JPH09289017A - Hydrogen storage alloy for battery and nickel hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce capacity drop in a low temperature region, obtain high electrode capacity over a wide temperature range, and lengthen the life by using a hydrogen storage alloy having a composition represented by the prescribed general formula. SOLUTION: An intermetallic compound based on a rare earth element and nickel are used as the base of an alloy component, and Ti, Zr, Hf and the like are added to the base to adjust the composition of the alloy in the prescribed range represented by the general formula of Ra Mb M'c Ad Ni100-a-b-c-d (wherein R is at least one element selected from Y, La, Ce, Sm, Nd, and Pr, M is at least one element selected from Ti, Zr, and Hf, M' is at least one element selected from Co, Fe, Cr, Mn, and Cu, A is at least one element selected from Al, Ga, Si, Ge, Sn, V, Nb, Ta, Mo, and W, and a, b, c, d are 10<=a<=30, 5<=b<=20, 0<=c<=30, 0<=d<=10 in atomic percent).

Description

Detailed Description of the Invention

[0001]

The present invention relates to a hydrogen storage alloy for a battery and a nickel-metal hydride battery using the alloy.
In particular, when alloy is used for the negative electrode of a battery, there is little decrease in capacity in low temperature range, high electrode capacity (battery capacity) and long life characteristics (long cycle characteristics) that can withstand repeated use in a wide operating temperature range. The present invention relates to a hydrogen storage alloy for batteries and a nickel-hydrogen secondary battery that can satisfy both requirements.

[0002]

2. Description of the Related Art Recent advances in electronic technology have led to power savings,
Due to the progress of packaging technology, electronic devices that have not been expected in the past are becoming smaller and more portable. 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 devices, telephones, and AV devices that are becoming more personalized and portable, there is a demand for the development of a high-performance battery, particularly for the purpose of reducing the size and weight and extending the use time of the device cordlessly. 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 has been spotlighted. 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.

[0004] 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 problems, 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 a plating method, a vapor deposition method 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.

As a hydrogen storage alloy used in the above alkaline secondary battery, there is an 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.

[0007]

However, the above L
electrode capacitance of m-Ni-Co-Al alloy (Lm is La enriched misch metal) consisting of AB ₅ hydrogen storage alloy,
The state is still as low as less than 300 mAh / g, and the cycle life due to charge and discharge 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.

Further, in the nickel-hydrogen battery using the above conventional hydrogen storage alloy as a negative electrode material, the battery capacity is lowered in the upper limit temperature range and the lower limit temperature region of the temperature range (-20 ° C. to + 80 ° C.) in which the battery is used. And the battery may not be discharged in some cases, resulting in a significant decrease in battery function. In particular, when used in cold regions, the voltage drop becomes large, and there is a problem that equipment malfunctions occur, and in any case the reliability of operation of equipment that uses a battery as a driving power source drops significantly. was there.

The present invention has been made in order to solve the above-mentioned problems, and in particular, a reduction in capacity in a low temperature range is small, a high electrode capacity can be obtained in a wide operating temperature range, and a long service life of a battery can be obtained. An object of the present invention is to provide a hydrogen storage alloy for a battery that can be realized and a nickel-hydrogen 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 the operating environment of a battery. As a result, when an IVa group element such as Ti, Zr, or Hf is further added to an intermetallic compound based on a rare earth element and nickel (Ni) as an alloy component to adjust the composition of the alloy to a predetermined range, hydrogen A hydrogen storage alloy having excellent storage characteristics and corrosion resistance can be obtained.
It was found that when this alloy is used as a negative electrode material, a nickel-hydrogen secondary battery having a balanced electrode capacity, life characteristics, and temperature characteristics of capacity can be obtained. The present invention has been completed based on the above findings.

[0011] That cell hydrogen-absorbing alloy according to the present invention have the general formula _{R a M b M 'c A} d Ni 100-abcd ( Here, R is selected Y, La, Ce, Sm, Nd, and Pr At least one element, M is Ti, Zr
And at least one element selected from Hf, M ′ is at least one element selected from Co, Fe, Cr, Mn and Cu, and A is Al, Ga,
At least one element selected from Si, Ge, Sn, V, Nb, Ta, Mo, and W, and a, b, c,
d is atomic% and 10 ≦ a ≦ 30, 5 ≦ b ≦ 20,
0 ≦ c ≦ 30 and 0 ≦ d ≦ 10. ). The average crystal grain size of the alloy is preferably in the range of 1 to 100 nm.

The hydrogen storage alloy for batteries according to the present invention can be manufactured by a usual vacuum melting / casting method. However, in order to relax the conditions of the homogenizing heat treatment performed after casting and solidification, which will be described later, the molten alloy having the above-described predetermined composition is brought into contact with a high-speed moving cooling body to cool at 100 ° C./min or more. It is desirable to manufacture by quenching and solidifying at a speed. By such rapid solidification treatment, a flake-shaped alloy sample having a thickness of about 20 to 300 μm can be obtained. In this case, it is also possible to make the alloy structure into an amorphous phase, and by heat-treating the alloy having this amorphous phase at a temperature above its crystallization temperature, an alloy composed of fine crystal grains can be obtained, and high capacity A long-life hydrogen storage alloy can be obtained.

By the above rapid solidification treatment, the additive components are uniformly dispersed in the alloy structure, and the grain boundary precipitation phase is also refined to prolong the life of the battery. Here, the size of the fine crystals of the alloy is about 1 to 100 nm on average. And, by making the crystal grains fine, the hydrogen storage rate by the alloy is increased, and the rise of the discharge capacity is quickened when the battery material is used.

In order to eliminate internal strain in the alloy prepared by the molten metal quenching method and homogenize the alloy, the alloy is kept at a temperature of 400 to 1100 ° C. in a non-oxidizing atmosphere.
A homogenizing heat treatment of heating for 10 hours is preferably performed.

Further, in the nickel-metal hydride secondary battery according to the present invention, a separator having electrical insulation is 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 storage alloy for a battery according to the present invention, in the general formula, R is an element having a hydrogen storage capacity which is the basis for increasing the capacity of the battery, and its content balances the capacity and the life. Considered, it is determined by the ratio with other constituents. R is at least one element selected from Y, La, Ce, Sm, Nd and Pr, and is usually used as a misch metal (Mm) which is a mixture of a plurality of rare earth elements. If the added amount a of the R component is less than 10 atomic%, the capacity becomes too small and the basic characteristics of the battery cannot be obtained.
On the other hand, when the added amount a exceeds 30 atomic%, the hydrogen equilibrium pressure is excessively lowered, and the battery function is impaired. The added amount a of the R component is set in the range of 10 to 30 atom%, and more preferably in the range of 15 to 25 atom%.

From the viewpoint of extending the life, it is preferable to use La, Ce and Pr as the R component, and La is particularly effective for achieving a high capacity.

M is at least one element selected from Ti, Zr and its Hf, and these M components are elements effective for increasing the hydrogen storage amount and stabilizing the life characteristics. If the addition amount b of the M component is less than 5 atom%, the above effect is insufficient, while if the addition amount b exceeds 20 atom%, the life characteristics are deteriorated. Therefore, the addition amount b of the M component is set to 5 to 20 atom%, but the range of 7 to 15 atom% is more preferable. From the viewpoint of extending the life, it is preferable to use Zr and Ti as the M component.

The M'component is Co, Fe, Cr, M
It is at least one element selected from n and Cu. These M'components enhance the catalytic action at the alloy interface,
It is a component that brings about the effect of accelerating the diffusion rate of hydrogen, and the addition amount C thereof is set in the range of 0 to 30 atomic%. If the added amount C exceeds 30 atom%, the battery capacity becomes too small,
It is difficult to satisfy the basic required characteristics as a battery. The preferable addition amount C is 25 atomic% or less.

Further, A is Al, Ga, Si, Ge, S
It is at least one selected from n, V, Nb, Ta, Mo and W, and all of these elements are effective for improving the life of the alloy. When the addition amount d of these A components exceeds 10 atomic%, the capacity is lowered.

Ni is alloyed with the rare earth component (R),
It is a basic element for forming a rare earth-Ni based hydrogen storage alloy having excellent corrosion resistance to store and release hydrogen, and is added as the balance component of the R, M, M ', and A components. Within the range of the amount of Ni added, the hydrogen storage equilibrium pressure in the sealed battery can be set appropriately.

Of the above M'components, Mn is effective in increasing the capacity of the negative electrode containing the hydrogen storage alloy, improving the corrosion resistance by promoting the formation of a passive film, and adjusting the hydrogen storage / release pressure (equilibrium pressure) to be lowered. Is. Al as the A component is Mn
In the same manner as described above, the hydrogen storage and release pressure (dissociation pressure) can be reduced to an operation pressure suitable for a sealed battery, and the durability can be increased.

Further, Co as the M'component is effective in improving the corrosion resistance of the alloy with respect to the electrolytic solution, etc., and the pulverization of the alloy is significantly suppressed, and the life characteristics of the battery are improved. Although the cycle life is improved as the amount of Co added increases, the electrode capacity tends to decrease, so it is necessary to optimize the amount of Co added depending on the application of the battery.

In addition, the hydrogen storage alloy according to the present invention includes
Elements such as Pb, C, N, O, F and Cl may be contained as impurities within a range that does not impair the characteristics of the alloy of the present invention. The content of each of these impurities is 6
It is preferably in the range of 000 ppm or less. More preferably 5000 ppm or less, still more preferably 400 ppm
0 ppm or less is good.

A hydrogen storage alloy having a hydrogen equilibrium pressure within a limited range is obtained by quenching and solidifying an alloy melt having a composition represented by the above general formula at a cooling rate of 100 ° C./min or more. When used as a negative electrode material for a battery, a hydrogen storage alloy that can maintain a high capacity over a wide temperature range and has little temperature dependence can be obtained. Specifically, the hydrogen equilibrium pressure of the alloy having a small temperature dependency is in the range of 0.05 to 0.6 atm based on the evaluation standard at a temperature of 60 ° C.

Here, the hydrogen equilibrium pressure is the hydrogen pressure when the number of hydrogen atoms stored per metal atom is 0.4.
If the hydrogen equilibrium pressure is less than 0.05 atm, the battery voltage will be too low, and the discharge capacity will be small especially under low temperature use conditions of 0 ° C or lower. On the other hand, when the hydrogen equilibrium pressure exceeds 0.6 atm, the capacity decrease at a high temperature of, for example, 80 ° C. or more becomes large, and it becomes difficult to use the battery under high temperature conditions.

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 made finer and necessary for storage and release of hydrogen. A sufficient route is 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.
Even under the following low temperature conditions, it is considered that as a result of effectively suppressing the decrease in capacity, a hydrogen storage alloy having little temperature dependence can be obtained.

The method for producing the hydrogen storage alloy for a battery according to the present invention is not particularly limited as long as the alloy composition can be made uniform to prevent segregation. That is, a raw material mixture prepared so as to have a predetermined composition is heated in an arc furnace or the like to prepare a molten alloy, and thereafter, a normal casting method, a gas atomizing method, or the like. 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 is 1
By setting it to 00 ° C./min or higher, preferably 300 ° C./min or higher, more preferably 2500 ° C./min or higher,
Even when a relatively large amount of La is contained as the misch metal, an alloy having a uniform structure and less segregation can be obtained. Examples of the cooling and solidifying method of the above-mentioned molten alloy include pouring the molten alloy onto a water-cooled Cu disk to obtain 10 to 50
A method of making an alloy block having a thickness on the order of mm may be used. By performing the cooling and solidifying treatment and the heat treatment described later, a high-capacity and long-life hydrogen-absorbing alloy for a battery can be obtained.

When the molten alloy is injected onto a cooling body moving at a higher speed to form a flake-like alloy having a thickness of about 20 to 300 μm, a hydrogen storage alloy composed of fine crystal grains of about 1 to 100 nm is obtained. It is possible to form a battery having high capacity and long life. 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 cooling and solidifying method for the molten alloy, a molten metal quenching method for quenching the molten molten alloy, such as a gas atomizing method, a rotating disk method, a centrifugal atomizing method, a single roll method, a twin roll method, etc., is used. The material and surface properties of the chill roll, the number of rotations of the chill roll (circumferential speed of the running surface), the temperature of the molten metal, the temperature of the cooling water for the cooling roll, the type of gas 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 stably manufactured in large quantities.

Single Roll Method FIG. 1 shows an apparatus for producing a hydrogen storage alloy by the 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 cooling rate of the cooling roll 5 and the injection amount of the hydrogen-absorbing alloy melt 3, but is generally set at 300 to 5000 rpm.

In the manufacturing apparatus shown in FIG. 1 described above, the molten hydrogen storage alloy 3 supplied from the ladle 2 is poured into the pouring nozzle 4.
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.

Twin Roll Method FIG. 2 shows an apparatus for producing a hydrogen storage alloy by the 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 made of a material having excellent heat conductivity such as copper and iron, and have a diameter of about 300 mm. The cooling rolls 5a and 5b are 0 to 0.5
300 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, the cooling directions are not aligned, and as a result, a hydrogen storage alloy in which the crystal growth directions are not aligned is manufactured. Therefore, it is preferably set to 0.2 mm or less.

In the above-mentioned manufacturing apparatus shown in FIG. 2, the molten hydrogen-absorbing alloy 3 is fed from the pouring nozzle 4 to 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 block-shaped, ribbon-shaped, flake-shaped or granular hydrogen storage alloy is produced by using the cooling solidification method as described above, the temperature gradient in the sample during the solidification of the molten alloy, the cooling roll or the rotating disk An equiaxed crystal structure, a columnar crystal structure, and an amorphous phase are formed in the alloy depending on the material, the amount of the molten alloy supplied, and the like.

In the manufacturing process of the above alloy particles, 100
C./min or more, preferably 300.degree. C./min or more, more preferably 1800.degree. C./min or more, when the molten metal is rapidly cooled to produce a hydrogen storage alloy, each crystal grain forming the alloy has a grain size of 1 to 100 nm. The degree of refinement and the alloy strength are increased, and the disorder of the grain boundaries is reduced, so that the hydrogen storage amount 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, passages of hydrogen molecules or hydrogen atoms are 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.

It is preferable to perform various heat treatments such as recrystallization heat treatment on the alloy prepared as described above according to demands such as adjustment of grain size. For example, an amorphous alloy is heat-treated at a temperature equal to or higher than the crystallization temperature of the alloy to adjust the crystal grain size.

Here, the recrystallization heat treatment is performed at + 50 ° C. which is a crystallization temperature obtained when the alloy is heated in a vacuum or an inert gas atmosphere at a temperature rising rate of 10 ° C./min.
It is carried out by heating in a temperature range of 200 ° C. for 10 minutes to 24 hours.

In the above heat treatment for crystallization, if the heating temperature is below the crystallization temperature of -50 ° C, crystallization does not easily occur, and if the heat treatment is carried out for a long time, oxidation of the alloy surface becomes remarkable. Further, at a heating temperature higher than the crystallization temperature by 200 ° C., coarsening of crystal grains begins to occur and the characteristics of the electrode using the alloy deteriorate. If the heat treatment time is less than 10 minutes, sufficient crystallization does not occur, and if it is 24 hours or more, oxidation of the alloy surface poses a problem.

In addition, in the alloy prepared by the cooling solidification method as described above, internal strain is apt to occur, while in the alloy prepared by the casting method, segregation is apt to occur. When used, the electrode capacity and life often decrease.

Then, the alloy prepared by cooling and solidifying is
In some cases, it is desirable to carry out a homogenizing heat treatment in which heating is performed at a temperature of 400 to 1100 ° C. for 1 to 10 hours.

When the temperature of the homogenizing heat treatment is less than 400 ° C., it becomes difficult to remove the internal strain, while the temperature is 11
If the temperature is higher than 00 ° C., the composition may change due to oxidation or evaporation of the rare earth element or the group IVa element, or the alloy strength may decrease due to secondary recrystallization. Therefore, the heat treatment temperature is set in the range of 400 to 1100 ° C.
In particular, in order to improve the electrode properties,
Is preferred.

When the heat treatment time is less than 1 hour, the effect of removing the internal strain is small. On the other hand, if the treatment time is prolonged to the extent of more than 10 hours, there is a high risk of causing coarsening of crystal grains, so 2 to 5 hours are preferable in consideration of production efficiency.

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 carrying out the homogenizing heat treatment under the conditions as described above, it becomes possible to effectively remove the internal strain while maintaining the homogeneity of the alloy, and further increase the electrode capacity and the life.

By subjecting the hydrogen storage alloy prepared as described above to the following surface treatment, the electrode characteristics such as activity and rising property can be improved when it is used as an electrode material. That is, by performing a surface treatment such as an acid treatment, an alkali treatment, or a fluorination treatment, it is possible to enhance the activity of the alloy surface and the rising property as a battery. Among the above surface treatments, especially KOH and NaO
Alkaline treatment using H 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-hydrogen secondary battery (cylindrical nickel-hydrogen secondary battery) according to the present invention using the above hydrogen storage alloy for a battery as a negative electrode active material will be described with reference to FIG.

A nickel-hydrogen secondary battery according to the present invention comprises a negative electrode 11 containing a hydrogen storage alloy for a battery represented by the above general formula R _a M _b M ′ _c A _d Ni _100-abcd and a positive electrode containing nickel oxide. A separator 13 having electrical insulation is interposed between the container 12 and the container 12, and the container 13 is housed in a closed container 14, 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 for pulverizing the hydrogen storage alloy, for example, a mechanical pulverization method such as a ball mill, a pulperizer, or a jet mill, or a method in which high-pressure hydrogen is occluded / released and pulverized by volume expansion at that time, is employed. .

Examples of the polymer binder include sodium polyacrylate and 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 reticulated sintered fiber substrate, or a felt-plated substrate obtained by plating a nonwoven fabric with a metal. 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 structure, the types and composition ratios of rare earth elements, group IVa elements, group VIII elements, group IVb elements, group IIIb elements constituting the alloy are appropriate for Ni. Since it is set to, a hydrogen storage alloy for batteries 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.

[0063]

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

Examples 1 to 12 Various metal raw material powders were mixed so as to have the alloy compositions shown in the left column of Table 1, and the obtained raw material mixture was heated and melted in a vacuum furnace to melt the alloy for each example. (Mother alloy) was prepared.

Next, the obtained molten alloy was cooled and solidified in an Ar atmosphere according to the following processing conditions to prepare block-shaped or flake-shaped alloy samples.

That is, the molten alloys for Examples 1 to 8 were rapidly solidified by a single roll method as shown in FIG. 1 to prepare flake-shaped alloy samples. As the cooling roll, a Cu-Be roll having a diameter of 400 mm was used, and the gap between the pouring nozzle (injection nozzle) and the cooling roll was 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 set at 25 m / sec.

On the other hand, the molten alloys for Examples 9 to 12 were rapidly solidified by the twin roll method as shown in FIG. 2 to prepare flaky alloy samples. 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.
Further, the roll circumferential 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 / cm ^2.
Set to.

Among the quenched alloy samples thus obtained, the quenched alloy samples produced by the single roll method and the twin roll method are both flakes and have a thickness of 150 to
It was 200 μm. These flaky alloy samples were subjected to a homogenizing heat treatment at 1000 ° C. for 10 hours,
Internal distortion was removed.

Comparative Examples 1 and 2 Raw material powders were blended so as to satisfy 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 to obtain a molten alloy for each comparative example. Each was prepared.

Then, each alloy melt was cooled and solidified by a casting method at a cooling rate of 5 to 60 ° C./min to prepare block-shaped alloy samples of Comparative Examples 1 and 2 having a thickness of 50 mm. For the obtained alloy sample, 100
The homogenized heat treatment was carried out by heating at 0 ° C. for 10 hours.

The obtained alloy samples were coarsely pulverized and then finely pulverized by a hammer mill, and the pulverized powder thus obtained was passed through a sieve to be classified into particles having a particle size of 75 μm or less to obtain a hydrogen storage alloy for each battery. It was made into powder. The average particle size is 35 to 40.
μm.

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

First, the hydrogen storage alloy powder for a battery, the PTFE powder, and the carbon powder according to the above Examples and Comparative Examples were adjusted to 95.5%, 4.0%, and 0.5% by weight, respectively. After weighing, 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 hydrogen storage alloy electrodes and a nickel electrode was measured by unipolar evaluation, while the life was evaluated by actually measuring the AA type (AA) nickel hydride battery of each example. Assembled. Here, as the electrolytic solution, a mixed aqueous solution of 8N potassium hydroxide and 1N lithium hydroxide was used.

Then, in the capacity evaluation of each hydrogen storage alloy electrode, after charging up to 400 mAh / g at a current value of 220 mA per 1 g of alloy (220 mA / g) in a thermostat at 25 ° C., Hg / HgO at the above current value was charged. For 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. After measuring the capacity at 25 ° C, the temperature in the constant temperature bath was adjusted to -20 ° C, and the capacity at that temperature was measured. And -20 ℃ to the capacity at 25 ℃
The temperature dependence of the capacity was evaluated by calculating the ratio with the capacity at.

In the life evaluation, 65
After charging at 0 mA for 1.5 hours, a charging / discharging cycle of discharging at a current of 1 A was repeated until the battery voltage became 1 V, and the number of cycles until the battery capacity reached 80% of the initial capacity was measured as the battery life. The results of each measurement are shown in Table 1 below. Further, the cooling rate from the molten metal at the time of alloy preparation was measured and is also shown in Table 1.

[0078]

[Table 1]

As is clear from the results shown in Table 1 above,
Each of the preparations was carried out by appropriately setting the composition ratio of the rare earth element which is the R site component in the general formula and the composition ratios of the other constituent elements such as IVa group, VIII group, IVb group and IIIb group, and cooling and solidifying. In the electrode and battery formed using the hydrogen storage alloy according to the example, compared to the battery of the comparative example having the conventional AB ₅ type composition ratio, the decrease in the capacity under the low temperature condition of −20 ° C. was small. It was found that the temperature dependence of the capacity was small in a wide operating temperature range.

Further, in the embodiment, the electrode capacity is increased by 85 to 135 mAh / g and the number of charge / discharge cycles is increased by about 3 to 4.2 times as compared with the comparative example, and the life of the battery is significantly increased. It was confirmed to be improved. That is, it was found that by setting the composition range specified in this example, a nickel-hydrogen secondary battery having a small temperature dependency, a high capacity, and a long life can be obtained.

[0081]

As described above, according to the hydrogen storage alloy for battery of the present invention, the rare earth element, IVa
Since the types of the groups, VIII, IVb, and IIIb and the composition ratios thereof are properly set for Ni, a hydrogen storage alloy for batteries 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.

[Brief description of 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;

[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) DESCRIPTION OF SYMBOLS 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

Claims (3)

[Claims] 1. The general formula R _a M _b M ′ _c A _d Ni
_100-abcd (where R is Y, La, Ce, Sm, Nd
And Pr, at least one element selected from Pr, M is at least one element selected from Ti, Zr, and Hf, and M ′ is at least selected from Co, Fe, Cr, Mn, and Cu. Is an element,
A is Al, Ga, Si, Ge, Sn, V, Nb, Ta,
It is at least one element selected from Mo and W, and a, b, c, and d are each atomic% of 10 ≦ a ≦ 3.
0,5 ≦ b ≦ 20, 0 ≦ c ≦ 30, 0 ≦ d ≦ 10. ) A hydrogen storage alloy for a battery having a composition represented by 2. The hydrogen storage alloy for batteries according to claim 1, wherein the average crystal grain size of the alloy is in the range of 1 to 100 nm. 3. The general formula R _a M _b M ′ _c A _d Ni
_100-abcd (where R is Y, La, Ce, Sm, Nd
And Pr, at least one element selected from Pr, M is at least one element selected from Ti, Zr, and Hf, and M ′ is at least selected from Co, Fe, Cr, Mn, and Cu. Is an element,
A is Al, Ga, Si, Ge, Sn, V, Nb, Ta,
It is at least one element selected from Mo and W, and a, b, c, and d are each atomic% of 10 ≦ a ≦ 3.
0,5 ≦ b ≦ 20, 0 ≦ c ≦ 30, 0 ≦ d ≦ 10. ) A negative electrode containing a hydrogen storage alloy for a battery having a composition represented by a) and a positive electrode containing nickel oxide are placed in a closed container with an electrically insulating separator interposed therebetween. A nickel-hydrogen secondary battery filled with an alkaline electrolyte.