JPH08120364A - Hydrogen storage alloy for battery, its production and nickel-hydrogen secondary battery - Google Patents

Abstract

PURPOSE: To produce a hydrogen storage alloy for a battery in which high electrode capacitance, good initial activity and, particularly, the long service life of a battery can be realized, to provide a method for producing the same and to produce a nickel-hydrogen secondary battery using the same alloy. CONSTITUTION: This alloy has a compsn. expressed by the general formula, ABx [wherein, A denotes at least one kind of element selected from rare earth elements including Y(yttrium); B denotes at least one kind of element selected from among Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag, Al, Ga, In, Si, Ge and Sn; and 4.5<=x<=5.5], and a film constituted of at least either of the nitrides and carbides of the same elements is formed on at least a part of the same alloy. Moreover, the same film is formed after the alloy is subjected to nitriding treatment or carbonizing treatment.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a hydrogen storage alloy for batteries,
The present invention relates to a method for producing the same and a nickel-hydrogen battery using the alloy, and particularly when an alloy is used for a negative electrode of the battery, high electrode capacity (battery capacity), long life characteristics (long cycle characteristics) that can withstand repeated use, and The present invention relates to a hydrogen storage alloy for batteries, which can satisfy the three major characteristics of good initial activity, a method for producing the same, and a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art Power saving due to recent advances in electronic technology,
Due to the progress of packaging technology, electronic devices that have not been expected in the past are becoming smaller and more portable. Along with this, there is a particular demand for higher capacity, longer life, and stable discharge current for the secondary battery that is the power source of the electronic device. For example, in OA devices, telephones, and AV devices that are becoming more personalized and portable, development of high-performance batteries is desired especially for the purpose of downsizing and weight reduction, and extension of device usage time without a cord. A non-sintered nickel-cadmium battery that uses the electrode substrate of a conventional sintered nickel-cadmium battery as a three-dimensional structure has been developed as a battery that meets such requirements, but a significant increase in capacity has not been achieved. .

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

However, since the negative electrode containing the hydrogen storage alloy is immersed in a concentrated alkaline aqueous solution which is an electrolytic solution when it is incorporated in a secondary battery, it is exposed to oxygen generated from the positive electrode especially during overcharge. However, the hydrogen storage alloy is corroded and the electrode characteristics are easily deteriorated. Furthermore, during charging / discharging, the volume of the hydrogen-absorbing alloy expands and contracts as it is absorbed and released into the hydrogen-absorbing alloy, so that the hydrogen-absorbing alloy is cracked and the hydrogen-absorbing alloy powder is pulverized. As the pulverization of the hydrogen storage alloy progresses, the specific surface area of the hydrogen storage alloy increases at an accelerating rate, so that the ratio of the area of deterioration of the surface of the hydrogen storage alloy due to 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, hydrogen storage alloys are made plural, or nickel thin films or copper thin films are attached to the surface of the hydrogen storage alloy powder or the surface of the negative electrode containing the hydrogen storage alloy by plating or vapor deposition. Prevents direct contact with electrolytic solution to improve corrosion resistance, increases mechanical strength to prevent cracking, or suppresses deterioration of hydrogen storage alloy surface by immersing in alkaline solution and drying. Although such a method has been proposed, it has not always been possible to achieve sufficient improvement, and in some cases, the electrode capacitance may be 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 this hexagonal structure is more effective per unit weight or unit volume of the battery than when using cadmium, which is a conventional typical negative electrode material for alkaline secondary batteries. It is possible to increase the energy density of the battery, increase the capacity of the battery, reduce the risk of environmental pollution such as cadmium pollution, and have good battery characteristics. .
Further, a battery using the AB ₅ alloy has an advantage that it can discharge a large current. By the way, Lm-Ni-C
The electrode capacity of the AB ₅ type hydrogen storage alloy made of o-Al type alloy (Lm is La-enriched misch metal) is 200 mAh /
The state is as low as less than g and the cycle life due to charge and discharge is about 400 cycles. Further, the battery using the AB ₅ alloy has an advantage that the discharge current can be set high. However, it has not reached the stage of satisfying both the electrode capacity and the cycle life, which are technically required levels in recent years.

Therefore, in order to increase the electrode capacity of the battery using the AB ₅ type hydrogen storage alloy, a method of relatively increasing the content ratio of A site is also adopted. According to this method, the electrode capacity can be increased by about 30%, but there is a drawback that the charge / discharge cycle life is shortened.

Further, misch metal (Mm: La is 10 to 50 wt%, Ce is 30 to 60) which is a constituent material of the A site.
wt%, Pr 2-10 wt%, Nd 10-45 wt
%, A method of increasing the La content in a rare earth element mixture) is also used. That is, by using the misch metal in which the Ce element in the misch metal is reduced and the La content is relatively increased, the electrode capacitance is 3
It is also possible to increase it by about 50%. However, also in this case, it was difficult to extend the cycle life.

As described above, the discharge capacity, the cycle life and the discharge voltage have been particularly emphasized as the reference characteristics for evaluating the secondary battery. Among these characteristics, in the case of a nickel-hydrogen secondary battery, the discharge voltage is almost determined by the redox reaction of the nickel oxide of the positive electrode and the hydrogen reaction of the negative electrode.Therefore, the discharge voltage is improved even if the hydrogen storage alloy is improved. The voltage does not change significantly. On the other hand, as the battery characteristics that are actually greatly improved by improving the hydrogen storage alloy,
There are two major characteristics: discharge capacity and cycle life.

In addition to these characteristics, as a battery characteristic improved by improving the hydrogen storage alloy, there is capacity rising property (ease of activation). That is, it is a characteristic that a high electrode capacity can be obtained by only a small number of activation operations (charging / discharging operations) after the battery is assembled. This capacity rising property is a characteristic that the user does not need to pay attention to when using the battery as a product, but if this capacity rising property is poor, the number of battery manufacturing steps increases and the battery manufacturing cost rises significantly. This is one of the important characteristics when the battery is designed by the manufacturer.

In batteries used in conventional handy camcorders and cellular phones, which have been mainly used in the past, the above-mentioned three major characteristics of discharge capacity, cycle life and capacity rising property are noticed and improved to improve the end user's ability. In addition to being able to provide a battery that fully satisfies the above requirement, it is also possible to reduce the manufacturing cost of the battery itself.

[0012]

However, due to the rapid spread of portable devices up to the present time, the demand for longer life of the batteries used as the power source for driving the devices is further increasing. It is becoming difficult to deal with it at the end of its life.

The present invention has been made to solve the above problems, and has a high hydrogen storage capacity for a battery, which can realize a long life of the battery, in addition to a high electrode capacity and a good initial activity. An object of the present invention is to provide a manufacturing method and a nickel-hydrogen secondary battery using the alloy.

[0014]

In order to achieve the above object, the inventors of the present invention have clarified the factors that hinder the extension of the battery life. As a result, in particular, the hydrogen storage alloy used for the negative electrode is pulverized at the time of charge / discharge of the battery, or the pulverized hydrogen storage alloy is corroded by the strong alkaline electrolytic solution, and hydroxide is formed on the alloy surface by the electrolytic solution. It was found that the formation of the battery and the deterioration of the battery function are major obstacles.

Then, various measures were taken to eliminate the above-mentioned inhibiting factors. As a result, when a film having a predetermined thickness made of nitride or carbide is integrally formed on the surface of the hydrogen-absorbing alloy powder, the hydrogen-absorbing alloy can be finely divided and electrolyzed without impairing the smooth hydrogen absorption-desorption reaction. It was found that the formation of hydroxide by the liquid can be effectively suppressed, and the life of the battery using the hydrogen storage alloy can be significantly extended. The present invention has been completed based on the above findings.

Further, the inventors of the present application have paid attention to the fact that the three major characteristics of the battery are good, the electrode capacity can be greatly increased, and that hydrogen can be absorbed and released at around room temperature and atmospheric pressure. Set the composition range, especially for AB ₅ and AB ₂
The hydrogen storage alloy of the system was selected for study.

That is, the first hydrogen storage alloy for a battery according to the present invention has a general formula ABx (where A is at least one element selected from rare earth elements including Y (yttrium), B is Ti, Zr, Hf, V, Nb, Ta, Cr,
Mo, W, Mn, Fe, Co, Ni, Cu, Ag, A
1, at least one element selected from Ga, In, Si, Ge and Sn, and an alloy having a composition represented by 4.5 ≦ x ≦ 5.5), and at least a nitride and a carbide of the above element. AB ₅ characterized in that a film consisting of one side is formed on at least a part of the surface of the above alloy.
System hydrogen storage alloy for batteries.

The second hydrogen storage alloy for batteries according to the present invention has the general formula ABx (where A is Ti, Zr, Hf, Y).
At least one element selected from rare earth elements including (yttrium), B is V, Nb, Ta, Cr, Mo,
W, Mn, Fe, Co, Ni, Cu, Ag, Al, G
at least one element selected from a, In, Si, Ge and Sn, and an alloy having a composition represented by 1.8 ≦ x ≦ 2.3), and comprising at least one of a nitride and a carbide of the above element. A hydrogen storage alloy for batteries of AB ₂ type, characterized in that the coating film formed on at least a part of the surface of the above alloy.

Further, in the AB ₅ type or AB ₂ type hydrogen storage alloy for batteries, it is preferable that the alloy has a columnar crystal structure in at least a part thereof.

Further, the method for producing a hydrogen storage alloy for a battery according to the present invention is to prepare an AB ₅ series or AB ₂ series hydrogen storage alloy having a predetermined composition as described above, and obtain the obtained alloy with nitrogen or carbonization. It is characterized in that a film made of at least one of a nitride and a carbide is formed on at least a part of the surface of the alloy by heat treatment in an atmosphere containing hydrogen.

Before forming the coating, it is preferable to carry out a homogenizing heat treatment in which the alloy is heated at a temperature of 400 to 1000 ° C. for 1 to 10 hours in a non-oxidizing atmosphere.

Further, the nickel-hydrogen secondary battery according to the present invention has an electrical insulation property between a negative electrode containing the above-mentioned AB ₅ type or AB ₂ type hydrogen storage alloy and a positive electrode containing nickel oxide. It is characterized in that it is housed in a hermetically sealed container via a separator having, and an alkaline electrolyte is filled in the hermetically sealed container.

The hydrogen storage alloy for batteries according to the present invention is represented by the general formula ABx, and the composition ratio X of B site is 4.5 to.
AB ₅ set to 5.5 or in the range of 1.8 to 2.3
It is a type alloy or AB ₂ type alloy. When the composition ratio X of B site is out of the above range, phases other than AB _{4.5 to 5.5} and AB _{1.8 to 2.3 in} the alloy (for example, AB, AB ₃ , A ₂
The production amount of the phase composed of B ₇ etc. and the phase composed of the element simple substance composing the B site [hereinafter referred to as the second phase] increases.

When the amount of the second phase other than the phase composed of AB _x increases in the alloy, the proportion of two or more alloy phases having different compositions containing the second phase in the hydrogen storage alloy that are in contact with each other increases.
The interface between the alloy phases having such different compositions has weak mechanical strength, and cracks are likely to occur from the interface as a starting point as hydrogen is absorbed and released.

Further, segregation is likely to occur at the interface, and corrosion of the hydrogen storage alloy is likely to occur from the segregation product as a starting point. Further, the second phase is
When an alloy containing less hydrogen than B _x and containing a large amount of the second phase is used as an electrode, the electrode capacity per unit volume decreases. In any case, when a hydrogen storage alloy is used as an electrode material, the electrode capacity and life are reduced.

After all, the reason why the value of X is limited is as follows. If the value of X is less than the lower limit, corrosion of the battery during charge / discharge is small, and it becomes impossible to obtain a hydrogen storage alloy that is resistant to cracking and pulverization. On the other hand, when the above x exceeds the upper limit, the formation of the second phase is recognized depending on the usual industrial alloy production method, and the characteristics of the hydrogen storage alloy cannot be improved. Therefore, the value of x is set within the above range.

The general formula ABx (x = 4.5 to 5.5)
The A site component of the alloy represented by is a component necessary for forming a hydride, and specifically, a rare earth element containing Y (specifically, Y, La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b, Lu).
The A site component of the alloy represented by the general formula ABx (x = 1.8 to 2.3) is at least one selected from rare earth elements containing Zr, Ti, Hf, and Y. In addition,
High-purity rare earth elements or simple rare earth elements are extremely expensive. Therefore, by using an inexpensive misch metal (hereinafter abbreviated as Lm) that is a mixture of a plurality of rare earth elements, it is possible to significantly reduce the material cost of the hydrogen storage alloy. The above Lm is usually La10.
70wt%, Ce0-50wt%, Pr2-10wt
%, Nd of 10 to 45 wt% is used.

The B component in the general formula is Co, Al, F.
e, Si, Cr, Cu, Ti, Zr, Hf, V, Nb,
At least one element selected from Ta, Mo, W, Ag, Ga, In, Si, Ge and Sn is shown. The B site component of the alloy represented by the general formula ABx (x = 1.8 to 2.3) is V, Nb, Ta, Cr, Mo, W, M.
n, Fe, Co, Ni, Cu, Al, Ga, In, A
At least one element selected from i, Ge and Sn is shown. Of the above B site components, Co, Al, F
e, Si, Cr, and Cu are elements that are particularly effective in extending the life of the hydrogen storage alloy.

Of the B-site components, Mn is effective for increasing the capacity of the negative electrode containing the hydrogen storage alloy and lowering the hydrogen storage / release pressure (equilibrium pressure), and Al is similar to Mn in hydrogen content. It has the effect of lowering the occlusion / release pressure (dissociation pressure) and can increase the durability. Also Co
Is effective in improving the corrosion resistance of the alloy against the electrolytic solution and the like, and the pulverization of the alloy is significantly suppressed. Note that Co
Although increasing the additive amount improves the cycle life, it tends to decrease the electrode capacity.
It is necessary to optimize the addition amount.

In addition, the hydrogen storage alloy according to the present invention includes
At least one element selected from Pd, B, Pb, C, N, O, F, Cl, S and P may be contained as an impurity in a range that does not impair the characteristics of the alloy of the present invention. The content of each of these impurities is 6000.
It is preferably in the range of ppm or less. More preferably 5000 ppm or less, still more preferably 4000 pp
m or less is good.

The method for producing the alloy used in the present invention is not particularly limited as long as it is a method capable of homogenizing the alloy composition and preventing 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.
It is formed by cooling and solidifying the alloy melt by using a rotating disk method, a centrifugal atomizing method, a single roll method, a twin roll method, or the like. When cooling the molten alloy, the cooling rate is 10 ° C /
By setting the time to be more than 2 seconds, an alloy having a uniform structure and less segregation can be obtained. In particular, using the melt quenching method for rapidly cooling the molten alloy in a molten state, such as the gas atomizing method, rotating disk method, centrifugal spraying method, single roll method, twin roll method, etc. By optimizing the manufacturing conditions such as the peripheral speed of the surface, the temperature of the molten metal, the cooling rate, the type of gas in the cooling chamber, the pressure, and the injection amount of the molten metal, a large amount of alloy can be stably manufactured.

When a ribbon-shaped, flake-shaped, or granular hydrogen storage alloy is produced by using the above-described molten metal quenching method, it is equiaxed depending on conditions such as the material of the cooling roll or the rotating disk and the cooling rate of the molten alloy. A crystal structure or a columnar crystal structure is formed in the alloy.

In the manufacturing process of the above alloy particles, 180
When a molten metal is quenched at a cooling rate of 0 ° C./sec or more to produce a hydrogen storage alloy, each crystal grain constituting the alloy is 1 to 1
As it becomes finer to about 00 μm and the alloy strength increases,
Since the disorder of the grain boundaries is reduced, the hydrogen storage amount is increased and the electrode capacity can be increased.

By the melt quenching treatment described above, a hydrogen storage alloy having a columnar crystal structure developed at least in part can be formed. Here, the columnar crystal refers to a columnar crystal grain having a ratio of a minor axis to a major axis (aspect ratio) of 1: 2 or more. In the columnar crystal structure, unlike the equiaxed crystal structure, the crystal orientations are aligned, so that the disorder of the grain boundaries is small, the hydrogen storage amount is increased, and the electrode capacity can be increased by the inventors' experiments. 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, the formation of local cells due to segregation is small, and it is possible to effectively prevent the shortening of the life due to the refinement of the alloy.

The crystal structure of the hydrogen storage alloy produced by the molten metal quenching treatment is a columnar crystal in the cross section in the thickness direction of the hydrogen storage alloy when it is incorporated into a battery as a hydrogen storage alloy electrode, from the viewpoint of improving battery characteristics. The area ratio of the tissue may be 50% or more, more preferably 70% or more, and further preferably 80% or more. Area ratio of columnar crystals is 50
%, The cycle life of the negative electrode using this alloy becomes longer than the cycle life of the negative electrode using the hydrogen storage alloy manufactured by the casting method. In particular, when the entire molten metal quenched alloy is formed of columnar crystals, segregation is particularly reduced, and the capacity and life of the alloy electrode can be further improved. On the other hand, when the area ratio is less than 50%, there is no remarkable difference in cycle life as compared with a negative electrode using a cast alloy.

As described above, internal strain is likely to occur in the alloy prepared by the melt quenching method, while segregation is likely to occur in the alloy prepared by the casting method. In any case, the alloy was used as the negative electrode material. In many cases, the electrode capacity and the service life are reduced.

Then, the alloy prepared by cooling and solidifying is
It is desirable to carry out a homogenizing heat treatment in which the temperature is 400 to 1000 ° C. for 1 to 10 hours in advance.

When the temperature of the homogenizing heat treatment is less than 400 ° C., it becomes difficult to remove the internal strain, but the temperature is 10
When the temperature is higher than 00 ° C., the composition changes due to the evaporation of alloy components such as Mn, and the alloy strength decreases due to secondary recrystallization. Therefore, the heat treatment temperature is 400
It is set in the range of -1000 ° C. Particularly, in order to improve the electrode characteristics, the range of 500 to 800 ° C. is preferable.

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 so as to exceed 10 hours, there is a high possibility that the crystal grains become coarse. Therefore, it is preferably about 2 to 5 hours in consideration of the production efficiency.

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

By carrying out 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 the life can be further enhanced. In particular, an alloy having a composition not containing Mn has a small effect of heat treatment, but for an alloy having a composition containing Mn, both the electrode capacity and the battery life are significantly improved by the heat treatment.

As described above, the alloy melt is cooled and solidified,
The hydrogen storage alloy for a battery according to the present invention is prepared by integrally forming a film made of a nitride or a carbide of an alloy component element on the surface of an alloy that has been subjected to a homogenizing heat treatment, if necessary.

The above coating is subjected to a nitriding / carburizing treatment by heating the alloy powder at a temperature of 300 to 800 ° C. for 10 minutes to 10 hours in a non-oxidizing atmosphere containing a gas serving as a nitrogen source or a carbon source, for example. It is formed by forming nitrides and carbides on the surface of the alloy powder.

The atmosphere during the nitriding / carburizing treatment is carried out in an inert gas such as Ar with a constant partial pressure ratio of N ₂ gas as a nitrogen source and hydrocarbon gas such as methane (CH ₄ ) as a carbon source. It is formed by diluting and mixing so that For example, Ar gas is used as an inert gas, while N is used as a nitrogen source.
_In order to form a uniform film using ₂ gas or CH ₄ gas as a carbon source, Ar gas and N ₂ gas or C are used.
The partial pressure ratio with the H ₄ gas may be adjusted within the range of 0: 100 to 95: 5.

The thickness of the film made of the nitride or carbide is set to 1 μm (10000 angstrom) or less. When the thickness of the film exceeds 1 μm, the permeability of hydrogen to the alloy is deteriorated and the battery function is likely to be hindered, and the ratio of the hydrogen storage alloy is relatively decreased, so that the battery capacity is decreased. Therefore, the film thickness is 1
Although it is set to be less than or equal to μm, in order to reduce the influence on hydrogen permeability and battery capacity, 0.1 μm (1000
Angstrom) or less is preferable, and further 0.05μ
It is more preferably m (500 angstroms) or less.

The thickness of the film can be arbitrarily set by appropriately adjusting the partial pressure ratio of the atmospheric gas, the heat treatment time and the temperature during the nitriding / carbonizing treatment.

Since the above-mentioned film is composed of a high hardness and stable nitride or carbide having a covalent bond structure, the structural strength of the alloy particles can be increased, and the fine powder of the alloy can be effectively prevented, and at the same time, the alkaline electrolysis can be performed. It is possible to effectively suppress the progress of corrosion of the alloy by the liquid and the formation of hydroxide. Therefore, when a battery is formed by using the above-mentioned hydrogen storage alloy having a film formed thereon as a negative electrode material, the life of the battery can be significantly extended as compared with the case where a hydrogen storage alloy without a film is used. it can.

By forming the above film so as to cover 20% or more of the alloy surface, the effect of improving battery life is exhibited, but preferably 50% or more of the alloy surface, more preferably the entire alloy surface. It is desirable to form a film at (100%). Further, oxides resulting from impurities such as oxygen contained in the alloy may be contained in the film as long as hydrogen permeability to the alloy is not impaired.

The hydrogen-absorbing alloy of the present invention having the above-mentioned coating may be formed by crushing alloy pieces which have been previously subjected to nitriding treatment or carbonization treatment into a predetermined particle size. The powder can be formed by nitriding treatment or carbonization treatment. In the case of the former, alloy powder whose entire surface is not covered with a film after pulverization is also generated in part, but even when these alloy powders are mixed and evaluated as an electrode, conventional alloy powders that have not been surface-treated The life can be significantly extended as compared with the case of using. That is, the effect of the present invention can be obtained with a negative electrode containing at least a part of the alloy having a film formed thereon.

Next, a nickel-hydrogen secondary battery (cylindrical nickel-hydrogen secondary battery) according to the present invention in which the above-mentioned hydrogen storage alloy for batteries having a coating film is used as a negative electrode active material will be described with reference to FIG. .

The nickel-hydrogen secondary battery according to the present invention has the above general formula ABx (x = 4.5 to 5.5 or x = 1.
On the surface of the alloy represented by 8 to 2.3), an electrically insulating separator 13 is interposed between a negative electrode 11 containing the hydrogen storage alloy for a battery and a positive electrode 12 containing nickel oxide, each having the above-mentioned coating formed thereon. It is housed in a closed container 14 and 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).
It is wound in a spiral shape with a separator 13 interposed therebetween and is 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 in 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 airtightly fixed via the gasket 17.
The positive electrode lead 18 has one end connected to the positive electrode 12 and the other end connected to the lower surface of the sealing plate 16. The cap-shaped positive electrode terminal 19 has the hole 15 on the sealing plate 16.
It is attached to cover. Rubber safety valve 20
Are arranged 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 fixes the positive electrode terminal 19 and the collar paper 22 placed on the upper ends of the container 14 so that the container 14 can be fixed.
It is attached near the top of the.

As the hydrogen storage alloy electrode 11, the paste type and non-paste type electrodes described below are used. (1) The paste-type hydrogen storage alloy electrode is a paste prepared by mixing the hydrogen storage alloy powder obtained by crushing the hydrogen storage alloy with a polymer binder and conductive powder added as necessary. Then, the paste is applied to a conductive substrate as a current collector, filled, dried, and then subjected to a roller press or the like to prepare. (2) In the non-paste type hydrogen storage alloy electrode, after stirring the above hydrogen storage alloy powder, the polymer binder, and the conductive powder added as necessary, and spraying them on the conductive substrate which is the current collector. It is produced by applying a roller press or the like.

As the pulverization method of the hydrogen storage alloy, for example, a mechanical pulverization method such as a ball mill, a pulperizer, a jet mill or the like, or a method of occluding and releasing high-pressure hydrogen and pulverizing by volume expansion at that time is adopted. .

Examples of the polymer binder include sodium polyacrylate and polytetrafluoroethylene (PTF).
E), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and the like can be mentioned. Such a polymer binder is preferably added in an amount of 0.1 to 5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy. However, in the case of producing the non-paste hydrogen storage alloy electrode of (2), the hydrogen storage alloy powder and the conductive powder added as necessary are made into a three-dimensional (mesh) form by fibrating by stirring. It is preferable to use polytetrafluoroethylene (PTFE), which can be fixed, as the polymer binder.

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

As the conductive substrate, for example, a two-dimensional substrate such as punched metal, expanded metal, or wire mesh, or a three-dimensional substrate such as a foam metal substrate, a mesh-like sintered fiber substrate, or a felt-plated substrate obtained by plating a nonwoven fabric with a metal. Can be mentioned. However, when the non-paste hydrogen storage alloy electrode of the above (2) is manufactured, a two-dimensional substrate is preferably used as the conductive substrate because the mixture containing the hydrogen storage alloy powder is scattered.

The non-sintered nickel electrode 12 combined with the hydrogen storage alloy electrode is, for example, nickel hydroxide and cobalt hydroxide (Co (O
H) ₂ ), cobalt monoxide (CoO), a mixture of metallic cobalt, etc., with carboxymethyl cellulose (CMC),
A polyacrylic acid salt such as polyacrylic acid soda is appropriately mixed 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 and then applying a roller press or the like.

Examples of the polymer fiber non-woven fabric used for the separator 13 include nylon, polypropylene,
Examples thereof include a single polymer fiber such as polyethylene, or a composite polymer fiber obtained by mixing and spinning these polymer fibers.

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

[0061]

According to the hydrogen storage alloy for a battery having the above structure,
Since the coating film made of nitride or carbide having high hardness and stability is formed on at least a part of the surface of the alloy, the structural strength of the alloy is enhanced and the deterioration due to the pulverization of the alloy can be effectively prevented. Further, the protective action of the above film can effectively prevent the corrosion of the alloy and the formation of hydroxide by the electrolytic solution. Therefore, when a battery is constructed by using the above-mentioned hydrogen storage alloy having a film formed thereon as a negative electrode material, the life of the battery can be significantly extended as compared with the case where no film is formed.

[0062]

EXAMPLES Examples of the present invention will be described more specifically below.

Examples 1 to 40 Various metal raw material powders were mixed so that the alloy compositions shown in the left column of Tables 1 and 2 were obtained, and the obtained raw material mixture was heated and melted in an Ar gas atmosphere. Each of the alloy melts was prepared. In the raw material powder, the misch metal (Lm) is 60 wt% La-5 wt% Ce-5 wt% Pr.
A La-rich Misch metal with a composition of -30 wt% Nd was used.

Next, Examples 1 to 4, 9 to 14, 27, 2
The alloy melts for 8, 33 to 38 were rapidly solidified by a single roll method to prepare alloy samples. Example 5
The alloy melts for ~ 8 were rapidly solidified by the twin roll method to prepare 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 was SUJ-2, and a roll having a diameter of 300 mm was used. Further, the rotation speed of the cooling roll was set to 800 rpm, the roll gap was set to zero, and a linear pressure of 5 tons was applied between the rolls. Example 1
Alloy melts for 5 to 19, 29, and 30 were rapidly cooled and solidified by a gas atomizing method to obtain alloy samples. Example 2
Alloy melts for 0 to 24, 31, and 32 were rapidly cooled and solidified by a centrifugal atomization method to obtain alloy samples. On the other hand, Examples 25 to 2
The alloy melts for Nos. 6, 39 and 40 were cast into a water-cooled mold having a mold interval of 40 mm to be solidified to prepare alloy samples.

Among the alloy samples thus obtained, the alloy samples for Examples 11 to 14, 18 to 19 and 23 to 24 were subjected to a homogenizing heat treatment of heating at a temperature of 600 ° C. for 4 hours in an Ar gas atmosphere. did. For the alloy samples of Examples 25 and 26, the temperature was 1 in the same Ar gas atmosphere.
A homogenizing heat treatment was performed at 000 ° C. for 4 hours.

Among the alloy samples thus homogenized as required, Examples 1, 2, 5, 6, 9 to 14, 2
With respect to the alloy samples of 5 to 28 and 33 to 38, hydrogen pulverization was carried out to obtain alloy powder having an average particle size of 30 μm. With respect to alloy samples other than those described above, classification treatment or optimization of production conditions was performed so as to obtain alloy powder having an average particle size of 30 μm.

Among the obtained alloy powders, each of the alloy powders for the odd-numbered examples was heated at a temperature of 600 ° C. in an atmosphere in which the partial pressure ratio of N ₂ gas and Ar gas was adjusted to 1: 1. A hydrogen storage alloy powder for each battery was prepared by performing a nitriding treatment by heating for 2 hours to form a film made of a nitride on almost the entire surface of the alloy powder.

On the other hand, each of the alloy powders for the even-numbered examples was carbonized by heating it at a temperature of 600 ° C. for 2 hours in an atmosphere in which the partial pressure ratio of CH ₄ gas and Ar gas was adjusted to 1: 1. The hydrogen storage alloy powder for each battery was prepared by forming a film of carbide on almost the entire surface of the alloy powder.

In Examples 3, 4, 7 and 8,
Prepare alloy flakes by each melt quenching process,
The obtained alloy flakes are previously subjected to a nitriding treatment or a carbonizing treatment to form a film, which is then pulverized into an alloy powder having a predetermined particle size. Further, in Example 37, carbonitriding treatment was carried out by heating the alloy powder at a temperature of 600 ° C. for 2 hours in an atmosphere in which Ar gas, N ₂ gas and CH ₄ gas were adjusted to a partial pressure ratio of 1: 1: 1. To prepare alloy powder.

The fracture surface structure of the hydrogen storage alloy for batteries according to each of the examples thus prepared was photographed with a scanning electron microscope (SEM), and the SEM photograph was subjected to image analysis.
The area ratio of columnar crystals to the entire fracture surface was measured. As described above, the columnar crystals are crystal grains having a ratio of major axis to minor axis (aspect ratio) of 2 or more.

Further, the type of the film formed on the alloy surface was identified by the Auger analysis method or the EPMA method, and the thickness was measured, and the results shown in Tables 1 and 2 were obtained.

Comparative Examples 1 to 9 On the other hand, Examples 5, 6 and 1 respectively except that the nitriding / carburizing treatment for forming the film was not performed and the film was not formed.
5, 21, 27, 29, 31, 39 were treated under the same conditions to prepare hydrogen storage alloy powders for batteries according to Comparative Examples 1, 2, 3, 4, 5, 6, 7, and 9, respectively.

The alloy composition is LmNi _3.9 Co _0.2 Mn.
Comparative Example 8 was performed under the same conditions as in Examples 25 to 26 except that _0.6 Al _0.2 Ti _0.1 was used, no homogenizing heat treatment was performed, and no nitriding / carburizing treatment was performed and no film was formed. A hydrogen storage alloy powder for a battery was prepared.

That is, the hydrogen storage alloys for batteries according to Comparative Examples 1, 2 and 5 were made of alloy samples manufactured by the single roll method, and Comparative Examples 3 and 6 were made of alloy samples manufactured by the gas atomizing method. In Comparative Examples 4 and 7, alloy samples manufactured by the centrifugal atomization method are used as materials, and in Comparative Examples 8 and 9, alloy samples manufactured by the casting method are used as materials.

The area ratio of columnar crystals to the entire fracture surface structure of the hydrogen storage alloy for batteries according to each comparative example was measured in the same manner, and the results shown in Table 3 were obtained.

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, the number of charge / discharge cycles, and the number of charge / discharge cycles required for initial activation (number of times of activation) were measured.

First, the hydrogen storage alloy powders for batteries, the PTFE powders, and the carbon powders according to the above-mentioned Examples and Comparative Examples were adjusted to 95.5%, 4.0%, and 0.5% by weight, respectively. After weighing, kneading was performed to prepare each electrode sheet.
The electrode sheet was cut into a predetermined size and pressure-bonded to a nickel current collector to prepare a hydrogen storage alloy electrode.

On the other hand, a small amount of CMC (carboxymethyl cellulose) 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 into a nickel porous body having a three-dimensional structure, dried, and then rolled by a roller press to produce a nickel electrode.

Then, the AA type (AA) nickel hydride batteries of the respective examples were assembled by combining the above hydrogen storage alloy electrodes and nickel electrodes. Here, the capacity of each battery was set to 650 mAh, which is the theoretical capacity of the nickel electrode, and a mixed aqueous solution of 7N potassium hydroxide and 1N lithium hydroxide was used as the electrolytic solution.

For each hydrogen storage alloy electrode, the current value of 220 mA per gram of alloy (220 mA / g) was 3
After charging to 00 mAh / g, Hg /
The maximum electrode capacity when the HgO reference electrode was discharged to a potential difference of −0.5 V was measured. Further, the number of times of activation of each electrode was measured. Here, the number of times of activation is the number of charge / discharge cycles required for the manufactured electrode to show the maximum capacity, and is an index for determining whether or not the battery characteristics of a battery manufactured using the alloy are good.

For each battery, 1.5 at 650 mA
After charging for an hour, a charge / discharge cycle of discharging with 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 measurement results are shown in Tables 1 to 3 below.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

[Table 3]

As is clear from the results shown in Tables 1 to 3, in the batteries formed by using the hydrogen storage alloys according to the respective examples in which the coatings made of nitrides, carbides and carbonitrides are formed, the coatings are In comparison with the battery of Comparative Example which does not form
It was confirmed that the change in the electrode capacity was small, but the number of charge / discharge cycles was increased by about 100 to 150 cycles, and the life of the battery was significantly improved.

Further, even if the alloy has a similar composition,
It was found that when the columnar crystal structure is formed in the alloy structure, the cycle life is prolonged as compared with the case where an alloy composed of equiaxed crystals is used.

[0087]

As described above, according to the hydrogen storage alloy for a battery of the present invention, since the coating film made of a nitride and carbide having high hardness and stability is formed on at least a part of the surface of the alloy, The structural strength of the alloy is enhanced, and deterioration due to pulverization of the alloy can be effectively prevented. Further, the protective action of the above film can effectively prevent the corrosion of the alloy and the formation of hydroxide by the electrolytic solution. Therefore, when a battery is constructed by using the above-mentioned hydrogen storage alloy having a film formed thereon as a negative electrode material, the life of the battery can be significantly extended as compared with the case where no film is formed.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing a configuration example of a nickel-hydrogen secondary battery according to the present invention.

[Explanation of symbols]

 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 Terminal 20 Safety Valve 21 Insulating Tube 22 Collar Paper

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01M 10/30 Z (72) Inventor Shusuke Inada 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama Works (72) Inventor Hiroyuki Hasebe 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside Toshiba Research and Development Center (72) Inventor Yoshiyuki Isazaki Komu-shishi-cho 1, Kawasaki-shi, Kanagawa Incorporated company Toshiba Research and Development Center

Claims (8)

[Claims] 1. A general formula ABx (where A is at least one element selected from rare earth elements including Y (yttrium), and B is Ti, Zr, Hf, V, Nb, Ta, C.
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
At least one element selected from Al, Ga, In, Si, Ge and Sn, and an alloy having a composition represented by 4.5 ≦ x ≦ 5.5), and at least a nitride and a carbide of the above element. A hydrogen storage alloy for a battery, wherein a film made of one is formed on at least a part of the surface of the above alloy. 2. A general formula ABx (where A is Zr, Ti,
At least one element selected from rare earth elements including Hf, Y (yttrium), B is V, Nb, Ta, C
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
At least one element selected from Al, Ga, In, Si, Ge, and Sn, and an alloy having a composition represented by 1.8 ≦ x ≦ 2.3), and at least a nitride and a carbide of the above element. A hydrogen storage alloy for a battery, wherein a film made of one is formed on at least a part of the surface of the above alloy. 3. The hydrogen storage alloy for batteries according to claim 1, wherein the alloy has a columnar crystal structure in at least a part thereof. 4. The general formula ABx (where A is at least one element selected from rare earth elements including Y (yttrium), and B is Ti, Zr, Hf, V, Nb, Ta, C.
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
At least one element selected from Al, Ga, In, Si, Ge and Sn, an alloy having a composition represented by 4.5 ≦ x ≦ 5.5) is prepared, and the obtained alloy is subjected to nitrogen or carbonization. A method for producing a hydrogen storage alloy for a battery, which comprises forming a film made of at least one of a nitride and a carbide of the above element on at least a part of the surface of the above alloy by heat treatment in an atmosphere containing hydrogen. 5. The general formula ABx (where A is Ti, Zr,
At least one element selected from rare earth elements including Hf, Y (yttrium), B is V, Nb, Ta, C
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
An alloy having a composition represented by at least one element selected from Al, Ga, In, Si, Ge and Sn, 1.8 ≦ x ≦ 2.3) is prepared, and the obtained alloy is subjected to nitrogen or carbonization. A method for producing a hydrogen storage alloy for a battery, which comprises forming a film made of at least one of a nitride and a carbide of the above element on at least a part of the surface of the above alloy by heat treatment in an atmosphere containing hydrogen. 6. The battery according to claim 4, wherein the alloy is subjected to a homogenizing heat treatment in a non-oxidizing atmosphere at a temperature of 400 to 1000 ° C. for 1 to 10 hours before forming the film. For producing hydrogen storage alloy for automobiles. 7. The general formula ABx (where A is at least one element selected from rare earth elements including Y (yttrium), and B is Ti, Zr, Hf, V, Nb, Ta, C.
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
At least one element selected from Al, Ga, In, Si, Ge and Sn, and an alloy having a composition represented by 4.5 ≦ x ≦ 5.5), and at least a nitride and a carbide of the above element. In a closed container with a separator having electrical insulation interposed between a negative electrode containing a hydrogen storage alloy for batteries and a positive electrode containing nickel oxide, in which a film composed of one is formed on at least part of the surface of the above alloy A nickel-hydrogen secondary battery, characterized in that the nickel-hydrogen secondary battery is housed in an airtight container and filled with an alkaline electrolyte in the closed container. 8. A general formula ABx (where A is Ti, Zr,
At least one element selected from rare earth elements including Hf, Y (yttrium), B is V, Nb, Ta, C
r, Mo, W, Mn, Fe, Co, Ni, Cu, Ag,
At least one element selected from Al, Ga, In, Si, Ge and Sn, and an alloy having a composition represented by 1.8 ≦ x ≦ 2.3), and at least a nitride and a carbide of the above element. In a closed container with a separator having electrical insulation interposed between a negative electrode containing a hydrogen storage alloy for batteries and a positive electrode containing nickel oxide, in which a film composed of one is formed on at least part of the surface of the above alloy A nickel-hydrogen secondary battery, characterized in that the nickel-hydrogen secondary battery is housed in an airtight container and filled with an alkaline electrolyte in the closed container.