Gallium-substituted solid electrolyte materials and all-solid-state lithium-ion secondary batteries

Abstract

A novel solid electrolyte material with high density and high ionic conductivity, and an all-solid-state lithium-ion secondary battery using the solid electrolyte material are provided. The chemical composition of the solid electrolyte material is expressed as Li 7‑3x Ga x La3Zr2O 12 (0.08 ≤ x < 0.5), the relative density is 99% or more, cubic crystal system, belonging to the space group I-43d, and has a garnet-type structure. The lithium-ion conductivity of the solid electrolyte material is 2.0×10 ‑3 S / cm or more. In addition, the lattice constant a of the solid electrolyte material is 1.29714 nm ≤ a ≤ 1.30433 nm, lithium ions occupy the 12a site, 12b site and two 48e sites in the crystal structure, and gallium occupies the 12a site and 12b site. The all-solid-state lithium-ion secondary battery has a positive electrode, a negative electrode and a solid electrolyte, and the solid electrolyte is composed of the solid electrolyte material of the present invention.

Description

Technical Field

[0001] The present invention relates to a gallium-substituted solid electrolyte material with high density and high ion conductivity, and an all-solid-state lithium-ion secondary battery using the solid electrolyte material. Background Art

[0002] Compared with secondary batteries such as nickel-cadmium batteries or nickel-metal hydride batteries, lithium-ion secondary batteries have higher energy density and can operate at high potentials, so they are widely used in small information devices such as mobile phones and laptops. In addition, in recent years, the demand for secondary batteries for hybrid vehicles and electric vehicles is increasing because they are easy to reduce in size and weight. Considering safety, all-solid-state lithium-ion secondary batteries that do not use flammable electrolytes are being developed. Solid electrolytes used in all-solid-state lithium-ion secondary batteries require high ion conductivity.

[0003] It is reported that materials having a cubic garnet structure have high ion conductivity (for example, see Patent Document 1), and research and development of materials having this structure is underway. In particular, it is reported that a material having a chemical composition of Li 7-x Ln3Z 2- x Ta x O 12 The material has high ion conductivity near x=0.5. In order to achieve high ion conductivity, it is necessary to reduce the grain boundary impedance or interface impedance as much as possible, so it is ideal as a solid material for a high-density formed (molded) body. In addition, as a solid material for a high-density formed body, since it can prevent short circuits between the positive and negative electrodes during the charge and discharge process and can be made into a thin film, it provides the possibility for the future miniaturization of all-solid-state lithium-ion secondary batteries. However, these materials with a cubic garnet structure are known to be difficult to sinter and it is difficult to prepare a high-density formed body.

[0004] Recently, Li with a garnet structure grown by melt method has been reported. 7-x Ln3Z 2-x Ta x O 12 or Li 7-x Ln3Z 2- x Nb x O 12 Single crystals have been reported (for example, see Patent Documents 2 and 3).

[0005] Recently, although there have been reports of the fabrication of gallium-substituted cubic garnet-type Li 7-3x Ga x La3Zr2O 12Although the sintered body has high lithium ion conductivity (for example, see Non-Patent Documents 1 and 2), there is no report on the production of single crystals by the melt method.

[0006] In order to achieve high ion conductivity, it is necessary to reduce the grain boundary resistance or interface resistance as much as possible, so it is ideal as a solid material for a high-density compact. In addition, since a single crystal high-density compact is not affected by the grain boundary, high lithium ion conductivity can be expected.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2011-195373

[0010] Patent document 2: WO2016068040

[0011] Patent document 3: WO2017130622

[0012] Non-patent literature

[0013] Non-patent document 1: Chemistry Materials, 28, 1861-1871 (2016)

[0014] Non-patent document 2: Crystallographic Communications, E72, 287-289, (2016) Summary of the invention

[0015] Problems to be solved by the invention

[0016] The present invention is made in view of the above situation, and its object is to provide a novel gallium-substituted solid electrolyte material with high density and high ion conductivity, and an all-solid-state lithium-ion secondary battery using the gallium-substituted solid electrolyte material.

[0017] Means for solving problems

[0018] The inventors have found that by (7-3x)y Ga xz La3Zr2O 12 (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3) is formed into a rod shape, and the polycrystal is melted / quenched by the FZ method using infrared focused heating to prepare a high-density single crystal rod of Li7-3xGaxLa3ZrO12 (0.08≤x<0.5).

[0019] The chemical composition of the solid electrolyte material of the present invention is expressed as Li 7-3x Gax La3Zr2O 12 (0.08≤x<0.5), the relative density is above 99%, it belongs to the cubic system, and has a garnet structure. In the solid electrolyte material of the present invention, the lithium ion conductivity can be 2.0×10 -3 S / cm or more. In the solid electrolyte material of the present invention, the lattice constant a can be 1.29714nm≤a≤1.30433nm. The single crystal solid electrolyte material of the present invention is grown by melting materials, and lithium ions can occupy the 12a site (coordinate x=0.75, y=0.625, z=0) and 12b site (coordinate x=0.75, y=0.125, z=0) in the crystal structure and two 48e (coordinate x=0.6678, y=0.5607, z=0.1735, coordinate x=0.6970, y=0.5738, z=0.0948), and gallium can occupy the 12a site (coordinate x=0.75, y=0.625, z=0) and 12b site (coordinate x=0.75, y=0.125, z=0). This is a new substance that is different from the crystal structure and the arrangement of lithium ions in the crystal structure reported in the past. In the solid electrolyte material of the present invention, the relative density is preferably 100%. In addition, when the composition ratio x of gallium is 0.5 or more, as shown in Non-Patent Document 2, since the lanthanum site is occupied by gallium, it becomes a material having a crystal structure different from that of the present invention.

[0020] In the method for producing the solid electrolyte material of the present invention, the chemical composition is expressed as Li (7-3x) y Ga xz La3Zr2O 12 At least a portion of the raw material (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3) is melted to form a molten portion, and the molten portion is moved at a moving speed of 8 mm / h or more, so that the chemical composition is expressed as Li 7- 3x Ga x La3Zr2O 12 (0.08≤x<0.5), the relative density is 99% or more, belongs to the cubic system, and has a garnet structure. In the method for manufacturing a solid electrolyte material of the present invention, the growth rate is preferably 8 mm / h or more and 19 mm / h or less. In the method for manufacturing a solid electrolyte material by the FZ method of the present invention, it is preferred that the rod-shaped raw material is melted while rotating it at a rotation speed of 30 rpm or more on a plane perpendicular to the length direction, and more preferably the rotation speed is 30 rpm or more and 60 rpm or less.

[0021] The all-solid-state lithium-ion secondary battery of the present invention comprises a positive electrode, a negative electrode and a solid electrolyte, and the solid electrolyte is composed of the solid electrolyte material of the present invention.

[0022] Effects of the Invention

[0023] According to the present invention, a gallium-substituted solid electrolyte material with high density and high ion conductivity and an all-solid-state lithium-ion secondary battery using the gallium-substituted solid electrolyte material can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] [ Figure 1 ] is the Li grown by FZ method obtained in Example 6.4 Ga 0.20 La3Zr2O 12 A photo of the appearance of a single crystal.

[0025] [ Figure 2 ] is Li obtained in the embodiment 6.4 Ga 0.20 La3Zr2O 12 Single crystal X-ray diffraction pattern of a single crystal.

[0026] [ Figure 3 ] is a graph showing Li obtained in the examples 6.4 Ga 0.20 La3Zr2O 12 Schematic diagram of the garnet structure of a single crystal.

[0027] [ Figure 4 ] is Li obtained in the embodiment 6.4 Ga 0.20 La3Zr2O 12 Nyquist plot of a single crystal using the AC impedance method.

[0028] [ Figure 5 ] is Li obtained in the embodiment 6.4 Ga 0.20 La3Zr2O 12 Powder X-ray diffraction pattern of a single crystal.

[0029] [ Figure 6 ] is the Li grown by FZ method obtained in Example 6.76 Ga 0.08 La3Zr2O 12 A photo of the appearance of a single crystal.

[0030] [ Figure 7 ] is the Li grown by FZ method obtained in Example 6.25 Ga 0.25 La3Zr2O 12 A photo of the appearance of a single crystal.

[0031] [ Figure 8 ] is Li grown by CZ method obtained in Example 6.64 Ga 0.12 La3Zr2O 12 A photo of the appearance of a single crystal.

[0032] [ Fig. 9 ] is Li obtained in the embodiment 6.64 Ga 0.12 La3Zr2O 12 Single crystal X-ray diffraction pattern of a single crystal.

[0033] [ Fig.10 ] is a graph showing Li obtained in the examples 6.64 Ga 0.12 La3Zr2O 12 Schematic diagram of the garnet structure of a single crystal.

[0034] [ Fig.11 ] is Li obtained in the embodiment 6.64 Ga 0.12 La3Zr2O 12 Powder X-ray diffraction pattern of a single crystal.

[0035] [ Fig.12 ] is Li obtained in the embodiment 6.64 Ga 0.12 La3Zr2O 12 Nyquist plot of a single crystal using the AC impedance method.

[0036] [ Fig.13 ] is a schematic diagram of the all-solid-state lithium-ion secondary battery prepared in the example. DETAILED DESCRIPTION

[0037] The present inventors have conducted in-depth research on a method of melting and cooling a mixed raw material at a high temperature, wherein the mixed raw material contains an excess of lithium and gallium compared to the composition ratio of the target solid electrolyte material, and have found that: Li+ having a cubic crystal system and a garnet-type structure can be prepared. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) single crystal, and confirmed that the single crystal can be mechanically thinned, thus completing the present invention. When growing a single crystal belonging to the cubic system and having a garnet structure by the FZ method, the sample rod is usually rotated at less than 20 rpm and lowered at a descending speed of about 2 mm / h. However, under this condition, Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) enters the gap and high-density crystals cannot be prepared.

[0038] In order to prepare a crystal without voids, the rod-shaped raw material is rotated at a rotation speed of 30 rpm or more, and the molten part is lowered at a moving speed of 8 mm / h or more, and the molten part is cooled at a high speed. Alternatively, the seed crystal is raised relative to the molten part of the raw material at a moving speed of 8 mm / h or more and cooled. The obtained high-density Li 7-3x Ga x La3Zr2O 12 The crystal rod (0.08≤x<0.5) can be cut into any thickness using a diamond cutter or the like. In addition, considering that lithium and gallium will volatilize at high temperatures, the high-density Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystals can be compared with the chemical composition of Li 7-3x Ga x La3Zr2O 12 The invention is produced by melting a mixed raw material in which the amounts of lithium and magnesium are increased according to the stoichiometric ratio of each metal.

[0039] The chemical composition of the solid electrolyte material of the present invention is expressed as Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5), the relative density is more than 99%, belongs to the cubic system, and has a garnet structure. Furthermore, the relative density is calculated by dividing the apparent density by the true density, wherein the apparent density is calculated by measuring the shape of the prepared thin film to calculate the apparent volume and the measured mass, and the true density is obtained based on the single crystal X-ray structure analysis results. Since the solid electrolyte material of the present invention is high-density, it can be easily cut into any thickness using a diamond tool or the like. In addition, the solid electrolyte material of the present invention has high ion conductivity. Specifically, it can be obtained that the lithium ion conductivity is 2.0×10 -3 S / cm or above solid electrolyte materials.

[0040] The solid electrolyte material of the present invention can be manufactured in the following manner: the chemical composition is expressed as Li (7-3x)y Ga xz La3Zr2O 12 At least a portion of the raw material (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3) is melted to form a molten portion, and the molten portion or seed crystal is moved at a moving speed of 8 mm / h or more. Specifically, the high-density Li2O3 of the present invention is grown by FZ method, Czochralski (CZ) method, Bridgeman method, pedestal method, etc. 7-3xGa x La3Zr2O 12 (0.08≤x<0.5) crystal. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) The size and shape of the crystal, etc., can be selected from these to produce an appropriate method. Li with a relative density of 100% can be produced by the FZ method or the CZ method. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystal, that is, the original Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) single crystal. Relative density is 100% Li 7-3x Ga x La3Zr2O 12 The lithium ion conductivity of the (0.08≤x<0.5) crystal is particularly excellent.

[0041] When the solid electrolyte material of the present invention is manufactured by the FZ method, the rod-shaped raw material is melted while rotating on a plane perpendicular to the length direction at a rotation speed of more than 30 rpm, and the crystal is grown by moving the molten portion in the length direction. By accelerating the moving speed of the molten portion to more than 8 mm / h, the decomposition of the raw material due to the volatilization of lithium and gallium can be avoided. When the solid electrolyte of the present invention is manufactured by the CZ method, the raw material is melted in a crucible, and the molten portion is moved in the length direction while rotating the seed crystal on a plane perpendicular to the length direction, thereby growing the crystal. By accelerating the moving speed of the seed crystal to more than 8 mm / h, the decomposition of the raw material due to the volatilization of lithium and gallium can be avoided. The moving speed of the molten portion or the seed crystal is preferably more than 8 mm / h and less than 19 mm / h. In addition, when grown by the FZ method, although lithium volatilizes in the molten portion and generates bubbles, bubbles can be removed by accelerating the rotation speed of the rod-shaped raw material to more than 30 rpm. The rotation speed of the raw material is preferably more than 30 rpm and less than 60 rpm. The melting of the raw material and the movement of the molten portion are preferably carried out in a dry air atmosphere.

[0042] In this way, Li with a relative density of more than 99% can be produced. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystal. Li with a relative density of more than 99%, belonging to the cubic system, and having a garnet structure 7-3x Ga x La3Zr2O 12Taking the growth of a (0.08≤x<0.5) crystal as an example, the method for manufacturing the solid electrolyte material of the present invention is described. First, a rod-shaped raw material is prepared in the following manner. At the beginning, considering that lithium will volatilize at high temperatures, the lithium compound, gallium compound, lanthanum compound and zirconium compound are weighed so that the molar ratio of Li:Ga:La:Zr is (7-3x)y:xz:3:2 (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3).

[0043] There are no particular restrictions on lithium compounds, as long as they contain lithium, and examples include oxides such as Li2O, carbonates such as Li2CO3, etc. There are no particular restrictions on gallium compounds, as long as they contain gallium, and examples include oxides such as Ga2O3, nitrates such as Ga(NO)3)3, etc. There are no particular restrictions on lanthanum compounds, as long as they contain lanthanum, and examples include oxides such as La2O3, hydroxides such as La(OH)3, etc. There are no particular restrictions on zirconium compounds, as long as they contain zirconium, and examples include oxides such as ZrO2, chlorides such as ZrCl4, etc.

[0044] In addition, a compound composed of two or more selected from lithium, gallium, lanthanum and zirconium can be used for weighing so that the molar ratio of Li:Ga:La:Zr is (7-3x)y:xz:3:2 (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3). As such a compound composed of two or more, lanthanum zirconium oxides such as La2Zr2O7, gallium lanthanum oxides such as GaLaO6, lithium gallium oxides such as Li5GaO4, lithium zirconium oxides such as Li2ZrO3, etc. can be listed.

[0045] Next, the weighed compounds are mixed. The mixing method is not particularly limited as long as the compounds can be uniformly mixed. For example, a mixer such as a stirrer can be used to mix the compounds in a wet or dry manner. The resulting mixture is then filled into a crucible with a lid, and then pre-calcined at 600° C. to 900° C., preferably 850° C., to obtain a powder as a raw material. Furthermore, it is further preferred that the raw material that has been pre-calcined once is repeatedly crushed, mixed, and calcined.

[0046] Next, in order to facilitate forming, the obtained raw material powder is crushed to make its particle size fine. There is no particular limitation on the crushing method, as long as the powder can be refined. For example, a planetary ball mill, a jar mill, a bead mill or other crushing equipment can be used for wet or dry crushing. Then, the obtained crushed material is filled into a rubber tube and then subjected to hydrostatic pressure to form it into a rod shape. Next, the obtained rod-shaped formed body is calcined at about 700°C to 1300°C, preferably 800°C to 1150°C for about 4 hours to obtain a rod-shaped raw material. At this time, the chemical composition of the raw material is Li(7-3x)y Ga xz La3Zr2O 12 (0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.3). In this way, a rod-shaped raw material can be manufactured.

[0047] Then, the rod-shaped raw material is melted in an infrared focusing heating furnace and then rapidly cooled to produce a Li 2O3 having a relative density of more than 99%, a cubic crystal system, and a garnet structure. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5). By this manufacturing method, a Li with a length of more than 2 cm can be obtained. 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystals. Therefore, thin sheets with the same quality can be easily prepared by cutting. In addition, when high-density Li 7- 3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystal, the following steps are performed. First, the raw material is placed in a crucible for heating and melting. Next, the seed crystal is immersed in the melt of the raw material and pulled while rotating. The rotation speed of the seed crystal is preferably above 3 rpm and below 30 rpm. By accelerating the movement speed of the seed crystal to above 8 mm / h, the volatilization of lithium and gallium is suppressed, so that a high-density Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) crystals. In addition, Li grown by the melt method 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) Compared with samples synthesized by the conventional solid phase method, the lattice constant tends to be longer.

[0048] In addition, due to the high density Li 7-3x Ga x La3Zr2O 12 (0.08≤x<0.5) The crystal has excellent lithium ion conductivity and can therefore be used as a solid electrolyte for an all-solid-state lithium ion secondary battery. That is, the all-solid-state lithium ion secondary battery of the present invention has a positive electrode, a negative electrode and a solid electrolyte, and the solid electrolyte is composed of the solid electrolyte material of the present invention. The present invention will be further specifically described below by way of examples, but the present invention is not limited to these examples.

[0049] Example 1

[0050] (Li 6.4 Ga 0.2 La3Zr2O 12 Mixing of raw materials

[0051] First, 15.318 g of lithium carbonate Li2CO3 (manufactured by RARE METALLIC, purity 99.99%), 2.061 g of gallium oxide Ga2O3 (manufactured by RARE METALLIC, purity 99.99%), 26.873 g of lanthanum oxide La2O3 (manufactured by RARE METALLIC, purity 99.99%), and 13.551 g of zirconium oxide ZrO2 (manufactured by RARE METALLIC, purity 99.99%) were placed in an agate mortar and uniformly mixed by a wet method using ethanol. Furthermore, the lanthanum oxide used was pre-calcined at 900°C in advance. The molar ratio of the metals in the mixture, Li:Ga:La:Zr, was 2.30% higher than that of the target Li 6.4 Ga 0.2 La3Zr2O 12 The stoichiometric ratio is 1.3 times the target composition, and the amount of gallium is 2 times the target composition. That is, the chemical composition is equivalent to Li 8.32 Ga 0.4 La3Zr2O 12 The amount.

[0052] Next, 57.1803g of the mixture was filled into an alumina crucible with a lid (NIKATTO manufactured, C3 type). Then, it was placed in a box-type electric furnace (Yamato Scientific Manufacturing, FP100 type) and pre-calcined at 850°C for 6 hours to obtain a powder. Then, the obtained powder was crushed. That is, 57g of powder, 300g of zirconia balls with a diameter of 5mm and 100g of isopropanol were filled into a zirconia crushing container with a capacity of 250mL, and a planetary ball mill (Germany FRITSCH manufactured, model P-6) was used to rotate at a revolution of 200rpm for a total of 300 minutes for crushing. The crushed powder was dried at 100°C for 24 hours and classified using a sieve with a mesh of 250μm.

[0053] (Preparation of rod-shaped raw materials)

[0054] Using the powder that passed through the sieve in the above process, a rod-shaped raw material was prepared by the following steps. First, 15.127g of the powder was filled into a rubber mold and degassed. Then, the mold was placed in water in a sealed state and kept at 40MPa for 5 minutes. Then, after reducing the pressure of the water, the mold was taken out from the mold. The mold was a cylindrical body with a diameter of 1.1cm and a height of 7.5cm. Then, a box-type electric furnace (DENKEN manufacturing, model KDF009) was used to calcine the cylindrical molded body at 1150°C for 4 hours. The taken-out molded body was a cylindrical body with a diameter of 0.75cm and a height of 5.2cm.

[0055] (Li 6.4 Ga 0.2 La3Zr2O 12 Crystal Growth)

[0056] First, the rod-shaped raw material obtained by the above process is placed in a four-elliptical infrared focusing heating furnace (FZ furnace) (manufactured by Crystal System, FZ-T-10000H model) equipped with a 1kW halogen lamp and placed in a dry air atmosphere. Next, the rod-shaped raw material is heated at an output power of 23.3% while rotating at 40 rpm on a plane perpendicular to the length direction. After a period of time, a part of the polycrystalline sample melts and forms a molten portion. Then, the rod-shaped raw material setting table is lowered at a moving speed of 10 mm / h to grow high-density Li 6.4 Ga 0.2 La3Zr2O 12 The chemical composition of sample 1 was analyzed by ICP-AES and single crystal X-ray crystal structure analysis. The results of ICP-AES showed that the chemical composition was Li:Ga:La:Zr=6.4:0.2:3.0:2.0. The appearance of sample 1 is as follows: Figure 1 As shown. Figure 1 As shown, a high-density Li 6.4 Ga 0.2 La3Zr2O 12 Crystal.

[0057] (High-density Li 6.4 Ga 0.2 La3Zr2O 12 Crystal Evaluation)

[0058] The structure of sample 1 was studied using a single crystal X-ray diffractometer (R-AXISRAPID-II, manufactured by RIGAKU) with a two-dimensional imaging plate detector. The X-ray diffraction pattern of sample 1 is shown in Figure 2 As shown. Figure 2As shown, clear diffraction points were measured. In addition, when the diffraction intensity data of sample 1 was collected and the crystal structure was studied by the crystal structure analysis program Jana2006, it was found that sample 1 was a cubic crystal. Sample 1 was cut with a diamond tool to prepare 4 thin slices with a thickness of 0.1 cm, and their relative densities were calculated by the above method. The results showed that their relative densities were 99.5%, 99.8%, 99.9%, and 100%, respectively.

[0059] Figure 3 The structure of sample 1 is schematically shown. Previously reported cubic garnet structure Li 7- 3x Ga x La3Zr2O 12 Belonging to space group I-43d, in non-patent document 1, the 12a site, 12b site, and 48e site in the crystal structure are lithium ion sites, and the 12a site and 12b site are gallium ion sites. In addition, in non-patent document 2, the 12a site, 12b site, and two types of 48e sites in the crystal structure are lithium ion sites, and the 12a site, 12b site, and the 24d site as a lanthanum site are gallium ion sites. On the other hand, in the crystal structure of sample 1 grown by the melting method, the 12a site (coordinates x = 0.75, y = 0.625, z = 0), the 12b site (coordinates x = 0.75, y = 0.125, z = 0), and two 48e sites (coordinates x = 0.6597, y = 0.5490, z = 0.1707, coordinates x = 0.6918, y = 0.5739, z = 0.0990) are lithium ion sites, and the 12a site and the 12b site are gallium ion sites. That is, sample 1 is a new substance with a crystal structure different from that of non-patent literature 1 and non-patent literature 2. Since the R factor indicating the reliability of the crystal structure analysis is 2.26%, it can be considered that the crystal structure analysis result is reasonable.

[0060] In addition, the lithium ions are arranged in the gallium-substituted cubic garnet structure with the shortest distance between the lithium ions, and the lithium ion sites are appropriately missing. Therefore, it can be considered that the lithium ion conductivity of sample 1 is higher than that of other cubic garnet structure compounds. Sample 1 was cut to prepare a thin sheet with a diameter of about 0.50 cm and a thickness of about 0.10 cm. Gold with a circular shape of 0.40 cm on one side of the bottom surface and a thickness of 40 nm was sputtered on the front and back of the thin sheet to form an electrode. When the lithium ion conductivity of the sample was measured in a nitrogen atmosphere at 25°C using the AC impedance method (measuring device: Solarton, 1260), the following was obtained: Figure 4 The Nyquist plot shown here is calculated based on the total impedance value, which is 2.4×10 -3S / cm. In addition, the lithium ion conductivity was calculated by changing the measurement temperature of the AC impedance measurement, and the activation energy was calculated from the Arrhenius plot composed of these, which was 0.23 eV.

[0061] The lattice constant a of sample 1 was calculated by the least square method using the reflection observed by the single crystal X-ray diffraction measurement, and it was a = 1.29714nm ± 0.00005nm. Based on this lattice constant, it can be known that sample 1 is a lithium composite oxide with a garnet structure. Sample 1 was crushed and subjected to powder X-ray diffraction measurement. The results are as follows: Figure 5 As shown. The powder X-ray diffraction pattern of sample 1 is the same as the single-phase diffraction pattern of the cubic garnet structure. The lattice constant a calculated based on the results of the powder X-ray structure analysis is a=1.29825nm±0.00001nm. Combining the results of single crystal X-ray diffraction measurement and powder X-ray structure analysis, the lattice constant of sample 1 is 1.29714nm≤a≤1.29825nm.

[0062] Example 2

[0063] (Li 6.76 Ga 0.08 La3Zr2O 12 Mixing of raw materials

[0064] First, 28.349 g of lithium carbonate Li2CO3 (manufactured by RARE METALLIC, purity 99.99%), 2.3979 g of gallium oxide Ga2O3 (manufactured by RARE METALLIC, purity 99.99%), 50.000 g of lanthanum oxide La2O3 (manufactured by RARE METALLIC, purity 99.99%) and 25.213 g of zirconium oxide ZrO2 (manufactured by RARE METALLIC, purity 99.99%) were put into an agate mortar and uniformly mixed by a wet method using ethanol. Furthermore, the lanthanum oxide used was pre-calcined at 900°C in advance. The molar ratio of the metals in the mixture, Li:Ga:La:Zr, was 2.349 g of the target Li2CO3. 6.76 Ga 0.08 La3Zr2O 12 The stoichiometric ratio is 1.2 times the target composition, and the amount of gallium is 3.2 times the target composition. That is, the chemical composition is equivalent to Li 8.11 Ga 0.25 La3Zr2O 12 The amount.

[0065] Next, 57.273g of this mixture is filled into an alumina crucible with a lid (NIKATTO manufacturing, C3 type). Then, it is placed in a box-type electric furnace (Yamato Science manufacturing, FP100 type) and pre-calcined at 850°C for 6 hours to obtain a powder. Then, the obtained powder is crushed. That is, 57g of powder, 300g of zirconia balls with a diameter of 5mm and 100g of isopropanol are filled into a zirconia crushing container with a capacity of 250mL, and a planetary ball mill (Germany FRITSCH manufacturing, model P-6) is used to rotate a total of 300 minutes at a revolution of 200rpm to crush. The crushed powder is dried at 100°C for 24 hours and classified using a sieve with a mesh of 250μm.

[0066] (Preparation of rod-shaped raw materials)

[0067] Using the powder that passed through the sieve in the above process, a rod-shaped raw material was prepared by the following steps. First, 15.098g of the powder was filled into a rubber mold and degassed. Then, the mold was placed in water in a sealed state and kept at 40MPa for 5 minutes. Then, after reducing the pressure of the water, the mold was taken out from the mold. The mold was a cylinder with a diameter of 1.1cm and a height of 7.5cm. Then, a box-type electric furnace (DENKEN manufacturing, model KDF009) was used to calcine the cylindrical molded body at 1150°C for 4 hours. The taken-out molded body was a cylinder with a diameter of 0.78cm and a height of 5.8cm.

[0068] (Li 6.76 Ga 0.08 La3Zr2O 12 Crystal Growth)

[0069] First, the rod-shaped raw material obtained by the above process is placed in a four-elliptical infrared focusing heating furnace (FZ furnace) (manufactured by Crystal System, FZ-T-10000H model) equipped with a 1kW halogen lamp and placed in a dry air atmosphere. Next, the rod-shaped raw material is heated at an output power of 22.9% while rotating at 40 rpm on a plane perpendicular to the length direction. After a period of time, a part of the polycrystalline sample melts and forms a molten portion. Then, the rod-shaped raw material setting table is lowered at a moving speed of 10 mm / h to grow high-density Li 6.76 Ga 0.08 La3Zr2O 12 The chemical composition of Sample 2 was analyzed by ICP-AES and single crystal X-ray crystal structure analysis. The ICP-AES results of Sample 2 showed that the chemical composition was Li:Ga:La:Zr=6.8:0.08:3.0:2.0, and its appearance was as follows: Figure 6 As shown. Figure 6 As shown, a high-density Li 6.76 Ga 0.08 La3Zr2O 12 Crystal.

[0070] (High-density Li 6.76 Ga 0.08 La3Zr2O 12 Crystal Evaluation)

[0071] The structure of sample 1 was studied using a single crystal X-ray diffractometer (R-AXISRAPID-II, AFC-7S, manufactured by RIGAKU) with a two-dimensional imaging plate detector. When the diffraction intensity data of sample 2 was collected and the crystal structure was studied using the crystal structure analysis program Jana2006, it was found that sample 2 and sample 1 had the same crystal structure.

[0072] Using the reflections observed by single crystal X-ray diffraction measurement of sample 2, the lattice constant a was calculated by the least squares method, which was a=1.30433nm±0.00014nm. Based on this lattice constant, it can be known that sample 2 is a lithium composite oxide with a garnet structure. Sample 2 was crushed and subjected to powder X-ray diffraction measurement. The lattice constant a calculated based on the results of powder X-ray structure analysis was a=1.29985nm±0.00001nm. Combining the results of single crystal X-ray diffraction measurement and powder X-ray structure analysis, the lattice constant of sample 1 is 1.29985nm≤a≤1.30433nm.

[0073] Example 3

[0074] (Li 6.25 Ga 0.25 La3Zr2O 12 Mixing of raw materials

[0075] First, 18.416 g of lithium carbonate Li2CO3 (manufactured by RARE METALLIC, purity 99.99%), 2.301 g of gallium oxide Ga2O3 (manufactured by RARE METALLIC, purity 99.99%), 30.000 g of lanthanum oxide La2O3 (manufactured by RARE METALLIC, purity 99.99%), and 15.128 g of zirconium oxide ZrO2 (manufactured by RARE METALLIC, purity 99.99%) were placed in an agate mortar and uniformly mixed by a wet method using ethanol. Furthermore, the lanthanum oxide used was pre-calcined at 900°C in advance. The molar ratio of the metals in the mixture, Li:Ga:La:Zr, was 2.301 g, which was 99.99% higher than that of the target Li 6.25 Ga 0.25La3Zr2O 12 The stoichiometric ratio is 1.3 times the target composition, and the amount of gallium is 1.6 times the target composition. That is, the chemical composition is equivalent to Li 8.13 Ga 0.40 La3Zr2O 12 The amount.

[0076] Next, 57.273g of this mixture is filled into an alumina crucible with a lid (NIKATTO manufacturing, C3 type). Then, it is placed in a box-type electric furnace (Yamato Science manufacturing, FP100 type) and pre-calcined at 850°C for 6 hours to obtain a powder. Then, the obtained powder is crushed. That is, 57g of powder, 300g of zirconia balls with a diameter of 5mm and 100g of isopropanol are filled into a zirconia crushing container with a capacity of 250mL, and a planetary ball mill (Germany FRITSCH manufacturing, model P-6) is used to rotate a total of 300 minutes at a revolution of 200rpm to crush. The crushed powder is dried at 100°C for 24 hours and classified using a sieve with a mesh of 250μm.

[0077] (Preparation of rod-shaped raw materials)

[0078] Using the powder that passed through the sieve in the above process, a rod-shaped raw material was prepared by the following steps. First, 15.128g of the powder was filled into a rubber mold and degassed. Then, the mold was placed in water in a sealed state and kept at 40MPa for 5 minutes. Then, after reducing the pressure of the water, the mold was taken out from the mold. The mold was a cylinder with a diameter of 1.1cm and a height of 7.5cm. Then, a box-type electric furnace (DENKEN manufacturing, model KDF009) was used to calcine the cylindrical molded body at 1150°C for 4 hours. The taken-out molded body was a cylinder with a diameter of 0.79cm and a height of 5.8cm.

[0079] (Li 6.25 Ga 0.25 La3Zr2O 12 Crystal Growth)

[0080] First, the rod-shaped raw material obtained by the above process is placed in a four-elliptical infrared focusing heating furnace (FZ furnace) (manufactured by Crystal System, FZ-T-10000H model) equipped with a 1kW halogen lamp and placed in a dry air atmosphere. Next, the rod-shaped raw material is heated at an output power of 23.1% while rotating at 40 rpm on a plane perpendicular to the length direction. After a period of time, a part of the polycrystalline sample melts and forms a molten portion. Then, the rod-shaped raw material setting table is lowered at a moving speed of 10 mm / h to grow high-density Li 6.25Ga 0.25 La3Zr2O 12 The chemical composition of Sample 3 was analyzed by ICP-AES and single crystal X-ray crystal structure analysis. The ICP-AES results of Sample 3 showed that the chemical composition was Li:Ga:La:Zr=6.25:0.25:3.0:2.0, and its appearance was as follows: Figure 7 As shown. Figure 7 As shown, a high-density Li 6.25 Ga 0.25 La3Zr2O 12 Crystal.

[0081] (High-density Li 6.25 Ga 0.25 La3Zr2O 12 Crystal Evaluation)

[0082] The structure of sample 3 was studied using a single crystal X-ray diffractometer (R-AXISRAPID-II manufactured by RIGAKU) with a two-dimensional imaging plate detector. When the diffraction intensity data of sample 3 was collected and the crystal structure was studied using the crystal structure analysis program Jana2006, it was found that sample 3 and sample 1 had the same crystal structure.

[0083] Using the reflections observed by single crystal X-ray diffraction measurement of sample 3, the lattice constant a was calculated by the least squares method, which was a=1.30364nm±0.00025nm. Based on this lattice constant, it can be known that sample 3 is a lithium composite oxide with a garnet structure. Sample 3 was crushed and subjected to powder X-ray diffraction measurement. The lattice constant a calculated based on the results of powder X-ray structure analysis was a=1.29993nm±0.00001nm. Combining the results of single crystal X-ray diffraction measurement and powder X-ray structure analysis, the lattice constant of sample 3 is 1.29993nm≤a≤1.30364nm.

[0084] Example 4

[0085] Li production based on CZ method 6.64 Ga 0.12 La3Zr2O 12 Crystal

[0086] (Li 6.64 Ga 0.12 La3Zr2O 12 Mixing of raw materials

[0087] First, 15.785 g of lithium carbonate Li2CO3 (manufactured by RARE METALLIC, purity 99.99%), 2.301 g of gallium oxide Ga2O3 (manufactured by RARE METALLIC, purity 99.99%), 30.000 g of lanthanum oxide La2O3 (manufactured by RARE METALLIC, purity 99.99%), and 15.128 g of zirconium oxide ZrO2 (manufactured by RARE METALLIC, purity 99.99%) were placed in an agate mortar and uniformly mixed by a wet method using ethanol. Furthermore, the lanthanum oxide used was pre-calcined at 900°C in advance. The molar ratio of the metals in the mixture, Li:Ga:La:Zr, was 2.301 g, which was 99.99% higher than that of the target Li 6.64 Ga 0.12 La3Zr2O 12 The stoichiometric ratio is 1.2 times the target composition, and the amount of gallium is 3.3 times the target composition. That is, the chemical composition is equivalent to Li 7.968 Ga 0.40 La3Zr2O 12 The amount.

[0088] (2)Li 6.64 Ga 0.12 La3Zr2O 12 Crystal Growth

[0089] First, a cylindrical iridium container with an inner diameter of 2.6 cm and a depth of 2.8 cm was filled with 28 g of polycrystalline Li obtained in the above process. 7.968 Ga 0.40 La3Zr2O 12 Then, the iridium container was placed in a single crystal pulling furnace (CZ furnace) (manufactured by Techno Search, TCH-3) with high-frequency induction heating function. Then, an iridium rod with a length of 50 mm was placed on the pulling part, and the CZ furnace was placed in a dry nitrogen atmosphere. Then, the high-frequency output power was gradually increased, and the iridium container was continuously heated at an output power of 58.8%. After a period of time, the Li filled in the iridium container 7.968 Ga 0.40 La3Zr2O 12 The powder melted.

[0090] Then, the iridium rod was immersed in Li while rotating at 3 rpm in a plane perpendicular to the length direction. 7.968 Ga 0.40 La3Zr2O 12 The iridium rod is then lifted at a moving speed of 10 mm / h to grow Li 6.64 Ga 0.12 La3Zr2O 12The grown Li 6.64 Ga 0.12 La3Zr2O 12 The appearance of the crystal (hereinafter also referred to as "sample 4") is as follows Figure 8 shown.

[0091] (High-density Li 6.64 Ga 0.12 La3Zr2O 12 Crystal Evaluation)

[0092] The structure of sample 4 was studied using a single crystal X-ray diffractometer (R-AXISRAPID-II manufactured by RIGAKU) with a two-dimensional imaging plate detector. The X-ray diffraction pattern of sample 4 is shown in Fig. 9 As shown. Fig. 9 As shown in the figure, clear diffraction points were measured. In addition, when the diffraction intensity data of sample 1 was collected and the crystal structure was studied using the crystal structure analysis program Jana2006, it was found that sample 4 was a cubic crystal and had a different crystal structure from the single crystal grown by the FZ method. In addition, the results of single crystal X-ray analysis showed that the chemical composition of sample 4 was Li 6.64 Ga 0.12 La3Zr2O 12 .

[0093] Fig.10 The structure of sample 4 is schematically shown. It is known that it has the same crystal structure as the crystal grown by the FZ method. 7-3x Ga x La3Zr2O 12Belonging to space group I-43d, in non-patent document 1, the 12a site, 12b site, and 48e site in the crystal structure are lithium ion sites, and the 12a site and 12b site are gallium ion sites. In addition, in non-patent document 2, the 12a site, 12b site, and two types of 48e sites in the crystal structure are lithium ion sites, and the 12a site, 12b site, and 24d site as a lanthanum site are gallium ion sites. On the other hand, in sample 4 grown by the melting method, lithium ions occupy the 12a site (coordinates x = 0.75, y = 0.625, z = 0) and 12b site (coordinates x = 0.75, y = 0.125, z = 0) and two types of 48e (coordinates x = 0.6678, y = 0.5607, z = 0.1735, coordinates x = 0.6970, y = 0.5738, z = 0.0948) in the crystal structure, and the gallium ion sites are the 12a site (coordinates x = 0.75, y = 0.625, z = 0) and 12b site (coordinates x = 0.75, y = 0.125, z = 0). That is, sample 4 is a new substance whose crystal structure is different from that of non-patent document 1 and non-patent document 2 and is the same as the single crystal grown by the FZ method. Since the R factor indicating the reliability of the crystal structure analysis is 3.35%, it can be considered that the crystal structure analysis result is reasonable.

[0094] The lattice constant a of sample 4 was calculated by the least square method using the observed reflections of the single crystal X-ray diffraction measurement, and it was a = 1.2994nm ± 0.0003nm. Based on this lattice constant, it can be known that sample 4 is a lithium composite oxide having a garnet structure. Sample 4 was crushed and subjected to powder X-ray diffraction measurement. The results are as follows: Fig.11 As shown. The powder X-ray diffraction pattern of sample 4 is the same as the single-phase diffraction pattern of the cubic garnet structure. The lattice constant a calculated based on the results of the powder X-ray structure analysis is a=1.29875nm±0.00001nm. Combining the results of single crystal X-ray diffraction measurement and powder X-ray structure analysis, the lattice constant of sample 4 is 1.29875nm≤a≤1.2994nm.

[0095] Sample 4 was cut to prepare a thin sheet with a diameter of about 0.70 cm and a thickness of about 0.10 cm. Gold with a thickness of 40 nm and a bottom side of 0.70 cm was sputtered on the front and back of the thin sheet to form electrodes. When the lithium ion conductivity of this sample was measured at 25°C in a nitrogen atmosphere using an AC impedance method (measurement device: Solarton, 1260), the following was obtained: Fig.12 The Nyquist plot shown here is calculated based on the total impedance value, which is 2.9×10 -3S / cm, which is no different from that of the single crystal grown by the FZ method. In addition, the activation energy was calculated from the Arrhenius plot composed of the lithium ion conductivity calculated by changing the measurement temperature of the AC impedance measurement, and was 0.22 eV, which is no different from that of the single crystal grown by the FZ method.

[0096] Example 5

[0097] Fabrication of all-solid-state lithium-ion secondary batteries

[0098] 0.0105 mol of lithium acetate dihydrate (manufactured by Sigma Aldorich) and 0.01 mol of cobalt acetate tetrahydrate (manufactured by Wako Pure Chemical Industries) were dissolved in 100 g of ethylene glycol (manufactured by Wako Pure Chemical Industries). Then, 10 g of polyvinyl pyrrolidone K-30 (manufactured by Wako Pure Chemical Industries) was added and dissolved to prepare a 0.1 mol / Kg lithium cobalt oxide precursor solution. The amount of lithium acetate was increased by 5% relative to the amount of cobalt acetate in terms of molar ratio because the amount of lithium evaporation during calcination was taken into account. Then, sample 1 was cut to prepare a thin sheet with a diameter of about 0.6 cm and a thickness of about 0.10 cm. 10 μL of the above solution was dripped on the thin sheet, and calcined at 400°C for 20 minutes, and then calcined at 850°C for 10 minutes, to synthesize lithium cobalt oxide as a positive electrode on the surface of sample 1 (hereinafter also referred to as "sample 2"). Then, in a glove box, as Fig.13 As shown, sample 1 and metal lithium punched into a diameter of 4 mm were placed in a commercially available HS battery for battery evaluation (manufactured by Hohsen Co., Ltd.) to prepare an all-solid-state lithium-ion secondary battery. The all-solid-state lithium-ion secondary battery showed 2.8 V at an open circuit voltage, confirming that it functioned as a battery.

[0099] Industrial Applicability

[0100] The high-density Li 7-3x Ga x La3Zr2O 12 Crystals can be used as solid electrolyte materials for all-solid-state lithium-ion secondary batteries, etc.

Claims

1. A solid electrolyte material, whose chemical composition is expressed as Li 7-3x Ga x La3Zr2O 12 , with a relative density of more than 99%, belongs to space group I-43d in the cubic crystal system, and has a garnet structure, in which, 0.08≤x<0.5， Lithium ions occupy the 12a site, 12b site and two 48e sites in the crystal structure, and gallium occupies the 12a site and 12b site.

2. The solid electrolyte material according to claim 1, wherein The lithium ion conductivity is 2.0×10 -3 S / cm or more.

3. The solid electrolyte material according to claim 1, wherein The lattice constant a is 1.29714nm≤a≤1.30433nm.

4. The solid electrolyte material according to any one of claims 1 to 3, wherein The relative density is 100%.

5. A method for manufacturing a solid electrolyte material, By expressing the chemical composition as Li (7-3x)y Ga xz La3Zr2O 12 At least a portion of the raw material is melted to form a molten portion, and the molten portion is moved at a moving speed of 8 mm / h or more or the seed crystal is moved relative to the molten portion so that its chemical composition is expressed as Li 7-3x Ga x La3Zr2O 12 , with a relative density of more than 99%, belongs to space group I-43d in the cubic crystal system, and has a garnet-type structure, in which, 0.08≤x<0.5, 1.1≤y≤1.4, 1.6≤z≤3.

3.

6. The method for producing a solid electrolyte material according to claim 5, wherein: The moving speed is greater than or equal to 8 mm / h and less than or equal to 19 mm / h.

7. The method for producing a solid electrolyte material according to claim 5 or 6, wherein: When the growth is performed by the FZ method, the rod-shaped raw material is melted while being rotated at a rotation speed of 30 rpm or more on a plane perpendicular to the longitudinal direction.

8. The method for producing a solid electrolyte material according to claim 7, wherein: The rotation speed is greater than or equal to 30 rpm and less than or equal to 60 rpm.

9. The method for producing a solid electrolyte material according to claim 5 or 6, wherein: When the growth is performed by the CZ method, the seed crystal is immersed in the molten portion and pulled up while being rotated at a rotation speed of 3 rpm to 30 rpm.

10. An all-solid-state lithium-ion secondary battery comprising a positive electrode, a negative electrode and a solid electrolyte, wherein: The solid electrolyte is composed of the solid electrolyte material according to any one of claims 1 to 4.

Images