JPH0797648A - Hydrogen storage alloy for battery, production thereof, and nickel-hydrogen secondary battery - Google Patents

Abstract

PURPOSE:To obtain a hydrogen storage alloy for battery having high electrode capacitance, long life characteristic, and superior rising characteristic by specifying a composition consisting of rare earth elements, Ni, Mn, Co, etc., and also forming a specific columnar crystal structure. CONSTITUTION:In an alloy represented by a general formula ANiaMnbMc (where A means rare earth elements including Y, M means Co, Al, Fe, Si, Cr, Cu, Ti, Zr, Zn, Hf, V, Nb, Ta, Mo, W, Ag, Pd, B, Ga, In, Ge, and Sn, 3.5<=a<=5, 0.1<=b<=1, 0<=c<=1, and 4.5<=a+b+c<=6), its structure is formed into a columnar crystal structure and the area ratio of columnar crystals having an aspect ratio not lower than 1:2 is regulated to >=50% and also it is preferable to regulate the average minor axis of the columnar crystals to <=39mum. This alloy can be obtained by rapidly solidifying a molten alloy on a rapidly rotating cooling roll at >=1800 deg.C/sec cooling rate. By using this alloy as negative electrode and an Ni oxide as positive electrode, together with alkaline electrolyte, an Ni-hydrogen secondary battery can be formed.

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 a battery, which is capable of satisfying the three major characteristics of good initial activity as well as potential stability (voltage flatness), 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 and longer life of 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 volume as compared with the conventional typical negative electrode material for alkaline secondary batteries, which is cadmium.
In addition to being able to increase the capacity of batteries, 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.

Further, the conventional hydrogen storage alloy is as described above.
The alkaline electrolyte causes a kind of corrosion reaction to deteriorate the electrode characteristics, but this reaction involves the consumption of the electrolyte. Therefore, in order to prevent the battery reaction from being hindered even if the amount of the electrolytic solution is reduced to some extent, the conventional battery should be filled with the electrolytic solution in excess of the amount necessary to accelerate the battery reaction. There is. However, when the amount of the electrolytic solution increases to cover the surface of the hydrogen storage alloy electrode, the consumption reaction rate of oxygen gas generated in the overcharge region decreases, which causes a problem that the internal pressure of the battery increases.

Further, the above-mentioned deterioration of the hydrogen storage alloy electrode poses a problem in battery design. That is, in order to seal the alkaline secondary battery, so that the hydrogen storage alloy electrode portion in a partially charged state usually remains even when the battery is discharged,
Further, the battery is designed so that when the battery is charged, a part of the hydrogen storage alloy electrode part which is in an uncharged state remains. However, the deterioration of the hydrogen storage alloy electrode progresses with the progress of charging and discharging. Therefore, in order to secure a sufficient cycle life as a battery, a large amount of the hydrogen storage alloy electrode must maintain the above relationship even if the alloy deteriorates. It is necessary to insert the above hydrogen storage alloy.
Therefore, the volume of the nickel electrode, which is the capacity control electrode, is reduced and the volume of the hydrogen storage alloy electrode is increased, which hinders the increase of the battery capacity, and the hydrogen storage alloy is expensive. Was inviting a rise.

By the way, as the hydrogen storage alloy, Z
r-Ti-Mn-Fe- Ag-V-Al-W and Ti ₁₅ Z
Examples thereof include AB ₂ or A ₂ B type hydrogen storage alloys represented by r ₂₁ V ₁₅ Ni ₂₉ Cr ₅ Co ₅ Fe ₁ Mn ₈ . These hydrogen storage alloys are manufactured by the usual method of crushing melt cast alloys. When these alloys are used for the negative electrode of the battery, the electrode capacity is high,
Good capacities of about 300 mAh / g and 400 mAh / g are obtained, and most of the metal materials constituting the alloy are inexpensive and economical.

However, these alloy systems generally have the drawback that it is difficult to produce them with a uniform composition distribution. In addition, a battery using the above alloy system as an electrode material has a slow capacity rise, and the activation operation (charge / discharge operation) of several tens of cycles after the battery is assembled.
There was a problem that a high electrode capacity could be obtained only after repeating the above. Moreover, there is a drawback that the discharge characteristics at large currents are poor,
Furthermore, there was a drawback that the voltage drop was large under low temperature conditions.
That is, of the three characteristics of high electrode capacity, long life, and initial activity that have been recently demanded, high capacity can be achieved, but it is difficult to satisfy the technical requirements in terms of initial activity (rising property). there were.

On the other hand, as another hydrogen storage alloy used for alkaline secondary batteries, there is an AB ₅ 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, Mm-Ni
The electrode capacity of the AB ₅ type hydrogen storage alloy made of —Co—Al type alloy (Mm is misch metal) is as low as less than 200 mAh / g, and the cycle life due to charge / discharge is about 400 cycles. It has not reached the stage where both the electrode capacity and the cycle life, which are the required standards, are satisfied.

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.

[0013]

[Problems to be Solved by the Invention] As described above,
Hydrogen storage alloys suitable for nickel-hydrogen secondary batteries, which satisfy all of the technically required levels of electrode capacity, cycle life, initial rising characteristics, and potential stability, have not yet been put into practical use.

The present invention has been made to solve the above problems, and the first object of the present invention is to satisfy all three major characteristics of high electrode capacitance, long life characteristics and good rising characteristics. A hydrogen storage alloy for a battery, a method for producing the same, and a nickel-hydrogen secondary battery using the alloy are provided.

A second object of the present invention is to use a hydrogen storage alloy as a negative electrode active material of a nickel hydrogen secondary battery,
Particularly, it is to provide a hydrogen storage alloy for a battery, which is excellent in long-life characteristics, and a nickel-hydrogen secondary battery using the same.

A third object of the present invention is to use a hydrogen-absorbing alloy electrode with little deterioration and to regulate the amount of electrolyte and the electrode capacity ratio, so that the capacity of the nickel-hydrogen alloy is high and the life is long, and the cost is low. It is about trying to provide the next battery.

[0017]

In order to achieve the above first object, the inventors of the present invention have focused on the fact that the electrode capacity can be easily increased and that hydrogen can be absorbed and released near room temperature and atmospheric pressure. Then, the AB ₅ type hydrogen storage alloy was selected as a research object. Then, hydrogen-absorbing alloys having various compositions were produced by substituting the AB ₅ type alloy components with various elements and changing the various production methods, and the effects of the composition, the production method, the heat treatment conditions and the like on the battery characteristics were comparatively studied. As a result, the following findings were obtained step by step.

First, the invention for achieving the first object will be described. It was found that when a part of the AB ₅ type hydrogen storage alloy was replaced with Mn, the electrode capacity was significantly improved to about 280 mAh / g. However, when the substitution amount of Mn exceeds a certain amount, the corrosion resistance of the hydrogen storage alloy decreases,
It has been found that the life characteristics of the battery using the alloy is rather deteriorated.

That is, it has become clear that corrosion is caused by a concentrated alkaline aqueous solution which is an electrolytic solution of an alkaline secondary battery, particularly when oxygen generated from the positive electrode at the time of overcharging coexists, and the electrode characteristics are deteriorated. It was

Therefore, the inventors of the present application have investigated the cause of the deterioration of the life characteristics of the battery due to the addition of Mn. When the constituent elements of various AB ₅ type alloy structures to which Mn was added were analyzed by an X-ray microanalyzer (EPMA), Mn in each alloy structure increased as the amount of Mn added increased.
It was confirmed that the amount of segregation of No. 1 increased. From this tendency, it was found that segregation of Mn was the main cause of the decrease in battery life that proceeded with an increase in the amount of Mn added.

In other words, in the conventional casting method of hydrogen storage alloy, which has a low cooling capacity, the crystal growth isotropic in the cooling process, so that grain boundaries are not formed in the hydrogen storage alloy particles. In addition to being easily ordered, segregation at the grain boundary portion is likely to occur because the time the alloy is present in the liquid phase is long. Further, even when the columnar crystals are partially formed by using the casting method having a high cooling ability, the columnar crystals grow in the minor axis direction, the segregation is large, and the corrosion resistance of the alloy is likely to decrease. In addition, Mn has a characteristic that it is more brittle than other alloy constituent elements. As a result, the segregation at the grain boundary portion serves as a starting point of corrosion and also lowers the mechanical strength, so that the pulverization of the alloy becomes remarkable due to the absorption and desorption of hydrogen.

Further, the segregation in the storage alloy easily forms a local battery, and Mn is eluted into the alkaline electrolyte due to its electrolytic corrosion action, or Mn on the surface of the alloy is changed to Mn (OH) _2. It is considered that the corrosion of the alloy is accelerated and the hydrogen storage amount of the hydrogen storage alloy itself is reduced, or the hydrogen storage alloy is peeled off from the electrode due to the corrosion, so that the capacity of the battery is reduced. Further, it is considered that the alloy becomes finer due to the decrease in the grain boundary strength due to the segregation and the deterioration of the battery characteristics with time also progresses.

From the above, it is expected that a hydrogen storage alloy electrode having a high capacity and a long life can be obtained by reducing the segregation of Mn.

Therefore, the following method was tried as a method for reducing segregation of Mn. (1) At the time of melting the alloy material, the constituent elements were made as fine as possible and well mixed, and then charged into a melting crucible. However, although they were relatively well mixed in the molten state, segregation with a size of several tens of μm to several hundreds of μm was formed during cooling. (2) As a heating device used during melting, a high-frequency heating device was used without using a resistance heating element, and the molten metal was forcibly stirred. In this case, although it was stirred very uniformly in the molten state, segregation having a size of several tens μm to several hundreds μm was formed during cooling. (3) When casting the molten alloy, the temperature of the molten alloy was raised as much as possible to lower the viscosity of the molten alloy, thereby homogenizing the molten alloy. In this case, segregation having a size of several tens μm to several hundreds μm was formed during cooling. (4) Heat treatment after casting (for example, 1000 ° C / 8
Segregation was reduced by carrying out h). In this case, although the effect was great, segregation with a size of several tens of μm remained.

Thus, even if one or more of the above-mentioned methods are combined and treated, segregation is reduced, but the required characteristics cannot be sufficiently satisfied.

As a result of various studies on the measures for preventing segregation of Mn and the like, the present inventors initially found that a molten alloy having a predetermined composition containing Mn at a temperature of 1000 to 1200 ° C./s which is faster than the cooling rate in the conventional casting method. The method of cooling at the cooling rate was adopted.

However, although the Mn segregation was reduced by this method, the required characteristics could not be sufficiently satisfied.

Therefore, the cooling rate is further increased to 1800 ° C./s.
The experiment was continued using the above high-speed cooling. as a result,
It was discovered that the experimental results were quite different from slow cooling in the range of 1000-1200 ° C / s. That is, the cooling rate is 1
At 800 ° C./s or more, the maximum value of Mn concentration distributed in the alloy becomes 1.3 times or less of the average value of Mn concentration of the entire alloy, and the maximum diameter of Mn segregated in the alloy. Was found to be 0.5 μm or less. Furthermore, it has been found that when an alloy having such Mn distribution is applied to a nickel-hydrogen secondary battery, the charge / discharge cycle life characteristics are dramatically improved without lowering the capacity characteristics.

First, the distribution of the Mn concentration will be described. The maximum value of Mn concentration distributed in the alloy is M of the entire alloy.
An alloy showing a value exceeding 1.3 times the average value of n concentration is M
Sites where the n concentration is locally high are dispersed in the alloy.
In such a portion, a corrosion reaction is likely to occur in a state where it is used as a negative electrode of a nickel-hydrogen battery, and deterioration of the hydrogen storage alloy itself is likely to proceed. In addition, if there is such a site having a different Mn concentration, the degree of expansion and contraction of the hydrogen storage alloy volume due to the absorption and desorption of hydrogen due to the electrode reaction will partly differ, so that stress is generated inside the alloy and pulverization progresses. As a result of increasing the specific surface area due to pulverization, the deterioration of the hydrogen storage alloy is further accelerated.

The above phenomenon hardly occurs in the hydrogen storage alloy in which the maximum value of Mn concentration distributed in the alloy is 1.3 times or less the average value of Mn concentration in the alloy. Therefore, when such an alloy is applied to the negative electrode, it is considered that the progress of corrosion of the alloy is suppressed and the cycle life characteristics of the nickel hydrogen battery are improved.

The ratio of the average value of Mn concentration of the entire alloy to the maximum value of Mn concentration in the alloy and the cycle life (the number of charge / discharge cycles) of the alloy electrode actually obtained from the experiments by the present inventors. The relationship is shown in FIG. In the diagram shown in FIG. 29, it became clear that a singular point exists when the maximum value of Mn concentration is around 1.3 times the average value. That is, Mn
The present inventors have for the first time discovered the fact that the battery life characteristics change drastically at the boundary of the singularity at which the maximum concentration is 1.3 times the average value.

Next, the maximum diameter of segregated Mn will be described. An alloy having a maximum segregated Mn diameter of more than 0.5 μm has a large segregation portion. Therefore, when such an alloy is used in a nickel-hydrogen battery, the segregation point serves as the starting point of the corrosion reaction, which causes Degradation is likely to progress. Further, when the alloy expands and contracts due to hydrogen absorption and desorption due to the electrode reaction, stress concentrates at the segregation point of Mn, so that cracks are likely to occur from the segregation point, and pulverization is further facilitated.

On the other hand, the maximum diameter of segregated Mn is 0.5.
In a hydrogen storage alloy having a thickness of μm or less, the above phenomenon hardly occurs. Therefore, when such an alloy is applied to the negative electrode of a nickel hydrogen battery, it is considered that the progress of corrosion of the negative electrode alloy is suppressed, and the cycle life characteristics of the nickel hydrogen battery are improved.

FIG. 30 shows the experimental results obtained by measuring the maximum diameter of Mn segregated in the alloy and the cycle life of the electrode using this alloy. In the diagram shown in FIG. 30, it was revealed that there is a singular point when the maximum diameter of Mn segregated in the alloy is around 0.5 μm. That is, the present inventors discovered for the first time the fact that the battery life greatly changes with the singular point at which the maximum diameter of segregated Mn becomes 0.5 μm as a boundary.

As described above, the present inventors have for the first time found that there is a singular point between the distribution of Mn concentration and the maximum diameter of segregated Mn and the required characteristics of the battery.
In order to achieve uniform Mn concentration and reduction of segregation, it is necessary to cool the molten alloy at a cooling rate of 1800 ° C./s or more to prepare a hydrogen storage alloy. It has been discovered that the above object cannot be achieved by slow cooling at about 1200 ° C / s. Again 180
By the high-speed cooling of 0 ° C./s or more, a columnar crystal structure having a new shape could be created for the first time (see Table 11).

Here, the columnar crystal structure having the novel shape means that the ratio (aspect ratio) of the minor axis to the major axis of the columnar crystal grains is 1: 2.
The above-mentioned crystal grains are referred to. The proportion of fine columnar crystals in the cross section of the crushed particles of the alloy is 50% or more, preferably 7%.
It has been discovered that higher electrode capacities and longer cycle lives can be achieved at the same time with 0% or more, more preferably 80% or more. That is, it was discovered for the first time that when the fine columnar crystal structure was formed, a high electrode capacity of 240 mAh / g or more and a long cycle life of 500 times or more were simultaneously achieved.

That is, as a result of various investigations by the present inventors, by forming fine crystal grains having a predetermined characteristic in the alloy by a melt quenching method at a cooling rate of 1800 ° C./s or more, a negative electrode material is obtained. It was found that the characteristics of can be greatly improved.

As a result of the study conducted by the present inventors, it was found that segregation of Mn and the like can be effectively prevented in the hydrogen storage alloy produced by the molten metal quenching method.

Furthermore, the inventors of the present invention have paid attention to the minute internal strain generated by the rapid cooling treatment, and have found that by removing this internal strain, a hydrogen storage alloy for a battery having further excellent characteristics can be obtained. That is, when the alloy material in a molten state is rapidly cooled by the method as described above, unlike the casting method, a large number of crystal nuclei are formed and the material is rapidly cooled, so that the alloy is likely to be distorted by cooling. It has been found that the formation of this internal strain makes it difficult for hydrogen to penetrate into and release from the inside of the alloy, resulting in deterioration of battery characteristics.

Therefore, as a result of various investigations by the present inventors, in the case of a melt-quenched alloy in which a fine crystal structure has been once formed by the melt-quenching method like the hydrogen storage alloy according to the present invention, the recrystallization temperature is Much lower than 200-500 ° C
For the first time, it was found that the internal strain can be effectively removed while maintaining the uniformity of the alloy and the hydrogen storage alloy for a battery with more excellent characteristics can be obtained only by performing the heat treatment for a short time in the temperature range. That is, it has been found that by relaxing this internal strain by the heat treatment, it is possible to further facilitate the penetration and release of hydrogen into the interior of the alloy and further improve the characteristics of the negative electrode material. The heat treatment time is at least 1 hour.

The present invention has been completed based on the above various findings. That is, the first hydrogen storage alloy for a battery according to the present invention has the general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium) and M is Co. , Al, Fe,
Si, Cr, Cu, Ti, Zr, Zn, Hf, V, N
b, Ta, Mo, W, Ag, Pd, B, Ga, In, G
a metal whose main component is at least one element selected from e and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦
1,0 ≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6), which has a columnar crystal structure, and the ratio of the minor axis to the major axis of the columnar structure (aspect ratio). The area ratio of columnar crystals having a ratio of 1: 2 or more is 50% or more. That is, a part of the B component of the AB ₅ type hydrogen storage alloy is replaced with Mn to increase the electrode capacity, and a hydrogen storage alloy capable of forming an electrode having a novel shape and long cycle life is formed. There is.

When the above alloy is produced by quenching, the thickness of the melt-quenched alloy may be set to 10 to 150 μm. The average minor axis of the columnar crystals is preferably 30 μm or less.

The second hydrogen storage alloy according to the present invention has the general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium) and M is Co. , Al, Fe, Si, Cr, Cu, T
i, Zr, Zn, Hf, V, Nb, Ta, Mo, W, A
a metal whose main component is at least one element selected from g, Pd, B, Ga, In, Ge and Sn;
3.5 ≦ a ≦ 5,0.1 ≦ b ≦ 1,0 ≦ c ≦ 1,4.5
≦ a + b + c ≦ 6), which is composed of an alloy having a composition represented by an X-ray microanalyzer,
A cross section of the alloy of 20 μm square is used as an observation area, and the observation area is divided into 100 units in the vertical direction and 100 units in the horizontal direction.
When observing the characteristic X-ray intensity of n, the characteristic X-ray intensity of Mn in each unit region was compared with the average value of the characteristic X-ray intensity of Mn in each unit region.
The hydrogen storage alloy is characterized in that the maximum value of the linear strength is 1.3 times or less.

As described above (maximum Mn concentration in alloy) /
The value of (average value of Mn concentration in the alloy) was measured by using an X-ray microanalyzer with a cross section of the alloy of 20 μm square as an observation region, and the observation region was divided into 100 units vertically and 100 units horizontally. When the characteristic X-ray intensity of Mn is observed, the value can be approximated to (maximum value of Mn characteristic X-ray intensity of each unit area) / (average value of Mn characteristic X-ray intensity of each unit area). . In the present invention, this value is 1.3 times or less. More preferably, it is 1.2 or less.

The third hydrogen storage alloy according to the present invention has the general formula A Ni _a Mn _b M _c (where A is Y).
At least one element selected from rare earth elements including (yttrium), M is Co, Al, Fe, Si, C
r, Cu, Ti, Zr, Zn, Hf, V, Nb, Ta,
Mo, W, Ag, Pd, B, Ga, In, Ge and S
a metal whose main component is at least one element selected from n, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦ 1, 0 ≦ c ≦
1, 4.5 ≦ a + b + c ≦ 6), and the Mn particles segregated in the alloy have a maximum diameter of 0.5 μm or less.

The first method for producing a hydrogen storage alloy for a battery according to the present invention is the general formula A Ni _a Mn _b M _c (where A
Is at least one element selected from rare earth elements including Y (yttrium), and M is Co, Al, Fe, Si,
Cr, Cu, Ti, Zr, Zn, Hf, V, Nb, T
a, Mo, W, Ag, Pd, B, Ga, In, Ge and Sn, a metal containing at least one element as a main component, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦ 1,0 ≦
When a molten alloy having a composition represented by c ≦ 1,4.5 ≦ a + b + c ≦ 6) is injected onto the running surface of a cooling roll that rotates at a high speed to quench and solidify, the alloy is rapidly cooled at a cooling rate of 1800 ° C./s or more. It is characterized by being processed to form a hydrogen storage alloy.

In the second manufacturing method, the molten alloy having the above composition is quenched at a cooling rate of 1800 ° C./s or more to prepare a molten alloy quenched alloy, and the obtained molten alloy is alloyed.
It is characterized by forming a hydrogen storage alloy for a battery by heat-treating at a temperature range of 200 to 500 ° C. for at least 1 hour.

Further, the quenching treatment of the molten alloy may be carried out under vacuum or in an atmosphere of an inert gas such as Ar. Further, the heat treatment may be performed in a vacuum or an inert gas atmosphere. In the first and second manufacturing methods, the molten metal quench alloy is formed by injecting the molten alloy onto the traveling surface of a cooling roll that rotates at a high speed and quenching and solidifying the molten alloy. The peripheral speed of the traveling surface of the cooling roll is 5 to 15 m. It is recommended to set it in the range of / second.

In all of the first to third hydrogen storage alloys for batteries according to the present invention, when Ni _a Mn _b M _c is represented by B, the alloy composition according to the present invention is 4.5 ≦ a + b + c ≦ 6.
A _{4.5 ~AB 6.} B composition ratio x (ie a + b
When the value of + c) is out of the above range, AB _4.5 to
Phases other than AB ₆ (eg AB, AB ₂ , AB ₃ , A ₂ B
The production amount of the phase composed of ₇ etc. and the phase composed of the element simple substance composing the B site [hereinafter referred to as the second phase]) is increased.

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 of 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 segregated material 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. When X is less than 4.5, the hydrogen storage alloy which is less likely to be corroded during charging / discharging of the battery and which is less likely to crack or become fine powder cannot be obtained. On the other hand, the x
When the value exceeds 6, the formation of the second phase is recognized depending on the usual industrially available alloy production method, and the characteristics of the hydrogen storage alloy cannot be improved. Therefore, x or (a + b
The value of + c) is set in the range of 4.5 to 6, more preferably 4.6 to 5.6, and further preferably 5.05.
The range is 5.5.

Further, according to the present invention, A Ni _a Mn _b M
_The A component constituting _c is a rare earth element containing Y (specifically, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, G
d, Tb, Dy, Ho, Er, Tm, Yb, Lu). High-purity rare earth elements or simple rare earth elements are extremely expensive. Therefore, by using a misch metal (hereinafter abbreviated as Mm or 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 Mm is usually La10 to 50.
wt%, Ce 30-60 wt%, Pr2-10 wt%,
A composition having an Nd of 10 to 45 wt% is used.

Further, the value of the composition ratio a of Ni is 3.5 to 5
The reason for limiting the range to is as follows. If the value of a is less than 3.5, the capacity of the electrode will decrease. On the other hand, when the value of a exceeds 5, the blending ratio of the other alloy components is relatively decreased, and it becomes difficult to increase the capacity.

Further, Mn is effective for increasing the capacity of the negative electrode containing the hydrogen storage alloy and for lowering the hydrogen storage / release pressure (equilibrium pressure), and is therefore an essential constituent element of the alloy of the present invention.
Mn is added in such a range that the composition ratio b is 0.1 to 1.0. If the composition ratio b exceeds 1, the alloy electrode is likely to be pulverized and the cycle life becomes short. Therefore, the upper limit of the composition ratio b is set to 1. On the other hand, when the composition ratio of Mn is less than 0.1, the improvement of the electrode capacity, which is one of the objects of the present invention, cannot be achieved.

The M component in the general formula is Co, Al, F.
e, Si, Cr, Cu, Ti, Zr, Zn, Hf, V,
Nb, Ta, Mo, W, Ag, Pd, B, Ga, In,
A metal whose main component is at least one element selected from Ge and Sn is shown. Of the above M components, Co, A
1, Fe, Si, Cr and Cu are elements that are particularly effective for extending the life of the hydrogen storage alloy. M component is the composition ratio c
Is added in a range of 1 or less. The composition ratio c is 1
If it exceeds, the capacity of the electrode formed of the alloy will decrease, so the upper limit was set to 1. Further, when the alloy is manufactured by using the melt quenching method, segregation is prevented, so that the life is extended to some extent. Therefore, the lower limit of the composition ratio c of the M component is set to 0.

Of the above M components, Al has a function of lowering the hydrogen storage / release pressure (dissociation pressure) as well as Mn, and can increase the durability.

Of the M components, 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. That is, when the amount of Co added is increased, the cycle life is improved, but the electrode capacity is reduced.
Since the high rate discharge characteristics tend to be impaired, 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
Hf, V, Nb, Ta, Mo, W, Ag, Pd, B, G
a, In, Ge, Sn, Pb, C, N, O, F, Cl,
At least one element selected from S, P and the like may be contained as an impurity as long as the characteristics of the alloy of the present invention are not impaired.

The content of each of these impurities is preferably in the range of 6000 ppm or less. More preferably 5000 ppm or less, still more preferably 40 ppm
00ppm or less is good.

The method for producing the hydrogen storage alloy for a battery according to the present invention is not particularly limited as long as it is a method for homogenizing the alloy composition to prevent segregation or to obtain the crystal structure according to the present invention. Using a molten metal quenching method such as a single roll method or a twin roll method, which will be described in detail with reference to the drawings, the material of the cooling roll, the rotation speed of the cooling roll (peripheral speed of the running surface), the temperature of the molten metal, By optimizing the gas species, pressure, and injection amount of molten metal, it is possible to stably manufacture a large amount.

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 300 mm, which is excellent in heat conductivity of copper, nickel, etc., and a hydrogen storage alloy molten metal 3 supplied from a ladle 2 and then jetting the same onto a running surface of the cooling roll 5. And a pouring nozzle 4 for pouring. The cooling roll 5 and the like are housed in a cooling chamber 1 adjusted to a vacuum or 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 set to approximately 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 sprayed further onto the running surface of the cooling roll 5, the molten alloy solidifies from the surface in contact with the cooling roll 5, crystal growth starts,
The solidification is completed by the time it is separated from the cooling roll 5. After that, the cooling further progresses while flying in the cooling chamber 1, and the hydrogen storage alloy 6 in which the concentration of the constituent elements is uniform, the segregation is small, and the crystal growth directions are aligned 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 5a, which are arranged in the cooling chamber 1 so that their traveling surfaces face each other.
5b, a melting furnace 7 for preparing a hydrogen storage alloy melt 3 by melting a raw material metal, and a hydrogen storage alloy melt 3 from this melting furnace 7.
Is provided with a pouring nozzle 4 for injecting between the cooling rolls 5a and 5b through 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 50 mm. The cooling rolls 5a and 5b are 0 to 0.5 m
300 to 2000 while maintaining a minute gap d of about m
It rotates at high speed at a rotation speed of about rpm. As the cooling roll, as shown in FIG. 2, in addition to the ones whose running surfaces are parallel to each other, so-called type rolls having a U-shaped or V-shaped cross-section can be used. Further, if the gap d between the cooling rolls 5a and 5b is excessively large, the cooling directions of the molten alloy are not aligned, and as a result, a hydrogen storage alloy in which the growth direction of columnar crystals is disturbed is produced, so it is set to 0.2 mm or less. It is preferable. Further, if the gap d is excessively large, the cooling rate is lowered, and the segregation of Mn is promoted, so that the concentration uniformity of Mn is lowered, and the size of the Mn segregated particles at the grain boundaries is large, so that the hydrogen storage alloy is grown. 0.2mm as it is manufactured
Set as follows.

In the manufacturing apparatus shown in FIG. 2 described above, the molten hydrogen storage alloy 3 is fed from the pouring nozzle 4 to the cooling rolls 5a,
When sprayed in the gap direction of 5b, the molten hydrogen storage alloy is solidified from the side in contact with the cooling rolls 5a and 5b on both sides, crystal growth starts, and completely solidifies by the time it is separated from the cooling rolls 5a and 5b. After that, the cooling further progresses while flying in the cooling chamber 1, and the hydrogen storage alloy 6 having columnar crystals according to the present invention with less segregation is manufactured.

Rotating Disc Method FIG. 32 shows an apparatus for producing hydrogen storage alloy particles by the rotating disc method. This manufacturing apparatus temporarily stores a disk-shaped rotating body 9 which is a high-speed rotating body arranged in a cooling chamber 1 in an argon gas atmosphere and a hydrogen storage alloy melt 3 supplied from a ladle 2, and The disk-shaped rotating body 9
And a pouring nozzle 4 for ejecting the molten metal on the traveling surface of. The rotating body 9 is made of a ceramic or metal material having relatively low wettability with respect to the molten metal for preventing the molten hydrogen storage alloy 3 from adhering and solidifying.

In the manufacturing apparatus of FIG. 32, when the molten hydrogen-absorbing alloy 3 supplied from the ladle 2 is injected from the pouring nozzle 4 onto the running surface of the disk-shaped rotor 9, the rotative force of the rotor 9 is generated. The particles are finely dispersed, and while flying inside the cooling chamber 1 without contacting the inner wall of the chamber 1, the particles are spheroidized by their surface tension, and are further cooled and solidified by an atmospheric gas such as argon gas. As a result, spherical hydrogen storage alloy particles 6 covered with the free cooling surface are produced. The hydrogen storage alloy particles 6 are recovered in the particle recovery container 10 arranged at the bottom of the cooling chamber 1.

Gas Atomizing Method FIG. 33 shows an apparatus for producing hydrogen storage alloy particles by the gas atomizing method. This manufacturing apparatus uses a heater 23 for a metal raw material disposed in a cooling chamber 1 in an argon gas atmosphere.
A melting furnace 24 for preparing a molten metal 3 for hydrogen storage alloy by heating and melting, and an inner diameter 2 formed at the bottom of the melting furnace 24.
The pouring nozzle 4 has a pouring nozzle 4 of about mm, a plurality of inert gas nozzles 25 attached so as to face the vicinity of the lower end opening of the pouring nozzle 4, and injecting a cooling inert gas such as argon gas. It has a structure including an on-off valve 26 that opens and closes.

In the manufacturing apparatus of FIG. 33, when argon gas is supplied into the melting furnace 24 containing the hydrogen storage alloy molten metal 3, the liquid surface of the molten metal 3 in the melting furnace 24 is pressurized and the melting furnace 24 Molten metal 3 is sprayed from the tip opening of the lower pouring nozzle 4. At this time, the inert gas nozzle 2 is arranged so as to face the ejection direction substantially at right angles.
An inert gas such as argon gas is injected from 5 toward the injected molten metal 3 at a high speed. As a result, the hydrogen storage alloy melt 3 is atomized and dispersed by the inert gas in the cooling chamber 1 without contacting the inner wall of the chamber 1, and is cooled and solidified while being extended downward along the swirl flow of the inert gas. . As a result, spherical hydrogen storage alloy particles 6 covered with the free cooling surface are produced.

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

The first to third hydrogen storage alloys according to the present invention are preferably obtained by quenching the molten alloy at a cooling rate of 1800 ° C./sec or more. 18 more
When a hydrogen absorbing alloy is produced by quenching a molten metal at a cooling rate of 00 ° C./s or more, each crystal grain constituting the alloy has 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.

The first hydrogen storage alloy for a battery according to the present invention has the columnar crystal structure developed particularly.

In the above-mentioned columnar crystal structure, unlike the equiaxed crystal structure, the crystal orientations are aligned, so that the grain boundaries are less disturbed, the hydrogen absorption amount is increased, and the electrode capacity can be increased. It was confirmed by these experiments. 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 a 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 must be 50% or more, more preferably 70% or more, and further preferably 80% or more. When the area ratio of the columnar crystals is 50% or more, 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 produced by the casting method. . In particular, when the entire melt-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%, no significant difference appears in the cycle life as compared with the negative electrode using the cast alloy. That is, by using the hydrogen storage alloy of the present invention which is produced by the above-mentioned melt quenching treatment and the area ratio of the columnar crystal structure in the cross section in the thickness direction is 50% or more, the electrode capacity is 240 mAh / g or more and the cycle life is 500. Excellent battery characteristics of more than once can be obtained at the same time. The more preferable value of the electrode capacity is 250 m
Ah / g or more, more preferably 255 mAh / g or more. The cycle life is more preferably 550 times or more, and further preferably 600 times or more.

Here, the columnar crystal means a columnar crystal grain having a ratio of a minor axis to a major axis (aspect ratio) of 1: 2 or more.

The method for producing the hydrogen storage alloy according to the present invention will be described in more detail.

The columnar crystal structure was developed as described above, and Mn
A hydrogen storage alloy for batteries with reduced segregation such as is produced by strictly controlling the preparation and cooling conditions of the molten alloy in the single roll method or the twin roll method.

That is, the molten alloy may be prepared by accommodating a hydrogen storage alloy (mother alloy) having the above-described composition produced by a casting method in advance in a melting crucible and melting it by high frequency. Alternatively, the amount of each constituent element added may be adjusted individually and directly dissolved in the crucible for preparation. At this time, among the constituent elements of the hydrogen storage alloy, it is preferable to add a relatively large amount of an element having a high vapor pressure such as a rare earth element or Mn.
That is, it is preferable to prevent the alloy composition from fluctuating due to volatilization of the element having a high vapor pressure, and to adjust the composition of the hydrogen storage alloy after quenching to a desired composition.

The obtained molten alloy is sprayed onto the running surface (cooling surface) of the cooling roll at a predetermined pressure, and is rapidly cooled and solidified into a ribbon-shaped or flake-shaped hydrogen storage alloy. At this time, columnar crystals grow from the surface of the cooling roll toward the high temperature part of the molten alloy, that is, in the direction perpendicular to the surface of the cooling roll. In order to sufficiently grow the columnar crystals, the thickness of the ribbon-shaped or flake-shaped hydrogen storage alloy is 10 to 150 μm, preferably 15 to 100 μm.
On the other hand, the peripheral speed of the running surface of the cooling roll is
In the case of a Cu roll, the range is 5 to 15 m / sec, and in the case of an Fe roll, the range is 8 to 30 m / sec. When the peripheral speed of the cooling roll is less than the lower limit of the above range, the cooling rate of the molten alloy is small, and it is difficult to sufficiently develop the columnar crystal structure in the above thickness range. On the other hand, when the peripheral speed exceeds the upper limit of the above range, the molten alloy is blown off at the moment of contact with the cooling roll, so that the cooling roll is not sufficiently cooled, the proportion of equiaxed crystals increases, and 50% in area ratio in the thickness direction
The above columnar crystal structure cannot be obtained.

The cooling rate of the molten metal quenching process is preferably 1800 ° C./s or more as described above. If this cooling rate is less than 1800 ° C./s, it is impossible to form a columnar structure having a special shape as described above. The cooling rate is preferably 2000 ° C./s or more, more preferably 2400 ° C./s or more.

The molten metal quenching treatment is preferably carried out in an atmosphere of an inert gas such as Ar or He in order to prevent deterioration of the molten alloy due to oxidation, but it is particularly preferably carried out in vacuum. That is, when the quenching process is performed in an inert gas atmosphere, the atmospheric gas may be caught between the cooling roll and the molten alloy, and the conditions under which a sufficient cooling effect can be obtained are narrowed. On the other hand, when the cooling process is performed in a vacuum, the entrainment of gas as described above does not occur,
The molten alloy is sufficiently cooled on the surface of the chill roll.

The constituent material of the cooling roll is Cu.
Materials having good thermal conductivity such as base alloys, Fe base alloys, and Ni base alloys are used. Further, a cooling roll formed by forming Cr plating or the like on the surface of the roll formed of the above material and hardening the surface may be used.

Further, as a constituent material of the crucible for preparing the molten alloy, conventional general-purpose quartz may be used.
However, since the quartz crucible does not generate heat due to high frequency heating, the molten alloy is cooled by the quartz when passing through the outlet, and as a result, the outlet is easily blocked. Therefore, by using a crucible made of a ceramic material such as Ti boride having good thermal conductivity, the above clogging can be effectively prevented.

In the hydrogen storage alloy prepared by the melt quenching method as described above, the crystal structure is fine and segregation of Mn and the like is small. Therefore, when the negative electrode for a battery is formed, its electrode capacity is 240 mAh / g or more. The level and the cycle life characteristics can be simultaneously improved at a level of 500 times or more. Also,
The present inventors have paid attention to the internal strain of the alloy generated by the quenching treatment, and have found by removing this internal strain that a hydrogen storage alloy for batteries with more excellent characteristics can be obtained.

Therefore, in the present invention, the internal strain is removed by heat-treating the hydrogen storage alloy of the above composition prepared by the melt quenching treatment at a relatively low temperature of 200 to 500 ° C. for 1 hour or more. That is, as a result of further study by the present inventors, by further subjecting the hydrogen storage alloy of the present invention prepared at the cooling rate of 1800 ° C./s or more to the heat treatment described above, both the capacity and the life are further improved. A new finding was obtained that it would be improved.

When the heat treatment temperature is lower than 200 ° C., it becomes difficult to remove the internal strain, while the temperature is 50.
If the temperature exceeds 0 ° C., compositional variation due to evaporation of alloying components such as Mn is caused, or alloy strength is reduced due to secondary recrystallization. Therefore, the heat treatment temperature is 200 ~
It is set in the range of 500 ° C. Particularly, in order to improve the electrode characteristics, the range of 250 to 350 ° C. is preferable.

If 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, the risk of causing coarsening of crystal grains increases, so that it is preferably about 2 to 5 hours in consideration of production efficiency.

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

By heat-treating the melt-quenched alloy at a relatively low temperature in this way, internal strain can be effectively removed while maintaining the homogeneity of the alloy, and the electrode capacity and life can be further increased. . In particular, the effect of heat treatment was small in the melt-quenched alloy containing no Mn, but the Mn-containing composition of the present invention significantly improved both the electrode capacity and the battery life.

Next, a fourth hydrogen storage alloy of the present invention which achieves the second object will be described.

In the fourth hydrogen storage alloy of the present application, at least 90% by volume is a single phase of AB _x (where A is at least one selected from rare earth elements including Y (yttrium), and B is Ni. And Co, Al, Fe, Si, Cr, C
u, Ti, Zr, Zn, Hf, V, Nb, Ta, Mo,
A metal containing at least one element selected from W, Ag, Pd, B, Ga, In, Ge and Sn as a main component, and X represents 5.05 ≦ X ≦ 6). And

The fourth hydrogen storage alloy for a battery according to the present invention needs to be a single phase in which at least 90% by volume is made of AB _x . Phases other than the phase consisting of AB _{x in the} alloy (for example, B, AB, AB ₂ , AB ₃ , A ₂ B ₇ , AB
₅ , the phase consisting of AB _1.4 etc. [hereinafter referred to as the second phase]) is 1
If it exceeds 0% by volume, two or more alloy phases of different compositions in the alloy often come into contact with each other. The interface between such alloy phases having different compositions has weak mechanical strength, and cracks are more likely to occur from the interface due to hydrogen absorption and desorption.
Further, segregation is likely to occur at the interface, and corrosion of the alloy is likely to occur from the segregation product as a starting point. Further, the second phase has a smaller hydrogen storage capacity than AB _x under the condition of using the electrode, and when an alloy containing more than 10% by volume of the second phase is used as an electrode, the electrode capacity per unit volume is lowered. To do.

The reason for limiting the value of X is as follows. When the above X is less than 5.05, the corrosion of the battery during charging / discharging is small, and it becomes impossible to obtain a hydrogen storage alloy that is unlikely to crack or be pulverized. On the other hand, when X exceeds 6, the formation of the second phase is recognized depending on the usual industrially available alloy production method, and the characteristics of the hydrogen storage alloy cannot be improved.

A that constitutes AB _x (5.05 ≦ X ≦ 6) is a rare earth element containing Y (specifically, Y, La, C).
e, Pr, Nd, Sm, Eu, Gd, Tb, Dy, H
o, Er, Tm, Lu) at least 1 selected from
Indicates the species. The element B is Ni, Co, Al, Fe, S.
i, Cr, Cu, Mn, Ti, Zr, Zn, Hf, V,
Nb, Ta, Mo, W, Ag, Pd, B, Ga, In,
A metal whose main component is at least one element selected from Ge and Sn is shown. In the present invention, the crystal form does not matter as long as the crystal system of the alloy maintains the CaCu ₅ system, but preferably the columnar crystals are formed.

As a method for producing the hydrogen storage alloy for batteries according to the present invention, a molten metal having a composition showing AB _x is used.
It is preferable to manufacture it by using various molten metal quenching methods because the hydrogen storage alloy can be stably obtained. Examples of the melt quenching method include the rotating disk method, the single roll method, the twin roll method, and the gas atomizing method.

Next, a nickel-hydrogen secondary battery (cylindrical nickel-hydrogen secondary battery) according to the present invention using the above-mentioned first to fourth hydrogen-absorbing alloys as a negative electrode active material will be described with reference to FIG. .

A hydrogen storage alloy electrode (negative electrode) 11 containing a hydrogen storage alloy is spirally wound with a separator 13 interposed between it and a non-sintered nickel electrode (positive electrode) 12 to form a bottomed cylindrical shape. It is stored in a 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. 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 the sealing plate 16 is attached to the container 14 by the caulking process to reduce the diameter of the upper opening inward. It is fixed airtightly through. 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 hat-shaped positive electrode terminal 19 is mounted on the sealing plate 16 so as to cover the hole 15. The rubber safety valve 20 is arranged so as to close the hole 15 in the space surrounded by the sealing plate 16 and the positive electrode terminal 19. Insulation tube 2
1 is attached near the upper end of the container 14 so as to fix the positive electrode terminal 19 and the collar paper 22 placed on the upper end of the container 14.

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 pulverizer, 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 blended in the range of 0.5 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.

The conductive substrate is, 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 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 polymeric fiber nonwoven 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.

Next, a nickel-hydrogen battery that achieves the third object of the present invention will be described.

In the nickel-hydrogen secondary battery according to the present invention, an alloy prepared by the molten metal quenching method is used as the hydrogen storage alloy constituting the hydrogen storage alloy electrode. The amount of the electrolyte solution of the nickel-hydrogen secondary battery constructed by using the hydrogen storage alloy electrode is in the range of 0.4 to 1.8 ml / Ah with respect to the capacity of the hydrogen storage alloy electrode. The capacity ratio of the uncharged state alloy in the battery discharge state of the hydrogen storage alloy electrode with respect to the capacity of is in the range of 1.1 to 2.0.

The hydrogen storage alloy is produced by a molten metal quenching method such as the above-mentioned rotating disk method, single roll method, twin roll method, or gas atomizing method.

The amount of the electrolytic solution is limited to the above range in relation to the capacity of the hydrogen storage alloy electrode for the following reason. When the amount of the electrolyte solution is less than 0.4 ml / Ah, the area of the hydrogen storage alloy electrode in contact with the electrolyte solution is reduced, which hinders a smooth battery reaction and reduces the capacity of the nickel electrode forming the battery. It cannot be fully withdrawn, resulting in a decrease in battery capacity. When the amount of the electrolyte solution exceeds 1.8 ml / Ah, the excess electrolyte solution covers the surface of the hydrogen storage alloy electrode, and the smooth reduction of oxygen gas generated from the nickel electrode in the overcharged state is hindered.
The internal pressure of the battery rises, which leads to deterioration of the battery characteristics accompanied by the safety valve operation.

The reason why the capacity ratio of the uncharged state alloy in the discharged state of the hydrogen storage alloy electrode to the capacity of the nickel electrode is limited to the above range is as follows. If the capacity ratio is less than 1.1, the battery capacity is regulated by the capacity of the hydrogen-absorbing alloy electrode. Therefore, unless a special charge control method or discharge control method is used, the battery internal pressure increases at the end of charge and the end of discharge. As a result, the battery characteristics are deteriorated with the operation of the safety valve. On the other hand, when the required amount ratio exceeds 2.0, the battery characteristics are not seriously hindered, but the void volume in the battery is decreased and the internal pressure of the battery is slightly increased, and the hydrogen storage alloy electrode occupies in the battery container. Since the volume is increased, the amount of the nickel electrode, which is the capacity regulating electrode, is reduced, and the battery capacity is reduced.

According to the first to third hydrogen storage alloys for a battery having the above structure, it is an AB ₅ type alloy containing Mn as an essential element and has a high capacity and excellent cycle life and initial characteristics.
Furthermore, it is possible to provide a negative electrode material for a nickel-hydrogen battery with a stable discharge potential. The above alloy is obtained by quenching molten alloy having a predetermined composition at a cooling rate of 1800 ° C./sec or more.

Although the behavior of the first hydrogen storage alloy having the above-mentioned crystal structure having the above-mentioned excellent characteristics is not clear, it is presumed to be due to the following action. That is, in the columnar crystal in which the crystal orientation of the hydrogen storage alloy is uniform, the expansion and contraction of the alloy during storage and desorption of hydrogen are performed in a certain direction, and the stress inside the alloy is reduced, so that the fine powder of the alloy Is suppressed. Therefore, the increase in the area in contact with the electrolytic solution is suppressed, and corrosion of the alloy is prevented. Further, in the hydrogen storage alloy produced by the conventional casting method, segregation is scattered at the grain boundary portion and becomes a starting point of corrosion. However, in the case of columnar crystals formed by growing crystals in one direction from the cooling surface as in the present application, segregation of elements is gathered at specific parts of the alloy as the crystals grow, and the starting point of corrosion inside the alloy decreases. It is thought to be to do.

Therefore, the cycle characteristics of the nickel-hydrogen secondary battery incorporating the electrode containing the hydrogen storage alloy are significantly improved.

The distribution of Mn concentration relating to the second hydrogen storage alloy of the present application will be described. In an alloy showing a maximum value of Mn concentration distributed in the alloy that exceeds 1.3 times the average value of the Mn concentration of the entire alloy, the regions where the Mn concentration is locally high are dispersed in the alloy. In such a portion, a corrosion reaction is likely to occur in a state where it is used as a negative electrode of a nickel-hydrogen battery, and deterioration of the hydrogen storage alloy itself is likely to proceed. In addition, if there is such a site having a different Mn concentration, the degree of expansion and contraction of the hydrogen storage alloy volume due to the absorption and desorption of hydrogen due to the electrode reaction will partly differ, so that stress is generated inside the alloy and pulverization progresses. As a result of increasing the specific surface area due to pulverization, the deterioration of the hydrogen storage alloy is further accelerated.

In a hydrogen storage alloy in which the maximum value of Mn concentration distributed in the alloy is 1.3 times or less of the average value of Mn concentration in the alloy, the above phenomenon hardly occurs. Therefore, when such an alloy is applied to the negative electrode, it is considered that the progress of corrosion of the alloy is suppressed and the cycle life characteristics of the nickel hydrogen battery are improved.

Next, the maximum diameter of Mn segregated in the third hydrogen storage alloy of the present application will be described. Segregated M
An alloy having a maximum n diameter of more than 0.5 μm has a large segregation portion. Therefore, when such an alloy is used in a nickel-hydrogen battery, the segregation point becomes the starting point of the corrosion reaction, and the hydrogen storage alloy itself deteriorates. It will be easier. Further, when the alloy expands and contracts due to hydrogen absorption and desorption due to the electrode reaction, stress concentrates at the segregation point of Mn, so that cracks are likely to occur from the segregation point, and pulverization is further facilitated.

On the other hand, the maximum diameter of segregated Mn is 0.5.
In a hydrogen storage alloy having a thickness of μm or less, the above phenomenon hardly occurs. Therefore, when such an alloy is applied to the negative electrode of a nickel hydrogen battery, it is considered that the progress of corrosion of the negative electrode alloy is suppressed, and the cycle life characteristics of the nickel hydrogen battery are improved.

Also, at least 90% by volume of single phase AB
_I (A is at least one rare earth element including Y, B is N
i and Co, Al, Fe, Si, Cr, Cu, Mn, T
i, Zr, Zn, Hf, V, Nb, Ta, Mo, W, A
a metal whose main component is at least one element selected from g, Pd, B, Ga, In, Ge and Sn;
When an electrode is formed by using the hydrogen storage alloy of the fourth invention of the present application where ≦ X ≦ 6) as an active material and the electrode is used to form a battery, the corrosion resistance to a concentrated alkaline electrolyte can be significantly improved. As a result, an alkaline secondary battery (for example, nickel-hydrogen secondary battery) with improved characteristics such as cycle life can be realized.

The reason why the hydrogen storage alloy having the single-phase AB _x alloy composition has the excellent corrosion resistance is not clear, but it is presumed to be due to the following behavior.

That is, first, in a hydrogen storage alloy containing 10% by volume or more of a plurality of phases instead of a single phase of CaCu ₅ type crystal structure by X-ray diffraction observation, alloy phases of different compositions should come into contact with each other. Will increase. The interface between such alloy phases having different compositions has weak mechanical strength, and cracks are more likely to occur from the interface due to hydrogen absorption and desorption. Further, corrosion due to segregation is likely to occur at the interface.
Further, the phase having a composition other than AB _x has a smaller storage amount of hydrogen ions under the electrode use conditions than that of AB _x .
As a result, when the nickel-hydrogen secondary electrode incorporating the electrode containing the hydrogen storage alloy as an active material was evaluated, not only the improvement of the life but also the reduction of the capacity were recognized.

From the above, by using at least 90% by volume of the hydrogen storage alloy as a single-phase AB _x , cracking and corrosion under the electrode use condition can be suppressed and the life can be improved. In addition, the crystal structure is CaCu
_Although it is type ₅ , the non-stoichiometric hydrogen storage alloy is
Since the crystal is strained, it can withstand expansion and contraction due to hydrogen absorption and desorption, and as a result, the cycle life of the electrode can be extended. Furthermore, the diffusion of hydrogen becomes faster. As a result, there is also an effect that the large current discharge characteristics when incorporated as a battery can be improved.

On the other hand, the hydrogen storage alloy produced by the melt quenching method is
Compared to the conventional hydrogen storage alloy produced by melting the raw material in a crucible in an inert atmosphere or vacuum and then casting it in a mold, the composition can be homogenized and the crystal size can be made smaller, and it is being cooled. It is possible to suppress the solidification segregation of. As a result, when an electrode is formed using the hydrogen storage alloy as an active material and a battery is formed using the electrode, the corrosion rate of the alkaline electrolyte can be reduced.

However, when the nickel-hydrogen secondary battery is constructed by using the negative electrode containing the hydrogen storage alloy produced by the melt quenching method, the hydrogen storage produced by the melt quenching method is used in the same battery design as the alloy by the conventional method. Not only can the characteristics of the alloy not be exhibited, but in particular, when the amount of electrolyte is too large, it may not be possible to reproduce from the battery characteristics of the conventional alloy.

Therefore, in the nickel-hydrogen secondary battery according to the present invention, the amount of the electrolytic solution is regulated within the range of 0.4 to 1.8 ml / Ah with respect to the capacity of the negative electrode of the hydrogen storage alloy. A smooth battery reaction is performed, the capacity of the nickel electrode can be sufficiently drawn out, and the capacity can be improved. Moreover, the oxygen gas generated from the nickel electrode can be smoothly reduced in the overcharged state, and the rise in the battery internal pressure can be suppressed.

By defining the capacity ratio of the uncharged state alloy in the discharged state of the hydrogen storage alloy negative electrode to the capacity of the nickel electrode in the range of 1.1 to 2.0,
It is possible to prevent the battery capacity from being regulated by the hydrogen storage alloy electrode capacity, and suppress an increase in the battery internal pressure at the end of charging and the end of discharging without using a special charge control method or discharge control method. At the same time, the volume of the hydrogen storage alloy electrode in the battery container can be reduced, and the amount of the nickel electrode, which is the capacity control electrode, can be increased by that amount, so that the capacity can be increased.

Therefore, it is possible to obtain a long-life and low-cost nickel-hydrogen secondary battery that has a high capacity and suppresses an increase in the battery internal pressure, while making the most of the characteristics of the hydrogen storage alloy produced by the melt quenching method.

Further, by heat-treating the above alloy at a relatively low temperature of about 200 to 500 ° C., it is possible to remove internal strain while maintaining the homogeneity of the alloy, and nickel which has more excellent battery characteristics. A hydrogen battery can be provided.

[0129]

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

Examples 1 to 9 Various raw material mixtures were prepared in consideration of wear during melting so that the melt-quenched alloys obtained by cooling by the melt-quenching method would have the compositions shown in Table 1. Each raw material mixture was put into a Ti boride crucible and melted by a high frequency induction heating method to prepare various alloy melts. Next, each of the obtained molten alloys was injected onto the surface of the cooling roll of the single roll method apparatus shown in FIG. 1 to prepare a flaky molten metal quench alloy having a thickness of 50 μm. Here, a copper roll having a diameter of 300 mm was used as the cooling roll, the gap width between the injection nozzle and the cooling roll was set to 50 mm, and the injection pressure was 0.02 kg.
It was set to f / cm ² . The quenching treatment was performed in vacuum, the rotation speed of the cooling roll was set to 600 rpm, and the average cooling rate of the molten alloy was adjusted to about 2400 ° C./s.

Next, each of the obtained melt-quenched alloys was crushed to 2
A hydrogen storage alloy powder for a battery was prepared by classifying the powder into a mesh of 00 mesh or less. Next, the prepared hydrogen storage alloy powder for a battery and P
9% by weight of TFE powder and carbon powder respectively
After weighing so as to be 5.5%, 4.0%, and 0.5%, 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.

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 discharged to a potential difference of −0.5 V with respect to the HgO reference electrode was measured, and the results shown in Table 1 were obtained. 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.

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 above-mentioned hydrogen storage alloy electrodes and nickel electrodes were combined to assemble the AA type (AA type) nickel hydrogen battery of each example. 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.

Then, 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.

After assembling each battery and charging / discharging for 10 cycles, the battery was disassembled and the metal structure of the hydrogen storage alloy used for the negative electrode was analyzed. The hydrogen-absorbing alloy powder once incorporated in the battery is integrated with the polymer binder, etc., and is partially corroded by the electrolytic solution and the etching solution used for observing the fine structure. Observing the tissue is difficult. Therefore, an analysis sample was prepared by the procedure of the following items (1) to (3), and the metal structure was analyzed by the method shown in the item (4).

(1) Removal of Negative Electrode When the battery is disassembled without being completely discharged, there is a risk of ignition of the hydrogen storage alloy contained in the negative electrode. Therefore, the battery is disassembled after the nickel-hydrogen battery is completely discharged. Then take out the negative electrode. In order to prevent ignition, the negative electrode taken out from the battery is thoroughly washed with water and dried. Insufficient washing or drying may result in poor compatibility with the resin and peeling during resin filling in the next step.

(2) Embedding of Negative Electrode with Resin Ten pieces of 10 mm × 5 mm sample are cut out from the dried negative electrode, and sample numbers 1 to 10 are given. Vertically stand these sample pieces in the mold with the long side down.
A resin is poured into the gap and cured to form a composite. As the resin for embedding, a resin having low viscosity such as epoxy resin is used. Further, in order to increase the degree of adhesion between the sample piece and the resin, it is advisable to raise the temperature of the resin and reduce the viscosity thereof before pouring it into the mold.

(3) Polishing of Composite The surface of the cured composite is coated with water resistant abrasive paper (# 600) to (# 600).
1500) are sequentially used for polishing to expose the cross section of the hydrogen storage alloy. This polishing operation may be performed by a polishing machine, but since the impact force is large, the hydrogen storage alloy in the electrode is likely to peel off. Therefore, it is preferable to carry out the polishing manually.

(4) Observation of Alloy Structure The metal structure of the hydrogen storage alloy contained in the above sample piece was SE.
When observed with M (scanning electron microscope), the hydrogen storage alloy is integrated with the polymer binder and the like, and in some cases, the metallographic structure cannot be clearly confirmed partially. Therefore, only alloys whose metallographic structure can be confirmed are to be observed.

In the above observation, the field of view was selected so that the most metallographic structure could be photographed, and the metallographic structure of the hydrogen storage alloy exposed on the electrode cross section was analyzed by SEM to 1500 to 20.
10 and 1 when taking a photograph at a magnification of about 00 times.
As shown in FIG. 6 and FIG. 22, it was carried out within the range of the region R defined by the largest rectangle inscribed in the crystal structure out of the entire amorphous crystal structure in which the crystal grains were visible. At this time, for each hydrogen storage alloy of the present invention contained in the negative electrode, the proportion of crystal particles having an aspect ratio of 1: 2 or more in the identifiable metal structure is preferably 50% or more. It is more preferably 70% or more, still more preferably 80% or more. This is because when the above ratio is less than 50%, the number of crystal grain boundaries increases, and as a result, segregation also increases and alloy particles are significantly deteriorated. Further, the ratio of the number of crystal grains having an aspect ratio of 1: 2 or more is 30% or more, more preferably 50% or more, and further preferably 70% or more with respect to the total number of particles contained in the metal structure that can be confirmed. It is necessary. This is because when the ratio of the number of crystal particles is less than 30%, the number of crystal particles that easily deteriorate becomes relatively large and the life of the battery is significantly shortened.

Here, the aspect ratio is the ratio of the minor axis to the major axis of the crystal grain, the major axis is the maximum length in the axial direction of the crystal grain, and the minor axis is the maximum length in the direction perpendicular to the axis. Say it.

In the metal structure of the hydrogen storage alloy according to the present invention, the average minor axis of the columnar crystal grains is preferably 30 μm or less, more preferably 20 μm or less, further preferably 10 μm or less. When the average minor axis is more than 30 μm, segregation occurs frequently, the corrosion resistance of the alloy is reduced, the life is shortened, and the charge / discharge cycle during battery production is significantly reduced. Furthermore, since the area of the grain boundary, which is a migration path of hydrogen in the alloy, becomes small, the diffusion resistance of hydrogen becomes large, and the battery voltage at the time of large current discharge tends to decrease.

Next, a method for obtaining the aspect ratio of the columnar crystals forming the metal structure of the hydrogen storage alloy will be specifically described.

FIG. 4 is an electron micrograph showing an example of the metallographic structure of the hydrogen storage alloy according to the example, showing a fracture surface in the thickness direction of the melt-quenched alloy in contact with the cooling roll of the single roll device. The hydrogen storage alloy is a flake-like melt quench alloy before crushing. In FIG. 4, the lower side of the fracture surface is the cooling surface that was in contact with the cooling roll, and the upper side is the free surface side. By the molten metal quenching treatment, it is possible to clearly identify the state where columnar crystals having various aspect ratios are grown vertically from the cooling surface side.

However, as the negative electrode of an actual battery, a pulverized melt-quenched alloy of the above flakes is used, and the pulverized powder may also be corroded by the electrolytic solution. When it is carried out, it is not always possible to observe clear columnar crystals. Figure 5 below
The case where the metal structure becomes unclear will be described with reference to FIGS.

5 to 8 are SEM photographs of the hydrogen storage alloy contained in the negative electrode taken out from the actually used battery. That is, in FIG. 5, a fracture surface in the direction perpendicular to the cooling surface of the cooling roll is observed, and the state in which columnar crystals are growing in the vertical direction can be identified. FIG. 6 shows a free surface side (free side) opposite to the side (roll side) contacting the cooling roll.
Represents the surface texture of the. In this case, only the end face corresponding to the minor axis of the columnar crystal is observed, so that it may be observed as if it is an equiaxed crystal. In FIG. 7, columnar crystals are partially observed in the central part, but it is difficult to clearly identify the metal structure as a whole because the upper right part is eroded by the electrolytic solution. Figure 8 shows the upper surface of the hydrogen storage alloy (white part)
However, an example in which the entire metallographic structure cannot be clearly discerned because it was eroded by the etching liquid used during SEM observation.

Therefore, when the metal structure of the hydrogen storage alloy contained in the negative electrode is analyzed, the target surface is mirror-polished and then an etching treatment is performed to expose the crystal grain boundaries of the metal structure. However, if the etching solution does not match the composition of the hydrogen storage alloy, the etching solution excessively corrodes the entire alloy, making it impossible to clearly expose the grain boundaries. Therefore, even if columnar crystals are formed, it is difficult to identify the entire metallographic structure if the degree of erosion is high.
On the other hand, even when the degree of erosion is small, the morphology of columnar crystals can barely be visually recognized, but it is difficult to clearly distinguish the crystal grain boundaries. In addition to the above, when a fractured surface oblique to the cooling roll surface is observed, columnar crystals may be observed as if they are equiaxed crystals depending on the angle between the cooling roll surface and the fractured surface. . Therefore, in this case, care must be taken when measuring the area ratio of columnar crystals.

FIGS. 9, 15 and 21 are SEM photographs of the hydrogen storage alloy particles contained in the negative electrode taken out from the actually used battery. FIG. 9, FIG. 15 and FIG.
The hydrogen storage alloy particles shown in are corresponding to Example 5, Example 1 and Example 8, respectively.

As shown in the central portion of FIG. 15, clear alloy particles having columnar crystals developed are observed, while the periphery thereof has
There are some alloy particles whose crystal structure cannot be clearly observed because they are corroded by the electrolytic solution of the battery and the etching solution used at the time of microscopy. In particular, when the etching solution is not suitable for the composition of the hydrogen storage alloy, the etching solution corrodes the alloy surface, making it impossible to observe the metal structure.

Next, a method for calculating the ratio of the crystal grains having an aspect ratio of 1: 2 or more to all the crystal grains based on the SEM photograph will be described. First, of all the hydrogen-absorbing alloy particles observed in the cross section of one polished negative electrode piece, the number of alloy particles having a distinct metal structure is counted, and the value is defined as N ₁ . At this time, in order to confirm that the alloy particles are hydrogen storage alloys, an X-ray microanalyzer (EPMA), an energy dispersive X-ray analyzer (EDX), or the like is used to obtain a unique signal from the rare earth element. To detect. When this peculiar signal is not detected, it is presumed that it is an adhered matter such as a crushed piece, it is determined that it is not a hydrogen storage alloy particle, and it is excluded from the number of alloy particles.

Next, among the N ₁ alloy particles, crystal grains having an aspect ratio of 1: 2 or more account for 50% of the metal structure area.
The number N ₁ ′ of alloy particles occupying the above is counted. Hereinafter, the negative electrode sample pieces 1 to 10 are similarly counted.

Thus obtained N _{1 to} N ₁₀ and N ₁ ′ to
The ratio of the columnar crystal structure is calculated by substituting the value of N ₁₀ ′ into the following formula.

[0154]

[Equation 1]

Next, a method of calculating the ratio of the columnar crystal structure in the metal structure will be described. As the columnar crystals, long crystal grains having an aspect ratio of 1: 2 or more were investigated. In addition, crystal grains having an aspect ratio of less than 1: 2 include not only equiaxed crystals but also chill crystals and various deposits. The area occupied by the columnar crystals is an image analyzer (LUZEX500 type, manufactured by Nippon Regulator KK).
Was measured using. That is, taking Example 5 as an example, to explain, an SEM of a metal structure photographed as shown in FIG.
Thin tracing paper on the photo (basis weight: 40 g / m ²
(Fig. 1) and the grain boundaries on the paper.
A map as shown in 0 is created. In the hydrogen storage alloy particles shown in FIG. 10, an eroded portion 30 eroded by the electrolytic solution is formed on the left side of the columnar crystal 31. Further, in the center of the region R, an adhering substance 33 such as a fragment of a crushed substance is interposed.

Next, in the created map, the portion corresponding to the columnar crystals having an aspect ratio of 1: 5 or more was painted black,
FIG. 11 is obtained. Similarly, the columnar crystal portion having an aspect ratio of 1: 4 or more is painted out to obtain FIG. Similarly, when the aspect ratio is 1: 3 and the aspect ratio is 1: 2 or more, painting is performed to obtain FIGS. 13 and 14, respectively. Next in FIG.
For 1 to 14, image processing is performed using an image analyzer, and the area ratio of columnar crystals corresponding to the aspect ratio is optically analyzed and calculated. That is, the image analyzer discriminates the presence or absence of columnar crystals in the target range R by the shade of color, and calculates the area ratio of the black portion corresponding to the columnar crystals.

15 to 20 and FIGS. 21 to 26 show examples in which the above area ratios are cumulatively calculated for other alloy structures. FIG. 15 is an SEM photograph showing the hydrogen storage alloy particles according to Example 1. Of the alloy particles shown in the SEM photograph of FIG. 15, the crystal structure of the alloy particles in the central portion where the crystal structure can be clearly identified is traced to obtain the map shown in FIG. In FIG. 16, the straight line at the upper edge is the contact surface 34 with respect to the cooling roll, and along this contact surface 34, the fine chill crystals 35 generated by the ultra-quenching action of the cooling roll.
Is being generated. Since the chill crystals 35 are fine, the crystal grain boundaries are not shown. On the right side of the area R, the deposit 3
3 intervenes.

In the same manner as in Example 5, the columnar crystal portions having an aspect ratio of 1: 5 or more, 1: 4 or more, 1: 3 or more, 1: 2 or more are filled in with black, and FIGS.
A map of 0 is obtained.

Also for the hydrogen storage alloy according to Example 8,
Similarly, from the SEM photograph shown in FIG. 21, a map of FIG. 22 showing the crystal structure is created, and the columnar crystals corresponding to each aspect ratio range are filled in, and FIGS. 23 to 26 are prepared. The area ratio of the columnar crystal portion is obtained by analyzing with an analyzer.

As is clear from FIGS. 9 to 26, it was confirmed that the columnar crystals 31 were sufficiently grown in all the crystal structures, while the equiaxed crystals 32 were partially present in the structures. It was

The range of the above analysis is shown in FIGS.
As shown in FIG. 6 and FIG. 22, it was set within the range of the region R defined by the largest rectangle inscribed in the crystal structure among all the amorphous crystal structures in which the crystal grains were visible. The columnar crystals existing on the boundary of the region R adopt the area only in the region R, while the aspect ratio was calculated from the shape of the entire columnar crystal including the part existing outside the region.

Thus, the area ratio of the columnar crystals of each hydrogen storage alloy according to Examples 1 to 9, the minor axis of the columnar crystals, the maximum electrode capacity of the battery using the hydrogen storage alloy, the number of charge / discharge cycles (lifetime). ) And the number of activities are summarized in Table 1 below.

[0163]

[Table 1]

As is clear from the results shown in Table 1, Mn
According to the hydrogen storage alloys for batteries according to Examples 1 to 9 prepared by quenching the molten alloy having the predetermined composition containing all of them, columnar crystals grow sufficiently in the crystal structure and segregation of the constituent elements is extremely high. Since the amount was small, the electrode capacity could be significantly improved without impairing the life when used as a negative electrode material.

Further, since the number of charge / discharge cycles required to reach the maximum electrode capacity, that is, the number of times of activation is as small as 2 to 3 cycles, the initial rise of the battery characteristics is quick, and the battery manufacturing cost can be reduced. It was

The metal structures of the hydrogen storage alloy powders prepared in Examples 1 to 9 were analyzed by the procedures shown in the following (A), (B) and (4) before the electrodes were prepared. I did.

(A) Resin embedding Approximately 100 mg of an alloy sample is sampled and scattered on the center of a resin embedding frame (made of polypropylene) for SEM samples having a diameter of 20 mm. Next, an epoxy resin commercially available as a resin for embedding a SEM sample (EPO-MI manufactured by Buhler Co., Ltd.
After mixing X) and the curing agent well, the mixture is poured into the embedding frame and cured. At this time, in order to improve the adhesiveness between the sample and the resin, it is possible to preheat the resin to about 60 ° C. to reduce the viscosity, or to inject the resin and then perform vacuuming in a vacuum desiccator to perform defoaming. desirable.

(B) Polishing The sample embedded by the above procedure is then polished by a polishing machine until a mirror finish is obtained. Since the hydrogen-absorbing alloy sample easily reacts with water, the roughness of the water-resistant abrasive paper should be 180, 400, while dropping methyl alcohol during polishing.
After polishing with a rotary polishing machine that rotates at 200 rpm while making it finer in order of 800, similarly set the felt on the rotary polishing machine and make the diamond paste finer in the order of 15 microns, 3 microns and 0.25 microns. It was mirror finished.

For each sample piece obtained by the above procedure,
The area ratio of the columnar crystals and the minor axis of the columnar crystals of the hydrogen storage alloy were measured by the method described in the item (4). as a result,
The hydrogen storage alloys according to Examples 1 to 9 show almost the same values as the respective measured values (Table 1) of the columnar crystals of the alloy contained in the negative electrode taken out from the nickel-hydrogen battery that had been charged and discharged for 10 cycles. It was confirmed.

Example 10 The composition of the melt-quenched alloy obtained by cooling by the melt-quenching method is LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 (Lm
Is La-enriched misch metal, Ce: 3% by weight, L
a: 50% by weight, Nd: 40% by weight, Pr: 5% by weight,
Other rare earth elements: Consists of 2% by weight. ),
A molten alloy was prepared by melting 200 g of an AB ₅ type hydrogen storage alloy ingot, the composition of which was adjusted in advance to anticipate wear during melting, in a high frequency induction heating furnace. Next, the obtained molten alloy was dropped onto the surface of the cooling roll of the single roll method apparatus shown in FIG. 1 to prepare a flaky molten metal quench alloy having a thickness of 50 μm.

This melt-quenched alloy was heat-treated in an argon atmosphere at a temperature of 300 ° C. for 4 hours and then pulverized, and the alloy powder classified to 200 mesh or less was used as a hydrogen storage alloy for batteries (alloy powder (A)).

On the other hand, a melt-quenched alloy was prepared in the same manner as the alloy powder (A), and the heat treatment temperatures were 150 ° C. and 200 ° C., respectively.
℃, 250 ℃, 350 ℃, 400 ℃, 500 ℃, 550
℃, 600 ℃, heat treatment for 4 hours, the alloy powder classified to 200 mesh or less (B) ~ (I) respectively
Alloy powder was used. Further, the heat treatment times for the (A) alloy powder were set to 0.5 hours, 1 hour, and 6 hours, respectively, to obtain (J) to (L) powders.

On the other hand, for comparison, a melt-quenched alloy was prepared in the same manner as the (A) alloy powder, and the alloy powder classified to 200 mesh or less without heat treatment was used as the (M) alloy powder.

Table 2 below shows the composition of each of the alloy powders (A) to (L) after the heat treatment and the composition of the alloy powder (M) not subjected to the heat treatment.

[0175]

[Table 2]

As is clear from the results shown in Table 2, the alloy powder (M) which was not heat-treated showed almost the desired composition. Further, in the alloy powders (A) to (G) and (J) to (L) which were heat-treated in the temperature range of 150 to 500 ° C, no large compositional change was observed. On the other hand, alloy powder (H)
In (1) and (I), since the heat treatment temperature was high, the amount of the rare earth element and manganese (Mn), which easily evaporate, was slightly reduced, and the composition variation was large. Thus, the heat treatment at a high temperature tends to change the alloy composition, so that it is desirable to carry out the heat treatment at a low temperature region.

Next, any of the prepared (A) to (M) powders, PTFE powder, and carbon powder were respectively added by weight%.
Was weighed so as to be 95.5%, 4.0%, and 0.5%, and kneaded to prepare each electrode sheet. The electrode sheet was cut into a predetermined size and pressed onto a nickel current collector to prepare a hydrogen storage alloy electrode. Alloy powder (A)
The electrodes created from (M) are electrodes (A) to (M), respectively.
And

Then, the hydrogen storage alloy electrodes (A) to
For (M), current value of 220 mA / g of alloy (2
After charging up to 300 mAh / g at 20 mA / g),
-0.5V with respect to the Hg / HgO reference electrode at the above current value
The maximum electrode capacity when discharged until the potential difference was measured was obtained and the results shown in Table 3 were obtained.

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 the mixture was stirred and mixed 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, each of the hydrogen storage alloy electrodes (A) to
AA type (AA type) by combining (M) and nickel electrode
A nickel metal hydride battery was assembled. Here, a battery using the alloy electrode (A) as a negative electrode is referred to as a battery (A), and hereinafter, similarly to batteries (B) to (M). 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.

Next, regarding each of the batteries (A) to (M), 65
After charging at 0 mA for 1.5 hours, the 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 results shown in Table 3 were obtained.

[0182]

[Table 3]

As is clear from the results shown in Table 3, when the heat-treated alloy powder was used, the alloy electrode (A),
As shown in (C) to (G) and (K) to (L), higher electrode capacitances were obtained in all cases. Also in terms of life characteristics, the batteries (A), (C) to (G), and (K) to (L) using the heat-treated alloy powder have 650 to 7
It was confirmed that the characteristics could be further improved with 94 cycles.

These phenomena are presumed to have been achieved by the following mechanism. That is, the alloy electrode (A),
In (C) to (G) and (K) to (L), the heat treatment effectively acted to remove the minute crystal strain in the alloy structure. Therefore, the hydrogen storage capacity per unit weight of the alloy was improved. Therefore, the electrode capacity was significantly increased as compared with the alloy electrode (M) which was not heat-treated. Furthermore, the stress at the time of hydrogen absorption and desorption was reduced, and the life characteristics of batteries using these alloy electrodes were also greatly improved. In particular, alloy powder (A) (D) (E) (K) heat-treated for 1 hour or more in the temperature range of 250 to 350 ° C.
It was proved that the improvement effect was particularly large when (L) was used.

On the other hand, in the case of the alloy powder (B), the heat treatment temperature was as low as 150 ° C., and in the case of the alloy powder (J), the heat treatment time was as short as 0.5 hours. Therefore, the electrode capacity and the battery life almost equal to those of the alloy powder (M) not subjected to the heat treatment were obtained.

For alloy powders (H) and (I),
Since the heat treatment temperature was too high at 550 to 600 ° C., the amount of highly volatile Mn and rare earth elements decreased, and the alloy composition fluctuated and the alloy strength decreased due to secondary recrystallization. Fell.

Example 11 Various melt-quenched alloys having different Mn addition amounts x were prepared by the same melt-quenching method as in Example 10. The composition formula of the melt-quenched alloy is LmNi _4.3-x Co _0.4 Mn _x Al _0.3 , and the Mn addition amount x is 0, 0.1, _0.3 , _0.5 , _0.8 , 1.2.
I changed it. Further, Lm is La-rich misch metal, and the same one as in Example 10 was used. The obtained melt-quenched alloy was used as it was without heat treatment to form an alloy electrode, and a battery was prepared by combining this alloy electrode and a nickel electrode, and the electrode capacity and the battery life were measured.

Further, for each alloy, the heat treatment conditions that were most effective in Example 10 (temperature 3 in Ar gas atmosphere) were obtained.
Heated at 00 ° C. for 4 hours). Example 1 below
Various hydrogen storage alloy electrodes and AA type nickel hydrogen batteries were prepared in the same manner as in Example 0, and the electrode capacity and the battery life were measured. The electrode capacity measurement method and the battery life measurement method are
The same procedure as in Example 10 was performed.

On the other hand, as a comparative example, LmNi _4.0 Co _0.4 Mn _0.3 was prepared by the melt casting method instead of the melt quenching method.
An electrode and a battery having the same specifications were manufactured using a hydrogen storage alloy ingot having a composition of Al _0.3 , and similarly, the electrode capacity and the battery life were measured and the results shown in Table 4 below were obtained.

[0190]

[Table 4]

As is clear from the results shown in Table 4, Mn
The effect of heat treatment is small in the alloy composition not containing. On the other hand, with the alloy composition containing Mn, a significant improvement effect was obtained in both electrode capacity and battery life. However, Mn
When the addition ratio of 1 exceeded 1.2 and became 1.2, the battery life was drastically reduced, and there was no significant difference in characteristics between the conventional melt-cast alloy ingot and the melt-quenched alloy.

On the other hand, in the melt cast alloy ingot, segregation of the constituents occurs in a wide range of the crystal structure. Therefore, the heat treatment conditions (300 ° C.) specified in the method of this embodiment are used.
After heating for 4 hours), homogenization of the alloy did not occur. Therefore, the effect of the heat treatment hardly appeared, and it was difficult to improve the battery characteristics.

Example 12 Six kinds of melt-quenched alloys having different Mn addition amounts were prepared by the same melt-quenching treatment method as in Example 11. The composition of the melt-quenched alloy is LmNi _4.3-x Co _0.4 Mn _x Cr _0.3.
And the Mn addition amount x is 0, 0.1, 0.3,
It was set to 0.5, 0.8 and 1.2.

On the other hand, as a comparative example, a hydrogen storage alloy ingot having a composition of LmNi _4.0 Co _0.4 Mn _0.3 Cr _0.3 prepared by a melting casting method was prepared.

Then, an alloy electrode and an AA type nickel-hydrogen battery were manufactured in the same manner as in Example 11 by using the various molten metal quench alloys and the hydrogen storage alloy ingots, and the electrode capacity and the battery life were measured.

Further, the various molten alloy quench alloys and hydrogen storage alloy ingots were heat-treated under the heat treatment conditions (300 ° C., 4 hours, Ar atmosphere) which had the highest effect in Example 10. Then, a hydrogen storage alloy electrode and an AA type nickel-hydrogen battery were manufactured using various heat-treated alloys, and the electrode capacity and battery life were measured by the same measurement method as in Example 10 to obtain the results shown in Table 5 below. .

[0197]

[Table 5]

As is clear from the results shown in Table 5, Mn
In the alloy composition not containing Al, the effect of improving the battery characteristics by the heat treatment is hardly exhibited. On the other hand, in the alloy composition in which the added amount x of Mn was in the range of 0.1 ≦ x ≦ 1, the increase of the electrode capacity and the prolongation of the battery life were achieved by the heat treatment.

However, it was confirmed that when the Mn addition amount x exceeds 1, the battery life is reduced to the same extent as when the cast alloy ingot is used, as in the case of Example 11.

Example 13 Five kinds of melt-quenched alloys having different Cu addition amounts x were prepared by the same melt-quenching treatment method as in Example 11. The composition of the melt-quenched alloy was LmNi _4.5-x Mn _0.5 Cu _x , and the Cu addition amounts x were 0, 0.3, 0.5, and
It was set to 0.8 and 1.2.

On the other hand, as a comparative example, a hydrogen storage alloy ingot having the composition LmNi _4.2 Mn _0.5 Cu _0.3 prepared by the melting casting method was prepared.

Then, an alloy electrode and an AA type nickel-hydrogen battery were manufactured in the same manner as in Example 11 by using the various molten metal quench alloys and hydrogen storage alloy ingots, and the electrode capacity and battery life were measured.

Further, the molten alloy quench alloy and the hydrogen storage alloy ingot were heated at a temperature of 300 in an Ar gas atmosphere.
It heat-processed at 4 degreeC. Then, a hydrogen storage alloy electrode and an AA type nickel-hydrogen battery were produced using the various heat-treated alloys, the electrode capacity and the battery life were measured by the same measurement method as in Example 10, and the results shown in Table 6 below were obtained. Obtained.

[0204]

[Table 6]

In the results shown in Table 6, since the addition amount of Mn, which has a large effect depending on the presence or absence of heat treatment, is constant, the change in the characteristics of the alloy electrode and the battery according to Example 13 is compared with those of Examples 10 to 12. And small. However, from the overall tendency, it was confirmed that the electrode capacity and the battery life were both increased by performing the heat treatment.

Further, it was confirmed that the electrode capacity decreased with an increase in the added amount of Cu, and especially when the added amount was 1 or more, a rapid decrease in the capacity was observed. It was also confirmed that if the addition amount exceeds 1, the life becomes sharply short.

According to the hydrogen storage alloys for batteries according to Examples 10 to 13 described above, since the molten alloy having a predetermined composition containing Mn as an essential component element was prepared by quenching, segregation was small, Alloy electrodes and batteries with high electrode capacity and long life can be formed.

In particular, the melt-quenched alloy is further added to 200 to 5
In the temperature range of 00 ° C, more preferably 200 to 350 ° C
By heat-treating for 1 hour or more in the low temperature range of 1, the internal strain can be removed while maintaining the homogeneity of the alloy. Therefore, it is possible to provide a nickel-hydrogen battery having more excellent battery characteristics.

Examples 1A to 9A Each of the melt-quenched alloys prepared by the single roll method in Examples 1 to 9 was further heated at a temperature of 3 in an Ar gas atmosphere.
Hydrogen storage alloy electrodes according to Examples 1A to 9A were prepared by treating under the same conditions as in Examples 1 to 9 except that the hydrogen storage alloy was produced by heat treatment at 00 ° C for 4 hours. Furthermore, each hydrogen storage alloy electrode (negative electrode) and nickel electrode (positive electrode)
Was combined to produce an AA-type nickel metal hydride electrode.

Under the same conditions as in Example 1, the area ratio of the columnar crystals of the hydrogen storage alloy, the minor axis of the columnar crystals, the maximum electrode capacity, the life (the number of charge / discharge cycles), and the rise of the initial electrode characteristics (the number of activations) were determined. It measured and obtained the result shown in the following table 7.

[0211]

[Table 7]

As is clear from the results shown in Table 7, 300
In the hydrogen storage alloys of the respective examples which are heat-treated at a relatively low temperature of ° C, the crystal strain is effectively corrected without impairing the homogeneity, so that the hydrogen storage / release is facilitated. Therefore,
It was proved that the electrode capacity and the battery life were significantly improved as compared with the batteries using the hydrogen storage alloys shown in Table 1 which were simply melt-quenched. Especially the electrode capacity is 10%
Increased.

Comparative Examples 1A to 1D Using a twin roll device as shown in FIG. 2 in which two cooling rolls made of iron having a diameter of 100 mm are opposed to each other, the alloy melt is quenched and finally Mm Ni _3.55 Mn _0.4. Al _0.3
Hydrogen storage alloys according to Comparative Examples 1A to 1D having a composition of Co _0.75 were prepared. The rotation speeds of the cooling rolls are 1500 rpm (Comparative Example 1A) and 2000 rpm, respectively.
(Comparative Example 1B), 2500 rpm (Comparative Example 1C), 30
It was set to 00 rpm (Comparative Example 1D).

Comparative Examples 2A to 2D, 3A, and 3B Comparative alloys 2A to 3D having a composition finally shown in Table 8 were obtained by quenching the molten alloy using a single roll apparatus having a cooling roll made of copper having a diameter of 300 mm. Hydrogen storage alloys according to 2D and 3A to 3B were prepared. The rotation speeds of the cooling rolls are 1000 rpm (Comparative Example 2A) and 1500 rpm, respectively.
(Comparative Example 2B), 2000 rpm (Comparative Examples 2B 'and 2C), 2500 rpm (Comparative Example 2D), 200 rpm
(Comparative Example 3A) and 200 rpm (Comparative Example 3B) were set. The quenching treatment was carried out in an Ar gas atmosphere of 1 atm, the distance between the tip of the injection nozzle for injecting the molten alloy and the cooling roll was 50 mm, and the injection pressure was 0.1 kgf / cm ² .

[0215] Using a single roll apparatus having a copper cooling roll of Comparative Example 4-6 in diameter 300 mm, and quenching the alloy melt, and finally hydrogen according to Comparative Examples 4 to 6 having the composition shown in Table 8 Each occlusion alloy was prepared. The quenching treatment was performed in an Ar gas atmosphere at 1 atm, the gap between the tip of the molten alloy injection nozzle and the cooling roll was 50 mm, the injection pressure was 0.02 kgf / cm ² ,
The rotation speed of the cooling roll was set to 1000 rpm.

As a crucible for preparing the molten alloy, a calcia crucible (Comparative Example 4), an alumina crucible (Comparative Example 5) and a quartz crucible (Comparative Example 6) were used, respectively.

Comparative Examples 7A to 7D Using a single roll device having a ceramics spraying roll having a diameter of 300 mm, the molten alloy was quenched, and finally L
Hydrogen storage alloys according to Comparative Examples 7A to 7D each having a composition of m Ni _4.2 Co _0.2 Mn _0.3 Al _0.3 were prepared. The rapid cooling treatment was performed in an Ar gas atmosphere at 1 atm, and the gap between the tip of the molten alloy injection nozzle and the cooling roll was set to 50 mm and the injection pressure was set to 0.1 kgf / cm ² . The rotation speeds of the ceramic spray rolls are 1000 rpm (Comparative Example 7A), 1500 rpm (Comparative Example 7B), 2000 rpm (Comparative Example 7C) and 2500 r, respectively.
pm (Comparative Example 7D).

Comparative Examples 8A to 9B The molten alloys were rapidly cooled using a single roll apparatus having a cooling roll made of copper and having a diameter of 200 mm, and finally the hydrogen according to Comparative Examples 8A to 9B having the composition shown in Table 9 was used. Each occlusion alloy was adjusted. In addition, the above-mentioned quenching treatment is performed at 1 atm of Ar.
Performed in a gas atmosphere, the gap between the tip of the molten alloy injection nozzle and the cooling roll is 50 mm, and the injection pressure is 100 mmH.
₂ O, the rotation speed of the cooling roll is 2000 rpm respectively
(Comparative Example 8A), 2500 rpm (Comparative Example 8B), 20
00 rpm (Comparative Example 9A), 2500 rpm (Comparative Example 9)
B).

Comparative Examples 10 to 13 The alloy ingots each have a composition of Mm Ni _3.0 Co.
_1.4 Al _0.6 (Comparative Example 10), Mm Ni _3.2 Co
_1.1 Al _0.7 (Comparative Example 11), Mm Ni _3.5 Co _0.7
Al _0.8 (Comparative Example 12), Mm Ni _3.7 Co _{0 4}
A hydrogen storage alloy powder raw material adjusted to have Al _0.9 (Comparative Example 13) was put into an alumina crucible and melted at 1400 ° C. by high frequency heating to prepare an alloy melt. Next, the molten alloy is poured into a steel water-cooled mold and solidified,
The hydrogen storage alloy ingots according to Comparative Examples 10 to 13 were manufactured.

Comparative Examples 14A to 14B The composition of the alloy ingot is Mm Ni _3.55 Co _0.75 M.
A hydrogen storage alloy powder raw material prepared to have n _0.4 Al _0.3 was put into a mullite crucible and heated to 1500 ° C. by a high frequency induction heating coil arranged on the outer periphery of the crucible to melt to prepare an alloy melt. Next, the obtained molten alloy was cast into a water-cooled mold made of copper, and the mold surface interval was 55 mm (Comparative Example 14
A), the same 35 mm (Comparative Example 14B), casting speed 3 kg / sec /
An alloy ingot was prepared at m ² . Further, the obtained alloy ingot was heat-treated at 1050 ° C. for 6 hours in an argon gas atmosphere to prepare hydrogen storage alloys according to Comparative Examples 14A to 14B.

Comparative Examples 15 to 20 As Comparative Examples 15, 16 and 18 to 20 , hydrogen absorbing alloy powder raw materials adjusted so that the composition of the alloy ingot has the values shown in Table 9 were put into an alumina crucible, A molten alloy was prepared by heating to 1400 ° C. by high frequency heating. In Comparative Example 17, a molten alloy was prepared by the arc melting method. Next, the obtained alloy melts were cast into a water-cooled iron mold and solidified to prepare hydrogen storage alloy ingots according to Comparative Examples 15 to 20. Furthermore, the hydrogen storage alloy ingot of Comparative Example 16 was further processed in an Ar gas atmosphere at 10
Heat treatment was carried out at 00 ° C. for 6 hours.

The melt-quenched alloys or hydrogen storage alloys of Comparative Examples 1A to 20 thus obtained were crushed using a stamp mill and classified to 200 mesh or less to prepare hydrogen storage alloy powders for batteries. Hereinafter, a hydrogen storage alloy electrode (negative electrode) was prepared in the same procedure as in Example 1 using the hydrogen storage alloy powder for each battery, and was combined with a nickel electrode (positive electrode) to assemble an AA type nickel hydrogen battery. Then, the electrode capacity, the number of charge / discharge cycles (lifetime) and the number of activations were measured according to the same measurement method as in Example 1, and the results shown in Tables 8 and 9 below were obtained.

[0223]

[Table 8]

[0224]

[Table 9]

As is clear from the results shown in Tables 8 and 9, in the hydrogen storage alloys shown in Comparative Examples 1A to 20,
In both cases, the area ratio of the columnar crystals in the metal structure is smaller than that in the examples shown in Tables 1 and 7. Therefore, it was confirmed that the electrode using this alloy had a low electrode capacity and the battery life indicated by the number of charge / discharge cycles was also short.

In the electrode of the comparative example, the number of charge / discharge cycles (the number of activations) required to obtain the maximum electrode capacity was 5
It was confirmed that the number of times was up to 9 times, which was more than twice that of Examples 2 to 3, and the initial rising property of the electrode was also low.

Particularly in the hydrogen storage alloys of Comparative Examples 1A to 1D, 2A to 2D, 3A to 3B, and 7A to 7D in which Mn was added as in the examples, the growth of columnar crystals was not sufficient and the equiaxed crystal structure In some cases, the battery characteristics were lower than those of the examples shown in Tables 1 and 7.

FIG. 27 is an electron microscope (SEM) photograph showing the metal structure of the fracture surface of the hydrogen storage alloy according to Comparative Example 7B. In FIG. 27, the lower part of the fracture surface is the cooling surface that was in contact with the cooling roll, and the upper part is the free surface. While columnar crystals are growing from the cooling surface toward the free surface,
Since the cooling rate was insufficient in the portion close to the free surface, an equiaxed crystal structure was formed. The area ratio occupied by columnar crystals is 50% or less in the entire crystal structure.

Comparative Examples 4, 5, 6 in which Mn is not added
In the battery using the hydrogen storage alloy according to 8A to 9B, the electrode capacity is about 200 to 225 mAh / g,
Moreover, the battery life was sluggish at 300 to 400 cycles.

Further, in the hydrogen storage alloys of Comparative Examples 10 to 13 produced by slow cooling by the casting method, the area ratio of columnar crystals was small, the electrode capacity was low, and the initial rising property of the electrode was poor. It has been found.

On the other hand, in the hydrogen storage alloys of Comparative Examples 14A to 14B manufactured by adding Mn and gradually cooling by the casting method, the columnar crystals were sufficiently grown, but the minor axis of the columnar crystals was 100. It can be seen that since the particle size is as coarse as 120 μm, a relatively high electrode capacity can be obtained, but the battery life is short and the initial rising property of the electrode is low.

Further, in the hydrogen storage alloys according to Comparative Examples 15 to 20 produced by slow cooling by the casting method without adding Mn, the crystal grain size becomes coarse to about 100 to 200 μm. The strength is low and the battery life is short.

As described above, comparing the respective examples shown in Tables 1 and 7 with the comparative examples shown in Tables 8 to 9, the hydrogen storage alloy and the battery according to this example show that the electrode capacity, the battery life and the It was found that the three major characteristics of initial rising property are both satisfied.

Next, the relationship between the crystal grain size of the hydrogen storage alloy and the battery life will be described with reference to the following examples and comparative examples.

Examples 14 to 17 and Comparative Examples 21 to 22 The composition of the hydrogen storage alloy was Lm Ni _4.0 Co _0.4 Mn.
An alloy powder raw material adjusted to _0.3 Al _0.3 was put into an alumina crucible and heated at high frequency to prepare a molten alloy.

As Examples 14 to 17, the above-mentioned molten alloys were rapidly cooled using a single roll machine having a cooling roll having a diameter of 300 mm to produce each hydrogen storage alloy. Here, the material and the rotation speed of the cooling roll were set as shown in Table 10.

On the other hand, as Comparative Examples 21 to 22, the molten alloy was put into a water-cooled mold made of copper and the mold surface interval was 45 mm.
Each hydrogen storage alloy was manufactured by casting under the conditions of (Comparative Example 21) and 80 mm (Comparative Example 22).

Examples 14 to 17 and Comparative Examples 21 to 21
The hydrogen storage alloy according to No. 22 was ground under the same conditions as in Example 1 to prepare a hydrogen storage alloy electrode (negative electrode), and further combined with a nickel electrode (positive electrode) to prepare a nickel hydrogen battery. The number of charge / discharge cycles of each battery was measured under the same conditions as in Example 1, and the results shown in Table 10 below were obtained.

[0239]

[Table 10]

FIG. 28 shows the relationship between the crystal grain size and the number of charge / discharge cycles. Example 14 in which columnar crystals developed
In Nos. 17 to 17, the crystal grain size is shown by the short diameter of the columnar crystal.

As is clear from the results shown in Table 10 and FIG. 28, it has been found that the battery life tends to be drastically reduced as the crystal grain size becomes coarser. In order to make the battery life (the number of charge / discharge cycles) 500 cycles or more, it is necessary to set the crystal grain size of the hydrogen storage alloy for the negative electrode to 30 μm or less.

Examples 18A to 18C and Comparative Example 23 In Examples 18A to 18C, the composition of the hydrogen storage alloy was Lm.
The alloy powder raw material adjusted to be Ni _0.4 Co _0.4 Mn _0.3 Al _0.3 was put into a titanium boride crucible, and high-frequency heating was performed to prepare a molten alloy. On the other hand, diameter 300 mm
2400 to 310 by using a single roll device having a Cu cooling roll (cooling water temperature: 20 ° C.)
Example 18A after quenching at an average cooling rate of 0 ° C./sec
A hydrogen storage alloy of ~ 18C was produced.

Here, the cooling rate was calculated as follows. When the molten alloy is injected from the nozzle, the heat is taken away by the cooling roll and rapidly solidified. Then, the rapidly solidified alloy is peeled off from the cooling roll and skipped. When the rotation speed of the cooling roll is about 600 rpm, the quenched alloy is peeled off from the cooling roll and skipped after the solidification is completed. On the other hand, when the rotation speed is about 1000 rpm,
Due to the strong centrifugal force of the cooling roll, the molten alloy peels off from the cooling roll and is skipped before solidification is completed. The moving distance from the time when the molten metal comes into contact with the cooling roll to the time when the molten metal peels changes depending on the composition of the alloy.
When the injection state of the molten metal was photographed with a high-speed video camera in the case of A (rotation speed: 600 rpm), the distance was equivalent to 1/8 rotation of the cooling roll. When the time for moving this distance is the cooling time, the cooling time is 1/80 second. The cooling rate is about 2400 ° C./s because the time for lowering the temperature from the molten alloy injection temperature 1380 ° C. to the freezing point 1350 ° C. is 1/80 second. However, since the position where the alloy peels off varies, the average value was adopted as the cooling rate.

On the other hand, as Comparative Example 23, an alloy powder raw material adjusted so that the composition of the hydrogen storage alloy was LmNi _3.5 Co _0.7 Mn _0.4 Zn _0.1 Al _0.3 was put into an alumina crucible and heated at high frequency to melt the alloy melt. Prepared. On the other hand, Fe cooling roll with a diameter of 300 mm (cooling water temperature: 50 ° C,
Using a single roll machine having a rotation speed of 200 rpm, the molten alloy was rapidly cooled at a cooling rate of 1150 ° C./sec to produce a hydrogen storage alloy.

Then, the hydrogen storage alloys according to Examples 18A to 18C and Comparative Example 23 were crushed under the same conditions as in Example 1 to prepare a hydrogen storage alloy electrode (negative electrode), and further combined with a nickel electrode (positive electrode). A nickel hydrogen battery was prepared. For each battery, the number of charge / discharge cycles was measured under the same conditions as in Example 1, the hydrogen storage alloy was taken out, and the proportion of columnar crystals in the metal structure was measured to obtain the results shown in Table 11 below.

[0246]

[Table 11]

As is clear from the results shown in Table 11, in the alloys of Examples 18A to 18C prepared by increasing the peripheral speed of the cooling roll and increasing the cooling rate, columnar crystals were sufficiently grown and the Excellent battery characteristics were exhibited as compared with the case of Comparative Example 23 that was cooled in.

Example 19 Next, in the hydrogen storage alloy of AB _x , the composition ratio x of the rare earth element A and the other element B was 4.4 to 6.1.
The effect of the change in the composition ratio x on the electrode capacity and the number of charge / discharge cycles was examined by changing the composition ratio in the range. That is, the alloy melt is rapidly cooled at a cooling rate of 2400 ° C / sec to obtain Lm.
Various hydrogen storage alloys represented by (Ni _0.8 Co _0.08 Mn _0.06 Al _0.06 ) _x were manufactured. The above composition ratio x = 5 corresponds to the hydrogen storage alloy of Example 1. Each hydrogen storage alloy thus obtained was treated in the same manner as in Example 1 to produce a negative electrode and measure its electrode capacity.
A nickel hydrogen battery was assembled in combination with the positive electrode and the number of charge / discharge cycles was measured to obtain the results shown in FIG.

As is clear from the results shown in FIG. 31, the electrode capacity is 240 mAh / g or more and the number of charge / discharge cycles is 500 or more within the range of 4.5 ≦ x ≦ 6.0 defined in the present invention. It was confirmed that the excellent battery characteristics were exhibited. Further, in a more preferable composition ratio x range (4.6 ≦ x ≦ 5.8), the electrode capacitance is 250 m.
It was also demonstrated that the number of charge / discharge cycles was 550 or more at Ah / g or more.

As described above, the hydrogen storage alloys for batteries according to the examples are AB ₅ type alloys in which Mn is an essential element, and since segregation of the constituents is small, the capacity is high and the cycle life and initial stage A negative electrode material for nickel-hydrogen secondary batteries having excellent characteristics can be provided. The above alloy is 1
It is obtained by quenching the molten alloy at a cooling rate of 800 ° C./s or more.

[0251] Further, the molten alloy quench alloy is added to 200 to 500
By heat treatment at a relatively low temperature of about 0 ° C., it is possible to remove internal strain while maintaining the homogeneity of the alloy, and it is possible to provide a nickel-hydrogen battery having more excellent battery characteristics.

Further, another embodiment of the present invention will be described together with a comparative example.

Example 20 (Preparation of Alloy) The stoichiometric composition was LmNi _4.0 Co _0.4 M.
In producing a hydrogen storage alloy that is n _0.3 Al _0.3 (Lm is a La-enriched misch metal), by reducing the amount of Lm when weighing the raw material elements, Ni, Co, Mn,
The raw materials were weighed in such a proportion that a non-stoichiometric composition was obtained without breaking the Al composition ratio. Next, these raw materials are melted in a high-frequency induction furnace, housed in the ladle 2 of the manufacturing apparatus by the single roll method shown in FIG. By appropriately lowering it to the roll 5, six types of flaky hydrogen storage alloys 6 (samples a to f) were obtained. The composition of each alloy obtained is shown in Table 12 below.
Further, these alloys were pulverized with a ball mill and classified with a 200-mesh sieve to obtain a hydrogen storage alloy for producing electrodes.

[0254]

[Table 12]

Further, the obtained hydrogen storage alloy (see Table 12 above)
Samples a to f) were subjected to X-ray diffraction measurement by the internal standard method. As a result, it was confirmed that the samples a to e had a single phase of AB _x of 95% by volume or more.
The sample f is a phase having a composition other than AB _x (second phase).
Was found to be produced in an amount of 10% by volume or more.

(Production of Electrode) The above hydrogen storage alloy powder, polytetrafluoroethylene (PTFE) powder, and Ketjen black were added at 95.5 wt% and 4 wt%, respectively.
After weighing so as to be 0.5% by weight, the mixture was stirred and mixed by a cutter mill until the PTFE was formed into fibers. The obtained cotton-like mixture was sprayed on a nickel wire mesh and rolled by a roller press to prepare a hydrogen storage alloy electrode (negative electrode).

(Production of battery) Nickel hydroxide 90% by weight
Nickel electrode by filling and drying a paste prepared by stirring and mixing a small amount of CMC and 50 wt% of water in 10 wt% of cobalt monoxide in a nickel porous body having a three-dimensional structure and rolling with a roller press. (Positive electrode) was produced.

The nickel electrode having a theoretical capacity of 1.1 Ah and the hydrogen storage alloy electrode were combined and wound with a separator made of a non-woven fabric to form an electrode group. This electrode group was inserted into an AA type battery can, a 30 wt% potassium hydroxide aqueous solution was injected, and the electrode was sealed with a positive electrode terminal plate having a safety valve with an operating pressure of 15 kg / cm ² . The next battery was assembled. In the secondary battery, the negative electrode / positive electrode ratio was 1.8, and the amount of the electrolytic solution for the hydrogen storage alloy electrode was 1.1 ml / Ah. However,
The negative electrode / positive electrode ratio means the capacity ratio of the hydrogen storage alloy electrode to the capacity of the nickel electrode in the uncharged state of the battery in the discharged state. In other words, it means the ratio of the capacity of the hydrogen storage alloy electrode to the capacity of the nickel electrode excluding the discharge reserve in the water storage alloy electrode generated by the oxidation of cobalt monoxide in the nickel electrode during the first charge after battery assembly. To do.

The cycle life of each secondary battery was evaluated. The conditions were such that the battery was charged at 1.1 A for 1.5 hours, and then the cycle of discharging at 1 A was repeated until the battery voltage reached 0.8 V. The cycle life was defined as the number of cycles until the battery capacity decreased to 50% of the initial capacity. Test temperature is 25
℃ was made. The results are shown in Table 13 below.

[0260]

[Table 13]

From Table 13, it can be seen that the cycle life is extended for non-stoichiometric compositions and that the cycle life is drastically shortened when _x of AB _x exceeds 6. Regarding the AB _6.2 alloy, the X-ray diffraction analysis showed that the second phase was formed in an amount of 10% by volume or more, and the EPMA observation showed that a large amount of La and Mn segregated at the grain boundaries. It has been found. From this, it was revealed that the formation of the second phase and the segregation at the grain boundaries significantly shorten the alloy life.

Comparative Example 24 A hydrogen storage alloy having the same composition as in Example 20 was prepared by a conventional casting method. Raw materials that were weighed so as to have the same composition as in Example 20 were put into a crucible, melted in a high frequency induction furnace, and then poured into an iron mold to obtain an alloy. Using the alloy thus obtained, a hydrogen storage alloy electrode was prepared in the same manner as in Example 20, and powder X-ray diffraction analysis was performed to observe the generation state of the second phase. The results are shown in Table 14.
In Table 14, ◯ indicates a single phase, × indicates that the second phase is generated, and Δ is not clear, but the second phase is 10
It indicates that more than volume% may be generated.

[0263]

[Table 14]

As is clear from Table 14, in the casting method, the second phase is likely to be generated when the alloy has a non-stoichiometric composition because the cooling rate is slow. This can be improved by using a water-cooled mold or by reducing the casting thickness, but it is very difficult to stably maintain a single phase up to around AB _5.5 where the performance is greatly improved.

From this, it is considered that the hydrogen storage alloy produced by the molten metal quenching method as described in Example 20 is suitable.

In Example 20, the single roll method was described as a method for easily and stably producing a hydrogen storage alloy having a stoichiometric composition, but another molten metal quenching method shown in FIG.
A hydrogen storage alloy having a non-stoichiometric composition was similarly stably obtained by the rotating disk method described in 2 above, the twin roll method described in FIG. 2, the gas atomizing method described in FIG. 33, and other rotating nozzle methods.

In Example 20, as the constituent elements of B of the hydrogen storage alloy represented by AB _x , Ni, Co,
Although Mn and Al were used, for example, Si, Fe, Cr, Cu
Similar results were obtained using the same method.

Example 21 Hydrogen storage alloy 500 having a composition of LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 (Lm is La-rich misch metal)
g is melted in a high-frequency induction furnace and is stored in the ladle 2 of the manufacturing apparatus by the single roll method shown in FIG. 1 described above, and the hydrogen storage alloy molten metal 4 is cooled from the ladle 2 (cooling roll for fine particles). 5), a flaky hydrogen storage alloy 6 was produced. This alloy 6 was ground with a ball mill and classified with a 200-mesh sieve to obtain a hydrogen storage alloy for electrode production. Then, the hydrogen-absorbing alloy powder, the PTFE powder, and the Ketjen black were each mixed at 95.5.
After weighing so that the weight%, 4% by weight, and 0.5% by weight were obtained, the mixture was stirred and mixed by a cutter mill until the PTFE became fibrous. The obtained cotton-like mixture was sprayed on a nickel wire mesh and rolled by a roller press to prepare a hydrogen storage alloy electrode (negative electrode).

Separately, 90% by weight of nickel hydroxide, 10% by weight of cobalt monoxide, a small amount of CMC and 50% by weight of water.
The mixture was stirred and mixed to form a paste, which was filled into a nickel porous body having a three-dimensional structure, dried, and rolled by a roller press to produce a nickel electrode (positive electrode).

Using the hydrogen storage alloy electrode and the nickel electrode produced by the above-described method, 30 kinds of AA type nickel-hydrogen secondary batteries having the above-mentioned negative electrode / positive electrode ratio and electrode liquid amount with respect to the hydrogen storage alloy electrode are shown in Table 15 below. Assembled
The capacity of these secondary batteries was set to 650 mAh as 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. A safety valve that operates at 18 kg / cm ² was used. It should be noted that, in Table 15, a portion where the battery symbol is not written indicates that it was impossible to inject a predetermined amount of the electrolytic solution because the electrode volume was too large.

[0271]

[Table 15]

Symbol A group shown in Table 15 (A1, A2,
A3, A4, A5, A6), group B (B1, B2, B3)
B4, B5, B6), C group (C1, C2, C3, C4
C5, C6), D group (D1, D2, D3, D4, D
5), group E (E1, E2, E3, E4) and group F (F
1, F2, F3) secondary batteries are charged at 650 mA for 1.5 hours, and then a charge / discharge cycle of discharging at 1 A is repeated until the battery voltage becomes 0.8 V, and the battery capacity is 50% of the initial capacity.
The number of cycles to reach% was examined. The result is shown in FIG.
Shown in. In FIG. 34, □ indicates the characteristics of the battery of the group A in Table 15, + indicates the characteristics of the battery of the group B of Table 15, ◇ indicates the characteristics of the battery of the group C of Table 15, and Δ indicates the characteristics. In Table 15, the characteristics of the group D battery are shown, × is the characteristics of the group E battery of Table 15, and ∇ is the characteristics of the group F battery of Table 15.

As is clear from FIG. 34, the cycle life of the secondary battery having a negative electrode / positive electrode ratio of 0.5 is remarkably short at all electrolyte amounts. This is because the battery configuration is regulated by hydrogen storage alloy electrodes, so the capacity is 0.5
In addition to the double output, the battery internal pressure rapidly increased to the safety valve operating pressure in the initial charge / discharge cycle, and electrolyte ran out because the electrolyte ran out of the safety valve. And it was confirmed by battery disassembly inspection.

On the other hand, the secondary battery having a negative electrode / positive electrode ratio of 1.1 or more achieves a cycle life of 150 cycles or more under these charge / discharge conditions unless the amount of the electrolyte is excessive or insufficient. This is a value that satisfies the practical cycle life of 500 cycles as a secondary battery under normal charge and discharge conditions, and is considered to be sufficient life. However, even if the anode / cathode ratio is 1.1 or more, the cycle life is about 50 cycles under the condition that the amount of electrolyte is 0.2 ml / Ah or 2.0 ml / Ah, and the cycle life is not sufficient. . This is because the amount of electrolyte is 0.2
Under the condition of ml / Ah, the liquid was exhausted from the beginning of the charge / discharge cycle, and under the condition of 2.0 ml / Ah, the battery internal pressure increased to the safety valve operating pressure at the end of charging, and the electrolyte was gradually exhausted. It became clear from the result of the measurement of the battery internal pressure that was separately performed.

Further, in order to investigate the battery internal pressure characteristics that greatly affect the battery life, the batteries when the secondary batteries of the groups A to F in Table 15 were charged for 5 hours at 650 mA which is a severe charging condition. The internal pressure was measured. The result is shown in FIG. In FIG. 35, □ indicates the characteristics of the battery of the group A in Table 15, + indicates the characteristics of the battery of the group B of table 15, and ◇ indicates the characteristics of the battery in the table 1.
5 shows the characteristics of the group C battery, Δ indicates the characteristics of the group D battery of Table 15, X indicates the characteristics of the group E battery of Table 15, and ▽ indicates the characteristics of the group F battery of the same table 15. Are shown respectively.

From FIG. 35, the secondary battery having a negative electrode / positive electrode ratio of 0.5 and the secondary battery having an electrolytic solution amount of 2 ml / Ah are all 18 kg / cm, which is the safety valve operating pressure because of the above-mentioned reason.
You can see that it has reached ² . When the weight of these secondary batteries was measured before and after the test, a weight reduction of 300 mg at the maximum and 40 mg at the minimum, which is considered to be caused by the ejection of the electrolytic solution, was observed.

In this experiment, all the internal pressures of the secondary battery having the amount of electrolyte of 0.2 ml / Ah were low. The amount of the electrolyte was very small, and the internal resistance of the battery rapidly increased at the end of charging. It was because the output range of the constant current power supply used for was exceeded and charging was not possible. From this, it can be understood that the secondary battery having the amount of electrolyte of 0.2 ml / Ah cannot be practically used.

From the above battery life and battery internal pressure measurement experiments, it is necessary that the anode / cathode ratio is 1.1 or more, and the amount of the electrolytic solution is 0.1% per 1 Ah of the hydrogen storage alloy electrode.
It has been found necessary to be in the range 4-1.8 ml.

Further, it was recognized that the battery internal pressure tended to increase when the negative electrode / positive electrode ratio exceeded 2. This is because the capacity of all secondary batteries was unified to 650 mAh,
It is considered that in a battery having a large positive electrode ratio, the volume occupied by the electrode group increased and the voids in the battery decreased.
From this, it is understood that the amount of electrolyte and the negative electrode / positive electrode ratio are mutually related values in battery design and cannot be independently determined.

Next, in order to confirm the high capacity, which is a major feature of the nickel-hydrogen secondary battery, an electrode group having the maximum capacity that can be accommodated in an AA type battery can when a certain negative / positive electrode ratio is given. Was prepared, an electrolyte solution was injected under various conditions to assemble a battery, and the battery capacity was measured when the initial battery was in a healthy state. The result is shown in FIG. In addition, □ in FIG. 36
Is 0.2 ml / A for the hydrogen storage alloy electrode
As for the characteristics of the secondary battery of h, + is 0.4 ml /
The characteristics of the Ah secondary battery are as follows:
/ Ah secondary battery characteristics, △ is the same amount of electrolyte is 1.5m
The characteristics of the secondary battery of 1 / Ah are as follows.
The characteristics of the secondary battery of ml / Ah are as follows.
The characteristics of the secondary battery of 2 ml / Ah are shown respectively.

From FIG. 36, it is understood that the capacity of the battery having the negative electrode / positive electrode ratio of 0.5 is low because the battery capacity is determined by the hydrogen storage alloy electrode containing only half the amount of the nickel electrode. Further, when the amount of the electrolytic solution is 0.2 ml / Ah, the electrolytic solution is still not sufficient to smoothly carry out the battery reaction, so that the battery capacity becomes low. Other than these, as the negative electrode / positive electrode ratio increases, the capacity of the nickel electrodes that can be assembled in the same electrode group volume decreases, so the battery capacity also decreases. It can be seen that when the anode / cathode ratio exceeds 0.2, the capacity is equal to or less than that of the current high capacity nickel cadmium battery.

By increasing the density of the active material of the electrode, it is possible to further increase the capacity even when the anode / cathode ratio is 2.0 or more. However, not only is it difficult to manufacture the electrode, but oxygen gas at the end of charging is also added. The reduction rate is remarkably reduced, and the large current discharge characteristics are also remarkably reduced, resulting in a battery that cannot be practically used.

From this experiment, it was found that it is necessary to set the negative electrode / positive electrode ratio to 2.0 or less in order to bring out the characteristic of the high capacity of the nickel-hydrogen secondary battery without sacrificing the battery characteristics. did.

In Example 21, the hydrogen-storing alloy electrode using the hydrogen-storing alloy, which was melt-quenched by the single roll method as the active material, and the non-sintered nickel electrode were mixed with 7N potassium hydroxide and 1N hydroxide. Although the example of forming the AA type battery by the mixed electrolytic solution with lithium has been described in detail, the present invention is not limited to the above method.

For example, as the molten metal quenching method, the rotating disk method explained in FIG. 32, the twin roll method explained in FIG. 2, and FIG.
The hydrogen storage alloy obtained by the gas atomizing method or the like described in Example 3 also showed the same characteristics as those of the single roll method of Example 21.

Further, in the method of manufacturing the electrode, after filling or coating the current collector with the kneaded material of the hydrogen storage alloy powder, the kneading agent and the water,
The characteristics of the present invention can also be exhibited by a so-called paste type electrode which is dried and rolled. As the hydrogen storage alloy, a powder obtained by mechanically pulverizing a hydrogen storage alloy produced by a molten metal quenching method, or a powder obtained by absorbing and desorbing hydrogen and pulverizing can be used. In particular, when the single roll method or the twin roll method is adopted, a flaky hydrogen storage alloy can be obtained under a wide range of manufacturing conditions. Since this flake-like alloy is generally thin, it can be crushed relatively easily. Therefore, the crushing before making the electrode should be limited to the coarse crushing of several 100 μm to several mm, and the rolling process in the electrode manufacturing process It is also possible to carry out further crushing together with rolling of the electrodes. By such a treatment, the specific surface area of the hydrogen storage alloy during electrode production can be reduced, the hydrogen storage alloy can be protected from surface oxidation / contamination during the production process, and the hydrogen storage alloy production process can be performed. Since the ignition probability inside can be lowered, it is possible to proceed with the work in a safe environment.

As for the electrolytic solution, for example, an 8N potassium hydroxide aqueous solution or an electrolytic solution in which an aqueous sodium hydroxide solution is mixed if necessary may be used.

Further, the battery size is, for example, 4 other than AA type.
/ 5A type and A type have the same results.

As described above in detail, according to the present embodiment, it is possible to provide a hydrogen storage alloy having little deterioration and long cycle life when used as a negative electrode active material of an alkaline secondary battery.
In addition, according to the present embodiment, a hydrogen storage alloy electrode with little deterioration is used, and by defining the amount of electrolyte and the electrode capacity ratio, a nickel-hydrogen secondary battery with high capacity, long life, and low cost is provided. it can.

Next, the influence of variations in the Mn concentration in the hydrogen storage alloy and the particle size of segregated Mn particles on the battery characteristics will be described with reference to the following examples and comparative examples.

The alloys of Examples 22 to 23 and Comparative Examples 25 to 27 had a composition of LmNi _4.3 Co _0.1 Mn _0.5 A.
l _0.1 (Lm is La enriched misch metal) so that, Lm anticipate depletion during dissolution advance, Ni, Co, M
n and Al were weighed. Next, these raw materials were melted in a high frequency induction furnace and poured into an ordinary mold to obtain an alloy of Comparative Example 25. Further, an alloy of Comparative Example 26 was obtained by pouring it into a water-cooled mold so that the thickness would be 10 mm. Further, in the single roll device shown in FIG. 1, a copper roll having a diameter of 300 mm was used as the cooling roll 5 and was rotated at 600 rpm in a vacuum, and the gap width between the injection nozzle 4 and the cooling roll 5 was set to 50 mm. Is 0.1 kgf / cm ² and the thickness is about 100 μm.
An alloy of Comparative Example 27 was obtained. The injection pressure is 0.05kg
An alloy of Example 22 having a thickness of 50 μm as f / cm ² was obtained. The injection pressure is 0.02 kgf / cm ² and the thickness is 20.
The alloy of Example 23 of μm was obtained, and a total of three types of flaky alloy samples were prepared. In addition to these, an average particle diameter of 20 μm was measured by the inert gas atomizing method apparatus shown in FIG.
The hydrogen-absorbing alloy powder of was prepared as Example 24.

The Mn concentration distribution of these alloy samples was examined by the method described below.

1) Resin embedding Approximately 100 mg of an alloy sample was sampled and dispersed in the center of a resin embedding frame (made of polypropylene) for SEM samples having a diameter of 20 mm. Next, a commercially available epoxy resin (EPO-MIX manufactured by Buehler Co.) for embedding a SEM sample is used.
After thoroughly mixing the resin and the curing agent, they were poured into the above-mentioned embedding frame and cured. At this time, in order to improve the adhesion between the sample and the resin, the resin is preheated to about 60 ° C. to reduce the viscosity, or after the resin is injected, vacuum is drawn in a vacuum desiccator to defoam. And more preferable.

2) Polishing The sample embedded in the above procedure is then polished by a polishing machine until it has a mirror finish. Since the hydrogen storage alloy sample easily reacts with water, the roughness of the water-resistant abrasive paper is adjusted to 180, 400, 80 by dropping methyl alcohol during polishing.
After polishing with a rotary polishing machine that rotates at 200 rpm while making it finer in the order of 0, the felt was set on the rotary polishing machine and the particle size of the diamond paste was 15 μm.
3 μm and 0.25 μm were successively finely ground to give a mirror finish.

3) Observation of EPMA Next, these samples were set in EPMA (V6 manufactured by Shimadzu Corporation). First, a region not containing Mn (for example, a sample stage) was observed, mapping observation was performed, and the intensity value of the characteristic X-ray of Mn when the Mn concentration was 0 was recorded. Next, the sample is moved so as to come to the center of the visual field, and the whole image of the Mn concentration distribution is grasped by mapping observation. In this measurement, the magnification was set so that the observation area was 20 μm square and fit in the visual field. At this time, care was taken so that the sample end did not enter the visual field. Then, the field of view was divided into 100 vertically and 100 horizontally to form 10000 unit areas, and the EPMA was set to measure the X-ray intensity value of each unit area.

The characteristic X-ray intensity distribution in the observation plane obtained by the above-mentioned observation was corrected by the intensity value in the region not containing Mn previously obtained. The average value in the observation plane was obtained by simply averaging the characteristic X-ray intensities corresponding to the respective unit areas thus obtained. The maximum value is the above X
The maximum value of the line strength was adopted. Further, the ratio of the maximum value to the average value of the X-ray intensity was calculated.

[0297] Each of the above analyzes was performed while changing the field of view.
Performed 0 times. The analysis results are shown in Table 16. In addition, Table 16 also shows the cooling rates at the time of sample production, which were measured by the same method as in Examples 18A to 18C.

[0298]

[Table 16]

Table 16 shows that the maximum strength value with respect to the average strength decreases in the order of Comparative Example 25, Comparative Example 26, Comparative Example 27, Example 22, Example 24, and Example 23.

Next, the crystal form of each sample was observed by the method described in Examples 1 to 9 and the results are shown in Table 17.

[0301]

[Table 17]

The reason why no numerical values are shown in Comparative Examples 25 and 24 in Table 17 is that in Comparative Example 25, an equiaxed crystal structure was observed over almost the entire cross section and no columnar crystal structure was observed. is there. Further, in Example 24, the structure could not be identified, but this is also because the structure other than the columnar crystals was formed.

Comparison between Table 16 and Table 17 shows that in Comparative Examples 26 and 27 and Examples 22 and 23 in which columnar crystals were observed,
The correspondence between the columnar crystal ratio and the uniformity of Mn distribution was
When the cooling rate is fast as in Examples 22 and 23, the solidification of the molten metal occurs rapidly, so that the solidification proceeds in one direction from the cooling surface, columnar crystals are likely to grow, and the proportion of columnar crystals increases. Further, since it rapidly solidifies, a specific element cannot exist in the molten state for the time required to form segregation in the grain or in the grain boundary. Therefore, in an element such as Mn, which tends to cause uneven distribution or segregation. It is also considered that the solidification occurred while maintaining the uniformity of distribution.

In Example 24, even though no columnar crystals were observed, the uniformity of the Mn distribution was excellent. It is considered that since it cannot exist in the molten state for the time required to form segregation in the boundary, even elements such as Mn that are likely to cause nonuniform distribution or segregation have solidified while maintaining uniform distribution.

Next, using these samples, electrodes were prepared in the following procedure. First, these alloys are crushed by a ball mill and then crushed to 200 by a 200 mesh sieve.
Particles larger than the mesh were excluded to obtain a hydrogen storage alloy powder. Next, these alloy powder, powdered PTFE, and Ketjen black were added at 95.5% by weight, 4% by weight, and 4% by weight, respectively.
After weighing so as to be 0.5% by weight, the mixture was stirred and mixed by a cutter mill until the PTFE was formed into fibers. The cotton-like mixture thus produced was sprayed on a nickel wire mesh and rolled by a roller press to obtain a hydrogen storage alloy electrode.

The cycle life was evaluated by sandwiching these electrodes between sintered nickel electrodes with a nylon separator interposed between them and immersing them in an 8N potassium hydroxide aqueous solution for charging and discharging.

The condition is 220 m per 1 g of alloy weight in the electrode.
After charging with the current of A for 1 hour, to the mercury oxide electrode,
220mA per gram of alloy until -0.5V
The cycle of discharging with the current of was repeated. The cycle life was defined as the number of cycles in which the electrode capacity decreased to 50% of the initial value. The evaluation temperature is 20 ° C. FIG. 37 shows the change in capacity with the progress of the cycle, and Table 18 shows the cycle life.

[0308]

[Table 18]

As described above, in Comparative Example 25 to Comparative Example 27 in which the X-ray intensity ratio corresponding to the Mn concentration in the hydrogen storage alloy was about 1.4, the cycle life at a single electrode was about 350 cycles. On the other hand, the concentration ratio is within the range of the present invention.
It was confirmed that in Examples 22 to 24 in which the number of cycles was 3 or less, the unipolar cycle life was significantly increased from 620 cycles to 740 cycles, respectively.

Next, in order to investigate the performance of an actual battery,
Using these alloys, batteries were prepared by the following procedure and the cycle life was evaluated.

The hydrogen storage alloy electrode was manufactured by the same manufacturing method as the above-mentioned electrode for electrode evaluation. Note that the amount of hydrogen storage alloy in the electrode was set to 9 g ± 0.2 g.

Nickel electrode is 90% by weight of nickel hydroxide
And 10% by weight of cobalt monoxide were mixed with a small amount of CMC and 50% by weight of water to form a paste, which was filled in a nickel porous body having a three-dimensional structure, dried, and rolled by a roller press. . At this time, the capacity calculated from the weight of nickel hydroxide in the electrode was set to 1.1 Ah.

The hydrogen storage alloy electrode thus prepared and the nickel electrode were combined and wound with a separator made of polypropylene blind cloth to form an electrode group.
Insert this electrode group into an AA type (AA type) battery can, inject a mixed aqueous solution of 7N potassium hydroxide + 1N lithium hydroxide as an electrolytic solution, and positive electrode terminal with a safety valve with an operating pressure of 15 kgf / cm ^2. The test battery shown in FIG. 3 was constructed by sealing with a plate.

Cycle life was evaluated using these batteries. The conditions were such that the battery was charged at 1.1 A for 1.5 hours, and then the cycle of discharging at 1 A was repeated until the battery voltage reached 0.8 V. The cycle life was defined as the number of cycles at which the battery capacity decreased to 50% of the initial capacity. Test temperature is 25 ℃
Is. FIG. 38 shows the change in battery capacity with the progress of the cycle, FIG. 39 shows the change in battery internal pressure with the progress of the cycle, and Table 19 shows the cycle life.

At this time, it was confirmed that the same procedure as in the case where the distribution of Mn was nonuniform was observed even in the electrode made into a battery by the following procedure.

1) Battery Discharge First, a battery is prepared as a sample in which charge / discharge cycles have not progressed after the battery was manufactured. Since the uniformity of Mn in the alloy changes as the charging / discharging cycle progresses, the charging / discharging cycle of the battery used as a sample is preferably 10 cycles or less if possible. This battery was discharged in a battery state at a current of 110 mA until the battery voltage became 0.8 V, and then a resistor of 10 KΩ was connected between both electrodes of the battery and left for 10 hours for complete discharge. The reason why the complete discharge is performed in two stages is to prevent ignition due to residual hydrogen.

2) Electrode washing with water After the above discharge is completed, the battery is disassembled and the hydrogen storage alloy electrode is taken out. The hydrogen storage alloy electrode taken out is for the purpose of removing hydrogen remaining as a discharge reserve in the electrode, and preventing the resin from being insufficiently solidified or the adhesion strength between the sample and the resin being lowered by the electrolytic solution. For this purpose, after thoroughly washing with pure water, it was completely dried with a vacuum dryer.

3) Resin Embedding The dried electrode is cut into a size of about 10 mm × 5 mm and scattered on the center of the resin embedding frame (made of polypropylene) for SEM sample with a diameter of 20 mm. Next, a commercially available epoxy resin (EPO-MIX manufactured by Buehler Co.) for embedding the SEM sample is thoroughly mixed with the resin and the curing agent, and then injected into the embedding frame to be cured. At this time, in order to improve the adhesion between the sample and the resin, the resin is heated in advance to about 60 ° C. to reduce the viscosity,
After injecting the resin, it is more preferable to degas by vacuuming in a vacuum desiccator.

4) Polishing The sample embedded by the above procedure is then polished by a polishing machine until it has a mirror finish. Since the hydrogen-absorbing alloy sample easily reacts with water, the roughness of the water-resistant abrasive paper should be 180, 400, 8 while dropping methyl alcohol during polishing.
After polishing with a rotary polishing machine that rotates at 200 rpm while making it finer in the order of 00, set felt on the rotary polishing machine and set the particle size of diamond paste to 15μ.
m, 3 μm, 0.25 μm in this order while polishing to obtain a mirror finish.

5) EPMA observation Next, with respect to these samples, EPM was conducted in the same procedure as described above.
A was used to measure the average and maximum of the X-ray intensity values corresponding to the Mn concentration in the sample. This measurement result is shown in Table 20.
Although it is shown in Table 1, it was confirmed that the same numerical values as those shown in Table 16 were obtained, and that they were sufficiently observable even after being made into an electrode or made into a battery.

[0321]

[Table 19]

[0322]

[Table 20]

As described above, in the batteries using the alloys of Comparative Examples 25 to 27, in which the uniformity of Mn distribution is low as in the result of the above-described electrode evaluation, the hydrogen storage alloys were formed from the relatively early stage of the charge / discharge cycle. An increase in battery internal pressure due to deterioration was observed. Due to the outflow of the electrolytic solution from the safety valve, the battery capacity decreased, and only a cycle life of about 130 cycles was obtained. On the other hand, in the batteries using Examples 22 to 24 with improved uniformity, the increase in internal pressure was relatively slow, and as a result, the cycle life was 410 to 510 cycles and the practical life of the secondary battery, respectively. We succeeded in obtaining a life significantly exceeding 300 cycles. Thus, even in an actual battery, M
It was confirmed that the cycle life can be significantly extended by setting the uniformity of the distribution of n within the range of the present invention.

When the alloys of Examples 25 and 26 and Comparative Examples 28 and 29 were used, the composition was LmNi _4.0 Co _0.4 Mn _0.3 A.
l _0.3 (Lm is La-enriched misch metal) Lm, Ni, Co, M
n and Al were weighed. Next, these raw materials were melted in a high frequency induction furnace and poured into an ordinary mold to prepare an alloy of Comparative Example 28. In addition, in the single roll device shown in FIG.
A copper roll with a diameter of 300 mm is used as a cooling roll, which is rotated at 800 rpm in vacuum, the gap width between the injection nozzle and the cooling roll is set to 50 mm, and the injection pressure is 0.1 kgf /
An alloy of Comparative Example 29 having a thickness of about 100 μm as cm ² was prepared. The injection pressure is 0.02 kgf / cm ² and the thickness is 2
A 0 μm flaky alloy sample of Example 25 was prepared. In addition to these, a hydrogen storage alloy powder having an average particle diameter of 20 μm was prepared by an inert gas atomizing method apparatus shown in FIG.

The size of Mn segregated in these alloy samples was examined by the following method. First, the alloy sample was sealed in a synthetic resin by the same procedure as in Examples 22 to 24, and then,
Polished to a mirror finish.

Then, the above sample was set in a SEM (ABT, ABT-55) equipped with EDX (KEVEX) and observed. First, mapping observation of Mn and other constituent elements of the hydrogen storage alloy is carried out by EDX, and a portion where Mn is segregated alone is searched for. However,
Since the resolution of EDX is lower than that of EPMA, it is difficult to directly determine the magnitude of segregation from the result of mapping observation. Therefore, in order to accurately know the magnitude of Mn segregation, the Mn concentration determined by EDX should be High points need to be observed by SEM. That is, the difference in the concentration of Mn and other elements compared with the alloy composition is observed on the SEM as the difference in the intensity of the reflected electron beam from the alloy portion. After making an assertion, the size of the region was determined from the results of observation with SEM.

Table 21 shows the results of observing the magnitude of Mn segregation by the above-mentioned SEM + EDX for Comparative Example 28, Comparative Example 29, Example 25, and Example 26. When preparing this table, observation was performed on 10 visual fields per sample.

[0328]

[Table 21]

Next, the crystal form of each sample was observed by the method described in Examples 1 to 9 and the results are shown in Table 22.

[0330]

[Table 22]

The reason why no numerical values are described in Comparative Example 28 and Example 26 in Table 22 is that in Comparative Example 28, an equiaxed crystal structure was observed over almost the entire surface and no columnar crystal structure was observed. . In Example 26, the structure could not be identified, but this is because the structure other than the columnar crystal was formed.

The comparison between Table 21 and Table 22 shows that columnar crystals were observed in Comparative Example 29 and Example 25, and there was a correspondence between the columnar crystal ratio and the magnitude of Mn segregation for the following reason. That is, when the cooling rate is high as in Comparative Example 29 and Example 25, solidification of the molten metal occurs rapidly, so that solidification proceeds more in one direction from the cooling surface and columnar crystals are more likely to grow. Will increase. Further, since it solidifies rapidly, it becomes difficult for a specific element to exist in a molten state until the time required for forming a segregation in a grain or a grain boundary. Even if segregation occurs, it becomes difficult for the segregated material to grow.
It is considered that even an element such as Mn that easily causes segregation does not become a large segregated product. Further, in Example 26, the size of the Mn segregation product is small in spite of the absence of columnar crystals, since the cooling rate is also very rapid, a specific element forms segregation in the grain or in the grain boundary. It is difficult to exist in the molten state until the time required for the formation, and even if segregation occurs, it is difficult to grow segregated substances. Therefore, even elements such as Mn that easily cause segregation do not become large segregated substances. Conceivable.

Next, 20 g of each of these samples was sealed in a closed container (volume: 50 cc) equipped with a gas introduction tube, and the sealed container was immersed in cooling water at 10 ° C., and 10 kg /
After absorbing hydrogen pressurized to cm ² , close the container at 60 ° C.
The pipe was connected to a vacuum pump while being immersed in the warm water described above to desorb the absorbed hydrogen. The particle size distribution of the sample after repeating the above occlusion and desorption for 1000 times was measured by a laser scattering type particle size distribution measuring device (manufactured by Seishin Enterprise Co., Ltd.). The results are shown in Table 23 below.

[0334]

[Table 23]

According to Table 23 above, in Example 25 in which the size of the Mn segregated product is small and is within the scope of the present invention, even after repeating hydrogen storage and desorption 1000 times, the average particle size of 35 μm before the test becomes 27 μm. In Example 26, the average particle size was 20μ
It can be seen that m is reduced to only 17 μm, and the pulverization by hydrogen storage / desorption in the hydrogen storage alloy is suppressed. On the other hand, in Comparative Examples 28 and 29, it was confirmed that the initial average particle size of 35 μm progressed to 9 μm and 13 μm, respectively.

Next, in order to investigate the effect of the difference in the pulverization behavior confirmed in the above test on the actual electrode characteristics, a cycle life test was performed on the electrodes.

Therefore, an electrode was manufactured by the following procedure.
First, each of the above alloys was pulverized by a ball mill, and then large particles of 200 mesh or more were removed by a 200 mesh sieve to obtain a hydrogen storage alloy powder. Next, these alloy powders, powdered PTFE, and Ketjen black were weighed so as to be 95.5% by weight, 4% by weight, and 0.5% by weight, respectively, and then the PTFE was made into fibers by a cutter mill. Stir and mix. The cotton-like mixture thus produced was sprayed on a nickel wire mesh and rolled by a roller press to obtain a hydrogen storage alloy electrode.

The cycle life was evaluated by sandwiching these electrodes between sintered nickel electrodes with a nylon separator interposed between them and immersing them in an 8N aqueous potassium hydroxide solution for charging and discharging.

The condition is 220 m per 1 g of alloy weight in the electrode.
After charging with the current of A for 1 hour, the mercury oxide electrode was
The cycle of discharging at a current of 220 mA / g of alloy was repeated until the voltage reached 0.5 V. The cycle life was defined as the number of cycles until the electrode capacity decreased to 50% of the initial value. The evaluation temperature is 20 ° C. The cycle life is shown in Table 24 below.

[0340]

[Table 24]

Comparing the results in Table 24 with the results in Table 23, the lifespans of Comparative Examples 28 and 29 in which pulverization is more likely to progress are shorter than those of Examples 25 and 26 in which pulverization is suppressed. It was confirmed that it is possible to significantly extend the cycle life by suppressing the progress of pulverization.

At this time, it was confirmed that the magnitude of segregation of Mn can be observed in the alloy formed into an electrode by the following procedure as in the case of the alloy alone.

1) Electrode Discharge First, an electrode in which the charging / discharging cycle has not progressed after electrode preparation is prepared as a sample. Since the state of Mn segregation in the alloy changes as the charge / discharge cycle progresses, the charge / discharge cycle of the electrode used as the sample is preferably 10 cycles or less if possible. This electrode was discharged at a current of 0.1 C until the electrode voltage became −0.5 V with respect to the mercury oxide electrode, and complete discharge was performed. The reason why the complete discharge is performed is to prevent ignition due to residual hydrogen.

2) Electrode water washing After the above-mentioned discharge is completed, the hydrogen storage alloy electrode is used for the purpose of removing hydrogen remaining as a discharge reserve in the electrode, and for insufficient solidification of the resin due to the electrolyte solution. For the purpose of preventing a decrease in adhesion strength between the sample and the resin, the sample was thoroughly washed with pure water and then completely dried with a vacuum dryer.

3) The dried electrode is 10 mm × 5 mm
It is cut to a size of about 20 mm and scattered on the center of a resin-embedded frame (made of polypropylene) for SEM samples with a diameter of 20 mm. Next, a commercially available epoxy resin (EPO-MIX manufactured by Buehler Co.) for embedding the SEM sample is thoroughly mixed with the resin and the curing agent, and then injected into the embedding frame and cured. At this time, in order to improve the adhesion between the sample and the resin, the resin is preheated to about 60 ° C. to reduce the viscosity, or after the resin is injected, vacuum is drawn in a vacuum desiccator to defoam. And more preferable.

4) Polishing The sample embedded according to the above procedure is then polished by a polishing machine until it has a mirror finish. Since the hydrogen-absorbing alloy sample easily reacts with water, the roughness of the water-resistant abrasive paper should be 180, 400, 8 while dropping methyl alcohol during polishing.
After polishing with a rotary polishing machine that rotates at 200 rpm while making it finer in the order of No. 00, set the felt on the rotary polishing machine and set the particle size of the diamond paste to 15μ.
m, 3 μm, 0.25 μm in this order while polishing to obtain a mirror finish.

5) EDX Observation Next, SEM (AB with EDX (manufactured by KEVEX))
The sample was set in ABT-55 manufactured by T. Co. and observed. First, mapping observation of Mn and other constituent elements of the hydrogen storage alloy is carried out by EDX, and a portion where Mn is segregated alone is searched for. However, EDX is EMP
Since the resolution is lower than that of A, it is difficult to directly obtain the size of segregation from the result of mapping observation.
In order to know the magnitude of Mn segregation accurately, it is necessary to observe with SEM the point of high Mn concentration obtained by EDX. That is, the difference in the concentration of Mn and other elements compared to the alloy composition is observed on the SEM as the difference in the intensity of the reflected electron beam from the alloy portion. After making an assertion, the size of the region was determined from the results of SEM observation.

Each of the above analyzes was carried out by changing the field of view.
Performed 0 times.

In the above examples, Ni, Co, Mn and Al were used as the constituent elements of B.
Si, Fe, Cu, Ag, Pd, Sn, In, Ga, G
Similar results were obtained even if partial substitution was performed with e, Ti, Zr, Zn, or the like.

As described above in detail, the maximum value of Mn concentration in the hydrogen storage alloy containing Mn, which is very effective for increasing the capacity of the hydrogen storage alloy, is 1.3 times the average value.
Or less, or by setting the maximum diameter of Mn segregated in the alloy to 0.5 μm or less, the corrosion resistance of the alloy with respect to a concentrated alkaline aqueous solution that is an electrolytic solution is improved, and the expansion due to hydrogen absorption and desorption It became possible to suppress pulverization due to shrinkage, and it became possible to extend the life of the hydrogen storage alloy. Therefore, it has become possible to extend the life of the nickel-hydrogen secondary battery using these alloys. Therefore, the industrial value of the hydrogen storage alloy according to the present invention is extremely large.

[0351]

As described above, according to the first to third hydrogen storage alloys for a battery of the present invention, it is an AB ₅ type alloy containing Mn as an essential element, and is used as an alkaline secondary battery. In addition, it is possible to provide a negative electrode material having a high capacity and excellent cycle life and initial characteristics.

By heat-treating the above alloy at a relatively low temperature of about 200 to 500 ° C., it is possible to remove internal strain while maintaining the homogeneity of the alloy. A hydrogen battery can be provided.

Further, according to the method for producing a hydrogen storage alloy of the present invention, it is possible to provide a negative electrode material for a nickel-hydrogen secondary battery which has a high capacity and is excellent in cycle life and initial characteristics.

Furthermore, according to the fourth hydrogen storage alloy of the present invention, when used as a negative electrode active material of an alkaline secondary battery, it is possible to form an electrode having little deterioration and long cycle life.

The nickel-hydrogen secondary battery according to the present invention has a high capacity, a long life, and a low price.

[Brief description of drawings]

FIG. 1 is a schematic view showing a molten metal quenching apparatus by a single roll method.

FIG. 2 is a schematic view showing a molten metal quenching apparatus by a twin roll method.

FIG. 3 is a perspective view showing a configuration example of a nickel hydrogen battery according to the present invention.

FIG. 4 is an electron micrograph showing a metallographic structure of a flake-shaped hydrogen storage alloy that has been subjected to melt quenching.

FIG. 5 is an electron micrograph showing a metal structure of hydrogen storage alloy particles contained in a negative electrode taken out from a battery.

FIG. 6 is an electron micrograph showing the metal structure of hydrogen storage alloy particles contained in the negative electrode taken out from the battery.

FIG. 7 is an electron micrograph showing the metal structure of hydrogen storage alloy particles contained in the negative electrode taken out from the battery.

FIG. 8 is an electron micrograph showing a metal structure of hydrogen storage alloy particles contained in a negative electrode taken out from a battery.

FIG. 9 is an electron micrograph showing the metal structure of the hydrogen storage alloy according to Example 9B.

FIG. 10 is a schematic view showing a columnar crystal of the metal structure shown in FIG.

11 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 5 or more in the metal structure shown in FIG.

12 is a schematic view showing a columnar crystal structure having an aspect ratio of 1: 4 or more in the metal structure shown in FIG.

13 is a schematic view showing a columnar crystal structure having an aspect ratio of 1: 3 or more in the metal structure shown in FIG.

FIG. 14 is a schematic view showing a columnar crystal structure having an aspect ratio of 1: 2 or more in the metal structure shown in FIG.

FIG. 15 is an electron micrograph showing the metal structure of the hydrogen storage alloy according to Example 5A.

FIG. 16 is a schematic view showing a columnar crystal of the metal structure shown in FIG.

17 is a schematic view showing a columnar crystal structure having an aspect ratio of 1: 5 or more in the metal structure shown in FIG.

18 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 4 or more in the metal structure shown in FIG.

19 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 3 or more in the metal structure shown in FIG.

20 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 2 or more in the metal structure shown in FIG.

FIG. 21 is an electron micrograph showing the metal structure of the hydrogen storage alloy according to Example 12A.

22 is a schematic view showing a columnar crystal of the metal structure shown in FIG.

23 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 5 or more in the metal structure shown in FIG.

24 is a schematic view showing a columnar crystal structure having an aspect ratio of 1: 4 or more in the metal structure shown in FIG.

25 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 3 or more in the metal structure shown in FIG.

26 is a schematic diagram showing a columnar crystal structure having an aspect ratio of 1: 2 or more in the metal structure shown in FIG. 21. FIG.

FIG. 27 is an electron micrograph showing the metal structure of the hydrogen storage alloy according to Comparative Example 7B.

FIG. 28 is a characteristic diagram showing the relationship between the crystal grain size of a hydrogen storage alloy and the number of charge / discharge cycles.

FIG. 29 is a characteristic diagram showing the relationship between the ratio of the maximum value to the average value of Mn concentration in the alloy and the number of charge / discharge cycles of the alloy electrode.

FIG. 30 is a characteristic diagram showing the relationship between the maximum diameter of Mn particles segregated in the alloy and the number of charge / discharge cycles.

FIG. 31 is a characteristic diagram showing the relationship between the composition ratio x, the electrode capacity, and the number of charge / discharge cycles in Example 19.

FIG. 32 is a schematic sectional view showing an apparatus for producing hydrogen storage alloy particles by a rotating disk method.

FIG. 33 is a schematic sectional view showing an apparatus for producing hydrogen storage alloy particles by a gas atomizing method.

FIG. 34 is a diagram comparing the battery cycle life with various negative electrode / positive electrode alloy capacity ratios and the amount of electrolyte.

FIG. 35 is a diagram comparing the negative electrode / positive electrode alloy capacity ratio and the maximum value of the battery internal pressure depending on the amount of the electrolytic solution.

FIG. 36 is a diagram comparing various negative electrode / positive electrode alloy capacity ratios and maximum battery capacities depending on the amount of electrolytic solution.

FIG. 37 is a graph showing the relationship between charge / discharge cycle and electrode capacity in Comparative Example 25, Comparative Example 26, Comparative Example 27, Example 22, Example 23, and Example 24.

FIG. 38 is a diagram showing the relationship between the charge / discharge cycle of an AA type battery and the battery capacity.

FIG. 39 is a diagram showing the relationship between the charge / discharge cycle of an AA type battery and the battery internal pressure.

[Explanation of symbols]

 1 Cooling Chamber 2 Ladle 3 Molten Alloy 4 Pouring Nozzle (Injection Nozzle) 5, 5a, 5b Cooling Roll 6 Hydrogen Storage Alloy 7 Melting Furnace 8 Tundish 9 Disc Rotating Body 10 Particle Collection Container 11 Hydrogen Storage Alloy Electrode (Negative Electrode) 12 Non-sintered nickel electrode (positive electrode) 13 Separator 14 Container 15 Hole 16 Sealing plate 17 Insulating gasket 18 Positive electrode lead 19 Positive electrode terminal 20 Safety valve 21 Insulating tube 22 Collar paper 23 Heater 24 Melting furnace 25 Inert gas nozzle 26 Opening valve 30 Erosion part 31 Columnar crystal 32 Equiaxed crystal 33 Adhered matter 34 Contact surface against cooling roll 35 Chill crystal

Front page continuation (72) Inventor Takao Sawa 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Pref., Toshiba Corporation Yokohama office (72) Inventor Hiromichi Horie, 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa (72) Inventor Noriaki Yagi No. 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa, Ltd. Incorporated Toshiba Yokohama Works (72) Inventor Hiromi Shizu, Shin-Sugita-cho, Isogo-ku, Yokohama, Kanagawa (72) Inventor Yoshiyuki Isazaki, 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research and Development Center, a stock company (72) Inventor, Ryoko Kanazawa 1 Komu-shi, Toshiba-cho, Kawasaki-shi, Kanagawa R & D Center

Claims (33)

[Claims] 1. A general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, Al, Fe,
Si, Cr, Cu, Ti, Zr, Zn, Hf, V, N
b, Ta, Mo, W, Ag, Pd, B, Ga, In, G
a metal whose main component is at least one element selected from e and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦
1,0 ≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6), and the alloy has a columnar crystal structure in which the ratio of the minor axis to the major axis (aspect ratio). A hydrogen storage alloy for batteries, characterized in that the area ratio of columnar crystals having a ratio of 1: 2 or more is 50% or more. 2. The hydrogen storage alloy for a battery according to claim 1, wherein the columnar crystals have an average minor axis of 30 μm or less. 3. The hydrogen storage alloy for a battery according to claim 1, wherein the alloy is a melt-quenched alloy, and the melt-quenched alloy has a thickness of 10 to 150 μm. 4. A general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, Al, Fe,
Si, Cr, Cu, Ti, Zr, Zn, Hf, V, N
b, Ta, Mo, W, Ag, Pd, B, Ga, In, G
a metal whose main component is at least one element selected from e and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦
1, 0 ≤ c ≤ 1,4.5 ≤ a + b + c ≤ 6), the alloy having an X-ray microanalyzer with a cross section of 20 µm as an observation region, The observation area is divided into 100 vertically and 100 horizontally
When observing the characteristic X-ray intensity of Mn for each of the divided unit regions, the average value of the characteristic X-ray intensity of Mn of each unit region was
The maximum value of the characteristic X-ray intensity of Mn in each unit region is 1.
A hydrogen storage alloy for batteries, which is 3 times or less. 5. The alloy has a columnar crystal structure, and in this columnar crystal structure, the ratio of the minor axis to the major axis (aspect ratio) is 1: 2.
The hydrogen storage alloy for a battery according to claim 4, wherein the area ratio of the columnar crystals is 50% or more. 6. The hydrogen storage alloy for batteries according to claim 5, wherein the columnar crystals have an average minor axis of 30 μm or less. 7. A general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, Al, Fe,
Si, Cr, Cu, Ti, Zr, Zn, Hf, V, N
b, Ta, Mo, W, Ag, Pd, B, Ga, In, G
a metal whose main component is at least one element selected from e and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≦
1, 0 ≤ c ≤ 1,4.5 ≤ a + b + c ≤ 6) for a battery, characterized in that the maximum diameter of Mn particles segregated in the alloy is 0.5 µm or less. Hydrogen storage alloy. 8. The alloy has a columnar crystal structure, and in this columnar crystal structure, the ratio of the minor axis to the major axis (aspect ratio) is 1: 2.
The hydrogen storage alloy for batteries according to claim 7, wherein the area ratio of the columnar crystals is 50% or more. 9. The hydrogen storage alloy for batteries according to claim 8, wherein the columnar crystals have an average minor axis of 30 μm or less. 10. The hydrogen storage alloy according to claim 7, wherein the alloy has an X-ray microanalyzer as an observation region with a cross section of 20 μm square, and the observation region has a length of 1 mm.
When observing the characteristic X-ray intensity of Mn in each of the unit regions divided into 00 and 100 in the horizontal direction, the characteristic X-ray intensity of Mn in each unit region is compared with the average value of the characteristic X-ray intensity of Mn in each unit region. A hydrogen storage alloy for batteries, wherein the maximum value is 1.3 times or less. 11. The hydrogen storage alloy according to claim 8, wherein the alloy has an X-ray microanalyzer as an observation region having a cross section of 20 μm square, and the observation region has a length of 1 mm.
When observing the characteristic X-ray intensity of Mn in each of the unit regions divided into 00 and 100 in the horizontal direction, the characteristic X-ray intensity of Mn in each unit region is compared with the average value of the characteristic X-ray intensity of Mn in each unit region. A hydrogen storage alloy for batteries, wherein the maximum value is 1.3 times or less. 12. The hydrogen storage alloy according to claim 9, wherein the alloy has an X-ray microanalyzer as an observation region with a cross section of 20 μm square, and the observation region has a length of 1 mm.
When observing the characteristic X-ray intensity of Mn in each of the unit regions divided into 00 and 100 in the horizontal direction, the characteristic X-ray intensity of Mn in each unit region is compared with the average value of the characteristic X-ray intensity of Mn in each unit region. A hydrogen storage alloy for batteries, wherein the maximum value is 1.3 times or less. 13. A general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium), and M is Co, Al, Fe, S).
i, Cr, Cu, Ti, Zr, Zn, Hf, V, Nb,
A metal containing at least one element selected from Ta, Mo, W, Ag, Pd, B, Ga, In, Ge and Sn as a main component, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≤1,0
≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6) When the molten alloy is sprayed onto the running surface of a chill roll that rotates at high speed to quench and solidify, it is rapidly cooled at a cooling rate of 1800 ° C./sec or more. A method for producing a hydrogen storage alloy for a battery, characterized by preparing a molten alloy quenching alloy to obtain a hydrogen storage alloy for a battery. 14. The method for producing a hydrogen storage alloy for a battery according to claim 13, wherein the melt quench alloy has a peripheral speed of a running surface of a cooling roll that rotates at a high speed in a range of 5 to 15 m / sec. 15. The method for producing a hydrogen storage alloy for a battery according to claim 13, wherein the quenching treatment of the molten alloy is carried out under vacuum. 16. A general formula A Ni _a Mn _b M _c (where A is at least one element selected from rare earth elements including Y (yttrium), and M is Co, Al, Fe, S).
i, Cr, Cu, Ti, Zr, Zn, Hf, V, Nb,
A metal containing at least one element selected from Ta, Mo, W, Ag, Pd, B, Ga, In, Ge and Sn as a main component, 3.5 ≦ a ≦ 5, 0.1 ≦ b ≤1,0
≤ c ≤ 1, 4.5 ≤ a + b + c ≤ 6) to rapidly cool an alloy melt to prepare a melt-quenched alloy, and obtain the melt-quenched alloy at least in a temperature range of 200 to 500 ° C. A method for producing a hydrogen storage alloy for a battery, which comprises heat-treating for 1 hour to form a hydrogen storage alloy for a battery. 17. The melt-quenched alloy is formed by injecting molten alloy onto the traveling surface of a cooling roll that rotates at a high speed and quenching and solidifying the molten alloy, and the peripheral speed of the traveling surface of the cooling roll is set in a range of 5 to 15 m / sec. The method for producing a hydrogen storage alloy for a battery according to claim 16, wherein: 18. The method for producing a hydrogen storage alloy for a battery according to claim 16, wherein the quenching treatment of the molten alloy is carried out under vacuum. 19. The method for producing a hydrogen storage alloy for a battery according to claim 16, wherein the heat treatment is carried out in vacuum or in an inert gas atmosphere. 20. AB having at least 90% by volume as a single phase
_x (where A is at least one selected from rare earth elements including Y (yttrium), B is Ni, Co, A
l, Fe, Si, Cr, Cu, Mn, Ti, Zr, Z
n, Hf, V, Nb, Ta, Mo, W, Ag, Pd,
A metal whose main component is at least one element selected from B, Ga, In, Ge and Sn, and x is 5.05.
≦ x ≦ 6)). A hydrogen storage alloy for a battery, wherein 21. In a nickel-hydrogen secondary battery in which a negative electrode containing a hydrogen storage alloy and a positive electrode containing nickel oxide are arranged with a separator interposed therebetween and sealed with an alkaline electrolyte, the hydrogen storage alloy has the general formula A Ni _a Mn _b
M _c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, A
l, Fe, Si, Cr, Cu, Ti, Zr, Zn, H
f, V, Nb, Ta, Mo, W, Ag, Pd, B, Ga,
At least one selected from In, Ge, and Sn
A metal whose main component is a seed element, 3.5 ≦ a ≦ 5, 0.1
≦ b ≦ 1,0 ≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6), and the alloy has a columnar crystal structure, and the columnar crystal structure has a minor axis and a major axis. The area ratio of columnar crystals with a ratio (aspect ratio) of 1: 2 or more is 5
Nickel-hydrogen secondary battery characterized by being 0% or more. 22. The nickel-hydrogen secondary battery according to claim 21, wherein the columnar crystals have an average minor axis of 30 μm or less. 23. In a nickel-hydrogen secondary battery in which a negative electrode containing a hydrogen storage alloy and a positive electrode containing nickel oxide are disposed with a separator interposed therebetween and sealed with an alkaline electrolyte, the hydrogen storage alloy is represented by the general formula A Ni _a Mn _b M
_c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, Al,
Fe, Si, Cr, Cu, Ti, Zr, Zn, Hf,
V, Nb, Ta, Mo, W, Ag, Pd, B, Ga, I
a metal whose main component is at least one element selected from n, Ge and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦
b ≦ 1,0 ≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6), the alloy having an X-ray microanalyzer with a cross section of 20 μm as an observation region. , The observation area is divided into 100 vertically and 1 horizontally
When observing the characteristic X-ray intensity of Mn for each of the 00 divided unit regions, the maximum value of the characteristic X-ray intensities of Mn of each unit region is compared with the average value of the characteristic X-ray intensity of Mn of each unit region. A nickel-hydrogen secondary battery characterized by being 1.3 times or less. 24. The alloy has a columnar crystal structure, and in this columnar crystal structure, the ratio of the minor axis to the major axis (aspect ratio) is 1 :.
The nickel-hydrogen secondary battery according to claim 23, wherein the area ratio of the two or more columnar crystals is 50% or more. 25. The nickel-hydrogen secondary battery according to claim 23, wherein the columnar crystals have an average minor axis of 30 μm or less. 26. In a nickel-hydrogen secondary battery in which a negative electrode containing a hydrogen storage alloy and a positive electrode containing nickel oxide are arranged with a separator interposed therebetween and sealed with an alkaline electrolyte, the hydrogen storage alloy has a general formula A Ni _a Mn _b M
_c (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, Al,
Fe, Si, Cr, Cu, Ti, Zr, Zn, Hf,
V, Nb, Ta, Mo, W, Ag, Pd, B, Ga, I
a metal whose main component is at least one element selected from n, Ge and Sn, 3.5 ≦ a ≦ 5, 0.1 ≦
b ≦ 1,0 ≦ c ≦ 1,4.5 ≦ a + b + c ≦ 6) which is an alloy having a composition represented by M and segregates in the alloy.
A nickel-hydrogen secondary battery having a maximum diameter of n particles of 0.5 μm or less. 27. The alloy has a columnar crystal structure, and in this columnar crystal structure, the ratio of the minor axis to the major axis (aspect ratio) is 1 :.
27. The nickel-hydrogen secondary battery according to claim 26, wherein an area ratio of two or more columnar crystals is 50% or more. 28. The nickel-hydrogen secondary battery according to claim 27, wherein the columnar crystals have an average minor axis of 30 μm or less. 29. The nickel-hydrogen secondary battery according to claim 26, wherein the alloy has an X-ray microanalyzer as an observation region having a cross section of 20 μm square, and the observation region is divided into 100 vertical and horizontal regions. When observing the characteristic X-ray intensity of Mn in each of 100 divided unit areas, Mn of each unit area
The maximum value of the characteristic X-ray intensities of Mn in each unit region is 1.3 times or less the average value of the characteristic X-ray intensities of 1. 30. The hydrogen storage alloy according to claim 27, wherein the alloy has an X-ray microanalyzer as an observation region having a cross section of 20 μm square, and the observation region has 100 vertical divisions and 100 horizontal divisions. When observing the characteristic X-ray intensity of Mn in each unit region, the maximum value of the characteristic X-ray intensities of Mn in each unit region was 1. A nickel-hydrogen secondary battery characterized by being 3 times or less. 31. The nickel-hydrogen secondary battery according to claim 30, wherein the columnar crystals have an average minor axis of 30 μm or less. 32. In a nickel-hydrogen secondary battery in which a negative electrode containing a hydrogen storage alloy and a positive electrode containing nickel oxide are arranged with a separator interposed therebetween and sealed with an alkaline electrolyte, at least 90% by volume of the hydrogen storage alloy is contained. Single phase A
B _x (where A is at least one element selected from rare earth elements including Y (yttrium), M is Co, A
l, Fe, Si, Cr, Cu, Ti, Zr, Zn, H
f, V, Nb, Ta, Mo, W, Ag, Pd, B, Ga,
At least one selected from In, Ge, and Sn
A metal whose main component is a seed element, and x is 5.05 ≦ x
≦ 6), A nickel-hydrogen secondary battery characterized by the following. 33. The hydrogen storage alloy is a melt-quenched alloy,
The amount of the alkaline electrolyte is in the range of 0.4 to 1.8 ml / Ah with respect to the capacity of the negative electrode hydrogen storage alloy, and the negative electrode hydrogen storage alloy with respect to the positive electrode nickel oxide capacity is in an uncharged state in a battery discharge state. Alloy volume ratio of 1.1-2.0
The nickel-hydrogen secondary battery is characterized in that