JP2019102420A - Lithium air battery - Google Patents

Abstract

To provide a technique which decreases the charge potential of a lithium air battery and which improves cycle characteristics thereof.SOLUTION: A lithium air battery (1) of the present disclosure includes: a negative electrode (12) configured to occlude and release lithium ions; a positive electrode (13) configured to enable oxygen in air, as a positive electrode active material, to be oxidized and reduced; and a nonaqueous lithium ion conductor (14) disposed between the negative electrode (12) and the positive electrode (13). The nonaqueous lithium ion conductor (14) contains: a compound represented by the following formula (1); and at least one selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to lithium air batteries.

  A lithium-air battery is a battery using oxygen in air as a positive electrode active material, and using a metal or a compound capable of inserting and extracting lithium ions as a negative electrode active material. The lithium air battery has advantages such as high energy density, easy miniaturization, and easy weight reduction. Therefore, the lithium air battery is attracting attention as a battery having an energy density exceeding that of the lithium ion battery currently considered to have the highest energy density.

  In a lithium-air battery, lithium peroxide is deposited on the positive electrode by a discharge reaction, and lithium peroxide is decomposed by a charge reaction. Due to the poor electronic conductivity of lithium peroxide, lithium air batteries generally exhibit large overpotentials during charging. As a result, the charging potential rises and the energy efficiency decreases.

Patent No. 4816693 Patent No. 5434086 gazette Patent No. 5315831 gazette

Benjamin J. Bergner et al, Understanding the fundamentals of redox mediators in Li-O2 batteries: a case study on nitroxides, Phys. Chem. Chem. Chem. Phys., 2015, 17, 31769-31779

  One aspect of the present disclosure provides a technique for reducing the charge potential of a lithium air battery and improving the cycle characteristics.

The lithium-air battery of one embodiment of the present disclosure is
An anode capable of absorbing and desorbing lithium ions;
A positive electrode configured to use oxygen in air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
Equipped with
The non-aqueous lithium ion conductor is
A compound represented by the following formula (1):
At least one selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone,
including.

In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a functional group exhibiting an electron donating property, and at least one functional group selected from R ₁ and R ₂ exhibits the electron donating property. It is. R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, a chain aliphatic group, a cyclic aliphatic group, a hydroxyl group, a nitro group, a nitroso group, an amino group, a sulfo group, a sulfuric acid group, an alkoxy It contains one selected from the group consisting of a carbonyl group, a vinyl group, an epoxy group, a methacryl group, an acryloyl group, a ureido group, a mercapto group and an isocyanate group, and the chain or cyclic aliphatic group is a halogen atom or a nitrogen atom And at least one selected from the group consisting of an oxygen atom, a sulfur atom, a silicon atom and a phosphorus atom.

  According to one aspect of the present disclosure, the charge potential of the lithium-air battery can be reduced, and the cycle characteristics can also be improved.

FIG. 1 is a schematic cross-sectional view of a lithium-air battery according to an embodiment of the present disclosure. FIG. 2 is a graph showing cyclic voltammograms of the compounds of Example 1 and Comparative Example 1. FIG. 3 is a graph showing the charge curves of the lithium air cells of Example 2, Comparative Example 2 and Comparative Example 3. FIG. 4 is a graph showing the charge curves of the lithium-air batteries of Example 2, Example 3, Example 4, Comparative Example 2 and Comparative Example 4.

(Findings that formed the basis of this disclosure)
It has been proposed to use an oxygen evolution catalyst (also called "redox mediator") to promote the decomposition of lithium peroxide.

  Derivatives of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (hereinafter referred to as "TEMPO derivative") as an oxygen generation catalyst in the lithium-air batteries described in Patent Documents 1 to 3 Is used. The TEMPO derivative is contained in the electrolytic solution or the positive electrode. The oxygen evolution catalyst promotes the decomposition of lithium peroxide by mediating the transfer of electrons between the positive electrode and the lithium peroxide to lower the charge potential.

  In the lithium-air battery described in Non-Patent Document 1, TEMPO derivatives, 2-azaadamantane-N-oxyl (AZADO) or 1-methyl-2-azaadamantane-N-oxyl (1-Me -AZADO) is used. These oxygen generating catalysts are dissolved in the electrolyte and lower the charge potential of the lithium air battery.

  These oxygen evolution catalysts described in the prior art are compounds which are one-electron oxidized to oxoammonium cations and are called nitroxyl radical compounds. The nitroxyl radical compound is reduced simultaneously with oxidative decomposition of lithium peroxide. This regenerates the nitroxyl radical. The regenerated nitroxyl radical is again converted to a cationic form on the surface of the positive electrode and reacts with lithium peroxide. Thus, the nitroxyl radical compound decomposes lithium peroxide while repeating oxidation and reduction.

The nitroxyl radical compounds described in Patent documents 1 to 3 and non-patent documents show an oxidation-reduction potential of 3.5 V (vs. Li ^/ Li ⁺ ) or more. The decomposition of lithium peroxide is initiated by the formation of a cationic form by the oxidation of the nitroxyl radical compound. Therefore, it is considered that the charge potential of the lithium-air battery can be further lowered by using a compound having a proper redox potential as the oxygen generation catalyst.

  Based on the above findings, the inventor of the present invention has intensively studied to solve the problem that the charge reaction does not easily proceed in the lithium-air battery and the charge-discharge cycle characteristics are not sufficient. As a result, the lithium-air battery of one embodiment of the present disclosure has been completed.

(Summary of one aspect according to the present disclosure)
The lithium-air battery according to the first aspect of the present disclosure is
An anode capable of absorbing and desorbing lithium ions;
A positive electrode configured to use oxygen in air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
Equipped with
The non-aqueous lithium ion conductor is
A compound represented by the following formula (1):
At least one selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone,
including.

In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a functional group exhibiting an electron donating property, and at least one functional group selected from R ₁ and R ₂ exhibits the electron donating property. It is. R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, a chain aliphatic group, a cyclic aliphatic group, a hydroxyl group, a nitro group, a nitroso group, an amino group, a sulfo group, a sulfuric acid group, an alkoxy It contains one selected from the group consisting of a carbonyl group, a vinyl group, an epoxy group, a methacryl group, an acryloyl group, a ureido group, a mercapto group and an isocyanate group, and the chain or cyclic aliphatic group is a halogen atom or a nitrogen atom And at least one selected from the group consisting of an oxygen atom, a sulfur atom, a silicon atom and a phosphorus atom.

  According to the first aspect, since the compound represented by the formula (1) functions as a charge catalyst which decomposes lithium peroxide efficiently, the charge potential is lowered. In addition to promoting the decomposition of lithium peroxide, the application of high voltage to each member of the lithium air battery can be avoided, so that the deterioration due to the oxidation of each member is suppressed and the cycle characteristics of the lithium air battery are also improved. Do. 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone have the effect of further reducing the charge potential.

  TEMPO derivatives described in the prior art have four methyl groups around the redox site NO (N-oxyl group) and are stabilized by sterically protected radicals. If four methyl groups are replaced by hydrogen atoms, TEMPO derivatives disproportionate rapidly to form nitrones and hydroxylamines.

  Compared to TEMPO derivatives described in the prior art, in the compound represented by formula (1), the stability of the radical is maintained while the steric hindrance around the redox site is smaller. Therefore, the reaction site of the compound represented by Formula (1) and lithium peroxide is large, and the reaction site is easily in contact with lithium peroxide. In addition, since the redox potential of the compound represented by the formula (1) is 比較 compared to the redox potential of the TEMPO derivative described in the prior art document, the compound represented by the formula (1) is Lithium peroxide can be decomposed at a lower potential. Therefore, by using the compound represented by the formula (1) as a redox mediator, it is possible to efficiently decompose lithium peroxide at the time of charging of the lithium-air battery. As a result, the charging potential can be sufficiently lowered. At the same time, improvement of the cycle characteristics of the lithium air battery can also be expected.

In the second aspect of the present disclosure, for example, in the lithium-air battery according to the first aspect, in the formula (1), both of R ₁ and R ₂ may be a functional group exhibiting an electron donating property. When both R ₁ and R ₂ are electron donating functional groups, the redox potential of the compound represented by the formula (1) can be sufficiently shifted to an extreme.

  In the third aspect of the present disclosure, for example, in the lithium-air battery according to the first or second aspect, the functional group exhibiting the electron donating property may be a hydrocarbon group. The hydrocarbon group reliably exhibits an electron donating property in the compound represented by the formula (1).

  In the fourth aspect of the present disclosure, for example, in the lithium-air battery according to the third aspect, the hydrocarbon group may have 1 to 3 carbon atoms. When the number of carbon atoms in the hydrocarbon group is 1 to 3, the redox potential can be shifted to 抑制 while suppressing the decrease in reactivity due to steric hindrance.

A lithium-air battery according to a fifth aspect of the present disclosure is
An anode capable of absorbing and desorbing lithium ions;
A positive electrode configured to use oxygen in air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
Equipped with
The non-aqueous lithium ion conductor contains a compound represented by the following formula (1).

In formula (1), R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 3 carbon atoms, and R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, or a chain Aliphatic group, cyclic aliphatic group, hydroxyl group, nitro group, nitroso group, amino group, sulfo group, sulfo group, sulfuric acid group, alkoxycarbonyl group, vinyl group, epoxy group, methacryl group, acryloyl group, ureido group, mercapto group And at least one selected from the group consisting of a halogen atom, a nitrogen atom, an oxygen atom, a sulfur atom, a silicon atom and a phosphorus atom, containing one selected from the group consisting of May be included.

  According to the fifth aspect, since the compound represented by the formula (1) functions as a charge catalyst which decomposes lithium peroxide efficiently, the charge potential is lowered. In addition to promoting the decomposition of lithium peroxide, the application of high voltage to each member of the lithium air battery can be avoided, so that the deterioration due to the oxidation of each member is suppressed and the cycle characteristics of the lithium air battery are also improved. Do.

  In the sixth aspect of the present disclosure, for example, in the lithium-air battery according to any one of the third to fifth aspects, the hydrocarbon group may be a methyl group. When the hydrocarbon group is a methyl group, the steric hindrance around the redox site is small, and the redox potential can also be shifted to 卑.

In the seventh aspect of the present disclosure, for example, in the lithium-air battery according to any one of the first to sixth aspects, each of R ₃ and R _{4 in} the formula (1) may be a hydrogen atom . When each of R ₃ and R ₄ is a hydrogen atom, the compound represented by Formula (1) exhibits excellent reactivity because it has a small molecular diameter.

  In the eighth aspect of the present disclosure, for example, in the lithium-air battery according to any one of the first to seventh aspects, the concentration of the compound in the non-aqueous lithium ion conductor is 0.01 mmol / L or more. It is also good. According to the eighth aspect, the effect of promoting the decomposition of lithium peroxide and the effect of improving the cycle characteristics of the lithium-air battery can be sufficiently obtained.

  In a ninth aspect of the present disclosure, for example, in the lithium-air battery according to any one of the first to fourth aspects, 2, 5-di-tert-butyl-1,4- 4 in the non-aqueous lithium ion conductor. At least one concentration selected from the group consisting of benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone may be 0.01 mmol / liter or more. When at least one concentration selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone is appropriately adjusted, The above effects can be sufficiently obtained.

  In the tenth aspect of the present disclosure, for example, in the lithium-air battery according to any one of the first to ninth aspects, the non-aqueous lithium ion conductor may further contain tetraethylene glycol dimethyl ether. Tetraethylene glycol dimethyl ether is suitable as a non-aqueous lithium ion conductor of a lithium air battery because it is difficult to volatilize and is stable to oxygen radicals.

(Embodiment)
Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

  FIG. 1 is a schematic cross-sectional view of a lithium-air battery according to an embodiment of the present disclosure. As shown in FIG. 1, the lithium-air battery 1 of the present embodiment includes a battery case 11, a negative electrode 12, a positive electrode 13, and an electrolyte layer 14 as a non-aqueous lithium ion conductor. The battery case 11 has a cylindrical portion 11a opened on both the top and bottom sides, a bottom portion 11b provided to close the opening on the bottom of the cylindrical portion 11a, and an opening on the upper surface of the cylindrical portion 11a. And a lid 11c provided to close the cover. The lid portion 11 c is provided with an air intake hole 15 for taking air into the battery case 11. The negative electrode 12 includes a negative electrode layer 12 a disposed on the inner bottom surface of the bottom portion 11 b of the battery case 11. The bottom portion 11 b of the battery case 11 also has the function of the negative electrode current collector of the negative electrode 12. That is, the negative electrode 12 is configured by the bottom portion 11 b which also serves as the negative electrode current collector and the negative electrode layer 12 a. The positive electrode 13 is configured of a positive electrode layer 13 a containing a carbon material, and a positive electrode current collector 13 b disposed between the positive electrode layer 13 a and the lid 11 c of the battery case 11. The electrolyte layer 14 of the lithium-air battery 1 may include a separator. A negative electrode current collector may be provided separately from the bottom 11b.

  The cell reaction in the lithium-air battery 1 having the above-described configuration is as follows.

Discharge reaction (ie reaction when using battery)
^{Negative: 2Li → 2Li + + 2e -} (A1)
Positive electrode: 2Li ⁺ + 2e ⁻ + O ₂ → Li ₂ O ₂ (A2)

Charging reaction (ie reaction during battery charging)
^{Negative: 2Li + + 2e - → 2Li} (A3)
Positive electrode: Li ₂ O ₂ → 2Li ⁺ + 2e ⁻ + O ₂ (A4)

  At the time of discharge, electrons and lithium ions are released from the negative electrode 12 as shown in the formulas (A1) and (A2). While electrons are taken into the positive electrode 13, at the same time, oxygen taken from the outside of the battery reacts with lithium ions in the positive electrode 13 to form lithium oxide. At the time of charge, electrons and lithium ions are taken into the negative electrode 12 as shown in the formulas (A3) and (A4). Electrons, lithium ions and oxygen are released from the positive electrode 13. The charge catalyst is a material that promotes the reaction represented by formula (A4).

  Next, each configuration of such a lithium air battery 1 will be described in detail.

1. Positive Electrode As described above, the positive electrode 13 includes the positive electrode layer 13a, and may further include the positive electrode current collector 13b. The positive electrode layer 13a and the positive electrode current collector 13b will be respectively described below.

(Positive layer)
The positive electrode layer 13 a contains oxygen in air as a positive electrode active material, and a material capable of oxidizing and reducing the oxygen. As such a material, the positive electrode layer 13a in the present embodiment includes a conductive porous body containing carbon. The carbon material used as the conductive porous body containing carbon may have high electron conductivity. Specifically, carbon materials such as acetylene black and ketjen black which are generally used as a conductive additive can be used. From the viewpoint of specific surface area and primary particle size, conductive carbon black such as ketjen black may be used. The carbon material is usually a powder. The specific surface area of the carbon material is, for example, 800 m ² / g or more and 2000 m ² / g or less, and may be 1200 m ² / g or more and 1600 m ² / g or less. When the specific surface area of the carbon material is in such a range, the positive electrode layer 13a having a pore structure is easily formed. The specific surface area is a value measured by the BET method.

  The positive electrode layer 13a may further contain a binder for immobilizing the above-mentioned conductive porous body. A well-known material can be used as a binder of the positive electrode layer 13a of the lithium air battery 1 as a binder. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). The content of the binder in the positive electrode layer 13a is not particularly limited, and is, for example, in the range of 1% by mass to 40% by mass.

  The thickness 13 a of the positive electrode layer is not particularly limited because it changes depending on the application of the lithium air battery 1 and the like. The thickness of the positive electrode layer 13a is, for example, in the range of 2 μm to 500 μm, and may be in the range of 5 μm to 300 μm.

  The positive electrode layer 13a can be produced, for example, by the method described below. The carbon material and the solvent are mixed to prepare a mixture. If necessary, additives such as a binder may be contained in the mixture. The obtained mixture (used as a coating solution) is coated on the positive electrode current collector 13b by a coating method such as a doctor blade method, and the coated film is dried. Thereby, the positive electrode 13 is obtained. The coated film of the mixture may be dried, and the dried coated film may be rolled by a method such as a roll press to produce the sheet-like positive electrode layer 13a having no positive electrode current collector 13b. You may produce the sheet-like positive electrode layer 13a by shape | molding a carbon material directly with a crimp press.

(Positive current collector)
The positive electrode current collector 13 b is a member that collects current from the positive electrode layer 13 a. It will not specifically limit, if it is a material which has electroconductivity as a material of the positive electrode collector 13b. Examples of the material of the positive electrode current collector 13b include stainless steel, nickel, aluminum, iron, titanium and carbon. Examples of the shape of the positive electrode current collector 13b include a foil shape, a plate shape, and a mesh (for example, grid) shape. In the present embodiment, the positive electrode current collector 13b may have a mesh shape. This is because the mesh-like positive electrode current collector 13b is excellent in current collection efficiency. In this case, the mesh-like positive electrode current collector 13b can be disposed inside the positive electrode layer 13a. The lithium-air battery 1 of the present embodiment further includes another positive electrode current collector 13 b (for example, a foil-like current collector) that collects the charge collected by the mesh-like positive electrode current collector 13 b. It is also good. In the present embodiment, a battery case 11 described later may have the function of the positive electrode current collector 13 b. The thickness of the positive electrode current collector 13b is, for example, in the range of 10 μm to 1000 μm, and may be in the range of 20 μm to 400 μm.

2. Negative Electrode As described above, the negative electrode 12 includes the negative electrode current collector, and may further include the negative electrode layer 12 a. Below, the negative electrode layer 12a and a negative electrode collector are each demonstrated.

(Anode layer)
The negative electrode layer 12a in the present embodiment may contain a negative electrode active material capable of inserting and extracting lithium ions. Such a negative electrode active material is not particularly limited as long as it is a substance containing a lithium element, for example, metal lithium which is a single metal, an alloy containing a lithium element, an oxide containing a lithium element and a lithium element And the like. Examples of the alloy containing lithium element include lithium aluminum alloy, lithium tin alloy, lithium lead alloy and lithium silicon alloy. As a metal oxide containing a lithium element, a lithium titanium oxide etc. are mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride and lithium manganese nitride.

  The negative electrode layer 12a may contain only the negative electrode active material, or may contain a binder in addition to the negative electrode active material. When the negative electrode active material is foil-like, the negative electrode layer 12a may contain only the negative electrode active material. When the negative electrode active material is in the form of powder, the negative electrode layer 12a may contain the negative electrode active material and a binder. A well-known material can be used as a binder of the negative electrode layer 12a of the lithium air battery 1, For example, PVdF, PTFE, etc. are mentioned. The content of the binder in the negative electrode layer 12a is not particularly limited, and is, for example, in the range of 1% by mass to 40% by mass. As a method of producing the negative electrode layer 12a using a powdery negative electrode active material, as in the method of producing the positive electrode layer 13a described above, it is possible to use a doctor blade method or a forming method using a pressure bonding press.

(Negative current collector)
The negative electrode current collector is a member that collects current from the negative electrode layer 12a. The material of the negative electrode current collector is not particularly limited as long as it has conductivity. A known material can be used as a negative electrode current collector of a lithium air battery. Examples of the material of the negative electrode current collector include copper, stainless steel, nickel and carbon. Examples of the shape of the negative electrode current collector include a foil shape, a plate shape, and a mesh (for example, grid) shape. The negative electrode current collector may be a porous body having irregularities on the surface. A battery case 11 described later may have the function of a negative electrode current collector.

3. Separator The lithium-air battery 1 of the present embodiment may include a separator disposed between the positive electrode 13 and the negative electrode 12. By arranging a separator between the positive electrode 13 and the negative electrode 12, a battery with high safety can be obtained. The separator is not particularly limited as long as it has a function of electrically separating the positive electrode layer 13a and the negative electrode layer 12a. As the separator, for example, porous films such as polyethylene (PE) porous film and polypropylene (PP) porous film, resin non-woven fabrics such as PE non-woven fabric and PP non-woven fabric, glass fiber non-woven fabrics, and porous insulating materials such as paper non-woven fabrics It can be mentioned.

  The porosity of the separator is, for example, in the range of 30% to 90%. When the porosity is in such a range, a sufficient amount of electrolyte is retained in the separator and the separator has sufficient strength. The porosity of the separator may be in the range of 35% to 60%. The porosity can be calculated from the true density of the material, the total volume and weight including the pores.

4. Electrolyte Layer The electrolyte layer 14 is a layer disposed between the positive electrode 13 and the negative electrode 12 to conduct lithium ions. The form of the electrolyte layer 14 is not particularly limited as long as it is a lithium ion conductor having lithium ion conductivity, and a solution system represented by an organic solvent system containing a salt of lithium as an electrolyte, and a salt of lithium It may be in any form of a solid membrane system represented by the system of the solid polymer electrolyte containing. Even if the electrolyte is solid or gel, the mediator contained in the electrolyte can cause an electrochemical reaction on the surface of the positive electrode 13.

  When the electrolyte layer 14 is a solution system, a non-aqueous electrolytic solution prepared by dissolving a lithium salt in a non-aqueous solvent can be used as the electrolyte layer 14.

Examples of the lithium salt contained as an electrolyte in the non-aqueous electrolytic solution include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), trifluoromethanesulfonic acid Examples include, but are not limited to, lithium (LiCF ₃ SO ₃ ) and bis trifluoromethanesulfonylamide lithium (LiN (CF ₃ SO ₂ ) ₂ ). A known lithium salt can be used as an electrolyte of the non-aqueous electrolytic solution of the lithium-air battery 1.

  The concentration of the electrolyte in the non-aqueous electrolytic solution is, for example, not less than 0.5 mol / liter and not more than 2.5 mol / liter. In the case of using a non-aqueous electrolytic solution that is a solution-based electrolyte layer 14, as described above, the non-aqueous electrolytic solution may be impregnated into a separator and held to form the electrolyte layer 14.

  As a non-aqueous solvent, a non-aqueous solvent known as a non-aqueous solvent of the non-aqueous electrolytic solution of the lithium-air battery 1 can be used. For example, a linear ether such as tetraethylene glycol dimethyl ether or tetraethylene glycol diethyl ether can be used as a solvent. The chain ether is less likely to cause a side reaction other than the oxidation-reduction reaction of oxygen in the positive electrode 13 as compared to the carbonate-based solvent. In particular, tetraethylene glycol dimethyl ether is suitable as an electrolyte for air batteries because it is difficult to volatilize and is stable against oxygen radicals. Other non-aqueous solvents include dimethylsulfoxide.

  The lithium-air battery 1 of the present embodiment further includes a nitroxyl radical compound as an oxygen generation catalyst. The nitroxyl radical compound of the present embodiment is represented by the following formula (1).

  The compound represented by the formula (1) is an organic compound having a bridged ring structure containing a nitroxyl radical. The compound represented by the formula (1) has a low distortion and a strong, highly symmetrical adamantane skeleton, and therefore can be extremely stably present in the free radical state.

  In the present embodiment, the nitroxyl radical compound is contained in the electrolyte layer 14 which is a non-aqueous lithium ion conductor. When the lithium-air battery 1 is charged, the nitroxyl radical compound is oxidized on the surface of the positive electrode 13 to change into a cation. This cation acts as a charge catalyst that promotes the decomposition of lithium peroxide.

  When the non-aqueous electrolytic solution is used as the electrolyte layer 14, the nitroxyl radical compound is dissolved in the non-aqueous solvent constituting the non-aqueous electrolytic solution. Therefore, the nitroxyl radical compound can be abundantly present around the positive electrode 13. The concentration of the nitroxyl radical compound in the non-aqueous electrolyte is, for example, 0.01 mmol / liter or more. The upper limit of the concentration of the nitroxyl radical compound in the non-aqueous electrolyte is, for example, 200 mmol / liter. When the concentration of the nitroxyl radical compound is properly adjusted, the above-mentioned effects can be sufficiently obtained.

In the compound represented by the formula (1), R ₁ and R ₂ are bonded to α carbon adjacent to the N-oxyl group which is a redox site. When at least one selected from R ₁ and R ₂ is an electron donating functional group, the redox potential of the compound represented by the formula (1) can be shifted to 卑. This effect is more fully obtained when both R ₁ and R ₂ are electron donating functional groups. The structures of R ₁ and R ₂ may be identical or different from each other.

  The functional group exhibiting an electron donating property includes a hydrocarbon group. The hydrocarbon group reliably exhibits an electron donating property in the compound represented by the formula (1).

The hydrocarbon group is typically an alkyl group such as a methyl group or an ethyl group. When electrons are partially donated from the σ bond of the alkyl group to the N-oxyl group, the radical is stabilized by the super conjugation effect. The longer the alkyl chain, the more the redox potential shifts. However, if the alkyl chain is too long, the influence of steric hindrance may increase, and the reactivity of the compound represented by the formula (1) with Li ₂ O ₂ may be reduced. When the number of carbon atoms in the hydrocarbon group is 1 to 3, the redox potential can be shifted to 抑制 while suppressing the decrease in reactivity due to steric hindrance. When the hydrocarbon group is a methyl group, the steric hindrance around the redox site is small, and the redox potential can also be shifted to 卑.

In the compound represented by the formula (1), R ₃ and R ₄ each independently represent a hydrogen atom, a halogen atom, a chain aliphatic group, a cyclic aliphatic group, a hydroxyl group, a nitro group or a nitroso group It may contain one selected from the group consisting of an amino group, a sulfo group, a sulfuric acid group, an alkoxycarbonyl group, a vinyl group, an epoxy group, a methacrylic group, an acryloyl group, a ureido group, a mercapto group and an isocyanate group. The chain or cyclic aliphatic group may contain at least one selected from the group consisting of a halogen atom, a nitrogen atom, an oxygen atom, a sulfur atom, a silicon atom and a phosphorus atom.

In the compounds represented by formula (1), R ₃ and R ₄ are separated from the redox site. Therefore, the influence of R ₃ and R ₄ on the redox potential is small. From this point of view, the structures of R ₃ and R ₄ are not limited. When each of R ₃ and R ₄ is a hydrogen atom, the compound represented by Formula (1) exhibits excellent reactivity because it has a small molecular diameter.

When each of R ₁ and R ₂ is a methyl group, the nitroxyl radical compound in the present disclosure is represented by the following formula (2). When each of R ₁ and R ₂ is a methyl group and each of R ₃ and R ₄ is a hydrogen atom, the nitroxyl radical compound in the present disclosure is represented by the following formula (3). The compound represented by the formula (3) is 1,5-dimethyl-9-azanoradamantane-N-oxyl (DMN-AZADO).

The presence of the compound represented by the formula (1) can be confirmed by, for example, ¹ H-NMR measurement.

  The lithium-air battery 1 of the present embodiment may further include an n-type redox molecule that mediates electron transfer in the discharge reaction. As an n-type redox molecule, 2,5-di-tert-butyl-1,4-benzoquinone represented by the following formula (4), and 2,6-di-tert- represented by the following formula (5) At least one selected from the group consisting of butyl-1,4-benzoquinone can be used.

2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone (both referred to as DBBQ) are both 2.6 V (vs. Li / Li) ^It is an n-type redox molecule having a redox potential in the vicinity of ⁺ ) and having similar redox characteristics, and receives an electron from the positive electrode 13 at the time of discharge and converts it into an anion (DBBQ ⁻ ). DBBQ ^- stabilizes to form Li ⁺ and O ₂ and complex (LiDBBQO _2). Thereafter, disproportionation of two molecules of this complex is considered to produce lithium peroxide.

  When DBBQ mediates the exchange of electrons, lithium peroxide can be formed not only on the surface of the positive electrode 13 but also in an electrolyte solution (in the vicinity of the positive electrode 13) slightly away from the surface of the positive electrode 13. That is, DBBQ that has received electrons from the positive electrode 13 diffuses into the electrolytic solution by the concentration gradient, and the reaction field for producing lithium peroxide is expanded. Thus, lithium peroxide is produced in such a manner that a large number of particles produced at different places are deposited on the surface of the positive electrode 13. When DBBQ is not used, since electron transfer is performed only on the surface of the positive electrode 13 almost, lithium peroxide is formed so as to cover the surface of the positive electrode 13. Assuming that the discharge capacities are equal, when using DBBQ, the surface area of lithium peroxide at the positive electrode 13 is larger than when DBBQ is not used. During charge, the reaction area of the cation of the redox mediator as the oxygen generation catalyst and lithium peroxide is expanded, the catalytic effect obtained is increased, and lithium peroxide can be decomposed more efficiently. As a result, the charge potential of the lithium air battery 1 is further lowered.

  When the non-aqueous electrolytic solution is used as the electrolyte layer 14, the DBBQ is dissolved in the non-aqueous solvent constituting the non-aqueous electrolytic solution. Therefore, DBBQ can be abundantly present around the positive electrode 13. The concentration of DBBQ in the non-aqueous electrolyte is, for example, 0.01 mmol / liter or more. The upper limit of the concentration of DBBQ in the non-aqueous electrolyte is, for example, 200 mmol / liter. When the concentration of DBBQ is properly adjusted, the above-mentioned effects can be sufficiently obtained. When both 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone are contained in the non-aqueous electrolyte as DBBQ, The total concentration is the concentration of DBBQ.

5. Battery Case The battery case 11 of the lithium-air battery 1 of the present embodiment is not particularly limited in shape, as long as it can accommodate the positive electrode 13, the negative electrode 12 and the electrolyte layer 14 as described above. The battery case 11 of the lithium-air battery 1 of the present embodiment is not limited to the shape shown in FIG. 1, and various shapes such as coin, flat, cylindrical and laminate types can be used. The battery case 11 may be an open-air battery case, or may be a closed battery case. The open-air battery case has a vent that allows the atmosphere to enter and exit, and is a case in which the atmosphere can be in contact with the positive electrode. In the case of the sealed battery case, the sealed battery case may be provided with a gas supply pipe and a gas discharge pipe. In this case, the gas supplied and discharged may be a dry gas. The gas supplied and discharged may have a high oxygen concentration, and may be pure oxygen (oxygen concentration 99.99%). The oxygen concentration may be high during discharge and low during charge.

  Hereinafter, the present disclosure will be described in more detail by way of examples. The following example is an example, and the present disclosure is not limited to the following example.

Example 1
LiTFSA (lithium bis trifluoromethane sulfonylamide, manufactured by Kishida Chemical Co., Ltd.) is mixed and dissolved in tetraethylene glycol dimethyl ether (TEGDME, manufactured by Kishda Chemical Co., Ltd.) to a concentration of 1 mol / liter to obtain a non-aqueous electrolytic solution. The In the obtained non-aqueous electrolyte, 1,5-dimethyl-9-azanoradamantane-N-oxyl (DMN-AZADO) was dissolved at a concentration of 2 mmol / liter. Cyclic voltammetry measurement was performed at a scanning speed of 10 mV / sec using a glassy carbon electrode as a working electrode, a platinum electrode as a counter electrode, and an Ag / Ag ⁺ electrode (all BAS Co., Ltd.) as a reference electrode. .

(Comparative example 1)
The cyclic voltammetry measurement was performed by the same method as Example 1 except having used TEMPO instead of DMN-AZADO.

  FIG. 2 shows cyclic voltammograms of the compounds of Example 1 and Comparative Example 1. As shown in FIG. 2, DMN-AZADO (Example 1) had a redox potential lower than that of TEMPO (Comparative Example 1).

According to theoretical calculation, in the compound represented by the formula (1), when R ₁ is a methyl group and R ₂ to R ₄ are hydrogen atoms, the redox of the compound represented by the formula (1) The potential is more noble than the redox potential of DMN-AZADO and more negative than the redox potential of TEMPO.

(Example 2)
A powder of ketjen black (manufactured by Lion Corporation) was used as a carbon material. A powder of PTFE (manufactured by Daikin Industries, Ltd.) was used as a binder. The carbon material and the binder were kneaded using an ethanol solvent at a mass ratio of 90:10 to obtain a mixture. The mixture was rolled by a roll press to produce an electrode sheet. The obtained electrode sheet was cut to obtain a positive electrode (positive electrode layer).

  LiTFSA (lithium bis trifluoromethanesulfonylamide, manufactured by Kishda Chemical Co., Ltd.) was mixed and dissolved in tetraethylene glycol dimethyl ether (TEGDME, manufactured by Kishda Chemical Co., Ltd.) to a concentration of 1 mol / liter. The mixed solution was stirred for 24 hours under a dry air atmosphere with a dew point of -50 degrees or less to obtain a non-aqueous electrolyte. In the obtained non-aqueous electrolyte, DMN-AZADO was dissolved at a concentration of 20 mmol / liter.

  A glass fiber separator was prepared as a separator. A SUS304 mesh as a current collector was attached to a metal lithium foil to obtain a negative electrode. Using the positive electrode, the separator, the non-aqueous electrolyte and the negative electrode, a lithium air battery having a structure shown in FIG. 1 was produced.

(Comparative example 2)
A lithium-air battery of Comparative Example 2 was made in the same manner as Example 2, except that DMN-AZADO was not used.

(Comparative example 3)
A lithium air battery of Comparative Example 3 was made in the same manner as Example 2, except that TEMPO was used instead of DMN-AZADO.

(Charge and discharge test)
After the lithium air batteries of Example 2, Comparative Example 2 and Comparative Example 3 were held for at least 20 minutes in an oxygen atmosphere, a charge / discharge test was performed. The current density at the time of discharge was 0.4 mA / cm ² , and the cutoff voltage was 2.0 V. The current density at the time of charge was 0.1 mA / cm ² and the cut-off voltage was 4.5V. After discharging, charging was performed. The obtained charging curve is shown in FIG. The SOC (State Of Charge) on the horizontal axis of FIG. 3 represents the charging rate, and the vertical axis Voltage represents the battery voltage relative to the redox potential of the negative electrode lithium.

  As shown in FIG. 3, the charge potential of the lithium air battery of Example 2 was lower than the charge potentials of the lithium air batteries of Comparative Example 2 and Comparative Example 3. In Example 2, it is presumed that DMN-AZADO is oxidized on the surface of the positive electrode to be converted to a cationic form, functions as a charge catalyst for efficiently decomposing lithium peroxide, and reduces the charge potential.

(Charge and discharge cycle test)
The charge-discharge cycle test of the lithium-air batteries of Example 2, Comparative Example 2 and Comparative Example 3 was conducted under the same conditions as the charge-discharge test described above. Specifically, discharge and charge were repeated three times each. The results of this charge-discharge cycle test are shown in Table 1. The capacity retention rate represents the ratio of the discharge capacity of each time to the discharge capacity of the first time.

  As shown in Table 1, compared to the lithium air batteries of Comparative Example 2 and Comparative Example 3, the discharge capacity of the lithium air battery of Example 2 was hard to decrease. In the lithium-air battery of Example 2, DMN-AZADO was used as an oxygen generation catalyst (redox mediator). The steric hindrance around the redox site of DMN-AZADO is small and the molecular size is also small. Therefore, it is inferred that DMN-AZADO functioned as a charge catalyst for efficiently decomposing lithium peroxide. In addition, DMN-AZADO is easily in contact with lithium peroxide and rapidly decomposes lithium peroxide. Therefore, in the lithium-air battery of Example 2, DMN-AZADO not only lowers the charge potential in the charging process but also promotes the decomposition of lithium peroxide and is considered to improve the cycle characteristics of the lithium-air battery.

As shown in the graph of FIG. 3, also in the lithium-air battery of Comparative Example 3, the lowering effect of the charge potential by TEMPO as the redox mediator was obtained. However, the lowering effect of the charge potential in Comparative Example 3 was lower than the effect obtained in Example 2. Therefore, the reactivity of TEMPO with Li ₂ O ₂ is considered to be lower than the reactivity of DMN-AZADO with Li ₂ O ₂ . TEMPO has greater steric hindrance around the N-oxyl group compared to DMN-AZADO. It is presumed that this has affected the lowering effect of the charge potential.

As shown in the graph of FIG. 3, the oxidation potential of TEMPO was reflected on the charge potential at the first cycle, and a low charge potential was obtained. However, when the reaction between TEMPO (TEMPO ⁺ ) in an oxidized state and Li ₂ O ₂ does not occur smoothly, a large amount of Li ₂ O ₂ remains in the positive electrode even after charging. The remaining Li ₂ O ₂ and Li ₂ O ₂ was precipitated in the second cycle of the discharge, most of the pores of the positive electrode filled, well resolved subsequent to Li ₂ O ₂ is weak action of TEMPO also in charge It can not be done, and it is presumed that the third cycle discharge was difficult to advance.

The reason why the capacity retention rate at the third cycle of Comparative Example 3 is inferior to that of Comparative Example 2 is that the redox mediator is inactivated on the surface of the negative electrode. The problem of deactivation can not be avoided unless the surface of the negative electrode is coated with a gel electrolyte or the like, or the solid electrolyte or the like blocks the contact between the redox mediator and lithium of the negative electrode. However, in the case of using a redox mediator such as TEMPO which does not have a high decomposition effect of Li ₂ O ₂ , it is estimated that the disadvantage due to deactivation exceeds the merit.

(Example 3)
The mass ratio of the carbon material to the binder was changed to 70:30, and 2,5-di-tert-butyl-1,4-benzoquinone (2,5-dibasic) at a concentration of 10 mmol / liter in the non-aqueous electrolyte. The lithium-air battery of Example 3 was made in the same manner as Example 2, except that DBBQ was additionally dissolved.

(Example 4)
2,6-di-tert-butyl-1,4-benzoquinone (2,6-DBBQ) was used in place of 2,5-di-tert-butyl-1,4-benzoquinone (2,5-DBBQ) The lithium air battery of Example 4 was produced in the same manner as in Example 3 except for the above.

(Comparative example 4)
The lithium air battery of Comparative Example 4 was prepared in the same manner as in Example 2 except that 2,5-di-tert-butyl-1,4-benzoquinone (2,5-DBBQ) was used instead of DMN-AZADO. Made.

(Charge and discharge test)
After the lithium air battery of Example 3 was held for at least 20 minutes in an oxygen atmosphere, a charge / discharge test was performed. The current density at the time of discharge was 0.4 mA / cm ² , and the cutoff voltage was 2.0 V. The current density at the time of charge was 0.1 mA / cm ² , and the cut-off voltage was 4.0V. After discharging, charging was performed. A charge and discharge test of the lithium air battery of Comparative Example 4 was also conducted. The obtained charging curve is shown in FIG.

  FIG. 4 also shows the charge curves of the lithium air cells of Example 2 and Comparative Example 2 in addition to the charge curves of the lithium air cells of Example 3 and Example 4 and Comparative Example 4. As shown in FIG. 4, the charge potentials of the lithium air batteries of Example 3 and Example 4 were lower than the charge potential of the lithium air battery of Example 2. That is, the charge potential was further lowered by adding 2,5-DBBQ or 2,6-DBBQ to the non-aqueous electrolyte.

  In the lithium-air battery of Comparative Example 4 containing only 2,5-DBBQ, the effect of lowering the charge potential was not obtained.

  As described above, according to the technology of the present disclosure, it is possible to promote the decomposition of lithium peroxide, which is a discharge product, to lower the charge potential of the lithium air battery, and to improve the cycle characteristics.

  According to the technology of the present disclosure, it is possible to reduce the charge potential of the lithium air battery while securing a high capacity, and to provide a lithium air battery having good charge and discharge cycle characteristics. Therefore, the lithium-air battery of the present disclosure is useful as a secondary battery.

DESCRIPTION OF SYMBOLS 1 lithium air battery 11 battery case 11a cylindrical part 11b bottom part 11c lid 12 negative electrode 12a negative electrode layer 13 positive electrode 13a positive electrode layer 13b positive electrode current collector 14 electrolyte layer 15 air intake hole

Claims (10)

An anode capable of absorbing and desorbing lithium ions;
A positive electrode configured to use oxygen in air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
Equipped with
The non-aqueous lithium ion conductor is
A compound represented by the following formula (1):
At least one selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone,
Including, lithium air battery.

[In formula (1), R ₁ and R ₂ each independently represent a hydrogen atom or a functional group exhibiting an electron donating property, and at least one selected from R ₁ and R ₂ exhibits the electron donating property] It is a group. R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, a chain aliphatic group, a cyclic aliphatic group, a hydroxyl group, a nitro group, a nitroso group, an amino group, a sulfo group, a sulfuric acid group, an alkoxy It contains one selected from the group consisting of a carbonyl group, a vinyl group, an epoxy group, a methacryl group, an acryloyl group, a ureido group, a mercapto group and an isocyanate group, and the chain or cyclic aliphatic group is a halogen atom or a nitrogen atom And at least one selected from the group consisting of an oxygen atom, a sulfur atom, a silicon atom and a phosphorus atom. ] The lithium air battery according to claim 1, wherein both R ₁ and R ₂ in the formula (1) are a functional group exhibiting an electron donating property.   The lithium air battery according to claim 1, wherein the electron donating functional group is a hydrocarbon group.   The lithium-air battery according to claim 3, wherein the hydrocarbon group has 1 to 3 carbon atoms. An anode capable of absorbing and desorbing lithium ions;
A positive electrode configured to use oxygen in air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
Equipped with
The lithium air battery, wherein the non-aqueous lithium ion conductor contains a compound represented by the following formula (1).

[In Formula (1), R ₁ and R ₂ are each independently a hydrocarbon group having 1 to 3 carbon atoms, and R ₃ and R ₄ are each independently a hydrogen atom, a halogen atom, or a chain Aliphatic group, cyclic aliphatic group, hydroxyl group, nitro group, nitroso group, amino group, sulfo group, sulfo group, sulfate group, alkoxycarbonyl group, vinyl group, epoxy group, methacryl group, acryloyl group, ureido group, mercapto And at least one selected from the group consisting of a halogen atom, a nitrogen atom, an oxygen atom, a sulfur atom, a silicon atom, and a phosphorus atom, containing one selected from the group consisting of a group and an isocyanate group; You may include one. ]   The lithium air battery according to any one of claims 3 to 5, wherein the hydrocarbon group is a methyl group. The lithium air battery according to any one of claims 1 to 6, wherein in the formula (1), each of R ₃ and R ₄ is a hydrogen atom.   The lithium air battery according to any one of claims 1 to 7, wherein the concentration of the compound in the non-aqueous lithium ion conductor is 0.01 mmol / liter or more.   At least one concentration selected from the group consisting of 2,5-di-tert-butyl-1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone in the non-aqueous lithium ion conductor The lithium air battery according to any one of claims 1 to 4, which is 0.01 mmol / liter or more.   The lithium air battery according to any one of claims 1 to 9, wherein the non-aqueous lithium ion conductor further comprises tetraethylene glycol dimethyl ether.

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