JP2016027563A - Solid electrolyte, lithium battery and lithium air battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte applicable to a battery using Li metal as an electrode active material and to provide a lithium battery using the same.SOLUTION: There is provided a solid electrolyte which contains Li, La and Zr and has a garnet-type structure, wherein the absorption coefficient measured at a wavelength range of 380 nm or more is 6.6 mmor less. There are provided a lithium battery and a lithium air battery having a positive electrode 2, a negative electrode 3 and a solid electrolyte 4.SELECTED DRAWING: None

Description

  The present invention relates to a solid electrolyte, a lithium battery using the solid electrolyte, and a lithium air battery.

  With the spread of notebook computers, mobile phones, digital cameras, etc., the demand for secondary batteries for driving these small electronic devices is increasing. Since these electronic devices can be increased in capacity, lithium batteries (particularly lithium ion secondary batteries) are being used.

  In lithium batteries currently on the market, an electrolytic solution containing a flammable organic solvent is used as an electrolyte. In this configuration, it is necessary to install a safety device that suppresses the temperature rise at the time of a short circuit and to improve the structure and material to prevent the short circuit.

  On the other hand, a lithium battery in which the electrolyte is changed to a solid electrolyte and the battery is completely solidified is being studied. The all solid-state lithium battery does not use a flammable organic solvent in the battery, so that the safety device can be simplified, and it is considered that the manufacturing cost and productivity are excellent.

  Li-La-Zr-O-based solid electrolytes are known as solid electrolytes used for all solid-state lithium batteries. For example, Patent Document 1 discloses a solid electrolyte that has Li, La, Zr, Al, Si, and O, has a garnet-type structure, and is a sintered body. Patent Document 2 discloses a solid electrolyte having Li, La, Zr, O, a specific composition, and a garnet-related structure. Patent Document 3 discloses a solid electrolyte having Li, La, Zr, Al, O, a specific composition, and a garnet structure or a garnet-related structure.

JP 2012-18792 A JP 2011-195373 A JP 2011-73963 A

  However, the conventional solid electrolyte has a problem in that a short circuit occurs when an electrode active material made of Li metal is attached to the surface of the solid electrolyte for ion conduction. That is, the conventional solid electrolyte has a problem that it cannot be applied to a battery using Li metal as an electrode active material.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the solid electrolyte applicable to the battery using the negative electrode active material which consists of Li metal, a lithium battery using the same, and a lithium air battery. .

In order to solve the above-mentioned problems, the present inventors have made studies and completed the present invention.
The solid electrolyte of the present invention is a solid electrolyte containing Li, La, Zr and having a garnet structure, and having an extinction coefficient measured in a wavelength range of 380 nm or more of 6.6 mm ⁻¹ or less. .

Since the solid electrolyte of the present invention has an extinction coefficient of 6.6 mm ⁻¹ or less, the ionic species responsible for conductivity exemplified by Li ions has a structure that regulates Li precipitation in the dense portion inside the solid electrolyte. ing. For this reason, it is suppressed that this ionic species crystallizes in the solid electrolyte to form dendrites. As a result, the solid electrolyte of the present invention does not cause a short circuit due to dendrites when a battery is formed.

The lithium battery of the present invention includes a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a negative electrode active material, and a positive electrode active material layer and a negative electrode active material layer. It has the solid electrolyte of any one of Claims 1-4 arrange | positioned, It is characterized by the above-mentioned.
The lithium battery of the present invention has the above-described solid electrolyte, and exhibits the effects obtained by the above-described solid electrolyte.
The lithium-air battery of the present invention includes a positive electrode having a positive electrode material having a means for introducing air using oxygen as a positive electrode active material and having a catalyst for reducing oxygen, and a negative electrode having a negative electrode material capable of occluding and releasing lithium. And a solid electrolyte layer containing the solid electrolyte according to any one of claims 1 to 4 interposed between the positive electrode and the negative electrode.
The lithium-air battery of the present invention is obtained by applying the above-described solid electrolyte to a lithium-air battery, and exhibits the effects obtained by the above-described solid electrolyte.

It is a schematic sectional drawing which shows the structure of the lithium battery of embodiment. It is a schematic sectional drawing which shows the structure of the lithium battery of another form. It is a schematic sectional drawing which shows the structure of the lithium air battery of embodiment. It is a diagram which shows the measurement result of the transmittance | permeability of the solid electrolyte of the sample 1 and the sample 11. FIG. 4 is an enlarged photograph showing the light transmittance of the solid electrolyte of Sample 1. FIG. 4 is an enlarged photograph showing the light transmittance of the solid electrolyte of Sample 10. 4 is an enlarged photograph showing light transmittance of a solid electrolyte of Sample 11. 3 is an enlarged photograph of a cross section of a solid electrolyte of Sample 11. It is a schematic sectional drawing which shows the structure of a test cell. 2 is a diagram showing the potential of an electrode of a test cell of sample 1. FIG. 2 is a diagram showing the potential of an electrode of a test cell of sample 10. FIG. 2 is a diagram showing the potential of an electrode of a test cell of sample 11. FIG.

  Hereinafter, the present invention will be described using embodiments. As an embodiment of the present invention, a solid electrolyte, a lithium battery using the solid electrolyte, and a lithium air battery will be described.

[Solid electrolyte]
The solid electrolyte of the present invention is a solid electrolyte containing Li, La, and Zr and having a garnet-type structure. With this configuration, it can function as a solid electrolyte responsible for ion conduction.

In the solid electrolyte of the present invention, the extinction coefficient measured in the wavelength range of 380 nm or more is 6.6 mm ⁻¹ or less. When the extinction coefficient is 6.6 mm ⁻¹ or less, a short circuit is suppressed when a battery is formed. When the extinction coefficient of the solid electrolyte is larger than 6.6 mm ⁻¹ , ionic conduction variation is likely to occur due to deterioration of crystallinity or increase in the amount of impurities, which causes a short circuit. The smaller the extinction coefficient, the better, and more preferably 1.7 mm ⁻¹ or less.

  The extinction coefficient is obtained from the transmittance of the solid electrolyte. Specifically, the transmittance of light having a wavelength range of 380 nm or more is measured with a transmittance meter (commercially available product) with respect to a solid electrolyte having a thickness of 0.8 mm. The transmittance is (transmitted light intensity) / (incident light intensity). When the surface reflection is ignored, the transmittance satisfies the relationship of transmittance T = exp (−α · x). Α: extinction coefficient, x: path length (solid electrolyte thickness). From the measured transmittance T and this equation, the extinction coefficient (α) can be obtained.

  When the transmittance is measured at a wavelength in the wavelength range of 380 nm or more and the transmittance fluctuates as shown in FIG. 4, the lower limit value of the transmittance within the measurement range is set as the transmittance of the solid electrolyte. be able to.

A light beam having a wavelength range of 380 nm or more used for measuring transmittance shows visible light. The upper limit of the light beam in the wavelength range of 380 nm or more is not limited, but can be in the visible light region (380 nm to 780 nm).
A solid electrolyte having an extinction coefficient of 6.6 mm ⁻¹ or less corresponds to a transmittance of 0.5% or more (solid electrolyte thickness: 0.8 mm) measured by a transmittance meter. A solid electrolyte having an extinction coefficient of 1.7 mm ⁻¹ or less corresponds to a transmittance of 25% or more (solid electrolyte thickness: 0.8 mm) measured by a transmittance meter.
The extinction coefficient of the solid electrolyte can be determined visually. For example, when the extinction coefficient is small in the visible light region of 500 nm or more (when the solid electrolyte is a transparent body), the solid electrolyte becomes yellow to orange.

  The extinction coefficient of the solid electrolyte increases when the solid electrolyte has pores therein. That is, when the solid electrolyte becomes a porous body, the extinction coefficient also increases. When the solid electrolyte becomes a porous body, ion species responsible for conductivity enter and crystallize into the pores of the solid electrolyte. The crystallized metal forms dendrites, causing a short circuit of the battery. This is also preferable because the dendrite is not formed in the solid electrolyte as the extinction coefficient decreases.

  The transmittance is preferably measured under conditions of a solid electrolyte thickness: 0.8 mm, a wavelength range of 380 nm or more, and a measurement range φ1 mm. When the transmittance measured under the condition of the measurement range φ1 mm is 0.5% or more, the extinction coefficient becomes 6.6 or less, and the solid electrolyte of the present invention can exhibit the above effect.

  The measurement of the transmittance under the condition of the measurement range φ1 mm described above can be performed at any point of the solid electrolyte. In other words, the transmittance of the solid electrolyte of the present invention is preferably 0.5% or more at any measurement point when the transmittance is measured at any point of the solid electrolyte under the condition of a measurement range φ1 mm.

  The solid electrolyte preferably has less than 0.5% impurities. Impurities contained in the solid electrolyte contribute to the formation and growth of dendrites. By reducing this impurity to less than 0.5%, generation (growth) of dendrite is suppressed. The smaller the impurity content, the better. If the impurity content exceeds 0.5%, dendrites are generated and grown. The content ratio of the impurity is a ratio (mass%) of the mass of the impurity when the mass of the solid electrolyte is 100%. The impurity in this embodiment is a compound other than a compound functioning as a solid electrolyte (a compound corresponding to a crystal grain in FIG. 8 described later), and includes not only inevitable impurities but also a compound having a crystal system different from that of the solid electrolyte. .

Here, as the proportion of impurities contained in the solid electrolyte increases, the extinction coefficient also increases. That is, the extinction coefficient is also affected by the content ratio of impurities in the solid electrolyte.
The solid electrolyte preferably has an extinction coefficient of 6.6 or less (transmittance of 0.5% or more) and an impurity content of less than 0.5%.

  The solid electrolyte preferably has a relative density of 99.5% or more. When the relative density is 99.5% or more, pores contributing to the formation of dendrites are not included in the solid electrolyte. Further, even if pores exist in the solid electrolyte, they become independent closed pores, and dendrite growth is restricted. That is, when the relative density is 99.5% or more, the generation of dendrites is reliably suppressed. When the relative density is as small as less than 99.5%, pores are formed in the solid electrolyte, and generation (growth) of dendrites cannot be suppressed.

  The relative density of the solid electrolyte is determined by (mass of solid electrolyte) / (mass of solid electrolyte when no impurities are included). The relative density of the solid electrolyte may be replaced with a value obtained by “100− (content ratio of the above-mentioned impurities)”.

  The solid electrolyte is preferably compressed by a hot isostatic pressing method. Hot isostatic pressing (HIP) does not cause a change in the composition of the solid electrolyte when the solid electrolyte is compressed to increase the relative density. More specifically, Li contained in the solid electrolyte moves in Li when heated, and escapes from the solid electrolyte. In heating without pressure (pressureless firing), Li is released from the solid electrolyte, the composition of the solid electrolyte changes, and the solid electrolyte cannot bear ionic conduction.

The compression by the hot isostatic pressing method is preferably performed so that the extinction coefficient is 6.6 or less (transmittance is 0.5% or more), and the relative density is 99.5% or more. It is more preferable. Such compression not only reduces the number of pores inside the solid electrolyte, but also eliminates continuous pores. When continuous pores are present, when used in a battery, the electrodes are electrically connected by the pores, and dendrites are generated in the continuous pores.
The compression by the hot isostatic pressing method can be performed using a commercially available HIP apparatus.

The composition of the solid electrolyte of the present invention is not limited as long as it contains Li, La, and Zr. The composition may be the same as that of a conventionally known solid electrolyte.
In the solid electrolyte of the present invention, the proportions of Li, La, and Zr are not particularly limited as long as the solid electrolyte having a garnet structure can be obtained. Usually, Li: La: Zr = 7: 3: 2 on a molar basis (molar ratio). This ratio includes a value that varies within a range in which a garnet-type structure can be formed. That is, Li: La: Zr = 7: 2.8-3.2: 1.8-2.2 is included. The proportions of Li, La, and Zr may be blended proportions of each element at the time of raw material preparation in the manufacturing method described later.

  The solid electrolyte of the present invention is preferably a Li—La—Zr—O-based oxide. The proportion of O contained in the solid electrolyte is basically determined so as to satisfy the principle of electrical neutrality in relation to each metal ion. Depending on the synthesis method, oxygen deficiency or oxygen excess may occur.

The solid electrolyte of the present invention may further contain another conventionally known element. By containing this other element, it is possible to adjust (improve) characteristics such as ionic conductivity of the solid electrolyte. Examples of other elements include elements such as Al, Ta, Nb, and Si.
The solid electrolyte of the present invention has a garnet structure. In the present invention, the garnet structure includes not only a garnet structure but also a garnet-like structure.

  The garnet structure can be identified by confirming the peak position of X-ray diffraction (XRD). For example, when XRD measurement using CuKα rays is performed, peaks are confirmed at 2θ = 17 °, 26 °, 28 °, 31 °, 34 °, 38 °, 43 °, 51 °, 52 °, and 53 °. it can.

(Production method)
If the solid electrolyte of this invention has said characteristic, the manufacturing method will not be limited. For example, a manufacturing process including a step of preparing a mixture of raw materials containing Li, La, and Zr (and another element), a step of firing (sintering) the mixture, and a step of compressing by a hot isostatic pressing method. I can give you a way.

The mixture of raw materials is a mixture of compounds containing one or more of Li, La, Zr and other contained elements. Examples of the compound containing Li (Li source) include compounds such as LiOH.H ₂ O, Li ₂ CO ₃ , CH ₃ COOLi, and LiNO ₃ . Examples of the compound containing La (La source) include La (OH) ₃ and La ₂ O ₃ . Examples of the compound containing Zr (Zr source) include ZrO ₂ .

  In the production of the solid electrolyte of the present invention, the composition of the produced solid electrolyte can be determined by adjusting the ratio of each element contained in these compounds (metal sources). Each raw material may be appropriately adjusted in consideration of the influence of volatilization (particularly, volatilization of Li during firing).

  The mixture of raw materials is preferably stirred so that the powders of these compounds (metal sources) are sufficiently mixed, and then compression molded into a predetermined shape. Moreover, it may be kneaded in a solvent for the purpose of improving dispersion, and the Li source, La source and Zr source to be used are not limited to powder but may be in a liquid state. When these solvents and liquid raw materials are used, it is necessary to dry them to obtain a mixture on the powder. A solid electrolyte having a desired shape can be obtained by compression molding a mixture of raw materials. Moreover, a sintered body having a high relative density can be obtained.

  The step of firing the mixture generates a solid electrolyte by firing (sintering, solid phase reaction) the mixture of raw materials. The firing conditions are not limited as long as the solid electrolyte can be generated.

  For example, the heating temperature at the time of baking should just be the temperature beyond the crystallization temperature of a solid electrolyte, for example, the range of 1200 to 1250 degreeC can be illustrated. The atmosphere during firing is not particularly limited, but is preferably an oxygen-containing atmosphere. In this case, oxygen in the oxygen-containing atmosphere becomes an O source constituting the solid electrolyte (composite oxide). The oxygen-containing atmosphere is obtained by, for example, a mixed gas of inert gas and oxygen gas, or air (air).

  The step of compressing by hot isostatic pressing is as described above. The method of compressing by hot isostatic pressing can be performed using a HIP device. The compression conditions in the HIP apparatus are not limited as long as the relative density of the solid electrolyte can be 99% or more.

  The solid electrolyte of the present invention is preferably subjected to a step of forming into a predetermined shape for assembling to a lithium battery. The method for forming the solid electrolyte is not limited, and examples thereof include cutting and polishing.

  When forming a solid electrolyte, it is preferable to process so that a defective location may be removed. The defective portion can be a portion having a low transmittance or relative density. By removing this defective portion, a solid electrolyte free from the defective portion is obtained. That is, it is possible to obtain a solid electrolyte excellent in ion conductivity in which generation of dendrites is suppressed.

[Lithium battery]
The lithium battery 1 of this embodiment is the lithium battery 1 shown in the cross-sectional view of FIG. 1, and includes a positive electrode 2, a negative electrode 3, and a solid electrolyte layer 4 housed in a battery case 5.

(Positive electrode)
The positive electrode 2 includes a positive electrode current collector 20 and a positive electrode active material layer 21 including a positive electrode active material disposed on the surface of the positive electrode current collector 20. The positive electrode active material layer 21 is a layer containing at least a positive electrode active material, and may contain a conductive material, a solid electrolyte, and a binder as necessary.
The positive electrode active material layer 21 is formed by applying a positive electrode mixture obtained by mixing a positive electrode active material, a conductive material, and a binder to the surface of the positive electrode current collector 20.

  The positive electrode active material of the positive electrode 2 is an active material capable of occluding and releasing lithium. As the positive electrode active material, a positive electrode active material of a conventional lithium battery (lithium ion secondary battery) can be selected. As the positive electrode active material, for example, various oxides, sulfides, lithium-containing oxides, conductive polymers, and the like can be used. The positive electrode active material is preferably a lithium-transition metal composite oxide.

Lithium - transition metal composite oxide is preferably a lithium metal compound polyanion structure ^{_{(Li α M 0 β X η}} O 4-γ Z γ). (Note that M ⁰ : one or more selected from Mn, Co, Ni, Fe, Cu, Cr, Mg, Ca, Zn, Ti, one or more selected from X: P, As, Si, Mo, Ge, Z: One or more selected from Al, Mg, Ca, Zn and Ti can be optionally contained, 0 ≦ α ≦ 2.0, 0 ≦ β ≦ 1.5, 1 ≦ η ≦ 1.5, 0 ≦ γ ≦ 1.5)

The lithium-transition metal composite oxide is preferably a lithium-transition metal composite oxide having an olivine structure. Examples of the olivine-structured lithium-transition metal composite oxide include LiFePO ₄ and LiFe _x Mn _1-x PO ₄ (0 ≦ x <1).

  The positive electrode active material layer 21 may further contain a solid electrolyte. By adding the solid electrolyte, the Li ion conductivity of the positive electrode active material layer 21 can be improved. Examples of solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes.

  The conductive material of the positive electrode 2 ensures the electrical conductivity of the positive electrode 2. Examples of the conductive material include, but are not limited to, graphite fine particles, acetylene black, ketjen black, carbon black such as carbon nanofiber, and amorphous carbon fine particles such as needle coke.

  The binder of the positive electrode 2 binds the positive electrode active material particles and the conductive material. As the binder, for example, PVDF, EPDM, SBR, NBR, fluororubber and the like can be used, but are not limited thereto.

  As the solvent for the positive electrode 2, an organic solvent that normally dissolves the binder is used. Examples thereof include, but are not limited to, NMP, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. In some cases, a positive electrode active material is slurried with PTFE or the like by adding a dispersant, a thickener, or the like to water.

  As the positive electrode current collector 20, for example, a material obtained by processing a metal such as aluminum or stainless steel, for example, a foil processed into a plate shape, a net, a punched metal, a foam metal, or the like can be used, but is not limited thereto.

(Negative electrode)
The negative electrode 3 is made of lithium (metal Li). The negative electrode 3 made of metal Li is disposed in contact with the negative electrode current collector 30. Note that the negative electrode 3 made of this metal Li corresponds to a negative electrode active material and a negative electrode active material layer 31 in another form described later. That is, the metal Li corresponds to the negative electrode active material, and corresponds to an aspect in which the negative electrode active material layer 31 is formed using only this negative electrode active material.
The negative electrode 3 made of metal Li is directly attached to the surface of the solid electrolyte 4 in an inert gas atmosphere, or is deposited on the surface that becomes the negative electrode 3 through the solid electrolyte 4, or metal Li is deposited on the surface of the solid electrolyte 4. It is formed by the method.

  As the negative electrode current collector 30, a current collector used in a conventional battery can be used, which is obtained by processing a metal such as copper, stainless steel, titanium, or nickel, for example, a foil processed into a plate, a net, or a punched Metal, foam metal, and the like can be used, but are not limited thereto.

(Solid electrolyte layer)
The solid electrolyte layer 4 has the above-described solid electrolyte of the present invention disposed between the positive electrode active material layer 21 and the negative electrode active material layer 31. The solid electrolyte layer 4 contains the above-described solid electrolyte, and may be composed of only the above-described solid electrolyte or may further contain another solid electrolyte.

(Battery case)
The battery case 5 used for the lithium battery of this embodiment is not limited, and a battery case of a conventional lithium battery can be used. The shape of the lithium battery (battery case) is not limited, and examples thereof include a coin type, a laminate type, a cylindrical type, and a square type.

  Examples of the battery case 5 include a battery case made of a metal such as SUS or a resin molded body. Moreover, as a battery case, the laminated exterior body formed from the laminated resin film which contains a plastic resin layer / metal foil / plastic resin layer in this order can be used.

(Other configurations of lithium battery)
The lithium battery 1 of this embodiment may be either a primary battery or a secondary battery. A secondary battery is preferred because it can be repeatedly charged and discharged.

  Moreover, the manufacturing method of a lithium battery will not be limited if it can manufacture the above-mentioned lithium battery, The method similar to the manufacturing method of a general lithium battery can be used. For example, a power generation element is manufactured by sequentially pressing a material constituting the positive electrode active material layer, a material constituting the solid electrolyte layer, and a material constituting the negative electrode active material layer, and the power generation element is placed inside the battery case. Examples of the method include housing and sealing the battery case by a method such as caulking.

[Another form of lithium battery]
In the lithium battery of the above form, the negative electrode 3 is made of metal Li, but the negative electrode can have the same configuration as a conventional lithium ion battery. The configuration of the lithium battery 1 of this embodiment is shown in a sectional view in FIG.
That is, the negative electrode 3 ′ includes a negative electrode current collector 30 and a negative electrode active material layer 31 including a negative electrode active material disposed on the surface of the negative electrode current collector 30. The negative electrode active material layer 31 is a layer containing at least a negative electrode active material, and may contain a conductive material, a solid electrolyte, and a binder as necessary.

Similarly to the positive electrode active material layer 21, the negative electrode active material layer 31 is formed by applying a negative electrode mixture obtained by mixing a negative electrode active material and a binder to the surface of the negative electrode current collector 30.
The negative electrode active material of the negative electrode 3 ′ is an active material capable of occluding and releasing lithium. As the negative electrode active material, a conventional negative electrode active material can be used. A negative electrode active material containing at least one element of Li, Sn, Si, Sb, Ge, and C can be given. Among these negative electrode active materials, C is preferably a carbon material capable of occluding and desorbing electrolyte ions of a lithium ion secondary battery (having Li storage ability), and more preferably amorphous coated natural graphite. preferable.

  Of these negative electrode active materials, Sn, Sb, and Ge are alloy materials that have a large volume change. These negative electrode active materials may form an alloy with another metal such as Ti—Si, Ag—Sn, Sn—Sb, Ag—Ge, Cu—Sn, and Ni—Sn.

  The negative electrode active material layer 31 may further contain a solid electrolyte. By adding the solid electrolyte, the Li ion conductivity of the negative electrode active material layer 31 can be improved. Examples of solid electrolytes include oxide solid electrolytes and sulfide solid electrolytes.

  As the conductive material of the negative electrode 3 ′, a carbon material, metal powder, conductive polymer, or the like can be used. From the viewpoint of conductivity and stability, it is preferable to use a carbon material such as acetylene black, ketjen black, or carbon black.

As the binder of the negative electrode 3 ′, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluororesin copolymer (tetrafluoroethylene / hexafluoropropylene copolymer) SBR, acrylic rubber, Fluorine rubber, polyvinyl alcohol (PVA), styrene / maleic acid resin, polyacrylate, carboxymethyl cellulose (CMC) and the like can be mentioned.
Examples of the solvent for the negative electrode 3 ′ include organic solvents such as N-methyl-2-pyrrolidone (NMP), water, and the like.
The negative electrode current collector 30 can be the same as that described above.

[Lithium air battery]
The lithium-air battery 7 of this embodiment is a lithium-air battery shown in the cross-sectional view of FIG. 3, and includes a positive electrode 72, a negative electrode 73, and a solid electrolyte layer 74 housed in a battery case 75.
(Positive electrode)
The positive electrode 72 includes a positive electrode material 720 that includes air introduction means for proceeding a battery reaction using oxygen as an active material, and includes a catalyst 721 that reduces oxygen. The positive electrode 72 includes a portion made of a positive electrode material 720 including a catalyst 721 and a positive electrode current collector (not shown). The positive electrode material 720 includes a solid electrolyte and a conductive material as necessary. The positive electrode material 720 includes a hole through which air can be introduced. A catalyst 721 and a conductive material are employed on the inner surface of the hole as necessary.

The catalyst 721 is a catalyst that promotes the reaction of oxygen, which is a positive electrode active material, in the positive electrode 72. The positive electrode active material uses oxygen in the air. The catalyst 721 is one or two selected from the group consisting of silver, platinum, iridium oxide, ruthenium oxide, manganese oxide, cobalt oxide, nickel oxide, iron oxide, copper oxide, and metal phthalocyanines. The above can be illustrated.
The catalyst 721 is integrally formed on the surface of the positive electrode material 720 or the solid electrolyte 74 by a method such as sputtering.

The positive electrode current collector is electrically connected to the catalyst 721. The positive electrode current collector has only to have electrical conductivity. The positive electrode 72 needs a means for introducing air into the positive electrode material 720, and the positive electrode current collector is desirably permeable to oxygen (having a structure capable of transmitting oxygen). For example, the positive electrode current collector is preferably a porous material composed of a metal such as stainless steel, nickel, aluminum, or copper, or a net / punched metal. Moreover, when using a porous material etc., it is desirable to employ | adopt the form with which the hole was filled with the electrically conductive material, the catalyst, etc.
The positive electrode current collector is electrically connected to the positive electrode terminal of the air battery 7. The positive electrode current collector may also serve as a positive electrode terminal or a conductive path (conductive wire) that electrically connects the catalyst 721 and the positive electrode terminal.

The positive electrode material 720 is preferably formed using a solid electrolyte as a base material. With this configuration, the positive electrode material 720 can hold the catalyst 721. Moreover, the positive electrode 72 and the solid electrolyte layer 74 can be joined. At this time, the positive electrode material 720 includes a hole into which air can be introduced.
As the solid electrolyte, the above solid electrolyte can be used.

  The conductive material is not particularly limited as long as it has conductivity. The conductive material is used as necessary. The conductive material is desirably a material having necessary stability under the atmosphere in the battery. For example, it is preferable to use a metal or alloy having high oxidation resistance. Here, the metal or alloy having high oxidation resistance is preferably silver, palladium, gold, platinum, aluminum, nickel or the like if it is specifically a metal. If it is an alloy, it is preferable that it is an alloy which consists of 2 or more types of metals chosen from silver, palladium, gold, platinum, copper, aluminum, and nickel. These oxides are also desirable.

(Negative electrode)
The negative electrode 73 includes a negative electrode material 730 capable of inserting and extracting lithium. The negative electrode 73 includes a negative electrode material 730 including a negative electrode active material and a negative electrode current collector 731. The negative electrode material 730 includes a solid electrolyte and a conductive material as necessary.

As the negative electrode current collector 731, for example, copper, nickel, or the like can be formed into a net, punched metal, foam metal, plate shape, foil shape, or the like. A battery casing can also be used as the negative electrode current collector.
The negative electrode current collector 731 is electrically connected to the negative electrode terminal of the air battery 7. The negative electrode current collector 731 may also serve as a negative electrode terminal or a conductive path (conductive wire) that electrically connects the catalyst 721 and the negative electrode terminal.

  Negative electrode active materials include metallic lithium, lithium alloys, metal materials that can store and release lithium, and alloy materials that can store and release lithium (not only alloys consisting of metals but also alloys of metals and metalloids). The structure consists of a solid solution, a eutectic (eutectic mixture), an intermetallic compound or a compound in which two or more of them coexist), and a compound capable of inserting and extracting lithium. One or more materials selected from the group.

Metal elements and metalloid elements that can constitute metal materials and alloy materials include tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), and antimony (Sb). ), Bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y ) And hafnium (Hf). Examples of these alloy materials or compounds include those represented by the chemical formula Ma _f Mb _g Li _h or the chemical formula Ma _s Mc _t Md _u . In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of non-metallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. Further, f> 0, g ≧ 0, h ≧ 0, s> 0, t> 0, u ≧ 0.

  In particular, the negative electrode material 730 is preferably a simple substance, alloy or compound of a group 4B metal element or metalloid element in the short-period type periodic table, particularly preferably silicon (Si) or tin (Sn), or an alloy thereof. A compound. These may be crystalline or amorphous.

Examples of the material capable of inserting and extracting lithium further include oxides, sulfides, and other metal compounds such as lithium nitrides such as LiN ₃ . Examples of the oxide include MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS. In addition, examples of the oxide that has a relatively low potential and can occlude and release lithium include iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, and tin oxide. Examples of the sulfide include NiS and MoS.

As the solid electrolyte contained in the negative electrode material 730, the above solid electrolyte can be used.
The conductive material is not limited, and the conductive material used as the conductive material in the positive electrode 720 can be used. The conductive material is used as necessary.

(Solid electrolyte layer)
The solid electrolyte layer 74 is interposed between the positive electrode 72 and the negative electrode 73, and has the solid electrolyte layer 74 containing the above-described solid electrolyte. The solid electrolyte layer 74 contains the above-described solid electrolyte, and may be composed of only the above-described solid electrolyte or may further contain another solid electrolyte.

(Battery case)
The battery case 75 is not limited, and a battery case of a conventional air battery can be used.
Examples of the battery case 75 include a battery case made of a metal such as SUS or a resin molded body. Moreover, as a battery case, the laminated exterior body formed from the laminated resin film which contains a plastic resin layer / metal foil / plastic resin layer in this order can be used.

The laminate outer package 75 of this embodiment is formed by combining a positive side laminate film 750 provided with holes for introducing oxygen into the catalyst 721 and a negative side laminate film 751 provided with no holes. The hole of the positive electrode side laminate film 750 is sealed with a sealing film 752 from the outside and the inside.
The holes in the positive laminate film 750 are opened so that the catalyst 721 is completely exposed.
Although not shown, the laminate outer package 75 has a conductive path (conductive wire) passing through the positive electrode 72 and the negative electrode 73 and the electrode terminal.

Hereinafter, the present invention will be described using examples.
As an example of the present invention, a solid electrolyte and a cell using the same were manufactured.
[Example]
(Solid electrolyte)
Li ₂ CO ₃ was prepared as a Li source, La ₂ O ₃ was prepared as a La source, and ZrO ₂ was prepared as a Zr source. Note that La ₂ O ₃ used was dried at 1000 ° C. for 1 h.

Each prepared compound was weighed so as to have a composition ratio of Li _7.7 La ₃ Zr ₂ O _{12 with} an excess of 10% of Li _7.7 La ₃ Zr ₂ O ₁₂ , pulverized and mixed, uniaxially pressed, hydrostatically pressed and pelletized A molded body was obtained.

The pellet-shaped molded body was calcined at 900 ° C. for 5 hours using a zirconia crucible in a firing furnace, then pulverized and mixed, pressure-molded, and hydrostatically pressurized, and then again calcined at 950 ° C. for 12 hours. Went. In addition, when pulverizing and mixing the pellets after calcination, γ-Al ₂ O ₃ was added at a predetermined ratio as an Al source, and pressure molding and hydrostatic pressing were performed. The Al source was added at a weight equivalent to 1.0 wt% when the weight of the pellets after calcination was 100 wt%.
Thereafter, firing (main firing) was performed under the conditions of 1180 ° C. and 36 h using the Powder Bed method.

The fired body was subjected to HIP treatment in order to further increase its denseness. The HIP treatment was performed in an Ar atmosphere under the conditions of a temperature of 1160 ° C., a holding time of 2 hrs, and a pressure of 12749 N (1300 kgf).
The sample after the HIP treatment was dry-polished (ground) until it became a transparent body. The transparent body indicates a state in which no dust is seen (having translucency) when the sample is visually observed. Samples with dust contain impurities and pores. A transparent body having translucency is a high-purity and high-density sample.

Thus, the solid electrolyte of Sample 1 corresponding to the example of the present invention was manufactured.
The content ratio of impurities in Sample 1 was determined to be 0.5%. That is, the relative density of Sample 1 was 99.5% (99.5% or more).

The transmittance of Sample 1 having a wavelength range of 380 nm or more and a thickness of 0.8 mm was measured using a transmittance meter (spectrophotometer, manufactured by JASCO Corporation, trade name: V-550). The measurement result of the transmittance of Sample 1 is shown in FIG. As shown in the figure, it can be seen that the solid electrolyte of Sample 1 has a transmittance higher than 0.5%, and a transmittance of about 30% which is much higher at 380 nm or more.
Then, calculation of the absorption coefficient of the solid electrolyte of the sample 1 ^was 1.5 mm -1 (1.7 mm ^-1 or less).

  The solid electrolyte of Sample 1 is shown as a photograph in FIG. As shown in FIG. 5, it can be seen that the solid electrolyte of the sample 1 is a transparent body with a high transmittance because the pattern (characters) of the table on which the sample is placed can be seen through.

[Comparative example]
(Sample 10)
The solid electrolyte of Sample 10 is a solid electrolyte manufactured in the same manner as Sample 1 except that the HIP treatment is not performed. Moreover, since the solid electrolyte of the sample 10 is an opaque body as will be described later, the dry polishing of the fired body was performed in order to shape it to a predetermined size.
When the content ratio of the impurities in Sample 10 was determined, it was 8.6% (0.5% or more). That is, the relative density of Sample 10 was 91.4% (less than 99.5%).

Moreover, the transmittance | permeability was measured similarly to the case of the sample 1, and the measurement result was shown according to FIG. As shown in FIG. 4, the transmittance of the solid electrolyte of Sample 10 was as low as 0.35% and less than 0.5% in the wavelength range of 380 nm or more. Extinction coefficient calculated from the transmittance ^is 7.26mm ^-1 (6.6mm -1 or higher).

  The solid electrolyte of sample 10 is shown in the photograph in FIG. As shown in FIG. 6, the solid electrolyte of the sample 10 has an opaque cream color, and it can be confirmed that the transmittance is low.

(Sample 11)
The solid electrolyte of Sample 11 is a solid electrolyte manufactured in the same manner as Sample 1 except that dry polishing is not performed.
When the content ratio of the impurities in Sample 11 was determined, it was 0.9% (0.5% or more). That is, the relative density of the sample 11 was 99.1% (less than 99.5%).
Further, when the transmittance was measured in the same manner as in the case of Sample 1, it was confirmed that a portion of 0.5% or more and a portion of less than 0.5% were mixed.

The solid electrolyte of Sample 11 is shown in the photograph in FIG. As shown in FIG. 7, the solid electrolyte of the sample 11 has high transparency, but the pattern (characters) on the table on which the sample is placed is not partially seen through, and there is a portion where the transmittance is low. It turns out that it is a transparent body.
A micrograph of a cross section of the solid electrolyte of Sample 11 was taken. The photograph taken is shown in FIG. As shown in FIG. 8, it can be confirmed that the solid electrolyte of the sample 11 is composed of crystal grains made of the solid electrolyte and impurities between the crystal grains. The solid electrolyte of sample 1 is made of this solid electrolyte and consists only of crystal grains.

(Samples 12 to 17)
The solid electrolytes of Samples 12 to 17 are solid electrolytes manufactured in the same manner as Sample 10 except that the processing conditions for the HIP treatment were changed.
As shown in Table 1, the solid electrolytes of Samples 12 to 17 are samples having different purities (relative densities). The solid electrolytes of Samples 12 to 17 are all translucent. The solid electrolyte of each sample is a solid electrolyte having a transmittance of less than 0.5%, and the extinction coefficient is 6.6 mm ⁻¹ or more.

[Evaluation]
As an evaluation of the solid electrolyte of each sample, a cell (test cell) was assembled, and a short circuit test was performed using the test cell.

(Test cell)
First, the solid electrolyte of each material is formed into a rectangular parallelepiped shape having a size of 1 × 1 mm and a thickness of 0.8 mm by cutting and polishing.
Li is vapor-deposited on both surfaces of the solid electrolyte 60 to form Li vapor-deposited films 61 and 61. The Li vapor deposition film 61 was formed with a thickness of 2 μm.

  A pair of electrodes 63 and 63 made of In are connected to the Li vapor deposition films 61 and 61 through copper foils 62 and 62. At this time, the pair of electrodes 63 and 63 press the solid electrolyte 60 in a compressing direction to hold the solid electrolyte 60 and the like.

  Thus, the test cell 6 was formed. The configuration of the test cell 6 is shown in FIG. Note that the test cell 6 is held in an inert gas atmosphere (dry atmosphere).

(Short-circuit test)
A current is applied to the pair of electrodes 63, 63 of the test cell 6 so as to be 0.5 mA / cm ² . At this time, the potential of the electrode 63 (potential difference between a pair of electrodes) is measured. The measurement results are shown in FIGS. 10 shows changes in the potential of the solid electrolytes of Sample 1 and Sample 10, FIG. 11 shows changes in the potential of the solid electrolyte of Sample 10, and FIG. 12 shows changes in the potential of the solid electrolyte of Sample 11. Shown respectively.

  As shown in FIG. 10, in the solid electrolyte of Sample 1, no significant change in potential is confirmed at about 1 V until the energization time is about 1100 (s). That is, Li forming the Li vapor deposition film 61 is ionically conducted through the solid electrolyte 60.

And when energization time passes about 1100 (s), it can confirm that the potential difference is rising. This increase in potential is due to the depletion of Li that conducts ions from the Li vapor deposition film 61.
On the other hand, as shown in FIGS. 11 to 12, in the solid electrolytes of Samples 10 to 11, the potential drops rapidly to 0 (zero) after a specific time has elapsed.

  Specifically, in the solid electrolyte of the sample 10, the potential gradually increases with time, and the potential drops to zero at about 250 (s). In the solid electrolyte of the sample 11, the potential gradually decreased with time, and the potential decreased to zero at about 100 (s). The rapid decrease in these potentials is due to the occurrence of a short circuit between the pair of electrodes 63 and 63. This short circuit occurs when Li from the Li vapor deposition film 61 crystallizes (generates and grows dendrites) in pores (such as pores that cause a decrease in relative density) present in the solid electrolyte 60, This was caused by electrical conduction between the electrodes 63 and 63.

As described above, the solid electrolyte 60 of the sample 1 corresponding to the embodiment of the present invention can be used as a solid electrolyte without causing Li crystallization even when applied to a battery using Li metal as an electrode active material. It can be confirmed that it can be used.
Furthermore, when the impedance and electric conductivity during the short circuit test of the solid electrolyte 60 of the sample 1 were confirmed, they were values usable as a lithium battery.
In addition, in each of the solid electrolytes of Samples 12 to 17, an internal short circuit occurred. In Table 1, an example in which a short circuit occurred is shown with ×.

  From the comparison between the solid electrolytes of Samples 12 to 17 and the solid electrolyte of Sample 1, by applying a solid electrolyte having a transmittance of 0.5% or more to a battery using Li metal as an electrode active material, It can be seen that it can be used as a solid electrolyte without causing crystallization of Li.

[Application to batteries]
As described above, the solid electrolyte of the example can be used as a solid electrolyte of a lithium battery without causing crystallization of Li, and the lithium battery of the above-described embodiment can be formed. Moreover, the lithium air battery of the above-described embodiment can also be formed.

1: Lithium battery 2: Positive electrode 3, 3 ′: Negative electrode 4: Solid electrolyte layer 5: Battery case 6: Test cell 60: Solid electrolyte 61: Lithium vapor deposition film 62: Copper foil 63: Electrode 7: Lithium air battery 72: Positive electrode 73: Negative electrode 74: Solid electrolyte layer 75: Battery case

Claims (8)

A solid electrolyte containing Li, La, Zr and having a garnet structure,
A solid electrolyte, wherein an extinction coefficient measured in a wavelength range of 380 nm or more is 6.6 mm ⁻¹ or less. The solid electrolyte according to claim ¹ , wherein the extinction coefficient is 1.7 mm ⁻¹ or less.   The solid electrolyte according to claim 1, wherein the solid electrolyte has an impurity content of less than 0.5%.   The solid electrolyte according to claim 1, wherein the solid electrolyte is compressed by a hot isostatic pressing method. A positive electrode (2) having a positive electrode active material layer (21) containing a positive electrode active material;
A negative electrode (3) having a negative electrode active material layer (31) containing a negative electrode active material;
The solid electrolyte (4) according to any one of claims 1 to 4, which is disposed between the positive electrode active material layer and the negative electrode active material layer,
A lithium battery (1) characterized by comprising:   The lithium battery according to claim 5, wherein the positive electrode active material and the negative electrode active material are active materials capable of occluding and releasing lithium.   The lithium battery according to claim 5, wherein the negative electrode is made of lithium. A positive electrode (72) comprising a positive electrode material (720) comprising means for introducing air with oxygen as a positive electrode active material and comprising a catalyst for reducing oxygen;
A negative electrode (73) having a negative electrode material capable of inserting and extracting lithium;
A solid electrolyte layer (74) containing the solid electrolyte according to any one of claims 1 to 4, interposed between the positive electrode and the negative electrode;
A lithium-air battery (7) characterized by comprising: