WO2019176148A1

WO2019176148A1 - Alloy powder for electrode, and alkaline storage battery negative electrode and alkaline storage battery using same

Info

Publication number: WO2019176148A1
Application number: PCT/JP2018/036628
Authority: WO
Inventors: 徹川勝; 大山　秀明; 後藤　浩之
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2018-03-16
Filing date: 2018-10-01
Publication date: 2019-09-19
Also published as: JP2021082376A

Abstract

This alloy powder for an electrode contains particles of a hydrogen storage alloy, wherein the particles include an aggregation portion in which nickel is aggregated. The hydrogen storage alloy contains an element L, an element E, Ni, and an element M. The element L is a Group-3 element in the periodic table, the element E is a Group-2 element in the periodic table, and the element M is at least one selected from the group consisting of Al and elements (exclusive of Ni) in the 4th to 6th periods of each of Groups 4 to 14 in the periodic table, and also contains Ag and Sn. With respect to the total of the elements L and E, the ratio x of Ni and the ratio y of the element M satisfy 2.50≤x+y≤4.50.

Description

Alloy powder for electrode, negative electrode for alkaline storage battery and alkaline storage battery using the same

The present disclosure relates to an electrode alloy powder containing a hydrogen storage alloy, an alkaline storage battery negative electrode and an alkaline storage battery using the same.

An alkaline storage battery (nickel metal hydride storage battery) using a negative electrode containing a hydrogen storage alloy as a negative electrode active material has been attracting attention as an alternative to a dry battery and a power source for an electric vehicle or the like.

The hydrogen storage alloy generally includes an element having a high hydrogen affinity and an element having a low hydrogen affinity. As the hydrogen storage alloy, for example, an alloy having a crystal structure such as AB ₅ type (for example, CaCu ₅ type), AB ₃ type (for example, CeNi ₃ type), or AB ₂ type (for example, MgCu ₂ type) is used. It has been. In these crystal structures, an element having high hydrogen affinity tends to be located at the A site, and an element having low hydrogen affinity tends to be located at the B site.

Attempts have been made to optimize the performance of the hydrogen storage alloy powder in order to improve the battery characteristics of alkaline storage batteries. For example, Patent Document 1 and Patent Document 2 propose a hydrogen storage electrode including a hydrogen storage alloy including a rare earth element, Ni, and another element as a hydrogen storage electrode having a large discharge capacity.

Japanese Patent Laid-Open No. 10-32223 JP 2014-88619 A

As the use of alkaline storage batteries expands, high discharge performance at low temperatures may be required. In order to enhance the discharge performance at low temperatures, it is generally necessary to increase the reactivity at low temperatures by increasing the reaction area of the hydrogen storage alloy. However, when the reaction area is increased, the deterioration of the hydrogen storage alloy tends to proceed and the life is shortened. Therefore, it is difficult to achieve both life performance and low temperature discharge performance in an alkaline storage battery using a hydrogen storage alloy.

One aspect of the present disclosure includes particles of a hydrogen storage alloy,
The particles include an agglomerated part in which nickel is agglomerated,
The hydrogen storage alloy includes element L, element E, Ni, and element M,
The element L is a periodic table group 3 element,
The element E is a periodic table group 2 element,
The element M is at least one selected from the group consisting of elements of the 4th to 6th periods (except for Ni) of the 4th to 14th groups of the periodic table, and Al, and Including Ag and Sn,
The ratio x of Ni and the ratio y of element M with respect to the total of element L and element E relate to electrode alloy powder satisfying 2.50 ≦ x + y ≦ 4.50.

Another aspect of the present disclosure relates to an alkaline storage battery negative electrode including the electrode alloy powder as a negative electrode active material.

Still another aspect of the present disclosure relates to an alkaline storage battery including a positive electrode, the negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.

In alkaline storage batteries, both life performance and low temperature discharge performance can be achieved.

It is a longitudinal section showing the structure of the alkaline storage battery concerning one embodiment of this indication typically.

[Alloy powder for electrodes]
The electrode alloy powder according to one aspect of the present disclosure includes particles of a hydrogen storage alloy. This particle includes an agglomerated part in which nickel is agglomerated. The hydrogen storage alloy includes an element L, an element E, Ni, and an element M. Element L is a periodic table group 3 element. Element E is a periodic table group 2 element. The element M is at least one selected from the group consisting of elements of the 4th to 6th periods (except for Ni) and Al of the 4th to 14th groups of the periodic table, and Ag. And Sn. The ratio x of Ni and the ratio y of element M with respect to the total of element L and element E satisfy 2.50 ≦ x + y ≦ 4.50.

In the above composition of the hydrogen storage alloy, x + y is a ratio of an element mainly located at the B site to an element mainly located at the A site, and is generally called a B / A ratio. The hydrogen storage alloy having a B / A ratio of 2.50 or more and 4.50 or less has an AB ₃ type crystal structure as a main crystal structure, and is sometimes called an AB ₃ type hydrogen storage alloy.

In order to enhance the discharge performance of alkaline storage batteries at low temperatures, it is generally necessary to increase the reaction area of hydrogen storage alloy particles to increase the reactivity at low temperatures. However, when the reaction area is increased, the deterioration of the hydrogen storage alloy particles easily progresses, so that the life performance of the battery decreases.

In this embodiment, particles of a hydrogen storage alloy having an agglomerated part (hereinafter also referred to as a Ni agglomerated part) in which nickel is aggregated and having the above composition (in particular, including Ag and Sn) are used. Thereby, while being able to ensure high reaction activity, the discharge | release of hydrogen at the time of discharge from a hydrogen storage alloy can be performed smoothly. Therefore, high discharge performance (or output performance) at low temperatures can be ensured without increasing the reaction area. Moreover, the fall of lifetime performance can be suppressed by the increase in the reaction area of a hydrogen storage alloy being suppressed. Therefore, both life performance and discharge performance at a low temperature can be achieved. Although the detailed mechanism that can achieve both the life performance and the discharge performance at low temperature is not clear, it is presumed mainly due to the following reasons.

Since Ag and Sn each easily form a hydride, they easily hold hydrogen. In particular, Sn present in the vicinity of Ag is more likely to form a hydride due to the high conductivity of Ag. And Ag becomes easier to hold | maintain hydrogen by interacting with Sn which exists near Ag. The Ni agglomerated part is formed by surface-treating the hydrogen storage alloy particles. When the hydrogen storage alloy particles contain Ag, Ag tends to segregate on the surface of the particles during the surface treatment. Therefore, particularly at the surface of the hydrogen storage alloy particles and in the vicinity thereof, a large amount of hydrogen is retained during charging due to the interaction between Ag and Sn. Hydrogen retained on the surface of such alloy particles and in the vicinity thereof is easily released during discharge even in a low temperature environment. The Ni agglomerated part is a magnetic substance cluster (magnetic substance) containing metallic nickel as a main component, has a catalytic action in diffusion of hydrogen, and has high conductivity. Due to this catalytic action and the Ni agglomerated part and the high conductivity of Ag, the hydrogen retained on the surface of the hydrogen storage alloy by Ag and Sn and in the vicinity thereof is more likely to be released during discharge even in a low temperature environment. The diffusion rate of hydrogen from inside the particles is also increased. Therefore, when hydrogen held on the surface of the alloy particles and the vicinity thereof is released during the discharge, hydrogen is successively supplied from the inside of the alloy particles to the surface of the alloy particles and the vicinity thereof, and the discharge reaction occurs smoothly. . That is, the release of hydrogen held on the surface of the alloy particles and in the vicinity thereof triggers the release of hydrogen from the alloy particles during discharge. Therefore, hydrogen release during discharge can proceed smoothly even in a low temperature environment.

In addition, the hydrogen storage alloy having an AB ₃ type crystal structure has a relatively high capacity, but is easily deteriorated by elution of constituent elements, and it is difficult to ensure high life performance. In the present disclosure, although the hydrogen storage alloy including the AB ₃ type crystal structure that easily deteriorates is used, the alloy particles contain Sn, thereby suppressing the pulverization of the alloy particles and increasing the reaction area. Is suppressed. Moreover, oxidation resistance improves by containing Ag. In addition to these effects, high hydrogen storage capacity and smooth hydrogen release described above can ensure high discharge performance at low temperatures without increasing the reaction area, and can also ensure high life performance. .

The discharge performance at low temperatures is often evaluated at temperatures up to about −20 ° C., but in recent years, high discharge performance is being demanded even at temperatures below −20 ° C. In the present disclosure, hydrogen discharge during discharge can proceed smoothly as described above, so that high discharge performance can be ensured even at temperatures lower than −20 ° C. (eg, about −30 ° C.).

Note that in the hydrogen storage alloy, 50% or more of the crystal structure may be an AB ₃ type crystal structure, and 70% or more may be an AB ₃ type crystal structure. When the crystal structure is measured at any of a plurality of locations (for example, 10 locations) on the cross section and / or the surface of the hydrogen storage alloy particles, the ratio is mainly 50% or more when the ratio of the locations showing the AB ₃ type crystal structure is 50% or more. It is assumed that the crystal structure has an AB ₃ type crystal structure. In addition, although the particle | grains which measure a crystal structure may be one, it is preferable to measure a crystal structure about several particle | grains selected arbitrarily. In the present disclosure, in the hydrogen storage alloy particles, the AB ₃ type crystal structure portion may have the above composition. The crystal structure of the hydrogen storage alloy can be evaluated by X-ray diffraction.

In the present disclosure, the ratio of elements in the hydrogen storage alloy is the atomic ratio of each element contained in the hydrogen storage alloy. For example, the Ni ratio x is the ratio of the number of Ni element atoms to the total number of element L and element E atoms in a hydrogen storage alloy (particularly at least part of the AB ₃ type crystal structure). The ratio of other elements is the same as that of Ni.

Hereinafter, the electrode alloy powder will be described in more detail.

The hydrogen storage alloy particles have Ni agglomerated parts. The Ni agglomerated part is a magnetic substance cluster (magnetic substance) whose main component is metallic nickel. For example, metallic nickel segregates on the surface or surface layer of the hydrogen storage alloy and aggregates to form magnetic clusters. In the magnetic substance cluster, the metallic nickel is aggregated in a crystalline form and / or an amorphous form. The magnetic substance cluster functions as a catalyst for a hydrogen transfer reaction (including a hydrogen diffusion reaction) by the hydrogen storage alloy.

The hydrogen storage alloy contains element L, element E, Ni and element M as essential components. In the hydrogen storage alloy, it is sufficient that at least a portion having an AB ₃ type crystal structure contains these essential components. The hydrogen storage alloy may contain other elements as optional components.

Element L is a periodic table group 3 element. The Group 3 elements of the periodic table include Sc, Y, lanthanoid elements, and actinoid elements. Lanthanoid elements include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Examples of actinoid elements include Ac, Th, Pa, and Np. The element L may contain one of these elements or a combination of two or more. The element L preferably includes at least one selected from the group consisting of Sc, Y, and a lanthanoid element, and particularly preferably includes at least one selected from the group consisting of Y and a lanthanoid element. When the element L contains Sc and / or a lanthanoid element, a high capacity is easily obtained. From the viewpoint of improving the corrosion resistance, the element L preferably contains Y.

Element E is a periodic table group 2 element. As the Group 2 element of the periodic table, Mg, Ca, Sr and Ba are preferable. The element E may contain 1 type of periodic table group 2 element, and may contain it in combination of 2 or more types. When the hydrogen storage alloy particles contain the element E, the activity with respect to hydrogen is increased, and the hydrogen storage amount is easily increased. From the viewpoint of securing a higher hydrogen storage amount, the element E preferably contains at least Mg. On the other hand, Mg easily elutes and tends to cause deterioration of the hydrogen storage alloy particles. According to the present disclosure, high discharge performance at a low temperature can be ensured without increasing the reaction area. Therefore, even when the hydrogen storage alloy particles contain Mg, deterioration of the hydrogen storage alloy particles can be suppressed. Therefore, the improvement effect of the hydrogen occlusion amount by Mg can be enjoyed effectively.

From the viewpoint of easily obtaining a high capacity while securing the Ni agglomerated part, the ratio x of Ni to the total of the elements L and E is preferably 3.0 or more. From the viewpoint of further increasing the capacity, the ratio x is more preferably 3.20 or more, further preferably 3.25 or more, and may be 3.30 or more. The upper limit of the ratio x may be determined so that x + y corresponding to the B / A ratio falls within the range described later.

The element M is at least one selected from the group consisting of elements in the 4th to 6th periods (except for Ni) of the 4th to 14th groups of the periodic table, and Al. Examples of Group 4 elements of the periodic table include Ti, Zr, Hf, and Rf. Examples of the Group 12 element include Zn. Examples of the Group 13 element include Ga and In in addition to Al. Examples of the Group 14 element include Ge and Sn. Among the elements M, examples of the transition metal element include V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Pd, Pt, Cu, Ag, and Au. Among the elements M, at least one selected from the group consisting of Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Ag, Zn, Al, Ga, In, Ge, and Sn Is preferred. When the hydrogen storage alloy contains these elements M, it is possible to suppress the formation of significant crystal defects accompanying the storage and release of hydrogen, and it is easy to obtain high charge / discharge characteristics and to reduce costs.

In the hydrogen storage alloy, element L and element E are likely to be located at the A site, and Ni and element M are likely to be located at the B site. 2. The ratio x of Ni to the sum of element L and element E and the ratio y of element M: x + y (= B / A ratio) is 2.50 or more, preferably 3.20 or more. 30 or more or. More preferably, it is 3.35 or more. x + y (= B / A ratio) is 4.50 or less, and preferably 3.90 or less. When x + y is in such a range, it is easier to achieve both life performance and low-temperature discharge performance. Further, high reaction activity and high capacity can be ensured. From the viewpoint of easily ensuring a higher capacity, it is more preferable that x + y is 3.80 or less or 3.75 or less. These lower limit values and upper limit values can be arbitrarily combined.

According to the present disclosure, the element M includes at least Ag and Sn. By combining Ag, Sn, and Ni agglomerated part, as described above, high discharge performance at a low temperature can be secured and high life performance can be obtained while suppressing an increase in reaction area.

The ratio y1 of Ag to the total of the elements L and E is preferably 0.010 or more, more preferably 0.012 or more, and further preferably 0.015 or more. When the ratio y1 is in such a range, a hydride is easily formed and high conductivity is easily secured, so that the discharge performance at a low temperature can be further enhanced. The ratio y1 is 0.045 or less, preferably 0.040 or less, more preferably 0.037 or less or 0.035 or less. When the ratio y1 is in such a range, excessive segregation of Ag is suppressed and the ratio of Sn is easily adjusted appropriately, so that the effect of suppressing an increase in reaction area can be enhanced. These lower limit values and upper limit values can be arbitrarily combined.

The ratio of the ratio y2 of Sn to the total of element L and element E to y1 (= y2 / y1) is preferably 0.30 or more, preferably 0.40 or more, and 0.70 or more. It may be. y2 / y1 is preferably 3.0 or less, more preferably 2.4 or less, and may be 1.5 or less. When y2 / y1 is in such a range, the balance between the life performance and the discharge performance at a low temperature can be easily improved. These lower limit values and upper limit values can be arbitrarily combined.

The total of y1 and y2 is preferably 0.070 or less, but from the viewpoint of securing a higher capacity, 0.060 or less is preferable, and 0.050 or less is more preferable.

The element M preferably contains at least Ag, Sn, and Al. When the element M contains Al, it is easy to lower the hydrogen equilibrium pressure and easily obtain a high hydrogen storage capacity, but Al is easy to elute and easily deteriorates the hydrogen storage alloy particles. According to the present disclosure, high discharge performance at a low temperature can be ensured without increasing the reaction area. Therefore, even when the hydrogen storage alloy particles contain Al, deterioration of the hydrogen storage alloy particles can be suppressed. Therefore, the effect of improving the hydrogen storage amount by Al can be enjoyed effectively.

When the element M includes Al, the ratio y3 of Al to the total of the elements L and E is, for example, 0.01 or more, and preferably 0.03 or more. When y3 is in such a range, the hydrogen equilibrium pressure is likely to be lowered, and a high hydrogen storage capacity is easily obtained. From the viewpoint of easily suppressing the deterioration of the hydrogen storage alloy particles, y3 is, for example, 0.30 or less, and preferably 0.10 or less. These lower limit values and upper limit values can be arbitrarily combined.

From the viewpoint of life performance and / or high capacity, the average particle size of the hydrogen storage alloy particles is, for example, preferably 15 μm or more and 60 μm or less, and more preferably 20 μm or more and 50 μm or less.

In the present disclosure, the average particle diameter means a median diameter (D ₅₀ ) in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measuring device or the like.

The electrode alloy powder is, for example,
(I) Step A of forming an alloy from simple elements constituting the hydrogen storage alloy,
(Ii) Step B for granulating the alloy obtained in Step A, and (iii) Step C for activating the granular material obtained in Step B.

(I) Process A (alloying process)
In step A, for example, an alloy can be formed from simple constituent components by using a known alloying method. Examples of the alloying method include a plasma arc melting method, a high frequency melting (die casting) method, a mechanical alloying method (mechanical alloy method), a mechanical milling method, and / or a rapid solidification method (specifically, a metal material). Roll spinning method, melt drag method, direct casting and rolling method, spinning solution spinning method, spray forming method, gas atomization method, wet spraying method, splat method, rapid solidification described in application literature (Industry Research Committee, 1999) A thin band crushing method, a gas spray splat method, a melt extraction method, and / or a rotating electrode method can be used. These methods may be used alone or a plurality of methods may be combined.

In step A, simple substances of the respective constituent elements are mixed, and the resulting mixture can be alloyed by the above method or the like. The mixture may be melted by heating to alloy the constituent elements. For such alloying, for example, a plasma arc melting method, a high frequency melting (die casting) method, and a rapid solidification method (rotating disk method, single roll method, twin roll method, etc.) are suitable. Further, the rapid solidification method and the mechanical alloying method may be combined. In the rapid solidification method, a hydrogen storage alloy can be obtained by pouring a molten alloy onto a rotating disk or cooling roll and solidifying it by rapid cooling.

In step A, when mixing each elemental element alone, the atomic ratio, mass ratio, etc. of each element are adjusted so that the hydrogen storage alloy has a desired composition.

The molten alloy is solidified prior to granulation in step B. Solidification of the alloy can be performed by supplying the molten alloy to a mold or the like as necessary, and cooling in the mold. From the viewpoint of increasing the dispersibility of the constituent elements in the alloy, the supply rate and the like may be appropriately adjusted.

The solidified alloy may be heated (annealed) as necessary. By performing the heat treatment, the dispersibility of the constituent elements in the hydrogen storage alloy can be easily adjusted, the degree of elution and / or segregation of the constituent elements can be easily controlled, and the hydrogen storage alloy can be easily activated.

The heating is not particularly limited, and can be performed, for example, at a temperature of 900 to 1100 ° C. in an atmosphere of an inert gas such as argon.

(Ii) Process B (granulation process)
In step B, the alloy obtained in step A is granulated. The granulation of the alloy can be performed by wet pulverization, dry pulverization, or the like, and these may be combined. The pulverization can be performed by a ball mill or the like. In the wet pulverization, the solidified alloy is pulverized using a liquid medium such as water. In addition, you may classify the obtained particle | grains as needed.

The alloy particles obtained in the process B may be referred to as a raw material powder for the electrode alloy powder.

(Iii) Process C (activation process)
In Step C, the pulverized product (raw material powder) can be activated by bringing the pulverized product into contact with an alkali or an acid. The activity may be performed by either a liquid phase method or a gas phase method. The activation may be performed under heating (for example, under heating at 100 ° C. or higher) as necessary. The alkali or acid is preferably used as an aqueous solution. The contact between the aqueous solution of alkali or acid and the raw material powder is, for example, immersing the raw material powder in the aqueous solution, adding the raw material powder into the aqueous solution, stirring, or spraying the aqueous solution onto the raw material powder. Can be done.

As the alkali, for example, alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and / or lithium hydroxide can be used. Of these, sodium hydroxide and / or potassium hydroxide are preferably used. Examples of the acid include organic acids such as acetic acid. In addition, inorganic acids such as carbonic acid and hydrochloric acid may be used.

From the viewpoint of activation efficiency, productivity, and / or process reproducibility, the concentration of alkali or acid in the aqueous solution is, for example, 5 mass% or more and 50 mass% or less.

After the activation treatment with alkali or acid, the obtained alloy powder may be washed with water. In order to reduce the remaining impurities on the surface of the alloy powder, the water washing is preferably finished after the pH of the water used for washing becomes 9 or less.

The alloy powder after the activation treatment is usually dried.

The electrode alloy powder according to an embodiment of the present disclosure can be obtained through such a process. The obtained alloy powder can achieve both life performance and discharge performance in a low temperature environment. Therefore, the electrode alloy powder is suitable for use as a negative electrode active material of an alkaline storage battery.

(Alkaline battery)
The alkaline storage battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.

The negative electrode contains the above-mentioned electrode alloy powder as a negative electrode active material.

Hereinafter, the components of the alkaline storage battery will be described in more detail.

(Negative electrode)
The negative electrode is not particularly limited as long as it includes the above-described electrode alloy powder as a negative electrode active material, and other constituent elements known in the alkaline storage battery can be used.

The negative electrode may include a core material and a negative electrode active material attached to the core material. Such a negative electrode can be formed by attaching a negative electrode paste containing at least a negative electrode active material to a core material.

As the negative electrode core material, known materials can be used, and examples thereof include a porous or non-porous substrate formed of stainless steel, nickel or an alloy thereof. When the core material is a porous substrate, the active material may be filled in the pores of the core material.

The negative electrode paste usually contains a dispersion medium, and a known component used for the negative electrode, for example, a conductive agent, a binder, and / or a thickener may be added as necessary.

The negative electrode can be formed, for example, by applying a negative electrode paste to the core, removing the dispersion medium by drying, and compressing (or rolling).

As the dispersion medium, a known medium such as water, an organic medium, or a mixed medium thereof can be used.

The conductive agent is not particularly limited as long as it is a material having electronic conductivity. Examples thereof include graphite (natural graphite, artificial graphite, etc.), carbon black, conductive fibers, and / or organic conductive materials.

The amount of the conductive agent is, for example, 0.01 to 50 parts by mass, preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the electrode alloy powder.

The conductive agent may be added to the negative electrode paste and mixed with other components. The surface of the electrode alloy powder may be coated with a conductive agent in advance.

As the binder, a resin material, for example, a rubber-like material such as styrene-butadiene copolymer rubber (SBR), a polyolefin resin, a fluororesin such as polyvinylidene fluoride, and / or an acrylic resin (including its Na ion crosslinked product) And the like.

The amount of the binder is, for example, 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the electrode alloy powder.

Examples of the thickener include cellulose derivatives such as carboxymethyl cellulose (CMC) and modified products thereof (including salts such as Na salt), polyvinyl alcohol, and / or polyethylene oxide.

The amount of the thickener is, for example, 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the electrode alloy powder.

(Positive electrode)
The positive electrode may include a core material and an active material or an active material layer attached to the core material. The positive electrode may be an electrode obtained by sintering active material powder.

The positive electrode can be formed, for example, by attaching a positive electrode paste containing at least a positive electrode active material to the core material. More specifically, the positive electrode can be formed by applying a positive electrode paste to a core material, removing the dispersion medium by drying, and compressing (or rolling).

As the positive electrode core material, known materials can be used, and examples thereof include a nickel foam, and a porous substrate formed of nickel or a nickel alloy such as a sintered nickel plate.

As the positive electrode active material, for example, a nickel compound such as nickel hydroxide and / or nickel oxyhydroxide is used.

The positive electrode paste usually contains a dispersion medium, and a known component used for the positive electrode, such as a conductive agent, a binder, and / or a thickener, may be added as necessary. The dispersion medium, the conductive agent, the binder, the thickener, and the amounts thereof can be selected from the same or range as in the case of the negative electrode paste. As the conductive agent, conductive cobalt oxide such as cobalt hydroxide and / or γ-type cobalt oxyhydroxide may be used. Further, the positive electrode paste may contain, as an additive, a metal compound (oxide, and / or hydroxide) such as zinc oxide and / or zinc hydroxide.

(Separator)
As a separator, the well-known thing used for an alkaline storage battery, for example, a microporous film, a nonwoven fabric, or these laminated bodies, etc. can be used. Examples of the material of the microporous film or the nonwoven fabric include polyolefin resins such as polyethylene and polypropylene, fluorine resins, and / or polyamide resins. From the viewpoint of high decomposition resistance to an alkaline electrolyte, it is preferable to use a separator made of polyolefin resin.

It is preferable to introduce a hydrophilic group into a separator formed of a highly hydrophobic material such as a polyolefin resin by a hydrophilic treatment. Examples of the hydrophilic treatment include corona discharge treatment, plasma treatment, and sulfonation treatment. The separator may have been subjected to one kind of treatment among these hydrophilization treatments, or may be obtained by combining two or more kinds of treatments.

The separator is preferably at least partially sulfonated. The degree of sulfonation of a separator (such as a resin separator) may be, for example, 1 × 10 ⁻³ to 4.3 × 10 ⁻³ . The degree of sulfonation of a separator (such as a resin separator) is represented by the ratio of sulfur atoms to carbon atoms contained in the separator.

The thickness of the separator can be appropriately selected from a range of 10 μm to 300 μm, for example.

The separator preferably has a non-woven structure. Examples of the separator having a nonwoven fabric structure include a nonwoven fabric or a laminate of a nonwoven fabric and a microporous membrane.

(Alkaline electrolyte)
As the alkaline electrolyte, for example, an aqueous solution containing an alkali is used. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and sodium hydroxide. These can be used individually by 1 type or in combination of 2 or more types.

The electrolytic solution contains an anion and a cation from which alkali is dissociated. As the anion, a hydroxide ion is preferable. Examples of the cation include sodium ion, potassium ion, and lithium ion. The electrolytic solution may contain one or more of these cations. The electrolytic solution may contain an alkali that has not been dissociated.

From the viewpoint of further enhancing the deterioration suppressing effect of the hydrogen storage alloy and suppressing the decrease in life performance at high temperatures, the alkaline electrolyte preferably contains sodium ions. The alkaline electrolyte may contain sodium ions and potassium ions and / or lithium ions. When alkaline electrolyte containing sodium ion and potassium ion is used, high ion conductivity can be secured while suppressing deterioration of life performance at high temperature by suppressing deterioration of hydrogen storage alloy. The discharge performance can be further improved.

The concentration of sodium ions in the alkaline electrolyte is, for example, 3.5 mol / L or more, preferably 3.7 mol / L or more, and more preferably 4.0 mol / L or more. When the sodium ion concentration is in such a range, moderate ion conductivity can be secured and the effect of suppressing the deterioration of the hydrogen storage alloy is further enhanced. The sodium ion concentration in the alkaline electrolyte is, for example, 5.5 mol / L or less, and preferably 5.0 mol / L or less. When the sodium ion concentration is in such a range, the effect of suppressing a decrease in discharge performance under a cold environment is further enhanced. These lower limit values and upper limit values can be arbitrarily combined. When the undissociated sodium ion source is included in the alkaline electrolyte, the above concentration is the sum of the concentrations of the undissociated sodium ion source and dissociated sodium ions.

When the alkaline electrolyte contains sodium ions and potassium ions, the concentration ratio of sodium ions to potassium ions (= Na / K) is, for example, 1.0 or more, and preferably 1.1 or more. Na / K is, for example, 1.5 or less, and more preferably 1.3 or less. These lower limit values and upper limit values can be arbitrarily combined. When Na / K is in such a range, it is possible to ensure high life performance at high temperatures while ensuring high discharge performance in a low temperature environment. When the undissociated potassium ion source is included in the alkaline electrolyte, the concentration of potassium ions is the sum of the concentrations of the undissociated potassium ion source and the dissociated potassium ions.

The specific gravity of the alkaline electrolyte is, for example, 1.03 to 1.55, preferably 1.11 to 1.32.

The configuration of the alkaline storage battery will be described below with reference to FIG. FIG. 1 is a longitudinal sectional view schematically showing the structure of an alkaline storage battery according to an embodiment of the present disclosure. The alkaline storage battery includes a bottomed cylindrical battery case 4 also serving as a negative electrode terminal, an electrode group housed in the battery case 4 and an alkaline electrolyte (not shown). In the electrode group, the negative electrode 1, the positive electrode 2, and the separator 3 interposed therebetween are spirally wound. A sealing plate 7 including a safety valve 6 is disposed in the opening of the battery case 4 via an insulating gasket 8, and the alkaline storage battery is hermetically sealed by caulking the opening end of the battery case 4 inward. The sealing plate 7 also serves as a positive electrode terminal, and is electrically connected to the positive electrode 2 via the positive electrode lead 9.

In such an alkaline storage battery, an electrode group is accommodated in a battery case 4, an alkaline electrolyte is injected, a sealing plate 7 is disposed in an opening of the battery case 4 via an insulating gasket 8, and the battery case 4 Can be obtained by caulking and sealing. At this time, the negative electrode 1 of the electrode group and the battery case 4 are electrically connected via a negative electrode current collector plate disposed between the electrode group and the inner bottom surface of the battery case 4. Further, the positive electrode 2 of the electrode group and the sealing plate 7 are electrically connected via the positive electrode lead 9.

[Example]
Hereinafter, although this indication is explained concretely based on an example and a comparative example, this indication is not limited to the following examples.

Examples 1 to 7 and Comparative Examples 1 to 8
(1) Preparation of raw material powder The simple substance of each element shown in Table 1 was mixed in the ratio which becomes a coefficient ratio shown in Table 1, and it fuse | melted with the high frequency melting furnace. The molten metal was poured into a mold to produce an ingot. The obtained ingot was heated at 1060 ° C. for 10 hours under an argon atmosphere. The heated ingot was pulverized into coarse particles. The obtained coarse particles were pulverized in the presence of water using a wet ball mill and sieved with a sieve having a mesh size of 75 μm in a wet state to obtain a raw material powder containing hydrogen storage alloy particles having an average particle size of 20 μm.

(2) Production of electrode alloy powder The raw material powder obtained in (1) above was mixed with an aqueous alkali solution containing 100% by mass of sodium hydroxide at a concentration of 40% by mass, and stirring was continued for 50 minutes. . The obtained powder was collected, washed with warm water, dehydrated and dried. Washing was performed until the pH of the hot water after use was 9 or less. As a result, an electrode alloy powder having a Ni agglomerated part was obtained. Hydrogen storage alloy electrode alloy powder composition formula can be expressed by _{_{_{L 1-α E α Ni x}}} M y. When the crystal structure of the hydrogen storage alloy was confirmed by X-ray diffraction, it was confirmed that it had an AB ₃ type crystal structure.

(3) Production of negative electrode 0.15 parts by mass of CMC (degree of etherification 0.7, degree of polymerization 1600), 0.3 parts by mass of acetylene black with respect to 100 parts by mass of the electrode alloy powder obtained in (2) above And 0.7 parts by mass of SBR were added, and water was further added and kneaded to prepare a negative electrode paste. The obtained negative electrode paste was applied to both surfaces of a core material made of nickel-plated iron punching metal (thickness 60 μm, hole diameter 1 mm, hole area ratio 42%). The coating film of the paste was pressed with a roller together with the core material after drying. Thus, a negative electrode having a thickness of 0.4 mm, a width of 35 mm, and a capacity of 2200 mAh was obtained. An exposed portion of the core material was provided at one end portion along the longitudinal direction of the negative electrode.

(4) Production of positive electrode A sintered positive electrode having a capacity of 1500 mAh obtained by filling a positive electrode core material composed of a porous sintered substrate with a positive electrode mixture was prepared. The positive electrode mixture comprises about 90 parts by mass of Ni (OH) ₂ (positive electrode active material), about 6 parts by mass of Zn (OH) ₂ as an additive, and about 4 parts by mass of Co (OH) ₂ as a conductive agent. Including. An exposed portion of the core material that does not hold an active material having a width of 35 mm was provided at one end portion along the longitudinal direction of the positive electrode core material.

(5) Preparation of alkaline storage battery Using the negative electrode and positive electrode obtained above, an alkaline storage battery (nickel metal hydride storage battery) having a nominal capacity of 1500 mAh and a size of 4 / 5A as shown in FIG. 1 was prepared. Specifically, the positive electrode 2 and the negative electrode 1 were wound through a separator 3 to produce a cylindrical electrode plate group. In the electrode plate group, the exposed portion of the positive electrode core material and the exposed portion of the negative electrode core material were exposed on the opposite end surfaces. For the separator 3, a sulfonated polypropylene nonwoven fabric (thickness: 100 μm) was used. A positive electrode lead 9 was welded to the end face of the electrode plate group from which the positive electrode core material was exposed.

The negative electrode current collector plate was welded to the end face of the electrode plate group where the negative electrode core material was exposed. The sealing plate 7 and the positive electrode 2 were electrically connected through the positive electrode lead 9. Thereafter, the negative electrode current collector plate was turned downward, and the electrode plate group was accommodated in a battery case 4 formed of a cylindrical bottomed can. The negative electrode lead connected to the negative electrode current collector plate was welded to the bottom of the battery case 4. After the electrolyte solution was injected into the battery case 4, the opening of the battery case 4 was sealed with a sealing plate 7 having a gasket 8 on the periphery, thereby completing an alkaline storage battery.

Note that an alkaline aqueous solution (specific gravity: 1.23) in which sodium hydroxide and potassium hydroxide were dissolved in water as an alkali was used as the electrolytic solution. The sodium ion concentration in the alkaline aqueous solution was 4.0 mol / L, and the concentration of sodium ions with respect to potassium ions (= Na / K) was 1.10.

(6) Evaluation After the alkaline storage battery was activated by charging / discharging (temperature: 20 ° C., charging condition: 150 mA for 16 hours, discharging condition: 300 mA for 5 hours), the following (a) to (d) Was evaluated.

In addition, each evaluation result is represented by a ratio (%) when the evaluation result of Example 1 is set to 100. (A) Low temperature discharge performance and (b) lifetime performance are evaluated based on the internal resistance of the battery, respectively, and a smaller value means better performance. On the other hand, (c) high temperature charging efficiency and (d) room temperature discharge capacity indicate that the larger the value, the higher the performance.

(A) Discharge performance in a low temperature environment (low temperature discharge performance)
Evaluation was performed according to the following procedure using the internal resistance of the battery as an index of discharge performance in a low temperature environment.

A discharge and charge test was performed by discharging at a current of 300 mA in a 20 ° C. atmosphere until the voltage reached 1.0 V, and then charging for 16 hours at a current of 150 mA.

Thereafter, pulse charge / discharge was performed under the following conditions (i) to (iv) in an atmosphere of −10 ° C., and the internal resistance was calculated from the voltage drop after 10 seconds of discharge.
(I) Discharge: Pulse discharge for 20 seconds at a current of 750 mA, pause for 5 minutes, charge: Pulse charge for 20 seconds at a current of 750 mA, and pause for 5 minutes.
(Ii) Discharge: pulse discharge for 20 seconds at a current of 1500 mA, pause for 5 minutes of discharge, charge: pulse charge for 20 seconds at a current of 1500 mA, and pause for 5 minutes of charge.
(Iii) Discharge: Pulse discharge for 20 seconds at a current of 3000 mA, pause for 5 minutes, Charge: Pulse charge for 20 seconds at a current of 3000 mA, and pause for 5 minutes.
(Iv) Discharge: pulse discharge for 20 seconds at a current of 4500 mA, pause for 5 minutes, charge: pulse charge for 20 seconds at a current of 4500 mA, pause for 5 minutes.

The internal resistance was calculated from the four current values under these conditions and the voltage drop after 10 seconds of discharge.

(B) Lifetime performance Trickle charging was performed under the following conditions in an atmosphere at 70 ° C., and then discharging was performed.

Trickle charge: Charge for 60 days at 75 mA current.

Discharge: Discharge until the voltage reaches 1.0 V at a current of 300 mA.

This trickle charge and discharge were repeated three times to make a life test. Thereafter, an internal resistance test was performed under the same conditions (i) to (iv) as in (a) above, and the internal resistance after the life test was determined.

(C) High temperature charge efficiency The room temperature charge / discharge test and the high temperature charge test shown below were performed, and the ratio of the discharge capacity of the high temperature charge test to the discharge capacity of the room temperature charge / discharge test was determined as the high temperature charge efficiency.

(Normal temperature charge / discharge test)
Charge and discharge were performed under the following conditions in an atmosphere of 20 ° C.

Charging: Charging at a current of 150 mA for 16 hours in an atmosphere at 20 ° C., then left for 1 hour.

Discharge: Discharge at 20 ° C atmosphere at 300 mA current until the voltage reaches 1.0V.

(High temperature charge test)
Charging: Charging for 16 hours at a current of 150 mA in a 60 ° C. atmosphere, and then leaving it for 3 hours in a 20 ° C. atmosphere.

(D) Room temperature discharge capacity The discharge capacity of the room temperature charge / discharge test shown in (c) above was defined as room temperature discharge capacity.

Comparative Example 9
Using the raw material powder obtained in (1) of Example 2 as it was, a negative electrode was produced in (3). Hydrogen storage alloy material powder composition formula: L _1-alpha can be represented by E _alpha Ni _x M _y, no Ni agglomeration unit. When the crystal structure of the hydrogen storage alloy was confirmed by X-ray diffraction, it was confirmed that it had an AB ₃ type crystal structure.

Except for using the obtained negative electrode, an alkaline storage battery was prepared and evaluated in the same manner as in Example 1.

Comparative Examples 10-13
In Example 1 (1), single elements of each element shown in Table 1 were mixed at a ratio such that the coefficient ratio shown in Table 1 was obtained, and raw material powder was obtained in the same manner as in Example 1. Using the obtained raw material powder as it was, a negative electrode was produced according to (3). Hydrogen storage alloy material powder composition formula: L _1-alpha can be represented by E _alpha Ni _x M _y, no Ni agglomeration unit.

Table 1 shows the results of Examples 1 to 7 and Comparative Examples 1 to 13 together with the composition of the hydrogen storage alloy. Examples 1 to 7 are A1 to A7, and Comparative Examples 1 to 13 are B1 to B13.

As shown in Table 1, the low temperature discharge performance and / or the life performance are low in the comparative example, whereas the low temperature discharge performance and the life performance are compatible in the embodiment.

Compared with B1 that does not use Ag and Sn, the improvement effect of the life performance in B3 to B5 that does not use Sn is 16 to 22%, and the improvement effect of the life performance in B6 to B8 that does not use Ag is 2%. ~ 12%. From these results, it is estimated that the effect of improving the life performance when Ag and Sn are used is about 18 to 34%. However, in A1 to A7, the life performance is far improved (as much as 45 to 52% compared to B1) compared with B3 to B5 and B6 to B8. Even when Ag and Sn are used, both the low-temperature discharge performance and the life performance are greatly deteriorated when there is no Ni aggregation portion. Even in conventional alloy compositions B10 to B13, both the low temperature discharge performance and the life performance are low.

Examples 8-10
As shown in Table 2, a raw material powder was obtained in the same manner as in Example 2 except that x + y (B / A ratio) was changed by changing the Ni ratio x. When the crystal structure of the hydrogen storage alloy was confirmed by X-ray diffraction, it was confirmed that it had an AB ₃ type crystal structure. A negative electrode and an alkaline storage battery were produced and evaluated in the same manner as in Example 2 except that the obtained raw material powder was used.

The results of Examples 8 to 10 are shown in Table 2 together with the composition of the hydrogen storage alloy. Examples 8 to 10 are A8 to A10. Table 2 also shows the results of A1 and A2.

As shown in Table 2, when the B / A ratio (x + y) is greater than 3.10, the case where the B / A ratio is greater than 3.10 has higher low temperature discharge performance and life performance, and the high temperature discharge capacity is also higher. The B / A ratio is preferably 3.20 or more. In addition, the high temperature discharge capacity was higher when the B / A ratio was smaller than 3.90, compared to when the B / A ratio was 3.90. The B / A ratio is preferably 3.80 or less.

Examples 11-14
An alkaline storage battery was produced and evaluated in the same manner as in Example 2 except that the sodium ion concentration and the Na / K ratio in the alkaline electrolyte were changed as shown in Table 3.

The results of Examples 11 to 14 are shown in Table 3. Examples 11 to 14 are A11 to A14. Table 3 also shows the results of A1 and A2.

As shown in Table 3, when the sodium ion concentration and / or the Na / K ratio in the alkaline electrolyte is increased, the high temperature charge efficiency and the high temperature discharge capacity are improved. The sodium ion concentration is preferably 4.0 mol / L or more. Moreover, it is preferable that Na / K ratio is 1.1 or more.

The electrode alloy powder, the negative electrode for an alkaline storage battery, and the alkaline storage battery according to the present disclosure are excellent in discharge performance in a low temperature environment and in life performance. Therefore, for example, it is suitable for use as a power source for various electronic devices, transportation devices, power storage devices, and / or for an auxiliary power source or an emergency power source.

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Separator 4 Battery case 6 Safety valve 7 Sealing plate 8 Insulating gasket 9 Positive electrode current collecting plate

Claims

Including particles of hydrogen storage alloy,
The particles include an agglomerated part in which nickel is agglomerated,
The hydrogen storage alloy includes element L, element E, Ni, and element M,
The element L is a periodic table group 3 element,
The element E is a periodic table group 2 element,
The element M is at least one selected from the group consisting of elements of the 4th to 6th periods (except for Ni) of the 4th to 14th groups of the periodic table, and Al, and Including Ag and Sn,
The alloy powder for an electrode, wherein the ratio x of Ni and the ratio y of the element M with respect to the total of the element L and the element E satisfies 2.50 ≦ x + y ≦ 4.50.
2. The electrode alloy powder according to claim 1, wherein the x and the y satisfy 3.20 ≦ x + y.
The alloy powder for electrodes according to claim 1 or 2, wherein x and y satisfy x + y≤3.80.
The alloy powder for an electrode according to any one of claims 1 to 3, wherein a ratio y1 of Ag with respect to a total of the element L and the element E is 0.010 or more and 0.040 or less.
The ratio of Sn to the total of the element L and the element E is y2,
The electrode alloy powder according to claim 4, wherein a ratio of y2 to y1 is 0.40 or more and 2.4 or less.
6. The electrode alloy powder according to claim 1, wherein the element E includes at least Mg.
The electrode alloy powder according to any one of claims 1 to 6, wherein the element M contains at least Ag, Sn, and Al.
A negative electrode for an alkaline storage battery comprising the electrode alloy powder according to any one of claims 1 to 7 as a negative electrode active material.
An alkaline storage battery comprising: a positive electrode; a negative electrode according to claim 8; a separator interposed between the positive electrode and the negative electrode; and an alkaline electrolyte.
The alkaline electrolyte contains sodium ions,
The alkaline storage battery according to claim 9, wherein the concentration of the sodium ions in the alkaline electrolyte is 4.0 mol / L or more.
The alkaline electrolyte contains sodium ions and potassium ions,
11. The alkaline storage battery according to claim 9, wherein a ratio of the sodium ion concentration to the potassium ion concentration is 1.1 or more.