JP2015106486A - Lithium air battery and positive electrode structure of lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium air battery which has an improved oxidation reduction capability of a positive electrode in the lithium air battery and can prevent the generation of hydrogen.SOLUTION: A lithium air battery unit cell 10 comprises a positive electrode structure 3, a negative electrode complex 4, a positive electrode collector 5, a negative electrode collector 6 and an electrolyte 7. The positive electrode structure 3 is obtained by laminating at least two or more positive electrodes 8. It is electrically connected to the positive electrode collector 5 and functions as one air electrode. The negative electrode complex 4 includes the negative collector 6, a negative electrode layer 11, a buffer layer 12, a solid electrolyte layer 13 and an outer periphery sealing member 14. The positive electrode 8 has a superficial area larger than that of the negative electrode layer 11.

Description

  The present invention relates to a lithium air battery and a positive electrode structure of a lithium air battery.

  In recent years, an air battery having an energy density much higher than that of a lithium ion battery has been expected mainly as an electric vehicle application. The air battery uses oxygen in the air as a positive electrode active material. As such an air battery, a lithium-air battery using a lithium metal, a lithium-based alloy, or a lithium-based compound as a negative electrode active material is known. Such a lithium-air battery is composed of a negative electrode, an electrolyte, and a positive electrode (air electrode), and an aqueous electrolyte or a non-aqueous electrolyte is used as the electrolyte.

  Among these, the lithium-air battery of an aqueous electrolyte generally has a negative electrode (for example, metallic lithium), a buffer layer (for example, cellulose impregnated with an organic electrolyte), a solid electrolyte layer (for example, lithium ion conductive glass). Ceramics, or lithium ion conductive glass ceramics, also expressed as lithium ion conductive glass ceramics), aqueous electrolyte (for example, lithium hydroxide aqueous solution) and positive electrode as air electrode (for example, platinum-supported carbon catalyst etc.) Carbon cloth). Compared with the non-aqueous electrolyte lithium-air battery, such an aqueous electrolyte lithium-air battery is advantageous in that it is not affected by moisture in the air, the electrolyte is inexpensive, and is nonflammable.

  By the way, Patent Document 1 describes that in a lithium-water battery, a reaction represented by the following formula (1) occurs at the positive electrode during discharge to generate hydrogen. In Patent Document 1, it is proposed that water is used as a storage material having a high hydrogen storage rate, hydrogen is freely supplied, and the supplied hydrogen is used as fuel for the fuel cell.

JP 2011-228162 A

In an aqueous electrolyte lithium-air battery, if the oxidation-reduction capability of the positive electrode can be maintained over a long discharge, the reaction of the following formula (2) occurs and hydrogen is not generated from the positive electrode. However, the inventors have shown that in a lithium-air battery using an aqueous electrolyte, the redox ability of the positive electrode is obtained when long-time discharge, particularly long-time discharge at a high current density (approximately 4 mA / cm ² or more) is performed. It was found that the reaction of formula (1) occurs and hydrogen is generated from the positive electrode. Moreover, when hydrogen generate | occur | produced in the positive electrode, the discharge voltage of the positive electrode fell and the problem that discharge time became short was discovered. Furthermore, as a result, the generated hydrogen is excessively present in the air. In addition, in order to improve the redox capacity of the positive electrode, when the amount of catalyst supported per unit area is increased, the catalyst activity decreases due to a decrease in the specific surface area of the catalyst, the catalyst activity becomes inefficient with respect to the catalyst amount, Issues such as increased costs have become issues.

  In view of the above problems, the present invention prevents lithium from being generated, thereby preventing a decrease in discharge voltage and a reduction in discharge time in a long-time discharge and preventing excessive hydrogen from being present in the air. The purpose is to provide.

  In order to achieve the above object, a lithium-air battery according to the present invention is a lithium-air battery including a negative electrode, a solid electrolyte, an electrolyte, and a positive electrode, and the positive electrode is larger than the surface area of the negative electrode. It has a surface area.

  In light of the above problems, by preventing the generation of hydrogen from the positive electrode of a lithium-air battery, it is possible to prevent a decrease in battery characteristics (discharge voltage and discharge time) due to high current density discharge over a long period of time, and hydrogen in the air. Is no longer present.

1 is a schematic perspective view showing a lithium air battery according to a first embodiment of the present invention. It is a schematic perspective view which shows the internal structure of the lithium air battery which concerns on 1st embodiment of this invention. It is a schematic sectional drawing which shows the internal structure of the lithium air battery single cell which concerns on 1st embodiment of this invention. It is a schematic perspective view which shows the internal structure of the lithium air battery which concerns on 2nd embodiment of this invention. It is a circuit diagram which shows the lithium air battery which concerns on 2nd embodiment of this invention. FIG. 6A is a schematic cross-sectional view showing the internal structure of a lithium-air battery unit cell according to the second embodiment of the present invention, and FIG. It is a schematic sectional drawing which shows an internal structure. It is a graph which shows transition of the discharge voltage of the lithium air battery in an Example. It is a graph which shows transition of the discharge voltage of the lithium air battery in an Example.

  1st Embodiment of the positive electrode structure of the lithium air battery and lithium air battery 1 which concerns on this invention is described with reference to FIGS.

  FIG. 1 is a schematic perspective view showing a lithium-air battery according to a first embodiment of the present invention.

  As shown in FIG. 1, a lithium-air battery 1 according to this embodiment includes a case 2 as an outer shell, a positive electrode current collector 6 and a negative electrode current collector as an air electrode current collector that is drawn out of the case 2 and exposed. Electric body 5.

  The case 2 is made of a material that is permeable to gas but impermeable to liquid. Case 2 is, for example, made of a fluoropolymer having a polyethylene or vinylidene fluoride unit and a tetrafluoroethylene unit, or a fluoropolymer having a vinylidene fluoride unit or a tetrafluoroethylene unit. A porous body of fluororesin, which is a hexahedron, for example, a hollow body having a rectangular parallelepiped shape. The case 2 may be a molded article made of a material that is impermeable to gas and liquid. In this case, a vent is provided on the side wall of the case 2. The vent is provided at a position where the electrolyte 7 described later does not leak out, and allows air to flow inside and outside the case 2.

  Only the positive electrode current collector 5 and the negative electrode current collector 6 are exposed outside the case 2.

  FIG. 2 is a schematic cross-sectional view showing the internal structure of the lithium-air battery 1 according to the first embodiment of the present invention.

  As shown in FIG. 2, the lithium-air battery 1 according to the present embodiment includes a case 2 that forms an outer shell, a positive electrode structure 3, a negative electrode composite 4, a positive electrode current collector 5, and a negative electrode current collector. A body 6 and an electrolyte 7 are provided.

  The positive electrode structure 3 and the negative electrode composite 4 are each electrically connected in parallel. The adjacent positive electrode structure 3 and negative electrode composite 4 are actually in contact with each other, but are separated from each other in FIG. 2 for easy identification. That is, a single air battery unit cell 10 is formed by the positive electrode structure 3, the negative electrode composite 4, and the electrolyte 7 included therein.

  The positive electrode current collector 5 may be present stably in the operating range of the lithium-air battery and may have a desired conductivity. For example, a plate-like or linear conductor made of a metal material such as stainless steel, nickel, aluminum, gold, or platinum, or a carbon material such as carbon cloth or carbon nonwoven fabric, and one end side of which is a part of the positive electrode structure 3 Alternatively, all are electrically connected.

  The negative electrode current collector 6 may be present stably in the operating range of the lithium-air battery and may have a desired conductivity. For example, it is made of a plate-like or linear conductor made of copper, nickel or the like, and one end thereof is electrically connected to a part or all of the negative electrode composite 4.

  FIG. 3 is a schematic cross-sectional view showing the internal structure of the lithium-air battery single cell 10 according to the present embodiment of the present invention.

  As shown in FIG. 3, the lithium-air battery unit cell 10 includes a positive electrode structure 3, a negative electrode complex 4, a positive electrode current collector 5, a negative electrode complex 6, and an electrolyte 7.

  The positive electrode structure 3 is formed by laminating at least two positive electrodes 8 and is electrically connected to the positive electrode current collector 5 and functions as one air electrode. More specifically, the positive electrode structure 3 is formed by, for example, sewing at least two or more positive electrodes 8 with carbon fiber, resin, or the like. In addition, it may be a structure formed by fixing a plurality of positive electrodes 8, for example, formed by pressing from the outside of adjacent positive electrodes 8 with a clip or the like, or formed by pressing from both sides with a mesh and fixed. Alternatively, the positive electrode structure 3 may be formed by fixing with a stapler or the like.

  The positive electrode 8 includes a main body portion 8 a and an air electrode layer 8 b containing a conductive material, and is electrically connected to the positive electrode current collector 5. Adjacent positive electrodes 8 may be separated from each other, but are desirably connected so that opposing surfaces are in contact with each other. In this case, the contact area between the adjacent positive electrodes 8 greatly contributes to the battery characteristics of the lithium air battery 1 and the lithium air battery single cell 10. Moreover, the shape of the positive electrode 8 is not particularly limited as long as it can be laminated, but the larger the contact area between the positive electrodes 8 adjacent to each other at the time of contact, the better.

  The air electrode layer 8 b is made of a conductive material such as carbon fiber and is electrically connected to the positive electrode current collector 5. The air electrode layer 8 b sucks up the electrolyte 7 and interposes between the positive electrode structure 3 and the negative electrode composite 4. Examples of the air electrode layer 8b include a porous structure, a mesh structure in which constituent fibers are regularly arranged, a nonwoven fabric structure in which the fibers are randomly arranged, and a three-dimensional network structure. For example, carbon paper, carbon cloth, carbon nonwoven fabric, porous nickel, porous aluminum and the like can be mentioned. The carbon cloth refers to a sheet shape in which carbon fibers are knitted with regularity, and the carbon non-woven fabric refers to a sheet shape in which carbon fibers are irregularly entangled. However, the present invention is not limited to this, and any material that exhibits corrosion resistance to the electrolyte 7 can be used as the air electrode layer 8b. As a material for the air electrode layer 8b, as described above, carbon fiber having high corrosion resistance, light weight, high gas diffusibility and high conductivity is preferable.

The air electrode layer 8b may include a conductive material, a catalyst such as a noble metal or a metal oxide, or a binder for binding these, if necessary. Examples of the conductive material include high specific surface area carbon materials such as carbon black and activated carbon. The catalyst may be a catalyst that promotes an oxygen reduction reaction during discharging and an oxygen oxidation reaction during charging. For _{example, MnO 2, CeO 2, Co} 3 O 4, NiO, V 2 O 5, Fe 2 O 3, ZnO, CuO, LiMnO 2, Li 2 MnO3, LiMn 2 O 4, Li 4 Ti 5 O 12, LiNiO 2 , LiVO ₃ , Li ₅ FeO ₄ , LiFeO ₂ , LiCrO ₂ , LiCoO ₂ , LiCuO ₂ , LiZnO ₂ , Li ₂ MoO 4, LiNbO ₃ , LiTaO ₃ , Li ₂ WO ₄ , Li ₂ ZrO ₃ , La _1.6 Sr _{0 .4} NiO ₄ , La ₂ NiO ₄ , La _0.6 Sr _0.4 FeO ₃ , La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ , La _0.8 Sr _0.2 MnO ₃ And metal oxides such as Mn _1.5 Co _1.5 O ₄ ; noble metals such as Au, Pt and Ag; and composites thereof. The method for producing the air electrode layer 8b containing the catalyst is not particularly limited. For example, the air electrode layer 8b is prepared by adhering a carbon carrying a catalytic metal such as platinum mixed with a binder and an organic solvent to a carbon cloth or the like. be able to. As the binder for mixing the carbon, a polyvinylidene fluoride (PVDF), a Nafion dispersion solution (registered trademark), a polytetrafluoroethylene (PTFE), a styrene-butadiene rubber (SBR) or the like is typically used as an electrode of a lithium ion battery. The polymer material used can be used. As the organic solvent for mixing the carbon, for example, N-methylpyrrolidone (NMP), acetonitrile, dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO) and the like can be used.

  The negative electrode composite 4 includes a negative electrode current collector 6, a negative electrode layer 11, a buffer layer 12 (protective layer), a solid electrolyte layer 13, and an outer peripheral sealing member 14.

  The negative electrode layer 11 is electrically connected to a part of the negative electrode current collector 6, and is bonded to one surface or both surfaces of the copper foil of the negative electrode current collector 6, for example. The negative electrode layer 11 is desirably made of metallic lithium from the viewpoint of increasing the capacity. However, the present invention is not limited thereto, and instead of metallic lithium, the negative electrode layer 11 may be an alloy containing lithium as a main component or a compound containing lithium as a main component. Examples of the lithium-based alloy include magnesium, calcium, aluminum, silicon, germanium, tin, lead, antimony, bismuth, silver, gold, and zinc. Moreover, as a compound which has the said lithium as a main component, Li3-xMxN (M = Co, Cu, Ni) is mentioned, for example. The thickness and area of the negative electrode layer 11 are changed according to the battery capacity.

The buffer layer 12 is formed between the negative electrode layer 11 and the solid electrolyte layer 13 to ensure lithium lithium ion conductivity between the two and prevent contact between the negative electrode layer 11 and the solid electrolyte layer 13. For example, when the material of the solid electrolyte layer 13 is LTAP represented by the general formula Li _{1 + x + y} Ti _2-x Al _x P _3-y Si _y O ₁₂ (x = 0.3, y = 0.2), the negative electrode layer When 11 and the solid electrolyte layer 13 come into contact with each other, there is a possibility that the LTAP reacts with the lithium of the negative electrode layer 11 and deteriorates. However, by inserting the buffer layer 12 between the negative electrode layer 11 and the solid electrolyte layer 13, these contacts are prevented, and thus the reaction as described above is suppressed. This contributes to extending the life of the lithium-air battery unit cell 10 and the lithium-air battery 1.

The buffer layer 12 is a lithium ion conductive polymer electrolyte or organic electrolyte. The lithium ion conductivity (also referred to as lithium ion conductivity) of the buffer layer 12 is desirably 10 ⁻⁵ S / cm or more.

The buffer layer 12 may be a solid electrolyte in which a lithium salt is dispersed in a polymer, or may be a gel electrolyte in which an organic electrolyte solution in which a lithium salt is dissolved is swollen in a polymer. Examples of the polymer serving as a host for the solid electrolyte include PEO (polyethylene oxide) and PPO (polypropylene oxide). Examples of the polymer serving as a host for the gel electrolyte include PEO (polyethylene oxide), PVDF (polyvinylidene fluoride), PVDF-HFP (copolymer of poly (vinylidene fluoride) and hexafluoropropylene). Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiTFSI (Li (CF ₃ SO ₂ ) ₂ N), Li (C ₂ F ₄ SO ₂ ) ₂ N, LiBOB (lithium bisoxalatoborate), and the like.

PEO is desirable as the host polymer. In this case, the molecular weight of PEO is desirably 10 ⁴ to 10 ⁵ , and the molar ratio of PEO and lithium salt is particularly desirably 8: 1 to 30: 1. Furthermore, in order to improve the strength and electrochemical characteristics of the buffer layer 12, a ceramic filler (for example, barium titanate: BaTiO ₃ powder) may be dispersed in the polymer. In this case, it is desirable that the mixing amount of the ceramic filler is 1 to 20 parts by weight with respect to 100 parts by weight of the remaining components.

The buffer layer 12 may be made of a material in which a porous separator is impregnated with an organic electrolyte. In this case, as the separator, paper (cellulose) or chemical fiber nonwoven fabric, porous polypropylene (PP), porous polyethylene (PE), porous polyimide (PI), or the like can be used. Further, as the organic electrolyte to be impregnated, propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL) LiPF ₆ , LiClO ₄ , LiBF ₄ , LiTFSI (LiN (CF ₃ SO ₂ ) ₂ N), Li (C ₂ F ₄ ) in an organic solvent such as 2-methyltetrahydrofuran (2-MeTHF) and dimethylformamide (DMH). A solution in which a lithium salt such as SO ₂ ) ₂ N or lithium bisoxalatoborate (LiBOB) is dissolved can be used.

  The buffer layer 12 is not necessarily provided in the negative electrode composite 4 and is an optional component. That is, in the negative electrode composite 4, the negative electrode layer 11 may be disposed so as to be directly adjacent to the solid electrolyte layer 13 without separating the buffer layer 12.

The solid electrolyte layer 13 is made of a material having lithium ion conductivity and low water permeability, and has a substantially flat plate shape or a film shape that is slightly larger than the negative electrode layer 11 and the buffer layer 12. The solid electrolyte layer 13 bears most of the outer shell of the negative electrode composite 4 to protect the negative electrode layer 11 and the buffer layer 12 from moisture, and selectively allows only lithium ions (Li ⁺ ) to pass therethrough.

As the solid electrolyte layer 13, glass ceramics having water resistance and lithium ion conductivity can be used. Desirably, the solid electrolyte layer 13 may be a NASICON (Na Superconducting Conductor) type lithium ion conductor. More preferably, the solid electrolyte layer 13 includes a part of the tetravalent cation M of the lithium ion conductor represented by the general formula Li3M2 (PO ₄ ) ₃ (M is a tetravalent cation such as Zr, Ti, Ge). Lithium ion conductor represented by the general formula Li _{1 + x} M _2−x M ′ _x (PO ₄ ) _{3 in} which lithium ion conductivity is improved by substitution with a trivalent cation M ′ such as In or Al. it can. In addition, the solid electrolyte layer 13 is a part of the tetravalent cation M of the lithium ion conductor represented by the general formula LiM ₂ (PO ₄ ) ₃ (M is a tetravalent cation such as Zr, Ti, Ge). it can be pentavalent "formula _{Li 1-x M 2-x} M with improved lithium ion conductivity by replacing" x _{(PO 4)} cation M lithium ion conductor represented by _3. It is also desirable to replace P in these lithium ion conductors with Si, and it is particularly desirable that the solid electrolyte layer 13 be LTAP. In this case, the lithium ion conductivity, nonflammability, water resistance and long-term stability are excellent, and the negative electrode layer 11 and the buffer layer 12 are reliably protected from moisture.

  The outer peripheral sealing member 14 encloses a part of the negative electrode current collector 4, the negative electrode layer 11, the buffer layer 12, and a part of the solid electrolyte layer 13, and excludes one surface of the solid electrolyte layer 13 on the positive electrode structure 3 side. Close the area. Examples of the outer peripheral sealing member 14 include an aluminum laminate film. The outer peripheral sealing member 14 may be formed by curing an epoxy resin adhesive, a silicone adhesive, a styrene-butadiene rubber adhesive, or the like. Since the outer peripheral sealing member 14 is exposed to both the electrolyte 7 and the buffer layer 12, it is preferable to have organic electrolyte resistance and alkali resistance.

  The electrolyte 7 is filled in the case 2, is in contact with at least the positive electrode structure 3 and the negative electrode complex 4, and is responsible for lithium ion conduction between the positive electrode structure 3 and the negative electrode complex 4. The electrolyte 7 exists at the bottom portion of the case 2 as shown in FIG. 3 and is sucked up by the air electrode layer 8 b, the material holding the electrolyte 7, etc., so that the electrolyte 7 is interposed between the positive electrode structure 3 and the negative electrode composite 4. It is preferable to intervene with the material etc. which hold | maintain. In this case, compared with the case where the electrolyte 7 exists in the whole case 2, the short circuit of the negative electrode composite 4 can be prevented.

Examples of the electrolyte 7 include an aqueous electrolyte in which a lithium salt is dissolved in water. In the case of the aqueous electrolyte, examples of the lithium salt dissolved in water include LiCl (lithium chloride), LiOH (lithium hydroxide), LiNO ₃ (lithium nitrate), CH ₃ CO ₂ Li, and the like.

According to the lithium air battery 1 and the positive electrode structure 3 of the lithium air battery 1 of the present embodiment,
The lithium-air battery 1 includes a negative electrode composite (negative electrode) 4, a solid electrolyte 13, an electrolyte 7, and a positive electrode (positive electrode structure) 3. The surface area that contributes to the battery reaction of the positive electrode structure 3 is conventional. Larger than a positive electrode structure with one positive electrode. Thereby, it is prevented that the oxidation-reduction reaction in the positive electrode structure 3 is lowered when discharged for a long time at a high current density. That is, hydrogen is prevented from being generated in the vicinity of the positive electrode structure 3 due to a high current density discharge for a long time. As a result, generation of hydrogen can be prevented, discharge characteristics (decrease in discharge voltage and shortening of discharge time), and generation of excessive hydrogen in the air can be prevented.

  The positive electrode structure 3 is formed by laminating at least one positive electrode 8 and functions as one air electrode. Thereby, the surface area of the air electrode contributing to the battery reaction can be increased, and the size in the stacking direction or the direction perpendicular to the stacking direction can be changed by adjusting the number of stacked positive electrodes 8 and the area of each. The size of the positive electrode structure 3 is preferably such that the surface area due to the surface area of the plurality of stacked positive electrodes 8 is larger than the surface area of one positive electrode 8. In this case, since the projected area of the surface having a large area in the positive electrode 8 can be reduced, the useless structure can be reduced and the entire surface area of the positive electrode structure 3 contributing to the battery reaction can be utilized as the positive electrode. Thereby, the structure of the lithium air battery single cell 10 and the lithium air battery 1 which consist of the positive electrode structure 3, the negative electrode composite body 4, and the electrolyte 7 can be optimized, made compact, and the size can be reduced.

  Further, by making the projected area of the positive electrode structure 3 substantially equal to the projected area of the surface of the negative electrode composite 4 having a large area, the size of the lithium-air battery single cell 10 is adjusted to the projected area of the negative electrode composite 4. For example, when a plurality of lithium air batteries 10 are stacked to form a stack structure, the lithium air battery 1 and the positive electrode structure 3 of the lithium air battery 1 having a more compact structure are obtained. Therefore, the size can be reduced by optimizing the structure of the lithium-air battery single cell 10 and the lithium-air battery 1.

  Furthermore, when the lithium-air battery 1 and the positive electrode structure 3 according to the present embodiment store a water-based electrolyte as the electrolyte 7 in the case 2, even if the electrolyte 7 volatilizes as the discharge proceeds, the lithium-air battery 1 and the positive electrode structure 3 can be used at any time. The electrolyte 7 is supplied to the positive electrode structure 3. Thereby, replenishment of the electrolyte 7 is not required over long-term discharge, and it is possible to eliminate the possibility that the battery performance deteriorates due to forgetting to replenish the electrolyte 7.

  Furthermore, according to the lithium air battery 1 and the positive electrode structure 3 according to the present embodiment, a compact structure can be realized even when the energy density and the input / output density are increased as compared with the conventional air battery. Suppressing the increase in size.

  A second embodiment of the lithium-air battery 1A and the positive electrode structure 3 of the lithium-air battery 1A according to the present invention will be described with reference to FIGS. 4 to 6B.

  FIG. 4 is a schematic perspective view showing the internal structure of the lithium-air battery 1A according to the second embodiment of the present invention. FIG. 5 is a circuit diagram showing a lithium-air battery 1A according to the second embodiment of the present invention. FIG. 6A is a schematic cross-sectional view showing the internal structure of the lithium-air battery unit cell according to the second embodiment of the present invention, and FIG. 6B is a negative electrode composite of the lithium-air battery unit cell. It is a schematic sectional drawing which shows the internal structure of a body. In addition, the same code | symbol is attached | subjected to the same structure as the lithium air battery 1 in the lithium air battery 1A, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 4, a lithium-air battery 1A includes a case 2, a plurality of positive electrode structures 3, a plurality of negative electrode composites 4A, a plurality of positive electrode current collectors 5 as a plurality of air electrode current collectors, Negative electrode current collector 6 and electrolyte 7.

  As shown in FIGS. 5-6 (b), the some positive electrode structure 3 and the negative electrode composite 4A are arranged in parallel by turns. Among these, one positive electrode structure 3 and one negative electrode complex 4A corresponding to this are one air battery single cell 10A. That is, the lithium-air battery 1A includes a configuration in which air battery single cells 10A configured by a pair of positive electrode structures 3 and negative electrode composites 4A are alternately arranged in parallel.

  Each of the plurality of positive electrode current collectors 5 has a linear or substantially plate shape, and is electrically connected to each of the plurality of positive electrode structures 3. Similarly, each of the plurality of negative electrode current collectors 6 has a linear shape or a substantially plate shape, and is electrically connected to each of the plurality of negative electrode composite bodies 4A. Also, at least one or more of the positive electrode current collector 5 and the negative electrode current collector 6 are exposed outside the case 2.

  The negative electrode composite 4A has a substantially plate shape, the negative electrode current collector 6, two negative electrode layers 11 that share a part of the negative electrode current collector 6 and are electrically connected, and two solid electrolyte layers. 13, an outer peripheral sealing member 14 </ b> A, and a gasket 20. The negative electrode composite 4A can include a buffer layer 12 having lithium ion conductivity and separating the negative electrode layer 11 and the solid electrolyte layer 13 as in the first embodiment.

  14 A of outer periphery sealing members close the area | region except the surface at the side of the positive electrode structure 3 to which each of the some solid electrolyte layer 13 respond | corresponds, a part of negative electrode collector 4A, the negative electrode layer 11, and solid A part of the electrolyte layer 13 is encapsulated. As the outer peripheral sealing member 14A, an aluminum laminate film is typically mentioned. The outer peripheral sealing member 14A may be formed by curing an epoxy resin adhesive, a silicone adhesive, an olefin adhesive, a styrene-butadiene rubber adhesive, or the like. Since the outer peripheral sealing member 14 </ b> A is exposed to both the electrolyte 7 and the buffer layer 12, it is preferable to have organic electrolyte resistance and alkali resistance.

  The gasket 20 is disposed between the two solid electrolyte layers 13 so as to surround the outer periphery of the negative electrode layer 11, and the two negative electrode layers 11 are disposed in the frame of the gasket 20. The gasket 20 may be fixed to the inner surface of each of the solid electrolyte layers 13 by an arbitrary method, but is preferably fixed by the adsorptivity and / or adhesiveness of the gasket 20 itself. The gasket 20 may be in contact with the outer periphery of the negative electrode layer 11 or may be separated from the outer periphery of the negative electrode layer 11. The gasket 20 is composed of two gaskets with the negative electrode current collector 6 interposed therebetween, and is superposed after being disposed on the inner surfaces of the two solid electrolyte layers 13. In this case, the two gaskets have an unillustrated overlapping surface and are in close contact with each other due to the adsorptivity and / or adhesiveness of the gasket itself. Thereby, the space in the gasket 20 is sealed. The negative electrode current collector 6 is led out of the negative electrode composite 4A through the overlapping surface. Alternatively, the gasket 20 may be configured as a single member. In such a case, a through hole (not shown) for allowing the negative electrode current collector 6 to penetrate is provided in the gasket 20.

  The material of the gasket 20 is not particularly limited as long as it is a rubber or an elastomer resistant to an organic electrolyte, but a rubber or an elastomer made of a copolymer of ethylene-propylene-diene or a fluorine-based rubber or an elastomer is preferable. Examples of the rubber formed by copolymerization of ethylene-propylene-diene include EPM, EPDM, EPT and the like. Examples of the fluorine-based rubber or elastomer include vinylidene fluoride (FKM), tetrafluoroethylene-propylene (FEPM), and tetrafluoroethylene-purple fluorovinyl ether (FFKM). The physical properties of the rubber or elastomer are preferably soft, and the hardness of the gasket material is preferably around Shore A 50-70. If the gasket material is extremely soft, there may be problems such as poor workability. In this case, since the gasket 20 has soft hardness, rubber elasticity, and both of these properties, the uniform height adjustment of the constituent members inside the negative electrode composite 4A is possible. That is, the overall adhesion of the contact surface between the buffer layer 12 and the solid electrolyte layer 13 can be improved by pressing one or both of the solid electrolyte layers 13 directly or indirectly. Thereby, the contact property of the negative electrode layer 11 and the solid electrolyte layer 13 through the buffer layer 12 can be improved. In addition, the rubber or elastomer is preferably a material in which the raw material before molding is liquid and has high adsorptivity and / or adhesiveness.

  The gasket 20 preferably has a rectangular window frame shape. The size of the gasket 20 has an internal dimension in which the negative electrode layer 11 can be disposed within the frame, and is an external dimension that is approximately the same size as the solid electrolyte layer 13. The thickness of the gasket 20 may be approximately the same as the total thickness of the constituent members laminated between the two solid electrolyte layers 13.

  According to the lithium air battery 1A and the positive electrode structure 3 of the lithium air battery 1A of the present embodiment, the negative electrode composite in which the same effects as those of the first embodiment are obtained and the two positive electrode structures 3 contribute to the battery reaction. Since the area contributing to the battery reaction of the body 4A is doubled, the input / output density is improved. Moreover, the number of parts of the lithium air battery 1A can be reduced, the structure of the lithium air battery 1A and the lithium air battery single cell 10A can be made more compact, and the weight thereof can be reduced.

  In addition, according to the lithium air battery 1A and the positive electrode structure 3 of the present embodiment, a plurality of lithium air battery units are compared with a conventional lithium air battery in which an aqueous electrolyte is included in each lithium air battery unit cell. The cells 10A are connected in parallel and accommodated in one case 2. Thereby, the lithium air battery 1A does not need to arrange | position the partition (equivalent to the exterior of the conventional lithium air battery) for every lithium air battery single cell 10A, and the electrolyte 7 is shared by several air battery single cell 10A. Thereby, the storage amount of the electrolyte 7 as the whole lithium air battery 1A can be optimized, and a weight and a volume can be reduced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the positive electrode structure of the lithium air battery and lithium battery which concerns on this invention is not restrict | limited by the following Example.

[Test Example 1]
(Preparation of positive electrode)
A positive electrode was produced by the following procedure.
(1) Weigh 80 mg of platinum-supported carbon (Pt: 45.8%) as a catalyst for oxygen reduction of the positive electrode and 20 mg of polyvinylidene fluoride (PVDF) as a binder (binder), and measure N-methylpyrrolidone ( A mixed solvent was prepared by adding 3.0 ml of NMP).
(2) The mixed solvent was stirred and dispersed for 15 minutes with a stirrer (AR-100 manufactured by Shinki Co., Ltd.) and 60 minutes with ultrasonic waves, and coated on carbon cloth using a coating machine (K202 control coater manufactured by Matsuo Sangyo Co., Ltd.). Then, it was placed on a hot plate and dried by heating at 110 ° C. for 1 hour to produce a positive electrode having a platinum loading of approximately 0.25 mg / cm 2.
(3) In the positive electrode of (2), the size (area) of the carbon cloth carrying platinum is set to 2.0 cm with the total area of both surfaces based on the size of metal lithium (2.0 cm ² ) of the negative electrode composite. ^2, 3.0 cm ^2, by distributing a 3.2 cm ² and 4.0 cm ^2, to prepare a sample 1, 2, 3 and 4 of the positive electrode.
(4) A positive electrode having a platinum carrying amount of about 0.45 mg / cm ² was prepared by setting the amount of platinum carrying carbon (Pt: 45.8%) of (1) to 160 mg.
(5) carbon cloth sized platinum supported in (4) (area) to prepare a sample 5 was 2.0 cm ² with respect to the size of the metallic lithium of the negative electrode mixture member (2.0 cm ²⁾ .

(Preparation of negative electrode composite)
A negative electrode composite was produced in the following procedure using constituent members such as specifications and sizes shown in Table 1.
(1) An aluminum laminate packaging material for a window material was bonded to one surface of a solid electrolyte with an SBR synthetic rubber adhesive. A cellulose separator as a buffer layer was placed on the other surface of the solid electrolyte, and 70.0 ml of an organic electrolyte (EC: EMC = 1: 1, 1M LiPF6) was dropped onto the cellulose separator and soaked.
(2) The metallic lithium affixed to the copper foil was placed on the cellulose separator.
(3) Since these members are packed between aluminum laminate packaging materials as outer peripheral sealing members, heat is applied with the ends of the four sides of the aluminum laminate packaging material for the outside and the window being overlapped. Welded and sealed.

(Preparation of aqueous electrolyte)
4.24 g of LiCl was dissolved in 500 ml of purified water to prepare a 2M (mol / L) LiCl aqueous solution. In order to hold the aqueous electrolyte, about 500 μl of the aqueous electrolyte was dropped onto the cellulose sheet and placed between the positive electrode structure and the negative electrode composite.

[Test Example 2]
(Preparation of positive electrode structure)
A positive electrode structure formed by laminating two positive electrodes was produced by the following procedure.
(1) Weigh 80 mg of platinum-supported carbon (Pt: 45.8%) as a catalyst for oxygen reduction of the positive electrode and 20 mg of polyvinylidene fluoride (PVDF) as a binder (binder), and measure N-methylpyrrolidone ( A mixed solvent was prepared by adding 3.0 ml of NMP).
(2) The mixed solvent was stirred and dispersed for 15 minutes with an agitator (AR-100 manufactured by Shinki Co., Ltd.) and 60 minutes with ultrasonic waves, and applied onto a carbon cloth using a coating machine (K202 control coater manufactured by Matsuo Sangyo Co., Ltd.). Then, it was placed on a hot plate and heated and dried at 110 ° C. for 1 hour to produce a positive electrode having a platinum loading of 0.25 mg / cm ² .
(3) A positive electrode structure was prepared by stacking two positive electrodes prepared in (2) and sewing them using a thread.
(4) In (2), the size (area) of the carbon cloth is based on the area (2.0 cm ² ) of metallic lithium of the negative electrode composite, and two positive electrodes having an area of 1.0 cm ^{2 on} one side are laminated. a sample 6 of a total area 2.0 cm ² Te, one side of the area to prepare a sample 7 of a total area 4.0 cm ² formed by laminating two sheets of positive electrode of 2.0 cm ^2.

(Preparation of negative electrode composite)
The same procedure as in Test Example 1 was used.

(Preparation of aqueous electrolyte)
The same procedure as in Test Example 1 was used.

(Discharge test)
The aqueous electrolyte filled in the beaker cell was charged with the negative electrode composite and the positive electrode (positive electrode structure) and discharged. Discharge was performed using the positive electrode or the positive electrode structure of any of Samples 1 to 7 as the positive electrode and the positive electrode structure. For each sample 1-7, the discharge voltage when discharging at a current density of 4 mA / cm ² (about 0.1 C discharge rate) was measured to confirm the presence or absence of hydrogen generation. Here, 1C means a current value at which discharge of a cell having a nominal capacity is constant-current discharged and the discharge is completed in exactly one hour.

  Table 2 shows the results of the discharge test performed on Samples 1 to 5 of Test Example 1. In Sample 1 and Sample 2 in which the area ratio of the positive electrode to the negative electrode was low, hydrogen was generated by long-time discharge. On the other hand, in Sample 3 and Sample 4 in which the area ratio of the positive electrode to the negative electrode was high, generation of hydrogen due to long-time discharge was not confirmed. In addition, generation of hydrogen was not confirmed in Sample 5 in which the amount of the platinum catalyst of the positive electrode was substantially the same as that of Sample 4, but the area ratio of the positive electrode to the negative electrode was low.

  FIG. 7 shows the transition of the discharge voltage between Sample 2 in which hydrogen was generated and Sample 3 in which no hydrogen was generated. In the discharge curve 15 of Sample 2, hydrogen was generated after 8.1 hours of discharge, and the discharge voltage was significantly reduced. On the other hand, in the discharge curve 16 of sample 3, no discharge voltage was observed in the long-time discharge. From these results, it was found that the oxygen reduction ability of the positive electrode was improved by increasing the area of the positive electrode, and it was possible to discharge for a long time without significantly reducing the discharge voltage.

  Table 3 shows the results of the discharge test performed on Samples 6 and 7 of Test Example 2. In Sample 6 having a low area ratio of the positive electrode structure to the negative electrode, hydrogen was generated by long-time discharge. On the other hand, in Sample 7 having a high area ratio of the positive electrode structure to the negative electrode, generation of hydrogen was not confirmed in a long-time discharge.

  FIG. 8 shows changes in discharge voltage between sample 6 in which hydrogen was generated and sample 7 in which no hydrogen was generated. In the discharge curve 17 of Sample 6, hydrogen was generated after 3.3 hours of discharge, and the discharge voltage was significantly reduced. On the other hand, in the discharge curve 18 of Sample 7, no significant decrease in the discharge voltage was observed. From these results, the area of the positive electrode structure in which the positive electrodes are stacked is increased, so that the oxygen reduction ability of the positive electrode structure is improved, and it is possible to perform long-time discharge without significantly reducing the discharge voltage. all right.

  In the above-described embodiment, an example in which an aqueous electrolyte is used as the electrolyte 7 has been described. However, the present invention is not limited to this. If it is a lithium air battery in which hydrogen is generated at the positive electrode, the electrolyte 7 can be used for the lithium air batteries 1 and 1A other than the aqueous electrolyte and the positive electrode structure 3 of the lithium air battery.

  According to the lithium-air battery and the positive electrode structure of the lithium-air battery according to the present invention, hydrogen generation from the positive electrode of the lithium-air battery is prevented, battery performance is prevented from being lowered, and hydrogen is excessively present in the air. A lithium-air battery and a positive electrode structure for a lithium-air battery are provided.

DESCRIPTION OF SYMBOLS 1, 1A Lithium air battery 2 Case 3 Positive electrode structure 4, 4A Negative electrode composite 5 Positive electrode current collector 6 Negative electrode current collector 7 Electrolyte 8 Positive electrode 8a Body part 8b Air electrode layer 10, 10A Air battery single cell 11 Negative electrode layer 12 Buffer layer (protective layer)
13 Solid electrolyte layer 14, 14A Outer peripheral sealing member 15, 16, 17, 18 Discharge curve 20 Gasket

Claims (14)

A lithium-air battery comprising a negative electrode, a solid electrolyte, an electrolyte, and a positive electrode,
The lithium air battery, wherein the positive electrode has a surface area larger than a surface area of the negative electrode.   The lithium air battery according to claim 1, wherein the positive electrode is a positive electrode structure formed by laminating at least two or more positive electrodes.   The lithium-air battery according to claim 2, wherein the positive electrode structure has a projected area substantially equal to a projected area of a surface of the negative electrode having a large area. The positive electrode structure is
An air electrode layer containing a conductive material and serving at least one surface of the positive electrode;
A plate-like or linear positive electrode current collector electrically connected to the air electrode layer;
Further comprising
The negative electrode is
A plate-like or linear negative electrode current collector;
A plate-like negative electrode layer made of metal lithium, an alloy containing lithium as a main component or a compound containing lithium as a main component, and electrically connected to a part of the negative electrode current collector;
A solid electrolyte that conducts lithium ions between the negative electrode layer and the electrolyte;
The negative electrode layer made of a glass ceramic material having lithium ion conductivity, while exposing the plate-shaped buffer layer partitioning between the negative electrode layer and the solid electrolyte layer, and the remainder of the negative electrode current collector to the outside , A joint portion that encloses and closes the buffer layer and the solid electrolyte;
A negative electrode composite comprising:
The lithium air battery according to claim 2, further comprising:   The lithium-air battery according to claim 4, wherein the positive electrode structure and the negative electrode composite are electrically connected in parallel.   6. The lithium air battery according to claim 4, wherein at least two or more of the positive electrode structures and at least one or more of the negative electrode composites are electrically alternately connected in parallel.   The lithium-air battery according to any one of claims 4 to 6, wherein the positive electrode current collector is made of stainless steel, nickel, aluminum, gold, platinum, or a carbon material.   The lithium air according to any one of claims 4 to 7, wherein the air electrode layer has a porous structure, a mesh structure in which constituent fibers are regularly arranged, a nonwoven fabric structure in which the fibers are randomly arranged, or a three-dimensional network structure. battery.   The lithium air battery according to claim 4, wherein the negative electrode current collector is made of copper or nickel. A case for accommodating the positive electrode structure and the negative electrode composite;
10. The electrolyte according to claim 4, wherein the electrolyte is stored in the case and is in contact with at least the positive electrode structure and conducts lithium ions between the positive electrode structure and the negative electrode composite. Lithium air battery.   The case is a fluororesin molded article made of a fluoropolymer having polyethylene, a vinylidene fluoride unit and a tetrafluoroethylene unit, or a fluororesin porous body made of a fluoropolymer having a vinylidene fluoride unit and a tetrafluoroethylene unit. The lithium air battery according to any one of Items 4 to 10.   12. The lithium air battery according to claim 1, wherein only the positive electrode current collector and the negative electrode current collector are exposed outside the case.   The lithium-air battery according to claim 1, wherein the electrolyte is an aqueous electrolyte. A linear or plate-like positive electrode current collector made of stainless steel, nickel, aluminum, gold, platinum or carbon material, a catalyst-supported porous structure, a mesh structure in which constituent fibers are regularly arranged, and randomly A positive electrode structure having a non-woven fabric structure or an air electrode layer having a three-dimensional network structure, and a positive electrode structure of a lithium-air battery,
The positive electrode contains a conductive material and is electrically connected to the positive electrode current collector; the air electrode layer bears at least one surface of the positive electrode;
The positive electrode structure is formed by stacking at least two positive electrodes.
A positive electrode structure for a lithium-air battery, wherein the projected area is changed by changing the number, size, or stacking direction of the positive electrodes.

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