JP6517606B2 - Air electrode, metal-air battery, air electrode material, and method of manufacturing air electrode material - Google Patents

Description

  The present invention relates to an air electrode, a metal-air battery, an air electrode material, and a method of manufacturing the air electrode material.

  Conventionally, an air electrode for a metal-air battery contains an electron conductive material as a main component, and contains a layered double hydroxide and a binder as accessory components (see, for example, Patent Document 1). A carbon material etc. are used as an electron conductive material. As the binder, so-called organic binders such as polyvinylidene fluoride, polytetrafluoroethylene and styrene / butadiene rubber are used.

JP 2012-43567 A

  On the other hand, there is a demand to further improve the characteristics of the air electrode (hydroxide ion conductivity, electron conductivity and catalytic reaction activity). The present inventors obtained a new finding that the characteristics of the air electrode can be further improved by using carbon nanotubes as a binder.

  The present invention has been made based on such new findings, and an object of the present invention is to provide an air electrode, a metal-air battery, an air electrode material, and a method of manufacturing the air electrode material whose characteristics can be improved.

  The air electrode according to the present invention is an air electrode used for a metal-air battery, and includes carbon nanotubes having electron conductivity and a layered double hydroxide having hydroxide ion conductivity.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the air electrode which can improve a characteristic, a metal air battery, air electrode material, and air electrode material can be provided.

Sectional view schematically showing the configuration of a zinc-air secondary battery 10 Cross section of air electrode Partially enlarged view of Figure 2 A schematic diagram for explaining the measurement method of cathode resistance SEM secondary electron image of cathode cross section SEM reflection electron image of air pole cross section

  A metal-air battery according to an embodiment will be described with reference to the drawings. The metal air battery is a concept including a zinc air secondary battery, a lithium air secondary battery, and the like. In the present embodiment, a zinc-air secondary battery will be described as an example of a metal-air battery.

  In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic, and ratios of dimensions may be different from actual ones.

(Configuration of Zinc Air Secondary Battery 10)
FIG. 1 is a cross-sectional view schematically showing the configuration of a zinc-air secondary battery 10. As shown in FIG. The zinc-air secondary battery 10 includes an air electrode 12, a hydroxide ion conductive separator 14, a negative electrode 16 immersed in an electrolytic solution, a positive electrode current collector 18, and a container 20.

1. Air pole 12
The air electrode 12 functions as a positive electrode which causes a reduction reaction and / or a generation reaction of O ₂ . The air electrode 12 is disposed on the hydroxide ion conductive separator 14. The air electrode 12 has a first major surface 12S and a second major surface 12T. The air electrode 12 contacts the hydroxide ion conductive separator 14 on the first major surface 12S. The air electrode 12 is in contact with the positive electrode current collector 18 at the second major surface 12T.

  The thickness of the air electrode 12 is not particularly limited, but may be 1 to 100 μm, preferably 1 to 75 μm, more preferably 1 to 50 μm, and still more preferably 1 to 30 μm. By this, the area of the three-phase interface of the hydroxide ion conduction phase, the electron conduction phase, and the gas phase can be secured to maintain the catalytic reaction activity of the air electrode 12.

  The air electrode 12 contains carbon nanotubes (hereinafter, abbreviated as "CNT") and layered double hydroxides (hereinafter, abbreviated as "LDH").

  CNT is a fibrous carbon material in which graphene having a hexagonal lattice structure is formed in a cylindrical shape. The CNTs may be single wall carbon nanotubes or multiwall carbon nanotubes. Both ends of the CNT may be closed or open.

  The CNTs function as an inorganic binder. The CNTs maintain the shape of the air electrode 12 by binding the LDH. CNT also functions as an oxygen reduction generation catalyst. By making the air electrode 12 contain CNT, the catalytic reaction activity of the air electrode 12 can be improved. CNTs also function as electron conductors. The electron conductivity of the air electrode 12 can be improved by containing CNTs in the air electrode 12.

  The CNTs are preferably present in the air electrode 12 not in a bundle but in a unwrapped state. By this, LDH can be bound efficiently. However, some of the CNTs may be present in a bundle in the air electrode 12.

LDH has hydroxide ion conductivity. LDH has the general formula ^{_{M 2+ 1-x M 3+ x}} (OH) 2 A n- x / n · mH 2 O (M 2+ is at least one divalent ^{cation, M 3+} is one or more A trivalent cation, A ⁿ⁻ is an n valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more. expressed. As M ^<2+> , Ni ^<2+> , Mg ^<2+> , Ca ^<2+> , Mn ^<2+> , Fe ^<2+> , Co ^<2+> , Cu ^<2+> , Zn ^<2+> is mentioned. As M ^<3+> , Fe ^<3+> , Al ^<3+> , Co ^<3+> , Cr ^<3+> , In ^<3+> is mentioned. As A ^{n −} , NO ³⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , OH ⁻ , Cl ⁻ , I ⁻ , Br ⁻ , F ⁻ can be mentioned. In ^particular, it includes ^{Mg 2+} as ^{M 2+,} LDH of Mg-Al type containing ^{Al 3+} as ^{M 3+} is preferred.

  The content of CNTs in the air electrode 12 can be 0.1 volume% or more and 40 volume% or less. Thus, CNTs that function as an oxygen reduction generation catalyst and an electron conductor can also function as an inorganic binder. Therefore, the air electrode 12 does not have to contain an organic binder that does not contribute to the characteristics (electron conductivity and catalytic activity) at all, and therefore, the air electrode 12 is compared to the case where LDH is bound using an organic binder. The 12 characteristics can be significantly improved. The content of CNTs in the air electrode 12 is preferably 0.1% by volume or more and 30% by volume or less, and more preferably 0.1% by volume or more and 20% by volume or less.

  The content of LDH in the air electrode 12 can be 60% by volume or more and 99.9% by volume or less. The content of LDH in the air electrode 12 is preferably 60% by volume or more and 90% by volume or less, and more preferably 60% by volume or more and 70% by volume or less.

  In the air electrode 12, the volume ratio of CNT to LDH (CNT volume / LDH volume) is preferably 0.001 or more. Thus, the LDH can be entirely enclosed by the CNTs, and the electron conductivity of the air electrode 12 can be further improved. In the air electrode 12, the volume ratio of CNT to LDH is preferably 1 or less. Thus, the hydroxide ion conductivity of the air electrode 12 can be further improved.

The air electrode 12 may contain a perovskite-type oxide represented by the general formula ABO _3-δ (δ ≦ 0.4). Such a perovskite type oxide preferably has electron conductivity, but may not have electron conductivity. The perovskite type oxide preferably functions as an oxygen reduction generation catalyst.

The perovskite type oxide is represented by the general formula ABO _3-δ (δ ≦ 0.4) and contains at least La at the A site and at least Ni, Fe and Cu at the B site. It is suitable. Such perovskite type oxide is represented by the composition formula _{LaNi 1-x-y Cu x} Fe y O 3-δ (x> 0, y> 0, x + y <1,0 ≦ δ ≦ 0.4) . In the following, the composition formula _{LaNi 1-x-y Cu x} Fe y O 3-δ perovskite oxide represented abbreviated as LNFCu.

  In the composition formula of LNFC u, x ≦ 0.5 is preferable, 0.01 ≦ x ≦ 0.5 is more preferable, and 0.05 ≦ x ≦ 0.3 is more preferable. In the composition formula of LNFC u, y ≦ 0.3 is preferable, and 0.01 ≦ y ≦ 0.3 is more preferable. By adjusting x and y to such a range, the electron conductivity, thermal expansion coefficient and catalytic reaction activity of the air electrode 12 can be improved.

  The LNFC u is preferably composed of a perovskite single phase. This can further improve the electron conductivity and the catalytic reaction activity of the air electrode 12.

  The perovskite oxide may contain LNFC u as a main component. In the present embodiment, the composition P “containing the substance Q as the main component” means that the substance Q accounts for 70% by volume or more, preferably 90% by volume or more, of the whole composition P. .

  The content of the perovskite oxide in the air electrode 12 can be 0.1 volume% or more and 50 volume% or less. The content of the perovskite oxide in the air electrode 12 is preferably 0.1% by volume or more and 40% by volume or less. In the air electrode 12, the volume ratio of CNT to perovskite oxide (CNT volume / perovskite oxide volume) can be 0.002 or more and 400 or less, and is preferably 0.02 or more and 40 or less.

  The air electrode 12 may contain a slight amount of organic binder. The content of the organic binder in the air electrode is preferably 10% by volume or less. As the organic binder, a thermoplastic resin or a thermosetting resin can be used, and it is not particularly limited.

  Preferred examples of the organic binder include carboxymethyl cellulose (CMC), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoro Ethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, Ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, Pyrene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer Polymers, ethylene-acrylic acid copolymers, and any mixtures thereof may be mentioned.

2. Hydroxide ion conductive separator 14
The hydroxide ion conductive separator 14 is disposed between the air electrode 12 and the negative electrode 16. The hydroxide ion conductive separator 14 is in contact with the first major surface 12S of the air electrode 12. The hydroxide ion conductive separator 14 is made of a material that can selectively transmit hydroxide ions generated and consumed at the air electrode 12.

  The hydroxide ion conductive separator 14 is preferably impervious to undesirable substances (such as carbon dioxide) other than oxygen contained in the air and alkali metal ions in the electrolyte. Such materials include dense ceramics which are inorganic solid electrolytes having hydroxide ion conductivity.

The inorganic solid electrolyte having hydroxide ion conductivity is represented by a general formula M 2 ⁺ _1−x M ³⁺ _x (OH) ₂ A ⁿ⁻ _{x / n} · _m H ₂ O, and a solidification method (eg, a hydrothermal solidification method) The LDH densified by) is preferred. Moreover, as the inorganic solid electrolyte having hydroxide ion conductivity, NaCo ₂ O ₄ , LaFe ₃ Sr ₃ O ₁₀ , Bi ₄ Sr ₁₄ Fe ₂₄ O ₅₆ , NaLaTiO ₄ , RbLaNb ₂ O ₇ , KLaNb ₂ O ₇ , And those having at least one basic composition selected from the group of Sr ₄ Co _1.6 Ti _1.4 O ₈ (OH) ₂ .xH ₂ O can also be used.

  These inorganic solid electrolytes are disclosed in WO 2011/108526 as solid electrolytes having hydroxide ion conductivity for fuel cells. By using an inorganic solid electrolyte having hydroxide ion conductivity as the hydroxide ion conductive separator 14, it is possible to suppress deterioration of the electrolyte solution due to the formation of carbonate ions, and zinc dendrite generated during charging is a hydroxide. The occurrence of a short circuit between positive and negative electrodes through the ion conductive separator 14 can be suppressed.

  The hydroxide ion conductive separator 14 may be a composite of a particle group including an inorganic solid electrolyte having hydroxide ion conductivity and a component that assists in densifying or curing the particle group.

  In addition, the hydroxide ion conductive separator 14 is a composite of an open-pored porous body as a substrate and an inorganic solid electrolyte deposited and grown in the pores so as to fill the pores of the porous body. It may be Examples of the porous body include insulating materials such as ceramics such as alumina and zirconia, and porous sheets made of a foamed resin or a fibrous substance.

  The relative density of the hydroxide ion conductive separator 14 calculated by the Archimedes method is preferably 88% or more, more preferably 90% or more, and still more preferably 94% or more.

  The shape of the hydroxide ion conductive separator 14 is not particularly limited, and may be a dense plate or film. When formed in a plate shape, the thickness of the hydroxide ion conductive separator can be 0.001 to 0.05 mm, preferably 0.001 to 0.01 mm, 0.001 to 0. More preferably, it is .005 mm.

The higher the hydroxide ion conductivity of the hydroxide ion conductive separator 14 is, the more desirable, but typically, 1 × 10 ⁻⁴ to 1 × 10 ⁻¹ S / m (1 × 10 ⁻³ to The conductivity of 1 × 10 ⁻⁴ to 1 × 10 ⁻² S / m (1 × 10 ⁻³ to 1 × 10 ⁻¹ mS / cm) is more typical than ¹ mS / cm.

3. Negative electrode 16
The negative electrode 16 is disposed on the opposite side of the air electrode 12 across the hydroxide ion conductive separator 14. The negative electrode 16 is immersed in the electrolytic solution.

  The negative electrode 16 contains zinc or a zinc alloy that functions as a negative electrode active material. The shape of the negative electrode 16 is not particularly limited, and may be in the form of particles, plates or gels, and is preferably in the form of particles or gels from the viewpoint of the reaction rate. The particle diameter of the particulate negative electrode 16 is preferably 30 to 350 μm. The gelled negative electrode 16 is preferably formed into a gel by mixing and stirring a non-boronized zinc alloy powder having a particle diameter of 100 to 300 μm, an alkaline electrolyte and a thickener (gelling agent).

  The zinc alloy may, for example, be a brazed alloy or a brazed alloy with magnesium, aluminum, lithium, bismuth, indium, lead or the like. As the zinc alloy, mercury-free and lead-free, non-boronized zinc alloy is preferable, and it is preferable to contain aluminum, bismuth, indium or a combination thereof. The zinc alloy more preferably contains 50 to 1000 ppm of bismuth, 100 to 1000 ppm of indium and 10 to 100 ppm of aluminum and / or calcium, and 100 to 500 ppm of bismuth and 300 to 700 ppm of indium and 20 to 50 ppm More preferably, it contains aluminum and / or calcium.

  The negative electrode 16 may be supported by a negative electrode current collector. Examples of the negative electrode current collector include stainless steel, metal plates such as copper and nickel, metal mesh, carbon paper and oxide conductors.

  As the electrolyte, known electrolytes generally used in zinc-air batteries can be used. As an electrolytic solution, an aqueous solution of an alkali metal hydroxide such as an aqueous solution of potassium hydroxide or aqueous sodium hydroxide, an aqueous solution containing zinc chloride or zinc perchlorate, a non-aqueous solvent containing zinc perchlorate, zinc bis (trifluoromethyl) Nonaqueous solvents containing sulfonyl) imide and the like can be mentioned. As an electrolyte solution, potassium hydroxide aqueous solution which is 1 type of alkali metal hydroxide aqueous solution is preferable, and it is more preferable to contain 3-50 weight% (for example, 30-45 weight%) of potassium hydroxide.

4. Positive electrode current collector 18
The positive electrode current collector 18 is disposed on the opposite side of the hydroxide ion conductive separator 14 with the air electrode 12 interposed therebetween. The positive electrode current collector 18 is in contact with the second major surface 12T of the air electrode 12.

The positive electrode current collector 18 is preferably breathable so that air can be supplied to the air electrode 12. Examples of the positive electrode current collector 18 include stainless steel, metal plates such as copper and nickel, metal mesh, carbon paper, oxide conductors, and the like.
5. Battery container 20
The battery case 20 accommodates the air electrode 12, the hydroxide ion conductive separator 14, the negative electrode 16 immersed in the electrolytic solution, and the positive electrode current collector 18. The battery container 20 has a positive electrode container 22, a negative electrode container 24, a positive electrode gasket 26 and a negative electrode gasket 28.

  The positive electrode container 22 accommodates the air electrode 12, the hydroxide ion conductive separator 14, and the positive electrode current collector 18. The positive electrode container 22 is formed with an air hole 20 a for passing external air. The negative electrode container 24 accommodates the negative electrode 16.

  The positive electrode gasket 26 is disposed along the inner peripheral edge of the positive electrode container 22. The negative electrode gasket 28 is disposed along the edge of the negative electrode container 24. The material, shape, and structure of the positive electrode gasket 26 and the negative electrode gasket 28 are not particularly limited, but it is preferable to be made of an insulating material such as nylon. When the positive electrode gasket 26 and the negative electrode gasket 28 sandwich the hydroxide ion conductive separator 14, the inside of the positive electrode container 22 and the negative electrode container 24 is hermetically sealed.

(Fine structure of air electrode 12)
Next, the detailed microstructure of the air electrode 12 will be described. FIG. 2 is an enlarged sectional view of the air electrode 12 shown in FIG. FIG. 3 is a partial enlarged view of FIG.

  As shown in FIGS. 2 and 3, the air electrode 12 is disposed between the hydroxide ion conductive separator 14 and the positive electrode current collector 18. The air electrode 12 includes a plurality of CNTs 12 a and a plurality of LDH particles 12 b.

  The shape of the CNTs 12a is a string shape. In the present embodiment, the CNTs 12a have a spirally wound structure, but may be linear or may be bent or curved. The average length of the CNTs 12a can be 0.1 μm or more, but is not particularly limited. The average diameter of the CNTs 12a can be 1.0 nm or more, but is not particularly limited.

  The plurality of CNTs 12 a entirely surround the plurality of LDHs 12 b. The plurality of CNTs 12a is preferably entangled with the plurality of LDHs 12b. By this, the shape of the air electrode 12 can be firmly maintained. At least some of the plurality of CNTs 12 a are preferably in contact with each other. This creates a long distance electron conduction path. It is preferable that at least a part of the CNTs 12 a among the plurality of CNTs 12 a be continuous in a direction perpendicular to the first major surface 12 S or the second major surface 12 T (hereinafter, referred to as “thickness direction”). By this, the electron conductivity of the air electrode 12 in the thickness direction can be improved.

  The particle shape of the LDH particles 12 b is plate-like. In the present embodiment, the LDH particles 12 b are formed in an elliptical plate shape, but may be a disk shape or a square plate shape. The average particle size of the LDH particles 12 b is preferably 10 μm or less. The average particle diameter of the LDH particles 12 b can be 0.01 μm or more and 5 μm or less. The average particle diameter of the LDH particles 12 b is preferably 1 μm or less. The average particle diameter of the LDH particles 12 b is the diameter of the plate-like particles when observing the particle shape with a SEM (scanning electron microscope).

  The LDH particles 12 b are supported by the string-like CNTs 12 a. The LDH particles 12b may be supported by the CNTs 12a indirectly through other LDH particles 12b, but are preferably supported by direct contact with the CNTs 12a. The LDH particles 12b may be in direct contact with several CNTs 12a. Direct contact between the LDH particles 12 b and the CNTs 12 a enables reactions between electrons passing through the CNTs 12 a and hydroxide ions passing through the LDH particles 12 b, thereby promoting the catalytic reaction activity of the air electrode 12. . The number ratio of the LDH particles 12 b in direct contact with the CNTs 12 a among the plurality of LDH particles 12 b is not particularly limited, but is preferably 90% or more.

  Preferably, at least some of the plurality of LDH particles 12 b are in contact with each other. By this, the conduction path of hydroxide ion can be formed. In particular, the plurality of LDH particles 12 b are preferably continuous in the thickness direction.

  As shown in FIGS. 2 and 3, the air electrode 12 preferably includes a plurality of perovskite-type oxide particles 12 c. The perovskite-type oxide particles 12c are preferably LN FC u particles.

  In the present embodiment, the particle shape of the perovskite-type oxide particles 12 c is spherical, but may not be spherical and may be complicated and irregular. The average particle diameter of the perovskite type oxide particles 12c can be 0.01 μm or more and 10 μm or less. The average particle size of the perovskite-type oxide particles 12c is preferably smaller than the average particle size of the LDH particles 12b. Specifically, the average particle diameter of the perovskite-type oxide particles 12c is preferably 0.1 μm or less. The average particle diameter of the perovskite-type oxide particles 12c is the diameter of the particles when observing the particle shape by SEM.

  The perovskite-type oxide particles 12c are preferably supported on the LDH particles 12b. The perovskite-type oxide particles 12c may be disposed on the two main surfaces of the plate-like LDH particles 12b, or may be disposed on the side surfaces of the plate-like LDH particles 12b. The perovskite-type oxide particles 12c preferably do not completely cover the entire surface of the LDH particles 12b. Since a part of the surface of the LDH particles 12 b can be exposed by this, connection between the LDH particles 12 b and connection between the CNTs 12 a and the LDH particles 12 b can be achieved.

  Preferably, at least some of the plurality of perovskite-type oxide particles 12c are in contact with each other. This forms a short distance electron conduction path. Preferably, at least some of the plurality of perovskite-type oxide particles 12c are in direct contact with the CNTs 12a. As a result, it is possible to connect the long-distance electron conduction path by the CNTs 12a and the short-distance electron conduction path by the perovskite oxide particles 12c.

(Method of manufacturing zinc air secondary battery 10)
Next, a method of manufacturing the zinc-air secondary battery 10 will be described.
1. Preparation of Air Electrode 12 First, a CNT dispersion is prepared. The CNT dispersion can be prepared by dispersing CNTs in a solvent (eg, water etc.). The concentration of CNTs in the CNT dispersion can be 0.1 wt% to 2.0 wt%, but is not particularly limited. In addition, since CNT has the property of being easily aggregated, it is difficult to disperse in liquid. Therefore, a commercially available CNT dispersion (for example, manufactured by Meijo Carbon Co., Ltd., product name SWNT dispersion) may be used.

  Next, the CNT dispersion is concentrated by heating the CNT dispersion to evaporate the solvent. Thus, by setting the viscosity of the CNT dispersion to 0.1 Pa · s or more and 200 Pa · s or less, the function of the CNT dispersion as a binder can be more effectively exhibited.

Next, prepare the LDH powder represented by the general formula ^{_{M 2+ 1-x M 3+ x}} (OH) 2 A n- x / n · mH 2 O as described above.

  Next, when a perovskite oxide is introduced into the air electrode 12, a perovskite oxide powder is prepared. Hereinafter, the case of using LNFCu powder as the perovskite-type oxide powder will be described. First, the lanthanum hydroxide powder, nickel oxide powder, copper oxide powder and iron oxide powder are dried (110 ° C., 12 hours). Next, each powder dried to have a desired molar ratio of La, Ni, Cu and Fe is weighed. Next, the weighed respective powders are wet-mixed with an aqueous medium and then dried, and then the mixture is sieved to prepare a mixed powder. Next, the mixed powder is put into an alumina crucible with a lid, and calcined (900 to 1200 ° C., 12 hours) in an oxygen atmosphere to prepare a calcined powder. Next, the calcined powder is crushed and uniaxially pressed, and then a compact is produced by CIP (Cold Isostatic Press). Next, the compact is placed in an alumina sheath and sintered in an oxygen atmosphere (900 to 1200 ° C., 12 hours) to prepare a sintered body. Next, the sintered body is wet-pulverized by a pot mill to prepare LNFCu powder.

  Next, each of the concentrated CNT dispersion and LDH powder is weighed. At this time, when the perovskite type oxide powder is prepared, the perovskite type oxide powder is also weighed.

  Next, the weighed CNT dispersion and LDH powder are charged into an agate mortar, and then the CNT dispersion and LDH powder are mixed while heating the agate mortar with a hot stirrer (60 to 90 ° C.) to prepare a mixed paste (air electrode material An example of

  At this time, the solvent is volatilized from the mixed paste to a viscosity at which printing of the next step is possible. The volume ratio of CNT to LDH (CNT volume / LDH volume) in the mixed paste is 0.001 or more and 1 or less. Thus, by preparing a mixed paste using a CNT dispersion, the uniform mixing properties of the CNTs in the mixed paste can be significantly improved as compared to the case of using powdery or sheet-like CNTs. As a result, the cathode 12 can be generally homogenized. When the perovskite-type oxide powder is weighed, the perovskite-type oxide powder may be mixed with the CNT dispersion and the LDH powder.

  Next, the mixed paste is printed on the positive electrode current collector 18 (for example, carbon paper and the like) by a printing method, and then dried (60 to 120 ° C., 1 hour to 12 hours) in the air. Thus, the laminate of the air electrode 12 and the positive electrode current collector 18 is completed.

2. Preparation of Hydroxide Ion Conductive Separator 14 Hereinafter, the case of producing an LDH separator as the hydroxide ion conductive separator 14 will be described.

First, a LDH powder represented by the general formula ^{_{M 2+ 1-x M 3+ x}} (OH) 2 A n- x / n · mH 2 O as described above.

  Next, an LDH compact having a relative density of 43 to 65% is produced by pressure molding (for example, CIP etc.) of the LDH powder. The relative density of the LDH compact is a value obtained by dividing the density calculated from the size and weight of the LDH compact by the theoretical density. In order to suppress the influence of the adsorbed water on the relative density, it is preferable to prepare an LDH molded body using LDH powder stored for 24 hours or more in a desiccator with a relative humidity of 20% or less.

  Next, the LDH molded body is manufactured by baking (400 to 850 ° C., 1 hour to 10 hours). The weight of the LDH fired body is preferably 57% to 65% of that of the LDH compact, and the volume of the LDH fired body is preferably 70% to 76% or less of that of the LDH compact.

Next, the LDH fired body is held in the aqueous solution containing n-valent anion (A ⁿ⁻ ) or immediately above, and regenerated into an LDH body by hydrothermal synthesis (20 to 200 ° C., 1 hour to 50 hours).

  Next, the LDH separator is completed by removing excess water from the LDH body under an environment of a temperature of 300 ° C. or less and a humidity of 25% or more.

3. Next, the negative electrode gasket 28 is attached to the negative electrode container 24 containing the negative electrode 16 immersed in the electrolytic solution.

  Next, the hydroxide ion conductive separator 14, the laminate of the air electrode 12 and the positive electrode current collector 18 and the positive electrode gasket 26 are sequentially disposed on the negative electrode gasket 28, and then the positive electrode container 22 attached with the positive electrode gasket 26 is Cover.

  Thus, the zinc-air secondary battery 10 is completed.

(Other embodiments)
The present invention is not limited to the embodiments as described above, and various modifications or changes can be made without departing from the scope of the present invention.

  Although the zinc-air secondary battery 10 has been described as an example of the metal-air battery, the air electrode 12 according to the present invention can also be used for other metal-air batteries such as a lithium-air secondary battery.

  The zinc-air secondary battery 10 includes the air electrode 12, the hydroxide ion conductive separator 14, the negative electrode 16 immersed in the electrolytic solution, the positive electrode current collector 18, and the container 20. It is sufficient if the negative electrode 16 and the electrolyte are provided.

  The shape of the zinc-air secondary battery 10 is not particularly limited, and may be, for example, a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, or a square type.

  The air electrode 12 is applicable not only to small secondary batteries but also to large secondary batteries used in electric vehicles and the like.

  The zinc-air secondary battery 10 may further include a positive electrode dedicated to charging. About the positive electrode only for charge, it describes, for example in Unexamined-Japanese-Patent No. 2010-176941. By providing the positive electrode for charging, even when the hydroxide ion conductivity of the hydroxide ion conductive separator 14 is low, high speed charging can be performed by using the positive electrode for charging at the time of charging. Furthermore, since the generation of oxygen at the air electrode 12 at the time of charge is suppressed, the corrosion and deterioration of the air electrode 12 can be suppressed. Examples of the positive electrode dedicated to charging include carbon and titanium metal mesh.

  Examples of the metal-air battery according to the present invention will be described below, but the present invention is not limited to the examples described below.

(Preparation of Examples 1 to 3)
Metal air batteries according to Examples 1 to 3 were produced as follows.

  First, CNT as an inorganic binder is dispersed in water, and the concentration of CNT is 0.1 wt. % CNT dispersion was prepared.

  Next, the viscosity of the CNT dispersion was adjusted to 25 Pa · s by heating the CNT dispersion to evaporate the solvent.

Next, a commercially available Mg _0.75 -Al _0.25- type LDH powder (manufactured by Kyowa Chemical Industry Co., Ltd., trade name DHT6) was prepared.

  Next, the concentrated CNT dispersion and LDH powder were weighed such that the mixing ratio of CNT and LDH was a value shown in Table 1.

  Next, the weighed CNT dispersion and LDH powder were charged into an agate mortar, and then the CNT dispersion and LDH powder were mixed while heating the agate mortar with a hot stirrer to produce a mixed paste (air electrode material). At this time, it was visually confirmed that the CNTs were uniformly mixed in the mixed paste. Although not shown in Table 1, in the mixture prepared by mixing the CNT powder (product No. EC-P, manufactured by Meijo Carbon Co., Ltd.) and the LDH powder, the CNTs are aggregated and uniformly mixed. I couldn't let it go. Similarly, although not shown in Table 1, it is difficult to cut the sheet sufficiently finely and uniformly in a mixture obtained by finely cutting a CNT sheet (manufactured by Meijo Carbon Co., Ltd., product number EC-P paper). It was not possible to mix uniformly.

  Next, the mixed paste was printed on carbon paper and then dried at 80 ° C. in the air. Thus, a laminate of the air electrode and the positive electrode current collector was completed.

  Next, an ion exchange membrane (manufactured by Astom Co., Ltd., model number Neosepta AHA) as a separator was prepared.

  Next, a negative electrode gasket is attached to a negative electrode container containing a polypropylene non-woven fabric impregnated with 1 M KOH aqueous solution, and a separator, a laminate of an air electrode and a positive electrode current collector and a positive electrode gasket are sequentially disposed on the negative electrode gasket , And a positive electrode container attached with a positive electrode gasket.

(Preparation of Example 4)
A metal-air battery according to Example 4 was produced as follows.

  First, CNT as an inorganic binder is dispersed in water, and the concentration of CNT is 0.1 wt. % CNT dispersion was prepared.

  Next, the viscosity of the CNT dispersion was adjusted to 25 Pa · s by heating the CNT dispersion to evaporate the solvent.

Next, a commercially available Mg _0.75 -Al _0.25- type LDH powder (manufactured by Kyowa Chemical Industry Co., Ltd., trade name DHT6) was prepared.

Next, the dried (110 ° C., 12 hours) lanthanum hydroxide powder, nickel oxide powder, copper oxide powder and iron oxide powder are subjected to the composition formula LaNi _1-x-y Cu _x Fe _y O _3-δ , x = 0 .2 Weighed so that y = 0.05. Next, each of the weighed powders was wet-mixed with an aqueous medium and dried, and then a sieve was used to produce a mixed powder. Next, the mixed powder was put into an alumina crucible with a lid, and calcined (1100 ° C., 12 hours) in an oxygen atmosphere to prepare a calcined powder. Next, the calcined powder is pulverized to prepare a compact by a uniaxial press, and then the compact is placed in an alumina sheath and fired in an oxygen atmosphere (1100 ° C., 12 hours) to produce a sintered body. did. Next, the sintered body was wet-pulverized using a pot mill to produce LNFCu powder as a perovskite oxide.

  Next, the concentrated CNT dispersion, LDH powder, and LNFCu powder were weighed such that the mixing ratio of CNT, LDH, and LNFCu was as shown in Table 1.

  Next, the weighed CNT dispersion, LDH powder and LNFCu powder are put into an agate mortar, and then the CNT dispersion, LDH powder and LNFCu powder are mixed while heating the agate mortar with a hot stirrer to obtain a mixed paste (air electrode material ) Was produced. At this time, it was visually confirmed that the CNTs were uniformly mixed in the mixed paste.

  Next, the mixed paste was printed on carbon paper and then dried at 80 ° C. in the air. Thus, a laminate of the air electrode and the positive electrode current collector was completed.

  Next, an ion exchange membrane (manufactured by Astom Co., Ltd., model number Neosepta AHA) as a separator was prepared.

  Next, a negative electrode gasket is attached to a negative electrode container containing a polypropylene non-woven fabric impregnated with 1 M KOH aqueous solution, and a separator, a laminate of an air electrode and a positive electrode current collector and a positive electrode gasket are sequentially disposed on the negative electrode gasket , And a positive electrode container attached with a positive electrode gasket.

(Preparation of Example 5)
A metal-air battery according to Example 5 was produced as follows.

  First, the same concentrated CNT dispersion as in Examples 1 to 3 was prepared.

  Next, the same LDH powder as in Examples 1 to 3 was prepared.

  Next, a dispersion of polytetrafluoroethylene (PTFE) as an organic binder (PTFE concentration: 60 wt.%) (Manufactured by Electrochem, trade name EC-TFE-500 ML) was prepared.

  Next, the CNT dispersion, the LNFCu powder and the PTFE dispersion were weighed such that the mixing ratio of CNT, LNFCu and PTFE was as shown in Table 1.

  Next, the weighed CNT dispersion, LNFCu powder and PTFE dispersion are put into an agate mortar, and then the CNT dispersion, LNFCu powder and PTFE dispersion are mixed while heating the agate mortar with a hot stirrer to obtain a mixed paste (air An electrode material was produced.

  Next, the mixed paste was printed on carbon paper and then dried at 80 ° C. in the air. Thus, a laminate of the air electrode and the positive electrode current collector was completed.

  Next, an ion exchange membrane (manufactured by Astom Co., Ltd., model number Neosepta AHA) as a separator was prepared.

  Next, a negative electrode gasket is attached to a negative electrode container containing a polypropylene non-woven fabric impregnated with 1 M KOH aqueous solution, and a separator, a laminate of an air electrode and a positive electrode current collector and a positive electrode gasket are sequentially disposed on the negative electrode gasket , And a positive electrode container attached with a positive electrode gasket.

(Production of Comparative Example 1)
A metal-air battery according to Comparative Example 1 was produced as follows.

  First, carbon black (manufactured by Denki Kagaku Kogyo, product number Denka black (powdery)) was prepared.

  Next, the same LDH powder as in Examples 1 to 3 was prepared.

  Next, a dispersion of PTFE as an organic binder was prepared.

  Next, carbon black, LNFCu powder and PTFE powder were weighed such that the mixing ratio of carbon black, LNFCu and PTFE was as shown in Table 1.

  Next, the weighed carbon black, LNFCu powder, and PTFE dispersion are introduced into an agate mortar, and then the carbon black, LNFCu powder, and a PTFE dispersion are mixed while heating the agate mortar with a hot stirrer to obtain a mixed paste (air electrode material ) Was produced.

  Next, the mixed paste was printed on carbon paper and then dried at 80 ° C. in the air. Thus, a laminate of the air electrode and the positive electrode current collector was completed.

  Next, an ion exchange membrane (manufactured by Astom Co., Ltd., model number Neosepta AHA) as a separator was prepared.

  Next, a negative electrode gasket is attached to a negative electrode container containing a polypropylene non-woven fabric impregnated with 1 M KOH aqueous solution, and a separator, a laminate of an air electrode and a positive electrode current collector and a positive electrode gasket are sequentially disposed on the negative electrode gasket , And a positive electrode container attached with a positive electrode gasket.

(Observation by SEM)
The microstructure of the air electrode was observed by observing the cross section of the air electrode of Examples 1 to 5 with an SEM. FIG. 5 is a SEM secondary electron image of the cross section of the air electrode of Example 4. FIG. 6 is a SEM reflection electron image of the cross section of the air electrode of Example 4. As an SEM, JSM-6610 LV manufactured by JEOL Ltd. was used, and the acceleration voltage was 20 kV.

  As shown in FIG. 5, it was possible to observe that the plurality of CNTs totally surrounded the plurality of LDHs and functioning as a binder. A long distance electron conduction path was formed by the plurality of CNTs contacting each other. A plurality of CNTs were entangled in entwining with a plurality of LDHs. Each of the plurality of LDHs was plate-shaped. A portion of the surface of each of the plurality of LDHs was exposed.

  Further, as shown in FIG. 6, the average particle size of the plurality of LNFC u particles was smaller than the average particle size of the plurality of LDHs. LNFC u particles were supported on LDH. A short distance electron conduction path was formed by contact between LNFC u particles. By direct contact of the LNFC u particles with the CNTs, the long distance electron conduction path by the CNTs was connected to the short distance electron conduction path by the LNFC u particles.

(Evaluation of overvoltage of air electrode)
FIG. 4 is a schematic view for explaining the method of measuring the overvoltage of the air electrode.

  First, a Pt wire as a reference electrode was inserted into the electrolyte, and a Zn plate as a counter electrode was disposed on the opposite side of the air electrode with the electrolyte interposed, and the working electrode was used as an air electrode.

Next, a current having a current density of 100 mA / cm ² was applied from the open circuit state, and after 10 minutes, the charge / discharge voltage of the counter electrode to the reference electrode was recorded.

  Next, the open circuit voltage of the counter electrode to the reference electrode was measured 10 minutes after returning to the open circuit state.

  Then, the difference between each of the charge and discharge voltages and the open circuit voltage was calculated as an overvoltage (V). The calculation results are summarized in Table 1 below. In Table 1, an overvoltage of less than 1.0 (V) is A (excellent), an overvoltage of 1.0 (V) or more and less than 1.5 (V) is B (good), 1.5 (V) or more. An overvoltage of less than 0 (V) was evaluated as C (acceptable), and an overvoltage of 2.0 (V) or more was evaluated as D (impossible).

  As shown in Table 1, in Examples 1 to 5, the overvoltage during charge and discharge was able to be reduced compared to Comparative Example 1. This is because the characteristics (hydroxide ion conductivity, electron conductivity, and catalytic reaction activity) of the air electrode can be improved by using the inorganic binder CNT instead of the organic binder.

  As shown in Table 1, in Examples 2 and 4, the overvoltage during charge and discharge was able to be reduced more than in Examples 1 and 3. From this, it was found that the content of CNT in the air electrode is preferably 5% by volume or less.

  As shown in Table 1, Example 4 was able to further reduce the overvoltage during charge and discharge as compared to Example 2. From this, it was found that introduction of a perovskite oxide (LNFCu) as a perovskite oxide is effective.

DESCRIPTION OF SYMBOLS 10 zinc air secondary battery 12 air pole 14 hydroxide ion conductive separator 16 negative electrode 18 positive electrode collector 20 container

Claims (15)

An air electrode used for a metal-air battery,
Carbon nanotubes having electron conductivity,
Layered double hydroxides having hydroxide ion conductivity,
Perovskite-type oxides represented by the general formula ABO _3-δ (δ ≦ 0.4),
Including the air electrode. The carbon nanotube functions as a binder,
The air electrode according to claim 1. The content of the carbon nanotube is 40% by volume or less,
The content of the layered double hydroxide is 60% by volume or more.
The air electrode according to claim 1 or 2. The content of the carbon nanotube is 0.1% by volume or more,
The air electrode according to any one of claims 1 to 3, wherein a content ratio of the layered double hydroxide is 99.9 volume% or less. The layered double hydroxide is plate-like,
The air electrode according to any one of claims 1 to 4. The perovskite oxide has electron conductivity,
The air electrode according to claim 1 . The perovskite oxide contains at least La at the A site and at least Ni, Fe and Cu at the B site,
The air electrode according to any one of claims 1 to 6 . The volume ratio of the perovskite oxide to the layered double hydroxide is 0.1% by volume or more and 40% by volume or less.
The air electrode according to any one of claims 1 to 7 . An air electrode according to any one of claims 1 to 8 ,
A negative electrode,
An electrolyte disposed between the air electrode and the negative electrode;
Metal-air battery comprising. The electrolyte is an inorganic solid electrolyte having hydroxide ion conductivity.
The metal air battery according to claim 9 . An air electrode material used for a metal-air battery,
Carbon nanotubes having electron conductivity,
Layered double hydroxides having hydroxide ion conductivity,
Perovskite-type oxides represented by the general formula ABO _3-δ (δ ≦ 0.4),
Including cathode material. A method of manufacturing an air electrode material used for a metal-air battery, comprising:
Weighing a carbon nanotube dispersion liquid in which carbon nanotubes are dispersed in a solvent;
Weighing the layered double hydroxide having hydroxide ion conductivity;
Mixing the weighed carbon nanotube dispersion and the weighed layered double hydroxide;
A method of manufacturing an air electrode material comprising: The volume ratio of the carbon nanotubes to the layered double hydroxide (carbon nanotube volume ÷ layered double hydroxide volume) is 0.001 or more and 1 or less.
A method of manufacturing the cathode material according to claim 12 . The method further comprises the step of weighing the perovskite type oxide,
Mixing the weighed perovskite-type oxides in the step of mixing the carbon nanotube dispersion and the layered double hydroxide;
A method of manufacturing an air electrode material according to claim 12 or 13 . The viscosity of the carbon nanotube dispersion is 0.1 Pa · s or more and 200 Pa · s or less.
A method of manufacturing the cathode material according to any one of claims 12 to 14 .