JP2011195373A - Lithium ion conductive oxide, method for producing the same, and electrochemical device using the same as member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cubic garnet-related type lithium ion conductive oxide having the long period property and the modulation property of a crystal structure to be suitable for the improvement of ion conductivity, and a method for producing the same and an electrochemical device using it as a member.SOLUTION: The lithium ion conductive oxide comprises lithium, lanthanum, zirconium and oxygen as a chemical composition and is expressed by a chemical composition formula: LiLaZrO(-3<x<2, x≠0). The method for producing the same and the electrochemical device containing the compound as a solid electrolyte member are provided.

Description

The present invention relates to a lithium ion conductive oxide, a method for producing the same, and an electrochemical device using the same as a member.

Currently, in Japan, most of the secondary batteries installed in portable electronic devices such as mobile phones and notebook computers are lithium secondary batteries. In addition, lithium secondary batteries are expected to be put into practical use as large batteries for hybrid cars and power load leveling systems in the future, and their importance is increasing.

This lithium secondary battery mainly comprises a positive electrode and a negative electrode containing materials capable of reversibly occluding and releasing lithium, an electrolyte solution in which a lithium ion conductor is dissolved in a non-aqueous organic solvent, and a separator. Element.

Among these components, the electrolytes that have been studied are electrolytes such as lithium perchlorate and lithium hexafluorophosphate, ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC). And those dissolved in a solvent such as diethyl carbonate (DEC).

Since these materials have good lithium ion conductivity, such liquid electrolytes are employed in almost all current lithium secondary batteries.

However, the lithium secondary battery employing such a liquid electrolyte has a safety problem because it easily causes a short circuit between the positive electrode and the negative electrode due to the battery structure, and causes heat generation and ignition due to the short circuit.

Further, since the electrolytic solution itself is decomposed at a high voltage of 4.3 V or higher, it is a problem in increasing the battery capacity that the operating voltage cannot be increased to 4.3 V or higher.

For this purpose, it is expected that safety can be ensured by solidifying the electrolyte instead of a liquid system, and a polymer polymer or an inorganic ceramic that is chemically stable even in a wide potential window is used as a battery. Development of a battery as an electrolyte has been studied.

Among these, oxide ceramic solid electrolytes are attracting attention from the viewpoint of safety because of their high chemical stability.

Among these, titanium oxides such as lithium aluminum titanium phosphorous oxide and perovskite type lithium lanthanum titanium oxide have been widely studied because they have good lithium conductivity.

However, it causes a redox reaction with the electrode material during charging and discharging, and a part of titanium is reduced from tetravalent to trivalent, so that there is a problem that electronic conductivity is born and there is a risk of short circuit. Met.

On the other hand, recently, lithium ion conductors having a cubic garnet-related type crystal structure have been studied and attracted attention because of their high chemical stability and stability in electrode reactions and high ionic conductivity in oxide systems. It was. (See Patent Document 1 and Non-Patent Document 1)

Among them, the lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ having a cubic garnet-related structure is attracting attention because it has the highest lithium ion conductivity among a series of cubic garnet-related oxides. (See Non-Patent Document 2)

This substance is known to have a garnet-related crystal structure belonging to a cubic system from the classification of the crystal lattice.

This crystal structure is characterized in that the lithium ion conduction path is formed by three-dimensionally combining one-dimensional spaces occupied by lithium.

However, from the viewpoint of practical lithium ion conductivity, a crystal structure capable of faster lithium diffusion was required.

In general, as a characteristic of the structure occupied by lithium ions, there are many disturbances in occupied seats, and when the occupied space is expanded, better conductivity can often be expressed.

When this is applied to this garnet-related lithium ion conductor, for the same lithium lanthanum zirconium oxide, by changing the chemical composition ratio, the lattice size is increased and the diffusion path is expanded, and the crystal structure has long periodicity and It was expected that structural control such as introducing modulation and disturbing the occupied seat of lithium would be effective in improving ion conductivity.

Further, as an example of the structure controlled by the composition ratio of zirconium and lanthanum, which are constituent elements of lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ , Zr _1-x La in which zirconium of the compound ZrO ₂ is substituted with lanthanum A compound having a chemical composition of _x O _2-0.5x (x = 0.1, 0.5) has been reported. It has been reported that the lattice size increases as the amount of lanthanum increases, and oxygen deficiency gives order to the crystal structure. (See Non-Patent Document 3)

In the lithium lanthanum zirconium oxide system, the lithium structure has been ordered by reducing the average structure as in the case of tetragonal lithium lanthanum zirconium oxide Li ₇ La ₃ Zr ₂ O ₁₂ so far. It was reported. (See Patent Document 2 and Non-Patent Document 4)

However, in a known cubic garnet-related lithium ion conductor, a compound having a long periodicity and a modulation property of a crystal structure suitable for improving the ionic conductivity has not been known.

Special table 2007-528108 gazette Japanese Patent Application No. 2008-321998

V. Thangadurai, W.H. Weppner, Advanced Functional Materials, 15, 107-112 (2005) R. Murugu, V.M. Thangadurai, W.H. Weppner, Agewandte Chemie-International Edition, 46, 7778-7781 (2007) C. -K. Long, J. et al. W. Richardson, Jr. , M.M. Ozawa, M .; Kimura, Journal of Alloys and Compounds, 207/208, 174-177 (1994) J. et al. Awaka, N .; Kijima, H .; Hayaka, J .; Akimoto, Journal of Solid State Chemistry, 182, 2046-2052 (2009)

Accordingly, the present invention is a cubic garnet-related lithium ion conductive oxide having a long period and a crystal structure suitable for improving ion conductivity, a method for producing the same, and a method for using the same. It is an object of the present invention to provide an electrochemical device.

Means for solving the problems are as follows.
(1) The chemical composition is composed of lithium, lanthanum, zirconium, and oxygen, and is represented by a chemical composition formula of Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0). Lithium ion conductive oxide characterized.
(2) The chemical composition is composed of lithium, lanthanum, zirconium, and oxygen, and Li _{7 + x-2y} La _{3 + x} Zr _2−x O _12−y (−3 <x <2, x ≠ 0, 0 <y <(3 .5 + 0.5x)) a lithium ion conductive oxide characterized by the chemical composition formula:
(3) The lithium ion conductive oxide according to (1) or (2), which has a cubic crystal structure as an average structure.
(4) The lithium ion conductive oxide according to (1) or (2), which has a cubic garnet-related crystal structure as an average structure.
(5) It has a cubic garnet-related crystal structure as an average structure, and its cubic lattice constant a is 12.98 to 13.20, (1) or (2) Lithium ion conductive oxide described in 1.
(6) It has a cubic garnet-related crystal structure as an average structure, and its cubic lattice constant a is not less than 12.98Å and not more than 13.20Å, and further, long-periodicity and modulation in its X-ray diffraction pattern The lithium ion conductive oxide according to (1) or (2), characterized in that splitting of the main reflection spot, appearance of a satellite reflection spot, and peak broadening reflecting the properties are observed.
(7) The composition according to any one of (1) to (6), characterized in that it is synthesized in a temperature range of 600 ° C. or more and 1300 ° C. or less using a mixture of raw material compounds of lithium, lanthanum, and zirconium as starting materials. A method for producing a lithium ion conductive oxide.
(8) The lithium ion according to any one of (1) to (6), characterized in that it is synthesized in a temperature range of 1100 ° C. to 1300 ° C. using tetragonal garnet-type lithium lanthanum zirconium oxide as a raw material. A method for producing a conductive oxide.
(9) An electrochemical device using the lithium ion conductive oxide according to any one of (1) to (6) as a solid electrolyte material.

According to the present invention, it is possible to produce a novel compound of a garnet-related lithium ion conductor having high-speed lithium ion conductivity and belonging to a cubic system as an average structure, and using this oxide as a solid electrolyte material By doing so, an electrochemical device such as a lithium secondary battery having excellent characteristics becomes possible.

It is a schematic diagram which shows one example of an all-solid-state lithium secondary battery. It is a figure which shows the average structure which a garnet related type compound has. 1 is a single crystal X-ray diffraction pattern of Li _7.1 La _3.1 Zr _1.9 O ₁₂ synthesized in Example 1. FIG. FIG. 4 is an enlarged view of FIG. 3. Powder of Li ₇ La ₃ Zr ₂ O ₁₂ (a) synthesized in Comparative Example 1 and Li _7.0 La _3.2 Zr _1.8 O _11.9 (b) of the present invention synthesized in Example 2 It is the figure which compared the X-ray diffraction pattern. _{2 is} a single crystal X-ray diffraction pattern of Li ₇ La ₃ Zr ₂ O ₁₂ synthesized in Comparative Example 1. FIG. FIG. 7 is an enlarged view of FIG. 6.

As a result of intensive studies on the chemical composition range of lithium lanthanum zirconium oxide, which is explained in the cubic garnet-related type, the average structure of the present inventors, it was found that a part of zirconium can be substituted with lanthanum, and the amount of lithium is It was found that it can be controlled by the amount of deficiency and found that there are novel compounds having different chemical compositions.

As a result, compared to the known cubic garnet-related Li ₇ La ₃ Zr ₂ O ₁₂ , the crystal lattice volume can be increased, and in the single crystal X-ray diffraction pattern, the long periodicity of the crystal structure, The present invention has been completed by observing cracks in the main reflection spot and satellite reflection spots showing the modulation property and confirming the broadening of diffraction peaks in the powder X-ray diffraction pattern.

In the lithium ion conductive oxide of the present invention, a part of lanthanum of the known compound Li ₇ La ₃ Zr ₂ O ₁₂ was substituted with zirconium or a part of zirconium with lanthanum, and the amount of lithium was changed for charge compensation. It is a compound having a chemical composition of Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0).
Alternatively, Li _{7 + x−2y} La _{3 + x} Zr _2−x O _12−y (−3 << 3) in which a part of lanthanum is replaced with zirconium or a part of zirconium is replaced with lanthanum and at the same time the amount of lithium and oxygen is changed for charge compensation. It is a novel compound having a chemical composition of x <2, x ≠ 0, 0 <y <(3.5 + 0.5x)).
The crystal structure is characterized by having a cubic garnet-related structure as an average structure, and the cubic lattice constant a is not less than 12.98 and not more than 13.20. It is a compound characterized by these.
As a more detailed characteristic of the crystal structure, it is a compound characterized in that the main reflection spot splitting, the appearance of the satellite reflection spot, and the peak broadening reflected in the X-ray diffraction pattern reflecting the long periodicity and modulation are observed. is there.
In addition, this method for producing a lithium ion conductive oxide is characterized by firing in a temperature range of 600 ° C. to 1300 ° C. using a mixture of raw material compounds of lithium, lanthanum, and zirconium as starting materials.
Furthermore, another method for producing this lithium ion conductive oxide is characterized by using tetragonal garnet-type lithium lanthanum zirconium oxide as a raw material and synthesizing in a temperature range of 1100 ° C. or higher and 1300 ° C. or lower.
Furthermore, lithium ion conductive oxides having these garnet-related structures can be used as solid electrolyte materials in electrochemical devices such as all-solid lithium secondary batteries, lithium-air secondary batteries, and lithium batteries.

The production method according to the present invention will be described in more detail.
(Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0) and Li _{7 + x−2y} La _{3 + x} Zr _2−x O _12−y (−3 <x <2, x ≠ 0, Synthesis with starting materials of lithium, lanthanum and zirconium starting materials of 0 <y <(3.5 + 0.5x))
The lithium ion conductive oxide of the present invention uses, as a raw material, at least one compound containing a lithium element, at least one compound containing a lanthanum element, and at least one compound containing a zirconium element, The starting materials can be weighed and mixed so as to be synthesized and heated in an atmosphere containing oxygen gas such as air.

As the lithium raw material, at least one of lithium (metallic lithium) and a lithium compound is used. The lithium compound is not particularly limited as long as it contains lithium, and examples thereof include oxides such as Li ₂ O ₂ , salts such as Li ₂ CO ₃ and LiNO ₃ , and hydroxides such as LiOH. . Among these, Li ₂ CO ₃ or LiNO ₃ is particularly preferable.

As the lanthanum raw material, at least one of lanthanum (metal lanthanum) and a lanthanum compound is used. The lanthanum compound is not particularly limited as long as it contains lanthanum, and examples thereof include oxides such as La ₂ O ₃ and salts such as La ₂ (CO ₃ ) ₃ and La (NO ₃ ) _3. . Among these, La ₂ O _{3 and the} like are particularly preferable.

As the zirconium raw material, at least one of zirconium (metallic zirconium) and a zirconium compound is used. The zirconium compound is not particularly limited as long as it contains zirconium, and examples thereof include oxides such as ZrO ₂ , carbides such as ZrC, and nitrides such as ZrN. Among these, ZrO ₂ is particularly preferable.

First, a mixture containing these is prepared. The mixing ratio of each starting material is such that the product composition is Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0) and Li _{7 + x−2y} La _{3 + x} Zr _2−x O ₁₂₋ It is preferable to mix such that the chemical composition is _y (−3 <x <2, x ≠ 0, 0 <y <(3.5 + 0.5x)). Among these, since Li easily volatilizes at a high temperature, it is more preferable to weigh 3 to 10% more than the target composition. The mixing method is not particularly limited as long as these can be uniformly mixed, and may be mixed by a wet method or a dry method using a known mixer such as a mixer.

Next, a powder sample with an adjusted particle size is molded. The molding method is not particularly limited, and may be molded by a known method using, for example, a tablet molding machine, a uniaxial press, a hydrostatic press, HIP, CIP or the like. Prior to the main firing, calcination and production of a sintered body may be performed in advance.

Next, the molded sample is put into a container such as a crucible. The crucible material is preferably made of a material that is usually stable at high temperatures, such as alumina or platinum.

Next, heat treatment is performed. The composition ratio can be appropriately set depending on the heat treatment temperature, but it is usually 600 ° C. to 1300 ° C., preferably 1100 ° C. to 1270 ° C. The atmosphere at the time of the heat treatment is not particularly limited, and may be usually performed in an oxidizing atmosphere or air. The heat treatment time can be appropriately changed according to the heat treatment temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling.

(Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0) and Li _{7 + x−2y} La _{3 + x} Zr _2−x O _12−y (−3 <x <2, x ≠ 0, Synthesis using tetragonal lithium lanthanum zirconium oxide of 0 <y <(3.5 + 0.5x)) as a starting material)
The lithium ion conductive oxide of the present invention, as another production method, uses tetragonal garnet-type lithium lanthanum zirconium oxide as a raw material, and is heated in an atmosphere containing oxygen gas such as in the air. It can be synthesized by involving a thermal decomposition reaction at.

The raw material tetragonal garnet-type lithium lanthanum zirconium oxide is not particularly limited as long as it is a compound that contains lithium, lanthanum, zirconium, and oxygen as main constituent elements and has a garnet-type crystal structure belonging to the tetragonal system. . For example, tetragonal garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ is preferable.

First, it is preferable to pulverize and mix tetragonal garnet-related lithium lanthanum zirconium oxide as a starting material. The pulverization / mixing method is not particularly limited as long as they can be uniformly pulverized / mixed, and may be pulverized / mixed in a wet or dry manner using a known pulverizer / mixer such as a mixer.

Next, a powder sample with an adjusted particle size is molded. The molding method is not particularly limited, and may be molded by a known method using, for example, a tablet molding machine, a uniaxial press, a hydrostatic press, HIP, CIP or the like. Prior to the main firing, calcination and production of a sintered body may be performed in advance.

Next, the molded sample is put into a container such as a crucible. The crucible material is preferably made of a material that is usually stable at high temperatures, such as alumina or platinum. Since it is important in this synthesis method that the lithium compound, zirconium compound, and lanthanum compound volatilize at a high temperature, it is preferable to control the sealing property of the crucible using a lid or the like.

Next, heat treatment is performed. The composition ratio can be set as appropriate depending on the heat treatment temperature, but it is usually 1100 ° C. to 1300 ° C., preferably 1130 ° C. to 1270 ° C., in which tetragonal crystals hardly exist stably. The atmosphere at the time of the heat treatment is not particularly limited, and may be usually performed in an oxidizing atmosphere or air. The heat treatment time can be appropriately changed according to the heat treatment temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling.

(Production of solid electrolyte)
Subsequently, the solid electrolyte material used for electrochemical devices, such as a lithium battery, is produced using the garnet related type lithium ion conductor compound obtained by the above.

That is, a solid electrolyte can be produced by forming a powder molded body, a sintered body, or a thin film of the lithium ion conductive oxide.

Among these, the sintered body was produced by using known powder / molding techniques such as uniaxial pressing or isostatic pressing, hot pressing, and current sintering using the previously synthesized powder as a raw material. The molded body can be produced by firing at 600 ° C. to 1400 ° C., preferably 800 ° C. to 1000 ° C. The firing atmosphere is not particularly limited, and the firing atmosphere is usually performed in an oxidizing atmosphere or air. The firing time can be appropriately changed according to the firing temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling. At this time, it is desirable to cover the molded body with the above powder in order to prevent the lithium from being decomposed due to high volatility at high temperature during firing.

In addition, for the production of solid electrolyte membranes, normal thin film and thick film production processes can be applied, such as sputtering, laser ablation (PLD), aerosol deposition (AD), or simple coating / drying processes. Such a method can be applied.

(Production of electrochemical devices)
The electrochemical device of the present invention uses a solid electrolyte using the above lithium ion conductive oxide as a member. That is, other than using the lithium ion conductive oxide of the present invention as one of the solid electrolyte materials, known lithium secondary batteries (coin type, button type, cylindrical type, all solid type, etc.), lithium batteries, alkaline batteries, Elemental technologies of electrochemical devices such as sensors can be used as they are.

FIG. 1 is a schematic view showing an example in which the present invention is applied to a coin-type lithium secondary battery as an electrochemical device of the present invention. The coin battery 1 includes a negative electrode terminal 2, a negative electrode 3, a solid electrolyte 4, an insulating packing 5, a positive electrode 6, and a positive electrode can 7.

In the electrochemical device (lithium secondary battery) of the present invention, the lithium ion conductive oxide of the present invention can be applied as a solid electrolyte material. Therefore, it is a great feature that it is not always necessary to use an organic electrolyte or a separator that is often used in known lithium secondary batteries.

In the lithium secondary battery of the present invention, the positive electrode material functions as a positive electrode such as lithium cobalt oxide (LiCoO ₂ ) or lithium manganese oxide (LiMn ₂ O ₄ ), and has a relatively high potential on the basis of lithium. In addition, a known material capable of occluding lithium can be employed. In particular, since this material is characterized by functioning stably as an electrolyte even at a high potential of about 5 V, a positive electrode material having a high potential can be used.

In the lithium secondary battery of the present invention, as the negative electrode material, for example, metallic lithium, lithium alloy, carbon material, lithium titanium oxide, etc., function as a negative electrode, have a relatively low potential with respect to lithium, and occlude lithium. Possible known ones can be employed. In particular, this material is not reduced against metallic lithium, and also functions stably as an electrolyte even at a high potential of about 5 V, so that a wide range of materials can be selected.
In the lithium secondary battery of the present invention, a known battery element may be adopted for the battery container and the like.

Hereinafter, examples will be shown to further clarify the features of the present invention. The present invention is not limited to these examples.

[Example 1]
(Synthesis of lithium ion conductive oxide _{Li 7 + x La 3 + x} Zr 2-x O 12)
As starting materials, lithium nitrate (LiNO ₃ ) powder having a purity of 99.9% or more, lanthanum oxide (La ₂ O ₃ ) powder having a purity of 99.9% or more, zirconium oxide (ZrO ₂ ) powder having a purity of 99.9% or more Was used so that the molar ratio of Li: La: Zr was 7.2: 3.1: 1.9. These were mixed in a mortar, then molded using a tablet molding machine, and placed in an alumina crucible (Al ₂ O ₃ 99.6%). This was put in an electric furnace and a sample was obtained by heating in air at 1150 ° C. for 4 hours.

One grain-grown particle was selected from the obtained samples, and single crystal X-ray diffraction measurement was performed using an imaging plate type single crystal X-ray diffractometer. FIG. 3 shows a single crystal X-ray diffraction pattern (vibration photograph) obtained, and FIG. 4 shows an enlarged view thereof. From FIG. 3, it was confirmed that the main reflection spot was appropriate in a cubic garnet-related crystal structure.

However, when the cubic lattice constant is obtained from the diffraction pattern, the following values are obtained, which are clearly longer than the known Li ₇ La ₃ Zr ₂ O ₁₂ lattice constant and have a difference in chemical composition. It was suggested that it was a new compound.
a = 13.134 mm (within an error of 0.004 mm)

Further, when the diffraction pattern of FIG. 4 is examined in detail, it is clear that the reflection spot cracks suggesting the long periodicity or modulation of the crystal structure, and the satellite reflection spot appears. Such a diffraction pattern has not been reported in the known cubic system Li ₇ La ₃ Zr ₂ O ₁₂ , and was confirmed to be a long periodicity of the crystal structure due to a change in chemical composition.

When the chemical composition of lanthanum and zirconium was analyzed for the obtained sample using an energy dispersive X-ray analyzer, La: Zr = 3.1: 1.9, and the chemical composition formula estimated from charge compensation As Li _7.1 La _3.1 Zr _1.9 O ₁₂ . From this result, compared with the publicly known Li ₇ La ₃ Zr ₂ O ₁₂ , the present lithium ion conductive oxide is Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (x = 0. 1) It became clear that it was a composition, and it became clear that the origin of the long periodicity of the crystal structure was a shift in chemical composition.

[Comparative Example 1]
(Synthesis of cubic Li ₇ La ₃ Zr ₂ O ₁₂ )
A tetragonal garnet-type lithium lanthanum zirconium oxide synthesized in advance by a known production method described in Non-Patent Document 4 is used as a raw material, pulverized and mixed in a mortar, and then molded using a tablet molding machine. In an alumina crucible with a lid (Al ₂ O ₃ , purity 99.6%). This was put into an electric furnace and heated in air at 1250 ° C. for 6 hours. After naturally cooling in an electric furnace, it was taken out.

The obtained sample was subjected to powder X-ray diffraction measurement using a powder X-ray diffractometer. As a result, it was found that the average structure was a single phase having a cubic system and a garnet-related structure. The powder X-ray diffraction pattern is shown in FIG. From this result, it was confirmed that it was a single phase sample having very good crystallinity.

Further, for the obtained sample, one grain-grown particle was selected, and a single crystal X-ray diffraction pattern was measured by an imaging plate type single crystal X-ray diffractometer. FIG. 6 shows a single crystal X-ray diffraction pattern (vibration photograph) obtained, and FIG. 7 shows an enlarged view thereof. The main reflection was observed as a clear single spot, and no long periodicity or modulation as in the case of FIG. 4 was observed, and the crystal structure was sufficiently explained by a cubic system. Further, when the lattice constant of the cubic garnet-related structure was obtained from the diffraction pattern, the following values were obtained, which was in good agreement with the known Li ₇ La ₃ Zr ₂ O ₁₂ described in Non-Patent Document 2. And the product was confirmed to be Li ₇ La ₃ Zr ₂ O ₁₂ .
a = 12.959 mm (within 0.002 mm error)

[Example 2]
(Synthesis of lithium ion conductive oxide _{Li 7 + x-2y La 3} + x Zr 2-x O 12-y (-3 <x <2,0 <y <(3.5 + 0.5x)))
Using tetragonal garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ synthesized in advance by a known production method described in Non-Patent Document 2 as a raw material, pulverized and mixed in a mortar, and then molded using a tablet molding machine The sample was placed in an alumina crucible (Al ₂ O ₃ , purity 99.6%) without a lid. This was put into an electric furnace and heated in air at 1150 ° C. for 6 hours. The obtained product was taken out by naturally cooling in an electric furnace.

The obtained sample was subjected to powder X-ray diffraction measurement using a powder X-ray diffractometer. As a result, it was revealed that the average structure was a single phase having a cubic system and a garnet-related structure. The powder X-ray diffraction pattern is shown in FIG.

Compared with the powder X-ray diffraction pattern of the known garnet-related Li ₇ La ₃ Zr ₂ O ₁₂ shown in FIG. 5 (a), the peak position of the pattern in FIG. 5 (b) is shifted to the low angle side, It became clear that the lattice constant was larger.

Furthermore, the peak is clearly broad, and it is confirmed that it has a shape with an especially wide skirt on the low angle side, suggesting the long period or modulation of the structure, etc. The single crystal X-ray diffraction of FIG. The result was in good agreement with the figure. Such a result was not reported in the known Li ₇ La ₃ Zr ₂ O ₁₂ , and was judged to be a difference in crystal structure due to a change in chemical composition.

Further, as a result of chemical composition analysis of this sample by ICP-AES method, Li _7.0 La _3.2 Zr _1.8 O _11.9 is valid, and Li _{7 + x-2y} La _{3 + x} Zr _2-x It was confirmed that the composition corresponds to x = 0.2 and y = 0.1 in the chemical composition formula of O _12-y .

Furthermore, in order to produce the lithium ion conductive oxide, it is necessary to volatilize lithium, zirconium, and oxygen from the sample, but in fact, the crystal phase precipitation of ZrO ₂ volatilized outside the crucible was confirmed. . This result suggests a zirconium deficient composition in the present lithium ion conductive oxide.

DESCRIPTION OF SYMBOLS 1 Coin type lithium secondary battery 2 Negative electrode terminal 3 Negative electrode 4 Solid electrolyte 5 Insulation packing 6 Positive electrode 7 Positive electrode can

Claims (9)

The chemical composition is composed of lithium, lanthanum, zirconium, and oxygen, and is represented by a chemical composition formula of Li _{7 + x} La _{3 + x} Zr _2−x O ₁₂ (−3 <x <2, x ≠ 0). Lithium ion conductive oxide. The chemical composition is composed of lithium, lanthanum, zirconium, and oxygen, and Li _{7 + x-2y} La _{3 + x} Zr _2-x O _12-y (-3 <x <2, x ≠ 0, 0 <y <(3.5 + 0. 5x)) Lithium ion conductive oxide characterized by the chemical composition formula 3. The lithium ion conductive oxide according to claim 1, wherein the lithium ion conductive oxide has a cubic crystal structure as an average structure. 3. The lithium ion conductive oxide according to claim 1, wherein the lithium ionic conductive oxide has a cubic garnet-related crystal structure as an average structure. 3. The lithium ion according to claim 1, wherein the lithium ion has a cubic garnet-related crystal structure as an average structure, and a cubic lattice constant a of 12.98 to 1320. Conductive oxide. It has a cubic garnet-related crystal structure as an average structure, and its cubic lattice constant a is not less than 12.98Å and not more than 13.20Å. Further, its X-ray diffraction pattern reflects long-periodity and modulation. The lithium ion conductive oxide according to claim 1, wherein splitting of the main reflection spot, appearance of a satellite reflection spot, and peak broadening are observed. The lithium ion conduction according to any one of claims 1 to 6, characterized by being synthesized in a temperature range of 600 ° C or higher and 1300 ° C or lower using a mixture of raw material compounds of lithium, lanthanum and zirconium as starting materials. Of producing a conductive oxide. 7. The lithium ion conductive oxidation according to claim 1, wherein tetragonal garnet-type lithium lanthanum zirconium oxide is used as a raw material and is synthesized in a temperature range of 1100 ° C. to 1300 ° C. 7. Manufacturing method. An electrochemical device using the lithium ion conductive oxide according to any one of claims 1 to 6 as a solid electrolyte material.