JP2011021262A - Hydrogen storage alloy and nickel-hydrogen storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy which can make the cycle properties of a nickel hydrogen storage battery excellent. <P>SOLUTION: The hydrogen storage alloy has a chemical composition expressed by general formula La<SB>v</SB>Sm<SB>w</SB>M1<SB>x</SB>M2<SB>y</SB>M3<SB>z</SB>; wherein, M1 denotes an element(s) of Pr and/or Nd; M2 denotes an element(s) at least including Mg in Mg and Ca; M3 is the one in which Ni or a part of Ni is substituted with one or more kinds of elements selected from the group consisting of the group 6A elements, the group 7A elements, the group 8A elements (excluding Ni and Pd), the group IB elements, the group 2B elements and the group 3B elements; and v, w, x, y and z satisfy inequality; 3.2≤z/(v+w+x+y)≤3.7, inequality; 0.60≤v(v+w+x)≤0.85, and inequality; 0.01≤w/(v+w+x)≤0.06. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hydrogen storage alloy and a nickel-metal hydride storage battery including a negative electrode containing the hydrogen storage alloy.

  Nickel metal hydride storage batteries have high energy density, so they are used as power sources for small electronic devices such as digital cameras and notebook computers, and because the operating voltage is equivalent to and compatible with primary batteries such as alkaline manganese batteries. As a substitute for the primary battery, the battery is widely used, and the demand for the battery is expanding dramatically.

  This type of nickel metal hydride storage battery is usually configured to include a nickel electrode including 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. Yes. Among these battery constituent materials, in particular, the hydrogen storage alloy that is the main material of the negative electrode has a great influence on the performance of the nickel-metal hydride storage battery such as discharge capacity and energy density. As the hydrogen storage alloy, Various things are being studied.

In recent years, as an alloy that exhibits a discharge capacity that exceeds the discharge capacity in the case of using an AB ₅ rare earth-Ni-based hydrogen storage alloy and that can suppress a decrease in battery capacity due to repeated charge and discharge (excellent cycle characteristics). Rare earth-Mg-Ni hydrogen storage alloys containing rare earth elements, Mg, and Ni are attracting attention. For example, rare earth-Mg-Ni hydrogen storage alloys are further blended with Al, Mn, Zn, etc. A hydrogen storage alloy is proposed (Patent Document 1).

JP 2007-169724 A

  In such rare earth-Mg-Ni-based hydrogen storage alloys, for example, the type and amount of metal added to the hydrogen storage alloy are adjusted in order to improve the cycle characteristics of a nickel-metal hydride storage battery equipped with a negative electrode containing the hydrogen storage alloy. There is something to do. However, such rare earth-Mg-Ni-based hydrogen storage alloys still do not always satisfy the cycle characteristics.

  Therefore, a hydrogen storage alloy that can improve the cycle characteristics of a nickel metal hydride storage battery is desired.

  This invention makes it a subject to provide the hydrogen storage alloy which can make the cycling characteristics of a nickel hydride storage battery excellent in view of said problem, a request point, etc. Another object of the present invention is to provide a nickel metal hydride storage battery having a negative electrode containing the hydrogen storage alloy and having excellent cycle characteristics.

In order to solve the above problems, the hydrogen-absorbing alloy according to the present invention, the chemical composition, a hydrogen storage alloy represented by the general formula _{La v Sm w M1 x M2 y} M3 z,
M1 is an element of Pr and / or Nd, M2 is an element containing at least Mg among Mg and Ca, M3 is a part of Ni or Ni, a group 6A element, a group 7A element, a group 8 element (Ni and (Except Pd), which is substituted with one or more elements selected from the group consisting of Group 1B elements, Group 2B elements, and Group 3B elements, and v, w, x, y and z are The following formula (1), formula (2) and formula (3)
3.2 ≦ z / (v + w + x + y) ≦ 3.7 Formula (1)
0.60 ≦ v / (v + w + x) ≦ 0.85 Formula (2)
0.01 ≦ w / (v + w + x) ≦ 0.06 Formula (3)
It is characterized by satisfying.

In the hydrogen storage alloy according to the present invention, M2 is Mg, and v, w, x, y, and z are the following formulas (4) and (5).
3.5 ≦ z / (v + w + x + y) ≦ 3.7 Formula (4)
0.71 ≦ v / (v + w + x) ≦ 0.83 Formula (5)
It is preferable to satisfy. With such a configuration, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved.

  In the hydrogen storage alloy according to the present invention, M3 is obtained by replacing Ni or a part of Ni with one or more elements selected from the group consisting of Al, Mn, Co, Cu, Fe, Cr and Zn. Including La, Sm and M1 in total from 17.3 atomic% to 19.2 atomic%, M2 from 3.0 atomic% to 3.9 atomic%, and M3 from 77.8 atomic% to 78 It is preferable to contain 7 atomic% or less. With such a configuration, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved.

  In the hydrogen storage alloy according to the present invention, M1 preferably contains at least Pr. With such a configuration, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved.

  The hydrogen storage alloy according to the present invention preferably contains no Co. With such a configuration, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved while suppressing an internal short circuit due to Co deposition in the nickel-metal hydride storage battery.

  The nickel-metal hydride storage battery according to the present invention includes a negative electrode containing the hydrogen storage alloy.

  In this specification, atomic% refers to the percentage of the number of specific atoms with respect to the total number of atoms present. Therefore, for example, an alloy containing 1 atomic% of nickel means an alloy having a ratio of including one nickel atom out of 100 atoms of the alloy.

  The hydrogen storage alloy according to the present invention can be contained in the negative electrode of a nickel metal hydride storage battery, and has an effect that the cycle characteristics of the nickel metal hydride storage battery can be improved.

The figure showing the relationship between the content rate of La in a hydrogen storage alloy, and the cycling characteristics of a nickel hydride storage battery.

  Hereinafter, an embodiment of the hydrogen storage alloy according to the present invention will be described.

The hydrogen storage alloy of the present embodiment is a hydrogen storage alloy having a chemical composition represented by a general formula La _v Sm _w M1 _x M2 _y M3 _z ,
M1 is an element of Pr and / or Nd, M2 is an element containing at least Mg among Mg and Ca, M3 is a part of Ni or Ni, a group 6A element, a group 7A element, a group 8 element (Ni and (Except Pd), which is substituted with one or more elements selected from the group consisting of Group 1B elements, Group 2B elements, and Group 3B elements, and v, w, x, y and z are The following formula (1), formula (2) and formula (3)
3.2 ≦ z / (v + w + x + y) ≦ 3.7 Formula (1)
0.60 ≦ v / (v + w + x) ≦ 0.85 Formula (2)
0.01 ≦ w / (v + w + x) ≦ 0.06 Formula (3)
It satisfies.
The hydrogen storage alloy is naturally an alloy represented by the above general formula, and may contain an element not defined by the general formula as an inevitable impurity, for example.

That is, in the hydrogen storage alloy of this embodiment, the so-called B / A ratio is not less than 3.2 and not more than 3.7 as shown in the formula (1), and is a rare earth as shown in the formula (2). The ratio of La to the total of La, Sm, Pr, and Nd is 0.60 or more and 0.85 or less, and the ratio of Sm to the total of La, Sm, Pr, and Nd that are rare earths as shown in Formula (3) Is 0.01 or more and 0.06 or less. For this reason, the cycle characteristics of the nickel-metal hydride storage battery using the hydrogen storage alloy can be excellent.
In the B / A ratio, A represents an element selected from the group consisting of rare earth elements such as La, Sm, Pr, and Nd, Mg, and Ca, and B represents a group 6A element, a group 7A element, and a group 8 element. It represents an element selected from the group consisting of transition metal elements such as Group 1B elements, Group 2B elements and the like and Al (excluding Pd).

  Specifically, in the hydrogen storage alloy, when the formula (1) is satisfied, that is, when the B / A ratio is 3.2 or more and 3.7 or less, the structure of the formed crystal phase is expanded. It is thought that it is difficult to be pulverized and stabilized by shrinkage. Therefore, the cycle characteristics of the nickel metal hydride storage battery using the hydrogen storage alloy can be excellent. On the other hand, when the formula (1) is not satisfied, the cycle characteristics of the nickel hydride storage battery using the hydrogen storage alloy can be deteriorated.

Further, in the hydrogen storage alloy, when the formula (2) is satisfied, the generation ratio of the Pr ₅ Co ₁₉ phase, the Ce ₅ Co ₁₉ phase, and the Ce ₂ Ni ₇ phase increases and the generation ratio of the CaCu ₅ phase decreases. In addition, a c-axis stacked structure in which the difference in change in the a-axis length during expansion and contraction is smaller between the crystal structures can be obtained. Therefore, it is considered that the structure of the formed crystal phase is hardly pulverized and stabilized even by expansion and contraction, and the cycle characteristics of the nickel-metal hydride storage battery using the hydrogen storage alloy can be improved. On the other hand, when the formula (2) is not satisfied, the cycle characteristics of the nickel hydride storage battery using the hydrogen storage alloy can be deteriorated.
The relationship between the structure of the crystal phase formed in the hydrogen storage alloy and the pulverization of the alloy due to expansion and contraction will be described later.

  Further, in the hydrogen storage alloy, by satisfying the formula (3), that is, the ratio of Sm to the total of La, Sm, Pr and Nd which are rare earths is 0.01 or more, the hydrogen storage alloy Therefore, the cycle characteristics of the nickel-metal hydride storage battery can be improved by the action described below. Moreover, when such a ratio is 0.06 or less, the structure of the formed crystal phase becomes difficult to be pulverized even by expansion and contraction, and the cycle characteristics can be excellent.

The relationship between the oxygen gas absorption performance of the hydrogen storage alloy and the cycle characteristics of the nickel metal hydride storage battery will be described.
In a nickel metal hydride storage battery equipped with a negative electrode containing a hydrogen storage alloy, oxygen is generated at the positive electrode when overcharged. The oxygen passes through the separator and reaches the negative electrode, and normally reacts with hydrogen stored in the hydrogen storage alloy to become water. However, when the battery is charged with a relatively large current exceeding the oxygen gas absorption rate of the hydrogen storage alloy, the reaction between oxygen gas and hydrogen at the negative electrode does not proceed rapidly, and the battery internal pressure increases. In order to release the gas inside the battery to the outside when the battery internal pressure reaches a predetermined pressure, the sealed battery is provided with a safety valve. However, when the gas is released from the safety valve, a part of the electrolyte is also released to the outside at the same time, so that the electrolyte is reduced and the electrolyte in the separator is depleted, thereby increasing the internal resistance of the battery. , The cycle life may be shortened and the cycle characteristics may deteriorate.
Therefore, when the oxygen gas absorption performance of the hydrogen storage alloy is enhanced by the ratio of Sm to the total of the rare earths La, Sm, Pr and Nd being 0.01 or more, the cycle characteristics of the nickel metal hydride storage battery are excellent. Can be.

In the hydrogen storage alloy, as described above, in the chemical composition expressed by the general formula _{La v Sm w M1 x M2 y} M3 z, by satisfying expressions (1) to (3) simultaneously, micronized is At the same time, the oxygen gas absorption performance is kept relatively high, and the nickel-metal hydride battery can have excellent cycle characteristics.

  Here, the relationship between the structure of the crystal phase formed in the hydrogen storage alloy and pulverization by expansion and contraction will be described below.

The hydrogen storage alloy 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 c-axis of the crystal structure. It is a rare earth-Mg-Ni-based hydrogen storage alloy laminated in the direction.
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 a Pr ₅ Co ₁₉ phase, a Ce ₅ Co ₁₉ phase, and a Ce ₂ Ni ₇ phase is preferable. The hydrogen storage alloy with these crystal phases has excellent characteristics that the difference in expansion and contraction between each crystal phase is small, so that distortion is difficult to occur, and deterioration (micronization) does not easily occur when hydrogen is stored and released repeatedly. Have

The Pr ₅ Co ₁₉ type crystal structure is a crystal structure in which three AB ₅ units are inserted between A ₂ B ₄ units, and the Ce ₅ Co ₁₉ type crystal structure is between A ₂ B ₄ units. Is a crystal structure in which 3 units of AB ₅ units are inserted into the crystal, and the Ce ₂ Ni ₇ type crystal structure is a crystal structure in which 2 units of AB ₅ units are inserted between A ₂ B ₄ units. ₂ the Co ₇ type crystal structure, a crystal structure AB ₅ unit is inserted 2 units worth between a ₂ B ₄ units, the La ₅ MgNi ₂₄ type crystal structure, AB between a ₂ B ₄ units _This is a crystal structure in which ₅ units are inserted by 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 repetition periodicity. The phase may be laminated randomly and without periodicity.

The content of each crystal phase in the hydrogen storage alloy is not particularly limited, but the content of the crystal phase having the Pr ₅ Co ₁₉ type crystal structure is 6 to 60% by mass, and the Ce ₅ Co ₁₉ type. The content of the crystal phase having the crystal structure is preferably 5 to 45% by mass, and the content of the crystal phase having the Ce ₂ Ni ₇ type crystal structure is preferably 22 to 55% by mass.

In the hydrogen storage alloy, it is preferable that two or more crystal phases having different crystal structures are laminated, and the content of the crystal phase having a CaCu ₅ type crystal structure is 5% by mass or less. When the content of the crystal phase having a CaCu ₅ type crystal structure is 5% by mass or less, there is an advantage that the pulverization is suppressed and the cycle life performance of the battery is improved.

  The crystal phase 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.

  Regarding the laminated structure of the crystal phase, for example, by observing the lattice image of the alloy by TEM, two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure. Can be confirmed.

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 is less prone to pulverization of the alloy even when the hydrogen is repeatedly stored and released by charging and discharging, the deterioration is suppressed, and the cycle characteristics of the nickel hydrogen storage battery are excellent. There is an advantage of getting.
Further, since the hydrogen storage alloy is a rare earth-Mg—Ni based hydrogen storage alloy having a relatively high capacity, a desired capacity in the battery can be achieved with a relatively small amount of use. And since the usage-amount of the positive electrode active material in a limited battery space can be increased by the part which the usage-amount decreased, it also has the effect | action that the discharge capacity of a nickel-metal hydride storage battery can be made comparatively large.

The composition of the hydrogen storage alloy in the chemical composition expressed by the general formula _{La v Sm w M1 x M2 y} M3 z, M2 is Mg, v, w, x, y and z satisfy the following formula (4) And formula (5)
3.5 ≦ z / (v + w + x + y) ≦ 3.7 Formula (4)
0.71 ≦ v / (v + w + x) ≦ 0.83 Formula (5)
It is preferable to satisfy.
With such a configuration, there is an advantage that the cycle characteristics of the nickel metal hydride storage battery can be further improved.

In the hydrogen storage alloy, M3 is obtained by substituting Ni or a part of Ni with one or more elements selected from the group consisting of Al, Mn, Co, Cu, Fe, Cr and Zn, La, Sm, and M1 are included in total from 17.3 atomic% to 19.2 atomic%, M2 is included from 3.0 atomic% to 3.9 atomic%, and M3 is included from 77.8 atomic% to 78.7 atomic%. % Or less is preferable. With such a configuration, there is an advantage that the cycle characteristics of the nickel metal hydride storage battery can be further improved.
Moreover, it is preferable that M2 contains Al and Ni at the point which can make the cycling characteristics of a nickel hydride storage battery further excellent.

  In the hydrogen storage alloy, M1 preferably contains at least Pr. When M1 contains at least Pr, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved.

  The hydrogen storage alloy preferably does not contain Co. Specifically, the hydrogen storage alloy is preferably prepared without blending Co even though Co may be contained as an impurity. Specifically, it is preferable that 0.2 atomic% or less of Co is contained in the hydrogen storage alloy. Since Co is not blended in the hydrogen storage alloy, there is an advantage that the cycle characteristics of the nickel hydride storage battery can be further improved while suppressing an internal short circuit due to Co deposition in the nickel hydride storage battery.

The hydrogen storage alloy, if containing Ca, expressed by a composition formula _{La v Sm w M1 x M2 y} M3 z, M1 is an element of Pr and / or Nd, M2 is located at the elements of Mg and Ca M3 is Ni or a part of Ni selected from the group consisting of Group 6A elements, Group 7A elements, Group 8 elements (excluding Ni and Pd), Group 1B elements, Group 2B elements, and Group 3B elements Or it is substituted with two or more elements, satisfies the following formula (6), the total of La, Sm and M1 is 14.8 atomic% or more and 19.1 atomic% or less, and M2 is 4.7 atoms % Or more and 7.4 atom% or less, and M3 is preferably contained in 76.2 atom% or more and 77.8 atom% or less. According to such a configuration, there is an advantage that the cycle characteristics of the nickel-metal hydride storage battery can be further improved while the hydrogen storage alloy contains Ca and is a relatively high capacity battery.
3.2 ≦ z / (v + w + x + y) ≦ 3.4 Formula (6)
In such a configuration, it is preferable that Mg is contained in an amount of 3.0 atomic% to 6.0 atomic%.

  Next, the manufacturing method of the hydrogen storage alloy of this embodiment is demonstrated.

  In the method for producing the hydrogen storage alloy of the present embodiment, for example, a melting step of melting an alloy raw material blended so as to have a predetermined composition ratio as described above, a cooling step of solidifying the molten alloy raw material, An annealing step of annealing the cooled alloy in a pressurized inert gas atmosphere in a temperature range of 860 ° C. to 1000 ° C. and a pulverizing step of pulverizing the alloy are performed.

  More specifically, each step will be described. 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, for example, 1200 ° C. or higher and 1600 ° C. or lower 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 may be so-called slow cooling, or 1000 K / second or more (also referred to as rapid cooling). By rapidly cooling at 1000 K / second or more, there is an effect that the alloy composition is refined and homogenized. The cooling rate can be set in a range of 1000000 K / second or less.

  As the cooling method, specifically, a water-cooled mold method, a melt spinning method with a cooling rate of 100000 K / sec or more, a gas atomizing method with a cooling rate of about 10,000 K / sec, or the like can be preferably used.

  In the annealing step, heating is performed at 860 ° C. or higher and 1000 ° C. or lower using, for example, an electric furnace in a pressurized state under an inert gas atmosphere. The pressurizing condition is preferably 0.2 MPa (gauge pressure) or more and 1.0 MPa (gauge pressure) or less. Moreover, it is preferable that the processing time in this annealing process shall be 3 hours or more and 50 hours or less.

The pulverization step may be performed either before or after annealing, but since the surface area is increased by pulverization, it is desirable to perform the pulverization step after the annealing step 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.
As the pulverization means, for example, mechanical pulverization, hydrogenation pulverization, or the like is used, and it is preferable that the hydrogen storage alloy particles after pulverization have a particle size of approximately 20 to 70 [μm].

  Hereinafter, an embodiment of a nickel metal hydride storage battery according to the present invention will be described.

The nickel-metal hydride storage battery of this embodiment includes a negative electrode containing the above-described hydrogen storage alloy as a hydrogen storage medium.
Since the nickel-metal hydride storage battery of this embodiment is provided with the negative electrode containing the said hydrogen storage alloy, it can become what was excellent in cycling characteristics.

Specifically, the nickel metal hydride storage battery of the present embodiment includes a negative electrode mainly composed of the above-described hydrogen storage alloy, and further includes, for example, a positive electrode (nickel electrode) including a positive electrode active material mainly composed of nickel hydroxide, a separator, And an alkaline electrolyte.
Examples of the negative electrode include those in which the hydrogen storage alloy powder is mixed with a conductive agent, a binder, a thickener, or the like, and pressed into a predetermined shape.

Although it does not specifically limit as a positive electrode of the nickel hydride storage battery of this embodiment, In general, the nickel hydroxide composite which has nickel hydroxide as a main component and zinc hydroxide and cobalt hydroxide are mixed. The positive electrode containing an oxide as a positive electrode active material is mentioned, Preferably, the positive electrode containing this nickel hydroxide complex oxide uniformly disperse | distributed by the coprecipitation method is mentioned.
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. And those obtained by oxidizing a part of these nickel hydroxide composite oxides using an oxygen or oxygen-containing gas, or a chemical such as K ₂ S ₂ O ₈ or hypochlorous acid.
Examples of the additive include compounds of rare earth elements such as Y and Yb, and Ca compounds as substances that improve oxygen overvoltage. 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 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, Examples thereof include ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, metal (nickel, gold, etc.) powder, one kind of conductive material such as metal fiber, or a mixture of two or more kinds.
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 Examples thereof include a single type of polymer having rubber elasticity such as a single type or a mixture of two or more types. 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.
Examples of the thickener include one kind of a polysaccharide such as carboxymethylcellulose, methylcellulose, and xanthan gum, or a mixture of two or more kinds. 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 any particular limitation. Examples of the current collector include those made of nickel or nickel-plated steel plate as a material from the viewpoint of reduction resistance and oxidation resistance. Examples of the shape of the current collector include a foam, a molded product of a fiber group, a three-dimensional base material subjected to uneven processing, or a two-dimensional base material such as a punching plate. Moreover, there is no limitation in particular also about the thickness of this electrical power collector, Usually, the thing of 5-700 micrometers is illustrated.
Among these current collectors, for the positive electrode, those made of nickel having excellent corrosion resistance and oxidation resistance to alkali and having a porous structure having a structure excellent in current collection are preferable. For the negative electrode, a punching plate obtained by nickel plating on an iron foil that is inexpensive and excellent in conductivity is preferable.
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.

The separator of the nickel metal hydride storage battery is preferably composed of a porous film or a nonwoven fabric exhibiting excellent rate characteristics 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.
Further, the separator is preferably subjected to a hydrophilic treatment. Examples of the separator include those obtained by subjecting the surface of a polyolefin resin fiber such as polypropylene to a sulfonation treatment, a corona treatment, a fluorine gas treatment, a 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 alkaline electrolyte constituting the nickel metal hydride storage battery preferably contains at least one of sodium ion, potassium ion and lithium ion, and the total ion concentration is 9.0 mol / liter or less, and the total ion concentration is What is 5.0-8.0 mol / liter is still more preferable.

  In addition, various additives may 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. Examples of the additive include oxides such as yttrium, ytterbium, erbium, calcium, and zinc, one kind of a hydroxide or the like, or a mixture of two or more kinds.

  When the nickel-metal hydride storage battery of this embodiment is an open-type nickel-metal hydride storage battery, the battery, for example, sandwiches the negative electrode with the positive electrode via a separator and fixes these electrodes so that a predetermined pressure is applied to these electrodes. Then, it can be produced by injecting an electrolyte and assembling an open cell.

  When the nickel metal hydride storage battery of this embodiment is a sealed nickel metal hydride storage battery, the battery is injected with the electrolyte before or after the positive electrode, the separator, and the negative electrode are stacked, and is sealed with an exterior material. Thus, it can be suitably manufactured. 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.

The hydrogen storage alloy of this embodiment and the nickel hydride storage battery of this embodiment are as illustrated above, but the present invention is not limited to the above illustrated hydrogen storage alloy and the above example nickel hydride storage battery.
That is, various forms used in a general hydrogen storage alloy can be adopted as long as the effects of the present invention are not impaired. Moreover, the various aspects used in a general nickel hydride storage battery can be employ | adopted in the range which does not impair the effect of this invention.
For example, the hydrogen storage alloy of the present embodiment, when one in which as described above chemical composition represented by the general formula _{La v Sm w M1 x M2 y} M3 z, in the hydrogen storage alloy of the present invention, the general formula As long as the above condition is satisfied, an element not defined by the general formula may be included as long as the effects of the present invention are not impaired.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
A hydrogen storage alloy was produced by the following method.
A predetermined amount of the raw material ingot was weighed so as to have the chemical composition of Example 1 shown in Table 1, placed in a crucible, and heated to 1500 ° C. using a high-frequency melting furnace in a reduced pressure argon gas atmosphere to dissolve the material. After melting, it was quenched by applying a melt spinning method to solidify the alloy.
Next, the obtained alloy was heat-treated at 910 ° C. for 5 hours under an argon gas atmosphere pressurized to 0.2 MPa (gauge pressure, the same applies hereinafter), and then the obtained hydrogen storage alloy was pulverized. Thus, a hydrogen storage alloy powder having an average particle size (D50) of 50 μm was obtained.

(Examples 2-9)
A hydrogen storage alloy was prepared in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to the composition shown in Examples 2 to 9 of Table 1.

(Comparative Example 1)
A hydrogen storage alloy was produced in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to the composition shown in Comparative Example 1 of Table 1.

(Comparative Examples 2 to 25)
A hydrogen storage alloy was prepared in the same manner as in Example 1 except that the composition of the hydrogen storage alloy was changed to the composition shown in Comparative Examples 2 to 25 in Table 1.

Each example, the values of the composition of the hydrogen storage alloy of the comparative example, in the chemical composition represented by the general formula _{La v Sm w M1 x M2 y} M3 z, [z / (v + w + x + y)] (B / A ratio), Table 1 shows values of [v / (v + w + x)] (namely, La / (La + Pr + Nd + Sm)) and values of [w / (v + w + x)] (namely, Sm / (La + Pr + Nd + Sm)).

(Production of open-type nickel metal hydride battery)
After adding and mixing 3 parts by mass of nickel powder (INCO # 210) to 100 parts by mass of the hydrogen storage alloy powder obtained as described above, an aqueous solution in which a thickener (methylcellulose) is dissolved is added. A paste made of 1 part by weight of a binder (styrene butadiene rubber) was applied to both sides of a 35 μm-thick perforated steel sheet (opening ratio 50%), dried, and then pressed to a thickness of 0.33 mm. Thus, a negative electrode plate was obtained.
In addition, a sintered nickel hydroxide electrode having a capacity three times as large as the negative electrode capacity was used for the positive electrode plate.
An open cell was assembled by sandwiching the negative electrode with the positive electrode through a separator, fixing these electrodes so that a pressure of 1 kgf was applied to these electrodes, and injecting a 7M potassium hydroxide aqueous solution.

<Evaluation of open nickel metal hydride batteries>
At 20 ° C., charging for 15 hours at 0.1 ItA (30 mA / g), resting for 1 hour, repeating a charge / discharge cycle of discharging to −0.6 V with respect to the Hg / HgO reference electrode at 0.2 ItA, The number of cycles to reach capacity was determined.
The results are shown in Table 1 for the number of cycles to reach the maximum capacity.

(Production of negative electrode of sealed nickel-metal hydride battery)
The hydrogen storage alloy powder obtained as described above was immersed in an 8M aqueous potassium hydroxide solution at 110 ° C. for 2 hours, and then washed with water until the pH reached 10. An aqueous solution in which a thickener (methylcellulose) is dissolved is added to 100 parts by mass of the powder after drying, and 1 part by mass of a binder (styrene butadiene rubber) is added to form a paste, and a perforated steel sheet having a thickness of 35 μm ( It was applied to both surfaces having an aperture ratio of 50%) and dried, and then pressed to a thickness of 0.33 mm to obtain a negative electrode plate.

(Preparation of sealed nickel metal hydride battery positive electrode)
As the positive electrode active material, a nickel hydroxide surface containing 3% by mass of zinc and 0.6% by mass of cobalt in a solid solution state and coated with 6% by mass of cobalt hydroxide was used in an 18M sodium hydroxide solution. What was air-oxidized at 1 degreeC for 1 hour was used. An aqueous solution in which a thickener (carboxymethylcellulose) is dissolved, an active material, and further 2% by mass of ytterbium oxide are mixed to prepare a paste, filled in a nickel foam substrate, dried, and then given a predetermined thickness ( The positive electrode plate was formed by pressing to 0.93 mm.

(Production of sealed nickel-metal hydride batteries)
The positive electrode and the negative electrode were wound on a spiral through a separator at a ratio of 1.45 with respect to the positive electrode capacity 1 to form an electrode group, and stored in a cylindrical metal case. The value calculated from the filling amount of the positive electrode active material was used for the positive electrode capacity. The calculation formula was as follows: filling amount of positive electrode active material (g) × ratio of nickel hydroxide (including higher-order nickel compound) in positive electrode active material × 289 (mAh / g). As the negative electrode capacity, the maximum capacity obtained in the evaluation of the open nickel-metal hydride battery negative electrode was used. Next, 1.95 ml of an electrolyte composed of 7M potassium hydroxide and 0.8M lithium hydroxide was injected and sealed with a metal lid provided with a safety valve to produce a 2000 mAh AA size nickel metal hydride storage battery. did.

<Initialization>
The sealed nickel-metal hydride battery using the hydrogen storage alloy of each example and each comparative example was initialized by the following procedure. Initial charging was performed by charging for 10 hours at 40 ° C. with 0.02 It (A) (40 mA) and charging at 20 ° C. with 0.2 It (A) (400 mA) for 3 hours. Next, discharging was performed at 20 ° C. and 0.2 It (A) until the final voltage reached 1V. Charging after the second cycle was performed at 20 ° C. and 0.1 It (A) for 12 hours, and discharging was performed until 0.2 It (A) and the final voltage reached 1 V, and chemical conversion was performed. Similarly, initialization was performed by charging and discharging up to the third cycle.

<Evaluation of cycle life>
For sealed nickel-metal hydride batteries using the hydrogen storage alloys of Examples and Comparative Examples, charging under conditions of 0.5 It (A) and −dV = 5 mV, rest for 30 minutes, and end voltage at 1 It (A) The discharge (25 ° C.) until the voltage reached 1 V was repeated, and the cycle number when the discharge capacity reached 50% of the initial capacity was defined as the cycle life.

<Measurement of maximum internal pressure>
The internal pressure was measured by forming a 2 mm round hole in the battery case and connecting a pressure gauge to the formed battery. The maximum internal pressure up to 120% charge of 1 ItA was recorded.

  Table 1 shows the cycle life as cycle characteristics in the nickel-metal hydride storage batteries using the hydrogen storage alloys of the examples and comparative examples. The results obtained for the maximum internal pressure are shown in Table 1.

Chemical composition, represented by the general formula _{La v Sm w M1 x M2 y} M3 z, hydrogen storage alloy that satisfies the following formula (1), i.e., the hydrogen storage alloy B / A ratio is 3.2 to 3.7 In, although the pulverization can be suppressed, when the formula (2) or the formula (3) is not satisfied, the cycle life is not sufficient. On the other hand, when the formulas (2) and (3) are further satisfied, the increase in internal pressure is suppressed while the pulverization is suppressed, and as a result, the cycle life is excellent.
3.2 ≦ z / (v + w + x + y) ≦ 3.7 Formula (1)
0.60 ≦ v / (v + w + x) ≦ 0.85 Formula (2)
0.01 ≦ w / (v + w + x) ≦ 0.06 Formula (3)
More specifically, by satisfying the formula (3), that is, when the ratio of Sm to the total of rare earths La, Sm, Pr and Nd is 0.01 or more, the initial activity of the alloy is increased (maximum It is considered that the number of cycles until the capacity is reached is reduced, and the oxygen gas absorption performance is increased by increasing the surface area of the alloy. Further, it is considered that the pulverization of the alloy is suppressed when the ratio of Sm to the total of La, Sm, Pr and Nd which are rare earths is 0.06 or less.

  FIG. 1 is a graph showing the ratio of La to the total of rare earths La, Sm, Pr, and Nd on the horizontal axis and the cycle life on the vertical axis for each of Examples and Comparative Examples 1-24.

Moreover, the leaving performance was investigated about the battery in which the hydrogen storage alloy of each Example and each comparative example was used.
That is, batteries different from those used for cycle life evaluation were prepared, and after charging and discharging were repeated 100 cycles, charging was conducted and then the discharging capacity when left for 14 days was examined.
As a result, for the batteries using the hydrogen storage alloy of Comparative Example 25, a significant decrease in discharge capacity was observed, but for the batteries using the hydrogen storage alloys of other Examples and Comparative Examples, there was a decrease in capacity. Almost not recognized. This means that a minute short circuit occurred inside the battery using the hydrogen storage alloy of Comparative Example 25. This minute short circuit is considered to be caused by the fact that cobalt contained in the alloy was precipitated inside the battery and caused an internal short circuit. Thus, it can be said that the hydrogen storage alloy in which cobalt is not blended as a constituent element has an advantage that the internal short circuit is suppressed, and the alloy of the example has a cycle life due to the structure in which cobalt is not blended. The performance is excellent and at the same time the performance of maintaining the capacity after being left is enhanced.

  In addition, the crystal structures of the hydrogen storage alloys produced in each example and each comparative example were examined.

<Lamination structure analysis of crystal phase by TEM observation>
When the hydrogen storage alloy produced in each Example and each Comparative Example was observed with a transmission electron microscope (TEM), it was confirmed that the primary particles were polycrystalline.

<Structural analysis of crystal phase by X-ray diffraction>
The hydrogen storage alloys produced in each Example and each Comparative Example were subjected to structural analysis by X-ray diffraction measurement.
Specifically, after pulverizing the obtained hydrogen storage alloy with a mortar, using a powder X-ray diffractometer (RINT2400, manufactured by Rigaku Corporation), a gonio radius of 185 mm, a divergence slit of 1 deg., A scattering slit of 1 deg. .15 mm, X-ray source CuKα ray, tube voltage 50 kV, tube current 200 mA. The diffraction angle was 2θ = 15.0 to 85.0 °, the scan speed was 4.000 ° / min., And the scan step was 0.020 °. Based on the obtained X-ray diffraction results, structural analysis was performed by the Rietveld method (analysis software, using RIETA 2000).

  Table 2 shows the content of the crystal phase in the hydrogen storage alloys produced in each example and each comparative example.

Claims (6)

Chemical composition, a hydrogen storage alloy represented by the general formula _{La v Sm w M1 x M2 y} M3 z,
M1 is an element of Pr and / or Nd, M2 is an element containing at least Mg among Mg and Ca, M3 is a part of Ni or Ni, a group 6A element, a group 7A element, a group 8 element (Ni and (Except Pd), which is substituted with one or more elements selected from the group consisting of Group 1B elements, Group 2B elements, and Group 3B elements, and v, w, x, y and z are The following formula (1), formula (2) and formula (3)
3.2 ≦ z / (v + w + x + y) ≦ 3.7 Formula (1)
0.60 ≦ v / (v + w + x) ≦ 0.85 Formula (2)
0.01 ≦ w / (v + w + x) ≦ 0.06 Formula (3)
The hydrogen storage alloy characterized by satisfy | filling. M2 is Mg, and v, w, x, y and z are the following formulas (4) and (5).
3.5 ≦ z / (v + w + x + y) ≦ 3.7 Formula (4)
0.71 ≦ v / (v + w + x) ≦ 0.83 Formula (5)
The hydrogen storage alloy according to claim 1, wherein:   M3 is obtained by substituting Ni or a part of Ni with one or more elements selected from the group consisting of Al, Mn, Co, Cu, Fe, Cr and Zn, and La, Sm and M1 Including 17.3 atomic% to 19.2 atomic% in total, M2 from 3.0 atomic% to 3.9 atomic%, M3 from 77.8 atomic% to 78.7 atomic% The hydrogen storage alloy according to claim 1 or 2.   M1 contains at least Pr, The hydrogen storage alloy in any one of Claims 1-3 characterized by the above-mentioned.   The hydrogen storage alloy according to any one of claims 1 to 4, wherein Co is not blended.   A nickel-metal hydride storage battery comprising a negative electrode containing the hydrogen storage alloy according to claim 1.

Images