JP2001279354A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the pulverization of a hydrogen storage alloy without causing the reduction of the amount of hydrogen to be occluded, and also to reduce the alloy cost by the reduction of the content of Co. SOLUTION: This hydrogen storage alloy has a two phase crystal structure of a base phase with a CaCu5 type crystal structure and a phase with a solidified structure of a three-dimensional network structure being present so as to be entangled in the base phase, these two phases have almost equal lattice constants, and also, the above phase with a three-dimensional network structure is the one similar to a CaCu5 type simuntaneously occulding or discharging hydrogen when the base phase occuludes or discharges hydrogen.

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 suitably used as a material for a secondary battery or a heat pump, and more particularly, to a fine powder of a hydrogen storage alloy which accompanies charge and discharge without reducing the amount of hydrogen storage. We propose a hydrogen storage alloy that exhibits excellent properties for preventing hydrogenation.

[0002]

Presently, many of the secondary battery for the hydrogen-absorbing alloy which is commercially available, those called Type ₅ AB, for example, M
mNiCoMnAl having a quinary composition having a CaCu _5- type crystal structure is used. This alloy is characterized by containing about 10 wt% of Co for preventing pulverization when storing and releasing hydrogen and for improving battery characteristics, particularly cycle characteristics. Also, for hydrogen storage alloys for heat pumps, in order to prevent a decrease in thermal conductivity,
Such Co is added.

[0003] Now, to prevent the pulverization of the hydrogen storage alloy as (耐微powder of characteristic improving) method, by reducing the Co content, the ratio of B site AB ₅ type alloys (non-stoichiometric) It is well known that increasing is effective. However, when the ratio of the B site in the AB _5- type alloy is increased, the pulverization resistance is improved, but there is a problem that the hydrogen storage amount is reduced.

In recent years, the use of large hydrogen secondary batteries has increased for applications such as electric vehicles (EV), hybrid EVs, and electric tools. As a hydrogen storage alloy mounted as a negative electrode of such a large battery, improvement in battery performance is required at the same time as improvement in the above-mentioned pulverization characteristics, and these characteristics can be obtained even under severe use conditions. In addition to the above, there is a demand for realizing low cost of the alloy itself. In order to meet such demands, it is considered effective to reduce Co, which is the most effective element for pulverization resistance among elements constituting the hydrogen storage alloy, but is expensive.

On the other hand, conventionally, there has been a proposal to maintain and improve the hydrogen storage alloy characteristics and the battery characteristics by improving the pulverization resistance. For example, Japanese Unexamined Patent Publication
The invention described in Japanese Patent No. 325790 relates to a sealed alkaline storage battery, and by adjusting the composition formula: Mm La and Nd in MmNi _{x Ay} to a specific ratio, pulverization by switching back and forth of hydrogen storage and release. This is a technology that tries to prevent Invention described in JP-A-4-202641, the composition formula: For LnNi _x Mn _y A _z alloy, after the grinding is segregated at a high concentration of Mn or La on the surface, trying to control the progress of the crack Technology. JP-A-4-16
The invention described in Japanese Patent No. 8239 is a hydrogen storage alloy for a nickel-metal hydride battery in which a network-like metal or alloy phase having higher toughness than the matrix is present in the hydrogen storage alloy. This is a technology that tries to prevent the progress of the game. It has also been proposed to improve the charge / discharge characteristics without deteriorating the cycle characteristics without adding any cobalt (Japanese Patent Application Laid-Open No.
No. 323468).

[0006] These conventional techniques improve various characteristics by paying attention to examination of alloy composition, surface treatment, heat treatment, and the like. Although there is a certain effect, the pulverization resistance of the hydrogen storage alloy is improved. There were still many issues to further improve.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to establish a technique capable of overcoming the above-mentioned problems of the prior art, and particularly to prevent the pulverization without reducing the hydrogen storage capacity. And at the same time, to reduce the Co content to reduce the alloy cost.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention proposes means for solving the problems with the following points as the gist. That is, the present invention is a hydrogen storage alloy in which a plurality of CaCu _5- type phases having substantially the same lattice constant form a three-dimensional network structure. Further, the present invention provides a hydrogen storage alloy having a two-phase crystal structure of a matrix having a CaCu _5- type crystal structure and a phase having a three-dimensional network solidification structure entangled in the matrix. The two phases have approximately equal lattice constants, and the three-dimensional network phase absorbs or releases hydrogen at the same time that the parent phase absorbs or releases hydrogen.
A hydrogen storage alloy characterized by having a phase similar to CaCu type ₅ . In the hydrogen storage alloy, the parent phase is an MmNi _5- based alloy phase containing Ca or Y, and the three-dimensional network structure phase is an MmNi _5- based alloy phase having a higher Ca or Y concentration than the parent phase. It is preferred that

In a preferred embodiment of the present invention, the following composition
CaCu with the formula₅Type hydrogen storage alloy, Ca or Y
Containing MmNi₅Matrix consisting of a base alloy,
MmNi having a composition with a high Ca or Y concentration in comparison
₅System alloy and entangled with the matrix alloy
Consisting of a three-dimensional network phase present in a combined state
A hydrogen storage alloy characterized by the following. Composition formula R_1-xB_xNi_aCo_bM_c  Here, 0.01 <x ≦ 0.30, 4.0 ≦ a ≦ 4.4, 0 <b ≦ 0.
6, 0 ≦ c ≦ 1.0, 5.00 ≦ a + b + c ≦ 5.30, R is a rare earth element
B is Ca or Y, M is Mn, Al, Fe, Cu, S
at least one selected from i, Cr and Sn
Is also a kind of element, 0.1-0.4 for Mn,
0.1 to 0.4, 0 to 0.3 for Cu, Fe, Cr and Sn

[0010] The rare earth element mixture preferably has a La content of 60 wt% or more, and this hydrogen storage alloy is preferable for nickel-metal hydride secondary batteries.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy according to the present invention has a crystal lattice constant (a-axis 5.00 to 5.10 °) substantially the same as that of the parent alloy in order to improve the resistance to pulverization. , C axis
Precipitating a three-dimensional network structure phase (4.00 to 4.10Å) that absorbs and releases hydrogen at the same pressure and at the same temperature (a network structure phase having a solidified structure that is three-dimensionally entangled with the matrix alloy). Thereby, the pulverization resistance is improved. In the present invention, such a three-dimensional network-structure phase is not simply a layer formed as a second phase on the surface of the matrix, but is diffused mutually with the matrix alloy to form a solidified structure in a three-dimensionally continuous state. Is a phase consisting of In addition, this phase is the crystal lattice constant of the above-described parent phase (a-axis 5.00 to 5.10 °, c-axis 4.
(A-axis 5.00-5.10)
Ｃ, c-axis 4.00 ~ 4.10Å), and at the same time, has a hydrogen storage capacity, and the presence of this phase can improve the pulverization resistance of the hydrogen storage alloy without reducing the storage capacity. is there.

[0012] In the hydrogen storage alloy according to the present invention, the mother phase, which occupies a part of the constitution, is Mm containing Ca or Y.
Preferably, it is a MmNi _5- based alloy phase, such as a NiCoMnAl alloy, and the three-dimensional network phase is compared to the parent phase.
It is preferably a Ca or Y rich MmNi _5- based alloy phase such as an MmNiCoMnAl alloy having a high Ca or Y concentration. The so-called three-dimensional network structure phase is the mother phase Ca
Alternatively, depending on the difference from the concentration of Y, it can be said that the phase has a reticulated solidified structure. In addition, this three-dimensional network structure phase absorbs and releases hydrogen as long as the parent phase absorbs and releases hydrogen.
It has the property of releasing, and exhibits the property of being able to simultaneously improve the resistance to pulverization without sacrificing each other. In the present invention, required Ca, Y
Is about 2 to 6 times, and as described above, the pulverization resistance can be improved without lowering the hydrogen storage properties as described above.

As described above, the three-dimensional network structure phase has both properties.
The reasons for the combination of functions are as follows.
In other words, according to the equilibrium diagram of the rare earth element and Ca, the rare earth element
In the case of alloys containing element and Co, especially in the case of
And rare earth elements have the property that Ca does not form a solid solution at all,
These are elements having strong repulsion. On the other hand,
Both elements have a very strong bond with nickel,
Each RNi₅, CaNi ₅CaCu₅Type crystal structure (6
(Interstitial) to form a hydrogen storage alloy.
You.

If a small amount of Ca is added to the MmNiCoMnAl-based hydrogen storage alloy, the rare-earth element and Ca have a large repulsive force. Is solidified so as to surround the periphery thereof, so that the solidified structure has a three-dimensional network structure.

Further, the phase having a low Ca content and the phase having a high Ca content have a CaCu _5- type structure having substantially the same lattice constant, and both functions as a hydrogen storage alloy, but have different characteristics. That is, by containing Ca in both phases, the lattice expansion at the time of hydrogen storage becomes small, and it becomes difficult to pulverize both.However, the phase with a smaller Ca content is a general phase that does not contain Ca. It has characteristics of high hydrogen storage relatively close to MmNiCoMnAl-based hydrogen storage alloys, and its pulverization characteristics are not exceptional. However, the phase having the higher Ca content has characteristics that are hardly pulverized. Therefore, the alloy according to the present invention has a structure in which a Ca-rich phase having characteristics that are difficult to pulverize three-dimensionally surrounds a Ca-rich phase having a small amount of hydrogen storage. Suppresses the pulverization and falling off of the high hydrogen storage phase in the center. As a result, a hydrogen storage alloy having a high hydrogen storage amount and excellent pulverization resistance as a whole can be obtained.

In this regard, the network structure phase disclosed in Japanese Patent Application Laid-Open No. 4-168239, which is reported to be expressed when Zr is blended, has a different crystal lattice constant and an equilibrium pressure from the parent phase. The alloy of the present invention differs from the alloy of the present invention in that the phase does not occlude or release hydrogen when storing or releasing hydrogen.

[0017] Incidentally, in the prior art, Ca in AB ₅ alloys
The technical idea of blending is disclosed in JP-A-60-24165.
It is known as seen in the invention of Japanese Patent Publication No. But,
The described in Japanese composition formula _{Ca 1-x Mm x Ni y} -z
The purpose of the _Mz alloy is to prevent the internal pressure of the battery due to overcharge, and to improve the pulverization resistance as in the alloy of the present invention.
Further, it is not a technique for reducing Co without decreasing the hydrogen storage amount. This means that in the examples,
The technique of substituting with Ca, and the amount of Co is 1.5, and only alloy examples in which a large amount of Co is blended are disclosed.
With such an alloy design, the above-described object of the present invention cannot be achieved.

In the hydrogen storage alloy according to the present invention, the suitable substitution amount of Ca of the structural phase precipitated in a three-dimensional network in the parent phase is more than 0.01 and does not exceed 0.3 with respect to the mixture R of the rare earth element. It is preferably in the range, particularly preferably 0.05 to 0.2. The reason is that the Ca or Y substitution amount is 0.
If it exceeds 3, the hydrogen storage capacity will decrease,
Below this, the network phase does not appear.

The hydrogen storage alloy of the present invention has a reduced Co content.
It is preferable that the hydrogen storage alloy has the following composition formula:
No. Composition formula R_1-xB_xNi_a4o_bM_c  Here, 0.01 <x ≦ 0.30, 4.0 ≦ a ≦ 4.4, 0 <b ≦ 0.
6, 0 ≦ c ≦ 1.0, 5.00 ≦ a + b + c ≦ 5.30, R is a rare earth element
B is Ca or Y, M is Mn, Al, Fe, Cu, S
at least one selected from i, Cr and Sn
Is also a kind of element, 0.1-0.4 for Mn,
0.1 to 0.4, 0 to 0.3 for Cu, Fe, Cr and Sn

In the above composition formula, since the improvement of the pulverization resistance is improved by exposing the three-dimensional network structure phase, the amount of Co substitution is not particularly limited. The lower limit is preferably set to a value larger than 0 in consideration of the case and the improvement in characteristics when used in a heat pump. Although the upper limit is not limited to 0.6, it is preferably 0.6 or less, more preferably 0.4 or less in consideration of economy.

In the case of Al, if the M element is less than 0.1, it is difficult to adjust the hydrogen equilibrium pressure, and if it exceeds 0.4, the amount of hydrogen occlusion is reduced. In the case of Mn, if it is less than 0.1, it becomes difficult to adjust the hydrogen equilibrium pressure and plateau property cannot be obtained. If it exceeds 0.4, corrosion occurs in the alkaline electrolyte, so 0.1 to 0.4 is preferable. Fe, C
In the case of r, Si, Cu, and Sn, it is not necessary to add, but when adding, the upper limit is about 0.3.

Further, in the alloy of the present invention, the non-stoichiometric ratio of the B site of the AB _5- type alloy having the CaCu _5- type crystal structure
If a + b + c + d is less than 5.00, the powdering resistance cannot be obtained, and 5.
Above 30 causes a decrease in hydrogen storage capacity, so AB
The ratio is preferably from 5.00 to 5.30, and more preferably from 5.15 to 5.20. In addition, Ni is the amount of other B-site-side constituent elements,
It is a value that is necessarily determined from the non-stoichiometric composition.

The above hydrogen storage alloy according to the present invention is preferably used for an alloy for a nickel-metal hydride secondary battery.
Further, the alloy of the present invention can be obtained by casting an iron mold having low thermal conductivity into a water-cooled mold to prevent erosion.

[0024]

EXAMPLES The composition of the hydrogen storage alloy used in this example was as follows:
R_1-xCa_xNi_4.24Co_{0.3 0}Mn_0.36Al
_0.30AB consisting of_5.20For the type, x =
Of 0.01, 0.025, 0.05, 0.10 and R_1-xCa_xNi
_4.15Co_0.30Mn_0.30Al _0.30AB consisting of
_5.05For the type, x = 0.05, 0.10, 0.20, 0.
It is 30. Set of hydrogen storage alloy used in comparative example
Naru is R_0.60Ca_0.40Ni_4.15Co_{0 . 30}Mn
_0.30Al_0.30AB consisting of_5.05Type, R
Ni_4.24Co_{0 . 30}Mn_0.36Al_0.30A consisting of
B_5.20Type, and RNi_{4.1 5}Co_0.30Mn
_0.30Al_0.30AB consisting of_5.05Use type
Was. Both of the above R have a La content of 0.8.
Was. The alloy was melted using a high-frequency melting furnace, and the temperature was 1000 ° C.
Heat treatment was performed in an Ar gas atmosphere for -7 hours.

As a characteristic evaluation, the structure was confirmed and identified with an analytical electron microscope. The hydrogen storage amount was determined by using a PCT measuring apparatus and the value of H / M at 80 ° C. and 10 atm was used.耐微powder of properties, was used as an index value of the alloy particle size distribution D ₅₀ after being once exhausted after absorbing hydrogen at a constant hydrogen pressurization.

Table 1 shows the results of the characteristic evaluation test. Compared to an alloy of the comparative example, the alloy of the present invention embodiment, the particle size D ₅₀ values after hydrogenation with the increase of Ca substitution amount was increased. In particular,
An alloy in which the metal structure with a Ca substitution amount of 0.025 or more has been converted to a dual phase.
_{The 50} value markedly increased, and the effect of suppressing pulverization increased. However, in the alloy I of the comparative example in which the Ca substitution amount was increased to 0.4, although the effect of suppressing pulverization was large, the hydrogen storage amount was significantly reduced, which was an undesirable result. Therefore, it was found that the upper limit of the Ca substitution amount is preferably about 0.3. On the other hand, in the alloys J and K of the comparative examples, the non-stoichiometric ratio A
In which it increased the D ₅₀ value by increasing the x values of B _x, but decreases the hydrogen storage capacity is large at the expense of the effect of micronized inhibition was found to be undesirable.

Here, as the representative examples of the metal structures that affected the pulverization suppressing effect, the metal structure photographs of the G alloy of the example and the K alloy of the comparative example are shown in FIGS. 1 and 2, respectively. From the figure, it can be seen that in the G alloy of Example, a light hue and a dark hue are observed, and the dark hue exists in a mesh around the light hue. Further, in the metallographic photograph by the backscattered electron image, the difference in the composition of the observed alloy appears as a light-dark contrast. According to the analysis result by EDS (optical electron micrograph), in the case of the G alloy, the light hue has a Ca content of about 1 at%, and the dark hue has a Ca content of about 5 at%.
It turned out to have a CaCu type ₅ crystal structure, and it is considered that this deep hue particularly suppresses pulverization. In contrast,
The K alloy of the comparative example had a uniform phase with uniform brightness except that cracks and the like were observed.

[0028]

[Table 1]

[0029]

According to the hydrogen storage alloy of the present invention having the above-described structure, pulverization can be suppressed without reducing the hydrogen storage amount. Further, even if the composition of the Co element is reduced, the pulverization resistance can be improved, so that the alloy cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of an alloy of the present invention.

FIG. 2 is an electron micrograph of a comparative alloy.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiaki Haneda 232 Okimachi, Oguni-machi, Oguni-machi, Nishiokitama-gun 5-7-6 Tokodai, Tsukuba, Japan Nihon Heavy Chemical Industry Co., Ltd., Tsukuba Research Laboratory (72) Inventor Tomohiro Yoshikawa 5-9-6, Tokodai, Tsukuba, Ibaraki Pref. 5H050 AA07 AA19 BA14 CB17 DA03 FA17 FA19 HA02

Claims (4)

[Claims] 1. A hydrogen storage alloy in which a plurality of CaCu _5- type phases having substantially the same lattice constant form a three-dimensional network structure. 2. A hydrogen storage alloy having a two-phase crystal structure of a matrix having a CaCu _5- type crystal structure and a phase having a three-dimensional network solidification structure entangled in the matrix. The two phases have approximately the same lattice constant, and the three-dimensional network structure phase is a CaCu _5- type-like phase that simultaneously absorbs or releases hydrogen when the mother phase absorbs or releases hydrogen. A hydrogen storage alloy characterized by the following. 3. The method according to claim 1, wherein the mother phase is MmNi ₅ containing Ca or Y.
Alloy phase, the three-dimensional network structure phase is
The hydrogen storage alloy according to claim 2, wherein the alloy is a MmNi _5- based alloy phase having a high Ca or Y concentration. 4. A CuCu having the following composition formula:₅Type hydrogen storage
MmNi containing gold or Ca or Y₅Consisting of base alloy
Compared to the parent phase and the parent alloy, the concentration of Ca or Y
MmNi with high composition₅Base alloy
Phase alloy is a three-dimensional network that exists in an intertwined state with each other
A hydrogen storage alloy, comprising: a structural phase. Composition formula R_1-xB_xNi_a1o_bM_c  Here, 0.01 <x ≦ 0.30, 4.0 ≦ a ≦ 4.4, 0 <b ≦ 0.
6, 0 ≦ c ≦ 1.0, 5.00 ≦ a + b + c ≦ 5.30, R is a rare earth element
B is Ca or Y, M is Mn, Al, Fe, Cu, S
at least one selected from i, Cr and Sn
Is also a kind of element, 0.1-0.4 for Mn,
0.1 to 0.4, 0 to 0.3 for Cu, Fe, Cr and Sn