WO2012081724A1 - 水素吸蔵合金粉末、負極及びニッケル水素二次電池 - Google Patents
水素吸蔵合金粉末、負極及びニッケル水素二次電池 Download PDFInfo
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- WO2012081724A1 WO2012081724A1 PCT/JP2011/079385 JP2011079385W WO2012081724A1 WO 2012081724 A1 WO2012081724 A1 WO 2012081724A1 JP 2011079385 W JP2011079385 W JP 2011079385W WO 2012081724 A1 WO2012081724 A1 WO 2012081724A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- 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
- H01M4/383—Hydrogen absorbing alloys
- H01M4/385—Hydrogen absorbing alloys of the type LaNi5
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/0433—Nickel- or cobalt-based alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C19/00—Alloys based on nickel or cobalt
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- 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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- 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
- H01M4/383—Hydrogen absorbing alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/34—Gastight accumulators
- H01M10/345—Gastight metal hydride accumulators
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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
Definitions
- the present invention relates to a hydrogen storage alloy powder, a negative electrode for a nickel metal hydride secondary battery, and a nickel metal hydride secondary battery.
- a nickel metal hydride secondary battery using a negative electrode containing a hydrogen storage alloy has a higher energy density than a nickel cadmium secondary battery, and does not use harmful Cd.
- Nickel metal hydride secondary batteries are also used in portable devices such as digital cameras, electric tools, and electric vehicles or hybrid electric vehicles, and various battery characteristics are required depending on the application.
- LaNi 5 -based hydrogen storage alloy which is a rare earth-Ni intermetallic compound having a CaCu 5 -type crystal structure as the main phase, and Ti, Zr, V and Ni as constituent elements
- a hydrogen storage alloy having a main phase of a Laves crystal structure is used.
- rare earth-Mg-Ni-based hydrogen storage alloys have been put into practical use, and nickel-metal hydride secondary batteries using this alloy as a negative electrode material are known to have a high capacity.
- Patent Document 1 the surface of a hydrogen storage alloy containing rare earth, nickel, magnesium and aluminum is acid-treated, so that the ratio of the surface of each element of nickel, magnesium and aluminum to the total amount of rare earth elements is within the alloy. It has been proposed that a hydrogen storage alloy having a larger composition can be obtained. It is disclosed that a nickel metal hydride secondary battery using such a hydrogen storage alloy as a negative electrode can suppress high-rate discharge characteristics at low temperatures and pulverization due to cracking of the alloy due to charge and discharge, and prevent a decrease in cycle life. Has been.
- Patent Document 2 discloses that a nickel-metal hydride battery produced by using an electrode containing La—Mg—Ni-based hydrogen storage alloy particles and Sn is charged and discharged while being immersed in an alkaline aqueous solution, whereby a compound containing Sn and Mg It has been disclosed that a compound containing can be precipitated on the surface of alloy particles, the discharge capacity of the nickel-metal hydride battery can be increased, and the cycle characteristics can be improved.
- the nickel-metal hydride secondary battery using the hydrogen storage alloy disclosed in Patent Documents 1 and 2 has not yet been able to satisfy all of the initial activity, discharge capacity, and cycle characteristics at the same time.
- the formula (1) R 1-a Mg a Ni b Al c M d (wherein R is a rare earth element including Sc and Y, Zr, Hf and Ca, and M is R And at least one element selected from elements other than Mg, Ni and Al, a is 0.005 ⁇ a ⁇ 0.40, b is 3.00 ⁇ b ⁇ 4.50, and c is 0 ⁇ c ⁇ 0.
- the outermost surface of the alloy powder has The molar ratio of Mg is larger than the molar ratio of Mg shown in formula (1) (a in formula (1)), and the molar ratio of Ni shown in formula (1) (b in formula (1) is Ni).
- Hydrogen-absorbing alloy powder and a Mg-Ni-containing region of the compositional molar ratio of Ni is large is provided.
- the nickel-hydrogen secondary battery using the negative electrode for nickel-metal hydride secondary batteries using this hydrogen storage alloy powder and this negative electrode is provided.
- the hydrogen storage alloy powder of the present invention (hereinafter sometimes abbreviated as alloy powder) has a specific composition, has the specific Mg enriched-Ni dilute region on the outermost surface, and inside the alloy powder, Since it has the specific Mg-Ni-containing region, the initial activity, discharge capacity, and cycle characteristics of the secondary battery should be excellent at the same time by using a negative electrode using this for a nickel-hydrogen secondary battery. Can do.
- FIG. 4 is a copy of a Comp image in a cross-sectional structure of the hydrogen storage alloy powder of Example 1.
- 2 is a copy of an Mg mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Example 1.
- 4 is a copy of an Al mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Example 1.
- 3 is a result of line analysis of Mg in a cross-sectional structure of the hydrogen storage alloy powder of Example 1.
- FIG. 3 is a result of Al line analysis in a cross-sectional structure of the hydrogen storage alloy powder of Example 1.
- FIG. 4 is a copy of a Comp image in a cross-sectional structure of the hydrogen storage alloy powder of Example 2.
- 4 is a copy of an Mg mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Example 2.
- 4 is a copy of an Al mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Example 2.
- 4 is a copy of a Comp image in a cross-sectional structure of the hydrogen storage alloy powder of Comparative Example 1.
- 4 is a copy of an Mg mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Comparative Example 1.
- 4 is a copy of an Al mapping image in a cross-sectional structure of the hydrogen storage alloy powder of Comparative Example 1.
- 3 is a result of line analysis of Mg in a cross-sectional structure of the hydrogen storage alloy powder of Comparative Example 1.
- FIG. 5 is a result of Al line analysis in a cross-sectional structure of the hydrogen storage alloy powder of Comparative Example 1.
- FIG. It is a copy of the Mg mapping image in the cross-sectional structure of the hydrogen storage alloy of Example 22. It is a copy of the Mg mapping image in the cross-sectional structure of the hydrogen storage alloy of Example 44.
- the alloy composition of the hydrogen storage alloy powder of the present invention is represented by the formula (1) R 1-a Mg a Ni b Al c M d .
- R is at least one element selected from rare earth elements including Sc and Y, Zr, Hf and Ca, and in particular, one or two of La, Nd, Pr, Sm, Y and Zr Preferably it contains more than one species.
- La tends to lower the equilibrium pressure at the time of hydrogen storage and release of the alloy, and Nd, Pr, Sm, Y, and Zr tend to increase.
- 1-a represents the content of R.
- 1-a is 0.60 ⁇ 1-a ⁇ 0.995, preferably 0.75 ⁇ 1-a ⁇ 0.99, and more preferably 0.85 ⁇ 1-a ⁇ 0.99.
- a represents the Mg content.
- a is 0.005 ⁇ a ⁇ 0.40, preferably 0.01 ⁇ a ⁇ 0.25, and more preferably 0.01 ⁇ a ⁇ 0.15. If the amount of Mg is small, a sufficient hydrogen storage amount cannot be obtained, and the discharge capacity may decrease when used in a secondary battery. If the amount of Mg is large, sufficient corrosion resistance cannot be obtained, and the cycle characteristics may deteriorate when used in a secondary battery. Mg tends to increase the hydrogen storage amount and to increase the equilibrium pressure at the time of hydrogen storage and release of the alloy powder.
- b represents the Ni content.
- b is 3.00 ⁇ b ⁇ 4.50, preferably 3.00 ⁇ b ⁇ 4.00, and more preferably 3.00 ⁇ b ⁇ 3.80. If the amount of Ni is small, pulverization tends to proceed, and the cycle characteristics may be deteriorated when used in a secondary battery. When the amount of Ni is large, a sufficient hydrogen storage amount cannot be obtained, and there is a possibility that a sufficient discharge capacity cannot be obtained when used in a secondary battery.
- c represents the Al content.
- c is 0 ⁇ c ⁇ 0.50, preferably 0.05 ⁇ c ⁇ 0.50, and more preferably 0.05 ⁇ c ⁇ 0.30.
- Al is not always necessary, but inclusion of Al improves the corrosion resistance and contributes to the improvement of cycle characteristics when used in a secondary battery.
- Al tends to lower the equilibrium pressure when the alloy powder absorbs and releases hydrogen, and contributes to improvement of the initial capacity and the like when a secondary battery is formed.
- the amount of Al is too large, a sufficient hydrogen storage amount cannot be obtained, and sufficient corrosion resistance may not be obtained due to segregation of Al.
- M represents at least one selected from elements other than R, Mg, Ni, and Al, and an element contributing to fine adjustment of the characteristics can be arbitrarily selected depending on the use of the battery.
- the M element include at least selected from Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Cu, Zn, B, Ga, Sn, Sb, In, C, Si, and P. 1 type is mentioned, Preferably, M element includes at least 1 type chosen from Ti, Nb, Mo, W, Mn, Fe, Co, Cu, B, and Sn.
- pulverization can be suppressed, or elution of Al into the electrolytic solution can be suppressed.
- d represents the content of the M element. d is 0 ⁇ d ⁇ 1.00, preferably 0 ⁇ d ⁇ 0.50, and is not necessarily required, but can be contained when fine adjustment of characteristics is required depending on the use of the battery.
- b + c + d represents the content of components other than R and Mg. These components mainly affect pulverization and contribute to improvement of cycle characteristics and the like particularly when a secondary battery is formed.
- b + c + d is 3.00 ⁇ b + c + d ⁇ 4.50, preferably 3.00 ⁇ b + c + d ⁇ 4.00, and more preferably 3.00 ⁇ b + c + d ⁇ 3.80.
- the composition of the alloy powder was confirmed by quantitative analysis with ICP (Inductively Coupled Plasma).
- the hydrogen storage alloy powder of the present invention has a Mg molar ratio larger than the molar ratio of Mg shown in Formula (1) (a in Formula (1)) on the outermost surface, and the molar ratio of Ni shown in Formula (1).
- the Mg concentration-Ni dilute region having a composition having a smaller Ni molar ratio than the ratio (b in the formula (1)), and the Mg and Ni in the Mg concentrated-Ni dilute region are contained inside the alloy powder.
- the Al content in the Mg enriched-Ni dilute region is arbitrary, but the molar ratio of Al shown in Formula (1) (c in Formula (1)) It is preferable to have a composition containing Al in a larger molar ratio. Further, the Al content in the Mg—Ni-containing region is arbitrary, but it is preferable to have a region having a composition having a smaller molar ratio of Al than the Mg-concentrated / Ni-diluted region.
- the Mg enriched-Ni dilute region By allowing the Mg enriched-Ni dilute region to exist on the outermost surface of the alloy powder, it is estimated that the movement of hydrogen within the Mg enriched-Ni diluted region and the alloy powder is performed smoothly. As a result, when used in a secondary battery, the initial activity, discharge capacity, and cycle characteristics can be improved simultaneously.
- the molar ratio of Mg is usually 1.05 times or more and 1.90 times or less, preferably 1.05 compared with the molar ratio of Mg and Ni shown in the formula (1). It is a region having a composition in which the molar ratio of Ni is usually not less than 0.45 times and not more than 0.95 times, preferably not less than 0.50 times and not more than 0.95 times.
- the Mg enriched-Ni dilute region is usually present in a part rather than the entire outermost surface of the alloy powder.
- the interface between the Mg enriched-Ni diluted region on the outermost surface and the other regions acts to smoothly move the hydrogen inside the Mg enriched-Ni diluted region and the alloy powder.
- the Mg enriched-Ni diluted region exists as a region having a thickness of usually 1 ⁇ m or more and 40 ⁇ m or less, preferably 2 ⁇ m or more and 40 ⁇ m or less from the outermost surface of the alloy powder toward the center.
- the major axis of the Mg enriched-Ni diluted region is preferably 5 ⁇ m or more and 60 ⁇ m or less.
- the ratio of the Mg enriched-Ni diluted region to the circumference of the alloy powder is preferably 1 to 60%, more preferably 1 to 30%.
- the Mg enriched-Ni dilute region and the Mg-Ni-containing region are element mapping images of Mg obtained by observing the cross section of the hydrogen storage alloy powder at 350 times with FE (Field Emission) -EPMA (Electron Probe Micro Analyzer). Use to confirm.
- the element mapping image of Mg adjusts contrast, level, etc., and reveals the density of Mg.
- the acceleration voltage is 15 kV
- the sample current is 5.0 ⁇ 10 ⁇ 8 A
- the beam diameter is ⁇ 1 ⁇ m or less
- Quantitative analysis is performed on the elements contained in the alloy powder in the off setting.
- the molar ratio of Mg and Ni in each region is in the above range, it is confirmed that they are a Mg enriched-Ni diluted region and a Mg—Ni-containing region.
- the thickness and major axis from the outermost surface of the Mg enriched-Ni dilute region were determined by observing the cross section of the alloy powder in the same manner as described above, and randomly selecting five alloy powders containing the Mg enriched-Ni dilute region. It is possible to measure by measuring the maximum value and the major axis of the thickness of all Mg-concentrated-Ni dilute regions existing on the surface, and obtaining the average of them.
- the ratio of the Mg enriched-Ni dilute region to the circumference of the outermost surface is the sum of the length of the Mg enriched-Ni dilute region occupying the circumference for the same five powders and divided by the total circumference of the five powders. To calculate.
- the Mg enriched-Ni dilute region includes an MgZn 2 type crystal structure, an MgCu 2 type crystal structure (hereinafter, the two structures are sometimes referred to as 1-2 phases), a CeNi 3 type crystal structure, and a PuNi 3 type. Crystal structure (hereinafter sometimes referred to as 1-3 phase without distinction between the two structures), Ce 2 Ni 7 type crystal structure, Gd 2 Co 7 type crystal structure (hereinafter referred to as 2-7 without distinction between the two structures) And a phase mainly composed of any one of these similar crystal structures.
- the crystal structure of the Mg—Ni-containing region is 1-3 phase, 2-7 phase, Ce 5 Ni 19 type crystal structure, Pr 5 Co 19 type crystal structure (hereinafter, the two structures are not distinguished, 5-19 It is presumed to be mainly composed of any one of the crystal structures similar to these.
- atoms occupying the B site of the unit cell of the CaCu 5 type crystal structure (hereinafter sometimes referred to as 1-5 phase) are replaced by atoms occupying a part of the A site, It seems that it is formed by generating an antiphase boundary which is a stacking fault.
- the hydrogen storage alloy powder of the present invention is presumed that the B site has a rich crystal structure from the outermost Mg enriched-Ni diluted region to the inside of the alloy powder (including the Mg-Ni-containing region).
- the Mg enriched-Ni diluted region is a phase mainly composed of either the 1-2 phase or a similar crystal structure
- the crystal structure inside the alloy powder is the Mg enriched-Ni diluted region. From the vicinity to the inside, it is estimated that there is a tendency to approach the 1-5 phase, such as a phase mainly composed of the 1-3 phase, 2-7 phase, and 5-19 phase.
- the crystal structure changes from the surface toward the center, it is presumed that this is one reason why hydrogen is absorbed and released smoothly.
- the alloy powder acts to relieve strain when expanding and contracting due to occlusion and release of hydrogen.
- the initial activity, the discharge capacity and the cycle characteristics are made particularly excellent at the same time.
- the crystal structure is estimated from the results of quantitative analysis of each element in the Mg enriched-Ni diluted region and the alloy powder by the FE-EPMA.
- the AB ratio (sum of b, c, d shown in the formula (1)) of the Mg enriched-Ni diluted region is 1.71, and as the inside of the alloy powder 3 .13, 3.56.
- the Mg enriched-Ni diluted region is a phase similar to the 1-2 phase, and as the inside of the alloy, it is a phase similar to the 1-3 phase, 2-7 phase, and 5-19 phase. Is done.
- the AB ratio becomes 3.16, 3.17, 3.36, 3.90 from the Mg enriched-Ni diluted region to the inside of the alloy powder. This is a phase similar to the 1-3 phase in which the Mg enriched-Ni diluted region is similar to the 1-3 phase, the 2-7 phase, the 5-19 phase, and the 1-5 phase. It is estimated that.
- the AB ratio does not take an integer value
- the AB ratio changes between 2 and 5 as the Mg concentration-Ni dilution region moves into the alloy powder.
- the crystal structures of the 1-2 phase to the 5-19 phase having different AB ratios are specifically described.
- the Mg—Ni-containing region preferably has at least two regions having compositions having different Mg molar ratios. At least two regions of the Mg—Ni-containing region include a region (a) and a region (b), and the region (a) has a molar ratio of Mg as compared with the molar ratio of Mg shown in Formula (1). Is a region having a composition of 0 times or more and 0.50 times or less. In the region (b), the molar ratio of Mg exceeds 0.50 times as compared with the molar ratio of Mg shown in the formula (1). This is a region having a composition of 95 times or less. Such at least two Mg—Ni-containing regions may be present in the alloy powder in any way.
- the Mg enriched-Ni dilute region and the at least two Mg-Ni-containing regions have concentration gradients in which the molar ratio of Ni decreases and the molar ratio of Ni increases from the outermost surface of the alloy powder toward the center. It is preferable to show.
- the crystal structure has a rich crystal structure at the B site from the outermost surface of the alloy powder toward the center, and the movement of hydrogen is smooth, and hydrogen is occluded. It is presumed that it acts to relieve the distortion of expansion / contraction due to release.
- the Mg enriched-Ni diluted region has a composition containing Al at a molar ratio larger than the molar ratio of Al shown in the above formula (1). Is preferably 1.05 times or more and 2.00 times or less of the molar ratio of Al shown in Formula (1).
- the hydrogen storage alloy powder composition of the present invention contains Al and there are at least two Mg-Ni-containing regions, the region (a ') and the region (b') include the region (a '),
- the molar ratio of Al is a region having a composition of 1.20 times or more and 2.00 times or less, and the region (b ′) is expressed by Formula (1).
- the Al molar ratio is preferably in the range of 0.50 times or more and 1.00 times or less.
- the region (a ′) is preferably present in the form of an island surrounded by the region (b ′) from the viewpoint of suppressing pulverization of the alloy powder.
- the region (a) and the region (a ′) as the Mg—Ni-containing region, or the region (b) and the region (b ′) may be the same or different.
- the hydrogen storage alloy powder of the present invention preferably has a volume average diameter (MV value) of 20 to 100 ⁇ m, more preferably 40 to 80 ⁇ m.
- MV value volume average diameter
- the alloy powder can be filled at a high density.
- the hydrogen storage alloy powder of the present invention can be produced, for example, by the following method.
- the manufacturing method of this alloy powder is not specifically limited, It performs by a well-known method.
- a strip casting method such as a single roll method, a twin roll method or a disk method, or a die casting method may be used.
- raw materials blended so as to have a predetermined alloy composition excluding Mg are prepared.
- the mixed raw materials are heated and melted in an inert gas atmosphere to form an alloy melt, and then the alloy melt is poured into a copper water-cooled roll, rapidly cooled and solidified to obtain an alloy cast.
- the alloy melt obtained by the above-described method is poured into a water-cooled copper mold, cooled and solidified to obtain an ingot.
- the strip casting method and the die casting method have different cooling rates, and the strip casting method is preferable when obtaining an alloy with little segregation and uniform composition distribution.
- the obtained alloy containing no Mg can be heat-treated.
- the alloy obtained by casting is pulverized to obtain an alloy powder. The pulverization can be performed using a known pulverizer.
- the particle diameter of the alloy powder is preferably 20 to 1000 ⁇ m, more preferably MV value. It is 20 to 400 ⁇ m, most preferably 20 to 100 ⁇ m.
- a metal Mg or Mg-containing alloy powder is prepared.
- the metal Mg powder can be prepared by pulverizing Mg metal using a known pulverizer.
- the Mg-containing alloy powder can be produced in the same manner as the above-described alloy powder not containing Mg.
- the melting point of the Mg-containing alloy is preferably as low as possible below the boiling point of the metal Mg in order to prevent Mg from evaporating in the heat treatment step described later.
- the element combined with the metal Mg includes at least one selected from Al, Cu, Zn, Ga, Sn, and In.
- Mg—Al alloys Mg—In alloys, Mg—Zn alloys, etc., whose melting point is lower than that of metal Mg.
- R combined with metallic Mg include La, Ce, Pr, Nd, Sm and Mm (Misch metal) containing them, Eu, Yb, and the like.
- the average particle diameter (D50) of the metal Mg or Mg-containing alloy powder is 20 to The thickness is preferably 2000 ⁇ m, more preferably 20 to 1500 ⁇ m.
- the alloy powder not containing Mg and the metal Mg or Mg-containing alloy powder are blended and mixed so as to have a desired composition of the hydrogen storage alloy powder.
- the mixed state be as uniform as possible.
- Mixing can be performed using a known mixer.
- a rotary mixer such as a double cone or V type, or a stirring type mixer such as a blade type or screw type.
- a pulverizer such as a ball mill or an attritor mill to mix while mixing the alloy powder not containing Mg and the powder of metal Mg or Mg-containing alloy.
- Mg diffusion and reaction is usually carried out at a relatively low temperature of 400 to 1090 ° C., so there is not much evaporation of components such as Mg, but strictly speaking, an alloy having a desired composition is considered in consideration of the yield of each component.
- an alloy powder not containing Mg and a metal Mg or Mg-containing alloy powder are blended.
- the obtained mixture is preferably heat-treated at 400 to 1090 ° C. for 0.5 to 240 hours.
- This heat treatment step can be performed in a known heat treatment furnace capable of controlling the atmosphere. At that time, heat treatment can be performed while mixing the mixture.
- a rotary furnace such as a rotary kiln furnace may be used.
- Mg diffuses and reacts from the metal Mg or Mg-containing alloy powder into the alloy powder not containing Mg, and the hydrogen storage alloy powder of the present invention can be obtained.
- the heat treatment temperature at this time is preferably a temperature and a time at which Mg evaporation is suppressed and diffusion / reaction is likely to proceed. Therefore, the heat treatment temperature is preferably 500 to 1080 ° C.
- the heat treatment time is preferably 1 to 24 hours. Since Mg is easily oxidized, the atmosphere in which the heat treatment is performed is preferably a vacuum or an inert gas atmosphere. More preferably, it is performed in an inert gas atmosphere and a pressurized atmosphere. In this case, it is possible to prevent evaporation of Mg and at the same time prevent evaporation.
- the heat treatment can be performed in two or more stages in the range of 400 to 1090 ° C. For example, it can be carried out by holding the metal Mg or Mg-containing alloy powder in a temperature range slightly exceeding the melting point and then raising the temperature and holding it in a higher temperature range. By carrying out like this, the above-mentioned diffusion and reaction can be carried out more uniformly. For example, it can be carried out by holding at 660 to 750 ° C. for 0.1 to 2.0 hours and then holding at 900 to 1080 ° C. for 4 to 24 hours.
- the particle size after crushing or pulverization preferably has an MV value of 20 to 100 ⁇ m, more preferably 40 to 80 ⁇ m.
- the method of crushing or crushing can be performed using a known crusher such as a feather mill, a hammer mill, a ball mill, an attritor mill, or the like.
- the negative electrode for a nickel metal hydride secondary battery of the present invention contains the hydrogen storage alloy powder of the present invention produced as described above.
- the hydrogen storage alloy powder of the present invention should be used after being subjected to a known treatment such as plating, surface coating with a polymer or the like, or surface treatment with a solution of acid, alkali, etc., depending on the desired properties. You can also.
- the content of the hydrogen storage alloy powder is 80% by mass or more based on the total amount of materials constituting the negative electrode other than the current collector such as a conductive agent and a binder. Preferably, it is 95 mass% or more.
- a conductive agent known ones can be used, and examples thereof include carbon black such as acetylene black and furnace black, carbonaceous materials such as graphite, copper, nickel, and cobalt.
- the binder known ones can be used.
- carboxymethyl cellulose polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethylene oxide, polytetrafluoroethylene (PTFE), 4-fluoroethylene-6-fluoropropylene copolymer A polymer (FEP) is mentioned.
- the current collector for example, punching metal or foam metal can be used.
- punching metal is used.
- the paste-type negative electrode is prepared by adding the hydrogen storage alloy powder of the present invention, the above-described binder, and, if necessary, a conductive agent, an antioxidant, a surfactant, a thickener, etc., mixing water as a solvent, The paste is applied to a current collector, filled, dried, and then subjected to a roller press or the like.
- the negative electrode for a nickel metal hydride secondary battery of the present invention can be formed with a water repellent layer, a conductive layer, or the like on the surface as necessary. These are performed by a known method. For example, the former is performed by applying and drying a fluororesin dispersion or the like, and the latter is performed by plating or the like.
- the nickel hydride secondary battery of the present invention includes the negative electrode for a nickel hydride secondary battery of the present invention.
- a publicly known thing can be used for the other composition.
- the nickel metal hydride secondary battery of the present invention can have various shapes such as a cylindrical shape, a stacked shape, and a coin shape. Regardless of the shape, the nickel metal hydride secondary battery stores an electrode group in which a negative electrode, a separator, and a positive electrode are stacked in a can body made of stainless steel or the like.
- the negative electrode and the negative electrode terminal are connected by winding the electrode group spirally with the negative electrode outside and inserting the electrode group into the can body.
- the positive electrode is usually connected to the positive terminal by a lead.
- a polymer fiber nonwoven fabric made of nylon, polypropylene, polyethylene or the like, a porous polymer film such as polyethylene, polypropylene, or the like can be used.
- the positive electrode usually contains nickel oxide, and for example, a non-sintered nickel electrode is used.
- a non-sintered nickel electrode is made by mixing nickel hydroxide and optionally added cobalt hydroxide, cobalt monoxide, metallic cobalt, etc. together with a binder and water as a solvent to form a paste. It is produced by filling a current collector such as foam metal and drying, and then applying a roller press or the like.
- the 6-8 N potassium hydroxide solution is injected as an alkaline electrolyte into the container containing the electrode group.
- An alkaline electrolyte to which lithium hydroxide, sodium hydroxide or the like is added can also be used.
- the container is usually provided with a gasket for sealing the battery and a safety valve that operates when the pressure in the battery rises.
- Example 1 In the alloy composition of the hydrogen storage powder shown in Table 1, raw materials excluding Mg were weighed and melted in an argon gas atmosphere in a high frequency melting furnace to obtain an alloy melt. Subsequently, the molten metal pouring temperature was set to 1400 ° C., and the slab having an average thickness of 0.4 mm was rapidly cooled and solidified by a strip casting method using a single roll casting apparatus using a copper water-cooled roll. Obtained. The obtained slab was pulverized with a ball mill to obtain an alloy powder having a particle size of 85 ⁇ m. When the composition of the obtained alloy was analyzed by ICP, it was La 0.66 Sm 0.13 Zr 0.01 Ni 3.42 Al 0.20 .
- the alloy powder obtained above and a metal Mg powder having an average particle size (D50) of 110 ⁇ m are mixed well in a mortar, held in an argon gas atmosphere at 700 ° C. for 30 minutes, and then heated to 970 ° C. for 12 hours. Retained.
- the composition of the obtained alloy powder was analyzed by ICP, it was La 0.66 Sm 0.13 Zr 0.01 Mg 0.20 Ni 3.42 Al 0.20 .
- the alloy powder after the heat treatment was crushed in a mortar to obtain a hydrogen storage alloy powder having an MV value of 70 ⁇ m.
- FIG. 1 shows a copy of the Comp image
- FIG. 2 shows a copy of the element mapping image of Mg
- FIG. 3 shows a copy of the element mapping image of Al
- FIG. 4 shows the results of line analysis of Al measured along the line segment shown in FIG.
- FE-EPMA manufactured by JEOL, trade name JXA8500F
- the element mapping image of Mg was adjusted so that contrast and level were adjusted so that the density of Mg could be clearly confirmed.
- a region having a higher Mg concentration than the inside was present on the outermost surface of the alloy powder.
- the region where Mg was further diluted was present in an island shape as compared with the surrounding region.
- Quantitative analysis was performed under conditions.
- the composition of the region having a higher Mg concentration than the inside on the outermost surface is La 0.63 Sm 0.12 Zr 0.01 Mg 0.24 Ni 2.96 Al 0.23
- the composition of the region where Mg is dilute and exists in an island shape is La 0.75 Sm. 0.15 Zr 0.01 Mg 0.09 Ni 3.60 Al 0.34
- the composition of the other region inside the alloy powder was La 0.68 Sm 0.13 Zr 0.01 Mg 0.18 Ni 3.11 Al 0.17 , La 0.70 Sm 0.14 Zr 0.01 Mg 0.15 Ni 3.32 Al 0.18 . Therefore, it was confirmed that the Mg concentration-Ni dilute region in which the Mg concentration is higher than the inside on the outermost surface is the Mg-Ni-containing region.
- the region where Mg is dilute and exists in an island shape is Al compared to the Al molar ratio (0.20) of La 0.66 Sm 0.13 Zr 0.01 Mg 0.20 Ni 3.42 Al 0.20 which is the overall composition of the alloy powder.
- a region having a composition with a molar ratio of 1.20 times or more and 2.00 times or less, and a region with a composition with a molar ratio of Al of 0.50 times or more and 1.00 times or less (the other region, La 0.68 Sm 0.13 Zr 0.01 Mg 0.18 Ni 3.11 Al 0.17 , La 0.70 Sm 0.14 Zr 0.01 Mg 0.15 Ni 3.32 Al 0.18 ) was confirmed to be surrounded.
- the ratio of the Mg enriched-Ni diluted region to the thickness of the Mg enriched-Ni diluted region, the long diameter, and the circumference of the alloy powder were measured to be 6 ⁇ m, 30 ⁇ m, and 18%, respectively. These results are shown in Table 7.
- the obtained negative electrode was immersed in an 8N-KOH aqueous solution together with a sintered nickel electrode as a counter electrode, and a charge / discharge cycle test was conducted at a temperature of 25 ° C.
- Charging / discharging was performed using a charging / discharging device (trade name BS2500-05R1 manufactured by Keiki Keiki Center Co., Ltd.) for 170 minutes with a current of 150 mA per gram of hydrogen storage alloy, and after resting for 10 minutes, 150 mA per gram of hydrogen storage alloy
- the cycle of discharging until the current was ⁇ 0.7 V with respect to the mercury oxide electrode was repeated 100 times.
- Examples 2 to 36, 41 to 43 A hydrogen storage alloy powder was produced in the same manner as in Example 1 except that the composition of the raw materials was changed to obtain a hydrogen storage alloy powder having the composition shown in Tables 1 to 3.
- a cross section of the hydrogen storage alloy powder of Example 2 is shown as a copy of the EPMA Comp image, FIG. 7 shows a copy of the Mg element mapping image, and FIG. 8 shows a copy of the Al element mapping image.
- the results of measuring the cross section of the hydrogen storage alloy powder by FE-EPMA are shown in Tables 1 to 3.
- the Mg—Ni containing region In the column of the composition of the Mg—Ni containing region in Tables 1 to 3, the Mg—Ni containing region, the mole of Al in comparison with the molar ratio of Al shown in the formula (1) representing the overall composition of the alloy powder.
- the molar ratio of Al is 0.50 times or more compared with the molar ratio of Al shown in Formula (1) and the region (a ′) having a composition of 1.20 times or more and 2.00 times or less.
- a region (b ′) having a composition less than or equal to 00 times, and the region (a ′) is present in an island shape surrounded by the region (b ′). It was written behind (Al enrichment).
- composition formulas without description of (Al enrichment) are described in order from the portion closer to the center from the portion closer to the center of the alloy powder than the Mg enriched-Ni diluted region.
- a copy of the elemental mapping image of Mg obtained by observing the cross section of the hydrogen storage alloy powder of Example 22 with FE-EPMA is shown in FIG. Quantitative analysis of each element contained was performed on the portions indicated by arrows (1) to (4) in FIG. (1) is the Mg enriched-Ni diluted region, and (2) to (4) are the Mg—Ni containing regions.
- (4) shows the molar ratio of Al in comparison with the molar ratio (0.15) of the Al composition of the hydrogen storage alloy powder of Example 22 (La 0.45 Gd 0.10 Pr 0.06 Nd 0.19 Mg 0.20 Ni 3.30 Al 0.15 ).
- the Mg—Ni-containing region that is surrounded by islands and exists in an island shape.
- Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1) Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1)
- Tables 4 to 6 show the molar ratio of Mg, the molar ratio of Ni, and the molar ratio of Al, respectively, in the Mg—Ni region compared with the molar ratio of Mg, Ni, and Al shown in Formula (1).
- the thickness of the Mg-concentrated-Ni diluted region, the long diameter, the ratio of the Mg-concentrated-Ni diluted region to the circumference of the alloy powder, and the results of the battery characteristics are shown in Tables 7-9. Shown in
- Examples 37 to 40 Except for changing the composition of the raw materials and casting the raw materials excluding Mg using a copper mold so as to obtain a 20 mm ingot, and obtaining a hydrogen storage alloy powder having the composition shown in Table 3.
- a hydrogen storage alloy powder was prepared.
- the results of measuring the cross section of the hydrogen storage alloy powder by FE-EPMA in the same manner as in Example 1 are shown in Table 3.
- Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1) Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1)
- Table 6 shows the molar ratio of Mg, the molar ratio of Ni, and the molar ratio of Al in the Mg—Ni region compared with the molar ratio of Mg, Ni, and Al shown in Formula (1).
- the thickness of the Mg-concentrated-Ni diluted region, the long diameter, the ratio of the Mg-concentrated-Ni diluted region to the circumference of the alloy powder, and the results of the battery characteristics are shown in Table 9. .
- Examples 44-52 The heat treatment time of the heat treatment carried out at 970 ° C. for 12 hours was changed to 3 hours (Examples 44, 47, 50), 6 hours (Examples 45, 48, 51), 9 hours (Example 46, 49, 52), and a hydrogen storage alloy powder was produced in the same manner as in Example 1 except that a hydrogen storage alloy powder having the composition shown in Table 3 was obtained.
- Table 3 The results of measuring the cross section of the hydrogen storage alloy powder by FE-EPMA in the same manner as in Example 1 are shown in Table 3.
- a copy of the FE-EPMA Mg mapping image of the cross section of the hydrogen storage alloy powder of Example 44 is shown in FIG.
- Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1) Mg concentration compared to the molar ratio of Mg, Ni and Al shown in formula (1)
- Table 6 shows the molar ratio of Mg, the molar ratio of Ni, and the molar ratio of Al in the Mg—Ni region compared with the molar ratio of Mg, Ni, and Al shown in Formula (1).
- the thickness of the Mg-concentrated-Ni diluted region, the long diameter, the ratio of the Mg-concentrated-Ni diluted region to the circumference of the alloy powder, and the results of the battery characteristics are shown in Table 9. .
- Comparative Example 1 All the raw materials containing metal Mg were blended at the same time so that an alloy having the same composition as the hydrogen storage alloy powder of Example 1 was obtained, and a slab was obtained by strip casting as in Example 1. The obtained slab was heat-treated at 950 ° C. for 6 hours in an argon gas atmosphere. The heat-treated cast slab was pulverized by a ball mill to obtain a hydrogen storage alloy powder having an MV value of 70 ⁇ m. When the composition of the obtained alloy powder was analyzed by ICP, it was La 0.66 Sm 0.13 Zr 0.01 Mg 0.20 Ni 3.42 Al 0.20 . A copy of the EPMA Comp image of the obtained hydrogen storage alloy powder is shown in FIG. 9, a copy of the Mg element mapping image is shown in FIG.
- FIG. 10 a copy of the Al element mapping image is shown in FIG. 11, and a line segment shown in FIG. FIG. 12 shows the results of Mg line analysis measured along the line, and FIG. 13 shows the results of Al line analysis measured along the line segment shown in FIG.
- Example 1 the cross section of the hydrogen storage alloy powder was measured by FE-EPMA. As a result, no Mg enriched-Ni diluted region was confirmed on the outermost surface of the alloy powder.
- the composition of the portion close to the surface is La 0.65 Sm 0.12 Zr 0.01 Mg 0.20 Ni 3.40 Al 0.21
- the composition of the portion close to the center is La 0.66 Sm 0.12 Zr 0.01 Mg 0.20 It was Ni 3.43 Al 0.20 .
- the battery characteristic measured similarly to Example 1 was measured. The results are shown in Table 9.
- Comparative Example 2 A hydrogen storage alloy powder was produced in the same manner as in Comparative Example 1 except that the composition of the raw materials was changed to obtain a hydrogen storage alloy powder having the composition shown in Table 3.
- the cross section of the hydrogen storage alloy powder was measured by FE-EPMA.
- no Mg enriched-Ni diluted region was confirmed on the outermost surface of the alloy powder.
- the quantitative analysis was performed on the two locations inside the alloy powder.
- the composition of the portion near the surface was La 0.15 Pr 0.47 Nd 0.24 Mg 0.15 Ni 3.31 Co 0.14 Al 0.08
- the composition near the center was La 0.16 Pr 0.46 Nd 0.25 Mg 0.15 Ni 3.30 Co 0.16 Al 0.07 .
- the battery characteristics were measured in the same manner as in Example 1. The results are shown in Table 9.
- Comparative Example 3 The hydrogen storage alloy was the same as in Comparative Example 1 except that the raw material composition was changed and a copper mold was used so that an ingot of 20 mm was obtained and a hydrogen storage alloy powder having the composition shown in Table 3 was obtained. A powder was prepared. As in Example 1, the cross section of the hydrogen storage alloy powder was measured by FE-EPMA. As a result, no Mg enriched-Ni diluted region was confirmed on the outermost surface of the alloy powder. As a result of quantitative analysis of two locations inside the alloy powder as in Comparative Example 1, the composition of the portion close to the surface was La 0.62 Sm 0.14 Zr 0.01 Mg 0.13 Ni 3.44 Al 0.10 , and the composition of the portion close to the center was La 0.69. Sm 0.14 Zr 0.01 Mg 0.17 Ni 3.37 Al 0.15 . Further, the battery characteristics were measured in the same manner as in Example 1. The results are shown in Table 9.
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Abstract
Description
近年、希土類-Mg-Ni系水素吸蔵合金が実用化され、この合金を負極材料として使用したニッケル水素二次電池は高容量であることが知られている。
特許文献2には、La-Mg-Ni系の水素吸蔵合金粒子とSnを含む電極を用いて作製したニッケル水素電池をアルカリ性水溶液に浸漬しながら充放電反応させることによって、Snを含む化合物およびMgを含む化合物を合金粒子表面に析出させることができ、このニッケル水素電池の放電容量を大きくし、かつサイクル特性を向上させうることが開示されている。
本発明の別の課題は、初期活性、放電容量及びサイクル特性の全てに優れたニッケル水素二次電池及び該二次電池に用いる負極を提供することにある。
また本発明によれば、上記水素吸蔵合金粉末を用いたニッケル水素二次電池用負極及び該負極を用いたニッケル水素二次電池が提供される。
本発明の水素吸蔵合金粉末の合金組成は、式(1) R1-aMgaNibAlcMdで示される。
式(1)中Rは、Sc、Yを含む希土類元素、Zr、HfおよびCaから選ばれる少なくとも1種の元素であり、特に、La、Nd、Pr、Sm、Y及びZrの1種又は2種以上を含むことが好ましい。Laは合金の水素吸蔵放出時の平衡圧を低くする傾向にあり、Nd、Pr、Sm、Y、Zrは高くする傾向にある。
式(1)中1-aは、Rの含有量を表す。1-aは、0.60≦1-a≦0.995であり、好ましくは0.75≦1-a≦0.99、さらに好ましくは0.85≦1-a≦0.99である。
式(1)中dは、M元素の含有量を表す。dは0≦d≦1.00、好ましくは0≦d≦0.50であり、必ずしも必要ではないが、電池の用途により特性の微調整が必要な場合に含有させることができる。
本発明において、前記合金粉末の組成は、ICP(Inductively Coupled Plasma)で定量分析することにより確認した。
本発明の水素吸蔵合金粉末がAlを含む場合、前記Mg濃化-Ni希薄領域におけるAlの含有割合は任意であるが、式(1)に示すAlのモル比(式(1)中のc)より大きいモル比でAlを含む組成を有することが好ましい。また、前記Mg-Ni含有領域におけるAlの含有割合は任意であるが、Mg濃化-Ni希薄領域よりAlのモル比が小さい組成の領域を有することが好ましい。
前記Mg濃化-Ni希薄領域は、式(1)に示すMgおよびNiのモル比と比較してMgのモル比が、通常1.05倍以上、1.90倍以下、好ましくは1.05倍以上、1.50倍以下であり、Niのモル比が、通常0.45倍以上、0.95倍以下、好ましくは0.50倍以上、0.95倍以下の組成の領域である。
前記Mg濃化-Ni希薄領域は、合金粉末の最表面から中心部に向かって、通常1μm以上、40μm以下、好ましくは2μm以上、40μm以下の厚みを有する領域として存在する。また、Mg濃化-Ni希薄領域の長径は、好ましくは5μm以上、60μm以下である。更に、Mg濃化-Ni希薄領域が、合金粉末の周長に占める割合は、好ましくは1~60%、さらに好ましくは1~30%である。
Mg濃化-Ni希薄領域の最表面からの厚み、長径は、合金粉末の断面を前述と同様に観察し、Mg濃化-Ni希薄領域が存在する合金粉末をランダムに5つ選択した合金粉末の表面に存在する全てのMg濃化-Ni希薄領域の厚みの最大値及び長径を測定し、それらの平均を求めることにより測定できる。Mg濃化-Ni希薄領域の最表面の周長に占める割合は、同じ5つの粉末について周長に占めるMg濃化-Ni希薄領域の長さを積算し、5つの粉末の全周長で割って算出する。
前記の結晶構造は、前記FE-EPMAによるMg濃化-Ni希薄領域および合金粉末内部の各元素の定量分析の結果から推測される。例えば、後述する実施例18の結果によるとMg濃化-Ni希薄領域のAB比(式(1)に示すb、c、dの和)が1.71であり、合金粉末内部になるにつれ3.13、3.56となっている。これはMg濃化-Ni希薄領域が1-2相に類似した相であり、合金内部になるにつれ、1-3相、2-7相、5-19相に類似した相であることが推測される。また実施例52は同様にMg濃化-Ni希薄領域から合金粉末内部になるにつれ、AB比が3.16、3.17、3.36、3.90となっている。これはMg濃化-Ni希薄領域が1-3相に類似した相であり、合金内部になるにつれ、1-3相、2-7相、5-19相、1-5相に類似した相であることが推測される。つまり、測定値はAB比が整数値はとらないものの、Mg濃化-Ni希薄領域から合金粉末内部になるにつれ、AB比が2近傍から5近傍までの間で変化することがわかる。ここでは、AB比が異なる1-2相から5-19相の結晶構造を具体的に記載した。近年、5-19相と1-5相の間のAB比をとる結晶構造の報告もあるが、これも前記した1-5相の単位格子においてBサイトを占める原子をAサイトをしめる原子である一定の周期で置換した結晶構造を有するものであって、本発明においてはそのような結晶構造を有することを除外するものではない。
前記Mg-Ni含有領域の少なくとも2種の領域は、領域(a)及び領域(b)を含み、領域(a)は、式(1)に示すMgのモル比と比較してMgのモル比が0倍以上、0.50倍以下の組成の領域であり、領域(b)は、式(1)に示すMgのモル比と比較してMgのモル比が0.50倍を超え、0.95倍以下の組成の領域である。このような少なくとも2種のMg-Ni含有領域は、合金粉末の内部にどのように存在しても良い。
本発明の水素吸蔵合金粉末組成がAlを含有し、前記Mg-Ni含有領域が少なくとも2種存在する場合、領域(a')及び領域(b')を含み、該領域(a')は、式(1)に示すAlのモル比と比較してAlのモル比が1.20倍以上、2.00倍以下の組成の領域であり、該領域(b')は、式(1)に示すAlのモル比と比較してAlのモル比が0.50倍以上、1.00倍以下の組成の領域であることが好ましい。更に、前記領域(a')は、前記領域(b')に周囲を囲まれた状態で島状に存在していることが、合金粉末の微粉化抑制の点で好ましい。ここで、Mg-Ni含有領域としての前記領域(a)と前記領域(a')、又は前記領域(b)と前記領域(b')とは、同一であっても異なっていても良い。
まず、水素吸蔵合金粉末の組成において、少なくともMgを含有しない合金粉末を調製する。該合金粉末の製造方法は特に限定されず、公知の方法により行われる。例えば、単ロール法、双ロール法又はディスク法等のストリップキャスト法や金型鋳造法が挙げられる。
ストリップキャスト法では、Mgを除く所定の合金組成となるように配合した原料を準備する。次いで不活性ガス雰囲気下、配合した原料を加熱溶解して合金溶融物とした後、該合金溶融物を銅製水冷ロールに注湯し、急冷却・凝固して合金鋳片を得る。一方、金型鋳造法では、前述の方法で得られた合金溶融物を水冷銅鋳型に注湯し、冷却・凝固して鋳塊を得る。ストリップキャスト法と金型鋳造法では冷却速度が異なり、偏析が少なく組成分布が均一な合金を得る場合にはストリップキャスト法が好ましい。また、偏析が少なく組成分布が均一な合金とするため、得られたMgを含有しない合金を熱処理することができる。
次に、鋳造して得られた合金を粉砕して合金粉末を得る。粉砕は公知の粉砕機を用いて行うことができる。このMgを含有しない合金粉末に対し、後述する熱処理工程においてMgの拡散・反応をスムーズに行うには、該合金粉末の粒径は、MV値で20~1000μmであるのが好ましく、さらに好ましくは20~400μm、最も好ましくは20~100μmである。
Mgの拡散・反応は通常400~1090℃と比較的低い温度で行うため、Mg等の成分の蒸発は多くはないが、厳密には各成分の歩留りを考慮して、所望する組成の合金が得られるように、Mgを含有しない合金粉末と、金属Mg又はMg含有合金の粉末とを配合する。
導電剤としては、既知のものが使用でき、例えば、アセチレンブラック、ファーネスブラック等カーボンブラック、黒鉛等の炭素質材料や、銅、ニッケル、コバルトが挙げられる。
結着剤としては、既知のものが使用でき、例えば、カルボキシメチルセルロース、ポリビニルアルコール、ポリビニルブチラール、ポリビニルピロリドン、ポリエチレンオキサイド、ポリテトラフルオロエチレン(PTFE)、4-フッ化エチレン-6-フッ化プロピレン共重合体(FEP)が挙げられる。
本発明のニッケル水素二次電池の形状は、円筒型、積層型、コイン型等、種々のものとすることができる。いずれの形状であっても、ニッケル水素二次電池は負極とセパレータと正極を積層した電極群をステンレス等からなる缶体に収納する。円筒形状の場合、通常、缶体を負極端子とするため、負極を外側にして電極群を渦巻き状に巻いて缶体に挿入することにより負極と負極端子は接続される。正極は通常、リードにより正極端子に接続される。
正極は、通常、ニッケル酸化物を含み、例えば、非焼結式ニッケル電極などが用いられる。非焼結式ニッケル電極は、水酸化ニッケルと必要に応じて添加される水酸化コバルト、一酸化コバルト、金属コバルトなどを結着剤とともに、水を溶媒として混合し、ペースト状とし、このペーストを発泡メタル等の集電体に充填、乾燥した後、ローラープレスなどを施すことにより作製される。
実施例1
表1に示す水素吸蔵粉末の合金組成においてMgを除く原料を秤量し、高周波溶解炉にてアルゴンガス雰囲気中で溶解し、合金溶融物とした。続いて、この溶融物の注湯温度を1400℃として、銅製水冷ロールを用いた単ロール鋳造装置を用いたストリップキャスト法にて急冷・凝固し、平均の厚みが0.4mmである鋳片を得た。得られた鋳片をボールミルにて、粉砕を行い、MV値が85μmの粒度の合金粉末を得た。得られた合金の組成をICPで分析したところ、La0.66Sm0.13Zr0.01Ni3.42Al0.20であった。
また、同水素吸蔵合金粉末の断面をFE-EPMA(日本電子製、商品名JXA8500F)により350倍で観察し、Mgの元素マッピング像を得た。Mgの元素マッピング像は、コントラスト、レベル調整を行い、Mgの濃淡が明らかに確認できるように調整した。合金粉末の最表面に内部よりMg濃度の高い領域が存在した。またその領域より内部のMgが希薄な領域には、周囲と比較し、さらにMgが希薄な領域が、島状に存在した。合金粉末の最表面の内部よりMg濃度の高い領域、その領域より内部にある周囲と比較し、さらにMgが希薄で、かつ島状に存在する領域および合金粉末内部のそれ以外の領域について、前記条件で定量分析を行った。その結果、最表面にある内部よりMg濃度の高い領域の組成は、La0.63Sm0.12Zr0.01Mg0.24Ni2.96Al0.23、Mgが希薄で、かつ島状に存在する領域の組成は、La0.75Sm0.15Zr0.01Mg0.09Ni3.60Al0.34、合金粉末内部のそれ以外の領域の組成は、La0.68Sm0.13Zr0.01Mg0.18Ni3.11Al0.17、La0.70Sm0.14Zr0.01Mg0.15Ni3.32Al0.18であった。したがって、最表面にある内部よりMg濃度の高い領域がMg濃化-Ni希薄領域であり、その他の領域がMg-Ni含有領域であることが確認された。また、Mgが希薄で、かつ島状に存在する領域は、合金粉末の全体組成であるLa0.66Sm0.13Zr0.01Mg0.20Ni3.42Al0.20のAlのモル比(0.20)と比較してAlのモル比が1.20倍以上、2.00倍以下の組成の領域であり、該Alのモル比が0.50倍以上、1.00倍以下の組成の領域(前記その他の領域、La0.68Sm0.13Zr0.01Mg0.18Ni3.11Al0.17、La0.70Sm0.14Zr0.01Mg0.15Ni3.32Al0.18)に周囲を囲まれていることが確認された。これらの結果を表1に示す。また、以上の結果から計算した、式(1)に示すMg、Ni及びAlのモル比と比較したMg濃化-Ni希薄領域におけるMgのモル比、Niのモル比及びAlのモル比、並びに式(1)に示すMg、Ni及びAlのモル比と比較したMg-Ni含有領域におけるMgのモル比、Niのモル比及びAlのモル比をそれぞれ表4に示す。
得られた水素吸蔵合金粉末の電池特性を下記の通り測定した。電池特性の評価結果を表7に示す。
(放電容量)
水素吸蔵合金粉末0.15gとカルボニルニッケル粉末0.45gを乳鉢でよく混合し、混合物を2000kgf/cm2で加圧プレスすることで直径10mmのペレットを作製した。次いで、ペレットをニッケル製金網の間に挟み込み、周辺をスポット溶接して圧接し、さらにニッケル製リードを前記金網にスポット溶接することで負極を作製した。得られた負極を対極の焼結式ニッケル電極と共に8N-KOH水溶液に浸漬し、25℃の温度下にて充放電サイクル試験を行った。
充放電は、充放電装置(計測器センター製、商品名BS2500-05R1)を使用し、水素吸蔵合金1g当たり150mAの電流で170分間充電し、10分間休止した後、水素吸蔵合金1g当たり150mAの電流で酸化水銀電極に対して-0.7Vになるまで放電を行うサイクルを100回繰り返した。
(サイクル特性)
サイクル特性として、上記充放電において最大放電容量、及び100サイクル時の放電容量を基に、以下で定義した。
サイクル特性=(100サイクル時の放電容量/最大放電容量)×100
原料の配合を変更し、表1~3に示す組成の水素吸蔵合金粉末を得た以外は、実施例1と同様にして水素吸蔵合金粉末を作製した。実施例2の水素吸蔵合金粉末の断面をEPMAのComp像の写しとして図6に、Mgの元素マッピング像の写しを図7に、Alの元素マッピング像の写しを図8に示す。
また、実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果を表1~3に示す。表1~3のMg-Ni含有領域の組成の欄には、Mg-Ni含有領域であって、合金粉末の全体組成を表す式(1)に示すAlのモル比と比較してAlのモル比が1.20倍以上、2.00倍以下の組成の領域(a')と、式(1)に示すAlのモル比と比較してAlのモル比が0.50倍以上、1.00倍以下の組成の領域(b')とを少なくとも含み、該領域(a')が、該領域(b')に周囲を囲まれた状態で島状に存在する場合については、組成式の後方に(Al濃化)と記載した。また、Mg-Ni含有領域の組成の欄に(Al濃化)と記載した組成式がない場合、Mgのマッピング像から同島状の領域が確認されなかったことを意味する。(Al濃化)の記載のない組成式は、Mg濃化-Ni希薄領域より内部にあり、合金粉末の表面に近い部分から中心に近い部分について、順番に記載している。
実施例22の水素吸蔵合金粉末の断面をFE-EPMAで観察したMgの元素マッピング像の写しを図14に示す。図14中の(1)~(4)の矢印で示す部分について、含有する各元素の定量分析を行った。(1)がMg濃化-Ni希薄領域、(2)~(4)がMg-Ni含有領域である。(4)は実施例22の水素吸蔵合金粉末の全体組成(La0.45Gd0.10Pr0.06Nd0.19Mg0.20Ni3.30Al0.15)のAlのモル比(0.15)と比較してAlのモル比が1.20倍以上、2.00倍以下の組成の領域であり、該Alのモル比が0.50倍以上、1.00倍以下の組成の領域((2)および(3))に周囲を囲まれ、かつ島状に存在するMg-Ni含有領域であった。
また、実施例1と同様にMg濃化-Ni希薄領域の厚み、長径、合金粉末の周長に対するMg濃化-Ni希薄領域の割合を測定した結果、並びに電池特性の結果を表7~9に示す。
原料の配合を変更し、Mgを除く原料の鋳造を、20mmの鋳塊が得られるように銅製金型を用いて行い、表3に示す組成の水素吸蔵合金粉末を得た以外は、実施例1と同様にして水素吸蔵合金粉末を作製した。実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果を表3に示す。
実施例1と同様に測定し算出した、式(1)に示すMg、Ni及びAlのモル比と比較したMg濃化-Ni希薄領域におけるMgのモル比、Niのモル比及びAlのモル比、並びに式(1)に示すMg、Ni及びAlのモル比と比較したMg-Ni領域におけるMgのモル比、Niのモル比及びAlのモル比をそれぞれ表6に示す。
また、実施例1と同様にMg濃化-Ni希薄領域の厚み、長径、合金粉末の周長に対するMg濃化-Ni希薄領域の割合を測定した結果、並びに電池特性の結果を表9に示す。
原料の配合を変更し、970℃、12時間行った熱処理の熱処理時間を3時間(実施例44、47、50)、6時間(実施例45、48、51)、9時間(実施例46、49、52)に変更し、表3に示す組成の水素吸蔵合金粉末を得た以外は、実施例1と同様にして水素吸蔵合金粉末を作製した。実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果を表3に示す。
実施例44の水素吸蔵合金粉末の断面のFE-EPMAのMgのマッピング像の写しを図15に示す。この合金粉末には、合金粉末の内部に周囲よりMgが希薄で、かつ島状に存在するMg-Ni含有領域は確認されなかった。図15中の(1)~(4)の矢印で示す部分について、含有する各元素の定量分析を行った。(1)がMg濃化-Ni希薄領域、(2)~(4)がMg-Ni含有領域である。
実施例1と同様に測定し算出した、式(1)に示すMg、Ni及びAlのモル比と比較したMg濃化-Ni希薄領域におけるMgのモル比、Niのモル比及びAlのモル比、並びに式(1)に示すMg、Ni及びAlのモル比と比較したMg-Ni領域におけるMgのモル比、Niのモル比及びAlのモル比をそれぞれ表6に示す。
また、実施例1と同様にMg濃化-Ni希薄領域の厚み、長径、合金粉末の周長に対するMg濃化-Ni希薄領域の割合を測定した結果、並びに電池特性の結果を表9に示す。
実施例1の水素吸蔵合金粉末と同じ組成の合金が得られるように、金属Mgを含むすべての原料を同時に配合し、実施例1と同様にストリップキャスティング法にて鋳片を得た。得られた鋳片をアルゴンガス雰囲気中、950℃で6時間熱処理を行った。熱処理後の鋳片をボールミルにて粉砕し、MV値が70μmの水素吸蔵合金粉末を得た。得られた合金粉末の組成をICPで分析したところLa0.66Sm0.13Zr0.01Mg0.20Ni3.42Al0.20であった。得られた水素吸蔵合金粉末のEPMAのComp像の写しを図9に、Mgの元素マッピング像の写しを図10に、Alの元素マッピング像の写しを図11に、図10に示す線分に沿って測定したMgのライン分析の結果を図12に、図11に示す線分に沿って測定したAlのライン分析の結果を図13に示す。
実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果、合金粉末の最表面にMg濃化-Ni希薄領域は確認されなかった。合金粉末の内部の2箇所について定量分析を行った結果、表面に近い部分の組成はLa0.65Sm0.12Zr0.01Mg0.20Ni3.40Al0.21、中心に近い部分の組成はLa0.66Sm0.12Zr0.01Mg0.20Ni3.43Al0.20であった。また実施例1と同様に測定した電池特性を測定した。結果を表9に示す。
原料の配合を変更し、表3に示す組成の水素吸蔵合金粉末を得た以外は、比較例1と同様にして水素吸蔵合金粉末を作製した。実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果、合金粉末の最表面にMg濃化-Ni希薄領域は確認されなかった。比較例1と同様に合金粉末の内部の2箇所について定量分析を行った結果、表面に近い部分の組成はLa0.15Pr0.47Nd0.24Mg0.15Ni3.31Co0.14Al0.08、中心に近い部分の組成はLa0.16Pr0.46Nd0.25Mg0.15Ni3.30Co0.16Al0.07であった。また実施例1と同様に電池特性を測定した。結果を表9に示す。
原料の配合を変更し、鋳造を20mmの鋳塊が得られるように銅製金型を用い、表3に示す組成の水素吸蔵合金粉末を得た以外は、比較例1と同様にして水素吸蔵合金粉末を作製した。実施例1と同様に同水素吸蔵合金粉末の断面をFE-EPMAで測定した結果、合金粉末の最表面にMg濃化-Ni希薄領域は確認されなかった。比較例1と同様に合金粉末の内部の2箇所について定量分析を行った結果、表面に近い部分の組成はLa0.62Sm0.14Zr0.01Mg0.13Ni3.44Al0.10、中心に近い部分の組成はLa0.69Sm0.14Zr0.01Mg0.17Ni3.37Al0.15であった。また実施例1と同様に電池特性を測定した。結果を表9に示す。
Claims (14)
- 式(1) R1-aMgaNibAlcMd(式中RはSc、Yを含む希土類元素、Zr、Hf及びCaから選ばれる少なくとも1種、MはR、Mg、Ni及びAl以外の元素から選ばれる少なくとも1種を示す。aは0.005≦a≦0.40、bは3.00≦b≦4.50、cは0≦c≦0.50、dは0≦d≦1.00、b+c+dは3.00≦b+c+d≦4.50である。)で表される組成を有する水素吸蔵合金粉末であって、
該合金粉末の最表面に、式(1)に示すMgのモル比(式(1)中のa)よりもMgのモル比が大きく、式(1)に示すNiのモル比(式(1)中のb)よりもNiのモル比が小さい組成のMg濃化-Ni希薄領域を有し、合金粉末の内部に、該Mg濃化-Ni希薄領域のMg及びNiのモル比よりもMgのモル比が小さく、Niのモル比が大きい組成のMg-Ni含有領域とを有する水素吸蔵合金粉末。 - 前記Mg濃化-Ni希薄領域は、式(1)に示すMgおよびNiのモル比と比較してMgのモル比が1.05倍以上、1.50倍以下、Niのモル比が0.50倍以上、0.95倍以下の組成の領域である請求項1記載の水素吸蔵合金粉末。
- 前記Mg-Ni含有領域として、Mgのモル比が異なる組成の少なくとも2種の領域が存在する請求項1又は2記載の水素吸蔵合金粉末。
- 前記Mg-Ni含有領域の少なくとも2種の領域が、領域(a)及び領域(b)を含み、領域(a)は、式(1)に示すMgのモル比と比較してMgのモル比が0倍以上、0.50倍以下の組成の領域であり、領域(b)は、0.50倍を超え、0.95倍以下の組成の領域である請求項3記載の水素吸蔵合金粉末。
- 前記Mg濃化-Ni希薄領域は、合金粉末の最表面から中心部に向かって、2μm以上、40μm以下の厚みを有する領域として存在している請求項1~4のいずれかに記載の水素吸蔵合金。
- 前記Mg濃化-Ni希薄領域及び前記少なくとも2種のMg-Ni含有領域は、合金粉末の最表面から中心部に向かって、Mgのモル比が小さく、Niのモル比が大きくなる濃度勾配を示す請求項3~5のいずれかに記載の水素吸蔵合金粉末。
- 前記Mg濃化-Ni希薄領域は、式(1)に示すAlのモル比(式(1)中のc)より大きいモル比でAlを含む組成を有し、前記Mg-Ni含有領域は、Mg濃化-Ni希薄領域よりAlのモル比が小さい組成の領域を有する請求項1~6のいずれかに記載の水素吸蔵合金粉末。
- 前記Mg濃化-Ni希薄領域は、式(1)に示すAlのモル比と比較してAlのモル比が1.05倍以上、2.00倍以下の組成の領域である請求項1~7記載の水素吸蔵合金粉末。
- 前記Mg-Ni含有領域の少なくとも2種の領域が、領域(a')及び領域(b')を含み、領域(a')は、式(1)に示すAlのモル比と比較してAlのモル比が1.20倍以上、2.00倍以下の組成の領域であり、領域(b')は、式(1)に示すAlのモル比と比較してAlのモル比が0.50倍以上、1.00倍以下の組成の領域であり、該領域(a')は、該領域(b')に周囲を囲まれた状態で島状に存在する請求項3~8記載の水素吸蔵合金粉末。
- 式(1)において、aは0.01≦a≦0.15、bは3.00≦b≦3.80、cは0.05≦c≦0.50、dは0≦d≦1.00、b+c+dは3.00≦b+c+d≦3.80である請求項1~9記載の水素吸蔵合金粉末。
- 体積平均径(MV値)が、20~100μmである請求項1~10のいずれかに記載の水素吸蔵合金粉末。
- 請求項1~11のいずれかに記載の水素吸蔵合金粉末からなるニッケル水素二次電池用負極活物質。
- 請求項12に記載の負極活物質を含むニッケル水素二次電池用負極。
- 請求項13に記載のニッケル水素二次電池用負極を備えたニッケル水素二次電池。
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JP2007063597A (ja) | 2005-08-30 | 2007-03-15 | Sanyo Electric Co Ltd | アルカリ蓄電池用水素吸蔵合金、アルカリ蓄電池用水素吸蔵合金の製造方法及びアルカリ蓄電池 |
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EP2653576A4 (en) | 2017-08-09 |
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JP5681729B2 (ja) | 2015-03-11 |
JPWO2012081724A1 (ja) | 2014-05-22 |
US9343737B2 (en) | 2016-05-17 |
KR20130130023A (ko) | 2013-11-29 |
EP2653576A1 (en) | 2013-10-23 |
US20130272918A1 (en) | 2013-10-17 |
CN103370431A (zh) | 2013-10-23 |
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