Lithium ion-conductive solid electrolyte and method for producing the same

Abstract

To provide a lithium ion-conductive solid electrolyte with presence of voids, high degree of sintering density, and excellent lithium ion conductivity.SOLUTION: A lithium ion-conductive solid electrolyte is composed of a garnet-type zirconium oxide sintered body containing Li and La. Within a rectangular region represented by 48 μm vertically and 64 μm horizontally in an SEM image, the solid electrolyte has a porosity of 2% to 15% as calculated by determining the ratio of voids having a size of 1 μm2 or more in area ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium ion conductive solid electrolyte and a method for producing the same. [Background technology]

[0002] Lithium-ion batteries, characterized by their high voltage and high energy density, are used in a variety of fields, including electronic devices and automobiles. Current lithium-ion batteries use liquid electrolytes containing electrolyte salts and organic solvents, which are flammable and therefore pose a risk of fire. Solid electrolytes eliminate the risk of fire and improve safety, so research and development of solid electrolytes has been actively conducted in recent years.

[0003] While batteries with solid electrolytes have a problem with high interfacial resistance between the electrodes and the solid electrolyte, sulfide-based solid electrolytes exhibit high lithium-ion conductivity due to the formation of a favorable interface between the electrodes and the solid electrolyte under pressure, bringing them closer to practical application. However, sulfides are difficult to handle because they react with water to generate toxic gases. In contrast, oxide-based solid electrolytes have the advantage of being easy to handle because they do not generate toxic gases, but they have a problem with low lithium-ion conductivity compared to sulfide-based solid electrolytes due to the high interfacial resistance between the electrodes and the solid electrolyte. Furthermore, the synthesis of oxide-based solid electrolytes requires high-temperature firing of the raw materials, which can lead to problems such as volatilization of the Li component and the introduction of impurities. Therefore, it is necessary to form a favorable electrode-solid electrolyte interface and grain boundaries in the oxide polycrystalline solid electrolyte that functions as a solid electrolyte.

[0004] Li7La3Zr2O, an oxide-based lithium ion conductor 12Lithium-ion lithium zeolite (LLZ) is known to have a cubic crystal structure at high temperatures and exhibit high ionic conductivity. However, LLZ has a tetragonal crystal structure at room temperature and exhibits low lithium ion conductivity. Therefore, doping LLZ with an element can stabilize the cubic crystal structure at room temperature. A known example of element-doped LLZ is a garnet-type oxide in which LLZ is doped with Al. Patent Document 1 (JP 2011-73963 A) discloses a ceramic material containing Li, La, Zr, Al, and O, having a garnet-type or garnet-like crystal structure, and in which the molar ratio of Li to La is 2.0 or more and 2.5 or less.

[0005] In addition to the garnet-type oxide disclosed in Patent Document 1, Ga-doped LLZ is known, which has the advantage of being synthesized at a lower temperature than Al-doped LLZ and exhibits high lithium ion conductivity, but further improvement in sinterability is required. Furthermore, garnet-type oxides obtained by doping Ta into LLZ are known to exhibit high lithium ion conductivity, but require high-temperature sintering to obtain a dense sintered body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-73963 Summary of the Invention [Problem to be solved by the invention]

[0007] The challenge for all of the above garnet-type oxides is to improve the sinterability by firing at low temperatures and for short periods. Currently, the lithium ion conductivity of oxide-based solid electrolytes is lower than that of liquid electrolytes in practical use, so further research is being conducted on LLZ doped with Ga, Ta, etc. The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a lithium ion conductive solid electrolyte that combines the sinterability of LLZ with high lithium ion conductivity. [Means for solving the problem]

[0008] The aspects of the present invention are as follows. [1] In a rectangular area of ​​48 μm in length and 64 μm in width in an SEM image, the area ratio is 1 μm 2 The porosity, which is the calculated value of the proportion of voids, is in the range of 2 to 15%. A lithium-ion conductive solid electrolyte consisting of a sintered garnet-type zirconium oxide containing Li and La. [2] The garnet-type zirconium oxide sintered body is Li 7-3x Ga x La3Zr2O 12 The lithium ion conductive solid electrolyte according to the above [1], which is composed of an oxide in which Al2O3 is added to Ga, and x, which is a Ga composition ratio, is 0.2 to 0.3. [3] The garnet-type zirconium oxide sintered body is Li 7-y La3Zr 2-y Ta y O 12 The lithium ion conductive solid electrolyte according to the above [1], which is composed of an oxide in which Al2O3 is added to Ta, and the Ta composition ratio y is 0.3 to 0.5. [4] The oxide is produced by a dry method and has a specific surface area of ​​30 to 130 m 2 The lithium ion conductive solid electrolyte according to the above [2] or [3], containing 0.1 to 1.7 wt % of Al2O3, where Al2O3 is 0.1 wt % or more and Al2O3 is 0.1 wt % or less. [5] Lithium ion conductivity is 2.0 × 10 -4 The lithium ion conductive solid electrolyte according to [1] above, having a conductivity of 0.5 S / cm or more. [6] The lithium ion conductive solid electrolyte according to [1] above, having an activation energy of 0.38 eV or less. [7] The lithium ion conductive solid electrolyte according to the above [1], which has a relative density of 85 to 98%. [8] A method for producing the lithium ion conductive solid electrolyte according to the above [2], The first firing process involves firing at atmospheric pressure, at a temperature of 900-1000°C, for a firing time of 4 hours or more. The second firing process involves firing at a temperature of 900-1100°C for a firing time of at least 4 hours. A method for producing a lithium ion conductive solid electrolyte comprising: [9] A method for producing the lithium ion conductive solid electrolyte according to the above [3], The first firing process involves firing at atmospheric pressure, at a temperature of 900-1000°C, for a firing time of 4 hours or more. The second firing process involves firing at a temperature of 900-1200°C for a firing time of 4 hours or more. A method for producing a lithium ion conductive solid electrolyte comprising:

[0009] The lithium ion conductive solid electrolyte provided by the present invention has an area ratio of 1 μm 2 The porosity, which is the calculated value of the proportion of voids, is in the range of 2 to 15%, which is different from that of conventional lithium ion conductive solid electrolytes. Thus, the presence of voids at a specific porosity in the lithium ion conductive solid electrolyte of the present invention can increase the contact area at the interface between the lithium ion conductive solid electrolyte and the electrode active material. This can be advantageous in reducing the interfacial resistance between the electrode and the solid electrolyte. Furthermore, the lithium ion conductive solid electrolyte provided by the present invention has voids, which allow an electrolyte solution to be contained as an additional component, and lithium dendrites precipitated during charge and discharge to be retained in the voids, which is expected to reduce the effects of dendrites. Conventional solid electrolytes usually have low lithium ion conductivity when voids are present, but the present invention can provide a lithium ion conductive solid electrolyte that has high lithium ion conductivity and voids by a simple method of simply adding alumina to the material and firing it. [Effects of the Invention]

[0010] It is possible to provide a lithium ion conductive solid electrolyte having voids, high sintering density, and excellent lithium ion conductivity. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing an SEM image of a lithium ion conductive solid electrolyte according to one embodiment. [Figure 2] FIG. 1 is a diagram showing an SEM image of a lithium ion conductive solid electrolyte according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Lithium ion conductive solid electrolyte) In the present invention, in a square region of an SEM image that is 48 μm long and 64 μm wide, the area ratio is 1 μm 2 The present invention relates to a lithium ion conductive solid electrolyte made of a garnet-type zirconium oxide sintered body containing Li and La, with a porosity of 2 to 15%, which is the calculated value of the proportion of the voids. The voids adequately hold the positive electrode active material, resulting in a lithium ion conductive solid electrolyte that exhibits excellent lithium ion conductivity. The area of ​​the voids in the garnet-type zirconium oxide sintered body is 1 μm 2 If the porosity is smaller than 1 μm, it is difficult to incorporate the positive electrode active material into the pores, and high lithium ion conductivity cannot be obtained. 2 The area of ​​voids smaller than this is not taken into consideration. Furthermore, if the porosity of the garnet-type zirconium oxide sintered body is less than 2%, it is not possible to incorporate a sufficient amount of positive electrode active material into the voids, and high lithium ion conductivity is not obtained. On the other hand, if the porosity of the garnet-type zirconium oxide sintered body is more than 15%, the ratio of the substrate to the matrix is ​​reduced, and sufficient lithium ion conductivity is not obtained.

[0013] Garnet-type zirconium oxide sintered body is Li 7-3x Ga x La3Zr2O 12(hereinafter, sometimes referred to as "LLZ-Ga") and Al2O3 is added to the LLZ-Ga oxide, and the Ga composition ratio x is preferably 0.2 to 0.3. If x is less than 0.2, sufficient lithium ion conductivity cannot be obtained. If x exceeds 0.3, the solid solubility range of Ga is exceeded, and a single phase may not be obtained.

[0014] Garnet-type zirconium oxide sintered body is Li 7-y La3Zr 2-y Ta y O 12 It is composed of an oxide obtained by adding Al2O3 to LLZ-Ta (hereinafter sometimes referred to as "LLZ-Ta"), and the Ta composition ratio y is preferably 0.3 to 0.5. If y is less than 0.3, sufficient lithium ion conductivity cannot be obtained. If y exceeds 0.5, the solid solubility range of Ta is exceeded, and a single phase may not be obtained.

[0015] Li 7-3x Ga x La3Zr2O 12 (x is 0.2-0.3) with Al2O3 added and Li 7-y La3Zr 2-y Ta y O 12 In the oxide in which Al2O3 is added to (y is 0.3 to 0.5), the oxide has a specific surface area of ​​30 to 130 m2 produced by a dry method. 2 It is preferable that the glass contains 0.1 to 1.7 wt % of Al2O3, which is / g.

[0016] The lithium ion conductivity of the lithium ion conductive solid electrolyte is 2.0×10 -4 It is preferably S / cm or more.

[0017] The activation energy of the lithium ion conductive solid electrolyte is preferably 0.38 eV or less. In the lithium ion conductive solid electrolyte of the present invention, the activation energy and its sinterability are closely related, and when the sinterability is sufficient, the activation energy is 0.38 eV or less. On the other hand, when the sinterability is insufficient, the activation energy exceeds 0.38 eV.

[0018] The relative density of the lithium ion conductive solid electrolyte is preferably 85 to 98%. If the relative density is less than 85%, the sintering property may be poor and sufficient lithium ion conductivity may not be obtained. On the other hand, if the relative density is more than 98%, it may not be possible to impregnate a sufficient amount of positive electrode active material into the pores. The relative density can be measured by the method shown in the examples.

[0019] (Method for producing lithium ion conductive solid electrolyte) Garnet-type zirconium oxide sintered body is Li 7-3x Ga x La3Zr2O 12A method for producing a lithium ion conductive solid electrolyte is described. The solid electrolyte is composed of an oxide containing Al2O3 and Ga, and the Ga composition ratio, x, is 0.2 to 0.3. The method comprises a first firing step, in which firing is performed under normal pressure at a temperature of 900 to 1000°C for at least four hours, and a second firing step, in which firing is performed at a temperature of 900 to 1100°C for at least four hours. This method requires the addition of alumina (Al2O3) to the raw materials between the two firing steps and the first and second firing steps. Adding alumina to the raw materials before the first firing step does not result in sufficient sinterability. In this method, the amount of alumina added must be 0.1 to 1.7 wt% of the total raw materials, and preferably 0.1 to 1 wt%. If the amount of alumina added is less than 0.1 wt%, sinterability will be significantly reduced. If the amount of alumina added exceeds 1.7 wt%, the doped Ga or Ta precipitates, preventing the formation of a garnet-type single phase. Furthermore, the firing temperature and firing time are crucial factors in this manufacturing method. To dope the raw materials with Ga, the firing temperature in the first firing step must be 900-1000°C, the firing temperature in the second firing step must be 900-1100°C, and the firing time in the first and second firing steps must be 4 hours or longer. If the firing temperature in the first and second firing steps is less than 900°C, the intended reaction will be insufficient, and the desired composition will not be obtained. The same applies if the firing time in the first and second firing steps is less than 4 hours. If the firing temperature in the first firing step is greater than 1000°C, the Li component will volatilize, preventing the desired composition from being obtained. Since the desired composition is obtained to a certain extent in the first firing step, the firing temperature in the second firing step can be set to 1000°C or higher. However, if the firing temperature in the second firing step exceeds 1100°C, the Li component will decrease, which is not preferable.

[0020] Garnet-type zirconium oxide sintered body is Li 7-y La3Zr 2-y Ta y O 12A method for producing a lithium ion conductive solid electrolyte, which is composed of an oxide containing Al2O3 added to Ta, and in which the Ta composition ratio (y) is 0.3 to 0.5, includes a first firing step in which firing is performed under normal pressure at a temperature of 900 to 1000°C for at least four hours, and a second firing step in which firing is performed at a temperature of 900 to 1200°C for at least four hours. To dope Ta in this production method, the firing temperature in the first firing step must be 900 to 1000°C, the firing temperature in the second firing step must be 900 to 1200°C, and the firing time for both the first and second firing steps must be at least four hours. If the firing temperature in the first and second firing steps is less than 900°C, the intended reaction will be insufficient, and the desired composition will not be obtained. The same problem occurs if the firing time in the first and second firing steps is less than four hours. If the firing temperature in the first firing step exceeds 1000°C, the Li component will volatilize and the desired composition will not be obtained. Since the desired composition is obtained to a certain extent in the first firing step, the firing temperature in the second firing step can be set to 1000°C or higher. However, if the firing temperature in the second firing step exceeds 1200°C, the Li component will decrease, which is not preferable.

[0021] X-ray diffraction measurements are used to confirm that sintered bodies made by adding Al2O3 to LLZ-Ga and LLZ-Ta produced by solid-state reaction have a garnet-type crystal structure. An example of a manufacturing method for LLZ-Ga and LLZ-Ta is described below.

[0022] In the LLZ-Ga manufacturing method, raw material powders were mixed in hexane using a ball mill for 0.5 to 3 hours, then dried and transferred to an alumina crucible lined with a gold sheet, where they were subjected to a first firing in air. Hexane was used as the solvent during ball mill mixing. The firing temperature must be 900 to 1000°C. To prevent reaction between the fired powder and moisture in the air or CO2 during cooling after firing, the resulting fired powder may be rapidly cooled at 400°C. The firing time is 4 hours or more, but typically 4 to 16 hours is preferred, and 10 to 14 hours is more preferred. The fired powder is then pulverized in hexane using a ball mill for 0.5 to 3 hours to obtain a powder. After drying, the powder is placed in a mold and formed into pellets under a pressure of 1 ton. It is then isostatically pressed at 150 MPa to obtain denser pellets. Finally, a second firing is performed to obtain LLZ-Ga. The firing temperature must be 900 to 1100° C., and more preferably 950 to 1050° C. In this case, the obtained LLZ-Ga may be rapidly cooled when it reaches 400° C.

[0023] The manufacturing method for LLZ-Ta is basically the same as that for LLZ-Ga, but the firing temperature during the first firing must be 900 to 1000°C. The firing temperature during the second firing must be 900 to 1200°C, with 950 to 1200°C being preferred. When firing at high temperatures, synthesis can also be performed using the powder bed method. In the powder bed method, a powder sample of LLZ-Ta is used as the base powder, and sample pellets are embedded in the base powder and fired.

[0024] The alumina powder added to LLZ-Ga and LLZ-Ta is manufactured by the dry method (or gas phase method) and has a specific surface area of ​​30 to 130 m 2 / g is preferable. Dry-process alumina powder is produced by introducing an alumina raw material into a flame, for example, an oxyhydrogen flame. The alumina powder added in the present invention is produced by a dry process; for example, alumina powder produced by a wet process has a large particle size and strong agglomeration, so it does not have sufficient fluidity with respect to the garnet-type zirconium oxide. On the other hand, alumina powder with a large specific surface area produced by a dry process has a small particle size and is finely divided, so it has good dispersibility and contributes to the uniformity of the reaction. The specific surface area of ​​available alumina powder obtained industrially by a dry process is in the range of 30 to 130 m 2 / g.

[0025] Fig. 1 shows an SEM image of the lithium ion conductive solid electrolyte obtained by adding 0.1 wt% of Al2O3 to LLZ-Ga, as obtained above. Fig. 2 shows an SEM image of the lithium ion conductive solid electrolyte obtained by adding 0.1 wt% of Al2O3 to LLZ-Ta, as obtained above. According to Figs. 1 and 2, the 1 μm 2 It is clear that the above voids are present effectively.

[0026] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention. [Example]

[0027] Next, examples will be described to further clarify the effects of the present invention, but the present invention is not limited to these examples.

[0028] (Examples 1 to 9, Comparative Examples 2 to 5 and 7 to 10) The raw material powders were mixed in a ball mill, dried, and transferred to a crucible, where they were subjected to the first firing in air under the conditions shown in Table 1. After firing, they were pulverized using a ball mill. The powder was dried and then pressed into a mold to form pellets. Next, a second firing was performed under the conditions shown in Table 1 to produce the lithium ion conductive solid electrolyte LLZ-Ga or LLZ-Ta shown in Table 1. Note that, because the Li component volatilizes during the production of the lithium ion conductive solid electrolyte, Li2CO3 was added in an amount 10 wt% in excess of the raw material powder. In addition, dry-process alumina with the specific surface area shown in Table 1 was added in the amount shown in Table 1 during the production of the lithium ion conductive solid electrolyte LLZ-Ga or LLZ-Ta.

[0029] Example 10 The lithium ion garnet-type zirconium oxide sintered body LLZ-Ga after the second firing in Example 1 was treated with a positive electrode active material LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Impregnated with O2.

[0030] (Comparative Examples 1 and 6) The raw material powders were mixed in a ball mill, dried, and transferred to a crucible, where they were fired a first time in air under the conditions shown in Table 1. After firing, they were pulverized using a ball mill. The powder was dried and then pressed into a mold to form pellets. Next, a second firing was performed under the conditions shown in Table 1 to produce the lithium ion conductive solid electrolyte LLZ-Ga or LLZ-Ta shown in Table 1. Note that, because the Li component volatilizes during the production of the lithium ion conductive solid electrolyte, the amount of Li2CO3 added was 10 wt% in excess of the weight of the raw material powder. Furthermore, dry-process alumina was not added during the production of the lithium ion conductive solid electrolyte LLZ-Ga or LLZ-Ta.

[0031] (Comparative Example 11) The lithium ion garnet-type zirconium oxide sintered body after the second firing of Comparative Example 1 was treated with the positive electrode active material LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 was included.

[0032] The lithium ion conductive solid electrolytes LLZ-Ga and LLZ-Ta of each example obtained as described above were measured for their properties (evaluation of single composition, relative density, porosity, lithium ion conductivity, activation energy). Note that, in the above examples, the primary goal was to obtain a lithium ion conductive solid electrolyte of single composition, and measurements of the properties (relative density, porosity, lithium ion conductivity, activation energy) were omitted for Comparative Examples 3, 4, and 7 to 10, in which a single composition was not obtained according to the evaluation in (2) below.

[0033] The manufacturing conditions and property values ​​of each example are shown in Table 1 below. [Table 1]

[0034] The characteristic values ​​shown in Table 1 were measured as follows. (1) Specific surface area of ​​dry-process alumina powder (m 2 / g) measurement The specific surface area of ​​the dry-process alumina powder was measured by a gas-phase adsorption method, in which gas molecules (nitrogen molecules) with a known occupied area are adsorbed onto the surface of the dry-process alumina powder, and the surface area of ​​the dry-process alumina powder is calculated from the amount of adsorption of these gas molecules.

[0035] (2) Evaluation of single compositions To evaluate the single composition, X-ray diffraction measurements were performed on the lithium ion conductive solid electrolyte, and the absence of peaks other than those attributable to the crystalline structure of the lithium ion conductive solid electrolyte was evaluated as a single composition. The X-ray diffraction measurements were performed using an X-ray diffractometer (D8-ADVANCE manufactured by Bruker) with CuKα radiation (λ = 0.15405 nm) at a scan rate of 4° / min and a step width of 0.02°.

[0036] (3) Measurement of relative density (%) The relative density was calculated by dividing the measured density of the lithium ion conductive solid electrolyte from the theoretical density. The theoretical density of the lithium ion conductive solid electrolyte was calculated using the lattice constant of the garnet-type zirconium oxide obtained from the X-ray diffraction measurement described above in (2). The measured density of the lithium ion conductive solid electrolyte was calculated from the volume and weight of the sample pellet.

[0037] (4) Measurement of porosity (%) To measure the voids, the lithium ion conductive solid electrolyte was observed using a scanning electron microscope (Hitachi High-Tech S-4800) at an accelerating voltage of 10.00 to 12.00 kV, and an SEM image was obtained having a rectangular area measuring at least 48 μm in length and 64 μm in width. To measure the porosity, image analysis was performed on a square area of ​​48 μm in length and 64 μm in width in the SEM image, and the area ratio was calculated as 1 μm 2 The porosity, which is the value obtained by calculating the proportion of the above voids, was calculated.

[0038] (5) Lithium ion conductivity (S / cm -1 ) measurement The ionic conductivity of the lithium-ion conductive solid electrolyte was measured using an impedance / gain-phase analyzer (Solartron 1260A). After Au electrodes were formed on both sides of the sample by sputtering, the sample was annealed at 800°C in an inert atmosphere, sealed in a laminate cell, and measurements were performed at frequencies of 0.1Hz to 10MHz, AC amplitude of 10mV, and temperatures of -20°C to 80°C.

[0039] (6) Measurement of activation energy (eV) The lithium ion conductivity obtained from the impedance measured at temperatures of -20°C to 80°C in the above (5) was plotted against the reciprocal of the temperature to prepare an Arrhenius plot, and the activation energy was calculated from the slope of the straight line of the Arrhenius plot.

[0040] The types of lithium ion conductive solid electrolytes shown in Table 1, "LLZ-Ga" and "LLZ-Ta," were manufactured from the following raw materials. Raw materials for LLZ-Ga: Li2CO3 (manufactured by Nacalai Tesque, purity: 99.0%), La(OH)3 (manufactured by Kojundo Chemical Co., Ltd., purity: 99.99%), ZrO2 (manufactured by Nacalai Tesque, purity: 98.0%), Ga2O3 (manufactured by Kojundo Chemical Co., Ltd., purity: 99.99%) Raw materials for LLZ-Ta: Li2CO3 (manufactured by Nacalai Tesque, purity: 99.0%), La(OH)3 (manufactured by Kojundo Chemical Co., Ltd., purity: 99.99%), ZrO2 (manufactured by Nacalai Tesque, purity: 98.0%), Ta2O5 (manufactured by Kojundo Chemical Co., Ltd., purity: 99.9%)

[0041] The dry-process alumina with each specific surface area shown in Table 1 is made of the following materials. Specific surface area 30m 2 / g dry alumina: Samples prepared by known dry methods Specific surface area 65m 2 / g dry-process alumina: AEROXIDE (registered trademark) Alu 65, manufactured by Evonik Specific surface area 100m 2 / g dry-process alumina: AEROXIDE (registered trademark) Alu C, manufactured by Evonik Specific surface area 130m 2 / g dry-process alumina: AEROXIDE (registered trademark) Alu 130, manufactured by Evonik

[0042] As shown in Table 1, the lithium ion conductive solid electrolytes of Examples 1 to 9 had a porosity of 2 to 15%, a relative density of 85 to 98%, and a surface area of ​​2.0 × 10 -4 The lithium ion conductive solid electrolyte of Example 10 had a lithium ion conductivity of 3.2 × 10 S / cm or more and an activation energy of 0.38 eV or less. -4 In contrast, the lithium ion conductive solid electrolytes of Comparative Examples 1 to 2 and 5 to 6 had a porosity of less than 2% or more than 15%, with a porosity of 1.9 × 10 -4The lithium ion conductivity was low at 1000 S / cm or less and the activation energy was high at 0.39 eV or more. Therefore, this experiment revealed that the lithium ion conductive solid electrolyte of the present invention exhibits high sintering density and excellent lithium ion conductivity due to the porosity of 2 to 15%. [Industrial Applicability]

[0043] Current lithium-ion secondary batteries using liquid electrolytes are used as energy storage devices in mobile phones, laptops, HEVs (Hybrid Electric Vehicles), EVs (Electric Vehicles), and renewable energy sources. Among these, all-solid-state lithium-ion batteries using solid electrolytes are expected to be used in IoT devices and electric vehicles in addition to EVs.

Claims

1. In a rectangular region of the SEM image that is 48 μm long and 64 μm wide, the area ratio is 1 μm ２ The porosity, which is the calculated value of the proportion of the voids, is in the range of 2 to 15%, A lithium ion conductive solid electrolyte comprising a sintered garnet-type zirconium oxide containing Li and La.

2. The garnet-type zirconium oxide sintered body is Li ７－３ｘ Ga ｘ La ３ Zr ２ O １２ Al ２ O ３ 2. The lithium ion conductive solid electrolyte according to claim 1, wherein the lithium ion conductive solid electrolyte is composed of an oxide to which Ga is added, and the Ga composition ratio x is 0.2 to 0.

3.

3. The garnet-type zirconium oxide sintered body is Li ７－ｙ La ３ Zr ２－ｙ Ta ｙ O １２ Al ２ O ３ 2. The lithium ion conductive solid electrolyte according to claim 1, wherein the lithium ion conductive solid electrolyte is composed of an oxide to which Ta is added, and the Ta composition ratio y is 0.3 to 0.

5.

4. The oxide is produced by a dry method and has a specific surface area of ​​30 to 130 m ２ / g of Al ２ O ３ The lithium ion conductive solid electrolyte according to claim 2 or 3, containing 0.1 to 1.7 wt % of

5. Lithium ion conductivity is 2.0 x 10 －４ 2. The lithium ion conductive solid electrolyte according to claim 1, wherein the ionic conductivity is 1.5 S / cm or more.

6. 2. The lithium ion conductive solid electrolyte according to claim 1, wherein the activation energy is 0.38 eV or less.

7. 2. The lithium ion conductive solid electrolyte according to claim 1, wherein the relative density is 85 to 98%.

8. 3. A method for producing the lithium ion conductive solid electrolyte according to claim 2, comprising: a first firing step in which firing is performed under normal pressure at a firing temperature of 900 to 1000°C for a firing time of 4 hours or more; a second firing step in which firing is performed at a firing temperature of 900 to 1100°C for a firing time of 4 hours or more; A method for producing a lithium ion conductive solid electrolyte comprising:

9. A method for producing the lithium ion conductive solid electrolyte according to claim 3, a first firing step in which firing is performed under normal pressure at a firing temperature of 900 to 1000°C for a firing time of 4 hours or more; a second firing step in which firing is performed at a firing temperature of 900 to 1200°C for a firing time of 4 hours or more; A method for producing a lithium ion conductive solid electrolyte comprising:

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