JPH0641663A - Hydrogen storage alloy and its manufacture, and hydrogen storage alloy electrode - Google Patents

Abstract

PURPOSE:To obtain an Ni-hydrogen secondary battery having a very high discharging capacitance and maintaining a high capacitance even after repeated charging-discharging. CONSTITUTION:This is a hydrogen storage alloy having a compsn. expressed by the formula: TiaZr1-a (NibVcMndMee) [in the formula, M=one or two or more kinds of elements selected among Cr, Fe, Co, Mo, W, Al, Cu and Nb as well as 0<=a<0.60, 1.00<b<1.50, 0.10<c<0.50, 0.10<d<0.70, 0.05<e<0.30 and 1.90<=b+c+d+e<=2.30] and substantially constituted of a Laves phase only, and this is a negative electrode for an Ni-hydrogen battery using the same as negative electrode active substance. The melting of the alloy is executed by rapid solidification of 500K/sec or faster from the state of the molten soln., and after the solidification, stress relief annealing may be executed at 550 to 750 deg.C for 1 to 4hr.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a hydrogen storage alloy based on Zr and Ni and having excellent hydrogen storage characteristics, a method for producing the same, and a high capacity Ni-hydrogen using the hydrogen storage alloy as an active material for a negative electrode. The present invention relates to a negative electrode for a secondary battery. The hydrogen storage alloy of the present invention is characterized in that it has a Laves phase having a basic crystal structure of C14 type (hexagonal) and / or C15 type (face centered cubic).

[0002]

2. Description of the Related Art At present, Ni-Cd batteries are the mainstream of secondary batteries used for memory backup of AV equipment and computers. However, from the viewpoints of the pollution problem of Cd, the problem of resource limitation that Cd is a by-product of zinc refining, and the development of secondary batteries with higher electric capacity, a hydrogen storage alloy was used instead of Cd as the negative electrode material (strictly speaking, the negative electrode A secondary battery called Ni-hydrogen battery used as an active material was developed. The secondary battery using this hydrogen storage alloy has a higher capacity than Ni-Cd batteries and Ni-Zn batteries, and is composed of pollution-free elements.
Therefore, Ni-hydrogen batteries are being considered for use as secondary batteries for electric vehicles whose use is expanding as pollution-free vehicles and energy-saving vehicles due to global environmental problems, and mass production is about to begin.

It was first developed as a hydrogen storage alloy for secondary batteries and is currently in the mainstream.
JP-A-1-162741 and Japanese Unexamined Patent Publication (Kokai) No. 1-162741 disclose hydrogen storage alloys based on rare earth metals and Ni. When these rare earth-Ni-based hydrogen storage alloys are used as electrodes, Ni-
A high electric capacity of about 1.5 times that of a Cd battery can be realized. However, development of high-performance lightweight secondary batteries for further miniaturization of AV equipment and electric vehicle applications has led to the development of hydrogen storage alloys for Ni-hydrogen batteries that can achieve higher discharge capacities. Has been requested.

In response to this request, Zr and Zr as disclosed in JP-A-2-220355 and JP-A-2-263944 are used.
Crystal structure of AB ₂ based on Ni or Zr, Ti and Ni
A hydrogen storage alloy having a (Laves phase) (hereinafter, also referred to as Zr-Ni system hydrogen storage alloy) has been proposed. This kind of alloy
The capacity is higher than that of the above rare earth metal-Ni system.

However, when a Zr-Ni system hydrogen storage alloy is produced by high-frequency induction heating melting, which is a usual method for producing hydrogen storage alloys, alloy phases other than the AB ₂ phase that do not contribute to charge and discharge are inevitable. The hydrogen storage alloy thus produced and produced has a reduced discharge capacity due to the inclusion of such a phase. Therefore, there is a possibility that the discharge capacity of the Zr-Ni-based hydrogen storage alloy may be further increased by forming the phase that does not contribute to charging / discharging substantially without being composed of the AB ₂ phase. . In addition, the conventional Zr-Ni-based hydrogen storage alloy has a drawback that the life is severely reduced by repeated use.

[0006]

A Zr-Ni-based hydrogen storage alloy for a Ni-hydrogen battery negative electrode having a basic crystal structure of AB ₂ Laves phase is prepared by strictly adjusting the composition to the stoichiometric composition of AB _2. However, in the conventional melting method, the AB ₂ single phase was not obtained,
The AB ₂ Laves phase and other phases were mixed, and the discharge capacity of the electrode was small due to the presence of the other phases.

The object of the present invention is to prevent the appearance of other phases,
Substantially completely AB ₂ Laves phase C15 type or C14
A Zr-Ni-based hydrogen storage alloy having a high discharge capacity in a single phase type or a two-phase state of a C15 type and a C14 type and a method for producing the same.

Another object of the present invention is to provide a hydrogen storage alloy for a negative electrode of a Ni-hydrogen battery, which has a high capacity and has a reduced lifespan due to repeated use, and a method for producing the same.

[0009]

Means for Solving the Problems The present inventor has conducted extensive studies to achieve the above-mentioned object and found that Zr and Ni or Zr
It has been found that a hydrogen storage alloy based on Ti and Ni and having a composition in which an appropriate amount of V, Mn and other elements are added has a high capacity and a small capacity decrease due to repeated charge and discharge.

Further, in order to further improve the capacity of this alloy system, the alloy obtained by melting is in a single phase state of C15 type or C14 type Laves phase, or a mixed phase state of only these two phases. In order to obtain, we tried heat treatment under various conditions,
Phases other than the Laves phase could not be completely eliminated even by heat treatment at high temperature for a long time.

Therefore, as a result of studying means for preventing the precipitation of phases other than the Laves phase during the solidification process during melting, it was found that when the melt was solidified by rapid cooling at a cooling rate above a certain level, the Laves phase The inventors have found that the precipitation of the other phases can be suppressed, and that a hydrogen storage alloy consisting essentially of the Laves phase can be obtained, and have completed the present invention.

With regard to the Laves phase alloy, it has been attempted to obtain an electrode substantially only by the alloy without using a Teflon-based binder or the like during sintering. If the electrode can be produced by sintering in this way, the packing density of the powder will be high, so that the capacity can be increased and the contact area between the powders will be large, which will reduce the resistance and enable the charging and discharging of a large current. There is an advantage that

For that purpose, there has been a demand for an alloy which does not precipitate any phase other than the Laves phase even if it is heated to a sintering temperature of 900 ° C. or higher, and which substantially consists of the Laves phase, and a method for producing the alloy.

With respect to these requirements, the present inventor, in the more specified alloy composition range, solidifies the melt by rapid cooling at a cooling rate of a certain rate or more, and then 550 to 11
The inventors have found that even if heated to 00 ° C. for a long time, the precipitation of phases other than the Laves phase is suppressed, and a hydrogen storage alloy consisting essentially of the Laves phase is obtained, and the present invention has been completed.

Here, the gist of the present invention is represented by the formula: Ti _a Zr
_1-a (Ni _b V _c Mn _{d Me} ) (wherein, one or more elements selected from the group consisting of M = Cr, Fe, Co, Mo, W, Al, Cu and Nb, 0 ≦
a <0.60, 1.00 <b <1.50, 0.10 <c <0.50, 0.10 <d
<0.70, 0.05 <e <0.30, 1.90 ≦ b + c + d + e ≦ 2.3
It is a hydrogen storage alloy having a composition represented by 0) and being substantially composed of only Laves phase.

Here, "substantially consisting of the Laves phase" means a measurement by an analytical electron microscope and electron beam diffraction.
This means that substantially no phases other than the Laves phase of C14 and C15 are detected.

When the alloy having the above composition is melted, this hydrogen storage alloy is rapidly cooled from the state of a melt at a cooling rate of 500 K / sec or more to solidify the alloy, preferably in an inert gas or vacuum. Can be manufactured by removing the strain during rapid solidification by heat treatment at 550 to 750 ° C. for 1 to 4 hours.

In a specific embodiment of the present invention,
Formula: Ti _a Zr _1-a (Ni _b V _c Mn _{d Me} ) (wherein M = Cr, Fe, Co, Mo, W, Al, Cu and Nb; More than one element, 0 ≦
a <0.20, 1.00 <b <1.50, 0.10 <c <0.50, 0.10 <d
<0.70, 0.05 <e <0.30, 1.95 <b + c + d + e ≦ 2.0
When a hydrogen storage alloy having the composition represented by 5) is rapidly cooled from the melt state at the time of melting at a cooling rate of 1.0 × 10 ³ K / sec or more, it is then placed in an inert gas or vacuum.
The Laves phase single phase is maintained even after heat treatment at 550 to 1100 ° C. for 1 to 20 hours. Hereinafter, this is referred to as a specific embodiment of the present invention.

In this case, the phases other than the C15 type Laves phase are substantially not detected by the measurement using an analytical electron microscope and electron diffraction. The present invention also relates to a negative electrode for a Ni-hydrogen battery, which uses the above hydrogen storage alloy as a negative electrode active material.

[0020]

The structure of the present invention will be described in detail below together with its operation. First, the detailed reason for limiting the composition of the hydrogen storage alloy of the present invention as described above will be described below.

(1) Ti and Zr (Ti _a Zr _1-a , 0 ≦ a <0.
60) The alloy of the present invention is basically in the form of an AB ₂ type compound. Ti and Zr are elements that occupy this A portion. There are various A elements for forming AB ₂ type compounds, but when Zr alone or Ti and Zr become A elements, a hydrogen storage alloy having a high hydrogen storage capacity and capable of reversibly absorbing and releasing hydrogen is obtained. Therefore, as the A element, Zr alone or Zr
I chose a combination of Ti. Therefore, in the above formula (I), the atomic ratio of Ti and Zr is 1.00 in total.

Further, when 0 ≦ a <0.60, the Ti content is 0.
The reason for limiting the atomic ratio to less than 60 is that, outside of this range, phases other than the Laves phase may appear even if the melting method by rapid cooling described above is used. Preferably 0
The range is ≦ a ≦ 0.30.

Further, as will be described later, 1.95 <b + c + d +
When e ≦ 2.05 and the solidification cooling rate is 1 × 10 ³ K / sec or more, if 0 ≦ a <0.20 and the Ti content is set to an atomic ratio of less than 0.20 of the A element, then (550- 1000) ° C × (1 to 20) h
The C15 type Laves phase single phase is maintained even when subjected to heat treatment at a high temperature of r for a long time. From this point, 0 ≦ a ≦ 0.10 is more desirable.

(2) Ni (Ni _b , 1.00 <b <1.50) Ni is an element occupying the B portion of the AB ₂ type basic form.
Ni acts as a catalyst for electrochemically storing and extracting hydrogen when the hydrogen storage alloy is used for a battery electrode. From this viewpoint, the alloy system of the present invention electrochemically absorbs a sufficient amount of hydrogen as a battery material.
As a result of obtaining the amount of Ni necessary to release it, the atomic ratio of Ni b
Was over 1.00, it was found that a high discharge capacity was obtained.
On the other hand, although Ni has an electrochemical catalytic action, it was also found that when the Ni content is too large, the hydrogen storage capacity of the alloy decreases, and the capacity when the battery is constructed becomes low. In order to realize the high capacity that is the object of the present invention, the upper limit of the Ni atomic ratio b is 1.
Must be less than 50. The preferred range of b is 1.10 ≦ b
≦ 1.30.

(3) V (V _c , 0.10 <c <0.50) V has a function of increasing the hydrogen storage amount of the alloy of the present invention. In order to obtain this effect, the atomic ratio c of V needs to be more than 0.10. However, V also has a function of lowering the hydrogen equilibrium pressure when the hydrogen storage amount is small. Therefore, V
When a large amount of is added, the hydrogen absorption equilibrium pressure becomes 10 ^-3 atm or less. When the hydrogen absorption equilibrium pressure falls below 10 ^-3 atmospheres, stored hydrogen that can be charged but cannot be discharged is generated, and the electric capacity that can be reversibly charged / discharged when a battery is constructed decreases. In order to avoid this, the atomic ratio c of V is limited to less than 0.50. The preferable range of c is 0.25 ≦ c ≦ 0.40.

(4) Mn (Mn _d , 0.10 <d <0.70) Mn improves the flatness of the hydrogen absorption / desorption plateau pressure of the alloy of the present invention (makes the plateau slope flat and long), It has the function of reducing the fluctuation range of the pressure due to the change in the hydrogen storage amount at the time of release. As a result, the hydrogen equilibrium pressure does not suddenly rise when the sealed battery is configured and charged, so that the internal pressure is prevented from rising and more charging is possible. To obtain this effect, the atomic ratio d of Mn needs to exceed 0.10. However, when Mn is contained in a large amount such as an atomic ratio of 0.70 or more, the corrosion resistance in the alkaline electrolyte is deteriorated and the repeated life of charge / discharge becomes short. Therefore, the atomic ratio of Mn is limited to 0.10 <d <0.70. The preferred range of d is
0.20 ≦ d ≦ 0.50.

(5) M = Cr, Fe, Co, Mo, W, Al, Cu, Nb
[ _Me , 0.05 <e <0.30] M element (one or more of Cr, Fe, Co, Mo, W, Al, Cu and Nb) has improved corrosion resistance without lowering hydrogen storage capacity. And has the function of improving battery life. In order to obtain these effects, it is necessary to add an M element whose atomic ratio exceeds 0.05 in total. On the other hand, when the content is 0.30 or more in atomic ratio, the function of lowering the hydrogen equilibrium pressure when the hydrogen storage amount is small becomes remarkable like V, and reversible charging / discharging is possible when the battery is constructed. The electric capacity will decrease. From this point, the total atomic ratio e of M element is 0.30.
Limited to less than. The preferred range of e is 0.10 ≦ e ≦ 0.20.

(6) 1.90 ≦ b + c + d + e ≦ 2.30 The alloy of the present invention takes the form of an AB ₂ type compound forming the Laves phase. b + c + d + e is the total atomic ratio of Ni, V, Mn, and M elements constituting the B portion of this structure, and therefore it is desired that b + c + d + e = 2.00.

When the solidification cooling rate during melting is less than 500 K / sec, in the melting by ordinary high frequency induction heating, b + c + d +
It has been confirmed that phases other than the Laves phase are precipitated even if e = 2.00 is adjusted. On the other hand, according to the present invention,
1.90 when solidifying at a cooling rate of 500 K / sec or more
It was found that in the range of ≤b + c + d + e≤2.30, a hydrogen storage alloy in a crystalline state substantially consisting of AB ₂ type Laves phase can be obtained. Preferably, 1.95 ≦ b + c + d
+ E ≦ 2.10.

According to a particular aspect of the present invention, 0≤a
When <0.20 and the solidification cooling rate is 1.0 × 10 ³ K / sec or more, if 1.95 <b + c + d + e ≦ 2.05, then (550 to 1000) ° C. × (1 to 20) hr high temperature, The C15 type Laves phase single phase is maintained even after long-term heat treatment. From this point, 1.98 ≦ b + c + d + e ≦ 2.02 is more desirable.

(7) Cooling Rate The hydrogen-absorbing alloy of the present invention is solidified by rapid cooling at a cooling rate of 500 K / sec or more from the melt state after melting together appropriate sources of each alloying element. It can be manufactured by any method that can be realized.

The melting can be carried out by an appropriate method such as arc melting, plasma melting, high frequency induction heating, resistance heating in an inert gas atmosphere or vacuum. The rapid solidification of the obtained melt may be performed by any method capable of rapid cooling at a cooling rate of 500 K / sec or more, such as a gas atomizing method, casting on a rotating drum, and a rotating electrode method.

Cooling rate during solidification from the melt is 500 K / sec
If it becomes smaller, it is not possible to reliably prevent precipitation of phases other than the Laves phase during solidification, making it difficult to produce a hydrogen storage alloy of the present invention consisting essentially of the Laves phase. . The cooling rate during solidification is preferably
1.0 × 10 ³ (= 1000) K / sec or more.

Particularly, 0 ≦ a <0.20, 1.95 <b + c + d +
If e ≦ 2.05, set the cooling rate during solidification from the melt
If it is 1.0 × 10 ³ K / sec or more, the subsequent heat treatment
The C15 type Laves phase single-phase state is maintained even at a high temperature of (550 to 1100) ° C x (1 to 20) hr for a long time.

(8) Strain-releasing heat treatment conditions Since the hydrogen storage alloy of the present invention is manufactured by rapid solidification as described above, strain may occur due to rapid cooling. As a result, the crystal lattice becomes distorted and the hydrogen absorption characteristics may change. This strain can be removed by heat treatment (strain relief annealing) in an inert gas or vacuum,
As the heat treatment condition, it is necessary to adopt a condition that phases other than the Laves phase do not precipitate during the treatment. As such a condition, a heat treatment condition of 550 to 750 ° C. for 1 to 4 hours was adopted.

550 ° C. is the minimum heat treatment temperature required for strain relief. On the other hand, if the heat treatment temperature is higher than 750 ° C,
Phases other than the Laves phase may precipitate. Further, the heat treatment time needs to be 1 hour or more for releasing the strain, and if it exceeds 4 hours, phases other than the Laves phase may be precipitated. Desirably, heat treatment is performed at 650 to 700 ° C. for about 3 hours.

However, with the component system and solidification cooling rate shown in the above-mentioned specific embodiment, precipitation other than the C15 type Laves phase is suppressed even when heated to 750 ° C. or higher. In this case also, 550 ° C is the minimum heat treatment temperature required for strain relief.
On the other hand, if the temperature exceeds 1100 ° C, phases other than the Laves phase will precipitate, and the C15 type Laves phase single phase state cannot be maintained.
-Ni phase etc. will precipitate. Therefore, it is necessary to perform heat treatment within the temperature range of 550 to 1100 ° C. Desirably 650
A temperature range of ℃ to 1050 ℃ is preferred. The heat treatment time required at least 1 hour to release the strain, and no precipitation other than C15 type Laves phase was observed up to 20 hours in this solidification cooling rate and component system. Therefore, from 1 hour to 20
The range was up to time. However, heat treatment for a too long time is not economically desirable, and is preferably 3 hours or more and 12 hours or less.

The production of the negative electrode for Ni-hydrogen battery from the hydrogen storage alloy of the present invention can be carried out by any method known to those skilled in the art. For example, if necessary, the hydrogen storage alloy of the present invention is pulverized into a powder in an inert atmosphere, and the obtained powder is mixed with a suitable binder (eg, a resin such as polyvinyl alcohol or polytetrafluoroethylene) and water. (Or other liquid) to form a paste. A negative electrode can be manufactured by filling this paste in a nickel porous body or a nickel-plated punching metal (a perforated steel sheet), drying and press-molding it into a desired electrode shape.

[0039]

EXAMPLES Example 1 Zr _1.0 (Ni _1.2 V _0.3 Mn _0.4 Co having the composition shown in Table 1 was used.
_0.1 ) based on the total atomic ratio (b +
Table 2 shows hydrogen storage alloys with various changes of c + d + e).
It was melted by various methods with different cooling rates during solidification as shown in. The raw materials used for the melting were as shown in Table 3.

With respect to various hydrogen storage alloys having different values of (b + c + d + e) and solidification cooling rates thus obtained,
The alloy phase existing in the alloy is analyzed by X-ray diffraction, transmission electron microscopy,
And electron diffraction-EDX analysis. The results are shown in Tables 4 and 5.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

As shown in Tables 4 and 5, when the alloy composition is within the range of the present invention and the alloy is melted at a solidification cooling rate of 500 K / sec or more, in all cases, it is a C15 type Laves phase single phase. Alternatively, a hydrogen storage alloy which is a mixed phase of the Laves phase of C15 type and C14 type and is substantially completely composed of the Laves phase was obtained. That is, it does not contain a phase with a low hydrogen storage capacity (Ni solid solution, Zr-Ni phase) or an α-Zr phase (hexagonal crystal), which is difficult to store hydrogen near room temperature, so it stores a very large amount of hydrogen. It becomes possible.

On the other hand, even if the alloy composition is within the range of the present invention, if the cooling rate is less than 500 K / sec, phases other than the Laves phase are precipitated. On the other hand, if the alloy composition is AB
_For compositions outside the scope of the invention that deviate significantly from ₂ , 500
Even with rapid cooling at a cooling rate of K / sec or more, α-Zr phase and
Precipitation of Zr-Ni phase cannot be avoided.

Example 2 The hydrogen storage alloy produced in Example 1 was used as a negative electrode material for Ni.
-A hydrogen battery was constructed and its discharge capacity was measured. The outline of the test method is shown below.

(1) Structure of Electrode The molten hydrogen storage alloy was pulverized to -63 μm, and the obtained alloy powder was made into a paste with an aqueous solution of 5 wt% of polyvinyl alcohol to form a foamed nickel porous body (for example, manufactured by Sumitomo Electric Industries, Ltd.). (Celmet) was filled and dried, and then pressure-molded by a vacuum hot press to obtain a hydrogen storage alloy electrode as a negative electrode. The amount of hydrogen storage alloy used was 2 g.

(2) Structure of Battery A hydrogen storage alloy electrode manufactured as described above is used as a negative electrode, and a commercially available sintered Ni electrode of nominal 2000 mA is used as a positive electrode, and a short circuit is prevented between the positive electrode and the negative electrode. For this purpose, a 6M-KOH aqueous solution was injected as an electrolytic solution with a polyamide non-woven fabric separator intervening, and then sealed to produce a sealed test Ni-hydrogen battery. This battery was a negative electrode capacity regulation type battery in which the capacity of the positive electrode was sufficiently larger than the capacity of the negative electrode.

(3) Evaluation of battery performance 100 mA / g (25 ° C) for 5 hours at 100 mA / g (25 ° C)
The discharge capacity was measured by repeating discharge up to a terminal voltage of 0.9 V at. The discharge capacity thus measured was used as the discharge capacity of the hydrogen storage alloy used for the negative electrode. The discharge capacity at the 50th cycle after repeated charge and discharge is shown in Table 6 below.

[0052]

[Table 6]

Despite the same alloy composition, a hydrogen storage alloy rapidly solidified at a cooling rate of 500 K / sec or more according to the present invention has a higher discharge capacity than a hydrogen storage alloy having a lower cooling rate. It can be seen that
It is considered that this high discharge capacity is due to the fact that the hydrogen storage alloy of the present invention substantially consists of the Laves phase, and no phase that does not participate in hydrogen storage has appeared.

Example 3 In the present invention, since rapid solidification is adopted, strain occurs,
The crystal lattice may be distorted and the hydrogen absorption characteristics may change. In this example, the results of tests conducted on heat treatment conditions for removing this strain are shown.

Among the hydrogen storage alloys of the present invention consisting of the Laves phase only, which were solidified from the melt at a cooling rate of 500 K / sec or more by the method of the present invention in Example 1, alloy compositions D and H of Table 1 were used. The alloy of 1 was heat-treated under various conditions (temperature and time) in argon gas for the purpose of removing the strain that might have occurred in the rapid solidification. The alloy phases existing in the hydrogen storage alloy after the heat treatment were identified in the same manner as in the method described in Example 1. The results are shown in Table 7 below regarding the presence or absence of a precipitation phase (a phase other than the Laves phase).

[0056]

[Table 7]

As shown in Table 7, the heat treatment temperature is 750.
When the temperature was higher than 0 ° C. or the heat treatment time was longer than 4 hours, the other phase, the precipitation of which was suppressed by quenching, was precipitated by the heat treatment. That is, due to the strain removal, the number of phases that are not involved in hydrogen storage leading to a decrease in the amount of absorbed hydrogen (discharge capacity) was increased, which was contrary to the object of the present invention. Therefore, the heat treatment for strain relief must be performed at 550 to 750 ° C. for 1 to 4 hours.

Example 4 In order to investigate the effect of strain relief by heat treatment after rapid solidification on discharge capacity, alloy E having a composition within the range of the present invention was melted by the melting method at various cooling rates shown in Table 2. After that, the heat treatment was performed in argon gas at 650 ° C. for 3 hours, which is the heat treatment condition within the scope of the present invention. The discharge capacity of the hydrogen storage alloy thus heat-treated was measured in the same manner as in Example 2. The discharge capacity at the 50th cycle of the heat-treated material is shown in the following Table 8 together with the discharge capacity without heat treatment.

[0059]

[Table 8]

As can be seen from Table 8, when melted by rapid solidification according to the present invention, the lattice strain was released by the heat treatment and the discharge capacity was increased. On the other hand, in the case of melting by the conventional method, since the cooling rate was low, almost no increase in discharge capacity due to heat treatment was observed. As already pointed out in Example 2, the rapid solidification method according to the present invention produces a hydrogen storage alloy having a higher discharge capacity than the conventional method. Can be further increased.

Example 5 Using the raw materials shown in Table 3, Zr-containing various compositions shown in Table 9 was used.
Ni-based hydrogen storage alloy was melted. The melting method includes the method b (solidification cooling rate of 35 K / sec, conventional method) and the method e (gas atomizing method of solidification cooling rate of 5 × 10 ³ to 1 × 10 ⁴ K / sec, the method of the present invention) shown in Table 2. I went with two types. No heat treatment was carried out for strain relief after melting. The discharge capacity of the obtained hydrogen storage alloy was measured by the same method as in Example 2. Ten
The discharge capacities at 0th, 300th and 500th cycles are also shown in Table 9.

[0062]

[Table 9]

As can be seen from the results shown in Table 9, according to the present invention, the alloy composition is appropriately selected, and the solidification cooling rate at the time of smelting is set to 500 K / sec or more for rapid cooling. By suppressing the precipitation of phases, a hydrogen storage alloy having a very high discharge capacity can be obtained. This is a result of the precipitation of phases other than the Laves phase being prevented by the rapid solidification, and the capacity of the Laves phase alloy, which originally has a high discharge capacity, can be fully utilized by the present invention.

When the alloy composition within the scope of the present invention is melted by the conventional method, or when the alloy composition is outside the scope of the present invention even in the melting method of the present invention, the appearance of phases other than the Laves phase appears. Could not be prevented and the discharge capacity decreased. As compared with the case where the same alloy composition was melted by the conventional method, the capacity of the hydrogen storage alloy of the present invention was increased by at least about 10%.

Example 6 The alloy having the composition range and the solidification cooling rate in the specific embodiment according to the present invention is substantially a C15 type Laves phase even if it is subjected to a high temperature heat treatment, and it is possible to secure a high discharge capacity. Tested to confirm. Table 10 shows the alloy composition used in the examples. Table 11 shows the melting method used in the examples.

(1) Heat treatment conditions and existing phases In the alloys having the compositions of K, L, M, N, O and P shown in Table 10, the relationship between the heat treatment conditions and the existing phases that can be confirmed was investigated.
The existence phase was confirmed by X-ray diffraction and an analytical transmission electron microscope. All of the examples shown in Table 12 belong to the scope of the present invention, but if 1.95 <b + c + d + e ≦ 2.05 and the cooling rate during solidification is 1.0 × 10 ³ K / sec or more, 55
No precipitation phase was observed even after heat treatment at 0 to 1100 ° C. for 1 to 20 hours, and it was a C15 type Laves phase single phase in the as-cast state. That is, in the range shown in the specific embodiment of the present invention, even if the heat treatment is performed up to a high temperature (up to 1100 ° C.), it is substantially a C15 type Laves phase single phase, and strain relief annealing is performed by the heat treatment of the present invention. An alloy consisting essentially of the C15 type Laves phase is obtained.

(2) Investigation of electrode characteristics The electrode characteristics of the alloy obtained as described above according to the present invention were investigated. The composition used in this example is as shown in Table 10. As a conventional method, the melting method shown in b of Table 2 is used.
Melt at a solidification cooling rate of K / sec, then in an Ar atmosphere
An alloy that was heat-treated at 1100 ° C for 20 hours was used. Further, as the method of the present invention, an Ar gas atomizing method capable of realizing a solidification cooling rate of 5 × 10 ³ K / sec to 1 × 10 ⁴ K / sec is used, and then an alloy is heat-treated at 1100 ° C. × 20 hr in an Ar atmosphere. Was used. An electrode was formed from the obtained alloy by the method described in Example 2 and its electrode characteristics were evaluated.

Table 13 shows the evaluation results. Both are compositions included in the specific embodiment of the present invention, but 1100 ° C. × 20
After the hr heat treatment, the alloys contained in this composition range have higher discharge capacity than the conventional alloys. On the other hand, the alloys of compositions K, P, and Q have the same discharge capacity as the solidification cooling rate of 35 K / sec which is the conventional method even if the solidification cooling rate in the present invention is used. The cause of this is as shown in Table 12.
By performing heat treatment at 1100 ° C for 20 hours, it is not necessary α for the alloy that was in the C15 type Laves phase state after being solidified by rapid solidification.
This is because precipitation of -Zr phase, Zr-Ni phase, etc. occurred.

Above all, within the scope of the present invention, particularly within the composition range shown as the above-mentioned specific embodiment and 1.0 × 10 ³ K
550 to 1100 for solidification cooling rate of / sec or more
Even if the heat treatment is carried out at a temperature of 1 ° C. for 1 to 20 hours, the alloy is substantially only the C15 type Laves phase, and a remarkably higher capacity than the alloy obtained by the usual melting method can be obtained. Therefore, even if an electrode is manufactured by sintering to increase the capacity, if the sintering condition is lower than 1100 ° C. × 20 hours for a short time, the electrode will be substantially only a C15 type Laves phase. There is a possibility that a higher capacity than that of the electrode obtained by using the alloy powder obtained by the melting method can be obtained.

[0070]

[Table 10]

[0071]

[Table 11]

[0072]

[Table 12]

[0073]

[Table 13]

Further, the hydrogen storage alloy of the present invention maintained a high capacity after repeated charge and discharge, and showed a high discharge capacity of 320 mAh / g or more after repeated charge and discharge of 500 cycles.

[0075]

As is clear from the results of the above examples, by using the hydrogen storage alloy according to the present invention as the cathode of a Ni-hydrogen secondary battery, a hydrogen storage alloy produced by a conventional melting method can be obtained. Higher discharge capacity is obtained compared to when used,
Moreover, 320 mA even after 500 cycles of charge and discharge.
It is possible to realize a Ni-hydrogen battery having a long life and a high discharge capacity capable of maintaining a high discharge capacity of h / g or more.

The Ni-hydrogen secondary battery using the hydrogen-absorbing alloy of the present invention is a Ni-hydrogen battery using the rare earth-based hydrogen-absorbing alloy currently in practical use, and other Laves phase-based batteries currently under development. The discharge capacity is higher than any of the Ni-hydrogen batteries using the hydrogen storage alloy of
It is a technology that can be expected to be applied to electricity storage at night and batteries for electric vehicles, which are applications that can be charged with a particularly high electric capacity, and can contribute to energy problems and global environmental conservation.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location H01M 4/38 A 8520-4K (72) Inventor Koichi Kamishiro 4-533 Kitahama, Chuo-ku, Osaka City No. Sumitomo Metal Industries Co., Ltd. (72) Inventor Kouki Takeshita 4-53-3 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Co., Ltd.

Claims (6)

[Claims] 1. The formula: Ti _a Zr _1-a (Ni _b V _c Mn _d M
_e ) (wherein, M = Cr, Fe, Co, Mo, W, Al, Cu and Nb, and one or more elements selected from the group of 0 ≦
a <0.60, 1.00 <b <1.50, 0.10 <c <0.50, 0.10 <d
<0.70, 0.05 <e <0.30, 1.90 ≦ b + c + d + e ≦ 2.3
A hydrogen storage alloy having a composition represented by 0) and being substantially composed only of a Laves phase. 2. When the alloy of the composition according to claim 1 is melted,
The method for producing a hydrogen storage alloy according to claim 1, wherein the alloy is solidified by rapidly cooling it from a melt state at a cooling rate of 500 K / sec or more. 3. The solidified alloy according to claim 2, wherein the obtained alloy is subjected to heat treatment at 550 to 750 ° C. for 1 to 4 hours in an inert gas or vacuum.
A method for producing the hydrogen storage alloy described. 4. The formula: Ti _a Zr _1-a (Ni _b V _c Mn _d M
_e ) (wherein, M = Cr, Fe, Co, Mo, W, Al, Cu and Nb, and one or more elements selected from the group of 0 ≦
a <0.20, 1.00 <b <1.50, 0.10 <c <0.50, 0.10 <d
<0.70, 0.05 <e <0.30, 1.95 <b + c + d + e ≦ 2.0
When melting the alloy with the composition represented by 5),
A method for producing a hydrogen storage alloy, which comprises substantially only C15 type Laves phase, characterized by rapidly cooling at a cooling rate of 1.0 × 10 ³ K / sec or more to solidify the alloy. 5. A substantially C15 type Laves, characterized in that, after solidification of the alloy according to claim 4, the obtained alloy is subjected to heat treatment at 550 to 1100 ° C. for 1 to 20 hours in an inert gas or vacuum. A method for producing a hydrogen storage alloy composed of only phases. 6. A negative electrode for a Ni-hydrogen battery, which uses the hydrogen storage alloy according to claim 1 as a negative electrode active material.