JPH09176774A - Hydrogen storage alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy extremely increased in hydrogen absorbing and releasing velocities and showing excellent initial activation at the time of practical use. SOLUTION: This hydrogen storage alloy is composed of an Ni-Zr-Mn alloy having a composition consisting of, by weight, 25-45% Zr, 1-12% Ti, 10-20% Mn, 2-12% V, 0.6-5% rare earth elements composed essentially of La and/or Ce, 0.1-4% Hf, and the balance Ni (contained by >=25%) with inevitable impurities and also having a cast structure in which lumpy (rare earth element)-Ni alloy phases are dispersedly distributed along the grain boundaries of the main phase of Zr-Ni-Mn alloy constituting a matrix and lamellar Ni-Zr alloy phases are discontinuously distributed adjacently to the lumpy (rare earth element)-Ni alloy phases, simillarly along the grain boundaries.

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 which has extremely fast hydrogen absorption and desorption rates and exhibits excellent initial activation when applied to, for example, a battery electrode.

[0002]

2. Description of the Related Art Conventionally, a large number of hydrogen storage alloys have been generally proposed, and recently, 6-11 November 1994.
Hydrogen storage alloys were announced at the "International Symposium on the Fundamentals and Applications of Metal-Hydrogen Systems" held in Fujiyoshida, Japan. This hydrogen storage alloy has a Zr: 22.1 to 25.5% by weight (hereinafter,% means% by weight).
%, Ti: 11.6-13.4%, Mn: 23.7
~ 24.6%, Cr: 22.4 to 23.3%, L
a: 7.5% or less, the rest of which has a composition of Ni and inevitable impurities, and Z which constitutes the base material as shown in the schematic enlarged structure diagram illustrating the representative structure in FIG.
It has a cast structure in which the La-Ni alloy phase is distributed and distributed along the grain boundaries of the main phase composed of the r-Ni-Mn alloy. In addition, the above hydrogen storage alloy is
The a-Ni alloy phase dissociates hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) by the catalytic action of the a-Ni alloy phase, and
The dissociated hydrogen atoms are absorbed at a much higher speed than the main phase of the Zr-Ni-Mn alloy, and therefore Zr-Ni is absorbed.
It is also known that the absorption of hydrogen atoms in the main phase of the -Mn-based alloy has a hydrogen absorption function mainly performed through the La-Ni-based alloy phase, while the hydrogen release is due to the opposite function. . Furthermore, when the hydrogen storage alloy is applied to, for example, an electrode of a battery, the hydrogen storage alloy is incorporated into the electrode until the electrode has a sufficient discharge capacity, that is, the hydrogen storage alloy. It is also known that initial activation in which charging and discharging are repeatedly performed is performed until the discharge capacity brought by is almost maximized, and the initial activation is performed for practical use.

[0003]

On the other hand, in recent years, there is a strong demand for higher output and higher performance of batteries and heat pumps to which hydrogen storage alloys are often applied and further energy saving. It is strongly desired for the alloy to have a much faster hydrogen absorption / desorption rate than the hydrogen absorption / desorption rate in the conventional hydrogen storage alloy, and to be activated in a shorter time in practical use.

[0004]

Means for Solving the Problems Accordingly, the present inventors have
From the above viewpoints, as a result of research to improve the hydrogen absorption / desorption rate and initial activation of the hydrogen storage alloy, (a) the hydrogen storage alloy, Zr: 25-45%,
Ti: 1 to 12%, Mn: 10 to 20%,
V: 2 to 12%, a rare earth element mainly composed of La and / or Ce, preferably 50% or more of the rare earth element in the ratio of La and / or Ce, more preferably substantially La and / or Or rare earth element composed of Ce: 0.6 to 5%, Hf:
Ni-Z having a composition of 0.1 to 4% and the balance of Ni (containing 25% or more) and inevitable impurities.
When composed of an r-Mn-based alloy, this Ni-Zr-Mn-based alloy constitutes a base material in a cast state (as-cast state) as shown in a schematic microstructure enlargement diagram illustrating a representative structure in FIG. The lumpy rare earth element-Ni-based alloy phase is dispersed and distributed along the grain boundaries of the main phase of the Zr-Ni-Mn-based alloy, and the plate-like Ni-Zr-based alloy phase is the rare earth element-
Also, it has a structure in which it is intermittently distributed along the crystal grain boundaries in the state of being adjacent to the Ni-based alloy phase. (B) In the hydrogen storage alloy of (a) above, as in the conventional hydrogen storage alloy having the structure shown in FIG. 2, the rare earth element-Ni alloy phase has hydrogen molecules in the atmosphere due to its catalytic action. (H ₂ ) dissociates into hydrogen atoms (H) at a relatively high rate and absorbs the dissociated hydrogen atoms.
Most of the hydrogen atoms absorbed in the rare earth element-Ni alloy phase are Zr-directly transferred from the rare earth element-Ni alloy phase.
Most of the plate-shaped N adjacent to the rare earth element-Ni alloy phase is not absorbed by the main phase of the Ni-Mn alloy.
i-Zr-based alloy phase shifts to hydrogen atom Zr-Ni-M
The main body of diffusion of the n-based alloy into the main phase is plate-like Ni-Zr.
Since it is carried out by surface diffusion through the alloy phase, it is possible to absorb hydrogen atoms at an extremely fast rate, while hydrogen desorption is also carried out by surface diffusion and recombination of the opposite hydrogen atoms. The rate is high, and the absorption rate of hydrogen atoms in the main phase at the time of initial activation is also increased due to surface diffusion, so that the initial activation can be remarkably promoted. The research results shown in (a) and (b) above were obtained.

The present invention has been made based on the above research results, and Zr: 25-45%,
Ti: 1 to 12%, Mn: 10 to 20%,
V: 2-12%, La and / or Ce-based rare earth element: 0.6-5%, Hf: 0.1-4
%, With the balance being Ni (but containing 25% or more) and inevitable impurities, and Zr constituting the matrix.
-The bulk rare earth element-Ni alloy phase is dispersed and distributed along the crystal grain boundaries of the main phase composed of -Ni-Mn alloy, and the plate-like Ni-Zr alloy phase is the rare earth element-Ni alloy phase. A hydrogen storage alloy composed of a Ni-Zr-Mn-based alloy having a structure which is also intermittently distributed along crystal grain boundaries in a state of being adjacent to each other, has a high hydrogen absorption / desorption rate and excellent initial activation. It is characterized by

Next, in the hydrogen storage alloy of the present invention, the reason why the composition of the Ni—Zr—Mn alloy constituting the hydrogen storage alloy is limited as described above will be explained. (A) Zr Zr component is combined with Ni and Mn as described above to form a main phase of a Zr-Ni-Mn alloy having hydrogen storage capacity, and is further combined with Ni to form a hydrogen atom in the main phase. Plate-like Ni that absorbs and releases nitrogen by surface diffusion
-Zr-based alloy phase is formed, but if the content ratio is less than 25%, the formation of the plate-like Ni-Zr-based alloy phase becomes insufficient in particular, and the hydrogen absorption / desorption rate and the initial activation ability are rapidly reduced. When the ratio exceeds 45%,
As the content of the plate-like Ni-Zr alloy phase having a small hydrogen storage amount increases and the content of the main phase having a large hydrogen storage amount relatively decreases, the hydrogen storage amount of the entire alloy decreases. Therefore, the content is set to 25 to 45%, preferably 30 to 38%.

(B) The Ti-Ti component has the function of making the equilibrium hydrogen dissociation pressure of the alloy lower than atmospheric pressure at room temperature, thereby contributing to promotion of absorption and desorption of hydrogen, and also in the main phase. Although it has the effect of increasing the hydrogen storage capacity, if the content ratio is less than 1%, the desired effect cannot be obtained, whereas if the content ratio exceeds 12%, the equilibrium hydrogen dissociation pressure is again at room temperature, for example. Since the pressure rises above atmospheric pressure and the absorption and release of hydrogen decrease, the ratio is set to 1 to 12%, preferably 4 to 8%.

(C) Mn The Mn component forms a main phase of a Zr-Ni-Mn alloy having a large hydrogen storage capacity by combining with Ni and Zr as described above, but its content is less than 10%. In the above, the formation of the main phase becomes insufficient and the hydrogen storage amount is unavoidably lowered. On the other hand, if the content ratio exceeds 20%, the absorption and release of hydrogen will be hindered. Was set to 10 to 20%, preferably 14 to 18%.

(D) The V V component, which is mainly in the main phase, acts to stabilize the equilibrium hydrogen dissociation pressure of the alloy and to increase the hydrogen storage amount. If the desired effect is not obtained, on the other hand, if the ratio exceeds 12%, the equilibrium hydrogen dissociation pressure becomes too low and it becomes difficult to release the stored hydrogen, and as a result, a decrease in the hydrogen storage amount is avoided. Therefore, the ratio is 2 to 12%, preferably 4 to 8
%.

(E) Rare earth element These components bond with Ni as described above to dissociate hydrogen molecules in the atmosphere at a faster rate than the main phase and the plate-like Ni-Zr alloy phase, Absorbing and forming a massive rare earth element-Ni based alloy phase that causes the absorbed hydrogen atoms to diffuse and transfer mainly to the adjacent plate-like Ni-Zr based alloy phase, but if the content ratio thereof is less than 0.1%, Bulk rare earth element −
If the proportion of the Ni-based alloy phase produced is too small to secure a desired high hydrogen absorption / desorption rate, and if the proportion thereof exceeds 5%, the massive rare earth element-Ni-based alloy having a low hydrogen storage capacity is obtained. Since the content ratio of the phase becomes too large and the hydrogen storage amount of the entire alloy decreases, the content ratio is set to 0.6 to 5%, preferably 1 to 4%. Further, in order to sufficiently exert the above-mentioned action by the rare earth element-Ni alloy phase, it is necessary to make La and / or Ce the main component of the rare earth element, and in this case, it is desirable that the ratio of La and / or Ce be set. The proportion of the rare earth element is preferably 50% or more, and more preferably the rare earth element is substantially composed of La and / or Ce.

(F) In the Hf Hf component, a Zr-Ni-Mn-based alloy main phase and a plate-like Ni-Zr-based alloy phase are formed together with the Zr component to form Zr.
Although it has the effect of sufficiently exerting the above-mentioned action brought about by the components, if the content is less than 0.1%, the desired effect cannot be exerted, while if the ratio exceeds 4%, the above-mentioned effect due to Zr is exerted. Since the action of is inhibited, its content is 0.1 to 4%, preferably 1 to
It was set at 1.7%.

(G) Ni If the Ni component content is less than 25%, the formation of the rare earth element-Ni-based alloy phase and the Ni-Zr-based alloy phase is insufficient as described above, and the desired hydrogen absorption / desorption rate and Since the initial activation cannot be secured, its content is set to 2
It was set at 5% or more.

The hydrogen storage alloy of the present invention can be made into powder having a predetermined particle size by ordinary mechanical crushing. However, mechanically coarsely crushed coarse particles are mixed with 10 to 2 in a pressurized hydrogen atmosphere.
A powder can also be obtained by hydrogen absorption by heating to a predetermined temperature within a range of 00 ° C. and hydrogenation pulverization by hydrogen release by evacuation, and all the resulting powders have a typical structure illustrated in FIG. It will have the organization as shown in the organization enlargement copy.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the hydrogen storage alloy of the present invention will be specifically described with reference to examples. Ni, Zr, Ti, Mn, V, La, Ce, Hf each having a purity of 99.9% or more as a raw material in an ordinary high frequency induction melting furnace
And Cr, and further misch metal, are melted in an Ar atmosphere to prepare alloy melts having the compositions shown in Tables 1 to 3, respectively, and cast into water-cooled copper molds to form ingots of the present invention. Storage alloys (hereinafter, referred to as alloys of the present invention) 1 to 45 and conventional hydrogen storage alloys (hereinafter, referred to as conventional alloys) were manufactured. As a result of observing the structure of the resulting alloy with a scanning electron microscope, the alloys 1 to 45 of the present invention are all the main phases of the Zr-Ni-Mn-based alloy forming the matrix as shown in FIG. Along with the crystal grain boundaries, the bulk rare earth element-Ni-based alloy phase is dispersed and distributed, and the plate-like Ni-Zr alloy phase is adjacent to the rare-earth element-Ni-based alloy phase. In the conventional alloy, as shown in FIG. 3, the bulk La—Ni-based alloy phase is dispersed and distributed along the grain boundaries of the main phase of the Zr—Ni—Mn-based alloy. I showed the organization to do.

Next, the hydrogen absorption rate and the hydrogen desorption rate of each of the above alloys 1 to 45 of the present invention and the conventional alloy were measured based on JIS H7202 "Hydrogen storage alloy hydrogenation rate test measuring method". Prior to the measurement, the alloys of the present invention 1 to 45 and the conventional alloy were coarsely crushed into coarse particles having a diameter of 2 mm or less by using a jaw crusher, and then these coarse particles were sealed in a pressure vessel and the hydrogen atmosphere pressure:
Hydrogenation and pulverization consisting of hydrogen absorption under the conditions of 8 atm, heating temperature: 200 ° C., holding time: 1 hour, and hydrogen release by evacuation were performed to obtain a powder having a particle size of 200 mesh or less. The measurement was performed under the following conditions.

First, regarding the hydrogen absorption rate, as shown in the schematic explanatory view of FIG. 4, (a) the powder is enclosed in a container immersed in a bath (oil or water), and the temperature of the bath is set to 200.
C, the valves Vb: closed, valves Va and Vc:
Pressurized hydrogen was introduced into the system from the hydrogen cylinder to open the valve, and when the pressure in the system was set to 30 atm, the valve Va was closed, and the system was allowed to stand until the pressure in the system dropped to a constant pressure (hydrogen absorption by powder was completed). When the initial activation of the powder is performed and (b) the pressure in the system is reduced to a constant pressure (about 20 atm), the valve V
b: Opened, the system was evacuated to a vacuum atmosphere of 10 ^-2 torr with a vacuum pump, the bath temperature was set to 20 ° C, and valves Vb: and Vc:
Close, valve Va: open and introduce hydrogen into the system excluding the container,
When the pressure reaches 30 atm, valve Va: closed, valve V
c: Open, pressure drop with respect to time in the system was measured in this state, and from the resulting pressure drop curve, the hydrogen storage amount at the time when the hydrogen storage amount of the powder became 80% and the time required until then were calculated. Then, (hydrogen storage amount at 80% storage) ÷ (80%
The time required for hydrogen storage) was calculated, and this value was used as the hydrogen absorption rate.

Regarding the hydrogen release rate, the state after the above hydrogen absorption rate measurement, that is, the valves Va and Vb:
Closed, valve Vc: open and the pressure in the system is constant (normally 20
(Atmospheric pressure), the bath temperature is set to an appropriate temperature for releasing hydrogen of powder in the range of 100 to 300 ° C., for example, 120 ° C., then the valve Vb is opened and the valve Vc is closed to remove the inside of the system. After exhausting to 10 ^-2 torr and then, with the valve Vb closed and the valve Vc open, the pressure rise over time in the system was measured and the resulting pressure rise curve showed that the hydrogen release of the powder was 80%. The amount of hydrogen released at the point of time and the time required up to that time were obtained, and (the amount of hydrogen released at the time of 80% release) / (the time required for the release of 80% hydrogen) was calculated. . The results are shown in Tables 1 to 3.

Further, for the purpose of evaluating the initial activation of the alloys 1 to 45 of the present invention and the conventional alloys, as detailed below, the powders were powdered and incorporated into a battery as an active material, and the battery was discharged at maximum discharge. It is repeatedly charged and discharged until the capacity is reached, and 90% of the maximum discharge capacity is reached.
The number of times of charge and discharge until a discharge capacity corresponding to ± 1% was shown was measured. That is, first, the alloys 1 to 45 of the present invention and the conventional alloys were coarsely crushed using a jaw crusher to obtain coarse particles having a diameter of 2 mm or less, and then finely pulverized using a ball mill to obtain a particle size of 200 mesh or less. , Polytetrafluoroethylene (PTFE) as a binder and carboxymethyl cellulose (CM as a thickener)
C) was added to form a paste, which was then filled in a commercially available porous Ni sintered plate having a porosity of 95%, dried, and pressed to obtain a plane size of 30 mm × 40 mm and a thickness of 0.40. ~ 0.
It has a shape of 43 mm (filling amount of the active material powder: about 1.8 g), and a Ni thin plate serving as a lead is attached to one side of this by welding to form a negative electrode, while the positive electrode is an active material in a weight ratio of 84:16. Of Ni (OH) ₂ and Co
O was used, and polytetrafluoroethylene (PTFE) as a binder and carboxymethyl cellulose (CMC) as a thickener were added thereto to form a paste, which was filled in the porous Ni sintered plate and dried. Then pressurize
Plane size: 30 mm x 40 mm, thickness: 0.71 to 0.73
mm shape, and also formed by attaching a Ni thin plate to one side of the same, and then disposing the positive electrode on both sides of the negative electrode via separator plates of polypropylene polyethylene copolymer, and further, each of the positive electrodes. For the purpose of preventing the active material from falling off from the outer surface, it is integrated by sandwiching it with a vinyl chloride protective plate, and this is put into a vinyl chloride cell, and 35% KO as an electrolytic solution is put in the cell.
A battery was manufactured by charging the H aqueous solution. Then, the battery was charged with a charging rate of 0.25 C and a discharging rate of:
0.18C, quantity of electricity charged: charging / discharging was performed under the condition of 135% of negative electrode capacity, and the charging and discharging were counted as one charging / discharging,
The charging and discharging were repeated until the battery reached the maximum discharge capacity. Tables 1 to 3 show the maximum discharge capacities measured as a result of this, and 95% ± of the maximum discharge capacities.
The number of times of charging / discharging required to show a discharge capacity of 1% was shown, and the initial activation was evaluated by this.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

As is clear from the results shown in Tables 1 to 3, in the alloys 1 to 45 of the present invention, the rare earth element-Ni.
The system alloy phase dissociates hydrogen molecules (H ₂ ) in the atmosphere into hydrogen atoms (H) at a relatively fast rate by the catalytic action of the alloy phase, and absorbs the dissociated hydrogen atoms. Most of the atoms are not directly absorbed from the rare earth element-Ni alloy phase into the main phase of the Zr-Ni-Mn alloy alloy, but are transferred to the plate-like Ni-Zr alloy phase adjacent to the rare earth element-Ni alloy alloy phase. However, since hydrogen atoms are mainly diffused into the main phase of the Zr-Ni-Mn-based alloy by plane diffusion through the plate-like Ni-Zr-based alloy phase, the hydrogen absorption rate is high, and Initial activation is also remarkably promoted, and as for hydrogen desorption, the main component of the absorbed hydrogen in the main phase moves to the plate-like Ni-Zr alloy by surface diffusion, so that the amount of hydrogen from the rare earth element-Ni alloy is increased. Release into the atmosphere becomes faster And than, whereas even in the conventional alloys, the hydrogen absorption and release primarily the bulk La-
Although hydrogen is diffused through the Ni-based alloy phase, hydrogen atoms are diffused between the La-Ni-based alloy phase and the Zr-Ni-Mn-based alloy main phase, so that hydrogen is relatively absorbed and released. The speed is inevitably slow, and the initial activation is also relatively slow. As mentioned above,
Since the hydrogen storage alloy of the present invention has extremely fast hydrogen absorption and desorption rates and exhibits excellent initial activation in practical use, it can be applied to various batteries and heat pumps to which it has high performance, high output, and energy saving. It will greatly contribute to the commercialization.

[Brief description of the drawings]

FIG. 1 is a schematic structure enlarged copy diagram illustrating a representative structure of a hydrogen storage alloy of the present invention.

FIG. 2 is a schematic structure enlarged copy diagram illustrating a representative structure of the hydrogen-absorbing alloy crushed powder of the present invention.

FIG. 3 is an enlarged schematic structure diagram illustrating a representative structure of a conventional hydrogen storage alloy.

FIG. 4 is a schematic explanatory diagram of an apparatus used for measuring a hydrogen absorption / desorption rate of a hydrogen storage alloy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Tamao 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Materials Co., Ltd.

Claims (1)

[Claims] 1. Zr: 25 to 45%, Ti: 1 to 12%, Mn: 10 to 20%, V: 2 to 12%, and a rare earth element mainly composed of La and / or Ce: 0 by weight%. ．
6 to 5%, Hf: 0.1 to 4%, and the balance is Ni (however, 2
5% or more) and inevitable impurities, and the bulk rare earth element-Ni-based alloy phase is dispersed and distributed along the grain boundaries of the main phase of the Zr-Ni-Mn-based alloy forming the matrix. Ni-Z having a cast structure in which the plate-like Ni-Zr alloy phase is adjacent to the rare earth element-Ni alloy phase and also intermittently distributed along the crystal grain boundaries.
A hydrogen storage alloy comprising an r-Mn-based alloy.