JPH11297319A - Hydrogen storage electrode material, and alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen storage electrode material, capable of properly controlling the ratio of rare-earth elements to transition metals in a hydrogen storage alloy after sintering, and to provide a negative electrode material for a metal-hydrogen alkaline storage battery having superior electrical capacity and charging-discharging cycle characteristic. SOLUTION: The composition of an alloy power is made identical among particles before sintering by dissolving a hydrogen storage alloy to be followed by quick cooling, so as to control the ratio of rare-earth elements to transition metals after sintering. The composition of the hydrogen storage alloy is preferably expressed by the formula R(Ni)a ,(Mn)b ,(Al)c (Co)d (M)e . (where, R is La or a mixture of La and one or more of rare earth elements (a), (b), (c), (d), (e) and (x) are coefficients expressing atomic ratios and respectively satisfies 1.8<=a<=5.5, 0.0<=b<=0.6, 0.0<=c<=0.4, 0.0<=d<=1.0, 0.0<=e<=0.2, and 4.0<=a+b+c+d+ e<=5.5; M is at least one kind of element selected from among the group comprising Si, Fe, Pb, Ti, Ca, Mg, Cu, In, Zn, Mo and Zr).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered porous body of a hydrogen storage electrode used as a negative electrode material of a metal-hydrogen alkaline storage battery and a method for producing the same.

[0002]

2. Description of the Related Art A hydrogen storage alloy is used as a negative electrode material of a secondary battery because it can electrochemically store and release hydrogen. The hydrogen storage alloy is hydrogenated and dehydrogenated during the charging and discharging of the battery, so that its volume changes. Therefore, when this alloy is used as it is, there is a problem that cracks occur, the powder is pulverized and falls off from the electrode, and its discharge capacity is reduced.

[0003] In order to solve such a problem, a method of manufacturing a paste-type electrode has heretofore generally been used to pulverize an alloy to several tens of μm and use a resin binder to form a support for an alloy such as punching metal or nickel foam. Coating prevents falling off. However, since the binder, the support and the separator are not deposited in the hydrogen storage in the battery,
The filling amount of the hydrogen storage alloy with respect to a certain volume is small. On the other hand, there has been considered a method of improving the strength against cracking by pulverizing the hydrogen storage alloy and directly sintering it to form an electrode. However, sintering by itself alone reduces the packing density of the alloy to a porosity of 20 to
To achieve 40%, a heat treatment at 1200 ° C. or higher is required. When such a high temperature is applied, there is a problem that the systematic fluctuation of the metal occurs greatly and the hydrogen storage characteristics are greatly reduced. Therefore, after pulverization, it has been proposed to coat the whole or a part with another metal or to lower the sintering temperature by adding a sintering aid such as another metal powder or metal fiber. is there. In this case, since a binder and a support are not required, the filling amount of the alloy is improved. However, even such a method is not preferable because the cost is increased due to the complicated manufacturing process, and the coating portion and the auxiliary agent are not included in the storage of hydrogen.

If the alloy is pulverized to an average particle size of 20 μm or less, sintering can be performed even at a sintering temperature of 1200 ° C. or less. However, the powder of an intermetallic compound containing a rare earth element is extremely oxidized. It is an easily alloyable alloy, and the amount of oxygen adsorbed during pulverization has a strong correlation with its surface area, so the influence of oxidation cannot be avoided. However, the present inventor has found that if the pulverization is performed in a low oxygen atmosphere, the amount of oxygen adsorbed on the fine powder can be reduced to some extent. For example, in the production of fine powder by liquid quenching such as the atomizing method, the average particle size is 7
When μm is obtained, the concentration of oxygen contained in the alloy can be reduced to 0.5% by weight or less based on the weight of the fine powder. With such an amount of oxygen, even if the oxygen generates an oxide, a fixed volume is used because the binder and the support used in the paste-type battery are not used and the amount of the separator used can be reduced. It is considered that the amount of alloy that can be filled therein is improved, and the charge capacity of a battery of the same volume is improved.

[0005] However, the rare earth contained in the intermetallic compound is highly reactive with the transition metal, and thus the adsorbed oxygen tends to mainly form a rare earth oxide. Considering LaNi ₅ , which is a typical hydrogen storage alloy, an La ₂ O ₃ type oxide is easily formed, but an alloy whose atomic weight of oxygen is 16 and that of lanthanum is 138.9 is lost due to oxidation. The lanthanum is about 6 times the oxygen weight ratio. For example, when 0.5% by weight of oxygen is contained in the alloy, the hydrogen storage alloy is usually composed of about 30% by weight of a rare earth element.
About 10% of rare earths will be lost by oxidation. During sintering, the inside of the grains becomes uniform by diffusion at the same time as oxidation, so that the composition becomes a compound in which the ratio of the transition metal is much larger than the composition before sintering. The value obtained by dividing the number of moles of the transition metal in the alloy, generally called the B / A ratio, by the number of moles of the rare earth is
In the case of a negative electrode material for an alkaline storage battery, the ratio is often 5.0. When the value of this ratio is near 5.0, as the value increases, the hydrogen storage equilibrium pressure of the alloy increases and the hydrogen storage amount increases. Causes a decline. Normally, hydrogen storage alloys have an equilibrium pressure,
The adjustment is performed by substituting nickel in the transition metal with another metal. However, an increase in the substitution amount undesirably further reduces the hydrogen storage capacity of the alloy and lowers the performance of the alkaline storage battery.

[0006] Intermetallic compounds of rare earth and transition metals called AB ₅ type is uniform region is very narrow in its composition, if slow cooling and dissolved at high frequency melting or the arc melting is a conventional manufacturing method, Even if the solution treatment is performed at a high temperature of about 1150 ° C. for a long time, the B / A ratio is at least about 4.9 at the minimum in order to obtain a uniform ingot without segregation. In a cast ingot having a composition of 4.9 or less, many segregated phases remain. When such a cast ingot having a large number of segregated phases is pulverized, the composition of the powder varies greatly depending on the grains.

The sintered body for an electrode must have a porosity of 20 to 40% in order to secure a reaction area. However, in sintering up to this porosity, diffusion beyond the grain boundaries is small. Even after sintering, a uniform structure is not obtained, and a segregated phase rich in rare earth remains. The presence of such a segregated phase results in deterioration of battery characteristics. Further, since the segregation phase rich in rare earth has a low melting point, sintering proceeds only around the segregation phase, the density inside becomes uneven, and the mechanical strength becomes insufficient. Therefore, when the quenching is not performed, the controllable range is narrow even if the composition after sintering is controlled. In order to make the B / A ratio 5.0 after sintering, the rare earth in the alloy is 30% by weight and the average atomic weight of the rare earth is 14%.
Assuming zero, the oxygen content contained must be less than about 0.1% by weight. Since it is industrially very difficult to reduce the oxygen content to 0.1% by weight or less in a powder sintered body having an average particle size of 1 to 20 μm in a hydrogen storage alloy comprising a rare earth and a transition metal, It is not enough to improve the properties of the alloy that has been cooled slowly after melting.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a hydrogen storage electrode material capable of appropriately controlling the ratio of a rare earth element to a transition metal in a hydrogen storage alloy after sintering, and having excellent electric capacity and charge / discharge cycle characteristics. It is an object of the present invention to provide a negative electrode material for a metal-hydrogen alkaline storage battery having the same.

[0009]

According to the present invention, the hydrogen storage alloy is cooled rapidly after melting, so that the alloy powder particles before sintering have the same composition as other particles, and the sintered rare earth and transition metal The ratio is controlled. The method of melting and quenching the hydrogen storage alloy according to the present invention is, for example, to produce a thin plate-shaped alloy by known roll quenching or the like, and then may be pulverized, or as a powder by a centrifugal spraying method or a gas atomizing method. good. Since the hydrogen storage alloy according to the present invention can be refined in structure and expanded in a uniform region by quenching, the width of controlling the composition of the alloy can be increased, and the oxygen content can be reduced to 0.1% by weight. %, Sufficient control can be performed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The composition of the hydrogen storage alloy used in the present invention is not particularly limited, but AB _n (n is 1 to 5).
Represents a positive number of 6. ) Can be used. In particular, those of AB ₅ type hydrogen absorbing alloy composition in the present invention is preferable in terms of battery life. In AB ₅ hydrogen storage alloy, as the A side element, La, Ce, N
A rare earth element selected from d and Pr alone or a mixture of the rare earth elements (in this case, La is preferably contained in the rare earth element mixture in an amount of 20% by weight or more) is more preferable. Note that the A-side element may include a rare earth element other than the above, or may include an element other than the rare earth element. (Ni) _a (Mn) _b (Al) _c (Co) _d as the B-side element
A composition consisting of (M) _e is preferred. Where a, b,
c, d and e are numbers, and 1.8 ≦ a ≦ 5.5 0.0 ≦ b ≦ 0.6 0.0 ≦ c ≦ 0.4 0.0 ≦ d ≦ 1.0. 0 ≦ e ≦ 0.2 4.0 ≦ a + b + c + d + e ≦ 5.5. M is Si, Fe, Pb, T
i, at least one element selected from the group consisting of Ca, Mg, Cu, In, Zn, Mo, and Zr.

In the present invention, after mixing each element having such a composition, the alloy is melted at a temperature of 1300 to 1600 ° C. in an atmosphere of an inert gas such as argon or helium.
A hydrogen storage alloy powder is prepared by a quenching method. In the present invention, a homogeneous alloy with less segregation is selected by obtaining a hydrogen storage alloy powder by a quenching method. The quenching method for obtaining such an alloy powder is not particularly limited. For example, a thin plate-shaped alloy is prepared by a known roll quenching method, and then pulverized to obtain a hydrogen storage alloy powder. When the roll quenching method (single roll, twin roll) is used, alloy powder is obtained by dry / wet pulverization using a jet mill, an attritor, or the like in an atmosphere of an inert gas such as argon, helium, or nitrogen. In particular, in the case of the present invention, it is desirable to sinter the hydrogen storage alloy powder obtained by using a jet mill. Fine particles (spherical, substantially spherical) of the hydrogen storage alloy powder can also be directly obtained by centrifugal spraying, gas atomizing, or the like.

In the present invention, rapid cooling refers to 100 ° C.
Cooling under the condition of a cooling rate of at least / second,
Particularly, a cooling condition of 10 ³ to 10 ⁵ ° C / sec is preferable. 10
If it is less than 0 ° C./sec, the cooling capacity is poor, and the alloy tends to segregate. In the case of using the roll quenching method, a molten alloy is flowed through a cooling roll, and quenched at the above-mentioned cooling rate while rotating the roll to obtain a thin strip alloy. In the centrifugal spraying method, a molten alloy is poured vertically on a rotating disk, and the alloy is scattered by the rotation of the disk to rapidly cool the alloy. The gas atomization method uses 10 kg of high-speed gas such as argon and helium.
The thin stream of the alloy is rapidly cooled while being exposed to the molten alloy under the condition of the gas pressure of f / cm ² or more. In the present invention, it is particularly preferable to use a hydrogen storage alloy powder obtained by pulverizing an alloy ribbon obtained by a roll quenching method.

In the present invention, the above-mentioned quenching method is used to form and sinter a hydrogen storage alloy powder having an average particle size of 1 to 20 μm, preferably 10 μm or less. Average particle size 20μ
When an alloy powder exceeding m is used for a sintered body, the binding force between the alloy particles due to sintering becomes weak, and the electrode cannot withstand the volume expansion and contraction forces caused by hydrogen storage and release, causing many cracks in the electrode. In addition, the current collecting function cannot be maintained as an electrode, and the battery life may be shortened. Further, the particle diameter is 1 to
It is good to keep it in the range of 0 μm.

According to the present invention, the hydrogen-absorbing alloy powder obtained by such a quenching method is charged into a mold so as to have a desired shape, molded under pressure, and under vacuum or in an inert gas atmosphere such as argon or helium. The alloy powder is directly sintered at 600 to 1100 ° C, preferably 950 to 1050 ° C for 0.5 to 5 hours. If the temperature is lower than 600 ° C., no sintering occurs because bonding between the alloy particles does not occur. If the temperature exceeds 1100 ° C., the sintering between the alloy particles progresses. It is not preferable because the capacity is reduced.

The sintered body obtained in this manner can be obtained by pressure molding and sintering, and can be directly used for an electrode. The sintered body can be sintered without using a current collecting support such as nickel. The body itself also has the function of a current collector, and can have the effect of greatly improving the electrode capacity per unit volume. Hydrogen storage alloy according to the present invention, since it is possible to microstructure and enlarge the uniform region by quenching, it is possible to increase the width of controlling the composition of the alloy,
Even when the oxygen content is 0.1% by weight or more, sufficient control can be performed. This is because even when the quenched alloy powder is sintered, it maintains a uniform structure without segregation.

According to the present invention, a lead is attached to a hydrogen storage alloy sintered body electrode having the above-mentioned features to form a negative electrode, and a positive electrode such as nickel hydroxide is disposed through a separator to form an electrode group. An alkaline storage battery that can be charged and discharged can be manufactured by injecting an electrolytic solution such as caustic potash into a sealed battery container of a mold type and sealing the can.

In the electrode of the present invention, the ratio between the rare earth and the transition metal of the sintered hydrogen storage alloy can be appropriately controlled.
By using this as a negative electrode material of an alkaline storage battery, excellent electric capacity and charge / discharge cycle characteristics are exhibited.

[0018]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.
The present invention can be appropriately changed and implemented without changing the gist. (Example) Commercially available Mm (Misch metal: 63% by weight of La, 7% by weight of Ce, 22% by weight of Pr, 8% by weight of Nd) and Ni, Co, Mn, and Al were weighed in a predetermined composition ratio under an argon atmosphere. The mixture is melted in an arc melting furnace to obtain a melt, and the melt is quenched by a known rotating roll (single roll, 3000 rpm, 4 × 10 ⁴ ° C./sec), and the composition (atomic ratio) of the alloy becomes Mm _1.05 Ni _3.65 Co _0.75
A ribbon-shaped ribbon made of Al _0.3 Mn _0.3 was obtained. The obtained ribbon was pulverized by a jet mill in a nitrogen atmosphere to obtain a powder having an average particle size of 7 μm. This powder was pressed and then sintered at 1,000 ° C. for 2 hours in a vacuum atmosphere to obtain a sintered body. When the oxygen concentration of the obtained sintered body (including the surface (the same applies hereinafter)) was measured, it was 0.30% by weight.
Met. The oxygen concentration was measured according to JIS Z 2613.

(Reference Example) Mm (same as the embodiment), Ni,
A composition (atomic ratio) obtained by weighing Co, Mn, and Al at a predetermined composition ratio in an arc melting furnace and subjecting the cast ingot to a heat treatment at 1050 ° C. for 10 hours in a vacuum and then slowly cooling was Mm _1.0
A cast mass consisting of Ni _3.65 Co _0.75 Al _0.3 Mn _0.3 was obtained. The cast lump was pulverized with a jet mill in a nitrogen atmosphere to obtain a powder having an average particle size of 7 μm. The oxygen concentration of the alloy powder was 0.25% by weight.

(Comparative Example 1) Mm (same as in Example), N
i, Co, Mn, and Al weighed to a predetermined composition ratio are added in an arc melting furnace, and the cast ingot is placed in a vacuum at 1050.
The composition (atomic ratio) slowly cooled after heat treatment at 10 ° C.
_A cast ingot consisting of _1.05 Ni _3.65 Co _0.75 Al _0.3 Mn _0.3 was obtained. The cast lump was pulverized with a jet mill in a nitrogen atmosphere to obtain a powder having an average particle size of 7 μm. This powder was molded and sintered in exactly the same manner as in the example to obtain a sintered body.
The oxygen concentration of the obtained sintered body was 0.3% by weight.

(Comparative Example 2) Mm (same as the embodiment), N
i, Co, Mn, and Al weighed to a predetermined composition ratio are added in an arc melting furnace, and the cast ingot is placed in a vacuum at 1050.
The composition (atomic ratio) slowly cooled after heat treatment at 10 ° C.
_A cast mass consisting of _1.0 Ni _3.65 Co _0.75 Al _0.3 Mn _0.3 was obtained. The cast lump was pulverized with a jet mill in a nitrogen atmosphere to obtain a powder having an average particle size of 7 μm. This powder was molded and sintered in exactly the same manner as in the example to obtain a sintered body.
The oxygen concentration of the obtained sintered body was 0.30% by weight.

FIG. 1 shows the results obtained by measuring the hydrogen storage characteristics of the sintered body obtained by the above-mentioned method by the known Sievert method. The vertical axis is hydrogen pressure, and the horizontal axis is hydrogen storage capacity (H / M ').
The hydrogen storage amounts are represented by hydrogen atoms H in the solid phase and alloy atoms M ′ (for example, in the embodiment, Mm _1.05 Ni _3.65 Co _0.75 A
l _0.3 Mn _0.3 ). As shown in the figure, the hydrogen storage alloy sintered body according to the embodiment of the present invention indicated by the solid line is similar to the reference example as the target value in the hydrogen storage equilibrium pressure. Comparative Example 1 has the same composition ratio as the example, but is inferior in flatness in the equilibrium region of hydrogen storage and in storage amount. FIG. 2 shows an example and comparative examples 1 and 2.
This is a result of preparing an open-type alkaline storage battery with a negative electrode regulation using the sintered body obtained in the above and a known nickel hydroxide, and performing a charge / discharge cycle test. The charge / discharge condition is 20 ° C
The battery is charged at 0.3 C for 5 hours at a constant temperature, and is repeatedly discharged to 0.2 V at 0.2 C after a lapse of 1 hour.

In the example, the charge / discharge characteristics show an improvement in the capacity as compared with the comparative examples 1 and 2 as in the hydrogen storage characteristics. Comparative Example 1 has a slight improvement in the initial capacity as compared with Comparative Example 2, but is slightly smaller than the improvement in the Example. In the Example, the cycle life is considerably improved as compared with the Comparative Example. Sample No. 1 has an extremely shorter cycle life than Comparative Example 2. This is because the B / A ratio of the alloy before sintering is 4.76 in the example and the comparative example 1, but the sintered body of the example is uniform, This is probably due to the presence of a rare earth-rich segregated phase in the body. Although the evaluation was made with an open type storage battery, when a sealed type battery was manufactured, the capacity of the sintered type battery can be significantly improved compared to the paste type battery of the same volume because the packing density of the negative electrode can be greatly improved compared with the paste type battery. Although improvement can be expected, the present invention is expected to be further improved.

Further, the present invention provides a conventional sintered electrode,
The hydrogen storage alloy may be used in combination with a case where the whole or a part of the hydrogen storage alloy is coated with a dissimilar metal or a case where various auxiliaries are added. Further, it is also possible to replace the Mm portion or the transition metal portion such as nickel or cobalt with a different element or to add a different element.

[0025]

As described above, according to the present invention, it is possible to increase the filling amount of the hydrogen storage alloy without providing a current collecting support as an alkaline storage battery. Therefore, the capacity density is greatly improved, and the cycle life is shortened. An excellent hydrogen storage electrode material for an alkaline secondary battery can be obtained.

[Brief description of the drawings]

FIG. 1 shows the results of measuring the hydrogen storage characteristics of a sintered body by a known Giebert method.

FIG. 2 shows the results of a charge / discharge cycle test of an open-type alkaline storage battery with a regulated anode using a sintered body and a known nickel hydroxide.

Claims (4)

[Claims] 1. A hydrogen storage electrode material obtained by molding and sintering a hydrogen storage alloy powder obtained by a quenching method. 2. The composition of the hydrogen-absorbing alloy has a general formula R (Ni) _a (Mn) _b (Al) _c (Co) _d (M) _e (wherein R is La alone or one or more of La) A, b, c, d, e, and x are coefficients representing an atomic ratio, and 1.8 ≦ a ≦ 5.5 0.0 ≦ b ≦ 0.60, respectively. 0.0 ≦ c ≦ 0.4 0.0 ≦ d ≦ 1.0 0.0 ≦ e ≦ 0.2 4.0 ≦ a + b + c + d + e ≦ 5.5 where M is Si, Fe, Pb, T
i, at least one element selected from the group consisting of Ca, Mg, Cu, In, Zn, Mo, and Zr. 2. The hydrogen storage electrode material according to claim 1, which is a hydrogen storage alloy represented by the formula: 3. The method according to claim 1, wherein the powder of the hydrogen storage alloy is 1 to 20 μm.
The hydrogen storage electrode material according to claim 1 or 2, having an average particle size of m. 4. An alkaline storage battery using the hydrogen storage electrode material according to claim 1 for a negative electrode.