JP2011044388A - Nickel-metal hydride storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the charging capacity of a nickel-metal hydride storage battery, and also to improve the cycle life characteristics thereof. <P>SOLUTION: The nickel-metal hydride storage battery includes a negative electrode that contains a hydrogen-absorbing alloy mainly composed of M1 elements, calcium, magnesium, and M2 elements, and aluminum hydride. The M1 elements is one or two or more kinds of elements (including at least a rare earth element) selected from a group consisting of rare earth elements, group 4A elements, group 5A elements, and Pd. The M2 elements is one or two or more kinds of elements (including at least nickel) selected from a group consisting of group 6A elements, group 7A elements, group 8 elements (excluding Pd), group 1B elements, group 2B elements, and group 3B elements. The content of the M2 elements in the hydrogen-absorbing alloy is larger than three times and less than five times the total content of the M1 elements, calcium, and magnesium. The content of calcium in the hydrogen-absorbing alloy is ≥0.5 atom%, and the content of aluminum as an M2 element in the hydrogen-absorbing alloy is ≥0 atom% and ≤1.5 atom%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nickel metal hydride storage battery.

  Nickel metal hydride storage battery, which is known for its high energy density, has been widely used as a power source for small electronic devices such as digital cameras and notebook computers, as well as primary batteries such as alkaline manganese batteries. Its use and demand are expected to expand in the future.

  By the way, this type of nickel metal hydride storage battery includes a nickel electrode containing a positive electrode active material mainly composed of nickel hydroxide, a negative electrode mainly composed of a hydrogen storage alloy, a separator, and an alkaline electrolyte. Is. Among these battery constituent materials, the hydrogen storage alloy, which is the main material of the negative electrode, has a great influence on the performance of nickel-metal hydride storage batteries such as discharge capacity and cycle characteristics. Various hydrogen storage alloys have been studied in the past. Has been.

As the hydrogen storage alloy, there is known a rare earth-Mg—Ni alloy that can increase the discharge capacity as compared with an AB ₅ rare earth-Ni alloy having a CaCu ₅ crystal structure. Has reported a La—Mg—Ca—Ni ₉ alloy having a PuNi ₃ type crystal structure and containing Ca as a rare earth-Mg—Ni alloy that can further increase the discharge capacity.

JP-A-11-217643

  However, a La—Mg—Ni based hydrogen storage alloy containing Ca (hereinafter also referred to as “La—Ca—Mg—Ni based hydrogen storage alloy”) has a hydrogen storage capacity due to the presence of calcium. On the other hand, there is a problem that the durability decreases as the amount of calcium added increases, and the cycle life of a battery constructed using the alloy decreases.

  In view of the above-described problems of the prior art, the present invention uses a La—Mg—Ca—Ni-based hydrogen storage alloy as an active material for a negative electrode to increase the hydrogen storage capacity, that is, the discharge capacity of a nickel-metal hydride storage battery. An object of the present invention is to provide a nickel-metal hydride storage battery excellent in cycle life characteristics by preventing the decrease in cycle life caused thereby.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, a La—Ca—Mg—Ni-based hydrogen storage alloy and aluminum hydroxide are mixed to form a negative electrode, whereby the La It has been found that the durability of a nickel-metal hydride storage battery using a —Ca—Mg—Ni-based hydrogen storage alloy as a negative electrode is improved, and the cycle life characteristics of the nickel-metal hydride storage battery are improved, and the present invention has been completed.

That is, the present invention includes a negative electrode composed of a hydrogen storage alloy mainly containing M1 element, calcium, magnesium and M2 element, and aluminum hydroxide,
The M1 element is one or more elements selected from the group consisting of rare earth elements, 4A group elements, 5A group elements and Pd (however, including at least rare earth elements);
The M2 element is one or more elements selected from the group consisting of Group 6A elements, Group 7A elements, Group 8 elements (excluding Pd), Group 1B elements, Group 2B elements and Group 3B elements (however, Including at least nickel)
The content ratio of the M2 element in the hydrogen storage alloy is more than 3 times and less than 5 times the total content ratio of each element of the M1 element, calcium and magnesium,
The calcium content in the hydrogen storage alloy is 0.5 atomic% or more, and
Provided is a nickel-metal hydride storage battery characterized in that the content ratio of aluminum as an M2 element in the hydrogen storage alloy is 0 atomic% or more and 1.5 atomic% or less.

Further, the present invention, the hydrogen storage alloy has the general formula _{M1 'u M1 "v Ca w} Mg x Ni y M2' z [ wherein, M1 'element of one or more kinds selected from rare earth elements M1 "element is one or more elements selected from the group consisting of Group 4A elements, Group 5A elements and Pd, and M2 'element is Group 6A element, Group 7A element, Group 8 element (Excluding Ni and Pd) are one or more elements selected from the group consisting of Group 1B elements, Group 2B elements and Group 3B elements, and u, v, w, x, y and z are: u + v + w + x + y + z = 100, 13.3 ≦ u ≦ 19.5, 0 ≦ v ≦ 1.2, 0.5 ≦ w ≦ 3.8, 2.2 ≦ x ≦ 5.8, 74.4 ≦ y ≦ 78. 7, a number satisfying 0 ≦ z ≦ 1.2. The nickel-metal hydride storage battery is characterized by having a composition represented by the following formula:

  The present invention also provides the nickel-metal hydride storage battery, wherein the aluminum hydroxide is 0.1 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy.

  According to the nickel metal hydride storage battery of the present invention, the hydrogen storage alloy having the above-described configuration, that is, the La—Ca—Mg—Ni-based hydrogen storage alloy containing calcium and aluminum hydroxide are used in combination as the constituent material of the negative electrode. As a result, the durability of the nickel-metal hydride storage battery is improved, and the cycle life characteristics are improved.

It is speculated that such an effect is exhibited by the fact that the aluminum hydroxide added to the negative electrode exhibits the action of suppressing the activity of the hydrogen storage alloy and the action of suppressing the elution of the composition elements of the hydrogen storage alloy. Is done. That is, by suppressing the activity of the hydrogen storage alloy, pulverization due to expansion and contraction of the alloy is suppressed, and as a result, cycle life characteristics are improved. Moreover, since the elution of the compositional elements of the hydrogen storage alloy is suppressed, the corrosion resistance of the alloy against the electrolytic solution is improved, so that the cycle life characteristics are improved.
According to the knowledge of the present inventors, among the constituent elements of the hydrogen storage alloy, rare earth elements and calcium have a large tendency to decrease the cycle life when eluted, and especially calcium that can contribute to an increase in hydrogen storage capacity is rare earth elements. It has been found that the cycle life is liable to be reduced due to the property of being easily eluted as compared with.
In the present invention, the hydrogen storage capacity is increased by adopting a hydrogen storage alloy containing calcium, and a negative electrode in which aluminum hydroxide coexists with the hydrogen storage alloy in which elution of rare earth elements and calcium is likely to be a problem. By adopting it, it was possible to improve the cycle life characteristics by suppressing the pulverization of the hydrogen storage alloy and elution of the constituent elements by the action as described above.

The nickel metal hydride storage battery according to the present invention includes a negative electrode configured to contain a hydrogen storage alloy mainly containing M1 element, calcium, magnesium, and M2 element, and aluminum hydroxide.
Here, the M1 element contained in the hydrogen storage alloy is one or two or more elements selected from the group consisting of rare earth elements, 4A group elements, 5A group elements and Pd (provided that at least the rare earth elements are included). And the M2 element is one or more selected from the group consisting of Group 6A elements, Group 7A elements, Group 8 elements (excluding Pd), Group 1B elements, Group 2B elements and Group 3B elements Element (however, including at least nickel).
Further, the content ratio of the M2 element in the hydrogen storage alloy is greater than 3 times and less than 5 times the total content ratio of each element of the M1 element, calcium and magnesium, and the content ratio of calcium in the hydrogen storage alloy Is 0.5 atomic% or more, and the content ratio of aluminum as the M2 element in the hydrogen storage alloy is 0 atomic% or more and 1.5 atomic% or less.

  In general, a La—Mg—Ni-based hydrogen storage alloy includes rare earth elements, Mg, and Ni, and the content ratio of Ni is greater than 3 times and less than 5 times the total content ratio of rare earth elements and Mg. Although it is an alloy, since the hydrogen storage alloy of the present invention contains Ca, the La—Ca—Mg—Ni-based hydrogen storage alloy contains rare earth elements, Mg, and Ni, and is made of Ni. The number of the alloys is more than 3 times and less than 5 times the total number of rare earth elements and Mg atoms and the number of Ca atoms added according to the present invention.

More specifically, the hydrogen storage alloy includes the following general formula:
_{M1 'u M1 "v Ca w} Mg x Ni y M2' z
What has a composition represented by these is preferable.

Here, in the general formula, the M1 ′ element and the M1 ″ element constitute the M1 element, and these are elements capable of forming a stable hydride.
Specifically, the M1 ′ element is one or more elements selected from rare earth elements, preferably one selected from the group consisting of La, Ce, Pr, Nd, Sm, and Y Or two or more elements.

  The M1 ″ element is an element other than the rare earth element of the M1 element, and specifically, one or more elements selected from the group consisting of a 4A group element, a 5A group element, and Pd. Preferably, it is an element that can be substituted for the rare earth element, Mg or Ca in the crystal structure of the alloy, and specifically, one kind selected from the group consisting of V, Nb, Ta, Ti, Zr and Hf Or 2 or more types of elements are preferable.

  The content of the M1 ″ element is preferably in a range that does not lose the action of the rare earth element, Mg or Ca. Therefore, the addition amount of the M1 ″ element may be 0 (zero). A small amount is preferable. Specifically, in the hydrogen storage alloy, the content is preferably 1.2 atomic percent or less, and more preferably 0 atomic percent or more and 0.2 atomic percent or less.

Further, the M2 ′ element and Ni constitute the M2 element, and these are elements in which hydrides are unstable.
The M2 ′ element is an element other than Ni that can replace Ni in the crystal structure of the alloy, and specifically includes a group 6A element, a group 7A element, a group 8 element (excluding Ni and Pd), 1B One or more elements selected from the group consisting of group elements, group 2B elements and group 3B elements, preferably selected from the group consisting of Co, Cu, Mn, Al, Cr, Fe and Zn Or one or more elements.

The content of the M2 ′ element is preferably in a range that does not eliminate the action of Ni. Therefore, the content may be 0 (zero), and even when added, it is preferably as small as possible. Specifically, the content of the M2 ′ element is preferably 0% by mass or more and 1.2% by mass or less in the hydrogen storage alloy.
However, among the M2 ′ elements, Al has a content of 0 atomic% or more and 1.5 atomic% or less in the hydrogen storage alloy.
Further, among the M2 ′ elements, Cr or Zn has an action of suppressing the pulverization of the alloy, and therefore, it is preferably added within the range of 1 atomic% or less in the hydrogen storage alloy.

  From such a viewpoint, in the general formula, u, v, w, x, y, and z are numbers satisfying u + v + w + x + y + z = 100, and u is preferably 13.3 ≦ u ≦ 19.5, 13 0.7 ≦ u ≦ 17.5 is more preferable, v is 0 ≦ v ≦ 1.2, preferably 0 ≦ v ≦ 0.2, and w is 0.5 ≦ w ≦ 3.8. Yes, preferably 1.2 ≦ w ≦ 3.5, x is 2.2 ≦ x ≦ 5.8, preferably 3.8 ≦ x ≦ 5.8, and y is 74. 4 ≦ y ≦ 78.7, preferably 75.0 ≦ y ≦ 77.8, and z is 0 ≦ z ≦ 1.2.

If the calcium content in the hydrogen storage alloy is less than 0.5 atomic%, not only will the effect of increasing the discharge capacity (hydrogen storage capacity) due to the addition of calcium be difficult, but the durability will be improved by aluminum hydroxide. The effect is difficult to be demonstrated. Further, if the calcium content is 3.8 atomic% or less, the pulverization of the alloy accompanying the storage and release of hydrogen is suppressed, and the alloy is further excellent in corrosion resistance.
From such a viewpoint, the content of calcium in the hydrogen storage alloy needs to be 0.5 atomic% or more, preferably 0.5 atomic% or more and 3.8 atomic% or less, more preferably It is 1.2 atomic% or more and 3.5 atomic% or less.

  In addition, the aluminum content in the hydrogen storage alloy needs to be 1.5 atomic% or less as described above. In the above hydrogen storage alloy having a calcium content of 0.5 atomic% or more, aluminum is difficult to be solid-dissolved uniformly in the crystal phase. Tend to increase. Therefore, by setting the aluminum content to 1.5 atomic% or less, it is possible to prevent such an increase in the segregation amount of aluminum and to obtain a hydrogen storage alloy having more excellent durability.

Here, the meaning that aluminum hardly dissolves uniformly in the crystal phase means that a crystal structure in which A ₂ B ₄ unit and AB ₅ unit peculiar to La—Ca—Mg—Ni alloy are laminated in the c-axis direction. Aluminum is difficult to solidify uniformly in a crystalline phase having a structure in which a predetermined number of AB ₅ units are inserted between A ₂ B ₄ units such as a Gd ₂ Co ₇ phase and a Ce ₂ Ni ₇ phase described later. That is.
The segregation phase of aluminum is considered to be formed as an alloy phase having a high aluminum concentration composition, and this segregation phase is considered to have a CaCu ₅ type crystal structure. Therefore, evaluation of the amount of segregation of aluminum can be performed by measuring the generation ratio of a phase having a CaCu ₅ type crystal structure.
For example, it can be seen that when the amount of aluminum is increased from 0 atomic% to 1.2 atomic%, the proportion of the CaCu ₅ phase increases from 0 mass% to 6.9 mass%. Specifically, four types of alloys of La _9.3 Nd _7.0 Ca _2.3 Mg _4.7 Ni _76.7-x Al _x (x = 0, 0.2, 0.7, 1.2) are manufactured and the presence of CaCu ₅ phase When the amount was examined, the production amounts of the CaCu ₅ phase were 0% by mass, 1.7% by mass, 3.5% by mass, and 6.9% by mass, respectively.

Incidentally, showing the case without calcium in the reference, for the case containing calcium, the tendency of the amount of CaCu ₅ phase upon addition of aluminum. La _5.1 Pr _14.1 Ca _0.0 Mg _2.1 Ni _78.7-x Al _x (x = 0, 1.7, 3.2, 4.3) alloys are manufactured, and the amount of CaCu ₅ phase formed therein is examined. And 3.0% by mass, 4.0% by mass, 4.5% by mass and 9.1% by mass, respectively. On the other hand, when each alloy of La _13.3 Ca _4.4 Mg _4.4 Ni _77.8-x Al _x (x = 0, 0.2) was manufactured and the amount of CaCu ₅ phase formed therein was examined, 0% by mass and It was 4.5% by mass. Thus, if it contains calcium, the amount of aluminum CaCu ₅ phase upon addition of it is recognized that there is a tendency to increase.

Moreover, it is preferable that the content rate of the said M2 element is 3.0 times or more and 3.7 times or less of the sum total of the content rate of each element of M1 element, calcium, and magnesium. With such a range, Gd ₂ Co ₇ phase, Ce ₂ Ni ₇ phase, at least two or more crystal phases of Ce ₅ Co ₁₉ phase and Pr ₅ Co ₁₉ phase is easily formed. By having these crystal phases, deterioration when the storage and release of hydrogen is repeated is suppressed. Since such a tendency is remarkable, it is more preferable that the content ratio of the M2 element is 3.2 times or more of the total content ratio of each element of the M1 element, calcium and magnesium, and more preferably 3.3. It is particularly preferable that the ratio is not less than twice and not more than 3.5.

  Therefore, in the above general formula, it is preferable to satisfy 3 ≦ (y + z) / (u + v + w + x) ≦ 3.7, more preferably 3.2 ≦ (y + z) / (u + v + w + x) ≦ 3.7, Particularly preferably satisfies 3.3 ≦ (y + z) / (u + v + w + x) ≦ 3.5.

  Thus, by constituting the negative electrode using the hydrogen storage alloy having the above composition, the cycle life characteristics can be improved while increasing the discharge capacity of the nickel-metal hydride storage battery.

  The hydrogen storage alloy in the present invention is a rare earth-Mg—Ni-based hydrogen storage alloy having two or more crystal phases having different crystal structures, and preferably the two or more crystal phases are It is a rare-earth-Mg-Ni-based hydrogen storage alloy laminated in the c-axis direction of the crystal structure.

Examples of the crystal phase include a crystal phase composed of a rhombohedral La ₅ MgNi ₂₄ type crystal structure (hereinafter also simply referred to as a La ₅ MgNi ₂₄ phase), and a crystal phase composed of a hexagonal Pr ₅ Co ₁₉ type crystal structure (hereinafter simply referred to as a simple phase). Pr ₅ Co ₁₉ phase), crystal phase composed of rhombohedral Ce ₅ Co ₁₉ type crystal structure (hereinafter also simply referred to as Ce ₅ Co ₁₉ phase), crystal phase composed of hexagonal Ce ₂ Ni ₇ type crystal structure (Hereinafter also simply referred to as Ce ₂ Ni ₇ phase), crystal phase composed of rhombohedral Gd ₂ Co ₇ type crystal structure (hereinafter also simply referred to as Gd ₂ Co ₇ phase), hexagonal CaCu ₅ type crystal structure Crystal phase (hereinafter also simply referred to as CaCu ₅ phase), crystal phase consisting of cubic AuBe ₅ type crystal structure (hereinafter also simply referred to as AuBe ₅ phase) crystal phase consisting of rhombohedral PuNi ₃ type crystal structure (hereinafter simply referred to as simply “AuBe ₅ phase”) PuNi _3-phase also called), and the like ani Rukoto can.

Among these, a hydrogen storage alloy having two or more selected from the group consisting of Gd ₂ Co ₇ phase, Pr ₅ Co ₁₉ phase, Ce ₅ Co ₁₉ phase, and Ce ₂ Ni ₇ phase is preferably used. The hydrogen storage alloy having these crystal phases has excellent characteristics that the difference between the expansion and contraction ratios between the crystal phases is small, so that the distortion is not easily generated and the deterioration is not easily caused by repeated storage and release of hydrogen.

Here, the La ₅ MgNi ₂₄ type crystal structure is a crystal structure in which _four AB ₅ units are inserted between A ₂ B ₄ units, and the Pr ₅ Co ₁₉ type crystal structure is A ₂ B It is a crystal structure in which 3 units of AB ₅ units are inserted between ₄ units, and Ce ₅ Co ₁₉ type crystal structure is that 3 units of AB ₅ units are inserted between A ₂ B ₄ units. It is a crystal structure, and the Ce ₂ Ni ₇ type crystal structure is a crystal structure in which _two AB ₅ units are inserted between A ₂ B ₄ units. What is the Gd ₂ Co ₇ type crystal structure? , ₂ units of AB ₅ units are inserted between A ₂ B ₄ units, and the AuBe ₅ type crystal structure is a crystal structure composed of only A ₂ B ₄ units.

The A ₂ B ₄ unit is a structural unit having a hexagonal MgZn ₂ type crystal structure (C14 structure) or a hexagonal MgCu ₂ type crystal structure (C15 structure), and the AB ₅ unit is a hexagonal CaCu ₅ unit. It is a structural unit with a type crystal structure.

  When the crystal phases are stacked, the stacking order of the crystal phases is not particularly limited, and a combination of specific crystal phases may be stacked with repeating periodicity. The phase may be laminated randomly and without periodicity.

The content of each crystal phase is not particularly limited, but the content of the crystal phase having the Gd ₂ Co ₇ type crystal structure is 0 to 80% by mass, and the Pr ₅ Co ₁₉ type crystal structure. The content of the crystal phase having _{3 to} 80% by mass, the content of the crystal phase having the Ce ₅ Co ₁₉ type crystal structure is 15 to 80% by mass, and the content of the crystal phase having the Ce ₂ Ni ₇ type crystal structure The rate is preferably 0 to 95% by mass.

In particular, the hydrogen storage alloy according to the present invention contains a crystal phase having a Ce ₂ Ni ₇ type crystal structure containing Ca or a crystal phase having a Gd ₂ Co ₇ type crystal structure containing Ca. Among them, it is preferable that the content of a crystal phase having a Ce ₂ Ni ₇ type crystal structure containing Ca is 20 to 90% by mass, and a Gd ₂ Co ₇ type crystal structure containing Ca. It is preferable that the content rate of the crystal phase which has 10-70 mass%.

  The crystal phase having each crystal structure can be identified by, for example, performing X-ray diffraction measurement on the pulverized alloy powder and analyzing the obtained X-ray diffraction pattern by the Rietveld method. .

  Moreover, it can be confirmed by observing the lattice image of the alloy using TEM that two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure.

When the hydrogen storage alloy is formed by laminating two or more crystal phases having different crystal structures in the c-axis direction of the crystal structure, the distortion of the crystal phase when hydrogen is stored by charging may be The crystal phase is relaxed. Therefore, the negative electrode comprising the hydrogen storage alloy has an effect that the alloy is less likely to be pulverized even if hydrogen storage and release are repeated by charging and discharging, and deterioration is unlikely to proceed.
Further, since the hydrogen storage alloy is a rare earth-Mg-Ni based hydrogen storage alloy, there is an effect that the discharge capacity is large.

The hydrogen storage alloy preferably has a hydrogen equilibrium pressure of 0.07 MPa or less. Conventional hydrogen storage alloys have the property that when hydrogen equilibrium pressure is high, it is difficult to absorb hydrogen and it is easy to release the absorbed hydrogen. When the high rate characteristics of the hydrogen storage alloy are enhanced, hydrogen self-releases. It was easy to do.
However, it is a rare earth-Mg-Ni-based hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated, and particularly when the content of the crystal phase having a CaCu ₅ type crystal structure is 15% by mass or less. In some hydrogen storage alloys, good high rate characteristics can be obtained even when the hydrogen equilibrium pressure is set to a low value of 0.07 MPa or less. A nickel metal hydride battery using the hydrogen storage alloy as a negative electrode has excellent high rate characteristics and Hydrogen self-release (self-discharge in a battery) is unlikely to occur. This is considered to be because the diffusibility of hydrogen in the alloy was improved.

  The hydrogen equilibrium pressure means an equilibrium pressure (release side) of H / M = 0.5 in the 80 ° C. PCT curve (pressure-composition isotherm).

The hydrogen storage alloy having such a configuration can be obtained by the following manufacturing method.
That is, the method for producing a hydrogen storage alloy as one embodiment includes a melting step of melting an alloy raw material blended to have a predetermined composition ratio, and rapid solidification of the molten alloy raw material at a cooling rate of 1000 K / second or more. And an annealing step of annealing the cooled alloy in a pressurized inert gas atmosphere in a temperature range of 860 to 1000 ° C.

More specifically, first, a predetermined amount of raw material ingot (alloy raw material) is weighed based on the chemical composition of the target hydrogen storage alloy.
In the melting step, the alloy raw material is put in a crucible and heated to 1200 to 1600 ° C., for example, in an inert gas atmosphere or in a vacuum to melt the alloy raw material.

  In the cooling step, the molten alloy material is cooled and solidified. The cooling rate is preferably 1000 K / second or more (also called rapid cooling). By rapidly cooling at 1000 K / second or more, there is an effect that the alloy composition is refined and homogenized.

  As the cooling method, specifically, a melt spinning method having a cooling rate of 100,000 K / second or more, a gas atomizing method having a cooling rate of about 10,000 K / second, or the like can be preferably used.

In the annealing step, heating is performed at 860 to 1000 ° C. using, for example, an electric furnace in a pressurized state under an inert gas atmosphere. As a pressurizing condition, 0.2 to 1.0 MPa (gauge pressure) is preferable. Moreover, it is preferable that the processing time in this annealing process shall be 3 to 50 hours.
The distortion of the crystal lattice is removed by such an annealing process, and the hydrogen storage alloy that has undergone the annealing process finally becomes a hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated.

After preparing a La—Mg—Ni-based hydrogen storage alloy containing calcium in a proportion of 0.5 atomic% to 3.3 atomic% by the above-described procedure, the hydrogen storage alloy is pulverized, and the negative electrode It is preferable to use it as a material.
The hydrogen storage alloy may be pulverized at the time of electrode fabrication either before or after annealing, but since the surface area is increased by pulverization, it is desirable to pulverize after annealing from the viewpoint of preventing surface oxidation of the alloy. The pulverization is preferably performed in an inert atmosphere to prevent oxidation of the alloy surface.
For the pulverization, for example, mechanical pulverization or hydrogenation pulverization is used.

Furthermore, in this invention, aluminum hydroxide is used as a constituent material of a negative electrode with this hydrogen storage alloy.
Specifically, aluminum hydroxide is added at a ratio of 0.1 parts by mass or more and 2 parts by mass or less, preferably 0.3 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the hydrogen storage alloy. . The aluminum hydroxide is preferably a powder having a particle size of 0.1 to 20 μm. The added aluminum hydroxide is distributed so as to coexist with the hydrogen storage alloy inside the negative electrode, and has the effect of improving the durability of the hydrogen storage alloy by the action as described above.

The hydrogen storage alloy used in the present invention can contain elements other than the M1 element, Ca, Mg, and M2 element as long as the effects of the present invention are obtained.
That is, the hydrogen storage alloy according to the present invention is naturally an alloy represented by the above general formula, and can contain an element not defined by the general formula as, for example, an inevitable impurity. Therefore, having the composition represented by the general formula has a composition that matches the general formula, or has a composition that includes the inevitable impurities and that excludes the impurities has the composition that matches the general formula. It means that.

  The alkaline electrolyte constituting the nickel metal hydride storage battery according to the present invention is not particularly limited, and a substance that moves ions during the electrochemical electromotive reaction at the positive and negative electrodes of the nickel metal hydride storage battery can be used. For example, an aqueous solution of potassium hydroxide, lithium hydroxide, or sodium hydroxide, or a mixture thereof can be used.

  In addition, various additives can be added to the electrolytic solution in order to improve the corrosion resistance to the alloy, improve the overvoltage at the positive electrode, improve the corrosion resistance of the negative electrode, and improve self-discharge. As this additive, oxides, hydroxides, etc., such as yttrium, ytterbium, erbium, calcium, and zinc, can be used singly or in combination.

On the other hand, the positive electrode of the nickel metal hydride storage battery is not particularly limited, but generally a nickel hydroxide composite oxide mainly composed of nickel hydroxide and mixed with zinc hydroxide or cobalt hydroxide. A positive electrode including a positive electrode active material can be preferably used, and a positive electrode including the nickel hydroxide composite oxide uniformly dispersed by a coprecipitation method can be more preferably used.
As additives other than the nickel hydroxide composite oxide, cobalt hydroxide, cobalt oxide and the like as a conductive modifier can be used, and the nickel hydroxide composite oxide is coated with cobalt hydroxide. A part of these nickel hydroxide composite oxides oxidized using oxygen or oxygen-containing gas, or a chemical such as K ₂ S ₂ O ₈ or hypochlorous acid can be used.
In addition, as the additive, as a substance for improving the oxygen overvoltage, a rare earth element compound such as Y or Yb or a Ca compound can be used. Since some of rare earth elements such as Y and Yb are dissolved and disposed on the negative electrode surface, an effect of suppressing corrosion of the negative electrode active material can be expected.

The positive electrode and the negative electrode may contain a conductive agent, a binder, a thickener, and the like as other components in addition to the main components as described above.
The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (such as scale-like graphite, scale-like graphite, earth-like graphite), artificial graphite, carbon black, acetylene black, A conductive material such as ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, metal (nickel, gold, etc.) powder, metal fiber, or the like can be included as one or a mixture of two or more.
Among these, as the conductive agent, acetylene black is preferable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by mass to 10% by mass with respect to the total weight of the positive electrode or the negative electrode. In particular, it is desirable to use acetylene black after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the necessary carbon amount can be reduced.
As a method of mixing them, a method that can be as uniform as possible is preferable. For example, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like may be dry or wet. The method used in the above can be adopted.
As the binder, usually, thermoplastic resins such as polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber A polymer having rubber elasticity such as can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 0.1 to 3% by mass with respect to the total amount of the positive electrode or the negative electrode.
As said thickener, polysaccharides, such as carboxymethylcellulose, methylcellulose, xanthan gum, etc. can be normally used as 1 type, or 2 or more types of mixtures. The addition amount of the thickener is preferably 0.1 to 0.3% by mass with respect to the total amount of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the active material, the conductive agent, and the binder in an organic solvent such as water, alcohol, and toluene, and then applying the obtained mixed liquid onto a current collector and drying it. Produced suitably. As the application method, for example, a method of applying an arbitrary thickness and an arbitrary shape using means such as roller coating such as an applicator roll, screen coating, blade coating, spin coating, and per coating is preferable. It is not limited to.

As the current collector, an electron conductor that does not adversely affect the exchange of electrons with the active material in the battery that is configured can be used without particular limitation. As the current collector, for example, from the viewpoint of reduction resistance and oxidation resistance, nickel or nickel-plated steel plate can be suitably used as a material, and as a shape, a foam, a molded body of a fiber group, A three-dimensional base material subjected to uneven processing or a two-dimensional base material such as a punching plate can be suitably used. Moreover, there is no limitation in particular also about the thickness of this electrical power collector, The thing of 5-700 micrometers is used suitably.
Among these current collectors, for the positive electrode, it is necessary to use a material having a porous structure, which is made of nickel having excellent corrosion resistance and oxidation resistance to alkali, and having a structure excellent in current collection. preferable. In addition, as a negative electrode, it is preferable to use a punching plate obtained by applying nickel plating for improving reduction resistance to an iron foil which is inexpensive and excellent in conductivity.
The punching diameter is preferably 2.0 mm or less, and the opening ratio is preferably 40% or more. This makes it possible to improve the adhesion between the negative electrode active material and the current collector even with a small amount of binder.

As a separator of a nickel metal hydride storage battery, it is preferable that a porous film or a nonwoven fabric exhibiting excellent rate characteristics be used alone or in combination of two or more. Examples of the material constituting the separator include polyolefin resins such as polyethylene and polypropylene, and nylon.
The basis weight of the separator is preferably 40 g / m ² to 100 g / m ² . If it is less than 40 g / m ² , the short circuit and the self-discharge performance may be deteriorated, and if it exceeds 100 g / m ² , the proportion of the separator per unit volume increases, so that the battery capacity tends to decrease. The air permeability of the separator is preferably 1 cm / sec to 50 cm / sec. If it is less than 1 cm / sec, the internal pressure of the battery may increase, and if it exceeds 50 cm / sec, the short circuit and the self-discharge performance may be deteriorated. The average fiber diameter of the separator is preferably 1 μm to 20 μm. When the thickness is less than 1 μm, the strength of the separator decreases, and the defect rate in the battery assembly process may increase. When the thickness exceeds 20 μm, the short circuit and the self-discharge performance may decrease.
The separator is preferably subjected to a hydrophilic treatment. For example, the surface of polyolefin resin fibers such as polypropylene may be subjected to sulfonation treatment, corona treatment, fluorine gas treatment, plasma treatment, or a mixture of those already subjected to these treatments. In particular, separators that have been sulfonated have a high ability to adsorb impurities such as NO ₃ ⁻ , NO ₂ ⁻ , and NH ₃ ⁻ that cause the shuttle phenomenon and elements eluted from the negative electrode. ,preferable.

  The sealed nickel-metal hydride storage battery as one embodiment of the present invention is preferably produced by injecting the electrolyte solution before or after laminating the positive electrode, the separator, and the negative electrode, and sealing with an exterior material. Is done. In a sealed nickel-metal hydride storage battery in which a power generation element in which a positive electrode and a negative electrode are stacked via the separator is wound, the electrolyte is injected into the power generation element before or after winding. preferable. As an injection method, it is possible to inject at normal pressure, but a vacuum impregnation method, a pressure impregnation method, and a centrifugal impregnation method can also be used. Examples of the material of the outer package of the sealed nickel-metal hydride storage battery include nickel-plated iron, stainless steel, polyolefin resin, and the like.

  The configuration of the sealed nickel-metal hydride storage battery is not particularly limited, and batteries including a positive electrode, a negative electrode, and a single-layer or multi-layer separator, such as a coin battery, a button battery, a square battery, a flat battery, Alternatively, a cylindrical battery having a roll-shaped positive electrode, a negative electrode, and a separator can be given.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Example 1>
(Preparation of positive electrode)
An ammonium complex and an aqueous sodium hydroxide solution were added to an aqueous solution in which nickel sulfate, zinc sulfate and cobalt sulfate were dissolved at a predetermined ratio to form an ammine complex. While vigorously stirring the reaction system, caustic soda is further added dropwise, the pH of the reaction system is controlled to 10 to 13, and the spherical high density nickel hydroxide particles serving as the core layer base material are converted into nickel hydroxide: zinc hydroxide: cobalt hydroxide. = 93: 5: 2 The weight ratio was synthesized.
The high-density nickel hydroxide particles were put into an alkaline aqueous solution adjusted to pH 10 to 13 with caustic soda, and an aqueous solution containing cobalt sulfate and ammonia at predetermined concentrations was added dropwise while stirring the solution. During this time, an aqueous caustic soda solution was appropriately added dropwise to maintain the pH of the reaction bath in the range of 10-13. The pH was maintained in the range of 10 to 13 for about 1 hour, and a surface layer made of a mixed hydroxide containing Co was formed on the surface of the nickel hydroxide particles. The ratio of the surface layer of the mixed hydroxide was 4% by mass with respect to hydroxide core layer base material particles (hereinafter simply referred to as core layer).
Furthermore, nickel hydroxide particles having a surface layer made of the mixed hydroxide were put into a 30% by mass (10 mol / liter) aqueous caustic soda solution at a temperature of 110 ° C. and sufficiently stirred. Subsequently, excess K ₂ S ₂ O ₈ was added to the equivalent of the cobalt hydroxide contained in the surface layer, and it was confirmed that oxygen gas was generated from the particle surface. The active material particles were filtered, washed with water and dried. To the obtained active material particles, 0.2% by mass of a carboxymethyl cellulose (CMC) aqueous solution, 0.3% by mass of polytetrafluoroethylene (PTFE), and 2% by mass of Yb ₂ O ₃ are added to obtain the active material particles. : CMC solute: PTFE: Yb ₂ O ₃ = 97.5: 0.2: 0.3: 2.0% by mass (solid content ratio) paste was filled in a nickel porous body of 350 g / m. . Then, after drying at 80 degreeC, it pressed to predetermined thickness and it was set as the 2000 mAh nickel positive electrode plate.

(Preparation of negative electrode)
A specified amount of a raw material ingot (alloy raw material) as shown in Table 1 is weighed into a crucible and heated to 1200 ° C. to 1600 ° C. in a low-pressure argon gas atmosphere using a high-frequency melting furnace to melt the material. did. After melting, a melt spinning method was applied and quenched at a cooling rate of 1000 K / second or more to solidify the alloy.
Next, the obtained alloy ingot was heated in an electric furnace at 930 ° C. for 5 hours in an argon gas atmosphere pressurized to 0.2 MPa (gauge pressure, the same applies hereinafter).
About each obtained hydrogen storage alloy, the equilibrium in H / M = 0.5 of the PCT curve (pressure-composition isotherm) in 80 degreeC was carried out using the Siebelz type PCT measuring apparatus (the Suzuki Shokan Co., Ltd. P73-07). The pressure was determined.
Furthermore, each hydrogen storage alloy was pulverized to an average particle diameter D50 = 50 μm, and the obtained powder was subjected to conditions of 40 kV, 100 mA (Cu tube) using an X-ray diffraction apparatus (manufactured by BrukerAXS, product number M06XCE). An X-ray diffraction test was performed. Furthermore, analysis by the Rietveld method (analysis software: Rietan 2000) was performed, and the generation ratio of the crystal phase was calculated. The results are shown in Table 2.
Next, the alloy powder, aluminum hydroxide powder (average particle diameter D50 = 1.6 μm), styrene butadiene copolymer (SBR) aqueous solution, and methyl cellulose (MC) aqueous solution,
50: 0.5: 0.0425: 0.3 was mixed at a solid mass ratio to form a paste, applied to a punched steel plate in which nickel was plated on iron, and dried at 80 ° C. using a blade coater. Then, it pressed to the predetermined thickness and was set as the negative electrode.

(Production of open evaluation battery)
The electrodes produced as described above were sandwiched between positive electrodes through separators and fixed with bolts so that a pressure of 1 kgf / cm ² was applied to these electrodes, and an open-type nickel-metal hydride storage battery was assembled. As the electrolytic solution, a mixed solution composed of a 6.8 mol / L KOH solution and a 0.8 mol / L LiOH solution was used.
The positive and negative electrode capacities of the open-type evaluation battery were designed under conditions where the positive electrode capacity is sufficiently larger than the negative electrode capacity, that is, so-called negative electrode regulation. Therefore, the charge / discharge capacity results obtained with this evaluation battery are for the negative electrode.

(Measurement of cycle life characteristics)
In a 20 ° C. water bath, charging at 150% at 0.1 ItA and discharging at 0.2 ItA with a final voltage of 0.6 V (vs. Hg / HgO) were repeated 50 cycles. And the discharge capacity of the 50th cycle with respect to the maximum discharge capacity was calculated | required as a capacity | capacitance maintenance factor (%). Table 3 shows the results of the maximum discharge capacity and capacity retention rate.

(Measurement of specific surface area)
The specific surface area of the alloy before and after the cycle test was measured according to the following procedure. The negative electrode was taken out from the battery before and after measuring the cycle life characteristics, washed with water and dried, and then the mixture layer portion and the substrate (punched steel plate in which iron was nickel-plated) were separated. Next, the composite material layer portion was pulverized with a mortar, placed in a specific surface area measuring device (manufactured by QUANTACHROME, MONOSORB), and the specific surface area was measured by the BET method.

(Measurement of average particle diameter D50)
The particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Microtrac, MT3000), and the average particle size D50 of the alloy before and after the cycle test was determined.

(Measurement of mass saturation magnetization)
Using a vibrating sample magnetometer (RHV Electronics, BHV-10H), the mass saturation magnetization of the alloy before and after the cycle test was measured.

<Comparative Example 1>
Do not add aluminum hydroxide as a negative electrode material, specifically, the alloy powder, styrene butadiene copolymer (SBR) aqueous solution, and methyl cellulose (MC) aqueous solution,
An open type evaluation battery was prepared in the same manner as in Example 1 except that the negative electrode was prepared by mixing at a solid mass ratio of 50: 0.0425: 0.3, and the same measurement was performed.

<Comparative Example 2>
An open type evaluation battery was prepared in the same manner as in Example 1 except that the chemical composition of the raw material ingot was changed to the composition shown in Table 1, and the same measurement was performed.

<Comparative Example 3>
An open type evaluation battery was prepared in the same manner as in Example 1 except that the chemical composition of the raw material ingot was changed to the composition shown in Table 1, and the same measurement was performed.

<Comparative example 4>
An open type evaluation battery was prepared in the same manner as in Example 1 except that the chemical composition of the raw material ingot was changed to the composition shown in Table 1, and the same measurement was performed.

<Comparative Example 5>
An open evaluation battery was prepared in the same manner as in Comparative Example 1 except that the chemical composition of the raw material ingot was changed to the composition shown in Table 1, and the same measurement was performed.

According to the results shown in Table 3, the rare earth-Mg—Ni-based hydrogen storage alloy containing Ca was compared with Comparative Examples 4 and 5 using the rare-earth-Mg—Ni-based hydrogen storage alloy containing no Ca. In the used Example 1 and Comparative Example 1, it is recognized that the maximum discharge capacity is increased.
When attention is paid to the effect of the addition of aluminum hydroxide, Comparative Examples 2 and 3 using a rare earth-Mg-Ni-based hydrogen storage alloy containing no Ca include Comparative Example 2 and aluminum hydroxide in which no aluminum hydroxide is added. It is recognized that the capacity retention rate is almost the same as that of Comparative Example 3 to which is added, and the effect of the addition of aluminum hydroxide is hardly exhibited. Further, in Comparative Examples 4 and 5, the capacity retention rate value did not change between Comparative Example 5 in which no aluminum hydroxide was added and Comparative Example 4 in which aluminum hydroxide was added, and the effect of the addition of aluminum hydroxide was effective. It is recognized that it has not been demonstrated.
On the other hand, in Example 1 and Comparative Example 1 using a rare earth-Mg—Ni-based hydrogen storage alloy containing Ca, Example in which aluminum hydroxide was added to Comparative Example 1 in which no aluminum hydroxide was added. The capacity retention rate of No. 1 is improved by 1.4%, and it is recognized that the effect of improving the capacity retention rate by adding aluminum hydroxide is remarkably exhibited.

  This is supported by changes in specific surface area, average particle diameter, and mass saturation magnetization before and after the cycle test, and Comparative Examples 4 and 5 using rare earth-Mg—Ni-based hydrogen storage alloys containing no Ca. In Comparative Example 5 in which no aluminum hydroxide was added and Comparative Example 4 in which aluminum hydroxide was added, these values hardly changed, whereas a rare earth-Mg—Ni-based hydrogen storage alloy containing Ca was used. In Example 1 and Comparative Example 1 used, the specific surface area, the average particle diameter, and the mass saturation magnetization of Example 1 to which aluminum hydroxide was added deteriorated with respect to Comparative Example 1 in which aluminum hydroxide was not added. It is recognized that it has changed to one with less.

<Examples 2 to 6>
An open type evaluation battery was prepared in the same manner as in Example 1 except that the chemical composition of the raw material ingot was changed to the composition shown in Table 4, and the capacity retention rate was measured.

<Comparative Examples 6 to 10>
Except that aluminum hydroxide was not added as a constituent material for the negative electrode, open type evaluation batteries were prepared in the same manner as in Examples 1 to 6, and the capacity retention rate was measured. The results are shown in Table 4 below.

  From Table 4, it can be seen that even if the alloy composition fluctuates within the scope of the present invention, the improvement effect of the capacity retention rate due to the addition of aluminum hydroxide as the constituent material of the negative electrode is exhibited.

Claims (3)

A negative electrode composed of a hydrogen storage alloy mainly containing M1 element, calcium, magnesium and M2 element, and aluminum hydroxide;
The M1 element is one or more elements selected from the group consisting of rare earth elements, 4A group elements, 5A group elements and Pd (however, including at least rare earth elements),
The M2 element is one or more elements selected from the group consisting of Group 6A elements, Group 7A elements, Group 8 elements (excluding Pd), Group 1B elements, Group 2B elements, and Group 3B elements (but at least Nickel)
The content of the M2 element in the hydrogen storage alloy is more than 3 times and less than 5 times the total content of each element of the M1 element, calcium and magnesium,
The calcium content in the hydrogen storage alloy is 0.5 atomic% or more, and
A nickel-metal hydride storage battery characterized in that the content of aluminum as the M2 element in the hydrogen storage alloy is 0 atomic% or more and 1.5 atomic% or less. The hydrogen storage alloy has the general formula _{M1 'u M1 "v Ca w} Mg x Ni y M2' z [ wherein, M1 'is one or more elements selected from rare earth elements, M1" is One or more elements selected from the group consisting of Group 4A elements, Group 5A elements and Pd, and M2 ′ is a Group 6A element, Group 7A element, Group 8 element (excluding Ni and Pd), 1B Is one or more elements selected from the group consisting of group elements, group 2B elements and group 3B elements, and u, v, w, x, y and z are u + v + w + x + y + z = 100, 13.3 ≦ u ≦ 19.5, 0 ≦ v ≦ 1.2, 0.5 ≦ w ≦ 3.8, 2.2 ≦ x ≦ 5.8, 74.4 ≦ y ≦ 78.7, 0 ≦ z ≦ 1.2 It is a number that satisfies The nickel-metal hydride storage battery according to claim 1, having a composition represented by:   3. The nickel-metal hydride storage battery according to claim 1, wherein the aluminum hydroxide is 0.1 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy.