JP2017076612A - Lithium air secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium air secondary battery capable of increasing current density, and achieving both high capacity and high output.SOLUTION: A lithium air secondary battery comprises: a positive electrode; and a negative electrode. The positive electrode has: a lithium conductive layer; a reaction layer; and an oxygen diffusion layer. The lithium conductive layer is located between the negative electrode and the oxygen diffusion layer, and includes a conductive material by 3-40 mass% to the mass of the lithium conductive layer. It is preferable that the lithium conductive layer includes a compound which enables the intercalation of lithium. It is also preferable that the conductive material includes a carbonaceous material.SELECTED DRAWING: None

Description

  The present invention relates to a lithium air secondary battery.

  A lithium air battery includes a negative electrode capable of occluding and releasing lithium ions, and a positive electrode including oxygen in the air as a positive electrode active material and containing an oxygen redox catalyst, and lithium ion conductivity between the negative electrode and the positive electrode. It has a structure with a medium. That is, a lithium-air battery is a battery having a positive electrode using oxygen in the air as an active material, and can be charged and discharged by performing an oxidation-reduction reaction of oxygen at the positive electrode. The lithium air battery theoretically has an energy density of 3000 Wh / kg or more, and this value corresponds to about 10 times the energy density of the lithium ion battery.

  For example, Patent Document 1 and Patent Document 2 are known as conventional techniques related to lithium-air batteries. The lithium-air battery described in Patent Document 1 includes a case having an air hole for supplying oxygen to the positive electrode, the positive electrode is composed of two layers having different compositions, and has an oxygen reducing ability on the air hole side. A layer is disposed, and a layer having a lithium ion storage capacity is disposed on the negative electrode side. The layer having the ability to occlude lithium ions is composed of an active material having an ability to occlude lithium ions at 2.0 V to 2.9 V (vs. Li), a conductive agent, and a binder. This lithium-air battery is described in Patent Document 1 as having a high capacity and excellent pulse discharge characteristics by having this configuration.

  The lithium-air battery described in Patent Document 2 is intended to solve the problems of the lithium-air battery described in Patent Document 1 described above, and the positive electrode layer has a first positive electrode having oxygen reducing ability. And a second positive electrode layer having a Li ion storage capacity. The second positive electrode layer contains a positive electrode active material having an average voltage smaller than 2.0 V (vs. Li) or an average voltage larger than 2.9 V (vs. Li). Patent Document 2 describes that by providing this configuration, a lithium battery can be obtained in which batteries having different characteristics can be used according to the current density during discharge. However, Patent Document 2 does not describe the test result of the above-described configuration according to an example.

JP 2006-286414 A International Publication No. 2010/073332 Pamphlet

  The lithium-air battery described in Patent Document 2 is characterized in that it functions as a high-capacity lithium-air battery at a small current discharge and functions as a high-power lithium-ion battery at a large current discharge. However, this lithium-air battery does not have both high capacity and high output at a high current density.

  Accordingly, an object of the present invention is to improve a lithium-air secondary battery, and more specifically, to provide a lithium-air secondary battery capable of increasing current density and having both high capacity and high output. is there.

  As a result of intensive investigations to solve the above problems, the present inventor has found that the above problems can be solved by increasing the diffusion rate until lithium ions released from the negative electrode reach the reaction layer of the positive electrode.

The present invention was made on the basis of the above knowledge, and is a lithium air secondary battery having a positive electrode and a negative electrode,
The positive electrode has a lithium conductive layer, a reaction layer and an oxygen diffusion layer;
By providing a lithium air secondary battery in which the lithium conductive layer is located between the negative electrode and the oxygen diffusion layer and contains 3% by mass to 40% by mass of a conductive material based on the mass of the lithium conductive layer. The problem is solved.

The present invention is also a positive electrode for a lithium air secondary battery having a lithium conductive layer, a reaction layer and an oxygen diffusion layer,
When the positive electrode is incorporated in a battery, the lithium conductive layer is disposed so as to be located between the negative electrode and the oxygen diffusion layer,
The lithium conductive layer provides a positive electrode for a lithium air secondary battery containing 3% by mass to 40% by mass of a conductive material based on the mass of the lithium conductive layer.

  ADVANTAGE OF THE INVENTION According to this invention, a lithium air secondary battery which can make a current density high and is compatible with high capacity | capacitance and high output is provided.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The lithium air secondary battery of the present invention has a negative electrode and a positive electrode. The negative electrode includes a negative electrode current collector and a negative electrode layer carried on the negative electrode current collector. The negative electrode layer can be made of a negative electrode active material and a binder. The negative electrode active material only needs to have a lithium ion releasing ability. As the negative electrode active material, various negative electrode active materials conventionally used as negative electrode materials for lithium primary batteries and lithium ion secondary batteries can be used without particular limitation.

  Examples of the negative electrode active material include metal oxide, metal sulfide, metal nitride, lithium metal, lithium alloy, lithium composite oxide, and carbonaceous material. Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. As the carbonaceous material, a carbonaceous material occluded with lithium ions can be used. Examples include graphite or coke, carbon fiber, graphite material such as spherical carbon or carbonaceous material, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase microspheres, etc. Examples include a graphite material obtained by heat treatment at 3000 ° C., or a carbonaceous material in which lithium ions are occluded.

  Examples of the binder used for binding the negative electrode active material include polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-butadiene rubber, styrene-butadiene rubber, and carboxymethylcellulose.

  As the negative electrode current collector carrying the negative electrode layer containing the negative electrode active material and the binder, for example, a conductive substrate having a porous structure or a nonporous conductive substrate can be used. These conductive substrates can be made of, for example, copper, aluminum, stainless steel, nickel, or the like. As the conductive substrate having a porous structure, for example, a mesh, a punched metal, an expanded metal, or the like can be used. Alternatively, a negative electrode active material supported on a metal foil and then a hole formed in the metal foil can be used as a conductive substrate having a porous structure.

  The negative electrode is disposed so as to face the positive electrode with the electrolyte interposed therebetween. As the electrolyte, various non-aqueous electrolytes that have been conventionally used as electrolytes for lithium ion secondary batteries can be used. For example, an organic solvent-based non-aqueous electrolyte obtained by dissolving a supporting electrolyte in an organic solvent or an ionic liquid-based non-aqueous electrolyte containing a supporting electrolyte can be used. Alternatively, a gel electrolyte solution composed of a polymer material and an organic solvent-based / ionic liquid-based non-aqueous electrolyte solution can also be used.

  Examples of the organic solvent used in the organic solvent-based non-aqueous electrolyte include carbonates such as propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and isopropyl methyl carbonate. . These solvents can be used alone or in combination of two or more.

Examples of the supporting electrolyte dissolved in the organic solvent include LiPF ₆ , Li [PF ₃ (C ₂ F ₅ ) ₃ ], Li [PF ₃ (CF ₃ ) ₃ ], LiBF ₄ , Li [BF ₂ (CF ₃ ). ₂ ], Li [BF ₂ (C ₂ F ₅ ) ₂ ], Li [BF ₃ (CF ₃ )], Li [BF ₃ (C ₂ F ₅ )], Li [B (COOCOO) ₂ ] (LiBOB), LiCF ₃ SO ₃ (LiTf), LiC ₄ F ₉ SO ₃ (LiNf), Li [(CF ₃ SO ₂ ) ₂ N] (LiTFSI), Li [(FSO ₂ ) ₂ N] (LiFSI), Li [(C _{2 F 5 SO 2) 2 N} ] (LiBETI), Li [(CF 3 SO 2) (C 4 F 9 SO 2) N], Li [(CN) 2 N] (LiDCA), Li [(CF 3 SO ₂ ) ₃ C], Li [(CN) ₃ C] and the like. The concentration of the supporting electrolyte in the organic solvent-based nonaqueous electrolytic solution is preferably 0.1 to 4 mol / L.

  Examples of the ionic liquid solvent used in the ionic liquid non-aqueous electrolyte include those composed of cations such as imidazolium ions and ammonium ions and various anions.

  Examples of the cation of the ionic liquid include N, N, N-trimethylbutylammonium ion, N-ethyl-N, N-dimethylpropylammonium ion, N-ethyl-N, N-dimethylbutylammonium ion, and N, N-dimethyl. -N-propylbutylammonium ion, N- (2-methoxyethyl) -N, N-dimethylethylammonium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1- Butyl-3-methylimidazolium ion, 1-ethyl-2,3-dimethylimidazolium ion, 1-ethyl-3,4-dimethylimidazolium ion, 1-ethyl-2,3,4-trimethylimidazolium ion, 1-ethyl-2,3,5-trimethylimidazolium ion, -Methyl-N-propylpyrrolidinium ion, N-butyl-N-methylpyrrolidinium ion, N-sec-butyl-N-methylpyrrolidinium ion, N- (2-methoxyethyl) -N-methylpyrrolidinium ion, N- (2-ethoxyethyl) -N-methylpyrrolidinium ion, N-methyl-N-propylpiperidinium ion, N-butyl-N-methylpiperidinium ion, N-sec-butyl-N-methylpiperidinium ion N- (2-methoxyethyl) -N-methylpiperidinium ion, N- (2-ethoxyethyl) -N-methylpiperidinium ion, and the like.

Examples of the anion of the ionic liquid include PF ₆ ⁻ , BF ₄ ⁻ , I ⁻ , Cl ⁻ , Br ⁻ , SCN ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ , CF ₃ COO ⁻ , CF ₃ SO ₃ ⁻ , and C ₆ F. ₅ SO ₃ ⁻ , [PF ₃ (C ₂ F ₅ ) ₃ ] ⁻ , [PF ₃ (CF ₃ ) ₃ ] ⁻ , [BF ₂ (CF ₃ ) ₂ ] ⁻ , [BF ₂ (C ₂ F ₅ ) _{2 ^{] -, [BF 3 (CF}} 3)] -, [BF 3 (C 2 F 5)] -, [(CF 3 SO 2) (C 4 F 9 SO 2) N] -, [(CF 3 SO 2 ) ₃ C] ⁻ , [(CN) ₃ C] ⁻ , [(CF ₃ SO ₂ ) ₂ N] ⁻ , [(FSO ₂ ) ₂ N] ⁻ , [(CF ₃ SO ₂ ) (FSO ₂ ) N] ^{_{-, [(CF 3 CF 2}} SO 2) 2 N] -, [(C 2 H 4 O 2) 2 B] - etc. Is mentioned.

  As the gel electrolyte, a mixture of the organic solvent-based non-aqueous electrolyte or the ionic liquid-based non-aqueous electrolyte and a polymer material can be used. Examples of the polymer material include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethacrylic acid or a salt thereof, polymethacrylic acid ester, polyacrylic acid or a salt thereof, and polyacrylic acid ester. These polymer materials can be contained in an amount of 1% by mass or more and 40% by mass or less based on the entire electrolyte solution on the gel.

  Of the various electrolytes described above, it is preferable to use the gel electrolyte solution containing an ionic liquid because volatilization of the components of the electrolyte solution can be suppressed. The suppression of volatilization contributes to the improvement of the cycle characteristics of the lithium air secondary battery.

  The positive electrode disposed at a position facing the negative electrode across the electrolyte is composed of a multilayer structure. The multilayer structure includes a lithium conductive layer, a reaction layer, and an oxygen diffusion layer. Among these layers, the oxygen diffusion layer is disposed at a position farthest away from the negative electrode. A lithium conductive layer is disposed between the negative electrode and the oxygen diffusion layer. Since the electrolyte is interposed between the negative electrode and the positive electrode as described above, it can be said that the lithium conductive layer is located between the electrolyte and the oxygen diffusion layer. The reaction layer is disposed between the lithium conductive layer and the oxygen diffusion layer. Thus, typically, in the positive electrode, the oxygen diffusion layer is disposed at a position farthest from the negative electrode, the reaction layer is disposed at a position closer to the negative electrode than the oxygen diffusion layer, and the positive electrode is viewed from the negative electrode. The lithium conductive layer is arranged at the closest position. It is preferable that the lithium conductive layer and the reaction layer are directly adjacent to each other, and no other layer is interposed between the two layers. Moreover, it is preferable that the reaction layer and the oxygen diffusion layer are directly adjacent to each other, and no other layer is interposed between the two layers.

  The oxygen diffusion layer preferably has water repellency and has a structure in which oxygen is diffused quickly. For this purpose, the oxygen diffusion layer preferably contains a fluorine-containing polymer such as polytetrafluoroethylene (PTFE) and has a porous structure. The oxygen diffusion layer preferably has a function as a current collector. From these viewpoints, the oxygen diffusion layer is preferably composed of a porous conductive material. Examples of such a conductive material include conductive cloth, conductive paper, conductive mesh, punched metal, expanded metal, and the like. Examples of materials for these conductive materials include carbon, stainless steel, nickel, aluminum, iron, and titanium. When the conductive material is composed of a metal, an oxidation resistant metal or alloy may be coated on the surface of the metal in order to suppress oxidation of the metal.

The reaction layer located closer to the negative electrode as viewed from the oxygen diffusion layer is a site where a reduction reaction of oxygen that has passed through the oxygen diffusion layer occurs during battery discharge. For this purpose, the reaction layer preferably contains a carbonaceous material or metal oxide having a high specific surface area (for example, 100 m ² / g or more). Examples of the carbonaceous material include ketjen black (registered trademark), acetylene black, carbon black, furnace black, activated carbon, activated carbon fiber, and charcoal. For activated carbons with low conductivity, it is preferable to add a highly conductive carbonaceous material such as acetylene black to the activated carbon to increase the conductivity of the reaction layer. On the other hand, examples of the metal oxide include manganese oxide, tin oxide, bismuth oxide, and tungsten oxide. In the reaction layer, a substance capable of lithium intercalation that is blended in the lithium conductive layer described later is not blended.

  In the reaction layer, the carbonaceous material or metal oxide is preferably mixed with a binder and present in a state of being held and fixed by the binder. As the binder, for example, polyamide, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-butadiene rubber, styrene-butadiene rubber, or the like can be used. A carbonaceous material or a metal oxide is mixed with a binder, and the resulting mixture is rolled into a film to form a film. The reaction layer can be formed by heating the film. Alternatively, for example, it can be formed by mixing a carbonaceous material or metal oxide and a binder in a solvent, applying the mixture to a current collector, drying and rolling. In general, the thickness of the reaction layer thus formed is preferably 1 μm or more and 200 μm or less, and more preferably 10 μm or more and 100 μm or less.

For the purpose of promoting the oxygen reduction reaction and / or oxidation reaction in the reaction layer, it is preferable that a catalyst for promoting the oxygen reduction reaction and / or the oxygen generation reaction coexists in the reaction layer. Examples of such a catalyst include noble metal catalysts such as ruthenium, platinum, rhodium or alloys thereof. Alternatively, cobalt phthalocyanine, cobalt porphyrin, cerium oxide (CeO ₂ ), aluminum (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), silver oxide (AgO), lanthanum calcium cobalt complex oxide (La _x Ca _y CoO _{3− z),} lanthanum calcium manganese iron composite oxide _{(La v Ca w Mn x Fe} y O 3-z), lanthanum strontium cobalt oxide _{(La x Sr y CoO 3-} z), sodium lanthanum manganate _(Na x La _y MnO _3), potassium lanthanum manganate _{(K x La y MnO 3-} z), lanthanum manganate rubidium _{(Rb x La y MnO 3-} z), copper-manganese composite oxide _(Cu x _Mn y _{O 4),} and the like It is done.

  The catalyst may be present in the reaction layer in a state of being mixed with the carbonaceous material or metal oxide, or may be present in the reaction layer in a state of being supported on the surface of the carbonaceous material. May be.

  As described above, the reaction layer may be a layer containing a carbonaceous material, or may be a layer containing a metal oxide in addition to the carbonaceous material. Alternatively, the reaction layer has a two-layer structure, the first reaction layer includes a carbonaceous material and does not include a metal oxide, and the second reaction layer adjacent to the first reaction layer is formed of a carbonaceous material and a metal. A layer containing an oxide may be used. In this case, it is preferable to dispose the first reaction layer on the oxygen diffusion layer side and the second reaction layer on the lithium conductive layer side. With this configuration, the capacity under a high current density can be further increased.

  Among the positive electrodes, the lithium conductive layer disposed at the position closest to the negative electrode is used for the purpose of increasing the mobility of lithium ions between the negative electrode and the reaction layer of the positive electrode. For this purpose, the lithium conductive layer preferably contains a conductive material. As the conductive material, the same carbonaceous material contained in the reaction layer can be used. Specifically, ketjen black (registered trademark), acetylene black, carbon black, furnace black, activated carbon, activated carbon fiber, charcoal and the like can be used.

In order to further improve the functions required of the lithium conductive layer, the lithium conductive layer preferably contains a substance capable of lithium intercalation. Examples of the substance capable of intercalating lithium ions include lithium transition metal composite oxides and lithium transition metal composite phosphates. Examples of such an oxide include a compound represented by LiMO ₂ (M represents one or more transition metals), LiM ₂ O ₄ (M represents one or more transition metals). And a compound represented by LiMPO ₄ (M represents one or more transition metals). Specifically, lithium cobaltate, lithium manganate, lithium nickel acid, nickel-cobalt-aluminum lithium _{(LiNi x Co y Al z O} 2), lithium nickel manganese cobalt oxide _{(LiNi x Mn y Co z O} 2), manganese Examples thereof include lithium nickel oxide (LiMn _x Ni _y O ₄ ), lithium manganese cobaltate (LiMn _x Co _y O ₄ ), olivine type lithium iron phosphate, olivine type lithium manganese phosphate, and lithium manganese spinel. Among these, it is more preferable to use a layered compound.

  In the lithium conductive layer, the ratio of the conductive material contained in the lithium conductive layer is preferably set within a specific range. Specifically, the proportion of the conductive material in the lithium conductive layer is preferably 3% by mass or more and 40% by mass or less based on the mass of the lithium conductive layer. By including the conductive material in the lithium conductive layer in this range, the mobility of lithium ions in the positive electrode is increased, and as a result, a high current density can be obtained during battery discharge, and a high capacity can be obtained. High output is compatible. In contrast, the lithium-air battery described in Patent Document 2 described above functions as a high-capacity lithium-air battery at a small current discharge, and functions as a high-power lithium-ion battery at a large current discharge. Designed to be In the lithium air secondary battery of the present invention, the batteries as described in Patent Document 2 are not properly used, and the lithium air secondary battery can be used for both large current discharge and small current discharge. Designed to work.

  Unlike the battery described in Patent Document 2, the lithium air secondary battery of the present invention functions as a lithium air secondary battery even during a large current discharge because a large amount of conductive material is contained in the lithium conductive layer. Because. Due to this, the main dominant factor for increasing the mobility of lithium ions in the lithium conductive layer can be the conductive material. As a result, even if the lithium conductive layer contains a substance capable of intercalating lithium, the inventor believes that the substance is difficult to function as a positive electrode active material of a lithium ion secondary battery. Yes. From another viewpoint, in the lithium conductive layer, a material capable of lithium intercalation functions to supplementarily increase the mobility of lithium ions. Therefore, the positive electrode active material in the lithium air secondary battery of the present invention is mainly oxygen, and unlike the lithium air battery described in Patent Document 2, a material capable of lithium intercalation is not a positive electrode active material.

  From the viewpoint of more effectively increasing the mobility of lithium ions in the lithium conductive layer, the proportion of the conductive material in the lithium conductive layer is 3% by mass or more and 40% by mass or less as described above based on the mass of the lithium conductive layer. It is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 20% by mass or less. Further, the value of A / B, which is the ratio between the mass A of the conductive material in the lithium conductive layer and the mass B of the substance capable of lithium intercalation, is preferably 0.03 or more and 1.33 or less, More preferably, it is 0.05 or more and 1.33 or less, and further preferably 0.11 or more and 0.40 or less.

  In the lithium conductive layer, it is preferable that the conductive material and the substance capable of intercalating lithium are mixed with the binder in the form of particles and are held and fixed by the binder. As the binder, those similar to those used in the reaction layer can be used. A lithium conductive layer is formed by mixing a conductive material and a lithium intercalable substance with a binder, rolling the resulting mixture into a film, and then heating the film. can do. In general, the thickness of the lithium conductive layer thus formed is preferably 10 μm or more and 100 μm or less, and more preferably 20 μm or more and 50 μm or less. Since the lithium conductive layer is configured in this manner, the electrolyte present adjacent to the lithium conductive layer is difficult to permeate toward the reaction layer side, and water in the air is also difficult to permeate the negative electrode side. Become. As a result, the charge / discharge cycle characteristics of the battery are improved.

  In the lithium air secondary battery of the present invention, the negative electrode and the positive electrode are separated from each other by an electrolyte, but in addition to this, a separator may be disposed between both the electrodes so that the both electrodes are reliably separated. As the separator, for example, a material similar to the material used as a separator of a lithium ion secondary battery can be used without particular limitation. For example, it consists of a porous membrane or non-woven fabric made of polyolefin, or glass fiber. In particular, it is preferable to use a separator coated with an ionic liquid from the viewpoint of further improving lithium ion conductivity and suppressing electrolyte depletion.

  The lithium-air secondary battery of the present invention is preferably used while being housed in a case. Examples of the shape of the case include a coin type, a flat plate type, a cylindrical type, and a laminate type. Further, the case may be an open air type or a sealed type. When the case is open to the atmosphere, a small hole for inflow of air can be provided at a position near the positive electrode of the case. On the other hand, when the case is a sealed type, it is preferable to provide an air supply pipe and a discharge pipe in the case.

  The lithium-air secondary battery of the present invention is suitably used for, for example, on-vehicle use, stationary power supply use, and household power supply use, taking advantage of its features such as high current density, high capacity, and high output.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. The amounts described in the examples and comparative examples are all amounts per evaluation cell. Unless otherwise specified, “%” means “mass%”.

[Example 1]
(1) Preparation of negative electrode Lithium foil was overlapped with copper foil as a current collector to form a negative electrode.
(2) Preparation of positive electrode (2a) Preparation of oxygen diffusion layer A conductive and water-repellent carbon sheet made of carbon fiber was used as the oxygen diffusion layer.
(2b) Formation of reaction layer 0.003 g of ketjen black ((registered trademark), hereinafter also referred to as “KB”) and 0.1 g of polyamic acid (solid content 20%) are kneaded and dispersed to obtain a paste. It was. This paste was applied to one surface of the carbon paper prepared in (2a) to form a coating film of the first reaction layer.
Next, 0.003 g of Ketjen Black (registered trademark), 0.003 g of Ru-supported α-MnO ₂ (Ru support amount 5%), and 0.1 g of polyamic acid (solid content 20%) are kneaded and dispersed. A paste was obtained. This paste was applied onto the coating film of the first reaction layer to form a coating film of the second reaction layer. Subsequently, it heated at 80 degreeC for 8 hours, and formed the reaction layer.
(2c) Formation of Lithium Conductive Layer 0.003 g of Ketjen Black (registered trademark), 0.0008 g of LiCoO ₂ (hereinafter also referred to as “LCO”), and 0.1 g of polyamic acid (solid content 20%) Were kneaded and dispersed to obtain a paste. This paste was applied on the reaction layer prepared in (2b). Next, heating was performed at 80 ° C. for 8 hours to form a lithium conductive layer.
(3) Preparation of electrolyte LiTFSI (lithium bistrifluoromethanesulfonimide) was used as a lithium salt and mixed with an organic solvent and a thickener to prepare an electrolyte.
(4) Assembly of lithium-air secondary battery A positive electrode and a negative electrode were disposed on each surface of the separator coated with the electrolyte obtained in (3). The positive electrode was disposed so that the lithium conductive layer was opposed to the separator. These were enclosed in a container to obtain a lithium air secondary battery. Air holes were formed in a portion of the container corresponding to the positive electrode.

[Example 2]
In the step (2c) of Example 1, the ratio of ketjen black (registered trademark) contained in the lithium conductive layer was increased as shown in Table 1 below. Other than that was carried out similarly to Example 1, and obtained the lithium air secondary battery.

Example 3
In Example 2, only the first reaction layer was formed without forming the second reaction layer. Other than that was carried out similarly to Example 2, and obtained the lithium air secondary battery.

Example 4
In Example 3, a positive electrode was formed using lithium manganese cobalt lithium {Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ } (hereinafter also referred to as “LSM111”) for the lithium conductive layer. . Other than that was carried out similarly to Example 3, and obtained the lithium air secondary battery.

Example 5
In Example 3, a positive electrode was formed using LiMn ₂ O ₄ (hereinafter also referred to as “LMO”) for the lithium conductive layer. Other than that was carried out similarly to Example 3, and obtained the lithium air secondary battery.

Example 6
In Example 3, a positive electrode was formed using LiFePO ₄ (hereinafter also referred to as “LFP”) for the lithium conductive layer. Other than that was carried out similarly to Example 3, and obtained the lithium air secondary battery.

[Comparative Example 1]
This comparative example is an example in which the step (2c) of Example 1 was not performed. Other than that was carried out similarly to Example 1, and obtained the lithium air secondary battery.

[Comparative Example 2]
This comparative example is an example in which the second reaction layer was not formed in Example 1, only the first reaction layer was formed, and the step (2c) of Example 1 was not performed. Other than that was carried out similarly to Example 1, and obtained the lithium air secondary battery.

[Comparative Example 3]
This comparative example is an example in which Ketjen Black (registered trademark) was not blended in the lithium conductive layer in the step (2c) of Example 1. Other than that was carried out similarly to Example 1, and obtained the lithium air secondary battery.

[Comparative Example 4]
In this comparative example, in the step (2c) of Example 1, the ratio of Ketjen Black (registered trademark) contained in the lithium conductive layer was significantly increased as shown in Table 1 below. Other than that was carried out similarly to Example 1, and obtained the lithium air secondary battery.

[Evaluation]
About the lithium air secondary battery obtained by the Example and the comparative example, the discharge capacity when charging / discharging with various current densities was measured. The results are shown in Tables 1 and 2 below.

  Subsequently, the cycle characteristics of Examples 1 to 3, which had good performance in the measurement of the discharge capacity, were also evaluated. The results are shown in Table 3 below.

As is clear from the results shown in Tables 1 to 3, the lithium air secondary batteries obtained in each example had a lower current density (for example, 1.0 mA / cm ²⁾ than the lithium air secondary batteries of the comparative examples. ) And a high current density (for example, 5.0 mA / cm ² ), it can be seen that a high capacity is maintained. Moreover, it turns out that a favorable cycle characteristic is shown. In particular, as is clear from the comparison of the results of the examples shown in Table 1, when the lithium conductive layer contains a layered compound as a compound capable of lithium intercalation, the battery is discharged at a low current density and a high current density. It can be seen that the high capacity is further maintained in any case.

Example 7
(1) Preparation of negative electrode Same as Example 1.
(2) Preparation of positive electrode (2a) Preparation of oxygen diffusion layer Same as Example 1.
(2b) Formation of reaction layer 0.02 g of carbon black (MK-1000 material manufactured by Nippon Graphite Industries Co., Ltd., hereinafter also referred to as “CB”) and 0.08 g of polyamic acid (solid content 20%) The paste was obtained by kneading and dispersing. This paste was applied to one surface of the carbon paper prepared in (2a) to form a coating film of the first reaction layer.
Next, 0.003 g of ketjen black (registered trademark) and 0.1 g of polyamic acid (solid content 20%) were kneaded and dispersed to obtain a paste. This paste was applied onto the coating film of the first reaction layer to form a coating film of the second reaction layer. Subsequently, it heated at 80 degreeC for 8 hours, and formed the reaction layer.
(2c) Formation of lithium conductive layer 0.002 g of carbon black (MK-1000 material manufactured by Nippon Graphite Industry Co., Ltd.), 0.0018 g of LiCoO ₂ , 0.1 g of polyamic acid (solid content 20%) Were kneaded and dispersed to obtain a paste. This paste was applied on the reaction layer prepared in (2b). Next, heating was performed at 80 ° C. for 8 hours to form a lithium conductive layer. A lithium air secondary battery was obtained in the same manner as Example 1 except for these.

Example 8
In “(2b) Formation of reaction layer” in Example 7, 0.003 g of ketjen black (registered trademark), 0.00015 g of Au-supported α-MnO ₂ (Au support amount 5%), 0.1 g A polyamic acid (solid content 20%) was kneaded and dispersed to obtain a paste. This paste was applied onto the coating film of the first reaction layer to form a coating film of the second reaction layer. A lithium air secondary battery was obtained in the same manner as in Example 7 except for this operation.

Example 9
Instead of Au-supported α-MnO ₂ (Au supported amount 5%) used in Example 8, Ru-supported α-MnO ₂ (Ru supported amount 5%) was used. Except this, it carried out similarly to Example 8, and obtained the lithium air secondary battery.

Example 10
Instead of Au-supported α-MnO ₂ (Au supported amount 5%) used in Example 8, Ag-supported α-MnO ₂ (Ag supported amount 5%) was used. Except this, it carried out similarly to Example 8, and obtained the lithium air secondary battery.

Example 11
Instead of Au-supported α-MnO ₂ (Au supported amount 5%) used in Example 8, Pt-supported α-MnO ₂ (Pt supported amount 5%) was used. Except this, it carried out similarly to Example 8, and obtained the lithium air secondary battery.

[Evaluation]
About the lithium air secondary battery obtained by the Example and the comparative example, the discharge capacity when charging / discharging with the current density shown in the following Table 4 was measured. The results are shown in the same table.

  As is clear from the comparison between the results shown in Table 4 and the results shown in Table 1 above, carbon black was used instead of Ketjen Black (registered trademark) in the lithium conductive layer and the first reaction layer. However, it can be seen that the lithium-air secondary battery exhibits a high discharge capacity. In particular, as is clear from the comparison between Example 7 and Examples 8 to 11, it can be seen that the discharge capacity is further increased when a catalyst is contained in the second reaction layer. In particular, it can be seen that when platinum is used as the catalyst used in the second reaction layer, the discharge capacity becomes extremely high.

Claims (7)

A lithium-air secondary battery having a positive electrode and a negative electrode,
The positive electrode has a lithium conductive layer, a reaction layer and an oxygen diffusion layer;
The lithium air secondary battery in which the lithium conductive layer is located between the negative electrode and the oxygen diffusion layer, and contains 3% by mass to 40% by mass of a conductive material based on the mass of the lithium conductive layer.   The lithium air secondary battery according to claim 1, wherein the lithium conductive layer contains a compound capable of intercalating lithium.   The lithium air secondary battery according to claim 1, wherein the conductive material includes a carbonaceous material.   The lithium air secondary battery according to any one of claims 1 to 3, wherein the reaction layer is located between the lithium conductive layer and the oxygen diffusion layer and includes a carbonaceous material or a metal oxide.   The lithium air secondary battery according to any one of claims 1 to 4, wherein the reaction layer includes a catalyst that promotes an oxygen reduction reaction and / or an oxygen generation reaction.   The lithium air secondary battery according to any one of claims 1 to 5, further comprising a separator between the positive electrode and the negative electrode, wherein the separator is coated with an ionic liquid. A positive electrode for a lithium air secondary battery having a lithium conductive layer, a reaction layer, and an oxygen diffusion layer,
When the positive electrode is incorporated in a battery, the lithium conductive layer is disposed so as to be located between the negative electrode and the oxygen diffusion layer,
The lithium conductive layer is a positive electrode for a lithium air secondary battery containing 3% by mass to 40% by mass of a conductive material based on the mass of the lithium conductive layer.