Method for manufacturing oxide-based materials

Abstract

The present invention provides a method for producing oxide-based materials that can reduce the degradation of their properties. [Solution] The method for manufacturing an oxide-based material includes a step of firing a lithium-containing material, and includes the operation of placing a firing jig containing the material into a furnace and firing the material, wherein an opening connecting the inside and outside of the firing jig is provided in the firing jig. The oxide-based material is, for example, a solid electrolyte having a garnet-type crystalline structure containing Li, La, and Zr.

Description

Technical Field

[0001] The present invention relates to a method for producing an oxide-based material including a step of firing a lithium-containing material.

Background Art

[0002] Oxide-based materials produced through a step of firing a lithium-containing material are known. Since lithium is likely to evaporate during firing, Patent Document 1 discloses a prior art in which the amount of lithium in the material is made excessive compared to the stoichiometric composition in consideration of the evaporation amount of lithium, and a prior art in which the material is covered with a firing jig to reduce the evaporation of lithium.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, since the material is covered with a firing jig, the gas generated from the material during firing stays inside the firing jig. When the concentration of the gas generated from the material inside the firing jig becomes high, reaction products having an unintended crystal structure are likely to be formed, resulting in a deterioration of the properties of the oxide-based material.

[0005] The present invention has been made to solve this problem, and an object thereof is to provide a method for producing an oxide-based material capable of reducing the deterioration of properties.

Means for Solving the Problems

[0006] A first aspect for achieving this object is a method for producing an oxide-based material including a step of firing a lithium-containing material, comprising putting a firing jig containing the material into a furnace, including an operation of firing the material, and an opening connecting the inside and the outside of the firing jig is provided in the firing jig.

[0007] In a second embodiment, the oxide material is a solid electrolyte having a garnet-type crystalline structure containing Li, La, and Zr, in the first embodiment.

[0008] The third aspect is that, in the first or second aspect, the ratio of the area of ​​the opening to the sum of the area of ​​the outer surface excluding the bottom of the firing jig and the area of ​​the opening is 0.02 or more and 0.30 or less.

[0009] The fourth aspect is that, in the third aspect, the value obtained by multiplying the ratio of the opening area, the maximum temperature (°C) during the firing operation, and the time (hours) at 1000°C or higher during the firing operation is 3700°C·h or less. [Effects of the Invention]

[0010] According to the present invention, a lithium-containing material is placed in a firing jig that has an opening connecting the inside and outside of the firing jig and fired there. This prevents the evaporation of lithium, while facilitating the exhaust of gases generated from the material during firing to the outside of the firing jig through the opening. This reduces the accumulation of gases generated from the material inside the firing jig and the evaporation of lithium, thereby reducing the formation of reaction products with unintended crystal structures, and thus reducing the deterioration of the properties of oxide-based materials. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the firing process of the material contained in the firing jig in the first embodiment. [Figure 2] (a) is a cross-sectional view of the firing jig containing the material, and (b) is a cross-sectional view of the firing jig showing its outer surface. [Figure 3] This is a schematic diagram showing the crystal structure of a garnet-type crystal. [Figure 4] This is a perspective view of the firing jig in the second embodiment. [Figure 5] (a) is a cross-sectional view of the firing jig along the Va-Va line in Figure 4, and (b) is a cross-sectional view of the firing jig showing its outer surface. [Figure 6]Perspective view of the firing jig in the third embodiment. [Figure 7] (a) is a cross-sectional view of the firing jig taken along line VIIa-VIIa of FIG. 6, and (b) is a cross-sectional view of the firing jig showing the outer surface of the firing jig.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram of the firing of the material 10 (see FIG. 2(a)) accommodated in the firing jig 11 in the first embodiment. The oxide-based material is manufactured through a process of firing the firing jig 11 containing the material 10 containing lithium in the furnace 20.

[0013] FIG. 2(a) is a cross-sectional view of the firing jig 11 containing the material 10. Examples of the oxide-based material manufactured through the process of firing the material 10 include a solid electrolyte having lithium ion conductivity, a positive electrode active material and a negative electrode active material that occlude or release lithium ions. Examples of the solid electrolyte include NASICON-based materials, LISICON-based materials, and oxides having a perovskite structure or a garnet structure.

[0014] Examples of the positive electrode active material and the negative electrode active material include oxides containing a transition metal and Li. Examples of the positive electrode active material include LiCoO2, LiNi x Co 0.15 Al 0.05 O2, LiMn2O4, LiNiVO4, LiNi<00000​​​​​​​​​​​​​​​​​​​​​2-x (PO4)3, Li 1+x Ge x Ti 2-x (PO4)3 is one example. LiSICON-based materials include Li 4-2x Zn x GeO4 (0 ≤ x ≤ 1) is an example. Oxides having a perovskite structure include Li x La (1-x) / 3 NbO3, La 2 / 3-X Li 3X One example is TiO3 (0 ≤ x ≤ 1). The crystal structure of garnet-type oxides is given by the general formula C3A2B3O 12 It is represented as follows.

[0016] Figure 3 schematically shows a garnet-type crystal structure. In the garnet-type crystal structure, the C site Sc is dodecahedral in coordination with the oxygen atom Oa, the A site Sa is octahedral in coordination with the oxygen atom Oa, and the B site Sb is tetrahedral in coordination with the oxygen atom Oa. In the garnet-type crystal structure, Li can be present in the void V, which is the site where the oxygen atom Oa is octahedral in coordination with the oxygen atom Oa. The void V is, for example, the area between B site Sb1 and B site Sb2. The Li present in void V is octahedral in coordination with the oxygen atom Oa that constitutes an octahedron including the tetrahedron face Fb1 forming B site Sb1 and the tetrahedron face Fb2 forming B site Sb2.

[0017] For example, Li7La3Zr2O 12 In a garnet-type solid electrolyte with this composition, La may occupy the C site Sc, Zr may occupy the A site Sa, and Li may occupy the B site Sb and the void V. Garnet-type solid electrolytes are found in the CSD (Cambridge Structural Database) X-ray diffraction file No. 422259 (Li7La3Zr2O 12 It has an XRD pattern similar to ).

[0018] In garnet-type solid electrolytes, various elements are substituted. For example, Ca, Sr, Ba, etc., are substituted at the C site; Nb, Ta, Sn, Hf, etc., are substituted at the A site; and Al, Ga, etc., are substituted at the B site. Elemental substitution changes the amount of lithium, altering the arrangement, occupancy, and occupancy sites of lithium ions within the crystal structure, thereby changing the ionic conductivity. Elemental substitution may result in differences in diffraction angles and intensity ratios compared to No. 422259.

[0019] Li7La3Zr2O 12 The constituent elements may be partially substituted with other elements, or trace amounts of other elements may be added without substituting any constituent elements. Examples of other elements include at least one element selected from the group consisting of Mg, Al, Si, Ca, Ti, V, Ga, Sr, Y, Nb, Sn, Sb, Ba, Hf, Ta, W, Bi, Rb, and lanthanides (excluding La).

[0020] For example, Li6La3Zr 1.5 W 0.5 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Al 0.2 O 12 ,Li 6.15 La3Zr 1.75 Ta 0.25 Ga 0.2 O 12 ,Li 6.25 La3Zr2Ga 0.25 O 12 ,Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ,Li 6.5 La3Zr 1.75 Te 0.25 O 12 ,Li 6.75 La3Zr 1.75 Nb 0.25 O 12 ,Li 6.9 La3Zr 1.675 Ta 0.289 Bi 0.036 O 12 ,Li 6.46 Ga0.23 La3Zr 1.85 Y 0.15 O 12 ,Li 6.8 La 2.95 Ca 0.05 Zr 1.75 Nb 0.25 O 12 ,Li 7.05 La 3.00 Zr 1.95 Gd 0.05 O 12 ,Li 6.20 Ba 0.30 La 2.95 Rb 0.05 Zr2O 12 These are some examples.

[0021] Garnet-type solid electrolytes are preferably those containing Mg and at least one of element A (where A is at least one element selected from the group consisting of Ca, Sr, and Ba), with the molar ratio of each element satisfying all of the following conditions (1) to (3), or those containing both Mg and element A, with the molar ratio of each element satisfying all of the following conditions (4) to (6). Element A is preferably Sr in order to increase the ionic conductivity of powder 19. (1) 1.33 ≤ Li / (La+A) ≤ 3 (2) 0 ≤ Mg / (La+A) ≤ 0.5 (3) 0 ≤ A / (La + A) ≤ 0.67 (4) 2.0 ≤ Li / (La+A) ≤ 2.6 (5) 0.01 ≤ Mg / (La+A) ≤ 0.14 (6) 0.04 ≤ A / (La + A) ≤ 0.17

[0022] Let's return to Figure 2(a) for explanation. Material 10 can be exemplified by powder, or molded bodies formed by applying pressure to the powder or agglomerating the powder. Examples of powders include mixtures of various metal salts such as oxides, hydroxides, and carbonates containing metal elements that constitute oxide-based materials, or powders prepared by solid-phase, liquid-phase, or gas-phase methods. Wet mixing and dry mixing can be used without limitation as means for mixing the various metal salts.

[0023] Material 10 is set so that the proportion of metal elements matches or approximates the stoichiometric composition to the extent that the desired oxide-based material can be obtained. Material 10 may contain certain metal elements, such as lithium, that tend to evaporate and disappear during firing, in excess of the stoichiometric composition.

[0024] The material 10 is fired in a firing jig 11 (refractory container). The firing jig 11 includes a container 12 and a lid 17. The container 12 includes a first bottom 13 and a wall 14 provided around the first bottom 13. The lid 17 rests on the wall 14. The lid 17 is a component that closes the opening of the container 12. By covering the container 12 with the lid 17 during firing, the evaporation of lithium contained in the material 10 and the incorporation of refractory materials and other materials falling from the furnace 20 (see Figure 1) can be reduced.

[0025] The shape of the first base 13 can be a polygon such as a triangle or square, or a circle such as an ellipse. One or more holes penetrating the first base 13 may be provided in the first base 13, as long as the mechanical strength of the first base 13 at the firing temperature is ensured. There are no particular restrictions on the shape or size of the holes, as long as the mechanical strength of the first base 13 is ensured.

[0026] The wall 14 is provided around the entire outer circumference of the first bottom 13, enclosing the entire first bottom 13. The wall 14 may be perpendicular to the first bottom 13, or it may extend outside the first bottom 13 such that the width of the wall 14 gradually increases as it moves away from the first bottom 13. The container 12 may be a single molded product in which the first bottom 13 and the wall 14 are integrated, or it may be made by bonding the first bottom 13 and the wall 14 together.

[0027] The second base 15 is placed on top of the first base 13. In order to reduce the distance (gap) between the outer circumference of the second base 15 and the wall 14, the shape of the second base 15 is almost identical to that of the first base 13. Reducing the gap is to decrease the amount of material 10 that gets between the edge of the second base 15 and the wall 14 and comes into contact with the first base 13. If the coefficient of linear expansion of the second base 15 between room temperature and the firing temperature is greater than the coefficient of linear expansion of the first base 13 between room temperature and the firing temperature, the dimensions of the second base 15 are set so that there is a small gap between the second base 15 and the wall 14 at room temperature. This is to prevent the wall 14 from being damaged by the second base 15 which expands relatively due to the heat during firing.

[0028] An opening 16 is provided in the firing jig 11, connecting the inside and outside of the firing jig 11. Gas generated from the material 10 inside the firing jig 11 during firing exits the firing jig 11 through the opening 16. Examples of gas include carbon dioxide and water vapor produced by the decomposition of metal salts contained in the material 10. To prevent the material 10 from spilling out of the firing jig 11 through the opening 16, the opening 16 is positioned higher than the volume of the material 10. In this embodiment, the opening 16 is provided in the wall 14.

[0029] Examples of materials for the firing jig 11 include inorganic materials such as alumina, cordierite, mullite, silica, magnesia, and zirconia, and metallic materials whose main component is at least one of W, Mo, and Ni. The main component means that the combined mass of W, Mo, and Ni is 50 wt% or more of the mass of the metallic material.

[0030] Examples of metallic materials with W as the main component include W, W-Fe alloy, W-ThO2 alloy, W-Mo alloy, W-Zr alloy, W-Ni-Cu alloy, W-Ni-Mo alloy, W-Ni-Fe alloy, W-Ni-Fe-Mo alloy, and W-Ni-Cu-Fe alloy. Examples of metallic materials with Mo as the main component include Mo, Mo-Cu alloy, Mo-Zr-Hf-C alloy, Mo-La2O3 alloy, and Mo-Re alloy. Examples of metallic materials with Ni as the main component include Ni, Ni-Cu alloy, Ni-Mo-Fe alloy, and Ni-Fe alloy.

[0031] Let's return to Figure 1 for explanation. Material 10 is generally fired two or more times. The main purpose of the first firing (hereinafter referred to as "primary firing") is the thermal decomposition of material 10. Primary firing can be carried out while an atmospheric gas flows through the furnace 20. The arrow G shown in Figure 1 indicates the direction in which the atmospheric gas flows through the furnace 20. Examples of atmospheric gases include air-modified gases such as dry air (air from which water vapor has been removed) and purified gas (air from which carbon dioxide has been removed), inert gases such as argon and helium, neutral gases such as nitrogen and ammonia, and reducing gases such as hydrogen and carbon monoxide.

[0032] In this embodiment, the furnace 20 is a continuous firing furnace in which a firing jig 11 placed on a base plate 21 is transported through a heating zone (not shown) by the movement of the base plate 21. Examples of continuous firing furnaces include roller hearth kilns, pusher kilns, tunnel kilns, walking beam furnaces, and mesh belt furnaces. If the furnace 20 is a mesh belt furnace, the base plate 21 may be omitted, and the firing jig 11 may be transported by placing it directly on the mesh belt.

[0033] The arrow W shown in Figure 1 indicates the direction in which the firing jig 11 moves within the furnace 20. As the material 10 contained within the firing jig 11 moves downstream in the direction of the firing jig 11's movement, phase changes and chemical reactions proceed due to firing. Since the material 10 is fired with a portion covered by the firing jig 11, the evaporation of lithium due to firing can be reduced. This makes it easier to obtain oxide-based materials with the desired crystal structure.

[0034] The furnace 20 transports the firing jigs 11 by arranging them in two rows, with one firing jig 11 placed on top of the lid 17 of the firing jig 11, but this is not the only way. To reduce the effects of temperature variations in the height and width directions inside the furnace 20, it is certainly possible to transport the firing jigs 11 one by one in a single row without stacking them.

[0035] In this embodiment, the walls 14 of the firing jig 11 are rectangular and cylindrical, and openings 16 are provided on each of the four sides of the wall 14. Since the gas generated from the material 10 during firing exits the firing jig 11 through the openings 16, the gas concentration inside the firing jig 11 can be reduced. This reduces the formation of reaction products with unintended crystalline structures, thereby reducing the deterioration of the properties of oxide-based materials.

[0036] When an atmospheric gas is flowing inside the furnace 20, it is preferable to position the firing jig 11 inside the furnace 20 such that the openings 16 provided in the firing jig 11 are located upstream and downstream of the atmospheric gas, respectively, along arrow G. This makes it easier for the atmospheric gas to enter the firing jig 11 through the upstream opening 16 and for the gas inside the firing jig 11 to exit through the downstream opening 16, thus facilitating the exchange between the gas generated from the material 10 and the atmospheric gas. Consequently, the deterioration of the properties of the oxide material can be further reduced.

[0037] It is preferable to align the conveying direction of the firing jig 11 (direction of arrow W) with the direction of the atmospheric gas flow (direction of arrow G). Since the material 10 is fired while the firing jig 11 is conveyed toward the upstream side of the atmospheric gas, the gases and evaporated elements generated from the material 10 are carried upstream in the conveying direction of the firing jig 11 by the atmospheric gas. Therefore, the concentration of gases and evaporated elements generated from the material 10 is lower upstream in the conveying direction of the firing jig 11 than downstream in the conveying direction of the firing jig 11. Downstream in the conveying direction of the firing jig 11, phase changes and chemical reactions of the material 10 are progressing, so by lowering the concentration of gases and evaporated elements generated from the material 10, contamination of the material 10, where phase changes and chemical reactions are progressing, by gases and the like can be reduced. Therefore, the deterioration of the properties of oxide-based materials can be further reduced.

[0038] Figure 2(b) is a cross-sectional view of the firing jig 11. The material 10 is not shown in Figure 2(b) (the same applies to Figures 5(b) and 7(b)). The outer surface of the firing jig 11 is defined as the side surface 22 of the container 12 that appears in the space inside the furnace 20 (see Figure 1), the bottom surface 23 of the container 12 that connects to the lower end of the side surface 22 and is in contact with the base plate 21 (see Figure 2(a)), and the top surface 24 that is made by the lid 17 and connects to the upper end of the side surface 22. The opening 16 is not included in the outer surface of the firing jig 11. The area of ​​the opening 16 is the area of ​​the part where the outer surface of the firing jig 11 and the opening 16 intersect.

[0039] The ratio R of the area of ​​the opening 16, when the sum of the area of ​​the outer surface (sides 22 and top surface 24) of the firing jig 11 excluding the bottom 23 and the area of ​​the opening 16 is taken as 1, is preferably between 0.02 and 0.30. This is to ensure gas exhaust from the opening 16 while reducing lithium evaporation. The reason for excluding the bottom 23 from the outer surface of the firing jig 11 when calculating the ratio R of the area of ​​the opening 16 is that the bottom 23 has little effect on the size of the space inside the firing jig 11 that is connected to the outside by the opening 16.

[0040] The material 10 that has undergone primary firing is more likely to form a crystalline structure of an oxide-based material during the second firing (hereinafter referred to as "secondary firing"). The material 10 after primary firing may already have a crystalline structure of an oxide-based material. Performing primary and secondary firing is just one example, and the number of firings is not limited to two. The number of firings may be more or less than two.

[0041] The main purpose of secondary calcination is the synthesis of oxide-based materials. When the oxide-based material is a garnet-type solid electrolyte, the primary calcination temperature is typically 850°C to 1150°C. Primary calcination may include steps of calcination at lower temperatures and steps of calcination at higher temperatures within this temperature range. Before proceeding to the next calcination step, the material 10 after each step may be crushed and mixed. It is desirable to crush the material 10 dry at this time. The primary calcination time is typically 10 to 15 hours at the set maximum temperature. The secondary calcination temperature is typically 1100°C to 1250°C. The secondary calcination time is typically 10 to 20 hours at the set maximum temperature.

[0042] It is preferable that the product of the maximum atmospheric temperature (°C) inside the furnace 20 during firing, the time (h) that the firing jig 11 is present in an atmosphere of 1000°C or higher during firing, and the ratio R of the area of ​​the opening 16, be 3700°C·h or less. This is to further reduce the evaporation of lithium from the material 10.

[0043] Alternatively, the material 10 after secondary firing may be removed from the firing jig 11, pressure may be applied to the removed material 10 to form a molded body, and the molded body may be placed in the firing jig 11 for firing. The firing temperature and time at this time are the same as those for secondary firing. Alternatively, the material 10 after primary firing may be removed from the firing jig 11, pressure may be applied to the removed material 10 to form a molded body, and the molded body may be placed in the firing jig 11 for secondary firing.

[0044] The fabricated oxide-based materials can be used as materials for energy storage devices such as secondary batteries and electrochemical capacitors. Examples of electrochemical capacitors include redox capacitors that utilize redox reactions and hybrid capacitors, which are asymmetric cells combining electric double-layer capacitors and solid electrolytes. Examples of materials for energy storage devices include mixtures of oxide-based material powder and electrolyte, slurries containing oxide-based material powder and dispersion medium, and active materials contained in electrodes.

[0045] A second embodiment will be described with reference to Figures 4 and 5. In the first embodiment, the case in which an opening 16 is provided in the wall 14 of the firing jig 11 was described. In the second embodiment, the case in which an opening 34 is provided between the wall 32 of the firing jig 31 and the lid 17 will be described. In the second embodiment, the same reference numerals are used for the same parts as in the first embodiment, and the description of the same parts is omitted.

[0046] Figure 4 is a perspective view of the firing jig 31 in the second embodiment. The firing jig 31, containing the material 10 (see Figure 5(a)), is placed in the furnace 20 in place of the firing jig 11 in the first embodiment. The firing jig 31 includes a wall 32 and a lid 17. In this embodiment, a rectangular lid 17 rests on a rectangular cylindrical wall 32. The lid 17 is positioned at a 45° rotation from its normal position where it is in close contact with the entire circumference of the upper end of the wall 32. This creates four triangular openings 34 between the four corners of the wall 32 and the lid 17.

[0047] Figure 5(a) is a cross-sectional view of the firing jig 31 along the Va-Va line in Figure 4. The firing jig 31 includes a bottom portion 33 positioned inside the wall 32. A material 10, which is a molded body formed by applying pressure to powder and solidifying it, rests on the bottom portion 33. In this embodiment, the bottom portion 33 is separate from the wall 32, but this is not the only possible configuration. It is certainly possible to connect the wall 32 and the bottom portion 33, making the wall 32 a bottomed cylindrical shape.

[0048] Figure 5(b) is a cross-sectional view of the firing jig 31. The outer surface of the firing jig 31 includes the side surface 35 of the wall 32 that appears in the space inside the furnace 20 (see Figure 1), and the upper surface 36 which is formed by the lid 17 and connects to the upper end of the side surface 35. The ratio R of the area of ​​the opening 34 to the sum of the area of ​​the outer surface (side surface 35 and upper surface 36) of the firing jig 31 and the area of ​​the opening 34 is preferably 0.02 or more and 0.30 or less. This is to reduce lithium evaporation while ensuring gas exhaust from the opening 34.

[0049] It is preferable that the product of the maximum atmospheric temperature (°C) inside the furnace 20 during firing, the time (h) that the firing jig 31 is present in an atmosphere of 1000°C or higher during firing, and the ratio R of the area of ​​the opening 34, be 3700°C·h or less. This is to further reduce the evaporation of lithium from the material 10.

[0050] A third embodiment will be described with reference to Figures 6 and 7. In the first and second embodiments, firing jigs 11 and 31 were described, in which a lid 17 was placed on walls 14 and 32 surrounding the material 10. In the third embodiment, a firing jig 41 is described, which includes a cover 43 that covers the material 10 placed on the bottom 42. In the third embodiment, the same reference numerals are used for the same parts as in the first embodiment, and the description of the same parts is omitted.

[0051] Figure 6 is a perspective view of the firing jig 41 in the third embodiment. Figure 7(a) is a cross-sectional view of the firing jig 41 along the line VIIa-VIIa in Figure 6. The firing jig 41 containing the material 10 is placed in the furnace 20 in place of the firing jig 11 in the first embodiment. The firing jig 41 includes a bottom 42 and a cover 43. A block-shaped molded body (material 10), formed by applying pressure to powder, is placed on the bottom 42.

[0052] The cover 43 includes a cylindrical wall 44 that surrounds the material 10 above the bottom 42, and a roof 45 that closes the upper end of the wall 44, covering the perimeter of the material 10. The cover 43 has rectangular notches 46 on the edges of the opposing walls 44. Two openings 47 are formed between the two notches 46 in the wall 44 and the bottom 42, connecting the inside and outside of the firing jig 41.

[0053] Figure 7(b) is a cross-sectional view of the firing jig 41. The outer surface of the firing jig 41 includes the side surface 48 of the wall 44 that appears in the space inside the furnace 20 (see Figure 1), and the upper surface 49 which is formed by the roof 45 and connects to the upper end of the side surface 48. The ratio R of the area of ​​the opening 47 to the sum of the area of ​​the outer surface (side surface 48 and upper surface 49) of the firing jig 41 and the area of ​​the opening 47 is preferably 0.02 or more and 0.30 or less. This is to reduce lithium evaporation while ensuring gas exhaust from the opening 47.

[0054] It is preferable that the product of the maximum atmospheric temperature (°C) inside the furnace 20 during firing, the time (h) that the firing jig 41 is present in an atmosphere of 1000°C or higher during firing, and the ratio R of the area of ​​the opening 47, be 3700°C·h or less. This is to further reduce the evaporation of lithium from the material 10. [Examples]

[0055] The present invention will be described in more detail by reference to examples, but the present invention is not limited to these examples.

[0056] Li 6.95 Mg 0.15 La 2.75 Sr 0.25 Zr 2.0 O 12 Li2CO3, MgO, La(OH)3, SrCO3, and ZrO2 were weighed accordingly. Li2CO3 was kept in excess by approximately 15 mol% in elemental terms, considering the volatilization of Li during calcination. The weighed raw materials were mixed in a dry mixer for 0.5 hours to obtain LLZ powder (material).

[0057] 300g of material was placed in a mold, and a force of 0.15kN was applied to the mold using a tabletop press to obtain a rectangular hexahedron molded body measuring 8cm in length, width, and height, and 4cm in thickness. The molded bodies were placed in firing jigs, which included a magnesia plate on which the molded bodies rested, and had nine different sized openings. These were designated as Samples No. 1-9. For Samples No. 1-9, the ratio R of the opening area was calculated, where the sum of the area of ​​the outer surface of the firing jig (excluding the bottom of the plate on which the molded body rests) and the area of ​​the openings was set to 1. The ratio R was rounded to the fifth decimal place.

[0058] The molded bodies, housed in firing jigs, were fired in a furnace circulating nitrogen gas. The firing process involved raising the temperature from room temperature to 1100°C, leaving the firing jigs in the 1100°C atmosphere for 10 hours, and then cooling them back to room temperature. In this firing process, the firing jigs were in an atmosphere above 1000°C for 12 hours. The value V (°C·h) was calculated by multiplying the ratio R of samples No. 1-9 by the maximum temperature of the furnace atmosphere during firing (1100°C) and the time the firing jigs were in an atmosphere above 1000°C (12h). The value V was rounded to one decimal place.

[0059] The molded bodies, after firing in an argon atmosphere glove box, were pulverized using a mortar and pestle to prepare samples for powder X-ray diffraction. After obtaining the X-ray diffraction patterns of the samples using powder X-ray diffraction with CuKα rays, the X-ray diffraction patterns were analyzed using the Rietveld method to determine the proportion of cubic crystals in samples No. 1-9.

[0060] It is known that the ionic conductivity of LLZ in the cubic crystal structure is higher than that of the tetragonal crystal structure. The cubic crystal structure of LLZ is the desired crystal structure, while the tetragonal crystal structure is the undesirable one. Therefore, samples with a cubic crystal ratio greater than 90 mass% (cubic:tetragonal = 90:10) were classified as A, samples with a cubic crystal ratio between 80 mass% and 90 mass% were classified as B, and samples with a cubic crystal ratio less than 80 mass% were classified as C.

[0061] Table 1 shows the ratio R of the opening area, the value V, and the Rietveld analysis results for samples No. 1-9. Sample No. 9 was fired on a plate without a wall surrounding the molded body. In sample No. 9, one side of the molded body was in contact with the magnesia plate, and five sides of the molded body were exposed to the space inside the furnace, so the ratio R of the opening area was 1.

[0062] [Table 1]

[0063] As shown in Table 1, sample No. 2-8, where the ratio R of the opening area was between 0.02 and 0.30, received a rating of A or B, indicating a high proportion of cubic crystals. It was revealed that a ratio R between 0.02 and 0.30 reduces gas retention and lithium evaporation from the molded body, thereby reducing reaction products with unintended crystal structures. Therefore, it is clear that the degradation of the properties of oxide-based materials can be reduced.

[0064] Samples No. 3-6, where the ratio R of the opening area was between 0.04 and 0.10, received a rating of A, indicating a particularly large proportion of cubic crystals. It was revealed that when the ratio R is between 0.04 and 0.10, gas retention and lithium evaporation from the molded body can be further reduced, thereby further reducing reaction products with unintended crystal structures.

[0065] Samples No. 2-8 had a V value of 3700°C·h or less. It was found that a V value of 3700°C·h or less can reduce the amount of reaction products with undesirable crystal structures.

[0066] Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention.

[0067] In this embodiment, the case of firing the material 10 using a continuous firing furnace has been described, but it is not limited to this. It is of course possible to fire the material 10 contained in firing jigs 11, 31, and 41 using a batch firing furnace. By providing openings 16, 34, and 47 in the firing jigs 11, 31, and 41, gases generated from the material 10 can be exhausted even in the case of a batch firing furnace.

[0068] The shapes, sizes, and number of openings 16, 34, and 47 described in the embodiment are just examples. The shapes, sizes, and number of openings 16, 34, and 47 are set appropriately according to the shapes and sizes of the firing jigs 11, 31, and 41. The shapes of walls 14, 32, and 44 described in the embodiment are also just examples, and polygonal cylindrical shapes such as triangles and squares, or circular cylindrical shapes such as circles and ellipses are set as appropriate.

[0069] In the embodiment, firing jigs 11, 31, and 41 equipped with lids 17 and roofs 45 have been described, but the invention is not necessarily limited to these. It is certainly possible to omit the lids 17 and roofs 45. If the lids 17 and roofs 45 are omitted, the areas where the lids 17 and roofs 45 were located will become openings. In this case as well, if the ratio R of the area of ​​the openings to the sum of the area of ​​the outer surfaces (sides 22, 35, 48) of the firing jigs 11, 31, and 41 is 0.02 or more and 0.30 or less, the deterioration of the properties of the oxide-based material can be further reduced.

[0070] In the first embodiment, a case was described in which the first bottom portion 13 and the second bottom portion 15 are placed on top of each other, but the invention is not limited to this. It is certainly possible to omit the second bottom portion 15. Also, a case was described in which the wall 14 and the first bottom portion 13 are joined together to form a bottomed cylindrical shape, but the invention is not limited to this. It is certainly possible to separate the first bottom portion 13 from the wall 14.

[0071] In the second embodiment, a case was described in which the lid 17 placed over the wall 32 is shifted to create an opening 34 between the wall 32 and the lid 17, but it is not limited to this. It is of course possible to make multiple openings (holes) in the lid 17 and to make the lid 17 tightly adhere to the entire circumference of the upper end of the wall 32. This is because gas can be exchanged between the inside and outside of the firing jig 31 through the holes made in the lid 17. [Explanation of symbols]

[0072] 10 materials 11, 31, 41 Firing jigs 16,34,47 aperture 20 furnace 23 bottom 22, 35, 48 Side view (part of the exterior) 24, 36, 49 Top surface (part of the outer surface)

Claims

1. A method for producing an oxide-based material, comprising a step of calcining a lithium-containing material, The above process includes placing the firing jig containing the material into a furnace and firing the material, A method for manufacturing an oxide-based material, wherein an opening connecting the inside and outside of the firing jig is provided in the firing jig.

2. The method for producing the oxide-based material according to claim 1, wherein the oxide-based material is a solid electrolyte having a garnet-type crystalline structure containing Li, La, and Zr.

3. A method for producing an oxide-based material according to claim 1 or 2, wherein the ratio of the area of ​​the opening to the sum of the area of ​​the outer surface of the firing jig excluding the bottom and the area of ​​the opening is 1 is 0.02 or more and 0.30 or less.

4. A method for producing an oxide-based material according to claim 3, wherein the value obtained by multiplying the ratio by the maximum temperature (°C) in the operation and the time (hours) at 1000°C or higher in the operation is 3700°C·h or less.

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