WO2016031942A1 - Electrolyte sheet and manufacturng method thereof - Google Patents

Abstract

　An electrolyte sheet, in one aspect of the present invention, in which a coating layer having a NASICON-type crystal structure that includes Li, Zr, and O and does not include a first transition metal derived from raw material is formed on a substrate having a NASICON-type crystal structure that includes Li, Ti, Al, P, and O.

Description

Electrolyte sheet and manufacturing method thereof

The present invention relates to an electrolyte sheet, a method for producing an electrolyte sheet, and an article.

Research on ceramic materials with excellent lithium ion conductivity has been actively conducted for application to lithium ion batteries, metal lithium-air batteries, and lithium ion capacitors.

Patent Document 1 discloses that a composite oxide represented by Li _{1 + x + y} Al _x Ti _2-x Si _y P _3-y O ₁₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is added to Zr, Hf, Y, Sm. A lithium ion conductive material containing a compound doped with at least one element selected from is disclosed.

International Publication No. 2013/024724

However, this lithium ion conductive material has low reduction resistance. When we want to use metallic lithium, which can be expected to improve energy density, as an electrode material, but when metallic lithium is used as an electrode material in direct contact with this lithium ion conductive material, titanium, the first transition metal element that is a constituent element Is reduced and deteriorated, and the ion conduction performance is lowered. Therefore, it is desired to improve the reduction deterioration resistance against metallic lithium.

An object of one embodiment of the present invention is to provide an electrolyte sheet having high lithium ion conductivity and excellent resistance to reduction deterioration with respect to metallic lithium in view of the above-described problems of the related art.

One embodiment of the present invention is the first transition since the raw material containing Li, Zr, P, and O on a substrate having a NASICON-type crystal structure containing Li, Ti, Al, P, and O in the electrolyte sheet. A coating layer having a NASICON crystal structure that does not contain a metal is formed.

One embodiment of the present invention is a process for producing a substrate having a NASICON type crystal structure by firing a raw material containing a Li-containing compound, a Ti-containing compound, an Al-containing compound, and a P-containing compound in a method for producing an electrolyte sheet. And a raw material containing a Li-containing compound, a Zr-containing compound and a P-containing compound and not containing a first transition metal-containing compound to produce a coating layer having a NASICON type crystal structure, or on the substrate Forming a step.

According to one embodiment of the present invention, it is possible to provide an electrolyte sheet having high lithium ion conductivity and excellent resistance to reduction deterioration with respect to metallic lithium.

It is a figure which shows the time-dependent change of the alternating current impedance of the coin cell produced using the electrolyte sheet of Example 1. FIG. It is a figure which shows the time-dependent change of the alternating current impedance of the coin cell produced using the electrolyte sheet of the comparative example 1. FIG. 6 is a graph showing the relationship of the lithium ion conductivity with the firing temperature of the electrolyte sheets of Examples 2-1-1 to 2-1-7. 2 is a cross-sectional SEM image of the electrolyte sheets of Examples 2-2-2 to 2-2-5. FIG. 6 is a graph showing the relationship of lithium ion conductivity with respect to the thickness of the coating layer of the electrolyte sheets of Examples 2-2-1 to 2-2-6 and Example 4. FIG. 3 is a graph showing changes in cell resistance over time when a coin cell produced using the electrolyte sheet of Example 2-2-3 is held at 25 ° C. for 100 hours and then heated at 85 ° C. for 12 hours. It is a figure which shows a time-dependent change of cell resistance at the time of heating the coin cell produced using the electrolyte sheet of Example 2-2-3 at 85 degreeC for 6 hours. It is a figure which shows the time-dependent change of the alternating current impedance of the coin cell produced using the electrolyte sheet of Example 3-2. It is a figure which shows the time-dependent change of the cell resistance of the coin cell produced using the electrolyte sheet of Example 3-2 and Comparative Example 3. 6 is a cross-sectional SEM image of the electrolyte sheet of Example 5. FIG.

Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

[Electrolyte sheet]
The electrolyte sheet according to the present embodiment includes Li, Zr, P, and O on a base material having a NASICON type crystal structure including Li, Ti, Al, P, and O, and includes a first transition metal derived from a raw material. A coating layer having no NASICON type crystal structure is formed.

The electrolyte sheet of the present embodiment can be applied to electrolyte membranes of lithium ion batteries, metal lithium-air batteries, separators, separators of lithium ion capacitors, and the like.

〔Base material〕
The base material has a NASICON type crystal structure containing Li, Ti, Al, P, and O. As the base material, a material having high lithium ion conductivity but not high resistance to reduction deterioration against metallic lithium is used.

As such a material, for example, a compound represented by Li _{1 + x} Al _x Ti _2-x P ₃ O ₁₂ (0 ≦ x ≦ 1) is preferably used.

It does not specifically limit about the raw material of a base material, A well-known compound can be used. For example, a base material can be produced by firing a compound containing an element constituting the compound, that is, a raw material containing a Li-containing compound, an Al-containing compound, a Ti-containing compound, or a P-containing compound. More specific examples include Li ₂ CO ₃ , Li ₂ TiO ₃ , TiO ₂ , H ₃ PO ₄ , Al ₂ (CO ₃ ) ₃ , AlPO ₄ , Al (PO ₃ ) ₃ , Al (OH) as raw materials. ) ₃ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO _{4 and the} like.

The raw materials are prepared in such a ratio that the composition when the raw materials of the base material are baked alone is the following composition ratio.

The content of Li in the substrate is preferably 5.5 to 13 mol%, more preferably 8 to 10 mol%, and still more preferably 8.5 to 9.5 mol%.

The content of Ti in the substrate is preferably 9 to 10 mol%, more preferably 8 to 10 mol%, and still more preferably 8.5 to 9.5 mol%.

The content of Al in the substrate is preferably 1 to 1.5 mol%, more preferably 1.2 to 1.4 mol%, and further preferably 1.2 to 1.3 mol%.

The content of P in the substrate is preferably 15 to 18 mol%, more preferably 15 to 16 mol%, and further preferably 15 to 15.5 mol%.

The content of O in the substrate is preferably 60 to 65 mol%, more preferably 61 to 65 mol%, still more preferably 63 to 64.5 mol%.

When the content of Li, Ti, Al, P, O in the substrate is within the above range, the ion conductivity and the sinterability are excellent.

It is preferable that the base material further includes one or more elements selected from the group consisting of Zr, Y, Si and B. As a result, the firing temperature can be reduced. Moreover, the density and bending strength of the base material can be improved, and further, lithium ion conductivity can be improved.

The raw material of one or more elements selected from the group consisting of Zr, Y, Si, and B is not particularly limited, and includes elements such as Zr, Y, Si, and B during firing using thermal diffusion. Addition from a contact material or a known compound can be used as a raw material. For example, a base material can be produced by firing a raw material containing a compound containing an element constituting the compound, that is, a Zr-containing compound, a Y-containing compound, a Si-containing compound, or a B-containing compound. As a more specific example, zirconia, yttria, yttria stabilized zirconia, silica, silicon, SiC, B ₂ O ₃ , LiBO ₃ or the like can be used as a raw material.

The content of Zr in the substrate is preferably 0.001 to 0.04 mol%, more preferably 0.01 to 0.04 mol%, still more preferably 0.02 to 0.03 mol%. . Sinterability improves that content of Zr in a base material is in the above-mentioned range.

The content of Y in the substrate is preferably 0.00001 to 0.03 mol%, more preferably 0.0001 to 0.01 mol%, and still more preferably 0.0005 to 0.0015 mol%. . Sinterability improves that content of Y in a base material is in the above-mentioned range.

The Si content in the substrate is preferably 0.8 to 1.5 mol%, more preferably 0.9 to 1.2 mol%, and still more preferably 1.0 to 1.1 mol%. . Sinterability improves that content of Si in a base material is in the said range.

The content of B in the substrate is preferably 0.01 to 0.2 mol%, more preferably 0.05 to 0.15 mol%, still more preferably 0.075 to 0.11 mol%. . Sinterability improves that content of B in a base material is in the said range.

The thickness of the substrate is not particularly limited, but is preferably 10 to 500 μm, more preferably 30 to 150 μm, and further preferably 40 to 80 μm. When the thickness of the substrate is within the above range, handling properties and low resistance can be expected.

(Coating layer)
The coating layer has a NASICON type crystal structure that includes Li, Zr, P, and O and does not include the first transition metal derived from the raw material. For the coating layer, it is preferable to use a material that is not sufficiently high in lithium ion conductivity but has high resistance to reduction deterioration against metallic lithium. However, it is desirable that the covering layer has higher lithium ion conductivity.

As such a material, for example, a compound represented by LiZr ₂ P ₃ O ₁₂ is preferably used.

The raw material for the coating layer is not particularly limited, and a known compound can be used. For example, a coating layer is prepared by firing a compound containing an element constituting the above compound, that is, a Li-containing compound, a Zr-containing compound, a P-containing compound, and a raw material not containing the first transition metal-containing compound, or Can be formed on a substrate. As a more specific example, Li ₂ CO ₃ , ZrO ₂ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ or the like can be used as a raw material.

In the present specification and claims, the “raw material-derived first transition metal” material is a material that is fired when the coating layer is formed or formed on a substrate.

When the raw materials for the coating layer are fired independently, the raw materials are prepared in such a ratio that the following composition ratio is obtained.

The content of Li in the coating layer is preferably 5.5 to 8 mol%, more preferably 5.5 to 7 mol%, and further preferably 5.7 to 6.6 mol%.

The content of Zr in the coating layer is preferably 10 to 11.5 mol%, more preferably 10.5 to 11.5 mol%, still more preferably 10.8 to 11.3 mol%.

The content of P in the coating layer is preferably 15 to 17.5 mol%, more preferably 16 to 17 mol%, and further preferably 16.3 to 16.8 mol%.

The content of O in the coating layer is preferably 65 to 68 mol%, more preferably 65 to 67 mol%, still more preferably 65.5 to 67 mol%.

When the content of Li, Zr, P, and O in the coating layer is within the above range, the sinterability and lithium ion conductivity are excellent.

Depending on the firing conditions, the composition changes due to transpiration of Li or the like. Further, when the coating layer is fired together with the base material, the constituent elements such as the first transition metal are diffused by thermal diffusion from the base material to the coating layer to form a part of the solid solution. For this reason, although the raw material of a coating layer is utilized in the ratio which becomes a predetermined composition ratio, the composition of the coating layer after baking changes with heating conditions. Furthermore, a composition gradient occurs in the coating layer. For this reason, the density | concentration of the 1st transition metal of the outermost surface of the coating layer after co-firing is remarkably low compared with a base material, and the 1st of the outermost surface of the coating layer after co-firing with a base material is The concentration of the transition metal is desirably ¼ or less of the base material. For that purpose, it is preferable to bake at a lower temperature to suppress thermal diffusion.

That is, a NASICON type crystal structure that includes Li, Zr, P, and O and does not include a first transition metal since the raw material on a base material having a NASICON type crystal structure containing Li, Ti, Al, P, and O. An electrolyte sheet in which the concentration of transition metal on the outermost surface of the coating layer is 1/4 or lower than that of the substrate is preferable, and the concentration of transition metal on the outermost surface of the coating layer An electrolyte sheet having a concentration of 1/10 or less as compared with the base material is more preferable.

The coating layer preferably further contains Ca and / or Y. Thereby, the density of a coating layer can be improved and, as a result, lithium ion conductivity can further be improved.

The raw materials for Ca and / or Y are not particularly limited, and addition from a contact material containing Ca and / or Y at the time of firing using thermal diffusion, or a known compound can be used as a raw material. For example, a base material can be produced by firing a material containing an element constituting the compound, that is, a raw material containing a Ca-containing compound and a Y-containing compound. As a more specific example, calcia, yttria, calcium carbonate, yttrium nitrate hexahydrate and the like can be used as a raw material.

The Ca content in the coating layer is preferably 0.05 to 0.6 mol%, more preferably 0.1 to 0.4 mol%, and still more preferably 0.2 to 0.3 mol%. . When the content of Ca in the coating layer is within the above range, an improvement in sinterability and an improvement in lithium ion conductivity can be expected.

The content of Y in the coating layer is preferably 0.01 to 0.7 mol%, more preferably 0.02 to 0.3 mol%, still more preferably 0.05 to 0.1 mol%. . If the Y content in the coating layer is within the above range, an improvement in sinterability can be expected.

The coating layer may be formed on one side of the base material, or may be formed on both sides of the base material.

Note that the coating layer may be a single layer or a multilayer (multilayer). When the coating layer has a multilayer structure, the composition controllability is excellent.

The thickness of the coating layer is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1.0 to 3 μm, and further preferably 1 to 1.5 μm. When the thickness of the coating layer is 0.5 μm or more, when forming the coating layer, the influence of the surface roughness of the substrate can be reduced, the generation of defects such as pinholes can be suppressed, and Resistance can be further improved. On the other hand, when the thickness of the coating layer is 10 μm or less, it is possible to suppress a decrease in lithium ion conductivity.

Here, when the coating layer is a multilayer, the thickness of the coating layer means the total thickness of the multilayer coating layers formed on the substrate.

[Specific example of manufacturing method of electrolyte sheet]
Hereinafter, the method for producing an electrolyte sheet will be described with a specific example, but is not limited to the following method.
(1) Production of substrate (1-1) Formation of sheet-like molded body An inorganic material for a substrate, a solvent, a binder, a plasticizer, and the like are mixed to prepare a raw material slurry or a kneaded product.

Here, the binder used is not particularly limited. For example, ethylene copolymer, styrene copolymer, acrylate and methacrylate copolymer, vinyl acetate copolymer, maleic acid copolymer, vinyl butyral resin, vinyl acetal resin, vinyl formal Examples thereof include conventionally known organic binders such as resins, vinyl alcohol resins, waxes, celluloses such as ethyl cellulose, and the like.

The solvent used is not limited, and water, alcohols such as methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol, ketones such as acetone and 2-butanone, pentane, hexane and heptane Aliphatic hydrocarbons such as benzene, toluene and xylene, and acetates such as methyl acetate, ethyl acetate and butyl acetate. In addition, it is not limited to 1 type, 2 or more types can also be mixed and used.

Furthermore, a dispersant for promoting peptization and dispersion of the raw material powder, a plasticizer for imparting flexibility to the sheet-like molded body, a surfactant, an antifoaming agent, and the like can be added.

Raw material slurry or raw material kneaded material is prepared by mixing an appropriate amount of the above components. At that time, in order to make each particle fine or to make the particle diameter uniform, mixing can be performed while pulverizing with a ball mill or the like.

(1-2) Production of sheet-like molded body (green sheet) The obtained raw material slurry or raw material kneaded material is formed into a sheet by various known methods such as slurry casting method, doctor blade method, extrusion molding method, screen printing method and the like. A shaped molded body (green sheet) can be molded.

At this time, the size of the sheet-like molded body (green sheet) is not particularly limited, and is appropriately selected according to the application.

(1-3) Firing Next, the sheet-like molded body (green sheet) is fired. Specifically, the sheet-like molded body is sandwiched and fired between materials containing at least one element selected from Zr, Hf, Y, and Sm.

The material containing at least one element selected from Zr, Hf, Y, and Sm used for firing is not limited as long as it is a material (substance) containing these elements. be able to. For example, the board which consists of these metals or oxides is mentioned. In addition, it is not necessary to contain only these elements, For example, the thing containing together another component like the zirconia board stabilized with calcia can also be used. In addition, for example, a material in which a foil, paste, powder, or the like containing the above elements is disposed on the surface of a plate having heat resistance such as alumina, mullite, or a platinum plate, at least on the surface in contact with the sheet molded body Can be used. Furthermore, a substance containing at least one element selected from Zr, Hf, Y, and Sm, for example, a molded body of such a metal or oxide powder (for example, a sheet or pellet) is also involved. It can be used as a material.

There is no particular limitation on the size of the material sandwiching the sheet-like molded body, as long as it covers the surface of the sheet-like molded body to be fired, depending on the size of the sheet-like molded body, the size of the firing furnace, etc. Can be selected as appropriate. In addition, it is sufficient if the sheet-like molded body is sandwiched between the materials as described above, and it is not necessary to apply a load or use a fixture, but it is possible to apply a load so that it does not move during firing, A fixing tool may be provided to easily carry-in work or the like.

Calcination temperature is selected according to the intended degree of ion conductivity, strength, etc., and is not limited. Although the sinterability varies depending on the presence or absence of additives, it is preferable to fire at 800 ° C. or higher, particularly preferable to fire at 825 ° C. or higher where ion conductivity and density increase, and more preferable to fire at 850 ° C. or higher. preferable. The upper limit of the temperature is not limited, but the temperature at which the ionic conductor melts and adheres to the material containing the predetermined element, the heat-resistant temperature of the material containing the predetermined element used, etc. are considered. And it is preferable to bake at a lower temperature. In particular, from the viewpoint of cost and prevention of transpiration of Li, firing at 900 ° C. or lower is preferable.

Thus, the base material is produced.

(2) Formation of coating layer (2-1) Preparation of coating solution An inorganic substance for the coating layer, a solvent, a binder, a plasticizer, and the like are mixed to prepare a coating solution.

Here, the binder used is not particularly limited. For example, ethylene copolymer, styrene copolymer, acrylate and methacrylate copolymer, vinyl acetate copolymer, maleic acid copolymer, vinyl butyral resin, vinyl acetal resin, vinyl formal Examples thereof include conventionally known organic binders such as resins, vinyl alcohol resins, waxes, celluloses such as ethyl cellulose, and the like.

The solvent used is not limited, and water, alcohols such as methanol, ethanol, 2-propanol, 1-butanol and 1-hexanol, ketones such as acetone and 2-butanone, pentane, hexane and heptane Aliphatic hydrocarbons such as benzene, toluene and xylene, and acetates such as methyl acetate, ethyl acetate and butyl acetate. In addition, it is not limited to 1 type, 2 or more types can also be mixed and used.

Furthermore, a dispersant for promoting peptization and dispersion of the raw material powder, a plasticizer for imparting flexibility to the sheet-like molded body, a surfactant, an antifoaming agent, and the like can be added.

(2-2) Formation of coating layer Next, a coating solution is applied to the substrate and dried. Application and drying may be repeated a plurality of times. By repeating the application and drying a plurality of times, the thickness of the coating layer can be controlled. The number of repetitions of application and drying is not particularly limited, but the formation of defects such as cracks can be suppressed if the thickness of the coating film formed by one application is not too thick. The thickness of the coating film formed by a single application depends on the size of the particles constituting the coating film, but is desirably about 5 μm or less. When the size of the particles constituting the coating film is 700 nm or less, it is desirable that the thickness of the coating film formed by one application is 1 μm or less.

(2-3) Firing Next, the substrate on which the coating layer is formed is fired.

The firing temperature is selected depending on the intended degree of ionic conductivity and the like, and is not limited. However, firing is preferably performed at 900 ° C. or higher, in particular, 1075 ° C. or higher at which ion conductivity and density are increased. Is preferably fired at 1100 ° C. or higher. The upper limit of the temperature is not limited, but the temperature at which the ionic conductor melts and adheres to the material containing the predetermined element, the heat-resistant temperature of the material containing the predetermined element used, etc. are considered. And it is preferable to bake at a lower temperature. In particular, firing at 1125 ° C. or lower is preferable from the viewpoint of cost and prevention of Li evaporation.

By the above preferred method, on the substrate having a NASICON type crystal structure containing Li, Ti, Al, P and O, Li, Zr, P and O are contained, but the first transition metal derived from the raw material is not contained. An electrolyte sheet having a coating layer having a NASICON crystal structure can be produced.

[Comparative Example 1]
Li ₂ CO ₃ , Li ₂ TiO ₃ , TiO ₂ , Al (PO ₃ ) ₃ , Al (OH) ₃ , SiO ₂ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ and ZrO ₂ to produce a Li ₂ O, TiO ₂ , Al ₂ O ₃ , SiO ₂ , P ₂ O ₅ and ZrO ₂ molar ratio of 1.5: 3.1: 2.2: 0.36: 2.6. : Weighed to 0.01 and mixed homogeneously. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 850 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, using a planetary ball mill P-6 (manufactured by Fritsch), the crystalline inorganic substance was pulverized in butanol at 600 rpm for 2 hours and then dried to obtain a powder. When pulverizing using a planetary ball mill, a zirconia pot was used and zirconia balls were used as media.

10% by weight of polyvinyl butyral and 0.2% by weight of N-tallow alkyl trimethylenediamine are added to the powder and mixed in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) for 24 hours. A slurry was obtained.

Using a sheet molding machine, the slurry was molded so as to have a thickness of 200 μm to obtain a sheet molded body (green sheet). The sheet compact was dried and cut into strips, sandwiched between two yttria-stabilized zirconia plates, and fired at 900 ° C. for 1 hour to obtain an electrolyte sheet. The electrolyte sheet had a lithium ion conductivity of 7.6 × 10 ⁻⁴ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Lithium ion conductivity]
A gold blocking electrode having a thickness of 500 nm was formed on both surfaces of the electrolyte sheet by sputtering, and then a coin cell was produced in an argon atmosphere. Next, using an impedance analyzer FRA1260 (manufactured by Solartron), the AC impedance of the coin cell at 25 ° C. was measured in the frequency range of 0.1 to 1 × 10 ⁶ Hz, and the lithium ion conductivity was calculated. The lithium ion conductivity is a group determined from the resistance within the crystal grains of the electrolyte sheet obtained by measuring the AC impedance of the coin cell, the sum of the intergranular resistance and the electrode interface resistance, the electrode area, and the cross-sectional SEM image. It calculated from the thickness of a material and a coating layer.

[Preparation of coating solution 1]
Li ₂ O ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ and ZrO ₂ are produced at a molar ratio of Li ₂ O, P ₂ O ₅ and ZrO ₂ of 1.1: After weighing to 3: 2, the mixture was mixed homogeneously. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, 2% by mass of N-tallow alkyl trimethylenediamine was added to the crystalline inorganic substance, and pulverized in butanol at 600 rpm for 2 hours using a planetary ball mill P-6 (manufactured by Fritsch). Thereafter, it was dried to obtain a powder. When measured using a particle size distribution analyzer ELSZ-2 (manufactured by Otsuka Electronics Co., Ltd.), the powder had a number average particle size of 1.4 μm. When pulverizing using a planetary ball mill, a zirconia pot was used and zirconia balls were used as media.

3% by mass of polyvinyl butyral was added to the powder and dispersed homogeneously in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) to obtain a cloudy coating solution 1.

[Example 1]
After dip-coating the coating solution 1, the drying operation was repeated a plurality of times to form a coating layer having a thickness of 10 μm on both surfaces of the electrolyte sheet (base material) of Comparative Example 1, and then an electric furnace HPM-1N (ASONE And manufactured at 930 ° C. to obtain an electrolyte sheet. The electrolyte sheet was confirmed to have a lithium ion conductivity of 7.4 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Comparative Example 2]
Li ₂ O ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ and ZrO ₂ are produced at a molar ratio of Li ₂ O, P ₂ O ₅ and ZrO ₂ of 1.1: After weighing to 3: 2, the mixture was mixed homogeneously. This composition is the same as that of the coating liquid 1. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, using a planetary ball mill P-6 (manufactured by Fritsch), the crystalline inorganic substance was pulverized in butanol at 600 rpm for 2 hours and then dried to obtain a powder. When pulverizing using a planetary ball mill, a zirconia pot was used and zirconia balls were used as media.

10% by weight of polyvinyl butyral and 0.2% by weight of N-tallow alkyl trimethylenediamine are added to the powder and mixed in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) for 24 hours. A slurry was obtained.

Using a sheet molding machine, the slurry was molded so as to have a thickness of 150 μm to obtain a sheet molded body (green sheet). The sheet compact was dried and cut into strips, and then fired at 1050 ° C. for 1 hour to obtain an electrolyte sheet. The electrolyte sheet had a lithium ion conductivity of 2.0 × 10 ⁻⁷ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

The lithium ion conductivity of the electrolyte sheet of Example 1 was larger than the calculated value calculated by the combined sum of the lithium ion conductivity of the electrolyte sheets of Comparative Example 1 and Comparative Example 2. For this reason, it turns out that the electrolyte sheet of Example 1 becomes a thing excellent in lithium ion conductivity by layering.

Next, the reduction deterioration resistance of the electrolyte sheets of Example 1 and Comparative Example 1 to metallic lithium was evaluated.

[Reduction degradation resistance to metallic lithium]
In an argon atmosphere, a coin cell was manufactured by pressure bonding a metal Li foil as an electrode on both surfaces of the electrolyte sheet. Next, hold in a constant temperature bath at 25 ° C., and measure the time-dependent change in the AC impedance of the coin cell at 25 ° C. in the frequency range of 0.05 to 1 × 10 ⁶ Hz using an impedance analyzer FRA1260 (manufactured by Solartron). Then, the reduction deterioration resistance against metallic lithium was evaluated.

FIG. 1 and FIG. 2 show the change over time of the alternating current impedance of coin cells prepared using the electrolyte sheets of Example 1 and Comparative Example 1, respectively.

1 and 2, it can be seen that in any of the electrolyte sheets of Example 1 and Comparative Example 1, the interfacial resistance with the electrode immediately after the coin cell is produced is large.

From FIG. 1, when the electrolyte sheet of Example 1 is held in a constant temperature bath at 25 ° C., the interfacial resistance with the electrode is reduced, and the resistance in the crystal grains and the grain boundary resistance are also reduced. It is understood that is superior. At this time, in the electrolyte sheet of Example 1, in addition to the improvement of the adhesion at the interface with the metallic lithium, it is considered that lithium ion deficiency is compensated and lithium ions are implanted.

From FIG. 2, when the electrolyte sheet of Comparative Example 1 is held in a constant temperature bath at 25 ° C., the interface resistance with the electrode slightly decreases, but the resistance in the crystal grains and the grain boundary resistance may increase rapidly. Recognize. This is considered to be because the electrolyte sheet of Comparative Example 1 is reduced and deteriorated by coming into contact with metallic lithium.

Next, the reduction deterioration resistance of the electrolyte sheet of Comparative Example 2 to metallic lithium was evaluated.

As a result, when the electrolyte sheet of Comparative Example 2 was held in a constant temperature bath at 25 ° C., the interface resistance with the electrode decreased, but the resistance in the crystal grains and the grain boundary resistance did not decrease. For this reason, it is thought that the electrolyte sheet of the comparative example 2 does not improve lithium ion conductivity by filling the defect of lithium ions and implanting lithium ions.

[Comparative Example 3]
An electrolyte sheet was obtained in the same manner as in Comparative Example 1 except that the slurry was formed to have a thickness of 150 μm and the firing temperature was changed to 930 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 8.4 × 10 ⁻⁴ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 2-1-1]
After dip-coating the coating solution 1, the drying operation was repeated a plurality of times to form a coating layer having a thickness of 30 μm on both surfaces of the electrolyte sheet (base material) of Comparative Example 3, and then electric furnace HPM-1N (ASONE And manufactured at 850 ° C. to obtain an electrolyte sheet. The pulling speed during dip coating was set to 0.1 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 5.2 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 2-1-2]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 900 ° C. The electrolyte sheet had a lithium ion conductivity of 5.4 × 10 ⁻⁶ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 2-1-3]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 920 ° C. The electrolyte sheet had a lithium ion conductivity of 9.4 × 10 ⁻⁶ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 2-1-4]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 940 ° C. The electrolyte sheet had a lithium ion conductivity of 1.4 × 10 ⁻⁵ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 2-1-5]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 950 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 1.5 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 2-1-6]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 980 ° C. The electrolyte sheet had a lithium ion conductivity of 1.3 × 10 ⁻⁵ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 2-1-7]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the firing temperature was changed to 1000 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 6.6 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

The lithium ion conductivities of the electrolyte sheets of Examples 2-1-1 to 2-1-7 were larger than the calculated values calculated by the combined sum of the lithium ion conductivities of the electrolyte sheets of Comparative Example 2 and Comparative Example 3. . Therefore, it can be seen that the electrolyte sheets of Examples 2-1-1 to 2-1-7 are excellent in lithium ion conductivity when layered.

FIG. 3 shows the relationship of the lithium ion conductivity to the firing temperature of the electrolyte sheets of Examples 2-1-1 to 2-1-7.

FIG. 3 shows that the lithium ion conductivity of the electrolyte sheet increases when the firing temperature is around 950 ° C.

Further, as a result of observing the sintered state of the coating layer with an electron microscope, a dense coating layer was formed in the electrolyte sheets of Examples 2-1-5 to 2-1-7.

Next, the reduction deterioration resistance of the electrolyte sheets of Examples 2-1-1 to 2-1-7 and Comparative Example 2 to metallic lithium was evaluated.

As a result, in the electrolyte sheets of Examples 2-1-1 to 2-1-7, the resistance in crystal grains and the grain boundary resistance did not increase even after two months or more. Therefore, it can be seen that the electrolyte sheets of Examples 2-1-1 to 2-1-7 are excellent in reduction deterioration resistance against metallic lithium.

On the other hand, in the electrolyte sheet of Comparative Example 3, as in the electrolyte sheet of Comparative Example 1, the resistance in crystal grains and the grain boundary resistance increased.

[Example 2-2-1]
The coating liquid 1 was dip-coated on both surfaces of the electrolyte sheet (base material) of Comparative Example 3, and then baked at 950 ° C. using an electric furnace HPM-1N (manufactured by ASONE) to obtain an electrolyte sheet. The pulling speed during dip coating was set to 0.005 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 4.6 × 10 ⁻⁴ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction. The electrolyte sheet was formed with a dense coating layer, and the coating layer had a thickness of 2 μm.

[Example 2-2-2]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the pulling rate during dip coating was 0.01 mm / s. The electrolyte sheet had a lithium ion conductivity of 2.5 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component. The electrolyte sheet was formed with a dense coating layer (see FIG. 4), and the coating layer had a thickness of 4 μm.

[Example 2-2-3]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the pulling rate during dip coating was set to 0.05 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 9.3 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction. The electrolyte sheet was formed with a dense coating layer (see FIG. 4), and the coating layer had a thickness of 7 μm.

[Example 2-2-4]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the pulling rate during dip coating was 0.1 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 6.3 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction. The electrolyte sheet was formed with a dense coating layer (see FIG. 4), and the coating layer had a thickness of 10 μm.

[Example 2-2-5]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the pulling rate during dip coating was 0.25 mm / s. The electrolyte sheet had a lithium ion conductivity of 3.1 × 10 ⁻⁶ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component. The electrolyte sheet was formed with a dense coating layer (see FIG. 4), and the coating layer had a thickness of 13 μm.

[Example 2-2-6]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the pulling rate during dip coating was set to 0.4 mm / s. The electrolyte sheet had a lithium ion conductivity of 1.7 × 10 ⁻⁶ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component. The electrolyte sheet had a dense coating layer, and the coating layer had a thickness of 20 μm.

FIG. 5 shows the relationship between the lithium ion conductivity and the thickness of the coating layer of the electrolyte sheets of Examples 2-2-1 to 2-2-6. In addition, in FIG. 5, the calculated value computed by the synthetic sum of the lithium ion conductivity of the electrolyte sheet of the comparative example 2 and the electrolyte sheet of the comparative example 3 is also shown.

From FIG. 5, the electrolyte sheets of Examples 2-2-1 to 2-2-6 have a lithium ion conductivity larger than the calculated value, and are excellent in lithium ion conductivity when layered. I understand. Furthermore, it can be seen that the electrolyte sheets of Examples 2-2-1 and 2-2-2 have a particularly large difference between the lithium ion conductivity and the calculated value, and are particularly excellent in lithium ion conductivity.

Next, the reduction deterioration resistance to metallic lithium in Examples 2-2-1 to 2-2-6 was evaluated.

As a result, the electrolyte sheets of Examples 2-2-1 to 2-2-6 did not increase the resistance in the crystal grains and the grain boundary resistance even when held in a constant temperature bath at 25 ° C. for 2 months or more. . Therefore, it can be seen that the electrolyte sheets of Examples 2-2-1 to 2-2-6 are excellent in reduction deterioration resistance against metallic lithium.

Next, in an argon atmosphere, a coin cell prepared by pressure-bonding a metal Li foil as an electrode on both surfaces of the electrolyte sheet of Example 2-2-3 was held in a thermostatic bath at 25 ° C. for 100 hours. The time-dependent change in cell resistance was confirmed when heated at 85 ° C. for 12 hours, cooled to 25 ° C. and held. At this time, the cell resistance was calculated from the resistance within the crystal grains of the electrolyte sheet obtained by measuring the alternating current impedance of the coin cell, the grain boundary resistance, the total interface resistance with the electrode, and the electrode area. As a result, when the electrolyte sheet of Example 2-2-3 is heated at 85 ° C. for 12 hours, the interface resistance with the electrode can be rapidly reduced as compared with the case where the electrolyte sheet is kept at 25 ° C. It was possible (see FIG. 6).

Further, in an argon atmosphere, a coin cell produced by pressing a metal Li foil as an electrode on both surfaces of the electrolyte sheet of Example 2-2-3 was heated at 85 ° C. for 6 hours and cooled to 25 ° C. The time-dependent change of the cell resistance when held was confirmed. At this time, the cell resistance was calculated from the resistance within the crystal grains of the electrolyte sheet obtained by measuring the alternating current impedance of the coin cell, the grain boundary resistance, the total interface resistance with the electrode, and the electrode area. As a result, the electrolyte sheet of Example 2-2-3 was able to rapidly reduce the interface resistance with the electrode by heating at 85 ° C. for 6 hours (see FIG. 7).

[Preparation of coating solution 2]
The molar ratio of Li ₂ O, P ₂ O ₅ , ZrO ₂ and CaO to produce Li ₂ CO ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , ZrO ₂ and CaCO ₃ Was weighed so as to be 1.2: 3: 1.9: 0.1, and then homogeneously mixed. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, 2% by mass of N-tallow alkyl trimethylenediamine was added to the crystalline inorganic substance, and pulverized in butanol at 600 rpm for 2 hours using a planetary ball mill P-6 (manufactured by Fritsch). Thereafter, it was dried to obtain a powder. When measured using a particle size distribution analyzer ELSZ-2 (manufactured by Otsuka Electronics Co., Ltd.), the powder had a number average particle size of 1.3 μm. A zirconia pot was used for pulverization using a planetary ball mill, and zirconia balls were used as media.

3% by mass of polyvinyl butyral was added to the powder and dispersed uniformly in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) to obtain a cloudy coating solution 2.

[Example 3-1-1]
An electrolyte sheet was obtained in the same manner as in Example 2-1-1 except that the coating liquid 2 was used instead of the coating liquid 1. The electrolyte sheet had a lithium ion conductivity of 6.2 × 10 ⁻⁶ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 3-1-2]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 900 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 6.8 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON type crystal structure as a main component by X-ray diffraction.

[Example 3-1-3]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 920 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 1.2 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 3-1-4]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 940 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 3.2 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 3-1-5]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 950 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 3.6 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 3-1-6]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 980 ° C. The electrolyte sheet had a lithium ion conductivity of 2.7 × 10 ⁻⁵ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 3-1-7]
An electrolyte sheet was obtained in the same manner as in Example 3-1-1 except that the firing temperature was changed to 1000 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 2.1 × 10 ⁻⁵ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

As a result of observing the sintered state of the coating layer using an electron microscope, a dense coating layer was formed in the electrolyte sheets of Examples 3-1-5 to 3-1-7.

[Comparative Example 4]
The molar ratio of Li ₂ O, P ₂ O ₅ , ZrO ₂ and CaO to produce Li ₂ CO ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , ZrO ₂ and CaCO ₃ Was weighed so as to be 1.2: 3: 1.9: 0.1, and then homogeneously mixed. This composition is the same as that of the coating liquid 2. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, using a planetary ball mill P-6 (manufactured by Fritsch), the crystalline inorganic substance was pulverized in butanol at 600 rpm for 2 hours and then dried to obtain a powder. When pulverizing using a planetary ball mill, a zirconia pot was used and zirconia balls were used as media.

10% by weight of polyvinyl butyral and 0.2% by weight of N-tallow alkyl trimethylenediamine are added to the powder and mixed in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) for 24 hours. A slurry was obtained.

Using a sheet molding machine, the slurry was molded so as to have a thickness of 150 μm to obtain a sheet molded body (green sheet). The sheet compact was dried and cut into strips, and then fired at 1050 ° C. for 1 hour to obtain an electrolyte sheet. The electrolyte sheet was confirmed to have a lithium ion conductivity of 5.0 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

The lithium ion conductivities of the electrolyte sheets of Examples 3-1-1 to 3-1-7 were larger than the calculated values calculated by the combined sum of the lithium ion conductivities of the electrolyte sheets of Comparative Example 3 and Comparative Example 4. . Therefore, it can be seen that the electrolyte sheets of Examples 3-1-1 to 3-1-7 become excellent in lithium ion conductivity when layered.

Next, the reduction deterioration resistance of the electrolyte sheets of Examples 3-1-1 to 3-1-7 and Comparative Example 4 to metallic lithium was evaluated.

As a result, in the electrolyte sheets of Examples 3-1-1 to 3-1-7, the resistance in the crystal grains and the grain boundary resistance did not increase even after two months or more. Therefore, it can be seen that the electrolyte sheets of Examples 3-1-1 to 3-1-7 are excellent in reduction deterioration resistance against metallic lithium.

In contrast, when the electrolyte sheet of Comparative Example 4 was held in a constant temperature bath at 25 ° C., the interface resistance with the electrode decreased, but the resistance within the crystal grains and the grain boundary resistance did not decrease. For this reason, it is thought that the electrolyte sheet of the comparative example 4 does not improve lithium ion conductivity by filling the defect of lithium ions and injecting lithium ions.

[Example 3-2]
An electrolyte sheet was obtained in the same manner as in Example 2-2-1 except that the coating liquid 2 was used instead of the coating liquid 1. The electrolyte sheet had a lithium ion conductivity of 4.8 × 10 ⁻⁴ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component. The electrolyte sheet was formed with a dense coating layer, and the coating layer had a thickness of 2 μm.

The lithium ion conductivity of the electrolyte sheet of Example 3-2 was larger than the calculated value calculated by the combined sum of the lithium ion conductivities of the electrolyte sheets of Comparative Example 3 and Comparative Example 4. Therefore, it can be seen that the electrolyte sheet of Example 3-2 is excellent in lithium ion conductivity by being layered.

Next, the reduction deterioration resistance of the electrolyte sheet of Example 3-2 to metallic lithium was evaluated.

As a result, the resistance in the crystal grains and the grain boundary resistance did not increase even when the electrolyte sheet of Example 3-2 was held in a constant temperature bath at 25 ° C. for 2 months or more. Therefore, it can be seen that the electrolyte sheet of Example 3-2 is excellent in reduction deterioration resistance against metallic lithium.

FIG. 8 shows the change over time in the AC impedance of the coin cell produced using the electrolyte sheet of Example 3-2.

FIG. 8 shows that when the electrolyte sheet of Example 3-2 is held in a thermostatic chamber at 25 ° C., the interfacial resistance with the electrode is decreased, and the resistance in the crystal grains and the grain boundary resistance are decreased. Therefore, it can be seen that the electrolyte sheet of Example 3-2 is excellent in reduction deterioration resistance against metallic lithium.

FIG. 9 shows the change over time of the cell resistance of the coin cells produced using the electrolyte sheets of Example 3-2 and Comparative Example 3.

From FIG. 9, it can be seen that the electrolyte sheet of Example 3-2 does not increase the cell resistance even when held in a thermostatic bath at 25 ° C. for 2 months or more, and is excellent in reduction deterioration resistance against metallic lithium.

On the other hand, when the electrolyte sheet of Comparative Example 3 is held in a constant temperature bath at 25 ° C., it can be seen that the cell resistance increases with time from immediately after the measurement, and the electrolyte is deteriorated.

[Preparation of coating solution 3]
Li ₂ CO ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , ZrO ₂ , Y ₂ O ₃ are produced to produce Li ₂ O, P ₂ O ₅ , ZrO ₂ and Y _2. After weighing so that the molar ratio of O ₃ was 1.2: 3: 1.94: 0.06, the mixture was homogeneously mixed. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, 2% by mass of N-tallow alkyl trimethylenediamine is added to the crystalline inorganic substance, and the mixture is pulverized in butanol at 4500 rpm using a spar apex mill (manufactured by Kotobuki Kogyo Co., Ltd.). A translucent sol was obtained. When measured using a particle size distribution analyzer ELSZ-2 (manufactured by Otsuka Electronics Co., Ltd.), the sol had a number average particle size of about 100 nm. When pulverizing using a bead mill, beads made of zirconia having a diameter of 0.3 mm were used as media.

After adding 3% by mass of polyvinyl butyral to the sol with respect to the dispersoid, they were mixed to obtain a coating solution 3.

[Example 4-1-1]
After dip-coating the coating solution 3, the drying operation was repeated a plurality of times to form a coating layer having a thickness of 3 μm on both surfaces of the electrolyte sheet (base material) of Comparative Example 3, and then an electric furnace HPM-1N (ASONE And manufactured at 825 ° C. to obtain an electrolyte sheet. The pulling speed during dip coating was set to 0.3 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 7.3 × 10 ⁻⁷ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Example 4-1-2]
An electrolyte sheet was obtained in the same manner as in Example 4-1-1 except that the firing temperature was changed to 850 ° C. The electrolyte sheet had a lithium ion conductivity of 4.2 × 10 ⁻⁵ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 4-1-3]
An electrolyte sheet was obtained in the same manner as in Example 4-1-1 except that the firing temperature was changed to 875 ° C. The electrolyte sheet had a lithium ion conductivity of 1.2 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 4-1-4]
An electrolyte sheet was obtained in the same manner as in Example 4-1-1 except that the firing temperature was changed to 900 ° C. The electrolyte sheet had a lithium ion conductivity of 1.3 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 4-1-5]
An electrolyte sheet was obtained in the same manner as in Example 4-1-1 except that the firing temperature was changed to 925 ° C. The electrolyte sheet was confirmed to have a lithium ion conductivity of 2.6 × 10 ⁻⁴ S / cm and a hexagonal NASICON type crystal structure as a main component by X-ray diffraction.

[Example 4-1-6]
An electrolyte sheet was obtained in the same manner as in Example 4-1-1 except that the firing temperature was changed to 950 ° C. The electrolyte sheet had a lithium ion conductivity of 1.4 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Comparative Example 5]
Li ₂ CO ₃ , H ₃ PO ₄ , NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , ZrO ₂ , Y ₂ O ₃ are produced to produce Li ₂ O, P ₂ O ₅ , ZrO ₂ and Y _2. After weighing so that the molar ratio of O ₃ was 1.2: 3: 1.94: 0.06, the mixture was homogeneously mixed. This composition is the same as that of the coating liquid 3. Next, the mixed powder was put in an aluminum crucible, fired at 600 ° C. for 2 hours using an electric furnace HPM-1N (manufactured by ASONE), and then cooled to room temperature. Furthermore, after taking out the sample from the aluminum crucible, it was placed on a zirconia substrate and fired at 1050 ° C. for 2 hours to obtain a crystalline inorganic substance. Next, using a planetary ball mill P-6 (manufactured by Fritsch), the crystalline inorganic substance was pulverized in butanol at 600 rpm for 2 hours and then dried to obtain a powder. When pulverizing using a planetary ball mill, a zirconia pot was used and zirconia balls were used as media.

10% by weight of polyvinyl butyral and 0.2% by weight of N-tallow alkyl trimethylenediamine are added to the powder and mixed in a mixed solvent of toluene and 1-butanol (volume ratio 85:15) for 24 hours. A slurry was obtained.

Using a sheet molding machine, the slurry was molded so as to have a thickness of 150 μm to obtain a sheet molded body (green sheet). The sheet compact was dried and cut into strips, and then fired at 1050 ° C. for 1 hour to obtain an electrolyte sheet. The electrolyte sheet was confirmed to have a lithium ion conductivity of 3.0 × 10 ⁻⁶ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

As a result of observing the sintered state of the coating layer with an electron microscope, in the electrolyte sheets of Examples 4-1-3 to 4-1-6, a dense coating layer was formed.

The lithium ion conductivities of the electrolyte sheets of Examples 4-1-1 to 4-1-6 were larger than the calculated values calculated by the combined sum of the lithium ion conductivities of the electrolyte sheets of Comparative Example 3 and Comparative Example 5. . Therefore, it can be seen that the electrolyte sheets of Examples 4-1-1 to 4-1-6 are excellent in lithium ion conductivity when layered.

Next, the reduction deterioration resistance of the electrolyte sheets of Examples 4-1-1 to 4-1-6 to metallic lithium was evaluated.

As a result, the electrolyte sheets of Examples 4-1-1 to 4-1-6 did not increase the resistance in the crystal grains and the grain boundary resistance even when held in a constant temperature bath at 25 ° C. for 2 months or more. . Therefore, it can be seen that the electrolyte sheets of Examples 4-1-1 to 4-1-6 are excellent in reduction deterioration resistance against metallic lithium.

[Example 4-2]
The coating liquid 3 was dip-coated on both surfaces of the electrolyte sheet (base material) of Comparative Example 3, and then baked at 875 ° C. using an electric furnace HPM-1N (manufactured by ASONE) to obtain an electrolyte sheet. The pulling speed during dip coating was set to 0.3 mm / s. The electrolyte sheet was confirmed to have a lithium ion conductivity of 4.2 × 10 ⁻⁴ S / cm and a hexagonal NASICON crystal structure as a main component by X-ray diffraction. The electrolyte sheet was formed with a dense coating layer, and the coating layer had a thickness of 1.5 μm.

The lithium ion conductivity of the electrolyte sheet of Example 4-2 was larger than the calculated value calculated by the combined sum of the lithium ion conductivities of the electrolyte sheets of Comparative Example 3 and Comparative Example 5. Therefore, it can be seen that the electrolyte sheet of Example 4-2 is excellent in lithium ion conductivity by being layered.

Next, the reduction deterioration resistance of the electrolyte sheet of Example 4-2 to metallic lithium was evaluated.

As a result, the resistivity of the electrolyte sheet of Example 4-2 did not increase even when held in a thermostatic bath at 25 ° C. for 2 months or more. For this reason, it turns out that the electrolyte sheet of Example 4-2 is excellent in the reduction deterioration tolerance with respect to metallic lithium.

[Example 5]
A green sheet (base material) produced in the same manner as in Comparative Example 1 except that the thickness was set to 170 μm, and a green sheet (coating layer) produced in the same manner as in Comparative Example 4 except that the thickness was set to 20 μm. Were pressed and bonded at 10 kN / cm ² and then fired at 950 ° C. to obtain an electrolyte sheet. The electrolyte sheet had a lithium ion conductivity of 8.5 × 10 ⁻⁶ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

FIG. 10 shows a cross-sectional SEM image of the electrolyte sheet.

The lithium ion conductivity of the electrolyte sheet of Example 5 was larger than the calculated value calculated by the combined sum of the lithium ion conductivity of the electrolyte sheets of Comparative Example 1 and Comparative Example 4. For this reason, it turns out that the electrolyte sheet of Example 5 becomes the thing excellent in lithium ion conductivity by layering.

Next, the reduction deterioration resistance of the electrolyte sheet of Example 5 to metallic lithium was evaluated.

[Reduction degradation resistance to metallic lithium]
After forming a gold blocking electrode having a thickness of 500 nm on the base material side of the electrolyte sheet by sputtering, a metal lithium foil as an electrode is pressure-bonded to the coating layer side of the electrolyte sheet in an argon atmosphere to form a coin cell. Produced. Next, it is held in a constant temperature bath at 25 ° C., and using an impedance analyzer FRA1260 (manufactured by Solartron), an AC impedance is measured over time in a frequency range of 0.1 to 1 × 10 ⁶ Hz. Reduction resistance was evaluated.

As a result, even when the electrolyte sheet of Example 5 was held in a thermostatic bath at 25 ° C. for 2 months or more, the resistance in crystal grains and the grain boundary resistance did not increase. For this reason, it turns out that the electrolyte sheet of Example 5 is excellent in the reduction deterioration tolerance with respect to metallic lithium.

[Comparative Example 6]
An electrolyte sheet was obtained in the same manner as in Comparative Example 1 except that the slurry was formed to have a thickness of 90 μm and the firing temperature was changed to 850 ° C. The electrolyte sheet had a lithium ion conductivity of 6.4 × 10 ⁻⁴ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Example 6]
After dip-coating the coating solution 3, the drying operation is repeated a plurality of times to form a coating layer having a thickness of approximately 1.5 μm on both surfaces of the electrolyte sheet (base material) of Comparative Example 6, and then the electric furnace HPM- The electrolyte sheet was obtained by firing at 900 ° C. using 1N (manufactured by ASONE). The pulling speed during dip coating was set to 0.5 mm / s. The electrolyte sheet had a lithium ion conductivity of 4.9 × 10 ⁻⁴ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component. By making the raw material particles used in the coating solution extremely fine, the firing temperature can be reduced, and a coating layer can be realized with smaller production energy.

In addition, the reduction deterioration resistance of the electrolyte sheet of Example 6 to metallic lithium was evaluated. As a result, in the Example 6 electrolyte sheet, the resistance in the crystal grains and the grain boundary resistance did not increase even after two months had passed. For this reason, it confirmed that the electrolyte sheet of Example 6 was excellent in the reduction deterioration tolerance with respect to metallic lithium.

[Comparative Example 7-1]
Prior to adding 10% by weight of polyvinyl butyral and 0.2% by weight of N-tallow alkyltrimethylenediamine, 0.05% by weight of LiBO ₃ was added to the powder, and planetary ball mill P-6 (Fritsch) was added. A slurry was obtained in the same manner as in Comparative Example 1 except that the mixture was sufficiently mixed.

Using a sheet molding machine, a sheet-like molded body (green sheet) was molded from the slurry so as to have a thickness of 100 μm. The sheet-like molded body was sufficiently dried and cut into strips, sandwiched between two yttria-stabilized zirconia plates, and baked at 830 ° C. for 2 hours to obtain an electrolyte sheet. The electrolyte sheet was confirmed to have a lithium ion conductivity of 8.6 × 10 ⁻⁴ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Comparative Example 7-2]
An electrolyte sheet was obtained in the same manner as in Comparative Example 7-1 except that the amount of LiBO ₃ added was changed to 0.1% by mass. The electrolyte sheet was confirmed to have a lithium ion conductivity of 7.9 × 10 ⁻⁴ S / cm and to have a hexagonal NASICON crystal structure as a main component by X-ray diffraction.

[Comparative Example 7-3]
An electrolyte sheet was obtained in the same manner as in Comparative Example 7-1 except that the addition amount of LiBO ₃ was changed to 0.25% by mass. The electrolyte sheet had a lithium ion conductivity of 7.1 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Comparative Example 7-4]
An electrolyte sheet was obtained in the same manner as in Comparative Example 7-1 except that the amount of LiBO ₃ added was changed to 0.5% by mass. The electrolyte sheet had a lithium ion conductivity of 5.4 × 10 ⁻⁴ S / cm, and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Comparative Example 7-5]
An electrolyte sheet was obtained in the same manner as in Comparative Example 7-1 except that the amount of LiBO ₃ added was changed to 1.0 mass%. The electrolyte sheet had a lithium ion conductivity of 4.1 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON crystal structure as a main component.

[Bending strength]
The same powder as in Comparative Example 1 and Comparative Examples 7-1 to 7-5 was formed into a rod shape using a uniaxial mold with an outer shape of 20 mm × 3 mm × 4 mm, and then baked at 830 ° C. for 2 hours to obtain a sample. . Next, the bending strength of the sample was measured by a three-point bending test under the conditions of a distance between supporting points of 16 mm and a crosshead speed of 0.5 mm / min.

Table 1 shows the measurement results of bending strength.

　表１に示すように、ＬｉＢＯ_３の添加量が０．２５質量％以上で曲げ強さが顕著に高くなった。対して、イオン伝導率は、ＬｉＢＯ_３の添加量の増加と共に低下する。このため基材へのＬｉＢＯ_３の添加量が０．２５～０．４質量％程度で、曲げ強さとイオン伝導率が高い試料が得られる。

As shown in Table 1, the bending strength was remarkably increased when the added amount of LiBO ₃ was 0.25% by mass or more. On the other hand, the ionic conductivity decreases with an increase in the amount of LiBO ₃ added. Therefore, a sample with high bending strength and high ionic conductivity can be obtained when the amount of LiBO ₃ added to the substrate is about 0.25 to 0.4 mass%.

[Example 7]
After the coating solution 3 is dip-coated, the drying operation is repeated a plurality of times to form a coating layer having a thickness of about 1.5 μm on both surfaces of the electrolyte sheet (base material) of Comparative Example 7-3. Using HPM-1N (manufactured by AS ONE), firing was performed at 900 ° C. to obtain an electrolyte sheet. The pulling speed during dip coating was set to 0.5 mm / s. The electrolyte sheet had a lithium ion conductivity of 3.1 × 10 ⁻⁴ S / cm and was confirmed by X-ray diffraction to have a hexagonal NASICON type crystal structure as a main component. By making the raw material particles used in the coating solution extremely fine, the firing temperature can be reduced, and a coating layer can be realized with smaller production energy.

In addition, the reduction deterioration resistance of the electrolyte sheet of Example 7 to metallic lithium was evaluated. As a result, in the electrolyte sheet of Example 7, the resistance within the crystal grains and the grain boundary resistance did not increase even after 2 months had passed. Furthermore, it was confirmed that the electrolyte sheet of Example 7 had high bending strength and excellent resistance to reduction deterioration against metallic lithium.

[Composition analysis]
The composition analysis in the fracture surface of the electrolyte sheet of Example 1 and Example 7 was performed by EDS. As a result, the ratio of the content of Ti on the outermost surface of the coating layer to the substrate was 0.04 and 0.23, respectively.

Tables 2 to 4 show the lithium ion conductivity of the electrolyte sheet.

　本国際出願は、２０１４年８月２９日に出願された日本国特許出願２０１４－１７６１３３号に基づく優先権を主張するものであり、日本国特許出願２０１４－１７６１３３号の全内容を本国際出願に援用する。

This international application claims priority based on Japanese Patent Application No. 2014-176133 filed on August 29, 2014. The entire contents of Japanese Patent Application No. 2014-176133 are incorporated herein by reference. Incorporate.

Claims (8)

On a base material having a NASICON type crystal structure containing Li, Ti, Al, P and O, it has a NASICON type crystal structure containing Li, Zr, P and O and not containing the first transition metal derived from the raw material. An electrolyte sheet, wherein a coating layer is formed. 2. The electrolyte sheet according to claim 1, wherein the coating layer has a thickness of 0.5 μm or more and 5 μm or less. 2. The electrolyte sheet according to claim 1, wherein the base material further contains one or more elements selected from the group consisting of Zr, Y, Si, and B. 3. The electrolyte sheet according to claim 1, wherein the coating layer further contains Ca and / or Y. Firing a raw material containing a Li-containing compound, a Ti-containing compound, an Al-containing compound and a P-containing compound to produce a substrate having a NASICON type crystal structure;
A raw material containing a Li-containing compound, a Zr-containing compound and a P-containing compound and not containing a first transition metal-containing compound is fired to produce a coating layer having a NASICON-type crystal structure, or formed on the substrate. The manufacturing method of the electrolyte sheet characterized by having the process to do. It is a manufacturing method of the electrolyte sheet given in any 1 paragraph of Claims 1 thru / or 4,
Forming a raw material slurry or kneaded material for a base material into a sheet-like molded body,
A step of firing the sheet-like molded body into a base material;
Forming a coating layer by applying a coating solution for the coating layer to the substrate;
And a step of firing the base material on which the coating layer has been formed. It is a manufacturing method of the electrolyte sheet given in any 1 paragraph of Claims 1 thru / or 4,
Forming a raw material slurry or kneaded material for a base material into a sheet-like molded body,
Forming a coating layer by applying a coating solution for the coating layer to the sheet-like molded body; and
And a step of firing the sheet-like molded body on which the coating layer is formed. An article comprising the electrolyte sheet according to claim 1.

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