposited on the surface of the Ti-Cr alloy base material. In the method for producing a hydrogen storage alloy according to the present invention, in the step (a), Ti—C containing 5 at% or less (not including 0) of Ni is used.
It is desirable to obtain an r-based alloy base material. Also, step (b)
It is effective that the Ni is adhered by mechanically. Furthermore, the Ti-Cr alloy base material obtained in the above-mentioned step (a) and the hydrogen storage alloy obtained after the above-mentioned step (c) are mainly composed of a phase (bcc phase) having a body-centered cubic crystal structure. Can be phases. Further, as the diffusion treatment in the step (c), 500 to 70
Heat treatment for 10 minutes to 3 hours in the temperature range of 0 ° C. can be adopted.

Prior to the step (b), the Ti-Cr alloy base material obtained in the step (a) is a phase (bcc phase) in which the Ti-Cr alloy base material has a body-centered cubic crystal structure. It is possible to further include a step (d) of performing a heat treatment in which a predetermined temperature period, for example, 1 minute to 1 hour is maintained in a temperature region in which is formed, for example, a temperature range of 1250 to 1450 ° C. At this time, after the step (d), a step (e) of forcibly cooling the Ti—Cr based alloy base material may be provided to rapidly cool the Ti—Cr based alloy base material. In particular, when Mo is contained in the Ti-Cr alloy base material, if the content of Mo is large, quenching
Equivalent characteristics can be obtained regardless of the cooling, but when the content is small, it can be expected to obtain good characteristics by performing rapid cooling.

The present invention also provides a hydrogen storage alloy electrode for a secondary battery, which has the following features. That is, the hydrogen storage alloy electrode for a secondary battery of the present invention has a composition of Ti
_{(100-abc -d) Cr a} X b X 'c Ni d Toshikatsu body-centered cubic type of crystalline structure phases (bcc phase) as the main phase Ti-C
It is characterized by including an r-based alloy base material and Ni-containing regions discretely formed on the surface of the Ti-Cr-based alloy base material. Here, in the composition of the Ti-Cr alloy base material, 2
0 ≦ a (at%) ≦ 80, 0 ≦ b (at%) ≦ 10,0
≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W and Al. It is desirable to use at least one element. Such an electrode is preferably formed of the hydrogen storage alloy manufactured by the manufacturing method of the present invention as described above.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy according to the present invention is b
A Ti-Cr alloy base material having a cc phase as a main phase, and this Ti
It is characterized by comprising Ni-containing regions discretely formed on the surface of the -Cr alloy base material. In the present specification, the Ni-containing region means a region containing Ni element in some form. That is, in the present specification, a region in which Ni exists alone (for example, a Ni adhered phase), a region in which Ni is alloyed with other elements (for example, a Ti—Ni alloy region), and the like are collectively referred to. This is referred to as "Ni-containing region".

FIG. 1 is a diagram schematically showing the structure of a hydrogen storage alloy according to the present invention. FIG. 1 (a) shows the state of the hydrogen storage alloy before the Ni diffusion treatment, and FIG. 1 (b) shows The states of the hydrogen storage alloy after the Ni diffusion treatment are shown respectively. In addition, as shown in FIG. 1, the hydrogen storage alloy is in the form of particles. The details of the Ni diffusion process will be described later.

First, with reference to FIG. 1A, the state of the hydrogen storage alloy before the Ni diffusion treatment will be described. Figure 1 (a)
As shown in, the surface of the Ti-Cr alloy base material 1 has N
The i adhered phase (Ni-containing region) 2 is discretely formed. Here, in the specification of the present application, “discretely” does not mean that the Ni-adhered phase 2 exists so as to cover the entire surface of the Ti—Cr alloy base material 1 as described above, but that it is Ti—C.
This means that the Ni adhered phase 2 is scattered on the surface of the r-based alloy base material 1. Therefore, as shown in FIG. 1A, a part of the Ti—Cr alloy base material 1 is exposed.

Next, the state of the hydrogen storage alloy after Ni diffusion treatment will be described with reference to FIG. 1 (b). By performing the Ni diffusion treatment, the Ni-deposited phase 2 is entirely or partially converted into a Ti-Ni-based alloy due to the diffusion that occurs between the Ni-adhered phase 2 and the Ti-Cr-based alloy base material 1. Then, a region where the Ni-adhered phase 2 is turned to become a Ti-Ni alloy (hereinafter,
The “Ti—Ni-based alloy region (Ni-containing region) 3” provides the hydrogen storage alloy with a catalytic ability for a reaction of electrochemically storing and releasing hydrogen, and also has an effect of oxidation resistance. be able to. Here, FIG. 1B shows a state in which a part of the Ni adhered phase 2 is changed to the Ti—Ni alloy region 3. The Ti—Ni based alloy region 3 is formed from the surface of the Ti—Ni based alloy base material 1 to Ni.
It can be formed by diffusing atoms. T
The i-Ni alloy region 3 is formed of, for example, Ti ₂ Ni or TiN.
i, TiNi _3, etc. In addition to Ti, alloy constituent elements such as Cr and Mo may be incorporated in the Ti—Ni based alloy region 3.

The structure of the hydrogen storage alloy according to the present invention has been schematically shown above with reference to FIG. Then, as described above, in the present specification, the region containing the Ni element is referred to as “Ni-containing region”. Therefore, the Ni adhered phase 2 and the Ti—Ni based alloy region 3 shown in FIG. 1 are both included in the “Ni-containing region” which is meant in the present invention. In the hydrogen storage alloy according to the present invention, the Ni-containing region is formed in a proportion of 1 to 10 wt% with respect to the Ti-Cr alloy base material 1.
The Ni-containing region preferably has a diameter of 5 μm or less (not including 0). A more desirable diameter of the Ni-containing region is 3 μm or less (not including 0), and further 0.5 to
It is 1.0 μm. As described above, the Ti—Ni-based alloy region 3 as the Ni-containing region provides the hydrogen storage alloy with a catalytic ability for a reaction of electrochemically storing and releasing hydrogen, but it does not absorb hydrogen. Is sufficient if the diameter of the Ni-containing region is 5 μm or less (not including 0). On the other hand, if the diameter of the Ni-containing region exceeds 5 μm, the alloy is destroyed (cracked) due to expansion accompanying hydrogen storage, which is not preferable. As will be described later, in the present invention, Ti-
The Cr-based alloy base material 1 can contain Ni at 5 at% or less in advance, but this means that it is contained in the Ti—Cr-based alloy base material 1 and is distinguished from the Ni-containing region.

The hydrogen storage alloy according to the present invention comprises Ti--Cr.
The Ni-containing region (Ni-deposited phase 2,
Instead of forming the Ti-Ni alloy region 3),
The greatest feature is that the containing regions are discretely formed on the surface of the Ti—Cr alloy base material 1. Due to this feature,
Since the heat treatment time for diffusing the Ni-containing region formed on the surface of the Ti-Cr alloy base material 1 is short,
Even after this heat treatment, it is possible to obtain a hydrogen storage alloy having the bcc phase as the main phase while suppressing the appearance of the Laves phase. As will be described in detail in Examples described later, according to the hydrogen storage alloy of the present invention, since a high hydrogen storage amount can be obtained, an electrode for a secondary battery using the hydrogen storage alloy of the present invention has a good cycle. Show the characteristics. Specifically, a high electric capacity can be maintained even after 20 cycles.

Next, the desirable composition of the Ti-Cr alloy base material 1 will be described. In the present invention, the alloy base material is T
The i-Cr alloy is used because a high hydrogen storage amount can be obtained by the Ti-Cr alloy as described above. Further, by setting the composition of the Ti-Cr alloy base material 1 as follows, it is possible to make the bcc phase the main phase even after the heat treatment for diffusing the Ni-adhered phase 2 is performed. Become. Hereinafter, a desirable composition of the Ti—Cr alloy base material 1 will be described in detail.

The Ti--Cr alloy has the general formula Ti.
_{(100-abc) Cr a X} b X 'c, where 20 ≦ a (at%) ≦
80, 0 ≦ b (at%) ≦ 10, 0 ≦ c (at%) ≦ 3
0, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W and A
It is preferable to have a composition of at least one element of l. The reasons for limiting the composition will be described below.

The atomic radius of Ti (0.146 nm) is Cr
Since the atomic radius is larger than the atomic radius (0.125 nm), the Ti content of the alloy is increased and the Cr content is decreased, the lattice constant of the bcc phase is increased and the plateau pressure is decreased. That is, the Ti—Cr alloy can control the plateau pressure by controlling the composition ratio of Ti and Cr. Therefore, although the plateau pressure of the hydrogen storage alloy changes depending on the alloy operating temperature, the Cr / Ti ratio that matches the target operating temperature may be selected.

However, when the Cr content a exceeds 80 at%, the plateau pressure remarkably rises, and when the Cr content a is less than 20 at%, the plateau pressure remarkably lowers and the practicability becomes poor. Therefore, 20 ≦ a (at%) ≦ The range is 80. It is preferable to select a Cr / Ti ratio suitable for the target operating temperature in the range of 30 ≦ a (at%) ≦ 70, and more preferably 45 ≦ a (at%) ≦ 65. Considering a certain practicality, it is desirable to have an appropriate plateau pressure at 20 ° C (293K) to 40 ° C (313K), in which case the Cr / Ti ratio should be in the range of 1.0 to 1.6. Is recommended. Specifically, Ti _(100-a) Cr _a , where 50 ≦ a
The composition is (at%) ≦ 62. However, the present invention is not limited to this composition.

Next, it is desirable to contain the X element, that is, at least one of Ru, Rh, Os and Ir in the range of 10 at% or less. The X element (hereinafter sometimes abbreviated as Ru, etc.) has a strong stabilizing effect on the bcc phase even when added in a small amount, and this effect is due to the conventionally known effects of V and M.
It surpasses bcc stabilizing elements such as o, W, and Al. The content of the X element in the present invention may be appropriately selected depending on the target operating temperature and operating pressure. But,
If it exceeds 10 at%, the hydrogen storage amount per unit weight decreases, and the cost becomes industrially too high. Therefore, the content is set to 10 at% or less. It may be selected in the range of preferably 7 at% or less, more preferably 5 at% or less. However, the Ni-deposited phase 2 is diffused to form Ti-Ni.
Even in the heat treatment for forming the base alloy region 3, bc
From the viewpoint of maintaining the c-phase, when at least one of Ru and Os is contained, 1.5 ≦ b (at
%) ≦ 5, further 2 ≦ b (at%) ≦ 4, and 2.5 ≦ when at least one of Rh and Ir is contained.
It is desirable that b (at%) ≦ 7, and further 3 ≦ b (at%) ≦ 5.

The reason why the element X of the present invention has the bcc phase stabilizing effect as described above is not clear. Regarding the stabilization of the bcc phase, the atomic radius is Ti (atomic radius: 0.1
It is effective to contain an element having an intermediate value between 46 nm) and Cr (atomic radius: 0.125 nm). Ra Beth phase expressed by a composition of the AB _2, to take an ideal geometry in these compositions, A, B both atomic atomic radius (R _A: R _B) is about 1.225 The atomic radius of Ti: Cr is 1.17: 1, which is slightly apart from the ideal geometrical structure. Then, in the Ti-Cr binary alloy, by increasing the amount of Ti, apparently more Ti penetrates into the B site, the atomic radius ratio between the A site and the B site is reduced, and the Laves phase is further increased. Can be separated from the ideal geometrical structure of. Further, if an element having a smaller atomic radius than the A site and a larger atomic radius than the B site is contained in the Ti-Cr binary alloy,
When this element enters either A or B site, R _A : R _B becomes smaller and hinders Laves phase formation, that is, bc
It is presumed to promote the formation of the c-phase. The X element of the present invention has an atomic radius of Ti as shown below.
(Atomic radius: 0.146 nm) and Cr (Atomic radius: 0.1
25 nm). Therefore, although the stabilizing effect of the bcc phase by the X element of the present invention is based on the above-mentioned assumption, the conventional stabilizing element of the bcc phase also has an atomic radius between Ti and Cr. Therefore, it has a remarkable effect that cannot be expected from the conventional bcc phase stabilizing element. (Atomic radius of X element) Ru: 0.133 nm, Rh: 0.134 nm Os: 0.134 nm, Ir: 0.135 nm

FIG. 2 shows Ti ₃₇ Cr ₅₈ V ₅ alloy, Ti ₃₉ C
It is a graph showing the results of measuring the phase transformation temperature to the color Beth phase from bcc phase r ₅₉ Mo ₂ alloy and Ti ₄₁ Cr ₅₇ Ru ₂ alloy (DTA curve). From FIG. 2, Ti ₄₁ Cr ₅₇ R
transformation temperature to the u ₂ alloy of error Beth phase, Ti ₃₇ Cr _{5 8} V ₅
It can be seen that it is higher than the transformation temperature of the alloy and the Ti ₃₉ Cr ₅₉ Mo ₂ alloy to the Laves phase. That is, FIG. 2 suggests that the Ru-containing alloy will have a large Laves phase suppressing effect even in the Ni diffusion treatment.

In the hydrogen storage alloy of the present invention, at least one of V, Mo, W and Al (X 'element) is used as a stabilizing element of the bcc phase in place of or together with the X element.
Can be included. By containing this X'element at the same time as the X element, the content of the X element can be further reduced, and a small amount of the X'element can be used.
The decrease in the hydrogen storage amount per unit weight can be suppressed to a slight level. As a result, it is possible to obtain a hydrogen storage alloy having high practicality, which is well balanced in cost and hydrogen storage amount per unit weight. In the present invention,
Although a small amount of the X'element can exert a predetermined effect, it cannot be denied that the X'element is contained in the same amount as the conventional one. Therefore, the inclusion of 30 at% or less is allowed. However, its content is preferably as small as possible within the range where a predetermined effect can be obtained. Therefore, in the present invention, the content of 20 at% or less, further 10 at% or less is recommended. Depending on the combination of the X element and the X element, the predetermined effect can be exhibited even with an extremely small content of 5 at% or less. An indication of the content of _c 'X when expressed in _c' a hydrogen storage alloy of the present invention the general formula _{Ti (100-abc) Cr a} X b X below. As one guideline, when Ru and / or Rh and V are added in combination, b + (c / 10) is 2 at% or more (b and c are symbols in the above general formula), Ru and / or Rh and Mo. B + (c / 3) when adding and
Is 2 at% or more, when Os and / or Ir and V are added in combination, b + (c × 3/20) is 3 at% or more, and when Os and / or Ir and Mo are added in combination, b + ( By setting c / 2) to 3 at% or more, a bcc single-phase structure can be obtained even after the heat treatment for diffusion treatment of the Ni-adhered phase 2.

In the present invention, the Ti-Cr alloy base material 1 is made of Ni.
One of the features is to appropriately contain 5% or less (not including 0). Ni in this range is previously set to T
By including it in the i-Cr alloy base material 1, the plateau pressure is arbitrarily controlled, the flatness of the plateau pressure is controlled, the melting temperature of the manufacturing process is controlled, the heat treatment temperature is controlled, the corrosion resistance of the alloy is improved, and the secondary battery electrode material is used. It is possible to control the current collecting characteristics and the like of the alloy. However, when Ni exceeding 5 at% is contained in the Ti-Cr alloy base material 1, the following problems occur. That is, Ni such as Ti and Cr
When elements other than the above and Ni are simultaneously dissolved, Ni segregation having a small hydrogen storage amount is formed in the entire Ti—Cr alloy base material 1 and the hydrogen storage amount is reduced. Therefore, Ti-Cr
In the base alloy base material 1, the amount of Ni contained in advance is 5a
t% or less (not including 0). A more desirable amount of Ni in the Ti-Cr alloy base material 1 is 3 at% or less, and more desirably 2 at% or less.

By the way, hydrogen absorption and desorption is repeated tens to hundreds of times (hereinafter, repeating hydrogen absorption and desorption tens to hundreds of times is appropriately referred to as "high cycle"), and hydrogen is gradually absorbed. It is known that the crystal structure of the alloy is distorted and the hydrogen storage alloy is easily cracked. And it is thought that this crack is the main cause of the characteristic deterioration of the hydrogen storage alloy. However, according to a study by the present inventor, Ti-C according to the present invention
In the r-based alloy base material 1, Ni was previously contained at 5 at% or less (0
(Not including), the Ti—Cr alloy base material 1 is less likely to crack even after a high cycle. That is, by preliminarily containing a predetermined amount of Ni in the Ti—Cr alloy base material 1, it is possible to mitigate cracking, which is the main cause of deterioration of the characteristics of the hydrogen storage alloy. Therefore, according to the hydrogen storage alloy of the present invention, it is possible to have desired properties even after a high cycle. In addition, when Ni is contained in the Ti-Cr alloy base material 1 in advance, even if the Ti-Cr alloy base material 1 is cracked, Ni is still present on the cracked surface, and therefore the secondary surface is still present. It can function as a battery electrode.

A general formula considering the case where the Ti—Cr alloy base material 1 of the present invention contains Ni element is as follows. _{Ti (100-abcd) Cr a} X b X 'c Ni d where 20 ≦ a (at%) ≦ 80,0 ≦ b (at%) ≦ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W And at least one element of Al

Further, the hydrogen storage alloy of the present invention comprises Y and lanthanoid series elements (La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b, Lu or less, and at least one of L elements including Y) can be contained in the range of 10 at% or less, preferably 5 at% or less, and more preferably 3 at% or less. Since the L element has a strong affinity with oxygen, it exerts an effect of removing oxygen existing in the alloy as an L element oxide. As a result, it becomes possible to stabilize the hydrogen storage amount and to effectively use industrially a raw material having a relatively large amount of oxygen. The general formula when the hydrogen storage alloy of the present invention contains L element is as follows. _{Ti (100-abcde) Cr a} X b X 'c Ni d L e where 20 ≦ a (at%) ≦ 80,0 ≦ b (at%) ≦ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5,
0 ≦ e (at%) ≦ 10, and X is Ru, Rh,
At least one element of Os and Ir, X ′ is at least one element of V, Mo, W and Al, and L is Y, La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu
At least one element of

Further, Mn, Fe and C are added to the alloy base material.
At least one element of O, Cu, Nb, Ta, B and C (hereinafter, T element) is 30 at% or less, preferably 2
It can be appropriately contained within a range of 0 at% or less, more preferably 10 at% or less. When the hydrogen storage alloy of the present invention contains T element, the general formula is as follows. _{Ti (100-abcdef) Cr a} X b X 'c Ni d L e T f where 20 ≦ a (at%) ≦ 80,0 ≦ b (at%) ≦ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5,
0 ≦ f (at%) ≦ 30, and X is Ru, R
at least one element of h, Os and Ir, the above X ′
Is at least one element of V, Mo, W and Al, and L is Y, La, Ce, Pr, Nd, Pm, Sm, E
at least one element of u, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, where T is Mn, Fe, C
at least one element of o, Cu, Nb, Ta, B and C

The hydrogen storage alloy of the present invention having the above structure has the bcc phase as the main phase. Whether or not the alloy has the bcc phase as the main phase can be determined by X-ray diffraction. Also in the present invention, whether or not the bcc phase is the main phase is determined by X-ray diffraction. More specifically, the ratio (%) according to the following formula based on the integrated intensity of the diffraction line is 50% or more.
The alloy is defined as the main phase. The hydrogen storage alloy of the present invention,
It is desirable that the proportion of the bcc phase is higher, and it is desirable that 70% or more, and further 90% or more, consist of the bcc phase. Needless to say, the present invention includes the case where the bcc phase is 100%, that is, the bcc phase is a single phase, and the hydrogen storage amount,
It is the most desirable form for other properties. In addition,
Not only the index (110) but also the index (2
The peak of the bcc phase is also observed in (00) and (211), but the higher-order indices (200) and (211) are not considered in the calculation of the ratio of the bcc phase in the present specification. bcc (110) / [bcc (110) + {C14Laves (201)
+ C15Laves (311)} × 2] In the present invention, the phase that may exist in addition to the bcc phase is the Laves phase. As mentioned above, the Laves phase is C
14-type crystal structure (βTiCr ₂ / Laves phase) and C
15-type crystal structure (αTiCr ₂ / Laves phase), and although not usually observed, C36-type crystal structure (γTiCr _2).
Laves phase).

The hydrogen storage alloy of the present invention can maintain the bcc single phase even after the Ni diffusion treatment for forming the Ti--Ni alloy region 3, specifically, the heat treatment. Moreover, this alloy contains the above-mentioned X element, namely Ru.
When such elements are included, it is sufficient to add a very small amount of 2 at% or 3 at%. This is known as V, Mo, W and A, which are known as conventional bcc phase stabilizing elements.
Less than 1 etc.

Next, a desirable manufacturing method for obtaining the hydrogen storage alloy of the present invention will be described with reference to FIG. FIG. 3 is a flowchart showing the method for producing a hydrogen storage alloy of the present invention. As shown in FIG. 3, in the method for producing a hydrogen storage alloy of the present invention, a step of obtaining a Ti—Cr alloy base material 1 (hereinafter referred to as “alloy production step”) and the obtained Ti—
A step of discretely depositing Ni on the surface of the Cr-based alloy base material 1 (hereinafter referred to as “Ni deposition step”), and a diffusion treatment of Ni deposited on the surface of the Ti—Cr-based alloy base material 1. (Hereinafter referred to as "Ni diffusion treatment step"). Hereinafter, each step will be described in detail.

<Alloy Making Step> First, the alloy making step (step S101) will be described. Ti according to the invention
The —Cr alloy base material 1 can be produced by, for example, an arc melting method. Here, Ti-
FIG. 4 shows a process for producing the Cr-based alloy base material 1.
As shown in FIG. 4, in the alloy preparation process in step S101, weighing of alloy elements (step S201), arc melting (step S202), crushing (step S203),
The heat treatment (step S204) and the rapid cooling (hereinafter, quenching) (step S205) are included. First, in step S201, an amount corresponding to the composition ratio is weighed for each metal forming the hydrogen storage alloy to be obtained. For example, the Ti-Cr alloy base material 1 is replaced with Ti-Cr-M.
When it is desired to form an o-Ni alloy, Ti, Cr, Mo, and Ni are weighed in an amount corresponding to the composition ratio. Similarly, T
When the i-Cr alloy base material 1 is desired to be a Ti-Cr-Ru alloy, Ti, Cr, and Ru may be weighed in an amount corresponding to the composition ratio.

After weighing the alloy elements in step S201, the process proceeds to step S202. Step S20
In No. 2, each weighed metal was put into an arc melting apparatus (not shown), and melting, stirring, and solidification were performed a predetermined number of times in an argon atmosphere of about 50 kPa (in the experimental example, it depends on the number of constituent elements, Repeat about 3 to 5 times). The reason for repeating melting, stirring and solidifying is to enhance the homogeneity of the alloy. The hydrogen storage alloy of the present invention can also obtain a single bcc phase in the as cast state after solidification.

After the arc melting is performed in step S202, the ingot homogenized by the arc melting is crushed if necessary (step S203). To crush the ingot, a stamp mill is used, and the particle size after crushing is
For example, it is set to 150 μm or less.

Further, the ingot or the crushed particles is subjected to a heat treatment for holding it in the temperature region immediately below the melting point for a predetermined time (step S204). Since the heating temperature during the heat treatment has a temperature range of bcc type immediately below the melting temperature of the alloy having the composition to be obtained, a temperature range of 1250 to 1450 just below the melting temperature of bcc type is present. It may be appropriately selected within (° C). For example, in the case of a composition containing about 60 at% of Cr, it is 140
The temperature may be maintained at about 0 ° C. However, if the temperature is low (about 1000 ° C. or less) even in the temperature range just below the melting temperature for bcc type, it is necessary to lengthen the heat treatment time. When the heating temperature is high, the heat treatment time is short, but the heating cost is increased. Therefore, the heating temperature may be selected in consideration of these points.

If the heating and holding time is too short, sufficient formation of the bcc phase cannot be obtained. Conversely, if the heating and holding time is too long, not only the heat treatment cost rises, but also a different phase precipitates to deteriorate the hydrogen storage characteristics. There may be side effects. Therefore, it may be appropriately selected in consideration of the heating temperature,
When the Ti-Cr alloy base material 1 contains an X element or an X'element excellent in the ability to form a bcc phase, 1 minute to
Heating in the range of 1 hour is sufficient. However, it does not prevent the heating and holding for more than 1 hour. The heating and holding is preferably performed in an inert gas such as Ar gas or in a vacuum. This is to prevent oxidation of the alloy.

After performing the heat treatment in step S204, the process proceeds to step S205. In step S205, the heated and held alloy is rapidly cooled. This quenching treatment is for holding the bcc phase formed by heating and holding to room temperature, and constitutes a bcc phase generation processing together with heating and holding. As a specific means for the rapid cooling treatment, charging into ice water or spraying with an inert gas can be mentioned. However, charging into ice water or spraying with an inert gas is a desirable mode of the present invention, but other cooling methods are not excluded. Here, the volume ratio of the bcc phase in the alloy changes depending on the cooling rate in the quenching process. That is, when the cooling rate is slow, the volume ratio of the bcc phase decreases, so it is desirable to perform rapid cooling at a cooling rate of 100 K / sec or more.

The alloy production process shown in FIG. 3 (step S1
01) includes, for example, steps S201 to S205 described above. After obtaining the Ti—Cr alloy base material 1 in the alloy preparation step (step S101), the process proceeds to the Ni deposition step (step S102) shown in FIG. In the Ni deposition step, Ni is deposited on the surface of the Ti—Cr alloy base material 1. Examples of the Ni deposition method include a plating method and a powder method. The powder method is preferable for discretely depositing Ni on the surface of the Ti—Cr alloy base material 1. The powder method is T
This is a method of adhering Ni powder to the surface of i-Cr alloy base material 1 and Ni powder by mixing them. It is desirable to apply mechanical impact during this mixing. Then, in order to deposit the Ni powder on the surface of the Ti—Cr alloy base material 1 by applying mechanical impact, for example, a stamp mill can be used.

Here, the addition amount of Ni powder is Ti--Cr.
It is 10 wt% or less (not including 0) with respect to the base alloy base material 1. More desirable addition amount of Ni powder is 5 wt% or less,
Furthermore, it is 3 wt% or less. According to the study by the present inventors, the hydrogen absorption / desorption amount of the hydrogen storage alloy reaches a peak value when the addition amount of Ni powder is around 5 wt%. Therefore, it is desirable that the added amount of Ni powder be 5 wt% or less (not including 0). Ni deposition process (step S10
The particle size of the Ni powder prepared in 2) may be 5 μm or less (not including 0), more preferably 3 μm or less, and further preferably about 0.5 to 1.0 μm.

Incidentally, as a method of depositing Ni, it is desirable to mechanically deposit Ni on the Ti—Cr alloy base material 1 using a powder method, particularly a stamp mill. When Ni is mechanically deposited using a stamp mill or the like, the N
The heat treatment for diffusing i (Ni diffusion treatment step) can be performed at a low temperature for a short time, which is effective for suppressing the precipitation of the Laves phase. However, the present invention includes any other method as long as Ni is discretely deposited on the alloy surface.

<Ni Diffusion Treatment Step> After Ni is discretely deposited on the surface of the Ti—Cr alloy base material 1 in the Ni deposition step (step S102), the process proceeds to the Ni diffusion treatment step (step S103). Ni diffusion treatment step (step S
In 103), a treatment for diffusing Ni on the surface of the Ti-Cr alloy base material 1, more specifically, a Ti-Cr alloy base material 1 to which Ni is adhered is applied in a predetermined temperature range for a predetermined time. A heat treatment for holding is performed. By this Ni diffusion treatment, Ti-
All or part of the Ni discretely deposited on the surface of the Cr-based alloy base material 1 becomes the Ti—Ni-based alloy region 3 as shown in FIG. 1B. The heat treatment in this Ni diffusion treatment step is preferably performed in a non-oxidizing atmosphere. The heating temperature of this heat treatment is preferably in the range of 500 to 1000 ° C, more preferably 500 to 700 ° C. If the heating temperature is less than 500 ° C., the diffusion of Ni will not proceed sufficiently even if the heating time is lengthened. On the other hand, the heating temperature is 100
When it exceeds 0 ° C, Ni diffuses further into the inside,
This is because the hydrogen storage amount may decrease.

When the heating temperature is in the range of 500 to 700 ° C., the heating time is 10 minutes to 3 hours. When the heating time exceeds 3 hours, the Laves phase appears in the Ti—Cr alloy base material 1 and the bcc phase decreases. As described above, a decrease in the bcc phase leads to a decrease in the hydrogen storage amount, which is not preferable. On the other hand, if the heating time is less than 10 minutes, the diffusion of Ni will not proceed sufficiently. Therefore, the heating temperature is 5
The heating time in the range of 00 to 700 ° C. is 1
0 minutes to 3 hours. In this case, a more preferable heating time is 10 minutes to 2 hours. However, it goes without saying that the desired heating time varies depending on the heating temperature.

The above steps S101 to S10
By going through the process of 3, the hydrogen storage alloy according to the present invention can be obtained. The hydrogen storage alloy according to the present invention has T
The greatest feature is that Ni-containing regions (Ni deposit phase 2, Ti-Ni alloy region 3) are discretely formed on the surface of the i-Cr alloy base material 1. Due to this feature, the heating time for the Ni diffusion treatment can be shortened as compared with the case where the Ni-containing region is formed on the entire surface of the Ti—Cr alloy base material 1. Therefore, it is possible to effectively suppress the appearance of the Laves phase in the Ti—Cr alloy base material 1. Therefore, the Ni diffusion treatment step (step S10
Even after 3), since the bcc phase of the Ti-Cr alloy base material 1 is maintained as a single phase or a main phase, according to the method for producing a hydrogen storage alloy of the present invention, hydrogen having excellent hydrogen storage characteristics is obtained. It is possible to obtain a storage battery and an electrode for a secondary battery having excellent cycle characteristics.

In the above embodiment, the heat treatment of heating, holding and quenching the ingot after melting, stirring and solidifying to obtain the ingot is shown in FIG. The Ti—Cr alloy base material 1 of the present invention can also be manufactured by a rapid solidification process in which For example, it is a process of obtaining a plate-shaped, ribbon-shaped, or powder-shaped alloy from a molten alloy by a method such as a strip casting method, a single roll method, or an atomizing method.
By using this rapid solidification process, it is possible to efficiently obtain the Ti—Cr based alloy base material 1 of the present invention having the bcc phase as the main phase, without performing the above-mentioned heat treatment of holding and quenching. Even if the alloy obtained by rapid solidification does not have the bcc phase as the main phase (Laves phase (main phase) + bcc phase or Laves phase), the heat treatment of heating and holding-quenching described above may be performed. it can. Of course, depending on the alloy composition, the bcc phase may become the main phase (including a single phase) without heat treatment after rapid solidification of the molten alloy. Even if the bcc single phase is obtained after rapid solidification, the composition is homogenized and the plateau flatness is improved by performing rapid solidification and heat treatment. The obtained hydrogen storage alloy has a pressure-composition isothermal (Pressure Com
By measuring the position Isotherms (PCT) line, its characteristics can be known. The measuring method of the PCT line is specified in JIS H7201, and the most common method is the vacuum origin method (JIS H7003 3003). The hydrogen storage amount of a hydrogen storage alloy is generally obtained by this vacuum origin method.

[0048]

EXAMPLES The hydrogen storage alloy of the present invention will be described below based on specific experimental examples. (Experimental Example 1) Ti ₄₈ Cr ₄₃ Mo was obtained by repeating melting, stirring, and solidification using the arc melting apparatus described above.
An alloy (ingot) having a composition of ₉ (at%) was obtained. The solidification is carried out by naturally cooling the molten alloy on a copper hearth. Next, the obtained alloy in the as cast state was crushed to 150 μm or less. 0.5 to this ground powder
Sample 1 was obtained by applying 5 wt% of Ni powder of ˜1 μm. Further, sample 2 and sample 3 were obtained by applying 5 wt% of Ni powder to the pulverized powder and then performing annealing (a) and (b) under the following conditions. The annealing (a) and (b) is supposed to be a process for diffusing Ni into the Ti—Cr alloy base material. The Ni was deposited using a stamp mill. Specifically, the alloy powder (pulverized powder) and the Ni powder were mixed by hand, and mechanical impact was applied using a stamp mill until the mixed powder became 75 μm or less. The Ni deposition method is the same in the following experimental examples.

Annealing (a): holding at 600 ° C. in vacuum for 1 hour and then furnace cooling Annealing (b): holding at 600 ° C. in vacuum for 10 hours and then furnace cooling

Sample 1, Sample 2 and Sample 3
Was identified by X-ray diffraction. Results are shown in FIG. 5A is a phase identification result of the as cast material, FIG. 5B is a phase identification result of the sample 2 subjected to the annealing (a), and FIG. 5C is a sample subjected to the annealing (b). The results of phase identification of 3 are shown respectively.

As shown in FIG. 5A, as cast
For sample 1 which is a material, pure N together with the bcc phase
Phase i was confirmed. It is considered that this is because the peak of the bcc phase in the alloy base material and the peak of the pure Ni phase adhered to the surface of the alloy base material overlapped each other. From the peaks observed in FIG. 5 (a), when the peak showing the pure Ni phase was subtracted, the index (11
Since only 0), (200) and (211) were observed, it can be seen that the alloy base material in the as cast state forms a bcc phase single phase structure. On the other hand, FIG.
As shown in (1), no pure Ni phase was observed in the sample 2 (annealed (a) material) that was treated to diffuse Ni into the alloy base material. It is considered that this is because Ni deposited on the surface of the alloy base material diffused into the alloy base material and was alloyed with Ti, Cr, etc. in the alloy base material. It can be seen from FIG. 5B that the alloy base material still maintains the bcc-phase single-phase structure after the annealing (a). In addition, for sample 3 (annealed (b) material) having a longer heating time than the annealed (a) material, the Laves phase was identified in addition to the bcc phase.

From the above results, even when Ni was deposited on the surface of the Ti-Cr alloy base material, Ni was added to Ti-
It was found that a bcc single-phase structure can be obtained by setting the treatment time for diffusing into the Cr-based alloy base material within an appropriate range. Also, when the processing time for diffusion becomes as long as 10 hours, the Laves phase appears and bcc
It was found that a monophasic structure could not be obtained. Here, since the sample 2 (annealed (a) material) having a heating temperature of 600 ° C. and a heating time of 1 hour has a bcc single-phase structure, a desirable heating time when the heating temperature is 500 to 700 ° C. Is assumed to be 10 minutes to 3 hours, more preferable heating time is 20 minutes to 2 hours, and further preferable heating time is about 30 minutes to 1 hour.

When the structure of Sample 2 was analyzed, as shown in FIG. 1, a Ni-containing region of 2 μm or less (Ni deposited phase 2, Ti deposited on the surface of the Ti—Cr alloy base material 1) was obtained.
-Ni-based alloy regions 3) were formed discretely. On the surface of the Ti—Cr alloy base material 1, a Ni deposit phase 2 and a Ti—Ni alloy region 3 surrounding the Ni deposit phase 2 were confirmed. It is considered that the Ti-Ni alloy region 3 was formed by the Ni-adhered phase 2 being inverted by the heat treatment.

(Experimental Example 2) Ni was used as the base material of the Ti-Cr alloy.
Hydrogen storage capacity of the hydrogen storage alloy obtained by depositing 5 wt% of
Experimental example 2 shows an experiment conducted to confirm the electric capacity and cycle characteristics of a secondary battery produced by using this hydrogen storage alloy for an electrode. After obtaining an alloy (ingot) having a composition of Ti ₄₈ Cr ₄₃ Mo ₉ (at%) by the same method as in Experimental Example 1, the alloy was pulverized to 150 μm or less. By applying 5 wt% of 0.5 to 1 μm Ni powder to this crushed powder and performing annealing (a),
Sample 4 was obtained. Note that Ni was adhered by using a stamp mill as in Example 1.

When the phase identification was performed on the sample 4 by X-ray diffraction, the same result as the phase identification result of the sample 2 shown in FIG. 5B was confirmed. That is, sample 4
It was also confirmed that the bcc single-phase structure was maintained.

Next, the PCT curve of Sample 4 was measured. The result is shown in FIG. For convenience of comparison, FIG. 6 also shows the measurement results of the PCT curve of the conventional material (MmNi ₅ : where Mm is misch metal).

It can be seen from FIG. 6 that Sample 4 exhibits a hydrogen storage capacity and a hydrogen release capacity which are superior to those of the conventional material. Specifically, the hydrogen storage capacity of the conventional material is about 1.25 wt.
%, The sample 4 showed a hydrogen storage amount of about 2.3 wt%, which is about twice as high as that of the conventional material.

Next, with respect to the secondary battery using the sample 4 and the conventional material as electrodes, the charge and discharge cycle conditions were set to 40 mA / g for 10 hours, and the electric capacity (calculated value from the Sibelts method) was obtained. The results are shown in Fig. 7. As shown in FIG. 7, the electric capacity of the conventional material is about 300 mAh / g in 30 cycles. On the other hand, the sample 4 according to the present invention in which 5 wt% of Ni was deposited using the stamp mill has a good electric capacity of 370 mAh / g or more even after 30 cycles. In addition, Sample 4 was obtained using the electric capacity at the 25th cycle (373.6 mAh / g) and the electric capacity at the first cycle (385.6 mAh / g).
When the capacity deterioration rate was measured, it was only 3.1%. Further, Sample 4 according to the present invention showed a good electric capacity of 350 mAh / g or more even after 60 cycles, and it was confirmed that the characteristics (electric capacity) as a secondary battery did not deteriorate until a high cycle. 6
When the surface of Sample 4 was observed after 0 cycles, no crack was observed. From the above results, Ti-
A hydrogen storage alloy in which Ni-containing regions are discretely formed on the surface of a Cr-based alloy base material exhibits a good hydrogen absorption / desorption amount, and a secondary battery using this hydrogen storage alloy as an electrode has a high electric capacity and a low electric capacity. It was found to show a capacity deterioration rate.

(Experimental Example 3) Experimental Example 3 is an experiment conducted to confirm the hydrogen absorption / desorption characteristics of the hydrogen storage alloy containing Ni in the Ti-Cr alloy base material in advance. An alloy (ingot) was obtained by repeating melting, stirring, and solidification of the alloy having the composition (at%) shown in Table 1 using the above-described arc melting apparatus. The solidification is carried out by naturally cooling the molten alloy on a copper hearth. About the obtained alloy, 0.1
After holding at 1350 ° C. for 3 minutes in an Ar atmosphere of MPa, the sample was obtained by pouring into ice water and quenching. This sample is called a quenching material. After quenching, 600 ° C in vacuum, 6
Annealing (a) in which the furnace is cooled after holding for a time was performed. The alloy (Ti ₅₀ Cr ₄₀ Ni ₃ Mo ₇ (at
%)) Was pulverized to 150 μm or less. Sample 5 was obtained by applying 5 wt% of Ni powder of 0.5 to 1 μm to this pulverized powder and annealing (a). Also,
Similarly, the obtained alloy (Ti ₄₉ Cr ₃₉ Ni ₅ Mo ₇ (at
%)) Is pulverized to 150 μm or less, and the pulverized powder is crushed with 0.1
Sample 6 was obtained by applying 5 wt% of Ni powder of 5 to 1 μm and annealing (a). Note that N
The deposition of i was performed using a stamp mill as in Example 1.

Then, the hydrogen storage amount of the sample 5 and the sample 6 was measured by the vacuum origin method. The results are shown in Table 1. In addition, the electric capacities (calculated values from the Sibelts method) of Sample 5 and Sample 6 were obtained under the same conditions as in Experimental Example 2. The results are also shown in Table 1. For convenience of comparison, Sample 4 (Ti—Cr alloy base metal containing no Ni) produced in Experimental Example 2
Table 1 also shows the hydrogen storage amount and the electric capacity of the.

[0061]

[Table 1]

As shown in Table 1, 3a is contained in the hydrogen storage alloy.
Sample 5 containing t% Ni in advance showed a hydrogen storage amount of 3.5 wt% in the first cycle, 2.2 wt% in the second cycle, and 2.1 wt% in the 30th cycle. Since these values are the same as those of Sample 4 in which the hydrogen storage alloy does not contain Ni in advance, it was found that the hydrogen storage amount would not be deteriorated if the Ni content was about 3 at%. However, the amount of Ni previously contained in the hydrogen storage alloy was 3 at% (Sample 5) to 5 at%.
When it becomes (Sample 6), the electric capacity is 400 mAh / g.
To 420 mAh / g, on the other hand, the hydrogen storage capacity is slightly reduced. Therefore, Ni contained in the hydrogen storage alloy in advance is preferably 5 wt% or less.

Further, when the phase identification was performed on the sample 5 and the sample 6 by X-ray diffraction, the same result as the phase identification result of the sample 2 shown in FIG. 5B was confirmed. In other words, for Sample 5 and Sample 6,
It was confirmed that the bcc single-phase structure was maintained.

From the above results, a predetermined amount of Ni was previously added to Ti.
It was found that the inclusion of the -Cr alloy base material makes it possible to obtain a high hydrogen storage amount and a high electric capacity even after a high cycle. However, comparing the hydrogen storage amounts of sample 5 and sample 6, since the sample 5 has a higher hydrogen storage amount, the amount of Ni contained in the Ti-Cr alloy base material is 5 at% or less, and further, 3 at
It can be said that it is effective to set it to be not more than%. Here, the result of measuring the PCT curve of Sample 6 is shown in FIG. Figure 8
It was found that Sample 6 shows a good hydrogen absorption / desorption amount as shown in FIG. Further, even after repeating hydrogen absorption and desorption 30 times, cracks did not occur in Sample 5 and Sample 6.

(Experimental Example 4) Next, Experimental Example 4 shows an experiment carried out to confirm the appearance phase when a predetermined amount of Ni is deposited on the alloy containing the X element. The composition shown in Table 2 (a
(t%) alloy using the above-mentioned arc melting device
Alloy (ingot) by repeating stirring and solidification
Got The solidification is carried out by naturally cooling the molten alloy on a copper hearth. A sample was obtained by holding the obtained alloy at 1400 ° C. for 10 minutes in an Ar atmosphere of 0.1 MPa, and then pouring it into ice water to rapidly cool it. This sample is called a quenching material. After the quenching treatment, the alloy was pulverized to 150 μm or less, and the pulverized powder was mixed with Ni powder to 3 by using a stamp mill.
wt% was applied, and then annealing (a) was performed. The obtained alloy was subjected to phase identification by X-ray diffraction. The results are also shown in Table 2. Table 2 also shows the proportion of the bcc phase calculated by the above-mentioned formula.

[0066]

[Table 2]

As shown in Table 2, the Ru content is 2 at
% Alloy Ti ₄₀ Cr ₅₈ Ru ₂ is annealed (a)
The ratio of the bcc phase after performing was 90%, and the bcc phase was the main phase. When the Ru content is 3 at% or more, the bcc single-phase structure can be maintained even after annealing (a). Also, the same Ru content is 2 at
% Of the alloy, Ti ₅₀ Cr ₄₈ Ru ₂ has a bcc single-phase structure after annealing (a). Thus, it is possible to obtain an Rcc that can obtain a bcc single phase structure.
The amount of u varies depending on the contents of Ti and Cr.
Specifically, if the Ti content is high, a bcc single-phase structure can be obtained with a smaller Ru content, but if the Ti content is low, the Ru content needs to be increased. As a result of observing the surface of the alloy, a Ti—Ni based alloy region, which is presumed to be due to diffusion between the deposited Ni and the alloy base material, was observed. Further, the Ti-Ni alloy region was formed dispersedly on the surface of the alloy base material.

The PCT curves of the quenched material and the annealed (a) material were measured. The results are shown in FIG. 9 (quenched material) and FIG.
(Annealed (a) material). In all cases, Ru amount (X)
It was confirmed that the hydrogen storage amount was high when the values of 2 at% and 3 at%. The PCT curves of the quenched material not annealed with Ni and the annealed (a) material were measured. The results are shown in FIG. 9 (quenched material) and FIG. 10 (annealed (a) material).
Shown in. The hydrogen storage capacity of the annealed (a) material containing Ru at 2 at% or 3 at% is comparable to that of the quenched material. This suggests that if the Ru amount (X) is contained in a predetermined amount, the structure has the bcc phase as the main phase or the single phase even after annealing (a).

(Experimental Example 5) In Experimental Example 5, which was carried out subsequently, T
After heat treatment of the i-Cr alloy base material, Ni was added to 5 w
This is an experiment conducted for confirming the characteristic change depending on the Mo content in the hydrogen storage alloy obtained by depositing t%.
In the same manner as in Experimental Example 1, Ti ₄₅ Cr _{55-X '} Mo _X' (at
%: X ′ = 0, 4, 4, 6, and 9), an alloy (ingot) having a composition was obtained, and then the alloy was pulverized to 150 μm or less. By applying 5 wt% of 0.5 to 1 μm Ni powder to this pulverized powder and annealing (a), sample 7a (Ti ₄₅ Cr ₅₅ ), sample 8a (T
i ₄₅ Cr ₅₃ Mo ₂ ), sample 9a (Ti ₄₅ Cr ₅₁ M
o ₄ ), sample 10a (Ti ₄₅ Cr ₄₉ Mo ₆ ) and sample 11a (Ti ₄₅ Cr ₄₃ Mo ₉ ) were obtained. Note that Ni was adhered by using a stamp mill as in Example 1.

Next, PCT was performed on each of the obtained samples.
The curve was measured. The result is shown in FIG. As shown in FIG. 11, Ti ₄₅ Cr, which is an alloy with a Mo content of 0 at%.
Compared with ₅₅ , Mo content is 2 at%, 4 at%, 6a
When t% and 9 at% increase, the hydrogen storage amount increases,
It can be seen that when the Mo content is 4 at% or more, high flatness can be obtained in the plateau region. This is because in a hydrogen storage alloy obtained by depositing 5 wt% of Ni after heat treatment of a Ti-Cr alloy base material, a high hydrogen storage amount can be obtained if Mo is contained in a predetermined amount or more. It suggests.

(Experimental Example 6) Subsequently, in a hydrogen storage alloy obtained by depositing 5 wt% of Ni on a Ti-Cr alloy base material, the characteristics obtained by performing heat treatment prior to depositing of Ni were measured. An experiment conducted for confirmation is shown as Experimental Example 6. Ti ₄₅ Cr _{55-X 'was} prepared in the same manner as in Experimental Example 1.
Mo _{X '} (at%: X' = 0, 2, 4, 6, 9)
After obtaining alloys (ingots) having the composition of, each alloy was pulverized to 150 μm or less. The pulverized powder was heat-treated by holding it in a furnace heated to 1400 ° C. for 10 minutes and then rapidly cooled in water.
By applying 5 wt% of Ni powder of 5-1 μm and annealing (a), sample 7b (Ti ₄₅ C
r ₅₅ ), sample 8b (Ti ₄₅ Cr ₅₃ Mo ₂ ), sample 9b (Ti ₄₅ Cr ₅₁ Mo ₄ ), sample 10b (Ti
₄₅ Cr ₄₉ Mo ₆ ), sample 11b (Ti ₄₅ Cr ₄₃ M
o ₉ ) was obtained. Note that Ni was adhered by using a stamp mill as in Example 1.

Next, the obtained samples 7b, 8b, 9
PCT curves were measured for b, 10b, and 11b. The result is shown in FIG. As shown in FIG. 12, sample 7a shown in FIG. 11 which is not heat-treated before Ni deposition,
Compared with the PCT curves of 8a, 9a, 10a, and 11a, N
Samples 7b, 8b, which are heat-treated before deposition of i,
It can be seen that 9b, 10b, and 11b have higher flatness of hydrogen pressure in the plateau region. The reason why the flatness of hydrogen pressure in the plateau region becomes low (the slope of the PCT curve becomes large) is considered to be that regions with different equilibrium pressures (different phases) coexist and nonuniformity of the alloy structure increases. In particular, the alloy obtained by the arc melting method is supported by the observation and consideration that the uniformity is inherently low. From the above results, it is suggested that the Ti—Cr alloy base material can be homogenized by performing a predetermined heat treatment before Ni deposition.

[0073]

According to the present invention, it is possible to obtain a hydrogen storage alloy which has a high hydrogen storage capacity and is excellent in cycle characteristics and suitable for a secondary battery.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the structure of a hydrogen storage alloy of the present invention.

FIG. 2 Ti₃₇Cr₅₈V_FiveAlloy, Ti₃₉Cr₅₉Mo₂Combined
Gold and Ti₄₁Cr ₅₇Ru₂Rabe from the bcc phase of the alloy
It is a graph showing the results of measuring the phase transformation temperature to the soot phase.
It

FIG. 3 is a flowchart showing a method for producing a hydrogen storage alloy of the present invention.

4 is a flowchart for explaining the contents of step S101 in FIG.

FIG. 5: Ti ₄₈ Cr ₄₃ Mo ₉ (a measured in Experimental Example 1
FIG. 3 is an X-ray diffraction diagram of a (t%) alloy.

FIG. 6 is a graph showing a PCT curve measured in Experimental Example 2.

FIG. 7 is a graph showing the electric capacity of a secondary battery using a hydrogen storage alloy with 5 wt% Ni deposited as an electrode.

FIG. 8 is a graph showing a PCT curve measured in Experimental Example 3.

9 is a graph showing a PCT curve measured in Experimental Example 4. FIG.

FIG. 10 is a graph showing a PCT curve measured in Experimental Example 4.

FIG. 11 is a graph showing a PCT curve measured in Experimental Example 5.

FIG. 12 is a graph showing a PCT curve measured in Experimental Example 6.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ti-Cr type alloy base material, 2 ... Ni adhered phase (Ni containing area), 3 ... Ti-Ni type alloy area (Ni containing area)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 4/24 H01M 4/24 J 4/38 4/38 A // C01B 3/00 C01B 3/00 B (72) Shinichi Yamashita Shinichi Yamashita 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Inventor Long-term 1-13-1, Nihonbashi, Nihonbashi, Chuo-ku, Tokyo F-Term ( Reference) 4G140 AA36 AA43 AA44 4K018 BA03 BA20 BC01 BC08 BC16 BC19 BC22 BD07 KA38 5H050 AA07 AA08 BA14 CA03 CB16 FA12 FA19 GA02 GA22 HA02 HA05 HA12 HA14

Claims (15)

[Claims] 1. A phase (bcc) having a body-centered cubic crystal structure
Phase) as the main phase, and a Ti-Cr alloy base material and N formed discretely on the surface of the Ti-Cr alloy base material.
A hydrogen storage alloy, comprising: an i-containing region. 2. The Ni-containing regions discretely formed on the surface of the Ti—Cr alloy base material are wholly or partly T-type.
The hydrogen storage alloy according to claim 1, wherein the hydrogen storage alloy is in an i-Ni alloy region. 3. The Ni-containing region discretely formed on the surface of the Ti—Cr alloy base material has a diameter of 5 μm or less (0
The hydrogen storage alloy according to claim 1, wherein 4. A phase (bcc) having a body-centered cubic crystal structure.
Phase) as a main phase, which is a hydrogen storage alloy composed of a Ti—Cr based alloy base material, wherein a Ti—Cr based alloy phase and a Ti— A hydrogen storage alloy characterized by the presence of a Ni-based alloy phase. 5. The Ti—Cr alloy base material has a composition of Ti _(100-abcd) Cr _{a Xb} X ′ _c Ni _d, where 20 ≦ a (at%) ≦ 80 and 0 ≦ b (at%). ) ≤ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W And at least one element of Al.
Alternatively, the hydrogen storage alloy according to item 4. 6. The hydrogen storage alloy according to claim 1, wherein the Ti—Cr alloy base material has a single-phase structure of a phase (bcc phase) having a body-centered cubic crystal structure. . 7. A step (a) of obtaining a Ti—Cr alloy base material.
A step (b) of discretely depositing Ni on the surface of the Ti—Cr based alloy base material obtained in the step (a), and a step of depositing Ni on the surface of the Ti—Cr based alloy base material. And a step (c) of diffusing Ni as described above, the method for producing a hydrogen storage alloy. 8. The production of a hydrogen storage alloy according to claim 7, wherein in the step (a), a Ti—Cr based alloy base material containing 5 at% or less (not including 0) of Ni is obtained. Method. 9. The Ti—C in the step (b).
The method for producing a hydrogen storage alloy according to claim 7, wherein the Ni is mechanically deposited on the surface of the r-based alloy base material. 10. The phase (bcc phase) having a body-centered cubic crystal structure, both of the Ti—Cr alloy base material obtained in the step (a) and the hydrogen storage alloy obtained after the step (c). The method for producing a hydrogen storage alloy according to claim 7, characterized in that 11. The hydrogen storage alloy according to claim 7, wherein the diffusion treatment in the step (c) is a heat treatment at a temperature range of 500 to 700 ° C. for 10 minutes to 3 hours. Manufacturing method. 12. Prior to the step (b), the Ti—Cr alloy base material obtained in the step (a),
The method further comprises a step (d) of subjecting the Ti-Cr alloy base material to a heat treatment for holding for a predetermined time in a temperature region where a phase (bcc phase) having a body centered cubic crystal structure is formed. Item 8. A method for producing a hydrogen storage alloy according to Item 7. 13. The heat treatment in the step (d) is performed by adding 1250 to 1450 to the Ti—Cr alloy base material.
The method for producing a hydrogen storage alloy according to claim 12, characterized in that the hydrogen storage alloy is held in the temperature range of 0 ° C for 1 minute to 1 hour. 14. The step (b) after the step (d)
The method for producing a hydrogen storage alloy according to claim 12, further comprising a step (e) forcibly cooling the heat-treated Ti-Cr alloy base material prior to the step (e). 15. The composition is _{Ti (100-abcd) Cr a} X b X 'c Ni d where 20 ≦ a (at%) ≦ 80,0 ≦ b (at%) ≦ 1
0, 0 ≦ c (at%) ≦ 30, 0 ≦ d (at%) ≦ 5, X is at least one element of Ru, Rh, Os and Ir, and X ′ is V, Mo, W And a Ti-Cr-based alloy base material having at least one element of Al and a main phase having a body-centered cubic crystal structure (bcc phase), and discretely on the surface of the Ti-Cr-based alloy base material Formed on N
An i-containing region, and a secondary battery electrode.