Composite oxide having a novel crystal structure, all-solid-state lithium ion secondary battery using the composite oxide as a solid electrolyte, and method for manufacturing the composite oxide

Abstract

The present invention provides a composite oxide having high density, high lithium ion conductivity, and low activation energy. The composite oxide has a chemical composition represented by Li 4－x Sr 2－x La x ZrO6 (0 ≦ x ≦ 1.0), and belongs to the space group P21 / n in the monoclinic system. The relative density of the composite oxide can be set to 100%. The lithium ion conductivity of the composite oxide can be set to 6.0×10 ‑ 4 S / cm or more. The composite oxide is manufactured by melting at least a part of a raw material having a chemical composition represented by Li (4－x)y Sr (2－x)z La x ZrO6 (0 ≦ x ≦ 1.0, 1 < y, 1 < z) to form a molten part, and moving the molten part at a moving speed of 8 mm / h or more.

Description

Technical Field

[0001] The present application relates to a composite oxide having a crystal structure with high density and high ionic conductivity, a method for manufacturing the composite oxide, and an all-solid-state lithium ion secondary battery using the composite oxide as a solid electrolyte material. Background Art

[0002] Compared with secondary batteries such as nickel-cadmium batteries and nickel-metal hydride batteries, lithium ion secondary batteries have a high energy density and can operate at high potentials. Therefore, lithium ion secondary batteries are widely used in small information devices such as mobile phones or laptop computers. In addition, lithium ion secondary batteries are easily miniaturized and lightened, so the demand for secondary batteries for hybrid vehicles or electric vehicles is increasing.

[0003] In addition, in consideration of safety, research and development of all-solid-state lithium ion secondary batteries that do not use a flammable electrolyte are underway. The solid electrolyte used for all-solid-state lithium ion secondary batteries requires a high lithium ion conductivity. As an oxide-based material having a high lithium ion conductivity, a material having a cubic garnet-type structure has been reported (Patent Document 1), and research and development of this material are underway. In particular, a material having a chemical composition of Li 7－x La 3 Zr 2－x Ta x O 12 has a high ionic conductivity near x = 0.5.

[0004] It is known that a material having this cubic garnet-type structure has poor sinterability and it is difficult to produce a high-density molded body. In addition, although a solid electrolyte having this cubic garnet-type structure has a high ionic conductivity at room temperature, the activation energy is around 0.45 eV, and the ionic conductivity decreases at low temperatures. In order to achieve a high ionic conductivity, it is necessary to reduce the grain boundary resistance and the interface resistance. Therefore, a solid material, particularly a single crystal material, as a high-density molded body is preferable as a solid electrolyte. Since a single crystal material is not affected by grain boundaries, high lithium ion conductivity can be expected. In addition, a single crystal material can prevent short circuits between the positive and negative electrodes during charge and discharge, and can be thinned, so it provides the possibility of miniaturization of all-solid-state lithium ion secondary batteries in the future.

[0005] Based on these problems, it has been reported that a melt method is used to grow Li having a garnet-type structure 7－x La 3 Zr 2－x Ta x O 12 or Li 7－x La 3 Zr 2－x Nb x O 12single crystals (Patent Documents 2 and 3). In addition, as other oxide-based materials showing high lithium ion conductivity, materials having a perovskite structure (Non-Patent Document 1), or polyanion-based materials having a NASICON structure (Non-Patent Document 2) have been reported. Thus, there are many reported examples of cubic garnet-type solid electrolytes, perovskite-type solid electrolytes, and NASICON-type solid electrolytes having high lithium ion conductivity, but there are few reported examples of materials having other structures.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2011-195373

[0009] Patent Document 2: WO 2016 / 068040

[0010] Patent Document 3: WO 2017 / 130622

[0011] Non-Patent Documents

[0012] Non-Patent Document 1: Solid state communicasions, 86, pp. 689-693, 1993

[0013] Non-Patent Document 2: Applied materials and interfaces, 10, pp. 10935-10944, 2018 Summary of the Invention

[0014] Problems to be Solved by the Invention

[0015] The present application has been studied in view of such circumstances, and the problem thereof is to develop a new solid electrolyte having high density, high lithium ion conductivity, and low activation energy.

[0016] Means for Solving the Problems

[0017] The inventors of the present application have found that by forming a mixed raw material of Li (4－x)y Sr (2－x)z La x ZrO 6 (0 ≦ x ≦ 1.0, y = 1.2, z = 1.2) into a rod shape and then melting and rapidly cooling the formed body by the FZ method using infrared focusing heating, it is possible to prepare Li 4－x Sr 2－x La x ZrO 6A high-density composite oxide single crystal rod represented by (0≦x≦1.0). That is, different from the cubic garnet-type structure, perovskite-type structure, and sodium superionic conductor-type structure, a single crystal of a solid electrolyte with a novel crystal structure for which no similar crystal structure has been reported was successfully grown.

[0018] Single crystal silicon can be thinned by using a wire saw for grinding. The high-density composite oxide single crystal rod of the present application is also high-strength. Therefore, the high-density composite oxide single crystal of the present application can be easily cut with a diamond cutting machine or the like. The inventors of the present application also found that a composite oxide single crystal represented by Li 4－x Sr 2－x La x ZrO 6 (0≦x≦1.0) can be made into a thin sheet with a thickness of about 0.1 mm. The composite oxide single crystal can be thinned to a thickness of about 0.03 mm.

[0019] The composite oxide of the present application has a chemical composition represented by Li 4－x Sr 2－x La x ZrO 6 (0≦x≦1.0), and belongs to the space group P2 1 / n in the monoclinic system.

[0020] The manufacturing method of the composite oxide of the present application is to form at least a part of a raw material having a chemical composition represented by Li (4－x)y Sr (2－x)z La x ZrO 6 (0≦x≦1.0, 1<y, 1<z) into a molten part, and move the molten part at a moving speed of 8 mm / h or more to manufacture a composite oxide having a chemical composition represented by Li 4－x Sr 2－x La x ZrO 6 (0≦x≦1.0), a relative density of 99% or more, and belonging to the space group P2 1 / n in the monoclinic system.

[0021] The all-solid-state lithium ion secondary battery of the present application has a positive electrode, a negative electrode, and a solid electrolyte, and the solid electrolyte is composed of the composite oxide of the present application.

[0022] Advantages of the Invention

[0023] According to the present application, Li with high density, high ionic conductivity, and low activation energy can be obtained, where the chemical composition is represented by Li 4－x Sr 2－x La x ZrO 6Composite oxide (0 ≦ x ≦ 1.0), and all-solid-state lithium ion secondary battery using the composite oxide as a solid electrolyte material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 Appearance photograph of the single crystal.

[0025] Figure 2 is the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 Single crystal X-ray diffraction pattern of the single crystal.

[0026] Figure 3 is the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 Energy-dispersive X-ray spectroscopy of the single crystal.

[0027] Figure 4 is a schematic diagram showing the crystal structure of the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 Schematic diagram of the crystal structure of the single crystal.

[0028] Figure 5 is the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 Nyquist plot of the single crystal by the AC impedance method.

[0029] Figure 6 is a diagram showing the relationship between the lithium ion conductivity and temperature of the Li obtained in Example 1 3.957 Sr 1.957 La 0.043 ZrO 6 obtained by the AC impedance method.

[0030] Figure 7 Exploded view of the all-solid-state lithium ion secondary battery fabricated in Example 1.

[0031] Figure 8 is the Li obtained in Example 2 4 Sr 2 ZrO 6 Appearance photograph of the single crystal.

[0032] Figure 9 is the Li obtained in Example 2 4 Sr 2 ZrO 6 single crystal X-ray diffraction pattern of the single crystal.

[0033] Figure 10 is the Li obtained in Example 3 3 SrLaZrO 6 appearance photograph of the single crystal.

[0034] Figure 11 is the Li obtained in Example 3 3 SrLaZrO 6 single crystal X-ray diffraction pattern of the single crystal. Detailed implementation manners

[0035] The inventors of the present application have deeply studied the melting and cooling methods of a mixed raw material containing excessive lithium and strontium compared with the composition ratio of the target composite oxide. The inventors of the present application have found that: by this method, a composite oxide single crystal of Li 4－ x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) can be fabricated. In addition, it was confirmed that the single crystal can be mechanically thinned, and the inventors of the present application have completed the invention disclosed in the present application. The composite oxide of the embodiment of the present application has a chemical composition represented by Li 4－x Sr 2－ x La x ZrO 6 (0 ≦ x ≦ 1.0), and belongs to the space group P2 1 / n in the monoclinic system.

[0036] The high-density single crystal of the present embodiment belonging to the monoclinic system and having a crystal structure for which no similar crystal structure has been reported so far cannot be fabricated by the usual FZ method in which the sample rod is rotated at a speed of less than 20 rpm and the molten part of the sample rod is lowered at a moving speed of about 2 mm / h. This is because there are voids in Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0). When the rod-shaped mixed raw material is rotated at a rotation speed of 20 rpm or more, and at the same time the molten part of the mixed raw material is lowered at a moving speed of 8 mm / h or more, and the molten part is rapidly cooled, a crystal without voids can be fabricated.

[0037] The obtained high-density Li 4－x Sr 2－x Lax ZrO 6 (0 ≦ x ≦ 1.0) composite oxide rods can be cut into any thickness by a diamond cutter or the like. In addition, considering the volatilization of lithium and strontium at high temperatures, the composite oxide single crystal of this embodiment can be obtained by melting a raw material with a chemical composition of Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) by increasing the mixed raw materials of lithium and strontium in the stoichiometric ratio of each metal.

[0038] The relative density of the composite oxide of this embodiment is preferably 99% or more, particularly preferably 100%. The relative density is calculated by measuring the outer shape of the produced thin sheet, calculating the apparent volume, and dividing the apparent density calculated from the measured mass by the true density obtained from the single crystal X-ray structure analysis result. Since the composite oxide of this embodiment has a high density, it can be cut into any thickness by a diamond cutter or the like.

[0039] In addition, the composite oxide of this embodiment can be used as a solid electrolyte material with a high ionic conductivity (e.g., 6.0×10 -4 S / cm or more) and a low activation energy (e.g., 0.20 eV or more and 0.30 eV or less). Specifically, Li 3.957 Sr 1.957 La 0.043 ZrO 6 can be used as a solid electrolyte material with a lithium ion conductivity of 6.0×10 -4 S / cm or more and an activation energy of 0.24 eV.

[0040] The composite oxide of this embodiment is manufactured by melting at least a part of a raw material having a chemical composition represented by Li (4－x)y Sr (2－x)z La x ZrO 6 (0 ≦ x ≦ 1.0, 1 < y, 1 < z) to form a molten part, and moving the molten part at a moving speed of 8 mm / h or more. Specifically, the single crystal of the composite oxide of this embodiment is grown by the FZ method, the Czochralski (Cz) method, the Bridgman method, or the pedestal method, etc. An appropriate manufacturing method can be selected from them according to the size and shape of the crystal of the composite oxide to be manufactured.

[0041] By the FZ method or the Cz method, a crystal of Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) with a relative density of 100%, that is, the original Li4－x Sr 2－x La x ZrO 6 Single crystal of a composite oxide of Li(0≤x≤1.0). The relative density is 100% 4－x Sr 2－x La x ZrO 6 Single crystal of a composite oxide of Li(0≤x≤1.0) has the characteristics of high lithium ion conductivity and low activation energy. When manufacturing the composite oxide of the present embodiment by the FZ method, the raw materials are melted while rotating at a rotation speed of 20 rpm or more on a plane perpendicular to the longitudinal direction of the rod-shaped raw material, and crystals are grown by moving the melting part in the longitudinal direction.

[0042] By increasing the moving speed of the melting part to 8 mm / h or more, decomposition of the raw materials accompanied by lithium volatilization can be avoided. The moving speed of the melting part is preferably 8 mm / h or more and 19 mm / h or less. In addition, in the melting part, bubbles are generated due to the volatilization of lithium, but by increasing the rotation speed of the rod-shaped raw material to 20 rpm or more, the bubbles can be removed. The rotation speed of the raw materials is preferably 20 rpm or more and 60 rpm or less. In addition, melting of the raw materials and movement of the melting part are preferably carried out in a dry air atmosphere. In this way, Li 4－x Sr 2－x La x ZrO 6 (0≤x≤1.0) crystals can be manufactured.

[0043] Taking the growth of Li 4－x Sr 2－ x La x ZrO 6 (0≤x≤1.0) crystals with a relative density of 99% or more, belonging to the monoclinic system and for which no similar crystal structure has been reported as an example, the manufacturing method of the composite oxide of the present embodiment will be described more specifically. First, a rod-shaped raw material is produced as follows. First, considering the volatilization of lithium salts and strontium salts at high temperatures, lithium compounds, strontium compounds, lanthanum compounds, and zirconium compounds are weighed in a stoichiometric ratio (so-called molar ratio) of Li:Sr:La:Zr of (4−x)y:(2−x)z:x:1 (0≤x≤1.0, 1<y, 1<z). y and z are preferably 1.1 or more, more preferably 1.15 or more and 1.25 or less.

[0044] As the lithium compound, there is no particular limitation as long as it contains lithium, and examples include oxides such as Li 2 O and Li 2 CO 3etc. carbonates, etc. As the strontium compound, there is no particular limitation as long as it contains strontium, and examples thereof include oxides such as SrO, SrCO 3 etc. carbonates and SrCl 2 etc. chlorides. As the lanthanum compound, there is no particular limitation as long as it contains lanthanum, and examples thereof include La 2 O 3 etc. oxides and La(OH) 3 etc. hydroxides, etc. As the zirconium compound, there is no particular limitation as long as it contains zirconium, and examples thereof include ZrO 2 etc. oxides and ZrCl 4 etc. chlorides, etc.

[0045] In addition, a compound composed of two or more selected from lithium, strontium, lanthanum, and zirconium can also be used, and it is weighed at a molar ratio of Li:Sr:La:Zr of (4−x)y:(2−x)z:x:1 (0≦x≦1.0, 1<y, 1<z). As such a compound composed of two or more, examples include lithium zirconium oxides such as LiZrO 3 etc. and strontium zirconium oxides such as SrZrO 4 etc.

[0046] Next, the weighed compounds are mixed. There is no particular limitation on the mixing method as long as these compounds can be uniformly mixed. For example, a mixer such as a stirrer can be used for wet or dry mixing. Then, the obtained mixture is filled into a crucible with a lid and pre-fired at 600°C to 900°C, preferably at 650°C. After filling it into a rubber tube or the like to form a rod shape, it is subjected to hydrostatic extrusion molding to obtain a powder as a raw material. In addition, it is more preferable to repeatedly pulverize, mix, and sinter the raw material pre-fired once.

[0047] Next, in order to facilitate molding, the obtained raw material powder is pulverized to make the particle size finer. There is no particular limitation on the pulverizing method as long as the powder can be made finer. For example, wet or dry pulverization can be performed using a pulverizing device such as a planetary ball mill, a pot mill, or a bead mill. Then, the obtained pulverized product is filled into a rubber tube and subjected to hydrostatic extrusion molding into a rod shape. Next, the obtained rod-shaped molded body is fired at about 600°C to 850°C, preferably at 700°C to 850°C for about 4 hours to obtain a rod-shaped raw material. At this time, the chemical composition of the raw material is Li (4－x)y Sr (2－x)z La x ZrO 6 (0≦x≦1.0, 1<y, 1<z).

[0048] Then, the rod-shaped raw material is melted by an infrared focusing heating furnace and rapidly cooled to manufacture Li with a relative density of 99% or more, belonging to the monoclinic system and having no similar crystal structure 4－xSr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0). By this production method, Li with a length of 2 cm or more is obtained 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) single crystal. Therefore, wafers of the same quality can be easily produced by cutting.

[0049] When manufacturing a high-density Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) single crystal by the CZ method, the following steps are carried out. First, the raw materials are put into a crucible and heated to melt. Then, a seed crystal is attached to the melt of the raw materials, and it is pulled up while rotating. By increasing the moving speed of the melting part, that is, the pulling speed of the seed crystal, to 8 mm / h or more, the volatilization of lithium and strontium can be suppressed, and thus a high-density Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) crystal is obtained.

[0050] In addition, the high-density Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) composite oxide can be used as a solid electrolyte for an all-solid-state lithium-ion secondary battery due to its excellent lithium-ion conductivity. That is, the all-solid-state lithium-ion secondary battery of the embodiment of the present application has a positive electrode, a negative electrode, and a solid electrolyte, and the solid electrolyte is composed of the composite oxide of the present embodiment. Hereinafter, the invention disclosed in the present application will be described more specifically by examples. The invention disclosed in the present application is not limited by any of these examples.

[0051] <Example 1>

[0052] (Preparation of powder mixed raw materials of Li 4.7484 Sr 2.3484 La 0.043 ZrO 6 )

[0053] 13.4461 g of lithium carbonate Li 2 CO 3 (made of rare metal, purity 99.99% (the same hereinafter)), 26.5725 g of strontium carbonate SrCO 3 (made of rare metal, purity 99.99% (the same hereinafter)), 0.5369 g of lanthanum oxide La 2 O3 (Made of rare metals, with a purity of 99.99% (the same hereinafter)), and 9.4445 g of zirconium oxide ZrO 2 (Made of rare metals, with a purity of 99.99% (the same hereinafter)) were placed in an agate mortar and mixed uniformly by a wet method using ethanol. Additionally, lanthanum oxide pre-fired at 900 °C in advance was used.

[0054] The metal molar ratio of this mixture, Li:Sr:La:Zr, compared to the target Li 3.957 Sr 1.957 La 0.043 ZrO 6 (Li 4－ x Sr (2－x) La x ZrO 6 in which x = 0.043) has 20 mol% more lithium and 20 mol% more strontium. That is, the chemical composition of this mixture is equivalent to Li 4.7484 Sr 2.3484 La 0.043 ZrO 6 (Li (4－x)y Sr (2－x)z La x ZrO 6 in which x = 0.043, y = 1.2, z = 1.2).

[0055] 50.000 g of this mixture was filled into a covered alumina crucible (made by NIKKATO, type C3). It was placed in a box-type electric furnace (made by Daiwa Kagaku, type FP100) and pre-fired at 650 °C for 6 hours to obtain a powder. 50 g of the obtained powder, 300 g of zirconia balls with a diameter of 5 mm, and 100 g of isopropanol were filled into a zirconia crushing container with a capacity of 250 mL, and using a planetary ball mill (made by Fritsch, Germany, model P-6), it was rotated at a revolution speed of 200 rpm for a total of 300 minutes to crush the powder. The crushed powder was dried at 100 °C for 24 hours and classified using a sieve with a pore size of 250 μm to obtain a powder mixed raw material.

[0056] (Production of rod-shaped raw material)

[0057] Using the powder mixed raw materials obtained above, rod-shaped raw materials are produced in the following order. 15.127 g of the powder mixed raw materials are filled into a rubber mold and degassed. The mold is placed in water in a sealed state and maintained at 40 MPa for 5 minutes. After reducing the water pressure, the molded body is taken out of the mold. The molded body is in the shape of a cylinder with a diameter of 1.1 cm and a height of 8.0 cm. Using a box-type electric furnace (manufactured by Danken, model KDF009), the cylindrical molded body is fired at 850 °C for 4 hours. The taken-out molded body, i.e., the rod-shaped raw material, is in the shape of a cylinder with a diameter of 1.0 cm and a height of 7.7 cm.

[0058] (Li 3.957 Sr 1.957 La 0.043 ZrO 6 Crystal cultivation)

[0059] The rod-shaped raw material obtained above is set in a four-elliptical infrared concentrating heating furnace (FZ furnace) (manufactured by Crystal System, model FZ-T-10000H) equipped with a 1 kW halogen lamp to form a dry air atmosphere. The rod-shaped raw material is rotated at 40 rpm on a plane perpendicular to the length direction, and heated at 21.3% power at the same time. Later, a part of the rod-shaped raw material as a polycrystalline specimen melts to form a molten part. The setting table of the rod-shaped raw material is lowered at a moving speed of 10 mm / h to cultivate a high-density Li 3.957 Sr 1.957 La 0.043 ZrO 6 composite oxide (hereinafter sometimes referred to as "specimen 1"). In addition, the chemical composition of specimen 1 is analyzed by single-crystal X-ray crystal structure analysis. Figure 1 Shows the appearance of specimen 1. As Figure 1 shown, a high-density Li with a length of 7 cm is produced 3.957 Sr 1.957 La 0.043 ZrO 6 crystal.

[0060] (Li 3.957 Sr 1.957 La 0.043 ZrO 6 Crystal evaluation)

[0061] Using a single-crystal X-ray diffractometer (manufactured by Rigaku, model R-AXISRAPID-II) with a two-dimensional IP detector, the structure of specimen 1 is studied. Figure 2 Shows the X-ray diffraction pattern of specimen 1. As Figure 2As shown, distinct diffraction points were measured. When calculating the lattice constants by the least squares method based on the diffraction points, the lattice constant a was 0.57506 nm ± 0.00014 nm, b was 0.62968 nm ± 0.00018 nm, c was 0.84906 nm ± 0.00026 nm, and the β angle was 97.048° ± 0.012°.

[0062] When collecting the diffraction intensity data of Specimen 1, constructing a model of the initial crystal structure using a program with the positive and negative alternating inversion method for super inversion, and studying the crystal structure through the crystal structure analysis program Jana2006, it was found that Specimen 1 belongs to the monoclinic system. Using a diamond cutter to cut Specimen 1, four thin slices with a thickness of 0.1 mm were made, and their relative densities were calculated by the above method. As a result, their relative densities were 99.5%, 99.8%, 99.9%, and 100% respectively. In this way, a composite oxide with a relative density of 99.5% or more was obtained.

[0063] Energy-dispersive X-ray spectroscopy measurement of Specimen 1 was carried out using an energy-dispersive X-ray spectroscopy device (manufactured by JEOL, JCM-6000) attached to a scanning electron microscope. As a result, the spectral data as shown in Figure 3 were obtained, and it was found that the elements contained in the single crystal are Sr, La, Zr, and O. The spectrum of carbon is the influence brought by the conductive band adhering to the specimen. In addition, an inductively coupled plasma mass spectrometry device (manufactured by Thermo Fisher SCIENTIFIC, iCAP Qs) using the single crystal was used to analyze the chemical composition. As a result, the molar ratio of Li:Sr:La:Zr in Specimen 1 was 3.96:1.96:0.04:1.

[0064] Figure 4 Schematically shows the structure of Specimen 1. Specimen 1 has a crystal structure for which there has been no report of a similar crystal structure so far. Li 3.957 Sr 1.957 La 0.043 ZrO 6 belongs to the space group P2 1 / n, lithium ions occupy two 4e sites within the crystal structure, strontium and lanthanum are solid-solved and occupy one 4e site, zirconium occupies the 2c site, and oxygen occupies three 4e sites. The R factor representing the reliability of the crystal structure analysis was 1.78%, so it can be said that the crystal structure analysis result is reasonable.

[0065] In addition, the lithium-ion arrangement in the crystal structure of this composite oxide has a three-dimensional lithium pathway. In particular, in one-dimensional direction, the distance between lithium ions is close to each other, and there are appropriately lithium-ion site defects. Therefore, it is considered that Sample 1 has high lithium-ion conductivity and can be applied to solid electrolyte materials. Sample 1 was cut to produce a thin slice with a diameter of about 0.50 cm and a thickness of about 0.10 cm. On the front and back sides of this thin slice, gold in the shape of a cylinder with a circular bottom side of 0.40 cm and a thickness of 40 nm was sputtered to form electrodes.

[0066] When measuring the lithium-ion conductivity of this sample by the AC impedance method (measurement device: Solarton, 1260) under a nitrogen atmosphere at 25 °C, Figure 5 the Nyquist curve shown was obtained. Based on the total resistance value, the lithium-ion conductivity of this sample was calculated to be 6.8×10 -4 S / cm. In addition, the lithium-ion conductivity of Sample 1 was measured in the temperature range of -20 °C to 40 °C. When applied to the Arrhenius equation, the activation energy was 0.24 eV. Figure 6 shows the temperature change of the lithium-ion conductivity of Sample 1. At -20 °C, the lithium-ion conductivity of Sample 1 (1.3×10 -4 S / cm) is higher than that of a solid electrolyte with a cubic garnet-type structure (6.2×10 -5 S / cm).

[0067] (Fabrication of All-Solid-State Lithium-Ion Secondary Battery)

[0068] 0.0105 mol of lithium acetate dihydrate (manufactured by Sigma-Aldrich) and 0.01 mol of cobalt(II) acetate tetrahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 100 g of ethylene glycol (manufactured by Wako Pure Chemical Industries, Ltd.). 10 g of polyvinylpyrrolidone K-30 (manufactured by Wako Pure Chemical Industries, Ltd.) was added thereto and dissolved to prepare a lithium cobaltate precursor solution with a concentration of 0.1 mol / kg. In terms of molar ratio, the amount of lithium acetate is 5% more than that of cobalt(II) acetate, taking into account the lithium evaporation amount during firing.

[0069] Sample 1 was cut to produce a thin slice with a diameter of about 0.6 cm and a thickness of about 0.10 cm. 10 μL of the above precursor solution was dropped onto one side of this thin slice and pre-fired at 400 °C for 20 minutes. Then, it was fired at 850 °C for 10 minutes to produce a sample (hereinafter sometimes referred to as "Sample 2") with a lithium cobaltate positive electrode formed on one side of Sample 1. In a glove box, Sample 2 and a punched metal lithium plate with a diameter of 4 mm were placed in a commercially available HS battery for battery evaluation (manufactured by Takizawa Co., Ltd.) to fabricate Figure 7 the all-solid-state lithium-ion secondary battery shown. This all-solid-state lithium-ion secondary battery showed an open-circuit voltage of 2.7 V, thereby confirming that it functions as a battery.

[0070] <Example 2>

[0071] (Preparation of powder mixed raw material of Li 4 Sr 2 ZrO 6 )

[0072] Except for using 14.1793 g of lithium carbonate Li 2 CO 3 , 25.9684 g of strontium carbonate SrCO 3 and 9.8524 g of zirconium oxide ZrO 2 , a powder mixed raw material was obtained in the same manner as in Example 1. The molar ratio of metals in this powder mixed raw material, Li:Sr:Zr, is 20 mol% higher in lithium and 20 mol% higher in strontium compared to the molar ratio of the target Li 4 Sr 2 ZrO 6 . That is, the chemical composition of this powder mixed raw material corresponds to Li 4.4 Sr 2.2 ZrO 6 (Li (4－

[0073] x)y Sr (2－x)z La x ZrO 6 where x = 0, y = 1.2, z = 1.2).

[0074] (Preparation of rod-shaped raw material)

[0075] Except for using 14.111 g of the powder mixed raw material obtained above, a molded body was obtained in the same manner as in Example 1. The molded body was in the shape of a cylinder with a diameter of 1.2 cm and a height of 6.0 cm. Then, it was fired under the same conditions as in Example 1 to obtain a rod-shaped raw material. The obtained rod-shaped raw material was in the shape of a cylinder with a diameter of 1.1 cm and a height of 5.3 cm.

[0076] (Crystal cultivation of Li 4 Sr 2 ZrO 6 )

[0077] Except for heating at a power of 19.8%, high-density Li 4 Sr 2 ZrO 6 composite oxide (hereinafter sometimes referred to as "Specimen 3") was cultivated in the same manner as in Example 1, and its chemical composition was analyzed. Figure 8 The appearance of Specimen 3 is shown. As Figure 8 shown, a high-density Li 4y Sr 2z ZrO6 crystals

[0078] (Li 4 Sr 2 ZrO 6 )(evaluation of the crystals of

[0079] The structure of Specimen 3 was studied in the same manner as in Example 1. Figure 9 Fig. shows the X-ray diffraction pattern of Specimen 3. As Figure 9 shown, distinct diffraction points were measured. When calculating the lattice constants by the least squares method based on the diffraction points, the lattice constant a was 0.573063 nm ± 0.000024 nm, b was 0.609683 nm ± 0.000025 nm, c was 0.847059 nm ± 0.000034 nm, and the β angle was 97.16628° ± 0.0129°.

[0080] When studying the crystal structure of Specimen 3 in the same manner as in Example 1, it was found that Specimen 3 belongs to the monoclinic system. Additionally, in the same manner as in Example 1, four thin slices of Specimen 3 with a thickness of 0.1 mm were prepared and the relative density was calculated. As a result, their relative densities were 99.8%, 99.7%, 99.9%, and 100% respectively. Thus, a composite oxide with a relative density of 99.5% or more was obtained.

[0081] Specimen 3 has a crystal structure as shown in Figure 4 which has not been reported to have a similar crystal structure so far. Li 4 Sr 2 ZrO 6 belongs to the space group P2 1 / n, lithium ions occupy two 4e sites within the crystal structure, strontium occupies one 4e site, zirconium occupies the 2c site, and oxygen occupies three 4e sites. The R factor indicating the reliability of the crystal structure analysis was 3.72%, and thus it can be said that the crystal structure analysis result is reasonable.

[0082] <Example 3>

[0083] (Preparation of the powder mixture raw material of (Li 3 SrLaZrO 6 )

[0084] Except for using 11.1527 g of lithium carbonate Li 2 CO 3 , 14.8549 g of strontium carbonate SrCO 3 , 13.6599 g of lanthanum oxide La 2 O 3 and 10.3325 g of zirconium oxide ZrO 2Except for this, a powder mixed raw material was obtained in the same manner as in Example 1. The molar ratio of metals in this powder mixed raw material, Li:Sr:La:Zr, has 20 mol% more lithium and 20 mol% more strontium compared to the molar ratio of the target Li 3 SrLaZrO 6 . That is, the chemical composition of this powder mixed raw material corresponds to Li 4.4 Sr 2.2 ZrO 6 (Li (4－x)y Sr (2－x)z La x ZrO 6 where x = 1, y = 1.2, and z = 1.2).

[0085] (Production of rod-shaped raw material)

[0086] Except for using 18.427 g of the powder mixed raw material obtained above, a molded body was obtained in the same manner as in Example 1. This molded body was in the shape of a cylinder with a diameter of 1.1 cm and a height of 8.0 cm. Then, it was fired under the same conditions as in Example 1 to obtain a rod-shaped raw material. The obtained rod-shaped raw material was in the shape of a cylinder with a diameter of 1.0 cm and a height of 8.0 cm.

[0087] (Cultivation of Li 3 SrLaZrO 6 crystals)

[0088] In the same manner as in Example 1, a high-density Li 3 SrLaZrO 6 composite oxide (hereinafter sometimes referred to as "Specimen 4") was cultivated, and its chemical composition was analyzed. Figure 10 The appearance of Specimen 4 is shown. As Figure 10 shown, a high-density Li 3 SrLaZrO 6 crystal with a length of 6 cm was produced.

[0089] (Evaluation of Li 3 SrLaZrO 6 crystals)

[0090] The structure of Specimen 4 was studied in the same manner as in Example 1. Figure 11 The X-ray diffraction pattern of Specimen 4 is shown. As Figure 11 shown, distinct diffraction points were measured. When calculating the lattice constants by the least squares method based on the diffraction points, the lattice constant a was 0.585780 nm ± 0.000220 nm, b was 0.639450 nm ± 0.00250 nm, c was 0.85860 nm ± 0.000300 nm, and the β angle was 96.84870° ± 0.01210°.

[0091] When studying the crystal structure of sample 4 in the same manner as in Example 1, it was found that sample 4 belongs to the monoclinic system. Additionally, in the same manner as in Example 1, four thin slices of sample 4 with a thickness of 0.1 mm were fabricated, and the relative density was calculated. As a result, their relative densities were 99.9%, 99.9%, 100%, and 99.7%, respectively. Thus, a composite oxide with a relative density of 99.5% or more was obtained.

[0092] Sample 4 has a crystal structure for which no similar reports have been made. Figure 4 as shown in the crystal structure. Li 3 SrLaZrO 6 belongs to the space group P2 1 / n, the lithium ions occupy two 4e sites within the crystal structure, strontium occupies one 4e site, zirconium occupies the 2c site, and oxygen occupies three 4e sites. The R factor indicating the reliability of the crystal structure analysis was 3.12%, and thus it can be said that the crystal structure analysis results are reasonable.

[0093] Combining the results of Examples 1 to 3, the lattice constants of Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) are a = 0.57 nm ± 0.02 nm, b = 0.62 nm ± 0.02 nm, c = 0.84 nm ± 0.02 nm, and the β angle is 97.0° ± 0.2°.

[0094] Industrial availability

[0095] The high-density Li 4－x Sr 2－x La x ZrO 6 (0 ≦ x ≦ 1.0) composite oxide can be used as a solid electrolyte material for all-solid-state lithium-ion secondary batteries, etc.

Claims

1. A composite oxide having a chemical composition represented by Li 4－x Sr 2－x La x ZrO 6 , where 0 ≦ x ≦ 1.0, and belonging to the space group P2 1 / n in the monoclinic system.

2. The composite oxide according to claim 1, wherein, The lithium ion conductivity is 6.0×10 -4 S / cm or more.

3. The composite oxide according to claim 1, wherein, the activation energy is 0.20 eV or more and 0.30 eV or less.

4. The composite oxide according to claim 1, wherein, the lattice constants a is 0.57 nm ± 0.02 nm, b is 0.62 nm ± 0.02 nm, c is 0.84 nm ± 0.02 nm, and the β angle is 97.0° ± 0.2°.

5. The composite oxide according to claim 1, wherein, lithium ions occupy two 4e sites within the crystal structure, strontium occupies one 4e site, or strontium and lanthanum are solid-soluted to occupy one 4e site, zirconium occupies the 2c site, and oxygen occupies three 4e sites.

6. The composite oxide according to any one of claims 1 to 5, wherein, the relative density is 100%.

7. A method for manufacturing a composite oxide, comprising: Melting process, melting at least a part of a raw material having a chemical composition represented by Li (4－x)y Sr (2－x)z La x ZrO 6 , where 0 ≦ x ≦ 1.0, 1 < y ≦ 1.25, 1 < z ≦ 1.25, to form a melting section, and a moving step of moving the molten part at a moving speed of 8 mm / h or more, to produce a composite oxide having a chemical composition represented by Li 4－x Sr 2－x La x ZrO 6 , where 0 ≦ x ≦ 1.0, a relative density of 99% or more, and belonging to the space group P2 1 / n in the monoclinic system; wherein, the raw material has a rod shape, while rotating the raw material at a rotation speed of 20 rpm or more on a plane perpendicular to the length direction of the raw material, melting the raw material to grow the composite oxide.

8. The method for manufacturing a composite oxide according to claim 7, wherein, the moving speed is 8 mm / h or more and 19 mm / h or less.

9. The method for manufacturing a composite oxide according to claim 8, wherein, the rotation speed is 20 rpm or more and 60 rpm or less.

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 composite oxide according to claim 1.

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