JP2016046039A - Metal air battery and electrolytic medium for metal air battery positive electrode side - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a superior metal air battery which can facilitate the manufacturing of a positive electrode of a metal air battery, and can prevent the decrease in discharge voltage; and an electrolytic medium for a positive electrode side of such metal air battery.SOLUTION: A metal air battery 1 comprises: a positive electrode part 30 including a carbon cloth; a negative electrode part 20 including a metallic lithium; and an electrolytic medium part 40 disposed between the positive and negative electrode parts, which is in contact with the positive electrode part. The electrolytic medium part 40 has an electrolytic medium 41 which is an electrolytic solution with a metal catalyst dissolved therein. The metal catalyst serves to facilitate an oxygen reductive reaction when the metal air battery is discharged.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a metal-air battery and an electrolytic medium for its positive electrode side.

  Due to the widespread use of electric vehicles, there are expectations for metal-air batteries such as lithium-air batteries that have a much higher energy density than lithium-ion batteries. The metal-air battery uses oxygen in the air as a positive electrode active material.

  Focusing on the type of electrolyte, lithium-air batteries are broadly divided into two types: non-aqueous electrolytes (Patent Documents 1 and 2) and aqueous electrolytes (Patent Documents 3 and 4).

JP 2012-84490 A JP 2014-2915 A JP 2013-201056 A Japanese Patent No. 5382573

  In any of Patent Documents 1 to 4, the catalyst on the positive electrode side of the metal-air battery is applied and supported on carbon fiber or the like, which is a positive electrode material. Therefore, in order to produce the positive electrode, a process of applying an appropriate amount of the catalyst and a process of drying after the application are necessary, and many processes are necessary to produce the positive electrode. In particular, when a catalyst is applied, the catalyst needs to be mixed with a binder and applied to the carbon fiber material. Therefore, there is a problem that the weight of the positive electrode increases and the energy density per weight decreases.

  In addition, when the reaction proceeds on the positive electrode side of the metal-air battery, a reaction product is generated on the catalyst surface or the reaction field of the catalyst, and the catalytic ability of the catalyst supported on the positive electrode material is reduced. there were. Furthermore, since the surface of the catalyst applied to the material surface of the positive electrode is hidden by another catalyst or an added binder, there is a possibility that it may not contribute to the reaction.

  Furthermore, as a general problem for metal-air batteries, when the discharge current value is increased, if the supply of oxygen at the positive electrode cannot catch up due to the bias of ions near the positive electrode, the reaction will not proceed and only the internal resistance will increase. There was a problem that the discharge voltage immediately decreased.

  Accordingly, an object of the present invention is to provide an excellent metal-air battery that can facilitate the production of a positive electrode of a metal-air battery and prevent a decrease in discharge voltage, and an electrolytic medium for the positive electrode side. And

  In order to solve the above-described problems, the present invention provides, as one aspect thereof, an electrolytic medium for a positive electrode side of a metal-air battery, which is a metal catalyst that promotes an oxygen reduction reaction during discharge of the metal-air battery. The electrolyte solution is dissolved.

The metal catalyst preferably contains a noble metal. The metal catalyst is preferably a metal complex. The metal complex is selected from the group consisting of I ⁻ , Br ⁻ , Cl ⁻ , F ⁻ , CN ⁻ , SCN ⁻ , S ²⁻ , OH ⁻ , NO ₃ ⁻ , NCS ⁻ , H ₂ O, NH ₃ and CO. Preferred are those containing at least one ligand that has been prepared. The electrolytic solution may be a non-aqueous electrolytic solution or an aqueous electrolytic solution.

  Moreover, the present invention, as another aspect, is a metal-air battery, comprising a positive electrode, a negative electrode, and an electrolytic medium disposed between and in contact with the positive electrode and the negative electrode. The metal-air battery includes an electrolytic solution in which a metal catalyst that promotes an oxygen reduction reaction is dissolved during discharge.

  The negative electrode preferably includes a negative electrode layer containing metallic lithium or a lithium-based alloy or compound, and two plate-shaped isolation layers sandwiching the negative electrode layer and having lithium ion conductivity.

  Conventionally, the metal catalyst that promotes the oxygen reduction reaction during discharge was supported on the carbon material of the positive electrode. However, according to the present invention, it is only dissolved in the electrolyte solution in contact with the positive electrode. Therefore, in the production of the positive electrode, the step of applying the catalyst to the carbon material and supporting it can be omitted, and the number of steps for producing the positive electrode can be reduced. In addition, a binder for fixing the catalyst becomes unnecessary, the positive electrode is reduced in weight, and the energy density per weight can be improved. In the present invention, since the metal catalyst dissolved in the electrolytic solution is present uniformly, the metal catalyst is not covered with another metal catalyst or a binder, and the generation of a catalyst that does not contribute to the promotion of the reaction can be prevented. .

  Furthermore, in the present invention, since the metal catalyst is dissolved in the electrolytic solution, the metal catalyst is present in the electrolytic solution uniformly and movably. Therefore, the solid catalyst surface supported on the carbon material of the conventional positive electrode. The reaction efficiency of the oxygen reduction reaction of the positive electrode can be improved as compared with the case where the reaction is promoted by. Thereby, even if the discharge current value is increased, it is possible to prevent the discharge voltage from being lowered. Further, even if the reaction proceeds at the positive electrode and a reaction product is generated, the metal catalyst is dissolved in the electrolytic solution, so that the reaction product does not cover the catalyst. A decrease in catalytic ability can be prevented, and a stable discharge voltage can be maintained.

1 is a cross-sectional view schematically showing one embodiment of a metal-air battery according to the present invention. It is a schematic diagram which expands and shows the frame II which is a boundary part of the positive electrode shown in FIG. 1, and an electrolysis medium. It is a perspective view which shows typically the metal air battery used by the Example and the comparative example. It is a graph which shows transition of the discharge voltage in an Example and a comparative example.

  Hereinafter, with reference to the accompanying drawings, an embodiment of a metal-air battery and an electrolytic medium for the positive electrode side according to the present invention will be described in more detail.

  As shown in FIG. 1, the metal-air battery 1 according to this embodiment mainly includes a negative electrode part 20, a positive electrode part 30, and an electrolytic medium part 40 located between the positive electrode part and the negative electrode part. The negative electrode part 20 has a negative electrode active material capable of occluding and releasing metal ions. The positive electrode portion 30 uses air containing oxygen that can be oxidized and reduced as a positive electrode active material, and is also referred to as an air electrode portion.

  The positive electrode part 30 is a composite in the present embodiment, a positive electrode layer 32 made of a material having conductivity and gas diffusibility, a positive electrode current collector 31 electrically connected to the positive electrode layer 32, And a positive electrode outer shell 33 partially covering the positive electrode layer 32.

  As the material having conductivity and gas diffusibility of the positive electrode layer 32, a conductive material having a porous structure may be used. Examples of the porous structure include 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. More specifically, there are carbon fiber materials such as carbon paper, carbon cloth, and carbon nonwoven fabric. The carbon cloth is in the form of a sheet in which carbon fibers are regularly knitted, and the carbon non-woven fabric is in the form of a sheet in which carbon fibers are randomly entangled. In addition, metal materials such as stainless steel, nickel, aluminum, and iron may be used as long as they have a porous structure. Among these, carbon fiber is more preferable from the viewpoint of weight reduction of the positive electrode and high corrosion resistance against the electrolytic solution.

  The positive electrode layer 32 has a thin plate shape. The positive electrode layer 32 is surrounded by the positive electrode outer shell 33, and one surface of the positive electrode layer 32 is opposed to at least one surface of the negative electrode part 20 (that is, a surface of an isolation layer 24 described later). The positive electrode outer shell 33 is provided with an opening. Further, another opening is provided in the positive electrode outer shell 33 so that air as the positive electrode active material is introduced into the positive electrode layer 32. Further, the positive electrode outer shell 33 is provided with an opening (not shown) for drawing out the positive electrode current collector 31 to the outside of the outer shell.

  The positive electrode current collector 31 may be present stably in the operating range of the metal-air battery and may have a desired conductivity. Examples of the material of the positive electrode current collector 31 include metal materials such as stainless steel, nickel, aluminum, gold, and platinum, and carbon fiber materials such as carbon cloth and carbon non-woven fabric.

  The electrolytic medium unit 40 includes an electrolytic medium 41 and an electrolytic medium outer shell 42 that houses the electrolytic medium 41. As shown in FIG. 2, the electrolytic medium 41 includes an electrolytic solution 43 in which a metal catalyst 44 is dissolved. The metal catalyst 44 has a catalytic activity that promotes at least the oxygen reduction reaction performed in the positive electrode layer 32 during the discharge of the metal-air battery 1. Of course, the metal catalyst 44 may have a catalytic activity that promotes the oxygen oxidation reaction performed in the positive electrode layer 32 when the metal-air battery 1 is charged.

  As such a metal catalyst 44, a noble metal or other transition metals can be used. Examples of the noble metal include Au, Ag, Pt, Pd, Rh, Ru, Ir, and oxides thereof. Examples of other transition metals include V, Mn, Fe, Co, Ni, Cu, Zn, La, Ce, and oxides thereof.

Since the metal catalyst 44 needs to be dissolved, it is preferably a metal complex. In particular, in the case of a complex, the complex is maintained even if the valence of the metal element changes, so that the reaction cycle of the metal catalyst can be easily maintained. As ligands of the metal ^{complex, I -, Br -, Cl} -, F -, CN -, SCN -, S 2-, OH -, NO 3 -, NCS -, H 2 O, NH 3, CO and the like can be mentioned It is done. Among these, when the electrolytic medium 41 is acidic, the discharge voltage can be maintained even when a large current flows, and therefore, halogen ions are preferable, and Cl ⁻ is more preferable.

  The concentration of the metal catalyst 44 is preferably 1.0 g or more, more preferably 2.0 g or more, and more preferably 4.0 g or more in order to exert the above catalytic effect. Is more preferable. If the concentration of the metal catalyst 44 becomes too high, the specific gravity of the electrolytic solution becomes heavy and the weight of the battery increases. Therefore, the upper limit is preferably 40 g or less per liter of the electrolytic solution.

  The electrolyte solution 43 may be an aqueous electrolyte solution or a non-aqueous electrolyte solution as long as it can dissolve the metal catalyst 44. As aqueous electrolyte, hydrochloric acid aqueous solution, nitric acid aqueous solution, boric acid aqueous solution, acetic acid aqueous solution, aqueous ammonia, etc. can be used. The pH of the electrolytic solution is not particularly limited, but in the case of an acidic electrolytic solution, the discharge voltage can be maintained even when a large current is passed. Of course, as long as the metal catalyst 44 can be dissolved, the pH of the electrolytic solution may be basic.

  The electrolytic solution 43 includes a liquid that has been made electrically conductive by dissolving a metal catalyst 44 such as a metal complex. For example, when a hexachloroplatinum (IV) complex is used as the metal catalyst, mere water (distilled water) can be used as a solvent for dissolving the metal catalyst. In this case, the electrolytic medium 41 has platinum dissolved as the metal catalyst 44. It contains an electrolytic solution 43 of hydrochloric acid.

As the non-aqueous electrolyte, a cyclic carbonate such as propylene carbonate (PC) or ethylene carbonate (EC), a chain carbonate such as dimethyl carbonate (DMC) or ethyl methyl carbonate (EMC), or a mixed solution thereof may be used. In order to provide conductivity, an electrolyte such as LiPF ₆ , LiClO ₄ , or LiBF ₄ may be added.

  In addition, the electrolytic medium 41 impregnates the porous body with the electrolytic solution in which the metal catalyst is dissolved as long as the metallic medium 44 exists uniformly in the electrolytic solution 43 and can move to the positive electrode layer 32. You may use it. As a porous body, you may use nonwoven fabrics, such as a resin nonwoven fabric and a glass fiber nonwoven fabric other than porous films, such as polyethylene and a polypropylene.

  Although the electrolytic medium 41 is accommodated in the electrolytic medium outer shell 42, the electrolytic medium outer shell 42 has an opening so that the electrolytic medium 32 is in contact with both a later-described isolation layer 24 and positive electrode layer 32 of the negative electrode unit 20. Is provided.

  The metal catalyst 44 that promotes the oxygen reduction reaction during discharge is conventionally supported on the carbon material of the positive electrode. However, in the present invention, the metal catalyst 44 is only dissolved in the electrolytic solution 43 in contact with the positive electrode layer 32. Therefore, when the positive electrode layer 33 is formed, the step of supporting the metal catalyst 44 by applying it to the carbon material can be omitted, and the number of manufacturing steps of the positive electrode can be reduced.

  Furthermore, conventionally, when the catalyst is supported on the carbon material of the positive electrode, it has been necessary to add a binder to fix the catalyst. However, in the present invention, the metal catalyst 44 is simply dissolved in the electrolytic solution 43. Therefore, it is not necessary to fix the metal catalyst 44, and it is not necessary to mix a binder. Therefore, the positive electrode layer 33 can be reduced in weight, and the energy density with respect to weight can be improved. In addition, in the conventional method of supporting the catalyst on the carbon material, the catalyst may not be fixed uniformly in the carbon material, or the binder may cover the catalyst. In the present invention, since the metal catalyst 44 dissolved in the electrolyte solution 43 is present uniformly, the metal catalyst is not covered with another metal catalyst or a binder. Generation of a catalyst that does not contribute to the promotion can be prevented.

  The negative electrode portion 20 is a composite in the present embodiment, and as shown in FIG. 1, a negative electrode current collector 21, a negative electrode layer 22 composed of a negative electrode active material, a buffer layer 23, and an isolation layer 24 are provided. These layers are provided in this order.

  The negative electrode current collector 21 has a linear shape or a plate shape. The material of the negative electrode current collector 21 may be present stably in the operating range of the metal-air battery, and may have any desired conductivity, such as copper or nickel.

The negative electrode active material of the negative electrode layer 22 is not particularly limited as long as it is a material capable of occluding and releasing metal ions. For example, metals such as sodium, calcium, magnesium, aluminum, zinc, and lithium can be used. Among these, an open circuit voltage is high and lithium is more preferable from a practical viewpoint. Further, the negative electrode active material is not limited to metallic lithium, and may be an alloy or compound containing lithium as a main component. The lithium-based alloy can include magnesium, calcium, aluminum, silicon, germanium, tin, lead, antimony, bismuth, silver, gold, zinc, and the like. Examples of the compound containing lithium as a main component include Li _3-x M _x N (M = Co, Cu, Ni).

The isolation layer 24 is located on the surface where the negative electrode portion 20 is in contact with the electrolytic medium portion 40, and protects the negative electrode layer 22 from moisture. The material of the isolation layer 24 is not particularly limited as long as it has water resistance and metal ion conductivity. For example, glass ceramics can be used. When metallic lithium is used as the negative electrode active material, the lithium ion conductivity of the isolation layer 24 is preferably 10 ⁻⁵ S / cm or more. Examples of the material of the isolation layer 24 include a NASICON (Na Superconducting Conductor) type lithium ion conductor. Further, 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) is trivalent such as In, Al, etc. And a 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 cation M ′. Further, 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) is converted to a pentavalent cation such as Ta. lithium ion conductor represented by "formula _{Li 1-x M 2-x} M with improved lithium ion conductivity by replacing" x _{(PO 4) 3} and the like M. P in these lithium ion conductors may be substituted with Si, and the lithium ion conductor represented by the general formula Li _{1 + x + y} Ti _2−x Al _x P _3−y Si _y O ₁₂ (LTAP) Desirable from the viewpoint of sex. In addition to these, sulfide-based ceramic electrolytes having high lithium ion conductivity are also included.

In the buffer layer 23, when the negative electrode layer 22 and the isolation layer 24 come into contact with each other, the negative electrode active material such as lithium of the negative electrode layer 22 and the glass ceramics of the isolation layer 24 may react to deteriorate the isolation layer 24. Therefore, the contact between the negative electrode layer 22 and the isolation layer 24 is prevented. The buffer layer 23 is a metal ion conductive polymer electrolyte or organic electrolyte. For example, you may use what made the organic electrolyte solution immerse in a separator (sheets, such as porous polyethylene, polypropylene, and cellulose). When metallic lithium is used as the negative electrode active material, it is desirable that the lithium ion conductivity (also referred to as lithium ion conductivity) of the buffer layer 23 is 10 ⁻⁵ S / cm or more. The organic electrolyte used is a mixture of ethylene carbonate mixed with diethyl carbonate or dimethyl carbonate and further added with a lithium salt. In addition, the buffer layer 23 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 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. .

Examples of the polymer include PEO (polyethylene oxide) and PPO (polypropylene oxide). The polymer serving as the host for the gel electrolyte is PEO (polyethylene oxide), PVA (polyvinyl alcohol), PAN (polyacrylonitrile), PVP (polyvinylpyrrolidone), PEO-PMA (crosslinked product of polyethylene oxide-modified polymethacrylate), PVdF (polyfluoride). And vinylidene fluoride), PVA (polyvinyl alcohol), PAA (polyacrylic acid), PVdF-HFP (copolymer of polyvinylidene fluoride and hexafluoropropylene), and the like. In addition, when using especially desirable PEO as a polymer of the buffer layer 23, 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. It is desirable. Further, in order to improve the strength and electrochemical characteristics of the buffer layer 23, a ceramic filler, for example, BaTiO ₃ powder may be 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.

  When a nonaqueous electrolytic solution is used as the electrolytic medium 41, the buffer layer 23 and the isolation layer 24 are not necessarily provided in the negative electrode part 20. That is, in the negative electrode part 20, the negative electrode layer 22 may be disposed so as to be directly adjacent to the electrolytic medium 41.

  The laminate of the negative electrode current collector 21, the negative electrode layer 22, the buffer layer 23, and the isolation layer 24 described above is covered with the negative electrode outer shell 25, and the surface of the isolation layer 24 of this laminate is the positive electrode of the positive electrode part 30. An opening is provided in the negative electrode outer shell 25 so as to face the surface of the layer 32. The negative electrode outer shell 25 is provided with an opening for drawing the negative electrode current collector 21 to the outer side of the outer shell.

Next, the operation of the metal-air battery 1 having such a configuration will be described. The discharge reaction of the metal-air battery 1 can be expressed by the following formula when the negative electrode layer 22 of the negative electrode part 20 uses metallic lithium as the negative electrode active material.
(Negative electrode side) 2Li → 2Li ⁺ + 2e ⁻ (Formula 1)
(Positive electrode side) 1 / 2O ₂ + H ₂ O + 2e ⁻ → 2OH ⁻ (Formula 2)

  As shown in FIG. 2, the metal catalyst 44 of the electrolytic medium unit 40 is movably present in the electrolytic solution 43 in contact with the positive electrode layer 32. 2) can be promoted. When platinum (Pt) is used as the metal catalyst 44, it can be expressed by the following formula.

  Since Pt (IV) of the catalyst exists uniformly and movably in the electrolytic solution 43, it easily accepts electrons from the negative electrode side to become Pt (II), but the oxygen reduction reaction ( In order to promote equation 2), electrons are emitted and returned to Pt (IV). Therefore, compared with the conventional case where the reaction is promoted on the surface of the solid phase catalyst supported on the carbon material of the positive electrode, the catalytic ability can be improved and the reaction efficiency of the oxygen reduction reaction of the positive electrode is improved. be able to. As a result, even if the discharge current value is increased, it is possible to avoid a state where oxygen supply is insufficient in the oxygen reduction reaction of the positive electrode, and it is possible to prevent the discharge voltage from being lowered.

  Further, even if the reaction proceeds in the positive electrode layer 32 and a reaction product is generated, the metal catalyst 44 is dissolved in the electrolytic solution 43, so that the reaction product does not cover the catalyst. Inhibition of reaction and reduction of catalytic ability can be prevented. As a result, a stable discharge voltage can be maintained even after a long discharge.

The charging reaction of the metal-air battery 1 can be expressed by the following formula under the same conditions as described above.
(Negative electrode side) 2Li ← 2Li ⁺ + 2e ⁻ (Formula 3)
(Positive electrode side) 1 / 2O ₂ + H ₂ O + 2e ⁻ ← 2OH ⁻ (Formula 4)

  Depending on the type of the metal catalyst 44, the oxygen oxidation reaction (formula 4) during charging can also be promoted. The action of the metal catalyst 44 at that time can improve the reaction efficiency of the oxygen oxidation reaction of the positive electrode in the same manner, only the electron emission and reception are reversed from those in the above-described discharge.

  In addition, the metal air battery 1 is not limited to the structure shown in FIG. 1, For example, it can also be set as the structure shown in FIG. As shown in FIG. 3, in the metal-air battery 100 of this embodiment, the electrolytic medium 140 is filled in the container 110, and the pair of negative electrode portions 120 and the positive electrode portions 130 are disposed in the electrolytic medium 140 so as to face each other. ing. In addition, you may arrange | position so that several pairs of the negative electrode part 120 and the positive electrode part 130 may laminate | stack.

  Since the structure of the positive electrode part 130 and the electrolytic medium 140 is the same as the structure of FIG. 1 mentioned above, description here is abbreviate | omitted. The negative electrode portion 120 includes a negative electrode current collector 121, two negative electrode layers 122, two buffer layers (separators) 123, two isolation layers (solid electrolyte) 124, a joint portion 125, and two gasket sheets 126, It has.

  The two negative electrode layers 122 have a plate shape sandwiching a part of the negative electrode current collector 121 and are made of a negative electrode active material. If the length of the negative electrode current collector 121 is a length between two negative electrode layers 122, the current collector 121 has an effect as a current collector. The two buffer layers 123 are sheet-like members that sandwich the two negative electrode layers 122. The two gasket sheets 126 are disposed between the two isolation layers 124 so as to surround the two negative electrode layers 22, and seal the space between the two isolation layers 124.

  The two isolation layers (solid electrolytes) 124 are disposed outside the two buffer layers 123, have a plate shape sandwiching all of the two negative electrode layers 122, and are solid electrolytes having lithium ion conductivity. The negative electrode layer 122 is protected by sandwiching the negative electrode layer 122 between the two solid electrolytes.

  The negative electrode part 120 is configured to sandwich two negative electrode layers 122 between two solid electrolytes. The negative electrode part 120 does not need to accommodate the negative electrode layer 122 in a packaging material such as aluminum laminate, and has a structure that allows the positive electrode part 130 and the negative electrode part 120 to be easily stacked as one cell.

  The joining portion 125 is formed so as to join and close the outer peripheral edge portions of the two isolation layers 124. The joining portion 125 in this example is provided at both ends of the solid electrolyte or the like.

  The material of the gasket 126 is not particularly limited as long as it is a rubber or elastomer resistant to an organic electrolyte, but an ethylene-propylene-diene copolymer rubber or elastomer, or a fluorine-based rubber or elastomer is suitable.

  For example, an adhesive can be used as the material of the bonding portion 125, and an adhesive having a low moisture permeability and a high sealing property is preferable. For example, an epoxy adhesive, an acrylic adhesive, Examples thereof include silicone adhesives, olefin adhesives, and synthetic rubber adhesives.

  Also in the metal-air battery 100 having such a configuration, as in the configuration of FIG. 1, the electrolytic medium 140 includes an electrolytic solution in which a metal catalyst is dissolved, so that the reaction efficiency of the oxygen reduction reaction of the positive electrode portion 130 is improved. In addition, it is possible to prevent inhibition of the catalytic reaction and decrease in catalytic ability, and to maintain a stable discharge voltage for a long time.

  Examples of the metal-air battery according to the present invention and comparative examples will be described below. The metal-air batteries used in Examples and Comparative Examples have the same configuration as that shown in FIG. 3, using a beaker as a container, using carbon cloth as a positive electrode part, and using metallic lithium as a negative electrode layer. Table 1 shows the electrolytic solution in which the metal catalyst is dissolved, the concentration of the metal catalyst, and the pH of the electrolytic solution.

The chloroplatinic acid solution (H ₂ PtCl ₆ ), palladium chloride solution (PdCl ₂ ), ruthenium chloride solution (RuCl ₃ ), and rhodium nitrate solution (Rh (NO ₃ ) ₃ ) of the examples are all manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. Is. In the comparative example, a simple hydrochloric acid solution that does not dissolve the metal catalyst and a 2M lithium chloride solution (LiCl) were used. All electrolytes had a capacity of 30 ml. The pH of each solution was measured with a pH meter (PH72) manufactured by Yokogawa Electric Corporation.

The negative electrode part was produced by sandwiching a copper foil current collector with double-sided metal lithium between two glass ceramics in a glove box under an argon atmosphere and sealing the periphery with an adhesive to produce a composite negative electrode. More specifically, first, a rubber gasket cut to a size where the outer periphery overlaps with the edge of the glass ceramic was prepared, and the inside was cut out to a size that could accommodate the metal lithium to be inserted later. Two of these were prepared and pasted on two glass ceramics. A separator (cellulose) and a copper foil current collector with lithium metal on both sides (made by Honjo Metal Co., Ltd.) are placed in this order in a glass ceramic rubber gasket, and a non-aqueous electrolyte (1M LiPF ₆ / EC: EMC produced by Kishida Chemical Co., Ltd.) = 1: 1). As the height of the liquid level, it is only necessary to reach a location where lithium metal exists. Finally, another glass ceramic was placed and fixed with a two-pack room temperature curing epoxy adhesive to produce a composite negative electrode.

The thickness of the metallic lithium part was 200 μm on one side and the copper foil part was 10 μm. LTAP (manufactured by OHARA) was used as the solid electrolyte. LTAP is lithium ion conductor represented by the general formula _{Li 1 + x + y Ti 2} -x Al x P 3-y Si y O 12, has the water resistance, he has a resistance to lithium metal Therefore, the isolation layer was composed of a separator and a non-aqueous electrolyte. As a material for the rubber gasket, ethylene propylene rubber (EPDM) having a thickness of 250 μm was used.

The conditions for the discharge test were discharging at a current density of ² mA / cm ² and measuring the discharge voltage after 200 seconds with a charge / discharge tester SD8 manufactured by Hokuto Denko. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 4, in comparison with Comparative Examples 1 and 2 using a simple hydrochloric acid solution or a lithium chloride solution that does not dissolve the metal catalyst, Examples 1 to 4 using an electrolytic solution in which the metal catalyst was dissolved were used. All the lithium air batteries showed high discharge voltage. It is known that the discharge voltage increases as the pH decreases, but the discharge of Example 1 containing the catalyst is larger than the result of Example 1 containing the catalyst and Comparative Example 1 containing no catalyst at the same pH. Since the voltage was shown, it can be said that the catalyst dissolved in the electrolyte functioned as a catalyst for the positive electrode reaction. Moreover, compared with Example 4 which used the nitric acid solution as electrolyte solution, the direction of Examples 1-3 using the hydrochloric acid solution showed all the high discharge voltage.

DESCRIPTION OF SYMBOLS 1,100 Metal-air battery 110 Container 20,120 Negative electrode part 21,121 Negative electrode collector 22,122 Negative electrode layer 23,123 Buffer layer 24,124 Isolation layer 25 Negative electrode outer shell 30,130 Positive electrode part 31 Positive electrode collector 32 Positive electrode layer 33 Positive electrode outer shell 40 Electrolytic medium portions 41 and 140 Electrolytic medium 42 Electrolytic medium outer shell 43 Electrolytic solution 44 Metal catalyst 125 Joint portion 126 Gasket

Claims (7)

  Electrolytic medium for positive electrode side of metal-air battery, wherein the electrolytic medium includes an electrolyte solution in which a metal catalyst that promotes oxygen reduction reaction is dissolved during discharge of the metal-air battery. Electrolytic medium for use.   The electrolysis medium according to claim 1, wherein the metal catalyst contains a noble metal.   The electrolytic medium according to claim 1, wherein the metal catalyst is a metal complex. Said metal ^{complex, I -, Br -, Cl} -, F -, CN -, SCN -, S 2-, OH -, NO 3 -, NCS -, selected from the group consisting of H 2 O, NH ₃ and CO The electrolytic medium according to claim 3, comprising at least one ligand formed.   The electrolytic medium according to any one of claims 1 to 4, wherein the electrolytic solution is a non-aqueous electrolytic solution or an aqueous electrolytic solution.   A metal-air battery comprising: a positive electrode; a negative electrode; and the electrolytic medium according to claim 1 disposed between the positive electrode and the negative electrode and in contact with the positive electrode.   The said negative electrode is equipped with the negative electrode layer containing the alloy or compound which has metal lithium or lithium as a main component, and this negative electrode layer, and has two plate-shaped isolation layers which have lithium ion conductivity. Metal-air battery.

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