JP2018133168A - Lithium-air battery and method of using the same - Google Patents

Abstract

A lithium-air battery having improved charge / discharge cycle characteristics while ensuring a high capacity is provided. A lithium-air battery 1 according to the present disclosure includes a negative electrode 12 including a negative electrode layer 12a capable of occluding and releasing lithium ions, a conductive porous material including carbon, and oxygen in the air as a positive electrode active material. A positive electrode 13 including a positive electrode layer capable of oxidizing and reducing oxygen, and a non-aqueous lithium ion conductor (for example, an electrolyte layer 14) disposed between the negative electrode 12 and the positive electrode 13 are provided. In the positive electrode layer, the first pore volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less is larger than the second pore volume occupied by pores having a pore diameter of more than 200 nm and 10000 nm or less. [Selection] Figure 1

Description

  The present disclosure relates to lithium-air batteries and methods of use thereof.

  A lithium air battery is a battery that uses oxygen in the air as a positive electrode active material and a metal or compound capable of occluding and releasing lithium ions as a negative electrode active material. Lithium-air batteries have advantages such as high energy density (amount of electric power that can be discharged with respect to weight), and easy miniaturization and weight reduction. Therefore, the lithium-air battery is attracting attention as a battery having an energy density exceeding that of the lithium ion battery that is considered to have the highest energy density.

  The lithium-air battery includes a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode. The lithium air battery may further include other components such as an oxygen permeable membrane disposed on the positive electrode. A conductive material is generally used for the positive electrode. As the conductive material, for example, a carbon material such as graphite and acetylene black is used.

  In the lithium air battery, further performance improvement is demanded while taking advantage of the high capacity inherent in the lithium air battery. For example, Patent Literature 1 proposes a lithium-air battery that has a further improved output characteristic while ensuring a high capacity. The lithium air battery proposed in Patent Document 1 uses porous carbon having a specific pore volume and pore size distribution for the positive electrode. The porous carbon has pores including mesopores and micropores having a pore diameter smaller than the mesopores, and the carbonaceous wall constituting the outline of the mesopores has a three-dimensional network structure. The micropores are formed, the mesopores are open pores, the pore portions continuously form connection pores, and the half-value width of the pore diameter distribution of the pores is 2 nm or less, The linking hole diameter distribution has a half-value width of 50 nm or more, and a pore volume occupied by pores having a pore diameter of 1 nm or more is 1.0 ml / g or more and 4.0 ml / g or less.

Japanese Patent No. 5852548

  However, a lithium air battery in which a carbon material having a specific pore volume and pore size distribution as described in Patent Document 1 is used for the positive electrode can be used as a secondary battery, although a large discharge capacity can be obtained. It has been found that the possible cycle characteristics are not sufficient. That is, the conventional lithium-air battery has a problem in making it a secondary battery before taking advantage of the high capacity that the lithium-air battery originally has due to insufficient charge / discharge cycle characteristics.

  Therefore, an object of the present disclosure is to provide a lithium-air battery having improved charge / discharge cycle characteristics while ensuring a high capacity.

This disclosure
A negative electrode including a negative electrode layer capable of occluding and releasing lithium ions;
A positive electrode including a conductive porous body containing carbon, and a positive electrode layer capable of oxidation-reduction of oxygen using oxygen in the air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
A lithium-air battery comprising:
In the positive electrode layer, the first pore volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less is larger than the second pore volume occupied by pores having a pore diameter of more than 200 nm and 10000 nm or less,
A lithium air battery is provided.

  The lithium-air battery of the present disclosure can improve charge / discharge cycle characteristics while ensuring a high capacity.

FIG. 1 is a schematic cross-sectional view illustrating a configuration example of a lithium air battery according to the present disclosure.

<Overview of one aspect according to the present disclosure>
A lithium air battery according to the first aspect of the present disclosure is provided.
A negative electrode including a negative electrode layer capable of occluding and releasing lithium ions;
A positive electrode including a conductive porous body containing carbon, and a positive electrode layer capable of oxidation-reduction of oxygen using oxygen in the air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
A lithium-air battery comprising:
In the positive electrode layer, the first pore volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less is larger than the second pore volume occupied by pores having a pore diameter of more than 200 nm and 10000 nm (= 10 μm) or less.

  When the first pore volume and the second pore volume in the positive electrode layer satisfy the above relationship, the lithium-air battery according to the first aspect improves charge / discharge cycle characteristics while ensuring a high capacity. Can do.

In the second aspect, for example, in the lithium air battery according to the first aspect, the electrode density of the positive electrode may be 0.2 to 0.4 g / cm ³ .

  In the lithium air battery according to the second aspect, the electrode density of the positive electrode satisfies the above range, in other words, it can be said that the positive electrode includes many pores having a small pore diameter. Therefore, in the lithium-air battery according to the second aspect, the lithium oxide generated during discharge tends to be small particles, and the charge / discharge cycle characteristics are improved.

  In the third aspect, for example, in the lithium air battery according to the first or second aspect, the surface functional group amount of the positive electrode layer may be 0.2 mmol / g or less.

  In the lithium air battery according to the third aspect, the surface functional group of the positive electrode layer is as low as 0.2 mmol / g or less. Therefore, the lithium ion which reacts with the surface functional group of the positive electrode layer and is not oxidized by the charging reaction and immobilized on the positive electrode layer is reduced. As a result, in the lithium air battery according to the third aspect, the charge / discharge cycle characteristics are improved.

  In the fourth aspect, for example, in the lithium air battery according to any one of the first to third aspects, the positive electrode layer may include pores having a pore diameter of 5 to 500 nm.

  In the lithium-air battery according to the fourth aspect, since the positive electrode includes pores having a pore diameter in the range of 5 to 500 nm, lithium oxide generated during discharge tends to be small particles, and charge / discharge cycle characteristics are improved.

  In the fifth aspect, for example, in the lithium air battery according to any one of the first to fourth aspects, the carbon contained in the conductive porous body may be conductive carbon black.

  In the lithium air battery according to the fifth aspect, since the carbon contained in the conductive porous body of the positive electrode layer is conductive carbon black, a positive electrode layer having excellent electronic conductivity can be realized.

  In the sixth aspect, for example, in the lithium air battery according to any one of the first to fifth aspects, the non-aqueous lithium ion conductor may include tetraethylene glycol dimethyl ether.

  Tetraethylene glycol dimethyl ether is less susceptible to side reactions than oxygen redox reactions in the positive electrode compared to carbonate solvents. Therefore, in the lithium air battery according to the sixth aspect, the charge / discharge reaction is hardly inhibited by the substance generated by the side reaction, so that the charge / discharge cycle characteristics can be improved.

  In the seventh aspect, for example, in the lithium-air battery according to any one of the first to sixth aspects, the negative electrode layer may contain metallic lithium.

  In the lithium-air battery according to the seventh aspect, since the negative electrode layer contains metallic lithium, a battery with higher energy density can be realized.

  A method for using a lithium air battery according to an eighth aspect of the present disclosure is a method for using a lithium air battery according to any one of the first to seventh aspects, wherein the discharge of the air battery is discharged. The depth is 25% or less.

  In the method of using the lithium-air battery according to the eighth aspect, since the discharge of the air battery is performed within a discharge depth of 25% or less, the lithium oxide produced on the positive electrode can be made into small particles, and further the discharge At the end, most of the voids in the positive electrode layer are not filled with lithium oxide having low electrical conductivity. Therefore, according to the usage method according to the eighth aspect, the charge / discharge cycle characteristics of the lithium-air battery can be improved.

<Embodiment>
Hereinafter, embodiments of the lithium-air battery of the present disclosure will be described in detail. In addition, the following embodiment is an example and this indication is not limited to the following forms.

  The lithium-air battery of the present embodiment includes a negative electrode including a negative electrode layer capable of occluding and releasing lithium ions, and a conductive porous body containing carbon, and the oxygen can be oxidized and reduced using oxygen in the air as a positive electrode active material. A positive electrode including a positive electrode layer, and a nonaqueous lithium ion conductor disposed between the negative electrode and the positive electrode. The positive electrode may further include a positive electrode current collector that collects current from the positive electrode layer. The negative electrode may further include a negative electrode current collector that collects current from the negative electrode layer. The lithium air battery according to the present embodiment may further include a separator disposed between the positive electrode and the negative electrode. A schematic cross-sectional view of one configuration example of such a lithium-air battery is shown in FIG.

  A lithium-air battery 1 illustrated in FIG. 1 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 includes a cylindrical portion 11a that is open on both the upper surface side and the bottom surface side, a bottom portion 11b that is provided so as to close an opening on the bottom surface side of the cylindrical portion 11a, and an opening on the upper surface side of the cylindrical portion 11a. And a lid portion 11c provided so as to close the door. 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 11 b of the battery case 11. The bottom part 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 11b that also serves as the negative electrode current collector and the negative electrode layer 12a. The positive electrode 13 includes a positive electrode layer 13a including a conductive porous body containing carbon, and an air intake hole 15 side of the lid portion 11c of the battery case 11 with respect to the positive electrode layer 13a (in other words, an electrolyte layer with respect to the positive electrode layer 13a). 14 and the positive electrode current collector 13b disposed on the opposite side. Although not shown, the lithium air battery 1 further includes a separator included in the electrolyte layer 14.

The battery reaction in the lithium air battery having the above-described configuration is as follows.
Discharge reaction (when using batteries)
Negative electrode: 2Li → 2Li ⁺ + 2e ⁻ (1)
Positive electrode: 2Li ⁺ + 2e ⁻ + O ₂ → Li ₂ O ₂ (2)
Charging reaction (during battery charging)
Negative electrode: 2Li ⁺ + 2e ⁻ → 2Li (3)
Positive electrode: Li ₂ O ₂ → 2Li ⁺ + 2e ⁻ + O ₂ (4)

  At the time of discharging, as shown in the formulas (1) and (2), electrons and lithium ions are released from the negative electrode, while at the positive electrode, oxygen and lithium ions taken from the outside of the battery simultaneously react with lithium. An oxide is formed. At the time of charging, as shown in equations (3) and (4), lithium ions are taken together with electrons in the negative electrode, and lithium ions and oxygen are released together with electrons in the positive electrode.

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

1. Positive electrode As described above, the positive electrode includes a positive electrode layer, and may further include a positive electrode current collector. Hereinafter, the positive electrode layer and the positive electrode current collector will be described.

(1) Positive electrode layer The positive electrode layer contains a material that allows oxygen in the air to be oxidized and reduced using oxygen in the air as a positive electrode active material. As such a material, the positive electrode layer in the present embodiment includes a conductive porous body containing carbon. The carbon material used as the conductive porous body containing carbon desirably has high electron conductivity. Specifically, carbon materials that are generally used as conductive aids, such as acetylene black and ketjen black, are preferred. Among these carbon materials, it is more preferable to use conductive carbon black such as ketjen black in view of specific surface area and primary particle size. The specific surface area of the carbon material, for example, be a 800~2000m ² / g, it is preferably 1200~1600m ² / g. By setting the specific surface area of the carbon material in such a range, it becomes easy to form a positive electrode layer having a characteristic pore structure described later. The specific surface area here is a value measured by the BET method.

  The positive electrode layer preferably includes pores having a pore diameter of 5 to 500 nm. Here, in the positive electrode layer, a volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less (first pore diameter range) is defined as “first pore volume”, and a pore diameter exceeding 200 nm and 10,000 nm or less (second pore diameter range) is defined. When the volume occupied by the pores is defined as “second pore volume”, the first pore volume is larger than the second pore volume. In other words, the pore volume of the positive electrode layer in the lithium-air battery of the present embodiment has a larger pore diameter in the second pore diameter range when the proportion formed by pores having a smaller pore diameter in the first pore diameter range is larger. In other words, it can be said that the positive electrode layer is a porous body in which many pores having a small pore diameter are present. As described above, lithium oxide is generated in the positive electrode during discharge. This lithium oxide is generated in the void portion of the positive electrode layer, that is, in the pores. Since the positive electrode layer in the present embodiment includes a large number of small pores, most of the lithium oxide generated during discharge becomes small particles. On the other hand, a decomposition reaction of the generated lithium oxide occurs during charging. Although the electrical conductivity of lithium oxide is low, in the lithium-air battery of this embodiment, since lithium oxide is small particles, the decomposition reaction of lithium oxide is likely to occur not only on the surface of the particles but also on the whole. As a result, most of the lithium oxide generated during discharge is decomposed and can contribute to charging. Thereby, the lithium air battery of this embodiment can improve charging / discharging cycling characteristics compared with the conventional lithium air battery.

  In order to further improve the charge / discharge cycle characteristics, it is preferable that the first pore volume is larger and the second pore volume is smaller. For example, by suppressing the second pore volume to 80% or less of the first pore volume, the proportion of lithium oxide that does not contribute to charging can be reduced, so that the charge / discharge cycle characteristics can be further improved. it can.

The 1st pore volume should just be larger than the 2nd pore volume, and the range is not specifically limited. In consideration of securing a higher capacity and improving charge / discharge cycle characteristics, the first pore volume is preferably set to 0.1 to 2.4 cm ³ / g, for example, 1.0 to 2.4 cm. More preferably, it is ³ / g. Further, the range of the second pore volume is not particularly limited, but is set to, for example, 0.1 to 2.2 cm ³ / g in consideration of securing a higher capacity and improving charge / discharge cycle characteristics. Is preferred.

For example, the electrode density of the positive electrode is preferably 0.2 g / cm ³ or more, and more preferably 0.3 g / cm ³ or more. In other words, the positive electrode has such a relatively high electrode density, which means that the positive electrode contains many small pores having a pore size of several nanometers. Therefore, according to the positive electrode having such an electrode density, the charge / discharge cycle characteristics can be improved. Incidentally, when the electrode density is too high, since the lithium oxide gap is too small that can be precipitated during the discharge, the electrode density is preferably for example 0.6 g / cm ³ or less, 0.4 g / cm ³ or less is more preferable. Here, the electrode density of the positive electrode is the density of the portion of the positive electrode where the electrode reaction occurs, and corresponds to the density of the positive electrode layer. That is, when the positive electrode includes a positive electrode current collector, the electrode density of the positive electrode is a density of a portion excluding the positive electrode current collector.

  It is preferable that the positive electrode layer has few surface functional groups (for example, OH groups). This is because when the surface functional group of the positive electrode layer is too much, the charge / discharge cycle characteristics may be deteriorated. Various factors can be considered as the cause of the deterioration of the charge / discharge cycle characteristics due to the surface functional groups of the positive electrode layer. When there are many surface functional groups, the OH groups on the surface react with Li ions to form O-Li. It is considered that the charge / discharge cycle characteristics deteriorate due to the occurrence of side reactions that occur and the O-Li becomes stable and immobilized without being oxidized by the charge reaction. On the other hand, in the case of the positive electrode layer having a small amount of surface functional groups, the amount of Li immobilized on the surface is small and the side reaction is small, so the charge / discharge cycle characteristics are improved. Therefore, the surface functional group amount of the positive electrode layer is preferably 0.5 mmol / g or less, and more preferably 0.2 mmol / g or less.

  Although the positive electrode layer should just contain said electroconductive porous body, it is preferable to further contain the binder which fixes said electroconductive porous body. As a binder, a well-known material can be used as a binder of the positive electrode layer of a lithium air battery, for example, a polyvinylidene fluoride (PVdF), a polytetrafluoroethylene (PTFE), etc. can be mentioned. Although content of the binder in a positive electrode layer is not specifically limited, For example, it is preferable to exist in the range of 1 mass%-40 mass%.

  The thickness of the positive electrode layer is not particularly limited because it varies depending on the use of the lithium-air battery, and can be, for example, in the range of 2 μm to 500 μm, and preferably in the range of 5 μm to 300 μm.

  As a method for forming the positive electrode layer, for example, a paint obtained by dispersing a composition containing the above-described conductive porous body and binder constituting the positive electrode layer in a solvent on a positive electrode current collector described below is used as a doctor blade. The method of apply | coating by the method etc. or the method of shape | molding the said composition with a crimping press etc. can be used.

(2) Positive electrode current collector The positive electrode current collector collects current from the positive electrode layer. Therefore, the material of the positive electrode current collector is not particularly limited as long as it has conductivity, and a known material can be used as the positive electrode current collector of the lithium air battery. Examples of the material of the positive electrode current collector include stainless steel, nickel, aluminum, iron, titanium, and carbon. Examples of the shape of the positive electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Among these, in the present embodiment, the shape of the positive electrode current collector is preferably a mesh shape. This is because the mesh-shaped positive electrode current collector is excellent in current collection efficiency. In this case, usually, a mesh-like positive electrode current collector is disposed inside the positive electrode layer. Furthermore, the lithium-air battery of this embodiment may further include another positive electrode current collector (for example, a foil-shaped current collector) that collects electric charges collected by the mesh-shaped positive electrode current collector. Good. In the present embodiment, a battery case, which will be described later, may have the function of a positive electrode current collector.

  The thickness of the positive electrode current collector can be, for example, in the range of 10 μm to 1000 μm, and preferably in the range of 20 μm to 400 μm.

2. Negative Electrode As described above, the negative electrode includes a negative electrode layer, and may further include a negative electrode current collector. Hereinafter, the negative electrode layer and the negative electrode current collector will be described.

(1) Negative electrode layer The negative electrode layer in this embodiment contains the negative electrode active material which can occlude / release lithium ion at least. Such a negative electrode active material is not particularly limited as long as it is a material containing lithium element. For example, a simple metal (metal lithium), an alloy containing lithium element, an oxide containing lithium element, and Examples thereof include a nitride containing lithium element. Examples of the alloy having a lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide containing a lithium element, lithium titanium oxide etc. can be 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 may contain only the negative electrode active material, or may contain a binder in addition to the negative electrode active material. For example, when the negative electrode active material is in the form of a foil, a negative electrode layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode layer having a negative electrode active material and a binder can be obtained. As a binder, a well-known material can be used as a binder of the negative electrode layer of a lithium air battery, for example, PVdF, PTFE, etc. can be mentioned. Although content of the binder in a negative electrode layer is not specifically limited, For example, it is preferable to exist in the range of 1 mass%-40 mass%. In addition, as a method for forming the negative electrode layer using the powdered negative electrode active material, a doctor blade method, a molding method using a pressure press, or the like can be used as in the above-described method for forming the positive electrode layer.

(2) Negative electrode current collector The negative electrode current collector collects current from the negative electrode layer. The material of the negative electrode current collector is not particularly limited as long as it has conductivity, and any known material can be used as the negative electrode current collector of the lithium-air battery. Examples of the material for 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 (grid) shape. In the present embodiment, a battery case to be described later may have the function of a negative electrode current collector.

3. Separator The lithium-air battery of this embodiment may include a separator disposed between the positive electrode (positive electrode layer) and the negative electrode (negative electrode layer). By disposing the separator between the positive electrode and the negative electrode, a highly safe battery can be obtained. The separator is not particularly limited as long as it has a function of electrically separating the positive electrode layer and the negative electrode layer. For example, porous films such as polyethylene (PE) and polypropylene (PP), PE and PP Examples thereof include porous insulating materials such as resin nonwoven fabrics, glass fiber nonwoven fabrics, and paper nonwoven fabrics.

  The separator preferably has a porosity in the range of 30 to 90%. When the porosity is less than 30%, when the separator holds the electrolyte, it may be difficult for the separator to hold the electrolyte sufficiently. On the other hand, if the porosity exceeds 90%, sufficient separator strength may not be obtained. A more preferable range of the porosity of the separator is 35 to 60%.

4). Electrolyte layer (lithium ion conductor)
The electrolyte layer is a layer that is disposed between the positive electrode (positive electrode layer) and the negative electrode (negative electrode layer) and conducts lithium ions. Therefore, the form of the electrolyte layer is not particularly limited as long as it has lithium ion conductivity (lithium ion conductor), and a solution system typified by an organic solvent system containing a lithium salt as an electrolyte, and Any form of a solid film system represented by a polymer solid electrolyte system containing a lithium salt may be used.

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

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

  The amount of the electrolyte dissolved in the nonaqueous solvent is, for example, 0.5 to 2.5 mol / l. When a solution-based electrolyte layer (non-aqueous electrolyte) is used, as described above, the electrolyte layer can be formed by impregnating and holding the non-aqueous electrolyte in a separator.

  As the non-aqueous solvent, a known non-aqueous solvent can be used as the non-aqueous solvent of the non-aqueous electrolyte of the lithium air battery. Among these, it is particularly preferable to use a chain ether such as tetraethylene glycol dimethyl ether as a solvent. This is because side reactions other than the oxidation-reduction reaction of oxygen in the positive electrode are less likely to occur than in the carbonate-based solvent.

5. Battery Case The battery case of the lithium-air battery of the present embodiment is not particularly limited because it only needs to accommodate the positive electrode, the negative electrode, and the electrolyte layer described above. Therefore, the battery case of the lithium-air battery of the present embodiment is not limited to the battery case 11 shown in FIG. 1, and various battery cases such as a coin type, a flat plate type, a cylindrical type, and a laminate type are used. Can do. The battery case is preferably an open-air battery case, but may be a sealed battery case. Note that the open air battery case has a vent hole through which air can enter and exit, and the air can come into contact with the positive electrode. On the other hand, in the case of a sealed battery case, it is preferable to provide a gas (air) supply pipe and a discharge pipe in the sealed battery case. In this case, the gas to be supplied and discharged is preferably a dry gas, in particular, preferably has a high oxygen concentration, and more preferably pure oxygen (99.99%). In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.

  Next, the preferable usage method of the lithium air battery of this embodiment is demonstrated.

  It is preferable to discharge the lithium air battery of this embodiment within a range of 50% or less of the depth of discharge (DOD). The discharge depth of the lithium-air battery in this embodiment is defined as the capacity at the time of complete discharge when the discharge potential of the positive electrode reaches 2.0 V with respect to the lithium reference potential. It is a ratio. By discharging at a DOD of 50% or less, the lithium oxide produced on the positive electrode can be made smaller particles, and at the end of the discharge, most of the voids in the positive electrode layer are filled with lithium oxide having low electrical conductivity. There is no end to it. Thereby, lithium oxide is decomposed | disassembled efficiently at the time of charge. As a result, according to the usage method of this embodiment, the charge / discharge cycle characteristics of the lithium-air battery of this embodiment can be improved. In order to improve the charge / discharge cycle characteristics, it is more preferable that the discharge of the lithium-air battery is performed within a range of DCD 25% or less.

  Hereinafter, the present disclosure will be described in more detail with reference to examples. Note that the following embodiments are examples, and the present disclosure is not limited to the following embodiments.

Example 1
As a material for forming a conductive porous body containing carbon, ketjen black (manufactured by ketjen black international, “ECP600”) was used. Moreover, PTFE (made by Daikin Industries, Ltd.) was used as a binder. This ketjen black and PTFE binder were kneaded with an ethanol solvent at a mass ratio of 90:10 and rolled by a roll press to prepare an electrode sheet. The obtained electrode sheet was used as a positive electrode (positive electrode layer). In addition, about the obtained electrode sheet | seat, pore diameter distribution, the electrode density, and the surface functional group amount were calculated | required by the below-mentioned method. Further, the first pore volume and the second pore volume were also determined from the obtained pore size distribution. The non-aqueous electrolyte is tetraethylene glycol dimethyl ether (TEGDME, manufactured by Kishida Chemical Co.), which is a non-aqueous solvent, and LiTFSA (lithium bistrifluoromethanesulfonylamide, manufactured by Kishida Chemical Co., Ltd.) is used as the electrolyte to a concentration of 1 mol / L. A dew point −50 ° C. or lower in a dry air atmosphere was used by stirring and mixing overnight. A glass fiber separator was used as the separator. As the negative electrode, metal lithium (Honjo Chemical) was used as a negative electrode layer, and SUS304 mesh (manufactured by Niraco) was attached to the negative electrode layer as a negative electrode current collector. These positive electrode (only the positive electrode layer), separator, non-aqueous electrolyte and negative electrode (negative electrode layer and negative electrode current collector) were arranged as shown in FIG. 1 to produce a lithium-air battery. The manufactured lithium air battery was subjected to a charge / discharge cycle test. Table 1 shows the results of the first pore volume, the second pore volume, the electrode density, and the surface functional group amount of the electrode sheet, and the results of the charge / discharge cycle test of the lithium air battery.

(Example 2)
A lithium air battery was produced in the same manner as in Example 1. Therefore, the pore size distribution, the first pore volume, the second pore volume, the electrode density, and the surface functional group amount of the electrode sheet produced as the positive electrode layer were the same as those of the electrode sheet of Example 1. The manufactured lithium air battery was subjected to a charge / discharge cycle test. Table 1 shows the results of the pore diameter distribution, the first pore volume, the second pore volume, the electrode density and the surface functional group amount of the electrode sheet, and the results of the charge / discharge cycle test of the lithium air battery.

(Example 3)
A lithium air battery was produced in the same manner as in Example 1. Therefore, the pore size distribution, electrode density, and surface functional group amount of the electrode sheet produced as the positive electrode layer were the same as those of the electrode sheet of Example 1. The manufactured lithium air battery was subjected to a charge / discharge cycle test. Table 1 shows the results of the pore diameter distribution, the first pore volume, the second pore volume, the electrode density and the surface functional group amount of the electrode sheet, and the results of the charge / discharge cycle test of the lithium air battery.

(Comparative Example 1)
A lithium-air battery was produced in the same manner as in Example 1, except that MgO-templated porous carbon (manufactured by Toyo Tanso Co., Ltd., “Cnovel P3”) was used as a material for forming a conductive porous body containing carbon. About the electrode sheet produced as a positive electrode layer, pore diameter distribution, electrode density, and surface functional group amount were measured by the method described later. About the produced lithium air battery, the charge / discharge cycle test was implemented by the method similar to Example 1. FIG. Table 1 shows the results of the pore size distribution, electrode density and surface functional group amount of the electrode sheet, and the results of the charge / discharge cycle test.

  About the measurement method of the pore diameter distribution, the first pore volume, the second pore volume, the electrode density and the surface functional group amount of the electrode sheet, and the test method of the charge / discharge cycle test, which were carried out in Examples and Comparative Examples, This will be specifically described below.

(Pore size distribution, first pore volume and second pore volume)
The first pore volume and the second pore volume are obtained by performing nitrogen adsorption measurement and mercury porosimetry measurement on the obtained electrode sheet, and using the BJH method from the obtained adsorption isotherm, the pore volume together with the pore diameter distribution. Asked.

(Electrode density)
The volume was measured from the thickness and area of the obtained electrode sheet, the mass was further measured, and the electrode density was calculated.

(Surface functional group amount)
The amount of surface functional groups is described in the literature Boehm, H .; P. , Advances in Catalysis, 16 179 (1966).

(Charge / discharge cycle test)
For the lithium air batteries of Example 1 and Comparative Example 1, after being held in an oxygen atmosphere for 20 minutes or more, the current density was 0.4 mA / cm ² , the discharge time was 3.5 hours (assuming DOD of 25%), and charge / discharge A cycle test was conducted. About the lithium air battery of Example 2, after hold | maintaining under oxygen atmosphere for 20 minutes or more, it was set as the current density of 0.4 mA / cm < ² >, discharge time 7 hours (DOD50% is assumed), and the charge / discharge cycle test was done. About the lithium air battery of Example 3, after hold | maintaining in oxygen atmosphere for 20 minutes or more, a current density was set to 0.4 mA / cm < ² >, the cut voltage at the time of discharge was set to 2.0V (DOD100%), and the charge / discharge cycle test was done. It was.

  As can be seen from the above results, the lithium air battery of Comparative Example 1 has a large capacity deterioration at the 10th cycle, whereas the lithium air battery of Example 1 shows almost no capacity deterioration even at the 10th cycle. Absent. From this result, it was found that the lithium-air battery of Example 1 having the positive electrode layer having the first pore volume larger than the second pore volume has good cycle characteristics.

  Further, in Examples 2 and 3 in which the same lithium-air battery as that in Example 1 was used and discharge was performed at a DOD different from that in Example 1, the initial capacity was larger than that of the lithium-air battery in Example 1. However, the capacity deteriorated as the cycle progressed, and became a value lower than that of Example 1 after 10 cycles. From this result, it was found that when the lithium air battery is used, the cycle characteristics can be improved by discharging at a DOD of 25% or less.

  The lithium-air battery of the present disclosure has good charge / discharge cycle characteristics while securing a high capacity. 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 Cover part 12 Negative electrode 12a Negative electrode layer 13 Positive electrode 13a Positive electrode layer 13b Positive electrode collector 14 Electrolyte layer (non-aqueous lithium ion conductor)
15 Air intake hole

Claims (8)

A negative electrode including a negative electrode layer capable of occluding and releasing lithium ions;
A positive electrode including a conductive porous body containing carbon, and a positive electrode layer capable of oxidation-reduction of oxygen using oxygen in the air as a positive electrode active material;
A non-aqueous lithium ion conductor disposed between the negative electrode and the positive electrode;
A lithium-air battery comprising:
In the positive electrode layer, the first pore volume occupied by pores having a pore diameter of 1 nm or more and 200 nm or less is larger than the second pore volume occupied by pores having a pore diameter of more than 200 nm and 10000 nm or less,
Lithium air battery. The electrode density of the positive electrode is 0.2 to 0.4 g / cm ³ .
The lithium air battery according to claim 1. The amount of surface functional groups of the positive electrode layer is 0.2 mmol / g or less,
The lithium air battery according to claim 1 or 2. The positive electrode layer includes pores having a pore size of 5 to 500 nm,
The lithium air battery according to claim 1. The carbon contained in the conductive porous body is conductive carbon black.
The lithium air battery of any one of Claims 1-4. The non-aqueous lithium ion conductor comprises tetraethylene glycol dimethyl ether;
The lithium air battery of any one of Claims 1-5. The negative electrode layer contains metallic lithium;
The lithium air battery according to any one of claims 1 to 6. It is a usage method of the lithium air battery of any one of Claims 1-7,
The discharge of the air battery is performed within a range of a discharge depth of 25% or less.
How to use lithium air battery.

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