WO2015068331A1 - 電極用合金粉末、それを用いたニッケル水素蓄電池用負極およびニッケル水素蓄電池 - Google Patents
電極用合金粉末、それを用いたニッケル水素蓄電池用負極およびニッケル水素蓄電池 Download PDFInfo
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- H01M4/383—Hydrogen absorbing alloys
- H01M4/385—Hydrogen absorbing alloys of the type LaNi5
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to an alloy powder for an electrode, a negative electrode for a nickel-metal hydride storage battery using the same, and a nickel-metal hydride storage battery, and more particularly, to improvement of an alloy powder for an electrode using a hydrogen storage alloy.
- An alkaline storage battery using a negative electrode including a hydrogen storage alloy as a negative electrode active material is excellent in output characteristics and high in durability (for example, life characteristics and / or storage characteristics). Therefore, such alkaline storage batteries are attracting attention as, for example, replacements for dry batteries and power sources for electric vehicles and the like.
- lithium ion secondary batteries are also used for such applications, and therefore battery characteristics such as capacity, output characteristics, and / or life characteristics are further improved from the viewpoint of highlighting the advantages of alkaline storage batteries It is hoped that
- a hydrogen storage alloy generally contains an element having a high hydrogen affinity and an element having a low hydrogen affinity.
- a hydrogen storage alloy for example, one 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 is done. In these crystal structures, elements having high hydrogen affinity tend to be located at the A site, and elements having low hydrogen affinity tend to be located at the B site.
- Patent Document 1 includes a hydrogen storage alloy containing Nd and having a ratio of an element having a low hydrogen affinity to an element having a high hydrogen affinity (B / A ratio) of 3.40 to 3.60, and La. And a hydrogen storage alloy having a B / A ratio of 3.50 to 3.70.
- Patent Document 2 a hydrogen storage alloy having a B / A ratio of 2.5 to 4.5, and a hydrogen storage alloy having a B / A ratio of 4.5 to 5.5 having a content of 50% by mass or less In combination.
- a hydrogen storage alloy having a framework structure of a continuous alloy in a network shape is studied in the matrix of a hydrogen storage alloy from the viewpoint of enhancing capacity and life characteristics.
- JP 2012-156101 A Japanese Patent Application Publication No. 2006-40847 Japanese Patent Application Laid-Open No. 7-278708
- the hydrogen storage alloy used in Patent Document 1 has an AB 3 type crystal structure, so a high capacity can be easily obtained, but because the corrosion resistance is low, the metal contained in the hydrogen storage alloy is alkaline electrolytic Elutes easily in solution.
- the content of a hydrogen storage alloy having a low corrosion-resistant AB 3 type crystal structure is high, and even in the case of an AB 5 type hydrogen storage alloy, a metal, for example, a metal located at B site (for example, Co, Mn, Al) are easily eluted in the alkaline electrolyte. That is, in Patent Document 2, it is difficult to sufficiently improve the corrosion resistance of the hydrogen storage alloy.
- the metal eluted from the hydrogen storage alloy is deposited on a separator and / or an electrode or the like to cause a micro short circuit, which tends to cause self discharge.
- Patent Document 3 a hydrogen storage alloy matrix and a skeleton of an alloy formed in the matrix form mixed crystals. However, such mixed crystals are difficult to produce.
- an object of the present invention is to provide an alloy powder for an electrode, an electrode for a nickel-metal hydride storage battery, and a nickel-metal hydride storage battery useful for obtaining a nickel-metal hydride storage battery having high battery capacity and reduced self-discharge. Do.
- One aspect of the present invention relates to particles of a first hydrogen storage alloy having an AB 5 type crystal structure, a hydrogen storage alloy a having an AB 2 type crystal structure, and a hydrogen storage alloy b having an AB 3 type crystal structure It is a mixture containing particles of at least one type of second hydrogen storage alloy selected from the group consisting of, and the content of the first hydrogen storage alloy in the mixture is more than 50% by mass.
- Another aspect of the present invention relates to a negative electrode for a nickel-metal hydride storage battery including the above-described alloy powder for an electrode as a negative electrode active material.
- Yet another aspect of the present invention relates to a nickel-metal hydride storage battery comprising a positive electrode, the above negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.
- the nickel-metal hydride storage battery it is possible to suppress self-discharge due to a micro short circuit while securing a high capacity.
- the alloy powder for an electrode comprises particles of a first hydrogen storage alloy having a crystal structure of type AB 5 and a crystal structure of hydrogen storage alloys a and AB 3 type having a crystal structure of type AB 2 And a mixture of particles of at least one second hydrogen storage alloy selected from the group consisting of hydrogen storage alloys b having the following:
- the content of the first hydrogen storage alloy (that is, the first hydrogen storage alloy particles) in the mixture is more than 50% by mass.
- a hydrogen storage alloy having a crystal structure of AB 2 type (hereinafter, also simply referred to as AB 2 type hydrogen storage alloy) can easily obtain a high capacity to some extent, expansion and contraction due to storage and release of hydrogen are severe. Deterioration due to the occurrence of cracking is large, and it is difficult to obtain sufficient cycle characteristics.
- a hydrogen storage alloy having a AB 3 type crystal structure (hereinafter, also simply referred to as AB 3 type hydrogen storage alloy) is advantageous in terms of high capacity, it has low corrosion resistance and the metal contained in the hydrogen storage alloy is alkali It is easy to elute in the electrolyte. When the degree of elution is too large, the hydrogen storage alloy is deteriorated, and the cycle characteristics are degraded.
- AB 5 type hydrogen storage alloy an AB 5 type crystal structure
- AB 2 type hydrogen storage alloy an AB 2 type hydrogen storage alloy
- the hydrogen storage alloy Elution of metals from water can be a problem.
- the metal for example, Co, Mn, and / or Al
- the metal located at the A site is easily eluted into the electrolytic solution.
- activation of the hydrogen storage alloy is also important.
- it is effective to elute the metal from the vicinity of the surface of the hydrogen storage alloy particles.
- the capacity tends to be reduced.
- metals located at the B site tend to precipitate.
- segregation which tends to precipitate partially tends to occur.
- the alloy powder for an electrode comprises a first hydrogen storage alloy particle having a crystal structure of AB 5 type, and a second hydrogen storage alloy of AB 2 type hydrogen storage alloy and / or AB 3 type hydrogen storage alloy It is a mixture with particles, and the content of the first hydrogen storage alloy is more than 50% by mass.
- the electrode alloy powder is a mixture of the first hydrogen storage alloy particles and the second hydrogen storage alloy particles.
- a metal between metals of each crystal structure is present at and near the interface of each crystal structure.
- a bond is formed (i.e., alloyed), and the dissolution towards alkaline electrolyte differs from that of the mixture. Therefore, the interaction between the metal eluted from the first hydrogen storage alloy and the metal eluted from the second hydrogen storage alloy as described above can not be obtained, and the self-discharge suppression effect can not be obtained.
- the first hydrogen storage alloy having the AB 5 type crystal structure means, for example, one having a B / A ratio of 4.5 to 5.5
- the hydrogen storage alloy a having the AB 2 type crystal structure is For example, it means that the B / A ratio is 1.5 to 2.5
- the hydrogen storage alloy b having a crystal structure of AB 3 type means, for example, one having a B / A ratio of more than 2.5 and less than 4.5.
- the first hydrogen storage alloy preferably contains the element L 1 , the element M 1 , and Ni.
- the first hydrogen storage alloy may contain the element E 1 as an optional component.
- the element L 1 is at least one selected from the group consisting of Group 3 elements and Group 4 elements in the periodic table, and the element M 1 is an alkaline earth metal element.
- the periodic table Group 3 element, Sc, Y include lanthanoid elements, and actinide elements.
- the lanthanoid elements include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
- Examples of actinide elements include Ac, Th, Pa, and Np.
- the periodic table Group 4 element, Ti include Zr, and Hf.
- the element L 1 may contain one or more of these elements in combination.
- the element L 1 preferably contains at least one selected from the group consisting of Sc, Y, a lanthanoid element, Ti and Zr.
- the element L 1 preferably contains at least one selected from the group consisting of Y and a lanthanoid element.
- the alkaline earth metal element of the element M 1 includes Mg, Ca, Sr and Ba.
- the element M 1 may contain one or more of these alkaline earth metal elements in combination. By including such an element M 1 , an ion-binding hydride is easily formed, and the hydrogen storage capacity is enhanced, so that the capacity can be easily increased. Of the elements M, Mg and / or Ca are preferred.
- the element M 1 preferably contains at least Mg. Since Mg easily attracts oxygen molecules and migrates to the surface of the hydrogen storage alloy, a corrosion resistant protective film containing an oxide and / or hydroxide containing Mg and the like is formed on the surface of the hydrogen storage alloy. It will be formed. Although Mg metal is easy to dissolve in alkaline electrolyte, such a protective film is stable, and it is easy to secure high discharge characteristics, and elution of metal (such as metal located at B site) from the first hydrogen storage alloy As a result, the self-discharge suppression effect can be further easily obtained.
- the ratio of Mg to the element M 1 is, for example, 70 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more.
- the ratio of Mg to the element M 1 is 100 mol% or less.
- Element M 1 comprises Mg alone (that is, the ratio of Mg to total element M 1 is 100 mol%) preferably may.
- the molar ratio ⁇ is, for example, 0.133 or less, preferably 0.132 or less, and more preferably 0.13 or less. These lower limit value and upper limit value can be arbitrarily combined.
- the molar ratio ⁇ may be, for example, 0.037 ⁇ ⁇ ⁇ 0.133 or 0.04 ⁇ ⁇ ⁇ 0.133. When the molar ratio ⁇ is in such a range, it is easy to suppress the deterioration of the first hydrogen storage alloy, in addition to easily suppressing the decrease in corrosion resistance and the hydrogen storage ability with respect to the electrolytic solution.
- the first hydrogen storage alloy contains Ni as an essential component.
- the molar ratio x 1 of Ni to the total of the element L 1 and the element M 1 is, for example, 3.5 or more, preferably 3.6 or more, and more preferably 3.8 or more.
- the molar ratio of x 1 is, for example, 4.32 or less, preferably 4.31 or less, more preferably 4.3 or less. These lower limit value and upper limit value can be arbitrarily combined.
- the molar ratio x 1 may be, for example, 3.5 ⁇ x 1 ⁇ 4.32 or 3.6 ⁇ x 1 ⁇ 4.31. When the molar ratio x 1 is in such a range, it is easy to suppress a decrease in corrosion resistance to decrease and the electrolyte volume of the hydrogen storage alloy.
- the element E 1 is, for example, a transition metal element of the periodic table group 5 to 11 group (except Ni), a group 12 element, an element of the second to fifth period of the group 13, a group 14 And at least one element selected from the group consisting of P and P elements of the third to fifth periods.
- transition metal elements include V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Pd, Cu, Ag and the like.
- group 12 element include Zn
- examples of the group 13 element include B, Al, Ga, and In.
- As a 14th group element, Si, Ge, Sn etc. can be illustrated.
- the first hydrogen storage alloy can contain the element E 1 as an essential component.
- the element E 1 is at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Ag, Zn, Al, Ga, In, Si, Ge, and Sn. It is preferably a species.
- the element E 1 preferably contains at least Co, Mn and / or Al. Co, Mn and Al (in particular, Co and Mn) are easily eluted in the alkaline electrolyte. In the embodiment of the present invention, the self-discharge can be suppressed even in the case where the first hydrogen storage alloy contains such an easily eluted metal element.
- the Co enters the B site and the bond with the surrounding elements of Co tends to be strengthened, so that when hydrogen is absorbed and released, crystal defects are caused along with expansion and contraction of the alloy. It is easy to suppress generation.
- the molar ratio z 1a of Co to the total of the element L 1 and the element M 1 is 0.13 or more, preferably 0.15 or more, more preferably 0.3 or more or 0 .37 or more.
- the molar ratio z 1a of Co is 0.5 or less, preferably 0.47 or less, and more preferably 0.45 or less. These lower limit value and upper limit value can be arbitrarily combined.
- the molar ratio z 1a of Co may be, for example, 0.13 ⁇ z 1a ⁇ 0.5, or 0.15 ⁇ z 1a ⁇ 0.47.
- the ratio of Co, Mn and Al to the element E 1 is, for example, 80 mol% or more, preferably 85 mol%, in total of Co, Mn and Al. The above, more preferably 90 mol% or more.
- the ratio of Co, Mn and Al to the element E 1 is 100 mol% or less in total of Co, Mn and Al. It is also preferred if the element E 1 consists only of Co, Mn and / or Al.
- the hydrogen equilibrium pressure is easily lowered, so that a high hydrogen storage capacity is easily obtained.
- the element E 1 contains Al, it is effective to suppress cracking of the alloy in addition to facilitating adjustment of the hydrogen equilibrium pressure.
- the element E 1 preferably contains both Mn and Al.
- the ratio is preferably 0.33, more preferably 0.5 / 0.5 to 0.63 / 0.37.
- x 1 + z 1 corresponds to the B / A ratio.
- x 1 + z 1 is 4.5 or more, preferably 4.78 or more, and more preferably 4.79 or more or 4.8 or more.
- x 1 + z 1 is 5.5 or less, preferably 5.2 or less.
- x 1 + z 1 may be less than 5.03, and is preferably 5.025 or less or 5.02 or less.
- x 1 + z 1 is 4.5 ⁇ x 1 + z 1 ⁇ 5.5, 4.78 ⁇ x 1 + z 1 ⁇ 5.2, 4.79 ⁇ x 1 + z 1 ⁇ 5.03, or 4. 8 ⁇ x 1 + z 1 ⁇ 5.025.
- ratio of Nd accounts for L 1 is less than 5 wt%
- the hydrogen storage alloy ratio of La occupying the first hydrogen-absorbing alloy is not more than 23 mass% (hereinafter, also referred to as a first hydrogen storage alloy a).
- the element E 1 preferably contains at least one selected from the group consisting of Co, Mn and Al.
- the molar ratio of each element and the B / A ratio can be selected from the ranges described above.
- the molar ratio ⁇ of the element M 1 is preferably 0.045 ⁇ ⁇ ⁇ 0.133, and more preferably 0.04 ⁇ ⁇ ⁇ 0.13.
- the molar ratio x 1 of Ni is preferably 3.5 ⁇ x 1 ⁇ 4.32, and more preferably 3.6 ⁇ x 1 ⁇ 4.3.
- x 1 + z 1 is 4.78 ⁇ x 1 + z 1 ⁇ 5.03, and more preferably 4.8 ⁇ x 1 + z 1 ⁇ 5.03.
- the molar ratio z 1a of Co is preferably 0.13 ⁇ z 1a ⁇ 0.5, and 0.15 ⁇ z 1a ⁇ 0.45. More preferable.
- the element L 1 is preferably a lanthanoid element.
- the ratio of La to the first hydrogen storage alloy A is, for example, 23% by mass or less, preferably 22.5% by mass or less, and more preferably 22.3% by mass or less.
- the ratio of La to the first hydrogen storage alloy A is, for example, 20% by mass or more, preferably 21% by mass or more, and more preferably 21.5% by mass or more. These upper limit value and lower limit value can be arbitrarily combined.
- the ratio of La to the first hydrogen storage alloy A may be, for example, 20 to 23% by mass, or 21 to 22.5% by mass.
- the element L 1 occupies Nd in the element L 1 even if it does not contain or contains Nd.
- the ratio of is less than 5% by mass, preferably 3.5% by mass or less, more preferably 2% by mass or less.
- the average particle diameter D 1 of the first hydrogen absorbing alloy particles is, for example, 20 ⁇ 60 [mu] m, preferably 30 ⁇ 50 [mu] m, more preferably 30 ⁇ 40 [mu] m.
- the average particle diameter D 1 is in such a range, while easy to activate a first hydrogen-absorbing alloy, it is easy to suppress the micro short circuit.
- the average particle diameter means a volume-based median diameter.
- the content of the first hydrogen storage alloy (that is, the first hydrogen storage alloy particles) in the mixture is more than 50% by mass, preferably 60% by mass or more, and more preferably 70% by mass or more or 80% by mass or more It is.
- the content of the first hydrogen storage alloy in the mixture is, for example, 97% by mass or less, preferably 95% by mass or less, and more preferably 90% by mass or less. These lower limit value and upper limit value can be arbitrarily combined.
- the content of the first hydrogen storage alloy in the mixture may be, for example, 60 to 97% by mass, 60 to 95% by mass, or 70 to 95% by mass.
- the content of the first hydrogen storage alloy is 50% by mass or less
- the content of the second hydrogen storage alloy is relatively large, so that the metal from the second hydrogen storage alloy (for example, located at the B site)
- the elution amount of metal etc. is too large, and it becomes impossible to suppress metal deposition. Therefore, self-discharge becomes remarkable without being able to suppress a micro short circuit.
- the second hydrogen storage alloy particles are at least one selected from the group consisting of particles of AB 2 type hydrogen storage alloy a and particles of AB 3 type hydrogen storage alloy b.
- Hydrogen storage alloys a includes, for example, an element L 2, and Ni, and the element E 2.
- the element L 2 is preferably at least one selected from the group consisting of periodic table group 4 elements.
- the periodic table group 4 elements include Ti, Zr, and Hf.
- the hydrogen storage alloy a contains the element L 2 , it is considered that the element L 2 eluted from the second hydrogen storage alloy can interact with the metal eluted from the first hydrogen storage alloy to suppress self-discharge.
- the element L 2 preferably contains at least one selected from the group consisting of Ti and Zr. When the element L 2 comprises Ti and / or Zr, self-discharge inhibitory effect is remarkable.
- the element L 2 contains Zr and / or Ti, and may optionally contain Hf.
- the ratio of Zr and Ti to the element L 2 is, for example, 80 mol% or more, preferably 85 mol% or more, and more preferably 90 mol% or more in total of Zr and Ti.
- the ratio of Zr and Ti to the element L 2 is 100 mol% or less in total of Zr and Ti. Also preferred if the element L 2 is composed of only Zr and / or Ti, the element L 2 is preferably also include at least Zr.
- the molar ratio of Zr to Ti is, for example, 0.5 / 0.5 to 0.99 / 0.01, preferably 0. 6 / 0.4 to 0.95 / 0.05, more preferably 0.7 / 0.3 to 0.95 / 0.05.
- the molar ratio x 2 of the Ni to elemental L 2 is, for example, 0.8 ⁇ x 2 ⁇ 1.5, preferably 0.9 ⁇ x 2 ⁇ 1.4, more preferably at 1 ⁇ x 2 ⁇ 1.3 is there.
- the molar ratio x 2 is in such a range, it is easy to suppress a decrease in corrosion resistance to decrease and the electrolyte volume of the hydrogen storage alloy.
- the element E 2 is a transition metal element of the periodic table group 5 to 11 (except Ni), a group 12 element, an element of the second to fifth periods of the group 13, a group 14 of the group It is at least one selected from the group consisting of an element having a period of 3 to a period 5 and P.
- transition metal elements include V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Pd, Cu, Ag and the like.
- Elements other than the transition metal element are the same as those exemplified for the element E 1.
- the element E 2 is at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Ag, Zn, Al, Ga, In, Si, Ge, and Sn. It is preferably a species.
- the element E 2 preferably contains at least one selected from the group consisting of Al and Mn.
- the element E 2 preferably contains at least Al, and may contain at least Al and Mn.
- the ratio of Mn and Al to the element E 2 is, for example, 80 mol% or more, preferably 85 mol% or more, more preferably 90 in total of Mn and Al. It is mol% or more.
- the ratio of Mn and Al to the element E 2 is 100 mol% or less in total of Mn and Al.
- Element E 2 is preferably also made of only Mn and / or Al.
- Al and Mn easily lower the hydrogen equilibrium pressure of the hydrogen storage alloy a, so that high hydrogen storage ability can be easily obtained.
- V can reduce the hydrogen equilibrium pressure, it is disadvantageous in cost because the raw material metal V is expensive.
- Mn is also advantageous in that it is easy to increase the reaction activity when storing hydrogen. Further, Mn and Al are easily eluted from the hydrogen storage alloy a as in the case of the first hydrogen storage alloy. In the embodiment of the present invention, even in the case where such an element that easily elutes is included, self-discharge due to a micro short circuit can be suppressed.
- the molar ratio z 2a of Al to the element L 2 is, for example, 0.05 ⁇ z 2a ⁇ 0.35, preferably 0.1 ⁇ z 2a ⁇ 0.3. Preferably, 0.15 ⁇ z 2a ⁇ 0.25.
- the capacity can be easily increased, and self-discharge can be suppressed more effectively.
- x 2 + z 2 corresponds to the B / A ratio.
- x 2 + z 2 is 1.5 or more, preferably 1.7 or more, and more preferably 1.8 or more.
- x 2 + z 2 is 2.5 or less, preferably 2.2 or less, more preferably 2.1 or less or 2 or less.
- x 2 + z 2 is, 1.5 ⁇ x 2 + z 2 ⁇ 2.5,1.7 ⁇ x 2 + z 2 ⁇ 2.2,1.8 ⁇ x 2 + z 2 ⁇ 2.2 or 1.8 ⁇ , It may be x 2 + z 2 ⁇ 2.1.
- x 2 + z 2 is in the above range, it is easy to suppress the decrease in the releasability of the stored hydrogen and to reduce the decrease in the phase of the hydride capable of storing and releasing, so the effective capacity decreases. It is easy to control.
- the hydrogen storage alloy b can contain the element L 3 , the element M 2 , and Ni as essential components.
- the hydrogen storage alloy b may contain the element E 3 as an optional component.
- the element L 3 is at least one selected from the group consisting of Group 3 elements and Group 4 elements of the periodic table. As the periodic table group 3 element and the group 4 element, those exemplified for the element L 1 can be mentioned.
- the element L 3 preferably contains at least one selected from the group consisting of Sc, Y and a lanthanoid element (in particular, the group consisting of Y and a lanthanoid element).
- a lanthanoid element in particular, the group consisting of Y and a lanthanoid element.
- the lanthanoid elements La, Ce, Pr, Nd and Sm are preferred, and in particular, La and Sm are preferred.
- the element L 3 preferably contains Sc and / or a lanthanoid element, and more preferably contains a lanthanoid element (in particular, at least La).
- the element L 3 may contain a lanthanoid element (in particular, at least La) and at least one selected from the group consisting of Sc and a periodic table group 4 element.
- the element L 3 preferably contains at least Y.
- the element L 3 may contain Y and a lanthanoid element (particularly, at least La), and is selected from the group consisting of Y, a lanthanoid element (particularly, at least La), Sc, and a periodic table group 4 element It may include at least one type.
- Y has a strong affinity for oxygen and has the ability to reduce surrounding oxides. Therefore, when the element L 3 comprises Y, corrosion of the hydrogen storage alloy (especially corrosion at high temperatures), it can be suppressed more effectively.
- the reducing ability of Y can be explained by Pauling's electronegativity. Pauling's electronegativity is a measure of the tendency of atoms to attract electrons. The binding energy of an element is related to the square of the Pauling's electronegativity difference. The larger the difference in electronegativity, the larger the binding energy.
- the Pauling's electronegativity of the elements contained in the above-mentioned hydrogen storage alloy is 1.2 for Y, 1.8 for Ni, 1.8 for Co, and 1.5 for Al.
- O is 3.5 and Y is the largest difference from oxygen, and Y has strong binding energy to oxygen. That is, it can be seen that there is a strong affinity for oxygen.
- the hydrogen storage alloy b comprises a periodic table Group 3 element and / or Group IV element as the element L 3, a metal element L 3 eluted from the second hydrogen-absorbing alloy is eluted from the first hydrogen absorbing alloy It is thought that they can interact to suppress self-discharge.
- an element L 3 if it contains at least one selected from the group consisting of Ti and Zr, more likely higher self-discharge inhibition effect can be obtained.
- the alkaline earth metal element of the element M 2 includes Mg, Ca, Sr and Ba.
- the element M 2 may contain one or two or more of these alkaline earth metal elements. By including such an element M 2 , the activity to hydrogen is increased, and the hydrogen storage amount can be easily increased.
- Mg and / or Ca are preferred.
- the element M 2 preferably contains at least Mg, from the viewpoint of higher activity to hydrogen. When the element M 2 contains Mg, the ratio of Mg in the element M 2 can be appropriately selected from the same range as the ratio of Mg in the element M 1 .
- the molar ratio ⁇ is 0.54 or less, preferably 0.52 or less, and more preferably 0.5 or less or 0.35 or less. These lower limit value and upper limit value can be arbitrarily combined.
- the molar ratio ⁇ may be, for example, 0.008 ⁇ ⁇ ⁇ 0.52, 0.01 ⁇ ⁇ ⁇ 0.5, or 0.25 ⁇ ⁇ ⁇ 0.35. When the molar ratio ⁇ is in such a range, it is easy to suppress the deterioration of the hydrogen storage alloy b and to easily suppress the deterioration of the corrosion resistance.
- the molar ratio x 3 of Ni to the total of the element L 3 and the element M 2 is, for example, 1.6 or more, preferably 1.8 or more, and more preferably 2 or more.
- the molar ratio x 3 is 4 or less, preferably 3.5 or less, more preferably 3.3 or less. These lower limit value and upper limit value can be arbitrarily combined.
- the molar ratio x 3 may be, for example, 1.6 ⁇ x 3 ⁇ 4 or 2 ⁇ x 3 ⁇ 3.5. When the molar ratio x 3 is in such a range, a sufficiently high capacity can be easily secured while suppressing self-discharge.
- Element E 3 is a transition metal element of the periodic table group 5 to 11 (except Ni), an element of group 12, an element of period 2 to 5 of group 13, a group of group 14 It is at least one selected from the group consisting of N, P, and S elements of the 3rd to 5th periods. As each element, the same thing as what was described about element E 1 and element E 2 is mentioned.
- the hydrogen storage alloy b can contain the element E 3 as an essential component.
- Element E 3 is a transition metal element in any of Groups 5 to 11 of the periodic table (except Ni) among the above-mentioned element E 3 , a Group 12 element, and a period 2 to 5 of Group 13
- At least one element E 3a selected from the group consisting of elements, Si, and P can be included. It is selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Ag, Zn, B, Al, Ga, In, Si, and P among these elements E 3a At least one is preferred.
- the hydrogen storage alloy b contains the element E 3a , the generation of remarkable crystal defects can be more effectively suppressed along with the storage and release of hydrogen. Moreover, in addition to the fact that high charge and discharge characteristics are easily obtained, the cost can be easily reduced.
- the element E 3a preferably contains at least Al.
- the self-discharge can be suppressed even in the case where the element E 3a contains Al having high solubility in the electrolytic solution (that is, when the hydrogen storage alloy b contains Al).
- the molar ratio ⁇ 1 of Al to the total of the element L 3 and the element M 2 is, for example, 0.008 or more, preferably 0.01 or more, and more preferably Is 0.015 or more or 0.02 or more.
- Molar ratio gamma 1 is, for example, 0.32 or less, preferably 0.3 or less, more preferably 0.15 or less, or 0.1 or less (or 0.07 or less). These lower limit value and upper limit value can be arbitrarily combined.
- Molar ratio gamma 1 is, for example, 0.008 ⁇ ⁇ 1 ⁇ 0.32,0.01 ⁇ ⁇ 1 ⁇ 0.3 or a 0.01 ⁇ ⁇ 1 ⁇ 0.15,.
- the element E 3a may contain Al (element E 3a-1 ) and an element E 3a (element E 3a-2 ) other than Al.
- Molar ratio gamma 2 elements L 3 and the element E 3a-2 to the total of the element M 2 is greater than or equal to 0, preferably 0.01 or more, or 0.05 or more, more preferably 0.1 or more or 0.2 It is above.
- Molar ratio gamma 2 is preferably 0.8 or less, more preferably 0.75 or less. These lower limit value and upper limit value can be arbitrarily combined.
- Molar ratio gamma 2 for example, may be 0.01 ⁇ ⁇ 2 ⁇ 0.8 or 0.2 ⁇ ⁇ 2 ⁇ 0.75,.
- the element E 3a (or the element E 3a-2 ) contains at least Co.
- the element E 3a contains Co, the quantitative details are not clear, but when Co enters the B site, the bond with elements around Co is strengthened, so when hydrogen is absorbed and released. The formation of crystal defects can be more effectively suppressed with the expansion and contraction of the alloy. Therefore, even if charge and discharge are repeated, cracking of the alloy can be more effectively suppressed, whereby life deterioration can be more effectively suppressed.
- the molar ratio ⁇ 3 of Co to the total of the element L 3 and the element M 2 is, for example, preferably 0.2 ⁇ ⁇ 3 ⁇ 0.8, 0.25 ⁇ ⁇ More preferably, 3 ⁇ 0.75.
- Molar ratio gamma 3 is the case of such a range, it is easy to suppress the formation of crystal defects during insertion and extraction of hydrogen, for easily secured hydrogen storage sites, easily increase the capacity.
- Element E 3 may include at least one element E 3b is selected from the group consisting of Ge and Sn.
- Element E 3 is, when containing an element E 3b, liable composite hydroxide containing an element E 3b is formed, can more effectively suppress the deterioration of the hydrogen storage alloy b.
- Sn has the ability to suppress expansion and contraction when storing and releasing hydrogen. Therefore, when the element E 3 b contains Sn, expansion and contraction more than necessary can be suppressed particularly when storing and releasing hydrogen at a high temperature, whereby corrosion of the hydrogen storage alloy can be suppressed.
- the elements E 3 b when Ge is combined with Y as the element L 3 , a composite hydroxide containing Ge and Y is easily formed, so deterioration of the alloy can be more effectively suppressed.
- Molar ratio gamma 4 elements E 3b to the total of the elements L 3 and the element M 2 is 0.01 or more, preferably 0.015 or more.
- the molar ratio of gamma 4 is 0.12 or less, preferably 0.11 or less, more preferably 0.1 or less. These lower limit value and upper limit value can be arbitrarily combined.
- Molar ratio gamma 4 for example, 0.01 ⁇ ⁇ 4 ⁇ 0.11 or a 0.01 ⁇ ⁇ 4 ⁇ 0.1,.
- the molar ratio gamma 4 When the molar ratio gamma 4 is in such a range, the constituent elements of the alloy other than the elements E 3b is replaced unnecessarily, the capacity may be lowered, and / or durability by lattice defects are introduced Deterioration or the like is suppressed. In addition, even when the element E 3 b contains Sn, excessive segregation of Sn can be suppressed, and the decrease in conductivity at low temperatures can be suppressed.
- a hydrogen storage alloy b1 containing an element L 3a , Mg, Ni, Al and an element Ma is preferable.
- elements L 3a, of the element L 3 an element except Y, element M a is, Ge, at least one selected from the group consisting of Y and Sn (or at least two kinds) It is.
- the molar ratio of Mg in the total of the element L 3a and Mg can be selected from the same range as the molar ratio ⁇ of the element M 2 .
- the molar ratio of Ni to the total of element L 3a and Mg can be selected from the same range as the molar ratio x 3 of Ni, and the molar ratio of Al to the total of element L 3a and Mg is the same range as the molar ratio ⁇ 1 of Al
- You can choose from Molar ratio of the element M a of the total of the elements L 3a and Mg may be selected from the same range as the molar ratio gamma 4 elements E 3b.
- Such a hydrogen storage alloy b1 can easily improve the surface activity, and thus can improve discharge characteristics such as low temperature discharge characteristics.
- the metal elution resistance is improved, the deterioration of the hydrogen storage alloy b1 is suppressed, the life characteristics can be improved, and the capacity can be easily increased.
- x 3 + z 3 corresponds to the B / A ratio.
- x 3 + z 3 is greater than 2.5, preferably 2.7 or more, and more preferably 2.8 or more.
- x 3 + z 3 is less than 4.5, preferably 4 or less, more preferably 3.5 or less or 3.3 or less.
- x 3 + z 3 may be 2.5 ⁇ x 3 + z 3 ⁇ 4.5, 2.7 ⁇ x 3 + z 3 ⁇ 4, or 2.8 ⁇ x 3 + z 3 ⁇ 4.
- the second hydrogen storage alloy particles may contain only particles of hydrogen storage alloy a or particles of hydrogen storage alloy b, or may contain both particles of hydrogen storage alloy a and particles of hydrogen storage alloy b.
- the average particle diameter D 2 of the particles of the second hydrogen-absorbing alloy for example, 15 ⁇ 50 [mu] m, preferably 20 ⁇ 30 [mu] m, more preferably 20 ⁇ 27 [mu] m.
- the metal from the second hydrogen-absorbing alloy particularly, metal, etc. which is located at the A site
- the alloy powder for electrodes may be a mixture of the first hydrogen storage alloy particles and the second hydrogen storage alloy particles, and the surface of the first hydrogen storage alloy particles may be covered with the second hydrogen storage alloy particles, or The surface of the second hydrogen storage alloy particles may be covered with the first hydrogen storage alloy particles. It is more preferable from the viewpoint of suppressing the deposition of the metal eluted from the first hydrogen storage alloy particles in the state where the second hydrogen storage alloy particles are covered with the surface of the first hydrogen storage alloy particles.
- the ratio of the average particle diameter D 1 of the particles of the first hydrogen storage alloy to the average particle diameter D 2 of the particles of the second hydrogen storage alloy: D 1 / D 2 is, for example, 0.4 It is preferably 4 to 4, more than 1 and preferably 3 or less, and still more preferably 1.1 to 2.
- the alloy powder for an electrode according to the embodiment of the present invention is suitable for use as a negative electrode active material of a nickel-metal hydride storage battery because self-discharge due to a micro short circuit can be suppressed while securing a high capacity.
- the alloy powder for electrodes can be obtained by mixing the first hydrogen storage alloy particles and the second hydrogen storage alloy particles.
- the first hydrogen storage alloy particles and the second hydrogen storage alloy particles are respectively (I) Step A of forming an alloy from a single element of a constituent element of a hydrogen storage alloy, (Ii) Step B of granulating the alloy obtained in Step A, and (iii) Step C of activating the particles obtained in Step B, Can be obtained by
- an alloy can be formed from a single component of a component by using a known alloying method.
- a known alloying method for example, plasma arc melting method, high frequency melting (mold casting) method, mechanical alloying method (mechanical alloy method), mechanical milling method, rapid solidification method (specifically, metal material) Roll spinning method, melt drag method, direct casting / rolling method, spinning in liquid spinning method, spray forming method, gas atomization method, wet spraying method, splat method, rapid solidification described in the Encyclopedia (industry study group, 1999) etc.
- a ribbon grinding method, a gas spray splat method, a melt extraction method, a rotary electrode method, etc. can be used. These methods may be used alone or in combination of a plurality of methods.
- step A simple substances of the respective constituent elements are mixed, and the obtained mixture can be alloyed by the above method or the like.
- the mixture may be melted by heating to alloy constituent elements.
- alloy constituent elements for example, plasma arc melting, high frequency melting (die casting), and rapid solidification are suitable. Further, the rapid solidification method and the mechanical alloying method may be combined.
- the step A when mixing the single elements of the respective constituent elements, the molar ratio, mass ratio, and the like of each single 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 carried out by supplying the molten alloy as required to a mold or the like and cooling in the mold. From the viewpoint of enhancing the dispersibility of the constituent elements in the alloy, the supply rate may be appropriately adjusted.
- the obtained alloy (ingot) in a solidified state may be heat-treated, if necessary.
- the heating is not particularly limited, and can be performed, for example, at a temperature of 900 to 1200 ° C. under an inert gas atmosphere such as argon.
- Process B (granulation process)
- the alloy (specifically, the ingot) obtained in step A is granulated.
- Granulation of the alloy can be performed by wet grinding, dry grinding or the like, and these may be combined.
- Pulverization can be performed by a ball mill or the like. In wet grinding, a liquid medium such as water is used to grind an ingot. The particles obtained may be classified if necessary.
- the alloy particles obtained in step B may be referred to as a raw material powder of an alloy powder for an electrode.
- Step C activation step
- activation of the pulverized material can be performed by bringing the pulverized material into contact with an aqueous alkali solution.
- the contact between the alkaline aqueous solution and the raw material powder is not particularly limited.
- the raw material powder is immersed in the alkaline aqueous solution, the raw material powder is added to the alkaline aqueous solution and stirred, or the alkaline aqueous solution is used as the raw material powder. It can be carried out by spraying or the like. Activation may be carried out under heating, if necessary.
- aqueous alkali solution for example, an aqueous solution containing an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, lithium hydroxide and the like as an alkali can be used.
- an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, lithium hydroxide and the like
- sodium hydroxide and / or potassium hydroxide is preferably used.
- the concentration of alkali in the aqueous alkali solution is, for example, 5 to 50% by mass, preferably 10 to 45% by mass.
- the obtained alloy powder may be washed with water.
- the washing be completed after the pH of the water used for washing reaches 9 or less.
- the alloy powder after activation treatment is usually dried.
- the nickel-metal hydride storage battery comprises 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-described alloy powder for an electrode as a negative electrode active material.
- FIG. 1 is a longitudinal sectional view schematically showing the structure of a nickel-metal hydride storage battery according to an embodiment of the present invention.
- the nickel-metal hydride storage battery includes a bottomed cylindrical battery case 4 which doubles as a negative electrode terminal, an electrode group accommodated 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 provided with a safety valve 6 is disposed at the opening of the battery case 4 via an insulating gasket 8, and the nickel hydrogen storage battery is sealed by the opening end of the battery case 4 being crimped inward. .
- the sealing plate 7 also serves as a positive electrode terminal, and is electrically connected to the positive electrode 2 through the positive electrode lead 9.
- the electrode group is accommodated in the battery case 4, an alkaline electrolyte is injected, and the sealing plate 7 is disposed at the opening of the battery case 4 via the insulating gasket 8.
- the open end of 4 can be obtained by caulking and sealing.
- the negative electrode 1 of the electrode group and the battery case 4 are electrically connected via the negative electrode current collector plate disposed between the electrode group and the inner bottom surface of the battery case 4.
- the positive electrode 2 of the electrode group and the sealing plate 7 are electrically connected via the positive electrode lead 9.
- the negative electrode is not particularly limited as long as it contains the above-mentioned alloy powder for an electrode as a negative electrode active material, and other known components used in nickel-metal hydride storage batteries can be used as other components.
- the negative electrode may include a core material and a negative electrode active material attached to the core material.
- a negative electrode can be formed by attaching a negative electrode paste containing at least a negative electrode active material to a core material.
- a well-known thing can be used as a negative electrode core material, The porous or non-porous board
- 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 if necessary, known components used for the negative electrode, for example, a conductive agent, a binder, a thickener and the like may be added.
- the negative electrode can be formed, for example, by applying a negative electrode paste to a core material, removing the dispersion medium by drying, and rolling.
- known media such as water, organic media, mixed media thereof and the like can be used.
- the conductive agent is not particularly limited as long as it is a material having electron conductivity.
- graphites such as natural graphite (scaly graphite and the like), artificial graphite, expanded graphite and the like; carbon blacks such as acetylene black and ketjen black; conductive fibers such as carbon fiber and metal fiber; metal particles such as copper powder And organic conductive materials such as polyphenylene derivatives can be exemplified.
- These conductive agents may be used alone or in combination of two or more.
- artificial graphite, ketjen black, carbon fiber and the like are preferable.
- the amount of the conductive agent is, for example, 0.01 to 50 parts by mass, preferably 0.1 to 30 parts by mass, and more preferably 0.1 to 10 parts by mass, with respect to 100 parts by mass of the alloy powder for an electrode.
- 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.
- the coating of the conductive agent can be performed by a known method, for example, coating the surface of the alloy powder for electrode with a conductive agent, adhering a dispersion containing the conductive agent and drying it, or mechanically coating it by a mechanochemical method or the like. It can be done by
- binder resin materials, for example, rubber-like materials such as styrene-butadiene copolymer rubber (SBR); polyolefin resins such as polyethylene and polypropylene; polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene Fluorine resins such as copolymers and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers; Acrylic resins such as ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl acrylate copolymers and the like A Na ion crosslinked body etc. can be illustrated. These binders may be used alone or in combination of two or more.
- 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 alloy powder for an electrode.
- a thickener for example, carboxymethyl cellulose (CMC) and its modified products (including salts such as Na salts), cellulose derivatives such as methyl cellulose; saponified polymers having a vinyl acetate unit such as polyvinyl alcohol; polyethylene oxide etc. And polyalkylene oxides of the like.
- CMC carboxymethyl cellulose
- saponified polymers having a vinyl acetate unit such as polyvinyl alcohol
- polyalkylene oxides of the like can be used singly or in combination of two or more.
- 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 alloy powder for an electrode.
- the positive electrode may include a core and an active material or an active material layer attached thereto. Further, the positive electrode may be an electrode obtained by sintering the 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 a 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 rolling.
- a well-known thing can be used as a positive electrode core material
- the porous substrate formed with nickel or nickel alloys, such as a nickel foam and a sintered nickel board, can be illustrated.
- nickel compounds such as nickel hydroxide and nickel oxyhydroxide, are used, for example.
- the positive electrode paste usually contains a dispersion medium, and if necessary, known components used for the positive electrode, for example, a conductive agent, a binder, a thickener and the like may be added.
- the dispersion medium, the conductive agent, the binder and the thickener, and the amount thereof can be respectively selected from the same as or in the range of the negative electrode paste.
- the conductive agent conductive cobalt oxide such as cobalt hydroxide or ⁇ -type cobalt oxyhydroxide may be used.
- the positive electrode paste may also contain, as an additive, a metal compound such as zinc oxide or zinc hydroxide (such as an oxide or hydroxide).
- separator As the separator, known ones used for nickel-metal hydride storage batteries, for example, microporous membranes, non-woven fabrics, laminates of these, etc. can be used. Examples of the material of the microporous film and the non-woven fabric include polyolefin resins such as polyethylene and polypropylene; fluoro resins; and polyamide resins. It is preferable to use a separator made of a polyolefin resin from the viewpoint of high resistance to decomposition by an alkaline electrolyte.
- a hydrophilic group by a hydrophilization treatment it is preferable to introduce a hydrophilic group by a hydrophilization treatment to a separator formed of a highly hydrophobic material such as a polyolefin resin.
- a hydrophilization treatment corona discharge treatment, plasma treatment, sulfonation treatment and the like can be exemplified.
- the separator may be one obtained by performing one of these hydrophilization treatments, or one obtained by combining two or more treatments.
- a separator subjected to both corona discharge treatment and sulfonation treatment may be used.
- the separator is preferably at least a sulfonation treatment. Since the sulfonic acid treatment is introduced into the separator by the sulfonation treatment, the sulfonated separator has a sulfonic acid group.
- the thickness of the separator can be appropriately selected, for example, from the range of 10 to 300 ⁇ m, and may be, for example, 15 to 200 ⁇ m.
- the thickness of the separator is, for example, 10 to 100 ⁇ m, preferably 10 to 50 ⁇ m, and more preferably 15 to 40 ⁇ m.
- the thickness of the separator is, for example, 50 to 300 ⁇ m, preferably 70 to 200 ⁇ m, and more preferably 80 to 150 ⁇ m.
- the separator preferably has a non-woven structure.
- a non-woven fabric or a laminate of non-woven fabric and a microporous membrane can be exemplified as a separator having a non-woven fabric structure.
- the basis weight of the separator having the non-woven fabric structure is, for example, 35 to 70 g / m 2 , preferably 40 to 65 g / m 2 , and more preferably 45 to 55 g / m 2 .
- alkaline electrolyte As the alkaline electrolyte, for example, an aqueous solution containing an alkali (alkaline electrolyte) is used.
- alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide. These can be used singly or in combination of two or more.
- the alkaline electrolyte preferably contains at least sodium hydroxide as an alkali.
- the alkaline electrolyte may contain sodium hydroxide and at least one selected from the group consisting of potassium hydroxide and lithium hydroxide.
- the concentration of sodium hydroxide in the alkaline electrolyte is, for example, 5 to 40% by mass, preferably 9.5 to 35% by mass, or 9.7 to 33% by mass or more.
- concentration of sodium hydroxide is in such a range, the self-discharge characteristics can be further enhanced.
- the potassium hydroxide concentration in the alkaline electrolyte can be selected, for example, in the range of 0 to 45% by mass, and may be 0.05 to 41% by mass or 0.1 to 33% by mass.
- the concentration of potassium hydroxide in the alkaline electrolyte may be higher than the concentration of sodium hydroxide, but from the viewpoint of more effectively suppressing the self-discharge, water It may be smaller than the sodium oxide concentration.
- the alkaline electrolyte contains lithium hydroxide
- the lithium hydroxide concentration in the alkaline electrolyte can be appropriately selected, for example, from the range of 0 to 5% by mass from the viewpoint of securing high ion conductivity of the alkaline electrolyte, It may be 0.1 to 3% by mass, or 0.1 to 1% by mass.
- the specific gravity of the alkaline electrolyte is, for example, 1.03 to 1.55, preferably 1.11 to 1.32.
- Example 1 Preparation of first hydrogen storage alloy particles La, Ce, Mg, Ni, Co, Mn, and Al simplex each, the composition of the hydrogen storage alloy is La 0.66 Ce 0.27 Mg 0.07 Ni 4.00 Co 0.30 Mn 0.40 Al 0.30 The mixture was mixed in such a ratio as to be melted in a high frequency melting furnace. The molten metal was poured (supplied) into a mold at a speed of 2 m / min to produce an ingot. The resulting ingot was heated at 1060 ° C. for 10 hours under an argon atmosphere. The heated ingot was crushed 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 diameter of 75 ⁇ m in a wet state to obtain a raw material powder containing a hydrogen storage alloy having an average particle diameter of 20 ⁇ m.
- the obtained raw material powder was mixed with an aqueous alkali solution containing sodium hydroxide at a concentration of 40% by mass and at a temperature of 100 ° C., and stirring was continued for 50 minutes.
- the obtained powder was collected, washed with warm water, dried and dried. The washing was performed until the pH of the hot water after use became 9 or less. As a result, first hydrogen storage alloy particles from which impurities were removed were obtained.
- Second Hydrogen Storage Alloy Particles The single elements of Zr, Ti, Ni, Mn, and Al are mixed at such a ratio that the composition of the hydrogen storage alloy is Zr 0.9 Ti 0.1 Ni 1.2 Mn 0.6 Al 0.2
- the raw material powder is prepared in the same manner as the above step (1) except that heating of the ingot is performed for 6 hours at a temperature of 850.degree. C., and second hydrogen storage alloy particles (average particles having AB 2 type crystal structure). A diameter of 20 ⁇ m was produced.
- the first hydrogen storage alloy particles obtained in the above step (1) and the second hydrogen storage alloy particles obtained in the above step (2) are uniformly dispersed at a mass ratio of 75:25.
- An alloy powder for an electrode was prepared by mixing. 0.15 parts by mass of CMC (etherification degree 0.7, polymerization degree 1600), 0.3 parts by mass of acetylene black and 0.7 parts by mass of SBR are added to 100 parts by mass of the alloy powder for electrodes, and water is further added.
- the electrode paste was prepared by kneading. The obtained electrode paste was applied to both sides of a core made of nickel-plated iron punching metal (thickness 60 ⁇ m, hole diameter 1 mm, hole area ratio 42%).
- the paste coating was pressed by a roller with a core material.
- 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 along the longitudinal direction of the negative electrode.
- a sintered positive electrode with a capacity of 1500 mAh which was obtained by filling a positive electrode core material made of a porous sintered substrate with nickel hydroxide, was prepared. About 90 parts by mass of Ni (OH) 2 is used for the positive electrode active material, about 6 parts by mass of Zn (OH) 2 is added as an additive, and about 4 parts by mass of Co (OH) 2 is added as a conductive material did. An exposed portion of the core material not holding the active material was provided at one end along the longitudinal direction of the positive electrode core material.
- a nickel metal hydride storage battery having a 4/5 A size and a nominal capacity of 1,500 mAh as shown in FIG. 1 was manufactured.
- the positive electrode 1 and the negative electrode 2 were wound around the separator 3 to produce a cylindrical electrode plate group.
- the exposed portion of the positive electrode core material to which the positive electrode mixture was not attached and the exposed portion of the negative electrode core member to which the negative electrode mixture was not attached were exposed on the opposite end surfaces.
- a non-woven fabric thickness 100 ⁇ m, basis weight 50 g / cm 2 ) made of a sulfonated polypropylene is used.
- a positive electrode current collector plate was welded to the end face of the electrode plate group where the positive electrode core material is exposed.
- a negative electrode current collector plate was welded to the end face of the electrode plate group where the negative electrode core member is exposed.
- the sealing plate 7 and the positive electrode current collector were electrically connected through the positive electrode lead 9. Thereafter, with the negative electrode current collector plate facing downward, the electrode plate group was housed in the 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 electrolytic 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 at the periphery, to complete a nickel hydrogen storage battery (battery A1).
- alkaline aqueous solution which contains sodium hydroxide 31 mass%, potassium hydroxide 1 mass%, and lithium hydroxide 0.5 mass% as an alkali was used for electrolyte solution.
- Examples 2 to 6 and Comparative Examples 1 to 4 Nickel hydrogen storage batteries A2 to A6 and B1 to B4 were prepared in the same manner as in Example 1 except that the content (% by mass) of the first hydrogen storage alloy particles in the alloy powder for electrodes was changed as shown in Table 1. And evaluated.
- Example 7 and Comparative Example 5 Nickel hydrogen storage batteries A7 and B5 are prepared and evaluated in the same manner as Example 1 and Comparative Example 1 except that the second hydrogen storage alloy particles having the AB 3 type crystal structure are used as the second hydrogen storage alloy particles. Did.
- each element of Zr, La, Y, Mg, Ni, Al, Co, and Ge is used as a second hydrogen storage alloy particle having a crystal structure of AB 3 type.
- the composition of the hydrogen storage alloy is Zr 0.05 La 0.93 Y 0.01
- a raw material powder is produced in the same manner as in step (1) of Example 1 except that mixing is performed at a ratio such that Mg 0.01 Ni 2.75 Al 0.03 Co 0.30 Ge 0.01 is obtained, and second hydrogen storage alloy particles (average particle diameter 20 ⁇ m) was used.
- the results of Examples 1 to 7 and Comparative Examples 1 to 5 are shown in Table 1.
- the batteries A1 to A7 are examples, and the batteries B1 to B5 are comparative examples.
- the single electrode capacity of the negative electrode was high and the self-discharge rate was low compared to B4 using only the first hydrogen storage alloy particles.
- the high single electrode capacity of the negative electrode also increases the capacity of the battery.
- the self-discharge rate is also high.
- the self-discharge rate is high.
- the content of the second hydrogen storage alloy is relatively large, the amount of metal elution from the second hydrogen storage alloy becomes too large, so that the metal deposition can not be suppressed, and a micro short circuit is caused. It is thought that it could not be suppressed.
- an alloy powder for an electrode that can increase the capacity of the nickel-metal hydride storage battery and can suppress self-discharge. Therefore, in addition to replacement of dry batteries, it can be expected to be used as a power source for various devices, and also for applications such as a power source for hybrid vehicles.
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Abstract
Description
例えば、特許文献1では、Ndを含み、水素親和性の高い元素に対する水素親和性の低い元素の比率(B/A比)が3.40~3.60である水素吸蔵合金と、Laを含み、B/A比が3.50~3.70である水素吸蔵合金とを組み合わせている。
特許文献3では、容量および寿命特性などを高める観点から、水素吸蔵合金のマトリックス中に、網目状に連続する合金の骨格構造を有する水素吸蔵合金が検討されている。
特許文献2では、耐食性の低いAB3型の結晶構造を有する水素吸蔵合金の含有量が多い上、AB5型の水素吸蔵合金でも、金属、例えば、Bサイトに位置する金属(例えば、Co、Mn、Al)が、アルカリ電解液中に溶出し易い。つまり、特許文献2では、水素吸蔵合金の耐食性を十分に向上することは困難である。
水素吸蔵合金から溶出した金属はセパレータおよび/または電極などに析出して、微小短絡を起こし、これにより、自己放電が起こり易くなる。
[電極用合金粉末]
本発明の一実施形態に係る電極用合金粉末は、AB5型の結晶構造を有する第1水素吸蔵合金の粒子と、AB2型の結晶構造を有する水素吸蔵合金aおよびAB3型の結晶構造を有する水素吸蔵合金bからなる群より選択される少なくとも一種の第2水素吸蔵合金の粒子とを含む混合物である。この混合物中の第1水素吸蔵合金(つまり、第1水素吸蔵合金粒子)の含有量は、50質量%よりも多い。
AB5型水素吸蔵合金では、B/A比が大きいため、Bサイトに位置する金属(例えば、Co、Mn、および/またはAl)が電解液中に溶出し易くなる。AB2型水素吸蔵合金およびAB3型水素吸蔵合金では、Aサイトに位置する金属(周期表第3族金属および/または第4族金属など)が電解液に溶出し易い。
(第1水素吸蔵合金粒子)
第1水素吸蔵合金は、元素L1、元素M1、およびNiを含むことが好ましい。第1水素吸蔵合金は、任意成分として、元素E1を含んでもよい。元素L1は、周期表第3族元素および第4族元素からなる群より選択される少なくとも一種であり、元素M1は、アルカリ土類金属元素である。
元素L1と元素M1の合計に対するNiのモル比x1は、例えば、3.5以上であり、好ましくは3.6以上、さらに好ましくは3.8以上である。また、モル比x1は、例えば、4.32以下であり、好ましくは4.31以下、さらに好ましくは4.3以下である。これらの下限値と上限値とは任意に組み合わせることができる。モル比x1は、例えば、3.5≦x1≦4.32、または3.6≦x1≦4.31であってもよい。モル比x1がこのような範囲である場合、水素吸蔵合金の容量の低下および電解液に対する耐食性の低下を抑制し易い。
特に、元素E1は、Co、Mnおよび/またはAlを少なくとも含むことが好ましい。Co、MnおよびAl(特に、CoおよびMn)は、アルカリ電解液に溶出し易い。本発明の実施形態では、このような溶出し易い金属元素を第1水素吸蔵合金が含む場合であっても、自己放電を抑制できる。
なお、本明細書中、平均粒子径とは、体積基準のメディアン径を意味する。
第2水素吸蔵合金粒子は、AB2型水素吸蔵合金aの粒子およびAB3型水素吸蔵合金bの粒子からなる群より選択される少なくとも一種である。
水素吸蔵合金aは、例えば、元素L2と、Niと、元素E2とを含む。
元素L2は、周期表第4族元素からなる群より選択される少なくとも一種であることが好ましい。周期表第4族元素には、Ti、Zr、およびHfが含まれる。水素吸蔵合金aが元素L2を含むことで、第2水素吸蔵合金から溶出した元素L2が第1水素吸蔵合金から溶出した金属と相互作用して、自己放電を抑制できると考えられる。元素L2は、TiおよびZrからなる群より選択される少なくとも一種を含むことが好ましい。元素L2がTiおよび/またはZrを含む場合、自己放電抑制効果が顕著になる。元素L2は、Zrおよび/またはTiを含み、必要に応じて、Hfを含んでもよい。
元素E2がMnおよび/またはAlを含む場合、元素E2に占めるMnおよびAlの比率は、MnおよびAlの合計で、例えば、80モル%以上、好ましくは85モル%以上、さらに好ましくは90モル%以上である。元素E2に占めるMnおよびAlの比率は、MnおよびAlの合計で、100モル%以下である。元素E2が、Mnおよび/またはAlのみからなる場合も好ましい。
x2+z2が上記のような範囲である場合、吸蔵した水素の放出性の低下を抑制し易く、吸蔵放出可能な水素化物の相の減少を抑制し易いため、実効的な容量の減少を抑制し易い。
水素吸蔵合金bは、必須成分として、元素L3、元素M2、およびNiを含むことができる。水素吸蔵合金bは、任意成分として元素E3を含んでもよい。
元素L3は、周期表第3族元素および第4族元素からなる群より選択される少なくとも一種である。周期表第3族元素および第4族元素としては、元素L1について例示したものが挙げられる。
なお、Yの還元能は、Paulingの電気陰性度で説明できる。原子が電子を引き付ける傾向を示す尺度として、Paulingの電気陰性度がある。元素の結合エネルギーは、Paulingの電気陰性度の差の二乗に関連する。電気陰性度の差が大きいほど、結合エネルギーは大きい。上記の水素吸蔵合金に含まれる元素のPaulingの電気陰性度は、Yが1.2、Niが1.8、Coが1.8、Alが1.5である。一方、Oは3.5であり、酸素との差が最も大きいのは、Yであり、Yが、酸素に対して、強い結合エネルギーを有する。すなわち、酸素に対して強い親和性があることが分かる。
元素E3は、上記元素E3のうち、周期表第5族~第11族の遷移金属元素(ただし、Niを除く)、第12族元素、第13族の第2周期~第5周期の元素、Si、およびPからなる群より選択される少なくとも一種の元素E3aを含むことができる。これらの元素E3aのうち、V、Nb、Ta、Cr、Mo、W、Mn、Fe、Co、Cu、Ag、Zn、B、Al、Ga、In、Si、およびPからなる群より選択される少なくとも一種が好ましい。水素吸蔵合金bが、元素E3aを含む場合、水素の吸蔵および放出に伴って、顕著な結晶欠陥が生成するのを、より効果的に抑制できる。また、高い充放電特性が得られ易いことに加え、コストを低減し易い。
元素L3と元素M2の合計に対する元素E3a-2のモル比γ2は、0以上であり、好ましくは0.01以上または0.05以上、さらに好ましくは0.1以上または0.2以上である。モル比γ2は、好ましくは0.8以下、さらに好ましくは0.75以下である。これらの下限値と上限値とは任意に組み合わせることができる。モル比γ2は、例えば、0.01≦γ2≦0.8、または0.2≦γ2≦0.75であってもよい。
元素E3bのうち、Geは、元素L3としてのYと組み合わせた場合、GeおよびYを含む複合水酸化物が形成され易いため、合金の劣化をより効果的に抑制できる。
x3+z3が、このような範囲である場合、反応活性および充放電可能な容量の低下を抑制し易い。
電極用合金粉末は、第1水素吸蔵合金粒子と第2水素吸蔵合金粒子とを混合することにより得ることができる。
第1水素吸蔵合金粒子、および第2水素吸蔵合金粒子(具体的には、水素吸蔵合金aの粒子、および水素吸蔵合金bの粒子)は、それぞれ、
(i)水素吸蔵合金の構成元素の単体から合金を形成する工程A、
(ii)工程Aで得られた合金を粒状化する工程B、および
(iii)工程Bで得られた粒状物を活性化処理する工程C、
を経ることにより、得ることができる。
工程Aでは、例えば、公知の合金化方法を利用することにより、構成成分の単体から合金を形成できる。このような合金化方法としては、例えば、プラズマアーク溶融法、高周波溶融(金型鋳造)法、メカニカルアロイング法(機械合金法)、メカニカルミリング法、急冷凝固法(具体的には、金属材料活用事典(産業調査会、1999)などに記載されているロールスピニング法、メルトドラッグ法、直接鋳造圧延法、回転液中紡糸法、スプレイフォーミング法、ガスアトマイズ法、湿式噴霧法、スプラット法、急冷凝固薄帯粉砕法、ガス噴霧スプラット法、メルトエクストラクション法、回転電極法など)を用いることができる。これらの方法は、単独で用いてもよく、複数の方法を組み合わせてもよい。
工程Aにおいて、各構成元素の単体を混合する際には、水素吸蔵合金が所望の組成となるように、各単体のモル比、質量比などを調整する。
加熱は、特に制限されず、例えば、900~1200℃の温度で、アルゴンなどの不活性ガス雰囲気下で行うことができる。
工程Bでは、工程Aで得られた合金(具体的には、インゴット)を粒状化する。合金の粒状化は、湿式粉砕、乾式粉砕などにより行うことができ、これらを組み合わせてもよい。粉砕は、ボールミルなどにより行うことができる。湿式粉砕では、水などの液体媒体を用いてインゴットを粉砕する。なお、得られた粒子は、必要に応じて分級してもよい。
工程Bで得られる合金粒子を、電極用合金粉末の原料粉末と称する場合がある。
工程Cにおいて、粉砕物(原料粉末)の活性化は、粉砕物を、アルカリ水溶液と接触させることにより行うことができる。アルカリ水溶液と原料粉末との接触は、特に制限されず、例えば、アルカリ水溶液中に、原料粉末を浸漬させたり、アルカリ水溶液中に原料粉末を添加して、撹拌したり、アルカリ水溶液を原料粉末に噴霧したりすることにより行うことができる。活性化は、必要に応じて、加熱下で行ってもよい。
活性化の効率、生産性、工程の再現性などの観点から、アルカリ水溶液中のアルカリの濃度は、例えば、5~50質量%、好ましくは10~45質量%である。
活性化処理後の合金粉末は、通常、乾燥される。
ニッケル水素蓄電池は、正極と、負極と、正極および負極の間に介在するセパレータと、アルカリ電解液とを具備する。
負極は、上記の電極用合金粉末を、負極活物質として含む。
(負極)
負極は、上記の電極用合金粉末を負極活物質として含む限り特に制限されず、他の構成要素としては、ニッケル水素蓄電池において使用される公知のものが使用できる。
負極芯材としては、公知のものが使用でき、ステンレス鋼、ニッケルまたはその合金などで形成された多孔性または無孔の基板が例示できる。芯材が多孔性基板の場合、活物質は、芯材の空孔に充填されていてもよい。
負極は、例えば、芯材に負極ペーストを塗布した後、乾燥により分散媒を除去し、圧延することにより形成できる。
分散媒としては、公知の媒体、例えば、水、有機媒体、これらの混合媒体などが使用できる。
導電剤の量は、電極用合金粉末100質量部に対して、例えば、0.01~50質量部、好ましくは0.1~30質量部、さらに好ましくは0.1~10質量部である。
結着剤の量は、電極用合金粉末100質量部に対して、例えば、0.01~10質量部、好ましくは0.05~5質量部である。
増粘剤の量は、電極用合金粉末100質量部に対して、例えば、0.01~10質量部、好ましくは0.05~5質量部である。
正極は、芯材と、これに付着した活物質または活物質層とを含んでもよい。また、正極は、活物質粉末を焼結した電極であってもよい。
正極は、例えば、芯材に少なくとも正極活物質を含む正極ペーストを付着させることにより形成できる。より具体的には、正極は、芯材に正極ペーストを塗布した後、乾燥により分散媒を除去し、圧延することにより形成できる。
正極活物質としては、例えば、水酸化ニッケル、オキシ水酸化ニッケルなどのニッケル化合物が使用される。
セパレータとしては、ニッケル水素蓄電池に使用される公知のもの、例えば、微多孔膜、不織布、これらの積層体などが使用できる。微多孔膜や不織布の材質としては、例えば、ポリエチレン、ポリプロピレンなどのポリオレフィン樹脂;フッ素樹脂;ポリアミド樹脂などが例示できる。アルカリ電解液に対する耐分解性が高い点からは、ポリオレフィン樹脂製のセパレータを用いることが好ましい。
アルカリ電解液としては、例えば、アルカリ(アルカリ電解質)を含む水溶液が使用される。アルカリとしては、水酸化リチウム、水酸化カリウム、水酸化ナトリウムなどのアルカリ金属水酸化物が例示できる。これらは、一種を単独でまたは二種以上を組み合わせて使用できる。
なお、アルカリ電解液の比重は、例えば、1.03~1.55、好ましくは1.11~1.32である。
(1)第1水素吸蔵合金粒子の作製
La、Ce、Mg、Ni、Co、Mn、およびAlの各単体を、水素吸蔵合金の組成がLa0.66Ce0.27Mg0.07Ni4.00Co0.30Mn0.40Al0.30となるような割合で混合し、高周波溶解炉で溶融した。溶融した金属を、2m/分の速度で、鋳型へ流し込み(供給し)、インゴットを作製した。得られたインゴットを、アルゴン雰囲気下、1060℃で10時間加熱した。加熱後のインゴットを、粗粒子に粉砕した。得られた粗粒子を、湿式ボールミルを用いて水の存在下で粉砕し、湿潤状態でメッシュ径が75μmの篩でふるい、平均粒子径20μmの水素吸蔵合金を含む原料粉末を得た。
Zr、Ti、Ni、Mn、およびAlの各単体を、水素吸蔵合金の組成がZr0.9Ti0.1Ni1.2Mn0.6Al0.2となるような割合で混合するとともに、インゴットの加熱を、温度850℃で6時間行う以外は、上記工程(1)と同様にして、原料粉末を作製し、AB2型の結晶構造を有する第2水素吸蔵合金粒子(平均粒子径20μm)を作製した。
上記工程(1)で得られた第1水素吸蔵合金粒子と、上記工程(2)で得られた第2水素吸蔵合金粒子とを、75:25の質量比で均一に混合することにより、電極用合金粉末を調製した。
電極用合金粉末100質量部に対して、CMC(エーテル化度0.7、重合度1600)0.15質量部、アセチレンブラック0.3質量部およびSBR0.7質量部を加え、さらに水を添加して練合することにより、電極ペーストを調製した。得られた電極ペーストを、ニッケルメッキを施した鉄製パンチングメタル(厚み60μm、孔径1mm、開孔率42%)からなる芯材の両面に塗布した。ペーストの塗膜は、乾燥後、芯材とともにローラでプレスした。こうして、厚み0.4mm、幅35mm、容量2200mAhの負極を得た。負極の長手方向に沿う一端部には、芯材の露出部を設けた。
多孔性焼結基板からなる正極芯材に水酸化ニッケルを充填させて得られた容量1500mAhの焼結式正極を準備した。正極活物質には約90質量部のNi(OH)2を用い、添加剤として約6質量部のZn(OH)2を添加し、導電材として約4質量部のCo(OH)2を添加した。正極芯材の長手方向に沿う一方の端部には、活物質を保持しない芯材の露出部を設けた。
上記で得られた負極および正極を用いて、図1に示すような4/5Aサイズで公称容量1500mAhのニッケル水素蓄電池を作製した。具体的には、正極1と負極2とを、セパレータ3を介して捲回し、円柱状の極板群を作製した。極板群では、正極合剤が付着していない正極芯材の露出部と、負極合剤が付着していない負極芯材の露出部とを、それぞれ反対側の端面に露出させた。セパレータ3には、スルホン化処理したポリプロピレン製の不織布(厚み100μm、目付50g/cm2)を用いた。
上記で得られた水素吸蔵合金粒子およびニッケル水素蓄電池について、下記の評価を行った。
(a)自己放電
ニッケル水素蓄電池を、25℃環境下にて10時間率(150mA)で15時間充電し、5時間率(300mA)で電池電圧が1.0Vになるまで放電した。このときの放電容量を求め、初期容量とした。
初期容量を測定した後のニッケル水素蓄電池を、25℃環境下にて10時間率(150mA)で15時間充電し、45℃で90日間放置した。放置後の電池を、5時間率(300mA)で電池電圧が1.0Vになるまで放電した。このときの放電容量を求め、初期容量に対する比率を容量維持率として百分率で求めた。この容量維持率を、100%から減じた値を自己放電率として評価した。
各実施例および比較例で得られた水素吸蔵合金粒子を用いて、設計容量が1000mAhである負極を、上記工程(3)に準じて作製した。得られた負極を用いる以外は、上記(5)と同様にして、負極規制のニッケル水素電池を作製した。得られた電池において、25℃環境下にて10時間率(100mA)で12時間充電し、Hg/HgO参照極を用いて、負極電位を測定しながら、水銀基準電位に対する負極の電位が-0.5Vとなるまで定電流(100mA)放電した。このときの時間を求め、負極の水素吸蔵合金重量当たりの単極容量を算出した。
電極用合金粉末中の第1水素吸蔵合金粒子の含有量(質量%)を表1に示すように変更する以外は、実施例1と同様に、ニッケル水素蓄電池A2~A6およびB1~B4を作製し、評価を行った。
第2水素吸蔵合金粒子として、AB3型の結晶構造を有する第2水素吸蔵合金粒子を用いる以外は、実施例1および比較例1と同様に、ニッケル水素蓄電池A7およびB5をそれぞれ作製し、評価を行った。
実施例1~7および比較例1~5の結果を表1に示す。なお、電池A1~A7は実施例、電池B1~B5は比較例である。
Claims (15)
- AB5型の結晶構造を有する第1水素吸蔵合金の粒子と、AB2型の結晶構造を有する水素吸蔵合金aおよびAB3型の結晶構造を有する水素吸蔵合金bからなる群より選択される少なくとも一種の第2水素吸蔵合金の粒子とを含む混合物であり、
前記混合物中の前記第1水素吸蔵合金の含有量は50質量%よりも多い、電極用合金粉末。 - 前記混合物中の前記第1水素吸蔵合金の含有量は、60~95質量%である請求項1に記載の電極用合金粉末。
- 前記第1水素吸蔵合金の粒子の平均粒子径D1は、20~60μmであり、
前記第2水素吸蔵合金の粒子の平均粒子径D2は、15~50μmである、請求項1または2に記載の電極用合金粉末。 - 前記水素吸蔵合金aは、元素L2と、Niと、元素E2とを含み、
前記元素L2は、TiおよびZrからなる群より選択される少なくとも一種を含む周期表第4族元素であり、
前記元素E2は、周期表第5族~第11族の遷移金属元素(ただし、Niを除く)、第12族元素、第13族の第2周期~第5周期の元素、第14族の第3周期~第5周期の元素、およびPからなる群より選択される少なくとも一種であり、
前記元素L2に対する、Niのモル比x2および前記元素E2のモル比z2の合計は、1.5≦x2+z2≦2.5を充足する、請求項1~3のいずれか1項に記載の電極用合金粉末。 - 前記水素吸蔵合金aにおいて、前記元素E2は、V、Nb、Ta、Cr、Mo、W、Mn、Fe、Co、Cu、Ag、Zn、Al、Ga、In、Si、Ge、およびSnからなる群より選択される少なくとも1種である、請求項4に記載の電極用合金粉末。
- 前記水素吸蔵合金aにおいて、
前記元素L2は、少なくともZrを含み、
前記元素E2は、少なくともAlを含み、
前記元素L2に対するAlのモル比z2aは、0.1≦z2a≦0.3である、請求項4または5に記載の電極用合金粉末。 - 前記元素E2は、Mnを含む、請求項4~6のいずれか1項に記載の電極用合金粉末。
- 前記水素吸蔵合金bは、必須成分としての元素L3、元素M2、およびNiと、任意成分としての元素E3とを含み、
前記元素L3は、周期表第3族元素および第4族元素からなる群より選択される少なくとも一種であり、
前記元素M2は、アルカリ土類金属元素であり、
前記元素E3は、周期表第5族~第11族の遷移金属元素(ただし、Niを除く)、第12族元素、第13族の第2周期~第5周期の元素、第14族の第3周期~第5周期の元素、N、P、およびSからなる群より選択される少なくとも一種であり、
前記元素L3と前記元素M2の合計に対する、Niのモル比x3および前記元素E3のモル比z3の合計は、2.5<x3+z3<4.5を充足する、請求項1~7のいずれか1項に記載の電極用合金粉末。 - 前記水素吸蔵合金bは、必須成分として前記元素E3を含み、
前記元素E3は元素E3aを含み、前記元素E3aは、V、Nb、Ta、Cr、Mo、W、Mn、Fe、Co、Cu、Ag、Zn、B、Al、Ga、In、Si、およびPからなる群より選択される少なくとも一種である、請求項8に記載の電極用合金粉末。 - 前記元素E3aは、少なくともAlを含み、
前記元素L3は、Yおよびランタノイド元素からなる群より選択される少なくとも一種を含み、
前記元素M2は、少なくともMgを含む、請求項9に記載の電極用合金粉末。 - 前記元素L3は、少なくともYを含む、請求項9または10に記載の電極用合金粉末。
- 前記第1水素吸蔵合金は、必須成分としての元素L1、元素M1、およびNiと、任意成分としての元素E1とを含み、
前記元素L1は、周期表第3族元素および第4族元素からなる群より選択される少なくとも一種であり、
前記元素M1は、アルカリ土類金属元素であり、
前記元素E1は、周期表第5族~第11族の遷移金属元素(ただし、Niを除く)、第12族元素、第13族の第2周期~第5周期の元素、第14族の第3周期~第5周期の元素、およびPからなる群より選択される少なくとも一種であり、
前記元素L1と前記元素M1の合計に対する、Niのモル比x1、および前記元素E1のモル比z1の合計は、4.5≦x1+z1≦5.5を充足する、請求項1~11のいずれか1項に記載の電極用合金粉末。 - 前記第1水素吸蔵合金は、必須成分として前記元素E1を含み、
前記元素E1は、V、Nb、Ta、Cr、Mo、W、Mn、Fe、Co、Cu、Ag、Zn、Al、Ga、In、Si、Ge、およびSnからなる群より選択される少なくとも1種である、請求項12に記載の電極用合金粉末。 - 請求項1~13のいずれか1項に記載の電極用合金粉末を、負極活物質として含むニッケル水素蓄電池用負極。
- 正極と、請求項14に記載の負極と、前記正極および前記負極の間に介在するセパレータと、アルカリ電解液とを具備する、ニッケル水素蓄電池。
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