JPH10102172A - Hydrogen storage alloy, its production, and nickel-hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hydrogen storage alloy for battery, excellent in hydrogen occlusion characteristic and corrosion resistance, by providing a pulverized powder of a rapidly solidified alloy having a specific composition and also specifying oxygen content in the pulverized powder. SOLUTION: This hydrogen storage alloy is composed of a pulverized powder of a rapidly solidified alloy having a composition represented by general formula ANia Mb M'c Td , and oxygen content in this pulverized powder is regulated to 0.01-0.4wt.%. At this time, A consists of La, Ce, Pr, Nd, and Y, and further, the contents of La, Ce, Pr, Nd, and Y in A are regulated, by weight, to 25-85%, 5-45%, 0-15%, 0-20%, and 0-10%, respectively. M is at least one element among Co, Fe, and Cu. M' is one element among Mn, Al, Si, and Zn. T is one element among B, S, Cr, Ga, Ge, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, and W. Moreover, the symbols (a), (b), (c), and (d) satisfy, by atomic ratio, 3.1<=a<=4.0, 0.4<=b<=1.2, 0.3<=c<=1.2, 0<=d<=0.2, and 4.7<=a+b+c+d<=5.1, respectively. By this method, the nickel-hydrogen secondary battery with long service life can be provided.

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, a method for producing the same, and a nickel-metal hydride battery using the alloy, and particularly to a high electrode capacity (battery capacity) when the alloy is used for a negative electrode of the battery. Also, the present invention relates to a hydrogen storage alloy capable of satisfying both long life characteristics (long cycle characteristics) that can withstand repeated use, a method for producing the same, and a nickel-metal hydride secondary battery.

[0002]

2. Description of the Related Art Unlike conventional fossil fuels such as petroleum-based fuels, hydrogen, which is converted into H ₂ O without generating harmful gases even when burned, has attracted attention as a clean energy source.
In order to realize this specific use of hydrogen, a method of storing and transporting hydrogen on a practical scale is important. However, when hydrogen is stored as a gas in a normal cylinder, the volume of the cylinder becomes excessive.On the other hand, when hydrogen is stored at a very low temperature as a liquid, auxiliary equipment such as a refrigeration facility is required. Anyway, there is a problem that the storage equipment becomes large. Therefore, a hydrogen storage alloy that absorbs hydrogen as a metal oxide by reacting with hydrogen and releases hydrogen by heating or the like has attracted attention as a means for storing and transporting hydrogen.
The application range of hydrogen storage alloys is wide, and in addition to the above-mentioned hydrogen storage means and transport means, fuel sources for hydrogen-powered vehicles, negative electrode materials for secondary batteries, hydrogen separation / recovery / purification equipment, heat pumps, cooling / heating systems, refrigeration Applications in various fields such as systems, heat storage devices, actuators, compressors, temperature sensors, and catalysts are being studied. In particular, applications of the hydrogen storage alloy as a negative electrode material of a secondary battery are steadily expanding.

In other words, recent advances in electronic technology have led to power savings, and advances in packaging technology have led to smaller and more portable electronic devices that could not be expected in the past. Accordingly, there is a particular demand for a secondary battery as a power source of the electronic device to have a high capacity, a long life, and a stable discharge current. For example, in OA equipment, telephones, and AV equipment that are becoming more personalized and portable, there is a demand for the development of high-performance batteries, particularly for the purpose of reducing the size and weight and extending the use time of cordless equipment. As a battery corresponding to such a demand, a non-sintered nickel cadmium battery having a three-dimensional structure using an electrode substrate of a conventional sintered nickel cadmium battery has been developed, but a remarkable capacity increase has not been achieved. .

Therefore, in recent years, an alkaline secondary battery (nickel-metal hydride secondary battery) using a structure in which a hydrogen storage alloy powder is fixed to a current collector as a negative electrode has been proposed and attracted attention. The negative electrode used in this nickel-metal hydride battery is
Generally, it is manufactured by the following procedure. That is, after the hydrogen storage alloy is melted by a high-frequency melting method or an arc melting method, the mixture is cooled and pulverized, and a conductive agent and a binder are added to the obtained pulverized powder to form a kneaded material, and the kneaded material is collected. It is manufactured by coating or crimping on an electric body. A negative electrode using this hydrogen storage alloy can increase the effective energy density per unit weight or unit volume as compared with cadmium, which is a conventional representative negative electrode material for an alkaline secondary battery. In addition to being able to increase the capacity of, it is characterized by low toxicity and low risk of environmental pollution.

[0005] However, the negative electrode containing the hydrogen storage alloy is immersed in a concentrated alkaline aqueous solution as an electrolytic solution in a state where the negative electrode is incorporated in a secondary battery, and is exposed to oxygen generated from the positive electrode particularly during overcharge. In addition, the hydrogen storage alloy is corroded and the electrode characteristics are likely to deteriorate. Further, at the time of charging and discharging, the volume expands and contracts in accordance with the occlusion and release of hydrogen in the hydrogen storage alloy, so that the hydrogen storage alloy cracks and the hydrogen storage alloy powder becomes finer. As the pulverization of the hydrogen storage alloy progresses, the specific surface area of the hydrogen storage alloy increases at an accelerated rate, so that the ratio of the area of the surface of the hydrogen storage alloy deteriorated by the alkaline electrolyte increases. Moreover, since the conductivity between the hydrogen storage alloy powder and the current collector also deteriorates,
The cycle life is reduced and the electrode characteristics are also deteriorated.

Therefore, in order to solve the above-mentioned problem, the hydrogen storage alloy is diversified, or a nickel thin film or a copper thin film is adhered to the surface of the hydrogen storage alloy powder or the negative electrode including the hydrogen storage alloy by plating, vapor deposition, or the like. Improve corrosion resistance by preventing direct contact with the electrolyte, prevent mechanical cracks by increasing mechanical strength, or suppress deterioration of the hydrogen storage alloy surface by immersing it in an alkaline solution and drying it. However, it has not always been possible to achieve a sufficient improvement, and in some cases, the electrode capacity is reduced.

[0007] As the hydrogen storage alloy used for the alkaline secondary battery, there is AB ₅ type alloy represented by LaNi _5. The negative electrode using the alloy system having the hexagonal structure has a more effective battery per unit weight or unit volume than the case of using cadmium which is a conventional representative negative electrode material for an alkaline secondary battery. Energy density can be increased, the battery capacity can be increased, and there is little risk of environmental pollution such as cadmium pollution, and the battery characteristics are good. .
Also, a battery using the above AB ₅ alloy has an advantage that a large current discharge is possible.

[0008]

[SUMMARY OF THE INVENTION However, for example, the electrode capacitance of the Lm-Ni-Co-Al alloy (Lm is La enriched misch metal) consisting of AB ₅ hydrogen storage alloy, slightly the current 300 mAh / g It is more than
The cycle life due to charging and discharging is about 200 cycles. Also, a battery using the above AB ₅ alloy has an advantage that the discharge current can be set high. However, it has not yet reached a stage that satisfies both the electrode capacity and the cycle life, which are the current technical requirements.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. When used as a negative electrode material of a battery, a high electrode capacity can be obtained, and hydrogen capable of prolonging the life of the battery can be realized. An object of the present invention is to provide a storage alloy, a method for producing the same, and a nickel-metal hydride secondary battery using the alloy.

[0010]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies on a hydrogen storage alloy suitable for increasing the capacity and extending the life of a battery. As a result, quench the molten alloy of a specific composition so as to form an intermetallic compound which is based on AB ₅ type alloy having a so-called CaCu ₅ type crystal structure, a further oxygen content of the alloy powder obtained by pulverizing By properly controlling, it is possible to obtain a hydrogen storage alloy with excellent hydrogen storage characteristics and corrosion resistance, and when this alloy is used as a negative electrode material, nickel-hydrogen that balances electrode capacity, life characteristics, and temperature characteristics of capacity The knowledge that a secondary battery can be obtained was obtained. In particular, it has been found from experiments that it is extremely effective to appropriately control the oxygen content of a rapidly cooled high-capacity alloy to prolong its life.
The present invention has been completed based on the above findings.

[0011] That the hydrogen storage alloy according to the present invention have the general formula _{ANi a M b M 'c T} d ( where, A is La, Ce,
It consists of Pr, Nd and Y, the La content in A is 25-85% by weight, the Ce content is 5-45%, Pr
The content is 0 to 15%, the Nd content is 0 to 20%, and the Y content is 0 to 10%, while M is Co, Fe and Cu.
M ′ is at least one element selected from
at least one selected from n, Al, Si and Zn
T is B, S, Cr, Ga, Ge, M
at least one element selected from the group consisting of o, Ru, Rh, Pd, Ag, In, Sn, Sb and W;
b, c, and d are 3.1 ≦ a ≦ 4.0 in atomic ratio, respectively.
0.4 ≦ b ≦ 1.2, 0.3 ≦ c ≦ 1.2, 0 ≦ d ≦
0.2, 4.7 ≦ a + b + c + d ≦ 5.1. ), Which is characterized by comprising a quenched alloy pulverized powder having a composition represented by the formula (1), wherein the pulverized powder has an oxygen content of 0.01 to 0.4% by weight. The average crystal grain size of the quenched alloy is 1 to 50.
It is good to be in the range of μm.

The method for producing a hydrogen storage alloy according to the present invention comprises:
A step of bringing the molten alloy having the above-mentioned predetermined composition into contact with a cooling medium to rapidly cool and solidify the alloy at a cooling rate of 100 ° C./sec or more; in a step of heat treatment, and a step of adjusting the grinding by grinding the quenched alloy heat treated in a non-oxidizing atmosphere powder, setting the vacuum degree of the atmosphere during the heat treatment process starts 10 ^-6 to 10 ² Torr After that, the oxygen content of the quenched alloy is adjusted to 0.01 to 0.4% by weight by performing heat treatment as it is or in a non-oxidizing atmosphere. By the rapid solidification treatment, the additional components are uniformly dispersed in the alloy structure, and the grain boundary precipitation phase is also refined, so that the battery life can be extended.

In order to eliminate internal strain in the alloy prepared by the above-mentioned quenching method and homogenize the alloy, the alloy is heated at a temperature of 600 to 1000 ° C. for 0.5 to 10 hours in a non-oxidizing atmosphere. It is preferable to perform a heat treatment for homogenization.
The degree of vacuum of the atmosphere at the start of this heat treatment step is 10 ^-6 to 1
O ² Torr, and by further adjusting the temperature and time of the heat treatment, the oxygen content of the quenched alloy is reduced to 0.01 to
It becomes possible to control to the range of 0.4% by weight.

Further, the nickel-metal hydride secondary battery according to the present invention comprises a separator having electrical insulation interposed between a negative electrode containing a hydrogen storage alloy having the above-mentioned predetermined composition and a positive electrode containing nickel oxide. It is housed in a closed container, and the closed container is filled with an alkaline electrolyte.

In the hydrogen-absorbing alloy according to the present invention, A in the general formula is an element having a hydrogen-absorbing ability which is the basis for increasing the capacity of a battery, and its content is determined in consideration of the balance between capacity and life. Therefore, it is determined by the ratio with the a + b + c + d value. A is a misch metal composed of La, Ce, Pr, Nd, and Y, and La is effective particularly for achieving high capacity. La content in the entire A component as a misch metal is 25 to 85% by weight, Ce content is 5 to 45% by weight, Pr content is 0 to 15% by weight, N
The d content is 0 to 20% by weight, and the Y content is 0 to 10% by weight.
Range. That is, when the La content in the misch metal is less than 25% by weight, the capacity of the battery is not sufficiently increased, while when the La content exceeds 85% by weight, the cycle life is shortened. When the Ce content is less than 5% by weight, the cycle life is short, while when it exceeds 45% by weight, it is difficult to increase the capacity. If the Pr content exceeds 15% by weight or the Y content exceeds 10% by weight, the life characteristics become insufficient. Therefore, the Pr content and the Y content in the misch metal are each 15% by weight. Hereinafter, the content is 10% by weight or less. If the Nd content exceeds 20% by weight, the life characteristics become insufficient, so that the Nd content is set in the range of 0 to 20% by weight.

In addition, components such as Ni, M, M ', and T are
It is a component that has an effect on catalytic action at the alloy interface, adjustment of hydrogen equilibrium pressure, and improvement of life characteristics.
+ B + c + d is set in the range of 4.7 to 5.1. When a + b + c + d is less than 4.7, the above-mentioned improvement effect is insufficient. On the other hand, when the atomic ratio exceeds 5.1, the battery capacity becomes too small, and it is difficult to satisfy the basic required characteristics as a battery. is there.

Among the above components, Ni is a basic element for absorbing and releasing hydrogen by forming a rare earth-Ni hydrogen storage alloy having excellent corrosion resistance by being alloyed with the rare earth component (A). , And the atomic ratio a is in the range of 3.1 to 4.0. The hydrogen storage equilibrium pressure in the sealed battery can be appropriately set within the above range of the atomic ratio of Ni, but Ni in the range of 3.3 to 3.9 can be properly set.
The addition amount is more preferable.

M is at least one element selected from the group consisting of Co, Fe and Cu. All of these elements improve the corrosion resistance of the alloy and reduce the occurrence of cracks due to the expansion of the lattice during hydrogen absorption. It is an element that effectively suppresses and exerts a life improving effect. When the addition amount b of these M components is less than 0.4, the above-mentioned improvement effect is insufficient, while when the addition amount exceeds 1.2, the capacity is significantly reduced.

M 'is at least one element selected from Mn, Al, Si and Zn, all of which contribute to improving the life of the alloy. When the added amount C of these M 'components is less than 0.3, the above-mentioned improvement effect is hardly exhibited, while when the added amount C exceeds 1.2, the hydrogen equilibrium pressure becomes too low and the capacity also decreases. It is not practical.

Further, T is B, S, Cr, Ga, Ge, M
o, Ru, Rh, Pd, Ag, In, Sn, Sb, W, and at least one of these elements is effective for improving the life of the alloy. When the addition amount d of these T components exceeds 0.2, the capacity is reduced.

The general formula A N of the hydrogen storage alloy according to the present invention
'In _c T _d, the A-site to form a hydride, does not form a hydride _{Ni a M b M' i a} M b M c
The T _d moiety and B site, and the a + b + c + d has a X, a hydrogen-absorbing alloy according to the present invention is represented by the general formula AB _X, the composition ratio X of the B site in the range of 4.7 to 5.1 it is set AB ₅ type alloy. Composition ratio X of B site
Is out of the above range, a phase other than AB _{4.7 to 5.1} (for example, a phase composed of AB, AB ₃ , A ₂ B _{7 and the} like, and a phase composed of a single element constituting the B site [hereinafter referred to as a second phase]) ) Increases.

In the alloy, the second phase other than the phase consisting of AB _X is used.
When the number of phases increases, the hydrogen-absorbing alloy contains the second phase 2
The rate at which alloy phases of different kinds or more in contact with each other increases. The interface between such alloy phases having different compositions has low mechanical strength, and cracks are likely to occur from this interface as a starting point for absorbing and releasing hydrogen.

Further, segregation is apt to occur at the interface, and corrosion of the hydrogen storage alloy is liable to occur starting from the segregated substance. In addition, the second phase may have A
Small storage amount of hydrogen as compared to the B _X, when using the second phase is often an alloy as the electrode, the electrode capacity per unit volume is lowered. In any case, when the hydrogen storage alloy is used as the electrode material, the electrode capacity and the life are reduced.

After all, the reason for limiting the value of X is as follows. When X is less than the lower limit (4.7), corrosion during charging and discharging of the battery is small, and it is not possible to obtain a hydrogen storage alloy that is difficult to crack or pulverize. On the other hand, when the X exceeds the upper limit (5.1), the formation of the second phase is recognized depending on an ordinary industrially feasible alloy manufacturing method, and the characteristics of the hydrogen storage alloy cannot be improved. Therefore, the value of X is set in the range of 4.7 to 5.1.

Of the M ′ component, Mn is effective in increasing the capacity of the negative electrode containing a hydrogen storage alloy, improving corrosion resistance by accelerating the formation of a passive film, and adjusting the decrease in hydrogen storage / release pressure (equilibrium pressure). Al, like Mn, has the effect of lowering the storage / release pressure (dissociation pressure) of hydrogen to an operation pressure suitable for a sealed battery and can increase durability. When the content of Mn and Al is less than 0.3 in atomic ratio, the above-mentioned improvement effect becomes insufficient. On the other hand, when the content of Mn and Al exceeds 1.2, the capacity is greatly reduced. I will. Therefore, the content of the M 'component such as Mn and Al is set in the range of 0.3 to 1.2.

Further, Co as the M component is effective in improving the corrosion resistance of the alloy against an electrolytic solution or the like, the pulverization of the alloy is remarkably suppressed, and the life characteristics of the battery are improved. When the amount of Co added is increased, the cycle life is improved, but the electrode capacity tends to decrease. Therefore, it is necessary to optimize the amount of Co added according to the use of the battery. The amount of Co added is related to the composition ratio of the rare earth element as the A-site component, but the atomic ratio of the composition range of the A-site component specified in the present invention is in the range of 0.4 to 1.2. It is suitable.

When the amount of Co is less than 0.4 in atomic ratio, the effect of improving the life is insufficient. On the other hand, when it exceeds 1.0, the capacity is significantly reduced. It is difficult to satisfy the two major required characteristics of the battery. From the above-mentioned viewpoints, it is desirable that Co and Mn are each added in a predetermined amount or more in atomic ratio as the B component of the hydrogen storage alloy of the present invention.

In addition, the hydrogen storage alloy according to the present invention includes:
Elements such as Pb, C, N, F and Cl may be contained as impurities as long as the properties of the alloy of the present invention are not impaired. The content of each of these impurities is 600
It is preferably in the range of 0 ppm or less. More preferably 5000 ppm or less, even more preferably 4000p
pm or less is good.

The hydrogen storage alloy of the present invention is obtained by rapidly cooling a molten alloy having the above-mentioned predetermined composition, further heat-treating and then pulverizing. The oxygen content of the pulverized powder is in the range of 0.01 to 0.4% by weight. The oxygen content affects the capacity and life when the alloy is used as a negative electrode material of a battery. That is, when the oxygen content is less than 0.01% by weight,
The coating thickness or coating area of oxides such as rare earths formed on the alloy surface becomes too small, and when the alloy comes into contact with a strong alkaline electrolyte such as KOH, corrosion tends to progress, shortening the battery life. Become. Particularly in a rapidly cooled alloy having a fine crystal grain size, intergranular corrosion tends to be promoted. On the other hand, when the oxygen content exceeds 0.4% by weight, the coating thickness or the coating area of the oxide becomes excessively large, and it becomes difficult to transmit hydrogen to the alloy, and the capacity of the battery is easily reduced.

Therefore, by setting the oxygen content in the pulverized powder after the heat treatment of the quenched alloy in the range of 0.01 to 0.4% by weight, a protective film having an appropriate thickness or an appropriate area can be obtained. Are formed, corrosion is suppressed, and the life can be extended, and a high-capacity battery can be obtained because the protective film does not inhibit the permeation of hydrogen. A more preferable range of the oxygen content is 0.03 to 0.3% by weight.

The oxygen content of the above alloy is increased by the surface oxidation of the alloy in the quenching, heat treatment or pulverization process of the molten alloy, but it greatly depends on the atmosphere during the quenching process and the temperature and time in the heat treatment process. I do.

Usually, the quenching treatment is performed in an inert gas atmosphere. However, the oxygen content can be adjusted by the degree of evacuation performed in advance. The heat treatment is also performed in an inert gas atmosphere, but the oxygen content should be adjusted and controlled according to the degree of evacuation (vacuum in the heating furnace at the start of the heat treatment) and the heat treatment conditions (temperature and time). Is more preferred. The degree of vacuum of the atmosphere is 10 ^-6 to 10 ² To
rr, but preferably 10 ^-5 to 10 ¹ Torr
Range.

In the hydrogen storage alloy according to the present invention, since the molten alloy having a predetermined composition is prepared by quenching, the crystal grains constituting the alloy structure are refined, and are necessary for storing and releasing hydrogen. The route is sufficiently secured. Then, the occlusion and release of hydrogen easily proceed through the route. That is, in the hydrogen transfer method, the ratio depending on the diffusion in the alloy, which is susceptible to the temperature, is reduced.
Under the following low-temperature conditions and under high-temperature conditions exceeding 60 ° C., it is considered that a decrease in capacity is effectively suppressed, and as a result, a hydrogen storage alloy with low temperature dependence can be obtained.

The hydrogen storage alloy according to the present invention is prepared by heating a raw material mixture prepared so as to have a predetermined composition in a high-frequency induction furnace or the like to prepare a molten alloy. The molten alloy is formed by cooling and solidifying the molten alloy using a rotating disk method, a centrifugal spray method, a single roll method, a twin roll method, or the like. When cooling the molten alloy, the cooling rate should be 10
By setting the temperature to 0 ° C./sec or more, preferably 300 ° C./sec or more, more preferably 1800 ° C./sec or more, even when La is contained in a relatively large amount as a misch metal, the structure is uniform, An alloy with less segregation can be obtained. By performing the cooling and solidifying treatment and the heat treatment described later, a high-capacity and long-life hydrogen storage alloy can be obtained.

Further, when the alloy melt is injected onto a cooling body moving at a high speed to form a flake-like alloy having a thickness of about 10 to 500 μm, a hydrogen storage alloy comprising fine crystal grains of about 1 to 50 μm is obtained. Thus, a high-capacity and long-life battery can be formed. Further, the refinement of the crystal grains increases the hydrogen absorption rate of the alloy, and the rise of the discharge capacity in a secondary battery becomes faster.

Further, as a method of cooling and solidifying the molten alloy, a molten metal quenching method for rapidly cooling the molten molten alloy such as a gas atomizing method, a rotating disk method, a centrifugal spraying method, a single roll method, a twin roll method, etc. is used. The material and surface properties of the cooling roll, the number of revolutions of the cooling roll (peripheral speed of the running surface), the temperature of the molten metal, the temperature of the cooling water for the cooling roll, the gas type in the cooling chamber, the pressure, the diameter of the molten metal injection nozzle, the injection amount By optimizing the manufacturing conditions, the alloy can be manufactured stably in large quantities.

Single Roll Method FIG. 1 shows an apparatus for producing a hydrogen storage alloy by a single roll method. This manufacturing apparatus stores a cooling roll 5 having a diameter of about 400 mm, which is excellent in heat conductivity such as copper and nickel, and a hydrogen storage alloy melt 3 supplied from a ladle 2 and then sprays the same onto the running surface of the cooling roll 5. And a pouring nozzle 4 to be used. The cooling roll 5 and the like are housed in a cooling chamber 1 adjusted to an inert gas atmosphere. The rotation speed of the cooling roll 5 depends on the wettability and the cooling speed of the cooling roll 5 and the injection amount of the hydrogen storage alloy melt 3, but is generally set to 100 to 5000 rpm.

In the manufacturing apparatus shown in FIG. 1 described above, the molten hydrogen storage alloy 3 supplied from the ladle 2
When the molten alloy is further sprayed onto the running surface of the cooling roll 5, the alloy melt solidifies from the surface in contact with the cooling roll 5, and crystal growth starts,
The solidification is completely completed before the solidification is removed from the cooling roll 5. Thereafter, the cooling proceeds further while flying in the cooling chamber 1, and the hydrogen storage alloy 6 with less segregation and a uniform crystal growth direction is manufactured.

The twin roll method Figure 2 is a hydrogen storage alloy manufacturing apparatus according twin roll method. This manufacturing apparatus includes one or more pairs of cooling rolls 5 a, which are arranged in the cooling chamber 1 such that respective running surfaces face each other.
5b, a melting furnace 7 for melting the raw material metal to prepare a hydrogen storage alloy melt 3, and a hydrogen storage alloy melt 3 from the melting furnace 7.
Is provided between the cooling rolls 5a and 5b via a tundish 8.

The cooling rolls 5a and 5b are formed of a material having excellent heat conductivity, such as copper or iron, and have a diameter of about 300 mm. The cooling rolls 5a and 5b are 0 to 0.5
100 to 200 while maintaining a small gap d of about mm.
It rotates at a high speed of about 0 rpm. In addition, as a cooling roll, as shown in FIG. 2, the running surface is parallel, and the running surface has a U-shaped or V-shaped cross-sectional shape.
A so-called mold roll can also be employed. Further, if the gap d between the cooling rolls 5a and 5b is excessively large, a cooling direction is not uniform, and as a result, a hydrogen storage alloy in which the crystal growth direction is not uniform is manufactured.

In the manufacturing apparatus shown in FIG. 2, the molten hydrogen storage alloy 3 is poured from the pouring nozzle 4 into the cooling rolls 5a,
When the molten hydrogen storage alloy is injected in the gap direction of 5b, solidification and crystal growth of the hydrogen storage alloy melt start from the sides in contact with the cooling rolls 5a, 5b on both sides, and complete solidification by the time the metal is separated from the cooling rolls 5a, 5b. Thereafter, the cooling proceeds further while flying in the cooling chamber 1, and the hydrogen storage alloy 6 with less segregation and a uniform crystal growth direction is manufactured.

When a ribbon-shaped, flake-shaped or granular hydrogen-absorbing alloy is produced by using the above-mentioned cooling and solidifying method, the temperature gradient in the sample during solidification of the molten alloy, the material of the cooling roll and the rotating disk, An equiaxed crystal structure and a columnar crystal structure are formed in the alloy depending on conditions such as the supply amount of the molten alloy.

In the manufacturing process of the alloy particles, 100
When the molten metal is quenched at a cooling rate of at least 300 ° C./sec, preferably at least 300 ° C./sec, more preferably at least 1800 ° C./sec to produce a hydrogen storage alloy, the crystal grains constituting the alloy have a size of 1 to 200 μm. The degree of fineness is increased, the alloy strength is increased, and the disorder of the grain boundaries is reduced. Therefore, the amount of hydrogen absorbed is increased, and the electrode capacity can be increased.

By the above-mentioned molten metal quenching treatment, a hydrogen storage alloy having a columnar crystal structure developed at least partially can be formed. Here, the columnar crystal refers to a columnar crystal grain having a ratio of minor axis to major axis (aspect ratio) of 1: 2 or more. In the above columnar crystal structure, unlike the equiaxed crystal structure, the crystal orientation is uniform, so that the disorder of the grain boundaries is small, the amount of hydrogen occlusion is increased, and the electrode capacity can be increased. Confirmed by That is, in the columnar crystal structure, a hydrogen molecule or a hydrogen atom path is formed along the interface, so that hydrogen is easily absorbed or released into the alloy, and the electrode capacity is increased. Further, segregation in the columnar crystal structure is extremely reduced. Therefore, formation of a local battery due to segregation is small, and a reduction in life due to miniaturization of the alloy structure can be effectively prevented.

In the alloy prepared by the cooling and solidification method as described above, internal strain is easily generated, and when the alloy is used as a negative electrode material, the electrode capacity and the life are often reduced.

Therefore, the alloy prepared by cooling and solidifying is
It is desirable to perform a homogenizing heat treatment at 0.5 to 10 hours at a temperature of 600 to 1000 ° C. in advance.

When the temperature of the homogenizing heat treatment is lower than 600 ° C., it is difficult to remove internal strain, while the temperature is lower than 10 ° C.
When the temperature is higher than 00 ° C., a composition change occurs due to oxidation or evaporation of the rare earth element or the group IVa element. Therefore, the heat treatment temperature is set in the range of 600 to 1000 ° C.
Particularly, in order to improve the electrode characteristics, 700 to 950 ° C.
Is preferable.

When the heat treatment time is less than 0.5 hours, the effect of removing internal strain is small and the variation in characteristics is large. On the other hand, if the treatment time is as long as more than 10 hours, the progress of oxidation becomes remarkable. Therefore, from the viewpoint of production efficiency, 0.5 to 10 hours is preferable.

The heat treatment atmosphere is preferably an inert gas atmosphere such as Ar or a vacuum in order to prevent high-temperature oxidation of the hydrogen storage alloy.

By performing the homogenizing heat treatment under the above conditions, the internal strain can be effectively removed while maintaining the homogeneity of the alloy, and the electrode capacity and life can be further increased.

At the start of the heat treatment step, vacuuming is performed to set the degree of vacuum in the heating furnace to about 10 ⁻⁶ to 10 ² Torr, and the heat treatment temperature and time are adjusted to obtain a rapidly cooled alloy. The oxygen content can be controlled in the range from 0.01 to 0.4% by weight.

By performing the following surface treatment on the hydrogen storage alloy prepared as described above, the electrode characteristics can be improved when the alloy is used as an electrode material. That is, by performing a surface treatment such as an acid treatment, an alkali treatment, and a fluoride treatment, the activity and corrosion resistance of the alloy surface can be increased. Among the above surface treatments, an alkali treatment using KOH or NaOH is particularly effective. These surface treatments may be performed in a state where the solidified solid remains rapidly quenched. Further, it may be carried out in a state after pulverization or in a state during pulverization.

Next, a nickel-metal hydride secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention using the above-mentioned battery hydrogen storage alloy as a negative electrode active material will be described with reference to FIG.

[0054] nickel-hydrogen secondary battery according to the present invention, between the positive electrode 12 including the negative electrode 11 and the nickel oxide comprising the formula ANi _a M _b M 'battery hydrogen storage alloy represented by _c T _d Is housed in a closed container 14 with a separator 13 having electrical insulation interposed therebetween, and the closed container 14 is filled with an alkaline electrolyte.

That is, the hydrogen storage alloy electrode (negative electrode) 11 containing a hydrogen storage alloy is a non-sintered nickel electrode (positive electrode).
12 are wound spirally with a separator 13 interposed therebetween, and housed in a bottomed cylindrical container 14. The alkaline electrolyte is contained in the container 14. A circular sealing plate 16 having a hole 15 in the center is arranged at the upper opening of the container 14. The ring-shaped insulating gasket 17 is disposed between the peripheral edge of the sealing plate 16 and the inner surface of the upper opening of the container 14, and is sealed to the container 14 by caulking to reduce the diameter of the upper opening inward. Board 1
6 is hermetically fixed via the gasket 17.
One end of the positive electrode lead 18 is connected to the positive electrode 12, and the other end is connected to the lower surface of the sealing plate 16. The cap-shaped positive electrode terminal 19 is provided on the sealing plate 16 with the hole 15.
It is attached to cover. Rubber safety valve 20
Is disposed so as to close the hole 15 in a space surrounded by the sealing plate 16 and the positive electrode terminal 19. The insulating tube 21 is used to fix the positive electrode terminal 19 and the flange paper 22 placed on the upper end of the container 14.
It is attached near the upper end of.

As the hydrogen storage alloy electrode 11, a paste type and a non-paste type described below are used. (1) The paste-type hydrogen storage alloy electrode is prepared by mixing a hydrogen storage alloy powder obtained by pulverizing the above-mentioned hydrogen storage alloy, a polymer binder, and a conductive powder to be added as necessary. The paste is applied to a conductive substrate serving as a current collector, filled, dried, and then subjected to a roller press or the like. (2) The non-paste type hydrogen storage alloy electrode is obtained by stirring the above-mentioned hydrogen storage alloy powder, the polymer binder, and the conductive powder to be added as required, and spraying the mixed powder on the conductive substrate serving as a current collector. It is produced by applying a roller press or the like.

As a method of pulverizing the hydrogen storage alloy, for example, a mechanical pulverization method such as a ball mill, a pulverizer, a jet mill or the like, or a method in which high-pressure hydrogen is occluded and released and pulverized by volume expansion at that time, are employed. .

As the polymer binder, for example, sodium polyacrylate, polytetrafluoroethylene (PTF)
E), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and the like. Such a polymer binder is preferably blended in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the hydrogen storage alloy. However, when preparing the non-paste type hydrogen storage alloy electrode of the above (2), the hydrogen storage alloy powder and the conductive powder to be added as required are formed into a three-dimensional shape (mesh shape) by fiberization by stirring. It is preferable to use immobilizable polytetrafluoroethylene (PTFE) as the polymer binder.

Examples of the conductive powder include carbon powder such as graphite powder and Ketjen black, and metal powder such as nickel, copper and cobalt. Such conductive powder can be used as the hydrogen storage alloy 10
It is preferable to add 0.1 to 5 parts by weight to 0 part by weight.

As the conductive substrate, for example, a two-dimensional substrate such as a punched metal, an expanded metal, or a wire mesh, or a three-dimensional substrate such as a foamed metal substrate, a mesh-like sintered fiber substrate, or a felt-plated substrate obtained by plating a metal on a nonwoven fabric is used. Can be mentioned. However, when producing the non-paste type hydrogen storage alloy electrode of the above (2), it is preferable to use a two-dimensional substrate as the conductive substrate since a mixture containing the hydrogen storage alloy powder is sprayed.

The non-sintered nickel electrode 12 combined with the hydrogen storage alloy electrode is made of, for example, nickel hydroxide and cobalt hydroxide (Co (O
H) ₂ ), carboxymethyl cellulose (CMC), a mixture with cobalt monoxide (CoO), metallic cobalt, etc.
A polyacrylic acid salt such as sodium polyacrylate is appropriately blended to form a paste, and this paste is used as a foam metal substrate,
It is prepared by filling a substrate having a three-dimensional structure such as a reticulated sintered fiber substrate or a felt-plated substrate obtained by plating a metal on a non-woven fabric, drying it, and then performing roller pressing or the like.

The polymer fiber non-woven fabric used for the separator 13 is, for example, nylon, polypropylene,
Examples thereof include simple polymer fibers such as polyethylene, and composite polymer fibers obtained by blending these polymer fibers.

As the alkaline electrolyte, for example, a potassium hydroxide solution having a concentration of 6N to 9N or a mixture of the potassium hydroxide solution with lithium hydroxide, sodium hydroxide or the like is used.

According to the hydrogen storage alloy for a battery having the above-described structure, the types and composition ratios of the rare earth elements constituting the alloy and the types and composition ratios of the elements to be replaced with Ni are properly set, and Since the oxygen content of the powder is strictly controlled, a hydrogen storage alloy for a battery having excellent hydrogen storage characteristics and corrosion resistance can be obtained. Therefore, when this alloy is used as the negative electrode material, the battery capacity is increased, and the pulverization of the alloy due to the alkali solution can be prevented from being deteriorated, so that a nickel-hydrogen secondary battery having a long life can be provided.

[0065]

Next, embodiments of the present invention will be described more specifically with reference to the following examples.

Examples 1 to 23 Various metal raw material powders were blended so as to have an A component (rare earth) composition and an alloy composition shown in the left column of Table 1, and the obtained raw material mixture was heated and melted in a vacuum furnace. An alloy melt (master alloy) for each example was prepared. Of the raw material powder,
As shown in Table 1, the misch metal (Lm) serving as the component A in the general formula has a La content of 68 to 95% by weight,
1 to 7% by weight of Nd, 0 to 3% by weight of Pr, 3 to 3% of Ce
La-enriched misch metal whose composition was changed in the range of 22% by weight was used.

Next, the obtained molten alloy was solidified by cooling in an Ar atmosphere according to the following processing conditions to prepare flake-shaped alloy samples.

That is, the alloy melts for Examples 1 to 15 were rapidly solidified by a single roll method as shown in FIG. 1 to prepare flake-shaped alloy samples. As a cooling roll, a Cu-Be roll having a diameter of 400 mm is used.
The gap between the pouring nozzle (injection nozzle) and the cooling roll is 10
mm and the injection pressure was 0.5 kg / cm ² . The quenching operation was performed in an Ar atmosphere, and the roll peripheral speed was 10 m / S
Set to.

On the other hand, the molten alloy for Examples 16 to 23
Flake-shaped alloy samples were prepared by rapid solidification by the twin-roll method as shown in FIG. The processing atmosphere in the twin roll method was an Ar gas atmosphere as in the case of the single roll method. The material of the cooling roll is Fe (SUJ
-2), and an iron roll having a diameter of 300 mm was used. Furthermore, the roll peripheral speed was set to 10 m / S with the roll gap of the cooling roll set to zero, and the injection pressure was set to 0.5 kg / S.
cm ² was set.

The quenched alloy samples produced by the single-roll method and the twin-roll method were each in the form of flakes, and had a thickness of 150 to 200 μm. These flake alloy samples were heat-treated under the conditions shown in Table 1, respectively. That is, the obtained alloy sample was put into a heating furnace, the degree of vacuum (initial vacuum degree) in the heating furnace at the start of the heat treatment was set to the value shown in Table 1, and then the atmosphere was returned to a normal pressure Ar atmosphere. By performing the heat treatment according to the temperature and time shown in Table 1, oxygen in the alloy sample was volatilized, and the internal strain was removed.

Comparative Examples 1 and 2 Raw material powders were blended so as to satisfy the misch metal (A) composition and the alloy composition shown in the left column of Table 1, and the obtained raw material mixture was heated and melted in a vacuum furnace. Molten alloys for comparative examples were prepared. In addition, among the raw material powders, as the misch metal (A) serving as the component A, those having an excessive Nd content (Comparative Example 1) and those having an excessive Ce content (Comparative Example 2) were used.

Then, each alloy melt was solidified by cooling at a cooling rate of 5 to 20 ° C./sec by a casting method, and block-shaped alloy samples of Comparative Examples 1 and 2 each having a thickness of 50 mm were prepared. Further, the obtained alloy samples were heated at 1000 ° C. for 5 hours and at 90 ° C. for 6 hours, respectively, to perform a homogenizing heat treatment. The initial degree of vacuum of the heating furnace at the start of the heat treatment was 1 × 10 ² Torr.

Next, each of the obtained alloy samples was finely pulverized by a hammer mill in an Ar gas atmosphere, and the obtained pulverized powder was passed through a sieve to classify the powder into a particle size of 75 μm or less. And The average particle size is 35-4.
It was 0 μm. Table 1 shows the results of analyzing the oxygen content of each alloy sample powder by the DECO method.

Next, in order to evaluate the characteristics of the hydrogen storage alloy according to each of the above Examples and Comparative Examples as a battery material, an electrode was formed using each of the above hydrogen storage alloys in the following procedure. The electrode capacity and the number of charge / discharge cycles (life) were measured.

First, the hydrogen storage alloy powder, PTFE powder, and carbon powder according to the above Examples and Comparative Examples were weighed to 95.5%, 4.0%, and 0.5% by weight, respectively. Each electrode sheet was prepared by kneading and rolling. The electrode sheet was cut out to a predetermined size, and pressed to a nickel current collector to prepare a hydrogen storage alloy electrode.

On the other hand, a small amount of CMC (carboxymethylcellulose) and water were added to 90% by weight of nickel hydroxide and 10% by weight of cobalt monoxide and mixed by stirring to prepare a paste. This paste was filled in a porous nickel body having a three-dimensional structure, dried, and then rolled by a roller press to produce a nickel electrode.

The capacity of each of the above-mentioned hydrogen storage alloy electrodes and the nickel electrode is combined, and the capacity is measured by monopolar evaluation. On the other hand, the life is evaluated by the AA type (AA) nickel-metal hydride battery of each embodiment. Was assembled. Here, an 8N aqueous potassium hydroxide solution was used as the electrolytic solution.

In the capacity evaluation of each hydrogen storage alloy electrode, the battery was charged to 400 mAh / g at a current value of 220 mA per gram of alloy (220 mA / g) in a constant temperature bath at 25 ° C., and then the Hg / HgO was charged at the above current value. With respect to the reference electrode,
The battery was discharged until the potential reached 0.5 V, and the charge and discharge were repeated, and the value when the amount of discharge reached the maximum was measured as the capacity.

In the life evaluation, 65% was obtained for each battery.
After charging at 0 mA for 1.5 hours, a charge / discharge cycle of discharging at a current of 1 A until the battery voltage becomes 0.9 V is repeated,
The number of cycles until the battery capacity reached 80% of the initial capacity was measured at 50 ° C. and evaluated as the battery life. Table 1 below shows the measurement results.

[0080]

[Table 1]

As is clear from the results shown in Table 1 above,
Examples in which the composition ratio of the rare earth element, which is the A-site component of the general formula, and the composition ratio of the other constituent elements are properly set, cooled and coagulated, and the oxygen content after pulverization is strictly controlled. In the electrode and the battery formed by using the hydrogen storage alloy according to the above, it was found that the decrease in the capacity was smaller than that of the battery of the comparative example having a different composition ratio or oxygen content.

Further, in the example, as compared with the comparative example, the electrode capacity is increased by 25 to 67 mAh / g, and the number of charge / discharge cycles is increased by about 50 at the maximum, so that the battery life is improved. It could be confirmed. That is, it was found that by setting the composition range and the oxygen content specified in the present example, a nickel hydrogen secondary battery having a high capacity and a long life can be obtained.

Example 24 (La _0.47 Ce _0.37 Pr _0.04 Nd _0.12 ) Ni _3.40 Co
_A molten alloy having a composition of _0.80 Mn _0.40 Al _0.20 was rapidly solidified by a single roll device as shown in FIG. 1 to prepare a flake-shaped alloy sample. As a cooling roll of the single roll device, a Cu-Be roll having a diameter of 400 mm was used, a gap between a pouring nozzle (injection nozzle) and the cooling roll was set to 10 mm, and an injection pressure was 0.5 kg / cm ² . did. The quenching operation was performed in an Ar atmosphere, and the roll peripheral speed was set at 8 m / S.

Next, the obtained alloy samples were separated and put into heating furnaces, respectively, and heat-treated at a temperature of 900 ° C. for 6 hours. At this time, it was varied degree of vacuum in the furnace during heat treatment start (initial degree of vacuum) for each sample in the range of 10 ^-8 ~10 ² Torr. Subsequently, the inside of the heating furnace was set to an Ar atmosphere, and heat treatment was performed at the above temperature and time.

Each of the obtained alloy samples was roughly pulverized and then finely pulverized by a hammer mill in the same manner as in Example 1. The obtained pulverized powder was passed through a sieve and classified to a particle size of 75 μm or less. The average particle size of the hydrogen storage alloy powder for a battery was 35 to 40 μm. When the oxygen content of each alloy powder was analyzed by the DECO method, it was in the range of 0.004 to 0.82% by weight.

Next, a negative electrode and a battery were assembled using each alloy powder in the same manner as in Example 1, and the capacity and life characteristics were measured. The results shown in FIG. 4 were obtained. FIG.
As can be seen from the results shown in Table 1, when the oxygen content of the alloy powder when incorporated into the battery is strictly controlled to be in the range of 0.01 to 0.4% by weight, the capacity becomes high and the long life characteristic is obtained. Was obtained.

On the other hand, it was confirmed that both the capacity and the life tended to decrease when the oxygen content exceeded 0.4% by weight. When the oxygen content was less than 0.01% by weight, it was found that the function of the oxide film as the protective film was not sufficiently exhibited, and thus the life of the alloy was shortened due to corrosion of the alloy.

[0088]

As described above, according to the hydrogen storage alloy according to the present invention, the types and composition ratios of the rare earth elements constituting the alloy, the types and composition ratios of the elements replacing Ni, and the Since the oxygen content is properly set, a hydrogen storage alloy for a battery having excellent hydrogen storage characteristics and corrosion resistance can be obtained. Therefore, when this alloy is used as a negative electrode material for a battery, a nickel-hydrogen secondary battery having a large battery capacity and a long life can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the configuration of a hydrogen storage alloy manufacturing apparatus using a single roll method.

FIG. 2 is a cross-sectional view showing a configuration of a hydrogen storage alloy manufacturing apparatus using a twin-roll method.

FIG. 3 is a perspective view showing a configuration example of a nickel-metal hydride secondary battery according to the present invention, partially cut away;

FIG. 4 is a graph showing a relationship between oxygen content, capacity, and life of the hydrogen storage alloy powder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling chamber 2 Ladle 3 Hydrogen storage alloy melt 4 Pouring nozzle 5, 5a, 5b Cooling roll 6 Hydrogen storage alloy 7 Melting furnace 8 Tundish 11 Hydrogen storage alloy electrode (negative electrode) 12 Non-sintered nickel electrode (positive electrode) 13 Separator 14 Container 15 Hole 16 Sealing Plate 17 Insulating Gasket 18 Positive Electrode Lead 19 Positive Electrode Terminal 20 Safety Valve 21 Insulating Tube 22 Flange Paper d Gap

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shusuke Inada 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Takamichi Inaba 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Noriaki Sato, Inventor, No. 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Prefecture, Japan (72) Masaki Okamura, No. 8, Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa, Japan Yokohama office

Claims (4)

[Claims] 1. A general formula _{ANi a M b M 'c T} d ( where,
A is composed of La, Ce, Pr, Nd and Y. The La content in A is 25 to 85% by weight, the Ce content is 5 to 45%, the Pr content is 0 to 15%, and the Nd content is A. 0
-20% and Y content is 0-10%, while M is C
o, at least one element selected from Fe and Cu, M 'is at least one element selected from Mn, Al, Si and Zn, and T is B, S, C
r, Ga, Ge, Mo, Ru, Rh, Pd, Ag, I
n, Sn, Sb and W are at least one element selected from the group consisting of a, b, c and d, each having an atomic ratio of 3.
1 ≦ a ≦ 4.0, 0.4 ≦ b ≦ 1.2, 0.3 ≦ c ≦
1.2, 0 ≦ d ≦ 0.2, 4.7 ≦ a + b + c + d ≦
5.1. ), Comprising a ground powder of a quenched alloy having a composition represented by the formula (1), wherein the oxygen content of the ground powder is 0.01 to 0.1.
A hydrogen storage alloy, which is 4% by weight. 2. The quenched alloy has an average crystal grain size of 1 to 50 μm.
The hydrogen storage alloy according to claim 1, wherein 3. A general formula _{ANi a M b M 'c T} d ( where,
A is composed of La, Ce, Pr, Nd and Y. The La content in A is 25 to 85% by weight, the Ce content is 5 to 45%, the Pr content is 0 to 15%, and the Nd content is A. 0
-20% and Y content is 0-10%, while M is C
o, at least one element selected from Fe and Cu, M 'is at least one element selected from Mn, Al, Si and Zn, and T is B, S, C
r, Ga, Ge, Mo, Ru, Rh, Pd, Ag, I
n, Sn, Sb and W are at least one element selected from the group consisting of a, b, c and d, each having an atomic ratio of 3.
1 ≦ a ≦ 4.0, 0.4 ≦ b ≦ 1.2, 0.3 ≦ c ≦
1.2, 0 ≦ d ≦ 0.2, 4.7 ≦ a + b + c + d ≦
5.1. A) contacting a molten alloy having a composition represented by the formula (1) with a cooling medium to rapidly cool and solidify the alloy at a cooling rate of 100 ° C./sec or more; and heat treating the obtained quenched alloy in a non-oxidizing atmosphere at a temperature of 600 to 1000 ° C. The process of
Adjusting the pulverized powder by pulverizing the heat-treated quenched alloy in a non-oxidizing atmosphere, and setting the degree of vacuum of the atmosphere at the start of the heat treatment step to 10 ⁻⁶ to 10 ² Torr, Alternatively, a method for producing a hydrogen storage alloy, wherein the oxygen content of the quenched alloy is adjusted to 0.01 to 0.4% by weight by performing heat treatment in a non-oxidizing atmosphere. 4. The general formula ANi _a M _b M ′ _c T _d (where:
A is composed of La, Ce, Pr, Nd and Y. The La content in A is 25 to 85% by weight, the Ce content is 5 to 45%, the Pr content is 0 to 15%, and the Nd content is A. 0
-20% and Y content is 0-10%, while M is C
o, at least one element selected from Fe and Cu, M 'is at least one element selected from Mn, Al, Si and Zn, and T is B, S, C
r, Ga, Ge, Mo, Ru, Rh, Pd, Ag, I
n, Sn, Sb and W are at least one element selected from the group consisting of a, b, c and d, each having an atomic ratio of 3.
1 ≦ a ≦ 4.0, 0.4 ≦ b ≦ 1.2, 0.3 ≦ c ≦
1.2, 0 ≦ d ≦ 0.2, 4.7 ≦ a + b + c + d ≦
5.1. ), Comprising a ground powder of a quenched alloy having a composition represented by the formula (1), wherein the oxygen content of the ground powder is 0.01 to 0.1.
A separator having electrical insulation is interposed between a negative electrode containing 4% by weight of a hydrogen storage alloy and a positive electrode containing nickel oxide, and housed in a closed container. A nickel-metal hydride secondary battery characterized by being filled.