JP2010244847A - Solid electrolyte material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte material made of lithium niobate and having a high Li-ion conductivity. <P>SOLUTION: The solid electrolyte material made of lithium niobate has a first group of X-ray diffraction peaks at (2θ)s of 23.7°±2.0°, 32.7°±2.0°, 34.8±2.0°, 38.9°±2.0°, 40.1°±2.0°, 42.5°±2.0° and a second group of X-ray diffraction peaks at (2θ)s of 25.5°±0.5°, 27.8°±1.0°, 31.0°±0.8°, 32.0°±0.8°, and when a strength of X-ray diffraction peak of the above (2θ) of 23.7°±2.0° is denoted by I<SB>A</SB>and a strength of the X-ray diffraction peak of the above (2θ) of 25.5°±0.5° is denoted by I<SB>B</SB>, a relation of I<SB>A</SB>/I<SB>B</SB>≤12.0 is satisfied. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solid electrolyte material made of lithium niobate and having high Li ion conductivity.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, the development of batteries (eg, lithium batteries) that are excellent as power sources has been regarded as important. In fields other than information-related equipment and communication-related equipment, for example, in the automobile industry, development of lithium batteries and the like used for electric cars and hybrid cars is being promoted.

  Here, since a commercially available lithium battery uses an organic electrolyte solution that uses a flammable organic solvent, it has a structure to prevent the installation of a safety device and to prevent a short circuit. Improvements in materials are necessary. In contrast, an all-solid-state battery in which the liquid electrolyte is changed to a solid electrolyte does not use a flammable organic solvent in the battery, so the safety device can be simplified, and the manufacturing cost and productivity are considered excellent. Yes.

Lithium niobate (LiNbO ₃ ) is known as a solid electrolyte material used for such all solid state batteries. For example, Patent Document 1 discloses a solid electrolyte battery using a lithium ion conductive glassy solid electrolyte mainly composed of lithium niobate, and a hexavalent metal oxide is added to the glassy solid electrolyte. Is disclosed. In this technique, lithium ion conductivity is improved by adding a hexavalent metal oxide to a glassy solid electrolyte mainly composed of lithium niobate. Further, Patent Document 2 discloses an amorphous lithium tantalate / lithium niobate thin film manufactured by a sputtering method. This technique aims to improve Li ion conductivity by setting the composition of the lithium tantalate / lithium niobate thin film within a specific range. Patent Document 3 discloses a sulfide-based glassy lithium ion conductive solid electrolyte containing lithium niobate. This technique aims to obtain a solid electrolyte material having a high glass transition temperature.

Japanese Patent Publication No. 3-51063 Japanese Patent Publication No. 3-43214 JP 2004-152659 A

  As described in Patent Document 1, lithium niobate shows almost no Li ion conductivity in the crystalline state. Therefore, when using lithium niobate as a solid electrolyte material, it is necessary to make it amorphous (amorphous) and to add other oxides and the like. The present invention has been made in view of the above circumstances, and a main object thereof is to provide a solid electrolyte material made of lithium niobate and having high Li ion conductivity.

In order to solve the above problems, in the present invention, a solid electrolyte material made of lithium niobate, 2θ = 23.7 ° ± 2.0 °, 32.7 ° ± 2.0 °, 34.8 First X-ray diffraction peak group of ° ± 2.0 °, 38.9 ° ± 2.0 °, 40.1 ° ± 2.0 °, 42.5 ° ± 2.0 °, and 2θ = 25 2nd X-ray diffraction peak group of 5 ° ± 0.5 °, 27.8 ° ± 1.0 °, 31.0 ° ± 0.8 °, 32.0 ° ± 0.8 ° and the intensity of X-ray diffraction peaks of the 2θ = 23.7 ° ± 2.0 ° and _{I a,} the intensity of X-ray diffraction peaks of the 2θ = 25.5 ° ± 0.5 ° was _{I B} In some cases, a solid electrolyte material is provided that satisfies the relationship of I _A / I _B ≦ 12.0.

According to the present invention, a first X-ray diffraction peaks, and a second X-ray diffraction peaks, further, by the I _A and I _B in a specific relationship, the Li ion conductivity It can be a high solid electrolyte material.

  Further, in the present invention, a cathode active material having an oxide cathode active material and a coat portion formed on the surface of the oxide cathode active material, wherein the coat portion is the solid electrolyte material described above. A positive electrode active material characterized by comprising:

  According to the present invention, by providing the coat portion, it is possible to suppress the generation of a high resistance layer caused by the reaction between the oxide positive electrode active material and the sulfide solid electrolyte material, and furthermore, the Li ion conductivity of the coat portion is high. The interface resistance between the oxide positive electrode active material and the sulfide solid electrolyte material can be reduced.

  Further, in the present invention, there is provided a method for producing the above-described solid electrolyte material, wherein a raw material solution containing Li alkoxide and Nb alkoxide is hydrolyzed to prepare a precursor solution of lithium niobate, and the precursor A precursor film forming step of forming a precursor film of lithium niobate using a body solution, and the precursor film at a temperature within a range of 345 ° C. to 355 ° C. and a time within a range of 4 hours to 6 hours A solid-state electrolyte material manufacturing method, comprising:

  According to the present invention, a solid electrolyte material having extremely high Li ion conductivity can be obtained by performing heat treatment under the above conditions.

It is a schematic sectional drawing explaining the solid electrolyte material of this invention. It is a schematic sectional drawing which shows an example of the positive electrode active material material of this invention. It is a schematic sectional drawing which shows an example of the manufacturing method of the solid electrolyte material of this invention. It is a result of the XRD measurement of the solid electrolyte material obtained in Example 1 and Comparative Examples 1-1 to 1-4. It is a result of the impedance measurement of the solid electrolyte material obtained in Example 1 and Comparative Examples 1-1 to 1-4. It is a result of the impedance measurement of the solid electrolyte material obtained in Example 1 and Comparative Examples 1-1 to 1-4. It is a result of the impedance measurement of the solid electrolyte material obtained in Example 1 and Comparative Examples 1-1 to 1-4. It is a simulation result which shows a part polyhedron structure of a single crystal structure and an amorphous structure. 3 is an XRD spectrum simulation result including actual measurement data of Example 1. FIG.

  Hereinafter, the manufacturing method of the solid electrolyte material, positive electrode active material, and solid electrolyte material of the present invention will be described in detail.

A. First, the solid electrolyte material of the present invention will be described. The solid electrolyte material of the present invention is a solid electrolyte material made of lithium niobate, and 2θ = 23.7 ° ± 2.0 °, 32.7 ° ± 2.0 °, 34.8 ° ± 2.0. °, 38.9 ° ± 2.0 °, 40.1 ° ± 2.0 °, first X-ray diffraction peak group of 42.5 ° ± 2.0 °, and 2θ = 25.5 ° ± 0 5 °, 27.8 ° ± 1.0 °, 31.0 ° ± 0.8 °, 32.0 ° ± 0.8 ° and the second X-ray diffraction peak group, and 2θ = the intensity of X-ray diffraction peaks of 23.7 ° ± 2.0 ° and _{I a,} the intensity of X-ray diffraction peaks of the 2θ = 25.5 ° ± 0.5 ° in the case of the _{I B, I a} / I _B ≦ 12.0 is satisfied.

According to the present invention, a first X-ray diffraction peaks, and a second X-ray diffraction peaks, further, by the I _A and I _B in a specific relationship, the Li ion conductivity It can be a high solid electrolyte material. As described above, since lithium niobate shows almost no Li ion conductivity in the crystalline state, when lithium niobate is used as a solid electrolyte material, it needs to be amorphous and further added with other oxides, etc. was there. On the other hand, according to the present invention, by having the above X-ray diffraction peak group, high Li ion conductivity can be exhibited even with, for example, only lithium niobate.

Furthermore, lithium niobate in the present invention is not intended to mean only LiNbO _3, but also including the vicinity of the composition. Here, when lithium niobate is represented by Li _x Nb _y O _z , x is usually 0.9 ≦ x ≦ 1.1, and preferably 0.95 ≦ x ≦ 1.05. y is usually 0.9 ≦ y ≦ 1.1, and preferably 0.95 ≦ y ≦ 1.05. z is usually 2.8 ≦ z ≦ 3.2, and preferably 2.9 ≦ z ≦ 3.1.

1. X-ray diffraction peak The solid electrolyte material of the present invention is characterized by having a first X-ray diffraction peak group and a second X-ray diffraction peak group. First, these X-ray peak groups will be described. The first X-ray diffraction peak group in the present invention is a peak group resulting from the crystal phase of the solid electrolyte material. Specifically, it is a group of peaks characteristic of a LiNbO ₃ single crystal. According to the X-ray diffraction (XRD) database, the peak at 2θ = 23.7 ° (23.681 °) is the peak of the (012) plane, and the peak at 2θ = 32.7 ° (32.667 °) is ( 104), the peak at 2θ = 34.8 ° (34.798 °) is the peak at (110), and the peak at 2θ = 38.9 ° (38.940 °) is (006). The peak at 2θ = 40.1 ° (40.58 °) is the peak at (113) plane, and the peak at 2θ = 42.5 ° (42.527 °) is at the (202) plane. It is a peak.

On the other hand, the second X-ray diffraction peak group in the present invention does not exist in the peak of the LiNbO ₃ single crystal, and is considered to be a peak group caused by the NbO ₃ tetrahedron. As will be described later, in the simulation using the molecular dynamics method, it is suggested that the NbO ₃ tetrahedrons are arranged with regularity, and the Li ion conduction path is formed so that the Li ion conductivity is high. It is thought that it has become. Moreover, since the solid electrolyte material of the present invention has the two types of X-ray diffraction peak groups described above, it is considered that the solid electrolyte material has a structure in which a crystalline phase and an amorphous phase are mixed. That is, it is considered that a high Li ion conductivity can be exhibited because the structure has an amorphous property and retains the crystal microstructure.

In the present invention, 2 [Theta] = 23.7 ° to the intensity of X-ray diffraction peak of ± 2.0 ° and _{I A,} the intensity of X-ray diffraction peaks of 2θ = 25.5 ° ± 0.5 ° I _In the case of _B , the relationship of I _A / I _B ≦ 12 is usually satisfied. Further, I _A / I _B preferably satisfies the relationship of I _A / I _B ≦ 10, and more preferably satisfies the relationship of I _A / I _B ≦ 8. This is because a solid electrolyte material having higher Li ion conductivity can be obtained.

2. Solid Electrolyte Material The impedance of the solid electrolyte material of the present invention is, for example, 100,000Ω or less, preferably 20,000Ω or less. The impedance value in the present invention is calculated by the AC impedance method described later.

  Examples of the shape of the solid electrolyte material of the present invention include a thin film shape and a particle shape. Hereinafter, a member having a thin-film solid electrolyte material and a member having a particulate solid electrolyte material will be exemplified. As an example of a member having a thin-film solid electrolyte material, as shown in FIG. 1A, an oxide positive electrode active material 2 and a thin-film solid electrolyte formed on the surface of the oxide positive electrode active material 2 A material having the material 1 can be given. In this case, the solid electrolyte material 1 functions as a coat portion that suppresses the generation of a high resistance layer generated by the reaction between the oxide positive electrode active material 2 and the sulfide solid electrolyte material (not shown). The high resistance layer and the like will be described in “B. Positive electrode active material” described later.

  As another example of a member having a thin film solid electrolyte material, as shown in FIG. 1B, a sulfide solid electrolyte material 3 and a thin film formed on the surface of the sulfide solid electrolyte material 3 What has the solid electrolyte material 1 can be mentioned. Also in this case, similarly to the above, the solid electrolyte material 1 functions as a coat portion that suppresses the generation of a high resistance layer caused by the reaction between the sulfide solid electrolyte material 3 and the oxide positive electrode active material (not shown). As another example of a member having a thin-film solid electrolyte material, as shown in FIG. 1C, a positive electrode active material layer 4 containing an oxide positive electrode active material, a thin-film solid electrolyte material 1, sulfide A power generation element in which the sulfide solid electrolyte layer 5 and the negative electrode active material layer 6 containing the solid electrolyte material are arranged in this order can be given. Also in this case, as described above, the solid electrolyte material 1 functions as a coat portion that suppresses the generation of a high resistance layer generated between the positive electrode active material layer 4 and the sulfide solid electrolyte layer 5.

  On the other hand, as an example of a member having a particulate solid electrolyte material, as shown in FIG. 1 (d), a positive electrode active material layer 4 containing an oxide positive electrode active material, a compression-molded particulate solid electrolyte material A power generation element in which 1 and the negative electrode active material layer 6 are arranged in this order can be given. In this case, the solid electrolyte material 1 functions as a solid electrolyte layer. The particulate solid electrolyte material may be added to the positive electrode active material layer or the negative electrode active material layer. In the present invention, members as shown in FIGS. 1A to 1D can also be provided. Further, the thickness of the coat portion is the same as the thickness described in “B. Positive electrode active material” described later.

B. Next, the positive electrode active material of the present invention will be described. The positive electrode active material of the present invention is a positive electrode active material having an oxide positive electrode active material and a coat portion formed on the surface of the oxide positive electrode active material, wherein the coat portion is the solid described above. It consists of an electrolyte material.

  According to the present invention, the provision of the coating portion can suppress the generation of a high resistance layer caused by the reaction between the oxide positive electrode active material and the sulfide solid electrolyte material, and furthermore, the coating portion has high Li ion conductivity. The interface resistance between the oxide positive electrode active material and the sulfide solid electrolyte material can be reduced. When the oxide positive electrode active material and the sulfide solid electrolyte material come into contact with each other, it is considered that both react and the reaction product acts as a high resistance layer. On the other hand, by providing the coat portion made of the above-described solid electrolyte material, the generation of the high resistance layer can be suppressed and the interface resistance can be reduced.

  FIG. 2 is a schematic cross-sectional view showing an example of the positive electrode active material of the present invention. A positive electrode active material 10 shown in FIG. 2 has an oxide positive electrode active material 2 and a coat portion 1a formed on the surface of the oxide positive electrode active material 2 and made of the above-described solid electrolyte material.

1. Coat part The coat part in this invention consists of a solid electrolyte material mentioned above. The solid electrolyte material is the same as the contents described in the above “A. Solid electrolyte material”, and the description thereof is omitted here. The average thickness of the coat part is, for example, preferably in the range of 0.1 nm to 30 nm, and more preferably in the range of 1 nm to 15 nm. This is because if the average thickness is too small, the generation of the high resistance layer may not be effectively suppressed, and if the average thickness is too large, the ionic conductivity may be reduced. Moreover, the coverage of the coating part in the surface of an oxide positive electrode active material is 50% or more, for example, and it is preferable to exist in the range of 75%-95%. It is because the production | generation of a high resistance layer can be suppressed more effectively if it is in the said range.

2. Next, the oxide cathode active material in the present invention will be described. In the present invention, by using an oxide positive electrode active material, for example, an all-solid battery having a high energy density can be obtained. Examples of the oxide positive electrode active material include a general formula Li _x M _y O _z (M is a transition metal element, x = 0.02 to 2.2, y = 1 to 2, z = 1.4 to 4). ) Can be used as the positive electrode active material. In the above general formula, M is preferably at least one selected from the group consisting of Co, Mn, Ni, V, Fe and Si, and is at least one selected from the group consisting of Co, Ni and Mn. It is more preferable. As such an oxide positive electrode active material, specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , Li ( _{Ni 0.5 Mn 1.5) O 4,} Li 2 FeSiO 4, Li 2 MnSiO 4 , and the like. Examples of the positive electrode active material other than the above general formula Li _x M _y O _z include olivine-type positive electrode active materials such as LiFePO ₄ and LiMnPO ₄ .

  Examples of the shape of the oxide positive electrode active material include a particle shape, and among them, a true spherical shape or an elliptical spherical shape is preferable. Moreover, when an oxide positive electrode active material is a particle shape, it is preferable that the average particle diameter exists in the range of 0.1 micrometer-50 micrometers.

3. Others Since the positive electrode active material of the present invention has a coat portion, it is possible to suppress the generation of a high resistance layer caused by the reaction between the oxide positive electrode active material and the sulfide solid electrolyte material. Examples of the sulfide solid electrolyte material include those having Li, S, and the third component A. Examples of the third component A include at least one selected from the group consisting of P, Ge, B, Si, I, Al, Ga, and As. Among them, in the present invention, the sulfide solid electrolyte material is preferably a compound using Li ₂ S and sulfide MS other than Li ₂ S. _{Specifically,} Li 2 _S-P 2 _{S 5 compound,} Li ₂ S-SiS 2 _compound, or the like can be mentioned Li ₂ S-GeS 2 compounds, among them _Li 2 _S-P 2 _{S 5} compound. This is because the Li ion conductivity is high. Furthermore, when the molar ratio between Li ₂ S and sulfide MS is xLi ₂ S- (100-x) MS, x preferably satisfies the relationship 50 ≦ x ≦ 95, and 60 ≦ x ≦ 85. It is more preferable to satisfy the relationship. _{Incidentally,} Li 2 _S-P 2 _{S 5} compound means a sulfide solid electrolyte material using Li ₂ S and _P 2 _{S 5.} The same applies to other compounds. For example, an amorphous Li ₂ S—P ₂ S ₅ compound can be obtained by performing a mechanical milling method or a melt quenching method using Li ₂ S and P ₂ S ₅ . Further, the sulfide solid electrolyte material of the present invention may be amorphous or crystalline. The crystalline sulfide solid electrolyte material can be obtained, for example, by firing an amorphous sulfide solid electrolyte material. Moreover, it is preferable that the sulfide solid electrolyte material of this invention has bridge | crosslinking sulfur. This is because the sulfide solid electrolyte material has high Li ion conductivity. Moreover, when it has bridge | crosslinking sulfur, a high resistance layer is easy to generate | occur | produce. In particular, in the present invention, it is preferable that the sulfide solid electrolyte material is Li ₇ P ₃ S ₁₁ . This is because the Li ion conductivity is high.

  Moreover, the positive electrode active material of this invention can be used for a lithium battery. That is, in the present invention, it is possible to provide a lithium battery characterized by having a positive electrode active material layer containing the above-described positive electrode active material. The lithium battery may be a lithium battery having an electrolytic solution or an all-solid lithium battery. Furthermore, the lithium battery preferably contains a sulfide solid electrolyte material in the positive electrode active material layer or the solid electrolyte layer.

C. Next, a method for producing a solid electrolyte material of the present invention will be described. The method for producing a solid electrolyte material of the present invention is a method for producing the above-described solid electrolyte material, wherein the raw material solution containing Li alkoxide and Nb alkoxide is hydrolyzed to prepare a precursor solution of lithium niobate. A precursor film forming step of forming a precursor film of lithium niobate using the precursor solution, and the precursor film at a temperature in the range of 345 ° C. to 355 ° C., and for 4 hours to 6 hours. And a heat treatment step of performing heat treatment for a time within the range.

  According to the present invention, a solid electrolyte material having extremely high Li ion conductivity can be obtained by performing heat treatment under the above conditions. In addition, about the solid electrolyte material by this invention, it is the same as that of the content described in the said "A. solid electrolyte material".

FIG. 3 is a schematic cross-sectional view showing an example of a method for producing a solid electrolyte material of the present invention. More specifically, a method for producing a solid electrolyte material formed on the surface of an oxide positive electrode active material by a sol-gel method is shown. In FIG. 3, a raw material solution containing lithium ethoxide, pentaethoxyniobium and ethanol is hydrolyzed by adding water diluted with ethanol and stirring to prepare a precursor solution of lithium niobate in advance. deep. Next, an oxide positive electrode active material 2 is prepared (FIG. 3A), a precursor solution is applied to the surface of the oxide positive electrode active material 2, and dried to form a precursor film 1b (FIG. 3). 3 (b)). Thereafter, the oxide positive electrode active material 2 having the precursor film 1b is subjected to heat treatment under predetermined conditions to form a thin-film solid electrolyte material 1 on the surface of the oxide positive electrode active material 2. Note that the method for manufacturing the solid electrolyte material shown in FIG. 3 can also be regarded as the method for manufacturing the positive electrode active material 10 described above.
Hereafter, the manufacturing method of the solid electrolyte material of this invention is demonstrated for every process.

1. Preparation Step The preparation step in the present invention is a step of preparing a precursor solution of lithium niobate by hydrolyzing a raw material solution containing Li alkoxide and Nb alkoxide. The raw material solution contains at least Li alkoxide and Nb alkoxide, and usually contains a solvent. Examples of the Li alkoxide include lithium methoxide and lithium ethoxide. On the other hand, examples of the Nb alkoxide include pentamethoxyniobium, pentaethoxyniobium, pentapropoxyniobium and pentaboxyniobium. Moreover, it is preferable to select suitably the ratio of Li alkoxide and Nb alkoxide contained in a raw material solution according to the composition of the target lithium niobate. Usually, the ratio of Li alkoxide and Nb alkoxide is determined by paying attention to the molar ratio of Li contained in Li alkoxide and Nb contained in Nb alkoxide. Furthermore, the molar ratio of Li and Nb is preferably in the same range as the numerical range of Li and Nb described above.

  In addition, the raw material solution in the present invention usually contains a solvent. The solvent is not particularly limited as long as it can dissolve and disperse Li alkoxide and Nb alkoxide. For example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol Etc. Furthermore, in the present invention, it is preferred that Li alkoxide and Nb alkoxide are dissolved in a solvent and then stirred and refluxed. Thereby, the composite alkoxide of Li alkoxide and Nb alkoxide can be obtained.

  In the present invention, the raw material solution is hydrolyzed to obtain a precursor solution of lithium niobate. Examples of the method for hydrolyzing the raw material solution include a method in which an aqueous solution containing water is prepared, and the aqueous solution is added to the raw material solution and mixed. The solvent of the aqueous solution is preferably the same as the solvent of the raw material solution. The water used is preferably decarbonated water from which carbonic acid has been removed. Furthermore, in this invention, you may stir and reflux for a hydrolysis reaction. Moreover, the ratio of Li contained in the precursor solution is, for example, preferably in the range of 0.05 mol / kg to 1.0 mol / kg, and more preferably in the range of 0.1 mol / kg to 0.6 mol / kg. The same applies to the proportion of Nb contained in the precursor solution.

2. Precursor film formation process The precursor film formation process in this invention is a process of forming the precursor film | membrane of lithium niobate using the said precursor solution. The method for forming the lithium niobate precursor film is not particularly limited, and examples thereof include a method in which a precursor solution is applied and dried. Examples of the method for applying the precursor solution include a spray method, a pulling method, and a spin coating method. In addition, the pulling-up method here is a method of applying the precursor solution on the surface of the coated body by immersing the coated body in the precursor solution and pulling up the coated body. The precursor solution to be coated is not particularly limited. For example, as shown in FIGS. 1A and 1B described above, the oxide positive electrode active material 2 and the sulfide solid electrolyte material are used. 3 etc. can be mentioned. In this case, you may apply | coat a precursor solution on the surface of the oxide positive electrode active material 2 using the coating apparatus which has a rolling fluidized bed. Moreover, it is preferable to select suitably the application quantity of a precursor solution according to the thickness of the target solid electrolyte material. Furthermore, in this invention, it is preferable to dry a precursor solution after apply | coating a precursor solution.

3. Heat treatment step The heat treatment step in the present invention is a step of heat-treating the precursor film at a temperature within a range of 345 ° C to 355 ° C and a time within a range of 4 hours to 6 hours. Furthermore, it is preferable that the temperature of heat processing exists in the range of 348 degreeC-352 degreeC. The heat treatment time is preferably in the range of 4.9 hours to 5.1 hours. In the present invention, first, the temperature is raised from room temperature, then heat treatment is performed within the above-described temperature and time ranges, and finally the temperature is lowered to room temperature. That is, the heat treatment time in the present invention is usually a holding time that does not include the temperature raising time and the temperature lowering time. In the present invention, the heat treatment is usually performed in an atmosphere containing oxygen, and it is particularly preferable to perform the heat treatment in an air atmosphere.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
(Preparation of LiNbO ₃ precursor solution)
First, in an inert gas atmosphere, lithium ethoxide (LiOC ₂ H ₅ ) and pentaethoxyniobium (Nb (OC ₂ H ₅ ) ₅ ) are mixed so that the molar ratio of Li: Nb is 1: 1. Mixed. Next, the obtained mixture was dissolved in dehydrated and purified ethanol in an inert gas atmosphere. Next, stirring and refluxing were performed for 24 hours in an inert gas atmosphere to obtain a composite alkoxide. Thereafter, decarboxylated water diluted with an appropriate amount of ethanol was added dropwise to the obtained composite alkoxide to perform hydrolysis. Next, stirring and refluxing were further continued to complete the hydrolysis reaction. Thereafter, ethanol was evaporated, and the concentration of the precursor solution of LiNbO ₃ was adjusted to 0.2 mol / L. Thereby, a precursor solution of LiNbO ₃ was obtained.

(Preparation of evaluation thin film)
First, a ready-made comb electrode composed of glass / insulating film / gold was prepared. Next, the comb electrode was immersed in the precursor solution of LiNbO ₃ obtained above. Thereafter, a precursor thin film was formed on the comb electrode by using a pulling method in which the comb electrode was pulled up at a constant speed. Next, the comb electrode on which the precursor thin film was formed was left to stand in an air atmosphere / room temperature for one day and dried. Next, the dried comb-shaped electrode was heat-treated at 350 ° C. for 5 hours. The heat treatment was performed according to the following procedure. That is, first, a comb-shaped electrode in an air atmosphere / room temperature was moved to an air atmosphere heat treatment chamber set at 350 ° C. and left for 5 hours. Next, the comb-shaped electrode subjected to the heat treatment was returned to the atmosphere and at room temperature, and was left until the temperature of the comb-shaped electrode became approximately the same as room temperature. Thereby, a thin film lithium niobate (solid electrolyte material) having a thickness of about 100 nm was obtained.

[Comparative Examples 1-1 to 1-4]
Except that the heat treatment conditions were changed to 200 ° C, 10 hours, 300 ° C, 2 hours, 350 ° C, 2 hours, 400 ° C, 2 hours, respectively. Thus, lithium niobate (solid electrolyte material) was obtained.

[Evaluation]
(X-ray diffraction measurement)
X-ray diffraction (XRD) measurement was performed on the solid electrolyte materials obtained in Example 1 and Comparative Examples 1-1 to 1-4. The result is shown in FIG. As shown in FIG. 4, in Example 1 and Comparative Example 1-4, 2θ = 23.7 ° ± 2.0 °, 32.7 ° ± 2.0 °, 34.8 ° ± 2.0 °. 38.9 ° ± 2.0 °, 40.1 ° ± 2.0 °, 42.5 ° ± 2.0 °, first X-ray diffraction peak group, and 2θ = 25.5 ° ± 0. A second X-ray diffraction peak group of 5 °, 27.8 ° ± 1.0 °, 31.0 ° ± 0.8 °, 32.0 ° ± 0.8 ° was confirmed. On the other hand, in Comparative Examples 1-1 to 1-3, all the above peaks were not detected. Incidentally, from the above results, the obtained solid electrolyte material, it was confirmed that a LiNbO ₃ single phase. In addition, it was found that the crystallization progresses by heat treatment because the flat portion decreases and the peak corresponding to each crystal plane becomes larger and narrower as the temperature is higher.

Further, as described above, the second X-ray diffraction peak group was confirmed in Example 1 and Comparative Example 1-4. Therefore, assuming that the intensity of the X-ray diffraction peak at 2θ = 23.7 ° ± 2.0 ° is I _A and the intensity of the X-ray diffraction peak at 2θ = 25.5 ° ± 0.5 ° is I _B , I _A / I was determined the value of _{I B.} As a result, in Example 1, I _A / I _B = 8.0, and in Comparative Example 1-4, I _A / I _B = 14.5.

(Li ion conductivity)
Li ion conductivity was evaluated for the solid electrolyte materials obtained in Example 1 and Comparative Examples 1-1 to 1-4 by the AC impedance method in a steady DC polarization state. The results are shown in FIGS. 5-7, the reciprocal of the diameter of the semicircle or arc closest to the zero is proportional to the Li ion conductivity. Those diameters are shown in Table 1.

  As shown in Table 1, in Example 1, it was confirmed that the impedance value was remarkably low and the Li ion conductivity was extremely high.

[Example 2]
First, a lead belt analysis was performed on the X-ray diffraction result of the ferroelectric phase LiNbO ₃ , and crystal structure data was created based on the existing identification result of the crystal structure. Next, based on the crystal structure data, the most stable structure data was prepared using the density functional theory based on plane waves. The obtained most stable crystal structure data, with the potential function of the existing Li-Nb-O system, by applying the melt-quench method while changing the condition in molecular dynamics calculations, amorphous LiNbO ₃ Structural data was prepared. The amorphous property was evaluated by qualitative evaluation by polyhedral display of (1) crystallization rate, (2) XRD spectrum, and (3) Nb—O bond of the crystal structure, using the obtained amorphous crystal structure data. FIG. 8 shows a partial polyhedral structure of the produced single crystal structure / amorphous structure.

Moreover, the XRD spectrum simulation result including the actual measurement value data of Example 1 is shown in FIG. 7, 8, and 9, it was found that the peak of the XRD spectrum of the LiNbO ₃ single crystal was caused by the microstructure of the NbO ₃ tetrahedron. When the crystallization rate was about 85%, the XRD simulation spectrum had very many peaks. In the actual measurement, it is considered that the observation is made broad for the sake of resolution, and it was found that the NbO ₃ tetrahedral structure is retained even in this case. In this case, it was found from the observation result of the polyhedral structure that the Li ion conduction path was very small, and it was confirmed that the Li ion conductivity was small even by actual measurement. On the other hand, when the crystallization rate was about 95%, the actual measurement and simulation of the XRD spectrum were similar and had a characteristic peak of a single crystal. When the polyhedral structure in this case is observed, it is confirmed that the NbO ₃ tetrahedron has regularity and a structure similar to the superionic conductor AgI, a Li ion conduction path is generated, and the Li ion conductivity is high even in actual measurement. It was.

DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte material 1a ... Coating part 1b ... Precursor film | membrane 2 ... Oxide positive electrode active material 3 ... Sulfide solid electrolyte material 4 ... Positive electrode active material layer 5 ... Sulfide solid electrolyte layer 6 ... Negative electrode active material layer 10 ... Positive electrode Active material

Claims (3)

A solid electrolyte material made of lithium niobate,
2θ = 23.7 ° ± 2.0 °, 32.7 ° ± 2.0 °, 34.8 ° ± 2.0 °, 38.9 ° ± 2.0 °, 40.1 ° ± 2.0 °, first X-ray diffraction peak group of 42.5 ° ± 2.0 °, 2θ = 25.5 ° ± 0.5 °, 27.8 ° ± 1.0 °, 31.0 ° ± 0 A second group of X-ray diffraction peaks at 8 °, 32.0 ° ± 0.8 °,
The intensity of X-ray diffraction peaks of the 2θ = 23.7 ° ± 2.0 ° and _{I A,} the intensity of X-ray diffraction peaks of the 2θ = 25.5 ° ± 0.5 ° in the case of the _{I B A} solid electrolyte material satisfying the relationship of I _A / I _B ≦ 12.0. A positive electrode active material having an oxide positive electrode active material and a coating portion formed on the surface of the oxide positive electrode active material,
The positive electrode active material, wherein the coat part is made of the solid electrolyte material according to claim 1. It is a manufacturing method of the solid electrolyte material according to claim 1,
Hydrolyzing a raw material solution containing Li alkoxide and Nb alkoxide to prepare a precursor solution of lithium niobate;
A precursor film forming step of forming a precursor film of lithium niobate using the precursor solution;
A heat treatment step of heat treating the precursor film at a temperature within a range of 345 ° C. to 355 ° C. and a time within a range of 4 hours to 6 hours;
A method for producing a solid electrolyte material, comprising: