JP2655074B2 - Hydrogen storage alloy and its electrode - Google Patents

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 reversibly storing and releasing hydrogen and an electrode using the hydrogen storage alloy.

[0002]

2. Description of the Related Art Hydrogen has attracted attention as clean energy. In particular, it has been proposed to use a hydrogen storage alloy capable of reversibly storing and releasing hydrogen for a negative electrode to form a chargeable and dischargeable secondary battery.

As hydrogen storage alloys capable of reversibly storing and releasing hydrogen, those having a CaCu ₅ structure such as LaNi ₅ and those having a Laves structure have been proposed. C
As a hydrogen storage alloy having an aCu ₅ structure, LaNi ₅
By improving the alloy, "it is possible to occlude a large amount of hydrogen in the form of hydride in a short time, and to easily release hydrogen by heating the hydride slightly or reducing the pressure. , release as complete having a characteristic such that reversibly performed ", the formula MmNi _5-x a hydrogen storage alloy for mischmetal represented by _xy B _y - nickel alloy has been proposed (Japanese Patent JP-B-58-39217). That is, La is replaced with Mm (Misch metal), and Ni is replaced with Ni.
Are partly A component (Al, Cu, Mn) and B component (A
l, Co, Cu, Mn, Si) to improve the hydrogen storage alloy properties.

[0004] These hydrogen-absorbing alloys reversibly absorb and release hydrogen also by an electrochemical reaction, and have been proposed to be used for electrodes. In particular, secondary batteries using nickel oxide or the like for the positive electrode have been proposed. It is widely used as a negative electrode of batteries. Usually, the rare earth has a CaCu ₅ structure used for these negative pole - nickel based hydrogen storage alloy, since the range of the stoichiometric composition is narrow, for example, MmNi _x Co _y M _z
The hydrogen storage alloy having a composition, 4 <x + y + z <5.5 range, i.e., used in the range of _{(Ni x Co y M z)} /Mm=4~5.5 ( JP 60-250558 Publication).

The production of a hydrogen storage alloy electrode used in these sealed secondary batteries is conventionally performed by a method of filling a hydrogen storage alloy powder into a foamed nickel base. For example, a hydrogen storage alloy powder pulverized to a particle size of 38 μm or less is mixed with an aqueous solution of polyvinyl alcohol to form a paste, filled in a predetermined amount of foamed nickel having a porosity of 93 to 94%, dried, and then pressed and cut. A sealed secondary battery is manufactured by using a negative electrode having a predetermined size according to the method described in JP-A-63-2362.
74, Examples of JP-A-1-132066 and the like).

However, Ni porous plates are expensive,
Since the cost of the whole battery is increased, an inexpensive electrode manufacturing method has been demanded. Further, the content of the alloy in the electrode is limited to 40 to 50%, and a further increase in capacity of the hydrogen storage alloy has been required. Further, since the diameter of the Ni porous body is large, the contact between the alloy powder and the porous body is also limited, which limits the high rate discharge characteristics. In addition, there was a problem that the alloy powder was dropped during charging and discharging, causing a reduction in cycle life.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to increase the content of a hydrogen storage alloy in an electrode without using a nickel porous body, thereby reducing the cost of the electrode. Along with a significant reduction and high capacity, the high-rate discharge characteristics are improved by integrating with the current collector. It was an object to provide a hydrogen storage alloy having excellent cycle life.

[0008]

SUMMARY OF THE INVENTION The present invention provides the following rare earth hydrogen storage alloys and electrodes.

1. A rare-earth hydrogen storage alloy that reversibly stores and releases hydrogen, wherein X (Ni _1-x M _x ) _d [X is Ti, Zr, T
a, Nb and Mo represent at least one element selected from the group consisting of Al, Co, Cu, Zn, F
e, at least one element selected from the group consisting of Mn, Cr and Si, where 1 ≦ d ≦ 3, 0 <x ≦ 0.
A rare earth hydrogen storage alloy having a skeletal structure mainly composed of an alloy having the composition of 3).

[0010] 2. R (Ni _(1-a) M _a ) _b (X (Ni _1−x M _x ) _d ) _c [wherein, R represents at least one element selected from lanthanoids, and M represents Al, Co , Cu, Zn, F
e, at least one element selected from the group consisting of Mn, Cr and Si, and X represents Ti, V, Ta, N
b, at least one element selected from the group consisting of Mo and Zr, where 0 <a ≦ 0.5, 4.8 <b ≦ 5.
5, 0 <c ≦ 2, 1 ≦ d ≦ 3, and 0 <x ≦ 0.3. [1] having a composition represented by the following formula: The rare earth hydrogen storage alloy according to 1.

3. 1. A hydrogen storage alloy electrode obtained by integrating the rare earth hydrogen storage alloy according to 1 above with a current collector.

Formation of three-dimensional skeletal structure The hydrogen storage alloy of the present invention contains X (Ni _1-x
M _x ) _d [X represents at least one element selected from the group consisting of Ti, Zr, Ta, Nb and Mo;
Represents Al, Co, Cu, Zn, Fe, Mn, Cr and S
i represents at least one element selected from the group consisting of i, and has a three-dimensional skeleton structure mainly composed of an alloy having a composition of 1 ≦ d ≦ 3 and 0 <x ≦ 0.3]. Things.

Have reported that when 0.1 atom of Mo is added to the rare earth-nickel hydrogen storage alloy AB _5.5 , MoCo ₃ forms a second phase and improves the catalytic activity (PHL Notten). and P. Hokkeling, JE
electrochem. Soc., 138, 1877 (1991)). The Hitoshi Nogami the case of adding B 0.09 atomic relative rare earth-based hydrogen storage alloy AB _5, MMCO ₄ B forms a second phase, the second phase dispersed in the hydrogen absorbing alloy is micronized And promotes the activation characteristics (Kouzo Nogami et al. Electrochemistry, 6
1, 1088 (1993)).

According to the present invention, a continuous flexible skeleton structure is formed in a rare earth-nickel-based hydrogen storage alloy by an additive element group represented by X. As a result, pulverization of the alloy is suppressed. It has been found that the cycle life is improved, and the catalytic activity and high-rate discharge characteristics are improved.

Hydrogen storage alloy An alloy composition representing a typical hydrogen storage alloy of the present invention: R (Ni _(1-a) M _a ) _b (X (Ni _1-x M _x ) _d ) _c , R represents at least one element selected from lanthanoids. ], R (Ni _(1-a) M _a ) _b corresponds to the composition of the hydrogen storage alloy particle phase, and M is an element forming a substitutional solid solution with Ni, and specifically, Al, Co, C
u, Zn, Fe, Mn, at least one element selected from the group consisting of Cr and Si, preferably Co, Mn
Or Al.

When M is composed of two or more elements, the mixing ratio of these elements is not limited, and it is sufficient that the total of the two or more elements is within the range represented by a. The hydrogen storage characteristics are adjusted by the amount of M added. a is 0 ≦ a ≦ 0.
The number is 5, preferably 0.1 ≦ a ≦ 0.3. When a is in the range of 0.1 ≦ a ≦ 0.3, the property of storing hydrogen is preferably maintained. b is 4.8 ≦
b ≦ 5.5.

The X component of the alloy represented by the above composition is T
It is at least one element selected from the group consisting of i, V, Ta, Nb, Mo, and Zr, and includes those in which two or more of the elements of M are partially dissolved. When X is composed of two or more elements, the mixing ratio of these elements is not limited, and the total of the two or more elements is d (Ni _1-x M _x ).
May be within the range represented by. d is in the range of 1 ≦ d ≦ 3. C is in the range of 0 <c ≦ 2, preferably 0.1 ≦ c ≦ 1. When c is larger than 2, the ability to occlude hydrogen is significantly reduced, which is not preferable.

[0018] X is an element a and earth to form the Ni and the intermetallic compound - the melting together nickel compounds AB _5, to form a crystallized out skeletal structure at the grain boundaries as an alloy or intermetallic compound of X and nickel . In the above alloy _{composition, X (Ni 1-X M} X) d is equivalent to the composition of the skeletal structure. Since rare earth elements are susceptible to oxidation and corrosion, the skeletal structure is easily broken, and the conductive network is also easily broken, resulting in a decrease in discharge characteristics and cycle life. Therefore, the ratio d of the (NiM) component in the X-Ni alloy needs to be 1 or more.

In producing the hydrogen storage alloy of the present invention, a mixture having a predetermined element ratio may be directly melted.
Before preparing the alloy, heat-melt the Ni and X components to form a nickel alloy or compound.
The X-Ni-based alloy is mixed with the R component and the M component, heated and melted, quenched, and heat-treated, whereby the rare-earth (R) -nickel-
The homogeneity of an alloy having a three-dimensional skeletal structure (hereinafter, sometimes simply referred to as a skeletal structure) holding a matrix (crystal grain phase) of an M-based alloy can be improved.

Since the skeleton diameter of the skeleton structure is determined by the crystal grain size, it can be controlled by the cooling rate of the alloy. For example, cooling rate = 10 ² k / sec and average diameter 50
μm or less, cooling rate = 10 ³ k / sec, average diameter 20 μm
Hereinafter, when the cooling rate is 10 ⁴ k / sec, the average diameter is 10 μm or less, and when the cooling rate is 10 ⁵ k / sec, the average diameter is 3 μm or less. The smaller the diameter is, the lower the hydrogen storage amount, that is, the electric capacity, but the cycle life and the high rate discharge characteristics are improved. The preferred cooling rate is 10 ² to 10 ³ k / sec, and the average diameter of the preferred skeletal structure is 20 to 50 μm.

The diameter (thickness) of the skeleton varies depending on the alloy composition and content, but can also be adjusted by the heat treatment temperature and time, and is preferably controlled in the range of 600 to 1400 ° C. Tend to be thicker (thicker) as is longer.

When a continuous three-dimensional skeleton of an X-Ni alloy (X = Ti, V, Ta, Nb, Mo, Zr) is formed in the matrix of the hydrogen storage alloy, the hydrogen storage alloy absorbs and releases hydrogen. At this time, pulverization due to expansion and contraction is suppressed, falling off is prevented, and the catalytic activity and corrosion resistance of the particle surface are improved, and high-rate discharge characteristics and cycle life can be improved.

The composition R (Ni _(1-a) M _a ) _b (X (Ni
When _1-x M _{x) d)} a c a _c is increased, since the occupancy of the skeletal structure of the alloy is increased, although the discharge capacity is reduced, corrosion resistance, cycle life characteristics are improved. The value of c is usually 0 <
c ≦ 2, preferably 0.1 ≦ c ≦ 1. When d in the X-nickel alloy is set to 1 or less, X (= Ti, V, T
a, Nb, Mo, and Zr) occlude hydrogen and easily become hydrogen embrittlement, so that the skeletal structure becomes less flexible and the volume of the rare earth-nickel-based hydrogen storage alloy crystal phase (matrix) associated with hydrogen absorption and release is reduced. Change cannot be absorbed. On the other hand, when d is larger than 3, the decrease in the hydrogen storage amount of the entire alloy is undesirably large. Therefore, 1 ≦ d ≦
3 is preferred.

X in X (Ni _1-x M _x ) _d is 0 ≦ x ≦
0.3. When x is larger than 0.3, the nickel content decreases, and the skeletal structure loses its flexibility.

Hydrogen Storage Alloy Electrode The hydrogen storage alloy of the present invention is bound as a powder on a current collector (eg, nickel mesh) to form an electrode having a three-dimensional skeleton structure of the current collector and the alloy. Can be made. In the integration of this alloy with the current collector, the alloy powder is pressed and pressed on a nickel mesh together with 2 to 10% by weight of nickel powder and sintered at 900 to 1100 ° C. from the viewpoint of electrode strength. However, since the electrode capacity is reduced, nickel powder need not be used. When the electrode is used in a cylindrical sealed battery, the sintering step can be omitted.

[0026]

As described above, in an electrode obtained by pressing a conventional alloy powder into a current collector and sintering it by heat treatment, the alloy is immediately pulverized and dropped off from the electrode due to charge and discharge, so that it can be put to practical use. Did not. However, in the electrode obtained by integrating the alloy having the three-dimensional skeletal structure of the present invention with the current collector by the above-described method, no falling off due to the pulverization of the alloy was observed even in a long charge / discharge cycle, and a practical electrode was used. It became possible to provide.

On the other hand, in the electrode manufacturing method in which the alloy is filled in the nickel porous body, the content of the alloy in the electrode is 40 to 50%.
% Is the limit and the capacity per unit volume is 1200 mA
h / cc is the limit. However, in the electrode in which the alloy of the present invention is integrated with the current collector, the amount of hydrogen absorbed per unit weight of the alloy powder itself is 10% by forming a skeleton structure in the alloy.
Although it is reduced to the extent, the electrode can be formed without using the nickel porous body required at the time of electrode molding, so that the capacity as an electrode can be increased by 10 to 30% per unit weight and unit volume, and the cost can be reduced. Becomes possible. Further, since a finer skeleton structure (diameter of 20 to 50 μm) is formed as compared with a conventional nickel porous body (diameter of 100 to 200 μm), it is possible to produce an electrode having excellent high-rate discharge characteristics.

In the production of the hydrogen storage alloy of the present invention, when the cooling rate of the alloy is increased, the matrix of the rare earth-nickel alloy remains crystalline and the skeleton structure of X (Ni _1-x
M _x ) _d [X = Ti, Ta, Nb, Mo] alone can be made amorphous. Since the amorphous alloy is not easily susceptible to hydrogen embrittlement, it works as a flexible frame in the hydrogen absorption / desorption cycle and prevents the entire alloy from being pulverized. Furthermore, by forming the skeleton structure continuously and densely with the surface of the rare earth-nickel alloy crystal particles (matrix), an electrode having a long cycle life can be obtained. In addition, the microscopic skeletal structure acts as a hydrogen diffusion path, and the electrode can be easily activated at the initial stage.

When the nickel-based hydrogen storage alloy powder of the present invention is used in a conventional nickel porous body, cost reduction and high capacity cannot be obtained. By the integration, improvement in the high rate discharge characteristics, cycle life characteristics, and initial activation characteristics is recognized.

[0030]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Examples 1 to 11 Ni and the X component element were weighed and mixed at the ratios shown in Table 1, and then heated and dissolved to form a Ni solid solution. After that, it was mixed with the R component and M component elements weighed to have the composition shown in Table 1 and mixed at 1600 ° C.
The high-frequency heating and melting were performed as described above, and the melt was poured into a water-cooled casting mold to be rapidly cooled. This alloy is heated and maintained in a range of 400 ° C. to 1500 ° C. for 10 to 50 hours in an inert atmosphere of Ar or vacuum to crystallize an alloy or compound containing nickel as a main component to form a skeletal structure.

This alloy was subjected to SEM (electron microscope) and EPM
Observation was performed by A (electron beam microanalyzer), and a continuous skeleton structure was observed at an arbitrary cross section of the ingot. Elemental analysis of the metal microstructure was performed to identify an element composition forming the skeleton structure. Further, an alloy forming a skeleton structure was identified by powder X-ray diffraction.

This alloy was pulverized in an inert atmosphere to obtain # 1
The alloy powder having passed through a 00 mesh was used.
i Pressure molding on wire mesh, 600-110 in inert atmosphere
1Ah by heating and holding in the range of 0 ° C for 3-6 hours
Was prepared.

A Ni-hydrogen battery with a negative electrode regulation of 0.2 C
At a rate of 0.2 C and a discharge cutoff voltage of 1 at a rate of 0.2 C.
Activation and cycling tests were performed at V. The activation characteristics were evaluated by the number of cycles at which the capacity was maximized. In the high-rate discharge test, the battery was charged at a rate of 0.2 C for 5 hours, a discharge end voltage of 1 V, and a rate of 3 C was performed.

In the alloys shown in Tables 1 to 11 as examples, a compound of Ni and an element corresponding to X (XNi
₃ ) formed a skeletal structure. This skeletal structure was maintained after the charge / discharge cycle, and no alloy was dropped from the electrode.

COMPARATIVE EXAMPLE 1 When the value of c becomes 0 as in the alloy composition of 1 in Table 2, the X-Ni alloy forming the skeletal structure does not crystallize, and no improvement in corrosion resistance or catalytic activity is observed. The effects of the present invention on the life and discharge characteristics are not recognized.

Comparative Examples 2 and 3 In the alloys shown in Table 2-2, b was small, and
In the alloy shown in No. 3, since d is small, the contained Ni is consumed by the generation of the compound of the X component and Ni, and therefore, the compound of the R component (rare earth element) and the Ni compound (RNi
₃ etc., the R component excess composition compared to RNi ₅ ) formed a parent phase.

COMPARATIVE EXAMPLES 4 AND 5 A hydrogen storage alloy capable of eutecticizing Ni and reversibly storing and releasing hydrogen because Ni is eutectic because alloy b of Table 2 has a large b and alloy b of Table 2 has a large d. Phase decreases, unit weight,
The discharge capacity per unit volume decreases, and it becomes difficult to increase the capacity of the secondary battery.

COMPARATIVE EXAMPLE 6 As shown in the alloy composition of 6 in Table 2, when c becomes 2 or more, XN
The amount of the i-compound becomes large, the amount of hydrogen storage alloy capable of reversibly storing and releasing hydrogen decreases, the discharge capacity per unit weight and unit volume decreases, and it becomes difficult to increase the capacity of the secondary battery.

COMPARATIVE EXAMPLE 7 When a is 0.5 or more, as in the alloy composition of 7 in Table 2, the hydrogen storage characteristics of the matrix greatly change, the corrosion resistance and the catalytic activity decrease, and the discharge characteristics decrease. Cycle life and discharge characteristics decrease.

COMPARATIVE EXAMPLE 8 When x is larger than 0.3, as in the alloy composition of 8 in Table 2, the nickel content decreases and the skeletal structure loses its flexibility.

[0042]

Example 1 Alloy composition number Initial capacity (mAh / cc) Activation 3C discharge (%) 300 cycles (%) 1 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (TiNi ₃ ) _0.2 1470 180 80 80 2 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (TaNi ₃ ) _0.2 1440 278 863 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (NbNi ₃ ) _0.2 1440 278 854 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ ( MoNi ₃ ) _0.2 1440 280 855 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (TiNi ₃ ) _2.0 1360 192 826 26 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (Ti (Ni _0.7 Co _0.3 ) ₃ ) _0.2 1420 180 877 La (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (Ti (Ni _0.7 Fe _0.3 ) ₃ ) _0.2 1430 178 818 8 La (Ni _0.7 Mn _0.1 Al _0.1 Co _0.1 ) ₅ (TiNi ₃ ) _0.1 1440 183 799 Mm (Ni _0.7 Mn _0.1 Al _0.1 Co _0.1 ) ₅ (TiNi ₃ ) _0.1 1390 181 82 10 La _0.7 Ce _0.3 (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (TiNi ₃ ) _0.1 1370 181 78 11 La _0.7 Nd _0.3 (Ni _0.8 Mn _0.1 Al _0.1 ) ₅ (TiNi ₃ ) _0.1 1360 181 81

[0043]

Table 2 Comparative Example Alloy Composition Number Initial Capacity (mAh / cc) Activation 3C Discharge (%) 300 Cycles (%) 1 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.0 1500 350 55 2 Mm (Ni _0.8 Co _0.1) Al _0.1 ) _4.5 (TaNi ₃ ) _0.2 1160 355 603 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.0 (Ti) _0.2 1380 140 454 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.8 (TiNi ₃ ) _0.2 1400 3 55 605 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.0 (TiNi ₅ ) _0.2 1050 157 606 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.0 (TiNi ₃ ) _4.0 560 145 307 Mm (Ni _0.4 Co _0.3 Al _0.3 ) _5.0 (TiNi ₃ ) _0.1 1290 460 508 Mm (Ni _0.8 Co _0.1 Al _0.1 ) _5.0 (TiNi _1.5 Co _1.5 ) _0.2 1310 155 60

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a hydrogen storage alloy having a skeletal structure according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Hiroshi Miyamura 1-8-31 Midorioka, Ikeda-shi, Osaka Prefecture Inside the Osaka Institute of Technology (72) Inventor Sei Uehara 1-81-31 Midorioka, Ikeda-shi, Osaka No. Examiner, Masaki Suzuki, Osaka Institute of Technology, National Institute of Advanced Industrial Science and Technology

Claims (3)

(57) [Claims] 1. A rare earth element that reversibly stores and releases hydrogen .
A nickel- based hydrogen storage alloy comprising a rare earth-nickel-based water
A matrix of an elemental storage alloy and X (Ni _1-x M _x ) _d [X is Ti, Z
represents at least one element selected from the group consisting of r, Ta, Nb and Mo, wherein M is Al, Co, Cu, Z
at least one element selected from the group consisting of n, Fe, Mn, Cr and Si, wherein 1 ≦ d ≦ 3, 0 <x ≦
0.3] having a skeletal structure mainly composed of an alloy having a composition of 0.3). 2. R (Ni _(1-a) M _a ) _b (X (Ni
_1-x M _x ) _d ) _c [wherein, R represents at least one element selected from lanthanoids, and M represents Al, Co, C
u, Zn, Fe, Mn, Cr and at least one element selected from the group consisting of Si, X is Ti,
At least one element selected from the group consisting of V, Ta, Nb, Mo, and Zr, where 0 <a ≦ 0.5;
8 <b ≦ 5.5, 0 <c ≦ 2, 1 ≦ d ≦ 3, 0 <x ≦
0.3. The rare earth hydrogen storage alloy according to claim 1, having a composition represented by the following formula: 3. A hydrogen storage alloy electrode obtained by integrating the rare earth hydrogen storage alloy according to claim 1 with a current collector.