JP6288511B2 - Negative electrode composite of lithium air battery and lithium air battery - Google Patents

Description

  The present invention relates to a negative electrode and a negative electrode composite of a lithium air battery, and a lithium air battery.

  An air battery is a battery that uses oxygen in the air as a positive electrode active material and metal as a negative electrode active material. As the negative electrode of the air battery, any battery that generates an electromotive force with the positive electrode can be used, and air batteries using various metals as the negative electrode have been studied.

  As one type of air battery, a lithium-air battery that uses metallic lithium as a negative electrode active material is considered promising as a next-generation battery from the viewpoint of increasing capacity. Lithium-air batteries are theoretically high in energy density, and are expected to be able to obtain an energy density of 700 Wh / kg, which is 7 times higher than lithium ion batteries, which is necessary for full-scale popularization of electric vehicles.

  Focusing on the type of electrolyte, lithium-air batteries are broadly divided into two types: aqueous electrolytes and nonaqueous electrolytes. Non-aqueous electrolyte lithium-air batteries have become the mainstream of research and development because they can utilize the technology of lithium-ion batteries other than the air electrode. On the other hand, research and development of an aqueous electrolyte-based lithium-air battery is also in progress, although the number is still small. Compared to lithium water batteries of non-aqueous electrolytes, lithium air batteries of aqueous electrolytes have the advantages that they are not affected by moisture in the air and that the electrolytes are inexpensive and incombustible. However, since lithium metal, which is the negative electrode active material, reacts when it comes into direct contact with oxygen or water, it is necessary to protect the negative electrode active material from the air or aqueous solution electrolyte with a solid electrolyte or the like in an aqueous electrolyte lithium battery. was there.

  Therefore, a negative electrode composite for a lithium-air battery having a three-layer structure in which a metal lithium plate as a negative electrode active material is coated with a solid electrolyte as a water-resistant layer and a buffer layer is inserted between the metal lithium plate and the solid electrolyte. Is known (for example, Patent Document 1).

  Further, it is known that in a secondary battery using lithium as a negative electrode active material, dendrites (dendritic crystals) are generated due to the uneven deposition of metallic lithium on the negative electrode during charging. Therefore, when dendrite grows by repeating charge and discharge, the separator is broken through, causing a decrease in discharge voltage and a decrease in discharge time. In the worst case, the dendrite reaches the positive electrode and causes a short circuit. In order to cope with this problem, a porous layer in which a plurality of porous bodies having different resistance temperature coefficients are adjacent to each other is arranged on the positive electrode side surface of the negative electrode, thereby making it difficult for unevenness of metal ion concentration to occur and depositing the metal uniformly. It is known to suppress dendrite growth (for example, Patent Document 2).

JP 2010-192313 A JP 2012-109164 A

  However, a conventional lithium-air battery uses, as a negative electrode, a sheet of lithium metal, a lithium alloy, or a lithium compound, or a powder obtained by bonding those powders with a binder. Therefore, there has been a problem that the shape of the negative electrode changes with the discharge reaction. This will be described with reference to FIG.

  A conventional lithium air battery 200 shown in FIG. 8 is a lithium air battery having a general configuration, and includes a lithium metal plate 201, a solid electrolyte 202, a buffer layer 203, an electrolyte 217, and an air electrode 219. The lithium metal plate 201, the solid electrolyte 202, and the buffer layer 203 constitute a negative electrode composite 210. FIG. 8A shows a state before use, and FIG. 8B shows a state after repeating the charge / discharge cycle.

  Generally, in a lithium-air battery, during charging, lithium ions in the electrolyte are deposited on the negative electrode layer as metallic lithium, and the volume of the negative electrode layer increases. On the other hand, at the time of discharge, since lithium metal is dissolved out as lithium ions, the volume of the negative electrode layer decreases. In the conventional lithium-air battery 200, after the lithium metal is eluted in the electrolyte during discharge, the deposition on the metal lithium plate 201 becomes non-uniform during charging. Therefore, the metal lithium plate 201 does not increase / decrease in volume uniformly in the plate thickness direction. As a result, the non-uniformity increases as the charge / discharge cycle increases, and the metal lithium plate 201 moves in the plate thickness direction. The shape was biased. When the shape change of the metal lithium plate 201 proceeds, in the worst case, the metal lithium plate 201 is divided. As a result, as the number of charge / discharge cycles increases, the charge / discharge performance decreases, and eventually charge / discharge cannot be performed.

  In particular, in the conventional lithium-air battery 200, dendrites are generated on the metal lithium plate 201 due to the uneven deposition of lithium ions during charging and discharging. When the dendrite grows, it breaks through the solid electrolyte 202 existing between the air electrode 219 and causes an internal short circuit. Further, when the thickness of the metal lithium plate 201 is reduced during discharge, a gap is generated between the metal lithium plate 201 and the solid electrolyte 202, the contact property is deteriorated, and the internal resistance is increased. Therefore, there has been a problem that the discharge voltage decreases as the discharge time increases. Furthermore, after a deep discharge, for example, a discharge of 90% or more of the theoretical capacity, the internal pressure decreases as the amount of metallic lithium decreases, and the central portion of the solid electrolyte 202 is bent and cracks occur. There was also a problem. Such a change in shape and internal short circuit of the metal lithium plate 201 is also a cause of shortening the charge / discharge cycle life of the lithium-air battery.

  The present invention has been made in view of the above problems, and suppresses the generation of dendrites, maintains the negative electrode shape, and reduces the charge / discharge performance even when the number of charge / discharge cycles increases. An object is to provide a negative electrode and a negative electrode composite of a lithium air battery, and a lithium air battery that can be suppressed.

  In order to achieve the above object, the present invention is a negative electrode of a lithium-air battery, comprising a porous metal having a large number of pores, wherein the pores are selected from metallic lithium, a lithium alloy, and a lithium compound. A negative electrode for a lithium-air battery that is filled with seeds is provided.

  In one aspect of the negative electrode of the lithium-air battery according to the present invention, it is preferable that the porous metal is foamed copper or foamed nickel.

  In another aspect, the present invention provides a negative electrode composite for a lithium-air battery, comprising a plate-like or linear negative electrode current collector and a porous metal having a large number of pores connected to the negative electrode current collector. The negative electrode layer in which the pores are filled with at least one selected from metallic lithium, lithium alloy, and lithium compound, and two plate-shaped isolations having lithium ion conductivity sandwiching the entire negative electrode layer And a negative electrode composite for a lithium-air battery.

  In one aspect of the negative electrode composite of the lithium-air battery according to the present invention, it is preferable that a buffer layer is further provided between the negative electrode layer and the isolation layer.

  In one aspect, the negative electrode composite of the lithium-air battery according to the present invention further includes a gasket disposed between the two isolation layers so as to surround the negative electrode layer, and sealing a space between the two isolation layers. Is preferred.

  In one aspect of the negative electrode composite for a lithium-air battery according to the present invention, it is preferable that an outer peripheral sealing member that hermetically seals the two isolation layers is further provided on an outer peripheral portion of the two isolation layers. .

  In another aspect, the present invention provides a lithium-air battery, the negative electrode composite, an air electrode layer containing a conductive material and facing at least one surface of the negative electrode composite, and the air electrode layer Provided is a lithium-air battery including an air electrode provided with a plate-like or linear air electrode current collector that is connected to the battery.

  In one aspect of the lithium-air battery according to this embodiment, one surface of the negative electrode composite and one surface of the air electrode layer facing one surface of the negative electrode composite constitute an air battery cell, It is preferable that the air battery cells are connected in parallel.

  In one aspect of the lithium-air battery according to the present invention, the air electrode layer is bent in a fold, and the plurality of negative electrode composites are sandwiched between flat portions between the folds of the air electrode layer. It is preferred that

  In one aspect, the lithium-air battery according to the present invention includes a case that houses the negative electrode composite and the air electrode, and the air electrode and the negative electrode composite that are stored in the case and are in contact with at least the air electrode. It is preferable to further include an electrolyte that conducts lithium ions between the body and the body.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode and negative electrode composite of a lithium air battery which suppresses the generation | occurrence | production of a dendrite, can suppress the fall of charge / discharge performance, even if the negative electrode shape is maintained and the number of charge / discharge cycles increases. Body, as well as a lithium-air battery.

It is typical sectional drawing which shows the negative electrode composite_body | complex of the lithium air battery which concerns on embodiment of this invention. It is a typical perspective view which shows the lithium air battery which concerns on embodiment of this invention. It is a typical perspective view which shows the internal structure of the lithium air battery which concerns on embodiment of this invention. It is a circuit diagram of the lithium air battery which concerns on embodiment of this invention. It is a typical perspective view which shows the other example of the internal structure of the lithium air battery which concerns on embodiment of this invention. It is a schematic diagram explaining the method of filling metal lithium into the pores of foamed copper. It is a schematic diagram which shows the foamed copper before and after filling with metallic lithium. It is a schematic diagram explaining the change after repeating charge and discharge of the conventional lithium air battery. 2 is a schematic cross-sectional view showing a negative electrode composite of a cell of Example 1. FIG. 3 is a schematic cross-sectional view showing a negative electrode composite of a cell of Comparative Example 1. FIG.

  Hereinafter, the negative electrode and the negative electrode composite of the lithium air battery and the lithium air battery according to the present invention will be described in more detail. The present invention is not limited to the following embodiments.

  FIG. 1 shows an embodiment of a negative electrode composite for a lithium-air battery according to the present invention. A negative electrode composite 10 for a lithium air battery shown in FIG. 1 includes a negative electrode layer 1, an isolation layer 2, a buffer layer 3, a negative electrode current collector 4, a gasket 7, and an outer peripheral sealing member 9 as main components. Yes. The negative electrode composite 10 includes a packaging structure in which both surfaces of the negative electrode layer 1 are covered with a buffer layer 3 and these are wrapped with two isolation layers 2 and a gasket 7.

  The negative electrode layer 1 is made of a porous metal having a large number of pores, and the pores are filled with at least one selected from metallic lithium, a lithium alloy, and a lithium compound (hereinafter also referred to as metallic lithium or the like). Yes. The negative electrode layer 1 has, for example, a rectangular flat plate shape. A negative electrode current collector 4 is connected to the negative electrode layer 1.

The lithium alloy is preferably at least one metal element selected from the group consisting of magnesium, calcium, aluminum, silicon, germanium, tin, lead, arsenic, antimony, bismuth, silver, gold, zinc, cadmium, It is an alloy with lithium. The lithium compound is not particularly limited as long as it can desorb and insert lithium ions. Examples of the lithium compound include Li _3-x M _x N (wherein M is Co, Cu, Ni, or the like).

  The porous metal is not particularly limited as long as it can store and release metallic lithium or the like in its pores, but is preferably a metal foam. The metal foam is a porous body in which a large number of bubbles are formed in a matrix metal. The porous substrate may be a porous body having a patterned structure, such as a lattice-like porous body in which cavities having a shape such as a cube are regularly arranged. The porous metal material may be present stably in the operating range of the negative electrode of the lithium-air battery and has a desired conductivity. Preferably, copper, nickel, or an alloy thereof is used. By using a material having good conductivity as the material of the porous substrate, the current collecting performance can be improved, and as a result, the discharge voltage and discharge time of the lithium-air battery can be improved. The porosity (porosity) of the porous metal is preferably 75 to 99%. When the porosity is within this range, there is an effect that a high-capacity air battery can be configured. The pore diameter of the pores of the metal foam is preferably several μm to 100 μm. When the pore size is in this range, the shape change due to expansion / contraction associated with charging / discharging is alleviated, and the negative electrode structure can be maintained. The pores of the porous metal are preferably filled with metallic lithium or the like at a filling rate of 75% or more (ratio of the volume of filled metallic lithium or the like to the bubble volume). It is desirable that the filling rate be as high as possible from the viewpoint of increasing the capacity of the air battery.

  Filling the pores of the porous metal with metal thyllium or the like is performed, for example, using a known means such as an electroplating method, a method of dissolving metal lithium or the like into the pores, a vacuum deposition method, or a sputtering method. The filling of the porous metal pores with metallic lithium or the like is preferably performed in advance before assembling the negative electrode composite 10, but after the negative electrode composite 10 is assembled, it may be charged by a charging process.

  Since the negative electrode layer 1 is composed of a porous metal, the porous metal serves as a pillar of the structure of the negative electrode layer 1, and the structure is maintained without thinning the negative electrode layer 1 during discharge. Furthermore, in the negative electrode layer 1, since metal lithium is deposited in the voids of the porous metal at the time of charging, uneven deposition of metal lithium can be suppressed, and dendrite growth and uneven shape can be prevented. Can be prevented. Therefore, the negative electrode layer 1 is less likely to change in shape of the negative electrode layer 1 even when the number of charge / discharge cycles is increased. Thus, since the shape change due to expansion / contraction of the negative electrode layer 1 can be alleviated, the negative electrode layer itself can be prevented from being broken and broken. Therefore, the negative electrode layer 1 can suppress a decrease in charge / discharge performance associated with the number of charge / discharge cycles. In addition to the negative electrode composite 10, the negative electrode layer 1 can also be used as a negative electrode layer in negative electrode composites having various structures, for example, negative electrode composites having an aluminum laminate film as a packaging material.

  The negative electrode current collector 4 may be made of any material as long as it can exist stably in the operating range of the lithium-air battery and has a desired conductivity. For example, copper, nickel, or alloys thereof can be used. The negative electrode current collector 4 has a plate shape or a linear shape. The negative electrode current collector 4 is connected to the negative electrode layer 1 and has a portion exposed to the outside of the isolation layer 2. This exposed portion can be electrically connected to the outside and functions as a negative electrode terminal.

  The isolation layer 2 is made of a solid electrolyte and constitutes most of the outer shell of the negative electrode composite 10. The isolation layer 2 has a rectangular flat plate shape that is slightly larger than the negative electrode layer 1, and the two isolation layers 2 sandwich the entire negative electrode layer 1. That is, the central portion of the isolation layer 2 faces the negative electrode layer 1, and the outer peripheral edge of the isolation layer 2 projects outward from the negative electrode layer 1 like a ridge or eaves. The isolation layer 2 serves as a separator that partitions the positive electrode layer containing the electrolyte and the negative electrode layer 1 and protects the negative electrode layer 1 from moisture. That is, the two isolation layers 2 face the air electrode layers of different air electrodes.

The isolation layer 2 is preferably made of glass ceramics having water resistance and lithium ion conductivity. The isolation layer 2 preferably has a lithium ion conductivity of 10 ⁻⁵ S / cm or more. Examples of the isolation layer 2 include a NASICON (Na Super Ionic Conductor) type lithium ion conductor. Further, as the isolation layer 2, a tetravalent cation M of a lithium ion conductor represented by the general formula LiM ₂ (PO ₄ ) ₃ (wherein M represents a tetravalent cation such as Zr, Ti, Ge, etc.). Li _{1 + x} M _2−x M ′ _x (PO ₄ ) ₃ (0 ≦ X ≦ 2) in which lithium ion conductivity is improved by substituting a part of trivalent cations M ′ such as In and Al The lithium ion conductor represented by these is mentioned. Further, as the isolation layer 2, a tetravalent cation M of a lithium ion conductor represented by the general formula LiM ₂ (PO ₄ ) ₃ (wherein M represents a tetravalent cation such as Zr, Ti, Ge, etc.). Is substituted with a pentavalent cation M ″ such as Ta to improve lithium ion conductivity. Li _1−x M _2−x M ″ _x (PO ₄ ) ₃ (0 ≦ X <1) The lithium ion conductor represented by these is mentioned. P in these lithium ion conductors may be substituted with Si, and is represented by the general formula Li _{1 + x + y} Ti _2−x Al _x P _3−y Si _y O ₁₂ (LTAP) (wherein x = 0.3, A lithium ion conductor represented by y = 0.2) is desirable from the viewpoint of ion conductivity.

The buffer layer 3 is a lithium ion conductive polymer electrolyte or an organic electrolyte. The lithium ion conductivity (also referred to as lithium ion conductivity) of the buffer layer 3 is desirably 10 ⁻⁵ S / cm or more. The buffer layer 3 is disposed between the negative electrode layer 1 and the isolation layer 2 and separates the negative electrode layer 1 and the isolation layer 2. The buffer layer 3 protects the isolation layer 2 from contact with the negative electrode layer 1 and enhances the ion conductivity of the negative electrode layer 1 and the isolation layer 2.

The buffer layer 3 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 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.

In addition, when using especially desirable PEO as a polymer of a solid electrolyte, it is desirable that the molecular weight of PEO is 10 ⁴ to 10 ⁵ , and the molar ratio of PEO and lithium salt is 8 to 30: 1. Is desirable.

In order to improve the strength and electrochemical characteristics of the buffer layer 3, a ceramic filler, for example, BaTiO ₃ powder, may be further dispersed in the polymer. The mixing amount of the ceramic filler is desirably 1 to 20 parts by weight with respect to 100 parts by weight of the remaining components.

Further, the buffer layer 3 may be formed by immersing an organic electrolyte in a separator (a sheet made of porous polyethylene, polypropylene, cellulose, or the like). In this case, the organic electrolyte used for the buffer layer 3 is obtained by mixing ethylene carbonate with diethyl carbonate or dimethyl carbonate and further adding a lithium salt such as LiPF ₆ (lithium hexafluorophosphate).

  Here, when the isolation layer 2 is made of glass ceramics, the negative electrode layer 1 and the isolation layer 2 may be in direct contact with each other, so that the glass ceramics of the isolation layer 2 may react with lithium in the negative electrode layer 1 and deteriorate. For example, when the material of the isolation layer 2 is LTAP, there is a possibility that the LTAP reacts with lithium and deteriorates. However, such a reaction is suppressed by inserting the buffer layer 3 to prevent contact between the negative electrode layer 1 and the isolation layer 2. This contributes to extending the life of the lithium-air battery.

  The buffer layer 3 is not necessarily provided in the negative electrode composite 10, and is an arbitrary component. That is, in the negative electrode composite 10, the negative electrode layer 1 may be disposed so as to be directly adjacent to the isolation layer 2 without the buffer layer 3 being separated.

  The gasket 7 is disposed between the two isolation layers 2 so as to surround the outer periphery of the negative electrode layer 1. The negative electrode layer 1 is disposed within the frame of the gasket 7. The gasket 7 may be fixed to the inner surface of each of the isolation layers 2 by an arbitrary method, but is preferably fixed by the adsorption and / or adhesiveness of the gasket 7 itself. The gasket 7 may be in contact with the outer periphery of the negative electrode layer 1 or may be separated from the outer periphery. The gasket 7 is composed of two gaskets and is disposed on the inner surface of each of the two isolation layers 2 and overlapped with each other. The two gaskets 7 are in close contact with each other on the overlapping surface 8, preferably due to the adsorptivity and / or adhesiveness of the gasket itself. That is, since the gaskets and the gasket 7 and the isolation layer 2 are fixed by adsorption and / or adhesion of the gasket 7, the space between the two isolation layers 2 is sealed. The negative electrode current collector 4 is led out of the negative electrode composite 10 through the overlapping surface 8. Alternatively, the gasket 7 may be configured as one member. In such a case, a through hole for the negative electrode current collector 4 is provided in the gasket 7.

  Since the space in the negative electrode composite 10 is sealed by the gasket 7, it is possible to prevent moisture and solution from entering the negative electrode composite 10. Further, since the gasket 7 is used for fixing, there is no problem that lateral displacement between the gaskets 7 or the isolation layer 2 and the gasket 7 occurs when an adhesive is applied as the outer peripheral sealing member 9. Therefore, workability in the manufacturing process of the negative electrode composite 10 can be improved.

  The gasket 7 preferably has a rectangular window frame shape. The size of the gasket 7 has an internal dimension in which the negative electrode layer 1 can be disposed in the frame, and is an external dimension that is almost the same size as the isolation layer 2. The thickness of the gasket 7 may be approximately the same as the total thickness of the components laminated between the isolation layers 2.

  Alternatively, the gasket 7 may have a window frame shape with a size such that a part of the gasket 7 protrudes outside the end of the isolation layer 2 in order to increase the area ratio of the negative electrode layer 1 to the isolation layer 2. By increasing the area ratio of the negative electrode layer 1 to the isolation layer 2, the battery capacity can be increased while maintaining the size of the negative electrode composite 10 compact.

  The material of the gasket 7 is not particularly limited as long as it is a rubber or elastomer resistant to an organic electrolyte. Since the gasket 7 is resistant to the organic electrolyte, the gasket 7 is not deteriorated even when an organic electrolyte that causes deterioration of an adhesive, resin, or the like is used in the negative electrode composite, and the hermeticity inside the negative electrode composite 10 is maintained. can do. The material of the gasket 7 is preferably a rubber or elastomer made of ethylene-propylene-diene copolymer, or a fluorine-based rubber or elastomer. Examples of the rubber made of ethylene-propylene-diene copolymer include EPM, EPDM, and EPT. Examples of the fluorine-based rubber or elastomer include vinylidene fluoride (FKM), tetrafluoroethylene-propylene (FEPM), tetrafluoroethylene-purple fluorovinyl ether (FFKM), and the like. The physical property of the rubber or elastomer is preferably a soft hardness. 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 processability. Since the gasket 7 has soft hardness and rubber elasticity, the height of the constituent members inside the negative electrode composite 10 can be adjusted uniformly. That is, it is possible to improve the overall adhesion of the contact surface between the buffer layer 3 and the isolation layer 2 by directly or indirectly pressing one or both of the isolation layers 2. Furthermore, this makes it possible to improve the contact between the isolation layer 2 and the negative electrode layer 1 via the buffer layer 3. As a result, the internal resistance of the lithium air battery can be reduced and the discharge voltage can be increased. Further, the rubber or elastomer is preferably a type in which the raw material before molding is liquid and has high adsorptivity and / or adhesiveness.

  The outer peripheral sealing member 9 is disposed at the outer peripheral ends of the two isolation layers 2 and hermetically seals the two isolation layers while exposing the remaining part of the negative electrode current collector 4 to the outside of the two isolation layers. The outer peripheral sealing member 9 is arranged so as to cover the gap between the two isolation layers on the entire periphery of the outer peripheral edge of the two isolation layers 2. The outer peripheral sealing member 9 preferably contacts the gasket 7 and fixes the isolation layer 2 and the gasket 7 from the outside. The outer periphery sealing member 9 can further improve the sealing performance of the negative electrode composite 10. The outer peripheral sealing member 9 is not particularly limited as long as it can be hermetically sealed between two isolation layers and can shrink in the thickness direction of the negative electrode composite 10, but is preferably an adhesive. Adhesives with low moisture permeability and high sealing properties are suitable, for example, epoxy adhesives, acrylic adhesives, silicone adhesives, olefin adhesives, and synthetic rubber adhesives. Can be mentioned. More preferably, the adhesive further has resistance to an aqueous electrolyte (preferably an organic electrolyte), such as an epoxy adhesive or an olefin adhesive. The adhesive preferably has curing conditions that cure in a short time at room temperature. In addition, the adhesive used as the outer peripheral sealing member 9 may contain an alcohol-based solvent or the like that degrades metallic lithium as a trace component, but since the space between the isolation layers is sealed by the gasket 7, Such an alcohol solvent can be prevented from entering the negative electrode composite 10. As a result, the degree of freedom of the type of adhesive that can be used for the external sealing member 9 can be improved. The adhesive has a penetrating portion through which the negative electrode current collector 4 penetrates.

  Alternatively, the outer peripheral sealing member 9 may be a member such as a clip that is fixed by pressing and sandwiching the outer surfaces of the two isolation layers 2 in the vicinity of the outer peripheral end. When the outer peripheral sealing member 9 is such a member, the adhesion between the buffer layer 3 and the isolation layer 2 and the negative electrode layer 1 and the isolation layer 2 can be performed without pressing one or both of the isolation layers 2. The adhesion through the buffer layer 3 can be maintained. Moreover, the sealing property between the two isolation layers by the gasket 7 can be enhanced. A member such as a clip as the external sealing member 9 can be used in combination with the above adhesive.

  The negative electrode composite 10 according to the present embodiment contributes both surfaces of the plate-shaped negative electrode composite 10 to power generation. By making the negative electrode composite 10 double-sided, it is possible to improve the input / output density by increasing the effective area for the battery reaction by a factor of two compared to the conventional lithium-air battery.

  Furthermore, in the negative electrode composite 10 according to this embodiment, the negative electrode layer 1 is made of a porous metal. Therefore, even if the discharge reaction proceeds and the amount of metallic lithium or the like in the negative electrode layer 1 decreases, the porous metal becomes a column and the structure of the negative electrode layer 1 is maintained. For this reason, a gap does not occur between the negative electrode layer 1 and the isolation layer 2, and the contact property between the negative electrode layer 1 and the isolation layer 2 via the buffer layer 3 can be maintained, and the contact resistance increases. There is no. Therefore, an increase in the internal resistance of the lithium air battery is suppressed, and as a result, the discharge voltage can be maintained. Furthermore, in the negative electrode composite 10 according to the present embodiment, high-depth discharge (100% discharge) is possible, and as a result, an increase in discharge capacity can be expected. On the other hand, in a conventional negative electrode that does not use a porous metal, a high-depth discharge of 80% or more is difficult because a gap is formed between the isolation layer and the negative-electrode layer by a high-depth discharge.

  Further, in the negative electrode composite 10 according to the present embodiment, even when the discharge reaction proceeds and the amount of metallic lithium or the like in the negative electrode layer 1 decreases, the structure of the negative electrode layer 1 is maintained and the shape change hardly occurs. Therefore, the internal pressure is not lowered due to the thinning of the negative electrode layer 1, and there is no possibility that the buffer layer 3 and the isolation layer 2 are deformed into a curved shape or the isolation layer 2 is cracked. Further, even if the number of charge / discharge cycles is increased, volume change due to expansion / contraction of the negative electrode layer 1 can be alleviated, so that the negative electrode layer itself can be prevented from being broken and broken.

  Furthermore, in the negative electrode composite 10 according to the present embodiment, when lithium is charged, metal lithium is deposited in the voids of the metal foam, so that uneven deposition of metal lithium can be suppressed, and the negative electrode layer 1 is biased. It can be prevented from changing to a different shape. In addition, generation and growth of dendrites due to uneven deposition of metallic lithium can be suppressed. For this reason, in the negative electrode composite 10 according to the present embodiment, since the tip of the grown dendrite does not come into contact with the isolation layer 2 and is damaged or pierced, it is possible to suppress a decrease in discharge voltage and a decrease in discharge time. There is no problem that the dendrite reaches the positive electrode and causes a short circuit. Therefore, the negative electrode composite 10 according to the present embodiment makes it possible to suppress a decrease in charge / discharge performance even when the number of charge / discharge cycles increases, thereby extending the life of the lithium-air battery. be able to.

  FIG. 2 shows an embodiment of a lithium air battery according to the present invention. FIG. 3 shows the internal structure of the lithium-air battery according to this embodiment. In FIG. 4, the circuit diagram of the lithium air battery which concerns on this embodiment is shown.

  The lithium-air battery 100 according to the embodiment shown in FIG. 2 and FIG. 3 includes, as main components, a case 12 that accommodates the negative electrode composite 10 and the air electrode 19, and a plurality of negative electrode composites that are alternately stacked. Body 10, negative electrode current collector 4 that is pulled out and exposed from inside case 12, air electrode current collector 16 as a positive electrode current collector, a plurality of air electrodes 19, and at least air stored in case 12 An electrolyte 17 that is in contact with the electrode 19 and that conducts lithium ions between the air electrode 19 and the negative electrode composite 10 is provided. In addition, the component which attached | subjected the same code | symbol has the same structure as embodiment described about FIG. 1, and the overlapping description is abbreviate | omitted.

  The adjacent negative electrode composite 10 and the air electrode 19 are actually in contact with each other, but are separated from each other in FIG. 3 so as to be easily identified.

  Case 12 is a gas-permeable but liquid-impermeable material, such as polyethylene, polypropylene, or a fluororesin molded product made of a fluoropolymer having vinylidene fluoride units and tetrafluoroethylene units, or vinylidene fluoride units. And a fluororesin porous body composed of a fluoropolymer having a tetrafluoroethylene unit, which is a hexahedron, for example, a hollow body having a rectangular parallelepiped shape. The case 12 may be a molded product 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 12. The vent is provided at a position where the electrolyte 17 described later does not leak out, and allows air to flow inside and outside the case.

  Only the negative electrode current collector 4 and the air electrode current collector 16 are exposed outside the case 12.

  One surface of the negative electrode composite 10 and one surface of the air electrode 19 facing the same are one air battery cell 21. That is, the lithium-air battery 1 is formed by connecting the number of facing air battery cells 21 of the negative electrode composite 10 and the air electrode 19 in parallel.

  The plurality of negative electrode composites 10 and the plurality of air electrodes 19 each have a plate shape. Further, the plurality of negative electrode composites 10 and the plurality of air electrodes 19 are electrically connected in parallel, respectively.

  The air electrode 19 has a larger projected area than the negative electrode composite 10. Specifically, it has a quadrilateral shape that is slightly larger than the negative electrode composite 10 having a quadrangular flat plate shape.

  The air electrode 19 includes a conductive material and is electrically connected to the air electrode layer 23 and the air electrode layer 23 facing at least one surface of the negative electrode composite 10 (that is, one surface of the isolation layer 2 described later). And a plate-like or linear air electrode current collector 16 connected to the.

The air electrode layer 23 is made of a conductive material such as carbon fiber, and has a thin plate shape. Specifically, the air electrode layer 23 may have a porous structure, for example, 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. Specifically, carbon materials such as carbon cloth, carbon non-woven fabric, and carbon paper. Further, as another material having a porous structure, for example, a metal material such as stainless steel, nickel, aluminum, or iron may be used. As a preferable material for the air electrode, a material having conductivity, light weight and high corrosion resistance is preferable, and an air electrode made of the above-described carbon material is desirable. The air electrode layer 23 sucks up the electrolyte 17 by capillary action and interposes between the negative electrode composite 10 and the air electrode 19. The air electrode layer 23 may include a catalyst such as a noble metal or a metal oxide. 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, La 1.6 Sr 0.4 NiO 4, La 2 NiO 4, La 0.6 Sr Metal oxidation such as _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 , Mn _1.5 Co _1.5 O ₄ A noble metal such as Au, Pt, and Ag; and a composite thereof. The method of producing the air electrode layer 23 containing the catalyst is not particularly limited. For example, a carbon cloth carrying a catalyst metal such as platinum mixed with a binder (binder) and an organic solvent (slurry) is used. It can be carried out by adhering to. As the organic solvent, for example, N-methyl-2-pyrrolidone (NMP), acetonitrile, dimethylformamide (DMF), dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO), acetone, ethanol, 1-propanol and the like are used. be able to. Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and the like. Specific examples of a method for attaching the catalyst to the air electrode layer 23 include a method in which the slurry is applied and adhered by a doctor blade method or a spray method.

  The air electrode current collector 16 may be present stably in the operating range of the lithium-air battery and has the desired conductivity. Examples of the material of the air electrode current collector 16 include metal materials such as stainless steel, nickel, aluminum, gold, and platinum, and carbon materials such as carbon cloth and carbon nonwoven fabric.

  The electrolyte 17 is a water based electrolyte. The electrolyte 17 may also be in contact with the negative electrode composite 10.

  The electrolyte 17 may be a polymer electrolyte. In this case, the electrolyte 17 is a thin film-like body sandwiched between the air electrode 19 and the negative electrode composite 10 or a film-like body that coats the surface of the air electrode layer 23.

  FIG. 5 shows another example of the internal structure of the lithium-air battery according to this embodiment. The internal structure of the lithium-air battery shown in FIG. 5 is characterized in that the air electrode layer 23A of the air electrode 19A is bent in a twisted manner. The plurality of negative electrode composites 10 are sandwiched between flat surfaces 23b between the folds 23a and the folds 23a of the air electrode layer 23A. In addition, the component which attached | subjected the same code | symbol has the same structure as embodiment described about FIG. 3, The overlapping description is abbreviate | omitted.

  Note that the adjacent negative electrode composite 10 and the air electrode 19A are actually in contact with each other, but are separated from each other in FIG. 5 for easy identification.

  One air electrode current collector 16 may be provided for one air electrode layer 23A sandwiching the plurality of negative electrode composites 10, and the number and total number of air electrode current collectors 16 are larger than those of the air electrode current collector 16 of the lithium-air battery 100. Extension length, weight, and volume can be reduced.

  The lithium air battery 100 according to the present embodiment is different from a conventional lithium air battery in which an aqueous electrolyte is included in each single cell in which a negative electrode composite and an air electrode are paired, and a plurality of air battery cells 21 are connected in parallel. And accommodated in one case 12. With such a structure, the lithium-air battery 100 according to the present embodiment does not require a partition for each air battery cell 21 (corresponding to the exterior of a conventional lithium-air battery), and the electrolyte 17 is composed of a plurality of air battery cells 21. The lithium-air battery 100 as a whole can optimize the storage amount of the electrolyte 17 and reduce the weight and volume.

  Further, in the conventional lithium-air battery, one surface of one air electrode faces one surface of one negative electrode composite and is enclosed in a container or a laminate film. In order to increase the input / output density (output per weight) in these conventional air batteries, it is necessary to simply use a large number of air batteries having the same structure or simply increase the size of the air battery having the same structure. In practice, it has been difficult to adopt an air battery, for example, when it is mounted on an electric vehicle in order to increase the mounting space of the air battery inefficiently. On the other hand, the lithium-air battery 100 according to the present embodiment eliminates the need for a laminate film in a conventional lithium-air battery, reduces the number of parts, and eliminates difficult adhesion in joining the laminate film polypropylene and glass ceramics.

  Therefore, according to the lithium air battery 100 according to the present embodiment, even if the energy density and the input / output density are increased as compared with the conventional air battery, it can be made compact by suppressing an extreme increase in size.

  Furthermore, in the lithium-air battery 100 according to this embodiment, since the negative electrode layer 1 is made of a porous metal, the generation of dendrite and the change in the negative electrode shape are suppressed, and charging accompanying an increase in the number of discharge / charge cycles. -It can alleviate the decrease in discharge performance and improve battery life.

  Furthermore, in the lithium-air battery 100 according to the present embodiment, when the aqueous electrolyte is stored in the case 12 as the electrolyte 17, even if the electrolyte 17 volatilizes as the discharge progresses, the electrolyte 17 is successively transferred to the air electrode 19. Can be replenished. Thereby, the lithium air battery 100 according to the present embodiment does not require replenishment of the electrolyte 17 over a long period of time, and prevents a performance deterioration due to the shortage of the electrolyte 17.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the negative electrode and negative electrode composite for lithium air batteries which concern on this invention, and a lithium air battery are not restrict | limited by the following Example.

[Example 1]
(Preparation of negative electrode composite)
1. The negative electrode composite 110 was assembled in the following procedure under an inert atmosphere with Ar having an oxygen concentration of 1 ppm or less and a dew point of −76 ° C. dp. FIG. 9 shows a schematic cross-sectional view of the negative electrode composite 110.
(1) Solid electrolyte 102 (lithium ion conductive glass ceramics (LTAP) thin plate, quadrilateral, two sheets), foamed copper 101 (porosity of about 90%, pore diameter 50 μm, quadrilateral, one sheet) which are constituent members of the negative electrode composite 110 Copper foil (attached to negative electrode current collector) 104), cellulose separator 103 (square, two sheets), and gasket sheet 107 (EPDM, square frame, two sheets) were prepared. One gasket sheet 107 was attached to each of the two solid electrolytes 102.
(2) The cellulose separator 103 is arranged on the first solid electrolyte 102 so as to enter the frame of the gasket sheet 107, and the organic electrolyte (EC: EMC = 1: 1, 1M LiPF ₆ ) is placed in the cellulose separator. It was dripped at 103 and soaked throughout. The foamed copper 101 was placed on the cellulose separator 103 so as to enter the frame of the gasket sheet 107, and the second cellulose separator 103 was placed on the foamed copper 101. The organic electrolyte was dropped into the second cellulose separator 103 and allowed to penetrate the whole, and it was confirmed that the cellulose separator 103 and the foamed copper 101 were in close contact with each other.
(3) The gasket sheet 107 attached to the second solid electrolyte 102 and the gasket sheet 107 attached to the first solid electrolyte 102 are the gasket overlapping surface 108. (2) was overlaid so that there was no deviation. Two gasket sheets 107 were attached and sealed by the adhesiveness of the gasket sheet 107 so that external air or the like did not enter. The components inside the negative electrode composite were fixed by pressing the whole from the outside so that the solid electrolyte 102 and the foamed copper 101 were in good contact with each other. Further, a part of the copper foil (negative electrode current collector) 104 attached to the foamed copper 101 was exposed to the outside of the solid electrolyte.
(4) An epoxy adhesive 109 (two-component room temperature curing type) is thinly applied to the entire periphery of the outer peripheral edge of the solid electrolyte 102 so that the space between the two solid electrolytes 102 is sealed. 109 was cured.

2. Next, metallic lithium was filled in the pores of the foamed copper 101. As shown in FIG. 6, the negative electrode composite 110 assembled in 1 above was immersed together with the positive electrode 113 in a container 115 containing 30 ml of a 5M LiOH aqueous solution 114. The negative electrode current collector 104 and the positive electrode current collector of the positive electrode 113 were respectively connected to the negative electrode and the positive electrode of the external power source (not shown), and charged at a current density of ² mA / cm ² for 20 hours. Before the current was applied, the pore p of the foamed copper 101 was hollow (FIG. 7 (a)). By this treatment, the metal lithium f was filled in the pore p of the foamed copper 101 (FIG. 7 (b)). )).

(Production of air electrode)
N-methyl-2-pyrrolidone (NMP) was measured by measuring 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). 3 ml was added to prepare a mixed solvent.
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 a carbon cloth having the same size as that of metallic lithium using a coating machine. It dried under reduced pressure and produced the air electrode with a platinum load of 0.25 mg / cm ² . An aluminum foil was attached to the air electrode as a current collector for the air electrode.

(Preparation of aqueous electrolyte)
4.24 g of LiCl was dissolved in 50 ml of purified water to prepare a 2M LiCl aqueous solution. In order to hold the aqueous electrolyte, the aqueous electrolyte was dropped onto the cellulose sheet and placed between the air electrode and the negative electrode.

(Production of cell)
An air electrode, a cellulose sheet in which an aqueous electrolyte is dropped, a negative electrode composite 110, a cellulose sheet in which an aqueous electrolyte is dropped, and an air electrode in a plastic case with a hole and a size that can accommodate the negative electrode composite 110 The stacks were stacked so that there was no deviation in this order, and the lithium-air battery cell of Example 1 was obtained.

[Comparative Example 1]
(Preparation of negative electrode composite)
The negative electrode composite 310 was produced by the following procedure in an inert atmosphere with Ar having an oxygen concentration of 1 ppm or less and a dew point of -76 ° C. dp. FIG. 10 shows a schematic cross-sectional view of the negative electrode composite 310. The negative electrode composite 310 has the same outer size as the negative electrode composite 110 of Example 1.
(1) Solid electrolyte 302 (lithium ion conductive glass ceramics (LTAP) thin plate, quadrilateral, two sheets), metallic lithium 301 (metal Li, quadrilateral, two sheets, copper foil (negative electrode collector), which are constituent members of the negative electrode composite 310 Attached to both surfaces of the electric body) 304) A cellulose separator 303 (square, two sheets) and a gasket sheet 307 (EPDM, square frame, two sheets) were prepared. A gasket sheet 307 was attached to each of the two solid electrolytes 302.
(2) On one solid electrolyte 302 shown on the lower side in FIG. 10, the cellulose separator 303 is disposed so as to enter the frame of the gasket sheet 307, and an organic electrolyte (EC: EMC = 1: 1, 1M). Of LiPF ₆ ) was dropped into the cellulose separator 303 so as to be soaked in the whole. The metallic lithium 301 was placed on the cellulose separator 303 so as to be within the frame of the gasket sheet 307, and the second cellulose separator 303 was placed on the metallic lithium 301. An organic electrolyte was dropped into the second cellulose separator 303 to be soaked throughout.
(3) The upper solid electrolyte 302 prepared in (1) is placed over the product in (2), and the upper and lower gasket sheets 307 are attached so as not to shift so that no external air enters. Thus, the gasket sheet 307 was sealed due to the adhesiveness. In addition, a part of the copper foil (negative electrode current collector) 304 attached to the metal lithium 301 was exposed to the outside of the solid electrolyte. The constituent members inside the negative electrode composite 310 were pressed and fixed from the outside so that the components contact each other with good adhesion.
(4) An epoxy adhesive 309 (two-component room temperature curing type) is thinly applied to the entire periphery of the outer peripheral edge of the solid electrolyte 302 so that the space between the two solid electrolytes 302 is sealed. 309 was cured.

(Production of air electrode)
The air electrode was produced in the same manner as in Example 1.

(Preparation of aqueous electrolyte)
The aqueous electrolyte was prepared in the same manner as in Example 1.

(Production of cell)
An air electrode, a cellulose sheet in which an aqueous electrolyte is dropped, a negative electrode composite 310, a cellulose sheet in which an aqueous electrolyte is dropped, and an air electrode in a plastic case with a hole and a size that can accommodate the negative electrode composite 310 The stacks were stacked so that there was no misalignment in this order, and the lithium-air battery cell of Comparative Example 1 was obtained.

[Discharge test]
In the cells of Example 1 and Comparative Example 1, the discharge voltage when discharged at 4 mA / cm ² (discharge rate of about 0.1 C) was measured using ALS608A manufactured by BAS. Here, 1C refers to a current value at which discharge of a cell having a nominal capacity is constant current and the discharge is completed in exactly one hour. The measurement results are shown in Table 1. As shown in Table 1, the cells of Example 1 and Comparative Example 1 all had high initial discharge voltages, but the cells of Example 1 had 10 charge / discharge cycles. As compared with the cell of Comparative Example 1, the decrease in the discharge voltage was suppressed. Further, in the cell of Example 1, dendrite was hardly generated even when the number of cycles was 5, and the growth of dendrite was suppressed as compared with the cell of Comparative Example 1. Further, in the cell of Example 1, the negative electrode layer was even more uniform in thickness than the cell of Comparative Example 1 even after repeated discharge.

DESCRIPTION OF SYMBOLS 1 Negative electrode layer 2 Separation layer 3 Buffer layer 4 Negative electrode collector 7 Gasket 8 Gasket overlapping surface 9 Outer peripheral sealing member 10 Negative electrode composite body 12 Case 16 Air electrode current collector 17 Electrolyte 19, 19A Air electrode 21 Air battery cell 23 , 23A Air electrode layer 23a Crease 23b Plane portion

100, 100A Lithium-air battery 101 Foamed copper 102 Solid electrolyte 103 Cellulose separator 104 Negative electrode current collector 107 Gasket 108 Gasket overlap surface 109 Epoxy adhesive 110 Negative electrode composite 113 Positive electrode 114 Lithium hydroxide aqueous solution 115 Container

200 Lithium-air battery 201 Metal lithium plate 202 Solid electrolyte 203 Buffer layer 217 Electrolyte 219 Air electrode 210 Negative electrode composite 212 Case

301 Metal Lithium 302 Solid Electrolyte 303 Cellulose Separator 304 Negative Electrode Current Collector 307 Gasket 309 Epoxy Adhesive 310 Negative Electrode Composite

f Metal lithium p Pore P Internal pressure

Claims (7)

A plate-like or linear negative electrode current collector;
A negative electrode layer comprising a porous metal having a plurality of pores connected to the negative electrode current collector, wherein the pores are filled with at least one selected from metallic lithium, a lithium alloy, and a lithium compound;
Two plate-shaped isolation layers having lithium ion conductivity sandwiching the whole negative electrode layer ;
A negative electrode composite of a lithium air battery , comprising: a gasket disposed between the two isolation layers so as to surround the negative electrode layer and sealing a space between the two isolation layers . The negative electrode composite according to claim 1 , further comprising a buffer layer between the negative electrode layer and the isolation layer. Wherein the outer peripheral sealing member of two isolated layers for hermetic seal, the anode composite of lithium-air battery according to claim 1 or 2 further comprising an outer peripheral portion of the two isolation layers. The negative electrode composite according to any one of claims 1 to 3 ,
An air electrode comprising a conductive material and an air electrode layer facing at least one surface of the negative electrode composite; and a plate-like or linear air electrode current collector electrically connected to the air electrode layer; A lithium-air battery comprising: And one surface of the negative electrode composite, the one surface of the air electrode layer opposite to the one surface of the negative electrode composite and constitute the air battery cell, a plurality of the air battery cells are connected in parallel, in claim 4 The lithium air battery as described. The air electrode layer is bent in a twisted manner,
5. The lithium-air battery according to claim 4 , wherein the plurality of negative electrode composites are sandwiched between flat portions between the folds of the air electrode layer. A case for housing the negative electrode composite and the air electrode;
The lithium air according to any one of claims 4 to 6 , further comprising an electrolyte stored in the case and in contact with at least the air electrode to conduct lithium ions between the air electrode and the negative electrode composite. battery.

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