WO2021166655A1 - Mg-BASED ALLOY NEGATIVE ELECTRODE MATERIAL, PRODUCTION METHOD THEREFOR, AND Mg SECONDARY BATTERY USING SAME - Google Patents

Mg-BASED ALLOY NEGATIVE ELECTRODE MATERIAL, PRODUCTION METHOD THEREFOR, AND Mg SECONDARY BATTERY USING SAME Download PDF

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WO2021166655A1
WO2021166655A1 PCT/JP2021/004058 JP2021004058W WO2021166655A1 WO 2021166655 A1 WO2021166655 A1 WO 2021166655A1 JP 2021004058 W JP2021004058 W JP 2021004058W WO 2021166655 A1 WO2021166655 A1 WO 2021166655A1
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negative electrode
based alloy
electrode material
alloy negative
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PCT/JP2021/004058
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French (fr)
Japanese (ja)
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英俊 染川
俊彦 万代
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国立研究開発法人物質・材料研究機構
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Priority to JP2022501775A priority Critical patent/JP7362164B2/en
Publication of WO2021166655A1 publication Critical patent/WO2021166655A1/en

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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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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
    • H01M4/46—Alloys based on magnesium or aluminium
    • 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 an Mg-based alloy negative electrode material and a method for producing the same.
  • the present invention also relates to an Mg secondary battery using an Mg-based alloy negative electrode material.
  • Mg (magnesium) metal When used as the negative electrode of a storage battery, Mg (magnesium) metal exhibits the highest theoretical capacity density among the metals in practical use and does not form a dendride-like precipitation part during electrodeposition, so that it is a high energy density storage battery. It is attracting attention as a negative electrode material for this purpose. However, unlike the Li (lithium) metal negative electrode and the Na (sodium) metal negative electrode, the Mg metal negative electrode is difficult to form an ionic conductive film at the interface with the electrolytic solution and is easily passivated, so that the dissolution and precipitation behavior is reversible. The problem is that it is unlikely to occur.
  • a storage battery such as a secondary battery includes a positive electrode active material and an electrolytic solution in addition to the negative electrode material. Therefore, as one means for solving the above-mentioned problems, the components other than the negative electrode material have been improved.
  • a positive electrode active material and an electrolytic solution effective for Mg secondary batteries have been developed, respectively.
  • the constituent materials can be roughly classified into two types: Mg metal negative electrode material (and Mg-based alloy negative electrode material) and Mg-containing intermetallic compounds.
  • Patent Documents 3 and 4 the above-mentioned problems are solved by utilizing the Mg-Bi intermetallic compound (Mg 3 Bi 2 ) and the Mg-Sn intermetallic compound (Mg 2 Sn) as the negative electrode material.
  • the intermetallic compound negative electrode has a problem that the potential is higher and the capacitance density is lower than that of the Mg metal negative electrode (and the Mg base alloy negative electrode).
  • Bi bismuth
  • Sn titanium
  • Patent Document 5 discloses an Mg metal negative electrode and an Mg-based alloy negative electrode using an Mg metal as a negative electrode without utilizing an intermetallic compound.
  • Patent Document 5 lists Mg—Al alloys, Mg—Zn alloys, and Mg—Mn alloys as Mg-based alloys constituting the negative electrode, but Mg— is shown in Examples. Only 6 mass% Al alloy. In this alloy, from the viewpoint of thermal equilibrium and metallographic structure, a large number of intermetallic compounds represented by Mg 17 Al 12 are dispersed in the Mg matrix at high density due to the high concentration of Al added. Will be done. Of course, since Al is spent on the formation of intermetallic compounds, it is obvious that solute element segregation does not occur at the grain boundaries.
  • Patent Document 6 discloses an Mg metal negative electrode and an Mg-based alloy negative electrode suitable for an Mg secondary battery containing 90% or more of Mg in terms of mass ratio.
  • a subcomponent that can be contained any one of Al (aluminum), Zn (zinc), Mn (manganese), Si (silicon), Ca (calcium), Fe (iron), Cu (copper), and Ni (nickel).
  • Al aluminum
  • Zn zinc
  • Mn manganese
  • Si silicon
  • Ca calcium
  • Fe iron
  • Cu copper
  • Ni nickel
  • Si, Fe, Cu, and Ni have a maximum solid solution amount of 0.01 mol% or less with respect to Mg, which is not a solid solution amount that affects mechanical properties and functional characteristics, and therefore are usually unavoidable impurity elements. Be treated.
  • Patent Document 7 discloses an Mg alloy containing 0.03 to 0.54 mol% of a solute atom having an atomic radius larger than that of Mg and having excellent strength and ductility.
  • the solute elements are unevenly distributed at the grain boundaries, but the average crystal grain size is 1.5 ⁇ m or less because the main purpose is to achieve high strength and high ductility of the bulk material.
  • Patent Document 8 discloses an Mg alloy containing 0.77 to 2 mass% of Mn
  • Patent Document 9 discloses an Mg alloy containing 0.25 to 9 mass% of Bi, both of which are excellent in room temperature ductility. It is said to be a Mg alloy.
  • Mg alloys are characterized in that the average crystal grain size is 10 ⁇ m or less, the elongation at break is about 100%, and the m value, which is an index of the contribution ratio of grain boundary slip to deformation, is 0.1 or more. There is.
  • the Mg alloys disclosed by the present inventors are intended to improve mechanical properties such as strength and ductility, and the electrochemical properties are unknown. As far as the present inventor knows, there is no literature or disclosure example related to the electrochemical properties of Mg-based binary alloys.
  • the first aspect of the present invention for solving the above-mentioned problems is to use at least one element (solute element) selected from Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth) and Zn.
  • This is an Mg-based alloy negative electrode material containing 0.02 mol% or more and 10 mol% or less in total, the balance of which is formed of an Mg-based alloy composed of Mg and an unavoidable component, and a thickness of 1 mm or less.
  • the Mg-based alloy negative electrode material may have an average particle size of 1000 ⁇ m or less as the Mg base material.
  • At least one of the solute elements may be segregated at the grain boundaries.
  • the Mg-based alloy negative electrode material may exhibit cycle characteristics of 5 times or more in cycle measurement using a tripolar cell.
  • the Mg-based alloy negative electrode material may exhibit characteristics of an overvoltage of 50 mV or less in an electrochemical precipitation / dissolution test of Mg metal.
  • the Mg-based alloy negative electrode material may exhibit a current density of ⁇ 10 mAcm ⁇ 2 or more when the electrode potential with respect to the Mg metal is ⁇ 0.5 V in the electrochemical precipitation / dissolution test of the Mg metal.
  • the second aspect of the present invention for solving the above-mentioned problems is to melt and cast a raw material to obtain an Mg-based alloy cast material, and to obtain an Mg-based alloy cast material at 400 ° C. or higher and 650 ° C. with respect to the Mg-based alloy cast material.
  • the solution treatment is performed at the following temperature for 0.5 hours or more and 48 hours or less, and the Mg-based alloy cast material after the solution treatment is subjected to plastic strain of 50 ° C. or higher and 550 ° C.
  • This is a method for producing an Mg-based alloy negative electrode material according to the first aspect, which comprises performing a spreading process having a cross-sectional reduction rate of 10% or more at the following temperature.
  • a third aspect of the present invention for solving the above problems is an Mg secondary battery composed of an Mg-based alloy negative electrode material according to the first aspect, an electrolyte and a positive electrode.
  • the Mg secondary battery may exhibit a cycle characteristic of 10 times or more by cycle measurement.
  • FIG. 1 It is a schematic diagram which shows the schematic structure of the Mg secondary battery which uses the Mg-based alloy negative electrode material which concerns on one aspect of this invention.
  • An example of an external photograph of the Mg-based alloy negative electrode material according to each embodiment of the present invention shows an external photograph after rolling.
  • An electron backscatter diffraction image is shown in an example of observing the microstructure of the Mg—Ca alloy according to an embodiment of the present invention.
  • a Z contrast image by high resolution electron microscopy is shown.
  • the electrochemical precipitation dissolution test example of the Mg—Ca alloy according to one embodiment of the present invention the relationship between the potential and the current density in each cycle is shown.
  • An electrochemical precipitation / dissolution test example of an Mg—Ag alloy according to an embodiment of the present invention shows the relationship between the potential and the current density in each cycle. It is an electrochemical precipitation dissolution curve of the Mg-based binary alloy which concerns on each Example of this invention.
  • the relationship between the potential and the current density at the time of two cycles is shown in the electrochemical precipitation dissolution test examples of Mg—Ca alloys having various Ca amounts according to one embodiment of the present invention.
  • the relationship between the potential and the current density at 10 cycles is shown in the electrochemical precipitation and dissolution test examples of Mg—Ca alloys having various Ca amounts according to one embodiment of the present invention.
  • the Mg-based alloy negative electrode material according to the first aspect of the present invention (hereinafter, may be simply referred to as “first aspect”) is substantially made of Mg—Amol% X as the Mg-based alloy material. That is, the balance of Amol% other than the X element is composed of Mg and an unavoidable component.
  • X is at least one element selected from Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earths) and Zn.
  • these elements may be collectively referred to as "solute elements”.
  • Rare earths among solute elements include lanthanoids such as Sc (scandium) and Y (yttrium), and Gd (gadolinium) and Ce (cerium).
  • the value of A is not more than the maximum solid solution value with respect to Mg, preferably 0.02 mol% or more and 10 mol% or less, more preferably 0.02 mol% or more and 5 mol% or less, still more preferably 0.02 mol%.
  • the above is 1 mol% or less.
  • the added solute element does not affect the mechanical properties and the electrochemical properties, and only acts in the same manner as the impurity element. From the viewpoint of sufficiently exerting a positive effect on the mechanical properties and electrochemical properties of the added solute element, it is preferable that each lower limit value in the range of A described above is 0.05 mol%.
  • the solid solution amount A is preferably 0.02 mol% or more and 0.2 mol% or less. It is more preferably 02 mol% or more and 0.1 mol% or less.
  • the thickness of the first side surface is 1 mm or less.
  • the thickness is preferably 0.5 mm or less, more preferably 0.3 mm or less.
  • the crystal grain size of the Mg matrix is preferably 1000 ⁇ m or less, more preferably 100 ⁇ m or less, and even more preferably 50 ⁇ m or less. In the dissolution of Mg by the negative electrode reaction, the grain boundaries tend to become sites.
  • the crystal grain size is measured by the section method based on the JIS standard (also referred to as a cutting method. See JIS H0501 and G0551). However, when the crystal grain size is fine or the grain boundaries are unclear, it is difficult to apply the section method. Therefore, a bright field image or an electron backscatter diffraction image obtained by a transmission electron microscope is used. The result of the measurement is taken as the crystal grain size.
  • the added solute element segregates at the grain boundaries and its concentration is 1.5 times or more higher than the concentration of the solute element present in the Mg matrix.
  • the presence or absence of grain boundary segregation is preferably identified by using the analysis result by the energy dispersive X-ray spectroscopy (EDX) apparatus attached to the transmission electron microscope (TEM), but it is preferable to use a method such as a three-dimensional atom probe. You may evaluate it.
  • EDX energy dispersive X-ray spectroscopy
  • TEM transmission electron microscope
  • the first aspect exhibits cycle characteristics of preferably 5 times or more, more preferably 25 times or more, still more preferably 50 times or more in cycle measurement using a tripolar cell.
  • the cycle characteristic is 5 times or more, the problem of side reaction with the electrolytic solution does not become apparent, so that it can be suitably used as a negative electrode.
  • the overvoltage obtained in the electrochemical precipitation / dissolution test using a tripolar cell is preferably 50 mV or less, more preferably 30 mV or less, still more preferably 20 mV or less. When the overvoltage is 50 mV or less, the loss of the battery voltage is small, so that it can be suitably used as a negative electrode.
  • the current density when the electrode potential with respect to Mg metal is ⁇ 0.5 V is preferably ⁇ 10 mAcm -2 or more, more preferably ⁇ 20 mA cm -2 or more. , More preferably ⁇ 25 mAcm -2 or more.
  • the current density is ⁇ 10 mAcm -2 or more, the electrochemical reaction is less likely to be rate-determined by the negative electrode, and it can be suitably used as the negative electrode.
  • the electrolytic solution used in the cycle measurement test and the electrochemical precipitation / dissolution test uses a fluoroalkoxyborate magnesium salt or a fluoroalkoxyaluminate magnesium salt of 0.1 mol / L or more and 1.5 mol / L or less as a solute, and the solute is organic. It shall be mixed with ethers. However, when the solute cannot be used, other magnesium compounds such as alkylmagnesium chloride, magnesium chloride, magnesium bistrifluoromethanesulfonylimide salt and magnesium hexamethyldisilazide salt may be substituted as the solute.
  • Mg and solute metal which are raw materials, are melted and cast to obtain an Mg-based alloy cast material.
  • the melting method is not limited as long as an alloy having the desired composition can be obtained, and atmospheric melting, vacuum melting, arc melting, plasma melting and the like can be adopted.
  • the casting method is not limited, and any method such as gravity casting, sand casting, die casting, etc. can be adopted as long as it can produce the desired Mg-based alloy casting material.
  • the molten Mg-based alloy cast material is subjected to a solution treatment at a temperature of 400 ° C.
  • the solution treatment time is preferably 0.5 hours or more and 48 hours or less. If the treatment time is less than 0.5 hours, the diffusion of the solute element in the matrix tends to be insufficient, so that segregation during casting remains and it becomes difficult to create a sound material. On the other hand, if the processing time exceeds 48 hours, the working time becomes long, which is not preferable from an industrial point of view.
  • the temperature of warm or hot working shall be 50 ° C or higher and 550 ° C or lower.
  • the temperature is preferably 75 ° C. or higher and 525 ° C. or lower, more preferably 100 ° C. or higher and 500 ° C. or lower.
  • the processing temperature is less than 50 ° C, many deformed twins that are the starting points of cracks and cracks are generated, and ear cracks and surface waviness occur at high density, so that a healthy foil material with a thickness of 1000 ⁇ m or less should be produced. Becomes difficult.
  • the amount of strain applied by warm or hot working is such that the cross-sectional reduction rate is 10% or more.
  • the cross-sectional reduction rate is preferably 20% or more, more preferably 50% or more.
  • strain cannot be uniformly applied to the inside of the work material, and it becomes difficult to control the crystal grain size and the grain boundary segregation.
  • the warm or hot working method is typically extrusion, forging, rolling, drawing, etc., but any working method can be used as long as it can apply strain and control the thickness. But it can be adopted.
  • the effect of the present invention cannot be obtained because the added solute element does not segregate at the grain boundaries only by solution-treating the cast material without executing warm or hot working.
  • the reason is that the grain boundary segregation phenomenon is caused by the interaction between the solute element and the strain introduced during warm or hot working.
  • FIG. 1 is a schematic view showing a schematic configuration of an Mg secondary battery in which the Mg-based alloy negative electrode material of the present invention is used.
  • the Mg secondary battery includes a positive electrode C, a negative electrode D, an electrolytic solution B, and a container A.
  • a positive electrode active material (not shown) is held by a positive electrode current collector (not shown).
  • the positive electrode current collector has a function of donating electrons to the positive electrode active material at the time of discharge.
  • the substance used as the positive electrode current collector nickel, iron, stainless steel, titanium, aluminum and the like are preferably used because they have relatively excellent corrosion resistance and are inexpensive.
  • the substance used as the positive electrode active material is not particularly limited as long as it can insert and remove Mg ions, but MgFeSiO 4 , MgMn 2 O 4 , or V 2 O 5 or the like is preferably used.
  • a specific configuration of the positive electrode C for example, a configuration in which V 2 O 5 is coated on stainless steel can be mentioned.
  • the Mg-based alloy negative electrode material As the negative electrode D, the Mg-based alloy negative electrode material according to the first side surface is used.
  • the electrolytic solution B is held by a separator (not shown) to generate ionic conductivity between the positive electrode C and the negative electrode D.
  • the electrolytic solution B contains Mg ions.
  • Mg ions cause a reduction reaction (for example, the reaction of the formula (1) described later) at the positive electrode C and an oxidation reaction (for example, the reaction of the formula (2) described later) at the negative electrode D.
  • Mg ions cause an oxidation reaction (for example, the reaction of the formula (3) described later) at the positive electrode C and a reduction reaction (for example, the reaction of the formula (4) described later) at the negative electrode D.
  • the electrolytic solution B in the third aspect may contain an organic solvent as a main solvent and a magnesium salt, or may be an inorganic solvent having Mg ion conductivity.
  • the magnesium salt dissolves in the organic solvent and dissociates to form a magnesium complex cation in which the organic solvent is coordinated. Since this complex cation is responsible for the activity in the electrochemical precipitation and dissolution of magnesium, good electrochemical properties tend to be obtained when a magnesium salt having higher dissociation is used.
  • the electrolytic solution exhibiting good electrochemical properties include an electrolytic solution in which a magnesium fluoroalkoxy borate salt or a magnesium fluoroalkoxyaluminate salt is mixed with organic ethers.
  • magnesium salt used in the electrolytic solution examples include those having a fluoroalkoxyborate anion or a fluoroalkoxyaluminate anion as a counter anion.
  • the fluoroalkoxy group of the magnesium salt used here is not particularly limited.
  • Specific examples of the magnesium salt used in the third aspect include tetrakis (hexafluoroisopropoxy) magnesium borate salt and tetrakis (hexafluoroisopropoxy) aluminate magnesium salt.
  • the positive electrode C, the negative electrode D, and the electrolytic solution B are sealed in the container A.
  • the material of the container A is not particularly limited as long as it does not leak the electrolytic solution and has corrosion resistance, but it is formed by pressing a metal plate such as iron, and the entire inner and outer surfaces are for corrosion resistance. Those on which a plating layer such as nickel is formed are preferably used.
  • the third aspect may include technical matters that are obvious in the technical field of Mg secondary batteries, in place of or in addition to the above matters.
  • the cast material after the solution treatment was machined into a cylindrical extruded billet having a diameter of 40 mm and a length of 60 mm.
  • the processed billet is held in a container set at 275 ° C. for 30 minutes, and then hot strain is applied by extrusion at an extrusion ratio of 19: 1 to extrude a material having a length of 500 mm or more (hereinafter, simply "extruded material”). ”) was prepared.
  • the extruded material was cut to a length of 100 mm and rolled. Before rolling, the extruded material is held in an electric furnace (muffle furnace) set at 400 ° C for 15 minutes or more, and then a rolling mill with a roll temperature set at 200 ° C is used to set the rolling reduction ratio of one pass to 10% and thicken. Rolling was carried out until the diameter became 0.30 mm.
  • rolled material the material after rolling is simply referred to as "rolled material”.
  • a rolled material containing Ag, Al, Bi, Li, Mn, Sn, Y and Zn as solute elements instead of Ca was produced by the same method.
  • Mn or Y having a melting point significantly different from that of Mg is used as a solute element
  • the iron crucible containing the raw material is heated by a high-frequency heating device to melt the alloy casting material.
  • the conditions for producing rolled material from each molten casting include the temperature inside the container that holds the cylindrical extruded billet, the temperature of the muffle furnace that holds the extruded material before rolling, and the roll temperature during rolling. Except for the items shown in Table 1, they were the same as the rolled materials containing Ca as a solute element.
  • FIG. 2 is an external photograph of each rolled material (Mg-based alloy negative electrode material).
  • the thickness t of each rolled material is 300 ⁇ m for Mg—Ca alloy, 300 ⁇ m for Mg—Y alloy, 300 ⁇ m for Mg—Mn alloy, 290 ⁇ m for Mg—Sn alloy, 300 ⁇ m for Mg—Zn alloy, and 300 ⁇ m for Mg—Li alloy.
  • Mg—Al alloy was 300 ⁇ m.
  • a fine structure image was obtained for each of the obtained rolled materials by an electron backscatter diffraction technique.
  • the microstructure image of the rolled Mg—Ca alloy material is shown in FIG. 3, and the same fine structure was obtained for the other rolled materials.
  • the lumps having the same contrast in the figure are individual crystal grains, and one typical crystal grain is surrounded by a black line, and the size is 20 ⁇ m.
  • Table 1 summarizes the average grain size of the binary alloy used in the examples and the extrusion processing and rolling processing conditions. The average crystal grain size is 100 ⁇ m or less regardless of the type of added element.
  • Z-contrast image obtained by high-resolution electron microscopy (HREM) of a rolled Mg-Ag alloy material.
  • HREM high-resolution electron microscopy
  • a portion where an element having a large atomic number is present is displayed brightly (whitish). Since the contrast of the grain boundaries indicated by the arrows is clear, it can be confirmed that the solute element is segregated at the grain boundaries. The grain boundary segregation was confirmed even when the solute element was not Bi among the rolled materials produced in the examples.
  • FIG. 5 shows the cycle voltage / current test results of the cell using the rolled Mg—Ca alloy material as the working electrode. 0V vs.
  • the redox currents observed near Mg 2+ / Mg correspond to the dissolution and precipitation of magnesium, respectively.
  • the overvoltage of dissolution and precipitation was about ⁇ 20 mV in the initial cycle, but the overvoltage of dissolution and precipitation gradually decreased as the cycle increased, and became 10 mV or less after 10 cycles.
  • the electrode potential with respect to Mg metal was ⁇ 0.5 V, the current density showed a value of ⁇ 30 mAcm -2 or more.
  • FIG. 6 shows the cycle voltage / current test results of the cell using the rolled Mg—Ag alloy material as the working electrode. 0V vs.
  • the redox currents observed near Mg 2+ / Mg correspond to the dissolution and precipitation of magnesium, respectively.
  • the overvoltage of dissolution precipitation was stable at about ⁇ 15 mV from the initial cycle to 50 cycles, and the fluctuation of the overvoltage with the cycle was minute.
  • the current density when the electrode potential with respect to Mg metal was ⁇ 0.5 V showed a value of ⁇ 30 mAcm -2 or more.
  • FIG. 7 shows the voltage / current measurement results of each cell at 10 cycles.
  • the voltage-current characteristics are affected by the added elements, and as described above, the rolled Mg—Ca alloy exhibits a small overvoltage.
  • Table 2 summarizes the current and voltage during 10 cycles. Table 2 also shows the results of checking the surface condition after immersing various Mg-based alloy negative electrode materials in the electrolytic solution for 3 days. The formation of pitting corrosion could not be confirmed in the alloy to which Ca was added, but pitting corrosion was observed in the other added element species. Decomposition products due to the reaction with the electrolytic solution adhered to the surface of the alloy where pitting corrosion was observed.
  • a tripolar cell was produced.
  • the cell structure was the same as described above except that a solution of ethyl magnesium chloride (C 2 H 5 MgCl) in tetrahydrofuran (THF) (concentration 2 mol / L) was used as the electrolytic solution.
  • the obtained 3-pole cell was subjected to a cycle voltage / current test under the above-mentioned conditions.
  • the voltage / current measurement results at 2 cycles of each cell are shown in FIG. 8, and the voltage / current measurement results at 10 cycles are shown in FIG. 9, respectively. From FIGS. 8 and 9, it can be seen that a large current density can be obtained in the cell using the Mg—Ca alloy negative electrode material having a Ca content of 0.05 mol% and 0.1 mol%. From these results, it can be said that the Mg—Ca alloy negative electrode material exhibits particularly excellent electrochemical properties when the Ca content is very small.
  • the Mg-based alloy of the present invention exhibits excellent electrochemical properties, it can be used as an Mg-based alloy negative electrode material for Mg secondary batteries as well as Mg primary batteries.
  • the Mg-based alloy negative electrode material of the present invention can be used for an Mg secondary battery.
  • Mg has a low density and a thin material, it can be applied as a lightweight foil material that can replace an aluminum foil as an Mg-based alloy foil having the composition of the Mg-based alloy negative electrode material of the present invention.

Abstract

[Problem] To provide an Mg-based alloy negative electrode material having excellent electrochemical properties. [Solution] An Mg-based alloy negative electrode material having a thickness of no more than 1 mm and being formed from an Mg-based alloy that includes a total of 0.02–10 mol% of at least one type of element selected from the group consisting of Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth), and Zn elements, with the remainder comprising Mg and unavoidable components.

Description

Ｍｇ基合金負極材及びその製造方法、並びにこれを用いたＭｇ二次電池Mg-based alloy negative electrode material and its manufacturing method, and Mg secondary battery using this
　本発明は、Ｍｇ基合金負極材及びその製造方法に関する。
　また、本発明はＭｇ基合金負極材を用いたＭｇ二次電池に関する。 The present invention relates to an Mg-based alloy negative electrode material and a method for producing the same.
The present invention also relates to an Mg secondary battery using an Mg-based alloy negative electrode material.
　Ｍｇ（マグネシウム）金属は、蓄電池の負極に用いた際に、実用されている金属の中でも高い理論容量密度を示すとともに、電析時にデンドライド状の析出部を形成しないことから、高エネルギー密度蓄電池のための負極材として注目を浴びている。しかし、Ｌｉ（リチウム）金属負極やＮａ（ナトリウム）金属負極と異なり、Ｍｇ金属負極は、電解液との界面にイオン伝導性の被膜を形成しにくく、不動態化しやすいため、可逆な溶解析出挙動が起こりにくいことが問題とされている。 When used as the negative electrode of a storage battery, Mg (magnesium) metal exhibits the highest theoretical capacity density among the metals in practical use and does not form a dendride-like precipitation part during electrodeposition, so that it is a high energy density storage battery. It is attracting attention as a negative electrode material for this purpose. However, unlike the Li (lithium) metal negative electrode and the Na (sodium) metal negative electrode, the Mg metal negative electrode is difficult to form an ionic conductive film at the interface with the electrolytic solution and is easily passivated, so that the dissolution and precipitation behavior is reversible. The problem is that it is unlikely to occur.
　通常、二次電池をはじめとする蓄電池は、負極材に加えて、正極活物質及び電解液を備える。このため、前述の問題を解決するための一手段として、負極材以外の構成要素の改良が行われている。例えば、特許文献１や２、非特許文献１に開示されるように、Ｍｇ二次電池に有効な正極活物質と電解液とがそれぞれ開発されている。翻って、負極材自体に注目すると、その構成材料は、Ｍｇ金属負極材（及びＭｇ基合金負極材）と、Ｍｇを含有する金属間化合物の二種類に大別できる。特許文献３、４では、Ｍｇ－Ｂｉ金属間化合物（Ｍｇ３Ｂｉ２）やＭｇ－Ｓｎ金属間化合物（Ｍｇ２Ｓｎ）を負極材に活用することで、前述の問題の解決を図っている。しかし、金属間化合物負極は、Ｍｇ金属負極（及びＭｇ基合金負極）と比較して電位が高くなり、容量密度も低下する問題がある。また、これらの金属間化合物を形成させるためには、Ｍｇと比較して密度の高いＢｉ（ビスマス）やＳｎ（スズ）を高濃度に添加する必要があるため、電池の重量低減の観点からは望ましくない。 Usually, a storage battery such as a secondary battery includes a positive electrode active material and an electrolytic solution in addition to the negative electrode material. Therefore, as one means for solving the above-mentioned problems, the components other than the negative electrode material have been improved. For example, as disclosed in Patent Documents 1 and 2 and Non-Patent Document 1, a positive electrode active material and an electrolytic solution effective for Mg secondary batteries have been developed, respectively. On the other hand, focusing on the negative electrode material itself, the constituent materials can be roughly classified into two types: Mg metal negative electrode material (and Mg-based alloy negative electrode material) and Mg-containing intermetallic compounds. In Patent Documents 3 and 4, the above-mentioned problems are solved by utilizing the Mg-Bi intermetallic compound (Mg 3 Bi 2 ) and the Mg-Sn intermetallic compound (Mg 2 Sn) as the negative electrode material. However, the intermetallic compound negative electrode has a problem that the potential is higher and the capacitance density is lower than that of the Mg metal negative electrode (and the Mg base alloy negative electrode). Further, in order to form these intermetallic compounds, it is necessary to add Bi (bismuth) and Sn (tin), which have a higher density than Mg, at a high concentration, and therefore, from the viewpoint of reducing the weight of the battery. Not desirable.
　一方、金属間化合物を活用せずに、Ｍｇ金属を負極としたＭｇ金属負極及びＭｇ基合金負極が、特許文献５に開示されている。特許文献５には、負極を構成するＭｇ基合金として、Ｍｇ－Ａｌ系合金、Ｍｇ－Ｚｎ系合金及びＭｇ－Ｍｎ系合金が列記されているが、実施例に示されているのはＭｇ－６ｍａｓｓ％Ａｌ合金のみである。この合金では、熱的平衡及び金属組織の観点からは、Ａｌ添加量の高濃度化に起因して、Ｍｇ１７Ａｌ１２を代表とする数多くの金属間化合物がＭｇ母相内に高密度に分散することとなる。もちろん、Ａｌは金属間化合物の形成に費やされるため、結晶粒界に溶質元素偏析が起こらないことは自明である。また、特許文献６は、Ｍｇを質量比で９０％以上含有するＭｇ二次電池に適したＭｇ金属負極及びＭｇ基合金負極を開示している。含有され得る副成分としては、Ａｌ（アルミニウム）、Ｚｎ（亜鉛）、Ｍｎ（マンガン）、Ｓｉ（ケイ素）、Ｃａ（カルシウム）、Ｆｅ（鉄）、Ｃｕ（銅）、Ｎｉ（ニッケル）のいずれかが例示されている。しかし、Ｍｇ合金の内部微細組織は創製方法により大きく異なり、例えば、押出や圧延加工に代表される展伸加工法の使用なしでは、溶質元素を結晶粒界に偏析させることはできない。また、Ｓｉ、Ｆｅ、Ｃｕ、Ｎｉは、Ｍｇに対する最大固溶量が０．０１ｍｏｌ％以下であり、力学特性や機能特性に影響を及ぼす固溶量ではないため、通常、不可避的な不純物元素として扱われる。 On the other hand, Patent Document 5 discloses an Mg metal negative electrode and an Mg-based alloy negative electrode using an Mg metal as a negative electrode without utilizing an intermetallic compound. Patent Document 5 lists Mg—Al alloys, Mg—Zn alloys, and Mg—Mn alloys as Mg-based alloys constituting the negative electrode, but Mg— is shown in Examples. Only 6 mass% Al alloy. In this alloy, from the viewpoint of thermal equilibrium and metallographic structure, a large number of intermetallic compounds represented by Mg 17 Al 12 are dispersed in the Mg matrix at high density due to the high concentration of Al added. Will be done. Of course, since Al is spent on the formation of intermetallic compounds, it is obvious that solute element segregation does not occur at the grain boundaries. Further, Patent Document 6 discloses an Mg metal negative electrode and an Mg-based alloy negative electrode suitable for an Mg secondary battery containing 90% or more of Mg in terms of mass ratio. As a subcomponent that can be contained, any one of Al (aluminum), Zn (zinc), Mn (manganese), Si (silicon), Ca (calcium), Fe (iron), Cu (copper), and Ni (nickel). Is illustrated. However, the internal microstructure of the Mg alloy differs greatly depending on the production method. For example, the solute element cannot be segregated at the grain boundaries without the use of a wrought processing method typified by extrusion or rolling processing. Further, Si, Fe, Cu, and Ni have a maximum solid solution amount of 0.01 mol% or less with respect to Mg, which is not a solid solution amount that affects mechanical properties and functional characteristics, and therefore are usually unavoidable impurity elements. Be treated.
　また、本発明者らは、Ｍｇに一種類のみの溶質元素を添加することに着目し、以下の提案を行っている。まず、特許文献７では、Ｍｇよりも原子半径が大きな溶質原子を０．０３～０．５４ｍｏｌ％含有し、強度と延性に優れるＭｇ合金を開示している。溶質元素が結晶粒界に偏在することを特徴とするが、バルク材の高強度・高延性化の達成を主眼としているため、平均結晶粒サイズが１．５μｍ以下であることを特徴としている。また、特許文献８ではＭｎを０．７７～２ｍａｓｓ％含有するＭｇ合金が、特許文献９ではＢｉを０．２５～９ｍａｓｓ％含有するＭｇ合金が、それぞれ開示されており、いずれも室温延性に優れたＭｇ合金とされている。これらのＭｇ合金は、平均結晶粒サイズが１０μｍ以下で、破断伸びが１００％程度を示し、変形に及ぼす粒界すべりの寄与率の指標であるｍ値が０．１以上を示すことを特徴としている。しかし、本発明者らが開示したいずれのＭｇ合金も、強度や延性をはじめとする力学特性の向上を目的とするものであり、電気化学の特性は不明である。本発明者の知る限りでは、Ｍｇ基二元系合金の電気化学特性に関連する文献や開示例はない。 In addition, the present inventors have focused on adding only one kind of solute element to Mg, and have made the following proposals. First, Patent Document 7 discloses an Mg alloy containing 0.03 to 0.54 mol% of a solute atom having an atomic radius larger than that of Mg and having excellent strength and ductility. The solute elements are unevenly distributed at the grain boundaries, but the average crystal grain size is 1.5 μm or less because the main purpose is to achieve high strength and high ductility of the bulk material. Further, Patent Document 8 discloses an Mg alloy containing 0.77 to 2 mass% of Mn, and Patent Document 9 discloses an Mg alloy containing 0.25 to 9 mass% of Bi, both of which are excellent in room temperature ductility. It is said to be a Mg alloy. These Mg alloys are characterized in that the average crystal grain size is 10 μm or less, the elongation at break is about 100%, and the m value, which is an index of the contribution ratio of grain boundary slip to deformation, is 0.1 or more. There is. However, all of the Mg alloys disclosed by the present inventors are intended to improve mechanical properties such as strength and ductility, and the electrochemical properties are unknown. As far as the present inventor knows, there is no literature or disclosure example related to the electrochemical properties of Mg-based binary alloys.
特開２０１２－１５０９２４号公報Japanese Unexamined Patent Publication No. 2012-150924 特開２０１６－９６０２４号公報Japanese Unexamined Patent Publication No. 2016-96024 特表２０１４－５１２６３７号公報Japanese Patent Application Laid-Open No. 2014-512637 特表２０１５－５１５７２８号公報Japanese Patent Application Laid-Open No. 2015-515728 特開２０１２－２２１６７０号公報Japanese Unexamined Patent Publication No. 2012-221670 特開２０１４－１４３１７０号公報Japanese Unexamined Patent Publication No. 2014-143170 特開２００６－１６６５８号公報Japanese Unexamined Patent Publication No. 2006-16658 特開２０１６－１７１８３号公報Japanese Unexamined Patent Publication No. 2016-17183 国際公開２０１７／１５４９６９号International release 2017/154996
　本発明は、優れた電気化学特性を有するＭｇ基合金負極材及びその製造方法を提供することを課題としている。
　また、本発明は、上記のＭｇ基合金負極材を用いたＭｇ二次電池を提供することを課題としている。 An object of the present invention is to provide an Mg-based alloy negative electrode material having excellent electrochemical properties and a method for producing the same.
Another object of the present invention is to provide an Mg secondary battery using the above-mentioned Mg-based alloy negative electrode material.
　前記課題を解決するための本発明の第１の側面は、Ａｌ、Ａｇ、Ｂｉ、Ｃａ、Ｓｎ、Ｍｎ、Ｌｉ、ＲＥ（希土類）及びＺｎから選択される少なくとも一種類の元素（溶質元素）を、合計で０．０２ｍｏｌ％以上、１０ｍｏｌ％以下の割合で含み、残部がＭｇと不可避的成分とからなるＭｇ基合金で形成され、かつ厚みが１ｍｍ以下であるＭｇ基合金負極材である。 The first aspect of the present invention for solving the above-mentioned problems is to use at least one element (solute element) selected from Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earth) and Zn. This is an Mg-based alloy negative electrode material containing 0.02 mol% or more and 10 mol% or less in total, the balance of which is formed of an Mg-based alloy composed of Mg and an unavoidable component, and a thickness of 1 mm or less.
　前記Ｍｇ基合金負極材は、Ｍｇ母材の平均粒子サイズが１０００μｍ以下であってもよい。 The Mg-based alloy negative electrode material may have an average particle size of 1000 μm or less as the Mg base material.
　前記Ｍｇ基合金負極材は、前記溶質元素の少なくとも１種が結晶粒界に偏析していてもよい。 In the Mg-based alloy negative electrode material, at least one of the solute elements may be segregated at the grain boundaries.
　前記Ｍｇ基合金負極材は、三極式セルを用いたサイクル計測において、５回以上のサイクル特性を示すものであってもよい。 The Mg-based alloy negative electrode material may exhibit cycle characteristics of 5 times or more in cycle measurement using a tripolar cell.
　前記Ｍｇ基合金負極材は、Ｍｇ金属の電気化学的析出溶解試験において、過電圧５０ｍＶ以下の特性を示すものであってもよい。 The Mg-based alloy negative electrode material may exhibit characteristics of an overvoltage of 50 mV or less in an electrochemical precipitation / dissolution test of Mg metal.
　前記Ｍｇ基合金負極材は、Ｍｇ金属の電気化学的析出溶解試験において、Ｍｇ金属に対する電極電位が±０．５Ｖのときに、±１０ｍＡｃｍ－２以上の電流密度を示すものであってもよい。 The Mg-based alloy negative electrode material may exhibit a current density of ± 10 mAcm − 2 or more when the electrode potential with respect to the Mg metal is ± 0.5 V in the electrochemical precipitation / dissolution test of the Mg metal.
　また、前記課題を解決するための本発明の第２の側面は、原料を溶解、鋳造してＭｇ基合金鋳造材を得ること、前記Ｍｇ基合金鋳造材に対して、４００℃以上、６５０℃以下の温度で、０．５時間以上、４８時間以下の溶体化処理を行うこと、及び前記溶体化処理後の前記Ｍｇ基合金鋳造材に対して、塑性ひずみ付与として、５０℃以上、５５０℃以下の温度で、断面減少率１０％以上の展伸加工を施すことを含む、前記第１の側面に係るＭｇ基合金負極材の製造方法である。 Further, the second aspect of the present invention for solving the above-mentioned problems is to melt and cast a raw material to obtain an Mg-based alloy cast material, and to obtain an Mg-based alloy cast material at 400 ° C. or higher and 650 ° C. with respect to the Mg-based alloy cast material. The solution treatment is performed at the following temperature for 0.5 hours or more and 48 hours or less, and the Mg-based alloy cast material after the solution treatment is subjected to plastic strain of 50 ° C. or higher and 550 ° C. This is a method for producing an Mg-based alloy negative electrode material according to the first aspect, which comprises performing a spreading process having a cross-sectional reduction rate of 10% or more at the following temperature.
　さらに、前記課題を解決するための本発明の第３の側面は、前記第１の側面に係るＭｇ基合金負極材と、電解質と正極とによって構成されたＭｇ二次電池である。
　前記Ｍｇ二次電池は、サイクル計測で１０回以上のサイクル特性を示すものであってもよい。 Further, a third aspect of the present invention for solving the above problems is an Mg secondary battery composed of an Mg-based alloy negative electrode material according to the first aspect, an electrolyte and a positive electrode.
The Mg secondary battery may exhibit a cycle characteristic of 10 times or more by cycle measurement.
本発明の一側面に係るＭｇ基合金負極材が使用されるＭｇ二次電池の概略的な構成を示す模式図である。It is a schematic diagram which shows the schematic structure of the Mg secondary battery which uses the Mg-based alloy negative electrode material which concerns on one aspect of this invention. 本発明の各実施例に係るＭｇ基合金負極材の外観写真例で、圧延加工後の外観写真を示している。An example of an external photograph of the Mg-based alloy negative electrode material according to each embodiment of the present invention shows an external photograph after rolling. 本発明の一実施例に係るＭｇ―Ｃａ合金の微細組織観察例で、電子線後方散乱回折像を示している。An electron backscatter diffraction image is shown in an example of observing the microstructure of the Mg—Ca alloy according to an embodiment of the present invention. 本発明の一実施例に係るＭｇ―Ａｇ合金の微細組織観察例で、高分解能電子顕微鏡法によるＺコントラスト像を示している。In the microstructure observation example of the Mg—Ag alloy according to one embodiment of the present invention, a Z contrast image by high resolution electron microscopy is shown. 本発明の一実施例に係るＭｇ―Ｃａ合金の電気化学的析出溶解試験例で、各サイクルでの電位と電流密度との関係を示している。In the electrochemical precipitation dissolution test example of the Mg—Ca alloy according to one embodiment of the present invention, the relationship between the potential and the current density in each cycle is shown. 本発明の一実施例に係るＭｇ―Ａｇ合金の電気化学的析出溶解試験例で、各サイクルでの電位と電流密度との関係を示している。An electrochemical precipitation / dissolution test example of an Mg—Ag alloy according to an embodiment of the present invention shows the relationship between the potential and the current density in each cycle. 本発明の各実施例に係るＭｇ基二元系合金の電気化学的析出溶解曲線である。It is an electrochemical precipitation dissolution curve of the Mg-based binary alloy which concerns on each Example of this invention. 本発明の一実施例に係る種々のＣａ量のＭｇ－Ｃａ合金の電気化学的析出溶解試験例で、２サイクル時の電位と電流密度との関係を示している。The relationship between the potential and the current density at the time of two cycles is shown in the electrochemical precipitation dissolution test examples of Mg—Ca alloys having various Ca amounts according to one embodiment of the present invention. 本発明の一実施例に係る種々のＣａ量のＭｇ－Ｃａ合金の電気化学的析出溶解試験例で、１０サイクル時の電位と電流密度との関係を示している。The relationship between the potential and the current density at 10 cycles is shown in the electrochemical precipitation and dissolution test examples of Mg—Ca alloys having various Ca amounts according to one embodiment of the present invention.
　本発明の第１の側面に係るＭｇ基合金負極材（以下、単に「第１側面」と記載することがある）は、Ｍｇ基合金素材として、Ｍｇ－Ａｍｏｌ％Ｘから実質的になる。すなわち、Ａｍｏｌ％のＸ元素以外の残部は、Ｍｇと不可避的成分とからなる。ここで、Ｘは、Ａｌ、Ａｇ、Ｂｉ、Ｃａ、Ｓｎ、Ｍｎ、Ｌｉ、ＲＥ（希土類）及びＺｎから選択される少なくとも一種類の元素である。以下、これらの元素を「溶質元素」と総称することがある。溶質元素のうち希土類には、Ｓｃ（スカンジウム）及びＹ（イットリウム）、並びにＧｄ（ガドリニウム）、Ｃｅ（セリウム）などのランタノイドが含まれる。Ａの値は、Ｍｇに対して最大固溶値以下であり、好ましくは０．０２ｍｏｌ％以上、１０ｍｏｌ％以下、より好ましくは０．０２ｍｏｌ％以上、５ｍｏｌ％以下、更により好ましくは０．０２ｍｏｌ％以上、１ｍｏｌ％以下である。Ａが０．０２ｍｏｌ％未満の場合、添加した溶質元素は、力学特性や電気化学的特性に影響を及ぼさず、不純物元素と同様に作用するのみである。添加した溶質元素の力学的特性や電気化学的特性への好影響を十分に発揮させる点からは、前述したＡの範囲の各下限値は、０．０５ｍｏｌ％とすることが好ましい。他方、Ａが１０ｍｏｌ％を超える場合、溶質元素が固溶状態であっても、粒界上にナノクラスターを形成し、粒界偏析が阻害されるため好ましくない。また、重量自体も大きくなるため、軽量化の観点から好ましくない。 The Mg-based alloy negative electrode material according to the first aspect of the present invention (hereinafter, may be simply referred to as “first aspect”) is substantially made of Mg—Amol% X as the Mg-based alloy material. That is, the balance of Amol% other than the X element is composed of Mg and an unavoidable component. Here, X is at least one element selected from Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earths) and Zn. Hereinafter, these elements may be collectively referred to as "solute elements". Rare earths among solute elements include lanthanoids such as Sc (scandium) and Y (yttrium), and Gd (gadolinium) and Ce (cerium). The value of A is not more than the maximum solid solution value with respect to Mg, preferably 0.02 mol% or more and 10 mol% or less, more preferably 0.02 mol% or more and 5 mol% or less, still more preferably 0.02 mol%. The above is 1 mol% or less. When A is less than 0.02 mol%, the added solute element does not affect the mechanical properties and the electrochemical properties, and only acts in the same manner as the impurity element. From the viewpoint of sufficiently exerting a positive effect on the mechanical properties and electrochemical properties of the added solute element, it is preferable that each lower limit value in the range of A described above is 0.05 mol%. On the other hand, when A exceeds 10 mol%, even if the solute element is in a solid solution state, nanoclusters are formed on the grain boundaries and segregation at the grain boundaries is hindered, which is not preferable. Moreover, since the weight itself becomes large, it is not preferable from the viewpoint of weight reduction.
　第１側面では、溶質元素ＸがＣａであると、電池を形成した際に、電解液との反応が顕著に抑制される点で好ましい。また、溶質元素ＸがＣａである場合には、ごく少量で大きな電流密度が得られることから、その固溶量Ａを０．０２ｍｏｌ％以上、０．２ｍｏｌ％以下とすることが好ましく、０．０２ｍｏｌ％以上、０．１ｍｏｌ％以下とすることがより好ましい。 On the first aspect, when the solute element X is Ca, the reaction with the electrolytic solution is remarkably suppressed when the battery is formed, which is preferable. When the solute element X is Ca, a large current density can be obtained with a very small amount. Therefore, the solid solution amount A is preferably 0.02 mol% or more and 0.2 mol% or less. It is more preferably 02 mol% or more and 0.1 mol% or less.
　第１側面は、その厚さが１ｍｍ以下である。該厚さは、好ましくは、０．５ｍｍ以下、より好ましくは０．３ｍｍ以下である。負極材では、電解液に接する表面積が大きいほど高い電気化学的効率が得られる。厚さが１ｍｍを超える負極材では、表面積が小さいことで、その電気化学的効率が低くなってしまう。また、二次電池の重量が大きくなり、軽量化のメリットが低減する。
　第１側面では、Ｍｇ母相の結晶粒サイズが１０００μｍ以下であることが好ましく、１００μｍ以下であることがより好ましく、５０μｍ以下であることがさらに好ましい。負極反応によるＭｇの溶解は、結晶粒界がサイトになりやすい。そのため、厚さが１ｍｍ（＝１０００μｍ）以下の箔材における結晶粒サイズを１０００μｍ以下とすることで、結晶粒界の体積率が十分なものとなり、均一に溶解挙動が起こることで、優れた電気化学的特性を取得することができる。結晶粒サイズの測定は、ＪＩＳ規格に基づいた切片法（切断法ともいう。ＪＩＳ　Ｈ０５０１、Ｇ０５５１参照）により行う。ただし、結晶粒サイズが微細な場合や、結晶粒界が不鮮明な場合には、切片法の適用が困難であるため、透過型電子顕微鏡によって得られる明視野像や電子線後方散乱回折像を用いて測定した結果を、結晶粒サイズとする。 The thickness of the first side surface is 1 mm or less. The thickness is preferably 0.5 mm or less, more preferably 0.3 mm or less. In the negative electrode material, the larger the surface area in contact with the electrolytic solution, the higher the electrochemical efficiency can be obtained. In a negative electrode material having a thickness of more than 1 mm, the electrochemical efficiency is lowered due to the small surface area. In addition, the weight of the secondary battery becomes large, and the merit of weight reduction is reduced.
On the first aspect, the crystal grain size of the Mg matrix is preferably 1000 μm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. In the dissolution of Mg by the negative electrode reaction, the grain boundaries tend to become sites. Therefore, by setting the crystal grain size of the foil material having a thickness of 1 mm (= 1000 μm) or less to 1000 μm or less, the volume fraction of the crystal grain boundaries becomes sufficient, and the dissolution behavior occurs uniformly, resulting in excellent electricity. Chemical properties can be obtained. The crystal grain size is measured by the section method based on the JIS standard (also referred to as a cutting method. See JIS H0501 and G0551). However, when the crystal grain size is fine or the grain boundaries are unclear, it is difficult to apply the section method. Therefore, a bright field image or an electron backscatter diffraction image obtained by a transmission electron microscope is used. The result of the measurement is taken as the crystal grain size.
　第１側面では、添加した溶質元素が結晶粒界に偏析し、その濃度はＭｇ母相に存在する溶質元素濃度よりも１．５倍以上高いことが好ましい。粒界偏析の有無の識別は、透過型電子顕微鏡（ＴＥＭ）に付属するエネルギー分散型Ｘ線分光（ＥＤＸ）装置による分析結果を使用して行うことが好ましいが、三次元アトムプローブなどの手法にて評価してもかまわない。 On the first aspect, it is preferable that the added solute element segregates at the grain boundaries and its concentration is 1.5 times or more higher than the concentration of the solute element present in the Mg matrix. The presence or absence of grain boundary segregation is preferably identified by using the analysis result by the energy dispersive X-ray spectroscopy (EDX) apparatus attached to the transmission electron microscope (TEM), but it is preferable to use a method such as a three-dimensional atom probe. You may evaluate it.
　第１側面は、三極式セルを用いたサイクル計測において、好ましくは５回以上、より好ましくは２５回以上、更に好ましくは５０回以上のサイクル特性を示す。サイクル特性が５回以上の場合、電解液との副反応の問題は顕在化しないため、負極として好適に使用できる。また、第１側面は、三極式セルを用いた電気化学的析出溶解試験にて取得される過電圧が、好ましくは５０ｍＶ以下、より好ましくは３０ｍＶ以下、さらに好ましくは２０ｍＶ以下となる。過電圧が５０ｍＶ以下であると、電池電圧の損失が小さいため、負極として好適に使用できる。さらに、第１側面は、前述の電気化学的析出溶解試験において、Ｍｇ金属に対する電極電位が±０．５Ｖのときの電流密度が、好ましくは±１０ｍＡｃｍ－２以上、より好ましくは±２０ｍＡｃｍ－２以上、さらに好ましくは±２５ｍＡｃｍ－２以上の値を示す。電流密度が±１０ｍＡｃｍ－２以上であることで、電気化学反応が負極により律速されにくくなり、負極として好適に使用できる。サイクル計測試験や電気化学的析出溶解試験に使用する電解液は、０．１ｍｏｌ／Ｌ以上１．５ｍｏｌ／Ｌ以下のフルオロアルコキシほう酸マグネシウム塩又はフルオロアルコキシアルミネートマグネシウム塩を溶質として、該溶質を有機エーテル類と配合したものとする。ただし、前記溶質を使用できない場合には、溶質として塩化アルキルマグネシウム、塩化マグネシウム、マグネシウムビストリフルオロメタンスルホニルイミド塩及びマグネシウムヘキサメチルジシラジド塩などの他のマグネシウム化合物を代用してもよい。 The first aspect exhibits cycle characteristics of preferably 5 times or more, more preferably 25 times or more, still more preferably 50 times or more in cycle measurement using a tripolar cell. When the cycle characteristic is 5 times or more, the problem of side reaction with the electrolytic solution does not become apparent, so that it can be suitably used as a negative electrode. On the first aspect, the overvoltage obtained in the electrochemical precipitation / dissolution test using a tripolar cell is preferably 50 mV or less, more preferably 30 mV or less, still more preferably 20 mV or less. When the overvoltage is 50 mV or less, the loss of the battery voltage is small, so that it can be suitably used as a negative electrode. Further, on the first aspect, in the above-mentioned electrochemical precipitation and dissolution test, the current density when the electrode potential with respect to Mg metal is ± 0.5 V is preferably ± 10 mAcm -2 or more, more preferably ± 20 mA cm -2 or more. , More preferably ± 25 mAcm -2 or more. When the current density is ± 10 mAcm -2 or more, the electrochemical reaction is less likely to be rate-determined by the negative electrode, and it can be suitably used as the negative electrode. The electrolytic solution used in the cycle measurement test and the electrochemical precipitation / dissolution test uses a fluoroalkoxyborate magnesium salt or a fluoroalkoxyaluminate magnesium salt of 0.1 mol / L or more and 1.5 mol / L or less as a solute, and the solute is organic. It shall be mixed with ethers. However, when the solute cannot be used, other magnesium compounds such as alkylmagnesium chloride, magnesium chloride, magnesium bistrifluoromethanesulfonylimide salt and magnesium hexamethyldisilazide salt may be substituted as the solute.
　次に、本発明の第２の側面に係るＭｇ基合金負極材の製造方法（以下、単に「第２側面」と記載することがある）を説明する。まず、原料であるＭｇ及び溶質金属を溶解、鋳造してＭｇ基合金鋳造材を得る。溶解方法は、所期の組成の合金が得られるものであれば限定されず、大気溶解、真空溶解、アーク溶解及びプラズマ溶解等が採用できる。また、鋳造方法についても限定されず、重力鋳造、砂型鋳造、ダイキャストなど、所期のＭｇ基合金鋳造材を作製できる手法であればいずれの方法も採用できる。次いで、溶製したＭｇ基合金鋳造材に対して、４００℃以上、６５０℃以下の温度で溶体化処理を行う。ここで、溶体化処理温度が４００℃未満の場合、添加した溶質元素を均質に固溶させるためには長時間の温度保持が必要となり、工業的観点から好ましくない。一方、６５０℃を超えると、固相温度以上であるため、局所溶解が始まり、作業上危険である。また、溶体化処理時間は、０．５時間以上、４８時間以下が好ましい。処理時間が０．５時間未満の場合、溶質元素の母相内での拡散が不十分となりやすいため、鋳造時の偏析が残存し、健全な素材を創製することが困難となる。他方、処理時間が４８時間を超える場合、作業時間が長くなるため、工業的観点から好ましくない。 Next, a method for manufacturing the Mg-based alloy negative electrode material according to the second aspect of the present invention (hereinafter, may be simply referred to as "second aspect") will be described. First, Mg and solute metal, which are raw materials, are melted and cast to obtain an Mg-based alloy cast material. The melting method is not limited as long as an alloy having the desired composition can be obtained, and atmospheric melting, vacuum melting, arc melting, plasma melting and the like can be adopted. Further, the casting method is not limited, and any method such as gravity casting, sand casting, die casting, etc. can be adopted as long as it can produce the desired Mg-based alloy casting material. Next, the molten Mg-based alloy cast material is subjected to a solution treatment at a temperature of 400 ° C. or higher and 650 ° C. or lower. Here, when the solution treatment temperature is less than 400 ° C., it is necessary to maintain the temperature for a long time in order to uniformly dissolve the added solute element, which is not preferable from an industrial point of view. On the other hand, if the temperature exceeds 650 ° C., since the temperature is above the solid phase temperature, local dissolution starts, which is dangerous in terms of work. The solution treatment time is preferably 0.5 hours or more and 48 hours or less. If the treatment time is less than 0.5 hours, the diffusion of the solute element in the matrix tends to be insufficient, so that segregation during casting remains and it becomes difficult to create a sound material. On the other hand, if the processing time exceeds 48 hours, the working time becomes long, which is not preferable from an industrial point of view.
　次いで、溶体化処理後のＭｇ基合金鋳造材に対して、温間又は熱間加工を行い、ひずみを付与する。温間又は熱間加工の温度は、５０℃以上、５５０℃以下とする。前記温度は、７５℃以上、５２５℃以下が好ましく、１００℃以上、５００℃以下がより好ましい。加工温度が５０℃未満の場合、割れや亀裂の起点となる変形双晶が数多く生じると共に、耳割れや表面の波うちが高密度に生じ、厚さ１０００μｍ以下の健全な箔材を作製することが困難となる。他方、加工温度が５５０℃を超える場合、加工中に再結晶化が進行して結晶粒微細化が阻害され、更に、加工に使用する金型の寿命の短縮にもつながる。温間又は熱間加工により付与されるひずみの量は、断面減少率が１０％以上となる量とする。前記断面減少率は、好ましくは２０％以上、より好ましくは５０％以上である。断面減少率が１０％未満の場合、被加工材の内部に至るまで均質にひずみ付与ができず、結晶粒サイズの制御と粒界偏析の制御が困難となる。なお、温間又は熱間加工方法は、押出、鍛造、圧延、引抜などが代表的であるが、ひずみを付与することができ、厚さを制御できる展伸加工法であればいずれの加工法でも採用できる。なお、温間又は熱間加工を実行せず、鋳造材を溶体化処理したのみでは、添加した溶質元素が結晶粒界に偏析しないため、本発明の効果が得られない。その理由は、粒界偏析現象が、温間又は熱間加工時に導入されるひずみと溶質元素との相互作用によって生じるためである。 Next, the Mg-based alloy cast material after the solution treatment is subjected to warm or hot working to impart strain. The temperature of warm or hot working shall be 50 ° C or higher and 550 ° C or lower. The temperature is preferably 75 ° C. or higher and 525 ° C. or lower, more preferably 100 ° C. or higher and 500 ° C. or lower. When the processing temperature is less than 50 ° C, many deformed twins that are the starting points of cracks and cracks are generated, and ear cracks and surface waviness occur at high density, so that a healthy foil material with a thickness of 1000 μm or less should be produced. Becomes difficult. On the other hand, when the processing temperature exceeds 550 ° C., recrystallization proceeds during processing to inhibit grain refinement, which further shortens the life of the mold used for processing. The amount of strain applied by warm or hot working is such that the cross-sectional reduction rate is 10% or more. The cross-sectional reduction rate is preferably 20% or more, more preferably 50% or more. When the cross-sectional reduction rate is less than 10%, strain cannot be uniformly applied to the inside of the work material, and it becomes difficult to control the crystal grain size and the grain boundary segregation. The warm or hot working method is typically extrusion, forging, rolling, drawing, etc., but any working method can be used as long as it can apply strain and control the thickness. But it can be adopted. It should be noted that the effect of the present invention cannot be obtained because the added solute element does not segregate at the grain boundaries only by solution-treating the cast material without executing warm or hot working. The reason is that the grain boundary segregation phenomenon is caused by the interaction between the solute element and the strain introduced during warm or hot working.
　次に、本発明の第３の側面に係るＭｇ二次電池（以下、単に「第３側面」と記載することがある）について説明する。図１は、本発明のＭｇ基合金負極材が使用されるＭｇ二次電池の概略的な構成を示す模式図である。図１に示す通り、Ｍｇ二次電池は、正極Ｃと、負極Ｄと、電解液Ｂと、容器Ａを備えている。 Next, the Mg secondary battery according to the third aspect of the present invention (hereinafter, may be simply referred to as "third aspect") will be described. FIG. 1 is a schematic view showing a schematic configuration of an Mg secondary battery in which the Mg-based alloy negative electrode material of the present invention is used. As shown in FIG. 1, the Mg secondary battery includes a positive electrode C, a negative electrode D, an electrolytic solution B, and a container A.
　正極Ｃにおいては、図示しない正極集電体によって、図示しない正極活物質が保持されている。正極集電体は、放電時に正極活物質に電子を供与する機能を有する。正極集電体として使用される物質は、ニッケル、鉄、ステンレス鋼、チタン、アルミニウム等が、耐食性が比較的優れていることと、安価であることから好ましく用いられる。正極活物質として使用される物質は、Ｍｇイオンを挿入及び脱離可能なものであれば特に制限されないが、ＭｇＦｅＳｉＯ４、ＭｇＭｎ２Ｏ４、又はＶ２Ｏ５等が好ましく用いられる。正極Ｃの具体的な構成としては、例えばステンレス上にＶ２Ｏ５を塗工した構成が挙げられる。 In the positive electrode C, a positive electrode active material (not shown) is held by a positive electrode current collector (not shown). The positive electrode current collector has a function of donating electrons to the positive electrode active material at the time of discharge. As the substance used as the positive electrode current collector, nickel, iron, stainless steel, titanium, aluminum and the like are preferably used because they have relatively excellent corrosion resistance and are inexpensive. The substance used as the positive electrode active material is not particularly limited as long as it can insert and remove Mg ions, but MgFeSiO 4 , MgMn 2 O 4 , or V 2 O 5 or the like is preferably used. As a specific configuration of the positive electrode C, for example, a configuration in which V 2 O 5 is coated on stainless steel can be mentioned.
　負極Ｄには、第１側面に係るＭｇ基合金負極材が用いられる。
　電解液Ｂは、図示しないセパレータによって保持され、正極Ｃと負極Ｄとの間にイオン伝導性を生じさせる。電解液Ｂは、Ｍｇイオンを含む。放電時にＭｇイオンは正極Ｃで還元反応（例えば、後述の式（１）の反応）を、負極Ｄで酸化反応（例えば、後述の式（２）の反応）を起こす。充電時にＭｇイオンは正極Ｃで酸化反応（例えば、後述の式（３）の反応）を、負極Ｄで還元反応（例えば、後述の式（４）の反応）を起こす。これら酸化還元反応により、Ｍｇ二次電池の充放電が可能となる。 As the negative electrode D, the Mg-based alloy negative electrode material according to the first side surface is used.
The electrolytic solution B is held by a separator (not shown) to generate ionic conductivity between the positive electrode C and the negative electrode D. The electrolytic solution B contains Mg ions. At the time of discharge, Mg ions cause a reduction reaction (for example, the reaction of the formula (1) described later) at the positive electrode C and an oxidation reaction (for example, the reaction of the formula (2) described later) at the negative electrode D. During charging, Mg ions cause an oxidation reaction (for example, the reaction of the formula (3) described later) at the positive electrode C and a reduction reaction (for example, the reaction of the formula (4) described later) at the negative electrode D. These redox reactions enable charging and discharging of the Mg secondary battery.
［化１］
　Ｖ２Ｏ５＋Ｍｇ２＋＋２ｅ－　→　ＭｇＶ２Ｏ５　…　式（１）
　Ｍｇ　→　Ｍｇ２＋＋２ｅ－　…　式（２）
　ＭｇＶ２Ｏ５　→　Ｖ２Ｏ５＋Ｍｇ２＋＋２ｅ－　…　式（３）
　Ｍｇ２＋＋２ｅ－　→　Ｍｇ　…　式（４） [Chemical 1]
V 2 O 5 + Mg 2+ + 2e - → MgV 2 O 5 ... formula (1)
Mg → Mg 2+ + 2e - ... formula (2)
MgV 2 O 5 → V 2 O 5 + Mg 2+ + 2e - ... formula (3)
Mg 2+ + 2e - → Mg ... formula (4)
　第３側面における電解液Ｂは、主溶媒としての有機溶媒と、マグネシウム塩を含むものでもよく、またＭｇイオン伝導性を有する無機溶媒でもよい。 The electrolytic solution B in the third aspect may contain an organic solvent as a main solvent and a magnesium salt, or may be an inorganic solvent having Mg ion conductivity.
　マグネシウム塩と有機溶媒とを含む電解液においては、マグネシウム塩が有機溶媒に溶解することで解離し、有機溶媒が配位したマグネシウム錯カチオンを形成する。この錯カチオンが、マグネシウムの電気化学的な析出及び溶解における活性を担うため、より解離性の高いマグネシウム塩を用いた場合に、良好な電気化学特性が得られる傾向にある。良好な電気化学特性を示す電解液として、フルオロアルコキシほう酸マグネシウム塩又はフルオロアルコキシアルミネートマグネシウム塩を、有機エーテル類と配合した電解液が挙げられる。 In an electrolytic solution containing a magnesium salt and an organic solvent, the magnesium salt dissolves in the organic solvent and dissociates to form a magnesium complex cation in which the organic solvent is coordinated. Since this complex cation is responsible for the activity in the electrochemical precipitation and dissolution of magnesium, good electrochemical properties tend to be obtained when a magnesium salt having higher dissociation is used. Examples of the electrolytic solution exhibiting good electrochemical properties include an electrolytic solution in which a magnesium fluoroalkoxy borate salt or a magnesium fluoroalkoxyaluminate salt is mixed with organic ethers.
　電解液に用いられるマグネシウム塩としては、フルオロアルコキシほう酸アニオン、あるいはフルオロアルコキシアルミネートアニオンを対アニオンとして有するものが例示される。なお、ここで用いられるマグネシウム塩のフルオロアルコキシ基は、特に限定しない。
　第３側面で用いられる具体的なマグネシウム塩としては、テトラキス（ヘキサフルオロイソプロポキシ）ほう酸マグネシウム塩及びテトラキス（ヘキサフルオロイソプロポキシ）アルミネートマグネシウム塩等が例示される。 Examples of the magnesium salt used in the electrolytic solution include those having a fluoroalkoxyborate anion or a fluoroalkoxyaluminate anion as a counter anion. The fluoroalkoxy group of the magnesium salt used here is not particularly limited.
Specific examples of the magnesium salt used in the third aspect include tetrakis (hexafluoroisopropoxy) magnesium borate salt and tetrakis (hexafluoroisopropoxy) aluminate magnesium salt.
　これら正極Ｃ、負極Ｄ、電解液Ｂは、容器Ａに封入される。容器Ａの材質等は、電解液の漏れがなく、耐食性を有するものであれば特に制限されないが、鉄等の金属板をプレス加工して形成され、内面及び外面の表面全体に耐食のためのニッケル等のめっき層が形成されたもの等が好ましく用いられる。 The positive electrode C, the negative electrode D, and the electrolytic solution B are sealed in the container A. The material of the container A is not particularly limited as long as it does not leak the electrolytic solution and has corrosion resistance, but it is formed by pressing a metal plate such as iron, and the entire inner and outer surfaces are for corrosion resistance. Those on which a plating layer such as nickel is formed are preferably used.
　なお、上記の実施形態は、第３側面に係るＭｇ二次電池の一例を説明したものにすぎず、制限的に解釈されるべきものではない。第３側面は、上記事項に代えて、又は上記事項に加えて、Ｍｇ二次電池の技術分野において自明な技術的事項を含んでもよい。 Note that the above embodiment is merely an explanation of an example of the Mg secondary battery according to the third aspect, and should not be interpreted in a restrictive manner. The third aspect may include technical matters that are obvious in the technical field of Mg secondary batteries, in place of or in addition to the above matters.
　以下、実施例により本発明の各側面をさらに具体的に説明するが、本発明は該実施例に限定されるものではない。 Hereinafter, each aspect of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the Examples.
［各種溶質元素を含むＭｇ基合金負極の作製及び特性確認］
　市販の純Ｍｇ（９９．９８ｍａｓｓ％）と市販の純Ｃａ（９９．９ｍａｓｓ％）を、目標含有量が、０．３ｍｏｌ％Ｃａとなるように秤量し、鉄製るつぼ中に投入して加熱することで溶解した。溶解の条件は、Ａｒ雰囲気にて、溶解温度を７００℃、溶解保持時間を５分とした。その後、直径５０ｍｍ、高さ２００ｍｍの鉄製鋳型に溶湯を注いで鋳造し、Ｍｇ－Ｃａ合金鋳造材を溶製した。その後、鋳造材を５００℃にて２時間保持して溶体化処理を行った。溶体化処理後の鋳造材を、機械加工により、直径４０ｍｍ、長さ６０ｍｍの円柱押出ビレットに加工した。加工後のビレットを２７５℃に設定したコンテナ内で３０分間保持した後、押出比１９：１にて押出による熱間ひずみ付与加工を行い、長さ５００ｍｍ以上の押出材（以下、単に「押出材」と記載する。）を作製した。 [Preparation of Mg-based alloy negative electrode containing various solute elements and confirmation of characteristics]
Weigh commercially available pure Mg (99.98 mass%) and commercially available pure Ca (99.9 mass%) so that the target content is 0.3 mol% Ca, put them into an iron crucible, and heat them. Dissolved in. The dissolution conditions were an Ar atmosphere, the dissolution temperature was 700 ° C., and the dissolution retention time was 5 minutes. Then, the molten metal was poured into an iron mold having a diameter of 50 mm and a height of 200 mm and cast to melt an Mg—Ca alloy cast material. Then, the cast material was held at 500 ° C. for 2 hours for solution treatment. The cast material after the solution treatment was machined into a cylindrical extruded billet having a diameter of 40 mm and a length of 60 mm. The processed billet is held in a container set at 275 ° C. for 30 minutes, and then hot strain is applied by extrusion at an extrusion ratio of 19: 1 to extrude a material having a length of 500 mm or more (hereinafter, simply "extruded material"). ”) Was prepared.
　押出材を長さ１００ｍｍに切断し、圧延加工を行った。圧延加工前に、押出材を４００℃に設定した電気炉（マッフル炉）に１５分間以上保持した後、ロール温度を２００℃に設定した圧延機により、１パスの圧下率を１０％として、厚さが０．３０ｍｍになるまで圧延加工を実施した。以下、圧延加工後の材料を、単に「圧延材」と記載する。 The extruded material was cut to a length of 100 mm and rolled. Before rolling, the extruded material is held in an electric furnace (muffle furnace) set at 400 ° C for 15 minutes or more, and then a rolling mill with a roll temperature set at 200 ° C is used to set the rolling reduction ratio of one pass to 10% and thicken. Rolling was carried out until the diameter became 0.30 mm. Hereinafter, the material after rolling is simply referred to as "rolled material".
　また、Ｃａに代えてＡｇ、Ａｌ、Ｂｉ、Ｌｉ、Ｍｎ、Ｓｎ、Ｙ及びＺｎをそれぞれ溶質元素とする圧延材を、同様の方法で作製した。ここで、Ｍｇに対して融点が大きく異なるＭｎやＹを溶質元素として使用する場合は、原料を投入した鉄製るつぼを高周波加熱装置により加熱して、合金鋳造材を溶製した。また、溶製した各鋳造材からの圧延材の製造条件は、円柱押出ビレットを保持するコンテナ内の温度、圧延加工前の押出材を保持するマッフル炉の温度、及び圧延加工時のロール温度をそれぞれ表１に示すものとした以外は、Ｃａを溶質元素とする圧延材と同一とした。例えばＭｇ－Ａｇの二元合金については、押出加工のコンテナ温度は２７５℃、圧延加工ではマッフル炉４００℃、ロール２００℃とし、厚さ３００μｍの箔材を得た。
　図２は、各圧延材（Ｍｇ基合金負極材）の外観写真である。各圧延材の厚さｔは、Ｍｇ－Ｃａ合金で３００μｍ、Ｍｇ－Ｙ合金で３００μｍ、Ｍｇ－Ｍｎ合金で３００μｍ、Ｍｇ－Ｓｎ合金で２９０μｍ、Ｍｇ－Ｚｎ合金で３００μｍ、Ｍｇ－Ｌｉ合金で３００μｍ、Ｍｇ－Ａｌ合金で３００μｍであった。 Further, a rolled material containing Ag, Al, Bi, Li, Mn, Sn, Y and Zn as solute elements instead of Ca was produced by the same method. Here, when Mn or Y having a melting point significantly different from that of Mg is used as a solute element, the iron crucible containing the raw material is heated by a high-frequency heating device to melt the alloy casting material. The conditions for producing rolled material from each molten casting include the temperature inside the container that holds the cylindrical extruded billet, the temperature of the muffle furnace that holds the extruded material before rolling, and the roll temperature during rolling. Except for the items shown in Table 1, they were the same as the rolled materials containing Ca as a solute element. For example, for a binary alloy of Mg—Ag, the container temperature for extrusion processing was 275 ° C., the muffle furnace 400 ° C. and roll 200 ° C. for rolling processing, and a foil material having a thickness of 300 μm was obtained.
FIG. 2 is an external photograph of each rolled material (Mg-based alloy negative electrode material). The thickness t of each rolled material is 300 μm for Mg—Ca alloy, 300 μm for Mg—Y alloy, 300 μm for Mg—Mn alloy, 290 μm for Mg—Sn alloy, 300 μm for Mg—Zn alloy, and 300 μm for Mg—Li alloy. , Mg—Al alloy was 300 μm.
　得られた各圧延材について、電子線後方散乱回折手法によって微細組織像を取得した。結果を代表して、Ｍｇ－Ｃａ合金圧延材の微細組織像を図３に示すが、他の圧延材についても同様の微細組織が得られた。図中における同一のコントラストからなる塊が個々の結晶粒であり、典型的な結晶粒ひとつを黒線で囲んでいるが、その大きさは２０μｍである。実施例で使用した二元系合金の平均結晶粒サイズと、押出加工と圧延加工条件を表１にまとめている。添加元素の種類に関係なく、いずれも平均結晶粒サイズが１００μｍ以下である。
　図４は、Ｍｇ－Ａｇ合金圧延材の高分解能電子顕微鏡法（ＨＲＥＭ：high-resolution　electron　microscopy）によって取得したＺコントラスト像である。Ｚコントラスト像では、原子番号の大きな元素が存在する箇所は、明るく（白っぽく）表示されることを特徴とする。矢印で示す結晶粒界のコントラストが明瞭であることから、溶質元素が結晶粒界に偏析していることが確認できる。なお、粒界偏析は、実施例で作製した圧延材のうち、溶質元素がＢｉのもの以外でも確認している。 A fine structure image was obtained for each of the obtained rolled materials by an electron backscatter diffraction technique. As a representative of the results, the microstructure image of the rolled Mg—Ca alloy material is shown in FIG. 3, and the same fine structure was obtained for the other rolled materials. The lumps having the same contrast in the figure are individual crystal grains, and one typical crystal grain is surrounded by a black line, and the size is 20 μm. Table 1 summarizes the average grain size of the binary alloy used in the examples and the extrusion processing and rolling processing conditions. The average crystal grain size is 100 μm or less regardless of the type of added element.
FIG. 4 is a Z-contrast image obtained by high-resolution electron microscopy (HREM) of a rolled Mg-Ag alloy material. In the Z-contrast image, a portion where an element having a large atomic number is present is displayed brightly (whitish). Since the contrast of the grain boundaries indicated by the arrows is clear, it can be confirmed that the solute element is segregated at the grain boundaries. The grain boundary segregation was confirmed even when the solute element was not Bi among the rolled materials produced in the examples.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　次に、電気化学評価によって取得した特性について説明する。電解液の調製、３極式セルの組み立てなどのすべての操作はアルゴン雰囲気のグローブボックスにおいて行った。テトラキス（ヘキサフルオロイソプロポキシ）ほう酸マグネシウム塩をジエチレングリコールジメチルエーテルと配合し、電解液を調製した。各圧延材（Ｍｇ基合金負極材）を作用電極とし、１．５ｍＬの上記電解液を入れ、白金を対電極、銀を参照電極として、３極式セルを組み立てた。アルゴン雰囲気のグローブボックスにおいて、１０ｍＶ／ｓのスキャン速度でサイクル電圧電流テストを行った。Ｍｇ－Ｃａ合金圧延材を作用電極に用いたセルのサイクル電圧電流テスト結果を図５に示す。０Ｖｖｓ．Ｍｇ２＋／Ｍｇ付近に観測された酸化還元電流は、それぞれマグネシウムの溶解析出に対応する。図５から分かるように、溶解析出の過電圧は初期サイクルでは±２０ｍＶ程度であるが、サイクルの増大に伴い溶解析出過電圧は徐々に低下し、１０サイクル以降では１０ｍＶ以下になった。またＭｇ金属に対する電極電位が±０．５Ｖのときに、電流密度が±３０ｍＡｃｍ－２以上の値を示した。 Next, the characteristics acquired by the electrochemical evaluation will be described. All operations, such as preparing the electrolyte and assembling the triode cell, were performed in a glove box with an argon atmosphere. A magnesium salt of tetrakis (hexafluoroisopropoxy) borate was mixed with diethylene glycol dimethyl ether to prepare an electrolytic solution. Each rolled material (Mg-based alloy negative electrode material) was used as a working electrode, 1.5 mL of the above electrolytic solution was added, and a three-pole cell was assembled using platinum as a counter electrode and silver as a reference electrode. A cycle voltage current test was performed at a scan speed of 10 mV / s in a glove box in an argon atmosphere. FIG. 5 shows the cycle voltage / current test results of the cell using the rolled Mg—Ca alloy material as the working electrode. 0V vs. The redox currents observed near Mg 2+ / Mg correspond to the dissolution and precipitation of magnesium, respectively. As can be seen from FIG. 5, the overvoltage of dissolution and precipitation was about ± 20 mV in the initial cycle, but the overvoltage of dissolution and precipitation gradually decreased as the cycle increased, and became 10 mV or less after 10 cycles. Further, when the electrode potential with respect to Mg metal was ± 0.5 V, the current density showed a value of ± 30 mAcm -2 or more.
　図６は、Ｍｇ－Ａｇ合金圧延材を作用電極に用いたセルのサイクル電圧電流テスト結果である。０Ｖｖｓ．Ｍｇ２＋／Ｍｇ付近に観測された酸化還元電流は、それぞれマグネシウムの溶解析出に対応する。溶解析出の過電圧は、初期サイクルから５０サイクルまで安定して±１５ｍＶ程度を示し、サイクルに伴う過電圧の変動は微小であった。またＭｇ金属に対する電極電位が±０．５Ｖのときの電流密度は±３０ｍＡｃｍ－２以上の値を示した。 FIG. 6 shows the cycle voltage / current test results of the cell using the rolled Mg—Ag alloy material as the working electrode. 0V vs. The redox currents observed near Mg 2+ / Mg correspond to the dissolution and precipitation of magnesium, respectively. The overvoltage of dissolution precipitation was stable at about ± 15 mV from the initial cycle to 50 cycles, and the fluctuation of the overvoltage with the cycle was minute. The current density when the electrode potential with respect to Mg metal was ± 0.5 V showed a value of ± 30 mAcm -2 or more.
　各セルの１０サイクル時の電圧電流測定結果を図７に示す。電圧電流特性は、添加元素に影響を受け、前述のとおりＭｇ－Ｃａ合金圧延材が小さな過電圧を示す。表２に１０サイクル時の電流と電圧をまとめている。また表２には、各種Ｍｇ基合金負極材を電解液に３日間浸漬した後の表面状態の確認結果も併記する。Ｃａを添加した合金は孔食の形成が確認できなかったが、その他添加元素種は孔食が観察された。孔食が観察された合金表面には電解液との反応による分解物が付着していた。 FIG. 7 shows the voltage / current measurement results of each cell at 10 cycles. The voltage-current characteristics are affected by the added elements, and as described above, the rolled Mg—Ca alloy exhibits a small overvoltage. Table 2 summarizes the current and voltage during 10 cycles. Table 2 also shows the results of checking the surface condition after immersing various Mg-based alloy negative electrode materials in the electrolytic solution for 3 days. The formation of pitting corrosion could not be confirmed in the alloy to which Ca was added, but pitting corrosion was observed in the other added element species. Decomposition products due to the reaction with the electrolytic solution adhered to the surface of the alloy where pitting corrosion was observed.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
［Ｍｇ－Ｃａ合金負極材におけるＣａ量の影響確認］
　純Ｍｇと純Ｃａとを、Ｃａ含有量が０．０５ｍｏｌ％、０．１ｍｏｌ％、０．６ｍｏｌ％、１．０ｍｏｌ％及び３．０ｍｏｌ％となるようにそれぞれ秤量し、鉄製るつぼ中に投入した以外は、上記Ｍｇ－０．３ｍｏｌ％Ｃａ合金負極材と同一の条件で、Ｃａ量の異なるＭｇ－Ｃａ合金負極材を作製した。 [Confirmation of the effect of Ca amount on Mg-Ca alloy negative electrode material]
Pure Mg and pure Ca were weighed so that the Ca contents were 0.05 mol%, 0.1 mol%, 0.6 mol%, 1.0 mol% and 3.0 mol%, respectively, and put into an iron crucible. Except for the above, Mg—Ca alloy negative electrode materials having different amounts of Ca were produced under the same conditions as the Mg—0.3 mol% Ca alloy negative electrode material.
　得られたＭｇ－Ｃａ合金負極材、及び上記Ｍｇ－０．３ｍｏｌ％Ｃａ合金負極材を用いて、３極式セルをそれぞれ作製した。セルの構造は、電解液にエチルマグネシウムクロリド（Ｃ２Ｈ５ＭｇＣｌ）のテトラヒドロフラン（ＴＨＦ）溶液（濃度２ｍｏｌ／Ｌ）を用いた以外は上述したものと同一とした。 Using the obtained Mg—Ca alloy negative electrode material and the above Mg—0.3 mol% Ca alloy negative electrode material, a tripolar cell was produced. The cell structure was the same as described above except that a solution of ethyl magnesium chloride (C 2 H 5 MgCl) in tetrahydrofuran (THF) (concentration 2 mol / L) was used as the electrolytic solution.
　得られた３極式セルについて、上述した条件にてサイクル電圧電流テストを行った。各セルの２サイクル時の電圧電流測定結果を図８に、１０サイクル時の電圧電流測定結果を図９に、それぞれ示す。図８及び図９からは、Ｃａの含有量が０．０５ｍｏｌ％及び０．１ｍｏｌ％のＭｇ－Ｃａ合金負極材を用いたセルにおいて、大きな電流密度が得られることが判る。これらの結果から、Ｍｇ－Ｃａ合金負極材においては、Ｃａの含有量がごく少量である場合に、特に優れた電気化学的特性を示すといえる。 The obtained 3-pole cell was subjected to a cycle voltage / current test under the above-mentioned conditions. The voltage / current measurement results at 2 cycles of each cell are shown in FIG. 8, and the voltage / current measurement results at 10 cycles are shown in FIG. 9, respectively. From FIGS. 8 and 9, it can be seen that a large current density can be obtained in the cell using the Mg—Ca alloy negative electrode material having a Ca content of 0.05 mol% and 0.1 mol%. From these results, it can be said that the Mg—Ca alloy negative electrode material exhibits particularly excellent electrochemical properties when the Ca content is very small.
　本発明のＭｇ基合金は、優れた電気化学特性を示すことから、Ｍｇ一次電池はもちろんのことＭｇ二次電池用のＭｇ基合金負極材として使用が可能である。
　本発明のＭｇ基合金負極材は、Ｍｇ二次電池に用いることができる。
　また、Ｍｇは低密度であり、素材の厚さが薄いため、本発明のＭｇ基合金負極材の組成を有するＭｇ基合金箔として、アルミニウム箔に代替できる軽量箔材として適応が可能である。 Since the Mg-based alloy of the present invention exhibits excellent electrochemical properties, it can be used as an Mg-based alloy negative electrode material for Mg secondary batteries as well as Mg primary batteries.
The Mg-based alloy negative electrode material of the present invention can be used for an Mg secondary battery.
Further, since Mg has a low density and a thin material, it can be applied as a lightweight foil material that can replace an aluminum foil as an Mg-based alloy foil having the composition of the Mg-based alloy negative electrode material of the present invention.
　Ａ…容器
　Ｂ…電解液
　Ｃ…正極
　Ｄ…負極 A ... Container B ... Electrolyte C ... Positive electrode D ... Negative electrode

Claims (9)

  1. 　Ａｌ、Ａｇ、Ｂｉ、Ｃａ、Ｓｎ、Ｍｎ、Ｌｉ、ＲＥ（希土類）及びＺｎから選択される少なくとも一種類の元素（溶質元素）を、合計で０．０２ｍｏｌ％以上、１０ｍｏｌ％以下の割合で含み、残部がＭｇと不可避的成分とからなるＭｇ基合金で形成され、かつ
    　厚みが１ｍｍ以下である
    Ｍｇ基合金負極材。     Contains at least one element (solute element) selected from Al, Ag, Bi, Ca, Sn, Mn, Li, RE (rare earths) and Zn in a total ratio of 0.02 mol% or more and 10 mol% or less. An Mg-based alloy negative electrode material in which the balance is made of an Mg-based alloy composed of Mg and an unavoidable component, and the thickness is 1 mm or less.
  2. 　Ｍｇ母材の平均粒子サイズが１０００μｍ以下である、請求項１に記載のＭｇ基合金負極材。 The Mg-based alloy negative electrode material according to claim 1, wherein the average particle size of the Mg base material is 1000 μm or less.
  3. 　前記溶質元素の少なくとも１種が結晶粒界に偏析している、請求項１又は２に記載のＭｇ基合金負極材。 The Mg-based alloy negative electrode material according to claim 1 or 2, wherein at least one of the solute elements is segregated at the grain boundaries.
  4. 　三極式セルを用いたサイクル計測において、５回以上のサイクル特性を示す、請求項１から３のいずれか１項に記載のＭｇ基合金負極材。 The Mg-based alloy negative electrode material according to any one of claims 1 to 3, which exhibits cycle characteristics of 5 times or more in cycle measurement using a tripolar cell.
  5. 　Ｍｇ金属の電気化学的析出溶解試験において、過電圧５０ｍＶ以下の特性を示す、請求項１から３のいずれか１項に記載のＭｇ基合金負極材。 The Mg-based alloy negative electrode material according to any one of claims 1 to 3, which exhibits characteristics of an overvoltage of 50 mV or less in an electrochemical precipitation / dissolution test of Mg metal.
  6. 　Ｍｇ金属の電気化学的析出溶解試験において、Ｍｇ金属に対する電極電位が±０．５Ｖのときに、±１０ｍＡｃｍ－２以上の電流密度を示す、請求項１から３のいずれか１項に記載のＭｇ基合金負極材。 The Mg according to any one of claims 1 to 3, which exhibits a current density of ± 10 mAcm -2 or more when the electrode potential with respect to the Mg metal is ± 0.5 V in the electrochemical precipitation / dissolution test of the Mg metal. Base alloy negative electrode material.
  7. 　原料を溶解、鋳造してＭｇ基合金鋳造材を得ること、
    　前記Ｍｇ基合金鋳造材に対して、４００℃以上、６５０℃以下の温度で、０．５時間以上、４８時間以下の溶体化処理を行うこと、及び
    　前記溶体化処理後の前記Ｍｇ基合金鋳造材に対して、塑性ひずみ付与として、５０℃以上、５５０℃以下の温度で、断面減少率１０％以上の展伸加工を施すこと
    を含む、請求項１から６のいずれか１項に記載のＭｇ基合金負極材の製造方法。     Melting and casting raw materials to obtain Mg-based alloy castings,
    The Mg-based alloy casting material is subjected to a solution treatment at a temperature of 400 ° C. or higher and 650 ° C. or lower for 0.5 hours or longer and 48 hours or shorter, and the Mg-based alloy casting after the solution treatment. 7. A method for manufacturing a Mg-based alloy negative electrode material.
  8. 　請求項１から６のいずれかに記載のＭｇ基合金負極材と、電解質と正極とによって構成されたＭｇ二次電池。 An Mg secondary battery composed of the Mg-based alloy negative electrode material according to any one of claims 1 to 6, an electrolyte, and a positive electrode.
  9. 　サイクル計測で１０回以上のサイクル特性を示す、請求項８に記載のＭｇ二次電池。 The Mg secondary battery according to claim 8, which exhibits cycle characteristics of 10 times or more in cycle measurement.
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